九州大学 研究者情報
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花田 和明(はなだ かずあき) データ更新日:2021.11.22

教授 /  応用力学研究所 附属高温プラズマ理工学研究センター 総合理工学府 総合理工学専攻 Ⅱ類 プラズマ・量子理工学メジャー


原著論文
1. Kazuo Nakamura, Nakoto Hasegawa, Kasutoshi Tokunaga, ARAKI Kuniaki, Irfan Jamil, Xiaolong Liu, Osamu Mitarai, Hideki Zushi, Kazuaki Hanada, Akihide Fujisawsa, Hiroshi Idei, Yoshihiko Nagashima, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Takahiro Nagata , Quaternion Analysis of Three-Phase Matrix Converter Switching Method, Proc. International Conference on Electrical Engineerintg (ICEE 2016),Okinawa, Session D2-4 Cat4-06:id90432, 2016.07.
2. 假家強,今井剛,南龍太郎,津村康平,江橋優斗,岡田麻希,中嶋洋輔,出射浩,花田和明,下妻隆,久保伸,小田靖久,池田亮介,坂本慶司,小野雅之 , 核融合炉へ向けた大電力ジャイロトロンの開発, プラズマ・核融合学会誌, 93, 3, 146-149, 2017.03.
3. 花田 和明 , 佐藤 浩之助, 図子 秀樹, 中村 一男, 坂本 瑞樹, 出射 浩, 長谷川 真, 高瀬 雄一, 前川 孝 , 御手洗 修, QUESTの設計と将来計画, 電気学会論文誌Vol.129,No.9「核融合炉実用化への課題と球状トカマク研究」 特集論文(Ⅰ), vol.129,No.9, 2009.09.
4. 中村 一男, 藤田 広樹, 劉 暁龍, 薛 二兵, 御手洗 修, 長谷川 真, 德永 和俊, 荒木 邦明, 図子 秀樹, 花田 和明, 藤澤 彰英, 松岡 啓介, 出射 浩, 永島 芳彦, 川崎 昌二, 中島 寿年, 東島 亜紀, クォターニオンによるマトリクスコンバータの解析, 電気学会研究会資料 電子デバイス/半導体電力変換研究会 合同研究会 大阪大学, EDD-13-61,SPC-13-123, 2013.10.
5. SK Sharma, H Zushi, N Yoshida, H Watanabe, M Osakabe, Y Takeiri, M Hasegava, K Tokunaga, K Hanada, H Idei, M Sakamoto, K Nakamura, A Fujisawa, M Ishiguro, S Tashima, Team QUEST, 25pGW-5 Effect of TF ripples on plasma wall interaction and localized damages due to loss of energetic electrons in QUEST, 日本物理学会講演概要集, 66.0, 1.0, 240.0, 67.0,2.0, 2011.09.
6. Santanu Banerjee, H Zushi, N Nishino, K Hanada, H Honma, HQ Liu, M Ishiguro, T Ryoukai, S Tashima, K Nakamura, H Idei, M Hasegawa, A Fujisawa, 26pGW-12 B_Z dependence of the higher order moments of density fluctuations in slab geometry plasma in QUEST, 日本物理学会講演概要集, 66.0, 1.0, 256.0, 2011.09.
7. HQ Liu, K Hanada, N Nishino, R Ogata, M Ishiguro, H Zushi, K Nakamura, A Fujisawa, H Idei, M Hasegawa, 26pGW-13 Experimental observation and Statistical Analysis of Blob-like Structures in QUEST, 日本物理学会講演概要集, 66.0, 1.0, 256.0, 2011.09.
8. Santanu BANERJEE, H ZUSHI, N NISHINO, Y NAGASHIMA, K HANADA, S TASHIMA, T INOUE, K NAKAMURA, H IDEI, M HASEGAWA, A FUJISAWA, K MATSUOKA, 18aFA-6 Fluctuation characteristics and flow at the SOL of ECRH driven plasma in QUEST, 日本物理学会講演概要集, 67.0, 2.0, 185.0, 2012.09.
9. Santanu BANERJEE, H ZUSHI, N NISHINO, K HANADA, HQ Liu, M ISHIGURO, T RYOUKAI, S TASHIMA, T INOUE, K NAKAMURA, H IDEI, H HASEGAWA, A FUJISAWA, K MATSUOKA, Y NAGASHIMA, 25pYG-5 Effect of poloidal magnetic field curvature variations on the edge turbulence of 8.2 GHz slab plasma in QUEST, 日本物理学会講演概要集, 67.0, 1.0, 271.0, 2012.09.
10. H Zushi, S Tashima, M Ishiguro, M Hasegawa, S Barnejee, H Nishino, M Isobe, K Hanada, H Idei, K Nakamura, A Fujisawa, Y Nagashima, K Matsuoka, I Toi, T Maekawa, Y Takase, M Kikuchi, A Ejin, Y Ueda, O Mitarai, S Okamura, 26pYG-2 QUEST 電流駆動における自発的内側 poloidal field null 配位の形成 (26pYG 核融合プラズマ (電流駆動・波動加熱), 領域 2 (プラズマ基礎・プラズマ科学・核融合プラズマ・プラズマ宇宙物理)), 日本物理学会講演概要集, 67.0, 1.0, 280.0, 2012.09.
11. Kishore, Mishra; Zushi, H; Idei, H; Tashima, S; Banerjee, S; Hasegawa, M; Hanada, K; Nakamura, K; Fujisawa, A; Nagashima, Y;, 28pKB-2 On formation of a natural inboard separatrix in ECW heated Ohmic plasma on the spherical tokamak QUEST, 日本物理学会講演概要集, 68.0, 2.0, 208.0, 2013.09.
12. Zushi, H; Tashima, S; Ishiguro, M; Hasegawa, M; Banerjee, S; Nishino, H; Isobe, M; Hanada, K; Idei, H; Nakamura, K;, 29aEC-9 非誘導電流駆動を用いた高ポロイダルベータ平衡とその解析 (29aEC 核融合プラズマ (数値解析・MHD 平衡・波動),領域 2 (プラズマ基礎・プラズマ科学・核融合プラズマ・プラズマ宇宙物理)), 日本物理学会講演概要集, 68.0, 1.0, 305.0, 2013.09.
13. 中村 一男、劉 暁龍、吉末竜也、御手洗 修、徳永 和俊、長谷川 真、図子 秀樹、花田 和明、藤澤 彰英、坂本 瑞樹、出射 浩、川崎 昌二、中島 寿年、東島 亜紀、荒木 邦明, マトリクスコンバータにおけるVenturini法と空間ベクトル法, 半導体電力変換研究会, SPC-11-024, 2011.03.
14. M. Hasegawa, K. Nakamura, K. N. Sato, K. Hanada, H. Zushi, M. Sakamoto, H. I dei, S. Kawasaki, H. Nakashima, A. Higashijima, QUEST装置における誘導電場による初期プラズマ生成, 九州大学大学院総合理工学報告, 第28巻第4号,pp. 391-398, 2007.04.
15. Wang, Feng; Nakamura, Kazuo; Mitarai, Osamu; Kurihara, Kenichi; Kawamata, Yoichi; Sueoka, Michiharu; Sato, Kohnosuke; Zushi, Hideki; Hanada, Kazuaki; Sakamoto, Mizuki;, Study on Plasma Shape Reproduction of Spherical, 九州大学大学院総合理工学報告, 29.0, 1.0, 7.0-12.0, 2007.11.
16. Xu, Handong; Hanada, Kazuaki; Hasegawa, Makoto; Zushi, Hideki; Nakamura, Kazuo;Sato, N;Sakamoto, Mizuki;Idei, Hiroshi;TRIAM Group, The plasma current control in the TRIAM-1M tokamak, 九州大学大学院総合理工学府,Interdisciplinary Graduate School of Engineering Sciences,Kyushu University, Vol. 29, No. 4, Pages 365-368, 2008.03.
17. Shunsuke Ide, Motomi Iida, Kazuo Ogura, Hitoshi Tanaka, Akira Yamazaki, Kazuaki Iwamura, Kazuaki Hanada, Takehiko Itou, Mikito Iwamasa, Yasushi Terumichi, Shigetoshi Tanaka, Takashi Maekawa, Akira Ando, Masahiko Nakamura, Electron Cyclotron Emission from Lower Hybrid Current Drive Plasma on the WT-3 Tokamak, journal of the physical society of japan, 10.1143/JPSJ.57.2605, 57, 8, 2605-2608, 1988.01, [URL], Electron cyclotron emission (ECE) from the lower hybrid current drive (LHCD) as well as the ohmic heating (OH) plasmas in WT-3 were measured along the horizontal chord in the equatorial plane and the vertical chord where the magnitude of the toroidal field is constant, respectively. Measurements show that the high energy tail electrons carrying the plasma current build up within 10 msec after the injection of the lower hybrid wave. The ECE spectrum from the LHCD plasma in a quasi-steady state can be fitted with a numerically calculated spectrum assuming that the electron velocity distribution function is Maxwellian with the temperature T=50 keV..
18. Motomi Iida, Takashi Maekawa, Hitoshi Tanaka, Shunsuke Ide, Kazuo Ogura, Kazuaki Hanada, Mikito Iwamasa, Takehiko Itoh, Yasushi Terumichi, Shigetoshi Tanaka, Stabilization and Destabilization of Sawtooth Oscillations by Lower Hybrid Current Drive in the WT-3 Tokamak, journal of the physical society of japan, 10.1143/JPSJ.57.3661, 57, 11, 3661-3664, 1988.01, [URL], Sawtooth oscillations appearing in Ohmically heated (OH) plasmas are suppressed by the lower hybrid current drive (LHCD) in the WT-3 tokamak (R = 65 cm, a = 20 cm, Ip ≃ 100 kA, ne = 1 – 2 × 1013 cm–3, qa ≃ 4.5, and PLH ≳ 100 kW). After the suppression, sawteeth reappear following m = 1 oscillations in the LHCD plasmas. The latter sawteeth have a large amplitude and long period (Ts = 2–5 msec), compared with the former one (Ts = 0.5–1.5 msec). Furthermore, they do not accompany a precursor and crash very fast..
19. A. Kuzmin, H. Zushi, I. Takagi, S. K. Sharma, Y. Hirooka, M. Kobayashi, M. Sakamoto, Kazuaki Hanada, Takumi Onchi, Y. Oyama, N. Youshida, K. Nakamura, akihide fujisawa, Hiroshi Idei, Yoshihiko Nagashima, Makoto Hasegawa, K. Mishra, Hydrogen flux measurements with permeation probes in spherical tokamak QUEST, Vacuum, 10.1016/j.vacuum.2016.04.025, 129, 178-182, 2016.07, [URL], Poloidal and radial distributions of the hydrogen flux, both atomic and ion, to the plasma facing materials (PFMs) are measured with four fixed and one movable PdCu membrane probes in the QUEST spherical tokamak. Direct information about hydrogen retention in the areas far from main plasma-wall interaction is essential because the significant part of the global retention is due to atomic hydrogen. Incident hydrogen flux Γinc is numerically reconstructed by fitting the experimentally measured hydrogen flux Γp, permeated through the membrane. The sensitivity of the probe is improved when compared with other work which allows dynamic changes of the retention flux to be monitored, allowing detection of 10% of the Γinc modulation, or ∼1017 H m−2s−1..
20. D. Yamaguchi, S.-I. Itoh, K. Hanada, T. Kubota, S. Toda, Transport Coefficient and Heat Pulse Propagation, Transaction of Fusion Technology, 10.13182/FST95-A11947137, 27,497-500(※Transaction of Fusion Technology Vol. 27 (1995) 497-500), 1995.01.
21. K. Hanada, T. Oikawa, K. Nozawa, H. Totsuka, K. Shinohara, E. Ishiyama, N. Shinoda, K. Yamagishi, H. Toyama, Low Aspect Ratio Tokamak Experiment in University of Tokyo, Transaction of Fusion Technology Vol. 27 (1995) 440-443, Transaction of Fusion Technology Vol. 27 (1995) 440-443, 1995.01.
22. Yoshinaga, T; Hanada, K; Sato, K; Nakamura, K; Zushi, H; Idei, H; Sakamoto, M; Hasegawa, M;, Non-Inductive Plasma Current Start-up Experiment by Electron Cyclotron Heating in the CPD Device, The Korean Vacuum Soiety, 185-185, 2007.08.
23. M. Sakamoto, K. N. Sato, M. Ogawa, K. Takaki, H. Zushi, K. Nakashima, N. Maezono, T. Sugata, Y. Nakashima, Y. Higashizono, Y. Kubota, A. Higashijima, H. Nakashima, S. Kawasaki, A. Iyomasa, M. Hasegawa, H. Idei, K. Hanada, K. Nakamura, Recent Global Wall Recycling Studies in Long Term Sustained TRIAM-1M Tokamak and its Development in New ST Device in Kyushu University, The 5th conference of Asia Plasma & Fusion Association (APFA 2005), August 29-31, 2005, Jeju (Korea), Proc. of the 5th conference of Asia Plasma & Fusion Association (APFA 2005),, 2005.08.
24. Kishore Mishra, H. Idei, H. Zushi, K. Nagata, R. Akimoto, M. K. Yamamoto, K. Hanada, M. Hasegawa, K. Nakamura, A. Fujisawa, Y. Nagashima, S. Banerjee, T. Onchi and A. Kuzmin, Thermal imaging of plasma with a phased array antenna in QUEST, Review of Scientific Instruments , 10.1063/1.4889903, 85, 11, 11E808, 2014.11, A thermal imaging system to measure plasma Electron Bernstein Emission (EBE) emanating from the mode conversion region in overdense plasma is discussed. Unlike conventional ECE/EBE imaging, this diagnostics does not employ any active mechanical scanning mirrors or focusing optics to scan for the emission cones in plasma. Instead, a standard 3 * 3 waveguide array antenna is used as a passive receiver to collect emission from plasma and imaging reconstruction is done by accurate measurements of phase and intensity of these signals by heterodyne detection technique. A broadband noise source simulating the EBE, is installed near the expected mode conversion region and its position is successfully reconstructed using phase array technique which is done in post processing..
25. Z. Wang, Kazuaki Hanada, N. Yoshida, T. Shimoji, M. Miyamoto, Y. Oya, H. Zushi, Hiroshi Idei, K. Nakamura, akihide fujisawa, Yoshihiko Nagashima, Makoto Hasegawa, S. Kawasaki, A. Higashijima, H. Nakashima, T. Nagata, A. Kawaguchi, T. Fujiwara, K. Araki, O. Mitarai, A. Fukuyama, Y. Takase, K. Matsumoto, Measurement of thickness of film deposited on the plasma-facing wall in the QUEST tokamak by colorimetry, Review of Scientific Instruments, 10.1063/1.5000739, 88, 9, 2017.09, [URL], After several experimental campaigns in the Kyushu University Experiment with Steady-state Spherical Tokamak (QUEST), the originally stainless steel plasma-facing wall (PFW) becomes completely covered with a deposited film composed of mixture materials, such as iron, chromium, carbon, and tungsten. In this work, an innovative colorimetry-based method was developed to measure the thickness of the deposited film on the actual QUEST wall. Because the optical constants of the deposited film on the PFW were position-dependent and the extinction coefficient k1 was about 1.0-2.0, which made the probing light not penetrate through some thick deposited films, the colorimetry method developed can only provide a rough value range of thickness of the metal-containing film deposited on the actual PFW in QUEST. However, the use of colorimetry is of great benefit to large-area inspections and to radioactive materials in future fusion devices that will be strictly prohibited from being taken out of the limited area..
26. Santanu Banerjee, H. Zushi, N. Nishino, K. Mishra, Takumi Onchi, A. Kuzmin, Yoshihiko Nagashima, Kazuaki Hanada, K. Nakamura, Hiroshi Idei, Makoto Hasegawa, akihide fujisawa, Dynamical programming based turbulence velocimetry for fast visible imaging of tokamak plasma, Review of Scientific Instruments, 10.1063/1.4914838, 86, 3, 2015.03, [URL], An orthogonal dynamic programming (ODP) based particle image velocimetry (PIV) technique is developed to measure the time resolved flow field of the fluctuating structures at the plasma edge and scrape off layer (SOL) of tokamaks. This non-intrusive technique can provide two dimensional velocity fields at high spatial and temporal resolution from a fast framing image sequence and hence can provide better insights into plasma flow as compared to conventional probe measurements. Applicability of the technique is tested with simulated image pairs. Finally, it is applied to tangential fast visible images of QUEST plasma to estimate the SOL flow in inboard poloidal null-natural divertor configuration. This technique is also applied to investigate the intricate features of the core of the run-away dominated phase following the injection of a large amount of neutrals in the target Ohmic plasma. Development of the ODP-PIV code and its applicability on actual plasma images is reported..
27. Hiroshi Idei, K. Nagata, K. Mishra, M. K. Yamamoto, T. Itado, R. Akimoto, Kazuaki Hanada, H. Zushi, Adaptive array technique for differential-phase reflectometry in QUEST, Review of Scientific Instruments, 10.1063/1.4891710, 85, 11, 2014.11, [URL], A Phased Array Antenna (PAA) was considered as launching and receiving antennae in reflectometry to attain good directivity in its applied microwave range. A well-focused beam was obtained in a launching antenna application, and differential-phase evolution was properly measured by using a metal reflector plate in the proof-of-principle experiment at low power test facilities. Differential-phase evolution was also evaluated by using the PAA in the Q-shu University Experiment with Steady State Spherical Tokamak (QUEST). A beam-forming technique was applied in receiving phased-array antenna measurements. In the QUEST device that should be considered as a large oversized cavity, standing wave effect was significantly observed with perturbed phase evolution. A new approach using derivative of measured field on propagating wavenumber was proposed to eliminate the standing wave effect..
28. J. Fujita, K. Matsuura, K. Kawahata, S. Fujiwaka, S. Itoh, K. N. Sato, K. Nakamura, H. Zushi, M. Sakamoto, Kazuaki Hanada, Eriko Jotaki, K. Makino, A rotating coil probe for the magnetic field measurement on a long pulsed tokamak, Review of Scientific Instruments, 70, 1 II, 445-448, 1999.01, In order to determine the magnitude and the position of the plasma current in a long pulsed tokamak such as the International Thermonuclear Experimental Reactor (ITER), it is urged to establish a reliable method which is free from the zero-level drift of the integrator as well as the radiation damage for the steady-state magnetic field measurement. For this purpose, we have developed a hybrid system, a combination of a conventional magnetic probe for the measurement of fast varying magnetic field and a rotating coil magnetic probe for that of slowly varying field. The rotating coil is energized by an air turbine to avoid electromagnetic interference and the induce signal with a constant rotation frequency is picked up through a transformer to eliminate mechanical contacts. An automatic gain control circuit is also designed for the compensation of rotation speed fluctuation. The system is proved to achieve a flat frequency response with a proper choice of cross over frequency for high- and low-frequency systems. The rotating coil probe is tested for over 170 h without any trouble. The probe was applied to the poloidal magnetic field measurement on the TRIAM-1M long pulsed tokamak, and proved to work satisfactorily..
29. Nakamura, Kazuo; Liu, Xiaolong; Tomoda, Masashi; Yoshisue, Tatsuya; Mitarai, Osamu; Hasegawa, Makoto; Tokunaga, Kazutoshi; Zushi, Hideki; Hanada, Kazuaki; Idei, Hiroshi;, Effect of Shell Cut and Diagnostic Port on Stabilizing Characteristics of Vertical Position Instability on QUEST, Research Institute for Applied Mechanics,Kyushu University, 143.0, 2012.09.
30. Sakamoto, Mizuki; Ogawa, Masanori; Higashizono, Yuta; Zushi, Hideki; Sato, Konosuke; Nakamura, Kazuo; Hanada, Kazuaki; Idei, Hiroshi; Hasegawa, Makoto; Kawasaki, Shoji;, Erosion and Re-deposition of Plasma-Facing material in Long Duration Discharges on TRIAM-1M, Reports of Research Institute for Applied Mechanics,Kyushu University, 136.0, 19.0-22.0, 43.0,CRPP-ARTICLE-2009-085, 2009.03.
31. Duorah, S; Ejiri, A; Lee, S; Iguchi, H; Fujisawa, A; Kojima, M; Matsuoka, K; Ishiyama, E; Hanada, K; Shiraiwa, S; Toyama, H; Takase, Y, Multilayer mirror based soft x-ray spectrometer as a high temperature plasma diagnostic, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.1324745, 72.0, 1.0, 1183.0-1187.0, 0.0, 2001.01, A fully calibrated multilayer mirror (MLM) based soft x-ray spectrometer has been developed and installed on the Compact Helical System (CHS). This MLM based spectrometer is a new approach to devising a soft x-ray spectrometer with medium time and energy resolutions. The spectrometer mainly consists of a MLM as the dispersive element and a 20-channel (p-i-n) pin diode array for the detection of the soft x-rays. Both the MLM and the pin diodes have been calibrated at the KEK (High Energy Accelerator Research Organization) Photon Factory for an energy range of 300-1200 eV. The reflectivity of the mirror was found to increase from 3% (photon energy of 335 eV) to 25% (photon energy of 1050 eV). The pin diodes were found to have almost 100% efficiency for creating electron-hole pairs in the calibrated energy range. The spectrometer was installed on the CHS with the aim of fast electron temperature measurement and study of fast magneto-hydrodynamic (MHD) events occurring in plasmas. The experiments show that in the energy range of measurement, the electron "temperature" determined from the slope of the soft x-ray spectrum is much lower than that measured by the Thomson scattering diagnostic. Analysis showed that the soft x-ray spectrum is highly contaminated by impurity emission. Therefore it may be possible to measure electron temperature with this diagnostic if we choose another energy range where we can measure the continuous spectrum. The present time resolution of the system is of the order similar to0.1 ms, which made it possible to study the behavior of the plasma during fast MHD events. Modulations in the soft x-ray intensity were observed during MHD events in CHS plasmas. Analysis of these shows that these may be due to modulations in the temperature or the impurity concentration. (C) 2001 American Institute of Physics..
32. L. G.Bruskin, N. Oyama, K. Shinohara, Y. Miura, Y. Kogi, A. Mase, M. Hasegawa, K. Hanada, Measurements of density fluctuations in reflectometry of cylindrical plasmas, REVIEW OF SCIENTIFIC INSTRUMENTS, https://doi.org/10.1063/1.1538355, 74.0, 3.0, 1473.0-1476.0, 2003.03, An analytical model of fluctuationreflectometry is developed, which is capable of handling the plasma profiles of arbitrary shape and curvature. The experimental profiles are piece-wise approximated by the functions, which allow for the integration of the full-wave O-mode equation. The model is applied to the reflectometry of the JT-60U tokamak plasma to provide a preliminary estimation of the fluctuation amplitude and spectral width..
33. Ishiguro, Masaki; Hanada, Kazuaki; Liu, Haiqing; Zushi, Hideki; Yoshida, Naoaki; Tokunaga, Tomonori; Nakamura, Kazuo; Fujisawa, Akihide; Idei, Hiroshi; Sakamoto, Mizuki; Hasegawa, Makoto; Tashima, Saya; Takase, Yuichi; Maekawa, Takashi; Kishimoto, Yasuaki; Mitarai, Osamu; Kawasaki, Shoji; Nakashima, Hisatoshi; Higashijima, Aki, Direct measurement of energetic electron flow in Q-shu University experiment with steady-state spherical tokamak, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.3662204, 82.0, 11.0, Article No. 113509, 2011.11, In magnetized plasmas, the presence of a significant number of energetic electrons has been observed but quantitative characteristics of these electrons are proving difficult to investigate. A Langmuir probe offers a means to provide quantitative measurement of these energetic electrons that takes into account electron emissions (secondary electron emission and electron reflection) from the probe tips and sheath expansion around the probe tips caused by a considerable negative potential. In this paper, these effects are experimentally confirmed and an analytical means to measure energetic electron characteristics are proposed. An analysis of plasmas produced by a high frequency wave is then applied leading to the successful detection of an asymmetric flow of energetic electrons. The estimated electron temperature and current density were approximately 4-5 keV and 2-3 kA/m(2). (C) 2011 American Institute of Physics. [doi:10.1063/1.3662204].
34. Banerjee, Santanu; Zushi, H.; Nishino, N.; Nagashima, Y.; Hanada, K.; Ishiguro, M.; Ryoukai, T.; Tashima, S.; Inoue, T.; Nakamura, K.; Idei, H.; Hasegawa, M.; Fujisawa, A.; Matsuoka, K., Fast visible imaging and edge turbulence analysis in QUEST, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.4739080, 83.0, 10.0, Article No. 10E524, 2012.10, A fast visible imaging system is installed on the spherical tokamak QUEST to study edge turbulence. The camera uses a complementary metal-oxide semiconductor detector with a maximum resolution of 1024 x 1024 at 7000 frames/s (fps) and can achieve 775 kfps at a resolution of 128 x 24. In this paper, we present the salient features of the system and its application to study edge turbulence in 8.2 GHz ECRH driven slab plasma, without plasma current. Vertical magnetic field (B-z) topology is varied with three sets of poloidal field (PF) coils and the variation in the edge turbulence is investigated as a function of the B-z strength and curvature. Fluctuation amplitude was highest for the shallow PF well. Cross-correlation coefficient shows distinct coherent mode along z direction at the steep density gradient region and it grows with the PF mirror ratio. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4739080].
35. H. Idei, H. Zushi, K. Hanada, K. Nakamura, A. Fujisawa, M. Hasegawa, N. Yoshida, M. Sakamoto, H. Watanebe, K. Tokunaga, Y. Nagashima, A. Ejiri, M. Sakaguchi, E. Kalinnikova, M. Ishiguro, S. Tashima, A. Fukuyama, H. Igami, S. Kubo, S. K. Sharma, T. Ryokai, H. Q. Liu, M. Isobe, K. Nagaoka, H. Nakanishi, N. Nishino, S. Kawasaki, H. Nakashima, A. Higashijima, Y. Takase, T. Maekawa, O. Mitarai, M. Kikuchi and K. Toi, Electron Cyclotron / Bernstein Wave Heating and Current Drive Experiments using Phased-array Antenna in QUEST, RADIO FREQUENCY POWER IN PLASMAS: Proceedings of the 19th Topical Conference, 1406.0, 1.0, 473.0-476.0, 2011.06, The phased‐array antenna system for Electron Cyclotron/Bernstein Wave Heating and Current Drive experiments has been developed in the QUEST. The antenna was designed to excite a pure O‐mode wave in the oblique injection for the O‐X‐B mode conversion experiments, and its good performances were confirmed at a low power level. The plasma current (<∼15 kA) with an aspect ratio of 1.5 was started up and sustained by only RF injection in the low‐density operations. The long pulse discharge of 10 kA was also attained for 37 s. The new density window to sustain the plasma current was observed in the high‐density plasmas. The single‐null divertor configuration with the high plasma current (<∼25 kA) was attained in the 17 s plasma sustainment..
36. Y. Takase, A. Ejiri, Kazuaki Hanada, S. Ide, O. Mitarai, S. Shiraiwa, M. Ushigome, Plasma current start-up by outboard PF coils in JT-60U and TST-2, RADIO FREQUENCY POWER IN PLASMAS: 16th Topical Conference on Radio Frequency Power in Plasmas
RADIO FREQUENCY POWER IN PLASMAS
16th Topical Conference on Radio Frequency Power in Plasmas
, 10.1063/1.2098259, 365-368, 2005.09, [URL], Plasma current (Ip) initiation and ramp-up utilizing induction by poloidal field (PF) coils located on the outboard side of the torus were demonstrated in both conventional aspect ratio tokamak (100 kA in JT-60U) and spherical tokamak (10 kA in TST-2). In the presence of sufficient source of plasma by RF ionization (1 MW in JT-60U, 100 kW in TST-2), Ip formation is possible without the existence of a PF null, with the initial vertical field (Bv) in the direction opposite to that required for equilibrium. Utilization of the extra flux swing provided by the PF coils before Bv switches sign is important in arriving at a high enough I p that matches Bv at the end of PF coil current ramp. In JT-60U, recharging of the OH coil was observed with only perpendicular and counter NB injection, suggesting overdrive by bootstrap current. In TST-2, a quasi-steady-state Ip of 4 kA was formed and sustained by RF power (PRF) alone, without the use of induction. The plasma current centroid of this type of plasma is located on the outboard side. The dependences of Ip on PRF and Bv were found to be weak. The results presented here offer encouragement to CS-less operation of a tokamak fusion reactor, which should have a large impact on the economic competitiveness..
37. H. Zushi, Y. Hirooka, M. Sakamoto, Y. Nakashima, R. Bhattacharyay, T. Yoshinaga, Y. Higashizono, K. Hanada, N. Nishino, N. Yoshida, K. Tokunaga, S. Kado, T. Shikama, Kawasaki, K. Okamoto, T. Miyazaki, H. Honma, K. N. Sato, K. Nakamura, H. Idei, M. Hasegawa, H. Nakashima, A. Higashijima, Particle recycling in the CPD Spherical Tokamak, Proceedings of the Joint Meeting of 4th IAEA Technical Meeting on Spherical Tori 14th International Workshop on Spherical Torus, 2008.10.
38. K. N. SATO, H. ZUSHI, K. HANADA, K. NAKAMURA, M. SAKAMOTO, H. IDEI, M. HASEGAWA, Y. HIGASHIZONO, S. KAWASAKI, H. NAKASHIMA, A. HIGASHIJIMA, ALL JAPAN ST RESEARCH GROUP, Project of Long Term Sustained Spherical Tokamak “QUEST”, Proceedings of the Joint Meeting of 4th IAEA Technical Meeting on Spherical Tori 14th International Workshop on Spherical Torus, (※), 2008.10.
39. Kalinnikova, E, Idei Hiroshi, zushi hideki, hanada kazuaki, Igami, H, Kubo, S, Fukuyama, A, Nuga, H., Multiple ray-tracing analysis for EBWH/CD experiments in QUEST, Proceedings of the 16th Joint Workshop on Electron Cyclotron Emission and Electron Cyclotron Resonance Heating, Vol. 1, No. , Pages 275-280, 2010.04.
40. Kishore Mishra, Hiroshi Idei, Hideki Zushi, Saya Tashima, Santanu Banerjee, Makoto Hasegawa, Kazuaki Hanada, Kazuo Nakamura, Akihide Fujisawa, Keisuke Matsuoka, Yoshihiko Nagashima, S. Kawasaki, A. Higashijima, H. Nakashima, and Quest Group, Characteristics of High Poloidal Beta (β p) Plasma Formed by Electron Cyclotron Waves in Spherical Tokamak QUEST, Proceedings of the 12th Asia Pacific Physics Conference (APPC12), 1.0, 5.0, Article No. 015031, 2013.07.
41. Santanu Banerjee, zushi hideki, N. Nishino, Y. Mahira, K. Nagaoka, K. Mishra, S. Tashima, Nagashima Yoshihiko, K.Hanada, Kazuo Nakamura, H. Idei, Makoto Hasegawa, Fujisawa Akihide, K. Matsuoka, Scrape Off Layer Flow Characteristics in the Spherical Tokamak QUEST, Proceedings of the 12th Asia Pacific Physics Conference, JPS Conf. Proc. ,015036 (2014), 2014.03.
42. H Idei, K Hanada, K Ohkubo, M Hasegawa, T Notake, S Kubo, T Shimozuma, S Ito, H Zushi, KN Sato, K Nakamura, M Sakamoto, A Iyomasa, H Hoshika, K Sasaki, S Kawasaki, H Nakashima, Remote Steering Antenna System and Its Application to ECH/ECCD Experiments on the TRIAM-1M tokamak, Proceedings of 13th Joint Workshop on ECE & ECRH, p. 326-331 (2004), 2004.01.
43. Hanada, K; Zushi, H; Idei, H; Nakamura, K; Ishiguro, M; Tashima, S; Kalinnikovab, EI; Sakamoto, M; Hasegawaa, M; Fujisawaa, A;, Recent experiments towards steady state operation of spherical tokamak QUEST, Proceeding of JSPS-CAS Core University Program Seminar on Production and Control of High Performance Plasmas with Advanced Plasma Heating and Diagnostic Systems 1-4 November, 2010, Guilin, China, Vol. , No. , Pages 42, 2011.01.
44. T. Yoshinaga, K. Hanada, H. Zushi, K. Nakamura, K. N. Sato, H. Idei, M. Sakamoto, M. Hasegawa, T. Morisaki, Y. Nakashima, N. Nishino, M. Nagata, N. Fukumoto, Y. Takase, T. Maekawa, Y. Kishimoto, O. Mitarai, N. Yoshida, K. Tokunaga, Y. Hirooka, Y. Higashizono, S. Kawasaki, H. Nakashima, A. Higashijima, R. Bhattacharyay, S. Kawano, S. Kawakami, T. Kikukawa, K. Dono, M. Ishiguro, H. Honma, T. Miyazaki, T. Ryokai, T. Sakimura, Y. Inada, S. Watanabe and Y. Wataya, Physics Study of EC-Excited Current Generation via Current Jump in the Compact Plasma-Wall-Interaction Experimental Device, Proc.22nd IAEA Fusion Energy Conference, (※), 2008.10.
45. Zushi, H.; Hirooka, Y.; Bhattacharyay, R.; Sakamoto, M.; Nakashima, Y.; Yoshinaga, T.; Higashizono, Y.; Hanada, K.; Nishino, N.; Yoshida, N.; Tokunaga, K.; Kado, S.; Shikama, T.; Kawasaki, S.; Okamoto, K.; Miyazaki, T.; Honma, H.; Sato, K. N.; Nakamura, K.; Idei, H.; Hasegawa, M.; Nakashima, H.; Higashijima, A., Active particle control experiments and critical particle flux discriminating between the wall pumping and fuelling in the compact plasma wall interaction device CPD spherical tokamak, Proc.22nd IAEA Fusion Energy Conference, 2008.10.
46. Sakamoto, M; Sato, KN; Zushi, H; Nakamura, K; Hanada, K; Idei, H; Hasegawa, M; Kawasaki, S; Nakashima, H; Higashijima, A;, Steady state plasma operation in the superconducting tokamak TRIAM-1M and the QUEST project, Proc. of Int. Symposium on Eco Topia Science, Pages 314-317, 2007.11.
47. M. Sakamoto, M. Ogawa, K. Takaki, H. Zushi, K, Nakashima, N. Maezono, T. Sugata, Y. Nakashima, Y. Higashizono, Y. Kubota, A. Higashijima, H. Nakashima, S. Kawasaki, A. Iyomasa, M. Hasegawa, H. Idei, K. Hanada, K. Nakamura, K. N. Sato, Impact of a movable limiter on the global wall recycling in TRIAM-1M, Proc. of 32nd EPS Conference on Plasma Physics, 1930-1933, 2005.01, In TRIAM-1M, the influence of the local structure of the first wall on the global wall recycling has been studied using the ML with good cooling capability. No wall saturation was observed in the 5 h 16 min discharge with the ML, since particle release was suppressed by less temperature rise of the main chamber. The global wall pumping rate without the ML, ~8.6 x 10
16
atoms m
-2
s
-1
, is 3.6 times higher than that of the long duration discharge without the ML. The temperature rise in the wall is attributed to the transition of the wall role from the particle sink to the source. The co-deposition of hydrogen with Mo is a key for the wall role of the particle sink. No clear difference of the growth rate of Mo deposits on the viewing window located from the limiter surface between with and without the ML. The growth rate is from ~2 x 10
-4
nm/s to ~8 x 10
-4
nm/s. The toroidal structure of hydrogen recycling changes significantly near at the ML. However, integration of H intensity with and without the ML over the whole toroidal length is about the same within 3% , which is less than the error, i.e. 15%..
48. Hanada, K; Iyomasa, A; Zushi, H; Hasegawa, M; Sasaki, K; Hoshika, H; Nakamura, K; Sakamoto, M; Sato, KN; Idei, H;, Transport barrier formation and its maintenance by LHCD on TRIAM-1M, Proc. of 20. IAEA fusion energy conference, IAEA-CN-116-EX/P4-25, 2005.01.
49. Sugata, Tomoya; Hanada, K; Imamura, N; Sakamoto, M; Zushi, H; Idei, H; Iyomasa, A; Kawasaki, S; Sato, K; Nakashima, H;, Estimation of Power Balance in Steady State LHCD Discharges on TRIAM-1M, Proc. of 12th International Congress on Plasma Physics, P3-094, 2004.10.
50. H Zushi, M Sakamoto, K Hanada, Y Matsuo, K Kuramoto, T Sugata, N Maezono, H Hoshika, A Iyomasa, K Sasaki, K Nakamura, KN Sato, H Idei, S Kawasaki, H Nakashima, A Higashijima, M Hasegawa, Very low frequency oscillations of heat load and recycling flux in steady-state tokamak discharge in TRIAM-1M, Proc. of 12. International Congress on Plasma Physics, (※), 2004.08.
51. NAKAMURA Kazuo, FUJITA Hiroki, LIU Xiaolong, XUE Erbing, XIA Fan, MITARAI Osamu, KURIHARA Kenichi, KAWAMATA Yoichi, SUEOKA Michiharu, HASEGAWA Makoto, TOKUNAGA Kazutoshi, ZUSHI Hideki, HANADA Kazuaki, FUJISAWA Akihide, IDEI Hiroshi, NAGASHIMA Yoshihiko, KAWASAKI Shoji, NAKASHIMA Hisatoshi, HIGASHIJIMA Aki, ARAKI Kuniaki, SHAPE RECONSTRUCTION OF RF-DRIVEN DIVERTOR PLASMA ON QUEST, Proc. Third Meeting for A3 Foresight Program Workshop on Critical Physics Issues Specific to Steady State Sustainment of High-Performance Plasmas,19-24 May 2013,Beijing,China,NIFS-PROC-95, 19-24 May 2013,Beijing,China,NIFS-PROC-95,48-55,2013.12., 2013.05.
52. H. ZUSHI, Y. HIROOKA, R. BHATTACHARYAY, M. SAKAMOTO, Y. NAKASHIMA, T. YOSHINAGA, Y. HIGASHIZONO, K. HANADA, N. NISHINO, N. YOSHIDA, K. TOKUNAGA, S. KADO, T. SHIKAMA, S. KAWASAKI, K. OKAMOTO, T. MIYAZAKI, H. HONMA, K. N. SATO, K. NAKAMURA, H. IDEI, M. HASEGAWA, H. NAKASHIMA, A. HIGASHIJIMA, Particle Recycling in the Compact Plasma wall interaction Device CPD Spherical Tokamak, Proc. Joint Meeting of the 4th IAEA Technical Meeting on Spherical Tori and the 14th International Workshop on Spherical Torus, (※), 2008.10.
53. H. ZUSHI, T. RYOUKAI, K. KIKUKAWA, T. MORISAKI, R. BHATTACHARYAY, T. YOSHINAGA, K. HANADA, H. IDEI, M. SAKAMOTO, Y. NAKASHIMA, Y. HIGASHIZONO, N. NISHINO, K. DONO, T. SAKIMURA, T. MIYAZAKI, H. HONMA, S. TASHIMA, K. N. SATO, K. NAKAMURA, M. HASEGAWA, S. KAWASAKI H. NAKASHIMA, A. HIGASHIJIMA, Study on Density Fluctuations during the RF Current Ramp-up Phase in the CPD Spherical Tokamak, Proc. Joint Meeting of the 4th IAEA Technical Meeting on Spherical Tori and the 14th International Workshop on Spherical Torus, 2008.10.
54. H. ZUSHI, T. RYOUKAI, K. KIKUKAWA, T. MORISAKI, R. BHATTACHARYAY, T. YOSHINAGA, K. HANADA, H. IDEI, M. SAKAMOTO, Y. NAKASHIMA, Y. HIGASHIZONO, N. NISHINO, K. DONO, T. SAKIMURA, T. MIYAZAKI, H. HONMA, S. TASHIMA, K. N. SATO, K. NAKAMURA, M. HASEGAWA, S. KAWASAKI H. NAKASHIMA, A. HIGASHIJIMA, Study on Fluctuations during the RF Current Ramp-up Phase in the CPD Spherical Tokamak, Proc. Joint Meeting of the 4th IAEA Technical Meeting on Spherical Tori and the 14th International Workshop on Spherical Torus,Frascati,Italy,October 7-10,2008, 2008.10.
55. M. Ogawa, M. Sakamoto, K. N. Sato, H. Zushi, K. Nakamura, K. Hanada, H. Idei, M. Hasegawa, S. Kawasaki, H. Nakashima, A. Higashijima, and TRIAM group, Effect of repetition of discharges on oxygen impurity behavior in long duration discharge on TRIAM-1M, Proc. International Conference on Plasma Surface Interactions in ControlledFusion Device,Hefei Anhui,China(2006), 2006.05.
56. K. Nakamura, X. L. Liu, T. Yoshisue, O. Mitarai, K. Tokunaga, M. Hasegawa, H. Zushi, K. Hanada, A. Fujisawa, M. Sakamoto, H. Idei, S. Kawasaki, H. Nakashima, A. Higashijima, K. Araki, Venturini Method and Space Vector Modulation Method in Matrix Converter, Proc. International Conference on Electrical Engineering (ICEE2011),Hong Kong,July 11-14,2011, (※), 2011.07.
57. LIU Xiaolong, YOSHISUE Tatsuya, NAKAMURA Kazuo, XUE Erbing, HASEGAWA Makoto, TOKUNAGA Kazutoshi, ZUSHI Hideki, HANADA Kazuaki, FUJISAWA Akihide, IDEI Hiroshi, NAGASHIMA Yoshihiko, KAWASAKI Shoji, NAKASHIMA Hisatoshi, HIGASHIJIMA Aki, ARAKI Kuniaki, Robust Control on Plasma Vertical Position Instability by a Matrix Converter as Power Supply of QUEST, Proc. International Conference on Electrical Engineering (ICEE 2012),Kanazawa,July 2012, (※), 2012.07.
58. NAKAMURA Kazuo, YOSHISUE Tatsuya, LIU Xiaolong, XUE Erbing, MITARAI Osamu, HASEGAWA Makoto, TOKUNAGA Kazutoshi, ZUSHI Hideki, HANADA Kazuaki, FUJISAWA Akihide, IDEI Hiroshi, NAGASHIMA Yoshihiko, KAWASAKI Shoji, NAKASHIMA Hisatoshi, HIGASHIJIMA Aki, ARAKI Kuniaki, Three Phase-to-Single Phase Matrix Converter Design for Feedback Stabilization by Magnetic Field Coil, Proc. International Conference on Electrical Engineering (ICEE 2012),Kanazawa,July 2012, (※), 2012.07.
59. Kazuo Nakamura, FUJITA Hiroki, LIU Xiaolong, XUE Erbing, MITARAI Osamu, Makoto Hasegawa, K. Tokunaga, zushi hideki, K.Hanada, Fujisawa Akihide, H. Idei, Nagashima Yoshihiko, KAWASAKI Shoji, NAKASHIMA Hisatoshi, HIGASHIJIMA Aki, ARAKI Kuniaki, Quaternion Concept in Matrix Converter Design for Feedback Stabilization by Magnetic Field Coil, Proc. International Conference on Electrical Engineering (ICEE 2013),Xiamen,July 2013, S7-02,FP0393, 2013.07.
60. K. Nakamura, J. R. Luo, H. Z. Wang, Z. S. Ji, H. Wang, F. Wang, N. Qi, K. N. Sato, K. Hanada, M. Sakamoto, H. Idei, M. Hasegawa, S. Kawasaki, H. Nakashima, A. Higashijima, Magnetic Sensorless Control of Plasma Position without Drift Problem in the HT-7 Tokamak, Proc. Int. Conf. on Electrical Engineering,2005,Kunming,China, (※), 2005.07.
61. K. Nakamura, F. Wang, K. N. Sato, H. Zushi, K. Hanada, M. Sakamoto, H. Idei, M. Hasegawa, S. Kawasaki, H. Nakashima, A. Higashijima, Hot Gas Flow Simulation Aimed for Integrative Optimization of GCB, Proc. Int. Conf. on Electrical Engineering, PS1-ME-17, 2006.07.
62. S. Watanabe, K. Hanada, Plasma current measurement on compact PWI experimental device, Proc. 8th Cross Straits Symposium on Materials,Energy and Environmental Sciences, (※), 2006.12.
63. M. Sakamoto, M. Ogawa, M. Tokitani, H. Zushi, K. Tokunaga, N. Yoshida, K. Nakamura, K. Hanada, K. N. Sato, H. Idei, M. Hasegawa, M. Miyamoto, S. Kawasaki, H. Nakashima, T. Fujiwara, A. Higashijima, B. Rajendraprasad, K. Sasaki, Global Wall Recycling and Hydrogen Retention in Co-deposites in Long Duration Discharges on TRIAM-1M, Proc. 5th IAEA Technical Meeting on Steady State Operation of Magnetic Fusion Devices, 2007.05.
64. Handong Xu, Kazuaki Hanada and TRIAM Group, The Feedback Control of Full Non-Inductive LHCD Plasma Current in TRIAM-1M, Proc. 5th IAEA Technical Meeting on Steady State Operation of Magnetic Fusion Devices, (※), 2007.05.
65. H. Idei, M. Sakaguchi, H. Kasahara, K. Saito, K. Hanada, H. Zushi, K. N. Sato, K. Nakamura, M. Sakamoto, M. Hasegawa, Y. Takase, T. Maekawa, O. Mitarai, Y. Kishimoto, S. Kawasaki, H. Nakashima, A.. Higashijima, Y. Higashizono, Phased-array antenna for Electron Bernstein Heating and Current Drive in QUEST, Proc. 34th International Conference on Infrared,Millimeter,and Terahertz Waves, 10.1109/ICIMW.2009.5324704, 2009.09, The phased-array antenna has been designed for steady-state electron Bernstein wave heating and current drive at 8.2 GHz in the QUEST tokamak. The prototype antenna had rather large side-lobe components. In the new designed antenna the side-lobe components were reduced by modification of the antenna structure. For the steady-state operation, forced water-cooling and thermal stress were analyzed for the antenna component using the HFSS/ePhysics/ANSYS codes..
66. K. Hanada, K. Sasaki, M. Hasegawa, H. Idei, H. Zushi, K. Nakamura, M. Sakamoto, K. N. Sato, S. Kawasaki, H. Nakashima, A. Higashijima and TRIAM group, Current profile estimation using Hard X-ray measurement along the top and bottom identical line of sight on TRIAM-1M, Proc. 33rd Conference on Control Fusion and Plasma Physics, Roma, Italy (2007), 1608-1611, 2006.06, A new technique to measure the current profile in lower hybrid current drive (LHCD) plasmas by using hard X-ray (HXR) energy spectrum measurement along the top and bottom identical line of sight (ILOS) is proposed. An angle between ILOS and the magnetic filed line is out of alignment from the perpendicular by the poloidal magnetic field. As the emission cross-section of HXR strongly depends on the angle to the drift direction of energetic electrons, that is the magnetic filed line, this disagreement of the angles makes significant difference between the signals of detectors located on the top and bottom. As the result, the poloidal magnetic field is able to be derived from the difference of the HXR emission along the top and bottom ILOS. The method was applied to the full LHCD plasmas on the TRIMA-1M tokamak and the plasma current around the magnetic axis was estimated..
67. H. Zushi, T. Kuramoto, M. Sakamoto, K. Hanada, T. Sugata, N. Maezono, SSTO study with real time measurements of recycling,heat load,and co-deposition, Proc. 31th EPS Conference on Control Fusion and Plasma Physics, Vol. 28G(2004),P2-129, 2004.01.
68. H. Zushi; S. Tashima; M. Ishiguro; M. Hasegawa; S. Banerjee; N. Nishino; M. Isobe; K. Hanada; H. Idei; K. Nakamura; A. Fujisawa; Y. Nagashima; K. Matsuoka, S. K. Sharma; H. Liu; K. Toi; T. Maekawa; A. Ejiri; T. Yamaguchi;J. Hiratsuka; Y. Takase; M. Kikuchi; A. Fukuyama; Y. Ueda; O. Mitarai; S. Okamura;, Non-inductive current start-up and plasma equilibrium with an inboard poloidal field null by means of electron cyclotron waves in QUEST, Proc. 24th Int. Conf. on Fusion Energy (San Diego, CA, 2012), (※), 2012.10.
69. H. Zushi, N. Nishino, K. Hanada H. Honma, H. Q. Liu, Y. Higashizono, M. Sakamoto, Y. Nakashima, M. Ishiguro, T. Ryoukai, S. Tashima, K. Nakamura, H. Idei, M. Hasegawa, A. Fujisawa, O. Mitarai, A. Fukuyama, Takeiri, Y. Takase, T. Maekawa, Y. Kishimoto, Study of Edge Turbulence from the Open to Closed Magnetic Field Configuration during the Current Ramp-up Phase in QUEST,, Proc. 23rd IAEA Fusion Energy Conference, 11-16 October 2010 Daejon, Korea, 2012.05.
70. H. Takahashi, K. Hanada, M. Ishiguro, H. Zushi, H. Fujisawa, K. Nakamura, H. Idei, Y. Nagashima, M. Hasegawa, S. Kawasaki, H. Nakashima, A, Higashijima, Y. Takase, A. Fukuyama, O. Mitarai, X. Gao, and H. Q. Liu, Measurement of ion saturation current and floating potential profile in divertor region on QUEST, Proc. 22nd International Toki Conference, (※), 2012.11.
71. Santanu Banerjee, H. Zushi, N. Nishino, Y. Nagashima, K. Hanada, S. Tashima, T. Inoue, K. Nakamura, H. Idei, M. Hasegawa, A. Fujisawa and K. Matsuoka, Edge turbulence characteristics of the Ohmic-ECRH driven plasma current phase investigated with fast visible imaging in QUEST, Proc. 22nd International Toki Conference November 19- 22,2012, P3-32, 2012.11.
72. N. Fukumoto, K. Hanada, S. Kawakami, S. Honma, M. Nagata, N. Nishino, H. Zushi, K. Sato, K. Nakamura, H. Idei, M. Sakamoto, M. Hasegawa, S. Kawasaki, H. Nakashima, A. Higashijima, R. Bhattachayay, K. Okamoto, Y. Kikuchi, Investigation of compact toroid penetration for fuelling spherical tokamak plasmas on CPD, Proc. 22nd IAEA Fusion Energy Conference, EX/P5-7, 2008.10.
73. K. N. Sato, H. Zushi, K. Nakamura, K. Hanada, M. Sakamoto, H. Idei, M. Hasegawa, S. Kawasaki, H. Nakashima, A. Higashijima, D. Thang, F. Wang, I. Rego, K. Sasaki, H. Xu, B. Rajendraprasad, M. Ogawa, K. Takagi, K. Nakashima, S. Nishi, T. Aoki, N. Kimura, Y. Inada, Y. Nozaki, Y. Wataya, H. Sakai, M. Matsubara, S. Watanabe, K. Goto, Y. Miyoshi, N. Yoshida, K. Tokunaga, T. Fujiwara, M. Miyamoto, M. Tokitani, K. Uehara, Y. Sadamoto, Y. Nakashima, Y. Higashizono, Y. Takase, A. Ejiri, S. Kado, T. Shikama, S. Iio, T. Takeda, Y. Hirooka, T. Morisaki, Y. Nakamura, K. Toi, T. Fujimoto, A. Iwamae, T. Maekawa, M. Nagata, N. Nishino, O. Mitarai, Overview of Recent Experimental Studies on TRIAM-1M, Proc. 21th IAEA Fusion Energy Conference, (※), 2006.10.
74. K. Hanada, H. Xu, H. Idei, H. Zushi, M. Hasegawa, K. Nakamura, M. Sakamoto, K. N. Sato, S. Kawasaki, H. Nakashima, A. Higashijima and K. Sasaki, Power dependence of density and current drive efficiency in full LHCD plasmas on TRIAM-1M, Proc. 21th IAEA Fusion Energy Conference, (※), 2006.10.
75. H. Zushi, K. Hanada, H. Idei, S. Nishi, T. Maekawa, M. Azumi, A. Fukuyama, S. Kubo, T. Shimozuma, T. Notake, K. Sasaki, B. Bhattacharyay, K. Nakashima, H. Hoshika, M. Sakamoto, M. Ogawa, K. Nakamura, K. N. Sato, M. Hasegawa, S. Kawasaki, H. Nakashima, A. Higashijima, K. Toi, Y. Takase, T. Shikama, S. Kado, O. Mitarai, K. Takahashi, K. Takaki, N. Maezono, M. Kitaguch, F. Wang, H. Xu, Y. Nozaki, Y. Wataya, N. Kimura, Bi-directional Lower Hybrid Current Drive and Electron Cyclotron Counter Current Drive Experiments in Full Current Drive Plasma in TRIAM-1M, Proc. 21th IAEA Fusion Energy Conference,Chengdu,China,16-21 October 2007, (※), 2006.10, In order to investigate the spectrum gap problem in LHCD and controllability for the current profile by means of counter current drive in full current drive plasma, experiments by combination of backward (BW) propagating LHW and/or ECW have been performed in a plasma sustained by forward (FW) propagating LHW. Three ctr-CD aspects have been investigated for relativistic resonance with respect to the power ratio of backward (PBW) to forward (PFW) LHWs; 1) a clear reduction of co-ICD for PBW/PFW < 0.8; 2) a rapid positive change in co-ICD and broadening in j(r) for PBW/PFW > 0.8 [H. Zushi et al., Nucl. Fusion 41 (2001) 1483]; and 3) a large positive change in co-ICD by ctr ECW into FW LHCD plasma and further changes to negative value in co-ΔICD depending on PBW/PFW of LHW..
76. Xiaolong Liu, Kazuo Nakamura, Tatsuya Yoshisue, Osamu Mitarai, Makoto Hasegawa, Kazutoshi Tokunaga, Hideki Zushi, Kazuaki Hanada, Akihide Fujisawa, Hiroshi Idei, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Kuniaki Araki, Study of Matrix Converter as Stabilizing Power Supply for Vertical Position Instability on QUEST Tokamak, Proc. 2011 Annual Conference of I.E.E. of Japan,Industry Applications Society,Okinawa,Sept. 6-8,2011, (※), 2011.09.
77. Y. Takase, S. Ide, S. Itoh, O. Mitarai, O. Naito, T. Ozeki, Y. Sakamoto, S. Shiraiwa, T. Suzuki, S. Tanaka, T. Taniguchi, M. Aramasu, T. Fujita, T. Fukuda, X. Gao, M. Gryaznevich, K. Hanada, E. Jotaki, Y. Kamada, T. Maekawa, Y. Miura, K. Nakamura, T. Nis, Formation of An Advanced Tokamak Plasma without the Use of Ohmic Heating Solenoid in JT-60U, Proc. 19th IAEA Fusion Energy Conference, IAEA-CN-94/PD/T-2, 2002.10.
78. K. Hanada, M. Hasegawa, K. Shinohara, S. Ohdach, et al. (Total 52), Investigation of Causality in H-L Transition on the JFT-2M Tokamak, Proc. 16th IAEA Fusion Energy Conference,Montreal (Canada),Vol.1 885-890,1996, 885.0-890.0, 1996.01.
79. Y. Miura, Y. Asahi, K. Hoshino, K. Ida, Y. Ishige, S. Kasai, T. Kawakami, H. Kawashima, K. Maeno, K. Nagashima, K. Ohasa, H. Ogawa, T. Ogawa, M. Sasaki, M. Sato, M. Sengoku, T. Shina, K. Hanada, K. Shinohara, S. Shiraiwa, A. Shoji, N. Suzuki, K. Uehara, T. Yamauchi, K. HAsegawa,, Divertor Biasing effects to Reduce L/H Power Threshold in the JFT-2M Tokamak, Proc. 16th IAEA Fusion Energy Conference,Montreal (Canada),Vol.1,167-175,(1996), (※), 1996.01.
80. H. Toyama, K. Hanada, K. Yamagishi, T. Oikawa, K. Shinohara, H. Totsuka, E. Ishiyama, H. Saito, S. Shiraiwa, M. HAsegawa, I. Nakajima, M. Ushigome, Helicity Injection Experiments and Turbulence Measurements on the Spherical Tokamak TST, Proc. 16th IAEA Fusion Energy Conference,Montreal (Canada),Vol.2 223-228,1996, 1996.01.
81. H. TOYAMA, S. OHDACHI, K. HANADA, K. SHINOHARA, T. OIKAWA, K. NOZAWA, H. TOTSUKA, E. ISHIYAMA, N. SHINODA, K. YAMAGISHI, T. SHOJI, H. TAMAI, K. HOSHINO, Y. MIURA, K. NAGASHIMA, H. KAWASHIMA, T. MATSUDA, H. OGAWA, M. MAENO, T. YAMAUCHI, K. UEHARA, T. SHHNA, S. SENGOKU, M. SATO, M. SASAKI, T. OGAWA, K. OASA, M. MORI, T. KAWAKAMI, S. KASAI, Y. ASAHI, H. AIKAWA, K. HASEGAWA, A. HONDA, Y. KASHIWA, K. KIKUCHI, F. OKANO, M. KOMATA, M. SAITO, E. SATO, M. SAWAHATA, N. SEKI, T. SHIBATA, N. SUZUKI, S. SUZUKI, T. TANAKA, T. TANI, T. TOKUTAKE, Y. TOMIYAMA, K. UMINO, H. MAEDA, Observation of turbulence suppression and transport reduction in the presence of sheared flow, Proc. 15th Intern. Conf. on Plasma Physics and Controlled Nuclear Fusion Research,Vol.1 575-581 (1994), 575.0-581.0, 1994.01.
82. Y. Terumichi, T. Maekawa, K. Hanada, S. Yoshimura, T. Maehara, S. Tabuchi, K. Nakamura, T. Iinuma, M. Nakamura, Control of MHD Activitys by ECH in the WT-3 Tokamak, Proc. 15th Intern. Conf. on Plasma Physics and Controlled Nuclear Fusion Research,Vol.2 189-196 (1994), 2.0, 189.0-195.0, 1994.01, A tearing mode with a poloidal mode number m = 2 and a toroidal mode number n = 1 can be suppressed by second harmonic electron cyclotron heating (ECH) on the q = 1 surface as well as on the q = 2 surface. Furthermore, sawtooth oscillations are modified by ECH on the q = 2 surface as well as on the q = 1 surface. Both results suggest that the mode coupling between the m = 1/r = 1 mode on the q = 1 surface and the m = 2/n = 1 mode on the q = 2 surface significantly overall affects the MHD activities..
83. H. TAMAI, T. SHOJI, Y. MIURA, K. NAGASHIMA, H. KAWASHIMA, T. MATSUDA, H. OGAWA, M. MAENO, T. YAMAUCHI, K. UEHARA, T. SHIINA, S. SENGOKU, M. SATO, M. SASAKI, T. OGAWA, K. OASA, M. MORI, H. MAEDA, T. KAWAKAMI, S. KASAI, K. HOSHINO, Y. ASAHI, H. AIKAWA, K. HASEGAWA, A. HONDA, Y. KASHIWA, K. KIKUCHI, F. OKANO, M. KOMATA, M. SAITO, E. SATO, M. SAWAHATA, N. SEKI, T. SHIBATA, N. SUZUKI, S. SUZUKI, T. TANAKA, T. TANI, T. TOKUTAKE, Y. TOMIYAMA, K. UMINO, H. TOYAMA, K. SHINOHARA, K. HANADA, N. OHYABU, S. OHDACHI, K. IDA, H. AMEMIYA, B. M. ANNARATONE, K. HOTHKER, ELM Control and Boundary Plasma Modification in the JFT-2M Tokamak, Proc. 15th Intern. Conf. on Plasma Physics and Controlled Nuclear Fusion Research,Vol.1 137-143 (1994), 137.0-144.0, 1994.09, Boundary plasmas around the separatrix are controlled by the application of an ergodic magnetic field and divertor biasing. ELMs in the quasi-steady-state H mode are controlled by the application of an ergodic field. ELMs are eliminated when the resonance with the effective ergodic field is far from the pedestal. ELM characteristics are affected by the safety factor qs, leading either to small and frequent ELMs with relatively low heat load on the divertor plates, or to large ELMs with higher flux and with more effective impurity exhaust. Divertor biasing controls the in-out asymmetry of heat and particle fluxes onto the divertor plates. Depending on the SOL current direction between inside and outside plates, the electron density at the ion side divertor and the electron temperature at the electron side are strongly influenced..
84. Xiaolong Liu, Kazuo Nakamura, Tatsuya Yoshisue, Osamu Mitarai, Makoto Hasegawa, Kazutoshi Tokunaga, Erbing Xue, Hideki Zushi, Kazuaki Hanada, Akihide Fujisawa, Hiroshi Idei, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Kuniaki Araki, Optimal Control on Plasma Vertical Position Instability in QUEST, Proc. 13th Cross Straits Symposium,Kyushu University,Fukuoka,Nov.,2011, 31.0-21.0, 2011.11.
85. Y. Terumichi, S. Tanaka, T. Maekawa, H. Tanaka, S. Ide, M. Iida, Kazuaki Hanada, T. Minami, M. Yoshida, T. Fukino, K. Ogura, M. Nakamura, T. Fujimoto, H. Suemitsu, Electron cyclotron lower hybrid current drive and heating on the WT-3 tokamak, Proc 13 Int Conf Plasma Phys Controlled Nucl Fusion Res, 777-782, 1991.01, A 70 kA (qm = 5) flat-top discharge and a 120 kA (qm = 3.6) flat-top discharge with zero loop voltage are realized by 2Ωe electron cyclotron current drive (ECCD) and lower hybrid current drive (LHCD), respectively. The figure of merit of current drive is 0.03-0.06 (1019 A·W-1·m-2) for ECCD and 0.3-0.6 for LHCD. 2Ωe ECH at the q(r) = 1 surface on the high field side of the midplane is more effective in stabilizing sawteeth than on the low field side. LHCD can stabilize sawteeth, m = 1 and m = 2 MHD activities. In the full LHCD discharge, there are no sawtooth, m = 1 and m = 2 MHD activities..
86. Wang, F; Nakamura, K; Mitarai, O; Kurihara, Kenichi; Kawamata, Yoichi; Sueoka, Michiharu; Sato, KN; Zushi, H; Hanada, K; Sakamoto, M;, Plasma Shape Reconstruction of Spherical Tokamak using CCS Method, Plasma and Fusion Research, 2.0, RA, Article No. S1095, 2007.01.
87. Haiqing LIU, Kazuaki HANADA, Nobuhiro NISHINO, Ryota OGATA, Masaki ISHIGURO, Hideki ZUSHI, Kazuo NAKAMURA, Mizuki SAKAMOTO, Hiroshi IDEI, Makoto HASEGAWA, Yuta HIGASHIZONO, Shoji KAWASAKI, Hisatoshi NAKASHIMA, Aki HIGASHIJIMA and QUEST GROUP, Measurement of Blob-Like Structures in Plasma with a Langmuir Probe and Fast Camera on QUEST, Plasma and Fusion Research, https://doi.org/10.1585/pfr.5.S2077, 5.0, RA, Article No. S2077, 2010.12, This paper presents a scheme for combining a Langmuir probe with a fast camera for measurement of the behavior of blob-like structures in the boundary region of an electron cyclotron resonance (ECR) heating plasma in Q-shu University Experiment with a Steady-State Spherical Tokamak (QUEST, major radius, R = 0.68 m, minor radius, a = 0.40 m, and toroidal magnetic field, Bt = 0.25 T at R = 0.64 m). The frame rate of the camera was typically set to 40,000 frames per second (FPS) with 192 × 144 pixels per frame. Radial motion of blob-like structures was observed in the half of the plasma space where the probe head was located. A radially movable and rotatable probe system was used to measure the floating potential from single unbiased tips, the potential of the positively biased tip, and the ion saturation current in two orthogonal directions in the outboard midplane region. Time series of the ion saturation current measured by the Langmuir probe and of pixels in a 40,000 FPS movie were compared and cross-correlated. The results of the two diagnostics agreed well, and the spatial scale was found to be of the same as the size of the probe head. The ion saturation current was asymmetric in terms of the time the blob-like structure was passing; fast camera imaging also clearly demonstrated the blobs' filamentary structures and radial motion at the edge of QUEST. This means that plasma in the blob-like structure hunches over, like blobs in other devices. The typical radial velocity of the structures is ∼1 km/s, and the structures were accelerated along their path of radial motion from the inner to the outer parts of the vacuum vessel..
88. Xiaolong LIU, Kazuo NAKAMURA, Yi JIANG, Tatsuya YOSHISUE, Osamu MITARAI, Makoto HASEGAWA, Kazutoshi TOKUNAGA, Hideki ZUSHI, Kazuaki HANADA, Akihide FUJISAWA, Hiroshi IDEI, Shoji KAWASAKI, Hisatoshi NAKASHIMA, Aki HIGASHIJIMA and Kuniaki ARAKI, Study of Matrix Converter as a Current-Controlled Power Supply in QUEST Tokamak, Plasma and Fusion Research, 6.0, RA, 5.0, Article No. 2405137, 2011.10, Because QUEST tokamak has a divertor configuration with a higher κ and a negative n-index, a precise power supply with a rapid response is needed to control the vertical position of the plasma. A matrix converter is a direct power conversion device that uses an array of controlled bidirectional switches as the main power elements for creating a variable-output current system. This paper presents a novel three-phase to two-phase topological matrix converter as a proposed power supply that stabilizes the plasma vertical position and achieves unity input power factor. An indirect control strategy in which the matrix converter is split into a virtual rectifier stage and a virtual inverter stage is adopted. In the virtual rectifier stage, the instantaneous active power and reactive power are decoupled on the basis of system equations derived from the DQ transformation; hence, unity power factor is achieved. Space vector pulse width modulation is adopted to determine the switching time of each switch in the virtual rectifier; the output voltage of the virtual rectifier is adjusted by the virtual inverter stage to obtain the desired load current. Theoretical analyses and simulation results are provided to verify its feasibility..
89. Saya TASHIMA, Hideki ZUSHI, Mitsutaka ISOBE, Hiroshi IDEI, Shoichi OKAMURA, Kazuaki HANADA, Kazuo NAKAMURA, Akihide FUJISAWA, Keisuke MATSUOKA, Makoto HASEGAWA, Yoshihiko NAGASHIMA, Shoji KAWASAKI, Hisatoshi NAKASHIMA, Aki HIGASHIJIMA and QUEST Team, Non-Inductive Current Drive by EC Waves in an Inboard Poloidal Magnetic Field Null Configuration on the Spherical Tokamak QUEST, Plasma and Fusion Research, https://doi.org/10.1585/pfr.8.2402118, 8.0, RA, 5.0, Article No. 2402118, 2013.09, To investigate the effects of confinement of fast electrons on poloidal beta equilibrium, experiments under different toroidal magnetic mirror ratios, MOMFC, were performed in electron cyclotron heated plasma in the spherical tokamak QUEST. The proportional constants of the relation between plasma current and vertical magnetic fields decreased with increase in MOMFC. The poloidal field null point appeared in the chamber for MOMFC > 1.8 at a plasma current value of ∼15 kA. Poloidal beta and temperature of hard X-rays increased with MOMFC. This suggests that high poloidal beta equilibrium plasma is produced by better confinement of energetic trapped particles..
90. Kishore MISHRA, Hideki ZUSHI, Hiroshi IDEI, Saya TASHIMA, Santanu BANERJEE, Makoto HASEGAWA, Kazuaki HANADA, Kazuo NAKAMURA, Akihide FUJISAWA, Yoshihiko NAGASHIMA, Keisuke MATSUOKA, Arseny KUZMIN, Takumi ONCHI and QUEST Team, Analytical Solution of High βp Equilibria with Natural Inboard Poloidal Null Configuration Obtained in the Spherical Tokamak QUEST, Plasma and Fusion Research, 10.1585/pfr.9.3402093, 9.0, RC, 5.0, Article No. 3402093, 2014.07, High βp (εβp ∼ 1) equilibria obtained in a ECW heated Ohmic plasma is investigated using a simple analytic solution of Grad-Shafranov equation. The formation of a natural inboard poloidal null associated with high βp is explained consistently by high diamagnetism and negative triangularity. As βp is increased, the poloidal null point penetrates further into the vacuum vessel, which is qualitatively explained by the analytic model. Transition from inboard (high field side) limiter bound to the natural divertor configuration is associated with a reduction of the edge safety factor without appreciable enhancement of MHD activities. Such a scenario is also addressed successfully with the model..
91. Kengoh Kuroda, Roger Raman, Kazuaki Hanada, Makoto Hasegawa, Takumi Onchi, Masayuki Ono, Thomas Jaboe, Brian A. Nelson, Masayoshi Nagata, Osamu Mitarai, Kazuo Nakamura, Hiroshi Idei, John Rogers, Shoji Kawasaki, Takahiro Nagata, Arseniy Kuzmin, Shinichiro Kojima, Osamu Watanabe, Aki Higashijima, Yuichi Takase, Atsushi Fukuyama, Current start-up using the new CHI system, Plasma and Fusion Research, 10.1585/pfr.12.1202020, 12, 2017.01, [URL], Coaxial Helicity Injection (CHI) has now been implemented in QUEST. The goals for the first transient CHI experiments were to establish reliable gas breakdown conditions, and to measure CHI-produced toroidal current generation. Both these objectives were successfully met. Toroidal currents up to 29 kA were measured. Interestingly, these first plasmas on QUEST also suggest the formation of small amounts of closed magnetic flux surfaces..
92. Yue Xu, Arseniy Kuzmin, Yoshi Hirooka, Kazuaki Hanada, Kazuaki Hanada, Hydrogen permeation through sputter-deposited tungsten coated F82H in QUEST, Plasma and Fusion Research, 10.1585/pfr.12.1305038, 12, 2017.01, [URL], Hydrogen plasma-driven permeation (PDP) experiments have been performed using a sputter-deposited tungsten (SP-W) coated F82H membrane in the spherical tokamak QUEST. It has been found that SP-W coatings tend to enhance hydrogen PDP compared with that of bare F82H membrane. Surface recombination is a key process determining the PDP flux, suggesting that surface effects on hydrogen PDP should be further investigated..
93. Hiroki Miura, Kazuaki Hanada, Hideki Zushi, Kazuo Nakamura, akihide fujisawa, Hiroshi Idei, Yoshihiko Nagashima, Makoto Hasegawa, Hisatoshi Nakashima, Shoji Kawasaki, Aki Higashijima, Osamu Mitarai, Atsushi Fukuyama, Yuichi Takase, Comparison between non-inductive plasma current start-up using ECRH with and without fundamental resonance on QUEST, Plasma and Fusion Research, 10.1585/pfr.10.3402066, 10, 2015.01, [URL], Comparison between non-inductive plasma current start-up using electron cyclotron resonance heating (ECRH) with and without fundamental (1st) resonance using 8.2-GHz microwave is experimentally performed on QUEST. Results of soft X-ray measurements in different energy ranges indicate significant difference in the number of current-carrying electrons with and without fundamental resonance. Numerical calculations show effective extendibility of electron energy in ECRH of fundamental resonance..
94. Yueng Kay Martin Peng, Akio Ishida, Yuichi Takase, Akira Ejiri, Naoto Tsujii, Takashi Maekawa, Masaki Uchida, Hideki Zushi, Kazuaki Hanada, Makoto Hasegawa, Two-Fluid Equilibrium Considerations of Te/Ti » 1, Collisionless ST Plasmas Sustained by RF Electron Heating, Plasma and Fusion Research, 10.1585/pfr.9.3403146, 9, SpecialIssue2, 2014.01, [URL], A solution of two-fluid (electron and ion), axisymmetric equilibrium is presented that approximates solenoidfree plasmas sustained only by RF electron heating that are recently studied in TST-2, LATE, QUEST. These plasmas indicate presence of orbit-confined energetic electrons carrying substantial toroidal current outside the last closed flux surface (LCFS); Te/Ti » 1 and low collisionality at modest densities within LCFS; and likely a positive plasma potential relative to the conductive vacuum vessel. A system of nonlinear second-order partial differential and algebraic equations constraining six functionals of poloidal magnetic flux or canonical angular momentum are solved. An example plasma measured in TST-2 is used to guide, by trial and error, the selection of these functionals to find appropriate solutions, while assuming peaked plasma profiles and 60% toroidal current within the LCFS. The numerical equilibrium obtained indicates a substantial ion toroidal flow and electrostatic potential so that the ion ∇pi, centrifugal, and electrostatic forces of nearly equal magnitudes combine to balance the Ji × B force, differently from the massless electron fluid that satisfies ∇pe = Je × B. The calculated properties suggest additional measurements needed to refine the choices of the functional forms and improve the two-fluid equilibrium fit to such plasmas..
95. , Saya Tashima, Hideki Zushi, Mitsutaka Isobe, Hiroshi Idei, Hiroshi Idei, Kazuaki Hanada, Kazuaki Hanada, Akihide Fujisawa, akihide fujisawa, Makoto Hasegawa, Makoto Hasegawa, Yoshihiko Nagashima, Hisatoshi Nakashima, Aki Higashijima, Non-inductive current drive by EC waves in an inboard poloidal magnetic field null configuration on the spherical tokamak QUEST, Plasma and Fusion Research, 10.1585/pfr.8.2402118, 8, 2013.01, [URL], To investigate the effects of confinement of fast electrons on poloidal beta equilibrium, experiments under different toroidal magnetic mirror ratios, MOMFC, were performed in electron cyclotron heated plasma in the spherical tokamak QUEST. The proportional constants of the relation between plasma current and vertical magnetic fields decreased with increase in MOMFC. The poloidal field null point appeared in the chamber for MOMFC > 1.8 at a plasma current value of ~15 kA. Poloidal beta and temperature of hard X-rays increased with MOMFC. This suggests that high poloidal beta equilibrium plasma is produced by better confinement of energetic trapped particles..
96. Santanu Banerjee, Hideki Zushi, Nobuhiro Nishino, Yoshihiko Nagashima, Kazuaki Hanada, Saya Tashima, Tsubasa Inoue, Kazuo Nakamura, Hiroshi Idei, Makoto Hasegawa, akihide fujisawa, Keisuke Matsuoka, Turbulence velocimetry of tangential fast imaging data on QUEST, Plasma and Fusion Research, 10.1585/pfr.8.2402098, 8, 2013.01, [URL], A particle image velocimetry technique based on orthogonal dynamic programming is developed to measure the time resolved flow field of the fluctuating structures at the plasma edge and scrape off layer. This nonintrusive technique can provide two dimensional velocity fields at high spatial and temporal resolution from a fast framing image sequence and hence can provide better insights in plasma flow as compared to conventional probe measurements. Applicability of the technique is tested with simulated image pairs. Finally, it is applied to tangential fast visible images of QUEST as a test case to estimate the scrape off layer flow in Ohmic and ECRH driven plasma discharges..
97. Hiroshi Idei, Hideki Zushi, Kazuaki Hanada, Evgeniya Kalinnikova, Kazuo Nakamura, akihide fujisawa, Yoshihiko Nagashima, Makoto Hasegawa, Keisuke Matsuoka, Tsuyoshi Kariya, Tsuyoshi Imai, Ryutaro Minami, Naoaki Yoshida, Mizuki Sakamoto, Hideo Watanabe, Kazutoshi Tokunaga, Akira Ejiri, Masatsugu Sakaguchi, Masaki Ishiguro, Saya Tashima, Atsushi Fukuyama, Hiroe Igami, Shin Kubo, Mitsutaka Isobe, Kenichi Nagaoka, Hideya Nakanishi, Nobuhiro Nishino, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Yuichi Takase, Takashi Maekawa, Osamu Mitarai, Mitsuru Kikuchi, Kazuo Toi, ECW/EBW heating and current drive experiment results and prospects for CW operation in QUEST, Plasma and Fusion Research, 10.1585/pfr.7.2402112, 7, SPL.ISS.1, 2012.12, [URL], A CW phased-array antenna system for electron cyclotron/Bernstein wave heating and current drive (ECWH/CD, EBWH/CD) experiments was developed in the QUEST. The antenna was designed to excite an elliptically polarized pure O-mode wave in oblique injection for the O-X-B mode conversion scenario, and its good performance was confirmed at a high power level. Long pulse discharges with a plasma current of 10 kA and 15 kA were non-inductively attained for 37 s and 20 s, respectively, with only radio frequency (RF) power. Divertor configurationswere also obtained in the RF-sustained plasmas. A new operational window for sustained plasma current was observed in the high-density plasma with a higher RF incident power. Two new heating and current drive systems with an 8.56GHz klystron and a 28GHz gyrotron are being prepared to conduct CW EBWH/CD experiments in the high-density plasma..
98. Osamu Mitarai, Kazuo Nakamura, Saya Tashima, Makoto Hasegawa, Hiroshi Idei, Mizuki Sakamoto, Kazuaki Hanada, Hideki Zushi, Kohnosuke Sato, Masaki Ishiguro, Hai Qing Liu, Yuta Higashizono, Aki Higashijima, Hisatoshi Nakashima, Shoji Kawasaki, Yuichi Takase, Takashi Maekawa, Nobuhiro Nishino, First ohmic discharge assisted with RF power in QUEST spherical tokamak, Plasma and Fusion Research, 10.1585/pfr.6.1402003, 6, 2011, 2011.12, [URL], Ohmic plasma currents of up to 17 kA with a discharge duration of 0.32 s have been obtained in the Kyushu University Experiment with Steady-State Spherical Tokamak (QUEST) with the help of electron cyclotron wave (ECW) and cancellation coils (CCs). The CCs, originally installed to create a field null in the plasma breakdown phase, are essential for producing plasma current in QUEST. Although the ohmic coil current is initially biased and then reduced completely to zero to induce the plasma current in 15-20 ms, we demonstrate that the flat top of the plasma current exceeding 20 ms is maintained by the vertical field after the ohmic current is switched off. This type of operation is quite favorable for extending pulsed operation to the steady state by electron Bernstein wave current drive (EBCD)..
99. Xiaolong Liu, Kazuo Nakamura, Yi Jiang, Tatsuya Yoshisue, Osamu Mitarai, Makoto Hasegawa, Kazutoshi Tokunaga, Hideki Zushi, Kazuaki Hanada, akihide fujisawa, Hiroshi Idei, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Kuniaki Araki, Study of matrix converter as a current-controlled power supply in QUEST tokamak, Plasma and Fusion Research, 10.1585/pfr.6.2405137, 6, 1 SPECIAL ISSUE, 2011.12, [URL], Because QUEST tokamak has a divertor configuration with a higher κ and a negative n-index, a precise power supply with a rapid response is needed to control the vertical position of the plasma. A matrix converter is a direct power conversion device that uses an array of controlled bidirectional switches as the main power elements for creating a variable-output current system. This paper presents a novel three-phase to two-phase topological matrix converter as a proposed power supply that stabilizes the plasma vertical position and achieves unity input power factor. An indirect control strategy in which the matrix converter is split into a virtual rectifier stage and a virtual inverter stage is adopted. In the virtual rectifier stage, the instantaneous active power and reactive power are decoupled on the basis of system equations derived from the DQ transformation; hence, unity power factor is achieved. Space vector pulse width modulation is adopted to determine the switching time of each switch in the virtual rectifier; the output voltage of the virtual rectifier is adjusted by the virtual inverter stage to obtain the desired load current. Theoretical analyses and simulation results are provided to verify its feasibility..
100. Haiqing Liu, Kazuaki Hanada, Nobuhiro Nishino, Ryota Ogata, Masaki Ishiguro, Hideki Zushi, Kazuo Nakamura, Mizuki Sakamoto, Hiroshi Idei, Makoto Hasegawa, Yuta Higashizono, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Measurement of blob-like structures in plasma with a Langmuir probe and fast camera on QUEST, Plasma and Fusion Research, 10.1585/pfr.5.S2077, 5, 2010.01, [URL], This paper presents a scheme for combining a Langmuir probe with a fast camera for measurement of the behavior of blob-like structures in the boundary region of an electron cyclotron resonance (ECR) heating plasma in Q-shu University Experiment with a Steady-State Spherical Tokamak (QUEST, major radius, R = 0.68 m, minor radius, a = 0.40 m, and toroidal magnetic field, Bt = 0.25T at R = 0.64 m). The frame rate of the camera was typically set to 40,000 frames per second (FPS) with 192 ×144 pixels per frame. Radial motion of blob-like structures was observed in the half of the plasma space where the probe head was located. A radially movable and rotatable probe system was used to measure the floating potential from single unbiased tips, the potential of the positively biased tip, and the ion saturation current in two orthogonal directions in the outboard midplane region. Time series of the ion saturation current measured by the Langmuir probe and of pixels in a 40,000 FPS movie were compared and cross-correlated. The results of the two diagnostics agreed well, and the spatial scale was found to be of the same as the size of the probe head. The ion saturation current was asymmetric in terms of the time the blob-like structure was passing; fast camera imaging also clearly demonstrated the blobs' filamentary structures and radial motion at the edge of QUEST. This means that plasma in the blob-like structure hunches over, like blobs in other devices. The typical radial velocity of the structures is ~1km/s, and the structures were accelerated along their path of radial motion from the inner to the outer parts of the vacuum vessel..
101. Mizuki Sakamoto, Yuta Higashizono, Hideki Zushi, Kazuo Nakamura, Kazuaki Hanada, Hiroshi Idei, Makoto Hasegawa, Younosuke Nakashima, Masayuki Tokitani, Mitsutaka Miyamoto, Kazutoshi Tokunaga, Shoji Kawasaki, Hisatoshi Nakashima, Tadashi Fujiwara, Aki Higashijima, Naoaki Yoshida, Kohnosuke Sato, Plasma-wall interaction study towards the steady state operation, Plasma and Fusion Research, 10.1585/pfr.5.S2009, 5, 2010.01, [URL], Various phenomena of plasma-wall interactions during long duration discharges in TRIAM-1M are investigated from macroscopic and microscopic viewpoints. It is found that the density dependence of the hydrogen neutral flux decay length is not very sensitive to the density (i.e. ne-0.2 ). Neutral transport through the scrape-off layer is important for structural formation of hydrogen recycling. The hydrogen retention in the co-deposited layer, which was obtained using a material probe during long duration discharges, is consistent with the global wall pumping rate estimated from particle balance analysis. The wall temperature and co-deposition play important roles on hydrogen re-emission and hydrogen absorption, respectively. Oxygen impurities should affect the erosion and deposition properties of the plasma-facing wall as well as the hydrogen retention property of the co-deposited layer. The co-deposition of hydrogen with molybdenum and the oxygen impurities both play important roles in the hydrogen recycling..
102. Masaki Ishiguro, Kazuaki Hanada, Kazuo Nakamura, Osamu Mitarai, Hideki Zushi, Hiroshi Idei, Mizuki Sakamoto, Makoto Hasegawa, Yuta Higashizono, Yuichi Takase, Takashi Maekawa, Yasuaki Kishimoto, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Reconstruction of vacuum magnetic flux in QUEST, Plasma and Fusion Research, 10.1585/pfr.5.S2083, 5, 2010.01, [URL], It is important to determine the best method for reconstructing the magnetic flux when eddy currents are significantly induced during magnetic measurement in spherical tokamaks (STs). Four methods for this reconstruction are investigated, and the calculated magnetic fluxes are compared to those measured in the cavity of a vacuum vessel. The results show that the best method is the one that uses currents from virtual coils for reconstruction. In this method, the placement of the virtual coils is optimized with numerical simulations using the Akaike information criterion (AIC), which indicates the goodness of fit of models used to fit measured data. The virtual coils are set on a line 15 cm outside the vacuum vessel..
103. Kazuaki Hanada, Kohnosuke Sato, Hideki Zushi, Kazuo Nakamura, Mizuki Sakamoto, Hiroshi Idei, Makoto Hasegawa, Yuichi Takase, Osamu Mitarai, Takashi Maekawa, Yasuaki Kishimoto, Masaki Ishiguro, Tomokazu Yoshinaga, Hiroe Igami, Nobuhiro Nishino, Hiroshi Honma, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Yuta Higashizono, Akira Ando, Nobuyuki Asakura, Akira Ejiri, Yoshihiko Hirooka, Akio Ishida, Akio Komori, Makoto Matsukawa, Osamu Motojima, Yuichi Ogawa, Noriyasu Ohno, Yasushi Ono, Martin Peng, Shigeru Sudo, Hiroshi Yamada, Naoaki Yoshida, Zensho Yoshida, Steady-state operation scenario and the first experimental result on QUEST, Plasma and Fusion Research, 10.1585/pfr.5.S1007, 5, 2010.01, [URL], QUEST focuses on the steady state operation of the spherical tokamak by controlled PWI and electron Bernstein wave current drive. One of the main purposes of QUEST is an achievement of long duration discharge with MW-class injected power. As the result, QUEST should be operated in the challenging region on heat and particle handling. To do the particle handling, high temperature all metal wall up to 623K and closed divertors are planned, which is to realize the steady-state operation under recycling ratio, R = 1. This is a dispensable check to DEMO, because wall pumping should be avoided as possible in the view of tritium retention. The QUEST project will be developed in increment step such as, I. low β steady state operation in limiter configuration, II. low β steady state operation in divertor configuration, III. relatively high β steady state operation in closed divertor configuration. Phase I in the project corresponds to these two years, and final goal of phase I is to make full current drive plasma up to 20 kA. Closed divertor will be designed and tested in the Phase II. QUEST is running from Oct., 2008 and the first results are introduced..
104. Tetsushi Kikukawa, Hideki Zushi, Tomohiro Morisaki, Rajendraprasad Bhattacharyay, Tomofumi Ryoukai, Tomokazu Yoshinaga, Makoto Hasegawa, Kazuaki Hanada, Hiroshi Idei, Experimental Group CPD Experimental Group, Visualization of magnetic surfaces during current ramp-up phase using thermal lithium sheet beam in CPD, Plasma and Fusion Research, 10.1585/pfr.3.010, 3, 2008.01, [URL], Two dimensional electron density profile measurement has been performed in the spherical tokamak CPD (Compact PWI experimental Device) using Li sheet beam imaging technique. The topological change from the open magnetic field line configuration to the closed one is visualized by this technique. The plasma current can be driven by RF waves itself in a weak mirror configuration and a clear change is observed in plasma boundary as well as magnetic field topology associated with the transition of the current from low (~1 kA) to high (~3kA) value..
105. N. Nishino, T. Mizuuchi, Z. Feng, S. Kobayashi, K. Nagasaki, H. Okada, F. Sano, K. Kondo, Y. Nakashima, Y. Higashizono, H. Kawano, T. Cho, M. Shoji, K. Sasaki, Kazuaki Hanada, H. Zushi, 2-D image diagnostic technique for edge turbulence using fast cameras, Plasma and Fusion Research, 10.1585/pfr.2.S1055, 2, 2007.01, [URL], Fast cameras are powerful tool to visualize the edge turbulence in peripheral plasmas. Under Bi-directional collaborations recently in Heliotron J and GAMMA10 filamentary structures along the magnetic field line were firstly observed with GPI (gas puff imaging) by fast camera. In both machines the filamentary structures had similar stripe pattern in the images and simultaneous measurements of the ion saturation current by electrostatic probes show that the filamentary structures were relatively higher electron density/temperature regions in peripheral plasmas. It is not sufficient to conclude both filamentary structures are the same, however, these phenomena were thought to be related to the energy confinement. Thus the physics mechanism should be solved in the near future..
106. Kazuaki Hanada, Keisuke Sasaki, Makoto Hasegawa, Hiroshi Idei, Hideki Zushi, Kazuo Nakamura, Mizuki Sakamoto, Konosuke Sato, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, group Triam group, Current profile estimation in full LHCD plasmas using hard X-ray measurement along the top and bottom identical line of sight on TRIAM-1M, Plasma and Fusion Research, 10.1585/pfr.2.S1071, 2, 2007.01, [URL], A new technique to measure the current profile in plasmas with asymmetric distribution function such as lower hybrid current drive (LHCD) by using hard X-ray (HXR) energy spectrum measurement along the top and bottom identical line of sights (ILOS) is proposed and is applied to the full and partially LHCD plasmas on the TRIAM-1M tokamak at the first time in the world. The pitch angles were measured at R - R
0
= ±2.5cm, where R, R
0
mean the major radii of the ILOS and the magnetic axis, respectively. The measured pitch angle of the magnetic field inverted at the magnetic axis estimated magnetic measurement in partially LHCD plasmas. This indicates that the difference of the measured pitch angles is caused by the plasma current in the plasma and this new method is available in detecting the current profile in tokamaks. In full LHCD plasma, no difference between the HXR signals along the top and bottomILOS appear. This indicates that the current density around the magnetic axis was reduced compared with that in partially LHCD plasmas. This observation is no contradiction with power deposition of LHCD..
107. F. Wang, K. Nakamura, O. Mitarai, K. Kurihara, Y. Kawamata, M. Sueoka, K. N. Sato, H. Zushi, Kazuaki Hanada, M. Sakamoto, Hiroshi Idei, Makoto Hasegawa, S. Kawasaki, H. Nakashima, A. Higashijima, Plasma shape reconstruction of spherical tokamak using CCS method, Plasma and Fusion Research, 10.1585/pfr.2.S1095, 2, 2007.01, [URL], Plasma shape reconstruction is important for plasma control of tokamak. Cauchy-Condition Surface (CCS) method is a numerical approach to reproduce plasma shape which has good precision in conventional tokamak. In order to apply it in the plasma shape reproduction of Compact PWI experimental Device (CPD) which is a new spherical tokamak in Kyushu University, the calculation precision of CCS method in CPD is analyzed in the paper..
108. Makoto Hasegawa, Kazuaki Hanada, Kohnosuke Sato, Kazuo Nakamura, Hideki Zushi, Mizuki Sakamoto, Hiroshi Idei, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Townsend avalanche breakdown assisted by radio frequency wave in tokamaks, Plasma and Fusion Research, 10.1585/pfr.2.007, 2, 2007.01, [URL], A simple model of radio frequency wave (RF) assisted breakdown based on Townsend avalanche theory is proposed for the purpose of evaluating the effect of RF on Townsend avalanche breakdown. According to this model, the required minimum electric field for RF-assisted breakdown can be decreased down to half of that for breakdown by the induction electric field alone. The electric field of RF reaches a minimum when the frequency of the RF is equal to the electron cyclotron frequency..
109. Hatem Elserafy, Kazuaki Hanada, Kengoh Kuroda, Hiroshi Idei, Ryota Yoneda, Canbin Huang, Shinichiro Kojima, Makoto Hasegawa, Yoshihiko Nagashima, Takumi Onchi, Ryuya Ikezoe, Aki Higashijima, Takahiro Nagata, Shoji Kawasaki, Shun Shimabukuro, Nicola Bertelli, Masayuki Ono, HFS injection of X-mode for EBW conversion in QUEST, Plasma and Fusion Research, 10.1585/pfr.14.1205038, 14, 1, 2019.01, [URL], High field side (HFS) injection of eXtra-ordinary X-mode for electron Bernstein wave (EBW) conversion was conducted in the QUEST tokamak. Radio frequency (RF; 8.2 GHz) power was delivered from the low field side (LFS) to the high field side HFS through waveguides, and from the HFS placed 20 cm above the midplane of the vacuum vessel. The aim was to compare the RF launches from the LFS and HFS. The plasma brightness, measured by a fast camera, as well as the H
α
signal captured along the mid-plane, was noticeably higher in the HFS launch than in the LFS launch. The HFS injection achieved a plasma current of approximately 130 A, versus 35A in the LFS injection. The electron density n
e
predicted from the position of the upper hybrid resonance agreed with the line-averaged n
e
measured by an interferometer, confirming the effective conversion and subsequent damping of the EBW mode. The RF leakage of the HFS injection was less than one-sixth that of the LFS injection. These results indicate that HFS delivers better RF coupling and conversion efficiency to EBW than LFS injection. Such efficient plasma heating via EBW will significantly enhance the plasma production..
110. Ryota Yoneda, Kazuaki Hanada, Hatem Elserafy, Nicola Bertelli, Masayuki Ono, High-field-side RF injection for excitation of electron Bernstein waves, Plasma and Fusion Research, 10.1585/PFR.13.3402115, 13, 2018.01, [URL], An evaluation of high-field-side (HFS) X-mode injection for the electron-Bernstein-wave (EBW) scenario is performed using the GENRAY ray-tracing code. In the early stage of low-density plasma start-up, when the electron cyclotron resonance and upper hybrid resonance layers are close to each other, efficient and localized heating by the EBW is attainable. We show that, when the electron density rises, the HFS scenario spontaneously shifts to current drive with successful electron heating. This shift can be explained as a change in heating mechanism from collisional to electron cyclotron damping. Also, we discuss a possible O-X-B scenario to continue the plasma current drive beyond the formation of an over-dense plasma..
111. Nao Yoneda, Taiichi Shikama, Hideki Zushi, Kazuaki Hanada, Akinobu Fujikawa, Takumi Onchi, Kengoh Kuroda, Kuniaki Nii, Masahiro Hasuo, Makoto Hasegawa, Hiroshi Idei, Kazuo Nakamura, Yoshihiko Nagashima, Aki Higashijima, Takahiro Nagata, Spectroscopic measurements of impurity ion toroidal and poloidal flow velocities and their dependence on vertical magnetic field in QUEST toroidal ECR plasmas, Plasma and Fusion Research, 10.1585/PFR.13.3402087, 13, 2018.01, [URL], Toroidal electron cyclotron resonance (ECR) plasma is an ECR heated plasma in an open toroidal magnetic field. The plasma contains no toroidal current and is used for the pre-ionization and non-inductive startup of a tokamak plasma. To obtain a deeper understanding of the basic properties of the plasmas produced in the spherical tokamak QUEST (Q-shu University Experiment with steady-state Spherical Tokamak), we have developed an optical emission spectroscopy system with multiple viewing chords and have used it to measure the spatial distributions of the toroidal and poloidal flow velocities of C2+ ions. We compare the measured velocities with those calculated from the ion drift equations using the plasma parameters reported for a similar spherical tokamak, LATE (the Low Aspect Ratio Torus Experiment)..
112. Kengoh Kuroda, Roger Raman, Stephen C. Jardin, Masayuki Ono, Kazuaki Hanada, TSC simulation of transient CHI in new electrode configuration on QUEST, Plasma and Fusion Research, 10.1585/PFR.13.3402059, 13, 2018.01, [URL], In QUEST, transient Coaxial Helicity Injection (CHI) has now been implemented using a new electrode configuration in which the CHI insulator is not part of the vacuum boundary. In this paper, for the first time, suitable conditions for generation of the CHI-produced toroidal current in the QUEST vessel configuration were investigated using the Tokamak Simulation Code (TSC). The simulation results show that the configuration in which the biased electrode is located farther away from the injector flux coil requires higher currents in the injector coil to generate the required injector flux. Additionally, energizing a lower inboard poloidal field coil and possibly lowering the electrode plate closer to the injector flux coil may be necessary to improve injector flux shaping to permit a configuration that is more favorable for inducing flux closure..
113. Kengoh Kuroda, Roger Raman, Kazuaki Hanada, Makoto Hasegawa, Takumi Onchi, Masayuki Ono, Thomas R. Jarboe, Brian A. Nelson, Masayoshi Nagata, Osamu Mitarai, Kazuo Nakamura, Hiroshi Idei, John Rogers, Shoji Kawasaki, Takahiro Nagata, Arseniy Kuzmin, Shinichiro Kojima, Osamu Watanabe, Aki Higashijima, Yuichi Takase, Atsushi Fukuyama, Erratum
Current Start-Up Using the New CHI System [Plasma Fusion Res., 12, (2017) (1202020)] DOI: 10.1585/pfr.12.1202020, Plasma and Fusion Research, 10.1585/pfr.12.1902026, 12, 2017.01, [URL], A typographical error of spelling occurred in author list of the published article. The correct author list is described as above on this page..
114. C. Huang, K. Hanada, K. Kuroda, S. Kojima, H. Fujiyoshi, H. Miura, T. Yamada, H. Idei, M. Hasegawa, and T. Onchi , Fast tangentially viewed soft X-ray imaging system based on image intensifier with microchannel plat detector on QUEST, Plasma and Fusion Research
, 10.1585/pfr.14.1402128, 14, 2019.06.
115. Masao MATSUYAMA, Hideki ZUSHI, Kazutoshi TOKUNAGA, Arseniy KUZMIN and Kazuaki HANADA , Effect of Re-Deposition Layers in Plasma-Facing Wall on Tritium Retention and Tritium Depth Profile
, Plasma and Fusion Research, 10.1585/pfr.14.1405125, 14, 2019.06.
116. Qilin Yue, Kazuaki Hanada, Makoto Oya, Shogo Matsuo, Shinichiro Kojima, Hiroshi Idei, Takumi Onchi, Kengoh Kuroda, Naoaki Yoshida, Ryuya Ikezoe, Yukai Liu, Makoto Hasegawa, Shun Shimabukuro, Aki Higashijima, Takahiro Nagata, Shoji Kawasaki, Measurement of dynamic retention with fast ejecting system of targeted sample (FESTA), Plasma and Fusion Research, 10.1585/PFR.15.2402013, 15, 1-5, 2020.04, [URL], Fast Ejecting System of Targeted sAmple called FESTA has been developed to carry out the measurement of dynamic hydrogen retention by a test sample. A sample can be exposed and extracted from the targeted plasma at any time using FESTA, however, when exposing the sample, the test chamber wall gets coated by some hydrogen as it is open to the QUEST vacuum vessel. We refer to this as the plasma-induced background. To measure the amount of hydrogen retained by the sample itself, the contribution from the plasma induced background must be subtracted from the measurements. To measure the accurate dynamic retention from plasma-exposed sample, a background subtraction model has been developed and tested. The initial testing shows that the FESTA system and model can estimate the dynamic hydrogen retention by a target test sample..
117. Kojima S., Elserafy H., Hanada K., Idei H., Ikezoe R., Nagashima Y., Hasegawa M., Onchi T., Kuroda K., Nakamura K., Murakami T., Fukuyama M., Kato R., Yoneda R., Ono M., Ejiri A., Takase Y., Murakami S. , Parametric Decay Wave Observation in HFS X-Mode Injection in QUEST, Plasma and Fusion Research, https://doi.org/10.1585/pfr.15.2402063, 15, 2402063, 2402063-1-2402063-6, 2020.08.
118. Makoto HASEGAWA, Kazuaki HANADA, Naoaki YOSHIDA, Hiroshi IDEI, Takeshi IDO, Yoshihiko NAGASHIMA, Ryuya IKEZOE, Takumi ONCHI, Kengoh KURODA, Shoji KAWASAKI, Aki HIGASHIJIMA, Takahiro NAGATA, Shun SHIMABUKURO, Kazuo NAKAMURA , Extension of Operation Region for Steady State Operation on QUEST by Integrated Control with Hot Walls
, Plasma and Fusion Research
, https://doi.org/10.1585/pfr.16.2402034, 16, 2021.03, The controllability of particle supply during long-term discharge in a high-temperature environment was investigated at the Q-shu University Experiment with steady state spherical tokamak (QUEST). QUEST has a high-temperature wall capable of active heating and cooling as a plasma-facing wall. With this hot wall, a temperature rise test was conducted with 673 K as the target temperature. It was confirmed that the hot wall could maintain the temperature above 600 K. Feedback control of particle fueling was conducted to control Hα emission, which is closely related to influx to the wall. Using this particle fueling control and setting the hot wall temperature to 473 K, it was possible to obtain a discharge of more than 6 h. In this discharge, the fueling rate of particles decreased with time, and finally became zero, losing the particle fueling controllability. However, as soon as the cooling water started to flow through the hot wall, particles could be supplied again, and controllability was restored. Thus, indicating that temperature control of the plasma first wall is important even in the high-temperature environment of 473 K to control particle retention of the wall..
119. Kazuo TOI, Takumi ONCHI, Kengo KURODA, Shinichiro KOJIMA, Hideki ZUSHI, Makoto HASEGAWA, Masaharu FUKUYAMA, Shoji KAWASAKI, Aki HIGASHIJIMA, Ryuya IKEZOE, Hiroshi IDEI, Takeshi IDO, Kazuaki HANADA, QUEST Experiment Group, Effects of Toroidally Distributed Divertor Biasing on Scrape-Off-Layer Plasma in the QUEST Spherical Tokamak, Plasma and Fusion Research, https://doi.org/10.1585/pfr.16.2402024, 16, 2021.03, A novel divertor biasing using four biasing plates that are arranged toroidally every 90◦ on the upper divertor plate is applied to low-density plasmas of the QUEST spherical tokamak. When some of these plates are biased in-phase by applying a sawtooth waveform voltage of 85-V amplitude and 50-Hz repetition, up to approximately 35% reduction of the particle flux to the divertor is observed during positive biasing. The input power for the flux reduction is approximately 0.2 kW for low-density tokamak plasmas produced by ∼130-kW electron cyclotron wave injection. Additionally, the signal of a plate probe placed in the low-field side of the mid-plane of the vacuum vessel indicates enhanced losses of fast electrons during positive biasing. The enhanced loss is attributed to small resonant magnetic perturbations produced by the bias-driven currents in the scrape-off layer. This novel divertor biasing is expected to provide a new experimental tool for studying divertor heat load control and fast electron confinement in a tokamak device..
120. Kazuo Nakamura,Yifan Zhang, Takumi Onchi, Hiroshi Idei,Makoto Hasegawa,Kazutoshi Tokunaga,Kazuaki Hanada,Osamu Mitarai,Shoji Kawasaki,Akihigashijima,Takahiro Nagata,Shun Shimabukuro , Quaternion Analysis of a Direct Matrix Conberter Based on Space-Vector Modulation
, Plasma and Fusion Research
, https://doi.org/10.1585/pfr.16.2405037, 16, 2021.03, In a three-phase matrix converter based on space-vector modulation (SVM), nine switches are controlled so that the instantaneous space vector of the line-to-line voltage rotates smoothly in two-dimensional space. The quaternion is a four-dimensional hypercomplex number that is good at describing three-dimensional rotation, such as that seen in three-dimensional game graphics programming theory. Utilizing the quaternion capability, we analyze a matrix converter by three-dimensional rotation instead of transforming to two-dimensional rotation in alpha-beta coordinates. It was clarified that the projection of the quaternion locus in three-dimensional space in the (1,1,1) direction is the same as an alpha-beta transformation locus in two-dimensional space. Concerning the direct matrix converter, we clarified that the (1,1,1)-directional superposition of three-fold higher harmonics cannot be eliminated. The quaternion can rotate and divide a three-dimensional vector. When the output voltage quaternion is divided by input one, the switching quaternion is obtained. The quaternion characteristics will be utilized to analyze a matrix converter based on direct SVM in more detail..
121. Kengoh KURODA, Roger RAMAN, Makoto HASEGAWA, Takumi ONCHI, Brian A. NELSON, John ROGERS, Osamu MITARAI, Kazuaki HANADA, Masayuki ONO, Thomas JARBOE, Masayoshi NAGATA, Hiroshi IDEI, Takeshi IDO,Ryuya IKEZOE, Shoji KAWASAKI, Takahiro NAGATA, Aki HIGASHIJIMA, Shun SHIMABUKURO, Ichiro NIIYA, Canbin HUANG, Shinichiro KOJIMA, Akihiro KIDANI, Takahiro MURAKAMI, Kazuo NAKAMURA, Yuichi TAKASE, Sadayoshi MURAKAMI , Initial Results from High-Field-Side Transient CHI Start-Up on QUEST
, Plasma and Fusion Research
, https://doi.org/10.1585/pfr.16.2402048, 16, 2021.03, Transient coaxial helicity injection (t-CHI) current start-up using a new design simple electrode configuration has been implemented on the QUEST. Discharges injected from the low field side (LFS) and from the high field side (HFS) were examined. Compared to the LFS injection case, the HFS injection has the advantages of providing access to a higher toroidal field and better controlling the location of the injector flux footprint location. Although the present PF coils on QUEST are not well positioned to form the injector flux on the HFS injector region and there has been a frequent occurrence of the spurious arcs, known as absorber arcs, HFS injection has shown flux evolution in a shape that is suitable for the formation of closed flux surfaces. The discharges were improved by installing an in-vessel-coil and adding a new cylindrical electrode to the existing CHI electrode. The results show that the new cylindrical electrode allowed the flux to evolve stably while allowing both the inner and the outer injector flux footprint to remain in the vicinity of the cylindrical electrode. This configuration which inherently generates a narrow injector flux footprint width resulted in discharges that strongly suggested the persistence of the CHI generated plasma after the injector current was reduced to zero. These studies have informed us of the need to improve the CHI gas injection system so that the absorber arcs could be better controlled in the HFS injection configuration..
122. Kazuaki Hanada, H. Zushi, Hiroshi Idei, K. Nakamura, M. Ishiguro, S. Tashima, E. I. Kalinnikova, Yoshihiko Nagashima, Makoto Hasegawa, akihide fujisawa, A. Higashijima, S. Kawasaki, H. Nakashima, O. Mitarai, A. Fukuyama, Y. Takase, X. Gao, H. Liu, J. Qian, M. Ono, R. Raman, Power Balance Estimation in Long Duration Discharges on QUEST, Plasma Science and Technology, 10.1088/1009-0630/18/11/03, 18, 11, 1069-1075, 2016.11, [URL], Fully non-inductive plasma start-up was successfully achieved by using a well-controlled microwave source on the spherical tokamak, QUEST. Non-inductive plasmas were maintained for approximately 3-5 min, during which time power balance estimates could be achieved by monitoring wall and cooling-water temperatures. Approximately 70%-90% of the injected power could be accounted for by calorimetric measurements and approximately half of the injected power was found to be deposited on the vessel wall, which is slightly dependent on the magnetic configuration. The power distribution to water-cooled limiters, which are expected to be exposed to local heat loads, depends significantly on the magnetic configuration, however some of the deposited power is due to energetic electrons, which have large poloidal orbits and are likely to be deposited on the plasma facing components..
123. Jinping Qian, L. L. Lao, Qilong Ren, Baonian Wan, Haiqin Liu, Long Zeng, Zhengping Luo, Kazuaki Hanada, Dalong Chen, Tonghui Shi, Youwen Sun, Biao Shen, Bingjia Xiao, Algorithm validation of the current profile reconstruction of EAST based on polarimeter/interferometer, Plasma Science and Technology, 10.1088/1009-0630/17/1/14, 17, 1, 75-79, 2015.01, [URL], The method of plasma current profile reconstruction using the polarimeter/interferometer (POINT) data from a simulated equilibrium is explored and validated. It is shown that the safety factor (q) profile can be generally reconstructed from the external magnetic and POINT data. The reconstructed q profile is found to reasonably agree with the initial equilibriums. Comparisons of reconstructed q and density profiles using the magnetic data and the POINT data with 3%, 5% and 10% random errors are investigated. The result shows that the POINT data could be used to a reasonably accurate determination of the q profile..
124. H. Zushi, T. Ryoukai, K. Kikukawa, T. Morisaki, R. Bhattacharyay, T. Yoshinaga, Kazuaki Hanada, T. Sakimura, Hiroshi Idei, K. Dono, N. Nishino, H. Honma, S. Tashima, T. Mutoh, S. Kubo, K. Nagasaki, M. Sakamoto, Y. Nakashima, Y. Higashizono, K. N. Sato, Kazuo Nakamura, Makoto Hasegawa, S. Kawasaki, H. Nakashima, A. Higashijima, Two dimensional density fluctuation measurements during the non-inductive current ramp-up phase in the compact plasma wall interaction experimental device CPD, Plasma Science and Technology, 10.1088/1009-0630/11/4/06, 11, 4, 397-401, 2009.12, [URL], Two-dimensional structure of density fluctuations is examined during the current jump phase, indicating a change from the open magnetic fields to the closed ones. During the smooth current ramp-up phase the two-dimensional contour of the LiI intensity shows vertically alignment, consistent with the magnetic surfaces. At the inflection point in Ip ramp-up the LiI intensity contour becomes flat in the observation regime and then suddenly a steep gradient and higher intensity regime are formed in the vertical direction. This higher intensity corresponds to a burst of LiI waveform. According to these changes in the contour, it is found that, within 1 ms around the burst of LiI, a low frequency coherent wave with a long wavelength rapidly grows. The relations with other signals (magnetic flux and microwave stray power) are discussed with respect to the topological change in the magnetic configuration and mode conversion of the incident electromagnetic waves..
125. Kazuo Nakamura, Jiarong Luo, Huazhong Wang, Zhenshan Ji, Hua Wang, Feng Wang, Na Qi, K. N. Sato, Kazuaki Hanada, M. Sakamoto, Hiroshi Idei, Makoto Hasegawa, S. Kawasaki, H. Nakashima, A. Higashijima, Magnetic sensorless control of plasma position and shape in a tokamak, Plasma Science and Technology, 10.1088/1009-0630/8/1/18, 8, 1, 80-83, 2006.01, [URL], Magnetic sensorless sensing and control experiments with the plasma horizontal position have been carried out in the superconducting tokamak HT-7. The sensing is made to focus on the ripple frequency component of the power supply with thyristor and directly from them without time integration. There is no drift problem with the integrator of magnetic sensors. Two kinds of control experiments have been carried out: to keep the position constant and swing the position in a triangular waveform. And magnetic sensorless sensing of plasma shape is discussed..
126. Nakamura, K; Ji, ZS; Shen, B; Qin, PJ; Itoh, S; Hanada, K; Sakamoto, M; Jotaki, E; Hasegawa, M; Iyomasa, A; Kawasaki, S; Nakashima, H, Magnetic sensorless sensing of plasma position in the superconducting tokamak HT-7, Plasma Science & Technology, 10.1088/1009-0630/6/5/006, 6.0, 5.0, 2459.0-2462.0, 0.0, 2004.10, Magnetic sensorless sensing experiments of the plasma horizontal position have been carried out in the superconducting tokamak HT-7. The horizontal position is calculated from the vertical field coil current and voltage without using signals of magnetic probes placed nearby a plasma. The calculations are focused on the ripple frequency component of the power supply. There is no drift problem with the time integration of magnetic probe signals. The error of the derived plasma position is lower than 2% of the plasma minor radius..
127. Y. K. Liu, N. Hamada, Kazuaki Hanada, X. Gao, H. Q. Liu, Y. W. Yu, J. P. Qian, L. Yang, T. J. Xu, Y. X. Jie, Y. Yao, S. S. Wang, J. C. Xu, Z. D. Yang, G. S. Li, Preliminary study on heat load using calorimetric measurement during long-pulse high-performance discharges on EAST, Plasma Physics and Controlled Fusion, 10.1088/1361-6587/aa5d88, 59, 4, 2017.03, [URL], Experimental Advanced Superconducting Tokamak (EAST) aims to demonstrate steady-state advanced high-performance H-mode plasmas with an ITER-like configuration, plasma control and heating schemes. The plasma-facing components in EAST are actively cooled, providing good conditions for researching long-pulse and high-energy discharges. A long-pulse high-performance plasma discharge (#59892 discharge) of up to 103 s with a core electron temperature of up to 4.5 keV was sustained with an injected energy exceeding 0.22 GJ in the 2015-2016 experimental campaign. A calorimetric measurement utilizing the temperature increment of cooling water is carried out to calculate the heat load on the strike point region of the lower divertor during long-pulse discharges in EAST. For the long-pulse and high-energy discharges, the comparison of the measurement results for the heat load measured by divertor Langmuir probes and the calorimetry diagnostic indicates that most of the heat load is delivered to the divertor panels as plasma, not radiation, and charge exchange neutrals. The ratio of the heat load on the strike point region of the lower divertor to the total injected energy is on average 42.5% per discharge with the lower single null divertor configuration. If the radiated energy loss measured by the fast bolometer diagnostic is taken into consideration, the ratio is found to be 61.6%. The experimental results and the analysis of the physics involved in these discharges are reported and discussed..
128. Takumi Onchi, H. Zushi, K. Mishra, Y. Oyama, Yoshihiko Nagashima, Kazuaki Hanada, Hiroshi Idei, Makoto Hasegawa, A. Kuzmin, H. Miura, K. Nakamura, akihide fujisawa, K. Nagaoka, Response of the far scrape-off layer plasma to strong gas puffing in the high poloidal beta configuration of the QUEST spherical tokamak, Plasma Physics and Controlled Fusion, 10.1088/0741-3335/58/11/115004, 58, 11, 2016.09, [URL], The response of the far scrape-off layer (far-SOL) to strong gas puffing (SGP), and its role as the boundary condition for core plasma, are investigated using a two-point Langmuir probe measurement in the high poloidal beta configuration in the QUEST spherical tokamak. The temperature and heat flux behave in an opposite way in the far-SOL and end-plate region after SGP, although SGP increases the density globally. The apparent density decay time in the far-SOL area is much longer than that in the core. Significant co-current flow is driven solely by the electron cyclotron wave in the far-SOL flow. Sheared flow is also observed in the perpendicular velocity profile during the recovered current flat-top phase, and such flow profiles are flattened by SGP. These flow profiles are attributed not only to drift-driven flow but also to transport-driven flow, the sink effect on the end-plate, and the balance of the neutral particle source..
129. K. Kuroda, R. Raman, Kazuaki Hanada, Makoto Hasegawa, Takumi Onchi, M. Ono, B. A. Nelson, T. R. Jarboe, M. Nagata, O. Mitarai, K. Nakamura, Hiroshi Idei, J. Rogers, S. Kawasaki, T. Nagata, A. Kuzmin, S. Kojima, C. Huang, O. Watanabe, A. Higashijima, Y. Takase, A. Fukuyama, S. Murakami, Initial results from solenoid-free plasma start-up using Transient CHI on QUEST, Plasma Physics and Controlled Fusion, 10.1088/1361-6587/aadcb7, 60, 11, 2018.09, [URL], Initial results from the recently implemented transient coaxial helicity injection (CHI) system on QUEST are reported. QUEST uses a new CHI electrode configuration in which the CHI insulator is not part of the vacuum boundary, making this configuration easier to implement in fusion reactors. Experimental results show that transient CHI startup in this alternate electrode configuration is indeed possible. Reliable gas breakdown was achieved, and toroidal currents up to 45 kA were generated..
130. Santanu Banerjee, H. Zushi, N. Nishino, Kazuaki Hanada, Hiroshi Idei, K. Nakamura, Makoto Hasegawa, akihide fujisawa, Yoshihiko Nagashima, K. Mishra, S. Tashima, Takumi Onchi, A. Kuzmin, K. Matsuoka, Effect of magnetic shear on edge turbulence in SOL-like open field line configuration in QUEST, Plasma Physics and Controlled Fusion, 10.1088/1361-6587/aacb69, 60, 8, 2018.06, [URL], Intensity fluctuations are investigated using the fast camera imaging technique in the slab annular plasma as a function of magnetic shear and connection length in the spherical tokamak QUEST. Note that here QUEST is operated as a simple magnetized torus with a tight aspect ratio. Slab annular plasmas feature open magnetic field lines and can mimic the tokamak edge-scrape off layer (SOL)-like plasma attributes reasonably well. Three magnetic shear regimes are realized using three poloidal magnetic field (PF) coil pairs. A whole range of connection lengths (∼∞ ≥ L c ≥ 5.5 m) is scanned by varying the PF strength for a given toroidal field for each magnetic shear regime. For the first time a systematic study of the effect of magnetic shear and field line pitch together on edge-SOL-like plasma fluctuations is being reported. Slab plasmas with intermediate magnetic shear are observed to be more susceptible to generate distinct blobs when L c is reduced by increasing the PF strength. A distinct coherent mode appears only at the lowest magnetic shear slab featuring a deep potential well. Such mode is not apparent at other magnetic shear cases even at the same L c. Finally, with a combination of PF coil pairs, both the features of intermediate and low magnetic shear slabs are shown to be realizable simultaneously. Significantly stronger blobs are observed with such combination of PF mirror ratios in the presence of a coherent mode. This study may provide better insight into the effect of magnetic configuration in the tokamak edge and SOL turbulence and can help in searching for better tools to control cross-field convective intermittent transport in tokamaks..
131. Kazuaki Hanada, Makoto Hasegawa, K. Shinohara, S. Ohdachi, T. Shoji, Y. Miura, H. Tamai, T. Oikawa, H. Totsuka, E. Ishiyama, N. Shinoda, S. Shiraiwa, H. Saito, Y. Endo, K. Yamagishi, H. Toyama, H-L transition caused by irregular probe insertion in the JFT-2M tokamak, Plasma Physics and Controlled Fusion, 10.1088/0741-3335/38/8/018, 38, 8, 1255-1259, 1996.12, [URL], A pair of probe pins whose lengths differ by 5 mm are inserted into the separatrix of H-mode plasmas. When the long pin is biased positively against the short one, the H-L transition takes place and the current through the resistor making a connection between these pins increases for 10 μs and the potential of the pin increases for 100 μs. The energy dissipated by the resistor during the H-L transition is comparable to the energy of the radial electric field in H-mode plasma. When the long pin is biased negatively, the H-L transition also occurs; however, it takes 1 ms to change the potential of the pin and the plasma returns to H-mode after the extraction of the probe..
132. Kazuaki Hanada, K. Ogura, S. Ide, H. Tanaka, M. Iida, T. Ito, M. Iwamasa, M. Yoshida, T. Minami, M. Nakamura, T. Maekawa, Y. Terumichi, S. Tanaka, Computer tomography of M=1 mode during sawtooth oscillation with three soft x-ray detector arrays on the WT-3 tokamak, Plasma Physics and Controlled Fusion, 10.1088/0741-3335/32/14/003, 32, 14, 1289-1299, 1990.12, [URL], Soft X-rays (SXRs) emitted from plasma in the WT-3 tokamak were measured by three SXR detector arrays, viewing the plasma from three different angles. From these experimental data, the authors reconstructed the two dimensional (2-D) contour of constant SXR emissivity as a function of time, using the technique of computer tomography (CT). Computer simulation results show that data from three or more sets of detector arrays are required to reconstruct the 2-D emissivity structure with sufficient accuracy to distinguish Kadomtsev's model from the quasi-interchange (Wesson's) model of sawtooth crash. Further, it is shown that if the noise amplitude is more than 1.5%, reconstruction of the real 2-D SXR emissivity structure is difficult..
133. Hatem Elserafy, Kazuaki Hanada, Shinichiro Kojima, Takumi Onchi, Ryuya Ikezoe, Kengoh Kuroda, Hiroshi Idei, Makoto Hasegawa, Ryota Yoneda, Masaharu Fukuyama, Arseniy Kuzmin, Aki Higashijima, Takahiro Nagata, Shoji Kawasaki, Shun Shimabukuro, Nicola Bertelli, Masayuki Ono, Electron Bernstein wave conversion of high-field side injected X-modes in QUEST, Plasma Physics and Controlled Fusion, 10.1088/1361-6587/ab6903, 62, 3, 2020.01, [URL], This paper presents a detailed design of the Q-shu University experimental steady state spherical tokamak's (QUEST's) high-field side (HFS) injection system for electron Bernstein wave (EBW) excitation and the results of an experimental comparison of the HFS eXtraordinary X-mode and low-field side (LFS) ordinary O-mode injection of 8.2 GHz radio frequency (RF) power. Waveguides, as an alternative to mirror polarizers for transmitting RF X-mode power from LFS to HFS for EBW conversion, were used instead of the installation of an RF mirror. Testing of LFS-to-HFS RF power transmission at 8.2 GHz, using an RG-50-type vacuum waveguide in a bench-scale device filled with SF6 gas at 0.03 Mpa, revealed that an RF power of 10.8 kW could traverse the fundamental electron cyclotron resonance layer for 60 s without breakdown. The short-length, open-ended waveguide antenna used in the HFS injection-induced wave diffraction reduced the efficiency of power delivery to the upper hybrid resonance (UHR) by approximately 7% at an electron temperature of 50 eV. The HFS injection was able to produce brighter camera images than the standard LFS injection. The location of the UHR, as estimated by measuring the density with an interferometer, agreed with its location as measured by plasma radiation low-field, side-edge positions shown by fast camera imaging. This indicates that the plasma was produced by mode-converted EBW. The HFS injection had an absorption efficiency of 96%, compared to 40% for LFS. A greater fluctuation of floating potential adjustable to the lower hybrid wave (LHW) was observed in the HFS case by installing a Langmuir probe, confirming that EBW conversion efficiency was higher in the HFS case. Moreover, after setting the poloidal field to BPF = 7.6 mT, plasma current (IP ) in the HFS peaked at 1.3 kA, as opposed to 0.3 kA for LFS, despite LFS injection having a total power of 55 kW, compared to 40 kW for HFS. However, as the impurity level was comparatively high, it is believed that this IP is dominated by pressure-drive, which makes it difficult to analyze EBWCD. Finally, the line-integrated density in the HFS injection peaked at 1.6 × 1018 m-2, compared to 8 × 1017 m-2 in the LFS one..
134. East Team, Y. K. Liu, N. Hamada, K. Hanada, X. Gao, H. Q. Liu, Y. W. Yu, J. P. Qian, L. Yang, T. J. Xu, Y. X. Jie, Y. Yao, S. S. Wang, J. C. Xu, Z. D. Yang, G. S. Li, Erratum
Preliminary study on heat load by using calorimetric measurement during long pulse high performance discharges on EAST, Plasma Physics and Controlled Fusion

, 10.1088/1361-6587/ab6b03, 62, 3, (2017) 59 (045009) , 2020.01, [URL], Figure 8 in [1] was partially incorrect because of the heat flux data derived from Langmuir probes which included the effect of arcing in long-pulse high-power heating plasmas on EAST tokamak. The new plot with corrected data and errorbar for figure 8 is presented here. (Figure Presented)..
135. R. Yoneda, Kazuaki Hanada, K. Nakamura, Hiroshi Idei, N. Yoshida, Makoto Hasegawa, Takumi Onchi, K. Kuroda, S. Kawasaki, A. Higashijima, T. Nagata, A. Isayama, O. Mitarai, A. Fukuyama, Y. Takase, Effect of magnetic structure on RF-induced breakdown in QUEST, Physics of Plasmas, 10.1063/1.4985142, 24, 6, 2017.06, [URL], In tokamak operations, breakdown of plasma is the first step of the plasma build-up. In this paper, we present a combinative investigation of radio frequency (RF)-induced breakdown experiments in QUEST (Q-shu University Experiment with Steady-State Spherical Tokamak) and a one-point model of hydrogen ionization. Experimental results with two different frequencies of 2.45 GHz and 8.2 GHz showed that the clear threshold on connection length, L, existed for breakdown with a negative n-index configuration n=-(R/Bv)·(∂Bv/∂R), where R is the major radius and Bv the is vertical magnetic field. In contrast, breakdown was always obtained with positive n-index when changing L. It indicates that a lifetime of an incubated electron plays a significant role in the plasma breakdown. According to one-point model calculation, the experimental threshold of L is well predicted by the lifetime of the incubated electron estimated by employing the loss term along with L. The model calculation also describes the requirement of the minimum electron temperature Te for RF-induced breakdown to realize an avalanche of electrons in the tokamak magnetic structure..
136. Santanu Banerjee, H. Zushi, N. Nishino, K. Mishra, Y. Mahira, S. Tashima, A. Ejiri, T. Yamaguchi, Takumi Onchi, Yoshihiko Nagashima, Kazuaki Hanada, K. Nakamura, Hiroshi Idei, Makoto Hasegawa, akihide fujisawa, A. Kuzmin, K. Matsuoka, Observation of an edge coherent mode and poloidal flow in the electron cyclotron wave induced high βp plasma in QUEST, Physics of Plasmas, 10.1063/1.4960117, 23, 8, 2016.08, [URL], Fluctuations are measured in the edge and scrape-off layer (SOL) of QUEST using fast visible imaging diagnostic. Electron cyclotron wave injection in the Ohmic plasma features excitation of low frequency coherent fluctuations near the separatrix and enhanced cross-field transport. Plasma shifts from initial high field side limiter bound (inboard limited, IL) towards inboard poloidal null (IPN) configuration with steepening of the density profile at the edge. This may have facilitated the increased edge and SOL fluctuation activities. Observation of the coherent mode, associated plasma flow, and particle out-flux, for the first time in the IPN plasma configuration in a spherical tokamak may provide further impetus to the edge and SOL turbulence studies in tokamaks..
137. Takumi Onchi, H. Zushi, K. Mishra, Y. Mahira, K. Nagaoka, Kazuaki Hanada, Hiroshi Idei, Makoto Hasegawa, K. Nakamura, akihide fujisawa, Yoshihiko Nagashima, K. Matsuoka, S. Tashima, S. Banerjee, A. Kuzmin, S. Kawasaki, H. Nakashima, A. Higashijima, O. Watanabe, Heat flux and plasma flow in the far scrape-off layer of the inboard poloidal field null configuration in QUEST, Physics of Plasmas, 10.1063/1.4928878, 22, 8, 2015.08, [URL], Heat flux and plasma flow in the scrape-off layer (SOL) are examined for the inboard poloidal field null (IPN) configuration of the spherical tokamak QUEST. In the plasma current (Ip) ramp-up phase, high heat flux (>1 MW/m2) and supersonic flow (Mach number M > 1) are found to be present simultaneously in the far-SOL. The heat flux is generated by energetic electrons excursed from the last closed flux surface. Supersonic flows in the poloidal and toroidal directions are correlated with each other. In the quasi-steady state, sawtooth-like oscillation of Ip at 20 Hz is observed. Heat flux and subsonic plasma flow in the far-SOL are modified corresponding to the Ip-oscillation. The heat flow caused by motion of energetic electrons and the bulk-particle transport to the far-SOL is enhanced during the low-Ip phase. Modification of plasma flow in the far SOL occurs earlier than the Ip crash. The M-Ip curve has a limit-cycle characteristic with sawtooth-like oscillation. Such a core-SOL relationship indicates that the far-SOL flow plays an important role in sustaining the oscillation of Ip in the IPN configuration..
138. T. Onchi,, H. Idei, M. Fukuyama, D. Ogata, R. Ashida, T. Kariya, A. Ejiri, K. Matsuzaki, Y. Osawa, Y. Peng, S. Kojima, O. Watanabe, M. Hasegawa, K. Nakamura, K. Kuroda, R. Ikezoe, T. Ido, K. Hanada, N. Bertelli, M. Ono, and A. Fukuyama, Non-inductive plasma current ramp-up through oblique injection of harmonic electron cyclotron waves on the QUEST spherical tokamak, Physics of Plasma, https://doi.org/10.1063/5.0031357, 28, 022505 (2021), 2021.01, The plasma current is ramped up primarily by a 28 GHz electron cyclotron wave (ECW) in the Q-shu University experiment Steady-State Spherical Tokamak (QUEST), with multiple harmonic resonance layers from the second to the fourth stay in the plasma core. A steering antenna comprising two quasi-optical mirrors enhances the power density of ECWs. The ECW beam is injected obliquely from the low-field side where the parallel refractive index is N∥ = 0.75 at the second-harmonic resonance layer. Analysis of the resonance condition has found that energetic electrons moving forward along the magnetic field resonate more effectively than those moving backward. Such symmetry breaking is consistent with the results of the current ramp-up experiment. The peak plasma current reaches Ip>70 kA, constantly injecting a beam of radio frequency power of 100 kW. Ray-tracing by the TASK/WR code demonstrates that the power of the 28 GHz extraordinary mode is absorbed by energetic electrons via single-pass cyclotron absorption.
I. INTRODUCTION.
139. Kazuaki Hanada, T. Maehara, K. Makino, Y. Kishigami, T. Kishino, T. Minami, H. Tanaka, M. Iida, M. Nakamura, T. Maekawa, Y. Terumichi, S. Tanaka, Sawtooth stabilization by localized electron cyclotron heating in the WT-3 tokamak, Physics of Fluids B, 10.1063/1.860375, 4, 11, 3675-3688, 1992.01, [URL], The effect on sawtooth oscillations (STO) by localized electron-cyclotron- resonance heating (ECH) on the WT-3 tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1988 (International Atomic Energy Agency, Vienna, 1989), Vol. 1, p. 563] is studied. STO are strongly modified or stabilized by ECH near the q=1 surface, where q refers to the safety factor. The effect of ECH is much stronger when it is applied on the high-field side as compared to the low-field side. Further, even when ECH is applied outside the q=1 surface, the amplitude of STO decreases and STO stabilizes. In the very high qL discharge, the excitation of STO can be obtained by applying ECH..
140. S. Tanaka, Kazuaki Hanada, H. Tanaka, M. Iida, S. Ide, T. Minami, M. Nakamura, T. Maekawa, Y. Terumichi, M. Yamada, J. Manickam, R. B. White, Sawtooth stabilization by electron cyclotron heating at the q=1 surface in the WT-3 tokamak, Physics of Fluids B, 10.1063/1.859636, 3, 8, 2200-2204, 1991.01, [URL], Sawtooth oscillations (STO) in the Ohmically heated (OH) WT-3 tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1988 (IAEA, Vienna, 1989), Vol. 1, p. 563] are strongly modified or suppressed by localized electron cyclotron resonance heating (ECH) near the q = 1 surface, where q refers to the safety factor. The effect of ECH is much stronger when it is applied on the high-field side, as compared to the low-field side. Complete suppression of the STO is achieved for the duration of the ECH when it is applied on the high-field side, in a low-density plasma, provided the ECH power exceeds a threshold value. This threshold decreases with the increasing safety factor at the limiter qL and the complete stabilization of STO can be obtained even when ECH is applied on the low-field side in the high-qL region. It is noticeable that these complete stabilizations can be obtained only by the localized ECH with the elliptic antenna. The STO stabilization is attributed to a modification of the current density profile by high-energy electrons generated by ECH, which reduces the shear in the q = 1 region..
141. T. Maehara, S. Yoshimura, Y. Kishigami, Kazuaki Hanada, T. Maekawa, M. Nakamura, Y. Terumichi, Fast electron momentum distributions in lower hybrid and electron cyclotron current drive plasmas, Physics Letters A, 10.1016/0375-9601(95)00741-K, 208, 1-2, 143-149, 1995.11, [URL], We investigate fast electron momentum distributions in lower hybrid (LH) and electron cyclotron (EC) current drive (CD) plasmas in the WT-3 tokamak by a new method for the reconstruction of momentum distribution from bremsstrahlung hard X-ray spectra measured at various viewing angles to the toroidal field. The results show that fast electrons in an LHCD plasma are further accelerated by an additional ECCD beyond the energy cut determined by the LH wave accessibility condition..
142. S. Shiraiwa, S. Ide, Sanae Itoh, O. Mitarai, O. Naito, T. Ozeki, Y. Sakamoto, T. Suzuki, Y. Takase, S. Tanaka, T. Taniguchi, M. Aramasu, T. Fujita, T. Fukuda, X. Gao, M. Gryaznevich, Kazuaki Hanada, Eriko Jotaki, Y. Kamada, T. Maekawa, Y. Miura, Kazuo Nakamura, T. Nishi, H. Tanaka, K. Ushigusa, Formation of Advanced Tokamak Plasmas without the Use of an Ohmic-Heating Solenoid, Physical Review Letters, 92, 3, 350011-350014, 2004.01, An integrated advanced scenario of tokamak formation without the use of an Ohmic heating (OH) solenoid in the JT-60U tokamak was investigated. The OH solenoid was not used but the electron cyclotron, lower hybrid waves, neutral beam injection and the loop voltage provided both the poloidal flux and vertical field. The plasma generated from this scenario had both internal and edge transport barriers with an energy confinement of 1.6 times H-mode scaling, poloidal beta of 3.6 and large bootstrap current fraction. The results show improved economic competitiveness of tokamak reactor without the use of OH solenoid..
143. T. Maekawa, T. Maehara, T. Minami, Y. Kishigami, T. Kishino, K. Makino, Kazuaki Hanada, M. Nakamura, Y. Terumichi, S. Tanaka, Up-shifted frequency electron-cyclotron current drive in a lower hybrid current drive plasma, Physical Review Letters, 10.1103/PhysRevLett.70.2561, 70, 17, 2561-2564, 1993.01, [URL], Using oblique injection of electron-cyclotron (EC) waves, launched from the low field side of the WT-3 tokamak, into a target plasma sustained by lower hybrid current drive (LHCD), the plasma current is ramped up at a rate corresponding to 100 kA/s. The current ramp-up is ascribed to selective EC heating of tail electrons in the LHCD plasma via fundamental EC resonance at an up-shifted frequency due to the Doppler effect..
144. Kazuaki Hanada, H. Tanaka, M. Iida, S. Ide, T. Minami, M. Nakamura, T. Maekawa, Y. Terumichi, S. Tanaka, M. Yamada, J. Manickam, R. B. White, Sawtooth stabilization by localized electron cyclotron heating in a tokamak plasma, Physical Review Letters, 10.1103/PhysRevLett.66.1974, 66, 15, 1974-1977, 1991.01, [URL], Sawtooth oscillations (STO) in the Ohmically heated WT-3 tokamak are strongly modified or suppressed by localized-electron cyclotron resonance heating (ECH) near the q=1 surface, where q refers to the safety factor. The efect of ECH is much stronger when it is applied on the high-field side as compared to the low-field side. Complete suppression of the STO is achieved for the duration of the ECH, in most cases, when it is applied on the high-field side of a low-density plasma, provided the ECH power exceeds a threshold value. The STO stabilization is attributed to a modification of the current-density profile by hot electrons generated by ECH, which reduces the shear in the q=1 region..
145. Hanada, K.; Zushi, H.; Idei, H.; Nakamura, K.; Ishiguro, M.; Tashima, S.; Kalinnikova, E. I.; Sakamoto, M.; Hasegawa, M.; Fujisawa, A.; Higashijima, A.; Kawasaki, S.; Nakashima, H.; Liu, H.; Mitarai, O.; Maekawa, T.; Fukuyama, A.; Takase, Y.; Qian, J., Non-Inductive Start up of QUEST Plasma by RF Power, PLASMA SCIENCE & TECHNOLOGY, 10.1088/1009-0630/13/3/08, 13.0, 3.0, 307.0-311.0, 0.0, 2011.06, Both start-up and sustainment of plasma were successfully achieved by fully non-inductive current drive using microwave with a frequency of 8.2 GHz. Plasmas current of 15 kA was implemented for 1 s. Magnetic surface reconstruction exhibited a plasma shape with an aspect ratio of below 1.5. The plasma current was dependent significantly on the launched microwave power and vertical magnetic field, while not affected by the mode of launched wave and the toroidal refractive index. Hard X-ray (HXR) emitted from energetic electrons accelerated by the microwave was observed, and the discharge with a plasma current over 4 kA followed the same trend as the number of photons of 10 keV to 12 keV. This suggests that the plasma current may be driven by energetic electrons. Based on the experimental conditions, alternative explanations of how the plasma current could be driven are discussed..
146. Liu Xiaolong, Kazuo Nakamura, Yoshisue, Tatsuya, Mitarai, Osamu, Makoto Hasegawa, K. Tokunaga, Xue Erbing, zushi hideki, K.Hanada, Fujisawa Akihide, H. Idei, H-infinity Loop Shaping Control for Plasma Vertical Position Instability on QUEST, PLASMA SCIENCE & TECHNOLOGY, 10.1088/1009-0630/15/3/21, 15.0, 3.0, 295.0-299.0, 0.0, 2013.03, QUEST has a divertor configuration with a high and a negative n-index, and the problem of plasma vertical position instability control in QUEST is still under extensive study for achieving high efficiency plasma. The instability we considered is that the toroidal plasma moves either up or down in the vacuum chamber until it meets the vessel wall and is extinguished. The actively controlled coils (HCU and HCL) outside the vacuum vessel are serially connected in feedback with a measurement of the plasma vertical position to provide stabilizing control. In this work, a robust controller is employed by using the loop synthesis method, and provides robust stability over a wide range of n-index. Moreover, the gain of the robust controller is lower than that of a typical proportional derivative (PD) controller in the operational frequency range; it indicates that the robust controller needs less power consumption than the PD controller does..
147. ITOH, S; NAKAMURA, Y; NAKAMURA, K; FUJITA, T; MAKINO, K; JOTAKI, E; KAWASAKI, S; ITOH, SI; MAEKAWA, T; TANAKA, S; TERUMICHI, Y; HANADA, K; MINAMI, T; MAEHARA, T; MAKINO, K; KISHIGAMI, Y; KISHINO, T; NAKAMURA, M, HIGH DENSITY AND LONG DURATION CURRENT DRIVE DISCHARGE WITH HIGH FREQUENCY LH WAVES IN TRIAM-1M .A. COMBINED CURRENT DRIVE OF ELECTRON CYCLOTRON AND LOWER HYBRID WAVES, AND ECH HEAT PULSE PROPAGATION IN THE WT-3 TOKAMAK .B., PLASMA PHYSICS AND CONTROLLED NUCLEAR FUSION RESEARCH 1992, VOL 1, 743.0-750.0, 0.0, 1993.11, Recent studies on particle and power control in long duration lower hybrid current drive (LHCD) operations in TRIAM-1M are presented. Particle control through gas puffing (t < 20 s) shows that steady coupling of LH waves is attained at 40 s from the initiation of the discharge. High power handling is carried out over 20 s under the power load of several MW/m2 for the poloidal limiters. Part B. Part B reports on an upshift frequency electron cyclotron current drive experiment in an LHCD plasma and on heat pulse propagation by means of localized EC heating in the WT-3 tokamak (R0 = 0.65 m, a = 0.2 m, Bt ≤ 1.75 T)..
148. Itoh, S; Sato, KN; Nakamura, K; Zushi, H; Sakamoto, M; Hanada, K; Jotaki, E; Makino, K; Kawasaki, S; Nakashima, H; Iyomasa, A, Recent progress in the superconducting tokamak TRIAM-1M, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/41/3A/052, 41.0, 3A, A587, 1999.03, Extensive studies of a steady-state tokamak reactor have been carried out on the superconducting tokamak TRIAM-1M. A discharge of (e) over tilde(e) = 2 x 10(18) m(-3) lasting more than 2 h has been demonstrated using a 2.45 GHz lower hybrid current drive (LHCD). A high-density plasma of ii, = 2 x 10(19) m(-3) has been sustained for 1 min using a 8.2 GHz LHCD under the high average wall loading of 5 MW m(-2) on the limiter. Recently, a single-null divertor configuration with high elongation (kappa = 1.5) was also successfully maintained for 1 min by the 2.45 GHz LHCD. A transition of the ion temperature (T-i) from 0.6 keV to about 2.5 keV is observed in 2.45 GHz LHCD plasmas; this operational regime, is called the 'high ion temperature (HIT)' mode. The 'HIT' mode is characterized by the existence of a steep T-i gradient (approximate to 50 keV m(-1)) near r/a similar to 0.4. It is found that the 'HIT' mode appears in a narrow window of the electron density and horizontal plasma position. The 'HIT' mode can be successfully maintained for over 1 min with accurate control of the density and position..
149. Bhattacharyay, R.; Zushi, H.; Morisaki, T.; Inada, Y.; Kikukawa, T.; Watanabe, S.; Sasaki, K.; Ryoukai, T.; Hasegawa, M.; Hanada, K.; Sato, K. N.; Nakamura, K.; Sakamoto, M.; Idei, H.; Yoshinaga, T.; Kawasaki, S.; Nakashima, H.; Higashijima, A., Study of magnetic configuration effects on plasma boundary and measurement of edge electron density in the spherical tokamak compact plasma wall interaction experimental device using Li sheet beam, PHYSICS OF PLASMAS, 10.1063/1.2839034, 15.0, 2.0, 0.0-0.0, 022504, 2008.02, Two-dimensional lithium beam imaging technique has been applied in the spherical tokamak CPD (compact plasma wall interaction experimental device) to study the effects of magnetic field configurations on rf plasma boundary in the absence of any plasma current, and also for the measurement of a two-dimensional edge electron density profile. With the present working condition of the diagnostics, the minimum measured electron density can be similar to 1.0 X 10 16 m(-3); this is considered to be the definition for the plasma boundary. The performance of the lithium sheet beam is absolutely calibrated using a quartz crystal monitor. Experimental results reveal that magnetic field configuration, either mirror or so-called null, critically affects the rf plasma boundary. A sharp lower boundary is found to exist in magnetic null configuration, which is quite different from that in the weak mirror configuration. Theoretical calculations of particle drift orbit and. magnetic connection length (wall-to-wall) suggest that only mirror trapped particles are confined within a region where the magnetic connection length is similar to 4.0 in or more. A two-dimensional edge electron density profile is obtained from the observed Li I intensity profile. Overdense plasma formation is discussed from the viewpoint of mode conversion of rf wave into electron Bernstein wave and its dependence on the electron density profile. (c) 2008 American Institute of Physics..
150. Ogata, R.; Hanada, K.; Nishino, N.; Liu, H. Q.; Zushi, H.; Ishiguro, M.; Ikeda, T.; Nakamura, K.; Fujisawa, A.; Idei, H.; Hasegawa, M.; Kawasaki, S.; Nakashima, H.; Higashijima, A., Investigations of the radial propagation of blob-like structure in a non-confined electron cyclotron resonance heated plasma on Q-shu University Experiment with a Steady-State Spherical Tokamak, PHYSICS OF PLASMAS, 10.1063/1.3640494, 18.0, 9.0, 0.0-0.0, Article No. 092306, 2011.09, A study of radial propagation and electric fields induced by charge separation in blob-like structures has been performed in a non-confined cylindrical electron cyclotron resonance heating plasma on Q-shu University Experiment with a Steady-State Spherical Tokamak using a fast-speed camera and a Langmuir probe. The radial propagation of the blob-like structures is found to be driven by E x B drift. Moreover, these blob-like structures were found to have been accelerated, and the property of the measured radial velocities agrees with the previously proposed model [C. Theiler et al., Phys. Rev. Lett. 103, 065001 (2009)]. Although the dependence of the radial velocity on the connection length of the magnetic field appeared to be different, a plausible explanation based on enhanced short-circuiting of the current path can be proposed. (C) 2011 American Institute of Physics. [doi:10.1063/1.3640494].
151. Ishiguro, Masaki; Hanada, Kazuaki; Liu, Haiqing; Zushi, Hideki; Nakamura, Kazuo; Fujisawa, Akihide; Idei, Hiroshi; Nagashima, Yoshihiko; Hasegawa, Makoto; Tashima, Saya; Takase, Yuichi; Kishimoto, Yasuaki; Mitarai, Osamu; Kawasaki, Shoji; Nakashima, Hisatoshi; Higashijima, Aki, Non-inductive current start-up assisted by energetic electrons in Q-shu University experiment with steady-state spherical tokamak, PHYSICS OF PLASMAS, 10.1063/1.4731700, 19.0, 6.0, Article No. 062508, 2012.06, After intensive discharge cleaning of the chamber wall, non-inductive current start-up experiments have been successfully performed in QUEST in moderate vertical fields of about 1.0-1.5mT with positive n-index. Simultaneously, with increasing plasma current, an asymmetric toroidal flow of energetic electrons was observed and direct measurements of current driven by this asymmetric flow were taken with a newly developed Langmuir probe technique. A numerical study of the energetic electron orbits indicates that the total current is enough to play a dominant role in the formation of a closed flux surface in QUEST. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4731700].
152. Banerjee, Santanu; Zushi, H.; Nishino, N.; Hanada, K.; Ishiguro, M.; Tashima, S.; Liu, H. Q.; Mishra, K.; Nakamura, K.; Idei, H.; Hasegawa, M.; Fujisawa, A.; Nagashima, Y.; Matsuoka, K., Role of stochasticity in turbulence and convective intermittent transport at the scrape off layer of Ohmic plasma in QUEST, PHYSICS OF PLASMAS, 10.1063/1.4890359, 21.0, 7.0, 0.0-0.0, 072311, 2014.07, Statistical features of fluctuations are investigated using the fast camera imaging technique in the scrape of layer (SOL) of electron cyclotron resonance heated Ohmic plasma. Fluctuations in the SOL towards low field side are dominated by coherent convective structures (blobs). Two dimensional structures of the higher order moments (skewness s and kurtosis k) representing the shape of probability density function (PDF) are studied. s and k are seen to be functions of the magnetic field lines. s and k are consistently higher towards the bottom half of the vessel in the SOL showing the blob trajectory along the field lines from the top towards bottom of the vessel. Parabolic relation (k = As-2 + C) is observed between s and k near the plasma boundary, featuring steep density gradient region and at the far SOL. The coefficient A, obtained experimentally, indicates a shift of prominence from pure drift-wave instabilities towards fully developed turbulence. Numerical coefficients characterizing the Pearson system are derived which demonstrates the progressive deviation of the PDF from Gaussian towards gamma from the density gradient region, towards the far SOL. Based on a simple stochastic differential equation, a direct correspondence between the multiplicative noise amplitude, increased intermittency, and hence change in PDF is discussed. (C) 2014 AIP Publishing LLC..
153. Shiraiwa, S; Hanada, K; Hasegawa, M; Idei, H; Kasahara, H; Mitarai, O; Nakamura, K; Nishino, N; Nozato, H; Sakamoto, M; Sasaki, K; Sato, K; Takase, Y; Yamada, T; Zushi, H, Heating by an electron Bernstein wave in a spherical tokamak plasma via mode conversion, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.96.185003, 96.0, 18.0, 0.0-0.0, Article No. 185003, 2006.05, The first successful high power heating of a high dielectric constant spherical tokamak plasma by an electron Bernstein wave (EBW) is reported. An EBW was excited by mode conversion (MC) of an X mode cyclotron wave injected from the low magnetic field side of the TST-2 spherical tokamak. Evidence of electron heating was observed as increases in the stored energy and soft x-ray emission. The increased emission was concentrated in the plasma core region. A heating efficiency of over 50% was achieved, when the density gradient in the MC region was sufficiently steep..
154. Jabir AL SALAMI, Changhong HU, mohamed.KAMRA,Kazuaki HANADA , Magnetic Induction and Electric Potential Smoothed Particle Magnetohydrodynamics for Incompressible Flows
, Numerical Methods in Fluids
, 10.1002/fld.4906, 2020.08, [URL].
155. H. Zushi, K. Nakamura, K. Hanada, K. N. Sato, M. Sakamoto, H. Idei M. Hasegawa, A. Iyomasa, S. Kawasaki, H. Nakashima, A. Higashijima, T. Kuramoto, A. Tanaka, Y. Matsuo, K. Esaki, H. Akanishi H. Ayatsuka, S. Imada, T. Sugata, H. Hoshika, K. Sasaki, N. Maez, Overview of steady state tokamak operation and current drive experiments in TRIAM-1M, Nuclear fusion, https://doi.org/10.1088/0029-5515/43/12/006, IAEA-CN-116-OV5-2

Proc. 20th IAEA Fusion Energy Conference, 2004.01.
156. A. Kuzmin, H. Zushi, I. Takagi, S. K. Sharma, M. Kobayashi, Y. Hirooka, Takumi Onchi, Kazuaki Hanada, N. Yoshida, K. Nakamura, akihide fujisawa, Hiroshi Idei, Yoshihiko Nagashima, Makoto Hasegawa, T. Mutoh, K. Mishra, H. Ohwada, Spatial distribution of atomic and ion hydrogen flux and its effect on hydrogen recycling in long duration confined and non-confined plasmas, Nuclear Materials and Energy, 10.1016/j.nme.2017.03.027, 12, 627-632, 2017.08, [URL], In order to understand the atomic hydrogen distribution in different kinds of plasma and its influence on the recycling, two kinds of plasmas were used: non-confined annular electron cyclotron resonance (ECR) and confined long duration plasmas. The permeation probes are used to measure directly the atomic hydrogen flux at several poloidal positions. The permeation through metals due to the ion and atom component of the hydrogen flux to the wall is indistinguishable. To estimate the contribution of the ions directly, Langmuir probes were used. The Гinc profile behind the plasma facing components (PFCs) is almost constant, ∼2 ×1018 H/s/m2..
157. M. Matsuyama, H. Zushi, Kazutoshi Tokunaga, A. Kuzmin, Kazuaki Hanada, Effect of heating temperature on tritium retention in stainless steel type 316 L, Nuclear Materials and Energy, 10.1016/j.nme.2018.05.024, 16, 52-59, 2018.08, [URL], Dependence of heating temperature on tritium retention behavior in stainless steel type 316 L (SS316L) has been examined about each process of degassing and tritium exposure. Two kinds of SS316L samples were employed: bare SS316L and plasma-exposed SS316L. The amount of tritium retained in surface layers of a sample was nondestructively measured by β-ray-induced X-ray spectrometry, and changes in the surface state with heating in vacuum were analyzed by X-ray photoelectron spectroscopy (XPS). Significant increase in tritium retention in bare SS316L samples appeared in a degassing temperature region above 600 K. Similar tendency of tritium retention was observed for the plasma-exposed sample. It was seen that the degassing process prior to tritium exposure significantly influenced to the tritium retention behavior. Furthermore, it was suggested from surface analysis by XPS that chemical states of SS316L surface at high temperatures play an important role for tritium retention behavior..
158. K. Hanada, N. Yoshida, I. Takagi, T. Hirata, A. Hatayama, K. Okamoto, Y. Oya, T. Shikama, Z. Wang, H. Long, C. Huang, M. Oya, H. Idei, Y. Nagashima, T. Onchi, M. Hasegawa, K. Nakamura, H. Zushi, K. Kuroda, S. Kawasaki, A. Higashijima, T. Nagata, S. Shimabukuro, Y. Takase, S. Murakami, X. Gao, H. Liu, J. Qian, R. Raman, M. Ono, Estimation of fuel particle balance in steady state operation with hydrogen barrier model, Nuclear Materials and Energy, 10.1016/j.nme.2019.03.015, 19, 544-549, 2019.05, [URL], This research investigated fuel particle balance during long duration discharge in an all-metal plasma facing wall (PFW)through intensive QUEST execution. A simple wall model including the plasma-induced deposition layer that creates hydrogen (H)barriers, called the H barrier model, was established. A simple calculation, based on a combination of H state rate equations and the H barrier model, was applied to real plasma in the early phase of its longest discharge. The model accurately reconstructed the evolutions of electron density and wall-stored H over time, proper values are chosen for the parameters that are difficult to determine experimentally. Comparative calculations that used the H barrier and a fully reflective models, predicted significant impacts of wall models on the plasma density time response and value of electron density, indicating that a proper wall model should be developed for all-metal PFW devices..
159. Ayaka Koike;Moeko Nakata;Shota Yamazaki;Takuro Wada;Fei Sun;MingzhongZhao;Naoaki Yoshida;KazuakiHanada;YasuhisaOya , Evaluation of hydrogen retention behavior in tungsten exposed to hydrogen plasma in QUEST
, Nuclear Materials and Energy
, https://doi.org/10.1016/j.nme.2020.100856, 26, 2021.03, The W (tungsten) samples were placed at Top, Equator and Bottom plasma facing walls of QUEST (Q-shu University Experiment with Steady-State-Spherical Tokamak) device and exposed to 754 shots of hydrogen plasma during 2017A/W (Autumn/Winter) campaign. Thereafter, their surface morphologies and chemical states were evaluated by TEM (Transmission Electron Microscope) and XPS (X-ray photoelectron spectroscopy). The XPS results showed that a thick carbon layer about 3–18 nm has formed throughout the wall surface. Among them, the Bottom wall had the deposition layer with the thickness of 2 nm, which was thinner than the top wall, namely erosion-dominated. On the other hand, a thick C layer about 18 nm was deposited on the Equator wall. The additional 1 keV D2+ was implanted into these samples and the D (deuterium) retention enhancement was estimated. The D2 TDS (Thermal Desorption Spectroscopy) spectra for all the samples had two major desorption stages at 400 K and 650 K, namely the desorption of D trapped by irradiation damages and deposition layer. The erosion/deposition profile would be caused by wall position and plasma condition, like a current start-up experiment. The desorption temperature of H2 (hydrogen) was shifted toward higher temperature side compared to that exposed to previous plasma campaign (2016 A/W), suggesting that H was mainly accumulated in the deposition layer with forming C–H bonds..
160. A.Kuzmin;M.Kobayashi;K.Hanada;H.Idei;T.Onchi;S.Mori;N.Yoneda;T.Shikama;M.Hasuo;T.Ido;Y.Nagashima;R.Ikezoe;M.Hasegawa;K.Kuroda;K.Kono;S.Matsuo;T.Nagata;S.Shimabukuro;H.Zushi , Investigation of radial distribution of atomic hydrogen flux to the plasma facing components in steady state discharges in QUEST tokamak
, Nuclear Materials and Energy
, https://doi.org/10.1016/j.nme.2020.100872, 26, 2021.03, Abstract
To study radial distribution of hydrogen flux in peripheral plasma in long duration tokamak discharges, permeation and Langmuir reciprocate probes are used. The atomic hydrogen flux to the walls at several radial positions is deduced from the permeation flux. Contribution of the ions to the hydrogen flow is deduced from the Langmuir probe ion saturation current. It is found, that the atomic hydrogen has the most contribution to the hydrogen flow behind the plasma facing components (PFCs), while the ion flux there is negligible. The atomic flux behind the PFCs drops to the value of , which is 6% of that just in front of PFCs, ..
161. N. Yoneda, T. Shikama, K. Hanada, S. Mori, T. Onchi, K. Kuroda, M. Hasuo, A. Ejiri,K. Matsuzaki, Y. Osawa, Y. Peng, Y. Kawamata, S. Sakamoto, H. Idei, T. Ido, K. Nakamura,Y. Nagashima, R. Ikezoe, M. Hasegawa, A. Higashijima, T. Nagata, S. Shimabukuro , Toroidal Flow Measurements of Impurity Ions in QUEST ECH Plasmas using Multiple Viewing Chords Emission Spectroscopy
, Nuclear Materials and Energy
, https://doi.org/10.1016/j.nme.2021.100905, 26, 2021.03, A spectroscopic system with multiple viewing chords was developed for QUEST (Q-shu University Experiment with Steady-State Spherical Tokamak) to measure the spatial distribution of ion toroidal velocities in discharges sustained by electron cyclotron resonance heating (ECH). Twenty-four viewing chords were aligned in the midplane and C III emission line spectra were measured for three types of ECH discharge under different magnetic field configurations. By applying an inversion method to the measured spectra, we evaluated the radial distributions of C2+ ion emissivity, temperature, and toroidal velocity. The error in the evaluated velocity was estimated to be less than 5 km/s. It was found that the velocity depends on the magnetic field configuration..
162. K. Hanada, N. Yoshida, M. Hasegawa, M. Oya, Y. Oya, I. Takagi, A. Hatayama, T. Shikama, H. Idei, Y. Nagashima, R. Ikezoe, T. Onchi, K. Kuroda, S. Kawasaki, A. Higashijima, T. Nagata, S. Shimabukuro,K. Nakamura, S. Murakami, Y. Takase, X. Gao, H. Liu, and J. Qian , Overview of recent progress on steady state operation of all-metal plasma facing wall device QUEST
, Nuclear Materials and Energy
, https://doi.org/10.1016/j.nme.2021.101013, 27, 2021.06, QUEST (Q-shu university experiment with steady state spherical tokamak) is a midsize spherical tokamak capable of steady-state operation, comprising all-metal plasma-facing walls and a hot wall (HW) to address issues pertaining to fuel particle balance. The HW was installed summer 2014. Quantitative analysis pertaining to the HW at 373 K is carried out, and clarify the quantitative impact of shot history that obviously appears in wall stored hydrogen just before the discharge at the wall temperature. The model indicates the plasma-induced deposition layer play an essential role in fuel particle balance. A clear temperature dependence of fuel recycling was observed using outgassing just after plasma termination and played an essential role in regulation of particle balance. Consequently, long duration discharges lasting more than 1 h has been obtained at wall temperature, TW < 423 K in the range of 40–60 kW of RF power and, similarly, a 6 h discharge could be achieved at TW = 473 K using 20 kW of injected RF power..
163. Liu, Yukai; Gao, Xiang; Hanada, Kazuaki; Yu, Yaowei; Liu, Haiqing; Yang, Lei; Zhang, Tao; Jie, Yinxian; Qian, Jinping; Zeng, Long; Ming, Tingfeng; Liu, Xiaoju; Liu, Shaocheng; Xu, Tiejun; Chen, Yue; Zhuang, Qing; Li, Yilong; Gan, Kaifu; Zhang, Bin; Chen, M; Zi, Pengfei; Wang, Yumin; Li, Gongshun; Zhu, Kezheng; Zhou, Tong; Li, Lei; Cao, Lei; Gong, Xianzu; Yao, Damao; Wang, Ke; Wang, Liang; Li, Jiangang , Power balance investigation in long-pulse high-performance discharges with ITER-like tungsten divertor on EAST, Nuclear Fusion
, 10.1088/1741-4326/aba0c6, 2020.08, [URL].
164. MISHRA KISHORE KANTI, zushi hideki, H.Idei, Makoto Hasegawa, Saya Tashima, Banerjee S, K.Hanada, H Togashi, T Yamaguchi, Akira Ejiri, Yuichi Takase, Kazuo Nakamura, Fujisawa Akihide, Nagashima Yoshihiko, Aleksandrovich Arseniy Kuzmin, Self Organization of High βp Plasma Equilibrium with an Inboard Proidal Magnetic Field Null in QUEST, Nuclear Fusion, 55 (2015) 083009 (13pp), 2015.07.
165. Hiroshi Idei, Takumi Onchi, T. Kariya, K.Hanada, T. Imai, A. Ejiri, O. Watanabe, K. Mishra, Kazuo Nakamura, Fujisawa Akihide, Nagashima Yoshihiko, Makoto Hasegawa, S, Kawasaki, T. Nakashima, A. Higashijima, H. Zushi, Y. Takase, A. Fukuyama, QUEST team, Non-inductive Electron Cyclotron Heating and Current Drive with Dual Frequency (8.2 /28 GHz) Waves in QUEST, Nuclear Fusion, 10.1088/1741-4326/aa7c20, 2017.10.
166. J. P. Qian, L. L. Lao, C. T. Holcomb, B. N. Wan, Y. W. Sun, D. Moreau, E. Li, L. Zeng, Kazuaki Hanada, A. M. Garofalo, X. Z. Gong, B. Shen, B. J. Xiao, An efficient technique for magnetic equilibrium reconstruction with q profile constraints and its application on the EAST tokamak, Nuclear Fusion, 10.1088/1741-4326/aa74eb, 57, 8, 2017.06, [URL], An efficient technique for building plasma equilibria with preset or constrained q profiles by solving the nonlinear Grad-Shafranov equation iteratively is proposed. The technique uses a set of dynamic virtual poloidal field probes in the plasma core region. Numerical examples are shown for monotonic q profiles and negative central magnetic shear equilibria which are obtained with this technique. As a proof of principle, the technique is applied on the EAST tokamak, to constrain the plasma equilibrium reconstruction with the experimental q = 1 surface information from the ECE diagnostic in addition to the external magnetic measurements..
167. Y. Takase, A. Ejiri, T. Fujita, N. Fukumoto, A. Fukuyama, Kazuaki Hanada, Hiroshi Idei, M. Nagata, Y. Ono, H. Tanaka, M. Uchida, R. Horiuchi, Y. Kamada, H. Kasahara, S. Masuzaki, Y. Nagayama, T. Oishi, K. Saito, Y. Takeiri, S. Tsuji-Iio, Overview of spherical tokamak research in Japan, Nuclear Fusion, 10.1088/1741-4326/aa62c1, 57, 10, 2017.06, [URL], Nationally coordinated research on spherical tokamak is being conducted in Japan. Recent achievements include: (i) plasma current start-up and ramp-up without the use of the central solenoid by RF waves (in electron cyclotron and lower hybrid frequency ranges), (ii) plasma current start-up by AC Ohmic operation and by coaxial helicity injection, (iii) development of an advanced fuelling technique by compact toroid injection, (iv) ultra-long-pulse operation and particle control using a high temperature metal wall, (v) access to the ultra-high-β regime by high-power reconnection heating, and (vi) improvement of spherical tokamak plasma stability by externally applied helical field..
168. T. Kariya, T. Imai, R. Minami, K. Sakamoto, Y. Oda, R. Ikeda, T. Shimozuma, S. Kubo, Hiroshi Idei, T. Numakura, K. Tsumura, Y. Ebashi, M. Okada, Y. Nakashima, Y. Yoshimura, H. Takahashi, S. Ito, Kazuaki Hanada, K. Nagasaki, M. Ono, T. Eguchi, Y. Mitsunaka, Development of over-MW gyrotrons for fusion at 14 GHz to sub-THz frequencies, Nuclear Fusion, 10.1088/1741-4326/aa6875, 57, 6, 2017.04, [URL], Megawatt power gyrotrons are being developed for collaborative electron cyclotron heating (ECH) studies of advanced fusion devices and demonstration power plant (DEMO). (1) In the first experiment of a 300 GHz gyrotron, an output power above 0.5 MW in the TE32,18 single mode was achieved with a pulse width of 2 ms. This was the first observation of MW-scale oscillations in a DEMO-relevant gyrotron mode. It was also found that the reflection at the output window affected the determination of the oscillation mode. Furthermore, several single mode oscillations in the 226-254 GHz range were confirmed, which is important for the step-frequency tunable gyrotron in the sub-THz frequency range. (2) Based on the successful results of the 77 and 154 GHz large helical device (LHD) tubes, a new 154/116 GHz dual-frequency gyrotron with an output of over 1.5 MW is being designed. (3) A new record output of 1.38 MW was obtained using an existing 28 GHz gyrotron. A newly designed tube aimed at achieving a dual-frequency output power of 2 MW at 28 GHz (0.4 MW continuous wave) and 1 MW at 35 GHz was built. In the first experimental test, main mode oscillations were observed at the frequencies of 28.036 and 34.831 GHz with Gaussian-like output beams and output power of 1.27 and 0.48 MW, respectively. A total efficiency of 50% was achieved at 28 GHz operation..
169. J. P. Qian, L. L. Lao, H. Q. Liu, W. X. Ding, L. Zeng, Z. P. Luo, Q. L. Ren, Y. Huang, J. Huang, D. L. Brower, Kazuaki Hanada, D. L. Chen, Y. W. Sun, B. Shen, X. Z. Gong, B. J. Xiao, B. N. Wan, EAST equilibrium current profile reconstruction using polarimeter-interferometer internal measurement constraints, Nuclear Fusion, 10.1088/1741-4326/aa4e58, 57, 3, 2017.03, [URL], The first equilibrium reconstruction of EAST current-density profile based on internal Faraday rotation measurements provided by the POlarimeter-INTerferometer (POINT) diagnostic is demonstrated using the EFIT equilibrium reconstruction code. EFIT incorporates 11 simultaneous line-integrated density and Faraday effect measurements from POINT to self-consistently reconstruct the equilibrium toroidal current density profile using a Faraday rotation reconstruction algorithm. It is shown that the POINT measurements can be applied to improve the accuracy of core plasma current density and q profile on EAST. Comparisons of magnetic surfaces and the q profile reconstructed using external magnetic data against those using magnetic and POINT data are presented. Equilibrium reconstructions using POINT data are found to be consistent with sawtooth phenomena. The sensitivity of equilibrium reconstruction to POINT measurements indicates Faraday rotation provides important constraints for determining the current profile..
170. Xiang Gao, Yao Yang, Tao Zhang, Haiqing Liu, Guoqiang Li, Tingfeng Ming, Zixi Liu, Yumin Wang, Long Zeng, Xiang Han, Yukai Liu, Muquan Wu, Hao Qu, Biao Shen, Qing Zang, Yaowei Yu, Defeng Kong, Wei Gao, Ling Zhang, Huishan Cai, Xuemei Wu, Kazuaki Hanada, Fubin Zhong, Yunfeng Liang, Chundong Hu, Fukun Liu, Xianzhu Gong, Bingjia Xiao, Baonian Wan, Xiaodong Zhang, Jiangang Li, Key issues for long-pulse high-β N operation with the Experimental Advanced Superconducting Tokamak (EAST), Nuclear Fusion, 10.1088/1741-4326/aa626c, 57, 5, 2017.03, [URL], In the last few years, long-pulse H-mode plasma discharges (with small edge-localized modes and normalized beta, β N ∼ 1) have been realized at the Experimental Advanced Superconducting Tokamak (EAST). This paper reports on high-β N (>1.5) discharges in the 2015 EAST campaign. The characteristics of these H-mode plasmas have been presented in a database. Analysis of the experimental limit of β N has revealed several main features of typical discharges. Firstly, efficient, stable high heating power is required. Secondly, control of impurity radiation (partly due to interaction between the plasma and the in-vessel components) is also a critical issue for the maintenance of high-β N discharges. In addition an internal transport barrier (ITB) has recently been observed in EAST, introducing further improvement in confinement surpassing H-mode plasmas. ITB dynamics is another key issue for high-β N plasmas in EAST. Each of these features is discussed in this paper. Study and improvement of these issues could be considered as the key to achieving long-pulse high-β N operation with EAST..
171. K. Hanada, N. Yoshida, T. Honda, Z. Wang, A. Kuzmin, I. Takagi, T. Hirata, Y.Oya, M.Miyamoto, H. Zushi, M. Hasegawa, K. Nakamura, A. Fujisawa, H. Idei, Y. Nagashima, O. Watanabe, T. Onchi, H. Watanabe, K. Tokunaga, A. Higashijima, S.Kawasaki, H.Nakashima, T.Nagata, Y.Takase, A.Fukuyama, and O.Mitarai, Investigation of hydrogen recycling property and its control with hot wall in long duration discharges on QUEST, Nuclear Fusion, 10.1088/1741-4326/aa8121, 57 (2017) 126061 (10pp), 2017.10, Abstract. Fully non-inductive plasma maintenance was achieved by a microwave of 8.2 GHz and 40 kW for more than 1 h 55 min with a well-controlled plasma-facing wall (PFW) temperature of 393 K using a hot wall on the middle-sized spherical tokamak QUEST until, finally, the discharge was terminated by the uncontrollability of the density. The PFW was composed of atmospheric plasma-sprayed tungsten and stainless steel. The hot wall plays essential roles in reducing the amount of wall-stored H and facilitating hydrogen recycling. The behaviour of fuel hydrogen in the PFW was investigated by monitoring the injection and evacuation of hydrogen into and from the plasma-producing vessel. A fuel particle balance equation based on the presence of a hydrogen transport barrier between the deposited layer and the substrate was applied to the long-duration discharges. It was found that the model could readily predict the observed behaviour that a higher wall temperature likely gives rise to faster wall saturation..
172. Hiroshi Idei, T. Kariya, T. Imai, K. Mishra, Takumi Onchi, O. Watanabe, H. Zushi, Kazuaki Hanada, J. Qian, A. Ejiri, M. M. Alam, K. Nakamura, akihide fujisawa, Yoshihiko Nagashima, Makoto Hasegawa, K. Matsuoka, A. Fukuyama, S. Kubo, T. Shimozuma, M. Yoshikawa, M. Sakamoto, S. Kawasaki, H. Nakashima, A. Higashijima, S. Ide, T. Maekawa, Y. Takase, K. Toi, Fully non-inductive second harmonic electron cyclotron plasma ramp-up in the QUEST spherical tokamak, Nuclear Fusion, 10.1088/1741-4326/aa7c20, 57, 12, 2017.10, [URL], Fully non-inductive second (2nd) harmonic electron cyclotron (EC) plasma current ramp-up was demonstrated with a newlly developed 28 GHz system in the QUEST spherical tokamak. A high plasma current of 54 kA was non-inductively ramped up and sustained stably for 0.9 s with a 270 kW 28 GHz wave. A higher plasma current of 66 kA was also non-inductively achieved with a slow ramp-up of the vertical field. We have achieved a significantly higher plasma current than those achieved previously with the 2nd harmonic EC waves. This fully non-inductive 2nd harmonic EC plasma ramp-up method might be useful for future burning plasma devices and fusion reactors, in particular for operations at half magnetic field with the same EC heating equipment..
173. S. Itoh, K. N. Sato, K. Nakamura, H. Zushi, M. Sakamoto, Kazuaki Hanada, Eriko Jotaki, K. Makino, S. Kawasaki, H. Nakashima, N. Yoshida, Recent progress on high performance steady state plasmas in the superconducting tokamak TRIAM-1M, Nuclear Fusion, 39, Special Issue, 1257-1270, 1999.09, An overview of TRIAM-1M experiments is presented. The current status of issues related to steady state operation is presented with reference to the achievement of super-ultra-long tokamak discharges sustained by LHCD for over 2 h. The importance of control of the initial phase of the plasma, the avoidance of high heat load concentration, wall conditioning and the avoidance of abrupt termination of long discharges are discussed as the crucial issues for the achievement of steady state operation of the tokamak. A high ion temperature (HIT) discharge fully sustained by 2.45 GHz LHCD with both high ion temperature and steep temperature gradient was successfully demonstrated for longer than 1 min in the limiter configuration. The HIT discharges can be obtained in a narrow window of density and position. The avoidance of heat load concentration on a limiter is the key point for the achievement and long sustainment of the HIT discharge. As the effective thermal insulation between the wall and the plasma is improved for the single null configuration, HIT discharges with peak ion temperature > 5 keV and a steeper temperature gradient of up to 85 keV/m can be achieved through the fine control of density and position. Plasmas with high κ ≈ 1.5 can also be demonstrated for longer than 1 min. The current profile is also well controlled for a time about 2 orders of magnitude longer than the current diffusion time using combined LHCD. The serious damage to the material of the first wall caused by energetic neutral particles produced by charge exchange is also described. As the neutral particles cannot be affected by a magnetic field, this damage by neutral particles must be prevented by a new technique..
174. T. Maehara, S. Yoshimura, T. Minami, Kazuaki Hanada, M. Nakamura, T. Maekawa, Y. Terumichi, Electron cyclotron current drive in a lower hybrid current drive plasma, Nuclear Fusion, 10.1088/0029-5515/38/1/304, 38, 1, 39-57, 1998.01, [URL], Electron cyclotron (EC) current drive experiments were carried out in lower hybrid current drive (LHCD) plasmas on the WT-3 tokamak. Using oblique injection of EC waves, plasma current is ramped up in a frequency range ω/Ωe ≃ 1.2-1.4, where Ωe is the EC frequency at the plasma centre. This ramp-up is ascribed to selective EC heating of fast electrons in LHCD plasmas via the fundamental EC resonance at the upshifted frequency due to the Doppler effect. Fast electron momentum distributions are estimated from bremsstrahlung hard X ray spectra. These distributions indicate that the parallel momentum input to the fast electrons in the relativistic energy range from oblique EC waves is effective for efficient EC current drive. Current ramp-up is also observed in the second harmonic frequency range ω/Ωe ≁ 1.9-2.2. In this case, bulk electrons are heated as well as fast electrons and no definite cause of current ramp-up is clarified..
175. S. Tanaka, Kazuaki Hanada, T. Minami, S. Ide, M. Iida, H. Tanaka, T. Maekawa, Y. Terumichi, Initiation of plasma current with the assistance of electron cyclotron waves in the WT-3 tokamak, Nuclear Fusion, 10.1088/0029-5515/33/3/I13, 33, 3, 505-513, 1993.12, [URL], In the WT-3 tokamak, the toroidal plasma current is started and ramped up to 6.3 kA by the electron cyclotron (EC) wave alone, without ohmic heating (OH) power. After generation of the plasma current by the EC wave, the OH current can be started up with a very low ohmically induced electric field, i.e. <0.32 V/m, which is extremely small compared with that (2.5 V/m) in an OH discharge with the assistance of EC resonance preionization. The low value of the starting loop voltage is in accordance with the requirements of the ITER design. It is demonstrated that the loop voltage and the flux of the OH transformer can be reduced considerably when the EC power is used for preionization and startup of the toroidal current before initiation of an OH discharge in tokamaks..
176. T. Maekawa, M. Nakamura, T. Komatsu, T. Kishino, Y. Kishigami, K. Makino, T. Maehara, T. Minami, Kazuaki Hanada, M. Iida, Y. Terumichi, S. Tanaka, Heat flux of fast electrons to the limiter in lower hybrid current drive plasma on WT-3, Nuclear Fusion, 10.1088/0029-5515/32/10/I05, 32, 10, 1755-1768, 1992.12, [URL], The heat flux of fast electrons to the local limiter in LHCD plasmas in WT-3 has been investigated by thermal measurement of the limiter. The amount of the heat flux (PFE) is found to be about on third of the net radiofrequency power (Prf) injected into the plasma for various discharge conditions. The results combined with other measurements show that the confinement of fast electrons deteriorates as Prf increases. This direct loss of fast electrons is one of the causes of the degradation of the current drive efficiency. Heat transport of the bulk electrons is also found to increase as Prf increases. Experimental results indicate that a significant part of the remaining RF power (2Prf/3) flows to the bulk electrons. The slowing down power of fast electrons in the energy range above several tens of keV is estimated to be quite small compared with 2P rf/3, suggesting that a significant part of the remaining power flows to the bulk electrons via other channels. A plausible channel is the absorption of RF power via lower energy electrons by an upshift of the parallel refractive index of the injected lower hybrid waves. This seems to be another cause of the degradation of the current drive efficiency..
177. H. Tanaka, K. Ogura, A. Ando, S. Ide, M. Iida, Kazuaki Hanada, T. Minami, M. Yoshida, M. Nakamura, T. Maekawa, Y. Terumichi, Non-inductive current drive using second harmonic electron cyclotron waves on the wt-3 tokamak, Nuclear Fusion, 10.1088/0029-5515/31/9/006, 31, 9, 1673-1687, 1991.01, [URL], A plasma current of up to 70 kA has been sustained in WT-3 discharges by second harmonic (2&OHgr;e) electron cyclotron (EC) waves alone, with zero loop voltage, after shutting off the Ohmic heating power. Further, in the case of high power EC wave injection, ramp-up discharges have been obtained. Pulse height analysis of hard X-rays in the line of sight at various angles to the toroidal field shows that the velocity distribution function of the high energy tail electrons is asymmetric in the toroidal direction. The 2&OHgr;e EC wave is mainly absorbed by the tail electrons, and a 2&OHgr;e EC driven current is generated by enhancing the asymmetry of the distribution. The figure of merit of 2&OHgr;e EC current drive (ECCD) is ηEC(2) = (3.2-6.4) × 10−2 (1019 A/W·m2), which is one order of magnitude smaller than that of lower hybrid current drive in WT-3. This low value of ηEC(2) can be attributed to low confinement of the current carrying, high energy tail electrons produced by 2&OHgr;e ECCD..
178. M. Nakamura, T. Minami, Kazuaki Hanada, M. Iida, S. Ide, H. Tanaka, T. Maekawa, Y. Terumichi, S. Tanaka, Particle confinement of lower hybrid current driven plasmas and electron cyclotron heated plasmas in the wt-3 tokamak, Nuclear Fusion, 10.1088/0029-5515/31/8/006, 31, 8, 1485-1494, 1991.01, [URL], Confinement properties of lower hybrid current driven (LHCD) plasmas and electron cyclotron heated (ECH) plasmas in the WT-3 tokamak are studied. The outward particle and energy fluxes are estimated from parameters of the scrape-off layer (SOL) plasma. During the LHCD period the density and temperature of the SOL plasma decrease drastically, while the density of the core plasma increases, suggesting a decrease of the outward flux. These results show that particle confinement is improved by LHCD. On the contrary, during ECH the density of the SOL plasma increases and the density of the core plasma decreases, suggesting a deterioration of particle confinement. Improved confinement is not obtained near the density limit of LHCD; the improvement is not related with MHD activities during LHCD..
179. T. Maekawa, M. Iida, H. Tanaka, S. Ide, Kazuaki Hanada, T. Minami, T. Fukino, Y. Terumichi, S. Tanaka, Production of high poloidal beta plasma by bidirectional lower hybrid current drive in the wt-3 tokamak, Nuclear Fusion, 10.1088/0029-5515/31/7/016, 31, 7, 1394-1398, 1991.01, [URL], Lower hybrid waves propagating both parallel and anti-parallel to the toroidal field (bidirectional waves) produce suprathermal electron tails in both directions. The contribution of these tails is additive for the pressure but subtractive for the plasma current Ip. Therefore, the poloidal beta due to tail electrons, ßptai1, becomes much larger than that in the usual case of unidirectional current drive, where ßptai1 exceeds unity only when Ip is smaller than the Alfvèn critical current IA. In the WT-3 tokamak, lower hybrid current drive plasmas produced by bidirectional and unidirectional injection have been compared in terms of ßp. The experimental results show that a high ßp plasma is generated with Ip larger than IA in the bidirectional case..
180. K. Ogura, H. Tanaka, S. Ide, M. Iida, Kazuaki Hanada, M. Yoshida, T. Minami, T. Cho, M. Nakamura, T. Maekawa, Y. Terumichi, S. Tanaka, Study of the fast electron distribution function in lower hybrid and electron cyclotron current driven plasmas in the wt-3 tokamak, Nuclear Fusion, 10.1088/0029-5515/31/6/002, 31, 6, 1015-1033, 1991.01, [URL], The distribution function f(p) of fast electrons produced by lower hybrid current drive (LHCD) is investigated in the WT-3 tokamak, using a combination of measurements of the hard X-ray (HXR) angular distribution with respect to the toroidal magnetic field and observations of the HXR radial profile. The data obtained indicate the formation of a plateau-like region in f(p) which corresponds to a region of resonant interaction between the lower hybrid (LH) wave and the electrons. The energy of the fast electrons in the peripheral plasma region is observed to be higher than that in the central plasma region under operational conditions with a high plasma current (Ip ≤ 80 kA). At low current (Ip ≤ 50 kA), however, the energy of fast electrons is constant along the plasma radius. In the current ramp-up phase, fast electrons are generated in the directions normal to and opposite to the LH wave propagation. The latter case is ascribed to a negatively biased toroidal electric field induced by the current ramp-up. To study the characteristic change of f(p) for various current drive mechanisms, HXR measurements are performed in electron cyclotron current driven (ECCD) plasma and in Ohmic heating (OH) plasma. In ECCD plasma, the perpendicular energy of fast electrons increases, which indicates that fast electrons are accelerated perpendicularly by electron cyclotron heating. In both LHCD and ECCD plasmas, fast electrons flow in the direction opposite to the wave propagation, while no such fast electrons are formed in OH plasma..
181. H. Tanaka, S. Ide, M. Iida, Kazuaki Hanada, M. Yoshida, T. Minami, T. Maekawa, Y. Terumichi, S. Tanaka, K. Ogura, M. Nakamura, Toroidal plasma current startup and sustainment by lower hybrid waves in the WT-3 tokamak, Nuclear Fusion, 10.1088/0029-5515/30/4/003, 30, 4, 611-624, 1990.01, [URL], In WT-3, lower hybrid waves are injected into a microwave discharge at the electron cyclotron resonance frequency to initiate the toroidal plasma current IP and to sustain it by radio frequency (RF) power alone without Ohmic heating power (this is called the ‘RF tokamak’). First, fast electrons in the range of several kilo-electron volts are generated by electron cyclotron and lower hybrid power which initiate a weak toroidal plasma current. Then, fast electrons above 100 keV are produced by the lower hybrid waves, and IP increases rapidly (ΔIp/Δt ∼ 780 kA·s−1) to almost 13 kA. Subsequently the toroidal plasma current is ramped up slowly (ΔIp/Δt ∼ 180 kA·s−1) to > 25 kA for low densities (̅e 6 × 1018 m−3). The fraction ∈R (≤8%) of injected lower hybrid power is converted into poloidal magnetic field energy. For high densities (̅e = (6−12) × 1018 m−3), a quasi-steady-state discharge is obtained with IP = 7−20 kA, and the figure of merit ηCD is about 0.05 × 1019 A·m−2·W−1. The experimental values of ∈R and ηCD are explained by the direct loss of fast electrons..
182. S. Ide, K. Ogura, H. Tanaka, M. Iida, Kazuaki Hanada, T. Itoh, M. Iwamasa, H. Sakakibara, T. Minami, M. Yoshida, T. Maekawa, Y. Terumichi, S. Tanaka, Investigation of high energy electrons in lower hybrid current drive plasma with electron cyclotron emission measurement in the WT-3 tokamak, Nuclear Fusion, 10.1088/0029-5515/29/8/009, 29, 8, 1325-1338, 1989.01, [URL], Electron cyclotron emission (ECE) from lower hybrid current drive plasma in the WT-3 tokamak has been measured along a vertical chord where the magnitude of the toroidal field is constant. From the frequency of the peak of the down-shifted second harmonic X-mode emission, the perpendicular temperature is evaluated to be about 50, 40 and 25 keV for plasmas with a current of 65, 50 and 24 kA, respectively. Also, the line integrated tail electron density is evaluated from the peak intensity for these plasmas and found to be 1.7, 0.9 and 0.5 × 1012 cm−2respectively. It is found that the perpendicular temperature is an increasing function of the component of the momentum parallel to the plasma current, p1and that the gradient of the perpendicular temperature along p1 increases as the plasma current decreases..
183. K. Hanada, N. Yoshida, M. Hasegawa, A. Hatayama, K. Okamoto, I. Takagi, T. Hirata, Y. Oya, M. Miyamoto, M. Oya, T. Shikama, A. Kuzmin, Z. X. Wang, H. Long, H. Idei, Y. Nagashima, K. Nakamura, O. Watanabe, T. Onchi, H. Watanabe, K. Tokunaga, A. Higashijima, S. Kawasaki, T. Nagata, S. Shimabukuro, Y. Takase, S. Murakami, X. Gao, H. Liu, J. Qian, R. Raman, M. Ono, Particle balance investigation with the combination of the hydrogen barrier model and rate equations of hydrogen state in long duration discharges on an all-metal plasma facing wall in QUEST, Nuclear Fusion, 10.1088/1741-4326/ab1858, 59, 7, 2019.05, [URL], The fuel particle balance during long duration discharges in the Q-shu University Experiment with steady state spherical tokamak (QUEST) was investigated. QUEST has all-metal plasma facing walls (PFWs) that were temperature controlled during the experiments. The presence of a transport barrier for hydrogen (H) at the interface between a plasma-induced deposition layer and metallic substrate was confirmed by nuclear reaction analysis with exposing deuterium plasma. An effective method to evaluate global hydrogen flux to PFWs is proposed, taking advantage of the nature of wall saturation. The outgoing flux of fuel particles from the PFWs just after the plasma termination was proportional to the square of wall-stored H, which indicates that enhanced recombination of solved hydrogen played an essential role in dynamic retention and was in agreement with predictions from the H-barrier model. A simple calculation based on the combination of wall modelling and rate equations of the H states denoted a significant impact of wall modelling on the time response of the plasma density. Hence, a proper wall model including the effects of the deposition layer creating the H barrier is required to be developed, even for all-metal PFW devices..
184. T. Kariya, R. Minami, T. Imai, M. Okada, F. Motoyoshi, T. Numakura, Y. Nakashima, H. Idei, T. Onchi, K. Hanada, T. Shimozuma, Y. Yoshimura, H. Takahashi, S. Kubo, Y. Oda, R. Ikeda, K. Sakamoto, M. Ono, K. Nagasaki, T. Eguchi, Y. Mitsunaka, Development of high power gyrotrons for advanced fusion devices, Nuclear Fusion, 10.1088/1741-4326/ab0e2c, 59, 6, 2019.04, [URL], Megawatt (MW) gyrotrons, with a wide frequency range from 14 to 300 GHz, are being developed as part of a collaborative electron cyclotron heating (ECH) study for advanced fusion devices and a demonstration power plant (DEMO). (1) Detailed designs for a 14 GHz 1 MW gyrotron are being developed for fabrication. For a 14 GHz radio frequency (RF) beam with high divergence, a calculated transmission efficiency of 94% to the corrugated waveguide coupling position was obtained initially by introducing the design concept (direct RF beam coupling by built-in waveguide) to minimize the RF transmission path. Installing a double-disk sapphire window will make it possible to develop a 1 MW gyrotron with a continuous wave (CW) at 14 GHz. (2) In experimental tests of a new 28/35 GHz dual-frequency gyrotron, the cooling characteristics of an optimal-structure double-disk sapphire window were evaluated. We confirmed that operating at 0.4 MW with a CW at 28 GHz is feasible, reaching twice the output power reported in previous studies. In a 2 ms short-pulse experimental test, maximum powers of 1.65 MW at 28.04 GHz and 1.21 MW at 34.83 GHz were achieved. (3) A design study of a 77/51 GHz dual-frequency gyrotron was performed. Oscillations above 1.5 MW for 77 GHz and 1.3 MW for 51.88 GHz are expected for a beam voltage V k = 80 kV and beam current I k = 60 A. (4) In an experiment with a 300 GHz gyrotron, the influence of the wave reflected from the window was reduced by tilting the output window, and mode competition in the cavity was suppressed. An output power of 0.62 MW with a pulse width of 1 ms, which is the new record for this frequency, was obtained. (5) We also performed a trial design study of a 240 GHz gyrotron for DEMO..
185. Y. Hirooka, M. Ono, R. Maingi, K. Hanada, M. Kondo, J. Miyazawa, M. Shimada, Conference report on the 1st US-Japan workshop on power and particle control by liquid metal plasma-facing components in a steady state magnetic fusion DEMO reactor, Nuclear Fusion, 10.1088/1741-4326/ab4ede, 60, 1, 2020.01, [URL], As part of the US-Japan bilateral collaboration program, a new series of workshops have been inaugurated on the subject of 'Power and Particle Control by Liquid Metal Plasma-Facing Components in a Steady State Magnetic Fusion DEMO Reactor'. The first workshop of this series was held at Princeton Plasma Physics Laboratory on 11-13 March 2019. This conference report is intended to share 24 technical presentations, discussion and the planning of future workshops with the world magnetic fusion community..
186. H. Idei, T. Onchi, K. Mishra, H. Zushi, T. Kariya, T. Imai, O. Watanabe, R. Ikezoe, K. Hanada, M. Ono, A. Ejiri, J. Qian, K. Nakamura, A. Fujisawa, Y. Nagashima, M. Hasegawa, K. Matsuoka, A. Fukuyama, S. Kubo, M. Yoshikawa, M. Sakamoto, S. Kawasaki, A. Higashijima, S. Ide, Y. Takase, S. Murakami, Electron heating of over-dense plasma with dual-frequency electron cyclotron waves in fully non-inductive plasma ramp-up on the QUEST spherical tokamak, Nuclear Fusion, 10.1088/1741-4326/ab4c12, 60, 1, 2020.01, [URL], A 28 GHz system with a high-power gyrotron tube has been used for the QUEST spherical tokamak to form an over-dense plasma for electron Bernstein wave (EBW) heating and current drive with an 8.2 GHz-wave. Non-inductive high-density plasma ramp-up experiments with dual-frequency (dual-f ) electron cyclotron (EC) (8.2 GHz and 28 GHz) waves were conducted. A spontaneous density jump (SDJ) to an over-dense state was first observed as a bifurcation phenomenon in the dual-f  wave experiment. The over-dense plasma on the 8.2 GHz wave was non-inductively ramped up to 25 kA, and was maintained for 0.4 s under stable plasma equilibrium after two such jumps in one shot. Heating to mildly energetic electrons and bulk electrons was observed even in the over-dense region. The electrostatic EBW heating effect on the mildly energetic electrons in the over-dense region is assessed following a dispersion analysis of the 8.2 GHz wave. The bulk electron heating effect observed is explained as heat exchange from mildly energetic electrons heated by the electrostatic EBW. Remarkably, a high hard-x-ray-radiation temperature of ∼500 keV was also observed in tangential viewing for current-carrying electrons in the over-dense core region. Synergetic heating from the overlap of different 28 GHz EC harmonic resonances as well as higher harmonic heating is discussed for maintaining the highly energetic electrons in the over-dense core region. In addition, the SDJ process and mechanism are considered based on the discussion of the electron heating effects with the 8.2 GHz wave..
187. Itoh S., Sato K. N., Nakamura K., Zushi H., Sakamoto M., Hanada K., Jotaki E., Makino K., Kawasaki S., Nakashima H., Yoshida N., Recent Progresses on High Performance Steady State Plasmas in the Superconducting Tokamak TRIAM-1M, NUCLEAR FUSION, 10.1088/0029-5515/39/9Y/304, 39.0, 9Y, Vol.39, No. 9Y, 1257-1270, 1999.09.
188. Zushi, H; Nakamura, K; Itoh, S; Sato, K; Sakamoto, M; Hanada, K; Jotaki, E; Makino, K; Kawasaki, S; Nakashima, H, High ion temperature discharge and its long sustainment in both limiter and single null configurations on TRIAM-1M, NUCLEAR FUSION, 10.1088/0029-5515/39/11Y/340, 39.0, 11Y, 1955.0-1963.0, IAEA-CN-69/EXP2/16, 1999.11, A high ion temperature discharge in the lower hybrid current drive scheme has been obtained for the first time in the world in the TRIAM-1M superconducting: tokamak. The high ion temperature mode is triggered by a transition which occurs within an operation window for the density, horizontal plasma position and antenna phasing. A steep ion temperature gradient (>80 keV/m) is formed near the core region at the transition. Long duration operation of this discharge has been successfully demonstrated in both the limiter and single null configurations by multiple control techniques..
189. Sakamoto, M; Itoh, S; Sato, KN; Nakamura, K; Zushi, H; Hanada, K; Jotaki, E; Makino, K; Kawasaki, S; Nakashima, H, Current profile control and improvement of current drive efficiency by combined lower hybrid waves in TRIAM-1M, NUCLEAR FUSION, 10.1088/0029-5515/40/3Y/303, 40.0, 3Y, 453.0-459.0, 0.0, 2000.03, Current profile control experiments were carried out in TRIAM-1M by the combination of two lower hybrid waves (LHWs) at 8.2 and 2.45 GHz with different spectra of parallel refractive index N-parallel to. In the combined lower hybrid current drive (LHCD) discharge, the current drive efficiency was improved by a factor of >1.5 compared with 8.2 GHz LHCD only and 2.45 GHz LHCD only. Measurements of the internal inductance and the radial profile of hard X ray emission indicated that the current profile can be controlled by changing the additional power of the 2.45 GHz LHW to the 8.2 GHz LHCD plasma. The improvement of the current drive efficiency and the modification of the current profile are considered to be attributable to the enhancement of the absorption of lower N-parallel to waves by higher N-parallel to waves in the two kinds of LHWs. Moreover, the controlled current profile can be successfully sustained for about two orders of magnitude longer than the current diffusion time..
190. Zushi, H; Itoh, S; Sato, KN; Nakamura, K; Sakamoto, M; Hanada, K; Jotaki, E; Makino, K; Pan, YD; Kawasaki, S; Nakashima, H, Recent progress on TRIAM-1M, NUCLEAR FUSION, 10.1088/0029-5515/40/6/315, 40.0, 6.0, 1183.0-1196.0, 0.0, 2000.06, A steady state plasma with high performance and high current drive efficiency is reported. In 2.45 GHz LHCD plasmas T-i is studied as a function of n(e) at the edge of the high ion temperature (HIT) window. Different characteristic timescales are found for T-i and n(e) to enter the HIT regime and the observed hysteresis behaviour of T-i with respect to n(e) is attributed to this difference. The electromagnetic emission (<3.5 GHz) is studied in order to understand ion heating mechanisms in the HIT regime. The spectrum shows several sidebands whose peak frequencies correspond to the ion plasma frequency. The spectral narrowing of the width of the sideband shows a clear correlation with ion heating. In 8.2 GHz LHCD plasmas an enhanced current drive (ECD) regime where both current drive efficiency eta(CD) (= (n) over bar(e)I(CD)R(o)/P-LH similar to 1 x 10(19) A m(-2)/W) and energy confinement time tau(E) (similar to 8-10 ms) are simultaneously improved is obtained at an (n) over bar(e) of 4.3 x 10(13) cm(-3) and B = 7 T under full current drive conditions. There exists a certain threshold power above which the ECD transition occurs. A hysteresis of eta(CD) is found around the threshold power, which is explained by the different characteristic time for the ECD transition in power rampup and rampdown schemes. Current profile control experiments are performed by using two opposite travelling LHWs. Current compensation (Delta I-CD/I-CD < -10%) is clearly seen when the backward (BW) travelling LHW (8.2 GHz) is added to a target plasma whose current is driven by a forward travelling LHW (8.2 GHz). As the BW wave power is increased, however, the current tends to flow in the forward direction. The mechanisms of this non-linear behaviour of the driven current with respect to the BW wave power are discussed..
191. Zushi, H; Itoh, S; Nakamura, K; Sakamoto, M; Hanada, K; Jotaki, E; Pan, YD; Hasegawa, M; Kawasaki, S; Nakashima, H, Steady state experiments on current profile control and long sustainment of high performance LHCD plasmas on the superconducting tokamak TRIAM-1M, NUCLEAR FUSION, 10.1088/0029-5515/41/10/315, 41.0, 10.0, 1483.0-1493.0, 0.0, 2001.10, The main purpose of TRIAM-1M (R-0 = 0.8 m, a x b = 0.12 m x 0.18 m, B = 8 T) is to study the route towards a high field compact steady state fusion reactor. In the advanced steady state operation programme, a heating mechanism for the high ion temperature mode with an internal transport barrier has been studied, an enhanced current drive mode in an extended (higher power and higher density) operation regime has been obtained, current density profile control experiments using multicurrent drive systems have been performed and the effects of wall recycling, wall pumping and wall saturation on particle control have been investigated..
192. Hanada, K; Itoh, S; Nakamura, K; Zushi, H; Sakamoto, M; Jotaki, E; Pan, YD; Hasegawa, M; Kawasaki, S; Nakashima, H, Enhanced current drive efficiency in a long discharge on TRIAM-1M, NUCLEAR FUSION, 10.1088/0029-5515/41/11/302, 41.0, 11.0, 1539.0-1542.0, 2001.11, The enhanced current drive (ECD) efficiency mode, which is characterized by a spontaneous increase of current drive efficiency eta (CD) from (0.3-0.4) x 10(19) A/W m(-2) to (0.6-1.0) x 10(19) A/W M(-2), is observed in long pure LHCD plasmas on TRIAM-1M. The energy confinement time is also improved due to the increase of line averaged electron density, and of the ion and electron temperatures. The current drive efficiency is proportional to the electron density. The transition to ECD mode occurs at a critical density, which depends slightly on the refractive index in the toroidal direction N(parallel to) of the injected wave..
193. Sakamoto, M; Itoh, S; Nakamura, K; Zushi, H; Hanada, K; Jotaki, E; Pan, YD; Kawasaki, S; Nakashima, H, Recycling and wall pumping in long duration discharges on TRIAM-1M, NUCLEAR FUSION, 10.1088/0029-5515/42/2/307, 42.0, 2.0, 165.0-168.0, PII S0029-5515(02)33450-1, 2002.02, Recycling and wall pumping have been studied comparing low (approximate to10(18) m(-3)) and high (approximate to10(19) m(-3)) density long duration plasmas in TRIAM-1M. The recycling coefficient of each plasma increases with time. There exist two time constants in the temporal evolution of the recycling coefficient. One is a few seconds and the other is about 30 s. The wall pumping rates of low and high density plasmas are evaluated to be approximate to1.5 x 10(16) atoms m(-2) s(-1) and approximate to4 x 10(17) atoms m(-2) s(-1), respectively. The difference may be caused by the total number of diffused ions and the charge exchange neutral flux with an energy of less than 0.7 keV. In an ultra-long discharge (approximate to70 min), the recycling coefficient becomes 1 or more before again decreasing below 1, i.e. the wall repeats the process of being saturated and refreshed. In high power and high density experiments, wall saturation phenomena have been observed. The discharge duration limited by wall saturation decreases with an increase in density..
194. Nakamura, K; Itoh, S; Zushi, H; Sakamoto, M; Hanada, K; Jotaki, E; Pan, YD; Kawasaki, S; Nakashima, H, Current profile control experiments in the LHCD plasma on TRIAM-1M, NUCLEAR FUSION, 10.1088/0029-5515/42/3/315, 42.0, 3.0, 340.0-343.0, PII S0029-5515(02)34176-0, 2002.03, Controllability of current profiles in long duration discharges is studied by two kinds of combination of wave spectra. First, by superposition of a higher N-parallel to spectrum wave at 2.45 GHz on a target plasma driven by a lower N-parallel to one at 8.2 GHz, a hollow j (r) profile has been achieved and sustained for 20 s. The current profile can be well controlled below a threshold power of 14 kW by varying the power at 2.45 GHz. A spontaneous transition phenomenon to a peaked j (r) profile, however, has occurred above the threshold power even after a reasonable steady state condition had been obtained. Second, using two oppositely travelling waves at 8.2 GHz the total current is clearly reduced, and the j (r) profile becomes peaked when the backward travelling lower hybrid waves (BWs) are superposed on the forward lower hybrid wave at a low power of 20 kW. When the BW power is increased above 27 kW, further current reduction is suppressed, and above 34 kW the direction of the current driven by the BWs is completely reversed and the j (r) profile becomes broad. Thus, current modification by BWs shows a highly non-linear behaviour with respect to the BW power..
195. Ishida, S; Abe, K; Ando, A; Cho, T; Fujii, T; Fujita, T; Goto, S; Hanada, K; Hatayama, A; Hino, T; Horiike, H; Hosogane, N; Ichimura, M; Tsuji-Iio, S; Itoh, S; Kamada, Y; Katsurai, M; Kikuchi, M; Kitsunezaki, A; Kohyama, A; Kubo, H; Kuriyama, M; Matsukawa, M; Matsuoka, M; Miura, Y; Miura, YM; Miya, N; Mizuuchi, T; Murakami, Y; Nagasaki, K; Ninomiya, H; Nishino, N; Ogawa, Y; Okano, K; Ozeki, T; Saigusa, M; Sakamoto, M; Sakasai, A; Satoh, M; Shimada, M; Shimada, R; Shimizu, M; Takagi, T; Takase, Y; Takeji, S; Tanabe, T; Toi, K; Ueda, Y; Uesugi, Y; Ushigusa, K; Wakatani, M; Yagi, Y; Yamaguchi, K; Yamamoto, T; Yatsu, K; Yoshikawa, K, Objectives and design of the JT-60 superconducting tokamak, NUCLEAR FUSION, 10.1088/0029-5515/43/7/314, 43.0, 7.0, 606.0-613.0, PII S0029-5515(03)64365-6, 2003.07, A fully superconducting tokamak named JT-60SC is designed for the modification programme of JT-60 to enhance economical and environmental attractiveness in tokamak fusion reactors. JT-60SC aims at realizing high-beta steady-state operation in the use of low radio-activation ferritic steel in a low v* and rho* regime relevant to the reactor plasmas. Objectives, research issues, plasma control schemes and a conceptual design for JT-60SC are presented..
196. Zushi, H; Itoh, S; Hanada, K; Nakamura, K; Sakamoto, M; Jotaki, E; Hasegawa, M; Pan, YD; Kulkarni, SV; Iyomasa, A; Kawasaki, S; Nakashima, H; Yoshida, N; Tokunaga, K; Fujiwara, T; Miyamoto, M; Nakano, H; Yuno, M; Murakami, A; Nakamura, S; Sakamoto, N; Shinoda, K; Yamazoe, S; Akanishi, H; Kuramoto, K; Matsuo, Y; Iwamae, A; Fuijimoto, T; Komori, A; Morisaki, T; Suzuki, H; Masuzaki, S; Hirooka, Y; Nakashima, Y; Mitarai, O, Overview of steady state tokamak plasma experiments in TRIAM-1M, NUCLEAR FUSION, 10.1088/0029-5515/43/12/006, 43.0, 12.0, 1600.0-1609.0, PII S0029-5515(03)71915-2, 2003.12, An overview of steady state tokamak studies in TRIAM-IM (R-0 = 0.8 m, a x b = 0.12 m x 0.18 m and B = 8 T) is presented. The current ramp-up scenario without using centre solenoid coils is reinvestigated with respect to controllability of the current ramp-up rate at the medium density region of (1-2) x 10(19) m(-3). The plasma is initiated by ECH (fundamental o-mode at 170 GHz with 200 kW) at B = 6.7 T, and the ramp-up rate below the technical limit of 150 kA s(-1) for ITER can be achieved by keeping the LH power less than 100 kW during the current ramp-up phase. The physics understanding of the enhanced current drive (ECD) mode around the threshold power level has progressed from a viewpoint of transition probability. A transition frequency, f(trans), for the ECD transition is determined as a function Of P-CD. At similar to70 kW no transition occurs for an f(trans), value of similar to0.017 Hz, meaning almost zero transition probability. With increasing P-CD > P-th, f(trans) increases up to 10 Hz, and the transition tends to occur with high probability. The record value of the discharge duration is updated to 3 h 10 min in a low (n) over tilde (e) similar to 1 x 10(18) m(-3) and low power (<10 kW) discharge. The global particle balance in long duration discharges is investigated, and the temporal change in wall pumping rate is determined. Although the density was low, the gas supply had to be stopped at 30 min after the plasma initiation to maintain the density constant. After that the density was sustained by the recycling flux alone until the end of the discharges. In addition to the recycling problem, in the high power and high density experiments, the localized PWI affects the SSO of the tokamak plasma. The effects of enhanced influx of metal impurities (Fe, Cr, Ni, Mo) on sustainment of the high performance ECD plasma are investigated. In order to evaluate the helium bombarding effects on the plasma facing component and hydrogen recycling in the future burning plasma, microscopic damage of metals exposed to long duration helium discharges was studied. The total exposure time was 128 s. From thermal desorption experiments for the specimens the amount of retained helium was evaluated as 3.9 x 10(20) He m(-2) and the scale length to be similar to1 mm in the SOL..
197. Hanada, K; Nakamura, K; Hasegawa, M; Itoh, S; Zushi, H; Sakamoto, M; Jotaki, E; Kulkarni, SV; Iyomasa, A; Kawasaki, S; Nakashima, H; Yoshida, N; Tokunaga, K; Fujiwara, T; Mitarai, O, Current ramp-up experiments in full current drive plasmas in TRIAM-1M, NUCLEAR FUSION, 10.1088/0029-5515/44/2/019, 44.0, 2.0, 357.0-361.0, PII S0029-5515(04)74023-5, 2004.02, Four types of plasma current ramp-up experiments in full non-inductively lower hybrid current driven (LHCD) plasmas were executed in TRIAM-1M: (1) current start-up by a combination of electron cyclotron resonance heating (ECRH) and LHCD, (2) tail heating by additional LHCD, (3) bulk heating by ECRH and (4) spontaneous ramp-up by a transition to enhanced current drive (ECD) mode. The time evolutions of plasma current during four types of ramp-up phase were adjusted by a simple model with two different time constants, which are a time defined by the total current diffusion time and a time constant for improving the current drive efficiency. In the case of (1) and (4), the latter time constant is significant during the current ramp-up phase. The improvement in the current drive efficiency in the ECD mode is likely to be caused by the increase in the effective refractive index along the magnetic field of the lower hybrid wave..
198. Sakamoto, M; Yuno, M; Itoh, S; Hanada, K; Nakamura, K; Zushi, H; Jotaki, E; Hasegawa, M; Kulkarni, S; Iyomasa, A; Kawasaki, S; Nakashima, H, Global particle balance and wall recycling properties of long duration discharges on TRIAM-1M, NUCLEAR FUSION, 10.1088/0029-5515/44/7/001, 44.0, 7.0, 693.0-698.0, PII S0029-5515(04)79641-6, 2004.07, The longest tokamak discharge, with a duration of 11406 s (3 It 10 min), has been achieved. The global particle balance has been investigated. In the longest discharge, the global balance between the particle absorption and release of the wall was achieved at t similar to 30 min. After that, the plasma density was maintained by the recycling flux alone until the end of the discharge. The maximum wall inventory is about 3.6 x 10(20) H at t similar to 30 min, but it is finally released from the wall at the end of the discharge. The hydrogen release seems to be caused by the temperature increase in the whole toroidal area of the main chamber. Moreover, it has been observed that there is a large difference between the properties of wall recycling in the continuous gas feed case (i.e. static condition) and in the additional gas puff case (i.e. dynamic condition). In the static condition, the effective particle confinement time increases to similar to 10 s during the I min discharge and it increases to similar to 100 s before the global balance in the longest discharge. In the dynamic condition, the decay time of the electron density just after the gas puff, i.e. the effective particle confinement time, is constant at 0.2-0.3 s during the discharge. The large difference in the effective particle confinement time between the static and dynamic conditions seems to be caused by the reduction in the recycling coefficient due to the enhanced wall pumping resulting from the additional gas puff..
199. Zushi, H; Nakamura, K; Hanada, K; Sato, KN; Sakamoto, M; Idei, H; Hasegawa, M; Iyomasa, A; Kawasaki, S; Nakashima, H; Higashijima, A; Kuramoto, T; Tanaka, A; Matsuo, Y; Esaki, K; Akanishi, H; Sugata, T; Hoshika, H; Sasaki, K; Maezono, N; Kitaguchi, M; Imamura, N; Yoshida, N; Tokunaga, K; Fujiwara, T; Miyamoto, M; Tokitani, M; Uehara, K; Sadamoto, Y; Nakashima, Y; Kubota, Y; Higasizono, Y; Takase, Y; Ejiri, A; Shiraiwa, S; Kado, S; Sikama, T; Tsuji-Iio, S; Takeda, T; Hirooka, Y; Ida, K; Nakamura, Y; Fujimoto, T; Iwamae, A; Maekawa, T; Mitarai, O, Steady-state tokamak operation, ITB transition and sustainment and ECCD experiments in TRIAM-1M, NUCLEAR FUSION, 10.1088/0029-5515/45/10/S12, 45.0, 10.0, #-#, 0.0, 2005.10, Experiments aiming at 'day long operation at high performance' have been carried out in TRIAM-1M. The record value of the discharge duration was updated to 5 h and 16 min. Steady-state tokamak operation is studied under the localized plasma wall interaction conditions. The distributions of the heat load, the particle recycling flux and impurity source are investigated to understand the co-deposition and wall pumping. The formation and sustainment of an internal transport barrier (ITB) in enhanced current drive mode has been investigated by controlling the lower hybrid driven current profile by changing the phase spectrum. An ITER relevant remote steering antenna for electron cyclotron wave injection was installed and a relativistic Doppler resonance of the oblique propagating extraordinary wave with energetic electrons driven by lower hybrid waves was studied..
200. Idei, H; Hanada, K; Zushi, H; Ohkubo, K; Hasegawa, M; Kubo, S; Nishi, S; Fukuyama, A; Sato, KN; Nakamura, K; Sakamoto, M; Yomasa, A; Kawasaki, S; Nakashima, H; Higashijima, A; Notake, T; Shimozuma, T; Ito, S; Hoshika, H; Maezono, N; Nakashima, K; Ogawa, M, Electron cyclotron current drive experiments in LHCD plasmas using a remote steering antenna on the TRIAM-1M tokamak, NUCLEAR FUSION, 10.1088/0029-5515/46/5/001, 46.0, 5.0, 489.0-499.0, 0.0, 2006.05, A remote steering antenna was recently developed for electron cyclotron heating and current drive (ECH/ECCD) experiments on the TRIAM- I M tokamak. This is the first application of the remote steering antenna concept for ECH/ECCD experiments, which have conditions relevant to the International Thermonuclear Experimental Reactor (ITER). Fundamental ECH and ECCD experiments were conducted in the ITER frequency from the low field using this antenna system. In addition to the angles near 0 degrees, the launcher was a symmetric direction antenna with an extended steering-angle capability of +/- (8 degrees-19 degrees). The output beam from the antenna was a well-defined Gaussian with a proper steering angle. The Gaussian content and the steering-angle accuracy were 0.85 and -0.5 degrees, respectively. The high power tests measured the antenna transmission efficiency at 0.90-0.94. The efficiencies obtained in the low and high power tests were consistent with the calculations using higher-order modes. In order to excite the pure O/X-modes in the oblique injection, two polarizers were used to control the elliptical polarization of the incident beam for the ECCD experiments. The fundamental O/X-mode ECH/ECCD was applied to lower hyrid current drive plasmas at the optimized incident polarization. In the X-mode experiment, at medium density (similar to 1 x 10(19) m(-3)), clear differences in the plasma current and the hard x-ray intensity were observed between the co- and counter-steering injections due to the ECCD effect on the coupling of forward fast electrons..
201. Ejiri, A.; Takase, Y.; Kasahara, H.; Yamada, T.; Hanada, K.; Sato, K. N.; Zushi, H.; Nakamura, K.; Sakamoto, M.; Idei, H.; Hasegawa, M.; Iyomasa, A.; Imamura, N.; Esaki, K.; Kitaguchi, M.; Sasaki, K.; Hoshika, H.; Mitarai, O.; Nishino, N., RF start-up and sustainment experiments on the TST-2@K spherical tokamak, NUCLEAR FUSION, 10.1088/0029-5515/46/7/003, 46.0, 7.0, 709.0-713.0, 0.0, 2006.07, Plasma start-up and sustainment without an inductive field have been studied in the TST-2@K spherical tokamak using high power RF sources (8.2 GHz/up to 170 kW). Steady state discharges with a plasma current of 4 kA were achieved. The line integrated density was about 3 x 10(17) m(-2) and the electron temperature was 160 eV. A truncated equilibrium was introduced to reproduce magnetic measurements. It was found that a positive Pfirsch-Schluter current in the open field line region at the outboard boundary makes a significant contribution to the current. Insensitivity of the current to variations in the vertical field and RF power variation was also found..
202. Takase, Y.; Ejiri, A.; Shiraiwa, S.; Adachi, Y.; Ishii, N.; Kasahara, H.; Nuga, H.; Ono, Y.; Oosako, T.; Sasaki, M.; Shimada, Y.; Sumitomo, N.; Taguchi, I.; Tojo, H.; Tsujimura, J.; Ushigome, M.; Yamada, T.; Hanada, K.; Hasegawa, M.; Idei, H.; Nakamura, K.; Sakamoto, M.; Sasaki, K.; Sato, K. N.; Zushi, H.; Nishino, N.; Mitarai, O., Plasma current start-up experiments without the central solenoid in the TST-2 spherical tokamak, NUCLEAR FUSION, 10.1088/0029-5515/46/8/S05, 46.0, 8.0, #-#, 0.0, 2006.08, Several techniques for initiating the plasma current without the use of the central solenoid are being developed in TST-2. While TST-2 was temporarily located at Kyushu University, two types of start-up scenarios were demonstrated. (1) A plasma current of 4 kA was generated and sustained for 0.28 s by either electron cyclotron wave or electron Bernstein wave, without induction. (2) A plasma current of 10 kA was obtained transiently by induction using only outboard poloidal field coils. In the second scenario, it is important to supply sufficient power for ionization (100 kW of EC power was sufficient in this case), since the vertical field during start-up is not adequate to maintain plasma equilibrium. In addition, electron heating experiments using the X-B mode conversion scenario were performed, and a heating efficiency of 60% was observed at a 100 kW RF power level. TST-2 is now located at the Kashiwa Campus of the University of Tokyo. Significant upgrades were made in both magnetic coil power supplies and RF systems, and plasma experiments have restarted. RF power of up to 400 kW is available in the high-harmonic fast wave frequency range around 20 MHz. Four 200 MHz transmitters are now being prepared for plasma current start-up experiments using RF power in the lower-hybrid frequency range. Preparations are in progress for a new plasma merging experiment (UTST) aimed at the formation and sustainment of ultra-high beta ST plasmas..
203. Bhattacharyay, R.; Zushi, H.; Nakashima, K.; Shikama, T.; Sakamoto, M.; Yoshida, N.; Kado, S.; Sawada, K.; Hirooka, Y.; Nakamura, K.; Hanada, K.; Idei, H.; Hasegawa, M.; Sato, K. N.; Ogawa, M.; Takaki, O.; Sasaki, K.; Xu, H.; Kawasaki, S.; Nakashima, H.; Higashijima, A., A study on temperature effects on hydrogen recycling and molybdenum impurity emission from a movable limiter in TRIAM-1M Tokamak, NUCLEAR FUSION, 10.1088/0029-5515/47/8/018, 47.0, 8.0, 864.0-874.0, 2007.08, In order to investigate the surface temperature effects on plasma fuel recycling and impurity release from the plasma facing components, plasma discharges have been performed under selected plasma-wall interaction (PWI) conditions in the high-field superconducting tokamak, TRIAM-1M. By moving a water-cooled molybdenum movable limiter (ML) beyond the last closed flux surface, as defined by poloidal limiters, the surface temperature profile on it is varied. Hot spots have been observed on the ML surface in such conditions. The release behaviour of fuel as well as impurity particles from the ML surface has been studied as a function of hot spot temperature (T-hot) by means of wide range spectroscopy (200-1600 nm). A critical Thot is found to be similar to 2100 K above which the emission of both hydrogen and impurity particles enhances significantly. This is indicative of some thermally activated process playing an important role in PWIs between the limiter and the edge plasma. With the rise in hot spot temperature localized PWI at the ML is found to dominate the global recycling even when external fuelling is stopped..
204. Zushi, H.; Hirooka, Y.; Bhattacharyay, R.; Sakamoto, M.; Nakashima, Y.; Yoshinaga, T.; Higashizono, Y.; Hanada, K.; Nishino, N.; Yoshida, N.; Tokunaga, K.; Kado, S.; Shikama, T.; Kawasaki, S.; Okamoto, K.; Miyazaki, T.; Honma, H.; Sato, K. N.; Nakamura, K.; Idei, H.; Hasegawa, M.; Nakashima, H.; Higashijima, A., Active particle control experiments and critical particle flux discriminating between the wall pumping and fuelling in the compact plasma wall interaction device CPD spherical tokamak, NUCLEAR FUSION, https://doi.org/10.1088/0029-5515/49/5/055020, 49.0, 5.0, 9.0, Article No. 055020, 2009.05, Two approaches associated with wall recycling have been performed in a small spherical tokamak device CPD (compact plasma wall interaction experimental device), that is, (1) demonstration of active particle recycling control, namely, 'active wall pumping' using a rotating poloidal limiter whose surface is continuously gettered by lithium and (2) a basic study of the key parameters which discriminates between 'wall pumping and fuelling'. For the former, active control of 'wall pumping' has been demonstrated during 50kW RF current drive discharges whose pulse length is typically similar to 300 ms. Although the rotating limiter is located at the outer board, as soon as the rotating drum is gettered with lithium, hydrogen recycling measured with H a spectroscopy decreases by about a factor of 3 not only near the limiter but also in the centre stack region. Also, the oxygen impurity level measured with O II spectroscopy is reduced by about a factor of 3. As a consequence of the reduced recycling and impurity level, RF driven current has nearly doubled at the same vertical magnetic field. For the latter, global plasma wall interaction with plasma facing components in the vessel is studied in a simple torus produced by electron cyclotron waves with I(p) < 1 kA. A static gas balance (pressure measurement) without external pumping systems has been performed to investigate the role of particle flux on a transition of 'wall fuelling' to 'wall pumping'. It is found that a critical particle flux exists to discriminate between them. Beyond the critical value, a large fraction (similar to 80%) of pressure drop ('wall pumping') is found, suggesting that almost all injected particles are retained in the wall. Below it, a significant pressure rise ('wall fuelling') is found, which indicates that particles are fuelled from the wall during/just after the discharge. Shot history effects (integrated particle recycling behaviour from the plasma facing surfaces) are seen on that the critical particle flux is reducing from 0.8 x 10(-4) to similar to 0.1 x 10(-4) Torr during the experimental campaign (similar to 3000 shots). In the wall pumping pressure range the wall pumping fraction is reduced with increasing surface temperature up to 150 degrees C..
205. Sharma, S. K.; Zushi, H.; Osakabe, M.; Takeiri, Y.; Yoshida, N.; Hasegava, M.; Yoshinaga, T.; Hanada, K.; Idei, H.; Sakamoto, M.; Nakamura, K.; Sato, K. N., Analysis of the footprint traces on the first walls of the compact plasma wall interaction device (CPD) using surface analysis and electron orbit calculations, NUCLEAR FUSION, 10.1088/0029-5515/50/2/025017, 50.0, 2.0, 0.0-0.0, Article No. 025017, 2010.02, After the non-inductive current startup experimental campaign on the spherical tokamak compact plasma wall interaction device (CPD), various localized damage tracks or footprint traces have been observed on plasma facing components (PFCs), such as the chamber walls and the 'stiffeners' that support them. Although the magnetic field configuration is mainly open, the footprint traces are classified as (1) radially distributed traces, (2) toroidal imperfect circular traces with small gaps, (3) arc-shaped traces and (4) vertically distributed traces. The surface analysis of the samples attached near the traces has been carried out by scanning electron microscopy and x-ray photoelectron spectroscopy. They suggest thin deposition of impurity materials (C, Cu, Ti, Fe and their oxides) over the traces. These footprint traces are analysed in view of the localized plasma wall interaction and the loss of energetic electrons using orbit calculations. Radially distributed traces correspond to the loss of co- and countermoving passing electrons mainly escaping along the magnetic field lines. The imperfect circular traces are found corresponding to lost orbits of the energetic trapped electrons largely crossing the magnetic field lines. Other traces are also discussed from a viewpoint of loss along the magnetic field lines and impurity deposition..
206. Stober, J.; Jackson, G. L.; Ascasibar, E.; Bae, Y-S.; Bucalossi, J.; Cappa, A.; Casper, T.; Cho, M-H.; Gribov, Y.; Granucci, G.; Hanada, K.; Hobirk, J.; Hyatt, A. W.; Ide, S.; Jeong, J-H.; Joung, M.; Luce, T.; Lunt, T.; Namkung, W.; Park, S-I.; Politzer, P. A.; Schweinzer, J.; Sips, A. C. C., ECRH-assisted plasma start-up with toroidally inclined launch: multi-machine comparison and perspectives for ITER, NUCLEAR FUSION, 10.1088/0029-5515/51/8/083031, 51.0, 8.0, 0.0-0.0, Article No. 083031, 2011.08, Electron cyclotron resonance heating (ECRH)-assisted plasma breakdown is foreseen with full and half magnetic field in ITER. As reported earlier, the corresponding O1- and X2-schemes have been successfully used to assist pre-ionization and breakdown in present-day devices. This contribution reports on common experiments studying the effect of toroidal inclination of the ECR beam, which is >= 20 degrees in ITER. All devices could demonstrate successful breakdown assistance for this case also, although in some experiments the necessary power was almost a factor of 2 higher compared with perpendicular launch. Differences between the devices with regard to the required power and vertical field are discussed and analysed. In contrast to most of these experiments, ITER will build up loop voltage prior to the formation of the field null due to the strong shielding by the vessel. Possible consequences of this difference are discussed..
207. Banerjee, Santanu; Zushi, H.; Nishino, N.; Hanada, K.; Sharma, S. K.; Honma, H.; Tashima, S.; Inoue, T.; Nakamura, K.; Idei, H.; Hasegawa, M.; Fujisawa, A., Statistical features of coherent structures at increasing magnetic field pitch investigated using fast imaging in QUEST, NUCLEAR FUSION, 10.1088/0029-5515/52/12/123016, 52.0, 12.0, 0.0-0.0, 123016, 2012.12, Fluctuations in slab plasma produced by electron cyclotron waves in an open magnetic configuration with vertical (B-z) and toroidal (B-t) fields are investigated as a function of B-z/B-t (field pitch) using a high speed visible camera in the spherical tokamak QUEST. Higher order moments (skewness s and kurtosis k) of spatio- temporal fluctuations are investigated. Background fluctuations, generation of coherent convective structures (blobs) and their propagation are analysed at the intensity gradient (R-im) and the source- free (essentially vacuum on the low- field side) regions, respectively. Parabolic relation (k = As-2 + C) is observed between s and k on the entire R- Z plane for a wide range of B-z/B-t. Progressive shift from the Gaussian statistics beyond R-im is observed with increasing B-z/B-t. From the moments of the probability density functions, possible location for blob generation is inferred to be R-im. Direct correspondence is observed with the prominence of the blobs and increase in stochastic forces with the increase in field pitch. Distribution of waiting time suggests that the blob generation may be a Poisson process. Accelerated cross field transport is observed for reasonably large-sized blobs..
208. Tashima, Saya; Zushi, H.; Isobe, M.; Hanada, K.; Idei, H.; Nakamura, K.; Fujisawa, A.; Matsuoka, K.; Hasegawa, M.; Nagashima, Y.; Okamura, S.; Banerjee, S.; Kawasaki, S.; Nakashima, H.; Higashijima, A., Role of energetic electrons during current ramp-up and production of high poloidal beta plasma in non-inductive current drive on QUEST, NUCLEAR FUSION, 10.1088/0029-5515/54/2/023010, 54.0, 2.0, 0.0-0.0, 023010, 2014.02, A scenario for non-inductive current ramp-up has been demonstrated using electron cyclotron waves in the spherical tokamak QUEST. The configuration was characterized by a high toroidal magnetic mirror ratio of 2 and a steady vertical magnetic field of more than 10% of the toroidal magnetic field. The generation and confinement of energetic electrons having energy greater than 10 keV were studied using hard x-rays. Because of the energetic electron pressure, a natural divertor formed with an inboard poloidal field null at the high poloidal beta (approximately 3-4)..
209. S. Itoh, E. Jotaki, K. Nakamura, M. Sakamoto, K. Hanada, H. Zushi, M. Hasegawa, S. Kawasaki, H. Nakasima, Current Ramp-up Experiments Using ECRW on TRIAM-1M, Juornal of Plasma and Fusion Science, 79.0, 4.0, 413.0-419.0, Vol. 79, No. 4, pp.413-419, 2003.04, The operation of tokamak devices is based on the principle of the transformer, so it has been considered that pulse operation of such devices is inevitable. But the superconducting high-field tokamak TRIAM-1M has been demonstrated continuous operation for last 15 years and succeeded in sustaining 3 hours of constant operation in 2001. Fusion reactors of the future will use the center solenoid (CS) coil only in the ramp-up phase of the plasma current. If the coil is removed from the tokamak device, the device can be simplified and its cost will be decreased. In TRIAM-1M experiments, a perfect CS-free ramp-up was demonstrated and succeeded in sustaining the plasma current longer than 30 s. In this paper, the operation scenario, especially plasma position control, and the results of the analysis of plasma control are described..
210. Kazuaki Hanada, Heat Flow during Sawtooth Collapse in Tokamak Plasmas, Journal of the Physical Society of Japan, 10.1143/JPSJ.63.967, 63, 3, 967-978, 1994.01, [URL], Heat flow during sawtooth collapse was studied on the WT-3 tokamak by using temporal evolution of soft X-ray intensity profile in the poloidal cross section in a lower hybrid current driven plasma as well as an electron cyclotron heated plasma. Two phases in sawtooth collapses were observed. In the first phase, the hottest spot that is the peak of the soft X-ray distribution approaches the inversion surface and heat flows out through a narrow gate on the inversion surface. In the second phase, the hottest spot stays on the inversion surface, and heat flows out through the whole inversion surface. This suggests that magnetic reconnection as predicted by Kadomtsev's model occurs in the first phase, but in the second phase, a different mechanism dominates heat flow..
211. Makoto Hasegwa, Kazuo Nakamura, Hideki Zushi, Kazuaki Hanada, akihide fujisawa, Keisuke Matsuoka, Hiroshi Idei, Yoshihiko Nagashima, Kazutoshi Tokunaga, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Development of a plasma control system for steady-state operation on QUEST, Journal of the Korean Physical Society, 10.3938/jkps.65.1191, 65, 8, 1191-1195, 2014.01, [URL], A drift error correction technique with machine vision and a real-time equilibrium calculation code have been developed on the QUEST (Q-shu university experiment with the steady-state spherical tokamak) for steady-state operation. The drift error caused by the long time-integration of magnetic raw signals has to be removed. With a captured image of the plasma’s cross section, the plasma’s position is identified by use of image filters. The measured magnetic flux values are corrected to the calculated flux values estimated by using this plasma position. The correction with the captured image work as expected in the preliminary result using a flashlight instead of a plasma..
212. K. Hanada, H. Zushi, E. Jotaki, Y. D.Pan, M. Sakamoto, K. Nakamura, S. Itoh, Enhancement of RF current drive efficiency on TRIAM-1M, Journal of Plasma and Fusion Research, 77.0, 3.0, 294.0-299.0, 2001.03.
213. SAKAMOTO Mizuki, ITOH Satoshi, NAKAMURA Kazuo, ZUSHI Hideki, HANADA Kazuaki, JOTAKI Eriko, HASEGAWA Makoto, PAN Yudong, KAWASAKI Shoji and NAKASHIMA Hisatoshi, Wall Recycling on the Superconducting Tokamak TRIAM-1M, Journal of Plasma and Fusion Research, 78.0, 1.0, 52.0-58.0, 2002.01.
214. MITARAI Osamu, TAKASE Yuichi, EJIRI Akira, SHIRAIWA Shun’ichi, KASAHARA Hiroshi, YAMADA Takuma, OHARA Shinya, TST-2 Team, NAKAMURA Kazuo, IYOMASA Atsuhiro, HASEGAWA Makoto, IDEI Hiroshi, SAKAMOTO Mizuki, HANADA Kazuaki, SATOH Kohnosuke, ZUSHI Hideki, TRIAM Group and NISHINO Nobuhiro, Plasma current start-up by ECW and vertical field in the TST-2 spherical tokamak, Journal of Plasma and Fusion Research SERIES, Vol. 80, No. , Pages 549, 2004.07.
215. H. Honma, K. Hanada, N. Fukumoto, M. Nagata, N. Nishino, K. N. Sato, K. Nakamura, H. Zushi, H. Idei, M. Sakamoto, M. Hasegawa, S. Kawasaki, H. Nakashima, A. Higashijima, S. Kawakami, T. Yoshinaga, Calorimetric measurement of kinetic energy of compact toroid in the spherical tokamak CPD, Journal of Plasma and Fusion Research, 8.0, 1015.0-1019.0, 2009.08.
216. Kazuo NAKAMURA, Shinji MATSUFUJI, Masashi TOMODA, Feng WANG, Osamu MITARAI, Kenichi KURIHARA, Yoichi KAWAMATA, Michiharu SUEOKA, Makoto HASEGAWA, Kazutoshi TOKUNAGA, Kohnosuke SATO, Hideki ZUSHI, Kazuaki HANADA, Mizuki SAKAMOTO, Hiroshi IDEI, Shoji KAWASAKI, Hisatoshi NAKASHIMA and Aki HIGASHIJIMA, Characteristics of SVD in ST Plasma Shape Reproduction Method Based on CCS, Journal of Plasma and Fusion Research, 8.0, 1048.0-1051.0, 2009.09.
217. Tomokazu YOSHINAGA, Kazuaki HANADA, Kohnosuke SATO, Hideki ZUSHI, Kazuo NAKAMURA, Hiroshi IDEI, Mizuki SAKAMOTO, Yousuke NAKASHIMA, Makoto HASEGAWA, Yuta HIGASHIZONO, Shoji KAWASAKI, Hisatoshi NAKASHIMA, Aki HIGASHIJIMA, Rajendraprasad BHATTACHARYAY, Kosuke DONO, Hiroshi HONMA, Masaki ISHIGURO, Takashi SAKIMURA, Tomofumi RYOKAI and Toshimasa MIYAZAKI, Non-inductive formation of spherical tokamak plasmas by ECH on CPD, Journal of Plasma and Fusion Research SERIES, 8.0, Vol.8,pp.100-104, 2009.09.
218. H. Idei, N. Takeuchi, S. Kubo, A. Fukuyama, H. Nuga, M. Sakaguchi, N. Nakamura, K. Hanada, H. Zushi, K. N. Sato, M. Sakamoto, M. Hasegawa, Y. Takase, O. Mitarai, Maekawa and Y. Kishimoto, Ray Trace and Fokker-Plank Analyses for Electron Bernstein Wave Heating and Current Drive in QUEST, Journal of Plasma and Fusion Research SERIES, 8.0, Vol.8,pp.1104-1107, 2009.09.
219. RYOUKAI, Tomofumi; ZUSHI, Hideki; MORISAKI, Tomohiro; IDEI, Hiroshi; HANADA, Kazuaki; DONO, Kousuke; MUTOH, Takashi; KUBO, Shin; NAGASAKI, Kazunobu;, The correlation analysis between electron density fluctuation and RF stray power in the CPD electron cyclotron plasma, Journal of Plasma and Fusion Research SERIES, 9.0, 310.0-315.0, https://inis.iaea.org/search/search.aspx?orig_q=journal:%22ISSN%201883-9630%22, 2010.01.
220. H. Idei, K. Nagata, M. Sakaguchi, K. Dono, Y. Wataya, A. Ohdachi, S. Inagaki, Y. Nagayama, K. Kawahata, H. Igami, T. Shimozuma, H. Zushi, K. Hanada, K. Nakamura, M. Sakamoto, M. Hassegawa, Y. Higashizono, S. Kawasaki, H. Nakashima, A. Higashijima, Y. Takase, T. Maekawa, O. Mitarai and Y. Kishimoto, Differential-Phase Reflectometry and Electron Bernstein Wave Radiometry using Phased-array Antenna System in the QUEST, Journal of Plasma and Fusion Research, 9.0, 112.0-117.0, (Proc.APFA2009/APPTC2009), 2010.08, The differential-phase reflectometry has been developed to measure the density profile evolution, concering electron Bernstein Wave (EBW) heating and current drive in the QUEST. The proper phase dependence was confirmed in developed single-side-band heterodyne differential-phase reflectometry at RIAM microwave/mm-wave test facilities. The phase time evolutions in the QUEST were also successfully measured, but the weak reflected-wave caused the small ratio of signal to noise in the measurements. The Phased Array Antenna (PAA) system was proposed for the reflectometry to obtain the large reflected-wave. The oblique viewing EBW emission can be measured by the precise phasearray measurements between the PAA waveguide elements. The PAA was confirmed to be effective, as a launching antenna for the reflectometry, and as a receiving antenna for the EBW radiometry. Keywords: AM reflectometry, Electron Bernstein wave, phased-array antenna, QUEST.
221. Osamu MITARAI, Kazuo NAKAMURA, Masaki ISHIGURO, Makoto HASEGAWA, Hiroshi IDEI, Mizuki SAKAMOTO, Kazuaki HANADA, Hideki ZUSHI, Hai Qing LIU, Saya TASHIMA, Yuta HIGASHIZONO, Aki HIGASHIJIMA, Hisatoshi NAKASHIMA, Shoji KAWASAKI and QUEST Group, Plasma Current Ramp-Up Experiments in QUEST, Journal of Plasma and Fusion Research, 9.0, (※), 2010.08.
222. S. Tashima, H. Zushi, M. Isobe, S. Okamura, H. Idei, K. Hanada, T. Ryoukai, M. Ishiguro, S. Sharma, SHU and the QUEST group, Hard X-ray measurement during the current startup phase in QUEST, Journal of Plasma and Fusion Research SERIES, 9.0, 316.0-321.0, 2010.08.
223. H. Q. LIU, K. HANADA, N. NISHINO, R. OGATA, M. ISHIGURO, H. ZUSHI, K. NAKAMURA, K. N. SATO, M. SAKAMOTO, H. IDEI, M. HASEGAWA, Y. HIGASHIZONO, S. KAWASAKI, H. NAKASHIMA, A. HIGASHIJIMA, and QUEST GROUP, Measurement of blob-like structure behavior in the plasma edge in QUEST, Journal of Plasma and Fusion Research SERIES, 9.0, 33.0-36.0, (※), 2010.08.
224. Y. Higashizono, M. Sakamoto, Y. Nakashima, R. Yonenaga, H. Zushi, K. Hanada, M. Ishiguro, K. Nakamura, H. Idei, M. Hasegawa, K. N. Sato, I. Gouda, S. Tsuru, S. Kawasaki, H. Nakashima, A. Higashijima, N. Nishino, O. Mitarai, T. Maekawa, Y. Kishimoto, Y. Takase and QUEST Group:, Observation of separated plasma structure in non inductive discharge in QUEST, Journal of Plasma and Fusion Research SERIES, 9.0, 007-011, (※), 2010.08.
225. S. K. Sharma, H. Zushi, I. Takagi, Y. Hisano, T. Shikama, S. Morita. T. Tanabe, N. Yoshida, M. Sakamoto, Y. Higashizono, K. Hanada, M. Hasegawa, O. Mitarai, K. Nakamura, H. Idei, K. N. Sato, S. Kawasaki, H. Nakashima, A. Higashijima, Y. Nakashima, N. Nishino, Y. Hatano, A. Sagara, Y. Nakamura, N. Ashikawa, T. Maekawa, Y. Kishimoto, Y. Takase and QUEST Group, Study of the plasma driven permeation of hydrogen through a nickel membrane in RF and ohmic plasmas in the spherical tokamak QUEST, Journal of Plasma and Fusion Research SERIES, 9.0, Volume 9 (2010,pp142-146, 2010.08.
226. M. Ishiguro, K. Hanada, H. Zushi, K. N. Sato, K. Nakamura, H. Idei, M. Sakamoto, M. Hasegawa, T. Yoshinaga, S. Kawasaki, H. Nakashima, A. Higashijima, The Study about the Relationship between Plasma Current in Open Magnetic Field and the Formation of Closed Flux Surface in CPD, Journal of Plasma and Fusion Research SERIES, 9.0, Vol.9,018-022(※Proceedings of the 7th General Scientific Assembly of the Asia Plasma and Fusion Association in 2009 (APFA2009) and Asia-Pacific Plasma Theory Conference in 2009 (APPTC2009),October 27-30,2009,Aomori,Japan), 2010.08.
227. H. Idei, K. Nagata, M. Sakaguchi, K. Dono, Y. Wataya, A. Ohdachi, S. Inagaki, Y. Nagayama, K. Kawahata, H. Igami, T. Shimozuma, H. Zushi, K. Hanada, K. Nakamura, M. Sakamoto, M. Hassegawa, Y. Higashizono, S. Kawasaki, H. Nakashima, A. Higashijima, Y. Takase, T. Maekawa, O. Mitarai and Y. Kishimoto, Differential-Phase Reflectometry and Electron Bernstein Wave Radiometry using Phased-array Antenna System in the QUEST, Journal of Plasma and Fusion Research, 10.1109/ICIMW.2010.5612434, 9.0, 0.0, 112.0-117.0, 2010.08, The differential-phase reflectometry has been developed to measure the density profile evolution, concering electron Bernstein Wave (EBW) heating and current drive in the QUEST. The proper phase dependence was confirmed in developed single-side-band heterodyne differential-phase reflectometry at RIAM microwave/mm-wave test facilities. The phase time evolutions in the QUEST were also successfully measured, but the weak reflected-wave caused the small ratio of signal to noise in the measurements. The Phased Array Antenna (PAA) system was proposed for the reflectometry to obtain the large reflected-wave. The oblique viewing EBW emission can be measured by the precise phasearray measurements between the PAA waveguide elements. The PAA was confirmed to be effective, as a launching antenna for the reflectometry, and as a receiving antenna for the EBW radiometry. Keywords: AM reflectometry, Electron Bernstein wave, phased-array antenna, QUEST.
228. Ishiguro, Masaki; Hanada, Kazuaki; Liu, Hiqing; Ogata, Ryota; Isobe, Mitsutaka; Tashima, Saya; Zushi, Hideki; Sato, Khonosuke; Fujisawa, Akihide; Nakamura, Kazuo; Idei, Hiroshi; Sakamoto, Mizuki; Hasegawa, Makoto; Takase, Yuichi; Maekawa, Takashi; Kishimoto, Yasuaki; Mitarai, Osamu; Kawasaki, Shoji; Nakashima, Hisatoshi; Higashijima, Aki, Investigation of Non-inductive Plasma Current Start-up by RF on QUEST, Journal of Physics Conference Series, 10.1088/1742-6596/511/1/012041, 511.0, 0.0, 0.0-0.0, Article No. 012041, 2014.09, Formations of a closed flux surface (CFS) on QUEST are achieved by fully non-inductive current start-up driven by RF, which is 8.2GHz in frequency and more than 40kW in power. It found that appropriate magnetic configuration with positive n-index and reduction of particle recycling was crucial to achieve the non-inductive plasma current start-up (PCS) successfully. Especially the controllability of particle recycling should be improved by wall conditioning based on successive plasma production and wall cleaning with electron cyclotron resonance heating (ECR) plasmas induced by RF in frequency of 2.45GHz..
229. Kazuaki Hanada, H. Zushi, N. Yoshida, N. Yugami, T. Honda, Makoto Hasegawa, K. Mishra, A. Kuzmin, K. Nakamura, akihide fujisawa, Hiroshi Idei, Yoshihiko Nagashima, O. Watanabe, Takumi Onchi, Hideo Watanabe, Kazutoshi Tokunaga, A. Higashijima, S. Kawasaki, H. Nakashima, Y. Takase, A. Fukuyama, O. Mitarai, Y. K.M. Peng, Particle balance in long duration RF driven plasmas on QUEST, Journal of Nuclear Materials, 10.1016/j.jnucmat.2015.01.013, 463, 1084-1086, 2015.07, [URL], Abstract Global particle balance in non-inductive long-duration plasma on QUEST has been investigated. Approximately 70% of the fuel hydrogen (H) was retained in the wall and then was almost exhausted just after the discharge. The global recycling ratio (Rg), defined as the ratio of the evacuated H2 flux to that injected, was found to gradually increase during discharges and subsequently rose rapidly. To study the growth of Rg, the thermal desorption spectra after deuterium implantation in a specimen exposed to QUEST plasma was analyzed with a model which includes reflection, diffusion, solution, recombination, trapping, and plasma-induced desorption in the re-deposition layer. The model reconstructs the growth of Rg during a long-duration plasma and indicates solution plays a dominant role in the growth..
230. A. Kuzmin, H. Zushi, I. Takagi, S.K. Sharma, A. Rusinov, Y. Inoue, Y. Hirooka, H. Zhou, M. Kobayashi, M. Sakamoto, K. Hanada, N. Yoshida, K. Nakamura, A. Fujisawa, K. Matsuoka, H. Idei, Y. Nagashima, M. Hasegawa, T. Onchi, S. Banerjee, K. Mishra, Global gas balance and influence of atomic hydrogen irradiation on the wall inventory in steady-state operation of QUEST tokamak, Journal of Nuclear Materials, 10.1016/j.jnucmat.2014.12.092, Available online, 2014.12.
231. Hiroshi Idei, K. Mishra, M. K. Yamamoto, M. Hamasaki, akihide fujisawa, Yoshihiko Nagashima, Y. Hayashi, Takumi Onchi, Kazuaki Hanada, H. Zushi, Adaptive-Array electron cyclotron emission diagnostics using data streaming in a software defined radio system, Journal of Instrumentation, 10.1088/1748-0221/11/04/C04010, 11, 4, 2016.04, [URL], Measurement of the Electron Cyclotron Emission (ECE) spectrum is one of the most popular electron temperature diagnostics in nuclear fusion plasma research. A 2-dimensional ECE imaging systemwas developed with an adaptive-Array approach. Aradio-frequency (RF) heterodyne detection system with Software Defined Radio (SDR) devices and a phased-Array receiver antenna was used to measure the phase and amplitude of the ECE wave. The SDR heterodyne system could continuously measure the phase and amplitude with sufficient accuracy and time resolution while the previous digitizer system could only acquire data at specific times. Robust streaming phase measurements for adaptive-Arrayed continuous ECE diagnostics were demonstrated using Fast Fourier Transform (FFT) analysis with the SDR system. The emission field pattern was reconstructed using adaptive-Array analysis. The reconstructed profileswere discussed using profiles calculated from coherent single-frequency radiation from the phase array antenna..
232. Hiroshi Idei, Shouji Kawasaki, Kazuaki Hanada, Hideki Zushi, Kohnosuke Sato, Kazuo Nakamura, Mizuki Sakamoto, Makoto Hasegawa, Hisatoshi Nakashima, Aki Higashijima, Yuichi Wataya, Shinji Matsubara, Shuhei Kawano, Initial results of AM reflectometory on CPD, Joint 32nd International Conference on Infrared and Millimetre Waves, and 15th International Conference on Terahertz Electronics, IRMMW-THz2007
IRMMW-THz2007 - Conference Digest of the Joint 32nd International Conference on Infrared and Millimetre Waves, and 15th International Conference on Terahertz Electronics
, 10.1109/icimw.2007.4516610, 518-519, 2007.12, The amplitude modulation reflectometer system has been developed to measure the density profile in detail on the Compact PWI ( plasma-wall interaction ) Device (CPD) experiments. The probing frequency range was 6-18 GHz, and its frequency-switching time was 10 μs in an arbitrary step. Using the broadband fast-scanning reflectometer, the wide-range density profile can be measured with high time resolution. In X-mode reflectometory, the developed system successfully measured the phase delay of propagating waves at 6.6, 8.8 and 13.2 GHz, reflected at the vessel wall of the CPD and the R-cutoff layers in the CPD plasma..
233. Hiroshi Idei, Shouji Kawasaki, Kazuaki Hanada, Hideki Zushi, Kohnosuke Sato, Kazuo Nakamura, Mizuki Sakamoto, Makoto Hasegawa, Hisatoshi Nakashima, Aki Higashijima, Yuichi Wataya, Shinji Matsubara, Shuhei Kawano, Initial results of AM reflectometory on CPD, Joint 32nd International Conference on Infrared and Millimetre Waves, and 15th International Conference on Terahertz Electronics, IRMMW-THz2007 IRMMW-THz2007 - Conference Digest of the Joint 32nd International Conference on Infrared and Millimetre Waves, and 15th International Conference on Terahertz Electronics, 10.1109/icimw.2007.4516610, 0.0, 0.0, 518-519, 2007.12, The amplitude modulation reflectometer system has been developed to measure the density profile in detail on the Compact PWI ( plasma-wall interaction ) Device (CPD) experiments. The probing frequency range was 6-18 GHz, and its frequency-switching time was 10 μs in an arbitrary step. Using the broadband fast-scanning reflectometer, the wide-range density profile can be measured with high time resolution. In X-mode reflectometory, the developed system successfully measured the phase delay of propagating waves at 6.6, 8.8 and 13.2 GHz, reflected at the vessel wall of the CPD and the R-cutoff layers in the CPD plasma..
234. Kouji Shinohara, Syun'ichi Shiraiwa, Katsumichi Hoshino, Yukitoshi Miura, Kazuaki Hanada, Hiroshi Toyama, A new method to analyze density fluctuation by microwave reflectometry, Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers, 10.1143/JJAP.36.7367, 36, 12 A, 7367-7374, 1997.01, [URL], The runaway phase phenomenon is a problem in reflectometry measurements. The change in the phase difference between the reflected wave and the reference one cannot be explained by the movement of the cut-off layer when the runaway phase phenomenon occurs. It is difficult to extract information of the density fluctuation from the data with the runaway phase. We show a model in which the runaway phase phenomenon comes from the wave scattered by the density fluctuations, and describe a new analysis method based on this model. The obtained results on plasma displacement and density fluctuation spectrum are presented..
235. K. Hanada, H. Zushi, H. Idei, K. Nakamura, M. Ishiguro, S. Tashima, E. I.Kalinnikova, M. Sakamoto, M. Hasegawa, A. Fujisawa, A. Higashijima, S. Kawasaki, H. Nakashima, H. Liu, O. Mitarai, T. Maekawa, A. Fukuyama, Y. Takase, J. Qian, Recent experiments and future collaborations on QUEST, JSPS-CAS Core University Program Seminar on Summary of 10-year Collaborations in Plasma and Nuclear Fusion Research Area 9?11 March 2011,Okinawa,Japan, 204.0, 204.0, 2011.07.
236. Sakamoto, M; Nakashima, H; Kawasaki, S; Iyomasa, A; Kulkarni, SV; Hasegawa, M; Jotaki, E; Zushi, H; Nakamura, K; Hanada, K; Itoh, S, Static and dynamic properties of wall recycling in TRIAM-1M, JOURNAL OF NUCLEAR MATERIALS, 10.1016/S0022-3115(02)01390-9, 313.0, 0.0, 519.0-523.0, PII S0022-3115(02)01390-9, 2003.03, A large difference between properties of wall recycling in the continuous gas feed case (i.e. static condition) and the additional gas puff case (i.e. dynamic condition) has been observed. In the static condition, the effective particle confinement time, tau(p)(*), increases almost linearly to about 10 s during the I min discharge. In the dynamic condition, tau(p)(*) is 0.2-0.3 s during the I min discharge. This difference of tau(p)(*) is also confirmed in the ultra-long discharge. tau(p)(*) in the static condition becomes similar to100 s before the global balance between particle absorption and release of the wall is achieved at t similar to30 min. tau(p)(*) in the dynamic condition is, however, still on the order of similar to0.3 s. The large difference between tau(p)(*) in the static and dynamic conditions is attributed to a reduction in the recycling coefficient due to enhanced wall pumping resulting from the gas puff. (C) 2003 Elsevier Science B.V. All rights reserved..
237. H. Zushi, S. Itoh, N. Yoshida, K. Hanada, K. Nakamura, M. Sakamoto, E. Jotaki, M. Hasegawa, K. Tokunaga, A. Iyomasa, A. Iwamae, Y. Hirooka, Physics and Technological Issues for Steady-State Tokamak Operation on TRIAM-1M, JOURNAL OF NUCLEAR MATERIALS, Vol.79, pp.1302-1316, 2003.12.
238. M. Hasegawa, K. Hanada, S. Itoh, K. Nakamura, H. Zushi, M. Sakamoto, E. Jotaki, S. V. Kulkarni, A. Iyomasa, S. Kawasaki, H. Nakashima, K. Nagasaki, Plasma Experiments Using a New 170GHz EC System and a Simple Model for Plasma Production, JOURNAL OF NUCLEAR MATERIALS, Vol.80, No.1 pp.53-58, 2004.01.
239. SHIRAIWA, Syun’ichi; Ejiri, Akira; Hanada, Kazuaki; Hasegawa, Makoto; Hoshika, Hiroyuki; Idei, Hiroshi; Iyomasa, Atsuhiro; Kamada, Yusuke; Kasahara, Hiroshi; Mitarai, Osamu;, Evidence of electron Bernstein wave heating on the TST-2 spherical tokamak, JOURNAL OF NUCLEAR MATERIALS, 81.0, 1.0, P3-P4, 2005.01.
240. Hanada, K.; Shinoda, N.; Sugata, T.; Sasaki, K.; Zushi, H.; Nakamura, K.; Sato, K. N.; Sakamoto, M.; Idei, H.; Hasegawa, M.; Kawasaki, S.; Nakashima, H.; Higashijima, A., Calorimetric measurement of heat load in full non-inductive LHCD plasmas on TRIAM-1M, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2007.01.255, 363.0, 1425.0-1428.0, 2007.06, Calorimetric measurements using the temperature increment of cooling-water were carried out to estimate the heat load distribution on the plasma facing components (PFCs) in the limiter discharges on TRIAM-1M. Line averaged electron density, n(e), and LH power, P-LH, dependences of the heat load on PFCs were measured. The heat load on the limiters was proportional to n(e)(1.5) in the range of n(e) = 0.2-1.0 x 10(19) m(-3) and P-LH(I) in the range of P-LH = 0.005-0.09 MW. For P-LH > 0.1 MW, the plasma transition to an enhanced current drive (ECD) mode appeared and the n(e) dependences on the heat load on the limiter moderated. This indicates that the heat flux to scrape-off layer (SOL) region was reduced due to the improvement of the plasma confinement. The up-down asymmetry of the heat load on the vacuum vessel was enhanced in the ECD mode, which may be caused by the increasing of the direct loss of energetic electrons. (c) 2007 Elsevier B.V. All rights reserved..
241. Ogawa, M.; Sakamoto, M.; Sato, K. N.; Zushi, H.; Nakamura, K.; Hanada, K.; Idei, H.; Hasegawa, M.; Kawasaki, S.; Nakashima, H.; Higashijima, A., Difference in oxygen impurity behavior between repetitive short discharges and one long discharge on TRIAM-1M, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2007.01.238, 363.0, 0.0, 1364.0-1368.0, 2007.06, Oxygen impurity behaviors of one long duration discharge and repetition of short duration discharges have been investigated in TRIAM-1M. In the former case, the OII line intensity divided by the line averaged electron density, which is considered as a monitor of oxygen concentration on the plasma facing surface (PFS), decreased with the time constant, tau(d), of 30-50 s during the discharge due to the hydrogen flux to PFS. In the latter case, tau(d) is in the range of 70-600 s. There exists a big difference of global behavior of oxygen impurity between both cases. The difference seems to result from the absence or presence of the interval time between the discharges. The oxygen concentration on PFS increases during the interval time due to adsorption of H2O. The time constant of the increase in the oxygen concentration is evaluated to be about 5500 s from Langmuir adsorption isotherms analysis. (c) 2007 Elsevier B.V. All rights reserved..
242. Sakamoto, M.; Ogawa, M.; Zushi, H.; Higashijima, A.; Nakashima, H.; Kawasaki, S.; Hasegawa, M.; Idei, H.; Hanada, K.; Nakamura, K.; Sato, K. N., In situ measurements of erosion and redeposition during long duration discharges on TRIAM-1M, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2007.01.055, 363.0, 0.0, 233.0-237.0, 2007.06, An in situ and real time measurement system of erosion and deposition has been developed, which is based on interference of light on a thin semi-transparent layer of redeposited material on substrate. It has been applied to long duration discharges in TRIAM-1M. The sapphire window is used as substrate. The deposition pattern on the window indicates up down and toroidal asymmetry. In the 5 h 16 min discharge, the thickness of the deposited layer increased monotonically with time and its deposition rate is similar to 1.5 x 10(16) Mo m(-2) S-1. In the low density and long duration discharge, the Mo deposition rate on the window depends on the ratio of Mo flux to hydrogen flux. (c) 2007 Elsevier B.V. All rights reserved..
243. Zushi, H.; Nozaki, Y.; Bhattacharyay, R.; Nakashima, K.; Sakamoto, M.; Hanada, K.; Idei, H.; Nakamura, K.; Sato, K. N.; Nishi, S.; Ogawa, M.; Takaki, K.; Sasaki, K.; Hirooka, Y.; Hasegawa, M.; Xu, H.; Kado, S.; Shikama, T.; Kawasaki, S.; Nakashima, H.; Higashijima, A., Relation between charge exchange flux and impurity influx studied by perturbation methods of gas puffing, heat load and confinement properties in TRIAM-1M, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2007.01.201, 363.0, 0.0, 1386.0-1394.0, 2007.06, A diagnostic technique to study the global structure of the recycling and impurity (molybdenum) influx from the plasma facing components is proposed and is tested using the three kinds of perturbations (gas puffing, transport oscillation, and localized heat deposition). Balmer line intensities I-H alpha, charge exchange flux Gamma(CX) and neutral molybdenum line I-Mol are measured and their correlations are analyzed with response to the perturbation parameters (I-H alpha at the gas port, density n(e), and hot spot temperature T-hot). A simple model calculation is done to understand these correlations. It is found that the phase reversal of Gamma(CX) with respect to n(e) modulation is well reproduced and a critical density exists for the phase reversal of I-Mol. The evaporation Mo flux evaluated with measured T-hot is also compared with enhanced I-Mol for the heat load perturbation and it contribution to the total content of Mo ions is evaluated by similar to 30% increment. (c) 2007 Elsevier B.V. All rights reserved..
244. Bhattacharyay, R.; Zushi, H.; Nakashima, K.; Shikama, T.; Sakamoto, M.; Ogawa, M.; Nakamura, K.; Yoshida, N.; Kado, S.; Sawada, K.; Hirooka, Y.; Hanada, K.; Sato, K. N.; Idei, H.; Sasaki, K.; Xu, H.; Hasegawa, M.; Uehara, K.; Tsushima, A.; Kimura, N.; Nozaki, Y.; Kawasaki, S.; Nakashima, H.; Higashijima, A., Surface temperature effects on hydrogen and impurity release from the limiter studied by means of visible and near infrared spectroscopic measurement in TRIAM-1M, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2007.01.117, 363.0, 0.0, 938.0-943.0, 2007.06, Tokamak operation has been performed under the localized plasma wall interaction conditions in TRIAM-1M, using a water cooled rail movable limiter (ML) made of Molybdenum. The limiter surface temperature dependence on hydrogen recycling and neutral molybdenum impurity production behaviour has been studied using visible as well as infrared spectroscopy during low power long pulse and high power short pulse discharges. In these experiments it is considered that escaped energetic electrons are lost mainly on ML and localised heat deposition makes a 'hot spot' on ML. It has been observed that H-2, H-alpha and MoI intensities critically depend on the hot spot temperature (T-hot) and enhanced recycling due to localized PWI on ML can fuel the discharge without any external fueling source. (c) 2007 Elsevier B.V. All rights reserved..
245. Sasaki, K.; Hanada, K.; Nishino, N.; Tokitani, M.; Yoshida, N.; Sato, K. N.; Zushi, H.; Nakamura, K.; Sakamoto, M.; Idei, H.; Hasegawa, M.; Kawasaki, S.; Nakasihma, H.; Higashijima, A., The observation of dust behavior in TRIAM-1M, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2007.01.199, 363.0, 0.0, 238.0-241.0, 2007.06, The observation of dusts in plasmas was carried out by high speed camera in full non-inductive lower hybrid current drive (LHCD) plasma on TRIAM-1M. The velocities of dusts were 10-50 m/s. The number of dust generated per second increased with the discharge duration in the range of 20-57 s. This suggests that a part of dusts were generated from a movable limiter whose the surface temperature increases with the discharge duration. Dusts were coming from various directions even close to the movable limiter. Dusts were collected in the vacuum vessel by use of a kind of cleaner and the composition and the size of dust were examined by Scanning Electron Microscope (SEM). Dust size was several mu m and composition was Molybdenum mixed with small amount of elements of stainless metal. The poloidal distribution of the collected mass of dusts was almost uniform. (c) 2007 Published by Elsevier B.V..
246. Zushi, H.; Morisaki, T.; Inada, Y.; Bouchard, J.; Nakashima, K.; Tsuchiya, H.; Hanada, K.; Sasaki, K.; Bhattacharyay, R.; Sato, K. N.; Nakamura, K.; Sakamoto, M.; Idei, H.; Hasegawa, M.; Kawasaki, S.; Nakashima, H.; Higashijima, A., Two-dimensional density profile measurement with a sheet thermal Li beam on CPD, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2007.01.259, 363.0, 0.0, 1429.0-1435.0, 2007.06, A sheet thermal Li beam to study the density contour near X-point and divertor strike points has been developed for the spherical tokamak CPD. The CCD camera with a time resolution of 1 ms and spatial resolution of similar to 1 mm can record two-dimensional images of LiI resonance line (300 mm x 500 mm). The performance of the sheet beam is absolutely calibrated by a quartz crystal monitor. The Li flux of 10(18)-10(19) m(-2) s(-1) is achieved near the X-point. The sheet characteristics of beam width and uniformity are also confirmed. This technique is applied during plasma initiation and electron cyclotron heating phase of plasma in a simple torus with a small vertical field. The formation of vertically stretched plasma at the position of the cyclotron resonance is clearly found. The expansion process towards the low field side is observed and an over dense plasma (> 1 x 10(18) m(-3)) is obtained. A model calculation of LiI emission with density range of 1-5 x 10(18) m(-3) agrees fairly well with the observations. Over dense plasma formation is also discussed. (c) 2007 Elsevier B.V. All rights reserved..
247. Tokitani, M.; Miyamoto, M.; Tokunaga, K.; Fujiwara, T.; Yoshida, N.; Sakamoto, M.; Zushi, H.; Hanada, K.; Nagata, S.; Tsuchiya, B., Hydrogen retention properties of co-deposition under high-density plasmas in TRIAM-1M, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2007.04.010, 367.0, 0.0, 1487.0-1491.0, 2007.08, Retention of hydrogen in co-deposits formed under high-density plasma discharge in TRIAM-1 M was studied. In order to quantify the retained hydrogen, material probe experiments were performed under the high-density ((n) over tilde (e) similar to 10(19) m(-3)) discharges. After the exposure to the plasma, the quantitative analysis of deposition, hydrogen retention, and microscopic modification of specimens were performed by means of ion beam analysis and transmission electron microscopy. The co-deposits mainly consisted of Mo. The deposition rate of Mo was about ten times higher than that of the low-density discharge case. The hydrogen concentrations (H/Mo) retained in the co-deposits were 0.06-0.17, which was much higher than that in bulk-Mo and almost equal to the low-density case. These results indicate that as long as the co-deposition layers are continuously formed.. strong wall pumping in TRIAM-1M is maintained during the discharges. (C) 2007 Elsevier B.V. All rights reserved..
248. Hasegawa, Makoto; Hanada, Kazuaki; Sato, Kohnosuke; Nakamura, Kazuo; Zushi, Hideki; Sakamoto, Mizuki; Idei, Hiroshi; Kawasaki, Shoji; Nakashima, Hisatoshi; Higashijima, Aki, Model of inductive plasma production assisted by radio-frequency wave in tokamaks, JOURNAL OF NUCLEAR MATERIALS, 10.1143/JPSJ.76.084501, 76.0, 8.0, 0.0-0.0, 084501, 2007.08, For initial plasma production, an induction electric field generated by applying voltage to a poloidal field (PF) coil system is used to produce a Townsend avalanche breakdown. When the avalanche margins are small, as for the International Thermonuclear Experimental Reactor (ITER) in which the induction electric field is about 0.3 V/m, the assistance of radio-frequency waves (RF) is provided to reduce the induction electric field required for reliable breakdown. However, the conditions of RF-assisted breakdown are not clear. Here, the effects of both RF and induction electric field on the RF-assisted breakdown are evaluated considering the electron loss. When traveling loss is the dominant loss, a simple model of an extended Townsend avalanche is proposed. In this model, the induction electric field required for RF-assisted breakdown can be decreased to half that required for induction breakdown..
249. Zushi, H.; Nishino, N.; Hanada, K.; Honma, H.; Liu, H. Q.; Higashizono, Y.; Sakamoto, M.; Tashima, S.; Ryoukai, T., Acceleration of blob driven by helical instability in a simple magnetic configuration in QUEST, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2010.11.040, 415.0, 1.0, S624-S627, 2011.08, Blob generation mechanisms have been studied in slab plasma produced by electron cyclotron waves in a simple magnetic configuration with vertical (B-z) and toroidal fields (B-t). Two dimensional high speed images are analyzed as plasma and fluctuation evolution. Near the outer boundary (source region) of the slab plasma helix-sinusoidal perturbations are exited, whose helix angle and vertical wavelength are consistent with pitch angle and turn distance of the magnetic field lines there. Two dimensional evolution of these helix instabilities are studied as a function of B-z/B-t. Steep gradient outside the source region triggers the plasma to expand radially as a blob ejection. Along the ridge line of the maximum inverse scale length a wave front of the helix perturbation moves outward. Radial ejection of blob with typical velocity of similar to 1 km/s is recognized as non-linear evolution of these helix instabilities. Acceleration of a blob is found in the source-free region. (C) 2010 Elsevier B.V. All rights reserved..
250. Hanada, K.; Sasaki, K.; Zushi, H.; Nakamura, K.; Sato, K. N.; Sakamoto, M.; Idei, H.; Hasegawa, M.; Kawasaki, S.; Nakashima, H.; Higashijima, A., Metallic dusts behavior in all-metal first wall on TRIAM-1M, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2010.11.017, 415.0, 1.0, S1123-S1126, 2011.08, Metallic dust behavior was observed in full lower hybrid current drive plasmas on TRIAM-1M, which had all-metal plasma facing components. TRIAM-1M was shut-down on December 2005 and then in-vessel dusts were collected with a suction aspirator through a membrane filter of 100 nm meshes. The toroidal distribution of the total mass of collected in-vessel dusts was measured and the largest amount was found to be near the vertical movable limiter (VML). The typical size of in-vessel dusts was 1-10 mu m and the impact on augmenting the surface area was not significant. Dusts were observed to be either flaky or spherical in form and the majority of the flakes had accumulated around the VML Eruption detritus were observed on the surface of large flakes and this suggests that the burst of blistering are one of the origins of in-vessel dusts. (C) 2010 Elsevier B.V. All rights reserved..
251. Liu, H. Q.; Hanada, K.; Nishino, N.; Ogata, R.; Ishiguro, M.; Zushi, H.; Nakamura, K.; Sakamoto, M.; Idei, H.; Fujisawa, A.; Hasegawa, M.; Higashizono, Y.; Kawasaki, S.; Nakashima, H.; Higashijima, A., Study of blob-like structures in QUEST, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2010.12.225, 415.0, 1.0, S620-S623, 2011.08, Blob-like structures are observed in an open magnetic field line configuration of electron cyclotron resonance (ECR) heating plasma in QUEST. The combined measurement with a fast camera and a movable Langmuir probe show that visible filamentary structures extended along field lines do correspond to over-dense plasma structures. Ion saturation current time trace shows a front-like asymmetric burst when a visible structure reaches the probe during its outward propagation. The typical radial velocity of the blob-like structure, V-b, was measured as similar to 1 km/s with the fast camera at the intermediate area. V-b increased as the blob-like structure moved along major radius, R (outward). The average velocity of E x B drift derived from the probe measurement, slightly larger than V-b, was also increased as the blob-like structure propagated to larger R. (C) 2010 Elsevier B.V. All rights reserved..
252. Sharma, S. K.; Zushi, H.; Takagi, I.; Hisano, Y.; Shikama, T.; Morita, S.; Tanabe, T.; Yoshida, N.; Sakamoto, M.; Higashizono, Y.; Hanada, K.; Hasegawa, M.; Nakamura, K.; Idei, H.; Sato, K. N.; Kawasaki, S.; Nakashima, H.; Higashijima, A.; Nakashima, Y.; Hatano, Y.; Sagara, A.; Nakamura, Y.; Ashikawa, N.; Maekawa, T.; Kishimoto, Y.; Takase, Y., Permeation measurements for investigating atomic hydrogen flux and wall pumping/fuelling dynamics in QUEST, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2011.09.026, 420.0, 13.0, 83.0-93.0, 2012.01, In order to investigate the overall atomic hydrogen background and the dynamic characteristics of wall pumping/fuelling phenomenon, a permeation probe system has been developed and applied in the spherical tokamak QUEST. Reliability of measurements, within +/- 3% accuracy and a positive correlation with the hydrogen line emission over three orders of magnitude have been demonstrated for more than 3000 various plasma discharges. By comparison of the experimental permeation (flux) curves with the numerically simulated curves, the net incident atomic hydrogen flux is evaluated in the range of 1 x 10(19) H m(-2) s(-1) 4 x 10(20) H m(-2) s(-1). The atomic flux has been investigated as a function of various plasma operation parameters like RF power, gas pressure and magnetic configuration. Using the static particle balance and permeation measurements, the progress in wall conditioning has been investigated. An inverse correlation between the atomic hydrogen flux and improvement in wall pumping has been observed over the two campaigns. (C) 2011 Elsevier B.V. All rights reserved..
253. Liu, H. Q.; Hanada, K.; Nishino, N.; Ogata, R.; Ishiguro, M.; Gao, X.; Zushi, H.; Nakamura, K.; Fujisawa, A.; Idei, H.; Hasegawa, M., Cross-field motion of plasma blob-filaments and related particle flux in an open magnetic field line configuration on QUEST, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2013.01.106, 438.0, S513-S517, 2013.07, Blob-filaments have been observed by combined measurement with a fast camera and a movable Langmuir probe in an open magnetic field line configuration of electron cyclotron resonance (ECR) heating plasma in QUEST. Blob-filaments extended along field lines do correspond to over-dense plasma structures and propagated across the field lines to the outer wall. The radial velocity of the blob structure, Vb, was obtained by three methods and was dominantly driven by the E x B force. The radial velocity, size of the blob showed good agreements with the results obtained by sheath-connected interchange theoretical model. Vb corresponds to roughly 0.02-0.07 of the local sound speed (Cs) in QUEST. The higher moments (skewness S and kurtosis K) representing the shape of PDF of density fluctuation are studied. Their least squares fitting with quadratic polynomial is K = (1.60 +/- 0.27) S-2 - (0.46 +/- 0.20). The larger blob structures, occurring only 10% of the time, can carry more than 60% loss of the entire radial particle flux. (C) 2013 Elsevier B.V. All rights reserved..
254. Takumi Onchi, Mahira, Y., Nagaoka, K., Tashima, S., BANERJEE SANTANU, MISHRA KISHORE KANTI, H.Idei, K.Hanada, Kazuo Nakamura, Fujisawa Akihide, Nagashima Yoshihiko, Makoto Hasegawa, Matsuoka, K., Aleksandrovich Arseniy Kuzmin, 渡邉 理, Kawasaki, S., Nakashima, H., Higashijima, A., Observation of heat flux and plasma flow in scrape off layer in QUEST, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2014.11.136, 463, 428-431, 2015.08.
255. Aleksandrovich Arseniy Kuzmin, zushi hideki, Takagi, I., Sharma, S. K., RUSINOV ALEKSANDR, Inoue, Y., Hirooka, Y., Zhou, H., Kobayashi, M., Sakamoto, M., K.Hanada, Naoaki Yoshida, Kazuo Nakamura, Fujisawa Akihide, Matsuoka, K., H.Idei, Nagashima Yoshihiko, Makoto Hasegawa, Takumi Onchi, Global gas balance and influence of atomic hydrogen irradiation on the wall inventory in steady-state operation of QUEST tokamak, JOURNAL OF NUCLEAR MATERIALS, 10.1016/j.jnucmat.2014.12.092, 463, 1087-1090, 2015.08.
256. H. Idei, K.Mishra, M.K.Yamamoto, Fujisawa Akihide, Nagashima Yoshihiko, M.Hamasaki, Y.Hayashi, Takumi Onchi, K.Hanada, zushi hideki, Multiple wall-reflection effect in adaptive-array differential-phase reflectometry on QUEST, JOURNAL OF INSTRUMENTATION, 10.1088/1748-0221/11/01/C01014, 11, 2016.01.
257. Liu, H. Q., Jie, Y. X., Ding, W. X., Brower, D. L., Zou, Z. Y., Qian, J. P., Li, W. M., Yang, Y., Zeng, L., Zhang, S. B., Lan, T., Wang, S. X., K.Hanada, Wei, X. C., Hu, L. Q., Wan, B. N., Internal magnetic field measurements by laser-based POlarimeter-INTerferometer (POINT) system on EAST, JOURNAL OF INSTRUMENTATION, 10.1088/1748-0221/11/01/C01049, 11, 2016.01.
258. Hasegawa, Makoto; Hanada, Kazuaki; Sato, Kohnosuke; Nakamura, Kazuo; Zushi, Hideki; Sakamoto, Mizuki; Idei, Hiroshi; Kawasaki, Shoji; Nakashima, Hisatoshi; Higashijima, Aki, Initial plasma production by Townsend avalanche breakdown on QUEST tokamak, JAPANESE JOURNAL OF APPLIED PHYSICS, 10.1143/JJAP.47.287, 47.0, 1.0, 287.0-292.0, 2008.01, On tokamak devices, an induction electric field induced by poloidal field (PF) coils plays a role to produce initial plasma. On a DIII-D tokamak, the required induction electric field for plasma breakdown agrees well with theoretical predictions based on the Townsend avalanche theory. According to the Townsend avalanche theory, the minimum induction electric field for plasma breakdown depends on neutral gas pressure and connection length. For stable plasma breakdown, a sufficiently large induction electric field is required. However, in the case of spherical tokamaks without electric insulation in the toroidal direction, the effect of eddy currents flowing in the toroidal direction should be considered in evaluating a feasible induction electric field because this effect suppresses the generation of an induction electric field. On a QUEST spherical tokamak, the possibility of Townsend avalanche breakdown is studied by evaluating the connection length and achievable induction electric field. The connection length is greater than 100 in in the case where a null point is set to be R = 0.56 in with a CS coil current of 2.0 kA and a PF26 coil current of 0.4 kA. Moreover, the induction electric field is about 1.5 V at this point including the effect of eddy currents. With these values, the initial plasma production by the induction electric field is sufficiently possible on QUEST..
259. Makoto Hasegawa, Kazuo Nakamura, Kazutoshi Tokunaga, Hideki Zushi, Kazuaki Hanada, akihide fujisawa, Hiroshi Idei, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, A plasma shape identification with magnetic analysis for the real-time control on QUEST, IEEJ Transactions on Fundamentals and Materials, 10.1541/ieejfms.132.477, 132, 7, 2012.10, [URL], In order to identify plasma shape, there is a way to represent the plasma current profile with several parameters, and adjust these parameters with least-square technique in order for calculated magnetic values to accord with measured ones. Here, the plasma shape parameters such as minor radius, elongation, and triangularity are chosen as the fitting parameters to represent plasma shape more directly, and the applicability to the control of the plasma shape are described by evaluating its calculation time. In order to find minimum of an objective function with least-square technique, two methods are compared, namely a linear approximation method and a downhill simplex method. While high accuracies of the measured magnetic signals are required, the good reproducibility is obtained, and the plasma shape identification can be done within several milliseconds in both methods..
260. Hiroshi Idei, Masatsugu Sakaguchi, Kazuya Nagata, Kazuaki Hanada, Hideki Zushi, Kazuo Nakamura, Makoto Hasegawa, Kohnosuke Sato, Mizuki Sakamoto, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Conceptual design and prototype performance of phased-array antenna for EBWH/CD experiments in QUEST, IEEJ Transactions on Fundamentals and Materials, 10.1541/ieejfms.132.511, 132, 7, 2012.10, [URL], Electron Bernstein Wave Heating and Current Drive (EBWH/CD) experiments have been conducted to sustain a spherical tokamak configuration in a steady state in QUEST. In the EBWH/CD experiments on QUEST, the O-X-B mode conversion scenario was selected for plasma current sustainment in rather lowdensity plasmas. A new phased-array antenna system was proposed to launch a pure elliptically-polarized O-mode in the oblique injection. The prototype antenna system was designed and its performance was checked at low power test facilities. Good focusing and steering properties were confirmed in the low power test..
261. Evgeniya Kalinnikova, Hiroshi Idei, Hiroe Igami, Shin Kubo, Atsushi Fukuyama, Hideo Nuga, Hideki Zushi, Kazuaki Hanada, Modeling of OXB mode conversion scenario for EBWH/CD experiments in QUEST, IEEJ Transactions on Fundamentals and Materials, 10.1541/ieejfms.132.505, 132, 7, 2012.10, [URL], The power deposition profiles were analyzed with a multiple ray tracing code for the Electron Bernstein Wave Heating and Current Drive (EBWH/CD) experiments in QUEST. In the EBWH/CD experiments in QUEST, the OXB mode conversion scenario was selected for the plasma current sustainment in the rather low-density case. The algorithm for the wave penetration through evanescent layer beyond a O-mode cutoff position was developed for the multiple-ray analysis. The launching antenna positions were considered to obtain the significant wave absorption in the specific propagating direction for current drive experiments using the developed ray-tracing code..
262. Kazuaki Hanada, Hideki Zushi, Hiroshi Idei, Kazuo Nakamura, Masaki Ishiguro, Saya Tashima, Evgeniya Kalinnikova, Mizuki Sakamoto, Makoto Hasegawa, akihide fujisawa, Konosuke Sato, Naoaki Yoshida, Hideo Watanabe, Kazutoshi Tokunaga, Yoshihiko Nagashima, Aki Higashijima, Shoji Kawasaki, Hisatoshi Nakashima, Haiqing Liu, Osamu Mitarai, Takashi Maekawa, Atsushi Fukuyama, Yuichi Takase, Jinping Qian, QUEST experiments towards steady state operation of spherical tokamaks, IEEJ Transactions on Fundamentals and Materials, 10.1541/ieejfms.132.490, 132, 7, 2012.10, [URL], Recent progress towards SSO of a spherical tokamak (ST) on QUEST is introduced. Zero-dimensional calculations of particle balance for QUEST experiment, refresh wall, and hot wall were performed showing that a SSO time of more than 1000s is required to obtain reliable results in regard to particle balance. Basic features of blobs were investigated in electron cyclotron resonance (ECR) heated plasmas. Formation and maintenance of a single-null divertor configuration was successfully obtained. Plasma duration in the divertor configuration was limited by out-gassing from a non-water-cooled first wall. Design studies for a hot wall are introduced..
263. Santanu Banerjee, Hideki Zushi, Nobuhiro Nishino, Kazuaki Hanada, Sanjeev Kumar Sharma, Tsubasa Inoue, Haiqing Liu, Masaki Ishiguro, Tomofumi Ryokai, Saya Tashima, Kazuo Nakamura, Hiroshi Idei, Makoto Hasegawa, akihide fujisawa, Keisuke Matsuoka, Statistical analysis of the convective intermittent transport at the edge region of QUEST, IEEJ Transactions on Fundamentals and Materials, 10.1541/ieejfms.132.545, 132, 7, 2012.10, [URL], Ambient fluctuations and the generation of coherent convective structures are investigated as a function of vertical to toroidal magnetic field ratio (B z/B t) in the spherical tokamak QUEST [K. Hanada et al., Plasma Fusion Research 5, S1007]. Fluctuation signals are obtained at a high spatial and temporal resolution using the fast visible camera. The coherent structures (blobs) were seen to be apparent only beyond a critical Bz/Bt ratio (∼ 10 -2). This clearly indicates a shift from the drift to the interchange mode with the increase in vertical magnetic field. The blobs are propagated radially at a high speed ∼ 10 3 m/s which is ∼ 1/10 th of the ion acoustic speed in QUEST. Lifetime of the blobs is about 700 μs. Second part of the study comprises of the investigation of the finer structures in the current ramp-up phase which is characterized by lower levels of fluctuations. Singular value decomposition (SVD) and principal component analysis (PCA) techniques are applied on the fast camera images to reveal the structures which are otherwise embedded in the overall intensity image. Electron banana orbits were seen to form from the slab annular plasma and grow wider to eventually shape the plasma current front..
264. Kazuaki Hanada, Kohnosuke Sato, Hideki Zushi, Kazuo Nakamura, Mizuki Sakamoto, Hiroshi Idei, Makoto Hasegawa, Yuichi Takase, Takashi Maekawa, Osamu Mitarai, Physical design and future plan of QUEST, IEEJ Transactions on Fundamentals and Materials, 10.1541/ieejfms.129.589, 129, 9, 2009.10, [URL], The QUEST (Kyushu, pronounced as "Q-shu" University Experiment with Steady-state spherical Tokamak) project is promoted from 2005 in the frame work of bi-directional collaboration organized by N1FS (National Institute for Fusion Science) to study plasma wall interaction on high temperature all-metal wall in long duration plasma on a spherical tokamak configuration. Present status and future plan of QUEST are presented..
265. Md Mahbub Alam, Kazuo Nakamura, Hiroshi Idei, Makoto Hasegawa, Kazutoshi Tokunaga, Kuniaki Araki, Kazuaki Hanada, akihide fujisawa, Yoshihiko Nagashima, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Fan Xia, Osamu Mitarai, Guiding Center Orbit Calculation for Evaluating the Current Density Distributions of the Electrons in Electron Cyclotron Heating on QUEST, IEEE Transactions on Plasma Science, 10.1109/TPS.2016.2570815, 44, 9, 1666-1671, 2016.09, [URL], In order to evaluate the magnetic surface current density distributions, the electron guiding center orbits were calculated with the equilibrium fitting plasma equilibrium analysis. The current density distributions in electron cyclotron-heated plasma were estimated from the orbit analyses in the equilibrium plasma shaping for the fundamental and the second-harmonic resonant electrons separately. The current density distribution profiles on the equatorial plane were obtained for the electrons with initially positive and negative velocities parallel to the magnetic field direction as well as the trapped electrons. The surface averaged current density profiles of the closed flux surfaces were also evaluated. A significant amount of the positive current density distributions appeared outside the last closed flux surface (LCFS), while all the negative current density distributions were evaluated inside the LCFS. The trapped electrons being the second-harmonic electron cyclotron resonant contributed the negative current inside the LCFS. The positive current density distributions outside the LCFS were significant for the driven current density for both the fundamental and second-harmonic resonances..
266. Kishore Mishra, Hideki Zushi, Hiroshi Idei, Takumi Onchi, Makoto Hasegawa, Kazuaki Hanada,, Origin and Evolution of Spontaneous Rotation in Plasma under Different Magnetic Field Geometries in Tokamak QUEST, IEEE Transactions on Plasma Science, 10.1109/TPS.2016.2522765, 44, 4, 441-447, 2016.04, [URL], Spontaneous toroidal rotation of the plasma is observed in the spherical tokamak QUEST with the help of electron cyclotron resonance (ECR) heating and without the use of any externally injected momentum. Several vertical magnetic field ( Bz) configurations with varying mirror ratio (M) (a measure of field curvature) are applied and evolution of rotation is studied with the help of Doppler spectroscopy of bulk and impurity ions. Significant toroidal rotation (Vφ-6km/s) is initiated in the open magnetic field configuration during the initial plasma breakdown phase, which is later sustained ( Vφ- 20km/s) in a closed magnetic field configuration in steady state. Rotational velocity is primarily along the cocurrent direction and is found to be proportional to the Bz strength and the resulting plasma current. High M and Bz are demonstrated to be the two specific external controls by which rotation can be initiated in the plasma. The rotation in open field lines is found to be initiated at the ECR layer in the slablike plasma, which is evolved to produce a sustained rotation in the natural divertor inboard poloidal field null equilibrium in QUEST..
267. Banerjee, Santanu; Zushi, H.; Nishino, N.; Hanada, K.; Liu, H. Q.; Ishiguro, M.; Ryoukai, T.; Tashima, S.; Nakamura, K.; Idei, H.; Hasegawa, M.; Fujisawa, A., Statistical Interpretation of the Density Fluctuations From the High-Speed Visible Images of Edge Turbulence on QUEST, IEEE TRANSACTIONS ON PLASMA SCIENCE, 10.1109/TPS.2011.2163423, 39.0, 11.0, 3006.0-3007.0, 0.0, 2011.11, Edge turbulence has been imaged on QUEST at high temporal resolution (50 kHz) using a fast framing visible camera. Statistical features of fluctuations including blobs are investigated in both open and closed magnetic configurations. Higher order moments of fluctuations including blobs and their mutual relationships are investigated. Close resemblance of the density pdf with Gaussian or beta distributions has earlier been predicted. Hence, an attempt has been made to characterize the density pdf with respect to the Pearson system to ascertain the implications of the stochastic forces..
268. Nakamura, Kazuo; Fujita, H.; Liu, X. L.; Xue, E. B.; Xia, Fan; Mitarai, Osamu; Kurihara, Kenichi; Kawamata, Y.; Sueoka, M.; Hasegawa, Makoto; Tokunaga, Kazutoshi; Zushi, H.; Hanada, K.; Fujisawa, A.; Matsuoka, K.; Idei, H.; Nagashima, Y.; Kawasaki, S.; Nakashima, H.; Higashijima, A.; Araki, Kuniaki; Fukuyama, A., Shape Reconstruction of RF-Driven Divertor Plasma on QUEST, IEEE TRANSACTIONS ON PLASMA SCIENCE, 10.1109/TPS.2014.2341616, 42.0, 9.0, 2309.0-2312.0, 2014.09, In the present RF-driven plasma with a lot of high-energy electrons, there may be anisotropic plasma pressure, which makes the usual equilibrium analysis difficult, but the Cauchy condition surface method can reconstruct the plasma shape precisely regardless of the anisotropy. In addition, the plasma current effect in the open magnetic surfaces outside of the closed magnetic surfaces is considered in the RF-driven divertor plasma. In the reconstruction process, singular value (SV) decomposition is used and optimal criterion function for generalized cross validation is estimated concerning truncation or reduction of the small-SV components..
269. K. Hanada, K. N.Sato, H. Zushi, K. Nakamura, M. Sakamoto, H. Idei, M. Hasegawa, Y. Takase, O. Mitarai, T. Maekawa, Y. Kishimoto, M. Ishiguro, T. Yoshinaga, H. Igami, S. Kawasaki, H. Nakashima, A. Higashijima, Y. Higashizono, A. Ando, N. Asakura, A. Ejiri, Y. Hirooka, A. Ishida, A. Komori, M. Matsukawa, O. Motojima, Y. Ogawa, N. Ohno, Y. Ono, M. Peng, S. Sudo, H. Yamada, N. Yoshida, Z. Yoshida, Physical design of MW-class steady-state spherical tokamak, QUEST, IAEA Fusion Energy Conference 2008, Proceedings of the 22nd IAEA Fusion Energy Conference, Geneva, 13-18 October 2008, FT/P3-25, 2008.10, QUEST (R=0.68m, a=0.4m) focuses on the steady state operation of the spherical tokamak (ST) by controlled PWI and electron Bernstain wave (EBW) current drive (CD). The QUEST project will be developed along two phases, phase I: steady state operation with plasma current, Ip=20-30kA on open divertor configuration and phase II: steady state operation with Ip=100kA and β of 10% in short pulse on closed divertor configuration. Feasibility of the missions on QUEST was investigated and the suitable machine size of QUEST was decided based on the physical view of plasma parameters. Electron Bernstein wave (EBW) current drive are planned to establish the maintenance of plasma current in steady state. Mode conversion efficiency to EBW was calculated and the conversion of 95% will be expected. A new type antenna for QUEST has been fabricated to excite EBW effectively. The situation of heat and particle handling is challenging, and W and high temperature wall is adopted. The start-up scenario of plasma current was investigated based on the driven current by energetic electron and the most favorable magnetic configuration for start-up is proposed..
270. Makoto Hasegawa, Kazuaki Hanada, Hiroshi Idei, Shoji Kawasaki, Takahiro Nagata, Ryuya Ikezoe, Takumi Onchi, Kengoh Kuroda, Aki Higashijima, Predictive maintenance and safety operation by device integration on the QUEST large experimental device, Heliyon, 10.1016/j.heliyon.2020.e04214, 6, 6, 2020.06, [URL], As technology has improved in recent years, it has become possible to create new valuable functions by combining various devices and sensors in a network. This concept is referred to as the Internet of Things (IoT), and predictive maintenance is a new valuable function associated with the IoT. In large-scale experimental facilities with many researchers, it is not desirable that experiments cannot be performed due to sudden failure of equipment. For this reason, it is important to predict the failure in advance based on the measurement results of sensors and to perform repairs in a planned manner. On the Q-shu University experiment with steady-state spherical tokamak (QUEST) large experimental device, it is necessary to drive a large current of 50 kA, and the diagnosis of its power line deterioration is well performed as predictive maintenance through the evaluation of its contact resistances of several micro ohms order on the network. In addition, as an example of the IoT, mechanisms to assist safe operation, such as a sound alarm system and an entrance management system, are built by sharing experimental information between devices via the network..
271. T. Kariya, R. Minami, T. Imai, T. Kato, Hiroshi Idei, Kazuaki Hanada, H. Zushi, T. Numakura, Y. Endo, M. Ichimura, Development of 28 GHz Gyrotron for Cooperative ECH Study, Fusion Science and Technology, 10.13182/FST14-848, 68, 1, 147-151, 2015.07, [URL], At the Plasma Research Center at University of Tsukuba, development of megawatt gyrotrons is being performed as a collaborative electron cyclotron heating (ECH) study with some research organizations. A 28 GHz 1 MW 1 s gyrotron has been developed to upgrade the GAMMA 10/PDX ECH systems. To improve the oscillation efficiency in high current regions, the magnetron injection gun (MIG) of the 28 GHz gyrotron has been modified. Output power of 1.25 MW has been achieved with this gyrotron. For the first step of the collaborative research between Tsukuba University and Kyushu University, the Tsukuba 28 GHz gyrotron was adapted to the Q-shu University Experiment with Steady-State Spherical Tokamak (QUEST) ECH system, and the plasma heating and current drive effect were demonstrated. We obtained successful results, including an electron cyclotron-driven plasma current of 66 kA in the QUEST plasma experiment. For the next step of the collaborative research, the design targets of a 2 MW 3 s and 0.4 MW continuous wave have been achieved in a design study of a new 28 GHz gyrotron..
272. S. K. Sharma, H. Zushi, I. Takagi, Y. Hisano, T. Shikama, S. Morita, T. Tanabe, N. Yoshida, M. Sakamoto, Y. Higashizono, Kazuaki Hanada, Makoto Hasegawa, O. Mitarai, Kazuo Nakamura, Hiroshi Idei, K. N. Sato, S. Kawasaki, H. Nakashima, A. Higashijima, Y. Nakashima, N. Nishino, Y. Hatano, A. Sagara, Y. Nakamura, N. Ashikawa, T. Maekawa, Y. Kishimoto, Y. Takase, Hydrogen permeation measurements in the spherical tokamak quest and its numerical modeling, Fusion Science and Technology, 10.13182/FST11-A12719, 60, 4, 1511-1514, 2011.01, [URL], A permeation measuring system with a nickel membrane of 30 pm thickness was installed near the mid plane of the spherical tokamak, QUEST. Hydrogen permeation through the membrane heated at fix temperatures (422 -506 K) was measured during short pulse (< 1 s) and long pulse (1 hour) plasma discharges. After the membrane was heated to a required temperature, hydrogen plasma was discharged using a 2.45 GHz or 8.2 GHzRF system. Significant plasma-driven permeation was observed even for very short plasma discharges (e.g. 0.1s). Numerical calculations with the use of diffusion equation under recombination boundary conditions were conducted to simulate the transient permeation behavior. The numerical calculations were also used to estimate diffusion coefficient and recombination coefficients of membrane material. Temperature dependence of both the coefficients was explained by the Arrhenius law. A one hour long permeation curve was also numerically reproduced using the same set of parameters except an increasing recombination coefficient on the plasma side of the membrane..
273. H. Zushi, Kazuaki Hanada, Hiroshi Idei, Makoto Hasegawa, K. Sasaki, R. Bhattacharyay, M. Sakamoto, Kazuo Nakamura, K. N. Sato, S. Kawasaki, H. Nakashima, A. Higashijima, Electron cyclotron counter current drive experiments in lower hybrid current drive plasma in triam-1m, Fusion Science and Technology, 10.13182/FST07-A1503, 52, 2, 240-249, 2007.01, [URL], Combined experiments with lower hybrid (LH) waves (LHWs) and electron cyclotron (EC) waves (ECWs) have been performed to study counter (ctr) current drive (CD) (ctr-CD) in LHCD plasma. Although there exists a large spectrum gap under the condition of the forward (FW) LHCD at high ratio (>13) of the thermal velocity and the phase velocity, the relativistic Doppler resonance for backward (BW) ECWs coupled with the energetic electrons streaming along the current direction is used to confirm that the gap in the opposite velocity region is also filled by BW LHWs and the counter current tends to be driven. Three experimental scenarios have been studied for ctr-CD by the following experiments: (a) BW-LHW injection into FW LHW, (b) BW-ECW injection into FW LHW, and (c) BW-ECW injection into bidirectional BW-LHCD and FW-LHCD plasma. A transition depending on the power ratio is observed in case (a). The Ohkawa current is discussed for the co-driven current observation for case (b). The role of the amount of the resonance electrons is understood as a function of the power ratio of BW LHW to FW LHW for case (c)..
274. Hiromasa Ninomiya, Akio Kitsunezaki, Masatsugu Shimizu, Masaaki Kuriyama, Haruyuki Kimura, Hisato Kawashima, Kazuhiro Tsuzuki, Masayasu Sato, Nobuaki Isei, Yukitoshi Miura, Katsumichi Hoshino, Kensaku Kamiya, Toshihide Ogawa, Hiroaki Ogawa, Kengo Miyachi, Satoshi Itoh, Naoaki Yoshida, Kazuaki Hanada, Kazuo Nakamura, Hideki Zushi, Mizuki Sakamoto, Eriko Jotaki, Makoto Hasegawa, Research activities on tokamaks in Japan
JT-60U, JFT-2M, and TRIAM-1M, Fusion Science and Technology, 10.13182/FST02-A210, 42, 1, 7-31, 2002.01, [URL], Research activities of the Japanese tokamaks JT-60U, JFT-2M, and TRIAM-1M are described. The recent JT-60 program is focused on the establishment of a scientific basis of advanced steady-state operation. Plasma performance in transient and quasi steady states has been significantly improved, utilizing reversed shear and weak shear (high-βp) ELMy H-modes characterized by both internal and edge transport barriers and high bootstrap current fractions. Development of each key issue for advanced steady-state operation has also been advanced. Advanced and basic research of JFT-2M has been performed to develop high-performance tokamak plasma as well as the structural material for a fusion reactor. Toroidal field ripple reduction with ferritic steel plates outside the vacuum vessel is successfully demonstrated. No adverse effects to the plasma were observed with poloidal fields inside the vacuum vessel (partial covering). Preparation is in progress for full-scale testing of the compatibility of the ferritic steel wall (full covering) with plasma. A heavy ion beam probe has been installed to study H-mode plasmas. Compact toroid (CT) injection experiments are performed, showing deep CT penetration into the core region of the H-mode. The TRIAM project has investigated steady-state operation and high-performance plasma of a tokamak with the high toroidal magnetic field superconducting tokamak. Four important contributions in the fields of fusion technology of superconducting tokamaks, steady-state operation, high-performance plasma, and startup of plasma current without the assistance of center solenoid coils have been achieved on TRIAM-1M, especially regarding steady-state operation by realization of a discharge for > 3 h..
275. Md Mahbub Alam, Kazuo Nakamura, Fan Xia, O.Mitara, Makoto Hasegawa, K. Tokunaga, K.Araki, zushi hideki, K.Hanada, Fujisawa Akihide, H.Idei, Nagashima Yoshihiko, S.Kawasaki, H.Nakashima, A.Higashijima, T.Nagata, Comparison of current density profiles based on particle orbit-driven current in steady-state plasma on QUEST, Fusion Engineering and Design, 10.1016/j.fusengdes.2015.11.007, 2016.11.
276. O.Mitarai, Kazuo Nakamura, Makoto Hasegawa, Takumi Onchi, H.Idei, Fujisawa Akihide, K.Hanada, zushi hideki, A.Higashijima, H.Nakashima, S.Kawasaki, K.Matsuoka, S.Koike, T.Takahashi, H.Tsutsui, Comparative studies of inner and outer divertor discharges and a fueling study in QUEST, Fusion Engineering and Design, 10.1016/j.fusengdes.2015.12.022, 2016.11.
277. K. Nakamura, M. M. Alam, Y. Z. Jiang, O. Mitarai, K. Kurihara, Y. Kawamata, M. Sueoka, M. Takechi, Makoto Hasegawa, K. Tokunaga, K. Araki, H. Zushi, Kazuaki Hanada, akihide fujisawa, Hiroshi Idei, Yoshihiko Nagashima, S. Kawasaki, H. Nakashima, A. Higashijima, T. Nagata, A. Fukuyama, Plasma equilibrium based on RF-driven current profile without assuming nested magnetic surfaces on QUEST, Fusion Engineering and Design, 10.1016/j.fusengdes.2017.05.070, 123, 532-534, 2017.11, [URL], In the present RF-driven (ECCD) steady-state plasma on QUEST, the plasma current seems to flow in the open magnetic surface outside of the closed magnetic surface in the low-field region according to the plasma current fitting (PCF) method. The current in the open magnetic surface is due to the orbit-driven current by high-energy particles in the RF-driven plasma. High-energy particles guiding center orbits are calculated as contour plots of conserved variables in the Hamiltonian formulation considering particles in the initial position with different energies and pitch angles satisfying the resonance condition. A negative current appears near the magnetic axis, and a hollow current profile is expected even if the pressure driven current is considered. The equilibrium is fitted within nested magnetic surfaces by J-EFIT coded by MATLAB using the hollow current profile shift toward the low-field region. Although the plasma boundary shape reflects the plasma current density profile, the equilibrium shape fitted by J-EFIT does not coincide with the orbit-driven current profile. However, introducing an extension of the current profile without assuming nested contours into the J-EFIT code appropriately fits the plasma shape with the hollow current profile to the measured magnetic data..
278. Makoto Hasegawa, Kazuo Nakamura, Hideki Zushi, Kazuaki Hanada, akihide fujisawa, Kazutoshi Tokunaga, Hiroshi Idei, Yoshihiko Nagashima, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Current status and prospect of plasma control system for steady-state operation on QUEST, Fusion Engineering and Design, 10.1016/j.fusengdes.2016.04.016, 112, 699-702, 2016.11, [URL], The plasma control system (PCS) of QUEST is developed according to the progress of QUEST project. Since one of the critical goals of the project is to achieve the steady-state operation with high temperature vacuum vessel wall, the PCS is also required to have the capability to control the plasma for a long period. For the increase of the loads to processing power of the PCS, the PCS is decentralized with the use of reflective memories (RFMs). The PCS controls the plasma edge position with the real-time identification of plasma current and its position. This identification is done with not only flux loops but also hall sensors. The gas fueling method by piezo valve with monitoring the Hα signal filtered by a digital low-pass filter are proposed and suitable for the steady-state operation on QUEST. The present status and prospect of the PCS are presented with recent topics..
279. Makoto Hasegawa, Kazuo Nakamura, Kazuaki Hanada, Shoji Kawasaki, Arseniy Kuzmin, Hiroshi Idei, Kazutoshi Tokunaga, Yoshihiko Nagashima, Takumi Onchi, Kengoh Kuroda, Osamu Watanabe, Aki Higashijima, Takahiro Nagata, Modification of plasma control system and hot-wall temperature control system for long-duration plasma sustainment in QUEST, Fusion Engineering and Design, 10.1016/j.fusengdes.2018.02.069, 129, 202-206, 2018.04, [URL], In tokamaks, the temperature of the plasma-facing wall is an important parameter for achieving particle balance and therefore steady-state operation. QUEST, which is a middle-sized spherical tokamak, has hot walls that act as plasma-facing walls. They can be actively heated with sheath heaters and actively cooled with water. To control the wall temperature, heating and cooling systems have been developed. These systems adjust the power of the sheath heaters and the motor valves of the cooling system, respectively. The two systems communicate via Ethernet through UDP and control the hot-wall temperature cooperatively. The plasma control system (PCS) in QUEST has also been modified, especially with respect to gas fueling, in order to enable long-duration plasma sustainment. A feedback controller has been installed in the PCS, together with a mass flow controller, allowing Hα emission from the plasma which is used as a reference signal, to be well controlled. Plasma density calculations using a field-programmable gate array are proposed for the feedback control system..
280. K. Shinohara, K. Hoshino, S. Shiraiwa, Kazuaki Hanada, H. Toyama, Y. Miura, N. Suzuki, K. Yamagishi, T. Oikawa, H. Totsuka, E. Ishiyama, N. Shinoda, Makoto Hasegawa, H. Saito, Y. Endo, Measurement of density fluctuations by JFT-2M reflectometer, Fusion Engineering and Design, 10.1016/S0920-3796(96)00644-8, 34-35, 433-436, 1997.01, [URL], The spectrum and the level of fluctuation have been evaluated from the phase data obtained with a reflectometer during the period without phase runaway on the JFT-2M tokamak. The estimated fluctuation level is about 1% in OH mode (at r/a < 0.8), about 4% in L mode (at r/a ≈ 0.8) and about 10% in H mode (r/a > 0.9), while the measured position changes according to the density profile..
281. S. Yoshimura, Kazuaki Hanada, Y. Kishigami, T. Maehara, S. Tabuchi, K. Nakamura, T. Iinuma, M. Nakamura, T. Maekawa, Y. Terumichi, Control of magnetohydrodynamic activities by electron cyclotron heating in WT-3, Fusion Engineering and Design, 10.1016/0920-3796(94)00172-4, 26, 1-4, 77-81, 1995.01, [URL], Control of the m = 2, n = 1, magnetohydrodynamic mode in an ohmically heated plasma by localized electron cyclotron heating is studied systematically in the WT-3 tokamak. It is found that both m = 2 and m = 2 modes can be simultaneously suppressed by electron cyclotron heating near the q = 1 surface as well as the q = 2 surface, where q is the safety factor..
282. Kazuaki Hanada, T. Maehara, S. Yoshimura, S. Tabuchi, K. Nakamura, M. Nakamura, T. Maekawa, Y. Terumichi, Electron cyclotron heating combined with lower hybrid current drive on WT-3, Fusion Engineering and Design, 10.1016/0920-3796(95)92542-T, 26, 1-4, 69-75, 1995.01, [URL], Lower hybrid current drive (LHCD) is applied to improve the confinement in the WT-3 tokamak. With increasing the lower hybrid (LH) power, a sharp decrease in electron thermal diffusivity χe is observed at a certain LF power. The χe is directly measured by applying the simple time-to-peak method to propagation of a heat pulse induced by a short electron cyclotron heating (ECH) pulse. A high electron temperature is obtained by applying ECH to the LHCD plasma with improved χe. The efficiency of ECH in the LHCD plasma with improved χe becomes three times that in ohmic heating plasmas..
283. Hiroshi Idei, Takumi Onchi, T. Kariya, T. I. Tsujimura, S. Kubo, S. Kobayashi, M. Sakaguchi, T. Imai, Makoto Hasegawa, K. Nakamura, K. Mishra, M. Fukuyama, M. Yunoki, S. Kojima, O. Watanabe, K. Kuroda, Kazuaki Hanada, Yoshihiko Nagashima, A. Ejiri, N. Matsumoto, M. Ono, A. Higashijima, T. Nagata, S. Shimabukoro, Y. Takase, A. Fukuyama, S. Murakami, 28-GHz ECHCD system with beam focusing launcher on the QUEST spherical tokamak, Fusion Engineering and Design, 10.1016/j.fusengdes.2019.02.027, 2019.01, [URL], New polarizer and launcher systems on a 28-GHz electron-cyclotron (EC) heating and current drive (HCD) system have been developed for non-inductive second-harmonic EC-plasma-current ramp-up in the QUEST spherical tokamak. A launcher system with two quasi-optical mirrors providing beam steering capability was designed to focus the incident beam to a small-sized waist of ∼0.05 m at the second-harmonic EC resonance layer. A relatively large focusing mirror was designed based on a Kirchhoff integral code developed to derive wave solutions. The focusing property of the launched beam was first confirmed with a 3-dimensional (3D) electromagnetic-wave simulator. Focusing characteristics were also checked at low-power test facilities, together with the steering capability. The performance of this launcher system was demonstrated to work as designed, and assembled in the QUEST device. The system was applied to the non-inductive second-harmonic EC plasma ramp-up experiments with no optimization required regarding the incident polarization. The results obtained for the non-inductive plasma ramp-up are also presented..
284. Takumi Onchi, Hiroshi Idei, K. Nakamura, T. Nagata, S. Kawasaki, R. Ashida, M. Fukuyama, Makoto Hasegawa, Ryuya Ikezoe, A. Higashijima, K. Kuroda, Yoshihiko Nagashima, Kazuaki Hanada, High voltage electrical system of 8.56 GHz CW klystron for electron cyclotron heating on QUEST spherical tokamak, Fusion Engineering and Design, 10.1016/j.fusengdes.2019.04.043, 146, 2567-2570, 2019.09, [URL], A high voltage DC power supply for the cathode of the 8.56 GHz CW klystron has been set up for electron cyclotron heating (ECH) in steady state tokamak operation on QUEST spherical tokamak. The power supply is equipped with an IGBT array and a reactor for fast shutoff of the voltage in 10 μs, where the influx of electric energy at the short circuit is limited to 5 J. AC switches also have been installed in the three-phase power lines. High voltage relays are useful to save electric energy consumption. Fast three-phase AC switching by IGBT-stack is applicable to reduce the electric load of the components of the klystron power supply..
285. K. Nakamura, M. M. Alam, Y. Z. Jiang, O. Mitarai, M. Takechi, M. Hasegawa, K. Tokunaga, K. Hanada, H. Idei, Y. Nagashima, T. Onchi, K. Kuroda, O. Watanabe, A. Higashijima, T. Nagata, S. Shimabukuro, S. Kawasaki, A. Fukuyama, Plasma equilibrium based on EC-driven current profile with toroidal rotation on QUEST, Fusion Engineering and Design, 10.1016/j.fusengdes.2019.04.059, 146, 2628-2631, 2019.09, [URL], In the EC-driven (8.2 GHz) steady-state plasma on QUEST, plasma current seems to flow in the open magnetic surface in the outside of the closed magnetic surface in the low-field region according to plasma current fitting method without taking equilibrium into account. In our previous work, plasma equilibrium solution was fitted assuming all plasma current is flowing in the inside of the Last Closed Flux Surface (LCFS). It was solved within isotropic pressure profile by EFIT code. Opposite-polarity current density region appeared in the high-field region. Here in this article, considering the toroidal rotation, the equilibrium is fitted within nested magnetic surfaces by SU-EFIT. Though the plasma magnetic axis shifts outward due to the centrifugal force, the opposite polarity current does not disappear in the high-field region. And relation between the toroidal rotation speed and the poloidal beta value will be discussed..
286. Yasuhisa Oya, Atsuko Sano, Yurina Sato, Moeko Nakata, Qilai Zhou, Akihiro Togari, Naoaki Yoshida, Kazuaki Hanada, Effect of carbon impurity reduction on hydrogen isotope retention in QUEST high temperature wall, Fusion Engineering and Design, 10.1016/j.fusengdes.2019.02.110, 146, 1480-1484, 2019.09, [URL], The W (tungsten) samples were placed at top, equator and bottom walls of QUEST (Q-shu University Experiment with Steady-State Spherical Tokamak) device and exposed 1238 shots of hydrogen plasma during 2016A/W (Autumn/Winter) campaign with normal wall temperature of 473 K (maximum temperature of 523 K). Thereafter, the surface morphology was evaluated by color measurement, TEM (Transmission Electron Microscope) and XPS (X-ray photoelectron spectroscopy). Thick deposition layers were formed on the samples placed at the equator and bottom walls. On the other hand, thin mixed material layer was deposited on the top wall, where large H (hydrogen) retention was observed, which would be caused by dynamic plasma wall interaction (erosion and deposition) with higher H flux. Low H retention was confirmed for bottom wall, where higher wall temperature without He discharge would contribute. The additional 1 keV D2 + was implanted into these samples and deuterium retention enhancement was estimated. It was clearly found that the irradiation damages would induce more deuterium trapping than the formation of C–D bond..
287. Masao Matsuyama;Hideki Zushi; Kazuaki Hanada; Yasuhisa Oya; Yuji Hatano , Effect of heating temperature on tritium retention in stainless steel type 316 L, Fusion Engineering and Design
, https://doi.org/10.1016/j.fusengdes.2021.112436, Volume 169, , August 2021, 112436, 2020.10, [URL].
288. YAMAGUCHI, H; ITOH, SI; HANADA, K; KUBOTA, T; TODA, S, TRANSPORT COEFFICIENT AND HEAT PULSE-PROPAGATION, FUSION SCIENCE AND TECHNOLOGY, 10.13182/FST95-A11947137, 27.0, 0.0, 497.0-500.0, 0.0, 1995.04, The problem of deducing chi(e) from heat pulse propagation measurements is addressed. It is indicated that diffusive models can not explain the experimental observations on WT-3 tokamak. The equation taking account of the convective term gives a good fit to experimental results. It may indicate that for the sawtooth free plasma, there exists an convection of heat pulse..
289. Sharma, S. K.; Zushi, H.; Takagi, I.; Hisano, Y.; Shikama, T.; Morita, S.; Tanabe, T.; Yoshida, N.; Sakamoto, M.; Higashizono, Y.; Hanada, K.; Hasegawa, M.; Mitarai, O.; Nakamura, K.; Idei, H.; Sato, K. N.; Kawasaki, S.; Nakashima, H.; Higashijima, A.; Nakashima, Y.; Nishino, N.; Hatano, Y.; Sagara, A.; Nakamura, Y.; Ashikawa, N.; Maekawa, T.; Kishimoto, Y.; Takase, Y., HYDROGEN PERMEATION MEASUREMENTS IN THE SPHERICAL TOKAMAK QUEST AND ITS NUMERICAL MODELING, FUSION SCIENCE AND TECHNOLOGY, 60.0, 4.0, 1511.0-1514.0, 0.0, 2011.11, A permeation measuring system with a nickel membrane of 30 ion thickness was installed near the mid plane of the spherical tokamak, QUEST Hydrogen permeation through the membrane heated at fix temperatures (422 - 506 K) was measured during short pulse (< 1 s) and long pulse (I hour) plasma discharges. After the membrane was heated to a required temperature, hydrogen plasma was discharged using a 2.45 GHz or 8.2 GHz RF system. Significant plasma-driven permeation was observed even for very short plasma discharges (e.g. 0.1s). Numerical calculations with the use of diffusion equation under recombination boundary conditions were conducted to simulate the transient permeation behavior. The numerical calculations were also used to estimate diffusion coefficient and recombination coefficients of membrane material. Temperature dependence of both the coefficients was explained by the Arrhenius law. A one hour long permeation curve was also numerically reproduced using the same set of parameters except an increasing recombination coefficient on the plasma side of the membrane..
290. Hanada, K; Jotaki, E; Sakamoto, M; Nakamura, K; Itoh, S, Wall conditioning using 2.45 GHz ECR-DC on superconducting tokamak TRIAM-1M, FUSION ENGINEERING AND DESIGN, 10.1016/S0920-3796(00)00434-8, 54.0, 1.0, 79.0-86.0, 0.0, 2001.02, Wall conditioning using electron cyclotron resonance-discharge cleaning (ECR-DC) was carried out for 35 h in a hydrogen plasma on superconducting tokamak, TRIAM-1M after ventilation of vacuum vessel for 2 months. The baking-out on extension ports was carried out before ECR-DC. As the wall of plasma chamber was cooled by water during ECR-DC about 25 degreesC, the pure effect of ECR-DC could be investigated. The ECR plasma of the electron density similar to 2x10(10) cm(-3) and electron temperature similar to6 eV was maintained by the microwave power up to 1 kW provided by a magnetron of frequency in 2.45 GHz. The decay time of the partial pressure of mass number 18 (H2O) and 28 (C2H4 and/or CO) were monitored during ECR-DC. The time evolution shows that oxygen and carbon was well removed from the surface of the wall by ECR-DC. The plasma resistivity of the first ohmic heated (OH) plasma just after the ECR-DC was the same as that of the final OH plasma after exposing the wall to tokamak plasmas for more than 7000 s. Intensity of the O II line, which was investigated in lower hybrid current drive (LHCD) plasma, did not change during an experimental campaign. These indicate that the wall conditioned by only ECR-DC is good in both OH and LHCD plasmas. A quantitative model of the efficiency for ECR-DC is presented. The model can explain the time evolution of partial pressure. From this model the duration required to clean up using ECR-DC was derived. This result may help in the design of the pump in large machines. (C) 2001 Elsevier Science B.V. All rights reserved..
291. Nakamura, K; Ji, ZS; Shun, B; Qin, PQ; Itoh, S; Hanada, K; Sakamoto, M; Jotaki, E; Hasegawa, M; Iyomasa, A; Kawasaki, S; Nakashima, H, Sensorless sensing of plasma horizontal position on HT-7, FUSION ENGINEERING AND DESIGN, 10.1016/S0920-3796(03)00308-9, #, 0.0, 771.0-777.0, 0.0, 2003.09, Sensorless sensing experiments of the plasma horizontal position have been carried out in the superconducting tokamak HT-7. The horizontal position is calculated from the vertical field coil current and voltage in two ways. The calculations are made focusing on the low frequency component and the ripple frequency component of the power supply. In the latter case, there is no drift problem and the error is lower than 2% of the plasma minor radius. (C) 2003 Elsevier Science B.V. All rights reserved..
292. Wang, F; Luo, JR; Nakamura, K; Sato, KN; Hanada, K; Sakamoto, M; Idei, H; Kawasaki, S; Nakashima, H, Continuous and real-time data acquisition system for superconducting tokamaks HT-7 and TRIAM-1M, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2005.09.055, 81.0, 8.0, 1621.0-1626.0, 2006.02, Conventional data acquisition systems cannot deal with data acquisition for a long-time discharge of a nuclear fusion reactor. Thus, continuous data acquisition with a real-time data presentation during discharge must be developed. Two data acquisition systems, which include alternating CAMAC data acquisition and long-time PCI data acquisition, are designed for the longtime operation of HT-7 tokamak. Since an effective alternating mode is adopted, the alternating CAMAC data acquisition can accurately and continuously acquire data at a rate of 10 kHz. The acquired data is immediately transmitted to a data server and real-time results can be presented during the plasma discharge. As for the long-time PCI data acquisition, a special kind of PCI A/D card, which has a hard disk on board, is designed to collect data at a max speed of 200 kHz. Thus, the total sampling duration is only related to the capacity of the hard disk on board. These two types of data acquisitions were applied to HT-7 tokamak and a 250 s discharge was acquired. These data acquisition systems were also successfully demonstrated on a 2500 s plasma discharge on TRIAM-1M. This paper describes the two data acquisitions in detail. (c) 2005 Elsevier B.V. All rights reserved..
293. Nakamura, K; Luo, JR; Wang, HZ; Ji, ZS; Wang, H; Wang, F; Qi, N; Sato, KN; Hanada, K; Sakamoto, M; Idei, H; Hasegawa, M; Iyomasa, A; Kawasaki, S; Nakashima, H; Higashijima, A, Magnetic sensorless control experiment without drift problem on HT-7, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2005.08.094, 81.0, 8.0, 1607.0-1612.0, 0.0, 2006.02, Magnetic sensorless control experiments of the plasma horizontal position have been carried out in the superconducting tokamak HT-7. Previously the horizontal position was calculated from the vertical field coil current and voltage without using signals of magnetic sensors like magnetic coils and flux loops placed near the plasma. The calculations are made focusing on the ripple frequency component of the power supply with thyristor and directly from them without time integration. There is no drift problem of integrator of magnetic sensors. Two kinds of experiments were carried out, to keep the position constant and swing the position in a triangular waveform. (c) 2005 Elsevier B.V. All rights reserved..
294. Hanada, K.; Sugata, T.; Sakamoto, M.; Zushi, H.; Nakamura, K.; Sato, K. N.; Idei, H.; Hasegawa, M.; Higashijima, A.; Kawasaki, S.; Nakashima, H., Power balance investigation in steady-state LHCD discharges on TRIAM-1M, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2006.03.004, 81.0, 19.0, 2257.0-2265.0, 0.0, 2006.09, A discharge longer than 5h was successfully achieved on TRIAM-1M by fully non-inductive lower hybrid current drive (LHCD). The heat load distribution into the plasma facing components (PFCs) during the 5 h discharge was investigated using calorimetric measurements, which estimated that the injected radio frequency (RF) power coincided with the total heat load amount to the PFCs. The power balance, including the portion of direct loss power of the fast electrons and the heat flux due to the charge exchange (CX) process, was also investigated. (c) 2006 Elsevier B.V. All rights reserved..
295. Nakamura, K.; Hasegawa, M.; Wang, R.; Kawasaki, S.; Nakashima, H.; Higashijima, A.; Sato, K. N.; Zushi, H.; Hanada, K.; Sakamoto, M.; Idei, H., Control system and the controllability of CPD and QUEST, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2008.01.004, 83.0, 2.0, 236.0-240.0, 2008.04, Superconducting tokamak TRIAM-1M has just ceased its operation in December 2005. However, in order to develop the systematic study on plasma-wall interaction in long duration discharges in the TRIAM-1M tokamak, spherical tokamak QUEST is under construction. To fulfill the mission of QUEST under a small group of the university in collaboration with other group, control and interlock system must be designed appropriately. Hence, a spherical tokamak CPD was constructed and the experiment is carried out for preparation of QUEST. The control and interlock system for QUEST is tested and developed during the experiment in the CPD. (c) 2008 Elsevier B.V. All rights reserved..
296. Hasegawa, M.; Nakamura, K.; Higashijima, A.; Kawasaki, S.; Nakashima, H.; Sato, K. N.; Zushi, H.; Hanada, K.; Sakamoto, A.; Idei, H., High accessible experimental information on CPD experiment, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2007.10.014, 83.0, 2.0, 402.0-405.0, 2008.04, On CPD [1] (Compact PWI experimental Device) experiment, information of electronic logbook and sequence status are distributed by Web services to prepare future experimental environment such as steady state operation and remote participation. Hence, all the researchers can acquire information with a Web browser installed on a personal computer if they are connected to the Internet. However, to carry a notebook computer all the time is a burden to researchers. Furthermore, the researchers may not be always connected to the Internet. Mobile phones are superior in portability compared to notebook computers, and are easy to connect with Internet through the wireless network of the telecom carriers. Moreover, since recent mobile phones have full browsing function, their affinities to the Web services are becoming high. On this account, Web services for mobile phones are developed to access experimental information. For sequence monitoring, a mobile application MIDlet that utilizes special functions of mobile phone such as sound and vibration is also developed to draw attentions of researchers to sequence status. (C) 2007 Elsevier B.V. All rights reserved..
297. Xu, Handong; Hanada, K.; Hasegawa, M.; Wang, M.; Shen, B.; Zushi, H.; Nakamura, K.; Sato, K. N.; Sakamoto, M.; Idei, H.; Bhattacharyay, R., The current control of steady-state plasma in TRIAM-1M and HT-7, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2008.01.018, 83.0, 2.0, 211.0-214.0, 0.0, 2008.04, Fully non-inductive lower hybrid current drive (LHCD) plasmas have been achieved in TRIAM-1M and HT-7 superconducting tokamaks, but the current control in toroidal plasma was performed in different way during their steady-state operation (SSO). In HT-7, the plasma current was controlled mainly by the ohmic field, and partially by LHCD through ohmic transformer magnetic flux feedback control. In TRIAM-1M, the plasma current was controlled by lower hybrid wave (LHW) power directly according to a simple simulation model. (c) 2008 Elsevier B.V. All rights reserved..
298. Hasegawa, M.; Higashijima, A.; Nakamura, K.; Hanada, K.; Sato, K. N.; Sakamoto, M.; Idei, H.; Kawasaki, S.; Nakashima, H., A WEB-based integrated data processing system for the TRIAM-1M, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2007.12.012, 83.0, 4.0, 588.0-593.0, 2008.05, In TRIAM-1M, plasma discharge can be sustained for over five hours [H. Zushi, et al., Steady-state tokamak operation, ITB transition and sustainment and ECCD experiments in TRIAM-1M, Nucl. Fusion 45 (2005) S142-S156]. In order to avoid sitting in front of one console for the purpose of monitoring the plasma discharge, it is recommended that the experimental information be accessible from any location at any time. In addition, simple services to access experimental information are required in order to promote the participation of multiple researchers in the TRIAM-1M experiment. Thus, A WEB-based integrated data processing system that provides management for experiment planning, an experimental log, numerical data, and plasma supervision has been installed in the TRIAM-1M. These services are composed primarily of an Apache WEB server, a Tomcat JSP/Servlet container, and a MySQL relational database. This system is constructed using the object-oriented Java language, which is easy to maintain and develop because of the intrinsic characteristics of the Java language. When participating in experiments, researchers are required only to prepare a WEB browser on any platform and are no longer required to memorize complex operations because all services are provided with a uniform user interface through a WEB browser. Furthermore, with the integration of these services, the required information and numerical data can be provided promptly by tracing HTML links that are created dynamically by server applications. (C) 2007 Elsevier B.V. All rights reserved..
299. Bhattacharyay, R.; Zushi, H.; Hirooka, Y.; Sakamoto, M.; Yoshinaga, T.; Okamoto, K.; Kawasaki, S.; Hanada, K.; Sato, K. N.; Nakamura, K.; Idei, H.; Ryoukai, T.; Nakashima, H.; Higashijima, A., Study on wall recycling behaviour in CPD spherical tokamak, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2008.05.009, 83.0, 7.0, 1114.0-1119.0, 0.0, 2008.12, Experiments to study wall recycling behaviour have been performed in the small spherical tokamak compact plasma-wall interaction experimental device (CPD) from the viewpoint of global as well as local plasma wall interaction condition. Electron cyclotron resonance (ECR) plasma of typically similar to 50 to 400 ms duration is produced using similar to 40 to 80 kW RF power. In order to study the global wall recycling behaviour, pressure measurements are carried out just before and after the ECR plasma in the absence of any external pumping. The recycling behaviour is found to change from release to pumping beyond a certain level of pressure value which is again found to be a function of shot history. The real-time local wall behaviour is studied in similar RF plasma using a rotating tungsten limiter, actively coated with lithium. Measurement of H. light intensity in front of the rotating surface has indicated a clear reduction (similar to 10%) in the steady-state hydrogen recycling with continuous Li gettering of several minutes. (C) 2008 Elsevier BY. All rights reserved..
300. Sharma, Sanjeev K.; Zushi, Hideki; Takagi, Ikuji; Hisano, Yuki; Sakamoto, Mizuki; Higashizono, Yuta; Shikama, Taichi; Morita, Sigeru; Tanabe, Tetsuo; Yoshida, Naoaki; Hanada, Kazuaki; Hasegawa, Makoto; Mitarai, Osamu; Nakamura, Kazuo; Idei, Hiroshi; Sato, Kohnosuke N.; Kawasaki, Shoji; Nakashima, Hisatoshi; Higashijima, Aki; Nakashima, Yousuke; Nishino, Nobuyuki; Hatano, Yuji; Sagara, Akira; Nakamura, Yukio; Ashikawa, Naoko; Maekawa, Takashi; Kishimoto, Yasuaki; Takase, Yuichi, Measurement of hydrogen permeation due to atomic flux using permeation probe in the spherical tokamak QUEST, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2010.08.032, 85.0, 6.0, 950.0-955.0, 0.0, 2010.11, Particle retention and recycling in plasma fusion devices are generally associated with the diffusion of atomic hydrogen into the materials. The resulted permeation of atomic hydrogen is known as plasma driven permeation (POP). This permeation may also be significant, even in the walls, which are not directly exposed to the plasma. Under similar conditions, the permeation flux (Gamma(perm)) of hydrogen through a 30 mu m thick Ni membrane heated at 412-575K has been measured in the spherical tokamak QUEST. Gamma(perm) is being measured during the scans of different operating parameters like RF power (P(RF)), chamber pressure (P(chamber)), discharge widths (tau(dis)) and vertical magnetic field (B(Z)). Simultaneously edge plasma density and spectral intensities of atomic (Balmer) lines and molecular (Fulcher) bands have been compared with the permeation measurements. A linear relationship has been established between the time integrated Gamma(perm) i.e. permeation fluence (Q(perm)) and the time integrated H(alpha) intensity i.e. H(alpha) fluence (Q(alpha)). Q(perm) also shows a strong relationship with the edge plasma density and various spectral fluences. The obtained results are discussed for exploring the applicability of the permeation probes in measuring the atomic flux near the first walls. (C) 2010 Elsevier B.V. All rights reserved..
301. Nakamura, K.; Jiang, Y.; Liu, X. L.; Mitarai, O.; Kurihara, K.; Kawamata, Y.; Sueoka, M.; Hasegawa, M.; Tokunaga, K.; Zushi, H.; Hanada, K.; Fujisawa, A.; Sakamoto, M.; Idei, H.; Kawasaki, S.; Nakashima, H.; Higashijima, A.; Araki, K., Eddy current-adjusted plasma shape reconstruction by Cauchy condition surface method on QUEST, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2011.04.045, 86.0, 6.0, 1080.0-1084.0, 2011.10, CCS (Cauchy Condition Surface) method is a numerical approach to reproduce plasma shape, which has good precision in conventional tokamaks. In order to apply it in plasma shape reproduction of ST (Spherical Tokamak). the calculation precision of the CCS method in a spherical tokamak CPD (Compact PWI experimental Device)(B(t) = 0.25 T, R = 0.3 m, a = 0.2 m) has been analyzed. The precision was confirmed also in ST and decided to be applied to a spherical tokamak QUEST (B(t), = 0.25 T, R = 0.68 m, a = 0.40 m).. In present stage from the magnetic measurement, it is known that the eddy current effect is large in QUEST experiment, and there are no special magnetic measurements for eddy current now, so some proper model should be selected to evaluate the eddy current effect. The eddy current density by not only CS (Center Solenoid) coil but also plasma current is calculated using EDDYCAL (JAEA). The eddy current magnitudes are taken as unknown variables and solved together with plasma shape reconstruction in ohmic discharge and ECCD (Electron Cyclotron Current Drive) discharge. (C) 2011 Elsevier B.V. All rights reserved..
302. Sharma, S. K.; Zushi, H.; Yoshida, N.; Watanabe, H.; Osakabe, M.; Takeri, Y.; Hasegawa, M.; Tanabe, T.; Tokunaga, K.; Hanada, K.; Idei, H.; Sakamoto, M.; Nakamura, K.; Fujisawa, A.; Ishiguro, M.; Tashima, S., Analysis of PWI footprint traces and material damage on the first walls of the spherical tokamak QUEST, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2011.10.001, 87.0, 1.0, 77.0-86.0, 2012.01, After several non-inductive current startup experimental campaigns in the spherical tokamak QUEST, its metallic first walls have revealed various kinds of damages as a signature of strong plasma wall interaction (PWI). Several types of footprint traces, namely colored regions formed due to material erosion/redeposition, melting of plasma facing components (PFCs) and numerous arc tracks on the chamber walls are recognized. Analysis of the re-deposited materials on collector probes is carried out using Xray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). Redeposition of several impurity materials such as carbon, oxygen and tungsten is identified. The footprint traces are majorly formed on the lower side PFCs, showing a large up/down asymmetry. Both toroidally symmetric and asymmetric footprint traces are formed on the bottoms side divertor plate and the lower part of the outboard side walls, respectively. Localized melting occurred on the outboard side limiters is attributed to the loss of energetic electrons produced via electron cyclotron resonance (ECR) heating. The observed damages are discussed in view of localized PWI, loss of energetic electrons, particle drifts, sputtering, arcing and redeposition of eroded materials. Material analysis and numerically calculated guiding center orbits of the charge particles are used to discuss these damages. (C) 2011 Elsevier B.V. All rights reserved..
303. Hasegawa, M.; Nakamura, K.; Zushi, H.; Hanada, K.; Fujisawa, A.; Matsuoka, K.; Mitarai, O.; Idei, H.; Nagashima, Y.; Tokunaga, K.; Kawasaki, S.; Nakashima, H.; Higashijima, A., Development of plasma control system for divertor configuration on QUEST, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2013.03.035, 88.0, 6.0, 1074.0-1077.0, 0.0, 2013.10, A plasma control system to sustain divertor configurations is developed on QUEST (Q-shu university experiment with steady-state spherical tokamak). Magnetic fluxes are numerically integrated at 100 kHz using FPGA (Field-Programmable Gate Array) modules and transferred to a main calculation loop at 4 kHz. With these signals, plasma shapes are identified in real time at 2 kHz under the assumption that the plasma current can be represented as one filament current. This calculation is done in another calculation loop in parallel by taking advantage of a multi-core processor of the plasma control system. The inside and outside plasma edge positions are controlled to their target positions using PID (proportional-integral-derivative) control loops. Whereas the outside edge position can not be controlled by the outer PF coil current, the inside edge position can be controlled by the inner PF coil current. (C) 2013 Elsevier B.V. All rights reserved..
304. Makoto Hasegawa, Kazuo Nakamura, zushi hideki, K.Hanada, Fujisawa Akihide, Mitarai, Osamu, K. Tokunaga, H.Idei, Nagashima Yoshihiko, Kawasaki, Shoji, Nakashima, Hisatoshi, Higashijima, Aid, Development of a high-performance control system by decentralization with reflective memory on QUEST, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2015.06.054, 96-97, 629-632, 2015.10.
305. Kazuo Nakamura, M.M. Alam, Y.Z. Jiang, O. Mitarai, K. Kurihara, Y. Kawamata, M. Sueoka, M. Takechi, Makoto Hasegawa, K. Tokunaga, K. Araki, H. Zushi, K.Hanada, Fujisawa Akihide, Hiroshi Idei, Nagashima Yoshihiko, S. Kawasaki, H. Nakashima, A. Higashijima, Analysis of plasma equilibrium based on orbit-driven current density profile in steady-state plasma on QUEST, FUSION ENGINEERING AND DESIGN, 10.1016/j.fusengdes.2015.11.035, 109, 1528-1533, 2016.11.
306. H. Idei, H. Zushi, K. Hanada, E. Kalinnikova, M. Sakaguchi, T. Itado, K. Nakamura, A. Fujisawa, Y. Nagashima, M. Hasegawa, K. Matsuoka, A. Fukuyama, S. Tashima, H. Watanabe, N. Yoshida, K. Tokunaga, A. Ejiri, H. Igami, S. Kubo, K. Toi, M . Isobe, K. Nagaoka, H. Nakanishi, N. Nishino, S. Kawasaki, H. Nakashima, A. Higashijima, Y. Ueda, M. Kikuchi, T. Fujita, O. Mitarai, T. Maekawa and Y. Takase, Electron Bernstein Wave Heating and Current Drive Effects in QUEST, FEC 2012: 24. IAEA Fusion Energy Conference; San Diego, CA (United States); 8-13 Oct 2012, 217.0, EX/P6-17, 2012.09.
307. Jabir Al Salami, Changhong Hu, Kazuaki Hanada, A study on smoothed particle hydrodynamics for liquid metal flow simulation, Evergreen, 6, 3, 190-199, 2019.09, In order to address the problem of heat and particle removal in tokamak-type, magnetic confinement nuclear fusion reactors, a divertor that utilizes liquid metal is suggested to replace solid tungsten divertors due to concerns regarding their structural integrity at high energy fluxes. The operation of such a device gives rise to phenomena spanning multiple disciplines of physics such as fluid dynamics, electromagnetics, thermodynamics and plasma physics. Smoothed Particle Hydrodynamics (SPH) is a Lagrangian, mesh-free numerical method that has been proven effective in a variety of disciplines. In this work, the hydrodynamic aspect of the liquid metal divertor is simulated using SPH, paving the way to implement additional physics in future work..
308. Nakano, Haruhiko ; Okazawa, Tomo ; Hasegawa, Makoto ; Hanada, Kazuaki ; Jotaki, Eriko ; Sakamoto, Mizuki ; Zushi, Hideki ; Nakamura, Kazuo ; Ito, Satoshi, Test of Wide-Band Reflectometer, Engineering Sciences Reports, Kyushu University, 22.0, 3.0, 267.0-300.0, 2000.12.
309. Xiaolong Liu, Kazuo Nakamura, Kazutoshi Tokunaga, Makoto Hasegawa, Kuniaki Araki, Yi Jiang, Tatsuya Yoshisue, Hideki Zushi, Kazuaki Hanada, Akihide Fujisawa, Hiroshi Idei, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Simulation on Toroidal Field Power Supply of HL-2A Tokamak: Application of Dual DQ0 Transformation for Six-Phase Synchronous Generator Model, Engineering Sciences Reports,Kyushu University, Vol.33,pp.7-10, 2011.06.
310. K. Okamoto, R. Tatsumi, K. Abe, A. Hatayama, Kazuaki Hanada, Modelling of plasma and its wall interaction for long-term tokamak operation, Contributions to Plasma Physics, 10.1002/ctpp.201700129, 58, 6-8, 602-607, 2018.07, [URL], Metal plasma-facing materials (PFMs) are expected to be candidates for future fusion power plants from the view point of tritium retention. The purpose of this study is to develop a model including a long timescale plasma interaction with metal PFMs. As a first step, we have developed a simple zero-dimensional (0D) model, which consists of particle balance equations for the following three different particle species: (a) hydrogen plasma (elec., H+, H+ 2 , H+ 3), (b) neutral hydrogen atoms (H) and molecules (H2) in the gas phase, and (c) the wall-stored H atoms. The model has been applied to simulate long-term operation in the limiter configuration of the QUEST tokamak. Modelling results of the long time evolution of the H atom wall inventory reasonably reproduce the experimental tendency. Although the present model is relatively simple, it is useful to understand the basic characteristics of overall plasma particle balance, the density control of the main plasma, and the H atom wall inventory for long-term tokamak operation..
311. Idei, H.; Shimozuma, T.; Ohkubo, K.; Kubo, S.; Notake, T.; Hanada, K.; Hasegawa, M., Operation range of remote steering antenna in anti-symmetric and symmetric directions, Conference Digest of the 2006 Joint 31st International Conference on Infrared and Millimeter Waves and 14th International Conference on Terahertz Electronics, 0.0, 0.0, 574.0-574.0, 0.0, 2006.04, Intensity and phase profiles of the output beams from a remote steering antenna were measured in the anti-symmetric and symmetric directions. The beam properties are discussed with the imaging property calculations..
312. Hiroshi Idei, Kazuaki Hanada, K. Ohkubo, Makoto Hasegawa, T. Notake, S. Kubo, T. Shimozuma, S. Ito, K. N. Sato, H. Zushi, Kazuo Nakamura, M. Sakamoto, A. Iyomasa, S. Kawasaki, H. Nakashima, A. Higashijima, S. Nishi, Remote steering antenna system on the TRIAM-1M Tokamak, Conference Digest of the 2004 Joint 29th International Conference on Infrared and Millimeter Waves and 12th International Conference on Terahertz Electronics
Conference Digest of the 2004 Joint 29th International Conference on Infrared and Millimeter Waves and 12th International Conference on Terahertz Electronics
, 725-726, 2004.12, A remote steering antenna designed as a symmetric direction antenna is prepared for Electron Cyclotron Heating (ECH) and Current Drive (ECCD) experiments on the TRIAM-1M tokamak. The steering angles of 8-19 degrees are available in the design, in addition to the angle near 0 degrees. The antenna is tested at both of high and low power levels. The fraction of radiated power to injected power at the antenna is roughly evaluated at the low power test. The angle radiated from the antenna is checked from both of the intensity and phase measurements at the low power test. Several percentage losses at the antenna are evaluated at the high power test. The antenna system is evaluated to work correctly..
313. Mori, S.; Shikama, T.; Hanada, K.; Yoneda, N.; Kuzmin, A.; Hasuo, M.; Idei, H.; Onchi, T.; Ejiri, A.; Osawa, Y.; Peng, Y.; Matsuzaki, K.; Kado, S.; Sawada, K.; Ido, T.; Nakamura, K.; Ikezoe, R.; Nagashima, Y.; Hasegawa, M.; Kuroda, K.; Higashijima, A.; Nagata, T.; Shimabukuro, S. Spectroscopic Measurement of Hydrogen Atom Density in a Plasma Produced with 28 GHz ECH in QUEST , Spectroscopic Measurement of Hydrogen Atom Density in a Plasma Produced with 28 GHz ECH in QUEST
, Atoms
, 10.3390/atoms8030044, 2020.06.
314. Takase, Y; Aramasu, M; Ejiri, A; Kasahara, H; Ohara, S; Shiraiwa, S; Yamada, T; Hanada, K; Hasegawa, M; Hoshika, H;, EBW and Outer PF Start-up on the TST-2 Spherical Tokamak, APS Meeting Abstracts, 1.0, 1063.0, 2003.01.
315. Takase, Y; Ejiri, A; Kamada, Y; Kasahara, H; Nozato, H; Ohara, S; Shiraiwa, S; Yamada, T; Esaki, K; Hanada, K;, ECW/EBW heating and current drive experiments on the TST-2 spherical tokamak, APS Meeting Abstracts, 1.0, 1014.0, 2004.01.
316. T. Ryoukai, H. Zushi, T. Morisaki, H. Idei, K. Hanada, T. Mutoh, S. Kubo, K. Nagasaki, and CPD experiment group, The correlation analysis between electron density fluctuation and RF stray power in the CPD electron cyclotron plasma, APPTC2009: Asia-Pacific plasma theory conference in 2009; Aomori (Japan); Aomori (Japan); 27-30 Oct 2009, 2009.10.
317. M. Ono, N. Bertelli, H. Idei, K. Hanada, T. Onchi, S. Kojima, and H. Elserafy, Modeling of solenoid-free start-up using 2nd harmonic electron cyclotron heating and current drive in QUEST, AIP Conference Proceedings , 10.1063/5.0013966, 2020.08.
318. S. Tashima, H. Zushi, M. Isobe, Hiroshi Idei, S. Okamura, Kazuaki Hanada, K. Nakamura, akihide fujisawa, K. Matsuoka, Makoto Hasegawa, Yoshihiko Nagashima, M. Ishiguro, S. Kawasaki, H. Nakashima, A. Higashijima, The role of energetic electrons on non-inductive current start-up and formation of an inboard poloidal field null configuration in the spherical tokamak QUEST, 39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics
39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics
, 1, 305-308, 2012.12.
319. TASHIMA, H ZUSHI, M ISOBE, H IDEI, S OKAMURA, K HANADA, K NAKAMURA, A FUJISAWA, K MATSUOKA, M HASEGAWA, Y NAGASHIMA, M ISHIGURO, S KAWASAKI, H NAKASHIMA, A HIGASHIJIMA, The role of energetic electrons on non-inductive current start-up and formation of an inboard poloidal field null configuration in the spherical tokamak QUEST, 39th EPS Conference & 16th Int. Congress on Plasma Physics, 1, 305-308, 2012.08.
320. S. TASHIMA, H. ZUSHI, M. ISOBE, S. OKAMURA, H. IDEI, K. HANADA, S. K. SHARMA, T. RYOUKAI, M. ISHIGURO, H. LIUand the QUEST group, The contribution of energetic electrons to the non-inductive current in QUEST, 37th EPS Conference on Plasma Physics, P5.136, 2010.06.
321. S. Tashima, H. Zushi, M. Isobe, S. Okamura, Hiroshi Idei, Kazuaki Hanada, S. K. Sharma, T. Ryoukai, M. Ishiguro, H. Liu, The role of fast electrons on the non-inductive current ramp-up in QUEST, 37th EPS Conference on Plasma Physics 2010, EPS 2010
37th EPS Conference on Plasma Physics 2010, EPS 2010
, 3, 1716-1719, 2010.12, The role of energetic electrons during the non-inductive current ramp-up is investigated in electron cyclotron heated plasma (≤ 60kW) in the spherical tokamak QUEST. The pulse height analysis of the hard X-ray (HX) is carried out with a fast time resolution of ≥1 ms, and acceleration of the electrons are studied by measuring the evolution of spectrum. It is found that wall recycling condition affects the formation of the tokamak configuration from an initial open magnetic field configuration. The vertical magnetic field Bz dependence of driven current Ip (~ 11 kA) is compared with those of HXs for studying contribution of fast electron. For high recycling case, Ip and HXs show peaks at an optimal low value of Bz/Bt = 7 ×10-3, however, for low recycling case, both increase monotonically with B z/Bt = 7 ×10-3 - 21×10 -3..
322. Hiroshi Idei, M. Sakaguchi, K. Nagata, E. Kalinnikova, A. Fukuyama, H. Zushi, Kazuaki Hanada, K. Nakamura, M. Sakamoto, Makoto Hasegawa, Y. Takase, T. Maekawa, O. Mitarai, S. Kawasaki, H. Nakashima, A. Higashijima, Development of CW 16-element phased-array antenna for electron bernstein wave heating and current drive experiments in QUEST, 36th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2011
IRMMW-THz 2011 - 36th International Conference on Infrared, Millimeter, and Terahertz Waves
, 10.1109/irmmw-THz.2011.6105070, 2011.12, [URL], The 16-element phased-array antenna has been developed for the EBWH/CD experiments. The 2-D k-spectra could be controlled. The heat load and stress were analyzed to be moderate in the 200kW CW operation. The symmetrically 2-D narrow-field distributions were excited by the developed antenna, indicating its good applicability to the EBWH/CD experiments..
323. Hiroshi Idei, M. Sakaguchi, E. Kalinnikova, K. Nagata, H. Zushi, Kazuaki Hanada, K. Nakamura, M. Sakamoto, Makoto Hasegawa, Y. Takase, T. Maekawa, O. Mitarai, A. Fukuyamaf, S. Kawasaki, H. Nakashima, A. Higashijima, Development of CW phased-array antenna system for electron Bernstein heating and current drive experiments in QUEST, 35th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2010
IRMMW-THz 2010 - 35th International Conference on Infrared, Millimeter, and Terahertz Waves, Conference Guide
, 10.1109/ICIMW.2010.5612352, 2010.11, [URL], The CW phased-array antenna for the EBWH/CD has been developed in QUEST. The measured fields were in excellent agreement with those evaluated by the Kirchhoff integral. The thermal load and stress were analyzed. The phase array has been fast scanned to control the incident polarization and angle..
324. K. Nagata, Hiroshi Idei, M. Sakaguchi, K. Dono, Y. Wataya, S. Kawasaki, H. Zushi, Kazuaki Hanada, K. Nakamura, M. Sakamoto, Makoto Hasegawa, Y. Higashizono, Y. Takase, T. Maekawa, O. Mitarai, Y. Kishimoto, H. Nakashima, A. Higashijima, Differential-phase reflectometry using phased-array antenna system in QUEST, 35th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2010
IRMMW-THz 2010 - 35th International Conference on Infrared, Millimeter, and Terahertz Waves, Conference Guide
, 10.1109/ICIMW.2010.5612434, 2010.11, [URL], The differential-phase reflectometry has been developed to measure the density profile, concerning electron Bernstein Wave (EBW) heating and current drive in the QUEST. The Phased Array Antenna (PAA) system was proposed for the reflectometry to improve the ratio of signal to noise. The PAA was confirmed to be effective, as a launching antenna to receive the larger reflected-wave signal..
325. Hiroshi Idei, K. Nagata, M. Sakaguchi, E. Kalinnikova, A. Fukuyama, S. Ohdachi, Inagaki Shigeru, Y. Nagayama, K. Kawahata, H. Igami, S. Kubo, T. Shimozuma, H. Zushi, Kazuaki Hanada, K. N. Sato, Kazuo Nakamura, M. Sakamoto, Makoto Hasegawa, Y. Takase, T. Maekawa, O. Mitarai, S. Kawasaki, H. Nakashima, A. Higashijima, Electron bernstein wave emission diagnostics using phased-array antenna system in QUEST, 35th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2010
IRMMW-THz 2010 - 35th International Conference on Infrared, Millimeter, and Terahertz Waves, Conference Guide
, 10.1109/ICIMW.2010.5612710, 2010.11, [URL], The square waveguide phased-array antenna system has been developed for Electron Bernstein Emission diagnostics. The broadband orthomode transducer was prepared to measure the wave polarization. The measured fields were in good agreements with those evaluated from the Kirchhoff integral..
326. Idei, H.; Nagata, K.; Sakaguchi, M.; Kalinnikova, E.; Fukuyama, A.; Ohdachi, S.; Inagaki, S.; Nagayama, Y.; Kawahata, K.; Igami, H.; Kubo, S.; Shimozuma, T.; Zushi, H.; Hanada, K.; Sato, K. N.; Nakamura, K.; Sakamoto, M.; Hasegawa, M.; Takase, Y.; Maekawa, T.; Mitarai, O.; Kawasaki, S.; Nakashima, H.; Higashijima, A., Electron Bernstein Wave Emission Diagnostics using Phased-array Antenna System in QUEST, 35TH INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER, AND TERAHERTZ WAVES (IRMMW-THZ 2010), https://doi.org/10.1109/ICIMW.2010.5612710, 1.0-3.0, 2010.09, The square waveguide phased-array antenna system has been developed for Electron Bernstein Emission diagnostics. The broadband orthomode transducer was prepared to measure the wave polarization. The measured fields were in good agreements with those evaluated from the Kirchhoff integral..
327. Hiroshi Idei, Nagata, K., Sakaguchi, M., Kalinnikova, E., Fukuyama, A., Ohdachi, S., Inagaki, S., Nagayama, Y., Kawahata, K., Igami, H., Kubo, S., Shimozuma, T., hideki zushi, kazuaki hanada, Electron Bernstein Wave Emission Diagnostics using Phased-array Antenna System in QUEST, 35TH INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER, AND TERAHERTZ WAVES (IRMMW-THZ 2010), 0.0-0.0, 2006.08.
328. Hiroshi Idei, M. Sakaguchi, H. Kasahara, K. Saito, M. Tsukamoto, Kazuaki Hanada, H. Zushi, K. N. Sato, Kazuo Nakamura, M. Sakamoto, Makoto Hasegawa, Y. Higashizono, Y. Takase, T. Maekawa, O. Mitarai, Y. Kishimoto, S. Kawasaki, H. Nakashima, A. Higashijima, Phased-array antenna for electron Bernstein wave heating and current drive in QUEST, 34th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2009
34th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2009
, 10.1109/ICIMW.2009.5324704, 2009.12, [URL], The phased-array antenna has been designed for steady-state electron Bernstein wave heating and current drive at 8.2 GHz in the QUEST tokamak. The prototype antenna had rather large side-lobe components. In the new designed antenna the side-lobe components were reduced by modification of the antenna structure. For the steady-state operation, forced water-cooling and thermal stress were analyzed for the antenna component using the HFSS/ePhysics/ANSYS codes..
329. Hiroshi Idei, K. Dono, Y. Wataya, K. Nagata, S. Kawasaki, H. Zushi, Kazuaki Hanada, K. N. Sato, Kazuo Nakamura, M. Sakamoto, Makoto Hasegawa, Y. Higashizono, Y. Takase, T. Maekawa, O. Mitarai, Y. Kishimoto, H. Nakashima, A. Higashijima, Single-side-band heterodyne differential-phase reflectometry in QUEST, 34th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2009
34th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2009
, 10.1109/ICIMW.2009.5324785, 2009.12, [URL], In a spherical tokamak (ST), an operating frequency of the reflectometry is low due to the low magnetic field of the device. In the large ST, the reflected wave signal level is weak in the large propagating length, and a direct coupling between the launching and receiving antennae may become comparable level to the reflected signal due to the diffraction effect in the low operating frequency at the ST. New single-side-band heterodyne differential-phase reflectometry is proposed on a large ST device of the QUEST, to remove the direct coupling effect in an amplitude modulation reflectometry..
330. Kazuaki Hanada, K. Sasaki, Makoto Hasegawa, Hiroshi Idei, H. Zushi, Kazuo Nakamura, M. Sakamoto, K. N. Sato, S. Kawasaki, H. Nakashima, A. Higashijima, Current profile estimation using Hard X-ray measurement along the top and bottom identical line of sight on TRIAM-1M, 33rd European Physical Society Conference on Plasma Physics 2006, EPS 2006
33rd EPS Conference on Plasma Physics 2006, EPS 2006 - Europhysics Conference Abstracts
, 1608-1611, 2006.12, A new technique to measure the current profile in lower hybrid current drive (LHCD) plasmas by using hard X-ray (HXR) energy spectrum measurement along the top and bottom identical line of sight (ILOS) is proposed. An angle between ILOS and the magnetic filed line is out of alignment from the perpendicular by the poloidal magnetic field. As the emission cross-section of HXR strongly depends on the angle to the drift direction of energetic electrons, that is the magnetic filed line, this disagreement of the angles makes significant difference between the signals of detectors located on the top and bottom. As the result, the poloidal magnetic field is able to be derived from the difference of the HXR emission along the top and bottom ILOS. The method was applied to the full LHCD plasmas on the TRIMA-1M tokamak and the plasma current around the magnetic axis was estimated..
331. H. Zushi, R. Bhattacharyay, M. Sakamoto, Y. Nozaki, K. Nakashima, M. Ogawa, K. Takaki, Kazuaki Hanada, Hiroshi Idei, Kazuo Nakamura, K. Sasaki, Y. Hirooka, Y. Nakashima, S. Kado, T. Shikama, Dynamics of recycling processes responding to the local particle and heat load perturbations on TRIAM-1M, 33rd European Physical Society Conference on Plasma Physics 2006, EPS 2006
33rd EPS Conference on Plasma Physics 2006, EPS 2006 - Europhysics Conference Abstracts
, 1604-1607, 2006.12, A new diagnostic technique to study the global structure of the recycling among the plasma facing components PFCs has been proposed and tested using the three kinds of perturbations (gas puffing, transport oscillation, and localized heat deposition) at the frequency less than a few Hz . H
α
intensities are measured at various toroidal and poloidal positions and FFT analysis shows that the propagation velocity of the neutral hydrogen in the toroidal direction is < 25 m/s for the gas puff modulation. For toroidally uniform transport oscillations, on the other hand, in-out asymmetry of recycling structure is found. The localized heat deposition causes the localized particle source distribution in the torus due to enhanced efflux of the hydrogen particles only fueled from the hot area..
332. K. Sasaki, Kazuaki Hanada, K. N. Sato, H. Zushi, K. Nakamura, M. Sakamoto, Hiroshi Idei, Makoto Hasegawa, S. Kawasaki, T. Nakashima, A. Higashijima, Y. Takase, A. Ejiri, S. Shiraiwa, H. Kasahara, Takuma Yamada, N. Nishino, Soft X-ray measurement in IRE on the TST-2 spherical tokamak, 33rd European Physical Society Conference on Plasma Physics 2006, EPS 2006
33rd EPS Conference on Plasma Physics 2006, EPS 2006 - Europhysics Conference Abstracts
, 1640-1643, 2006.12, Internal Reconnection Event (IRE) is a characteristic relaxation phenomenon in STs (Sperical Tokamaks). To investigate the deformation of the plasma shape during IRE, four PIN diode arrays of 20 channels were installed on the TST-2@K (TST-2 at Kyushu University). Precursor of IRE was observed for several milli-seconds. The fluctuation was composed of two dominant components in frequency of 10kHz and 4kHz. The mode structure of 10kHz component is n/m=1/1 helical structure and 4kHz is n/m= 3/4. The overlap of modes (10kHz and 4kHz) was considered to be cause of IRE in TST-2 from the position and the growth of the modes..
333. M. Sakamoto, M. Ogawa, K. Takaki, H. Zushi, K. Nakashima, N. Maezono, T. Sugata, Y. Nakashima, Y. Higashizono, Y. Kubota, A. Higashijima, H. Nakashima, S. Kawasaki, A. Iyomasa, Makoto Hasegawa, Hiroshi Idei, Kazuaki Hanada, Kazuo Nakamura, K. N. Sato, Impact of a movable limiter on the global wall recycling in TRIAM-1M, 32nd European Physical Society Conference on Plasma Physics and Controlled Fusion combined with the 8th International Workshop on Fast Ignition of Fusion Targets
32nd EPS Conference on Plasma Physics 2005, EPS 2005, Held with the 8th International Workshop on Fast Ignition of Fusion Targets - Europhysics Conference Abstracts
, 1930-1933, 2005.12, In TRIAM-1M, the influence of the local structure of the first wall on the global wall recycling has been studied using the ML with good cooling capability. No wall saturation was observed in the 5 h 16 min discharge with the ML, since particle release was suppressed by less temperature rise of the main chamber. The global wall pumping rate without the ML, ~8.6 x 10
16
atoms m
-2
s
-1
, is 3.6 times higher than that of the long duration discharge without the ML. The temperature rise in the wall is attributed to the transition of the wall role from the particle sink to the source. The co-deposition of hydrogen with Mo is a key for the wall role of the particle sink. No clear difference of the growth rate of Mo deposits on the viewing window located from the limiter surface between with and without the ML. The growth rate is from ~2 x 10
-4
nm/s to ~8 x 10
-4
nm/s. The toroidal structure of hydrogen recycling changes significantly near at the ML. However, integration of H intensity with and without the ML over the whole toroidal length is about the same within 3% , which is less than the error, i.e. 15%..
334. H. Zushi, T. Kuramoto, M. Sakamoto, Y. Matsuo, K. Hanada, T. Sugata, N. Maezono, N. Yoshida, K. Tokunaga, T. Fujiwara, M. Miyamoto, M. Tokitani, S. Kado, T. Sikama, Y. Nakashima, Y. Hirooka, and TRIAM exp. Group, Steady State Tokomak Operation with Real Time Measurements of Recycling, Heat Load, and Molybdenum Deposition in TRIAM-1M, 31th EPS Conference on Control Fusion and Plasma Physics, Vol. 28G,P2-129, 2004.06.
335. T. KURAMOTO, H. ZUSHI, S. NAKAMURA, K. HANADA, K. SHINODA, M. SAKAMOTO, K. NAKAMURA, M. HASEGAWA, A. IYOMASA, S. KAWASAKI, H. NAKASHIMA, The effects of the hot spot on sustainment of LHCDplasma on TRIAM-1M, 30th EPS Conference on Contr. Fusion and Plasma Phys., St. Petersburg, 7-11 July 2003 ECA Vol. 27A, P-2.125, 27A, P-2.125, 2003.07.
336. K. Hanada, Y. Shinoda, M. Sakamoto, S. Itoh, K. Nakamura, H. Zushi, E. Jotaki, M. Hasegawa, S. V.Kulkarni, S. Kawasaki, H. Nakashima, A. Iyomasa, N. Yoshida, K. Tokunaga, T. Fujiwara, Measurement of prompt loss of energetic electrons in a long LHCD discharge on TRIAM-1M, 29th European Physical Society Conference on Plasma Physics and Controlled Fusion, P-2.085, 2002.01.
337. Md Mahbub Alam, Kazuo Nakamura, Makoto Hasegawa, Kazutoshi Tokunaga, Kuniaki Araki, Hideki Zushi, Kazuaki Hanada, akihide fujisawa, Hiroshi Idei, Yoshihiko Nagashima, Shoji Kawasaki, Hisatoshi Nakashima, Aki Higashijima, Fan Xia, Osamu Mitarai, Current density calculation from particle orbit in RF-driven divertor plasma on QUEST, 26th IEEE Symposium on Fusion Engineering, SOFE 2015
2015 IEEE 26th Symposium on Fusion Engineering, SOFE 2015
, 10.1109/SOFE.2015.7482308, 2016-May, 2016.05, [URL], We investigate and calculate particle orbits and the effect of particle orbits on plasma current density for nonrelativistic resonance condition in the present RF-driven divertor plasma on QUEST. We surveyed particle orbits for different values of parallel refractive index, particle initial positions and pitch angles on fundamental and second harmonic resonance conditions. We observed that for fundamental harmonic resonance condition when particle orbits are plotted on the poloidal cross-section for positive values of parallel refractive index, these orbits are started from the resonance surface and produced their orbits around the LCFS (Large Closed Flux Surface). These orbits carry positive current. When particle orbits are plotted for negative values of parallel refractive index, these orbits are started from resonance surface, but remained at the inside of the LCFS. These orbits carry negative current that reduced the overall plasma current. For second harmonic resonance condition when particle orbits are plotted on the poloidal cross-section most of the orbits remained in inside the LCFS and carry positive current. When we consider the value of parallel refractive index-0.4 and +0.4 some particle orbits arrived at the limiter and become lost particles. On the other hand, when we consider particle initial positions 0.16 m or more vertically far from the mid plane some banana orbits are produced. These banana orbits make the current density profile maximum at low field side region. From this calculation we got a hollow current density profile with current density peak at the low field side region outside of the LCFS. From this calculation we can infer that parabolic current density profile is possible, if we set the resonance surface outside of the magnetic axis by increasing the toroidal magnetic field coil current and make the plasma position inward by increasing vertical field coil current..
338. K. Nakashima, H. Zushi, N. Maezono, M. Sakamoto, N. Yoshida, Kazutoshi Tokunaga, Y. Hirooka, T. Shikama, S. Kado, N. Nishino, Y. Nakahima, Kazuaki Hanada, K. Sasaki, Hiroshi Idei, A. Iyomasa, S. Kawasaki, K. N. Sato, H. Nakashima, Kazuo Nakamura, Makoto Hasegawa, A. Higashijima, Surface temperature dependence of hydrogen balmar and molybdenum neutral lines from the Mo limiter in TRIAM-1M, 21st IEEE/NPS Symposium on Fusion Engineering, SOFE'05
21st IEEE/NPS Symposium on Fusion Engineering, SOFE'05
, 10.1109/FUSION.2005.252980, 2006.12, [URL], The limiter surface temperature dependence on hydrogen recycling and molybdenum impurity production behavior was studied with optical spectroscopy during long pulse plasma discharges in TRIAM-1M. It has been observed that the H
α
intensity critically depends on the limiter surface temperature. The Mo-I intensity from the hot spot has shown a negative temperature dependence. This is believed to be due to the reduction of heat load and enhanced CX flux due to ion temperature rise..
339. M. Sakamoto, M. Ogawa, H. Zushi, K. Takaki, M. Tokitani, K. Tokunaga, N. Yoshida, Y. Higashizono, Y. Nakashima, K. Nakamura, K. Hanada, K. N. Sato, H. Idei, M. Hasegawa, S. Kawasaki, H. Nakashima, T. Fujiwara, A. Higashijima, T. Shikama, S. Kado, A. Tsushi, Multiscale Phenomena of Plasma-Wall Interaction in Long Duration Discharges on TRIAM-1M, 21st IAEA Fusion Energy Conference, 16-21,EX/P4-25, 2006.10.
340. M Sakamoto, Y Matsuo, T Kuramoto, M Kitaguchi, T Sugata, N Maezono, M Tokitani, H Zushi, K Nakamura, K Hanada, KN Sato, H Idei, M Hasegawa, A Iyomasa, S Kawasaki, H Nakashima, A Higashijima, N Yoshida, K Tokunaga, T Fujiwara, M Miyamoto, Y Nakashima, Y Kubota, Y Higashizono, Y Hirooka, S Kado, T Shikama, Toroidal Structure of Hydrogen Recycling in Ultra-long Discharges on TRIAM-1M, 20th IAEA Fusion Energy Conference 2004. Conference proceedings, IAEA-OV-EX/P5-30, 2004.11.
341. H. Idei, K. Hanada, H. Zushi, K. Ohkubo, M. Hasegawa, S. Kubo, S. Nishi, K. N. Sato, K. Nakamura, M. Sakamoto, A. Iyomasa, S. Kawasaki, H. Nakashima, A. Higashijima, T. Notake, T. Shimozuma, S. Ito, H. Hoshika, N. Maezono, K. Nakashima, M. Ogawa, TRIAM Gro, Fundamental X-mode Electron Cyclotron Current Drive using Remote-Steering Symmetric Direction Antenna at Larger Steering Angles, 20th IAEA Fusion Energy Conference,IAEA-CN-116-PD-1-2(2004), IAEA-CN-116-PD-1-2, 2004.11.
342. Kazuo Nakamura, H. Fujita, X. L. Liu, E. B. Xue, F. Xia, O. Mitarai, K. Kurihara, Y. Kawamata, M. Sueoka, Makoto Hasegawa, Kazutoshi Tokunaga, H. Zushi, Kazuaki Hanada, akihide fujisawa, K. Matsuoka, Hiroshi Idei, Yoshihiko Nagashima, S. Kawasaki, H. Nakashima, A. Higashijima, K. Araki, A. Fukuyama, Shape reconstruction of RF-driven divertor plasma on QUEST, 2013 IEEE 25th Symposium on Fusion Engineering, SOFE 2013
2013 IEEE 25th Symposium on Fusion Engineering, SOFE 2013
, 10.1109/SOFE.2013.6635507, 2013.12, [URL], In the present RF-driven plasma with a lot of high-energy electrons, there may be anisotropic plasma pressure, which makes difficult a usual equilibrium analysis, but the CCS method can reconstruct the plasma shape precisely regardless of the anisotropy. And the plasma current effect in the open magnetic surfaces outside of the closed magnetic surfaces is considered in the RF-driven plasma. Further high-energy particle guiding center orbits are calculated aiming at estimation of the open-magnetic-surface current distribution..
343. Idei, H.; Sakaguchi, M.; Nagata, K.; Kalinnikova, E.; Fukuyama, A.; Zushi, H.; Hanada, K.; Nakamura, K.; Sakamoto, M.; Hasegawa, M.; Takase, Y.; Maekawa, T.; Mitarai, O.; Kawasaki, S.; Nakashima, H.; Higashijima, A., Development of CW 16-element Phased-array Antenna for Electron Bernstein Wave Heating and Current Drive Experiments in QUEST, 2011 36TH INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER, AND TERAHERTZ WAVES (IRMMW-THZ), 10.1109/irmmw-THz.2011.6105070, 0.0, 0.0, 686.0-687.0, 2011.09, The 16-element phased-array antenna has been developed for the EBWH/CD experiments. The 2-D k-spectra could be controlled. The heat load and stress were analyzed to be moderate in the 200kW CW operation. The symmetrically 2-D narrow-field distributions were excited by the developed antenna, indicating its good applicability to the EBWH/CD experiments..
344. Hiroshi Idei, H. Zushi, Kazuaki Hanada, Kazuo Nakamura, akihide fujisawa, Makoto Hasegawa, N. Yoshida, M. Sakamoto, H. Watanebe, Kazutoshi Tokunaga, Yoshihiko Nagashima, A. Ejiri, M. Sakaguchi, E. Kalinnikova, M. Ishiguro, S. Tashima, A. Fukuyama, H. Igami, S. Kubo, S. K. Sharma, T. Ryokai, H. Q. Liu, M. Isobe, K. Nagaoka, H. Nakanishi, N. Nishino, S. Kawasaki, H. Nakashima, A. Higashijima, Y. Takase, T. Maekawa, O. Mitarai, M. Kikuchi, K. Toi, Electron Cyclotron / Bernstein wave heating and current drive experiments using phased-array antenna in QUEST, 19th Topical Conference on Radio Frequency Power in Plasmas
Radio Frequency Power in Plasmas - Proceedings of the 19th Topical Conference
, 10.1063/1.3665017, 473-476, 2011.12, [URL], The phased-array antenna system for Electron Cyclotron/Bernstein Wave Heating and Current Drive experiments has been developed in the QUEST. The antenna was designed to excite a pure O-mode wave in the oblique injection for the O-X-B mode conversion experiments, and its good performances were confirmed at a low power level. The plasma current (<∼15kA) with an aspect ratio of 1.5 was started up and sustained by only RF injection in the low-density operations. The long pulse discharge of 10 kA was also attained for 37 s. The new density window to sustain the plasma current was observed in the high-density plasmas. The single-null divertor configuration with the high plasma current (<∼25kA) was attained in the 17 s plasma sustainment..
345. M. Sakamoto, M. Yuno, S. Itoh, K. Hanada, K. Nakamura, H. Zushi, E. Jotaki, M. Hasegawa, S. V. Kulkani, A. Iyomasa, S. Kawasaki, H. Nakashima, Global particle balance and wall recycling properties of long duration discharges on TRIAM-1M, 19th IAEA Fusion Energy Conference, 2002.10.
346. H. Zushi, S. Itoh, K. Hanada, K. Nakamura, M. Sakamoto, E. Jotaki, M. Hasegawa, Y. D. Pan, S. V. Kulkarni, A. Iyomasa, S. Kawasaki, H. Nakashima, N. Yoshida, K. Tokunaga, T. Fujiwara, M. Miyamoto, H. Nakano, M. Yuno, A. Murakami, S. Nakamura, N. Sakamoto, K. Shinoda, S. Yamazoe, H. Akanishi, K. Kuramoto, Y. Matsuo, A. Iwamae, T. Fuijimoto, A. Komori, T. Morisaki, H. Suzuki, S. Masuzaki, Y. Hirooka, Y. Nakashima and O. Mitarai, Overview of Steady State Tokamak Plasma Experiments on TRIAM-1M, 19th IAEA Fusion Energy Conference(Lyon,2002), 2002.03.
347. , Kishore Mishra, H. Zushi, H. Idei, Hiroshi Idei, Kazuaki Hanada, High βp plasma formation using off-axis ECCD in Ohmic heated plasma in the spherical tokamak QUEST, 18th Joint Workshop on Electron Cyclotron Emission and Electron Cyclotron Resonance Heating, EC 2014
EPJ Web of Conferences
, 10.1051/epjconf/20158702012, 87, 2015.01, [URL], High poloidal beta (εβp ~ 1) operation in steady state condition in tokamaks is of great interest and has previously been demonstrated using NBI, LHCD and low current (Ip) plasma for a short time (<0.5 s). A very few experiments however, have been performed towards the investigation of highest obtainable βp in tokamak plasma. In this work we report the first result of high βp production and its sustainment though an off axis ECCD at two different frequencies (fundamental and second harmonic) in Ohmic (OH) target plasma. With application of ECCD, plasma βp increased to encounter an equilibrium limit and the standard limiter configuration is transformed to an Inboard Poloidal field Null (IPN) configuration. Both off-axis and on-axis ECCD is studied and found to have some distinctive features, which are discussed in this paper..
348. K. Nakamura, S. Itoh, H. Zushi, M. Sakamoto, K. Hanada, E. Jotaki, Y. D. Pan, S. Kawasaki, H. Nakashima, Current Profile Control Experiments in the LHCD Plasma on TRIAM-1M, 18th Intern. Conf. on Fusion Energy, IAEA-CN-77/EXP4/5 (2000), 2000.10.
349. M. Sakamoto, S. Itoh, K. Nakamura, H. Zushi, K. Hanada, E. Jotaki, U. D. Pan, S. Kawasaki, H. Nakashima, Recycling and Wall Pumping in Long Duration Discharges on TRIAM-1M, 18th Intern. Conf. on Fusion Energy, 2000.10.
350. K. Hanada, S. Itoh, K. Nakamura, H. Zushi, M. Sakamoto, E. Jotaki, Y. D. Pan 1), M. Hasegawa, S. Kawasaki, H. Nakashima, New Transition Phenomena in a Long Discharge on TRIAM-1M, 18th IAEA Fusion Energy Conference (Sorrento),IAEA-CN-77/EXP5/25, IAEA-CN-77/EXP5/26, 2000.10.
351. Zushi, H; Itoh, S; Nakamura, K; Sakamoto, M; Hanada, K; Jotaki, E; Pan, YD; Hasegawa, M; Kawasaki, S; Nakashima, H;, Steady State Experiments on High Performance,Current Profile Control and Long Sustainment of LHCD Plasmas on the Superconducting Tokamak TRIAM-1M, 18th IAEA Fusion Energy Conference (Sorrento),IAEA-CN-77/OV5/3, IAEA-CN-77/OV5/3 (2000), 2000.10.
352. H. Idei, M. Sakaguchi, E. I. Kalinnikova, K. Nagata, H. Zushi, K. Hanada, S. Tashima, M. Ishiguro, , H. Q. Liu, H. Igami3, S. Kubo, K. Nakamura, A. Fujisawa, M. Sakamoto, M. Hassegawa, Y. Higashizono, R. Ogata, T. Ryokai, S. K. Sharma, S. Kawasaki, H. Nakashima, A. Higashijima, Y. Takase, T. Maekawa, O. Mitarai and Y. Kishimoto, Development of Phased-array Antenna System and Its Application to EBWH/CD Experiments in QUEST, 16th Joint Workshop on Electron Cyclotron Emission and Electron Cyclotron Resonance Heating,Sanya,China, 269.0-274.0, (※), 2010.04.
353. Sasaki, K; Hanada, K; Sato, KN; Zushi, H; Nakamura, K; Sakamoto, M; Idei, H; Hasegawa, M; Kawasaki, S; Nakashima, T;, Soft X-ray measurement in IRE on the TST-2 tokamak, 16th International Toki Conference, P6-28, 2006.12.
354. H. Zushi, K. Hanada, H. Idei, M. Hasegawa, K. Sasaki, R. Bhattacharyay, M. Sakamoto, K. Nakamura, K. N. Sato, S. Kawasaki, H. Nakashima, A. Higashijima, ELECTRON CYCLOTRON COUNTER CURRENT DRIVE EXPERIMENTS IN BI-DIRECTIONAL LOWER HYBRID CURRENT DRIVE PLASMA IN TRIAM-1M, 14th Joint Workshop on Electron Cyclotron Emission and Electron Cyclotron Resonance Heating, Thira, Santorini Island, Greece, 9-12 May 2006, 2006.05.
355. K. Hanada, A. Iyomasa, H. Zushi, M. Hasegawa, K. Sasaki, H. Hoshika, K. Nakamura, M. Sakamoto, K. N. Sato, H. Idei, S. Kawasaki, H. Nakashima, A. Higashijima, Transport barrier formation by LHCD on TRIAM-1M, 12th International Congress on Plasma Physics,25-29 October 2004,Nice (France), (※), 2004.10, Internal transport barrier (ITB) has been obtained in full lower hybrid current driven (LHCD) plasmas on a superconducting tokamak, TRIMA-1M (R=0.84m, a x b=0.12mx0.18m, BT<8T). The formation of ITB depends on the current density profile, j(r), varied by the power deposition of the lower hybrid (LH). The plasma with ITB can be maintained by the LH power deposited around the foot point of ITB up to 25 sec, which corresponds to more than 100 times of current diffusion time, τL/R. ITB is terminated by the reduction of current drive efficiency caused by metal impurities accumulation. In some condition, self-organized slow sawtooth oscillations (SSSO) of plasma current, density, temperature, and so on with the period comparable to the current diffusion time have been also observed during ITB discharge. The oscillation has the capability of particle exhaust, as the result, it may play an role in the avoidance of the impurity accumulation and the dilution in the future steady state fusion plasma with ITB, as the edge-localized mode in H-mode..
356. Hiroyuki Hoshika, H. Zushi, M. Aramasu, H. Idei, A. Iyomasa, A. Ejiri, S. Ohara, H. Kasahara, Y. Kamada, S. Kawasaki, M. Sakamoto, K. Sasaki, K. Sato, S. Shiraiwa, Y. Takagi, Y. Takase, H. Nakashima, K. Nakamura, M. Hasegawa, K. Hanada, A. Higashijima, T. Yamada, Ion acceleration during internal magnetic reconnection events in TST-2, 12th International Congress on Plasma Physics,25-29 October 2004,Nice (France), arXiv preprint physics/0410229, P1-078, 2004.10, Characteristics of ion acceleration in the internal magnetic reconnection events (IRE) have been studied by means of a neutral particle energy analyzer (NPA) in Tokyo Spherical Tokamak (TST-2). The major and minor radii are 0.38 m and 0.25m, respectively. The magnetic field strength is 0.3T and the maximum plasma current is up to 140 kA. The electron and ion temperatures are 0.4-0.5 keV and 0.1 keV, respectively and the electron density is ~1x1019 m-3. The NPA can be scanned toroidally from q = 74° (cw) to q = 114° (ccw), where q = 90° corresponds to the perpendicular sightline. The direction of the plasma current is cw. The NPA signals are digitized at every 50 ms. The NPA is calibrated in the energy range of 0.1 keV < E < 8.4 keV. When the IRE occurs, it is observed that the plasma current increases by ~ 20% and the loop voltage drops from 0.6 V to-5 V for ~ 0.1 ms. The enhanced charge exchange flux is observed by more than one order of magnitude at ~ 1 keV for this reconnection phase. The ion temperature increases by 80 eV at IREs. The angle q dependence of increment of Ti shows that DTi (q = 74°) is higher than that for q = 114°. This observation suggests that an ion is accelerated initially in the direction of magnetic field lines. The time evolution of the ion distribution function is simulated with a Fokker-Planck code taking into account the electric field effects..
357. T. Kariya, T. Imai, R. Minami, K. Tsumura, Y. Ebashi, Hiroshi Idei, Kazuaki Hanada, M. Ono, K. Komurasaki, T. Numakura, Y. Endo, Y. Nakashima, Development of 28/35 GHz dual-frequency gyrotron for ECH study, 11th International Conference on Open Magnetic Systems for Plasma Confinement, OS 2016
Open Magnetic Systems for Plasma Confinement, OS 2016
Proceedings of the 11th International Conference on Open Magnetic Systems for Plasma Confinement
, 10.1063/1.4964176, 1771, 2016.10, [URL], The high power and long pulse operation of the gyrotron as well as efficient transmission of its output are quite important for achieving improved plasma performances. A 28 GHz 1 MW gyrotron developed for GAMMA 10/PDX achieved an output power of 1.38 MW in 2015 experiment after the power supply was improved. Furthermore, a new 28/35 GHz dual-frequency gyrotron (2 MW 3 s and 0.4 MW CW) for QUEST, NSTX-U, Heliotron J and GAMMA 10/PDX has been fabricated, after the preliminary test of a double-disk sapphire window installed in the gyrotron was performed. In the first experimental test, the oscillation of the main mode was confirmed at a frequency of 28.036 GHz with a Gaussian-like beam and an output power of 1.22 MW..
358. S. K. Sharma, H. Zushi, I. Takagi, Y. Hisano, T. Shikama, S. Morita, T. Tanabe, N. Yoshida, M. Sakamoto, Y. Higashizono, K. Hanada, M. Hasegawa, O. Mitarai, K. Nakamura, H. Idei, K. N. Sato, S. Kawasaki, H. Nakashima, A. Higashijima, Y. Nakashima, N. Nishino, Y. Hatano, A. Sagara, Y. Nakamura, N. Ashikawa, T. Maekawa, Y. Kishimoto, Y. Takase and QUEST GroupS, Wall pumping studies in spherical tokamak QUEST using permeation measurements and a static gas balance method,, 10th International Workshop on Hydrogen Isotopes in Fusion Reactor Materials, Pleasanton,and the Livermore Valley,California,May 31 - June 1,2010, 2010.05.

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