Updated on 2024/12/24

Information

 

写真a

 
IDO TAKESHI
 
Organization
Research Institute for Applied Mechanics Advanced Fusion Research Center Professor
Interdisciplinary Graduate School of Engineering Sciences Department of Interdisciplinary Engineering Sciences(Concurrent)
Title
Professor
Contact information
メールアドレス
Tel
0925837695
Profile
・磁場閉じ込めプラズマ中に発生する不安定性、乱流及び電場形成に関する実験研究 ・重イオンビームを用いた計測器の開発
External link

Research Areas

  • Energy Engineering / Nuclear fusion

Degree

  • Ph.D.

Research History

  • Kyushu University Research Institute for Applied Mechanics Professor 

    2019.10 - Present

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    Country:Japan

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  • 2000年4月―2019年9月 核融合科学研究所   

Education

  • Nagoya University   工学研究科   エネルギー理工学

    - 2000

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    Country:Japan

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  • Nagoya University   Graduate School, Division of Engineering  

    - 2000

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  • Osaka University   Faculty of Science  

    - 1994

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  • Osaka University   School of Science   物理学

    - 1994

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    Country:Japan

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Research Interests・Research Keywords

  • Research theme: プラズマ物理学

    Keyword: プラズマ物理学

    Research period: 2024

  • Research theme: Plasma physics

    Keyword: Plasma physics

    Research period: 2024

  • Research theme: Development of Heavy Ion Beam Probes for QUEST spherical tokamak and PLATO tokamak

    Keyword: Heavy ion beam probe, HIBP, turbulence, tokamak, plasma confinement

    Research period: 2019.10

  • Research theme: Investigation of the physical mechanism of formation of the electric potential profiles and turbulent transport in the magnetically confined plasmas

    Keyword: Magnetically confined plasma, electric potential profile, Heavy Ion Beam Probe, turbulence, nuclear fusion

    Research period: 2004.4

  • Research theme: Development of Heavy Ion Beam Probe on the Large Helical Device

    Keyword: Heavy Ion Beam Probe (HIBP), Electric Potential Measurement

    Research period: 2000.4

  • Research theme: Investigation of spatio-temporal evolution of electric potential in JFT-2Mトカマク

    Keyword: magnetically confined plasma, L-H transition, electric field, turbulence, turubulent transport, Heavy Ion Beam Probe (HIBP)

    Research period: 1999.4 - 2006.3

  • Research theme: Development of Heavy Ion Beam Probe on JFT-2M tokamak

    Keyword: Heavy Ion Beam Probe (HIBP)

    Research period: 1997.10 - 2004.3

Awards

  • 自然科学研究機構若手研究者賞

    2012.6   自然科学研究機構  

  • 第15回技術進歩賞

    2010.11   プラズマ・核融合学会   大型ヘリカル装置における重イオンビームプローブの開発

Papers

  • Development of a heavy ion beam probe diagnostic for HL-2A tokamak Reviewed International journal

    H.R. Fan, L.T. Gao, A.D. Liu, G. Zhuang, T. Ido, M. Xu, J.C. Huang, J. Zhang, C.Q. Feng, C. Zhou, H. Liu, L. Nie, Y.X. Liu, B.Z. Fu, J.Q. Li and W.D. Liu

    Journal of Instrumentation   18 ( 1 )   2023.1

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    Language:English   Publishing type:Research paper (scientific journal)  

    A heavy ion beam probe (HIBP) is being developed and tested on the HL-2A tokamak. To focus on the turbulence measurement in high beta scenarios with the toroidal magnetic field of 1.35 T, a 500 kV thallium beam is chosen and optimized. The locations of the injection and detection system are determined based on the probing beam trajectory calculations. The status of the accelerator, sweep system, analyzer, and control system is described. Four pairs of sweep plates are positioned in both primary and secondary beamlines to actively control the beam trajectory, where the poloidal sweepers require a maximum of 15 kV voltages to be applied. A parallel-plate energy analyzer with multi-slits is supplied by 100 kV high voltage for the electric potential measurement. The signal intensity is also evaluated to be hundreds of nA levels, 5 × 107 V/A amplifiers are therefore designed. Software is also developed to include the data acquisition as well as the control and monitoring of HIBP subsystems.

    DOI: 10.1088/1748-0221/18/01/P01008

  • Conceptual design of a heavy ion beam probe for the QUEST spherical tokamak

    T. Ido, M. Hasegawa, R. Ikezoe, T. Onchi, K. Hanada, H. Idei, K. Kuroda, Y. Nagashima

    Review of Scientific Instruments   2022.11

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    Language:Others   Publishing type:Research paper (scientific journal)  

    DOI: 10.1063/5.0101770

  • Geodesic acoustic modes in magnetic confinement devices Invited Reviewed International journal

    Conway, G.D., Smolyakov, A.I., Ido, T.

    Nuclear Fusion   62 ( 1 )   013001-1 - 013001-149   2022.1

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    Language:English   Publishing type:Research paper (scientific journal)  

    Geodesic acoustic modes (GAMs) are ubiquitous oscillatory flow phenomena observed in toroidal magnetic confinement fusion plasmas, such as tokamaks and stellarators. They are recognized as the non-stationary branch of the turbulence driven zonal flows which play a critical regulatory role in cross-field turbulent transport. GAMs are supported by the plasma compressibility due to magnetic geodesic curvature—an intrinsic feature of any toroidal confinement device. GAMs impact the plasma confinement via velocity shearing of turbulent eddies, modulation of transport, and by providing additional routes for energy dissipation. GAMs can also be driven by energetic particles (so-called EGAMs) or even pumped by a variety of other mechanisms, both internal and external to the plasma, opening-up possibilities for plasma diagnosis and turbulence control. In recent years there have been major advances in all areas of GAM research: measurements, theory, and numerical simulations. This review assesses the status of these developments and the progress made towards a unified understanding of the GAM behaviour and its role in plasma confinement. The review begins with tutorial-like reviews of the basic concepts and theory, followed by a series of topic orientated sections covering different aspects of the GAM. The approach adopted here is to present and contrast experimental observations alongside the predictions from theory and numerical simulations. The review concludes with a comprehensive summary of the field, highlighting outstanding issues and prospects for future developments.

    DOI: https://doi.org/10.1088/1741-4326/ac0dd1

  • Conceptual design of heavy ion beam probes on the PLATO tokamak Reviewed International journal

    T. Ido, A. Fujisawa, K. Takemura, T.-K. Kobayashi, D. Nishimura, N. Kasuya, A. Fukuyama, C. Moon, K. Yamasaki, S. Inagaki, Y. Nagashima, and T. Yamada

    Review of Scientific Instruments   92   053553   2021.5

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    Language:English   Publishing type:Research paper (scientific journal)  

    Heavy ion beam probe (HIBP) systems have been designed for the new tokamak, PLATO [A. Fujisawa, AIP Conf. Proc. 1993, 020011 (2018)]. The designs have been completed, and the installations are in progress. Two HIBPs are being installed in toroidal sections 180○ apart to investigate long-range correlations in the toroidal direction. Each HIBP consists of an injection beamline and a detection beamline as usual. Yet, one of the HIBPs is equipped with an additional detection beamline; the measurement positions of its two detection beamlines can be placed on almost the same magnetic surface yet at poloidal angles that differ by ∼180○. The use of three detection beamlines allows us to investigate spatial asymmetry and long-range correlations in both the toroidal and poloidal directions, simultaneously. The detected beam intensity is expected to be enough for turbulence measurements in almost the entire plasma region when the electron density is up to 1 × 10^19 m−3 by selecting appropriate ion species for the probe beam. Each detector has three channels 10 mm apart, allowing measurement of local structures of micro-scale turbulence. Therefore, using the HIBPs on the PLATO tokamak will enable both local and global properties of plasma turbulence to be investigated, simultaneously.

    DOI: 10.1063/5.0041814

    Other Link: https://doi.org/10.1063/5.0041814

  • Observation of subcritical geodesic acoustic mode excitation in the large helical device Reviewed International journal

    T. Ido, K. Itoh, M. Lesur, M. Osakabe, A. Shimizu, K. Ogawa, M. Nishiura, I. Yamada, R. Yasuhara, Y. Kosuga, M. Sasaki, K. Ida, S. Inagaki, S.-I. Itoh and the LHD Experiment Group

    Nuclear Fusion   57   072009   2017.4

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    The abrupt and strong excitation of the geodesic acoustic mode (GAM) has been found in the
    large helical device (LHD), when the frequency of a chirping energetic particle-driven GAM
    (EGAM) approaches twice that of the GAM frequency. The temporal evolution of the phase
    relation between the abrupt GAM and the chirping EGAM is common in all events. The result
    indicates a coupling between the GAM and the EGAM. In addition, the nonlinear evolution
    of the growth rate of the GAM is observed, and there is a threshold in the amplitude of the
    GAM for the appearance of nonlinear behavior. A threshold in the amplitude of the EGAM for
    the abrupt excitation of the GAM is also observed. According to one theory (Lesur et al 2016
    Phys. Rev. Lett. 116 015003, Itoh et al 2016 Plasma Phys. Rep. 42 418) the observed abrupt
    phenomenon can be interpreted as the excitation of the subcritical instability of the GAM. The excitation of a subcritical instability requires a trigger and a seed with sufficient amplitude. The observed threshold in the amplitude of the GAM seems to correspond with the threshold in the seed, and the threshold in the amplitude of the EGAM seems to correspond with the threshold in the magnitude of the trigger. Thus, the observed threshold supports the interpretation that the abrupt phenomenon is the excitation of a subcritical instability of the GAM.

    DOI: 10.1088/1741-4326/aa665a

  • Strong Destabilization of Stable Modes with a Half-Frequency Associated with Chirping Geodesic Acoustic Modes in the Large Helical Device Reviewed International journal

    T. Ido, K. Itoh, M. Osakabe, M. Lesur, A. Shimizu, K. Ogawa, K. Toi, M. Nishiura, S. Kato, M. Sasaki, K. Ida, S. Inagaki, S.-I. Itoh, the LHD Experiment Group

    Physical Review Letters   116   015002   2016.1

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    Language:English   Publishing type:Research paper (scientific journal)  

    Abrupt and strong excitation of a mode has been observed when the frequency of a chirping energetic-particle driven geodesic acoustic mode (EGAM) reaches twice the geodesic acoustic mode (GAM) frequency. The frequency of the secondary mode is the GAM frequency, which is a half-frequency of the primary EGAM. Based on the analysis of spatial structures, the secondary mode is identified as a GAM. The phase relation between the secondary mode and the primary EGAM is locked, and the evolution of the growth rate of the secondary mode indicates nonlinear excitation. The results suggest that the primary mode (EGAM) contributes to nonlinear destabilization of a subcritical mode.

    DOI: 10.1103/PhysRevLett.116.015002

  • Electrostatic Potential Measurement by Using 6-MeV Heavy Ion Beam Probe on LHD Invited Reviewed International journal

    Takeshi IDO, Akihiro SHIMIZU, Masaki NISHIURA, Shinji KATO, Haruhisa NAKANO, Akimitsu NISHIZAWA, Yasuji HAMADA, Mitsuhiro YOKOTA, Kiwamu TSUKADA, Hideki OGAWA, Tomoyuki INOUE, Katsumi IDA, Mikiro YOSHINUMA, Sadayoshi MURAKAMI, Kenji TANAKA, Kazumichi NARIHARA, Ichihiro YAMADA, Kazuo KAWAHATA, Naoki TAMURA and the LHD Experimental Group

    Plasma and Fusion Research   3   031   2008.4

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    Language:English   Publishing type:Research paper (scientific journal)  

    A heavy ion beam probe (HIBP) using a 3 MV tandem accelerator was installed in Large Helical Device (LHD). It is designed to measure the electrostatic potential in the core region directly. It is calibrated and can be used to measure the electrostatic potential profiles in LHD plasmas. The radial electric field (Er) obtained from the potential profiles measured using the HIBP agrees with that measured by charge exchange spectroscopy (CXS). Er predicted by the neoclassical theory is also compared to that measured using the HIBP, and is in good agreement with the experimental results in the core region.

    DOI: 10.1585/pfr.3.031

    Other Link: http://www.jspf.or.jp/PFR/PFR_articles/pfr2008/pfr2008_03-031.html

  • Geodesic–acoustic-mode in JFT-2M tokamak plasmas Invited Reviewed International journal

    T Ido, Y Miura, K Kamiya, Y Hamada, K Hoshino, A Fujisawa, K Itoh, S-I Itoh, A Nishizawa, H Ogawa, Y Kusama and JFT-2M group

    Plasma Physics and Controlled Fusion   48   S41   2006.3

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    Language:English   Publishing type:Research paper (scientific journal)  

    The characteristics of geodesic–acoustic-mode (GAM) are investigated through direct and simultaneous measurement of electrostatic and density fluctuations with a heavy ion beam probe. The amplitude of the GAM changes in relation to the radial position; it is small near the separatrix, reaches a local maximum at 3 cm inside the separatrix and then decreases again to 5 cm inside the separatrix. The frequency is constant in the range, though the predicted GAM frequency varies according to the temperature gradient. The correlation length is about 6 cm and comparable to the structure of the amplitude of the GAM. The results indicate the GAM has a radial structure which reflects the local condition at about 3 m inside the separatrix. The phase relation between the GAM oscillation indicates that the GAM is a radial propagating wave.
    The interaction between the GAM and the ambient density fluctuation is shown by the high coherence between the GAM oscillation and the temporal behaviour of the ambient density fluctuation. Moreover, the phase relation between the electric field fluctuation of the GAM (E˜r,GAM) and the amplitude of the density fluctuation indicates that the modulation of the ambient density fluctuation delays the E˜r,GAM. The causality between the GAM and the modulation of the density fluctuation is revealed.

    DOI: 10.1088/0741-3335/48/4/S04

    Other Link: https://iopscience.iop.org/article/10.1088/0741-3335/48/4/S04

  • Observation of the interaction between the geodesic acoustic mode and ambient fluctuation in the JFT-2M tokamak Reviewed International journal

    T. Ido, Y. Miura, K. Hoshino, K. Kamiya, Y. Hamada, A. Nishizawa, Y. Kawasumi, H. Ogawa, Y. Nagashima, K. Shinohara, Y. Kusama, JFT-2M group

    Nuclear Fusion   46 ( 5 )   512   2006.3

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    Language:English   Publishing type:Research paper (scientific journal)  

    The electrostatic and density fluctuation are measured simultaneously with a heavy ion beam probe. The electrostatic fluctuation with the geodesic acoustic mode (GAM) frequency is observed in L-mode plasmas and not in H-mode plasmas. The poloidal and radial structure is consistent with the GAM. So the fluctuation is concluded to be the GAM. The amplitude of the GAM changes in the radial direction; it is small near the separatrix, has a maximum at 3 cm inside the separatrix and decreases again to 5 cm inside the separatrix. The GAM and the temporal behaviour of the ambient density fluctuation show a significant coherence, and the phase of modulation of the ambient density fluctuation tends to delay the potential oscillation of the GAM. It is clearly verified that the GAM affects ambient fluctuation and also the local particle transport through modulation of the amplitude of the ambient fluctuation.

    DOI: 10.1088/0029-5515/46/5/003

    Other Link: https://iopscience.iop.org/article/10.1088/0029-5515/46/5/003

  • Overview of Large Helical Device experiments of basic plasma physics for solving crucial issues in reaching burning plasma conditions

    Ida, K; Yoshinuma, M; Kobayashi, M; Kobayashi, T; Kenmochi, N; Nespoli, F; Magee, RM; Warmer, F; Dinklage, A; Matsuyama, A; Sakamoto, R; Nasu, T; Tokuzawa, T; Kinoshita, T; Tanaka, K; Tamura, N; Nagaoka, K; Nishiura, M; Takemura, Y; Ogawa, K; Motojima, G; Oishi, T; Morishita, Y; Varela, J; Hayashi, WHJ; Markl, M; Bouvain, H; Liang, Y; Leconte, M; Moseev, D; Moiseenko, VE; Albert, CG; Allfrey, I; Alonso, A; Arellano, FJ; Ashikawa, N; Azegami, A; Bardoczi, L; Van Berkel, M; Beurskens, M; Binderbaue, MW; Bortolon, A; Brezinsek, S; Bussiahn, R; Cappa, A; Carralero, D; Chan, IC; Cheng, J; Dai, X; Den Hartog, DJ; Dhard, CP; Ding, F; Ejiri, A; Ertmer, S; Fornal, T; Fujita, K; Fujiwara, Y; Funaba, H; Garcia, L; Garcia-Regana, JM; Garcia-Cortés, I; Garkusha, IE; Gates, DA; Ghai, Y; Gilson, EP; Gota, H; Goto, M; Green, EM; Haak, V; Hamaguchi, S; Hanada, K; Hara, H; Hartmann, D; Hayashi, Y; Henning, T; Hidalgo, C; Hillairet, J; Hutton, R; Ido, T; Igami, H; Ikeda, K; Inagaki, S; Ishizawa, A; Ito, S; Isobe, M; Isobe, Y; Ivkovic, M; Jiang, Z; Jo, J; Kamio, S; Kasahara, H; Kato, D; Katoh, Y; Kawachi, Y; Kawamoto, Y; Kawamura, G; Kawate, T; Kazakov, YO; Klumper, V; Knieps, A; Ko, WH; Kobayashi, S; Koike, F; Kovtun, YV; Kubkowska, M; Kubo, S; Lam, SSH; Langenberg, A; Laqua, H; Lazerson, S; Lestz, J; Li, B; Liao, L; Lin, Z; Lunsford, R; Masuzaki, S; Matsuura, H; McCarthy, KJ; Medina-Roque, D; Mitarai, O; Mollen, A; Moon, C; Mori, Y; Morisaki, T; Morita, S; Mukai, K; Murakami, I; Murakami, S; Murase, T; Muscatello, CM; Nagasaki, K; Naujoks, D; Nakano, H; Nakata, M; Narushima, Y; Nagy, A; Nicolau, JH; Nishizawa, T; Nishimoto, S; Nuga, H; Nunami, M; Ochoukov, R; Ohdachi, S; Ongena, J; Osakabe, M; Pablant, NA; Panadero, N; Peterson, B; Villén, JD; Romazanov, J; Rosato, J; Rud, M; Sakakibara, S; Sakaue, HA; Sakai, H; Sakon, I; Salewski, M; Sangaroon, S; Sereda, S; Stange, T; Saito, K; Satake, S; Seki, R; Seki, T; Sharapov, S; Shimizu, A; Shimozuma, T; Shivam, G; Shoji, M; Spong, DA; Sugama, H; Sun, Z; Suzuki, C; Suzuki, Y; Tajima, T; Takada, E; Takahashi, H; Toi, K; Tsuchibushi, Y; Tsujii, N; Tsumori, K; Tsujimurai, TI; Ueno, G; Uehara, H; Velasco, JL; Wang, E; Watanabe, KY; Wauter, T; Wenzel, U; Yajima, M; Yamada, H; Yamada, I; Yanagihara, K; Yamaguchi, H; Yanai, R; Yasuhara, R; Yokoyama, M; Yoshimura, Y; Zarnstorff, M; Zhao, M; Zhong, GQ; Zhou, Q; Ziaei, S

    NUCLEAR FUSION   64 ( 11 )   2024.11   ISSN:0029-5515 eISSN:1741-4326

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    Publisher:Nuclear Fusion  

    Recently, experiments on basic plasma physics issues for solving future problems in fusion energy have been performed on a Large Helical Device. There are several problems to be solved in future devices for fusion energy. Emerging issues in burning plasma are: alpha-channeling (ion heating by alpha particles), turbulence and transport in electron dominant heating helium ash exhaust, reduction of the divertor heat load. To solve these problems, understanding the basic plasma physics of (1) wave-particle interaction through (inverse) Landau damping, (2) characteristics of electron-scale (high-k) turbulence, (3) ion mixing and the isotope effect, and (4) turbulence spreading and detachment, is necessary. This overview discusses the experimental studies on these issues and turbulent transport in multi-ion plasma and other issues in the appendix.

    DOI: 10.1088/1741-4326/ad3a7a

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  • Heating characteristic of electron Bernstein wave using high-field side X-mode injection in QUEST

    Murakami, T; Kojima, S; Hanada, K; Idei, H; Ido, T; Ikezoe, R; Hasegawa, M; Onchi, T; Kono, K; Kuroda, K; Ejiri, A

    PLASMA PHYSICS AND CONTROLLED FUSION   66 ( 11 )   2024.11   ISSN:0741-3335 eISSN:1361-6587

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    Publisher:Plasma Physics and Controlled Fusion  

    A comparative investigation was conducted to assess the impact of high-field side (HFS) extraordinary (X) mode (HFS X) injection and low-field side (LFS) ordinary (O) mode (LFS O) injection of 8.2 GHz radio frequency (RF) power in the Q-shu University experimental steady-state spherical tokamak. In the case of the HFS X injection, the ratio of electron plasma frequency and RF frequency f pe / f RF was 1.3, indicating an overdense plasma, whereas in the LFS O injection, this ratio was 0.9. Distinctive features emerged in the electron temperature and density profiles between the two injection scenarios. In the HFS X injection, the profiles peaked between the fundamental electron cyclotron resonance (ECR) layer and the upper hybrid resonance layer. Conversely, in the LFS O injection, the peaks were situated near the 1st ECR layer. This implies effective excitation of the electron Bernstein wave (EBW) in the case of the HFS X injection, with the wave power being absorbed through the doppler-shifted ECR of the EBW. Density and temperature oscillations were observed only in the start-up phase of the HFS X injection, which may correlate with the presence of the left-hand cutoff of the X-mode. These findings will be contributed to understand the distinctive characteristics associated with plasma heating through EBW excitation in the HFS X injection.

    DOI: 10.1088/1361-6587/ad802e

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  • Electron cyclotron current start-up using a retarding electric field in the QUEST spherical tokamak

    Onchi, T; Idei, H; Hanada, K; Watanabe, O; Miyata, R; Zhang, Y; Koide, Y; Otsuka, Y; Yamaguchi, T; Higashijima, A; Nagata, T; Sekiya, I; Shimabukuro, S; Niiya, I; Kono, K; Zennifa, F; Nakamura, K; Ikezoe, R; Hasegawa, M; Kuroda, K; Nagashima, Y; Ido, T; Kariya, T; Ejiri, A; Murakami, S; Fukuyama, A; Kosuga, Y

    NUCLEAR FUSION   64 ( 10 )   2024.10   ISSN:0029-5515 eISSN:1741-4326

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    Publisher:Nuclear Fusion  

    The plasma current start-up experiment is conducted through electron cyclotron (EC) heating in the QUEST spherical tokamak. During the EC heating, the application of a toroidal electric field in the opposite direction to the plasma current effectively inhibits the growth of energetic electrons. Observations show rapid increases in plasma current and hard x-ray count immediately following the cancellation of the retarding electric field. When a compact tokamak configuration maintains equilibrium on the high field side, along with the retarding field, it leads to effective bulk electron heating. This heating achieved an electron temperature of Te ≈ 1 keV at electron density ne > 1.0 × 1018 m−3. Ray tracing of the EC wave verifies that more power absorption into plasma through a single-pass occurs around the second resonance layer with higher values of electron density and temperature.

    DOI: 10.1088/1741-4326/ad6914

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  • Hydrogen removal by electron cyclotron wall conditioning with neon gas and its impact of tokamak plasma start-up on the QUEST spherical tokamak

    Fukumoto, M; Yue, QL; Hanada, K; Kojima, S; Nakano, T; Yoshida, N; Ikezoe, R; Nagashima, Y; Ido, T; Onchi, T; Idei, H; Iguchi, H; Komiyama, T; Shikama, T; Ejiri, A; Masuzaki, S; Sakamoto, M; Ueda, Y; Kuroda, K; Kono, K; Shimabukuro, S; Higashijima, A

    NUCLEAR FUSION   64 ( 6 )   2024.6   ISSN:0029-5515 eISSN:1741-4326

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    Publisher:Nuclear Fusion  

    Electron cyclotron wall conditioning with neon gas (Ne-ECWC) has been performed on the normal conducting spherial tokamak QUEST with metal walls under a trapped particle configuration with O-mode EC waves including X-mode polarization with a frequency of 8.2 GHz and an injection power of 16 kW. The Ne-ECWC removes hydrogen from the wall with small neon retention. The Ne-ECWC decreases hydrogen recycling at the following tokamak discharges, contributing to an improvement of the following tokamak plasma start-up: the plasma current increases and the start-up timing of the plasma current shifts forward. However, defects such as voids and bubbles are formed on tungsten surface exposed to the Ne-ECWC plasma.

    DOI: 10.1088/1741-4326/ad3d6e

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  • Improving Current Distribution Model for EBWCD using Flux Loops in QUEST

    Junyao Zhou, Hanada Kazuaki, Kuroda Kengoh, Onchi Takumi, Idei Hiroshi, Ikezoe Ryuya, Hasegawa Makoto, Nagashima Yoshihiko, Ido Takeshi, Kinoshita Toshiki

    Evergreen   11 ( 2 )   555 - 562   2024.6   ISSN:21890420 eISSN:24325953

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    Language:English   Publisher:Transdisciplinary Research and Education Center for Green Technologies, Kyushu University  

    During the early phase of tokamak plasma start-up prior to the formation of a closed magnetic surface, various plasma current profiles are expected to be observed. Especially, the noninductive current drive (CD) by the electron Bernstein wave (EBW) is likely to be the most dominant, and the current profile is expected to focus on a local area predicted by the theoretical model. In addition, the EBWCD direction could be affected by a horizontal magnetic field induced by a toroidal magnetic field coil and feed-through. The magnetic flux data cannot be fitted by using a previous model described by Yoshinaga23), and hence, this model needs improvement. Consequently, an improved model is introduced in this paper based on the theoretical prediction of EBWCD. This model can be applied to reproduce the complex plasma current profile accurately during the early phase of the tokamak plasma start-up.

    DOI: 10.5109/7183306

    CiNii Research

  • Core density profile control by energetic ion anisotropy in LHD

    Nishiura, M; Shimizu, A; Ido, T; Satake, S; Yoshinuma, M; Yanai, R; Nunami, M; Yamaguchi, H; Nuga, H; Seki, R; Fujita, K; Salewski, M

    PHYSICS OF PLASMAS   31 ( 6 )   2024.6   ISSN:1070-664X eISSN:1089-7674

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    Publisher:Physics of Plasmas  

    Electron and impurity ion density profiles have been controlled by using tangential and perpendicular neutral beams for plasma heating in a stellarator/heliotron for the first time. Reduced anisotropy of stored energy for energetic ion En⊥/Enǁ has resulted in an inward electron and impurity transport, forming a core electron density peaking. Increased anisotropy leads to a flat or hollowed electron density profile with an impurity exhaust in a core region [Yoshinuma et al., Nucl. Fusion 49, 062002 (2009)]. A high confinement state of particles in LHD has yet to be achieved, except for a temporal state of an electron density peaking created by a pellet injection. As a pioneering and crucial research result, the operation of energetic ion anisotropy by neutral beams has newly demonstrated that the direction of the radial transport of bulk and impurity ions can be controlled. At the same time, the overall plasma performance rises in neutron flux and stored energy. On the other hand, the increase in the anisotropy flattens the density profile. This new finding holds promise for a control knob of nuclear fusion reactors to enhance fusion power output.

    DOI: 10.1063/5.0201440

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  • Identification of nonlinear effects of background asymmetry on solitary oscillations in a cylindrical plasma

    Kobayashi, T; Fujisawa, A; Nagashima, Y; Moon, C; Yamasaki, K; Nishimura, D; Inagaki, S; Shimizu, A; Tokuzawa, T; Ido, T

    SCIENTIFIC REPORTS   14 ( 1 )   12175   2024.5   ISSN:2045-2322

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    Language:English   Publisher:Scientific Reports  

    A symmetry-breaking in rotational spatial pattern of quasi-periodic solitary oscillations is revealed with tomography measurement of plasma emission, simultaneously with background asymmetry in stationary plasma structure. Although the oscillatory pattern deformation is a natural course in the presence of asymmetry, elaborate analyses identify existence unfeatured nonlinear effects of the background asymmetry, i.e., its nonlinear couplings with harmonic modes of rotational symmetry, to produce non-harmonic mode to break the symmetry and cause the oscillatory pattern to be chaotic. The findings suggest the unrecognized fundamental process for plasmas to be turbulent.

    DOI: 10.1038/s41598-024-62969-1

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  • Comparison of electron temperature and density measured by helium line intensity ratio and Thomson scattering methods in ECH spherical tokamak plasma

    Komiyama, T; Shikama, T; Hanada, K; Ido, T; Onchi, T; Kono, K; Ejiri, A; Hasegawa, M; Inoue, S; Hasuo, M; Idei, H; Yue, QL; Kuroda, K; Higashijima, A; Prapan, P

    PLASMA PHYSICS AND CONTROLLED FUSION   66 ( 4 )   2024.4   ISSN:0741-3335 eISSN:1361-6587

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    The electron temperature and density profiles in the midplane of a spherical tokamak plasma produced by electron cyclotron heating (ECH) in Q-shu University experiment with steady-state spherical tokamak (QUEST) are measured by the helium line intensity ratio method. The measured profiles are compared with those obtained by the Thomson scattering method, and the measured temperatures and densities are found to agree within factors of ∼2 and ∼6, respectively. Taken together with the previous results of comparisons performed in the scrape-off layers of several toroidal devices, the same degree of agreement between the helium line intensity ratio method and other methods is obtained in the ranges of 7-100 eV for temperature and 4 × 1016-1 × 1019 m−3 for density.

    DOI: 10.1088/1361-6587/ad2c2a

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  • A Method to Analyze Plasma Images Using Modified Fourier-Bessel Functions

    NISHIMURA Yuki, FUJISAWA Akihide, NAGASHIMA Yoshihiko, MOON Chanho, NISHIZAWA Takashi, KOBAYASHI Tatsuya, SHIMIZU Akihiro, TOKUZAWA Tokihiko, IDO Takeshi, NISHIMURA Daiki, KOBAYASHI Taiki

    Plasma and Fusion Research   19 ( 0 )   1201014 - 1201014   2024.3   ISSN:1880-6821 eISSN:18806821

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    <p>A new method is proposed to analyze plasma image of tomography using modified Fourier-Bessel Functions (FBF) instead of the original FBF analysis. The application of the method to an assumed plasma image shows that the difference between the original and the fitting image is improved considerably to that of FBF, owing to giving a better fitting inside the plasma and eliminating the ghost values outside the plasma, without any disadvantages in analysis of plasma structures and patterns.</p>

    DOI: 10.1585/pfr.19.1201014

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  • Demonstration of transient CHI startup using a floating biased electrode configuration

    Kuroda, K; Raman, R; Onchi, T; Hasegawa, M; Hanada, K; Ono, M; Nelson, BA; Rogers, J; Ikezoe, R; Idei, H; Ido, T; Nagata, M; Mitarai, O; Nishino, N; Otsuka, Y; Zhang, Y; Kono, K; Kawasaki, S; Nagata, T; Higashijima, A; Shimabukuro, S; Niiya, I; Sekiya, I; Nakamura, K; Takase, Y; Ejiri, A; Murakami, S

    NUCLEAR FUSION   64 ( 1 )   2024.1   ISSN:0029-5515 eISSN:1741-4326

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    Results from the successful solenoid-free plasma startup using the method of transient coaxial helicity injection (transient CHI) in the QUEST spherical tokamak (ST) are reported. Unlike previous applications of CHI on HIT-II and on NSTX which required two toroidal insulating breaks to the vacuum vessel, QUEST uses a first of its kind, floating single biased electrode configuration, which does not use such a vacuum break. Instead, the CHI electrode is simply insulated from the outer lower divertor plate support structure. This configuration is much more suitable for implementation in a fusion reactor than the previous configurations. Transient CHI generated toroidal currents of 135 kA were obtained. The toroidal current during the formation of a closed flux configuration was over 50 kA. These results bode well for the application of transient CHI in a new generation of compact high-field STs and tokamaks in which the space for the central solenoid is very restricted.

    DOI: 10.1088/1741-4326/ad0dd6

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  • Effects of toroidally-distributed-divertor biasing on scrape-off-layer (SOL) current drive, divertor particle flux and fast electron confinement in the QUEST spherical tokamak

    Toi, K; Onchi, T; Zushi, H; Kuroda, K; Idei, H; Hanada, K; Hasegawa, M; Kojima, S; Ikezoe, R; Ido, T; Kawasaki, S; Higashijima, A

    NUCLEAR FUSION   63 ( 10 )   2023.10   ISSN:0029-5515 eISSN:1741-4326

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    A novel divertor biasing by four biasing plates distributed toroidally (TDDB) on the upper divertor target plate is applied to low density tokamak plasmas started-up by 28 GHz 2nd harmonic electron cyclotron current drive (ECCD) in a quasi-double null configuration of the QUEST spherical tokamak (ST). In the ST plasmas of line averaged electron density < n e > ∼0.7-1 × 1018 m−3, about 20%-40% of the current I bias driven by ∼85 V sawtooth bias voltage reaches the lower divertor plate along the biased scrape-off-layer (SOL) flux tube as the SOL current I SOL . The fact I SOL is noticeably lower than I bias indicates an appreciable leakage of parallel current from the biased SOL flux tube. The leakage currents in the toroidal and radial directions are confirmed by detection of them using the unbiased plates in the TDDB experiments. From the ion saturation current density profile obtained by a divertor Langmuir probe array, the fall-off lengths of divertor particle flux are estimated together with the strike line position. Total particle flux to the upper divertor, evaluated by the integrated ion saturation current density profile is reduced by up to 45% during positive biasing of the TDDB, depending on the position of the strike line to the biased plate. In addition, the TDDB also induces a noticeable loss of fast electrons produced by ECCD, leading to an ∼2% reduction in the maximum toroidal current of the ST plasma compared to a shot without the TDDB. Reduction of the divertor particle flux and enhancement of the fast electron losses are thought to be dominantly caused by E × B drift induced by the TDDB. In the present experimental conditions, the effects of magnetic perturbations produced by the SOL currents on the fast electron losses can be neglected because of a too small SOL current.

    DOI: 10.1088/1741-4326/acee13

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  • Rotational movement analysis based on Fourier-rectangular function transform for cylindrical plasma

    Nishimura, D; Fujisawa, A; Yamasaki, K; Nagashima, Y; Moon, C; Nishizawa, T; Kobayashi, TK; Kobayashi, T; Shimizu, A; Tokuzawa, T; Ido, T

    JOURNAL OF APPLIED PHYSICS   134 ( 11 )   2023.9   ISSN:0021-8979 eISSN:1089-7550

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    This article presents a method to estimate the rotational velocity of a cylindrical plasma from its two-dimensional images by an extended use of the Fourier-rectangular function transform, which was proposed to analyze the structure and dynamics of a cylindrical plasma [K. Yamasaki e t a l ., J. Appl. Phys. 126 , 043304 (2019)]. The proposed method is applied to tomography images of plasmas produced in a linear cylindrical device and succeeds in obtaining the radial distribution of rotational velocity and its fluctuations, providing an interesting finding, that is, the existence of flow modulation associated with m = 1 mode fluctuations.

    DOI: 10.1063/5.0165318

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  • Spectroscopic measurement of increases in hydrogen molecular rotational temperature with plasma-facing surface temperature and due to collisional-radiative processes in tokamaks

    Yoneda, N; Shikama, T; Scotti, F; Hanada, K; Iguchi, H; Idei, H; Onchi, T; Ejiri, A; Ido, T; Kono, K; Peng, Y; Osawa, Y; Yatomi, G; Kidani, A; Kudo, M; Hiraka, R; Takeda, K; Bell, RE; Maan, A; Boyle, DP; Majeski, R; Soukhanovskii, VA; Groth, M; McLean, AG; Wilcox, RS; Lasnier, C; Nakamura, K; Nagashima, Y; Ikezoe, R; Hasegawa, M; Kuroda, K; Higashijima, A; Nagata, T; Shimabukuro, S; Niiya, I; Sekiya, I; Hasuo, M

    NUCLEAR FUSION   63 ( 9 )   2023.9   ISSN:0029-5515 eISSN:1741-4326

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    Spatially resolved rotational temperature of ground state hydrogen molecules desorbed from plasma-facing surface was measured in QUEST, LTX-β, and DIII-D tokamaks, and the increases of the rotational temperature with the surface temperature and due to collisional-radiative processes in the plasmas were evaluated. The increase due to collisional-radiative processes was calculated by solving rate equations considering electron and proton collisional excitation and deexcitation and spontaneous emission. The calculation results suggest a high sensitivity for the rotational temperature to electron and proton densities, but a negligible sensitivity to the electron, proton, and surface temperatures. In the three tokamaks with different plasma parameters and plasma-facing surface materials, the spatial profile of the rotational temperature was estimated using Fulcher-α emission lines (600-608 nm). In QUEST, the spatial profile of the rotational temperature was estimated from spatially resolved spectra. In the other tokamaks, the rotational temperature was evaluated assuming a single point emission with a location determined from the Fulcher-α emission profile as measured with a filtered camera. In metal-walled devices QUEST and LTX-β, the rotational temperature increased with the surface temperature, and the calculated collisional-radiative increase is consistent with measured increase assuming that the rotational temperature at the surface is approximately 500-600 K higher than the surface temperature. In DIII-D with carbon walls, a larger collisional-radiative increase than the other tokamaks was observed because of the higher density leading to a large difference from the calculated increase compared to the other smaller tokamaks. Measurement of the Fulcher-α emission profile with higher spatial resolution in DIII-D may reduce the difference and reveal the effect of the surface temperature on the rotational temperature. These results show the increases in the rotational temperature with the surface temperature and due to the collisional-radiative processes.

    DOI: 10.1088/1741-4326/acd4d1

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  • Spectroscopic measurement of increases in hydrogen molecular rotational temperature with plasma-facing surface temperature and due to collisional-radiative processes in tokamaks

    Yoneda N., Shikama T., Scotti F., Hanada K., Iguchi H., Idei H., Onchi T., Ejiri A., Ido T., Kono K., Peng Y., Osawa Y., Yatomi G., Kidani A., Kudo M., Hiraka R., Takeda K., Bell R.E., Maan A., Boyle D.P., Majeski R., Soukhanovskii V.A., Groth M., McLean A.G., Wilcox R.S., Lasnier C., Nakamura K., Nagashima Y., Ikezoe R., Hasegawa M., Kuroda K., Higashijima A., Nagata T., Shimabukuro S., Niiya I., Sekiya I., Hasuo M.

    Nuclear Fusion   63 ( 9 )   2023.9   ISSN:00295515 eISSN:17414326

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    Spatially resolved rotational temperature of ground state hydrogen molecules desorbed from plasma-facing surface was measured in QUEST, LTX-β, and DIII-D tokamaks, and the increases of the rotational temperature with the surface temperature and due to collisional-radiative processes in the plasmas were evaluated. The increase due to collisional-radiative processes was calculated by solving rate equations considering electron and proton collisional excitation and deexcitation and spontaneous emission. The calculation results suggest a high sensitivity for the rotational temperature to electron and proton densities, but a negligible sensitivity to the electron, proton, and surface temperatures. In the three tokamaks with different plasma parameters and plasma-facing surface materials, the spatial profile of the rotational temperature was estimated using Fulcher-α emission lines (600–608 nm). In QUEST, the spatial profile of the rotational temperature was estimated from spatially resolved spectra. In the other tokamaks, the rotational temperature was evaluated assuming a single point emission with a location determined from the Fulcher-α emission profile as measured with a filtered camera. In metal-walled devices QUEST and LTX-β, the rotational temperature increased with the surface temperature, and the calculated collisional-radiative increase is consistent with measured increase assuming that the rotational temperature at the surface is approximately 500–600 K higher than the surface temperature. In DIII-D with carbon walls, a larger collisional-radiative increase than the other tokamaks was observed because of the higher density leading to a large difference from the calculated increase compared to the other smaller tokamaks. Measurement of the Fulcher-α emission profile with higher spatial resolution in DIII-D may reduce the difference and reveal the effect of the surface temperature on the rotational temperature. These results show the increases in the rotational temperature with the surface temperature and due to the collisional-radiative processes.

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  • Circuit design for doubling the toroidal magnetic field on the QUEST spherical tokamak

    Onchi, T; Idei, H; Yanagi, N; Zhang, YF; Nakamura, K; Kuroda, K; Hasegawa, M; Ikezoe, R; Hanada, K; Ido, T; Kobayashi, M; Ogawa, Y; Yoshitani, M; Kawamura, T

    FUSION ENGINEERING AND DESIGN   192   2023.7   ISSN:0920-3796 eISSN:1873-7196

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    Various scenarios of electron cyclotron heating can be explored in a spherical tokamak with a high toroidal field. On the QUEST spherical tokamak, doubling the toroidal field results in the emergence of the fundamental resonance layer for 28 GHz electron cyclotron waves. The second-harmonic resonance layer shifts toward the plasma central area. To increase the coil current from 50 to 100 kA, a current source is designed with 125 modules in parallel. The module power supply comprises a bank of lithium-ion capacitors and a DC–DC buck converter. In the bench test of a single module, the current was found to increase linearly and maintained the flat-top as programmed.

    DOI: 10.1016/j.fusengdes.2023.113794

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  • Sudden Change Events of Plasma Current during Electron-Cyclotron Current Start-Up on the QUESTB Spherical Tokamak Reviewed International journal

    Ryuya IKEZOE, Kosuke TAKEDA, Kengoh KURODA, Takumi ONCHI, Takahiro NAGATA, Izumi SEKIYA, Hiroshi IDEI, Fadilla ZENNIFA, Yifan ZHANG, Seiya SAKAI, Rikuya MIYATA, Takahiro YAMAGUCHI, Makoto HASEGAWA, Yoshihiko NAGASHIMA, Takeshi IDO, Kazuaki HANADA

    Plasma and Fusion Research   18   402066   2023.6

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    Non-inductive plasma current start-up experiments have been conducted using 2nd harmonic electroncyclotron resonance heating (ECRH) on the QUEST spherical tokamak. Sudden or abrupt changes in plasma current, referred to as sudden change events (SCEs), have been frequently observed during these experiments. To investigate these events, fast magnetic activity was measured globally by installing arrays of magnetic pick-up coils inside the vacuum vessel on QUEST. Analysis revealed that all observed SCEs could be classified into three categories based on their magnetic characteristics. In one type of event, called SCE–III, the plasma current suddenly decreases by up to 50% instantaneously, occurring in a wide discharge region achieved using 2nd ECRH start-up on QUEST. These SCE–III events may potentially lead to disruptions in future discharges at higher powers.

    DOI: 10.1585/pfr.18.2402066

  • A versatile power supply system for the central solenoid of the QUEST spherical tokamak

    Zhang, YF; Onchi, T; Nakamura, K; Otsuka, Y; Koide, Y; Yue, QL; Nagata, T; Kawasaki, S; Kuroda, K; Hasegawa, M; Ikezoe, R; Ido, T; Hanada, K; Idei, H

    FUSION ENGINEERING AND DESIGN   191   2023.6   ISSN:0920-3796 eISSN:1873-7196

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    Here, a versatile power supply system, consisting of two current sources, insulated-gate bipolar transistor stacks, and a capacitor bank, is proposed for application in various operations of the QUEST spherical tokamak. The central solenoid coil in this system can carrying a maximum current and voltage of ±8 kA and ±375 V, respectively. In plasma start-up experiments based on ohmic heating through double flux swing, a plasma current of over 100 kA is stably obtained. Moreover, the feedback control of the thyristor power supply is utilized to control the plasma current, plasma shape, and position. The oscillating central-solenoid current applies a bipolar loop voltage at constant time intervals, and the capacitor bank discharge facilitates a co-axial helicity injection as well as amplifies the toroidal current.

    DOI: 10.1016/j.fusengdes.2023.113648

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  • Initial testing of ohmic heating through double flux swing during electron cyclotron start-up in the QUEST spherical tokamak

    Zhang, YF; Onchi, T; Nakamura, K; Yue, QL; Nagata, T; Kawasaki, S; Kuroda, K; Hasegawa, M; Ikezoe, R; Ido, T; Hanada, K; Idei, H

    PLASMA SCIENCE & TECHNOLOGY   25 ( 5 )   2023.5   ISSN:1009-0630 eISSN:2058-6272

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    A power-supply system was developed for Ohmic heating (OH) to double × 1018 the amount of change magnetic flux in the primary central solenoid (CS) on the QUEST spherical tokamak. Two power supplies are connected with stacks of insulated-gate bipolar transistors, and sequentially operated to generate positive and negative CS currents. This bipolar power-supply system is controlled via a field-programmable gate array, which guarantees the safety of the entire system operation. The new OH system, assisted by electron cyclotron heating, enables the stable generation of plasma currents exceeding 100 kA. Moreover, the achieved electron density over the wide range in the major radial direction exceeds the cut-off density for one of the high-power microwave sources in QUEST. This strategy yields target plasmas for future experiments with the electron Bernstein wave.

    DOI: 10.1088/2058-6272/acafc2

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  • Design Study of a Line Integrated Thomson Scattering System for TST-2 Spherical Tokamak Device

    EJIRI Akira, LIN Yu-Ting, JANG Seowon, PENG Yi, SHINOHARA Kouji, IDO Takeshi, KONO Kaori, NAGASHIMA Yoshihiko

    Plasma and Fusion Research   18 ( 0 )   2402025 - 2402025   2023.4   ISSN:1880-6821 eISSN:18806821

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    <p>A design study of a line integrated Thomson scattering (TS) system with a complete backscattering configuration has been performed to clarify practical problems. Installation on the TST-2 spherical tokamak was assumed, and an optical system design with ready-made components, are adopted. Some practical aspects, such as aberration, masking effect of the laser combining mirror, misalignment are investigated by ray tracing calculations. The performance of density profile reconstruction was also investigated. It was found that a tangential-multi-chord measurement configuration on the midplane shows a good effective localization, and error enhancement in the reconstruction is small. In addition, the efficiency of the system is about an order of magnitude larger than the present conventional TS system in TST-2. The attractiveness of the line integrated TS measurements was demonstrated.</p>

    DOI: 10.1585/pfr.18.2402025

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  • QUEST Database for Tokamak Big Data Reviewed International journal

    Makoto HASEGAWA, Aki HIGASHIJIMA, Ichiro NIIYA, Kazuaki HANADA, Hiroshi IDEI, Takeshi IDO, Ryuya IKEZOE, Takumi ONCHI, Kengo KURODA and Daisuke SAKURA

    18   1305048   2023.4

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    A database has been developed to provide a highly efficient data analysis environment by registering various types of data obtained in the QUEST (Q-shu University Experiment with Steady-State Spherical Tokamak) experiments and providing the data to researchers through standard SQL query output. In conventional experiments, measurements are usually obtained using several instruments, and the results are often stored separately in proprietary formats. An analysis to collect distributed files and convert them into appropriate formats individually was necessary, which led to a decrease in analysis efficiency. In order to build a system to centrally store and provide data, we constructed new servers, each for registering data in a database and for extracting data from the database and visualizing the data. As a result, various real-time monitoring data can be registered in the database, and data retrieval for analysis can be performed easily with a unified user interface. The construction of this database has made it possible to easily retrieve real-time monitoring data and a wide variety of table data, enabling analysis from a new perspective, and improving analysis efficiency.

    DOI: 10.1585/pfr.18.1305048

  • 8.56-GHz quasi-optical launcher system with incident-mode selectivity on the QUEST spherical tokamak

    Idei, H; Sakaguchi, M; Mishra, K; Onchi, T; Ikezoe, R; Watanabe, O; Tanaka, Y; Saito, T; Ido, T; Hanada, K

    FUSION ENGINEERING AND DESIGN   189   2023.4   ISSN:0920-3796 eISSN:1873-7196

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    An 8.56-GHz quasi-optical launcher system with incident-mode selectivity was developed for non-inductive electron cyclotron (EC) plasma ramp-up and long-pulse sustainment, and effective bulk-electron heating on the Q-shu University experiment with steady-state spherical tokamak (QUEST). A novel polarization-selective system was proposed to conduct fundamental and second harmonic EC heating and current drive experiments with ordinary and extra-ordinary mode waves, respectively. Selectivity of the incident modes or polarizations was confirmed using the whole developed system at a low power level. A large-sized mirror launcher was developed to inject the beam whose size was as small as possible near the QUEST major radius. The designed mirror performance was checked using a three-dimensional electromagnetic-wave simulator and a low-power test. Ultimately, 0.15-m sized beams for both the two polarizations were successfully attained near the QUEST major radius, even in low-frequency applications with long propagation.

    DOI: 10.1016/j.fusengdes.2023.113479

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  • Quaternion Analysis of Transient Phenomena of Motor-Generator Reviewed International journal

    Kazuo NAKAMURA, Yifan ZHANG, Takumi ONCHI, Hiroshi IDEI, Makoto HASEGAWA, Kazutoshi TOKUNAGA, Kazuaki HANADA, Takeshi IDO, Ryuya IKEZOE, Hirotaka CHIKARAISHI, Osamu MITARAI, Shoji KAWASAKI, Aki HIGASHIJIMA, Takahiro NAGATA, Shun SHIMABUKURO

    Plasma and Fusion Research   18   2405035   2023.3

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    A motor-generator slowly converts low electrical power to the large rotating energy of the induction motor, which is then converted to the higher electrical power of the synchronous generator through a pulse. Such a cycle is repeated in a tokamak plasma experiment. In the transient phase at the start of the synchronous generator, high transient voltage appears in the armature windings repeatedly. Due to the repeatability, it is imperative to estimate the high voltage and control it so that the maximum voltage is kept under a tolerable value. A quaternion is a four-dimensional hypercomplex number that is good at describing three-dimensional rotation. Utilizing the quaternion capability, a three-phase motor-generator is analyzed using three-dimensional rotation. The mechanical rotation was anlyzed by the rotation quaternion. The salient pole-type rotating field can be manipulated by direct-quadrature conversion even in quaternion analysis. The rotating dynamics and electrical phenomena of a motor-generator can be analyzed by considering the quaternion power from the motor-generator and the electrical load for plasma control.

    DOI: 10.1585/pfr.18.2405035

  • A Proposal to Evaluate Electron Temperature and Electron Density Fluctuations Using Dual Wavelength Emission Intensity Tomography in a Linear Plasma

    Yoshihiko Nagashima, Akihide Fujisawa, Kotaro Yamasaki, Shigeru Inagaki, Chanho Moon, Fumiyoshi Kin, Yuichi Kawachi, Hiroyuki Arakawa, Takuma Yamada, Tatsuya Kobayashi, Naohiro Kasuya, Yusuke Kosuga, Makoto Sasaki, Takeshi Ido

    Journal of the Physical Society of Japan   92 ( 3 )   2023.3

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    DOI: 10.7566/jpsj.92.033501

  • Development of Thomson Scattering Measurement System for Long Duration Discharges on the QUEST Spherical Tokamak

    KONO Kaori, IDO Takeshi, EJIRI Akira, HANADA Kazuaki, YUE Qilin, HASEGAWA Makoto, PENG Yi, SAKAI Seiya, IKEZOE Ryuya, IDEI Hiroshi, KAWASAKI Syoji, KURODA Kengoh, ONCHI Takumi, NAGASHIMA Yoshihiko, JANG Seowon

    Plasma and Fusion Research   18 ( 0 )   1405012 - 1405012   2023.2   ISSN:1880-6821 eISSN:18806821

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    <p>The Thomson scattering control system has been modified to measure the time evolution of the electron density and temperature profiles during long duration discharges in the QUEST spherical tokamak. The system consists of a signal generator and a control circuit. The former accepts a QUEST main trigger and provides multiple triggers, each of which starts a short-term (e.g. 15 s) measurement. The latter provides triggers to synchronize the oscilloscope and laser oscillation during a short-term measurement. The system was used in 1000 s long duration discharges in QUEST, and the temporal evolutions of density and temperature profiles were obtained successfully. It was found the profiles are stationary after about 300 s.</p>

    DOI: 10.1585/pfr.18.1405012

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  • Hydrogen isotope effect on self-organized electron internal transport barrier criticality and role of radial electric field in toroidal plasmas

    T. Kobayashi, A. Shimizu, M. Nishiura, T. Ido, S. Satake, T. Tokuzawa, T. Ii Tsujimura, K. Nagaoka, K. Ida

    Scientific Reports   12 ( 1 )   2022.12

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    Abstract

    Self-organized structure formation in magnetically confined plasmas is one of the most attractive subjects in modern experimental physics. Nonequilibrium media are known to often exhibit phenomena that cannot be predicted by superposition of linear theories. One representative example of such phenomena is the hydrogen isotope effect in fusion plasmas, where the larger the mass of the hydrogen isotope fuel is the better the plasma confinement becomes, contrary to what simple scaling models anticipate. In this article, threshold condition of a plasma structure formation is shown to have a strong hydrogen isotope effect. To investigate the underlying mechanism of this isotope effect, the electrostatic potential is directly measured by a heavy ion beam probe. It is elucidated that the core electrostatic potential transition occurs with less input power normalized by plasma density in plasmas with larger isotope mass across the structure formation. This observation is suggestive of the isotope effect in the radial electric field structure formation.

    DOI: 10.1038/s41598-022-09526-w

  • Behavior of geodesic acoustic mode and limit-cycle oscillation approaching L-H transition in JFT-2M tokamak

    Kobayashi, T; Sasaki, M; Ido, T; Kamiya, K; Miura, Y; Ida, K; Itoh, K

    PLASMA PHYSICS AND CONTROLLED FUSION   64 ( 11 )   2022.11   ISSN:0741-3335 eISSN:1361-6587

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    In this paper, a phenomenology of competing behavior between the geodesic acoustic mode (GAM) and the limit-cycle oscillation (LCO) is presented. Before the LCO occurs, the GAM can grow to the observable amplitude via the turbulent Reynolds stress force. Approaching the L-H transition, the LCO is excited and the GAM decays. In the LCO phase, the GAM driving force is possibly suppressed by the nonlocal turbulence amplitude modulation by the LCO.

    DOI: 10.1088/1361-6587/ac9333

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  • 3D metal powder additive manufacturing phased array antenna for multichannel Doppler reflectometer

    T. Tokuzawa, T. Nasu, S. Inagaki, C. Moon, T. Ido, H. Idei, A. Ejiri, R. Imazawa, M. Yoshida, N. Oyama, K. Tanaka, K. Ida

    Review of Scientific Instruments   2022.11

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    DOI: 10.1063/5.0101723

  • Design Considerations for the Implementation of a High-Field-Side Transient CHI System on QUEST Invited Reviewed International journal

    R. Raman, K. Kuroda, K. Hanada, M. Ono, M. Hasegawa, T. Onchi, R. Ikezoe, H. Idei, T. Ido, J.A. Rogers

    Journal of Fusion Energy   4171 - 4176   2022.11

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    Transient coaxial helicity injection (T-CHI), a method first developed on the small helicity injected torus (HIT-II) experiment and then validated on the much larger National Spherical Torus Experiment (NSTX) device, is a method to initiate an inductive-like tokamak plasma discharge without reliance on the central solenoid. A CHI discharge is initiated by driving current along magnetic flux that connects the inner and outer divertor plates on one end of the tokamak. To permit this, on both HIT-II and NSTX, toroidal ceramic insulators were used to electrically separate the inner and outer vessel components. The use of such large toroidal vacuum insulators may not be easy to implement in reactors. To address this issue, the Q-shu University experiments with steady-state spherical tokamak (ST) (QUEST) is developing a reactor-relevant CHI configuration in which one of the divertor plates is electrically insulated from the rest of the vessel. The first application of T-CHI on QUEST biased the CHI electrode to the outer vessel. While the CHI discharges could be easily generated, it was found that as the discharge filled the vessel, the separation distance between the injector magnetic flux footprints widened, a condition that is not favorable for the generation of closed flux surfaces. Biasing the electrode to the inner wall is a configuration similar to that used on NSTX and HIT-II, but initial testing in this configuration has proved to be challenging. The design described here overcomes the present limitation by locating the CHI electrode much closer to the CHI injector flux coil and using an NSTX-like gas injection manifold to enable high-field-side T-CHI startup on QUEST. The concepts described in this article should also benefit the future implementation of T-CHI systems in other tokamaks and spherical tokamaks.

    DOI: 10.1109/TPS.2022.3193069

  • Improvements to the High-Field-Side Transient CHI System on QUEST Reviewed International journal

    K. Kuroda, R. Raman, M. Hasegawa, T. Onchi, K. Hanada, M. Ono, B. A. Nelson, J. Rogers, R. Ikezoe, H. Idei, T. Ido, O. Mitarai, M. Nagata, S. Kawasaki, T. Nagata, A. Higashijima, S. Shimabukuro, I. Niiya, I. Sekiya, S. Kojima, K. Nakamura, Y. Takase & S. Murakami

    Journal of Fusion Energy   41 ( 2 )   25   2022.11

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    Transient coaxial helicity injection (CHI) is a promising candidate for solenoid-free plasma current start-up in a low-aspect-ratio tokamak in support of developing fully non-inductive scenarios. The aim of the transient CHI research on QUEST is to develop a reactor-relevant CHI design. On QUEST, a CHI discharge is initiated by driving current along magnetic field lines that connect an electrically insulated electrode plate (which is referred to as a bias electrode) to a vessel component at the bottom region of the spherical tokamak. In the first application of CHI on QUEST, the electrically insulated electrode plate was biased with respect to the outer vessel in a configuration referred to as low-field-side (LFS) injection. To maintain a narrow injector flux footprint width throughout the discharge, QUEST is now developing a high-field-side (HFS) injection configuration, in which the electrically insulated electrode plate is biased with respect to the inner vessel components. Through the implementation of a CHI-dedicated gas injection system, studies in the HFS injection configuration have now demonstrated good magnetic flux evolution into the vacuum vessel. Toroidal currents up to 43 kA have been achieved, and the generated current has increased in proportion to the magnetic flux connecting the electrodes. These results which show agreement with the CHI-scaling suggest that much higher levels of toroidal current can be generated on QUEST in an optimized CHI system in which the magnetic flux connecting the CHI electrodes is further increased.

    DOI: 10.1007/s10894-022-00338-4

  • Adaptive Capon beamforming for lensless electron cyclotron emission imaging with high spatial resolution Reviewed International journal

    H. Idei, M. Fukuyama, S. Sakai, K. Mishra, K. Nishimura, R. Ikezoe, T. Onchi, T. Ido, K. Hanada

    Review of Scientific Instruments   20   103531   2022.10

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    Electron cyclotron emission (ECE) imaging diagnostics incorporating a lensless approach have been developed for measurements involving active spatial selectivity and direction-of-arrival estimation. The Capon method for adaptive-array analysis was proposed to improve the spatial resolution of the two-dimensional ECE imaging technique. Broadband noise source emissions were used to simulate the ECE to verify the practical effectiveness of the Capon method in the ECE imaging. Multiple noise source emission positions were properly estimated with a high spatial resolution using the Capon method.

    DOI: 10.1063/5.0101632

  • Towards automated gas leak detection through cluster analysis of mass spectrometer data

    Makoto Hasegawa, Daisuke Sakurai, Aki Higashijima, Ichiro Niiya, Keiji Matsushima, Kazuaki Hanada, Hiroshi Idei, Takeshi Ido, Ryuya Ikezoe, Takumi Onchi, Kengo Kuroda

    Fusion Engineering and Design   180   113199 - 113199   2022.7

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    DOI: 10.1016/j.fusengdes.2022.113199

  • Geodesic acoustic modes in magnetic confinement devices

    G.D. Conway, A.I. Smolyakov, T. Ido

    Nuclear Fusion   62 ( 1 )   013001 - 013001   2022.1   ISSN:0029-5515 eISSN:1741-4326

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    Abstract

    Geodesic acoustic modes (GAMs) are ubiquitous oscillatory flow phenomena observed in toroidal magnetic confinement fusion plasmas, such as tokamaks and stellarators. They are recognized as the non-stationary branch of the turbulence driven zonal flows which play a critical regulatory role in cross-field turbulent transport. GAMs are supported by the plasma compressibility due to magnetic geodesic curvature—an intrinsic feature of any toroidal confinement device. GAMs impact the plasma confinement via velocity shearing of turbulent eddies, modulation of transport, and by providing additional routes for energy dissipation. GAMs can also be driven by energetic particles (so-called EGAMs) or even pumped by a variety of other mechanisms, both internal and external to the plasma, opening-up possibilities for plasma diagnosis and turbulence control. In recent years there have been major advances in all areas of GAM research: measurements, theory, and numerical simulations. This review assesses the status of these developments and the progress made towards a unified understanding of the GAM behaviour and its role in plasma confinement. The review begins with tutorial-like reviews of the basic concepts and theory, followed by a series of topic orientated sections covering different aspects of the GAM. The approach adopted here is to present and contrast experimental observations alongside the predictions from theory and numerical simulations. The review concludes with a comprehensive summary of the field, highlighting outstanding issues and prospects for future developments.

    DOI: 10.1088/1741-4326/ac0dd1

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  • Conceptual design of a heavy ion beam probe diagnostic for HL-2M tokamak Reviewed

    H.R. Fan, T. Ido, A.D. Liu, Min Xu, Z.Y. Liu, Ge Zhuang, L.J. Cai, J.X. Li, L.T. Gao, Chu Zhou, Lin Nie, J.Q. Li, W.D. Liu

    Fusion Engineering and Design   173   112845 - 112845   2021.12

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    DOI: 10.1016/j.fusengdes.2021.112845

  • The first observation of 4D tomography measurement of plasma structures and fluctuations Reviewed

    Chanho Moon, Kotaro Yamasaki, Yoshihiko Nagashima, Shigeru Inagaki, Takeshi Ido, Takuma Yamada, Naohiro Kasuya, Yusuke Kosuga, Makoto Sasaki, Yuichi Kawachi, Daiki Nishimura, Taiki Kobayashi, Akihide Fujisawa

    Scientific Reports   11 ( 1 )   2021.12

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    <title>Abstract</title>A tomography system is installed as one of the diagnostics of new age to examine the three-dimensional characteristics of structure and dynamics including fluctuations of a linear magnetized helicon plasma. The system is composed of three sets of tomography components located at different axial positions. Each tomography component can measure the two-dimensional emission profile over the entire cross-section of plasma at different axial positions in a sufficient temporal scale to detect the fluctuations. The four-dimensional measurement including time and space successfully obtains the following three results that have never been found without three-dimensional measurement: (1) in the production phase, the plasma front propagates from the antenna toward the end plate with an ion acoustic velocity. (2) In the steady state, the plasma emission profile is inhomogeneous, and decreases along the axial direction in the presence of the azimuthal asymmetry. Furthermore, (3) in the steady state, the fluctuations should originate from a particular axial position located downward from the helicon antenna.

    DOI: 10.1038/s41598-021-83191-3

  • Investigation of radial distribution of atomic hydrogen flux to the plasma facing components in steady state discharges in QUEST tokamak Reviewed

    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, A. Higashijima, I. Niiya, H. Zushi

    Nuclear Materials and Energy   26   2021.3

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    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 F~4.3×1015H/m2/s, which is ~6 % of that just in front of PFCs, F~7.7×1016H/m2/s.

    DOI: 10.1016/j.nme.2020.100872

  • Toroidal flow measurements of impurity ions in QUEST ECH plasmas using multiple viewing chords emission spectroscopy Reviewed

    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

    Nuclear Materials and Energy   26   2021.3

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    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.

    DOI: 10.1016/j.nme.2021.100905

  • Non-inductive plasma current ramp-up through oblique injection of harmonic electron cyclotron waves on the QUEST spherical tokamak Reviewed

    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, A. Fukuyama

    Physics of Plasmas   28 ( 2 )   2021.2

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    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 I p > 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.

    DOI: 10.1063/5.0031357

  • The systematic investigation of energetic-particle-driven geodesic acoustic mode channeling using MEGA code Reviewed

    Hao Wang, Yasushi Todo, Masaki Osakabe, Takeshi Ido, Yasuhiro Suzuki

    Nuclear Fusion   60 ( 11 )   2020.11

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    Energetic-particle-driven geodesic acoustic modes (EGAMs) channeling in the Large Helical Device (LHD) plasmas are systematically investigated for the first time using MEGA code. MEGA is a hybrid simulation code for energetic particles interacting with a magnetohydrodynamic (MHD) fluid. In the present work, both the energetic particles and the bulk ions are described kinetically. The EGAM profiles in the three-dimensional form is illustrated. Then, EGAM channeling behaviors are analyzed under different conditions. During the EGAM activities without frequency chirping, EGAM channeling occurs in the linear growth stage but terminates in the decay stage after the saturation. During the EGAM activities with frequency chirping, EGAM channeling occurs continuously. Also, low-frequency EGAM makes the energy transfer efficiency () higher, and this is confirmed by changing the energetic particle pressure, energetic particle beam velocity, and energetic particle pitch angle. Moreover, higher bulk ion temperature makes the energy transfer efficiency higher. In addition, under a certain condition, the energy transfer efficiency in the deuterium plasma is lower than that in the hydrogen plasma.

    DOI: 10.1088/1741-4326/ab8a04

  • Comparison between Tomography and Langmuir Probe Data in PANTA Reviewed

    Yoshihiko Nagashima, Akihide Fujisawa, Kotaro Yamasaki, Shigeru Inagaki, Chanho Moon, Fumiyoshi Kin, Yuichi Kawachi, Hiroyuki Arakawa, Takuma Yamada, Tatsuya Kobayashi, Naohiro Kasuya, Yusuke Kosuga, Makoto Sasaki, Takeshi Ido

    Journal of the Physical Society of Japan   89 ( 9 )   093501 - 093501   2020.9

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    Emission intensity ε from plasmas is a complicated function of electron temperature Te and electron density ne. To understand the dependence of ε on Te and ne, an experimental comparison between tomography data (local ε of ArII) and Langmuir probe data (Te and ne) in a linear plasma device PANTA is presented in this paper. In the comparison, the local emission intensity is modeled as εmodel / Teαn2e, and the model is validated by calculating both cross-correlation function and least squares of residuals between the fluctuations of ε and εmodel. The comparison reveals that the both methods provide α = 2.3–2.7, higher than 2 that of the exponent of ne. This result confirms that dependence of Te on ε is larger than that of ne when Te is low, as in PANTA.

    DOI: 10.7566/jpsj.89.093501

  • Spectroscopic Measurement of Hydrogen Atom Density in a Plasma Produced with 28 GHz ECH in QUEST Reviewed

    Satoru Mori, Taiichi Shikama, Kazuaki Hanada, Nao Yoneda, Arseniy Kuzmin, Masahiro Hasuo, Hiroshi Idei, Takumi Onchi, Akira Ejiri, Yuki Osawa, Yi Peng, Kyohei Matsuzaki, Shinichiro Kado, Keiji Sawada, Takeshi Ido, Kazuo Nakamura, Ryuya Ikezoe, Yoshihiko Nagashima, Makoto Hasegawa, Kengo Kuroda, Aki Higashijima, Takahiro Nagata, Shun Shimabukuro

    ATOMS   8 ( 3 )   2020.9

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    The spatial distribution of the hydrogen atom density was evaluated in a spherical tokamak (ST) plasma sustained only with 28 GHz electron cyclotron heating (ECH). The radially resolved H-delta emissivity was measured using multiple viewing chord spectroscopy and Abel inversion. A collisional-radiative (CR) model analysis of the emissivity resulted in a ground-state hydrogen atom density of 10(15)-10(16) m(-3) and an ionization degree of 1-0.85 in the plasma.

    DOI: 10.3390/atoms8030044

  • Erratum: Impact of a resonant magnetic perturbation field on impurity radiation, divertor footprint, and core plasma transport in attached and detached plasmas in the Large Helical Device (Nuclear Fusion (2019) 59 (096009) DOI: 10.1088/1741-4326/ab26e6) Reviewed

    M. Kobayashi, R. Seki, S. Masuzaki, S. Morita, H. M. Zhang, Y. Narushima, H. Tanaka, K. Tanaka, T. Tokuzawa, M. Yokoyama, T. Ido, I. Yamada

    Nuclear Fusion   59 ( 10 )   2019.8

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    Due to an error in the production process, figures 6 and 13 had overlapping labels on their y axes. The correct figures are shown below. (Figure Presented).

    DOI: 10.1088/1741-4326/ab3a13

  • Simulation of energetic particle driven geodesic acoustic modes and the energy channeling in the Large Helical Device plasmas Reviewed

    Hao Wang, Yasushi Todo, Masaki Oasakabe, Takeshi Ido, Yasuhiro Suzuki

    Nuclear Fusion   59 ( 9 )   2019.8

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    Energetic particle driven geodesic acoustic modes (EGAMs) in Large Helical Device plasmas are investigated using MEGA code. MEGA is a hybrid simulation code for energetic particles interacting with a magneto-hydrodynamic (MHD) fluid and in the present work, both the energetic particles and bulk ions are described by the kinetic equations. The low frequency EGAMs are reproduced. Also, the energy transfer is analyzed and the bulk ion heating during the EGAM activity is observed. The ions obtain energy when the energetic particles lose energy, and this indicates that an energy channel is established by the EGAM. EGAM channeling is reproduced by simulation with realistic parameters for the first time. The heating power to bulk ions is 3.4 kW m-3. It is found that sideband resonance is dominant during the energy transfer from EGAM to the bulk ions, and the transit frequencies of resonant bulk ions are one-half of the EGAM frequency.

    DOI: 10.1088/1741-4326/ab26e5

  • Core plasma confinement during detachment transition with RMP application in LHD Reviewed

    M. Kobayashi, S. Masuzaki, K. Tanaka, T. Tokuzawa, M. Yokoyama, Y. Narushima, I. Yamada, T. Ido, R. Seki

    Nuclear Materials and Energy   17   137 - 141   2018.12

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    The core plasma confinement during detachment phase is investigated in the discharges with application of resonant magnetic perturbation (RMP) field in LHD. The RMP application creates a remnant magnetic island in the edge stochastic layer, which largely changes the plasma parameter profiles including impurity radiation. The electron temperature and pressure profiles are flattened at the island, while the electron density is slightly peaked at the edge of the island. The estimated impurity radiation profile is enhanced and fixed around the magnetic island during the detached phase, where the discharge is stably sustained with controlled level of radiation. Without RMP, the radiation penetrates the confinement region, leading to radiation collapse. It is found that in the case of the RMP application the plasma stored energy increases discontinuously at the detachment transition. In spite of the reduced effective plasma volume caused by the edge magnetic island and by the enhanced radiation there, the central plasma pressure finally exceeds the case without RMP. This is caused by the pressure profile peaking at the central region in the case with RMP. These results indicate clear change of core plasma confinement during the detached phase with RMP.

    DOI: 10.1016/j.nme.2018.10.003

  • Abrupt excitation of energetic-particle-driven geodesic acoustic mode in the large helical device Reviewed International journal

    Takeshi Ido

    AIP Conference Proceedings   1993   020002   2018.8

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    DOI: 10.1063/1.5048712

  • Realization of high T <inf>i</inf> plasmas and confinement characteristics of ITB plasmas in the LHD deuterium experiments Reviewed

    H. Takahashi, K. Nagaoka, K. Mukai, M. Yokoyama, S. Murakami, S. Ohdachi, T. Bando, Y. Narushima, H. Nakano, M. Osakabe, K. Ida, M. Yoshinuma, R. Seki, H. Yamaguchi, K. Tanaka, M. Nakata, F. Warmer, T. Oishi, M. Goto, S. Morita, T. I. Tsujimura, S. Kubo, T. Kobayashi, I. Yamada, C. Suzuki, M. Emoto, T. Ido, A. Shimizu, T. Tokuzawa, K. Nagasaki, T. Morisaki, Y. Takeiri

    Nuclear Fusion   58 ( 10 )   2018.8

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    The deuterium (D) operation was initiated in the LHD in 2017. In the first campaign of the D experiments, we successfully extended the high temperature regime in the LHD. The new record of the ion temperature (T i) of 10 keV associated with the ion internal transport barrier (ITB) was achieved due to several operational optimization. The thermal confinement characteristics of ITB plasmas were compared between hydrogen and D discharges. The effective ion thermal diffusivity of the ion-ITB plasmas was found to be smaller in the D discharges than that in the H discharges. The profiles of the T i, the electron density, and the impurity of the high T i plasmas strongly depended on the magnetic configuration and these profiles tended to peaked in the inward-shifted configuration. It was also found that the electron thermal confinement of the electron-ITB plasmas was clearly improved in the deuterium case. The GKV simulation showed the linear growth rate of TEM/ITG reduced in the plasmas with D both for the ion ITB and the electron ITB plasmas and qualitatively agreed with the tendency of the change in the thermal diffusivity obtained from the power balance analysis.

    DOI: 10.1088/1741-4326/aad87e

  • Energy confinement of hydrogen and deuterium electron-root plasmas in the Large Helical Device Reviewed

    Felix Warmer, H. Takahashi, K. Tanaka, Y. Yoshimura, C. D. Beidler, B. Peterson, H. Igami, T. Ido, R. Seki, M. Nakata, M. Yokoyama, T. Akiyama, H. Funaba, K. Ida, S. Kubo, A. Shimizu, T. Shimozuma, T. Tokuzawa, T. I. Tsujimura, H. Yamada, I. Yamada, R. Yasuhara, M. Yoshinuma, S. Yoshimura, T. Morisaki, M. Osakabe

    Nuclear Fusion   58 ( 10 )   2018.8

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    © 2018 IAEA, Vienna. The dependence of the energy confinement and energy transport on the isotope mass is a long-standing open question in the stellarator community. With the recent upgrade of the Large Helical Device to allow for deuterium plasma operation, systematic isotope experiments could be carried out for the first time in a major non-axisymmetric device. Within this framework, electron-cyclotron-resonance heated (ECRH) hydrogen and deuterium plasmas were investigated varying both density and heating power to establish a broad data set. Even at low power the central ECRH heating is sufficient to lead to stellarator-specific core-electron-root-confinement which features a peaked electron temperature profile and a positive radial electric field. For this data set, the energy confinement time and energy transport is investigated in detail and compared to the neoclassical theory. Over the whole data set, the energy confinement time of deuterium is statistically 10%-20% larger than in hydrogen indicating that the 'isotope effect' also exists in non-axisymmetric devices. Both the electron and ion temperature are elevated in deuterium compared to hydrogen at the same effective absorbed power and density. From a neoclassical point-of-view, the electron-root and the positive electric field extend over nearly the entire plasma radius. Good agreement is found between the measured and theoretical neoclassical ambipolar electric field. The neoclassical energy-flux can account for up to half the experimental flux implying that turbulence is responsible for a significant fraction of the entire energy-flux.

    DOI: 10.1088/1741-4326/aad611

  • Excitation of helically-trapped-energetic-ion driven resistive interchange modes with intense deuterium beam injection and enhanced effect on beam ions/bulk plasmas of LHD Reviewed

    T. Bando, S. Ohdachi, M. Isobe, Y. Suzuki, K. Toi, K. Nagaoka, H. Takahashi, R. Seki, X. D. Du, K. Ogawa, T. Ido, A. Shimizu, T. Ozaki

    Nuclear Fusion   58 ( 8 )   2018.6

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    Energetic ion driven resistive InterChange modes (EICs) accompanying repeated bursts of the magnetic fluctuations were found in hydrogen campaign of large helical device. The pressure gradient of helically trapped energetic particles, which are mainly produced by perpendicularly injected beams, drives this mode. Recently, perpendicular neutral beam injection (PERP-NBI) systems are upgraded for deuterium plasma campaign. The beam energies of the two PERP-NBIs are increased from 40/40 keV to 60/80 keV, respectively. And the injection powers increase from 6/6 MW to 9/9 MW, as well. As results of these upgrades of NBIs, the β value of helically trapped energetic ions, , has increased up to ∼0.35% and induced EICs with larger bursts and smaller repetition frequencies. It is found that the threshold of to excite EICs increases with deuterium PERP-NBIs. The amplitude of each burst and effect on energetic beam ions become larger when is larger. In addition, a large electrostatic potential about -25 kV is observed when EICs are excited, which is about two times larger than the potential observed in hydrogen campaign. The transient increases of the electron density and temperature in edge regions are clearly observed when the electrostatic potential is formed.

    DOI: 10.1088/1741-4326/aac699

  • Quantification of Turbulent Driving Forces for the Geodesic Acoustic Mode in the JFT-2M Tokamak Reviewed

    T. Kobayashi, M. Sasaki, T. Ido, K. Kamiya, Y. Miura, Y. Nagashima, K. Ida, S. Inagaki, A. Fujisawa, S. I. Itoh, K. Itoh

    Physical Review Letters   120 ( 4 )   2018.1

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    We investigate spatial structures of turbulence and turbulent transport modulated by the geodesic acoustic mode (GAM), from which the excitation mechanism of the GAM is discussed. The GAM is found to be predominantly excited through a localized Reynolds stress force, rather than the dynamic shearing force. The evaluated growth rate is larger than the linear damping coefficients and is on the same order of magnitude as the effective growth rate evaluated from time evolution in the GAM kinetic energy.

    DOI: 10.1103/PhysRevLett.120.045002

  • Turbulent transport reduction induced by transition on radial electric field shear and curvature through amplitude and cross-phase in torus plasma Reviewed

    T. Kobayashi, K. Itoh, T. Ido, K. Kamiya, S. I. Itoh, Y. Miura, Y. Nagashima, A. Fujisawa, S. Inagaki, K. Ida

    Scientific Reports   7 ( 1 )   2017.12

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    Spatiotemporal evolutions of radial electric field and turbulence are measured simultaneously in the H-mode transition, which is a prototypical example of turbulence structure formation in higherature plasmas. In the dynamical phase where transport barrier is established abruptly, the time-space-frequency-resolved turbulent particle flux is obtained. Here we report the validation of the mechanism of transport barrier formation quantitatively. It is found that the particle flux is suppressed predominantly by reducing density fluctuation amplitude and cross phase between density fluctuation and potential fluctuation. Both radial electric field shear and curvature are responsible for the amplitude suppression as was predicted by theory. Turbulence amplitude reduction immediately responds to the growth of the radial electric field non-uniformity and saturates, while cross phase continuously approaches zero.

    DOI: 10.1038/s41598-017-14821-y

  • Extended capability of the integrated transport analysis suite, TASK3D-a, for LHD experiment Reviewed

    M. Yokoyama, R. Seki, C. Suzuki, M. Sato, M. Emoto, S. Murakami, M. Osakabe, T. Ii Tsujimura, Y. Yoshimura, T. Ido, K. Ogawa, S. Satake, Y. Suzuki, T. Goto, K. Ida, N. Pablant, D. Gates, F. Warmer, P. Vincenzi

    Nuclear Fusion   57 ( 12 )   2017.9

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    The integrated transport analysis suite, TASK3D-a (Analysis), has been developed to be capable for routine whole-discharge analyses of plasmas confined in three-dimensional (3D) magnetic configurations such as the LHD. The routine dynamic energy balance analysis for NBI-heated plasmas was made possible in the first version released in September 2012. The suite has been further extended through implementing additional modules for neoclassical transport and ECH deposition for 3D configurations. A module has also been added for creating systematic data for the International Stellarator-Heliotron Confinement and Profile Database. Improvement of neutral beam injection modules for multiple-ion species plasmas and loose coupling with a large-simulation code are also highlights of recent developments.

    DOI: 10.1088/1741-4326/aa800a

  • Extension of the operational regime of the LHD towards a deuterium experiment Reviewed

    Y. Takeiri, T. Morisaki, M. Osakabe, M. Yokoyama, S. Sakakibara, H. Takahashi, Y. Nakamura, T. Oishi, G. Motojima, S. Murakami, K. Ito, A. Ejiri, S. Imagawa, S. Inagaki, M. Isobe, S. Kubo, S. Masamune, T. Mito, I. Murakami, K. Nagaoka, K. Nagasaki, K. Nishimura, M. Sakamoto, R. Sakamoto, T. Shimozuma, K. Shinohara, H. Sugama, K. Y. Watanabe, J. W. Ahn, N. Akata, T. Akiyama, N. Ashikawa, J. Baldzuhn, T. Bando, E. Bernard, F. Castejón, H. Chikaraishi, M. Emoto, T. Evans, N. Ezumi, K. Fujii, H. Funaba, M. Goto, T. Goto, D. Gradic, Y. Gunsu, S. Hamaguchi, H. Hasegawa, Y. Hayashi, C. Hidalgo, T. Higashiguchi, Y. Hirooka, Y. Hishinuma, R. Horiuchi, K. Ichiguchi, K. Ida, T. Ido, H. Igami, K. Ikeda, S. Ishiguro, R. Ishizaki, A. Ishizawa, A. Ito, Y. Ito, A. Iwamoto, S. Kamio, K. Kamiya, O. Kaneko, R. Kanno, H. Kasahara, D. Kato, T. Kato, K. Kawahata, G. Kawamura, M. Kisaki, S. Kitajima, W. H. Ko, M. Kobayashi, S. Kobayashi, T. Kobayashi, K. Koga, A. Kohyama, R. Kumazawa, J. H. Lee, D. López-Bruna, R. Makino, S. Masuzaki, Y. Matsumoto, H. Matsuura, O. Mitarai, H. Miura, J. Miyazawa, N. Mizuguchi, C. Moon, S. Morita, T. Moritaka, K. Mukai, T. Muroga, S. Muto, T. Mutoh

    Nuclear Fusion   57 ( 10 )   2017.8

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    As the finalization of a hydrogen experiment towards the deuterium phase, the exploration of the best performance of hydrogen plasma was intensively performed in the large helical device. High ion and electron temperatures, T i and T e, of more than 6 keV were simultaneously achieved by superimposing high-power electron cyclotron resonance heating onneutral beam injection (NBI) heated plasma. Although flattening of the ion temperature profile in the core region was observed during the discharges, one could avoid degradation by increasing the electron density. Another key parameter to present plasma performance is an averaged beta value . The high regime around 4% was extended to an order of magnitude lower than the earlier collisional regime. Impurity behaviour in hydrogen discharges with NBI heating was also classified with a wide range of edge plasma parameters. The existence of a no impurity accumulation regime, where the high performance plasma is maintained with high power heating >10 MW, was identified. Wide parameter scan experiments suggest that the toroidal rotation and the turbulence are the candidates for expelling impurities from the core region.

    DOI: 10.1088/1741-4326/aa7fc2

  • Extension of operational regime in high-temperature plasmas and effect of ECRH on ion thermal transport in the LHD Reviewed

    H. Takahashi, K. Nagaoka, S. Murakami, M. Osakabe, H. Nakano, K. Ida, T. I. Tsujimura, S. Kubo, T. Kobayashi, K. Tanaka, R. Seki, Y. Takeiri, M. Yokoyama, S. Maeta, M. Nakata, M. Yoshinuma, I. Yamada, R. Yasuhara, T. Ido, A. Shimizu, H. Tsuchiya, T. Tokuzawa, M. Goto, T. Oishi, S. Morita, C. Suzuki, M. Emoto, K. Tsumori, K. Ikeda, M. Kisaki, T. Shimozuma, Y. Yoshimura, H. Igami, R. Makino, T. Seki, H. Kasahara, K. Saito, S. Kamio, K. Nagasaki, T. Mutoh, O. Kaneko, T. Morisaki

    Nuclear Fusion   57 ( 8 )   2017.7

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    A simultaneous high ion temperature (T i) and high electron temperature (T e) regime was successfully extended due to an optimized heating scenario in the LHD. Such high-temperature plasmas were realized by the simultaneous formation of an electron internal transport barrier (ITB) and an ion ITB by the combination of high power NBI and ECRH. Although the ion thermal confinement was degraded in the plasma core with an increase of T e/T i by the on-axis ECRH, it was found that the ion thermal confinement was improved at the plasma edge. The normalized ion thermal diffusivity at the plasma edge was reduced by 70%. The improvement of the ion thermal confinement at the edge led to an increase in T i in the entire plasma region, even though the core transport was degraded.

    DOI: 10.1088/1741-4326/aa754b

  • Model validation for radial electric field excitation during L-H transition in JFT-2M tokamak Reviewed

    T. Kobayashi, K. Itoh, T. Ido, K. Kamiya, S. -I. Itoh, Y. Miura, Y. Nagashima, A. Fujisawa, S. Inagaki, K. Ida, K. Hoshino

    NUCLEAR FUSION   57 ( 7 )   2017.7

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    In this paper, we elaborate the electric field excitation mechanism during the L-H transition in the JFT-2M tokamak. Using time derivative of the Poisson's equation, models of the radial electric field excitation is examined. The sum of the loss-cone loss current and the neoclassical bulk viscosity current is found to behave as the experimentally evaluated radial current that excites the radial electric field. The turbulent Reynolds stress only plays a minor role. The wave convection current that produces a negative current at the edge can be important to explain the ambipolar condition in the L-mode.

    DOI: 10.1088/1741-4326/aa5d03

  • Suppression of Trapped Energetic Ions Driven Resistive Interchange Modes with Electron Cyclotron Heating in a Helical Plasma Reviewed

    X. D. Du, K. Toi, S. Ohdachi, K. Y. Watanabe, H. Takahashi, Y. Yoshimura, M. Osakabe, R. Seki, T. Nicolas, H. Tsuchiya, K. Nagaoka, K. Ogawa, K. Tanaka, M. Isobe, M. Yokoyama, M. Yoshinuma, S. Kubo, S. Sakakibara, T. Bando, T. Ido, T. Ozaki, Y. Suzuki, Y. Takemura

    Physical Review Letters   118 ( 12 )   2017.3

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    The resistive interchange mode destabilized by the resonant interaction with the trapped energetic ions is fully suppressed when the injected power of electron cyclotron heating exceeds a certain threshold. It is shown for the first time that the complete stabilization of the energetic-particle-driven mode without relaxing the energetic particle (EP) pressure gradient is possible by reducing the radial width of the eigenmodes δw, especially when δw narrows to a small enough value relative to the finite orbit width of EP.

    DOI: 10.1103/PhysRevLett.118.125001

  • 2D spatial profile measurements of potential fluctuation with heavy ion beam probe on the Large Helical Device Reviewed

    A. Shimizu, T. Ido, T. Ido, M. Nishiura, S. Kato, K. Ogawa, K. Ogawa, H. Takahashi, H. Takahashi, H. Igami, Y. Yoshimura, S. Kubo, T. Shimozuma

    Review of Scientific Instruments   87 ( 11 )   2016.11

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    2D spatial profile measurements of potential fluctuation with heavy ion beam probe on the Large Helical Device
    © 2016 Author(s).Two-dimensional spatial profiles of potential fluctuation were measured with the heavy ion beam probe (HIBP) in the Large Helical Device (LHD). For 2D spatial profile measurements, the probe beam energy has to be changed, which requires the adjustment of many deflectors in the beam transport line to optimize the beam trajectory, since the transport line of LHD-HIBP system is long. The automatic beam adjustment system was developed, which allows us to adjust the beam trajectory easily. By analyzing coherence between potential fluctuation and magnetic probe signal, the noise level of the mode power spectrum of the potential fluctuation can be reduced. By using this method, the 2D spatial profile of potential fluctuation profile was successfully obtained.

    DOI: 10.1063/1.4963908

  • Resistive interchange mode destabilized by helically trapped energetic ions and its effects on energetic ions and bulk plasma in a helical plasma Reviewed

    X. D. Du, K. Toi, S. Ohdachi, M. Osakabe, T. Ido, K. Tanaka, M. Yokoyama, M. Yoshinuma, K. Ogawa, K. Y, Watanabe, T. Akiyama, M. Isobe, K. Nagaoka, T. Ozaki, S. Sakakibara, R. Seki, A. Shimizu, Y. Suzuki, H. Tsuchiya

    Nuclear Fusion   56 ( 1 )   2016.11

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    Resistive interchange mode destabilized by helically trapped energetic ions and its effects on energetic ions and bulk plasma in a helical plasma
    © 2016 IAEA, Vienna. A resistive interchange mode of the structure (, : poloidal and toroidal mode numbers, respectively) with a bursting character and rapid frequency chirping in the range less than 10 kHz is observed for the first time in the edge region of the net current-free, low beta LHD (Large Helical Device) plasmas during high power injection of perpendicular neutral beams. The mode resonates with the precession motion of helically trapped energetic ions (EPs), following the resonant condition. The radial mode structure is recognized to be similar to that of the pressure-driven resistive interchange mode, of which radial displacement eigenfunction quite localizes around the mode rational surface, and evolves into an odd-type (or island-type) during the late of frequency chirping phase. This beam driven mode is excited when the beta value of helically trapped EPs exceeds a certain threshold. This instability is thought to be a new branch of resistive interchange mode destabilized by the trapped energetic ions. The radial transport, i.e. redistribution and losses, of helically trapped energetic ions induced by the mode transiently generates significant radial electric field near the plasma peripheral region. The large shear of thus generated radial electric field is thought to contribute to the observed suppression of micro-turbulence and transient increases of the temperature of fully ionized carbon impurity ions and electron density, suggesting improvement of bulk plasma confinement.

    DOI: 10.1088/0029-5515/56/1/016002

  • Experimental Identification of Electric Field Excitation Mechanisms in a Structural Transition of Tokamak Plasmas Reviewed

    T. Kobayashi, K. Itoh, T. Ido, K. Kamiya, S. -I. Itoh, Y. Miura, Y. Nagashima, A. Fujisawa, S. Inagaki, K. Ida, K. Hoshino

    Scientific Reports   6   2016.8

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    Self-regulation between structure and turbulence, which is a fundamental process in the complex system, has been widely regarded as one of the central issues in modern physics. A typical example of that in magnetically confined plasmas is the Low confinement mode to High confinement mode (L-H) transition, which is intensely studied for more than thirty years since it provides a confinement improvement necessary for the realization of the fusion reactor. An essential issue in the L-H transition physics is the mechanism of the abrupt "radial" electric field generation in toroidal plasmas. To date, several models for the L-H transition have been proposed but the systematic experimental validation is still challenging. Here we report the systematic and quantitative model validations of the radial electric field excitation mechanism for the first time, using a data set of the turbulence and the radial electric field having a high spatiotemporal resolution. Examining time derivative of Poisson's equation, the sum of the loss-cone loss current and the neoclassical bulk viscosity current is found to behave as the experimentally observed radial current that excites the radial electric field within a few factors of magnitude.

    DOI: 10.1038/srep30720

  • On the Origin of Steep and Localized Radial Electric Field in the Transport Barrier at Plasma Edge Reviewed

    K. Itoh, S. I. Itoh, T. Kobayashi, K. Kamiya, T. Ido, T. Tokuzawa, S. Inagaki, N. Kasuya

    Contributions to Plasma Physics   56 ( 6-8 )   522 - 527   2016.8

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    Theories to understand the steep and localized radial electric field in the edge of toroidal plasma, which appears in conjunction with H-mode, is revisited based on the electric field bifurcation model. Key elements in the models of the L-H transition (including the toroidal effects on the dielectric constant and the effects of the curvature of radial electric field on turbulence suppression) are assessed. Results are applied to tokamak and helical plasmas, for which data with high-resolution have been obtained recently. The status of quantitative tests on various mechanisms through comparison with experimental observations is also addressed. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).

    DOI: 10.1002/ctpp.201610042

  • Transition from chirping to steady NBI-driven Alfvén modes caused by magnetic configuration variations in the TJ-II stellarator Reviewed

    A. V. Melnikov, L. G. Eliseev, E. Ascasíbar, A. Cappa, F. Castejón, C. Hidalgo, T. Ido, J. A. Jiménez, A. S. Kozachek, L. I. Krupnik, M. Liniers, S. E. Lysenko, K. Nagaoka, J. L. De Pablos, A. Shimizu, S. E. Sharapov, M. V. Ufimtsev, S. Yamamoto

    Nuclear Fusion   56 ( 7 )   2016.6

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    Beam-driven Alfvén eigenmodes (AEs) have been studied in the TJ-II low-magnetic-shear flexible heliac (B 0 = 0.95 T, R = 1.5 m, a = 0.22 m), in L-mode hydrogen plasmas with hydrogen NBI and ECR heating (P NBI 1.0 MW, E NBI = 32 keV, P ECRH 0.6 MW). In low-density plasmas in the range = (0.3-1.5) ×1019 m-3, a large variety of AEs have been observed in the plasma core with the heavy ion beam probe diagnostic and Mirnov coils, in the frequency range 50 kHz < f AE < 380 kHz. In experiments in which the vacuum rotational transform is varied during the shot (dynamic configuration scan), some AEs exhibit changes in their nonlinear evolution from bursting-amplitude AEs with chirping frequency to steady-frequency AEs, and back. The range of intervals within which the AEs studied are chirping or steady-state is determined.

    DOI: 10.1088/0029-5515/56/7/076001

  • Onset condition of the subcritical geodesic acoustic mode instability in the presence of energetic-particle-driven geodesic acoustic mode Reviewed

    K. Itoh, S. I. Itoh, Y. Kosuga, M. Lesur, T. Ido

    Plasma Physics Reports   42 ( 5 )   418 - 423   2016.5

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    An analytic model is developed for understanding the abrupt onset of geodesic acoustic mode (GAM) in the presence of chirping energetic-particle-driven GAM (EGAM). This abrupt excitation phenomenon has been observed on LHD plasma. Threshold conditions for the onset of abrupt growth of GAM are derived, and the period doubling phenomenon is explained. The phase relation between the mother mode (EGAM) and the daughter mode (GAM) is also discussed. This result contributes to the understanding of “trigger problems” of laboratory and nature plasmas.

    DOI: 10.1134/S1063780X16050056

  • Nonlinear excitation of subcritical fast ion-driven modes Reviewed

    M. Lesur, M. Lesur, K. Itoh, K. Itoh, T. Ido, S. I. Itoh, S. I. Itoh, Y. Kosuga, Y. Kosuga, M. Sasaki, S. Inagaki, S. Inagaki, M. Osakabe, M. Osakabe, K. Ogawa, K. Ogawa, A. Shimizu, K. Ida, K. Ida

    Nuclear Fusion   56 ( 5 )   2016.4

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    Nonlinear excitation of subcritical fast ion-driven modes
    © 2016 IAEA, Vienna.In collisionless plasma, it is known that linearly stable modes can be destabilized (subcritically) by the presence of structures in phase-space. The growth of such structures is a nonlinear, kinetic mechanism, which provides a channel for free-energy extraction, different from conventional inverse Landau damping. However, such nonlinear growth requires the presence of a seed structure with a relatively large threshold in amplitude. We demonstrate that, in the presence of another, linearly unstable (supercritical) mode, wave-wave coupling can provide a seed, which can lead to subcritical instability by either one of two mechanisms. Both mechanisms hinge on a collaboration between fluid nonlinearity and kinetic nonlinearity. If collisional velocity diffusion is low enough, the seed provided by the supercritical mode overcomes the threshold for nonlinear growth of phase-space structure. Then, the supercritical mode triggers the conventional subcritical instability. If collisional velocity diffusion is too large, the seed is significantly below the threshold, but can still grow by a sustained collaboration between fluid and kinetic nonlinearities. Both of these subcritical instabilities can be triggered, even when the frequency of the supercritical mode is rapidly sweeping. These results were obtained by modeling the subcritical mode kinetically, and the impact of the supercritical mode by simple wave-wave coupling equations. This model is applied to bursty onset of geodesic acoustic modes in an LHD experiment. The model recovers several key features such as relative amplitude, timescales, and phase relations. It suggests that the strongest bursts are subcritical instabilities, with sustained collaboration between fluid and kinetic nonlinearities.

    DOI: 10.1088/0029-5515/56/5/056009

  • Nonlinear Excitation of Subcritical Instabilities in a Toroidal Plasma Reviewed

    M. Lesur, K. Itoh, T. Ido, M. Osakabe, K. Ogawa, A. Shimizu, M. Sasaki, K. Ida, S. Inagaki, S. -I. Itoh

    PHYSICAL REVIEW LETTERS   116 ( 1 )   2016.1

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    In a collisionless plasma, it is known that linearly stable modes can be destabilized (subcritically) by the presence of structures in phase space. However, nonlinear growth requires the presence of a seed structure with a relatively large threshold in amplitude. We demonstrate that, in the presence of another, linearly unstable (supercritical) mode, wave-wave coupling can provide a seed, which is significantly below the threshold, but can still grow by (and only by) the collaboration of fluid and kinetic nonlinearities. By modeling the subcritical mode kinetically, and the impact of the supercritical mode by simple wave-wave coupling equations, it is shown that this new kind of subcritical instability can be triggered, even when the frequency of the supercritical mode is rapidly sweeping. The model is applied to the bursty onset of geodesic acoustic modes in a LHD experiment. The model recovers several key features such as relative amplitude, time scales, and phase relations. It suggests that the strongest bursts are subcritical instabilities, driven by this mechanism of combined fluid and kinetic nonlinearities.

    DOI: 10.1103/PhysRevLett.116.015003

  • Contribution of geodesic acoustic modes in the limit cycle oscillation near H-mode transition in JFT-2M plasmas Reviewed

    K. Itoh, T. Kobayashi, T. Ido, S-I Itoh, K. Kamiya

    PLASMA PHYSICS AND CONTROLLED FUSION   57 ( 9 )   2015.9

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    The magnitude of geodesic acoustic modes (GAMs) is analyzed, which are driven by the oscillating Reynolds stress force in poloidal direction in the limit cycle oscillation (LCO) of tokamaks near the condition of H-mode transition. Although the frequency of LCO is much lower than the natural frequency, the forced oscillation of GAMs at the LCO frequency is excited. The amplitude of excited GAMs can be similar to that of low frequency zonal flows. The result is compared with the observation of the JFT-2M tokamak.

    DOI: 10.1088/0741-3335/57/9/092001

  • Simulation study of high-frequency energetic particle driven geodesic acoustic mode

    Hao Wang, Yasushi Todo, Takeshi Ido, Masaki Osakabe

    Physics of Plasmas   22 ( 9 )   2015.9

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    High-frequency energetic particle driven geodesic acoustic modes (EGAM) observed in the large helical device plasmas are investigated using a hybrid simulation code for energetic particles and magnetohydrodynamics (MHD). Energetic particle inertia is incorporated in the MHD momentum equation for the simulation where the beam ion density is comparable to the bulk plasma density. Bump-on-tail type beam ion velocity distribution created by slowing down and charge exchange is considered. It is demonstrated that EGAMs have frequencies higher than the geodesic acoustic modes and the dependence on bulk plasma temperature is weak if (1) energetic particle density is comparable to the bulk plasma density and (2) charge exchange time (τcx) is sufficiently shorter than the slowing down time (τs) to create a bump-on-tail type distribution. The frequency of high-frequency EGAM rises as the energetic particle pressure increases under the condition of high energetic particle pressure. The frequency also increases as the energetic particle pitch angle distribution shifts to higher transit frequency. It is found that there are two kinds of particles resonant with EGAM: (1) trapped particles and (2) passing particles with transit frequency close to the mode frequency. The EGAMs investigated in this work are destabilized primarily by the passing particles whose transit frequencies are close to the EGAM frequency.

    DOI: 10.1063/1.4930130

  • Integrated discharge scenario for high-temperature helical plasma in LHD Reviewed

    K. Nagaoka, H. Takahashi, S. Murakami, H. Nakano, Y. Takeiri, H. Tsuchiya, M. Osakabe, K. Ida, M. Yokoyama, M. Yoshinuma, S. Morita, M. Goto, T. Oishi, N. Pablant, K. Fujii, K. Tanaka, N. Tamura, Y. Nakamura, X. Du, T. Ido, A. Shimizu, S. Kubo, H. Igami, R. Seki, C. Suzuki, Y. Suzuki, K. Tsumori, K. Ikeda, M. Kisaki, Y. Yoshimura, T. Shimozuma, T. Seki, K. Saito, H. Kasahara, S. Kamio, T. Mutoh, O. Kaneko, H. Yamada, A. Komori

    Nuclear Fusion   55 ( 11 )   2015.9

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    The discharge scenario of high temperature plasma with a helical configuration has significantly progressed. The increase of central ion temperature due to the reduction of wall recycling was clearly observed. The peaking of the ion heating profile and the reduction of charge exchange loss of energetic ions play an important role for further improvement of ion heat transport in the ion internal transport barrier (ITB) core. The ion ITB and electron ITB have been successfully integrated due to the superposition of centrally focused electron cyclotron heating to the ion ITB plasma, and the high temperature regime of the ion temperature comparable to the electron temperature (Ti ∼ Te) has been significantly extended. The width of the ion ITB formed with electron ITB is wider than the width of electron ITB. The positive radial electric field was observed in the integrated ITB plasma by a heavy ion beam probe, while the negative radial electric field was observed in ion ITB plasmas. The ion temperature gradient decreases with the increase of the temperature ratio (Te /Ti).

    DOI: 10.1088/0029-5515/55/11/113020

  • Identification of the energetic-particle driven GAM in the LHD Reviewed International journal

    T. Ido, M. Osakabe, A. Shimizu, T. Watari, M. Nishiura, K. Toi, K. Ogawa, K. Itoh, I. Yamada, R. Yasuhara, Y. Yoshimura, S. Kato and The LHD Experiment Group

    Nuclear Fusion   55   083024   2015.7

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    n = 0 modes with frequency chirping have been observed by a heavy ion beam probe and
    Mirnov coils in the large helical device plasmas, where n is the toroidal mode number.
    The spatial structures of the electrostatic potential fluctuation and the density fluctuation
    correspond to those of the geodesic acoustic mode (GAM). The modes are observed only
    during the tangential neutral beam injection with the energy of 175 keV. The energy spectra
    of fast ions measured by a neutral particle analyzer implies that the modes are excited by
    the fast ions through the inverse Landau damping. The absolute values and the temperature
    dependence of the frequency of the mode can be interpreted by the dispersion relation taking
    into account the measured energy spectra of the fast ions. Therefore, the observed n = 0 modes
    are identified as the energetic-particle driven GAM.

    DOI: 10.1088/0029-5515/55/8/083024

    Other Link: https://iopscience.iop.org/article/10.1088/0029-5515/55/8/083024

  • Overview of transport and MHD stability study: Focusing on the impact of magnetic field topology in the Large Helical Device

    K. Ida, K. Nagaoka, S. Inagaki, H. Kasahara, T. Evans, M. Yoshinuma, K. Kamiya, S. Ohdach, M. Osakabe, M. Kobayashi, S. Sudo, K. Itoh, T. Akiyama, M. Emoto, A. Dinklage, X. Du, K. Fujii, M. Goto, T. Goto, M. Hasuo, C. Hidalgo, K. Ichiguchi, A. Ishizawa, M. Jakubowski, G. Kawamura, D. Kato, S. Morita, K. Mukai, I. Murakami, S. Murakami, Y. Narushima, M. Nunami, N. Ohno, N. Pablant, S. Sakakibara, T. Seki, T. Shimozuma, M. Shoji, K. Tanaka, T. Tokuzawa, Y. Todo, H. Wang, M. Yokoyama, H. Yamada, Y. Takeiri, T. Mutoh, S. Imagawa, T. Mito, Y. Nagayama, K. Y. Watanabe, N. Ashikawa, H. Chikaraishi, A. Ejiri, M. Furukawa, T. Fujita, S. Hamaguchi, H. Igami, M. Isobe, S. Masuzaki, T. Morisaki, G. Motojima, K. Nagasaki, H. Nakano, Y. Oya, C. Suzuki, Y. Suzuki, R. Sakamoto, M. Sakamoto, A. Sanpei, H. Takahashi, H. Tsuchiya, M. Tokitani, Y. Ueda, Y. Yoshimura, S. Yamamoto, K. Nishimura, H. Sugama, T. Yamamoto, H. Idei, A. Isayama, S. Kitajima, S. Masamune, K. Shinohara, P. S. Bawankar, E. Bernard, M. Von Berkel, H. Funaba, X. L. Huang, T. Ii, T. Ido, K. Ikeda, S. Kamio, R. Kumazawa, T. Kobayashi, C. Moon, S. Muto, J. Miyazawa, T. Ming, Y. Nakamura, S. Nishimura

    Nuclear Fusion   55 ( 10 )   2015.7

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    The progress in the understanding of the physics and the concurrent parameter extension in the large helical device since the last IAEA-FEC, in 2012 (Kaneko O et al 2013 Nucl. Fusion 53 095024), is reviewed. Plasma with high ion and electron temperatures (Ti(0)∼Te(0)∼6keV) with simultaneous ion and electron internal transport barriers is obtained by controlling recycling and heating deposition. A sign flip of the nondiffusive term of impurity/momentum transport (residual stress and convection flow) is observed, which is associated with the formation of a transport barrier. The impact of the topology of three-dimensional magnetic fields (stochastic magnetic fields and magnetic islands) on heat momentum, particle/impurity transport and magnetohydrodynamic stability is also discussed. In the steady state operation, a 48min discharge with a line-averaged electron density of 1 1019m-3 and with high electron and ion temperatures (Ti(0)∼Te(0)∼2keV), resulting in 3.36GJ of input energy, is achieved.

    DOI: 10.1088/0029-5515/55/10/104018

  • Edge plasma dynamics during L-H transition in the JFT-2M tokamak Reviewed

    T. Kobayashi, K. Itoh, T. Ido, K. Kamiya, S. -I. Itoh, Y. Miura, Y. Nagashima, A. Fujisawa, S. Inagaki, K. Ida, K. Hoshino

    NUCLEAR FUSION   55 ( 6 )   2015.6

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    This article presents a radial electric field measurement by a heavy ion beam probe in the JFT-2M tokamak, during the L-H transition. An abrupt increase (time scale of O(100 mu s)) of the strong edge radial electric field (localized in the radius with FWHM similar to 7 mm) results in the increase of density gradient and turbulence reduction. Rapid inward propagation of the turbulence suppression front is observed at the transition. After the transition, the electric field structure in the tiny edge localized modes (ELMs) is analyzed. Transport self-regulation events observed in the vicinity of the L-H transition, i.e. the limit cycle oscillation (LCO) in the L-mode, the tiny ELM in the H-mode, as well as the L-H transition itself, are summarized in a single Lissajous diagram in the electric field-density gradient space, which provides a comprehensive explanation of the transition dynamics.

    DOI: 10.1088/0029-5515/55/6/063009

  • Microtearing mode (MTM) turbulence in JIPPT-IIU tokamak plasmas Reviewed

    Y. Hamada, T. Watari, A. Nishizawa, O. Yamagishi, K. Narihara, K. Ida, Y. Kawasumi, T. Ido, M. Kojima, K. Toi

    NUCLEAR FUSION   55 ( 4 )   2015.4

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    Magnetic, density and potential fluctuations up to 500 kHz at several spatial points have been observed in the core region of JIPPT-IIU tokamak plasmas using a heavy ion beam probe. The frequency spectra of the density and magnetic oscillations are found to be similar, whereas there are large differences in the phase, coherence and frequency dependences deduced from signals at adjacent sample volumes. These differences allow us to ascribe the detected magnetic fluctuations to the microtearing mode (MTM) by simple dispersion relations of the MTM in collisionless and intermediate regimes. The frequency-integrated level of magnetic fluctuations around 150 kHz (100-200 kHz) is (B) over tilde (r)/B-t approximate to 1 x 10(-4), a level high enough for the ergodization of the magnetic surface and enhanced electron heat loss as derived by Rechester and Rosenbluth (1978 Phys. Rev. Lett. 40 38). This level is consistent with the measurements performed using cross-polarization scattering of microwaves in the Tore Supra tokamak. Our results are the first direct experimental verification of the MTM in the core region of tokamak plasmas, which has been recently observed in gyrokinetic simulations using a very fine mesh in tokamak and ST plasmas.

    DOI: 10.1088/0029-5515/55/4/043008

  • Resistive interchange modes destabilized by helically trapped energetic ions in a helical plasma Reviewed

    X. D. Du, K. Toi, M. Osakabe, S. Ohdachi, T. Ido, K. Tanaka, M. Yokoyama, M. Yoshinuma, K. Ogawa, K. Y, Watanabe, M. Isobe, K. Nagaoka, T. Ozaki, S. Sakakibara, R. Seki, A. Shimizu, Y. Suzuki, H. Tsuchiya

    Physical Review Letters   114 ( 15 )   2015.4

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    Resistive interchange modes destabilized by helically trapped energetic ions in a helical plasma
    © 2015 American Physical Society. A new bursting m=1/n=1 instability (m,n: poloidal and toroidal mode numbers) with rapid frequency chirping down has been observed for the first time in a helical plasma with intense perpendicular neutral beam injection. This is destabilized in the plasma peripheral region by resonant interaction between helically trapped energetic ions and the resistive interchange mode. A large radial electric field is induced near the edge due to enhanced radial transport of the trapped energetic ions by the mode, and leads to clear change in toroidal plasma flow, suppression of microturbulence, and triggering an improvement of bulk plasma confinement.

    DOI: 10.1103/PhysRevLett.114.155003

  • Flow damping due to stochastization of the magnetic field

    K. Ida, M. Yoshinuma, H. Tsuchiya, T. Kobayashi, C. Suzuki, M. Yokoyama, A. Shimizu, K. Nagaoka, S. Inagaki, K. Itoh, T. Akiyama, M. Emoto, T. Evans, A. Dinklage, X. Du, K. Fujii, M. Goto, T. Goto, M. Hasuo, C. Hidalgo, K. Ichiguchi, A. Ishizawa, M. Jakubowski, K. Kamiya, H. Kasahara, G. Kawamura, D. Kato, M. Kobayashi, S. Morita, K. Mukai, I. Murakami, S. Murakami, Y. Narushima, M. Nunami, S. Ohdach, N. Ohno, M. Osakabe, N. Pablant, S. Sakakibara, T. Seki, T. Shimozuma, M. Shoji, S. Sudo, K. Tanaka, T. Tokuzawa, Y. Todo, H. Wang, H. Yamada, Y. Takeiri, T. Mutoh, S. Imagawa, T. Mito, Y. Nagayama, K. Y. Watanabe, N. Ashikawa, H. Chikaraishi, A. Ejiri, M. Furukawa, T. Fujita, S. Hamaguchi, H. Igami, M. Isobe, S. Masuzaki, T. Morisaki, G. Motojima, K. Nagasaki, H. Nakano, Y. Oya, Y. Suzuki, R. Sakamoto, M. Sakamoto, A. Sanpei, H. Takahashi, M. Tokitani, Y. Ueda, Y. Yoshimura, S. Yamamoto, K. Nishimura, H. Sugama, T. Yamamoto, H. Idei, A. Isayama, S. Kitajima, S. Masamune, K. Shinohara, P. S. Bawankar, E. Bernard, M. Von Berkel, H. Funaba, X. L. Huang, T. Ii, T. Ido, K. Ikeda, S. Kamio, R. Kumazawa, C. Moon, S. Muto, J. Miyazawa, T. Ming, Y. Nakamura

    Nature Communications   6   2015.1

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    The driving and damping mechanism of plasma flow is an important issue because flow shear has a significant impact on turbulence in a plasma, which determines the transport in the magnetized plasma. Here we report clear evidence of the flow damping due to stochastization of the magnetic field. Abrupt damping of the toroidal flow associated with a transition from a nested magnetic flux surface to a stochastic magnetic field is observed when the magnetic shear at the rational surface decreases to 0.5 in the large helical device. This flow damping and resulting profile flattening are much stronger than expected from the Rechester-Rosenbluth model. The toroidal flow shear shows a linear decay, while the ion temperature gradient shows an exponential decay. This observation suggests that the flow damping is due to the change in the non-diffusive term of momentum transport.

    DOI: 10.1038/ncomms6816

  • 2D potential measurements by applying automatic beam adjustment system to heavy ion beam probe diagnostic on the Large Helical Device Reviewed

    A. Shimizu, T. Ido, M. Kurachi, R. Makino, M. Nishiura, S. Kato, A. Nishizawa, Y. Hamada

    REVIEW OF SCIENTIFIC INSTRUMENTS   85 ( 11 )   2014.11

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    Two-dimensional potential profiles in the Large Helical Device (LHD) were measured with heavy ion beam probe (HIBP). To measure the two-dimensional profile, the probe beam energy has to be changed. However, this task is not easy, because the beam transport line of LHD-HIBP system is very long (similar to 20 m), and the required beam adjustment consumes much time. To reduce the probe beam energy adjustment time, an automatic beam adjustment system has been developed. Using this system, required time to change the probe beam energy is dramatically reduced, such that two-dimensional potential profiles were able to be successfully measured with HIBP by changing the probe beam energy shot to shot. (C) 2014 AIP Publishing LLC.

    DOI: 10.1063/1.4891975

  • Dynamics of edge limit cycle oscillation in the JFT-2M Tokamak

    T. Kobayashi, K. Itoh, T. Ido, K. Kamiya, S. I. Itoh, Y. Miura, Y. Nagashima, A. Fujisawa, S. Inagaki, K. Ida, N. Kasuya, K. Hoshino

    Nuclear Fusion   54 ( 7 )   2014.7

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    In the JFT-2M tokamak (JFT standing for JAERI Fusion Torus), the limit cycle oscillation (LCO), together with several variables, i.e., the electrostatic potential, radial electric field, electron density, turbulence intensity, and Dα emission from the divertor region, is observed before the L-to-H transition. The spatiotemporal dynamics of the LCO is analysed in detail. Zonal flows are not seen, while modulation is observed in the edge-localized poloidal flow and density gradient. Modulation is also seen in the Reynolds stress, caused by that in the turbulence intensity and turbulence wavenumber. However, flow acceleration cannot be explained by the modulation in the Reynolds stress. Rapid inward propagation is also observed for the density gradient and turbulence packet. The characteristics of the propagation are verified by means of turbulence spreading theory and diffusion theory. © 2014 IAEA, Vienna.

    DOI: 10.1088/0029-5515/54/7/073017

  • Extension of high T <inf>e</inf> regime with upgraded electron cyclotron resonance heating system in the Large Helical Device

    H. Takahashi, T. Shimozuma, S. Kubo, Y. Yoshimura, H. Igami, S. Ito, S. Kobayashi, Y. Mizuno, K. Okada, T. Mutoh, K. Nagaoka, S. Murakami, M. Osakabe, I. Yamada, H. Nakano, M. Yokoyama, T. Ido, A. Shimizu, R. Seki, K. Ida, M. Yoshinuma, T. Kariya, R. Minami, T. Imai, N. B. Marushchenko, Y. Turkin

    Physics of Plasmas   21 ( 6 )   2014.6

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    Enhancement of the output power per gyrotron has been planned in the Large Helical Device (LHD). Three 77-GHz gyrotrons with an output power of more than 1 MW have been operated. In addition, a high power gyrotron with the frequency of 154 GHz (1 MW/5 s, 0.5 MW/CW) was newly installed in 2012, and the total injection power of Electron cyclotron resonance heating (ECRH) reached 4.6 MW. The operational regime of ECRH plasma on the LHD has been extended due to the upgraded ECRH system such as the central electron temperature of 13.5 keV with the line-averaged electron density ne-fir = 1 × 1019 m-3. The electron thermal confinement clearly improved inside the electron internal transport barrier, and the electron thermal diffusivity reached neoclassical level. The global energy confinement time increased with increase of ne-fir. The plasma stored energy of 530 kJ with n e-fir = 3.2 × 1019 m-3, which is 1.7 times larger than the previous record in the ECRH plasma in the LHD, has been successfully achieved. © 2014 AIP Publishing LLC.

    DOI: 10.1063/1.4884365

  • Observation of multi-scale turbulence and non-local transport in LHD plasmas

    T. Tokuzawa, S. Inagaki, K. Ida, K. Itoh, T. Ido, A. Shimizu, H. Takahashi, S. Kitajima, N. Tamura, M. Yoshinuma, H. Tsuchiya, I. Yamada, K. Tanaka, T. Akiyama, Y. Nagayama, K. Kawahata, K. Y. Watanabe, H. Yamada

    Physics of Plasmas   21 ( 5 )   2014.5

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    We have studied two types of spatio-temporal turbulence dynamics in plasmas in the Large Helical Device, based on turbulence measurements with high spatial and temporal resolution. Applying conditional ensemble-averaging to a plasma with Edge-Localized Modes (ELMs), fast radial inward propagation of a micro-scale turbulence front is observed just after ELM event, and the propagation speed is evaluated as ∼ 100m/s. A self-organized radial electric field structure is observed in an electrode biasing experiment, and it is found to realize a multi-valued state. The curvature of the radial electric field is found to play an important role for turbulence reduction. © 2014 AIP Publishing LLC.

    DOI: 10.1063/1.4876619

  • How is turbulence intensity determined by macroscopic variables in a toroidal plasma? Reviewed

    S. Inagaki, T. Tokuzawa, N. Tamura, S. -I. Itoh, T. Kobayashi, K. Ida, T. Shimozuma, S. Kubo, K. Tanaka, T. Ido, A. Shimizu, H. Tsuchiya, N. Kasuya, Y. Nagayama, K. Kawahata, S. Sudo, H. Yamada, A. Fujisawa, K. Itoh

    NUCLEAR FUSION   53 ( 11 )   2013.11

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    We report observations of the dynamic response of micro-fluctuations and turbulent flux to a low-frequency heating power modulation in the Large Helical Device. The responses of heat flux and micro-fluctuation intensity differ from that of the change in temperature gradient. This result violates the local transport model, where turbulence is determined by the local temperature gradient. A new relationship between flux, gradient and turbulence is found. In addition to the temperature gradient, the heating rate is proposed as a new, direct controlling parameter of turbulence to explain the fast response of turbulence against periodic modulation of heating power.

    DOI: 10.1088/0029-5515/53/11/113006

  • Extension of operation regimes and investigation of three-dimensional currentless plasmas in the Large Helical Device

    O. Kaneko, H. Yamada, S. Inagaki, M. Jakubowski, S. Kajita, S. Kitajima, Kobayashi, K. Koga, T. Morisaki, S. Morita, T. Mutoh, S. Sakakibara, Y. Suzuki, H. Takahashi, K. Tanaka, K. Toi, Y. Yoshimura, T. Akiyama, Y. Asahi, N. Ashikawa, H. Chikaraishi, A. Cooper, D. S. Darrow, E. Drapiko, P. Drewelow, X. Du, A. Ejiri, M. Emoto, T. Evans, N. Ezumi, K. Fujii, T. Fukuda, H. Funaba, M. Furukawa, D. A. Gates, M. Goto, T. Goto, W. Guttenfelder, S. Hamaguchi, M. Hasuo, T. Hino, Y. Hirooka, K. Ichiguchi, K. Ida, H. Idei, T. Ido, H. Igami, K. Ikeda, S. Imagawa, T. Imai, M. Isobe, M. Itagaki, T. Ito, K. Itoh, S. Itoh, A. Iwamoto, K. Kamiya, T. Kariya, H. Kasahara, N. Kasuya, D. Kato, T. Kato, K. Kawahata, F. Koike, S. Kubo, R. Kumazawa, D. Kuwahara, S. Lazerson, H. Lee, S. Masuzaki, S. Matsuoka, H. Matsuura, A. Matsuyama, C. Michael, D. Mikkelsen, O. Mitarai, T. Mito, J. Miyazawa, G. Motojima, K. Mukai, A. Murakami, I. Murakami, S. Murakami, T. Muroga, S. Muto, K. Nagaoka, K. Nagasaki, Y. Nagayama, N. Nakajima, H. Nakamura, Y. Nakamura, H. Nakanishi, H. Nakano, T. Nakano, K. Narihara, Y. Narushima, K. Nishimura, S. Nishimura, M. Nishiura, Y. M. Nunami

    Nuclear Fusion   53 ( 10 )   2013.10

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    The progress of physical understanding as well as parameter improvement of net-current-free helical plasma is reported for the Large Helical Device since the last Fusion Energy Conference in Daejeon in 2010. The second low-energy neutral beam line was installed, and the central ion temperature has exceeded 7 keV, which was obtained by carbon pellet injection. Transport analysis of the high-Ti plasmas shows that the ion-thermal conductivity and viscosity decreased after the pellet injection although the improvement does not last long. The effort has been focused on the optimization of plasma edge conditions to extend the operation regime towards higher ion temperature and more stable high density and high beta. For this purpose a portion of the open helical divertors are being modified to the baffle-structured closed ones aimed at active control of the edge plasma. It is compared with the open case that the neutral pressure in the closed helical divertor increased by ten times as predicted by modelling. Studies of physics in a three-dimensional geometry are highlighted in the topics related to the response to a resonant magnetic perturbation at the plasma periphery such as edge-localized-mode mitigation and divertor detachment. Novel approaches of non-local and non-diffusive transport have also been advanced. © 2013 IAEA, Vienna.

    DOI: 10.1088/0029-5515/53/10/104015

  • Spatiotemporal Structures of Edge Limit-Cycle Oscillation before L-to-H Transition in the JFT-2M Tokamak Reviewed

    T. Kobayashi, K. Itoh, T. Ido, K. Kamiya, S. -I. Itoh, Y. Miura, Y. Nagashima, A. Fujisawa, S. Inagaki, K. Ida, K. Hoshino

    PHYSICAL REVIEW LETTERS   111 ( 3 )   2013.7

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    In this Letter, we report analyses of spatiotemporal dynamics of turbulence and structure in the limit-cycle oscillation (LCO) that precedes an L-to-H transition. Zonal flows are not observed during LCO, and the oscillation is the periodic generations or decays of barrier with edge-localized mean flow. Oscillatory Reynolds stress is found to be too small to accelerate the LCO flow, by considering the dielectric constant in magnetized toroidal plasmas. Propagation of changes of the density gradient and turbulence amplitude into the core is also observed.

    DOI: 10.1103/PhysRevLett.111.035002

  • Regions of kinetic geodesic acoustic modes and streamers in JIPPT-IIU tokamak plasmas Reviewed

    Y. Hamada, T. Watari, A. Nishizawa, O. Yamagishi, K. Narihara, Y. Kawasumi, T. Ido, M. Kojima, K. Toi

    NUCLEAR FUSION   52 ( 6 )   2012.6

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    The radial extent of kinetic geodesic acoustic modes (KGAMs) and streamers is measured using a heavy ion beam probe. Intense KGAM oscillations are observed in the core region of a low-density ohmic (OH) plasma where T-e >> T-i and outside this region, streamers characterized by steepening fronts are observed. The radial profile of plasma density stays flat in the region of the streamers, showing a rise in the plasma density in two regions, one at the scrape-off layer and the other in the core region during the radial scan of sample volumes. Intense (up to e Phi / kT(e) similar to 0.1) and broad GAM oscillations (delta f / f similar to 0.5) are observed in the r < a(p)/2 region of tokamak plasmas. GAM oscillations and streamers are strongly reduced in the heated phase. In addition, the radial profile of the spectra of GAM in the heated phase is very different from that of a low-density OH plasma. The streamers and the two-step rise in the density radial profile disappear in the heated phase.

    DOI: 10.1088/0029-5515/52/6/063023

  • Long range temperature fluctuation in LHD Reviewed

    Shigeru Inagaki, Tokihiko Tokuzawa, Kimitaka Itoh, Katsumi Ida, Sanae I. Itoh, Naoki Tamura, Satoru Sakakibara, Naohiro Kasuya, Akihide Fujisawa, Shin Kubo, Takashi Shimozuma, Takeshi Ido, Seiya Nishimura, Hiroyuki Arakawa, Tatsuya Kobayashi, Masatoshi Yagi, Kenji Tanaka, Yoshio Nagayama, Kazuo Kawahata, Shigeru Sudo, Hiroshi Yamada, Akio Komori

    Plasma and Fusion Research   6   2011.12

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    Long range temperature fluctuation in LHD
    We report a detailed correlation technique to identify the long-range temperature fluctuation in the Large Helical Device. Correlation hunting has successfully realized the observation of electron temperature fluctuations, which are characterized by their correlation length comparable to the plasma minor radius, with low frequency of ~ 1-3kHz, ballistic radial propagation (at a speed of ~1km/s, of the order of diamagnetic drift velocity), spatial mode number of m/n = 1/1 (or 2/1), and amplitude of ~2% at the maximum. Bicoherence analysis confirmed their nonlinear coupling with local microscopic turbulent fluctuations. This long-range temperature fluctuation is a possible carrier of fast propagation in transport processes observed so far. We also comment on the theoretical interpretation. © 2011 The Japan Society of Plasma Science and Nuclear Fusion Research.

    DOI: 10.1585/pfr.6.1402017

  • A New Simulation Method of Geodesic Acoustic Mode in Toroidal Plasmas by Using Band-Limited White Noise in a δf Neoclassical Transport Code Reviewed

    Shinsuke SATAKE, Hideo SUGAMA, Ryutaro KANNO, Takeshi IDO, Seikichi MATSUOKA, Masayuki YOKOYAMA

    Progress in Nuclear Science and Technology   2 ( 0 )   72   2011.10

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    A New Simulation Method of Geodesic Acoustic Mode in Toroidal Plasmas by Using Band-Limited White Noise in a δf Neoclassical Transport Code

    DOI: 10.15669/pnst.2.72

  • Observation of Long-Distance Radial Correlation in Toroidal Plasma Turbulence Reviewed

    S. Inagaki, T. Tokuzawa, K. Itoh, K. Ida, S. -I. Itoh, N. Tamura, S. Sakakibara, N. Kasuya, A. Fujisawa, S. Kubo, T. Shimozuma, T. Ido, S. Nishimura, H. Arakawa, T. Kobayashi, K. Tanaka, Y. Nagayama, K. Kawahata, S. Sudo, H. Yamada, A. Komori

    PHYSICAL REVIEW LETTERS   107 ( 11 )   2011.9

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    This Letter presents the discovery of macroscale electron temperature fluctuations with a long radial correlation length comparable to the plasma minor radius in a toroidal plasma. Their spatiotemporal structure is characterized by a low frequency of similar to 1-3 kHz, ballistic radial propagation, a poloidal or toroidal mode number of m/n = 1/1 (or 2/1), and an amplitude of similar to 2% at maximum. Nonlinear coupling between the long-range fluctuations and the microscopic fluctuations is identified. A change of the amplitude of the long-range fluctuation is transmitted across the plasma radius at the velocity which is of the order of the drift velocity.

    DOI: 10.1103/PhysRevLett.107.115001

  • Heat and momentum transport of ion internal transport barrier plasmas on the Large Helical Device Reviewed

    K. Nagaoka, K. Ida, M. Yoshinuma, Y. Takeiri, M. Yokoyama, S. Morita, K. Tanaka, T. Ido, A. Shimizu, N. Tamura, H. Funaba, S. Murakami, M. Goto, H. Takahashi, C. Suzuki, Y. Suzuki, K. Ikeda, M. Osakabe, K. Tsumori, H. Nakano, O. Kaneko, H. Yamada

    NUCLEAR FUSION   51 ( 8 )   2011.8

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    The peaked ion-temperature profile with steep gradient, the so-called ion internal transport barrier (ion ITB), was formed in the neutral beam heated plasmas on the Large Helical Device and the high-ion-temperature regime of helical plasmas has been significantly extended. The ion thermal diffusivity in the ion ITB plasma decreases down to the neoclassical transport level. The heavy ion beam probe observed the smooth potential profile with negative radial electric field (ion root) in the core region where the ion thermal diffusivity decreases significantly. The large toroidal rotation was also observed in the ion ITB core and the transport of toroidal momentum was analysed qualitatively. The decrease in momentum diffusivity with ion temperature increase was observed in the ion ITB core. The toroidal rotation driven by ion-temperature gradient, the so-called intrinsic rotation, is also identified.

    DOI: 10.1088/0029-5515/51/8/083022

  • 金イオンビームとガスターゲットの衝突時の反応断面積測定システムの作製

    谷池 晃, 忍 友彰, 望月 翔, 井戸 毅, 西浦 正樹, 清水 昭博, 古山 雄一, 北村 晃

    神戸大学大学院海事科学研究科紀要 = Review of the Faculty of Maritime Sciences, Kobe University   8   47 - 58   2011.7

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    Fabrication of the measurement system for the cross sections in collisions between Au beams and gas targets

    DOI: 10.24546/81003310

  • Potential fluctuation associated with the energetic-particle-induced geodesic acoustic mode in the Large Helical Device Reviewed International journal

    T. Ido, A. Shimizu, M. Nishiura, S. Nakamura, S. Kato, H. Nakano, Y. Yoshimura, K. Toi, K. Ida, M. Yoshinuma, S. Satake, F. Watanabe, S. Morita, M. Goto, K. Itoh, S. Kubo, T. Shimozuma, H. Igami, H. Takahashi, I. Yamada, K. Narihara and the LHD Experiment Group

    Nuclear Fusion   51   073046   2011.6

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    Geodesic acoustic modes (GAM) driven by energetic particles are observed in the Large Helical Device (LHD) by a heavy ion beam probe. The GAM localizes near the magnetic axis. It is confirmed that the energetic-particle-induced GAM is accompanied by an electrostatic potential fluctuation and radial electric field fluctuation. The amplitude of the potential fluctuation is several hundred volts, and it is much larger than the potential fluctuation associated with turbulence-induced GAMs observed in the edge region in tokamak plasmas. The energetic-particle-induced GAM modulates the amplitude of the density fluctuation in a high-frequency range. The observed GAM frequency is constant at the predicted GAM frequency in plasmas with reversed magnetic shear. On the other hand, it shifts upwards from the predicted GAM frequency in plasmas with monotonic magnetic shear.

    DOI: 10.1088/0029-5515/51/7/073046

    Other Link: https://iopscience.iop.org/article/10.1088/0029-5515/51/7/073046

  • Detection of the kinetic geodesic acoustic mode (KGAM) near the centre region of JIPPT-IIU tokamak plasmas Reviewed

    Y. Hamada, T. Watari, A. Nishizawa, O. Yamagishi, K. Narihara, K. Ida, Y. Kawasumi, T. Ido, M. Kojima, K. Toi

    NUCLEAR FUSION   51 ( 3 )   2011.3

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    The broad and intense spectrum of the geodesic acoustic mode (GAM) oscillations near the magnetic axis of tokamak plasmas with T-e/T-i >> 1 becomes narrow and weak during neutral beam heating. It then becomes wide and weak during third harmonics ICRF heating. The wide spectra of GAMs are generally consistent with recent kinetic GAM (KGAM) theories.

    DOI: 10.1088/0029-5515/51/3/033005

  • Production of Sub-MeV Positive Gold Ion Beams with Various Gas Targets to Improve the Tandem Accelerator of the LHD-HIBP Reviewed

    Akira Taniike, Takeshi Ido, Masaki Nishiura, Akihiro Shimizu, Yuichi Furuyama, Akira Kitamura

    Plasma and Fusion Research   5, S2087 (2010)   2010.12

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    Production of Sub-MeV Positive Gold Ion Beams with Various Gas Targets to Improve the Tandem Accelerator of the LHD-HIBP

    DOI: 10.1585/pfr.5.S2087

  • Observation of reversed-shear Alfvén eigenmodes excited by energetic ions in a helical plasma Reviewed

    K. Toi, F. Watanabe, T. Tokuzawa, K. Ida, S. Morita, T. Ido, A. Shimizu, M. Isobe, K. Ogawa, D. A. Spong, Y. Todo, T. Watari, S. Ohdachi, S. Sakakibara, S. Yamamoto, S. Inagaki, K. Narihara, M. Osakabe, K. Nagaoka, Y. Narushima, K. Y. Watanabe, H. Funaba, M. Goto, K. Ikeda, T. Ito, O. Kaneko, S. Kubo, S. Murakami, T. Minami, J. Miyazawa, Y. Nagayama, M. Nishiura, Y. Oka, R. Sakamoto, T. Shimozuma, Y. Takeiri, K. Tanaka, K. Tsumori, I. Yamada, M. Yoshinuma, K. Kawahata, A. Komori

    Physical Review Letters   105 ( 14 )   2010.10

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    Observation of Reversed-Shear Alfven Eigenmodes Excited by Energetic Ions in a Helical Plasma
    Reversed-shear Alfven eigenmodes were observed for the first time in a helical plasma having negative q(0)(II) ( the curvature of the safety factor q at the zero shear layer). The frequency is swept downward and upward sequentially via the time variation in the maximum of q. The eigenmodes calculated by ideal MHD theory are consistent with the experimental data. The frequency sweeping is mainly determined by the effects of energetic ions and the bulk pressure gradient. Coupling of reversed-shear Alfven eigenmodes with energetic ion driven geodesic acoustic modes generates a multitude of frequency-sweeping modes.

    DOI: 10.1103/PhysRevLett.105.145003

  • Potential measurements with heavy ion beam probe system on LHD Reviewed

    A. Shimizu, T. Ido, S. Nakamura, K. Toi, M. Nishiura, S. Kato

    REVIEW OF SCIENTIFIC INSTRUMENTS   81 ( 10 )   2010.10

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    The heavy ion beam probe system in the Large Helical Device (LHD) was improved as follows. At first, the additional new sweeper was installed into the diagnostic port to extend the observable region. By using this sweeper, the potential profile was measured in a wider minor radius range than in previous experiments, in the case of outward shifted magnetic configuration of LHD. Next, the real time control system was installed to control the probe beam orbit for measuring the potential in plasma with large plasma current. In this system, a digital signal processor was used to control the probe beam in real time. The system worked well in the fixed position observation mode. In the sweeping mode for profile measurement, this control system became unstable. The details of this system and the experimental results are reported in this article. (c) 2010 American Institute of Physics. [doi:10.1063/1.3491317]

    DOI: 10.1063/1.3491317

  • Experimental study of radial electric field and electrostatic potential fluctuation in the Large Helical Device Invited Reviewed International journal

    T Ido, A Shimizu, M Nishiura, K Nagaoka, M Yokoyama, K Ida, M Yoshinuma, K Toi, K Itoh, H Nakano, S Nakamura, F Watanabe, S Satake, Y Yoshimura, M Osakabe, K Tanaka, T Tokuzawa, Y Takeiri, K Tsumori, K Ikeda, S Kubo, T Shimozuma, H Igami, H Takahashi, N Tamura and LHD Experiment Group

    Plasma Physics and Controlled Fusion   52   124025   2010.9

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    A heavy ion beam probe was installed on the Large Helical Device (LHD) to investigate the roles of radial electric fields (Er ) in magnetically confined high-temperature plasmas. Two new observations are presented. One is the observation of electrostatic potential profiles during the formation of extremely hollow density profiles of impurities, called the impurity hole (Ida K et al 2009 Phys. Plasmas 16 056111), in the LHD plasmas. The measured Er is negative, and the Er determined by the ambipolarity condition of neoclassical particle fluxes is consistent with this observation. However, the transport analysis indicates that the formation of the extremely hollow profile is not attributable to the impurity fluxes driven by Er and the density and temperature gradients of the impurity. The other new observation is on the geodesic acoustic mode (GAM). The electrostatic potential fluctuation associated with the GAM, which is probably induced by energetic particles, in plasmas with the reversed or weak magnetic shear is identified. The GAM is localized in the core region of the plasma.

    DOI: 10.1088/0741-3335/52/12/124025

    Other Link: https://iopscience.iop.org/article/10.1088/0741-3335/52/12/124025

  • 24pQJ-3 イオンITBプラズマにおける熱・運動量輸送特性(24pQJ 核融合プラズマ(輸送・閉じ込め(2)/揺動・乱流特性),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))

    永岡 賢一, 居田 克巳, 吉沼 幹朗, 横山 雅之, 竹入 康彦, 森田 繁, 田中 謙治, 田村 直樹, 徳沢 季彦, 井戸 毅, 清水 昭博, 村上 定義, 中野 治久, 池田 勝則, 長壁 正樹, 津守 克嘉, 金子 修, LHD実験グループ

    日本物理学会講演概要集   65 ( 2 )   2010.8

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  • GAM generation by drift waves in JIPP T-llU tokamak core plasmas Reviewed

    Y. Hamada, T. Watari, A. Nishizawa, O. Yamagishi, K. Narihara, Y. Kawasumi, T. Ido, M. Kojima, K. Toi

    NUCLEAR FUSION   50 ( 2 )   2010.2

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    Density and potential fluctuations were measured in the core region of the JIPP-TIIU plasma using a heavy ion beam probe. By applying a new technique of wavenumber resolved bicoherence, the coupling of the drift waves with zonal flows was clearly observed. In addition, nonlinear energy flow from drift-wave turbulence to high-frequency zonal flows using Ritz's model equation was first observed in the core region of low-density tokamak plasmas, which means there is generation of GAM by drift waves. The nonlinear growth rate of high-frequency zonal flow was estimated to be in the order of 10(4) s(-1) or higher. In additionally heated plasmas where low-frequency ion temperature gradient mode is dominant, the bicoherence pattern changes drastically.

    DOI: 10.1088/0029-5515/50/2/025001

  • Development of a heavy ion beam probe for measuring electrostatic potential profile and its fluctuation in LHD Reviewed International journal

    Takeshi Ido, Akihiro Shimizu, Masaki Nishiura, Haruhisa Nakano, Shinji Kato, Shinsuke Ohshima, Yasuo Yoshimura, Shin Kubo, Takashi Shimozuma, Hiroe Igami, Hiromi Takahashi, Kazuo Toi, Fumitake Watanabe, Kazumichi Narihara and Ichihiro Yamada

    Plasma Science and Technology   11   460 - 464   2009.8

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    DOI: 10.1088/1009-0630/11/4/19

  • DEVELOPMENT OF 6-MeV HEAVY ION BEAM PROBE ON LHD Invited Reviewed International journal

    T. IDO, A. SHIMIZU, M. NISHIURA, S. KATO, H. NAKANO, S. OHSHIMA, M. YOKOYAMA, S. MURAKAMI, A. WAKASA, S. NAKAMURA, M. YOKOTA, K. TSUKADA, H. OGAWA, T. INOUE, and LHD EXPERIMENT GROUP

    Fusion Science and Technology   58   436   2009.7

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    A heavy–ion beam probe (HIBP) using a 3-MV tandem accelerator was installed in Large Helical Device (LHD). It is designed to measure the electrostatic potential in the core region directly. The electrostatic potential profiles can be measured successfully using the HIBP,and the radial electric field predicted by the neoclassical theory is consistent with that measured using the HIBP as long as the ambipolarity condition of the neoclassical particle flux has a single solution. Although the turbulent fluctuation is not detected because of low signal-to-noise ratio, several coherent fluctuations, which are inferred to be reversed-shear-induced Alfvén eigenmode and the geodesic acoustic mode, are observed directly in core plasmas, and the spatial distribution is revealed.

    DOI: 10.13182/FST10-A10829

    Other Link: https://www.tandfonline.com/doi/abs/10.13182/FST10-A10829

  • Extension of Improved Particle and Energy Confinement Regime in the Core of LHD Plasma Reviewed

    KANEKO Osamu, EMOTO Masahiko, FUNABA Hisamichi, GONCHAROV Pavel, GOTO Motoshi, GOTO Takuya, HAMAGUCHI Shinji, ICHIGUCHI Katsuji, IDO Takeshi, IGAMI Hiroe, IKEDA Katsunori, YOKOYAMA Masayuki, IMAGAWA Shinsaku, ISOBE Mitsutaka, ITOH Kimitaka, IWAMOTO Akifumi, KANNO Ryutaro, KASAHARA Hiroshi, KASUYA Naohiro, KATO Daiji, KAWAHATA Kazuo, KOBAYASHI Masahiro, YOSHINUMA Mikiro, KUBO Shin, KUMAZAWA Ryuhei, MAEKAWA Ryuji, MASUZAKI Suguru, MITO Toshiyuki, MIYAZAWA Jun-ichi, MIZUGUCHI Naoki, MORISAKI Tomohiro, MORITA Shigeru, MOTOJIMA Gen, NAGAOKA Ken-ichi, MUTO Sadatsugu, MUTOH Takashi, NAGAYAMA Yoshio, NAKAJIMA Noriyoshi, NAKAMURA Yukio, NAKANISHI Hideya, NARIHARA Kazumichi, NARUSHIMA Yoshiro, NISHIMURA Kiyohiko, NISHIURA Masaki, IDA Katsumi, OBANA Tetsuhiro, OHDACHI Satoshi, OHYABU Nobuyoshi, OSAKABE Masaki, OZAKI Tetsuo, PETERSON Byron J, SAGARA Akio, SAITO Kenji, SAKAKIBARA Satoru, SATAKE Shinsuke, SAKAMOTO Ryuichi, SATO Kuninori, SEKI Tetsuo, SHIMIZU Akihiro, SHIMOZUMA Takashi, SHOJI Mamoru, SUDO Shigeru, SUGAMA Hideo, SUZUKI Chihiro, SUZUKI Yasuhiro, TAKAHASHI Hiromi, AKIYAMA Tsuyoshi, TAKAHATA Kazuya, TAKEIRI Yasuhiko, TAMURA Hitoshi, TAMURA Naoki, TANAKA Kenji, TODA Shinichiro, TOI Kazuo, TOKITANI Masayuki, TOKUZAWA Tokihiko, TSUMORI Katsuyoshi, ASHIKAWA Naoko, WATANABE Kiyomasa, YAMADA Ichihiro, YAMADA Hiroshi, YAMAGISHI Osamu, YANAGI Nagato, YOSHIMURA Shinji, YOSHIMURA Yasuo, KOMORI Akio, CHIKARAISHI Hirotaka

    Plasma and Fusion Research   4   27 - 27   2009.1

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    Extension of Improved Particle and Energy Confinement Regime in the Core of LHD Plasma
    Recent two major topics of Large Helical Device (LHD) towards fusion relevant conditions, high-density operation and high-ion-temperature operation, are reported. Super dense core plasma was obtained by the combination of repetitive hydrogen ice pellet injection and high power neutral beam injection (NBI) heating. A very peaked density profile with the highest central density of 1.1 &times; 1021 m-3 was produced showing that the particle transport was suppressed very well in the plasma core. The spatial density profile varies as the position of magnetic axis (Rax), and the steepest profile is obtained at Rax = 3.95 m. The highest central ion temperature of 5.6 keV was obtained in hydrogen plasma at electron density of 1.6 &times; 1019 m-3 by NBI, where a peaked ion-temperature profile with internal ion energy transport barrier was observed. The profile of electron temperature did not change much and was broad even when the ion temperature had a peaked profile. The central ion temperature is higher than the electron temperature, which is a new operation regime of LHD. High central ion temperature accompanied strong toroidal rotation and an extreme hollow profile of carbon ions (impurity hole). These steep temperature profiles were obtained so far at around Rax = 3.6 m. The compatibility between particle and energy confinement is a new issue of LHD to explore a new operation regime for attractive fusion reactor.

    DOI: 10.1585/pfr.4.027

  • Measurements of spatial structure of plasma potential and density fluctuations by multichannel heavy ion beam probe on large helical device Reviewed

    Shinsuke Ohshima, Takeshi Ido, Akihiro Shimizu, Masaki Nishiura, Haruhisa Nakano

    Review of Scientific Instruments   79 ( 10 )   10F320   2008.10

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    Measurements of spatial structure of plasma potential and density fluctuations by multichannel heavy ion beam probe on large helical device

    DOI: 10.1063/1.2981177

  • Measurement of Electrostatic Potential Fluctuation using Heavy Ion Beam Probe in Large Helical Device Reviewed International journal

    Takeshi Ido, Akihiro Shimizu, Masaki Nishiura, Haruhisa Nakano, Shinsuke Ohshima, Shinji Kato, Yasuji Hamada, Yasuo Yoshimura, Shin Kubo, Takashi Shimozuma, Hiroe Igami, Hiromi Takahashi, Kazuo Toi, and Fumitake Watanabe

    Review of Scientific Instruments   79   10F318   2008.7

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    Heavy ion beam probe (HIBP) for large helical device (LHD) has been improved to measure the potential fluctuation in high-temperature plasmas. The spatial resolution is improved to about 10 mm by controlling the focus of a probe beam. The HIBP is applied to measure the potential fluctuation in plasmas where the rotational transform is controlled by electron cyclotron current drive. The fluctuations whose frequencies change with the time constant of a few hundreds of milliseconds and that with a constant frequency are observed. The characteristics of the latter fluctuation are similar to those of the geodesic acoustic mode oscillation. The spatial profiles of the fluctuations are also obtained.

    DOI: 10.1063/1.2971207

  • Experimental studies of zonal flow and field in compact helical system plasma Reviewed

    A. Fujisawa, K. Itoh, A. Shimizu, H. Nakano, S. Ohshima, H. Iguchi, K. Matsuoka, S. Okamura, T. Minami, Y. Yoshimura, K. Nagaoka, K. Ida, K. Toi, C. Takahashi, M. Kojima, S. Nishimura, M. Isobe, C. Suzuki, T. Akiyama, T. Ido, Y. Nagashima, S. -I. Itoh, P. H. Diamond

    PHYSICS OF PLASMAS   15 ( 5 )   055906   2008.5

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    The experimental studies on zonal flows and turbulence have been carried out in Compact Helical System [K. Matsuoka, S. Kubo, M. Hosokawa , in Plasma Physics and Controlled Nuclear Fusion Research, Proc. 12th Int. Conf., Nice, 1988 (International Atomic Energy Agency, Vienna, 1989, Vol. 2, p. 411] using twin heavy ion beam probes. The paper presents the experimental observations of stationary zonal flow, nonlinear couplings between zonal flow and turbulence, and the role of zonal flow in the improved confinement, together with the recent discovery of zonal magnetic field. The presented experimental results strongly support the new paradigm that the plasma transport should be considered as a system of drift wave and zonal flows, and provides the first direct evidence for turbulence dynamo that the structured magnetic field can be really generated by turbulence. (C) 2008 American Institute of Physics.

    DOI: 10.1063/1.2889012

  • Status of the heavy ion beam probe system in the Large Helical Device Reviewed

    M. Nishiura, T. Ido, A. Shimizu, H. Nakano, T. Kato, S. Kato, Y. Hamada, V. P. Shevelko, R. K. Janev, M. Wada

    Review of Scientific Instruments   79   2008.3

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    Status of the heavy ion beam probe system in the Large Helical Device
    A heavy ion beam probe (HIBP) system has been installed into the Large Helical Device (LHD) to measure the spatial profile of the plasma potential and density fluctuations. The optimization of the HIBP system, especially the beam injector, is described. The negative ion beam is required for the MeV beam production in a tandem accelerator. A sputter-type heavy negative ion source has been developed as an intense Au- beam source to produce Au+ beams with energy in the MeV range. The extraction electrodes and the Einzel lens system of the ion source have been designed taking into account the beam optics, and installed into the real machine. Throughout the plasma diagnostics on LHD experiments, the consumptions of vaporized caesium and gold target are being characterized for practical operations. In addition, the experimental charge fractions are compared with the theoretical fractions for understanding the charge-changing behavior of Au- ions and optimizing the fraction of Au+ ions at the exit of the tandem accelerator of the HIBP system. © 2008 American Institute of Physics.

    DOI: 10.1063/1.2819323

  • Experimental progress on zonal flow physics in toroidal plasmas Reviewed

    A. Fujisawa, T. Ido, A. Shimizu, S. Okamura, K. Matsuoka, H. Iguchi, Y. Hamada, H. Nakano, S. Ohshima, K. Itoh, K. Hoshino, K. Shinohara, Y. Miura, Y. Nagashima, S. I. Itoh, M. Shats, H. Xia, J. Q. Dong, L. W. Yan, K. J. Zhao, G. D. Conway, U. Stroth, A. V. Melnikov, L. G. Eliseev, S. E. Lysenko, S. V. Perfilov, C. Hidalgo, G. R. Tynan, C. Holland, P. H. Diamond, G. R. McKee, R. J. Fonck, D. K. Gupta, P. M. Schoch

    Nuclear Fusion   47   2007.10

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    Experimental progress on zonal flow physics in toroidal plasmas
    The present status of experiments on zonal flows in magnetic confinement experiments is examined. The innovative use of traditional and modern diagnostics has revealed unambiguously the existence of zonal flows, their spatio-temporal characteristics, their relationship to turbulence and their effects on confinement. In particular, a number of observations have been accumulated on the oscillatory branch of zonal flows, named geodesic acoustic modes, suggesting the necessity for theories to give their proper description. In addition to these basic properties of zonal flows, several new methods have elucidated the processes of zonal flow generation from turbulence. Further investigation of the relationship between zonal flows and confinement is strongly encouraged as cross-device activity including low temperature, toroidal and linear devices. © 2007 IAEA.

    DOI: 10.1088/0029-5515/47/10/S19

  • In search of zonal flows by using direct density fluctuation measurements Reviewed

    Y. Nagashima, K. Itoh, S-I Itoh, A. Fujisawa, M. Yagi, K. Hoshino, K. Shinohara, A. Ejiri, Y. Takase, T. Ido, K. Uehara, Y. Miura

    PLASMA PHYSICS AND CONTROLLED FUSION   49 ( 10 )   1611 - 1625   2007.10

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    A method for zonal flow study by using direct density fluctuation measurements is proposed. When ambient drift-wave turbulence is modulated by zonal flows (i.e. in the drift-wave-zonal flow systems), an envelope of the ambient density fluctuations has spectral peaks around zonal flow frequencies. A spectral peak at the geodesic acoustic mode (GAM) frequency is observed in the envelope of the ambient density fluctuations measured in edge plasma of the JFT-2M tokamak. The significant cross-bicoherence is also found between the ambient density fluctuations and its envelope in the GAM frequency. This result demonstrates that we can measure the GAM only by using density fluctuation data. This method provides a possibility of zonal flow research in burning core plasma by density fluctuation diagnostics such as microwave reflectometry.

    DOI: 10.1088/0741-3335/49/10/002

  • Spatial resolution of the heavy ion beam probe on LHD Invited Reviewed International journal

    T. IDO, A. SHIMIZU, M. NISHIURA, Y. HAMADA, S. KATO, A. NISHIZAWA, H. NAKANO

    Plasma and Fusion Research   2   S1100   2007.3

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    DOI: 10.1585/pfr.2.S1100

  • Intermittent characteristics in coupling between turbulence and zonal flows Reviewed

    A. Fujisawa, A. Shimizu, H. Nakano, S. Ohshima, K. Itoh, Y. Nagashima, S. -I Itoh, H. Iguchi, Y. Yoshimura, T. Minami, K. Nagaoka, C. Takahashi, M. Kojima, S. Nishimura, M. Isobe, C. Suzuki, T. Akiyama, T. Ido, K. Matsuoka, S. Okamura, P. H. Diamond

    PLASMA PHYSICS AND CONTROLLED FUSION   49 ( 3 )   211 - 217   2007.3

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    An extended application of Gabour's wavelet to bicoherence analysis succeeds in resolving the instantaneous structure of three wave couplings between disparate scale electric field fluctuations in the high temperature core in a toroidal plasma device named the compact helical system. The obtained results quantify an intermittent linkage between turbulence and zonal flows - a highlighted issue in the present plasma research. This is the first demonstration that the intermittent nature of the three wave coupling should underlie the turbulence power modulation due to zonal flows.

    DOI: 10.1088/0741-3335/49/3/002

  • 6 MeV heavy ion beam probe on Large Helical Device Reviewed International journal

    T. Ido, A. Shimizu, M. Nishiura, A. Nishizawa, S. Katoh, K. Tsukada, M. Yokota, H. Ogawa, T. Inoue, Y. Hamada, T. P. Crowley, LHD Experimental Group

    Review of Scientific Instruments   77   10F523   2006.10

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    A heavy ion beam probe (HIBP) has been installed on the Large Helical Device (LHD). A MeV-range beam is required for the LHD-HIBP. The probing beam is accelerated up to 6 MeV by use of a tandem accelerator. A new energy analyzer with tandem electrodes has also been developed to analyze such a high energy beam. As a result, a secondary beam can be detected and its energy successfully analyzed. It is verified, in principle, that the potential profile can be measured using the HIBP.

    DOI: 10.1063/1.2338311

  • Turbulence and transport characteristics of a barrier in a toroidal plasma

    A Fujisawa, A Shimizu, H Nakano, S Ohsima, K Itoh, H Iguchi, Y Yoshimura, T Minami, K Nagaoka, C Takahashi, M Kojima, S Nishimura, M Isobe, C Suzuki, T Akiyama, Y Nagashima, K Ida, K Toi, T Ido, SI Itoh, K Matsuoka, S Okamura, PH Diamond

    PLASMA PHYSICS AND CONTROLLED FUSION   48 ( 4 )   S205 - S212   2006.4

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    Turbulence and zonal flow at, a transport barrier are studied with twin heavy ion beam probes in a toroidal helical plasma. A wavelet analysis is used to extract turbulence properties, e.g. spectra of both density and potential fluctuations, the coherence and the phase between them and the dispersion relation. Particle transport estimated from the fundamental characteristics is found to clearly rise with their intermittent activities after the barrier is broken down. Time-dependent analysis reveals that the intermittency of turbulence is correlated with the evolution of the stationary zonal flow.

    DOI: 10.1088/0741-3335/48/4/S15

  • Wavelet and Fourier analysis of zonal flows and density fluctuations in JIPP T-IIU tokamak plasmas Reviewed

    Y. Hamada, T. Watari, A. Nishizawa, T. Ido, M. Kojima, Y. Kawasumi, K. Toi

    PLASMA PHYSICS AND CONTROLLED FUSION   48 ( 4 )   S177 - S191   2006.4

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    Wavelet and two-dimensional Fourier analyses of local potential and density signals were conducted. These signals were obtained in the core region of tokamak plasmas by a multiple-sample-volume heavy ion beam probe. In the low-density Ohmic plasma where the electron temperature is much higher than that of the ions, the high-frequency (HF) zonal flow in geodesic acoustic mode frequency region is more energetic than the low-frequency zonal flow from 10 to 1000Hz in terms of integrated intensity. This result is in sharp contrast to the results of ITG simulations, of the tokamak plasmas. The HF zonal flow has a short lifetime, (a few cycles). The wavelet spectra of density are much,more chaotic than those of potential turbulence, changing the amplitude and frequency of the dominant modes more rapidly within the lifetime of the HF zonal flows. It, was. also found that HF parts of the density fluctuations are highly modulated by the HF zonal flows.

    DOI: 10.1088/0741-3335/48/4/S13

  • Optimization of negative ion sources for a heavy-ion-beam probe

    和田 元

    Review of Scientific Instruments   77 ( 03A )   537 - 539   2006.3

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    Optimization of negative ion sources for a heavy-ion-beam probe
    The development of plasma-sputter-type negative ion sources is underway for the heavy-ion-beam probe system as plasma diagnostic beams of the large helical device (LHD) for potential and fluctuation field measurements. Our purpose is to increase the doubly charged exchanged Au+ beam intensity to enhance the detection signal after passing through the plasmas of the LHD. For this purpose, the characterization of the Au- ion source and the beam optics has been carried out both experimentally and numerically. Based on these results, a new plasma-sputter-type negative ion source is designed and tested. © 2006 American Institute of Physics.

    DOI: 10.1063/1.2170094

  • Characteristics of plasma operation with the ferritic inside wall and its compatibility with high-performance plasmas in JFT-2M

    K. Tsuzuki, H. Kimura, Y. Kusama, M. Sato, H. Kawashima, K. Kamiya, K. Shinohara, H. Ogawa, K. Uehara, G. Kurita, S. Kasai, K. Hoshino, N. Isei, Y. Miura, M. Yamamoto, K. Kikuchi, T. Shibata, M. Bakhtiari, T. Hino, Y. Hirohata, Y. Yamauchi, K. Yamaguchi, H. Tsutsui, R. Shimada, H. Amemiya, Y. Nagashima, T. Ido, Y. Hamada

    Fusion Science and Technology   49 ( 2 )   197 - 208   2006.2

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    Compatibility between plasma and reduced activation ferritic steel, which is the leading candidate for the structural material of a fusion demonstration reactor, has been investigated in the Advanced Material Tokamak EXperiment (AMTEX). Ferritic plates (FPs) were installed progressively in the JFT-2M tokamak. The effect of ferromagnetism on plasma production, control, confinement, and stability has been investigated. Impurity release behavior has also been investigated. Even when the inside vacuum vessel wall was fully covered with the FPs and the tokamak plasma was operated close to the wall, no deleterious effect was observed, and the normalized beta could be increased up to ∼3.5. Thus, encouraging results are obtained for application of this material to the demonstration reactor.

    DOI: 10.13182/FST06-A1095

  • Studies of radial electric field formation and its effect on fluctuations and transport barriers in the JFT-2M tokamak Reviewed

    K Ida, Y Miura, T Ido, Y Nagashima, K Shinohara

    FUSION SCIENCE AND TECHNOLOGY   49 ( 2 )   122 - 138   2006.2

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    The mechanism of E x B flow formation, the effect of the E X B flow on parallel flow, the reduction of fluctuations by the shearing effect of the E x B flow shear, and the relation between the geodesic acoustic mode (GAM) and density fluctuations are discussed based on the experiments using various Er measurements in the JFT-2M tokamak. The experiments in plasmas with H-mode and counter-neutral beam injection (NBI) mode show that the feedback loop of the E x B flow shear, the fluctuation suppression, and an increase of ion diamagnetic flow are key to the formation of the transport barrier in toroidal plasmas. Two important effects of the radial electric field are presented: One is fluctuation suppression by the E x B flow shear, and the other is a drive of the parallel flow by radial electric field, which explains the driving mechanism of a spontaneous toroidal flow. The relation between the GAM and the density fluctuations is also discussed. The GAM is observed to be excited by the nonlinear coupling of density fluctuations, while the GAM itself affects the amplitude of the density fluctuations.

  • Reduced divertor heat loads, plasma shape effects, and radial electric field structures in JFT-2M HRS H-mode plasmas Reviewed

    K Kamiya, H Kawashima, T Ido, N Oyama, M Bakhtiari, S Kasai, Y Kusama, Y Miura, H Ogawa, K Tsuzuki, K Uehara

    NUCLEAR FUSION   46 ( 2 )   272 - 276   2006.2

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    A key feature of the 'high recycling steady' (HRS) H-mode regimes is the reduction of the transient heat load to the divertor target due to large ELMS. The heat flux to the divertor targets measured by means of a Langmuir probe in the scrape-off layer on the target plate is about similar to 0.3 MW m(-2) in the typical HRS plasmas, which is very small in comparison with the transient heat load in the ELMy H-mode discharge. In addition, the effects of the plasma shaping on the access to and improved plasma performance of HRS H-mode regimes have been investigated. Furthermore, simultaneous measurements of both density fluctuations and potential profiles at the plasma edge region using a heavy ion beam probe are also presented.

    DOI: 10.1088/0029-5515/46/2/010

  • Observation of nonlinear coupling between small-poloidal wave-number potential fluctuations and turbulent potential fluctuations in ohmically heated plasmas in the JFT-2M tokamak Reviewed

    Y Nagashima, K Hoshino, A Ejiri, K Shinohara, Y Takase, K Tsuzuki, K Uehara, H Kawashima, H Ogawa, T Ido, Y Kusama, Y Miura

    PHYSICAL REVIEW LETTERS   95 ( 9 )   2005.8

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    Two types of electrostatic modes with small-poloidal wave numbers (similar to 1 and 10-15 kHz) are observed in the edge region of Ohmically heated plasmas in the JFT-2M tokamak. The envelope of the higher frequency coherent mode is modulated at the frequency of the lower frequency mode. A bispectral analysis revealed that a significant nonlinear coupling among the two types of fluctuations and the broadband background turbulent potential fluctuations occurs inside the last closed magnetic flux surface, suggesting that a nonlinear process such as the parametric-modulational instability is involved.

  • Zonal flows in the geodesic acoustic mode frequency range in the JIPP T-IIU tokamak plasmas Reviewed

    Y Hamada, A Nishizawa, T Ido, T Watari, M Kojima, Y Kawasumi, K Narihara, K Toi

    NUCLEAR FUSION   45 ( 2 )   81 - 88   2005.2

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    Large potential oscillations were detected in JIPPT-IIU tokamak plasmas in a wide range of plasma cross-sections in measurements using a multi-sample-volume heavy ion beam probe. These oscillations have large amplitudes reaching a few hundreds of volts and their frequencies are in the range of the geodesic acoustic mode (GAM). They are found over a wide range of plasma cross-sections and commonly have m = 0 structures. As they were Fourier analysed, it was found that the central frequency is higher in the core of the plasma and lower in the edge of the plasma. These observations agree with the properties of theoretically predicted GAM oscillations. It was also found that the frequency spectrum is peaked in the core and broad in the edge, which may have something to do with damping mechanisms of the GAM. The phase relation between the density and the electric field fluctuations was studied extensively in terms of the cross-correlation function. The level of the density fluctuation was low as it should be,, and the expected 90 degrees phase difference was found in a limited radial domain.

    DOI: 10.1088/0029-5515/45/2/002

  • Recent diagnostic developments on LHD

    S. Sudo, Y. Nagayama, B. J. Peterson, K. Kawahata, T. Akiyama, N. Ashikawa, M. Emoto, M. Goto, Y. Hamada, K. Ida, T. Ido, H. Iguchi, S. Inagaki, M. Isobe, T. Kobuchi, A. Komori, Y. Liang, S. Masuzaki, T. Minami, T. Morisaki, S. Morita, S. Muto, Y. Nakamura, H. Nakanishi, M. Narushima, K. Narihara, M. Nishiura, A. Nishizawa, S. Ohdachi, M. Osakabe, T. Ozaki, R. O. Pavlichenko, S. Sakakibara, K. Sato, M. Shoji, N. Tamura, K. Tanaka, K. Toi, T. Tokuzawa, K. Y. Watanabe, T. Watanabe, H. Yamada, I. Yamada, M. Yoshinuma, P. Goncharov, D. Kalinina, T. Kanaba, T. Sugimoto, A. Ejiri, Y. Ono, H. Hojo, K. Ishii, N. Iwama, Y. Kogi, A. Mase, M. Sakamoto, K. Kondo, H. Nagasaki, S. Yamamoto, N. Nishino, S. Okajima, T. Saida, M. Sasao, T. Takeda, S. Tsuji-Iio, D. S. Darrow, H. Takahashi, Y. Liu, J. F. Lyon, A. Yu Kostrioukov, V. B. Kuteev, V. Sergeev, I. Viniar, A. V. Krasilnikov, A. Sanin, L. N. Vyacheslavov, D. Stutman, M. Finkenthal, O. Motojima

    Plasma Physics and Controlled Fusion   45 ( 12 A )   2003.12

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    Standard diagnostics for fundamental plasma parameters and for plasma physics are routinely utilized for daily operation and physics studies in the large helical device (LHD) with high reliability. Diagnostics for steady-state plasma are under intensive development, especially for Te, ne (yttrium-aluminium garnet (YAG) laser Thomson, CO2 laser polarimeter), data acquisition in steady-state and heat-resistant probes. To clarify the plasma properties of the helical structure, two- or three-dimensional diagnostics are being aggressively developed: tangential cameras (fast SX TV, photon counting CCD, Hα TV); tomography (tangential SX CCD, bolometer); imaging (bolometer, ECE, reflectometer). Divertor and edge physics are important key issues for steady-state operation. Diagnostics for neutral flux (Hα array, Zeeman spectroscopy) and ne (fast scanning probe, Li beam probe, pulsed radar reflectometer) are also in advanced stages of development. In addition to these, advanced diagnostics are being intensively developed in LHD through domestic and international collaborations.

    DOI: 10.1088/0741-3335/45/12A/027

  • Calibration of heavy ion beam probe energy analyzer using mesh probe in the JFT-2M tokamak Reviewed

    K Kamiya, Y Miura, T Ido, Y Hamada

    REVIEW OF SCIENTIFIC INSTRUMENTS   74 ( 9 )   4206 - 4208   2003.9

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    A direct calibration technique for a heavy ion beam probe (HIBP) parallel plate electrostatic energy analyzer using the mesh probe is established. When an ac bias voltage (+/-1.0 kV, 50 Hz) is applied to the inner mesh box and He gas is puffed into the vacuum vessel after setting the sample volume within the inner mesh box, it is confirmed that the normalized difference (ND) depends linearly on the applied bias voltage. The slope of the ND with respect to the bias voltage, d(ND)/d(Phi(bias)), shows the clear dependence on the in-plane entrance angle to the analyzer slit that is expected from the ideal analyzer model. Although the mesh transparency of the beam is about 40%, good signal to noise ratio is obtained with a beam current of about 10 muA, and the uncertainty for an absolute calibration of the energy analyzer is less than 10%. Calibration results are in good agreement with previous results using a standard gas target method. (C) 2003 American Institute of Physics.

    DOI: 10.1063/1.1599057

  • Recent diagnostic developments on LHD

    S. Sudo, T. Ozaki, N. Ashikawa, M. Emoto, M. Goto, Y. Hamada, K. Ida, T. Ido, H. Iguchi, S. Inagaki, M. Isobe, K. Kawahata, K. Khlopenkov, T. Kobuchi, Y. Liang, S. Masuzaki, T. Minami, S. Morita, S. Muto, Y. Nagayama, H. Nakanishi, K. Narihara, A. Nishizawa, S. Ohdachi, M. Osakabe, B. J. Peterson, S. Sakakibara, M. Sasao, K. Sato, M. Shoji, N. Tamura, K. Tanaka, K. Toi, T. Tokuzawa, K. Watanabe, T. Watanabe, I. Yamada, P. Goncharov, A. Ejiri, S. Okajima, A. Mase, S. Tsuji-Iio, T. Akiyama, J. F. Lyon, L. N. Vyacheslavov, A. Sanin

    Plasma Physics and Controlled Fusion   45 ( 7 )   1127 - 1142   2003.7

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    The recent diagnostic developments on the large helical device (LHD) are described briefly. LHD is the largest helical machine with all superconducting coils, and its purpose is to prove the ability of a helical system to confine a fusion-relevant plasma in steady state. According to the missions of LHD research, the diagnostic devices are categorized as follows: diagnostics for (i) high nτET plasmas and transport physics; (ii) magnetohydrodynamic stability; (iii) long pulse operation and divertor function; and (iv) energetic particles. These are briefly described focusing on the recent developments of the devices. Since the LHD experiment started in March 1998, five series of experimental campaigns have been carried out. The LHD diagnostics during these periods were operated successfully, and contributed to the analysis of the experimental results.

    DOI: 10.1088/0741-3335/45/7/307

  • Observation of the fast potential change at L-H transition by a heavy-ion-beam probe on JFT-2M Reviewed

    T Ido, K Kamiya, Y Miura, Y Hamada, A Nishizawa, Y Kawasumi

    PHYSICAL REVIEW LETTERS   88 ( 5 )   2002.2

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    The fast potential change near the separatrix is measured directly at the L-H transition by a heavy-ion-beam probe. The potential changes with two different time scales at the L-H transition triggered by a sawtooth crash: it drops at first with the time scale of 10-100 mus just after the arrival of the heat pulse due to the sawtooth crash. Then, it decreases again at a few 100 mus after the first drop at a time scale of about 200 mus.

    DOI: 10.1103/PhysRevLett.88.055006

    Other Link: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.88.055006

  • Relations among potential change, fluctuation change and transport barrier in the JFT-2M tokamak

    Y Miura, T Ido, K Kamiya, Y Hamada

    NUCLEAR FUSION   41 ( 8 )   973 - 979   2001.8

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    Potential and density/temperature fluctuations at the L-H transition axe measured by the heavy ion beam probe on JFT-2M. It has been observed that the timescale of the potential change is as fast as 10-100 mus when the input power (P(in)) is larger than the L-H threshold power (P(th)). When P(in) similar to P(th), the confinement is improved gradually step by step with sawtooth crashes, After a few sawtooth crashes, the potential drops rapidly to the level of the ELM free H mode. From the gradual change of the potential, assuming that dE(r)/dr is a key to forming and sustaining the transport barrier, the criterion of dE(r)/dr is less than (1.2+/-0.4) x 10(3) kV/m(2). At an ELM just before the H-L transition the potential inside the separatrix also shows a rapid positive jump. The timescales of the positive jump and of thc recovery of the potential to its negative value are about 40 and 150 mus, respectively. Before the H L transition, the time between ELMs and/or dithering transition becomes shorter and the plasma finally goes back to the L mode.

    DOI: 10.1088/0029-5515/41/8/301

  • Development of mesh probe for the calibration of the HIBP diagnostic system in the JFT-2M tokamak Reviewed

    K Kamiya, Y Miura, K Tsuzuki, T Ido, Y Hamada, T Nakayama

    REVIEW OF SCIENTIFIC INSTRUMENTS   72 ( 1 )   579 - 582   2001.1

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    A direct calibration technique for the heavy ion beam probe system using the mesh probe is established. The mesh probe makes it possible to calibrate the diagnostic system with the same condition as a real plasma measurement. The location of the sample volume could be determined with the spatial resolution of about 7.5 mm. It shows good agreement with this expected result by the trajectory code with an accuracy of about 1%. (C) 2001 American Institute of Physics.

  • Temporal behaviour of the potential and fluctuations at the L-H transition on JFT-2M Reviewed

    T Ido, K Kamiya, Y Miura, Y Hamada, A Nishizawa, Y Kawasumi

    PLASMA PHYSICS AND CONTROLLED FUSION   42   A309 - A315   2000.5

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    Potential and density/temperature fluctuations at the L-H transition are measured by a heavy ion beam probe (HIBP) on JFT-2M. It has been observed that the time scale of potential change is as fast as 10-100 mu s when the input power (P-in) is larger than the L-H threshold power (P-th). When P-in = P-th, the confinement is improved step by step, with sawteeth crashes accompanied by a decrease of potential. After a few sawteeth crashes, the potential drops rapidly to the level of the ELM-free H-mode. At that time, the density/temperature fluctuations are suppressed simultaneously. The observations of the temporal behaviour of the potential and fluctuations in such all L-H transition are reported.

  • Behaviour of sample volumes of the heavy ion beam probe on JFT-2M Reviewed

    T Ido, K Kamiya, Y Hamada, A Nishizawa, Y Kawasumi, Y Miura

    PLASMA PHYSICS AND CONTROLLED FUSION   41 ( 8 )   1013 - 1024   1999.8

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    Complex behaviour of sample volumes in heavy ion beam probe (HIBP) is numerically and experimentally explored. Three types of the sample volume divergences are established experimentally. It is found that the comparison of the results of experiments and trajectory calculation can provide calibrations of the HIBP.

    DOI: 10.1088/0741-3335/41/8/307

  • Heavy ion beam probe diagnostic system on JFT-2M Reviewed

    T Ido, Y Hamada, A Nishizawa, Y Kawasumi, Y Miura, K Kamiya

    REVIEW OF SCIENTIFIC INSTRUMENTS   70 ( 1 )   955 - 958   1999.1

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    Heavy ion beam probe (HIBP) on JFT-2M has been installed. The diagnostic system is described briefly alone with a detailed description of planned calibration experiments. Two sets of poloidal and toroidal sweepers are used, one set at the entrance port and the other set at the exit port. These are used to measure a potential profile from the edge to the core of the plasma and to reduce the error due to the change of the angle to the energy analyzer. The calibration of the required voltages on electrodes of these sweepers for the potential profile measurement will be performed by the ionization of the injected beams with the neutral gas puffed into the tokamak chamber, with special emphasis on the effects of peculiar behaviors of the double sample volumes and sample volume divergence. It is found that in JFT-2M HIBP these phenomena do not disturb the calibration of the potential measurement. These peculiar behaviors will be useful for accurately determining the location of the observation point. (C) 1999 American Institute of Physics. [S0034-6748(99)75501-2].

    DOI: 10.1063/1.1149474

  • Strong electron heating in CHS ICRF heating experiments

    S. Masuda, R. Kumazawa, K. Nishimura, T. Mutoh, T. Watari, F. Simbo, T. Seki, T. Ido, R. Akiyama, A. Ando, A. Ejiri, H. Idei, K. Ida, H. Iguchi, M. Isobe, M. Iwase, S. Kubo, K. Matsuoka, T. Morisaki, S. Morita, S. Mutoh, S. Murakami, S. Okamura, T. Ozaki, S. Sakakibara, M. Sasao, C. Takahashi, T. Kawamoto, K. Tanaka, J. Xu, H. Yamada, I. Yamada, D. A. Rasmussen, J. F. Lyon, J. B. Wilgen, D. E. Greenwood, D. J. Hoffman, E. F. Jaeger, M. Murakami

    Nuclear Fusion   37 ( 1 )   53 - 68   1997.1

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    An ion cyclotron range of frequencies (ICRF) heating experiment was performed on the Compact Helical System (CHS) device in order to identify the problems in establishing this as a reliable heating method. Radiofrequency heating was applied to plasmas with two ion species produced by ECH. Stored energy increased up to 2.2 kJ with the application of a 590 kW ICRF heating pulse, giving a heating efficiency comparable to that of NBI heating. More importantly, the 'flat-top' of the stored energy was maintained during the pulse. Good heating was realized with 30% proton and 70% deuteron plasmas at high density (4 ×19 m-3). It was found that the best discharges are dominated by electron ICRF heating, which seems to be the reason for the successful results. On the contrary, a flat-top in stored energy has never been obtained in discharges where ion heating dominates. The loss of high energy ions with large pitch angles produced by ion heating appears to degrade the performance and limit the duration of the heating. A similar degradation was encountered in previous ICRF heating experiments in helical systems. A newly designed detector was used to study the loss of the helically trapped particles.

    DOI: 10.1088/0029-5515/37/1/I12

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Presentations

  • LHDにおいて垂直NBIにより形成される電位及び密度の空間構造

    井戸毅, 清水昭博, 西浦正樹, 田窪英法, 西澤章光

    第39回プラズマ・核融合学会年会  2022.11 

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    Event date: 2022.11

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:富山   Country:Japan  

    近年不純物ホール等、不純物輸送の解明を契機として磁気面上における電位の非一様性の影響が注目されている。この非一様性を形成する要因の一つとして、高エネルギーの中性粒子入射(NBI)に起因する捕捉高速イオンの影響が数値シミュレーションに指摘されている(H. Yamaguchi and S. Murakami, Nucl. Fusion 58 016029 (2018))。本研究では、核融合科学研究所のLHDにおいて垂直NBIに対するプラズマ内部における電位分布及び密度分布の応答の計測を行った。
    図1に垂直NBIの有無に対する電位分布及び重イオンビームプローブ(HIBP)の信号強度分布の違いを示す。ここでHIBPの信号強度はプラズマの密度及び高速イオンの密度を反映する。電位分布、信号強度分布ともにNBI時に特徴的な空間構造が形成されることが観測された。この構造はNBが入射されている間は維持されており、再現性があることも確認された。また、LHDには2基の垂直NBIが設置されているが、上記の特徴的な構造は、計測位置からトロイダル方向に近い位置でのNBI時には顕著であるが、遠い位置でのNBI時には観測されない。この結果は、垂直NBI時にトロイダル方向に局在した電位構造が形成されており、磁気面上の非一様性の存在を示唆している。ただし、この構造は上記数値シミュレーションとは異なり、磁気軸近傍で顕著に現れる。今後この2次元構造や高速イオンの分布の解析を含め、物理機構を検討する必要がある。

  • Conceptual Design of a Heavy Ion Beam Probe for the QUEST spherical tokamak International conference

    T. Ido, M. Hasegawa, R. Ikezoe, T. Onchi, K. Hanada, H. Idei, K. Kuroda, Y. Nagashima

    24th Topical Conference on High Temperature Plasma Diagnostics  2022.5 

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    Event date: 2022.5

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Rochester, New York   Country:United States  

    A heavy ion beam probe (HIBP) has been designed for the QUEST spherical tokamak to measure plasma turbulence and the electric potential profiles. By using a cesium ion beam with the energy of several keV, the observable region covers most of the upper half of the plasma. Although the probe beam is deflected by the poloidal magnetic field produced by plasma current and poloidal coil currents, it can be detected under the plasma current up to 150 kA by modifying the trajectories with two electrostatic sweepers. According to numerical estimation of the detected beam intensity, sufficient signal intensity for measuring plasma turbulence can be obtained over almost the measurable region when the electron density is up to 1×10^19 m^(-3) which is larger than the cut-off density of ECH in QUEST. The performance of the designed HIBP is sufficient for the QUEST project.

  • Dynamics of energetic particle-driven oscillatory zonal flow in toroidal plasmas Invited

    Takeshi Ido

    第38回 プラズマ・核融合学会  2021.11 

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    Event date: 2021.11 - 2021.6

    Language:English   Presentation type:Symposium, workshop panel (public)  

    Venue:オンライン   Country:Japan  

  • Design of Heavy Ion Beam Probes on the PLATO tokamak International conference

    Takeshi Ido, Akihide Fujisawa, Keiji Takemura, Naohiro Kasuya, Shigeru Inagaki, Atsushi Fukuyama, Yoshihiko Nagashima, Chanho Moon, Kotaro Yamasaki, Takuma Yamada, Yusuke Kosuga, Makoto Sasaki

    High-Temperature Plasma Diagnostics Conference  2020.12 

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    Event date: 2020.12

    Language:English   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

    Plasma turbulence plays a decisive role in determining dynamics of plasmas not only in laboratories but also in the space. Especially, recent studies have indicated the importance of not only local but also global properties of the turbulence such as symmetry breaking and multi-scale interaction. In order to explore dynamics of plasmas through measuring plasma turbulence precisely and globally, a new tokamak named Plasma Turbulence Observatory (PLATO) is being constructed in Kyushu University.
    One of the key diagnostic systems for the PLATO project is Heavy Ion Beam Probe (HIBP), by which the electric potential, its fluctuations, density fluctuations, and magnetic fluctuations are measured directly and simultaneously without any perturbation to the plasmas. The HIBPs are installed in two toroidal sections to observe long range correlation in the toroidal direction. In addition, two energy analyzers in a poloidal cross section to observe the poloidal asymmetry and the correlation in the poloidal direction. The measurable area covers almost the whole plasma with a circular poloidal cross section and approximately 80 % of a poloidal cross section of the plasma with \kappa of 1.5 and \delta of 0.5, where \kappa is the ellipticity and \delta is the triangularity. The beam energy is 10 – 50 keV for Rubidium (Rb) beam or 50 – 150 keV for Sodium (Na) beam. According to a numerical calculation under the condition in which the central electron density is 1x10^19 (m^-3) and the density profile is parabolic, the detected beam intensity will be sufficient for micro-turbulence measurement in the region from the normalized minor radius(rho) of 0.2 to the plasma edge by Rb beam and in whole measurable region by Na beam. Therefore, we will be able to investigate nature of turbulence through multi-scale and simultaneous measurement.

  • QUEST用重イオンビームプローブの設計

    井戸毅,長谷川真,池添竜也,恩地拓己,出射浩,黒田賢剛,吉田直亮,永島芳彦

    プラズマ・核融合学会  2020.12 

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    Event date: 2020.12

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  • 乱流抑制配位創成に向けたHIBP設置可能性の検討

    井戸毅,清水昭博,西浦正樹,濱田泰司,新配位創成研究チーム

    プラズマ・核融合学会  2020.11 

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    Event date: 2020.12

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:オンライン   Country:Japan  

  • LHDにおける高速イオン励起測地線音波バーストが電位分布に及ぼす影響

    井戸毅, 一ノ瀬薫, 清水昭博, 佐々木真, 王 灏, 西浦正樹

    第36回プラズマ・核融合学会年会  2019.11 

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    Event date: 2019.11 - 2019.12

    Language:Japanese   Presentation type:Oral presentation (invited, special)  

    Venue:中部大学   Country:Japan  

    LHDにおいてNBI時に高速イオン励起測地線音波(EGAM)がバースト的に発生する。この時、GAMの周期より十分長く、バースト継続時間より短い時間で平均した平均電位の変動が観測された。電位はプラズマ中心領域で負に、規格化小半径0.2より外では正に変動しており、中心近傍で負電場が形成されている。この電場形成は高速イオンの損失を示唆している。中心近傍においてはEGAM発生時に電位揺動及び密度揺動も減少しており、負電場形成との関連が考えられる。

  • Nonlinear wave-particle interaction in magnetized high temperature plasmas confined in Large Helical Device Invited International conference

    Takeshi Ido, Akihiro Shimizu, Masaki Osakabe, Kimitaka Itoh, Maxime Lesur, Kunihiro Ogawa, Hao Wang, Makoto Sasaki, Yusuke Kosuga, Shigeru Inagaki, Sanae.–I. Itoh, and the LHD Experiment Group

    3rd Asia-Pacific Conference on Plasma Physics  2019.11 

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    Event date: 2019.11

    Language:English   Presentation type:Oral presentation (general)  

    Venue:Hefei, China   Country:China  

    Wave-particle interactions are ubiquitous in plasmas, and they are observed as interesting phenomena. In this presentation, observed subcritical instability driven by nonlinear wave-particle interaction in magnetized plasmas will be shown.
    In magnetized high temperature plasmas confined in the Large Helical Device (LHD), it is observed that an instability named geodesic acoustic mode(GAM) is excited abruptly by energetic particles existing through the inverse Landau damping. The frequency of this instability usually increases with the time scale of a few milliseconds, and the temporal evolution of the frequency reflects the evolution of the velocity distribution which is a result of wave-particle interaction.
    When the frequency of the GAM reaches twice the ordinary GAM frequency and the amplitude of the GAM exceeds a threshold, another GAM is abruptly excited with the shorter time scale of 1 ms or less. The phase relation between the originally-existing GAM, hereinafter referred to as the primary mode, and the abruptly excited GAM, hereinafter referred to as the secondary mode, is locked, and the evolution of the growth rate of the secondary mode indicates nonlinear excitation. These behaviors can be interpreted as the excitation of the subcritical instability of the secondary mode through nonlinear wave-particle interaction triggered by the primary mode. Abrupt excitation phenomena have been wildly observed in laboratory plasmas (e.g. sawtooth oscillation and disruption) and astro-plasmas(e.g. solar flare), and subcritical instabilities are one of the working hypotheses of the onset of abrupt phenomena. The finding of the abrupt excitation of the GAM and the understanding of the phenomena as the subcritical instability demonstrate an experimental path to the understanding of the physical mechanism of the onset of the abrupt phenomena.

  • PLATOトカマクにおける重イオンビームプローブ設置計画

    井戸毅、藤澤彰英、稲垣滋、永島芳彦、文贊鎬、山崎広太郎、糟谷直宏、小菅佑輔、佐々木真、山田琢磨

    日本物理学会  2019.9 

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    Event date: 2019.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:岐阜大学   Country:Japan  

  • Calibration of a Heavy Ion Beam Probe on the PLATO tokamak International conference

    T. Suetsugu, T. Ido, A. Fujisawa, T. Nishizawa, D. Kobayashi, D. Nishimura, C. Moon, Y. Nagashima, N. Kasuya, Y. Kosuga, T. Yamada

    7th Asia-Pacific Conference on Plasma Physics  2023.11 

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    Language:English   Presentation type:Oral presentation (general)  

    Venue:Nagoya   Country:Japan  

  • QUEST 用重イオンビームプローブのビームラインの設計

    山奥亮汰,井戸毅,末継寅英,長谷川真,木下稔基,河野香,QUEST実験グループ

    プラズマ・核融合学会  2023.11 

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    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:岩手   Country:Japan  

  • 8p-YM-6 JFT-2Mにおける重イオンビームプローブ計測

    井戸 毅, 西澤 章光, 川澄 義明, 濱田 泰司, 三浦 幸俊

    日本物理学会講演概要集  1997.9 

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    Language:Japanese  

    Country:Japan  

    8p-YM-6 Heavy ion beam probe measurement in JFT-2M tokamak

  • 28pUD-2 JFT-2Mトカマクのポテンシャル揺動(28pUD 核融合プラズマ(輸送・閉じ込め特性),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))

    星野 克道, 永島 芳彦, 井戸 毅, JFT-2Mグループ

    日本物理学会講演概要集  2006.3 

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    Country:Japan  

    28pUD-2 Potential fluctuations in the JFT-2M Tokamak

  • 27aXE-4 LHDにおける反転磁気シア配位形成時に励起される高速イオン励起アルヴェン固有モードとGAM周波数揺動の空間構造の観測(27aXE 核融合プラズマ(波動・安定性),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))

    井戸 毅, 清水 昭博, 西浦 正樹, 中野 治久, 加藤 眞治, 東井 和夫, 渡辺 文武, 吉村 泰夫, 久保 伸, 下妻 隆, 伊神 弘恵, 高橋 裕己

    日本物理学会講演概要集  2009.3 

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    Country:Japan  

    27aXE-4 Observation of Alfven eigenmode and Geodesic-acoustic-mode excited by energetic ions in LHD plasmas with the reversed magnetic shear

  • 金イオンビームとガスターゲットの衝突時の反応断面積測定システムの作製

    谷池 晃, 忍 友彰, 望月 翔, 井戸 毅, 西浦 正樹, 清水 昭博, 古山 雄一, 北村 晃

    神戸大学大学院海事科学研究科紀要  2011.7 

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    Country:Japan  

    Fabrication of the measuremente system for the cross sections in collisions between Au beams and gas targets

  • 26pYG-11 LHDにおける磁場リップルトップ及びボトムECHに対するプラズマの応答(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))

    牧野 良平, 久保 伸, 井戸 毅, 下妻 隆, 吉村 泰夫, 西浦 正樹, 伊神 弘恵, 高橋 裕己, 清水 昭博, 小笠原 慎弥

    日本物理学会講演概要集  2012.3 

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    Language:Japanese  

    Country:Japan  

    26pYG-11 Plasmas response to magnetic ripple top and bottom ECH in LHD

  • 24aYG-3 LHDプラズマにおける高速イオン励起GAMによる大振幅電位揺動とイオン温度上昇(24aYG 核融合プラズマ(MHD平衡・不安定性・磁気リコネクション,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)

    東井 和夫, 中村 充希, 井戸 毅, 清水 昭博, 小川 国大, 磯部 光孝, 長壁 正樹, 森田 繁, 後藤 基志, Pablant N. A., LHD実験グループ

    日本物理学会講演概要集  2012.3 

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    Language:Japanese  

    Country:Japan  

  • PLATOトカマクにおける重イオンビームプローブの校正実験

    末継寅英, 井戸毅, 藤澤彰英, 小林大輝, 西村大輝, 清水昭博, 西澤敬之, 永島芳彦, 文贊鎬, 糟谷直宏, 小菅祐輔, 山田琢磨

    プラズマ・核融合学会  2023.11 

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    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:岩手   Country:Japan  

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MISC

Professional Memberships

  • The Physical Society of Japan

  • The Japan Society of Plasma Science and Nuclear Fusion

  • The Physical Society of Japan

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  • The Japan Society of Plasma Science and Nuclear Fusion

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Committee Memberships

  • プラズマ・核融合学会   編集委員  

    2021.7 - 2023.6   

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    Committee type:Academic society

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  • 日本物理学会   Steering committee member   Domestic

    2013.10 - 2016.9   

  • 日本物理学会   領域2 領域運営委員,役員   Domestic

    2013.10 - 2016.9   

Academic Activities

  • 伊藤賞審査委員 International contribution

    ヨーロッパ物理学会プラズマ物理分科会  ( France ) 2023.7

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    Type:Competition, symposium, etc. 

  • 伊藤賞審査委員 International contribution

    ヨーロッパ物理学会プラズマ物理分科会  ( Japan ) 2022.6 - 2022.7

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    Type:Competition, symposium, etc. 

  • Screening of academic papers

    Role(s): Peer review

    2022

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    Type:Peer review 

    Number of peer-reviewed articles in foreign language journals:4

  • プラズマ・核融合学会誌

    2021.7 - 2023.6

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    Type:Academic society, research group, etc. 

  • Screening of academic papers

    Role(s): Peer review

    2021

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    Type:Peer review 

    Number of peer-reviewed articles in foreign language journals:3

    Number of peer-reviewed articles in Japanese journals:0

    Proceedings of International Conference Number of peer-reviewed papers:0

    Proceedings of domestic conference Number of peer-reviewed papers:0

  • プログラム委員,座長 International contribution

    4th Asia Pacific Conference on Plasma Physics (AAPPS-DPP2020)  ( Korea ) 2020.10

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    Type:Competition, symposium, etc. 

    Number of participants:550

  • Screening of academic papers

    Role(s): Peer review

    2020

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    Type:Peer review 

    Number of peer-reviewed articles in foreign language journals:5

    Number of peer-reviewed articles in Japanese journals:0

    Proceedings of International Conference Number of peer-reviewed papers:0

    Proceedings of domestic conference Number of peer-reviewed papers:0

  • Screening of academic papers

    Role(s): Peer review

    2019

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    Type:Peer review 

    Number of peer-reviewed articles in foreign language journals:3

    Number of peer-reviewed articles in Japanese journals:0

    Proceedings of International Conference Number of peer-reviewed papers:0

    Proceedings of domestic conference Number of peer-reviewed papers:0

  • Plasma and Fusion Research International contribution

    2018.10 - 2026.9

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    Type:Academic society, research group, etc. 

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Research Projects

  • QUESTにおける電磁揺動計測に基づく熱・粒子輸送研究の推進

    2024.4 - 2025.3

    Joint research

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    Authorship:Principal investigator  Grant type:Other funds from industry-academia collaboration

  • 磁場閉じ込めプラズマにおける高エネルギー粒子による電位構造形成機構の研究

    2024.4 - 2025.3

    Joint research

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    Authorship:Principal investigator  Grant type:Other funds from industry-academia collaboration

  • 軸対称プラズマの閉じ込め性能のアスペクト比依存性の起源の解明

    Grant number:24K00613  2024 - 2027

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (B)

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    Authorship:Principal investigator  Grant type:Scientific research funding

  • Development of a group of particle transport codes connecting the wall, peripheral, and core regions including dependence of ro-vibrational states of molecular hydrogen

    Grant number:23K03362  2023.4 - 2028.3

    Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

    中村 浩章, 澤田 圭司, 齋藤 誠紀, 森高 外征雄, 井戸 毅, 田村 祐一

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    Grant type:Scientific research funding

    非接触プラズマの生成には周辺領域での中性粒子輸送が影響する。また、炉心プラズマを高い効率で閉じ込め状態(Hモード)を維持するためには、壁からの中性粒子発生を低減する必要がある。非接触プラズマ・Hモードの両立条件を求める手法は未だ確立されていない。本研究では、(1)衝突輻射モデルを組み込んだ中性粒子輸送コード(2)分子動力学法と熱伝導方程式のハイブリッドコード、(3)ジャイロ運動論PICコードの改良も重ねてきた。これら3つのコードを紡ぎあい「壁の水素リサイクリング状態と分子の振動回転状態が、周辺の非接触プラズマ/炉心プラズマ閉じ込めにどのような影響を与えるか?」という課題に取り組む

    CiNii Research

  • Breakthrough of turbulent transport mechanism of self-burning plasma by high energy ion and tubulence analysis

    Grant number:23K25857  2023.4 - 2026.3

    Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (B)

    西浦 正樹, 矢内 亮馬, 釼持 尚輝, 田中 謙治, 井戸 毅, 關 良輔, 山口 裕之

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    Grant type:Scientific research funding

    核融合炉の高エネルギーイオンによる自律燃焼条件には,高エネルギーイオンとバルクイオ
    ンの良好な閉じ込めの両立が必須となる.本研究はミリ波協同トムソン散乱(CTS)と相関電子温度揺動(CECE)計測を用いて高エネルギーイオンが駆動するプラズマ中の電場と乱流に着目した電場・乱流励起・輸送メカニズムの解明を目的とする.そのために従来の高エネルギーイオン計測用のCTS受信機を基に,高ダイナミックレンジ化(30dB)と低ノイズ化した新CTS/CECE計測システムを開発しCECE計測を実現する.燃焼プラズマ閉じ込め物理機構に於ける高エネルギーイオンの役割を解明することで原型炉研究の新学術基盤を構築する.

    CiNii Research

  • QUESTにおける電磁揺動計測に基づく熱・粒子輸送研究の推進

    2023.4 - 2024.3

    Joint research

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    Authorship:Principal investigator  Grant type:Other funds from industry-academia collaboration

  • LHDプラズマにおける熱・粒子輸送への高速イオン駆動電磁場の影響

    2022.4 - 2023.3

    Joint research

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    Authorship:Principal investigator  Grant type:Other funds from industry-academia collaboration

  • 磁場閉じ込め高温プラズマ内部における2次元電磁揺動計測手法の開発

    2022.4 - 2023.3

    Joint research

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    Authorship:Principal investigator  Grant type:Other funds from industry-academia collaboration

  • LHDプラズマにおける熱・粒子輸送への高速イオン駆動電磁場の影響

    2021.4 - 2022.3

    Joint research

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    Authorship:Principal investigator  Grant type:Other funds from industry-academia collaboration

  • 磁場閉じ込め高温プラズマ内部における2次元電磁揺動計測手法の開発

    2021.4 - 2022.3

    Joint research

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    Authorship:Principal investigator  Grant type:Other funds from industry-academia collaboration

  • QUESTプロジェクト

    2019.10 - 2026.3

    日本 

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    Authorship:Coinvestigator(s) 

  • 高エネルギー粒子駆動揺動場とプラズマ乱流場のスケール間相互作用の検証

    2018 - 2020

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

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    Authorship:Principal investigator  Grant type:Scientific research funding

  • PLATOプロジェクト

    2017.4 - 2022.3

    九州大学 

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    Authorship:Coinvestigator(s) 

  • 統合観測システムで解き明かす乱流プラズマの構造形成原理と機能発現機構

    2017 - 2021

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Specially Promoted Research

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    Authorship:Coinvestigator(s)  Grant type:Scientific research funding

  • 微視的乱流と大域的揺らぎの同時計測による磁場閉じ込めプラズマにおける熱輸送の研究

    Grant number:15K06653  2015 - 2017

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

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    Authorship:Principal investigator  Grant type:Scientific research funding

  • 高効率多チャンネル重イオン検出器の開発による電場形成とプラズマ乱流の研究

    Grant number:24561031  2012 - 2014

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (C)

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    Authorship:Principal investigator  Grant type:Scientific research funding

  • 多チャンネル重イオンビームプローブの開発による電位構造形成過程の研究

    Grant number:20686062  2008 - 2010

    Grants-in-Aid for Scientific Research  Grant-in-Aid for Young Scientists(A)or(B)

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    Authorship:Principal investigator  Grant type:Scientific research funding

  • 統合観測システムで解き明かす乱流プラズマの構造形成原理と機能発現機構

    Grant number:17H06089 

    藤澤 彰英, 井戸 毅, 稲垣 滋, 飯尾 俊二

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    Grant type:Scientific research funding

    変容する自然の理解および核融合炉実現のための磁場閉じ込めプラズマの学術体系化を目指した乱流プラズマの統合大域精密観測装置PLATOが完成し運転を開始している。その建設過程において装置電源としての誘導型フライホイールほか1000チャンネルを超えるトモグラフィーデータ記録装置などの経済的技術も生まれている。PLATOプロジェクトを支援する研究としての直線プラズマ装置PANTAにおいては準3次元トモグラフィーが完成しそのための画像解析法(Fourier-Rectangular級数展開法など)も開発された。理論シミュレーショ研究では、広く乱流プラズマに関連した成果が多数上がっている。

    CiNii Research

  • 高エネルギー粒子駆動揺動場とプラズマ乱流場のスケール間相互作用の検証

    Grant number:18K03589 

    井戸 毅, 清水 昭博, 谷池 晃

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    Grant type:Scientific research funding

    磁場閉じ込めプラズマの閉じ込め性能を左右する電位や密度の揺らぎを計測するための計測器であるHIBPの高精度化を行い、これを用いてプラズマ中の高速イオンによって励起される不安定性とプラズマ乱流の計測に成功した。高速イオン励起不安定性とプラズマ乱流の直接相互作用は観測されなかったが、これまで観測されたことのない、高速イオン励起不安定性の2次元構造や高速イオンによる電場形成など新しい現象を見出すことに成功した。

    CiNii Research

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Class subject

  • 物理概論

    2024.4 - 2024.9   First semester

  • 物理概論

    2023.4 - 2023.9   First semester

  • 総合理工学修士実験

    2022.4 - 2023.3   Full year

  • 総合理工学修士演習

    2022.4 - 2023.3   Full year

  • 物理概論

    2022.4 - 2022.9   First semester

  • 物理概論

    2021.4 - 2021.9   First semester

  • 物理数学基礎

    2020.4 - 2020.6   Spring quarter

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Activities contributing to policy formation, academic promotion, etc.

  • 2021.4 - 2022.3   プラズマ・核融合学会

    プラズマ・核融合学会専門委員会「データサイエンスとの連携によるプラズマ・核融合データ利活用の推進」