| 井戸 毅（いど たけし） | データ更新日：2023.06.26 |
教授 ／
応用力学研究所
附属高温プラズマ理工学研究センター
| 1. | Makoto Hasegawa, Daisuke Sakurai, Aki Higashijima, Ichiro Niiya, Keiji Matsushima, Kazuaki Hanada, Hiroshi Idei, Takeshi Ido, Ryuya Ikezoe, Takumi Onchi, Kengo Kuroda, Towards automated gas leak detection through cluster analysis of mass spectrometer data, Fusion Engineering and Design, 10.1016/j.fusengdes.2022.113199, 180, 113199-113199, 2022.07. |
| 2. | T. Kobayashi, A. Shimizu, M. Nishiura, T. Ido, S. Satake, T. Tokuzawa, T. Ii Tsujimura, K. Nagaoka, K. Ida, Hydrogen isotope effect on self-organized electron internal transport barrier criticality and role of radial electric field in toroidal plasmas, Scientific Reports, 10.1038/s41598-022-09526-w, 12, 1, 2022.12, 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.. |
| 3. | T. Ido, M. Hasegawa, R. Ikezoe, T. Onchi, K. Hanada, H. Idei, K. Kuroda, Y. Nagashima, Conceptual design of a heavy ion beam probe for the QUEST spherical tokamak, Review of Scientific Instruments, 10.1063/5.0101770, 2022.11. |
| 4. | T. Tokuzawa, T. Nasu, S. Inagaki, C. Moon, T. Ido, H. Idei, A. Ejiri, R. Imazawa, M. Yoshida, N. Oyama, K. Tanaka, K. Ida, 3D metal powder additive manufacturing phased array antenna for multichannel Doppler reflectometer, Review of Scientific Instruments, 10.1063/5.0101723, 2022.11. |
| 5. | 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, A Proposal to Evaluate Electron Temperature and Electron Density Fluctuations Using Dual Wavelength Emission Intensity Tomography in a Linear Plasma, Journal of the Physical Society of Japan, 10.7566/jpsj.92.033501, 92, 3, 2023.03. |
| 6. | Conway, G.D., Smolyakov, A.I., Ido, T., Geodesic acoustic modes in magnetic confinement devices, Nuclear Fusion, https://doi.org/10.1088/1741-4326/ac0dd1, 62, 1, 013001-1-013001-149, vol.62, No.1, 013001, 2022.01, [URL], 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.. |
| 7. | 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, Conceptual design of a heavy ion beam probe diagnostic for HL-2M tokamak, Fusion Engineering and Design, 10.1016/j.fusengdes.2021.112845, 173, 112845-112845, 2021.12. |
| 8. | 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, The first observation of 4D tomography measurement of plasma structures and fluctuations, Scientific Reports, 10.1038/s41598-021-83191-3, 11, 1, 2021.12, |
| 9. | 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, Conceptual design of heavy ion beam probes on the PLATO tokamak, Review of Scientific Instruments , 10.1063/5.0041814, 92, 053553, 2021.05, [URL], 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.. |
| 10. | 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, Investigation of radial distribution of atomic hydrogen flux to the plasma facing components in steady state discharges in QUEST tokamak, Nuclear Materials and Energy, 10.1016/j.nme.2020.100872, 26, 2021.03, 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.. |
| 11. | N. Yoneda, T. Shikama, K. Hanada, S. Mori, T. Onchi, K. Kuroda, M. Hasuo, A. Ejiri, K. Matsuzaki, Y. Osawa, Y. Peng, Y. Kawamata, S. Sakamoto, H. Idei, T. Ido, K. Nakamura, Y. Nagashima, R. Ikezoe, M. Hasegawa, A. Higashijima, T. Nagata, S. Shimabukuro, Toroidal flow measurements of impurity ions in QUEST ECH plasmas using multiple viewing chords emission spectroscopy, Nuclear Materials and Energy, 10.1016/j.nme.2021.100905, 26, 2021.03, A spectroscopic system with multiple viewing chords was developed for QUEST (Q-shu University Experiment with Steady-State Spherical Tokamak) to measure the spatial distribution of ion toroidal velocities in discharges sustained by electron cyclotron resonance heating (ECH). Twenty-four viewing chords were aligned in the midplane and C III emission line spectra were measured for three types of ECH discharge under different magnetic field configurations. By applying an inversion method to the measured spectra, we evaluated the radial distributions of C2+ ion emissivity, temperature, and toroidal velocity. The error in the evaluated velocity was estimated to be less than 5 km/s. It was found that the velocity depends on the magnetic field configuration.. |
| 12. | 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, Non-inductive plasma current ramp-up through oblique injection of harmonic electron cyclotron waves on the QUEST spherical tokamak, Physics of Plasmas, 10.1063/5.0031357, 28, 2, 2021.02, 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.. |
| 13. | Hao Wang, Yasushi Todo, Masaki Osakabe, Takeshi Ido, Yasuhiro Suzuki, The systematic investigation of energetic-particle-driven geodesic acoustic mode channeling using MEGA code, Nuclear Fusion, 10.1088/1741-4326/ab8a04, 60, 11, 2020.11, 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.. |
| 14. | 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, Comparison between Tomography and Langmuir Probe Data in PANTA, Journal of the Physical Society of Japan, 10.7566/jpsj.89.093501, 89, 9, 093501-093501, 2020.09, 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.. |
| 15. | 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, Spectroscopic Measurement of Hydrogen Atom Density in a Plasma Produced with 28 GHz ECH in QUEST, ATOMS, 10.3390/atoms8030044, 8, 3, 2020.09, 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.. |
| 16. | 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, 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), Nuclear Fusion, 10.1088/1741-4326/ab3a13, 59, 10, 2019.08, 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).. |
| 17. | Hao Wang, Yasushi Todo, Masaki Oasakabe, Takeshi Ido, Yasuhiro Suzuki, Simulation of energetic particle driven geodesic acoustic modes and the energy channeling in the Large Helical Device plasmas, Nuclear Fusion, 10.1088/1741-4326/ab26e5, 59, 9, 2019.08, 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.. |
| 18. | M. Kobayashi, S. Masuzaki, K. Tanaka, T. Tokuzawa, M. Yokoyama, Y. Narushima, I. Yamada, T. Ido, R. Seki, Core plasma confinement during detachment transition with RMP application in LHD, Nuclear Materials and Energy, 10.1016/j.nme.2018.10.003, 17, 137-141, 2018.12, 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.. |
| 19. | Takeshi Ido, Abrupt excitation of energetic-particle-driven geodesic acoustic mode in the large helical device, AIP Conference Proceedings, 10.1063/1.5048712, 1993, 020002, 2018.08. |
| 20. | 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, Energy confinement of hydrogen and deuterium electron-root plasmas in the Large Helical Device, Nuclear Fusion, 10.1088/1741-4326/aad611, 58, 10, 2018.08, © 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.. |
| 21. | 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, Realization of high T |
| 22. | 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, 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, Nuclear Fusion, 10.1088/1741-4326/aac699, 58, 8, 2018.06, 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.. |
| 23. | T. Kobayashi, M. Sasaki, T. Ido, K. Kamiya, Y. Miura, Y. Nagashima, K. Ida, S. Inagaki, A. Fujisawa, S. I. Itoh, K. Itoh, Quantification of Turbulent Driving Forces for the Geodesic Acoustic Mode in the JFT-2M Tokamak, Physical Review Letters, 10.1103/PhysRevLett.120.045002, 120, 4, 2018.01, 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.. |
| 24. | T. Kobayashi, K. Itoh, T. Ido, K. Kamiya, S. I. Itoh, Y. Miura, Y. Nagashima, A. Fujisawa, S. Inagaki, K. Ida, Turbulent transport reduction induced by transition on radial electric field shear and curvature through amplitude and cross-phase in torus plasma, Scientific Reports, 10.1038/s41598-017-14821-y, 7, 1, 2017.12, 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.. |
| 25. | 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, Extended capability of the integrated transport analysis suite, TASK3D-a, for LHD experiment, Nuclear Fusion, 10.1088/1741-4326/aa800a, 57, 12, 2017.09, 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.. |
| 26. | 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, Extension of the operational regime of the LHD towards a deuterium experiment, Nuclear Fusion, 10.1088/1741-4326/aa7fc2, 57, 10, 2017.08, 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.. |
| 27. | 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, Extension of operational regime in high-temperature plasmas and effect of ECRH on ion thermal transport in the LHD, Nuclear Fusion, 10.1088/1741-4326/aa754b, 57, 8, 2017.07, 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.. |
| 28. | T. Kobayashi, K. Itoh, T. Ido, K. Kamiya, S. -I. Itoh, Y. Miura, Y. Nagashima, A. Fujisawa, S. Inagaki, K. Ida, K. Hoshino, Model validation for radial electric field excitation during L-H transition in JFT-2M tokamak, NUCLEAR FUSION, 10.1088/1741-4326/aa5d03, 57, 7, 2017.07, 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.. |
| 29. | 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, Observation of subcritical geodesic acoustic mode excitation in the large helical device, Nuclear Fusion, 10.1088/1741-4326/aa665a, 57, 072009 , 2017.04, [URL], 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.. |
| 30. | 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, Suppression of Trapped Energetic Ions Driven Resistive Interchange Modes with Electron Cyclotron Heating in a Helical Plasma, Physical Review Letters, 10.1103/PhysRevLett.118.125001, 118, 12, 2017.03, 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.. |
| 31. | 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, 2D spatial profile measurements of potential fluctuation with heavy ion beam probe on the Large Helical Device, Review of Scientific Instruments, 10.1063/1.4963908, 87, 11, 2016.11, © 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.. |
| 32. | 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, Resistive interchange mode destabilized by helically trapped energetic ions and its effects on energetic ions and bulk plasma in a helical plasma, Nuclear Fusion, 10.1088/0029-5515/56/1/016002, 56, 1, 2016.11, © 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.. |
| 33. | T. Kobayashi, K. Itoh, T. Ido, K. Kamiya, S. -I. Itoh, Y. Miura, Y. Nagashima, A. Fujisawa, S. Inagaki, K. Ida, K. Hoshino, Experimental Identification of Electric Field Excitation Mechanisms in a Structural Transition of Tokamak Plasmas, Scientific Reports, 10.1038/srep30720, 6, 2016.08, 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.. |
| 34. | K. Itoh, S. I. Itoh, T. Kobayashi, K. Kamiya, T. Ido, T. Tokuzawa, S. Inagaki, N. Kasuya, On the Origin of Steep and Localized Radial Electric Field in the Transport Barrier at Plasma Edge, Contributions to Plasma Physics, 10.1002/ctpp.201610042, 56, 6-8, 522-527, 2016.08, 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).. |
| 35. | 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, Transition from chirping to steady NBI-driven Alfvén modes caused by magnetic configuration variations in the TJ-II stellarator, Nuclear Fusion, 10.1088/0029-5515/56/7/076001, 56, 7, 2016.06, 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 |
| 36. | K. Itoh, S. I. Itoh, Y. Kosuga, M. Lesur, T. Ido, Onset condition of the subcritical geodesic acoustic mode instability in the presence of energetic-particle-driven geodesic acoustic mode, Plasma Physics Reports, 10.1134/S1063780X16050056, 42, 5, 418-423, 2016.05, 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.. |
| 37. | 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, Nonlinear excitation of subcritical fast ion-driven modes, Nuclear Fusion, 10.1088/0029-5515/56/5/056009, 56, 5, 2016.04, © 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.. |
| 38. | 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, Strong Destabilization of Stable Modes with a Half-Frequency Associated with Chirping Geodesic Acoustic Modes in the Large Helical Device, Physical Review Letters, 10.1103/PhysRevLett.116.015002, 116, 015002, 2016.01, [URL], 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.. |
| 39. | M. Lesur, K. Itoh, T. Ido, M. Osakabe, K. Ogawa, A. Shimizu, M. Sasaki, K. Ida, S. Inagaki, S. -I. Itoh, Nonlinear Excitation of Subcritical Instabilities in a Toroidal Plasma, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.116.015003, 116, 1, 2016.01, 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.. |
| 40. | K. Itoh, T. Kobayashi, T. Ido, S-I Itoh, K. Kamiya, Contribution of geodesic acoustic modes in the limit cycle oscillation near H-mode transition in JFT-2M plasmas, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/57/9/092001, 57, 9, 2015.09, 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.. |
| 41. | 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, Integrated discharge scenario for high-temperature helical plasma in LHD, Nuclear Fusion, 10.1088/0029-5515/55/11/113020, 55, 11, 2015.09, 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).. |
| 42. | Hao Wang, Yasushi Todo, Takeshi Ido, Masaki Osakabe, Simulation study of high-frequency energetic particle driven geodesic acoustic mode, Physics of Plasmas, 10.1063/1.4930130, 22, 9, 2015.09, 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.. |
| 43. | 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, Identification of the energetic-particle driven GAM in the LHD, Nuclear Fusion, 10.1088/0029-5515/55/8/083024, 55, 083024, 2015.07, [URL], 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.. |
| 44. | 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, Overview of transport and MHD stability study: Focusing on the impact of magnetic field topology in the Large Helical Device, Nuclear Fusion, 10.1088/0029-5515/55/10/104018, 55, 10, 2015.07, 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.. |
| 45. | T. Kobayashi, K. Itoh, T. Ido, K. Kamiya, S. -I. Itoh, Y. Miura, Y. Nagashima, A. Fujisawa, S. Inagaki, K. Ida, K. Hoshino, Edge plasma dynamics during L-H transition in the JFT-2M tokamak, NUCLEAR FUSION, 10.1088/0029-5515/55/6/063009, 55, 6, 2015.06, 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.. |
| 46. | Y. Hamada, T. Watari, A. Nishizawa, O. Yamagishi, K. Narihara, K. Ida, Y. Kawasumi, T. Ido, M. Kojima, K. Toi, Microtearing mode (MTM) turbulence in JIPPT-IIU tokamak plasmas, NUCLEAR FUSION, 10.1088/0029-5515/55/4/043008, 55, 4, 2015.04, 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.. |
| 47. | 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, Resistive interchange modes destabilized by helically trapped energetic ions in a helical plasma, Physical Review Letters, 10.1103/PhysRevLett.114.155003, 114, 15, 2015.04, © 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.. |
| 48. | 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, Flow damping due to stochastization of the magnetic field, Nature Communications, 10.1038/ncomms6816, 6, 2015.01, 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.. |
| 49. | A. Shimizu, T. Ido, M. Kurachi, R. Makino, M. Nishiura, S. Kato, A. Nishizawa, Y. Hamada, 2D potential measurements by applying automatic beam adjustment system to heavy ion beam probe diagnostic on the Large Helical Device, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.4891975, 85, 11, 2014.11, 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.. |
| 50. | 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, Dynamics of edge limit cycle oscillation in the JFT-2M Tokamak, Nuclear Fusion, 10.1088/0029-5515/54/7/073017, 54, 7, 2014.07, 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.. |
| 51. | 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, Extension of high T |
| 52. | 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, Observation of multi-scale turbulence and non-local transport in LHD plasmas, Physics of Plasmas, 10.1063/1.4876619, 21, 5, 2014.05, 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.. |
| 53. | 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, How is turbulence intensity determined by macroscopic variables in a toroidal plasma?, NUCLEAR FUSION, 10.1088/0029-5515/53/11/113006, 53, 11, 2013.11, 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.. |
| 54. | 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, Extension of operation regimes and investigation of three-dimensional currentless plasmas in the Large Helical Device, Nuclear Fusion, 10.1088/0029-5515/53/10/104015, 53, 10, 2013.10, 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.. |
| 55. | T. Kobayashi, K. Itoh, T. Ido, K. Kamiya, S. -I. Itoh, Y. Miura, Y. Nagashima, A. Fujisawa, S. Inagaki, K. Ida, K. Hoshino, Spatiotemporal Structures of Edge Limit-Cycle Oscillation before L-to-H Transition in the JFT-2M Tokamak, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.111.035002, 111, 3, 2013.07, 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.. |
| 56. | Y. Hamada, T. Watari, A. Nishizawa, O. Yamagishi, K. Narihara, Y. Kawasumi, T. Ido, M. Kojima, K. Toi, Regions of kinetic geodesic acoustic modes and streamers in JIPPT-IIU tokamak plasmas, NUCLEAR FUSION, 10.1088/0029-5515/52/6/063023, 52, 6, 2012.06, 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 |
| 57. | 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, Long range temperature fluctuation in LHD, Plasma and Fusion Research, 10.1585/pfr.6.1402017, 6, 2011.12, 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.. |
| 58. | Shinsuke SATAKE, Hideo SUGAMA, Ryutaro KANNO, Takeshi IDO, Seikichi MATSUOKA, Masayuki YOKOYAMA, A New Simulation Method of Geodesic Acoustic Mode in Toroidal Plasmas by Using Band-Limited White Noise in a δf Neoclassical Transport Code, Progress in Nuclear Science and Technology, 10.15669/pnst.2.72, 2, 0, 72, 2011.10. |
| 59. | 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, Observation of Long-Distance Radial Correlation in Toroidal Plasma Turbulence, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.107.115001, 107, 11, 2011.09, 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.. |
| 60. | 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, Heat and momentum transport of ion internal transport barrier plasmas on the Large Helical Device, NUCLEAR FUSION, 10.1088/0029-5515/51/8/083022, 51, 8, 2011.08, 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.. |
| 61. | 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, 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, 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, 10.24546/81003310, 8, 47-58, 2011.07. |
| 62. | 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, Potential fluctuation associated with the energetic-particle-induced geodesic acoustic mode in the Large Helical Device, Nuclear Fusion, 10.1088/0029-5515/51/7/073046, 51, 073046, 2011.06, [URL], 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.. |
| 63. | Y. Hamada, T. Watari, A. Nishizawa, O. Yamagishi, K. Narihara, K. Ida, Y. Kawasumi, T. Ido, M. Kojima, K. Toi, Detection of the kinetic geodesic acoustic mode (KGAM) near the centre region of JIPPT-IIU tokamak plasmas, NUCLEAR FUSION, 10.1088/0029-5515/51/3/033005, 51, 3, 2011.03, 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.. |
| 64. | Akira Taniike, Takeshi Ido, Masaki Nishiura, Akihiro Shimizu, Yuichi Furuyama, Akira Kitamura, Production of Sub-MeV Positive Gold Ion Beams with Various Gas Targets to Improve the Tandem Accelerator of the LHD-HIBP, Plasma and Fusion Research, 10.1585/pfr.5.S2087, 5, S2087 (2010), 2010.12. |
| 65. | 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, Observation of reversed-shear Alfvén eigenmodes excited by energetic ions in a helical plasma, Physical Review Letters, 10.1103/PhysRevLett.105.145003, 105, 14, 2010.10, Reversed-shear Alfvén eigenmodes were observed for the first time in a helical plasma having negative q0′′ (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 Alfvén eigenmodes with energetic ion driven geodesic acoustic modes generates a multitude of frequency-sweeping modes. © 2010 The American Physical Society.. |
| 66. | A. Shimizu, T. Ido, S. Nakamura, K. Toi, M. Nishiura, S. Kato, Potential measurements with heavy ion beam probe system on LHD, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.3491317, 81, 10, 2010.10, 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]. |
| 67. | 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, Experimental study of radial electric field and electrostatic potential fluctuation in the Large Helical Device, Plasma Physics and Controlled Fusion, 10.1088/0741-3335/52/12/124025, 52, 124025, 2010.09, [URL], 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.. |
| 68. | 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, 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)), 日本物理学会講演概要集, 65, 2, 2010.08. |
| 69. | Y. Hamada, T. Watari, A. Nishizawa, O. Yamagishi, K. Narihara, Y. Kawasumi, T. Ido, M. Kojima, K. Toi, GAM generation by drift waves in JIPP T-llU tokamak core plasmas, NUCLEAR FUSION, 10.1088/0029-5515/50/2/025001, 50, 2, 2010.02, 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.. |
| 70. | 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, Development of a heavy ion beam probe for measuring electrostatic potential profile and its fluctuation in LHD, Plasma Science and Technology, 10.1088/1009-0630/11/4/19, 11, 460-464, 2009.08. |
| 71. | 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, DEVELOPMENT OF 6-MeV HEAVY ION BEAM PROBE ON LHD, Fusion Science and Technology, 10.13182/FST10-A10829, 58, 436, 2009.07, [URL], 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.. |
| 72. | 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, Extension of Improved Particle and Energy Confinement Regime in the Core of LHD Plasma, Plasma and Fusion Research, 10.1585/pfr.4.027, 4, 27-27, 2009.01, 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 × 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 × 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.. |
| 73. | Shinsuke Ohshima, Takeshi Ido, Akihiro Shimizu, Masaki Nishiura, Haruhisa Nakano, Measurements of spatial structure of plasma potential and density fluctuations by multichannel heavy ion beam probe on large helical device, Review of Scientific Instruments, 10.1063/1.2981177, 79, 10, 10F320, 2008.10. |
| 74. | 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, Measurement of Electrostatic Potential Fluctuation using Heavy Ion Beam Probe in Large Helical Device, Review of Scientific Instruments, 10.1063/1.2971207, 79, 10F318, 2008.07, [URL], 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.. |
| 75. | 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, Experimental studies of zonal flow and field in compact helical system plasma, PHYSICS OF PLASMAS, 10.1063/1.2889012, 15, 5, 055906, 2008.05, 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.. |
| 76. | 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, Electrostatic Potential Measurement by Using 6-MeV Heavy Ion Beam Probe on LHD, Plasma and Fusion Research, 10.1585/pfr.3.031, 3, 031, 2008.04, [URL], 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.. |
| 77. | M. Nishiura, T. Ido, A. Shimizu, H. Nakano, T. Kato, S. Kato, Y. Hamada, V. P. Shevelko, R. K. Janev, M. Wada, Status of the heavy ion beam probe system in the Large Helical Device, Review of Scientific Instruments, 10.1063/1.2819323, 79, 2008.03, 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.. |
| 78. | 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, Experimental progress on zonal flow physics in toroidal plasmas, Nuclear Fusion, 10.1088/0029-5515/47/10/S19, 47, 2007.10, 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.. |
| 79. | 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, In search of zonal flows by using direct density fluctuation measurements, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/49/10/002, 49, 10, 1611-1625, 2007.10, 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.. |
| 80. | T. IDO, A. SHIMIZU, M. NISHIURA, Y. HAMADA, S. KATO, A. NISHIZAWA, H. NAKANO, Spatial resolution of the heavy ion beam probe on LHD, Plasma and Fusion Research, 10.1585/pfr.2.S1100, 2, S1100, 2007.03, [URL]. |
| 81. | 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, Intermittent characteristics in coupling between turbulence and zonal flows, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/49/3/002, 49, 3, 211-217, 2007.03, 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.. |
| 82. | 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 , 6 MeV heavy ion beam probe on Large Helical Device, Review of Scientific Instruments, 10.1063/1.2338311, 77, 10F523, 2006.10, [URL], 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. . |
| 83. | 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, Turbulence and transport characteristics of a barrier in a toroidal plasma, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/48/4/S15, 48, 4, S205-S212, 2006.04, 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.. |
| 84. | Y. Hamada, T. Watari, A. Nishizawa, T. Ido, M. Kojima, Y. Kawasumi, K. Toi, Wavelet and Fourier analysis of zonal flows and density fluctuations in JIPP T-IIU tokamak plasmas, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/48/4/S13, 48, 4, S177-S191, 2006.04, 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.. |
| 85. | 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, Geodesic–acoustic-mode in JFT-2M tokamak plasmas, Plasma Physics and Controlled Fusion, 10.1088/0741-3335/48/4/S04, 48, S41, 2006.03, [URL], 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.. |
| 86. | 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, Observation of the interaction between the geodesic acoustic mode and ambient fluctuation in the JFT-2M tokamak, Nuclear Fusion, 10.1088/0029-5515/46/5/003, 46, 5, 512, 2006.03, [URL], 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.. |
| 87. | 和田 元, Optimization of negative ion sources for a heavy-ion-beam probe, Review of Scientific Instruments, 10.1063/1.2170094, 77, 03A, 537-539, 2006.03, 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.. |
| 88. | 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, Characteristics of plasma operation with the ferritic inside wall and its compatibility with high-performance plasmas in JFT-2M, Fusion Science and Technology, 10.13182/FST06-A1095, 49, 2, 197-208, 2006.02, 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.. |
| 89. | K Kamiya, H Kawashima, T Ido, N Oyama, M Bakhtiari, S Kasai, Y Kusama, Y Miura, H Ogawa, K Tsuzuki, K Uehara, Reduced divertor heat loads, plasma shape effects, and radial electric field structures in JFT-2M HRS H-mode plasmas, NUCLEAR FUSION, 10.1088/0029-5515/46/2/010, 46, 2, 272-276, 2006.02, 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.. |
| 90. | K Ida, Y Miura, T Ido, Y Nagashima, K Shinohara, Studies of radial electric field formation and its effect on fluctuations and transport barriers in the JFT-2M tokamak, FUSION SCIENCE AND TECHNOLOGY, 49, 2, 122-138, 2006.02, 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.. |
| 91. | Y Nagashima, K Hoshino, A Ejiri, K Shinohara, Y Takase, K Tsuzuki, K Uehara, H Kawashima, H Ogawa, T Ido, Y Kusama, Y Miura, Observation of nonlinear coupling between small-poloidal wave-number potential fluctuations and turbulent potential fluctuations in ohmically heated plasmas in the JFT-2M tokamak, PHYSICAL REVIEW LETTERS, 95, 9, 2005.08, 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.. |
| 92. | Y Hamada, A Nishizawa, T Ido, T Watari, M Kojima, Y Kawasumi, K Narihara, K Toi, Zonal flows in the geodesic acoustic mode frequency range in the JIPP T-IIU tokamak plasmas, NUCLEAR FUSION, 10.1088/0029-5515/45/2/002, 45, 2, 81-88, 2005.02, 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.. |
| 93. | 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, Recent diagnostic developments on LHD, Plasma Physics and Controlled Fusion, 10.1088/0741-3335/45/12A/027, 45, 12 A, 2003.12, 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.. |
| 94. | K Kamiya, Y Miura, T Ido, Y Hamada, Calibration of heavy ion beam probe energy analyzer using mesh probe in the JFT-2M tokamak, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.1599057, 74, 9, 4206-4208, 2003.09, 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.. |
| 95. | 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, Recent diagnostic developments on LHD, Plasma Physics and Controlled Fusion, 10.1088/0741-3335/45/7/307, 45, 7, 1127-1142, 2003.07, 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.. |
| 96. | T Ido, K Kamiya, Y Miura, Y Hamada, A Nishizawa, Y Kawasumi, Observation of the fast potential change at L-H transition by a heavy-ion-beam probe on JFT-2M, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.88.055006, 88, 5, 2002.02, [URL], 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.. |
| 97. | Y Miura, T Ido, K Kamiya, Y Hamada, Relations among potential change, fluctuation change and transport barrier in the JFT-2M tokamak, NUCLEAR FUSION, 10.1088/0029-5515/41/8/301, 41, 8, 973-979, 2001.08, 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.. |
| 98. | K Kamiya, Y Miura, K Tsuzuki, T Ido, Y Hamada, T Nakayama, Development of mesh probe for the calibration of the HIBP diagnostic system in the JFT-2M tokamak, REVIEW OF SCIENTIFIC INSTRUMENTS, 72, 1, 579-582, 2001.01, 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.. |
| 99. | T Ido, K Kamiya, Y Miura, Y Hamada, A Nishizawa, Y Kawasumi, Temporal behaviour of the potential and fluctuations at the L-H transition on JFT-2M, PLASMA PHYSICS AND CONTROLLED FUSION, 42, A309-A315, 2000.05, 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.. |
| 100. | T Ido, K Kamiya, Y Hamada, A Nishizawa, Y Kawasumi, Y Miura, Behaviour of sample volumes of the heavy ion beam probe on JFT-2M, PLASMA PHYSICS AND CONTROLLED FUSION, 10.1088/0741-3335/41/8/307, 41, 8, 1013-1024, 1999.08, [URL], 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.. |
| 101. | T Ido, Y Hamada, A Nishizawa, Y Kawasumi, Y Miura, K Kamiya, Heavy ion beam probe diagnostic system on JFT-2M, REVIEW OF SCIENTIFIC INSTRUMENTS, 10.1063/1.1149474, 70, 1, 955-958, 1999.01, [URL], 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].. |
| 102. | 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, Strong electron heating in CHS ICRF heating experiments, Nuclear Fusion, 10.1088/0029-5515/37/1/I12, 37, 1, 53-68, 1997.01, 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.. |
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