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(EX/S3-2) MHD Instabilities and Their Effects on Plasma Confinement in the Large Helical Device Plasmas

K. Toi1), S. Ohdachi1), S. Yamamoto2), N. Nakajima1), S. Sakakibara1), K.Y. Watanabe1), S. Inagaki1), Y. Nagayama1), Y. Narushima1), H. Yamada1), K. Narihara1), S. Morita1), T. Akiyama3), N. Asikwa1), X. Ding4), M. Emoto1), H. Funaba1), M. Goto1), K. Ida1), H. Idei1), T. Ido1), K. Ikeda1), S. Imagawa1), M. Isobe1), K. Itoh1), O. Kaneko1), K. Kawahata1), T. Kobuchi1), A. Komori1), S. Kubo1), R. Kumazawa1), J. Li5), Y. Liang1), S. Masuzaki1), T. Mito1), J. Miyazawa1), T. Morisaki1), S. Murakami1), S. Muto1), T. Mutoh1), K. Nagaoka1), Y. Nakamura1), H. Nakanishi1), K. Nishimura1), A. Nishizawa1), N. Noda1), T. Notake2), K. Ohkubo1), I. Ohtake1), N. Ohyabu1), Y. Oka1), S. Okamura1), T. Ozaki1), B.J. Peterson1), A. Sagara1), T. Saida6), K. Saito1), R. Sakamoto1), M. Sasao1), K. Sato1), M. Sato1), T. Satow1), T. Seki1), T. Shimozuma1), M. Shoji1), S. Sudo1), M.Y. Tanaka1), N. Tamura6), K. Tanaka1), K. Tsumori1), T. Uda1), T. Watari1), A. Weller7), Y. Xu1), I. Yamada1), M. Yokoyama1), S. Yoshimura1), Y. Yoshimura1), K. Yamazaki1), K. Matsuoka1), O. Motojima1), Y. Hamada1), M. Fujiwara1)
1) National Institute for Fusion Science, Toki, Japan
2) Dep. of Energy Eng. and Science, Nagoya Univ., Nagoya, Japan
3) Res. Lab. for Nucl. Reactors, Tokyo Inst. Tech., Tokyo, Japan
4) Southwestern Institute of Physics, Chengdu, China
5) Institute of Plasma Physics, Akademia Sinica, Hefei, China
6) Dep. Of Fusion Science, Graduate Univ. of Advanced Studies, Hayama, Japan
7) Max-Planck-Instutut für Plasmaphysik, Garching, Germany

Abstract.  MHD stability of NBI heated plasmas and impacts of MHD modes on plasma confinement are intensively studied in the Large Helical Device (LHD). Three characteristic MHD instabilities were observed, that is, (1) pressure driven modes excited in the plasma edge, (2) pressure driven mode in the plasma core, and (3) Alfvén eigenmodes (AEs) driven by energetic ions. MHD mode excited in the edge region accompanies multiple satellites, and is called Edge Harmonic Modes (EHMs). EHM sometimes has a bursting character. The bursting EHM transiently decreases the stored energy by about 15 percents. In the plasma core region, m=2/n=1 pressure driven mode is typically destabilized. The mode often induces internal collapse in the higher beta regime more than 1 percent. The internal collapse appreciably affects the global confinement. Energetic ion driven AEs are often detected in NBI-heated LHD plasmas. Particular AE with the frequency 8-10 times larger than TAE-frequency was detected in high beta plasmas more than 2 percent. The AE may be related to helicity-induced AE. Excitation of these three types of MHD instabilities and their impacts on plasma confinement are discussed.

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IAEA 2003