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(EX/C5-1) Plasma Performance and Impurity Behavior in Long Pulse Discharges on LHD

Y. Nakamura¹⁾, Y. Takeiri¹⁾, R. Kumazawa¹⁾, M. Osakabe¹⁾, T. Seki¹⁾, B.J. Peterson¹⁾, K. Ida¹⁾, H. Funaba¹⁾, M. Yokoyama¹⁾, N. Tamura¹⁾, A. Komori¹⁾, S. Morita¹⁾, K. Sato¹⁾, K. Narihara¹⁾, S. Inagaki¹⁾, T. Tokuzawa¹⁾, S. Masuzaki¹⁾, J. Miyazawa¹⁾, N. Noda¹⁾, T. Mutoh¹⁾, T. Shimozuma¹⁾, K. Kawahata¹⁾, Y. Oka¹⁾, H. Suzuki¹⁾, N. Ohyabu¹⁾, T. Akiyama²⁾, N. Ashikawa¹⁾, M. Emoto¹⁾, P. Goncharov³⁾, M. Goto¹⁾, H. Idei¹⁾, K. Ikeda¹⁾, S. Imagawa¹⁾, M. Isobe¹⁾, O. Kaneko¹⁾, H. Kawazome⁴⁾, K. Khlopenkov¹⁾, T. Kobuchi¹⁾, A. Kostrioukov¹⁾, S. Kubo¹⁾, Y. Liang¹⁾, T. Minami¹⁾, T. Morisaki¹⁾, S. Murakami¹⁾, S. Muto¹⁾, K. Nagaoka¹⁾, Y. Nagayama¹⁾, H. Nakanishi¹⁾, Y. Narushima¹⁾, K. Nishimura¹⁾, T. Notake⁵⁾, H. Nozato⁶⁾, S. Ohdachi¹⁾, S. Okamura¹⁾, T. Ozaki¹⁾, A. Sagara¹⁾, T. Saida³⁾, K. Saito¹⁾, S. Sakakibara¹⁾, R. Sakamoto¹⁾, M. Sasao¹⁾, M. Sato¹⁾, M. Shoji¹⁾, N. Takeuchi⁵⁾, K. Tanaka¹⁾, M.Y. Tanaka¹⁾, K. Toi¹⁾, Y. Torii⁵⁾ K. Tsumori¹⁾, K.Y. Watanabe¹⁾, T. Watari¹⁾, Y. Xu¹⁾, H. Yamada¹⁾, I. Yamada¹⁾, S. Yamamoto⁵⁾, T. Yamamoto⁵⁾, S. Yoshimura¹⁾, Y. Yoshimura¹⁾, M. Yoshinuma¹⁾, K. Itoh¹⁾, T. Mito¹⁾, K. Ohkubo¹⁾, I. Otake¹⁾, T. Satow¹⁾, S. Sudo¹⁾, T. Uda¹⁾, K. Yamazaki¹⁾, K. Matsuoka¹⁾, O. Motojima¹⁾, Y. Hamada¹⁾, M. Fujiwara^1)
 
1) National Institute for Fusion Science, Toki, Japan
²⁾ Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, Tokyo, Japan
³⁾ Department of Fusion Science, School of Mathematical and Physical Science, Graduate University for Advanced Studies, Hayama, Japan
⁴⁾ Graduate School of Energy Science, Kyoto University, Uji Japan
⁵⁾ Department of Energy Engineering and Science, Nagoya University, Japan
⁶⁾ Graduate School of Frontier Sciences, The University of Tokyo, Japan

Abstract.  Demonstration of high confinement and long-duration discharges is one of the most challenging issues for magnetic fusion research. The superconducting Large Helical Device (LHD) provides a new platform for solving particle and heat flux problems in steady state as well as the physics study of plasma confinement in helical devices. Since the last IAEA meeting, long pulse experiments in an extended parameter range at LHD were performed with high heating power of up to 2 MW. The operational density was extended up to 6.5×10¹⁹m^{- 3} for NBI discharges and the discharge duration up to 127 s for ICH discharges. Physics studies on confinement characteristics and impurity behavior distinguished in long pulse discharges are presented. Confinement properties were completely the same as those in short pulse discharges and high performance plasmas were maintained over a period of long time. Impurity accumulation was observed in a specific density range of around 2×10¹⁹m^{- 3} for NBI heated pure hydrogen discharges. The impurity behavior is in qualitative agreement with neoclassical impurity transport.

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