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Author(s):
K. Ida, M. Osakabe, K. Tanaka, T. Minami, S. Nishimura, S. Okamura, A. Fujisawa, Y. Yoshimura, S. Kubo, R. Akiyama, D.S.Darrow, H. Idei, H. Iguchi, M. Isobe, S. Kado, T. Kondo, S. Lee, K. Matsuoka, S. Morita, I. Nomura, S. Ohdachi, M. Sasao, A. Shimizu, K. Tumori, S. Takayama, M. Takechi, S. Takagi, C. Takahashi, K. Toi and T. Watari
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Title:
Transition from L Mode to High Ion Temperature Mode in CHS Heliotron/Torsatron Plasmas
Date of publication:
Oct. 1998
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Key words:
IAEA, fusion energy conference, Yokohama
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Abstract:
A high ion temperature mode (high T_i mode) is observed for neutral beam heated plasmas in the Compact Helical System (CHS) Heliotron/torsatron. The high T_i mode plasma is characterized by a high central ion temperature, T_i(0), and is associated with a peaked electron density profile produced by neutral beam fueling with low wall recycling. Transition from L mode to high T_i mode has been studied in CHS. The central ion temperature in the high T_i mode discharges reaches to 1 keV which is 2.5 times higher than that in the L mode discharges. The ion thermal diffusivity is significantly reduced by a factor of more than 2 - 3 in the high T_i mode plasma. The ion loss cone is observed in neutral particle flux in the energy range of 1 - 6 keV with a narrow range of pitch angle (90 pm 10 degree) in the high T_i mode. However, the degradation of ion energy confinement due to thls loss cone is negligible.
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