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Author(s):
S. Morita, H. Yamada, H. Iguchi, K. Adati, R. Akiyama, H. Arimoto, M. Fujiwara, Y. Hamada, K. Ida, H. Idei, O. Kaneko, K. Kawahata, T. Kawamoto, S. Kubo, R. Kumazawa, K. Matsuoka, T. Morisaki, K. Nishimura, S. Okamura, T. Ozaki, T. Seki, M. Sakurai, S, Sakakibara, A. Sagara, C. Takahashi, Y. Takeiri, H. Takenaga, Y. Takita, K. Toi, K. Tsumori, K. Uchino, M. Ueda, T. Watari, I. Yamada
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Title:
A Role of Neutral Hydrogen in CHS Plasmas with Reheat and Collapse and Comparison with JIPP T-IIU Tokamak Plasmas
Date of publication:
Sep. 1992
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Key words:
CHS, JIPPT-IIU, neutral hydrogen, collapse, confinement improvement, IOC-mode, H-mode, density peaking, impurity accumulation
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Abstract:
Results are described on NBI plasmas of the Compact Helical System (CHS). An increase in the stored energy, which is called plasma 'reheat', is observed with density peaking when gas puffing is turned off in the high density region. A plasma collapse with large increase in radiation loss occurs even in discharges whose Z_eff values (typically, less than 2-3) do not show any increase when the gas puffing is continued. Both phenomena are basically explained by the edge electron temperature due to the difference in the amount of edge hydrogen neutrals. After turning off the gas puffing, the central electron density n_e0 shows an increase of 80% and the density peaking factor (n_e0 / bar{n}_e) changes from 1.0 to 2.0, in typical cases, and a high inward velocity of the impurities appears (v = 20 m/s). The accumulation is studied in relation to the poloidal rotation and the edge temperature. These results are compared with results from plasmas with IOC- and H-modes in the JIPPT-IIU tokamak.
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