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Author(s):
O. Kaneko, S. Kubo, K. Nishimura, T. Shoji, M. Hosokawa, K. Ida, H. Idei, H. Iguchi, K. Matsuoka, S. Morita, N. Noda, S. Okamura, T. Ozaki, A. Sagara, H. Sanuki, C. Takahashi, Y. Takeiri, Y. Takita, K. Tsuzuki, H. Yamada, T. Amano, A. Ando, M. Fujiwara, K. Hanatani, A. Karita, T. Kohmoto, A. Komori, K. Masai, T. Morisaki, O. Motojima, N. Nakajima, Y. Oka, M. Okamoto, S. Sobhanian and J. Todoroki
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Title:
Confinement Characteristics of High Power Heated Plasma in CHS
Date of publication:
Sep. 1990
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Key words:
helical system, confinement, high beta, OHKAWA current, bootstrap current
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Abstract:
High-power-heated discharges in CHS are studied from the view point of optimizing the plasma performance in low-aspect-ratio heliotron/torsatron ( R/a= 100 cm/ 20 cm ) . With tangential neutral injection, the stored energy, especially the electron temperature, strongly depends on the location of magnetic axis. The optimal magnetic axis (R_{ax}=92cm) , however, does not coincide with the location where the theory predicts the most favorable drift surface (R_{ax}=88cm) . High beta plasma (< B >=1.5%) can also be obtained in inward shifted configurations at the toroidal field B_t=0.47-0.6T. The optimal location is also R_{ax}=92cm although the observed plasma center shifts outward by several cm due to Shafranov shift. So far, the obtained stored energy stays in the range that the LHD scaling predicts. This fact means that the performance of CHS. i.e. Iow-aspect-ratio helical system, is as good as other helical systems . The induced currents are observed both in ECH and NBH discharges. In NBH discharges, the currents consist of bootstrap and OHKAWA currents. In fact, the current reversal is often observed when the density is high or B_t is low, which is consistent with the theory of bootstrap current in the plateau regime.
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