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Author(s):
K. Toi, S. Okamura, H. Iguchi, H. Yamada, S. Morita, S. Sakakibara, K. Ida, K. Nishimura, K. Matsuoka, R. Akiyama, H. Arimoto, M. Fujiwara, M. Hosokawa, H. Idei, O. Kaneko, S. Kubo, A. Sagara, C. Takahashi, Y. Takeiri, Y. Takita, K. Tsumori, I. Yamada and H. Zushi
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Title:
Formation of H-mode Like Transport Barrier in the CHS Heliotron / Torsatron
Date of publication:
Oct. 1992
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Key words:
H-mode, transport barrier, heliotron/torsatron, rotational transform, confinement improvement, edge localized modes, threshold plasma current, edge poloidal rotation
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Abstract:
Control of rotational transform profile with a small ohmic heating ( OH-) current to increase the rotational transform has led to a continuous rise in the line-averaged electron density with reduction of H alpha-lights around the torus, in a heliotron/torsatron plasma heated by neutral beams. During the density rise, the transport barrier with steep temperature and density gradients near the plasma edge has been formed. Edge localized modes ( ELM )-like activity is also observed. Incoherent magnetic fluctuations in the frequency range f > 20 kHz are clearly suppressed during the density rise phase, while low frequency coherent part remains almost unchanged. Global energy confinement time in the density rise phase is improved by ~15 %, compared with that of the discharge without the OH-current. These experimental observations are very similar to the H-mode in tokamaks. There is a threshold of the current for the transition, where the increment of rotational transform by the threshold current corresponds to ~ 0.1 at the edge. No obvious increase in the edge poloidal rotation velocity, however, is observed during the density rise phase, that is, at most ~ 3 km/s.
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