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Author(s):
S. Okamura, K. Matsuoka, K. Nishimura, K. Tsumori, R. Akiyama, S. Sakakibara, H. Yamada, S. Morita, T. Morisaki,. N. Nakajima, K. Tanaka, J. Xu, K. Ida, H. Iguchi, A. Lazaros, T. Ozaki, H. Arimoto, A. Ejiri, M. Fujiwara, H. Idei. O. Kaneko, K. Kawahata, T. Kawamoto, A. Komori, S. Kubo, O. Motojima, V.D. Pustovitov, C. Takahashi, K. Toi and I. Yamada
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Title:
High-Beta Discharges with Neutral Beam Injection in CHS
Date of publication:
May 1994
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Key words:
CHS, high beta, heliotron/torsatron, self-stablilization, titanium gettering, LHD scaling, magnetic well, Mercier stability, Shafranov shift, position control, magnetic fluctuation
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Abstract:
High-beta plasmas with a volume-averaged equilibrium beta value 2.1 % were produced in CHS using tangential neutral beam injection. This beta value was achieved with the confinement improvement (reheat mode) observed after turning off a strong gas puffing. The wall conditioning with titanium gettering was used to made a high density operation (bar{ne} &It; 8x10^19m^-3) possible for low magnetic field (B_t=0.6 T). The discharges start with the magnetic hill configuration (in vacuum) and finally get Mercier stable equilibrium due to the self-stabilization effect given by the magnetic well which is produced by the plasma pressure. The Shafranov shift was about 40% of a plasma minor radius. Magnetic fluctuations did not increase with increasing plasma pressure when beta value exceeded 1%. The dynamic poloidal field control was applied to suppress the outward plasma shift with increasing plasma pressure. Such operation gave an additional increase of beta value compared with the constant poloidal field operation.
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