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(CDP/15) Quasi-steady State High Confinement at High Density by LH Waves in the HT-6M Tokamak

J. Li, J. R. Luo, B. N. Wan, Y. X. Liu, F. X. Yin, X. Z. Gong, D. C. Li, S. Liu, Y. X. Jie, X. Gao, N. C. Luo, J. G. Jiang, Y. Q. Han, M. J. Wu, G. X. Wang, Y. F. Liang, A. L. Yao, Z. W. Wu, S. Y. Zhang, J. S. Mao, L. Z. Cui, Y. H. Xu, Y. D. Meng, J. Y. Zhao, B. N. Ding, G. M. Li, X. D. Xu, B. L. Lin, W. W. Yie

Institute of Plasma Physics, Academia Sinica, 230031, Hefei, P.R.China

Abstract.  The quasi-steady-state ( t_H > 10$\tau_{\mathrm{Eoh}}^{}$) H-mode with high plasma density (ELMy and ELMy free) was routinely obtained by the injection of Lower Hybrid Heating (LHH) and Lower Hybrid Current Drive (LHCD) with a power threshold of 50 kW . The antenna spectrum was scanned in wide range and $\tau_{\mathrm{E}}^{}$ was about 1.5 $\sim$ 2.0 times of the L-mode scaling. The density increases almost three times during the H-phase by gas puffing and the particle confinement time increases more than two times even with a line average density of 3×10¹³cm^{- 3} , which is about 60% the Greenwald density limit. A hollow T_e profile was achieved in the high density case. The experimental results reproducibly show a good agreement with the theoretical prediction for the LH off-axis power deposition profile. When a certain of fraction of the plasma current is non-inductively sustained by the LH waves, a hollow current density profile is formed and the magnetic shear is reversed. This off-axis hollow current profile and enhanced confinement improvement are attributed to a strong reduction of electron thermal diffusivity in the reversed shear region.

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