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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 ( $\rm t_H > 10 \tau_{Eoh}$) 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 $\rm\tau_E$ 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 $\rm 3 \times 10^{13} cm^{-3}$ , which is about 60% the Greenwald density limit. A hollow $\rm T_e$ 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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