Quasi-steady State High Confinement at High Density by LH Waves in the HT-6M Tokamak

摘要

The quasi-steady-state (t_H> 10_(τEoh)) H-mode with high plasma density (ELMy and ELMy free) wasrnroutinely obtained by the injection of Lower Hybrid Heating (LHH) and Lower Hybrid Current Drive (LHCD) withrna power threshold of 50 kW . The antenna spectrum was scanned in wide range and tE was about 1.5～2.0 times ofrnthe L-mode scaling. The density increases almost three times during the H-phase by gas puffing and the particlernconfinement time increases more than two times even with a line average density of 3×10~(13)cm~(-3) , which is about 60%rnthe Greenwald density limit. A hollow T_e profile was achieved in the high density case. The experimental resultsrnreproducibly show a good agreement with the theoretical prediction for the LH off-axis power deposition profile.rnWhen a certain of fraction of the plasma current is non-inductively sustained by the LH waves, a hollow currentrndensity profile is formed and the magnetic shear is reversed. This off-axis hollow current profile and enhancedrnconfinement improvement are attributed to a strong reduction of electron thermal diffusivity in the reversed shearrnregion.