LOWER-HYBRID CURRENT DRIVE EFFECTS ON HT-7 SUPERCONDUCTING TOKAMAK

Lower hybrid current drive (LHCD) experiments have been done on the su perconducting Tokamak HT-7 by using a new developed long pulse megawat t lower hybrid wave system. An LHCD efficiency of 0.5 x 10(19) A.m(-2) /W in a pulse length of several hundreds of milliseconds has been achi eved. After boronization of the tokamak vacuum vessel, considerable im provements of plasma energy confinement and particle confinement durin g LHCD phase have been achieved by adjusting wave spectra. An energy t ransfer from the lower hybrid wave to plasma bulk electrons has been d emonstrated experimentally. A computer simulation of the LHCD experime nts by using a ray tracing code combined with a two dimensional Fokker -Planck code is in good accordance with experimental measurements and suggests an important role of plasma current profile.