Modification of Boundary Parameters and Fluctuations by IBW and LHCD in the HT-7 Tokamak

Abstract Measurements of boundary parameters and their fluctuations have been performedin ohmic (OH) plasma and Ion Bernstein Wabe (IBW) and Lower Hybrid Current Drive (LHCD)enhanced confinement plasma using a pneumatically driven Langmuir probe array on HT-7 toka-mak. In the enhanced confinement plasma, the gradients of electron density and temperaturebecome higher and a transport barrier comes into being in the vicinity of the limiter. The bound-ary potential shows a clear modification in the same region. The fluctuation levels are significantlydepressed and the coherences between fluctuations are reduced evidelltly in the enhanced plasma.Meanwhile, we obtained the spectral features and the poloidal phase velocity of fluctuations us-ing a two-point correlation technique and found obvious modifications of the turbulence and thepoloidal flow. The results suggest that the improved confinement in the IBW and LHCD en-hanced plasma is at least partially due to the modification of the boundary parameters and