Effects of Resonant Magnetic Fluctuations on Plasma Confinement in Current Carrying high-β Plasmas of LHD

Abstract

The effects of resonant magnetic fluctuations on plasma confinement have been investigated in current carrying high-β plasmas in magnetic hill configurations of the Large Helical Device. The m/n= 2/1 mode excited in core region was dominantly observed in the unstable configuration as predicted by linear theory on ideal instability, and the plasma current decreasing magnetic shear enhances the mode activity. The disappearance of the m/n = 2/1 mode was observed with an increase in plasma current, and then the plasma confinement and the beta value increase by less than 10 % with the recovery of core pressure. When the plasma current exceeds a certain value, the plasma confinement is improved by 20 % with the reduction of the amplitudes of the modes in the peripheral region in addition to the disappearance of the m/n = 2/1 mode. Then the beta value increases by 38 %. MHD activities led to no disruption even in such an unstable configuration, and the moderate plasma current mitigated the effect of MHD activity on the plasma confinement.