Fusion Science and Technology / Volume 50 / Number 2 / August 2006 / Pages 177-185
Technical Paper / Stellarators
This paper describes recent progress in magnetohydrodynamics (MHD) study of high-beta plasmas of the Large Helical Device. Control of the plasma aspect ratio (Ap) in the range of 6.3 to 8.3 was done in order to optimize the configuration for high-beta plasma production and to investigate the MHD characteristics. The experiments brought a maximum average beta of 4.3% at the Ap = 6.6 configuration. MHD activities in the periphery are dominantly observed in such a high-beta region, and their amplitudes increase with decreasing magnetic Reynolds number (S) and have clear dependence on the S parameter. When the plasma aspect ratio is increased, minor collapse due to the m/n = 1/1 mode without rotation occurs. It is enhanced further by the plasma current reducing magnetic shear and degrades the beta value by >50%. The results are expected to give important information on the operation regime and the future design of the helical fusion reactor and to contribute to experimental knowledge of ideal and resistive instability.