Study of MHD activity in the HT-7 superconducting tokamak

Abstract An attempt is made to explain the behavior of the magneto-hydrodynamic (MHD) instabilities observed at values of the edge safety factor 3 q ( a ) 4 , on the HT-7 superconducting tokamak. For the poloidal-magnetic-field fluctuations observed at the Mirnov coils, Mirnov-coil analysis shows that the MHD activity consists predominantly of m = 2 mode. Estimates are given for the characteristic growth time of the m = 2 mode, τ g , and the related rate of island growth, d W / d t . The experimental value of τ g is found to be smaller than the linear theoretical one, and thus satisfy the condition τ A τ g τ S (where ideal timescale is τ A , and the resistive timescale is τ S ). However, the experimental and theoretical calculation of d W / d t are found to be in reasonable agreement with each other.