STABILITY OF RESISTIVE AND IDEAL BALLOONING MODES IN THE TEXAS-EXPERIMENTAL-TOKAMAK AND DIII-D

The stability of drift resistive ballooning modes is examined using the reduced Braginskii equations, which include electron temperature and magnetic fluctuations. The Texas Experimental Tokamak (TEXT) [Phys. Fluids B 2, 2879 (1990)] edge plasma is found to be unstable for a broad range of mode numbers. For low mode numbers (m < 70), the plasma is unstable to the drift resistive ballooning mode, which has a growth rate that scales linearly with the resistivity (gamma approximately eta). As the mode number increases, a transistion is found to the resistive ballooning mode with the usual scaling of gamma approximately eta-1/3. A similar analysis is made for parameters from DIII-D [Phys. Fluids B 2, 1405 (1990)] for both the L mode and the H mode. It is found that the L mode is unstable to the resistive mode, but beta almost-equal-to beta(I)/6, where beta(I) is the critical-beta for the ideal instability. The H mode is weakly unstable to the resistive mode and is only about a factor of 2 below the beta-threshold for the more robustly unstable ideal mode.