Application of the low-frequency energy principle to wall modes

The effects of trapped particles on the stability of the n=1 resistive wall mode are investigated by means of a generalized energy principle. The analysis is carried out for the stationary high-β plasma equilibrium of the International Thermonuclear Experimental Reactor (ITER) [ K. Tomabechi Nucl. Fusion 31, 1135 (1991)] advanced-tokamak scenario. It is found that the trapped particle compressibility and the dissipation induced by the mode resonance with the trapped particle precession motion are stabilizing. By retaining the contribution of trapped thermal ions, electrons, and α particles, the resistive wall mode growth rate is significantly reduced and the mode almost fully suppressed. This effect vanishes for fast flowing plasmas rotating toroidally with a frequency above the ion diamagnetic frequency.