Active Stabilization of the Resistive-Wall Mode in High-Beta, Low-Rotation Plasmas

The resistive-wall mode is actively stabilized in the National Spherical Torus Experiment in high-beta plasmas rotating significantly below the critical rotation speed for passive stability and in the range predicted for the International Thermonuclear Experimental Reactor. Variation of feedback stabilization parameters shows mode excitation or suppression. Stabilization of toroidal mode number unity did not lead to instability of toroidal mode number two. The mode can become unstable by deforming poloidally, an important consideration for stabilization system design.