Rotational Stabilization of Resistive Wall Mode on JT-60U

Abstract

We have carried out experiments to clarify the stabilizing effect of a plasma rotation on the resistive wall mode (RWM) that could limit the achievable-βN in high-βN plasmas above the no-wall ideal βN-limit. On JT-60U plasma rotations are controlled using neutral beams with varying combinations of net torque input while keeping βN constant. The RWM is destabilized as the plasma rotation is being reduced. Detailed measurements of the mode structure revealed that the RWM has a global structure that rotates with the order of the resistive wall time. In these experiments, it is found that the critical toroidal rotation speed for the RWM stabilization is less than 1% of the Alfvén speed. Moreover, the critical rotation does not strongly depend on βN. The results suggest that high-βN operation up to the ideal wall βN-limit could be possible by suppressing the RWM with a slow plasma rotation in fusion reactors.