Control of the resistive wall mode in advanced tokamak plasmas on DIII-D

Resistive wall mode (RWM) instabilities are found to be a limiting factor in advanced tokamak regimes with low internal inductance. Even small amplitude modes can affect the rotation profile and the performance of these ELMing H mode discharges. Although complete stabilization of the RWM by plasma rotation has not yet been observed, several discharges with increased beam momentum and power injection sustained good steady state performance for record durations. The first investigation of active feedback control of the RWM has shown promising results: the leakage of radial magnetic flux through the resistive wall can be successfully controlled and the duration of the high beta phase can be prolonged. The results provide a comparative test of several approaches to active feedback control, and are being used to benchmark the analysis and computational models of active control.

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