Study of RWM Stability and RWM Feedback Control in Reactor Relevant Low-Rotation Discharges in DIII-D*

Advanced tokamak operation in ITER is expected to require active control of the resistive wall mode (RWM) [1]. After the re-orientation of 1 of 4 neutral beam injectors DIII-D is now ideally suited to address the stability of non-rotating high-beta plasmas. In discharges with balanced NBI heating the RWM becomes unstable at the no-wall stability limit. Only a modest increase of the plasma rotation is sufficient to remain stable beyond this limit suggesting a lower rotation threshold than anticipated from previous experiments, which used non-axisymmetic magnetic fields to lower the plasma rotation. Feedback experiments using an upgraded audio-amplifier system to stabilize the RWM in low-rotation plasmas have begun and comparisons with feedback modeling will be shown.\par \vskip6pt \noindent [1]~Y.\ Liu, et al., Nucl.\ Fusion {\bf 45}, 1131 (2005).