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(EXP3/01(R)) Resistive Wall Mode Dynamics and Active Feedback Control in DIII-D

A. M. Garofalo¹⁾, J. Bialek¹⁾, A. H. Boozer¹⁾, M. S. Chu²⁾, E. Fredrickson³⁾, M. Gryaznevich³⁾, T. H. Jensen²⁾, L. C. Johnson⁴⁾, R. J. La Haye²⁾, G. A. Navratil¹⁾, M. Okabayashi⁴⁾, E. J. Strait²⁾, J. T. Scoville²⁾, A. D. Turnbull²⁾, and the DIII-D Team
 
¹⁾ Columbia University, New York, New York, USA
²⁾ General Atomics, San Diego, California USA
³⁾ Princeton Plasma Physics Laboratory, Princeton, New Jersey, USA
⁴⁾ UKAEA-Culham Laboratory, Abingdon, United Kingdom

Abstract.  Recent DIII-D experiments have shown that the n=1 resistive wall mode (RWM) can be controlled by an external magnetic field applied in closed loop feedback using the six element error field correction coil (C-coil). The RWM constitutes the primary limitation to normalized beta in recent DIII-D advanced tokamak plasma experiments. The toroidal rotation of DIII-D plasmas does not seem sufficient to completely suppress the RWM: a very slowly growing RWM (growth rate $\gamma$ $\ll$ 1/$\tau_{\mathrm{w}}^{}$) is often observed at normalized beta above the no-wall limit and this small RWM slows the rotation. As the rotation decreases, there is a transition to more rapid growth ( $\gamma$ $\sim$ 1/$\tau_{\mathrm{w}}^{}$). The application of magnetic feedback is able to hold the RWM to a very small amplitude, prolonging the plasma duration above the no-wall limit for durations much longer than the growth time of the RWM. These initial experimental results are being used to compare control algorithms, to benchmark models of the feedback stabilization process and to guide the design of an upgraded coil-sensor system for stabilization of the RWM at normalized beta values closer to the ideal-wall limit.

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