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E. J. Strait, M. S. Chu, L. L. Lao, R. J. La
Haye, J. T. Scoville, T. S. Taylor, A. D. Turnbull,
M. Walker, and the DIII-D Team
General Atomics, P.O. Box 85608, San Diego, California 92186-9784,
U.S.A.
A. Garofalo, J. Bialek, G. A. Navratil,
S. Sabbagh
Columbia University, New York, New York, U.S.A.
Princeton Plasma Physics Laboratory, Princeton, New Jersey, U.S.A.
Oak Ridge National Laboratory, Oak Ridge, Tennessee, U.S.A.
University of Texas at Austin, Austin, Texas, U.S.A.
University of Wisconsin-Madison, Madison, Wisconsin, U.S.A.
B. W. Rice
Lawrence Livermore National Laboratory, Livermore, California,
U.S.A.
Abstract. Two approaches to achieving long-time scale stabilization of the
ideal kink mode with a real, finite conductivity wall are considered: plasma
rotation and active feedback control. DIII-D experiments have demonstrated
stabilization of the resistive wall mode (RWM) by sustaining beta greater than
the no-wall limit for up to 200 ms, much longer than the wall penetration time
of a few ms. These plasmas are typically terminated by an m=3, n=1 mode as the
plasma rotation slows below a few kHz. Recent temperature profile data shows
an ideal MHD mode structure, as expected for the resistive wall mode at beta
above the no-wall limit. The critical rotation rate for stabilization is in
qualitative agreement with recent theories for dissipative stabilization in
the absence of magnetic islands. However, drag by small-amplitude RWMs or
damping of stable RWMs may contribute to an observed slowing of rotation at
high beta, rendering rotational stabilization more difficult. An initial
open-loop active control experiment, using non-axisymmetric external coils and
a new array of saddle loop detectors, has yielded encouraging results,
delaying the onset of the RWM.
IAEA 2001
