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(EX/S2-1) Resistive Wall Stabilization of High Beta Plasmas in DIII-D

E.J. Strait1), J. Bialek2), N. Bogatu3), M. Chance4), M.S. Chu1), D. Edgell3), A.M. Garofalo2), G.L. Jackson1), T.H. Jensen1), L.C. Johnson4), J.S. Kim3), R.J. La Haye1), G. Navratil2), M. Okabayashi4), H. Reimerdes2), J.T. Scoville1), A.D. Turnbull1), M.L. Walker1), DIII-D Team
1) General Atomics, San Diego, USA
2) Columbia University, New York, New York, USA
3) Fartech, Inc., San Diego, USA
4) Princeton Plasma Physics Laboratory, Princeton, New Jersey, USA

Abstract.  Recent DIII-D experiments have demonstrated sustained stable operation well above the free-boundary stability limit. The n=1 ideal kink mode is stabilized at high beta by a resistive wall and a combination of plasma rotation and active feedback, or by rotation alone. The key to this achievement has been to minimize resonant asymmetries of the magnetic field. Theory predicts that a resonant plasma response to any static n=1 field asymmetry will enhance the drag on plasma rotation at high beta, leading to loss of rotation followed by growth of an instability. This resonant plasma response has been directly observed in DIII-D experiments, and a new technique makes use of the resonant response to reduce the magnetic field asymmetry through feedback control. With reduction of the resonant drag, beta has been sustained at more than 1.5 times the free-boundary stability limit for longer than 1 s. The ideal wall-stabilized beta limit has been reached, at approximately twice the free-boundary limit. *Work supported by U.S. Department of Energy under Contracts DE-AC03-99ER54464, DE-AC05-00OR22725, and Grant DE-FG02-89ER53297.

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IAEA 2003