Stabilization of the external kink and control of the resistive wall mode in tokamaks
- Columbia University, New York, New York 10027 (United States)
- General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States)
- The University of Texas at Austin, Austin, Texas 87812 (United States)
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)
- Oak Ridge National Laboratory, Oak Ridge, Tennessee 73831 (United States)
- Lawrence Livermore National Laboratory, Livermore, California 94551 (United States)
One promising approach to maintaining stability of high beta tokamak plasmas is the use of a conducting wall near the plasma to stabilize low-{ital n} ideal magnetohydrodynamic instabilities. However, with a resistive wall, either plasma rotation or active feedback control is required to stabilize the more slowly growing resistive wall modes (RWMs). Previous experiments have demonstrated that plasmas with a nearby conducting wall can remain stable to the n=1 ideal external kink above the beta limit predicted with the wall at infinity. Recently, extension of the wall stabilized lifetime {tau}{sub L} to more than 30 times the resistive wall time constant {tau}{sub w} and detailed, reproducible observation of the n=1 RWM have been possible in DIII-D [Plasma Physics and Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1986), p. 159] plasmas above the no-wall beta limit. The DIII-D measurements confirm characteristics common to several RWM theories. The mode is destabilized as the plasma rotation at the q=3 surface decreases below a critical frequency of 1{endash}7 kHz ({approximately}1{percent} of the toroidal Alfv{acute e}n frequency). The measured mode growth times of 2{endash}8 ms agree with measurements and numerical calculations of the dominant DIII-D vessel eigenmode time constant {tau}{sub w}. From its onset, the RWM has little or no toroidal rotation ({omega}{sub mode}{le}{tau}{sub w}{sup {minus}1}{lt}{omega}{sub plasma}), and rapidly reduces the plasma rotation to zero. These slowly growing RWMs can in principle be destabilized using external coils controlled by a feedback loop. In this paper, the encouraging results from the first open loop experimental tests of active control of the RWM, conducted in DIII-D, are reported. {copyright} {ital 1999 American Institute of Physics.}
- OSTI ID:
- 344923
- Report Number(s):
- CONF-981127-; ISSN 1070-664X; TRN: 99:005508
- Journal Information:
- Physics of Plasmas, Vol. 6, Issue 5; Conference: 40. annual physics of plasmas meeting, APS Division of Plasma Physics, New Orleans, LA (United States), 16-20 Nov 1998; Other Information: PBD: May 1999
- Country of Publication:
- United States
- Language:
- English
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