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Title: Stabilization of the external kink and control of the resistive wall mode in tokamaks

Abstract

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,more » 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.}« less

Authors:
; ; ;  [1]; ; ; ; ; ; ; ;  [2];  [3]; ;  [4];  [5];  [6]
  1. Columbia University, New York, New York 10027 (United States)
  2. General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States)
  3. The University of Texas at Austin, Austin, Texas 87812 (United States)
  4. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)
  5. Oak Ridge National Laboratory, Oak Ridge, Tennessee 73831 (United States)
  6. Lawrence Livermore National Laboratory, Livermore, California 94551 (United States)
Publication Date:
OSTI Identifier:
344923
Report Number(s):
CONF-981127-
Journal ID: PHPAEN; ISSN 1070-664X; TRN: 99:005508
Resource Type:
Journal Article
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 6; Journal 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
Subject:
70 PLASMA PHYSICS AND FUSION; PLASMA INSTABILITY; KINK INSTABILITY; PLASMA CONFINEMENT; TOKAMAK DEVICES; PLASMA DIAGNOSTICS; THERMONUCLEAR REACTOR WALLS; WALL EFFECTS; STABILIZATION

Citation Formats

Garofalo, A M, Bialek, J, Navratil, G A, Sabbagh, S A, Turnbull, A D, Strait, E J, Chu, M S, La Haye, R J, Lao, L L, Scoville, J T, Taylor, T S, Walker, M L, Austin, M E, Fredrickson, E, Okabayashi, M, Lazarus, E A, and Rice, B W. Stabilization of the external kink and control of the resistive wall mode in tokamaks. United States: N. p., 1999. Web. doi:10.1063/1.873495.
Garofalo, A M, Bialek, J, Navratil, G A, Sabbagh, S A, Turnbull, A D, Strait, E J, Chu, M S, La Haye, R J, Lao, L L, Scoville, J T, Taylor, T S, Walker, M L, Austin, M E, Fredrickson, E, Okabayashi, M, Lazarus, E A, & Rice, B W. Stabilization of the external kink and control of the resistive wall mode in tokamaks. United States. doi:10.1063/1.873495.
Garofalo, A M, Bialek, J, Navratil, G A, Sabbagh, S A, Turnbull, A D, Strait, E J, Chu, M S, La Haye, R J, Lao, L L, Scoville, J T, Taylor, T S, Walker, M L, Austin, M E, Fredrickson, E, Okabayashi, M, Lazarus, E A, and Rice, B W. Sat . "Stabilization of the external kink and control of the resistive wall mode in tokamaks". United States. doi:10.1063/1.873495.
@article{osti_344923,
title = {Stabilization of the external kink and control of the resistive wall mode in tokamaks},
author = {Garofalo, A M and Bialek, J and Navratil, G A and Sabbagh, S A and Turnbull, A D and Strait, E J and Chu, M S and La Haye, R J and Lao, L L and Scoville, J T and Taylor, T S and Walker, M L and Austin, M E and Fredrickson, E and Okabayashi, M and Lazarus, E A and Rice, B W},
abstractNote = {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.}},
doi = {10.1063/1.873495},
journal = {Physics of Plasmas},
number = 5,
volume = 6,
place = {United States},
year = {1999},
month = {5}
}