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Title: Off-axis fishbone-like instability and excitation of resistive wall modes in JT-60U and DIII-D

Abstract

An energetic-particle (EP)-driven ''off-axis-fishbone-like mode (OFM)'' often triggers a resistive wall mode (RWM) in JT-60U and DIII-D devices, preventing long-duration high-{beta}{sub N} discharges. In these experiments, the EPs are energetic ions (70-85 keV) injected by neutral beams to produce high-pressure plasmas. EP-driven bursting events reduce the EP density and the plasma rotation simultaneously. These changes are significant in high-{beta}{sub N} low-rotation plasmas, where the RWM stability is predicted to be strongly influenced by the EP precession drift resonance and by the plasma rotation near the q=2 surface (kinetic effects). Analysis of these effects on stability with a self-consistent perturbation to the mode structure using the MARS-K code showed that the impact of EP losses and rotation drop is sufficient to destabilize the RWM in low-rotation plasmas, when the plasma rotation normalized by Alfven frequency is only a few tenths of a percent near the q=2 surface. The OFM characteristics are very similar in JT-60U and DIII-D, including nonlinear mode evolution. The modes grow initially like a classical fishbone, and then the mode structure becomes strongly distorted. The dynamic response of the OFM to an applied n=1 external field indicates that the mode retains its external kink character. These comparative studiesmore » suggest that an energetic particle-driven 'off-axis-fishbone-like mode' is a new EP-driven branch of the external kink mode in wall-stabilized plasmas, analogous to the relationship of the classical fishbone branch to the internal kink mode.« less

Authors:
; ; ;  [1]; ; ; ;  [2]; ; ; ;  [3]; ;  [4];  [5];  [6]; ; ;  [7]
  1. Princeton Plasma Physics Laboratory, PO Box 451, Princeton, New Jersey 08543-0451 (United States)
  2. Japan Atomic Energy Agency, 801-1, Mukouyama, Naka, Ibaraki 311-0193 (Japan)
  3. General Atomics, PO Box 85608, San Diego, California 92186-5608 (United States)
  4. Department of Physics and Astronomy, University of California-Irvine, Irvine, California 92697 (United States)
  5. FAR-TECH, Inc., 3550 General Atomics Ct, San Diego, California 92121 (United States)
  6. Euratom/CCFE Fusion Association, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom)
  7. Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027-6900 (United States)
Publication Date:
OSTI Identifier:
21537875
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 18; Journal Issue: 5; Other Information: DOI: 10.1063/1.3575159; (c) 2011 American Institute of Physics
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BEAM INJECTION HEATING; DOUBLET-3 DEVICE; EXCITATION; FISHBONE INSTABILITY; HIGH-BETA PLASMA; JT-60U TOKAMAK; KINK INSTABILITY; PLASMA PRESSURE; CLOSED PLASMA DEVICES; ENERGY-LEVEL TRANSITIONS; HEATING; INSTABILITY; PLASMA; PLASMA HEATING; PLASMA INSTABILITY; PLASMA MACROINSTABILITIES; THERMONUCLEAR DEVICES; TOKAMAK DEVICES

Citation Formats

Okabayashi, M., Solomon, W. M., Budny, R. V., Manickam, J., Matsunaga, G., Takechi, M., Asakura, N., Shinohara, K., Grassie, J. S. de, Strait, E. J., Jackson, G. L., La Haye, R. J., Heidbrink, W. W., Zhu, Y. B., In, Y., Liu, Y. Q., Reimerdes, H., Hanson, J. M., and Lanctot, M. J. Off-axis fishbone-like instability and excitation of resistive wall modes in JT-60U and DIII-D. United States: N. p., 2011. Web. doi:10.1063/1.3575159.
Okabayashi, M., Solomon, W. M., Budny, R. V., Manickam, J., Matsunaga, G., Takechi, M., Asakura, N., Shinohara, K., Grassie, J. S. de, Strait, E. J., Jackson, G. L., La Haye, R. J., Heidbrink, W. W., Zhu, Y. B., In, Y., Liu, Y. Q., Reimerdes, H., Hanson, J. M., & Lanctot, M. J. Off-axis fishbone-like instability and excitation of resistive wall modes in JT-60U and DIII-D. United States. doi:10.1063/1.3575159.
Okabayashi, M., Solomon, W. M., Budny, R. V., Manickam, J., Matsunaga, G., Takechi, M., Asakura, N., Shinohara, K., Grassie, J. S. de, Strait, E. J., Jackson, G. L., La Haye, R. J., Heidbrink, W. W., Zhu, Y. B., In, Y., Liu, Y. Q., Reimerdes, H., Hanson, J. M., and Lanctot, M. J. Sun . "Off-axis fishbone-like instability and excitation of resistive wall modes in JT-60U and DIII-D". United States. doi:10.1063/1.3575159.
@article{osti_21537875,
title = {Off-axis fishbone-like instability and excitation of resistive wall modes in JT-60U and DIII-D},
author = {Okabayashi, M. and Solomon, W. M. and Budny, R. V. and Manickam, J. and Matsunaga, G. and Takechi, M. and Asakura, N. and Shinohara, K. and Grassie, J. S. de and Strait, E. J. and Jackson, G. L. and La Haye, R. J. and Heidbrink, W. W. and Zhu, Y. B. and In, Y. and Liu, Y. Q. and Reimerdes, H. and Hanson, J. M. and Lanctot, M. J.},
abstractNote = {An energetic-particle (EP)-driven ''off-axis-fishbone-like mode (OFM)'' often triggers a resistive wall mode (RWM) in JT-60U and DIII-D devices, preventing long-duration high-{beta}{sub N} discharges. In these experiments, the EPs are energetic ions (70-85 keV) injected by neutral beams to produce high-pressure plasmas. EP-driven bursting events reduce the EP density and the plasma rotation simultaneously. These changes are significant in high-{beta}{sub N} low-rotation plasmas, where the RWM stability is predicted to be strongly influenced by the EP precession drift resonance and by the plasma rotation near the q=2 surface (kinetic effects). Analysis of these effects on stability with a self-consistent perturbation to the mode structure using the MARS-K code showed that the impact of EP losses and rotation drop is sufficient to destabilize the RWM in low-rotation plasmas, when the plasma rotation normalized by Alfven frequency is only a few tenths of a percent near the q=2 surface. The OFM characteristics are very similar in JT-60U and DIII-D, including nonlinear mode evolution. The modes grow initially like a classical fishbone, and then the mode structure becomes strongly distorted. The dynamic response of the OFM to an applied n=1 external field indicates that the mode retains its external kink character. These comparative studies suggest that an energetic particle-driven 'off-axis-fishbone-like mode' is a new EP-driven branch of the external kink mode in wall-stabilized plasmas, analogous to the relationship of the classical fishbone branch to the internal kink mode.},
doi = {10.1063/1.3575159},
journal = {Physics of Plasmas},
number = 5,
volume = 18,
place = {United States},
year = {Sun May 15 00:00:00 EDT 2011},
month = {Sun May 15 00:00:00 EDT 2011}
}