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

Journal Article · Sun May 15 04:00:00 EDT 2011 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.3575159· OSTI ID:21537875

Okabayashi, M; Solomon, W M; Budny, R V; Manickam, J ^[1]; Matsunaga, G; Takechi, M; Asakura, N; Shinohara, K ^[2]; Grassie, J S. de; Strait, E J; Jackson, G L; La Haye, R J ^[3]; Heidbrink, W W; Zhu, Y B ^[4]; In, Y ^[5]; Liu, Y Q ^[6]; Reimerdes, H; Hanson, J M; Lanctot, M J ^[7]

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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)

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.

• OSTI ID: 21537875
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 5 Vol. 18; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BEAM INJECTION HEATING
CLOSED PLASMA DEVICES
DOUBLET-3 DEVICE
ENERGY-LEVEL TRANSITIONS
EXCITATION
FISHBONE INSTABILITY
HEATING
HIGH-BETA PLASMA
INSTABILITY
JT-60U TOKAMAK
KINK INSTABILITY
PLASMA
PLASMA HEATING
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
PLASMA PRESSURE
THERMONUCLEAR DEVICES
TOKAMAK DEVICES