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Off-axis Fishbone-like Instability and Excitation of Resistive Wall Mode in JT-60U and DIII-D

M. Okabayashi ; G. Matsunaga ; M. Takechi ; J.S. deGrassie ; W.W. Heidbrink ; Y. In ; Yueqiang Liu (Institutionen för rymd- och geovetenskap, Transportteori) ; E.J. Strait ; N. Asakiura ; R. Budny ; Jackson G ; J. Hanson ; R.J. La Haye ; M.J. Lanctot ; J.Manickam ; H. Reimerdes ; K. Shinohara
Physics of Plasmas (1070-664X). Vol. 18 (2011), p. 056121.
[Artikel, refereegranskad vetenskaplig]

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-βN 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-βN 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 Alfvén 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.

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Denna post skapades 2011-12-14. Senast ändrad 2012-09-19.
CPL Pubid: 150075


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Institutioner (Chalmers)

Institutionen för rymd- och geovetenskap, Transportteori (2010-2012)



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