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Cross-machine comparison of ressonant field amplification and resistive wall mode stabilization by plasma rotation |
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Reimerdes, H., T.C. Hender, S.A. Sabbagh, J.M. Bialek, M.S. Chu, A.M. Garofalo, M.P. Gryaznevich, D.F. Howell, G.L. Jackson, R.J. La Haye, Y.Q. Liu, J.E. Menard, G.A. Navratil, M. Okabayashi, S.D. Pinches, A.C. Sontag, E.J. Strait, W. Zhu, M. Bigi, M. de Baar, P. de Vries, D.A. Gates, P. Gohil, R.J. Groebner, D. Mueller, R. Raman, J.T. Scoville, W.M. Solomon, the DIII-D Team, JET-EFDA Contributors e a Equipa NSTX |
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2006 |
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DOI |
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Resumo |
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Dedicated experiments in the DIII-D tokamak J. L. Luxon, Nucl. Fusion, 42, 614 (2002), the Joint
European Torus (JET) (P. H. Rebut, R. J. Bickerton, and B. E. Keen, Nucl. Fusion 25, 1011 (1985)],
and the National Spherical Torus Experiment (NSTX) [M. Ono, S. M. Kaye, Y.-K. M. Peng et al.,
Nucl. Fusion 40, 557 (2000)] reveal the commonalities of resistive wall mode (RWM) stabilization
by sufficiently fast toroidal plasma rotation in devices of different size and aspect ratio. In each
device the weakly damped n=1 RWM manifests itself by resonant field amplification (RFA) of
externally applied n=1 magnetic fields, which increases with the plasma pressure. Probing DIII-D
and JET plasmas with similar ideal magnetohydrodynamic (MHD) stability properties with
externally applied magnetic n=1 fields, shows that the resulting RFA is independent of the machine
size. In each device the drag resulting from RFA slows the toroidal plasma rotation and can lead to
the onset of an unstable RWM. The critical plasma rotation required for stable operation in the
plasma center decreases with increasing q95, which is explained by the inward shift of q surfaces
where the critical rotation remains constant. The quantitative agreement of the critical rotation
normalized to the inverse Alfvén time at the q=2 surface in similar DIII-D and JET plasmas
supports the independence of the RWM stabilization mechanism of machine size and indicates the
importance of the q=2 surface. At low aspect ratio the required fraction of the Alfvén velocity
increases significantly. The ratio of the critical rotation in similar NSTX and DIII-D plasmas can be
explained by trapped particles not contributing to the RWM stabilization, which is consistent with
stabilization mechanisms that are based on ion Landau damping. Alternatively, the ratio of the
required rotation to the sound wave velocity remains independent of aspect ratio. |
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