β-Suppression of Alfvén Cascade Modes in the National Spherical Torus Experiment
Authors: E.D. Fredrickson, N.A. Crocker, N.N. Gorelenkov, W.W. Heidbrink, S. Kubota, F.M. Levinton, H. Yuh, J.E. Menard, and R.E. Bell
Abstract:
The coupling of Alfvén Cascade (AC) modes or reversed-shear Alfvén eigenmodes (rsAE) to Geodesic Acoustic Modes (GAM) implies that the range of the AC frequency sweep is reduced as the electron β is increased. This model provides an explanation for the otherwise surprising absence of AC modes in reverse shear NSTX plasmas, given the rich spectrum of beam-driven instabilities typically seen in NSTX. In experiments done at very low β to investigate this prediction, AC modes were seen, and as the βe was increased from shot to shot, the range of the AC frequency sweep was reduced, in agreement with this theoretical prediction.
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Presented at the Thirty-fourth EPS Conference on Plasma Physics, 2–6 July, 2007, Warsaw, Poland.
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Download PPPL-4253 July 2007 (pdf 660 kb)
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