| P11 · Observation of Compressional Alfven Eigenmodes
in a Conventional Tokamak W.W. Heidbrink1, M.S. Kim1, E.D. Fredrickson2, N.N. Gorelenkov2, T. Rhodes3, G. Wang3, M.A. VanZeeland4 1University of California, Irvine
2Princeton Plasma Physics Laboratory
3University of California, Los Angeles
4ORISE
Abstract: Fast-ion instabilities with frequencies somewhat below the ion cyclotron frequency occur frequently in spherical tokamaks such as the National Spherical Torus Experiment (NSTX). NSTX and the DIII-D tokamak are nearly ideal for fast-ion similarity experiments, having similar neutral beams, fast-ion to Alfven speed vf/vA, fast-ion pressure, and shape of the plasma, but with a factor of two difference in the major radius. When DIII-D is operated at low field (0.6 T), compressional Alfven eigenmode (CAE) instabilities appear that closely resemble the NSTX instabilities. In particular, the mode frequencies, polarization, and beam-energy threshold are nearly identical to NSTX. CAE in high-field discharges and
emission at cyclotron harmonics are also observed. As on NSTX, the basic stability properties are consistent with the idea that the instability is driven by anisotropy in the fast-ion velocity distribution and is damped predominately by Landau damping of electrons. The results suggest that these modes could be unstable in ITER.
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