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| IT13 · Discrete
compressional Alfvén eigenmode spectrum in tokamaks N. N. Gorelenkov1, E. D. Fredrickson2, W. W.
Heidbrink1, N. A. Crocker3,
S. Kubota3, W. A. Peebles3 1University of California, Irvine, CA, USA Abstract: The spectrum of Compressional Alfvén Eigenmodes (CAE) is analyzed and shown to be discrete in tokamaks with low aspect ratio, such as the National Spherical Torus Experiment (NSTX), as well as in the conventional tokamaks, such as DIII-D. The study is focused on recent similarity experiments on NSTX and DIII-D in which sub-cyclotron frequency instabilities of CAEs were observed at similar plasma conditions [W.W. Heidbrink, et.al. Nuclear Fusion 46, 2006, in press]. The global ideal MHD code NOVA recovers the main properties of these modes predicted by theory and observed in both devices. The discrete spectrum of CAEs is characterized by three quantum mode numbers for each eigenmode, (M;S;n), where M, S, and n are poloidal, radial and toroidal mode numbers, respectively. The expected mode frequency splitting corresponding to each of these mode numbers seems to be observed in experiments and is consistent with our numerical analysis. The polarization of the observed magnetic _eld oscillations in NSTX was measured and is also consistent with the numerical analysis, which helps to identify them as CAE activity. CAE mode structure was obtained and shown to be localized in both radial and poloidal directions with typical radial localization toward the plasma edge and poloidal localization at the low _eld side of the plasma cross section. Note: In special issue in Nuclear Fusion - volume 46, issue 10
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