PPPL-3828 is available in <a href="PPPL-3828.pdf">pdf</a> format (1.2 MB).

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<b> Theory and Observations of High Frequency Alfv&#233;n Eigenmodes in Low Aspect Ratio Plasmas </b>
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<b>Authors:</b> N.N. Gorelenkov, E. Fredrickson, E. Belova, C.Z. Cheng, D. Gates, S. Kaye, and R. White
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<b>Date of PPPL Report:</b> June 2003
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<b>Published:</b> Nuclear Fusion <b>43</b> (April 2003) 228-233.</p>


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New observations of sub-cyclotron frequency instability in low aspect ratio plasma in National Spherical Torus Experiments (NSTX) are reported. The frequencies of observed instabilities correlate with the characteristic Alfv&#233;n velocity of the plasma. A theory of localized Compressional Alfv&#233;n Eigenmodes (CAE) and Global shear Alfv&#233;n Eigenmodes (GAE) in low aspect ratio plasma is presented to explain the observed high frequency instabilities. CAE's/GAE's are driven by the velocity space gradient of energetic super-Alfv&#233;n beam ions via Doppler shifted cyclotron resonances. One of the main damping mechanisms of GAE's, the continuum damping, is treated perturbatively within the framework of ideal MHD. Properties of these cyclotron instabilities ions are presented.


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