Showing papers by "Herbert L Berk published in 2009"

Beta-induced Alfvén-acoustic eigenmodes in National Spherical Torus Experiment and DIII-D driven by beam ions

Abstract: Kinetic theory and experimental observations of a special class of energetic particle driven instabilities called here beta-induced Alfven-acoustic eigenmodes (BAAEs) are reported confirming, previous results [N. N. Gorelenkov et al., Plasma Phys. Controlled Fusion 49, B371 (2007)]. The kinetic theory is based on the ballooning dispersion relation where the drift frequency effects are retained. BAAE gaps are recovered in kinetic theory. It is shown that the observed certain low-frequency instabilities on DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] and National Spherical Torus Experiment [M. Ono, S. M. Kaye, Y.-K. M. Peng et al., Nucl. Fusion 40, 557 (2000)] are consistent with their identification as BAAEs. BAAEs deteriorate the fast ion confinement in DIII-D and can have a similar effect in next-step fusion plasmas, especially if excited together with multiple global toroidicity-induced shear Alfven eigenmode instabilities. BAAEs can also be used to diagnose safety factor profiles, a technique known as magnetohydrodynamic spectroscopy.

Drift-Wave Eigenmodes and Spectral Gaps in Tandem Mirrors

Abstract: In recent years, breakthroughs in the GAMMA-10 tandem mirror device and new designs such as the Kinetically Stabilized Tandem Mirror have renewed enthusiasm for investigation of mirror plasmas. 1 With a discrete eigenmode solver and shooting code we calculate kinetic Alfven waves in a model GAMMA-10 experiment, and then examine the nature of the spectral gaps. We validate the results of these calculations by comparing with magnetic probe signals recorded in the LAPD as a function of frequency of the antenna and the axial position.