Stability of global drift-kinetic Alfven eigenmodes in DIII-D
Global Alfven eigenmodes are studied using two different models for the plasma and the results compared with the instability threshold measured experimentally. Fluid-resistive models predict that continuum damped toroidicity induced Alfven modes (TAE) are formed in the frequency range of the experimental instabilities, but using realistic values of the resistivity makes a stability analysis impossible for computational reasons. The kinetic plasma model solves this problem by taking into account the ion Larmor radius and the resonant Landau interactions between the particles and the wavefield. As a consequence drift-kinetic Alfven eigenmodes (DKAE) are created by toroidal coupling between the global TAE wavefield, the mode converted kinetic Alfven, ion-acoustic and drift waves. The power transfers between the wave and the particles show that the drift character of the wavefield in the core destabilizes DKAE modes through resonant interactions with the fast beam ions. The predicted beam pressure instability threshold is in agreement with the one measured experimentally. (C) 1997 American Institute of Physics.