Effects of an alpha particle slowing-down distribution on tokamak ballooning modes

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Abstract
Energetic trapped alpha particles interact through their precessional drift with high-mode-number ballooning modes in tokamaks. Due to the energy dependence of the precessional drift, the consequences of this interaction depend on the form of the alpha distribution function. Results are compared here for two forms of alpha distribution: a Maxwellian and a slowing-down distribution. The latter has a significantly greater influence on ballooning stability because of the larger fraction of particles in the energy range of the drift resonance. Also, due to the dependence on the critical velocity (..alpha.. T/sub e/sup 1/2/), the stability boundaries and growth rates now are strong functions of the background electron temperature T/sub e/. Parameters typical of tokamak breakeven experiments such as the Tokamak Fusion Test Reactor (TFTR) are considered. 7 refs., 7 figs.

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