Radial Dependence of the Collisional Trapped-Particle Instability

Abstract

We investigate the effects of temperature gradient and magnetic shear on the radial dependence of the collisional trapped-particle mode. The former produces a reflecting layer at the edge of the plasma, while the latter introduces fine structure in the untrapped-particle terms. It is concluded, contrary to a published result, that unstable eigenmodes are likely to occur in large Tokamaks. Untrapped-ion resonances near the rational flux surfaces provided a stabilizing effect, however.