STABILIZATION OF COLLISIONLESS TRAPPED-PARTICLE MODES IN TOKAMAKS

A quadratic form is derived to study the stability of collisionless trapped particle modes in tokamaks. Marginal stability criteria show that stability can be obtained by controlling the electron temperature profile. In a low aspect ratio equilibrium (such as the recently proposed Comet [Comments Plasma Phys. XII, 125 (1989)]), the stability requirement is ηc≃O(1) (ηe = ∂ ln Te/η ln ne); in a standard large aspect ratio tokamak with a broad density profile, the requirement is LTe/R≃O(1) (L Te-1 = - ∂ ln Te/∂r). Possible application of the second scenario to H-mode plasmas is noted. © 1990 American Institute of Physics.