Studies on the behaviors of minority ions under ICRF wave heating

Abstract

Bounce averaged quasilinear kinetic equation is solved numerically by finete element method (FEM) to obtain the lowest order minority ion distribution function driven by an ion cyclotron range of frequency (ICRF) wave at the fundamental harmonic in tokamak geometry. The resulting solutions show similar charateristics in both energy and pitch angle profiles to previous Fokker-Planck simulation results. A reasonably simple and accurate analytical expression which can well represent the numerical solution is obtained. The analytical representation may be applicable to whole ICRF heated minority ions, since it is valid over whole region of the velocity space. The resonant minority ions can be treated as linear combinations of two(or three) separate species with different particle densities and temperatures. Neoclassical transport of energetic minority tail ions is also studied analytically. The total tail ion transport is expressed by the sum of the Coulomb collision-driven transprot and the wave-driven transport, whcih is due to the ICRF wave scattering of the tail ions as reported in the literature. In the present work the effect of coulomb collisions on the tail ion transport is investigated. The transport include both convetive and diffusive terms. It is found that the rate of radial particle transport is smaller than that of usual neoclassecal theory and the rate of radial diffusive energy transport occurs in a tail ion-electron momentum transfer time with a stepsize to be about one banana width. There are strong radially inward convective energy transport, which is driven by the gradient of the magnetic field.