Anisotropic distribution function of minority tail ions generated by strong ion-cyclotron resonance heating

The highly anisotropic particle distribution function of minority tail ions driven by ion-cyclotron resonance heating at the fundamental harmonic is calculated in a two-dimensional velocity space. It is assumed that the heating is strong enough to drive most of the resonant ions above the ion–electron critical slowing-down energy. Simple analytic expressions for the tail distribution are obtained for the cases when the bounce-averaged quasilinear heating coefficient Db is assumed to be constant in pitch angle and energy, when the Doppler effect is sufficiently large to flatten the sharp pitch angle dependence in Db but the energy dependence is allowed, and when the sharp pitch angle dependence is retained. It is found that a simple constant-Db solution can be used instead of the more complicated velocity-dependent-Db solutions for many analytic purposes.