ICRF wave absorption by alpha particles

Absorption of ICRF waves by alpha particles is investigated. Higher harmonic cyclotron damping of the waves is examined not only for the slowing-down distribution of alpha particles but also for the distribution given by the Fokker-Planck calculation. The right and left hand circularly polarized amplitudes of the RF electric field are taken into account in the RF diffusion coefficient. The linear absorption rate for the alpha slowing-down distribution increases with decreasing ratio of electron plasma to electron cyclotron frequency and increasing cyclotron harmonic number. Unless this absorption rate is nearly unity, the bulk formation of alpha particles results in a further increase of the rate of absorption by alphas. Fusion reactivity enhancement due to the ICRF induced ion tail and fusion energy multiplication in the presence of alpha particles are also discussed. (author). Letter-to-the-editor. 17 refs, 4 figs