Effect of ion loss on ICRF heating

The effect of spatial loss on ICRF (ion cyclotron range of frequency) wave heating is studied. A simple model for the energy-dependent loss term is adopted in the Fokker-Planck equation. The case of the minority ion heating by fundamental cyclotron resonance is analysed. It is found that the high energy particle loss imposes a limit on the heating power density, above which an increase in the heating power does not raise the energy transfer to the bulk particles, i.e. the heating efficiency deteriorates. This power limit is serious for losses with strong energy dependence such as ripple diffusion. Small spatial loss can annihilate the increment of the fusion reaction by tail generation.