FINITE ORBIT EFFECTS IN ICRF HEATED TOKAMAK PLASMAS

A Monte Carlo investigation of ion cyclotron resonance beating of tokamak plasmas is undertaken to study the finite orbit width effects. For minority heating schemes with peaked power deposition profiles, there is a significant reduction in absorbed and transferred power in the centre of the discharge, as compared with zero orbit width calculations. The broader power absorption profiles also give rise to a large reduction of tail energy in the centre. Although the total fast ion energy content and the total thermonuclear yield are less affected, the radial profiles of these quantities differ substantially from those in the zero orbit width limit. The reduction of the power absorption in the centre with fixed wave field profiles arises because of the broadening of the orbits and the enhanced diffusion and drift of the heated ions. The importance of these effects is assessed.