Thermalization of a Fast Ion in a Plasma

The question of the precise rate of thermalization of a fast ion in a plasma is of some interest in connection with several existing or proposed controlled thermonuclear devices. In this paper we follow a fast ion which is injected into a plasma in equilibrium. Specifically, we determine the time history of the probability distribution of this ion in velocity space. This is done by numerical integration of the linearized, space-independent Fokker-Planck equation with both the ion-ion and ion-electron interaction terms retained. The mean time of thermalization is calculated for several widely separated injection velocities. Some other properties of this single-ion probability distribution are analyzed.