CONFINED ALPHA-PARTICLES NEAR THE PLASMA EDGE IN TOKAMAKS

The properties of classically confined high-energy alpha particles nea r the outer midplane of a tokamak torus are considered in order to pro vide the basic information required for theoretical studies of the sup erthermal ion cyclotron emission which has been observed in tokamak ex periments. An analytical expression for the velocity distribution func tion of fusion reaction products has been derived, which generalizes p revious results. The alpha-particle distribution function for test cas e data corresponding to typical parameters of the JET preliminary trit ium experiment has been calculated using a three-dimensional Fokker-Pl anck code and it has been shown that this function can be well approxi mated by the derived analytical expression. The number of alpha partic les produced in a pure deuterium plasma due to secondary fusion reacti ons has been evaluated. It is shown that, due to orbital effects, the local alpha-particle density in a deuterium plasma can be comparable t o the density of protons which are produced directly by the DD reactio ns.