Monte Carlo studies of charge-exchange first wall heat fluxes from neutral beam injection in tandem mirror reactors

Monte Carlo methods are employed to compute surface heat fluxes at the first walls of three representative tandem mirror reactors: TDF, TASKA-M, and MARS, resulting from charge-exchange (CX) of high power neutral beams with the fusion plasmas. The full three-dimensional nature of the anisotropic interaction processes of neutral beams with mirror-confined plasmas is retained in the calculations, and resulting CX heat fluxes are mapped both azimuthally and axially on the first wall surfaces. The angular distribution of heat fluxes at the first wall shows strong backward-peaking for TDF with maximum power densities of ～ 2.4 kW cm^?2 occurring at 180° relative to the incident beam direction. By contrast, the angular distributions for TASKA-M and MARS exhibit strong forward-peaking, resulting in hot spots of 1140 and 700 W cm^?2, respectively, at the first wall. Physical arguments are presented for the behavior of these CX heat flux distributions in terms of the plasma and beam parameters of each system. Particular emphasis is given to the engineering implications of the results and methods for ameliorating these high first wall heat fluxes are discussed.