SIMPLE-MODELS FOR EVALUATING THE ROLE OF ATOMIC PROCESSES IN HELIUM ENRICHMENT

An analytical solution to a one-dimensional linear kinetic transport equation (slab model) is obtained to investigate the influence of elastic collisions between neutral atoms and plasma ions on neutral gas transport under typical tokamak boundary conditions. By comparing solutions obtained for neutral helium and neutral hydrogen the possibility of local helium enrichment in divertors or pump limiters is investigated. By using a general Monte Carlo algorithm to solve the same kinetic equations, the analytical solutions are verified. Furthermore some of the simplifying approximations in the collision integral and in the boundary conditions, which were necessary to obtain closed form analytical solutions, are then removed in the Monte Carlo solution. This allows a critical assessment of such approximations.