Simulation of plasma flow and potential formation in the non-uniform divertor magnetic field of a stellarator

A kinetic code for simulation of collisionless magnetized plasma flow along expanding magnetic field lines to a neutralizer plate is developed and presented. A Monte Carlo description for the ion dynamics coupled with Boltzmann electrons is used to develop an iterative scheme for solution of the Vlasov equation and quasi-neutrality. The code has been used to simulate plasma flow in the edge region of stellarators with expanding magnetic field lines and neutral gas recycling at the neutralizer plate. The results show that the presence of a divergent magnetic field increases the pre-sheath potential drop above that obtained with a uniform field calculation. The increased potential drop generates an electrostatic barrier retarding the flow of high-Z impurity ions from the target plate towards the confined plasma. Neutral gas recycling increases the ion density and hence decreases the potential drop, amplifies the particle and energy fluxes to the wall, and reduces the average energy carried by each particle to the neutralizer plate. (author). 10 refs, 10 figs