Coupled plasma-neutral transport model for the scrape-off region

Analysis of the scrape-off region requires treatment of the plasma transport along and across the field lines and inclusion of the neutral transport effects. A method for modeling the scrape-off region which uses separate models for each of these aspects that are coupled together through an iteration procedure that requires only minimal numerical effort is presented. The method is applied to estimate the neutral pumping rates in the pump-limiter and divertor options for a proposed deuterium-tritium (D-T) ignition experiment. High neutral recycling in the vicinity of the neutralizer plate dramatically affects pumping rates for both the pump-limiter and divertor. In both cases, the plasma flow into the channel surrounding the neutralizer plate is greatly reduced by the neutral recycling. The fraction of this flow that is pumped can be large, but in general it is dependent on the particular geometry and plasma conditions. It is estimated that pumping speeds approximately greater than 10(5) L/s are adequate for the exhaust requirements in the pump-limiter and the divertor cases. High neutral recycling on the front surface of the limiter tends to increase the neutral pumping rate.