Monte carlo simulation of the ISX pumped limiter

Abstract This paper presents the results of Monte Carlo simulations of the neutral particle transport inside the pumped limiters installed on the ISX Tokamak. An overview is given of both the experiment and the computer code, DEGAS, used for the calculations. Two configurations of the limiters are treated in both the pumped and the unpumped modes. A variety of scrape-off densities and temperatures typical of those observed experimentally are considered. A number of quantities of interest are calculated including the fate of the neutralized particles, the particle confinement time in the chamber, and the recycling at the neutralizer plate as well as the neutral densities, temperatures and pressures. The calculated pressures are found to be somewhat larger than those measured. The discrepancy is most probably due to uncertainty in the current of ions to the neutralizer plate. The calculations are limited by the inability to include the changes in the plasma parameters due to the neutral processes and by the 2D nature of the code compared with the definitely 3D nature of the limiters. The results and their significance in the understanding of the limiter behavior are discussed.