Divertor design study using LEDGE and DEGAS

The authors have used the multispecies fluid simulation code LEDGE and Monte Carlo neutral transport code DEGAS to study various divertor designs applicable to TPX and DIII-D, with the objective of optimizing the configuration with respect to radiative loss and backflow of particles to the plasma core. After the two-fluid neutrals model currently implemented in LEDGE was benchmarked by comparing its predictions for the neutral and ionization-source densities with those of DEGAS for a simple slot geometry, a fixed plasma generated by LEDGE was used as a target for several DEGAS runs. The plasma grid was large enough to include various internal DEGAS boundaries intended to simulate a variety of divertor configurations: (1) rectangular slot; (2) box, i.e., a slot with baffles perpendicular to poloidal field lines upstream from the divertor plate; (3) open-quotes venetian blinds,close quotes a series of perpendicular baffles parallel to one another. The approach attempts to take advantage of the ability of the Monte Carlo technique to deal with complicated geometries and the relative speed of fluid simulations without a full-scale iterative coupling of the two, and should give at least a qualitative measure of the relative merits of the different designs. The authors have also performed gas-target simulations with LEDGE for the divertor region of an ITER geometry using gas injection from the side walls near the divertor plate. They observed that even though temperature reduction can be accomplished, most of the power still flows to the plate