CORE DIVERTOR/WALL PARTICLE DYNAMICS IN THE DIII-D TOKAMAK/

A wall model developed for the analysis of Tore Supra wall loading exp eriments has been applied to an experiment on DIII-D which demonstrate d a substantial capacity for retention of deuterium gas in an all-grap hite environment, and which showed the efficacy of the pumped divertor to deplete a gas-loaded wall. The Tore Supra model has been extended and applied to evaluate the particle exchange mechanisms between the c ore, divertor, and wall. Data-constrained plasma modeling is done for the discharges of the load/unload sequence. The poloidal distribution of the charge exchange flux profile to the divertor and outer wall is determined from the Eirene neutral transport code, to estimate the eff ective working areas for particle exchange and saturation. The deposit ion and saturation of the hydrogenic efflux in the aC:H layer and grap hite is modeled with the 1-D WDIFFUSE code, applied to the regions fue lled by charge exchange flux to predict the instantaneous local wall r ecycling coefficient. A mechanism is proposed to explain the previous paradoxical result that exhaust quickly (similar to 3 s) balances the only particle input, due to beam fueling, whereas a long term net wall depletion is observed over similar to 10 discharges. The saturation a nd depletion of wall layers fuelled by energetic charge exchange parti cles provides such a mechanism.