Divertor helium pumping in TdeV-96 under various conditions

In this paper, we report on the effects of density, divertor geometry and E CRH heating on divertor pressure and helium enrichment. Low, medium and hig h (semi-detached) densities were investigated with outboard pumping (OB) an d private region pumping (PR). For OH discharges, density and geometry effe cts are compared with B2-EIRENE simulations. There is general agreement wit h experiments, except for the high density, private region pumping case whe re the experimental enrichment is lower than predicted. We studied the effe ct of H- and L-modes on He pumping. L-modes gave the highest divertor press ures and enrichment. H-modes did not affect appreciably the total pressure but the enrichment decreased. Finally, the effects of baffling, biasing and divertor fuelling are discussed; and a comparison is made between a two-re servoir and four-reservoir model for particle balance. (C) 1999 Elsevier Sc ience B.V. All rights reserved.