Plasma edge fluid models for recycling at near tangential surfaces

2D-plasma edge fluid modeling has become a common tool to investigate aspec ts of plasma surface interaction (PSI) in fusion devices. Recycling at expo sed surfaces is included, typically, via Bokm-type boundary conditions for the plasma flow held along the B-field. Only very crude prescriptions are i n use for near tangential surfaces. Such structures are, however, crucial f or limiter configurations, for the baffles in diverters and for main chambe r recycling. Experimentally the recycling at web surfaces is often found to be much stronger than predicted if sheath theory is extrapolated to very s mall field line inclination angles. In this paper we present extensions of the B2-EIRENE code system to study such effects in detail, and we apply thi s to evaluate, quantitatively, some of the assumptions behind one particula r ('funneling-') model proposed earlier for plasma fluxes onto tangential s urfaces. (C) 2001 Elsevier Science B.V. All rights reserved.