Assessment of critical physical assumptions in consistent 2D plasma edge modelling

Two dimensional multifluid plasma edge transport codes, combined with complete Monte Carlo models for the neutral particles, have become a standard tool to investigate tokamak boundary layer physics. In this paper one of the most widely applied plasma edge codes, i.e. the BRAAMS (B2) code, is evaluated firstly by testing the influence of different neutral particle source term models of various degrees of sophistication, ranging from the original "minimal" analytic description in B2 to the fully three-dimensional Monte Carlo code EIRENE. Secondly, by comparison with another plasma edge transport code, the assumption of ambipolarity and the absence of diamagnetic fluxes, resulting in the omission of contributions to ion-electron energy transfer, is investigated. It is demonstrated that already in a low recycling open limiter tokamak, plasma conditions are very sensitive to details of the neutral particle transport. Therefore, it is expected to be even more sensitive in higher recycling divertor configurations. Furthermore, it is shown that the assumption of ambipolarity may lead in some circumstances to spurious features in radial profiles, in particular for the ion temperature.