Simulation of transient wall pumping, fuelling effects and density control in tokamaks

Abstract

A dynamical model has been developed which solves a time-dependent coupled system of equations for the (1) plasma density and (2) hydrogenic concentrations in the implantation layer of several representative plasma facing/limiting walls in tokamaks in order to examine the density behaviour during the transient phase of discharges as well as long pulse discharges, which are dominated by the wall pumping/fuelling characteristics. A 1-D plasma particle transport code including a model for the SOL and an analytical neutral transport model has been used to describe the plasma particle transport processes. The Local Mixing Model with some adaptations has been used to describe the behaviour of the hydrogenic concentrations in the walls. The new model significantly improves the simulation of a Tore Supra experiment with a transition from limiting the plasma on the outer limiter to limiting the plasma on the inner wall compared our previous, more simple model. Long pulse discharges in Tore Supra are examined by the more simplified model to identify the dominant mechanisms for the constant particle absorption mechanisms.