Impurity recycling and retention on Au and C surfaces exposed to the scrape-off layer of the TCA tokamak

Abstract

In addition to impurity trapping, surfaces exposed to the boundary layer of a tokamak and other fusion devices are subjected to erosion phenomena. On local surface regions which do not experience unipolar arcing, these processes are due to the energetic fluxes of impurity and plasma particles which induce sputtering. Data are presented on collection probe experiments in the TCA tokamak which demonstrate that this erosion behavior may be evaluated from a knowledge of the shot dependence of the areal concentrations and impact energies of the trapped particles within the surface. Furthermore, a semiempirical parameter, which we call the ‘‘impurity recycling factor’’ (k), can be used to describe impurity retention and sputtering behavior for local plasma-surface interactions. Data on impurity retention and reemission are presented with respect to the impurity recycling factor as a function of the distance from the plasma edge.