The Relative Importance of Wall and Target Impurity Sources in Divertor Tokamaks

Abstract

Experiments in JET operated with X-point discharges have shown that wallproduced impurity influxes can be significantly more effective at contaminating the core plasma than plate-produced influxes. The DlVlMP (Wertor b u r i t y ) Monte Carlo impurity productionfiransport code is used to study core contamination efficiency assuming a wide variety of models/assurnptions for the plasma edge behaviour, including forced fuel recirculation (pumped divertor mode) and spontaneous flow reversal. It is found that for an open (X-point) divertor geometry and for plasma conditions typical of low Tie operation that a wall source is -3-5x more effective at contaminating the core than a target source of equal strength. For high iie conditions the wall source is >lox more effective than the target source.