Impurity transport at the DIII-D divertor strike points

Impurities are recognized as a serious problem for present and future high Q tokamak experiments. The study of the plasma boundary is therefore of increasing importance. In a tokamak fusion reactor the largest impurity source is expected at the divertor strike points. Design studies for machines, such as ITER, suggest that entrainment of these impurities in the hydrogenic flow close to the target plates will provide effective screening of the core. In this paper we discuss experiments on DIII-D which attempt to test the impurity transport predictions in the critical zone just in front of the divertor target plates. 9 refs., 6 figs