STUDY OF ELECTRIC-ARC EROSION OF DIVERTOR PLATES IN A TOKAMAK

The are erosion of two samples cut from an insulating tile mounted in the region of the most intense energy delivery to the divertor plate i n the DIII-D tokamak is examined. The surface material was a boron-car bide coating on a graphite base. The dimensions of the cathode-spot tr acks are determined, and the total erosion produced by an individual a re discharge is estimated. For typical dimensions of melted craters, t he parameters of the heat source are estimated. The role of polarizati on currents related to the ion inertia in carrying a current across th e magnetic field in the cathode region of the unipolar are is discusse d.