Temperature limit of a graphite divertor surface due to self-sputtering and radiation enhanced sublimation

The surface temperature limit of a graphite coated tokamak divertor due to particle erosion has been examined theoretically. The analysis uses models for physical sputtering, radiation enhanced sublimation, and redeposition phemomena. An upper bound on surface temperature is computed based on the necessary condition that self-sputtering be finite. The allowable graphite surface temperature is found to depend strongly on the plasma edge temperature, being limited to < or approx.800deg C for medium plasma edge temperatures (≅ 150 eV). (orig.)