Erosion/redeposition analysis: Status of modeling and code validation for semi-detached tokamak edge plasmas

We are analyzing erosion and tritium codeposition for ITER, DIII-D, and other devices with a focus on carbon divertor and metallic wall sputtering, for detached and semi-detached edge plasmas. Carbon chemical-sputtering/hydrocarbon-transport is computed in detail using upgraded models for sputtering yields, species, and atomic and molecular processes. For the DIII-D analysis this includes proton impact and dissociative recombination for the full methane and higher hydrocarbon chains. Several mixed material (Si-C doping and Be/C) effects on erosion are examined. A semi-detached reactor plasma regime yields peak net wall erosion rates of approximately 1.0 (Be), approximately 0.3 (Fe), and approximately 0.01 (W) cm/burn-yr, and approximately 50 cm/burn-yr for a carbon divertor. Net carbon erosion is dominated by chemical sputtering in the approximately 1-3 eV detached plasma zone. Tritium codeposition in divertor-sputtered redeposited carbon is high (approximately 10-20 g T/1000 s). Silicon and beryllium mixing tends to reduce carbon erosion. Initial hydrocarbon transport calculations for the DIII-D DiMES-73 detached plasma experiment show a broad spectrum of redeposited molecules with approximately 90% redeposition fraction.