Erosion Redeposition Analysis: Status of Modeling and Code Validation for Semi-Detached Tokamak Edge Plasmas

J. Nuclear Materials, 266-269, 58-66 (1999).

Brooks, J. N., Alman, D., Federici, G., Ruzic, D. N., Whyte, D. G.

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 1.0 (Be), 0.3 (Fe), and 0.01 (W) cm/burn-yr, and 50 cm/burn-yr for a carbon divertor. Net carbon erosion is dominated by chemical sputtering in the 1–3 eV detached plasma zone. Tritium codeposition in divertor-sputtered redeposited carbon is high (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 90% redeposition fraction.