Sputtering erosion of beryllium coated plasma facing components - General considerations and analysis for ITER detached plasma regime

Sputtering erosion is a key performance issue for beryllium coatings in future fusion reactors. Past analysis of this subject for various edge plasma regimes - as briefly reviewed here - shows acceptable erosion only for low duty factor devices. Erosion analysis is now focusing on a very low boundary temperature ( ≤ 2 eV) 'detached plasma' regime for the International Thermonuclear Experimental Reactor (ITER) Vertical Director design. Erosion and tritium codeposition calculations are made for this regime using a coupled WBC/REDEP/DEGAS⁺ code analysis. The analysis includes calculations of low energy, oblique incidence, sputtering yields using the VFTRIM-3D code calibrated to fit recent data on D-Be sputtering. We find that beryllium performs better than carbon for detached conditions due to the absence of chemical sputtering. Beryllium performs worse than vanadium or tungsten. Net erosion rates of beryllium coated first wall components, due mainly to physical sputtering by charge exchange D-T neutrals, vary from ∼ 0 to 2 cm per burn-year along the wall. Tritium co-deposition in redeposited beryllium surface layers may be high.