Advances in the modeling of chemical erosion/redeposition of carbon divertors and application to the JET tritium codeposition problem

We have improved the modeling of chemically eroded carbon transport and applied this to JET and ITER. New features are: (1) coupled REDEP and ERO-JET impurity transport code calculations for sputtered wall/divertor carbon, (2) MolDyn molecular dynamics calculations of carbon/hydrocarbon particle reflection at hydrogen-saturated carbon surfaces, (3) ADAS full collisional radiative carbon ion recombination rate coefficients. At low incident particle energies relevant to chemical-erosion (∼0.1–15 eV), we predict high reflection coefficients (∼20–100%), implying more net erosion and T/C codeposition than for full-sticking models. Calculated tritium codeposition rates for the JET MkIIA divertor, using ‘reference’ chemical erosion yields of order 1% – while higher than previously estimated are well short ( X∼1/40) of published data. Possible explanations include much higher chemical erosion yields.