Divertor erosion study for TPX and implications for steady-state fusion reactors

A sputtering erosion analysis was performed for the tilted plate divertor design of the proposed TPX tokamak. High temperature ({approximately} 100 eV), non-radiative, steady-state compatible, plasma edge conditions were used as input to the REDEP erosion/redeposition code. For the reference carbon surface the results show a stable erosion profile, i.e., non-runaway self-sputtering, in spite of carbon self-sputtering coefficients that are locally in excess of unity. The resulting net erosion rates are high (peak {approx} 1--2.5 m/burn-yr) but may be acceptable for a low duty factor experimental device such as TPX. Other surface materials were also analyzed, in part to obtain insight for fusion reactor designs using a similar plasma regime. Both medium and high-Z materials are predicted not to work, due to runaway self-sputtering. Beryllium is stable but has erosion rates as high or higher than carbon. A liquid metal lithium surface has stable sputtering with a zero-erosion potential and may thus be an attractive future material choice