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

Abstract

A sputtering erosion analysis was performed for the tilted plate divertor design of the proposed TPX tokamak. High temperature (-100 eV), non-radiative, steady-state compatible, plasma edge conditions were used as input to the REDEP erosiodredeposition code. For the reference carbon surface the results show a stable erosion profile, i.e., non-runaway selfsputtering, in spite of carbon self-sputtering coefficients that are locally in excess of unity. The resulting net erosion rates are high (peak =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.

First measurements of the ion energy distribution at the divertor strike point during DIII-D disruptions

“…The angular and energy distribution of ions impinging on the divertor plate is. needed in order to calculate and benchmark surface erosion, in plasma transport, and redeposition of impurity atoms/ions due to sputtering [1,2]. The ion distribution near the target plate also controls the thickness of the vapor shield [3] and the erosion rate.…”