Modeling of Impurity Sourcing and Transport from High-Temperature Silicon Carbide Walls for Next-Step Tokamaks

Simulations of a DIII-D size tokamak with high-temperature silicon carbide (SiC) walls demonstrate reduced plasma-facing component (PFC) erosion rates and upstream impurity accumulation relative to all-graphite PFCs. The total erosion of SiC is reduced by 10× relative to graphite at a divertor surface temperature 800 K. The upstream impurity content also decreases from 2.4% to 0.7% but the higher mass of Si implies similar values of Z-effective (~1.5) between the two cases. Impurity source rates and upstream density decrease at 1000-1200 K for graphite PFCs but not for the SiC cases since most of the erosion is via physical sputtering. Background plasmas were generated with the SOLPS-ITER code package using the DIII-D geometry (3 MW heating power) and then coupled to the DIVIMP impurity transport model. Inclusion of drifts in the favorable B×▽B direction results in minimal changes to the divertor density but increases upstream impurity densities by a factor of 2× due to changes in the parallel force balance. Results are sensitive to the surface temperature of both the inner and outer targets but not the main walls. Parameter scans to higher heating power and in the unfavorable B×▽B drift direction will also be presented.