Evaluation of Silicon Carbide Coatings as Primary Armor Material in DIII-D H-Mode Discharges

Silicon carbide coatings on ATJ graphite exposed to 25 H-mode plasma discharges with edge localized modes (ELMs) in the DIII-D lower divertor demonstrated minimal changes to the macroscopic or microscopic surface morphology. Post-exposure compositional analysis reveals Si enrichment of about 10{\%}. To interpret these results, an analytic surface model is developed using calculated physical and temperature-dependent chemical sputtering yields from Si, SiC, and C (graphite). The Si content in the plasma-facing surface layer is predicted to increase with both surface temperature and divertor electron temperature, T$_{\mathrm{e,div}}$, due to more efficient physical and chemical sputtering yields of C relative to Si. The total gross erosion of Si from this mixed Si-C-SiC layer increases strongly with T$_{\mathrm{e,div}}$ but erosion of C stays relatively constant. These trends are reproduced by measurements obtained via spectroscopic inference using the S/XB method. Quantitatively, the model slightly under-predicts the measured erosion rates; this is attributed to ELMs, which have minimal (but non-zero) impact on SiC erosion. Extrapolating to a case with all-SiC walls in DIII-D, an order-of-magnitude decrease of the overall C source is predicted, motivating further investigation of SiC as a non-metallic plasma-facing material with favorable erosion properties.