Evaluation of silicon carbide as a divertor armor material in DIII-D H-mode discharges

TL;DR

This study develops and tests an erosion model for silicon carbide as a plasma-facing material in fusion devices, showing promising results for its use in future reactors due to its low erosion and impurity sourcing.

Contribution

The paper introduces a novel analytic erosion model for SiC in fusion environments and validates it with experimental data from DIII-D tokamak discharges.

Findings

Si enrichment occurs during plasma bombardment, mainly from sputtering of the enriched Si layer.

Experimental erosion rates are close to model predictions, with slight underestimation.

SiC coatings show minimal surface damage after exposure, supporting its durability as a PFM.

Abstract

Silicon carbide (SiC) represents a promising but largely untested plasma-facing material (PFM) for next-step fusion devices. In this work, an analytic mixed-material erosion model is developed by calculating the physical (via SDTrimSP) and chemical (via empirical scalings) sputtering yield from SiC, Si, and C. The Si content in the near-surface SiC layer is predicted to increase during D plasma bombardment due to more efficient physical and chemical sputtering of C relative to Si. Silicon erosion from SiC thereby occurs primarily from sputtering of the enriched Si layer, rather than directly from the SiC itself. SiC coatings on ATJ graphite, manufactured via chemical vapor deposition, were exposed to repeated H-mode plasma discharges in the DIII-D tokamak to test this model. The qualitative trends from analytic modeling are reproduced by the experimental measurements, obtained via spectroscopic inference using the S/XB method. Quantitatively the model slightly under-predicts measured erosion rates, which is attributed to uncertainties in the ion impact angle distribution, as well as the effect of edge-localized modes. After exposure, minimal changes to the macroscopic or microscopic surface morphology of the SiC coatings were observed. Compositional analysis reveals Si enrichment of about 10%, in line with expectations from the erosion model. Extrapolating to a DEMO-type device, an order-of-magnitude decrease in impurity sourcing, and up to a factor of 2 decrease in impurity radiation, is expected with SiC walls, relative to graphite, if low C plasma impurity content can be achieved. These favorable erosion properties motivate further investigations of SiC as a low-Z, non-metallic PFM.