Performance and damage mechanisms of dispersion-strengthened tungsten under H-mode plasma in DIII-D

Dispersion strengthened tungsten (DSW) alloys are promising materials for plasma facing components, displaying improved mechanical properties and microstructure stability compared to pure tungsten. In this work, the performance of DSW reinforced with 1 wt% transition-metal carbide (TaC, TiC, or ZrC) has been examined under H-mode plasma in the DIII-D tokamak. DSW samples were mounted both flush with the divertor floor and at a 10° angle towards the incoming plasma fluxes to further increase the heat and particle loading. To simulate the impact of prolonged tokamak operation, similar plasma exposures were repeated on two additional sets of DSW samples: one set pre-implanted with 10 22 m -2 helium, and another set heated in-situ to an additional 500°C. Flush mounted samples exhibited good surface stability, with no evidence of melting or cracking regardless of composition or treatment. Carbon redeposition was observed on most samples, likely due to the graphite environment of DIII-D. Under coupled thermal loading and helium implantation, surface nanostructuring developed in some DSW samples; however, DSW containing tantalum dispersion phases showed strong resistance to such surface modification. In contrast, obvious surface melting was observed on 10° angled samples containing TaC and ZrC dispersoids, likely associated with dispersoid oxidation during fabrication, which reduced thermal conductivity and promoted elevated surface temperatures during plasma exposure. The grain morphology of DSW containing TiC remained largely unchanged, although near-surface dispersoids on the angled TiC sample were missing after plasma exposure. The loss is associated with oxidation of the dispersoids during fabrication, followed by sublimation during plasma exposure. Through systematic comparison of DSW performance under H-mode plasma conditions, this study identifies key degradation mechanisms and highlights strategies to improve the performance of DSW as plasma facing materials.