Synergistic effects of W–Ta alloys exposed to various ELM-like fusion events

Abstract

Recently tungsten alloys have shown capabilities in suppressing morphological changes when exposed to harsh fusion conditions. Morphological changes due to He+ and D+ ions at high temperatures (1000 - 2000 K) can lead to easier erosion and sputtering of W particles towards quenching the fusion plasma. This study investigated W-3Ta alloy as potential plasma facing materials (PFMs) exposed to different edge-localized mode (ELM)-like energies and ion loadings. Performance of W-3Ta has been tested as a function of ELM-like energies (0.6 - 1.5 GWm-2) and varying He+ and D+ ion concentrations (100% He+, 50% He+:50% D+,10% He+:90% D+ (similar ELM-like reactor condition), and 100% D+ ions). Early-stage fuzz formation and surface pores were observed during 100% He+ ion irradiation and mixed ion loadings but not observed during 100% D+ ion loadings. Pores decreased in quantity and increased in size with increasing transient heat loading. Grain boundaries acted as trapping sites of helium and deuterium atoms during dual beam ion irradiations, as observed through increased pore size along the grain boundary. Qualitative erosion estimates were measured using witness plates. Increased erosion was observed with increasing D+ ion concentration, which is attributed to D supersaturation in the near surface region affecting thermal and mechanical properties. More erosion was observed for W-3Ta samples compared to pure W, evident through large (>10 µm) cracks on the surface, and an increase in W metal XPS peaks under similar loading conditions. The slight enhancement in erosion is attributed to the slightly decreased thermal properties, ~10% thermal diffusivity drop, of W-3Ta at high temperatures. The damage threshold was impacted by ion loading, where distinct cracking was observed for 100% He+ at a lower heat loading. This matrix study using reactor-like loading supports the need for extensive studies on future W alloy PFMs before selecting one as an alternative.