Performance of tungsten-tantalum alloys under dual ion beam irradiation and transient heat loading environments

Tungsten alloys are candidates to replace pure W divertors in future DEMO tokamak reactors with capabilities to suppress surface morphologies but may suffer with their decrease in thermal properties. This investigation focuses on W-3Ta due to its fuzz suppression capabilities, and lower cracking compared to other W-Ta alloys. Samples were exposed to different ELM-like energies and different He⁺ and D⁺ dual beam ion concentrations. Early-stage fuzz growth was observed during He⁺ exposures via surface and sub surface imaging, seen with mixed ion loadings via sub surface imaging, and was absent in pure D⁺ loading. Surface pores were visible with all ion loadings except pure D⁺, with decreasing quantity and increasing size with increasing transient heat loading. Grain boundaries grew larger with increasing D⁺ loading and acted as paths for rapid desorption of He⁺ and D⁺ due to an increase in pore size along the grain boundary. Erosion measurements using Mo witness plates and XPS indicated higher erosions with mixed He⁺ and D⁺ ions over pure He⁺. Optical profilometry aided in measuring changes in melting threshold between different loadings. This matrix study of various ELM-like events on materials supports the need for novel advanced alloys as potential plasma facing materials.