Deciphering surface behavior and deuterium retention in tin-lithium-coated fuzzy tungsten substrates

Abstract

Tungsten will be used as plasma-facing material in the divertor in ITER, but it undergoes detrimental surface-subsurface morphological changes under irradiation. One type of tungsten that may mitigate such morphologies is porous tungsten due to higher defect sink areal density. While surface nanostructures such as fuzz may compromise plasma performance, their intrinsic porosity offers a proxy for a porous material and strategies to prevent high-Z impurity emission. Liquid metal coatings have been proposed as plasma facing materials to counteract the erosion issues faced by tungsten. Tin-lithium eutectics are an understudied class of potential liquid metal coatings for their low melting points and reduced erosion and fuel retention compared to pure lithium coatings. A 95 at.% tin-lithium eutectic was deposited on fuzzy tungsten samples and exposed to 250 eV deuterium ions at 250 °C and varying fluences. Mitigation of fuzz erosion and deuterium retention were examined post-mortem with SEM and secondary mass ion spectroscopy (SIMS) of tungsten samples and witness samples used to collect eroded material. The SnLi film persisted after irradiation and protected underlying fuzz. SIMS results demonstrate surface mixing of the liquid metal and tungsten substrate and increased lithium erosion at high fluence and non-structured surfaces. The highest concentration and deepest penetration of retained deuterium was observed in the sample exposed to the lowest fluence. Results may indicate intercalation of liquid metal with tungsten tendrils at elevated temperatures.