Deuterium retention in solid and liquid tin after low-temperature plasma exposure

摘要

Recently, plasma-facing components based on liquid metals were proposed for a prospective nuclear fusion reactor in order to circumvent challenges that occur for solid metal components, such as erosion lifetime, neutron embrittlement or transient overloading. One candidate material is liquid tin. We present a systematic study of the behavior of solid and liquid tin exposed to a low-temperature deuterium plasma at temperatures between 300 and 515 K, focusing on deuterium retention and thermal release as well as on tin erosion and re-deposition. We find strong variations of deuterium depth profiles, deuterium release spectra, and tin erosion rates, which are correlated to dramatic changes in the surface morphology. In particular, we find evidence for massive gas bubble formation in tin, which can lead to the evolution of a thick, sponge-like layer for tin exposed to deuterium plasma just below the melting point, and to the rapid formation of a macroscopic gas pocket below liquid tin. We present evidence for strongly temperature-dependent chemical erosion of tin by deuterium plasma in the solid state. In the liquid state, a high tin erosion rate occurs, which is apparently induced by ejection of tin microdroplets. Furthermore, we observed strong plasma-assisted, low-temperature wetting of tin on tungsten near the melting point of tin. We tentatively propose the hypothesis that all of the observed effects may be influenced by tin-deuterium chemistry, e.g. the formation and de-composition of stannane molecules.