Deuterium plasma interactions with liquid gallium

Liquid metals such as gallium, tin and lithium are potential plasma-facing materials that may be used to withstand the high heat and particle fluxes in a fusion plasma environment. The interaction of plasma with liquid gallium surfaces has been examined experimentally because of the liquid's wide temperature range (303-2478 K) and relatively low chemical reactivity. The deuterium retention in liquid gallium samples following plasma exposure in the PISCES experimental plasma device is measured using thermal desorption spectroscopy and is found to be independent of exposure temperature. The retention level saturates at a value of roughly 3x1023 D m-3 (or about 5 ppm) for sample exposure temperatures ranging from 333 to 800 K and incident ion fluences up to 1.5x1026 D m-2. Results from the analyses of the surface after plasma exposure using Auger electron spectroscopy is reported. Micropitting is observed in scanning electron microscope pictures taken after plasma exposure and after resolidification of the gallium surface. Calculations based on the observed retained concentration of deuterium in gallium show that the pumping capabilities of a flowing gallium surface will be small. In addition, measurements of the erosion yield of deuterium-bombarded gallium are presented and compare favourably with results from sputtering yield calculations. (author)