Scanning electron microscopy analyses of an ITER plasma-facing unit mockup exposed to extreme ion fluences in Magnum-PSI

A small-scale tungsten monoblock mockup was exposed to continuous Magnum-PSI plasma beams under six different conditions, including pure hydrogen, deuterium and helium (He) plasmas as well as mixed D/He plasmas with low electron temperature (1.5–5 eV), with maximum surface temperatures up to 1600 °C, and with ion fluences up to 10 30 m−2. The recrystallization in the centre of the hottest exposure spots, the absence of cracking on all monoblocks, the formation of a nanostructured fuzz layer several microns thick by pure He exposure, and the presence of various impurities from the exposure in Magnum-PSI on the surface were observed and analysed with a dedicated scanning electron microscope able to handle the entire mockup without any prior cutting.