Sub-surface structures of ITER-grade W (Japan) and re-crystallized W after ITER-similar low-energy and high-flux D plasma loadings

Tungsten is a promising candidate for plasma-facing materials in fusion reactors. In this work, two types of W materials were investigated: (i) sintered and forged tungsten (ITER-grade Japan, grain sizes 2-100 μm, elongated normal to the surface) and (ii) the same W grade, but after additional re-crystallization (at 2073 K, grain size ∼50 μm). The samples were exposed to deuterium with an ion energy of 38 eV D-1, a fluence of 1027 D m-2 and a flux of ∼1022 D m-2 s-1 in a plasma generator at elevated temperatures (320-700 K). The D retention (determined by thermal desorption spectroscopy and nuclear reaction analysis) of both sample types is compared. The samples were analysed with scanning electron microscopy combined with a focused ion beam for iterative cross-sectioning to obtain three-dimensional (3D) data of the sub-surface. Electron backscattered diffraction was applied to determine the grain orientation and deformation. First nano-secondary ion mass spectroscopy investigations were performed on a D-loaded sample to analyse the lateral accumulation of H/D on the surface.