Formation of helium induced nanostructure ‘fuzz’ on various tungsten grades

The response of a variety of W material grades to nanostructure ‘fuzz’ formation is explored. W targets are exposed to He or D2–0.2He plasmas in PISCES-B at 900–1320 K to below sputter threshold He+ ions of energy 25–60 eV for up to 2.2 × 104 s. SEM and XPS reveal nanoscopic reorganization of the W surface to a layer of ‘fuzz’ of porosity ∼90% as determined by a ‘fuzz’ removal/weight loss method. The variability of ‘fuzz’ growth is examined at 1120 K for 1 h durations: SR, SC and doped W grades – La2O3 (1% wt.), Re (5% and 10% wt.), and TiC (1.5% wt.) developed 2–3 μm thick ‘fuzz’ layers, while a VPS grade developed a layer 4 μm thick. An RC grade revealed additional ‘fuzz’ at deep (>100 μm) grain boundaries. However, heat treatment up to 1900 K produced reintegration of ‘fuzz’ with the bulk and He release at ∼1000 K and ∼1400–1800 K due to depopulation from vacancy complexes.