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 D(2)-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 x 10(4) s. SEM and XPS reveal nanoscopic reorganization of the W surface to a layer of 'fuzz' of porosity similar to 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 - La(2)O(3) (1% wt.), Re (5% and 10% wt.), and TiC (1.5% wt.) developed 2-3 mu m thick 'fuzz' layers, while a VPS grade developed a layer 4 mu m thick. An RC grade revealed additional 'fuzz' at deep (>100 mu m) grain boundaries. However, heat treatment up to 1900 K produced reintegration of 'fuzz' with the bulk and He release at similar to 1000 K and similar to 1400-1800 K due to depopulation from vacancy complexes. (C) 2010 Elsevier B.V. All rights reserved.