Sputtering properties of tungsten 'fuzzy' surfaces

Sputtering yields of He-induced W 'fuzzy' surfaces bombarded by Ar have been measured in the linear divertor plasma simulator PISCES-B. It is found that the sputtering yield of a fuzzy surface, Yfuzzy, decreases with increasing fuzzy layer thickness, L, and saturates at ∼10% of that of a smooth surface, Ysmooth, at L > 1 μm. The reduction in the sputtering yield is suspected to be due mainly to the porous structure of fuzz, since the ratio, Yfuzzy/Ysmooth follows (1 − pfuzz), where pfuzz is the fuzz porosity. Further, Yfuzzy/Ysmooth is observed to increase with incident ion energy, Ei. This may be explained by an energy dependent change in the angular distribution of sputtered W atoms, since at lower Ei, the angular distribution is observed to become more butterfly-shaped. That is, a larger fraction of sputtered W atoms can line-of-sight deposit/stick onto neighboring fuzz nanostructures for lower Ei butterfly distributions, resulting in lower ratio of Yfuzzy/Ysmooth.