Model of fuzz formation on a tungsten surface

Abstract

A model of fuzz formation on a tungsten surface exposed to helium plasma is proposed. According to this model, the fuzz structure forms due to the growth of fuzz fibers from adatoms generated under bombardment by helium ions. The threshold energy of adatom formation by He⁺ ions is about one-third of the sputtering threshold. The kinetics of adatom diffusion over fibers describes the temporal dependence of the fuzz layer thickness in quantitative agreement with the experiment. In addition to generating adatoms, the role of helium ions consists in the formation of a nonuniform surface as a result of the opening of helium bubbles and, probably, in providing conditions for the aggregation of adatoms over bubbles with extended shells. These factors favor the appearance of clusters that serve as nuclei for the growth of fibers from adatoms and the formation of a fuzz structure.