Angular Effects in the Sputtering of Stainless Steel by Hydrogen Ions

One major source of plasma contamination in tokamaks results from sputtering of the first wall of the plasma chamber by hydrogenic species. Charge transfer neutrals and escaping ions will have different incident angle distributions and it is therefore important to study the angular behavior of the sputtering mechanism. Laboratory experiments are reported in which the angular and energy distribution of Cr+ sputtered from 304 stainless steel by H+3 is measured as a function of angle of incidence of the H+3 beam. A change in both the angular distribution and the energy distribution is observed toward grazing incidence, which is taken as evidence of the increasing contribution of surface recoils. The effects of surface contamination on the yield, angular distribution, and energy distribution of sputtered ions are also reported.