SURFACE BEHAVIOR OF FIRST-WALL MATERIALS DUE TO THE SYNERGISTIC EFFECT OF HELIUM AND HYDROGEN ISOTOPES

Scanning electron microscopy has been used to investigate changes in s urface morphology due to helium implantation and hydrogen charging. Pu re polycrystalline nickel, OFHC copper and Cu-1.8Be-0.2Co (CAD 172) al loy have been studied. The influence of helium implantation parameters on blister formation and growth was investigated. Hydrogen charging ( cathodic or thermal-gas) was found to lower the helium content needed for blistering and surface exfoliation. The effect of heating, carried out after hydrogen charging, was also studied. For the copper samples , hydrogen damage was produced by oxide reduction at the oxide-metal i nterface. This damage was found to be lower when the sputtering due to helium implantation increased. The CuBe alloy showed a greater hydrog en resistance due to the stability of the surface BeO.