Effects of Helium Ions on Hydrogen Isotope Behavior in Tungsten

Simultaneous irradiation effects of He on tungsten blistering with hydrogen and carbon mixed ion beam were investigated. It was found that only 0.1% addition of He ions to 1 keV H and C mixed ion beam (C:0.8-1.0%) reduced (at 473 K) or completely suppressed (at 653 K and 723 K) blister formation. In order to obtain more detailed result, two ion sources were used to irradiate tungsten with H and He ions with different energies. In the He energy of 0.6 keV (1.5 keV H&C),significant blistering was observed, while in the He energies of 1.0 keV and 1.5 keV, blister formation was suppressed. These results suggested that a He bubble layer reduced hydrogen diffusion through the layer. A He bubble size and a volume rate were about 1-2 nm and ~2% at 653 K, respectively. To evaluate T retention in the ITER tungsten wall, this effect should be included.