Modification of Tungsten Surface Irradiated by Hydrogen and Helium Plasma

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(Hydrogen Plasma Irradiation)Blister formation is clearly observed on tungsten surface under a low energy (<100 eV) and high flux(>l0^<21> m^<-2> s^<-1>) hydrogen plasma irradiation at the surface temperature less than 950 K and the fluence higher than 3 x 10^<24> m^<-2>. The size of maximum hydrogen blisters is up to 300micron at higher fluence irradiation. The dependence of blister formation on sample temperature is clearly obtained. When the surface temperature is higher than 950 K no blisters are observed on tungsten surface at various incident fluence. These results indicate that such large hydrogen blister formation due to low energy particles irradiation at low temperature can also make a great effect on the hydrogen retention in fusion devices and reactors.(Helium Plasma Irradiation)Tungsten (W) specimens were irradiated by low energy (<65 eV) and high flux (>10^<23> m^<-2> s^<-1>) helium plasma to investigate the incident ion energy dependence of helium bubble formation. Experimental results indicate the existence of the incident ion energy threshold for the bubble formation. The threshold energy around 15 eV could associate with the surface potential for He ions entering to the W surface.