Effects of helium implantation on damage during pulsed high heat loading of tungsten

A cyclic helium beam with energy 18.7 keV has been used to irradiate stress relieved and recrystallized powder metallurgy tungsten up to a fluence of ∼1023 He/m2. After the helium irradiations, the samples have been exposed to pulsed high heat loading by an electron beam with a heat flux of 1 GW/m2 and duration of 1, 1.5 or 2 ms. Surfaces of irradiated samples become smooth as a result of the electron beam irradiation of 1 GW/m2 for 1 ms, due to atom migration on the surface at high temperature. On the other hands, the surface of irradiated samples is partially melted and resolidified. However, smoothing does not occur around the melted area. Stress relieved tungsten is melted by irradiation of a heat flux of 1 GW/m2 and duration of 1.5 ms, but recrystallized tungsten is not melted by the same heat loading.