Helium irradiation effects on the surface modification and recrystallization of tungsten

Helium (He) irradiation has previously been observed to alter surface modifications and the recrystallization properties of tungsten (W). In this study, He irradiations in the NAGDIS-II linear plasma device, at temperatures below recrystallization and low energies (50 eV) followed by annealing at 1470 K were carried out. Additionally, high energy (28 keV) hydrogen (H) with an admixture of 6 at% He irradiations in the neutral beam facility GLADIS were performed at temperatures above recrystallization (1770 K). These are compared to pure H irradiations under the same conditions. In the low temperature cases, following irradiation, an undulating microstructure is observed on the surface of the samples after irradiation. After annealing at 1470 K, it is observed that the inhibition effect of He irradiation is more pronounced following lower temperature exposures. The effect of He irradiation on inhibition of recrystallization with grain growth is also observed to saturate at the highest fluences. In the high temperature, high energy case, He irradiation and recrystallization happens simultaneously. Following the irradiation a coral like microstructure is observed on the surface of the sample. The introduction of He is not seen to have a significant effect on the recrystallization process of W when the irradiation is carried out at temperatures above recrystallization.