Irradiation effects of H/He neutral beam on different forged tungsten materials

Tungsten has been considered as the most promising plasma-facing materials(PFMs)for the future fusion reactor due to its excellent chemical and physical properties.In this work,different kinds of tungsten-based PFMs including pure W,W-K,and W-Y_(2)O_(3)alloys were prepared via powder metallurgy.Then,high-energy rate forging was used for the plastic deformation to refine the grain size of the samples and increase their densities.To evaluate the service performance of these tungsten-based PFMs under edge plasma conditions,the deformed samples were exposed to high-energy hydrogen(H)neutral beam doped with 6 at%helium(He).Sequentially,edge-localized mode-like transient loadings(1 ms,100 cycles)were carried out on the specimens with neutral beam pre-loading to study the impact of H/He pre-loading on the generation and propaga-tion of cracks.The microstructural changes of the exposed surfaces were observed by scanning electron microscopy with the help of focused ion beam.The experimental results indicate that H/He neutral beam irradiation could induce obvious surface damages of the tested samples.For example,pinhole and coral-like nanostructures were formed on the surfaces of the exposed samples,as the surface temperatures were relatively high.The cracking thresholds of the W-Y_(2)O_(3)samples with and without neutral beam pre-irradiations were both between 0.22 and 0.33 GW m^(−2),while the cracking thresholds of pure W and W-K samples were less than 0.22 GW m^(−2).This result indicates that the H/He neutral beam pre-loading has no significant impact on the cracking threshold.In addition,the crack pattern on the surface of the exposed samples closely depends on the grain boundary pattern.