Evolution of surface morphology and helium bubble in tungsten under 40 keV helium ions implantation followed by deuterium plasma exposure

Surface morphology and internal microstructure of tungsten (W) pre-implanted by 40 keV mass-separated helium (He) ions with different fluences at room temperature were investigated in this work. The morphology changes of the samples were analyzed almost in situ, by repetitively examined the specified irradiation area which is marked by focused ion beam technology. As the samples were implanted by He ion with a fluence of 6 × 1020 He m-2, no He blisters or other microstructures could be found on the surface. When the fluence reaches 6 × 1021 He m-2, a large number of He blisters with the size of 1/41 μm were observed on the W specimens. For the results of the subsequent deuterium plasma exposure, instead of deuterium-induced blistering, no changes on the W surface which pre-irradiated by He ion irradiation at low fluence (6 × 1020 He m-2). Surprisingly, for He ions pre-implanted W with high fluence (6 × 1021 He m-2), almost all the He blisters were cracked and their lids even peeled off. It could be attributed to the lateral stress caused by subsequent D exposure. Moreover, the size of He bubbles was also increased under subsequent deuterium exposure, suggesting that He atoms can attract D atoms. No deuterium blisters were found on these samples which were pre-implanted with high and low fluences, suggesting that He ion pre implantation can effectively inhibit the surface blistering caused by deuterium exposure.