Effects of helium irradiation on high heat load properties of tungsten

He ion pre-implanted tungsten has been irradiated by electrons to examine synergistic effects of He implantation and high heat load. Depth profile measurements show that He distributes on the surface locally and most of He is distributed in the projected range, however, some of the helium atoms diffuse to deeper region. Blisters are observed on the sample irradiated to a fluence of 1×10²² He/m² at 300 K. However, at 1073 K, such blisters are not observed and no noticeable modification occurs. There is no large difference in surface modification by electron beam irradiation between the samples irradiated or not with He when the sample is at the high temperature (2773 K) for 6 s. Two large He release peaks are observed from the sample irradiated to a fluence of 1×10²² He/m² at 1073 K. It is thought that He release in the first peak is due to microcrack formation near the surface and that the second He release peak is due to the exfoliation or rupture of blisters.