Helium retention and early stages of helium-vacancy complexes formation in low energy helium-implanted tungsten

Tungsten has been selected as the material of the divertor of the ITER fusion reactor. In operation, tungsten will be submitted to high alpha particles bombardment. The consequence of helium implantation is a major issue for the reliability of tungsten components. The aim of the study was to investigate the behavior of helium implanted in tungsten at low energy and low flux. 320eV Helium ions were introduced by plasma immersion at the flux of 2.5×1018ion/m−2/s−1. The helium behavior was investigated by Nuclear Reaction Analysis and the evolution of the tungsten lattice by Positron Annihilation Spectroscopy (PAS). Helium-implanted tungsten exhibits a low retention rate (13.6% at 9.4×1019Hem−2) which decreases with the implantation fluence. The desorption of helium starts at low temperature (