Synergistic effects of high energy helium irradiation and damage introduction at high temperature on hydrogen isotope retention in plasma facing materials

In this study, energetic helium (He) ion irradiation was performed to obtain bulk He distribution in tungsten (W) materials, concurrent with damage introduction at high temperature. Then, deuterium (D) implantation and thermal desorption spectrometry were performed to evaluate D retention. At the same time, the surface tritium (T) concentration and depth distribution were evaluated by imaging plate (IP) and β-ray induced X-ray spectroscopy (BIXS) measurements after mixed D-T gas exposure. Numerical simulations were applied to evaluate changes in binding energies, diffusion depths, and trapping sites under different irradiation conditions. The results showed that weak trapping sites with higher concentration, such as vacancies, were produced during only energetic He⁺ irradiation events, leading to enhancement of D retention. Fe³⁺-He⁺ simultaneous irradiation promoted the formation of He_xV_y complexes, which reduced the concentration of vacancy trapping sites and changed the stress field around defects, leading to the suppression of D trapping behavior. From the reduced effects of D retention caused by He_xV_y complexes at higher temperatures, the results suggested that defect recovery was the dominant mechanism. With increasing damage level at higher temperatures, more weak trapping sites, such as dislocations and vacancies sites, were produced, leading to a more dominant influence on D retention than He_xV_y complex effects. It was also found that He_xV_y complexes prevented D diffusion to the bulk and that simulation results showed that the damage level had little impact on D diffusion depth.