Trapping and de-trapping behavior of hydrogen isotopes in <100> interstitial dislocation loops of tungsten

Abstract In fusion reactors, plasma-facing materials (PFMs) work under a complex irradiation environment. A lot of irradiation defects will be generated in tungsten (W), primary candidate for PFMs, leading to a substantial amount of hydrogen fuel retention. Among various irradiation induced defects, <100> interstitial dislocation loops can stably exist and trap hydrogen isotopes, significantly threatening the safety of fusion reactors. Therefore, understanding the mechanism behind the trapping and de-trapping behavior in <100> interstitial dislocation loops for hydrogen isotopes is an urgent challenge. In this work, the microscopic kinetic behavior of deuterium (D) trapping/de-trapping in <100> interstitial dislocation loops was systematically investigated. It shows that <100> dislocation loops exhibit the highest D atom binding energy near the loop, approximately 1.5 eV. As a result, D atoms tend to be trapped in the regions closest to the loop. Two possible migration pathways for the trapped D were explored, and the results indicate that D prefers to migrate along the dislocation loop. As temperature increases, the trapped D atoms gradually transition from short-range vibrations within the dislocation loop to long-range migration along the loop and can de-trap from the loop at higher temperatures. Calculations of the activation energy for D de-trapping from the dislocation loop suggest that D trapping in the loop follows a multi-level mechanism. Comparison with the binding energies and thermal desorption spectra of other defects reveals that <100> dislocation loops are the strongest trapping sites for hydrogen isotopes among dislocation-type defects. This study provided a comprehensive understanding of the trapping and de-trapping behavior of hydrogen isotopes in <100> interstitial dislocation loops under a fusion environment, which carries practical implications for evaluating tritium retention in PFMs.