Deuterium trapping and diffusion in monocrystalline and polycrystalline plasma facing materials

Comprehensive understanding of hydrogen isotopes' trapping and de-trapping mechanisms on plasma facing materials (PFMs) is critical to commercial fusion devices in terms of fuel, economics, and safety concerns. Studies focusing on deuterium trapping on tungsten and tungsten alloys show that nano-sized bubbles are formed in subsurface region of tungsten because of high deuterium concentration. In our recent study, employing molecular dynamics to study deuterium trapping and bubble formation on tungsten, the formation of D bubble in tungsten subsurface was also observed for tungsten temperature of 600K or higher. Another outcome of that study was the effects of grain boundary on retention of deuterium in tungsten. In this study, deuterium bombardment with various energies on tungsten structures including both monocrystalline (MC) and polycrystalline (PC) with grain boundary at various temperatures was analyzed using molecular dynamics (MD) methods. Large-scale Atomic/Molecular Parallel Simulator (LAMMPS) code was employed using Tersoff interatomic potential determining interaction between particles. The deuterium trapping mechanism parameters such as retention rate and implantation depth for MC- and PC-tungsten structures were analyzed. Our preliminary results show that the retention rate of deuterium could be explained in two regimes based on deuterium energy. While retention rate of deuterium with higher energies (>100 eV) in tungsten is dominated by the energies of deuterium particles, however, deuterium with lower energies, the structure of tungsten influences the retention rate. The goal of this study is to provide comprehensive understanding of deuterium trapping mechanism in tungsten to determine hydrogen isotopes' concentration in plasma facing components and the overall performance in future fusion devices.