Molecular dynamics simulation analysis of helium cluster growth conditions under tungsten surfaces

AY Hamid and JZ Sun and HY Zhang and T Stirner, COMPUTATIONAL MATERIALS SCIENCE, 186, 109994 (2021).

DOI: 10.1016/j.commatsci.2020.109994

Molecular dynamics simulations have been performed to study the effects of helium fluxes on helium cluster size underneath tungsten surfaces under bombardment of helium atoms with incident energy 30 (similar to) 100 eV at temperature 300 (similar to) 2100 K. The simulation results show that the helium cluster size depends on the magnitude of the helium flux: at a higher flux, the helium clusters on average form in smaller size in tungsten but with larger number; while the clusters form further away from the surface at a lower flux. The coalescence of He atoms and helium bubbles depends on the tungsten temperature: at elevated temperatures around 2000 K, the incident He atoms in tungsten slow down more rapidly than at 1000 K but the number of vacancies per He cluster is smaller. The incident energy has a strong effect on the retention of helium atoms: The helium retention rate increases with the incident energy, and the helium retention depends weakly on temperature in the low energy range of interest. It is also found that the surface orientation plays an important role not only in determining the depth distribution but also in determining the helium retention and cluster size: at the surface 110, the retention rate of helium atoms is the lowest, and at the surface 111, the clusters grow easily in the lateral direction. The present simulation results suggest that the 001 surface is favorable for fuzz growth. The results obtained in the present work provide insight to the reasons why the fuzz only grows within a certain parameter range at the atomic level.

Return to Publications page