Molecular Dynamics Simulation on Diffusion Behavior of Self-interstitial Atom Cluster in Tungsten

Tungsten is considered as the most potential plasma-facing material in the future fusion reactor. However, in the real environment of future fusion reactor, 14 MeV high-energy neutron irradiation produced by deuterium-tritium fusion reaction will cause serious atoms displacement and various defects accumulation in materials. Here, self-interstitial atom and its clusters are the most common defects in neutron irradiation damage situation. Molecular dynamics simulation was used to study the stable structures and formation energy of 1/2〈111〉 and 〈100〉 self-interstitial atom clusters in tungsten. It is found that the most stable structure of SIA cluster in W is 1/2〈111〉 SIA cluster, which would be stable after aggregation. The diffusion behavior of 1/2〈111〉 self-interstitial atom clusters with different sizes was also studied, and it is found that a single SIA cluster is easy to diffuse and turn when the temperature is higher than 700 K, while two or more SIA clusters shows one-dimensional motion when the temperature is 300-900 K. In order to accurately describe the dynamic behavior of SIA clusters of various sizes, a set of empirical parameters for calculating the transition frequency of SIA clusters was presented. The results will provide accurate and complete input parameters for larger-scale simulations such as kinetic Monte Carlo and cluster dynamics, and provide the basis for correctly understanding and evaluating the neutron irradiation behavior in tungsten.