Accelerated Molecular Dynamics Simulations of Dislocation-Obstacle Interactions in Tungsten: Enabling Micro-Second Simulations

Plasma Facing Materials (PFMs) in fusion reactors have to withstand extreme temperatures and high particle flux of Hydrogen (H) isotopes and Helium (He). Tungsten (W) is the main candidate for PFM in the International Thermonuclear Experimental Reactor but He irradiation of W results in modification of surface microstructure due to creation of Helium-Vacancy (He_nV_m) complexes. This leads to increased retention of H isotopes and degradation of thermomechanical stability. In this work, we study the interaction of these He_nV_m complexes with edge dislocations using accelerated molecular dynamics. We use a novel Parallel Replica Dynamics method where states and transitions are identified on-the-fly using a diffusion distance metric calculated from an approximation of the Koopman operator of the dynamics. Using up to 600 replicas, we are able to investigate the interactions between edge dislocations and He_nV_m complexes at temperatures ranging from 300-1200 K and applied stresses well below the critical resolved shear stress. The calculated rates for the dislocation to overcome the obstacle span ≈3 orders of magnitude, reaching micro-second timescales at low temperatures/stresses, and show a strong dependence on the applied stress.