Speaker
Description
In magnetic confinement nuclear fusion devices, Tungsten (W) is considered the most promising plasma-facing materials (PFMs) for divertor, which will be exposed to high-energy neutron irradiation, high flux plasma irradiation at high temperatures (up to 1200 °C during steady-state operation). High-energy neutron irradiation can directly generate dislocation loops through collision cascades, or produce self-interstitial atom (SIA) that subsequently aggregate to form loops. Moreover, during the accumulation of helium from plasma irradiation and the subsequent formation of nano-scale helium bubbles, SIAs can also be created; these can further aggregate into dislocation loops as the bubbles grow. To simulate the long-term defect evolution of tungsten at the mesoscale, it is of great significance to conduct detailed studies on processes such as cluster migration. For body-centered cubic (bcc) metals like tungsten, the 1/2<111> dislocation loop is widely recognized as the most energetically favourable configuration and can undergo rapid one-dimensional (1D) migration along the <111> direction even at relatively low temperatures. However, due to the considerable difficulty in experimentally observing their thermal migration directly, research on the migration behavior of dislocation loops remains insufficient.
In this study, molecular dynamics (MD) simulations were performed using Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) to investigate the 1D migration of 1/2<111> dislocation loops containing 13 to 99 SIAs NI over a temperature range of 400–2000 K for a duration of 5 ns. To ensure statistical reliability, each combination of size and temperature was simulated 10 times with different random seeds. The mean square displacement (MSD) of the center of mass of the loop was analyzed as a function of time. Based on the Arrhenius equation, the pre-exponential factor D0 and activation energy Ea for the migration of smaller loops were fitted as functions of NI. Furthermore, a sharp decrease in migration coefficient was observed for larger dislocation loops, similar to that reported in iron, and a further study of this phenomenon was carried out.