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Molecular dynamics (MD) simulations have been performed to investigate the diffusion properties of hydrogen (H) atoms in body-center-cubic (bcc) iron (Fe) with point defects, i.e., vacancies (Vs) and self-interstitial atoms (SIAs). Firstly, the binding energies of a H atom to a H/SIA-H cluster have been calculated by molecular statics simulations. The results show that single-H diffusion should be the major diffusion mechanism in perfect bcc Fe and bcc Fe with SIAs, but for bcc Fe with Vs, results from literatures show that multi-H diffusion should be taken into account. Further, the mean squared displacements method has been employed to determine the diffusivities and diffusion energy barriers of single-H at different temperatures in perfect bcc Fe. The diffusion energy barrier varies with the temperature. Furthermore, the H diffusion properties with different point defect concentrations have also been demonstrated, which showed that diffusivities reduce as the point defect concentration increases and the influence of point defects reduces as the temperature increases. Especially, SIAs exhibit negligible effect when the temperature is higher than 600 K. [ABSTRACT FROM AUTHOR]

The interactions between dust and plasma-facing material (PFM) relate to the lifetime of PFM and impurity production. Series results have been obtained theoretically and experimentally but more detailed studies are needed. In present research, we investigate the evolution of kinetic, potential and total energy of plasma-facing material (PFM) in order to understand the dust/PFM interaction process. Three typical impacting energy are selected, i.e., 1, 10 and 100 keV/dust for low-, high- and hyper-energy impacting cases. For low impacting energy, dust particles stick on PFM surface without damaging it. Two typical time points exist and the temperature of PFM grows all the time but PFM structure experience a modifying process. Under high energy case, three typical points appear. The temperature curve fluctuates in the whole interaction process which indicates there are dust/PFM and kinetic/potential energy exchanges. In the hyper-energy case in present simulation, the violence dust/PFM interactions cause sputtering and crater investigating on energy evolution curves. We further propose the statistics of energy distribution. Results show that about half of impacting energy consumes on heating plasma-facing material meanwhile the other half on PFM structure deformation. Only a small proportion becomes kinetic energy of interstitial or sputtering atoms. [ABSTRACT FROM AUTHOR]