Molecular Dynamics Simulation Of Low-energetic Hydrogen And Isotopes Bombarding The Tungsten (001)Surface

Tungsten (W) or its alloys are the most promising candidate materials for the divertor plates of ITER, attributed to their resistance to chemical erosion, and their excellent thermal performance. However, as plasma facing material (PFM) for the future fusion devices, W are subjected to high heat and hydrogen (H) isotopes fluxes from the plasma. Being the lightest element, H atoms can easily diffuse into the bulk, immobilized by point defects and lead to the modification of the thermal and mechanical properties of W. Therefore, the interaction between H atoms and W has been one of the most import issues for developing W as PFM. Previously, a large number of experimental studies on the interaction of H atoms and W surface. In the thesis, the first and second chapters introduce the research background and the basic principles of this work, respectively. The third and fourth chapters report the main work of this project. The content of this thesis is arranged as follows.-In the third chapter molecular dynamics simulations are performed to the diffusion behavior of low-energy hydrogen atoms in bcc tungsten (001). The simulation results show that when the energy of vertically incident hydrogen atoms is in a range of0.0-20.0eV, their retention probability increases rapidly; in the whole incident energy range0.5--50.0eV, the reflection probability gradually drops, but still exceeds60%. By varying the incident angle, the retention probability may increase in some energy ranges compared with those in the case of vertical incidence, but the reflection probability still dominates. In this paper, also presents the depth distribution of energy deposition of incident hydrogen and its isotopes. It is found that tritium atoms deposit more energy in the surface region than hydrogen.In the chapter4, the energy deposition of low-energy incident H and its isotopes in W is investigated. The reflection of H atoms at different incident energies from (001) W surface is always dominant, more than60%of incident events for all incident angles. The reflection rate of either D or T is a little lower than that of H, still more than50%. In an energy range from0.5to15.0eV, the reflectivity for any incident species decreases as the incident energy increases. At the same incident angle and energy, the reflection rate of T is the lowest, and comparatively, T atoms distribute closest to the W surface. H atoms occupy mainly the tetrahedral interstitial sites of W. It is also found that the substrate W temperature has a big effect on the reflectivity of incident H isotopic atoms and their retention.