| The divertor has been proved to be an essential part for a nuclear fusion reactor in handling large particle fluxes. Carbon based materials due to its excellent thermal resistance and low atomic number has been chosen as a primary material for the divertor target plates for the International Thermonuclear Experimental Reactor (ITER). However, two major issues-large erosion yield and hydrogen/tritium retention-are questioning whether the carbon-based materials can be used in future fusion devices. Further study on carbon-based materials is needed to answer the inescapable question.As well known, the energy of the particles incident on the divertor plates seldom exceeds one hundred electron volts; this energy range cannot be described adequately by the potentials used in Trim code and its variants. Up to now no macroscopic theoretical model available can predict reasonably the sputtering yield of Carbon based materials caused by low-energy hydrogen impact. Microscopic model, taking into account the C-H bond forming and breaking, is desperately needed. Brenner et al. developed a set of reactive empirical bond-order (REBO) potentials and applied it successfully to studying chemical vapor growth of diamond. Recently, many studies have been carried out on C-H systems for explaining the chemical erosion of carbon-based materials and even hydrogen (or its isotope) retention. However, the knowledge of chemical erosion process of carbon-based materials is still limited.We develop a molecular dynamic simulation code with REBO potential for analyzing chemical erosion processes of graphite. In the first part of this thesis, the collision processes between incident hydrogen atom and single graphite sheet are modeled in detail. Since the structure of graphene has great effects on the interaction between hydrogen and carbon, the energy and bombarding location of incident hydrogen atom are critical parameters. To characterize the structural effects, the high symmetrical points, corresponding toΓ, M, K in the energy band, are chosen as the impacting targets. The evolutions of kinetic and potential energy of incident hydrogen atom as well as C-C and C-H bond energy are evaluated during collision processes. The simulation results show that the interaction between hydrogen and carbon atom cannot be described theoretically by two-body approximation and must take into account the effects of multi-body interaction. At different incident locations, the states of incident hydrogen exhibit very different characteristics. The adsorption, reflection, and penetration coefficients of incident atoms are accessed. It is found that the incident hydrogen with energy lower than 0.35 eV is 100 percent reflected. When one hydrogen atom is adsorbed to one carbon atom, the bond energy of this carbon with its nearest neighbors is reduced by 1.2 eV from 4.9 eV.In the second part of this thesis, the collision processes between one hydrogen atom and graphene with single vacancy defect have been investigated. Energy transfers between hydrocarbon particles have been studied during the collision processes at the edge of vacancy defects. Energy losses for C-C and C-H bond also have been studied. The results show:The monovacancy has a big influence on adsorption between hydrocarbon particles; In certain areas of the graphite sheet, an incident hydrogen atom can be reflected backwards in two different energy ranges; hydrocarbon particles, which adsorbed at the monovacancy edge, form a bond in sp2 configuration, without an overhang configuration. However, C-C bond energy does not reduce while previous work found that theirs bond energy decreased byl.2 eV during hydrocarbon bond forming. We also found that, the carbon atom, at the vacancy edge, has more capacity to absorb incident energy, but has less capacity to spread the gained energy. These results will be of great help to understand the chemical erosion and tritium retention in fusion devices.
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