Dynamic Behavior of Carbon Deposited on Tungsten Surface due to Carbon Ion Bombardment and Its Influence on Ion-Solid Interactions

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The fluence evolution of C deposited on a W surface due to C ion impact and its influence on ion–solid interactions such as physical sputtering and ion reflection are studied using a dynamic Monte Carlo code, EDDY. In particular, attention is focused on their impact energy dependence. In the code, the fluence evolution of surface composition changes due to collisional mixing resulting from the ion impact and also due to thermal activated diffusion of the deposited C resulting from the elevated surface temperature is simulated along with the particle emissions from the C-contaminated W surface. The physical sputtering of the deposited C is enhanced by the reflective scattering collision in the vicinity of the surface, which results from a difference between the C ion reflection from C and that from W. The energy dependence of the physical sputtering is dependent upon the fluence amount. As the energy increases, the physical sputtering is enhanced, and it is then suppressed above a certain impact energy which varies depending on the fluence amount. This results from the difference between a mixed layer of C and W formed at a low fluence and a C film formed on the W surface at a high fluence. In addition, its surface temperature dependence is strongly dependent upon the fluence amount. For a low fluence the physical sputtering is suppressed with increasing surface temperature, whereas it is enhanced for a high fluence. This is attributed to a remarkable growth of the mixed layer due to the diffusion of the deposited C.

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