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Obtaining Distributions of Plasma Impurities Using Atomistic Simulations

Carbon-based materials are widely used and studied divertor materials for tokamak fusion devices. During investigations of their plasma-facing properties, the carbon sputtering yields at all energies have received much attention. However, the chemical composition of the sputtered species is also very important as the species that leave the surface either redeposit on the original surface or drift elsewhere in the vacuum chamber, possibly entering the core plasma. Determining the fusion plasma dilution and the growth of hydrocarbon films in the fusion device vacuum chamber requires a good knowledge of the type of the eroded hydrocarbon species. We use molecular dynamics simulations to model the erosion of carbon surfaces under low energy (5 - 30 eV) H/D bombardment. The atomistic nature of the modeling allows us to unambiguously recognize the sputtered hydrocarbon species. Our results show that the predominant eroded species are the small hydrocarbons CH x /CD x and C 2 H x /C 2 D x , in agreement with experiments. Only a small fraction of heavier hydrocarbons are seen.