Molecular dynamics modeling of chemical erosion of carbon films

Full text of publication follows: The divertors of fusion experiments like ITER have to withstand extraordinary power loads and high particle fluxes. Due to the excellent plasma-facing properties carbon has been chosen for the ITER divertor. The major disadvantage of carbon as plasma-facing material is the pronounced chemical erosion and subsequent formation of co-deposited layers in remote areas capable of trapping large amounts of tritium. We employ molecular dynamics simulations (MD) using a reactive hydrocarbon potential to clarify the erosion mechanism of amorphous hydrocarbon (aCH)-films on an atomistic level. On annealed a-CH samples cumulative bombardments simulations with hydrogen atoms and energetic noble gas atoms were performed with several hydrogen to noble gas atom ratios and the effects on erosion yields and the distribution of the eroded species are examined. The presented approach allows the separation of chemically activated processes and momentum induced changes of the atomic structure. This also yielded an explanation for the recently experimentally observed enhanced erosion yields for co-bombarded aCH-films with hydrogen and noble gas ions. (authors)