Simulation of hydrocarbon reflection from carbon and tungsten surfaces and its impact on codeposition patterns on plasma facing components

In order to investigate the redeposition characteristics of hydrocarbons released by chemical sputtering, a Monte Carlo simulation of the transport in edge plasmas is performed, where the reflection and dissociation efficiencies at tungsten (W) and carbon (C) surfaces are calculated using molecular dynamics simulation. The redeposition probability for W and W–C mixed material is strongly suppressed due to strong break-up of hydrocarbons on the surface. Sticking coefficient for ion species increases with increasing plasma temperature, whereas for low plasma temperature (<3 eV) it approaches to the value for neutral species which is independent of the temperature. Our calculations reproduce the redeposition distribution and the difference between C and W roof-like limiters in 13CH4 injection experiments at TEXTOR. The redeposition distribution is more localized for physical sputtering at a W–C mixed layer formed on the W limiter than for chemical sputtering of hydrogenated and amorphized carbon on the C limiter.