Molecular dynamics study on hydrocarbon interaction with plasma facing walls

A molecular dynamics (MD) simulation was undertaken to investigate hydrocarbon interactions with fusion related W and C surfaces. W–C mixed and hydrogenated amorphous C layers on the surface were prepared by collisions of C and H atoms at different impact energies on a W crystalline cell. The reflection coefficient for CHy and C2Hy and the distribution of the reflected species were calculated and we determined their dependence on energy and angle. The mixing of W with C reduces the reflection coefficient where C atoms dominate the distribution at energies of 30 eV or more, and this is similar to non-doped W. The amorphization of graphite strongly decreases the reflection coefficient where the emission of small hydrocarbons is suppressed but hydrogen uptake in the amorphous C increases it slightly. The amount of injected hydrogen per hydrocarbon impact on different material surfaces is discussed in relation to the fuel retention of plasma facing walls.