CD4 production from mixed W–C–D surface during simultaneous irradiation of W with C+ and D+

Simultaneous irradiation of W was performed with 6 keV C+ and 0.1–0.4 keV D+ ion beams; the C fraction in the combined total flux was ∼4%. Beam energies and fluxes were selected to provide continuous erosion of the mixed W–C–D surface, preventing the formation of a carbon overlayer. The temperature-dependent features of the methane production curves confirm the occurrence of chemical erosion from the mixed-material surface. In general, the curves exhibit the highest erosion rates at room temperature (∼300 K) followed by a decreasing trend with increasing temperature. Methane yield (CD4/D+) estimates are ∼1–1.5% at RT, decreasing to ∼0.5% at 500 K, and levelling off at higher temperatures. XPS depth profiles confirm the depletion of C from the mixed W–C–D surface layer; however, at present we cannot determine what fraction of this is due to physical or chemical sputtering.