Detailed study of radiation enhanced sublimation of graphite under high flux beam irradiation

The dependence of the erosion yield on angle of incidence and irradiation flux for graphite materials at elevated temperature (1980 K) and at room temperature was studied in high flux regime close to edge plasma condition. Irradiation was made with 5 keV Ar beam with the highest flux of 1021 m−2 s−1. It is found that similar reduction of the yield at 1980 K with flux was observed for isotropic graphite (IG-430 and ISO-630) and pyrolytic graphite at normal incidence and for IG-430 at 60° incidence. The yield at RT (physical sputtering) increased with angle of incidence in the same manner for isotropic and pyrolytic graphite. The irradiated surface of pyrolytic graphite at RT shows dense spinous processes, which could relate to the result. The RES yield at 1980 K, defined as total yield at 1980 K minus physical sputtering yield at RT, is almost constant with angle of incidence in low flux but shows some decrease in high flux. The RES yield calculated based on an interstitial diffusion model shows very weak angular dependence.