DETAILED STUDY OF RADIATION-ENHANCED SUBLIMATION OF GRAPHITE UNDER HIGH-FLUX BEAM IRRADIATION

The dependence of the erosion yield on angle of incidence and irradiat ion flux for graphite materials at elevated temperature (1980 K) and a t room temperature was studied in high flux regime close to edge plasm a condition. Irradiation was made with 5 keV Ar beam with the highest flux of 10(21) 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 degrees incidence. The yield at RT (physical sputtering) increa sed with angle of incidence in the same manner for isotropic and pyrol ytic graphite. The irradiated surface of pyrolytic graphite at RT show s dense spinous processes, which could relate to the result. The RES y ield at 1980 K, defined as total yield at 1980 K minus physical sputte ring yield at RT, is almost constant with angle of incidence in low fl ux but shows some decrease in high flux. The RES yield calculated base d on an interstitial diffusion model shows very weak angular dependenc e. (C) 1998 Elsevier Science S.A. All rights reserved.