Dynamics of ion irradiation defects

We have investigated radiation enhanced sublimation of graphite and chemical sputtering of graphite under high flux beam irradiation(up to 10 I D 122 I D 1 m I D 1-2 I D 1 s I D 1-1 D 1)to study the dynamics of ion irradiation defects and its effects on the above-mentioned erosion processes of graphite.The obtained results are as follows：1.Radiation enhanced sublimation of isotropic graphite was investgated with 5keV Ar beam with the flux up to 10 I D 121 I D 1 m I D 1-2 I D 1 s I D 1-1 I D 1)。It is found that as irradiation flux exceeds10个D120个D1m个D1-2个D1s个D1-1个D1 erosion yield decreases rapidly with flux asΦD1-0.26个D1(Φ：flux)。This flux dependence is much stronger than the previous low flux results(&lt；10个D 120个D 1m I D1-2个D1s个D1-1个D1，Φ个D1-0.1个D1)。According to self-interstitial diffusion theory，flux dependence of erosion yield of radiation enhanced sublimation might be elucidated provided that sinks for interstitials are stable defects for low irradiation flux(&lt；10 I D120 I D1-2…More I D 1 s I D 1-1 I D 1)and vacancies for high irradiation flux(&gt；10 I D 120 I D 1米I D 1-2 I D 1 s I D 1-1 I D 1).2.Measurements of chemically sputtered methane(CD)D24-D2)were made with 5keV D-D3+(/)3-D3beam irradiation by a quadrupole mass analyser installed in a differential pumping chamber.Samples were isotropic graphite(JG-430)，CFC graphite(CX2002)，boron-doped graphite(GB series，boron content0%to20%)，and silicon-doped graphite(TS Processed Graphite)。It is found that peak temperature at which methane signals took maximum increased with flux up to about1000K.This temperature was not observed previously(Less Than850K)and could be considered as a high flux effect。In addition，methane yield(Methane Signal Divided By Flux)did not show flux dependence。These results are not consistent with a typical chemical sputtering model made by Roth et al.Under the assumption that the annealing effects of graphite prevents methyl group formation above the temperature of 800K.Chemical sputtering yield of boron-doped graphite is reduced by about a factor of3compared with pure graphite samples。For silicon-doped graphite with the atomic ration of about1/1.Chemical sputtering was almost suppressed。Less：Less

We have investigated radiation enhanced sublimation of graphite and chemical sputtering of graphite under high flux beam irradiation (up to 10ィイD122ィエD1 mィイD1-2ィエD1sィイD1-1ィエD1) to study the dynamics of ion irradiation defects and its effects on the above-mentioned erosion processes of graphite. The obtained results are as follows :1. Radiation enhanced sublimation of isotropic graphite was investgated with 5keV Ar beam with the flux up to 10ィイD121ィエD1mィイD1-2ィエD1sィイD1-1ィエD1). It is found that as irradiation flux exceeds 10ィイD120ィエD1mィイD1-2ィエD1sィイD1-1ィエD1 erosion yield decreases rapidly with flux as ΦィイD1-0.26ィエD1 (Φ : flux). This flux dependence is much stronger than the previous low flux results (< 10ィイD120ィエD1mィイD1-2ィエD1sィイD1-1ィエD1, ΦィイD1-0.1ィエD1). According to self-interstitial diffusion theory, flux dependence of erosion yield of radiation enhanced sublimation might be elucidated provided that sinks for interstitials are stable defects for low irradiation flux (< 10ィイD120ィエD1mィイD1-2 … More ィエD1sィイD1-1ィエD1) and vacancies for high irradiation flux (>10ィイD120ィエD1mィイD1-2ィエD1sィイD1-1ィエD1).2. Measurements of chemically sputtered methane (CDィイD24ィエD2) were made with 5 keV DィイD3+(/)3ィエD3 beam irradiation by a quadrupole mass analyser installed in a differential pumping chamber. Samples were isotropic graphite (JG-430), CFC graphite (CX2002), boron-doped graphite (GB series, boron content 0% to 20%), and silicon-doped graphite (TS processed graphite). It is found that peak temperature at which methane signals took maximum increased with flux up to about 1000 K. This temperature was not observed previously (less than 850 K) and could be considered as a high flux effect. In addition, methane yield (methane signal divided by flux) did not show flux dependence. These results are not consistent with a typical chemical sputtering model made by Roth et al. under the assumption that the annealing effects of graphite prevents methyl group formation above the temperature of 800 K. Chemical sputtering yield of boron-doped graphite is reduced by about a factor of 3 compared with pure graphite samples. For silicon-doped graphite with the atomic ration of about 1/1. Chemical sputtering was almost suppressed. Less