Simulation calculation of ion-induced sputtering yields for plasma-irradiated solid surfaces

Abstract

A computer code ACAT, is used to evaluate the self-sputtering of graphite by carbon ions, taking into account finite temperature effect, the boundary sheath potential and the angle δ between the magnetic field vector and the normal to the surface. These yields are calculated for many initial energies and angles — which obey the shifted Maxwellian distribution — using the Monte Carlo random number technique and then averaged. It is found that for the precise understandings of sputtering thresholds and sputtering yields we should use the distributed ion sources such as the shifted Maxwellian as the ion source, not the average angles and average energies of the distributed ion source, because both the energy dependences of the near threshold sputtering and the bombarding angle dependence of the grazing angle sputtering are very strong. The influences of T i, of the temperature ratio T i/ T e and δ are also discussed. The sputtering yield becomes larger than unity for T e > 100 eV, when T i/ T e > 5. This is a very severe problem for erosion of divertor plates. It means that we need a more precise knowledge of ion temperature on the operating conditions.