Effects of carbon impurity in fusion plasmas on erosion of RAF first wall

Sputtering erosion of RAF (reduced-activation ferritic/martensitic steel) was studied under hydrogen and carbon mixed ion beam irradiation. Ion beam energy, flux, and fluence were 1 keV H3+ (dominant species), ∼1.5 × 1020 H/m2 s and ∼5 × 1024 H/m2, respectively. Erosion yields of RAF irradiated by the mixed ion beams are found to be temperature dependent. For carbon concentration in the beam of 0.84% (1.3%), an effective erosion yield at 453 K is lower than that at 773 K by 18% (34%). For 0.8% C in the beam, the surface carbon composition at 453 K is about 20%, while at 773 K it is very low (∼3%), which suggests swift carbon diffusion into the bulk. This experimental surface carbon concentration agrees with simulation results by the EDDY code. The change in the effective erosion yield with temperature is consistent with the change in surface carbon concentration.