Simulation study of material mixing process on tungsten surfaces at elevated temperatures due to boundary plasma exposure and its influence on plasma wall interactions

Using a dynamic plasma–surface interaction code EDDY, phenomena associated with material mixing, which result from the simultaneous use of W and C as plasma-facing materials, have been simulated. A comparison of the simulation results with the growth of W–C mixed contamination layers at a W surface that was measured in TEXTOR-94 shows good agreement. The agreement shows that this growth is due to thermal diffusion of the deposited C impurity into the W surface, depending on the surface temperature. Also, C+ penetration from the W–C mixed contamination layers into the plasma has been simulated along with chemical erosion including CD4 transport in the plasma. The simulation results have been compared with CII light emission distributions measured in front of a W–C twin test limiter exposed to TEXTOR-94 plasmas. These comparisons show that the contribution of chemical erosion to the C release is suppressed due to the W–C mixed contamination layers.