Simulation Study on Influence of Chemically Eroded Carbon Impurity Transport on Net Sputtering Erosion of Carbon Materials Exposed to Edge Fusion Plasmas

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Regarding TEXTOR and ITER-FEAT fusion devices, the net sputtering erosion rate of C targets exposed to their edge fusion plasmas has been investigated using a simulation code for plasma surface interactions, EDDY. The influence of the transport of chemically eroded CD4 molecules on the net erosion rate is presented. Emphasis is put on the difference in the simulated results between the CD4 reaction chain with e−, the CD4 reaction chain with e− plus D+, and the sticking coefficients of CDx locally returned back to the targets, which are related closely to the local redeposition, for a variety of plasma densities and temperatures. In particular, at a high density such as 1019 m−3 and low temperatures of less than 10 eV, the net erosion rate is found to be suppressed by a significant contribution of the local redeposition resulting from the charge exchange reactions of CDx with D+ if all the locally returned CDx radicals stick. For the ITER-FEAT divertor plasma, the profile of the net erosion rate along the outer vertical target is significantly changed by the C impurity concentration in the plasma, which is eroded from other wall surfaces and then transported by the plasma. For the D+ plasma exposure only, the net erosion rate is highest around the separatrix strike point. On the other hand, it is highest at the private plasma region if a few percent of the C impurity concentration is added to the D+ plasma exposure. The local redeposition resulting from the charge exchange reactions significantly suppresses the net erosion rates at these plasma regions, but does not bring about a significant change in the erosion/deposition profile along the outer vertical target.

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