Influence of Carbon Impurity on Net Erosion of Reduced-Activation Ferritic/Martensitic Steel and Tungsten Materials Exposed to Hydrogen and Carbon Mixed Ion Beam Relevant to Fusion Plasma Boundary

Abstract

Using a simulation code for dynamic interactions between energetic ions and solid materials, the influence of C impurity concentration on net erosion of reduced-activation ferritic/martensitic steel, RAF (Fe in the simulation), and W materials exposed to a 0.33 keV H+ and 1 keV C+ impurity mixed ion beam relevant to a fusion plasma boundary has been studied. A comparison of the simulation results between the Fe and W materials at C impurity concentrations less than C: 1.00% is described and discussed. In particular, emphasis is paid to a quantitative comparison between depth profiles of C impurity deposited on the materials and the experimental data, which were obtained by the H and C mixed ion beam exposure experiments of RAF (F82H in the experiment) and W materials. For the W material, chemical erosion (CH4 emission) of the deposited C impurity by the H+ impact is taken into account in the simulation. The C impurity concentration causes a significant difference in net erosion between the two materials. For the Fe material, net erosion is suppressed with increasing C impurity concentration. In contrast, for the W material, net erosion is enhanced. In the depth profile, there is also a significant difference between the two materials. At C: 0.11%, the impinging C impurity is hardly deposited on the Fe material. For the W material, the depth profile at C: 0.11% shows a local peak around a certain depth, which is in good agreement with the experimental data at 653 K. This agreement indicates no contribution of the chemical erosion in the H–C–W system, which is quite different from that in the H–C system where the chemical erosion occurs. The difference seems to indicate that the chemical erosion in the H–C–W system is dependent upon amounts of the deposited C impurity or the binary alloy phase change between W and C. When the C impurity concentration increases to C: 0.84%, the impinging C impurity is deposited on the Fe material. The depth profile shows a maximum at the top surface, which reproduces the experimental data at 453 K. For the W material, the depth profile at C: 0.84% shows almost the same tendency as that at C: 0.11%, but shows a larger amount of the deposited C impurity. The simulation result at C: 0.84% is in disagreement with the experimental result at 653 K, which shows a maximum at the top surface. This disagreement is not fully explained by only the chemical erosion.