Improvement of Carbon Properties used as PFCs in Tokamaks by Nitrogen Irradiation

摘要

Many properties of carbon make it suitable for plasma facing components (PFC). However, chemical erosion of carbon by hydrogen and oxygen at high temperature causes a dilution of the plasma and an important loss of energy by radiation. Diffusion of hydrogen in carbon as well as its poor retention constitute other major obstacles concerning the use of carbon in PFCs. Inspired by the work done for synthesis of C_2N_4 and its promising properties, we have studied the use of carbon implanted with nitrogen as PFC's. Thermal annealing used in combination with surface analysis tools (ERD ExB, RBS, XPS) were used to characterise in laboratory the influence of N implantation on the retention of hydrogen and the chemical erosion of two kinds of carbon (a-C and CFC). Results from laboratory experiments show the N implantation in carbon slows down the diffusion of hydrogen and causes an improvement of its retention without a significant increase in methane and ethylene emission during thermal annealing for an appropriate implantation dose (N/C～0.2). These results suggest that implantation of N in carbon is a valuable tool to improve the properties of carbon in PFC's.