SIMS analysis of the interaction between plasmas and the graphite first wall in RFX-mod

Modified Reversed-Field eXperiment is an experiment of magnetic confinement of thermonuclear plasma in the Reversed-Field Pinch configuration. The toroidal device is designed to operate with hydrogen plasmas, and the most internal wall is entirely covered with polycrystalline graphite tiles. The disadvantage of graphite walls is the progressive hydrogen accumulation in graphite during operation. To overcome this problem, some graphite conditioning procedures are necessary (e.g. boronization, lithization and glow discharge). The critical role of graphite walls on plasma control suggested the use of secondary ion mass spectrometry (SIMS) technique for the evaluation of conditioning procedures efficacy. SIMS analyses of graphite samples after their exposure to plasmas or wall conditioning treatments are presented in this work. The SIMS technique resulted fundamental on the investigation of the boron distribution in the graphite tiles, and sample comparisons indicated the need for glow discharge cleaning system upgrading to improve the conditioning process and boronization uniformity.