Plasma cleaning of boron-based contaminants for fusion diagnostic first mirrors

Plasma–material interaction (PMI) is one of the major challenges in the development of future fusion reactors, as it critically affects plasma–facing components and, in particular, the performance of diagnostic first mirrors. This work investigates PMI phenomena relevant for the cleaning of diagnostic first mirrors in fusion reactors. Representative rhodium mirrors have been produced and contaminated with boron and boron–tungsten deposits, to resemble redeposition phenomena occurring during operation, and exposed to deuterium and argon plasmas in the GyM linear device at ISTP, in Milan. The outcome of the study showed that deuterium plasmas effectively removed boron nanoparticles with minimal mirror damage, while argon plasmas were most effective for tungsten removal and induced surface nanostructuring. The study demonstrates the complementarity of argon and deuterium plasmas for cleaning purposes and establishes a laboratory-scale framework to assess erosion and cleaning efficiency, providing insights for optimizing in-situ mirror cleaning in ITER and future fusion devices.