Experimental investigation on laser removal of carbon and tungsten particles

During the operation of the ITER fusion facility, particles with size from 10 nm to 100 μm, mainly composed of carbon, beryllium, and tungsten, will be produced. Since dust could lead to safety issues, it must be periodically removed from the facility in order to keep their quantity below the safety limit requirements. In this context, laser cleaning appeared as a very promising technique, and investigations have to be done to understand the physical processes and optimize the procedure. Several experiments were carried out to improve the understanding of the phenomena involved during the laser-induced removal of Carbon particles. The ejection mechanisms have been experimentally studied for different irradiation conditions with nanosecond laser pulses. The removal efficiency and the fluence threshold were determined by optical microscopy. The influence of the substrate was studied for the dry laser cleaning configuration. This study presents scanning electronic microscopy pictures which show that the particle removal leads to a damage of the substrate. These damages give evidences on the ablation mechanism. The laser shock cleaning was also studied. In this configuration, the laser-induced shock wave can be used to push the particles away from the surface. This technique appears to be very useful to clean shadowed areas.