Laser dust removal: mechanisms and applications
Résumé
The presence of particles on surfaces can be a strong problem in terms of pollution (optics), defect (microelectronics) or security (nuclear). In this context, the removal of highly adhering particles from surfaces (silicon or other materials) remains a challenge. Many studies have been performed in the field of microelectronics to evaluate the potentiality of various cleaning techniques. Among them, dry laser cleaning appeared as a very powerful process to eject small particles from surfaces. The purpose of this work is to apply this technique in the frame of the ITER project to remove C, W and Be particles from the reactor walls. The aim of this presentation is to describe the laser-induced particle removal technique based on fast energy transfer between the incident beam and matter. The ejection mechanisms have been experimentally studied for different conditions of laser or material. They are related to photochemical, mechanical or thermal effects. The relative importance of these processes will be discussed as a function of the dust material and structure and of the laser irradiation characteristics. Preliminary experiments related to the ITER project will be also described. The first step was to create W and C particles representatives to those formed in a Tokamak. For this purpose, we collected on a W substrate the aggregates formed during laser ablation of CFC or W targets. The shapes of such particles are very similar to those observed in the fusion reactors. A brief theoretical description of the processes leading to the formation of these aggregates in the laser-produced plasmas will be given. Then, the removal efficiency of such particles will be discussed as a function of the irradiation characteristics (laser fluence and wavelength). The velocity of the ejected particles will be also determined.