In Situ Characterization of Dust Mobilized by Laser Cleaning Methods and Loss of Vacuum Accidents

We investigate the ability of light extinction spectrometry (LES) to characterize, at long distances, the size distribution and concentration of dust mobilized by laser cleaning methods (ITER wall detritiation and characterization of deposition layers) or by experiments dealing with a loss-of-vacuum accident. Potentially harmful effects induced by wall proximity, plasma plume broadband emission, and associated shock waves are shown to have a negligible influence on LES measurements, which demonstrates the interest in this optical technique for the aforementioned studies. However, our experimental results, based on aerosols of silica and tungsten powder aggregates, show that the present setup allows the characterization of dust volume fractions of less than [approximately equal]1-10 ppb for a probing length of 1 m (or by extrapolation [approximately equal]0.1-1 ppb for a probing length of 10 m).