Shadowgraph technique applied to stardust facility for dust tracking: first results

The problem of dust resuspension in case of Loss Of Vacuum Accident (LOVA) in a nuclear fusion plant (ITER or DEMO like) is an important issue for the safety of workers and the security of environment. The Quantum Electronics and Plasma Physics Research Group has implemented an optical set-up to track dust during a LOVA reproduction inside the experimental facility STARDUST. The shadowgraph technique, in this work, it is applied to track dark dust (like Tungsten). The shadowgraph technique is based on an expanded collimated beam of light emitted by a laser (or a lamp) transversely to the flow field direction. Inside STARDUST the dust moving in the air flow causes variations of refractive index of light that can be detected by the means of a CCD camera. A spatial modulation of the light-intensity distribution on the camera can be measured. The resulting pattern is a shadow of the refractive index field that prevails in the region of the disturbance. The authors use an incandescent white lamp to illuminate the vacuum vessel of STARDUST facility. The light-area passes through the test section that has to be investigated and the images of the dust shadows are collected with a fast CCD camera. The images are then elaborated with mathematical algorithms to obtain information about the velocity fields of dust during the accidents reproduction. The experimental set-up together with a critical analysis of the first results are presented in this paper.