Laser-Induced Breakdown Spectroscopy as Diagnostics for Plasma-Wall Interactions Monitoring in Tokamaks
P. G─ůsior
IFPILM, Hery 23, 01-497 Warszawa, Poland
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Plasma-wall interactions in tokamaks inflict local erosion which often leads to the deposition of the removed material in distant areas, mainly lower temperature zones of the divertor. This phenomenon is accompanied with the accumulation of fuel particles in deposits, which is called fuel retention, and in future will be particularly important in the case of radioactive tritium. The fuel inventory needs to be monitored which therefore requires a measurement method which, due to the harsh thermonuclear conditions, must be contactless and highly resistant to electromagnetic interference. The method which satisfies these prerequisites is laser-induced breakdown spectroscopy basing on the remote acquisition of the optical signal which may be induced by a laser head installed on a remotely controlled conveyor or even outside the device. The presented method was originally applied for the carbon-based plasma-facing components which manifested intensive chemical erosion and therefore unacceptably high rate of fuel retention. Nevertheless, the method proved its capability for these conditions and furthermore was found to be even more advantageous for plasma-facing components manufactured with the use of mixed materials (beryllium and tungsten) since it allowed for the monitoring of the material transport to the divertor. At the IPPLM, research on laser-induced breakdown spectroscopy originated from the former investigation of the possibility of employing pulse lasers in the laser cleaning of the fuel inventory. The recent work outlines the progress of the method: starting from a spin-off application for monitoring of the laser cleaning process, through the adaptation to mixed material components, to the advanced alternatives such as dual pulse or calibration-free laser-induced breakdown spectroscopy which are currently under development in EUROfusion collaboration with such international partners as ENEA Frascati, FZJ and others.

topics: thermonuclear fusion, plasm-wall interactions, laser-induced breakdown spectroscopy, LIBS