Accessory laboratory measurements to support quantification of hydrogen isotopes by in-situ LIBS from a robotic arm inside a fusion vessel

In order to try to improve spectral separation for hydrogen isotope detection in plasma facing components, a flow of noble gas at reduced pressure is proposed as alternative to atmospheric pressure experiments in air during maintenance of fusion vessels. To this aim the already realized compact LIBS probe has been equipped with a sealable tip where a noble gas could flow. The tip was in contact with the selected point of the target and its proper positioning was guaranteed by an adjustable metallic cone. Laboratory measurements were carried out by flowing either He or Ar on ITER-like tiles. A positive effect of Ar flow on Hα signal intensity was observed, while a significant narrowing of the Hα band was obtained upon He addition. Additional measurements on deuterium doped samples simulating the tile's composition in ITER divertor region were performed by applying a local vacuum in the point of analysis or utilizing the set-up in double pulse (DP) mode. These experiments were aimed at optimizing the acquisition parameters of the LIBS setup (e.g, single or double pulse excitation, gate delay, gate width, interpulse delay) when operated in different conditions (vacuum, atmospheric pressure, under gas flow) in order to resolve the two nearby emission bands Hα and Dα, still preserving a satisfactory Signal-to-Noise-Ratio (SNR). Finally, considerations on applicability of Calibration Free (CF) method for the quantification of hydrogen isotopes are presented.