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  • Laser-induced breakdown spe...
    Jõgi, Indrek; Paris, Peeter; Ristkok, Jasper; Roldán, Alicia Marin; Bhat, Pavitra Ganapati; Veis, Pavel; Karhunen, Juuso; Almaviva, Salvatore; Gromelski, Wojciech; Dinca, Paul; Porosnicu, Corneliu; Radović, Iva Bogdanović; Siketić, Zdravko; Gąsior, Paweł; Likonen, Jari; Hakola, Antti

    Nuclear materials and energy, June 2024, 2024-06-00, 2024-06-01, Volume: 39
    Journal Article

    •He detection by LIBS method was investigated in He containing Be coatings.•At optimized conditions, 2.8 % of He was confidently detectable with LOD 0.7 %•There was an upper limit of 20 mbar Ar background pressure for reliable He detection.•He detection was limited due to the He line broadening and increased noise.•Very high excitation energy of He atom complicates the application of CF-LIBS. Laser Induced Breakdown Spectroscopy (LIBS) method is considered to be a promising tool for analyzing the retention of hydrogen isotopes (D and T) and helium (He) on the first walls and divertor regions of future fusion reactors. Helium will be produced in DT reactions but could also be used in the initial non-nuclear phases of DEMO concepts. The present study investigates the He detection by LIBS method in the Be coatings simulating the deposits on the divertor plasma-facing components of JET while the results are also relevant for He detection in the deposits of other wall materials. The study was carried out in a vacuum vessel filled with 2–40 mbar argon background gas. It was shown that 2.8 at. % of He was confidently detectable by LIBS at optimized measurement conditions and the estimated limit of detection at used experimental conditions is approximately 0.7 at. %. The intensity of the He emission line at 587.56 nm was the strongest at the center of the laser-induced plasma plume. The He line intensity increased with the pressure of Ar gas but the broadening of the He line and the increase of the background emission and noise set an upper limit to the Ar background pressure usable for He detection. The application of the calibration-free LIBS procedure resulted in the overestimation of the He/Be ratio by several orders of magnitude. The overestimation can be explained by the deviation of LIBS plasma from the local thermodynamic equilibrium, which is caused by the very high excitation energy of He atoms.