In-vessel and depth-resolved semi-quantitative analysis on hydrogen isotopes and wall materials in JET by LIBS operated on a remote handling arm

The tokamak JET achieved a groundbreaking milestone in nuclear fusion during its final deuterium–tritium experimental campaign (DTE-3) by setting a new world energy record [1]. To investigate in-vessel the fuel retention and wall material migration in JET post DT operation and clean-up phase with baking and glow discharge cleaning, a laptop-sized laser-induced breakdown spectroscopy (LIBS) system was deployed and mounted on a remote handling arm inside JET. The 800 ps (10 mJ) laser (wavelength 1064 nm) achieved a spatial and depth resolution of 130 μm and 180 nm on tungsten plasma-facing components (1000 pulses), respectively. Over 800 positions including beryllium first wall and tungsten divertor were studied by LIBS and provided both the spatial distribution and depth profiles of retained hydrogen (H) isotopes. LIBS spectra from four spectrometer systems enabled both high-resolution, high-sensitivity measurements and a broad spectral range simultaneously. Among them, a high throughput and high spectral resolution spectrometer in Littrow-arrangement was applied to distinguish the hydrogen isotopes. This in-vessel analysis demonstration provides vital information about the applicability of the technique for retention studies in future fusion reactors.