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Laser-induced breakdown spectroscopy (LIBS) is a technique developed for determining fuel retention in ITER plasma-facing components (PFCs) [1]. It can also analyse the formation of various layers on PFCs caused by material redeposition eroded from other regions. A series of experiments was conducted at the JET tokamak after the third deuterium-tritium campaign, DTE3, to demonstrate the feasibility of using the LIBS tool for in-situ fuel retention measurements and material migration analysis. [2]. The LIBS instrument, operated on the remote handling arm system MASCOT, included a sub-nanosecond laser with focusing optics inside a compact enclosure [2]. Emission from the LIBS plasma plume was directed into a 20 m optical fibre and then through a multi-channel fibre bundle to various spectrometers. An Echelle-type spectrometer captured spectra over a broad range of 260-760 nm to determine the elemental depth profiles of elements present in the PFC layers [2]. A custom-made Littrow-type spectrometer recorded spectra in a narrow wavelength range of 654-658 nm with good spectral resolution and was used to measure the emission line intensities of hydrogen isotopes T, D and H [3].
LIBS experiments were conducted at 840 different locations on the JET wall and divertor. This study presents experimental results from various locations on the inner wall guard limiter (IWGL), including 2X beam tiles in upper, central and lower poloidal positions, as well as wing and central toroidal positions. The in-situ LIBS results aligned with previous studies using ex-situ characterization methods after the ILW1-ILW3 campaigns [4-5]. On the wings of the tiles, LIBS depth profiles revealed Ni-, Cr-, and W-containing surface layers, which were absent in the central tile regions. The D signal was present on the surface of all investigated positions. On the wings of the tiles, the D signal remained detectable at a deeper level within the tile but was relatively weaker at the surface.
[1] H.J. Meiden, S. Almaviva, J. Butikova et al. Nucl. Fusion 61 (2021) 125001
[2] J. Likonen, S. Almaviva, R. Rayaprolu et al. Nucl. Mater. Energy 45 (2025) 102021
[3] R. Yi, R. Rayaprolu, J. Likonen et al. Nucl. Mater. Energy 45 (2025) 102016
[4] A. Baron-Wiechec, A. Widdowson, E. Alves et al. J. Nucl. Mater 463 (2015) 157
[5] A. Widdowson, J.P. Coad, E. Alves et al. Nucl. Mater. Energy 19 (2019) 218