Speaker
Description
Laser-Induced Breakdown Spectroscopy (LIBS) is a key diagnostic for analysing plasma-facing components in fusion devices [1], where erosion, migration, redeposition and fuel retention produce complex multi-element layers containing Be, W, Mo, H/D/T isotopes and various impurities [2,3]. Accurate characterisation of these layers is essential for understanding material migration, surface composition and fuel retention in ITER and future pilot fusion plants.
In this work, we analyse in-situ LIBS data from the JET robotic wall-inspection system acquired during recent D/T campaigns to obtain quantitative depth profiles of major and minor elements and retained hydrogen isotopes. Sub-nanosecond LIBS spectra were recorded at 840 wall positions, with several hundred laser shots per location, using a broadband echelle spectrometer (255–760 nm) and a narrow-band Littrow spectrometer centred on the Hα line (656 nm). The experimental setup is described in detail in [4–6].
Quantification uses the Calibration-Free LIBS (CF-LIBS) method applied to interference-free lines of W, Mo, Be, Ti, Ni and Cr. Electron temperature (approximately 0.7 eV) is obtained from multi-element Boltzmann plots using several hundred lines, while electron density is evaluated with the Saha equation. This ensures the precision required for reliable CF-LIBS quantification. Spectral averaging is necessary to reduce noise, but it directly affects depth resolution: minimal averaging (2–5 shots) preserves high resolution for major elements, while minor-element detection requires stronger averaging, reducing depth precision. Case studies on inner divertor tiles demonstrate CF-LIBS depth profiles over ~500 laser shots with depth resolution down to only a few shots. Quantified species include W, Mo, Be, H/D/T, Ti, Ni, Cr and impurities such as Cu and Ca, while C and O could not be detected due to the limited spectral range.
References:
[1] G. S. Maurya et al., Journal of Nuclear Materials, 541 (2020) 152417.
[2] J. P. Coad et al., Journal of Nuclear Materials, 313–316 (2003) 419.
[3] P. Veis et al., Nuclear Materials and Energy, 25 (2020) 100809.
[4] J. Likonen et al., Nuclear Materials and Energy, 45 (2025) 102021.
[5] J. Ristkok et al., Nuclear Materials and Energy, 44 (2025) 101968.
[6] R. Yi et al., Nuclear Materials and Energy, 45 (2025) 102016.
[7] A. Ciucci et al., Appl Spectrosc, 53 (1999) 960.
[8] P. Veis et al., Phys. Scr., T171 (2020) 014073.
[9] M. Hornackova et al., Eur. Phys. J. Appl. Phys., 66 (2014) 10702.