Speaker
Description
Monitoring and detection of deuterium (D) retention in plasma-facing components in a tokamak is essential for safety and fuel management. In this work, we present femtosecond laser-induced ablation coupled to quadrupole mass spectrometry (fs-LIA-QMS) to investigate D depth profiles in Fe–Zr/Y+D–Fe multilayer samples (each layer ~1 µm) prepared on Si substrates. Fs-LIA-QMS combines ultrafast laser ablation, which removes material layer by layer with minimal thermal damage, with real-time mass spectrometry detection of the ablated species. This approach allows quantitative analysis of gaseous species like hydrogen isotopes with high depth resolution (~10–20 nm per pulse) and minimal sample modification [1].
A comparative study of top-hat and Gaussian beam profiles and their impact on depth resolution was performed. The top-hat beam was produced using an Airy beam shaper (320–450 nm) combined with a theta lens (f = 163 mm) positioned at 162.6 mm along the focal axis, producing a uniform ablation profile with uniformity ~0.71. Analysis using a confocal microscope yields crater radii of approximately 14 µm (top-hat) and 6.5 µm (Gaussian) at 5.6 µJ/pulse. The top-hat beam was selected for its uniform intensity distribution, providing better layer-by-layer depth information of D retention. Each layer was irradiated with 256 laser pulses at 10 kHz, with two QMS measurement cycles synchronized to each laser cycle. Depth profiling was performed over 500 laser cycles, enabling high-resolution ablation in depth. Real-time QMS quantification of D₂ released during ablation was performed, and the D concentration as a function of depth was determined using a calibrated deconvolution procedure.
The obtained fs-LIA-QMS depth profiles are compared with Nuclear Reaction Analysis (NRA) based depth profiles and both resolve the D retained in the Zr layer. A detailed discussion of the obtainable depth-resolved information from fs-LIA-QMS in comparison to the NRA measurement will be presented. The results demonstrate that fs-LIA-QMS is a sensitive, high-resolution technique for characterizing hydrogen isotope retention in fusion-relevant multilayer structures but also highlight the importance of beam-shape selection for accurate depth profiling.
Reference:
[1] S. Mittelmann, M. Mayer, U. von Toussaint, B. Buchner, A. Theodorou, T. Dürbeck, W. Jacob, and T. Schwarz-Selinger, “Femtosecond Laser-Induced Ablation – Quadrupole Mass Spectrometry (fs-LIA-QMS) experiment for the detection of trapped hydrogen isotopes and helium in nuclear fusion relevant materials,” Spectrochim. Acta Part B: At. Spectrosc., vol. 233, p. 107283, 2025. https://doi.org/10.1016/j.sab.2025.107283