Towards ultra-sensitive in-situ helium retention monitoring in high-Z fusion materials via combined LIBS and LID-QMS

In-situ monitoring of helium (He) retention in plasma-facing materials (PFMs) of nuclear fusion devices is critical for understanding plasma-wall interactions (PWIs). This study introduces a transformative approach to optimize He detection in high-Z materials—tungsten (W) and molybdenum (Mo)—using laser-induced breakdown spectroscopy (LIBS) under vacuum conditions. The He I 587.56 nm spectral line was identified as the optimal analytical signal for LIBS due to its dominant intensity and resilience to spectral interference from high-Z elements. By systematically optimizing gate delay timing and leveraging spatial plasma emission characteristics, a threefold improvement in signal-to-noise ratio (S/N) was achieved through the exclusion of core plasma emissions, where bremsstrahlung background and matrix interference are most pronounced. Quantitative calibration curves were established using laser-induced desorption quadrupole mass spectrometry (LID-QMS) as a reference, with internal standardization reducing prediction errors to ≤10%—significantly enhancing accuracy in the face of variable laser ablation rates. The achieved limits of detection (LODs) for He in Mo and W co-deposited layers are 0.72×1014 He/mm2 (0.09 at.%) and 0.84×1014 He/mm2 (0.11 at.%), respectively—the lowest reported values for high-Z materials to date. This work delivers critical calibration parameters and a robust methodology for in-situ LIBS diagnostics, addressing the long-standing challenge of real-time He retention monitoring in fusion devices. The proposed approach paves the way for practical applications in tokamaks such as ITER and EAST, enabling precise characterization of plasma-wall interactions and facilitating advancements in plasma-facing component design.