Towards ultra-sensitive <i>in situ</i> helium retention monitoring in high-<i>Z</i> fusion materials via combined laser-induced breakdown spectroscopy and laser-induced desorption– quadrupole mass spectrometry

Abstract In situ monitoring of helium (He) retention in plasma-facing materials 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 the signal-to-noise ratio 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 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 for He in Mo and W co-deposited layers are 0.72 × 10 14 He mm −2 (0.09 at.%) and 0.84 × 10 14 He mm −2 (0.11 at.%), respectively, being 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 longstanding 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 PWIs and facilitating advancements in plasma-facing component design.