Quantitative characterization of helium in the ITER-like co-deposition layer by laser-induced breakdown spectroscopy

Abstract

As a product of the D-T burning plasma in tokamak fusion reactors, helium (He) ash would be retained in plasma-facing components like the first wall and divertor, harming the stable operation of burning plasma. The quantitative monitoring of He retention is critical for He removal in these regions. Laser-induced breakdown spectroscopy (LIBS) is a promising technique for this task due to its remote, in-situ, online, and all-element monitoring capabilities. In this work, the LIBS method was employed to quantitatively determine He retention in ITER-like wall material under a vacuum. The characteristic line of He I at 587.56 nm was clearly observed in the collected emission spectrum of the laser-induced plasma, and it was used for the subsequent quantitative analysis. The parameters of LIBS, i.e., the laser fluence and the gate delay of the spectrometer, were optimized to obtain He lines with high signal-to-noise ratios. The absolute concentration of He retained in the ITER-like co-deposition layer was measured by thermal desorption mass spectrometry (TDS) for calibration. The calibration curve exhibited a highly linear relationship between the LIBS intensity of the He I at 587.56 nm line and the He concentration in the co-deposition layer with a fitting coefficient R2 of 0.995. The limit of detection for He areal density using the current LIBS approach with the optimized parameters is achieved to be 1.8 × 1020 He/m2.

Keywords

• Helium retention
• Tokamak
• LIBS
• Quantitative analysis
• Areal density