Calibration-free analysis of a tungsten-based target for diagnostics of relevant fusion materials comparing picosecond and nanosecond LIBS

Highlights

• Surface characterization of W-based materials by LIBS using 5 ns and ~30 ps pulses.

• The electron temperature and density were evaluated to perform CF-LIBS.

• The quantitative analysis of the sample achieved the nominal composition.

• Better results are obtained by ps regime as it provides narrower lines.

Abstract

The elemental analysis of plasma-facing components (PFCs) with deposits is vital for the study of the material erosion, deposition, and fuel retention. For ITER-like divertor, first wall is formed by W-based deposit containing Be, O, D, H and other impurities. The quantification of fuel retention in these materials, including the depth dependence of the fuel retention and the elemental composition, is important. Calibration free laser-induced breakdown spectroscopy (CF-LIBS) is the only technique possible for online remote diagnostics with recognition of the hydrogen isotopes. But the most commonly used ns-LIBS leads to material's overheating; thus, larger non-realistic retention of hydrogen isotopes is generally obtained. In this work, we report the quantitative ps- and ns-CF LIBS analysis of W-based model material (WCu). A WCu alloy has been selected to permit the analysis of tungsten spectral lines in a binary alloy with an element with not too many weak lines. Surface experiments are performed by LIBS using ~30 ps and 5 ns, 1064 nm laser pulses at atmospheric pressure. One of the advantages of ps laser is that it ablates the surface more efficiently, without overheating the ablated material. The laser ablation threshold for the plasma creation in the ps regime is situated at lower energy, thus less material is needed and better depth resolution can be obtained. Suitable Cu and W spectral lines have been selected for the precise evaluation of the electron temperature using the Saha-Boltzmman plots. The electron density values were found from the Saha-Boltzmann plots and the Stark broadening of the H_α spectral line. The results demonstrate the successful detection of W and Cu spectral lines using ps- and ns-LIBS and its quantification.