CF-LIBS study of pure Ta, and WTa + D coating as fusion-relevant materials: a step towards future in situ compositional quantification at atmospheric pressure

Tungsten (W) and its alloys are being considered as a major candidate for the plasma-facing components (PFCs) in future fusion devices. Being versatile and able to perform in situ measurements, laser-induced breakdown spectroscopy (LIBS) is the most promising analytical tool for the elemental characterization of fusion-relevant materials. The present article studies the use of calibration free (CF)-LIBS for the characterization of the plasma generated from tantalum (Ta) and elemental quantification of WTa (5 at.%) + Deuterium (D) (10 at.%) sample (coating thickness ~ 3 µm) on molybdenum (Mo) substrate, using a high energy Nd:YAG laser (1064 nm, pulse duration 8 ns). The laser energy has been optimized (58 mJ/pulse) for given samples, and the laser-induced plasma was generated on the surface by means of focussing the laser. All the experimental measurements have been performed in air at atmospheric pressure and room temperature. For the quantification of WTa + D coating, measurements have also been performed under the flow of nitrogen gas. For the detection of the analytes, both gate delay ( t d ) and gate width ( t g ) were optimized. For the CF quantification, it has been found that the most appropriate gate times were t d = t g = 1 µs, considering thermodynamic equilibrium. Suitable emission from both neutral and ionic species has been considered for the evaluation of the plasma temperature and electron density using the Boltzmann and Saha–Boltzmann plots approaches, respectively. This work provides a step towards CF-LIBS quantification and depth profile analysis studies for WTa-based materials and D retention in it. These results have been compared with those obtained by other analytical techniques (TOF-ERDA and GDOES).