Selection of molybdenum lines by quantitative analysis of molybdenum- zirconium-titanium alloy by CF-LIBS for future fusion applications

Molybdenum and its alloys have been chosen as substrate and support material for tungsten thin layers at special limiters and divertors parts of tokamak devices. These Molybdenum parts of the tokamak walls are used for mapping and quantification of material migration and redeposition. In this work, we used Laser Induced Breakdown Spectroscopy (LIBS) as a diagnostic method to analyse Mo-Zr-Ti alloy (TZM) under three different ambient conditions expected in a tokamak in between periods of plasma operation. LIBS spectra were measured under air atmosphere and under Argon and Nitrogen flow at the laser spot on the sample. The resulting plasma plume was created using Nd:YAG (1064 nm) laser operating at the fourth harmonic frequency (266 nm). Atomic and ionic spectral lines of Mo, Ti and Zr were selected from spectra and used for analysis. The evolution of plasma parameters – electron density (ne) and electron temperature (Te) - has been observed by choosing different gate windows and delays relative to the laser pulse. Finally, the elemental concentration of the TZM sample has been calculated by the calibration free LIBS approach. The results are showing that most suitable conditions for elemental analysis are gate delay and gate width equal to 750, 1000, 1500 ns respectively, where we observed similar elementary concentrations in all three conditions.