Influence of sample temperature on the laser-induced breakdown spectroscopy of a molybdenum–tungsten alloy

Abstract

The analytical capabilities of laser-induced breakdown spectroscopy (LIBS) for in situ elemental analysis of nuclear materials at elevated temperatures were estimated. A certified molybdenum–tungsten alloy (Mo 70 wt% and W 30 wt%) was chosen as a replacement for the high Z impurities deposited on plasma facing components (PFCs) in tokamak. The influence of sample temperature (T_s) on the optical emission of the laser-induced molybdenum–tungsten plasma was investigated with a nanosecond infrared (1064 nm) laser pulse. LIBS experiments were carried out in a wide temperature range from 20 to 410 °C. Surface morphology and depth profiling measurements of the ablated crater for the different temperature conditions were performed. A noticeable dependence of signal emission intensity on T_s has been found. An increase in T_s leads to an increase in the spectral line emissions. In the laser ablation process, the ablation rate, plasma temperature and electron density increase significantly with T_s. In addition, the reflectivity of the alloy surface drops dramatically once oxidation occurs. The decrease of surface reflectivity leads to a greater laser energy coupled to the target and a higher LIBS signal. These results will help improve the LIBS quantitative analysis of high Z impurities in the tokamak device.