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

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 (Ts) on the optical emission of laser-induced molybdenum-tungsten plasma was investigated with nanosecond infrared (1064 nm) laser pulse. LIBS experiments were carried out in a wide temperature range from 20 to 410 ℃. Surface morphology and depth profiling of the ablated crater for the different temperature conditions were performed. A noticeable dependence of signal emission intensity on Ts has been found. An increase in Ts 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 Ts. 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 signals. These results will help improve the LIBS quantitative analysis of high Z impurities in tokamak device.