Experimental and model study of LIBS depth profile for multilayer deposition materials

Abstract

The patterns of erosion and deposition occurred in the plasma-facing materials (PFMs) of a magnetic confinement fusion device are crucial for the investigation of plasma-wall interaction (PWI). The deposition behavior can be identified by the elemental depth profile of the deposition layer. As an effective remote monitoring method for the wall in nuclear fusion devices, laser-induced breakdown spectroscopy (LIBS) shows excellent potential for the depth profiling of the deposition layer on the PFMs. However, some potentially influencing factors lead to the difficulty of distinguishing and identifying the interfaces between the deposition layers and substrate. The measuring accuracy of the deposition layer thickness plays an essential role in PWI research. In this paper, depth profiling of multilayer samples with Ni layers on Cu were performed using LIBS with an ns-pulse laser. The experiment was carried out under 5 × 10−5 mbar to simulate the operation of a nuclear fusion device. Meanwhile, a two-dimensional model for multi-pulse LIBS depth analysis based on the laser beam profile factor and interface roughness factor was established to reconstruct and predict the elemental depth profile distribution of NiCu multilayer materials. The correlation coefficients between the experimental and modeling data were all >0.99. We introduced a locating approach for the interface based on model prediction, and the relative errors of all Ni layer thicknesses were < 5.1%, demonstrating the feasibility and accuracy of the model. All the results show that the two-dimensional numerical model can improve the accuracy of LIBS depth profile on layer thickness analysis and further promote the application of in situ LIBS diagnosis in PWI research.