Spatiotemporal dynamic characterization of the laser-induced plasma of a mixed material (WCCu) under variable ablation angles in a vacuum

Abstract

The real-time composition information of the surfaces of the plasma-facing components (PFCs) in the tokamak, especially the divertor region, is of great significance for understanding and revealing the plasma–wall interaction (PWI) process. As a promising in situ diagnostic method of wall surfaces, laser-induced breakdown spectroscopy (LIBS) has been well proven to detect the elemental distribution of PFCs on the Experimental Advanced Superconducting Tokamak (EAST). Under the limitation of complex working conditions, the influence of laser ablation angles (LAAs) on the LIBS spectra needs to be paid much attention to ensure the accuracy of measurement results. Meanwhile, due to the processes of fuel retention, erosion and redeposition, the PFC surface is always composed of mixed layers of high and low Z elements, so it is significative to investigate the spatiotemporal dynamic evolution of high and low Z elements in the detecting region of LIBS under different LAAs. In this paper, a LIBS system with a coaxial collection configuration based on a linear array fiber bundle is developed to investigate the features of a laser-induced tungsten carbide copper (WCCu) plasma at variable LAAs under simulated EAST vacuum conditions. The spatial and temporal distribution of optical emission shows that the spectra of the three elements with different charge states are significantly different under orthogonal and oblique ablation. Inappropriate spectral acquisition parameters can significantly increase measurement errors under variable LAAs. The spatiotemporal dynamic evolution of the characteristic spectral lines of the three elements under orthogonal ablation and oblique ablation has been systematically characterized by optical emission spectroscopy and fast plasma imaging methods, respectively, and their differences are also discussed in detail. Moreover, the spectral intensity under variable LAAs is corrected by optimizing the spectral acquisition parameters and the obtained relationship between the spectral intensity and the laser power density.