Spatial Resolution Measurements of C, Si and Mo Using LIBS for Diagnostics of Plasma Facing Materials in a Fusion Device**supported by the National Magnetic Confinement Fusion Science Program of China (No. 2013GB109005), National Natural Science Foundation of China (Nos. 11175035, 11475039), Chinesisch-Deutsches Forschungs Project (GZ768) and the Fundamental Research Funds for the Central Universities of China (Nos. DUT12ZD(G)01, DUT14ZD(G)04)

Abstract

Recently, a laser-induced breakdown spectroscopic (LIBS) system has been developed for in situ measurements of the chemical compositions of plasma facing materials (PFMs) in the Experimental Advanced Superconducting Tokamak (EAST). In this study, a LIBS system, which was used in a similar optical configuration to the in situ LIBS system in EAST, has been developed to investigate the spatial distribution of PFM elements at 10−4 Pa. The aim of this study was to understand the nature of the spatial distribution of atoms or ions of different elements in the plasma plume and optimize the signal to background ratio for the in situ LIBS diagnosis in EAST. The spatial profiles of the LIBS signals of C, Si, Mo and the continuous background were measured. Moreover, the influence of laser spot size and laser energy density on the LIBS signals of C, Si, Mo and H was also investigated. The results show that the distribution of the C, Si and Mo peaks' intensities first increased and then decreased from the center to the edge of the plasma plume. There was a maximum value at R ≈ 1.5 mm from the center of the plasma plume. This work aims to improve the understanding of ablating plasma dynamics in very low pressure environments and give guidance to optimize the LIBS system in the EAST device.