Characterization of impurity distribution and composition on the shutter plate for an optical diagnosis in EAST tokamak using laser-induced breakdown spectroscopy

The quantification of impurities in tokamak devices is of great significance as it allows for a better understanding of the plasma performance and the lifetime of plasma-facing components (PFCs). This study focuses on the characterization of the impurity distribution and composition on the surface of a shutter plate for an optical diagnosis in the Experimental Advanced Superconducting Tokamak (EAST) by Laser-Induced Breakdown Spectroscopy (LIBS). The primary impurity elements, including copper (Cu), tungsten (W), molybdenum (Mo), lithium (Li), and Sodium(Na), were identified by analyzing the LIBS spectra obtained from the surface of the shutter plate. The spatial distribution of these impurities on both sides of the plate was investigated. The analysis results indicate an increase in impurity content on the outer surface of the shutter plate as proximity to Last Closed Flux Surface (LCFS), followed by a near-linear decrease with the distance from the LCFS. The results of the inner ring on the inner side facing the glass window show fewer metal impurities than the outer rings on the edge for the inner side of the plate. Moreover, the thickness of the deposition layer was determined by estimating the Average Ablation Rate (AAR) through the measurement by confocal microscopy. In addition, Calibration-Free LIBS method were performed to determine the relative content of impurities. The results of this study provide valuable references for studying the migration and transportation of impurities.