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The quantification of impurities in fusion devices is important to improve understanding of all impurity-related issues and their solutions. In this study, the deposition of the impurity layer on the lower hybrid wave gas puffing pipe (LHW-GPP) used in the Experimental Advanced Superconducting Tokamak (EAST) was characterized. The calibration-free laser-induced breakdown spectroscopy (CF-LIBS) was employed to resolve the impurity deposition of the unknown standard by focusing the laser at various spot positions on the sample surface. The impurity elements that appeared in the spectrum of deposition are copper (Cu), tungsten (W), molybdenum (Mo), lithium (Li), silicon (Si), and carbon (C). The laser ablation of impurity showed an uneven deposition pattern. Each laser pulse depicted the different concentrations of the impurity elements. The results obtained from the quantification and the depth profiling showed that the impurity deposition was composed of eroded materials caused by the plasma-surface interactions with the divertors, main wall, limiters, and supporting structure materials. The exponential decrease in impurity signals and constant behavior of substrate intensity were also observed during consecutive laser shots. The study provided the estimation of impurity contents in the fusion plasma. [Display omitted] • Diagnostic study of impurity deposition in the EAST. • Quantification and depth profiling of unknown contents in the mixed materials. • Ablation behavior evolution of the signal intensity of deposition and substrate materials. • calibration-free LIBS for quantification of the trace elements in the matrix. • LIBS is an optical and remote technique to analyze the plasma-facing components. [ABSTRACT FROM AUTHOR]

Laser-induced breakdown spectroscopy (LIBS) has been demonstrated to diagnose the surface element distribution of plasma-facing components (PFC S) in fusion devices. However, the magnetic field intensity and polarity near the wall surface change frequently and cannot be measured in real time, which will affect the analytical accuracy of LIBS results. The determination of the strength and polarity direction of the magnetic field near the surface will be conducive to the quantitative analysis of LIBS and provide valuable information for the distribution of the magnetic field near the surface of PFCs. In this work, the effects of magnetic fields on the characteristics of laser-induced Mo plasma, such as the ablation depth and mass, the spatio-temporal evolution behavior of spectrum and the plasma parameters, were first systematically investigated. The different phenomenon of continuum radiation, Mo I line and Mo II line under the magnetic field were mutually verified by optical emission spectroscopy and fast plasma imaging methods. Meanwhile, an approach for measurement of the magnetic field intensity and polarity near the surface of PFCS by LIBS method has been proposed and investigated. When the magnetic field polarity is changed, the spatial distribution profile of Mo spectrum will drift in the opposite direction affected by of the Lorentz force, which realizes the measurement of magnetic field polarity. Moreover, the splitting distance of Mo I line caused by Zeeman effect with the variable magnetic fields were preliminarily calculated. The experimental values of splitting distance agree well with the theoretical values that calculated by the known magnetic field strength. These results confirm the feasibility of measuring the magnetic field intensity and polarity of PFCs surface by LIBS approach. [Display omitted] • The LIBS approach to measure the magnetic field near the surface of PFCs has been proposed and investigated. • The ablation depth and mass of Mo targets remain unchanged under different magnetic field strengths in a vacuum. • The spatiotemporal characteristics of spectrum enables LIBS to distinguish the polarity of the magnetic field. • The magnetic field strengths were determined by Zeeman splitting based on the Mo I line. [ABSTRACT FROM AUTHOR]

Laser-induced breakdown spectroscopy (LIBS) has been proposed as a promising in-situ diagnostic approach for the elemental analysis of the co-deposition impurities on plasma-facing components (PFCs) of the experimental advanced superconducting tokamak (EAST) as well as ITER tokamak. The EAST has been equipped with an ITER-like tungsten (W) divertor, and impurities of W originating from divertor erosion can be transported into core plasma as impurities, which seriously reduces the plasma performance with power radiation losses and fuel dilution. In the present work, to achieve a more reliable quantitative analysis, a variation of the CF-LIBS algorithm, the so-called one-point calibration LIBS (OPC-LIBS), is examined for major and minor constituents in a set of W-Mo-Fe-Cr steel samples (chosen as a proxy of the co-deposition layers on the lower hybrid wave gas puffing pipe of EAST) at 5 × 10−5 mbar. The OPC-LIBS essentially employs one matrix-matched standard sample of known composition to evaluate the comprehensive correction factors of crucial experimental and spectroscopic parameters. These are essential for empirically correcting the LIBS line intensities to achieve a more precise quantitative analysis compared with the conventional CF-LIBS. In the case of OPC-LIBS measurement in vacuum, the relative error of major elements such as Fe (85.24–88.69a.t.%) is below 1.64%, while that of minor elements like W (1.91–6.27a.t.%) is within 24.79%. It is substantially better than the predicted results of CF-LIBS, in which the relative error of Fe and W in order are within 10.75% and 202.03%. The obtained results confirm the quantitative analysis capability of the OPC methodology in a tokamak environment for the in-situ LIBS system. [Display omitted] • Compared with CF-LIBS, OPC-LIBS has significantly improved the quantitative accuracy for both major and trace elements. • This study examined how OPC-LIBS could enhance the quantitative LIBS analysis in vacuum. • The achieved results revealed that the relative errors of W (1.91–6.27a.t.%) are below 24.79%. • The results confirm the quantitative analysis capability of the OPC methodology for the in-situ LIBS system of EAST. [ABSTRACT FROM AUTHOR]