Quantitative analysis of tungsten in steel by one-point calibration laser-induced breakdown spectroscopy in vacuum

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 ITERlike 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 x 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.