Collinear double-pulse laser-induced breakdown spectroscopy as an in-situ diagnostic tool for wall composition in fusion devices

Our recent investigations have indicated the potential of double-pulse laser-induced breakdown spectroscopy (DP-LIBS) for analysis of the deposited impurity on divertor tiles in the experimental advanced superconducting tokamak (EAST). The collinear DP-LIBS configuration was suggested with the aim of overcoming the sensitivity shortcomings of the conventional single pulse laser-induced breakdown spectroscopy (SP-LIBS) technique in vacuum conditions. A systematic study of plasma emission signal dependence on the inter-pulse delay at 3.5 × 10−3 Pa was performed, and the results were compared with the ones obtained with a single laser pulse of energy corresponding to the sum of the two pulses. For a molybdenum tile, it was found that the atomic spectral lines of Mo were enhanced by a factor of 6.5 when an inter-delay time of 1.5 μs was installed. For an exposed divertor tile, significant increases in the emission line intensities of various minor elements (such as Mo, Si, Fe, Cr, Ti, Ni and Ca) were observed in DP-LIBS, while no spectra signal was achieved in SP-LIBS. This collinear DP-LIBS technique would help us to develop a more promising system to monitor the fuel retention and impurity deposition on plasma facing components of EAST.