Compositions and chemical states on the co-deposition layer of lithiated tungsten of plasma-facing components of EAST

Lithiation is beneficial to enhance plasma performance in EAST by reducing hydrogen and impurities recycling via lithium (Li) wall conditioning. High-Z materials like tungsten (W) have been selected as up-divertor in EAST tokamak. However, the nature of the chemical compositions and states on Li-W co-deposition layer is still unclear. In this paper, pure W plasma-facing component experiments with Li deposition layer were carried out by a cascaded-arc linear plasma generator. An in-situ laser-induced breakdown spectroscopy (LIBS) system with spatial resolution about 1 mm and depth resolution about 200 nm was developed to real time monitor the composition and distribution on Li-W co-deposition layer. The chemical states of the co-deposition layer and laser ablation spots were determined by a post-mortem analysis of X-ray photoelectron spectroscopy (XPS). Both LIBS and XPS results shew that higher concentration of Li could be observed at the region closed to the Li source. The XPS spectra indicated that Li2CO3 peaks intensities at 289 eV and 531.6 eV were obviously changed with the Li distribution. In addition, high proportional W oxides were formed on the surface of Li-W co-deposition layer in the lithiated W sample. Elemental W signals corresponding to the laser ablation spots were much more obvious than them in the area of Li-W co-deposition layer surface without laser ablation. This work could improve the understanding of the Li-wall conditioning for tungsten divertor in EAST tokamak. (C) 2017 Published by Elsevier Ltd.