Depth-resolved analysis of multi-element impurity deposition on test tiles in EAST tokamak by using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was employed for the depth-resolved identification of impurities deposited on the small test tiles used in the experimental advanced superconducting tokamak (EAST). LIBS spectra show the impurity elements of molybdenum (Mo), tungsten (W), carbon (C), copper (Cu), lithium (Li), titanium (Ti), silicon (Si), iron (Fe), and chromium (Cr) in the impurity deposition on the test tiles used in the EAST. The analysis of impurities was performed at various spot positions on the surfaces of the tiles. The impurity deposition is the final destination of the migrating eroded materials in the EAST. The interaction of high-heat plasma with the plasma-facing components (PFCs) causes the erosion of W upper and lower divertors, Mo main wall, the doped graphite (C, Si & Ti) limiters, Li wall conditioning, and CuCrZr heat conductors. Surface morphology was performed by using the scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX). Depth profile analysis showed the thickness of impurity deposition is in fractions of micrometers because the impurity signals appeared just in a few laser shots. The spectral intensity of impurity was observed differently during the consecutive laser shots on various spot positions that showed the impurity deposition is uneven on the tiles' surfaces.