Raman spectroscopy and X-ray diffraction studies of some deposited carbon layers in Tore Supra

Carbon deposited layers collected in Tore Supra on the neutralizers, on the toroidal pumped limiter and on the vertical outboard limiter have been analysed by X-ray diffraction and Raman spectroscopy. Both techniques show that these samples are highly disordered, mainly consisting of graphite-like nanoparticles. They are not similar to amorphous or hydrogenated amorphous carbons: this is consistent with the low amount of deuterium found trapped inside. Their structure can be related to their vicinity to plasma, particle bombardment inducing high temperature and preventing full amorphization. Samples exposed to the highest fluency in the machine show the largest degree of disorder, with probably a minor contribution of three-dimensional disorder, which may be due to the formation of bonds with deuterium.