Localization by TEM and EELS of deuterium trapping sites in CFC exposed to plasma irradiation in Tore Supra

Carbon fiber composite (CFC) Sepcarb (R) N11 is used in the tokamak Tore Supra as plasma-facing components. To investigate the fuel retention capability of this material, a mobile sample holder was used to expose CFC N11 samples to direct irradiation by the scrape-off layer plasma of Tore Supra at fluences up to 1 x 10(25) m(-2). Deuterium (D) elemental mapping using nuclear reaction analysis for the most-exposed CFC sample showed that D retention occurs at depths greater than 8 Elm due to the presence of deep (>3.5 mu m) local retention sites. In this work, combining transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS), we describe at a high spatial resolution where and how D atoms are trapped in these sites. TEM experiments performed on thin cross-sections of the plasma-modified surface show evidence of the presence of a 3.5 mu m-thick deuterated amorphous carbon layer deposited on the CFC surface. We show that specific localized retention sites correspond to the filling of relatively large (similar to 3 mu m.) and deep (at least 3 mu m below the initial CFC surface) cracks between fibres and matrix by the deuterated amorphous carbon layer. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.