Fuel Inventory in Carbon Fiber Composites from Tokamaks, Detailed Mapping and Quantification

Full text: The major issues to be tackled in the field of Plasma-wall interaction (PWI) are lifetime of plasma-facing materials (PFM), fuel inventory and dust formation. The aim of this work was to investigate fuel retention and its distribution in a CFC material, NB41 which is an EU reference material for divertor tiles in ITER. Samples of NB41 were exposed to high flux deuterium plasmas in a plasma-wall interaction simulator PISCES-A at the University of California at San Diego, USA, and in the TEXTOR tokamak in Julich Germany. CFC from Tore Supra at Cadarache France have also been investigated. The reaction 2D(3He,p)4He was used for deuterium and 12C(3He,p)14N for carbon detection using both a broad beam and a nuclear microbeam at the 5 MV Tandem Accelerator in Uppsala. After the exposure in PISCES-A, two regions with distinctly different deuterium content can be distinguished. They correspond to two different types of fibres, ex-PAN and ex-pitch where the larger roughness of the broken fibres of the ex-pitch region can explain the higher retention in this region. Micro-distribution of deuterium and carbon in the erosion zone of the target exposed in TEXTOR is shows that the distributions of D and C are not uniform. In complex pattern there are some spots, up to 100-200 μm wide, with high deuterium content (8x1017 cm-2), whereas the remaining part retains less fuel. There are also places with very small relative carbon content, thus indicating the presence of other species accumulated in those areas. Over a distance of less then 1 mm differences in the deuterium concentration was found to be as large as 4% and as low as 0.2% from CFC samples from Tore Supra first wall. Work supported by EURATOM and carried out under EFDA. (author)