C. Adelhelm (Sp), M. Balden, Max Planck Institute for Plasma Physics, Garching (Germany); P. Starke,
University of Augsburg (Germany); A. Centeno, C. Blanco, CSIC, Oviedo (Spain); I. López Galilea, C.
García-Rosales, University of Navarra, San Sebastián (Spain)
Carbon (i.e. CFC) is considered as plasma-facing material (PFM) for the divertor in future fusion devices, like ITER. The reactivity of carbon against hydrogen species (chemical erosion) is the main drawback, causing life time problems of the components and formation of hydrocarbon layers. This is of safety concern if radioactive tritium – the fuel for fusion – is used. Doping of carbon with transition metals strongly reduces chemical erosion. This is shown with D ion beam and plasma exposure experiments for different doped carbon materials. Ion beam experiments were performed for 30 and 200 eV D at 300 and ~750 K. During plasma exposure the materials were subjected to neutral and 30 eV deuterium at 300 K. For both experiments the absolute erosion yield (eroded C per impacting D) was determined by measuring the weight loss. As reference material, well-defined metal-doped amorphous carbon films (a-C:Me, Me = Ti, V, Zr, W) were produced using dual-source magnetron sputter deposition with metal concentrations up to 20 at%. Their structural characterization (using RBS, XRD, and XAS) revealed that the metal is homogenously distributed in the carbon matrix and shows the formation of nm-sized carbide crystallites after annealing to 1100 K prior the erosion
experiments. Depending on metal type and concentration, the total erosion yield of a-C:Me films is always reduced by a factor of up to 20 compared to pure carbon. Novel Ti and Zr-doped fine grain graphite and CFC materials with carbide grain sizes of 80 – 200 nm were eroded using the ion beam and plasma exposure facility. First experiments showed promising results for Ti-doped graphite with erosion yields of 2 % for 30 eV D and 6 % for 200 eV D. Ti-doped CFC suffered from weak fibermatrix bonding which results in macroscopic particle loss.