Emission of solid particles from carbon materials under pulsed surface heat loads

The emission of solid particles from strongly heated carbon surfaces may contribute to the erosion of plasma facing components. This process concurs with the thermal sublimation of carbon and is assumed to be dependent on the kind of carbon material. With regard to the application as plasma facing material it is of importance to investigate the mechanism and the process of particle emission with relation to the material structure and to quantify the loss of material due to particle emission depending on the material (e.g. graphite, CFC). In the experiments an electron beam facility has been used to deposit surface heat loads onto specimens of different carbon materials, esp. fine and coarse grain graphites, CFCs, and pyrolytic carbon. The heat load was applied with power densities of 0.5 to 1.5 GW/m(2) for pulse durations of 0.1s to Is. The eroded material was collected by catcher probes which were arranged to allow the quantitative determination of the angular dependence of the particle emission from the heated specimen surface. The evaluation of the probe surfaces by means of high resolution SEM and image analysis gave information on the size distribution of the eroded particles. A small fraction of the particles detected from heated fine grain graphite had sizes of the order of the graphite grains itself (a few mu m), and a considerable amount of material was deposited on the probes in form of sub-mu m particles. The structure of these particles was examined by TEM. In addition, photographs of the particle emission during heating were taken showing the trajectories of the emitted particles and allowing further comparison with the post-experimental analysis.