Brittle destruction of carbon based materials under severe thermal loads

To evaluate the dust formation under severe surface heat loads, 120 keV electron beam pulses have been applied to different specimens of carbon based materials, especially fine and coarse grain graphites, CFCs, and pyrolytic carbon. The incident heat load was up to 1.5 GW m-2 for pulse durations of 0.1-2 s. The eroded material was collected by catcher probes or within a volumetric trap. The evaluation of the probe and trap surfaces by means of high resolution scanning electron microscopy (SEM) and image analysis gave information on the size distribution of the eroded particles. A fraction of the particles detected from heated fine grain graphite had sizes of the order of the graphite grains itself (several ten microns), and a considerable amount of material was deposited on the probes in form of sub-μm particles. The structure of these particles was examined by TEM. Furthermore, the morphology of electron beam generated carbon dust particles was compared to carbon fragments collected in tokamak facilities