High heat flux test by high current and low energy electron beam

High thermal shock resistance is required for plasma facing materials in nuclear fusion devices. Graphite and carbon based composites are the primary candidates for high heat flux materials to be used for limiter or armor plates at present. In this study, thermal shock tests of commercially available isotropic graphite were conducted using a hot hollow cathode type electron gun with a high current (200 A) and low voltage (50 V). Heat flux was 1-2 kW/cm², flux diameter was 18 mm, and specimen size was 25 mm×25 mm×1 mm. Specimens fractured into 2 or 3 pieces within l s of heat load duration. A magnitude of flux when a specimen fractured for l s of heat load duration was used as a measure of thermal shock resistance. The thermal shock resistance of the most anisotropic sample was the highest in this experiment. Correlations between thermal shock resistance and various material properties were examined among samples, except the anisotropic samples. The thermal shock resistance was higher for samples with lower fracture strength and lower apparent density and larger pore size. This result is not in accordance with a simple model based on thermo-elastic theory. It may suggest that thermal shock resistance is controlled by a crack propagation process rather than a crack initiation process.