Damage structure in divertor armor materials exposed to multiple ITER relevant ELM loads

The damage threshold and damage mechanisms of divertor armor materials, i.e. CFC and tungsten, were studied under the impact of ITER relevant ELM-like loads. These experiments were carried out in a Quasi-Stationary Plasma Accelerator applying repetitive pulses of 500 μs up to 100 cycles. CFC showed preferential erosion of the PAN fiber-bundles above 0.6 MJ/m2 and cracking of pitch fiber-bundles. Tungsten showed cracking already at 0.2 MJ/m2 and melting at flat surfaces above 1 MJ/m2. Cracks in tungsten were identified as primary and secondary cracks which all propagated in the vertical direction, which was considered to be less critical. At an energy density of 1.5 MJ/m2, the melt-layer completely covered the surface and bridged the castellation slots.