Transient heat load challenges for plasma-facing materials during long-term operation

The study summarizes the experimental results on fusion relevant pure heat load exposures of different tungsten products in the electron beam devices JUDITH 1 and 2. Besides steady state heat loading, up to 106 transient ELM-like pulses were applied. A detailed postmortem analysis reveals a wide and complex range of thermally-induced surface modifications and damages, such as roughening due to plastic deformation, cracking, and melting of parts of the material surface. Different industrially available tungsten products with varying thermal and mechanical properties were investigated in order to examine their influence on the thermal shock response. Furthermore, recrystallisation of the material, which will take place during long term operation, will additionally deteriorate the mechanical strength of the plasma facing material. The results show that the mechanical strength of the material has a significant influence on the formation and evolution of damage. Especially, recrystallisation and melting/resolidification will make the material more prone to thermal shock and fatigue, accelerating the evolution of damages. The combination of different material modifications/damages accompanied by the degradation of mechanical properties will have a strong impact on the plasma performance and lifetime of plasma facing materials/components.