Long-pulse high heat flux testing of tungsten monoblock target mock-ups for investigation of creep fatigue interaction

Divertor components for ITER and even beyond will be subjected to cyclic steady state heat loads with a duration of several minutes to hours, repeatedly occurring slow transients during reattachment or ramp-up and down, as well as heat loads during ELMs applying a combination of low cycle fatigue and creep as well as high cycle fatigue via thermal shock loads. While for the qualification of components the duration of the fatigue cycles up to now has been kept small, i.e., close to the required time to reach thermal saturation which is 10 s for typical divertor components, creep in these components has not yet been assessed. In this study divertor tungsten monoblock mock-up manufactured via hot radial pressing in the ITER-like geometry consisting of 4 monoblocks and quality checked via ultrasonic testing are exposed to high heat flux loads in the electron beam facility JUDITH 2 using a high temperature cooling circuit with controlled water chemistry. Thereby, cyclic loads up to 1000 cycles with a duration of 10 to 600 s and a power density of 20 MW/m2 were applied, representing strike point loading conditions in DEMO during strike point sweeping scenarios. Each of the tungsten monoblocks is loaded individually providing the possibility to study different scenarios on one single mock-up. The aim is to assess the performance and degradation of performance due to the applied loads, which is supported by characterization via metallography, profilometry, SEM and hardness testing after the high heat flux tests.