Degradation of plasma facing materials due to severe thermal shocks

During off-normal plasma operation scenarios the high heat flux components in future thermonuclear devices such as ITER will be subjected to severe thermal shocks. Plasma disruptions with deposited energy densities of 100 MJm^-2 and beyond are the most essential damaging mechanisms. However, a significant fraction of the incident energy will be absorbed by a dense cloud of ablation vapor, hence reducing the effective energy density at the plasma facing surface significantly. Beside material erosion, the formation of cracks in the recrystallized zone and in the underlying material will have strong impact on the integrity of the PFM. Also plasma instabilities on a much longer time scale, i.e. with a duration of 0.3 to 1.0 s have to be anticipated. These VDEs (vertical displacement events) result in deposited energy densities of approx. 60 MJm^-2. In contrast to the rather short disruption events in addition to surface effects, also material damage to the bulk material and to the joining zone has to be considered