Conceptual design of a pre-loaded liquid lithium divertor target forNSTX-U

In this work, a conceptual design for a pre-filled liquid lithium divertor target for the National SphericalTorus Experiment Upgrade (NSTX-U) is presented. The design is aimed at facilitating experiments withhigh lithium flux from the plasma facing components (PFCs) in NSTX-U and investigating the potentialof capillary based liquid lithium components. In the design, lithium is supplied from a reservoir in thePFC to the plasma facing surface via capillary action in a wicking structure. This working principle isalso demonstrated experimentally. Next, a titanium zirconium molybdenum (TZM) prototype design ispresented, required to withstand a steady state heat flux peaking at 10 MW m−2for 5 s and edge localizedmodes depositing (130 kJ in 2 ms at 10 Hz). The main challenge is to sufficiently reduce the thermalstresses. This is achieved by dividing the surface into brushes and filling the slots in between with liquidlithium. The principle of using this liquid “interlayer” allows for thermal expansion and simultaneouslyheat conduction, and could be used to significantly reduce the demands to solids in future PFCs. Lithiumflow to the surface is analyzed using a novel analytical model, ideally suited for design purposes. Thermalstresses in the PFC are analyzed using the finite element method. The requirements are met, and thus aprototype will be manufactured for physical testing.