Electron Beam Exposure on a Flowing Lithium Surface in the Actively Pumped Open-Surface Lithium LOop (APOLLO)

Liquid lithium is a promising material for plasma-facing components (PFCs) due to its ability to enhance plasma performance, protect solid substrate material, and avoid the transient melting that affects solid PFCs. As a low-Z material, lithium provides strong gettering capabilities and enables operation in a low-recycling regime. The University of Illinois at Urbana-Champaign (UIUC) with Tokamak Energy Ltd. is developing the Actively Pumped Open-Surface Lithium LOop (APOLLO) which consists of a flowing lithium loop, a free-surface PFC within a magnetic field, a deuterium plasma source or electron beam heating, and a distillation column for the extraction of hydrogenic species. The APOLLO will increase the technological readiness level of liquid lithium PFCs. The APOLLO PFC module consists of a computationally optimized distributor that evenly distributes lithium from the inlet pipe across a 3” wide 3D-printed refractory metal ordered mesh located in a free surface flow channel. The PFC can be exposed to an electron beam characterized by continuous flow calorimetry capable of supplying a heat flux up to 7 MW/m² to the free surface. Alternatively, the PFC can be exposed to an Electron Cyclotron Resonance (ECR) hydrogen/deuterium/helium plasma source that has been characterized with an array of 16 Langmuir probes, a Retarding Field Energy Analyzer (RFEA), and actinometric spectroscopy. Lithium flows across the PFC with average surface velocities up to 10 cm/s and mass flow rates up to 12 g/s. The PFC module is surrounded by a Helmholtz coil capable of creating an 800 Gauss magnetic field. Results from both electron beam and helium ECR plasma exposures on a flowing liquid lithium surface will be presented. The electron beam results are focused on Thermo-Electric MagnetoHydroDynamic (TEMHD) drive on the open surface and the helium plasma exposure results investigate the trapping of helium within the lithium flow.