Deuterium Implantation and Thermal Extraction in the Actively Pumped Open-Surface Lithium LOop (APOLLO)

Liquid lithium plasma-facing components (PFCs) offer numerous advantages, including improved plasma performance, protection of solid substrate material, and avoidance of the transient melting seen in solid PFCs. Lithium is a low-Z element that exhibits strong gettering properties and allows access to a low-recycling plasma regime. However, lithium's uptake of hydrogenic species presents an issue for future fusion plants that must limit tritium inventory. To explore solutions, 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 PFC 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. Lithium flows across the plate with average surface velocities up to 10 cm/s and mass flow rates up to 12 g/s while simultaneously exposed to an Electron Cyclotron Resonance (ECR) hydrogen/deuterium plasma source. The plasma has been characterized with an array of 16 Langmuir probes, a Retarding Field Energy Analyzer (RFEA), and actinometric spectroscopy. After lithium exits the plate via the collector, it flows to an inductively heated Hydrogen Distillation Experiment (HyDE) chamber which thermally treats the lithium at temperatures up to 700℃ to remove hydrogenic species and impurities. Deuterium uptake in flowing liquid lithium exposed to an ECR plasma is studied for different lithium flowrates and plasma parameters. Deuterium thermal extraction efficiency is measured with a resistive impurity probe and thermal desorption analysis. A 0D model of the APOLLO is used to explain experimental observations.