Speaker
Description
Liquid lithium plasma-facing components (PFCs) present several advantages for fusion applications, including enhanced plasma performance, protection of underlying structural materials, and mitigation of transient melting phenomena associated with solid PFCs. As a low atomic number (low-Z) material, lithium exhibits strong gettering capabilities and enables operation in a low-recycling plasma regime. However, the absorption of hydrogenic species by lithium poses a significant challenge for future fusion reactors, where stringent limits on tritium inventory must be maintained.
To address this issue, the University of Illinois Urbana-Champaign (UIUC), in collaboration with Tokamak Energy Ltd., has developed the Actively Pumped Open-Surface Lithium Loop (APOLLO). This experimental platform comprises a circulating liquid lithium loop, a free-surface lithium PFC operating within a magnetic field, a deuterium plasma source or electron beam heating system, and a distillation column designed for the extraction of hydrogenic species. The PFC incorporates a computationally optimized distributor that uniformly delivers lithium from an inlet pipe across a 7.5 cm-wide, additively manufactured refractory metal ordered mesh situated within a free-surface flow channel. Lithium flows across the mesh with average surface velocities of up to 10 cm/s and mass flow rates reaching 12 g/s, while being simultaneously exposed to an electron cyclotron resonance (ECR) hydrogen/deuterium plasma source.
Plasma characteristics are diagnosed using an array of 16 Langmuir probes, a retarding field energy analyzer (RFEA), and actinometric spectroscopy. After exiting the PFC via a collector, the lithium is transported to the inductively heated Hydrogen Distillation Experiment (HyDE), where it undergoes thermal treatment at temperatures up to 700 °C to remove hydrogenic species and other impurities. Deuterium uptake in flowing liquid lithium exposed to an ECR plasma is investigated as a function of lithium flow rate and plasma operating conditions. The efficiency of deuterium thermal extraction is quantified using a resistive impurity probe and thermal desorption analysis. A zero-dimensional (0D) model of the APOLLO system is employed to interpret and contextualize the experimental results.