Demonstration of low recycling and NBI fueling with liquid lithium walls in the Lithium Tokamak Experiment-β (LTX-β)

Low-recycling liquid lithium surfaces are a potential solution to the two main obstacles for fusion - confinement and power handling. Several critical prerequisites for the low-recycling, liquid Li approach have been recently achieved in the Lithium Tokamak Experiment-β. Improved conditioning techniques in LTX-β created clean, mirror-like liquid Li surfaces that fully surround the plasma, without significant operational problems. Experiments with liquid Li walls have reproduced key results previously demonstrated with solid Li, including a hot, low-recycling edge (R~0.6) with a unique, low-collisionality scrape-off layer. A hot edge is predicted to greatly improve confinement by suppressing temperature gradients that drive turbulent losses. As gas puffing cools the edge, core fueling is essential in the low-recycling regime. LTX-β has recently achieved neutral beam fueling and heating with a ~20% increase in plasma density and high normalized confinement not seen to degrade with P_NBI. Recent improvements to the neutral beam, liquid Li techniques, plasma operational systems, and diagnostics will extend the initial proof-of-principle results to higher levels of performance and steadier-state, as well as investigate new, unique aspects of the low-recycling liquid Li regime.