The meeting focused on how liquid metals could protect the components that face the extreme heat of fusion plasmas and at the same time enhance overall system performance. This discussion built on priorities laid out in the Department of Energy Fusion Science and Technology Roadmap released in October 2025, which highlights liquid metals as a key cross cutting technology. Organizers sought to align public research capabilities with the requirements emerging from private sector fusion designs.
"Our Roadmap identified liquid metals as a potentially game changing technology on the path to achieving fusion power. Your insights and expertise will help inform what's needed for a world leading U.S. liquid metal program," said Jean Paul Allain, associate director of Fusion Energy Sciences, in his opening remarks. Allain emphasized that the roadmap calls for coordinated efforts to move liquid metal ideas from experimental facilities into devices relevant for power generation.
The Department of Energy aims to enable a competitive U.S. fusion power industry in which demonstration plants feed electricity into the grid. Fusion concepts such as tokamaks confine hot, electrically charged plasma in a doughnut shaped vessel using powerful magnetic fields so that the plasma ions fuse and release energy. Deciding how best to employ liquid metals in these harsh environments is now a central question for designers of next generation systems.
"We're here to think about what the public program can deliver that will help us win not only the fusion energy race, not just delivering the first power plant, but the first economically competitive power plant and an economically competitive industry," said Heather Jackson, division director for Fusion Enabling Science and Partnerships at Fusion Energy Sciences and organizer of the first day. She noted that industrial competitiveness will depend on materials and components that can operate reliably for long periods under intense thermal and particle loads.
On the second day of the meeting, program manager Josh King underscored the importance of direct input from private fusion developers. "Hearing directly from both private companies - whether they are currently exploring liquid metals for their fusion systems or are still holding back and don't see it as their roadmap presently - helps us understand the full landscape of research needs and identify where investments will have the greatest impact," King said. The discussions highlighted both near term validation experiments and longer term technology development needs.
Princeton Plasma Physics Laboratory occupies a central role in this emerging liquid metal ecosystem because of its long standing focus on liquid lithium for fusion applications. The laboratory collaborates with partners worldwide and leads the national Fusion Innovation Research Engine collaborative dedicated to liquid metal technology and science. PPPL's flagship device, the National Spherical Torus Experiment Upgrade, is being prepared to serve as a test bed for components that use liquid metals directly facing the plasma.
"Bringing liquid lithium technology from the laboratory to a fusion power grid requires building significant infrastructure: additional test facilities to validate how liquid metals behave in strong magnetic fields and under intense plasma bombardment, reliable methods to efficiently extract and purify the fusion fuel tritium from flowing lithium, and a domestic supply chain for the specialized materials these systems require," said Rajesh Maingi, head of tokamak experimental science at PPPL. "With decades of liquid metal research, PPPL is well positioned to help build that foundation." His remarks underscored the need for dedicated facilities and industrial capabilities that go well beyond existing experiments.
PPPL's current liquid metal portfolio spans experimental and theoretical work. The Lithium Tokamak Experiment beta, a compact tokamak whose walls can be almost completely coated in liquid lithium, has already produced a wealth of data on how liquid surfaces influence plasma behavior and wall conditions. Researchers are also developing a lithium vapor divertor that generates and controls lithium vapor to reduce extreme heat fluxes that would otherwise damage solid walls, while carefully measuring how vapor production varies with surface temperature and impurities.
The lithium program includes the Lithium EXposure and Interaction (LEXI) experiment, one of PPPL's newest liquid metal facilities. LEXI maintains more than 100 grams of liquid lithium at temperatures above 300 degrees Celsius for periods exceeding 600 hours so that scientists can monitor how metals and porous structures that contain the lithium evolve over time. The experiment, now in operation and open to users, provides a platform to study long term compatibility between structural materials and this highly reactive liquid metal.
PPPL scientists are also pursuing theoretical studies that address how liquid metal blankets can capture heat from fusion reactions, how plasmas interact with liquid surfaces and how liquid metals flow in the presence of strong magnetic fields. These models guide experimental design and help identify operating regimes that maximize performance and component lifetime. The theoretical work feeds directly into concepts for integrated power plant blankets that breed fuel and remove heat.
Several new initiatives are being launched to extend the laboratory's capabilities. A liquid lithium magnetic centrifuge under development will investigate how to separate protium and deuterium, two forms of hydrogen, from liquid lithium using magnetically driven flows. This approach draws on principles tested in a more general liquid metal centrifuge and is considered important for future systems that must manage different hydrogen isotopes efficiently.
Another project, the liquid metal ultrasonic diagnostic development effort, seeks to measure liquid metal flow speed without relying on visible cameras, which can be difficult to use in opaque and radioactive environments. The first diagnostic system will operate in Galinstan, a surrogate liquid metal for lithium, before later versions are adapted to work with actual liquid lithium. Reliable, non invasive flow measurements are viewed as essential for both experimental devices and commercial reactors.
The Lithium Experimental Application Program, or LEAP, represents the first in a planned sequence of platforms that will expose liquid metals to conditions similar to those expected in advanced fusion concepts. LEAP will handle roughly 100 times more lithium than PPPL has previously been licensed to store on site and will employ a suite of diagnostics to track how liquid metal plasma facing components respond under realistic heat and particle loads. By scaling up both inventory and measurement capability, the laboratory aims to provide data that can directly inform engineering choices for future plants.
Participants at the January meeting agreed that realizing the potential of liquid metals will require coordinated national investments in test stands, diagnostics, materials development and fuel cycle technologies. The discussions at PPPL marked an early step in defining a U.S. research program that can support both public missions and private sector fusion ventures. As fusion developers refine their designs, the emerging liquid metal strategy is expected to play an increasingly prominent role in plans for practical, economically competitive fusion power.
Related Links
Princeton Plasma Physics Laboratory
Powering The World in the 21st Century at Energy-Daily.com
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