A national research program strategy on the use of liquid metals in fusion systems was discussed on Jan. 22 at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL). The meeting, which was the first of its kind, also provided valuable insights into liquid metal infrastructure needs, along with current technology and science gaps, outlined in the DOE's Fusion Science and Technology Roadmap published in October 2025.
Research suggests that liquid metals could protect the components that directly face the intense heat of plasma and improve fusion system performance. Partly due to its strong expertise in liquid metals, PPPL was chosen as the host site for the meeting. More than 75 people attended in person and online, including researchers from U.S. national labs, universities, DOE personnel and fusion leaders from the private sector.
"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," FES Associate Director Jean Paul Allain told the audience.
The DOE's ultimate goal is to support a competitive U.S. fusion power industry, and demonstration of fusion power plants in this country is a critical step. Fusion could provide a stable source of electricity to diversify the power grid and ensure energy independence for America. One way to harness that energy involves a doughnut-shaped vessel called a tokamak, which confines particles of electrically charged matter known as plasma using magnetic fields, creating conditions that cause the plasma particles to fuse together and release energy. Refining ideas about the best ways to use liquid metals in tokamaks is an important aspect of fusion research.
From laboratory to power grid
"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 FES and organizer of the first day of the meeting.
Josh King, a program manager at the DOE's FES and organizer of the second day of the meeting, thanked the private sector fusion companies for their input. "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.
PPPL brings a breadth of liquid metals research to the table
PPPL is a leader in liquid metals research for fusion applications, with a particular focus on liquid lithium, collaborating with public and private partners worldwide. PPPL also leads a national Fusion Innovation Research Engine collaborative to advance liquid metal technology and science. PPPL's primary fusion experiment, the National Spherical Torus Experiment-Upgrade, is intended to eventually serve as a test bed for liquid metal components.
"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."
PPPL's liquid metals work currently includes the following projects:
- Lithium Tokamak Experiment-𝛽: This small, doughnut-shaped tokamak has already yielded numerous insights into the effects of liquid metal coatings in tokamaks, as its walls can be almost completely coated in liquid lithium.
- Lithium Vapor Divertor Development: The lithium vapor divertor aims to reduce very high plasma heat flux that would otherwise melt the solid walls in a fusion system. The goal of these experiments is to measure how the lithium vapor generation changes with the surface temperature and impurities.
- Lithium EXposure and Interaction (LEXI) Experiment: One of the Lab's newest liquid metal experiments, LEXI reveals how liquid lithium interacts with the metals and porous structures that contain it. LEXI maintains more than 100 grams of liquid lithium at temperatures above 300 degrees Celsius for more than 600 hours, allowing researchers to observe how materials change over time when immersed in the bulk volume of this reactive metal. This facility is now operating and available to scientists for research.
- Theoretical Work: Scientists are conducting theoretical work on liquid metal blankets for capturing the heat from fusion, plasma-wall interactions and liquid metal flows in magnetic fields.
Recently initiated liquid metals projects at PPPL include:
- Liquid Lithium Magnetic Centrifuge: The liquid lithium magnetic centrifuge will allow researchers to study how to separate varieties of hydrogen atoms known as protium and deuterium from liquid lithium. This technology is key to designing a future fusion system and will use the principles being tested in the liquid metal centrifuge described below.
- Liquid Metal Ultrasonic Diagnostic Development: This new system will enable measurement of the liquid metal flow speed without the need for visible cameras. The first system will be tested in Galinstan, a surrogate liquid metal for lithium, and future versions will work with liquid lithium.
- Lithium Experimental Application Program (LEAP): This is the first in a series of platforms that will enable scientists to study how liquid metal behaves in conditions that replicate those projected to exist inside future fusion systems. To accomplish this goal, LEAP will handle 100 times more lithium than the Lab has ever been licensed to store on-site. With this amount of lithium and a variety of measurement tools, PPPL will be able to test various concepts for liquid metal plasma-facing components suitable for fusion systems.
