Princeton Plasma Lab Hosts First National Meeting on Liquid Metals for Fusion Power

Fusion energy requires containing plasma at temperatures exceeding 100 million degrees Celsius - hotter than the core of the sun. The materials that directly face this plasma absorb enormous heat and particle fluxes, erode over time, and must withstand conditions that have no industrial parallel. How those plasma-facing components are designed and cooled may ultimately determine whether fusion power is economically viable.

Liquid metals - particularly liquid lithium - have attracted attention as a potential solution. Unlike solid walls, liquid metal surfaces can continuously replenish themselves, carrying heat away efficiently and potentially trapping the hydrogen isotopes that plasma sheds. In January 2026, the U.S. Department of Energy convened the first national meeting specifically dedicated to coordinating liquid metal research for fusion at Princeton Plasma Physics Laboratory (PPPL). More than 75 people attended in person and online, including researchers from national laboratories, universities, DOE program officers, and leaders from the private fusion sector.

Why Liquid Metals Now

The DOE's Fusion Science and Technology Roadmap, published in October 2025, identified liquid metals as a technology warranting dedicated national investment. The roadmap reflected a broader shift in fusion development: private companies are now pursuing commercial fusion reactors on timelines measured in years rather than decades, and they need technical foundations in areas like plasma-facing component design that the public program can most efficiently develop.

"Our Roadmap identified liquid metals as a potentially important 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.

PPPL was a natural host for the meeting. The laboratory has maintained an active liquid metals research program for decades, with particular expertise in liquid lithium. It leads a national Fusion Innovation Research Engine collaborative focused on liquid metal technology and serves as the home of the National Spherical Torus Experiment-Upgrade, which is intended to eventually serve as a test bed for liquid metal plasma-facing components.

Infrastructure Gaps and Technical Challenges

The meeting produced a detailed picture of what a world-leading U.S. liquid metals program would require. Several areas stood out as priorities.

Test facilities capable of validating how liquid metals behave in strong magnetic fields and under intense plasma bombardment are needed at a scale not currently available domestically. The interaction between liquid lithium and magnetic fields - magnetohydrodynamics - creates complex flow patterns that affect both heat removal efficiency and tritium extraction. Building the experimental infrastructure to study these interactions at relevant scales requires sustained investment.

Tritium extraction presents a distinct challenge. Liquid lithium absorbs tritium, the hydrogen isotope used as fusion fuel, as it flows through the reactor. Recovering that tritium efficiently - to recycle it as fuel and to prevent radiological contamination - requires reliable separation technology. Current methods need development and validation at fusion-relevant scales.

"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.

Active PPPL Experiments

Several PPPL liquid metal experiments are already generating data relevant to reactor design. The Lithium EXposure and Interaction (LEXI) experiment maintains more than 100 grams of liquid lithium at temperatures above 300 degrees Celsius for more than 600 hours, studying how materials change when immersed in bulk reactive liquid metal - directly relevant to the long-term durability of components in a real reactor. The new Lithium Experimental Application Program (LEAP) will handle 100 times more lithium than the laboratory has ever been licensed to store on-site, enabling tests of plasma-facing component concepts at realistic scales.

Theoretical work on liquid metal blankets for heat capture and on plasma-wall interaction modeling complements the experimental program. New diagnostic tools being developed include an ultrasonic flow measurement system designed to work with liquid lithium in strong magnetic fields - environments where conventional optical or electronic diagnostics cannot easily operate.

Private Sector Input

A distinctive feature of the meeting was direct engagement with private fusion companies, some of which are evaluating liquid metals for their systems and some of which have not included liquid metals in their current plans. Both perspectives proved informative for setting public program priorities.

"Hearing directly from both private companies - whether they are currently exploring liquid metals for their fusion systems or are still holding back - helps us understand the full landscape of research needs and identify where investments will have the greatest impact," said Josh King, a program manager at DOE's Fusion Energy Sciences office.

The interaction highlights a structural shift in the fusion field: public laboratories increasingly see their role partly as technical service providers for private developers, addressing the fundamental science and infrastructure questions that are too long-term and expensive for individual companies to carry alone.