Surprising Plateau in Low Energy Fusion
Unexpected Discovery at Low Energies
Fusion reactions do more than promise limitless energy. They also produce neutrons — subatomic particles used in medical imaging, cargo screening, planetary science, and national security research. Controlling fusion for these applications has long been a goal separate from power generation.
Scientists at the University of California, Davis and the Department of Energy’s Lawrence Berkeley National Laboratory have now found that the materials surrounding a fusion reaction can dramatically increase how often it occurs. The effect is strongest at low energies, where fusion is normally extremely rare. The discovery came while researchers were testing how different materials behave under deuterium bombardment.
At energies below 2.5 kiloelectronvolts — a very low range for nuclear reactions — theory predicts fusion rates should drop sharply. Instead, the team observed a surprising plateau. Some samples showed fusion rates roughly a quintillion times higher than bare fusion reactions without any material. [1] A quintillion is a 1 followed by 18 zeros, a number so large it is hard to grasp.
The findings were published in Nature Communications on July 18. The study marks the first time a solid material has been shown to actively boost low-energy fusion rather than merely contain it [2]
The Next Step: Probing the Mechanism
The team now plans to explore a much wider range of materials. They want to understand exactly why the fusion rate plateaus at low energies instead of falling off. “It comes down to better understanding the mechanism so that we can try to enhance it,” said Jeremy Munday, a professor at UC Davis and the study’s corresponding author. [1]
The researchers suspect that electrons and defects within the metal may shield the repulsive electrostatic forces between deuterium nuclei. When two deuterium atoms try to fuse, their positive charges repel each other. If the material’s electronic structure or crystal defects reduce that repulsion, the nuclei can get close enough to fuse more easily. Tuning these properties could allow engineers to design materials that speed up nuclear reactions in specific conditions.
This approach opens a new field the team calls “materials-driven fusion.” Instead of designing materials just to survive the harsh conditions of a fusion reactor, researchers might shape them to actively boost reactions — similar to how catalysts accelerate chemical reactions. Arun Persaud, head of the Fusion Science and Ion Beam Technology group at Berkeley Lab, said the effect gives scientists a new knob to turn. “If we understand this effect better,” Persaud said, “it opens the door to engineering new materials that would affect the fusion rate under certain conditions.” [2] Someday, he added, that progress might lead to more compact and efficient neutron generators for cargo screening, planetary science, and medical therapy and imaging.
The team will systematically test different metals and different ways of loading deuterium into them. They will also probe the unexpected fusion plateau at even lower energies to find its true limit. The goal is to learn enough about the underlying physics to translate the effect to other areas of nuclear science.
What Changes and What Remains Open
For decades, materials in fusion experiments were viewed as passive containers — they needed to survive intense heat and radiation but were not thought to influence the fusion reaction itself. This study overturns that assumption. “The work shows conclusively that the material environment where fusion occurs at low temperatures is an active participant rather than a passive container,” said Cameron Geddes, director of the Accelerator Technology and Applied Physics division at Berkeley Lab. That insight adds a new dimension to fusion research.
In the experiment, researchers used two methods to pack deuterium — a heavy form of hydrogen — into thin foils of palladium and titanium. They then fired a beam of deuterium ions at the foils at different energies and measured how often fusion took place. The fusion rate depended on how the deuterium was loaded. Some samples showed the enormous rate increase at low energies, while others did not. This suggests that the microscopic arrangement of deuterium atoms within the metal is critical.
The finding changes the way scientists think about low-energy nuclear reactions. It connects fusion science with materials science and chemistry in a way that was not previously considered. The work establishes a reproducible experimental platform for studying how solid materials influence nuclear reactions, creating a test bed for future research.
Yet the exact mechanism remains unknown. Researchers have hypotheses — electron shielding, defect-assisted tunneling — but no confirmed explanation. They do not yet know how far the fusion rate can be enhanced or whether the effect can be extended to room-temperature conditions. The long-term applications, such as compact neutron generators, depend on answering these fundamental questions. For now, the plateau at low energies stands as a puzzle that could reshape the field if its cause is fully understood.