Researchers led by Jure Zupan propose that energetic neutrons striking lithium-rich breeding blankets in deuterium–tritium fusion reactors could produce axion-like particles via neutron-capture reactions and neutron bremsstrahlung. Their models predict ALP fluxes that may be substantially larger than plasma-based mechanisms and potentially detectable outside the reactor vessel. If confirmed experimentally, fusion facilities could become controllable, complementary laboratories for dark-matter searches.
Fusion Reactors Could Produce Detectable Axion-Like Dark Matter Particles, Study Suggests
Fusion Reactors Might Create Dark Matter Particles, Physicists Show
Reactors built to generate power by fusing atomic nuclei may offer an unexpected opportunity for fundamental physics: they could produce low-mass dark-sector particles, such as axions or axion-like particles (ALPs), not directly from the fusion plasma but from interactions between energetic neutrons and reactor materials.
Neutrons, Lithium Blankets and New Particles
An international team of researchers led by physicist Jure Zupan (University of Cincinnati) has proposed a concrete theoretical pathway for axion production in deuterium–tritium fusion reactors. In these designs, a lithium-rich "breeding blanket" surrounds the vacuum vessel. The fusion plasma emits a massive flux of high-energy neutrons that strike the blanket and inner walls, converting kinetic energy into heat and breeding tritium by neutron capture on lithium.
How Axions Could Be Produced
The authors identify two neutron-driven processes that could generate ALPs at rates higher than previously considered plasma mechanisms:
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- Neutron Capture Reactions: When neutrons are captured by lithium or other nuclei in the blanket, nuclear transitions can, in principle, emit axion-like particles alongside conventional radiation.
- Neutron Bremsstrahlung: As high-energy neutrons scatter and slow in the reactor materials, they can radiate energy. Under certain models, part of that radiation can take the form of light, weakly interacting bosons such as ALPs.
The researchers' calculations indicate that the ALP flux from these neutron-driven mechanisms can exceed the flux expected from solar-like plasma emission in a man-made reactor. Crucially, under plausible reactor conditions the emitted ALP flux might be large enough to be detectable outside the reactor vessel, opening a practical path for experimental searches at operating or future fusion facilities.
"The Sun is a huge object producing a lot of power. The chance of having new particles produced from the Sun that would stream to Earth is larger than having them produced in fusion reactors using the same processes as in the Sun," Zupan says. "However, one can still produce them in reactors using a different set of processes."
Implications And Next Steps
If experimental searches near fusion reactors confirm these predictions, it would provide a controlled, repeatable laboratory window onto the dark sector that complements astrophysical searches. The paper models the relevant nuclear processes and estimates fluxes, and the authors suggest that deuterium–tritium reactors with lithium breeding blankets could be instrumented or adapted to look for the predicted ALP signal.
The work is published in the Journal of High Energy Physics. While theoretical estimates are promising, realizing a detection will require careful experimental design to separate any ALP signal from backgrounds and to account for reactor-specific geometry and materials.
Context: Axions and axion-like particles remain among the leading theoretical candidates to explain dark matter, a non-luminous component that makes up roughly 84% of the Universe’s matter budget while ordinary baryonic matter accounts for about 16%. This proposal reframes fusion reactors not only as potential energy sources but also as novel laboratories for probing fundamental physics.
