A new theoretical study suggests that future fusion reactors could produce axions, elusive particles potentially linked to dark matter. Led by a University of Cincinnati physicist, the research outlines how neutrons in these reactors might trigger reactions creating such particles. The idea echoes a puzzle from the TV show The Big Bang Theory that fictional scientists could not solve.
Physicists have proposed a method for detecting axions inside fusion reactors, building on decades of dark matter research. Jure Zupan, a physics professor at the University of Cincinnati, collaborated with scientists from Fermi National Laboratory, MIT, and Technion-Israel Institute of Technology. Their findings, published in the Journal of High Energy Physics, explore how these reactors could serve as particle detectors.
Axions are hypothetical subatomic particles that could constitute dark matter, which influences the universe's structure through gravity despite being invisible and non-interacting with light. Ordinary matter comprises only a small portion of the cosmos, with dark matter inferred from galactic motions.
The study focuses on a fusion reactor design using deuterium and tritium fuel within a lithium-lined vessel, part of an international project in southern France. High-energy neutrons generated during fusion would interact with the reactor walls, sparking nuclear reactions that might produce axions or similar particles. Another pathway involves neutrons slowing down and emitting bremsstrahlung radiation, potentially yielding these elusive particles.
"Neutrons interact with material in the walls. The resulting nuclear reactions can then create new particles," Zupan explained.
This concept revives an idea from season 5 of the sitcom The Big Bang Theory, where characters Sheldon Cooper and Leonard Hofstadter attempted but failed to make it work. "The general idea from our paper was discussed in 'The Big Bang Theory' years ago, but Sheldon and Leonard couldn't make it work," Zupan noted. The show featured equations comparing axion production in the sun versus reactors, highlighting the sun's greater output but suggesting reactors could use distinct processes.
While the sun offers higher chances for axion detection due to its scale, the researchers argue that fusion reactors provide a controlled environment for probing the dark sector. The work, detailed in a paper titled 'Searching for exotic scalars at fusion reactors' by Chaja Baruch and colleagues (DOI: 10.1007/JHEP10(2025)215), opens avenues for experimental verification as fusion technology advances.