Fusion Reactors Could Generate Axions, Offering a New Path to Detect Dark Matter

Fusion reactors are designed for clean power, but a new study by U.S. physicists suggests they could also be mysterious dark matter factories. Axions, theorized dark matter particles, may be born when fusion-generated neutrons smash into reactor walls. Dark matter makes up most of the universe's matter yet has never been directly seen. The key insight is that axions would not come from the hot fusion plasma but from the reactor's solid walls.

Fusion reactors as dark matter factories

According to the new study, fast neutrons from deuterium–tritium fusion slam into reactor walls, triggering nuclear reactions that could emit axions. The team models a lithium-lined reactor vessel (as planned in ITER) and finds its huge neutron flux could yield dark-sector particles. Neutron capture can leave nuclei excited, which then emit axions as they de-excite; these 'ghost' particles would slip out through the reactor's shielding. Although the Sun generates many more axions, researchers say fusion reactors offer a new production channel.

Implications and detection

The results suggest that future fusion plants may serve as dark matter research facilities. A heavy-water tank close to the reactor, for instance, could serve as a detector since an axion striking deuterium splits it into a neutron and a proton, leaving a distinct signal. It would be possible to separate genuine signals from backgrounds such as solar neutrinos by comparing data with the reactor on and off. The experiment would still limit theoretical models even in the absence of axions. To test the concept, more work will include intricate reactor simulations and unique detector designs.