In a turn of events more suited to prime-time TV, physicists have laid out the details of how the same reactors that will power the future could potentially unlock one of the biggest mysteries of cosmology, reports ScienceDaily of a theoretical study that shows that deuterium-tritium fusion reactors like those proposed for deployment in projects like ITER and DEMO could produce axions a hypothetical particle thought by many scientists to comprise the hidden framework of our universe.
Axions have always held a strange position in the world of physics, ever since they were posited in the late 1970s. They were originally hypothesized to fix a symmetry problem within Quantum Chromodynamics, but they soon found a new lease on life as a potential candidate for Dark Matter, the invisible mass that constitutes about 85 percent of the matter in the universe. Dark matter does not shine nor absorb light, but its effects, due to gravity, determine the way galaxies move within the cosmos. Discovery of axions would not only validate a part of the Standard Model of Particle Physics, but would also throw valuable insight into the aftermath of the Big Bang.
The new research, initiated by University of Cincinnati physicist Jure Zupan in collaboration with scientists at Fermi National Laboratory, M.I.T., and Technion – Israel Institute of Technology, takes a different approach to conventional methods seeking to detect axions in astrophysical sources or in nuclear fission reactors. Rather, the new research seeks to detect the strong neutron flux emitted inside a fusion reactor with a lithium-lined chamber. Normally, the fusion of a deuterium nucleus with a tritium nucleus (existing in every 1 cm³ of fusion fuel) yields a net release of 17.6 MeV per fusion, with 3.5 MeV trapped within the helium nucleus inside the plasma, while 14.1 MeV is converted to high-energy neutrons.
Nevertheless, because a 2,000 megawatt fusion reactor could achieve a neutron flux as high as 10¹⁵ per square centimeter per second, which might be 100 times higher compared to fission reactors with a similar capacity, it is highly possible that a detection could be achieved through this novel method. Such a detection could be possible because the higher velocities attained
These neutrons, of course, reacting with either the lithium in the breeding blankets or steel in the reactor walls, might cause nuclear reactions resulting in exotic particle emissions in addition to gamma rays in certain reactions. In regards to Axion-Like Particles (ALPs), there are production estimates based on comparisons to gamma dipole magnetic transitions in lithium and iron. Then another method would be through Neutron Bremsstrahlung. This would be a neutron collision resulting in a nuclear scatter, a loss of energy, creating a production of new particles. This theoretical analysis demonstrates a means of a possible flux-level of ALPs that would be much higher than in the plasma found in a reactor.
Detection is the biggest challenge here. They recommend the use of a heavy water detector with a detector such as the Sudbury Neutrino Observatory setup positioned 10 meters away from the reactor core. Since this will have 1,000 tons of heavy water with 6 × 10³³ deuterium nuclei, the detector could record the decay of these alpine particles into protons and neutrons. It would be identifiable compared to sources such as the solar neutrinos that cause 4,800 such events every year for the reactor-on and reactor-off periods and the position of the sun.
Although such a strategy is currently only theoretical in a laboratory setting, it can be considered in the context of the progress observed in condensed matter physics, making axion-like phenomena more feasible. Recent research uses materials like manganese bismuth telluride, a topological antiferromagnet, which can be used as a host for axion-like quasiparticles. The theoretical particles behave in the same way as regular axions in the universe. In fact, the detection mechanism may be compared to a kind of “cosmic car radio” listening to the frequency of dark matter. This can be achieved through the merging of high flux neutron sources obtained from fusion reactors and quantum materials.
There is an element of irony linking axion research with popular culture. In a few episodes of The Big Bang Theory TV show, imaginary particle physicists Sheldon Cooper, Ph.D., and his assistant, Leonard Hofstadter, struggled with the issue of axion production in a fusion reactor before resignedly abandoning hope, utili. Via a whiteboard equation accompanied by a sad face. Zupan points out, however, that what they did mirror axion production in the Sun, where the main player, of course, was its enormous scale. Yet a entirely different set of nuclear reactions occurring in the reactor walls holds the secret key to a viable axion production method.
However, if realized, fusion reactors would be playing a dual role: supporting clean energy production and facilitating basic physics research. Moreover, by installing dark matter detectors within the already-under-construction infrastructure, scientists would be attempting to detect dark matter particles without having to undertake large-scale projects to establish specialized research facilities. In doing so, they would be trying to find proof of axions for the first time in nearly half a century despite being potentially essential for unlocking the hidden structure of the universe.
