Searching for exotic scalars at fusion reactors

Abstract

Part of the energy created in deuterium-tritium fusion reactors is carried away from plasma by a high-intensity neutron flux, which is then absorbed by the reactor’s inner walls. The neutron flux can be used to sustain the reaction by the following mechanism: the walls are coated with lithium-rich breeding blankets, in which a fraction of neutrons interacts with lithium, creating tritium, which can be, in turn, used a fuel for the main reaction. The interactions of neutrons with the materials within the breeding blanket can also result in the production of dark sector particles, feebly interacting light scalars or pseudoscalars, via nuclear transitions. We estimate the potential size of such dark sector flux outside the reactor and consider possible detection methods at current and future thermonuclear fusion reactors. In our analysis, we take into account all other current bounds, recasting also the SNO axion bound for a CP even scalar. We find that year-long searches at current and future reactors can set leading constraints on dark scalar- and dark pseudoscalar-nucleon couplings.