there was a Scientific American article on this a few o months back (sadly paywalled). Essentially they can ringfence the potential masses/energies of axions b

there was a Scientific American article on this a few o months back (sadly paywalled). Essentially they can ringfence the potential masses/energies of axions based on other things, if they exist, this device contains a resonant cavity that should be able to detect them breaking down across most of the theoretical energy range