The ADMX Orpheus experiment: first results and future operations*

Orpheus is an axion haloscope using an open cavity design with dielectrics to search for axions with masses around 70 μeV. The axion is a hypothetical particle and an especially promising dark matter candidate. While it was predicted as a consequence of a solution to the strong CP problem, it could have been created in sufficient quantities in the early universe to solve the dark matter problem. Currently, the most sensitive axion haloscope, ADMX, uses a closed resonant cavity with a tunable frequency to couple to axions with masses of order 1 μeV (f0~1 GHz). However, higher order modes of standard closed cavity haloscopes do not couple strongly to the axion. They therefore require smaller cavity volumes for detecting axions at higher frequencies, significantly decreasing sensitivity. Orpheus modifies higher order modes to couple to the axion, and is thus able to explore higher frequencies and axion masses. As with any axion haloscope, data from Orpheus can also be used to search for dark photons, another dark matter candidate. In this talk, I will give an overview of the design and construction of Orpheus and present results from a dark photon search conducted in 2021. Finally, I will outline plans for Orpheus in 2022, when we expect to conduct our first axion search.