A tunable dielectric-loaded copper resonator for axion searches at 11 GHz

In the context of axion searches with haloscopes, tunable cavity resonators with high quality factor and high effective volume at frequencies above about 8 GHz are central for probing the axion-photon coupling with the required sensitivity to reach the quantum chromodynamics axion models. Higher order modes in dielectric-loaded cavities allow for higher effective volumes and larger quality factors compared to basic cylindrical cavities, but a proper cavity frequency tuning mechanism to probe broad axion mass ranges is not yet available. In this work, we report about the design and construction of a tunable prototype of a single-shell dielectric-boosted resonator with its axion-sensitive pseudo-TM030 high-order mode at about 11 GHz frequency. A clamshell tuning method previously tested for empty cylindrical resonators has been perfected for this geometry through simulations and in situ tests conducted at cryogenic temperature. Tuning is accomplished in a range of about 2% of the central frequency, without significantly impacting the unloaded quality factor of about 175 000. The experimental results presented in this work demonstrate the tunability of this type of resonator, definitely confirming its applicability to high frequency axion searches.