High-volume tunable resonator for axion searches above 7 GHz

While haloscope experiments searching for axion dark matter with cylindrical microwave cavity resonators are the most sensitive to date, that sensitivity is degraded at high frequencies, due to geometric scaling. The authors demonstrate a prototype thin-shell cavity resonator that decouples volume from resonant frequency, and thus avoids such degradation. As the resonator comprises two mechanically isolated pieces, a protocol is developed for robust, automated precision alignment, which enables a wide tuning range for the resonator's axion-sensitive TM₀₁₀ mode. A discussion of the instrument's feasibility for high-frequency probes of the post-inflationary scenario is also offered.