Characterization of a Resonant Cavity for the Princeton Axion Search

A key element of the Princeton aXion Search (PXS) is a copper tunable resonator with high quality factor operating in the 200-500 MHz frequency range (corresponding to 0.8-2.1 ueV mass). This is a transitional range between the DMRadio program, which operates below any cavity modes, and the higher-frequency cavity regime. We discuss cavity designs and tuning strategies for covering this 200-500 MHz range, including COMSOL simulations of the internal cavity geometry. We also present experimental studies of a room-temperature cavity. We compare the resonant frequency and quality factor of the empty cavity to simulation to elucidate loss mechanisms associated with the fabrication and welding processes. We produce maps of the cavity mode electric and magnetic fields through bead-pull measurements with dielectric and metallic beads.