Exploration of Non-Mechanical Tuning Methods for Microwave Axion Search Cavities

Dark matter axion haloscopes aim to amplify and measure the signal from the conversion of axions to photons in the presence of a strong magnetic field. The frequency of the resulting signal is related to the unknown mass of the axion. Microwave cavities are used to couple the converted photon with a resonant cavity mode for readout, but in order to search the wide range of well-motivated masses the cavity must be able to efficiently sweep through many resonant frequencies. Current experiments are able to tune over a frequency range using rotating mechanical rods. This method introduces imperfect geometry that increasingly impacts signal strength as experiments try to reach higher frequencies. We explore non-mechanical tuning methods that could aid in the goal of tuning at higher frequencies while preserving the signal strength of the cavity. We present an investigation of materials with tunable permittivity with the potential to tune the resonant frequency of an axion search cavity, with further applications to hidden photon searches. We conduct a preliminary analysis of how such a tuning method may be best utilized within the cavity.