Avoided mode crossings in cylindrical microwave cavities

TL;DR

This paper investigates how longitudinal symmetry breaking causes avoided mode crossings in cylindrical microwave cavities, impacting the design of high-Q tunable cavities for axion detection.

Contribution

It provides an analytical understanding of the mechanism behind avoided mode crossings due to symmetry breaking in cylindrical cavities.

Findings

Avoided mode crossings are caused by longitudinal symmetry breaking.

The size of the frequency gaps due to AMC is proportional to the symmetry breaking magnitude.

The study enhances cavity design for axion haloscope detectors.

Abstract

Axion haloscope detectors require high-$Q$ cavities with tunable TM$_{010}$ modes whose resonant electric field occupies as much of the full volume of the cavity as possible. An analytical study of the effects of longitudinal symmetry breaking within microwave cavities was conducted to better understand the mode structure. The study revealed longitudinal symmetry breaking of the cavities was the mechanism for avoided mode crossings (AMC) in cylindrical microwave cavities. The results showed the size of the gaps in the search frequency spectrum due to an AMC was roughly proportional to the magnitude of symmetry breaking for small perturbations.