Uniform Field in Microwave Cavities Through the Use of Effective Magnetic Walls

TL;DR

This paper introduces a novel method to enhance the form factor of microwave cavities for axion detection by shifting metal walls to create uniform electromagnetic fields, validated through theoretical, simulation, and experimental results.

Contribution

The study proposes a quarter-wavelength wall shift technique to convert electric boundary conditions into magnetic ones, significantly improving the mode uniformity and form factor in WM plasma haloscopes.

Findings

Enhanced form factor confirmed by simulations and experiments.

Uniform electric field mode achieved in modified resonator.

Method allows simple control of field profiles in WM cavities.

Abstract

Wire media (WM) resonators have emerged as promising realization for plasma haloscopes -- devices designed to detect axions, a potential component of dark matter. Key factors influencing the detection probability include cavity volume, resonance quality factor, and form factor. While the form factor has been explored for resonant frequency tuning, its optimization for axion detection remains unexplored. In this work, we present a novel approach to significantly enhance the form factor of WM plasma haloscopes. By shifting the metal walls of the resonator by a quarter wavelength, we effectively convert an electric wall boundary condition into a magnetic wall one, allowing for an almost uniform mode. Theoretical analysis and numerical simulations confirm that this modification improves the electric field profile and boosts the form factor. We validate these findings through experimental results from two prototype resonators: one with a standard geometry and another with a quarter-wave air gap between the WM and the walls. Additionally, our method provides a simple way to control the field profile within WM cavities, which can be explored for further applications.