Resonant Cavity Characterization for Project 8 Neutrino Mass Experiment

The observation of neutrino flavor oscillations confirms that neutrinos, long thought to be massless, in fact have non-zero masses. However, the actual mass value is still unknown. The Project 8 Neutrino Mass Experiment aims to improve the sensitivity of neutrino mass measurements, through an experimental technique known as Cyclotron Radiation Emission Spectroscopy (CRES). In this technique, we reconstruct the electron energy spectrum endpoint from tritium beta decays, in which electrons and antineutrinos are produced, by measuring the cyclotron radiation emitted by the electrons trapped in a cylindrical open-ended resonant cavity. The electromagnetic fields in the cavity can be mapped using the bead-pull technique and used as an input to model the electron-coupling to the cavity. The bead-pull technique consists of placing a small object in the cavity and observing the resonant frequency change as the object is moved throughout the cavity. Using a metal bead and a dielectric bead, resonant frequency data was collected using a vector network analyzer for a range of positions throughout the cavity. The resonant frequency maps for the metal and dielectric beads are converted into field maps and the shape of the resonant modes can be found and compared to analytical models.