Speaker
Description
This work was performed as part of the international Project 8 collaboration. The goal of the Project 8 experiment is to measure the absolute neutrino mass using tritium beta decays, which involves precisely measuring the energies of the beta-decay electrons in the high-energy tail of the spectrum.
To achieve its design sensitivity of $m_\beta\sim$ 40 meV, Project 8 has chosen an $\textit{atomic}$ tritium source to eliminate the energy smearing inherent to past and current molecular tritium experiments. The design sensitivity assumes a fiducial population of at least $10^{18}$ tritium atoms. The second key element which enables this sensitivity is a frequency-based energy measurement invented by Project 8 called Cyclotron Radiation Emission Spectroscopy. The CRES technique, however, has optimal sensitivity at an atom density of $10^{12}$ cm$^{-3}$. At this density, $10^{18}$ atoms occupy 10 m$^3$.
To prevent recombination of the tritium atoms on the container walls, it is necessary to trap them in a magnetic minimum. The baseline trap depth is $\Delta B = 2$ T, but even this substantial depth can only trap a population of atoms below $\sim30$ mK. The atom trapping field minimum simultaneously traps the beta decay electrons. I will discuss a candidate magnetic velocity and state selector to supply a sufficient trappable flux of atoms.
CRES further relies on a highly uniform magnetic field and precise knowledge of that field to convert the measured frequency into the electron energy. Our baseline is a background solenoid field of 1 T and a field uniformity in the fiducial volume of well below $10^{-5}$. With a fiducial volume fraction of perhaps 50%, the magnet itself takes on quite sizable proportions. I will discuss a preliminary design for a NbTi superconducting multipole (Ioffe-Pritchard) trap in the context of this large scale as required for a next-generation neutrino mass measurement.
