Implementation and Optimization of the PTOLEMY Transverse Drift Electromagnetic Filter

TL;DR

This paper describes the implementation and optimization of the PTOLEMY transverse drift electromagnetic filter, demonstrating low-energy electron transport suitable for tritium beta-decay spectrum analysis, with a focus on magnetic field design and electrode voltage settings.

Contribution

It introduces a novel filter design with optimized electrode configurations and demonstrates its effectiveness through simulation for precise electron energy measurement.

Findings

Achieved electron energy reduction from 18.6 keV to <10 eV in simulations.

Designed a three-potential-well system to improve electron acceptance.

Validated the filter's performance with a 1 T or 3 T magnetic field in simulation.

Abstract

The PTOLEMY transverse drift filter is a new concept to enable precision analysis of the energy spectrum of electrons near the tritium beta-decay endpoint. This paper details the implementation and optimization methods for successful operation of the filter. We present the first demonstrator that produces the required magnetic field properties with an iron return-flux magnet. Two methods for the setting of filter electrode voltages are detailed. The challenges of low-energy electron transport in cases of low field are discussed, such as the growth of the cyclotron radius with decreasing magnetic field, which puts a ceiling on filter performance relative to fixed filter dimensions. Additionally, low pitch angle trajectories are dominated by motion parallel to the magnetic field lines and introduce non-adiabatic conditions and curvature drift. To minimize these effects and maximize electron acceptance into the filter, we present a three-potential-well design to simultaneously drain the parallel and transverse kinetic energies throughout the length of the filter. These optimizations are shown, in simulation, to achieve low-energy electron transport from a 1 T iron core (or 3 T superconducting) starting field with initial kinetic energy of 18.6 keV drained to <10 eV (<1 eV) in about 80 cm. This result for low field operation paves the way for the first demonstrator of the PTOLEMY spectrometer for measurement of electrons near the tritium endpoint to be constructed at the Gran Sasso National Laboratary (LNGS) in Italy.