A Design for an Electromagnetic Filter for Precision Energy Measurements at the Tritium Endpoint

TL;DR

This paper describes a novel electromagnetic filter design for the PTOLEMY project, enabling precise energy measurements of electrons near the tritium endpoint to detect the Cosmic Neutrino Background.

Contribution

It introduces a compact electromagnetic filter that uses higher-order drift processes to improve energy resolution for neutrino detection.

Findings

The filter achieves exponentially increasing precision on electron transverse velocity.

It maintains phase-space volume conservation validating its theoretical basis.

The design is more compact than previous electromagnetic filtering techniques.

Abstract

We present a detailed description of the electromagnetic filter for the PTOLEMY project to directly detect the Cosmic Neutrino Background (CNB). Starting with an initial estimate for the orbital magnetic moment, the higher-order drift process of ExB is configured to balance the gradient-B drift motion of the electron in such a way as to guide the trajectory into the standing voltage potential along the mid-plane of the filter. As a function of drift distance along the length of the filter, the filter zooms in with exponentially increasing precision on the transverse velocity component of the electron kinetic energy. This yields a linear dimension for the total filter length that is exceptionally compact compared to previous techniques for electromagnetic filtering. The parallel velocity component of the electron kinetic energy oscillates in an electrostatic harmonic trap as the electron drifts along the length of the filter. An analysis of the phase-space volume conservation validates the expected behavior of the filter from the adiabatic invariance of the orbital magnetic moment and energy conservation following Liouville's theorem for Hamiltonian systems.