Electromagnetic design of the KATRIN large-volume air coil system

TL;DR

This paper discusses the electromagnetic design of a large-volume air coil system crucial for guiding electrons and reducing background in the KATRIN neutrino mass experiment, ensuring precise magnetic field control.

Contribution

It presents the design considerations and solutions for the large air coil system used in KATRIN to optimize electron transmission and background suppression.

Findings

Successful design of the coil system for precise magnetic field control.

Enhanced electron transmission efficiency in the spectrometer.

Effective compensation of Earth's magnetic field effects.

Abstract

The KATRIN experiment is designed to determine the absolute neutrino mass scale with a sensitivity of 200 meV (90 % CL) by measuring the electron energy spectrum close to the endpoint of molecular tritium beta decay. Electrons from a high-intensity gaseous tritium source are guided by a strong magnetic field of a few T to the analyzing plane of the main spectrometer where an integral energy analysis takes place in a low field region (B<0.5 mT). An essential design feature to obtain adiabatic electron transport through this spectrometer is a large volume air coil system surrounding the vessel. The system has two key tasks: to adjust and fine-tune the magnetic guiding field (Low Field Correction System), as well as to compensate the distorting effects of the earth magnetic field (Earth Field Compensation System). In this paper we outline the key electromagnetic design issues for this very large air coil system, which allows for well-defined electron transmission and optimized background reduction in the KATRIN main spectrometer.