Technical design and commissioning of the KATRIN large-volume air coil system

TL;DR

The paper details the design, commissioning, and verification of a large-volume air coil system crucial for optimizing magnetic fields in the KATRIN neutrino mass experiment, enhancing signal transmission and background suppression.

Contribution

It presents the technical design, operational modes, and validation of the air coil system, a key component for precise magnetic field control in KATRIN.

Findings

Magnetic field measurements matched simulations, confirming system functionality.

The air coil system enables versatile operation modes for background suppression.

Successful commissioning supports accurate neutrino mass measurements.

Abstract

The KATRIN experiment is a next-generation direct neutrino mass experiment with a sensitivity of 0.2 eV (90% C.L.) to the effective mass of the electron neutrino. It measures the tritium $\beta$-decay spectrum close to its endpoint with a spectrometer based on the MAC-E filter technique. The $\beta$-decay electrons are guided by a magnetic field that operates in the mT range in the central spectrometer volume; it is fine-tuned by a large-volume air coil system surrounding the spectrometer vessel. The purpose of the system is to provide optimal transmission properties for signal electrons and to achieve efficient magnetic shielding against background. In this paper we describe the technical design of the air coil system, including its mechanical and electrical properties. We outline the importance of its versatile operation modes in background investigation and suppression techniques. We compare magnetic field measurements in the inner spectrometer volume during system commissioning with corresponding simulations, which allows to verify the system's functionality in fine-tuning the magnetic field configuration. This is of major importance for a successful neutrino mass measurement at KATRIN.