A large 'Active Magnetic Shield' for a high-precision experiment

TL;DR

This paper introduces a novel Active Magnetic Shield system designed for high-precision neutron electric dipole moment experiments, providing stable, uniform magnetic environments within spatial constraints.

Contribution

The paper presents a new feedback-controlled AMS with complex coil arrangements that effectively stabilizes magnetic fields in a compact setup for sensitive experiments.

Findings

Achieves magnetic field suppression to a few microtesla in sub-Hertz range.

Provides stable, uniform magnetic environment around a large passive shield.

Design fulfills specific experimental requirements and can be adapted for other applications.

Abstract

We present a novel Active Magnetic Shield (AMS), designed and implemented for the n2EDM experiment at the Paul Scherrer Institute. The experiment will perform a high-sensitivity search for the electric dipole moment of the neutron. Magnetic-field stability and control is of key importance for n2EDM. A large, cubic, 5m side length, magnetically shielded room (MSR) provides a passive, quasi-static shielding-factor of about 10^5 for its inner sensitive volume. The AMS consists of a system of eight complex, feedback-controlled compensation coils constructed on an irregular grid spanned on a volume of less than 1000m^3 around the MSR. The AMS is designed to provide a stable and uniform magnetic-field environment around the MSR, while being reasonably compact. The system can compensate static and variable magnetic fields up to +-50muT (homogeneous components) and +-5muT (first-order gradients), suppressing them to a few muT in the sub-Hertz frequency range. The presented design concept and implementation of the AMS fulfills the requirements of the n2EDM experiment and can be useful for other applications, where magnetically silent environments are important and spatial constraints inhibit simpler geometrical solutions.