Degaussing Procedure and Performance Enhancement by Low-Frequency Shaking of a 3-Layer Magnetically Shielded Room

TL;DR

This paper presents an optimized degaussing procedure and a low-frequency shaking method to significantly improve the magnetic shielding performance of a large, multi-layer magnetically shielded room used for sensitive co-magnetometer experiments.

Contribution

It introduces a novel degaussing protocol using frequency sweep and exponential decay, and demonstrates that low-frequency shaking enhances shielding factors by a factor of four.

Findings

Residual magnetic field can be reliably reduced below 1 nT.

The degaussing procedure takes 21 minutes for the entire MSR.

Low-frequency shaking of the outer layer improves shielding factors by approximately four times.

Abstract

We report on the performance of a Magnetically Shielded Room (MSR) intended for next level $^3$He/$^{129}$Xe co-magnetometer experiments which require improved magnetic conditions. The MSR consists of three layers of Mu-metal with a thickness of 3 mm each, and one additional highly conductive copper-coated aluminum layer with a thickness of 10 mm. It has a cubical shape with an walk-in interior volume with an edge length of 2560 mm. An optimized degaussing (magnetic equilibration) procedure using a frequency sweep with constant amplitude followed by an exponential decay of the amplitude will be presented. The procedure for the whole MSR takes 21 minutes and measurements of the residual magnetic field at the center of the MSR show that $|B|<1$ nT can be reached reliably. The chosen degaussing procedure will be motivated by online hysteresis measurements of the assembled MSR and by Eddy current simulations showing that saturation at the center of the Mu-metal layer is reached. Shielding Factors can be improved by a factor $\approx 4$ in all directions by low frequency (0.2 Hz), low current (1 A) shaking of the outermost Mu-metal layer.