Initial Performance of the TUCAN Magnetically Shielded Room

TL;DR

The paper reports initial performance metrics of a magnetically shielded room designed for ultra-precise neutron electric dipole moment measurements, demonstrating high shielding factors and low residual fields.

Contribution

This work presents the commissioning results and initial magnetic shielding performance of a large, multi-layer MuMetal and copper shielded room for nEDM experiments.

Findings

Shielding factor of 3.25×10^4 at 0.01 Hz within ambient cyclotron field.

Shielding factor of 3.75×10^4 at 0.01 Hz without cyclotron field.

Residual magnetic field at room center is approximately 1.8 nT.

Abstract

The TRIUMF Ultracold Advanced Neutron (TUCAN) collaboration has commissioned a large magnetically shielded room to be used for measuring the neutron electric dipole moment (nEDM) to a precision of $10^{-27}~e\mathrm{cm}$. The room is composed of five layers of MuMetal and one layer of copper and sits within the $\lesssim 370~\mu\mathrm{T}$ ambient field produced by the TRIUMF cyclotron. Within this environment, the quasi-static shielding factor was measured to be $3.25(2) \times 10^4$ at $0.01~\mathrm{Hz}$ with an external peak-to-peak perturbation of $2~\mu\mathrm{T}$. Without the large ambient cyclotron field, the shielding factor improves to $3.75(4)\times 10^4$ at the same perturbation amplitude and frequency. After idealization in the cyclotron field, the residual field at the room center was $B = 1.8(2)~\mathrm{nT}$ and the vertical first-order gradient across the central 1~m$^3$ ($dB_{\mathrm{z}}/dz$) was $-279(64)~\mathrm{pT/m}$. With additional improvement to the idealization, and with active compensation, we expect the room to be adequate for a $10^{-27}~e\mathrm{cm}$ nEDM search.