Suppression of Nonuniform Magnetic Fields in Magnetic Shielding System for SERF Co-Magnetometer

Spin-exchange relaxation-free (SERF) co-magnetometer typically uses a low-noise magnetic shield system, which is composed of outer mu-metal shields and inner low-noise magnetic shields, to provide the required magnetic environment. Proper degaussing is essential for the co-magnetometer to obtain low remanence and field gradient. In this article, an improved design method of degaussing device suitable for the SERF co-magnetometer is proposed, which considers the degaussing performance demand of multimaterial magnetic shields and the introduction of magnetic noise by metal materials. Based on this, a coil-shaped degaussing device in a separate type is designed and compared with the existing detachable pole-shaped degaussing device. The experimental results show that this degaussing device can reduce the residual magnetic field in the three-axis directions by more than 65% and reduce the magnetic gradient within +/- 10 mm of the shields' center by more than 80%. As a result, the nonuniform magnetic fields can be effectively reduced, which greatly suppresses the electron relaxation so that the signal-to-noise ratio (SNR) is improved. Furthermore, the signal noise of the SERF co-magnetometer is reduced by about 25%.