Abstract
In a varying low-frequency external magnetic field, such as that experienced by a satellite in low Earth orbit, the effect of hysteresis should be considered for any magnetic-field-sensitive device placed inside a magnetic shield. We divided the residual magnetic field inside the shielding into two parts: an attenuated magnetic field and a magnetization-induced magnetic field. To calculate the residual magnetic field accurately, we introduced the hysteresis Jiles–Atherton model to predict and calculate the magnetization-induced magnetic field. To mimic the varying magnetic field of low Earth orbits, we developed a quasi-Helmholtz coil by controlling the coil current and placed a magnetic-field-sensitive device—a cold atom clock—inside the coil. This clock was operating inside three layers of magnetic shielding. For the Jiles–Atherton model, we adjusted the current of the compensation coil in real time to maintain a stable magnetic field inside the shield. With this compensation strategy, the test result showed that the field variation is reduced from 14.8nT to 1.4nT. Compared with other strategies, this method provides a more accurate and more universal magnetic-field compensation scheme.
Highlights
Magnetic shielding is important for devices with magnetically susceptible atoms such as atomic clocks, atomic interferometers, and atomic gravimeters
Three or more layers of magnetic shielding enclosing the reference atoms in an atomic clock are needed to ensure that the residual magnetic field is near zero
A cold atomic clock or an atom interferometers running in low Earth orbit experiences a periodically varying external magnetic field
Summary
Magnetic shielding is important for devices with magnetically susceptible atoms such as atomic clocks, atomic interferometers, and atomic gravimeters. To reduce the residual magnetic field from hysteresis for the space-bound cold atomic clocks, Projet d’Horloge Atomique par Refroidissement d’Atomes en Orbite (PHARAO) and Cold Atom Clock Experiment in Space (CACES), active compensation methods employing a quadratic-function algorithm and a linear-function algorithm, respectively, were developed. These active compensation algorithms were developed for specific magnetic-shield structures and a specific near Earth-orbit magnetic field. A more general model to calculate and predict the scitation.org/journal/adv hysteresis inside the magnetic shields would be useful This is pivotal in finding a better compensation strategy or to design certain types of new magnetic shields for a system exposed to a varying magnetic field
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