Magnetic field stabilization for magnetically shielded volumes by external field coils

摘要

New results on an active stabilization system for improving the performance of a four-layer Ferromagnetic shield are presented. The system is based on measuring the magnetic field outside (but Close to) the shield by a fluxgate sensor. The output of this sensor is used to feed a Current through an external coil system surrounding the shield, thus stabilizing the ambient external field in one direction at a predefined value. Here we report on the construction and the characterization of the system in the magnetic test facility at PSI with special emphasis on a potential future application in a measurement of the neutron electric dipole moment (nEDM). Because of the long integration times in the nEDM experiment (about 100s or more) only slow disturbances have to be corrected for. With stabilization, suppression factors around 200 have been observed for stationary, localized sources and for vehicles moving on a road at 10 m distance. The ambient magnetic noise is reduced by a factor 10-20 for integration times of 100-1000s. (c) 2005 Elsevier B.V. All rights reserved.