Active shield for EDM measurement

We are developing an active shield for the measurement of neutron electric dipole moment using ultracold neutron. The disturbing geomagnetism and environmental magnetic fields are cancelled by the active shield. We introduced proportional-integral-differential control to the feedback loop of the system to improve the performance of the active shield. A quadrupole-coil arrangement was adopted to control the diagonal components of the field gradient. The influence of magnetic shielding inside the active shield was studied. It was found that this effect caused no critical problems in the detection of zero-field conditions.