Development of Homogeneous Magnetic Field for the Measurement of Neutron EDM

   Toward measurement of nEDM (neutron electric dipole moment) using polarized UCN from the UCN source, we are developing a magnetic field with high homogeneity for Ramsey resonance.  Our goal is to measure nEDM with the 10 times better precision than the present world record.  We are now developing an active filed compensation system to cancel out relatively high magnetic field from environment including the geomagnetism, as a preparation for a homogenous magnetic field by the spherical coils.

   Our half scale test system is 2m x 2m x 2m in size, and is composed of 4 square coils in one direction, and can be graded up to 3D system which is composed of 12 coils in total.  Using signals from magnetic field sensors in feed back loops, our system automatically cancels out both the center magnetic field and the field gradient at the same time.  Distance between coils are optimized for the better magnetic field homogeneity. We report present status of the development, including performance, e.g., field suppression factor, time response, field homogeneity, etc.