Progress on the Design, Construction and Test of the Full Size Magnet for the SNS Neutron Electric Dipole Moment Search

The SNS nEDM project aims to search for a neutron electric dipole moment (nEDM) at a goal sensitivity of 3x10^-28 e-cm at the Spallation Neutron Source (SNS) of Oak Ridge National Laboratory (ORNL). The nEDM signal will appear as a change of the procession frequency of polarized ultracold neutrons (UCN) induced by the application of a high electric field. A uniform magnetic field over the UCN storage volume of 0.4 m long with a gradient less than 3 ppm/cm is crucial to suppress the false nEDM signal due to the geometric phase effect, and the field strength will be monitored by comagnetometer He-3. The magnetic fields will be generated by superconducting cosine-theta coils of 1.5—2 m in diameter, enclosed in a nearly-hermetic superconducting lead shield. In this talk, we will present the progress of design, construction and tests of the full size magnets and magnetic shielding as well as the cryogenic systems. The challenges and solutions will be discussed.