Cryogenic Engineering for the Magnetic Field System in the nEDM@SNS Experiment

The nEDM@SNS experiment aims to measure the electric dipole moment of neutrons at a new level of sensitivity. The Magnetic Field System is designed to generate a holding field with uniformity < 3 ppm/cm as well as a spin dressing field. The entire magnet package is cooled to below 6K to maintain functioning of the superconducting wires and shields with two pulse-tube cryocoolers. In order to minimize distortion of the fields, these cryocoolers are installed in a separate vessel at a distance, and the cooling power is delivered via circulation of supercritical helium. Heating of the metglas flux return by the alternating dressing field is eliminated by a passive copper shield. A magnetic probe will be installed in a warm bore located in the center of the magnet to characterize the generated fields. A Cu-G10 woven 100K thermal shield around the warm bore is fabricated to minimize the distortion on the dressing field in the field mapping.