Characterization of a 1/2-scale prototype magnet at cryogenic temperatures for the SNS nEDM experiment

The observation of a permanent electric dipole moment of the neutron at the current level of experimental sensitivity would indicate new physics beyond the Standard Model of particle interactions. In addition, it might also explain the mystery behind the matter-antimatter asymmetry of the Universe. Given these tantalizing implications, a new multi-institutional effort to measure the neutron electric dipole moment (nEDM) using ultra-cold neutrons and polarized $^{3}$He in a bath of superfluid $^{4}$He is currently underway at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. The search for the nEDM asks for stringent requirements on the uniformity of the magnetic environment at cryogenic temperatures. We present measurements of the uniformity of a half-scale version of the coil that will be used for the experiment. The measurements are performed while the coil is at a temperature of $\approx$~90 K. The results are in good agreement with previous room temperature measurements which suggest that magnetic non-uniformities due to thermal contraction are under control.