Magnetic Field Persistence for nEDM Experiments*

Neutron electric dipole moment experiments require extremely stable magnetic fields for sensitivity to electric precession frequencies at least 10 orders of magnitude smaller than the Larmor precession.  In cryogenic experiments, a superconductor is used to shield the precession chamber from external magnetic fields.  However, during cooldown, some areas go superconducting before others, which can trap inhomogeneous magnetic fields in the shield.  A superconducting mesh provides the same persistence as a solid superconducting shield while not displacing the magnetic flux, creating more predictable fields.  This allows the precession field to be generated outside the cryostat. We fabricated a rectangular prism out of a lead mesh with two temperature probes and magnetic field probe inside to test persistence of the magnetic field inside the superconducting mesh both during and after the superconducting transition.