YBCO films as Meissner screens in the control of polarized neutron beams — Observations and calculations

The expulsion of magnetic induction from a thin film of superconducting YBa2Cu3O7(YBCO) — the Meissner effect, was used to permit the reversal of magnetic fields across the film that produced spin reversal of a polarized neutron beam. We report the design and performance of such a device called a cryo-flipper. We compare the measured performance of the YBCO-cryo-flipper to the performance expected on the basis of calculations of the magnetic fields around the film and the precession of neutron spins through these fields, and comment on the advantages of such a system compared to cryo-flippers based on a superconducting niobium foil.