Neutron spin manipulation devices using YBCO films

The Meissner effect in a thin-film superconductor can be used to create a sharp boundary between regions of different magnetic field and hence can be used as a component of neutron spin manipulation devices. We have developed two cryogenic neutron spin manipulation devices using single-crystal, high-T _c, YBCO films, which can be cooled without using liquid cryogens and eliminate small angle scattering associated with polycrystalline films. The devices are a spin flipper and a spin precession device both of which use 350-nm-thick YBCO films covered with gold on a 0.5 mm thick sapphire substrate. The spin flipper consists of one such film mounted on an oxygen-free copper frame and connected to a closed-cycle He refrigerator. The flipper is capable of working with a maximum neutron beam size of 42 x 42 mm² and can be used with both vertical and horizontal guide fields. The spin precession device was constructed by mounting two of the YBCO films parallel to one another with an H-magnet between them. By changing the current through the H-magnet, the precession of the neutron polarisation between the films can be controlled. Tests at the Low Energy Neutron Source (LENS) show that this device is capable of generating controlled spin precession for a neutron beam up to 20 x 20 mm² in cross section.