title: Superconducting magnetic Wollaston prism for neutron spin encoding.
abstract: A magnetic Wollaston prism can spatially split a polarized neutron beam into two beams with different neutron spin states, in a manner analogous to an optical Wollaston prism. Such a Wollaston prism can be used to encode the trajectory of neutrons into the Larmor phase associated with their spin degree of freedom. This encoding can be used for neutron phase-contrast radiography and in spin echo scattering angle measurement (SESAME). In this paper, we show that magnetic Wollaston prisms with highly uniform magnetic fields and low Larmor phase aberration can be constructed to preserve neutron polarization using high temperature superconducting (HTS) materials. The Meissner effect of HTS films is used to confine magnetic fields produced electromagnetically by current-carrying HTS tape wound on suitably shaped soft iron pole pieces. The device is cooled to ~30 K by a closed cycle refrigerator, eliminating the need to replenish liquid cryogens and greatly simplifying operation and maintenance. A HTS film ensures that the magnetic field transition within the prism is sharp, well-defined, and planar due to the Meissner effect. The spin transport efficiency across the device was measured to be ~98.5% independent of neutron wavelength and energizing current. The position-dependent Larmor phase of neutron spins was measured at the NIST Center for Neutron Research facility and found to agree well with detailed simulations. The phase varies linearly with horizontal position, as required, and the neutron beam shows little depolarization. Consequently, the device has advantages over existing devices with similar functionality and provides the capability for a large neutron beam (20 mm × 30 mm) and an increase in length scales accessible to SESAME to beyond 10 μm. With further improvements of the external coupling guide field in the prototype device, a larger neutron beam could be employed.
authors.affiliation: Center for Exploration of Energy and Matter, Indiana University, Bloomington, Indiana 47408, USA.
authors.forename: F
authors.initials: F
authors.lastname: Li
authors.affiliation: Center for Exploration of Energy and Matter, Indiana University, Bloomington, Indiana 47408, USA.
authors.forename: S R
authors.initials: SR
authors.lastname: Parnell
authors.affiliation: Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA.
authors.forename: W A
authors.initials: WA
authors.lastname: Hamilton
authors.affiliation: National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
authors.forename: B B
authors.initials: BB
authors.lastname: Maranville
authors.affiliation: Center for Exploration of Energy and Matter, Indiana University, Bloomington, Indiana 47408, USA.
authors.forename: T
authors.initials: T
authors.lastname: Wang
authors.affiliation: Ceraco Ceramic Coating GmbH, Ismaning 85737, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Semerad
authors.affiliation: Center for Exploration of Energy and Matter, Indiana University, Bloomington, Indiana 47408, USA.
authors.forename: D V
authors.initials: DV
authors.lastname: Baxter
authors.affiliation: Adelphi Technology Inc., Redwood City, California 94063, USA.
authors.forename: J T
authors.initials: JT
authors.lastname: Cremer
authors.affiliation: Center for Exploration of Energy and Matter, Indiana University, Bloomington, Indiana 47408, USA.
authors.forename: R
authors.initials: R
authors.lastname: Pynn