Neutron polarization evolution calculations along the SNS magnetism reflectometer beam line

In polarized neutron scattering instruments, most polarization devices apply magnetic fields of different space and time profiles for achieving the desired conditioning of the beam. Magnetic fields created at each device impose fringe/stray fields onto other devices in the beam line, which may affect their functionalities as well as the evolution of the neutron polarization. For the SNS magnetism reflectometer, it is desirable that different sample environment magnets and beam conditioning devices can be used in variable experimental conditions. Spin polarizers and analyzers, broad-band spin flippers and other polarized neutron devices must be capable of working reliably in the vicinity of small magnetic fields generated by an iron-yoke electromagnet and of much larger magnetic fields created, for example, by a high-field superconducting magnet. The latter may not only impose relatively large stray fields along the beam path, but also produce relatively large field gradients. In this paper, we present calculations treating the magnetic field interference between devices, the effect of sample environment magnets and the resultant neutron polarization evolution along the beam line. Calculations are presented for polarized instrumentation configurations that will typically be applied in standard experimental conditions at the SNS magnetism reflectometer.