Conceptual design of supermirror polarizers at the European Spallation Source

Abstract

Polarized neutrons will be made available on many European Spallation Source (ESS) instruments. There are a number of technologies available for polarizers and polarization analyzers which will be used at the ESS. The selection of the technology for an instrument is based on the performance and the constraints of the instrument. We will focus on the design of polarizing supermirror devices using Monte Carlo ray tracing simulation as an integral part of instrument design process. A McStas module has been developed to simulate a multichannel V-cavity polarizer, seeking the appropriate parameters to be incorporated into the respective instrument. The performance of such polarizers is studied for three instruments at ESS (MIRACLES (backscattering spectrometer), BIFROST (indirect geometry spectrometer) and ODIN (imaging)) with different requirements and constraints, where the suitability of this kind of devices can be assessed. For the first two instruments, where there is no strong constraint on the placement of the polarizer, the optimal configurations show excellent performance over the whole required wavelength ranges. However, in ODIN, due to more strict constraints in the placement of the polarizer, the performance is more dependent on the wavelength in the required wavelength range and other options may need to be considered.