Speaker
Description
Neutron polariser and analyser based on polarising supermirror technology [1-3] have been enabling the widespread use of polarised neutrons in the past decades. Polarising supermirror operates on polarised neutron reflectometry principles and is highly sensitive to incident neutron’s wavelength and incident angle. Modern neutron beamline often uses neutron optical elements such as a combination of curved and elliptical neutron guides to get out of the line of sight to the moderator, increase the transport of selected neutrons and focus the beam onto a sample. A polariser is placed either inline in a section of the neutron guides or at the guide exit in the experimental enclosure. At those locations, the beam characteristics are complex, making it necessary to use simulation for the design evaluation of the polariser. At present, the leading simulation software are McStas [4,5] and Vitess [6]. While many polarising devices have been incorporated, the complexity of the interaction between neutron and polarising supermirror and the increasing sophistication of beamline design demand further development of the simulation code to include physical processes that could previously be omitted [7]. We report here a development that, in addition to polarisation-dependent reflection and transmission at the supermirror coating, also includes transmission and absorption in substrate, refraction at the substrate interface, and multiple internal reflection in double-side coated supermirror. At the device level, multiple reflection between supermirrors has also been included in, e.g. v-cavity polariser. The results revealed internal reflections in a substrate and cross-talk between supermirrors can significantly affect the performance. Consequently, mitigations have been incorporated in our polariser designs to archive, for instance, 95% polarisation and 42% transmission at 2 Å for a v-cavity polariser. We will present our findings and the results of polariser design for ESS instruments using the new code.
[1] P. Böni, Physica B 234-236, 1038 (1997).
[2] T. Krist, C. Lartigue, F. Mezei, Physica B 180-181, 1005 (1992).
[3] T. Bigault, et. al., J. Phys.: Conf. Ser. 528, 012017 (2014).
[4] P. Willendrup and K. Lefmann, J. Neutron Res. 22, 1 (2020).
[5] P. Willendrup and K. Lefmann, J. Neutron Res. 23, 7 (2021).
[6] K. Lieutenant, et. al., Proc. SPIE Int. Soc. Opt. Eng. 5536, 134 (2004).
[7] D. M. Rodríguez, et. al., EPJ Web of Conferences 286, 03008 (2023).
E-mail of the corresponding author: waitung.lee@ess.eu
