Montel optics: Tailoring phase-space in neutron beam extraction

TL;DR

This paper presents a method for designing neutron beam transport systems using Montel optics, enabling precise, low-background beams suitable for small samples and extreme conditions, with verified simulations demonstrating effective brilliance transfer.

Contribution

It introduces simple numeric tools for designing Montel mirror-based neutron transport systems, verified by Monte-Carlo simulations including gravity and beam size effects.

Findings

Effective brilliance transfer from moderator to sample.

Montel optics produce homogeneous, low-background neutron beams.

Design tools are validated for use in advanced neutron instruments.

Abstract

In view of the trend towards smaller samples and experiments under extreme conditions it is important to deliver small and homogeneous neutron beams to the sample area. For this purpose, elliptic and/or Montel mirrors are ideally suited as the phase space of the neutrons can be defined far away from the sample. Therefore, only the useful neutrons will arrive at the sample position leading to a very low background. We demonstrate the ease of designing neutron transport systems using simple numeric tools, which are verified using Monte-Carlo simulations that allow to take into account effects of gravity and finite beam size. It is shown that a significant part of the brilliance can be transferred from the moderator to the sample. Our results may have a serious impact on the design of instruments at spallation sources such as the European Spallation Source (ESS) in Lund, Sweden.