From x-ray telescopes to neutron scattering: using axisymmetric mirrors to focus a neutron beam

TL;DR

This paper demonstrates the use of Wolter mirror systems, originally for x-ray telescopes, to focus neutron beams, enabling improved neutron scattering techniques through nested axisymmetric mirrors tested at MIT.

Contribution

It introduces a novel application of Wolter mirror configurations for neutron beam focusing, including experimental implementation and ray-tracing simulations.

Findings

Successful focusing of neutron beams with nested Ni mirrors

Enhanced collection efficiency through nesting of mirror pairs

Aberration-free focusing performance demonstrated

Abstract

We demonstrate neutron beam focusing by axisymmetric mirror systems based on a pair of mirrors consisting of a confocal ellipsoid and hyperboloid. Such a system, known as a Wolter mirror configuration, is commonly used in x-ray telescopes. The axisymmetric Wolter geometry allows nesting of several mirror pairs to increase collection efficiency. We have implemented a system containing four nested Ni mirror pairs, which was tested by focusing a polychromatic neutron beam at the MIT Reactor. In addition, we have carried out extensive ray-tracing simulations of the mirrors and their performance in different situations. The major advantages of the Wolter mirrors are nesting for large angular collection, and aberration-free performance. We discuss how these advantages can be utilized to benefit various neutron scattering methods, such as imaging, SANS, and time-of-flight spectroscopy.