Bi-spectral beam extraction in combination with a focusing feeder

TL;DR

This paper proposes a shortened bi-spectral neutron beam extraction system using multiple mirrors, enhancing spectral range and instrument utilization, especially for compact focusing designs at the European Spallation Source.

Contribution

It introduces a novel multi-mirror extraction system that improves bi-spectral neutron beam delivery for short-distance, focused instrument designs.

Findings

Shortened mirror system enhances spectral range.

Multiple mirrors improve beam extraction efficiency.

Suitable for compact, focused neutron instruments.

Abstract

Bi-spectral beam extraction combines neutrons from two different kind of moderators into one beamline, expanding the spectral range and thereby the utilization of an instrument. This idea can be realized by a mirror that reflects long wavelength neutrons from an off-axis colder moderator into a neutron guide aligned with another moderator emitting neutrons with shorter wavelengths which will be transmitted through the mirror. The mirror used in such systems is typically several meters long, which is a severe disadvantage because it reduces the possible length of a focusing device in design concepts requiring a narrow beam at a short distance from the source, as used in many instruments under development for the planned European Spallation Source (ESS). We propose a shortened extraction system consisting of several mirrors, and show that such an extraction system is better suited for combination with a feeder in an eye of the needle design, illustrated here in the context of a possible ESS imaging beamline.