Multi-mirror imaging optics for low-loss transport of divergent neutron beams and tailored wavelength spectra

TL;DR

This paper proposes a multi-mirror neutron optical system that efficiently transports divergent neutron beams with minimal losses and allows spectral tailoring, potentially replacing traditional guides at large facilities.

Contribution

It introduces a novel multi-mirror imaging system using nested elliptical mirrors for low-loss neutron transport and spectral control, enhancing current neutron guide technology.

Findings

Efficient transport of cold neutrons with minimal geometric losses.

Ability to discriminate neutron wavelengths and achieve beam monochromation.

Potential to replace conventional neutron guides at large-scale facilities.

Abstract

A neutron optical transport system is proposed which comprises nested short elliptical mirrors located halfway between two common focal points M and M'. It images cold neutrons from a diverging beam or a source with finite size at M by single reflections onto a spot of similar size at M'. Direct view onto the neutron source is blocked by a central absorber with little impact on the transported solid angle. Geometric neutron losses due to source size can be kept small using modern supermirrors and distances M-M' of a few tens of metres. Very short flat mirrors can be used in practical implementations. Transport with a minimum of reflections remedies losses due to multiple reflections that are common in long elliptical neutron guides. Moreover, well-defined reflection angles lead to new possibilities for enhancing the spectral quality of primary beams, such as clear-cut discrimination of short neutron wavelengths or beam monochromation using bandpass supermirrors. Multi-mirror imaging systems may thus complement or even replace ordinary neutron guides, in particular at the European Spallation Source.