Correction of Optical Aberrations in Elliptic Neutron Guides

Published

November 21, 2012

Author(s)

Phllip M. Bentley, Shane J. Kennedy, Ken H. Andersen, Damian Martin Rodriguez, David F. Mildner

Abstract

Modern, nonlinear ballistic neutron guides are an attractive concept in neutron beam delivery and instrumentation, because they offer increased performance over straight or linearly tapered guides. However, like other ballistic geometries they have the potential to create significantly non-trivial instrumental resolution functions. We address the source of the most prominent optical aberration, namely coma, where off-axis rays have a different focal length from on-axis rays. We illustrate how the interplay between coma, sources of finite size, and mirrors with non-perfect reflectivity can conspire to produce uneven distributions in the neutron beam divergence, the source of complicated resolution functions. To solve these problems, we propose a hybrid elliptic-parabolic guide geometry. Using this new kind of neutron guide shape, it is possible to condition the neutron beam and remove almost all of the aberrations, whilst providing the same performance in beam current as a standard elliptic neutron guide. We highlight the positive implications for a number of neutron scattering instrument types that this new shape can bring.

Citation

Nuclear Instruments & Methods in Physics Research A

Volume

693

Pub Type

Journals

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Keywords

neutron guide, elliptic, parabolic, ballistic, conic section

Citation

Bentley, P. , Kennedy, S. , Andersen, K. , Rodriguez, D. and Mildner, D. (2012), Correction of Optical Aberrations in Elliptic Neutron Guides, Nuclear Instruments & Methods in Physics Research A, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=909598 (Accessed April 25, 2024)