Parabolic versus elliptic focusing - Optimization of the focusing design of a cold triple-axis neutron spectrometer by Monte-Carlo simulations

TL;DR

This paper uses Monte-Carlo simulations to compare parabolic and elliptic focusing designs for a cold-neutron triple-axis spectrometer, finding the parabolic design offers superior neutron intensity and homogeneity.

Contribution

It introduces a simulation-based comparison of focusing geometries for neutron spectrometers, optimizing design parameters for improved performance.

Findings

Parabolic focusing yields higher neutron intensity.

Parabolic design provides more homogeneous divergence distribution.

Elliptic focusing results in inhomogeneous divergence distribution.

Abstract

We present Monte-Carlo simulations for the focusing design of a novel cold-neutron triple-axis spectrometer to be installed at the end position of the cold guide NL-1 of the research reactor FRM-II in Munich, Germany. Our simulations are of general relevance for the design of triple-axis spectrometers at end positions of neutron guides. Using the McStas program code we performed ray trajectories to compare parabolic and elliptic focusing concepts. In addition the design of the monochromator was optimized concerning crystal size and mosaic spread. The parabolic focusing concept is superior to the elliptic alternative in view of the neutron intensity distribution as a function of energy and divergence. In particular, the elliptical configuration leads to an inhomogeneous divergence distribution.