Effects of ground movements on realistic guide models for the European Spallation Source

TL;DR

This study uses ray-tracing simulations to assess how ground movements affect neutron guide efficiency at the European Spallation Source, finding smaller losses in realistic models than previously predicted, thus informing guide design.

Contribution

It provides a detailed simulation-based analysis of ground movement effects on neutron guides, demonstrating reduced losses with realistic engineering models compared to earlier simple models.

Findings

Losses are about 7% for the BIFROST guide at 2.3-4.0 Å.

Realistic guide mounting reduces predicted losses.

Overillumination is unnecessary for mitigation.

Abstract

We model the effect of ground movement, based on empirical experience, on the transport properties of long neutron guides by ray-tracing simulations. Our results reproduce the large losses found by an earlier study for a simple model, while for a more realistic engineering model of guide mounting, we find the losses to be significantly smaller than earlier predicted. A detailed study of the guide for the cold neutron spectrometer BIFROST at the European Spallation Source shows that the loss is 7.0(5) % for wavelengths of 2.3-4.0 {\AA}; the typical operational wavelength range of the instrument. This amount of loss does not call for mitigation by overillumination as suggested in the previous work. Our work serves to quantify the robustness of the transport properties of long neutron guides, in construction or planning at neutron facilities worldwide.