Physical design of cold neutron direct geometry inelastic spectrometer at China Spallation Neutron Source

TL;DR

The paper details the design of CNIS, a cold-neutron spectrometer at CSNS, emphasizing its innovative features for enhanced low-energy excitation measurements and operational flexibility.

Contribution

It introduces a novel instrument design combining optimized flight path, chopper systems, and modular features for improved cold-neutron inelastic scattering capabilities.

Findings

Achieves approximately 1% energy resolution in high-resolution mode.

Features modular design for versatile sample environment integration.

Provides a flexible platform planned for operation in 2029.

Abstract

The Cold-Neutron Inelastic Spectrometer (CNIS) is a direct-geometry, time-of-flight instrument designed for China Spallation Neutron Source (CSNS) and optimized to probe low-energy lattice and magnetic excitations. The instrument integrates a long flight path with bent supermirror guides and an elliptical-focusing geometry to suppress high-energy background while improving cold-neutron delivery to the sample. A flexible multi-disk chopper suite provides pulse shaping, band selection and monochromatization, enabling multi-$E_\textrm{i}$ operation. Modular features, including an interchangeable high-focusing guide insert, radial collimation and a vacuum ``airbox'' for simplified sample-environment integration, enhance signal-to-noise and operational versatility. Through combined flight-path and chopper optimization, CNIS achieves excellent routine-mode energy resolution and can reach approximately $\sim 1\%$ in a dedicated high-resolution configuration. CNIS is planned to commence user operation in 2029, offering a highly flexible platform for cold-neutron inelastic scattering studies.