Development and extension of a monochromatic neutron beamline for neutron polarimetry device characterization at the Spallation Neutron Source

TL;DR

This work addresses the need for well-characterized polarized neutron beams to test and validate polarimetry devices. It describes the design, extension, and commissioning of an 8.9 Å monochromatic beamline at the SNS, including a flight tube, shielding, and diagnostics, and demonstrates a proof-of-concept polarimetry suite using a supermirror polarizer, Mezei spin flipper, and in situ $^{3}$He spin analyzer. Key results include a flipping efficiency of $0.93$, an in situ analyzing power of $P_n^{3He}=0.70$, and a beam polarization of $P_n=0.83 \pm 0.07$, confirming strong spin contrast and stable operation. The extended beamline serves as a practical testbed for polarimetry technologies, with significance for polarized neutron EDM searches and other fundamental neutron physics and materials research.

Abstract

The precise manipulation and analysis of neutron spin states are foundational for a wide range of physics experiments, from fundamental symmetry tests to materials science. To enable systematic characterization of neutron polarimetry devices, we have constructed and extended a monochromatic neutron beamline at the Spallation Neutron Source, Oak Ridge National Laboratory. The beamline delivers monochromatic neutrons and provides a flexible platform for deploying and evaluating advanced neutron spin manipulation instruments. We describe the design and commissioning of the extended beamline and present a proof-of-concept neutron polarimetry study using three devices: a supermirror neutron polarizer, a Mezei spin flipper, and an in situ neutron 3He spin analyzer system. Performance metrics, optimization strategies, and systematic effects are discussed, demonstrating the beamline utility for neutron instrumentation testing. These results establish the extended monochromatic beamline as a useful resource for the development and validation of neutron polarimetry technologies.

Figures (2)

• Figure 1: Spectrum from the SNS monochromatic neutron beamline measured as a function of neutron wavelength.
• Figure 2: 8.9 Å neutron count rate while sweeping the flipper coil current for the guide field cancellation coil current of -17.5 A.