NSF: New Spin-echo Spectrometer on NG-A

With the postponed cold source upgrade and while waiting for the returning reactor cycles, we have accelerated the installation plan for the new NSE spectrometer on NG-A. This instrument is being developed in collaboration with the University of Delaware’s Center for Neutron Science, led by Prof. Norm Wagner.  It is funded by the Mid-scale Research Infrastructure program (NSF DMR-1935956), one of NSF’s 10 Big Ideas.  The instrument will essentially be a copy of the new J-NSE Phoenix instrument built by JCNS and located at the MLZ in Garching, Germany. The accelerated plan is coordinated with the operating neutron cycles to commission the instrument before the cold source upgrade begins.

The new instrument will employ optimally designed superconducting precession coils (OSCPCs), increasing the maximum Fourier time by 2.5x.  This is expected to increase the data acquisition rate by roughly an order of magnitude for a given time window.  Combining the new design with the increased flux provided by the upcoming cold source and several instrument elements optimized for long wavelength operation, we expect to achieve a Fourier time of 300 ns routinely. Because of the improved long wavelength performance, which should provide the same flux at 20 Å as we now have at 17 Å, we hope to reach 700 ns for strongly scattering samples.

Figure 1. a) The old NSE capable time and space domain is presented in orange, while the extended area shown in blue results from the upgrade project, with a possibility of reaching further to the dashed area for strongly scattered samples. b) The 2x flux gain by D2 cold source at longer wavelengths, λ > 7 Å, and the optimally designed superconducting precession coils increase the Fourier time corresponding to each routinely used wavelength.

The OSCPC twin arrived at NCNR in early Nov 2022 and has successfully passed inspection and site-acceptance tests. The ultimate goal of these tests was to ensure the superconductor coils work correctly at the below-critical temperature of the superconducting material – Nb₃Sn.

Figure 2. The optimized superconducting precession coils (OSCPCs) under a three-week cooling process with a target cryogenic temperature of ~4K. Each superconducting coil is cooled by two large cryocoolers.

Along with OSCPCs, several other critical components have also been fabricated by our local NCNR engineers or partner manufacturers, passed factory and site-acceptance tests, and delivered to NCNR. These components include a neutron velocity selector (NVS) and an exchange table, a polarizer and an exchange station, an updated position-sensitive detector (PSD), warm zone components including Pythagoras coils and other correction coils going into OSCPCs, new support structures, and an updated power supply system. While the new NVS and single-V cavity polarizer are designed to work effectively with long neutron wavelengths, the old NVS and double-V cavity polarizer will be reused for the shorter neutron wavelength applications. The new ³He PSD consists of an array of tube detectors with improved maximum count rate and sensitivity over long neutron wavelengths.

Figure 3. The left pictures are fabricated air pad-assisted carriage systems, which are bigger than the old ones to accommodate the new, bigger superconducting coils. The middle images show two neutron velocity selectors (NVSs) sitting on a newly fabricated exchange table and their control panel in the CAD design. The old NVS (smaller one) will be reused for short wavelengths, while the new NVS (bigger one) is designed for use at longer wavelengths. On the right, is an exchangeable polarizer station, which will host double-V (reused) and single-V cavity (new) polarizers for short and long wavelengths, respectively.

The new NSE instrument should be installed and ready for testing by the end of August.

As part of the educational outreach of the NSE upgrade project, we are planning a 2^nd NSE workshop on September 18^th-21^st, 2023. The fundamentals of NSE spectroscopy applied to soft matter and biology will prepare the scientists to use NSE techniques. The basics of static and quasi-elastic neutron scattering, NSE instrumentation, and NSE experimental design and data analysis will be covered.

Further information and updates on the project’s progress and the upcoming workshop can be found on the Center for Neutron Science website and social media Twitter.