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NSF: New Neutron Spin Echo Spectrometer on NG-A

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NSF

With the postponed cold source upgrade and while waiting for the returning reactor cycles, we 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, one of NSF’s 10 Big Ideas.  The instrument is essentially a copy of the new J-NSE Phoenix instrument built by JCNS and located at the MLZ in Garching, Germany. The accelerated plan was coordinated with the operating neutron cycles to perform the hot commissioning of the instrument.

The new instrument employs optimally designed superconducting precession coils (OSCPCs), increasing the maximum Fourier time by 2.5x. It enables using shorter wavelengths with significantly higher intensities and increases 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, possibly reaching 700 ns for strongly scattered samples. The extended accessible time scale will expand the opportunities to study various material systems, especially in soft matter.

NG-A
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 passed inspection and site-acceptance tests. These tests aimed to ensure the superconductor coils work correctly at the below-critical temperature of ~9K for the superconducting material – NbTi. Installation of the cryo-compressors and warm zones for both OSCPCs was completed by late June and early July 2023, followed by the success of leak tests by circulating water through the coils. The primary OSCPC sitting on its carriage system is now at the final spot, while the secondary precession coil is still waiting for the newly poured epoxy dancing floor to be 100% cured.

Primary optimized superconducting precession coil (OSCPC) sitting on its stationary carriage
Figure 2. The primary optimized superconducting precession coil (OSCPC) sitting on its stationary carriage is at the final spot. The installation of warm zones for both OSCPCs has been completed. However, the 2nd precession coil still waits for the newly poured epoxy dancing floor (bottom left) to be fully cured. The Pythagoras coil, one of the correction elements of the warm zone inside the OSCPC, is shown in the bottom middle picture. Each superconducting coil is cooled by two large cryocoolers (bottom right), which are ready in place.

Along with OSCPCs, several other critical components were 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 its exchange table, a polarizer and its exchange station, an updated position-sensitive detector (PSD), warm zone components including Pythagoras coils and other correction coils mounted inside 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 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.

Neutron velocity selectors, control panel, correction coil, and polarizer station
Figure 3. The top left picture shows two neutron velocity selectors (NVSs) sitting on a newly fabricated exchange table, and their control panel is bottom left. The old NVS (smaller one) will be reused for short wavelengths, while the new NVS (bigger one) is designed for longer wavelengths. The top right picture is the state-of-art Pythagoras correction coil shown in Fig. 2 when mounted inside OSCPC. The bottom right is an exchangeable polarizer station, which hosts double-V (reused) and single-V cavity (new) polarizers for short and long wavelengths.

The new NSE instrument is on track to finish the installation by early December and will be ready to perform the hot commissioning when the reactor shutter opens.

As part of the educational outreach of the NSE upgrade project, we are planning a 2nd NSE workshop on September 18th-21st, 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, 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 on Twitter.

Created April 8, 2020, Updated August 9, 2023