MULTI-AXIS CRYSTAL SPECTROMETER
The Multi-Axis Crystal Spectrometer (MACS), which has been operating for 8 years, is currently a world-class instrument for studying magnetic dynamics with high flux and low backgrounds, allowing a sensitivity in detecting small signals that is unmatched anywhere in the world. This instrument is critical in the search for quantum spin liquids, a phase of quantum matter that has long been predicted, but whose existence has never fully been established. Recent experiments on MACS are bringing us closer than ever before to establishing its existence. MACS is also critical for the study of unconventional superconductivity.
Opportunities and Challenges
Planned developments of MACS include lowering the background for better signal-to-noise ratio (e.g., it is critical for weak magnetic signals in the quantum spin liquid) and the development of event-mode neutron detection, which will greatly increase experimental throughput, enable instruments to collect data while the instrument is moving, and provide tools to study time-dependent phenomena.
MACS is losing its leading-edge because of the development of competing capabilities at both spallation-based and reactor-based neutron sources around the world—for example, instruments at the Spallation Neutron Source, Paul Scherrer Institute, and the European Spallation Source (ESS). The putative MACS-II upgrade of MACS is needed to turn MACS into a polychromatic multi-plexed instrument. Importantly, however, funds have not been secured for this project. The existing MACS instrument will continue to be the one of choice for experiments that require a few fixed-energy cuts in reciprocal-space, so a complementary suite of MACS-II, which would reside on the revamped NG4 line after the replacement of the cold-source, and MACS-I, on its dedicated cold-source with highly optimized optics, will leave the NCNR well-placed to tackle the emerging challenges in quantum magnetism.
Neutrons and photons interact with matter differently and, thus, provide complementary information about its structure and properties. While this has been widely understood and exploited to do absorption, emission, and scattering experiments, the advantages of neutron imaging have been far less appreciated than have those of photon imaging. the NCNR is now, and continues to be, a world leader in neutron imaging.
NIST’s Neutron and X-Ray Tomography (NeXT) system has been available to users since June 2016 and has already contributed to advances in the study of novel batteries, concrete degradation, geologic flows, and shale composition. This instrument—the only one of its kind—can simultaneously carry out neutron and X-ray tomography experiments on samples. This instrument makes it possible to do structural, compositional, temporal, and functional experiments on essentially any sample under a variety of environments and operational conditions. Substantial improvements in both the spatial and the temporal resolution of the NeXT instrument are expected to materialize over the next 4 years. Improvements in spatial resolution obtained using the 1.5 micron detector on this instrument have already led to new insights into fuel-cell operation, owing to the neutron’s unequalled sensitivity to water. Later in 2018, this detector will be upgraded with a higher frame-rate camera and other improvements in its optics.
Opportunities and Challenges
Introduction of Wolter optics to the NeXT instrument in coming years will enable improved time and spatial resolution, permitting more detailed exploitation of more complex sample environments. The neutron phase-imaging option on this instrument provides enhanced sensitivity to structural thickness and other structural properties by more than an order of magnitude. New neutron-grating interferometers are under development and will permit even greater sensitivity. Far-field interferometry is a promising tool for a wide variety of materials science problems, but its development faces significant challenges in the near term. New gratings will be required for improved fringe visibility, and a dynamic source grating also has to be developed. New data analysis strategies and software will be needed. All of these require increased funding over what is now available. The NCNR is now seeking internal funding through NIST’s Innovation in Measurement Sciences (IMS) Program for these initiatives, which needs to be given appropriate attention by NIST decision makers.
Opportunities and Challenges
The BT8 beam guide, along with the residual stress diffractometer it feeds and its associated instrumentation, was introduced in the mid-1990s. It is currently undergoing a series of upgrades that will increase its data acquisition rate by a factor of 20 or more. It provides a platform for the noninvasive study of inhomogeneous stresses and strains produced in materials by industrial processes such as stamping of automotive hoods, fastening two metals together, or additive manufacturing. Its strain-measuring devices were built to support the NIST Center for Automotive Lightweighting, an industrial consortium led by the NIST Material Measurement Laboratory (MML). Users of this facility include academic researchers, industrial laboratories, and the U.S. Army.
Software is essential for interpreting data. In many instances, the lack of consensus across the scientific community about how best to analyze particular types of data creates confusion. The NCNR is to be commended for leading efforts to develop consensus by developing software that can analyze scattering data measured at any facility (globally). This software includes the packages SASSIE, SASView, and Refl1D, widely used by the user community, for analyzing small-angle scattering and reflectivity. Reductus, a browser-based online analysis platform for reflectivity data, has been rolled out and looks promising.
Challenges and Opportunities
Software development is absolutely essential for instrument control and data acquisition. The NCNR has a small, but effective, software group of five people, although it is facing a challenge, which is unlikely to disappear anytime soon, in recruiting and retaining talent in this area, because enticing opportunities abound for people skilled in software development. On the controls/data acquisition side, the staged rollout of the NICE software platform continues, and it is now used to control nine instruments, apparently with good user satisfaction overall. This rollout will continue in the upcoming period.
Developments are in progress to improve the analysis of polarized, time-resolved, and two-dimensional (2D) anisotropic data. There is a significant need to develop software that will make it easier to relate real-space structures to scattering measurements in Fourier space and to complement scattering measurements with simulations.
NIST actively seeks outside resources to support software development through joint development projects with other facilities and through direct government funding. Refl1D, the NCNR reflectometry program, was initially developed under the DANSE (Distributed Data Analysis for Neutron Scattering Experiments)1-reflectometry National Science Foundation grant. It is arguably the most complete and versatile package for analyzing specular reflection data, but it has not been embraced globally. The DANSE project also supported the precursor to SasView, and SasView itself is in the process of being transitioned into what is being called the “community collaborative” software project. It currently has European Union funding through 2020 under the SINE2020 (Science and Innovation with Neutrons in Europe in 2020).2 Further development will likely come in the form of programming resources from three main facilities: NCNR, ESS, and the ISIS Neutron and Muon Source.
Very Small Angle Neutron Scattering
The commissioning of the Very Small Angle Neutron Scattering (v-SANS) instrument will markedly improve the capabilities that the NCNR can offer the soft-matter community. This long-awaited, long-in-development instrument will give researchers access to length scales from 1 micron down to 1 nm using a three-detector system, with high flux on the sample. Using either a white beam, a velocity selector, or a graphite monochromator, the wavelength and wavelength resolution can be selected by the user to optimize the beam either for time-resolved studies or for very high spatial resolution.
2 SINE2020 is a consortium of 18 partner institutions from 12 countries, funded by the European Union through the H2020 programme. Further information is available at the SINE2010 website at https://www.sine2020.eu/.
Experiments can be performed either with multi-pinhole focusing optics, which requires large samples, or with a single-pinhole or a slit geometry, in which case the data must, by default, be de-smeared. The versatility and flexibility designed into this instrument will make it suitable for carrying out a wide variety of experiments such as the study of membrane proteins or of micelles for use in drug-delivery systems.
Preliminary data indicate that v-SANS can achieve the ultrahigh resolution it was designed for while at the same time delivering a high-flux beam to the samples. In fact, initial experiments indicate that, for otherwise similar operating conditions, the flux on the sample in the v-SANS instrument is about twice that provided by existing SANS instruments at the NCNR. During the next cycle, the instrument will be made available to users for one-third of the beam time and in the following cycle for two-thirds of the beam time.
Chromatic Analysis Neutron Diffractometer Or Reflector
The Chromatic Analysis Neutron Diffractometer Or Reflector (CANDOR) instrument, scheduled to be fully operational in 2019, has a novel reflectometer design for reactor sources that involves the delivery of multiple streams of neutrons with different wavelengths onto the sample at the same area using an array of monochromators. A single CANDOR detector array consist of 54 highly oriented pyrolytic graphite crystals set at different takeoff angles to diffract neutrons into 6 LiF:ZnS(Ag) proportional counters. Specular reflectivity at multiple scattering vectors can be measured simultaneously, greatly reducing the time of measurement, and opening the possibility of performing time-resolved reflectivity studies or allowing measurement on very small samples, which is particularly important for polarized reflectivity measurements on magnetic systems. The science that will be enabled with CANDOR will include time-resolved interfacial and thin-film behavior of soft matter and polarized reflectivity measurements on very small magnetic multilayer samples.