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Adequacy of Instrumentation
The National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) hosts a suite of 30 neutron beam instruments, of which 17 are neutron scattering instruments operated by NCNR; 11 are imaging, analytical chemistry, and neutron physics instruments operated by the NIST Physical and Materials Measurement Laboratories (MML); and 1 is a test station.1 The nSoft Small-Angle Neutron Scattering (SANS) instrument is operated collaboratively by MML and NCNR.
The team at NCNR has continued to upgrade and enhance the instrument suite in a rolling program, building on their strengths and ensuring that they remain on, or close to, the cutting edge of neutron scattering instrumentation. The work is leveraged with additional funding from National Science Foundation (NSF) and NIST programs, and NCNR has been successful in being responsive to such opportunities. It is essential for continued success at NCNR that this program of upgrades and enhancements is supported as a core part of facility operations to meet their mission to the user community.
The comparison of the performance of the instruments against existing and known future facilities took into account uniqueness, key technical parameters, scientific capability, and quality of measured data.
As an example, the Chromatic Analysis Neutron Diffractometer or Reflector (CANDoR) is a unique instrument in a technical sense that brings scientific capabilities for time-resolved reflectometry over a wide Q range that are beyond what is available elsewhere. The data quality, in terms of both signal to noise and the absolute background level are also world leading. Such measurements are traditionally seen as the domain of time-of-flight instruments, but here the team has brought the benefits of a continuous source to bear and produced a world-leading instrument. In comparison, the two reflectometers planned at the European Spallation Source (ESS) will eventually provide for a wider simultaneous Q range, but will struggle to match the signal-to-noise and low absolute background seen on CANDoR, and furthermore are currently at least 5 years from reliable user operations. The instrumentation proposed for the Spallation Neutron Source (SNS) second target station is even further in the future, but will again struggle to match the low background obtainable at a reactor source.
A second example is provided by the Multi-Axis Crystal Spectrometer (MACS-II), which is world class for a neutron spectrometer in terms of monochromatic cold-neutron flux and energy resolution, and which, combined with the very large solid-angle of its detector and a very low neutron background, gives it world-class capability when compared with counterparts at the Institut Laue-Langevin (ILL) and SNS to map out weak, diffuse excitations characteristic of the quantum and/or frustrated magnetic systems that are of greatest interest now and for the foreseeable future. Performance has been enhanced further to provide unique capabilities in studying dynamic systems through the provision of event capability that may be combined with synchronization of external probes or fields applied to the sample. Instruments planned for ESS to provide similar scientific capability will not be distinctly more highly performing in their early years and are unlikely to be available until 2028 at the earliest. The planned spectrometers at
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1 The current instruments are shown in Appendix A.
the SNS second target station should be world leading in this area, but are currently at least a decade away from operation.
The NCNR has some unique and world-leading instruments that can deliver significant scientific impact. The timelines of new sources suggest that with appropriate levels of continued investment—for example, completion of the detector coverage on CANDoR and the build-out of the Polarized Large Angle Resolution Spectrometer (PoLAR)—and investment in staff to provide support for users wanting to do challenging experiments as with MACS, NCNR can readily maintain a world-leading role in neutron scattering instrumentation for the next decade. It is also important to note that new sources do not reduce the performance of existing instruments elsewhere!
NEUTRON SPIN-ECHO SPECTROMETER
Accomplishments
The NCNR team, working with partners at the University of Delaware, have successfully attracted funding through the National Science Foundation (NSF) Mid-Scale Research Instrumentation (MSRI) program to upgrade the Neutron Spin-Echo Spectrometer (NSE). This upgrade will significantly extend the accessible Fourier times on the instrument, modernize the controls and operations, and provide for training of a new instrument scientist. The plan to work with Forschungzentrum Jülich, a partnership that delivered the current NSE instrument, to deliver this new instrument is a prudent one. The team at the Jülich Centre for Neutron Science is a world leader in constructing this type of instrument, and the new NCNR instrument will take advantage of all of the recent advances that have been made in NSE design in order to extract maximum performance from the National Bureau of Standards Reactor (NBSR) neutron flux.
A strong link to the Small-Angle Neutron Scattering (SANS) instrument team has been developed, and access to SANS measurements is made available to NSE users. This is a key part of the increasing productivity of the NSE program, as it allows measurement of the static structure in order to support the dynamics measurements.
Challenges and Opportunities
The new instrument, combined with the new cold source, will deliver a significant step in performance over the current NSE, which has a successful and growing scientific impact. However, there will still be limitations owing to lower flux compared to reactor-based instruments elsewhere, but a focus on the bioscience areas where the team are world leading will ensure that the upgrade delivers scientifically.
The new instrument presents an opportunity to extend the user base beyond the current users and collaborations. This will involve the challenge of further community building beyond the currently supportable base. The gains in throughput and accessible Fourier time will open the potential for lower sample concentrations and new biological systems for study.
CANDOR
The CANDoR instrument is a multiplexed, “white-beam” neutron reflectometer that makes use of banks of graphite monochromators, closely coupled with detectors, to measure reflectivity curves at multiple wavelengths simultaneously. The design, construction, and commissioning of this complex instrument is impressive and to be commended. It has taken a significant, coordinated effort from across the facility to execute this project.
Accomplishments
The instrument has now been commissioned and entered the user program in 2020. Despite the restrictions owing to the COVID pandemic, the team successfully executed several user proposals and is expecting these results to start to appear in papers soon. The early results are particularly notable in the low background achieved and thus the extension in Q range possible. The team has also demonstrated a noticeably improved signal to noise ratio.
Despite the delayed development and commissioning, which allowed some design changes to enhance performance over the original baseline, the instrument performance has now been demonstrated and represents a significant advance on the state of the art.
Challenges and Opportunities
CANDoR has the capability, when fully fitted out with the complete detector bank, to be a transformative instrument for neutron reflectometry. This opportunity can be realized only by executing a fully resourced plan for finalization of the instrument construction. Completion of the instrument with installation of the remaining detector banks should be prioritized after the 2023 outage.
The capabilities of CANDoR present challenges in data processing and analysis, with the increased rate and complexity of measurements calling for the development of software tools that will empower users of the instrument. The reflectometry team has been very successful, with a strongly collaborative approach thus far. This model has the instrument scientists doing the bulk of data processing and analysis for the users, but this will not be sustainable on CANDoR without investment in staff and software. The expertise in reflectometry software exists at NCNR and should be supported and expanded.
While the most obvious benefit of the CANDoR instrument is the ability to make more measurements in the same amount of time, the opportunity should be taken to expand into new science areas that take advantage of the capabilities beyond increased throughput. Large parametric studies, building a library of biomolecular structures at interfaces (as proposed by Dr. Frank Heinrich),2 and examining interfacial kinetics are all possible areas of interest. In terms of kinetics, if the reflectometry team can take full advantage of the opportunity presented by the Center for High Resolution Neutron Scattering (CHRNS) project on time-resolved measurements, CANDoR is well positioned to deliver a strong return on investment in this area.
VSANS
Accomplishments
The Very Small Angle Neutron Scattering (vSANS) instrument has now been commissioned and has started operations. The user program was unfortunately interrupted by the pandemic and unplanned outage, but the team has worked well to ensure that experiments were still performed and that users obtained data.
Challenges and Opportunities
The closures of the Orphee reactor at the Laboratoire Leon Brillouin (Saclay, France), and the BER II reactor at the Helmholtz Zentrum Berlin (Berlin, Germany) have left the NCNR vSANS as a unique
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2 F. Heinrich, Carnegie Mellon University, 2021, “The Structure of Membrane-Associated Proteins,” presentation to the Panel on Assessment of the Center for Neutron Research, July 21.
instrument worldwide. There remain challenges with the high-resolution detector and the slit collimation system, which have been exacerbated by the unplanned outage. The vSANS capabilities are much sought after in the user community and represent an opportunity to enable experiments that cannot be performed elsewhere.
BT-8/DARTS UPGRADE
Accomplishments
The engineering diffractometer has been significantly upgraded, with a new detector, a new multilayer monochromator, new sample strain equipment, and a new sample positioning assembly. These upgrades combined provide the potential for a 20× gain in count rate for cubic systems and represent a significant advance for this instrument.
Challenges and Opportunities
The instrument is currently operated successfully in a collaborative mode by one instrument scientist, but the increased performance presents a challenge to this model. The potential for increased throughput presents possible challenges in data quantity, and additional scientific staff will be needed if the opportunities presented by these performance gains are to be fully realized. If additional funding could be secured, there is the opportunity to expand the engineering diffraction program and impact, as the industrial connection is very strong for this technique. The team should consider developing and strengthening its connections to university-based engineering research groups with links to industry as a mechanism for increased usage, and potentially as a mechanism for support for additional staffing.
NEUTRON INTERFEROMETRIC MICROSCOPY—FAR FIELD IMAGING
Accomplishments
The imaging team from the Physical Measurement Laboratory (PML) has collaborated with the SANS team from NCNR and successfully obtained internal NIST Innovations in Measurement Science (IMS) funding to develop its concept for far field imaging. Proof of concept measurements have been made, and there is a good collaboration under way with the Materials Measurement Laboratory (MML) on production of microchannel phase gratings.
Challenges and Opportunities
This technique, when used for materials characterization, will generate larger data volumes than the team has been used to dealing with; this challenge needs to be addressed through investment in automated data processing and integrated data analysis if the opportunities of this technique are to be realized. Even with these larger data volumes, there will still be significantly less data than obtained at synchrotron tomography beamlines and there is an opportunity to learn from the X-ray community and the software tools they employ. The team should resist the urge to develop its own software tools from scratch and ensure that it makes use of community efforts in image reconstruction and analysis and maintains its good connection to the neutron and X-ray imaging community.
If the development project is successful, it will provide a unique materials characterization facility when deployed on the NG-7/SANS instrument and open new experimental opportunities for the NCNR user community.
SPINS REPLACEMENT—POLAR
Accomplishments
The NCNR team has collaborated with the University of California, Santa Barbara, to develop a proposal for a Continuous Angle Multiple Energy Analysis (CAMEA)-type secondary spectrometer for the Spin Polarized Inelastic Neutron Spectrometer (SPINS) replacement. This proposal has successfully moved to the second round in the NSF Mid-Scale Research Instrumentation Program (MSRI).
Challenges and Opportunities
The PoLAR proposal would deliver a high-performance cold triple-axis instrument for NCNR that would be competitive with instruments at other facilities and provide a unique tool for U.S. neutron users. There is an opportunity for the team to work with the Paul Scherrer Institute in Switzerland (RITA-2/CAMEA) and European Spallation Source (ESS/BIFROST3) teams on development of the instrument to minimize effort at NCNR. The new instrument will present challenges in data processing and analysis, but there is again an opportunity to learn from similar instruments elsewhere.
D2 COLD SOURCE
The D2 cold source project will replace liquid hydrogen with liquid deuterium as a moderator to produce cold neutrons. It will help to compensate for the reduced neutron flux when the reactor is converted from high enriched uranium (HEU) to low enriched uranium (LEU).
Accomplishments
The D2 cold source project is currently on track and well managed.
Challenges and Opportunities
The project is currently reported to be on schedule, but with some key procurements needing to be executed this year. There needs to be very close monitoring to ensure that the installation can be executed within the planned outage.
The outage presents challenges for the user program, particularly with the unplanned outage limiting access in 2021. The NCNR has been successful in working with other facilities to obtain time for U.S. users during the pandemic and unplanned outage, and these collaborations provide an opportunity to make a more formal plan for user access during the 2023 shutdown.
The opportunity to have enhanced long-wavelength flux for the cold neutron instruments is notable, and with the conversion to LEU now scheduled to occur in 2029 at the earliest, there will be a significant period of operations where the user community will benefit from this flux enhancement.
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3 BIFROST is the name of a high-flux extreme environment spectrometer.
NG-5, NG-6, AND NG-7 GUIDE REPLACEMENTS
Accomplishments
The Neutron Guide (NG) design for replacement of NG-5, NG-6, and NG-7 has been optimized for the instruments currently installed or planned in the future, making use of modern supermirror optics to enhance flux at all instruments using the guides.
Challenges and Opportunities
There will be challenges with the procurement and installation timing for the optics, but careful project management should be able to mitigate this risk. The loss of the free-liquids reflectometer on NG-7 could lead to reduced capabilities at NCNR, but this could present an opportunity to further play to the strengths of the reflectometry team in bio-membranes and magnetism.
TIME-RESOLVED DATA ACQUISITION
Accomplishments
The NCNR team has implemented time stamping of the neutron data (event mode data acquisition) on the Multi-Axis Crystal Spectrometer (MACS), and tour de force experiments by the Broholm group have demonstrated the scientific value of these types of experiments for NCNR and provided a technical testbed for further development. The integration of this complex sample environment equipment with the data acquisition system is a strong example of the focus of NCNR on doing what is needed to deliver the highest quality science from the facility.
Challenges and Opportunities
The NSF-CHRNS project to deliver time-stamped, and hence time-resolved, data acquisition across the neutron scattering instrument suite presents a significant opportunity for new experiments and new science. The use of time-stamped data recording at a continuous source represents technical challenges in
- The design and deployment of a new timing network to put all equipment on the same clock;
- The integration of detector systems and data acquisition systems with the new timing system; and
- Efficient data storage and data processing.
The team at NCNR should be sure to take advantage of advances in these methods at other reactors—for example, at the Australian Nuclear Science and Technology Organisation (ANSTO) and the Institut Laue-Langevin (ILL)—as well as building on their own experience of operating the SANS instruments in event mode, the work done on time-involved small-angle experiments (TISANEs), and the knowledge gained from the MACS experiments. The flexibility designed into the instrument control and data acquisition system in accordance with the National Initiative for Cybersecurity Education (NICE) will benefit these efforts.
When deploying the new systems, care needs to be taken to ensure that implementation of these advanced measurement methods does not compromise the existing capabilities that users depend on.
Finding: There is a critical need for the United States to develop a compelling future vision for powerful neutron facilities, including reactors to maintain competitiveness with Europe and Asia with better resourced and staffed facilities.
Conclusion: The prolonged shutdown of the NCNR reactor, newer facilities, and better staffing abroad may cause leading-edge scientists, both instrument scientists and users, to move to work and do their research at the best facilities, not in the United States.
Finding: Remote use of the instruments by outside users is hampered by NIST firewalls. After the restart of operations during COVID-19, only on-site staff and users could perform experiments, with samples sent to NCNR. This requires more staff to perform the “remote” experiments. Automation of sample environments and experiments are beginning to be realized.
Conclusion: The future staffing needs and systems that allow automation for instruments will increase owing to the likely increase in users wanting to conduct remote experiments. This is especially the case for serving the needs of industry, which is important for enabling NIST’s mission.
RECOMMENDATION: The National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) leadership and staff should continue to work on enhancements to systems and/or staffing to serve remote users and to increase automation to better serve the user community into the future. The team should consider developing and strengthening its connections to university-based engineering research groups with links to industry as a mechanism for increased usage of the engineering diffractometer, and potentially as a mechanism for support for additional staffing.
Finding: NCNR has been successful at recruiting and retaining high-quality staff, and this is one of the key factors in the good productivity and outsized scientific impact. There is a very successful postdoctoral program that is quite diverse and results in a relatively high number of placements into academic positions at the end of the postdoctorate.
Key Conclusion: Excellent in-house staff attracts and enables effective partnerships with excellent external groups and is essential to world-class scientific output. It is critical to continue to maintain a pipeline of such staff (e.g., through Ph.D. and postdoctoral programs) with a broad portfolio of instrumentation capacity and capability.
Key Finding: The long-term impact of 7 years of flat budgets has caused a reduction of NCNR instrument staff by 20 percent, to a level significantly below international standards.
Key Conclusion: The reduction of instrument staff, already low by international standards, is reducing capabilities essential for a world-class user facility and reducing NCNR’s ability to develop and continuously upgrade cutting-edge instruments, necessary for a very old reactor to increase scientific productivity. Improvements in efficiency and technology developments have reached their limits of maximizing the efforts of the current staff over the past 7 years of flat budgets. If this continues, it is likely to even more greatly impact staff morale and the scientific productivity of the facility. More staff is needed in hardware and especially software to realize the potential of time-resolved studies.
KEY RECOMMENDATION: The National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) leadership should work with NIST leadership to ensure the support of NCNR at the level of staffing it needs to continue to develop upgrades and enhancements to instruments to ensure a world-class user facility.
Finding: NCNR hosts a suite of 30 neutron beam instruments, of which 17 are neutron scattering instruments operated by NCNR and 13 are imaging, analytical chemistry, and neutron physics instruments operated by the NIST Physical Measurement and Materials Measurement Laboratories.
Finding: The staff and users at NCNR have continued to upgrade and enhance the instrument suite in a rolling program, building on their strengths and ensuring that they remain on, or close to, the cutting edge of neutron scattering instrumentation. The work is leveraged with additional funding from NSF and NIST programs, and NCNR has been successful in being responsive to such opportunities.
Key Conclusion: The upgrades and continual enhancements to instruments are owing to the outstanding quality of NCNR staff, with time to perform its own research and to collaborate on science with external users. It is essential for continued success at NCNR that the instrument staff can continue to perform its own research, thus attracting and retaining the best staff and users, and that this program of upgrades and enhancements is supported as a core part of facility operations to meet its mission to the user community.
Finding: The D2 cold source project is currently on track and well managed.
Conclusion: The opportunity to have enhanced long-wavelength flux for the cold neutron instruments is notable, and with the conversion to LEU now scheduled to occur in 2029 at the earliest, there will be a significant period of operations where the user community will benefit from this flux enhancement.
Finding: Several instruments at NCNR are unique in the world or will be world class with continuing development, allowing research that can be done nowhere else. These are (1) the Chromatic Analysis Neutron Diffractometer or Reflector (CANDoR) instrument, a multiplexed, “white-beam” neutron reflectometer that makes use of banks of graphite monochromators, closely coupled with detectors, to measure reflectivity curves at multiple wavelengths simultaneously; (2) the Very Small Angle Neutron Scattering (vSANS) instrument; (3) the Neutron Interferometric Microscopy-Far Field Imaging system conceptual design; and (4) the new capability of time-resolved data acquisition at the Multi-Axis Crystal Spectrometer (MACS) enabled by sophisticated complex sample environments.
Key Finding: Upgrades or planned upgrades to several instruments will bring them to par or nearly to par with global counterparts. These are the Neutron Spin Echo Spectrometer (NSE) upgrade and the Polarized Large Angle Resolution Spectrometer (PoLAR) secondary continuous-angle multiple energy analysis spectrometer for the Spin Polarized Inelastic Neutron Spectrometer (SPINS) replacement.
Finding: Planned upgrades to the BT-8 engineering diffractometer and planned replacement of the NG-5, NG-6, and NG-7 beam guides using supermirror optics will represent significant advances.
