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Summary
The Precision Electro-Mechanical Experiments (PREME) program develops precision electro-mechanical measurements for fundamental traceability of the SI units and the determination of fundamental constants. By taking full advantage of the intrinsic scaling and multiple realization paths now offered by the new SI, PREME is developing projects for in-situ, fit for purpose direct realization of the SI units based on the defined values of the Planck constant, elementary charge, and the Josephson and von Klitzing constants. PREME has several projects, as discussed below.
Description
NIST-4 Kibble Balance
Previously called ‘the Electronic Kilogram’ Project, a major component of PREME is the realization of SI unit of mass, the kilogram, using the NIST-4 Kibble balance, the fourth generation of Kibble balances at NIST. This is accomplished through a high-accuracy comparison of power as measured in mechanical (force and velocity) and electrical (voltage and resistance) units. Because of the quantum nature of all but the kilogram mass unit (laser length, atomic time, Josephson effect voltage, and Quantum Hall effect resistance), the two measurements provide a high-accuracy determination of a kilogram artifact based on the defined value of the Planck Constant.
In operation since 2015 NIST-4 has provided valuable data for the 2016 pilot study for the future realization of mass in the new SI, a final NIST value of the Planck constant for the CODATA Special adjustment of the fundamental constants for the assignment of the exact values of the defining constants that now form the foundational basis of the new SI, and the first Key Comparison of mass within the new SI.
Contact:
Darine Haddad
darine.haddad@nist.gov
301-975-6552
REFERENCES of Major Accomplishments:
“Report on the CCM key comparison of kilogram realizations CCM.m-k8.2019,” M Stock et al, Metrologia, 57(1A):07030-07030, jan 2020
https://doi.org/10.1088/0026-1394/57/1a/07030.
“Measurement of the Planck constant at the National Institute of Standards and Technology from 2015 to 2017” D. Haddad et al, Metrologia, 54(5):633, 2017
https://doi.org/10.1088/1681-7575/aa7bf2
“A precise instrument to determine the Planck constant, and the future kilogram” D. Haddad et al., Invited article, Review of Scientific Instruments, 87(6), 2016.
https://doi.org/10.1063/1.4953825
“A LEGO Watt balance: An apparatus to determine a mass based on the new SI,” L S Chao et al., American Journal of Physics 83(913) 2015
https://doi.org/10.1119/1.4929898
QEMMS
The Quantum Electro-Mechanical Metrology suite (QEMMs) under development will provide Primary Standard Laboratories quantum voltage, resistance, current, and mass dissemination traceable to the new SI at or below present uncertainties. Using graphene quantum Hall resistance standards (GQHR) developed by NIST that are capable of transport currents of 1 mA and the redefinition of the kilogram allowing primary mass realizations at values other than 1 kg, it is now possible to combine Programmable Josephson Voltage Standards (PJVS) and a GQHR to provide a quantum current source (10 V/12.9kohm = 770 µA) that can be directly injected into a Kibble Balance operating in the range of 10 g to 200 g. The Kibble Balance provides mass dissemination traceable to the Planck constant while the robust quantum voltage, resistance, and current standards can be independently accessed for other electrical metrology needs.
The 100 g Kibble balance has been designed on a single degree of freedom flexure-constrained motion and is in the process of being manufactured.
Contact:
Darine Haddad
darine.haddad@nist.gov
301-975-6552
REFERENCES of Major Accomplishments:
“Magnet system for the Quantum Electro-Mechanical Metrology Suite”, R R Marangoni et al, IEEE Trans. Instrum. Meas., 69(8): 5736 – 5744, 2019
https://doi.org/10.1109/TIM.2019.2959852
KIBB-g2
PREME researchers have successfully demonstrated the first Kibble balance operating in air at the gram level (KIBB-g1) with relative accuracies at a few parts in 106. KIBB -g1 is rated at a Technology Readiness Level (TRL) 6 as a proof of concept, functional prototype as shown in the photograph below [1]. Pushing KIBB-g1 toward commercialization requires collaboration with potential end users as well as balance manufacturers.
Based on the success of KIBB-g1, NIST has entered into an arrangement with the DoD through the NIST on a Chip program to deliver a version of KIBB-g1 (KIBB-g2) that will be robust and fit for deployment to primary metrology labs throughout the armed services. KIBB-g2 will be the first step in streamlining and modernizing mass metrology, replacing legacy infrastructure which is both labor and time intensive, in addition to being inherently vulnerable due to damage during handling and logistical difficulties in shipping physical artifacts. Merging mass and electrical metrology at the primary metrology labs will make the entire chain of traceability to the SI more efficient by providing direct traceability of mass based on in house quantum traceable electrical standards.
Contact:
Leon Chao
leon.chao@nist.gov
301-975-4763
REFERENCES of Major Accomplishments:
“The design and development of a tabletop Kibble balance at NIST,” L. Chao, F. Seifert, D. Haddad, J. Stirling, D. Newell, and S. Schlamminger, IEEE Transactions on Instrumentation and Measurement, 68(6):2176-2182, 2019
https://doi.org/10.1109/TIM.2019.2901550
ENTR
PREME researchers have begun exploring the possibility of directly realizing small torque ranging from 1 mN m to 1 N m using the rotational form of the Kibble principle. This self-calibrating tabletop instrument would utilize a free-spinning electromagnet to generate a torque to directly calibrate torque tools thereby truncating the present convoluted traceability chain to mass and length. A direct realization of torque traceable to the revised SI in terms of electrical quantities would be a first for NIST and hopefully inspires more SI-related twists for new applications.
The DoD has shown interest in becoming early adopters of direct torque realization and has recently collaborated with PREME researchers, laying out the steps for modernizing their existing torque metrology infrastructure and developing a prototype Electronic NIST Torque Realizer (ENTR) with a dynamic range of 1 mN m to 1 N m and relative uncertainties on the order of parts in 103, a target aimed to be competitive with commercial torque transducers. The long term goal is to expand coverage of a wider measurement range with commercial ENTRs. Presently the concept is rated at a Technology Readiness Level (TRL) 2 with encouraging signs of success.
Contact:
Leon Chao
leon.chao@nist.gov
301-975-4763
PhoMo
PREME researchers have made significant progress toward building electro-mechanical devices to measure high laser power through photon momentum transfer (PhoMo). Measuring the power of lasers at nominal power levels above 10 kW is very cumbersome. Conventionally, the measurement is done by absorbing the laser power and capturing the absorber's temperature rise. However, this method has three disadvantages. (1) Large absorbers are needed, (2) the absorbers are not perfect, limiting the reachable uncertainties at the percent level, and (3) the laser beam is no longer available after it has been absorbed, rendering this method unusable for process control.
Researchers at the Sources and Detectors group at NIST Boulder are working on measuring the laser in reflection for high-power laser applications. The laser is reflected on a nearly perfect mirror, and the photon pressure force that acts on the mirror is measured. The PREME team and the Small Mass and Force Project in Gaithersburg working with the group in Boulder has now built a mechanical device to aid the effort. The dedicated weighing cell, shown in the Figure above, is optimized to measure large powers by comparing the laser pressure force to an electrostatic force generated by a capacitor plate. The electrostatic force is directly traceable to the revised SI. All sensitive parts of the instrument are mechanically removed from the laser's line of sight, even behind the mirror, to avoid heating by non-reflected light. The mechanism has been optimized to reduce the measurement uncertainty to the required application.
Contact:
Stephan Schlamminger
stephan.schlamminger@nist.gov
301-975-3609
Big G
The universal constant of gravitation, G –known as “big G” to distinguish it from little g, the acceleration due to Earth’s gravity – is a fundamental constant of nature. It is the parameter that describes the gravitational force of attraction between any two objects in the universe, whether they are planets or people or office supplies. But despite centuries of measurement, the constant is still only known to 5 significant figures, much less than any other fundamental constant of nature. Moreover, the spread of the input data for the determination of G is over 20 times larger than the CODATA-18 stated uncertainty.
To this end NIST has acquired the experimental apparatus of the two most significant outliners in the determination of G – the results from the International Bureau of Weights and measures (BIPM) and JILA, the joint effort between the University of Colorado and NIST. Progress on reconstructing the BIPM experiment has been slow but steady with an expected first results in time for the 2020 CODATA adjustment of the fundamental constants.
Contact:
Stephan Schlamminger
stephan.schlamminger@nist.gov
301-975-3609
REFERENCES of Major Accomplishments:
“Closed form expressions for gravitationalmultipole moments of elementary solids, “J. Stirling and S. Schlamminger, Phys. Rev. D, 100:124053, 2019
https://doi.org/10.1103/PhysRevD.100.124053