The irony of the magnet system for Kibble balances -- a review

Abstract

The magnet system is an essential component of the Kibble balance, a device that is used to realize the unit of mass. It is the source of the magnetic flux, and its importance is captured in the geometric factor $Bl$. Ironically, the $Bl$ factor cancels out and does not appear in the final Kibble equation. Nevertheless, care must be taken to design and build the magnet system because the cancellation is perfect only if the $Bl$ is the same in both modes: the weighing and velocity mode. This review provides the knowledge necessary to build a magnetic circuit for the Kibble balance. In addition, this article discusses the design considerations, parameter optimizations, practical adjustments to the finished product, and an assessment of systematic uncertainties associated with the magnet system.

arXiv comment69 pages, 20 figures

References in corpus (10)

• Measurement of the Planck constant at the National Institute of Standards and Technology from 2015 to 2017
• Determination of the Planck constant using a watt balance with a superconducting magnet system at the National Institute of Standards and Technology
• Construction, Measurement, Shimming, and Performance of the NIST-4 Magnet System
• A summary of the Planck constant measurements using a watt balance with a superconducting solenoid at NIST
• Preliminary Planck constant measurements via UME oscillating - magnet Kibble balance
• Removal of zero-point drift from AB data and the statistical cost
• Coils and the Electromagnet Used in the Joule Balance at the NIM
• A nonlinearity in permanent-magnet systems used in watt balances
• Magnet system for the Quantum Electro-Mechanical Metrology Suite
• A discussion of $Bl$ conservation on a two dimensional magnetic field plane in watt balances