Magnet system for the Quantum Electro-Mechanical Metrology Suite

TL;DR

This paper details the design and analysis of a magnet system for the Quantum Electro-Mechanical Metrology Suite (QEMMS), enabling precise mass measurements with low uncertainty at NIST.

Contribution

It introduces a novel magnet system design for QEMMS, adapting the NIST-4 magnet with improvements for a smaller Kibble balance and practical installation considerations.

Findings

Analytical models accurately predict coil-current effects and forces.

Finite element analysis and measurements validate the models.

Design improvements enable precise, low-uncertainty mass measurements.

Abstract

The design of the permanent magnet system for the new Quantum Electro-Mechanical Metrology Suite (QEMMS) is described. The QEMMS, developed at the National Institute of Standards and Technology (NIST), consists of a Kibble balance, a programmable Josephson voltage standard, and a quantum Hall resistance standard. It will be used to measure masses up to $100\,\mathrm{g}$ with relative uncertainties below $2\times 10^{-8}$. The magnet system is based on the design of the NIST-4 magnet system with significant changes to adopt to a smaller Kibble balance and to overcome known practical limitations. Analytical models are provided to describe the coil-current effect and model the forces required to split the magnet in two parts to install the coil. Both models are compared to simulation results obtained with finite element analysis and measurement results. Other aspects, such as the coil design and flatness of $Bl$ profile are considered.