A Compact Magnet System for the Tsinghua Tabletop Kibble Balance

TL;DR

This paper presents a compact, easy-to-assemble magnet system for the Tsinghua tabletop Kibble balance, achieving high $Bl$ values and low weight, crucial for precise mass measurements and quantum traceability.

Contribution

The study introduces a novel, streamlined magnet design that simplifies assembly and enhances magnetic uniformity, improving the performance of tabletop Kibble balances.

Findings

High $Bl$ values achieved (400 Tm and 800 Tm)

Magnet system weight reduced to 40 kg

Systematic effects like current effect are minimized

Abstract

Although the so-called magnetic geometrical factor, $Bl$, of a Kibble balance does not appear in the Kibble equations, it offers the precision link between electrical and mechanical quantities and furthers a quasi-quantum traceability path for mass metrology. This feature makes the magnet system, supplying the $Bl$ in Kibble equations, play a core role in Kibble balances. Following the open-hardware idea, we report here on the design, manufacture, assembly, optimization, and finally performance of a compact magnet system for the Tsinghua tabletop Kibble balance. Notably, the magnet system showcased in this study facilitates a straightforward upper levitation of splitting through a streamlined mechanism guide, substantially enhancing the ease of open and close operations. Experimental tests show the realized magnet systems can yield a high $Bl$ value (e.g., 400 Tm for a bifilar coil and 800 Tm for a single coil with a wire gauge of 0.2 mm) meanwhile a low volume/weight (40 kg) thanks to the uniformity improvement of magnetic profiles. Furthermore, important parameters related to systematic effects, such as the current effect, are checked, aiming for a final mass-realization accuracy at the $10^{-8}$ level.