A quantitative investigation of the effect of a close-fitting superconducting shield on the coil-factor of a solenoid

TL;DR

This paper investigates how superconducting shields can significantly alter the coil-factor in solenoids, affecting precision in cryogenic magnetic experiments, and proposes a solution using high-permeability materials.

Contribution

It demonstrates the impact of superconducting shields on coil-factor accuracy and introduces a method to mitigate this effect with high-permeability inserts.

Findings

Superconducting shields can cause nearly tenfold errors in coil-factor measurements.

The magnetic environment significantly influences coil-factor beyond geometric considerations.

Inserting high-permeability sheets reduces the error caused by superconducting shields.

Abstract

Superconducting shields are commonly used to suppress external magnetic interference. We show, that an error of almost an order of magnitude can occur in the coil-factor in realistic configurations of the solenoid and the shield. The reason is that the coil-factor is determined by not only the geometry of the solenoid, but also the nearby magnetic environment. This has important consequences for many cryogenic experiments involving magnetic fields such as the determination of the parameters of Josephson junctions, as well as other superconducting devices. It is proposed to solve the problem by inserting a thin sheet of high-permeability material, and the result numerically tested.