Magnetic shielding properties of high-temperature superconducting tubes subjected to axial fields

TL;DR

This study experimentally investigates the magnetic shielding properties of high-temperature superconducting tubes under AC axial magnetic fields, analyzing how dimensions, field strength, and frequency affect shielding effectiveness and spatial variation.

Contribution

It provides the first detailed spatial analysis of shielding factors along HTS tubes and explains the frequency dependence using a power law related to flux creep.

Findings

Shielding factor is constant near the tube center.

Shielding factor decreases exponentially near the ends.

Frequency dependence follows a power law due to flux creep.

Abstract

We have experimentally studied the magnetic shielding properties of a cylindrical shell of BiPbSrCaCuO subjected to low frequency AC axial magnetic fields. The magnetic response has been investigated as a function of the dimensions of the tube, the magnitude of the applied field and the frequency. These results are explained quantitatively by employing the method of Brandt (1998 Phys. Rev. B 58 6506) with a Jc(B) law appropriate for a polycrystalline material. Specifically, we observe that the applied field can sweep into the central region either through the thickness of the shield or through the opening ends, the latter mechanism being suppressed for long tubes. For the first time, we systematically detail the spatial variation of the shielding factor (the ratio of the applied field over the internal magnetic field) along the axis of a high-temperature superconducting tube. The shielding factor is shown to be constant in a region around the centre of the tube, and to decrease as an exponential in the vicinity of the ends. This spatial dependence comes from the competition between two mechanisms of field penetration. The frequency dependence of the shielding factor is also discussed and shown to follow a power law arising from the finite creep exponent n.