Bulk superconducting tube subjected to the stray magnetic field of a solenoid

Abstract

Hard type-II hollow superconductors are well suited for low frequency magnetic shielding. The properties and performances of superconducting magnetic shields subjected to homogeneous magnetic fields have been extensively discussed in the literature. In the present work, we investigate the magnetic shielding and the penetration of magnetic flux in a bulk high temperature superconducting tube subjected to the inhomogeneous fringe field of a solenoidal coil. Thanks to a bespoke microdisplacement measurement system, we measure the magnetic field distribution around the tube. We develop a full 3D finite element model based on an H formulation to understand the flux penetration mechanisms and predict the shape of the current loops. Using constitutive law parameters obtained from previous independent experiments, our model is found to be in excellent agreement with the measurements. We discuss how to assess the degree of inhomogeneity of the magnetic field and show that, in our case study, the field can be treated as the magnetic field of an equivalent magnetic dipole. We also show that some features of the flux penetration in inhomogeneous field can be also observed when the tube is subjected to an oblique homogeneous magnetic field, which offers a better understanding of the shielding current density distribution inside the shield. Finally, we discuss the magnetic field concentration occurring around the shield for different magnetic field configurations. In particular, we show that the extremities of the tube on the side not facing the magnetic field source experience the highest flux concentration.

Magnetic shielding of various geometries of bulk semi-closed superconducting cylinders subjected to axial and transverse fields

“…This will be done by investigating numerically the magnetic shielding properties of various assemblies of bulk superconductors, all of them having an axisymmetric geometry. In a real case, the direction of the magnetic field to be shielded is inhomogeneous and could be applied at any angle [36], justifying the need to consider the shielding properties of the investigated structures when they are subjected to both an axial field and a transverse field. In the latter case, symmetry is lost and 3D modelling of the electromagnetic properties [37][38][39][40][41] needs to be used.…”

Fast time-varying current triggering flux jumps of multi-filamentary Nb3Sn wire exposed to oblique magnetic field

“…It is worth nothing that oblique magnetic field has two direct consequences. Firstly, the shielding currents are usually affected by the axial and transverse components of the magnetic field, producing very different responses [17]. Secondly, the complex current distribution leads to a loss of symmetry in the study problem [18].…”

Improvement of the homogeneity of magnetic field by the attenuation of a selected component with an open superconducting shield made of commercial tapes

“…Bulk superconductors are capable of full shielding below a penetration magnetic eld 8 . Hogan et al analyzed the behavior of bulks in an inhomogeneous fringe magnetic eld 9 . Notably, no homogenization of magnetic eld was observed.…”