Abstract
Superconductors are strategic materials for the fabrication of magnetic shields, and within this class, MgB has been proven to be a very promising option. However, a successful approach to produce devices with high shielding ability also requires the availability of suitable simulation tools guiding the optimization process. In this paper, we report on a 3D numerical model based on a vector potential (A)-formulation, exploited to investigate the properties of superconducting (SC) shielding structures with cylindrical symmetry and an aspect ratio of height to diameter approaching one. To this aim, we first explored the viability of this model by solving a benchmark problem and comparing the computation outputs with those obtained with the most used approach based on the H-formulation. This comparison evidenced the full agreement of the computation outcomes as well as the much better performance of the model based on the A-formulation in terms of computation time. Relying on this result, the latter model was exploited to predict the shielding properties of open and single capped MgB tubes with and without the superimposition of a ferromagnetic (FM) shield. This investigation highlighted that the addition of the FM shell is very efficient in increasing the shielding factors of the SC screen when the applied magnetic field is tilted with respect to the shield axis. This effect is already significant at low tilt angles and allows compensating the strong decrease in the shielding ability that affects the short tubular SC screens when the external field is applied out of their axis.
Highlights
Sensitive magnetic measurement systems, such as those employed in biomagnetic imaging or in other radiation/particle detection systems, need efficient magnetic shields to reduce the effects of the external magnetic disturbances [1,2,3,4,5]
Since the aim is to assemble shielding shells that combine the practical requirement of a small size and a high shielding factor, we focused on MgB2 samples with a height/diameter aspect ratio close to unity
The study was carried out by applying the external field parallel and perpendicular to the tube axis, i.e., in the Axial Field (AF) and Transverse Field (TF) orientation, respectively, up to a maximum value μ0 Happ = 1.7 T, at which the superconductor is fully penetrated by the magnetic field
Summary
Sensitive magnetic measurement systems, such as those employed in biomagnetic imaging or in other radiation/particle detection systems, need efficient magnetic shields to reduce the effects of the external magnetic disturbances [1,2,3,4,5]. Promising improvements of the shielding ability have been achieved by superimposing SC and ferromagnetic (FM) materials [18,19,20,21,22,23,24], including the possibility to cloak static (DC) and alternating (AC) magnetic fields in suitably shaped SC/FM heterostructures [25,26,27,28,29,30] In this framework, being able to model the electromagnetic behavior of an SC material as well as to guarantee high shielding factors for magnetic fields of arbitrary direction is a needed and successful approach for the development and optimization of novel screening devices [31]. This approach allows the implementation of the problem by self-developed programs or commercial software packages taking advantages of various formulations already developed
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