Modelling and Performance Analysis of MgB2 and Hybrid Magnetic Shields

Abstract

Superconductors are strategic materials for the fabrication of magnetic shields, and within this class, MgB2 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 MgB2 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.

Soft Magnetic Properties and Electromagnetic Shielding Performance of Fe40Ni40B20 Microfibers

“…The measurement of the magnetic flux density in the center of the two tubular arrangements of MG2 microfibers allowed the evaluation of their static magnetic field shielding efficiency via the evaluation of the shielding factor (SF), defined as the ratio between the applied magnetic field and the measured magnetic flux density (SF = B app /B z ). [43] All the measurements indicate an anisotropic behavior of both the shield arrangements according to the microfibers anisotropic behavior. Indeed, the shielding performances are greater when the microfiber orientations and the applied magnetic field are placed on the same plane/direction.…”

“…The measurement of the magnetic flux density in the center of the two tubular arrangements of MG2 microfibers allowed the evaluation of their static magnetic field shielding efficiency via the evaluation of the shielding factor (SF), defined as the ratio between the applied magnetic field and the measured magnetic flux density ( SF = B app / B z ). [ 43 ]…”

“…The attenuation constant of the composite is 20-25 times larger than that of the matrix and increases slightly with frequency. The value of the attenuation constant 𝛼 can then be used to estimate the absorption contribution to the shielding efficiency (SE A = 8.868𝛼t) for an infinite slab of thickness t. [43] This contribution is usually the dominant one for the total shielding efficiency and is a good measure of the performance of the material for high-frequency attenuation. We find for the FeNiB composite an excellent SE A that ranges 37.5 dB at 2 GHz to 77.9 at 14 GHz when a thickness of 1 cm is considered.…”

Magnetization AC losses in multilayer superconducting round cables with coinciding and opposite lay angles

“…E c is the parameter that defines the sharpness of the transition between the positive and negative critical current densities. The electric field is represented by its module, |E|, and three components E x , E y , E z in the Cartesian coordinate system with unit vectors î, ĵ, k. Equation (3) presented here is a slightly corrected version of the final equation presented in [37], and its correctness was already tested in [38]. This correction removes the operation with single components of the electric field from the highly nonlinear hyperbolic tangent function that may produce local non-collinearity between the vectors ⃗ E and ⃗ J in some rare cases.…”

Measurement of Magnetic Hysteresis Loops of the Ni-5at.%W Alloy Substrate as a Function of Temperature in a Stack of 2G HTS-Coated Conductor Annuli

“…This is the case for low frequency passive magnetic shielding, for which two advantages can be noticed. Due to its ability to channel magnetic flux lines, a ferromagnetic substrate may improve the shielding process itself, similarly to the impact of combining bulk ferromagnetic and superconducting shields [22]- [26]. The second advantage is that a non-zero magnetic shielding persists above T c [27], thereby increasing the reliability of the shield.…”