Monel Contribution to AC Losses in MgB<sub>2</sub> Wires in Frequencies Up To 18 kHz

Nikulshin, Yasha; Wolfus, Shuki; Friedman, A.; Ginodman, V.; Grasso, G.; Tropeano, M.; Bovone, Gianmarco; Vignolo, M.; Yeshurun, Y.

doi:10.1109/tasc.2018.2841926

Cited by 9 publications

(11 citation statements)

References 27 publications

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“…First, the wire is in a self-field state, carrying either AC current or DC with superimposed AC currents. The AC current of 8 A rms was chosen to be within the range used in previous experiments [13,14], while convenient and sufficient for modelling yet far from the critical current. This case is representative of cables and current leads in general use.…”

Section: Model Detailsmentioning

confidence: 99%

“…The DC bias current used in both cases is either zero or 40 A. It was experimentally proven [13] that this current is enough to saturate the Monel and reduce dramatically the effects related to the magnetic properties of the Monel.…”

Section: Model Detailsmentioning

confidence: 99%

“…In this section we analyze the AC losses in the common case where AC current is superimposed on DC current. Specifically, we select here 40 A DC and 8 A rms AC currents, to match the values in our previous experimental studies [13,14]. For this relatively low DC bias value the current flows in the outer filament layer without fully penetrating the filaments.…”

Section: Biasmentioning

confidence: 99%

“…The simulations show clearly that the total AC losses depend strongly on the magnetic properties of the wire matrix and sheath. In particular, the eddy currents in the Monel matrix are enhanced [13,14], and its high permeability changes the magnetic field penetration pattern inside the superconducting filaments, contributing to additional hysteresis loss in the superconducting material itself.…”

Section: Introductionmentioning

confidence: 99%

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Effect of magnetic sheath on filament AC losses and current distribution in MgB₂ superconducting wires: numerical analysis

Nikulshin¹,

Yeshurun²,

Wolfus³

2019

Supercond. Sci. Technol.

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Finite element method (FEM) analysis is employed to study and compare AC losses in a wide frequency range in two MgB 2 superconducting wires in self-field and in the presence of external AC field. The modelled wires, of the same external dimensions, are mono-and 36-superconducting filaments embedded in either magnetic Monel or a nonmagnetic metallic wire sheath. We demonstrate that in a multifilamentary wire in self-field the Monel sheath serves as a 'pole piece' at the filament outer surface and alters local magnetic fields, current flow and AC losses distribution within the filament. In comparison with the nonmagnetic sheath with the same electrical conductivity, AC current in the wire with the magnetic sheath penetrates significantly deeper into the filaments and AC losses in the filament and in the magnetic sheath increase significantly. In contrast, the symmetry of the monofilament wire makes the current and loss distributions in the filament practically indifferent to the sheath composition. Still, losses in the magnetic sheath are much higher than in the nonmagnetic sheath due to increased flux dynamics. The application of DC current, on which the AC current is superimposed, sharply reduces the AC losses in the magnetic sheath material due to the drop in its permeability. Filament losses are also reduced in the presence of DC current, but to a much lesser extent. Results also show that in the kHz frequency range, the magnetic permeability of the sheath increases the skin effect in both the wire and filaments complex. As a result, at such frequencies, a significant portion of the current is carried by the metallic part of the wire instead of the superconductor, contributing to a further increase in losses. The analysis also shows that in the presence of external AC magnetic field, the Monel can provide magnetic shielding for inner filaments, thus reducing coupling effects between filaments. However, if magnetically saturated by the DC current, the Monel behaves quite similarly to a nonmagnetic sheath.

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Section: Model Detailsmentioning

confidence: 99%

Section: Model Detailsmentioning

confidence: 99%

Section: Biasmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effect of magnetic sheath on filament AC losses and current distribution in MgB₂ superconducting wires: numerical analysis

Nikulshin¹,

Yeshurun²,

Wolfus³

2019

Supercond. Sci. Technol.

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“…The aforementioned problems have been somehow ignored, partly due to the engineering prospects of reducing the AC losses in multifilamentary superconductors by the magnetic screening effect of the SFM coatings. Another problem that is still to be solved [ 19 , 54 , 55 , 56 , 57 , 58 , 59 ] is due to the intrinsic difficulty added by the uncertainty on the physical mechanism that couples the electromagnetic properties of SCs and SFMs at a local level (i.e., inside both materials but within a macroscopical approach). Even in the most ideal of the cases, a perfectly cylindrical type-II SC wire of infinite length obeying the general CST [ 45 ], that is, a case in which a fully analytic solution for the time dynamics of the flux-front profiles exists [ 60 ], it is apparently impossible to determine the cause of the increment in the AC-losses for an SC embedded within a closed SFM sheath.…”

Section: Introductionmentioning

confidence: 99%

Critical State Theory for the Magnetic Coupling between Soft Ferromagnetic Materials and Type-II Superconductors

Fareed

2021

Materials

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Improving our understanding of the physical coupling between type-II superconductors (SC) and soft ferromagnetic materials (SFM) is the root for progressing to the application of SC-SFM metastructures in scenarios such as magnetic cloaking, magnetic shielding, and power transmission systems. However, in the latter, some intriguing and yet unexplained phenomena occurred, such as a noticeable rise in the SC energy losses, and a local but not isotropic deformation of its magnetic flux density. These phenomena, which are in apparent contradiction with the most fundamental theory of electromagnetism for superconductivity, that is, the critical state theory (CST), have remained unexplained for about 20 years, given the acceptance of the controversial and yet paradigmatic existence of the so-called overcritical current densities. Therefore, aiming to resolve these long-standing problems, we extended the CST by incorporating a semi-analytical model for cylindrical monocore SC-SFM heterostructures, setting the standards for its validation with a variational approach of multipole functionals for the magnetic coupling between Sc and SFM materials. It is accompanied by a comprehensive numerical study for SFM sheaths of arbitrary dimensions and magnetic relative permeabilities μr, ranging from μr=5 (NiZn ferrites) to μr = 350,000 (pure Iron), showing how the AC-losses of the SC-SFM metastructure radically changes as a function of the SC and the SFM radius for μr≥100. Our numerical technique and simulations also revealed a good qualitative agreement with the magneto optical imaging observations that were questioning the CST validness, proving therefore that the reported phenomena for self-field SC-SFM heterostructures can be understood without including the ansatz of overcritical currents.

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Maximum reduction of energy losses in multicore MgB2 wires by metastructured soft-ferromagnetic coatings

Kapolka

2022

Sci Rep

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When compared with rare-earth coated conductors, magnesium diboride superconducting cables are known to show significant advantages by cost and easy production. However, the inherent difficulty for achieving a significant reduction of their magnetization losses in multifilamentary wires, without degrading the high critical current density that is so characteristic of the monowire, is considered as one of the major drawbacks for their practical use in high power density applications. Being this one of the major markets for superconducting cables, from fundamental principles and computational optimization techniques, in this paper we demonstrate how the embedding of the superconducting filaments into soft-ferromagnetic metastructures can render to their full magnetic decoupling, and therefore, to the maximum reduction of the energy losses that can be achieved without deteriorate the critical current density of the cable. The designed multifilamentary metastructure is made of NbTi coated MgB2 superconducting filaments in a Cu-matrix, serving as a reference for validating our model with actual experimental measurements in monowires and multifilamentary wires. The novelty in our computationally aided multifilamentary wires, is that each one of the filaments is embedded within a thin metastructure made of a soft-ferromagnetic layer and a resistive layer. We have found that for soft-ferromagnetic layers with magnetic permeabilities in the range of $$\mu _{r}=$$ μ r = 20–100, nearly a full magnetic decoupling between the superconducting filaments can be achieved, leading to efficiencies higher than $$92\%$$ 92 % , and an overall reduction of the AC-losses (including eddy currents at the Cu-matrix) higher than $$50\%$$ 50 % .

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Monel Contribution to AC Losses in MgB₂ Wires in Frequencies Up To 18 kHz

Cited by 9 publications

References 27 publications

Effect of magnetic sheath on filament AC losses and current distribution in MgB₂ superconducting wires: numerical analysis

Effect of magnetic sheath on filament AC losses and current distribution in MgB₂ superconducting wires: numerical analysis

Critical State Theory for the Magnetic Coupling between Soft Ferromagnetic Materials and Type-II Superconductors

Maximum reduction of energy losses in multicore MgB2 wires by metastructured soft-ferromagnetic coatings

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Monel Contribution to AC Losses in MgB2 Wires in Frequencies Up To 18 kHz

Cited by 9 publications

References 27 publications

Effect of magnetic sheath on filament AC losses and current distribution in MgB2 superconducting wires: numerical analysis

Effect of magnetic sheath on filament AC losses and current distribution in MgB2 superconducting wires: numerical analysis

Critical State Theory for the Magnetic Coupling between Soft Ferromagnetic Materials and Type-II Superconductors

Maximum reduction of energy losses in multicore MgB2 wires by metastructured soft-ferromagnetic coatings

Contact Info

Product

Resources

About

Monel Contribution to AC Losses in MgB₂ Wires in Frequencies Up To 18 kHz

Effect of magnetic sheath on filament AC losses and current distribution in MgB₂ superconducting wires: numerical analysis

Effect of magnetic sheath on filament AC losses and current distribution in MgB₂ superconducting wires: numerical analysis