The effect of geometry on the trapped magnetic field in bulk superconductors

Fukai, Hironobu; Tomita, Masaru; Murakami, Masato; Nagatomo, Takao

doi:10.1088/0953-2048/15/7/311

Cited by 21 publications

(15 citation statements)

References 8 publications

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“…There exist a number of different numerical techniques that have been applied variously to the modelling of superconducting materials [30,46], including the finite difference (FD) method [47], the combined sand-pile/Biot-Savart method [48][49][50][51], the Fourier Transform method [29], minimisation or variational techniques [52][53][54][55][56][57][58] and the finite element method (FEM). In general, FEM techniques are the most commonly used and developed methods, and these can be applied to superconducting material problems using a variety of formulations [30,59,60]: namely the A-V [61][62][63], T-Ω [64][65][66], H [67][68][69][70][71][72][73][74][75][76][77][78] and E [59,[79][80][81] formulations, and Campbell's equation [63,82].…”

Section: Numerical Techniquesmentioning

confidence: 99%

“…Equation ( 3) has been applied variously to bulk superconductors in [97][98][99][100][101][102]. The material-dependent constants can be estimated via the trapped field profile of the bulk (for example, [97]) or by measurements of the magnetic moment hysteresis (m-H) loops of sub-specimens taken from the bulk (for example, [15,103,104]) at different temperatures.…”

Section: Understanding Flux Dynamicsmentioning

confidence: 99%

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Modelling of bulk superconductor magnetization

Ainslie

Fujishiro

2015

Supercond. Sci. Technol.

184

166

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This paper presents a topical review of the current state of the art in modelling the magnetization of bulk superconductors, including both (RE)BCO (where RE = rare earth or Y) and MgB 2 materials. Such modelling is a powerful tool to understand the physical mechanisms of their magnetization, to assist in interpretation of experimental results, and to predict the performance of practical bulk superconductor-based devices, which is particularly important as many superconducting applications head towards the commercialisation stage of their development in the coming years. In addition to the analytical and numerical techniques currently used by researchers for modelling such materials, the commonly used practical techniques to magnetize bulk superconductors are summarised with a particular focus on pulsed field magnetization (PFM), which is promising as a compact, mobile and relatively inexpensive magnetizing technique. A number of numerical models developed to analyse the issues related to PFM and optimise the technique are described in detail, including understanding the dynamics of the magnetic flux penetration and the influence of material inhomogeneities, thermal properties, pulse duration, magnitude and shape, and the shape of the magnetization coil(s). The effect of externally applied magnetic fields in different configurations on the attenuation of the trapped field is also discussed. A number of novel and hybrid bulk superconductor structures are described, including improved thermal conductivity structures and ferromagnet-superconductor structures, which have been designed to overcome some of the issues related to bulk superconductors and their magnetization and enhance the intrinsic properties of bulk superconductors acting as trapped field magnets (TFMs). Finally, the use of hollow bulk cylinders/tubes for shielding is analysed.

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Section: Numerical Techniquesmentioning

confidence: 99%

Section: Understanding Flux Dynamicsmentioning

confidence: 99%

Modelling of bulk superconductor magnetization

Ainslie

Fujishiro

2015

Supercond. Sci. Technol.

184

166

View full text Add to dashboard Cite

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“…. The trapped field saturates as the thickness, H, of the bulk approaches D, which can be deduced from (3) and (4), and is observed for bulk (RE)BCO superconductors [20], as well as bulk MgB 2 [10]. From these results, the geometry of the bulk can be optimised, and as found in [21] for bulk (RE)BCO superconductors, an aspect ratio of between 1 and 1.5 for R/H (radius/thickness) would also be an appropriate compromise between the accessible, surface trapped field and volume of superconducting material for bulk Ba122 magnets.…”

Section: Fixed Thickness Diameter Variationmentioning

confidence: 62%

Numerical modelling of iron-pnictide bulk superconductor magnetization

Ainslie

Yamamoto

Fujishiro

et al. 2017

Supercond. Sci. Technol.

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Iron-based superconductors exhibit a number of properties attractive for applications, including low anisotropy, high upper critical magnetic fields (H c2) in excess of 90 T and intrinsic critical current densities above 1 MA cm −2 (0 T, 4.2 K). It was shown recently that bulk iron-pnictide superconducting magnets capable of trapping over 1 T (5 K) and 0.5 T (20 K) can be fabricated with fine-grain polycrystalline Ba 0.6 K 0.4 Fe 2 As 2 (Ba122). These Ba122 magnets were processed by a scalable, versatile and low-cost method using common industrial ceramic processing techniques. In this paper, a standard numerical modelling technique, based on a 2D axisymmetric finite-element model implementing the H-formulation, is used to investigate the magnetisation properties of such iron-pnictide bulk superconductors. Using the measured J c (B, T) characteristics of a small specimen taken from a bulk Ba122 sample, experimentally measured trapped fields are reproduced well for a single bulk, as well as a stack of bulks. Additionally, the influence of the geometric dimensions (thickness and diameter) on the trapped field is analysed, with a view of fabricating larger samples to increase the magnetic field available from such trapped field magnets. It is shown that, with current state-of-the-art superconducting properties, surface trapped fields >2 T could readily be achieved at 5 K (and >1 T at 20 K) with a sample of diameter 50 mm. Finally, an aspect ratio of between 1 and 1.5 for R/H (radius/thickness) would be an appropriate compromise between the accessible, surface trapped field and volume of superconducting material for bulk Ba122 magnets.

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“…1) generates a field B at any point P in space which can be derived by Biot-Savart law. Simple expressions for B components are derived in [5] or [7]. Bean model [8] is considered, meaning that current flowing in each loop is determined by constant critical current density of the sample, J C .…”

Section: A Sand Pile Modeling Of One Single Grainmentioning

confidence: 99%

“…In a previous work, the force developed by an all superconducting linear motor was derived by averaging magnetic flux density of two trapped flux magnets over the volume of superconducting coils in the armature of the motor [4]. This flux density was calculated by means of sand pile model [5], where persistent currents are assumed to flow in concentric loops parallel to sample edges. Biot-Savart law is then used for straightforward calculation of flux density components in any point in space.…”

Section: Introductionmentioning

confidence: 99%

Validation and Application of Sand Pile Modeling of Multiseeded HTS Bulk Superconductors

Pina

Pereira

Ceballos

et al. 2015

IEEE Trans. Appl. Supercond.

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Sand pile and Bean models have already been applied to describe single grain HTS bulks. An extension to that approach was used to model multiseed bulks, needed for several practical applications as electric motors or flywheels with superconducting bearings. The use of genetic algorithms was then proposed to determine intra-and intergrain current densities, and application to two and three seeds samples using trapped flux experimental measurements was exemplified. However, this model assumed some simplifications, as equal properties in grain boundaries between neighboring grains. In this paper an extension to this methodology is proposed and evaluated by analyzing measurements performed in plans at different distances from surfaces of samples with three seeds. Discussion of its influence on a practical application is also explored.

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The effect of geometry on the trapped magnetic field in bulk superconductors

Cited by 21 publications

References 8 publications

Modelling of bulk superconductor magnetization

Modelling of bulk superconductor magnetization

Numerical modelling of iron-pnictide bulk superconductor magnetization

Validation and Application of Sand Pile Modeling of Multiseeded HTS Bulk Superconductors

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