Modelling and comparison of trapped fields in (RE)BCO bulk superconductors for activation using...

Modelling and comparison of trapped fields in

(RE)BCO bulk superconductors for activation

using pulsed field magnetisation

1Department of Engineering, University of Cambridge2Department of Materials Science & Engineering, Iwate University

Mark Ainslie1, H. Fujishiro2, T. Ujiie2, J. Zou1, A.R. Dennis1, Y-H. Shi1,

D.A. Cardwell1

2015 Joint UK-Japan Workshop on Physics and Applications of Superconductivity

13 April 2015

Presentation Outline

• Bulk high-temperature superconducting materials

• Properties & applications

• Practical magnetization techniques & pulsed field magnetization

(PFM)

• Experimental PFM of Y-Ba-Cu-O, Gd-Ba-Cu-O samples at 40 & 65 K

• Numerical simulation using 3D FEM

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Bulk High Temperature Superconductors

• Conventional magnets (NdFeB, SmCo) limited by material properties

• Magnetisation independent of sample volume

• Bulk HTS trap magnetic flux via macroscopic electrical currents

• Magnetisation increases with sample volume

• Trapped field given by

Btrap = A µ0 Jc d

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A large, single grain

bulk superconductor


• Btrap = A µ0 Jc d

• Candidate materials must be able to:

• Pin magnetic flux effectively

• Carry large current density, Jc, over large length scales

• Be insensitive to application of large magnetic fields, Jc(B)

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Example field dependence of critical

current density, Jc(B), for bulk YBCO


• Demonstrated trapped fields over 17 T

• 17.24 T at 29 K

2 x 26.5 mm YBCO

Tomita, Murakami Nature 2003

• 17.6 T at 26 K

2 x 25 mm GdBCO

Durrell, Dennis, Jaroszynski,

Ainslie et al. Supercond. Sci.

Technol. 2014

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Stack of 2 x GdBCO samples

that achieved 17.6 T at 26 K


• Significant potential at 77 K

• Jc = up to 5 x 104 A/cm2 at 1 T

• Btrap up to 1 ~ 1.5 T for YBCO

• Btrap > 2 T for (RE)-BCO

• Record trapped field =

3 T at 77 K

• 1 x 65 mm GdBCO

• Nariki, Sakai, Murakami Supercond.

Sci. Technol. 2005

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Typical trapped field profile of

GdBCO at 77 K

Bulk HTS Applications

• Can be utilised in three ways:

• Flux trapping (trapped field magnet)

• Flux shielding

• Flux pinning

• Leading to applications in:

• Magnetic separation

• Magnetic levitation

• Flywheels & bearings

• Trapped flux-type electric machines

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(top) Yokoyama et al. IEEE Trans. Appl. Supercond. 13 (2003) 1592-5

(bottom) Oka et al. Supercond. Sci. Technol. 18 (2005) S72-S76




• Flux shielding

• Flux pinning






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• Flux shielding

• Flux pinning









• Flux shielding

• Flux pinning





• Trapped flux-type rotating machines

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Axial gap, trapped-flux motor

Magnetization of Bulk HTS

• Three magnetisationtechniques:

• Field Cooling (FC)

• Zero Field Cooling (ZFC)

• Pulse Field Magnetisation(PFM)

• To trap Btrap, need at least Btrapor higher

• FC and ZFC require large magnetising coils

• Impractical for applications/devices

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ZFC FC

Pulse Field Magnetization

• Achieving in-situ magnetisation is crucial for trapped-flux-type rotating machines

• PFM technique = compact, mobile, relatively inexpensive

• Issues = Btrap [PFM] < Btrap [FC], [ZFC]

• Temperature rise ΔT due to rapid movement of magnetic flux

• Record PFM trapped field = 5.2 T at 29 K (45 mm diameter Gd-BCO) [Fujishiro et al. Physica C 2006]

• Many considerations:

• Pulse magnitude, pulse duration, temperature, number of pulses, shape of magnetising coil(s)

• Dynamics of magnetic flux during PFM process

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Bulk Modelling in 3D – Pulsed Field Magnetisation

YBCO

d = 32 mm

t = 15 mm

Btrap = 0.692 T

GdBCO

d = 41 mm

t = 16 mm

Btrap = 1.19 T

Ainslie et al. Supercond. Sci. Technol. 27 (2014) 065008

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Bulk Modelling In 3D – Pulsed Field Magnetisation


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Key findings:

• GdBCO has more homogeneous Jc

distribution than YBCO

• GdBCO has higher Jc overall,

leading to higher trapped field,but

also higher ‘full activation’ field



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Key findings:

• Lower operating temperature =

stronger pinning/higher Jc

• BUT Trapped field not significantly

higher more heating, reduced

specific heat

• Higher ‘full activation’ field

• Observed flux dynamics similar


• Finite Element Method (FEM)

using commercial software

Comsol Multiphysics

• Governing equations:

• Maxwell’s equations (H

formulation)

• PFM needs to include thermal

equations

• Jc(B,T)

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• Finite Element Method (FEM)

using commercial software

Comsol Multiphysics

• Governing equations:

• Maxwell’s equations (H

formulation)

• PFM needs to include thermal

equations

• Jc(B, T)

• E-J power law, E α Jn, n = 21

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77 K


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Thank you for listening

ご清聴ありがとうございました。

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Contact email: [email protected]

Website: http://www.eng.cam.ac.uk/~mda36/

mailto:[email protected]

http://www.eng.cam.ac.uk/~mda36/

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