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

B S G

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

B S G

A large, single grain

bulk superconductor

Bulk High Temperature Superconductors

• 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)

B S G

Example field dependence of critical

current density, Jc(B), for bulk YBCO

Bulk High Temperature Superconductors

• 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

B S G

Stack of 2 x GdBCO samples

that achieved 17.6 T at 26 K

Bulk High Temperature Superconductors

• 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

B S G

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

B S G

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

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

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

B S G

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

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 rotating machines

B S G

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

B S G

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

B S G

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

B S G

Bulk Modelling In 3D – Pulsed Field Magnetisation

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

B S G

Bulk Modelling In 3D – Pulsed Field Magnetisation

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

B S G

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

Bulk Modelling In 3D – Pulsed Field Magnetisation

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

B S G

Bulk Modelling In 3D – Pulsed Field Magnetisation

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

B S G

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

Bulk Modelling In 3D – Pulsed Field Magnetisation

• 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)

B S G

Bulk Modelling In 3D – Pulsed Field Magnetisation

• 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

B S G

Bulk Modelling in 3D – Pulsed Field Magnetisation

77 K

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

B S G

Bulk Modelling in 3D – Pulsed Field Magnetisation

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

B S G

Bulk Modelling in 3D – Pulsed Field Magnetisation

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

B S G

Thank you for listening

ご清聴ありがとうございました。

B S G

Contact email: mark.ainslie@eng.cam.ac.uk

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