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: [email protected]
Website: http://www.eng.cam.ac.uk/~mda36/
Top Related