Technology for High Field Magnets with YBCO Conductors

1
Technology for High Field Magnets with YBCO
Conductors

• Presented by H.W.Weijers
• Collaborators
• U. P. Trociewitz, W. D. Markiewicz, D. C.
  Larbalestier and many others at NHMFL
• SuperPower
• US-Japan workshop, Dec 14, 2009

2
Outline

• General considerations
• Coated conductors, Bi-2223, Bi-2212
• Technology for 32 T
• and beyond
• Summary

3
Definitions

• Je I/(conductor area)
• Jave NI/(winding area)
• JavelJe
• l fill factor

4
Applications of high-field HTS magnets

• Research magnets
• NMR magnets
• Scattering magnets
• HEP
• Dipoles
• Muon cooling
• Very high field hybrids

Multi-kA cable preferred
5
What does it take?

• Current density in windings
• Manageable stress levels

Key enabling parameters
6
What does it take?

• Current density in windings
• Manageable stress levels
• Stability against disturbance
• Protection against quench and other fault
  conditions
• AC-loss/ ramping losses
• Magnetic field quality

Key enabling parameters
7
What does it take?

• Current density in windings
• Manageable stress levels
• Stability against disturbance
• Protection against quench and other fault
  conditions
• AC-loss/ ramping losses
• Magnetic field quality
• Joints, terminals, insulation
• Fabrication technology
• Reliability
• Desirable Flexible architecture (I), wind-as-is

Key enabling parameters
8
What does it take?

• For 4 to 5 cm bore magnets
• 25 T Jave 100 A/mm2, smax 200 MPa
• 30 T Jave 200 A/mm2, smax gt 400 MPa for
  reasonably compact magnet
• Stress goes up significantly for larger diameters

Cross-section of an imaginary 25 T magnet based
on NHMFL 21 T NMR magnet
9
Conductor comparison
Property Comments YBCO Bi-2223 Bi-2212 (wire)
Strength Current density for 25 T for 25 T
Strength Current density for compact 30 T for compact 30 T - /- - -
Piece length /-
Reproducibility batch-batch Ic size/shape transverse resistivity anisotropy 4K, 30 T /- ? ? /- /-
Flexible architecture stabilizer amount strength/reinforcement width/diameter - - /- - /-
AC loss /- ?
All have something (most), none have everything
proven for 30T right now
10
Ready for high field magnets?(modest bore
solenoids)

• 25 T magnets Bi-2223 yes, Bi-2212 close
• 30 T magnets Bi-2223 marginal, 2212 lacking Je
• YBCO best Je and strength
• suitable for 25 and 30 T
• flexible architecture
• Reproducibility/predictability beyond JeTBD
• Fast conductor development is double-edged (not
  magnet pull)
• Lengths available
• Lack of broad experience
• Hopefully coated conductor technology will be
  ready soon

11
32 T Magnet Parameters
Total field 32 T Field inner YBCO coils 17
T Field outer LTS coils 15 T Cold inner bore 32
mm Uniformity 5x10-4 1cm
DSV Current 186 A Inductance 436 H Stored
Energy 7.54 MJ
YBCO
Nb3Sn
NbTi
Tentative pancake winding for inner coil, layer
winding for 2 larger HTS coils
User magnet for NHMFL milliKelvin facilty
12
32 T YBCO Coil Parameters
YBCO coil 1 2 3 Inner radius
(mm) 20 47 77 Outer radius (mm) 42 71 101 Coil
length (mm) 144 240 340 Field increment
(T) 5.7 5.7 5.6 Jave (A/mm2) 225 211 211 Curren
t density copper (A/mm2) 426 426 426 Maximum
stress (MPa) 305 400 435 Conductor length
(km) 0.75 2.4 5.2
The proposal design is intended to be compact and
yet practical in stress and copper content for
protection.
13
YBCO Test Coils
SuperPower I. Bmax 26.8 T ?B 7.8 T
SuperPower II. Bmax 27 T ?B 7 T
NHMFL I. Bmax 33.8 T ?B 2.8 T
NHMFL II. Bmax 20.4 T ?B 0.4 T
During construction
14
YBCO Test Coils and 32 T YBCO Coils

• Maximum field increment in highest background
  field

• Homogeneous stress distribution
• Self-supporting windings
• Special terminals to avoid winding reinforcement
• 1.5 mm thick, 25 mm tall windings
• Standard SP4050
• 30 um Cu plating
• Layer wound, epoxy impregnated
• Instrumented with multiple V-taps, strain gages

NHMFL I.
SuperPower I.
NHMFL II.
32 T YBCO Coils
SuperPower II.
3 built
Images are to scale
15
Results so far

• Very high Jave gt 30 T (gt 460 A/mm2 in test coil)
• Without reaching conductor limits
• Large diameter stress coils
• Have not reached conductor limits at 760 MPa,
  0.6 strain, Jave 300 A/mm2
  at 20 T
• Terminals on thin coils that provide minimal
  reinforcement of windings are difficult
• Compares favorably with benchmark and design Jave
  and s
• Need to account for larger field angle (20º) in
  user magnet
• Repeated (protected) quenches do not affect Je
• Also at self-field
• Magnet technology in relatively early stage

16
32 T YBCO RD topics

• Winding techniques
• New layer winding equipt
• Quench protection
• Amount Cu needed
• Heaters
• Terminals
• Joints (Walsh)
• Insulation
• Varnish, paper, UV-cure epoxy

17
Beyond 32 T YBCO RD topics

• Insulation
• mm-level coatings (oxide, ..)
• Support magnet conductor development
• Reduced anisotropy at low T, high B
• Round wire
• Find limits, towards full potential
• NMR with HTS
• Focus on field quality (not high field yet)
• Multi-kA cables
• Test of cable at 4 K, 20 T

18
Summary

• Breakthrough coated conductor developments in
  last few years
• Stress tolerance and Jave for 30 T demonstrated
  in conductor and coils
• 32 T YBCO project pushing high-field magnet
  technology development
• Development required in many areas
• Broader supporting RD at NHMFL
• Starting research on HTS NMR and multi-kA cables