superior performance. powerful technology.

SuperPower Inc. is a subsidiary of Furukawa Electric Co. Ltd.

2G HTS Coil Technology Development at SuperPower Inc.

Honghai Song, Paul Brownsey, Yifei Zhang, Justin Waterman, Toru Fukushima and Drew HazeltonSuperPower Inc., Schenectady, NY 12304 USA

2JB-01, The Applied Superconductivity ConferencePortland, Oregon October 7-12, 2012

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Outline

• 2G HTS coil development– General conductor / coil mechanical performance – Challenges in epoxied coils– Develop alternative approaches in coil winding and post‐wire‐

production• An example:  high quality 2G HTS pancake coil developments

– Practices, winding, conductor splice, coil joint and testing• Other coil‐related areas

– Layer wound coils, alternative insulation• Conclusions

SuperPower’s wire exhibits robust mechanical properties

• Conductor mechanical properties can be characterized in three dimensions– ab plane along the length– ab plane along the width– Along the c‐axis direction, 

perpendicular to ab plane• Mechanical properties are a function of 

copper thickness and temperature

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Conductor Stress‐Strain at RT, 77K and 4 K with Various Copper Thickness

W.D. Markiewicz et al. IEEE TAS, 22(3), 2012

(RT)40 um60 um

100 um

0

200

400

600

800

1000

1200

0.000 0.002 0.004 0.006 0.008 0.010 0.012

stress (M

Pa)

strain

Copper thickness

40 µm

60 µm

100 µm

Data from NHMFL

(77 K and 4 K)

Robust mechanical properties exhibited in  2G HTS coilsalong the width in ab plane

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• Stress upon DPC coils up to 100 MPa, 77 K

• No observable change in critical current

• Repeat 100 timesW.B. Sampson et al., PAC11, NYC, March 28, 2011

(Brookhaven National Laboratory)

• Mechanical properties in 3D– ab plane along the length 

Azimuthal direction– ab plane along the width  axial 

direction (z axis)– Along the c‐axis direction, 

perpendicular to ab plane radial direction

r axis (c‐axis)

z axis (ab plane)

Robust mechanical properties along c‐axis (compressive)

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Static Compression Test – Effect on Ic

r axis (c‐axis)

z axis (ab plane)

• RT compression, Ic tested at 77 K• No measurable degradation in critical current

Challenge: reported degradation (Ic reduction) in epoxy impregnated 2G HTS coils

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Reported degradation in wet (epoxied) coil weak mechanical properties along c‐axis• Takematsu et al., Physica C 674‐677, 470, 

2010• Yanagisawa et al., Physica C 471, 480, 2011

Adhesion strength along c‐axisrelated to c‐axis peel strength

Some reported solutions 

• Thin wall (~20 μm) cryogenically compatible polyester shrink tube.

• U. Trociewitz et al. APL 99, 202506, 2011• Generation of 24 T at 4.2K with 2G HTS insert, 

impregnated with Paraffin• Matsumoto et al., Physica C 025017, 2012

r axis (c‐axis)

z axis (ab plane)

Addressing the degradation issue in epoxied coils

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C‐axis peel strength & Coil Degradation

Defining Problem

C‐axis peel strengthMeasurement

Characterization& Analysis

Technical Solution(Wire Fabrication)

Technical Solution(Coil Development)

Approach #2: 

Stronger wires, higher c‐axis strength from 2G HTS wire production

Approach #1: 

Develop coil winding techniques to tolerate lower peel strength conductor (focus of this presentation)

Wire Delamination

Coil Degradation

C‐axis peel strength test used at SuperPower to guide conductor performance in coils

• Degradation in some epoxied coils also observed at SuperPower• Phenomenon: Ic drops in thermal cycles from RT to 77 K• Peel strength of 2G HTS tape is a good indicator of conductor performance in 

epoxied coils

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(Y. Zhang et al., Physica C, 473, 41‐47, 2012)

P β

T-peel test

θ

Translation Stage

Angular Jig

SampleP

Fixed peeling angle peel test

• Load vs displacement curves• Peel strength is reliable and sensitive method 

T‐peel test on 2G HTS wire 

Peel strength test setup at SuperPower, 

Good correlation between c‐axis peel strength result and epoxied coil performance

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• Correlation between c‐axis adhesion (peel) strength and coil performance

• 50 cm cut for peel test• All the rest wound into wet wind 

epoxied coil• Ic test in three thermal cycles (three Ic

run in each cycle)

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.020

0 5 10 15 20 25 30 35 40 45 50

Current (A)

Volta

ge (V

)

Dry TC1 Run 1Wet TC1 Run 1Wet TC1 Run 2Wet TC1 Run 3Wet TC2 Run 1Wet TC2 Run 2Wet TC2 Run 3Wet TC3 Run 1Wet TC3 Run 2Wet TC3 Run 3Dry TC1 Run 2

Low peel strength ‐gradual degradation

Higher peel strength ‐ No degradation

Multiple coil fabrication approaches evaluated for winding epoxied coils without degradation

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Epoxy change alone is not a solutionEpoxy

Former Material with less shrinkage ratio 

Release Significant improvement found in coils

Co-windingReduce weight ratio between epoxy/coil, unify epoxy distribution

Insulation Alternative insulations 

• Improved fixturing for winding control

• Mandrel design improvement

• Winding tension control (on‐going)

Winding Tech

Siemens presented their positive results at EUCAS 2011(M. Oomen et al, 2‐LB‐11)

MIT/FBML, NHMFL, BNL

NHMFL, MIT/FBML

Metal strip co‐winding with HTS conductor for high field magnet has been effectively used by many groups• 1995, MIT/Sumitomo, SS co‐winding, 1G HTS Bi2223

– Generation of 24.0 T at 4.2 K and 23.4 T at 27 K with a high‐temperature superconductor coil in a 22.54 T background field 

• APL, 67, 1923, 1995• 2003, NHMFL/OST, co‐wind SS (28 μm), 1G HTS Bi2212

– Development of a 5T HTS Insert Magnet as Part of 25T Class Magnets• IEEE Trans. Appl. Supercond., 13 (2), 1396‐1399, 2003

• 2011, MIT/FBML, co‐wind Cu (0.2 mm with one side polyester) for ReBCO, co‐wind SS (50 um) for Bi‐2223 – A 1.3 GHz LTS/HTS NMR magnet – a progress report

• IEEE Trans. Appl. Supercond., 21 (3), 2092, 2011• 2011, BNL, co‐wind SS or Kapton (25 μm), 2G HTS ReBCO

– High field HTS R&D soldenoid for Muon Collider• IEEE Trans. Appl. Supercond., 21, (3), 1884, 2011

• 2012, NHMFL, plain co‐wind  SS, 2G HTS ReBCO– Superconducting 32 T magnet with ReBCO high field coils, NHMFL

• IEEE Trans. Appl. Supercond., 22 (3), 4300704, 2012

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Pros and cons of SS co‐winding• Pros

– Mechanical reinforcement– Less contained epoxy, improvement w/r to cool‐down– Insulation may become stabilizer during transient/local quench– Increased thermal conductivity, compared to conventional insulation

• Cons– Ramping loss (low ramping rate, HTS larger thermal margin)– Current re‐distribution during quench (may need modeling for large 

magnet)– Impact on current densityPartial epoxy impregnation offers positive results – Side applied, epoxy partially penetrated into turns, 30‐40% of epoxy 

coverage for 4 mm wide wire– Seals the coil, protects it from moisture– Mechanically fixes turn‐turn and layer‐layer

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Key technologies demonstrated in high quality pancake coil development

1. Release layer  decouple coil and former, reduce radial tensile stress2. Metal strip co‐winding coil geometry quality, very flat side wall, which 

impacts magnet design & assembly3. Partial epoxy impregnation  physical quality, no Ic drop after cool‐down4. Winding tension  alignment, reduce tensile stress during cool‐down

In-plane view Side view

DPC development process highlights

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Building former first is recommended.Wind the coil and then cut former is risky.

With internal crossover, winding the first PC, the other half conductor stored on another spool

Double pancake coil, Interleaf layer added.finishing.

Multi‐roller winding system. SS‐cowinding.

In coil splice methodology fully developed

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Typical conductor splice resistance

In coil splice

Typical double pancake coil testing

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0.0E+00

2.0E‐03

4.0E‐03

6.0E‐03

8.0E‐03

1.0E‐02

1.2E‐02

0 10 20 30 40

Volta

ge (V

)

Current (A)

Coil ETE

V 1‐2

V 2‐3

V 3‐4

‐1.5E‐02

‐1.0E‐02

‐5.0E‐03

0.0E+00

5.0E‐03

1.0E‐02

1.5E‐02

2.0E‐02

0 5 10 15 20 25 30 35Volta

ge (V

)

Current (A)

• Test procedure• Slow ramping is recommended

• minimizes induced voltage• Ramp current, dynamic data• Hold current for 10 s, static data• Smaller step during transition, divider =5• cooling, warm‐up (slow)

• Use static data for Ic and n‐value• Two DPC (1‐2, 3‐4)• bridge joint (2‐3)• ETE voltage 

Layer wound coil for high field insert

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• 2G HTS ReBCO is prime candidate for high performance coils required for high magnetic field applications

• Layer wound coil technology being developed

• Layer wound, epoxied coils tend to be less susceptible to degradation on thermal cycling

Alternative insulation systems – promising solutions being evaluated• In‐situ insulation applied to 2G 

HTS tape

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• Test coil, ID=50 mm, G10 former, release layer on former, Stycast 1266 epoxy, 4 thermal cycles, no degradation

• More test coils to be wound

• Test coil, ID=50 mm, G10 former, 124 turns, Stycast 1266 epoxy, 5 thermal cycles, no degradation 

• More test coils to be studied

• Insulation by VPI

Before After

Conclusions

• Coil winding techniques in epoxied coils have been demonstrated that mitigate coil degradation on thermal cycling– An example of a successful DPC coil development

• SS co‐winding, epoxy side application• DPC coil winding• Developed a superconductor bridge joint between coils• Achieve good Ic and n‐value, no degradation found.

– The effectiveness of the partial epoxy side application technique to mitigate degradation of epoxied coils has been demonstrated. 

• Dry wind , Partial wet wind (epoxy on coil edges) , Full epoxy coils (Wet wind, VPI)  under development

• Coil geometries:  Pancake → , Layer wound → , Racetracks  next• Stronger conductor (high peel strength) being researched and developed

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