20 K test of ExoCable epoxy impregnated...

20 K test of ExoCable epoxy impregnated coils

Slowa Solovyov1, Saad Rabbani1, Zachary Mendelson1, Tim Haugan2, Martin Rupich3, Vladimir Kashikhin4 and Paul Farrell1

1Brookhaven Technology Group Inc., Stony Brook, NY2Write Patterson Air Base, Dayton, OH

3American Superconductor Corporation, Ayer, MA4Fermi National Accelerator Facility, Batavia, IL

www.brookhaventech.com

LTSW 2019, Charleston, SC February 11-13 2019 1

Supported by: U.S. DOE Office of Science SBIR Phase I award DE-SC0018737, Phase II award DE-SC0017797

Motivation: we need defect tolerant cable

LTSW 2019, Charleston, SC February 11-13 20192

Across-tape defects

Along-tape defects

Deposition malfunction

Epitaxy failure

Some defects emergeduring coil operation

Courtesy of Anatolii PolyanskiiNHMFL

✓ Avoiding defects in YBCO layers is difficult

✓ Some defects are hidden, get revealed only after coil tests

Solution: electrically coupled cable

2G wire stack BTG exfoliated filament stack

Buffer

Substrate

Sharing current path

Sharing current path


We are solving the following problems:▪ Single-filament magnets proven difficult to protect against burnout

▪ Substrate prevents efficient current sharing

▪ Multifilamentary cable is far more expensive than a single tape

▪ Not compatible with epoxy impregnation

Timeline of the exfoliated YBCO development


2015 2016 2017 2018 2019

10 cm coupons

Phase I HEP Phase II HEP

Phase I HEP Phase I Fusion

EERE AMO BAA: AMSC, BTG, BNL

2 m coupons

2.5 mm laser sliced

1 mm filaments

15 m cable20 K coil tests

Irradiation enhancement Double sided tape

Transposed cableDistributed splices

YBCO on insulator

Signallines

Current leads

Cables

Trapped fieldcoils

Multi-filamentary cable architecture


Copper stabilizerNichrome cladding Solder YBCO

✓ Electrically connected filaments are the key element for a stable cable structure

Test coil manufacturing process


Dry wound Vacuum impregnation, Stycast 1266

Upper current lead

Voltage taps Voltage taps

Cooling collar attached

12 coils, over 100 meters of cable tested

77 K performance after re-flow and impregnation


✓No Ic and n-value degradation after multiple rapid cool-downs to 77 K

✓Solder reflow significantly reduces the winding noise, but reduces Ic by 8%

1 2 3 4 5 6 7 8 9 100

100

200

300

400

500

C5, onel layer, W14

C3, six layers

C3, one layer

C1, one layer

Cri

tica

l cu

rre

nt,

Ic (

A)

Number of cycles, room temperature - 77 K

C2, three layers

0.2

0.4

0.6

0.8

1.0

0 100 200 300 400 5000.0

0.5

1.0

1.5

2.0

10-7

V/m

10-6

V/cm

10-7

V/m

10-6

V/cm

Solder re-flow

Three layer coil I20

Epoxy-impregnation

As-wound

Solder re-flow

Six layer coil I17

Epoxy-impregnation

Vo

ltag

e, V

(m

V)

Applied current, I (A)

As-wound

Cycling RT to 77 K

Winding noise


8

Effect of solder re-flow on the winding noise: FFT of coil signal

✓ Winding noise is most likely originates by collapse of inter-filament current loops

✓ Reliable electrical connection between the filaments is essential in suppressing the winding noise

10-14

10-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

0.01 0.1 110

-1410

-1310

-1210

-1110

-1010

-910

-810

-710

-6As-wound 300 A

200 A100 A

0 A

200 A

100 A

300 A

Aftter filament fusion, 182oC 10 min

0 A

Am

plit

ud

e (

a.u

.)

Frequency, (Hz)

x200

increase

Transient current loops

High field AC loss and field error (winding magnetization)


0 1 2 3 4 5 6 7 8 9 10 11 12 130.0

0.2

0.4

0.6

0.8

2.4 mm BTG cable

4 mm SP tape stack

Loss

at

10

0 H

z, El(W

/m A

cyc

le)

Cable width (mm)

12 mm SP tape

0 20 40 60 80 100 120 1400

20

40

60

80

100

Fused stack

Loss

, (W

/m)

Frequency, Hz

0.59 T

Wraped stack

0.6 Tesla AC loss measurement

✓ AC los and field error is reduced proportionally to the filament width

0 50 100 150 2000.000

0.005

0.010

0.015

0.020

0.025

0.030

C3, six layers

C1, one layer

C2, three layers

No

rmal

ize

d h

yste

resi

s, H/H

max

Coil current, I (A)

Double pancake

12 mm tape

Technology deployment: quadrupole coil for Fermilab


✓ Layer-wound, epoxy impregnated Exocable coil was tested independently in aquadrupole structure by FermiLab

25 K testing-conduction cooled


12” chamber Cryomech compressor Cryomech coldhead

Mounted coilWith scanning Hall probe

Central field hysteresis at 77 and 25 K


0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 200 400 600 800 1000 1200

-40

-20

0

20

Ce

nte

r fi

eld

, 0H

(T) 22 K, C3, 6 layer coil

4 A/s

Relaxation

Fie

ld h

yste

resi

s, 0H

(m

T)

Coil current, Icoil

(A)

77 K 22 K

✓At 22 K field dynamics is defined by relaxation at high currents

✓The coil excited up to 1,300 A, generation 0.7 T in the center

Flux dynamics at 77 and 25 K


0 200 400 600 800 1000 1200 14001.000

1.001

1.002

1.003

1.004

1.005

1.006

50 A (0.02 T)

100 A (0.05 T)

No

rmal

ize

d f

ield

, H(t)/H(0)

(a.u

.)

Time(s)

6 layer coil, 77 K 200 A (0.10 T)

0 1000 2000 3000 4000 5000 60000.0

0.2

0.4

0.6

0.8

1.0

Coil center, 1,000 A (0.5 T)

Decay rate, 300 A

Coil outer edge, 300 A

Coil center, 300 A (0.15 T)

No

rmal

ize

d f

ield

, H(t)/H(0)

(a.u

.)

Time (s)

6 layer coil, 25 K

0

2

4

6

8

10 Field

time

de

rivative H/t/H

(10

-5/s)

77 K 25 K

✓Completely different field settling profile at 77 and 25 K

✓ The field increases at 77 K and decreases at 25 K

Settling time 3 min at 0.1 T

Settling time 2 hrs at 0.1 T

Field settling time for flat cable coils


0 200 400 600 800 1000 1200 140010

2

103

104

One layer

Three layers

Six layers

Fie

ld s

ett

lin

g ti

me

, s(s

)

Coil current, I (A)

25 K

500 1000 1500 2000 25000.8

0.85

0.9

0.95

1 Single layer, 25 K

700 A600 A

400 A

300 A

200 A

100 A

No

rmal

ize

d f

ield

, H(t)/H(0)

(a.u

.)

Time (s)

✓Field settling time strongly depends on current: not just coupling

✓The time does not depends on the cable length: coupling loops are not global

Settling time 1-2 min

Time profile of magnetic field inside and outside the bore


0 100 200 300 400 500 600

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Radial component, innner

Axial component, innner

Radial component, outer

Axial component, outer

No

rma

lize

d m

agn

eti

c fi

eld

, (a

.u.)

Time (s)

Relaxation at 300 A

Magnet axis

✓The central field reduction is probably explained by the flux diffusion through the

winding

Vertical Hall probe scan: field penetration into the winding


0 1 2 3 4-0.3

-0.2

-0.1

0.0

0.1

0.2

Ouside scan, 300 A

0.15 T in center, 25 K

Radial field

Mag

ne

tic

fie

ld, 0H

(T)

Vertical Distance (cm)

Axial field

✓Magnetization is determined by the radial component penetrating the winding

Scan range

10 min intervals

Magnet axis

Coupling and supercurrents in LTS and HTS

LTSW 2019, Charleston, SC February 11-13 201917

Supercurrent loop

Coupling current loop 2G wire stackLTS cable, un-transposed

LTS cable, transposed

Reduced coupling loop size

Supercurrent

Coupling current

Simplified flux penetration model into a coupled cable, highly anisotropic filament


Cross-filament loop (coupling currents)Cross-filament dipole

Persistent current loop (in-plane currents)In-plane dipole (same as in pancakes)

Radial field, Hr

Axial field, Ha

Solenoidal field Hs

In-plane dipoleShields Hr

Subtracts from Hs

Cross-filament dipoleShields Ha shields in the windingAdds to Hs in the bore

Transposition: Twisted 1 mm vs. flat 2.4 mm, 240 A at 25 K


0 200 400 600 800 10000.90

0.95

1.00

1.05

1.10

Twisted cable, 1 mm

No

rma

lize

d m

agn

eti

c fi

eld

(a

.u)

Time(s)

25 K, one layer cable

Flat cable, 2 mm

✓Twisting seem to improve the field stability: more tests needed

Twisted cable coil

Conclusion

▪ Demonstrated operation of epoxy-impregnated multi-filamentary cable in conduction cooled mode

▪ Transposition is non-essential at 77 K: coupling current play a minimal role at 77 K

▪ Generated maximum 0.7 T in conduction cooled regime at 25 K

▪ Winding magnetization at 25 K is not well understood, transposition maybe needed due to possible coupling effects

▪ Testing coils at low temperature is critical

▪ Flux behavior at 77 K and < 30 K seems to be very different!

Acknowledgement

▪ DOE Office of Science, High Energy Physics (Phase I and Phase II awards DE-SC0017797 )

▪ DOE Office of Science, Office of Fusion Sciences (Phase I funding DE-SC0018737,

▪ American Superconductor Corporation

▪ Wright-Patterson Air Force Lab

▪ Fermi National Accelerator Facility

▪ Advanced Energy Center incubator at Stony Brook University

▪ Office of Strategic Partnership for Industrial Resurgence at Stony Brook University


Continuous slicing and cabling: Phase I funded by Fusion Science


Laser head

Cabled filament array

Linear transport

Tape tensioner operation


✓ Tensioner tested

Cabling of solder-coated superconducting filaments


0 20 40 60 80 100 1200.0

0.2

0.4

0.6

0.8

1.0

10 N5 N 2 N Flat3 mm former radius

YBCO down

Pitch 15 mm

Variable tension

Vo

ltag

e, V

(m

V)


✓ Critical bending radius of the solder-coated filaments is too large

Uncoated tape cabling test


0 20 40 60 80 1000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

15 mm

Flat10 mm

Vo

ltag

e, V

(m

V)


13 mm

3 mm former radius

YBCO down configuration

Pitch dependence

Irradiated tape

0 10 20 30 40 50 60 700.0

0.2

0.4

0.6

0.8

1.0Aftre re-flowSix layer coil,

14 meters of cable

Cowound with stabilization

Vo

ltag

e, V

(m

V)


Flat

Cabling pitch dependence Co-wound stabilizer

✓ Co-winding the stabilizer allows reducing the effect of cabling degradation✓ Even narrower filaments are needed

20 K test of ExoCable epoxy impregnated...

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