Axial and transverse stress–strain characterization of the EU dipole high

Jc RRP Nb3Sn strand

A. Nijhuis, Y. Ilyin, W. Abbas, H.J.G. Krooshoop, W.A.J. Wessel, Y. Miyoshi, L. Feng, E.P.A. van Lanen

Geneva, 20 May 2008

IntroductionIntroduction

Strain sensitivity Nb3Sn strands / ITER CICC application:evaluate sensitivity various applied strandscabled conductor design (limiting peak strains).

CICC: axial strain, periodic transverse bending strain and periodic contact stress, axial and transverse stiffness.

Besides pacman disc spring for axial Ic() measurements, we used the TARSIS test set-up with probes for bending, contact stress and stiffness (axial & transverse).

We concentrate on results of high Jc OST RRP type of strand (EU Dipole strand, EUDIPO) and make a few comparisons with ITER type strands.

Relation cabling pattern and performance degradation in CICC.

IIc (c (VIVI) and strand deformation in ) and strand deformation in TARSISTARSIS

TARSIS test set-up with probes for bending, contact stress and stiffness (axial & transverse).

Bending between contact points, various wavelengths.

Reduced Ic vs force for SMI strand for 3 wavelengths.

LMI

0

0.2

0.4

0.6

0.8

1

0 2,000 4,000 6,000 8,000 10,000 12,000

load per meter [N/m]

I c/I

c0 [-

]

Lw=5.01 mm

Lw=7.15 mm

Lw=10.01 mm

Crossing strands for contact stress characterisation.

Ic vs stress for crossing strands, 11 T and 12 T for EM-LMI strand.

Strand tensile stress-strain tests at various temperatures (participation in VAMAS).

Stress-strain curve for EM-LMI (TFMC) strand

HITX-strand

Lw=4.7 mm

0

0.2

0.4

0.6

0.8

1

0 50 100 150 200 250 300

stress [MPa]

I c/I c

0 [-

]

contour

F-release

OST RRP Nb3Sn Dipole strandOST RRP Nb3Sn Dipole strand

Jc>2060 A/mm2Ternary Nb + Nb-47Ti = 0.81 mmCu:nonCu= 191 x 84 stack designbillet number 8712

Courtesy of ENEA

A Nijhuis, Y Ilyin and W Abbas, ‘Axial and transverse stress–strain characterization of the EU dipole high current density Nb3Sn strand’Supercond. Sci. Technol. 21 No 6 (June 2008) 065001 (10pp)

Uni-axial strain & Uni-axial strain & IIc (Pacman)c (Pacman)

Sample wire

Pacman spring

Torque transfer pins

Temperature variations by placing the Pacman spring under an insulator cup, creating a helium gas volume.

With heaters and thermometers arranged symmetrically the temperature can be balanced within ±20 mK.

Strand soldered on perimeter disc shaped spring Standard procedure VI curves

I =1000 A,-appl =-0.9 to + 0.9 %B=6 to 15 TT=4.2 to 12 K.First we explore the compressive strain range, then B,T dependency and finally the tensile range for irreversibility

Uni-axial Uni-axial IIc-strain (OST-DIP)c-strain (OST-DIP)

VI curves for OST-dipole strandI > 800 A,-appl =-0.9 to + 0.9 %B=6 to 14 TT=4.2 to 10 K.

Uni-axial Uni-axial IIcc((,B,T,B,T) (OST-DIP)) (OST-DIP)

Measured Ic @ 10 V/mOST-dipole strand

Fit to Dev Strain Model,30 data points requiredfor description of entire Ic(B-T- space reversible behaviourStandard: 50 data points+ irreversible tensile.

OST-DIP strand degrades immediately, actually before passing zero strain (peak), red markers are after irreversible degradation

General conductor scaling parameters:Deviatoric strain (~2nd inv.: slope) Ca1 49.05Deviatoric strain (~3rd inv.: asymmetry) Ca2 13.05Hydrostatic strain (~1st inv.: peak rounding) eps_0a 0.374%Thermal pre-strain (axial) eps_m -0.143%Maximum upper critical field Bc2m(0) 29.40 TMaximum critical temperature Tcm 15.97 KPre-constant [ =(constant*Bc2m(0)^2)/kappa_1m(0) ] C 47095 AT

EFDA DipoleOST strand

Pacman

0

100

200

300

400

500

600

700

800

900

-1 -0.8 -0.6 -0.4 -0.2 0 0.2

strain, [%]

criti

cal c

urr

en

t, I c

[A]

measured

dev strain model

after eps-applied > 0.1 %

IIcc((B,TB,T) () (applappl=0)=0)

Measured Ic @ 10 V/mOST-dipole strand

Fit to Dev Strain Model

OST Dipole strandPacman

T=constant

0

100

200

300

400

500

600

700

800

900

5 7 9 11 13 15

B [T]cr

itica

l cu

rre

nt,

I c [A

]

T=6 K, measT=8 K, measT=4.2 K, measT=4.2 K, modelT=8 K, modelT=6 K, modelT=10 K, measT=10 K, model

OST Dipole strandPacman

0

100

200

300

400

500

600

700

800

900

1000

4 5 6 7 8 9 10 11

T [K]

criti

cal c

urr

en

t, I c

[A]

B=12 T, meas B=12 T, modelB=6 T, meas B=6 T, modelB=8 T, meas B=8 T, modelB=10 T, meas B=10 T, modelB=14 T, meas B=14 T, model

nn-value (OST-DIP)-value (OST-DIP)

n-value 10-100 V/mOST-dipole strand

OST-DIP strand degrades immediately when passing zero (peak) strain, the n-value is good indicator (red markers)

OST-DipoleB=12 T

0

10

20

30

40

50

60

-1 -0.8 -0.6 -0.4 -0.2 0 0.2

strain [%]

n-v

alu

e [-

]

T=4.2 KT=6 KT=8 KT=10 KT=4.2 K, e-appl > 0.1 %

OST-Dipole

y = 2.1684x0.456

0

10

20

30

40

50

60

0 200 400 600 800 1000

I c [A]

n-v

alu

e [-

]

n-value (10-100uV/m)

after eps-applied > 0.1 %

all n-values eps-appl < 0.1 %Power (n-value (10-100uV/m))

Axial strain irreversibility limitAxial strain irreversibility limit

Hitachi bronze strand with irr=0.63 %

HitachiBronze

Pacman

0

50

100

150

200

250

-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

strain, [%]

Ic [

A]

0

10

20

30

40

50

60

70

80

90

100

n-v

alu

e [-

]Ic reversiblen reversiblen-value, irreversibility limit

Ic

OST-I

0

50

100

150

200

250

300

-0.1 0 0.1 0.2 0.3 0.4 0.5

strain [%]

Ic [A

]0

5

10

15

20

25

30

35

40

45

50

n-v

alu

e [-

]

Ic, reversibleIc, irreversiblen-value, reversiblen-value, irreversiblen-value, irreversibility limit

Irreversibility strain limit determined by intersection of two lines through n-values vs. strain for two ITER type of strands (Ic criterion 10 V/m, n- value between 10 and 100 V/m)

OST internal tin strand with irr=0.25 %

Strain irreversibility limit OST-DIPStrain irreversibility limit OST-DIP

Ic & n-valueOST-dipole strandB=12 TT=4.2 K.

Determine irreversibility strain limit by intersection of two lines through n-values vs. strain.For ODT-DIP irr=-0.03 %, so irreversibility appears already before intrinsic zero axial strain is reached

EFDA DipoleOST strand

Pacman

0

100

200

300

400

500

600

700

-0.2 -0.1 0 0.1 0.2

strain, [%]

criti

cal c

urr

en

t, I c

[A]

0

10

20

30

40

50

60

70

n-v

alu

e [-

]

Ic

n-value

n-value, irreversibility limit

Uni-axial Uni-axial IIcc((,B,T,B,T) (OST-DIP & ) (OST-DIP &

HEP prototype DIP)HEP prototype DIP)

Other high Jc OST-RRP (HEP prototype DIP) strand (127 filaments) also degrades immediately when passing zero strain (peak), two samples tested.

normalised I c

T =4.2 K, B=12 T

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2

strain, [%]

I c/ c

I max

[-]

OST Dipole

OST prototype HEP Dipole

prototype HEP Dipole2 samples on Pacman

0

100

200

300

400

500

600

700

800

900

-1 -0.8 -0.6 -0.4 -0.2 0 0.2

strain, [%]

criti

cal c

urre

nt, I

c [A

]

#1, measured, 12 T

#2, measured, 11 T

Both types high Jc OST-RRP strands, HEP prototype and Dipole (91 filaments) degrade around zero strain (peak).Different strain sensitivity, DIP strand less sensitive (materials not analysed).

Strain irreversibility limit OST-DIPStrain irreversibility limit OST-DIP

For OST-DIP irr=-0.03 % (just before reaching peak) and prototype HEP DIP irr= ~0.07 %

EFDA DipoleOST strand

Pacman

0

100

200

300

400

500

600

700

-0.2 -0.1 0 0.1 0.2

strain, [%]

criti

cal c

urr

en

t, I c

[A]

0

10

20

30

40

50

60

70

n-v

alu

e [-

]

Ic

n-value

n-value, irreversibility limit prototype HEP Dipole

0

100

200

300

400

500

600

700

800

-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2

strain, [%]cr

itica

l cu

rre

nt,

I c [A

]

0

10

20

30

40

50

60

70

80

90

100

n-v

alu

e [-

]

Ic-meas

n-value

Uni-axial Uni-axial IIc-strain, overviewc-strain, overview

Ic() @ 12 T & 4.2 K of 16 Nb3Sn strands

High Jc OST RRP: 600 AITER Advanced: 200-300 AITER Model Coil: 150 A

measused I c

T=4.2 K, B=12 T

0

100

200

300

400

500

600

700

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8

strain, [%]

I c/ c

I max

[-]

OST DipoleOST-I, 2nd sampleOST-II, scaled B=11 TEASNIN&WST, 0.77 mmVAC (CSMC) DUEM-LMI (TFMC) DUSMI-PIT 504 (binary)OST prototype HEP DipoleMitsubishiHitachiRF IntTin CuNbLuvata Pori (TFAS)OCSI (TFAS)KOR-1NIN-WST 45-5

Uni-axial Uni-axial IIc-strain sensitivity, c-strain sensitivity, overviewoverview

Normalised Ic @ 12 T & 4.2 K

High Jc OST RRP: 600 AITER Advanced: 200-300 AITER Model Coil: 150 A

normalised I c

T=4.2 K, B=12 T

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8

strain, [%]

I c/ c

I max

[-]

OST Dipole

OST prototype HEP DipoleThe relative strain sensitivity for strands is defined as the slope of the reduced Ic (Ic/Ico) vs. the strain between -0.7 % < < -0.3 %.

Relative Relative IIc-strain sensitivityc-strain sensitivity

The average relative strain sensitivity of all strands is 1.01 and the stdev is 0.08.

OST RRP DIP strand is least sensitive int. tin strand while the HEP prototype is one of the most sensitive.(Materials not analysed).

Recent bronze is least sensitive except (VAC-CSMC)

0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

Hitach

iEAS

OST-D

IP

ITER-IT

ITER-IT

ITER-IT

ITER-IT

ITER-IT

ITER-IT

ITER-IT

VAC (CSM

C)

ITER-IT

ITER-IT

ITER-IT

OST-p

roto

HEP D

IP

ITER-IT

rel.

Ic s

en

sitiv

ity Ic

vs

stra

in [-

]

Irreversibility strain limitIrreversibility strain limit

Irreversibility strain limit for tested strandsLow limit for high Jc OST RRP type of strands (near peak) and bronze high limit.ITER internal tin mostly between 0.2 % and 0.4 % (average 0.33 % stdev 0.11 %).(EAS strand to be measured, here based on micrography from Matt Jewell on Twente samples)

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

OST-D

IP

OST-p

roto

HEP D

IP

ITER-IT

ITER-IT

ITER-IT

ITER-IT

ITER-IT

ITER-IT

ITER-IT

ITER-IT

ITER-IT

ITER-IT

ITER-IT

VAC (CSM

C)

Hitach

iEAS

irre

vers

ibili

ty s

tra

in li

mit

[%]

HitachiBronze

Pacman

0

50

100

150

200

250

-0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

strain, [%]

Ic [

A]

0

10

20

30

40

50

60

70

80

90

100

n-v

alu

e [-

]

Ic reversiblen reversiblen-value, irreversibility limit

Ic

TARSIS stress-strain results, 4.2 KTARSIS stress-strain results, 4.2 K

Stress-strain curves on ITER and Model Coil strands at 4.2 K: racture: 0.9 % - 1.2 % strain

TARSIS 4.2 K stress-strain test TARSIS 4.2 K stress-strain test OST-DipoleOST-Dipole

OST-Dip stress-strain4.2 K tests

0

50

100

150

200

250

300

0 0.005 0.01 0.015

strain [%]

stre

ss [M

Pa

]He_noCr_bht 1

He_noCr_bht 3

He_Cr 1

He_Cr 2

He_noCr_aht 1

Strand failure just beyond 0.5 % strain (T=4.2 K).

Cr layer removed before HT: slightly weaker stiffness. Confirmed with other strand types.All TARSIS tests are done with Cr layer removed before HT.

necking

fracture

yielding

TARSIS bendingTARSIS bending

TARSIS bending test OST-DipoleTARSIS bending test OST-Dipole

OST-DipoleBending

Lw=7 & 10 mm

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1 1.2 1.4

peak bending strain [%]

I c/I

c0 [-

]

V1, 10mm

V3, 7mm

LRL

HRL

OST-DipoleBending

Lw=7 & 10 mm

0

5

10

15

20

25

30

35

40

45

50

0 0.2 0.4 0.6 0.8 1 1.2 1.4

peak bending strain [ ]

n-v

alu

e [-

]

ext1

ext2

ext3

V3, 7mm

V1, 7mm

EFDA Dipole strand:Initially following the LRL (good IF redistribution).Failure at 0.5 % strain.

Correlation between fracture strain and deviation from bending-LRL:

OST-Dip stress-strain4.2 K tests

0

50

100

150

200

250

300

0 0.005 0.01 0.015

strain [%]st

ress

[MP

a]

He_noCr_bht 1

He_noCr_bht 3

He_Cr 1

He_Cr 2

He_noCr_aht 1

TARSIS bending, resultsTARSIS bending, results

Reduced Ic vs peak bending strain for several tested strands illustrating the spread in sensitivity but in particular the high sensitivity for OST-DIP (> 0.5 %).

Bending

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5 2 2.5

peak bending strain [%]

I c /

I c0

[-]

OST Dipole

TARSIS crossing strands test: TARSIS crossing strands test: IIcc

Probe for X-strands test with periodicity 4.7 mm and 90 angle.Reacted straight X-strands, are pressed by top plate (not visible).

Ic() for OST-DIP strand also showing Ic release of load and irreversibility up to 50 MPa () transverse stiffness

OST-DipoleX-strand

Lw=4.7 mm

0

0.2

0.4

0.6

0.8

1

0 50 100 150 200 250

stress [MPa]

I c/I c

0 [-

]

contour

released load

OST-DipoleX-strand

Lw=4.7 mm

0.8

0.85

0.9

0.95

1

0 10 20 30 40 50 60 70 80

stress [MPa]

I c/I c

0 [-

]

contour

released load

OST-DipoleX-strands

Lw=4.7 mm

0

50

100

150

200

250

300

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

strain [-]

stre

ss [M

Pa

]

stress [MPa]

TARSIS crossing strands:TARSIS crossing strands:IIc and n-valuec and n-value

OST-II strand most sensitive to transverse contact stress (and binary SMI-PIT) followed by EM-LMI, OST-DIP, MIT and less sensitive HIT and EAS bronze strands.n-value OST-II degrades rapidly between 10 and 30 MPa.

0

0.2

0.4

0.6

0.8

1

0 50 100 150 200 250 300stress [MPa]

I c/I c

0 [-

]

EASOST-IOST-IIHitachiEM-LMIMitsubishiOST-DipSMI-504, binaryKOR-1

0

0.2

0.4

0.6

0.8

1

1.2

0 50 100 150 200 250 300

stress [MPa]

n/n

0 [-

]

EASOST-IOST-IIHitachiMitsubishiOST-DipEM-LMISMI-504, binaryKOR-1

Is it possible to use strain sensitive strands like the high Jc OST RRP for CICC??

Influence of cabling in CICCInfluence of cabling in CICC

April 2006 (Barcelona), a priori TEMLOP prediction postulating influence characteristic bending wavelength (Lw), no experimental data available at that time to prove it.

Influence of cabling in CICCInfluence of cabling in CICC

vf =0.36E // = 29 Gpa

IxB =750 kN/m

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

0 0.005 0.01 0.015 0.02

bending wavelength, L w [m]

red

uce

d I

c [-

]

0.0%

0.2%

0.4%

0.6%

0.8%

1.0%

1.2%

1.4%

1.6%

1.8%

2.0%

pe

ak

be

nd

ing

str

ain

[%]

reduced Ic @ peak load

peak strain

`

August 2007: relation for Lw and Lp (1st stage twist pitch) ]1[

21

21

1

m

L

N

LL p

Lp

pw

A. Nijhuis and Y. Ilyin, ‘Transverse Load Optimisation in Nb3Sn CICC Design; Influence of Cabling, Void Fraction and Strand Stiffness’, Supercond. Sci. Technol. 19 (2006) 945-962.

A. Nijhuis, ‘A solution for transverse load degradation in ITER Nb3Sn CICCs, effect of cabling on Lorentz forces response’ Supercond. Sci. Technol. 21 (2008) 054011 (15pp)

April 2007 SULTAN test first verification of a priori prediction influence bending wavelength for long pitches.

Influence of cabling in CICCInfluence of cabling in CICC

TFPRO-2 SULTAN sample: two legs, one reference ITER cabling pattern gave Tcs= 5.5 K and very low n-value, other leg with roughly twice longer pitches gave best performance ever of Tcs=7.3 K and high n-value.

TFPRO-2 ITER reference cabling pattern

0 200 400 600 800 10005.0

5.5

6.0

6.5

7.0

7.5

Tcs

, K

Cycle

OST2 OST1

TFPRO2

TFPRO-2 long pitches

Required:Influence current non-uniformity induced at joints and terminations must be excludedRoughly similar cable design (relevant # strand layers / ratio of copper strands)

Influence of cabling in CICCInfluence of cabling in CICC

Sample PITSAM2 (LF2)PITSAM5

Short pitchesPITSAM5

Long pitches

EDIPO LF2 LF2 LF2

Cable pattern (3x3)x3x4 3x3x3x4 3x3x3x4

Sc strand number 48 48 48

Sc strand Cr plated OST dipole 0.81 mm

Cr plated OST dipole 0.81 mm

Cr plated OST dipole 0.81 mm

Cu strand number 60 60 60

Twist pitch 58/95/139/213 34/95/139/213 83/140/192/213

Outer conductor dimensions (mm)

12.6 x 12.6 12.6 x 12.6 12.6 x 12.6

vf (%)(calculated)

30 30 30

PITSAM SULTAN test of similar CICC shape but different cabling patternPITSAM 2, 5L & 5SFully soldered joints

Dipole PITSAM 2 & 5, and ITER TFPRO2 (long pitches) Lw has been determined by:

Influence of cabling in CICCInfluence of cabling in CICC

]1[

21

21

1

m

L

N

LL p

Lp

pw

Conductor type 1st stage Lp Lw [m]

PITSAM1, 2, 3, 4 0.058 0.0098

PITSAM5 Long = ITER Option II 0.083 0.0161

PITSAM5 Short 0.033 0.0048

TFPRO2/OST1 = ITER Option I * 0.045 0.007

TFPRO2/OST2, Long Lp 0.116 0.0263

USTF1 (alternate 6x1)* 0.025 0.0011

* For USTF1 the strand properties are not available so the virgin performance, and thus the degradation can not be determined. For TFPRO2/OST1 Option I influence of the joint non-uniformity can not be excluded.

PITSAM and TFPRO2 (long pitches) performance for (virgin) zero load condition is determined by Jackpot Model (Jacket Potential) for =0.6 %.

Influence of cabling in CICCInfluence of cabling in CICC

JackPot model:PITSAM 2, 548 SC strands60 Cu strands

Good agreement with TEMLOP prediction.

Measured degradation:

Tcs/Tcs0 vs Lw

with Tcs0 computed for =-0.6 %

0.6

0.7

0.8

0.9

1.0

1.1

0 0.005 0.01 0.015 0.02 0.025 0.03

characteristic bending wavelength L w [m]

Tcs

/Tcs

0 [-

]

PITSAM LF2 (2 & 5)

TFPRO2/OST2, Long Lp

polyn. fit

SummarySummary

Ic vs. uni-axial strain, bending, contact stress and stiffness is characterised on OST RRP high Jc Nb3Sn strands.

Strain sensitivity I/ in the range of ITER Int tin. Irreversibility strain limits: ~ 0% for OST-DIP, from +0.2% to

+0.4% for ITER Int tin and > +0.6% for (recent) bronze. Bending behaviour follows the LRL until failure strain is

reached: 0.5% peak bending strain for OST DIP. Intermediate twist pitch length in CICC causes degraded

performance: TEMLOP prediction influence pitches further confirmed.