Effects of Fast Neutron Irradiation onState-of-the-Art Nb3Sn Wires

Thomas Baumgartner

May 12, 2014

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

Results

Conclusions

Outline

1 Introduction

2 Experimental

3 Results

4 Conclusions

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

Results

Conclusions

Acknowledgments

CERN has been an important partner throughoutthe past four years and funded the Nb3Snirradiation study discussed in this presentation.

Rainer Prokopec provided the presented data oninsulating materials.

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

IntroductionTechnologicalobjective

Nb3Sn wire samples

Expectations

Experimental

Results

Conclusions

Outline

1 IntroductionTechnological objectiveNb3Sn wire samplesExpectations

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

IntroductionTechnologicalobjective

Nb3Sn wire samples

Expectations

Experimental

Results

Conclusions

Technological objective

Collaboration with CERNExamined Nb3Sn wires are candidates for LHC upgradeReplacing the Nb-Ti inner triplets (quadrupole magnetassemblies for focusing) with Nb3Sn can improve theluminosityIntense and complex radiation field near the interactionpoints (neutrons, protons, pions, . . . )What is the life expectancy of a Nb3Sn inner tripletmagnet under these conditions?

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

IntroductionTechnologicalobjective

Nb3Sn wire samples

Expectations

Experimental

Results

Conclusions

Nb3Sn wire samplesFive types of multifilamentary wires

Ta alloyed RRP0.8mm, 54 sub-elementsTi alloyed RRP0.8mm, 108 sub-elementsBinary IT1.25mm, 246 sub-elementsTa alloyed PIT1.0mm, 192 sub-elementsTa alloyed PIT0.7mm, 114 sub-elements

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

IntroductionTechnologicalobjective

Nb3Sn wire samples

Expectations

Experimental

Results

Conclusions

ExpectationsEffects of radiation damage on Nb3Sn

Critical temperature Tc decreasesExplanation: Disorder leads to a reduction of theelectronic density of statesUpper critical field Bc2 increasesExplanation: Mean free path of electrons decreases, thusnormal state resistivity increasesκ= κ0 +C

pγρn, Bc2 = κ

p2Bc

Critical current density Jc increases up to a certain fluence,then decreases againExplanation: Sum of the above effects

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

IntroductionTechnologicalobjective

Nb3Sn wire samples

Expectations

Experimental

Results

Conclusions

ExpectationsBehavior of Jc(Φt)

0

0.5

1.0

1.5

0 0.2 0.4 0.6 0.8 1.0

Jc(

Φt)

/ J

c(0)

Φt (arb. units)

approx. lifetime fluence

Jc increases at low fluencesUsually explained with anincrease in Bc2

Some reports on changesin flux pinning due toradiation induced pinningcenters1,2

Tc degradation dominatesat high fluences

1M. W. Guinan et al.: Informal Report, LLNL, 1984

2T. Okada et al.: J. Appl. Phys. 63 (9), pp. 4580–4585, 1988

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

ExperimentalIrradiation

SQUIDmagnetometry

Transportmeasurements

Bc2 (T) measurements

Results

Conclusions

Outline

2 ExperimentalIrradiationSQUID magnetometryTransport measurementsBc2(T) measurements

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

ExperimentalIrradiation

SQUIDmagnetometry

Transportmeasurements

Bc2 (T) measurements

Results

Conclusions

Irradiation

TRIGA Mark-II reactor in ViennaFast neutron flux densityΦf = 4.1·1016 m−2 ·s−1

(E > 0.1MeV)Sequential irradiation of shortwire samples for magnetometryRadioactivity reduced by 2 ordersof magnitude relative to transportsamplesFluence step size: ∼2·1021 m−2

Ni samples included for fluencemonitoring (reaction threshold≈ 1MeV → fast neutrons only)

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

ExperimentalIrradiation

SQUIDmagnetometry

Transportmeasurements

Bc2 (T) measurements

Results

Conclusions

SQUID magnetometryJc from magnetization loops

Quantum Design MPMS XLmax. field: 7TIrreversible magnetic momentmirr(B,T) obtained frommagnetization loops in thetemperature range 4.2 – 15KJc(B) evaluated at eachtemperature using mirr andsub-element geometry3

Tc obtained from AC susceptibilitymeasurements

3T. Baumgartner et al.: IEEE Trans. Appl. Supercond. 22 (3), 6000604, 2012

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

ExperimentalIrradiation

SQUIDmagnetometry

Transportmeasurements

Bc2 (T) measurements

Results

Conclusions

SQUID magnetometryJc from magnetization loops

108

109

1010

1011

0 1 2 3 4 5 6 7

Jc (

A⋅m

-2)

B (T)

4.2 K

5 K

6 K

7 K

8 K

9 K

10 K

11 K

12 K

13 K

14 K

15 K

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

ExperimentalIrradiation

SQUIDmagnetometry

Transportmeasurements

Bc2 (T) measurements

Results

Conclusions

Transport measurements

0

10

20

30

40

50

60

0 200 400 600 800 1000

V (

µV)

I (A)

∼ 0.5m of wire onTi-6Al-4V barrel (miniVAMAS, Ø 23mm)Measurementsperformed in appliedfields of up to 15TMaximum current of1000A in liquid helium

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

ExperimentalIrradiation

SQUIDmagnetometry

Transportmeasurements

Bc2 (T) measurements

Results

Conclusions

Transport measurementsComparison with magnetometry results

102

103

104

0 2 4 6 8 10 12 14 16

I c (

A)

B (T)

Magnetometry

Extrapolation

Transport

RRP-Ti-1084.2K

Good agreementbetween magnetometryresults and transportcritical currentmeasurementsLess than 15%deviation betweenextrapolatedmagnetometry dataand transport results

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

ExperimentalIrradiation

SQUIDmagnetometry

Transportmeasurements

Bc2 (T) measurements

Results

Conclusions

Bc2(T ) measurements

Bc2(T) obtained from resistivitymeasurements (temperaturesweep at constant field)Direct measurements possible forT & Tc/2 (15T max. field)Extrapolation to lowertemperaturesMeasurements performed on 1unirradiated sample of each wiretype, and 3 irradiated samples

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

ResultsCritical temperature

Critical currentdensity

Upper critical field

Volume pinning force

Two-mechanismmodel

Conclusions

Outline

3 ResultsCritical temperatureCritical current densityUpper critical fieldVolume pinning forceTwo-mechanism model

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

ResultsCritical temperature

Critical currentdensity

Upper critical field

Volume pinning force

Two-mechanismmodel

Conclusions

Critical temperature

Small Tc degradation within the examined fluence range(∼2% at Φf t = 1022 m−2)Can be described with a linear relationshipTc(Φf t) = Tc(0)−kTΦf t

Slope kT is smaller by about 1/3 in the binary wire,probably due to a higher initial degree of order

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

ResultsCritical temperature

Critical currentdensity

Upper critical field

Volume pinning force

Two-mechanismmodel

Conclusions

Critical temperature

16.6

16.8

17.0

17.2

17.4

17.6

17.8

18.0

0 0.5 1.0 1.5 2.0 2.5

Tc

(K)

Φft (1022 m-2)

RRP-Ta-54

PIT-Ta-192

RRP-Ti-108

IT-246

PIT-Ta-114

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

ResultsCritical temperature

Critical currentdensity

Upper critical field

Volume pinning force

Two-mechanismmodel

Conclusions

Critical current density

Jc(T ,B) obtained from magnetometry data after eachirradiation stepData used to assess Jc(Φf t)/Jc(0)

7T max. applied field ⇒ evaluation at lower field valuesSignificant increase found in all examined wire types

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

ResultsCritical temperature

Critical currentdensity

Upper critical field

Volume pinning force

Two-mechanismmodel

Conclusions

Critical current density

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

0 0.5 1.0 1.5 2.0

Jc(

Φft)

/ Jc(

0)

Φft (1022 m-2)

RRP-Ta-54

PIT-Ta-192

RRP-Ti-108

IT-246

PIT-Ta-114

T = 4.2K, B = 6T

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

ResultsCritical temperature

Critical currentdensity

Upper critical field

Volume pinning force

Two-mechanismmodel

Conclusions

Critical current density“Old” irradiation studies

E > 1MeV 4

binary wire

E = 14MeV 5

binary wire Ti alloyed wire

4C. L. Snead Jr., D. M. Parkin.: Nucl. Technol. 29 (3), pp. 264–267, 1976

5F. Weiss et al.: IEEE Trans. Mag. 23 (2), pp. 976–979, 1987

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

ResultsCritical temperature

Critical currentdensity

Upper critical field

Volume pinning force

Two-mechanismmodel

Conclusions

Upper critical field

Data obtained at T & Tc/2 (15T max. field)Extrapolation based on the dirty limit WHH function6

Unexpectedly low irradiation induced increase of Bc2 foundin the 3 examined samples

6E. Helfand, N. R. Werthamer: Phys. Rev. 147 (1), pp. 288–294, 1966

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

ResultsCritical temperature

Critical currentdensity

Upper critical field

Volume pinning force

Two-mechanismmodel

Conclusions

Upper critical field

0

5

10

15

20

25

0 2 4 6 8 10 12 14 16 18

Bc2

(T

)

T (K)

unirradiated

Φft = 1.0 ⋅ 1022 m-2

Binary wire IT-246Φf t = 1.0 · 1022 m−2

Bc2(T = 0) increases by∼ 3% relative to theunirradiated stateSimilar behavior foundin RRP-Ti-108 andPIT-Ta-114

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

ResultsCritical temperature

Critical currentdensity

Upper critical field

Volume pinning force

Two-mechanismmodel

Conclusions

What is going on?

Jc exhibits a considerable increase as a result of irradiationBc2 increases only slightlyChanges in the flux pinning behavior must be responsiblefor the large Jc increase

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

ResultsCritical temperature

Critical currentdensity

Upper critical field

Volume pinning force

Two-mechanismmodel

Conclusions

Volume pinning forceThe concept of scaling

0

0.2

0.4

0.6

0.8

1.0

0 0.2 0.4 0.6 0.8 1.0

Fp

/ Fp(m

ax)

b = B / B*c2

In Nb3Sn the volumepinning force Fp = ∣∣~Jc ×~B

∣∣exhibits scaling behaviorPlotting the normalizedvolume pinning force vs.the reduced field yields thesame curve at differenttemperaturesFp(b) ∝ f (b) = bp (1−b)q

p = 0.5, q = 2 for puregrain boundary pinning7

7D. Dew-Hughes: Phil. Mag. 30 (2), pp. 293–305, 1974

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

ResultsCritical temperature

Critical currentdensity

Upper critical field

Volume pinning force

Two-mechanismmodel

Conclusions

Volume pinning forceAnalysis of unirradiated samples

Fp = Jc B from magnetometry data normalized at eachtemperaturef (b) = C bp (1−b)q used as a fit functionAlgorithm finds p and q which minimize the global error(all temperatures included)

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

ResultsCritical temperature

Critical currentdensity

Upper critical field

Volume pinning force

Two-mechanismmodel

Conclusions

Volume pinning forceAnalysis of unirradiated samples

0

0.2

0.4

0.6

0.8

1.0

0 0.2 0.4 0.6 0.8 1.0

Fp

/ Fp(m

ax)

b = B / B*c2

4.2 K

5 K

6 K

7 K

8 K

9 K

10 K

11 K

12 K

13 K

14 K

15 K

0

5

10

15

20

25

0 5 10 15 20

Bc2

, B* c2

(T

)T (K)

upper crit. field

scaling field

Binary wire IT-246, unirradiated, p = 0.49, q = 2.16

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

ResultsCritical temperature

Critical currentdensity

Upper critical field

Volume pinning force

Two-mechanismmodel

Conclusions

Volume pinning forceAnalysis of irradiated samples

Optimal p and q change with fluencePeak in the pinning function at bmax = p/(p+q) is shiftedto higher valuesScaling field values changed only slightly, in agreementwith the Bc2(T) measurements

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

ResultsCritical temperature

Critical currentdensity

Upper critical field

Volume pinning force

Two-mechanismmodel

Conclusions

Volume pinning forceAnalysis of irradiated samples

0

0.2

0.4

0.6

0.8

1.0

0 0.2 0.4 0.6 0.8 1.0

Fp

/ Fp(m

ax)

b = B / B*c2

unirradiated

Φft = 1.0 ⋅ 1022 m-2

Binary wire IT-246, before and after irradiation

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

ResultsCritical temperature

Critical currentdensity

Upper critical field

Volume pinning force

Two-mechanismmodel

Conclusions

Two-mechanism model

Observed behavior is inconsistent with grain boundarypinning (p = 0.5, q = 2)Contribution of a second mechanism was investigated 8,9

f (b) =αbp1 (1−b)q1 +βbp2 (1−b)q2 , α+β= 1

Second mechanism was identified as pinning by coreinteraction between vortices and normal conductingpoint-like structures (p2 = 1, q2 = 2)7

Point-pinning contribution β was evaluated as a functionof fluence for all samples

8H. Küpfer et al.: J. Appl. Phys. 51 (2), pp. 1121–1126, 1980

9P. Maier, E. Seibt.: Appl. Phys. Lett. 39 (2), pp. 175–177, 1981

7D. Dew-Hughes: Phil. Mag. 30 (2), pp. 293–305, 1974

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

ResultsCritical temperature

Critical currentdensity

Upper critical field

Volume pinning force

Two-mechanismmodel

Conclusions

Two-mechanism modelPoint-pinning contribution vs. fluence

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 0.5 1.0 1.5 2.0

β

Φft (1022 m-2)

RRP-Ta-54

PIT-Ta-192

RRP-Ti-108

IT-246

PIT-Ta-114

f (b) =αbp1 (1−b)q1 +βbp2 (1−b)q2 , p2 = 1, q2 = 2

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

Results

ConclusionsSummary

Outlook

Outline

4 ConclusionsSummaryOutlook

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

Results

ConclusionsSummary

Outlook

Summary

Five Nb3Sn wire types were subjected to sequential fastneutron irradiation up to Φf t = 2·1022 m−2

They appear to be more resilient to radiation than wiresused in previous studiesTc as a function of fluence shows a linear degradationBc2 increases only slightly with fluence ⇒ large Jc increaseis due to changes in the volume pinning forceChanges in the pinning behavior can be described with afluence dependent point-pinning contribution using atwo-mechanism model10

10T. Baumgartner et al.: Supercond. Sci. Technol. 27 (1), 015005, 2014

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

Results

ConclusionsSummary

Outlook

Outlook

Maximum in Jc(Φf t) is relevant to life time estimation andcomparison with other irradiation studies (different wires ordifferent particles) ⇒ irradiation program will be continuedTransport samples will be irradiated for comparison withmagnetometry results and to obtain more high-field dataMagnetometry measurements will be attempted in fields ofup to 15T using our self-built vibrating coil magnetometerOur group is also active in the field of insulating materials

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

Results

ConclusionsSummary

Outlook

Excursus: insulating materialsRadiation effects on resins

epoxy cyanate ester

Similar impregnation processCosts for CE higher by afactor of up to 10

CE can be mixed with epoxyto reduce costs

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

Results

ConclusionsSummary

Outlook

Excursus: insulating materialsQualification of resins for the ITER TF coils11

Demands for ITER:Mixing ratio:40% CE / 60% epoxyLong pot life:viscosity < 100mPa·sfor more than 100 hMaximum curingtemperature:160±10℃ for 24 h

3 suppliers, 4 resins:Huntsman, Switzerland:LMB 6653 / LMB 6622-4Composite TechnologiesDevelopment, USA:CTD-425CTD-435Industrial SummitTechnology, Japan:IST

11K. Humer et al.: Fusion Eng. Des., 88 (5), pp. 350–360, 2013

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

Results

ConclusionsSummary

Outlook

Excursus: insulating materialsMechanical properties before and after irradiation

ITER design fluence: 1.0 · 1022 m−2 (E > 0.1MeV)

Effects ofFast NeutronIrradiation onState-of-the-Art Nb3Sn

Wires

ThomasBaumgartner

Outline

Introduction

Experimental

Results

ConclusionsSummary

Outlook

Excursus: insulating materialsMaterial tests for CERN

S-glass fiber reinforced composites3 different types of epoxy resinsSeveral irradiations up to a total absorbeddose of 50MGyGlass fibers are wrapped before Nb3Snheat treatmentPossible surface degradation orcontaminationEffects on the resin / fiber / conductorinterfaces must be examined

Thank you for your attention.

If we knew what it was we were doing,it would not be called research, would it?

Albert Einstein