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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?
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