TrappedFluxMeasurementsandThermalBoundaryResistanceAnalysisforanECRfilm

Thin Film Workshop 2016Sarah Aull

Acknowledgements toA. Miyazaki, W. Venturini Delsolaro and the HIE-Isolde team (CERN)A.-M. Valente-Feliciano (JLab)

WhereweleftatSRF2015

FirstNb/Cucoatingbyenergeticcondensationshowed• astronglymitigatedQ-slope• (still)lowtrappedflux

sensitivity• strongdependenceonthe

cooldowndynamics

Summary

15/09/2015 sarah.aull@cern.ch 13

withaQ-Slopecomparabletobulk

niobiumat4K

severelyaffectedbythermalcurrents

stilllesssensitivetotrappedflux

Abulk-likeNb/Cufilm…

sarah.aull@cern.chThinFilmWorkshop2016 2

ThermalBoundaryResistanceModel

• SmalldefectsattheNb-CuinterfaceleadtomicroscopicquencheswhichcausetheNb\CuQ-slope.

• Q(Eacc)curvecanbeconvertedintoadistributionfunctionofthermalcontactresistances.

sarah.aull@cern.chThinFilmWorkshop2016

VPalmieriandRVaglio,Supercond.Sci.Technol.29(2016)015004

Tc

RNb/Cu

Nb

Cu

Integrationyieldsdetachedsurfacearea:I =

Zf�RNb/Cu

�dRNb/Cu

3

ThermalBoundaryResistanceModel

• SmalldefectsattheNb-CuinterfaceleadtomicroscopicquencheswhichcausetheNb\CuQ-slope.

• Q(Eacc)curvecanbeconvertedintoadistributionfunctionofthermalcontactresistances.

sarah.aull@cern.chThinFilmWorkshop2016

VPalmieriandRVaglio,Supercond.Sci.Technol.29(2016)015004

Tc

RNb/Cu

Nb

Cu

Integrationyieldsdetachedsurfacearea:I =

Zf�RNb/Cu

�dRNb/Cu

Conversion is not a fit

Difficult to test experimentally

3

ExamplesofDetachedSurfaces

4sarah.aull@cern.chThinFilmWorkshop2016

CourtesyB.B

arbo

raCo

urtesyR.Valizad

eh

CourtesyR.Valizad

ehCo

urtesyP.Jac

ob

ECR

Sputtering Sputtering

Sputtering

ThermalContactResistanceoftheECR1

• CompareTBRanalysisforRFmeasurementsontheECRcoatingatdifferenttemperaturesandfrequencycombinations.

sarah.aull@cern.chThinFilmWorkshop2016 5

400 MHz

800 MHz

2.5 K

4 K

Detachedsurfacearea:

I =

Zf�RNb/Cu

�dRNb/Cu

ThermalContactResistanceoftheECR1

• CompareTBRanalysisforRFmeasurementsontheECRcoatingatdifferenttemperaturesandfrequencycombinations.

sarah.aull@cern.chThinFilmWorkshop2016 5

400 MHz

800 MHz

2.5 K

4 K

Detachedsurfacearea:

I=(3.4±0.7)10-5«(10-3-10-4)

I =

Zf�RNb/Cu

�dRNb/Cu

ThermalContactResistanceoftheECR1

• CompareTBRanalysisforRFmeasurementsontheECRcoatingatdifferenttemperaturesandfrequencycombinations.

sarah.aull@cern.chThinFilmWorkshop2016 5

400 MHz

800 MHz

2.5 K

4 K

Detachedsurfacearea:

I=(3.4±0.7)10-5«(10-3-10-4)

I =

Zf�RNb/Cu

�dRNb/Cu

Same result for all curves supports

validity of TBR model

TestingtheThermalContactResistanceModel

• CompareTBRanalysisforRFmeasurementsonbulkNbreferenceatdifferenttemperaturesandfrequencycombinations.

sarah.aull@cern.chThinFilmWorkshop2016 6

400 MHz

800 MHz

2.5 K

4 K

Detachedsurfacearea:

I =

Zf�RNb/Cu

�dRNb/Cu

TestingtheThermalContactResistanceModel

• CompareTBRanalysisforRFmeasurementsonbulkNbreferenceatdifferenttemperaturesandfrequencycombinations.

sarah.aull@cern.chThinFilmWorkshop2016 6

400 MHz

800 MHz

2.5 K

4 K

Detachedsurfacearea:

I =

Zf�RNb/Cu

�dRNb/Cu

No meaningful

result for bulk Nb

TBRAnalysisforHIE-Isolde

CompareQ(E)at2.5Kand4.5K:

HIE-Isoldecavitiesshownalsosamedistributionfunctionforfordifferenttemperatures

7CourtesyAkiraMiyazaki(CERN)ThinFilmWorkshop2016

TBRAnalysisforHIE-Isolde

CompareQ(E)at2.5Kand4.5K:

HIE-Isoldecavitiesshownalsosamedistributionfunctionforfordifferenttemperatures

7CourtesyAkiraMiyazaki(CERN)ThinFilmWorkshop2016

Consistent with • thermal boundary resistance being

a main Q-slope contributor • mitigated Q-slope for improved

microstructure due to energetic condensation.

CoolDownDynamics:ThinFilmWorkshop2014

8sarah.aull@cern.chThinFilmWorkshop2016

SimulationofCoolDownDynamics

• HeattransfersimulationwithCOMSOLtostudycooldowndynamicsintheQuadrupoleResonatorgeometry.

• TemperaturedependentmaterialpropertiesforNb,Cuandstainlesssteel.

sarah.aull@cern.chThinFilmWorkshop2016 9

SimulationofCoolDownDynamics

• HeattransfersimulationwithCOMSOLtostudycooldowndynamicsintheQuadrupoleResonatorgeometry.

• TemperaturedependentmaterialpropertiesforNb,Cuandstainlesssteel.

sarah.aull@cern.chThinFilmWorkshop2016 9

the slower the cool down, the bigger the

temperature gradient across the surface

InfluenceofCoolDown

• Thelowfieldsurfaceresistanceincreasesforslowcooling,resp.large(r)temperaturegradients

• Thehigherthelowfieldresistance,thestrongertheQ-slope.

• Theinfluenceofanambientfieldisnegligible.

sarah.aull@cern.chThinFilmWorkshop2016 10

400MHz,2K

InfluenceofCoolDown

• Thelowfieldsurfaceresistanceincreasesforslowcooling,resp.large(r)temperaturegradients

• Thehigherthelowfieldresistance,thestrongertheQ-slope.

• Theinfluenceofanambientfieldisnegligible.

sarah.aull@cern.chThinFilmWorkshop2016 10

400MHz,2K 400MHz,2K

FluxTrappingorFluxExpulsion?

Asolenoidunderthesampleallowstrappedfluxstudies.

11sarah.aull@cern.chThinFilmWorkshop2016

FluxTrappingorFluxExpulsion?

Asolenoidunderthesampleallowstrappedfluxstudies.

11sarah.aull@cern.chThinFilmWorkshop2016

Allambientfieldistrappeduptoathresholdfieldabovewhichfieldcanbeexpelled

FluxTrapping• Belowthethresholdfield,allfieldistrappedindependentlyof

cooldowndynamics.

• Thedependenceoncooldowndynamicsissignificantlystrongerthanlossesduetotrappedflux.

12sarah.aull@cern.chThinFilmWorkshop2016

FluxTrapping• Belowthethresholdfield,allfieldistrappedindependentlyof

cooldowndynamics.

• Thedependenceoncooldowndynamicsissignificantlystrongerthanlossesduetotrappedflux.

12sarah.aull@cern.chThinFilmWorkshop2016

400MHz,2K

FluxTrapping• Thedependenceoncooldowndynamicsissignificantly

strongerthanlossesduetotrappedflux.

• ECRcoatingstillshowslowtrappedfluxsensitivity

SECR (400MHz) = (0.022± 0.001) n⌦/µT

13sarah.aull@cern.chThinFilmWorkshop2016

400MHz,2K

SECR (800MHz) = (0.075± 0.009) n⌦/µT

FluxTrapping• Thedependenceoncooldowndynamicsissignificantly

strongerthanlossesduetotrappedflux.

• ECRcoatingstillshowslowtrappedfluxsensitivity

SECR (400MHz) = (0.022± 0.001) n⌦/µT

13sarah.aull@cern.chThinFilmWorkshop2016

400MHz,2K

SECR (800MHz) = (0.075± 0.009) n⌦/µT

What causes the strong surface resistance dependence on cool

down dynamics?

ECR2• Measureforthreedifferentthermal

cycles.

• Fitwith

• Findunchangedsuperconductinggap—>re-runfitwithcommon∆

14sarah.aull@cern.chThinFilmWorkshop2016

400MHz

RS (T ) =ABCS

Texp

✓�

kBT

◆+Rres

RS (400MHz, 10mT, T )

EffectofThermalCycling

• BCSfactorstronglyincreaseswithresidualresistance

•

• Hinttowardsstrongmagneticfields?Duetothermalcurrents?

15sarah.aull@cern.chThinFilmWorkshop2016

ABCS ⇠ !2 · ` · � (T, `)3�4

Conclusion• AnalysisofvariousRFdataincombinationwithFIB-SEMsupports

thatadhesionplaysthekeyroleincuringtheQ-slopeinNb/Cu.

• ConsistentpictureforNb/Cu:TemperaturegradientswhencrossingTcincreaselowfieldsurfaceresistance.

• Magneticfluxexpulsiononlyabovethresholdfield.

• Nocorrelation(sofar)betweencooldownrate/temperaturegradientandamountoffluxexpulsion.

• Effectoftemperaturegradientsignificantlystrongerthantrappedflux.

• Thermalcyclingappearstochangetheeffectivepenetrationdepth.

16sarah.aull@cern.chThinFilmWorkshop2016