thin films technologies for srf eucard2 wp12.2 thin films prospectives

THIN FILMS TECHNOLOGIES FOR SRFEUCARD2 WP12.2 THIN FILMS PROSPECTIVES

C. Z. ANTOINE, CEA, Irfu, SACM, Centre d'Etudes de Saclay, 91191 Gif-sur-Yvette Cedex, France

OUTLOOK

Introduction

Characterization tools

Deposition technique

Physics of SRF and advanced superconductors

Multilayers

Conclusion

INTRODUCTION

2014-04-16

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Claire Antoine Eucard2 WP12 Meeting @ Saclay

Nb : l~50 nm => only a few 100s nm of SC necessary

(the remaining thickness= mechanical support only) => Make thin films !

Advantages

Thermal stability (substrate cavity = copper)CostInnovative materialsOptimization of RBCS possible

Disadvantages

Fabrication and surface preparation (at least) as difficult as for bulkSuperconductivity very sensitive to crystalline quality (lower in thin films for now)

2014-04-16 Claire Antoine Eucard2 WP12 Meeting @ Saclay | PAGE 4

WHY THIN FILMS ? 2 REASONS

Making cheaper cavities :

Bulk like Nb on copper (1-5 µm)

Overcoming Nb monopoly:

Nb3Sn, MgB2, Multilayers…

Advantages

Can also be deposited onto copperHigher Tc => higher Q0Higher HSH or HC1 => higher accelerating field

Disadvantages

Fabrication and surface preparation (at least) as difficult as for bulkSuperconductivity very sensitive to crystalline quality (lower in thin films for now)Deposition of innovative (compound) materials is very difficultTheoretical limit (HSH vs HC1) still controverted => choice of ideal material !?

Advantages

Structure /composition can be optimized with conventional techniquesIdeal structure and composition can be achieved on model sample (guide for deposition of cavities)Cost

Disadvantages

RF performances cannot be directly measuredSpecific measurement tools need to be developed (sample cavity, magnetometer…)Ultimately a cavity deposition set-up will be needed, but with a known aimed structure


THIN FILMS CHALLENGES: DEPENDS ON THE STRATEGY

Optimizing

structure/composition of the

films on samples

Optimizing deposition inside

cavities

Advantages

RF testing easy and gives direct performanceWork is done only once, direct cavity production

Disadvantages

Very heavy and lengthy, many parametersNeed to develop a specific cavity deposition set-upDifficult to optimize set-up and film togetherOptimization of the structure/composition of the film is difficult

STRUCTURE OF THE TASK 12.2 (EUCARD2)

Niobium on copper (µm)

After ~ 20 years stagnation : new revolutionary deposition techniques Great expectations in cost reduction No improved performances/ bulk Nb

Higher Tc material (µm)

Based on superheating model. Higher field and lower Q0 expected

Higher Tc material (nm), multilayer

Based on trapped vortices model (Gurevich) Higher field and lower Q0 expected Recent experimental evidences

Specific characterization tools needed

Better understanding of SRF physics needed

Subtask

1

Subtask 2

Subtask

3


CHARACTERIZATION TOOLS DEVELOPMENTS(TASK 3)

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“SAMPLE CAVITIES”

Quadrupole resonnator developed at HZBSee O. Kugeler’s talk (HZB activities)

TE011 cavity developped at IPNO


LOCAL MAGNETOMETRY DEVELOPED @CEA

Measurement of HC1 on sample without edge/demagnetization effect (local measurement: field decreases quickly far from the coil: rcoil = 2,5 mm; rsample~1 cm ~ rcoil x 4 )

= T/Tc

1 2 3 4 5 6

Br (

a,u,

)

Bz (a

,u,)

1 2 3 4 5 60r/r0

r/r0

0

0

Excitation/Detection coil (small/sample)

Differential Locking Amplifier


DEPOSITION TECHNIQUES ISSUES(TASK 1 AND TASK 2)

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3 MAJORS DEPOSITION TECHNIQUES


High-energy deposition techniques line of sight techniques issues: getting uniform thickness/structure limited in complex geometry

Thermal diffusion films limited compositions available non uniform composition

Chemical techniques CVD, ALD conformational even in complex shape very quick for large surfaces issues: get the proper crystalline structure

DEPOSITION TECHNIQUES: INTERNATIONAL SITUATION

CERN Nb bulk like: Magnetron sputtering, HPIMS (collaboration with Sheafield University)Nb3Sn (diffusion furnace) : in project

Grenoble INPML: ALD and CVD

STFCNb, ML: PVD and ECR –CVD

Jlab and collaboratorsAt Jlab : ECR, HPIMSAlmeda Corpn: CED (Plasma)W&M : magnetron sputtering + Complete material characterization

CornellNb3Sn (diffusion furnace)

Temple UniversityMgB2 (HP-CVD), ML in collaboration with LANL and FNAL

ANLML: ALD

INFN LegnaroNbN (diffusion furnace)Large experience on sputtering, Nb3Sn…


Publications on that topic at SRF 2013: 23

HPIMS @ CERN: bulk-like thin films

See G. Terenziani’s talk


CVD/ ALD @ GRENOBLE INP

Received special R&D ALD set-up

Need to develop a suitable coordination chemistry for the ALD precursors (+ plasma ALD to help)

Process scaling up to cavity deposition will be performed with specific simulation tools.


See F. Weiss’s talk

UNDERSTANDING THE PHYSICS OF SRF(TASK 3)ADVANCED SUPERCONDUCTORS(TASK 2)

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SRF LIMITS : BACK TO BASICS


Q0 (1/Thermal dissipations) depends on surface resistance … which depends on TcHigher Tc => higher Q0 => lower operation cost

Ultimate limit in Eacc: when the SC becomes dissipative! Transition : when T and/or B↑Vortices in RF highly dissipative => keep Meissner state

At w < 3 GHz: we are limited by BRF !!!

HC1Nb

= 180-190 mT

Cavities : Meissner State, no vortex please !!!

? HSH

SRF : HC1 VS HSH

Cavities : Meissner State, H~ HC1, J~JD (@ HC1), T~2-4 K

Coils : higher TC, butmixed state (low HC1) Generally low magnetic field

2014-04-16 Claire Antoine Eucard2 WP12 Meeting @ Saclay | PAGE

Reaching higher field (Eacc/BRF) => Reach superheating field (metastable Meissner state) : Nb3Sn, MgB2…=> Artificially enhance HC1 : Multilayers

Nb3Sn : RECENT BREAKTHROUGH


At 4,2 K Q0Nb3Sn =

20 x Q0Nb !!!

At 2 KQ0Nb3Sn ~

Q0Nb

Limited in Eacc

Nb3Sn: RECENT BREAKTHROUGH


HC1Nb3Sn (~27mT)

Recent results from CornellCW

Cornell, 1997pulsed

HC1 is not a fundamental limit for SRFbut

Is it a practical limitation ?NB : HSH is more easily observed :

Close to Tc (cf Yogi)Pulsed RF

Hays. "Measuring the RF critical field of Pb, Nb, NbSn". in SRF 97. 1997.

HP Nb 0.12 T (H°C1=0.17 T)

1E+08

1E+09

1E+10

1E+11

1E+12

0 5 10 15 20 25 30 35

Epk (MV/m)

Qo

QUENCH

10 20 30 40 50 60 70

HP Nb3Sn 0.03T (H°C1=0.05 T)

Nb3Sn

Nb

1.5 GHz Nb3Sn cavity (Wuppertal, 1985) 1.3 GHz Nb cavity (Saclay, 1999)

Nb3Sn : A LOT OF ROOM FOR IMPROVEMENT


ADVANCED SUPERCONDUCTORS :MULTILAYERS

2014-04-16

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Multilayers: Nb / insulator/ superconductor / insulator /superconductor… :

Surface screening and low Rs Thin SC films. d< l => artificial enhancement of HC1

*

The thin layers stand high fields without vortex nucleation Niobium surface screening: allows higher field in the cavity

=> Q0multi >> Q0

Nb RR NbS

NbNS 10

1

0 10 20 30 40 50 601E+09

1E+11

200100

Eacc (MV/m)

B(mT)

Q0

ALTERNATIVE TO BULK SC: MULTILAYERS

(SC with higher Tc than Nb)

**lNdeHH applNb

Cavity's internal surface →Outside wall

Happlied

HNb

Nb I-S-I-S-

* In theory 20 nm NbN : HC1 x ~200** Simplified model from Gurevich

In principle :


FIELD SCREENING / THIN FIELD

Modified Model (Kubo, 2013)

T. Kubo @ SRF 2013

Made the calculation for exact boundaries condition

l, x : known bulk values (not necessary exact for thin films)

Applied to NbN, Nb3Sn, MgB2

Similar calculation also proposed by S. Posen for Nb3Sn only

Simple Model (Gurevich, 2006) (1 of the reasons why measurements with Squid are ambiguous)

B B B B

Single layerInfinite plane Thin film in a uniform field


OPTIMUM THICKNESS FOR SL ?

T. KuboSL/ML structures not effective for Nb3Sn

Contrary to simple model, very thin layers are not interestingOptimum thickness around 100 nm for NbN ?How does that compare with exp. Measurements ?

=> Series of SL with various thicknesses (50 nm to 150 nm) is needed


RESULTS FROM OTHER LABS

Compare with what is expected for bulk Nb : ~1300 Oe @ 4.5 K !

[Lukaszew, W&M 2012]

*

**


MgO (100) substrate

600(*) / 250(**) nm Nb “bulk like”

~ 15 nm insulator (MgO)

~30(*) or 50 nm (**) NbN

Alternating MgB2-insulator structures have been fabricated on sapphire substrate: 40 nm MgO as insulating layer, sputtered. MgB2 deposited by HPCVD ex situ. 150,

100, and 75 nm in thickness.

Tc near 40 K for 100 and 150 nm films. Lower for 75 nm film.

Multilayer films with thin MgB2 layers show higher HC1 than the 300 nm film even though the total thickness are the same.

SapphireMgB2

MgOMgB2

MgOMgB2

[Teng, Xi – Temple University]

MgB2-MgO MULTILAYER FILMS



[Tajima, SRF 2011]

Magnetic screening evidenced for ML4 up to 38 mT, at T~7K

Dramatic transition around 38 mT => rcoil << rsample not valid anymore ?

Magnetometer is effective up to 1500 mA (equivalent field 150 mT) Tp° 2-40 K

Use of larger samples/smaller coil is mandatory

MAGNETOMETRY EARLY RESULTS

4 5 6 7 8 9 10 11 12 13 14 15 16

0,0000

0,0005

0,0010

0,0015

0,0020

0,0025

0,0030

0,0035

0,0040

0,0045

0,0050

V3

(V)

Température (K)

0,2 0,9 18,56 3,7 7,5 1,2 15 18,6 22 26,5 36,6 36,7 52,4 52,5 52,6 52,6 61,3 61,3

CZ Antoine, JC Villegier, G Martinet, Applied Physics Letters 102 (10), 102603-102603-4


THERMAL ANALYSIS

Strong indication that RBCS is improved with MLCould probably be improved with the use of thicker layers (complete screening)Rres is higher for ML than for Nb, but strongly influenced by substrate ?Very promising preliminary results

Same calibrationRs rf-ML2<< Rs Nb

NB. Current: ½I in Nb½I in NbN

Polycrystalline Nb substrateLarge grain Nb substrate


Bulk LG Nb

~ 15 nm insulator (MgO)

50 nm NbN

CONCLUSIONS AND PERSPECTIVES

Renewed activity on bulk-like Nb films (cost issues) and high HSH SC e.g. Nb3Sn or NbN (higher performances)

ML structures seem to be a promising way to go beyond Nb for accelerator cavities

Look for higher Q0, not only Eacc !

WE ARE ON THE EVE OF A TECHNOLOGICAL REVOLUTION FOR SRF CAVITIES !

Few labs involved

EUCARD 2 : only large scale program in Europe in this domain, big opportunity


DSMIrfuSACMLIDC2

Commissariat à l’énergie atomique et aux énergies alternativesCentre de Saclay | 91191 Gif-sur-Yvette CedexT. +33 (0)1 69 08 73 28| F. +33 (0)1 69 08 64 42

Etablissement public à caractère industriel et commercial | RCS Paris B 775 685 019


THANK YOU FOR YOUR ATTENTION

2014-04-16

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SPARES

2014-04-16

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COAXIAL ENERGETIC DEPOSITION (CED)

• Ions Energy 60-120 eV• Arc source is scalable for large scale cavity coatings• UHV and clean walls important

Substrate RRR

Single crystal insulatorMgO (100) 176MgO (110) 424MgO (111) 197

a-Al2O3 488c-Al2O3 247

Cu large grains 289

Record 585

Nb films grown by Jlab and AASC Almeda Applied Science Corporation. Balk like RRR values

Ch. Reece; JLab

Coaxial Energetic Deposition (CEDTM)

Cathodic arc plasma.

2014-04-16 Claire Antoine Eucard2 WP12 Meeting @ Saclay | PAGE

T

J

H HC2

HSH

HC1

thin films technologies for srf eucard2 wp12.2 thin films prospectives

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