THIN FILMS TECHNOLOGIES FOR SRF EUCARD 2 WP

THIN FILMS TECHNOLOGIES FOR SRF EUCARD 2 WP 12. 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 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 3 2014 -04 -16

WHY THIN FILMS ? 2 REASONS Making cheaper cavities : Overcoming Nb monopoly: Bulk like Nb on copper (1 -5 µm) Nb 3 Sn, Mg. B 2, Multilayers… Advantages Nb : l~50 nm => only a few 100 s nm of SC necessary (the remaining thickness= mechanical support only) => Make thin films ! Advantages Thermal stability (substrate cavity = copper) Cost Innovative materials Optimization of RBCS possible Disadvantages Fabrication and surface preparation (at least) as difficult as for bulk Superconductivity very sensitive to crystalline quality (lower in thin films for now) 2014 -04 -16 Can also be deposited onto copper Higher Tc => higher Q 0 Higher HSH or HC 1 => higher accelerating field Disadvantages Fabrication and surface preparation (at least) as difficult as for bulk Superconductivity very sensitive to crystalline quality (lower in thin films for now) Deposition of innovative (compound) materials is very difficult Theoretical limit (HSH vs HC 1) still controverted => choice of ideal material !? Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 4

THIN FILMS CHALLENGES: DEPENDS ON THE STRATEGY Optimizing structure/composition of the Optimizing deposition inside cavities films on samples Advantages Structure /composition can be optimized with conventional techniques Ideal structure and composition can be achieved on model sample (guide for deposition of cavities) Cost Disadvantages RF performances cannot be directly measured Specific measurement tools need to be developed (sample cavity, magnetometer…) Ultimately a cavity deposition set-up will be needed, but with a known aimed structure 2014 -04 -16 Advantages RF testing easy and gives direct performance Work is done only once, direct cavity production Disadvantages Very heavy and lengthy, many parameters Need to develop a specific cavity deposition set-up Difficult to optimize set-up and film together Optimization of the structure/composition of the film is difficult Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 5

STRUCTURE OF THE TASK 12. 2 (EUCARD 2) Niobium on copper (µm) After ~ 20 years stagnation : new revolutionary deposition techniques Great expectations in cost reduction No improved performances/ bulk Nb k tas b Su 1 Higher Tc material (µm) Based on superheating model. Higher field and lower Q 0 expected Subtask 2 Higher Tc material (nm), multilayer Based on trapped vortices model (Gurevich) Higher field and lower Q 0 expected Recent experimental evidences Specific characterization tools needed k Better understanding of SRF physics needed 2014 -04 -16 tas b Su 3 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 6

CHARACTERIZATION TOOLS DEVELOPMENTS (TASK 3) Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 7 2014 -04 -16

“SAMPLE CAVITIES” Quadrupole resonnator developed at HZB See O. Kugeler’s talk (HZB activities) TE 011 cavity developped at IPNO 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 8

LOCAL MAGNETOMETRY DEVELOPED @CEA Measurement of HC 1 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 ) Bz (a, u, ) Differential Locking Amplifier Br (a, u, ) 0 0 1 2 3 4 r/r 0 5 6 Excitation/Detection coil (small/sample) 0 1 2 3 4 5 6 r/r 0 = T/Tc 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 9

DEPOSITION TECHNIQUES ISSUES (TASK 1 AND TASK 2) Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 10 2014 -04 -16

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 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 11

DEPOSITION TECHNIQUES: INTERNATIONAL SITUATION CERN Nb bulk like: Magnetron sputtering, HPIMS (collaboration with Sheafield University) Nb 3 Sn (diffusion furnace) : in project Grenoble INP ML: ALD and CVD STFC Nb, ML: PVD and ECR –CVD Jlab and collaborators At Jlab : ECR, HPIMS Almeda Corpn: CED (Plasma) W&M : magnetron sputtering + Complete material characterization Cornell Nb 3 Sn (diffusion furnace) Temple University Mg. B 2 (HP-CVD), ML in collaboration with LANL and FNAL ANL ML: ALD INFN Legnaro Nb. N (diffusion furnace) Large experience on sputtering, Nb 3 Sn… 2014 -04 -16 Publications on that topic at SRF 2013: 23 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 12

HPIMS @ CERN: bulk-like thin films See G. Terenziani’s talk 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 13

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 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 14

UNDERSTANDING THE PHYSICS OF SRF (TASK 3) ADVANCED SUPERCONDUCTORS (TASK 2) Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 15 2014 -04 -16

SRF LIMITS : BACK TO BASICS Q 0 ( 1/Thermal dissipations) depends on surface resistance … which depends on Tc Higher Tc => higher Q 0 => 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 HC 1 Nb = 180 -190 m. T At w < 3 GHz: we are limited by BRF !!! Cavities : Meissner State, no vortex please !!! 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 16

SRF : HC 1 VS HSH Cavities : Meissner State, H~ HC 1, J~JD (@ HC 1), T~2 -4 K ? HSH Coils : higher TC, but mixed state (low HC 1) Generally low magnetic field Reaching higher field (Eacc/BRF) => Reach superheating field (metastable Meissner state) : Nb 3 Sn, Mg. B 2… => Artificially enhance HC 1 : Multilayers 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE

Nb 3 Sn : RECENT BREAKTHROUGH At 4, 2 K Q 0 Nb 3 Sn = 20 x Q 0 Nb !!! At 2 KQ 0 Nb 3 Sn ~ Q 0 Nb Limited in Eacc 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 18

Nb 3 Sn: RECENT BREAKTHROUGH Hays. "Measuring the RF critical field of Pb, Nb. Sn". in SRF 97. 1997. Cornell, 1997 pulsed Recent results from Cornell CW HC 1 Nb 3 Sn (~27 m. T) but HC 1 is not a fundamental limit for SRF Is it a practical limitation ? NB : HSH is more easily observed : Close to Tc (cf Yogi) Pulsed RF 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 19

Nb 3 Sn : A LOT OF ROOM FOR IMPROVEMENT HP Nb 3 Sn 0. 03 T (H°C 1=0. 05 T) HP Nb 0. 12 T (H°C 1=0. 17 T) Nb 3 Sn Nb 1. 5 GHz Nb 3 Sn cavity (Wuppertal, 1985) 1. 3 GHz Nb cavity (Saclay, 1999) 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 20

ADVANCED SUPERCONDUCTORS : MULTILAYERS Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 21 2014 -04 -16

ALTERNATIVE TO BULK SC: MULTILAYERS Multilayers: Nb / insulator/ superconductor / insulator /superconductor… superconductor : Surface screening and low Rs Thin SC films. d< l => artificial enhancement of HC 1* (SC high with e than r Tc Nb) The thin layers stand high fields without vortex nucleation Niobium surface screening: allows higher field in the cavity => Q 0 multi >> Q 0 Nb In principle : Nb I-S- Happlied B(m. T) 100 HNb Outside wall Cavity's internal surface → Q 0 1 E+12 200 1 E+11 1 E+10 1 E+09 0 20 40 Eacc (MV/m) 60 * In theory 20 nm Nb. N : HC 1 x ~200 ** Simplified model from Gurevich 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 22

FIELD SCREENING / THIN FIELD Infinite plane Single layer B B Simple Model (Gurevich, 2006) Modified Model (Kubo, 2013) Thin film in a uniform field B B (1 of the reasons why measurements with Squid are ambiguous) T. Kubo @ SRF 2013 Made the calculation for exact boundaries condition l, x : known bulk values (not necessary exact for thin films) Applied to Nb. N, Nb 3 Sn, Mg. B 2 Similar calculation also proposed by S. Posen for Nb 3 Sn only 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 23

OPTIMUM THICKNESS FOR SL ? SL/ML structures not effective for Nb 3 Sn T. Kubo Contrary to simple model, very thin layers are not interesting Optimum thickness around 100 nm for Nb. N ? How does that compare with exp. Measurements ? => Series of SL with various thicknesses (50 nm to 150 nm) is needed 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 24

RESULTS FROM OTHER LABS [Lukaszew, W&M 2012] ~30(*) or 50 nm (**) Nb. N ~ 15 nm insulator (Mg. O) * 600(*) / 250(**) nm Nb “bulk like” Mg. O (100) substrate ** Compare with what is expected for bulk Nb : ~1300 Oe @ 4. 5 K ! 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 25

Mg. B 2 -Mg. O MULTILAYER FILMS Mg. B 2 Mg. O Mg. B 2 Sapphire Alternating Mg. B 2 -insulator structures have been fabricated on sapphire substrate: § 40 nm Mg. O as insulating layer, sputtered. § Mg. B 2 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 Mg. B 2 layers show higher HC 1 than the 300 nm film even though the total thickness are the same. 2014 -04 -16 [Teng, Xi – Temple University] Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 26

[Tajima, SRF 2011] 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 27

MAGNETOMETRY EARLY RESULTS CZ Antoine, JC Villegier, G Martinet, Applied Physics Letters 102 (10), 102603 -4 Magnetic screening evidenced for ML 4 up to 38 m. T, at T~7 K Dramatic transition around 38 m. T => rcoil << rsample not valid anymore ? Magnetometer is effective up to 1500 m. A (equivalent field 150 m. T) Tp° 2 -40 K Use of larger samples/smaller coil is mandatory 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 28

THERMAL ANALYSIS 50 nm Nb. N ~ 15 nm insulator (Mg. O) Bulk LG Nb Polycrystalline Nb substrate Large grain Nb substrate Same calibration Rs rf-ML 2<< Rs Nb NB. Current: ½I in Nb. N Strong indication that RBCS is improved with ML Could 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 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 29

CONCLUSIONS AND PERSPECTIVES Renewed activity on bulk-like Nb films (cost issues) and high HSH SC e. g. Nb 3 Sn or Nb. N (higher performances) ML structures seem to be a promising way to go beyond Nb for accelerator cavities Look for higher Q 0, 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 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 30

THANK YOU FOR YOUR ATTENTION | PAGE 31 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay 2014 -04 -16 Commissariat à l’énergie atomique et aux énergies alternatives Centre de Saclay | 91191 Gif-sur-Yvette Cedex T. +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 DSM Irfu SACM LIDC 2

SPARES Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE 32 2014 -04 -16

COAXIAL ENERGETIC DEPOSITION (CED) Substrate RRR Single crystal insulator Mg. O (100) 176 Mg. O (110) 424 Mg. O (111) 197 a-Al 2 O 3 488 c-Al 2 O 3 247 Cu large grains 289 Record 585 Cathodic arc plasma. • Ions Energy 60 -120 e. V • Arc source is scalable for large scale cavity coatings • UHV and clean walls important Ch. Reece; JLab Nb films grown by Jlab and AASC Almeda Applied Science Corporation. Balk like RRR values Coaxial Energetic Deposition (CEDTM)

H HC 2 HSH HC 1 T J 2014 -04 -16 Claire Antoine Eucard 2 WP 12 Meeting @ Saclay | PAGE