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Thin films technologies for SRF EUcard2 WP12.2 Thin films prospectives

Thin films technologies for SRF EUcard2 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

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Thin films technologies for SRF EUcard2 WP12.2 Thin films prospectives

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  1. 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

  2. Outlook • Introduction • Characterization tools • Deposition technique • Physics of SRF and advanced superconductors • Multilayers • Conclusion

  3. Introduction Claire Antoine Eucard2 WP12 Meeting @ Saclay

  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 copper • Higher Tc => higher Q0 • Higher HSH or HC1 => 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 (HSHvs HC1) still controverted => choice of ideal material !? • 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) • Cost • Innovative materials • Optimization of RBCSpossible • Disadvantages • Fabrication and surface preparation (at least) as difficult as for bulk • Superconductivity very sensitive to crystalline quality (lower in thin films for now) Claire Antoine Eucard2 WP12 Meeting @ Saclay

  5. Thin films Challenges: depends on the strategy Optimizing structure/composition of the films on samples Optimizing deposition inside cavities • 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 • 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 Eucard2 WP12 Meeting @ Saclay

  6. 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 Claire Antoine Eucard2 WP12 Meeting @ Saclay

  7. Characterization tools developments(task 3) Claire Antoine Eucard2 WP12 Meeting @ Saclay

  8. “Sample cavities” • Quadrupole resonnator developed at HZB • See O. Kugeler’s talk (HZB activities) • TE011 cavity developped at IPNO Claire Antoine Eucard2 WP12 Meeting @ Saclay

  9. Differential Locking Amplifier Excitation/Detection coil (small/sample) = T/Tc 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 ) Bz(a,u,) 0 Br (a,u,) 0 1 2 3 4 5 6 r/r0 0 1 2 3 4 5 6 r/r0 Claire Antoine Eucard2 WP12 Meeting @ Saclay

  10. Deposition techniques Issues(task 1 and task 2) Claire Antoine Eucard2 WP12 Meeting @ Saclay

  11. 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 Claire Antoine Eucard2 WP12 Meeting @ Saclay

  12. Deposition techniques: International situation • CERN • Nb bulk like: Magnetron sputtering, HPIMS (collaboration with Sheafield University) • Nb3Sn (diffusion furnace) : in project • Grenoble INP • ML: ALD and CVD • STFC • Nb, ML: PVD and ECR –CVD • Jlab and collaborators • At Jlab : ECR, HPIMS • AlmedaCorpn: CED (Plasma) • W&M : magnetron sputtering + Complete material characterization • Cornell • Nb3Sn (diffusion furnace) • Temple University • MgB2 (HP-CVD), ML in collaboration with LANL and FNAL • ANL • ML: ALD • INFN Legnaro • NbN(diffusion furnace) • Large experience on sputtering, Nb3Sn… Publications on that topic at SRF 2013: 23 Claire Antoine Eucard2 WP12 Meeting @ Saclay

  13. HPIMS @ cern: bulk-like thin films • See G. Terenziani’s talk Claire Antoine Eucard2 WP12 Meeting @ Saclay

  14. 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 Claire Antoine Eucard2 WP12 Meeting @ Saclay

  15. Understanding the physics of SRF(task 3)Advanced superconductors(task 2) Claire Antoine Eucard2 WP12 Meeting @ Saclay

  16. SRF limits : back to basics • Q0 (1/Thermal dissipations) • depends on surface resistance … which depends on Tc • Higher 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 !!! Claire Antoine Eucard2 WP12 Meeting @ Saclay

  17. SRf : HC1 vs HSH Cavities : Meissner State, H~ HC1, J~JD (@ HC1), T~2-4 K ? HSH Coils : higher TC, but mixed state (low HC1) Generally low magnetic field • Reaching higher field (Eacc/BRF) • => Reach superheating field (metastable Meissner state) : Nb3Sn, MgB2… • => Artificially enhance HC1 : Multilayers Claire Antoine Eucard2 WP12 Meeting @ Saclay

  18. Nb3Sn: recent breakthrough • At 4,2 K Q0Nb3Sn = 20 x Q0Nb !!! • At 2 KQ0Nb3Sn ~ Q0Nb • Limited in Eacc Claire Antoine Eucard2 WP12 Meeting @ Saclay

  19. Nb3Sn: recent breakthrough Hays. "Measuring the RF critical field of Pb, Nb, NbSn". in SRF 97. 1997. Cornell, 1997 pulsed Recent results from Cornell CW HC1Nb3Sn(~27mT) • HC1 is not a fundamental limit for SRF • but • Is it a practical limitation ? • NB : HSH is more easily observed : • Close to Tc (cf Yogi) • Pulsed RF Claire Antoine Eucard2 WP12 Meeting @ Saclay

  20. 1.5 GHz Nb3Sn cavity (Wuppertal, 1985) 1.3 GHz Nb cavity (Saclay, 1999) Nb3Sn: a lot of room for improvement HP Nb3Sn 0.03T (H°C1=0.05 T) HPNb 0.12 T (H°C1=0.17 T) Nb3Sn Nb Claire Antoine Eucard2 WP12 Meeting @ Saclay

  21. Advanced superconductors :Multilayers Claire Antoine Eucard2 WP12 Meeting @ Saclay

  22. B(mT) Q0 Eacc(MV/m) Alternative to bulk SC: Multilayers • 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 >> Q0Nb (SC with higher Tc than Nb) In principle : Nb I-S-I-S- Happlied HNb Cavity'sinternal surface → Outsidewall  * In theory 20 nm NbN : HC1 x ~200 ** Simplified model from Gurevich Claire Antoine Eucard2 WP12 Meeting @ Saclay

  23. Field screening / thin field Infinite plane Single layer Thin film in a uniform field B B B B Simple Model (Gurevich, 2006) Modified Model (Kubo, 2013) (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 NbN, Nb3Sn, MgB2 • Similar calculation also proposed by S. Posen for Nb3Sn only Claire Antoine Eucard2 WP12 Meeting @ Saclay

  24. Optimum thickness for SL ? • T. Kubo • SL/ML structures not effective for Nb3Sn • Contrary to simple model, very thin layers are not interesting • Optimum 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 Claire Antoine Eucard2 WP12 Meeting @ Saclay

  25. results from other labs [Lukaszew, W&M 2012] ~30(*) or 50 nm (**)NbN * ~ 15 nm insulator (MgO) 600(*) / 250(**) nm Nb “bulk like” MgO (100) substrate ** • Compare with what is expected for bulk Nb : ~1300 Oe @ 4.5 K ! Claire Antoine Eucard2 WP12 Meeting @ Saclay

  26. MgB2-MgO Multilayer Films MgB2 MgO MgB2 MgO MgB2 Sapphire • 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 HC1than the 300 nm film even though the total thickness are the same. [Teng, Xi – Temple University] Claire Antoine Eucard2 WP12 Meeting @ Saclay

  27. [Tajima, SRF 2011] Claire Antoine Eucard2 WP12 Meeting @ Saclay

  28. Magnetometry Early results CZ Antoine, JC Villegier, G Martinet, Applied Physics Letters 102 (10), 102603-102603-4 • 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 Claire Antoine Eucard2 WP12 Meeting @ Saclay

  29. Thermal analysis 50 nm NbN ~ 15 nm insulator (MgO) Bulk LG Nb Polycrystalline Nb substrate Large grain Nb substrate • Same calibration • Rs rf-ML2<< Rs Nb • NB. Current: ½I in Nb • ½I in NbN • Strong indication that RBCS is improved with ML • Could probably be improved with the use of thicker layers (complete screening) • Rresis higher for ML than for Nb, but strongly influenced by substrate ? • Very promising preliminary results Claire Antoine Eucard2 WP12 Meeting @ Saclay

  30. 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 Claire Antoine Eucard2 WP12 Meeting @ Saclay

  31. Thank you for your attention 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 IrfuSACMLIDC2 Claire Antoine Eucard2 WP12 Meeting @ Saclay

  32. Spares Claire Antoine Eucard2 WP12 Meeting @ Saclay

  33. Coaxial Energetic Deposition (CED) Cathodic arc plasma. • Ions Energy 60-120 eV • Arc source is scalable for large scale cavity coatings • UHV and clean walls important Coaxial Energetic Deposition (CEDTM) Nb films grown by Jlab and AASC Almeda Applied Science Corporation. Balk like RRR values Ch. Reece; JLab

  34. H HC2 HSH HC1 T J Claire Antoine Eucard2 WP12 Meeting @ Saclay

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