Enhancement of First Penetration
Field in Superconducting Multi-layers
              Samples



                          ...
High field dissipations
  Theoretical Work from Gurevich : Non linear BCS resistance

 A. Gurevich, "Multiscale mechanisms...
High field dissipations

           HC1 Nb3Sn (0.05 T)                             HC1 Nb (0.17 T)

        1E+12

       ...
High field dissipations
  Theoretical Work from Gurevich : Non linear BCS resistance

 A. Gurevich, "Multiscale mechanisms...
Breaking Niobium monopoly
Overcoming niobium limits (A.Gurevich, 2006) :

        Keep niobium but shield its surface from...
High Tc nanometric SC films : low RS, high HC1
                                                                           ...
Samples and HC1 issues
 Choice of model samples:
        It is easier to change parameters on sample than on cavities : e....
High quality model samples
  Choice of NbN:
          ML structure = close to Josephson junction preparation (SC/insulator...
Characterization:
          Standard characterization : material quality (collabn
        CEA/INAC-Grenoble)
            Q...
Magnetic characterization : SQUID (1)
Principle of measurement (5x5mm2 samples) :
 Parallel and perpendicular field tested...
SQUID (2) : references @ 4.5 K

Nb(250 nm) :
                                                           NbN(30 nm)




   ...
SQUID (3) : SL Sample @ 4.5 K




  High quality NbN film (Tc =16.37K)

  Strong anisotropic behavior

  Longitudinal mome...
SQUID (4) : ML Sample @ 4.5 K
  ML sample : 250 nm Nb + 4 x (14 nm MgO + 12 nm NbN )
  Similar behavior as SL
  Instabilit...
SQUID : ISSUES

  Strong screening effect observed although
sample is in uniform field (!?)
    Edge, shape, alignment iss...
Local magnetometry (1)
3rd harmonic measurement, coll. INFM Napoli
    M. Aurino, et al., Journal of Applied Physics, 2005...
Local magnetometry (2)
         3rd harmonic measurement, coll. INFM Napoli
                 b0cos         ) applied in th...
Local magnetometry (3)
                        18
                         100

                        16 90
            ...
Local magnetometry (4)
               Sample SL : small Nb signal @ ~TcNb : Nb is sensed through the NbN layer !
         ...
Local magnetometry (4)
                                                                  copper rod
                      ...
Future : Depositing and testing RF cavities
                                                     TE011,
            deposi...
Conclusions et perspectives:

    When no edge effect (i.e. demagnetization factor) is
involved, magnetic screening of NbN...
Compléments




CEA/DSM/Irfu/SACM/Lesar       Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010   23
Adjustment of coil distance
                                   glue                                              glue + co...
Multilayers optimization
SC structure optimization
Deposition techniques optimization                          Nb
        ...
Bulk Nb ultimate limits : not far from here !
                                                                            ...
Rappels sur les principaux supras


   Matériau         TC (K)      n        HC           HC1              HC2            ...
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Antoine - Enhancement of First Penetration Field in Superconducting Multi-layers Samples

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Enhancement of First Penetration Field in Superconducting Multi-layers Samples (Claire Antoine - 30')
Speaker: Claire Antoine - CEA | Duration: 30 min.
Abstract
In 2006 Gurevich proposed to use nanoscale layers of superconducting materials with high values of Hc > Hc (Nb) for magnetic shielding of bulk niobium to increase the breakdown field of Nb RF cavities.

We have deposited high quality “model” samples by DC magnetron reactive sputtering on R-plane cut sapphire substrates. A 250 nm layer of niobium figures the bulk material as in rf cavities. Such Nb layers were coated with a single or multiple stacks of NbN layers (25 nm or 12 nm) separated by 15 nm MgO barriers, and characterized by X-rays reflectivity and DC transport measurements.

The first magnetic penetration field HC1 has been measured with dc magnetization curves in a SQUID system and with a local probe method based on 3rd harmonic analysis. The Nb samples coated with NbN multi-layers clearly exhibit a higher first penetration field, and the screening effect of the NbN layer was evidenced.

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Antoine - Enhancement of First Penetration Field in Superconducting Multi-layers Samples

  1. 1. Enhancement of First Penetration Field in Superconducting Multi-layers Samples C. Z. ANTOINE, S. BERRY CEA, Irfu, Centre d'Etudes de Saclay, 91191 Gif-sur-Yvette Cedex, France M. AURINO, J-F. JACQUOT, J-C. VILLEGIER, CEA, INAC, 17 Rue des Martyrs, 38054 Grenoble-Cedex-9, France G. LAMURA CNR-SPIN-GE, corso Perrone 24, 16124 Genova, Italy A. ANDREONE CNR-SPIN-NA and Dipartimento di Scienze Fisiche, Università di Napoli Federico II, Piazzale Tecchio 80, 80125 Napoli, Italy The Fourth International Workshop on Thin Films and New Ideas for pushing the limits of RF Superconductivity CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 1
  2. 2. High field dissipations Theoretical Work from Gurevich : Non linear BCS resistance A. Gurevich, "Multiscale mechanisms of SRF breakdown". Physica C, 2006. 441(1-2): p. 38-43 A. Gurevich, "Enhancement of RF breakdown field of SC by multilayer coating". Appl. Phys.Lett., 2006. 88: p. 12511. P. Bauer, et al., "Evidence for non-linear BCS resistance in SRF cavities ". Physica C, 2006. 441: p. 51–56 Classical model (BCS) : dissipations calculated @ T ~Tc, clean limit “rf pair breaking” induces non linear corrections which increase when T At high field : quadratic variation of RBCS => Vortex ~ some nm Hot spot ~ some mm cm (comparable to what is observed on cavities) High field dissipation threshold = 1st penetration des vortex (HC1) Nb is the best for SRF because it has the highest HC1, …. CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 2
  3. 3. High field dissipations HC1 Nb3Sn (0.05 T) HC1 Nb (0.17 T) 1E+12 Nb3Sn 1E+11 Nb Bulk Nb3Sn cavity : Qo 1E+10 • High Q0 @ low field QUENCH => low Rres 1E+09 • Early Q slope 1E+08 0 10 5 20 10 30 15 40 20 50 25 60 30 70 35 Epk (MV/m) 1.5 GHz Nb3Sn cavity (Wuppertal, 1985) 1.3 GHz Nb cavity (Saclay, 1999) CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 3
  4. 4. High field dissipations Theoretical Work from Gurevich : Non linear BCS resistance A. Gurevich, "Multiscale mechanisms of SRF breakdown". Physica C, 2006. 441(1-2): p. 38-43 A. Gurevich, "Enhancement of RF breakdown field of SC by multilayer coating". Appl. Phys.Lett., 2006. 88: p. 12511. P. Bauer, et al., "Evidence for non-linear BCS resistance in SRF cavities ". Physica C, 2006. 441: p. 51–56 Classical model (BCS) : dissipations calculated @ T ~Tc, clean limit “rf pair breaking” induces non linear corrections which increase when T At high field : quadratic variation of RBCS => Vortex ~ some nm Hot spot ~ some mm cm (comparable to what is observed on cavities) High field dissipation threshold = 1st penetration des vortex (HC1) Nb is the best for SRF because it has the highest HC1, Nb is close to its ultimate limits (normal state transition) Increasing the field = > avoiding vortices penetration CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 4
  5. 5. Breaking Niobium monopoly Overcoming niobium limits (A.Gurevich, 2006) : Keep niobium but shield its surface from RF field and prevent vortex penetration Use nanometric films (w. d < ) of higher Tc SC : => HC1 et Hs enhancement Example : NbN , = 5 nm, = 200 nm HC1 = 0,02 T & Hs = 0,23 T, x 200 x ~ 30 20 nm film => H’C1 = 4,2 T & H’s = 6,37 T (similar improvement with MgB2 or Nb3Sn) NbN 1 Nb R BCS 10 R BCS => Q0multi >> Q0Nb CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 5
  6. 6. High Tc nanometric SC films : low RS, high HC1 Magnetic field B (mT) 160 Happlied 1E+12 80 Quality coefficient Q0 1E+11 HNb Cavity's internal Outside wall surface → 1E+10 Nd HNb Happl e 1E+09 0 20 40 60 Accelerating Field Eacc (MV/m) Composite nanometric SC : Multilayers Nb / insulator/ superconductor / insulator /superconductor… Bulk Nb prevents perpendicular vortex penetration (surrounding field) Insulating layer ~ 15 nm : Josephson decoupling High Tc SC : d ~ some 10 nm High HS Magnetic screening for parallel vortex Lower RBCS Q0 ↑↑ CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 6
  7. 7. Samples and HC1 issues Choice of model samples: It is easier to change parameters on sample than on cavities : e.g. Easier to get good quality layers on small surfaces Change of substrate nature : sapphire, monocrystalline Nb, polycrystalline Nb, surface preparation. Optimization of SC thickness, number of layer, etc. But ! HC1 measurement is more difficult with classical means (DC). Note that HC1DC ≤ HC1RF ≤ HC => any DC or low frequency measurement is conservative compare to what is expected if RF. HC1 give an estimation of the maximum field achievable without dissipation : if I keep below HC1, I don't really have to care about what exactly HSH is, what the (complex!) behavior of vortices is, etc. Still need RF test to estimate RS/Q0 CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 7
  8. 8. High quality model samples Choice of NbN: ML structure = close to Josephson junction preparation (SC/insulator compatibility) Use of asserted techniques for superconducting electronics circuits preparation: Magnetron sputtering Flat monocrystalline substrates ~ 25 nm NbN ~ 15 nm insulator (MgO) 250 nm Nb “bulk” Reference sample R Test sample SL Monocrystalline sapphire ~ 12 nm NbN x4 14 nm insulator (MgO) 250 nm Nb “bulk” Monocrystalline sapphire Test sample ML Collaboration avec J.C. Villégier, CEA-Inac / Grenoble CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 8
  9. 9. Characterization: Standard characterization : material quality (collabn CEA/INAC-Grenoble) Quantum design PPMS: Tc, conductivity X Rays : low angle diffusion : Peaks/phases Identification : Monocrystalline or highly (200) textured layers Distortions :d(200) on NbN expanded: ~ 0,5 % X Rays : reflectivity: thickness and interface roughness Quantum design physical properties measurement system (PPMS): Reference Thickness Roughness Sample SL Thickness Roughness Sample ML** Thicknes Roughness Sample R* (nm) (nm) Tc = 16.37 K (nm) (nm) Tc = 15.48 K s (nm) (nm) Tc = 8.9 K Nb 250 1 Nb 250 1 Nb 250 1 MgO 14 1 MgO 14 1 MgO *** 14 1 NbN 0 0 NbN 25 1.5 NbN 12 1.5 * Sample R contains only Nb capped with a layer of NbO. Obtained by RIE etching of sample SL. ** In ML the motive MgO/NbN is repeated 4 times. *** except the external, capping layer which is 5 nm CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 9
  10. 10. Magnetic characterization : SQUID (1) Principle of measurement (5x5mm2 samples) : Parallel and perpendicular field tested B //, longitudinal moment Thin films in parallel configuration (B//): Quartz 1. Strong transverse signal vs longitudinal => the longitudinal holder component appears non purely dipolar (superposition of 2 signals) Detection 2. Strong sensitivity of M to the angle between the sample coils B Sample surface and the applied field B (alignment should be better than 0.005°). Development of a dedicated fitting procedure 1. Fourier transform 2. Separation of the odd signal from the even signal B //, transverse moment 3. Reverse Fourier transform 4. Fitting Sample Oriented quartz Longitudinal signal holder Actual longitudinal B component Detection Transverse coils component (cross talk) Usual dipolar signal Signal as detected in the long. Loop : strong even signal is due to “crosstalk " with the transverse moment CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010
  11. 11. SQUID (2) : references @ 4.5 K Nb(250 nm) : NbN(30 nm) "Elemental" layers : isotropic. HP ~ 18 mT = compatible with magnetron sputtered films No field enhancement on 30 nm NbN layer !? CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010
  12. 12. SQUID (3) : SL Sample @ 4.5 K High quality NbN film (Tc =16.37K) Strong anisotropic behavior Longitudinal moment : Fishtail shape characteristic of layered SC HP ~ 96 mT (+ 78 mT /Nb alone) !!! Similar behavior with ML CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010
  13. 13. SQUID (4) : ML Sample @ 4.5 K ML sample : 250 nm Nb + 4 x (14 nm MgO + 12 nm NbN ) Similar behavior as SL Instabilities in 1rst and 3rd quadrant (vortices jumps ?) NbN lowest quality (Tc= 15.48K) CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010
  14. 14. SQUID : ISSUES Strong screening effect observed although sample is in uniform field (!?) Edge, shape, alignment issues => is BP ~ BC1 ? Perpendicular remnant moment => what is the exact local field ? DC instead of RF : not a problem; BC1 is expected to be higher in RF => need to get rid of edge effects => need to get local measurement ! CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010
  15. 15. Local magnetometry (1) 3rd harmonic measurement, coll. INFM Napoli M. Aurino, et al., Journal of Applied Physics, 2005. 98: p. 123901. Perpendicular field : field distribution can be determined analytically. If rsample> 4 rcoil : Sample ≡ infinite plate Applied field : perpendicular, induction (B ) // surface Differential Locking Amplifier Excitation/Detection coil (small/sample) CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 15
  16. 16. Local magnetometry (2) 3rd harmonic measurement, coll. INFM Napoli b0cos ) applied in the coil temperature ramp third harmonic signal appears @ Tb0 series of b0 => series of transition temperature => BC1 (T)) = T/Tc Sample SL : third harmonic signal for various b0 CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 16
  17. 17. Local magnetometry (3) 18 100 16 90 ref ref 14 80 SL 12 70 SL 60 B (mT) 10 B (mT) 50 8 SQUID results 40 6 30 4 20 2 10 0 0 0 0 2 2 4 4 6 6 8 8 10 10 12 12 14 14 16 16 18 18 T (K)(K) T SL sample : 250 nm Nb + 14 nm MgO + 25 nm NbN 8.90K < Tp° < 16K : behavior ~ NbN alone Tp°< 8.90K, i.e. when Nb substrate is SC , => BC1SL >> BC1Nb Need to extend measure @ higher field and lower temperature CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 17
  18. 18. Local magnetometry (4) Sample SL : small Nb signal @ ~TcNb : Nb is sensed through the NbN layer ! Since the Nb layer feels a field attenuated by the NbN layer, the apparent transition field is higher. This curve provides a direct measurement of the attenuation of the field due to the NbN layer 2 Nb Ref 1.5 Nb/SL B (mT) 1 0.5 0.04 0.03 Nd 0 0.02 HNb Happl e 8 8.5 9 0.01 0 BC1 curves for Niobium in the reference (direct T (K) 5 7 9 measurement) and in SL (under the NbN layer). CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 18
  19. 19. Local magnetometry (4) copper rod (thermalization of electrical wires) spring coil support (high glass coil conductivity bead copper) Coil :  ∅int : sample 1mm, ∅ ext : thermal 5mm, L : 2,25 braid mm  Wire: ∅ 32µm  Spires : 2800  Bmax ~ 30 mT sample support High (estimation from temperature heating steel (high conductivity conductivity sensor max J) wire rods copper) copper plate coil with ext. ∅ : 5 mm => samples with ∅> 13 mm ≡ infinite plane thermal regulation : 1.6 K <Tp°< 40K, automated 100 to 200 mT available soon CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 20
  20. 20. Future : Depositing and testing RF cavities TE011, depositing and testing RF Cavities: ~3 GHz IPNO IPN (Orsay) : 3GHz, LKB (Paris) : 50GHz Cavités 1.3 GHz @ Saclay (what deposition technique?!) 1.3 GHz Irfu 50 GHz LKB CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 21
  21. 21. Conclusions et perspectives: When no edge effect (i.e. demagnetization factor) is involved, magnetic screening of NbN is effective even in perpendicular field This result is very encouraging regarding cavities situation Local magnetometry is a convenient tool for sample characterization : ML structure optimization (SC, thickness, number of layers, substrate preparation…) Evaluation of various deposition techniques We are open to collaboration if you want to test samples ! CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 22
  22. 22. Compléments CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 23
  23. 23. Adjustment of coil distance glue glue + copper powder glass bead wedge : 60 µm coil CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 24
  24. 24. Multilayers optimization SC structure optimization Deposition techniques optimization Nb NbN Magnetron sputtering Inac (Grenoble), Al2O3 Atomic Layer Deposition INP (Grenoble) MgO Cu Metallic substrates more realistic): From samples to cavities : ALD involves the use of a pair of reagents Application of this AB Scheme Reforms a new surface Adds precisely 1 monolayer Viscous flow (~1 Torr) allows rapid growth No line of site requirements => uniform layers, larges surfaces, well adapted to complex shapes : cavities! up grade of existing cavities ? CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 26
  25. 25. Bulk Nb ultimate limits : not far from here ! Cavité 1DE3 : EP @ Saclay T- map @ DESY Film : courtoisie A. Gössel + D. Reschke (DESY, Début 2008) The hot spot is not localized : the material is ~ equivalent at each location => cavity not limited /local defect, but by material properties ? CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 27
  26. 26. Rappels sur les principaux supras Matériau TC (K) n HC HC1 HC2 L Type (µWcm) (Tesla)* (Tesla)* (Tesla)* (nm)* Pb 7,1 0,08 n.a. n.a. 48 I Nb 9,22 2 0,2 0,17 0,4 40 II Mo3Re 15 0,43 0,03 3,5 140 II NbN 16,2 70 0,23 0,02 15 200 II V3Si 17 II NbTiN 17,5 35 0,03 151 II Nb3Sn 18,3 20 0,54 0,05 30 85 II Mg2B2 40 0,43 0,03 3,5 140 II- 2gaps YBCO 93 1,4 0,01 100 150 d-wave CEA/DSM/Irfu/SACM/Lesar Claire Antoine –Thin Films Workshop, Padua, October 4 –6, 2010 28

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