Lobanov - Nb-sputtered 150 MHz Quarter-wave Resonators for ANU Linac Upgrade

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Nb sputtered 150 MHz quarter-wave resonators for ANU LINAC Upgrade (Nikolai Lobanov - 20')
Speaker: Nikolai Lobanov - The Australian National University | Duration: 20 min.

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Lobanov - Nb-sputtered 150 MHz Quarter-wave Resonators for ANU Linac Upgrade

  1. 1. Nb-sputtered 150 MHz Quarter-wave Resonators for ANU Linac Upgrade <ul><li>Pb-Sn technology </li></ul><ul><li>Multi-stub resonators update </li></ul><ul><li>Choice of Nb-coated QWRs </li></ul><ul><li>Other thin films srf applications </li></ul>October 2010 Nikolai Lobanov Nuclear Physics, RSPE, ANU
  2. 2. October 2010
  3. 3. Largest scale application of sc in Australia October 2010
  4. 4. Module cryostat with 3 SLRs October 2010
  5. 5. October 2010 Phase Diagram of Superconductors Ginzburg-Landau Parameter k GL =  L /  0 : k GL <0.71 Type I k GL >0.71 Type II  nucleate fluxoide ~10 -6 s » T rf ~10 -9 s so s/c persists up to H sh >H c H sh  0.89H c / k GL 0.5 for k GL « 1 H sh  1.2H c for k GL  1 H sh  0.75H c for k GL » 1 Phase diagram from Yogi Thesis 1977
  6. 6. Properties of Superconductors October 2010 Lattices from cst-www.nrl.navy.mil/lattice/struk Material Pb Pb96 % Sn4% Nb (bulk) Nb (film) Nb 3 Sn YBCO MgB 2 (dirty) T c , K 7.2 9.2 18.2 90 39  /kT c 2.1 1.86 2.25  L(o) , nm  ( 20C150MHz ) ,  28 18.7 36 15.6 65 200 a-b 1000 c 140  0 , nm 111 64 6 1.5 6 l (0) , nm Mean free path 1000 90 30 1.0 k GL 0.5-2 ~1 3-12 20 100 H c1 , Oe - 1700 200 H c (term) , Oe 800 2000 5350 H c2 , Oe - 2400 22000 >100 T 24500 H SH , Oe 1000 2400 4000 Lattice FCC Sn:BCT BCC
  7. 7. Low field surface resistance: Pb, Nb, Nb 3 Sn October 2010 In RF shielding of E field by supercurrent is incomplete due to inertia of e - so normal e - interact with E-field dissipating energy (two-fluid model by London) RF surface resistance based on Bardeen Cooper Schrieffer (BCS) theory: R BCS =A (  L ,  0 ,v F , l ) T -1 f  exp(-  (T) /kT)+R 0 ,  2, R 0 - residual resistance R BCS calculated from Halbritter program R BCS =0.89x10 -4 T -1 f 2 exp(-17.67/T) R BCS =0.94x10 -4 T -1 f 2 exp(-39.6/T) R BCS =0.69x10 -4 T -1 f 1.9 exp(-15.1/T) Pb98%Sn2% NIM PR A284(1989) 294 Nb Padamsee RFS for Acclerators 1998 p88 Nb 3 Sn Padamsee Supercond.Sci.Tech.14 (2001)R39
  8. 8. October 2010 Low field BCS & Residual Resistance: Pb Delayen 3 rd SRF Yogi Thesis high frequency: R s is dominated by R BCS at T >2.5 K low frequency: R s is dominated by R res at T=1.8-4.3 K R (T) =R BCS +R RES  117 n 
  9. 9. October 2010 High-field Performance: low  Nb and Nb/Cu Bulk Nb cavities M Kelly RFSC Limits 160 MHz 11% Nb/Cu ALPI QWRs:  =29  R BCS =70-145 n  Porcellato 12 th SRF
  10. 10. October 2010 High H -field Performance: Pb Yogi Thesis Test with sample in the middle of Helical s/c Nb coil low E-field Below H tr : loss due to week s/c links in grain boundaries Above H tr : loss due to H-field enhancement by sharp edges As thin as possible!
  11. 11. Pb-Sn Plating SLRs at ANU: Problems Low melting point metals like Pb and Sn take a long time to solidify and the corresponding surface diffusion distance becomes long resulting in formation of large grains. October 2010 At some plating condition a dendrite can be generated.
  12. 12. High E,H - fields Performance: Pb (cont) October 2010 <ul><li>Mechanical polishing of pre-plated 1 µ PbSn surface </li></ul><ul><li>Reverse pulse plating high quality 0.3 µ PbSn cosmetic layer over it </li></ul>H tr =370 Oe Plating Pb96%-Sn4% at ANU, R SURF  130 n  at 6 W H tr =262 Oe Delayen 3 rd SRF+2005 discussion @ Jefferson Curve E: decreased FE and increased other loss mechanisms
  13. 13. Pb-Sn Plating SLRs: Results October 2010 This procedure has proven to be successful in re-plating 12 ANU SLRs including 4 resonators with cracks in electron-beam weld.
  14. 14. Substrate preparation October 2010 tumbling degreasing
  15. 15. Superconductor coating laboratory October 2010 high pressure rinsing GN 2 drying PbSn plating
  16. 16. Clean room facilities class ~500 October 2010 assembling SLR and module cryostat
  17. 17. Characterization of sc films October 2010
  18. 18. Intermodulation distortion technique for SLRs October 2010
  19. 19. Twin stub resonator status I October 2010
  20. 20. Twin stub resonator status II October 2010 <ul><li>Cold test delayed due to vacuum failure </li></ul><ul><li>Doughnuts geometry is </li></ul><ul><li>to be changed to suppress </li></ul><ul><li>multipackting </li></ul>
  21. 21. October 2010 Pushing the Limits of SRF Pb For SLR H p /E acc = 105 Oe/MV/m leading to E acc =5 MV/m (limited by H c ) and E acc =6.1 MV/m (limited by H sh ) For Pb at 4.3 K H c =H (0) (1-(T/T c ) 2 )= 530 Oe and H sh =1.2H c =636 Oe Data for PbSn alloys is not available, the best ANU SLR operates at E acc =3.9 MV/m limited by FE <ul><li>Plating final layer ~0.1  at over-potential (higher current density) </li></ul><ul><li>Plating multi-layers of Pb and PbSn alloys </li></ul><ul><li>Vacuum annealing or melting crystalline Pb film to make it amorphous </li></ul><ul><li>High power and helium processing on-line at 1kW peak RF power </li></ul><ul><li>RF gasket conditioning (PbSn pre-plating of lead wire) </li></ul><ul><li>Fundamental SRF properties of Pb, PbSn films shall be further investigated </li></ul><ul><li>ANY MORE IDEAS? </li></ul>Pushing the Limits of Pb:
  22. 22. October 2010 Nb/Cu SRF & TF Technology Common features: Base Pressure <10 -8 Torr; Bias Substrate –60  -100 V; Substrate temperature 100-500 C°. Challenges: Complex Geometry and Hydrides in bulk-like films Magnetron CERN, ACCEL, Cornell, ANU DC Cathode INFN Legnaro ECR *) JLAB Vacuum Arc *) , INFN A.Soltan HPPM *) , CERN Laser Ablation, JLAB Dep. Rate  /hour 0.5-6 0.5 1.5 2-3 10 6-72 RRR 5-10 10 20-100 20-100 - -
  23. 23. Latest developments <ul><li>EIF Funds available over the next 4 years to upgrade Linac with 4-8 resonators: Nb-coated QWRs ? Collaborators are welcome </li></ul><ul><li>Another EIF project is Re-buncher @1.2 MV/m. Can we make it of MgB2 or HTS? </li></ul><ul><li>What about sc (HTS) phase detector installed in the Linac cryostat? </li></ul><ul><li>ACAS collaboration between ANU, UM, ANSTO and AS has been launched on 13 th July 2010 http://epp.physics.unimelb.edu.au/ACAS </li></ul>October 2010
  24. 24. <ul><li>Thank you ! </li></ul>October 2010

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