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