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

Thin Films and New Ideas for SRF 2010

October 2010 1

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

Nikolai Lobanov

Nuclear Physics, RSPE, ANU

Pb-Sn technologyMulti-stub resonators updateChoice of Nb-coated QWRsOther thin films srf applications


October 2010 2


October 2010 3

Largest scale application of sc in Australia


October 2010 4

Module cryostat with 3 SLRs


October 2010 5

Phase Diagram of Superconductors

Ginzburg-Landau ParameterkGL= λL/ ξ0 :

kGL <0.71 Type I

kGL >0.71 Type II

τnucleate fluxoide~10-6 s » Trf~10-9 sso s/c persists up to Hsh>Hc

Hsh≈0.89Hc/ kGL0.5 for kGL«1

Hsh≈1.2Hcfor kGL ≈ 1

Hsh≈0.75Hc for kGL»1

Phase diagram from Yogi Thesis 1977


October 2010 6

Properties of Superconductors

Material

Pb Pb96%

Sn4%Nb (bulk)

Nb (film)

Nb3Sn YBCO MgB2

(dirty)

Tc, K 7.2 9.2 18.2 90 39

∆/kTc 2.1 1.86 2.25λL(o), nm

δ(20C150MHz) ,µ28

18.736

15.665 200 a-b

1000 c140

ξ0, nm 111 64 6 1.5 6l(0), nmMean free path

1000 90 30 1.0

kGL0.5-2 ~1 3-12 20 100

Hc1, Oe - 1700 200

Hc (term), Oe 800 2000 5350

Hc2, Oe - 2400 22000 >100 T 24500

HSH, Oe 1000 2400 4000

Lattice FCC Sn:BCT BCC

Lattices from cst-www.nrl.navy.mil/lattice/struk


October 2010 7

Low field surface resistance: Pb, Nb, Nb3Sn

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:

RBCS=A(λL,ξ0,vF, l) T-1f αexp(-∆(T)/kT)+R0 , α≈2, R0- residual resistance

RBCS calculated from Halbritter program

RBCS=0.89x10-4T-1f 2exp(-17.67/T)

RBCS=0.94x10-4T-1f 2exp(-39.6/T)

RBCS=0.69x10-4T-1f 1.9exp(-15.1/T)

Pb98%Sn2% NIM PR A284(1989) 294

Nb Padamsee RFS for Acclerators 1998 p88

Nb3Sn Padamsee Supercond.Sci.Tech.14 (2001)R39


October 2010 8

Low field BCS & Residual Resistance: Pb

Delayen 3rd SRF

Yogi Thesis

high frequency:Rs is dominated by RBCS

at T >2.5 K

low frequency:Rs is dominated by Rres

at T=1.8-4.3 K

R(T) =RBCS+RRES ≈117 nΩ


October 2010 9

High-field Performance: low β Nb and Nb/Cu

Bulk Nb cavities

M Kelly RFSC Limits

160 MHz 11% Nb/Cu ALPI QWRs:

Γ=29 Ω

RBCS=70-145 nΩPorcellato 12th SRF


October 2010 10

High H-field Performance: Pb

Yogi Thesis Test with sample in the middle of Helical s/c Nb coil low E-field

Below Htr: loss due to week s/c links in grain boundariesAbove Htr: loss due to H-field enhancement by sharp edges

As thin as possible!


October 2010 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.

At some plating condition a At some plating condition a

dendrite can be generated.dendrite can be generated.


October 2010 12

High E,H- fields Performance: Pb (cont) Mechanical polishing of pre-plated 1 µ PbSn

surface Reverse pulse plating high quality 0.3 µ PbSn

cosmetic layer over itHtr=370 Oe

Plating Pb96%-Sn4% at ANU, RSURF ≈130 nΩ at 6 W

Htr=262 Oe

Delayen 3rd SRF+2005 discussion @ Jefferson

Curve E: decreased FE and increased other loss mechanisms


October 2010 13

Pb-Sn Plating SLRs: Results

This procedure has proven to be successful in re-plating 12 ANU

SLRs including 4 resonators with cracks in electron-beam weld.


October 2010 14

Substrate preparation

tumbling

degreasing


October 2010 15

Superconductor coating laboratory

high pressure rinsing

GN2 dryingPbSn plating


October 2010 16

Clean room facilities class ~500

assembling SLR and module cryostat


October 2010 17

Characterization of sc films


October 2010 18

Intermodulation distortion technique for SLRs


October 2010 19

Twin stub resonator status I


October 2010 20

Twin stub resonator status II

Cold test delayed due to vacuum failure

Doughnuts geometry is

to be changed to suppress

multipackting


October 2010 21

Pushing the Limits of SRF Pb

For SLR Hp/Eacc= 105 Oe/MV/m leading to

Eacc =5 MV/m (limited by Hc) and Eacc =6.1 MV/m (limited by Hsh )

For Pb at 4.3 K Hc=H(0)(1-(T/Tc)2)= 530 Oe and Hsh =1.2Hc =636 Oe

Data for PbSn alloys is not available, the best ANU SLR operates at Eacc=3.9 MV/m limited by FE

Plating final layer ~0.1 µ at over-potential (higher current density)

Plating multi-layers of Pb and PbSn alloys

Vacuum annealing or melting crystalline Pb film to make it amorphous

High power and helium processing on-line at 1kW peak RF power

RF gasket conditioning (PbSn pre-plating of lead wire)

Fundamental SRF properties of Pb, PbSn films shall be further investigated

ANY MORE IDEAS?

Pushing the Limits of Pb:


October 2010 22

Nb/Cu SRF & TF Technology

MagnetronCERN, ACCEL, Cornell, ANU

DC CathodeINFN Legnaro

ECR *)

JLAB

Vacuum Arc*), INFNA.Soltan

HPPM *),CERN

Laser Ablation,JLAB

Dep. Rateµ/hour

0.5-6 0.5 1.5 2-3 10 6-72

RRR 5-10 10 20-100 20-100 - -

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


October 2010 23

Latest developments

EIF Funds available over the next 4 years to upgrade Linac with 4-8 resonators: Nb-coated QWRs ? Collaborators are welcomeAnother EIF project is Re-buncher @1.2 MV/m. Can we make it of MgB2 or HTS?What about sc (HTS) phase detector installed in the Linac cryostat?ACAS collaboration between ANU, UM, ANSTO and AS has been launched on 13th July 2010 http://epp.physics.unimelb.edu.au/ACAS


October 2010 24

Thank you !