http://www.surfacetreatments.it/thinfilms Commissioning of the JLab Surface Impedance Characterization (SIC) System (Charles Reece - 20') Speaker: Charles Reece - Jefferson Lab, Newport News (VA) USA | Duration: 20 min. Abstract Binping Xiao, Larry Phillips, and Charles Reece A system for making direct calorimetric measurements of the surface resistance at 7.5 GHz of small samples of variously prepared superconducting surfaces has been commissioned at JLab. The flat, 50 mm diameter sample temperature is regulated independently of the balance of the TE011 sapphire-loaded cavity, enabling Rs and Δλ measurements from 2 K to Tc of the sample. Initial operation, limited by available rf power, has extended to Bpk of 18 mT. The calorimeter resolution is better than 10 nΩ, and the sampled surface area is ~ 0.8 cm2. The SIC has been commissioned with a bulk Nb sample, demonstrating excellent agreement with standard BCS characterizations. Initial application to SRF thin films has begun. We are eager to apply it to non-niobium materials. Preparations for a second generation with extended dynamic range have already begun.

1. Commissioning the JLab 7.5 GHz Surface
Impedance Characterization (SIC) System
Charles Reece
for
Binping Xiao
Oct 4, 2010

2. Outline
• A 7.5 GHz surface impedance characterization system
based on a sapphire-loaded TE011 Nb cavity has been
under development at JLab for several years.
• The system provides calorimetric measurements of Rs
and ∆λ vs T and Bpk on area < 1 cm2 in the center of
5.0 cm diameter disk sample.
• The system has recently completed initial
commissioning and is well suited for characterization
of higher Tc candidate films.
• A next generation system capable of measurements
approaching Bpk ~160 mT is under development.

3. Characterization of Potential Materials
for SRF Cavities
Surface Characterization :
Morphology : SEM, AFM
Structure & Orientation : XRD, EBSD, TEM
Chemistry : XPS, SIMS
RF Characterization :
Field- and temperature-dependent SRF properties of
new candidate materials
How to correlate these two?
Small flat sample surface characterization (SIC System)

4. SIC System Design
Sapphire rod
Nb cavity
Sample under test
Calorimeter

5. SIC System Key RF Parameters
Prf f − f ref
Zs = 2
+ iωµ 0 (λref + )
Surface Impedance: kB pk M
Key parameters from Microwave Studio simulation

6. RF Calibration
7.52
7.51
7.5 -34.4±0.1Hz /nm , m eas ured at 4K
7.49
Freq [GHz]
7.48
7.47
7.46
-30.0±0.5Hz/nm,
7.45 MWS simulation
7.44
-31±2Hz/nm, measured at room T
7.43
0 0.2 0.4 0.6 0.8 1 1.2
Gap [mm]
Sample position tuning sensitivity of TE011 mode.
Confirms the mode correspondence with MWS simulation.
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7. SIC System: Characterization of Calorimeter
The thermal impedance
of the calorimeter
determines the
envelope of accessible
calorimetric heat
measurements as a
function of sample
temperature.
Roughly, 1 mK
temperature increase
corresponds to 1 μW @
2 K and 6 μW @ 9 K.
Sample temperature versus heater power under
equilibrium with bath temperature at 2 K,
without RF . Solid line is calculation based on
standard materials database.

8. SIC System: Characterization of Calorimeter
Characterization
of delta-T
between sample
and sample
holder for
standard Cu-Cu
interface.
■ Apply heat on sample
◆ Apply heat on holder

9. (T, Rs, Bpk) Measurement Range of SIC
Present 2.0 K
working range
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10. (T, Rs, Bpk) Measurement Range of SIC
10

11. SIC Commissioning Test: Rs vs T for Bulk Nb
Rs for bulk Nb sample brazed to Cu.
Solid line is BCS fit.
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12. SIC Measurements: ∆λ vs T
Penetration depth temperature dependence
for bulk Nb sample brazed to Cu. Solid line is BCS fit.
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13. SIC Measurements: BCS Fit Parameters for
Nb-brazed-to-Cu sample
Δ/k Tc = 1.87
Tc = 9.26 K
London penetration depth = 45.5 nm
Coherence length = 102 nm
Mean free path = 571 nm
λ(0) = 26.9 nm
Residual resistance = 1.13 µΩ
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14. Summary
• SIC measurement capability has been demonstrated
with bulk niobium.
• The resolution of the surface resistance in this
system can be as low as 1.2 nΩ at 5 mT peak
magnetic field and will be higher with higher fields.
• The maximum peak magnetic field presently attained
is 14 mT, limited by RF power and cavity Q.
• Since sample temperature is independent of cavity
temperature, the SIC system is ideally suited for
characterizing samples of higher-Tc materials.
14

15. Future of SIC
2nd Generation:
• A CW 200 Watt RF source
seeking
• A higher quality factor cavity
For increased Bpk
design -> draw -> machine -> assemble -> test
• A new calorimetry system
For increase heat dynamic range
design -> draw -> machine -> assemble -> test
15

16. (T, Rs, Bpk) Measurement Range
Expected of 2nd Generation SIC System
16

17. (T, Rs, Bpk) Measurement Range
Expected of 2nd Generation SIC System
Anticipated 2.0 K working range
without Q improvement
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18. (T, Rs, Bpk) Measurement Range
Expected of 2nd Generation SIC System
Full 2.0 K working
range with Q
improvement
Anticipated 2.0 K working range
without Q improvement
18

19. Thanks to J. Delayen, S. Dutton, R. Geng, P.
Kushnick, F. Marhauser, M. Morrone, J. Nance, J.
Ozelis, L. Phillips, T. Powers, H. Wang for their
contributions and support during the
development of this system.
See Reference:
“Radio Frequency Surface Impedance Characterization System for Superconducting
Samples at 7.5 GHz,” B. P. Xiao, C. E. Reece, H. L. Phillips, R. L. Geng, H. Wang,
F. Marhauser, and M. J. Kelley, Rev. Sci. Inst. (submitted) (2010).
Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.