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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.
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Commissioning the JLab 7.5 GHz Surface Impedance Characterization (SIC) System
Charles Reece
for
Binping Xiao
Oct 4, 2010
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 Rsand ∆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.
Characterization of Potential Materials for SRF Cavities
Surface Characterization : Morphology : SEM, AFM Structure & Orientation : XRD, EBSD, TEMChemistry : 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)
SIC System Design
Calorimeter
Nb cavity
Sapphire rod
Sample under test
)(02 Mff
ikB
PZ ref
refpk
rfs
−++= λωµSurface Impedance:
SIC System Key RF Parameters
Key parameters from Microwave Studio simulation
6
RF Calibration
Sample position tuning sensitivity of TE011 mode.Confirms the mode correspondence with MWS simulation.
7.43
7.44
7.45
7.46
7.47
7.48
7.49
7.5
7.51
7.52
0 0.2 0.4 0.6 0.8 1 1.2
Gap [mm]
Freq
[GH
z]
-30.0±0.5Hz/nm,MWS simulation
-34.4±0.1Hz/nm, measured at 4K
-31±2Hz/nm, measured at room T
SIC System: Characterization of Calorimeter
Sample temperature versus heater power under equilibrium with bath temperature at 2 K,without RF . Solid line is calculation based on standard materials database.
The thermal impedance of the calorimeter determines the envelope of accessible calorimetric heat measurements as a function of sample temperature.
Roughly, 1 mKtemperature increase corresponds to 1 μW @ 2 K and 6 μW @ 9 K.
Apply heat on sample Apply heat on holder
SIC System: Characterization of Calorimeter
Characterization of delta-Tbetween sample and sample holder for standard Cu-Cu interface.
9
(T, Rs, Bpk) Measurement Range of SIC
Present 2.0 K working range
10
(T, Rs, Bpk) Measurement Range of SIC
11
SIC Commissioning Test: Rs vs T for Bulk Nb
Rs for bulk Nb sample brazed to Cu.Solid line is BCS fit.
12
SIC Measurements: ∆λ vs T
Penetration depth temperature dependencefor bulk Nb sample brazed to Cu. Solid line is BCS fit.
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
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.
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
16
(T, Rs, Bpk) Measurement Range Expected of 2nd Generation SIC System
17
(T, Rs, Bpk) Measurement Range Expected of 2nd Generation SIC System
Anticipated 2.0 K working range without Q improvement
18
(T, Rs, Bpk) Measurement Range Expected of 2nd Generation SIC System
Anticipated 2.0 K working range without Q improvement
Full 2.0 K working range with Q improvement
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.
