Commissioning the JLab 7.5 GHz Surface
Impedance Characterization (SIC) System

              Charles Reece
              ...
Outline
• A 7.5 GHz surface impedance characterization system
  based on a sapphire-loaded TE011 Nb cavity has been
  unde...
Characterization of Potential Materials
           for SRF Cavities
Surface Characterization :
Morphology : SEM, AFM
Struc...
SIC System Design
    Sapphire rod




Nb cavity




                                Sample under test
            Calorim...
SIC System Key RF Parameters

                              Prf                          f − f ref
                      Z...
RF Calibration
              7.52

              7.51

               7.5                     -34.4±0.1Hz /nm , m eas ured...
SIC System: Characterization of Calorimeter

The thermal impedance
of the calorimeter
determines the
envelope of accessibl...
SIC System: Characterization of Calorimeter



Characterization
of delta-T
between sample
and sample
holder for
standard C...
(T, Rs, Bpk) Measurement Range of SIC




         Present 2.0 K
         working range




                              ...
(T, Rs, Bpk) Measurement Range of SIC




                                    10
SIC Commissioning Test: Rs vs T for Bulk Nb




              Rs for bulk Nb sample brazed to Cu.
              Solid line...
SIC Measurements: ∆λ vs T




Penetration depth temperature dependence
for bulk Nb sample brazed to Cu. Solid line is BCS ...
SIC Measurements: BCS Fit Parameters for
        Nb-brazed-to-Cu sample
   Δ/k Tc = 1.87
   Tc = 9.26 K
   London penetrat...
Summary
• SIC measurement capability has been demonstrated
  with bulk niobium.
• The resolution of the surface resistance...
Future of SIC
2nd Generation:
• A CW 200 Watt RF source
     seeking
• A higher quality factor cavity
     For increased B...
(T, Rs, Bpk) Measurement Range
Expected of 2nd Generation SIC System




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




        Anticipated 2.0 K working range
        w...
(T, Rs, Bpk) Measurement Range
Expected of 2nd Generation SIC System


         Full 2.0 K working
         range with Q
 ...
Thanks to J. Delayen, S. Dutton, R. Geng, P.
   Kushnick, F. Marhauser, M. Morrone, J. Nance, J.
   Ozelis, L. Phillips, T...
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Reece - Commissioning the JLab 7.5 GHz Surface Impedance Characterization (SIC) System

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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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Reece - Commissioning the JLab 7.5 GHz Surface Impedance Characterization (SIC) System

  1. 1. Commissioning the JLab 7.5 GHz Surface Impedance Characterization (SIC) System Charles Reece for Binping Xiao Oct 4, 2010
  2. 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. 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. 4. SIC System Design Sapphire rod Nb cavity Sample under test Calorimeter
  5. 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. 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. 6
  7. 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. 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. 9. (T, Rs, Bpk) Measurement Range of SIC Present 2.0 K working range 9
  10. 10. (T, Rs, Bpk) Measurement Range of SIC 10
  11. 11. SIC Commissioning Test: Rs vs T for Bulk Nb Rs for bulk Nb sample brazed to Cu. Solid line is BCS fit. 11
  12. 12. SIC Measurements: ∆λ vs T Penetration depth temperature dependence for bulk Nb sample brazed to Cu. Solid line is BCS fit. 12
  13. 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 13
  14. 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. 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. 16. (T, Rs, Bpk) Measurement Range Expected of 2nd Generation SIC System 16
  17. 17. (T, Rs, Bpk) Measurement Range Expected of 2nd Generation SIC System Anticipated 2.0 K working range without Q improvement 17
  18. 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. 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.

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