Fundamental R&D - non Nb
Nb coating
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TUFUB8 CVD Coated Copper Substrate SRF Cavity Research at Cornell University 381
 
  • M. Ge, T. Gruber, J.J. Kaufman, M. Liepe, J.T. Maniscalco, T.E. Oseroff, R.D. Porter, Z. Sun
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • V.M. Arrieta, S.R. McNeal
    Ultramet, Pacoima, California, USA
 
  Chemical vapor deposition (CVD) is a promising alternative to conventional sputter techniques for coating copper substrate cavities with high-quality superconducting films. Through multiple SRF-related DOE SBIR projects, Ultramet has developed CVD processes and CVD reactor designs for SRF cavities, and Cornell University has conducted extensive RF testing of CVD coated surfaces. Here we report results from thin-film CVD Nb3Sn coated copper test plates, and for thick-film CVD niobium on copper including full-scale single cell 1.3 GHz copper substrate cavities. Detailed optical inspection and surface characterization show high-quality and well-adhered coatings. No copper contamination is found. The Nb3Sn coated plates have a uniform Nb3Sn coating with a slightly low tin concentration (19 -22%), but a BCS resistance well in agreement with predictions. The CVD Nb coatings on copper plates demonstrate excellent adhesion characteristics and exceeded surface fields of 50 mT without showing signs of a strong Q-slope that is frequently observed in sputtered Nb cavities. Multiple single-cell 1.3 GHz copper cavities have been coated to date at Ultramet, and results from RF testing of these are presented and discussed.  
slides icon Slides TUFUB8 [12.488 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUB8  
About • paper received ※ 01 July 2019       paper accepted ※ 05 July 2019       issue date ※ 14 August 2019  
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TUP068 Study of Surface Treatment of 1.3 GHz Single-cell Copper Cavity for Niobium Sputtering 605
SUSP018   use link to see paper's listing under its alternate paper code  
 
  • F.Y. Yang, J. Dai, P. He, Z.Q. Li, Y. Ma, P. Zhang
    IHEP, Beijing, People’s Republic of China
 
  Funding: This work has been supported in part by PAPS project and National Key Programme for S&T Research and Development (Grant NO.: 2016YFA0400400)
A R&D program on niobium sputtering on copper cavities has started at IHEP in 2017. Single-cell 1.3 GHz copper cavity has been chosen as a substrate. A chemical polishing system has subsequently developed and commissioned recently to accommodate the etching of both copper samples and a cavity. Different polishing agents have been tested on copper samples and later characterized. The results of these surface treatment tests are presented.
 
poster icon Poster TUP068 [1.228 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP068  
About • paper received ※ 20 June 2019       paper accepted ※ 03 July 2019       issue date ※ 14 August 2019  
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TUP070 The SRF Thin Film Test Facility in LHe-Free Cryostat 610
 
  • O.B. Malyshev, J.A. Conlon, P. Goudket, N. Pattalwar, S.M. Pattalwar
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • G. Burt
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • G. Burt
    Lancaster University, Lancaster, United Kingdom
 
  An ongoing programme of development superconducting thin film coating for SRF cavities requires a facility for a quick sample evaluation at the RF conditions. One of the key specifications is a simplicity of the testing procedure, allowing an easy installation and quick turnover of the testing samples. Choked test cavities operating at 7.8 GHz with three RF chokes have been designed and tested at DL in a LHe cryostat verifying that the system could perform as required. Having a sample and a cavity physically separate reduces the complexity involved in changing samples (major causes of low throughput rate and high running costs for other test cavities) and also allows direct measurement of the RF power dissipated in the sample via power calorimetry. However, changing a sample and preparation for a test requires about two-week effort per sample. In order to simplify the measurements and achieve a faster turnaround, a new cryostat cooled with a closed-cycle refrigerator has been designed, built and tested. Changing a sample, cooling down and testing can be reduced to 2-3 days per sample. Detailed design and results of testing of this facility will be reported at the conference.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP070  
About • paper received ※ 21 June 2019       paper accepted ※ 02 July 2019       issue date ※ 14 August 2019  
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TUP072 The Development of Niobium Sputtering on Copper Cavities at IHEP 613
 
  • J. Dai, P. He, Z.Q. Li, Y. Ma, F.Y. Yang, P. Zhang
    IHEP, Beijing, People’s Republic of China
 
  A R&D program focusing on niobium sputtering on copper cavities started at IHEP in 2017. Single-cell 1.3 GHz elliptical cavity shape has been initially chosen as sputtering substrate. A magnetron sputtering system have been developed in 2018. In addition, a surface treatment facility to polish the copper substrate before sputtering has been developed and commissioned. This paper will present the Nb/Cu coating activities at IHEP.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP072  
About • paper received ※ 19 June 2019       paper accepted ※ 04 July 2019       issue date ※ 14 August 2019  
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TUP073 Superconducting Thin Films Characterization at HZB with the Quadrupole Resonator 616
 
  • D.B. Tikhonov, S. Keckert, J. Knobloch, O. Kugeler, Y. Tamashevich
    HZB, Berlin, Germany
  • A-M. Valente-Feliciano
    JLab, Newport News, Virginia, USA
 
  Funding: EASITrain - European Advanced Superconductivity Innovation and Training. This Marie Sklodowska-Curie Action Innovative Training Networks founded by H2020 under Grant Agreement no. 764879
Superconducting thin films have great potential as post-Nb material for use in SRF applications in future accelerators and industry. To test the RF-performance of such films in practice, would require the building and coating of a full RF cavity. Deposition of thin films on such scales in test facilities are challenging, in particular when curved surfaces have to be coated. This greatly complicates their systematic research. In this contribution we report on the method we use to characterize small and flat thin film samples (Deposited onto both Nb and Cu substrates) in an actual cavity named the Quadrupole Resonator (QPR). We also summarize the latest measurement results of NbTiN thin films. The Quadrupole Resonator at HZB is a tool that is able to perform SRF characterizations at frequencies ~415, 847, 1300 MHz with RF fields using an RF-DC power compensation technique.
 
poster icon Poster TUP073 [2.318 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP073  
About • paper received ※ 23 June 2019       paper accepted ※ 02 July 2019       issue date ※ 14 August 2019  
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TUP075 New Progress for Nb Sputtered 325 MHz QWR Cavities in IMP 621
 
  • F. Pan, H. Guo, Y. He, T.C. Jiang, C.L. Li, M. Lu, T. Tan
    IMP/CAS, Lanzhou, People’s Republic of China
 
  Comparing with bulk niobium cavities, the Nb/Cu cavities feature a much better stability at 4.5 K. Last year, two 325 MHz QWR copper cavities coated with biased DC diode sputterred Nb for CiADS has been accomplished at IMP. But vertical tests showed the cavities had low Q0 at 4 K. To solve the issue, a new coating system was designed and built. The sputtering target was redesigned and manufactured. The coating parameters were selected again and auxiliary heating was used to control the coating temperature in the process of sputtering. The power and Ar pressure during coating were also carefully selected. The paper covers resulting film characters, vertical tests with the evolution of the sputtering process, and improvements we made since last year.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP075  
About • paper received ※ 22 June 2019       paper accepted ※ 14 August 2019       issue date ※ 14 August 2019  
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THFUB2 Progress with Nb Hipims Films on 1.3 GHz Cu Cavities 823
 
  • M.C. Burton, A.D. Palczewski, C.E. Reece, A-M. Valente-Feliciano
    JLab, Newport News, Virginia, USA
 
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
In recent years, efforts have been invested to leverage the different processes involved in energetic condensation to tailor Nb film growth in sequential steps. The resulting Nb/Cu films display high quality material properties and show promise of high RF performance. The lessons learned are now applied to 1.3 GHz Nb on Cu cavity deposition via high power impulse magnetron sputtering (HiPIMS). RF performance is measured at different temperatures. Particular attention is given to the effect of cooldown and sensitivity to external applied magnetic fields. The results are evaluated in light of the Nb film material and superconducting properties measured with various microscopy and magnetometry techniques in order to better understand the contributing factors to the residual and flux induced surface resistances. This contribution presents the insights gained in exploiting energetic condensation as a path towards RF Q-slope mitigation for Nb/Cu films, correlating film material characteristics with RF performance.
 
slides icon Slides THFUB2 [7.869 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THFUB2  
About • paper received ※ 02 July 2019       paper accepted ※ 03 July 2019       issue date ※ 14 August 2019  
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THFUB3
Nb/Cu Coatings Characterization in HiPIMS With Biased Substrate and Application of a Positive Pulse  
 
  • F. Avino, S. Calatroni, D. Fonnesu, A. Grudiev, P. Naisson, H. Neupert, A.T. Perez Fontenla, T. Richard, G.J. Rosaz, A. Sublet, M. Taborelli
    CERN, Geneva, Switzerland
 
  In this work, we present results on the characterization of Nb on Cu films obtained in High Power Impulse Magnetron Sputtering (HiPIMS) with a negatively biased substrate, or with a positive pulse after the main negative one [1]. This allows to accelerate the Nb+ atoms towards substrates with small grazing angles of incidence to obtain a dense and defect-free Nb film. Samples reproducing the shape of a 1.3 GHz SRF cavity are coated by varying the timing of the substrate bias with respect to the main HiPIMS. The Nb film residual stress and estimations of the amount of trapped discharge gas (Kr) are also presented. The effect of applying a positive pulse after the main HIPIMS pulse on Nb/Cu samples coated in Ar is further explored. Crystallites size characterization is obtained with X-Ray Diffraction. First SRF properties by measurement of the critical temperature are provided. Preliminary results of Nb/Cu coatings of Cu samples reproducing the real geometry of the Wide Open Waveguide Crab cavity [2] are presented.
[1] F Avino et al., Plasma Sources Sci. Technol., vol. 28 pp. 01LT03, 2019.
[2] A. Grudiev, Proceedings of SRF 2015.
 
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