Keyword: radio-frequency
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SUPCAV008 Design and Construction of Nb3Sn Vapor Diffusion Coating System at KEK cavity, vacuum, MMI, operation 23
 
  • K. Takahashi, T. Okada
    Sokendai, Ibaraki, Japan
  • H. Ito, E. Kako, T. Konomi, H. Sakai, K. Umemori
    KEK, Ibaraki, Japan
 
  Vapor diffusion Nb3Sn coating system was developed at KEK. At most 1.3GHz 3-cell cavity can be coat with the coating system. The coating system consists of a coating chamber made of Nb, a vacuum furnace for heating the Nb chamber, and a heating device of Tin in the crucible. The Nb chamber vacuum and the furnace vacuum are isolated to prevent contamination from the furnace. There is a heating device for increasing Tin vapor pressure. In this presentation, the design and construction of the coating system are reported.  
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-SUPCAV008  
About • Received ※ 21 June 2021 — Accepted ※ 18 November 2021 — Issue date; ※ 11 April 2022  
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SUPCAV009 First Nb3Sn Coating and Cavity Performance Result at KEK cavity, SRF, experiment, superconducting-RF 27
 
  • K. Takahashi, T. Okada
    Sokendai, Ibaraki, Japan
  • H. Ito, E. Kako, T. Konomi, H. Sakai, K. Umemori
    KEK, Ibaraki, Japan
 
  At KEK, Nb3Sn vapor diffusion R&D for High-Q has just started. We have performed Nb3Sn coating on niobium samples and characterized these samples. We optimized the cavity coating parameter from the result of characterized samples. After optimizing the parameter, we have performed Nb3Sn coating on a TESLA-like single-cell Nb cavity and measured cavity performance in vertical tests. This presentation presents the result of the cavity coating and performance results.  
poster icon Poster SUPCAV009 [1.477 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-SUPCAV009  
About • Received ※ 21 June 2021 — Accepted ※ 18 March 2022 — Issue date; ※ 16 May 2022  
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SUPFDV003 Effect of Mean Free Path on Nonlinear Losses of Trapped Vortices Driven by a RF Field Field cavity, ECR, linear-dynamics, simulation 67
 
  • M.R.P. Walive Pathiranage, A.V. Gurevich
    ODU, Norfolk, Virginia, USA
 
  Funding: This work was supported by NSF under Grants PHY 100614-010 and PHY 1734075, and by DOE under Grant DE-SC 100387-020.
We report extensive numerical simulations on nonlinear dynamics of a trapped elastic vortex under rf field, and its dependence on electron mean free path li. Our calculations of the field-dependent residual surface resistance Ri(H) take into account the vortex line tension, the linear Bardeen-Stephen viscous drag and random distributions of pinning centers. We showed that Ri(H) decreases significantly at small fields as the material gets dirtier while showing field independent behavior at higher fields for clean and dirty limit. At low frequencies Ri(H) increases smoothly with the field amplitude at small H and levels off at higher fields. The mean free path dependency of viscosity and pinning strength can result in a nonmonotonic mean free path dependence of Ri, which decreases with li at higher fields and weak pinning strength.
 
poster icon Poster SUPFDV003 [1.339 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-SUPFDV003  
About • Received ※ 20 June 2021 — Accepted ※ 19 December 2021 — Issue date; ※ 09 April 2022  
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SUPFDV006 Investigation of SIS Multilayer Films at HZB SRF, superconductivity, cavity, quadrupole 72
 
  • D.B. Tikhonov, S. Keckert, J. Knobloch, O. Kugeler
    HZB, Berlin, Germany
  • E. Chyhyrynets, C. Pira
    INFN/LNL, Legnaro (PD), Italy
  • J. Knobloch
    University of Siegen, Siegen, Germany
  • S.B. Leith, M. Vogel
    University Siegen, Siegen, Germany
 
  Funding: The manufacture of the QPR samples received funding from the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement No 730871
The systematic study of multilayer SIS films (Superconductor-Insulator-Superconductor) is being conducted in Helmholtz-Zentrum Berlin. Such films theoretically should boost the performance of superconducting cavities, and reduce some problems related to bulk Nb such as magnetic flux trapping. Up to now such films have been presented in theory, but the RF performance of those structures have not been widely studied. In this contribution we present the results of the latest tests of AlN-NbN films, deposited on micrometers-thick Nb layers on copper. It has, also, been shown previously at HZB that such SIS films may show some unexpected behavior in surface resistance versus temperature parameter space. In this contribution we continue to investigate those effects with the variation of different parameters of films (such as insulator thickness) and production recipes.
 
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-SUPFDV006  
About • Received ※ 21 June 2021 — Revised ※ 09 July 2021 — Accepted ※ 12 August 2021 — Issue date ※ 21 December 2021
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SUPFDV009 Thermal Annealing of Sputtered Nb3Sn and V3Si Thin Films for Superconducting RF Cavities SRF, cavity, ECR, target 82
 
  • K. Howard, M. Liepe, Z. Sun
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Funding: U.S. National Science Foundation under Award PHY-1549132, the Center for Bright Beams and Cornell Center for Materials Research Shared Facilities supported through the NSF MRSEC program (DMR-1719875)
Nb3Sn and V3Si thin films are alternative material candidates for the next-generation of superconducting radio frequency (SRF) cavities. However, past sputtered films suffer from stoichiometry and strain issues during deposition and post annealing. As such, we aim to explore the structural and chemical effects of thermal annealing, both in-situ and post-sputtering, on DC-sputtered Nb3Sn and V3Si with varying thickness on Nb or Cu substrates. We successfully enabled recrystallization of 100 nm thin Nb3Sn films with stoichiometric and strain-free grains at 950 C annealing. For 2 um films, we observed removal of strain and slight increase in grain size with increasing temperature. A phase transformation from unstable to stable structure appeared on thick V3Si samples, while we observed significant Sn loss in thick Nb3Sn films at high temperature anneals. For films on Cu substrates, we observed similar Sn and Si loss during annealing likely due to Cu-Sn and Cu-Si phase generation and subsequent Sn and Si evaporation. These results encourage us to refine our process to obtain high quality films for SRF use.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-SUPFDV009  
About • Received ※ 22 June 2021 — Revised ※ 06 July 2021 — Accepted ※ 12 August 2021 — Issue date ※ 17 March 2022
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SUPTEV010 Electrical and Thermal Properties of Cold-Sprayed Bulk Copper and Copper-Tungsten Samples at Cryogenic Temperatures cavity, site, SRF, vacuum 142
 
  • H. Pokhrel
    ODU, Norfolk, Virginia, USA
  • G. Ciovati, P. Dhakal, J.K. Spradlin
    JLab, Newport News, Virginia, USA
  • C.-J. Jing, A. Kanareykin
    Euclid TechLabs, Solon, Ohio, USA
 
  Funding: Work supported by the U.S. Department of Energy, Office of Science, SBIR grant DE-SC00195589
The development of high thermal conductivity coatings with pure copper or copper-tungsten alloy could be beneficial to improve the heat transfer of bulk Nb cavities for conduction cooling applications and to increase the stiffness of bulk Nb cavities cooled by liquid helium. Cold-spray is an additive manufacturing technique suitable to grow thick coatings of either Cu or CuW on a Nb substrate. Bulk (~5 mm thick) coatings of Cu and CuW were deposited on standard 3 mm thick, high-purity Nb samples and smaller samples with 2 mm x 2 mm cross section were cut for measuring the thermal conductivity and the residual resistivity ratio. The samples were subjected to annealing at different temperatures and a maximum RRR of ~130 and ~40 were measured for the Cu samples and CuW samples, respectively.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-SUPTEV010  
About • Received ※ 21 June 2021 — Revised ※ 13 August 2021 — Accepted ※ 15 November 2021 — Issue date ※ 21 March 2022
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MOPTEV012 Extra-Cold EP Process at Fermilab cavity, controls, niobium, SRF 230
 
  • F. Furuta, D.J. Bice, M. Martinello, T.J. Ring
    Fermilab, Batavia, Illinois, USA
 
  FNAL has established a cold Electro-Polishing (EP) method which maintains the outer surface temperature of cavity cell around 12~15°C during EP process. Cold EP has been applied on the various SRF cavities and contributed to achieve high RF performances with them. To investigate more feasibility and capability of EP at lower temperature, the FNAL EP temperature control tool was recently improved. Extra-cold EP process below 0°C at cavity cell region was successfully performed on 1.3 GHz 1-cell cavity. A compatible RF performance with cold EP method was also demonstrated during the cavity vertical testing. The details of extra-cold EP process and the cavity test results will be presented.  
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-MOPTEV012  
About • Received ※ 21 June 2021 — Accepted ※ 14 December 2021 — Issue date; ※ 16 May 2022  
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MOPTEV017 Development and Operation of PIP-II Injector Test, SSR1 Cryomodule, 325 MHz Amplifiers cavity, operation, rf-amplifier, cryomodule 245
 
  • J. Steimel, V.M. Grzelak, D.W. Peterson
    Fermilab, Batavia, Illinois, USA
  • V.R. Bala, S.K. Bharade, G. Joshi, R. Keshwani, J.K. Mishra, M.M. Pande, S. Shrotriya, H. Shukla, S. Singh, C.I. Sujo
    BARC, Mumbai, India
  • D. Balakrishna, N. Chikte, S. Dubey, C. G, V. Gollapalli, J. K Chandra, V. Kumar, M. M, A. Maheshwari, S.N. Nagaratnam, G. Poornima, T.V.S. Thalluri
    ECIL, Hyderabad, India
 
  Funding: 1Fermilab, U.S.Department of Energy 2 Bhabha Atomic Research Centre, Department of Atomic Energy, Government of India 3 Electronic Corporation of India, Department of Atomic Energy, Government of India
The PIP-II Injector Test (PIP2IT) has successfully accelerated ionized hydrogen up to 17MeV through a superconducting, single spoke resonator (SSR1) cryomodule at Fermi National Accelerator Laboratory (FNAL). Each of the SSR1 cavities is tuned to 325MHz and requires up to 6 kW of RF power to accelerate 2mA of ionized hydrogen at the design gradients. RF power amplifiers, specialized for SRF cavity beam operations, were designed by Bhabha Atomic Research Center (BARC) and constructed in a collaboration between the BARC in Mumbai, India and the Electronics Corporation of India Limited (ECIL) in Hyderabad, India. The RF amplifiers meet the specifications and requirements mutually approved between BARC and FNAL. They operate at 325 MHz with a linear power output of 7 kW in both CW and pulse mode. The amplifiers are compatible with the FNAL accelerator personnel safety system and the cavity protection interlocks. Access to controls and internal diagnostic instrumentation are compatible with EPICS control standards. This paper gives details about RF power amplifier development within the Department of Atomic Energy (DAE), India and the operational details with PIP2IT at FNAL.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-MOPTEV017  
About • Received ※ 28 June 2021 — Revised ※ 08 September 2021 — Accepted ※ 18 November 2021 — Issue date ※ 14 May 2022
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TUPFAV006 The Superconducting Radio Frequency System of Shenzhen Industrial Synchrotron Radiation Source FacilityRIAL SYNCHROTRON RADIATION SOURCE FACILITY cavity, radiation, synchrotron, storage-ring 392
 
  • W. Ma, Y.B. Sun, N. Yuan
    Sun Yat-sen University, Zhuhai, Guangdong, People’s Republic of China
  • L.G. Liu
    SSRF, Shanghai, People’s Republic of China
  • L. Lu, L. Yang, Z.L. Zhang
    IMP/CAS, Lanzhou, People’s Republic of China
 
  Shenzhen industrial synchrotron radiation source is a 3 GeV synchrotron radiation diffraction-limited source. It consists of three parts, linear accelerator, booster, and storage ring. As a basic part of the storage ring, the superconducting radio frequency system provides energy for the beam to supplement the beam power loss caused by synchrotron radiation and higher-order modes, and provide the longitudinal bunch for the electron beam. The superconducting radio frequency cavity of the storage ring consists of two 500 MHz single-cell cavities and a third harmonic 1500 MHz double-cell cavity. This paper will introduce the superconducting cavity, radio frequency amplifier, and low-level radio frequency system in the Shenzhen industrial synchrotron radiation source facility.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-TUPFAV006  
About • Received ※ 20 June 2021 — Revised ※ 16 August 2021 — Accepted ※ 21 August 2021 — Issue date ※ 26 November 2021
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TUPFDV007 Surface Impedance of Nb3Sn and YBa2Cu3O7-δ in High Magnetic Fields impedance, cavity, framework, electron 416
 
  • N. Pompeo, A. Alimenti, E. Silva, K. Torokhtii
    Università degli Studi Roma III, Roma, Italy
  • G. Celentano, V. Pinto, F. Rizzo
    ENEA C.R. Frascati, Frascati (Roma), Italy
  • R. Flükiger
    UNIGE, Geneva, Switzerland
  • T. Spina
    Fermilab, Batavia, Illinois, USA
 
  Funding: This work has been partially carried out within the framework of the EUROfusion consortium, funding from the Euratom research and training programme 2014-18 and 2019-20 under grant agreement No 633053
New potential rf applications of superconductors emerged with the need to operate in high dc magnetic fields (up to 16 T) where vortex motion dictates the response: the beam screen coating of the Future Circular Collider (FCC) [1] and haloscopes, i.e. rf cavities for the axions detection [2]. However, very few data are available in the required regimes. We present in this work measurements of the surface impedance Z up to 12 T on bulk Nb3Sn and YBCO thin films grown by different techniques. The measurements are performed with a dielectric loaded resonator operating at 15 GHz. We obtained the vortex motion resistivity and extracted the high frequency vortex motion parameters [3]: the depinning frequency, the flux-flow resistivity and the pinning constant, as well as their temperature and field dependences. Substantial differences are highlighted in the high frequency pinning properties of the studied materials, providing useful information on possible improvements in view of applications. A comparison with the results obtained in the microwave frequency range at lower fields (up to 1 T) is given.
[1] S. Calatroni, IEEE Trans. Appl. Supercond., vol. 26 p. 3500204, 2016.
[2] D. Alesini et al., Phys. Rev. D, vol. 99, p. 101101, 2019.
[3] J.I. Gittleman and B. Rosenblum, Phys. Rev. Lett., vol. 16, p.734, 1966.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-TUPFDV007  
About • Received ※ 21 June 2021 — Accepted ※ 21 August 2021 — Issue date; ※ 02 January 2022  
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TUPTEV003 Progress of MgB2 Deposition Technique for SRF Cavities at LANL cavity, SRF, experiment, superconductivity 482
 
  • P. Pizzol, L. Civale, D.N. Kelly, I. Nekrashevich, A. Poudel, H.R. Salazar, R.K. Schulze, T. Tajima
    LANL, Los Alamos, New Mexico, USA
 
  Since its discovery in 2001, Magnesium Diboride (MgB2) has had the potential to become a material for cavity manufacturing. Having a transition temperature (Tc) at ~39 K, there is a potential to operate the cavity at ~20 K with cryocoolers. This will open up a variety of applications that benefit from compact high-efficiency superconducting accelerators. We have found a 2-step deposition technique as a viable technique for cavity coating, i.e., coating of a pure boron layer with chemical vapor deposition using a diborane gas in the first step and react it with Mg vapor in the second step. In this paper, we will show some recent results with up to Tc ~38 K using a small furnace and describe a new coating system under construction with a new 3-zone furnace to coat a 1.3-GHz single-cell cavity.  
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-TUPTEV003  
About • Received ※ 21 June 2021 — Accepted ※ 16 October 2021 — Issue date; ※ 02 May 2022  
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WEPFDV005 Tensile Tests of Large Grain Ingot Niobium at Liquid He Temperature niobium, cavity, experiment, SRF 562
 
  • M. Yamanaka
    KEK, Ibaraki, Japan
  • K. Enami
    Tsukuba University, Ibaraki, Japan
 
  Tensile tests at liquid He temperature were performed using specimen taken from high purity large grain niobium ingot produced by CBMM. The measured RRR is 242. The ingot is 260 mm in diameter and sliced by a multi wire saw to 2.8 thickness. 5 specimens were cut off from one sliced disk. 3 disks were set in same phase to obtain same grain distribution. 3 specimens each of 5 grain patterns 5, 15 in total were used for the tensile test. The tensile test stand using a cryostat and liquid He was manufactured by ourselves. The measured tensile strength varied 379 to 808 MPa. The average value is 611 MPa. The tensile strength at room temperature is 84 MPa. The strength becomes high at low temperature like a fine grain niobium. The specimen includes a grain boundary, and causes the variation of strength. The different result was obtained in same grain patterns. The relationship between crystal orientation and strength is discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-WEPFDV005  
About • Received ※ 08 June 2021 — Accepted ※ 12 September 2021 — Issue date; ※ 02 May 2022  
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WEPFDV007 Main Highlights of ARIES WP15 Collaboration SRF, site, cavity, laser 571
 
  • O.B. Malyshev, P. Goudket, R. Valizadeh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • C.Z. Antoine
    CEA-IRFU, Gif-sur-Yvette, France
  • O. Azzolini, E. Chyhyrynets, G. Keppel, C. Pira, F. Stivanello
    INFN/LNL, Legnaro (PD), Italy
  • G. Burt, D.J. Seal, D.A. Turner
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • G. Burt, B.S. Sian
    Lancaster University, Lancaster, United Kingdom
  • O. Kugeler, D.B. Tikhonov
    HZB, Berlin, Germany
  • S.B. Leith, A.O. Sezgin, M. Vogel
    University Siegen, Siegen, Germany
  • A. Medvids, P. Onufrijevs
    Riga Technical University, Riga, Latvia
  • R. Ries, E. Seiler
    Slovak Academy of Sciences, Institute of Electrical Engineering, Bratislava, Slovak Republic
  • B.S. Sian
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • A. Sublet, G. Vandoni, L. Vega Cid, W. Venturini Delsolaro, P. Vidal Garcia
    CERN, Meyrin, Switzerland
  • D.A. Turner
    STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
 
  Funding: European Commission’s ARIES collaboration H2020 Research and Innovation Programme under Grant Agreement no. 730871
An international collaboration of research teams from CEA (France), CERN (Switzerland), INFN/LNL (Italy), HZB and USI (Germany), IEE (Slovakia), RTU (Latvia) and STFC/DL (UK), are working together on better understanding of how to improve the properties of superconducting thin films (ScTF) for RF cavities. The collaboration has been formed as WP15 in the H2020 ARIES project funded by EC. The systematic study of ScTF covers: Cu substrate polishing with different techniques (EP, SUBU, EP+SUBU, tumbling, laser), Nb, NbN, Nb3Sn and SIS film deposition and characterisation, Laser post deposition treatments, DC magnetisation characterisation, application of all obtained knowledge on polishing, deposition and characterisation, Laser post deposition treatments, DC magnetisation characterisation, application to the QPR samples for testing the films at RF conditions. The preparation, deposition and characterisation of each sample involves 3-5 partners enhancing the capability of each other and resulting in a more complete analysis of each film. The talk will give an overview of the collaborative research and will be an introduction to the detailed talks given by the team members.
 
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-WEPFDV007  
About • Received ※ 19 June 2021 — Accepted ※ 12 February 2022 — Issue date; ※ 10 April 2022  
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WEPFDV008 Thermal Conductivity of Electroplated Copper Onto Bulk Niobium at Cryogenic Temperatures cavity, SRF, niobium, site 576
 
  • G. Ciovati, P. Dhakal
    JLab, Newport News, Virginia, USA
  • I.P. Parajuli, M.R.P. Walive Pathiranage
    ODU, Norfolk, Virginia, USA
  • T. Saeki
    KEK, Ibaraki, Japan
 
  Funding: U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177.
Superconducting radio-frequency (SRF) cavities made of high-purity bulk niobium are widely used in modern particle accelerators. The development of metallic outer coatings with high thermal conductivity would have a beneficial impact in terms of improved thermal stability, reduced material cost and for the development of conduction-cooled, cryogenic-free SRF cavities. Several high-purity, fine-grain Nb samples have been coated with 2’4 mm thick copper by electroplating. Measurements of the thermal conductivity of the bimetallic Nb/Cu samples in the range 2’7 K showed values of the order of 1 kW/(m K) at 4.3 K. Very good adhesion between copper and niobium was achieved by depositing a thin Cu layer by cold spray on the niobium, prior to electroplating the bulk Cu layer.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-WEPFDV008  
About • Received ※ 17 June 2021 — Accepted ※ 10 September 2021 — Issue date; ※ 01 March 2022  
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THPFDV003 SIMS Investigation of Furnace Baked Nb cavity, vacuum, niobium, SRF 761
 
  • E.M. Lechner, M.J. Kelley, A.D. Palczewski, C.E. Reece
    JLab, Newport News, Virginia, USA
  • J.W. Angle, M.J. Kelley
    Virginia Polytechnic Institute and State University, Blacksburg, USA
 
  Funding: U.S. DOE Contract No. DE-AC05-06OR23177
Results recently published by Ito et al. showed that "furnace baking" Nb SRF cavities after electropolishing yields high quality factors and anti-Q-slopes resembling that of N doped cavities. Small Nb samples were prepared following the recipe outlined by Ito. These samples were measured by SIMS to examine impurity contributions to the RF penetration layer. These diffusion profiles are modeled, and their consequences on RF properties discussed.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-THPFDV003  
About • Received ※ 22 June 2021 — Accepted ※ 24 November 2021 — Issue date; ※ 15 May 2022  
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THPTEV015 Cylindrical Magnetron Development for Nb3sn Deposition via Magnetron Sputtering cavity, SRF, target, site 868
 
  • Md.N. Sayeed, H. Elsayed-Ali
    ODU, Norfolk, Virginia, USA
  • C. Côté, M.A. Farzad, A. Sarkissian
    PLASMIONIQUE Inc., Varennes, Québec, Canada
  • G.V. Eremeev
    Fermilab, Batavia, Illinois, USA
  • A-M. Valente-Feliciano
    JLab, Newport News, Virginia, USA
 
  Funding: This work was supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under Contract No. DE-AC05-06OR23177.
Due to its better superconducting properties (critical temperature Tc~ 18.3 K, superheating field Hsh~ 400 mT), Nb3Sn is considered as a potential alternative to niobium (Tc~ 9.25 K, Hsh~ 200 mT) for superconducting radiofrequency (SRF) cavities for particle acceleration. Magnetron sputtering is an effective method to produce superconducting Nb3Sn films. We deposited superconducting Nb3Sn films on samples with magnetron sputtering using co-sputtering, sequential sputtering, and sputtering from a stoichiometric target. Nb3Sn films produced by magnetron sputtering in our previous experiments have achieved DC superconducting critical temperature up to 17.93 K and RF superconducting transition at 17.2 K. A magnetron sputtering system with two identical cylindrical cathodes that can be used to sputter Nb3Sn films on cavities has been designed and is under development now. We report on the design and the current progress on the development of the system.
 
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-THPTEV015  
About • Received ※ 22 June 2021 — Revised ※ 12 August 2021 — Accepted ※ 21 August 2021 — Issue date ※ 27 September 2021
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THPTEV016 The Role of Oxygen Concentration in Enabling High Gradients in Niobium SRF Cavities cavity, niobium, SRF, ECR 871
 
  • D. Bafia, A. Grassellino, A.S. Romanenko
    Fermilab, Batavia, Illinois, USA
 
  We studied the role of O concentration with depth in the performance of Nb SRF cavities. An ensemble of electropolished 1.3 GHz cavities, which initially showed high field Q-slope (HFQS), was subjected to sequential testing and treatment with in-situ low temperature baking at various temperatures. We find that increasing the bake duration causes (i) an increase in the onset of HFQS until it is absent up to quench (ii) a non-monotonic relationship with the quench field (iii) an evolution of the RBCS toward a non-equilibrium behavior that drives anti-Q slope. Our data is qualitatively explained by assuming an O diffusion model and suggests that the mitigation of HFQS that arises from 120°C in-situ LTB is mediated by the diffusion of O from the native oxide which prevents the precipitation of proximity-coupled Nb nano-hydrides, in turn enabling higher quench fields. The decrease in quench field for cavities in which O has been diffused >90 nm from the RF surface may be due to a reduction of the field limit in the SS bilayer structure. We also suggest that the evolution of the RBCS occurs due to the absence of proximity coupled inclusions, bringing about non-equilibrium effects.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-THPTEV016  
About • Received ※ 22 June 2021 — Revised ※ 13 September 2021 — Accepted ※ 13 October 2021 — Issue date ※ 23 November 2021
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