Author: Antoine, C.Z.
Paper Title Page
THFUA3
 Material and Superconducting Properties of NbTiN/AlN Multilayer Films  
 
  • A-M. Valente-Feliciano, D.R. Beverstock, C.E. Reece
    JLab, Newport News, Virginia, USA
  • C.Z. Antoine
    CEA-DRF-IRFU, France
  • S. Keckert, O. Kugeler, D.B. Tikhonov
    HZB, Berlin, Germany
  • M.J. Kelley
    The College of William and Mary, Williamsburg, Virginia, USA
  • R. Valizadeh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 and DARPA-BAA MIPR No. HD0011728910
In the pursuit of increasing the range of surface magnetic fields sustainable in SRF cavities, new standards in quality of thin multi-layer superconductor/insulator/superconductor (SIS) structures are being achieved. With the synergistic development of multilayered metamaterials based on 3 to 1 nm NbTiN and AlN films, the interface between films is improved. Based on bulk film values, the maximum magnetic field contour plot is also established for NbTiN to guide the choice of each layer thickness and quickly converge to optimized SIS structures. The delayed DC flux entry is measured for standalone NbTiN films and multilayer stacked structures on ideal substrates and Nb substrates. Some SIS structures along with standalone NbTiN films have been deposited on Nb and their superconducting properties and RF surface impedance are evaluated. 		 
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FRTU4
 Materials Beyond Bulk Nb  
 
  • C.Z. Antoine
    CEA-IRFU, Gif-sur-Yvette, France
  
  Materials Beyond Bulk Nb Bulk Niobium is approaching its ultimate limits. New materials are needed as wellas to decrease the production costs or get improved performances. This tutorials describe the criteria of choice for these material, along with the challenges to be met during their fabrications. Keywords: SRF, superconducting thin films, NbN, MgB2, Nb3Sn, pnictides, deposition techniques  
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TUP078 Lower Critical Field Measurement of NbN Multilayer Thin Film Superconductor at KEK 632
SUSP013   use link to see paper's listing under its alternate paper code  
 
  • H. Ito
    Sokendai, Ibaraki, Japan
  • C.Z. Antoine
    CEA-IRFU, Gif-sur-Yvette, France
  • H. Hayano, R. Katayama, T. Kubo, T. Saeki
    KEK, Ibaraki, Japan
  • R. Ito, T. Nagata
    ULVAC, Inc, Chiba, Japan
  • Y. Iwashita, H. Tongu
    Kyoto ICR, Uji, Kyoto, Japan
  
  Funding: The work is supported by Japan Society for the Promotion of Science Grant-in-Aid for Young Scientist (A) No.17H04839.
The multilayer thin film structure of the superconductor has been proposed by A. Gurevich to enhance the maximum gradient of SRF cavities. The lower critical field Hc1 at which the vortex start penetrating the superconducting material will be improved by coating Nb with thin film superconductor such as NbN. It is expected that the enhancement of Hc1 depends on the thickness of each layer. In order to determine the optimum thickness of each layer and to compare the measurement results with the theoretical prediction proposed by T. Kubo, we developed the Hc1 measurement system using the third harmonic response of the applied AC magnetic field at KEK. For the Hc1 measurement without the influence of the edge or the shape effects, the AC magnetic field can be applied locally by the solenoid coil of 5mm diameter in our measurement system. ULVAC made the NbN-SiO2 multilayer thin film samples of various NbN thicknesses. In this report, the measurement result of the bulk Nb sample and NbN-SiO2 multilayer thin film samples of different thickness of NbN layer will be discussed. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP078  
About • paper received ※ 23 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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THFUA2 Evaluation of the Superconducting Characteristics of Multi-Layer Thin-Film Structures of NbN and SiO2 on Pure Nb Substrate 807
 
  • R. Katayama, H. Hayano, T. Kubo, T. Saeki
    KEK, Ibaraki, Japan
  • C.Z. Antoine
    CEA-IRFU, Gif-sur-Yvette, France
  • H. Ito
    Sokendai, Ibaraki, Japan
  • R. Ito
    ULVAC, Inc, Chiba, Japan
  • Y. Iwashita, H. Tongu
    Kyoto ICR, Uji, Kyoto, Japan
  • T. Nagata
    ULVAC, Inc., Tsukuba, Japan
  
  In recent years, it has been pointed out that the maximum accelerating gradient of a superconducting RF cavity can be increased by coating the inner surface of the cavity with a multilayer thin-film structure consisting of alternating insulating and superconducting layers. In this structure, the principal parameter that limits the performance of the cavity is the critical magnetic field or effective Hc1 at which vortices begin penetrating into the superconductor layer. This is predicted to depend on the combination of the film thickness. We made samples that have a NbN/SiO2 thin-film structure on a pure Nb substrate with several layers of NbN film deposited using DC magnetron sputtering method. Here, we report the measurement results of effective Hc1 of NbN/SiO2(30 nm)/Nb multilayer samples with thicknesses of NbN layers in the range from 50 nm to 800 nm by using the third-harmonic voltage method. Experimental results show that an optimum thickness exists, which increases the effective Hc1 by 23.8 %.  
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THFUA2  
About • paper received ※ 03 July 2019       paper accepted ※ 05 July 2019       issue date ※ 14 August 2019  
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THP002 Metallographic Polishing Pathway to the Future of Large Scale SRF Facilities 828
SUSP011   use link to see paper's listing under its alternate paper code  
 
  • O. Hryhorenko, M. Chabot
    Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
  • C.Z. Antoine
    CEA-IRFU, Gif-sur-Yvette, France
  • D. Longuevergne
    FLUO, Orsay, France
  
  Funding: The financial support from the European Nuclear Science and Applications Research 2 (ENSAR 2) under grant agreeement N°654002.
Optimization of SRF cavities mainly focuses on pushing the limits of bulk Niobium, cost reduction of cavity fabrication and development of new SRF materials for future accelerators (ILC, FCC). Nowadays chemical etching is the only surface treatment used to prepare SRF surface made of Nb. However the operational cost of chemical facilities is high and these present a very bad ecological footprint. The search of an alternative technique could make the construction of these future large scale facilities possible. Metallographic polishing (MP) is a candidate not only for bulk Nb treatment, but could also provide the mirror-finished substrate for alternative SRF thin films deposition. Recent R&D studies, conducted at IPNO & IRFU, focused on the development of 2-steps MP procedure of Nb flat samples. Roughness of polished surface has been proven better than standard EP treatment and less polluted than CBP. MP provides on flat surfaces a high removal rate (above 1 µm/min) and high reproducibility. The paper will describe the optimized method and present all the surface analysis performed. The first RF characterization of a polished disk will be presented. 		 
poster icon Poster THP002 [2.902 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP002  
About • paper received ※ 20 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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THP041 Impact of the Cu Substrate Surface Preparation on the Morphological, Superconductive and RF Properties of the Nb Superconductive Coatings 935
 
  • C. Pira, E. Chyhyrynets
    INFN/LNL, Legnaro (PD), Italy
  • C.Z. Antoine
    CEA-IRFU, Gif-sur-Yvette, France
  • X. Jiang, S.B. Leith, M. Vogel
    University Siegen, Siegen, Germany
  • A. Katasevs, J. Kaupužs, A. Medvids, P. Onufrijevs
    Riga Technical University, Riga, Latvia
  • O. Kugeler
    HZB, Berlin, Germany
  • O.B. Malyshev, R. Valizadeh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • R. Ries, E. Seiler
    Slovak Academy of Sciences, Institute of Electrical Engineering, Bratislava, Slovak Republic
  • A. Sublet
    CERN, Meyrin, Switzerland
  
  Funding: This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement No 730871.
Nowadays, one of the main issues of the superconducting thin film resonant cavities is the Cu surface preparation. A better understanding of the impact of copper surface preparation on the morphological, superconductive (SC) and RF properties of the coating, is mandatory in order to improve the performances of superconducting cavities by coating techniques. ARIES H2020 collaboration includes a specific work package (WP15) to study the influence of Cu surface polishing on the SRF performances of Nb coatings that involves a team of 8 research groups from 7 different countries. In the present work, a comparison of 4 different polishing processes for Cu (Tumbling, EP, SUBU, EP+SUBU) is presented through the evaluation of the SC and morphological properties of Nb thin film coated on Cu planar samples and QPR samples, polished with different procedures. Effects of laser annealing on Nb thin films have also been studied. Different surface characterizations have been applied: roughness measurements, SEM, EDS, XRD, AFM, and thermal and photo-stimulated exoelectrons measurements. SC properties were evaluated with PPMS, and QPR measurements will be carry out at HZB in the beginning of 2019. 		 
poster icon Poster THP041 [3.196 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP041  
About • paper received ※ 23 June 2019       paper accepted ※ 05 July 2019       issue date ※ 14 August 2019  
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