Author: Sublet, A.
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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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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.
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About • paper received ※ 23 June 2019       paper accepted ※ 05 July 2019       issue date ※ 14 August 2019  
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