Author: Perez Fontenla, A.T.
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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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Electrodeposition of Copper Applied to the Manufacture of Seamless SRF Cavities  
  • G.J. Rosaz, S. Atieh, S. Calatroni, L.M.A. Ferreira, E. Garcia-Tabares Valdivieso, C. Garion, L. Lain-Amador, A.T. Perez Fontenla, K. Scibor, M. Taborelli, C. Yin Vallgren
    CERN, Geneva, Switzerland
  Nb thin film SRF cavities have demonstrated for many years their strong potential as being an alternative to bulk Nb cavities [1]. However most of the defects observed in the Nb layers originate from defects inherited from the substrate itself [2]. Two routes are used to manufacture Cu cavities. The first one consists of forming the half-cells independently by either spinning or electro-hydroforming. The latter are then joined together and to the cut-offs by electron-beam welding. The second one is a seamless process in which the cell is entirely spun around a mandrel and then electron-beam welded to the cut-offs. Both approaches require welding, leading to potential formation of porosities. We propose an innovative route, inspired from a technology used to form small diameter vacuum chambers [3]. The cavity is formed by electrodeposition of Cu on a sacrificial mandrel whose surface state will determine the inner cavity’s surface quality. The strength of the process relies on the total absence of welding. We present the values obtained for Young Modulus, Ultimate Tensile Stress, roughness and RRR on dedicated samples. We will then discuss the fabrication route of a real cavity.
[1] C. Benvenuti et al., IEEE transactions on applied superconductivity, vol. 9, No. 2, June 1999.
[2] G. Rosaz et al., FCC week 2018
[3] L. Lain Amador et al., JVSTA, vol. 36, pp. 021601, 2018.
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