Author: Rosaz, G.J.
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THFUA7
RF Performances of Nb3Sn Coatings on a Copper Substrate for Accelerating Cavities Applications  
 
  • M. Arzeo, S. Fernandez, E.A. Ilyina, G.J. Rosaz, W. Venturini Delsolaro
    CERN, Geneva, Switzerland
  • M. Bonura, C. Senatore
    UNIGE, Geneva, Switzerland
 
  In the last decades, with the advancement of the bulk niobium technology for making superconducting RF (SRF) accelerating cavities, the expected theoretical limitations are being reached. For this reason superconducting materials alternative to niobium are being considered. One of the most promising among them is the Nb3Sn alloy. The higher critical temperature and field makes it very attractive for SRF applications. The coating of superconducting Nb3Sn films on a copper substrate has been optimized at CERN. Few micron thick films with excellent structural and morphological properties are prepared via DC magnetron sputtering of stoichiometric targets. While DC superconducting properties were measured along with the optimization of the coating methods, the RF performances were still unknown. In this talk we shall report on the results from the first complete RF characterization of such films. The surface resistance Rs is estimated as a function of both temperature and RF peak magnetic field at three different frequencies by means of the quadrupole resonator at CERN. The sensitivity of Rs to thermal cycling around Tc, and to trapped magnetic field, is also studied and presented.  
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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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THP031 Operation Experience with the LHC ACS RF System 911
 
  • K. Turaj, L. Arnaudon, P. Baudrenghien, O. Brunner, A.C. Butterworth, F. Gerigk, M. Karppinen, P. Maesen, E. Montesinos, F. Peauger, G.J. Rosaz, E.N. Shaposhnikova, D. Smekens, M. Taborelli, M. Therasse, H. Timko, D. Valuch, N. Valverde Alonso, W. Venturini Delsolaro
    CERN, Meyrin, Switzerland
 
  The LHC accelerating RF system consists of two cryomodules per beam, each containing four single-cell niobium sputtered 400.8 MHz superconducting cavities working at 4.5 K and an average accelerating voltage of 2 MV. The paper summarises the experience, availability and evolution of the system within 10 years of operation. The lessons learned from the successful replacement and re-commissioning of one cryomodule with a spare module, and the recent re-test of the originally installed module on the test stand are also included. Finally, a review of currently launched spare cavity production and long-term developments are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP031  
About • paper received ※ 23 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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FRCAB2
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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