WEPFDV —  Wednesday Poster Fundamental Development and Research   (30-Jun-21   11:10—12:10)
Paper Title Page
WEPFDV004 A New Model for Q-Slope in SRF Cavities: RF Heating at Multiple Josephson Junctions Due to Weakly-Linked Grain Boundaries or Dislocations 556
 
  • K. Saito
    KEK, Ibaraki, Japan
  • K. Saito
    FRIB, East Lansing, Michigan, USA
 
  Several models are already proposed for Q-slopes in SRF cavity performance, medium field Q-slope (MFQS), high field Q-slope (HFQS). However, these does not explain both in a way unified. Here, a new model by multiple Josephson junctions on weakly linked grain boundaries or dislocations is proposed for the unified explanation. This model suggests two kind of junctions: ceramic like one and weak superconductor one. If plotted the field vs. RF power dissipation, an increase of RF loss is remarkably observed in proportional to the cube of fields, on both BCP’ed and EP’ed cavity (MFQS). An exponential RF dissipation is often observed at high fields for BCP’ed cavity (HFQS). If supposed the number of J-junctions linearly increases with the fields (this is explained by the flux quantum penetration condition), these behaviors are easily explained. In addition, this model has a potential to explain the anti-Q slope behavior observed in Nitrogen doped or mid-temperature baked cavity. In this paper, this model will be explained, then several data analysis results will be presented.  
poster icon Poster WEPFDV004 [2.201 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2021-WEPFDV004  
About • Received ※ 21 June 2021 — Accepted ※ 11 November 2021 — Issue date ※ 16 May 2022  
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WEPFDV005 Tensile Tests of Large Grain Ingot Niobium at Liquid Helium Temperature 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 ※ doi:10.18429/JACoW-SRF2021-WEPFDV005  
About • Received ※ 08 June 2021 — Accepted ※ 12 September 2021 — Issue date ※ 02 May 2022  
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WEPFDV006 Activities at NCBJ Towards Development of the Future, Fully-Superconducting, XFEL-Type, RF Electron Gun 566
 
  • J. Lorkiewicz, P.J. Czuma, A.M. Kosińska, P. Krawczyk, R. Mirowski, R. Nietubyć, M. Staszczak, K. Szamota-Leandersson
    NCBJ, Świerk/Otwock, Poland
  • J.K. Sekutowicz
    DESY, Hamburg, Germany
 
  Our group at NCBJ works on upgrade of 1.6-cell, SRF, XFEL-type injector in collaboration with DESY and other laboratories. The work is focused on preparation of lead-on-niobium photocathode, its positioning in the gun cavity and on the UV laser system for photocurrent excitation. RF focusing effect was used to minimize the predicted emittance and transverse size of accelerated e- beam. Following beam dynamics computation, it has been proposed that the photocathode be recessed 0.45 mm into the rear wall of the gun cavity. It helps focusing e- beam in its low-energy part. Preparation of sc cathodes of Pb layer on Nb plugs (*, **) is reported, aimed at reaching clean, planar and uniform Pb films. The laser system will consist of commercially available Pharos laser and a 4-th harmonic generator. A gaussian, 300 fs long, 257 nm in wavelength UV pulse will be transformed in time by a pulse stretcher/stacker and in space by pi-shaper. The planned optical system will generate cylindrical photoelectron bunch 2 - 30 ps long and 0.2 - 3 mm wide.
* J. Lorkiewicz et al., Vacuum 179 (2020) 109524
** R. Nietubyc et al., NIM A891 (2018) pp. 78-86
 
poster icon Poster WEPFDV006 [2.018 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2021-WEPFDV006  
About • Received ※ 21 June 2021 — Accepted ※ 13 April 2022 — Issue date ※ 03 May 2022  
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WEPFDV007 Main Highlights of ARIES WP15 Collaboration 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.Ö. 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 García
    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.
 
poster icon Poster WEPFDV007 [2.013 MB]  
DOI • reference for this paper ※ doi: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 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 ※ doi:10.18429/JACoW-SRF2021-WEPFDV008  
About • Received ※ 17 June 2021 — Accepted ※ 10 September 2021 — Issue date ※ 01 March 2022  
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WEPFDV010 Structural Investigation of Nitrogen-Doped Niobium for SRF Cavities 581
 
  • M. Major, L. Alff, M. Arnold, J. Conrad, S. Flege, R. Grewe, N. Pietralla
    TU Darmstadt, Darmstadt, Germany
 
  Funding: Work supported by the German Federal Ministry for Education and Research (BMBF) through grant 05H18RDRB2 and the German Research Foundation (DFG) via the AccelencE Research Training Group (GRK 2128).
Niobium is the standard material for superconducting RF (SRF) cavities for particle acceleration. Superconducting materials with higher critical temperature or higher critical magnetic field allow cavities to work at higher operating temperatures or higher accelerating fields, respectively. One direction of search for new materials with better properties is the modification of bulk niobium by nitrogen doping. In the Nb-N phase diagram, the cubic delta-phase of NbN has the highest critical temperature. Niobium samples were annealed and doped with nitrogen in the high-temperature furnace at TU Darmstadt and investigated at its Materials Research Department with respect to structural modifications. X-ray diffraction (XRD) confirmed the appearance of Nb4N3 and Nb2N phases on the surface of the samples. A single cell cavity was annealed under optimized doping conditions. The test samples treated together with the cavity showed almost single Nb4N3 phase. XRD pole figures also showed grain growth during sample annealing.
 
DOI • reference for this paper ※ doi:10.18429/JACoW-SRF2021-WEPFDV010  
About • Received ※ 22 June 2021 — Revised ※ 18 August 2021 — Accepted ※ 17 November 2021 — Issue date ※ 19 November 2021
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