Fundamental R&D - Nb
material studies
Paper Title Page
TUFUA7 Review of Muon Spin Rotation Studies of SRF Materials 360
 
  • T. Junginger
    Lancaster University, Lancaster, United Kingdom
  • R.E. Laxdal
    TRIUMF, Vancouver, Canada
 
  Muons spin rotate in magnetic fields and emit a positron preferentially in spin direction after decay. These properties enable muon spin rotation (muSR) as a precise probe for local magnetism. muSR has been used to characterize SRF materials since 2010. At TRIUMF a so called surface beam implants muons at a material dependent depth of about 150 µm in the bulk. A dedicated spectrometer was developed for field of first vortex penetration and pinning strength measurements of SRF materials in parallel magnetic fields of up to 300 mT. A low energy beam available at PSI implants muons at variable depth in the London layer allowing for direct measurements of the London penetration depth from which the lower critical field and the superheating field can be calculated. This facility is limited to parallel magnetic fields of up to 25 mT. Here, surface and low energy muSR results on SRF materials are reviewed and cross-correlated to each other and to further results from additional experiments. Finally, we present the status of a new facility based on the similar beta-NMR technique enabling measurements in the London layer of SRF materials exposed to parallel magnetic fields above 200 mT.  
slides icon Slides TUFUA7 [4.063 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUA7  
About • paper received ※ 01 July 2019       paper accepted ※ 12 July 2019       issue date ※ 14 August 2019  
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TUFUB1
Direct Correlation of State of the Art Cavity Performance With Surface Nb Nano-Hydrides Cutouts Observed via Cryogenic AFM  
 
  • Z-H. Sung
    Fermilab, Batavia, Illinois, USA
 
  There was no abstract provided by the author.  
slides icon Slides TUFUB1 [8.368 MB]  
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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, D. Longuevergne
    IPN, Orsay, France
  • C.Z. Antoine
    CEA-IRFU, Gif-sur-Yvette, 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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THP003 Results on Bulk Niobium Surface Resistance Measurement With Pillbox Cavity on TE011 and TE012 Modes 833
 
  • G. Martinet
    IPN, Orsay, France
 
  Surface measurement of superconducting samples is required to characterize processes of bulk niobium preparation for SRF resonators. In order to reduce characterization cost and improve measurement performances, a pill-box cavity has been developed at IPN Orsay. Using TE011 and TE012 modes, we describe the latest results based on calorimetric method.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP003  
About • paper received ※ 23 June 2019       paper accepted ※ 03 July 2019       issue date ※ 14 August 2019  
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THP004 Design and Fabrication of a Quadrupole-Resonator for Sample R&D 838
SUSP042   use link to see paper's listing under its alternate paper code  
 
  • R. Monroy-Villa, D. Reschke, M. Wenskat
    DESY, Hamburg, Germany
  • W. Hillert, R. Monroy-Villa, M. Wenskat
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  • S. Keckert, O. Kugeler, D.B. Tikhonov
    HZB, Berlin, Germany
  • P. Putek, S.G. Zadeh, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  • U. van Rienen
    University of Rostock, Rostock, Germany
 
  Being able to obtain BCS and material properties from the same surface is necessary to gain a fundamental understanding of the evolution of SRF surfaces. A test resonator which will allow to obtain BCS properties from samples is currently under development at the University of Hamburg and DESY and is based on the Quadrupole Resonators developed and operated at CERN and HZB. The current status of the necessary infrastructure, the procurement process and design considerations are shown. In addition, an outline of the planed R&D project with the Quadrupole Resonator will be presented and first RF measurements and surface analysis results of samples will be shown  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP004  
About • paper received ※ 23 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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THP007 In-Situ EXAFS Investigations of Nb-Treatments in N2 at Elevated Temperatures 842
THP005   use link to see paper's listing under its alternate paper code  
 
  • P. Rothweiler, B. Bornmann, J. Klaes, D. Lützenkirchen-Hecht, R. Wagner, S. von Polheim
    University of Wuppertal, Wuppertal, Germany
 
  Funding: We gratefully acknowledge financial support by the German Federal Ministry of Education and Research (BMBF) under project No. 05H15PXRB1.
Smooth polycrystalline Nb metal foils were exposed to dilute N2 and Kr atmospheres at elevated temperatures of up to 900°C. Transmission mode X-ray absorption spectroscopy (EXAFS) experiments were used to study the resulting changes of the atomic short range order structure in-situ. EXAFS data were collected prior to any heat treatment as well as during the different process steps at elevated temperatures with a time resolution of about 1 s, and the samples were also studied after cooling to room temperature. In general, only very small changes of the Nb-EXAFS data could be detected after the processing in N2-atmospheres, and no evidence for bulk formation of Nb-nitrides was found. In contrast, the quantitative EXAFS data evaluation revealed slightly distorted Nb-Nb coordinations, suggesting that N-atoms are increasingly incorporated on octahedral interstitial sites in the host lattice with increasing N2-exposure. For the treatments in Kr-atmospheres, simultaneous measurements are feasible at both the K-edge of the Nb host and the Kr dopant. Those studies gave clear evidence for a Kr uptake during the heat treatment, and will be discussed in more detail at the conference.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP007  
About • paper received ※ 23 June 2019       paper accepted ※ 01 July 2019       issue date ※ 14 August 2019  
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THP008 The Technical Study of Nb3Sn Film Deposition on Copper by HiPIMS 846
 
  • L. Xiao, X.Y. Lu, W.W. Tan, D. Xie, Y. Yang, L. Zhu
    PKU, Beijing, People’s Republic of China
 
  Our work is mainly focused on the deposition methods of Nb3Sn films on Cu substrates and film‘s properties. The superconducting transition temperature(Tc) of Nb3Sn film is 12K. There are diffraction peaks of Nb3Sn in the X-ray diffraction patterns in which without diffraction peaks of copper compounds. Scanning electron micro-structures of Nb3Sn film reflect its nice compactness and binding force between film and substrate.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP008  
About • paper received ※ 23 June 2019       paper accepted ※ 01 July 2019       issue date ※ 14 August 2019  
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THP009 Pulse Laser Annealing of Niobium Film on Copper for SRF Cavities 848
 
  • Y. Yang, X.Y. Lu, W.W. Tan, L. Xiao, D. Xie, L. Zhu
    PKU, Beijing, People’s Republic of China
 
  Thin film cavities were proposed as the most promis-ing next generation superconducting cavities. The chal-lenges are improving the surface superconducting per-formance and reducing defects of the coating film, which can be greatly solved by laser annealing. Laser annealing system has been set up in Peking University, and experi-ments with niobium thin film sample have been carried out. Superconducting performance and other properties of Nb/Cu samples before and after annealing were com-pared. Recrystallization happened and surface structure improved a lot according to the results.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP009  
About • paper received ※ 22 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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THP010 The Mechanism of Electropolishing of Niobium from Choline Chloride-based Deep Eutectic Solvents 852
 
  • Q.W. Chu, H. Guo, S.C. Huang, A.D. Wu, Z.M. You
    IMP/CAS, Lanzhou, People’s Republic of China
 
  Funding: National Natural Science Foundation (11705252)
The mechanism of electropolishing of niobium (Nb) from choline chloride-based deep eutectic solvent (DES) was studied by anodic polarization tests and electrochemical impedance spectroscopy (EIS) using a Nb rotating disk electrode (RDE). Based on the results of an anodic polarisation test, the electropolishing of Nb is mass transport controlled. EIS results are consistent with the compact salt film mechanism for niobium electropolishing in this electrolyte. The influence of rotation rate, applied potential and electrolyte temperature on the electropolishing mechanism of Nb was investigated. As the applied potential positively shift, Rct, Rp and L increase, CPE decrease and Rs unchanged. The increase in rotation rate and electrolyte temperature leads to a decrease of Rs, Rct, Rp and L, and an increase of CPE.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP010  
About • paper received ※ 18 June 2019       paper accepted ※ 02 July 2019       issue date ※ 14 August 2019  
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THP011 Niobium Semiproducts for the Superconducting Strands and SRF Cavities in Russia 857
 
  • M.V. Alekseev, I.M. Abdyukhanov, V.A. Drobyshev, M.V. Kravtsova, M.V. Krylova, P.A. Lykianov, K.A. Mareev, V.I. Pantsyrny, M.V. Polikarpova, M.M. Potapenko, A.G. Silaev, A.S. Tsapleva
    SC A A Bochvar High-Technology Research Institute of Inorganic Materials, Moscow, Russia
  • M.Y. Shlyakhov, S.M. Zernov
    JSC - TVEL, Moscow, Russia
 
  The melting regimes of the niobium ingots with high chemical purity and low hardness for the Nb3Sn, NbTi and other superconducting materials manufacture have been developed at SC "VNIINM". Using this niobium material and by the SC "VNIINM" manufacture regimes at the SC "Chepetsky Mechanical Plant" 220 tons of Nb3Sn and NbTi strands for ITER and 12 km of Nb3Sn strands for HL-LHC (CERN) with the required characteristics have been successfully produced. The review of the characteristics of the different semiproducts (sheets, tubes, rods), made in Russia from the special grade niobium, and of the superconducting strands, manufactured with the use of them, is presented in the paper. The ways of the further improvement of the niobium ingots melting regimes and niobium sheets deformation and annealing regimes with the target of achieving RRR > 300 for the SRF cavities application are discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP011  
About • paper received ※ 23 June 2019       paper accepted ※ 04 July 2019       issue date ※ 14 August 2019  
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THP012 Assessment of the Mechanical Properties of Ultra-High Purity Niobium After Cold Work and Heat Treatment With the HL-LHC Crab Cavities as Benchmark 860
 
  • A. Gallifa Terricabras, A. Amorim Carvalho, I. Aviles Santillana, S. Barrière, R. Calaga, E. Cano-Pleite, O. Capatina, M.D. Crouvizier, L. Dassa, M.S. Meyer, N. Valverde Alonso
    CERN, Geneva, Switzerland
  • M. Benke, A.B. Palotas, G. Szabó, M. Szűcs
    University of Miskolc, Faculty of Materials Science and Engineering, Miskolc-Egyetemváros, Hungary
  • A. Hlavács, G.J. Krallics, V. Mertinger, M. Sepsi
    University of Miskolc, Miskolc, Hungary
 
  The High Luminosity Large Hadron Collider (HL-LHC) is the upgrade of the world’s largest particle collider; it will allow the full exploitation of the LHC potential and its operation beyond 2025. An essential part of the HL-LHC project are the Crab Cavities, that are particle deflecting SRF cavities of non-axisymmetric shape made of bulk ultra-high purity Nb. Since the cavities are produced by complex metal sheet forming processes, followed by a heat treatment (HT) for H outgassing (650 °C, 24 h), there is uncertainty on their mechanical properties after manufacturing and in service conditions (2 K). Mechanical tests at room temperature have been conducted on RRR300 pure Nb samples. The samples were previously submitted, by cold cross-rolling, to different levels of plastic deformation representative of the effective plastic strain seen by the Nb sheets during forming operations. Moreover, a comparison of the mechanical properties of cold cross-rolled samples before and after HT has been established. Results of evolution of the microstructure and hardness are also presented. This study can be of interest for Nb cavities to be sub-mitted to HT at 650 °C, and may help to push the design of novel SRF cavities.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP012  
About • paper received ※ 22 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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THP014 First Direct Imaging and Profiling TOF-SIMS Studies on Cutouts from Cavities Prepared by State-of-the-Art Treatments 866
 
  • A.S. Romanenko, A. Grassellino, M. Martinello, Y. Trenikhina
    Fermilab, Batavia, Illinois, USA
  • D. Bafia
    Illinois Institute of Technology, Chicago, Illinois, USA
 
  Funding: This work has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
Small amounts of interstitial impurities in the penetra-tion depth of superconducting radio frequency (SRF) cavities have a dramatic effect on the quality factors and maximum accelerating gradients. Here we report the first TOF-SIMS studies of cutouts from cavities prepared by all modern surface treatments, which allow a direct corre-lation of the impurity distribution with the observed cavity performance. Imaging capability of our instrument allows to avoid the possible issues associated with the ‘‘ghost’’ depth profiles appearing as a consequence of particulate surface contamination, which likely caused the inconclusive SIMS results on e.g. oxygen diffusion in the past.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP014  
About • paper received ※ 02 July 2019       paper accepted ※ 04 July 2019       issue date ※ 14 August 2019  
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THP017 Crystallographic Characterization of Nb3Sn Coatings and N-Doped Niobium via EBSD and SIMS 871
SUSP001   use link to see paper's listing under its alternate paper code  
 
  • J.W. Angle, M.J. Kelley, J. Tuggle
    Virginia Polytechnic Institute and State University, Blacksburg, USA
  • G.V. Eremeev, M.J. Kelley, C.E. Reece
    JLab, Newport News, Virginia, USA
  • M.J. Kelley, U. Pudasaini
    The College of William and Mary, Williamsburg, Virginia, USA
 
  Historically, niobium has been used as the superconducting material in SRF cavities. Due the high operational costs, other materials are currently being considered. Nb3Sn coatings have been investigated over the past several decades, motivated by potentially higher operating temperatures. More recently niobium has been doped with nitrogen to improve the quality factor (Q). Currently, a need for better understanding still exists for both mechanisms. EBSD has been shown to be a viable technique to determine the crystallographic orientation and the size of the Nb3Sn grains. The EBSD maps obtained show a bimodal distribution of grain sizes with smaller Nb3Sn grains found present near the Nb3Sn/Nb interface. In addition to the Nb3Sn coatings, N-doped niobium coupons were analyzed by EBSD and found that the coupon had preferred surface orientation. The EBSD analysis was found to be vital as specific grains could be targeted in SIMS to better understand the diffusion of nitrogen with respect to crystal orientation.  
poster icon Poster THP017 [2.571 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP017  
About • paper received ※ 23 June 2019       paper accepted ※ 29 June 2019       issue date ※ 14 August 2019  
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THP020 Study of Dislocation Content Near Grain Boundaries using Electron Channeling Contrast Imaging and its Effect on Superconducting Properties of Niobium 876
 
  • M. Wang, T.R. Bieler
    Michigan State University, East Lansing, Michigan, USA
  • S. Balachandran, S. Chetri, P.J. Lee
    NHMFL, Tallahassee, Florida, USA
  • S. Chetri, A. Polyanskii
    ASC, Tallahassee, Florida, USA
  • C. Compton, C. Compton
    FRIB, East Lansing, Michigan, USA
  • C. Compton
    NSCL, East Lansing, Michigan, USA
 
  Funding: U.S. Department of Energy. National Science Foundation Cooperative Agreement No. DMR-1157490 (-2017) DMR-1644779 (2018-) and the State of Florida
Trapped micro-Tesla levels of magnetic flux degrade the performance of Nb superconducting radio frequency (SRF) accelerators. Recent studies have revisited the role of small deformation (dislocation substructure influence) on cavity performance. However, the link between microstructural defects and mechanisms leading to poor performance is still unresolved. To examine the mechanism of flux pinning by dislocations and grain boundaries, systematic studies on bi-crystal Nb tensile samples were designed with strategically chosen orientation relationships between neighboring crystals with respect to the grain boundaries. Laue X-ray diffraction and electron backscatter diffraction analysis was used to measure crystal orientations of a large-grain Nb slice, from which the bi-crystals were extracted. Dislocation structures near the grain boundaries were characterized before and after 5% tensile deformation using electron channeling contrast imaging (ECCI), after which the magnetic flux behavior was observed using cryogenic magneto-optical imaging (MOI). We discuss the conditions under which we observe increased flux pinning in regions of high dislocation density.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP020  
About • paper received ※ 23 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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THP043 Deposition Parameter Effects on Niobium Nitride (NbN) Thin Films Deposited Onto Copper Substrates with DC Magnetron Sputtering 945
SUSP008   use link to see paper's listing under its alternate paper code  
 
  • S.B. Leith, X. Jiang, M. Vogel
    University Siegen, Siegen, Germany
  • R. Ries, E. Seiler
    Slovak Academy of Sciences, Institute of Electrical Engineering, Bratislava, Slovak Republic
 
  Funding: The EASITrain project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant No 764879.
As part of efforts to improve the performance of SRF cavities, to that prescribed by future operating requirements, alternative materials are currently being investigated. NbN is one of the alternatives under investigation to provide these better performance figures. In this contribution, a summary of results from an investigation into DC magnetron sputtered NbN thin films deposited onto copper substrates is presented. The copper substrates were prepared using a mechanical polishing process, followed by a chemical etching process. The NbN films were prepared in a large scale commercial coating system. A high and low value for the substrate temperature, process pressure, bias voltage, cathode power, nitrogen gas percentage, and the working gas type, using either Argon or Krypton, constitute the parameters of this study. The base pressure of the system prior to deposition was 5x107 hPa for all coatings. The resulting films have been characterised using various surface characterisation methods to determine the effects of the deposition parameters during the film growth process. The deposition parameters have been optimised based on the characterisation results.
 
poster icon Poster THP043 [1.169 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP043  
About • paper received ※ 23 June 2019       paper accepted ※ 29 June 2019       issue date ※ 14 August 2019  
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