Fundamental R&D - non Nb
non-Nb films
Paper Title Page
MOP003 Development of Nb3Sn Cavity Coating at IMP 21
 
  • Z.Q. Yang, H. Guo, Y. He, C.L. Li, Z.Q. Lin, M. Lu, T. Tan, P.R. Xiong, S.H. Zhang, S.X. Zhang
    IMP/CAS, Lanzhou, People’s Republic of China
 
  The A15 superconductor Nb3Sn is one of the most promising alternative materials to standard niobium for SRF applications. In this paper, we report our progress in the development of Nb3Sn cavity coating by vapor diffusion method at IMP. The evolutionary process of nucleation was analyzed. Influence of SnCl2 partial pressure inhomogeneity was studied. Less-nuclear zones were found on the surfaces of nucleation samples. The Nb3Sn film structure and composition were investigated and analyzed. In light of knowledge obtained above, the coating process was optimized. Finally, both 1.3 GHz and 650 MHz single cell cavities were coated and vertically tested both at 4 K and 2 K. Effect of low temperature baking (1000°C for 48 hs) on the RF performance of Nb3Sn cavity was studied. After baking, the Q drop in the low field region was eliminated and the Q in the intermediate field region was increased 8 times. The Q was 10 times larger than that of the Nb cavity at 4.2 K even in the case of the ambient field larger than 20 mGs. This study shows that the low temperature baking is an effective enrichment to the post treatment of the Nb3Sn cavity.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP003  
About • paper received ※ 23 June 2019       paper accepted ※ 03 July 2019       issue date ※ 14 August 2019  
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MOP004 Preparation of Pb-Photocathodes at National Centre for Nuclear Research in Poland – State of the Art 25
 
  • J. Lorkiewicz, I. Cieślik, P.J. Czuma, A.M. Kosińska, R. Nietubyć
    NCBJ, Świerk/Otwock, Poland
  • J.K. Sekutowicz
    DESY, Hamburg, Germany
 
  Funding: We are currently using a financial support within "PolFEL - Polish Free Electron Laser" cofounded by the European Regional Development Fund.
R&D activities related to preparation of the superconducting Pb photocathode layer on niobium substrate are ongoing at the National Centre for Nuclear Research (NCBJ) in cooperation with DESY, HZDR, HZB, BNL and other research institutes. The activities are part of the R&D program at DESY for the cw-upgrade of E-XFEL and for the newly approved free electron laser facility PolFEL to be built and operated at NCBJ. The optimization results obtained for the lead deposition on niobium and smoothing of the coated layers are reported. The photocathodes samples were tested for their surface morphology, microstructure and quantum efficiency in terms of the impact on the operation of all-superconducting RF electron injector, proposed for both facilities.
 
poster icon Poster MOP004 [1.446 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP004  
About • paper received ※ 23 June 2019       paper accepted ※ 29 June 2019       issue date ※ 14 August 2019  
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MOP010 Ab Initio Calculations on the Growth and Superconducting Properties of Nb3Sn 39
SUSP023   use link to see paper's listing under its alternate paper code  
 
  • N. Sitaraman, T. Arias, P. Cueva, M.M. Kelley, D.A. Muller
    Cornell University, Ithaca, New York, USA
  • J.M. Carlson, A.R. Pack, M.K. Transtrum
    Brigham Young University, Provo, USA
  • M. Liepe, R.D. Porter, Z. Sun
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Funding: This research was funded by the Center for Bright Beams.
In this work, we employ theoretical ab initio techniques to solve mysteries and gain new insights in Nb3Sn SRF physics. We determine the temperature dependence of Nb3Sn antisite defect formation energies, and discuss the implications of these results for defect segregation. We calculate the phonon spectral function for Nb3Sn cells with different combinations of antisite defects and use these results to determine Tc as a function of stoichiometry. These results allow for the first-ever determination of Tc in the tin-rich regime, where experimental measurements are unavailable and which is critical to understanding the impact of tin-rich grain boundaries on superconducting cavity performance. Finally, we propose a theory for the growth mechanism of Nb3Sn growth on a thick oxide, explaining the puzzling disappearing droplet behavior of Sn on Nb oxide and suggesting how in general an oxide layer reacts with Sn to produce a uniform Nb3Sn layer.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP010  
About • paper received ※ 02 July 2019       paper accepted ※ 03 July 2019       issue date ※ 14 August 2019  
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MOP011 High Frequency Nb3Sn Cavities 44
SUSP020   use link to see paper's listing under its alternate paper code  
 
  • R.D. Porter, M. Liepe, J.T. Maniscalco
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Niobium-3 Tin (Nb3Sn) is an alternative material to Nb for SRF cavities. This material is capable of higher temperature operation and has high theoretical maximum accelerating gradients. Cornell University is a leader in the development of this material for SRF applications, and current Nb3Sn 1.3 GHz single cells produced at Cornell achieve quality factors above 10zEhNZeHn at 4.2 K at medium fields, far above what can be reached with niobium. Most of the recent Nb3Sn cavity development has been done at 1.3 GHz. In this paper, we present new results from Nb3Sn cavities at 2.6 GHz and 3.9 GHz. We compare relative cavity performance and flux trapping sensitivities, and extract frequency dependencies. Results show that the frequency can be increased without degrading the performance of the cavities, opening the path towards a new generation of compact and efficient SRF cavities for a wide range of future applications.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP011  
About • paper received ※ 05 July 2019       paper accepted ※ 12 July 2019       issue date ※ 14 August 2019  
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MOP013 Reducing Surface Roughness of Nb3Sn Through Chemical Polishing Treatments 48
 
  • H. Hu, M. Liepe, R.D. Porter
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Niobium-3 tin (Nb3Sn) is a promising alternative material for SRF cavities, with theoretical limits for critical temperatures and superheating fields reaching twice that of conventional Nb cavities. However, currently achievable accelerating gradients in Nb3Sn cavities are much lower than their theoretical limit. One limitation to the maximum accelerating gradient is surface magnetic field enhancement caused by the surface roughness of Nb3Sn. However, there are currently no standard techniques used to reduce Nb3Sn surface roughness. Since Nb3Sn is only 2-3 microns thick, it is difficult to selectively polish Nb3Sn without removing the entire layer. Here, we investigate reducing the surface roughness of Nb3Sn through applying chemical polishing treatments, including modified versions of standard techniques such as Buffered Chemical Polishing (BCP) and Electropolishing (EP). Through data acquired from Atomic Force Microscope (AFM) scans, SEM scans, and SEM-EDS analysis, we show the effects of these chemical treatments in reducing surface roughness and consider the changes in the chemical composition of Nb3Sn that may occur through the etching process. We find that BCP with a 1:1:8 solution is ineffective while EP halves the surface roughness of Nb3Sn.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP013  
About • paper received ※ 01 July 2019       paper accepted ※ 04 July 2019       issue date ※ 14 August 2019  
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MOP014 Electroplating of Sn Film on Nb Substrate for Generating Nb3Sn Thin Films and Post Laser Annealing 51
SUSP036   use link to see paper's listing under its alternate paper code  
 
  • Z. Sun, M. Liepe, T.E. Oseroff, R.D. Porter
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • T. Arias, A.B. Connolly, J.M. Scholtz, N. Sitaraman, M.O. Thompson
    Cornell University, Ithaca, New York, USA
  • X. Deng
    University of Virginia, Charlottesville, Virginia, USA
  • K.D. Dobson
    University of Delaware, Newark, Delaware, USA
 
  Controlling film quality of Nb3Sn is critical to its SRF cavity performance. The state-of-the-art vapor diffusion approach for Nb3Sn deposition observed surface roughness, thin grain regions, and misfit dislocations which negatively affect the RF performance. The Sn deficiency and non-uniformity at the nucleation stage of vapor deposition is believed to be the fundamental reason to cause these roughness and defects issues. Thus, we propose to pre-deposit a uniform Sn film on the Nb substrate, which is able to provide sufficient Sn source during the following heat treatment for Nb3Sn nucleation and growth. Here, we demonstrated successful electrodeposition of a low-roughness, dendrite-free, excellent-adhesion Sn film on the Nb substrate. More importantly, we further achieved a uniform, low-roughness (Ra = 66 nm), pure-stoichiometric Nb3Sn film through thermal treatment of this electroplated Sn film in the furnace. Additionally, we provide preliminary results of laser annealing as a post treatment for epitaxial grain growth and roughness reduction.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP014  
About • paper received ※ 22 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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MOP015 RF Performance Sensitivity to Tuning of Nb3Sn Coated CEBAF Cavities 55
 
  • G.V. Eremeev, W. Crahen, J. Henry, F. Marhauser, C.E. Reece
    JLab, Newport News, Virginia, USA
  • U. Pudasaini
    The College of William and Mary, Williamsburg, Virginia, USA
 
  Funding: Co-Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics.
Nb3Sn has the potential to surpass niobium as the material of choice for SRF applications. The potential of this material stems from a larger superconducting energy gap, which leads to expectations of a higher RF critical field and a lower RF surface resistance. The appeal of better superconducting properties is offset by the relative complexity of producing practical Nb3Sn structures, and Nb3Sn sensitivity to lattice disorder challenges the use of the material for practical applications. Such sensitivity is indirectly probed during SRF cavity development, when the cavity is tuned to match the desired accelerator frequency. In the course of recent experiments we have coated and tuned several multi-cell cavities. Cold RF measurements before and after tuning showed degradation in cavity performance after tuning. The results of RF measurement were compared against strain evolution on Nb3Sn surface during tuning based on CST and ANSYS models.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP015  
About • paper received ※ 26 June 2019       paper accepted ※ 01 July 2019       issue date ※ 14 August 2019  
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MOP016 Insights Into Nb3Sn Coating of CEBAF Cavities From Witness Sample Analysis 60
 
  • 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
 
  Funding: Co-Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics.
With the progress made in the Nb3Sn coatings on single-cell SRF cavities, development is ongoing to reproduce single-cell cavity results on practical structures such as CEBAF 5-cell cavities. During CEBAF cavity coating development, several changes from the single-cell procedure to the coating setup and the heating profile were introduced to improve the quality of Nb3Sn films. To witness the properties of grown Nb3Sn films in different cavity locations, 10 mm x 10 mm samples were positioned in strategic places within the coating chamber. Composition and structure of the samples were analyzed with surface analytic techniques and correlated with sample location during coatings. Implications from sample analysis to Nb3Sn coatings on different geometries are discussed in this contribution.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP016  
About • paper received ※ 26 June 2019       paper accepted ※ 29 June 2019       issue date ※ 14 August 2019  
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MOP018 Recent Results From Nb3Sn Single Cell Cavities Coated at Jefferson Lab 65
 
  • U. Pudasaini, M.J. Kelley
    The College of William and Mary, Williamsburg, Virginia, USA
  • G. Ciovati, G.V. Eremeev, M.J. Kelley, C.E. Reece
    JLab, Newport News, Virginia, USA
  • I.P. Parajuli, Md.N. Sayeed
    ODU, Norfolk, Virginia, USA
 
  Funding: Partially authored by Jefferson Science Associates under contract no. DE¬AC05¬06OR23177. Supported by Office of High Energy Physics under grants DE-SC-0014475 to the College of William and DE-SC-0018918 to Virginia Tech
Because of superior superconducting properties (Tc ~ 18.3K, Hs h ~ 425 mT and delta ~ 3.1 meV) compared to niobium, Nb3Sn promise better RF performance (Q0 and Eacc) and/or higher operating temperature (2 K Vs 4.2 K) for SRF cavities. Nb3Sn-coated SRF cavities are produced routinely by depositing a few micron-thick Nb3Sn films on the interior surface of Nb cavities via tin vapor diffusion technique. Early results from Nb3Sn cavities coated with this technique exhibited precipi-tous low field Q-slope, also known as Wuppertal slope. Several Nb3Sn single cell cavities coated at JLab ap-peared to exhibit similar Q-slope. RF testing of cavi-ties and materials study of witness samples were con-tinuously used to modify the coating protocol. At best condition, we were able to produce Nb3Sn cavity with Q0 in excess of ~ 5×1010 at 2 K and ~ 2×1010 at 4 K up the accelerating gradient of ~15 MV/m, without any significant Q-slope. In this presentation, we will dis-cuss recent results from several Nb3Sn coated single-cell cavities linked with material studies of witness samples, coating process modifications and the possi-ble causative factors to Wuppertal slope.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP018  
About • paper received ※ 23 June 2019       paper accepted ※ 29 June 2019       issue date ※ 14 August 2019  
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THFUA5
Field Limitation in Nb3Sn Cavities  
 
  • R.D. Porter
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Niobium-3 Tin (Nb3Sn) is the most promising alternative material to Nb for SRF cavities, allowing for twice the operating temperature and potentially twice the accelerating gradient compared to Nb. According to the superheating field, an elliptical Nb3Sn cavity could reach 96 MV/m. However, current Cornell Nb3Sn cavities quench between 14 and 18 MV/m in CW operation. Previous work has shown that cavity quench occurs at a thermal surface defect, but the details of the defect are not yet understood. Here we present further studies of the defect/quench mechanism conducted at Cornell and with collaborators. These studies suggest new quench mechanisms and rule out older hypotheses.  
slides icon Slides THFUA5 [12.734 MB]  
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THFUA6 Nb3Sn Films for SRF Cavities: Genesis and RF Properties 810
 
  • U. Pudasaini, M.J. Kelley
    The College of William and Mary, Williamsburg, Virginia, USA
  • 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
 
  Funding: Partially authored by Jefferson Science Associates under contract no. DE¬AC05¬06OR23177. Supported by Office of High Energy Physics under grants DE-SC-0014475 to the College of William and DE-SC-0018918 to Virginia Tech.
Understanding of Nb3Sn nucleation and growth is essential to the progress with Nb3Sn vapor diffusion coatings of SRF cavities. Samples representing different stages of Nb3Sn formation have been produced and examined to elucidate the effects of nucleation, growth, process conditions, and impurities. Nb3Sn films from few hundreds of nm up to ~15 µm were grown and characterized using AFM, SEM/EDS, XPS, EBSD, SIMS, and SAM. Microscopic examinations of samples suggest the mechanisms behind Nb3Sn thin film nucleation and growth. RF measurements of coated cavities were combined with material characterization of witness samples to adapt the coating process in "Siemens" coating configuration. Understanding obtained from sample studies, applied to cavities, resulted in Nb3Sn cavity with quality factor 2 ×1010 at 15 MV/m accelerating gradient at 4 K, without "Wuppertal" Q-slope. We discuss the genesis of the Nb3Sn thin film in a typical tin vapor diffusion process, and its consequences to the coating of SRF cavities.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THFUA6  
About • paper received ※ 23 June 2019       paper accepted ※ 29 June 2019       issue date ※ 14 August 2019  
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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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THFUB1 Nb3Sn at Fermilab: Exploring Performance 818
 
  • S. Posen, J. Lee, O.S. Melnychuk, Y.M. Pischalnikov, D.A. Sergatskov, B. Tennis
    Fermilab, Batavia, Illinois, USA
  • J. Lee, D.N. Seidman
    NU, Evanston, Illinois, USA
 
  Fermilab’s Nb3Sn coating program produced its first 1.3 GHz single cell cavities in early 2017 and since then has explored the performance of Nb3Sn on a wide variety of cavity substrates and performed microscopic studies down to atomic resolution. Results to present in this talk include a study of frequency dependence from 650 MHz to 1.3 GHz of BCS resistance, residual resistance, and magnetic flux sensitivity. We show microscopic studies performed in collaboration with Northwestern University’s Materials Science and Engineering Department of limitation mechanisms in Nb3Sn, including thin film regions and tin segregation at grain boundaries, discussing correlations with RF performance and mechanisms for the formation of these features during growth. Finally, we present results of the first 1.3 GHz 9-cell cavity coated with Nb3Sn.  
slides icon Slides THFUB1 [27.194 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THFUB1  
About • paper received ※ 29 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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