Keyword: niobium
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TUZGBE5 A Combined Temperature and Magnetic Field Mapping System for SRF Cavities cavity, operation, SRF, experiment 1228
 
  • J.M. Köszegi, K. Alomari, J. Knobloch, O. Kugeler, B. Schmitz
    HZB, Berlin, Germany
  
  In the past decade, a significant improvement of SRF cavity performance has been achieved, yet a number of performance limiting mechanisms, such as magnetic flux trapping, still exist. We present a diagnostics tool which combines flux expulsion measurement during the superconducting phase transition with temperature mapping during operation. This system has a time resolution for both temperature and magnetic field mapping of 2 ms for full cavity coverage, so that short-lived events, including cavity quenches, can easily be resolved.  
slides icon Slides TUZGBE5 [1.358 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUZGBE5  
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WEYGBF3 Nb3Sn Multicell Cavity Coating at JLab cavity, factory, SRF, superconductivity 1798
 
  • 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
  • M.J. Kelley
    Virginia Polytechnic Institute and State University, Blacksburg, USA
  • I.P. Parajuli, MNS. Sayeed
    ODU, Norfolk, Virginia, USA
  
  Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics.
Following encouraging results with Nb3Sn-coated R&D cavities, the existing coating system was upgraded to allow for Nb3Sn coating of CEBAF accelerator cavities. The upgrade was designed to allow Nb3Sn coating of original CEBAF 5-cell cavities with the vapor diffusion technique. Several CEBAF cavities were coated in the upgraded system to investigate vapor diffusion coatings on extended structures. Witness samples coated along with the cavities were characterized with material science techniques, while coated cavities were measured at 4 and 2 K. The progress, lessons learned, and the pathforward are discussed. 		 
slides icon Slides WEYGBF3 [2.381 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEYGBF3  
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WEPAK005 A Cryogenic Current Comparators (CCC) Customized for FAIR-Project pick-up, shielding, cryogenics, electronics 2088
 
  • J. Golm, R. Neubert, F. Schmidl, P. Seidel
    FSU Jena, Jena, Germany
  • J. Golm, T. Stöhlker, V. Tympel
    HIJ, Jena, Germany
  • D.M. Haider, F. Kurian, M. Schwickert, T. Sieber, T. Stöhlker
    GSI, Darmstadt, Germany
  • R. Neubert
    Thuringia Observatory Tautenburg, Tautenburg, Germany
  • M. Schmelz, R. Stolz
    IPHT, Jena, Germany
  • T. Stöhlker
    IOQ, Jena, Germany
  • V. Zakosarenko
    Supracon AG, Jena, Germany
  
  The principle of non-destructive measurement of ion beams by detection of the azimuthal magnetic field, using low temperature Superconducting Quantum Interference Device (SQUID) sensors, has been established at GSI already in the mid 90's. After more recent developments at Jena, GSI and CERN, a CCC was installed in the CERN Antiproton Decelerator (AD) and is operated there routinely as the first stand-alone CCC system. For the Facility for Antiproton and Ion Research (FAIR) a new version of the CCC with eXtended Dimensions (CCC-XD) - especially with a larger inner diameter and adapted parameters - was constructed and first lab tests have already been performed. In parallel, a concept for a dedicated UHV beamline cryostat has been worked out. The CCC-XD system - together with the new cryostat - will be ready for testing in the CRYRING at GSI before the end of 2018. In this contribution, experimental results for the resolution, frequency range, slew rate and pulse-signal obtained by electrical laboratory measurements with the CCC-XD are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAK005  
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WEPMF009 Influence of Argon-Ion Irradiation on Field Emission from Polycrystalline Cu and Large-Grain NB Surfaces radiation, experiment, cavity, vacuum 2384
 
  • S. Soykarci
    University of Wuppertal, Wuppertal, Germany
  • D. Lützenkirchen-Hecht, V. Porshyn, P. Serbun
    Bergische Universität Wuppertal, Wuppertal, Germany
  
  Funding: This work is funded by the BMBF project 05H15PXRB1.
In the present work, systematic investigations of the enhanced field emission (EFE) from polycrystalline copper and large grain niobium surfaces before and after argon-ion irradiation with an energy of 5 keV were performed with a variation of the irradiation time. Results show that the suppression of the EFE might be achievable. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF009  
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WEPMF010 Laser Treatment of Niobium Surface for SRF Aplications laser, cavity, experiment, electron 2387
 
  • V. Porshyn, D. Lützenkirchen-Hecht, P. Serbun
    Bergische Universität Wuppertal, Wuppertal, Germany
  • H. Bürger, S. Soykarci
    University of Wuppertal, Wuppertal, Germany
  
  Funding: The research was funded by the German Federal Ministry of Education and Research (BMBF) under project number 05H15PXRB1.
We report on a laser surface treatment of high purity niobium (110) single crystals. Typical surface defects like scratches, pits, sharp rims and holes were eliminated by a focused pulsed ns-laser beam. A laser fluence of about 0.68 J/cm2 and 40 - 80 pulses per spot were required to induce well detectable surface modifications. The remelted surface was sufficiently smooth, but exhibited also a number of wave structures. Thus, the surface roughness slightly increased with increasing number of pulses. Finally, boiling traces and μm-deep ablation were observed and studied as well. Local field electron emission measurements showed no emission up to 700 MV/m from a moderate remelted area below the boiling point. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF010  
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WEPMF035 Investigating the Effect of Inhomogeneous Resistivity on Bulk RRR and Heat Conductivity Using a Lattice Green's Functions Method cavity, network, lattice, HOM 2436
 
  • N.C. Shipman, A. Macpherson
    CERN, Geneva, Switzerland
  • G. Burt
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • J.A. Mitchell
    Lancaster University, Lancaster, United Kingdom
  
  A method was developed to calculate the bulk RRR (residual resistivity ratio) which would be measured on a superconducting cavity or sample with an inhomogeneous resistivity and arbitrary geometry. The method involves modelling the object as a network of resistors and employs lattice Green's functions. A further adaptation of the method which allows the heat transport characteristics of such an object to be predicted is also described.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF035  
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WEPMF036 RF Test Result of a BNL N-Doped 500 MHz B-Cell Cavity at Cornell cavity, SRF, vacuum, superconducting-cavity 2440
 
  • F. Furuta, M. Ge, T. Gruber, J.J. Kaufman, M. Liepe, J.T. Maniscalco, J. Sears
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • F. Gao, J. Rose
    BNL, Upton, Long Island, New York, USA
  
  Cornell's SRF group has collaborated with Brookhaven National Laboratory (BNL) on one 500 MHz CESR type SRF "B-cell" cavity (BNL B-cell) for the National Synchrotron Light Source II. Cornell has been responsible for RF surface preparation, vertical testing, and short cavity string assembly. As a state-of-the-art surface preparation protocol, Cornell selected Nitrogen doping for the BNL B-cell. N-doping has been well demonstrated and established to push the cavity quality factor (Q0) higher in 1.3GHz SRF cavities at many laboratories. Cornell calculated that N-doping could also be beneficial on a 500MHz SRF cavity, with a potential to increase its Q0 by a factor of two compared with the traditional chemical polishing based surface preparation protocol. Here we report on the detailed surface preparation and vertical test result of the BNL B-cell.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF036  
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WEPMF037 HF Free Bipolar Electro-Polishing Studies on Niobium SRF Cavities at Cornell With Faraday Technology cavity, SRF, MMI, radio-frequency 2443
 
  • F. Furuta, M. Ge, T. Gruber, J.J. Kaufman, P.N. Koufalis, M. Liepe, J. Sears
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • T.D. Hall, M.E. Inman, R. Radhakrishnan, S.T. Snyder, E.J. Taylor
    Faraday Technology, Inc., Clayton, Ohio, USA
  
  Cornell's SRF group and Faraday Technology have been collaborating on two phase-II SBIR projects. One of them is the development and commissioning of a 9-cell scale HF free Bipolar Electro-Polishing (BEP) system. Faraday Technology has upgraded their 1.3 GHz single-cell BEP system for hosting 9-cell cavities. Initial commissioning of the new system was done with a three single-cell cavity string, and high a gradient of 40MV/m was demonstrated during the RF tests at Cornell. After this success with the test string, the 9-cell cavity was processed with the new system at Faraday and RF test was performed at Cornell. Here we report detailed results from these 9-cell scale HF free BEP studies.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF037  
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WEPMF039 Experimental Results on the Field and Frequency Dependence of the Surface Resistance of Niobium Cavities cavity, vacuum, experiment, electron 2451
 
  • P.N. Koufalis, M. Liepe, J.T. Maniscalco, T.E. Oseroff
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  We investigate the field and frequency dependence of the surface resistance of single-cell niobium cavities as a function of surface treatment at 1.3, 2.6, and 3.9 GHz. The surface resistance is broken down into two parts: the temperature-independent residual resistance and the temperature-dependent BCS resistance. While the low-field BCS resistance is known to vary quadratically with frequency, the exact dependence of the BCS and residual resistances on field at higher frequencies are important topics for further investigation. We offer results on a systematic experimental study of the residual and BCS resistance as a function of frequency and field for clean niobium and high-temperature nitrogen-doped niobium.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF039  
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WEPMF041 Insights into the Role of C, N, and O Introduced by Low Temperature Baking on Niobium Cavity Performance cavity, experiment, ECR, superconductivity 2455
 
  • P.N. Koufalis, M. Liepe
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  Previous experiments have shown that introducing nitrogen gas during low temperature bakes (120-160 C) of niobium cavities introduces C, N, and O impurities to the first 10-100 nm of the surface. This new treatment results in higher quality factors and even 'anti-Q-slope' in some cases. However, it is not entirely clear the role that each of these impurities plays in the performance enhancement of the cavities. It has been suggested that interstitial N within the first few nm of the surface is solely responsible for the observed enhancement, but little work has been done on the role of C and O. Because both C and O are abundant in much higher quantities than N near the surface, it is important to understand whether they are beneficial or detrimental to cavity performance. We provide further insight into the effects of C and O on cavity performance by baking in an ambient atmosphere rich in CO2 as opposed to N2.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF041  
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WEPMF042 A Computational Method for More Accurate Measurements of the Surface Resistance in SRF Cavities cavity, SRF, operation, radio-frequency 2458
 
  • J.T. Maniscalco, M. Liepe
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  The principal loss mechanism for superconducting RF cavities in normal operation is Ohmic heating due to the microwave surface resistance in the superconducting surface. The typical method for calculating this field-dependent surface resistance Rs(H) from RF measurements of quality factor Q0 implicitly returns a weighted average of Rs over the surface as a function of peak surface magnetic field H, not the true value of Rs as a function of the local magnitude of H. In this work we present a computational method to convert a measured Q0 vs. Hpeak to a more accurate Rs vs. Hlocal, given knowledge about cavity geometry and field distribution.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF042  
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WEPMF044 Updates on the DC Field Dependence Cavity cavity, multipactoring, SRF, simulation 2465
 
  • J.T. Maniscalco, M. Liepe
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  Work at Cornell has demonstrated good agreement between a theoretical model by A. Gurevich of the anti-Q-slope (a field-dependent decrease of the microwave surface resistance) and experimental results from impurity-doped niobium. As a corollary, the model predicts that a strong DC magnetic field applied parallel to the RF surface will produce a similar decrease in surface resistance. In order to explore this prediction for many materials, we have designed a new coaxial cavity with a strong, uniform DC field superimposed over a weak RF field on a removable and replaceable niobium sample. Here we present updates on the progress of this new cavity.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF044  
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WEPMF046 Modeling of the Frequency and Field Dependence of the Surface Resistance of Impurity-Doped Niobium cavity, experiment, ECR, SRF 2471
 
  • J.T. Maniscalco, P.N. Koufalis, M. Liepe
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  The anti-Q-slope, a field-dependent decrease in surface resistance observed in impurity-doped niobium, has been investigated extensively in 1.3 GHz cavities. New early research into this effect has recently been performed at higher and lower frequencies, revealing an additional dependence on frequency: the anti-Q-slope is stronger at higher frequencies and weaker at lower frequencies. Several models have been proposed to explain the anti-Q-slope, with varying success in this new frequency-dependent regime. In this work, we analyze recent experimental data from a low-temperature-doped 1.3 GHz cavity and a high-temperature nitrogen-doped 2.6 GHz cavity and discuss the implications of these results on the proposed models.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF046  
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WEPMF047 Performance of Samples With Novel SRF Materials and Growth Techniques cavity, SRF, superconducting-RF, site 2475
 
  • T.E. Oseroff, M. Ge, M. Liepe, J.T. Maniscalco, R.D. Porter
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • S.R. McNeal
    Ultramet, Pacoima, California, USA
  • M.J. Sowa
    Veeco-CNT, Medford, USA
  
  Novel materials are currently being studied in an attempt to push accelerating superconducting RF cavities to support higher accelerating fields and to operate with lower power loss. Growing layers of these materials of the quality necessary has proven to be difficult. In this work, we present the SRF performance of planar samples of the promising materials, NbN and Nb¬3Sn, grown using atomic layer deposition (ALD) and chemical vapor deposition (CVD) respectively. Results are promising.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF047  
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WEPMF050 Update on Nb3Sn Progress at Cornell University cavity, SRF, accelerating-gradient, site 2479
 
  • R.D. Porter, J. Ding, D.L. Hall, M. Liepe
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • T.A. Arias, P. Cueva, D.A. Muller, N. Sitaraman
    Cornell University, Ithaca, New York, USA
  
  Niobium-3 Tin (Nb3Sn) is the most promising alternative material for SRF accelerator cavities. The material can achieve higher quality factors, higher temperature operation and potentially higher accelerating gradients compared to conventional niobium. Cornell University has a leading program to produce 2 - 3 micrometer thick coatings of Nb3Sn on Nb for SRF applications using vapor diffusion. This program has been the first to produce quality factors higher than achievable with conventional Nb at usable accelerating gradients. Here we present an update on progress at Cornell University, including studies of the formation of the Nb3Sn layer, density functional theory calculations of Nb3Sn growth, and designs for a sample host cavity for measuring the quench field of Nb3Sn.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMF050  
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WEPMK014 A New Design for the Hilumi Radio-Frequency Dipole Bare Cavity cavity, GUI, resonance, SRF 2659
 
  • M. Parise, P. Berrutti, L. Ristori
    Fermilab, Batavia, Illinois, USA
  
  Crabbing cavities are one of the technological landmark that will allow the LHC to optimize its per-formance and maximize its integrated luminosity by allowing a head-on collision between the bunches despite the non-zero crossing angle. A total of 8 crab cavities will be installed in the interaction region of each of the two experiments, ATLAS and CMS. In the last years, the two types of crab cavities were de-signed, built and tested under the US-LARP R&D pro-gram. Horizontal crabbing is obtained with a radio-frequency dipole cavity (RFD) designed by Old Do-minion University (ODU), SLAC and Fermilab (FNAL). In this paper a new mechanical design, that uses passive stiffeners, is presented. This design leads to a decrease of the Lorentz Force Detuning frequency shift, satisfy the requirements on pressure sensitivity, validate the structural integrity and increase the tuner sensitivity and the maximum elastic tuning range. Furthermore, it will be possible to greatly simplify the shape of the magnetic shield and Helium vessel with respect to the current design.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMK014  
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WEPMK016 New Insight on Nitrogen Infusion Revealed by Successive Nanometric Material Removal cavity, SRF, accelerating-gradient, factory 2665
 
  • M. Checchin, A. Grassellino, M. Martinello, O.S. Melnychuk, S. Posen, A.S. Romanenko, D.A. Sergatskov
    Fermilab, Batavia, Illinois, USA
  
  In this study we present new insight on low temperature nitrogen infusion on bulk niobium superconducting radio-frequency (SRF) cavities. Nitrogen infusion is a thermal treatment recently discovered at Fermilab that allows to reach high accelerating gradients, of the order of 45MV/m, with high Q-factors, of the order of 2 · 1010. Detailed depth dependent RF studies (by means of subsequent HF rinses) and comparisonwith SIMS results pinpointed interstitial nitrogen as the responsible for the improved performance and uncovered the extension of its profile inside the material.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMK016  
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WEPML005 Testing of SSR1 Production Tuner for PIP-II cavity, linac, SRF, cryomodule 2681
 
  • J.P. Holzbauer, D. Passarelli, Y.M. Pischalnikov
    Fermilab, Batavia, Illinois, USA
  
  Funding: This manuscript 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.
The PIP-II project at Fermilab is a proton driver linac calling for the use of five different, novel cavity geometries. Prototyping at Fermilab is in the advanced stages for the low-beta single-spoke resonator (SSR1) and associated technologies. A production tuner design has been fabricated and tested, both warm and cold in the Spoke Test Cryostat (STC). This paper will present the detailed studies on this tuner, including slow motor/piezoelectric tuner range and hysteresis as well as dynamic mechanical system characterization. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML005  
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WEPML010 Operation Regime Analysis of Conduction Cooled Cavities Through Multi-Physics Simulation cavity, operation, SRF, simulation 2697
 
  • R.A. Kostin, R. Dhuley, M.G. Geelhoed, R.D. Kephart, T.K. Kroc, O.V. Prokofiev, J.C.T. Thangaraj
    Fermilab, Batavia, Illinois, USA
  • A. Kanareykin
    Euclid TechLabs, LLC, Solon, Ohio, USA
  
  Funding: Department of Energy
Euclid Techlabs in collaboration with Fermilab IARC (Batavia, IL) is developing industrial superconducting 10MeV electron linac. Conduction cooling is used for cooling instead of liquid helium bath to simplify linac maintenance. The cavity linked to commercially available cryo-cooler cold head through highly conductive aluminium strips. However, this solution raises a problem of contact thermal resistance. This paper shows some results of Comsol multyphysics simulations of the cavity cooling by AL strips. Some insight was obtained on the acceptable range of contact resistance. Operation regimes were obtained at different accelerating gradients and cavity temperatures. The results of simulation are presented and discussed. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML010  
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WEPML013 Anti-Q-slope enhancement in high-frequency niobium cavities cavity, ECR, SRF, experiment 2707
 
  • M. Martinello, S. Aderhold, S.K. Chandrasekaran, M. Checchin, A. Grassellino, O.S. Melnychuk, S. Posen, A.S. Romanenko, D.A. Sergatskov
    Fermilab, Batavia, Illinois, USA
  
  N-doped 1.3 GHz niobium cavities showed for the first time the so-called anti-Q-slope, i.e. the increasing of the Q-factor as a function of the accelerating field. It was verified that the anti-Q-slope is consequence of the decreasing of the temperature-dependent component of the surface resistance as a function of the field. This trend is opposite compared to the increasing of the surface resistance previously observed in 1.3 GHz standard (EP, BCP, 120 C baked) niobium cavities. The effect of the different state-of-the-art surface treatments on the field dependence of the surface resistance is studied for 650 MHz, 1.3 GHz, 2.6 GHz and 3.9 Ghz cavities. This proceeding shows that the field dependence of the temperature-dependent component of the surface resistance has a strong frequency dependence and that the anti-Q-slope may appear even in clean niobium cavities if the resonant frequency is high enough, suggesting new routes toward the understanding of the anti-Q-slope effect.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML013  
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WEPML078 Development of a Superconducting Double-Spoke Cavity at IMP cavity, accelerating-gradient, SRF, ion-source 2869
 
  • T.C. Jiang, H. Guo, Y. He, C.L. Li, L.B. Liu, T. Tan, P.R. Xiong, Z.M. You, W.M. Yue, S.H. Zhang, S.X. Zhang
    IMP/CAS, Lanzhou, People's Republic of China
  
  Superconducting multi-spoke cavities are well-known optional choice for acceleration of heavy ions in medium velocity regimes. The paper describes the design, fabrication and test results of the superconducting double-spoke cavity developed at IMP. After Buffered Chemical Polishing and High pressure Rinsing, one cavity has undergone high gradient RF testing at 4 K in the Vertical Test Stand. We present measurements of the quality factor as a function of accelerating field and maximum field on the surface. Accelerating gradient of more than 15 MV/m is reached with peak electric field of 61 MV/m, and peak magnetic field of 118 mT.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPML078  
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THPAL012 Soft Chemical Polishing and Surface Analysis of Niobium Samples cavity, SRF, linac, operation 3641
 
  • J. Conrad, L. Alff, M. Arnold, S. Flege, R. Grewe, M. Major, N. Pietralla
    TU Darmstadt, Darmstadt, Germany
  • F. Hug
    IKP, Mainz, Germany
  
  Funding: Work supported by the German Federal Ministry for Education and Research (BMBF) under Grant No. 05H15RDRBA
The Superconducting Darmstadt Linear Accelerator S-DALINAC uses twelve Niobium Cavities with a RRR of 280 which are operated at 2 K. The operating frequency is 3 GHz; the design value of the accelerating gradient is 5 MV/m. To achieve the target value of 3 x 10˄9 for Q0, different surface preparation methods were applied and systematically tested using a vertical 2 K cryostat. A well-established technique is the so called Darmstadt Soft Chemical Polishing, which consists of an ultrasonic cleaning of the cavity with ultrapure water followed by oxidizing the inner surface with nitric acid. After rinsing with water the niobium oxide layer is removed with hydrofluoric acid in a separate second step. Finally the structure is rinsed and then dried by a nitrogen flow. Until now each cavity in operation was chemically treated with a proven record of success. In order to understand and to optimize the process on the niobium surface, systematic tests with samples were performed and analyzed using material science techniques like SEM, SIMS and EDX. We will report on the results of our research and we will give a review on our experiences with varied chemical procedures. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL012  
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THPAL029 Comparison of Horizontal and Vertical Electropolishing Methods using Niobium Single-Cell Coupon Cavity cavity, cathode, accumulation, experiment 3692
 
  • V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi
    MGH, Hyogo-ken, Japan
  • H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe
    KEK, Ibaraki, Japan
  
  Horizontal electropolishing (HEP) is an established tech-nique for surface treatment of niobium accelerating cavi-ties. Vertical electropolishing (VEP), in which the cavity is electropolished in the vertical posture, is in R&D phase for parameter optimization. We performed HEP and VEP of a niobium single-cell coupon cavity to compare the effect of both the methods on surface state and removal at different positions of the cavity. HEP was performed at STF, KEK with the standard EP parameters. VEP was performed at Marui Galvanizing Company with a cathode called 'Ninja cathode' that can be rotated during the VEP process. The optimized cathode design and VEP parame-ters resulted in symmetric removal as obtained with the HEP technique and yielded a smooth inner surface of the entire cavity  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL029  
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THPAL030 Vertical Electropolishing of 1.3 GHz Niobium 9-Cell Cavity: Parameter Study and Cavity Performance cavity, cathode, accumulation, linac 3695
 
  • V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi
    MGH, Hyogo-ken, Japan
  • H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe
    KEK, Ibaraki, Japan
  • H. Ito
    Sokendai, Ibaraki, Japan
  • H. Oikawa
    Utsunomiya University, Utsunomiya, Japan
  
  VEP parameters and process have been already optimized with single-cell 1.3 GHz niobium cavity at Marui Galva-nizing Company working in collaboration with KEK. A unique cathode called 'Ninja cathode' with an optimized shape was applied to single-cell cavities. The cathode was effective to stop the bubble accumulation in the upper half-cell of the cavity and yielded smooth surface and uniform removal in the cell. This work shows parameter study with the Ninja cathode and a 9-cell coupon cavity which contains totally 9 coupons and viewports in the first, fifth, and ninth cells. Effects of temperature and acid flow in the cathode housing were studied using coupon currents and by observing bubbles through the viewports. The adequate parameters found with 9-cell coupon cavity were applied on a 9-cell cavity to be tested in vertical cryostat. The VEP and vertical test results are reported.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL030  
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THPAL031 Development of a Vertical Electropolishing Facility for Nb 9-Cell Cavity cavity, cathode, controls, site 3699
 
  • Y.I. Ida, V. Chouhan, K.N. Nii
    MGH, Hyogo-ken, Japan
  • akabori. Akabori, G.M. Mitoya, K. Miyano
    HKK, Morioka, Japan
  • Y. Anetai, F. Takahashi
    WING. Co.Ltd, Iwate-ken, Japan
  • H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe
    KEK, Ibaraki, Japan
  
  Our Nb accelerating cavity vertical electropolishing (VEP) facility development group which was led by KEK started single-cell VEP facility development from 2014. This is based on horizontal electropolishing (HEP) techniques developed by KEK over 10 years and stainless steel electropolishing techniques developed by Marui over 30 years. We have reported results of Nb cavity VEP with Ninja cathode so far. In order to achieve international linear collider (ILC) construction, it is said that cost reduction and productivity improvement are necessary, however in case of 9-cell cavity, uniform inner surface polishing is difficult, as well known to predecessors. In this article, we will present the first report of VEP facility development from initial transparent plastic mock-up to improvement for Nb 9-cell cavity.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL031  
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THPAL035 Design of β=0.65, 5 Cells, 644 MHz Elliptical Cavity for FRIB Upgrade cavity, linac, cryomodule, operation 3712
 
  • M. Xu, C. Compton, C. Contreras-Martinez, W. Hartung, S.H. Kim, S.J. Miller, P.N. Ostroumov, A.S. Plastun, J.T. Popielarski, L. Popielarski, M.A. Reaume, K. Saito, A. Taylor, J. Wei, T. Xu, Q. Zhao
    FRIB, East Lansing, USA
  • I.V. Gonin, T.N. Khabiboulline, V.P. Yakovlev
    Fermilab, Batavia, Illinois, USA
  
  Funding: Work supported by the U.S. DOE Office of Science under Cooperative Agreement DE-SC0000661 and the NSF under Cooperative Agreement PHY-1102511, the State of Michigan and Michigan State University.
The superconducting (SC) linac of the Facility for Rare Isotope Beams (FRIB) under construction will deliver 200 MeV/u, 400 kW beam to the target for producing rare isotopes at Michigan State of University (MSU). For further beam energy upgrade, we have designed the β = 0.65, 5 cells, 644 MHz elliptical cavity. The beam energy can be upgraded to 400 MeV/u by installing 11 cryomodules to the available space in the FRIB tunnel. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL035  
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THPAL036 Nb3Sn Thin Films for the Production of Higher Gradient SRF Cavities at Reduced Cost cavity, SRF, superconductivity, site 3716
 
  • S.A. Kahn, M.A. Cummings
    Muons, Inc, Illinois, USA
  • E.Z. Barzi, D. Turrioni
    Fermilab, Batavia, Illinois, USA
  • S. Falletta
    Politecnico di Torino, Torino, Italy
  • A. Kikuchi
    NIMS, Tsukuba, Ibaraki, Japan
  
  High gradient superconducting cavities (SRF) will be needed for future accelerators. The higher gradient can achieve the high energy with fewer cavities. However the accelerating field of niobium cavities is limited by the peak magnetic field on the cavity surface. Cavities coated with Nb3Sn have a significantly larger Hc2 allowing the cavity to achieve a larger gradient. Measurements of Nb3Sn coated cavities have achieved about half the theoretical predicted gradient. It is possible to improve Nb3Sn plated cavity performance.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL036  
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THPAL065 Improving the Work Function of Nitrogen-Doped Niobium Surfaces for SRF Cavities by Plasma Processing plasma, cavity, SRF, accelerating-gradient 3802
 
  • K.E. Tippey, R. Afanador, M. Doleans, S.-H. Kim, J.D. Mammosser, C.J. McMahan
    ORNL, Oak Ridge, Tennessee, USA
  • M. Martinello
    Fermilab, Batavia, Illinois, USA
  
  Funding: DOE research grant FWP-ERKCSA2; DOE contract DE-AC05-00OR22725
Work function and surface chemistries of SiC-polished, electropolished, and nitrogen-doped niobium coupons were analyzed before and after plasma processing using a neon-oxygen gas mixture. These studies represent an initial enquiry into the feasibility of applying the plasma processing technique designed at ORNL for the Spallation Neutron Source (SNS) to the nitrogen-doped Nb cavities for the Coherent Light Source II (LCLS-II). Work function of all measured samples was increased after plasma processing, which indicates the strong potential of the plasma processing technique as a tool for increasing the accelerating gradient of nitrogen-doped cavities. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL065  
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THPAL086 Superconducting Thin Film RF Measurements cavity, SRF, vacuum, operation 3856
 
  • P. Goudket, L. Bizel-Bizellot, L. Gurran, O.B. Malyshev, S.M. Pattalwar, R. Valizadeh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • G. Burt, L. Gurran
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • P. Goudket, T. Junginger, O.B. Malyshev, S.M. Pattalwar, R. Valizadeh
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • L. Gurran, T. Junginger
    Lancaster University, Lancaster, United Kingdom
  
  As part of an ongoing programme of SRF Thin Films development, a radiofrequency (RF) cavity and cryostat dedicated to the measurement of superconducting coatings at GHz frequencies was designed to evaluate surface resistive losses on a flat sample. The resonator has now been used for measurements on Thin Film samples. Results from a test on a sample previously tested at Cornell University are presented. In order to simplify the measurements and achieve a faster turnaround, the experiment will be moved to a new cryostat fitted with a cryocooler. This will limit the measurements to low power only, but will allow a much faster sorting of samples to identify those that would benefit from further investigation. A description of the system and initial results will be presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL086  
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THPAL118 Critical Fields of SRF Materials cavity, FEL, interface, superconductivity 3921
 
  • T. Junginger
    TRIUMF, Vancouver, Canada
  • T. Prokscha, Z. Salman, A. Suter
    PSI, Villigen PSI, Switzerland
  • A-M. Valente-Feliciano
    JLab, Newport News, Virginia, USA
  
  Nb3Sn and NbTiN are two potential alternative materials to niobium for superconducting RF cavities. In this study direct measurements of the magnetic penetration depth using the low energy muon spin rotation technique are presented, from which the lower critical field and the superheating field are derived. Comparison with RF data confirms that the lower critical field is not a fundamental limitation and predict a potential performance clearly exceeding current state of the art of niobium technology if the superheating field can be achieved. As a potential pathway to avoid premature vortex penetration and reaching the superheating field it is suggested to use a bilayer structure with the outer layer having a larger magnetic penetration depth.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL118  
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THPAL123 Fabrication and Test of β=0.3 325MHz Balloon Single Spoke Resonator cavity, multipactoring, linac, TRIUMF 3934
 
  • Z.Y. Yao, J.J. Keir, D. Kishi, D. Lang, R.E. Laxdal, H.L. Liu, Y. Ma, B. Matheson, B.S. Waraich, Q. Zheng, V. Zvyagintsev
    TRIUMF, Vancouver, Canada
  
  A novel balloon variant of the single spoke resonator (SSR) has been designed, fabricated and tested at TRIUMF. The cavity is the β=0.3 325 MHz SSR1 prototype for the Rare Isotope Science Project (RISP) in Korea. The balloon variant is specifically designed to reduce the likelihood of multipacting barriers near the operating point. A systematic multipacting study led to a novel geometry, a spherical cavity with re-entrant irises plus a spoke. The balloon cavity provides competitive RF parameters and a robust mechanical structure. Cold tests demonstrated the principle of the balloon concept. The fabrication experience and the preliminary test results will be reported in this paper.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL123  
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THPAL126 Nitrogen Bake-out Procedures at the Vertical High-Temperature UHV-Furnace of the S-DALINAC cavity, SRF, vacuum, linac 3937
 
  • R. Grewe, L. Alff, M. Arnold, J. Conrad, S. Flege, M. Major, N. Pietralla
    TU Darmstadt, Darmstadt, Germany
  • F. Hug
    IKP, Mainz, Germany
  
  Funding: Work supported by the Federal Ministry of Education and Research through grant No. 05H15RDRBA.
As the performance limits of bulk Nb srf cavities are reached, our research is focused on materials with superior srf properties like Nb3Sn and NbN. Research on NbN resulted in the "nitrogen-doping" process used for increasing the quality factors of srf cavities for the LCLS-II project. This process leads to delta-phase Nb-N, a phase with higher critical sc parameters than bulk Nb. This phase is formed at temperatures of 800°C in nitrogen atmospheres of 10-2 mbar. Other crystalline phases of NbN have even better sc parameters. We concentrate our research on applicability of delta-phase NbN for cavities. The delta-phase forms at temperatures of above 1300°C, which is more than most of the furnaces at accelerator facilites are capable of. Since 2005 the Institute for Nuclear Physics at the Technische Universität Darmstadt operates a high temperature vacuum furnace which has been upgraded to allow temperatures of up to 1750°C and bakeouts of niobium samples and cavities in nitrogen atmospheres. We will report on the current status of our research on nitrogen bake-out procedures on Nb samples. The samples have been analyzed at the Material Science Departement with SIMS, REM and XRD. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL126  
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THPAL127 Structural Investigations of Nitrogen-Doped Niobium for Superconducting RF Cavities cavity, vacuum, ECR, experiment 3940
 
  • M. Major, L. Alff, M. Arnold, J. Conrad, S. Flege, R. Grewe, M. Mahr, N. Pietralla
    TU Darmstadt, Darmstadt, Germany
  • F. Hug
    KPH, Mainz, Germany
  
  Funding: Work supported by the German Federal Ministry for Education and Research (BMBF) through grant 05H15RDRBA.
Niobium is the standard material for superconducting RF (SRF) cavities. Superconducting materials with higher critical temperature or higher critical magnetic field allow cavities to work at higher operating temperatures or higher accelerating fields, respectively. Enhancing the surface properties of the superconducting material in the range of the penetration depth is also beneficial. 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 (16 K). Already slight nitrogen doping of the alpha-Nb phase results in higher quality factors.* Nb samples were N-doped at the refurbished UHV furnace at IKP Darmstadt. Reference samples were annealed in 1 bar nitrogen atmosphere at different temperatures. In this contribution the results on the structural investigations (x-ray diffraction and pole figure, secondary ion mass spectroscopy, scanning electron microscopy) at the Materials Research Department of TU Darmstadt will be presented.
*Grassellino et al., Proc. SRF2015, MOBA06, 48. 		 
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THPAL130 Effect of Deposition Temperature and Duration on Nb3Sn Diffusion Coating SRF, cavity, experiment, superconductivity 3950
 
  • U. Pudasaini, M.J. Kelley
    The College of William and Mary, Williamsburg, Virginia, USA
  • G.V. Eremeev, M.J. Kelley, C.E. Reece
    JLab, Newport News, Virginia, USA
  • M.J. Kelley, J. Tuggle
    Virginia Polytechnic Institute and State University, Blacksburg, USA
  
  Funding: Partially authored by Jefferson Science Associates under contract no. DE¬AC05¬06OR23177. Work at College of William & Mary supported by Office of High Energy Physics under grant SC0014475.
Nb3Sn is a potential candidate to replace Nb in SRF accelerator cavities to reduce cost and advance perfor-mance. Tin vapor diffusion is the preferred technique to realize such cavities by growing a few microns thick Nb3Sn coating on the interior surface of the niobium cavity. The coating process typically uses temperatures of 1100-1200 °C for 3-6 hours. It is important to better understand the coating process, and optimize the coating parameters to overcome the current limitation on the performance of Nb3Sn coated SRF cavities. We investi-gate Nb3Sn coatings prepared in the temperature range of 900-1200 °C and duration of 3 - 12 hours using various material characterization tools. Variation of these pa-rameters appears to have notable effect on microstructure and topography of the obtained surface. 		 
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THPAL131 Studies of Electropolishing and Oxypolishing Treated Diffusion Coated Nb3Sn Surfaces cavity, SRF, experiment, superconductivity 3954
 
  • U. Pudasaini, M.J. Kelley
    The College of William and Mary, Williamsburg, Virginia, USA
  • G.V. Eremeev, M.J. Kelley, C.E. Reece
    JLab, Newport News, Virginia, USA
  • M.J. Kelley, J. Tuggle
    Virginia Polytechnic Institute and State University, Blacksburg, USA
  
  The Nb3Sn-coated cavities aim to enhance perfor-mance and significantly reduce cost. Their fabrication involves tin vapor diffusion coating of Nb3Sn on the interior surface of a Nb cavity. Controlled removal of first few layers to obtain a smoother and cleaner surface could be desirable to improve the high field RF perfor-mance. Our first results from the application of elec-tropolishing and oxypolishing techniques on Nb3Sn-coated surfaces indicated reduced surface roughness, and the surface composition appeared nominally unchanged. Systematic studies explore the effect of different polish-ing parameters into the roughness and composition. We present the latest results from SEM/EDS and AFM studies of Nb3Sn-coated samples treated with electropolishing and oxypolishing.  
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THPAL140 Rework Recipe Development, Analysis and Results of Select 9-Cell Cavities for LCLS-II cavity, embedded, site, linac 3968
 
  • A.D. Palczewski, K. Macha, H. Park, C.E. Reece, K.M. Wilson
    JLab, Newport News, Virginia, USA
  • A. Burrill, D. Gonnella
    SLAC, Menlo Park, California, USA
  
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The SLAC National Accelerator Laboratory is currently constructing a major upgrade to its accelerator, the Linac Coherent Light Source II (LCLS-II). Several Department of Energy laboratories, including the Thomas Jefferson National Accelerator Facility (JLab) and Fermi National Accelerator Laboratory (FNAL), are collaborating in this project. The cryomodules for this project each consist of eight 1.3-GHz cavities produced by two vendors, Research Instruments GmbH in Germany (RI*) and Ettore Zanon S.p.a. in Italy (EZ*), using niobium cell material from Tokyo Denkai Co., Ltd. (TD) and Ningxia Orient Tantalum Industry Co., Ltd. (OTIC/NX)). During the initial production run, cavity performance from one of the vendors (Vendor A) was far below expectation. All the cavities had low Q0, later attributed to minimal EP as well as high-flux-trapping NX material, early quench behaviour below 18 MV/m, with many having Q0 roll-off at 12-16 MV/m. Production was stopped multiple times over the following 6 months, with test batches of cavities being made to ascertain the root cause of the problem. The final root cause of the problem was found to be inappropriate grinding of the RF surface prior to welding which left normal conducting inclusions in the surface. In addition, most cavities showed internal and external weld spatter which required post weld grinding and a very rough surface from operating the electropolishing machine in an etching rather than polishing regime. All issues have been corrected on new cavities and rework is underway on the originally effected cavities. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL140  
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THPAL141 Optimizing Procurement Strategies for LCLS-II cavity, cryomodule, HOM, status 3972
 
  • K.M. Wilson, G. Cheng, E. Daly, J.A. Fitzpatrick, N.A. Huque, M.L. Laney, F. Marhauser, A.D. Palczewski, H. Park, T. Peshehonoff, G. Tenbusch, M. Torres
    JLab, Newport News, Virginia, USA
  
  Funding: This work was supported by the LCLS-II Project and the U.S. Department of Energy, Contract DE-AC02-76SF00515
The SLAC National Accelerator Laboratory is currently constructing a major upgrade to its accelerator, the Linac Coherent Light Source II (LCLS-II). Several Department of Energy national laboratories, including the Thomas Jefferson National Accelerator Facility (JLab), are participating in this project. JLab is responsible for procuring a number of critical components. Over the course of this project, JLab has evolved several procurement strategies to minimize risk and improve performance while working within the constraints of budget and schedule. This paper discusses the impact of procurement choices on project technical success. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL141  
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THPAL143 Commissioning of JLab Vertical Cavity Processing System for SRF Nb Single Cell and Multicell Cavity With HF-Free Pulse-Reverse Electopolishing cavity, SRF, controls, MMI 3978
 
  • H. Tian, M. Lester, J. Musson, H.L. Phillips, C.E. Reece, C. Seaton
    JLab, Newport News, Virginia, USA
  
  Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177
Pulse reversed electropolishing of niobium SRF cavities, using a dilute aqueous H2SO4 electrolyte without HF yields equivalent RF performance with traditional EP. Comparing with present EP process for Nb SRF cavity which uses 1:10 volume ratio of HF (49%) and H2SO4 (98%), pulse reverse EP (also known as bipolar EP (BPEP)) is ecologically friendly and uses relatively benign electrolyte options for cavity processing. In this study, we report the commissioning of a new vertical cavity processing system for SRF Nb single cell and multi-cell cavities with HF-free pulse-reverse electropolishing at Jefferson Lab, together with RF test of cavities being processed. We report the scale-up challenges and interpretations from process R&D to implementation. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL143  
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THPMF032 Preparation and Testing of the BERLinPro Gun 1.1 Cavity cavity, gun, cathode, pick-up 4117
 
  • H.-W. Glock, J. Knobloch, A. Neumann, Y. Tamashevich
    HZB, Berlin, Germany
  
  Funding: Work supported by German Bundesministerium für Bildung und Forschung, Land Berlin, and grants of the Helmholtz Association
For the BERLinPro energy recovery LINAC, HZB is developing a superconducting 1.4-cell electron gun, which, in its final version, is planned to be capable of CW 1.3 GHz operation with 77 pC/bunch. For this purpose a series of three superconducting cavities, denoted as Gun 1.0, Gun 1.1 (both designed for 6 mA) and Gun 2.0 (100 mA) is foreseen. Here the status of the Gun 1.1 cavity is described, including results of the recent vertical testing. Lessons learned from the production and preparation process are summarized, also in order to identify issues critical for the production of Gun 2.0. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMF032  
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THPML132 Cryogenic Performance of an SRF Deflecting Cavity Fabricated Using Alternative Techniques for the ARIEL eLinac cavity, SRF, linac, cryogenics 4992
 
  • D.W. Storey
    Victoria University, Victoria, B.C., Canada
  • R.E. Laxdal, Z.Y. Yao
    TRIUMF, Vancouver, Canada
  
  A 650 MHz SRF deflecting mode cavity has been built and tested for use as a three-way beam separator in the ARIEL eLinac. The cavity operates in a TE-like mode, and has been optimized for high shunt impedance with minimal longitudinal footprint. The device is the first SRF cavity to be fully fabricated in house at TRIUMF. The requirements of the cavity allowed for the development of low cost manufacturing techniques, including the use of Reactor grade niobium and atmospheric pressure TIG welding. The cavity has been fabricated and tested at 4 K and 2 K, obtaining a 4 K Qo of 4·108 at the operating voltage of 0.3 MV, surpassing the goal voltage and quality factor required for operation. Results of the cryogenic tests of the cavity will be presented here.  
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