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MOBA05 Nature of Quality Factor Degradation in SRF Cavities due to Quench cavity, superconductivity, simulation, cryogenics 41
 
  • M. Checchin
    Fermilab, Batavia, Illinois, USA
  
  Superconductive quench is a well-known phenomenon that causes magnetic flux trapping in superconducting accelerating cavities increasing the radio-frequency surface resistance. This paper is addressed to the understanding of the quench-induced losses nature. We present the proof that the real origin of quench-related quality factor degradation is consequence only of ambient magnetic field trapped at the quench spot. Also, we show how the quality factor can be fully recovered after it was highly deteriorated quenching several times in presence of external magnetic field. Such phenomenon was found to be completely reliable up to certain values of applied magnetic field, above that the cavity quality factor cannot be fully recovered anymore.  
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MOPB010 Field-Dependent Surface Resistance for Superconducting Niobium Accelerating Cavities: The Case of N-Doping niobium, cavity, data-analysis, superconductivity 95
 
  • W. Weingarten
    Private Address, SERGY, France
  • R.G. Eichhorn
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  The dependence of the Q-value on the RF field (Q-slope) for superconducting RF cavities is actively studied in various accelerator laboratories. Although remedies against this dependence have been found, the physical cause still remains obscure. A rather straightforward two-fluid model description of the Q-slope in the low and high field domains is extended to the case of the recently experimentally identified increase of the Q-value with the RF field obtained by so-called "N-doping”.
This paper was initiated when one of the authors (W.W., retiree from CERN) visited Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, NY. 		 
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MOPB018 Introduction of Precisely Controlled Microstructural Defects into SRF Cavity Niobium Sheets and Their Impact on Local Superconducting Properties niobium, cavity, SRF, superconductivity 120
 
  • M. Wang, T.R. Bieler, D. Kang
    Michigan State University, East Lansing, Michigan, USA
  • C. Compton
    FRIB, East Lansing, Michigan, USA
  • D.C. Larbalestier, A. Polyanskii, Z-H. Sung
    ASC, Tallahassee, Florida, USA
  • P.J. Lee
    NHMFL, Tallahassee, Florida, USA
  
  Funding: Research supported by DOE/OHEP (contract number DE-FG02-09ER41638 at MSU and DE-SC0009960 at FSU) and the State of Florida.
When SRF cavity shapes are formed from Nb sheets, the metallurgical processing introduces microstructural defects such as dislocations and low-angle grain boundaries that can serve as pinning centers for magnetic flux that may degrade cavity performance. Therefore, the relationship between magnetic flux behavior and microstructural defects in carefully strained SRF Nb sheet was investigated. Laue X-ray and EBSD-OIM crystallographic analyses of large grain ingot slices were used to characterize microstructural defects and then predict which grains and sample orientations will produce desired model defects due to tensile deformation. Grain orientations were chosen to favor specific slip systems, which generate dislocations with special angles with respect to the sample surface. Nb bicrystals were also prepared to investigate the effects of grain boundaries on flux pinning. The generated defect structures were confirmed by OIM and TEM. Cryogenic magneto-optical imaging was used to directly observe the penetration of magnetic flux into the deformed Nb. These model samples have deformation that is similar to that expected in typical cavity forming processes. 		 
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MOPB020 Mean Free Path Dependence of the Trapped Flux Surface Resistance SRF, niobium, simulation, superconductivity 129
 
  • M. Checchin, A. Grassellino, M. Martinello, A. Romanenko
    Fermilab, Batavia, Illinois, USA
  • M. Martinello
    Illinois Institute of Technology, Chicago, Illlinois, USA
  • J. Zasadzinski
    IIT, Chicago, Illinois, USA
  
  Funding: Work supported by the US Department of Energy, Office of High Energy Physics
In this article a calculation of the trapped flux surface resistance is presented. The two main mechanisms considered in such approach are the oscillation of the magnetic flux trapped in the superconductor due to the Lorentz force, and the static resistance associated to the normal conducting vortex core. The model derived shows a good description of the available experimental data, highlighting that the radio frequency vortex dissipation is mostly due to the static part of the surface resistance. We show that the surface resistance for 100% trapped flux normalized to the trapped field (expressed in nOhm/mG) can be approximated to R/B=18.3*(l f)1/2/(50.1+l) with l the mean free path in nm and f the frequency in GHz. 		 
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MOPB047 Secondary Electron Yield of Electron Beam Welded Areas of SRF Cavities cavity, gun, niobium, vacuum 196
 
  • M. Basovic, S. Popović, M. Tomovic, L. Vušković
    ODU, Norfolk, Virginia, USA
  • F. Čučkov, A. Samolov
    University of Massachusetts Boston, Boston, Massachusetts, USA
  
  Secondary Electron Emission (SEE) is a phenomenon that contributes to the total electron activity inside the Superconducting Radiofrequency (SRF) cavities during the accelerator operation. SEE is highly dependent on the state of the surface. During electron beam welding process, significant amount of heat is introduced into the material causing the microstructure change of Niobium (Nb). Currently, all simulation codes for field emission and multipacting are treating the inside of the cavity as a uniform, homogeneous surface. Due to its complex shape and fabricating procedure, and the sensitivity of the SEE on the surface state, it would be interesting to see if the Secondary Electron Yield (SEY) parameters vary in the surface area on and near the equator weld. For that purpose, we have developed experimental setup that can measure accurately the energy distribution of the SEY of coupon-like like samples. To test the influence of the weld area on the SEY of Nb, dedicated samples are made from a welded plate using electron beam welding parameters common for cavity fabrication. SEY data matrix of those samples will be presented.  
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MOPB055 Characterization of Nitrogen Doping Recipes for the Nb SRF Cavities niobium, cavity, SRF, cryogenics 223
 
  • Y. Trenikhina, A. Grassellino, O.S. Melnychuk, A. Romanenko
    Fermilab, Batavia, Illinois, USA
  
  For the future development of the nitrogen doping technology, it’s vital to understand the mechanisms behind the performance benefits of N-doped cavities as well as the performance limitations, such as quench field. Following various doping recipes, cavity cutouts and flat niobium samples have been evaluated with XRD, SEM, SIMS and TEM in order to relate structural and compositional changes in the niobium near-surface to SRF performance. Annealing of Nb cavities with nitrogen for various durations and at various temperatures lead to a layer containing inclusions of non-superconducting Nb nitride phases, followed by unreacted Nb with an elevated N-interstitials concentration. We found that EP of the N-treated cavities removes the unwanted niobium nitride phases, confirming that performance benefits are originating from the elevated concentration of N interstitials. The role of low temperature Nb hydride precipitants in the performance limitation of N-doped cavities was evaluated by TEM temperature dependent studies. Finally, extended characterization of the original cavity cutouts from the N-doped RF tested cavity sheds some light on quenching mechanisms.  
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MOPB059 Field Emission Investigation of Centrifugal-Barrel-Polished Nb Samples cavity, site, vacuum, survey 237
 
  • S. Lagotzky, G. Müller
    Bergische Universität Wuppertal, Wuppertal, Germany
  • A. Navitski
    DESY, Hamburg, Germany
  • A.L. Prudnikava, Y. Tamashevich
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  
  Funding: This work was funded by BMBF project 05H12PX6.
Actual and future SRF-accelerators require high accelerating gradient Eacc and quality factor Q0, which are often limited by enhanced field emission (EFE)* caused by surface roughness or particulates**. Various expensive surface preparation techniques (e.g. BCP, EP, HPR etc.) have been developed to obtain the required surface quality and remove the emitters. Recently, centrifugal barrel polishing (CBP) has been reconsidered to obtain a comparable surface roughness as EP with less effort***. We have started to investigate Nb samples, which were prepared as coupons in a single cell 1.3 GHz cavity by an optimized five step CBP process with a final dry ice cleaning. EFE maps showed the first emitter (1 nA) at 60 MV/m, and 32 emitters at 110 MV/m. SEM/EDX analysis of the emitting sites revealed many Al2O3 inclusions with sharp edges. Therefore, subsequent BCP (~20 μm removal) was applied to the sample. Surface analysis as well as EFE characterization of CBP treated Nb coupons with/without BCP step will be presented.
*D. Reschke et al., THPP021, LINAC14.
**A. Navitski et al., PRSTAB 16, 112001 (2013).
***C.A. Cooper, L.D. Cooley, Supercond. Sci. Technol. 26, 015011 (2013). 		 
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MOPB061 Suppression of Upstream Field Emission in RF Accelerators cavity, cryomodule, SRF, site 246
 
  • F. Marhauser, S.V. Benson, D. Douglas
    JLab, Newport News, Virginia, USA
  • L.J.P. Ament
    ASML US Inc., Wilton, CT, USA
  
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
So-called electron loading is the primary cause for cavity performance limitations in modern RF accelerating cavities. In superconducting RF cavities in particular, the onset of parasitic electron effects may start at field levels as low as a few MV/m. Electron loading can be attributed to mainly three phenomena: field emission, multiple impact electron amplification, and RF electrical breakdown. Field emission has been a persistent issue despite advances in SRF technology, whereas RF electrical breakdown and multipacting can be controlled by appropriate cavity design choices. Field emission becomes a major concern when the electrons emitted are captured by the accelerating RF field and directed along the beam axis through a series of cavities or even entire cryomodules. Consequently, electrons can accumulate energy comparable to that of the main beam over similar distances. This can represent a considerable dark current, which can travel downstream or upstream depending on the field-emitting site of origin. In this paper, a method is presented that can significantly suppress the upstream field emission by design. 		 
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MOPB094 Inspection and Repair Techniques for the EXFEL Superconducting 1.3 GHz Cavities at Ettore Zanon S.p.A: Methods and Results cavity, operation, accelerating-gradient, controls 368
 
  • G. Massaro, G. Corniani, N. Maragno
    Ettore Zanon S.p.A., Schio, Italy
  • A. Matheisen, A. Navitski
    DESY, Hamburg, Germany
  • P. Michelato, L. Monaco
    INFN/LASA, Segrate (MI), Italy
  
  The quality control of the inner surface of superconducting RF cavities is essential in order to assure high accelerating gradient and quality factor. Ettore Zanon S.p.A. (EZ) has implemented in the serial production an optical system that use an high-resolution camera, in order to detect various types of defects. This system is added to a grinding machine, that was specifically designed and built to repair imperfections of the cavities inner surface. This inspection and repair system is applied to recover performance limited cavities of the 1.3 GHz European XFEL project, where surface irregularities are detected, either by the Obacht inspection system at Desy or the optical system at EZ. The optical system and the grinding procedure are qualified using two series cavities limited in gradient and showing different types of surface defects. The performances of these cavities have been recovered to reach the specifications of the project. Until now, all the series XFEL cavities built by EZ, repaired with this technique, have shown an accelerating gradient well above the EXFEL goal.  
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TUAA02 Commissioning of the SRF Linac for ARIEL cavity, cryomodule, linac, TRIUMF 457
 
  • V. Zvyagintsev, Z.T. Ang, T. Au, S. Calic, K. Fong, P.R. Harmer, B. Jakovljevic, J.J. Keir, D. Kishi, P. Kolb, S.R. Koscielniak, A. Koveshnikov, C. Laforge, D. Lang, M.P. Laverty, R.E. Laxdal, Y. Ma, A.K. Mitra, N. Muller, R.R. Nagimov, W.R. Rawnsley, R.W. Shanks, R. Smith, B.S. Waraich, L. Yang, Z.Y. Yao, Q. Zheng
    TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
  
  This paper is reporting commissioning results for the SRF linac of ARIEL facility at TRIUMF. The paper is focused on the SRF challenges: cavity design and performance, ancillaries design and preparation, cryomodule design and performance, RF system and final beam test results.  
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TUAA04 Rapid Growth of SRF in India cavity, niobium, linac, SRF 467
 
  • D. Kanjilal
    IUAC, New Delhi, India
  
  Funding: Funding received from Ministry of Higher Education through University Grants Commission of India and from Department of Atomic Energy are gratefully acknowledged.
The talk shall summarize the recent advances in the SRF program in various research centres in India. The SRF related activities at Inter-University Accelerator Centre (IUAC) at Delhi , Raja Ramanna Centre for Advanced Technology (RRCAT) at Indore, Bhabha Atomic Research Centre (BARC) and Tata Institute of Fundamental Research (TIFR) both at Mumbai, and Variable Energy Cyclotron Centre (VECC) at Kolkata shall be addressed. In particular indigenous niobium resonator fabrication and test facilities of IUAC operational for more than a decade which have been used extensively for development, fabrication and utilization of various types of resonators will be discussed. The results from the commissioning of the full three linac modules having eight niobium quarter wave resonators in each module of the heavy ion linac at IUAC for regular scheduled experiments will be presented. The technology and infrastructure developments at RRCAT, BARC, TIFR and VECC for fabrication, processing and tests of future cavities will be discussed. 		 
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TUPB014 First Operation of a Superconducting RF Electron Test Accelerator at Fermilab gun, cavity, operation, superconducting-RF 571
 
  • E.R. Harms, R. Andrews, C.M. Baffes, D.R. Broemmelsiek, K. Carlson, D.J. Crawford, N. Eddy, D.R. Edstrom, J.R. Leibfritz, A.H. Lumpkin, S. Nagaitsev, P. Piot, P.S. Prieto, J. Reid, J. Ruan, J.K. Santucci, V.D. Shiltsev, W.M. Soyars, D. Sun, R.M. Thurman-Keup, A. Valishev, A. Warner
    Fermilab, Batavia, Illinois, USA
  
  Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
A test accelerator utilizing SRF technology recently accelerated its first electrons to 20 MeV at Fermilab. Foreseen enhancements will make acceleration to 300 MeV possible at a maximum beam power of 80 kW. A summary of commissioning steps and first experiments as well as current beam parameters compared to design is presented. Plans for expansion and the future physics program are also summarized. 		 
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TUPB016 Progress on Superconducting Linac for the RAON Heavy Ion Accelerator cavity, linac, cryomodule, ion 578
 
  • H.J. Kim
    IBS, Daejeon, Republic of Korea
  
  The RISP (Rare Isotope Science Project) has been proposed as a multi-purpose accelerator facility for providing beams of exotic rare isotopes of various energies. It can deliver ions from proton to uranium. Proton and uranium ions are accelerated upto 600 MeV and 200 MeV/u respectively. The facility consists of three superconducting linacs of which superconducting cavities are independently phased. Requirement of the linac design is especially high for acceleration of multiple charge beams. In this paper, we present the RISP linac design, the prototyping of superconducting cavity and cryomodule.  
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TUPB045 Surface Analysis and Material Property Studies of Nb3Sn on Niobium for Use in SRF Cavities cavity, niobium, radio-frequency, klystron 665
 
  • D.L. Hall, H. Conklin, T. Gruber, J.J. Kaufman, M. Liepe, J.T. Maniscalco, B. Yu
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • Th. Proslier
    ANL, Argonne, Illinois, USA
  
  Funding: Work supported by DOE grant DE-SC0008431 and NSF grant PHY-141638. Use of CCMR via NSF MRSEC program (DMR-1120296)
Studies of superconducting Nb3Sn cavities and samples at Cornell University and Argonne National Lab have shown that current state-of-the-art Nb3Sn cavities are limited by material properties and imperfections. In particular, the presence of regions within the Nb3Sn layer that are deficient in tin are suspected to be the cause of the lower than expected peak accelerating gradient. In this paper we present results from a material study of the Nb3Sn layer fabricated using the vapour deposition method, with data collected using AFM, SEM, TEM, EDX, and XRD methods as well as with pulsed RF testing. 		 
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TUPB046 Structure and Composition of Nb3Sn Diffusion Coated Films on Nb ion, niobium, SRF, cavity 669
 
  • J. Tuggle, M.J. Kelley
    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, H. Xu
    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. College of William & Mary supported by U.S. DOE Office of High Energy Physics under grant DE-SC-0014475
The structure and composition of Nb3Sn films obtained by diffusion coating niobium coupons and SRF cavities were investigated by x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and scanning electron microscopy (SEM) with energy-dispersive x-ray spectroscopy (EDS) and electron back-scatter diffraction (EBSD), including native surfaces, depth profiles and cross-sections. We find that the native surface oxide is significantly tin-rich, we have measured depth profiles. We find that the grains apparent in the SEM images are individual crystallites having no evident relationship to the substrate or each other. 		 
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TUPB047 Next Generation of SRF-Guns: Low Secondary Electron Yield Based on a Thin Film Approach target, gun, cathode, SRF 673
 
  • C. Schlemper, X. Jiang, M. Vogel
    University Siegen, Siegen, Germany
  
  Multipacting is a common issue in the context of cathode units of superconducting radiofrequency photoinjectors (SRF-guns) utilized in linear accelerators under resonant conditions. In this study, Titanium Nitride (TiN) and Carbon thin films have been prepared by DC and RF magnetron sputtering in a Nitrogen and Argon plasma discharge, respectively. Films featuring a thickness of about 600 nm were produced under various deposition conditions on substrates such as Copper, Molybdenum, and Silicon. Materials characterization was carried out utilizing SEM, Raman and FTIR spectroscopy, XRD and AFM. In order to evaluate the SEY a new device is introduced, which is capable of quasi in-situ measurements. The latter is realized by connecting the coating-, the SEY- and a contamination chamber into one setup allowing sample transfer under UHV conditions. Even after an exposure to air carbon shows SEY values down to 0.69. This value, however, turns out to be quite sensitive with respect to the actual surface morphology. Clean TiN surfaces, on the other hand, displayed a SEY value as low as 1.4. In this case the SEY value is strongly affected by potential surface contamination.  
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TUPB049 Cutout Study of a Nb3Sn Cavity cavity, niobium, SRF, accelerating-gradient 681
 
  • S. Posen, O.S. Melnychuk, A. Romanenko, D.A. Sergatskov, Y. Trenikhina
    Fermilab, Batavia, Illinois, USA
  • D.L. Hall, M. Liepe
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  The first 1.3 GHz single cell Nb3Sn cavity coated at Cornell was shown in RF measurements at Cornell and FNAL to have poor RF performance. Though subsequent cavities showed much higher quality factors, this cavity exhibited Q0 on the order of 109 caused by strong heating concentrated in one of the half cells. This paper presents an investigation into the source of this excess heating, for the purpose of process improvement, so that similar degradation can be avoided in future coatings. Through the use of temperature mapping both at Cornell and at FNAL, locations with high and low surface resistance were located, cut out from the cavity, and studied with microscopic tools. We present the RF measurements and temperature maps as well as the microscopic analyses, then conclude with plans for continued studies.  
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TUPB050 Secondary Electron Yield of SRF Materials niobium, SRF, vacuum, cavity 686
 
  • S. Aull, T. Junginger, H. Neupert
    CERN, Geneva, Switzerland
  • S. Aull, J. Knobloch
    University of Siegen, Siegen, Germany
  • J. Knobloch
    HZB, Berlin, Germany
  
  The secondary electron yield (SEY) describes the number of electrons emitted to the vacuum per arriving electron at the surface. For a given geometry, the SEY is the defining factor for multipacting activity. In the quest of superconducting RF materials beyond bulk niobium, we studied the SEY of the currently most important candidates for future SRF applications: Nb3Sn, NbTiN and MgB2. All studies were done on clean but technical surfaces, i.e. on clean surfaces exposed to air and with their native oxides as it would be the case for SRF cavities.  
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TUPB053 Research on MgB2 at LANL for the Application to SRF Structures SRF, vacuum, superconductivity, status 700
 
  • T. Tajima, L. Civale, R.K. Schulze
    LANL, Los Alamos, New Mexico, USA
  
  Funding: U.S. Department of Energy (DOE) Office of Science Office of Nuclear Physics Early Career Research Program
This paper is focused on the development of MgB2 coating technique at LANL. Using boron film samples obtained at a large furnace system, we succeeded in obtaining superconducting MgB2 films (Tc of up to 37 K so far) by reacting them with Mg vapor. The major improvements were 1) confinement of the Mg vapor in a hot zone to mitigate the insufficient Mg pressure due to condensation on low temperature surfaces of the connected vacuum pipes and 2) reduction of cooldown time, i.e., ~13 minutes instead of ~1 day with the large system to prevent MgB2 from decomposing. 		 
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TUPB054 Local Composition and Topography of Nb3Sn Diffusion Coatings on Niobium niobium, cavity, site, accelerating-gradient 703
 
  • 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
  
  Funding: Co-authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. College of William & Mary supported by U.S. DOE Office of High Energy Physics under grant DE-SC-0014475.
The potential for energy savings and for increased gradient continues to bring attention to Nb3Sn-coated niobium as a future SRF cavity technology. We prepared these materials by vapor diffusion coating on polycrystalline and single crystal niobium. The effect of changing substrate preparation, coating parameters and post-treatment were examined by AFM and SEM/EDS. The AFM data were analyzed in terms of power spectral density (PSD). We found little effect of pre-coating topography on the result. The PSD’s show some surprising kinship to those obtained from BCP-treated surfaces. SEM/EDS revealed no composition non-uniformities at the micron scale. 		 
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TUPB056 Characterization of Nb3Sn Coated Nb Samples SRF, cavity, ion, niobium 708
 
  • Y. Trenikhina, S. Posen, A. Romanenko
    Fermilab, Batavia, Illinois, USA
  • D.L. Hall
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • M. Liepe
    Cornell University, Ithaca, New York, USA
  
  Nb3Sn has a great potential to replace traditional Nb for the fabrication of SRF cavities. The higher critical temperature of Nb3Sn potentially allows for an increased operational temperature for SRF cavities, which promises cryogenic cost savings. We present preliminary characterization of Nb3Sn layer grown on flat Nb sample prepared by the same chemical vapor deposition method that is used for the cavity coating. SEM, TEM/EDS, TEM imaging and diffraction characterization was used in order to evaluate any chemical and structural defects that could be responsible for the limited quench field and high residual resistance. Variation of local stoichiometry was found in the Nb3Sn layer, which is in line with previous studies. Regions of decreased Sn content can have a lower Tc in comparison to the stoichiometric composition, which may be responsible for the limited performance. AES investigations of the Nb3Sn surface before and after HF-rinse were done in order to explore the mechanism that is responsible for the performance degradation of HF-rinsed Nb3Sn coated cavities.  
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TUPB063 A Multi-Sample Residual Resistivity Ratio System for High Quality Superconductor Measurements ECR, niobium, cavity, feedback 726
 
  • J.K. Spradlin, C.E. Reece, A-M. Valente-Feliciano
    JLab, Newport News, Virginia, USA
  
  Funding: This work is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR2317.
For developing accelerator cavity materials, superconducting transition temperature (TC), transition width (ΔTC), and residual resistivity ratio (RRR), are useful parameters to correlate with SRF performance and fabrication processes of bulk, thin film, and novel materials. The RRR gauges the purity and structure of the superconductor based on the temperature dependence of electron scattering in the normal conducting state. Combining a four point probe delta pulse setup with a switch allows multiplexing of the electrical measurements to 32 samples per cooldown cycle. The samples are measured inside of an isothermal setup in a liquid helium (LHe) dewar. The isothermal setup is required for a quasistatic warmup of the samples through TC. This contribution details the current setup for collecting RRR and TC data, the current standard of throughput, measurement quality of the setup, and the improvements underway to increase the system’s resolution and ease of use. 		 
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TUPB073 Cold Tests of SSR1 Resonators Manufactured by IUAC for the Fermilab PIP-II Project cavity, niobium, proton, radio-frequency 750
 
  • L. Ristori, A. Grassellino, O.S. Melnychuk, D.A. Sergatskov, A.I. Sukhanov
    Fermilab, Batavia, Illinois, USA
  • K.K. Mistri, P.N. Potukuchi, A. Rai, J. Sacharias, S.S.K. Sonti
    IUAC, New Delhi, India
  
  In the framework of the Indian Institutions and Fermilab Collaboration (IIFC) within the PIP-II project, two Superconducting Single Spoke Resonators were manufactured at the Inter-University Accelerator Centre (IUAC) in New Delhi and tested at Fermilab. The resonators were subject to the routine series of inspections and later processed chemically by means of Buffered Chemical Polishing, heat-treated at 600 C and cold-tested at Fermilab in the Vertical Test Stand. In this paper we present the findings of the inspections and the results of the cold-tests.  
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TUPB076 The Multipacting Study of Niobium Sputtered High-Beta Quarter-Wave Resonators for HIE-ISOLDE cavity, simulation, pick-up, niobium 760
 
  • P. Zhang, W. Venturini Delsolaro
    CERN, Geneva, Switzerland
  
  Funding: This work has been supported partly by a Marie Curie Early Initial Training Network Fellowship of the European Community’s 7th Programme under contract number PITN-GA-2010-264330-CATHI.
Superconducting quarter-Wave Resonators (QWRs) will be used in the superconducting linac upgrade in the frame of HIE-ISOLDE project at CERN. The cavities are made of bulk copper with thin niobium film coated. They will be operated at 101.28 MHz at 4.5 K providing 6 MV/m accelerating gradient with 10 W power dissipation. Multipacting (MP) has been studied for the high-beta (β=10.9%) QWRs and two MP barriers have been found: Eacc at around 0.05MV/m and 1.5MV/m. We have used both CST Microwave Studio & Particle Studio and the parallel codes Omega3P & Track3P developed at SLAC. The results from the two codes are consistent and are in good agreement with cavity vertical cold test results. Both MP barriers can be processed by RF during the cavity cold test. 		 
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TUPB085 Characterization of Optical Surface Properties of 1.3 GHz SRF Cavities for the European XFEL cavity, background, niobium, SRF 795
 
  • M. Wenskat, L. Steder
    DESY, Hamburg, Germany
  
  The optical inspection of the inner surface of superconducting rf cavities is a well-established tool at many laboratories. Its purpose is to recognise and understand field limitations and to allow optical quality assurance during cavity production. Within the ILC-HiGrade programme at DESY, as part of the XFEL cavity production, an automated image processing and analysis algorithm has been developed that recognises structural boundaries. The count of features, the length of boundaries and their orientation can be used for characterisation. Appreciable differences are observed depending on the fabrication process at the vendor and the chemical treatment applied. The potential of this framework for automated quality assurance as an integral part of large-scale cavity production will be outlined. In addition, correlations between geometrical surface properties and the maximal accelerating field of twenty cavities have been found. These observations coincide with quench localisation by second sound of two cavities. The distribution of the limiting cell is vendor dependent, indicating weaknesses in the fabrication procedure.  
poster icon Poster TUPB085 [2.272 MB]  
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WEA1A04 Commissioning Results of the HZB Quadrupole Resonator niobium, cavity, quadrupole, SRF 930
 
  • R. Kleindienst, A. Burrill, S. Keckert, J. Knobloch, O. Kugeler
    HZB, Berlin, Germany
  
  Funding: The research leading to these results has received funding from the European Commission under the FP7 Research Infrastructures project EuCARD-2, grant agreement no.312453
Recent cavity results with niobium have demonstrated the necessity of a good understanding of both the BCS and residual resistance. For a complete picture, and comparison with theory, it is essential that one can measure the RF properties as a function of applied magnetic field, temperature, frequency and ambient magnetic field. Standard cavity measurements are limited in their ability to change all parameters freely and in a controlled manner. On the other hand, most sample measurement setups operate at fairly high frequency, where the surface resistance is always BCS dominated. The quadrupole resonator, originally developed at CERN, is ideally suited for RF characterization of samples at frequencies of 400 and 1300 MHz, between which many of today’s SRF cavities operate. We report on a modified version of the QPR with improved RF figures of merit for high-field operation. Experimental challenges in the commissioning run and alternate designs towards a simpler sample change are shown alongside measurement results of a large grain niobium sample. 		 
slides icon Slides WEA1A04 [5.611 MB]  
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WEA1A05 Nanostructure of the Penetration Depth in Nb Cavities: Debunking the Myths and New Findings niobium, cavity, cryogenics, SRF 937
 
  • Y. Trenikhina, A. Romanenko
    Fermilab, Batavia, Illinois, USA
  • J. Kwon, J.-M. Zuo
    UIUC, Urbana, USA
  
  Nanoscale defect structure within the magnetic penetration depth of ~100 nm is key to the performance limitations of niobium superconducting radio frequency (SRF) cavities. Using a unique combination of advanced thermometry during cavity RF measurements, and TEM structural and compositional characterization of the samples extracted from cavity walls at both room and cryogenic temperatures, we directly discover the existence of nanoscale hydrides in SRF cavities limited by the high field Q slope, and show the decreased hydride formation after 120C baking. Crucially, in extended studies we demonstrate that adding 800C hydrogen degassing - both with AND without light BCP afterwards - restores the hydride formation to the pre-120C bake level correlating perfectly with the observed high field Q slope behavior. We also show absence of niobium oxides along the grain boundaries and the modifications of the surface oxide upon 120C bake, which contradicts some of the widely used models of niobium surface.  
slides icon Slides WEA1A05 [31.768 MB]  
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THAA02 SRF Gun Development Overview gun, cathode, cavity, SRF 994
 
  • J.K. Sekutowicz
    DESY, Hamburg, Germany
  
  The most demanding component of a continuous wave (cw) injector is cw operating RF-gun, delivering highly populated low emittance bunches. RF-guns, both working at room temperature and superconducting, when they generate highly populated low emittance bunches have to be operated at high accelerating gradients to suppress space charge effects diluting emittance. Superconducting RF-guns are technically superior to the normal conducting devices because they dissipate orders of magnitude less power when operating at very high gradients in cw mode. In this contribution progress since 2013 in the R&D programs, designing and operation of the SRF-injectors at KEK, HZB, HZDR, PKU and DESY will be discussed.  
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THAA03 SRF Gun at BNL: First Beam and Other Commissioning Results cathode, gun, SRF, cavity 1001
 
  • W. Xu, Z. Altinbas, S.A. Belomestnykh, I. Ben-Zvi, L. DeSanto, S. Deonarine, D.M. Gassner, R.C. Gupta, H. Hahn, L.R. Hammons, C. Ho, J.P. Jamilkowski, P. K. Kankiya, D. Kayran, R. Kellermann, N. Laloudakis, R.F. Lambiase, C.J. Liaw, V. Litvinenko, G.J. Mahler, L. Masi, G.T. McIntyre, T.A. Miller, D. Phillips, V. Ptitsyn, T. Rao, T. Seda, B. Sheehy, K.S. Smith, A.N. Steszyn, T.N. Tallerico, R. Than, J.E. Tuozzolo, E. Wang, D. Weiss, M. Wilinski, A. Zaltsman, Z. Zhao
    BNL, Upton, Long Island, New York, USA
  • S.A. Belomestnykh, I. Ben-Zvi, V. Litvinenko
    Stony Brook University, Stony Brook, USA
  
  The talk shall cover two SRF photoemission electron guns under commissioning at BNL: a 704 MHz elliptical ERL gun and a 112 MHz quarter-wave gun for coherent electron cooling experiment. In particular, the speaker shall report on generating first photoemission beam current from the 704 MHz SRF gun, multipacting issues in the SRF guns, photocathode behavior as well as other commissioning experiences and results.  
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THAA04 Comparison of Cavity Fabrication and Performances Between Fine Grains, Large Grains and Seamless Cavities cavity, SRF, niobium, vacuum 1006
 
  • K. Umemori, H. Inoue, T. Kubo, H. Shimizu, Y. Watanabe, M. Yamanaka
    KEK, Ibaraki, Japan
  • A. Hocker
    Fermilab, Batavia, Illinois, USA
  • T. Tajima
    LANL, Los Alamos, New Mexico, USA
  
  In KEK-CFF, L-band SRF cavity fabrication studies have been actively proceeded. Main target of the R&D is investigation of cavity fabrication methods using different Nb materials. In this talk, we report mainly focus on the experiences obtained from single cell cavity fabrications. First, different Nb materials are compared, between fine grain Nb and large grain(LG) Nb from different vendors including low RRR LG Nb, in which, cavities were fabricated by electron beam welding method. Difficulty on LG cavity fabrication come from deformation due to stressed grain boundaries. In addition to nominal electron beam welded cavities, hydro-formed seamless cavities have been fabricated. Relatively large difference of equator and iris ratio cause difficulty on expansion of Nb pipes. Good qualified Nb pipe is essential and control of hydro-forming steps including annealing of materials is also important. In order to evaluate these cavity performances, vertical tests were carried out. Generally, they showed good performances. In this presentation, fabrication processes, technical difficulties, mitigation strategies and vertical test results are presented.  
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THPB013 A Novel Design and Development of 650 MHz, β=0.61, 5-Cell SRF Cavity for High Intensity Proton Linac cavity, niobium, impedance, HOM 1088
 
  • S.S. Som, P. Bhattacharyya, A. Dutta Gupta, S. Ghosh, A. Mandal, S. Seth
    VECC, Kolkata, India
  
  Funding: DAE, Govt. of India
DAE laboratories in India are involved in R&D activities on SRF cavity technology for the proposed high intensity proton linacs for ISNS/IADS and also FERMILAB PIP-II program under IIFC. VECC is responsible for design, analysis and development of a 650 MHz, β=0.61, 5-cell elliptical cavity. This paper describes the novel design of the cavity, with different aperture and wall angle, having better field flatness and mechanical stability, reliable surface processing facility and less beam loss. The cavity geometry has been optimized to get acceptable values of field enhancement factors, R/Q, Geometric factor, cell-to-cell coupling etc. The effective impedance of transverse and longitudinal HOMs are low enough to get rid of HOM damper for low beam current. 2-D analysis shows no possibility of multipacting. However, 3-D analysis using CST Particle Studio code confirms its presence and it can be suppressed by introducing a small convexity in the equator region. Two niobium half cells and beam pipes for the single cell cavity have been fabricated. Measurement and RF characterisation of half cells, prototype 1-cell and 5-cell and also 1-cell niobium cavities have been carried out.
email:ssom@vecc.gov.in 		 
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THPB021 Balloon Variant of Single Spoke Resonator resonance, simulation, cavity, superconductivity 1110
 
  • Z.Y. Yao, R.E. Laxdal, V. Zvyagintsev
    TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
  
  Spoke resonators have been widely proposed and optimized for various applications. Good performance has been demonstrated by many cavity tests. Accompanying the great progress, the adverse impact of strong multipacting (MP) is also noted by recent test reports, consistent with modern 3D simulations. This paper will discuss MP behaviors in the single spoke resonator. In particular a phenomenological theory is developed to highlight the details of the geometry that affect MP. The analysis leads to an optimized geometry of a single spoke resonator defined here as the ‘balloon geometry’. A 325MHz β=0.3 single spoke resonator based on 'balloon' concept is under development by the RISP-TRIUMF Collaboration. The RF and mechanical design of this cavity will also be reported.  
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THPB029 MHI's Production Activities of Superconducting Cavity cavity, superconducting-RF, gun, SRF 1141
 
  • A. Miyamoto, H. Hara, K. Kanaoka, K. Okihira, K. Sennyu, T. Yanagisawa
    MHI, Hiroshima, Japan
  
  Mitsubishi Heavy Industries (MHI) have developed manufacturing process of superconducting cavities for a long time. In this presentation, recent progress will be reported.  
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THPB030 Fabrication and Evaluation of Low RRR Large Grain 1-Cell Cavity cavity, niobium, SRF, accelerating-gradient 1146
 
  • H. Shimizu, H. Inoue, E. Kako, T. Saeki, K. Umemori, Y. Watanabe, M. Yamanaka
    KEK, Ibaraki, Japan
  
  Successive R&D studies of SRF cavities are ongoing at KEK by using existing facilities of Cavity Fabrication Facility (CFF) and other equipment of Superconducting Test facility (STF). Recently, there are studies on the low RRR of niobium material with high and uniform concentration of tantalum which could be used for the fabrication of high performance SRF cavity, and hence it could reduce the fabrication cost of cavities [1]. In order to confirm the advantage of the material, a large-grain single-cell cavity was fabricated at CFF/KEK with sheets sliced from a low RRR niobium ingot with high and uniform concentration of tantalum. The resistivity measurement of sample from sliced sheet showed the RRR value of 100, whereas it is about 400 for the nominal qualification of fine-grain sheets at KEK. The low RRR large-grain single-cell cavity was already fabricated at CFF/KEK. The quality control of the fabrication processes are well under control. Then several vertical tests of the cavity were done at STF/KEK. In this presentation, the results of the vertical tests are shown. The potential of the low RRR niobium material for SRF cavity are discussed.
*P.Kneisel et al, NIM A774(2015)133 		 
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THPB033 Frequency Measurement and Tuning of a 9-Cell Superconducting Cavity Developed with UK Industry cavity, simulation, superconducting-RF, niobium 1158
 
  • L.S. Cowie, P. Goudket, A.R. Goulden, P.A. McIntosh, A.E. Wheelhouse
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • J.R. Everard, N. Shakespeare
    Shakespeare Engineering, South Woodham Ferrers, Essex, United Kingdom
  • B. Lamb, S. Postlethwaite, N. Templeton
    STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
  
  As part of an STFC Innovations Partnership Scheme (IPS) grant, in support of enabling UK industry to address the large potential market for superconducting RF structures, Daresbury Laboratory and Shakespeare Engineering Ltd are collaborating to produce a 1.3 GHz 9 cell niobium cavity. This paper describes the procedures to ensure the cavity reaches the required frequency and field flatness. The frequency of each half-cell was measured using a custom measurement apparatus. Combined mechanical and RF simulations were used to compensate for cavity deformation during measurement. Results of Coordinate Measurement Machine measurements of one half-cell are presented. The same procedure will be used to trim the cells at the dumbbell stage, and the full 9-cell cavity will be tuned once welded.  
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THPB040 Hydroforming of Large Grain Niobium Tube niobium, cavity, experiment, vacuum 1171
 
  • A. Mapar, F. Pourboghrat
    MSU, East Lansing, Michigan, USA
  • T.R. Bieler
    Michigan State University, East Lansing, Michigan, USA
  • C. Compton
    FRIB, East Lansing, Michigan, USA
  • J.E. Murphy
    University of Nevada, Reno, Reno, Nevada, USA
  
  Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-FG02-09ER41638.
Currently most of Niobium (Nb) cavities are manufactured from fine grain Nb sheets. As-cast ingots go through a series of steps including forging, milling, rolling, and intermediate annealing, before they are deep-drawn into a half-cell shape and subsequently electron beam welded to make a full cavity. Tube hydroforming, a manufacturing technique where a tube is deformed using a pressurized fluid, is an alternative to the current costly manufacturing process. A whole cavity can be made from a tube using tube hydroforming. This study focuses on deformation of large grain Nb tubes during hydroforming. The crystal orientation of the grains is recorded. The tube is marked with a square-circle-grid which is used to measure the strain after deformation. The deformation of the tube is going to be modeled with crystal plasticity finite element and compared with experiments. This paper only covers the characterization of the tube and the hydroforming process. 		 
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THPB042 Advance Additive Manufacturing Method for SRF Cavities of Various Geometries niobium, cavity, SRF, vacuum 1181
 
  • P. Frigola, R.B. Agustsson, L. Faillace, A.Y. Murokh
    RadiaBeam, Santa Monica, California, USA
  • G. Ciovati, W.A. Clemens, P. Dhakal, F. Marhauser, R.A. Rimmer, J.K. Spradlin, R.S. Williams
    JLab, Newport News, Virginia, USA
  • J. Mireles, P.A. Morton, R.B. Wicker
    University of Texas El Paso, W.M. Keck Center for 3D Innovation, El Paso, Texas, USA
  
  An alternative fabrication method for superconducting radio frequency (SRF) cavities is presented. The novel fabrication method, based on 3D printing (or additive manufacturing, AM) technology capable of producing net-shape functional metallic parts of virtually any geometry, promises to greatly expand possibilities for advance cavity and end-group component designs. A description of the AM method and conceptual cavity designs are presented along with material analysis and RF measurement results of additively manufactured niobium samples.  
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THPB044 A Superconducting RF Deflecting Cavity for the ARIEL e-Linac Separator cavity, HOM, linac, impedance 1187
 
  • D.W. Storey
    Victoria University, Victoria, B.C., Canada
  • R.E. Laxdal, L. Merminga, B.S. Waraich, Z.Y. Yao, V. Zvyagintsev
    TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
  
  A 650 MHz SRF deflecting mode cavity has been designed for the ARIEL e-Linac to separate interleaved beams heading towards either Rare Ion Beam production or a recirculation loop for energy recovery, allowing the e-Linac to provide beam delivery to multiple users simultaneously. The cavity geometry has been optimized for the ARIEL specifications, resulting in a very compact cavity with high shunt impedance and low dissipated power. Analyses have been performed on the susceptibility to multipacting, input coupling considering beam loading and microphonics, and extensive studies into the damping of transverse and longitudinal higher order modes. The pressure sensitivity, frequency tuning, and thermal behaviour have also been studied using ANSYS. The cavity design resulting from these considerations will be discussed here.  
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THPB050 Performance Evaluation of HL-LHC Crab Cavity Prototypes in a CERN Vertical Test Cryostat cavity, SRF, monitoring, HOM 1210
 
  • K.G. Hernández-Chahín
    DCI-UG, León, Mexico
  • G. Burt
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • C. Christophe, A. Macpherson, M. Navarro-Tapia, R. Torres-Sanchez
    CERN, Geneva, Switzerland
  • S.U. De Silva
    ODU, Norfolk, Virginia, USA
  • A.R.J. Tutte
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • S. Verdú-Andrés
    BNL, Upton, Long Island, New York, USA
  
  Funding: My work is supported by the Mexican CONACYT(Consejo Nacional de Ciencia y Tecnologia) program through the Mexican national scholarship (Becas Nacionales y Becas Mixtas).
Three proof-of-principle compact crab cavity designs have been fabricated in bulk niobium and cold tested at their home labs, as a first validation step towards the High Luminosity LHC project. As a cross check, all three bare cavities have been retested at CERN, in order to cross check their performance, and cross-calibrate the CERN SRF cold test facilities. While achievable transverse deflecting voltage is the key performance indicator, secondary performance aspects derived from multiple cavity monitoring systems are also discussed. Temperature mapping profiles, quench detection, material properties, and trapped magnetic flux effects have been assessed, and the influence on performance discussed. The significant effort invested in developing expertise in preparation and testing of these crab cavities has already been fruitful for all partners, and more is to come within this ongoing program. 		 
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THPB055 RF Performance Results of the 2nd ELBE SRF Gun gun, SRF, cavity, cathode 1227
 
  • A. Arnold, M. Freitag, P.N. Lu, P. Murcek, J. Teichert, H. Vennekate, R. Xiang
    HZDR, Dresden, Germany
  • G. Ciovati, P. Kneisel, M. Stirbet, L. Turlington
    JLab, Newport News, Virginia, USA
  
  As in 2007 the first 3.5 cell superconducting radio frequency (SRF) gun was taken into operation at Helmholtz-Zentrum Dresden-Rossendorf, it turned out that the specified performance to realize an electron energy of 9.4 MeV has not been achieved. Instead, the resonator of the gun was limited by field emission to about one third of this value and the measured beam parameters remained significantly below its expectations. However, to demonstrate the full potential of this electron source for the ELBE linear accelerator, a second and slightly modified SRF gun was developed and built in collaboration with Thomas Jefferson National Accelerator Facility. We will report on commissioning of this new SRF gun and present a full set of RF performance results. Additionally, investigations are shown that try to explain a particle contamination that happened recently during our first cathode transfer.  
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THPB058 Commissioning of the 112 MHz SRF Gun gun, cathode, SRF, laser 1240
 
  • S.A. Belomestnykh, I. Ben-Zvi, J.C. Brutus, T. Hayes, V. Litvinenko, K. Mernick, G. Narayan, P. Orfin, I. Pinayev, T. Rao, F. Severino, J. Skaritka, K.S. Smith, R. Than, J.E. Tuozzolo, E. Wang, Q. Wu, B. P. Xiao, A. Zaltsman
    BNL, Upton, Long Island, New York, USA
  • S.A. Belomestnykh, I. Ben-Zvi, V. Litvinenko, T. Xin
    Stony Brook University, Stony Brook, USA
  
  Funding: Work is supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the US DOE.
A 112 MHz superconducting RF photoemission gun was designed, fabricated and installed in RHIC for the Coherent electron Cooling Proof-of-Principle (CeC PoP) experiment at BNL. The gun was commissioned first without beam. This was followed by generating the first photoemission beam from a multi-alkali cathode. The paper presents the commissioning results. 		 
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THPB076 Quality Control of Welding, Brazing Joints and Cu Deposition on EU-XFEL Coupler Parts controls, interface, Windows, vacuum 1301
 
  • A. Ermakov, D. Kostin, W.-D. Möller
    DESY, Hamburg, Germany
  
  In frames of EU-XFEL Project the quality control of fundamental 1.3GHz power couplers is very important task. The power coupler consists of a several number of parts including itself the different types of welding and brazing joints between ceramic, copper and stainless steel components. The quality of these joints is subject to be investigated and controlled according to EU-XFEL Coupler specification taking into account the different coupler manufacturers involved. The quality of Cu deposition on some EU-XFEL coupler parts is also the issue to be qualified according to specs. The number of microscope images of different types of joints and Cu deposition on some EU-XFEL 1.3GHz coupler parts are presented.  
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THPB087 Design and Simulation of High Power Input Coupler for C-ADS Linac 5-Cell Elliptical Cavities simulation, cavity, RF-structure, impedance 1343
 
  • K.X. Gu
    Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China
  • X. Chen, T.M. Huang, Q. Ma, W.M. Pan
    IHEP, Beijing, People's Republic of China
  
  Two 650 MHz elliptical cavity sections (elliptical 063, elliptical 082) are chosen to accelerate medium energy protons for China Accelerator Driven sub-critical System (C-ADS) linac. For each 5-cell cavity, RF power up to 150 kW in CW mode is required to be fed by a fundamental power coupler (FPC). A coaxial type coupler is designed to meet the power and RF coupling requirements. This paper presents the RF design, thermal analysis and multipacting simulations of the coupler for C-ADS 5-cell elliptical cavities.  
poster icon Poster THPB087 [0.593 MB]  
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THPB088 20 kW CW Power Couplers for the APS-U Harmonic Cavity cavity, Windows, operation, storage-ring 1346
 
  • M.P. Kelly, A. Barcikowski, Z.A. Conway, D. Horan, M. Kedzie, S.H. Kim, P.N. Ostroumov
    ANL, Argonne, Illinois, USA
  • S.V. Kutsaev
    RadiaBeam, Santa Monica, California, USA
  • J. Rathke
    AES, Medford, New York, USA
  
  Funding: This work supported by the U.S. DOE, Office of Nuclear Physics, Contract No. DE-AC02-06CH11357. This research used resources of ANL’s ATLAS facility, which is a DOE Office of Science User Facility.
A pair of 20 kW CW adjustable RF power couplers optimized for 1.4 GHz have been designed and are being built as part of the APS-U bunch lengthening system. The system uses one superconducting RF cavity to be installed into the APS Upgrade electron storage ring and will provide a tremendous practical benefit to the majority of users by increasing the beam lifetime by 2-3 times. The 80 mm diameter, 50 Ω coaxial couplers include 4 cm (~20 dB) of adjustability. This allows optimization of bunch lengthening for a range of storage ring beam currents and fill patterns while, simultaneously, maintaining the required 0.84 MV harmonic cavity voltage. To provide bunch lengthening, the cavity/coupler system must extract RF power (up to 32 kW) from the beam. Each coupler will transmit roughly half of the total extracted power to external water-cooled loads. The design extends upon on a well-tested ANL two RF window concept, using a pair of simple rugged 80 mm diameter alumina disks. A new feature is the ‘hourglass-shaped’ inner conductor chosen to maximize transmission at 1.4 GHz. Results of electromagnetic and thermal simulations, as well as, prototyping and initial RF testing are presented. 		 
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THPB093 A 1.3 GHz Waveguide to Coax Coupler for Superconducting Cavities With a Minimum Kick cavity, emittance, niobium, dipole 1360
 
  • J.A. Robbins, C. Egerer, R.G. Eichhorn, V. Veshcherevich
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  Transversal forces as a result of asymmetric field generated by the fundamental power couplers have become a concern for low emittance beam in future accelerators. In pushing for smallest emittances, Cornell has finished a physics design for a symmetric coupler for superconducting accelerating cavities. This coupler consists of a rectangular waveguide that transforms into a coaxial line inside the beam pipe, eventually feeding the cavity. We will report on the RF design yielding to the extremely low transversal kick. In addition, heating, heat transfer and thermal stability of this coupler has been evaluated.  
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THPB097 New Possible Configuration of 3.9 GHz Coupler Windows, multipactoring, simulation, cavity 1373
 
  • S. Kazakov
    Fermilab, Batavia, Illinois, USA
  
  The LCLS-II superconducting accelerator supposedly will use 3.9 GHz (3-d harmonic) superconductive cavities. A new possible configuration of 3.9 GHz main coupler is presented in the papar. This configuration contains two coaxial ceramic windows, a cold and a warm one. Inner conductors of windows are connected through the capacitive gap and have no mechanical no thermal contacts. It allows to avoid using bellows and thus avoid the problem of heating and cooling. The windows have shields protecting shields against the electron, and this prevents the window ceramics from charging. Results of computer simulation of the new coupler are posted.  
poster icon Poster THPB097 [1.036 MB]  
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THPB102 RF Conditioning of the XFEL Power Couplers at the Industrial Scale vacuum, pick-up, monitoring, controls 1387
 
  • H. Guler, A. Gallas, W. Kaabi, D.J.M. Le Pinvidic, C. Magueur, M. Oublaid, A. Thiebault, A. Verguet
    LAL, Orsay, France
  
  LAL has in charge the production monitoring and the RF conditioning of 800 power couplers to equip 100 XFEL cryomodules. The conditioning process and all the preceding preparation steps are performed in a 70m2 clean room. This infrastructure, its equipment and the RF station are designed to allow the treatment of 8 couplers in the same time, after a ramp-up phase. Clean room process and conditioning results are presented and discussed.  
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THPB116 Modified ELBE Type Cryomodules for the Mainz Energy-Recovering Superconducting Accelerator MESA cryomodule, HOM, operation, niobium 1413
 
  • T. Stengler, K. Aulenbacher, R.G. Heine, F. Schlander, D. Simon
    IKP, Mainz, Germany
  • M. Pekeler, D. Trompetter
    RI Research Instruments GmbH, Bergisch Gladbach, Germany
  
  At the Institut für Kernphysik of Johannes Gutenberg-Universität Mainz, the new multiturn energy recovery linac MESA is under construction. Two modified ELBE-type cryomodules with two 9-cell TESLA/XFEL cavities each will provide an energy gain of 50 MeV per turn. Those are currently in the production process at RI Research Instruments GmbH, Bergisch Gladbach, Germany. Modifications for the tuner and the HOM damper are under development. In addition, a 4K/2K Joule Thomson expansion stage will also be integrated into the cryomodule. The current status of the development of the cryomodules and their modifications will be discussed.  
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FRBA03 SRF, Compact Accelerators for Industry & Society cavity, SRF, cathode, gun 1467
 
  • R.D. Kephart, B.E. Chase, I.V. Gonin, A. Grassellino, S. Kazakov, T.N. Khabiboulline, S. Nagaitsev, R.J. Pasquinelli, S. Posen, O.V. Pronitchev, A. Romanenko, V.P. Yakovlev
    Fermilab, Batavia, Illinois, USA
  • S. Biedron, S.V. Milton, N. Sipahi
    CSU, Fort Collins, Colorado, USA
  • S. Chattopadhyay
    Northern Illinois Univerity, Dekalb, Illinois, USA
  • P. Piot
    Northern Illinois University, DeKalb, Illinois, USA
  
  Accelerators developed for Science now are used broadly for industrial, medical, and security applications. Over 30,000 accelerators touch over $500B/yr in products producing a major impact on our economy, health, and well being. Industrial accelerators must be cost effective, simple, versatile, efficient, and robust. Many industrial applications require high average beam power. Exploiting recent advances in Superconducting Radio Frequency (SRF) cavities and RF power sources as well as innovative solutions for the SRF gun and cathode system, a collaboration of Fermilab-CSU-NIU has developed a design for a compact SRF high-average power electron linac. Capable of 5-50 kW average power and continuous wave operation this accelerator will produce electron beam energies up to 10 MeV and small and light enough to mount on mobile platforms, such accelerators will enable new in-situ environmental remediation methods and new applications involving in-situ crosslinking of materials. More importantly, we believe this accelerator will be the first of a new class of simple, turn-key SRF accelerators that will find broad application in industry, medicine, security, and science.  
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