3 Technology
3A Superconducting RF
Paper Title Page
MOPRC025 Final Design of the Fully Equipped HWR Cavities for SARAF 123
 
  • G. Ferrand
    CEA/DSM/IRFU, France
  • L. Boudjaoui, P. Hardy, F. Leseigneur, C. Madec, N. Misiara, N. Pichoff
    CEA/IRFU, Gif-sur-Yvette, France
  
  SNRC and CEA collaborate to the upgrade of the SARAF accelerator to 5 mA CW 40 MeV deuteron and proton beams (Phase 2). CEA is in charge of the design, construction and commissioning of the superconducting linac (SARAF-LINAC Project). The SCL is made up of 4 cryomodules: the first two will host each 6 half-wave resonator (HWR) low beta cavities (β = 0.09) at 176 MHz; the last two will host each 7 HWR high-beta cavities (β = 0.18) at 176 MHz. The fully equipped cavity includes the niobium cavity with a helium tank, an input power couplers and a frequency tuning system. The final RF design of the low and high beta cavities will be presented in this poster, as well as the RF design of the couplers, the expected tuning range of the cavities and the multipactor analysis.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPRC025  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPRC026 Mechanical Design of the HWR Cavities for the SARAF SRF LINAC 126
 
  • N. Misiara, L. Boudjaoui, G. Ferrand, P. Hardy, F. Leseigneur, C. Madec, N. Pichoff
    CEA/IRFU, Gif-sur-Yvette, France
  
  SNRC and CEA collaborate to the upgrade of the SARAF accelerator to 5 mA CW 40 MeV deuteron and proton beams (Phase 2). CEA is in charge of the design, construction and commissioning of the superconducting linac (SARAF-LINAC Project). The SCL consists in 4 cryomodules. The first two identical cryomodules host 6 half-wave resonator (HWR) low beta cavities (β = 0.09) at 176 MHz. The last two identical cryomodules will host 7 HWR high-beta cavities (β = 0.18) at 176 MHz. The fully equipped cavity includes the niobium cavity with its helium tank, the couplers and the frequency tuning system. In this paper, the mechanical design and the foreseen qualification procedures for both cavities and tuning systems are presented with compliance, to the best extent, to the rules of Unfired Pressure Vessels NF-EN 13445 (1-5) standards.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPRC026  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPRC027 Surface Roughness Effect on the Performance of Nb3Sn Cavities 129
SPWR032   use link to see paper's listing under its alternate paper code  
 
  • R.D. Porter, D.L. Hall, M. Liepe, J.T. Maniscalco
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  Funding: DOE award DE-SC0008431
Surface roughness of current Niobium-3 Tin (Nb3Sn) superconducting radio-frequency (SRF) accelerator cavities can cause enhancement of the surface magnetic field. This enhancement can push the surface magnetic field beyond the critical field, which, if it occurs over a large enough area, can cause the cavity to quench. This paper presents simulations of the surface magnetic field enhancements in SRF cavities caused by the surface roughness of current Cornell Nb3Sn cavities, which have achieved record efficiency. Simple, smooth cavity geometry is defined and surface magnetic fields calculated using SLANS2. The cavity geometry is modified with a small rough region for which the geometry is determined from AFM scans of a Nb3Sn coated sample and the surface fields are calculated again. The calculated surface fields of the smooth and rough cavities are compared to determine the extent of the field enhancement, the area over which the enhancement is significant, and which surface features cause large field enhancement. We find that 1% of the surface analyzed has fields enhance by more than 45%. On average the Q-factor is increased by (3.8 ± 1.0) \%. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPRC027  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPRC029 Experiment of Plasma Discharge on HWR Cavity for In-Situ Surface Cleaning Study 133
SPWR008   use link to see paper's listing under its alternate paper code  
 
  • A.D. Wu, Y. He, T.C. Jiang, C.L. Li, Y.M. Li, W.M. Yue, S.H. Zhang, H.W. Zhao
    IMP/CAS, Lanzhou, People's Republic of China
  • L.M. Chen
    Institute of Physics, Chinese Academy of Sciences, Beijing, People's Republic of China
  • L. Yang
    IHEP, Beijing, People's Republic of China
  
  Hydrocarbons, which migrate from the vacuum bumps system, will absorb on the cavity surface after periods of operation. The contaminants can reduce the surface electron work function to enhance the field emission effect and restrict the cavity accelerating gradient. The room temperature in-situ plasma surface processing to clean the hydrocarbon contaminants can act as a convenient and efficient technology for the accelerator on line performance recovery. For better control of the discharge inside the cavity, the experiment works on a single HWR cavity aims to research the ignition between the swarm parameters (gas flow, pressure, forward power).  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPRC029  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPLR022 Commissioning and First Results from the Fermilab Cryomodule Test Stand 185
 
  • E.R. Harms, M.H. Awida, C.M. Baffes, K. Carlson, S.K. Chandrasekaran, B.E. Chase, E. Cullerton, J.P. Edelen, J. Einstein, C.M. Ginsburg, A. Grassellino, B.J. Hansen, J.P. Holzbauer, S. Kazakov, T.N. Khabiboulline, M.J. Kucera, J.R. Leibfritz, A. Lunin, D. McDowell, M.W. McGee, D.J. Nicklaus, D.F. Orris, J.P. Ozelis, J.F. Patrick, T.B. Petersen, Y.M. Pischalnikov, P.S. Prieto, O.V. Prokofiev, J. Reid, W. Schappert, D.A. Sergatskov, N. Solyak, R.P. Stanek, D. Sun, M.J. White, C. Worel, G. Wu
    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 new test stand dedicated to SRF cryomodule testing, CMTS1, has been commissioned and is now in operation at Fermilab. The first device to be cooled down and powered in this facility is the prototype 1.3 GHz cryomodule assembled at Fermilab for LCLS-II. We describe the demonstrated capabilities of CMTS1, report on steps taken during commissioning, provide an overview of first test results, and survey future plans. 		 
poster icon Poster MOPLR022 [3.431 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR022  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPLR023 Examination of Cutouts Inner Surfaces from Nb3Sn Coated Cavity 189
 
  • U. Pudasaini, M.J. Kelley
    The College of William and Mary, Williamsburg, Virginia, USA
  • G.V. Eremeev, C.E. Reece
    JLab, Newport News, Virginia, USA
  • J. Tuggle
    Virginia Polytechnic Institute and State University, Blacksburg, USA
  
  Funding: Supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177 and Office of High Energy Physics under grant SC00144475.
The potential for higher operating temperature and higher gradient have motivated SRF cavity researchers to pursue Nb3Sn as an alternative to Nb for nearly fifty years. Far and away the most common embodiment has been a few micron-thick Nb3Sn layer on the cavity interior surface obtained by vapor diffusion coating, with one or another set of parameters. While many cavities have been made and RF tested, reports of dissecting a cavity in detail to examine the coating and relate it to RF measurements are rare. We coated a BCP-treated single cell cavity in a typical process of tin/tin chloride activation at 500 C followed by tin vapor deposition at 1200 C. After RF-testing, we cut and examined sections from several locations to learn composition, thickness topography of the interior surface. The effect of process variables, such as surface preparation, process temperature and duration, and vapor chemistry needs to be explored. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR023  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPLR024 Progress Towards Nb3Sn CEBAF Injector Cryomodule 193
 
  • G.V. Eremeev, K. Macha, U. Pudasaini, C.E. Reece, A-M. Valente-Feliciano
    JLab, Newport News, Virginia, USA
  
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Operations at 4 K instead of 2 K have the potential to reduce the operational cost of an SRF linac by a factor of 3, if the cavity quality factor can be maintained. Cavities coated with Nb3Sn have been shown to achieve the accelerating gradients above 10 MV/m with a quality factor around 1010 at 4 K. Because such performance is already pertinent for CEBAF injector cryomodule, we are working to extend these results to CEBAF accelerator cavities envisioning coating of two CEBAF 5-cell cavities with Nb3Sn. They will be installed in an injector cryomodule and tested with beam. The progress on this path is reported in this contribution. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR024  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPLR025 Investigation of Low-Level Nitrogen in Niobium by Secondary Ion Mass Spectrometry 196
 
  • J. Tuggle
    Virginia Polytechnic Institute and State University, Blacksburg, USA
  • M.J. Kelley
    The College of William and Mary, Williamsburg, Virginia, USA
  • A.D. Palczewski, C.E. Reece
    JLab, Newport News, Virginia, USA
  • F.A. Stevie
    NCSU AIF, Raleigh, North Carolina, USA
  
  Funding: Supported by the U.S. DOE Office of Science, ONP contract DE-AC05-06OR23177 and OHEP grant SC00144475. Tuggle is supported by Nanoscale Characterization and Fabrication Laboratory at Virginia Tech.
Understanding the improvement of the SRF cavity quality factor by low-level nitrogen addition ("N-doping") is attracting much attention from researchers. Precise, repeatable measurement of the nitrogen profile in the parts-per-thousand to parts-per-million range is vital. Secondary Ion Mass Spectrometry (SIMS) is the approach of choice because of excellent sensitivity and depth resolution. Accurate quantitation must consider sample properties, such as surface topography and crystal structure, calibration of the instrument with reference materials, and data analysis. We report the results of a SIMS study in which polycrystal and single crystal coupons were N-doped, each accompanied by new SRF-grade niobium sheet equivalent to a single cell cavity. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR025  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPLR026 Material Qualification of LCLS-II Production Niobium Material Including RF and Flux Expulsion Measurements on Single Cell Cavities 199
 
  • A.D. Palczewski, F. Marhauser
    JLab, Newport News, Virginia, USA
  • A. Grassellino, S. Posen
    Fermilab, Batavia, Illinois, USA
  
  Funding: Work at JLab is supported by the U.S. Department of Energy under contract DE-AC05-06OR23177 and Fermilab is operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359.
It has been shown that cooldown details through transition temperature can significantly affect the amount of trapped magnetic flux in SRF cavities, which can lead to performance degradation proportional to the magnitude of the ambient magnetic field.[*] It has also more recently been shown that depending on the exact material properties - even when the material used originated from the same batch from the same vendor - and subsequent heat treatment, the percent of flux trapped during a cool-down could vary widely for identical cool-down parameters.[**] For LCLS-II, two material vendors have produced half of the niobium used for the cavity cells (Tokyo Denkai Co., Ltd. (TD) and Ningxia Orient Tantalum Industry Co., Ltd. (NX)). Both vendors delivered material well within specifications set out by the project (according to ASTM B 393-05), which allows yet some variation of material characteristics such as grain size and defect density. In this contribution, we present RF and magnetic flux expulsion measurements of four single cell cavities made out of two different niobium batches from each of the two LCLS-II material suppliers and draw conclusions on potential correlations of flux expulsion capability with material parameters. We present observations of limited flux expulsion in cavities made from the production material and treated with the baseline LCLS-II recipe.
[*] A. Romanenko et al J. Appl. Phys. 115, 184903 (2014)
[**] S. Posenet et al., Journal of Applied Physics 119, 213903 (2016). 		 
poster icon Poster MOPLR026 [0.861 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR026  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPLR030 Electromagnetic Design of a Superconducting Twin Axis Cavity 203
 
  • S.U. De Silva, J.R. Delayen, H. Park
    ODU, Norfolk, Virginia, USA
  • A. Hutton, F. Marhauser, H. Park
    JLab, Newport News, Virginia, USA
  
  The twin-axis cavity is a new kind of rf superconducting cavity that consists of two parallel beam pipes, which can accelerate or decelerate two spatially separated beams in the same cavity. This configuration is particularly effective for high-current beams with low-energy electrons that will be used for bunched beam cooling of high-energy protons or ions. The new cavity geometry was designed to create a uniform accelerating or decelerating fields for both beams by utilizing a TM110 dipole mode. This paper presents the design rf optimization of a 1497 MHz twin-axis single-cell cavity, which is currently under fabrication.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR030  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPLR031 Wakefield Analysis of Superconducting RF-Dipole Cavities 206
 
  • S.U. De Silva, J.R. Delayen
    ODU, Norfolk, Virginia, USA
  
  RF-dipole crabbing cavities are being considered for a variety of crabbing applications. Some of the applications are the crabbing cavity systems for LHC High Luminosity Upgrade and the proposed Electron-Ion Collider for Jefferson Lab. The design requirements in the current applications require the cavities to incorporate complex damping schemes to suppress the higher order modes that may be excited by the high intensity proton or electron beams traversing through the cavities. The number of cavities required to achieve the desired high transverse voltage, and the complexity in the cavity geometries also contributes to the wakefields generated by beams. This paper characterizes the wakefield analysis for single cell and multi-cell rf-dipole cavities.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR031  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPLR032 Preparation for Cavity Material Studies at the Vertical High-Temperature UHV-Furnace of the S-DALINAC 209
 
  • R. Grewe, L. Alff, J. Conrad, T. Kürzeder, 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.
Since 2005 the Institute for Nuclear Physics at the Technische Universität Darmstadt operates a high temperature vacuum furnace. It is designed to reach temperatures of up to 1800°C. It has been used for baking out several niobium superconducting RF cavities at 850°C with proven success*. Current research for improving the performance of SRF cavities is focused on nitrogen treatment of such cavities. Nitrogen doping of SRF cavtities results in an up to four times higher quality-factor as compared to untreated cavities**. At higher temperatures between 1300°C and 1700°C the so-called delta-phase of NbN forms, which is highly interesting for applications to superconducting accelerator technology***. The UHV-furnace at the S-DALINAC offers the possibility to treat niobium samples at considerably higher temperatures than what has been done up to now in order to study the effect of delta-phase NbN and N-doping on superconducting properties. The furnace has been refurbished and recommissioned to realize research on nitrogen treatment of niobium samples. We will report on our first experiences with operating the upgraded furnace.
*Araz et al., Proceedings of SRF05, 2015
**Grasselino et al., Superconducting Science and Technology, 2013
***Pham Tu et al., Proceedings of SRF87, 1987 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR032  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPLR035 Fabrication of Superconducting Spoke Cavity for Compact Photon Source 212
 
  • M. Sawamura, R. Hajima
    QST, Tokai, Japan
  • H. Hokonohara, Y. Iwashita, H. Tongu
    Kyoto ICR, Uji, Kyoto, Japan
  • T. Kubo, T. Saeki
    KEK, Ibaraki, Japan
  
  Funding: This study is supported by Photon and Quantum Basic Research Coordinated Development Program of MEXT, Japan.
The spoke cavity is expected to have advantages for compact ERL accelerator for X-ray source based on laser Compton scattering. We have been developing the spoke cavity under a research program of MEXT, Japan to establish the fabrication process. Since our designed shape of the spoke is complicated due to increase the RF properties, one-step press forming with one set of molds will cause so large strain to break the sheet. We designed the mold components including the process of press work. The press forming tests of the spoke cavity have been done with the various materials of sheets to check molding performance. In this paper we present status of the spoke cavity fabrication. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR035  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPLR036 Study on Multilayer Thin Film Coating on Superconducting Cavity 215
 
  • Y. Iwashita, Y. Fuwa, H. Tongu
    Kyoto ICR, Uji, Kyoto, Japan
  • H. Hayano, T. Kubo, T. Saeki
    KEK, Ibaraki, Japan
  • M. Hino
    Kyoto University, Research Reactor Institute, Osaka, Japan
  • H. Oikawa
    Utsunomiya University, Utsunomiya, Japan
  
  Funding: This research is supported by following programs: Grant-in-Aid for Exploratory Research 26600142 and Photon and Quantum Basic Research Coordinated Development Program from the MEXT.
Multilayer thin film coating is a promising technology to enhance performance of superconducting cavities. Until recently, principal parameters to achieve the sufficient performance had not been known, such as the thickness of each layer. We proposed a method to deduce a set of the parameters to exhibit a good performances. In order to verify the scheme, we are trying to make some experiments on the subject at Kyoto. The sample preparation and the test setup for the measurement apparatus will be discussed. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR036  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPLR037 Study of the Surface and Performance of Single-Cell Nb Cavities After Vertical EP Using Ninja Cathodes 217
 
  • V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi
    MGH, Hyogo-ken, Japan
  • P. Carbonnier, F. Éozénou, Y. Gasser, L. Maurice, C. Servouin
    CEA/DSM/IRFU, France
  • F. Furuta, M. Ge, T. Gruber, J.J. Kaufman, J. Sears
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe
    KEK, Ibaraki, Japan
  • K. Ishimi
    MGI, Chiba, Japan
  
  A 1.3 GHz single-cell niobium (Nb) coupon cavity was vertically electropolished (VEPed) with three different Ninja cathodes which were specially designed for VEP of 1.3 GHz superconducting RF elliptical (ILC/Tesla type) cavities. The cathodes were fabricated to have different surface areas and different distances between cathode surface and the equator. The Ninja cathode prepared with an enhanced cathode surface area was covered with a meshed shield to avoid bubble attack on the surface of the cavity cell. It has been turned out that the anode-cathode distance and the cathode area affect surface morphology of the equator. A smooth equator surface was obtained in the cases in which the cathode surface was geometrically close to the equator or instead the cathode surface area was sufficiently larger. Two 1.3 GHz ILC/Tesla type single-cell cavities VEPed with the Ninja cathodes and using optimized conditions showed good performance in vertical tests.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR037  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPLR038 Fabrication of 9 Cell Coupon Cavity for Vertical Electropolishing Test 220
 
  • S. Kato, H. Hayano, H. Inoue, H. Monjushiro, T. Saeki, M. Sawabe
    KEK, Ibaraki, Japan
  • V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi
    MGH, Hyogo-ken, Japan
  
  We have been using single cell coupon cavities to establish vertical electropolishing (VEP) process for a couple of years. A series of in-situ measurements of an EP current at an individual coupon in a coupon cavity can help determination of appropriate EP conditions. VEPed coupons which are surface analysed with XPS, SEM and the other tools can also bring lot information and expertise to development of VEP cathode and optimization of VEP conditions. This time we fabricated the world first 9-cell coupon cavity where 3 sample coupons at the equators and 6 sample coupons at positions close to the irises can be installed. VEP of this coupon cavity with a newly developed Ninja cathode brought useful information for improvement of the VEP facility and optimization of the VEP conditions.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR038  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPLR039 Development of New Type "Ninja" Cathode for Nb 9-cell Cavity and Experiment of Vertical Electro-Polishing 223
 
  • K.N. Nii, V. Chouhan, Y.I. Ida, T.Y. Yamaguchi
    MGH, Hyogo-ken, Japan
  • H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe
    KEK, Ibaraki, Japan
  • K. Ishimi
    MGI, Chiba, Japan
  
  Marui Galvanizing Co. Ltd. has been improving Vertical Electro-Polishing (VEP) technologies and facilities for Nb 9-cell superconducting accelerator cavity for International Linear Collider (ILC) in collaboration with KEK. This time, we developed new type 'Ninja' cathode in order to improve VEP uniformity of Nb 9-cell cavity inner surface based on the results of 1-cell cavity VEP experiment. In this article, we will report construction of new type "Ninja" cathode for Nb 9-cell cavity and experiment of VEP using this.  
poster icon Poster MOPLR039 [0.610 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR039  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPLR041 Design and Fabrication of β=0.3 SSR1 for RISP 226
 
  • Z.Y. Yao, R.E. Laxdal, B.S. Waraich, V. Zvyagintsev
    TRIUMF, Vancouver, Canada
  • R. Edinger
    PAVAC, Richmond, B.C., Canada
  
  A 325MHz β=0.30 balloon variant of single spoke resonator, which was proposed to suppress multipacting around operational gradient, was chosen as the prototype cavity of SSR1 for Rare Isotope Science Project (RISP). It was also demonstrated to achieve good RF and mechanical properties by geometry optimization for both cavity and helium jacket. The details of RISP SSR1 design will be reported in this paper, accompanying with some particular considerations of fabrication for this new member to the spoke family.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR041  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPLR043 Cavity Processing and Preparation of 650 MHz Elliptical Cell Cavities for PIP-II 229
 
  • A.M. Rowe, S.K. Chandrasekaran, A. Grassellino, O.S. Melnychuk, M. Merio, D.A. Sergatskov
    Fermilab, Batavia, Illinois, USA
  • T. Reid
    ANL, Argonne, Illinois, USA
  
  Funding: Operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy.
The PIP-II project at Fermilab requires fifteen 650 MHz SRF cryomodules as part of the 800 MeV LINAC that will provide a high intensity proton beam to the Fermilab neutrino program. A total of fifty-seven high-performance SRF cavities will populate the cryomodules and will operate in both pulsed and continuous wave modes. These cavities will be processed and prepared for performance testing utilizing adapted cavity processing infrastructure already in place at Fermilab and Argonne. The processing recipes implemented for these structures will incorporate state-of-the art processing and cleaning techniques developed for 1.3 GHz SRF cavities for the ILC, XFEL, and LCLS-II projects. This paper describes the details of the processing recipes and associated chemistry, heat treatment, and cleanroom processes at the Fermilab and Argonne cavity processing facilities. This paper also presents single and multi-cell cavity test results with quality factors above 5·1010 and accelerating gradients above 30 MV/m. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR043  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
MOPLR047 Advanced Vertical Electro-Polishing studies at Cornell with Faraday 233
 
  • F. Furuta, M. Ge, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, 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, S.T. Snyder, E.J. Taylor
    Faraday Technology, Inc., Clayton, Ohio, USA
  
  Cornell's SRF group and Faraday Technology Inc. have started collaborations on two phase-II SBIR projects. Both projects are aiming for the development of advanced Vertical Electro-Polishing (VEP) for Nb SRF cavities, such as HF free or acid free VEP protocols. These could be eco-friendlier alternatives for the standard, HF-based EP electrolyte used, and could bring new breakthrough performance for Nb SRF cavities. Here we give a status update and report first results from these two projects.  
poster icon Poster MOPLR047 [2.852 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR047  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
TU2A03 Resonance Control for Future Linear Accelerators 363
 
  • W. Schappert
    Fermilab, Batavia, Illinois, USA
  
  Many of the next generation of particle accelerators (LCLS II, PIP II) are designed for relatively low beam loading. Low beam loading requirement means the cavities can operate with narrow bandwidths, minimizing capital and base operational costs of the RF power system. With such narrow bandwidths, however, cavity detuning from microphonics or dynamic Lorentz Force Detuning becomes a significant factor, and in some cases can significantly increase both the acquisition cost and the operational cost of the machine. In addition to the efforts to passive environmental detuning reduction (microphonics) active resonance control for the SRF cavities for next generation linear machine will be required. State of the art in the field of the SRF Cavity active resonance control and the results from the recent efforts at FNAL will be presented in this talk.  
slides icon Slides TU2A03 [0.897 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TU2A03  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
TUOP07 High Performance Next-Generation Nb3Sn Cavities for Future High Efficiency SRF Linacs 398
TUPRC031   use link to see paper's listing under its alternate paper code  
 
  • D.L. Hall, J.J. Kaufman, M. Liepe, J.T. Maniscalco, R.D. Porter
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  Funding: DOE
A 1.3 GHz ILC-shape single-cell Nb3Sn cavity fabricated at Cornell has shown record performance, exceeding the cryogenic efficiency of niobium cavities at the gradients and quality factors demanded by some contemporary accelerator designs. An optimisation of the coating process has resulted in more cavities of the same design that achieve similar performance, proving the reproducibility of the method. In this paper, we discuss the current limitations on the peak accelerating gradients achieved by these cavities. In particular, high-pulsed-power RF testing, and thermometry mapping of the cavity during CW operation, are used to draw conclusions regarding the nature of the quench limitation. In light of these promising results, the feasibility and utility of applying the current state of the technology to a real-life application is discussed. 		 
slides icon Slides TUOP07 [1.506 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUOP07  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
TUOP08 On Magnetic Flux Trapping in Superconductors 402
TUPRC030   use link to see paper's listing under its alternate paper code  
 
  • R.G. Eichhorn, J. Hoke, Z. Mayle
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  Magnetic flux trapped on the cool-down has become an important factor in the performance in superconducting cavities. We have conducted flux trapping experiments on samples that reveal a very interesting feature of the mechanism on flux trapping which might impact magnetic shielding concepts of future cryomodules.  
slides icon Slides TUOP08 [1.787 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUOP08  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
TUPRC024 Design and Implementation of an Automated High-Pressure Water Rinse System for FRIB SRF Cavity Processing 468
 
  • I.M. Malloch, E.S. Metzgar, L. Popielarski, S. Stanley
    FRIB, East Lansing, Michigan, USA
  
  Funding: This material is based upon work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE SC0000661, the State of Michigan and Michigan State University.
Traditionally, high-pressure water rinse (HPR) systems have consisted of relatively simple pump and rinse wand actuator systems intended to clean superconducting radio frequency (SRF) cavities during processing prior to test assembly. While these types of systems have proven effective at achieving satisfactory levels of cleanliness, large amounts of operator touch-labor are involved, especially in SRF cavities with complex geometries, where several fixture changes and cavity manipulations may be required. With this labor comes the risk of cavity damage or contamination, and the expense of the operator's time. To reduce this operator intervention and maximize cavity cleanliness and process throughput, a new, fully-automated, robotic HPR system has been commissioned in the Facility for Rare Isotope Beams (FRIB) cavity processing facility. This paper summarizes the design and commissioning process of the HPR system, and demonstrates improvements to the FRIB processing facility through the minimization of cavity contamination risk and reduction of technician labor through system automation. Comparative cavity RF test results are presented to further demonstrate system effectiveness. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPRC024  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
TUPRC025 Low Temperature Nitrogen Baking of a Q0 SRF Cavities 472
 
  • P.N. Koufalis, F. Furuta, M. Ge, D. Gonnella, J.J. Kaufman, M. Liepe, J.T. Maniscalco, R.D. Porter
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  Nitrogen-doping has led to an unprecedented increase in the intrinsic quality factor of bulk-niobium superconducting RF cavities. So far, high temperature baking in a nitrogen atmosphere is used almost exclusively to dope cavities. Recently, we have set focus on low temperature baking to produce similar performance increases and we present those results here.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPRC025  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
TUPLR022 Particulate Study on Materials for Cleanroom Assembly of SRF Cavities 512
 
  • L. Zhao, A.V. Reilly
    JLab, Newport News, Virginia, USA
  
  Reducing particulates is an important aspect for clean-room operation. Knowing that it is impossible to completely eliminate all particulates in a clean room, efforts have been made to prevent particulates from entering SRF cavities during high pressure rinsing (HPR) and assembly. At Jefferson Lab, one practice to achieve this goal has been clamping covers to cavity open flanges during assembly. Several cover materials that have been used are examined and alternative candidate materials are under development. Clamps as a known particulate generator are carefully examined and cleaning efficiency of different methods is studied. Cover tests were done on different cavity flanges, including an LCLS-II beam pipe flange, which helps the selection of cover materials for prototype and production of the project.
Authored by Jefferson Science Associates, LLC under U.S. DOE Contracts DE-AC05-06OR23177 and DE-AC02-76SF00515 for the LCLS-II Project. 		 
poster icon Poster TUPLR022 [1.282 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR022  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
TUPLR023 Impurity Content Optimization to Maximize Q-Factors of Superconducting Resonators 515
SPWR016   use link to see paper's listing under its alternate paper code  
 
  • M. Martinello, M. Checchin, A. Grassellino, O.S. Melnychuk, S. Posen, A. Romanenko, D.A. Sergatskov
    Fermilab, Batavia, Illinois, USA
  • M. Checchin
    Illinois Institute of Technology, Chicago, Illlinois, USA
  • J. Zasadzinski
    IIT, Chicago, Illinois, USA
  
  Quality factor of superconducting radio-frequency (SRF) cavities is degraded whenever magnetic flux is trapped in the cavity walls during the cooldown. In this contribution we study how the trapped flux sensitivity, defined as the trapped flux surface resistance normalized for the amount of trapped flux, depends on the mean free path. A systematic study of a variety of 1.3 GHz cavities with different surface treatments (EP, 120 C bake and different N-doping) is carried out. A bell shaped trend appears for the range of mean free path studied. Over-doped cavities fall at the maximum of this curve defining the largest values of sensitivity. In addition, we have studied the trend of the BCS surface resistance contribution as a function of mean free path, showing that N-doped cavities follow close to the theoretical minimum. Adding these results together we show that the 2/6 N-doping treatment gives the highest Q-factor values at 2 K and 16 MV/m, as long as the magnetic field fully trapped during the cavity cooldown is lower than 10 mG.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR023  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
TUPLR024 Enhancement of the Accelerating Gradient in Superconducting Microwave Resonators 519
SPWR017   use link to see paper's listing under its alternate paper code  
 
  • M. Checchin, A. Grassellino, M. Martinello, S. Posen, A. Romanenko
    Fermilab, Batavia, Illinois, USA
  • M. Martinello
    Illinois Institute of Technology, Chicago, Illlinois, USA
  • J. Zasadzinski
    IIT, Chicago, Illinois, USA
  
  Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. DEAC02-07CH11359 with the United States Department of Energy.
The accelerating gradient of superconducting resonators can be enhanced by engineering the thickness of a dirty layer grown at the cavity's rf surface. In this paper the description of the physics behind the accelerating gradient enhancement by meaning of the dirty layer is carried out by solving numerically the the Ginzburg-Landau (GL) equations for the layered system. The calculation shows that the presence of the dirty layer stabilizes the Meissner state up to the lower critical field of the bulk, increasing the maximum accelerating gradient. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR024  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
TUPLR025 Optimal Nitrogen Doping Level to Reach High Q0 523
 
  • D. Gonnella, T. Gruber, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  Funding: NSF and US DOE
New continuous wave (CW) accelerators such as LCLS-II at SLAC require many SRF cavities operating in the medium field region at unprecedented high Q. In order to achieve this demanding goal, nitrogen-doping of the SRF cavities will be used. Nitrogen-doping has been shown to affect the BCS resistance both by a lowering of Rbcs at low fields and by the introduction of an anti-Q slope which enables the Q to continue increasing as the RF field is increased. The exact strength of this anti-Q slope is heavily dependent on the doping recipe and specifically the mean free path of the RF penetration layer of the doped cavities. In addition to its effect on Rbcs, the mean free path affects the amount of residual resistance obtained due to trapped magnetic flux. We have analyzed nine cavities prepared with different levels of nitrogen-doping to understand how BCS and residual resistance are affected by changes in the mean free path. Here we present a model based on these experimental results to predict the optimal doping level to reach the maximum Q at 16 MV/m based on the ambient magnetic field conditions. We find that if the cavities can be cooled with small amounts of trapped flux, moderate nitrogen-doping is better, while if they will have large amounts of trapped flux, lighter dopings should be used. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR025  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
TUPLR027 Magnetic Field Management in LCLS-II 1.3 GHz Cryomodules 527
 
  • S.K. Chandrasekaran, A. Grassellino, C.J. Grimm, G. Wu
    Fermilab, Batavia, Illinois, USA
  
  Funding: Operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy.
The ambient magnetic field at the SRF cavity surface of the LCLS-II 1.3 GHz cryomodules is specified to be less than 0.5 μT (5 mG). Multiple methods were designed to lower the magnetic fields inside the prototype cryomodule. The resulting ambient magnetic field in this cryomodule just prior to its first cool down was <0.15 μT (1.5 mG), as measured using fluxgates inside and outside the cavity helium vessels. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR027  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
TUPLR029 FRIB HWR Tuner Development 535
 
  • S. Stark, A. Facco, S.J. Miller, P.N. Ostroumov, J.T. Popielarski, K. Saito, B.P. Tousignant, T. Xu
    FRIB, East Lansing, USA
  • A. Facco
    INFN/LNL, Legnaro (PD), Italy
  • S.M. Gerbick, M.P. Kelly
    ANL, Argonne, USA
  
  Funding: * This material is based upon work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661, the State of Michigan and Michigan State University
During the last two years the HWR pneumatic tuner development at FRIB evolved from the first prototypes to the final production design. A lot of warm testing and several cryogenic integrated tests with cavity were performed to optimize the tuner features. The main challenges included the bellow bushings binding and very tight space limitations for the assembly on the rail. The final design, based on the acquired experience, was prepared in collaboration with ANL and entered the preproduction phase. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR029  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
TUPLR030 First FRIB β=0.53 Prototype Coldmasss Build 538
 
  • D.R. Victory, K. Elliott, B. Oja, J.T. Popielarski, M.S. Wilbur
    FRIB, East Lansing, USA
  
  Funding: This material is based upon work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE SC0000661, the State of Michigan and Michigan State University.
The β=0.53 coldmass consists of eight Superconducting Radio Frequency (SRF) β=0.53 cavities, eight Fundamental mode Power Couplers (FPC), and one 8 T solenoid. This is the first coldmass with this version of cavity and it has brought new challenges to overcome. The Facility for Rare Isotope Beams (FRIB) contains 18 cryomodules with β=0.53 cavity coldmasses, and this type of coldmass is the highest power and most produced ones in FRIB. During the final cleaning stage and the cavity assembly, particle detection equipment is used to verify the cavity cleanliness levels for cavity certification test and for coldmass assembly. This method allows for cleanliness detection of specific areas inside the cavity at any time a vacuum flange is off. The fixtures, techniques and procedures used to build the β=0.53 coldmasses will be presented. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR030  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
TUPLR033 First FRIB β=0.041 Production Coldmass Build 541
 
  • K. Elliott, S.J. Miller, B. Oja, J.T. Popielarski, L. Popielarski, D.R. Victory, M.S. Wilbur, T. Xu
    FRIB, East Lansing, USA
  • M. Wiseman
    JLab, Newport News, Virginia, USA
  
  Funding: This material is based upon work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE SC0000661, the State of Michigan and Michigan State University.
Three β=0.041 cryomodules are required for the Facility for Rare Isotope Beams (FRIB) accelerator. Cleanroom assembly of all three coldmasses for these cryomodules has been completed. The cleanroom assembly includes; the superconducting radio frequency (SRF) cavities, the superconducting solenoids, fundamental power couplers (FPC), beam position monitors, alignment rail, and transport cart. This paper will provide an overview of the techniques and procedures used to assemble this cavity string such that it can be used in the FRIB accelerator. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR033  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
WE1A03 The Superconducting Radio-Frequency Linear Accelerator Components for the European Spallation Source: First Test Results 651
 
  • C. Darve, N. Elias, F. Schlander
    ESS, Lund, Sweden
  • C. Arcambal, P. Bosland, E. Cenni, G. Devanz
    CEA/IRFU, Gif-sur-Yvette, France
  • S. Bousson, P. Duthil, G. Olivier, G. Olry, D. Reynet
    IPN, Orsay, France
  • G. Costanza
    Lund University, Lund, Sweden
  • H. Li, R.J.M.Y. Ruber, R. Santiago Kern
    Uppsala University, Uppsala, Sweden
  • F. Peauger
    CEA/DSM/IRFU, France
  
  The European Spallation Source requires a pulsed Linac with an average beam power on the target of 5MW which is about five times higher than the most powerful spallation source in operation today. Over 97% of the acceleration occurs in superconducting cavities. ESS will be the first accelerator to employ double spoke cavities to accelerate beam. Accelerating gradients of 9MV/meter is required in the spoke section. The spoke section will be followed by 36 elliptical 704 MHz cavities with a geometrical beta of 0.67 and elliptical 704 MHz cavities with a geometrical beta of 0.86. Accelerating gradients of 20MV/m is required in the elliptical section. Initial gradient test results will be presented in which results exceed expected requirements.  
slides icon Slides WE1A03 [6.533 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-WE1A03  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
WE1A04 Performance Analysis of the European XFEL SRF Cavities, From Vertical Test to Operation in Modules 657
 
  • N. Walker, D. Reschke, J. Schaffran, L. Steder, M. Wenskat
    DESY, Hamburg, Germany
  • L. Monaco
    INFN/LASA, Segrate (MI), Italy
  
  More than 800 resonators have been fabricated, vertically qualified and operated in module tests before the accelerating module installation in the linac, which will be completed before the conference. An analysis of this experience, with correlation of the final cavity performances with production, preparation and assembly stages, is underway and at the time of the conference a summary of the activities will be available.  
slides icon Slides WE1A04 [3.436 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-WE1A04  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
WE2A01
 N-Doping: The New Breakthrough Technology for SRF Cavities  
 
  • M. Martinello
    Fermilab, Batavia, Illinois, USA
  
  Modern projects of accelerators for High Energy Physics and FEL accelerators (PIP II, LCLS II, etc.) demand operation of the SRF cavities in CW regime. In this situation, low cryogenic losses are essential. Decrease of the losses or, thus, increase of the cavity unloaded quality factor Q0 allows great savings in capital and operational cost. The new N-doping technique for the SRF cavity processing in order to achieve high Q0 is described, which is now a ready-to-use technology for SRF accelerators. The current implementation of this technique for the LCLS-II cavity production, allow us to present how ultra-high Q-factors can be maintained from the vertical to the horizontal test. In particular, efficient cooling and optimization of shielding design will be discussed to address potential Q degradation from the remnant magnetic fields in the cryomodule. The talk will go through the physics and fundamental studies that allowed us a) to define the best nitrogen doping treatment which minimizes the Q sensitivity to trapped magnetic field, b) to maximize magnetic flux expulsion based on cavity treatment.  
slides icon Slides WE2A01 [3.101 MB]  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
WE2A03 Plasma Processing to Improve the Performance of the SNS Superconducting Linac 679
 
  • M. Doleans, R. Afanador, J.A. Ball, D.L. Barnhart, W. Blokland, M.T. Crofford, B. DeGraff, S.W. Gold, B.S. Hannah, M.P. Howell, S.-H. Kim, S.W. Lee, J.D. Mammosser, C.J. McMahan, T.S. Neustadt, J. Saunders, S.E. Stewart, W.H. Strong, P.V. Tyagi, D.J. Vandygriff, D.M. Vandygriff
    ORNL, Oak Ridge, Tennessee, USA
  
  Funding: This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE.
An in-situ plasma processing technique has been developed at the Spallation Neutron Source (SNS) to improve the performance of the superconducting radio-frequency (SRF) cavities in operation. The technique uses a low-density reactive neon-oxygen plasma at room-temperature to improve the surface work function, to help removing adsorbed gases on the RF surface and to reduce its secondary emission yield. Recently, the plasma processing technique has been applied to one offline cryomodule and to two cryomodules in the linac tunnel. Improvement of the accelerating gradient has been observed in all three cryomodules. 		 
slides icon Slides WE2A03 [4.433 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-WE2A03  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
THOP01 Experimental Study of Nucleation for Nb3Sn Diffusion Coatings on Niobium SRF Cavities 740
SPWR042   use link to see paper's listing under its alternate paper code  
THPRC002   use link to see paper's listing under its alternate paper code  
 
  • 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: Partially authored by Jefferson Science Associates under Contract No. DE-AC05-06OR23177. Work at William & Mary supported by Office of High Energy Physics under grant SC0014475
Nb3Sn has the potential to achieve superior performance both in terms of operating temperature (4.2 K vs 2 K) and accelerating gradient resulting in significant reduction in both initial and operating costs of SRF linacs. Cavity interior surface coatings are obtained by two-step vapor diffusion: nucleation followed by deposition. To gain more understanding of nucleation and its effect on the subsequent coating, we investigated the effect of varying parameters in a typical tin/tin chloride process. We report findings obtained by SEM/EDS, AFM, SAM and other materials characterization approaches. 		 
slides icon Slides THOP01 [2.784 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THOP01  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
THOP02 Investigation of Nitrogen Absorption Rate and Nitride Growth on SRF Cavity Grade RRR Niobium as a Function of Furnace Temperature 744
THPRC003   use link to see paper's listing under its alternate paper code  
 
  • A.D. Palczewski, C.E. Reece
    JLab, Newport News, Virginia, USA
  • M.J. Kelley
    The College of William and Mary, Williamsburg, Virginia, USA
  • J. Tuggle
    Virginia Polytechnic Institute and State University, Blacksburg, USA
  
  Funding: Notice: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The current state of the art processing of niobium superconducting radio frequency cavities with nitrogen diffusion is performed at 800C in a furnace with a partial pressure of approximately ~20 mtorr of nitrogen. Multiple studies have shown the bulk of the nitrogen absorbed by the niobium forms a thick (1-3 microns) non-superconducting nitride layer which must be removed to produce optimal RF results. The depth profiling of interstitial nitrogen and surface nitrides has already been probed using SIMS measurements. These measurements have also been modeled by extrapolating data from nitride growth studies performed at atmospheric pressure and temperatures above 1000 C (**). One open question is whether there is a diffusion zone at lower temperature in which the niobium will absorb nitrogen but not create a non-superconducting nitride layer; or is the absorption of nitrogen only possible by first forming a nitride buffer layer which then frees up nitrogen for absorption. A systematic study of absorption rate vs. temperature and correlated SIMS measurements needs to be performed to answer this question. We report on the absorption rate vs. temperature from 400 C to 900 C of cavity grade niobium with metallurgically flat witness samples. The witness samples surface depth profile of NbN via SIMS's will be presented and correlated to the absorption.**
* Gonnella et al., Proceedings of SRF2015 Pre-release MOPB042 (2015)
** Tuggle et al., Investigation of Low-Level Nitrogen in Niobium by Secondary Ion Mass Spectrometry, these proceedings (2016) 		 
poster icon Poster THOP02 [2.235 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THOP02  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
THOP03 Cold Bead-Pull Test Stand for SRF Cavities 748
THPRC004   use link to see paper's listing under its alternate paper code  
 
  • A.V. Vélez, A. Frahm, J. Knobloch, A. Neumann
    HZB, Berlin, Germany
  
  Bead-pull measurements represent a final step in the fabrication process of an SRF cavity. These tests allow to characterize the flatness of the field profile in order to perform mechanical tuning if needed. These test has been always performed at room temperature, where material properties differ from the superconducting state properties. Still questions like mechanical deformation due to assymetrical thermal shrincage have not yet been answered experimentaly. In this paper, an upgrade of the former Cold-Bead pull system developed by HZB [1] is presented. This test stand is capable of holding a 9-cell Tesla cavity at LHe temperature providing a realistic insight to cavity parameters under realistic conditions. A copper test pill-box is placed in series with the multi-cell cavity in order to perform 1.8K calibration of the bead. Results will be presented on this paper and compared to electromagnetic simulations.  
slides icon Slides THOP03 [2.731 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THOP03  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
THPLR069 Quality Factor Measurement Method Using Multi Decay Time Constants on Cavity 1011
 
  • J.W. Kim, H. Kim
    IBS, Daejeon, Republic of Korea
  
  Quality factor measurement method using multi decay time constants on superconducting cavity is suggested. In most cases of vertical test, one decay time constant is measured around critical coupling and coupling constants are measured using forward and reflected rf power to get intrinsic quality factor. We use multi decay time constants method to measure the quality factor, which uses three decay time constants. Two more switches before and after the cavity are added to the measurement system. Decay time constants are measured by switching off the rf power switch in front of rf source, the forward power switch in front of input power coupler, and then the pickup power switch behind the pickup coupler, respectively, at the same power of steady state.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THPLR069  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
THPLR074 N-Doped Niobium Accelerating Cavities: Analyzing Model Applicability 1014
 
  • R.G. Eichhorn, N.A. Stilin
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • W. Weingarten
    CERN, Geneva, Switzerland
  
  So-called Nitrogen-doped cavities show a rather strange field dependent behavior of the surface resistance. We had come up with a rather straightforward two fluid model description of the Q-slope in the low and high field domains in an earlier publication based on one dataset of a cavity. In this contribution we report on successfully applying this model to other cavity performance data as well as cases were the model fails.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THPLR074  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)