LINAC2016 - List of Keywords (niobium)

Paper	Title	Other Keywords	Page
MOOP05	Dry-Ice Cleaning of RF-Structures at DESY	cavity, gun, RF-structure, coupling	52
	A. Brinkmann, J. Ziegler DESY, Hamburg, Germany
	Dry-Ice cleaning is today a well established cleaning method in matters of reducing harmful dark current and field emission in copper RF-structures like RF-Guns such as for the European XFEL, FLASH and REGAE. This led to the idea to clean longer RF-structures, in particular 3GHz transverse deflecting structures for the European XFEL. We developed a cleaning device with the possibility to clean up to 2 m long structures in horizontal position with an inner diameter of not more than 40 mm. Furthermore this device also allows to clean 9-cell TESLA-type Nb-cavities as well. A report of the technical layout and results of RF-tests will be given.
	Slides MOOP05 [0.969 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOOP05
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MOPRC027	Surface Roughness Effect on the Performance of Nb3Sn Cavities	cavity, SRF, pulsed-power, klystron	129
	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
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MOPLR023	Examination of Cutouts Inner Surfaces from Nb3Sn Coated Cavity	cavity, SRF, ion, accelerating-gradient	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
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MOPLR024	Progress Towards Nb3Sn CEBAF Injector Cryomodule	cavity, cryomodule, operation, electron	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
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MOPLR025	Investigation of Low-Level Nitrogen in Niobium by Secondary Ion Mass Spectrometry	ion, SRF, cavity, factory	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
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MOPLR026	Material Qualification of LCLS-II Production Niobium Material Including RF and Flux Expulsion Measurements on Single Cell Cavities	cavity, cryomodule, SRF, controls	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 MOPLR026 [0.861 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR026
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MOPLR032	Preparation for Cavity Material Studies at the Vertical High-Temperature UHV-Furnace of the S-DALINAC	vacuum, simulation, SRF, superconductivity	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
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MOPLR037	Study of the Surface and Performance of Single-Cell Nb Cavities After Vertical EP Using Ninja Cathodes	cathode, cavity, experiment, polarization	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
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MOPLR041	Design and Fabrication of β=0.3 SSR1 for RISP	cavity, TRIUMF, cryogenics, linac	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
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MOPLR047	Advanced Vertical Electro-Polishing studies at Cornell with Faraday	cavity, SRF, status, target	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 MOPLR047 [2.852 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-MOPLR047
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TUOP07	High Performance Next-Generation Nb3Sn Cavities for Future High Efficiency SRF Linacs	cavity, SRF, accelerating-gradient, pulsed-power	398
	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 TUOP07 [1.506 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUOP07
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TUOP08	On Magnetic Flux Trapping in Superconductors	solenoid, experiment, cavity, SRF	402
	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 TUOP08 [1.787 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUOP08
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TUPRC025	Low Temperature Nitrogen Baking of a Q0 SRF Cavities	cavity, SRF, radio-frequency, impedance	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
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TUPLR022	Particulate Study on Materials for Cleanroom Assembly of SRF Cavities	cavity, SRF, operation, experiment	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 TUPLR022 [1.282 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUPLR022
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TUPLR023	Impurity Content Optimization to Maximize Q-Factors of Superconducting Resonators	cavity, SRF, factory, superconductivity	515
	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
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TUPLR025	Optimal Nitrogen Doping Level to Reach High Q0	cavity, cryomodule, SRF, electron	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
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TUP106004	Status of RRR Analysis for RAON Accelerator	cavity, vacuum, SRF, superconductivity	628
	Y. Jung, H. Kim, W.K. Kim IBS, Daejeon, Republic of Korea J. Lee, J. Seo Vitzrotech Co., Ltd., Ansan City, Kyunggi-Do, Republic of Korea
	Residual resistance ratio (RRR) of 300-grade niobium has been analyzed to find optimal welding condition for a superconducting cavity. RRR values were not only measured along the welding directions, but also perpendicular to the welding lines. In this presentation, we will show the RRR analysis as a function of the distance, the welding speed, and the welding pressure.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-TUP106004
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THOP01	Experimental Study of Nucleation for Nb3Sn Diffusion Coatings on Niobium SRF Cavities	SRF, experiment, background, accelerating-gradient	740
	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 THOP01 [2.784 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THOP01
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THOP02	Investigation of Nitrogen Absorption Rate and Nitride Growth on SRF Cavity Grade RRR Niobium as a Function of Furnace Temperature	SRF, cavity, ion, injection	744
	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 THOP02 [2.235 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THOP02
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THOP03	Cold Bead-Pull Test Stand for SRF Cavities	cavity, HOM, SRF, simulation	748
	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 THOP03 [2.731 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THOP03
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THPLR004	Development of 1.3 Ghz Single-Cell Superconducting Cavities With Nb Material Developed by Ulba Metallurgical Plant	cavity, accelerating-gradient, vacuum, radiation	849
	T. Ota, N. Kuroiwa, S. Nomura, Y. Otani, M. Takasaki, M. Yamada Toshiba, Yokohama, Japan H. Hayano, T. Saeki KEK, Ibaraki, Japan Y.V. Krygin, V. Kuznetsov, A.A. Tsorayev Ulba Metallurgical Plant, Ust-Kamenogorak, Kazakhstan Y. Shirota BE International Corporation, Tokyo, Japan T. Tosaka Toshiba Corporation, Power And Industrial Systems Research and Development Center, Yokohama, Japan
	TOSHIBA has been developing high purity niobium (Nb) material for superconducting cavities with ULBA Metallurgical Plant (UMP) since 2008. Recently, we have produced the high purity Nb plates. Two 1.3 GHz single-cell superconducting cavities using UMP's Nb plates have been fabricated by TOSHIBA and RF tested at High Energy Accelerator Research Organization (KEK). One of the cavities has achieved the accelerating gradient of Eacc=31.8 MV/m. The development of high purity Nb plates, details of the fabrication of the cavities and the RF test results are presented in this article.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THPLR004
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THPLR037	Development of a Superconducting Twin Axis Cavity	cavity, HOM, linac, SRF	932
	H. Park, A. Hutton, F. Marhauser JLab, Newport News, Virginia, USA S.U. De Silva, J.R. Delayen, H. Park ODU, Norfolk, Virginia, USA
	Superconducting cavities with two separate accelerating axes have been proposed in the past for energy recovery linac applications. While the study showed the advantages of such cavity, the designs present serious fabrication challenges. Hence the proposed cavities have never been built. The new design, elliptical twin cavity, proposed by Jefferson Lab and optimized by Center for Accelerator Science at Old Dominion University, allows similar level of engineering and fabrication techniques of a typical elliptical cavity. This paper describes preliminary LOM and HOM spectrum, engineering and fabrication processes of the twin axis cavity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THPLR037
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THPLR074	N-Doped Niobium Accelerating Cavities: Analyzing Model Applicability	electron, cavity, vacuum, embedded	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.
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Paper

Title

Other Keywords

Page

MOOP05

Dry-Ice Cleaning of RF-Structures at DESY

cavity, gun, RF-structure, coupling

52

A. Brinkmann, J. Ziegler
DESY, Hamburg, Germany

Dry-Ice cleaning is today a well established cleaning method in matters of reducing harmful dark current and field emission in copper RF-structures like RF-Guns such as for the European XFEL, FLASH and REGAE. This led to the idea to clean longer RF-structures, in particular 3GHz transverse deflecting structures for the European XFEL. We developed a cleaning device with the possibility to clean up to 2 m long structures in horizontal position with an inner diameter of not more than 40 mm. Furthermore this device also allows to clean 9-cell TESLA-type Nb-cavities as well. A report of the technical layout and results of RF-tests will be given.

Slides MOOP05 [0.969 MB]

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MOPRC027

Surface Roughness Effect on the Performance of Nb3Sn Cavities

cavity, SRF, pulsed-power, klystron

129

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) \%.

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MOPLR023

Examination of Cutouts Inner Surfaces from Nb3Sn Coated Cavity

cavity, SRF, ion, accelerating-gradient

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.

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MOPLR024

Progress Towards Nb3Sn CEBAF Injector Cryomodule

cavity, cryomodule, operation, electron

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.

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MOPLR025

Investigation of Low-Level Nitrogen in Niobium by Secondary Ion Mass Spectrometry

ion, SRF, cavity, factory

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.

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MOPLR026

Material Qualification of LCLS-II Production Niobium Material Including RF and Flux Expulsion Measurements on Single Cell Cavities

cavity, cryomodule, SRF, controls

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 MOPLR026 [0.861 MB]

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MOPLR032

Preparation for Cavity Material Studies at the Vertical High-Temperature UHV-Furnace of the S-DALINAC

vacuum, simulation, SRF, superconductivity

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

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MOPLR037

Study of the Surface and Performance of Single-Cell Nb Cavities After Vertical EP Using Ninja Cathodes

cathode, cavity, experiment, polarization

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.

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MOPLR041

Design and Fabrication of β=0.3 SSR1 for RISP

cavity, TRIUMF, cryogenics, linac

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.

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MOPLR047

Advanced Vertical Electro-Polishing studies at Cornell with Faraday

cavity, SRF, status, target

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 MOPLR047 [2.852 MB]

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TUOP07

High Performance Next-Generation Nb3Sn Cavities for Future High Efficiency SRF Linacs

cavity, SRF, accelerating-gradient, pulsed-power

398

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 TUOP07 [1.506 MB]

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TUOP08

On Magnetic Flux Trapping in Superconductors

solenoid, experiment, cavity, SRF

402

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 TUOP08 [1.787 MB]

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TUPRC025

Low Temperature Nitrogen Baking of a Q0 SRF Cavities

cavity, SRF, radio-frequency, impedance

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.

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TUPLR022

Particulate Study on Materials for Cleanroom Assembly of SRF Cavities

cavity, SRF, operation, experiment

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 TUPLR022 [1.282 MB]

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TUPLR023

Impurity Content Optimization to Maximize Q-Factors of Superconducting Resonators

cavity, SRF, factory, superconductivity

515

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.

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TUPLR025

Optimal Nitrogen Doping Level to Reach High Q0

cavity, cryomodule, SRF, electron

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.

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TUP106004

Status of RRR Analysis for RAON Accelerator

cavity, vacuum, SRF, superconductivity

628

Y. Jung, H. Kim, W.K. Kim
IBS, Daejeon, Republic of Korea
J. Lee, J. Seo
Vitzrotech Co., Ltd., Ansan City, Kyunggi-Do, Republic of Korea

Residual resistance ratio (RRR) of 300-grade niobium has been analyzed to find optimal welding condition for a superconducting cavity. RRR values were not only measured along the welding directions, but also perpendicular to the welding lines. In this presentation, we will show the RRR analysis as a function of the distance, the welding speed, and the welding pressure.

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THOP01

Experimental Study of Nucleation for Nb3Sn Diffusion Coatings on Niobium SRF Cavities

SRF, experiment, background, accelerating-gradient

740

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 THOP01 [2.784 MB]

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THOP02

Investigation of Nitrogen Absorption Rate and Nitride Growth on SRF Cavity Grade RRR Niobium as a Function of Furnace Temperature

SRF, cavity, ion, injection

744

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 THOP02 [2.235 MB]

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THOP03

Cold Bead-Pull Test Stand for SRF Cavities

cavity, HOM, SRF, simulation

748

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 THOP03 [2.731 MB]

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THPLR004

Development of 1.3 Ghz Single-Cell Superconducting Cavities With Nb Material Developed by Ulba Metallurgical Plant

cavity, accelerating-gradient, vacuum, radiation

849

T. Ota, N. Kuroiwa, S. Nomura, Y. Otani, M. Takasaki, M. Yamada
Toshiba, Yokohama, Japan
H. Hayano, T. Saeki
KEK, Ibaraki, Japan
Y.V. Krygin, V. Kuznetsov, A.A. Tsorayev
Ulba Metallurgical Plant, Ust-Kamenogorak, Kazakhstan
Y. Shirota
BE International Corporation, Tokyo, Japan
T. Tosaka
Toshiba Corporation, Power And Industrial Systems Research and Development Center, Yokohama, Japan

TOSHIBA has been developing high purity niobium (Nb) material for superconducting cavities with ULBA Metallurgical Plant (UMP) since 2008. Recently, we have produced the high purity Nb plates. Two 1.3 GHz single-cell superconducting cavities using UMP's Nb plates have been fabricated by TOSHIBA and RF tested at High Energy Accelerator Research Organization (KEK). One of the cavities has achieved the accelerating gradient of Eacc=31.8 MV/m. The development of high purity Nb plates, details of the fabrication of the cavities and the RF test results are presented in this article.

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reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THPLR004

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THPLR037

Development of a Superconducting Twin Axis Cavity

cavity, HOM, linac, SRF

932

H. Park, A. Hutton, F. Marhauser
JLab, Newport News, Virginia, USA
S.U. De Silva, J.R. Delayen, H. Park
ODU, Norfolk, Virginia, USA

Superconducting cavities with two separate accelerating axes have been proposed in the past for energy recovery linac applications. While the study showed the advantages of such cavity, the designs present serious fabrication challenges. Hence the proposed cavities have never been built. The new design, elliptical twin cavity, proposed by Jefferson Lab and optimized by Center for Accelerator Science at Old Dominion University, allows similar level of engineering and fabrication techniques of a typical elliptical cavity. This paper describes preliminary LOM and HOM spectrum, engineering and fabrication processes of the twin axis cavity.

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reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THPLR037

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THPLR074

N-Doped Niobium Accelerating Cavities: Analyzing Model Applicability

electron, cavity, vacuum, embedded

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.

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reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2016-THPLR074

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