SRF2019 - List of Keywords (niobium)

Paper	Title	Other Keywords	Page
MOP003	Development of Nb₃Sn Cavity Coating at IMP	cavity, SRF, radio-frequency, experiment	21
	Z.Q. Yang, H. Guo, Y. He, C.L. Li, Z.Q. Lin, M. Lu, T. Tan, P.R. Xiong, S.H. Zhang, S.X. Zhang IMP/CAS, Lanzhou, People’s Republic of China
	The A15 superconductor Nb₃Sn is one of the most promising alternative materials to standard niobium for SRF applications. In this paper, we report our progress in the development of Nb₃Sn cavity coating by vapor diffusion method at IMP. The evolutionary process of nucleation was analyzed. Influence of S_nCl₂ partial pressure inhomogeneity was studied. Less-nuclear zones were found on the surfaces of nucleation samples. The Nb₃Sn film structure and composition were investigated and analyzed. In light of knowledge obtained above, the coating process was optimized. Finally, both 1.3 GHz and 650 MHz single cell cavities were coated and vertically tested both at 4 K and 2 K. Effect of low temperature baking (1000°C for 48 hs) on the RF performance of Nb₃Sn cavity was studied. After baking, the Q drop in the low field region was eliminated and the Q in the intermediate field region was increased 8 times. The Q was 10 times larger than that of the Nb cavity at 4.2 K even in the case of the ambient field larger than 20 mGs. This study shows that the low temperature baking is an effective enrichment to the post treatment of the Nb₃Sn cavity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP003
About •	paper received ※ 23 June 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019
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MOP005	The Facility for Rare Isotope Beams Superconducting Cavity Production Status and Findings Concerning Surface Defects	cavity, linac, SRF, status	31
	C. Compton NSCL, East Lansing, Michigan, USA H. Ao, J. Asciutto, K. Elliott, W. Hartung, S.H. Kim, E.S. Metzgar, S.J. Miller, J.T. Popielarski, L. Popielarski, K. Saito, T. Xu FRIB, East Lansing, Michigan, USA J. Craft SLAC, Menlo Park, California, 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 Facility for Rare Isotope Beams (FRIB), located on the campus of Michigan State University (MSU) will require 324 Superconducting Radio Frequency (SRF) cavities in the driver linac. Four types of cavities of two classes, quarter-wave (β=0.041 and 0.085) and half-wave (β=0.29 and 0.53), will be housed in 46 cryomodules. To date, FRIB has tested over 300 cavities in vertical Dewar tests as part of the certification procedures. Incoming cavities, fabricated in industry, are sequenced through acceptance inspection and checked for non-conformance. If accepted, the cavities are processed, assembled onto a vertical test stand, and cold tested. A large database of cavity surface images has been collected with the aid of a borescope camera. Borescope inspection is a standard step that is performed at incoming inspection, post-acid bulk etch, and after failed tests (if necessary) for each cavity, in order to locate any non-conformances. Findings of surface defects relating to degraded cavity performance will be presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP005
About •	paper received ※ 02 July 2019 paper accepted ※ 13 August 2019 issue date ※ 14 August 2019
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MOP010	Ab Initio Calculations on the Growth and Superconducting Properties of Nb₃Sn	site, cavity, SRF, electron	39
	N. Sitaraman, T. Arias, P. Cueva, M.M. Kelley, D.A. Muller Cornell University, Ithaca, New York, USA J.M. Carlson, A.R. Pack, M.K. Transtrum Brigham Young University, Provo, USA M. Liepe, R.D. Porter, Z. Sun Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: This research was funded by the Center for Bright Beams. In this work, we employ theoretical ab initio techniques to solve mysteries and gain new insights in Nb₃Sn SRF physics. We determine the temperature dependence of Nb₃Sn antisite defect formation energies, and discuss the implications of these results for defect segregation. We calculate the phonon spectral function for Nb₃Sn cells with different combinations of antisite defects and use these results to determine Tc as a function of stoichiometry. These results allow for the first-ever determination of Tc in the tin-rich regime, where experimental measurements are unavailable and which is critical to understanding the impact of tin-rich grain boundaries on superconducting cavity performance. Finally, we propose a theory for the growth mechanism of Nb₃Sn growth on a thick oxide, explaining the puzzling disappearing droplet behavior of Sn on Nb oxide and suggesting how in general an oxide layer reacts with Sn to produce a uniform Nb₃Sn layer.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP010
About •	paper received ※ 02 July 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019
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MOP011	High Frequency Nb₃Sn Cavities	cavity, SRF, radio-frequency, factory	44
	R.D. Porter, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Niobium-3 Tin (Nb₃Sn) is an alternative material to Nb for SRF cavities. This material is capable of higher temperature operation and has high theoretical maximum accelerating gradients. Cornell University is a leader in the development of this material for SRF applications, and current Nb₃Sn 1.3 GHz single cells produced at Cornell achieve quality factors above 10^zEhNZeHn at 4.2 K at medium fields, far above what can be reached with niobium. Most of the recent Nb₃Sn cavity development has been done at 1.3 GHz. In this paper, we present new results from Nb₃Sn cavities at 2.6 GHz and 3.9 GHz. We compare relative cavity performance and flux trapping sensitivities, and extract frequency dependencies. Results show that the frequency can be increased without degrading the performance of the cavities, opening the path towards a new generation of compact and efficient SRF cavities for a wide range of future applications.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP011
About •	paper received ※ 05 July 2019 paper accepted ※ 12 July 2019 issue date ※ 14 August 2019
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MOP013	Reducing Surface Roughness of Nb₃Sn Through Chemical Polishing Treatments	cavity, superconductivity, controls, SRF	48
	H. Hu, M. Liepe, R.D. Porter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Niobium-3 tin (Nb₃Sn) is a promising alternative material for SRF cavities, with theoretical limits for critical temperatures and superheating fields reaching twice that of conventional Nb cavities. However, currently achievable accelerating gradients in Nb₃Sn cavities are much lower than their theoretical limit. One limitation to the maximum accelerating gradient is surface magnetic field enhancement caused by the surface roughness of Nb₃Sn. However, there are currently no standard techniques used to reduce Nb₃Sn surface roughness. Since Nb₃Sn is only 2-3 microns thick, it is difficult to selectively polish Nb₃Sn without removing the entire layer. Here, we investigate reducing the surface roughness of Nb₃Sn through applying chemical polishing treatments, including modified versions of standard techniques such as Buffered Chemical Polishing (BCP) and Electropolishing (EP). Through data acquired from Atomic Force Microscope (AFM) scans, SEM scans, and SEM-EDS analysis, we show the effects of these chemical treatments in reducing surface roughness and consider the changes in the chemical composition of Nb₃Sn that may occur through the etching process. We find that BCP with a 1:1:8 solution is ineffective while EP halves the surface roughness of Nb₃Sn.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP013
About •	paper received ※ 01 July 2019 paper accepted ※ 04 July 2019 issue date ※ 14 August 2019
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MOP016	Insights Into Nb₃Sn Coating of CEBAF Cavities From Witness Sample Analysis	cavity, SRF, HOM, hardware	60
	G.V. Eremeev, M.J. Kelley, C.E. Reece JLab, Newport News, Virginia, USA M.J. Kelley, U. Pudasaini The College of William and Mary, Williamsburg, Virginia, USA
	Funding: Co-Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics. With the progress made in the Nb₃Sn coatings on single-cell SRF cavities, development is ongoing to reproduce single-cell cavity results on practical structures such as CEBAF 5-cell cavities. During CEBAF cavity coating development, several changes from the single-cell procedure to the coating setup and the heating profile were introduced to improve the quality of Nb₃Sn films. To witness the properties of grown Nb₃Sn films in different cavity locations, 10 mm x 10 mm samples were positioned in strategic places within the coating chamber. Composition and structure of the samples were analyzed with surface analytic techniques and correlated with sample location during coatings. Implications from sample analysis to Nb₃Sn coatings on different geometries are discussed in this contribution.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP016
About •	paper received ※ 26 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019
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MOP018	Recent Results From Nb₃Sn Single Cell Cavities Coated at Jefferson Lab	cavity, SRF, experiment, factory	65
	U. Pudasaini, M.J. Kelley The College of William and Mary, Williamsburg, Virginia, USA G. Ciovati, G.V. Eremeev, M.J. Kelley, C.E. Reece JLab, Newport News, Virginia, USA I.P. Parajuli, Md.N. Sayeed ODU, Norfolk, Virginia, USA
	Funding: Partially authored by Jefferson Science Associates under contract no. DE¬AC05¬06OR23177. Supported by Office of High Energy Physics under grants DE-SC-0014475 to the College of William and DE-SC-0018918 to Virginia Tech Because of superior superconducting properties (Tc ~ 18.3K, Hs h ~ 425 mT and delta ~ 3.1 meV) compared to niobium, Nb₃Sn promise better RF performance (Q₀ and E_acc) and/or higher operating temperature (2 K Vs 4.2 K) for SRF cavities. Nb₃Sn-coated SRF cavities are produced routinely by depositing a few micron-thick Nb₃Sn films on the interior surface of Nb cavities via tin vapor diffusion technique. Early results from Nb₃Sn cavities coated with this technique exhibited precipi-tous low field Q-slope, also known as Wuppertal slope. Several Nb₃Sn single cell cavities coated at JLab ap-peared to exhibit similar Q-slope. RF testing of cavi-ties and materials study of witness samples were con-tinuously used to modify the coating protocol. At best condition, we were able to produce Nb₃Sn cavity with Q₀ in excess of ~ 5×10¹⁰ at 2 K and ~ 2×1010 at 4 K up the accelerating gradient of ~15 MV/m, without any significant Q-slope. In this presentation, we will dis-cuss recent results from several Nb₃Sn coated single-cell cavities linked with material studies of witness samples, coating process modifications and the possi-ble causative factors to Wuppertal slope.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP018
About •	paper received ※ 23 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019
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MOP022	Superconducting RF Cavity Materials Research at the S-DALINAC	cavity, linac, SRF, simulation	74
	R. Grewe, L. Alff, M. Arnold, J. Conrad, S. Flege, M. Major, N. Pietralla TU Darmstadt, Darmstadt, Germany F. Hug IKP, Mainz, Germany
	Funding: Supported by BMBF Through 05H18RDRB2 Current state-of-the-art superconducting rf (srf) accelerators are mostly using cavities made of high RRR bulk niobium (Nb). The maximum field gradients and quality factors (Q₀) of these cavities are basically reached now. To further increase the srf cavity properties for future accelerator facilities, research of new materials for srf cavity applications is necessary. The current research at the S-DALINAC* is focused on the development of bake-out procedures of Nb samples and cavities in nitrogen (N) atmosphere of up to 100 mbar to nucleate the delta-phase (d-phase) of the Nb-N binary system. The d-phase has superconducting properties which exceed the properties of bulk Nb. This makes the d-phase attractive for srf applications. The vertical test cryostat (vt) at the S-DALINAC has been upgraded and recommissioned to allow investigations of the quality factor and accelerating field gradients of cavities before and after bake-out. The vt upgrade includes a newly developed variable input coupling to allow matching of the external q-factor (Qex) to Q₀. The results of the ongoing research of the nitrogen atmosphere bake-out procedures and the upgrade of the vt will be presented. *N. Pietralla, Nuclear Physics News, Vol. 28, No. 2, 4 (2018)
	Poster MOP022 [1.759 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP022
About •	paper received ※ 21 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019
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MOP023	Nitrogen Infusion Sample R&D at DESY	cavity, vacuum, SRF, HOM	77
	C. Bate, A. Dangwal Pandey, A. Ermakov, B. Foster, T.F. Keller, D. Reschke, J. Schaffran, S. Sievers, N. Walker, H. Weise, M. Wenskat DESY, Hamburg, Germany W. Hillert University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany G.D.L. Semione, V. Vonk DESY Nanolab, FS-NL, Hamburg, Germany A. Stierle University of Hamburg, Hamburg, Germany
	The European XFEL continuous wave upgrade requires cavities with reduced surface resistance (high Q-values) for high duty cycle while maintaining high accelerating gradient for short-pulse operation. A possible way to meet the requirements is the so-called nitrogen infusion procedure. However, a fundamental understanding and a theoretical model of this method are still missing. The approach shown here is based on sample R&D, with the goal to identify key parameters of the process and establish a stable, reproducible recipe. To understand the underlying processes of the surface evolution, which gives improved cavity performance, advanced surface analysis techniques (e.g. SEM/EDX, TEM, XPS, TOF-SIMS) are utilized. Additionally, a small furnace just for samples was set up to change and explore the parameter space of the infusion recipe. Results of these analyses, their implications for the cavity R&D and next steps are presented.
	Poster MOP023 [3.759 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP023
About •	paper received ※ 23 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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MOP024	Vacancy-Hydrogen Dynamics in Samples During Low Temperature Baking	positron, cavity, lattice, electron	83
	M. Wenskat, C. Bate, D. Reschke, H. Weise DESY, Hamburg, Germany C. Bate University of Hamburg, Hamburg, Germany M. Butterling, E. Hirschmann, M.O. Liedke, A. Wagner HZDR, Dresden, Germany J. Cizek Charles University, Prague, Czech Republic
	Funding: This work was supported by the Helmholtz Association within the topic Accelerator Research and Development (ARD) of the Matter and Technologies (MT) Program and by the BMBF under the research grant 05H18GURB1. The recent discovery of a modified low temperature baking process lead to a reduction of surface losses and an increase of the accelerating gradient of TESLA shape cavities. The hypothesis linking the accelerator performance and the treatment is the suppression of lossy nanohydrides via defect trapping, with vacancy-hydrogen complexes forming at the lower temperatures. Utilizing Doppler broadening Positron Annihilation Spectroscopy and Positron Annihilation Lifetime Spectroscopy samples made from European XFEL niobium sheets and cavity cut-outs were investigated. The evolution of vacancies, hydrogen and their interaction at different temperature levels have been studied during in-situ annealing. Measurements of niobium samples and a correlation between RF, material properties, and V-H distribution in cavity cut-outs has been done.
	Poster MOP024 [1.087 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP024
About •	paper received ※ 20 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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MOP025	Cavity Cut-out Studies of a 1.3 GHz Single-cell Cavity After a Failed Nitrogen Infusion Process	cavity, SRF, electron, superconductivity	87
	M. Wenskat, C. Bate, T.F. Keller, D. Reschke DESY, Hamburg, Germany C. Bate University of Hamburg, Hamburg, Germany A. Jeromin DESY Nanolab, FS-NL, Hamburg, Germany J. Knobloch, F. Kramer, O. Kugeler, J.M. Köszegi HZB, Berlin, Germany J. Knobloch University of Siegen, Siegen, Germany
	Funding: This work was supported by the Helmholtz Association within the topic Accelerator Research and Development (ARD) of the Matter and Technologies (MT) Program and by the BMBF under the research grant 05H18GURB1. R&D on the nitrogen infusion process at DESY produced at the beginning a series of 1.3 GHz single-cell cavities which have shown severe deterioration in the vertical cold test which was completely unexpected and could not be explained. To investigate the reason for the deterioration, one of those cavities was optically inspected and a T- and H-Map test was done in collaboration with HZB. Together with 2nd Sound data, regions of interests were identified and cut from the cavity. Subsequent surface analysis techniques (SEM/EDX, SIMS, PIXE, EBSD, DB-PAS, PALS, XPS) were applied in order to identify the reason for the deterioration. Especially the differences between hot and cold spots as well as quench spots identified by T-Mapping were investigated.
	Poster MOP025 [0.975 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP025
About •	paper received ※ 20 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019
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MOP026	A Cross-Lab Qualification of Modified 120°C Baked Cavities	cavity, shielding, multipactoring, factory	90
	M. Wenskat, D. Reschke, J. Schaffran, L. Steder, M. Wiencek DESY, Hamburg, Germany D. Bafia, A. Grassellino, O.S. Melnychuk Fermilab, Batavia, Illinois, USA A.D. Palczewski JLab, Newport News, Virginia, USA M. Wiencek IFJ-PAN, Kraków, Poland
	Funding: This work was supported by the Helmholtz Association within the topic Accelerator Research and Development (ARD) of the Matter and Technologies (MT) Program and by the BMBF under the research grant 05H18GURB1. Within a global effort to understand and standardize the nitrogen-infusion and the low T bake procedure, one large grain and two fine grain single-cell cavity were treated and tested at FNAL and then send to other labs including DESY and JLab for further studies.
	Poster MOP026 [0.813 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP026
About •	paper received ※ 20 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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MOP028	Materials Science Investigations of Nitrogen-Doped Niobium for SRF Cavities	cavity, SRF, superconducting-RF, collider	99
	M. Major, L. Alff, M. Arnold, J. Conrad, S. Flege, R. Grewe, N. Pietralla TU Darmstadt, Darmstadt, Germany
	Funding: Work supported by the German Federal Ministry for Education and Research (BMBF) through grant 05H18RDRB2. Niobium is the standard material for superconducting RF (SRF) cavities for particle acceleration. Superconducting materials with higher critical temperature or higher critical magnetic field allow cavities to work at higher operating temperatures or higher accelerating fields, respectively. Enhancing the surface properties of the superconducting material in the range of the penetration depth is also beneficial. One direction of search for new materials with better properties is the modification of bulk niobium by nitrogen doping. In the Nb-N phase diagram, the cubic delta-phase of NbN has the highest critical temperature. Niobium samples were annealed and N-doped in the high-temperature furnace at TU Darmstadt and investigated at its Materials Research Department with respect to structural modifications. Secondary ion mass spectrometry showed at which conditions N-diffusion takes place. X-ray diffraction (XRD) confirmed the appearance of NbN and Nb₂N phases for the optimized doping process. XRD pole figures also showed grain growth during sample annealing.
	Poster MOP028 [2.555 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP028
About •	paper received ※ 05 July 2019 paper accepted ※ 12 July 2019 issue date ※ 14 August 2019
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MOP029	N-Doping Studies With Single-Cell Cavities for the SHINE Project	cavity, SRF, FEL, ECR	102
	J.F. Chen, H.T. Hou, Y.F. Liu, D. Wang, Y. Wang SARI-CAS, Pudong, Shanghai, People’s Republic of China Y.W. Huang ShanghaiTech University, Shanghai, People’s Republic of China Z. Wang SINAP, Shanghai, People’s Republic of China
	The SHINE SRF accelerator is designed to operate in CW mode with more than six hundred superconducting cavities. In order to reduce the high cost of construction and operation of the cryogenic system, high-Q cavities with nitrogen-doping technology together with tradition-ally treated large-grain cavities have been considered as two possible options. In this paper, we present N-doping studies on single-cell cavities fabricated with fine-grain and large-grain niobium.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP029
About •	paper received ※ 23 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019
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MOP030	Analysis of Surface Nitrides Created During "Doping" Heat Treatments of Niobium	cavity, SRF, lattice, controls	106
	J.K. Spradlin, A.D. Palczewski, C.E. Reece, H. Tian JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The benefits of reduced RF losses from interstitial "doping" of niobium are well established. Many of the details involved in the process remain yet to be elucidated. The niobium surface reacted with low-pressure nitrogen at 800°C presents a surface with chemical reactivity different than standard niobium. While standard "recipes" are being used to produce cavities, we seek additional insight into the chemical processes that may be used to remove the "undesirable" as-formed surface layer. This may lead to new processing routes or quality assurance methods to build confidence that all surface "nitrides" have been removed. We report a series of alternate chemistry treatments and subsequent morphological examinations and interpret the results. We also introduce a new standardized Nb sample system in use for efficient characterization of varying doping protocols and cross-laboratory calibration.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP030
About •	paper received ※ 23 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019
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MOP031	Investigation of Frequency Behavior Near Tc of Niobium Superconducting Radio-Frequency Cavities	cavity, SRF, electron, ECR	112
	D. Bafia, J. Zasadzinski IIT, Chicago, Illinois, USA D. Bafia, M. Checchin, A. Grassellino, O.S. Melnychuk, A.S. Romanenko, D.A. Sergatskov Fermilab, Batavia, Illinois, USA
	This paper will present a systematic investigation of the resonant frequency behavior of niobium SRF cavities subject to different surface processing (nitrogen doping, nitrogen infusion, 120°C bake, EP, etc.) near the critical transition temperature. We find features occurring in frequency versus temperature (FvsT) data near Tc that seem to vary with surface processing. Emphasis is placed on one of the observed features: a dip in the superconducting resonant frequency below the normal conducting value which is prominent in nitrogen doped cavities and appears to be a signature of nitrogen doping. This gives further insights on the mechanisms responsible for the large increase in performance of cavities subject to this surface treatment. The magnitude of this dip in frequency is studied and related to possible physical parameters such as the concentration of impurities near the surface and the design resonant frequency of the cavity. A possible explanation for the meaning of this dip is discussed, namely, that it is a result of strong coupling between electrons and phonons within the resonator.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP031
About •	paper received ※ 23 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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MOP032	Effect of Low Temperature Infusion Heat Treatments and "2/0" Doping on Superconducting Cavity Performance	cavity, ECR, SRF, background	118
	P.N. Koufalis, M. Ge, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Under specific circumstances, low temperature infusion heat treatments of niobium cavities have resulted in the ubiquitous "Q-rise". This is an increase in quality factor with increasing field strength or equivalently a decrease in the temperature-dependent component of the surface resistance. We investigate the results of various infusion conditions with infusion bake time as a free parameter. To study the very near surface effects of infusion, we employ HF rinsing, light VEP, and oxypolishing to remove several or tens of nm at a time. We present results from RF performance tests of low temperature infusion heat treated niobium cavities, and correlate these with SIMS impurity depth profiles obtained from witness samples. We also present results of a cavity doped at 800 C with the "2/0" recipe.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP032
About •	paper received ※ 26 June 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019
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MOP039	Nitrogen Doping Studies of Superconducting Cavities at Peking University	cavity, accelerating-gradient, superconducting-cavity, ECR	141
	S. Chen, M. Chen, L.W. Feng, J.K. Hao, L. Lin, K.X. Liu, S.W. Quan, F. Wang, F. Zhu PKU, Beijing, People’s Republic of China
	Nitrogen doping studies with 1.3 GHz superconducting cavities were carried out at Peking University in recent years. We have realized 4×10¹⁰ of high quality factor at 12 MV/m and 2.0 K with large grain single cell cavities by heavy doping. To improve the accelerating gradient of high Q cavities, light doping recipe is adopted. Accelerating gradient is improved to 20 MV/m and the quality factor is larger than 3×10¹⁰ at 16 MV/m and 2.0 K for light doped cavities. The nitrogen treatment, test and analysis are presented in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP039
About •	paper received ※ 21 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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MOP040	Low Temperature Thermal Conductivity of Niobium and Materials for SRF Cavities	SRF, cavity, experiment, controls	144
	M. Fouaidy Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
	A test facility, allowing the test of 4 samples simultaneously during each run, was developed for measuring at low temperature (T= 1.5 K - 10 K) the thermal conductivity k(T) of niobium and other materials used for the fabrication of SRF cavities. The measurements are performed using steady-state axial heat flow method with a careful control of heat leaks to the surrounding. Several samples of different materials (industrial Nb sheets, Ti¿) were either tested as received or/and subjected to various Heat Treatment (H.T) prior to the experiment then tested. The resulting experimental data are presented and compared to the experimental results previously reported by other groups. As expected, H.T @ 1200°C with Ti gettering improves the Nb RRR by a factor of 3 and consequently k(T). Finally, the correlation between the Niobium RRR and the thermal conductivity. at T=4.2 K is confirmed in good agreement with the Wiedemann-Franz law.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP040
About •	paper received ※ 04 July 2019 paper accepted ※ 05 July 2019 issue date ※ 14 August 2019
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MOP041	Comparison of the Lattice Thermal Conductivity of Superconducting Tantalum and Niobium	scattering, electron, lattice, simulation	148
	P. Xu, N.T. Wright MSU, East Lansing, Michigan, USA T.R. Bieler Michigan State University, East Lansing, Michigan, USA
	Funding: This work is supported by the U.S. Department of Energy, Office of High Energy Physics through Grant No. DE-FG02-13ER41974. The thermal conductivity k of superconducting Ta behaves similarly to that of superconducting Nb, albeit at colder temperatures. This shift is due to the superconducting transition temperature of Ta being 4.3 K, versus 9.25 K for Nb. For example, the temperature of the phonon peak of properly treated Ta is about 1 K as opposed to a phonon peak at about 2 K for Nb. The typical value of k of Ta is smaller than Nb with the value at the phonon peak for Ta being O(10) W/ m/ K. Like Nb, k is dominated by phonons at these temperatures. This lattice k can be modeled by the Boltzmann transport equation, solved here by a Monte Carlo method using the relaxation time approximation. Individual scattering mechanisms due to boundaries, dislocations, and residual normal electrons are examined, and the phonon dispersion relation is included. Differences in the thermal response of deformed Ta, as compared with Nb, may be attributed to differences in dislocation densities of the two metals following similar levels of deformation. Boundary scattering dominates at the coldest temperatures. The phonon peak decreases and shifts to warmer temperatures with deformation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP041
About •	paper received ※ 19 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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MOP045	The LCLS-II HE High Q and Gradient R&D Program	cavity, SRF, cryomodule, linac	154
	D. Gonnella, S. Aderhold, A. Burrill, G.R. Hays, T.O. Raubenheimer, M.C. Ross SLAC, Menlo Park, California, USA D. Bafia, M. Checchin, A. Grassellino, M. Martinello, A.S. Romanenko Fermilab, Batavia, Illinois, USA M. Ge, M. Liepe, S. Posen Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA A.D. Palczewski, C.E. Reece JLab, Newport News, Virginia, USA
	Funding: US DOE and the LCLS-II HE Project The LCLS-II HE project is a high energy upgrade to the superconducting LCLS-II linac. It consists of adding twenty additional 1.3 GHz cryomodules to the linac, with cavities operating at a gradient of 20.8 MV/m with a Q₀ of 2.7·10¹⁰. Performance of LCLS-II cryomodules has suggested that operations at this high of a gradient will not be achievable with the existing cavity recipe employed. Therefore a research program was developed between SLAC, Fermilab, Thomas Jefferson National Accelerator Facility, and Cornell University in order to improve the cavity processing method of the SRF cavities and reach the HE goals. This program explores the doping regime beyond what was done for LCLS-II and also has looked to further developed nitrogen-infusion. Here we will summarize the results from this R\&D program, showing significant improvement on both single-cell and 9-cell cavities compared with the original LCLS-II cavity recipe.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP045
About •	paper received ※ 25 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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MOP049	Prototypes Fabrication of 1.3 GHz Superconducting Rf Components for SHINE	cavity, FEL, HOM, SRF	164
	H.T. Hou, J.F. Chen, Z.Y. Ma, J. Shi, Y. Wang SARI-CAS, Pudong, Shanghai, People’s Republic of China F.S. He IHEP, Beijing, People’s Republic of China S.W. Quan PKU, Beijing, People’s Republic of China
	Aiming to high repetition rate hard X-ray facility, con-struction of Shanghai HIgh repetition rate XFEL aNd Extreme light facility (SHINE) project has been ap-proved. During the R & D phase, prototypes fabrication of key components of 1.3GHz superconducting rf system have been proposed, especially 1.3 GHz 9-cell niobium cavities. Here the paper will present the progress of the fabrication status and performance of the prototypes, together with the analysis of not only the quality factor and gradient of the cavities. Consideration of HOM feed-throughs and absorbers are also reported.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP049
About •	paper received ※ 23 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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MOP056	Surface Treatments for the Series Production of ESS Medium Beta Cavities	cavity, recirculation, SRF, simulation	188
	M. Bertucci, A. Bosotti, A. D’Ambros, P. Michelato, L. Monaco, C. Pagani, R. Paparella, D. Sertore INFN/LASA, Segrate (MI), Italy C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy D. Rizzetto, M. Rizzi Ettore Zanon S.p.A., Schio, Italy A. Visentin Ettore Zanon S.p.A., Nuclear Division, Schio, Italy
	The surface treatment of ESS 704 MHz medium beta cavities consists of a bulk BCP 200 micron removal, a 10 h 600°C heat treatment and a final 20 micron BCP performed after tank integration. The facility currently employed for the BCP treatment, settled in Ettore Zanon SpA, is here presented, together with the results so far obtained on the first series cavities in terms of frequency sensitivity, removal rate and surface external temperature. The optimization of BCP treatment by a preliminary fluid-dynamical finite element model is also discussed. Some details about the visual inspection procedure and the furnace qualification are also presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP056
About •	paper received ※ 23 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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MOP060	INFN-LASA for the PIP-II Project	cavity, SRF, interface, linac	205
	R. Paparella, M. Bertucci, A. Bignami, A. Bosotti, M. Chiodini, A. D’Ambros, P. Michelato, L. Monaco, D. Sertore INFN/LASA, Segrate (MI), Italy J.F. Chen SARI-CAS, Pudong, Shanghai, People’s Republic of China C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy L. Sagliano ESS, Lund, Sweden
	INFN-LASA joined the international effort for the PIP-II project in Fermilab to build the 650 MHz superconducting cavities realizing the low-beta section of the 800 MeV proton linac. After developing the electro-magnetic and mechanical design, INFN-Milano started the prototyping phase by producing five single-cells and two complete 5-cells cavities. This paper reports the status of PIP-II activities at INFN-LASA summarizing manufacturing experience and preliminary experimental results.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP060
About •	paper received ※ 24 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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MOP061	State of the Art of Niobium Machining for SRF Applications	SRF, cavity, electron, alignment	210
	P. Naisson, S. Atieh, K. Scibor, P. Trubacova CERN, Geneva, Switzerland F. Dumont, D. Fabre, F. Valiorgue ENISE, Saint Etienne, France
	Niobium is a demanding material to be machined. Its low hardness, high melting temperature and abrasivity leads to poor cutting condition, and surface quality and shape accuracy could be difficult to achieve, especially for complex shapes such as HOM antennas. Recent CERN developements concerning DQW crab cavity for HL-LHC project had implied extensive research program to better understand and master the machining of this material. In this frame, the present article will introduce actual state of the art machining condition used at CERN and their consequences about the surface roughness, shape accuracy and taking into account the tool wear in order to maintain this level of quality. Morevoer, advance machning solution, such as cryogenic cooling could be used.
	Poster MOP061 [2.921 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP061
About •	paper received ※ 30 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019
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MOP064	Performance of First Prototype Multi-Cell Low-Surface-Field Shape Cavity	cavity, SRF, electron, experiment	222
	R.L. Geng JLab, Newport News, Virginia, USA Y. Fuwa, Y. Iwashita Kyoto ICR, Uji, Kyoto, Japan H. Hayano KEK, Ibaraki, Japan H. Ito Sokendai, Ibaraki, Japan Z. Li SLAC, Menlo Park, California, USA
	The idea of cavity shaping for higher ultimate acceleration gradients has been proposed for some time, Low Loss/Ichiro and Re-entrant being examples, both seeking a lower Hpk/E_acc at the expense of a higher Epk/E_acc. While experimental verification in single-cell cavities of those shapes was very successful including the record gradient of 59 MV/m, pushing multi-cell cavities of those shapes to higher gradients was prevented by field emission. The Low-Surface-Field (LSF) shape seeks not only a lower Hpk/E_acc but also a lower Epk/E_acc, therefore it has the advantage of raising ultimate gradient at reduced field emission. The first multi-cell LSF shape prototype cavity was built using the standard forming and welding techniques. RF tests have been carried out, following standard ILC TDR baseline surface processing and treatment recipe. Three out of five cells achieved Hpk values corresponding to E_acc 50 MV/m. The current limit is the field emission in end cells. Instrumented testing following end-cell wiping and HPR with larger nozzles is in progress. We will present detailed experimental results and preparation procedures.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP064
About •	paper received ※ 24 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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MOP070	Investigation of the Critical RF Fields of Superconducting Cavity Connections	cavity, simulation, vacuum, impedance	230
	J.C. Wolff, J.I. Iversen, D. Klinke, D. Kostin, D. Reschke, S. Sievers, A. Sulimov, J.H. Thie, M. Wiencek DESY, Hamburg, Germany R. Wendel, J.C. Wolff HAW Hamburg, Hamburg, Germany
	To optimise the length of the drift tube of a superconducting cavity (SC), it is required to know the critical value of the RF fields to prevent a potential early quench at the flange connection in case of a drift tube length reduction. To avoid changes on the SC which has been used for the tests, all RF cryogenic experiments have been carried out by using a cylinder in the center of a 1-cell cavity drift tube to increase the field magnitude at the connection. This cylinder has been designed and optimised by RF simulations to provide a field density at the connection twice as high as at a chosen reference point near the iris. Hence also a test SC with a comparatively low gradient can be used without causing field restrictions. In this contribution an approach to investigate the field limitations of 1.3 GHz TESLA-Shape SC connections and thereby the minimal drift tube length based on simulations will be presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP070
About •	paper received ※ 23 June 2019 paper accepted ※ 04 July 2019 issue date ※ 14 August 2019
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TUFUA1	The Field-Dependent Surface Resistance of Doped Niobium: New Experimental and Theoretical Results	cavity, SRF, electron, ECR	340
	J.T. Maniscalco, M. Ge, P.N. Koufalis, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA T. Arias, D. Liarte, J.P. Sethna, N. Sitaraman Cornell University, Ithaca, New York, USA
	We present systematic work investigating how different doping and post-doping treatments affect the BCS surface resistance at 1.3~GHz and higher frequencies. We examine the field-dependent BCS resistance at many temperatures as well as the field-dependent residual resistance and use the results to reveal how impurity species and concentration levels affect the field-dependent RF properties. We further demonstrate the importance of thermal effects and their direct dependence on doping level. We use the tools of Density Functional Theory to work towards an {\em ab initio} model of electron overheating to theoretically confirm the impact of doping, create a full model that includes thermal effects to predict the field dependent resistance, and show that the predictions of the model agree with results from doped and non-doped cavities ({\em e.g.} the strength of the anti-Q-slope and the high-field Q slope). Finally, we use our experimental results to systematically assess and compare theories of the field-dependent BCS resistance, showing that the current theory on smearing of the density of states is incomplete.
	Slides TUFUA1 [6.780 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUA1
About •	paper received ※ 01 July 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019
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TUFUA4	New Insights on Nitrogen Doping	cavity, electron, SRF, ECR	347
	D. Bafia, J. Zasadzinski IIT, Chicago, Illinois, USA D. Bafia, M. Checchin, A. Grassellino, O.S. Melnychuk, A.S. Romanenko, D.A. Sergatskov Fermilab, Batavia, Illinois, USA
	This paper covers a systematic study of the quench in nitrogen doped cavities: a cavity was sequentially treated/reset with different N-doping recipes which are known to produce different levels of quench field. Analysis of cavity heating profiles using TMAP are used to gain insight on the origins of quench; new recipes demonstrate the possibility to increase quench fields well beyond 30 MV/m. In addition, a new signature of nitrogen doping is explored, namely, a dip in the superconducting resonant frequency below the normal conducting value just below the critical transition temperature, giving further insights on the mechanisms responsible for the large increase in performance of cavities subject to this surface treatment.
	Slides TUFUA4 [3.097 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUA4
About •	paper received ※ 23 June 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019
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TUFUA5	Recent Development on Nitrogen Infusion Work Towards High Q and High Gradient	cavity, SRF, injection, radio-frequency	355
	P. Dhakal JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. A quality factor as high as 2 × 10¹⁰ at 1.5 GHz was achieved at a gradient of 35 MV/m by 800 °C annealing and N-infusion at 140 °C. A comparison of the field dependence of the surface resistance after N-infusion with a recent theoretical model that extends the calculation of the BCS surface resistance to high rf fields suggests an increase in the quasiparticles¿ relaxation time with increasing infusion temperature, which could be due to a decreasing density of subgap states. Nb coupons treated similarly showed the formation of thicker oxynitride layer on the surface beneath thin dielectric Nb₂O₅ layer. A plausible explanation for the improved Q₀ is that the oxynitride layer on the Nb surface adds additional electron scattering within RF penetration depth.
	Slides TUFUA5 [6.077 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUA5
About •	paper received ※ 19 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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TUFUA7	Review of Muon Spin Rotation Studies of SRF Materials	SRF, cavity, experiment, FEL	360
	T. Junginger Lancaster University, Lancaster, United Kingdom R.E. Laxdal TRIUMF, Vancouver, Canada
	Muons spin rotate in magnetic fields and emit a positron preferentially in spin direction after decay. These properties enable muon spin rotation (muSR) as a precise probe for local magnetism. muSR has been used to characterize SRF materials since 2010. At TRIUMF a so called surface beam implants muons at a material dependent depth of about 150 µm in the bulk. A dedicated spectrometer was developed for field of first vortex penetration and pinning strength measurements of SRF materials in parallel magnetic fields of up to 300 mT. A low energy beam available at PSI implants muons at variable depth in the London layer allowing for direct measurements of the London penetration depth from which the lower critical field and the superheating field can be calculated. This facility is limited to parallel magnetic fields of up to 25 mT. Here, surface and low energy muSR results on SRF materials are reviewed and cross-correlated to each other and to further results from additional experiments. Finally, we present the status of a new facility based on the similar beta-NMR technique enabling measurements in the London layer of SRF materials exposed to parallel magnetic fields above 200 mT.
	Slides TUFUA7 [4.063 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUA7
About •	paper received ※ 01 July 2019 paper accepted ※ 12 July 2019 issue date ※ 14 August 2019
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TUFUB3	Mapping Flux Trapping in SRF Cavities to Analyze the Impact of Geometry	cavity, experiment, HOM, simulation	364
	F. Kramer, J. Knobloch, O. Kugeler, J.M. Köszegi HZB, Berlin, Germany J. Knobloch University of Siegen, Siegen, Germany
	A combined temperature and magnetic field mapping system was used to investigate the impact of an ambient field on trapped flux and on the resulting local surface resistance. For this, a 1.3 GHz TESLA single cell cavity was cooled through the superconducting transition at different magnetic field angles with respect to the cavity axis. The measurements suggest, that the field is trapped homogeneously over the cavity volume, without changing its orientation. Flux trapped perpendicular the surface contributed significantly more to the surface resistance, than trapped flux parallel to the surface.
	Slides TUFUB3 [12.777 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUB3
About •	paper received ※ 21 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019
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TUFUB5	Effects of Static Magnetic Fields on a Low-frequency TEM Class Superconducting Cavity	cavity, shielding, SRF, superconductivity	370
	M.K. Ng, Z.A. Conway, M.P. Kelly, K.W. Shepard ANL, Lemont, Illinois, USA
	Systematic studies on the effect of magnetic fields on a 330 MHz superconducting (TEM-mode) half-wave cavity are presented. The practical application of the results is for a possible future 2 K operation in the ATLAS heavy-ion accelerator at Argonne. The low frequency and the integral stainless steel jacket, rather than titanium, provide important new data for this full production model low-beta cavity. The studies include multi-axial magnetic field measurements near the cavity surface due to ambient and applied fields. Cavity performance under different conditions is measured at temperatures ranging between 1.6 K and 4.5 K. A residual resistance of approximately 5-7 nΩ at 1.6 K is observed. Data suggest that an appreciable fraction arises from losses that are not due to flux trapping.
	Slides TUFUB5 [1.195 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUB5
About •	paper received ※ 24 June 2019 paper accepted ※ 14 August 2019 issue date ※ 14 August 2019
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TUFUB8	CVD Coated Copper Substrate SRF Cavity Research at Cornell University	cavity, SRF, interface, target	381
	M. Ge, T. Gruber, J.J. Kaufman, M. Liepe, J.T. Maniscalco, T.E. Oseroff, R.D. Porter, Z. Sun Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA V.M. Arrieta, S.R. McNeal Ultramet, Pacoima, California, USA
	Chemical vapor deposition (CVD) is a promising alternative to conventional sputter techniques for coating copper substrate cavities with high-quality superconducting films. Through multiple SRF-related DOE SBIR projects, Ultramet has developed CVD processes and CVD reactor designs for SRF cavities, and Cornell University has conducted extensive RF testing of CVD coated surfaces. Here we report results from thin-film CVD Nb₃Sn coated copper test plates, and for thick-film CVD niobium on copper including full-scale single cell 1.3 GHz copper substrate cavities. Detailed optical inspection and surface characterization show high-quality and well-adhered coatings. No copper contamination is found. The Nb₃Sn coated plates have a uniform Nb₃Sn coating with a slightly low tin concentration (19 -22%), but a BCS resistance well in agreement with predictions. The CVD Nb coatings on copper plates demonstrate excellent adhesion characteristics and exceeded surface fields of 50 mT without showing signs of a strong Q-slope that is frequently observed in sputtered Nb cavities. Multiple single-cell 1.3 GHz copper cavities have been coated to date at Ultramet, and results from RF testing of these are presented and discussed.
	Slides TUFUB8 [12.488 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUB8
About •	paper received ※ 01 July 2019 paper accepted ※ 05 July 2019 issue date ※ 14 August 2019
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TUP011	QWR085 Design for Bisol Post Accelerator SCL2	ISOL, cavity, simulation, LEBT	413
	M. Chen, S. Chen, A.Q. Cheng, J.K. Hao, K.X. Liu, Y.Q. Liu, D.M. Ouyang, S.W. Quan, F. Zhu PKU, Beijing, People’s Republic of China Z. Peng CIAE, Beijing, People’s Republic of China
	BISOL(Beijing Isotope-Separation-On-Line Neutron-Rich Beam Facility) is a new generation radioactive ion beam(RIB) facility[1]. It consists a CARR nuclear reactor, a high intensity deuteron accelerator and a post accelera-tor. QWR085 cavity is supposed to be used in SCL2 of post accelerator. This paper mainly talks about the elec-tromagnetic design, mechanical design and vibration damper design of QWR085.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP011
About •	paper received ※ 23 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019
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TUP012	Evaluation of High Performance Large Grain Medium Purity SRF Cavity From KEK	cavity, SRF, experiment, cryogenics	415
	P. Dhakal, G. Ciovati, G.R. Myneni JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. We presented the RF measurement on a 1.3 GHz single cell cavity fabricated at KEK using large grain ingot niobium with RRR=10⁷. The cavity reached to 35 MV/m with Q₀ = 2.0×10^zEhNZeHn at 2.0 K, record performance on the cavity made from medium purity ingot niobium. The cavity was cool down with different temperature gradient along the cavity axis in order to understand the flux expulsion mechanism when the cavity does through the superconducting transition and effect of trap residual magnetic field on the residual resistance. The measurement showed the excellent flux expulsion with the flux trapping sensitivity of 0.29 nΩ/mG for electro polished surface and 0.44 nΩ/mG for cavity followed by low temperature baking at 120°C for 12 hours. We acknowledge KEK for sending this cavity for evaluations.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP012
About •	paper received ※ 17 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019
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TUP016	Quarter-wave Resonator with the Optimized Shape for Quantum Information Systems	cavity, photon, shielding, factory	430
	S.V. Kutsaev, R.B. Agustsson, P.R. Carriere, A. Moro, A.Yu. Smirnov, K.V. Taletski RadiaBeam, Santa Monica, California, USA A.N. Cleland, É. Dumur The University of Chicago, Chicago, Illinois, USA Z.A. Conway ANL, Lemont, Illinois, USA K.V. Taletski MEPhI, Moscow, Russia
	Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, under SBIR grant DE-SC0018753 Quantum computers (QC), if realized, could disrupt many computationally intense fields of science. The building block element of a QC is a quantum bit (qubit). Qubits enable the use of quantum superposition and multi-state entanglement in QC calculations, allowing a QC to simultaneously calculate millions of computations at once. However, quantum states stored in a qubit degrade with decreased quality factors and interactions with the environment. One technical solution to improve qubit lifetimes and network interactions is a circuit comprised of a Josephson junction located inside of a high Q-factor superconducting 3D cavity. RadiaBeam, in collaboration with Argonne National Laboratory and The University of Chicago, has developed a superconducting radio-frequency quarter-wave resonant cavity (QWR) for quantum computation. Here a 6 GHz QWR was optimized to include tapering of the inner and outer conductors, a toroidal shape for the resonator shorting plane, and the inner conductor to reduce parasitic capacitance. In this paper, we present the results of the qubit cavity design optimization, fabrication, processing and testing in a single-photon regime at mK temperatures.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP016
About •	paper received ※ 23 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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TUP018	New SRF Structures Processed at the ANL Cavity Processing Facility	cavity, cathode, SRF, dipole	434
	T. Reid, Z.A. Conway, B.M. Guilfoyle, M. Kedzie, M.P. Kelly, M.K. Ng ANL, Lemont, Illinois, USA
	Argonne National Laboratory (ANL) has extended high quality cavity processing techniques based on those developed for the International Linear Collider to several more complex superconducting RF cavities. Recently, these include a bunch lengthening harmonic cavity, a crabbing rf-dipole cavity, a compact half-wave cavity, and both medium and high frequency elliptical cavities. These systems are an improved version of the one originally developed for 1.3 GHz 9-cell cavities and include a second rotating electrical contact that can support multiple cathodes, necessary for optimum polishing in difficult cavity geometries. All include the possibility for external water cooling.
	Poster TUP018 [4.322 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP018
About •	paper received ※ 28 June 2019 paper accepted ※ 12 July 2019 issue date ※ 14 August 2019
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TUP019	Status of High Temperature Vacuum Heat Treatment Program at IPN Orsay	cavity, SRF, MMI, vacuum	438
	M. Fouaidy, F. Chatelet, V. Delpech, F. Galet, D. Le Dréan, R. Martret, G. Olry, T. Pépin-Donat Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France M. Baudrier, P. Carbonnier, E. Fayette, X. Hanus, Th. Proslier, D. Roudier, P. Sahuquet, C. Servouin CEA-DRF-IRFU, France E. Cenni, L. Maurice CEA-IRFU, Gif-sur-Yvette, France D. Longuevergne FLUO, Orsay, France
	In the framework of ESS, a vacuum furnace dedicated to High Temperature Heat Treatment under Vacuum (VH2T2) of SRF bulk Nb cavities was developed and commissioned in May 2016. This furnace is currently used for interstitial hydrogen removal (10h00 @ 650 °C) of two type of cavities: 1) the whole series of 26 ESS 352 MHz spoke resonators equipped with their Ti LHe tank well, 2) some prototypes of ESS high beta and medium beta cavities. Up to know IPN Orsay VH2T2 (10h00 @ 650 °C) was successfully applied to more than 16 cavities. In this paper we will first report about these VH2T2 tests. Finally, we have just started testing nitrogen infusion and nitrogen doping processes on samples and 1.3 GHz cavities: the preliminary results will be discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP019
About •	paper received ※ 03 July 2019 paper accepted ※ 04 July 2019 issue date ※ 14 August 2019
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TUP020	Statistical Analysis of the 120°C Bake Procedure of Superconducting Radio Frequency Cavities	cavity, accelerating-gradient, FEL, SRF	444
	L. Steder, D. Reschke DESY, Hamburg, Germany
	DESY is and was very active in R&D related to SRF cavities. Many single and nine cell cavities with different surface treatment histories were tested vertically. Results of these cold tests are accelerating gradient and quality factor of the cavities. Using the large number of available datasets the parameters of the 120°C bake procedure, which is applied to avoid high-field Q-slope, are analysed. The impact of different durations and temperatures on accelerating gradient, quality factor and residual resistance is studied in detail and is compared to results obtained with the recently proposed procedure of modified low temperature bake. For this procedure additional four hours at temperatures around 75°C are implemented before the standard bake at about 120°C. Since the claim is, that cavities treated with such a modified procedure achieve extra-ordinary large accelerating gradients it is a very interesting research field for the European XFEL continuous wave mode upgrade. For this purpose cavities with high quality factors are needed, but in addition large maximal accelerating fields are required to maintain high energies in the pulsed operation mode of the accelerator.
	Poster TUP020 [0.747 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP020
About •	paper received ※ 21 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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TUP021	Effect of Cathode Rotation and Acid Flow in Vertical Electropolishing of 1.3 GHz Niobium Nine-Cell Cavity	cavity, cathode, experiment, SRF	448
	V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi MGH, Hyogo-ken, Japan H. Hayano, S. Kato, H. Monjushiro, T. Saeki KEK, Ibaraki, Japan
	We have been carrying out R&D on vertical electropolishing (VEP) technique to establish it as an alternate of the horizontal EP (HEP) technique used for the surface treatment of niobium (Nb) superconducting RF (SRF) cavities. We have earlier reported on a VEP parameter study for 1.3 GHz single and nine-cell Nb cavities. The optimized VEP parameters and a unique rotating cathode yielded uniform removal and a smooth surface in the single cell cavity. The unique cathode and a dual flow mechanism for acid circulation were applied to improve the removal uniformity in the nine-cell cavity. The vertically electropolished single and nine cell cavities achieved the same RF performance as achieved after the HEP processes. We are making efforts to further improve the removal uniformity in the nine-cell cavity. Here, we report on a VEP of the 1.3 GHz Nb nine-cell cavity at a higher cathode rotation speed of 50 rpm. The VEP results reveal that the speed could be considered for improving the uniformity in removal while maintaining the surface smoothness. Required improvements in the VEP facility and acid flow condition for achieving uniform EP and a smooth surface are also described.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP021
About •	paper received ※ 23 June 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019
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TUP022	Fermilab EP Facility Improvement	cavity, target, controls, SRF	453
	F. Furuta, D.J. Bice, A.C. Crawford, T.J. Ring Fermilab, Batavia, Illinois, USA
	Electro-chemical Polishing (EP) is one of the key technologies of surface treatments for niobium superconducting cavities. We have established a single-cell scale horizontal electro-polishing facility at Fermilab and routinely processed the niobium cavities with the frequencies of 1.3 GHz to 3.9 GHz. The precise control of EP parameters, especially the temperatures of cavity outside wall, allows the uniform removal over the cell with the variation of ±15%. Here we report the details of our EP process and recent improvements on our EP facility at Fermilab.
	Poster TUP022 [1.711 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP022
About •	paper received ※ 10 July 2019 paper accepted ※ 17 August 2019 issue date ※ 14 August 2019
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TUP024	Radial Tuning Devices for 1.3 GHz TESLA Shape Cavities	cavity, SRF, HOM, FEL	459
	A. Sulimov, J.H. Thie DESY, Hamburg, Germany
	Radial tuning devices at DESY can be applied to any TESLA shape 1.3 GHz cavity to reduce its elongation due to excessive additional material removal (>300 µm) or to compensate critical manufacturing uncertainties. Radial deformation of cavity cells can be provided by a special chain or a rolling device with three rollers. The chain distributes the radial forces on the equator area around the cell. The rollers are moving radially in relation to the rotating cavity and provide an equator diameter reduction. Both devices have the contour close to the cell shape at the equator area. The required equator radius deviation depends on the tuning target and usually varies between (0.02…0.60) mm. Different aspects of the tuning procedure and material properties are described using the example of cavity rolling.
	Poster TUP024 [0.252 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP024
About •	paper received ※ 23 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019
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TUP027	Vertical Electropolishing of Niobium Nine-Cell Cavity with a Cavity Flipping System for Uniform Removal	cavity, cathode, experiment, SRF	467
	K.N. Nii, V. Chouhan, Y.I. Ida, T.Y. Yamaguchi MGH, Hyogo-ken, Japan H. Hayano, S. Kato, H. Monjushiro, T. Saeki KEK, Ibaraki, Japan
	Marui Galvanizing Co., Ltd. has been developing vertical electropolishing (VEP) technology for single and nine-cell niobium superconducting radio frequency cavities using a unique cathode namely Ninja cathode in collaboration with KEK. The VEP process usually results in non-uniform removal with a large asymmetry along the cavity length. In order to suppress the asymmetry in removal, we are making different approaches. Flipping of the cavity during the VEP process is one of the approaches applied so far. A unique VEP setup, which allows the flipping of a multi-cell cavity, has been developed as reported earlier. Here, we report the improvement in the setup with automation for cavity flipping. VEP experiments were conducted with the improved system. VEP parameters were studied and the VEP results including the removal trend are discussed in detail.
	Poster TUP027 [1.347 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP027
About •	paper received ※ 24 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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TUP029	An Experimental Analysis of Effective EP Parameters for Low-Frequency Cylindrical Nb Cavities	cavity, cathode, SRF, polarization	472
	C.E. Reece JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Work supported by the U.S. DoE, Office of Science, Office of Basic Energy Sciences. While the basic process of electropolishing niobium with 1:9 HF:H₂SO₄ electrolyte has been well characterized, the specific process parameters used to electropolish different superconducting radio frequency (SRF) cavity geometries requires thoughtful attention. One seeks to realize confidently local diffusion-limited polishing at each point on the surface while maximizing uniformity of removal rate. Since the reaction rate is temperature dependent, this implies that one must manage the cavity surface temperature during polishing. Too-high applied voltage aggravates temperature and thus removal non-uniformity, but too-low applied voltage risks placing the large-diameter locations "off the current plateau," yielding etching rather than polishing. The majority of recent experience has been with elliptical L-band SRF cavities and some half-wave cavities at ANL. Lower frequency cavities with increased surface area and larger cathode-to-equator distance require fresh analysis and optimization. In preparation for SNS PPU project, JLab performed some EP process development runs with SNS high beta cavities to help identify viable parameter regimes for communication to cavity vendors. Results from this study are presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP029
About •	paper received ※ 23 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019
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TUP042	Measurement of Mechanical Vibration of SRILAC Cavities	cavity, linac, ECR, cryomodule	513
	O. Kamigaito, K. Ozeki, N. Sakamoto, K. Suda, K. Yamada RIKEN Nishina Center, Wako, Japan
	Mechanical vibration of quarter-wavelength resonators of SRILAC, the superconducting booster of the RIKEN heavy-ion linac, was measured during a vertical cold test. The measurements were performed for fully assembled cavities as well as for bare niobium cavities without the titanium jacket. In the procedure, the instantaneous resonant frequencies were measured for 10 seconds at a time interval of 1 ms and were recorded as a time series. The frequencies were analyzed by means of conventional signal analysis. The power spectrum was deduced from the autocorrelation function calculated with the fluctuation of resonant frequencies. Although the vibration amplitudes were smaller in the cavities assembled with the titanium jacket, we could not find a clear reason for this.
	Poster TUP042 [6.957 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP042
About •	paper received ※ 27 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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TUP043	Ab-initio Study of Atomic Scale Interaction Among Nb, Sn, Cl, and O	cavity, electron, SRF, superconductivity	518
	A.B. Tesfamichael, T. Arias Cornell University, Ithaca, New York, USA
	Funding: Center for Bright Beam (CBB) We employed a combination of ab-initio calculations and statistical mechanical models to understand the nature of atomic scale interaction among Nb, Sn, Cl, and O. Because of the profound nature of the interaction, we began our study by focusing only on the interaction of Nb with Sn in the absence of Cl and O. Using Density Functional Theory (DFT) we calculated: (1), binding energy of both vacant and interstitial of the super cell for both Nb and Sn atoms (2), rate of diffusion and re-evaporation upon transportation of Sn atom across z-axis from bulk Nb layer (3), electron transfer and electric field upon transportation of Sn atom both across z-axis and xy-plane from bulk Nb layer. Our calculation indicated 30-40% difference from experimental results. Therefore, we conclude that the presence of oxides is important and also Cl impurity can not not be avoided.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP043
About •	paper received ※ 24 June 2019 paper accepted ※ 04 July 2019 issue date ※ 14 August 2019
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TUP045	Ab Initio Calculations on Impurity Doped Niobium and Niobium Surfaces	scattering, electron, experiment, lattice	523
	N. Sitaraman, T. Arias Cornell University, Ithaca, New York, USA R.G. Farber, S.J. Sibener, R.D. Veit The University of Chicago, Chicago, Illinois, USA M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: This work was funded by the Center for Bright Beams We develop and apply new tools to understand Nb surface chemistry and fundamental electronic processes using theoretical ab initio methods. We study the thermodynamics of impurities and hydrides in the near-surface region as well as their effect on the surface band gap. This makes it possible for experimentalists to relate changes in STM dI/dV measurements resulting from different preparations to changes in subsurface structure. We also calculate matrix elements for electron-impurity scattering in Nb for common impurities O, N, C, and H. By transforming these matrix elements into a Wannier function basis, we calculate lifetimes for a dense set of states on the Fermi surface and determine the mean free path as a function of impurity density. This technique can be generalized to calculate other scattering amplitudes and timescales relevant to SRF theory.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP045
About •	paper received ※ 02 July 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019
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TUP046	Low Frequency, Low Beta Cavity Performance Improvement Studies	cavity, SRF, factory, vacuum	527
	P. Kolb, R.E. Laxdal, Z.Y. Yao TRIUMF, Vancouver, Canada
	In recent years, new discoveries such as N₂ doping and infusion lead to a significant increases in Q₀ and accelerating gradient for 1.3 GHz, β=1 elliptical cavities. To understand and to adapt these treatments for lower frequency, \beta < 1 cavities, two coaxial test cavities, one quarter-wave resonator (QWR) and one half-wave resonator (HWR), have been built and put through a systematic study of these new treatments to show the effectiveness of these treatments at different frequencies. These cavities are tested in their fundamental mode and several higher order modes to study the frequency dependence of new cavity treatments such as N₂ doping and infusion. Results of these studies are presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP046
About •	paper received ※ 22 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019
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TUP049	Maximum Performance of Cavities Affected by the High-field Q-slope (HFQS)	cavity, SRF, experiment, radio-frequency	533
	G. Ciovati JLab, Newport News, Virginia, USA A.V. Gurevich, I.P. Parajuli ODU, Norfolk, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The work of I. P. and A. G. is supported by NSF Grant PHY 100614-010. The performance of high-purity, bulk niobium SRF cavities treated by chemical processes such as BCP or EP is limited by the so-called high-field Q-slope (HFQS). Several models and experimental studies have been proposed and performed over the years to understand the origin of these anomalous losses but a general consensus on what these orgins are is yet to be established. In this contribution, we present the results from the RF tests of several 1.3 GHz single-cell cavities limited by the HFQS and tested using a variable input coupler. This allowed to maintain close to critical coupling even at high field and the data showed that the HFQS did not saturate and that in some cases a power dissipation of up to 200 W at 2 K could be sustained without quench.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP049
About •	paper received ※ 21 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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TUP050	A Multi-layered SRF Cavity for Conduction Cooling Applications	cavity, SRF, cryogenics, ECR	538
	G. Ciovati, G. Cheng, E. Daly, G.V. Eremeev, J. Henry, R.A. Rimmer JLab, Newport News, Virginia, USA I.P. Parajuli ODU, Norfolk, Virginia, USA U. Pudasaini The College of William and Mary, Williamsburg, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Some of the work was supported by the 2008 PECASE Award of G. Ciovati. I. Parajuli is supported by NSF Grant PHYS-100614-010 Industrial application of SRF technology would favor the use of cryocoolers to conductively cool SRF cavities for particle accelerators, operating at or above 4.3 K. In order to achieve a lower surface resistance than Nb at 4.3 K, a superconductor with higher critical temperature should be used, whereas a metal with higher thermal conductivity than Nb should be used to conduct the heat to the cryocoolers. A standard 1.5 GHz bulk Nb single-cell cavity has been coated with a ~2 µm thick layer of Nb₃Sn on the inner surface and with a 5 mm thick Cu layer on the outer surface for conduction cooled applications. The cavity performance has been measured at 4.3 K and 2.0 K in liquid He. The cavity reached a peak surface magnetic field of ~40 mT with a quality factor of 6×10⁹ and 3.5×10⁹ at 4.3 K, before and after applying the thick Cu layer, respectively.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP050
About •	paper received ※ 21 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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TUP051	Progress Towards Commissioning the Cornell DC Field Dependence Cavity	cavity, multipactoring, SRF, solenoid	543
	J.T. Maniscalco, T. Gruber, A.T. Holic, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The Cornell DC Field Dependence Cavity is a new coaxial test resonator designed to study the impact of strong (up to 200 mT or more) DC surface magnetic fields on the superconducting surface resistance, providing physical insight into the root of the ‘‘anti-Q-slope’’ and probing critical fields. In this report we report progress in the commissioning of this new apparatus, including finalized design elements and results of prototype tests.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP051
About •	paper received ※ 25 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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TUP053	Optimal Thermal Gradient for Flux Expulsion in 600°C Heat-treated CEBAF 12 GeV Upgrade Cavities	cavity, HOM, experiment, controls	550
	R.L. Geng, F. Marhauser, P.D. Owen JLab, Newport News, Virginia, USA
	We will present results on measurement of flux expulsion in CEBAF 12 GeV upgrade cavities and original CEBAF cavities and the search for optimal thermal gradient for reducing the trapped flux in cavities installed in CEBAF linacs. Preliminary measurements of one C100 cavities has shown that a nearly perfect flux expulsion can be achieved at an optimal thermal gradient - a surprising result contrary to the expectation of zero flux expulsion for 600°C heat treated niobium cavities. These results could lead to a cost-effective path for improving the quality factor of cavities installed in CEBAF and ultimately saving accelerator operation cost.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP053
About •	paper received ※ 24 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019
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TUP054	How Is Flux Expulsion Affected by Geometry: Experimental Evidence and Model	cavity, experiment, SRF, accelerating-gradient	555
	D. Longuevergne Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
	Measurements of magnetic sensitivity to trapped flux on several type of cavity geometries have been performed at IPNO showing a clear geometrical effect. Magnetic sensitivity depends not only on material quality but also on the cavity geometry and on the residual magnetic field orientation. A presentation of experimental data will be done. These will be as well compared to the theoretical magnetic sensitivities calculated thanks to a simple Labview routine
	Poster TUP054 [1.312 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP054
About •	paper received ※ 03 July 2019 paper accepted ※ 04 July 2019 issue date ※ 14 August 2019
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TUP055	Nonlinear Dynamics and Dissipation of Vortex Lines Driven by Strong RF Fields	cavity, ECR, radio-frequency, electron	560
	M.R.P. Walive Pathiranage, A.V. Gurevich ODU, Norfolk, Virginia, USA
	Trapped vortices can contribute significantly to a residual surface resistance of superconducting radio frequency (SRF) cavities but the nonlinear dynamics of flexible vortex lines driven by strong rf currents has not been well understood. Here we report extensive numerical simulations of large-amplitude oscillations of a trapped vortex line under the strong rf magnetic field. The rf power dissipated by an oscillating vortex segment driven by the rf Meissner currents was calculated by taking into account the nonlinear vortex line tension, vortex mass and a nonlinear Larkin-Ovchinnikov and overheating viscous drag force. We calculated the field dependence of the surface resistance Rs and showed that at low frequencies Rs(H) increases with H but as the frequency increases, Rs(H) becomes a non-monotonic function of H which decreases with H at higher fields. These results suggest that trapped vortices can contribute to the extended Q(H) rise observed on the SRF cavities.
	Poster TUP055 [1.744 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP055
About •	paper received ※ 23 June 2019 paper accepted ※ 05 July 2019 issue date ※ 14 August 2019
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TUP056	A First-Principles Study on Magnetic Flux Trapping at Niobium Grain Boundaries	electron, cavity, simulation, radio-frequency	565
	P. Garg, K.N. Solanki Arizona State University, Tempe, USA T.R. Bieler Michigan State University, East Lansing, Michigan, USA L.D. Cooley NHMFL, Tallahassee, Florida, USA
	Niobium is basis for all superconducting radio frequency cavities, a technology that accelerates charged particle beams to energy levels not possible by other means. When cavities are pushed to limits, significant heating appears at extended material defects, like grain boundaries. Therefore, it is crucial to understand how grain boundary (GB) structure and associated properties lead to trapping of magnetic field, and whether GB itself has any unusual magnetic behavior. Using first-principles calculations, external magnetic field along the GB plane was simulated within an all-electron full-potential linearized augmented plane-wave framework. A ground state with non-zero flux, indicative of flux trapping, was obtained at some grain boundaries, this outcome being influenced strongly by GB local structure. Furthermore, electronic density of states and charge-transfer calculations suggested non-zero spin polarization at grain boundaries, which may be consistent with recent observations of unusual paramagnetic magnetization as a function of specimen surface area for cavity-grade niobium.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP056
About •	paper received ※ 23 June 2019 paper accepted ※ 04 July 2019 issue date ※ 14 August 2019
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TUP057	Study of Flux Trapping Variability between Batches of Tokyo Denkai Niobium used for the LCLS-II Project and Subsequent 9-cell RF Loss Distribution between the Batches	cavity, SRF, FEL, superconductivity	570
	A.D. Palczewski JLab, Newport News, Virginia, USA D. Gonnella SLAC, Menlo Park, California, USA O.S. Melnychuk, D.A. Sergatskov Fermilab, Batavia, Illinois, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. During the LCLS-II project a second batch of niobium was procured from Tokyo Denkai Co Ltd in order to make additional cavities. The original production material came from Two vendors Tokyo Denkai Co., Ltd. (TD) and Ningxia Orient Tantalum Industry Co., Ltd. (OTIC/NX)). It was found TD niobium required a lower annealing temperature (900°C) to obtain satisfactory flux expulsion characteristics compared to NX which required a slightly higher annealing temperature (950°-975°C). In order to ensure the new TD material performed equivalent to the niobium produced 4 year before after 900°C annealing; each heat lot of niobium had its flux expulsion characteristics parametrized and custom thermal treatments developed for each lot. Subsequent pure heat lot 9 cell cavities were made and tested. We will look at the flux expulsion characteristics of each lot, and RF loss of the 9-cell cavities produced using the individual heat lots.
	Poster TUP057 [1.446 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP057
About •	paper received ※ 25 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019
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TUP061	Gradients of 50 MV/m in TESLA Shaped Cavities via Modified Low Temperature Bake	cavity, SRF, ECR, site	586
	D. Bafia, J. Zasadzinski IIT, Chicago, Illinois, USA D. Bafia, A. Grassellino, O.S. Melnychuk, A.S. Romanenko, Z-H. Sung Fermilab, Batavia, Illinois, USA
	This paper will discuss the 75/120 C modified low temperature bake capable of giving unprecedented accel-erating gradients of above 50 MV/m for 1.3 GHz TESLA-shaped niobium SRF cavities in CW operation. A bifurca-tion in the Q₀ vs E_acc curve is observed after retesting cavities without disassembly in between, yielding per-formance that ranges from exceptional to above state-of-the-art. Atomic Force Microscopy studies on cavity cut-outs gives a possible mechanism responsible for this branching in performance, namely, the dissociation and growth of room temperature niobium nano-hydrides that exist near the RF surface, which are made superconduct-ing only through the proximity effect. In-situ low temper-ature baking of cavity cutouts reveals a dissociation of these room temperature nano-hydrides, which could ex-plain the higher performance of cavities subject to similar in-situ heating in the dewar.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP061
About •	paper received ※ 23 June 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019
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TUP062	New Insights in the Quench Mechanisms in Nitrogen Doped Cavities	cavity, SRF, accelerating-gradient, factory	592
	D. Bafia, J. Zasadzinski IIT, Chicago, Illinois, USA D. Bafia, D.J. Bice, A. Grassellino, O.S. Melnychuk, A.S. Romanenko, D.A. Sergatskov Fermilab, Batavia, Illinois, USA D. Gonnella SLAC, Menlo Park, California, USA A.D. Palczewski JLab, Newport News, Virginia, USA
	This paper will cover a systematic study of the quench in nitrogen doped cavities: three cavities were sequentially treated/reset with different doping recipes which are known to produce different levels of quench field. Analysis of mean free path and TMAP coupled with sample analysis reveals new insights on the physics of the premature quench in nitrogen doped cavities; new recipes demonstrate the possibility to increase quench fields well beyond 30 MV/m.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP062
About •	paper received ※ 23 June 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019
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TUP068	Study of Surface Treatment of 1.3 GHz Single-cell Copper Cavity for Niobium Sputtering	cavity, SRF, experiment, MMI	605
	F.Y. Yang, J. Dai, P. He, Z.Q. Li, Y. Ma, P. Zhang IHEP, Beijing, People’s Republic of China
	Funding: This work has been supported in part by PAPS project and National Key Programme for S&T Research and Development (Grant NO.: 2016YFA0400400) A R&D program on niobium sputtering on copper cavities has started at IHEP in 2017. Single-cell 1.3 GHz copper cavity has been chosen as a substrate. A chemical polishing system has subsequently developed and commissioned recently to accommodate the etching of both copper samples and a cavity. Different polishing agents have been tested on copper samples and later characterized. The results of these surface treatment tests are presented.
	Poster TUP068 [1.228 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP068
About •	paper received ※ 20 June 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019
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TUP072	The Development of Niobium Sputtering on Copper Cavities at IHEP	cavity, vacuum, SRF, photon	613
	J. Dai, P. He, Z.Q. Li, Y. Ma, F.Y. Yang, P. Zhang IHEP, Beijing, People’s Republic of China
	A R&D program focusing on niobium sputtering on copper cavities started at IHEP in 2017. Single-cell 1.3 GHz elliptical cavity shape has been initially chosen as sputtering substrate. A magnetron sputtering system have been developed in 2018. In addition, a surface treatment facility to polish the copper substrate before sputtering has been developed and commissioned. This paper will present the Nb/Cu coating activities at IHEP.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP072
About •	paper received ※ 19 June 2019 paper accepted ※ 04 July 2019 issue date ※ 14 August 2019
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TUP073	Superconducting Thin Films Characterization at HZB with the Quadrupole Resonator	cavity, SRF, quadrupole, FEL	616
	D.B. Tikhonov, S. Keckert, J. Knobloch, O. Kugeler, Y. Tamashevich HZB, Berlin, Germany A-M. Valente-Feliciano JLab, Newport News, Virginia, USA
	Funding: EASITrain - European Advanced Superconductivity Innovation and Training. This Marie Sklodowska-Curie Action Innovative Training Networks founded by H₂020 under Grant Agreement no. 764879 Superconducting thin films have great potential as post-Nb material for use in SRF applications in future accelerators and industry. To test the RF-performance of such films in practice, would require the building and coating of a full RF cavity. Deposition of thin films on such scales in test facilities are challenging, in particular when curved surfaces have to be coated. This greatly complicates their systematic research. In this contribution we report on the method we use to characterize small and flat thin film samples (Deposited onto both Nb and Cu substrates) in an actual cavity named the Quadrupole Resonator (QPR). We also summarize the latest measurement results of NbTiN thin films. The Quadrupole Resonator at HZB is a tool that is able to perform SRF characterizations at frequencies ~415, 847, 1300 MHz with RF fields using an RF-DC power compensation technique.
	Poster TUP073 [2.318 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP073
About •	paper received ※ 23 June 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019
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TUP075	New Progress for Nb Sputtered 325 MHz QWR Cavities in IMP	cavity, target, experiment, SRF	621
	F. Pan, H. Guo, Y. He, T.C. Jiang, C.L. Li, M. Lu, T. Tan IMP/CAS, Lanzhou, People’s Republic of China
	Comparing with bulk niobium cavities, the Nb/Cu cavities feature a much better stability at 4.5 K. Last year, two 325 MHz QWR copper cavities coated with biased DC diode sputterred Nb for CiADS has been accomplished at IMP. But vertical tests showed the cavities had low Q₀ at 4 K. To solve the issue, a new coating system was designed and built. The sputtering target was redesigned and manufactured. The coating parameters were selected again and auxiliary heating was used to control the coating temperature in the process of sputtering. The power and Ar pressure during coating were also carefully selected. The paper covers resulting film characters, vertical tests with the evolution of the sputtering process, and improvements we made since last year.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP075
About •	paper received ※ 22 June 2019 paper accepted ※ 14 August 2019 issue date ※ 14 August 2019
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TUP076	Electrochemical Deposition of Nb₃Sn on the Surface of Cu Substrates	cavity, site, controls, SRF	624
	M. Lu, Q.W. Chu, Y. He, Z.Q. Lin, F. Pan, T. Tan, Z.Q. Yang IMP/CAS, Lanzhou, People’s Republic of China
	Coating superconducting Nb₃Sn thin film on the inner surface of a superconducting RF cavity is one of the most promising approaches to improve the performance of the accelerating cavity. Compared with traditional evaporation and sputtering, electrochemical coating has the advantages on process simplicity, low cost and mass production. However, the conventional electroplating, because of its low growth temperature and aqueous reaction environment, tends to produce porous, loosely bonded, and often contaminated film. All these properties result in excessive pinning center and deteriorate the superconducting radio frequency cavities performance. In this paper, a new method including multi-layer electroplating and heat treatment is used to deposit Nb₃Sn thin film on top of copper substrates. Important growth parameters, e.g. electrical current density, layer thickness ratio, and annealing temperature are studied. The morphology of the film surfaces was observed by scanning electron microscope (SEM) and the structure of the film was analyzed by X-ray diffraction (XRD). The results showed that a flat and uniform Nb₃Sn layer on copper can be obtained, and the thickness is about 7 micron.
	Poster TUP076 [0.716 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP076
About •	paper received ※ 23 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019
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TUP079	Deposition of Nb₃Sn Films by Multilayer Sequential Sputtering for SRF Cavity Application	cavity, SRF, site, FEL	637
	Md.N. Sayeed, H. Elsayed-Ali ODU, Norfolk, Virginia, USA M.C. Burton, G.V. Eremeev, C.E. Reece, A-M. Valente-Feliciano JLab, Newport News, Virginia, USA U. Pudasaini The College of William and Mary, Williamsburg, Virginia, USA
	Nb₃Sn is considered as an alternative of Nb for SRF accelerator cavity application due to its potential to obtain higher quality factors and higher accelerating gradients at a higher operating temperature. Magnetron sputtering is one of the effective techniques that can be used to fabricate Nb₃Sn on SRF cavity surface. We report on the surface properties of Nb₃Sn films fabricated by sputtering multiple layers of Nb and Sn on sapphire and niobium substrates followed by annealing at 950°C for 3 h. The crystal structure, film microstructure, composition and surface roughness were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM). The RF performance of the Nb₃Sn coated Nb substrates were measured by a surface impedance characterization system. We also report on the design of a multilayer sputter deposition system to coat a single-cell SRF cavity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP079
About •	paper received ※ 22 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019
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TUP093	Summary of FRIB Cavity Processing in the SRF Coldmass Processing Facility and Lessons Learned	cavity, SRF, linac, controls	680
	E.S. Metzgar, B.W. Barker, K. Elliott, W. Hartung, L. Popielarski, G.V. Simpson, D.R. Victory, J.D. Whaley FRIB, East Lansing, Michigan, USA
	Funding: Work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661 and the National Science Foundation under Cooperative Agreement PHY-1102511. Baseline coldmass production for the linear particle accelerator at the Facility for Rare Isotope Beams (FRIB) is nearing completion. This paper will review the processing of cavities through the FRIB superconducting radio frequency (SRF) coldmass production facility focusing on chemical processing and high-pressure rinsing. Key processing data will be compiled and correlations between processing variables and cavity RF testing results will be examined.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP093
About •	paper received ※ 22 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019
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THFUA1	RF Characterization of an S-I-S’ Multilayer Sample	quadrupole, ECR, SRF, cavity	800
	S. Keckert, J. Knobloch, O. Kugeler, D.B. Tikhonov HZB, Berlin, Germany A-M. Valente-Feliciano JLab, Newport News, Virginia, USA
	S-I-S’ multilayers promise to boost the performance of bulk superconductors in terms of maximum field and surface resistance. At HZB, RF-surface resistance measurements were performed with a Quadrupole Resonator (QPR) and an S-I-S’ sample (75 nm NbTiN on 15 nm AlN insulator on bulk Nb) prepared at JLab. Measurements were performed at 414, 845, and 1286 MHz at sample temperatures from 2 K up to well above the transition temperature of NbTiN of ~17.3 K. The Rs exhibits an unexpected temperature dependence: Rather than rising monotonically, as expected from BCS theory, a local maximum is observed. There is a temperature range where Rs decreases with increasing temperature. Such behavior indicates that an additional interaction between the superconducting layers may have to be included in the surface resistance model. Measurements of the baseline Nb sample prior to coating exhibited no such behavior; hence systematic measurement errors can be excluded as the explanation. The maximum field was limited by a hard magnetic quench near 20 mT, close to Hc1 of NbTiN, suggesting that the sample is limited by early flux penetration.
	Slides THFUA1 [1.004 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THFUA1
About •	paper received ※ 22 June 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019
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THFUA6	Nb₃Sn Films for SRF Cavities: Genesis and RF Properties	cavity, SRF, interface, experiment	810
	U. Pudasaini, M.J. Kelley The College of William and Mary, Williamsburg, Virginia, USA J.W. Angle, M.J. Kelley, J. Tuggle Virginia Polytechnic Institute and State University, Blacksburg, USA G.V. Eremeev, M.J. Kelley, C.E. Reece JLab, Newport News, Virginia, USA
	Funding: Partially authored by Jefferson Science Associates under contract no. DE¬AC05¬06OR23177. Supported by Office of High Energy Physics under grants DE-SC-0014475 to the College of William and DE-SC-0018918 to Virginia Tech. Understanding of Nb₃Sn nucleation and growth is essential to the progress with Nb₃Sn vapor diffusion coatings of SRF cavities. Samples representing different stages of Nb₃Sn formation have been produced and examined to elucidate the effects of nucleation, growth, process conditions, and impurities. Nb₃Sn films from few hundreds of nm up to ~15 µm were grown and characterized using AFM, SEM/EDS, XPS, EBSD, SIMS, and SAM. Microscopic examinations of samples suggest the mechanisms behind Nb₃Sn thin film nucleation and growth. RF measurements of coated cavities were combined with material characterization of witness samples to adapt the coating process in "Siemens" coating configuration. Understanding obtained from sample studies, applied to cavities, resulted in Nb₃Sn cavity with quality factor 2 ×10¹⁰ at 15 MV/m accelerating gradient at 4 K, without "Wuppertal" Q-slope. We discuss the genesis of the Nb₃Sn thin film in a typical tin vapor diffusion process, and its consequences to the coating of SRF cavities.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THFUA6

Paper

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MOP003

Development of Nb₃Sn Cavity Coating at IMP

cavity, SRF, radio-frequency, experiment

21

Z.Q. Yang, H. Guo, Y. He, C.L. Li, Z.Q. Lin, M. Lu, T. Tan, P.R. Xiong, S.H. Zhang, S.X. Zhang
IMP/CAS, Lanzhou, People’s Republic of China

The A15 superconductor Nb₃Sn is one of the most promising alternative materials to standard niobium for SRF applications. In this paper, we report our progress in the development of Nb₃Sn cavity coating by vapor diffusion method at IMP. The evolutionary process of nucleation was analyzed. Influence of S_nCl₂ partial pressure inhomogeneity was studied. Less-nuclear zones were found on the surfaces of nucleation samples. The Nb₃Sn film structure and composition were investigated and analyzed. In light of knowledge obtained above, the coating process was optimized. Finally, both 1.3 GHz and 650 MHz single cell cavities were coated and vertically tested both at 4 K and 2 K. Effect of low temperature baking (1000°C for 48 hs) on the RF performance of Nb₃Sn cavity was studied. After baking, the Q drop in the low field region was eliminated and the Q in the intermediate field region was increased 8 times. The Q was 10 times larger than that of the Nb cavity at 4.2 K even in the case of the ambient field larger than 20 mGs. This study shows that the low temperature baking is an effective enrichment to the post treatment of the Nb₃Sn cavity.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP003

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paper received ※ 23 June 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019

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MOP005

The Facility for Rare Isotope Beams Superconducting Cavity Production Status and Findings Concerning Surface Defects

cavity, linac, SRF, status

31

C. Compton
NSCL, East Lansing, Michigan, USA
H. Ao, J. Asciutto, K. Elliott, W. Hartung, S.H. Kim, E.S. Metzgar, S.J. Miller, J.T. Popielarski, L. Popielarski, K. Saito, T. Xu
FRIB, East Lansing, Michigan, USA
J. Craft
SLAC, Menlo Park, California, 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 Facility for Rare Isotope Beams (FRIB), located on the campus of Michigan State University (MSU) will require 324 Superconducting Radio Frequency (SRF) cavities in the driver linac. Four types of cavities of two classes, quarter-wave (β=0.041 and 0.085) and half-wave (β=0.29 and 0.53), will be housed in 46 cryomodules. To date, FRIB has tested over 300 cavities in vertical Dewar tests as part of the certification procedures. Incoming cavities, fabricated in industry, are sequenced through acceptance inspection and checked for non-conformance. If accepted, the cavities are processed, assembled onto a vertical test stand, and cold tested. A large database of cavity surface images has been collected with the aid of a borescope camera. Borescope inspection is a standard step that is performed at incoming inspection, post-acid bulk etch, and after failed tests (if necessary) for each cavity, in order to locate any non-conformances. Findings of surface defects relating to degraded cavity performance will be presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP005

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paper received ※ 02 July 2019 paper accepted ※ 13 August 2019 issue date ※ 14 August 2019

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MOP010

Ab Initio Calculations on the Growth and Superconducting Properties of Nb₃Sn

site, cavity, SRF, electron

39

N. Sitaraman, T. Arias, P. Cueva, M.M. Kelley, D.A. Muller
Cornell University, Ithaca, New York, USA
J.M. Carlson, A.R. Pack, M.K. Transtrum
Brigham Young University, Provo, USA
M. Liepe, R.D. Porter, Z. Sun
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: This research was funded by the Center for Bright Beams.
In this work, we employ theoretical ab initio techniques to solve mysteries and gain new insights in Nb₃Sn SRF physics. We determine the temperature dependence of Nb₃Sn antisite defect formation energies, and discuss the implications of these results for defect segregation. We calculate the phonon spectral function for Nb₃Sn cells with different combinations of antisite defects and use these results to determine Tc as a function of stoichiometry. These results allow for the first-ever determination of Tc in the tin-rich regime, where experimental measurements are unavailable and which is critical to understanding the impact of tin-rich grain boundaries on superconducting cavity performance. Finally, we propose a theory for the growth mechanism of Nb₃Sn growth on a thick oxide, explaining the puzzling disappearing droplet behavior of Sn on Nb oxide and suggesting how in general an oxide layer reacts with Sn to produce a uniform Nb₃Sn layer.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP010

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paper received ※ 02 July 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019

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MOP011

High Frequency Nb₃Sn Cavities

cavity, SRF, radio-frequency, factory

44

R.D. Porter, M. Liepe, J.T. Maniscalco
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Niobium-3 Tin (Nb₃Sn) is an alternative material to Nb for SRF cavities. This material is capable of higher temperature operation and has high theoretical maximum accelerating gradients. Cornell University is a leader in the development of this material for SRF applications, and current Nb₃Sn 1.3 GHz single cells produced at Cornell achieve quality factors above 10^zEhNZeHn at 4.2 K at medium fields, far above what can be reached with niobium. Most of the recent Nb₃Sn cavity development has been done at 1.3 GHz. In this paper, we present new results from Nb₃Sn cavities at 2.6 GHz and 3.9 GHz. We compare relative cavity performance and flux trapping sensitivities, and extract frequency dependencies. Results show that the frequency can be increased without degrading the performance of the cavities, opening the path towards a new generation of compact and efficient SRF cavities for a wide range of future applications.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP011

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paper received ※ 05 July 2019 paper accepted ※ 12 July 2019 issue date ※ 14 August 2019

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MOP013

Reducing Surface Roughness of Nb₃Sn Through Chemical Polishing Treatments

cavity, superconductivity, controls, SRF

48

H. Hu, M. Liepe, R.D. Porter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Niobium-3 tin (Nb₃Sn) is a promising alternative material for SRF cavities, with theoretical limits for critical temperatures and superheating fields reaching twice that of conventional Nb cavities. However, currently achievable accelerating gradients in Nb₃Sn cavities are much lower than their theoretical limit. One limitation to the maximum accelerating gradient is surface magnetic field enhancement caused by the surface roughness of Nb₃Sn. However, there are currently no standard techniques used to reduce Nb₃Sn surface roughness. Since Nb₃Sn is only 2-3 microns thick, it is difficult to selectively polish Nb₃Sn without removing the entire layer. Here, we investigate reducing the surface roughness of Nb₃Sn through applying chemical polishing treatments, including modified versions of standard techniques such as Buffered Chemical Polishing (BCP) and Electropolishing (EP). Through data acquired from Atomic Force Microscope (AFM) scans, SEM scans, and SEM-EDS analysis, we show the effects of these chemical treatments in reducing surface roughness and consider the changes in the chemical composition of Nb₃Sn that may occur through the etching process. We find that BCP with a 1:1:8 solution is ineffective while EP halves the surface roughness of Nb₃Sn.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP013

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paper received ※ 01 July 2019 paper accepted ※ 04 July 2019 issue date ※ 14 August 2019

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MOP016

Insights Into Nb₃Sn Coating of CEBAF Cavities From Witness Sample Analysis

cavity, SRF, HOM, hardware

60

G.V. Eremeev, M.J. Kelley, C.E. Reece
JLab, Newport News, Virginia, USA
M.J. Kelley, U. Pudasaini
The College of William and Mary, Williamsburg, Virginia, USA

Funding: Co-Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics.
With the progress made in the Nb₃Sn coatings on single-cell SRF cavities, development is ongoing to reproduce single-cell cavity results on practical structures such as CEBAF 5-cell cavities. During CEBAF cavity coating development, several changes from the single-cell procedure to the coating setup and the heating profile were introduced to improve the quality of Nb₃Sn films. To witness the properties of grown Nb₃Sn films in different cavity locations, 10 mm x 10 mm samples were positioned in strategic places within the coating chamber. Composition and structure of the samples were analyzed with surface analytic techniques and correlated with sample location during coatings. Implications from sample analysis to Nb₃Sn coatings on different geometries are discussed in this contribution.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP016

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paper received ※ 26 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019

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MOP018

Recent Results From Nb₃Sn Single Cell Cavities Coated at Jefferson Lab

cavity, SRF, experiment, factory

65

U. Pudasaini, M.J. Kelley
The College of William and Mary, Williamsburg, Virginia, USA
G. Ciovati, G.V. Eremeev, M.J. Kelley, C.E. Reece
JLab, Newport News, Virginia, USA
I.P. Parajuli, Md.N. Sayeed
ODU, Norfolk, Virginia, USA

Funding: Partially authored by Jefferson Science Associates under contract no. DE¬AC05¬06OR23177. Supported by Office of High Energy Physics under grants DE-SC-0014475 to the College of William and DE-SC-0018918 to Virginia Tech
Because of superior superconducting properties (Tc ~ 18.3K, Hs h ~ 425 mT and delta ~ 3.1 meV) compared to niobium, Nb₃Sn promise better RF performance (Q₀ and E_acc) and/or higher operating temperature (2 K Vs 4.2 K) for SRF cavities. Nb₃Sn-coated SRF cavities are produced routinely by depositing a few micron-thick Nb₃Sn films on the interior surface of Nb cavities via tin vapor diffusion technique. Early results from Nb₃Sn cavities coated with this technique exhibited precipi-tous low field Q-slope, also known as Wuppertal slope. Several Nb₃Sn single cell cavities coated at JLab ap-peared to exhibit similar Q-slope. RF testing of cavi-ties and materials study of witness samples were con-tinuously used to modify the coating protocol. At best condition, we were able to produce Nb₃Sn cavity with Q₀ in excess of ~ 5×10¹⁰ at 2 K and ~ 2×1010 at 4 K up the accelerating gradient of ~15 MV/m, without any significant Q-slope. In this presentation, we will dis-cuss recent results from several Nb₃Sn coated single-cell cavities linked with material studies of witness samples, coating process modifications and the possi-ble causative factors to Wuppertal slope.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP018

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paper received ※ 23 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019

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MOP022

Superconducting RF Cavity Materials Research at the S-DALINAC

cavity, linac, SRF, simulation

74

R. Grewe, L. Alff, M. Arnold, J. Conrad, S. Flege, M. Major, N. Pietralla
TU Darmstadt, Darmstadt, Germany
F. Hug
IKP, Mainz, Germany

Funding: Supported by BMBF Through 05H18RDRB2
Current state-of-the-art superconducting rf (srf) accelerators are mostly using cavities made of high RRR bulk niobium (Nb). The maximum field gradients and quality factors (Q₀) of these cavities are basically reached now. To further increase the srf cavity properties for future accelerator facilities, research of new materials for srf cavity applications is necessary. The current research at the S-DALINAC* is focused on the development of bake-out procedures of Nb samples and cavities in nitrogen (N) atmosphere of up to 100 mbar to nucleate the delta-phase (d-phase) of the Nb-N binary system. The d-phase has superconducting properties which exceed the properties of bulk Nb. This makes the d-phase attractive for srf applications. The vertical test cryostat (vt) at the S-DALINAC has been upgraded and recommissioned to allow investigations of the quality factor and accelerating field gradients of cavities before and after bake-out. The vt upgrade includes a newly developed variable input coupling to allow matching of the external q-factor (Qex) to Q₀. The results of the ongoing research of the nitrogen atmosphere bake-out procedures and the upgrade of the vt will be presented.
*N. Pietralla, Nuclear Physics News, Vol. 28, No. 2, 4 (2018)

Poster MOP022 [1.759 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP022

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paper received ※ 21 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019

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MOP023

Nitrogen Infusion Sample R&D at DESY

cavity, vacuum, SRF, HOM

77

C. Bate, A. Dangwal Pandey, A. Ermakov, B. Foster, T.F. Keller, D. Reschke, J. Schaffran, S. Sievers, N. Walker, H. Weise, M. Wenskat
DESY, Hamburg, Germany
W. Hillert
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
G.D.L. Semione, V. Vonk
DESY Nanolab, FS-NL, Hamburg, Germany
A. Stierle
University of Hamburg, Hamburg, Germany

The European XFEL continuous wave upgrade requires cavities with reduced surface resistance (high Q-values) for high duty cycle while maintaining high accelerating gradient for short-pulse operation. A possible way to meet the requirements is the so-called nitrogen infusion procedure. However, a fundamental understanding and a theoretical model of this method are still missing. The approach shown here is based on sample R&D, with the goal to identify key parameters of the process and establish a stable, reproducible recipe. To understand the underlying processes of the surface evolution, which gives improved cavity performance, advanced surface analysis techniques (e.g. SEM/EDX, TEM, XPS, TOF-SIMS) are utilized. Additionally, a small furnace just for samples was set up to change and explore the parameter space of the infusion recipe. Results of these analyses, their implications for the cavity R&D and next steps are presented.

Poster MOP023 [3.759 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP023

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paper received ※ 23 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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MOP024

Vacancy-Hydrogen Dynamics in Samples During Low Temperature Baking

positron, cavity, lattice, electron

83

M. Wenskat, C. Bate, D. Reschke, H. Weise
DESY, Hamburg, Germany
C. Bate
University of Hamburg, Hamburg, Germany
M. Butterling, E. Hirschmann, M.O. Liedke, A. Wagner
HZDR, Dresden, Germany
J. Cizek
Charles University, Prague, Czech Republic

Funding: This work was supported by the Helmholtz Association within the topic Accelerator Research and Development (ARD) of the Matter and Technologies (MT) Program and by the BMBF under the research grant 05H18GURB1.
The recent discovery of a modified low temperature baking process lead to a reduction of surface losses and an increase of the accelerating gradient of TESLA shape cavities. The hypothesis linking the accelerator performance and the treatment is the suppression of lossy nanohydrides via defect trapping, with vacancy-hydrogen complexes forming at the lower temperatures. Utilizing Doppler broadening Positron Annihilation Spectroscopy and Positron Annihilation Lifetime Spectroscopy samples made from European XFEL niobium sheets and cavity cut-outs were investigated. The evolution of vacancies, hydrogen and their interaction at different temperature levels have been studied during in-situ annealing. Measurements of niobium samples and a correlation between RF, material properties, and V-H distribution in cavity cut-outs has been done.

Poster MOP024 [1.087 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP024

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paper received ※ 20 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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MOP025

Cavity Cut-out Studies of a 1.3 GHz Single-cell Cavity After a Failed Nitrogen Infusion Process

cavity, SRF, electron, superconductivity

87

M. Wenskat, C. Bate, T.F. Keller, D. Reschke
DESY, Hamburg, Germany
C. Bate
University of Hamburg, Hamburg, Germany
A. Jeromin
DESY Nanolab, FS-NL, Hamburg, Germany
J. Knobloch, F. Kramer, O. Kugeler, J.M. Köszegi
HZB, Berlin, Germany
J. Knobloch
University of Siegen, Siegen, Germany

Funding: This work was supported by the Helmholtz Association within the topic Accelerator Research and Development (ARD) of the Matter and Technologies (MT) Program and by the BMBF under the research grant 05H18GURB1.
R&D on the nitrogen infusion process at DESY produced at the beginning a series of 1.3 GHz single-cell cavities which have shown severe deterioration in the vertical cold test which was completely unexpected and could not be explained. To investigate the reason for the deterioration, one of those cavities was optically inspected and a T- and H-Map test was done in collaboration with HZB. Together with 2nd Sound data, regions of interests were identified and cut from the cavity. Subsequent surface analysis techniques (SEM/EDX, SIMS, PIXE, EBSD, DB-PAS, PALS, XPS) were applied in order to identify the reason for the deterioration. Especially the differences between hot and cold spots as well as quench spots identified by T-Mapping were investigated.

Poster MOP025 [0.975 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP025

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paper received ※ 20 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019

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MOP026

A Cross-Lab Qualification of Modified 120°C Baked Cavities

cavity, shielding, multipactoring, factory

90

M. Wenskat, D. Reschke, J. Schaffran, L. Steder, M. Wiencek
DESY, Hamburg, Germany
D. Bafia, A. Grassellino, O.S. Melnychuk
Fermilab, Batavia, Illinois, USA
A.D. Palczewski
JLab, Newport News, Virginia, USA
M. Wiencek
IFJ-PAN, Kraków, Poland

Funding: This work was supported by the Helmholtz Association within the topic Accelerator Research and Development (ARD) of the Matter and Technologies (MT) Program and by the BMBF under the research grant 05H18GURB1.
Within a global effort to understand and standardize the nitrogen-infusion and the low T bake procedure, one large grain and two fine grain single-cell cavity were treated and tested at FNAL and then send to other labs including DESY and JLab for further studies.

Poster MOP026 [0.813 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP026

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paper received ※ 20 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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MOP028

Materials Science Investigations of Nitrogen-Doped Niobium for SRF Cavities

cavity, SRF, superconducting-RF, collider

99

M. Major, L. Alff, M. Arnold, J. Conrad, S. Flege, R. Grewe, N. Pietralla
TU Darmstadt, Darmstadt, Germany

Funding: Work supported by the German Federal Ministry for Education and Research (BMBF) through grant 05H18RDRB2.
Niobium is the standard material for superconducting RF (SRF) cavities for particle acceleration. Superconducting materials with higher critical temperature or higher critical magnetic field allow cavities to work at higher operating temperatures or higher accelerating fields, respectively. Enhancing the surface properties of the superconducting material in the range of the penetration depth is also beneficial. One direction of search for new materials with better properties is the modification of bulk niobium by nitrogen doping. In the Nb-N phase diagram, the cubic delta-phase of NbN has the highest critical temperature. Niobium samples were annealed and N-doped in the high-temperature furnace at TU Darmstadt and investigated at its Materials Research Department with respect to structural modifications. Secondary ion mass spectrometry showed at which conditions N-diffusion takes place. X-ray diffraction (XRD) confirmed the appearance of NbN and Nb₂N phases for the optimized doping process. XRD pole figures also showed grain growth during sample annealing.

Poster MOP028 [2.555 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP028

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paper received ※ 05 July 2019 paper accepted ※ 12 July 2019 issue date ※ 14 August 2019

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MOP029

N-Doping Studies With Single-Cell Cavities for the SHINE Project

cavity, SRF, FEL, ECR

102

J.F. Chen, H.T. Hou, Y.F. Liu, D. Wang, Y. Wang
SARI-CAS, Pudong, Shanghai, People’s Republic of China
Y.W. Huang
ShanghaiTech University, Shanghai, People’s Republic of China
Z. Wang
SINAP, Shanghai, People’s Republic of China

The SHINE SRF accelerator is designed to operate in CW mode with more than six hundred superconducting cavities. In order to reduce the high cost of construction and operation of the cryogenic system, high-Q cavities with nitrogen-doping technology together with tradition-ally treated large-grain cavities have been considered as two possible options. In this paper, we present N-doping studies on single-cell cavities fabricated with fine-grain and large-grain niobium.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP029

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paper received ※ 23 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019

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MOP030

Analysis of Surface Nitrides Created During "Doping" Heat Treatments of Niobium

cavity, SRF, lattice, controls

106

J.K. Spradlin, A.D. Palczewski, C.E. Reece, H. Tian
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The benefits of reduced RF losses from interstitial "doping" of niobium are well established. Many of the details involved in the process remain yet to be elucidated. The niobium surface reacted with low-pressure nitrogen at 800°C presents a surface with chemical reactivity different than standard niobium. While standard "recipes" are being used to produce cavities, we seek additional insight into the chemical processes that may be used to remove the "undesirable" as-formed surface layer. This may lead to new processing routes or quality assurance methods to build confidence that all surface "nitrides" have been removed. We report a series of alternate chemistry treatments and subsequent morphological examinations and interpret the results. We also introduce a new standardized Nb sample system in use for efficient characterization of varying doping protocols and cross-laboratory calibration.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP030

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paper received ※ 23 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019

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MOP031

Investigation of Frequency Behavior Near Tc of Niobium Superconducting Radio-Frequency Cavities

cavity, SRF, electron, ECR

112

D. Bafia, J. Zasadzinski
IIT, Chicago, Illinois, USA
D. Bafia, M. Checchin, A. Grassellino, O.S. Melnychuk, A.S. Romanenko, D.A. Sergatskov
Fermilab, Batavia, Illinois, USA

This paper will present a systematic investigation of the resonant frequency behavior of niobium SRF cavities subject to different surface processing (nitrogen doping, nitrogen infusion, 120°C bake, EP, etc.) near the critical transition temperature. We find features occurring in frequency versus temperature (FvsT) data near Tc that seem to vary with surface processing. Emphasis is placed on one of the observed features: a dip in the superconducting resonant frequency below the normal conducting value which is prominent in nitrogen doped cavities and appears to be a signature of nitrogen doping. This gives further insights on the mechanisms responsible for the large increase in performance of cavities subject to this surface treatment. The magnitude of this dip in frequency is studied and related to possible physical parameters such as the concentration of impurities near the surface and the design resonant frequency of the cavity. A possible explanation for the meaning of this dip is discussed, namely, that it is a result of strong coupling between electrons and phonons within the resonator.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP031

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paper received ※ 23 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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MOP032

Effect of Low Temperature Infusion Heat Treatments and "2/0" Doping on Superconducting Cavity Performance

cavity, ECR, SRF, background

118

P.N. Koufalis, M. Ge, M. Liepe, J.T. Maniscalco
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Under specific circumstances, low temperature infusion heat treatments of niobium cavities have resulted in the ubiquitous "Q-rise". This is an increase in quality factor with increasing field strength or equivalently a decrease in the temperature-dependent component of the surface resistance. We investigate the results of various infusion conditions with infusion bake time as a free parameter. To study the very near surface effects of infusion, we employ HF rinsing, light VEP, and oxypolishing to remove several or tens of nm at a time. We present results from RF performance tests of low temperature infusion heat treated niobium cavities, and correlate these with SIMS impurity depth profiles obtained from witness samples. We also present results of a cavity doped at 800 C with the "2/0" recipe.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP032

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paper received ※ 26 June 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019

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MOP039

Nitrogen Doping Studies of Superconducting Cavities at Peking University

cavity, accelerating-gradient, superconducting-cavity, ECR

141

S. Chen, M. Chen, L.W. Feng, J.K. Hao, L. Lin, K.X. Liu, S.W. Quan, F. Wang, F. Zhu
PKU, Beijing, People’s Republic of China

Nitrogen doping studies with 1.3 GHz superconducting cavities were carried out at Peking University in recent years. We have realized 4×10¹⁰ of high quality factor at 12 MV/m and 2.0 K with large grain single cell cavities by heavy doping. To improve the accelerating gradient of high Q cavities, light doping recipe is adopted. Accelerating gradient is improved to 20 MV/m and the quality factor is larger than 3×10¹⁰ at 16 MV/m and 2.0 K for light doped cavities. The nitrogen treatment, test and analysis are presented in this paper.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP039

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paper received ※ 21 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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MOP040

Low Temperature Thermal Conductivity of Niobium and Materials for SRF Cavities

SRF, cavity, experiment, controls

144

M. Fouaidy
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France

A test facility, allowing the test of 4 samples simultaneously during each run, was developed for measuring at low temperature (T= 1.5 K - 10 K) the thermal conductivity k(T) of niobium and other materials used for the fabrication of SRF cavities. The measurements are performed using steady-state axial heat flow method with a careful control of heat leaks to the surrounding. Several samples of different materials (industrial Nb sheets, Ti¿) were either tested as received or/and subjected to various Heat Treatment (H.T) prior to the experiment then tested. The resulting experimental data are presented and compared to the experimental results previously reported by other groups. As expected, H.T @ 1200°C with Ti gettering improves the Nb RRR by a factor of 3 and consequently k(T). Finally, the correlation between the Niobium RRR and the thermal conductivity. at T=4.2 K is confirmed in good agreement with the Wiedemann-Franz law.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP040

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paper received ※ 04 July 2019 paper accepted ※ 05 July 2019 issue date ※ 14 August 2019

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MOP041

Comparison of the Lattice Thermal Conductivity of Superconducting Tantalum and Niobium

scattering, electron, lattice, simulation

148

P. Xu, N.T. Wright
MSU, East Lansing, Michigan, USA
T.R. Bieler
Michigan State University, East Lansing, Michigan, USA

Funding: This work is supported by the U.S. Department of Energy, Office of High Energy Physics through Grant No. DE-FG02-13ER41974.
The thermal conductivity k of superconducting Ta behaves similarly to that of superconducting Nb, albeit at colder temperatures. This shift is due to the superconducting transition temperature of Ta being 4.3 K, versus 9.25 K for Nb. For example, the temperature of the phonon peak of properly treated Ta is about 1 K as opposed to a phonon peak at about 2 K for Nb. The typical value of k of Ta is smaller than Nb with the value at the phonon peak for Ta being O(10) W/ m/ K. Like Nb, k is dominated by phonons at these temperatures. This lattice k can be modeled by the Boltzmann transport equation, solved here by a Monte Carlo method using the relaxation time approximation. Individual scattering mechanisms due to boundaries, dislocations, and residual normal electrons are examined, and the phonon dispersion relation is included. Differences in the thermal response of deformed Ta, as compared with Nb, may be attributed to differences in dislocation densities of the two metals following similar levels of deformation. Boundary scattering dominates at the coldest temperatures. The phonon peak decreases and shifts to warmer temperatures with deformation.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP041

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paper received ※ 19 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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MOP045

The LCLS-II HE High Q and Gradient R&D Program

cavity, SRF, cryomodule, linac

154

D. Gonnella, S. Aderhold, A. Burrill, G.R. Hays, T.O. Raubenheimer, M.C. Ross
SLAC, Menlo Park, California, USA
D. Bafia, M. Checchin, A. Grassellino, M. Martinello, A.S. Romanenko
Fermilab, Batavia, Illinois, USA
M. Ge, M. Liepe, S. Posen
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
A.D. Palczewski, C.E. Reece
JLab, Newport News, Virginia, USA

Funding: US DOE and the LCLS-II HE Project
The LCLS-II HE project is a high energy upgrade to the superconducting LCLS-II linac. It consists of adding twenty additional 1.3 GHz cryomodules to the linac, with cavities operating at a gradient of 20.8 MV/m with a Q₀ of 2.7·10¹⁰. Performance of LCLS-II cryomodules has suggested that operations at this high of a gradient will not be achievable with the existing cavity recipe employed. Therefore a research program was developed between SLAC, Fermilab, Thomas Jefferson National Accelerator Facility, and Cornell University in order to improve the cavity processing method of the SRF cavities and reach the HE goals. This program explores the doping regime beyond what was done for LCLS-II and also has looked to further developed nitrogen-infusion. Here we will summarize the results from this R\&D program, showing significant improvement on both single-cell and 9-cell cavities compared with the original LCLS-II cavity recipe.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP045

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paper received ※ 25 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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MOP049

Prototypes Fabrication of 1.3 GHz Superconducting Rf Components for SHINE

cavity, FEL, HOM, SRF

164

H.T. Hou, J.F. Chen, Z.Y. Ma, J. Shi, Y. Wang
SARI-CAS, Pudong, Shanghai, People’s Republic of China
F.S. He
IHEP, Beijing, People’s Republic of China
S.W. Quan
PKU, Beijing, People’s Republic of China

Aiming to high repetition rate hard X-ray facility, con-struction of Shanghai HIgh repetition rate XFEL aNd Extreme light facility (SHINE) project has been ap-proved. During the R & D phase, prototypes fabrication of key components of 1.3GHz superconducting rf system have been proposed, especially 1.3 GHz 9-cell niobium cavities. Here the paper will present the progress of the fabrication status and performance of the prototypes, together with the analysis of not only the quality factor and gradient of the cavities. Consideration of HOM feed-throughs and absorbers are also reported.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP049

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paper received ※ 23 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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MOP056

Surface Treatments for the Series Production of ESS Medium Beta Cavities

cavity, recirculation, SRF, simulation

188

M. Bertucci, A. Bosotti, A. D’Ambros, P. Michelato, L. Monaco, C. Pagani, R. Paparella, D. Sertore
INFN/LASA, Segrate (MI), Italy
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy
D. Rizzetto, M. Rizzi
Ettore Zanon S.p.A., Schio, Italy
A. Visentin
Ettore Zanon S.p.A., Nuclear Division, Schio, Italy

The surface treatment of ESS 704 MHz medium beta cavities consists of a bulk BCP 200 micron removal, a 10 h 600°C heat treatment and a final 20 micron BCP performed after tank integration. The facility currently employed for the BCP treatment, settled in Ettore Zanon SpA, is here presented, together with the results so far obtained on the first series cavities in terms of frequency sensitivity, removal rate and surface external temperature. The optimization of BCP treatment by a preliminary fluid-dynamical finite element model is also discussed. Some details about the visual inspection procedure and the furnace qualification are also presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP056

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paper received ※ 23 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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MOP060

INFN-LASA for the PIP-II Project

cavity, SRF, interface, linac

205

R. Paparella, M. Bertucci, A. Bignami, A. Bosotti, M. Chiodini, A. D’Ambros, P. Michelato, L. Monaco, D. Sertore
INFN/LASA, Segrate (MI), Italy
J.F. Chen
SARI-CAS, Pudong, Shanghai, People’s Republic of China
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy
L. Sagliano
ESS, Lund, Sweden

INFN-LASA joined the international effort for the PIP-II project in Fermilab to build the 650 MHz superconducting cavities realizing the low-beta section of the 800 MeV proton linac. After developing the electro-magnetic and mechanical design, INFN-Milano started the prototyping phase by producing five single-cells and two complete 5-cells cavities. This paper reports the status of PIP-II activities at INFN-LASA summarizing manufacturing experience and preliminary experimental results.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP060

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paper received ※ 24 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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MOP061

State of the Art of Niobium Machining for SRF Applications

SRF, cavity, electron, alignment

210

P. Naisson, S. Atieh, K. Scibor, P. Trubacova
CERN, Geneva, Switzerland
F. Dumont, D. Fabre, F. Valiorgue
ENISE, Saint Etienne, France

Niobium is a demanding material to be machined. Its low hardness, high melting temperature and abrasivity leads to poor cutting condition, and surface quality and shape accuracy could be difficult to achieve, especially for complex shapes such as HOM antennas. Recent CERN developements concerning DQW crab cavity for HL-LHC project had implied extensive research program to better understand and master the machining of this material. In this frame, the present article will introduce actual state of the art machining condition used at CERN and their consequences about the surface roughness, shape accuracy and taking into account the tool wear in order to maintain this level of quality. Morevoer, advance machning solution, such as cryogenic cooling could be used.

Poster MOP061 [2.921 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP061

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paper received ※ 30 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019

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MOP064

Performance of First Prototype Multi-Cell Low-Surface-Field Shape Cavity

cavity, SRF, electron, experiment

222

R.L. Geng
JLab, Newport News, Virginia, USA
Y. Fuwa, Y. Iwashita
Kyoto ICR, Uji, Kyoto, Japan
H. Hayano
KEK, Ibaraki, Japan
H. Ito
Sokendai, Ibaraki, Japan
Z. Li
SLAC, Menlo Park, California, USA

The idea of cavity shaping for higher ultimate acceleration gradients has been proposed for some time, Low Loss/Ichiro and Re-entrant being examples, both seeking a lower Hpk/E_acc at the expense of a higher Epk/E_acc. While experimental verification in single-cell cavities of those shapes was very successful including the record gradient of 59 MV/m, pushing multi-cell cavities of those shapes to higher gradients was prevented by field emission. The Low-Surface-Field (LSF) shape seeks not only a lower Hpk/E_acc but also a lower Epk/E_acc, therefore it has the advantage of raising ultimate gradient at reduced field emission. The first multi-cell LSF shape prototype cavity was built using the standard forming and welding techniques. RF tests have been carried out, following standard ILC TDR baseline surface processing and treatment recipe. Three out of five cells achieved Hpk values corresponding to E_acc 50 MV/m. The current limit is the field emission in end cells. Instrumented testing following end-cell wiping and HPR with larger nozzles is in progress. We will present detailed experimental results and preparation procedures.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP064

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paper received ※ 24 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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MOP070

Investigation of the Critical RF Fields of Superconducting Cavity Connections

cavity, simulation, vacuum, impedance

230

J.C. Wolff, J.I. Iversen, D. Klinke, D. Kostin, D. Reschke, S. Sievers, A. Sulimov, J.H. Thie, M. Wiencek
DESY, Hamburg, Germany
R. Wendel, J.C. Wolff
HAW Hamburg, Hamburg, Germany

To optimise the length of the drift tube of a superconducting cavity (SC), it is required to know the critical value of the RF fields to prevent a potential early quench at the flange connection in case of a drift tube length reduction. To avoid changes on the SC which has been used for the tests, all RF cryogenic experiments have been carried out by using a cylinder in the center of a 1-cell cavity drift tube to increase the field magnitude at the connection. This cylinder has been designed and optimised by RF simulations to provide a field density at the connection twice as high as at a chosen reference point near the iris. Hence also a test SC with a comparatively low gradient can be used without causing field restrictions. In this contribution an approach to investigate the field limitations of 1.3 GHz TESLA-Shape SC connections and thereby the minimal drift tube length based on simulations will be presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-MOP070

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paper received ※ 23 June 2019 paper accepted ※ 04 July 2019 issue date ※ 14 August 2019

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TUFUA1

The Field-Dependent Surface Resistance of Doped Niobium: New Experimental and Theoretical Results

cavity, SRF, electron, ECR

340

J.T. Maniscalco, M. Ge, P.N. Koufalis, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
T. Arias, D. Liarte, J.P. Sethna, N. Sitaraman
Cornell University, Ithaca, New York, USA

We present systematic work investigating how different doping and post-doping treatments affect the BCS surface resistance at 1.3~GHz and higher frequencies. We examine the field-dependent BCS resistance at many temperatures as well as the field-dependent residual resistance and use the results to reveal how impurity species and concentration levels affect the field-dependent RF properties. We further demonstrate the importance of thermal effects and their direct dependence on doping level. We use the tools of Density Functional Theory to work towards an {\em ab initio} model of electron overheating to theoretically confirm the impact of doping, create a full model that includes thermal effects to predict the field dependent resistance, and show that the predictions of the model agree with results from doped and non-doped cavities ({\em e.g.} the strength of the anti-Q-slope and the high-field Q slope). Finally, we use our experimental results to systematically assess and compare theories of the field-dependent BCS resistance, showing that the current theory on smearing of the density of states is incomplete.

Slides TUFUA1 [6.780 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUA1

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paper received ※ 01 July 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019

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TUFUA4

New Insights on Nitrogen Doping

cavity, electron, SRF, ECR

347

D. Bafia, J. Zasadzinski
IIT, Chicago, Illinois, USA
D. Bafia, M. Checchin, A. Grassellino, O.S. Melnychuk, A.S. Romanenko, D.A. Sergatskov
Fermilab, Batavia, Illinois, USA

This paper covers a systematic study of the quench in nitrogen doped cavities: a cavity was sequentially treated/reset with different N-doping recipes which are known to produce different levels of quench field. Analysis of cavity heating profiles using TMAP are used to gain insight on the origins of quench; new recipes demonstrate the possibility to increase quench fields well beyond 30 MV/m. In addition, a new signature of nitrogen doping is explored, namely, a dip in the superconducting resonant frequency below the normal conducting value just below the critical transition temperature, giving further insights on the mechanisms responsible for the large increase in performance of cavities subject to this surface treatment.

Slides TUFUA4 [3.097 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUA4

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paper received ※ 23 June 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019

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TUFUA5

Recent Development on Nitrogen Infusion Work Towards High Q and High Gradient

cavity, SRF, injection, radio-frequency

355

P. Dhakal
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
A quality factor as high as 2 × 10¹⁰ at 1.5 GHz was achieved at a gradient of 35 MV/m by 800 °C annealing and N-infusion at 140 °C. A comparison of the field dependence of the surface resistance after N-infusion with a recent theoretical model that extends the calculation of the BCS surface resistance to high rf fields suggests an increase in the quasiparticles¿ relaxation time with increasing infusion temperature, which could be due to a decreasing density of subgap states. Nb coupons treated similarly showed the formation of thicker oxynitride layer on the surface beneath thin dielectric Nb₂O₅ layer. A plausible explanation for the improved Q₀ is that the oxynitride layer on the Nb surface adds additional electron scattering within RF penetration depth.

Slides TUFUA5 [6.077 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUA5

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paper received ※ 19 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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TUFUA7

Review of Muon Spin Rotation Studies of SRF Materials

SRF, cavity, experiment, FEL

360

T. Junginger
Lancaster University, Lancaster, United Kingdom
R.E. Laxdal
TRIUMF, Vancouver, Canada

Muons spin rotate in magnetic fields and emit a positron preferentially in spin direction after decay. These properties enable muon spin rotation (muSR) as a precise probe for local magnetism. muSR has been used to characterize SRF materials since 2010. At TRIUMF a so called surface beam implants muons at a material dependent depth of about 150 µm in the bulk. A dedicated spectrometer was developed for field of first vortex penetration and pinning strength measurements of SRF materials in parallel magnetic fields of up to 300 mT. A low energy beam available at PSI implants muons at variable depth in the London layer allowing for direct measurements of the London penetration depth from which the lower critical field and the superheating field can be calculated. This facility is limited to parallel magnetic fields of up to 25 mT. Here, surface and low energy muSR results on SRF materials are reviewed and cross-correlated to each other and to further results from additional experiments. Finally, we present the status of a new facility based on the similar beta-NMR technique enabling measurements in the London layer of SRF materials exposed to parallel magnetic fields above 200 mT.

Slides TUFUA7 [4.063 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUA7

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paper received ※ 01 July 2019 paper accepted ※ 12 July 2019 issue date ※ 14 August 2019

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TUFUB3

Mapping Flux Trapping in SRF Cavities to Analyze the Impact of Geometry

cavity, experiment, HOM, simulation

364

F. Kramer, J. Knobloch, O. Kugeler, J.M. Köszegi
HZB, Berlin, Germany
J. Knobloch
University of Siegen, Siegen, Germany

A combined temperature and magnetic field mapping system was used to investigate the impact of an ambient field on trapped flux and on the resulting local surface resistance. For this, a 1.3 GHz TESLA single cell cavity was cooled through the superconducting transition at different magnetic field angles with respect to the cavity axis. The measurements suggest, that the field is trapped homogeneously over the cavity volume, without changing its orientation. Flux trapped perpendicular the surface contributed significantly more to the surface resistance, than trapped flux parallel to the surface.

Slides TUFUB3 [12.777 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUB3

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paper received ※ 21 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019

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TUFUB5

Effects of Static Magnetic Fields on a Low-frequency TEM Class Superconducting Cavity

cavity, shielding, SRF, superconductivity

370

M.K. Ng, Z.A. Conway, M.P. Kelly, K.W. Shepard
ANL, Lemont, Illinois, USA

Systematic studies on the effect of magnetic fields on a 330 MHz superconducting (TEM-mode) half-wave cavity are presented. The practical application of the results is for a possible future 2 K operation in the ATLAS heavy-ion accelerator at Argonne. The low frequency and the integral stainless steel jacket, rather than titanium, provide important new data for this full production model low-beta cavity. The studies include multi-axial magnetic field measurements near the cavity surface due to ambient and applied fields. Cavity performance under different conditions is measured at temperatures ranging between 1.6 K and 4.5 K. A residual resistance of approximately 5-7 nΩ at 1.6 K is observed. Data suggest that an appreciable fraction arises from losses that are not due to flux trapping.

Slides TUFUB5 [1.195 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUB5

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paper received ※ 24 June 2019 paper accepted ※ 14 August 2019 issue date ※ 14 August 2019

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TUFUB8

CVD Coated Copper Substrate SRF Cavity Research at Cornell University

cavity, SRF, interface, target

381

M. Ge, T. Gruber, J.J. Kaufman, M. Liepe, J.T. Maniscalco, T.E. Oseroff, R.D. Porter, Z. Sun
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
V.M. Arrieta, S.R. McNeal
Ultramet, Pacoima, California, USA

Chemical vapor deposition (CVD) is a promising alternative to conventional sputter techniques for coating copper substrate cavities with high-quality superconducting films. Through multiple SRF-related DOE SBIR projects, Ultramet has developed CVD processes and CVD reactor designs for SRF cavities, and Cornell University has conducted extensive RF testing of CVD coated surfaces. Here we report results from thin-film CVD Nb₃Sn coated copper test plates, and for thick-film CVD niobium on copper including full-scale single cell 1.3 GHz copper substrate cavities. Detailed optical inspection and surface characterization show high-quality and well-adhered coatings. No copper contamination is found. The Nb₃Sn coated plates have a uniform Nb₃Sn coating with a slightly low tin concentration (19 -22%), but a BCS resistance well in agreement with predictions. The CVD Nb coatings on copper plates demonstrate excellent adhesion characteristics and exceeded surface fields of 50 mT without showing signs of a strong Q-slope that is frequently observed in sputtered Nb cavities. Multiple single-cell 1.3 GHz copper cavities have been coated to date at Ultramet, and results from RF testing of these are presented and discussed.

Slides TUFUB8 [12.488 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUB8

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paper received ※ 01 July 2019 paper accepted ※ 05 July 2019 issue date ※ 14 August 2019

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TUP011

QWR085 Design for Bisol Post Accelerator SCL2

ISOL, cavity, simulation, LEBT

413

M. Chen, S. Chen, A.Q. Cheng, J.K. Hao, K.X. Liu, Y.Q. Liu, D.M. Ouyang, S.W. Quan, F. Zhu
PKU, Beijing, People’s Republic of China
Z. Peng
CIAE, Beijing, People’s Republic of China

BISOL(Beijing Isotope-Separation-On-Line Neutron-Rich Beam Facility) is a new generation radioactive ion beam(RIB) facility[1]. It consists a CARR nuclear reactor, a high intensity deuteron accelerator and a post accelera-tor. QWR085 cavity is supposed to be used in SCL2 of post accelerator. This paper mainly talks about the elec-tromagnetic design, mechanical design and vibration damper design of QWR085.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP011

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paper received ※ 23 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019

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TUP012

Evaluation of High Performance Large Grain Medium Purity SRF Cavity From KEK

cavity, SRF, experiment, cryogenics

415

P. Dhakal, G. Ciovati, G.R. Myneni
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
We presented the RF measurement on a 1.3 GHz single cell cavity fabricated at KEK using large grain ingot niobium with RRR=10⁷. The cavity reached to 35 MV/m with Q₀ = 2.0×10^zEhNZeHn at 2.0 K, record performance on the cavity made from medium purity ingot niobium. The cavity was cool down with different temperature gradient along the cavity axis in order to understand the flux expulsion mechanism when the cavity does through the superconducting transition and effect of trap residual magnetic field on the residual resistance. The measurement showed the excellent flux expulsion with the flux trapping sensitivity of 0.29 nΩ/mG for electro polished surface and 0.44 nΩ/mG for cavity followed by low temperature baking at 120°C for 12 hours.
We acknowledge KEK for sending this cavity for evaluations.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP012

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paper received ※ 17 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019

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TUP016

Quarter-wave Resonator with the Optimized Shape for Quantum Information Systems

cavity, photon, shielding, factory

430

S.V. Kutsaev, R.B. Agustsson, P.R. Carriere, A. Moro, A.Yu. Smirnov, K.V. Taletski
RadiaBeam, Santa Monica, California, USA
A.N. Cleland, É. Dumur
The University of Chicago, Chicago, Illinois, USA
Z.A. Conway
ANL, Lemont, Illinois, USA
K.V. Taletski
MEPhI, Moscow, Russia

Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, under SBIR grant DE-SC0018753
Quantum computers (QC), if realized, could disrupt many computationally intense fields of science. The building block element of a QC is a quantum bit (qubit). Qubits enable the use of quantum superposition and multi-state entanglement in QC calculations, allowing a QC to simultaneously calculate millions of computations at once. However, quantum states stored in a qubit degrade with decreased quality factors and interactions with the environment. One technical solution to improve qubit lifetimes and network interactions is a circuit comprised of a Josephson junction located inside of a high Q-factor superconducting 3D cavity. RadiaBeam, in collaboration with Argonne National Laboratory and The University of Chicago, has developed a superconducting radio-frequency quarter-wave resonant cavity (QWR) for quantum computation. Here a 6 GHz QWR was optimized to include tapering of the inner and outer conductors, a toroidal shape for the resonator shorting plane, and the inner conductor to reduce parasitic capacitance. In this paper, we present the results of the qubit cavity design optimization, fabrication, processing and testing in a single-photon regime at mK temperatures.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP016

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paper received ※ 23 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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TUP018

New SRF Structures Processed at the ANL Cavity Processing Facility

cavity, cathode, SRF, dipole

434

T. Reid, Z.A. Conway, B.M. Guilfoyle, M. Kedzie, M.P. Kelly, M.K. Ng
ANL, Lemont, Illinois, USA

Argonne National Laboratory (ANL) has extended high quality cavity processing techniques based on those developed for the International Linear Collider to several more complex superconducting RF cavities. Recently, these include a bunch lengthening harmonic cavity, a crabbing rf-dipole cavity, a compact half-wave cavity, and both medium and high frequency elliptical cavities. These systems are an improved version of the one originally developed for 1.3 GHz 9-cell cavities and include a second rotating electrical contact that can support multiple cathodes, necessary for optimum polishing in difficult cavity geometries. All include the possibility for external water cooling.

Poster TUP018 [4.322 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP018

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paper received ※ 28 June 2019 paper accepted ※ 12 July 2019 issue date ※ 14 August 2019

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TUP019

Status of High Temperature Vacuum Heat Treatment Program at IPN Orsay

cavity, SRF, MMI, vacuum

438

M. Fouaidy, F. Chatelet, V. Delpech, F. Galet, D. Le Dréan, R. Martret, G. Olry, T. Pépin-Donat
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
M. Baudrier, P. Carbonnier, E. Fayette, X. Hanus, Th. Proslier, D. Roudier, P. Sahuquet, C. Servouin
CEA-DRF-IRFU, France
E. Cenni, L. Maurice
CEA-IRFU, Gif-sur-Yvette, France
D. Longuevergne
FLUO, Orsay, France

In the framework of ESS, a vacuum furnace dedicated to High Temperature Heat Treatment under Vacuum (VH2T2) of SRF bulk Nb cavities was developed and commissioned in May 2016. This furnace is currently used for interstitial hydrogen removal (10h00 @ 650 °C) of two type of cavities: 1) the whole series of 26 ESS 352 MHz spoke resonators equipped with their Ti LHe tank well, 2) some prototypes of ESS high beta and medium beta cavities. Up to know IPN Orsay VH2T2 (10h00 @ 650 °C) was successfully applied to more than 16 cavities. In this paper we will first report about these VH2T2 tests. Finally, we have just started testing nitrogen infusion and nitrogen doping processes on samples and 1.3 GHz cavities: the preliminary results will be discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP019

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paper received ※ 03 July 2019 paper accepted ※ 04 July 2019 issue date ※ 14 August 2019

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TUP020

Statistical Analysis of the 120°C Bake Procedure of Superconducting Radio Frequency Cavities

cavity, accelerating-gradient, FEL, SRF

444

L. Steder, D. Reschke
DESY, Hamburg, Germany

DESY is and was very active in R&D related to SRF cavities. Many single and nine cell cavities with different surface treatment histories were tested vertically. Results of these cold tests are accelerating gradient and quality factor of the cavities. Using the large number of available datasets the parameters of the 120°C bake procedure, which is applied to avoid high-field Q-slope, are analysed. The impact of different durations and temperatures on accelerating gradient, quality factor and residual resistance is studied in detail and is compared to results obtained with the recently proposed procedure of modified low temperature bake. For this procedure additional four hours at temperatures around 75°C are implemented before the standard bake at about 120°C. Since the claim is, that cavities treated with such a modified procedure achieve extra-ordinary large accelerating gradients it is a very interesting research field for the European XFEL continuous wave mode upgrade. For this purpose cavities with high quality factors are needed, but in addition large maximal accelerating fields are required to maintain high energies in the pulsed operation mode of the accelerator.

Poster TUP020 [0.747 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP020

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paper received ※ 21 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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TUP021

Effect of Cathode Rotation and Acid Flow in Vertical Electropolishing of 1.3 GHz Niobium Nine-Cell Cavity

cavity, cathode, experiment, SRF

448

V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi
MGH, Hyogo-ken, Japan
H. Hayano, S. Kato, H. Monjushiro, T. Saeki
KEK, Ibaraki, Japan

We have been carrying out R&D on vertical electropolishing (VEP) technique to establish it as an alternate of the horizontal EP (HEP) technique used for the surface treatment of niobium (Nb) superconducting RF (SRF) cavities. We have earlier reported on a VEP parameter study for 1.3 GHz single and nine-cell Nb cavities. The optimized VEP parameters and a unique rotating cathode yielded uniform removal and a smooth surface in the single cell cavity. The unique cathode and a dual flow mechanism for acid circulation were applied to improve the removal uniformity in the nine-cell cavity. The vertically electropolished single and nine cell cavities achieved the same RF performance as achieved after the HEP processes. We are making efforts to further improve the removal uniformity in the nine-cell cavity. Here, we report on a VEP of the 1.3 GHz Nb nine-cell cavity at a higher cathode rotation speed of 50 rpm. The VEP results reveal that the speed could be considered for improving the uniformity in removal while maintaining the surface smoothness. Required improvements in the VEP facility and acid flow condition for achieving uniform EP and a smooth surface are also described.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP021

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paper received ※ 23 June 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019

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TUP022

Fermilab EP Facility Improvement

cavity, target, controls, SRF

453

F. Furuta, D.J. Bice, A.C. Crawford, T.J. Ring
Fermilab, Batavia, Illinois, USA

Electro-chemical Polishing (EP) is one of the key technologies of surface treatments for niobium superconducting cavities. We have established a single-cell scale horizontal electro-polishing facility at Fermilab and routinely processed the niobium cavities with the frequencies of 1.3 GHz to 3.9 GHz. The precise control of EP parameters, especially the temperatures of cavity outside wall, allows the uniform removal over the cell with the variation of ±15%. Here we report the details of our EP process and recent improvements on our EP facility at Fermilab.

Poster TUP022 [1.711 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP022

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paper received ※ 10 July 2019 paper accepted ※ 17 August 2019 issue date ※ 14 August 2019

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TUP024

Radial Tuning Devices for 1.3 GHz TESLA Shape Cavities

cavity, SRF, HOM, FEL

459

A. Sulimov, J.H. Thie
DESY, Hamburg, Germany

Radial tuning devices at DESY can be applied to any TESLA shape 1.3 GHz cavity to reduce its elongation due to excessive additional material removal (>300 µm) or to compensate critical manufacturing uncertainties. Radial deformation of cavity cells can be provided by a special chain or a rolling device with three rollers. The chain distributes the radial forces on the equator area around the cell. The rollers are moving radially in relation to the rotating cavity and provide an equator diameter reduction. Both devices have the contour close to the cell shape at the equator area. The required equator radius deviation depends on the tuning target and usually varies between (0.02…0.60) mm. Different aspects of the tuning procedure and material properties are described using the example of cavity rolling.

Poster TUP024 [0.252 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP024

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paper received ※ 23 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019

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TUP027

Vertical Electropolishing of Niobium Nine-Cell Cavity with a Cavity Flipping System for Uniform Removal

cavity, cathode, experiment, SRF

467

K.N. Nii, V. Chouhan, Y.I. Ida, T.Y. Yamaguchi
MGH, Hyogo-ken, Japan
H. Hayano, S. Kato, H. Monjushiro, T. Saeki
KEK, Ibaraki, Japan

Marui Galvanizing Co., Ltd. has been developing vertical electropolishing (VEP) technology for single and nine-cell niobium superconducting radio frequency cavities using a unique cathode namely Ninja cathode in collaboration with KEK. The VEP process usually results in non-uniform removal with a large asymmetry along the cavity length. In order to suppress the asymmetry in removal, we are making different approaches. Flipping of the cavity during the VEP process is one of the approaches applied so far. A unique VEP setup, which allows the flipping of a multi-cell cavity, has been developed as reported earlier. Here, we report the improvement in the setup with automation for cavity flipping. VEP experiments were conducted with the improved system. VEP parameters were studied and the VEP results including the removal trend are discussed in detail.

Poster TUP027 [1.347 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP027

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paper received ※ 24 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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TUP029

An Experimental Analysis of Effective EP Parameters for Low-Frequency Cylindrical Nb Cavities

cavity, cathode, SRF, polarization

472

C.E. Reece
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Work supported by the U.S. DoE, Office of Science, Office of Basic Energy Sciences.
While the basic process of electropolishing niobium with 1:9 HF:H₂SO₄ electrolyte has been well characterized, the specific process parameters used to electropolish different superconducting radio frequency (SRF) cavity geometries requires thoughtful attention. One seeks to realize confidently local diffusion-limited polishing at each point on the surface while maximizing uniformity of removal rate. Since the reaction rate is temperature dependent, this implies that one must manage the cavity surface temperature during polishing. Too-high applied voltage aggravates temperature and thus removal non-uniformity, but too-low applied voltage risks placing the large-diameter locations "off the current plateau," yielding etching rather than polishing. The majority of recent experience has been with elliptical L-band SRF cavities and some half-wave cavities at ANL. Lower frequency cavities with increased surface area and larger cathode-to-equator distance require fresh analysis and optimization. In preparation for SNS PPU project, JLab performed some EP process development runs with SNS high beta cavities to help identify viable parameter regimes for communication to cavity vendors. Results from this study are presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP029

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paper received ※ 23 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019

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TUP042

Measurement of Mechanical Vibration of SRILAC Cavities

cavity, linac, ECR, cryomodule

513

O. Kamigaito, K. Ozeki, N. Sakamoto, K. Suda, K. Yamada
RIKEN Nishina Center, Wako, Japan

Mechanical vibration of quarter-wavelength resonators of SRILAC, the superconducting booster of the RIKEN heavy-ion linac, was measured during a vertical cold test. The measurements were performed for fully assembled cavities as well as for bare niobium cavities without the titanium jacket. In the procedure, the instantaneous resonant frequencies were measured for 10 seconds at a time interval of 1 ms and were recorded as a time series. The frequencies were analyzed by means of conventional signal analysis. The power spectrum was deduced from the autocorrelation function calculated with the fluctuation of resonant frequencies. Although the vibration amplitudes were smaller in the cavities assembled with the titanium jacket, we could not find a clear reason for this.

Poster TUP042 [6.957 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP042

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paper received ※ 27 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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TUP043

Ab-initio Study of Atomic Scale Interaction Among Nb, Sn, Cl, and O

cavity, electron, SRF, superconductivity

518

A.B. Tesfamichael, T. Arias
Cornell University, Ithaca, New York, USA

Funding: Center for Bright Beam (CBB)
We employed a combination of ab-initio calculations and statistical mechanical models to understand the nature of atomic scale interaction among Nb, Sn, Cl, and O. Because of the profound nature of the interaction, we began our study by focusing only on the interaction of Nb with Sn in the absence of Cl and O. Using Density Functional Theory (DFT) we calculated: (1), binding energy of both vacant and interstitial of the super cell for both Nb and Sn atoms (2), rate of diffusion and re-evaporation upon transportation of Sn atom across z-axis from bulk Nb layer (3), electron transfer and electric field upon transportation of Sn atom both across z-axis and xy-plane from bulk Nb layer. Our calculation indicated 30-40% difference from experimental results. Therefore, we conclude that the presence of oxides is important and also Cl impurity can not not be avoided.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP043

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paper received ※ 24 June 2019 paper accepted ※ 04 July 2019 issue date ※ 14 August 2019

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TUP045

Ab Initio Calculations on Impurity Doped Niobium and Niobium Surfaces

scattering, electron, experiment, lattice

523

N. Sitaraman, T. Arias
Cornell University, Ithaca, New York, USA
R.G. Farber, S.J. Sibener, R.D. Veit
The University of Chicago, Chicago, Illinois, USA
M. Liepe, J.T. Maniscalco
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: This work was funded by the Center for Bright Beams
We develop and apply new tools to understand Nb surface chemistry and fundamental electronic processes using theoretical ab initio methods. We study the thermodynamics of impurities and hydrides in the near-surface region as well as their effect on the surface band gap. This makes it possible for experimentalists to relate changes in STM dI/dV measurements resulting from different preparations to changes in subsurface structure. We also calculate matrix elements for electron-impurity scattering in Nb for common impurities O, N, C, and H. By transforming these matrix elements into a Wannier function basis, we calculate lifetimes for a dense set of states on the Fermi surface and determine the mean free path as a function of impurity density. This technique can be generalized to calculate other scattering amplitudes and timescales relevant to SRF theory.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP045

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paper received ※ 02 July 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019

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TUP046

Low Frequency, Low Beta Cavity Performance Improvement Studies

cavity, SRF, factory, vacuum

527

P. Kolb, R.E. Laxdal, Z.Y. Yao
TRIUMF, Vancouver, Canada

In recent years, new discoveries such as N₂ doping and infusion lead to a significant increases in Q₀ and accelerating gradient for 1.3 GHz, β=1 elliptical cavities. To understand and to adapt these treatments for lower frequency, \beta < 1 cavities, two coaxial test cavities, one quarter-wave resonator (QWR) and one half-wave resonator (HWR), have been built and put through a systematic study of these new treatments to show the effectiveness of these treatments at different frequencies. These cavities are tested in their fundamental mode and several higher order modes to study the frequency dependence of new cavity treatments such as N₂ doping and infusion. Results of these studies are presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP046

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paper received ※ 22 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019

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TUP049

Maximum Performance of Cavities Affected by the High-field Q-slope (HFQS)

cavity, SRF, experiment, radio-frequency

533

G. Ciovati
JLab, Newport News, Virginia, USA
A.V. Gurevich, I.P. Parajuli
ODU, Norfolk, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The work of I. P. and A. G. is supported by NSF Grant PHY 100614-010.
The performance of high-purity, bulk niobium SRF cavities treated by chemical processes such as BCP or EP is limited by the so-called high-field Q-slope (HFQS). Several models and experimental studies have been proposed and performed over the years to understand the origin of these anomalous losses but a general consensus on what these orgins are is yet to be established. In this contribution, we present the results from the RF tests of several 1.3 GHz single-cell cavities limited by the HFQS and tested using a variable input coupler. This allowed to maintain close to critical coupling even at high field and the data showed that the HFQS did not saturate and that in some cases a power dissipation of up to 200 W at 2 K could be sustained without quench.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP049

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paper received ※ 21 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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TUP050

A Multi-layered SRF Cavity for Conduction Cooling Applications

cavity, SRF, cryogenics, ECR

538

G. Ciovati, G. Cheng, E. Daly, G.V. Eremeev, J. Henry, R.A. Rimmer
JLab, Newport News, Virginia, USA
I.P. Parajuli
ODU, Norfolk, Virginia, USA
U. Pudasaini
The College of William and Mary, Williamsburg, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Some of the work was supported by the 2008 PECASE Award of G. Ciovati. I. Parajuli is supported by NSF Grant PHYS-100614-010
Industrial application of SRF technology would favor the use of cryocoolers to conductively cool SRF cavities for particle accelerators, operating at or above 4.3 K. In order to achieve a lower surface resistance than Nb at 4.3 K, a superconductor with higher critical temperature should be used, whereas a metal with higher thermal conductivity than Nb should be used to conduct the heat to the cryocoolers. A standard 1.5 GHz bulk Nb single-cell cavity has been coated with a ~2 µm thick layer of Nb₃Sn on the inner surface and with a 5 mm thick Cu layer on the outer surface for conduction cooled applications. The cavity performance has been measured at 4.3 K and 2.0 K in liquid He. The cavity reached a peak surface magnetic field of ~40 mT with a quality factor of 6×10⁹ and 3.5×10⁹ at 4.3 K, before and after applying the thick Cu layer, respectively.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP050

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paper received ※ 21 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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TUP051

Progress Towards Commissioning the Cornell DC Field Dependence Cavity

cavity, multipactoring, SRF, solenoid

543

J.T. Maniscalco, T. Gruber, A.T. Holic, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

The Cornell DC Field Dependence Cavity is a new coaxial test resonator designed to study the impact of strong (up to 200 mT or more) DC surface magnetic fields on the superconducting surface resistance, providing physical insight into the root of the ‘‘anti-Q-slope’’ and probing critical fields. In this report we report progress in the commissioning of this new apparatus, including finalized design elements and results of prototype tests.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP051

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paper received ※ 25 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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TUP053

Optimal Thermal Gradient for Flux Expulsion in 600°C Heat-treated CEBAF 12 GeV Upgrade Cavities

cavity, HOM, experiment, controls

550

R.L. Geng, F. Marhauser, P.D. Owen
JLab, Newport News, Virginia, USA

We will present results on measurement of flux expulsion in CEBAF 12 GeV upgrade cavities and original CEBAF cavities and the search for optimal thermal gradient for reducing the trapped flux in cavities installed in CEBAF linacs. Preliminary measurements of one C100 cavities has shown that a nearly perfect flux expulsion can be achieved at an optimal thermal gradient - a surprising result contrary to the expectation of zero flux expulsion for 600°C heat treated niobium cavities. These results could lead to a cost-effective path for improving the quality factor of cavities installed in CEBAF and ultimately saving accelerator operation cost.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP053

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paper received ※ 24 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019

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TUP054

How Is Flux Expulsion Affected by Geometry: Experimental Evidence and Model

cavity, experiment, SRF, accelerating-gradient

555

D. Longuevergne
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France

Measurements of magnetic sensitivity to trapped flux on several type of cavity geometries have been performed at IPNO showing a clear geometrical effect. Magnetic sensitivity depends not only on material quality but also on the cavity geometry and on the residual magnetic field orientation. A presentation of experimental data will be done. These will be as well compared to the theoretical magnetic sensitivities calculated thanks to a simple Labview routine

Poster TUP054 [1.312 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP054

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paper received ※ 03 July 2019 paper accepted ※ 04 July 2019 issue date ※ 14 August 2019

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TUP055

Nonlinear Dynamics and Dissipation of Vortex Lines Driven by Strong RF Fields

cavity, ECR, radio-frequency, electron

560

M.R.P. Walive Pathiranage, A.V. Gurevich
ODU, Norfolk, Virginia, USA

Trapped vortices can contribute significantly to a residual surface resistance of superconducting radio frequency (SRF) cavities but the nonlinear dynamics of flexible vortex lines driven by strong rf currents has not been well understood. Here we report extensive numerical simulations of large-amplitude oscillations of a trapped vortex line under the strong rf magnetic field. The rf power dissipated by an oscillating vortex segment driven by the rf Meissner currents was calculated by taking into account the nonlinear vortex line tension, vortex mass and a nonlinear Larkin-Ovchinnikov and overheating viscous drag force. We calculated the field dependence of the surface resistance Rs and showed that at low frequencies Rs(H) increases with H but as the frequency increases, Rs(H) becomes a non-monotonic function of H which decreases with H at higher fields. These results suggest that trapped vortices can contribute to the extended Q(H) rise observed on the SRF cavities.

Poster TUP055 [1.744 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP055

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paper received ※ 23 June 2019 paper accepted ※ 05 July 2019 issue date ※ 14 August 2019

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TUP056

A First-Principles Study on Magnetic Flux Trapping at Niobium Grain Boundaries

electron, cavity, simulation, radio-frequency

565

P. Garg, K.N. Solanki
Arizona State University, Tempe, USA
T.R. Bieler
Michigan State University, East Lansing, Michigan, USA
L.D. Cooley
NHMFL, Tallahassee, Florida, USA

Niobium is basis for all superconducting radio frequency cavities, a technology that accelerates charged particle beams to energy levels not possible by other means. When cavities are pushed to limits, significant heating appears at extended material defects, like grain boundaries. Therefore, it is crucial to understand how grain boundary (GB) structure and associated properties lead to trapping of magnetic field, and whether GB itself has any unusual magnetic behavior. Using first-principles calculations, external magnetic field along the GB plane was simulated within an all-electron full-potential linearized augmented plane-wave framework. A ground state with non-zero flux, indicative of flux trapping, was obtained at some grain boundaries, this outcome being influenced strongly by GB local structure. Furthermore, electronic density of states and charge-transfer calculations suggested non-zero spin polarization at grain boundaries, which may be consistent with recent observations of unusual paramagnetic magnetization as a function of specimen surface area for cavity-grade niobium.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP056

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paper received ※ 23 June 2019 paper accepted ※ 04 July 2019 issue date ※ 14 August 2019

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TUP057

Study of Flux Trapping Variability between Batches of Tokyo Denkai Niobium used for the LCLS-II Project and Subsequent 9-cell RF Loss Distribution between the Batches

cavity, SRF, FEL, superconductivity

570

A.D. Palczewski
JLab, Newport News, Virginia, USA
D. Gonnella
SLAC, Menlo Park, California, USA
O.S. Melnychuk, D.A. Sergatskov
Fermilab, Batavia, Illinois, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
During the LCLS-II project a second batch of niobium was procured from Tokyo Denkai Co Ltd in order to make additional cavities. The original production material came from Two vendors Tokyo Denkai Co., Ltd. (TD) and Ningxia Orient Tantalum Industry Co., Ltd. (OTIC/NX)). It was found TD niobium required a lower annealing temperature (900°C) to obtain satisfactory flux expulsion characteristics compared to NX which required a slightly higher annealing temperature (950°-975°C). In order to ensure the new TD material performed equivalent to the niobium produced 4 year before after 900°C annealing; each heat lot of niobium had its flux expulsion characteristics parametrized and custom thermal treatments developed for each lot. Subsequent pure heat lot 9 cell cavities were made and tested. We will look at the flux expulsion characteristics of each lot, and RF loss of the 9-cell cavities produced using the individual heat lots.

Poster TUP057 [1.446 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP057

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paper received ※ 25 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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TUP061

Gradients of 50 MV/m in TESLA Shaped Cavities via Modified Low Temperature Bake

cavity, SRF, ECR, site

586

D. Bafia, J. Zasadzinski
IIT, Chicago, Illinois, USA
D. Bafia, A. Grassellino, O.S. Melnychuk, A.S. Romanenko, Z-H. Sung
Fermilab, Batavia, Illinois, USA

This paper will discuss the 75/120 C modified low temperature bake capable of giving unprecedented accel-erating gradients of above 50 MV/m for 1.3 GHz TESLA-shaped niobium SRF cavities in CW operation. A bifurca-tion in the Q₀ vs E_acc curve is observed after retesting cavities without disassembly in between, yielding per-formance that ranges from exceptional to above state-of-the-art. Atomic Force Microscopy studies on cavity cut-outs gives a possible mechanism responsible for this branching in performance, namely, the dissociation and growth of room temperature niobium nano-hydrides that exist near the RF surface, which are made superconduct-ing only through the proximity effect. In-situ low temper-ature baking of cavity cutouts reveals a dissociation of these room temperature nano-hydrides, which could ex-plain the higher performance of cavities subject to similar in-situ heating in the dewar.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP061

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paper received ※ 23 June 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019

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TUP062

New Insights in the Quench Mechanisms in Nitrogen Doped Cavities

cavity, SRF, accelerating-gradient, factory

592

D. Bafia, J. Zasadzinski
IIT, Chicago, Illinois, USA
D. Bafia, D.J. Bice, A. Grassellino, O.S. Melnychuk, A.S. Romanenko, D.A. Sergatskov
Fermilab, Batavia, Illinois, USA
D. Gonnella
SLAC, Menlo Park, California, USA
A.D. Palczewski
JLab, Newport News, Virginia, USA

This paper will cover a systematic study of the quench in nitrogen doped cavities: three cavities were sequentially treated/reset with different doping recipes which are known to produce different levels of quench field. Analysis of mean free path and TMAP coupled with sample analysis reveals new insights on the physics of the premature quench in nitrogen doped cavities; new recipes demonstrate the possibility to increase quench fields well beyond 30 MV/m.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP062

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paper received ※ 23 June 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019

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TUP068

Study of Surface Treatment of 1.3 GHz Single-cell Copper Cavity for Niobium Sputtering

cavity, SRF, experiment, MMI

605

F.Y. Yang, J. Dai, P. He, Z.Q. Li, Y. Ma, P. Zhang
IHEP, Beijing, People’s Republic of China

Funding: This work has been supported in part by PAPS project and National Key Programme for S&T Research and Development (Grant NO.: 2016YFA0400400)
A R&D program on niobium sputtering on copper cavities has started at IHEP in 2017. Single-cell 1.3 GHz copper cavity has been chosen as a substrate. A chemical polishing system has subsequently developed and commissioned recently to accommodate the etching of both copper samples and a cavity. Different polishing agents have been tested on copper samples and later characterized. The results of these surface treatment tests are presented.

Poster TUP068 [1.228 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP068

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paper received ※ 20 June 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019

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TUP072

The Development of Niobium Sputtering on Copper Cavities at IHEP

cavity, vacuum, SRF, photon

613

J. Dai, P. He, Z.Q. Li, Y. Ma, F.Y. Yang, P. Zhang
IHEP, Beijing, People’s Republic of China

A R&D program focusing on niobium sputtering on copper cavities started at IHEP in 2017. Single-cell 1.3 GHz elliptical cavity shape has been initially chosen as sputtering substrate. A magnetron sputtering system have been developed in 2018. In addition, a surface treatment facility to polish the copper substrate before sputtering has been developed and commissioned. This paper will present the Nb/Cu coating activities at IHEP.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP072

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paper received ※ 19 June 2019 paper accepted ※ 04 July 2019 issue date ※ 14 August 2019

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TUP073

Superconducting Thin Films Characterization at HZB with the Quadrupole Resonator

cavity, SRF, quadrupole, FEL

616

D.B. Tikhonov, S. Keckert, J. Knobloch, O. Kugeler, Y. Tamashevich
HZB, Berlin, Germany
A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA

Funding: EASITrain - European Advanced Superconductivity Innovation and Training. This Marie Sklodowska-Curie Action Innovative Training Networks founded by H₂020 under Grant Agreement no. 764879
Superconducting thin films have great potential as post-Nb material for use in SRF applications in future accelerators and industry. To test the RF-performance of such films in practice, would require the building and coating of a full RF cavity. Deposition of thin films on such scales in test facilities are challenging, in particular when curved surfaces have to be coated. This greatly complicates their systematic research. In this contribution we report on the method we use to characterize small and flat thin film samples (Deposited onto both Nb and Cu substrates) in an actual cavity named the Quadrupole Resonator (QPR). We also summarize the latest measurement results of NbTiN thin films. The Quadrupole Resonator at HZB is a tool that is able to perform SRF characterizations at frequencies ~415, 847, 1300 MHz with RF fields using an RF-DC power compensation technique.

Poster TUP073 [2.318 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP073

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paper received ※ 23 June 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019

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TUP075

New Progress for Nb Sputtered 325 MHz QWR Cavities in IMP

cavity, target, experiment, SRF

621

F. Pan, H. Guo, Y. He, T.C. Jiang, C.L. Li, M. Lu, T. Tan
IMP/CAS, Lanzhou, People’s Republic of China

Comparing with bulk niobium cavities, the Nb/Cu cavities feature a much better stability at 4.5 K. Last year, two 325 MHz QWR copper cavities coated with biased DC diode sputterred Nb for CiADS has been accomplished at IMP. But vertical tests showed the cavities had low Q₀ at 4 K. To solve the issue, a new coating system was designed and built. The sputtering target was redesigned and manufactured. The coating parameters were selected again and auxiliary heating was used to control the coating temperature in the process of sputtering. The power and Ar pressure during coating were also carefully selected. The paper covers resulting film characters, vertical tests with the evolution of the sputtering process, and improvements we made since last year.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP075

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paper received ※ 22 June 2019 paper accepted ※ 14 August 2019 issue date ※ 14 August 2019

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TUP076

Electrochemical Deposition of Nb₃Sn on the Surface of Cu Substrates

cavity, site, controls, SRF

624

M. Lu, Q.W. Chu, Y. He, Z.Q. Lin, F. Pan, T. Tan, Z.Q. Yang
IMP/CAS, Lanzhou, People’s Republic of China

Coating superconducting Nb₃Sn thin film on the inner surface of a superconducting RF cavity is one of the most promising approaches to improve the performance of the accelerating cavity. Compared with traditional evaporation and sputtering, electrochemical coating has the advantages on process simplicity, low cost and mass production. However, the conventional electroplating, because of its low growth temperature and aqueous reaction environment, tends to produce porous, loosely bonded, and often contaminated film. All these properties result in excessive pinning center and deteriorate the superconducting radio frequency cavities performance. In this paper, a new method including multi-layer electroplating and heat treatment is used to deposit Nb₃Sn thin film on top of copper substrates. Important growth parameters, e.g. electrical current density, layer thickness ratio, and annealing temperature are studied. The morphology of the film surfaces was observed by scanning electron microscope (SEM) and the structure of the film was analyzed by X-ray diffraction (XRD). The results showed that a flat and uniform Nb₃Sn layer on copper can be obtained, and the thickness is about 7 micron.

Poster TUP076 [0.716 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP076

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paper received ※ 23 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019

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TUP079

Deposition of Nb₃Sn Films by Multilayer Sequential Sputtering for SRF Cavity Application

cavity, SRF, site, FEL

637

Md.N. Sayeed, H. Elsayed-Ali
ODU, Norfolk, Virginia, USA
M.C. Burton, G.V. Eremeev, C.E. Reece, A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA
U. Pudasaini
The College of William and Mary, Williamsburg, Virginia, USA

Nb₃Sn is considered as an alternative of Nb for SRF accelerator cavity application due to its potential to obtain higher quality factors and higher accelerating gradients at a higher operating temperature. Magnetron sputtering is one of the effective techniques that can be used to fabricate Nb₃Sn on SRF cavity surface. We report on the surface properties of Nb₃Sn films fabricated by sputtering multiple layers of Nb and Sn on sapphire and niobium substrates followed by annealing at 950°C for 3 h. The crystal structure, film microstructure, composition and surface roughness were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM). The RF performance of the Nb₃Sn coated Nb substrates were measured by a surface impedance characterization system. We also report on the design of a multilayer sputter deposition system to coat a single-cell SRF cavity.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP079

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paper received ※ 22 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019

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TUP093

Summary of FRIB Cavity Processing in the SRF Coldmass Processing Facility and Lessons Learned

cavity, SRF, linac, controls

680

E.S. Metzgar, B.W. Barker, K. Elliott, W. Hartung, L. Popielarski, G.V. Simpson, D.R. Victory, J.D. Whaley
FRIB, East Lansing, Michigan, USA

Funding: Work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661 and the National Science Foundation under Cooperative Agreement PHY-1102511.
Baseline coldmass production for the linear particle accelerator at the Facility for Rare Isotope Beams (FRIB) is nearing completion. This paper will review the processing of cavities through the FRIB superconducting radio frequency (SRF) coldmass production facility focusing on chemical processing and high-pressure rinsing. Key processing data will be compiled and correlations between processing variables and cavity RF testing results will be examined.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP093

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paper received ※ 22 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019

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THFUA1

RF Characterization of an S-I-S’ Multilayer Sample

quadrupole, ECR, SRF, cavity

800

S. Keckert, J. Knobloch, O. Kugeler, D.B. Tikhonov
HZB, Berlin, Germany
A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA

S-I-S’ multilayers promise to boost the performance of bulk superconductors in terms of maximum field and surface resistance. At HZB, RF-surface resistance measurements were performed with a Quadrupole Resonator (QPR) and an S-I-S’ sample (75 nm NbTiN on 15 nm AlN insulator on bulk Nb) prepared at JLab. Measurements were performed at 414, 845, and 1286 MHz at sample temperatures from 2 K up to well above the transition temperature of NbTiN of ~17.3 K. The Rs exhibits an unexpected temperature dependence: Rather than rising monotonically, as expected from BCS theory, a local maximum is observed. There is a temperature range where Rs decreases with increasing temperature. Such behavior indicates that an additional interaction between the superconducting layers may have to be included in the surface resistance model. Measurements of the baseline Nb sample prior to coating exhibited no such behavior; hence systematic measurement errors can be excluded as the explanation. The maximum field was limited by a hard magnetic quench near 20 mT, close to Hc1 of NbTiN, suggesting that the sample is limited by early flux penetration.

Slides THFUA1 [1.004 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THFUA1

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paper received ※ 22 June 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019

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THFUA6

Nb₃Sn Films for SRF Cavities: Genesis and RF Properties

cavity, SRF, interface, experiment

810

U. Pudasaini, M.J. Kelley
The College of William and Mary, Williamsburg, Virginia, USA
J.W. Angle, M.J. Kelley, J. Tuggle
Virginia Polytechnic Institute and State University, Blacksburg, USA
G.V. Eremeev, M.J. Kelley, C.E. Reece
JLab, Newport News, Virginia, USA

Funding: Partially authored by Jefferson Science Associates under contract no. DE¬AC05¬06OR23177. Supported by Office of High Energy Physics under grants DE-SC-0014475 to the College of William and DE-SC-0018918 to Virginia Tech.
Understanding of Nb₃Sn nucleation and growth is essential to the progress with Nb₃Sn vapor diffusion coatings of SRF cavities. Samples representing different stages of Nb₃Sn formation have been produced and examined to elucidate the effects of nucleation, growth, process conditions, and impurities. Nb₃Sn films from few hundreds of nm up to ~15 µm were grown and characterized using AFM, SEM/EDS, XPS, EBSD, SIMS, and SAM. Microscopic examinations of samples suggest the mechanisms behind Nb₃Sn thin film nucleation and growth. RF measurements of coated cavities were combined with material characterization of witness samples to adapt the coating process in "Siemens" coating configuration. Understanding obtained from sample studies, applied to cavities, resulted in Nb₃Sn cavity with quality factor 2 ×10¹⁰ at 15 MV/m accelerating gradient at 4 K, without "Wuppertal" Q-slope. We discuss the genesis of the Nb₃Sn thin film in a typical tin vapor diffusion process, and its consequences to the coating of SRF cavities.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THFUA6

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paper received ※ 23 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019

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THFUB1

Nb₃Sn at Fermilab: Exploring Performance

cavity, SRF, multipactoring, superconductivity

818

S. Posen, J. Lee, O.S. Melnychuk, Y.M. Pischalnikov, D.A. Sergatskov, B. Tennis
Fermilab, Batavia, Illinois, USA
J. Lee, D.N. Seidman
NU, Evanston, Illinois, USA

Fermilab’s Nb₃Sn coating program produced its first 1.3 GHz single cell cavities in early 2017 and since then has explored the performance of Nb₃Sn on a wide variety of cavity substrates and performed microscopic studies down to atomic resolution. Results to present in this talk include a study of frequency dependence from 650 MHz to 1.3 GHz of BCS resistance, residual resistance, and magnetic flux sensitivity. We show microscopic studies performed in collaboration with Northwestern University¿s Materials Science and Engineering Department of limitation mechanisms in Nb₃Sn, including thin film regions and tin segregation at grain boundaries, discussing correlations with RF performance and mechanisms for the formation of these features during growth. Finally, we present results of the first 1.3 GHz 9-cell cavity coated with Nb₃Sn.

Slides THFUB1 [27.194 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THFUB1

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paper received ※ 29 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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THP002

Metallographic Polishing Pathway to the Future of Large Scale SRF Facilities

SRF, cavity, embedded, cryogenics

828

O. Hryhorenko, M. Chabot
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
C.Z. Antoine
CEA-IRFU, Gif-sur-Yvette, France
D. Longuevergne
FLUO, Orsay, France

Funding: The financial support from the European Nuclear Science and Applications Research 2 (ENSAR 2) under grant agreeement N°654002.
Optimization of SRF cavities mainly focuses on pushing the limits of bulk Niobium, cost reduction of cavity fabrication and development of new SRF materials for future accelerators (ILC, FCC). Nowadays chemical etching is the only surface treatment used to prepare SRF surface made of Nb. However the operational cost of chemical facilities is high and these present a very bad ecological footprint. The search of an alternative technique could make the construction of these future large scale facilities possible. Metallographic polishing (MP) is a candidate not only for bulk Nb treatment, but could also provide the mirror-finished substrate for alternative SRF thin films deposition. Recent R&D studies, conducted at IPNO & IRFU, focused on the development of 2-steps MP procedure of Nb flat samples. Roughness of polished surface has been proven better than standard EP treatment and less polluted than CBP. MP provides on flat surfaces a high removal rate (above 1 µm/min) and high reproducibility. The paper will describe the optimized method and present all the surface analysis performed. The first RF characterization of a polished disk will be presented.

Poster THP002 [2.902 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP002

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paper received ※ 20 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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THP003

Results on Bulk Niobium Surface Resistance Measurement With Pillbox Cavity on TE011 and TE012 Modes

cavity, coupling, SRF, experiment

833

G. Martinet
Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France

Surface measurement of superconducting samples is required to characterize processes of bulk niobium preparation for SRF resonators. In order to reduce characterization cost and improve measurement performances, a pill-box cavity has been developed at IPN Orsay. Using TE011 and TE012 modes, we describe the latest results based on calorimetric method.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP003

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paper received ※ 23 June 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019

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THP004

Design and Fabrication of a Quadrupole-Resonator for Sample R&D

quadrupole, cavity, SRF, simulation

838

R. Monroy-Villa, D. Reschke, M. Wenskat
DESY, Hamburg, Germany
W. Hillert, R. Monroy-Villa, M. Wenskat
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
S. Keckert, O. Kugeler, D.B. Tikhonov
HZB, Berlin, Germany
P. Putek, S.G. Zadeh, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
U. van Rienen
University of Rostock, Rostock, Germany

Being able to obtain BCS and material properties from the same surface is necessary to gain a fundamental understanding of the evolution of SRF surfaces. A test resonator which will allow to obtain BCS properties from samples is currently under development at the University of Hamburg and DESY and is based on the Quadrupole Resonators developed and operated at CERN and HZB. The current status of the necessary infrastructure, the procurement process and design considerations are shown. In addition, an outline of the planed R&D project with the Quadrupole Resonator will be presented and first RF measurements and surface analysis results of samples will be shown

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP004

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paper received ※ 23 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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THP007

In-Situ EXAFS Investigations of Nb-Treatments in N₂ at Elevated Temperatures

experiment, cavity, vacuum, lattice

842

P. Rothweiler, B. Bornmann, J. Klaes, D. Lützenkirchen-Hecht, R. Wagner, S. von Polheim
University of Wuppertal, Wuppertal, Germany

Funding: We gratefully acknowledge financial support by the German Federal Ministry of Education and Research (BMBF) under project No. 05H15PXRB1.
Smooth polycrystalline Nb metal foils were exposed to dilute N₂ and Kr atmospheres at elevated temperatures of up to 900°C. Transmission mode X-ray absorption spectroscopy (EXAFS) experiments were used to study the resulting changes of the atomic short range order structure in-situ. EXAFS data were collected prior to any heat treatment as well as during the different process steps at elevated temperatures with a time resolution of about 1 s, and the samples were also studied after cooling to room temperature. In general, only very small changes of the Nb-EXAFS data could be detected after the processing in N₂-atmospheres, and no evidence for bulk formation of Nb-nitrides was found. In contrast, the quantitative EXAFS data evaluation revealed slightly distorted Nb-Nb coordinations, suggesting that N-atoms are increasingly incorporated on octahedral interstitial sites in the host lattice with increasing N₂-exposure. For the treatments in Kr-atmospheres, simultaneous measurements are feasible at both the K-edge of the Nb host and the Kr dopant. Those studies gave clear evidence for a Kr uptake during the heat treatment, and will be discussed in more detail at the conference.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP007

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paper received ※ 23 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019

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THP008

The Technical Study of Nb₃Sn Film Deposition on Copper by HiPIMS

SRF, cavity, electron, superconductivity

846

L. Xiao, X.Y. Lu, W.W. Tan, D. Xie, Y. Yang, L. Zhu
PKU, Beijing, People’s Republic of China

Our work is mainly focused on the deposition methods of Nb₃Sn films on Cu substrates and film‘s properties. The superconducting transition temperature(Tc) of Nb₃Sn film is 12K. There are diffraction peaks of Nb₃Sn in the X-ray diffraction patterns in which without diffraction peaks of copper compounds. Scanning electron micro-structures of Nb₃Sn film reflect its nice compactness and binding force between film and substrate.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP008

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paper received ※ 23 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019

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THP009

Pulse Laser Annealing of Niobium Film on Copper for SRF Cavities

laser, cavity, experiment, interface

848

Y. Yang, X.Y. Lu, W.W. Tan, L. Xiao, D. Xie, L. Zhu
PKU, Beijing, People’s Republic of China

Thin film cavities were proposed as the most promis-ing next generation superconducting cavities. The chal-lenges are improving the surface superconducting per-formance and reducing defects of the coating film, which can be greatly solved by laser annealing. Laser annealing system has been set up in Peking University, and experi-ments with niobium thin film sample have been carried out. Superconducting performance and other properties of Nb/Cu samples before and after annealing were com-pared. Recrystallization happened and surface structure improved a lot according to the results.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP009

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paper received ※ 22 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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THP010

The Mechanism of Electropolishing of Niobium from Choline Chloride-based Deep Eutectic Solvents

ECR, polarization, impedance, cavity

852

Q.W. Chu, H. Guo, S.C. Huang, A.D. Wu, Z.M. You
IMP/CAS, Lanzhou, People’s Republic of China

Funding: National Natural Science Foundation (11705252)
The mechanism of electropolishing of niobium (Nb) from choline chloride-based deep eutectic solvent (DES) was studied by anodic polarization tests and electrochemical impedance spectroscopy (EIS) using a Nb rotating disk electrode (RDE). Based on the results of an anodic polarisation test, the electropolishing of Nb is mass transport controlled. EIS results are consistent with the compact salt film mechanism for niobium electropolishing in this electrolyte. The influence of rotation rate, applied potential and electrolyte temperature on the electropolishing mechanism of Nb was investigated. As the applied potential positively shift, Rct, Rp and L increase, CPE decrease and Rs unchanged. The increase in rotation rate and electrolyte temperature leads to a decrease of Rs, Rct, Rp and L, and an increase of CPE.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP010

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paper received ※ 18 June 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019

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THP011

Niobium Semiproducts for the Superconducting Strands and SRF Cavities in Russia

ECR, SRF, cavity, target

857

M.V. Alekseev, I.M. Abdyukhanov, V.A. Drobyshev, M.V. Kravtsova, M.V. Krylova, P.A. Lykianov, K.A. Mareev, V.I. Pantsyrny, M.V. Polikarpova, M.M. Potapenko, A.G. Silaev, A.S. Tsapleva
SC A A Bochvar High-Technology Research Institute of Inorganic Materials, Moscow, Russia
M.Y. Shlyakhov, S.M. Zernov
JSC - TVEL, Moscow, Russia

The melting regimes of the niobium ingots with high chemical purity and low hardness for the Nb₃Sn, NbTi and other superconducting materials manufacture have been developed at SC "VNIINM". Using this niobium material and by the SC "VNIINM" manufacture regimes at the SC "Chepetsky Mechanical Plant" 220 tons of Nb₃Sn and NbTi strands for ITER and 12 km of Nb₃Sn strands for HL-LHC (CERN) with the required characteristics have been successfully produced. The review of the characteristics of the different semiproducts (sheets, tubes, rods), made in Russia from the special grade niobium, and of the superconducting strands, manufactured with the use of them, is presented in the paper. The ways of the further improvement of the niobium ingots melting regimes and niobium sheets deformation and annealing regimes with the target of achieving RRR > 300 for the SRF cavities application are discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP011

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paper received ※ 23 June 2019 paper accepted ※ 04 July 2019 issue date ※ 14 August 2019

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THP012

Assessment of the Mechanical Properties of Ultra-High Purity Niobium After Cold Work and Heat Treatment With the HL-LHC Crab Cavities as Benchmark

cavity, ECR, operation, simulation

860

A. Gallifa Terricabras, A. Amorim Carvalho, I. Aviles Santillana, S. Barrière, R. Calaga, E. Cano-Pleite, O. Capatina, M.D. Crouvizier, L. Dassa, M.S. Meyer, N. Valverde Alonso
CERN, Geneva, Switzerland
M. Benke, A.B. Palotas, G. Szabó, M. Szűcs
University of Miskolc, Faculty of Materials Science and Engineering, Miskolc-Egyetemváros, Hungary
A. Hlavács, G.J. Krallics, V. Mertinger, M. Sepsi
University of Miskolc, Miskolc, Hungary

The High Luminosity Large Hadron Collider (HL-LHC) is the upgrade of the world’s largest particle collider; it will allow the full exploitation of the LHC potential and its operation beyond 2025. An essential part of the HL-LHC project are the Crab Cavities, that are particle deflecting SRF cavities of non-axisymmetric shape made of bulk ultra-high purity Nb. Since the cavities are produced by complex metal sheet forming processes, followed by a heat treatment (HT) for H outgassing (650 °C, 24 h), there is uncertainty on their mechanical properties after manufacturing and in service conditions (2 K). Mechanical tests at room temperature have been conducted on RRR300 pure Nb samples. The samples were previously submitted, by cold cross-rolling, to different levels of plastic deformation representative of the effective plastic strain seen by the Nb sheets during forming operations. Moreover, a comparison of the mechanical properties of cold cross-rolled samples before and after HT has been established. Results of evolution of the microstructure and hardness are also presented. This study can be of interest for Nb cavities to be sub-mitted to HT at 650 °C, and may help to push the design of novel SRF cavities.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP012

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paper received ※ 22 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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THP014

First Direct Imaging and Profiling TOF-SIMS Studies on Cutouts from Cavities Prepared by State-of-the-Art Treatments

cavity, SRF, GUI, superconductivity

866

A.S. Romanenko, A. Grassellino, M. Martinello, Y. Trenikhina
Fermilab, Batavia, Illinois, USA
D. Bafia
Illinois Institute of Technology, Chicago, Illinois, USA

Funding: This work has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
Small amounts of interstitial impurities in the penetra-tion depth of superconducting radio frequency (SRF) cavities have a dramatic effect on the quality factors and maximum accelerating gradients. Here we report the first TOF-SIMS studies of cutouts from cavities prepared by all modern surface treatments, which allow a direct corre-lation of the impurity distribution with the observed cavity performance. Imaging capability of our instrument allows to avoid the possible issues associated with the ‘‘ghost’’ depth profiles appearing as a consequence of particulate surface contamination, which likely caused the inconclusive SIMS results on e.g. oxygen diffusion in the past.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP014

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paper received ※ 02 July 2019 paper accepted ※ 04 July 2019 issue date ※ 14 August 2019

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THP017

Crystallographic Characterization of Nb₃Sn Coatings and N-Doped Niobium via EBSD and SIMS

interface, SRF, electron, cavity

871

J.W. Angle, M.J. Kelley, J. Tuggle
Virginia Polytechnic Institute and State University, Blacksburg, USA
G.V. Eremeev, M.J. Kelley, C.E. Reece
JLab, Newport News, Virginia, USA
M.J. Kelley, U. Pudasaini
The College of William and Mary, Williamsburg, Virginia, USA

Historically, niobium has been used as the superconducting material in SRF cavities. Due the high operational costs, other materials are currently being considered. Nb₃Sn coatings have been investigated over the past several decades, motivated by potentially higher operating temperatures. More recently niobium has been doped with nitrogen to improve the quality factor (Q). Currently, a need for better understanding still exists for both mechanisms. EBSD has been shown to be a viable technique to determine the crystallographic orientation and the size of the Nb₃Sn grains. The EBSD maps obtained show a bimodal distribution of grain sizes with smaller Nb₃Sn grains found present near the Nb₃Sn/Nb interface. In addition to the Nb₃Sn coatings, N-doped niobium coupons were analyzed by EBSD and found that the coupon had preferred surface orientation. The EBSD analysis was found to be vital as specific grains could be targeted in SIMS to better understand the diffusion of nitrogen with respect to crystal orientation.

Poster THP017 [2.571 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP017

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paper received ※ 23 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019

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THP020

Study of Dislocation Content Near Grain Boundaries using Electron Channeling Contrast Imaging and its Effect on Superconducting Properties of Niobium

cavity, electron, SRF, superconductivity

876

M. Wang, T.R. Bieler
Michigan State University, East Lansing, Michigan, USA
S. Balachandran, S. Chetri, P.J. Lee
NHMFL, Tallahassee, Florida, USA
S. Chetri, A. Polyanskii
ASC, Tallahassee, Florida, USA
C. Compton, C. Compton
FRIB, East Lansing, Michigan, USA
C. Compton
NSCL, East Lansing, Michigan, USA

Funding: U.S. Department of Energy. National Science Foundation Cooperative Agreement No. DMR-1157490 (-2017) DMR-1644779 (2018-) and the State of Florida
Trapped micro-Tesla levels of magnetic flux degrade the performance of Nb superconducting radio frequency (SRF) accelerators. Recent studies have revisited the role of small deformation (dislocation substructure influence) on cavity performance. However, the link between microstructural defects and mechanisms leading to poor performance is still unresolved. To examine the mechanism of flux pinning by dislocations and grain boundaries, systematic studies on bi-crystal Nb tensile samples were designed with strategically chosen orientation relationships between neighboring crystals with respect to the grain boundaries. Laue X-ray diffraction and electron backscatter diffraction analysis was used to measure crystal orientations of a large-grain Nb slice, from which the bi-crystals were extracted. Dislocation structures near the grain boundaries were characterized before and after 5% tensile deformation using electron channeling contrast imaging (ECCI), after which the magnetic flux behavior was observed using cryogenic magneto-optical imaging (MOI). We discuss the conditions under which we observe increased flux pinning in regions of high dislocation density.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP020

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paper received ※ 23 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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THP041

Impact of the Cu Substrate Surface Preparation on the Morphological, Superconductive and RF Properties of the Nb Superconductive Coatings

laser, cavity, SRF, radiation

935

C. Pira, E. Chyhyrynets
INFN/LNL, Legnaro (PD), Italy
C.Z. Antoine
CEA-IRFU, Gif-sur-Yvette, France
X. Jiang, S.B. Leith, M. Vogel
University Siegen, Siegen, Germany
A. Katasevs, J. Kaupužs, A. Medvids, P. Onufrijevs
Riga Technical University, Riga, Latvia
O. Kugeler
HZB, Berlin, Germany
O.B. Malyshev, R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
R. Ries, E. Seiler
Slovak Academy of Sciences, Institute of Electrical Engineering, Bratislava, Slovak Republic
A. Sublet
CERN, Meyrin, Switzerland

Funding: This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement No 730871.
Nowadays, one of the main issues of the superconducting thin film resonant cavities is the Cu surface preparation. A better understanding of the impact of copper surface preparation on the morphological, superconductive (SC) and RF properties of the coating, is mandatory in order to improve the performances of superconducting cavities by coating techniques. ARIES H₂020 collaboration includes a specific work package (WP15) to study the influence of Cu surface polishing on the SRF performances of Nb coatings that involves a team of 8 research groups from 7 different countries. In the present work, a comparison of 4 different polishing processes for Cu (Tumbling, EP, SUBU, EP+SUBU) is presented through the evaluation of the SC and morphological properties of Nb thin film coated on Cu planar samples and QPR samples, polished with different procedures. Effects of laser annealing on Nb thin films have also been studied. Different surface characterizations have been applied: roughness measurements, SEM, EDS, XRD, AFM, and thermal and photo-stimulated exoelectrons measurements. SC properties were evaluated with PPMS, and QPR measurements will be carry out at HZB in the beginning of 2019.

Poster THP041 [3.196 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP041

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paper received ※ 23 June 2019 paper accepted ※ 05 July 2019 issue date ※ 14 August 2019

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THP043

Deposition Parameter Effects on Niobium Nitride (NbN) Thin Films Deposited Onto Copper Substrates with DC Magnetron Sputtering

site, cathode, ECR, cavity

945

S.B. Leith, X. Jiang, M. Vogel
University Siegen, Siegen, Germany
R. Ries, E. Seiler
Slovak Academy of Sciences, Institute of Electrical Engineering, Bratislava, Slovak Republic

Funding: The EASITrain project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant No 764879.
As part of efforts to improve the performance of SRF cavities, to that prescribed by future operating requirements, alternative materials are currently being investigated. NbN is one of the alternatives under investigation to provide these better performance figures. In this contribution, a summary of results from an investigation into DC magnetron sputtered NbN thin films deposited onto copper substrates is presented. The copper substrates were prepared using a mechanical polishing process, followed by a chemical etching process. The NbN films were prepared in a large scale commercial coating system. A high and low value for the substrate temperature, process pressure, bias voltage, cathode power, nitrogen gas percentage, and the working gas type, using either Argon or Krypton, constitute the parameters of this study. The base pressure of the system prior to deposition was 5x10⁷ hPa for all coatings. The resulting films have been characterised using various surface characterisation methods to determine the effects of the deposition parameters during the film growth process. The deposition parameters have been optimised based on the characterisation results.

Poster THP043 [1.169 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP043

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paper received ※ 23 June 2019 paper accepted ※ 29 June 2019 issue date ※ 14 August 2019

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THP044

RF Characterization of Novel Superconducting Materials and Multilayers

cavity, SRF, site, plasma

950

T.E. Oseroff, M. Liepe, Z. Sun
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
B. Moeckly
STI, Santa Barbara, California, USA
M.J. Sowa
Veeco-CNT, Medford, USA

Cutting edge SRF technology is likely approaching the fundamental limitations of niobium cavities operating in the Meissner state. This combined with the obvious advantages of using higher critical temperature superconductors and thin film depositions leads to interest in the RF characterization of such materials. A TE mode niobium sample host cavity was used to characterize the RF performance of 5" (12.7 cm) diameter sample plates as a function of field and temperature at 4 GHz. Materials studied include MgB₂ and thin film atomic layer deposition (ALD) NbN and NbTiN on Nb substrates. These higher critical temperature superconductors all having coherence lengths on the order of a few nm. It is therefore likely that defects on the order of the coherence lengths will cause early flux penetration well before the theorized superheating field of an ideal superconducting surface. Superconductor-insulator-superconductor (SIS) multilayers have been proposed as a mechanism of arresting these early penetration flux avalanches and are therefore studied here as well, using the same NbN and NbTiN films, but over thin layers of insulating AlN on Nb substrates.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP044

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paper received ※ 02 July 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019

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THP045

Improvements to the Cornell Sample Host System

cavity, SRF, coupling, quadrupole

956

T.E. Oseroff, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

RF characterization of arbitrary superconducting samples has been of interest for many years but, due to the experimental complexities, has never been achieved to its full potential. A TE mode niobium sample host cavity has been used at Cornell to characterize the RF performance of 5" (12.7 cm) diameter sample plates. It was designed and built in 2012 – 2013 and since then has encountered a range of problems. The focus of this work is to highlight these and to present solutions to assist future researchers hoping to design novel RF characterization instruments. Topics covered include coupler design, cryostat support structure, sample preparation, and a discussion of potential systematic errors introduced by the data extraction and calibration methods applied to this device.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP045

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paper received ※ 01 July 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019

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THP047

Progress of TRIUMF Beta-SRF Facility for Novel SRF Materials

SRF, cavity, optics, radio-frequency

964

E. Thoeng
UBC & TRIUMF, Vancouver, British Columbia, Canada
R.A. Baartman, P. Kolb, R.E. Laxdal, B. Matheson, G. Morris, N. Muller, S. Saminathan
TRIUMF, Vancouver, Canada
T. Junginger
UVIC, Victoria, Canada

Funding: NSERC (Natural Sciences and Engineering Research Council of Canada)
SRF cavities made with bulk Nb have been the backbone of high-power modern linear accelerators. Demands for higher energy and more efficient linear accelerators, however, have strained the capabilities of bulk Nb close to its fundamental limit. Several routes have been proposed using thin film novel superconductors (e.g. Nb₃Sn), SIS multilayer, and N-doping. Beta-NMR techniques are more suitable for the characterization of Meissner state in these materials, due to the capability of soft-landing radioactive ions on the nanometer scale of London penetration depth, as compared to micrometer probe of the muSR technique. Upgrade of the existing beta-NQR beamline, combined with the capability of high parallel magnetic field (200 mT) are the scope of the beta-SRF facility which has been fully funded. All hardware required for the upgrade has also been procured. The status of the commissioning, which is currently in phase I, is reported here, together with the future schedule of phase II with the fully installed beta-SRF beamline. Finally, the detail layout of the completed beamline and sample requirements will be included in this paper which might be of interest of future users.

Poster THP047 [1.372 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP047

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paper received ※ 23 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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THP055

Magnetic Field Induced by Thermo Electric Current in LCLS-II Cryomodules

cavity, cryomodule, SRF, vacuum

1003

G. Wu, S.K. Chandrasekaran
Fermilab, Batavia, Illinois, USA

Funding: The work is supported by Fermilab which is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
Seebeck effect of metals play an important role in cryomodule design. As cryomodule cools down from room temperature down to nominal cavity operating temperature, components in a cryomodule experiences different temperatures. Some components such as power couplers cross from room temperature to 2 K. Thermo electric current forms loops circulating through and around cavities. Such current loops will generate additional magnetic field that could be trapped into cavity wall during superconducting transition as well as during cavity quench. These trapped field can degrade cavity quality factor and increase heat load. Simple circuit model is proposed and compared to calculated trapped field during cryomodule tests.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP055

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paper received ※ 26 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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THP080

Status of the All Superconducting Gun Cavity at DESY

cavity, cathode, SRF, gun

1087

E. Vogel, S. Barbanotti, A. Brinkmann, Th. Buettner, J.I. Iversen, K. Jensch, D. Klinke, D. Kostin, W.-D. Möller, A. Muhs, J. Schaffran, M. Schmökel, J.K. Sekutowicz, S. Sievers, L. Steder, N. Steinhau-Kühl, A. Sulimov, J.H. Thie, H. Weise, M. Wenskat, M. Wiencek, L. Winkelmann, B. van der Horst
DESY, Hamburg, Germany

At DESY, the development of a 1.6-cell, 1.3 GHz all superconducting gun cavity with a lead cathode attached to its back wall is ongoing. The special features of the structure like the back wall of the half-cell and cathode hole require adaptations of the procedures used for the treatment of nine-cell TESLA cavities. Unsatisfactory test results of two prototype cavities motivated us to re-consider the back-wall design and production steps. In this contribution we present the status of the modified cavity design including accessories causing accelerating field asymmetries, like a pick up antenna located at the back wall and fundamental power- and HOM couplers. Additionally, we discuss preliminary considerations for the compensation of kicks caused by these components.

Poster THP080 [7.365 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP080

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paper received ※ 20 June 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019

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THP089

Development of Superconducting RF Double Spoke Cavity at IHEP

cavity, coupling, SRF, linac

1114

Q. Zhou, F.S. He, W.M. Pan
IHEP, Beijing, People’s Republic of China

The China Spallation Neutron Source (CSNS) is de-signed to produce spallation neutrons. CSNS upgrade is planned to increase beam power by inserting a SRF linac after drift tube linac (DTL). IHEP is developing a 325MHz double spoke cavity at ¿0 of 0.5 for the CSNS SRF linac. The cavity shape was optimized to minimize Ep/Ea while keeping Bp/Ep reasonably low. Meanwhile, mechanical design was applied to check stress, Lorentz force detuning and microphonic effects, and to minimize pressure sensitivity. A new RF coupling scheme was pro-posed to avoid electrons hitting directly on ceramic win-dow. After fabrication and post processing of cavity, the cavity reached Bp of 120mT at E_acc = 13.8MV/m and Q₀ = 1.72·10¹⁰ under vertical test at 2K.

Poster THP089 [2.176 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP089

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paper received ※ 22 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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THP095

Direct Measurement of Thermoelectric Currents During Cool Down

cavity, simulation, experiment, coupling

1139

A.E. Ivanov, F. Gerigk, A. Macpherson
CERN, Geneva, Switzerland

In recent years there has been much discussion on thermoelectric effects and their role in flux expulsion during cool down of SRF cavities. Magnetic field is often measured to asses both flux expulsion as the cavity undergoes superconducting transition, and thermoelectric currents due to spatial thermal gradients. As a complementary view, in this paper we show direct measurement of the thermoelectric current independent from the expulsion measurement of the magnetic field. In our setup the azimuthally symmetric cavity is vertically installed and the thermal gradient is along the symmetry axis allowing to describe the cool down behavior of the thermoelectric current using simple coupled simulations.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP095

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paper received ※ 21 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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THP096

ESS Prototype Cavities Developed at CEA Saclay

cavity, SRF, HOM, linac

1143

E. Cenni
CEA-IRFU, Gif-sur-Yvette, France
M. Baudrier, P. Carbonnier, G. Devanz, X. Hanus, L. Maurice, J. Plouin, D. Roudier, P. Sahuquet
CEA-DRF-IRFU, France

The ESS elliptical superconducting Linac consists of two types of 704.42 MHz cavities, medium and high beta, to accelerate the beam from 216 MeV up to the final energy at 2 GeV. The medium and high-beta parts of the Linac are composed of 36 and 84 elliptical cavities, with geometrical beta values of 0.67 and 0.86 respectively. CEA Saclay is in charge of the cavity prototypes that is designing, manufacturing, testing and integrating them into demonstrator cryomodules. We have manufactured 6 medium beta and 5 high beta cavities and we present here the latest results concerning these activities.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP096

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paper received ※ 22 June 2019 paper accepted ※ 02 July 2019 issue date ※ 14 August 2019

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THP100

Insight into DESY’s Test Laboratory for Niobium Raw Material and Semi-finished Products

cavity, FEL, SRF, controls

1157

J.I. Iversen, A. Brinkmann, A. Ermakov, A. Muhs, J. Ziegler
DESY, Hamburg, Germany

DESY has started setting up a test laboratory for niobium more than 20 years ago. The initial application was to assure required surface quality of niobium sheets before its forming to half cells for the 1.3 GHz SRF Tesla shape cavities. As a first test equipment DESY developed a basic eddy current test device which was refined continuously. Since that time the laboratory grew with the requirements on R&D activities for niobium raw material and its semi-finished products. To be able to assure the Quality of niobium products needed for the European XFEL series cavity production, the Lab¿s infrastructure was updated significantly. Now the capabilities of the test laboratory cover the investigation of the fundamental physical properties of various materials including for example mechanical properties, surface, microstructure and chemical composition analysis. The Quality Assurance for the European XFEL was performed successfully on an outstanding level and in the meantime the laboratory was used for several other projects like LCLS-II and ESS. We present DESY’s test infrastructure as well as applied methods for the Quality Assurance and R&D activities and we report about experiences.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP100

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paper received ※ 25 June 2019 paper accepted ※ 30 June 2019 issue date ※ 14 August 2019

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FRCAA3

Industrial Cavity Production: Lessons Learned to Push the Boundaries of Nitrogen-Doping

cavity, cryomodule, SRF, linac

1199

D. Gonnella, S. Aderhold, A. Burrill, M.C. Ross
SLAC, Menlo Park, California, USA
E. Daly, G.K. Davis, F. Marhauser, A.D. Palczewski, K.M. Wilson
JLab, Newport News, Virginia, USA
A. Grassellino, C.J. Grimm, T.N. Khabiboulline, O.S. Melnychuk, S. Posen, D.A. Sergatskov
Fermilab, Batavia, Illinois, USA

Funding: Work supported by US DOE Contract DE-AC02-76SF00515.
Nitrogen doping has been proven now in several labs to enhance Q₀ values of 1.3 GHz cavities in the gradient domain favored by CW operation. The choice of doping for the LCLS-II project has given the community a wealth of statistics and experience on the challenge of transferring the doping technology to industry. Overall, industry-produced nitrogen-doped cavities have shown excellent performance, however some technical issues have arisen. This talk focuses on lessons learned from the production of over 300 nitrogen-doped cavities for LCLS-II and how issues were mitigated to further improve performance. Finally, I will discuss pushing the boundaries of nitrogen-doping further by exploring different doping regimes in order to maintain excellent Q₀ performance, while reaching higher quench fields.

Slides FRCAA3 [16.880 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-FRCAA3

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paper received ※ 02 July 2019 paper accepted ※ 03 July 2019 issue date ※ 14 August 2019

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FRCAA6

Investigation on 1, 3 and 9-Cell SRF Elliptical Cavities made of Large Grain Niobium

cavity, SRF, cryomodule, radio-frequency

1213

T. Dohmae, H. Inoue, T. Kubo, H. Shimizu, K. Umemori, Y. Watanabe, M. Yamanaka
KEK, Ibaraki, Japan

Large grain (LG) niobium is directly sliced from niobium ingot. LG niobium sheet has larger crystal size than that of fine grain (FG) niobium which is forged and rolled, and normally used as the SRF cavity materials. It is expected that higher Q-value can be achieved using LG niobium sheet. And, effective reduction in material cost can be also achieved by LG niobium since forge and rolling process are skipped. On the other hand, there are some difficulties in fabrication since it has large deformation due to strong anisotropy. Cavity fabrication facility in KEK has been fabricated 1, 3 and 9-cell elliptical cavities made by LG niobium and RF tested in vertical cryostat. In this talk, the fabrication process and test results from these cavities will be presented.

Slides FRCAA6 [5.819 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-FRCAA6

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paper received ※ 23 June 2019 paper accepted ※ 01 July 2019 issue date ※ 14 August 2019

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