Keyword: niobium
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TUOXSP2 Analysis of Low RRR SRF Cavities cavity, SRF, accelerating-gradient, radio-frequency 783
 
  • K. Howard, Y.K. Kim
    University of Chicago, Chicago, Illinois, USA
  • D. Bafia, A. Grassellino
    Fermilab, Batavia, Illinois, USA
 
  Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. This work was supported by the University of Chicago.
Recent findings in the superconducting radio-frequency (SRF) community have shown that introducing certain impurities into high-purity niobium can improve quality factors and accelerating gradients. Success has been found in nitrogen-doping, diffusion of the native oxide into the niobium surface, and thin films of alternate superconductors atop a niobium bulk cavity. We question why some impurities improve RF performance while others hinder it. The purpose of this study is to characterize the impurity profile of niobium with a low residual resistance ratio (RRR) and correlate these impurities with the RF performance of low RRR cavities so that the mechanism of recent impurity-based improvements can be better understood and improved upon. Additionally, we perform a low temperature bake on the low RRR cavity to evaluate how the intentional addition of oxygen to the RF layer affects performance. We have found that low RRR cavities experience low temperature-dependent BCS resistance behavior more prominently than their high RRR counterparts. The results of this study have the potential to unlock a new understanding on SRF materials.
 
slides icon Slides TUOXSP2 [1.495 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUOXSP2  
About • Received ※ 08 June 2022 — Accepted ※ 11 June 2022 — Issue date ※ 25 June 2022  
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TUPOTK005 Mitigation of Parasitic Losses in the Quadrupole Resonator Enabling Direct Measurements of Low Residual Resistances of SRF Samples quadrupole, SRF, cavity, simulation 1196
 
  • S. Keckert, R. Kleindienst, J. Knobloch, F. Kramer, O. Kugeler, D.B. Tikhonov
    HZB, Berlin, Germany
  • W. Ackermann, H. De Gersem
    TEMF, TU Darmstadt, Darmstadt, Germany
  • X. Jiang, A.O. Sezgin, M. Vogel
    University Siegen, Siegen, Germany
  • J. Knobloch
    University of Siegen, Siegen, Germany
  • M. Wenskat
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
 
  The quadrupole resonator (QPR) is a dedicated sample-test cavity for the RF characterization of superconducting samples in a wide temperature, RF field and frequency range. Its main purpose are high resolution measurements of the surface resistance with direct access to the residual resistance thanks to the low frequency of the first operating quadrupole mode. Besides the well-known high resolution of the QPR, a bias of measurement data towards higher values has been observed, especially at higher harmonic quadrupole modes. Numerical studies show that this can be explained by parasitic RF losses on the adapter flange used to mount samples into the QPR. Coating several micrometer of niobium on those surfaces of the stainless steel flange that are exposed to the RF fields significantly reduced this bias, enabling a direct measurement of a residual resistance smaller than 5 nano-Ohm at 2 K and 413 MHz.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK005  
About • Received ※ 08 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 28 June 2022
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TUPOTK006 Systematic Investigation of Flux Trapping Dynamics in Niobium Samples cavity, experiment, SRF, controls 1200
 
  • F. Kramer, S. Keckert, S. Keckert, J. Knobloch, J. Knobloch, O. Kugeler
    HZB, Berlin, Germany
  • J. Knobloch, O. Kugeler
    BESSY GmbH, Berlin, Germany
  • J. Knobloch
    University of Siegen, Siegen, Germany
 
  Trapped magnetic flux in superconducting cavities can significantly increase surface resistance, and, thereby, limits the cavities’ performance. To reduce trapped flux in cavities, a better understanding of the fundamental mechanism of flux trapping is vital. We develop a new experimental design: measuring magnetic flux density at 15 points just above a niobium sheet of dimensions (100 x 60 x 3) mm with a time resolution of up to 2 ms and a flux resolution better than 0.5 µT. This setup allows us to control the temperature gradient and cooldown rate, both independently of each other, as well as the magnitude and direction of an external magnetic field. We present data gathered on a large-grain sample as well as on a fine-grain sample. Our data suggests that not only the temperature gradient but also the cooldown rate affects trapped flux. Additionally, we detect a non-trivial relationship between trapped flux and magnitude of applied field.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK006  
About • Received ※ 08 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 16 June 2022
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TUPOTK008 Cavity Designs for the Ch3 to Ch11 and Bellow Tuner Investigation of the Superconducting Heavy Ion Accelerator Heliac cavity, SRF, heavy-ion, simulation 1204
 
  • T. Conrad, M. Busch, H. Podlech, M. Schwarz
    IAP, Frankfurt am Main, Germany
  • K. Aulenbacher
    IKP, Mainz, Germany
  • K. Aulenbacher, W.A. Barth, F.D. Dziuba, V. Gettmann, T. Kürzeder, S. Lauber, J. List, M. Miski-Oglu
    HIM, Mainz, Germany
  • W.A. Barth, M. Basten, F.D. Dziuba, M. Heilmann, A. Rubin, A. Schnase, S. Yaramyshev
    GSI, Darmstadt, Germany
 
  New CH-DTL cavities designs of the planned Helmholtz Linear Accelerator (HELIAC) are developed in collaboration of HIM, GSI and IAP Frankfurt. The linac, operated in cw-mode with a final energy of 7.3 MeV/u, is intended for various experiments, in particular with heavy ions at energies close to the Coulomb barrier for research on SHE. Twelve sc CH cavities are foreseen, divided into four different cryostats. Each cavity will be equipped with dynamic bellow tuner. After successful beam tests with CH0, CH3 to CH11 are being designed. Based on the experience gained so far, optimization will be made, which will lead to both an increase in performance in terms of reducing the peak fields limiting superconductivity and a reduction in manufacturing costs and time. In order to optimize manufacturing, attention was paid to design many parts of the cavity, such as lids, spokes, tuner and helium shell, with the same geometrical dimensions. In addition, a tuner test rig was developed, which will be used to investigate the mechanical properties of the bellow tuner. For this purpose, different simulations were made in order to realize conditions as close as possible to reality in the test rig.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK008  
About • Received ※ 08 June 2022 — Revised ※ 13 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 17 June 2022
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TUPOTK010 Nitric Acid Soaking after Imperfect Furnace Treatments cavity, SRF, radio-frequency, linac 1211
 
  • R. Ghanbari, A. Dangwal Pandey
    DESY, Hamburg, Germany
  • C. Bate
    University of Hamburg, Hamburg, Germany
  • W. Hillert, M. Wenskat
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
 
  Annealings of niobium cavities in UHV or nitrogen atmospheres are crucial for the performance in the later cryogenic tests and operation. Recovery methods for imperfect annealing conditions have been discussed, and a more recent proposal, the so-called "nitric acid soak" has been studied here in detail. It shows surprising recovery potential, albeit the unclear origin of this improvement. We present our investigation on the several potential origins. For this, we used SEM, SIMS and XPS measurements of niobium samples to study the surface morphology and contaminations. We can reject the favored hypothesis on the origin of the improvement, and propose an alternative origin.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK010  
About • Received ※ 10 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 18 June 2022
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TUPOTK011 Commissioning of a New Magnetometric Mapping System for SRF Cavity Performance Tests cavity, SRF, ECR, superconducting-cavity 1215
 
  • J.C. Wolff, J. Eschke, A. Gössel, D. Reschke, L. Steder, L. Trelle
    DESY, Hamburg, Germany
  • W. Hillert
    University of Hamburg, Institut für Experimentalphysik, Hamburg, 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.
Magnetic flux trapped in the niobium bulk material of superconducting radio frequency (SRF) cavities degrades their quality factor and the accelerating gradient. The sensitivity for flux trapping is mainly determined by the treatment and the geometry of the cavity as well as the niobium grain size and orientation. To potentially improve the flux expulsion characteristics of SRF cavities and hence the efficiency of future accelerator facilities, further studies of the trapping behavior are essential. For this purpose a magnetometric mapping system to monitor the magnetic flux along the outer cavity surface of 1.3 GHz TESLA-Type single-cell SRF cavities has been developed and is currently in the commissioning phase at DESY. Contrary to similar approaches, this system digitizes the sensor signals already inside of the cryostat to extensively reduce the number of required cable feedthroughs. Furthermore, the signal-to-noise ratio (SNR) and consequently the measuring sensitivity can be enhanced by shorter analog signal lines, less thermal noise and the Mu-metal shielding of the cryostat. In this contribution test results gained by a prototype of the mapping system are presented.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK011  
About • Received ※ 10 June 2022 — Revised ※ 16 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 29 June 2022
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TUPOTK012 Nitrogen Infusion Sample R&D at DESY cavity, vacuum, ECR, accelerating-gradient 1219
 
  • C. Bate
    University of Hamburg, Hamburg, Germany
  • A. Ermakov, D. Reschke, J. Schaffran
    DESY, Hamburg, Germany
  • W. Hillert, M. Wenskat
    University of Hamburg, Institut für Experimentalphysik, Hamburg, 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.
Many accelerator projects such as the ILC would benefit from cavities with reduced surface resistance (high Q-values) while maintaining a high accelerating gradient. A possible way to meet the requirements is the so-called nitrogen-infusion procedure on Niobium cavities. However, a fundamental understanding and a theoretical model of this method are still missing. One important parameter is the residual resistance ratio (RRR) which is related to the impurity content of the material. We report the investigated RRR on samples in a wide temperature range in a vacuum and under a nitrogen atmosphere. This comparison made it possible to make statements about the differences in the concentration of nitrogen by varying the temperature. The samples are pure cavity-grade niobium and treated in the same manner as cavities. For this purpose, a small furnace dedicated to sample treatment was set up to change and explore the parameter space of the infusion recipe. Care was taken to achieve the highest level of purity possible in the furnace and in a pressure range of 1.0·10-8 mbar in order to meet the high requirements of nitrogen infusion.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK012  
About • Received ※ 08 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 01 July 2022
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TUPOTK013 PEALD SIS Studies for SRF Cavities cavity, SRF, site, plasma 1222
 
  • I. González Díaz-Palacio, R.H. Blick, A. Stierle, R. Zierold
    University of Hamburg, Hamburg, Germany
  • W. Hillert, M. Wenskat
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  • A. Jeromin
    DESY Nanolab, FS-NL, Hamburg, Germany
  • T.F. Keller, N. Krupka, M. Wenskat
    DESY, Hamburg, Germany
 
  Recent technological advances and material treatments have pushed Nb SRF cavities to their maximum RF performance. A novel approach for overcoming this limitation, which takes advantage of RF field only penetrates into the superconductor at a certain distance called London penetration depth, is nano-structuring multilayers with PEALD (plasma-enhanced atomic layer deposition). SIS (superconductor-insulator-superconductor) multilayers provide magnetic screening of the bulk Nb cavity, increasing the field at which the vortex penetration starts, and higher quality factor. ALD is closely related to chemical vapor deposition and bases on sequential self-limit gas-solid surface reactions facilitating conformal coatings with sub-nm precision even on complex substrates such as the interior of a cavity. As a preliminary study for SIS SRF cavities, we investigated the AlN-NbTiN/NbN multilayers grown by PEALD. Different compositions, thicknesses, and post-deposition thermal treatments have been investigated. The characterization results of superconducting properties, elemental composition, crystallinity, and cross-section are shown in this contribution.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK013  
About • Received ※ 09 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 27 June 2022
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TUPOTK016 HiPIMS-Coated Novel S(I)S Multilayers for SRF Cavities SRF, cavity, target, cathode 1234
 
  • A.Ö. Sezgin, X. Jiang, M. Vogel
    University Siegen, Siegen, Germany
  • I. González Díaz-Palacio, R. Zierold
    University of Hamburg, Hamburg, Germany
  • S. Keckert, J. Knobloch, O. Kugeler, D.B. Tikhonov
    HZB, Berlin, Germany
  • J. Knobloch
    University of Siegen, Siegen, Germany
  • R. Ries, E. Seiler
    Slovak Academy of Sciences, Institute of Electrical Engineering, Bratislava, Slovak Republic
 
  Funding: Material syntheses and characterizations via SMART, BMBF, Germany (05K19PSA). Superconducting characterizations via iFAST, H2020, EU (101004730). Part of this work via the MNaF, University of Siegen.
Pushing beyond the existing bulk niobium SRF cavities is indispensable along the path towards obtaining more sustainable next generation compact particle accelerators. One of the promising candidates to push the limits of the bulk niobium is thin film-based multilayer structures in the form of superconductor-insulator-superconductor (SIS). In this work, S(I)S multilayer structures were coated by high power impulse magnetron sputtering (HiPIMS), having industrial upscaling potential along with provid-ing higher quality films with respect to conventional magnetron sputtering techniques (e.g., DCMS), combined with (PE)-ALD techniques for deposition of the ex-situ insulating layers. On the path towards formulating opti-mized recipes for these materials to be coated on the inner walls of (S)RF cavities, the research focuses on innovat-ing the best performing S(I)S multilayer structures con-sisting of alternating superconducting thin films (e.g., NbN) with insulating layers of metal nitrides (e.g., AlN) and/or metal oxides (e.g., AlxOy) on niobium lay-ers/substrates (i.e., Nb/AlN/NbN) in comparison to the so-called SS multilayer structures (i.e., Nb/NbN). This con-tribution presents the initial materials and superconduct-ing and RF characterization results of the aforementioned multilayer systems on flat samples.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK016  
About • Received ※ 11 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 18 June 2022
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TUPOTK018 Combined In-Situ QEXAFS and XRD Investigations on Nb-Treatments in N2 Gas Atmospheres at Elevated Temperatures vacuum, site, cavity, SRF 1238
 
  • P. Rothweiler, F. Eckelt, D. Lützenkirchen-Hecht, S. Paripsa, L. Voß
    University of Wuppertal, Wuppertal, Germany
 
  Funding: We gratefully acknowledge financial support by the German Federal Ministry of Education and Research (BMBF) under project No. 05H18PXRB1.
Thin polycrystalline Nb metal foils were treated in N2 gas atmospheres at elevated temperatures of 900 °C up to 1200 °C. A combination of transmission mode Quick X-ray absorption spectroscopy (QEXAFS) at the Nb-K-edge and X-ray diffraction (XRD) used in parallel were used to investigate changes in the atomic short and long-range structure of the bulk Nb-material in-situ. A dedicated high-vacuum heating cell with a base pressure of 10-6 mbar was used to perform the heat treatments under vacuum and nitrogen gas atmosphere. The treatments typically included (i) a preheating at 900 °C under high-vacuum, (ii) a treatment in 3 mbar nitrogen gas at the desired temperature and (iii) a cooldown to room temperature under vacuum conditions. The QEXAFS and XRD data were collected in parallel during the entire process with a time resolution of 4 s. While the samples treated at 900 °C show the typical N-uptake to the octahedral interstitial sites, the samples treated at higher temperatures show the growth of distinct niobium nitride phases. The results will be discussed in more details during the conference.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK018  
About • Received ※ 08 June 2022 — Revised ※ 09 June 2022 — Accepted ※ 12 June 2022 — Issue date ※ 18 June 2022
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TUPOTK034 Evaluating the Effects of Nitrogen Doping and Oxygen Doping on SRF Cavity Performance cavity, SRF, ECR, simulation 1287
 
  • H. Hu, Y.K. Kim
    University of Chicago, Chicago, Illinois, USA
  • D. Bafia
    Fermilab, Batavia, Illinois, USA
 
  Superconducting radiofrequency (SRF) cavities are resonators with extremely low surface resistance that enable accelerating cavities to have extremely high quality factors (Q0). High Q0 decreases the capital required to keep the accelerators cold by reducing power loss. The performance of SRF cavities is largely governed by the surface composition of the first §I{100}{nm} of the cavity surface. Impurities such as oxygen and nitrogen have been observed to yield high Q0, but their precise roles are still being studied. Here, we compare the performance of cavities doped with nitrogen and oxygen in terms of surface composition and heating behavior with field. A simulation of the diffusion of oxygen into the bulk of the cavity was built using COMSOL Multiphysics software. Simulated results were compared to the actual surface composition of the cavities as determined from secondary ion mass spectrometry analysis. Understanding how these impurities affects performance allows us to have further insight into the underlying mechanisms that enable these surface treatments to yield high Q0.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK034  
About • Received ※ 08 June 2022 — Revised ※ 10 June 2022 — Accepted ※ 12 June 2022 — Issue date ※ 30 June 2022
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TUPOTK035 CVD Nb3Sn-on-Copper SRF Accelerator Cavities cavity, SRF, radio-frequency, factory 1291
 
  • G. Gaitan, P.N. Koufalis, M. Liepe
    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
  • M. Liepe
    Cornell University, Ithaca, New York, USA
 
  Funding: This work is supported by the US Department of Energy SBIR program under grant number DE-SC0017902. Gabriel Gaitan is supported by the National Science Foundation under Grant No. PHY-1549132.
Nb3Sn is the most promising alternative material for achieving superior performance in Superconducting Radio-Frequency (SRF) cavities, compared to conventional bulk Nb cavities now used in accelerators. Chemical vapor deposition (CVD) is an alternative to the vapor diffusion-based Nb3Sn growth technique predominantly used on bulk niobium cavities and may enable reaching superior RF performance at reduced cost. In collaboration with Cornell, Ultramet has developed CVD process capabilities and reactor designs to coat copper SRF cavities with thick and thin films of Nb and Nb3Sn. In this paper, we present our latest research efforts on CVD Nb3Sn-on-copper SRF cavities, including RF performance test results from two 1.3 GHz SRF cavities coated by Ultramet.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK035  
About • Received ※ 15 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 21 June 2022
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TUPOTK036 Study of Chemical Treatments to Optimize Niobium-3 Tin Growth in the Nucleation Phase cavity, SRF, radio-frequency, site 1295
 
  • L. Shpani, S.G. Arnold, G. Gaitan, M. Liepe, Z. Sun
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • T. Arias, M.M. Kelley, N. Sitaraman
    Cornell University, Ithaca, New York, USA
 
  Funding: This research is funded by the National Science Foundation under Grant No. PHY-1549132, the Center for Bright Beams.
Niobium-3 Tin (Nb3Sn) is a high-potential material for next-generation Superconducting Radiofrequency (SRF) cavities in particle accelerators. The most promising growth method to date is based on vapor diffusion of tin into a niobium substrate with nucleating agent Tin Chloride (SnCl2). Still, the current vapor diffusion recipe has significant room for realizing further performance improvement. We are investigating how different chemical treatments on the niobium substrate before coating influence the growth of a smooth and uniform Nb3Sn layer. More specifically, this study focuses on the interaction between the SnCl2 nucleating agent and the niobium surface oxides. We compare the effect of different chemical treatments with different pH values on the tin droplet distribution on niobium after the nucleation stage of coating. We also look at the effect that the nucleation temperature has on the smoothness and uniformity of the tin distribution, with the ultimate goal of optimizing the recipe to coat smooth Nb3Sn cavities.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK036  
About • Received ※ 12 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 17 June 2022
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TUPOTK042 Challenges to Reliable Production Nitrogen Doping of Nb for SRF Accelerating Cavities cavity, SRF, vacuum, controls 1311
 
  • C.E. Reece, M.J. Kelley, E.M. Lechner, A.D. Palczewski
    JLab, Newport News, Virginia, USA
  • J.W. Angle, M.J. Kelley
    Virginia Polytechnic Institute and State University, Blacksburg, USA
  • F.A. Stevie
    NCSU AIF, Raleigh, North Carolina, USA
 
  Funding: This work was authored by JSA LLC under U.S. DOE contract DE-AC05-06OR23177. This material is based on work supported by the U.S. DOE Early Career Award to A. Palczewski, with supplemental support from DOE BES via the LCLS-II HE R&D program. J. Angle’s support was from the Office of High Energy Physics, under grant DE-SC-0014475 to Virginia Tech.
Over the last several years, alloying of the surface layer of niobium SRF cavities has been demonstrated to beneficially lower the superconducting RF surface resistance. Nitrogen, titanium, and oxygen have all been demonstrated as effective alloying agents, occupying interstitial sites in the niobium lattice within the RF penetration depth and even deeper, when allowed to thermally diffuse into the surface at appropriate temperatures. The use of nitrogen for this function has been often termed ’nitrogen doping’ and is being applied in the LCLS-II and LCLS-II HE projects. We report characterization studies of the distribution of nitrogen into the exposed niobium surface and how such distribution is affected by the quality of the vacuum furnace environment in which the doping takes place, and the complexity of nitride crystal growth on different grain orientations of surface niobium. Using state-of-the-art quantification methods by dynamic secondary ion mass spectrometry (SIMS) depth profiling in niobium, we identify several phenomena involving furnace-sourced contamination. We also highlight a potential issue with N2 flow constraints from the flange ’caps’ used during heat treatments.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK042  
About • Received ※ 07 June 2022 — Revised ※ 09 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 05 July 2022
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TUPOTK044 Preliminary Results of a Magnetic and Temperature Map System for 3 GHz Superconducting Radio Frequency Cavities cavity, SRF, MMI, radio-frequency 1315
 
  • I.P. Parajuli, G. Ciovati, J.R. Delayen, A.V. Gurevich, B.D. Khanal
    ODU, Norfolk, Virginia, USA
  • G. Ciovati, J.R. Delayen
    JLab, Newport News, Virginia, USA
 
  Funding: Work supported by NSF Grant 100614-010. Jlab work is supported by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Superconducting radio frequency (SRF) cavities are fundamental building blocks of modern particle accelerators. A surface resistance in the tens of nanoOhm range is achieved when cooling these cavities to liquid helium temperature, ~2 - 4 K. One of the leading sources of residual losses in SRF cavities is trapped magnetic flux. Flux trapping mechanism depends on different surface preparations and cool-down conditions. We have designed, developed and commissioned a combined magnetic and temperature mapping system using anisotropic magneto-resistance sensors and carbon resistors, respectively, to study the flux trap mechanism in 3 GHz single-cell niobium cavities. In this contribution, we will describe the experimental apparatus and present preliminary test results.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK044  
About • Received ※ 02 June 2022 — Revised ※ 11 June 2022 — Accepted ※ 24 June 2022 — Issue date ※ 25 June 2022
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TUPOTK045 Magnetic Field Mapping of 1.3 GHz Superconducting Radio Frequency Niobium Cavities cavity, SRF, MMI, radio-frequency 1319
 
  • I.P. Parajuli, G. Ciovati, J.R. Delayen, A.V. Gurevich
    ODU, Norfolk, Virginia, USA
  • G. Ciovati, J.R. Delayen
    JLab, Newport News, Virginia, USA
 
  Funding: Work supported by NSF Grant 100614-010. Jlab work is supported by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Niobium is the material of choice to build superconducting radio frequency (SRF) cavities, which are fundamental building blocks of modern particle accelerators. These cavities require a cryogenic cool-down to ~2 - 4 K for optimum performance minimizing RF losses on the inner cavity surface. However, temperature-independent residual losses in SRF cavities cannot be prevented entirely. One of the significant contributor to residual losses is trapped magnetic flux. The flux trapping mechanism depends on different factors, such as surface preparations and cool-down conditions. We have developed a diagnostic magnetic field scanning system (MFSS) using Hall probes and anisotropic magneto-resistance sensors to study the spatial distribution of trapped flux in 1.3 GHz single-cell cavities. The first result from this newly commissioned system revealed that the trapped flux on the cavity surface might redistribute with increasing RF power. The MFSS was also able to capture significant magnetic field enhancement at specific cavity locations after a quench.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK045  
About • Received ※ 02 June 2022 — Revised ※ 09 June 2022 — Accepted ※ 20 June 2022 — Issue date ※ 27 June 2022
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TUPOTK059 Modeling O and N Alloying in Nb for SRF Applications cavity, SRF, radio-frequency, vacuum 1354
 
  • E.M. Lechner, M.J. Kelley, A.D. Palczewski, C.E. Reece
    JLab, Newport News, Virginia, USA
  • J.W. Angle, M.J. Kelley
    Virginia Polytechnic Institute and State University, Blacksburg, USA
  • F.A. Stevie
    NCSU AIF, Raleigh, North Carolina, USA
 
  Funding: This work was coauthored by Jefferson Science Associates LLC under U.S. DOE Contract No. DE-AC05-06OR23177 and grant No. DE-SC-0014475 to Virginia Tech for the support of J. Angle.
N and O-alloyed superconducting radio frequency cavities exhibit extraordinary quality factors. Developing diffusion models that describe interstitial N and O in Nb is important for optimizing alloyed cavity quality factors and accelerating gradients. N and O-alloyed Nb samples are examined with SEM AND SIMS and their diffusion profiles modeled.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK059  
About • Received ※ 08 June 2022 — Revised ※ 10 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 17 June 2022
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THPOMS052 Magnetic Field Shield for SC-Cavity with Thin Nb Sheet cavity, shielding, experiment, cryogenics 3090
 
  • Y. Iwashita, Y. Kuriyama
    Kyoto University, Research Reactor Institute, Osaka, Japan
  • Y. Fuwa
    JAEA/J-PARC, Tokai-mura, Japan
  • H. Tongu
    Kyoto ICR, Uji, Kyoto, Japan
 
  Funding: This work was partly supported by JSPS KAKENHI Grant Number 19K21877.
Shielding the superconducting accelerating cavity made of niobium from the weak environmental magnetic field is an important subject. Niobium is a type-II superconductor, which traps the environmental magnetic flux in the material during the superconducting transition, resulting in increase of residual resistance and heating during operation during operation. Shielding from a weak magnetic field is essential for high performance operations. A magnetic shielding method that uses the diamagnetism of superconducting materials instead of magnetic flux absorption by high magnetic permeability materials is discussed.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOMS052  
About • Received ※ 14 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 18 June 2022
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