MC7: Accelerator Technology
T07: Superconducting RF
Paper Title Page
TUOXSP2 Analysis of Low RRR SRF Cavities 783
SUSPMF110   use link to see paper's listing under its alternate paper code  
 
  • 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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TUPOTK002 Results of the RF Power Tests of the ESS Cryomodules Tested at CEA 1186
 
  • O. Piquet, S. Berry, A. Bouygues, E. Cenni, G. Devanz, C. Madec, C. Mayri, P. Sahuquet
    CEA-DRF-IRFU, France
  • C. Arcambal, Q. Bertrand, P. Bosland, T. Hamelin
    CEA-IRFU, Gif-sur-Yvette, France
  • M.J. Ellis
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • P. Pierini
    ESS, Lund, Sweden
  • D. Sertore
    INFN/LASA, Segrate (MI), Italy
  
  Eight of the medium and high beta cryomodules deliv-ered to ESS by CEA are tested at CEA before delivery; the two medium and high beta prototypes and the three first of each type of the series. The goal of these tests is to validate the assembly and the performances on few cryomodules before the next cryomodules of the series are delivered to ESS. This paper summarizes the general results obtained during the tests at 2 K and at high RF power, Pmax = 1.1 MW. The cavities reach the ESS re-quirements, Eacc = 16.7 MV/m (Medium beta) and 19.9 MV/m (High beta) with an efficient compensation of the Lorentz detuning by the piezo tuner over the full RF pulse length of 3.6 ms at 14 Hz. After the successful tests at CEA, the first cryomodules have been shipped to ESS where the final acceptance test are performed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK002  
About • Received ※ 03 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 21 June 2022
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TUPOTK004 Time Resolved Field Emission Detection During ESS Cryomodule Tests 1192
 
  • E. Cenni, G. Devanz, O. Piquet
    CEA-IRFU, Gif-sur-Yvette, France
  • M. Baudrier, L. Maurice
    CEA-DRF-IRFU, France
  
  At CEA-Saclay we are currently testing the European Spallation Source (ESS) high beta cryomodules (CM). Each cryomodule is equipped with four superconducting elliptical cavities with their ancillaries (fundamental power couplers (FPC), frequency tuners and magnetic shields). The cavity are designed to accelerate protons with relativistic speed about β=0.86 and operate at an accelerating field of 19.9MV/m. During cryomodule test, operational parameters are inspected by powering up one cavity at the time. A dedicated gamma ray detection system has been designed and installed around the cryomodule in order to have a more precise insight into field emission phenomenon occurring during cryomodule operation. Recently we were able to obtain time resolved data concerning radiation emerging from the cavities due to field emission.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK004  
About • Received ※ 08 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 02 July 2022
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TUPOTK005 Mitigation of Parasitic Losses in the Quadrupole Resonator Enabling Direct Measurements of Low Residual Resistances of SRF Samples 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.Ö. 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 1200
SUSPMF103   use link to see paper's listing under its alternate paper code  
 
  • 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 1204
SUSPMF104   use link to see paper's listing under its alternate paper code  
 
  • 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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TUPOTK009 Development of Superconducting CH Cavity Preparation at IAP 1208
 
  • P. Müller, H. Podlech
    IAP, Frankfurt am Main, Germany
  • K. Aulenbacher, F.D. Dziuba, V. Gettmann, T. Kürzeder, M. Miski-Oglu
    HIM, Mainz, Germany
  • W.A. Barth, M. Basten, V. Gettmann, T. Kürzeder, M. Miski-Oglu
    GSI, Darmstadt, Germany
  
  Funding: HIC for FAIR, BMBF Contr. No. 05P21RFRB2 and HFHF
Goethe University (GU), Gesellschaft für Schwerionenforschung (GSI) and Helmholtz Institut Mainz (HIM) work in collaboration on the Helmholtz Linear Accelerator (HELIAC). A new superconducting (sc) continous wave (cw) high intensity heavy ion linear accelerator (Linac) will provide ion beams with maximum duty factor up to beam energies of 7.3 MeV/u. The acceleration voltage will be provided by sc Crossbar-H-mode (CH) cavities, developed of Institute for Applied Physics (IAP) at GU. Cavity preparation is researched and optimized towards widely used elliptical multicell cavities. A standardized preparation protocol for CH cavities is researched in collaboration between GU, GSI and HIM on a 360 MHz 19 gap CH prototype. Baseline measurements and a 120°C 48 hour bake produced higher maximum gradient, higher intrinsic quality factor and a shorter cavity conditioning phase. As a critical preparation step, High Pressure Rinsing (HPR) with ultra pure water will be performed at HIM and is currently in preparation. HPR cycles are currently tested on a CH dummy with a new nozzle layout that is optimized towards CH cavity geometry. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK009  
About • Received ※ 08 June 2022 — Revised ※ 16 June 2022 — Accepted ※ 18 June 2022 — Issue date ※ 02 July 2022
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TUPOTK010 Nitric Acid Soaking after Imperfect Furnace Treatments 1211
SUSPMF105   use link to see paper's listing under its alternate paper code  
 
  • 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 1215
SUSPMF106   use link to see paper's listing under its alternate paper code  
 
  • 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 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 1222
SUSPMF107   use link to see paper's listing under its alternate paper code  
 
  • 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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TUPOTK014 Refurbishment of SRF Cavities and HOM Antenna Coating Studies for the Mainz Energy-Recovering Superconducting Accelerator (MESA) 1226
 
  • P.S. Plattner, F. Hug, T. Stengler
    KPH, Mainz, Germany
  
  Funding: The work received funding by BMBF through 05H21UMRB1.
The Mainz Energy-Recovering Superconducting Accelerator (MESA) will be a new recirculating accelerator, which can operate in an external beam mode and an energy recovering mode. In the ERL-mode the electrons cross an internal gas-target at MAGIX and give their kinetic energy into the Superconducting Radio Frequency (SRF) system back after experimental use. The MESA cryomodules are based on ELBE-type cryomodules, which contain two 9-cell TESLA/XFEL-type cavities. For any maintenance the clean room infrastructure at the Helmholtz Institute Mainz (HIM) can be used. Currently, a cryomodule from the decommissioned ALICE ERL at Daresbury, UK is in the process of refurbishment. The refurbishment includes an HPR rinse of the cavities suffering from field emission at present and various adjustments of the module for a future use in MESA, which includes adding piezo tuners and new HOM antennas. For the new antennas, different superconducting coatings (Nb3Sn and NbTiN) will be tested to reach higher critical temperatures in the future for giving the possibility to couple out more HOM power without quenching as the prospected cw beamload lays above 4 mA in MESA ERL operation. Using a superconducting 3 GHz six-cell injector cavity for the S-DALINAC the successful refurbishment of a SRF cavity by applying a high pressure rinse in the clean room infrastructure at HIM was demonstrated the first time.
* The authors acknowledge the transfer of one cryomodule to Mainz by STFC Daresbury. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK014  
About • Received ※ 07 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 18 June 2022 — Issue date ※ 23 June 2022
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TUPOTK015 HOM Coupler Design and Optimization for the FCC-ee W Working Point 1230
SUSPMF108   use link to see paper's listing under its alternate paper code  
 
  • S. Udongwo, S.G. Zadeh, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  • R. Calaga
    CERN, Meyrin, Switzerland
  
  Funding: Funded by CERN under ADDENDUM FCC-GOV-CC-00213 (KE4978/ ATS) to FCC-GOV-CC- 0213/2431149/KE4978 VERSION 1.0.
The Future Circular electron-positron Collider (FCC-ee) is planned to operate with beam energies from 45.6 to 182.5 GeV and beam currents from 5.4 to 1390 mA. The purpose is to study the properties of the Z-, W- and Higgs boson and the top and anti-top quarks in four operation points. The beam current of 147 mA of the W working point requires particular care to string damp HOMs. This paper proposes 2-cell 400 MHz SRF cavities with improved damping as an alternative to the baseline 4-cell cavities for this working point. The resulting impedance of the HOM-damped cavity is then calculated and compared with the impedance budget. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK015  
About • Received ※ 08 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 16 June 2022
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TUPOTK016 HiPIMS-Coated Novel S(I)S Multilayers for SRF Cavities 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 1238
SUSPMF109   use link to see paper's listing under its alternate paper code  
 
  • 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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TUPOTK020 Status of LASA-INFN R&D Activity on PIP-II Low-beta Prototypes 1241
 
  • M. Bertucci, A. Bosotti, A. D’Ambros, E. Del Core, A.T. Grimaldi, P. Michelato, L. Monaco, C. Pagani, R. Paparella, D. Sertore
    INFN/LASA, Segrate (MI), Italy
  • A. Gresele
    Zanon Research & Innovation, Schio, VI, Italy
  • C. Pagani
    Università degli Studi di Milano & INFN, Segrate, Italy
  
  LASA-INFN is developing some PIP-II β=0.61 cavity prototypes so to set up a high-Q recipe allowing to reach the PIP-II performance target in view of the series production. A single-cell cavity was treated with a XFEL-like baseline recipe, whereas a multicell cavity underwent a mid-T bake step as final surface treatment. Both cavities have been then tested at the LASA vertical experimental facility. The test results are here reported and discussed. Basing on the satisfactory results so far obtained, a strategy for the qualification and upgrade of the LASA vertical test facility is outlined.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK020  
About • Received ※ 08 June 2022 — Revised ※ 13 June 2022 — Accepted ※ 14 June 2022 — Issue date ※ 16 June 2022
Cite • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
TUPOTK021 Recent Update on ESS Medium Beta Cavities at INFN LASA 1245
 
  • D. Sertore, M. Bertucci, M. Bonezzi, A. Bosotti, D. Cardelli, A. D’Ambros, A.T. Grimaldi, L. Monaco, R. Paparella, G.M. Zaggia
    INFN/LASA, Segrate (MI), Italy
  • C. Pagani
    Università degli Studi di Milano & INFN, Segrate, Italy
  
  The INFN LASA contribution to the European Spallation Source ERIC (European Research Infrastructure Consortium) Superconducting Linac is focused on supplying 36 cavities for the Medium Beta section of the proton accelerator. Twenty eight cavities have been fully qualified and delivered to CEA for integration into the cryomodules. We present the status of the activities dedicated to completing our contribution both by applying alternative surface treatments with respect to the series vertical BCP and by procuring new cavities.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK021  
About • Received ※ 09 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 25 June 2022  
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TUPOTK022 INFN-LASA for the Fermilab PIP-II 1249
 
  • R. Paparella, M. Bertucci, M. Bonezzi, A. Bosotti, D. Cardelli, A. D’Ambros, E. Del Core, A.T. Grimaldi, L. Monaco, D. Sertore, G.M. Zaggia
    INFN/LASA, Segrate (MI), Italy
  • C. Pagani
    Università degli Studi di Milano & INFN, Segrate, Italy
  
  The status of INFN-LASA contribution to the PIP-II project at Fermilab is reported in this paper. Experimental results and ongoing activities on prototypes are summarized together with the development of related testing infrastructures. The series production of the 38 5-cell, beta 0.61 cavities designed by INFN-LASA for the LB650 section of the PIP-II linac recently commenced, the status of major procurements and associated activities is here below presented. All cavities will be produced and surface treated in industry to reach the unprecedented performances required, qualified through vertical cold test at qualified infrastructures and delivered as linac-ready at the string assembly site.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK022  
About • Received ※ 09 June 2022 — Revised ※ 10 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 04 July 2022
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TUPOTK023 Study on Commercial Diodes as Thermometers at Low Temperature for Temperature Mapping System of Nb3sn Superconducting Radiofrequency Cavities 1252
 
  • R. Wanison, K. Umemori, T. Yamada
    KEK, Ibaraki, Japan
  • K. Takahashi
    Sokendai, Ibaraki, Japan
  • R. Wanison
    Department of Mechanical Engineering, Faculty of Engineering, Chiang Mai University, Chiang Mai, Thailand
  
  Nb3Sn Superconducting radiofrequency (SRF) cavities has been researched and developed at Center for Applied Superconducting Accelerator (CASA), KEK. One of effec-tive tools for research on the performance of SRF cavities is a temperature mapping (T-map) system for detecting small increases in temperature. It is a thermometer array positioned precisely on an outer surface of cavity wall. Thermometer should cover at least from the range of typi-cal operating temperature of 4 K to the transition tempera-ture of 18 K, for the Nb3Sn SRF cavities. Therefore, car-bon resistor can not be used as a cheap thermometer due to low sensitivity at this temperature range. In this pro-ceeding, we report the results of the test for various com-mercially available diodes as a thermometer for T-map system. The sensitivity, stability and the repeatability are measured, cooled by a GM cryocooler.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK023  
About • Received ※ 08 June 2022 — Revised ※ 11 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 07 July 2022
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TUPOTK024 Multipacting Simulation on Half-Wave Resonator for 200 MeV Energy Upgrade of Komac Proton Linac 1255
 
  • J.J. Dang, H.S. Kim, H.-J. Kwon, S. Lee
    KOMAC, KAERI, Gyeongju, Republic of Korea
  
  Funding: This work was supported through KOMAC operation fund of KAERI by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (KAERI-524320-22).
A superconducting linac is developed at KOrea Multi-purpose Accelerator Complex (KOMAC) for proton beam energy upgrade from 100 MeV to 200 MeV. The SRF linac consists of thirty-six half-wave resonator (HWR) cavities. 350 MHz, β = 0.56 HWR is designed to provide 3.6 MV accelerating voltage. After a fundamental RF design study, an analysis on a multipacting (MP) of HWR is carried out. The MP simulation for the HWR is performed by using CST Particle Studio. To understand a feature of the MP occurrence in the HWR, a particle-in-cell simulation is conducted while changing various conditions such as an RF amplitude, an RF phase, and an emission surface. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK024  
About • Received ※ 08 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 04 July 2022
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TUPOTK025 Design Study of the Third Harmonic Superconducting Cavity for a Bunch Lengthening 1258
 
  • J.Y. Yoon, E.-S. Kim
    KUS, Sejong, Republic of Korea
  • J.H. Han, H.S. Park
    Kiswire Advanced Technology Ltd., Daejeon, Republic of Korea
  • E. Kako
    KEK, Ibaraki, Japan
  
  The bunch lengthening by the 3rd harmonic cavity reduces the electron collisions in a bunch and increases the Touschek lifetime of a storage ring. We performed the multi-physics simulations including the electromagnetic, thermal, and mechanical analysis of the cavity. In the electromagnetic simulation, the geometry is optimized for the required performance of the cavity. The elliptical double-cell geometry is selected to increase the accelerating voltage and reduce the power losses of the cavity. Thermal/mechanical analyses were performed to check the deformation of the thermal and pressure contraction. The prototype cavity does not require the power coupler as it is a passive type. The conceptual design and copper prototype of the 3rd harmonic cavity will be described in this paper. Based on this design, the fabrication of Niobium cavity is in progress.
Superconducting RF, Cavity 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK025  
About • Received ※ 02 June 2022 — Revised ※ 13 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 09 July 2022
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TUPOTK026 ESS Elliptical Cryomodules Tests at Lund Test Stand 1261
 
  • C.G. Maiano, E. Asensi Conejero, N. Elias, P. Goudket, W. Hees, P. Pierini, L. Sagliano, F. Schlander, M.Y. Wang
    ESS, Lund, Sweden
  • D. Bocian, W. Gaj, P. Halczynski, M. Sienkiewicz, F.D. Skalka, J. Swierblewski, K.M. Wartak, M. Wartak
    IFJ-PAN, Kraków, Poland
  
  We present an overview and description of the elliptical cryomodules test activities at Lund Test Stand 2. During 2021 the test facility was commissioned with one prototype, and four series medium beta modules have now been successfully tested at ESS in Lund. This activity allowed the joint ESS and IFJ PAN team to develop all the procedures and the necessary automated tools for the different phases of the site acceptance test campaign (e.g. incoming inspections, coupler conditioning, cooldown strategies, tuning to resonance and electromagnetic/cryogenic performance verification). During the initial test period techniques for diagnostics of limiting mechanisms have been developed and improved up to a consolidated and mature state for the rest of the test campaign. Tests results and the initial statistics is presented and commented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK026  
About • Received ※ 07 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 16 June 2022
Cite • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
TUPOTK027 Field Emission Measurements at Lund Test Stand 1265
 
  • C.G. Maiano, N. Elias, E. Laface, P. Pierini, L. Sagliano, M.Y. Wang
    ESS, Lund, Sweden
  • E. Cenni
    CEA-IRFU, Gif-sur-Yvette, France
  
  We present here a description of field emission (FE) measurements set-up developed for elliptical cryomodules test activities at Lund Test Stand 2. A test campaign of field emission measurements has been developed and optimized during cryomodules tests. The scintillator detectors (and their respective shields), chosen for these measurements, have been characterized and optimized. The field emission application has been developed and integrated in the cryomodules tests operator interface. The Initial test results are presented and commented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK027  
About • Received ※ 07 June 2022 — Revised ※ 13 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 10 July 2022
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TUPOTK028 Tuning of Superconducting Cavities Using the FFT of Transmitted Power 1268
 
  • E. Laface, C.G. Maiano, P. Pierini, M.Y. Wang
    ESS, Lund, Sweden
  
  We implemented a method to tune the ESS superconducting cavities based on the spectral analysis of the high resolution data available from the Low Level RF system (LLRF) for the transmitted power, without the need of connecting a network analyzer or any other dedicated instrumentation along the RF chain. A frequency peak up to 4 MHz off from the resonating frequency can be detected and used to control the stepper motor of the tuner until the cavity is stretched to the proper length to reach the correct operation frequency. Experience of its use at the ESS Test Stand 2 (TS2) facility at Lund during cryomodule acceptance testing is presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK028  
About • Received ※ 16 May 2022 — Revised ※ 11 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 14 June 2022
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TUPOTK031 A First 6 GHz Cavity Deposition with B1 Superconducting Thin Film at ASTeC 1279
 
  • R. Valizadeh, A.N. Hannah, O.B. Malyshev
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • E. Chyhyrynets, V.A. Garcia Diaz, C. Pira
    INFN/LNL, Legnaro (PD), Italy
  • V.R. Dhanak
    The University of Liverpool, Liverpool, United Kingdom
  • O.B. Malyshev
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • G.B.G. Stenning
    STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
  
  Nb3Sn, NbTiN and NbN are superconductors with critical temperatures of 18.3, 12.6-17 and 11.6-17.5 K, respectively, these are higher than that of Nb at 9.3 K. Hence, at 4 K, they have an RF resistance, an order of magnitude lower than that of Nb, which leads to quality factors above those of Nb. In recent years, there has been an extensive effort converting Nb cavities into Nb3Sn. Alloying the top inner layer of the cavity using Sn diffusion at a high temperature has had some degree of success, however, the reproducibility remains a major hindering and limiting factor. In this study, we report on the PVD deposition of NbTiN inside a 6 GHz cavity, using an external magnetic coil configuration. The deposition is done at an elevated temperature of about 650 C. We report on the superconducting properties, film structure and its stoichiometry and surface chemical state. The films have been characterised with SEM, XRD, XPS, EDS and SQUID magnetometer.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK031  
About • Received ※ 07 June 2022 — Revised ※ 09 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 06 July 2022
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TUPOTK033 First RF Measurements of Planar SRF Thin Films with a High Throughput Test Facility at Daresbury Laboratory 1283
 
  • D.J. Seal, G. Burt, P. Goudket, O.B. Malyshev, B.S. Sian, R. Valizadeh
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • G. Burt, D.J. Seal, B.S. Sian
    Lancaster University, Lancaster, United Kingdom
  • P. Goudket, O.B. Malyshev, R. Valizadeh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • P. Goudket
    ESS, Lund, Sweden
  • H.S. Marks
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  
  The research on superconducting thin films for future radio frequency (RF) cavities requires measuring the RF properties of these films. However, coating and testing thin films on full-sized cavities is both challenging and timeconsuming. As a result, films are typically deposited on small, flat samples and characterised using a test cavity. At Daresbury Laboratory, a facility for testing 10 cm diameter samples has recently been commissioned. The cavity uses RF chokes to allow physical and thermal separation between itself and the sample under test. The facility allows for surface resistance measurements at a resonant frequency of 7.8 GHz, at temperatures down to 4 K, maximum RF power of 1 W and peak magnetic fields of a few mT. The main advantage of this system is the simple sample mounting procedure due to no physical welding between the sample and test cavity. This allows for a fast turnaround time of two to three days between samples. As such, this system can be used to quickly identify which samples are performing well under RF and should require further testing at higher gradient. Details of recent upgrades to this facility, together with measurements of both bulk niobium and thin film samples, will be presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK033  
About • Received ※ 08 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 30 June 2022 — Issue date ※ 02 July 2022
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TUPOTK034 Evaluating the Effects of Nitrogen Doping and Oxygen Doping on SRF Cavity Performance 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 1291
SUSPMF111   use link to see paper's listing under its alternate paper code  
 
  • 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 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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TUPOTK037 Status Update on Cornell’s SRF Compact Conduction Cooled Cryomodule 1299
SUSPMF112   use link to see paper's listing under its alternate paper code  
 
  • N.A. Stilin, A.T. Holic, M. Liepe, T.I. O’Connell, J. Sears, V.D. Shemelin, J. Turco
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  A new frontier in Superconducting RF (SRF) development is increasing the accessibility of SRF technology to small-scale accelerator operations which are used in various industrial or research applications. This is made possible by using commercial cryocoolers as a cooling source, which removes the need for expensive liquid cryogenics and their supporting infrastructure. Cornell University is currently developing a new cryomodule based on a conduction cooling scheme. This cryomodule will use two pulse tube cryocoolers in place of liquid cryogenics in order to cool the system. A new 1.3 GHz cavity has been designed with a set of four niobium rings welded at the equator and irises which allow for a direct thermal link between the cavity and cryocooler cold heads. The cavity will use two coaxial RF input couplers capable of delivering up to 100 kW total RF power for high-current beam operation. This coupler design was modified from the Cornell ERL injector couplers, including simplifications such as removing the cold RF window and most outer bellows, while retaining inner bellows for adjustable coupling.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK037  
About • Received ※ 12 June 2022 — Revised ※ 11 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 16 June 2022
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TUPOTK038 Next Generation SRF Cavities at Cornell University 1303
SUSPMF113   use link to see paper's listing under its alternate paper code  
 
  • N.M. Verboncoeur, M. Liepe, R.D. Porter, L. Shpani
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  
  Our goal is to develop new materials and protocols for the growth and preparation of thin-film and layered superconductors for next generation SRF cavities with higher performance for future accelerators. We are working primarily with Nb3Sn to achieve this goal, as well as other materials which aim to optimize the RF field penetration layer of the cavity. This contribution gives a general update on our most recent cavity test results. A deeper insight into RF loss distribution and dynamics during cavity testing is gained using a new global high-speed temperature mapping system (T-Map).  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK038  
About • Received ※ 11 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 22 June 2022
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TUPOTK040 Design of the Electron Ion Collider Electron Storage Ring SRF Cavity 1307
 
  • J. Guo, E. Daly, J. Henry, J. Matalevich, G.-T. Park, R.A. Rimmer, H. Wang, S. Wang
    JLab, Newport News, Virginia, USA
  • D. Holmes, K.S. Smith, W. Xu, A. Zaltsman
    BNL, Upton, New York, USA
  
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
The Electron Ion Collider (EIC) under construction at Brookhaven National Laboratory is a high luminosity collider as the next major research facility for the nuclear physics community. Among the numerous RF subsystems in the EIC, the electron storage ring (ESR) fundamental RF cavities system is one of the most challenging. This system will handle a high beam current of up to 2.5 A and replenish up to 10 MW of beam power losses from synchrotron radiation and HOM. Variable coupling is required in the cavities due to the wide range of required total RF voltage and beam current combinations. In this paper, we will present the status of the design and future plans. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK040  
About • Received ※ 16 June 2022 — Revised ※ 11 June 2022 — Accepted ※ 23 June 2022 — Issue date ※ 28 June 2022
Cite • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
TUPOTK042 Challenges to Reliable Production Nitrogen Doping of Nb for SRF Accelerating Cavities 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 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 1319
SUSPMF114   use link to see paper's listing under its alternate paper code  
 
  • 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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TUPOTK048 Optimization of a 600 MHz Two-Cell Slotted Waveguide Elliptical Cavity for FCC-ee 1323
 
  • S. Gorgi Zadeh, O. Brunner, F. Peauger, I. Syratchev
    CERN, Meyrin, Switzerland
  
  The radio-frequency (RF) system of the future circular lepton collider (FCC-ee) must cope with different machine parameters ranging from Ampere-class operation required for the Z-peak working point to the high-gradient operation for the ttbar threshold. The Superconducting Slotted Waveguide Elliptical cavity (SWELL) concept was recently proposed as an alternative to the challenging RF baseline design of the FCC-ee. In this paper, random optimization methods are used to minimize the peak surface magnetic field and the maximum longitudinal impedance of the higher order modes (HOM) of a two-cell \unit[600]{MHz} SWELL cavity. In the next step, the waveguide slots are optimized to first have a smooth transition from the cavity to the slots to avoid large peak surface fields and second to achieve high transmission at dipole mode frequencies and low transmission at fundamental mode frequency while keeping the design compact.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK048  
About • Received ※ 23 May 2022 — Revised ※ 12 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 15 June 2022
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TUPOTK059 Modeling O and N Alloying in Nb for SRF Applications 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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TUPOTK064 HL-LHC Crab Cavity HOM Couplers: Challenges and Results 1374
 
  • J.A. Mitchell, R. Calaga, E. Montesinos
    CERN, Meyrin, Switzerland
  
  To compensate for the detrimental effect of the crossing angle on luminosity production in the High Luminosity Large Hadron Collider’s (HL-LHC) interaction regions, superconducting crab cavities (vertical and horizontal) will be installed at the two interaction regions of the ATLAS and CMS experiments. Both cavity designs use multiple Higher Order Mode (HOM) couplers to reduce beam instabilities and heat loads caused by the very high proton current in the HL-LHC. The conceptual RF designs of the HOM couplers are firstly presented, evaluating HOM damping requirements, fundamental mode rejection and dynamic heat load constraints. A special focus is given to the coupler’s characteristic impedance (Z0), to improve the robustness during transport and operation. Following this, RF measurements of the HOM couplers before installation, installed on the superconducting cavities and with a circulating proton beam are detailed, analysing deviations from the simulated cases.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK064  
About • Received ※ 07 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 10 July 2022
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TUPOTK065 Design of a Passive Superconducting Harmonic Cavity for HALF Storage Ring 1378
 
  • Y. Wei, B. Du, G. Feng, D. Jia, J. Pang, S.C. Zhang
    USTC/NSRL, Hefei, Anhui, People’s Republic of China
  • C.P. Welsch, H.D. Zhang
    The University of Liverpool, Liverpool, United Kingdom
  • C.P. Welsch, H.D. Zhang
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  
  Higher harmonic cavities, also known as Landau cavities, have been proposed to improve beam lifetime and provide Landau damping by lengthening the bunch without energy spread for stable operations of present and future low-emittance storage rings. This contribution presents design of a passive superconducting 3rd-harmonic cavity (super-3HC) for the planned Hefei Advanced Light Facility (HALF) at University of Science and Technology of China. It is designed to provide 0.43 MV at 1499.4 MHz for the nominal 2.2 GeV, 350 mA electron beam, and 1.44 MV main RF voltage in storage ring. Through optimizations it has a low R/Q < 45 Ohm, which has potential to achieve a good bunch lengthening. Higher-order-modes are strongly damped using a pair of room-temperature silicon carbide (SiC) rings to meet the requirement of beam instabilities. In addition, preliminary engineering design for the super-3HC cryomodule is also described in this contribution.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK065  
About • Received ※ 03 June 2022 — Revised ※ 09 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 17 June 2022
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