Keyword: niobium
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MOYE3 Experiments on a Conduction Cooled Superconducting Radio Frequency Cavity with Field Emission Cathode cavity, experiment, SRF, accelerating-gradient 16
  • Y. Ji, R. Dhuley, C.J. Edwards, J.C.T. Thangaraj
    Fermilab, Batavia, Illinois, USA
  • V. Korampally, D. Mihalcea, O. Mohsen, P. Piot, I. Salehinia
    Northern Illinois University, DeKalb, Illinois, USA
  Funding: The project is supported by DOE HEP Accelerator Stewardship award to Fermilab and Northern Illinois University
To achieve Ampere-class electron beam accelerators the pulse delivery rate need to be much higher than the typical photo injector repetition rate of the order of a few kilohertz. We propose here an injector which can, in principle, generate electron bunches at the same rate as the operating RF frequency. A conduction-cooled superconducting radio frequency (SRF) cavity operating in the CW mode and housing a field emission element at its region of high axial electric field can be a viable method of generating high-repetition-rate electron bunches. In this paper, we report the development and experiments on a conduction-cooled Nb3Sn cavity with a niobium rod intended as a field emitter support. The initial experiments demonstrate ~0.4 MV/m average accelerating gradient, which is equivalent of peak gradient of 3.2 MV/m. The measured RF cavity quality factor is 1.4 × 108 slightly above our goal. The achieved field gradient is limited by the relatively low input RF power and by the poor coupling between the external power supply and the RF cavity. With ideal coupling the field gradient can be as high as 0.6 MV/m still below our goal of about 1 MV/m
slides icon Slides MOYE3 [1.444 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOYE3  
About • Received ※ 01 August 2022 — Revised ※ 03 August 2022 — Accepted ※ 05 August 2022 — Issue date ※ 30 September 2022
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MOPA21 Effect of Electropolishing on Nitrogen Doped and Undoped Niobium Surfaces cavity, SRF, factory, superconducting-RF 93
  • V. Chouhan, F. Furuta, M. Martinello, T.J. Ring, G. Wu
    Fermilab, Batavia, Illinois, USA
  Cold electropolishing (EP) of a nitrogen-doped (N-doped) niobium (Nb) superconducting RF (SRF) cavity was found to improve its quality factor. In order to understand the effect of EP temperature on N-doped and undoped surfaces, a systematic EP study was conducted with 2/0 N-doped and heat-treated Nb samples in a beaker. The Nb samples were electropolished at different surface temperatures ranging from 0 to 42 C. The results showed that the doped surface was susceptible to the sample temperature during EP. EP resulted in the surface pitting on the doped samples where the number density of pits increased at a higher temperature. The surface results were compared with the surface of cutouts from a 9-cell cavity which was 2/0 N-doped and electropolished. This paper shows de-tailed surface features of the N-doped and undoped Nb surfaces electropolished at different temperatures.  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA21  
About • Received ※ 20 July 2022 — Revised ※ 24 July 2022 — Accepted ※ 09 August 2022 — Issue date ※ 11 August 2022
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MOPA22 Study on Electropolishing Conditions for 650 MHz Niobium SRF Cavity cavity, cathode, SRF, power-supply 97
  • V. Chouhan, D.J. Bice, F. Furuta, M. Martinello, M.K. Ng, H. Park, T.J. Ring, G. Wu
    Fermilab, Batavia, Illinois, USA
  • B.M. Guilfoyle, M.P. Kelly, T. Reid
    ANL, Lemont, Illinois, USA
  The PIP II linear accelerator includes different types of niobium SRF cavities including 650 MHz elliptical low (0.61) and high (0.92) beta cavities. The elliptical cavity surface is processed with the electropolishing method. The elliptical cavities especially the low-beta 650 MHz cavities showed a rough equator surface after the EP was performed with the standard EP conditions. This work was focused to study the effect of different EP parameters, including cathode surface area, temperature and voltage, and optimize them to improve the cavity surface.  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA22  
About • Received ※ 02 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 03 September 2022
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MOPA24 LCLS-II and HE Cryomodule Microphonics at CMTF at Fermilab cavity, cryomodule, cryogenics, SRF 103
  • C. Contreras-Martinez, B.E. Chase, A.T. Cravatta, J.A. Einstein-Curtis, E.R. Harms, J.P. Holzbauer, J.N. Makara, S. Posen, R. Wang
    Fermilab, Batavia, Illinois, USA
  • L.R. Doolittle
    LBNL, Berkeley, California, USA
  Microphonics causes the cavity to detune. This study discusses the microphonics of 16 cryomodules, 14 for LCLS-II and 2 for LCLS-II HE tested at CMTF. The peak detuning, as well as the RMS detuning for each cryomodule, will be discussed. For each cryomodule, the data was taken with enough soaking time to prevent any thermalization effects which can show up in the detuning. Each data capture taken was 30 minutes or longer and sampled at 1 kHz.  
poster icon Poster MOPA24 [1.428 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA24  
About • Received ※ 03 August 2022 — Revised ※ 10 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 20 September 2022
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MOPA42 Considerations Concerning the Use of HTS Conductor for Accelerator Dipoles with Inductions above 15 T dipole, induction, quadrupole, superconductivity 143
  • M.A. Green
    LBNL, Berkeley, California, USA
  Funding: This work was supported by the office of Science, under US Department of Energy contract number DE-AC-02-05CH11231.
The use of high temperature superconductors for accelerator dipole has been discussed for about twenty years and maybe a little more. Conductors that can potentially be used for accelerator magnets have been available for about fifteen years. These conductors are REBCO tape conductors, which can be wound into coils with no reaction after winding, and BISSCO cable conductors, which require reaction after winding and insulation after reaction in a process similar to Nb3Sn cables. Both conductors are expensive and the process after reacting is expensive. Some unknown factors that remain: Will either conductor degrade in current carrying capacity with repeated cycling like Nb3Sn cables do? The other two issues are problems for both types of HTS conductors and they are; 1) quench protection in the event of a normal region run-away and 2) dealing with the superconducting magnetization inherent with HTS cables and tapes. This paper will discuss the last two issues and maybe will provide a partial solution to these problems.
poster icon Poster MOPA42 [1.498 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA42  
About • Received ※ 01 August 2022 — Revised ※ 08 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 23 August 2022
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MOPA62 High Quality Conformal Coatings on Accelerator Components via Novel Radial Magnetron with High-Power Impulse Magnetron Sputtering GUI, target, plasma, SRF 182
  • W.M. Huber, I. Haehnlein, T.J. Houlahan, B.E. Jurczyk, A.S. Morrice, R.A. Stubbers
    Starfire Industries LLC, Champaign, USA
  Funding: This material is based upon work supported by the U.S. Department of Energy under Award Numbers DE-SC0019784 and DE-SC0020481.
In this work, we present two configurations of a novel radial magnetron design that are suitable for coating the complex inner surfaces of a variety of modern particle accelerator components. These devices have been used in conjunction with high-power impulse magnetron sputtering (HiPIMS) to deposit copper and niobium films onto the inner surfaces of bellows assemblies, waveguides, and SRF cavities. These films, with thicknesses of up to 3 µm and 40 µm for niobium and copper, respectively, have been shown to be conformal, adherent, and conductive. In the case of copper, the post-bake RRR values of the resulting films are well within the range specified for electroplating of the LCLS-II bellows and CEBAF waveguide assemblies. In addition to requiring no chemical processing beyond a detergent rinse and solvent degrease, this magnetron design exhibits over 80% target material utilization. Further, in the case of niobium, an enhancement in RRR over that of the bulk (target) material has been observed.
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA62  
About • Received ※ 02 August 2022 — Revised ※ 05 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 21 August 2022
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MOPA67 Examining the Effects of Oxygen Doping on SRF Cavity Performance cavity, SRF, ECR, radio-frequency 196
  • 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 accelerators cold by reducing power loss. The performance of SRF cavities is largely governed by the surface composition of the first 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 fundamental material properties to understand how these impurities affect performance. This enables us to have further insight into the underlying mechanisms that enable these surface treatments to yield high Q0 performance.  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA67  
About • Received ※ 02 August 2022 — Accepted ※ 05 August 2022 — Issue date ※ 03 October 2022  
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WEZE5 Magnetic Flux Expulsion in Superconducting Radio-Frequency Niobium Cavities Made from Cold Worked Niobium cavity, SRF, radio-frequency, ECR 611
  • B.D. Khanal
    ODU, Norfolk, Virginia, USA
  • S. Balachandran, P.J. Lee
    NHMFL, Tallahassee, Florida, USA
  • S. Chetri
    ASC, Tallahassee, Florida, USA
  • P. Dhakal
    JLab, Newport News, Virginia, USA
  Trapped residual magnetic field during the cool down of superconducting radio frequency (SRF) cavities is one of the primary sources of RF residual losses leading to lower quality factor. Historically, SRF cavities have been fabricated from high purity fine grain niobium with grain size ~50 to 100 µm as well as large grain with grain size of the order of few centimeters. Non-uniform recrystallization of fine-grain Nb cavities after the post fabrication heat treatment leads to higher flux trapping during the cool down, and hence the lower quality factor. We fabricated two 1.3 GHz single cell cavities from cold-worked niobium from different vendors and processed along with cavities made from SRF grade Nb. The flux expulsion and flux trapping sensitivity were measured after successive heat treatments in the range 800 to 1000°C. The flux expulsion from cold-worked fine-grain Nb cavities improves after 800°C/3h heat treatments and it becomes similar to that of standard fine-grain Nb cavities when the heat treatment temperature is higher than 900°C.  
slides icon Slides WEZE5 [2.029 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEZE5  
About • Received ※ 01 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 31 August 2022
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WEPA27 Effect of Duration of 120 °C Baking on the Performance of Superconducting Radio Frequency Niobium Cavities cavity, SRF, radio-frequency, accelerating-gradient 683
  • B.D. Khanal
    ODU, Norfolk, Virginia, USA
  • P. Dhakal
    JLab, Newport News, Virginia, USA
  Over the last decade much attention was given in increasing the quality factor of superconducting radio frequency (SRF) cavities by impurity doping. Prior to the era of doping, the final cavity processing technique to achieve the high accelerating gradient includes the "in situ" low temperature baking of SRF cavities at temperature ~ 120°C for several hours. Here, we present the results of a series of measurements on 1.3 GHz TESLA shape single-cell cavities with successive low temperature baking at 120°C up to 96 hours. The experimental data were analyzed with available theory of superconductivity to elucidate the effect of the duration of low temperature baking on the superconducting properties of cavity materials as well as the RF performance. In addition, the RF loss related to the trapping of residual magnetic field refereed as flux trapping sensitivity was measured with respect to the duration of 120°C bake.  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA27  
About • Received ※ 01 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 19 August 2022
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WEPA52 Demonstration of Twice-Reduced Lorentz-Force Detuning in SRF Cavity by Copper Cold Spraying cavity, SRF, site, accelerating-gradient 749
  • R.A. Kostin, C.-J. Jing, A. Kanareykin
    Euclid TechLabs, Solon, Ohio, USA
  • G. Ciovati
    JLab, Newport News, Virginia, USA
  Funding: The project is funded by DOE SBIR # DE-SC0019589
Superconducting RF (SRF) cavities usually are made from thin-walled high RRR Niobium and are susceptible to Lorentz Force Detuning (LFD) ’ cavity deformation phenomena by RF fields. In this paper, we present high gradient cryogenic results of an SRF cavity with two times reduced LFD achieved by copper cold spray reinforcement without sacrificing cavity flexibility for tuning. Finite-element model was developed first to find the best geometry for LFD reduction, which incorporated coupled RF, structural and thermal modules, and is also presented.
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA52  
About • Received ※ 27 July 2022 — Revised ※ 03 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 16 August 2022
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THYE5 Analysis of Low RRR SRF Cavities cavity, SRF, accelerating-gradient, radio-frequency 877
  • K. Howard, Y.K. Kim
    University of Chicago, Chicago, Illinois, USA
  • D. Bafia, A. Grassellino
    Fermilab, Batavia, Illinois, USA
  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 performed surface treatments, low temperature baking and nitrogen-doping, on low RRR cavities to evaluate how the intentional addition of more impurities 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 THYE5 [5.013 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-THYE5  
About • Received ※ 03 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 01 October 2022
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