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SUPCAV018 First N-Doping and Mid-T Baking of Medium-ß 644 MHz 5-Cell Elliptical Superconducting RF Cavities for Michigan State University’s Facility for Rare Isotope Beams cavity, SRF, linac, cryomodule 53
  • K.E. McGee, S.H. Kim, P.N. Ostroumov, A. Taylor
    FRIB, East Lansing, Michigan, USA
  • G.V. Eremeev, M. Martinello, A.V. Netepenko
    Fermilab, Batavia, Illinois, USA
  • M.P. Kelly, T. Reid
    ANL, Lemont, Illinois, USA
  Funding: Work supported by the 2020 US DoE, Office of Science Graduate Student Research award (SCGSR), and US DoE, Office of Science, High Energy Physics under Cooperative Agreement award number DE-SC0018362
Two hadron linacs currently under development in the US, the PIP-II linac at Fermi National Accelerator Laboratory (FNAL) and the upgrade for Michigan State University’s Facility For Rare Isotope Beams (FRIB), will employ 650 and 644 MHz ß-0.6 elliptical superconducting cavities respectively to meet their design energy requirements. The desired CW operation modes of these two linacs sets Q-factor requirements well above any previously achieved for cavities at this operating frequency and velocity, driving the need to explore new high-Q treatments. The N-doping technique developed at FNAL and employed at an industrial scale to the LCLS-II cryomodules is a strong candidate for high-Q treatments, but work is needed to refine the treatment to the lower operating frequency and velocity regime. We present the first results of the first N-doping tests and a "mid-T" bake test in the FRIB 644 MHz 5-cell elliptical cavities.
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About • Received ※ 23 June 2021 — Revised ※ 16 November 2021 — Accepted ※ 08 May 2022 — Issue date ※ 08 May 2022
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SUPFDV013 HiPIMS NbN Thin Film Development for Use in Multilayer SIS Films site, lattice, ECR, cavity 91
  • S.B. Leith, B. Bai, X. Jiang, M. Vogel
    University Siegen, Siegen, Germany
  • R. Ries, E. Seiler
    Slovak Academy of Sciences, Institute of Electrical Engineering, Bratislava, Slovak Republic
  Funding: Authors acknowledge both the EASITrain, Marie Sklodowska-Curie Action (MSCA) Innovative Training Network (ITN), Grant Agreement no. 764879 and the ARIES collaboration, Grant Agreement no. 730871
As part of efforts to improve the performance of SRF cavities, the use of alternative structures, such as superconductor-insulator-superconductor (SIS) film coatings have been extensively investigated. Initial efforts using DC magnetron sputtering (MS) deposited NbN films showed the efficacy of this approach. The use of energetic condensation methods, such as high power impulse magnetron sputtering (HiPIMS), have already improved the performance of Nb thin films for SRF cavities and have already been used for nitride film coatings in the tool industry. In this contribution, the results from the deposition of HiPIMS NbN thin films onto oxygen free high conductivity (OFHC) Cu substrates are presented. The effects of the different deposition parameters on the deposited films were elucidated through various characterisation methods, resulting in an optimum coating procedure. This allowed for further comparison between the HiPIMS NbN films and the previously presented DC MS NbN films. The results indicate the improvements offered by HiPIMS deposition, most notably, the significant increase in the entry field, and its applicability to the deposition of SIS films on Cu.
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About • Received ※ 20 June 2021 — Revised ※ 08 July 2021 — Accepted ※ 12 August 2021 — Issue date ※ 25 October 2021
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SUPTEV002 Application of Plasma Electrolytic Polishing onto SRF Substrates SRF, plasma, cavity, power-supply 116
  • E. Chyhyrynets, O. Azzolini, R. Caforio, V.A. Garcia Diaz, G. Keppel, C. Pira, F. Stivanello, M. Zanierato
    INFN/LNL, Legnaro (PD), Italy
  Funding: Work supported by the INFN CSNV experiment TEFEN. This project has received funding from the Euro-pean Union’s Horizon 2020 Research and Innovation programme under GA No 101004730.
A new promising approach of SRF substrates surface treatment has been studied - Plasma Electrolytic Polishing (PEP). The possible application of PEP can be used not only on conventional elliptical resonators, but also on other components of SRF such as, for example, couplers or Quadrupole resonators (QPRs). However, SRF application of PEP represents a challenge since it requires a different approach to treat the inner surface of elliptical cavities respect to electropolishing. In this work, the main problematics and possible solutions, the equipment, and the polishing system requirements will be shown. A proposed polishing system for 6 GHz elliptical cavities and QPRs will be shown and discussed.
poster icon Poster SUPTEV002 [2.710 MB]  
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About • Received ※ 21 June 2021 — Revised ※ 08 July 2021 — Accepted ※ 12 August 2021 — Issue date ※ 22 April 2022
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MOPTEV014 New Improved Horizontal Electropolishing System for SRF Cavities cavity, controls, operation, MMI 237
  • C.E. Reece, S. Castagnola, P. Denny, A.L.A. Mitchell
    JLab, Newport News, Virginia, USA
  Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OThR23177.
The best performance of niobium SRF accelerating cavities is obtained with surfaces smoothed with electropolishing chemical finishing. Jefferson Lab has recently specified, procured, installed, and commissioned a new versatile production electropolishing (EP) tool. Experience with EP research and operations at JLab as well as vendor interactions and experience guided development of the system specification. Detailed design and fabrication was awarded by contract to Semiconductor Process Equipment Corporation (SPEC). The delivered system was integrated into the JLab chemroom infrastructure and commissioned in 2020. The new EP tool provides much improved heat exchange from the circulating H2SO4/HF electrolyte and also the cavity via variable temperature external cooling water flow, resulting in quite uniform cavity wall temperature control and thus improved removal uniformity. With the JLab infrastructure, stabilized process temperature as low as 5 C is available. We describe the system and illustrate operational modes in this contribution.
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About • Received ※ 21 June 2021 — Revised ※ 08 July 2021 — Accepted ※ 19 August 2021 — Issue date ※ 31 March 2022
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TUPCAV001 Vertical Electro-Polishing of 704 MHz Resonators Using Ninja Cathode: First Results cavity, niobium, experiment, linac 431
  • F. Éozénou, M. Baudrier, E. Cenni, E. Fayette, L. Maurice, C. Servouin
    CEA-DRF-IRFU, France
  • V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi
    MGH, Hyogo-ken, Japan
  • H. Hayano, H. Ito, S. Kato, T. Kubo, H. Monjushiro, T. Saeki
    KEK, Ibaraki, Japan
  • G. Jullien
    CEA-IRFU, Gif-sur-Yvette, France
  Vertical Electro-Polishing (VEP) of elliptical cavities using rotating Ninja cathodes (Marui Company patented technology) has continually been improved since 2012 and successfully applied for 1300MHz multicell ILC-type resonators. The goal of the presented study is to apply this technology to 704 MHz ESS-type resonators with both better Q0 and accelerating gradients in mind. We intend to demonstrate the superiority of VEP compared to standard Buffer Chemical Polishing (BCP), for possible applications such as MYRRHA accelerator. We describe here the promising results achieved on β=0.86 single-cell cavity after 200 µm uniform removal. The cavity quenched at 27 MV/m without any heat treatment. The surface resistance achieved was less than 5nΩ at 1.8K. Substantial performance improvement is expected after heat treatment of the cavity and additional 20 µm VEP sequence. A cathode for 5-Cell ESS cavity is concomitantly under design stage.  
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About • Received ※ 21 June 2021 — Revised ※ 16 August 2021 — Accepted ※ 23 August 2021 — Issue date ※ 17 March 2022
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TUPTEV001 RF Experience from 6 Years of ELBE SRF-Gun II Operation cavity, gun, SRF, operation 477
  • A. Arnold, P.N. Lu, S. Ma, P. Murcek, A.A. Ryzhov, J. Schaber, J. Teichert, H. Vennekate, R. Xiang
    HZDR, Dresden, Germany
  • G. Ciovati, P. Kneisel
    JLab, Newport News, Virginia, USA
  At the electron accelerator for beams with high brilliance and low emittance (ELBE), the second version of a superconducting radio-frequency (SRF) photoinjector was brought into operation in 2014. After a period of commissioning, a gradual transfer to routine operation took place in 2017 and 2018, so that more than 3000h of user beam have already been generated since 2019. During this time, a total of 20 cathodes (2 Cu, 12 Mg, 6 Cs2Te) were used, but no serious cavity degradation was observed. In this paper, we summarize the operational experience of the last 6 years of SRF gun operation, with special emphasis on the main RF properties of the cavity. This includes the evolution of QvsE, dark current, multipacting, but also mechanical properties such as Lorentz force detuning, helium pressure sensitivity as well as microphonics. The latter is closely connected to an active compensation by a so-called low-level RF feedback loop, which is also briefly presented.  
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About • Received ※ 21 June 2021 — Revised ※ 25 December 2021 — Accepted ※ 22 February 2022 — Issue date ※ 16 April 2022
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TUPTEV006 Development and Adustment of Tools for Superconducting RF Gun Cavities cavity, gun, SRF, FEL 495
  • B. van der Horst, D. Klinke, A. Muhs, M. Schmökel, J.K. Sekutowicz, S. Sievers, N. Steinhau-Kühl, A. Sulimov, J.H. Thie, L. Trelle, E. Vogel
    DESY, Hamburg, Germany
  For the superconducting radio frequency (SRF) 1.6-cell gun cavities (CV) developed at DESY, a similar fabrication and treatment process, as for the European XFEL 9-cell cavities is foreseen. The different length and geometry of these cavities lead to a number of adjustments to existing and the development of new tools. This paper covers the new designs and adaptations of a tuning tool, chemistry flanges, a wall thickness measurement device, as well as a new high-pressure rinsing spray head and an optical inspection camera for the 1.6-cell 1.3 GHz DESY SRF gun cavities under the development for the European XFEL.  
poster icon Poster TUPTEV006 [1.397 MB]  
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About • Received ※ 21 June 2021 — Revised ※ 05 August 2021 — Accepted ※ 18 September 2021 — Issue date ※ 18 November 2021
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WEPFDV006 Activities at NCBJ Towards Development of the Future, Fully-Superconducting, XFEL-Type, RF Electron Gun gun, electron, cavity, plasma 566
  • J. Lorkiewicz, P.J. Czuma, A.M. Kosińska, P. Krawczyk, R.M. Mirowski, R. Nietubyć, M. Staszczak, K. Szamota-Leandersson
    NCBJ, Świerk/Otwock, Poland
  • J.K. Sekutowicz
    DESY, Hamburg, Germany
  Our group at NCBJ works on upgrade of 1.6-cell, SRF, XFEL-type injector in collaboration with DESY and other laboratories. The work is focused on preparation of lead-on-niobium photocathode, its positioning in the gun cavity and on the UV laser system for photocurrent excitation. RF focusing effect was used to minimize the predicted emittance and transverse size of accelerated e- beam. Following beam dynamics computation, it has been proposed that the photocathode be recessed 0.45 mm into the rear wall of the gun cavity. It helps focusing e- beam in its low-energy part. Preparation of sc cathodes of Pb layer on Nb plugs (*, **) is reported, aimed at reaching clean, planar and uniform Pb films. The laser system will consist of commercially available Pharos laser and a 4-th harmonic generator. A gaussian, 300 fs long, 257 nm in wavelength UV pulse will be transformed in time by a pulse stretcher/stacker and in space by pi-shaper. The planned optical system will generate cylindrical photoelectron bunch 2 - 30 ps long and 0.2 - 3 mm wide.
* J. Lorkiewicz et al., Vacuum 179 (2020) 109524
** R. Nietubyc et al., NIM A891 (2018) pp. 78-86
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About • Received ※ 21 June 2021 — Accepted ※ 13 April 2022 — Issue date; ※ 03 May 2022  
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THOTEV06 Plasma Electrolytic Polishing as a Promising Treatment Replacement of Electropolishing in the Copper and Niobium Substrate Preparation for SRF plasma, cavity, SRF, niobium 718
  • C. Pira, O. Azzolini, R. Caforio, E. Chyhyrynets, V.A. Garcia, G. Keppel, F. Stivanello
    INFN/LNL, Legnaro (PD), Italy
  Superconducting radio frequency (SRF) cavities performances strongly depend on the substrate preparation. Currently, the conventional protocol of SRF surface preparation includes electropolishing (EP) as the main treatment achieving low roughness, clean and non-contaminated surfaces, both for bulk Nb and Cu substrates. Harsh and non-environmentally friendly solutions are typically used: HF and H2SO4 mixture for Nb, and H3PO4 with Butanol mixtures for EP of Cu. This research is focused on the application of a relatively new technique "Plasma Electrolytic Polishing" (PEP) for the SRF needs. PEP technology is an evolution of EP with a list of advantages that SRF community can benefit from. PEP requires diluted salt solutions moving to a greener approach in respect to EP. PEP can in principle substitute, or completely eliminate, intermediate steps, like mechanical and/or (electro) chemical polishing. Thanks to the superior removing rate in the field (up to 3.5 µm/min of Nb, and 10 µm/min of Cu) in one single treatment roughness below 100 nm Ra has been obtained both for Nb and Cu. In the present work a proof of concept is shown on Nb and Cu planar samples.  
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About • Received ※ 21 June 2021 — Accepted ※ 18 October 2021 — Issue date; ※ 01 May 2022  
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THPCAV003 Impact of Vertical Electropolishing with Flipping System on Removal Uniformity and Surface State: Study with 9-Cell Niobium Coupon Cavity cavity, experiment, niobium, status 783
  • K.N. Nii, V. Chouhan, Y.I. Ida, T.Y. Yamaguchi
    MGH, Hyogo-ken, Japan
  • H. Hayano, S. Kato, H. Monjushiro, T. Saeki
    KEK, Ibaraki, Japan
  We have been developing a vertical electropolishing (VEP) method for niobium superconducting RF cavities using a novel setup that allows periodic flipping of the cavity to put it upside down in the VEP process. The purpose of using the novel setup named as flipping system is to achieve uniform removal and smooth surface of the cavity. Previously, we have already introduced the VEP system and showed the preliminary results of VEP performed with the flipping system. In this article, we report VEP results obtained with a nine-cell coupon cavity. The results include detail on coupon currents with I-V curves for coupons, and impact of the cavity flipping on removal uniformity and surface morphology of the cavity.  
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About • Received ※ 19 June 2021 — Revised ※ 10 August 2021 — Accepted ※ 22 October 2021 — Issue date ※ 23 November 2021
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