Author: Longuevergne, D.
Paper Title Page
SUPCAV013 Multipacting Analysis of the Quadripolar Resonator (QPR) at HZB 42
 
  • S. Bira, D. Longuevergne
    Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
  • Y. Kalboussi
    CEA-IRFU, Gif-sur-Yvette, France
  • S. Keckert, J. Knobloch, O. Kugeler
    HZB, Berlin, Germany
  • Th. Proslier
    CEA-DRF-IRFU, France
 
  Multipacting (MP) is a resonating electron discharge, often plaguing radio-frequency (RF) structures, produced by the synchronization of emitted electrons with the RF fields and the electron multiplication at the impact point with the surface structure. The electron multiplication can take place only if the secondary emission yield (SEY, i.e. the number of electrons emitted due to the impact of one incoming electron), , is higher than 1. The SEY value depends strongly on the material and the surface contamination. Multipacting simulations are crucial in high-frenquency (HF) vacuum structures to localize and potentially improve the geometry. In this work, multipacting simulations were carried out on the geometry of the Quadrupole Resonator (QPR) in operation at HZB using the Spark 3D module in Microwave Studio suite (CST). These simulations helped to understand a particular behavior observed during the QPR tests, and furthermore made it possible to suggest enhancement ways in order to limit this phenomenon and facilitate its operation.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-SUPCAV013  
About • Received ※ 09 July 2021 — Revised ※ 09 July 2021 — Accepted ※ 09 April 2022 — Issue date ※ 07 May 2022
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MOPFDV001 Investigation of an Alternative Path for SRF Cavity Fabrication and Surface Processing 319
 
  • O. Hryhorenko, D. Longuevergne
    Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
  • C.Z. Antoine
    CEA-IRFU, Gif-sur-Yvette, France
  • F. Brisset
    ICMMO, Orsay, France
  • T. Dohmae
    KEK, Ibaraki, Japan
 
  The preparation of SRF cavities includes a lengthy, costly, and safety issued electrochemical polishing (EP or BCP) step to remove the damaged layer coming from the cavity fabrication. We have shown that most of the damage layer is originated from the rolling process during the preparation of the sheet material, while subsequent deep drawing tends to leave only µm thick damage layer. We propose a 2-steps mechanical process that allows us to easily get rid of the thick damage layer on the sheets before cavity forming. The process has been established on samples and extended to large disks ready for 1.3 GHz half-cell forming. The polished sheets will be then sent to KEK for half-cell forming and subsequent surface and material analysis before proceeding to half-cell welding. Former studies on the sample demonstrated that damages induced by forming can successfully be removed by recrystallization and less than 10 µm final chemistry.  
poster icon Poster MOPFDV001 [2.303 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-MOPFDV001  
About • Received ※ 25 June 2021 — Revised ※ 11 July 2021 — Accepted ※ 21 August 2021 — Issue date ※ 15 May 2022
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TUOFDV04
Evidence of Reduced Magnetic Sensitivities in Low Beta SRF Cavities  
 
  • D. Longuevergne
    Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
  • A. Miyazaki
    Uppsala University, Uppsala, Sweden
 
  Dedicated flux trapping experiments have been carried out on different types of low-beta superconducting accelerating cavities. The measured magnetic sensitivities of these complex geometries can be significantly lower than the predicted values calculated by commonly-used material-based models. In this paper, we suggest a new approach beyond the present material based models. Indeed, both the ambient magnetic field orientation and cavity geometry have a significant impact on the cavity performance degradation due to magnetic trapped flux. Experimental data are presented, and a new model to interpret the geometrical effect is introduced, assessed and shows as well very good agreement with data from the literature.  
slides icon Slides TUOFDV04 [1.259 MB]  
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TUPCAV002 HOM Excitation in Spoke Resonator for SRF Studies 435
 
  • D. Longuevergne, N. Bippus, F. Chatelet, V. Delpech, N. Hu, C. Joly, T. Pépin-Donat, F. Rabehasy, L. Renard
    Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
  • M. Baudrier
    CEA-DRF-IRFU, France
  • E. Cenni, L. Maurice
    CEA-IRFU, Gif-sur-Yvette, France
 
  The excitation of Higher Order Modes (HOM) or Lower Order Modes (LOM) has been performed for years on multi-cell superconducting accelerating cavities as a mean to coarsely locate a quench, a defective area or ignite a plasma for surface cleaning. Moreover, such multi-mode testing is very useful to understand more accurately the frequency dependence of the surface resistance in a wide range of surface magnetic fields (0<B<150mT). In that sense, several type of dedicated non-accelerating resonators like Quadrupole Resonator (QPR), Half- or Quarter- Wave resonators have been built to specifically study new superconducting materials or new surface or heat treatments. What is proposed in this paper is to perform such multi-mode analysis (352 MHz, 720 MHz and 1300 MHz) in an existing accelerating cavity, in particular a Spoke Resonator. Baseline results will be presented and perspectives of such technique will be discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-TUPCAV002  
About • Received ※ 22 June 2021 — Revised ※ 19 July 2021 — Accepted ※ 23 August 2021 — Issue date ※ 15 April 2022
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WEPCAV002 Improvement of Chemical Etching Capabilities (BCP) for SRF Spoke Resonators at IJCLab 590
 
  • J. Demercastel-Soulier, P. Duchesne, D. Longuevergne, G. Olry, T. Pépin-Donat, F. Rabehasy, D. Reynet, S. Roset, L.M. Vogt
    Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
 
  Buffered chemical polishing (BPC) is the reference surface polishing adopted for ESS and MYRRHA SRF spoke resonators at IJCLab. This chemical treatment, in addition to improving the RF performance, fits into the frequency adjustment strategy of the jacketed cavity during its preparation phase. In the framework of the collaboration with Fermilab for PIP-II project, IJCLab has developed a new setup to perform rotational BCP. The implementation of a rotation during chemical etching improves significantly the homogeneity and quality of surface polishing. In this paper, we present the numerical analysis based on a fluid dynamics model. The goal is to estimate the acid flow characteristics inside the cavity, determine the influence of several parameters as mass flow rate and rotation speed and propose the best configuration for the new experimental setup  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-WEPCAV002  
About • Received ※ 23 June 2021 — Revised ※ 18 August 2021 — Accepted ※ 21 August 2021 — Issue date ※ 14 January 2022
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FROFDV07
Material Engineering of ALD- Deposited Multilayer to Improve the Superconducting Performances of RF Cavities Under Intense RF Fields  
 
  • Y. Kalboussi
    CEA, DES-ISAS-DM2S, Université Paris-Saclay, Gif-sur-Yvette, France
  • C.Z. Antoine, B. Delatte
    CEA-IRFU, Gif-sur-Yvette, France
  • S. Bira, D. Longuevergne
    Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
  • D. Dragoe
    ICMMO, Orsay, France
  • J. Leroy
    CEA/DRF/IRAMIS/SIS2M, Gif sur Yvette, France
  • Th. Proslier
    CEA-DRF-IRFU, France
  • S. Tusseau-Nenez
    Ecole Polytechnique, Palaiseau, France
 
  We are exploring an original approach to improve the performance of bulk Niobium RF cavities through surface engineering with ALD superconducting multilayer capable of screening efficiently the magnetic fields and therefore inhibiting vortices penetration in Niobium cavities. As a first step for the multilayer, we aim at replacing the deleterious niobium native oxide by a clean interface between an insulator synthesized by ALD (Al2O3, Y2O3 and MgO) and the Niobium metal. To that end I will present the results obtained on both flat niobium samples and 1.3 GHz elliptical cavities. Our study shows that ALD deposited films are a good diffusion barrier, resist to thermal treatments and reduce significantly the presence of the niobium native oxide on the surface. Low SEY material such as TiN was also deposited on top of the insulator film to reduce multipacting phenomena. RF test on ALD coated cavities shows already a slight improvement of the superconducting performances. In parallel we started synthesizing superconducting NbTiN alloys by ALD. I will present preliminary results on the superconducting properties of NbTiN films grown on AlN by ALD with various compositions on Nbiobium.  
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