Author: Powers, T.
Paper Title Page
MOPTEV009 A Method for In-Situ Q0 Measurements of High-Quality SRF Resonators 221
 
  • S.V. Kuzikov, P.V. Avrakhov, C.-J. Jing, R.A. Kostin, Y. Zhao
    Euclid TechLabs, Solon, Ohio, USA
  • C.-J. Jing, C.-J. Jing
    ANL, Lemont, Illinois, USA
  • C.-J. Jing, R.A. Kostin
    Euclid Beamlabs, Bolingbrook, USA
  • R.A. Kostin, V.P. Yakovlev
    Fermilab, Batavia, Illinois, USA
  • T. Powers, R.A. Rimmer
    JLab, Newport News, Virginia, USA
 
  Funding: The work was supported in the part by DoE SBIR grant #DE-SC0019687.
Accelerator projects such as LCLS-II naturally require low-loss superconducting (SRF) cavities. Due to strong demand for improving intrinsic quality factor (Q0), importance of accurate cavity characterization increases. We propose a method to measure Q0 in situ for an SRF resonator installed in its cryogenic module and connected with a RF feed source via a fixed RF coupler. The method exploits measurements of a response for an SRF resonator fed by an amplitude-modulated signal. Such a signal can be synthesized as a beat-wave composed of two frequencies that are close to the resonant frequency. Analyzing the envelope of the reflected signal, one can find the difference in reflection for the chosen frequencies and use them to compute the intrinsic Q. We also develop the methodology to carry out measurements of Q0 at the nominal cavity operating voltage. We verified our method in experiments with a room temperature copper resonator and with two SRF resonators including Fermilab’s 650 MHz cavity and JLab’s 1500 MHz cavity.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-MOPTEV009  
About • Received ※ 15 June 2021 — Revised ※ 26 August 2021 — Accepted ※ 19 February 2022 — Issue date ※ 06 April 2022
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TUPTEV004 In Situ Plasma Processing of Superconducting Cavities at JLAB 485
 
  • T. Powers, N.C. Brock, T.D. Ganey
    JLab, Newport News, Virginia, USA
 
  Funding: Funding provided by SC Nuclear Physics Program through DOE SC Lab funding announcement Lab-20-2310
Jefferson Lab began a plasma processing program starting in the spring of 2019. Plasma processing is a common technique for removing hydrocarbons from surfaces, which increases the work function and reduces the secondary emission coefficient. Unlike helium processing which relies on ion bombardment of the field emitters, plasma processing uses free oxygen produced in the plasma to break down the hydrocarbons on the surface of the cavity. The residuals of the hydrocarbons in the form of water, carbon monoxide and carbon dioxide are removed from the cryomodule as part of the process gas flow. The initial focus of the effort is processing C100 cavities by injecting RF power into the HOM coupler ports. We will then start investigating processing of C50 cavities by introducing RF into the fundamental power coupler. The plan is to start processing cryomodules in the CEBAF tunnel in the mid-term future, with a goal of improving the operational gradients and the energy margin of the linacs. This work will describe the systems and methods used at JLAB for processing cavities using an argon oxygen gas mixture. Before and after plasma processing results will also be presented.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2021-TUPTEV004  
About • Received ※ 21 June 2021 — Accepted ※ 05 October 2021 — Issue date; ※ 02 May 2022  
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