Author: Kuzikov, S.V.
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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 ※  
About • Received ※ 15 June 2021 — Revised ※ 26 August 2021 — Accepted ※ 19 February 2022 — Issue date ※ 06 April 2022
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WEPCAV008 A Fast Mechanical Tuner for SRF Cavities 600
  • S.V. Kuzikov
    Euclid TechLabs, Solon, Ohio, USA
  • V.P. Yakovlev
    Fermilab, Batavia, Illinois, USA
  There is a particular need for fast tuners and phase shifters for advanced superconducting accelerator RF systems. The tuners based on ferrite, ferroelectric and piezo materials are commonly used. However, those methods suffer from one or another issue of high power loss, slow response, and narrow tuning range. We propose a robust, fast (up to ~5 MHz/sec), high efficient mechanical tuner for SRF cavities operating at the frequency 50 MHz. We develop an external mechanical tuner that is strongly coupled to the cavity. The tuner design represents a trade-off of high efficiency (low RF losses and low heat flux) and frequency tunability range. Our approach solves this trade-off issue. We propose RF design which exploits two coupled resonators so that a main high-field cavity is controlled with a small tunable resonator with a flexible metallic wall operating in a relatively low RF field. Simulations, carried out for a 7.5 MV/m 50 MHz SRF Quarter Wave Resonator (QWR), show that frequency tunability at level 10-3 is obtainable.  
DOI • reference for this paper ※  
About • Received ※ 17 June 2021 — Revised ※ 06 August 2021 — Accepted ※ 22 November 2021 — Issue date ※ 04 February 2022
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