Author: Kim, Y.K.
Paper Title Page
MOPA34 Noise in Intense Electron Bunches 128
  • S. Nagaitsev, D.R. Broemmelsiek, J.D. Jarvis, A.H. Lumpkin, J. Ruan, G.W. Saewert, R.M. Thurman-Keup
    Fermilab, Batavia, Illinois, USA
  • Z. Huang, G. Stupakov
    SLAC, Menlo Park, California, USA
  • Y.K. Kim
    University of Chicago, Chicago, Illinois, USA
  We report on our investigations into density fluctuations in electron bunches. Noise and density fluctuations in relativistic electron bunches, accelerated in a linac, are of critical importance to various Coherent Electron Cooling (CEC) concepts as well as to free-electron lasers (FELs). For CEC, the beam noise results in additional diffusion that counteracts cooling. In SASE FELs, a microwave instability starts from the initial noise in the beam and eventually leads to the beam microbunching yielding coherent radiation, and the initial noise in the FEL bandwidth plays a useful role. In seeded FELs, in contrast, such noise interferes with the seed signal, so that reducing noise at the initial seed wavelength would lower the seed laser power requirement. Status of the project will be presented.  
poster icon Poster MOPA34 [0.638 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA34  
About • Received ※ 10 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 14 August 2022 — Issue date ※ 24 August 2022
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MOPA67 Examining the Effects of Oxygen Doping on SRF Cavity Performance 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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WEYE6 Thermionic Sources for Electron Cooling at IOTA 588
  • M.K. Bossard, Y.K. Kim
    University of Chicago, Chicago, Illinois, USA
  • N. Banerjee, J.A. Brandt
    Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA
  • B.L. Cathey, S. Nagaitsev, G. Stancari
    Fermilab, Batavia, Illinois, USA
  • M.A. Krieg
    Saint Olaf College, Northfield, MN, USA
  We are planning a new electron cooling experiment at the Integrable Optics Test Accelerator (IOTA) at Fermilab for cooling ~2.5 MeV protons in the presence of intense space-charge. Here we present the simulations and design of a thermionic electron source for cooling at IOTA. We particularly discuss parameters of the thermionic source electrodes, as well as the simulation results. We also present a new electron source test-stand at the University of Chicago, which will be used to test the new thermionic electron source, as well as other electron sources. In addition, we discuss results from analyzing the test stand operations with a currently existing electron source. Furthermore, we present future steps for the test stand as well as production and commissioning of the thermionic source at IOTA.  
slides icon Slides WEYE6 [3.182 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEYE6  
About • Received ※ 02 August 2022 — Revised ※ 07 August 2022 — Accepted ※ 08 August 2022 — Issue date ※ 28 August 2022
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THYE5 Analysis of Low RRR SRF Cavities 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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