Author: Carlsten, B.E.
Paper Title Page
TUP016 Beam-Dynamics Analysis of Long-Range Wakefield Effects on the SCRF Cavities at the Fast Facility 1
  • Y.-M. Shin
    Northern Illinois University, DeKalb, Illinois, USA
  • K. Bishofberger, B.E. Carlsten, F.L. Krawczyk
    LANL, Los Alamos, New Mexico, USA
  • A.H. Lumpkin, J. Ruan, R.M. Thurman-Keup
    Fermilab, Batavia, Illinois, USA
  Funding: Work supported by the subcontract (contract No: G2A62653) of LANL-LDRD program and DOE contract No. DEAC02-07CH11359 to the Fermi Research Alliance LLC.
Long-range wakefields in superconducting RF (SCRF) cavities create complicated effects on beam dynamics in SCRF-based FEL beamlines. The driving bunch excites effectively an infinite number of structure modes (including HOMs) which oscillate within the SCRF cavity. Couplers with loads are used to damp the HOMs. However, these HOMs can persist for long periods of time in superconducting structures, which leads to long-range wakefields. Clear understanding of the long-range wakefield effects is a critical element for risk mitigation of future SCRF accelerators such as XFEL at DESY, LCLS-II XFEL, and MaRIE XFEL. We are currently developing numerical tools for simulating long-range wakefields in SCRF accelerators and plan to experimentally verify the tools by measuring these wakefields at the Fermilab Accelerator Science and Technology (FAST) facility. This paper previews the experimental conditions at the FAST 50 MeV beamline based on the simulation results.
WEP034 Diagnostics Upgrades for Investigations of HOM Effects in TESLA-type SCRF Cavities 1
  • A.H. Lumpkin, N. Eddy, D.R. Edstrom, P.S. Prieto, J. Ruan, Y.-M. Shin, R.M. Thurman-Keup
    Fermilab, Batavia, Illinois, USA
  • B.E. Carlsten
    LANL, Los Alamos, New Mexico, USA
  Funding: Work at FNAL supported by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. DoE. Work at LANL supported by U.S. DoE through the LANL/LDRD Program.
We describe the upgrades to diagnostic capabilities on the Fermilab Accelerator Science and Technology (FAST) electron linear accelerator that will allow investigations of the effects of high-order modes (HOMs) in SCRF cavities on macropulse-average beam quality. We focus here on the dipole modes in the first pass-band generally observed in the 1.6-1.9 GHz regime in TESLA-type SCRF cavities due to uniform transverse beam offsets of the electron beam. Such cavities are the basis of the accelerator for the European XFEL and the proposed MaRIE XFEL facility. Initial HOM data indicate that the mode intensities oscillate for about 10 microseconds after the micropulse enters the cavity, resulting in centroid shifts throughout the train. This results in a blurring of the averaged beam image size. The upgrades will include optimizing the HOM detectors' bandpass filters and adding a 1.3-GHz notch filter, converting the BPM electronics to bunch-by-bunch processing, and using the C5680 streak camera in a framing mode for bunch-by-bunch spatial information at the <20-micron level. The preliminary HOM detector data, prototype BPM test data, and first framing camera OTR data will be presented.