Author: Lindberg, R.R.
Paper Title Page
Higher Harmonic XFELO with the Planned 4 GeV LCLS II SCRF Linac  
  • K.-J. Kim, B.W. Adams, R.R. Lindberg, D. Shu, Yu. Shvyd'ko
    ANL, Argonne, Ilinois, USA
  • Z. Huang
    SLAC, Menlo Park, California, USA
  Funding: This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences under contract No. DE-AC02-06CH11357 (ANL) and DE-AC02-76SF00515 (SLAC)
An x-ray FEL oscillator (XFELO) will produce hard x-ray pulses of ultra-fine spectral resolution (~ meV) that combines FEL brightness with storage ring stability [1]. Thus, for example, the long-standing problem of high-TC superconductivity could be solved by inelastic x-ray scattering. In addition, an x-ray spectral comb can in principle be generated, vastly expanding the reach of experimental x-ray quantum optics. The accelerator for an XFELO should optimally be of the CW superconducting type. The linac for the European XFEL can be operated in CW mode without adding more cooling capacity if the energy is lowered from 14 to 7 GeV [2]. It is also possible to drive a hard x-ray XFELO at lower than 7 GeV, if a higher harmonic is chosen as the operating wavelength [3]. We have studied XFELO for 1 Å x-rays operating at the third or fifth harmonic using the 4 GeV SCRF linac planned for LCLS-II. Assuming bunch charge=50 pC, normalized rms emittance=0.2 mm-mrad, rms energy spread=500 keV, rms bunch length=190 fs, and undulator period length=2.6 cm, the gain at 1 Å as a 5th harmonic is found to be about 40%, sufficient for lasing allowing for the various losses.
[1] K.-J. Kim, Y. Shvyd’ko, and S. Reiche, Phys. Rev. Lett. 100,244802 (2008)
[2] J.K. Sekutowicz, et al., 2013 FEL Conf.(2013)
[3] J. Dai, H. Deng, and Z. Dai, Phys. Rev. Lett. 108,034802(2012)
slides icon Slides WEA03 [2.703 MB]  
THP039 Commissioning of the Photo-Cathode RF Gun at APS 803
  • Y.-E. Sun, J.C. Dooling, R.R. Lindberg, A. Nassiri, S.J. Pasky, H. Shang, T.L. Smith, A. Zholents
    ANL, Argonne, Ilinois, USA
  A S-band RF gun is recently RF conditioned and commissioned at APS, Argonne. In this paper we report the high-power RF conditioning process of the gun. Dark currents are monitored during the RF conditioning and found to be less than 150pC. Following the RF conditioning, photo-electron beams are generated from the gun and the copper cathode quantum efficiency is monitored. We study the quantum efficiency as gun gradient varies and vacuum condition improves. Photo-electron beam enery and emittance are measured as RF gun gradient and solenoid, as well as drive-laser conditions are varied. Finally we compare our experimental results with numerical simulations.
Work supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.
FRB02 A Collinear Wakefield Accelerator for a High Repetition Rate Multi-beamline Soft X-ray FEL Facility 993
  • A. Zholents, W. Gai, R.R. Lindberg, J.G. Power, Y.-E. Sun
    ANL, Argonne, Ilinois, USA
  • C.-J. Jing, A. Kanareykin
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • C. Li, C.-X. Tang
    TUB, Beijing, People's Republic of China
  • D.Y. Shchegolkov, E.I. Simakov
    LANL, Los Alamos, New Mexico, USA
  Funding: Supported by U.S. Department of Energy under Contract No. DE-AC02-06CH11357 and by the U.S. Department of Energy Laboratory LDRD program at Los Alamos National Laboratory.
A concept is presented for a multi beamline soft x-ray free-electron laser (FEL) facility where several FEL undulator lines are driven by an equal number of high repetition rate single-stage collinear wakefield accelerators (CWA). A practical design of the CWA, extending over 30 meters and embedded into a quadrupole wiggler, is considered. The wiggler’s structure of alternating focusing and defocusing quadrupoles is used to control single-bunch breakup instability. It is shown that practical restrictions on the maximum attainable quadrupole field limit the maximum attainable charge in the drive bunch whose sole purpose is to produce a high accelerating field in the CWA for the following main bunch. It is also pointed out that the distance between drive and main bunches varies along the accelerator, causing a measurable impact on the energy gain by the main bunch and on the energy spread of electrons in it. Means to mitigate these effects are proposed and results are presented for numerical simulations demonstrating the main bunch with plausible parameters for FEL application including a relatively small energy spread. Finally, results are presented for the expected FEL performance using an appropriately chosen undulator.
slides icon Slides FRB02 [6.512 MB]