Author: Lumpkin, A.H.
Paper Title Page
MOPSO51 Feasibility of an XUV FEL Oscillator at ASTA 88
 
  • A.H. Lumpkin
    Fermilab, Batavia, USA
  • H. Freund
    LANL, Los Alamos, New Mexico, USA
  • M.W. Reinsch
    LBNL, Berkeley, California, USA
 
  Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
A significant opportunity exists at the Advanced Superconducting Test Accelerator (ASTA) facility presently under construction at Fermilab to enable the first XUV free electron laser (FEL) oscillator experiments. The ultrabright beam from the L-band photoinjector will provide sufficient gain to compensate for reduced mirror reflectances in the VUV-XUV regimes, the 3-MHz micropulse repetition rate for 1 ms will support an oscillator configuration, the SCRF linac will provide stable energy, and the eventual GeV-scale energy with three TESLA-type cryomodules will satisfy the FEL resonance condition in the XUV regime. Concepts based on combining such beams with a 5-cm-period undulator and optical resonator cavity for an FEL oscillator are described. We used the 68% reflectances for normal incidence on multilayer metal mirrors developed at LBNL*. Initial simulations using GINGER with an oscillator module and MEDUSA:OPC show saturation for the 13.4-nm case after 300 and 350 passes, respectively,of the 3000 pulses. Initially, VUV experiments could begin in the 180- to 120-nm regime using MgF2-coated Al mirrors with only one cryomodule installed and beam energies of 250-300 MeV.
*LBNL X-ray optics site: http://xdb.lbl.gov/Section4
 
 
TUOBNO01 Beam Diagnostics for Coherent Optical Radiation Induced by the Microbunching Instability 169
 
  • A.H. Lumpkin
    Fermilab, Batavia, USA
 
  Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
The generation of the ultrabright beams required by modern free-electron lasers (FELs) has generally relied on chicane-based bunch compressions that often result in the microbunching instability. Following compression, spectral enhancements can extend even into the visible wavelengths through the longitudinal space charge impedances. Optical transition radiation (OTR) screens have been extensively used for transverse electron beam size measurements for the bright beams, but the presence of longitudinal microstructures (microbunching) in the electron beam or the leading edge spikes can result in strong, localized coherent enhancements (COTR) that mask the actual beam profile. We now have evidence for the effects in both rf photocathode-gun injected linacs* and thermionic-cathode-gun injected linacs**. Since the first observations, significant efforts have been made to characterize, model, and mitigate COTR effects on beam diagnostics. An update on the state-of-the-art for diagnosing these effects will be given as illustrated by examples at APS, LCLS, SCSS, SACLA, and NLCTA.
*A.H. Lumpkin et al.,Phys. Rev. ST Accel. Beams 12, 040704 (2009).
**H. Tanaka,"Commissioning of the Japanese XFEL at Spring8, Proceedings of IPAC2011, San Sebastián, Spain, 21-25 (2011).
 
slides icon Slides TUOBNO01 [1.805 MB]  
 
TUPSO45 Initial Streak Camera Measurements of the S-band Linac Beam for the University of Hawaii FEL Oscillator 325
 
  • A.H. Lumpkin
    Fermilab, Batavia, USA
  • M.R. Hadmack, J.M.D. Kowalczyk, J. Madey, E.B. Szarmes
    University of Hawaii, Honolulu, HI, USA
 
  Funding: Work at Fermilab supported by Fermi Research Alliance, LLC under U.S.DOE Contract No.DE-AC02-07CH11359. Work at UH supported by U.S. Dept. of Homeland Security grant No. 20120-DN-077-AR1045-02.
The S-band linac driven Mark V free-electron laser oscillator (FELO) at the University of Hawai‘i operates in the mid-IR at electron beam energies of 40-45 MeV with a four microsecond macropulse length. Recently investigations of the electron beam micropulse bunch length and phase as a function of macropulse time became of interest for potentially optimizing the FELO performance. These studies involved the implementation of a Hamamatsu C5680 streak camera with dual sweep capabilities and the transport of optical transition radiation (OTR) generated at an upstream Cu mirror and of coherent spontaneous emission radiation (CSER) generated in the undulator to the streak camera location outside of the linac tunnel. Both a fast single-sweep vertical unit and a synchroscan unit tuned to 119.0 MHz were used. Initial results include measurements of the individual CSER (on the FEL7th harmonic at 652 nm) micropulse bunch lengths (3 to 5 ps FWHM), the CSER signal intensity variation along macropulse time, and a detected phase slew of 4 ps over the last 700 ns of the macropulse. Complementary OTR measurements are also being evaluated and will be presented as available.