Author: Lumpkin, A.H.
Paper Title Page
MOOBB01 Transverse-to-longitudinal Emittance-exchange with an Energy Chirped Beam 49
  • J.C.T. Thangaraj, H.T. Edwards, A.S. Johnson, A.H. Lumpkin, T.J. Maxwell, J. Ruan, J.K. Santucci, Y.-E. Sun, R.M. Thurman-Keup
    Fermilab, Batavia, USA
  Emittance exchange has been proposed to increase the performance of free electron lasers by tailoring the phase space of an electron beam. The principle of emittance exchange - where the transverse phase space of the electron beam is exchanged with the longitudinal phase space - has been demonstrated recently at the A0 photoinjector. The experiment used a low charge bunch (250 pC) with no energy chirp. Theory predicts an improvement in the emittance exchange scheme when the incoming beam has an energy chirp imparted on it. The energy chirp helps to overcome the thick lens effect of the deflecting mode cavity and other second order effects that might lead to an incomplete emittance exchange at higher charges. In this work, we report experimental and simulation results from operating the emittance exchange beam line using an energy chirped beam with higher charge (500 pC) at different RF-chirp settings.  
slides icon Slides MOOBB01 [2.338 MB]  
MOPPR071 Initial Results of Transverse Beam Profile Measurements Using a LYSO:Ce Crystal 951
  • A.S. Johnson, A.H. Lumpkin, T.J. Maxwell, J. Ruan, J.K. Santucci, C.C. Tan, R.M. Thurman-Keup, M. Wendt
    Fermilab, Batavia, USA
  A prototype transverse beam profile monitor for eventual use at the Advanced Superconducting Test Accelerator (ASTA) has been tested at the Fermilab A0 Photoinjector. Results from low-charge (20 pC) studies indicate that a LYSO:Ce scintillator will be a viable replacement for a YAG:Ce scintillator when using intercepting radiation convertor screens for beam profiling. We will also describe the planned implementation of LYSO:Ce crystals to mitigate the coherent optical transition radiation due to the microbunching instability through the use of band-pass filters and specially timed cameras.  
WEPPP030 Experimental Generation of a Double-bunch Electron Beam by Transverse-to-Longitudinal Phase Space Exchange 2789
  • T.J. Maxwell, P. Piot
    Northern Illinois University, DeKalb, Illinois, USA
  • A.S. Johnson, A.H. Lumpkin, J. Ruan, Y.-E. Sun, R.M. Thurman-Keup
    Fermilab, Batavia, USA
  Funding: Supported by Fermi Research Alliance, LLC under U.S. Dept. of Energy Contract No. DE-AC02-07CH11359, and Northern Illinois Univ. under US Dept. of Defense DURIP program Contract N00014-08-1-1064.
In this paper we demonstrate the generation of a tunable, longitudinal double-pulse electron beam. Experimental results on the generation of electron bunch trains with sub-picosecond structure have been previously reported where an initial transverse electron beam modulation was produced by masking the electron beam directly*. Here the initial transverse structure is imparted by masking of the photoinjector drive laser to effectively produce two horizontally offset beams at photoemission in the RF gun. A longitudinal double-pulse modulation is then realized after a transverse-to-longitudinal phase-space exchange beamline. Longitudinal profile tuning is demonstrated by upstream beam focusing in conjunction with downstream monitoring of single-shot electro-optic spectral decoding of coherent transition radiation.
* Y.-E. Sun et al., Tunable Subpicosecond Electron-Bunch-Train Generation Using a Transverse-To-Longitudinal Phase-Space Exchange Technique, Phys. Rev. Lett. 105, 234801 (2010).
WEPPP072 Beam Characterization and Coherent Optical Transition Radiation Studies at the Advanced Photon Source Linac 2876
  • J.C. Dooling, R.R. Lindberg, N. Sereno, C.-X. Wang
    ANL, Argonne, USA
  • A.H. Lumpkin
    Fermilab, Batavia, USA
  Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract number DE-AC02-06CH11357.
The Advanced Photon Source facility includes a 450-MeV S-band linac with the option for injection from a photocathode (PC) rf gun. A diode-pumped, twice-frequency doubled Nd:glass regen laser (263 nm) is used with the Cu PC to generate the electron beams. Characterization of these beams and studies of the microbunching instability following beam compression in the four-dipole magnetic chicane are described. A suite of diagnostics is employed including a three-screen emittance section, a FIR coherent transition radiation autocorrelator, electron spectrometers, and an optical diagnostics end station. An energy chirp impressed on the beam is used to compress the 1-2 ps, rms bunch as it passes through the chicane. With compression, bunch lengths of 170-200 fs, rms at 450 pC are measured, and coherent optical transition radiation (COTR) due to the microbunching instability is observed. Mitigation techniques of the COTR in the beam profile diagnostics are demonstrated both spectrally and temporally. At 100 pC without compression normalized transverse emittances of 1.8 and 2.7 microns are observed in the x and y planes, in reasonable agreement with initial ASTRA simulations.