THOC —  Electron and X-ray Diagnostics   (25-Aug-11   13:30—15:00)
Chair: J.M. Byrd, LBNL, Berkeley, California, USA
Paper Title Page
THOCI1
 Measurement and Control of the Longitudinal Phase Space at High-Gain Free-electron Lasers  
 
  • C. Behrens, C. Gerth
    DESY, Hamburg, Germany
  
  Free-electron lasers provide a high degree of flexibility in terms of pulse intensity and wavelength range. In the case of high-gain FELs with a two-frequency accelerator in front of the bunch compressors, the flexibility is extended with electron bunch shape and length tunability. The final goal is to get control of the FEL photon pulses which might be achieved by controlling the longitudinal phase space (LPS) of the driving electron bunch. This can be achieved by using transverse deflecting structures/cavities (TDS/C) in combination with energy spectrometers which provide a direct measurement method with high resolutions in both energy and time. In this talk, the basic concepts of longitudinal phase space diagnostics, using transverse deflecting structures/cavities in combination with energy spectrometers, will be discussed with examples from FLASH at DESY and LCLS at SLAC. The obtainable resolutions and limitations due to the accelerator optics, induced energy spread by the TDS/C itself, and coherent synchrotron radiation will be shown by simulations and measurements. Finally, an overview of planned LPS diagnostics at other facilities, like the European XFEL, will be presented.  
slides icon Slides THOCI1 [3.849 MB]  
 
THOCI2
 Measurement of Ultrashort Electron and X-ray Beams for X-ray FELs  
 
  • Y.T. Ding
    SLAC, Menlo Park, California, USA
  
  Measurement of ultrashort electron and X-ray pulses is a challenging but important subject for X-ray free electron lasers. After a brief overview of the common temporal diagnostics for X-ray FEL facilities, we discuss new techniques developed recently to push the temporal resolution to the femtosecond level and below. One of them is the longitudinal transformation method that directly maps time to energy by adjusting the accelerator settings [1]. Experiments at LCLS using a high-resolution spectrometer demonstrate that the bunch profile can be measured with a temporal resolution approaching 1 fs rms [2]. Another single-shot method is to use an X-band transverse cavity, not yet installed, after the FEL undulator to reconstruct both the electron and X-ray temporal profiles by measuring electron beam longitudinal phase space. Simulation studies show that about 1 fs rms time resolution may be achievable in the LCLS and is applicable to a wide range of FEL wavelengths and operating facilities. Other techniques including optical streaking methods will also be discussed.
[1] Z. Huang, K. Bane, Y. Ding and P. Emma, Phys. Rev. ST Accel. Beams, 13, 092801 (2010);
[2] Z. Huang et al, PAC11, THP183. 		 
slides icon Slides THOCI2 [3.321 MB]  
 
THOC3
 Few-fs X-ray Pulse Length Measurement at LCLS  
 
  • A.R. Maier, F. Grüner
    LMU, Garching, Germany
  • J.D. Bozek, R.N. Coffee
    SLAC, Menlo Park, California, USA
  • A.L. Cavalieri, I. Grguras
    CFEL, Hamburg, Germany
  • J.T. Costello
    DCU, Dublin, Republic of Ireland
  • G. Doumy
    ANL, Argonne, USA
  • S. Düsterer
    DESY, Hamburg, Germany
  • J. Gagnon, W. Helml, R. Kienberger, W. Schweinberger, V.S. Yakovlev
    MPQ, Garching, Munich, Germany
  • M. Meyer, P. Radcliffe, T. Tschentscher
    European XFEL GmbH, Hamburg, Germany
  • C. Roedig
    Ohio State University, USA
  
  The Linac Coherent Light Source (LCLS) has an unique operating mode, delivering X-ray pulses of only a few femtoseconds (fs) length, though so far the precise X-ray pulse length has been experimentally inaccessible. In a recent experiment we measured the LCLS pulse length in this regime to be 4 fs fwhm by overlapping the FEL pulse with an optical infrared laser in a Neon gas jet. The IR laser maps the temporal X-ray pulse profile into the energy spectrum of the generated photolectrons. By measuring the photoelectron spectrum a direct characterization of the FEL pulse is possible. In the experiment we were able to directly access the temporal substructure of the X-ray pulses, measured the typical pulse length in the LCLS low charge mode to be 4 fs fwhm and showed single-spike, single-fs X-ray pulses.  
slides icon Slides THOC3 [2.818 MB]  
 
THOC4 Transverse Size and Distribution of FEL X-ray Radiation of the LCLS 465
 
  • J.L. Turner, F.-J. Decker, Y.T. Ding, P. Emma, J.C. Frisch, K. Horovitz, Z. Huang, R.H. Iverson, J. Krzywinski, H. Loos, M. Messerschmidt, S.P. Moeller, H.-D. Nuhn, D.F. Ratner, J.J. Welch, J. Wu
    SLAC, Menlo Park, California, USA
  
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515
Understanding and controlling the transverse size and distribution of FEL X-ray radiation of the LCLS at the SLAC National Accelerator Laboratory is discussed. Understanding divergence, source size, and distributions under various conditions is a convolution of many effects such as the electron distribution, the undulator alignment, micro-bunching suppression, and beta-match. Measurements of transverse size along the X-ray pulse and other studies designed to sort out the dominant effects are presented and discussed. 		 
slides icon Slides THOC4 [1.874 MB]