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TUBAU01 FLASH Upgraded - Preparing for the European XFEL laser, electron, feedback, radiation 211
 
  • H. Schlarb
    DESY, Hamburg
  Since 2005, the Free electron LASer in Hamburg, FLASH, has delivered a high brilliance photon beam to users in a wavelength range between 13 nm and 40 nm. To meet the user demands for 4 nm wavelengths, sub-50fs timing stability, and better pointing stability, the accelerator will be continuously upgraded within the next few years. The upgrade to an energy of 1.3 GeV, the transverse and longitudinal intra-train feedback system, and a 3rd harmonic cavity at 3.9 GHz are key prototype tests for the European XFEL. FLASH also serves as a test bench for an entirely new approach to accelerator facility synchronisation involving optical pulses distributed in length stabilized fibres. Increased stabilization of the electron beam peak current and its arrival time should provide the possibility to reliably seed the electron bunch with higher laser harmonics. In this paper, an overview of the planned upgrade for FLASH will be presented with respect to its usefulness for the European XFEL. The status of the XFEL project will also be briefly summarized.  
slides icon Slides  
 
TUPPH015 Diffraction Effects in the Coherent Transition Radiation Bunch Length Diagnostics electron, radiation, diagnostics, injection 256
 
  • V. A. Lebedev, S. Nagaitsev, G. M. Kazakevich
    Fermilab, Batavia, Illinois
  Diffraction effects in the Coherent Transition Radiation (CTR) bunch length diagnostics were considered for the A0 Photoinjector and the ILC injection module. The effects can cause a noticeable distortion of the measured CTR spectra dependently on the experimental setup and the bunch parameters. The distortion results in the the errors of the bunch length determination. Presented calculations show possible errors in determination of the bunch length in assumed experiments based on the CTR spectra measurements at A0 Photo injector and the ILC injection module.  
 
WEBAU03 Performance Tests of the Photon Monochromator for Self-seeding at FLASH undulator, electron, radiation, vacuum 306
 
  • H. K. Bechtold, J. Hartvig, H. Juul, V. Toft
    Aarhus University, Aarhus
  • R. Follath, G. Reichardt, F. Senf, F. Siewert
    BESSY GmbH, Berlin
  • U. Hahn, J. Viefhaus, R. Treusch
    DESY, Hamburg
  • S. V. Hoffmann
    ISA, Aarhus
  • Ch. Knoechel
    LBNL, Berkeley, California
  • R. Reininger
    UW-Madison/SRC, Madison, Wisconsin
  A single pass FEL amplifier can produce extremely intense and fully coherent radiation at short wavelengths if it is seeded by a coherent light beam resonant with the magnetic structure and collinear with the electron beam. Since at the present time a single pass SASE FEL is the only source of sufficiently intense, tunable radiation in the soft X-ray region, it has been proposed to use such a source in combination with a narrow-band monochromator for seeding an FEL amplifier*. By means of such a "Self-Seeding", the soft X-ray free electron laser FLASH at DESY will be modified so that it can provide coherent radiation in space and time in a wavelength range from about 60-6nm (~20-200eV). In this presentation, we will focus on the performance of the photon monochromator beamline which was setup and tested at the synchrotron radiation storage ring ASTRID in Aarhus, Denmark. The optical, mechanical and vacuum design will be described along with results on the resolving power of the monochromator which have been obtained scanning across rare gas resonance lines at various energies. Based on these results we will conclude that the monochromator is mechanically very stable and reproducible and behaves according to its specifications with resolving powers between 10000 and 20000, i.e. bandwidths of a few meV only.

* J. Feldhaus, E. L. Saldin, J. R. Schneider, E. A. Schneidmiller, and M. V. Yurkov, Opt. Commun. 140, 341 (1997)

 
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WEPPH004 Numerical Calculations of the Radiation Emitted from the FLASH Infrared Undulator undulator, radiation, synchrotron, synchrotron-radiation 322
 
  • V. Kocharyan, J. Rossbach, O. Grimm
    DESY, Hamburg
  The results from the magnetic measurements with the FLASH infrared electromagnetic undulator reported in a companion paper where used as input for calculations of the expected radiation spectrum. Especially the behaviour of the device at small first harmonic wavelengths, i.e. small excitation currents, is important for beam diagnostics, as here the high intensity in a narrow band is a distinct advantage over broad-band sources to detect small bunch structures. The field quality is reduced at small currents due to imperfections in the yoke construction and limited compensation by correction windings. A determination of the lower limit for useful operation of the device follows from these calculations.  
 
WEPPH006 Study of Undulator Deformation Tolerance for the European XFEL undulator, simulation, radiation, electron 330
 
  • B. Faatz, J. Pflueger, Y. Li
    DESY, Hamburg
  The undulators for the European XFEL use NdFeB type permanent magnets. Even for perfect magnet material, the undulator quality degrades due to mechanical limitations, such as girder deformation, and temperature variation. Since the beam orbit can always be corrected, the main effect will be a variation in slippage between electrons and photon beam along the undulator. A careful estimation of the error budget is needed to avoid cost driving hardware efforts. We modeled deformation, gap variation and temperature error and used GENESIS to simulate the effect on the performance of the European XFEL.  
 
WEPPH007 MCP-based Photon Detector with Extended Wavelength Range for FLASH radiation, target, undulator, background 334
 
  • O. I. Brovko, D. Kharlamov, E. A. Matyushevskiy, A. V. Shabunov
    JINR/LHE, Moscow
  • J. Feldhaus, U. Hahn, M. Hesse, U. Jastrow, V. Kocharyan, P. Radcliffe, E. Saldin, E. Schneidmiller, K. I. Tiedtke, R. Treusch, M. V. Yurkov, N. von Bargen, L. Bittner
    DESY, Hamburg
  • V. I. Lokhmatov, E. Syresin
    JINR, Dubna, Moscow Region
  Experimental experience gained at the extreme ultraviolet SASE FEL FLASH (DESY, Hamburg) has shown that successful operation of the facility strongly depends on the quality of the radiation detectors. Here key issues are: wide wavelength range (6 to 100 nm for FLASH), wide dynamic range (from the level of spontaneous emission to the saturation level), and high relative accuracy of measurements which is crucial for detection of a signature of amplification and characterization of statistical properties of the radiation. In this report we describe MCP-based radiation detector for FLASH which meets these requirements. Key element of the detector is wide dynamic range micro-channel plate (MCP) which detects scattered radiation from a target. With five different targets and MCPs in combination with optical attenuators present detector covers operating wavelength range from 6 to 100 nm, and dynamic range of the radiation intensities, from the level of spontaneous emission up to the saturation level of SASE FEL.  
 
WEPPH029 Development of the Longitudinal Phase-Space Monitor for the L-band Electron Linac at ISIR, Osaka University electron, radiation, linac, vacuum 409
 
  • T. Igo, G. Isoyama, S. Kashiwagi, M. Morio, R. Kato
    ISIR, Osaka
  The correlation between longitudinal positions of electrons in a bunch and their energies has a critical effect on the temporal evolution of SASE, and various methods are being developed to measure the longitudinal phase-space profile. We are developing a system to measure the longitudinal phase-space distribution of electrons by a combination of a bending magnet, a profile monitor, and a streak camera at the Institute of Scientific and Industrial Research (ISIR), Osaka University. In the preliminary experiments using a profile monitor utilizing optical transition radiation (OTR), it was confirmed that the monitor had higher momentum resolution than the presently used momentum analyzer consisting of a slit and a current meter*. However, we could not obtain the sufficient number of photons to obtain the phase-space image since, in addition to a low photon yield, the angular distribution of OTR emitted by the electron beam in the energy region of 10 – 20 MeV, with which THz-SASE and THz-FEL experiments are conducted at this laboratory, is too large to concentrate it efficiently on a streak camera. In order to increase the number of photons, we try to use silica aerogel as a radiator of the profile monitor by following the example of PITZ**. We will present an outline of the phase-space monitor we are developing and its experimental results.

* R. Kato et al, FEL’06, Berlin, Germany, August 2006, THPPH041, p.676, http://www.jacow.org.** J. Roensch et al, FEL’06, Berlin, Germany, August 2006, THPPH019, p.597, http://www.jacow.org

 
 
WEPPH048 XPS Studies of Cs2Te Photocathodes cathode, electron, laser, survey 457
 
  • H. A. Duerr, R. Ovsyannikov, M. Sperling, A. Vollmer
    BESSY GmbH, Berlin
  • J. H. Han, S. Schreiber, S. Lederer
    DESY, Hamburg
  • P. Michelato, L. Monaco, C. Pagani, D. Sertore
    INFN/LASA, Segrate (MI)
  • F. Stephan
    DESY Zeuthen, Zeuthen
  Cesium Telluride (Cs2Te) photocathodes are used as sources for electron beams because of their high quantum efficiency (QE) and their ability to release high peak current electron bunches in a high gradient RF-gun. Starting from a high QE level of about 10% the quantum efficiency of these cathodes decreases during operation in a photo-injector to below 0.5%. To understand this behaviour, XPS investigations on the chemical composition were performed at BESSY. In this contribution we compare two fresh cathodes from INFN with one used under normal operation at FLASH and one used at PITZ at a higher than usual RF-gradient of 60 MV/m.