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MOPPH073 An Enhanced GINGER Simulation Code with Harmonic Emission and HDF5 IO Capabilities radiation, simulation, undulator, diagnostics 218
 
  • W. M. Fawley
    LBNL, Berkeley, California
  GINGER* is an axisymmetric, polychromatic (r-z-t) FEL simulation code originally developed in the mid-1980's to model the performance of single-pass amplifiers. Over the past 15 years GINGER's capabilities have been extended to include more complicated configurations such as undulators with drift spaces, dispersive sections, and vacuum chamber wakefield effects; multi-pass oscillators; and multi-stage harmonic cascades. Its coding base has been tuned to permit running effectively on platforms ranging from desktop PC's to massively parallel processors such as the IBM-SP. Recently, we have made significant changes to GINGER by replacing the original predictor-corrector field solver with a new direct implicit algorithm, adding harmonic emission capability, and switching to the HDF5 IO library** for output diagnostics. In this paper, we discuss some details regarding these changes and also present simulation results for a number of test cases ranging from LCLS SASE emission to performance of the FERMI@ELETTRA two-stage, harmonic cascade.

* http://www-ssrl.slac.stanford.edu/lcls/technotes/LCLS-TN-04-3.pdf (also LBNL-49625-Rev. 1)
** http://hdf.ncsa.uiuc.edu/HDF5/

 
 
TUBAU05 Technical Aspects of the Integration of the Optical Replica Synthesizer for the Diagnostics of Ultra-short Bunches into FLASH at DESY laser, electron, undulator, diagnostics 296
 
  • P. van der Meulen, N. X. Javahiraly, M. Larsson
    FYSIKUM, AlbaNova, Stockholm University, Stockholm
  • E. Saldin, H. Schlarb, E. Schneidmiller, A. Winter, M. V. Yurkov
    DESY, Hamburg
  • V. G. Ziemann
    UU/ISV, Uppsala
  Recently, Saldin et al.* introduced a novel scheme to characterise ultra-short electron bunches in a FEL. The method is based on producing an 'optical copy' of the electron bunch, which can then be easily analysed using well-known non-linear optical techniques. To this end, a near-IR laser beam is overlapped with the electron beam in the first undulator of an optical klystron. In the following dispersive section the laser-induced energy modulation is transformed into a density modulation . The modulated electron bunch then produces a strong optical pulse in the second undulator. Analysis of this near-IR pulse (the optical copy) then provides information about the length, the slice emittance and the slice energy spread of the original electron bunch. We discuss the implementation of such a measurement set-up at the VUV-FEL at DESY and investigate the influence of various parameters on the performance of the device. Topics we address include the electron beam optics of the undulators, quadrupoles and the dispersive chicane, as well as the requirements for the seed laser pulses. The detection and analysis of the near-IR pulse and an extension to the XUV-FEL are also covered.

* E. Saldin, et al. "A simple method for the determination of the structure of ultrashort relativistic electron bunches," Nucl. Inst. and Methods A 539 (2005) 499.

 
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TUPPH007 JAEA Photocathode DC-Gun for an ERL Injector electron, gun, laser, ion 319
 
  • T. Nishitani, R. Hajima, H. Iijima, N. Kikuzawa, E. J. Minehara, R. Nagai, N. Nishimori, M. Sawamura
    JAEA/ERL, Ibaraki
  • H. Hayashitani, Y. Noritake, M. Tabuchi, Y. Takeda
    Nagoya University, Nagoya
  ERL light source and FEL require an electron beam of large current and small emittance. In order to realize an electron gun satisfying such requirements, we started developments of a photocathode DC-gun and a new-type NEA-photocathode. The DC-gun consists of a chamber to activate NEA-surface, a 250keV acceleration chamber, and a mode-locked Ti:Sapphire laser. Since extreme high vacuum is essential to obtain a long-life photocathode, we adopt a load-lock system for transporting a photocathode between the chambers, each of which is equipped with an NEG pump. Up to now, we fabricated an electrodes chamber and a high voltage terminal of 250kV and we succeeded in a 250kV high voltage test. We also have suggested a superlattice photocathode as a new-type photocathode with higher performance than an existing technology. Up to now, we fabricated photocathode samples by molecular beam epitaxy and measured quantum efficiency after NEA-surface activation.  
 
TUPPH016 The Partial-Waveguide Resonator of the U100-FEL at FZ Rossendorf undulator, laser, alignment, electron 345
 
  • R. Wuensch, M. Freitag, R. Schlenk, W. Seidel, U. Willkommen, D. Wohlfarth, B. Wustmann
    FZR, Dresden
  The U100-FEL, which is under construction at the Forschungszentrum Rossendorf, will be equipped with a parallel-plate waveguide which is 10 mm high (inside), almost 8 m long and covers more than two third of the total resonator length. Its horizontal width varies from 70 mm within the undulator up to 130 mm at the downstream resonator mirror. A special diagnostics had to be developed to align the electron and the IR beam within this waveguide. A drive system has been designed for the cylindrical downstream resonator mirror. It allows to shift and tilt the mirror, which is completely embedded in the waveguide. The size and the curvature of the bifocal upstream resonator mirror has been fitted to minimize the optical loss in the resonator. To adjust the outcoupling to the varying beam size on the mirror surface a set of three collocated, relocatable mirrors with different outcoupling hole sizes will be applied. We present various sophisticated design concepts which comply with the large wavelength range and the special requirements caused by the bulky waveguide construction and its small free space in vertical direction.  
 
TUPPH054 Beam Pickup Designs Suited for an Optical Sampling Technique pick-up, laser, simulation, electron 451
 
  • K. E. Hacker, F. Loehl, H. Schlarb
    DESY, Hamburg
  A beam position monitor with a large horizontal aperture is being developed for use in dispersive regions of magnetic chicanes as part of an energy measurement. It will have a horizontal detection range of 10 cm or more and a resolution of better than 30 um. This is achievable with a stripline design, mounted perpendicularly to the electron beam direction. A high-precision phase measurement at both ends of the stripline will allow for determination of the beam postion. The phase measurement of the short RF pulses from the stripline will be done with a technique that utilizes a timing laser that samples the RF pulse traveling though an electro-optical modulator.  
 
TUPPH071 Simulation of Mirror Distortion in Free-Electron LASER Oscillators wiggler, simulation, electron, emittance 477
 
  • H. Freund
    SAIC, McLean
  • S. V. Benson, M. D. Shinn
    Jefferson Lab, Newport News, Virginia
  Thermal distortion in cavity mirrors in high-power FELs can alter mode quality and degrade performance. Hence, it is important to be able to predict the character of the distortions to model their effect on FEL performance. To this end, we address these key issues by developing modeling and simulation tools that can accomplish these goals, and then benchmarking the simulation against observations on the 10 kW-Upgrade experiment at the Thomas Jefferson National Accelerator Facility. The modeling and simulation will rely on the MEDUSA code, which is a 3-D FEL simulation code capable of treating both amplifiers and oscillators in both the steady-state and time-dependent regimes. MEDUSA employs a Gaussian modal expansion, and treats oscillators by decomposing the modal representation at the exit of the wiggler into the vacuum Gaussian resonantor modes and then analytically propagating these modes through the resonator back to the entrance of the wiggler in synchronism with the next electron bunch. Knowledge of the power loading on the mirrors allows us to model the mode distortions using Zernicke polynomials and this technique has been incorporated into MEDUSA.  
 
THBAU01 APPLE Undulators for HGHG-FELs undulator, electron, controls, radiation 521
 
  • J. Bahrdt
    BESSY GmbH, Berlin
  Cascaded HGHG-FEL facilities have been proposed by several groups. In these machines the beam characteristics of the initial seeding laser like short pulses and a small bandwidth are transformed to shorter wavelengths where lasers are not available. The first stages are equipped with planar devices. For full polarization control the last amplifier and the final radiator can be realized as APPLE devices. The specific demands on the polarizing devices as compared to planar hybrid devices are discussed for the example of the proposed BESSY HE-FEL to be operated at 1nm: the small good field region implies tight geometrical tolerances. Gap and phase dependent focussing effects have to be compensated. The field optimization procedure requires specific strategies. An improvement of the magnetic material is helpful in this context. Other important issues are the radiation protection system and the complexity of the control system.  
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THPPH009 Cryomodule and Tuning System of the Superconducting RF Photo-Injector gun, cathode, acceleration, emittance 575
 
  • J. Teichert, A. Arnold, H. Buettig, R. Hempel, D. Janssen, U. Lehnert, P. Michel, K. Moeller, P. Murcek, Ch. Schneider, R. Schurig, F. Staufenbiel, R. Xiang
    FZR, Dresden
  • T. Kamps, D. Lipka
    BESSY GmbH, Berlin
  • G. Klemz
    DESY Zeuthen, Zeuthen
  • W.-D. Lehmann
    IfE, Dresden
  • J. Stephan
    IKST, Drsden
  • I. Will
    MBI, Berlin
  We present the designs and report on the progress in construction and testing of the cryomodule and the tuning system for the SRF gun. The SRF gun project, a collaboration of BESSY, DESY, MBI and FZR, aims at the installation of a high average current CW photo injector at the ELBE linac with a Nb cavity. The cryostat consists of a stainless steel vacuum vessel, a warm magnetic shield, a liquid N cooled thermal shield, and a He tank with two-phase supply tube. A heater pot in the He input port will be used for He level control. The 10 kW power coupler is adopted from ELBE module. A cooling and support system for the NC photo cathode has been developed and tested. It allows the adjustment of the cathode with respect to the cavity from outside. The cryomodule will be connected with the 220 W He refrigerator of ELBE and will operate at 1.8 to 2 K. The static thermal loss is expected to be less than 20 W. Two tuners will be installed for separate tuning of the three TESLA cells and the half-cell. The tuners are dual spindle-lever systems with step motors and low-vibration gears outside the cryostat. Functionality, tuning range and accuracy have been tested in cryogenic environment.  
 
THPPH054 Linac Coherent Light Source Undulator RF BPM System dipole, undulator, coupling, linac 706
 
  • R. M. Lill, L. H. Morrison, G. J. Waldschmidt, D. R. Walters
    ANL, Argonne, Illinois
  • R. Johnson, Z. Li, S. Smith, T. Straumann
    SLAC, Menlo Park, California
  The LCLS will be the world's first x-ray free electron laser when it becomes operational in 2009. LCLS is currently in the construction phase. The beam position monitor (BPM) system planned for the LCLS undulator will incorporate a high resolution X-band cavity BPM system described in this paper. The X-band cavity BPM system will provide high-resolution measurements of the electron beam trajectory on a pulse-to-pulse basis and over many shots. The X-band cavity BPM size, simple fabrication and high resolution make it an ideal choice for the LCLS beam position detection. We will discuss the system specifications, design, and prototype test results.  
 
THCAU04 Peak Current Performances from Electron Sources based on Field Emission (Single Tip and Field Emitter Arrays (FEAs)) laser, electron, emittance, gun 781
 
  • R. Ganter, R. J. Bakker, M. Dehler, G. J. Gobrecht, C. Gough, E. Kirk, F. Le Pimpec, S. C. Leemann, K. L. Li, M. Paraliev, M. Pedrozzi, J.-Y. Raguin, L. Rivkin, V. Schlott, H. Sehr, S. Tsujino, A. F. Wrulich
    PSI, Villigen
  Reducing beam emittance while keeping high brightness is the most direct way to reduce the cost and size of Free Electron Lasers (FELs). Ultimately, beam emittance is limited by the thermal emittance at the electron source. In order to find electron sources with low thermal emittance (<5.10-8 m.rad) and high brightness (>5.1013 A.m-2.rad-2), cathodes based on single tip field emitter as well as field emitters arrays (FEAs) are investigated. Maximum peak current, measured from single tip in ZrC with a typical apex radius around one micrometer, are presented. Voltage pulses of two nanoseconds duration and up to 50 kilovolts amplitude lead to field emission current up to 470 mA from one ZrC tip. Combination of high applied electric field with laser illumination gives the possibility to modulate the emission with laser pulses. Sub-nanoseconds current pulses have been emitted with laser pulses at 1064nm illuminating a ZrC tip under high electric field. The dependence of photo-field emitted current with the applied voltage can be explained by the Schottky effect.  
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FRAAU04 A New Generation of X-Ray Optics Based on Pyrolytic Graphite photon, focusing, optics, alignment 798
 
  • H. Legall, H. Stiel
    MBI, Berlin
  • A. Antonov, I. Grigorieva
    Optigraph GmbH, Berlin
  • V. Arkadiev
    IAP, Berlin
  • A. Bjeoumikhov
    IfG, Berlin
  • A. Erko
    BESSY GmbH, Berlin
  Highly Oriented Pyrolytic Graphite (HOPG) is a mosaic crystal, which consists of a large number of small nearly perfect crystallites. The unique structure of HOPG crystals enables them to be highly efficient in an energy range between 2 keV up to several 10 keV. The mosaicity of the crystal is responsible for the dramatic increase of integral reflectivity in comparison to perfect crystals. Furthermore thin HOPG crystal films can be easily bent and exhibit a very high thermal conductivity making them interesting for application in experiments with high average power x-ray sources. For application in x-ray spectroscopy the achievable spectral resolution of the crystal optics is in particular of interest. Recently performed measurements with very low foil thickness have revealed a spectral resolution of E/DeltaE=2900 in 004-reflection (H. Legall et al., Opt. Expr. 14 (2006)). This is by far the highest spectral resolution reported for HOPG crystals. The integral reflectivity of these films is still comparable to that of ideal Ge crystals. In the present work we will present new results concerning the energy resolution, integral reflectivity and application of thin bent Graphite films.  
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