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SASE

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MOPCH002 Seeding the FEL of the SCSS Phase 1 Facility with the 13th Laser Harmonic of a Ti: Sa Laser Produced in Gas laser, FEL, undulator, radiation 44
 
  • G. Lambert, M. Bougeard, W. Boutu, P. Breger, B. Carré, D. Garzella, M. Labat, H. Merdji, P. Monchicourt, P. Salieres
    CEA, Gif-sur-Yvette
  • O.V. Chubar, M.-E. Couprie
    SOLEIL, Gif-sur-Yvette
  • T. Hara, H. Kitamura, T. Shintake
    RIKEN Spring-8 Harima, Hyogo
  • D. Nutarelli
    LAC, Orsay
  A seeding configuration, in which the 13th harmonic (60 nm) of a Ti: Sa laser (50 mJ, 10 Hz, 130 fs) generated in a gas cell is used as the external source, will be tested in 2006 on the SCSS test facility (SPring-8 Compact Sase Source, Japan). This facility is based on a thermionic cathode electron gun (1 nC of bunch charge), a C-band LINAC (5712 MHz, 35 MV/m) and two in-vacuum undulators (15 mm of period). The maximum electron beam energy is 250 MeV and the SASE emission from visible to 60 nm can be obtained. The High order Harmonic Generation (HHG) experiment was mounted off-line at the end of last December. A first chamber is dedicated to harmonic generation. A second one is used for spectral selection and adaptation of the harmonic waist in the modulator. The tests are performed in Saclay with the LUCA (Laser Ultra Court Accordable) laser (15 mJ, 10 Hz, 50 fs) from January to March at 266 nm, 160 nm and 60 nm and its results are presented here. Also, before performing the real tests in SPring-8 FEL presence, final theoretical estimations of the performances relying on 1D simulations using PERSEO code and 3D simulations using GENESIS and SRW codes are given.  
 
MOPCH015 Impact of Undulator Wakefileds and Tapering on European X-ray FEL Performance undulator, radiation, FEL, simulation 83
 
  • I. Zagorodnov, M. Dohlus, T. Limberg
    DESY, Hamburg
  The European X-ray Free-Electron Laser (XFEL) based on self-amplified spontaneous emission (SASE) requires an electron beam with a few kA peak current and a small-gap undulator system up to 250 m in length. The interaction between the high-current electron bunch and the undulator vacuum chamber affects the FEL performance. In this paper we estimate the induced wakefields in elliptical pipe geometry, taking into account the main geometrical variations of the chamber. To study the expected performance in the presence of the calculated wakefields, we are doing start-to-end simulations with the tracking codes ASTRA, CSRtrack and GENESIS. To compensate the wakefield impact on the FEL performance, an adiabatic change of undulator parameters is considered.  
 
MOPCH016 Bunch Compression Monitor radiation, electron, FEL, acceleration 86
 
  • H. Delsim-Hashemi, J. Rossbach, P. Schmüser
    Uni HH, Hamburg
  • O. Grimm, H. Schlarb, B. Schmidt
    DESY, Hamburg
  • A.F.G. van der Meer
    FOM Rijnhuizen, Nieuwegein
  An accelerated bunch of electrons radiates coherently at wavelengths longer than or comparable to the bunch length. The first generation Bunch Compression Monitor (BCM) that is installed at the VUV-FEL applies this principle by measuring the total radiation intensity. For a better control on the degree of the compression, the radiated intensity in different bandwidth can be used. Dependent on the changes in the structure of the bunch, its radiation spectrum changes correspondingly. A new generation BCM uses wavelength dependent diffracting devices and multi-channel sensors to measure the signal in different wavelength channels simultaneously. This paper describes the construction of the first prototypes and experimental results in different short wavelength bands measured at the linac of the VUV-FEL at DESY, Hamburg.  
 
TUPCH024 Comparative Study of Bunch Length and Arrival Time Measurements at FLASH laser, electron, FEL, DESY 1049
 
  • H. Schlarb, A. Azima, S. Düsterer, M. Huening, E.-A. Knabbe, M. Roehrs, R. Rybnikov, B. Schmidt, B. Steffen
    DESY, Hamburg
  • M.C. Ross
    SLAC, Menlo Park, California
  • P. Schmüser, A. Winter
    Uni HH, Hamburg
  Diagnostic devices to precisely measure the longitudinal electron beam profile and the bunch arrival time require elaborate new instrumentation techniques. At the VUV-FEL, two entirely different methods are used. The bunch profile can be determined with high precision by a transverse deflecting RF structure. The method is disruptive and does not allow to monitor multiple bunches in a macro-pulse train. Therefore, it is augmented by two non-disruptive electro-optical devices, called EO and TEO. The EO setup uses a dedicated diagnostic laser synchronized to the machine RF. The longitudinal electron beam profile is encoded in the intensity profile of a chirped laser pulse and analyzed by looking at the spectral composition of the pulse. The second setup, TEO, utilizes the TiSa-based laser system used for pump-probe experiments. Here, the temporal electron shape is encoded into a spatial dimension of laser pulse by an intersection angle between the laser and the electron beam at the EO-crystal. In this paper, we present a comparative study of bunch length and arrival time measurements performed simultaneously with all three experimental techniques.  
 
TUPCH026 Single Shot Longitudinal Bunch Profile Measurements at FLASH using Electro-optic Techniques electron, laser, linac, FEL 1055
 
  • B. Steffen, E.-A. Knabbe, B. Schmidt
    DESY, Hamburg
  • G. Berden, A.F.G. van der Meer
    FOM Rijnhuizen, Nieuwegein
  • W.A. Gillespie, P.J. Phillips
    University of Dundee, Nethergate, Dundee, Scotland
  • S.P. Jamison, A. MacLeod
    UAD, Dundee
  • P. Schmüser
    Uni HH, Hamburg
  For the high-gain operation of a SASE FEL, extremly short electron bunches are essential to generate sufficiently high peak currents. At the superconducting linac of the VUV-FEL at DESY, we have installed an electro-optic experiment with temporal decoding and spectral decoding to probe the time structure of the electric field of single sub 200fs e-bunches. In this technique, the field-induced birefringence in an electro-optic crystal is encoded on a chirped ps laser pulse. The longitudinal electric field profile of the electron bunch is then obtained from the encoded optical pulse by a single-shot cross correlation with a 30 fs laser pulse using a second-harmonic crystal (temporal decoding) or by a single-shot measurement of its spectrum (spectral decoding). In the temporal decoding measurements an electro-optic signal of 230fs FWHM was observed, and is limited by the material properties of the particular electro-optic crystal used. Bunch profile and time jitter measurements were obtained simultaneously with VUV SASE operation.  
 
TUPCH053 Bunch Length Characterization Downstream from the Second Bunch Compressor at FLASH DESY, Hamburg electron, radiation, FEL, CDR 1127
 
  • E. Chiadroni
    INFN-Roma II, Roma
  The characterization of the longitudinal density profile of picosecond and sub-picosecond relativistic particle bunches is a fundamental requirement in many particle accelerator facilities, since knowledge of the characteristics of the accelerated beams is of utmost importance for the successful development of the next generation light sources and linear colliders. The development of non-intercepting beam diagnostics is thus necessary to produce and control such beams. First experimental evidences of the non-intercepting nature of diffraction radiation diagnostics are given. The longitudinal bunch distribution downstream of the second bunch compressor of the DESY TTF VUV-FEL has been reconstructed using a frequency-domain technique based on the autocorrelation of coherent diffraction radiation. Due to the low and high frequency suppression, introduced by the experimental apparatus, only a portion of the CDR spectrum participates to the reconstruction of the longitudinal bunch profile. The knowledge of the system frequency response is then crucial in order to correct the results and extrapolate a bunch shape as close as possible to the real one.  
 
THPCH150 Double-pulse Generation with the FLASH Injector Laser for Pump/Probe Experiments laser, FEL, radiation, polarization 3143
 
  • O. Grimm, K. Klose, S. Schreiber
    DESY, Hamburg
  The injector laser of the VUV-FEL at DESY, Hamburg, was modified to allow the generation of double-pulses, separated by a few cycles of the 1.3 GHz radio-frequency. Such double pulses are needed for driving the planned infrared/VUV pump/probe facility. Construction constraints of the facility will result in an optical path length about 80 cm longer for the infrared. Although the VUV can be delayed using normal-incidence multilayer mirrors at selected wavelengths, a fully flexible scheme is achieved by accelerating two electron bunches separated by more than the path length difference and then combine the infrared radiation from the first with the VUV from the second. This paper explains schemes for the generation of double-pulses with the laser system. It summarizes experimental studies of the effect on the operation of diagnostic instrumentation and on the tunability of the machine. Of special concern is the effect of wakefields on the quality of the second bunch, critical for achieving lasing.  
 
THPLS132 Physics Requirement of a PLS-XFEL Undulator undulator, radiation, FEL, XFEL 3592
 
  • D.E. Kim, C.W. Chung, I.S. Ko, J.-S. Oh, K.-H. Park
    PAL, Pohang, Kyungbuk
  Pohang Accelerator Laboratory(PAL)is planning a 0.3nm SASE (Self Amplification of Spontaneous Emission) XFEL based on a 3.7GeV linear accelerator. For short saturation length, application of the SPring8 type in the vacuum undulator is needed. This reflects the experiences from the Spring8 SCSS project. The end structures were designed to be asymmetric along the beam direction to ensure systematic zero 1st field integral. The thickness of the last magnets was adjusted to minimize the transition distance to the fully developed periodic field. This approach is more convenient to control than adjusting the strength of the end magnets. The final design features 4mm minimum pole gap, 15mm period, and peak effective field of 1.09 Tesla. In this article, the physical design of the undulator, the design of the end structure, and the physics requirements of the undulator system will be presented.