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radiation

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MOBAU02 Technology Challenges Towards Short-Wavelength FELs electron, emittance, undulator, space-charge 9
 
  • J. Rossbach
    Uni HH, Hamburg
  Since the very first proposal of high-gain FELs for the X-ray wavelength regime it was obvious that realization of such a device, potentially rewarding revolutionary science opportunities, would impose extraordinary challenges in terms of accelerator physics and technology. The talk will review the major steps that had to be taken to finally construct an FEL user facility for soft X-rays. Also, a few issues will be pointed out that are to be addressed in order to make full profit of the FEL principle at X-ray wavelengts.  
slides icon Slides  
 
MOPPH003 VOLC: Volume Free Electron Laser Simulation Code electron, simulation, free-electron-laser, laser 14
 
  • S. Sytova
    Belarussian State University, Scientific Research Institute of Nuclear Problems, Minsk
  First lasing of Volume Free Electron Laser (VFEL) in mm wavelength range was obtained recently*. Мulti-wave volume distributed feedback where electromagnetic waves and electron beam spread angularly one to other in a spatially-periodic target is the VFEL distinctive feature**. Mathematical model and numerical methods for VFEL nonlinear stage simulation were proposed*** and implemented in computer code VOLC that means "VOLume Code". It was developed on the basis of multiple Fortran codes created in 1991-2006 years. VOLC allows to simulate different geometries of two- and three-wave VFEL in amplifier and oscillator regimes. Electron beam is modelled by averaging over initial phases of electrons. Dimensionality is 2D (one spatial coordinate and one phase space coordinate) plus time. All numerical results obtained using VOLC are in good agreement with analytical predictions of VFEL theory. Different roots to chaos in VFEL were investigated using VOLC. Some successful simulations of VFEL experimental setup at INP were carried out. A description of VOLC possibilities and representative numerical results are presented.

* V. G. Baryshevsky et al., NIMA483 (2002) 21. ** V. G. Baryshevsky, NIMA445 (2000) 281. *** K. Batrakov, S. Sytova, Computational Mathematics and Mathematical Physics 45 (2005) 666.

 
 
MOPPH006 Longitudinal Wake Field for an Electron Beam Accelerated through a Ultra-High Field Gradient electron, impedance, acceleration, undulator 26
 
  • E. Saldin, E. Schneidmiller, M. V. Yurkov, G. Geloni
    DESY, Hamburg
  Electron accelerators with higher longitudinal field gradients can produce high-energy beams with compact, cheap setups. Laser-plasma acceleration appears to constitute the more promising breakthrough in this direction, delivering field gradients up to TV/m. Here we describe the impact of longitudinal wake fields on the electron beam, based on solution of Maxwell's equations for the longitudinal field. We consider an acceleration distance much smaller than the overtaking length (the length that electrons travel as a light signal from the tail of the bunch overtakes the head of the bunch), that is the case for laser-plasma devices. We give expressions for impedance and wake function that may be evaluated numerically. We show that the rate of energy loss in the bunch due to radiative interaction is equal to that of coherently radiated energy in the far-zone. A limiting expression is found for a large distance of the electron beam from the accelerator compared with the overtaking length. We derive analytical solutions for a Gaussian transverse and longitudinal bunch shape. We apply our analytical asymptote by studying the feasibility of a Table-Top FEL based on laser-plasma driver. Numerical estimations indicate that the effects of the time-dependent energy change induced by the longitudinal wake pose a serious threat to the operation of this device. (See DESY 06-222)  
 
MOPPH007 Theory of Nonlinear Harmonic Generation in Free-Electron Lasers with Helical Wigglers electron, undulator, wiggler, resonance 30
 
  • E. Saldin, E. Schneidmiller, M. V. Yurkov, G. Geloni
    DESY, Hamburg
  Coherent Harmonic Generation (CHG), and in particular Nonlinear Harmonic Generation (NHG), is of importance for both short wavelength Free-Electron Lasers (FELs), in relation with the achievement of shorter wavelengths with a fixed electron-beam energy, and high-average power FEL resonators, in relation with destructive effects of higher harmonics radiation on mirrors. In this paper we present a treatment of NHG from helical wigglers with particular emphasis on the second harmonic. Our study is based on an exact analytical solution of Maxwell's equations, derived with the help of a Green's function method. In particular, we demonstrate that nonlinear harmonic generation (NHG) from helical wigglers vanishes on axis. Our conclusion is in open contrast with results in literature, that include a kinematical mistake in the description of the electron motion. (See DESY 07-058)  
 
MOPPH009 Undulator Radiation in a Waveguide undulator, resonance, vacuum, diagnostics 34
 
  • E. Saldin, E. Schneidmiller, M. V. Yurkov, G. Geloni
    DESY, Hamburg
  We propose an analytical approach to characterize undulator radiation near resonance, when the presence of the vacuum-pipe considerably affects radiation properties. This is the case of the far-infrared undulator beamline at the Free-electron LASer (FEL) in Hamburg (FLASH), that is designed to deliver pulses in the TeraHertz (THz) range. This undulator can be used for pump-probe experiments where THz pulses are naturally synchronized to the VUV pulse from the FEL, as well as the development of novel electron-beam diagnostics techniques. Since the THz radiation diffraction-size exceeds the vacuum-chamber dimensions, characterization of infrared radiation must be performed accounting for the presence of a waveguide. We developed a theory of undulator radiation in a waveguide based on paraxial and resonance approximation. We solved the field equation with a tensor Green's function technique, and extracted figure of merits describing in a simple way the influence of the vacuum-pipe on the radiation pulse as a function of the problem parameters. Our theory, that makes consistent use of dimensionless analysis, allows treatment and physical understanding of many asymptotes of the parameter space, together with their region of applicability. (See DESY 07-031)  
 
MOPPH011 Comparison Between Kinetic and Fluid Description of Plasma-Loladed Free-Electron Laser plasma, electron, wiggler, space-charge 42
 
  • S. Babaei, B. Maraghechi
    AUT, Tehran
  In the kinetic treatment of the plasma-loaded FEL in Ref.* single particle equation of motion, for both beam and plasma electrons in the radiation fields, are used. Therefore, interaction terms between the wiggler and the space-charge wave, in the transverse velocity of electrons, which are important elements in the fluid model, are neglected. A dispersion relation of a plasma-loaded FEL with kinetic theory is found in Ref.* that takes into account the velocity spread of both beam and plasma electrons. In the present analysis, a dispersion relation is obtained, by the fluid theory, with the interaction terms between the wiggler and the space-charge wave in the transverse velocity of electrons taken into account. Since these interaction terms are inherently missing in the kinetic theory the two dispersion relation are compared to find out about the importance of these terms. It was found that although the absence of these terms has considerable effects on the growth rate, the general kinetic dispersion relation may be used to study the temperature effects of a warm beam/plasma on the instability of a free-electron laser with a plasma background.

* S. Babaei and B. Maraghechi, "Kinetic description of plasma-loaded free-electron laser", Phys. Plasmas, to be published.

 
 
MOPPH015 Limit for Harmonic Conversion in a Single Cascade of Coherent Harmonic Generation bunching, electron, laser, simulation 50
 
  • G. De Ninno, E. Allaria
    ELETTRA, Basovizza, Trieste
  Harmonic generation is a reliable method for producing coherent high-brightness photon pulses from relativistic electron bunches. The standard process leading to Coherent Harmonic Generation (CHG) is initiated by a powerful seed laser. As a consequence, reaching short wavelengths generally requires a high order frequency conversion. For that reason some of the projects which are presently under development for coherent VUV and soft-Xray emission are based on a series of two or more consecutive "cascades". In these setups, the radiation produced into one CHG stage is used as a seed in a following CHG cascade. The required number of cascades is related to the maximum harmonic conversion which can be obtained in single stages. In this paper the mechanism underlying the CHG, i.e. the bunching creation into the modulator, is studied in detail and the physical limits for the single-stage CHG are investigated. The identification of the limiting parameters may allow the implementation of new methods for enhancing the conversion efficiency. One of these methods, which relies on a simple modification of the standard CHG scheme, has been recently proposed* and shown to be able to significantly improve the system performance. Results are confirmed by numerical simulations using the codes Ginger and Genesis. Expected impact on some of the existing projects for CHG is also presented.

* E. Allaria, G. De Ninno, Phys. Rev. Lett., to be published.

 
 
MOPPH017 1D Linear Intensity Spiking Evolution in a Single Shot of a SASE FEL electron, undulator, free-electron-laser, laser 54
 
  • V. Petrillo
    Universita' degli Studi di Milano, Milano
  • L. Serafini, C. Maroli
    INFN-Milano, Milano
  The analysis is based on the 1D Maxwell-Lorentz equations which are reduced to the usual averaged linear equation in the limit of vanishingly small radiation field A(z,t) and average length lm. It is shown that if this equation is solved with initial shot noise conditions in which the widths of the spikes and the average distance between successive spikes are both uniformly smaller than the cooperation length Lc, it may lead to large amplitude coherent signals. The intensity spiking RMS relative amplitude decreases from the 100% values it has at t=0, down to values of the order or less than 0.1% in time intervals from ten to twenty gain times.  
 
MOPPH020 FEL with Orotron Type Feedback electron, coupling, feedback, undulator 61
 
  • R. Ando, K. Kamada
    Kanazawa University, Kanazawa
  • N. S. Ginzburg, N. Yu. Peskov, R. M. Rozental, A. Sergeev, V. Yu. Zaslavsky, A. Malkin
    IAP/RAS, Nizhny Novgorod
  In microwave electronics orotron is widely used as a source of RF radiation in millimeter and submillimeter wavebands. In this device an electron beam is coupled to a mode of quasi-optical resonator by means of the periodical grating one of the resonator mirror. In our paper we discuss a relativistic modification of such a device. A novel FEL scheme is suggested in which the slow wave structure of orotron is replaced by shallow Bragg corrugation which provides the coupling of the transverse (with respect to direction of beam propagation) mode of a two-mirror cavity with longitudinally propagating wave. The latter can be excited by the electron beam wiggling in undulator field. Described scheme allows to combine selective properties of an orotron with relativistic frequency conversion of a free electron laser. The transverse mode provides the feedback in the system thus leading to self-excitation, while the propagating wave is responsible for energy extraction in the steady-state regime of operation. The discussed system was investigated both analytically and numerically using direct codes and averaged equations approach.  
 
MOPPH022 A Description of Guided FEL Radiation Using Dielectric Waveguide Eigenmodes undulator, coupling, electron, bunching 65
 
  • A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
  • J. B. Rosenzweig, E. Hemsing
    UCLA, Los Angeles, California
  An analysis of the radiation field of an FEL in terms of eigenmodes of a linear dielectric waveguide is presented.  
 
MOPPH023 Enhancing FEL Power with Phase Shifters undulator, electron, simulation, linac 69
 
  • A. Chao, Z. Huang
    SLAC, Menlo Park, California
  • D. F. Ratner
    Stanford University, Stanford, Califormia
  Undulator taper is a well-known technique to increase the FEL efficiency past saturation by maintaining the resonant condition. In this paper, we demonstrate that shifting the electron bunch phase relative to the radiation is equivalent to tapering the undulator parameter. Using discrete phase changes derived from optimized undulator tapers for the LCLS x-ray FEL, we show that placing appropriate phase shifters between undulator sections can reproduce the power enhancement of these undulator tapers. The phase shifters are relatively easy to implement and operate, and hence can be used to aid or replace the undulator taper for optimizing the FEL performance.  
 
MOPPH025 Three-dimensional Theory of the Cerenkov Free-Electron Laser electron, laser, free-electron-laser, feedback 73
 
  • C. A. Brau, H. L. Andrews
    Vanderbilt University, Nashville, Tennessee
  We present an analytical theory for the operation of a Cerenkov free-electron laser which includes diffraction of the optical mode in the direction transverse to the electron beam. Because the width of the optical mode depends on the gain, the usual cubic dispersion relation is replaced by a 5/2-power dispersion relation, however, only two of these roots are allowed. These two roots both have positive real parts, indicating that they are slow waves. For a narrow electron beam, the optical mode is much wider than the beam, thus reducing the gain by an order of magnitude from that predicted by the two dimensional theory. In the limit of a wide electron beam, the two dimensional theory is recovered.  
 
MOPPH026 Three-Dimensional Theory of the Smith-Purcell Free-Electron Laser electron, laser, free-electron-laser, synchrotron 77
 
  • H. L. Andrews, C. A. Brau, J. D. Jarvis
    Vanderbilt University, Nashville, Tennessee
  We present an analytic theory for the operation of a Smith-Purcell free-electron laser (SPFEL) that includes transverse diffraction of the optical beam. For the case of an infinitely wide electron beam, this theory agrees with previous two-dimensional analyses. When the electron beam is narrow compared to the mode, the gain (amplifier regime) is substantially reduced by diffraction, while its dependence on the beam current is increased due to gain guiding. A 5/2-power dispersion relation replaces the conventional cubic dispersion relation. Additionally, the constituent waves of the laser mode are found to have different transverse decay rates. An estimate of the start current (oscillator regime) of the device is obtained by satisfying the appropriate boundary conditions on the beam axis.  
 
MOPPH030 Terahertz Imaging and Radioscopy with 160x120 Microbolometer 90 fps Camera free-electron-laser, laser, electron, controls 83
 
  • A. L. Aseev, M. A. Dem'yanenko, D. G. Esaev, I. V. Marchishin
    ISP, Novosibirsk
  • G. N. Kulipanov, N. Vinokurov, B. A. Knyazev
    BINP SB RAS, Novosibirsk
  Uncooled micromolometer camera for IR and THz high-speed imaging has been developed. The 160x120 focal plane array consists of resistive vanadium oxide elements on a silicon nitride bridge. The element size is 48x48 micron at 51 micron array period. We describe device fabrication process and focal plane array operational characteristics. The camera was used as a recorder in quasi-optical systems with Novosibirsk terahertz free electron laser as a radiation source. Radioscopy of the objects, which are of interest for biology and security applications, has been demonstrated. The recording rate up to 90 frames per second has been obtained.  
 
MOPPH031 Spectroscopy and Spectrally Resolved Radioscopy of Biological Substances Using Terahertz Free Electron Laser Radiation free-electron-laser, laser, diagnostics, electron 86
 
  • V. V. Gerasimov
    NSU, Novosibirsk
  • A. M. Gonchar
    ICG SB RAS, Novosibirsk
  • B. A. Knyazev
    BINP SB RAS, Novosibirsk
  High average power and monochromacity of terahertz Novosibirsk free electron laser are favorable for the development of time and space resolved spectroscopic and radioscopic techniques for study of highly absorbing substances, in particular, biological ones. To study highly absorbing objects we applied a homemade attenuated total reflection spectrometer, which enables operation in both conventional and imaging mode. By measuring the reflection coefficients for p- and s-polarized radiation, the real (n) and imaginary (k) parts of refractive index can be derived. Using a microbolometer matrix (see the paper by Esaev et al. at this conference), imaging radioscopy of the samples containing amino acids and DNA had been performed. The methods developed were applied also for examination of bones of intact and senescence-accelerated mice that, probably, would lead to study osteoporosis development.  
 
MOPPH032 Development of Metal Mesh Based Quasi-optical Selective Components and Their Application in High-power Experiments at Novosibirsk Terahertz FEL laser, synchrotron, controls, synchrotron-radiation 89
 
  • B. G. Goldenberg, P. V. Kalinin, V. V. Kubarev, N. Vinokurov, S. A. Kuznetsov
    BINP SB RAS, Novosibirsk
  Successful realization of terahertz research programs at the Novosibirsk FEL-facility requires detailed development, designing and optimization of passive quasi-optical selective components, intended for polarization and frequency gating of powerful THz-beams of NovoFEL radiation. Along with desired selective characteristics such components should be capable of operating over a long period of time under high-power load conditions (a few hundred Watts of average incident radiation power) without noticeable degradation of their properties. It admits to employ in selective components only low absorbing and thermostable materials, such as high conductivity metals and special types of polymers. This report is devoted to development of metal mesh based selective structures, such as polarizing beamsplitters (attenuators) and different frequency filters, and their application in high-power THz-experiments. Possibilities and prospects of two main production technologies are discussed: 1) conventional photolithography destined for manufacturing thin metal structures deposited on low-absorbing thermostable polymer films; 2) LIGA-technique intended for producing thick substrate-free metal structures.  
 
MOPPH033 Diffraction Optical Elements and Optical Systems with a High Power Monochromatic Terahertz Source focusing, free-electron-laser, laser, electron 93
 
  • H. J. Cha, Y. U. Jeong
    KAERI, Daejon
  • V. S. Cherkassky, L. A. Merzhievsky, S. A. Zhigach
    NSU, Novosibirsk
  • A. V. Fanova, B. A. Knyazev, G. N. Kulipanov, N. Vinokurov, I. A. Polskikh
    BINP SB RAS, Novosibirsk
  We have developed reflective diffraction optical elements (DOE) for focusing radiation of terahertz free electron lasers (FEL). Metal-dielectric Fresnel zone plates and metallic kinoform "lenses" were fabricated and tested using FEL radiation. A microbolometer camera (see the paper by Esaev et al. at this conference) sensitive to THz radiation had been applied for recording both terahertz beam caustic and terahertz images. Diffraction efficiency of a kinoform lens appears to be about unity. Quality of images obtained with the kinoform lens was studied. The lens was used as a key element for a Toepler optical system, which were used for studying condense matter non-uniformities and deformations. The experiments were performed at Novosibirsk and KAERI FELs.  
 
MOPPH034 Diagnostics of an Electron Beam using Coherent Cherenkov Radiation electron, laser, diagnostics, undulator 95
 
  • R. Tikhoplav
    UCLA, Los Angeles, California
  A comparison of coherent Cherenkov and transition radiations as a diagnostic tool for longitudinal distribution of an electron beam is studied in this paper. Two methods will be used for the 7th harmonic bunching experiment at Neptune linear accelerator facility at UCLA. Coherent Cherenkov radiation is produced in an aerogel with an index of refraction close to unity.  
 
MOPPH036 First Experiences with the FIR-FEL at ELBE electron, laser, undulator, free-electron-laser 97
 
  • P. Michel, W. Seidel, G. Staats, J. Teichert, R. Wuensch, U. Lehnert
    FZD, Dresden
  We show the design and the parameters of operation of the long-wavelength (U100) FEL of ELBE. First lasing has been shown in August, 2006. Since then, the laser has undergone thorough commissioning and is available for user experiments since fall, 2006. Besides in-house users the IR beam is available to external users in the FELBE (FEL@ELBE) program witch is a part of the integrated activity on synchrotron and free electron laser science in the EU. At the beginning of 2007 lasing in the full designed wavelength range from 20μm to 200μm was demonstrated. The laser power typically reaches several W in CW operation but drops for very long wavelengths depending on the size of the used outcoupling hole. However, there exists a serious problem with small gaps in the providable wavelength spectrum. We attribute this behaviour to the transmission characteristics of the overmoded partial waveguide used from the undulator entrance to the first mirror.  
 
MOPPH041 Comparative Study of Electro-Optic Effect between Simulation and Measurement laser, electron, simulation, controls 104
 
  • J. Y. Huang, C. Kim, I. S. Ko, Y. W. Parc
    PAL, Pohang, Kyungbuk
  The short, intense, and low emittance electron beams are crucial to make high quality X-ray beam for X-ray free electron laser (XFEL). Electro-Optic Sampling (EOS) is a promising method to measure the electron bunch length non-destructively. A simulation study is done with the pulse propagation method, which utilizes Fourier transform to investigate the evolution of electromagnetic pulse inside the electro-optic (EO) crystal. The experimental result measured with spatial decoding method at Free electron LASer in Hamburg (FLASH) facility in Deutsches Elektronen-Synchrotron (DESY) is analyzed in terms of the relative phase shift between the horizontal and vertical component of the laser pulse. In this report, the experimental results expressed in terms of the "Relative Phase Shift Г" are compared with the simulation result. The simulation and the experimental result show similar values within reasonable error. The way to increase the signal level is also proposed.  
 
MOPPH042 Losses in Optical Resonator of Novosibirsk Terahertz Free Electron Laser: Theory and Experiment coupling, laser, electron, free-electron-laser 107
 
  • V. V. Kubarev
    BINP SB RAS, Novosibirsk
  Design of optical resonator of Novosibirsk terahertz free electron laser (NovoFEL)was made on base simple analitical theory discribed in paper*. Direct comparison of the theory and many experiments on NovoFEL is presented.

* Kubarev V. V. Babinet principle and diffraction losses in laser resonators. Quantum Electronics 30(9)824-826(2000).

 
 
MOPPH043 Control and Diagnostic System of Novosibirsk FEL Radiation controls, undulator, diagnostics, linac 111
 
  • V. V. Kubarev, E. V. Makashov, K. S. Palagin, S. S. Serednyakov
    BINP SB RAS, Novosibirsk
  The architecture the main capabilities of control and diagnostic system of the Novosibirsk FEL coherent radiation are described. The client-server model is used for software, controlling this system. The developed software is capable to work both in client and server mode. Also it can control various equipment – from FEL optical cavity mirrors to local equipment of users stations. The mode of control program operation and controlled equipment are determinates by external configuration files. Some results of the system operation are also presented.  
 
MOPPH050 Status of the Undulator System of the Seeded HGHG-FEL Test Bench at MAX-lab electron, undulator, simulation, laser 122
 
  • M. Brandin, F. Lindau, D. Pugachov, S. Thorin, S. Werin
    MAX-lab, Lund
  • W. Frentrup, A. Gaupp, K. Goldammer, K. Holldack, M. Scheer, J. Bahrdt
    BESSY GmbH, Berlin
  Within the EUROFEL Design Study a seeded HGHG-FEL will be set up at the 400 MeV linac at MAX-lab. The undulators and the dispersive section have been installed. A glass fibre based power meter system for integrated dose measurements as well as a Cherenkov system for a fast detection of electron losses have been integrated. We report on the performance of all components. Simulations on the acceptable radiation doses inside the undulator magnets will be presented. In the first step of commissioning the THz radiation as produced by the bunched electron beam inside the dispersive section will be used for the optimization of the longitudinal and transverse overlap of the electron beam and the laser beam.  
 
MOPPH051 Nonlinear Harmonic Generation in the BESSY Soft X-Ray FEL undulator, electron, simulation, laser 126
 
  • K. Goldammer
    BESSY GmbH, Berlin
  Free Electron Lasers do not only radiate at the fundamental frequency, they may also radiate coherently at higher harmonics. This process is referred to as nonlinear harmonic generation or NHG. NHG is of high interest, because it extends the FEL output wavelength of FELs to several harmonics of the FEL resonant frequency. In cascaded High Gain Harmonic Generation (HGHG) FELs, harmonic radiation may be used to improve frequency-conversion and reduce the number of HGHG-stages. BESSY proposes to build a cascaded HGHG FEL with three FEL lines. They cover a wavelength range of 51 nm (Low-Energy FEL) to 1.2 nm (High-Energy FEL) and consist of up to four HGHG-stages. In this paper, we present studies of the BESSY High-Energy FEL harmonic content performed with the upgraded version of the simulation code Genesis 1.3.  
 
MOPPH052 Output Performance of the STARS HGHG Demonstrator at BESSY undulator, emittance, laser, electron 130
 
  • K. Goldammer, A. Meseck, B. C. Kuske
    BESSY GmbH, Berlin
  BESSY is planning to construct a free-electron laser facility (STARS) to demonstrate cascaded high-gain harmonic generation (HGHG) FELs. A 325MeV superconducting linear accelerator will drive two HGHG-stages, where the second stage is seeded by the radiation from the first stage. Such a cascading of the HGHG scheme, originally pioneered by L. H. Yu, allows a reduction of the STARS output wavelength down to the few 10nm range. This paper describes the expected performance of the facility, the achievable wavelength range, the harmonic content of the radiation, the potential of super-radiant pulses and first considerations about the stability of the source.  
 
MOPPH054 Small-Aperture Vacuum-Chamber Design for STARS electron, vacuum, undulator, scattering 134
 
  • J. Bahrdt, V. Duerr, M. Scheer, G. Wuestefeld, A. Meseck
    BESSY GmbH, Berlin
  To demonstrate and investigate the cascaded HGHG-scheme proposed for the BESSY Soft X-ray FEL, BESSY plans to build a test-facility called STARS consisting of two HGHG stages. The radiator in the second stage is planned as an APPLE III device which provides the highest field for a circular beam pipe. The minimum Gap of 7 mm translates into a 5 mm inner diameter of the vacuum chamber. An analysis of the impact of the wakefields and the expected vacuum profile is thus required. Results of this analysis an vacuum measurements are presented.  
 
MOPPH058 Status of the SPARX Project emittance, linac, undulator, simulation 142
 
  • D. Filippetto
    INFN/LNF, Frascati (Roma)
  The SPARX project consists in an Soft-X-ray-FEL facility jointly supported by MUR(Research Department of Italian Government), Regione Lazio, CNR, ENEA, INFN and the University of Roma Tor Vergata. It is the natural extension of the ongoing activities of the SPARC collaboration. The aim is the generation of electron beams characterized by ultra-high peak brightness at the energy of 1 and 2 GeV, for the first and the second phase respectively. The beam is expected to drive a single pass FEL experiment in the range of 13.5-6 nm and 6-1.5 nm, at 1 GeV and 2 GeV respectively, both in SASE and SEEDED FEL configurations. A hybrid scheme of RF and magnetic compression will be adopted, based on the expertise achieved at the SPARC. high brightness photoinjector presently under commissioning at Frascati INFN-LNF Laboratory.  
 
MOPPH062 Features of the PAL-XFEL Design undulator, electron, emittance, brightness 152
 
  • J. Choi, H.-S. Kang, T.-Y. Lee
    PAL, Pohang, Kyungbuk
  The PAL-XFEL design has been revised since the previous conference. The 2nd bunch compressor has been moved to a higher energy to eliminate the space charge effect and the total linac energy has been increased from 3.7 GeV to 4.0 GeV. Details and reasons of these design revisions are explained in this paper.  
 
MOPPH063 Potentialities of ELMI Device for Submillimeter Generation by Stimulated Intercavity Scattering in Planar FEM scattering, electron, simulation, cathode 156
 
  • N. S. Ginzburg, N. Yu. Peskov, A. Sergeev, V. Yu. Zaslavsky, I. V. Zotova
    IAP/RAS, Nizhny Novgorod
  • P. V. Kalinin, S. A. Kuznetsov, A. V. Arzhannikov
    BINP SB RAS, Novosibirsk
  Paper describes main features of a project on two-stage generation of submillimeter radiation at the ELMI device. This novel variant of a two-stage scheme based on stimulated intercavity scattering was proposed earlier in the paper*. In accordance with the scheme, at the first stage a sheet electron beam drives a 2D Bragg free electron maser (FEM) of planar geometry to generate 4-mm pump wave. At the second stage this wave undergoes stimulated scattering at the supplementary electron beam to produce submillimeter radiation. A key feature of a proposed scheme is to use two sheet beams with a few kiloampers currents that transported in parallel channels, which are connected by a special waveguide* for synchronization of beam radiation in different channels**. Production of two sheet beams by one accelerator diode with two cathodes is also similar to the process of operation of the multibeam diode described in Ref.**. Two-stage scheme allows us to use high power 4-mm radiation produced in the first channel by the sheet beam moving in an undulator quasi-static magnetic field, as an EM-undulator for the secondary stage FEL operating in Terahertz wave range. In the paper we describe results of theoretical and experimental investigations of various aspects of the two-stage scheme and some testing experiments on units for realization of this scheme at the ELMI device.

* A. V.Arzhannikov et al. Proc. Int. Workshop, N. Novgorod, Vol.1,p.228-232,2006.** A. V.Arzhannikov et al. Digest Tech. Papers, PPPS-2001, Las Vegas, Nevada, Vol.1, p.561-564,2001.

 
 
MOPPH068 The NCAS-FEL: an FEL Oscillator with High Slippage undulator, electron, simulation, laser 163
 
  • K.-J. Boller, E. van Geijin
    Mesa+, Enschede
  • J. Jalink, W. J. van der Zande
    Radboud University Nijmegen, Institute of Molecules and Materials, Nijmegen
  • P. J.M. van der Slot
    Twente University, Laser Physics and Non-Linear Optics Group, Enschede
  In normal operation of FEL oscillators with little or no slippage, the cavity length needs to be slightly smaller than the synchronous value due to the lethargy in the gain build-up. If the FEL experiences high slippage, i.e., when the slippage becomes comparable or even larger than the length of the electron pulse, a different cavity detuning may be required. We use the one dimensional Medusa1D code to study the NCAS-FEL* as an example of an FEL oscillator having high slippage. Medusa1d is basically equal to the fully three dimensional Medusa code** with the 3D effects stripped out. It includes multiple wiggler segments, electron beam transport elements, harmonics and a simple oscillator model. Medusa1D can also include 3D effects using the fitting formula of Xie***. The NCAS-FEL is a RF-linac based FEL dedicated for high resolution spectroscopic studies in the wavelength range from 100 micron to 1.5 mm. The design of the NCAS-FEL is currently under way, and we report here initial results of this design and focus on the effects of high slippage on cavity detuning and the development of coherence within the optical pulse.

* Proceedings of FEL 2006, Berlin, Germany (2006) p485 - 487 ** Phys. Rev. ST-AB 8, 110701 (2005)*** Nucl. Instrum. Methods Phys. Res., Sect. A 445, 59 (2000)

 
 
MOPPH069 3D Modelling of the ERLP IR-FEL simulation, electron, alignment, wiggler 167
 
  • J. A. Clarke, N. Thompson, D. J. Dunning
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • B. W.J. McNeil
    USTRAT/SUPA, Glasgow
  An Energy Recovery Linac Prototype (ERLP) facility is currently being commissioned at Daresbury Laboratory; it serves as a testbed for technologies to be used in the proposed 4th Generation Light Source (4GLS) facility. As part of the ERLP facility, an infra-red oscillator FEL is due to be commissioned early in 2008. In this paper we present full three dimensional, time-dependent modelling of the ERLP IR-FEL using Genesis 1.3 in combination with a paraxial optical propagation code (OPC). We also discuss how this work will be used to inform commissioning of the FEL.  
 
MOPPH072 The IR-Beam Transport System from the ELBE-FELs to the User Labs diagnostics, laser, electron, focusing 171
 
  • M. Justus, K.-W. Leege, D. Proehl, R. Schlenk, A. Winter, D. Wohlfarth, R. Wuensch, W. Seidel
    FZD, Dresden
  In the Forschungszentrum Dresden-Rossendorf, two free-electron lasers (FELs) have been put into operation. They produce laser light in the medium and the far infrared wavelength range (4-200 microns). The IR light is transported to several laboratories in the same building and to the adjacent building of the High Magnetic Field Laboratory (HLD) as well. The latter is up to 70m away from the FELs. Constructional peculiarities, the large wavelength range (a factor of 50 between the shortest and the longest wavelengths), the high average power in cw regime, and the beam property requirements of the users pose a challenge to the beam line design. The transport system includes vacuum pipes, plane and toroidal gold-covered copper mirrors, exit windows, and diagnostic elements. The designed transport system produces a beam waist at selected spots in each laboratory representing an image of the outcoupling hole. Spot size and position are independent of the wavelength. In the HLD the beam is fed into a circulare waveguide, guiding the radiation to the sample inside of a cryostat. To ensure the desired beam properties, the transport system has been analyzed by means of various ray and wave optical models.  
 
MOPPH074 Preliminary Design of the Proposed IR-FEL in India electron, simulation, undulator, linac 179
 
  • V. Kumar, S. Krishnagopal
    RRCAT, Indore (M. P.)
  We propose to build a infra-red free-electron laser facility in India. We present details of the preliminary design of the FEL.  
 
MOCAU01 Short Wavelength Regenerative Amplifier FELs feedback, simulation, electron, undulator 182
 
  • D. J. Dunning, N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • B. W.J. McNeil
    USTRAT/SUPA, Glasgow
  In this paper we discuss the possibility of extending the operating wavelength range of tunable Regenerative Amplifier FELs to shorter wavelengths than current design proposals, notably into the XUV regions of the spectrum and beyond where the reflectivity of broadband optics is very low. Simulation studies are presented which demonstrate the development of good temporal coherence in generic systems with a broadband radiation feedback of less than one part in ten thousand.  
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MOCAU02 Numerical Solution of the FEL Correlation Function Equation undulator, electron, simulation 188
 
  • N. Vinokurov, O. A. Shevchenko
    BINP SB RAS, Novosibirsk
  The equation for two-particle correlation function in FEL was derived recently to provide a new way of noise calculations in FELs*. In this paper this equation is solved numerically for the simplest case of narrow electron beam. Time independent solution with saturation is obtained. It is compared with the results of quasilinear theory and results of previous SASE linewidth estimates.

* O. A. Shevchenko, N. A. Vinokurov, NIM A507 (2003) 84-88

 
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MOCAU04 Impact of Longitudinal Space-charge Wake from FEL Undulators on Current-enhanced SASE Schemes impedance, undulator, space-charge, electron 196
 
  • E. Saldin, E. Schneidmiller, M. V. Yurkov, G. Geloni
    DESY, Hamburg
  In this article we present a description of longitudinal wake fields in X-ray Free-Electron Lasers (XFELs) that is of relevance in relation with Enhanced Self-Amplified Spontaneous Emission (ESASE) schemes. We consider wakes in XFELs, in the limit when the electron beam has gone inside the undulator for a distance longer than the overtaking length (the length that electrons travel as a light signal from the tail of the bunch overtakes the head of the bunch). We find that the magnitude of the resulting energy chirp constitutes a reason of concern for the practical realization of ESASE schemes.  
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MOCAU05 Space Charge Effect in an Accelerated Beam acceleration, space-charge, electron, electromagnetic-fields 200
 
  • Z. Huang, G. V. Stupakov
    SLAC, Menlo Park, California
  It is usually assumed that the space charge effects in relativistic beams scale with the energy of the beam as the inverse relativistic factor gamma factor squared. We show that for a beam accelerated in the longitudinal direction there is an additional space charge effect in free space that scales as the ratio of the accelerating field to the gamma factor. This space charge field has the same origin as the "electromagnetic mass of the electron" discussed in textbooks on electrodynamics. It keeps the balance between the kinetic energy of the beam and the energy of the electromagnetic field of the beam. We then consider the effect of this field on a beam generated in an RF gun and calculate the energy spread produced by this field in the beam.  
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TUAAU02 Electron Outcoupling Scheme for the Novosibirsk FEL undulator, electron, bunching, simulation 204
 
  • O. A. Shevchenko, V. G. Tcheskidov, N. Vinokurov, A. N. Matveenko
    BINP SB RAS, Novosibirsk
  One of the main problems of contemporary high power FELs is the mirror heating. One of the possible solutions of this problem is the use of electron outcoupling*. In this case the mirrors of optical resonator are not transparent and the coherent radiation from an additional undulator in the FEL magnetic system is used. To provide the output of this radiation the electron beam in the auxiliary undulator is deflected from the optical resonator axis. To save bunching it is preferable to use the achromatic deflecting bend. The project of electron outcoupling for the Novosibirsk FEL is described. Simulation results are presented.

* N. G. Gavrilov et al., NIM A304 (1991) 63-65

 
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TUAAU05 Modelling Mirror Aberrations in FEL Oscillators Using OPC undulator, laser, simulation, free-electron-laser 207
 
  • K.-J. Boller, J. G. Karssenberg, P. J.M. van der Slot
    Mesa+, Enschede
  Thermal distortion in mirrors used in high average power FEL oscillators, like the JLAB FEL and the 4GLS VUV-FEL, will influence the mode quality and affect the FEL performance. In order to quantify these effects, these distortions needs to be characterised. Mirror aberrations are generally described using Zernike polynomials and also in case of thermal distortions, it has been shown that these polynomials can be used to describe the mirror distortion*. The Optical Propagation Code (OPC)** is a general optical propagation package in the paraxial approximation, that works together with gain codes like Medusa and Genesis 1.3 to model FEL oscillators. We have extended OPC to include phase masks, that can either be generated by an external program or internally using Zernike polynomials. This allows OPC to model mirror aberrations. We will present a few examples, illustrating the capabilities of OPC.

* Nucl. Instrum. Meth. A407 (1998)401** J. Appl. Phys. 100, 093106 (2006)

 
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TUBAU01 FLASH Upgraded - Preparing for the European XFEL laser, electron, feedback, photon 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.  
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TUBAU03 STARS – an FEL to Demonstrate Cascaded HGHG linac, emittance, electron, laser 220
 
  • M. Abo-Bakr, W. Anders, J. Bahrdt, R. Follath, K. Goldammer, S. C. Hessler, K. Holldack, T. Kamps, B. C. Kuske, A. Meseck, T. Quast, J. Knobloch
    BESSY GmbH, Berlin
  BESSY plans to build the BESSY Soft X-ray FEL facility, a second generation FEL for the VUV and soft x-ray range. The TDR was evaluated by the German Science Council and recommended for funding subject to the condition that cascaded high-gain harmonic generation (HGHG) be demonstrated beforehand. To this end, BESSY is proposing the demonstration facility STARS for a two-stage HGHG FEL. For efficient lasing from 40 nm to 70 nm, a 325 MeV driver linac is required. It consists of a normal-conducting gun, superconducting TESLA-type modules modified for CW operation and a bunch compressor. The two-stage HGHG cascade employs variable gap undulators, with the final amplifier being an APPLE-III device for full polarization control. A beamline with user experiment completes STARS, which is planned to remain operational even after the BESSY FEL comes online. This paper summarizes the layout of STARS, the main parameters and the expected performance.  
 
TUPPH011 Analytical Studies of Transverse Coherence Properties of X-ray FELs electron, undulator, emittance, free-electron-laser 240
 
  • E. Schneidmiller, M. V. Yurkov, E. Saldin
    DESY, Hamburg
  We describe analytically the process of formation of transverse coherence in X-ray SASE FELs.  
 
TUPPH012 Compact X-ray Free-Electron-Laser Based on an Optical Undulator laser, undulator, electron, emittance 244
 
  • A. Bacci, C. Maroli, A. R. Rossi, L. Serafini
    INFN-Milano, Milano
  • V. Petrillo
    Universita' degli Studi di Milano, Milano
  • P. Tomassini
    INFN-Pisa, Pisa
  The interaction between a very high brightness electron beam and a relativistically intense optical laser pulse produces X rays via coherent Thomson back scattering with FEL collective amplification. The phenomenon is, however, very selective, so that the characteristics of both electron and laser beam must satisfy tight requirements in terms of beam current, emittance, energy spread and laser amplitude stability within the pulse. The three-dimensional equations governing the radiation phenomena have been studied in both linear and non linear regime and solved numerically for the particularly interesting values of wavelengths of 1 Ang, 1 nm and 12 nm. The performance of the collective Thomson source has been compared with that of an equivalent static undulator. A set of scaling laws ruling the phenomenon is also presented. The possibility of using an electron beam produced via LWFA in the bubble regime is investigated.  
 
TUPPH013 Production of Ultra-short Radiation Pulses in Frequency Doubler undulator, electron, laser, simulation 248
 
  • E. Schneidmiller, M. V. Yurkov, E. Saldin
    DESY, Hamburg
  Typically beam formation system of driver linac for SASE FEL produces electron beams with small local energy spread. This feature opens up extra possibilities for implementation of different FEL schemes. One of them is an effective frequency doubler*. It consists of an undulator tuned to the fundamental harmonic, dispersion section, and undulator tuned to the second harmonic. The first stage is a conventional soft X-ray SASE FEL. Its gain is controlled in such a way that the maximum energy modulation of the electron beam at the XFEL exit is about equal to the local energy spread, but still far away from saturation. When electron bunch passes through dispersion section this energy modulation leads to effective compression of the particles. Then bunched electron beam enters the 2nd harmonic undulator, and produces the radiation at the 2nd harmonic. Recently SASE FEL FLASH in Hamburg demonstrated unique mode of operation generating sub-10-fs radiation pulses**. In this paper we study an option of frequency doubler for FLASH operating in the femtosecond mode of operation.

* J. Feldhaus et al., NIM A 528 (2004) 471.** W. Ackermann et al., "Operation of a free electron laser from the extreme ultraviolet to the water window", Nature Photonics, in press.

 
 
TUPPH014 Generation of X-ray FEL Light Using Laser Wakefield Accelerated Electron Beams undulator, electron, laser, simulation 252
 
  • A. Rousse, K. Ta Phuoc
    LOA, Palaiseau
  • N. Vinokurov, O. A. Shevchenko
    BINP SB RAS, Novosibirsk
  We consider a new class of high gain FELs based on femtosecond electron bunches with extra high current density produced by Laser Wake Field Acceleration (LWFA). The FELs of this kind can be used for generation of high power femtosecond x-ray pulses. We present the results of simulations of FEL operation with some reasonable beam parameters which will be obtained in future. We focus our attention on the advantages which can be gained from the unique possibility of the use of femtosecond hundred-kiloamperes bunches, generated by LWFA. We also consider the impact of the relatively poor electron beam properties on FEL characteristics.  
 
TUPPH015 Diffraction Effects in the Coherent Transition Radiation Bunch Length Diagnostics electron, diagnostics, injection, photon 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.  
 
WEAAU01 Commissioning Results of the SLAC LCLS Gun laser, cathode, gun, emittance 276
 
  • R. Akre, J. Castro, P. Emma, J. C. Frisch, A. Gilevich, G. R. Hays, P. Hering, R. H. Iverson, P. Krejcik, C. Limborg-Deprey, H. Loos, A. Miahnahri, J. F. Schmerge, J. L. Turner, J. J. Welch, W. E. White, J. Wu, D. Dowell
    SLAC, Menlo Park, California
  The beam quality and operational requirements for the Linac Coherent Light Source (LCLS) currently being constructed at SLAC are exceptional, requiring the design of a new s-band RF photocathode gun for the electron source. Two guns (Gun1 and Gun2) have been fabricated and tested at high RF power. Gun1 was installed March 17, 2007 and began providing beams for the LCLS injector commissioning on April 5, 2007. Gun2 is reserved as a backup gun. The results and analysis of the gun’s performance in the LCLS injector will be presented.  
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WEAAU05 A Compact Electron Spectrometer for an LWFA electron, laser, undulator, plasma 294
 
  • R. A. Crowell, K.-J. Kim, A. H. Lumpkin
    ANL, Argonne, Illinois
  The use of a laser wakefield accelerator (LWFA) beam as a driver for a compact Free-Electron Laser (FEL) has been proposed recently. A project is underway at Argonnne National Laboratory (ANL) to operate an LWFA in the bubble regime and to use the quasi-monoenergetic electron beam as a driver for a 3-m long undulator for generation of sub-ps UV radiation. The Terawatt Ultrafast High Field Facility (TUHFF) in the Chemistry division provides the 20 TW peak power laser. Towards this goal, a compact electron spectrometer whose initial fields of 0.45 T provide energy coverage of 30-200 MeV has been selected to characterize the electron beams. The system is based on the Ecole Polytechnique design* used for their LWFA and incorporates the 5-cm long permanent magnet dipole, the LANEX scintillator screen located at the dispersive plane, a Roper Scientific 16-bit MCP-intensified CCD camera, and a Bergoz ICT for complementary charge measurements. Test results on the magnets, the 16-bit camera, and the ICT will be described, and initial electron beam data will be presented as available.

*Y. Glinnec et al., "Broadrange Single Shot Electron Spectrometer", Report dated July 6, 2006, Ecole Polytechnique.

 
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WEBAU03 Performance Tests of the Photon Monochromator for Self-seeding at FLASH photon, undulator, electron, 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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WEPPH003 Magnetic Measurements of the FLASH Infrared Undulator undulator, simulation, electron, power-supply 318
 
  • A. Chesnov, E. A. Matushevsky, D. Petrov, E. Syresin, N. A. Morozov
    JINR, Dubna, Moscow Region
  • O. Grimm, Y. Holler
    DESY, Hamburg
  • J. Rossbach
    Uni HH, Hamburg
  The FLASH free-electron laser at DESY, Hamburg, will be equipped with an infrared electromagnetic undulator during the current shut-down, providing radiation in the range 1-200 um. It will be used both for electron beam diagnostics purposes and as a powerful source synchronized to the VUV and soft X-ray pulses of the FEL. The undulator was constructed at the Joint Institute of Nuclear Research (JINR). This paper summarizes the extensive magnetic measurements that where performed both at JINR and DESY prior to installation of the undulator.  
 
WEPPH004 Numerical Calculations of the Radiation Emitted from the FLASH Infrared Undulator undulator, photon, 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, electron, photon 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 target, photon, 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.  
 
WEPPH021 Wide Band Seeding and Wavelength Compression laser, electron, undulator, cathode 378
 
  • T. Shintake
    RIKEN Spring-8 Harima, Hyogo
  Seeding with optical laser and compressing wavelength in chicane bunch compressor has been studied theoretically. Overlapping laser beam with in comming electron beam in free space, with oblique crossing, we may apply energy modulation on relativisitic electron beam. When we use forth harmonic YAG-laser, 255 nm, and compressing 20 times, we have 13 nm density modulation period. Passing in undulator, which resonates to the compressed wavelength, the super-radiation mode beam will be generated. In contrast with SASE-FEL, this type of radiation source does not require high quality beam, ease to operate and coherent.  
 
WEPPH028 Development of a Compact Cherenkov Free-Electron Laser Operating Terahertz Wave Range electron, vacuum, cathode, free-electron-laser 406
 
  • M. R. Asakawa, N. M. Miyabe
    Kansai University, Osaka
  • A. Ikeda, M. Kusaba, Y. Tsunawaki
    OSU, Daito, Osaka
  We designed a compact Cherenkov Free-Electron Laser(CFEL) device capable of delivering mW-level output power at frequencies of up to THz from 10GHz to 1 THz. CFEL has the advantage of generating higher frequencies at lower electron beam energy. Due to lower electron beam CFEL device is compact. Our CFEL device consists of a waveguide partially filled with two lined parallel dielectric slabs through which a relativistic electron beam propagates. We call this structure "double-slab". In our device, the electron beam is generated using the Spindt cathode. We used a super conducting magnet to compress and guide the electron beam along the dielectric slabs. Assuming a dielectric slab thickness of 0.65mm,length of 11cm and electron beam energy 50keV ,the output power generated by the device was numerically calculated to be mW-level at 46GHz. Currently , we are conducting the POP experiment at millimeter wave range.  
 
WEPPH029 Development of the Longitudinal Phase-Space Monitor for the L-band Electron Linac at ISIR, Osaka University electron, photon, 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

 
 
WEPPH032 Electron-Linac Based Femtosecond THz Radiation Source at PAL electron, linac, simulation, target 421
 
  • J. Choi, Y. G. Jung, C. Kim, H.-G. Kim, S.-C. Kim, I. S. Ko, W. W. Lee, B. R. Park, H. S. Suh, I. H. Yu, H.-S. Kang
    PAL, Pohang, Kyungbuk
  A 60-MeV electron linac for intense femto-second THz radiation is under construction at PAL, which is the beamline construction project to be completed by 2008. To get intense femto-second THz radiation up to 100 cm-1, the electron beam should be compressed down to below 100 fs. The linac will use an S-band photocathode RF-gun as an electron beam source, two S-band accelerating structures to accelerate the beam to 60 MeV, a chicane-type bunch compressor to get femto-second electron bunch, and an optical transition radiation (OTR) target as a radiator. The PARMELA code simulation result shows that the 0.2 nC beam can be compressed down to a few tens of femto-seconds, and even the higher charge of 0.5nC to about one hundred femto-seconds. Also, the linac will be able to provide a femto-second electron beam for electron pulse radiolysis and compton-scattering experiment for fs X-ray.  
 
WEPPH038 Low Power Consuming Hybrid Bending Magnet at the XFEL Beam Dump electron, permanent-magnet, dipole, laser 435
 
  • H. Danared, A. Hedqvist, F. Hellberg
    MSL, Stockholm
  • W. Decking, B. Krause, A. Petrov, J. Pflueger, M. Schmitz
    DESY, Hamburg
  At the end of the European XFEL the electron beam is separated from the photon beam and directed towards the beam dump with a bending magnet.* This dipole magnet is designed to bend 10-25 GeV electrons by 1 degree/m and is 10 meter long in total. By integrating permanent magnet material into a conventional electromagnet, this so called hybrid magnet with a 1 T bias magnetic field consumes no power at the nominal energy of the XFEL, 17.5 GeV. The magnetic field can be increased or decreased by magnet coils to obtain 1 degree/m deflection for all energies between 10 and 25 GeV. In case of component failures a passive safety system is needed to prevent the electron beam from reaching the experimental hall. The bias field of the permanent magnet not only saves power, but also works as a safety system for the XFEL. Here a proposal for such a hybrid configuration is presented together with its characteristics. The magnet is designed to use small amount of permanent magnet material and to consume less power than a conventional electromagnet.

*European XFEL Technical design report, edited by M. Altarelli et. al.,DESY 2006.

 
 
WEPPH047 Electro-Optic Spectral Decoding for Single-Shot Characterisation of the Coherent Transition Radiation Time Structure at FLASH laser, vacuum, electron, background 453
 
  • E.-A. Knabbe, B. Schmidt, P. Schmüser, B. Steffen, V. R. Arsov
    DESY, Hamburg
  Characterisation of the longitudinal profiles of ultrashort electron bunches is of primary importance for controlling the lasing process of SASE FEL. Non-destructive, single-shot techniques, are preferable. Presently the most promising ones are the Electro-Оptic (EO) laser diagnostics and the THz spectroscopy of coherent transition radiation (CTR). Whereas the former are applied directly in the electron beam line, the latter offer possibility to detect shorter temporal structures, but outside the tunnel. Therefore it is important to know the transfer function of the CTR beam line. We present a single-shot EO detection of temporal CTR profiles, generated from electron bunches, kicked to an off-axis screen at DESY's VUV-FEL (FLASH). The THz radiation is transported through a 20 m long line from the accelerator tunnel to an experimental station outside. The measurements are performed in air and in vacuum with 0.5 mm ZnTe and 0.175 mm GaP crystals in crossed-polarisers detection scheme. Pulses with less than 1 ps FWHM have been measured.  
 
WEPPH054 Coherent THz Light Source Using Very Short Electron Bunches from a Thermionic RF Gun gun, electron, undulator, simulation 476
 
  • K. Akiyama, H. Hama, F. Hinode, K. Kasamsook, M. Kawai, K. Nanbu, T. Tanaka, M. Yasuda, T. Muto
    Tohoku University, School of Scinece, Sendai
  To develop a narrowband coherent Terahertz (THz) light source, a project for producing very short electron bunch has been progressed at Laboratory of Nuclear Science, Tohoku University. Coherent synchrotron radiation is another promising source for generation of high-power THz light. Passing through a conventional undulator with a field period length of ~ 10 cm, the very short electron bunch at the energy around 15 MeV can produce coherent THz radiation. The electron beams of which the bunch length is less than 100 femto-second will be generated by a combined injector system of a thermionic RF gun and a bunch compressor. We have developed an independently-tunable-cells (ITC) RF gun consisted with two uncoupled cavities in order to manipulate the longitudinal phase space. It was found out that the ITC-RF gun is possibly quite suitable to produce such a very short bunch employing a magnetic bunch compressor. In theoretical investigation at the moment, a bunch length of less than 50 fs has been achieved in the numerical tracking simulation. Employing Lienard-Weichert potential, we have performed a 3-D simulation of the coherent THz radiation. The paper will describes the latest status of development of the ITC RF gun and tracking simulations for the bunch compressor as well. Characteristics of the coherent THz radiation resulted from the simulation will be also reported  
 
WEPPH055 Experimental Investigation of Smith-Purcell Radiation From Gratings of Different Profile target, electron, vacuum, microtron 480
 
  • V. A. Cha, D. V. Karlovets, Yu. A. Popov, A. Potylitsyn, L. G. Sukhikh, G. A. Naumenko
    TPU, Tomsk
  • B. N. Kalinin, G. A. Saruev
    INPR, Tomsk
  Smith-Purcell radiation (SPR) is widely considered as the spontaneous mechanism for FEL. There are a few theoretical SPR models, which predict large difference between radiation intensity from relativistic electrons for grating with different profile. To choose the most effective grating we carried out the absolute coherent SPR intensity measurements on the 6.2 MeV electron beam. The coherent SPR spectra and angular distributions were investigated. Gratings with lamellar, triangular and so-called "flat" gratings were studied. It was shown the grating consisted of the conductive strips is more preferable target for SPR generation.  
 
WEPPH056 Gain and Coherence Enhancement for SASE FEL using Laser pre-modulated Electrons electron, bunching, acceleration, wiggler 484
 
  • H.-L. Chang, C. H. Chen, W. C. Cheng, A.-C. Chiang, Y.-C. Huang
    NTHU, Hsinchu
  • W. K. Lau, G.-H. Luo
    NSRRC, Hsinchu
  SASE FEL built up from shot noises exhibits noisy temporal and spectral structures at the output. We propose to use a laser to modulate the electron density at low beam energy and improve the emission characteristics of the SASE FEL at high beam energy. In this scheme, a laser beat wave is incident on the photocathode of an electron gun to generate periodically bunched electrons at the beat-wave frequency. The density modulated electrons can generate superradiance at the harmonics of the beat frequency in all types of single-pass FEL, including Smith-Purcell FEL, Cherenkov FEL, and undulator FEL. The bunching frequency can be further increased by a factor of 10-100 by compressing a chirped, density-modulated, low-energy electron pulse in an alpha magnet, which is subsequently accelerated to high energy for SASE FEL. Computer simulation using particle-in-cell codes, including ASTRA, ELEGANT, and GINGER, shows significant improvements on the gain and coherence of SASE FEL. We will report our detailed study and experimental progress in the conference.  
 
WEPPH058 Modeling a RF Linac Based Short Pulse Waveguide FEL electron, simulation, interaction-region, bunching 487
 
  • Y. Pinhasi, Yu. Lurie
    CJS, Ariel
  • M. Tecimer
    NHMFL, Tallahassee, Florida
  We discuss modeling a highly slippage dominated short pulse, long wavelength rf linac based THz FEL in a waveguide cavity.  
 
THAAU01 Experience and Plans of the JLAB FEL Facility as a User Facility laser, free-electron-laser, electron, linac 491
 
  • M. D. Shinn
    Jefferson Lab, Newport News, Virginia
  Jefferson Lab’s IR Upgrade FEL building was planned from the beginning to be a user facility, and includes an associated 600 sq. m area containing seven laboratories. The high average power capability (multikilowatt-level) in the near-infrared (1-3 microns), and many hundreds of watts at longer wavelengths, along with an ultrafast (~ 1 ps) high PRF (10’s MHz) temporal structure makes this laser a unique source for both applied and basic research. In addition to the FEL, we have a dedicated laboratory capable of delivering high power (many tens of watts) of broadband THz light. After commissioning the IR Upgrade, we once again began delivering beam to users in 2005. In this presentation, I will give an overview of the FEL facility and its current performance, lessons learned over the last two years, and a synopsis of current and future experiments.  
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THAAU03 Experimental Study of Volume Free Electron Laser Using a "Grid" Photonic Crystal with Variable Period electron, free-electron-laser, laser, feedback 496
 
  • V. G. Baryshevsky, N. A. Belous, V. A. Evdokimov, A. Gurinovich, A. S. Lobko, A. V. Oskin, P. F. Safronov, P. V. Molchanov
    Belarussian State University, Scientific Research Institute of Nuclear Problems, Minsk
  Electrodynamical properties of a crystal-like artificial periodic structure (photonic crystal) formed by a periodically strained metallic threads were studied both theoretically and experimentally*,**. In the present paper operation of Volume Free Electron Laser using a "grid" photonic crystal with variable period is experimentally studied. Dependence of the generation threshold on photonic crystal length is investigated along with the frequency characteristics of generated radiation.

* Baryshevsky V. G. et al. NIM section B. Vol252 (2006) P.92-101 ** Baryshevsky V. G. et al. Proc. of the 28th FEL Conference PP.331-338

 
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THBAU01 Research Highlights from FLASH free-electron-laser, laser, electron, vacuum 499
 
  • J. Feldhaus, R. Treusch
    DESY, Hamburg
  The Free electron LASer in Hamburg (FLASH) has started regular user operation in summer 2005, providing XUV radiation pulses with pulse energies in the 10 - 100 μJ range and pulse durations of 10 - 50 fs. The science programme at FLASH covers a broad range of novel applications including fundamental studies on atoms, ions, molecules and clusters, creation and characterisation of warm dense matter, diffraction imaging of nanoparticles, spectroscopy of bulk solids and surfaces, investigation of surface reactions and spin dynamics, and the development of advanced photon diagnostics and experimental techniques. So far, 16 science projects have been pursued involving approximately 200 scientists from 11 countries. Some of the research highlights will be presented.  
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THBAU04 Millimeter Waves Sensing Behind Walls - Feasibility Study with FEL Radiation polarization, controls, coupling, survey 501
 
  • M. Einat, M. Kanter, B. Litvak, A. Yahalom, B. Yu. Kapilevich
    CJS, Ariel
  • A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
  The existing through-wall imaging (TWI) systems operate in 1 – 10 GHz, basically, in order to reduce an attenuation caused by building material. However, the spatial resolution is drastically degraded when the operating frequency is relatively low. On the other hand, a majority of building materials demonstrate increased losses as the frequency increases. As a result, higher RF power from the source is required. The Israeli mm-wave FEL provides unique opportunity to solve the above TWI problem permitting to deliver output power 100-1000W at 85-105 GHz. Design of TWI system operating on mm-waves needs comprehensive study of constitutive parameters of different building materials. This paper describes systematic measurements of effective attenuation constant of typical building materials such as concrete bricks, wood, tiles, sand, gypsum, etc. on mm-waves using powerful FEL radiation. Since the Rayleigh criterion for surface roughness cannot be satisfied for some of measured materials, scattering and depolarization effects lead to increasing measured attenuation in comparison with bulky material. Additional experiments were performed to estimate a contribution of these effects into the measured attenuation.  
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FRAAU01 Source of Radiation on ARC-EN-CIEL Proposal undulator, electron, laser, cryogenics 505
 
  • O. V. Chubar, M. Labat, G. Lambert, O. Marcouillé, M.-E. Couprie
    SOLEIL, Gif-sur-Yvette
  The ARC-EN-CIEL project proposes a panoply of light sources for the scientific community. The phase 1 (220 MeV superconducting Linac, down to 30 nm) and phase 2 (1 GeV, down to 1 nm) choice to provide 30-100 fs HGHG radiation and their Non Linear Harmonics seeded with the High order Harmonics generated in Gas is further confirmed with the suceesfull demonstration experiment of such a scheme at SPA. New optimizations of the undulatros lead to in vacuum undulators of period 26 mm for the modulator, and APPLE-type radiators of period 30 mm, close to the standard SOLEIL insertion devices. New calculations have been carried out using PERSEO TD and GENESIS coupled to SRW for further propagation of the FEL wavefront to the beamlines. In addition, THz radiation from the magnets of the compression chicanes will be provided and has been calculated using SRW. ARC-EN-CIEL Phase 3 incorporates ERL loops, for hard X ray spontaneous emission above 10 keV from short period in vacuum undulators (20 mm period typically), one Soft-X ray spontaneous emission beamline using an variable polarisation undulator, and an FEL oscillator in the 10-60 nm spectral range. Recent calculations and optimisations will be presented.  
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FRAAU03 Compact Ring FEL as a Source of High Power Infrared Radiation undulator, electron, bunching, simulation 517
 
  • A. N. Matveenko, N. Vinokurov, O. A. Shevchenko
    BINP SB RAS, Novosibirsk
  Ring FELs* were proposed mainly to improve the quality of radiation of x-ray FELs. Their main advantage is the absence of mirrors. It appears that this advantage is also useful for high power FELs. Another reason to build infrared ring FEL is the proof-of-principle for shorter wavelength FELs. Therefore we considered the scheme of infrared ring FEL which requires ERL with beam energy 50 MeV. Using extensive simulations we developed requirements for electron beam parameters and magnetic system of ring FEL. In spite of rather compact design such FEL may provide more than 10 kW average power.

* N. A. Vinokurov, O. A. Shevchenko, NIM A528 (2004) 491-496

 
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