X-ray FELs

Paper Title Page
TUBAU01 FLASH Upgraded - Preparing for the European XFEL 211
 
  • H. Schlarb
    DESY, Hamburg
  
  Since 2005, the Free electron LASer in Hamburg, FLASH, has delivered a high brilliance photon beam to users in a wavelength range between 13 nm and 40 nm. To meet the user demands for 4 nm wavelengths, sub-50fs timing stability, and better pointing stability, the accelerator will be continuously upgraded within the next few years. The upgrade to an energy of 1.3 GeV, the transverse and longitudinal intra-train feedback system, and a 3rd harmonic cavity at 3.9 GHz are key prototype tests for the European XFEL. FLASH also serves as a test bench for an entirely new approach to accelerator facility synchronisation involving optical pulses distributed in length stabilized fibres. Increased stabilization of the electron beam peak current and its arrival time should provide the possibility to reliably seed the electron bunch with higher laser harmonics. In this paper, an overview of the planned upgrade for FLASH will be presented with respect to its usefulness for the European XFEL. The status of the XFEL project will also be briefly summarized.  
slides icon Slides  
TUBAU02 Status of SCSS & X-ray FEL Project in Japan 216
 
  • T. Shintake
    RIKEN Spring-8 Harima, Hyogo
  
  Staus of SCSS project after the first lasing last year will be reported. The X-ray FEL, which uses 8 GeV C-band, is under construction, whose status will be reported.  
slides icon Slides  
TUBAU03 STARS – an FEL to Demonstrate Cascaded HGHG 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.  
slides icon Slides  
TUBAU04 Towards a Low Emittance X-ray FEL at PSI 224
 
  • A. Adelmann, A. Anghel, R. J. Bakker, M. Dehler, R. Ganter, C. Gough, S. Ivkovic, F. Jenni, C. Kraus, F. Le Pimpec, S. C. Leemann, K. B. Li, P. Ming, B. S.C. Oswald, M. Paraliev, M. Pedrozzi, J.-Y. Raguin, L. Rivkin, T. Schietinger, V. Schlott, L. Schulz, A. Streun, F. Stulle, D. Vermeulen, F. Q. Wei, A. F. Wrulich, A. Oppelt
    PSI, Villigen
  
  The Paul Scherrer Institute (PSI) in Switzerland aims at building a compact and cost-effective X-ray FEL facility for the wavelength range 0.1 - 10 nm. Based on the generation of very low emittance beams, it consists of a low-emittance electron gun (LEG) followed by high-gradient acceleration, and advanced accelerator technology for preserving the initial low emittance during further acceleration and bunch compression. In order to demonstrate the feasibility of the concept and the emittance preservation, a 250 MeV test facility will be built. This machine has been designed to be used as injector for the X-ray FEL at a later date. The accelerator design of the 250 MeV linac will be presented in the paper together with the status of the LEG and high gradient acceleration.  
slides icon Slides  
TUBAU05 One Angstrom FEL Oscillator using ERL Beams
 
  • S. Reiche
    UCLA, Los Angeles, California
  • s. Shvydko, K.-J. Kim
    ANL, Argonne, Illinois
  
  An oscillator X-ray FEL for 1-Å is feasible with ERLs. We have studied a 1-Å FEL using electron beams extrapolated from the "high coherence" mode of the proposed Cornell ERL, using the electron energy = 7 GeV, the undulator parameter K=1.4, and period length=1.88 cm. With a 30-m undulator the small signal gain is about 20%, sufficient for "lasing" if one round trip reflectivity is greater than 90%. The gain will be higher for a higher bunch current achievable with further optimization of the gun. The peak power of the circulating optical beam at saturation is about 20 MW and its bandwidth 10-6. The increased energy spread of the electron beam due to the FEL interaction does not pose problem for the recirculation optics. Two possible schemes for optical cavity are possible. One is a cavity of regular triangle with three crystal reflectors. Another is to use a cavity consisting of two Bragg reflectors at near-backscattering configuration and a grazing incidence mirror in between. Parasitic diffraction in backscattering of a cubic crystal provides a convenient out-coupling mechanism. The fraction of parasitic diffraction can be set to a small, desired value while keeping the high reflectivity in the main diffraction by suitably orienting the crystals away from the exact backscattering geometry. The mirror serves also the important function of focusing the x-ray beam.  
slides icon Slides  
TUPPH009 SASE FEL Simulations for the European XFEL with the Codes Simplex and Genesis
 
  • W. Decking
    DESY, Hamburg
  • V. M. Tsakanov, V. G. Khachatryan
    CANDLE, Yerevan
  
  Numerical simulation studies of the FEL process have been carried out for the European XFEL project. The impact of the undulator lattice quadrupole magnets misalignments on the FEL performance has been investigated using the FEL simulation codes SIMPLEX and GENESIS. The choice of the optimal beta function for the undulator has been investigated as well. The problem of the reduction of the number of quadrupole magnets in the undulator lattice is considered.  
TUPPH010 Gamma Laser on the Base of Diffraction Scattering an Intense 4.3 GeV Electron Beam on a Crystal
 
  • A. O. Aganyants
    YerPhI, Yerevan
  
  Difficulties of creating gamma lasers are generally known. Difficulties of creating gamma lasers are generally known. However such gamma laser as a phenomenon of nature has unexpectedly manifested in our experiments on the Yerevan synchrotron. A nonlinear increase in gamma ray emission depending on the electron beam intensity had been shown in the foregoing. New striking results will be presented, among them: swelling a gamma beam profile or growth of the spatial coherent length of electron-photon interaction in crystal and tending produced photons to coalescence at their interaction with substance. New data give evidence: gamma laser takes place when electron beam touches the crystal.  
TUPPH011 Analytical Studies of Transverse Coherence Properties of X-ray FELs 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 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 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 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 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.  
TUPPH018 Development of Ultra-short Pulse, Single Coherent Spike for SASE X-ray FELs
 
  • P. Musumeci, C. Pellegrini, S. Reiche, J. B. Rosenzweig
    UCLA, Los Angeles, California
  
  There is a large interest in the production of high power, ultra-short, one femtoseconds or less, coherent X-ray pulses, for atomic physics and other applications. However the present design of X-ray SASE FELs leads to an X-ray pulse about 100 times longer. Several methods to reduce the bunch length to the 10-1 fs region have been proposed. These methods are based on electron bunch manipulation to cut the lasing part of the bunch to a fraction of the total length, thus reducing the X-ray pulse length. We are considering here a different method, using ultra-short, very low charge electron bunches, with a length of the order or shorter than the FEL cooperation length. In this case the X-ray pulse length after amplification in the undulator is a few times the electron bunch length. Our simulations show that in an LCLS-like case we can obtain coherent, Fourier transform limited, X-ray pulses, consisting of a single spike, with a FWHM of about 0.1 um, corresponding to about 300 as, a peak power of about 5 GW, and an intensity of about 10 uJ.  
TUPPH019 Simulations for the LCLS Injector 260
 
  • Y. T. Ding, D. Dowell, P. Emma, J. C. Frisch, A. Gilevich, G. R. Hays, P. Hering, Z. Huang, R. H. Iverson, P. Krejcik, H. Loos, A. Miahnahri, J. F. Schmerge, J. L. Turner, W. E. White, J. Wu, C. Limborg-Deprey
    SLAC, Menlo Park, California
  
  The commissioning of the LCLS Injector has started this year. The electron beam quality for producing high power SASE X-rays is very challenging to reach. In this paper, we will describe comparisons between simulations made with multi-particle tracking code and electron beam measurements performed on the LCLS injector.  
TUPPH020 Quiet Start Method in small signal HGHG FEL Simulation 264
 
  • Y. Hao, Y. Hao
    IUCF, Bloomington, Indiana
  • L.-H. Yu
    BNL, Upton, Long Island, New York
  
  Quiet start scheme is broadly utilized in Self Amplified Spontaneous Radiation (SASE)FEL simulations, which is proven to be correct and efficient. Nevertheless, due to the energy modulation and dispersion section, the High Gain Harmonic Generation (HGHG) FEL simulation will not be improved by the traditional quiet start method. A new approach is presented to largely decrease the number of macro-partilces per slice that can be implemented in both time-independent and time-dependent simulation, accordingly expedites the high order harmonic cascade simulation or other small signal HGHG cases.