Keyword: bunching
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MOPSO09 Investigation of a 2-Colour Undulator FEL Using Puffin undulator, FEL, electron, radiation 47
 
  • L.T. Campbell, B.W.J. MᶜNeil
    USTRAT/SUPA, Glasgow, United Kingdom
  • S. Reiche
    PSI, Villigen PSI, Switzerland
 
  The unaveraged FEL code Puffin* is used to investigate a 2 color FEL. In the scheme under investigation, undulator modules are tuned alternately to generate 2 frequencies quasi-simultaneously, which should result in greater stability than generating them consecutively. The advantage of using Puffin is that it provides the capability of modelling a broad bandwidth spectrum. For example, radiation at 1nm and 2.4nm is difficult to model simultaneously in standard averaged FEL codes. An unaveraged code like Puffin is able to model 2 (or more) wavelengths with a much wider spacing.
* LT Campbell and BWJ McNeil, Phys. Plasmas 19, 093119 (2012)
 
 
MOPSO49 Numerical Accuracy When Solving the FEL Equations FEL, simulation, electron, undulator 82
 
  • R.R. Lindberg
    ANL, Argonne, USA
 
  Funding: U.S. Dept. of Energy Office of Sciences under Contract No. DE-AC02-06CH11357
The usual method of numerically solving the FEL equations involves dividing both the e-beam and radiation field into "slices" that are loaded one at a time into memory. This scheme is only first order accurate in the discretization of the ponderomotive phase because having only one slice in memory effectively results in a first order interpolation of the field-particle coupling. While experience has shown that FEL simulations work quite well, the first order accuracy opens the door to two possible ways of speeding up simulation time. First, one can consider higher order algorithms; unfortunately, these methods appear to require all the particle and field data in memory at the same time, and therefore will typically only be important for either small (probably 1D) problems or for parallel simulations run on many processors. Second, one may consistently solving the equations to some low order using faster, simpler algorithms (replacing, for example, the usual RK4). The latter is particularly attractive, although in practice it may be desirable to retain higher order methods when integrating along z. We investigate some of the possibilities.
 
 
TUPSO32 Project of the Short Pulse Facility at KAERI electron, quadrupole, gun, kicker 287
 
  • N. Vinokurov, S.V. Miginsky
    BINP SB RAS, Novosibirsk, Russia
  • S. Bae, B.A. Gudkov, B. Han, K.H. Jang, Y.U. Jeong, H.W. Kim, K. Lee, S.V. Miginsky, J. Mun, S. H. Park, G.I. Shim, N. Vinokurov
    KAERI, Daejon, Republic of Korea
  • N. Vinokurov
    NSU, Novosibirsk, Russia
 
  Funding: This work is supported by the WCI Program of the National Research Foundation of Korea funded by the Ministry of Education, Science, and Technology of Korea (NRF Grant No. WCI 2011-001).
The low-energy electron accelerator with subpicosecond electron bunches is under construction at Korea Atomic Energy Research Institute (KAERI). It will serve as the user facility for high-energy ultrafast electron difraction and synchronized high-power terahertz pulse and short x-ray pulse generation. The accelerator consists of RF gun with photocathode and 20-MeV linac. The bunching of accelerated beam is achieved in the ninety-degree achromatic bend. After that fast kicker deflects some of bunches to the target for x-ray generation, other bunches come to terahertz radiator (undulator or multifoil). Bunches from the RF gun are also planned to use for ultrafast electron difraction. Some detailes of the design, current status of the project and future plans are described.
 
 
WEOBNO03 Intense Emission of Smith-Purcell Radiation at the Fundamental Frequency from a Grating Equipped with Sidewalls radiation, simulation, electron, solenoid 477
 
  • J.T. Donohue
    CENBG, Gradignan, France
  • J. Gardelle, P. Modin
    CEA, LE BARP cedex, France
 
  The two-dimensional theory of the Smith-Purcell free-electron laser predicts that coherent Smith-Purcell radiation can occur only at harmonics of the frequency of the evanescent wave that is resonant with the beam. Particle-in-cell simulations have shown that in a three-dimensional context, where the lamellar grating has sidewalls, coherent Smith-Purcell radiation can be copiously emitted at the fundamental frequency, for a well-defined range of beam energy. An experiment at microwave frequencies has confirmed this prediction . The power output is considerably greater than for the previously observed emission at the second harmonic, in agreement with three-dimensional simulations . The dependence of frequency on beam energy and emission angle is in good agreement with three-dimensional theory and simulations. Provided that a reduction in scale can be achieved, a path is open to coherent Smith-Purcell radiation at Terahertz frequencies.
(1) J. Gardelle, P. Modin and J.T. Donohue, Appl. Phys. Lett. 100, 131103 (2012).
(2) J. T. Donohue and J. Gardelle, Appl. Phys. Lett. 99, 161112 (2011).
 
slides icon Slides WEOBNO03 [11.891 MB]  
 
WEPSO14 Towards High Frequency Operation with a Multi-Grating Smith-Purcell FEL simulation, radiation, electron, FEL 525
 
  • J.T. Donohue
    CENBG, Gradignan, France
  • J. Gardelle
    CEA, LE BARP cedex, France
 
  Three-dimensional simulations and experiments have shown that, for a grating equipped with sidewalls, copious emission of coherent Smith-Purcell (SP) radiation at the fundamental frequency of the evanescent surface wave is possible 1, 2. Since the underlying theory is scale invariant, the wavelength emitted is reduced in proportion to a uniform rescaling of the grating. In order to increase our 5 GHz to 100 GHz , the grating surface would be reduced by a factor of 400, which would lead to greatly reduced power. In addition, the required beam might be hard to generate. To avoid this, we propose to use several gratings in parallel with no overall reduction in the total width and the same beam as in our microwave experiment. For this scheme to succeed, it is essential that the bunching in the different gratings be coherent. . Simulations suggest that this occurs for as much as a ten-fold scale reduction. To test this idea, an experiment is using several gratings is being performed.
1. J. T. Donohue and J. Gardelle, Appl. Phys. Lett. 99, 161112 (2011).
2. J. Gardelle, P. Modin and J.T. Donohue, Appl. Phys. Lett. 100, 131103 (2012),.
 
 
WEPSO19 A Full Beam 1D Simulation Code for Modeling Hybrid HGHG/EEHG Seeding Schemes for Evaluating the Dependence of Bunching Factor Bandwidth on Multiple Parameters laser, simulation, FEL, electron 533
 
  • C.M. Fortgang, B.E. Carlsten, Q.R. Marksteiner, N.A. Yampolsky
    LANL, Los Alamos, New Mexico, USA
 
  Multiple seeding schemes are available for design of narrow-band, short-wavelength FELs. Analysis of such schemes often focus on the amplitude of the final bunching factor b, and how far it is above shot noise. Only under ideal conditions is the bandwidth of b FT limited. We have developed a 1D simulation tool that models complex hybrid seeding schemes using macro properties of the entire beam bunch to assess effects on both the amplitude and bandwidth of b. In particular the effects on bunching factor from using non-ideal beam driven radiators for downstream modulators, energy slew and curvature, and energy spread are investigated with the 1D tool.  
 
WEPSO41 Feasibility Studies for Echo-enabled Harmonic Generation on CLARA laser, electron, FEL, radiation 588
 
  • I.P.S. Martin, R. Bartolini
    Diamond, Oxfordshire, United Kingdom
  • R. Bartolini
    JAI, Oxford, United Kingdom
  • N. Thompson
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
 
  The Compact Linear Accelerator for Research and Applications (CLARA) is a proposed single-pass FEL test facility, designed to facilitate experimental studies of advanced FEL techniques applicable to the next generation of light source facilities. One such scheme under consideration is Echo-Enabled Harmonic Generation (EEHG). In this paper we explore the suitability of CLARA for carrying out studies of this scheme, combining analytical and numerical calculations to determine likely hardware operating ranges, parameters tolerances and estimated FEL performance. A possible adaptation to convert EEHG into a short-pulse scheme is also considered.  
 
WEPSO60 A Method for Obtaining High Degree of Circular Polarization at X-ray FELs undulator, FEL, radiation, polarization 651
 
  • E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg, Germany
 
  Baseline design of many X-ray FEL undulators assumes a planar configuration which results in a linear polarization of SASE FEL radiation. However, many users experiments would profit from using a circularly polarized radiation. As a cheap upgrade one can consider an installation of a helical afterburner, but then one should have an efficient method to suppress linearly polarized background from the main undulator. In this paper we consider a new method for such a suppression which is illustrated with the parameters of the soft X-ray undulator SASE3 of the European X-ray FEL.  
 
WEPSO68 Effect of Coulomb Collisions on Echo-enabled Harmonic Generation undulator, laser, scattering, FEL 684
 
  • G.V. Stupakov
    SLAC, Menlo Park, California, USA
 
  Echo Enabled Harmonic Generation (EEHG) for FEL seeding is sensitive to the intrabeam scattering (IBS) effect. The reason for this is that in the process of generation high-harmonic density modulation in the beam the phase space evolves through a stage with narrow energy bands, which are characterized by the energy spread many times smaller than the beam energy spread. Energy diffusion caused by IBS tends to smear our these bands leading to diminished bunching factors at high harmonics. In the previous work [1] IBS in EEHG was studied in a simple model of a drift. This work extends the analysis of [1] to realistic lattices, and is applied to some of the existing practical designs of EEHG seeding.
[1] G. Stupakov, Effect of Coulomb Collisions on Echo-Enabled Harmonic Generation (EEHG), in Proceedings of the 2011 FEL Conference, Shanghai, China, 2011.
 
 
THIANO01 Double Stage Seeded FEL with Fresh Bunch Injection Technique at FERMI FEL, electron, undulator, laser 723
 
  • E. Allaria, D. Castronovo, P. Cinquegrana, G. D'Auria, M. Dal Forno, M.B. Danailov, G. De Ninno, A.A. Demidovich, S. Di Mitri, B. Diviacco, W.M. Fawley, M. Ferianis, E. Ferrari, L. Fröhlich, G. Gaio, L. Giannessi, R. Ivanov, B. Mahieu, N. Mahne, I. Nikolov, F. Parmigiani, G. Penco, L. Raimondi, C. Serpico, P. Sigalotti, C. Spezzani, M. Svandrlik, C. Svetina, M. Trovò, M. Veronese, D. Zangrando, M. Zangrando
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • M. Dal Forno
    DEEI, Trieste, Italy
  • G. De Ninno, D. Gauthier
    University of Nova Gorica, Nova Gorica, Slovenia
  • E. Ferrari, F. Parmigiani
    Università degli Studi di Trieste, Trieste, Italy
  • L. Giannessi
    ENEA C.R. Frascati, Frascati (Roma), Italy
  • B. Mahieu
    CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette, France
  • M. Zangrando
    IOM-CNR, Trieste, Italy
 
  Seeding a FEL with an external coherent source has been extensively studied in the last decades as it can provide a way to enhance the radiation brightness and stability, with respect to that available from SASE. An efficient scheme for seed a VUV-soft x ray FEL uses, a powerful, long wavelength external laser to induce on the electron beam coherent bunching at the harmonics of the laser wavelength. When the bunching is further amplified by FEL interaction in the radiator, the scheme is called high gain harmonic generation (HGHG). The need of high power seed sources and of small energy spread are at the main limits for a direct extension of the HGHG scheme to short wavelengths. The fresh bunch scheme was proposed as a way to overcome these limitations; the scheme foresees the FEL radiation produced by one HGHG stage as an external seed in a second HGHG stage. We report the latest results obtained at FERMI that uses the two-stage HGHG scheme for generation of FEL pulses in the soft x-ray. A characterization of the FEL performance in terms of power, bandwidth and stability is reported. Starting from the FERMI results we will discuss extension of the scheme toward shorter wavelengths.  
slides icon Slides THIANO01 [9.355 MB]