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bunching

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MOPPH015 Limit for Harmonic Conversion in a Single Cascade of Coherent Harmonic Generation electron, radiation, 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.

 
 
MOPPH022 A Description of Guided FEL Radiation Using Dielectric Waveguide Eigenmodes radiation, undulator, coupling, electron 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.  
 
TUAAU02 Electron Outcoupling Scheme for the Novosibirsk FEL undulator, electron, radiation, 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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TUPPH020 Quiet Start Method in small signal HGHG FEL Simulation simulation, electron, laser, resonance 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.  
 
WEPPH041 7th Harmonic Buncher Experiment at Neptune Laboratory laser, undulator, electron, coupling 441
 
  • R. Tikhoplav, S. Tochitsky, P. Musumeci
    UCLA, Los Angeles, California
  Since typically FEL undulator magnets have period length in the cm range, and the normalized magnetic field strength K is maintained close to unity to guarantee a good coupling, a very high energy electron beam is needed to access the far UV and x-ray region of the electromagnetic spectrum. One way to reduce the beam energy necessary for short wavelength light sources consists of exploiting the FEL harmonic interaction. An experiment aimed at demonstrating the efficiency of harmonically coupled schemes is proposed for the Neptune Laboratory at UCLA. We plan to inject the 12.4 MeV beam from the split photoinjector in an already available undulator with period = 3.3 cm and K = 1.8. The FEL resonant wavelength with these parameters is 74.2 um. A copropagating high power 10.6 um CO2 laser bunches the beam via 7th harmonic FEL/IFEL interaction. Preliminary calculations show that even though the interaction is weakened by the high harmonic number, it is required to use only 5 -10 MW of power in order to induce full bunching on the beam in the 10 period long undulator.  
 
WEPPH056 Gain and Coherence Enhancement for SASE FEL using Laser pre-modulated Electrons electron, acceleration, wiggler, radiation 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 radiation, electron, simulation, interaction-region 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.  
 
FRAAU03 Compact Ring FEL as a Source of High Power Infrared Radiation radiation, undulator, electron, 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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