Author: Gover, A.
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MOP078 Sub-Radiance and Enhanced-Radiance of Undulator Radiation from a Correlated Electron Beam 221
 
  • R. Ianconescu
    Shenkar College of Engineering and Design, Ramat Gan, Israel
  • A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
  • E. Hemsing, A. Marinelli
    SLAC, Menlo Park, California, USA
  • A. Nause
    UCLA, Los Angeles, USA
 
  Funding: We acknowledge the United States - Israel Binational Science Foundation (BSF)
The radiant intensity of Synchrotron Undulator Radiation (UR) depends on the current noise spectrum of the electron beam injected into the wiggler. The current noise spectrum and intensity can be controlled (suppressed or enhanced relative to the shot-noise level) by the effect of collective longitudinal space charge interaction in a drift and dispersion sections[1]. This new control lever is of significant interest for possible control of SASE in FEL, since UR is the incoherent seed of SASE. Thus, control of spontaneous UR is a way to enhance the coherence of seeded FEL [2], or alternatively, obtain enhanced radiation from a cascade noise-amplified electron beam [3]. The dependence of UR emission on the current noise is primarily a result of the longitudinal correlation of the e-beam distribution due to the longitudinal space charge effect. However, at short wavelengths, 3-D effects of transverse correlation and effects of emittance disrupts the proportionality relation between the UR intensity and e-beam current noise. We present analysis and simulation of UR subradiance/superradiance under various ranges of beam parameters, and compare to recent experimental observations [1].
[1] D. Ratner et al., PRST - ACCELERATORS AND BEAMS 18, 050703 (2015)
[2] E. Allaria et al., Nat. Photonics 7, 913 (2013)
[3] A. Marinelli et al., Phys. Rev. Lett. 110, 264802 (27 June 2013)
 
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TUP069 THz Based Phase-Space Manipulation in a Guided IFEL 519
 
  • E.J. Curry, S. Fabbri, P. Musumeci
    UCLA, Los Angeles, California, USA
  • A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
 
  Funding: This work has been supported by DOE grant DE-FG02-92ER40693, and NSF grant PHY-1415583.
We propose a guided IFEL interaction driven by a broadband THz source to compress a relativistic electron bunch and synchronize it with an external laser pulse. A high field single-cycle THz pulse is group velocity-matched to the electron bunch inside a waveguide, allowing for a sustained interaction in a magnetic undulator. The THz pulse is generated via optical rectification from the external laser source, with peak field of up to 4.6 MV/m. We present measurements of the THz waveform before and after a parallel plate waveguide with varying aperture size and estimate the group velocity. We also present results from a preliminary 1-D multi-frequency simulation code we are developing to model the guided broadband IFEL interaction. Given a 6 MeV, 100 fs electron bunch with an initial 10-3 energy spread, as can be readily produced at the UCLA Pegasus laboratory, the simulations predict a phase space rotation of the bunch distribution that will reduce the initial timing jitter and compress the electron bunch by nearly an order of magnitude.
 
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WEB04 Saturation Dynamics, Fine Spectrum, and Chirp Control in a CW FEL Oscillator 580
 
  • H. S. Marks, A. Gover, H. Kleinman
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
  • D. Borodin, A. Damti, A. Friedman, Y. Vashdi
    Ariel University, Ariel, Israel
  • M. Einat, M. Kanter, Y. Lasser, Yu. Lurie, A. Yahalom
    Ariel University Center of Samaria, Faculty of Engineering, Ariel, Israel
 
  As in conventional laser physics, the saturation dynamics of a long-pulse Electrostatic Accelerator FEL (EA-FEL) oscillator consists of oscillations build-up, resonator modes competition, and establishment of narrow linewidth single mode lasing. In EA-FEL the gain curve drifts to lower frequencies during the long laser pulse due to inevitable droop in the acceleration voltage. This post-saturation drift renders fine chirp of the single mode laser frequency due to the oscillator frequency pulling effect. We have integrated a voltage-ramping element into the electrostatic accelerator terminal that makes it possible to control the acceleration voltage throughout the lasing pulse. This allows us to keep the voltage constant throughout the e-beam pulse, and so increase the single mode lasing time, avoiding mode-hopping during the pulse due to the drift of the gain curve. Furthermore, by adjusting the voltage ramp rate and polarity we obtained controllable positive/negative laser frequency chirp that can be used in a single pulse sweep for fine spectral line (10-6) gas-spectroscopy. The study was conducted on the Israeli EA-FEL that operates at tunable frequencies between 95-110 GHz.  
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WEC04
Subradiant Spontaneous Undulator Emission through Collective Suppression of Shot Noise  
 
  • D.F. Ratner, E. Hemsing, A. Marinelli
    SLAC, Menlo Park, California, USA
  • A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
  • A. Nause
    UCLA, Los Angeles, USA
 
  The phenomenon of Dicke's subradiance, in which the collective properties of a system suppress radiation, has received broad interest in atomic physics, but can also be applied to relativistic electron beams. The resulting "quiet" beam generates less spontaneous undulator radiation than emitted even by a random shot noise beam. Quiet beams could have diverse accelerator applications, including lowering power requirements for seeded FELs. Here we present recent experimental observations at the Next Linear Collider Test Accelerator and discuss prospects for pushing the phenomenon to X-ray wavelengths.  
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WEP085 Conceptual Theory of Spontaneous and Taper-Enhanced Superradiance and Stimulated Superradiance 746
 
  • A. Gover, R. Ianconescu
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
  • C. Emma, P. Musumeci
    UCLA, Los Angeles, USA
  • A. Friedman
    Ariel University, Ariel, Israel
 
  Funding: We acknowledge partial support by the U.S. Israel Binational Science Foundation (BSF)Jerusalem, Israel
In the context of radiation emission from an electron beam Dicke's superradiance (SR) is the enhanced radiation emission from a pre-bunched beam. Stimulated Superradiance (ST-SR) is the further enhanced emission of the bunched beam in the presence of a phase-matched radiation wave. These processes were analyzed for Undulator radiation in the framework of radiation field mode-excitation theory[1]. In the nonlinear saturation regime the synchronism of the bunched beam and an injected radiation wave may be sustained by wiggler tapering [2]. Same processes are instrumental also in enhancing the radiative emission in the tapered wiggler section of seeded FEL[3]. In a long tapered wiggler the diffraction of the emitted radiation wave is not negligible even at Angstroms wavelengths (as in LCLS). A Fresnel diffraction model was provided in [4] for the SR process only. Here we outline the fundamental physical concepts of Spontaneous Superradiadce (SR), Stimulated Superradiance (ST-SR), Taper-Enhanced Superradiance (TES) and Taper-Enhanced Stimulated Superradiance Amplification (TESSA), and compare their Fourier and Phasor formulations in the radiation mode expansion and free-diffraction models. Detailed further analysis can provide better design concepts of high power FELs and improved tapering strategy for enhancing the power of seeded short wavelength FELs
1. A. Gover, PR ST-AB 8, (030701) ; (030702) (2005)
2. J. Duris et al., arxiv 2015.
3. Y. Jiao et al., PR ST-AB 15 050704 2012
4. E.A. Schneidmiller, M.V. Yurkov, PR ST-AB 18, 030705 (2015)
 
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