Author: Gover, A.
Paper Title Page
TUC04 Enhancement of Radiative Energy Extraction in an FEL Oscillator by Post-Saturation Beam Energy Ramping 1
  • H. S. Marks, A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
  • E. Dyunin, Yu. Lurie
    Ariel University, Ariel, Israel
  We present experimental results showing a greater than 50% increase in post-saturation radiation power extraction from a Free Electron Laser oscillator based on an electrostatic accelerator. Electrostatic accelerator free electron laser oscillators have the potential for CW operation. Present day operating oscillators rely on long pulses of electrons, tens of microseconds in duration; they generate correspondingly long radiation pulses, at a single longitudinal mode after a mode competition process. The presented post-saturation power extraction enhancement process is based on temporal tapering (up-ramping) of the beam energy, enabling a large synchrotron oscillation swing of the trapped electron bunches in passage along the interaction length. We further discuss the theoretical limits of the temporal tapering efficiency enhancement process.  
Group and Phase Velocity Matching in THz IFEL interaction  
  • E.J. Curry, S.S. Fabbri, P. Musumeci
    UCLA, Los Angeles, California, USA
  • A. Gover
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
  Funding: Work supported by DOE grant DE-FG02-92ER40693 and NSF grant PHY-1415583.
We review results from the recent guided-THz IFEL experiment at the UCLA PEGASUS facility. Using a parallel plate waveguide, the group velocity of a near-single cycle THz pulse was reduced to match electron beam propagation in an undulator, resulting in a ponderomotive interaction sustained for 30 cm. With a 1-uJ THz pulse obtained by optical rectification in a LN source, the projected beam energy distribution increased from a full peak width of 30 keV to more than 100 keV. When using a long (multi-ps) electron beam, longitudinal phase-space measurements reveal the snake-like energy modulation from the ps-scale THz pulse. Using a short beam configuration, we also measure bunch compression, limited by the available drift length to a factor of two. Finally, we explore the application of this technique to amplification of the THz seed using the 1-D multi-frequency simulation code we have developed for this novel zero-slippage interaction scheme.
Stimulated Emission/Absorption of Radiation by a Single Electron Quantum Wavepacket  
  • A. Gover, Y. Pan
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
  Funding: Partial support by Deutsche-Israelische Projektkooperation (DIP) and US-Israel Binational Science Foundation (BSF).
We analyze the stimulated (emission/absorption) interaction of a single electron quantum wavepacket with coherent radiation, using perturbation theory and numerical solution. The analysis applies to a wide class of free electron radiative-interaction schemes, and is exemplified for Smith-Purcell radiation. Contrary to spontaneous emission, stimulated radiative interaction depends on the wavepacket characteristics in a certain quantum range. If the electron drifts beyond a critical length, then dimension-dependent acceleration of the wavepacket is fundamentally impossible because of the wavepacket spread. Below this range, such acceleration is possible, approaching the limit of classical 'point particle' linear acceleration, at the conditions of small wavepacket dimensions relative to the radiation wavelength and multi-photon exchange. Our analysis emulates the FEL gain in the limit of negligible recoil, and the quantum momentum recoil sidebands characteristics of PINEM - when recoil effect is significant. We use the platform for discussing the fundamental physics question of measurability of the quantum wavepacket size and the limitation of the classical 'white' shot-noise model.
FRB03 Dynamics of Superradiant Emission by a Prebunched E-Beam and its Spontaneous Emission Self-Interaction 1
  • R. Ianconescu, A. Gover
    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: Partial support by US-Israel Binational Science Foundation (BSF) and by Deutsche-Israelische Projektkooperation (DIP).
In the context of radiation emission from an electron beam, Dicke's superradiance (SR) is the enhanced coherent spontaneous radiation emission from a prebunched beam, and Stimulated-Superradiance (ST-SR) is the further enhanced emission of the bunched beam in the presence of a phase-matched radiation wave.* These processes are analyzed for undulator radiation in the framework of radiation field mode-excitation theory. In the nonlinear saturation regime the synchronicity of the bunched beam and an injected radiation wave may be sustained by wiggler tapering: Tapering-Enhanced Superradiance (TES) and Tapering-Enhanced Stimulated Superradiance Amplification (TESSA).** Identifying these processes is useful for understanding the enhancement of radiative emission in the tapered wiggler section of seeded FELs.***,**** The nonlinear formulation of the energy transfer dynamics between the radiation wave and the bunched beam fully conserves energy. This includes conservation of energy without radiation reaction terms in the interesting case of spontaneous self-interaction (no input radiation).
* A. Gover, Phys. Rev. ST-AB 8, 030701 (2005).
** J. Duris et al., New J.Phys. 17 063036 (2015).
*** E. A. Schneidmiller et al., PRST-AB 18, 03070 (2015).
**** C. Emma et al., this conference.
slides icon Slides FRB03 [2.656 MB]