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| MOPPH020 |
Enhancement of a Coherent (Super Radiant) Emission in FEL by Means of Energy Modulation of an Emitting Short Electron Bunch
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79 |
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- Yu. Lurie, Y. Pinhasi
CJS, Ariel
- A. Gover
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
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The developing techniques for generation of short bunches of relativistic electron beams enable construction of high-power, compact super-radiant free-electron lasers (FELs). Optimal efficiency of the super-radiant emission is achieved with ultra-short pulses (the beam duration is much less then the period of radiation). Unfortunately, the minimum duration of the pulse that can be achieved in practice is technologically limited, restricting the frequency of the radiation. We demonstrate that a super-radiant emission can be strongly enhanced by means of a proper energy modulation of the driving beam pulse, as suggested by A. Doria et al.*. In this way, a THz FEL source driven by short electron bunches generated by photo-cathode injection can be realized. Numerical simulations carried out using the WB3D code** show that linear energy modulation of a driving electron bunch enables one to increase the power of the super-radiant emission by a few orders of magnitude, approaching the power that can be achieved if ultra-short e-beam bunches are available. Possible limitations for the application of this method are also discussed, as well as the spectral purity of enhanced radiation.
* A. Doria et al., Phys. Rev. Lett. 80, 2841 (1998).** Y. Pinhasi, Yu. Lurie and A. Yahalom, Nucl. Instr. and Meth. in Phys. Res. A 475, 147 (2001).
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| TUPPH018 |
New Resonator for the Israeli FEL
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349 |
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- A. Faingersh, J. Dadoun, Kh. Garb, A. Gover, Y. Socol
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
- G. G. Denisov, M. Y. Shmelyov
IAP/RAS, Nizhny Novgorod
- M. Einat, B. Kapilevich, B. Litvak, Y. Pinhasi, A. Yahalom
CJS, Ariel
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The Israeli FEL resonator was re-designed in order to reduce the overall round-trip losses and achieve control on the radiation output-coupling. In its new configuration, the resonator consists of overmoded corrugated rectangular waveguide and two radiation mode splitters, separating the high-energy e-beam from the laser radiation. The electron input splitter is based on Talbot effect in an overmoded rectangular waveguide. The radiation out-coupling is done in the output splitter. It is based on novel design and it combines Talbot effect between two parallel plates with free space propagation, and focusing by two curved cylindrical mirrors in a confocal imaging scheme. The waveguide and the splitters were tested experimentally, showing improved performance in comparison with the former resonator. The measured unloaded Q-factor of the new version is increased by a factor of ~ 3, attaining up to Q=30,000. Accordingly, the round-trip losses are ~15%. Rotating grids control the radiation out-coupling allowing wide variation for maximization of the radiation output power and extraction efficiency. The design layout and the testing results are presented.
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| TUPPH019 |
Present Status of the Israeli FEL: Increasing FEL Power by Electron Beam Energy Boosting
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352 |
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- Y. Socol, E. Dyunin, A. Gover, M. Volshonok
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
- M. Einat, Yu. Lurie, Y. Pinhasi, A. Yahalom
CJS, Ariel
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The status of R&D work aimed on increasing FEL power by boosting the electron beam energy after the radiation build-up is reported. A fine control of the electron beam energy during the radiation pulse is designed to compensate the small energy degradation during the pulse. Also, a controlled ramp (up or down) in the electron energy during the pulse will be applicable as well. Theoretical estimations of the output power in the presence of electron energy change during the pulse compared to the obtained experimental results are presented. 2 models, showing good agreement between them and with the existing data, are compared: low-gain analytical model based on the pendulum equation, and rigorous 3D FEL interaction model solved numerically. Another expected result of the design is to further extend the pulse duration with stable conditions and to obtain improved coherency. The electrical and mechanical lay-outs of the high-voltage boosting (leading to electron beam energy boosting) are also presented.
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| THAAU05 |
Space-Frequency Model of Ultra Wide-Band Interactions in Free-Electron Lasers
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513 |
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- Y. Pinhasi, Yu. Lurie, A. Yahalom
CJS, Ariel
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The principle of operation of intense radiation devices such as microwave tubes, free-electron lasers (FELs) and masers, is based on a distributed interaction between an electron beam and radiation. We developed a three-dimensional, space-frequency theory for the analysis and simulation of radiation excitation and propagation in electron devices and free-electron lasers operating in an ultra wide range of frequencies*. The total electromagnetic field is presented in the frequency domain as an expansion in terms of cavity eigen-modes. The mutual interaction between the electron beam and the field is fully described by coupled equations, expressing the evolution of mode amplitudes and electron beam dynamics. The approach is applied in a numerical particle code WB3D, simulating wide band interactions in free-electron lasers operating in the linear and non-linear regimes. The code is used to study the statistical and spectral characteristics of multimode radiation generation in a free-electron laser, operating in various operational parameters. The theory is demonstrated also in the case of "grazing", resulting in a wide-band interaction between the electron beam and the radiation.
* Y. Pinhasi, Yu. Lurie, A. Yahalom: Space-frequency model of ultra wide-band interactions in millimeter wave masers, Phys. Rev. E 71, (2005), 036503- 1-8
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Slides
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Talk
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