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| MOAAU01 |
FEL Prize Lecture: Coherent Electron-Beam Radiation Sources and FELs: A Theoretical Overview
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- A. Gover, E. Dyunin
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
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The theory of Coherent electron beam radiation devices in general, and FEL in particular, is reviewed in terms of a general simple formulation based on modal expansion of the radiation field. A variety of e-beam radiation mechanisms (FEL, TWT, Cerenkov Radiation) have common features. All these radiation mechanisms can emit coherent or partially coherent radiation by means of three basic kinds of radiation processes: Spontaneous emission (shot-noise radiation), Superradiance (bunched-beam coherent radiation) and Stimulated emission. The common radiation processes and their relations are explained, in both frequency and time domains, in terms of the radiation modes expansion formulation. It is shown that the coherence properties of the emitted radiation, in each radiation process, depend on the phase relations between the radiation wave-packets, emitted by the individual electrons and their entrance distribution statistics. In the high gain linear regime all these radiation mechanisms satisfy the Pierce dispersion equation, and all radiation characteristics are derived from the Pierce transfer functions. I employ the formulation to delineate limits of coherence of electron beam radiation sources, and particularly examine possible schemes for turning SASE FELs to operate as coherent radiation sources.
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Slides
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Talk
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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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- 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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| TUPPH032 |
Development of Powerful FEMs for X, Ka and W Bands for Physical and Industrial Applications
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- M. Einat
CJS, Ariel
- N. S. Ginzburg, N. Yu. Peskov, M. I. Petelin
IAP/RAS, Nizhny Novgorod
- A. Gover, Y. Socol
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
- A. Kaminsky, S. Sedykh
JINR, Dubna, Moscow Region
- J. Lucas
University of Liverpool, Liverpool
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FEMs are among the main sources of powerful microwave pulses from X to W-bands. Interest to such sources is caused by the large number of potential physical and industrial applications, requiring a wide variety of the radiation parameters. The new generation of the accelerators (SLAC, CERN) requires sources of ~100 MW pulse RF power at 30-38 GHz with a narrow spectrum. Material processing stations require kW-level average power. Alternatively, spectroscopic and biological experiments require lower power but for a specific frequency spectrum. The possibility to develop such sources is being studied at Tel-Aviv University, IAP RAS, JINR and The University of Liverpool within the framework of the INTAS collaboration project. Three successful FEM experiments have been carried out:- Electrostatic-accelerator driven 70-130 GHz Tandem-FEM with kW-level pulse power (Tel-Aviv University.)
- Linac-driven 30-GHz FEM-oscillator with pulse RF power of ~ 20 MW (JINR + IAP RAS)
- Sub-relativistic e-beam industrial FEM tunable over X-band with output power up 1 kW (The University of Liverpool).
The presentation summarizes the progress in the development of FEMs and their applications.
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