| Paper | Title | Page |
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| MOPPH034 | Production of 'Giant' Pulses of Scattered Radiation from Pump Wave Spot Runing over the Electron Beam | 115 |
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| To generate ultrashort electromagnetic pulses it is suggested to use the superradiance (SR) effects in the process of stimulatted scattering when the spot illuminated by pump wave shifts along the electron beam with group velocity of scattered radiation. According to theoretical consideration it is shown that in such conditions the amplitude of scattered SR pulse is proportional to interaction distance. This process is not sensitive to the dispersion of beam parameters due to extremely short time of wave interaction with every electron. In the case of scattering of laser radiation by a moderately relativistic electron beam it is possible to produce intense SR pulses either at terahertz (down conversion) or at UV (up conversion) frequency band depending on direction of pump wave propagation with respect to electron beam. In principle, to shift the illuminated spot along the electron beam, reflection of the pump wave by rotating mirror can be used. More realistic method is the transmission of the frequency-modulated pump wave through an optical prism. | ||
| TUPPH026 | Dispersion Effects in Short Pulse Waveguide FEL | 378 |
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The influence of waveguide dispersion on the FEL operation driven by short electron bunches is studied. Under the assumption of a high quality resonator a parabolic equation for the evolution of electromagnetic pulse profile is derived. Based on an analytical theory describing the linear stage of generation a starting condition is determined. A structure of supermodes representing the sum of resonator eigenmodes with locked phases is found as well. It is demonstrated that due to waveguide dispersion FEL is able to generate not only for positive but also for negative cavity detuning. The computer simulation of a nonlinear regime taking into account electromagnetic pulse dispersion defines a stationary profile of electromagnetic pulse in good agreement with experimental results*,**. It is shown that regimes with periodic and chaotic self-modulation of the pulse profile are realized for considerable exceeding of the length of interaction region over the threshold. A superradiant (transient) regime of short pulse generation is found for small cavity detuning.
* Jeong Y. U., et al. Proc. of the 2004 FEL Conference, Trieste, Italy, 2004, P.667. ** Doria A., Bartolini R., Feinstein J. IEEE J. Quantum Electron., 1993, V.29, P.1428. |
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| TUPPH034 | Generation of Narrow Band Short mm Wave Superradiance Pulses in a Non-uniform Planar Waveguide | 397 |
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Recently significant progress was achieved in production of ultrashort pulses in millimeter wave band based on intense electron bunch supperradiance*,**,***. One of the problems for advance similar mechanisms in shorter wave bands is spectrum broadening caused by the simultaneous bunch interaction with several waveguide modes. To suppress spurious interaction we suggest to use the non-uniform planar waveguide. In such a waveguide the phase velocities of the different modes varied over longitudinal coordinate, with the exception of the fundamental TEM mode. As a result it is possible to suppress interaction of the short electron bunch with higher-orders modes responsible for lower frequencies radiation including cut-off modes. We studied 200-500 GHz superradiance of a 2 MV, 100 A, 100-300 ps electron bunch in a planar regular wiggler. It is shown that narrow band superradiance pulses could be produced in the 2 m long planar waveguide with the gap between plates linear increasing from 1-2 to 5-8 wavelength. The peak power of the pulses amounted 3 MW and hundreds of kW for the 200 GHz and 500 GHz bands correspondingly.
*Ginzburg N. S, et al. // Nucl. Instr. Meth. Phys. Res., 1999, A429 (1), 94 **N. S.Ginzburg, et al. // Opt. Comm., 2000, 175 (1-3), 139 ***A. G.Reutova, et al. // JETP Lett., 2005, 82(5), 263 |
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| TUPPH035 | Generation of Superradiant Pulses by Backscattering of Pumping Wave on the Intense Electron Bunch | 400 |
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| Recently significant progress was archived in the generation of multimegawatt subnanosecond pulses in millimeter wave band utilizing the cyclotron and Cherenkov mechanisms of superradiance (SR). We study the novel mechanism of SR when the powerful pumping wave undergoes the stimulated backscattering on the intense electron bunch. Due to the Doppler up shift the radiation frequency can significantly exceed the frequency of the pumping wave. With the relativistic microwave generator as a pumping wave source such a mechanism can be used for generation of the powerful pulse radiation in the short millimeter and submillimeter wave bands. Experiments on the observation of the stimulated scattering in the superradiance regime were carried out at Institute of Electrophysics RAS with two synchronized accelerators. The 4 ns electron beam from the first accelerator is used for generation of the 38 GHz 100 MW pumping wave which subsequently scattered on the subnanosecond 250 keV 1 kA electron bunch produced by the second accelerator. The SR pulses with duration 200 ps and peak power about 1 MW were generated. The spectrum of scattered signal included the frequencies up to 150 GHz. |