| 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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| TUPPH032 | Development of Powerful FEMs for X, Ka and W Bands for Physical and Industrial Applications | 390 |
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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:
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| TUPPH033 | A FEL Amplifier Based on Planar Bragg Waveguides | 393 |
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A planar periodic Bragg structure can be used for wave guiding in the direction transverse to the lattice vector. Open Bragg waveguide can provide high selectivity over the transverse coordinate when its size essentially exceeds wavelength. We study several new schemes of FEL amplifiers based on these structures. In a transverse current amplifier scheme it is beneficial to use a grating with a step of corrugation, that results in the existence of a single low dissipative mode located near defect. The sheet electron beam moves across the waveguide to be resonant to one of partial waves forming the operating mode. Another way is a traditional traveling wave amplifier scheme where electron beam moves along waveguide axis. To increase effective size of operating mode is suggested a structure with regular longitudinal corrugation that couples two partial waves propagating at some angle to the axis to the wave propagating directly along the axis. This wave, which in moving reference frame is transformed into a cut off mode*, is excited by the electrons. Analysis shows rather high gain and efficiency of the novel application schemes with simultaneous discrimination of parasitic modes.
*1. N.S. Ginzburg, A. M.Malkin, N. Yu. Peskov et. al. Improving selectivity of free electron maser with 1D Bragg resonator using coupling of propagating and trapped waves, PR ST-AB 8,040705(2005) |
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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. |