| Paper | Title | Page |
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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 |