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ISSN Print: 0040-2508
ISSN Online: 1943-6009
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On the Feedback in Smith-Purcell Experiments
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ABSTRACT
Excitation of fast (bulk) waves 0.9 and 3.6 mm band and at angles close to 90° from an electron beam which is not modulated by an external signal has been experimentally detected. The above experiments were similar to those of Smith-Purcell, but they were made over the millimeter wavelength range and at an accelerating voltage from 2.5 to 5.2 kV. The minus first space harmonic of a slow (surface) wave of the periodic structure excited in the wavelength range from 11 to 0.5 mm in the BWT regime has been used for the self-modulation of the electron beam.
Analysis of the known conditions has been performed notably the excitation of fast and slow waves, modulation of an electron beam by a slow wave, both spatial and time retardation of the higher-order harmonics of an electron beam. The results have been verified experimentally.
It is stated that a principally unavoidable positive feedback via a slow wave of a plane grating has been used to obtain the electron beam modulation in the Smith-Purcell experiments as in the case of this particular experiment.
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