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Longitudinal electrostatic field effect on width of multiharmonic space-charge wave frequency spectrum in two-stream superheterodyne FEL with a helical electron beam

Lysenko, AV, Oleksiienko, GA, Volk, II


Sumy State University
2, Rimsky Korsakov St., Sumy, 40007, Ukraine

E-mail: lysenko_@ukr.net

Language: russian


Subject and Purpose. The research subject is spectral characteristics of the space-charge wave propagating in klystron-type two-stream superheterodyne free-electron laser (TSFEL) with a helical relativistic electron beam. The aim is to theoretically investigate the longitudinal electrostatic field action on the multiharmonic space-charge wave forming in the device under study.

Methods and Methodology. We proceed from the quasi-hydrodynamical equation, continuity equation, and Maxwell's equations. Methods of hierarchical approach to the theory of oscillations and waves, namely the modernized method of averaged characteristics, are employed to solve the problems of motion and continuity. The method of slowly varying amplitudes is used to solve the field problem.

Results. A differential equation system has been obtained in cubical non-linear approximation, describing the dynamics of multiharmonic space-charge wave harmonics in the TSFEL transit section in the presence of a longitudinal electrostatic field. A regime has been studied where the frequency of the first-order space-charge wave harmonic is much less than the critical frequency of the two-stream instability. It has been demonstrated that the accelerating longitudinal electrostatic field application broadens the frequency spectrum. In the decelerating electrostatic field, the multiharmonic space-charge waves have higher amplitudes and narrower frequency spectra. The transit section length decreases then. It has been revealed that the longitudinal electrostatic field application for controlling the frequency spectrum width is more effective with helical electron beams than with straight ones.

Conclusion. We propose to use a longitudinal electrostatic field in the TSFEL transit section for controlling the width of space-charge wave frequency spectrum and the level of output signal amplitudes in multiharmonic two-stream free-electron lasers of klystron type with a helical relativistic electron beam.

Keywords: helical electron beam, longitudinal electrostatic field, superheterodyne free-electron laser, three-wave parametric resonance, two-stream instability

Manuscript submitted 02.05.2019
PACS 41.60.Cr; 52.35.Mw​
Radiofiz. elektron. 2020, 25(1): 70-79
Full text (PDF)

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