Wave–particle interactions in a long traveling wave tube with upgraded helix

We investigate the interaction of electromagnetic waves and electron beams in a 4 m long traveling wave tube (TWT). The device is specifically designed to simulate beam-plasma experiments without appreciable noise. This TWT presents an upgraded slow wave structure (SWS) that results in more precise...

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Bibliographic Details
Published in:Physics of plasmas 2020-09, Vol.27 (9)
Main Authors: C. de Sousa, M., Doveil, F., Elskens, Y., L. Caldas, I.
Format: Article
Language:English
Subjects:
Amplitudes
Chaotic Dynamics
Computer simulation
Electromagnetic radiation
Electromagnetism
Electron beams
Electrons
Engineering Sciences
Nonlinear analysis
Nonlinear Sciences
Particle interactions
Physics
Plasma Physics
Saturation
Space charge
Traveling wave tubes
Traveling waves
Wave interaction
Wave propagation
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Summary:We investigate the interaction of electromagnetic waves and electron beams in a 4 m long traveling wave tube (TWT). The device is specifically designed to simulate beam-plasma experiments without appreciable noise. This TWT presents an upgraded slow wave structure (SWS) that results in more precise measurements and makes new experiments possible. We introduce a theoretical model describing wave propagation through the SWS and validated by the experimental dispersion relation, impedance, and phase and group velocities. We analyze nonlinear effects arising from the beam–wave interaction, such as the modulation of the electron beam and the wave growth and saturation process. When the beam current is low, the wave growth coefficient and saturation amplitude follow the linear theory predictions. However, for high values of current, nonlinear space charge effects become important and these parameters deviate from the linear predictions, tending to a constant value. After saturation, we also observe trapping of the beam electrons, which alters the wave amplitude along the TWT.
ISSN:1070-664X
1089-7674
DOI:10.1063/5.0018959