Harmonic Content in the Beam Current in a Traveling-Wave Tube

Abstract

In a klystron, charge overtaking of electrons leads to an infinity of ac current on the electron beam. This paper extends the klystron theory of orbital bunching to a travelingwave tube (TWT). We calculate the harmonic content of the beam current in a TWT that results from an input signal of a single frequency. We assume that the electron orbits are governed by Pierce's classical three-wave, linear theory. The crowding of these linear orbits may lead to charge overtaking and, therefore, harmonic generation on the beam current, as in a klystron. We analytically calculate the buildup of harmonic content as a function of tube length from the input, and compare the results with the CHRISTINE code. Good agreement is found. Also found is the surprisingly high level of harmonic contents in the electron beam current, even when the TWT operates in the small signal regime. A dimensionless bunching parameter for a TWT, X = (2 P in /( P b C)) 1/2 , is identified, which characterizes the harmonic content in the ac beam current, where P in is the input power of the signal, P b is the dc beam power, and C is Pierce's gain parameter.

High current nonlinear transmission line based electron beam driver

“…9 also shows a relative increase in the amplitude of higher frequency content compared to the amplitude of the peak signal frequency. Although the drift tube lacks a slow wave structure, generation of harmonic content, such as the peak around 1.9 GHz in the 1A and 4A traces and around 2.9 GHz in the 4A trace is likely a result of the charge overtaking effect described in [21,22]. observed at the NLTL Stage 58 D-dot.…”

Traveling Wave Amplifier Driven by a Large Diameter Annular Electron Beam in a Disk-Loaded Structure

“…Even in the linear regime, there could be significant harmonic content in the beam current due to crowding of an electron orbit [13]. It would be of interest to see if the Disk-on-Rod TWT can function as a bi-frequency amplifier.…”

Multi-frequency recirculating planar magnetrons

“…Later in the chapter, § 2.3 explores whether the second harmonic of the LBO, which has a frequency near 2 GHz, can injection-lock the SBO, which also has a frequency near 2 GHz. The harmonic content of electron beams has been the focus of study in many microwave vacuum electron devices, such as klystrons [63] and TWTAs [64,65]. Another consequence is the gradual reduction in magnetron efficiency as the current density is increased due to the energy invested in focusing the electrons by overcoming their electrostatic repulsion.…”