Tuning of the self-modulation period in a relativistic BWO with strong reflections

Abstract

We show the possibility of re-adjusting the self-modulation period in the variant of the backward wave oscillator with an external reflector by changing the position of the reflector. Thus, the possibility to partially control the generation spectrum is demonstrated. The theory is confirmed by the results of numerical modeling by the Particle-In-Cell method.1. The possibilities of using high-power multi-frequency microwave signals (including chaotic ones) in various applications have been actively discussed in recent years. The range of these applications includes radar systems [1], interference-immune data transfer [2], radio acoustic atmospheric probing [3], and radar countermeasures [4]. All this stimulates significantly the development of the research associated with the issues of generating and controlling the parameters of high-power multi-frequency microwaves.As applied to the relativistic backward-wave oscillator (BWO), the possibilities of controlling the spectrum of multi-frequency generation were first discussed in [5], where it was shown that the generation of several closely spaced frequencies can be realized in a sectioned system with stepwise variation of synchronism detuning between the beam and the operating mode, which is achieved by changing the period of the slowwave system in individual sections. Correspondingly, the difference of the generated frequencies is regulated by the detuning step, i.e., the period of the system.In this paper, we study an alternative way to generate signals with complex spectra, which is based on realization of the self-modulation regime in the BWO with an external reflector. In this case, we have an attractive possibility to change the generation spectrum by varying the position of the external reflector under conditions of invariable geometry of the interaction space and the parameters of the electron beam. It is known that in BWOs with strong external reflections, the spectral radiation lines in the regime of periodic self-modulation are close to the resonant frequencies of the aggregate electrodynamic system [6]. Correspondingly, one can adjust the self-modulation frequency by changing the distance to the reflector.2. Consider a model of the BWO with the electrodynamic system shaped as a section of a circular corrugated waveguide with a tubular electron beam. Suppose that a part of the signal from the BWO output is reflected from the reflector with the reflection coefficient R and is transmitted to the generator input with the delay t 0 . Within the approximation of a relatively small change in the electron energy in the interaction process, the dynamics of the BWO can be described by the system of equations (see [7])