A. S. Fokin

Turbulent electron beams as sources of broadband noise-like microwave oscillations

We report the results obtained from the theoretical and experimental analyses of multivelocity turbulent charged-particle beams, space-charge bunches of which are sources of broadband noise-like microwave oscillations.

An experimental study of the interaction between a pulsed electron beam and a large-amplitude electromagnetic wave

We experimentally investigate the interaction between an electron beam with a periodically varying diameter and a large-amplitude electromagnetic wave. The effect of different factors on the pulsed beam formation and current density in bunches is established. Compared with the electron beam deceleration circuits (low-voltage vircator systems), the generators based on pulsed turbulent beams have a broader band due to the formation of a large number of space charge bunches and an integral power efficiency that is higher by a factor of 2–2.5.

Transparent traveling wave tubes with electron-beam modulation at the cathode

We consider the results of an experimental investigation of a laboratory prototype of a microwave amplifier based on a transparent traveling wave tube (TWT) with the input signal applied either to a beam-modulating near-cathode grid or (traditional scheme) to the input helix of a slow-wave system. Dependences of the amplifier gain and efficiency on the input-power level are presented. In the TWT scheme with a modulating grid, the electron efficiency reaches 50–56% at a gain of 12–13 dB.

Experimental study of scenarios of transitioning to broadband generation in a laboratory model of a low-voltage vircator

The results from experimental investigations of the transition from single-frequency generation to broadband generation in a laboratory model of a low-voltage vircator are presented. It is found that the transition to broadband generation is realized via intermittency or through a cascade of period-doubling bifurcations.

Higher harmonics in the output spectrum of a generator with turbulent electron beam

Formation of electron bunches in turbulent electron beams is numerically simulated and experimentally studied. A prototype of a laboratory generator is proposed, and control parameters (in particular, electron spread with respect to longitudinal velocities and additional deceleration of electron beam by electrostatic field of collector) that affect the characteristics of electron bunches and provide an increase in the number and amplitude of higher harmonics in the output spectrum are determined.

Formation of space-charge bunches in a multivelocity-electron-beam-based microwave oscillator with a cathode unshielded from the magnetic field

The influence of the magnitude and configuration of the magnetic field on the parameters of electron bunches formed in a multivelocity electron beam is analyzed. It is shown that the use of a cathode unshielded from the magnetic field and a nonuniform magnetic field increasing along the drift space enables the formation of compact electron bunches. The ratio between the current density in such bunches and the beam current density at the entrance to the drift space reaches 106, which results in a substantial broadening of the output microwave spectrum due to an increase in the amplitudes of the higher harmonics of the fundamental frequency.

Effect of the ion background on the spectral and amplitude characteristics of the output signal from the oscillator with the turbulent electron beam

The effect of the residual gas pressure on the spectral and amplitude characteristics of the output signal from the oscillator with the turbulent electron beam is examined. It is shown that ions resulting from gas ionization in the drift region promote formation of denser and more compact space charge bunches. Denser bunches increase the output signal power and aid in appearance of higher-order components in the spectrum, thus extending the working range to a higher-frequency region. When the device operates in the regime of noiselike signal generation, ions contribute to a decrease in the irregularity of the output power spectrum to about 0.3 dB in the working frequency range up to two octaves.

TURBULENCE IN MICROWAVE ELECTRONICS: TEORETICAL APPROACHES AND EXPERIMENTAL RESULTS

A review of the current state of different theoretical approaches to the description of turbulence in electron beams and electronic devices at microwave frequencies is shown. A three types of turbulent (nonlaminar) electron beams were considered. The first type of turbulent electron beam is caused by the intersection of electronic trajectories (e.g., due to thermal velocity) and it is common to the flow of electrons at all. The turbulence of the second type is due to the instability of the electron beams, because of which a small perturbations grow for an exponentially (such instabilities include diocotron and slipping-instability). The third type – vortex turbulence, the cause of which is filamentarization of electron flow. Formed charged filaments interact among themselves, that leads to the formation of vortex structures; the presence of this structures increases the number of collective degrees of freedom and may lead to turbulence. The results of an experimental study of turbulent flows and electronic generators with their use in standalone mode and when an external signal were shown. Various types of broadband broadband microwave oscillators oscillations were investigated. We discuss the phenomenological model of turbulent the electron beam, which is a chain of superradiant clots containing electron-oscillators, chain of «vortices» ( «vortices» are describes by the modified equations of van der Pol).

Intensive multiple-velocity electron beams (formation methods, using for broadband generation)

We consider the results obtained from the theoretical and experimental analyses of intensive multiple-velocity electron beams, space-charge bunches of which are sources of broadband noise-like microwave oscillations. Different concepts of forming such beams are considered. The results of the experimental study of the oscillations generated by the developed laboratory layout of the wideband microwave generator are reported.

Investigation of the influence of electron-velocity dispersion on the output characteristics of a laboratory breadboard of a low-voltage vircator

Some ways of forming multivelocity electron beams are considered, and experimental dependences (obtained on a laboratory breadboard of a low-voltage vircator) of the integral output power and generation band on the electron-velocity dispersion in a beam are shown.