Microwave generation power in a nonrelativistic electron beam with virtual cathode in a retarding electric field

The power of microwave generation in a nonrelativistic electron beam with virtual cathode formed in a static retarding electric field (low-voltage vircator system) has been studied experimentally and by means of numerical simulation within the framework of a one-dimensional theory. The limits of applicability of the one-dimensional theory have been experimentally determined.     

Nonlinear dynamics of electron beam with virtual cathode in external inhomogeneous magnetic field

Nonlinear dynamics of virtual cathode (VC) formed in electron beam in a strongly inhomogeneous external magnetic field generated by a ring magnet has been numerically simulated using a two-dimensional model. It is established that the field characteristics strongly influence the VC dynamics. Physical processes responsible for this strong dependence are considered. The output power of generation in a model system with VC is determined as a function of the field parameters.     

The electron beam with virtual cathode in a two-section drift tube

An analysis based on the law of conservation of the z component of field and particle momentum in a thin annular magnetized monoenergetic electron beam in a two-section drift tube composed of tube segments with different radii (R ₁<R ₂) allowed the critical injected beam current to be determined for which a virtual cathode, formed in the wider tube at the joint section, starts traveling through the narrower tube toward the beam injection region. A region behind the traveling virtual cathode features a “squeezed” single-flux state of the beam (corresponding to the “slow” left branch of the current characteristic, high charge density, but low relativistic factor). When the injected current decreases below a critical transition level (I _in<I _Tr), the virtual cathode returns to the initial position and restores the double-flux electron beam. This current is smaller than (I _lim1+I _lim2)/2, and, depending on R ₂, varies from the limiting transport current for the narrower section (I _lim1) up to I _F/2, where I _F is the Fedosov current for this tube section.     

Statistical properties of oscillations of a microwave chaos generator based on a virtual cathode

The statistical properties of signals of a microwave generator of chaotic oscillations based on a virtual cathode have been experimentally studied. It is established that variations in the coefficient of electron beam deceleration not only modifies the spectral characteristics, but also changes the statistical properties of generated signals.     

The effect of the conductivity of drift chamber walls on the dynamics of a relativistic electron beam with a virtual cathode

The effect of conductivity of walls of a drift chamber of the axial vircator on the behavior of a relativistic electron beam with a supercritical current was investigated. The dynamics of a relativistic electron beam is shown to be characterized by the formation of a virtual cathode of complex structure with two or three potential minima in the azimuthal direction, which rotate around the drift space axis. It is established that variation in the conductivity of drift chamber walls leads to stepwise switching of the generation frequency and a sharp change in the output power. Dependences of the output radiation power of the investigated vircator system on the conductivity of drift chamber walls for two characteristic regimes of the dynamics of a relativistic electron beam were obtained.     

The current of an annular electron beam with virtual cathode in a drift tube

An analysis based on the laws of conservation of energy and the z components of the field and particle momentum shows that a thin magnetized annular electron beam in a homogeneous drift tube behind a virtual cathode under stationary conditions occurs in a “squeezed” state corresponding to a slow left-hand branch of the current characteristic with a relativistic factor in the interval 1≤γ≤Γ^1/3. The beam current I ₁ behind the virtual cathode in a homogeneous drift tube can vary from zero up to a limiting value I _lim, while the injection currents (I ₂) and the current of electrons reflected from the virtual cathode (I ₃) for every stationary state are single-valued functions of I ₁ and fall within the intervals I _F/2≤I ₂≤I _lim and 0≤I ₃≤I _F/2, respectively, where I _F is the Fedosov current.     

Influence of feedback on the complex dynamics of an electron beam with a virtual cathode in a virtode

Results are presented of a numerical simulation of the nonlinear dynamics of a relativistic electron beam with a virtual cathode in a drift relativistic-electron-beam vircator system with and without external feedback. Pis’ma Zh. Tekh. Fiz. 24, 51–57 (March 12, 1998)     

The virtual cathode velocity during electron beam transport in a drift tube

Technical Physics Letters - A solution corresponding to a thin annular electron beam in a homogeneous drift tube featuring a uniformly moving virtual cathode (VC) has been obtained. The dependence...     

Bicoherent wavelet analysis of the structure formation in an electron beam with virtual cathode

The supercritical electron beam structure formation in a diode gap with inhomogeneous ion background density are analyzed by the bicoherent wavelet transformation method. By studying the wavelet bicoherency of the spatiotemporal data about oscillations in the system, it is possible to effectively reveal and analyze local spatial structures formed in the electron beam.     

The current of an annular electron beam behind virtual cathode

The output current I _out of a magnetized annular electron beam transported in a homogeneous drift tube of a SINUS-7 setup has been studied as a function of the injected beam current I _inj. The electron beam was injected via an anode inset of smaller radius and had a current above the Fedosov limit for the given drift tube (I _inj ≥ I _F). It is established that, to within the experimental uncertainty, a virtual cathode (VC) is formed when the injected beam current exceeds the corresponding limiting I _lim. In this state, the current transmitted behind VC is approximately equal to the limiting value (I _out ≈ I _lim).     

Virtual cathode formation in annular electron beam in an external magnetic field

The conditions of virtual cathode (VC) formation in an annular electron beam in the presence of an external focusing magnetic field have been studied by means of numerical simulation within the framework of a two-dimensional model. The dependences of a critical beam current (at which the VC is formed) on the magnetic field and of the optimum field (at which the critical current is minimal) on the beam geometry are determined. The optimum magnetic field depends on the Brillouin field value.     

Spontaneous and stimulated emission in microwave oscillators with a virtual cathode

A one-dimensional model of electron beam emission with a virtual cathode is used to show that spontaneous emission occurs in a reditron while stimulated emission is observed in vircators and negative triodes. However, at a certain stage in the latter, the radiative instability is quenched as a result of the evolution of turbulence in the electron beam. The idea is therefore put forward that this quenching may be eliminated by specially shaping the leading edge of the high-voltage supply pulse to the diode of the microwave oscillator. Pis’ma Zh. Tekh. Fiz. 24, 41–46 (February 26, 1998)     

Ultralow-voltage generator of chaotic microwave oscillations with secondary-emission cathode

A new scheme of an effective ultralow-voltage generator of broadband chaotic microwave oscillations is considered. The device operates on counterpropagating turbulent electron beams, one of which is created by a secondary-emission cathode. Results of an experimental investigation of the device prototype operating in various regimes are summarized. Promising features of the proposed ultralow-voltage oscillator are the relatively low accelerating voltages (below 500 V), increased efficiency (up to 14–15%) compared to analogs, broad band of generated oscillation frequencies, high level of integral output power (up to 35 W), the possibility of fast and easy control over the generation regimes (from almost monochromatic to broadband), and small dimensions of the device.     

Experimental study of the effect of external noise-like signal on the dynamics of vircator with magnetron injection gun

The effect of an external noise-like signal on the operation of a low-voltage vircator with magnetron injection gun has been experimentally studied. The results show that the noise-like input signal allows the output characteristics of the low-voltage vircator to be controlled so as to drive it to operate at either maximum output power or maximum generation bandwidth.     

Dynamics of the transverse oscillations of an electron beam in a tellarator

The transverse oscillations of a thin electron beam in a stellarator or in a modified betatron were theoretically studied. The analysis is based on the relativistic Lorentz equation for intrinsic fields of the electron beam calculated by the method of retarded potential. Conditions for an instability development caused by the stellarator field inhomogeneity are determined. It is shown that a stellarator may also feature other instabilities of the transverse oscillations which are not related to the stellarator field inhomogeneity.     

Experimental study of the electron beam compressed state breakup

The dynamics of breakup of the compressed state of an electron beam with a virtual cathode (VC) transported in a two-section drift tube of a high-current electron accelerator has been studied. Based on the results of numerical simulations, the method of partial capture of the injected beam current during the applied voltage pulse is proposed and implemented, which can ensure the conditions necessary for the breakup of the electron beam compressed state. The VC velocity during the breakup of the electron beam compressed state amounts to 6–8% of the velocity of light in vacuum. The experimental data qualitatively agree with the results of analytical estimations and numerical simulations.     

Experimental study of the effect of acoustic oscillations on heat transfer in a gas flow

The influence of acoustic oscillations on heat transfer in a high-temperature turbulent flow is determined. It is shown how the heat transfer at resonance frequencies differs at nodes and antinodes of the standing acoustic wave.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 1, pp. 61–67, January, 1977.     

Generator of broadband noiselike microwave oscillations on turbulent electron beams

Generator of chaotic microwave oscillations on turbulent electron beams has been studied by experimental and theoretical methods. The presence of a magnetic field with sufficiently large amplitude and period leads to the formation of space charge bunches in the electron beam, which results in the generation of broadband noiselike oscillations.     

Ultralow-voltage generator of chaotic microwave oscillations on counterpropagating electron beams

Technical Physics Letters - The new scheme of an ultralow-voltage generator of broadband chaotic microwave oscillations is considered, which operates on counterpropagating turbulent electron beams....     

Ultrabroadband generators of noiselike high-frequency and microwave oscillations with electron feedback

It is experimentally established that oscillators, such as a low-voltage vircator with electron feedback, are characterized by an ultrabroad generation band (up to four octaves and above). The minimum frequency of oscillations is on the order of 50 MHz, while the maximum frequency is about 3–3.5 GHz. The low-frequency part of the spectrum is related to the oscillations of positive ions in the interaction space.