Output microwave radiation power of low-voltage vircator with external inhomogeneous magnetic field

Dependence of the power of a broadband microwave radiation generated by a low-voltage oscillator with virtual cathode (vircator) on the parameters of an external inhomogeneous magnetic field has been studied by numerical simulations using a two-dimensional model. It is established that there are optimum parameters of the generator (configuration of the external magnetic field, electron beam current) for which the output radiation power is maximum. A relationship between the optimum conditions of virtual cathode formation in the electron beam and the microwave generation regime is established.     

Chaotic signal generation in low-voltage vircator with electron source shielded from external magnetic field

The effect of shielding an electron source from a homogeneous external magnetic field of the drift chamber on the nonlinear dynamics of the electron beam with a virtual cathode (VC) and on the characteristics of output microwave radiation in a low-voltage vircator have been numerically simulated within the framework of a two-dimensional model. It is established that the increased degree of shielding of the electron source from the external magnetic field leads to the complication of the VC dynamics in the system and the corresponding chaotization of the output microwave radiation. Physical processes that account for the observed effect of shielding are analyzed.     

Effect of positive ions on the microwave generation in a low-voltage vircator

The effect of vacuum conditions on the characteristics of microwave generation in a nonrelativistic electron beam with a virtual cathode (VC) formed in a retarding field (low-voltage vircator) has been experimentally studied. The ionization of residual gases in the working chamber of a low-voltage vircator leads to displacement of the VC out of the interaction space, which results in breakdown of the microwave generation. The experimental data agree with the results of numerical simulations.     

Experimental study of the effect of external signal on microwave oscillations in a nonrelativistic electron beam with virtual cathode

The effect of an external harmonic signal on the characteristics of microwave generation in a non-relativistic electron beam with virtual cathode (VC) formed in a static retarding electric field (low-voltage vircator system) has been experimentally studied. A significant increase in the vircator generation power is observed when the frequency of the external signal is close to the frequency of VC oscillations. At large detunings, a broadband chaotic generation is observed.     

Microwave generation features in a vircator with an inhomogeneous magnetic field in the interaction region

A vircator with an inhomogeneous external magnetic field superimposed onto the cathode-anode-virtual cathode potential well was studied by methods of computer modeling. It is shown that the application of such additional field allows a significant (almost fivefold) increase in the microwave generation efficiency, which is explained by the gyrotron effect development.     

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.     

An S-band vircator with premodulated electron beam based on a compact generator with inductive energy storage

An experimental S-band vircator with premodulated electron beam based on a compact generator with inductive energy storage is described. The vircator radiation power was 300 MW at a power efficiency of about 5% and a pulse duration of 50 ns. The oscillation frequency, determined by the electrodynamic system parameters, remained unchanged during the pulse.     

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.     

3D simulation of electron beam squeezed-state generation in a two-section drift tube and analysis of its characteristics

A 3D numerical electromagnetic simulation of a vircator in the mode of electron-beam squeezedstate generation is performed. Detailed numerical investigations are carried out, and the dynamics of charged particles in the squeezed state is analyzed. It is shown that the electron beam density (and, as a consequence, effective beam plasma frequency) can be significantly increased in the squeezed state. Hence, the vircator generation frequency and power can also be increased.     

Vircator radiation controlled by axial current-carrying filament

The operation of a vircator system with an axial current-carrying filament was studied by computer modeling. It is demonstrated that, by correctly selecting the value of current in the filament, the electron beam dynamics can be controlled so as to excite the output feeder in an optimum regime, which provides for a fourfold increase in the output power.     

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.     

Self-similarity and branching of wavelet transforms of microwave signals generated by a vircator

The turbulence regimes of an electron flow with a virtual cathode are studied. The microwave signals generated by a vircator are calculated by the method of large particles. The wavelet transforms of these signals are constructed, and it is shown that they have a complicated self-similar and branching structure. It is concluded that the turbulence of an electron flow is caused by macroscopic instabilities. Pis’ma Zh. Tekh. Fiz. 22, 92–96 (December 26, 1996)     

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)     

Effect of external signal on the output power of an oscillator with electron feedback

The effect of an external single-frequency harmonic signal on the output power of an oscillator with electron feedback has been studied by analytical and numerical methods. It is established that an increase in the input signal power leads to sharp growth in the output power of the nonautonomous oscillator. Physical processes that take place in the electron beam with virtual cathode under the action of an external harmonic signal, which leads to velocity modulation in the electron beam entering the interaction space, have been analyzed. The obtained results well agree with the data of previous experimental investigations of the signal gain in a low-voltage vircator.     

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.     

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.     

Scenario for the establishment of an electron beam “squeezed state” in a magnetically insulated vircator

A 2.5-dimensional particle-in-cell code was used to simulate different scenarios for the establishment of an electron beam “squeezed state” in a magnetically insulated vircator. Vircators with and without anode foils were compared. It was found that the squeezed state is established in both cases but the dynamics of establishment differ. Pis’ma Zh. Tekh. Fiz. 23, 29–33 (November 26, 1997)     

The influence of vacuum conditions on the microwave generation in a vircator

The effect of residual gases on the lifetime of a virtual cathode (VC) was studied. Dependence of the output pulse energy of a high-power vircator on the vacuum conditions was studied. It is demonstrated that a rough vacuum of 5×10^?4 Torr achieved with a mechanical pump is sufficient for a vircator operation without significant loss of the output radiation energy. The experimental data agree with a model of the mechanism of VC degradation as a result of the gas ionization.     

Vircator generation spectrum controlled by an external SHF signal

The possibility of controlling the vircator generation spectrum by an external SHF signal is confirmed by the results of computer simulation using the method of large particles. Duration of the vircator adjustment process is evaluated.     

Small-size ultralow-voltage generator of chaotic microwave oscillations

The scheme of a small-size ultralow-voltage generator of broadband chaotic microwave oscillations is considered. Results of numerical modeling and experimental investigation of the device prototype operating in various regimes are summarized. Good prospects of the proposed ultralow-voltage generator (vircator) are related to the relatively low accelerating voltages (below 1000 V), rather high electron beam currents (up to 800 mA), good efficiency (up to 5%), and small dimensions of the device.