Nikita S. Frolov

High-power microwave amplifier based on overcritical relativistic electron beam without external magnetic field

The high-power scheme for the amplification of powerful microwave signals based on the overcritical electron beam with a virtual cathode (virtual cathode amplifier) has been proposed and investigated numerically. General output characteristics of the virtual cathode amplifier including the dependencies of the power gain on the input signal frequency and amplitude have been obtained and analyzed. The possibility of the geometrical working frequency tuning over the range about 8%–10% has been shown. The obtained results demonstrate that the proposed virtual cathode amplifier scheme may be considered as the perspective high-power microwave amplifier with gain up to 18 dB, and with the following important advantages: the absence of external magnetic field, the simplicity of construction, the possibility of geometrical frequency tuning, and the amplification of relatively powerful microwave signals.

Generalized synchronization in the action of a chaotic signal on a periodic system

Generalized synchronization is observed during the action of a chaotic signal on generators of periodic oscillations. The features in the behavior of the synchronous regime threshold upon a change in the chaotic signal parameters are investigated. The possibility of using such devices for concealed information transfer is demonstrated.

Artificial neural network detects human uncertainty

Artificial neural networks (ANNs) are known to be a powerful tool for data analysis. They are used in social science, robotics, and neurophysiology for solving tasks of classification, forecasting, pattern recognition, etc. In neuroscience, ANNs allow the recognition of specific forms of brain activity from multichannel EEG or MEG data. This makes the ANN an efficient computational core for brain-machine systems. However, despite significant achievements of artificial intelligence in recognition and classification of well-reproducible patterns of neural activity, the use of ANNs for recognition and classification of patterns in neural networks still requires additional attention, especially in ambiguous situations. According to this, in this research, we demonstrate the efficiency of application of the ANN for classification of human MEG trials corresponding to the perception of bistable visual stimuli with different degrees of ambiguity. We show that along with classification of brain states associated with multistable image interpretations, in the case of significant ambiguity, the ANN can detect an uncertain state when the observer doubts about the image interpretation. With the obtained results, we describe the possible application of ANNs for detection of bistable brain activity associated with difficulties in the decision-making process.

Beam-plasma instability in charged plasma in the absence of ions

In the present work we have studied the novel nonlinear phenomenon of plasma physics - beam-plasma instability in a charged plasma in the absence of ions. We have shown the possibility of the instability development and analyzed the characteristics of physical processes taking place during the beam-plasma interaction.

Theoretical and experimental analysis of the microwave radiation power of a generator on a virtual cathode subjected to external harmonic exposure

Analytical, numerical, and experimental investigations of the output power of a generator are performed on a virtual cathode under the effect of an external harmonic signal. It is shown theoretically that an increase in the power of the external effect leads to an increase in the output power of a nonautonomous oscillator. The results from our theoretical analysis are in good agreement with the results from a pilot study.

Amplification through chaotic synchronization in spatially extended beam-plasma systems

In this paper, we have studied the relationship between chaotic synchronization and microwave signal amplification in coupled beam-plasma systems. We have considered a 1D particle-in-cell numerical model of unidirectionally coupled beam-plasma oscillatory media being in the regime of electron pattern formation. We have shown the significant gain of microwave oscillation power in coupled beam-plasma media being in the different regimes of generation. The discovered effect has a close connection with the chaotic synchronization phenomenon, so we have observed that amplification appears after the onset of the complete time scale synchronization regime in the analyzed coupled spatially extended systems. We have also provided the numerical study of physical processes in the chain of beam-plasma systems leading to the chaotic synchronization and the amplification of microwave oscillations power, respectively.

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.

Modeling Instabilities in Relativistic Electronic Beams in the CST Particle Studio Environment

The paper is devoted to the development of the classical vircator model in the CST Particle Studio for the investigation of the physical mechanisms of the development, coexistence, and interaction of Pierce/Bursian and diocotron instabilities in relativistic electronic streams. Such a model is numerically analyzed by the CST Particle Studio. We find that a numerical instability develops, which leads to an additional small-scale space density modulation in the electron beam during its motion in the system. We find the character time scale of the instability and determine its relation with a spatial mesh step. We study the instability in detail and propose a method to suppress it by the CST Particle Studio. Also, important notes concerning the development of models of microwave devices in the CST Particle Studio are presented.

Virpertron: A novel approach for a virtual cathode oscillator design

In this paper, we propose a novel approach for the design of a virtual cathode oscillator. As a new concept, we suggest a microwave system containing an annular relativistic electron beam travelling through the drift space with dielectric inserts characterized by different values of permittivity. In this case, a virtual cathode which is the source of powerful electromagnetic oscillations forms at the junction of different dielectric materials. According to the mechanism of virtual cathode formation, we have called this device as a virpertron. We have carried out a detailed numerical investigation of virtual cathode formation features in this system via 3D electromagnetic PIC-simulation using CST Particle Studio. We have also studied the spectral properties of the microwave radiation generated by the virpertron.

Perspective sub-THz powerful microwave generator nanovircator for T-rays biomedical diagnostics

In this paper we suggest the new approach of powerful sub-THz signal generation based on intense electron beams containing oscillating virtual cathode. Suggested compact microwave source complies with a number of biomedical applications such as imaging, preventive healthcare, etc. In this work we discuss the results of numerical simulation and optimization of the novel device called “nanovircator” that have been carried out. The results of the numerical study show the possibility of “nanovircator” operation at 0.1-0.4 THz frequency range.