A. A. Badarin

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.

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.

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.

Multistability in a relativistic electron beam with an overcritical current

The multistability effect of relativistic electron beam behavior, particularly the coexistence of three modes of typical behavior, is revealed in a numerical investigation. These modes are characterized by a virtual cathode with two, four, or five potential minima in the azimuthal direction rotating around the drift space axis.

Brain-computer interface on the basis of EEG system Encephalan

We have proposed brain-computer interface (BCI) for the estimation of the brain response on the presented visual tasks. Proposed BCI is based on the EEG recorder Encephalan-EEGR-19/26 (Medicom MTD, Russia) supplemented by a special home-made developed acquisition software. BCI is tested during experimental session while subject is perceiving the bistable visual stimuli and classifying them according to the interpretation. We have subjected the participant to the different external conditions and observed the significant decrease in the response, associated with the perceiving the bistable visual stimuli, during the presence of distraction. Based on the obtained results we have proposed possibility to use of BCI for estimation of the human alertness during solving the tasks required substantial visual attention.

Processes of virtual cathodes interaction in multibeam system

Two variants of schemes of a multibeam vircator are proposed and studied in this paper. Numerical analysis of the influence of various parameters of these systems (magnitude of the external magnetic field and detuning of beam currents) on the generation characteristics was conducted. The possibility of synchronizing several virtual cathodes in a single drift space of a multibeam vircator is demonstrated. The regime maps of basic control parameters of the system are built. The possibility of effective interaction of several virtual cathodes in a single drift space is analyzed, and the conditions for implementing an effective addition of powers of each beam at the output load are determined.

Simulation of the development and interaction of instabilities in a relativistic electron beam under variation of the beam wall thickness

The development and interaction of Bursian and diocotron instabilities in an annular relativistic electron beam propagating in a cylindrical drift chamber are investigated analytically and numerically as functions of the beam wall thickness and the magnitude of the external uniform magnetic field. It is found that the interaction of instabilities results in the formation of a virtual cathode with a complicated rotating helical structure and several reflection regions (electron bunches) in the azimuthal direction. It is shown that the number of electron bunches in the azimuthal direction increases with decreasing beam wall thickness and depends in a complicated manner on the magnitude of the external magnetic field.

Recuperation in superpower Cherenkov generators with a nonuniform magnetic field

We consider an effective method for increasing the total efficiency of relativistic Cherenkov generators, viz., recuperation. It has been found that, for a generator with an efficiency smaller than 15%, recuperation makes it possible to obtain an increase in the efficiency that exceeds 50% (from 12% to 68%). In generators with initially high efficiency (more than 50%), recuperation may turn out to be ineffective.

Generation of higher harmonics in relativistic electron beam with virtual cathode

The study of the generation regimes with intense higher harmonics taking place in a high-power vircator [1] consisting of a relativistic electron beam (REB) with a virtual cathode (VC) has been made. The characteristics of these regimes, in particular, the typical spectra of output signal and their variations with the change of the system parameters (beam current, the induction of external magnetic field) as well as physical processes occurring in the system have been analyzed by means of 3D electromagnetic simulation in CST Particle Studio. The model under study consists of the perfect electric conducting finite-length cylindrical waveguide region (electron beam drift chamber) with the grid electrodes at both ends under the same potential and axially symmetrical at the entrance monoenergetic overcritical annular REB travelling through the drift chamber. Let us note, that the frequency of the fundamental component (the first harmonic) in the spectrum is determined by the value of the disturbed plasma frequency [1].

Study of oscillation modeswith intensive higher harmonics in a relativistic electron beam with a virtual cathode

This work presents the results of the study of nonlinear oscillations of a relativistic electron beam with a virtual cathode in the cylindrical drift space depending on external magnetic field values, current and initial energy of injected electrons of the relativistic beam. Special attention was given to the analysis of higher harmonics of fundamental frequency of virtual cathode oscillations with the change of system control parameters. The numerical simulation was carried out by means of CST Particle Studio software package for three-dimensional electromagnetic simulation. The complex dynamics of virtual cathode in the relativistic electron beam were found out. Particularly, these were defined areas in the plane of the control parameters “beam current - magnetic field” where the first/second/third harmonic of current oscillations was maximal.