Vladimir N. Kornienko

Development of the system for visualization of electric conductivity distribution in human brain and its activity by the magnetic induction tomography (MIT) method

Currently rapid development of functional activity researches of human brain sets the problem of reliable and non-invasive detection of mental processes and states. At present we know some traditional methods of rapid and contactless acquisition of brain activity characteristics, such as functional tomography (fMRI) and magnetoencephalography. But these methods have low temporal resolution, complicated and ambiguous association of measured values with information processes in brain. So possibility of MIT application is investigated. Estimation of possibility of such changes registration is performed. Investigations of magnetic field configuration, schematics of transmit-receive modules and numerical algorithms are in progress. It may allow us to register high speed conductivity changes in brain tissues.

Efficiency improvement in relativistic Cerenkov devices due to dynamic cyclotron resonance

The efficiency enhancement in relativistic electron devices with linear electron beams guided by homogeneous magnetic fields due to combined Cerenkov-cyclotron interaction has been studied. The case considered is when electrons do not satisfy the cyclotron resonance condition initially, but start interaction with an electromagnetic field under the condition of pure Cerenkov synchronism. Then, the changes in electron energy due to the Cerenkov interaction lead some electrons to satisfy the cyclotron resonance condition. This effect, called the dynamic cyclotron resonance, may play a significant role in strongly nonlinear regimes of a primary interaction when an electron beam is separated into groups of accelerated and decelerated particles. For the case of the primary Cerenkov interaction, two groups of accelerated and decelerated electrons can exist which interact with the RF field under the same Cerenkov resonance condition, but due to dynamic shifts in electron cyclotron frequencies, can resonantly interact with different harmonics or the gyrofrequency. It is shown by numerical simulations that the efficiency can be improved 25-28% for typical Cerenkov interaction up to 50% by choosing an appropriate value of the focusing magnetic field.

Nonstationary fluid dynamics under exposure to nanosecond voltage pulses

A numerical analysis of the liquid motion in a spherical capacitor under the applied voltage pulse with a duration of several nanoseconds and a peak value to 300 kV is performed. A system of hydrodynamics equations written in the general form in the spherical coordinate system and the Tait equation of state are used to simulate the liquid motion. The electrostrictive pressure is calculated for a liquid in the form of a dipole dielectric.

Optimization of a combined high-power ultrawideband antenna

The results of optimization of the geometry of a combined ultrawideband antenna excited by a 1-ns bipolar pulse are presented. Numerical and physical experiments have been performed to optimize the increase in the electric-field strength in the direction of the antenna main beam. It has been shown that the peak field strength can be increased by 6%.

Generation of attosecond relativistic electron jets in laser pulse interaction with gas targets

Formation of attosecond relativistic electron jets from tape gas targets of subcritical concentration with a powerful ultra-short laser pulse is considered. Achievable characteristics of the jets are found. It is shown that for some range of parameters, a single relativistic electron mirror can be formed, which is appropriate for generation of coherent attosecond x-ray pulse using the counter reflection of the probe laser pulse.

Nonlinear reflection of high-amplitude laser pulses from relativistic electron mirrors

A coherent X-ray pulse of attosecond duration can be formed in the reflection of a counterpropagating laser pulse from a relativistic electron mirror. The reflection of a high-amplitude laser pulse from the relativistic electron mirror located in the field of an accelerating laser pulse is investigated by means of two-dimensional (2D) numerical simulation. It is shown that provided the amplitude of the counterpropagating laser pulse is several times greater than the amplitude of the accelerating laser pulse, the reflection process is highly nonlinear, which causes a significant change in the X-ray pulse shape and its shortening up to generation of quasi-unipolar pulses and single-cycle pulses. A physical mechanism responsible for this nonlinearity of the reflection process is explained, and the parameters of the reflected X-ray pulses are determined. It is shown that the duration of these pulses may constitute 50 – 60 as, while their amplitude may be sub-relativistic.

Dynamics of an ensemble of cyclotron oscillators in the field of a charged filament

The effect of an external static radial electric field on the characteristics of a superradiation pulse of an ensemble of cyclotron oscillators is investigated in a numerical experiment. It is demonstrated that this external field alters the amplitude, the width, and the peak time of the radiation generated by this active medium.

Nonstationary fluid dynamics in inhomogeneous electric field

Summary form only given. Formation of voids (micro-pores) in a vicinity of a pin electrode in a highly non-uniform electric field applied within a few nanoseconds was proposed recently as a main mechanism of electrical breakdown of liquid dielectrics1. We solve the problem of fluid dynamics when voltage pulse duration of 7 ns with a peak value of 300 kV was applied to a spherical electrode - plane setup. Motion of liquid (water) is described by the system of equations of hydrodynamics written in general terms in the spherical coordinates and the Tait equation of state. Electrostrictive force is taken in a form proposed for polar dielectrics2.Action of electrostrictive forces results in the formation of a shock wave, which propagates from the spherical electrode. The speed of the shock front reaches 3 Mach numbers. The rarefaction region is formed before the shock front, duration and peak value of which increases in a few nanoseconds. At some point, the negative pressure reaches a value at which liquid is ruptured and microcavity can be formed. The size of the cavities is determined by the rate a shock front growth. It is demonstrated that the size of cavities is sufficient to accelerate electrons to the energies of ionization of molecules of water vapor in the cavity.

Response of an isolated ensemble of cyclotron oscillators with discrete spectrum to a short electromagnetic pulse

Electromagnetic radiation of a wideband ensemble of cyclotron oscillators after the action of a short pulse is considered. It is shown that a periodic response is formed in the system. The energy and spectral characteristics of this response are studied. Possible collective mechanism of formation of this response is proposed.

3D computer simulation of the coherent radiation formation in multiwave cerenkov generator

Summary form only given. Earlier (34th ICOPS-2007) we presented the results of computer simulation of the multiwave cerenkov generator (MWCG) obtained by means of an axially symmetric numerical model. However, many physical processes accompanying the formation of coherent radiation remained unclear.