I. N. Onishchenko

Dielectric wake-field generator

Wake-fields excited in a dielectric media can be applied both for particles acceleration and for HF-power generation. In the present work theoretical and experimental investigations are represented on the generation of the electromagnetic wake-fields in the dielectric tube by a sequence of the relativistic electron bunches. The obtaining of the peaked high power due to the coherent superposition of the wake-fields of the regular sequence of bunches and multi-mode operation has been investigated. The measurements of wake-fields output power and the beam electron energy losses and were performed.

Obtainment of electromagnetic radiation at interaction of electron beam with ring plasma waveguide

One of the principle purposes is the research of the most effective method of extraction of energy of the oscillations excited by an electron beam from plasma into the outer space or high frequency (HF) tracks. The most attractive solution of this problem, is presented with hybrid plasma waveguides that combine advantages of the both plasma waveguides and the standard slow wave structures.

Electrodynamics of plasma-filled diffraction generator

For determining the possibility of the creating beam-plasma generators in mm range the electrodynamic properties of the structure that consists of a sequence of metallic rings filled with plasma and surrounded by a metallic screen has been investigated. The excitation of HF-oscillations is produced by an electron beam. The dispersion characteristics, field topography, and HF-power flow distribution and their dependence on plasma density have been determined. The dispersion equation was obtained using the method of partial regions: I-inside of rings space, II-outside of rings up to metallic screen, and III-boundary region between them. Finding fields from Maxwell equations with permeability tensor and matching them at region III using the condition of Pointing vector continuity transcendental equation was derived for numerical analysis. Dispersion curves shifted with plasma density increase and allows to regulate the generated frequency. In the vacuum case, modes resonant with the e-beam have surface characteristics that result in low amplification coefficient. The ratio of power flow in region II to one in region I is 0.48 for the principle mode for the parameters considered. This demonstrates the possibility of such systems to take off the generated HF-power. Thus, plasma filling was considered as a tool for generation enhancement.

The exciting of the wake field in the dielectric waveguide

A theoretical analysis and numerical simulation of wake-field excitation in a dielectric-lined waveguide for the generation of peaked high power emission are carried out. The theory of wake-field excitation by a single electron bunch in a dielectric-lined circular waveguide is developed, and simulation results of wake-field excitation for linear and nonlinear stages of the process are presented.

Electrodynamics of wide spectrum plasma waveguide surrounding with a periodic succession of metallic rings

Summary form only given, as follows. Hybrid plasma slow-wave structure as a combination of conventional structure and plasma waveguide is promising for wideband HF-devices with enhanced efficiency. In the present investigations the periodic succession of metallic rings surrounding a plasma waveguide is considered. The dispersion characteristics, field topography, HF-power distribution, growth rate and efficiency estimations are presented. The possibility of wide-band high frequency generation in the structures considered is shown.

Focusing of relativistic electron bunches at the wake-field excitation in plasma

Analytical and numerical investigations of the trajectories of probing beam electrons in a two dimensional wake-field, generated in a plasma by a dense bunch of relativistic electrons with Gaussian longitudinal and transverse distributions of density have been carried out. Based on the calculations of probing beam deviations, the diagnostic instruments are developed for the parameters of experiments conducted at NSC KIPT. The diagnostic instruments include an electron gun generating a 10 keV electron beam with a current of 10 /spl mu/A and 2 mm in diameter, which passes through the chamber of interaction and falls on the collector of 10 mm diameter. The collector (screen) is placed in front of the first plate of a microchannel amplifier which consists of three microchannel plates (MCP) with sizes between 20 and 30 mm. The 3 kV voltage was applied to each plate. The total amplification of MCP amplifier is 10/sup 4/ to 10/sup 5/ depending on the number of particles incident on the first plate. As a result of probing beam deviations due to the excited wake-field, the electrons fall on the first plate of the amplifier and are registered by its anode located behind the third plate. The calculated probing beam deviations and the amplification attained with the MCP amplifier permit one to detect and investigate the electrical wake-fields excited by a sequence of relativistic bunches ( number of particles in a bunch is 2/spl middot/10/sup 9/, energy is 14 MeV) in a plasma of 10/sup 11/-10/sup 13/ cm/sup -3/ density. The intensity of the fields registered by this technique is no less than 2 kV/cm.

RF-breakdown in ionosphere by two-frequencies radiation

The HF-breakdown in ionosphere by electric fields of two electromagnetic waves with close frequencies is studied. The essence of this type of discharge concludes in the following. Under the action of the ponderomotive force caused by the fields of two electromagnetic waves, the electrons gain the energy /spl epsiv//sub p/ that is compares to the ionization energy of the gas /spl epsiv//sub p//spl sim//spl epsiv//sub i/. This process is faster than direct ionization in the field of separate waves. Consequently the power of the HF source is essentially decreasing. As a result of this breakdown mechanism the plasma is produced of density needed for resonant excitation of plasma wave at parametric three-waves interaction. In the field of the plasma wave the essential acceleration of the breakdown process occurs. It is explained by the fact that the threshold field lowers with frequency decreasing linearly and maximum value of the plasma wave field that is saturated at nonlinear three-waves interaction stage is proportional to the squared root of frequency. Hence, if plasma frequency is more less comparatively to wave frequencies the ionization of the gas will occur in the plasma wave field even at the amplitudes of electromagnetic waves less the threshold breakdown value. The maximum value of plasma waves and growth rate of breakdown are found for the given power of two electromagnetic waves. Some experimental examples are represented on beat-wave excitation of plasma wave and breakdown in ionosphere. It is considered the plasma wake field by using high power short electromagnetic pulse or succession such pulses.