K. V. Aleksandrov

Investigations of Subcritical Streamer Microwave Discharge in Reverse-Vortex Combustion Chamber

In this paper, we report on the experimental investigations of two innovative technologies combined in one device, namely, the application of an initiated streamer microwave (MW) discharge for ignition and flame control in a reverse-vortex combustion chamber, also known as a Tornado combustor. The pulsed subcritical streamer MW discharge (SSD) in a quasi-optical wave beam was experimentally investigated in the atmospheric-pressure model of a Tornado combustor with transparent dielectric walls. The possibility of a surface MW streamer discharge formation at new conditions, particularly on the dielectric walls of the cylindrical combustion chamber, has been confirmed. The mechanism of SSD realization, at which the discharge development takes place in a volume of the combustion chamber, has been proposed. It was shown that SSD could be applied for ignition of fuel/air mixtures in an axial area of the reverse-vortex combustion-chamber bottom plate, which is normally used for a fuel feeding.

Domains of Existence of Various Types of Microwave Discharge in Quasi-Optical Electromagnetic Beams

High-and medium-pressure discharges excited by quasi-optical microwave beams in air are classified using experimental data. Diffuse, streamer, overcritical, undercritical, and deeply undercritical discharges are distinguished. The domains of existence of each type of discharge are determined as functions of the air pressure and field strength for two particular electromagnetic wavelengths.

Microwave breakdown of air initiated by a short electromagnetic vibrator

The electrical breakdown of air (under a pressure from several tens of Torr to several hundreds of Torr) is initiated in a linearly polarized quasi-optical microwave beam using a rounded-end cylindrical metallic electromagnetic vibrator placed parallel to the electric component of the microwave field. The vibrator is much shorter than the wavelength of the field. The field strength at the top of the vibrator as a function of its length is determined. An empiric expression relating the field strength at the top with the vibrator length-to-diameter ratio is found for the vibrator length range studied. The practicability of locally measuring the field in a quasioptical microwave beam is substantiated. The idea is to determine the maximal air pressure at which electrical breakdown of air initiated by a short vibrator placed at a given point of the beam takes place.

Surface streamer microwave discharge

An atmospheric-pressure pulsed microwave discharge on the surface of an insulating plate and between two insulating fllms is considered. The discharge is initiated in a quasi-optical microwave beam away from the beam-forming elements. The TEM field of the beam is less than the critical breakdown value. The initiator is a metallic dipole placed either directly on the plate surface facing away from the radiation source or between the films. The discharge has the form of branching streamer channels adjacent to the surface and filling up the cross section of the microwave beam with a field level higher than the value separating the subcritical and highly subcritical forms of the microwave streamer discharge.

Electromagnetic vibrator: An initiator of air breakdown in the subcritical field of a quasi-optical microwave beam

The subject of investigation is the resonance properties of cylindrical electromagnetic vibrators with different diameters and spherically rounded ends acting as initiators of air breakdown in the subcritical field of a quasi-optical microwave beam. The vibrator is placed both in the field of a traveling electromagnetic wave and at the antinode of the field above a screen inserted in the microwave beam. The shortening of the half-wave vibrator that governs its ability to initiate air breakdown, the field at the top-pole of this vibrator, and a tolerance on its resonance length are found from experimental data.

Electric discharge in air in a deeply subcritical field of a quasi-optical microwave beam

We describe the results of experiments on initiation of an electric discharge in air in a quasi-optical microwave beam by an electromagnetic vibrator fixed above the screen. This method for initiating the electrical breakdown makes it possible to obtain a discharge at a level of the electric field component in the microwave, which two orders of magnitude lower than the minimal critical field of the electrodeless breakdown of air. In our experiments, the threshold value of the air pressure determining the low- and high-temperature forms of the microwave discharge are determined depending on the field level.

An electromagnetic vibrator fixed on a screen initiates gas breakdown in the subcritical field of a microwave beam

Results of experimental investigation of the electric breakdown of air in a quasi-optical microwave beam with a deep subcritical field level are presented. The breakdown was initiated by a linear or Γ-shaped electromagnetic (EM) vibrator fixed on a screen. It is established that a vibrator positioned above the screen at a distance shorter than quarter-wavelength of the EM field can induce the electric breakdown of air at high pressures and relatively low field level. Using a Γ-shaped EM vibrator, it is possible to preset the spatial region of breakdown.

Regular set of gas discharges on the surface of a dielectric in a quasi-optical microwave beam

Various ways of producing a regular set of plasma objects in the field of a quasi-optical microwave beam using passive vibrators are considered. These objects provide the basis for a periodic vortex structure on the surface of an immersed dielectric body. The properties of a deeply subcritical surface discharge in the flow, as well as its structure and spatial and energy characteristics, are described.

Boundary-Layer Control Based on Localized Plasma Generation: Development of the Microwave System

,The brief review of the results of theoretical and experimental investigations of advanced method of boundary-layer control based on localized plasma generation obtained in frames of the three-year joint project CRDF #UKE2-1508-KV-05 are presented in this paper. Emphasis is placed on the electrodynamic aspects of the developed method in laboratory conditions in Moscow Radiotechnical Institute and at carrying out of final experiments on multidisciplinary wind-tunnel installation in Institute of Hydromechanics and National Aviation University in Kiev. The main problem had fundamental character and consisted in development of unique electrodynamic multisystem of close located initiators of microwave (MW) discharges on a dielectric surface in “free-space” conditions. Herewith it was initially necessary to solve the problem of creation of a uniform field distribution in such system in a field of plane electromagnetic (EM) wave, i.e. to solve the problem of multimode excitation of such arrays of EM vibrators. At the same time already the first experiments have highlighted a number of other engineering problems. First, it was necessary to develop new irradiating electrodynamic system providing quite uniform field distribution on a model surface in real conditions of experiment in the working chamber of the wind tunnel. Secondly, the periodic system of multiple MW discharges had to be generated at a remote irradiation of model and simultaneously at limited power of the MW radiation source. All the specified problems have been successfully solved. Physical grounds of creation of regular system of multiple MW discharges on a dielectric surface of a streamline body were developed. This allowed not only to confirm feasibility and high efficiency of the proposed method but also to determine prospects of its further development.

Pulsed microwave discharge in atmospheric air in the focus of a two-mirror resonator

Free-localized pulsed microwave discharge in atmospheric air in the focus of an open two-mirror high-Q resonator excited by linearly polarized electromagnetic radiation with a wavelength of 4.3 cm is described. This discharge is analogous to the previously studied streamer resonance microwave discharge ignited under similar conditions but with an electromagnetic radiation wavelength of 8.9 cm. Starting from a certain overcritical electric field, the discharge plasma channel has a high-temperature core.