Search

We consider the realization of rotation of particles with a photoinduced dipole moment in the absence of an external field source. The effects considered here are based on the mechanism of the orientational interaction of at least a pair of particles that are photodipoles. We consider examples of realization of this mechanism including the geometry corresponding to the Quincke photorotation. From the point of view of applications, the variety of self-rotation in the case of a single photodipole located on or near a metal surface can be of interest. The torque for spherical particles with a radius of 10 μm is estimated.

We report on the results of experimental investigation of forced action of a deeply subcritical microwave discharge initiated in a quasi-optical electromagnetic beam on bodies placed into a supersonic air flow.

The results of experimental studies of combustion of propane–air gaseous mixture when it was ignited by a microwave discharge have been described. The mixture with different propane content fills a sealed radio-transparent tube placed along the axis of a focused linearly polarized quasi-optical microwave beam at atmospheric pressure. Multi-point ignition of the mixture is carried out near one end of the tube by a pulsed microwave discharge with a surface-developed streamer structure. The growth of gas pressure in the tube as propane burned was recorded in the experiments. The microwave pulse energy being invested in high-temperature discharge plasma has been estimated in them. The minimum percentage of propane in the mixture at which the microwave discharge ignites it has been determined in experiments. The time dependence of the pressure increase in the tube as the propane burns determines the combustion process dynamics.

The feasibility of air breakdown initiation by a quasi-optical subcritical-field microwave beam has been studied experimentally. Breakdown has been initiated by a linear electromagnetic vibrator, which was placed in a traveling electromagnetic wave (i) on the surface of a dielectric sheet that faces wavevector k of the wave, (ii) on the opposite surface of the sheet, and (iii) near the sheet. Fields induced at the ends of the vibrator have been calculated theoretically for all arrangements. Numerical estimates and experimental data have shown that when a vibrator is placed on a dielectric surface, electrical breakdown of air may be initiated in a much deeper subcritical field of the microwave beam than when it is placed in the field of a traveling microwave.

Microwave discharges initiated by an electromagnetic (EM) vibrator and ignited on the inner surface of a dielectric tube in a quasi-optical EM beam are experimentally studied. A threshold level of the microwave field that separates domains of subcritical and deeply subcritical microwave discharges is determined in experiments. Experiments show that streamer channels of the subcritical discharge propagate from the initiator along the propagation direction of the EM wave and in the opposite direction under certain conditions. Variations in the power of the microwave beam can be used to change length of the plasma region of the subcritical discharge along the wave vector of the microwave beam and control the level of the EM energy absorbed in the plasma regions of the deeply subcritical microwave discharge.

Results of experiments on a propagation of a pressure wave with a shock-wave leading front through a gas region excited by a pulsed freely localized discharge of the microwave wavelength range are described. The discharge was realized in air at a pressure from 14 to 100 Torr in the focal region of a quasi-optical electromagnetic beam of the microwave wavelength range. The experiments revealed three types of interaction of the gas-dynamic pulse with the region excited by the discharge in the post-discharge mode. The specific type of interaction is defined by the initial structure of the discharge and the delay time of the gas-dynamic pulse passage through the excited region. Keywords: aerodynamics, microwave discharge, pressure wave.

The rotation of a spherical particle in a constant electric field (an effect found earlier) has been analyzed. The particle is illuminated to induce the electric dipole moment of the sphere. The dynamics of the rotation effect has been considered in general terms to refine conditions for adiabatic rotation. The features of the particle’s nonadiabatic rotation have been demonstrated with a sphere placed in a medium with an infinitesimal viscosity. It has been shown that the nonadiabatic rotation dynamics to a great extent depends on a relationship between the electrical and photoinduced dipole moments of the sphere. The rotation dynamics of a particle with a slightly nonspherical shape has been briefly analyzed.

Experiments on initiating an electrical discharge with a developed streamer structure in atmospheric pressure air are described. The discharge was initiated in a quasi-optical linearly polarized microwave beam with a subcritical field. Air breakdown was initiated by an electromagnetic vibrator placed in free space, on the surface of a dielectric plate, and on the outer or inner surface of a quartz tube. From experimental data, the velocity of the discharge front propagation toward the wavevector of the electromagnetic wave has been estimated.

Experimental data on electrical breakdown of air in a linearly polarized traveling microwave with a deeply subcritical field are presented. Breakdown is initiated by a linear electromagnetic vibrator or a set of vibrators. They are placed over a metal surface the plane of which contains the wavevector of the microwave and its electrical component. The axes of the vibrators are parallel to this component, and their distances to the metal surface are shorter than the quarter-wavelength of the field. In experiments with the single vibrator, this distance is varied. When the set of vibrators is used, they were placed one after another along the wavevector of the field.

The results of experimental studies on using an electrical discharge with an extended streamer structure in a quasioptical microwave beam in the multipoint ignition of a propane–air mixture have been reported. The pulsed microwave discharge was initiated at the interior surface of a quartz tube that was filled with the mentioned flammable mixture and introduced into a microwave beam with a subbreakdown initial field. Gas breakdown was initiated by an electromagnetic vibrator. The dependence of the type of discharge on the microwave field strength was examined, the lower concentration threshold of ignition of the propane–air mixture by the studied discharge was determined, and the dynamics of combustion of the flammable mixture with local and multipoint ignition were compared.