V.A. Chernikov

Freely localized microwave discharge in a supersonic gas flow

A discharge produced by a focused microwave beam in a supersonic gas flow has been investigated experimentally. It is shown that the degree of ionization and the gas temperature in the discharge are fairly high and that the main properties of the discharge plasma are only slightly affected by the supersonic air flow. Discharges produced by focused microwave beams can find application in supersonic plasma aerodynamics.

Experimental investigations of the distribution of pulsed-plasma-generator radiation at its various spatial orientation and global anisotropy of space

Abstract Results of experimental investigation of plasma luminous emittance (integrated with respect to time and quartz transmission band spectrum) of a pulsed plasma generator depending on its axis spatial position, are presented. It is shown that the spatial distribution of plasma radiant intensity is of clearly anisotropic character, that is, there exists a cone of the plasma generator axial directions in which the radiation of plasma reaches its peak. A possible explanation of the results obtained based on a hypothesis of global anisotropy of space caused by the existence of a cosmological vectorial potential A g , is given. It is shown that the vector A g has the following coordinates in the second equatorial coordinate system: right ascension α=293°±10°, declination δ=36°±10°. The experimental results are in accordance with those of the earlier experiments on determining the direction of A g .

Microwave and Direct-Current Discharges in High-Speed Flow: Fundamentals and Application to Ignition

DOI: 10.2514/1.24803 The main parameters and properties of an electrodeless freely localized microwave discharge, a surface microwave discharge, transversal in relation to the gas flow direct-current and pulse-periodic electrode discharges, andacombined microwavedirect-current dischargeareexperimentally investigated.It isshown thatalltypesof the discharges result in a reliable ignition of hydrocarbon fuel. Combustion of a propane–air supersonic stream is realized under condition of the combined surface microwave and direct-current discharge. To find out the influence ofdifferent channels ofenergy transfer onignition ofcombustible mixtures in asupersonic flow,the kinetic modelof ignition of hydrocarbons–air mixtures, and taking into account the influence of electric field on processes of dissociation molecules and creation of the active radicals, excited and charged (electrons, positive and negative ions) particlesunderconditionsofnonequilibriumplasmaofthegasdischargewasdeveloped.Mathematicalmodelinghas revealed a strong influence of the reduced electric field on induction period. The microwave discharges may find applications in different fields of supersonic plasma aerodynamics and in development of new-generation plasma sources for plasma chemistry, nano- and microelectronics purposes (plasma treatment of surfaces, etching, and film deposition), and so on.

Surface microwave discharges in air

A microwave discharge excited on the outer surface of a dielectric antenna has been investigated. The transverse and longitudinal dimensions and propagation velocities of the discharge have been measured as functions of the air pressure and the power and duration of the exciting microwave pulse. The spatial distributions and time evolution of the gas temperature, electron density, and radiation intensity of the discharge have been determined. It is shown that the degree of ionization of the discharge plasma can exceed 10%. The spatial distribution of the electron density is found to depend strongly on the air pressure.

Microwave Discharge on the Surface of a Dielectric Antenna

A microwave discharge initiated by a surface wave on a dielectric body placed in a supersonic air flow is studied. The discharge is shown to represent a thin plasma layer that uniformly covers the antenna surface. In experiments, the discharge propagation velocity may be as high as 100 km/s, which is several orders of magnitude higher than the velocity of sound in air. The peak pulse power necessary to excite the discharge in a wide range of air pressures (from 10−3 to 103 Torr) is no higher than 100 kW. It is shown that the gas temperature may rise to 1000–2000 K, rapidly increasing (with a rate of ≈50 K/μs) at the early stage of discharge evolution. The discharge of this type may find applications in super-and hypersonic plasma aerodynamics (such as control of the flow near the surface of a body moving in a dense atmosphere, reduction of surface friction, optimization of ignition and combustion conditions for supersonic flows of gaseous fuel, etc.). It may also be used to advantage in development of new-generation plasma sources for micro-and nanoelectronics purposes (plasma treatment of surfaces, etching, and film deposition).

High-voltage pulse discharge propagating along a water surface

The results are presented of experimental studies of electrical discharge occurring in the atmosphere along a free water surface between a spike above the water surface and a remote submerged electrode during quasi-rectangular high voltage pulses. Three stages of such discharge are identified, and the stage of the discharge gliding along the water surface is investigated.

Transverse Electric Discharges in Supersonic Air Flows: Microscopic Characteristics of Discharge

The spectroscopic and probe methods are used to measure the microscopic parameters of plasma of pulsed and stationary transverse discharges in a supersonic air jet flowing into a submerged space. The measurements are performed for the Mach number of flow M = 2, submerged space pressure p = 5 to 30 kPa, degree of the jet being off-design n ∼ 2, and discharge current I = 1 to 10 A. The discharge current dependences of the average values of gas temperature, charged particle concentration, and reduced electric field are measured for a discharge mode close to that of current generator. The measured values of gas temperature lie in the range of 1 to 3 kK, those of charged particles concentration — of 1013 to 1014 cm-3 , and of reduced electric field — of 40 to 20 Td. The axial distribution of temperature is characterized by high values of temperature even at short distances from the electrodes and by a slow decrease along the flow.

Corona Discharge Over Liquids With Powder Addition

Corona discharge over a surface of alcohol, water, and kerosene with aluminum powder addition is applied to realize and visualize a number of electrohydrodynamic phenomena at the interaction of the discharge with a surface of the liquid. Thin aluminum powder film allows to visualize funnels and motion in them appearing under an ion wind impact.

Negative Corona Discharge Over a Surface of Alcohol

Negative corona discharge over a surface of alcohol was applied to realize and visualize a number of electrohydrodynamic phenomena at the interaction of the discharge with a surface of the liquid (alcohol). Two phenomena - a bursting jet and a liquid column with charged head - are presented.

Combined M W-DC Discharge in a High Speed Propane -Butane -Air Stream

The mechanism of the gas -phase oxidation of various combustible gases, including hydrocarbons and hydrogen, has been thoroughly studied, with the emphasis on their ignition mechanism. The great majority of publications in this field have dealt with factors determining the induction per iod preceding the ignition event. In recent decades, there has also been much literature discussing the possibility of effectively controlling combustion processes by various physical means. Use of the gas discharge is one of such ways , promoting an intens ification of chain combustion of hydrocarbons. However, the ignition kinetics is not completely understood even for the rather simple model system hydrogen -oxygen under low -temperature gas -discharge plasma conditions, which are established at large values of the reduced electric field. Therefore, for a deeper insight in the physicochemical processes occurring in the low -temperature plasma initiation of the ignition of a combustible gas, the experimental study of the effect of a gas discharge on the ignition event should be fulfilled and accompanied by mathematical modeling. The study of the ignition and combustion of hydrogen -containing mixtures under low -temperature plasma conditions is of importance from various standpoints: it is necessary to carry out b oth fundamental research in the mechanism and kinetics of atom -molecule reactions in a strong electric field and an analysis of a variety of applied problems, including the optimization of plasma chemical processes. One important problem is to develop the physical principles of the burning of high speed flow of combustible gases. Under such conditions it is necessary to ensure a rapid space ignition of the high -velocity hydrocarbon flow. To do this, it is necessary to minimize the induction period. In our l aboratory, we initiate d ignition with dc discharges (either longitudinal or transverse to the flow), periodic pulsed discharges, and freely localized and surface microwave discharges. Initially, the effect of low temperature plasma on the combustion kineti cs of a gaseous fuel was experimentally studied for a propane -butane air flow with a Mach number of M=2. Our experimental setup consists of a cylindrical vacuum chamber with an inner diameter of 1 m and a length of 3 m, a high -pressure air receiver, a high -pressure propane -butane receiver, a system for mixing the propane -butane mixture with air, a system for producing a high speed propane -butane -air flow, an aerodynamic channel, a discharge section, different plasma generators, a pulsed high -voltage power s upply, a synchronization system, and a diagnostic system. The air flow rate can be varied between 25 and 100 g/s; the propane -butane flow rate, between 1 and 8 g/s. The basic part of this setup is the vacuum chamber, which serves to produce a high speed fl ow and is a reservoir for the exhaust gases and combustion products. The vacuum systems allows operation in a wide pressure range of p=10 -3 -10 3 torr . We used some types of a gas discharge for ignition: freely localized microwave discharge , surface microwav e discharge, direct current discharge, and pulsed transverse electrode discharge. The ignition of the high speed stream was detected as a glow in the aerodynamic channel downstream of the discharge section. No glow was observed when a gas discharge was gen erated in an air flow, when it was generated in a high speed propane -butane -air flow but its parameters (pulse duration, discharge current, electric field strength in the plasma, and the electric power deposited in the discharge) were inappropriate for ign ition, or when the mixture was far from stoichiometric. Induction time was simultaneously derived from different measurements: (1) the minimum pulse duration resulting in a glowing flame in the aerodynamic channel downstream of the discharge section; (2) the time taken by the intensity of the molecular band of the excited CH * radical (the (0;0) band due to the A 2 ��X 2 � transition), with an edge wavelength of �=431.5 nm, to achieve the maximum growth rate;