Gas-dynamics of the propagation of a microwave discharge excited by the H 10 waveguide mode

A two-dimensional gas-dynamic model is applied to calculate the characteristics of the steady-state propagation of a microwave discharge excited by the H ₁₀ waveguide mode. The stream pattern is found on the basis of gas dynamics of a slowly propagating discharge, taking into account the non-one-dimensional character of the gas flow ahead of the discharge front. The calculated values of the propagation velocity agree with the experimental results.     

Studies of pulsed and continuous microwave discharges used to deposit diamond films

Results are presented from optical measurements of the atomic hydrogen density and the gas temperature in a reactor for depositing diamond films from the plasmas of pulsed and continuous microwave discharges at a fixed mean microwave power. The results obtained make it possible to explain the fact that the growth rate of diamond films in the plasma of a pulsed microwave discharge is larger than that in a continuous microwave discharge.     

Spectroscopic measurements and numerical simulations of the electrode plasma of an electrode microwave discharge in hydrogen

The structure of an electrode microwave discharge in hydrogen at pressures of 1–8 torr and incident powers of 20–100 W is studied using optical spectroscopy. A two-dimensional computer code is developed for self-consistently simulating a self-sustained steady-sate electrode microwave discharge ignited at the end of the inner conductor of a coaxial line. The model is based on simultaneously solving time-dependent Maxwell’s equations, the balance equations for charged particles, and a homogeneous Boltzmann equation. The numerical results referring to the electrode region of the discharge are in fair agreement with the experimental data. This confirms the early suggestion (inferred from experimental data) of the combined “self-sustained-non-self-sustained” character of the electrode discharge. It is shown that the self-sustained discharge domain is located in the electrode region of the discharge.     

Multipactor discharge on a dielectric at different inclination angles of the microwave electric field relative to the dielectric surface

Multipactor discharge on a dielectric is studied numerically and analytically for different inclination angles α of the microwave electric field with respect to the dielectric surface. The power absorbed in the discharge is calculated, and analytic estimates for the average current density of secondary electrons and the average energy of electrons bombarding the dielectric surface are obtained as functions of the angle α and the electron oscillation energy in the microwave field. It is found that the dependence of the absorbed power on the inclination angle of the external microwave field has a minimum at α ～20°–30°.     

Low-pressure discharge induced by microwave radiation with a stochastically jumping phase

Results are presented from experimental studies on the unique beam-plasma generator of microwave radiation with a stochastically jumping phase (MWRSJP). To interpret the experimental results, a computer code was developed that allows one to simulate the process of gas ionization by electrons heated in the MWRSJP field and the behavior of plasma particles in such a field. The conditions for ignition and maintenance of a microwave discharge in air by MWRSJP are found both experimentally and theoretically, and the pressure range in which the power required for discharge ignition and maintenance is minimum are determined.     

Pulsed microwave discharge in a capillary filled with atmospheric-pressure gas

A pulsed microwave coaxial capillary plasma source generating a thin plasma filament along the capillary axis in an atmospheric-pressure argon flow is described. The dynamics of filament formation is studied, and the parameters of the gas and plasma in the contraction region are determined. A physical model of discharge formation and propagation is proposed. The model is based on the assumption that, under the conditions in which the electric fields is substantially below the threshold value, the discharge operates in a specific form known as a self-sustained-non-self-sustained (SNS) microwave discharge.     

Microwave cellular discharge in fine powder mixtures

The excitation of microwave discharges in fine semiconductor powders and powder mixtures of metals and dielectrics is studied. The plasma is produced due to local sparks generated in microsecond microwave pulses. The time delay in the onset of a discharge amounts to several milliseconds for intensities on the order of 10 kW/cm². As the discharge develops, both microwave absorption and the discharge glow intensity increase. Intense nonuniform heating of the powder is observed.     

Electrode microwave discharge in nitrogen: Structure and gas temperature

Electrode microwave discharges in nitrogen at pressures of 1–16 Torr and input microwave powers of 30–180 W have been studied by space-resolved emission spectroscopy. It is shown that the discharge is highly nonuniform. The relative intensities of the first and second positive nitrogen bands, as well as of the first negative band of nitrogen ions, are found to vary significantly throughout a discharge because, in different discharge regions, emitting particles are excited by different mechanisms. The gas temperature was determined by the method of the unresolved rotational structure of different sequences of the emission spectra of the second positive system of nitrogen.     

Theoretical and experimental study of microwave power absorption by a single-sided multipactor discharge on a dielectric

The coefficient of microwave power absorption by a single-sided multipactor discharge on a dielectric surface is studied analytically and numerically as a function of the incident microwave power. It is shown that taking into account electron reflections from the dielectric surface leads to a substantial increase in the absorption coefficient. The analytical and numerical results are compared with experimental data.     

Structure of a discharge induced by a coaxial microwave plasmatron with a gas-supply channel in the inner electrode

The structure of a discharge induced by a coaxial microwave plasmatron with a gas-supply channel in the inner electrode of a coaxial waveguide is investigated. A plasmatron with a power of up to 10 W operates at a frequency of 10 GHz. Depending on the operation regime, the discharge takes either a filament or torch form. A plasma filament arises at low flow rates of the working gas (argon) and occurs at the border of the potential core of the gas jet. A torch discharge occurs at high flow rates and has the form of a hollow cone. In both cases, the discharge arises in the potential core of the gas jet and does not spread beyond it. The distribution of the microwave field in the discharge plasma is determined.     

Spatial distribution of the electron component parameters in the nitrogen plasma of a low-pressure electrode microwave Discharge

Spatial distributions of charged particle concentration, electron temperature, and DC potential in an electrode microwave discharge in nitrogen at a pressure of 1 Torr have been measured using the double electric probe method. It has been shown that, near the electrode/antenna, the charged particle concentration exceeds a critical value. The concentration and heterogeneity of the discharge increase with increasing microwave power.     

Numerical investigation of a microwave discharge driven by the H 10-type wave

A two-dimensional numerical model is proposed for studying a steady microwave discharge driven by the H ₁₀-type wave. The parameters of a discharge in nitrogen at atmospheric pressure are calculated. The results obtained agree qualitatively with the experimental data.     

Experimental study of a multipactor discharge on a dielectrics surface in a high-Q microwave cavity

Results from experimental studies of multipactor discharges on the surfaces of various dielectrics placed in a high-Q cylindrical microwave cavity excited at the TE₀₁₃ mode in the X-band are presented. The thresholds for the onset and maintenance of a multipactor discharge on quartz, polycrystalline diamond, lithium fluoride, and Teflon surfaces possessing different roughness are determined. It is shown that, in such a resonance system, a steady multipactor discharge can operate without transition into the stage of microwave breakdown of the desorbed gas. It is found that, due to long-term action of the discharge, a thin carbon-containing film is deposited on the dielectric surface, which leads to an increase in the breakdown threshold.     

Microwave processes in the SPD-ATON stationary plasma thruster

Results of experimental studies of microwave processes accompanying plasma acceleration in the SPD-ATON stationary plasma thruster are presented. Specific features of the generation of microwave oscillations in both the acceleration channel and the plasma flow outgoing from the thruster are analyzed on the basis of local measurements of the spectra of the plasma wave fields. Mechanisms for generation of microwave oscillations are considered with allowance for the inhomogeneity of the electron density and magnetic field behind the edge of the acceleration channel. The effect of microwave oscillations on the electron transport and the formation of the discharge current in the acceleration channel is discussed.     

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.     

Calculation of a coaxial microwave torch

Parameters of an equilibrium microwave discharge in an atmospheric-pressure argon flow in a coaxial waveguide with a truncated inner electrode are calculated numerically by using a self-consistent two-dimensional MHD model. The results obtained agree satisfactorily with the experimental data.     

Discharge in a Subthreshold Microwave Beam as an Unusual Type of Ionization Wave

Plasma Physics Reports - Ionization−overheating instability of a non-self-sustained discharge in air in a subthreshold microwave field creates a self-sustained discharge with a fine cellular...     

Stability of the low-temperature states of high-pressure microwave discharges

Symmetric (planar, cylindrical, and spherical) models of microwave discharges in air are considered assuming that the deposited energy is removed via heat conduction. The characteristic features of spherical discharges are analyzed in detail, and the conditions for discharge stability are examined. It is shown that discharges in the low-temperature (unstable) state can be stabilized by varying the power of a feedback-controlled microwave source.     

A pulse-periodic torch in a coaxial waveguide: Formation dynamics and spatial structure

Results are presented from experimental studies of the formation dynamics, spatial structure, and parameters of a pulse-periodic microwave discharge excited in a coaxial waveguide. The experimental setup allows the stable generation of a plasma jet in molecular and atomic gas flows at pressures close to atmospheric pressure without applying additional initiators. The complicated sequence of processes leading to torch formation cannot be adequately described with conventional models of a discharge sustained by a surface electromagnetic wave.     

Resonance microwave discharge as a source of UV radiation

Results are presented from theoretical and experimental studies of an optical radiation source based on a microwave discharge excited in an Ar + Hg mixture. The main attention is paid to the so-called “resonance” discharge operating at low pressures of the working gas (argon). It is shown that a decrease in the Ar pressure leads to significant increase in the Hg radiation intensity (including biologically active UV radiation) and considerable decrease in the intensity of argon emission lines. The intensity of discharge radiation is calculated in the framework of the collisional-radiative model. The results of calculation agree qualitatively with experimental data.