Plasma Chemical Kinetics Research Articles

Effects of pulse rise time and pulse width on discharge mode transition of SDBD plasma under repetitive pulses

Abstract Affected by environmental states and power supply parameters, the discharge mode of surface dielectric barrier discharge plasma may gradually transfer from O3 mode to NOx mode, resulting in various gas-phase species for different applications. Despite the intensive study of attempts to control this discharge mode transition by changing discharge conditions and power excitations in recent years, the effects of the pulse rise time and the pulse width on the discharge mode transition have not been discussed. In the present study, a surface dielectric barrier discharge was excited by repetitive pulses with different pulse rise times or pulse widths, and the time-varying concentrations of key long-lived species (O3 and NO2) were quantified. The results demonstrated that it was possible to modulate the discharge mode by adjusting pulse rise time/pulse width. The quenching of O3 was observed to occur at a faster rate and the mode transition was noted to occur at an earlier point in time as the pulse rise time decreased from 225 ns to 125 ns and the pulse width increased from 0.5 μs to 4 μs. The employment of a zero-dimensional model for the analysis of plasma chemical kinetics revealed that the reduction in pulse rise time and the prolongation of pulse width resulted in an increase in the mean vibrational energy of N2(v) and a more rapid electrode temperature rise caused by plasma heating. The former enhanced the generation of NO, while the latter accelerated the thermal decomposition of O3, thereby promoting the speed of mode transition.

ThunderBoltz: an open-source direct simulation Monte Carlo Boltzmann solver for plasma transport, chemical kinetics, and 0D modeling

Abstract Plasma-neutral interactions, including reactive kinetics, are often either studied in 0D using ODE-based descriptions, or in multi-dimensional fluid or particle-based plasma codes. The latter case involves a complex assembly of procedures that are not always necessary to test effects of underlying physical models and mechanisms for particle-based descriptions. Here we present ThunderBoltz, a lightweight, publicly available 0D direct simulation Monte Carlo code designed to accommodate a generalized combination of species and arbitrary cross sections without the overhead of expensive field solves. It can produce electron, ion, and neutral velocity distributions in applied AC/DC E-field and/or static B-field scenarios. The code is built in the C++ standard library and includes a convenient Python interface that allows for input file generation (including compatibility with cross section data from the LXCat database), electron transport and reaction rate constant post-processing, input parameter constraint satisfaction, calculation scheduling, and diagnostic plotting. These codes can be accessed at the repository: https://github.com/lanl/ThunderBoltz. In this work we compare ThunderBoltz transport calculations against Bolsig+ calculations, benchmark test problems, and swarm experiment data, finding good agreement with all three in the appropriate field regimes. In addition, we present example use cases where the electron, ion, and background neutral particle species are self-consistently evolved to model the background kinetics, a feature that is absent in fixed-background Monte Carlo and n-term Boltzmann solvers. The latter functionality allows for the possibility of particle-based chemical kinetics simulations of the plasma and neutral species as a new alternative to ODE-based approaches.

Numerical investigation of vacuum ultra-violet emission in Ar/O2 inductively coupled plasmas

Abstract Controlling fluxes of vacuum ultraviolet (VUV) radiation is important in a number of industrial and biomedical applications of low pressure plasma sources because, depending on the process, VUV radiation may be desired, required to a certain degree, or unwanted. In this work, the emission of VUV radiation from O atoms is investigated in low-pressure Ar/O2 inductively coupled plasmas via numerical simulations. For this purpose, a self-consistent Ar/O2 plasma-chemical reaction scheme has been implemented in a zero dimensional plasma chemical kinetics model and is used to investigate VUV emission from excited O atoms (3s 5S 2 0 and 3s 3S 1 0 ) at 130 and 135 nm. The model is extensively compared with experimental measurements of absolute VUV emission intensities, electron densities and Ar excited state densities. In addition, oxygen VUV emission intensities are investigated as a function of pressure, Ar/O2 mixture, and power deposition and the dominant reaction pathways leading to oxygen VUV emission are identified and described. In general terms, absolute oxygen VUV emission intensities increase with power and oxygen fraction over the ranges investigated and peak emission intensities are found for pressures between 5–50 Pa. The emission is dominated by the 130 nm resonance line from the decay of the O(3s 3S 1 0 ) state to the ground state. Besides, at low pressure (0.3–1 Pa), the flux of oxygen VUV photons to surfaces is much lower than that of positive ions, whereas oxygen VUV fluxes dominate at higher pressure, ≳ 5–50 Pa depending on O2 fraction. Finally, oxygen atom fluxes to surfaces are, in general, larger than those of VUV photons for the parameter space investigated.

Theoretical cross sections for electron collisions relevant for ammonia discharges part 1: NH3, NH2, and NH

Besides being the worlds’ most important fertilizer precursor, ammonia could play an important role as hydrogen carrier in a decarbonized future. The efficient production and decomposition (or cracking) of ammonia are essential to this end. An electricity-driven technology of interest for both these processes are non-thermal plasmas. Plasma processes have the advantage of activating—even inert—molecules and initiating chemical reactions through electron collisions, rather than through conventional heating. However, a complete set of low-energy cross section data is not available for the electron collisions with ammonia (NH3) and its radicals, amidogen (NH2) and imidogen (NH). Here, we used the ab initio R-matrix method to determine theoretical cross sections for the low-energy electron collision processes with NH3, NH2, and NH. Additionally, we explored the contribution of the different processes towards dissociation (especially from electronic excited states). Where possible, we compared our theoretical cross section data with experimental data and/or previous recommendations. Lastly, our own recommended cross section data for the electron collisions are presented. Use of this complete set of electron collision data should contribute to a more accurate description of and better insights into the plasma-chemical kinetics behind plasma-assisted ammonia production and decomposition processes.

Numerical modeling of plasma assisted ignition of CH4/O2/He mixture by the nanosecond repetitive pulsed surface dielectric barrier discharge

A nanosecond repetitive pulsed surface dielectric barrier discharge (NRP-SDBD) is a promising method for generation of non-equilibrium plasma with more kinetic activity. This paper presents numerical studies on the effects of pulse repetition frequency (PRF) on low temperature ignition of lean and stoichiometric CH4/O2/He mixture in NRP-SDBD plasma. A skeletal plasma kinetics mechanism is primary developed and calibrated, to mitigate the computationalloads of modeling SDBD discharge by the two-dimensional plasma solver PASSKEy coupled with Poisson's equation. The discharge current was well predicted, meanwhile the sequential and spatial reduced electric field (E/N) is revealed as the ionization wave propagates forward. Special attention is placed on time-evolution of electric field strength used as inputs in simulation of plasma assisted ignition (PAI) conducted by zero-dimensional ZDPlasKin-CHEMKIN code. The principle of PAI on lean and stoichiometric CH4/O2/He mixture via varied PRF is analyzed in details from view of plasma kinetics and chemical kinetics. Ultimately, the important role of plasma active species O, O(1D), O2(a1Δg) on promoting ignition chain reactions is highlighted. It is also concluded that high PRF is beneficial for the accumulation of short lifetime species such as CH4(v13) and O(1D), which participate in the formation of important intermediate CH3.

Plasma-Assisted Dry Reforming of CH4: How Small Amounts of O2 Addition Can Drastically Enhance the Oxygenate Production─Experiments and Insights from Plasma Chemical Kinetics Modeling

Plasma-Assisted Dry Reforming of CH₄: How Small Amounts of O₂ Addition Can Drastically Enhance the Oxygenate Production─Experiments and Insights from Plasma Chemical Kinetics Modeling

The influence of pulse repetition frequency on reactive oxygen species production in pulsed He+H2O plasmas at atmospheric pressure

Atmospheric pressure plasmas generated from a helium gas with admixtures of water vapor have numerous applications in biomedicine. It is important that the chemistry of such plasmas can be tightly controlled so that they may be tailored for their intended use. In this study, computational modeling is used to vary the pulse repetition frequency of a nanosecond-pulsed, pin-to-pin He + 0.25% H2O discharge in the range of 1–100 kHz to determine the influence of the pulse repetition frequency on the resulting densities of reactive oxygen species and the rates of dominant reaction pathways involving them. The plasma is simulated using the 0D plasma-chemical kinetics model GlobalKin. The pulse shape is kept constant. The afterglow duration is, therefore, dependent on the repetition frequency. Analysis of the bulk plasma chemistry after the plasma has reached equilibrium shows that the peak electron density is only weakly dependent on the pulse repetition frequency. Increasing the pulse repetition frequency is shown to increase the density of H, O, and OH radicals, while the relationship between the repetition frequency and the densities of species with longer lifetimes, namely, H2O2 and O3, is found to be more complex. These are formed throughout the afterglow, and their density depends on the availability of reactant species, the afterglow duration, and the background gas temperature. This work concludes that the pulse repetition frequency is not a simple control parameter, especially for species that are predominantly produced in the afterglow. Detailed modeling is required for accurate control of species densities using the pulse repetition frequency.

Plasma–liquid interactions: an experiment and simulation study on plasma dynamic behaviors near the gas–liquid interfacial layer

Plasma–liquid interaction processes are essential to various plasma applications such as sewage disposal, biomedicine, and synthesis of nanomaterials. However, the near gas–liquid interfacial behavior of plasma property remains inadequately understood, hindering the controllability of the application process. This study combines experimental diagnostics and simulations to investigate the production and transport of plasma-generated reactive species near (∼35 μm) the gas–liquid interfacial layer. The experimental results are used to benchmark densities obtained from a zero-dimensional plasma chemical kinetics simulation, which reveals the time evolutions of plasma-generated active species. A large number of neutral particles (like OH, H2O2) and water cluster ions (like H9O4 +) were produced as a result of the evaporation effect of the cathode solution surface. The estimation of energy flux from the gaseous plasma to liquid surface showed that the hydration process of positive ions plays the key role in the resulted water evaporation at the gas–liquid interfacial layer.

The temporal behavior of O atom of a nonequilibrium atmospheric pressure plasma driven by kHz nanosecond voltage pulses

AbstractThis work investigates the temporal dynamics of O atoms in nonequilibrium atmospheric pressure plasma (NAPP) generated by kHz nanosecond pulsed discharge. Two‐photon laser‐induced fluorescence (TALIF) method is used to measure the time resolution of O atom density from the first discharge pulse in two gas mixtures, He + 0.4%O2 and He + 0.4%air. The discharge frequencies of 1 and 10 kHz are considered in the experiment. The results show that the O atom density does not accumulate with increasing number of pulses in both gas environments at 1 kHz. However, at 10 kHz, a cumulative effect of O atom density with the number of pulses is observed in both gas mixtures. After 10 and 300 discharge pulses in He + 0.4%O2 and He + 0.4%air, respectively, the O atom density saturates at the same moment after each discharge cycle. It was found that even after a long operating period of discharge, the decay of O atom density during each discharge cycle is not negligible. The O atom density in He + 0.4%O2 varies in the range of 2.85 × 1021 m−3–4.29 × 1021 m−3 while the O atom density in He + 0.4%air varies in the range of 2.60 × 1021 m−3–3.19 × 1021 m−3. This indicates that the choice of diagnostic time points is important for the O atom density measurements when using TALIF to diagnose kHz pulsed NAPP. In addition, 0D plasma chemical kinetics models are developed for the two gas mixtures to investigate O atoms' production and consumption processes. The causes of the cumulative effect of O atom density at 10 kHz, the saturation effect, and the formation of the periodic variation trend are also investigated. The simulation results show that the consumption rate of O atoms and the O atom density are directly correlated. As the number of pulses increases, the O atom consumption rate increases, which gradually counteracts the number of O atoms generated during the pulse discharge. This leads to delay and saturation of the cumulative effect of O atoms.

Key Modes of Ignition and Maintenance of Corona Discharge in Air

Theoretical and experimental studies of various modes of corona discharge operation in atmospheric pressure air are presented in this short review. The original results of modeling negative corona discharges are presented, taking into account the non-stationary plasma-chemical kinetics of charged particles in air plasma. The space–time evolution of the discharge in needle-to-plane geometry is investigated and analyzed. Several stages of discharge development are revealed from the moment of initiation of a low-negative current corona to the quasi-stationary mode of a glow discharge. Experimental data of the authors are presented. Modern technology and diagnostic equipment with a wide variation of the main parameters (the shape and polarity of the applied voltage, the type of gap, etc.) was used. The measurement of the optical characteristics of the plasma glow was carried out with high spatial resolution. Corona discharge current pulse profiles in the air at atmospheric pressure have been recorded with subnanosecond time resolution. With a positive polarity of the pin electrode and high voltage, a transition from a spherical streamer initiating a corona discharge to a cylindrical streamer is shown. The author’s results are rigorously evaluated through a critical comparison with findings from other research groups.

Power concentration determined by thermodynamic properties in complex gas mixtures: the case of plasma-based dry reforming of methane

We investigate discharge contraction in a microwave plasma at sub-atmospheric pressure, operating in CO2 and CO2/CH4 mixtures. The rise of the electron number density with plasma contraction intensifies the gas heating in the core of the plasma. This, in turn, initiates fast core-periphery transport and defines the rate of thermal chemistry over plasma chemistry. In this context, power concentration describes the overall mechanism including plasma contraction and chemical kinetics. In a complex chemistry such as dry reforming of methane, transport of reactive species is essential to define the performance of the reactor and achieve the desired outputs. Thus, we couple experimental observations and thermodynamic calculations for model validation and understanding of reactor performance. Adding CH4 alters the thermodynamic properties of the mixture, especially the reactive component of the heat conductivity. The increase in reactive heat conductivity increases the pressure at which plasma contraction occurs, because higher rates of gas heating are required to reach the same temperature. In addition, we suggest that the predominance of heat conduction over convection is a key condition to observe the effect of heat conductivity on gas temperature.

Generation and decay of N2(A3Σu +) molecules in reacting CO2 and CH4 plasmas

Time-resolved number densities of N2(A3Σu +, v = 0, 1) molecules in diffuse ns pulse discharge plasmas in N2, N2–H2, N2–CH4, N2–CO2, and N2–CO2–CH4 are measured by tunable diode laser absorption spectroscopy (TDLAS). The first series of measurements is made in the discharge pulse bursts at a relatively low pulse repetition rate (3 kHz), when the N2(A3Σu +) generation and decay after individual discharge pulses is fully resolved. The second set of data is taken during a sequence of two pulse bursts generated at a higher pulse repetition rate (100 kHz), for different delay times between the first and second bursts. This approach is used to determine the effect of accumulation and decay of reacting species generated in the plasma, including N, H, and O atoms, CO molecules, and C2 hydrocarbon product species, on the rate of N2(A3Σu +) production and quenching. The effect of these species can be isolated since the rates of N2(A3Σu +) quenching by the initial reactant species (H2, CH4, and CO2) are slow. Comparison of the measurement results with the kinetic modeling predictions is used to obtain insight into the plasma chemical reaction kinetics. The results complement the measurements of N, H, O, and CO in high-pressure reacting plasmas, and help quantify the plasma chemical processes driven by the electron impact dissociation, electronic excitation, and reactive quenching of the excited electronic states. The present results may be used for the development and validation of higher fidelity kinetic models of reacting plasmas, incorporating state-specific electronic and vibrational energy transfer and chemical reactions.

Chemical Kinetics Simulation of Hydrogen Generation in Rotating Gliding Arc Plasma

This work reports hydrogen (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) formation using methane nitrogen gas mixture as a feed stream in a rotating gliding arc (RGA) reactor. The H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> formation in the RGA was quantified by experimental studies, and the results were validated by simulating plasma chemical kinetics using the Chemical Workbench software. The simulation was performed for an experimental condition, where methane (1%) and nitrogen (99%) gas mixture was fed to an RGA at 5, 10, 25, and 40 lpm. For these flow rates, the simulation predicted 1417, 802, 299, and 67 ppm of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , respectively. Also, the results show that at these flow rates, the reduced electric field (E/N) of the discharge was 78, 83, 92, and 101 Td and the gas temperature was 3800, 4108, 4590, and 4975 K respectively. The simulation result was in reasonable agreement with the experimental data, which shows 1276, 717, 213, and 61 ppm of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in the product gas, respectively, at 5, 10, 25, and 40 lpm. This work marks the first step toward process optimization through the simulation approach.

A numerical methodology based on CFD and plasma chemical kinetics simulations: a focus on the cyano radical

A numerical methodology based on CFD and plasma chemical kinetics simulations: a focus on the cyano radical

Nonheating ozone suppression in pulsed air discharges: role of pulse duration and repetition rate

Facilitating the separate production of ozone (O3) and nitrogen oxides (NO x ) in air discharges without a thermal process is of most merit in diversifying plasma technology; in particular, it is a primary requirement in certain cold, heat-sensitive plasma applications. Here, we propose a new method of nonheating ozone suppression in air discharges. The present work demonstrates that controlling the plasma chemical kinetics by adjusting the duration (width) and/or repetition frequency of the high-voltage DC pulse is effective in suppressing ozone formation in a surface dielectric barrier discharge in static ambient air. The temporal development of each oxygen- and nitrogen-related species in air discharge is complicated and shows different trends in the time range <10 µs; relatively long-lived O3 and NO x are strongly governed by the temporal behavior of short-lived reactive species, such as excited N2(A) and N2(v). To quantify time-varying O3 and NO x , an in situ UV absorption spectroscopy is applied to our gas-tight plasma reactor, which is operated in air at 21 °C. With a fixed frequency at 10 kHz and decreasing pulse duration from 10 μs to 0.18 μs, ozone is quenched faster in the plasma reactor, resulting in an irreversible chemical mode transition from an O3- to NO-rich environment. From a different set of experiment (with a 200 ns pulse duration and a frequency range of 1–10 kHz), we can conclude that the off-pulse period also plays a crucial role in the temporal evolution of O3 and NO x ; the larger the applied driving frequency is, the earlier the ozone-free phenomenon appears over the discharge time. Our findings represent a breakthrough in expanding the usage of air discharges and their application in various fields of interest.

Chemical kinetics and density measurements of OH in an atmospheric pressure He + O2 + H2O radiofrequency plasma

This work presents experiments and modelling of OH densities in a radio-frequency driven atmospheric-pressure plasma in a plane-parallel geometry, operated in helium with small admixtures of oxygen and water vapour (He + O2 + H2O). The density of OH is measured under a wide range of conditions by absorption spectroscopy, using an ultra-stable laser-driven broad-band light source. These measurements are compared with 0D plasma chemical kinetics simulations adapted for high levels of O2 (1%). Without O2 admixture, the measured density of OH increases from 1.0 × 1014 to 4.0 × 1014 cm−3 for H2O admixtures from 0.05% to 1%. The density of atomic oxygen is about 1 × 1013 cm−3 and grows with humidity content. With O2 admixture, the OH density stays relatively constant, showing only a small maximum at 0.1% O2. The simulations predict that the atomic oxygen density is strongly increased by O2 addition. It reaches ∼1015 cm−3 without humidity, but is limited to ∼1014 cm−3 beyond 0.05% water content. The addition of O2 has a weak effect on the OH density because, while atomic oxygen becomes a dominant precursor for the formation of OH, it makes a nearly equal contribution to the loss processes of OH. The small increase in the density of OH with the addition of O2 is instead due to reaction pathways involving increased production of HO2 and O3. The simulations show that the densities of OH, O and O3 can be tailored relatively independently over a wide range of conditions. The densities of O and O3 are strongly affected by the presence of small quantities (0.05%) of water vapour, but further water addition has little effect. Therefore, a greater range and control of the reactive species mix from the plasma can be obtained by the use of well-controlled multiple gas admixtures, instead of relying on ambient air mixing.

Flowing Atmospheric Pressure Afterglow for Ambient Ionization: Reaction Pathways Revealed by Modeling.

We describe the plasma chemistry in a helium flowing atmospheric pressure afterglow (FAPA) used for analytical spectrometry, by means of a quasi-one-dimensional (1D) plasma chemical kinetics model. We study the effect of typical impurities present in the feed gas, as well as the afterglow in ambient humid air. The model provides the species density profiles in the discharge and afterglow regions and the chemical pathways. We demonstrate that H, N, and O atoms are formed in the discharge region, while the dominant reactive neutral species in the afterglow are O3 and NO. He* and He2* are responsible for Penning ionization of O2, N2, H2O, H2, and N, and especially O and H atoms. Besides, He2+ also contributes to ionization of N2, O2, H2O, and O through charge transfer reactions. From the pool of ions created in the discharge, NO+ and (H2O)3H+ are the dominant ions in the afterglow. Moreover, negatively charged clusters, such as NO3H2O- and NO2H2O-, are formed and their pathway is discussed as well. Our model predictions are in line with earlier observations in the literature about the important reagent ions and provide a comprehensive overview of the underlying pathways. The model explains in detail why helium provides a high analytical sensitivity because of high reagent ion formation by both Penning ionization and charge transfer. Such insights are very valuable for improving the analytical performance of this (and other) ambient desorption/ionization source(s).

Inevitable chemical effect of balance gas in low temperature plasma assisted combustion

Abstract Electrical discharges (or plasmas) have attracted researchers’ attention to improve combustion characteristics. One of its key effects, which is not fully understood yet, is the in-situ production of chemically reactive species. Since most related low temperature kinetic studies to-date have been performed under highly diluted conditions (> 99%), here we present the inevitable and undesirable chemical effect of a balance gas (Ar, He, N2) on the plasma-chemical kinetics. We employ a zero dimensional plasma-chemical kinetics model in combination with a (detailed and reduced) H2/O2/Ar reaction mechanism. The presented results indicate that (dissociative) quenching of excited (metastable) states dominates the H2 and O2 dissociation processes under highly diluted conditions. Additionally, in the reduced field intensity (E/N) domain, the type and amount of the balance gas significantly alters the fraction of electron energy transferred to the other species in the mixture. Therefore, we propose essential steps for the design of future kinetic studies for plasma assisted combustion.

Time-resolved in situ measurements and predictions of plasma-assisted methane reforming in a nanosecond-pulsed discharge

This study investigates the plasma properties and chemical kinetics of plasma-assisted methane reforming in a He diluted nanosecond-pulsed plane-to-plane dielectric barrier discharge (ns-DBD) through the combination of time-resolved in situ laser diagnostics and a 1-D numerical model. Plasma-assisted fuel reforming kinetic mechanisms have predominantly been evaluated on the basis of matching reactant conversion and syngas production to steady-state measurements, which cannot describe the full range of chemistry and physics necessary to validate the model. It was found that adding 1% CH4 to a pure He ns-DBD led to a faster breakdown along the rising edge of the applied voltage pulse, thereby lowering the reduced electric field (E/N), electron number density, and electron temperature. Further addition of CH4 did not continue to alter the E/N in the model. Laser absorption spectroscopy was used to measure gas temperature, C2H2, H2O, and CH2O in a CH4/CO2/He discharge to serve as validation targets for the predicted reaction pathways. CH2O was predicted within 25% of the measured value, while H2O and C2H2 were under-predicted by a factor of two and three, respectively. From path flux analysis, the major pathway for CH2O formation was through the reaction between CH3 and O, while C2H2 formation had multi-step pathways that relied on ions like CH3+ and C2H5+. The path flux analysis also shows that CH2 is a significant intermediate for production of both CH2O and C2H2, and increased CH2 concentration could improve model predictions. The results show that the use of reaction rate constants with lower uncertainties and inclusion of He2+ are needed to improve the predictions. Finally, varying the ”equivalence ratio”, defined by the CH4 dry reforming reaction to H2 and CO, from 0.5 to 2 was shown to have a weak effect on measured product species and experimental trends were explained based on pathways extracted from the model.

Study of the microwave streamer evolution using a new semi-analytical model

A microwave (MW) plasma channel (filament, plasmoid, and plasma dipole) shows promise for its applications for off-body non-electrode modification of a gas flow (plasma aerodynamics) and in the plasma assisted combustion process. A full-scale study of the plasma channel evolution requires a self-consistent solution of Maxwell's equations, plasma chemical kinetics equations, and gasdynamics equations. An attempt is made to develop a simple electrodynamic (based on the solution of Maxwell's equations) “fast” model for studying the evolution of the plasma channel in conjunction with a fairly complete system of plasma chemical reactions. The model is based on a simplifying assumption about the shape of the channel, which converts a 3D problem into a 1D one. The results of numerical calculations in air within the pressure range P = 20–150 Torr are presented. An experimental study of plasmoid development was carried out to verify the predictions of the model. The calculated results agree well with all available experimental data within the pressure range P = 20–150 Torr. The proposed electrodynamic approach made it possible to reveal (i) the mechanism of self-organization during the development of a MW streamer and (ii) the reason for a sharp decrease in the velocity of its elongation, as well as to obtain relations connecting the main characteristics of the streamer (the amplitude of the electric field in the channel and on its heads, the velocity of ionization waves, and the characteristic scale of their fronts). The proposed model will be useful both for estimating the channel parameters and for deciphering the dynamics of radiation scattered by the plasma dipole. The development of such an approach will allow one to study the evolution of multiplasmoid structures of a high-pressure MW discharge.