The study of the effect of the initial conditions on the features of the formation and development of the anodic ionization wave between two electrodes with a tip-plane gap geometry in argon at atmospheric pressure is performed on the basis of a two-dimensional axisymmetric drift-diffusion model. Keywords: gas discharge, low-temperature plasma, gas breakdown, ionization waves, simulation.

The paper presents a computational and theoretical analysis of kinetic processes in methane, nitrogen, and oxygen mixtures for non-self-sustaining direct current discharges supported by an electron beam. Within an approximate approach, the kinetic coefficients in plasma under the simultaneous action of an applied electric field and an electron beam are determined. In a zero-dimensional (spatially homogeneous) approximation, the quasi-stationary composition of charged particles is calculated. The rate constants for generation of chemically active neutral particles of various types in plasma are calculated along with the energy efficiencies (G-factors) of the production of these particles depending on the magnitudes of the reduced electric field and the beam current. Similarity rules are proposed for the relation between the rates of production of active particles under the action of an electric field and an electron beam. It is shown that, by varying the applied field, it is possible to influence the composition of the produced hydrocarbon radicals.

In this paper, we investigate the spatial-local electron energy distribution function (eEDF) interacting with a background gas at the sub-atmospheric pressure in a wide range of applied crossed electric and magnetic fields using the Boltzmann kinetic equation. We compare solutions obtained using two numerical approaches (deterministic two-term approximation and stochastic Monte Carlo method) to identify their applicability in the context of determining drift velocity and reaction constants for electrons. For argon and helium, the upper limit of the reduced electric field applicability of the two-term approximation is discussed. It has been shown that the presence of a magnetic field can reduce this limit. Two explanations are given, one is based on the math of two-term formalism, and the other is based on velocity-space analysis. Two-term approximation fails due to it's inability to resolve underlying cyclotron oscillation (it should result in an energy variation along the electron's trajectory). The absence of this feature causes an incorrect estimation of momentum-transfer rate. This results an inaccuracy in the estimation of the angle between electric field and drift velocity.

Available experimental data show that the use of voltage pulses with subnanosecond rise times and amplitudes that essentially exceed the breakdown voltage leads to the formation of wide spherical or conical streamers. In this paper, the structure and dynamics of atmospheric pressure wide negative streamers in air and helium by applying high overvoltages with a short rise time to a sharp needle electrode are investigated experimentally and computationally. In the simulations, the two-dimensional fluid and kinetic electron Monte Carlo simulation models are used. All the streamers were simulated with the conventional photoionization term S ph that was never turned off. By including an additional source S MC , responsible for the generation of fast electrons, wide and diffuse streamers are obtained. We compare the shapes, width and velocities of conventional streamers in air and helium with those for streamers driven by fast electrons. We show that a conventional streamer in air has a cylindrical form. The conventional streamer in helium is wider than that in air and has a shape of an expanding cone. While accounting for fast electrons, different streamer shapes were obtained. In air, the gap was closed by a spherical streamer. In helium, the shape of a streamer resembles that of a pumpkin. We also demonstrate that near the flat anode, velocities of conventional streamers in air and helium were as high as 5 × 10 9 cm s −1 and reached values greater than 10 10 cm s −1 when fast electrons were taken into account. By the application of high (by a factor of four or greater) overvoltages to a sharp needle electrode, the formation of a discharge with several parallel streamers was observed. In this regime, the trajectories of fast electrons originated not only from the cathode, but also from the region of a streamer front where the electric field is high. As a result, the so-called diffuse discharge was formed with high intensity plasma channels surrounded by an aureole of smaller electron density.

In this paper, we examine the energy distribution function of electrons in the case of a very weakly ionized argon plasma at sub-atmospheric pressure and external electric field using Boltzmann kinetic equation. We consider a spatially uniform model because our primary interest is the behavior of the collisional part of the equation. The purpose of the study is to compare two different numerical approaches: a deterministic one (using two-term local non-stationary approximation) and a stochastic approach (using the Monte Carlo method) over a wide range of reduced electric fields. We compare steady-state and time-dependent solutions, isotropic and anisotropic parts of the electron energy distribution function, and reaction constants. The research will also help to identify any limitations and challenges of these methods.

The modelling method based on decoupling the simulation of the cathodic part of the arc (the cathode and the near-cathode non-equilibrium plasma layer) from the simulation of the arc on the whole has been extended to cathodes of arc plasma torches, consisting of an insert with a conical tip, made of pure or doped tungsten, and a surrounding water-cooled copper holder. The method was validated by comparison with the experiment, performed on a 200 A DC arc in atmospheric-pressure argon. Standard work function of polycrystalline tungsten of 4.54 eV was used for modelling of pure-tungsten insert and a good agreement with the experiment was found with respect to both the insert tip shape and the temperature distribution in the tip, recorded in the stable operation mode. There are no unambiguous data on the work function for arc cathodes made of doped tungsten, although in situ measurements of the effective work function of cathodes of high-pressure arc discharges provide useful hints. On the other hand, the experiments reported in this work show that the tip temperatures of inserts made of tungsten doped with 1.5%

Experiments were carried out to study the stable attachment of an atmospheric pressured argon dc arc to the surface of pure, thoriated and lanthanated tungsten. Using spectroscopic methods electron temperatures and concentrations were obtained in the positive plasma column near the cathode. With a current of 200 A and a plasma gas flow rate of 1.5 g/s, the average values of temperatures were T e ~ 2.6 eV for pure tungsten, T e ~ 2 eV for thoriated and lanthanated tungesten, and concentrations n e ~ 10 17 cm –3 . In these experiments, the cathode with an insert of lanthanated tungsten (3100 K) had the lowest working surface temperature due to the lower effective work function, while for thoriated and pure tungsten surface temperatures were 3300 and 3800 K, respectively. It was found that at a current of 200 A, the tip of the pure tungsten cathode was in the liquid phase, in contrast to thoriated and lanthanated tungsten that remained in solid phase.

In this paper, the effect of appearance of fast electrons behind the grid cathode in the direction reverse to the anode is studied computationally. Fast electrons are observed within 0.5 ns after application of a short voltage pulse. The results obtained confirm the possibility of generation of backward fast electrons (some of them are in a runaway mode) and explain the main trends of this process. It is shown that backward fast electrons are supported by the ionization wave (IW). The IW evolution proceeds via two phases. During the first phase, first fast electrons are observed moving toward the anode. Then, multiple individual IWs starting from each individual cathode wire are formed in the anode–cathode gap. The duration of this stage is 0.3 ns and corresponds to the pulse rise time. At the second phase, the separate individual IWs merge in a single flat ionization wave. The IW penetrates through the cathode wires and propagates in the direction reverse to the anode. The preferred direction of fast electrons propagation also reverses. Now, the trajectories of fast electrons are mainly directed away from the anode. The duration of the recorded flux of fast electrons is of the order of a few picoseconds. This time interval correlates with the available experimental data.

Numerical simulations of the production of nitrogen oxide NO and dioxide NO2 in the pulse-periodic regime in atmospheric pressure air were performed for four different time dependences of the energy deposition power. The time dynamics of the temperature in the center of the discharge gap and the absolute number of particles of nitrogen oxides NO and NO2 were shown. It was found that the number of produced NO particles becomes stationary almost immediately after the end of the pulse while the number of NO2 particles continues to increase monotonously. The results of this study can be in demand for the design of nitrogen oxide generators for medical applications.

In the present study, we computationally investigate the splitting of CO2 to carbon monoxide and oxygen in an atmospheric pressure microwave (MW) plasma torch. We demonstrate different stages of CO2 conversion while using 2D and 1D models. For both models, we use identical sets of chemical reactions, cross sections, power profiles and dimensions of the plasma region. Based on the real MW plasma torch device, we first constructed two-dimensional geometry and obtained results using the 2D model. Then, the 1D plug-flow model was employed. With 1D model we expected to obtain the results close to those we already had from the 2D approach. However, we revealed that the gas temperature and plasma species behaviour in 1D model was quite different from those obtained with the 2D code. We revisited the 2D results and found that the reverse (upstream) gas flow near the central electrode was responsible for the observed discrepancies. In 2D model, the residence time of a certain portion of gas was much longer. When the flow rate in 1D model was adjusted, the reasonable agreement between both models was achieved.

Using the method of shadow photographing, the formation of a spark discharge in the "tip (cathode)-plane" interval with a length of 1.5 mm is investigated. Two types of shock waves have been registered cylindrical, created when the discharge channel expands, and cathode, presumably generated by cathode flares near the surface of the tip electrode. The computational and theoretical consideration of the proposed mechanism is carried out. Keywords: gas discharge, microstructure, electron temperature, degree of gas ionization.

The genome of Stellaria media contains a gene family for hevein-like antimicrobial peptides, some of which are known to encode two peptides released from the translation product as a result of post-translational proteolysis. These peptides have been shown to inhibit the growth of bacteria and fungi, including potato pathogens Alternaria solani and Alternaria alternata. One of these genes, ProSmAMP1, was introduced into the potato genome under the control of the light-inducible promoter of Cab gene from common wheat. The resulting transgenic lines expressed ProSmAMP1 mRNA during several vegetative passages, and their resistance to early blight was assessed by several indicators of detached leaf infection, with plants having the highest expression of the transgene also showing the highest resistance.

Using the method of shadow photographing, the formation of a spark discharge in the "tip (cathode) – plane" interval with a length of 1.5 mm is investigated. Two types of shock waves have been registered – cylindrical, created when the discharge channel expands, and cathode, presumably generated by cathode flares near the surface of the tip electrode. The computational and theoretical consideration of the proposed mechanism is carried out.

Проведены эксперименты по исследованию стационарной привязки аргоновой дуги атмосферного давления к поверхности чистого, торированного и лантанированного вольфрама. Спектральными методами получены температуры и концентрации электронов в плазме положительного столба вблизи катода при токе дуги 200 А и расходе плазмообразующего газа 1.5 г/с, средние значения которых T e ~ 2.6 эВ для чистого вольфрама, T e ~ 2 эВ для торированного и лантанированного с n e ~ 10 17 см –3 . При этом наименьшей температурой рабочей поверхности обладает катод со вставкой из лантанированного вольфрама (3100 К) из-за меньшей эффективной работы выхода, когда как для торированного и чистого вольфрама 3300 К и 3800 К соответственно. При этом установлено, что при токе 200 А вершина поверхности чистого вольфрама находится в жидкой фазе в отличие от торированного и лантанированного вольфрама.

The spatio-temporal structure and plasma parameters of a new type of glow discharge—atmospheric-pressure interelectrode microwave discharge in gas flow—were studied experimentally and numerically. A multi-electrode coaxial-type cold plasma torch developed for large-area surface treatment was used as a gas discharge device. The torch was supplied with microwave power (2.45 GHz, ∼100 W) via a coaxial cable by a typical wave-guide plasmatron. Self-sustained glow discharges were excited between the round ends of the rod-like electrodes and inner wall of the cylindrical discharge chamber near the outlet. The filamentation of the discharge channel in the near-electrode regions was detected by high-speed video filming. The dendritic self-similar (fractal) character of the filaments’ structure was revealed and analyzed. The branching factor and fractal dimension of this structure were estimated as 3 and 1.1–1.3, respectively. Using discharge gas temperature T g = 1200 ± 100 K, as determined from the emission spectroscopy measurements, the following discharge plasma parameters were obtained from numerical calculations: electron temperature T e = 1.14 eV and concentration n e ∼ 10 21 – 10 22 m −3 , conductivity σ ∼ 400 Ω − 1 m − 1 , current density j ∼ 10 6 A m −2 , and electric field strength E ∼ 10 4 V m −1 .

The results of experimental and computational studies of the pulsed periodic microsecond diffuse discharge excited in the air flow under atmospheric pressure in a sharply heterogeneous interval are described. It is shown that effective synthesis of nitric oxide is ensured in such a discharge. A model of the production of nitrogen oxides in the late stage of discharge has been developed, which takes into account the main plasmachemical reactions and gasdynamics. Simulation shows the combined effect of plasmachemical and gasdynamics processes on the spatiotemporal characteristics of the discharge, which determinethe generation of nitric oxide among others. The values of the main parameters of the discharge are determined, and satisfactory agreement between the calculated and experimental data is shown.

Numerical simulation of the development of ionization waves—streamers—in pure argon at atmospheric pressure in a plane-parallel gap has been performed. The velocities and plasma parameters of cathode- and anode-directed ionization waves are obtained, and the streamer dynamics and structure are analyzed. The effects of variation of the background density of charged species are considered. The roles of various ionization mechanisms (the direct and stepwise ionization, and the Penning reaction) during streamer formation and propagation are revealed.

The paper considers various causes of explosions on the cathodes surface in the region of arc attachment in a direct current arc discharge. Estimates of the characteristic times of the development of instabilities during the passage of current through the liquid tip of the cathode are made. As a result, an assumption was put forward that, starting from the moment of formation of the stretched tip and up to the explosion, at different stages of the stretches development, various instabilities alternately play the main roles.

В настоящей работе выполнен расчет локального нестационарного кинетического уравнения Больцмана (КУБ) двумя принципиально разными подходами (детерминистическим и стохастическим) для электронов в аргоне для трех значений приведенного электрического поля 10, 100, 1000.Представлено сравнение решений КУБ для изотропной и анизотропной частей функции распределения энергии электронов на основе двучленного приближения и метода Монте-Карло.Показан диапазон значений приведенного электрического поля, где решения, полученные с помощью двух подходов, совпадают.Ключевые слова: кинетическое уравнение Больцмана, функция распределения, аргон, метод Монте-Карло

The study of the effect of the initial conditions on the features of the formation and development of the anodic ionization wave between two electrodes with a tip – plane gap geometry in argon at atmospheric pressure is performed on the basis of a two-dimensional axisymmetric drift-diffusion model.