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Optical emission spectroscopy (OES) is an important technique for plasma diagnostics. Random deviation is inevitable during the measurement of plasma emission spectra due to the imperfection of instruments and other interferences. On the other hand, inaccuracies in the collision cross-section data can lead to distortion of the collisional-radiative (CR) model. The coupling of theoretical and experimental error factors can pose difficulties for accurate diagnostics of plasma. This work presents the development of the OES method for xenon plasma that employs a neural network model to integrate prior information on the characteristics of instrument noise and model distortions, thereby improving the accuracy of OES diagnostics. The neural network model takes emission line ratios as input and normalized electron density as output and is trained using a dataset that is generated with a CR model and an instrument disturbance model. The neural network-based OES method is implemented to determine the electron density in a microwave discharge chamber and compared with a traditional OES method with a multi-variant fitting technique. A significant improvement on relative deviation of diagnostic results is observed, which promises a good prospect for further development. [ABSTRACT FROM AUTHOR]

Number density of plasma-generated atoms or molecules is an important parameter for both fundamental research and applications. It can be measured in a straightforward manner, using vacuum-ultraviolet absorption spectroscopy, which is mainly possible in laboratory conditions as it may require bulky equipment, such as lasers. By contrast, optical actinometry is an alternative approach that only uses spontaneous emission from the plasma. This technique relies on the so-called corona excitation and uses emission line ratios between the gases with unknown and known concentrations (called actinometer in the last case). As a result of using line ratios, the additional density calibration is not required if the excitation cross sections are known. This study discusses Ar-based actinometry in low-pressure (roughly < 1 kPa) plasma discharges with an emphasis on multiple line ratios. The work is particularly focused on the method's applicability, the choice of Ar cross sections, and potential error sources. The influence of the additional excitation mechanisms is analyzed based on both experiments and modeling. The optical transitions for F, O, H, N, and P atoms along with expressions for their number density are presented, not requiring high optical resolution for measurements. For the sake of method validation, it is shown that in low-pressure radiofrequency discharges, a nearly excellent agreement between the actinometry data and the calibrated measurements can be achieved by careful selection of optical transitions. [ABSTRACT FROM AUTHOR]

ABSTRACT This study explores nitrogen fixation in the Martian atmosphere using plasma technology. By combining microwave and dielectric barrier discharges (DBD), nitrogen was converted into water‐soluble nitrogen fertilizer (N₂O₅) for agriculture. Despite the low pressure and temperature of Mars, optimized discharge conditions and reactor design significantly boosted the generation efficiency of N₂O₅ precursors, NO₂, and O₃ production. The microwave discharge achieved NOx concentrations of 63.6 ppm, close to experimental values; adjusting DBD pressure to 760 Torr enhanced O₃ concentration by 105 times, yielding 3.8 mol/m³ N₂O₅. The findings lay a technological foundation for future Martian ecosystem development and highlight the need for further experimental validation and system optimization. [ABSTRACT FROM AUTHOR]

A two-dimensional axisymmetric plasma model of a radio frequency induction discharge of low pressure (13–133 Pa) with gas blowing is presented. The model includes the Navier−Stokes equations, the continuity equations for ions, electrons, and metastable atoms, the equations for the conservation of energy of electrons and atoms in the ground state, and the Maxwell equations with the corresponding boundary conditions. A feature of the model is that the initial approximation for the concentration of electrons is chosen by solving a one-dimensional eigenvalue problem. The results of numerical calculations of the characteristics of RF discharge with gas blowing are presented. [ABSTRACT FROM AUTHOR]

The characteristics of a high-frequency discharge during plasma-liquid treatment of the surface of a metal plate made of copper grade M1 under atmospheric illumination were studied. The high-frequency (HF) discharge is ignited by supplying an electrolyte to the surface of a metal electrode. The surface temperatures of the electrodes during the burning of an HF discharge were studied using infrared thermography. The types and shapes of plasma structures generated in the interelectrode gap are described. The crystal composition, electron concentration, variable and rotational temperatures were determined using optical emission spectroscopy (OES). The morphology and surface of the plates were studied before and after processing. [ABSTRACT FROM AUTHOR]

The work carried out numerical studies of the dynamics of plasma parameters in a microwave discharge in a tube in argon at low pressures. Numerical calculations were carried out for various values of the discharge power input and taking into account the gas flow. The results demonstrated that at a pressure of 10 Torr and power input into the discharge of 100 and 1000 W, the gas temperature in the discharge reaches values of 304 and 345 K, respectively. [ABSTRACT FROM AUTHOR]

Liquid-phase processing of oxygen-containing organic compounds in a chemical microfluidic plasma reactor has been implemented. Excitation of a microdischarge in vapor–gas bubbles in a treated liquid stream by an external electric field makes it possible to intensify redox processes in order to obtain valuable components and intermediate products of organic synthesis without the introduction of complex and unstable oxidizing agents. By controlling the parameters of the microreactor, it is possible to create conditions for the preferential occurrence of a desired chemical reaction: partial or deep liquid-phase oxidation of alcohols, oxidative rearrangement of ketones, and cracking or oxidative degradation of the carbon skeleton. [ABSTRACT FROM AUTHOR]

The paper describes methods for preparing natural fabrics for direct printing. The influence of preliminary plasma treatment of natural fabrics on color fastness to washing has been studied. Cotton fabrics and Tencel fabric made from eucalyptus fibers have been examined. Plasma treatment was used to modify the fabrics. The plasma type was nonequilibrium, low-temperature; capacitively coupled radiofrequency discharge plasma in air. It has been established that the plasma treatment of the fabrics in air at a power of 2000 W helps to increase color fastness to washing by up to 82%. [ABSTRACT FROM AUTHOR]

This study investigates the ionization pressure threshold of a gas (air, helium, argon, and SF6 across a wide pressure range) filled dielectric tube when a ∼300 MW, ∼0.7 ns, 9.6 GHz high-power microwave (HPM) pulse propagates through it. The thresholds are determined as the pressure for which the energy of the transmitted HPM pulse decreases to ∼30%, which is close to the same HPM pulse's transmission coefficient when a metal rod fills the tube. These thresholds are found to be 0.4 × 105 Pa,105 Pa, 1.8 × 105 Pa, and 0.2 × 105 Pa, for air, argon, helium, and SF6, respectively. The measured intensity of the plasma light emission starts to decrease at a pressure which coincides with the pressure threshold determined by HPM pulse propagation. Additionally, at gas pressures <5 × 104 Pa, it is shown that time- and space-resolved images of the light emission display a diffused plasma which at higher pressures >105 Pa transforms into streamer like plasma. Simplified numerical simulations of a microwave discharge in air at 1 × 105 Pa and 4 × 105 Pa are consistent with the experimental plasma light observations. [ABSTRACT FROM AUTHOR]

When the power converter connects to the high-frequency transformer breaks through the bottleneck and reaches a frequency of 100 kHz or even higher, the high-frequency transformer's inter-turn insulation faces more serious high-frequency discharge and high-temperature problems. In order to improve the service performance of oil-immersed high-frequency transformer insulation paper, composite K-BNNS particles are prepared by ultrasonic stripping, heat treatment, and thermomagnetic stirring. Then, K-BNNS particles are mixed with PMIA (polymeric m-phenylenediamine solution) slurry to produce composite aramid paper. And the effects of K-BNNS particles with different contents on the thermal conductivity, dielectric properties, partial discharge properties, and mechanical properties of aramid paper are explored. It can be found that, when the addition of composite particles (K-BNNS) is 10%, the comprehensive performance of composite aramid paper is the best. Compared with Nomex paper, the in-plane and through-plane thermal conductivity of composite insulating paper F-10 increased by 668.33% and 760.66%, respectively. Moreover, the high-frequency breakdown voltage increased by 48.73% and the tensile strength increased by 2.49%. The main reason is that the composite particles form a complete thermal conductive network in the aramid paper matrix and a large number of hydrogen bonds with the matrix, which enhances the internal interface bonding force of the material and changes the charge transport mechanism. [ABSTRACT FROM AUTHOR]

Hydrogen is often envisioned as a green fuel and energy carrier. However, a greenhouse gas‐free production method is still needed for this purpose. A promising method is the pyrolysis of methane. In this study, we present the three‐dimensional simulation of methane pyrolysis in a microwave plasma torch operated in an argon–methane mixture. Due to the high gas temperatures, the chemistry is dominated by reactions between neutral particles. Therefore, the plasma is treated only as a heat source using space‐resolved gas temperature measurements as input. The end‐of‐pipe results of the simulation are compared to measured values, showing good agreement for methane conversion. [ABSTRACT FROM AUTHOR]

• A feedback control platform is built to reduce thrust noise in various operations. • Variations of AG current with feedback control are related with interception rate. • CEX process affects AG current with feedback control through the types of ions. High thrust noise limits the application of microwave discharge ion thruster (MDIT) on space gravitational waves (GWs) detection, which needs to be suppressed by a feedback control system. A feedback control experimental platform is established for MDIT choosing microwave power and ion beam current respectively as controlled variable and feedback parameter. Experiments show the feedback control system adjusts screen grid (SG) current by regulating microwave power to compensate for fluctuations of acceleration grid (AG) current, which is mainly because the ability of microwave power to adjust SG current is dramatically stronger than that to adjust AG current. Faced with fluctuations of decreasing flow rate, the feedback control system boosts microwave power to stabilize ion beam current. However, the AG current shows diametrically opposed characteristics for operations with different interception rates under regulation of a feedback control system. Further study shows this phenomenon is the macroscopic reflection of ion trajectories variations on AG current under the function of specific electric field when feedback control system changes the proportions of primary ions and charge exchange (CEX) ions by influencing CEX reaction intensity in the grid system and its downstream region. Analysis of mean free path shows the CEX reaction intensity in the grid system is stronger than that downstream from AG. Therefore, the physical process in the grid system dominates variations of AG current. [ABSTRACT FROM AUTHOR]

Recently, two completely different types of lasers—a fiber laser and a gas-discharge laser—were combined into a single device by demonstrating 2.03 µm laser generation in He-Xe plasma that was produced by a microwave discharge directly inside a hollow-core fiber. This new type of laser—a gas-discharge fiber laser—provides excellent opportunities to greatly enrich the wavelength range of the operation of fiber lasers. In this work, we investigate a He-Kr gas mixture as an active medium of this new type of laser. As a result, a He-Kr gas-discharge fiber laser is demonstrated for the first time. The laser was pumped by a microwave discharge in a He:Kr (40:1) mixture that was filled into a revolver fiber with the hollow-core diameter of 130 µm. The total gas pressure was about 100 torr. With broadband mirrors of the laser resonator, generation was observed simultaneously at wavelengths of 2190 and 2523 nm. The output power of the He-Kr gas-discharge fiber laser was about 1 mW. [ABSTRACT FROM AUTHOR]

The dynamics of the neutral atoms in Hall thrusters affects several plasma processes, from ionization to electrons' mobility. In the context of Hall thruster's particle-in-cell (PIC) modeling, the neutrals are often treated kinetically, similar to the plasma species, and their interactions with themselves and the ions are resolved using the direct-simulation Monte–Carlo (DSMC) algorithm. However, the DSMC approach is computationally resource demanding. Therefore, modeling the neutrals as a 1D fluid has been also pursued in simulations that do not involve the radial coordinate and, hence, do not resolve the neutrals' radial expansion. In this article, we present an extensive study on the sensitivity of the PIC simulations of Hall thruster discharge to the model used for the neutral dynamics. We carried out 1D axial PIC simulations with various fluid and kinetic models of the neutrals as well as self-consistent quasi-2D axial-azimuthal simulations with different neutrals' fluid descriptions. Our results show that the predictions of the simulations in either 1D or 2D configurations are highly sensitive to the neutrals' model, and that different treatments of the neutrals change the spatiotemporal evolution of the discharge. Moreover, we observed that considering the ion-neutral collisions causes a significant variation in the neutral temperature, thus requiring that the neutrals' energy equation to be included as well in their fluid system of equations. Finally, the self-consistent axial-azimuthal simulations highlighted that a neutrals' model based on the continuity conservation equation only is not an appropriate choice and leads to physically unexpected high-frequency global discharge oscillations. [ABSTRACT FROM AUTHOR]

The dynamical behavior of the capacitively coupled Ar plasma driven by four frequencies (54, 80, 94 and 100 MHz) at fixed pressure are simulated by the particle-in-cell/Monte-Carlo collisions (PIC/MCC) model based on the electromagnetic field. The magnetic field is generated by plasma current itself. The results show that the electron density, charge density, and electron temperature increase with the frequency increase when radio frequency (RF) power is 40 W. The electron heating rate and argon ion heating rate near the sheath increase with the frequency increase. The high-energy electron density (> 3 0   eV) varies nonlinearly with the frequency increase. The high-energy electron density is highest at 80 MHz among the four frequencies. The electron density, charge density, and high-energy electron density increase with RF power (30, 45, 60, and 75 W) increase at 80 MHz. The electron temperature decreases with RF power increase at 80 MHz. The electron heating rate and argon ion heating rate near the sheath have no change with RF power increase at 80 MHz. The electron energy probability distributions (EEPF) show that the number of high-energy electrons (> 3 0   eV) is highest at 80 MHz. The reason may be the electron resonant heating that occurs in the plasma when the electron cyclotron frequency equals source frequency at 80 MHz. The electron dynamics of capacitively coupled plasma is important for microelectronics etching and membrane deposition. [ABSTRACT FROM AUTHOR]

Due to the high stability and less maintenance, the radio frequency (RF) driven ion source is preferred for the neutral beam injection (NBI) system. In a popular design of the RF ion source for NBI application, a Faraday shield (FS) is installed inside the RF plasma driver to protect the discharge tube. However, the FS also brings some drawbacks, such as lowering the RF power transfer and increasing the processing difficulty. A prototype of the RF plasma driver without FS and with mature manufacturing technology has been developed by using a water-cooled discharge tube. After basic testing, this prototype was further tested under the RF plasma discharge experiments in views of high power, long pulse, and long term. The reliability and its plasma characteristics were the focus of these experiments, also for the hidden issues. The results show that the prototype could generate stable and high-density plasma without any damage or sputtering mark. An RF plasma discharge of 50 kW and 20 s has been achieved. The expected frequency tuning was equally effective on the prototype. Moreover, compared to the RF plasma driver with FS, the prototype could produce higher electron density in the extraction region under the same RF power. Of course, some of the shortcomings of the prototype have also been exposed in the experiments and will be improved in subsequent experiments. [ABSTRACT FROM AUTHOR]

A parametric study in terms of a global model has been performed on the kinetic processes in iodine plasma generated by electrodeless inductively coupled radiofrequency and microwave discharges. The formation dynamics of the plasma component composition has been obtained for various regimes. It has been shown that ion–ion plasma is formed at short times and a transition from ion–ion to electron–ion plasma occurs at times from several fractions to several milliseconds. The model made it possible to determine the most optimal regimes of iodine plasma generation in modern electric rocket engines. [ABSTRACT FROM AUTHOR]

Charging and dynamics of a spherical dust grain injected into a continuous and pulsed radio frequency (RF) discharge have been studied using a one‐dimensional fluid model. First, the plasma characteristics of the two types of discharges are computed and compared. In the pulsed discharge, it is found that the central electron density exhibits a periodic variation while the averaged electron density is lower compared to that in the continuous discharge due to the decrease in the total ionization rate. Further, the dust charge is computed using the plasma characteristics. It is found that the dust charge negatively increases as the duty cycle ratio increases. Also, the charge in the pulsed discharge is lower in comparison to the continuous discharge due to the shorter duration of the pulsed RF discharge limiting the amount of energy transferred to electrons. On the other hand, the dust particle remains in the powered sheath region exhibiting a damped oscillation in the two discharges with higher oscillation frequency in the continuous discharge. [ABSTRACT FROM AUTHOR]

Chondrules are tiny particles that occur in stony meteorites and are considered as the building blocks of early asteroids and planets. It is believed that they were formed by the fast heating of the dust in the solar nebula. To date, there is no lab-scale experimental study of the formation of chondrules from the initial gas phase precursors following fast heating and crystallisation. The motivation of this work is a pre-trial study of the formation of chnodrule-like particles. The formation of meteorites in the space environment is associated with the aggregation of small particles or molecular clouds under the influence of shock waves or high-energy gas discharges in the solar nebula. In this work, the properties of product formation at the nanoscale-level were investigated using different feedstock materials which are the dominant elements in the meteorite. The structural and morphological properties of the synthesised Si-Fe nanomaterials were analysed by scanning/transmission electron microscopy (SEM/TEM), and chemical composition was analysed by X-ray energy-dispersive spectroscopy (EDS). The identification of crystalline phases was carried out by X-ray diffraction (XRD), whereas the presence of an Fe-Si system in the synthesised particles was demonstrated by Mössbauer spectroscopy. The obtained materials were exposed to the relatively high-energy pulsed plasma beam on the substrate with the aim to emulate the possible fast heating and melting of the formed nanoparticles. The formation steps of growing synthetic (engineered) chondro-like particles and nanostructures in laboratory conditions is discussed. [ABSTRACT FROM AUTHOR]

Placing metals within microwave ovens has been generally viewed as a dangerous practice because of occurrence of violent discharge, but in recent years such discharge phenomenon has attracted increasing attention and has enabled a variety of exciting applications. In this work, we provide a comprehensive review of fundamental understanding of microwave–metal discharge interaction and its state-of-the-art application for nanomaterials synthesis. We introduce the microscopic interaction between different categories of materials and the electric and magnetic field of microwaves. For microwave–metal interaction, we highlight its size-dependence and point out the influence of the oxide layer on the surface of metals. We discuss the required conditions for occurrence of discharge, microscopic formation mechanism, and characteristic features of microwave–metal discharge processes. Through analyzing the influence from the microwave input, discharging metals, and surrounding discharging media, we discuss the strategy for systematical regulation of the discharge process. We describe the applications of the microwave–metal discharge for facile synthesis of various functional nanomaterials including core–shell carbon/metal, metal oxides, metal chalcogenides, intermetallic compounds, metallic nanoparticles and metallic compounds, and organic compounds. Finally, the challenges in precise characterization and dynamic regulation of the discharge process as well as exciting application opportunities are discussed. [ABSTRACT FROM AUTHOR]

This investigation conducted an experimental study of flow control in a Mach 2.5 cavity combustor using arc plasma energy deposition (APED), implemented both with and without injection. APED was produced by a pulsed arc discharge plasma actuator at frequencies of 5, 10, 15, and 20 kHz. The objective is to elucidate the influence and underlying mechanisms of APED on the flow dynamics by statistically evaluating time-resolved schlieren images and monitoring pressure fluctuations throughout the control process. The findings indicate that APED significantly modifies the energy distribution across unsteady modes and alters the pressure distribution within the flow field. In scenarios without injection, high-frequency discharge triggers oscillations in the shear layer; the impact of precursor shocks and thermal bubbles diminishes the magnitude and fluctuations of both shear layer-induced and internal shocks. Conversely, in the injection scenario, high-frequency discharge, in conjunction with oscillations of the boundary layer and bow shocks, amplifies the oscillation amplitude and frequency of jet vortex shedding. Additionally, APED intensifies the pulsation and penetration depth of the jet, which is essential for enhancing the mixing efficiency of the incoming flow with fuel. The effectiveness of the control is positively correlated with the actuator's discharge frequency, or its average power, within the confines of this study. [ABSTRACT FROM AUTHOR]

The effect of external gas injection near the plume on the performance of a microwave discharge cathode is investigated. Experiments were conducted under two gas injection conditions: gas addition and gas distribution. Gas distribution tended to lead to better performance than gas addition. In the gas distribution experiments, the total gas consumption was kept constant, the internal gas flow rate was reduced, and external gas was supplied. The electron current increased from 0.26 to 0.49 A at 35 V when the microwave power was 15 W. When the sum of the internal and external gas flow rates was held constant, external gas injection lowered the neutralization costs and increased the gas utilization efficiency. The neutralization current was successfully increased by 48 % at 12 W of microwave power compared with 8 W of microwave power with the same level of naturalization cost and gas utilization efficiency. The electron temperature and plasma density in the plume, as measured using a Langmuir probe, suggested that an increase of ionization in the plume by the external gas injection enhanced the cathode's performance. • Supplying gas into the plume of a microwave discharge cathode improves its performance. • Neutralization current increased by 58 % with external gas injection. • External gas injection decrease naturalization cost and increase gas utilization efficiency. • An increase of ionization in the plume by the external gas injection enhanced the cathode's performance. [ABSTRACT FROM AUTHOR]

Gas chromatography was used to study the products of an atmospheric pressure microwave discharge in water with methane bubbling at incident microwave power ranging between 500 and 650 W and methane flow rate ranging between 25 and 75 mL/min. The main components of products are H2, CO, CO2, and CH4. The concentration of H2 reaches 75% with the energy consumption for hydrogen formation of 25 L/kWh. A zero‐dimensional self‐consistent nonstationary discharge model, which takes into account the process of quenching of reaction products, was developed to analyze experimental results and study mechanisms of the formation of hydrogen and carbon oxides. Taking into account the quenching of reaction products is an important and necessary part of modeling discharges in liquids. [ABSTRACT FROM AUTHOR]

A system is described for introducing microwave power into the vacuum chamber of a tokamak for preionization of the gaseous medium located there in order to facilitate subsequent discharge in it. Three main problems arising in this case are considered and a way to solve them is proposed. The calculation model of the electromagnetic structure includes a mode converter, a dielectric transformer, and a galvanic isolation unit. All geometric parameters of the device components were optimized. The described microwave power input device is made of nonmagnetic stainless steel and is currently used at the MEPhI training and demonstration tokamak. [ABSTRACT FROM AUTHOR]

A microwave discharge inside of a methane bubble in boiling water is modeled in a 0D approximation taking into account the change in the size of the plasma bubble. The process of quenching the reaction products after the bubble detaches from the electrode surface is also simulated. The working pressure is 1 atm. It is shown that the main reaction products are H2, CO2, and CO. The ratio of CO2 and CO concentrations depends on the ratio of the initial flows of water vapor and methane. The calculated concentrations of the main decomposition products of methane and water are in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

A characterization of plasma parameters and neutral particle energies and fluxes has been performed for radio frequency and microwave discharges in the Toroidal Magnetized System (TOMAS). A movable triple Langmuir probe was used to study the electron densities and temperatures, and a time-of-flight neutral particle analyzer was used to measure the energy and fluxes of neutral particles, as a function of the total injected power and the antenna frequency used to generate the plasma. The experimental results can provide information on the behavior of neutral particles at low energies in wall conditioning plasmas. [ABSTRACT FROM AUTHOR]

The diagnostic of magnetized radio frequency complex plasma via probing techniques and spectroscopy is challenging. However, a self-excited dust ion acoustic waves (DIAWs) have been observed employing laser scattering. Inspired by the current high enthusiasm for the theoretical description of complex plasma, we study the propagation of DIAWs in a three-dimensional collisional and magnetized dusty plasma medium. We consider the fluid model for dust and ion particles, while we neglect the inertia of electrons considering the Boltzmann distribution. A linear dispersion relation is obtained and a nonlinear modified Zakharov–Kuznetsov equation is derived utilizing the reductive perturbation technique. The effects of ion-neutral and dust-neutral collisions on the dynamics of the nonlinear DIAWs are considered. The phase portrait analysis and numerical illustration of a rarefactive DIA cnoidal waves and solitons are also presented. Our findings agree with experimental observations by Choudhary M, Bergert R, Mitic S, and Thomas MH. [Influence of external magnetic field on dust acoustic waves in a capacitive rf discharge. Contrib Plasma Phys. 2020;60:e201900115] as the growth of nonlinear periodic waves is recorded when the magnetic field is roughly 0.05 T and vanishes when the magnetic field is close to 0.1 T. Moreover, the model reveals that the electrostatic cnoidal and soliton waves propagate with low frequencies up to 140 Hz. [ABSTRACT FROM AUTHOR]

A magnetized capacitively coupled oxygen plasma was studied synergistically using phase resolved optical emission spectroscopy and particle‐based kinetic simulation. Discharge mode transitions from ambipolar mode into drift mode and finally into α mode induced by increasing the magnetic field were observed at different driving frequencies and different electrode gaps. The simulation results demonstrate that the discharge operating in the same mode exhibits a similar degree of electronegativity. By increasing driving frequency or electrode gap, the same discharge mode transition tends to occur at a lower magnetic field, and, meanwhile, the high electric field and electron power absorption shift from the bulk region to the sheath edge. [ABSTRACT FROM AUTHOR]

The work studied the effect of a low-pressure RF discharge on the structure of leather from the skins of sea and river fish. The volumetric nature of plasma processing of natural materials has been determined, because the surface of the skin is exposed to a flow of ions with an ion energy of 50–100 eV, and the treatment of the internal surfaces of the material becomes possible due to the instantaneous potential difference of the SZ on opposite sides of the sample, which occurs during HF oscillations of the electron gas in the plasma and reaches values of 80–160 V. [ABSTRACT FROM AUTHOR]

The paper considers the main stages of constructing a two-dimensional model of the constant conductivity of a finite-length RF induction discharge. The system of equations describing the quasi-stationary electromagnetic field of a high-pressure discharge allows only a numerical analysis of its structure. An analytical model is required to study the discharge structure in the axial region. To construct it, it is necessary to proceed to the complex form of Maxwell's equations. This approach was first used by J.J. Thomson to describe a one-dimensional RF discharge. In this case, the nonlinear differential equations of the electromagnetic field in physical variables turn into linear differential equations for complex quantities, which allow accurate solutions using special Bessel and Kelvin functions for a complex argument. The obtained relations allow us to formulate several conclusions that relate to the structure of a quasi-stationary electromagnetic field in a finite-length discharge. The results obtained in this work may be useful to specialists in the field of physics and technology of RF induction discharge. [ABSTRACT FROM AUTHOR]

A pulsed microwave surfaguide-type discharge used for nitrogen fixation in N 2 –O 2 gas mixtures is characterized by optical emission spectroscopy. Results show that both rotational and vibrational temperatures are elevated in the active zone near the waveguide, decaying along the discharge tube in both upstream and downstream. The characteristic length of optical emission from NO(A - X) transition gets contracted when pressure increases, specifically at P ≥ 2 Torr. The degree of vibrational non-equilibrium (defined as the ratio between vibrational and rotational temperatures) is decreased by a factor of two when pressure changes from 0.6 to 10 Torr. Non-equilibrium likely disappears as the discharge pressure rises, resulting in a gas temperature elevation. A correlation between gas residence time, pulse duration, and characteristic times for different energy transfer channels is discussed. The rotational–vibrational dynamics differs for NO and N 2 during the pulse. Both species lose vibrational excitation at the beginning of the pulse, whereas N 2 gets re-excited again during the second half of the pulse, which may occur as a result of an efficient pumping-up effect through the vibrational–vibrational energy transfer. At the same time, vibrational relaxation of NO takes place primarily due to a strong vibrational–translational exchange via NO–O 2 and NO–O collisions. [ABSTRACT FROM AUTHOR]

Bands of the g 6Φ-X 4Δ, g 6Φ-A 4Π, g 6Φ-a 6Δ, and g 6Φ-b 6Π electronic transitions of iron monodeuteride (FeD) have been measured in laser excitation and in dispersed fluorescence. The molecules were produced both in a cold supersonic molecular jet source and in a chemical reaction between iron pentacarbonyl [Fe(CO5)] and a microwave discharge of argon and hydrogen gases. Dispersed fluorescence from the latter source was detected at high resolution with a Fourier transform spectrometer, yielding a large number of the transitions observed. The data reveal that FeD experiences strong interstate couplings that compromise fitting of the data with traditional Hamiltonians but that the problem is less severe than in corresponding spectra of FeH. This work greatly expands the available data on FeD, which were previously characterized only through the F 4Δ-X 4Δ spectrum and pure rotational data in the ground state. [ABSTRACT FROM AUTHOR]

Microwave machining is considered a potential technique to process some nonmetals and a few metals. The technique is found promising at low microwave power. This work analyzes effects of drilling time while drilling stainless steel sheets at low average microwave power. Microwave drilling trials were conducted inside domestic microwave oven at an average microwave power level of 70 W. Interaction of a pointed thoriated tungsten tool (diameter: 1 mm, minimum tip diameter ≈ 0.1 mm) with microwaves triggered metal-microwave discharge plasma column to ablate stainless steel sheet. Tool wear was observed to increase with drilling time, which influenced the plasma column and the resulting quality of drilled holes. Overcut increased with drilling time due to progressive expansion of the plasma column. Similarly, heat-affected zone widened with increase in drilling time. Circularity degraded due to declining uniformity of plasma column with longer drilling. Imaging of plasma column was discussed. Moreover, measures for improving performance parameters are discussed. [ABSTRACT FROM AUTHOR]

The paper shows that upon ignition of the combined gas discharge in the resonator chamber, there appears a double layer with diode properties that consists of layers of positive and negative charges surrounding the workpiece. An increase in the level of microwave power supplied to the chamber leads to a decrease in the equivalent diode resistance in open and closed modes and an increase in the current flowing through the unit. The ions of the process gas (nitrogen or argon) ionized by the microwave field fall on the product surface and diffuse into it as a result of the thermal diffusion process, which hardens the surface layer. The product is heated when a positive bias potential is applied to it by a stream of high-energy electrons arriving at the surface and accelerated to energies of tens and hundreds eV in the discharge acceleration zone. Ion-plasma implantation leads to a significant increase in the strength, wear resistance and corrosion resistance of the surface of the processed product. [ABSTRACT FROM AUTHOR]

Experimental study has been made of the ignition of a subcritical microwave discharge at pressures in the range 55–79 Torr with the initiation by pulsed laser radiation (58 mJ in a pulse). A rise of 36% in the critical pressure was obtained to form the discharge with the orientation of the laser beam along the vector of the microwave-field strength. Computer modeling has shown that upon the traversal of a focused laser beam, a highly conductive laser trail can be formed with a peak ionization degree as high as 10%, which, for a period of the order of 1 μs, locally enhances the electric microwave field up to supercritical values. [ABSTRACT FROM AUTHOR]

The great advantage of plasma technology in harnessing abundant clean energy for electrifying and decentralizing the chemical industry holds the promise of attaining carbon neutrality. Therefore, recent research efforts have been dedicated to reducing the energy costs of plasma processes to facilitate the commercialization of this technology. However, it has been noted an inconsistency in reporting energy costs across the literature resulted from inaccurate estimation of power consumption within the system, leading to the misevaluation of the process, its underlying mechanism, and the significance of critical factors. This study comprehensively addresses these challenges by discussing and refining methods for estimating power consumption in a plasma system. Insights are drawn from our ongoing research in plasma NOx synthesis, specifically a thorough analysis of the discharge dynamics in a recently developed reactor "high-frequency spark discharge" using a high-speed camera, ICCD camera, and high-performance oscilloscope at various pulse widths of the applied voltage. The investigation revealed the importance of accounting for the post-spark period in the voltage cycle during power estimation, as it demonstrates an influence on NOx synthesis. Furthermore, the study highlighted and addressed critical errors in power measurement and energy cost estimation in the literature. It is found that a significant error, exceeding ± 70%, arises from overlooking signals delay in the setup and improper adjustment of oscilloscope functions, particularly channel impedance, data averaging, bandwidth, and sampling rate. This paper serves as a valuable guide towards establishing standardized measurements toward the precise estimation of energy costs in plasma processes. [ABSTRACT FROM AUTHOR]

This report describes an investigation by experimentation to elucidate atmospheric discharge plasma induced using a 50 kW millimeter-wave beam at 94 GHz. Millimeter-wave discharge plasma is useful for an ultraviolet light source, radioactive material detection, chemical decomposition, and beamed energy propulsion (BEP). The gyrotron used in this study is the "UT-94" with a frequency of 94 GHz and an output power of 100 kW, which was developed at the University of Tokyo specifically for BEP research. The 94 GHz frequency is promising for atmospheric energy beaming because of its low atmospheric attenuation, small beam divergence, and existing utilization track records in the atmosphere. This study experimentally investigated the relationship between the incident beam power density and propagation velocity of an ionization-wave front, which is particularly critical to thrust performance. In addition, the plasma structures were also clarified at 94 GHz and compared with other microwave and millimeter-wave frequencies, such as 28 GHz and those higher than 100 GHz. As a result, finer microscopic structure in the H–k plane was observed than those reported in earlier studies. Furthermore, we found a clear relation between structures and propagation velocities in terms of the electric field concentration of the incoming electromagnetic-waves. [ABSTRACT FROM AUTHOR]

Carbon deposits consisting of vertically oriented multilayer graphene sheets on metallic foils represent an interesting alternative to activated carbon in electrical and electrochemical devices such as super-capacitors because of the superior electrical conductivity of graphene and huge surface–mass ratio. The graphene sheets were deposited on cobalt foils by plasma-enhanced chemical vapor deposition using propane as the carbon precursor. Plasma was sustained by an inductively coupled radiofrequency discharge in the H mode at a power of 500 W and a propane pressure of 17 Pa. The precursor effectively dissociated in plasma conditions and enabled the growth of porous films consisting of multilayer graphene sheets. The deposition rate varied with time and peaked at 100 nm/s. The evolution of surface wettability was determined by the sessile drop method. The untreated substrates were moderately hydrophobic at a water contact angle of about 110°. The contact angle dropped to about 50° after plasma treatment for less than a second and increased monotonously thereafter. The maximal contact angle of 130° appeared at a treatment time of about 30 s. Thereafter, it slowly decreased, with a prolonged deposition time. The evolution of the wettability was explained by surface composition and morphology. A brief treatment with oxygen plasma enabled a super-hydrophilic surface finish of the films consisting of multilayer graphene sheets. [ABSTRACT FROM AUTHOR]

The work is devoted to the study of the characteristics of a low-temperature plasma of a high-frequency (HF) discharge (f = 13.56 MHz) ignited between metallic and electrolytic electrodes at atmospheric pressure. Burning of an RF discharge in a diffuse (volumetric) form is observed at the interface between the media between the electrodes. Numerical calculations of the electric field strength and the distribution of the volumetric power density of the Joule heat release before breakdown in a vapor-gas mixture near a metal electrode are presented. The discharge radiation spectrum, plasma composition, and electron density were studied by optical emission spectroscopy. The thermograms of the electrode surface under the conditions of an RF discharge are considered. [ABSTRACT FROM AUTHOR]

An understanding of the degradation mechanism of a microwave discharge cathode is the key to extending the lifetime of microwave ion thruster systems. This study investigates the effect of nozzle contamination by sputtered Ag-polytetrafluoroethylene (PTFE) on microwave discharge cathode performance. The current–voltage characteristics were measured for nominal and contaminated (by PTFE spray with 0.2 µm thick or tape with 0.15 mm thick) cathodes. The contamination thickness and area on the nozzle were varied to investigate the characteristic differences. It was confirmed that the anode voltage increased by 20 V or more in the case of the contaminated cathode. The anode voltage was measured for the sputter-contaminated cathode to evaluate the effect of contamination under more realistic conditions. After 630 h of sputter-contamination operation, it is estimated that sputtered particles were deposited to a thickness of 77 µm at most, and the anode voltage increased by 8 V. The results show that the downstream surface of the nozzle is critical for maintaining cathode performance. The insulating coating formed by the sputtered PTFE may interfere with ion absorption and degrade electron emission capability. A theoretical model based on the extended Brophy model supports these results. This study provides important information for the use of PTFE-based materials around ion thrusters. [ABSTRACT FROM AUTHOR]

We report on electron spin resonance studies of H atoms stabilized in solid H 2 films at temperature 0.7 K and in a magnetic field of 4.6 T. The H atoms were produced by bombarding H 2 films with 100 eV electrons from a radiofrequency discharge run in the sample cell. We observed a one order of magnitude faster H atom accumulation in the films made of para-H 2 gas with a small ortho-H 2 concentration (0.2% ortho-H 2 ) as compared with those made from normal H 2 gas content (75% ortho-H 2 ). We also studied the influence of ortho-H 2 molecules on spatial diffusion of H atoms in solid H 2 films. The spatial diffusion of H atoms in both normal and para-H 2 films is faster than the diffusion obtained from the measurement of H atom recombination. The rate of spatial diffusion of H atoms in para-H 2 films was slower in comparison with that in the normal H 2 films. We discuss possible explanations of these observations. [ABSTRACT FROM AUTHOR]

In the experiment, plasma–dust clouds were obtained from the substance of the Tsarev meteorite, a simulant of lunar regolith LMS-1D and ilmenite concentrate using a microwave discharge in powder media. For each of the samples, the dynamics of the development of the discharge and the formation of a plasma–dust cloud with subsequent relaxation after the end of the microwave pulse were recorded. From the emission spectra of the plasma and the surface of a solid body, the temperatures of the gas, electrons and surface were determined. A comparison of the phase and elemental composition of the initial samples and samples after exposure to plasma showed that there is no significant change in the composition. However, scanning electron microscopy results clearly indicate spheroidization of the original angular and irregularly shaped particles. The appearance of spherical particles is also observed, the dimensions of which are larger than the linear dimensions of the particles in the original sample. The results obtained indicate the possibility of using such experiments to study chemical and plasma-chemical processes of synthesis and modification of substances under conditions of plasma–dust clouds encountered in space phenomena. [ABSTRACT FROM AUTHOR]

The work presents the results of an experimental study of the characteristics of the RF capacitive discharge placed in a magnetic field with a predominant radial component. The experiments are performed in the plasma source, which has the geometry of a Hall thruster. The integrated characteristics of the discharge, as well as the axial distribution of the probe ion current in the channel of the plasma source, are measured using three diagrams of the organization of the external discharge circuit: with the open for DC discharge circuit, as well as in the combination of a capacitive discharge with a direct current discharge. The main measurements are made in the argon in the flowrate range of 0.75–1.8 mg/s and the power of the generator 80–300 W at a frequencies of 2, 4, and 13.56 MHz, the induction of the magnetic field lying in the range of 100–300 G. Evaluation of the parameters of the plasma engine based on capacitive RF discharge when working in air, argon and krypton are made. [ABSTRACT FROM AUTHOR]

We present the preliminary results of experimental studies on hydrogen production through methane pyrolysis. Based on the analytical review, the technology of methane pyrolysis in the plasma of a microwave discharge was chosen. To implement this method, an installation for applied research PM-6 was developed, and experimental data on the possibility of producing hydrogen was obtained. The methods of mass spectrometry and optical emission spectrometry were used to analyze the products of the methane decomposition reaction. It has been established that at a microwave forward power of 0.6 kW, plasma pyrolysis of methane occurs with the formation of hydrogen, carbon, and hydrocarbons. Preliminary calculations of methane conversion, as a result of the conducted studies, showed a hydrogen selectivity of 4–5%. The developed installation and the applied method are under modernization at the present time. [ABSTRACT FROM AUTHOR]

Dielectric barrier discharge (DBD) plasma has several applications in different fields. One of these fundamental applications is medical usages, where various methods are employed to improve the plasma treatment process. The combination of different gases is one of the important strategies to improve the performance of plasma in treatment. In this paper, the optimized plasma parameters for one-dimensional radiofrequency discharge produced at low pressures in a helium gas combination is studied. In this research, the optimal combination of H2O and He is identified to attain the highest amount of reactive oxygen species (ROS). Considered mixture are 5, 10, 15 and 20 precent of H2O for one dimensional helium gas discharge. The results show that the parameters of the output plasma are highly dependent on the composition of the input gases. It is found that the greatest concentrations of H+, H+, Hes (excited helium), and OH densities are observed when the H2O percentage was at 10%. Moreover, the density distributions of various species and the temperatures of electrons are numerically calculated during the electrical discharge process. These findings provide useful knowledge on how to optimize plasma parameters for biomedical applications, which may lead to improved treatment results in several therapeutic areas. [ABSTRACT FROM AUTHOR]

Thermal stability and the kinetics of thermal decomposition of the thermally reduced graphene oxide (TRGO) treated by a pulsed high-frequency discharge in a hydrogen atmosphere have been studied. The modified Hummers method was used for obtaining the initial graphite oxide from graphite powder. Thermal exfoliation of the graphene oxide powder has been done in vacuum conditions with a heating rate of 5–7 degrees per minute to a temperature of 300 °С. TRGO has been treated by pulsed high-frequency discharge in a hydrogen atmosphere for partial graphene hydrogenation (chemical addition of atomic hydrogen) that leads to structural changes in the carbon planes and formation of C–H sp3 bonds. The thermogravimetry analysis measurements of the mass loss have been carried from room temperature to 1000 °C in a nitrogen atmosphere with a nitrogen flow rate of 20 mL/min and different heating rates: 50, 75 100, 125, 150, and 200 K/min, respectively. Kissinger's multiple heating rate method has been used to determine the activation energy for decomposing substances. Activation energies Ea1, Ea2, and Ea3 equal 28, 50, and 148 kJ/mol, respectively, have been compared with the energies of the activation of thermal defunctionalization of multiwalled carbon nanotubes (MWCNTs). The activation energy Ea3 = 148 kJ/mol is close to that of the thermal decomposition of anhydride functional groups in MWCNT. The value of Ea2 = 50 kJ/mol indicates the presence of the keto and hydroxy acid's function groups on TRGO. Activation energy Ea1 = 28 kJ/mol related with all other groups including the lighter C–H bonds that destructed due to dehydrogenation of the TRGO. Obtained experimental results are useful for further proposing the kinetic model of the mechanism of the most probable reaction of TRGO decomposition. [ABSTRACT FROM AUTHOR]

Ammonia have been attractive as one of the alternative fuels for reducing greenhouse gas (GHG) emissions. However, ammonia combustion has lower combustion performance than common hydrocarbon fuels. Furthermore, it may emit nitrous oxide (N 2 O), which is one of the GHGs. This paper presents the experimental investigations of plasma-assisted ammonia combustion (PAAC) using a rod-electrode-type microwave plasma source (MPS) at atmospheric pressure. The equivalence ratios of premixed ammonia/dry air (NH 3 /Air) gas are set below the stoichiometric combustion of NH 3 to reduce toxic NH 3 in the combustion gas. Under the condition of the equivalence ratios, the experiments are focused on reducing the unburned NH 3 and produced N 2 O concentrations in the combustion gas. In the experiments, the unburned NH 3 , nitrogen oxide (NO x) (the sum of nitric oxide (NO) and nitrogen dioxide (NO 2)), and N 2 O concentrations in the combustion gas are investigated in terms of the flow velocity of premixed NH 3 /Air gas inside the rod-electrode-type MPS and the transmission power to the rod-electrode-type MPS. In conclusion, the rod-electrode-type MPS is identified to be useful for PAAC. The NH 3 and N 2 O concentrations in the combustion gas reach approximately 25 and 4 parts per million (ppm), respectively, under the conditions of the equivalence ratio of 1.0, flow velocity of approximately 0.167 m/s, and transmission power of about 84 W. At that time, the NO x concentration is approximately 4300 ppm, and the power transmission efficiency is approximately 68 %. • Plasma-assisted ammonia combustion (PAAC) was conducted using microwave discharge. • The microwave discharge was generated using a rod-electrode-type microwave plasma source (MPS). • The experiments were conducted without a swirler and below the stoichiometric combustion. • The minimum concentrations of NH 3 and N 2 O in the combustion gas reached 25 and 4 ppm. • The rod-electrode-type MPS was identified to be useful for PAAC. [ABSTRACT FROM AUTHOR]

A one-dimensional (1D) fluid model is developed to investigate the effect of multi-frequency excitation consisting of consecutive harmonics on the charge of a single dust grain in a weakly collisional capacitively coupled plasma discharge. The spatial distributions of the electron density, the electrons temperature, and the charged particle flux are obtained and analyzed under the effects of the number of harmonics. It is shown that the number of harmonics considerably affects the discharge properties and the sheath thickness. In order to analyze the charge of an injected dust particle under the effect of different operating parameters, the model takes into account the electron and ion currents, as well as the effect of collisions between ions and neutral atoms. The results showed that as the number of harmonics increases, the particle charge increases in the powered sheath region while it decreases in the grounded sheath due to the electrical asymmetry effect. However, the charge remains constant in the central region where the electron temperature is constant. The present study further shows that the gas pressure and the driving frequency affect the dust charge oppositely, where an increase in pressure leads to a decrease in the dust charge, especially in the sheath regions, while the particle charge negatively increases as the driving frequency increases for all excitation waveforms. [ABSTRACT FROM AUTHOR]

Using chromatography, the gas composition in a cold plasma jet, which is a flowing afterglow of a microwave glow discharge at atmospheric pressure, is analyzed. The plasma jet is formed by the interaction of the discharge plasma with atmospheric air behind the outlet of the 6-electrode plasma torch, electrical power to which is supplied from the waveguide microwave (2.45 GHz) plasmatron. An analysis of the gas samples of the jet shows that when plasma-forming argon flows through the microwave discharge, hydrogen and methane are formed behind the discharge region, and the concentration of carbon monoxide increases by 5–6 times. The reactive oxygen species in the cold plasma jet is studied using liquid chromatography of an aqueous solution of isopropyl alcohol after treatment with the plasma jet. It is found that because of plasma treatment, partial oxidation of isopropyl alcohol to acetone occurs. This makes it possible to consider acetone as an indicator of reactive oxygen species (hydroxyl radicals, atomic oxygen and ozone) in a cold plasma jet. [ABSTRACT FROM AUTHOR]

A method for activating water by plasma of an electrodeless torch discharge in a microwave electromagnetic field in argon in an environment of water vapor, at atmospheric pressure, to obtain a pure solution of hydrogen peroxide H2O2 without impurities in distilled water is proposed. It is shown that the main mechanism for the formation of atomic hydrogen H• and hydroxyl HO• radicals in the water decomposition is photolysis under the influence of excimer vacuum ultraviolet radiation of argon plasma. Hydrated electrons can be an additional source of radicals in liquid water when the plasma torch comes into contact with the water surface. Today plasma technologies are widely used to produce activated water containing hydrogen peroxide, to solve environmental problems, to increase productivity in agriculture, and for medical use. [ABSTRACT FROM AUTHOR]