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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]

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]

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]

In recent years, interest in striation phenomena in radio frequency (rf) discharges has risen due to the availability of new experimental data and the implementation of new computational models. Depending on the conditions, different mechanisms of discharge striations are realized. These are the ionization instability, the instability due to the electron attachment to electronegative gases, or the instability due to thermoelectric transport. Although the first two mechanisms were modeled quite extensively in recent years, the understanding of the influence of the Dufour effect originating from plasma density gradients on the stability of radio frequency discharges in long tubes remains poor. In this paper, the influence of this mechanism on the longitudinal striations of radio frequency discharge is presented using a one-dimensional model of argon discharge driven with rf excitation under intermediate pressure conditions of 0.5 Torr. It is found that striation formation is sensitive to the value of the thermoelectric heat transport coefficient in the low electron temperature range. The critical value of this coefficient necessary for the instability onset is derived using the linear stability analysis. [ABSTRACT FROM AUTHOR]

The possibilities of igniting a combustible mixture in a high-speed flow using a microwave streamer discharge are considered. The results of experimental studies of the streamer discharge structure at various pressures are presented. To quantitatively characterize the intensity of combustion of fuel ignited by a microwave discharge, pressure and temperature measurements are used in various sections of the jet in the discharge wake. The results obtained demonstrate the possibility of igniting a model combustible mixture when propane or its mixture with air is sup-plied to the discharge region. The main physical mechanisms responsible for heating the discharge plasma to the ignition temperature of the combustible mixture and their characteristic time scales are revealed. The change in the dimensions of the combustion zone with a decrease in the initial proportion of propane in the mixture is discussed. The minimum duration and minimum level of microwave radiation required to ignite a model combustible mixture under various conditions are determined. [ABSTRACT FROM AUTHOR]

Ignition of combustible air/propane mixture in a high-speed flow with a microwave streamer discharge is considered. The experimental results of structure of streamer discharge and quantities at various pressures are presented. Pressure and temperature measurements in various sections of the streamer discharge in high-speed flow are analysed. The results obtained demonstrate the possibility of ignition of air/propane combustible mixture. The main physical mechanisms responsible for heating the discharge plasma to the ignition temperature of the combustible mixture and their characteristic time scales are discussed. The minimum time and minimum level of microwave radiation required to ignite a combustible mixture under various conditions are determined. • Streamer discharge structure at various pressures in high-speed flow is presented. • Streamer discharge provides reliable ignition in a high-speed flow. • Minimum time and pulse energy required to ignite a mixture are determined. [ABSTRACT FROM AUTHOR]

As a method to optimize the power frequency of dual-frequency plasma, we propose an optimization method that combines genetic algorithm and plasma simulation. A two-dimensional plasma simulation model of Ar plasma was constructed with a fluid model. Combining this simulation model with a genetic algorithm, 300 cases of plasma conditions with high plasma density and small variation in electron density were calculated. As a result, the optimum conditions were 175 to 210 MHz for the high-frequency generator and 1.0 to 2.5 MHz for the low-frequency generator. Furthermore, two types of single objective functions that combine the electron density and the variation rate were proposed. The single objective functions with emphasis on electron density and with emphasis on variation rate were introduced, and each objective function was optimized. [ABSTRACT FROM AUTHOR]

Manganese dioxide is one of the key materials in battery, adsorption media, and catalytic materials in the environmental field because of its excellent properties. In this investigation, new synthetical technology—the microwave discharge plasma in liquid method was used directly to make manganese dioxide with potassium permanganate (KMnO4) solution. The synthesis was realized in one step by the microwave discharging plasma in potassium permanganate aqueous solution without using any dispersants or stabilizers. The reduction time was very short, it only takes 3 min to complete the reduction of the 0.2 mmol l−1 potassium permanganate solution for the formation of MnO2. The structure characteristics and adsorption-desorption curves were studied by X-ray diffractometer (XRD), transmission electron microscopy and x-ray photoelectron spectroscopy, XRD, etc. it was found that the synthesized manganese dioxide nano-sheet had a layered structure and a large specific surface area (248.89 m2 g−1). The methylene blue was used to validate the effectiveness of the prepared manganese dioxide. The results showed that the synthesized manganese dioxide had good adsorption and photocatalytic properties. In conclusion, the microwave liquid-phase discharge plasma is a very effective reduction method with potential development. [ABSTRACT FROM AUTHOR]

In this paper we developed a model of the ICRF plasma flow in a geometry of the two following regions: a plasma torch (narrow area) and a chamber (broad area). We used the numerical model developed in the COMSOL-multiphysics software with the given parameters of outlet pressure p = 133 Pa, drive power W = 1.3 kW, drive frequency f = 1.76 MHz and gas flow G = 0–0.4 g/s. We obtained the spatial dependencies of the electron density, electron temperature, pressure in the chamber, gas velocity and performed the analysis of effects in the broadening area. As a result, we noticed some features, which include an anomalous increase of the electron density in the broadening area. [ABSTRACT FROM AUTHOR]

The results of an experimental study of the initiation, development and maintenance of a plasma surface discharge initiated by microwave (microwave) radiation of a gyrotron (75 GHz, 300 kW, 6 ms) in air under normal conditions on the surface of a quartz substrate with metal inclusions are presented. It is shown that the velocity of the propagation of the discharge ionization front reaches 40 m/s, which corresponds to the thermal conduction propagation mechanism. In this case, the maximum calculated gas temperature of the plasma reaches 5500 K, which leads to the sublimation of metal inclusions. For the first time, the plasma parameters of a surface microwave discharge on metal-dielectric targets, which have been used in various aeroplasma and plasma-chemical applications, are presented. [ABSTRACT FROM AUTHOR]

We demonstrate similarity-based scaling networks for capacitive radio frequency (RF) plasmas, which extensively correlate discharge characteristics under varied conditions, incorporating the transition from original to similarity states. Based on fully kinetic particle-in-cell simulations, similar RF discharges in argon are demonstrated with three external control parameters (gas pressure, gap distance, and driving frequency) simultaneously tuned. A complete set of scaling pathways regarding fundamental discharge parameters is obtained, from which each plasma state finds its neighboring node with only one control parameter tuned. The results from this study provide a promising strategy for plasma multi-parameter mapping, enabling effective cross-comparisons, prediction, and manipulation of RF discharge plasmas. [ABSTRACT FROM AUTHOR]

The effect of driving frequency in the range of 13.56–73 MHz on electron energy distribution and electron heating modes in a 50 mTorr capacitively coupled argon plasma discharge is studied using 1D-3V particle-in-cell simulations. Calculated electron energy probability functions exhibit three distinct "temperatures" for low-, mid-, and high-energy electrons at all the studied driving frequencies. When compared to published experimental data, the calculated probability functions show a reasonable agreement for the energy range resolved in the measurements (about 2–10 eV). Discrepancies due to limitations in experimental energy resolution outside this range lead to differences between computational and experimental values of the electron number density determined from the distribution functions, and the predicted effective electron temperature is within 25% of experimental values. The impedance of the discharge is interpreted in terms of a homogeneous equivalent circuit model, and the driving frequency dependence of the inferred combined sheath thickness is found to obey a known, theoretically derived, power law. The average power transferred from the field to the electrons (electron heating) is computed, and a region of negative heating near the sheath edge, particularly at higher driving frequencies, is identified. Analysis of the electron momentum equation shows that electron inertia, which on temporal averaging would be zero in a linear regime, is responsible for negative values of power deposition near the sheath edge at high driving frequencies due to the highly nonlinear behavior of the discharge. [ABSTRACT FROM AUTHOR]

Plasma asymmetry generation in capacitively coupled plasma (CCP) discharges provides control over vital parameters that are useful in many plasma processing applications. In this article, using the particle-in-cell simulation technique, we investigated the spatial plasma asymmetry creation by a temporally asymmetric (sawtooth) waveform by varying its number of harmonics (N). The simulation results predict a non-linear increase in the plasma density and ion flux with an increase in N, i.e., it first decreases, reaching to a minimum value for a critical value of N and then increases almost linearly with a further rise in N. The ionization asymmetry increases with N, and higher harmonics on the instantaneous sheath position are observed for higher values of N. These higher harmonics generate multiple ionization beams that are generated near the expanding sheath edge and are responsible for an enhanced plasma density. The ion energy distribution function (IEDF) depicts a bi-modal shape for different values of N. DC self-bias is observed on the powered electrode, its magnitude with respect to the plasma potential decreases with increasing N, and therefore, the corresponding ion energy on the powered electrode decreases. The results conclude that by changing N of a sawtooth waveform in a collisionless CCP system, the ion flux asymmetry is not altered, whereas sheath symmetry could be significantly affected causing a systematic variation in the ion energy asymmetry. Due to an increase in the higher harmonic contents in the sawtooth waveform, a transition from broad bi-modal to narrow-shaped IEDFs is found. [ABSTRACT FROM AUTHOR]

In the past three decades, first principles-based fully kinetic particle-in-cell Monte Carlo collision (PIC/MCC) simulations have been proven to be an important tool for the understanding of the physics of low pressure capacitive discharges. However, there is a long-standing issue that the plasma density determined by PIC/MCC simulations shows quantitative deviations from experimental measurements, even in argon discharges, indicating that certain physics may be missing in previous modeling of the low pressure radio frequency (rf) driven capacitive discharges. In this work, we report that the energetic electron-induced secondary electron emission (SEE) and excited state atoms play an important role in low pressure rf capacitive argon plasma discharges. The ion-induced secondary electrons are accelerated by the high sheath field to strike the opposite electrode and produce a considerable number of secondary electrons that lead to additional ionizing impacts and further increase of the plasma density. Importantly, the presence of excited state species even further enhances the plasma density via excited state neutral and resonant state photon-induced SEE on the electrode surface. The PIC/MCC simulation results show good agreement with the recent experimental measurements in the low pressure range (1–10 Pa) that is commonly used for etching in the semiconductor industry. At the highest pressure (20 Pa) and driving voltage amplitudes 250 and 350 V explored here, the plasma densities from PIC/MCC simulations considering excited state neutrals and resonant photon-induced SEE are quantitatively higher than observed in the experiments, requiring further investigation on high pressure discharges. [ABSTRACT FROM AUTHOR]

Parametric study and nonlinear dynamical analysis of the discharge parameter variations are presented here for a hollow cathode source in the glow discharge regime and later in the radio frequency (RF) discharge regime. A plasma source consisting of a semi‐transparent hollow cathode leads to the generation of nonthermal energetic charged particles and the formation of multiple potential regimes in the plasma column during both the glow discharge as well as the RF discharge regimes. The hollow cathode discharge obtained using this single plasma source exhibits significant mixed‐mode oscillations (MMOs) during the glow discharge regime. Various regular and irregular sequences of MMOs evolved during the progressive change of discharge voltage in the glow discharge regime. During the RF power application across the hollow cathode source, the charged particles oscillate and appear in bursts in the time series. The present study investigates energy distribution among the coherent modes of discharge through the application of the Empirical Mode Decomposition technique. Multiple coherent modes are identified during both discharge regimes that carry most of the discharge energy. [ABSTRACT FROM AUTHOR]

In this paper, we discuss a number of problems found in the literature related to experimental measurements of rf discharge electrical and plasma parameters with different electromagnetic probes. Incorrect evaluations of discharge power and the inaccurate measurement of basic plasma parameters with electrical (Langmuir), magnetic (B-dot), and microwave probes are among the troubling issues found in many recent publications on rf plasma. The purpose of this review is to show the origination of errors and ways to their mitigation based on the three-decade development of contemporary rf discharge diagnostics. [ABSTRACT FROM AUTHOR]

This study analyzes the dependence of electron extraction efficiency, which is defined as the ratio of the extracted electron current to the generated electron current, on the orifice shapes and magnetic fields of a miniature microwave discharge xenon neutralizer via three-dimensional particle-in-cell simulations with Monte Carlo collisions (PIC–MCCs). The PIC–MCC simulation results show that the orifice shapes do not significantly affect the discharge characteristics or the electron extraction efficiency. However, the efficiency achieves a 1.5-times higher value in a new magnetic field configuration, referred to as MF-2, where the magnetic field lines pass through nearly the entire area of the orifices. This improvement is attributed to the reduction in the electron backflow and the electron loss toward both the downstream inside surface and the outside wall of the discharge chamber. In addition, there are relatively small plasma fluctuations in the discharge chamber for MF-2 due to its low Bohm diffusion coefficient, where no rotating spokes, which are often seen in other E × B devices, are observed. As a result, the electron loss toward the downstream surface inside the discharge chamber is reduced, and this decrease in the electron loss also contributes to the increase in the extraction efficiency. [ABSTRACT FROM AUTHOR]

This article reports experimental observation of rotating plasma discharges in a coaxial structure at a frequency of 2.45 GHz and under atmospheric pressure. In contrast to other cases, the discharge in our case spins without external static magnetic field or moving electrodes. Its formation and impact factors are experimentally explored. Results show that the rotating discharge, especially the peculiarities of its rotation velocity, is attributed to the combined action of gas flow and electromagnetic field intensity between the conductors. Raising the electromagnetic field intensity or reducing the gas flow rate in appropriate ranges can result in a notable increase of the rotation speed. Experiments also demonstrate that the rotation properties are independent of the coaxial dimensions. This article is supposed to provide a new thinking and guidelines for inducing rotating discharge in a coaxial structure without electrodes moving or external magnetic field. [ABSTRACT FROM AUTHOR]

We present the results of an experimental and analytical study of the structural and dynamic properties of a monolayer consisting of dust grains in an electrostatic trap in an RF discharge plasma. The possibility of forming a monolayer with an isotropic distribution for interparticle distance and kinetic energy of particles in the structure has been experimentally shown. Isotropy has crucial importance for the study of various processes in such systems, including the kinetics of phase transitions, the formation of directed flows, wave propagation, and others. [ABSTRACT FROM AUTHOR]

An analysis of the formation of a void in the PK3 setup in dusty plasma with 3.4-μm-diameter melamine–formaldehyde particles—in an RF discharge in argon at a pressure of 12–50 Pa under microgravity conditions at the ISS is presented. The uniform state of the plasma can only be obtained at a voltage close to the discharge extinction voltage. The application of a low-frequency voltage of 20–50 Hz stabilizes the state of the dusty plasma and shifts the void formation threshold towards higher RF voltages. It is shown that the formation of a void is associated with non-local ionization of the plasma at the center of the discharge by fast electrons, which are heated in the near-electrode layers. [ABSTRACT FROM AUTHOR]

The radiation spectra of the RF discharge plasma of dichlorodifluoromethane during copper etching are obtained and analyzed. It is shown that radiation of the RF discharge plasma is represented by atomic and molecular components and it is assumed that the dependences of the intensities of the lines and bands on the external discharge conditions are determined by the excitation of the emissive states on direct electron impact. Moreover, their behavior agrees with the character of the dependences of the etching rate under the same conditions. [ABSTRACT FROM AUTHOR]

Carbon nanoparticles were synthesized using a 13.56 MHz radiofrequency (RF) discharge of Ar/CH4 plasma in pulsed mode to control the nanoparticle size. Experimental observations have shown that the size of carbon nanoparticles increases with the frequency of the pulse signal. It was also found that by using a frequency modulated pulsed RF signal it is possible to control the size of carbon nanoparticles in the 40–70 nm range, where the plasma‐enhanced chemical vapour deposition method is the main mechanism for nanoparticle growth. Transmission electron microscopy image analysis showed two types of nanoparticles, some of which are an agglomerate of nanoparticles with an amorphous structure, while the others are nanometre‐sized with crystalline structures. Changes in the modulation frequency and synthesis time help to obtain different films with different values of the contact angle. [ABSTRACT FROM AUTHOR]

A microwave plasma generator (MPG) of a sub-millimeter scale might be suitable for biomedical applications. However, there are still many unknowns regarding the MPG discharge behavior at this scale and specific conditions. A two-dimensional MPG model at the millimeter scale and its simulation and relative calculation in the COMSOL Multiphysics software are presented. A MPG filled with argon and helium is simulated, respectively. The frequency of a microwave source of about 5 GHz is considered. The number density and temperature of electrons as well as chemical composition are obtained at different power and pressure conditions. The electron density peaks slightly downstream of the crossing point, and the electron density is slightly asymmetrically in the y-plane due to the fact that the electromagnetic waves are absorbed asymmetrically. The electron temperature is relatively low everywhere, in part, due to the high operating pressure. The electron temperature peaks directly underneath the wave guide where the wave is absorbed. The electron density increases with the increase in the internal pressure and the input power of the MPG, the electron temperature decreases with the increase in the internal pressure of the MPG, but the electron temperature cannot be affected by the input power change of MPG. The amount of excited Ar+ and Ars (metastable atom) increases with the increase in the input power and pressure of MPG, but the amount of excited Ar almost remained unchanged. In addition, the amount of excited He almost remained unchanged, while the amount of excited He+, Hes (metastable atom), and He2+ increased with the increase in the input power and pressure of MPG. The simulation results of this model are thus informative for understanding the physical characteristics of millimeter-sized MPG, and it will provide a solid basis for the future development of such hardware in small plasma capsules for cancer therapy. [ABSTRACT FROM AUTHOR]

We present measurements of the time evolution of plasma and electrical parameters in a pulsed capacitively coupled argon discharge operated at a radio frequency of 12.5 MHz, whose amplitude is ‘step-up’ and ‘step-down’ modulated. The ‘step-up (-down)’ amplitude-modulated waveform consists of three segments, i.e., a low (high)-voltage, a high (low)-voltage, and a zero-voltage stage. Here, we focus on the effect of the ratio (ζ = V L/ V H ⩽ 1) of the low-(V L) to high-voltage (V H) amplitude (measured at the end of the respective segment) on the time evolution of discharge parameters. We monitor the behavior of the discharge by measuring (i) the optical emission intensity (OEI) of a selected Ar-I spectral line, (ii) the electron density at the center of the plasma (using a hairpin probe) as well as (iii) the electrical characteristics (by voltage and current probes). It is found that at relatively large ζ (i.e., at low disparity between the two voltage amplitudes), for both the ‘step-up’ and ‘step-down’ cases, these parameters evolve relatively smoothly with time upon changing the voltage amplitude, and the ignition process strongly depends on the duration of the zero-voltage period. At low ζ (i.e., at high disparity between the voltage amplitudes), an abnormal evolution of the parameters can be observed during the low-voltage period for both cases. Specifically, the voltage amplitude and the modulus of the system impedance increase to a higher value, while the relative phase, φ vi, between the voltage and the current approaches 90°, resulting in a reduction of the power deposition and the OEI. The enhanced voltage amplitude decreases to a steady-state value, accompanied by a decline of φ vi, and an abnormal increase of the current amplitude and the electron density after some time, of which the duration increases with the decrease of ζ. The ζ -dependent evolution of the electron density during the low-voltage period was found to significantly affect the subsequent ignition process and electron power absorption mode at the beginning of the high-voltage period. [ABSTRACT FROM AUTHOR]

Despite the progress made in the treatment of nephrolithiasis, the existing methods of renal calculi destruction are not ideal and have both advantages and disadvantages. Considering the process of high-frequency glow discharge formation on the surface of an electrode and in an electrolyte solution, we obtained the results on the destruction of renal calculi in vitro. It was shown that the destruction of kidney stones by glow discharge plasma was caused by several processes—the plasma induced effect of hydrated electrons and shock wave effect of the electrolyte stimulated by electrical breakdowns in the plasma. The plasma generation modes were configured by estimating the thickness of the vapor–gas layer in which the plasma burns. Thus, the average rate of contact destruction of renal calculi was measured depending on the plasma generator input power and time of plasma exposure. We conclude that the method of stone fragmentation by high-frequency electrolyte plasma is rather perspective and can be used in endoscopic urology for percutaneous and transurethral lithotripsy. [ABSTRACT FROM AUTHOR]

Results of optical and gas-dynamic investigations of the microwave discharge plasma under conditions of gas-jet synthesis of diamond are reported. The data are analyzed for determining the temperature and composition of the mixture in the discharge chamber for the purpose of further optimization of the method. The influence of the flow rate of the injected gas mixture on the macroparameters of the gas mixture flow at the exit of the discharge chamber is studied. The temperature and pressure measured in the discharge chamber are used for the numerical analysis of the mixture composition depending on the injected gas flow rate. It is demonstrated that the mixture composition at the exit of the discharge chamber correlates with the rate of diamond synthesis. [ABSTRACT FROM AUTHOR]

High-frequency discharge plasma in halogen-containing gases is widely used in micro- and nanoelectronic technology for cleaning and dry etching the surface of semiconductor wafers and IC functional layers. In this paper, we study the surface quality (based on roughness data) of a semiconductor after plasma-chemical etching in R-23 freon plasma. Freon R-23 is widely used in the technology of etching Si, Ge, and a number of other materials (GaAs, GaP, InP), providing technologically acceptable interaction rates, and also satisfying the anisotropy and selectivity requirements. Nevertheless, the quality control of the surface of IC layers remains an urgent task of modern submicron electronics. [ABSTRACT FROM AUTHOR]

Plasma potential is a key parameter in plasma discharge or fusion plasma to control plasma–wall interaction or ExB drift. The magnitude of plasma potential depends on the overall energy transmitted to the plasma via direct current (dc) or radio frequency (RF) devices such as electrodes or antennas. Knowing the plasma potential from the exciting source is useful to prevent high energetic fluxes to the wall or to improve the plasma confinement or explaining shear velocity. The aim of the present model is to calculate this plasma potential with respect to a dc or RF source in a magnetized or unmagnetized plasma. This double saturated probe (DSP) model takes into account the electron saturation current and is able to derive the plasma potential as a function of the electrode/wall area ratio for a dc or RF discharge in a helium/argon plasma with or without a magnetic field. The results of the model are compared with Aanesland’s model in the case of unmagnetized capacitive sheath and particle-in-cell (PIC) simulations. The magnetized model is applied to a plasma column with a perpendicular capacitive current in an RF discharge. It appears that the plasma potential can increase to almost the RF potential value at a low wall/electrode area ratio ($A_{\text {wall}}/A_{\text {el}}$ lower than 5), while the same potential collapses as soon as the area ratio (perpendicular over the parallel current area) is higher than the electron/ion saturation current ratio. This is directly due to the saturation of electron current, preventing the plasma potential from following the imposed RF potential by the electrode, so that the maximum value can be as lower as the floating potential. The perpendicular current involved is mainly a conduction current modeled as a resistive collisional current. In fusion plasma, the maximum plasma potential can rise to higher values than in plasma discharges, but the collapse of the potential still occurs for long collisional biased flux tubes. [ABSTRACT FROM AUTHOR]

Presently, an atmospheric-pressure non-equilibrium microwave discharge plasma jet is expected to be applicable in the sterilization and disinfection equipment for dental implants. However, since the atmospheric-pressure plasma is in non-equilibrium state, there have been no simplified means established to measure basic properties of the plasma. We successfully developed a radical sensor, a simplified tool for detecting oxygen radicals released from plasma by using polyester fiber as base material, and methylene blue as dye. When this sensor detects an oxygen radical, the color of the radical sensor changes from blue, the original color, to white. In this report, we are going to explain the results of the experiments in the fabrication process to verify the behavior of this radical sensor. We combined polyester fiber, the base material of the radical sensor, and methylene blue, the dye, to prototype the radical sensor and used it in our experiments. The radical sensor features the mechanism in which the color changes from blue to white when plasma-irradiated. We used the angle meter to measure the hydrophilicity level and verified the etching effects of the oxygen radicals on the base material in order to clarify this discoloration mechanism. From this result, we found out that the hydrophilicity varied greatly as the flow rate of the oxygen gas used as plasma gas changed and that the color-changing mechanism was due to the adsorption effect of the oxygen radicals. We also used X-ray photoelectron spectroscopy (XPS) to analyze the components to further understand the adsorption effect of the oxygen radicals and clarified that the oxygen radicals accounted for the color-changing mechanism of the radical sensor. [ABSTRACT FROM AUTHOR]

In this paper, we show and discuss a set of cross sections for electron collisions with dimethyl ether (DME, C2H6O) obtained by the standard swarm analysis of experimental data for drift velocities and ionization coefficients measured in pure DME and its mixtures with Ar and Ne by E. Oettinger and coworkers. While the existing cross section set gave relatively good predictions for drift velocities, it proved necessary to modify the inelastic cross sections in order to achieve a better agreement with drift velocities in gas mixtures and a good agreement for the ionization coefficient. Furthermore, the derived set of cross sections was used to calculate the electron transport and rate coefficients under the influence of a constant electric field and crossed electric and magnetic DC and RF orthogonal configuration fields. The effect of the magnitude and frequency of the fields on electron transport was studied separately. Our work has resulted in a database of collision and transport data which can be used in modeling of both DC and RF discharges and plasma applications containing pure DME and its mixtures. [ABSTRACT FROM AUTHOR]

This article is devoted to the study of the glow intensity of radio-frequency capacitive discharge plasma with nanoparticles for further use in lighting devices. The process of carbon nanoparticles synthesis in the radiofrequency discharge was investigated, and the influence of plasma parameters on the formation and growth of the material was also studied. A method for determining the diameter of nanoparticles based on self-bias voltage and electron density is considered. It is revealed that the diameter of nanoparticles has a considerable influence on the optical properties of the plasma, in particular, on the emission intensity. Based on the obtained data, laboratory samples of lighting devices with improved luminous intensities were developed. [ABSTRACT FROM AUTHOR]

Plasma density in a magnetized, capacitive-coupled, radio frequency (RF) discharge has been determined using the electrical impedance characteristics of the discharge. The effective impedance between the parallel plate electrodes has been treated as an equivalent electric circuit consisting of resistive and reactive components, expressed in terms of high-frequency plasma conductivity. Hence the model is used to connect the externally measured RF voltage, current, and their relative phase to plasma density. Additionally, a triple Langmuir probe (TLP) is used to substantiate the results of the electrical impedance model. The plasma density obtained using the direct probe measurement is found to be in good agreement with those determined from the passive measurements based on electrical impedance of the discharge as outlined in this article. [ABSTRACT FROM AUTHOR]

This study was carried out to investigate the efficacy of the non-thermal atmospheric pressure plasma produced with dielectric barrier discharge (APPD) using air as a processing gas and microwave energy to control Tribolium castaneum and Trogoderma granarium adults and larvae in wheat grains. Insects' mortality was found to be power and time-dependent. The results indicated that non-thermal APPD and the microwave have enough insecticidal effect on the target pests. From the bioassay, LT50's and LT90's levels were estimated, T. granarium larvae appeared more tolerant to non-thermal APPD and the microwave energy than adults 7 days post-exposure. The germination percentage of wheat grains increased as the time of exposure to the non-thermal APPD increased. On the contrary, the germination percentage of wheat grains decreased as the time of exposure to the microwave increased. In addition, changes in antioxidant enzyme activities, catalase (CAT), glutathione S-transferase (GST) and peroxidase, in adults and larvae were examined after 24 h post-treatment to non-thermal APPD at 15.9 W power level, which caused 50% mortality. The activity of CAT, GST and lipid peroxide in the treated larvae showed a significant increase post-exposure to the non-thermal APPD at 15.9 W power level. On the other hand, no significant change in GSH-Px activity was observed. Reductions in the level of glutathione (GSH) and protein content occurred in treated larvae in comparison with the control. [ABSTRACT FROM AUTHOR]

Some types of the slot input of high energy into cylindrical and rectangular cavities are considered. The energy input through slot waveguiding apertures located at the central circle of the cavity is selected and optimized. The standing wave ratio of the system is determined. The change in the electrical field energy in the cavity, when the position of the slot waveguide is shifted, is simulated. The optimum (best for processing with microwave discharge plasma) positions of the objects and waveguide slots as well as critical positions (choosing which can put the oscillator out of action) are shown. The increase in the field density between two metallic objects is calculated. The results demonstrating the inacceptable way of the slot input of energy for solving some types of problems related to processing of complex surfaces with the microwave discharge are obtained. [ABSTRACT FROM AUTHOR]

Chlorine-containing plasma and its mixtures with molecular and inert gases, as well as plasmas of complex polyatomic gases, such as freons, are often used to form the topology on the surface of semiconductors. This article examines the surface quality (based on the roughness data) of the semiconductor structure of GaAs after plasma-chemical etching in the plasma of mixtures of HCl/Ar, HCl/Cl2, and HCl/H2, as well as R-12 freon and its mixture with argon. Freon R-12 is often used for etching Si, Ge, and a number of other materials (GaAs, GaP, InP), providing technologically acceptable interaction rates, and also meets the requirements for anisotropy and selectivity. Also, mixtures of active gases with inert (He, Ar) gases have become widespread, which can act both as simply diluent gases and as sources of ions for the ion bombardment of the sample for the further ionic stimulation of the desorption of the interaction products, which improves the functional properties surface, with a slight decrease in the speed of interaction. Nevertheless, controlling the surface quality of samples remains an urgent task in modern electronics. [ABSTRACT FROM AUTHOR]

A microwave beam (wavelength 4 mm, power 150–300 kW) generates an ionization wave in air in the subthreshold field in the shape of a conglomerate of thread-like channels that moves toward the beam. The periphery of the beam refracts in the plasma of the non-self-sustained discharge in the UV halo of the thread-like discharges and self-focuses in the recombining plasma behind the front of the plasmoid that consists of thread-like channels. The self-focusing of the peripheral regions of the wave beam causes local bursts of ionization behind the front of the leading plasmoid. [ABSTRACT FROM AUTHOR]

The fluid model, also called the macroscopic model, is commonly used to simulate low temperature and low pressure radiofrequency plasma discharges. By varying the parameters of the model, numerical simulation allows us to study several cases, providing us the physico-chemical information that is often difficult to obtain experimentally. In this work, using the fluid model, we employ numerical simulation to show the effect of pressure and space between the reactor electrodes on the fundamental properties of silicon plasma diluted with ammonia and hydrogen. The results show the evolution of the fundamental characteristics of the plasma discharge as a function of the variation of the pressure and the distance between the electrodes. By examining the pressure-distance product in a range between 0.3 Torr 2.7 cm and 0.7 Torr 4 cm, we have determined the optimal pressure-distance product that allows better deposition of hydrogenated silicon nitride (SiNxHy) films which is 0.7 Torr 2.7 cm. [ABSTRACT FROM AUTHOR]

The influence of solid particles produced in plasma of microwave discharge in liquid n-heptane at atmospheric pressure on the electron energy distribution functionand detailed analysis of ion composition of plasma are presented. [ABSTRACT FROM AUTHOR]

The vibrational kinetics model of the dissociation process CO2 + M → CO + O + M based on the two-modes (symmetric–asymmetric) approximation is presented. The model has shown to produce the effective dissociation rate of CO2 under conditions of thermal equilibrium close to that obtained experimentally. Results of the 0D calculations of the CO2 conversion in non-equilibrium conditions of a microwave plasma discharge are discussed. The chemical energy efficiency obtained in the calculations at translational-rotational temperature 300 K and degree of ionization 10−5 is between 42 and 56% depending on the assumptions. The efficiency is found to reduce and eventually vanish at elevated temperatures. [ABSTRACT FROM AUTHOR]

This paper is the first from a set of two companion papers on radio-frequency (RF) discharges. These two papers are in turn part of a larger series on the foundations of plasma and discharge physics. In this part we cover the basics of non-magnetized capacitive and inductive RF discharges, introduce the main concepts related to them and provide reference literature for further reading. In the second part we concentrate on RF discharges in the presence of external magnetic field. These types of RF discharges find a wide range of applications in various industries. Among the most prominent examples are the microelectronics industry for etching and deposition of thin films, the medical and food industry for the application of various coatings and changing the wettability of surfaces, the space industry to power ion-gridded thrusters for satellites, the fusion and elementary particle research for the production of beams of energetic ions or atoms. The paper introduces the basic concepts of RF power deposition and describes in more detail the operating conditions of the plasma reactors. The most important physical phenomena encountered in these discharges are outlined through the use of simplified models. The paper is intended as an entry point for newcomers to the field and provides ample of references (including textbooks) for further reading on the more specific and/or subtle aspects of the operation of these types of RF discharges. [ABSTRACT FROM AUTHOR]

A program to simulate gas-discharge kinetics with allowance for the temporal evolution of the electron-energy distribution function is developed on the example of microwave discharge in molecular deuterium with electron cyclotron resonance. The model includes the averaged heating effect of the microwave field at cyclotron resonance, elastic collisions of electrons with electrons and heavy discharge components, and inelastic excitation and transformation reactions. The program considers the temporal evolution of the electron distribution function within these processes, and an algorithm that changes the boundaries of the design range of the distribution function depending on its current values is developed for it. This makes it possible to consider the function variations over a wide energy range. The conditions determining the algorithm accuracy are developed, and the counting-error dynamics upon variation of the parameters of these conditions is given. The adequacy and reliability of the simulation results, which are estimated based on the values of the introduced errors and comparison with third-party models, are shown. [ABSTRACT FROM AUTHOR]

We consider the excitation and absorption of waves in a magnetoactive rf discharge plasma in the conditions when the generator frequency is lower than the electron cyclotron frequency. We consider the cases of unconfined and confined plasmas in the cylindrical geometry and different regimes of excitation of plasma waves with different dispersion relations and field polarizations. The power input to the plasma depends on the distribution of external-source currents initiating the discharge and on the density parameter characterizing the plasma density and transverse sizes of the system. In the case of a plasma cylinder with a free surface or a plasma cylinder in a large conducting casing, which is most interesting for applications, plasma contains only potential and nonpotential E-type oblique Langmuir waves as well as a strongly nonpotential surface wave. The latter wave is practically not excited by external currents flowing over the cylinder surface for real parameters of the system. For high values of the density parameter, the effective resistance of the plasma with inducting excitation of the discharge is predominant. For moderate and low values of this parameter, capacitive excitation of the wave by the current on the plasma cylinder surface is found to be most effective. [ABSTRACT FROM AUTHOR]

Biogas production is an important component of an environmentally benign renewable energy strategy. However, the cost-effectiveness of biogas production from biomass is limited by the presence of polymeric structures, which are recalcitrant to digestion by bacteria. Therefore, pretreatments must often be applied prior to anaerobic fermentation to increase yields of biogas. Many physico-chemical pretreatments have a high energy demand and are generally costly. An alternative could be the ignition of a plasma directly in the biomass substrate. The reactive species that are generated by plasma–liquid interactions, such as hydroxyl radicals and hydrogen peroxides, could contribute significantly to the disintegration of cell walls and the breakage of poorly digestible polymers. With respect to economic, processing, and other potential benefits, a microwave instigated and sustained plasma was investigated. A microwave circuit transmitted 2-kW pulses into a recirculated sodium carboxymethyl cellulose solution, which mimicked the rheological properties of biomass. Each microwave pulse had a duration of 12.5 ms and caused the ignition of a discharge after a vapor bubble had formed. Microwaves were absorbed in the process with an efficiency of ∼97%. Slow-motion imaging showed the development of the discharge. The plasma discharges provoked a decrease in the viscosity, probably caused by the shortening of polymer chains of the cellulose derivative. The decrease in viscosity by itself could reduce processing costs and promotes bacterial activity in actual biomass. The results demonstrate the potential of microwave in-liquid plasma discharges for the pretreatment of biomass. [ABSTRACT FROM AUTHOR]

The mixing of N2 with H2 leads to very different plasmas from pure N2 and H2 plasma discharges. Numerous issues are therefore raised involving the processes leading to ammonia (NH3) formation. The aim of this work is to better characterize capacitively-coupled radiofrequency plasma discharges in N2 with few percents of H2 (up to 5%), at low pressure (0.3–1 mbar) and low coupled power (3–13 W). Both experimental measurements and numerical simulations are performed. For clarity, we separated the results in two complementary parts. The actual one (first part), presents the details on the experimental measurements, while the second focuses on the simulation, a hybrid model combining a 2D fluid module and a 0D kinetic module. Electron density is measured by a resonant cavity method. It varies from 0.4 to 5 × 109 cm−3, corresponding to ionization degrees from 2 × 10−8 to 4 × 10−7. Ammonia density is quantified by combining IR absorption and mass spectrometry. It increases linearly with the amount of H2 (up to 3 × 1013 cm−3 at 5% H2). On the contrary, it is constant with pressure, which suggests the dominance of surface processes on the formation of ammonia. Positive ions are measured by mass spectrometry. Nitrogen-bearing ions are hydrogenated by the injection of H2, N2H+ being the major ion as soon as the amount of H2 is >1%. The increase of pressure leads to an increase of secondary ions formed by ion/radical–neutral collisions (ex: N2H+, NH4+, H3+), while an increase of the coupled power favours ions formed by direct ionization (ex: N2+, NH3+, H2+). [ABSTRACT FROM AUTHOR]

The characteristics of dust coagulation process in gravitational direction are investigated in an ethylene RF (radio frequency) discharge plasma system. The experiment shows that dust particles can aggregate into the huge fractal structure (centimeter scale). The coagulation process is mainly characterized by the scattering laser intensity, the distribution of dust clouds, and the fractal dimension. In this experiment, the rotational characteristics of the huge fractal structure can be observed and investigated by the oscillation of the scattering spectrum. These results provide an experimental basis for the investigation of dust coagulations. [ABSTRACT FROM AUTHOR]

It is shown that microbial cells can be immobilized on polymer matrices modified via plasma treatment. On the example of microbial cells Azospirillum brasilense Sp 7, A. lipoferum Sp59b, and Escherichia coli XL-1, it was found that the immobilization efficiency of biological objects depends on the film processing time in plasma. Treatment of a polystyrene film in a high-frequency discharge plasma allowed a significant increase in the lifetime of microbial cells immobilized on its surface. It was shown that the optimal time for film processing in plasma was 30 s, the time to immobilize microbial cells was ~ 20 min, and bacteria remained viable for up to 6 months after immobilization. The use of matrices modified with plasma treatment as a carrier for immobilized the microbial cells to production biosensors is proposed. [ABSTRACT FROM AUTHOR]

A high efficiency of power coupling from the incident microwave to the discharge is a general demand for large-scale and high-power applications of microwave plasma torches. This paper aims to experimentally explore the possibility of improving the power coupling efficiency by choosing a proper glass tube in a microwave plasma torch with a metallic enclosure, rather than using additional tuning measures such as a movable short-circuited ending plunger or a three-stub tuner. The power coupling efficiencies for the glass tubes with different wall thicknesses were experimentally measured under different incident microwave powers and different pressures. The results showed that the power coupling efficiency was improved with the increase in the glass tube wall thickness in a wide range of operating conditions for the microwave plasma torch with specific dimensions. An efficiency higher than 85% can be achieved once the wall thickness of the glass tube is in a particular range. This indicates that external tuning measures can be reduced for the microwave plasma torch with a proper glass tube, which helps to save the cost of tuning devices and enhance the flexibility in different working environments. [ABSTRACT FROM AUTHOR]

Particle-in-cell/Monte Carlo collision simulations are performed to investigate the effects of using realistic models for secondary electron emission induced by different plasma species on the discharge characteristics in direct current (DC) superposed radio-frequency (RF) capacitively coupled plasmas (CCPs). A dual-frequency (DF, 60/2 MHz) source is applied on one of the electrodes to sustain the discharge, and an auxiliary DC source is fixed on the opposite electrode to generate energetic secondary electrons (SEs). Realistic models are employed to calculate the secondary electron yields (SEYs) induced by electrons and heavy particles (i.e. ions and fast neutrals) impacting the 'dirty' surfaces (e.g. oxidized metal), respectively, in argon discharge at a fixed pressure of 1.5 Pa. The results are compared to those obtained by assuming a constant ion-induced SEYs of γ = 0.1, and a constant elastic reflected electron yield of ηel. = 0.2. As the effective SEY γ* (arising from heavy particle impact) calculated from the realistic model is enhanced at the DC electrode, numerous γ-electrons can be induced under the effect of the DC-bias. These γ-electrons then bombard the opposite RF electrode with mean energies corresponding to the value of DC-bias, which further induce significant emission of δ-electrons (i.e. electron-induced SEs). Moreover, the δ-electrons originating from the RF electrode can be trapped and bounced back by the opposite DC sheath toward the RF electrode, inducing δ-electron emission once more. Consequently, this positive-feedback source of δ-electrons, leads to an enhanced ionization in the first half-cycle of the low frequency period, and a further growth in plasma density in hybrid DC/RF discharge. [ABSTRACT FROM AUTHOR]

In an inductively coupled high-frequency discharge plasma, SiCxNy:H films are obtained from a mixture of hexamethylcyclotrisilazane vapor and argon at substrate temperatures of 100 to 400°C and a discharge power of 200 W. The simplest plasma components (nitrogen, cyan, silicon atoms, CH free radicals, and C2 dimers) are determined. Some physicochemical properties of the films, including the growth rate, types of chemical bonds, refractive index, transparency interval, and contact angle, are studied. The synthesized films have a polymer-like structure. [ABSTRACT FROM AUTHOR]

The results of experimental studies of combustion of propane–air gaseous mixture when it was ignited by a microwave discharge have been described. The mixture with different propane content fills a sealed radio-transparent tube placed along the axis of a focused linearly polarized quasi-optical microwave beam at atmospheric pressure. Multi-point ignition of the mixture is carried out near one end of the tube by a pulsed microwave discharge with a surface-developed streamer structure. The growth of gas pressure in the tube as propane burned was recorded in the experiments. The microwave pulse energy being invested in high-temperature discharge plasma has been estimated in them. The minimum percentage of propane in the mixture at which the microwave discharge ignites it has been determined in experiments. The time dependence of the pressure increase in the tube as the propane burns determines the combustion process dynamics. [ABSTRACT FROM AUTHOR]