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The effects of Argon (Ar) on the Synthesis and Photocatalytic activities of monolayer Graphene under the flow of Methane (CH4) and Hydrogen (H2) gas has been studied. The Chemical Vapor Deposition (CVD) method was used to create a large area of monolayer graphene with features that meet the needs of a wide variety of applications. With this, the possibility of varying the dimensions of graphene by differing the argon gas while keeping other parameters constant was demonstrated. This helps with the ability to control the size and number of layers of graphene for different applications. Further, the photocatalytic activities of produced graphene were examined during CVD at various argon gas flow rates to observe their effects on the performances of graphene. The result shows that the synthesized graphene at Ar = 80 sccm is a monolayer with perfectly shaped edges. After exfoliation, the graphene obtained was properly formed with a large surface area, which helped achieve the results of higher photocatalytic activity. [ABSTRACT FROM AUTHOR]

We measured breakdown voltage ${V}_{\text {b}}$ , gas temperature ${T}_{{\text {g}}}$ , and gas density ${N}$ with the corresponding critical electric field ${E}_{{\textit {cr}}}/{N}$ in hot dissociated mixtures initially involving SF6, C2F4, and Cu highly diluted in argon. These gas mixtures are heated by a microwave source generating a plasma flame that ablates Cu atoms from a thin copper filament placed inside the cell of the hot gas conditioning. Densities of Ar, SF6, and C2F4 are controlled by flowmeters, while the density of ablated Cu is estimated from optical emission spectroscopy, which is also used for ${T}_{{\text {g}}}$ and ${N}$ estimation. The measured ${E}_{{\textit {cr}}}/{N}$ data in the considered experimental cases of gas temperatures and mixture compositions are needed to analyze the sets of the collision cross sections of species involved in hot dissociated SF6 (11 species), C2F4 (19 species), crossed species (two species), and copper byproducts (five species). The sets of collision cross sections of SF6/C2F4 byproducts were taken from a previous work and those of copper byproducts are fit and validated in the present work. Then, the sets of collision cross sections of all species are considered without argon in some hot specific SF6/C2F4/Cu mixtures to analyze the effect of more particularly copper on ${E}_{{\textit {cr}}}/{N}$ for large ranges of ${T}_{{\text {g}}}$ (up to 4000 K) at a given gas pressure using a rigorous multiterm solution of Boltzmann equation for electron energy distribution function (EEDF) while calculating based on thermodynamic equilibrium formalisms of hot gas composition for species proportions. [ABSTRACT FROM AUTHOR]

In this work, high-performance GaN vertical Schottky barrier diodes (SBDs) are successfully fabricated on the GaN-on-GaN substrate by using the self-alignment trench structure and argon (Ar) ion implantation. The fabricated diodes achieve a high current ON/ OFF ratio of 108 and high breakdown voltage (BV) of 656 V due to the reduced surface electric field effect. Besides, the temperature-dependent reverse leakage characteristics show that two Poole–Frenkel emission (PFE) processes dominate the carrier transport. This work shows great potential of the self-alignment trench structure in fabricating GaN vertical SBDs to improve the BV with simply fabrication process. [ABSTRACT FROM AUTHOR]

It is demonstrated that the phenomenon of absolute negative electron mobility (ANG) in the homogeneous stationary plasma has a subtle effect when the solution of the Boltzmann kinetic equation is exclusively reduced to the local plasma-chemical balance of electron production and loss. Even if strong electron attachment allows to realize an inverse electron distribution function (EDF), the sign of the electron mobility depends on whether the contribution of the electronegative impurity is also taken into account or not in the increase of the electron scattering transport frequency. In an example of a typical argon–fluorine mixture, it is shown that when real electron collision cross sections are used, the ANG of electrons is not realized even for an inverse EDF. A similar result is obtained when solving a model problem with strong electron attachment: even EDF inversion near-zero energies does not ensure the creation of an ANG. Since a real laboratory plasma is spatially inhomogeneous, in order to find the EDF, it is necessary to solve the complete kinetic equation, which depends on both energy and space variables. Under these conditions, the divergence of the spatial flow is an additional source (or sink), which can thereby ensure the formation of a stationary absolute negative conductivity (ANC). [ABSTRACT FROM AUTHOR]

Graphite samples, used in first-wall and divertor of nuclear fusion reactors like tokamaks, were irradiated using hydrogen and argon ions produced in an MTPF-2 plasma focus device in 20 shots to study radiation damages. Ion energy spectra are $dN_{\text {H}}\left ({E_{\text {H}} }\right)/ dE_{\text {H}}\approx E_{\text {H}}^{-2.8}$ with a minimum energy of 120 keV to a maximum of 1 MeV for hydrogen ions and ${dN_{\text {Ar}}\left ({E_{\text {Ar}} }\right)} / {dE_{\text {Ar}}}\approx E_{\text {Ar}}^{-3.5}$ with a minimum energy of 200 keV and a maximum energy of 2 MeV for argon ions. Based on the results of the SRIM code, the maximum destruction of hydrogen ions is at a depth of 900 nm, and a rate of 0.025 DPA/shot and highest hydrogen density is 0.5% at 920 nm. Conversely, the highest degradation of argon ions is at a depth of 120 nm and 0.23 DPA/shot, and the highest density of argon ions at a depth of 200 nm is 0.07%. Different maximum degradation locations and the maximum density of argon ions are due to their heavy mass compared to hydrogen. SEM micrographs show holes with high population density and some sublimated areas on hydrogen-irradiated surfaces. The predominant phenomenon due to argon ion irradiation is physical sputtering, leading to cavities with a depth of several micrometers. Based on the X-ray diffraction (XRD) spectrum, the location and intensity of peaks are changed, and irradiation reduces graphitization and increases the size of the graphite crystal. [ABSTRACT FROM AUTHOR]

The objective of this article is to enhance the dc insulation strength of poly- ${m}$ -phenylene isophthalamide (PMIA) paper by surface treatment. CF4/Ar plasma is used to modify the surface of PMIA paper by fluorination, and the effects of fluorination on the microstructure, electrical parameters, and insulation properties of the material are investigated, and the optimized treatment parameters of CF4 concentration and treatment time are obtained, and the mechanism is further explained from the perspective of carrier traps. The results show that the moderate CF4/Ar plasma treatment can improve the surface insulation properties of PMIA paper without damaging its overall insulation properties. [ABSTRACT FROM AUTHOR]

In this article, we investigate the influence of external discharge conditions on plasma parameters in the plasma discharge chamber of the radome configuration. We designed a conformal cavity and then used the multiphysics simulation software COMSOL to establish a 2-D axisymmetric model for discharge simulation research. In the study, we found that the changes in coil power and pressure have a noticeable effect on the distribution of plasma parameters. First, the maximum electron density, electric potential, and electron temperature are obtained by changing the power of the coil in a certain pressure argon environment. Then, under the condition of constant coil power, the discharge characteristics of plasma are studied by changing the gas pressure in the cavity. The results show that the change of coil power has a significant impact on the parameter distribution of plasma discharge. The greater the coil power, the greater the electron density, and the more concentrated the distribution. At the same time, the potential induced in the heating zone and the corresponding electron temperature decreased after the reaction stabilized. The increase of gas pressure significantly increases the peak value of electron density and changes the parameter distribution of discharge. However, when the argon pressure exceeds a certain threshold, it will no longer have a significant effect on the distribution of discharge parameters. The general conclusion is that the increase of power and argon pressure plays an essential role in improving the electron density distribution. This conclusion has guiding significance for exploring the law of plasma parameter distribution on electromagnetic scattering characteristics. [ABSTRACT FROM AUTHOR]

In this work, a 1-D extended fluid model is built to investigate the effects of the electric waveform supplying a dielectric barrier microdischarge plasma. Three symmetric waveforms (sine, square, and triangle) are used in this study in addition to one asymmetric waveform (positive ramp). The results of numerical experiments show that the discharge activity is strongly affected by the applied voltage waveform, where the dielectric-barrier glow discharge (DBD) in case of the sine and triangle waveforms is more filamentary (with series of narrow current density peaks) when compared with the square waveforms. Although the discharge period of the sine and triangle waveforms is high, the rms value of its current is lower than that in the case of the square waveforms. [ABSTRACT FROM AUTHOR]

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

To study the electromagnetic radiation effect of a thermal control layer (TCL) on the surface of general spacecraft in a space environment, a model of thermal control material irradiated with microwaves was established, a particle-in-cell (PIC)-Monte Carlo collisions (MCC) simulation was used, and the processes of field emission, multipacting, outgassing, and impact ionization on the surface of thermal control materials were simulated. By comparing the primary electrons, secondary electrons, and impact ionization electrons produced under different field intensities and frequencies of electromagnetic waves, different compositions of outgassing, and different thermal control materials, the influencing factors and critical thresholds of avalanche ionization were obtained. The simulation results show that whether avalanche ionization occurs in outgassing on the surface of the TCL is affected by the electromagnetic wave amplitude, electromagnetic wave frequency, outgassing composition, and the material of the TCL. This provides a theoretical reference for the safe operation of spacecraft. [ABSTRACT FROM AUTHOR]

To study the electromagnetic radiation effect of a thermal control layer (TCL) on the surface of general spacecraft in a space environment, a model of a metal aluminum film material irradiated with microwaves was established, particle-in-cell (PIC)-Monte Carlo collisions (MCCs) simulation was used, and the processes of field emission, multipacting, outgassing, and impact ionization on the surface of thermal control materials were simulated. By comparing the primary-, secondary-, and impact ionization electrons produced under different gas densities, the influence of the process on metal aluminum film was analyzed. The simulation results show that the field emission, multipacting, and collisional ionization on the material surface all strengthened when the outgassing density exceeded the threshold value, and outgassing collision ionization was dominant among them. Avalanche ionization occurred on the material surface to generate plasma, which absorbs electromagnetic wave energy, and the total increase in the energy of ions and electrons may cause damage to the aluminum film, which is very important in its practical application. [ABSTRACT FROM AUTHOR]

Parameter studies of plasma treatment are informative about the optimal use of this technology in biomedical applications such as the argon radio-frequency plasma jet kINPen. However, the interdependence of the plasma-dissipated power in relation to input current and feed gas modulation on the resulting biological consequences has not been studied so far. To this end, a parameter study is presented, and the effect on human immune cell viability was investigated across different input current power and argon with oxygen/nitrogen feed gas admixture settings. It was found that with both nitrogen and oxygen admixtures, a concentration-dependent change in plasma-dissipated power emerged, which converged at 27.5 and 26.5 mA, respectively. The extent of cytotoxicity in immune cells confirmed the relevance of these findings, which were in congruency with the plasma-dissipated powers identified. These findings underline the critical role and input parameter-dependent action of plasma sources for biomedical application. [ABSTRACT FROM AUTHOR]

This article presents a new type of microwave-induced atmospheric-pressure low-temperature dielectric barrier discharge source, based on the principle of parallel plate transmission lines (PPTLs). This source is a simple structure with small size, large plasma discharge area, and low discharge temperature. Experiments show that linear plasma discharge with width of 15 mm can be obtained with input power of only 25 W at 2.45 GHz. The temperature of sample placed 1 mm vertically away from the nozzle and treated for 3 min is about 45 °C even with 60-W microwave input power, which proved its thermal safety even for the biomedical applications. Emission spectroscopy diagnosis indicates that the electron density of plasma can be controlled easily by adjusting the discharge gap and the dielectric thickness. It makes this source available for various applications. This work provides a new approach to obtain uniform linear plasma. [ABSTRACT FROM AUTHOR]

A device, which is designed based on strip line, is proposed for dual-channel plasma jets. Based on electromagnetic theory and DRUDE model, finite difference time domain algorithm and finite element algorithm are adopted to obtain the dimensions of designed device. An experimental system is established, and microwave power of 70 W can process 30 L of argon per minute, which is extremely efficient compared with traditional microwave plasma jet. Meanwhile, reflected power is measured to be 8% of incident power using a power meter, which is in good agreement with simulation results. [ABSTRACT FROM AUTHOR]

In this article, the investigation has been carried out for the characterization of the proposed tapered geometry of dielectric barrier discharge (DBD)-based cold atmospheric pressure plasma jet (C-APPJ) on the basis of optical emission spectroscopy (OES) and imaging for different operating parameters, such as argon gas flow rates, applied voltages, and frequencies. The detailed characteristics for the formation of the plasma plume using argon as a working gas have been presented for a wide range of flow rates [1–3 standard liter per minute (SLM)] and frequencies (15–25 kHz). Increasing the pulse frequency, the length and the diameter of the plasma plume increase, while the length of the plasma plume increases when increasing the gas flow rate up to 2 SLM. Time-integrated images have been captured using the intensified charge couple device (ICCD) camera, which illustrates that the plasma plume comprises different emission layers of definite patterns. The propagation dynamics and formation of different emission layers of the plasma plume have also been investigated using the COMSOL Multiphysics simulation. It has been observed that the local electric field of 6 kV/cm is responsible for the propagation of the plasma bullet and the generation of the electron with an average energy of ~9 eV. OES has also been performed to understand the plasma chemistry and identify the reactive species in the C-APPJ. The discharge analysis and characteristics performed through experiment and simulation would certainly be helpful for the design and development of C-APPJ sources. [ABSTRACT FROM AUTHOR]

To examine the influence of radiative transitions on the performance of nonequilibrium seed-free argon plasma magnetohydrodynamic (MHD) generators, we developed MHD numerical simulation technique with a collisional-radiative (C-R) model, where neutral argon atoms with 45 discrete effective electronic excitation levels, singly ionized argon ions, and free electrons were considered under a two-temperature, low-magnetic Reynolds number MHD approximation. Furthermore, a so-called escape factor was implemented in the C-R model to consider the effects of radiation trapping by ground-state neutral atoms. Using the developed technique, we computed the performance characteristics of a nonequilibrium seed-free argon plasma MHD generator. The numerical results showed that the generator performance gets higher as the escape factor decreases, i.e., the optical thickness for radiative transitions to the ground state of neutral atoms increases. The numerical results also suggested that when the escape factor is $1.0\times 10^{-3}$ or less, the generator performance is almost the same as that for the escape factor of 0 corresponding to completely optical-thick plasma case for the radiative transitions to the ground state of neutral atoms. Furthermore, realistic escape factor values for resonance lines in the power generation channel were evaluated using a well-known estimation model. Consequently, the estimated values had the order of $10^{-4}$. We also showed that under such relatively optically thick plasma cases, a collisional (C) model and a widely used global ionization-recombination rate model with no explicit consideration of electronically excited-state neutral atoms can reproduce the generator performance predicted by the C-R model with relatively good accuracy. [ABSTRACT FROM AUTHOR]

In this article, the Vlasov–Maxwell equations have been integrated by the forward semi-Lagrangian method to compute the soft X-ray (SXR) emission from a dense plasma focus device filled with pure and impure argon. The impurity has been assumed as copper of which the electrodes were made. The results have shown that, in the case of pure argon, the emission power reached up to $3.5 \times 10^{9}{\mathrm {W}}$. However, for the impurity with a 10% volumetric fraction and with the effective charge number of 10, the emission power reduced to $4\times 10^{5}{\mathrm {W}}$. With the further increase in the impurity amount, the emission power reduced again. However, if the impurity charge number is close to the pure gas charge number, the attenuation of the SXR emission decreases. [ABSTRACT FROM AUTHOR]

Present article discusses the role of plasma parameters on the morphology of nanocrystalline powders of lanthanum hexaboride (LaB6) synthesized by arc plasma gas-phase condensation method. The nanocrystalline powders so obtained were used to fabricate pellet-shaped cathodes of 5 mm diameter and thickness of 1 mm. Moreover, thermal plasma plume was used for sintering the cathodes and achieve desired densification. Prior to fabrication of cathodes, the synthesized powders of LaB6 were characterized using X-ray diffraction, Raman spectroscopy, and transmission electron microscopy to investigate phase purity and morphological properties. Finally, an indigenously developed thermionic emission experimental set-up was used to record thermionic emission current obtained from LaB6 cathode at different temperatures. Richardson Dushman equation was used to find out the work function of the cathode under investigation. [ABSTRACT FROM AUTHOR]

Optical emission spectroscopy (OES) has been used as an in-situ method to monitor the film deposition carried out using a combination of two plasma-assisted techniques; pulsed laser deposition (PLD) and magnetron sputtering (MS). In this work, the plasmas produced during the PLD ablation of a gold target in an argon atmosphere and its simultaneous use with MS of ZnO were characterized by OES. Neutral atoms of Au, Ar, and Zn and ions of Au were identified, and the temporal and spatial evolution of their emission lines was studied along the axis of the PLD plasma expansion. During the PLD of Au an increment in the emission intensity of neutral Au near the substrates, as a function of the laser pulse fluence, demonstrated resputtering of the Au deposit by the high energy species produced by PLD. When the combination of PLD of Au and MS of ZnO was performed, a similar increment was observed in the emission intensity, but in this case of neutral Zn that was caused by the preferential resputtering of Zn from the ZnO–Au deposit. The MS plasma neither significantly affect the PLD plasma expansion nor did it affect the resputtering of the films. [ABSTRACT FROM AUTHOR]

An isotropic etching, etch rate and surface roughness of Si, Ge and Si0.8Ge0.2 subjected to CF4/Ar/O2 plasma has been studied using inductively coupled plasma (ICP) system. First, we applied the etching parameters on the silicon substrate to observe the etching rate using carbon tetrafluoride (CF4) under different flow rates and choose the parameters of high etch rate. The chosen parameters for silicon was CF4 (60 sccm) and etching in different ratios of argon (Ar) and oxygen (O2) were also discussed. Second, it also reports on selective isotropic etching for germanium (Ge) and Si0.8Ge0.2 by ultrahigh vacuum chemical vapor deposition (UHVCVD) and was etched under selected conditions used for silicon under different atmospheres in an inductively coupled plasma system. Starting from a pure CF4 gas that etches Ge and Si0.8Ge0.2 with a good selectivity to silicon, the modification of gas mixture was also investigated. A possible mechanism based on the favored action of CF4 is investigated. Relative etch rate between Si, Ge and Si0.8Ge0.2 are explained with etch rate reductions achieved by selective CF4 plasma chemistries with Ar/O2. Etched profile, surface roughness was examined and measured by using SEM and AFM technique. [ABSTRACT FROM AUTHOR]

A plasma jet at atmospheric pressure using a dielectric barrier discharge (DBD) can be very useful in the biomedical field. In this article, a numerical simulation of such plasma jet operating in argon gas and launched in the open air was developed using COMSOL Multiphysics software. Three coupled models are considered in this study. A hydrodynamic investigation is conducted and the dilution of argon in air is considered an initial value in the plasma model. An electrostatic study is developed in order to preview the initial electric field. Finally, a plasma study is carried out and discussed in terms of electron density, electric field distribution, and plasma length. This study is validated by comparing the results to those measured in a similar system in the literature. The results are in good agreement with the literature and correspond to the physics of the plasma jet. [ABSTRACT FROM AUTHOR]

This article presents a systematic investigation on the behavior of electrons in the bullet in the Ar/H2O plasma jet in increasing the applied voltage and water vapor concentration based on a needle-plate discharge configuration and a 1-D particle-in-cell Monte Carlo method. The scattering angle of the electron in the bullet is described using the angle between the electron scattering direction and the bullet propagation direction. The following results are obtained. The evolution characteristic of the angle spectrum of electrons in the bullet in increasing the applied voltage is the same as that in increasing water vapor concentration, namely, the electrons scattered toward the target get increasingly less. When increasing the applied voltage, the OH density, the electron density, and the average electron energy Eave increase. However, the increase in water vapor concentration leads to an evidently increasing OH density and a decrease in both the electron density and Eave. In the range of electron scattering angles below 90° in the bullet, the percentage of electrons with energy above 3.27 eV (the threshold of inducing dissociative electron attachment to water molecule) increases with increasing applied voltage but presents a slight decrease in increasing water vapor concentration. The majority of electrons to most probably interact with the target are of energies higher than 3.27 eV. Finally, a notable effect of H2O admixture is that it gives rise to the decrease in not only Eave but also the electron density in the bullet, especially the latter decreases evidently. [ABSTRACT FROM AUTHOR]

The 6-D Vlasov–Maxwell equations in the cylindrical coordinates have been solved to calculate the electron beam emission from mixtures of argon and neon. The forward semi-Lagrangian approach was used for solutions. The simulation of the electron velocity field has shown that at the early stage of the pinch evolution of a 4-mbar 90% Ar–10% Ne mixture, the sausage instabilities began to develop from the top parts of the pinch due to bigger Bθ with respect to Bz. In the turbulence regions, the electrons could accelerate up to speeds of 905 × 105 and 2387.5 × 105 m/s at 90.9 and 181.82 ns, respectively. It has been observed that in the high turbulence region, Ez = −2.04 × 107 V/m, while in the weak turbulence region, Ez = −1.46 × 107 V/m. Increasing the neon percentage in the mixture changed the turbulence regions and the upstream and downstream emissions. [ABSTRACT FROM AUTHOR]

This work is an extensive study of the plasma chemical etching (PCE) process of single-crystalline lithium niobate (LiNbO3) in the SF6/O2 based inductively coupled plasma (ICP). The influence of the main technological parameters of the LiNbO3 PCE process, including the distance between the sample and the lower edge of the discharge chamber, as well as the temperature of the substrate holder on the etching process rate, has been studied. It was shown that changing the temperature of the substrate holder in the range from 100 to 200°C leads to a gradual rise of the etching rate from 127 to 282 nm/min. A further increase in the temperature to 250°C results in a sharp increase in the etching rate to 711 nm/min. The maximum achieved etching rate in experimental series which were aimed at determining the dependence of the LiNbO3 etching rate on the temperature of the substrate holder was 812 nm/min at a substrate holder temperature of 325°C. With the help of X-ray photoelectron spectroscopy (XPS) technique was found and shown that during the etching process in fluorinated plasma the nonvolatile LiF compound is formed on the surface of the treated LiNbO3. On the basis of the obtained results, the optimal process of deep ($> 80~\mu \text{m}$) LiNbO3 PCE was developed, with an etched wall inclination angle of ≈110°, with selectivity ratio to Cr mask of ≈ 20, and an etching rate of about 300 nm/min. [2020-0317] [ABSTRACT FROM AUTHOR]

In the present work, a numerical study of the influence of discharge current, gas pressure, and axial magnetic field on the formation of the spatial distributions of parameters of a dusty argon plasma of the positive column of a dc glow discharge is reported. It is found that an increase in current, pressure, or magnetic field enhances the degree of dust influence on the spatial distribution of particles and on the fluxes in the plasma and can lead to the implementation of a variety of outcomes from the flattening of the radial density profile of charged particles to the formation of uniform and even nonmonotonic radial distributions with the reversal of the ambipolar field direction. Three different modes of transition to nonmonotonic radial density profiles, depending on the parameter being changed, are reported. [ABSTRACT FROM AUTHOR]

Array of microplasma jets has been produced in atmospheric conditions using a high-voltage ac power source for the degradation of malachite green (MG) dye in the aqueous solution. The effect of plasma forming gases (air, oxygen, and argon) on the degradation was analyzed by UV-Vis spectrophotometer, and the formation of hydrogen peroxide during plasma–water interaction was quantified. Oxygen plasma produced a relatively high amount of hydrogen peroxide than air and argon, leading to efficient degradation. Oxygen plasma medium exhibited 14.78% and 9.85% higher energy yield than air and argon plasma, respectively. Observation shows that the degradation of MG dye in the aqueous solution follows the first-order kinetics irrespective of plasma forming gases. Phytotoxicity of untreated and oxygen microplasma treated MG dye solution was examined with the germination of tomato seeds. The results illustrate that the toxicity of MG dye was considerably reduced with the microplasma discharge treatment, as it induced 17.4% higher germination percentage than control. The study delineates that oxygen microplasma is an effective, economic and eco-friendly tool for detoxification of huge amount of MG dye in the aqueous medium. [ABSTRACT FROM AUTHOR]

CO2 gas is being considered as one of the potential plasma forming gases in plasma arc material processes due to its thermophysical properties, cost, and easy availability. The understanding of the thermal behavior of CO2 plasma arc is essential for an effective utilization of it. However, the studies on CO2 arc characteristics are scanty. In this study, a 2-D axisymmetric model is built for the simulation of CO2 and Ar arcs with and without evaporation of anode. The thermal characteristics of CO2 arc are compared with those of Ar arc at different arc currents and anode materials. CO2 arc possesses higher temperature compared to Ar arc and the arc current strongly influences the temperature of CO2 arc. The anode flux in CO2 arc is higher compared to that of Ar arc and the effects of arc current and nature of the anode material on the same are stronger in CO2 arc. The arc heating efficiency in CO2 is higher than that in Ar and it reduces with increasing arc current. [ABSTRACT FROM AUTHOR]

This article investigates the wettability distribution of a surface treated by an atmospheric-pressure plasma jet at different flow rates and aims to apply on microfluidic channel plotting. It is well known that plasma is capable of modifying the wettability of a surface, and a plasma jet, due to its finite nozzle size, has a great advantage that can modify only a local area on a surface. The feasibility of plotting wall-less microfluidic channel has been confirmed by our recent works. In this work, we present a quantitative study on the wettability distribution with different flow rates. Argon is used as the working gas, and six different flow rates, including 0, 0.1, 0.5, 1, 3, and 5 L/min, have been tested. According to the results, the wettability distribution is significantly affected by the flow rate. A higher flow rate would lead to a wider range of modified area, as well as more hydrophilic. The flow rates are also employed for plotting wall-less microfluidic channels, and the width of the channel can be directly controlled by the flow rates. Optical emission spectroscopy (OES) is used to verify the plasma dosages at both the nozzle outlet and on the treated surface. Based on the OES results, the intensity of OH radical is positively correlated with the flow rate. The features and properties of the modification with different flow rates are discussed. [ABSTRACT FROM AUTHOR]

In recent years, global warming has become a worldwide problem. Carbon dioxide (CO2) is one of the primary substances causing global warming, and its emission should be reduced. A promising technology is the conversion of CO2 to carbon monoxide (CO) using plasma treatment, so that the CO itself or its conversion to methane can be used as fuel for combustion engines. In this article, a CO2 dissociation or reduction treatment system using an adsorbent and nonthermal plasma (NTP) flow is investigated. To improve the conversion efficiency, the conversion efficiency for Ar or He plasma is evaluated. In the physical adsorption process, ∼10% CO2 gas with a flow rate of 10 L/min is prepared, and then, it is introduced into the flow channel; CO2 is adsorbed by the adsorbent. After the adsorption process, the circulation flow channel is set, and then, the Ar or He NTP flow is generated with a blower. As a result, the adsorbed CO2 is desorbed with CO2 concentrations of 20% and 23% by the Ar NTP flow and the He NTP flow, respectively. The CO2 conversion efficiency reaches 21%, and the energy efficiencies reach 13% and 10% with plasma in the cases using the Ar and He NTP flows, respectively. The energy efficiency with regard to CO is better with the Ar plasma, but more atomic carbon can be generated using the He plasma. [ABSTRACT FROM AUTHOR]

This article presents a comparative investigation on behaviors of electrons in the Ar and He plasma jets by means of the numerical simulation based on a typical needle-plate discharge configuration with positive applied pulsed voltage and a 1-D particle-in-cell Monte-Carlo collision (PIC-MCC) method. Emphasis is placed on the electrons in the bullet in the jets. In Ar, the bullet velocity is low and the electron density in the bullet is high, compared to He. In He, the energy spectrum of electrons (ESEs) in the bullet is of a low peak and a wide distribution, and the corresponding average electron energy is evidently high, contrary to Ar. The reason for this evident difference is mainly due to their different excitation energies and ionization energies as well as their different cross sections. In Ar and He, two electron densities $N_{e}$ and $N_{\mathrm {ext}}$ in the bullet have been calculated. The former is the electron density in the bullet and the latter refers to a density of electrons in the bullet with energy above the lowest excitation threshold inducing the dissociative electron attachment (DEA) to water molecules. Consequently, not only $N_{e}$ but also $N_{\mathrm {ext}}$ in Ar is higher than in He, meaning more generation of reactive species in aqueous solution via DEA mechanism. The ESEs in the bullet in Ar are more sensitive to the applied voltage amplitude than in He, thus in Ar, the increase in the applied voltage amplitude induces more evident increase in the average electron energy in the bullet than in He. [ABSTRACT FROM AUTHOR]

Electrons are generated abundantly in the plasma jet and play an active role in the mass transfer of reactive species in the aqueous solution in plasma medicine. Such an importance requires knowledge of the behavior of electrons in the plasma jet. The objective of this work is to understand the electron behaviors in the bullet in the plasma jet, including the angle spectrum of electrons (ASEs) and the related energy spectrum, so as to have an insight into those electrons which most probably interact with the target. The numerical modeling based on a needle–plate discharge configuration in conjunction with a 1-D Particle-in-Cell Monte-Carlo Collision (PIC-MCC) simulation method was used to achieve this task. The scattering angle of electron in the bullet is described using the angle between the electron scattering direction and the bullet propagation direction. The ASE in the bullet is close to a sinusoidal distribution. As the bullet propagates, the temporal evolution of ASE indicates that relatively more electrons in the bullet are scattered into the angle range below 90°, but at any moment when the propagating bullet is close to the target, ASE in the bullet generally remains unchanged. In addition, relatively less electrons in the bullet are scattered into the angle range below 90° due to the increase of the applied voltage amplitude. For the considered voltage amplitudes below 7 kV, the number of electrons in the angle range below 90° is within 47% of electrons in the bullet and, in these electrons, the proportion of non-subionization electrons reaches about 12%. These results may be taken into consideration in investigating the mass transfer of reactive species in plasma medicine. [ABSTRACT FROM AUTHOR]

A steady-state kinetic model of argon–helium high-pressure radio frequency dielectric barrier discharge is developed using a simplified reaction rate package appropriate for pressures ranging from 200 to 500 torr. Electron production and loss rates are analyzed as a function of pressure and Ar–He mixture, highlighting the importance of the Ar2* dimer for higher pressures and Ar rich mixtures. As pressure increases, the primary ionization mechanism shifts between ionization of ground state Ar to dimer ionization, which affects the steady-state reduced electric field due to the electron energy required for the two dominant ionization mechanisms. The resulting reduced electric field profile controls the metastable Ar(1s5) production, which, combined with the Ar(1s5) loss rates, reveals the metastable density as a function of pressure and Ar-fraction. This simplified 0-D steady-state model shows close agreement with previous time-dependent simulations using a robust reaction rate package. [ABSTRACT FROM AUTHOR]

Mitigating disruptions is essential for the longevity of future large tokamak experimental devices and reactors. Currently, shattered pellet injection (SPI) technique is the most effective mitigation technique found thus far, and has been chosen for the baseline disruption mitigation (DM) system for ITER. To optimally design SPI systems, the survivability of the pellet throughout the pre-shatter flight and the resulting shatter spray must be better understood. Experimental tests of low-angle single strike impacts of neon and argon pellets were conducted to determine the minimum normal kinetic impact energy that pellets can withstand throughout guide tube travel. Knowing the maximum normal kinetic energy that pellets of relevant materials and temperatures can withstand during flight will allow for an optimal SPI system design. Characterization of the downstream shatter spray was performed for various shatter tube geometries using pure argon and neon pellets. The experimentally measured post-shatter fragment size distribution is compared to theoretical models. The most accurate model found from this comparison is a statistics-based model for brittle material shattering that is correlated with the relevant physical parameters of SPI pellets. Extrapolation of the model to ITER size pellets is presented. [ABSTRACT FROM AUTHOR]

In this article, a multigap pseudospark (PS) discharge-based plasma cathode electron (PD-PCE) source is considered for the generation of high density and energetic pulsed electron beams using electrostatic 2-D kinetic particle-in-cell (PIC) simulation code OOPIC Pro. The characteristics of the generated electron beams are very much dependent on the geometrical and operating parameters of PD-PCE source. The size, uniformities, and irregularities of electrode apertures play a significant role on the generation of high density and energetic electron beams. Investigation has been carried out to analyze the effect of the irregular electrode apertures in PD-PCE source for the generation of electron beams. The combinations of irregularities considered in the diameter of electrode apertures are 2, 4, 6, and 8 mm, mostly used for the development of PD-PCE sources. It has been observed that the aperture size of first electrode decides the delay in breakdown of first gap at constant operating conditions. The delay primarily depends on the penetrating behavior of equipotential lines which leads the successive breakdowns in the remaining gaps of multigap PD-PCE source. The latter electrodes of multigap geometry are responsible for guiding the size of electron beams. Dips in the electron beam currents have been observed during its rise, which are dependent on the sequence of irregular electrode apertures and operating conditions. The gas pressure and electrode apertures control the voltage falls in gaps and rise of electron beam current. The study would support the design and the development of PD-PCE sources suitable for extreme ultraviolet (EUV)/soft X-ray, microwave, and surface modification applications. [ABSTRACT FROM AUTHOR]

This article deals with the proof of concept and the preliminary evaluation of decontamination performances obtained with a plasma jet generated by a piezoelectric transformer (PT). This low-voltage supply solution (<10 V) is investigated as a plasma jet device, compact and safe solution for the decontamination of medical thermo-sensitive devices. The principle of the piezoelectric generator is presented, followed by the optical s–protocol conditions for the bactericidal effect observations, and finally the reduction rates obtained on Pseudomonas aeruginosa and Staphylococcus aureus bacteria strains with an argon plasma jet at atmospheric pressure about 2.5-W electrical input power. [ABSTRACT FROM AUTHOR]

This article aims to understand the physics of pulsed plasmas by investigating the ionization and recombination of pulsed plasmas on the nanosecond timescale and how operating conditions affect the time-resolved electron temperature and electron density of a pulsed plasma. A nanosecond-pulsed argon plasma discharge was generated at various pulse frequencies, widths, and pressures. The argon emission lines were analyzed with a time-synchronized, intensified charge-coupled device (ICCD) spectrometer assembly that gated at 4 ns, and relative intensities of strong argon neutral and ion lines were used in line-ratio calculations. These experimentally determined ratios were compared to theoretical ratios generated from PrismSPECT, a collisional-radiative spectral analysis software, to obtain time-resolved electron temperature ($\sim 1$ eV) and electron density ($10^{14}-10^{15}$ cm $^{-3}$) over the various operating conditions as well as to discover trends of these plasma parameters over the lifetime of the pulsed plasma. Increasing pulse repetition frequency of the plasma increased the value of maximum $T_{e}$ , shortened the $T_{e}$ rise and decay times, and increased the excited argon neutral population. While $n_{e}$ was relatively independent of pulse frequency, higher pulse frequencies resulted in a faster $n_{e}$ decay. Maximum $T_{e}$ and $n_{e}$ were weakly dependent on applied discharge voltage, but both parameters decayed sooner in time with increasing voltage. Lastly, $T_{e}$ was inversely proportional to pressure, but $n_{e}$ was approximately linear. All three pressures had similar but time-shifted temporal profiles for $n_{e}$. Plasmas in all operating conditions had ionization and recombination times in the tens of nanoseconds. [ABSTRACT FROM AUTHOR]

In this article, the results of numerical simulation regarding the influence of different dust particles’ spatial distributions in the plasma of a positive column (PC) of direct current glow discharge in argon are presented. The effect of homogeneous dust clouds of different radii located on the axis of a gas discharge tube, uniform annular clouds of dust particles, and clouds with inhomogeneous dust density on the formation of the main scenarios of radial distributions of particles and fluxes in the PC plasma was studied for a wide range of dust particle densities. It was found that similar (when all three density profiles of electrons, ions, and charged dust inside the dust cloud are parallel) and nonmonotonic radial distributions of charged particles are formed only when the external region between the boundary of the dust cloud and the wall of the tube is of sufficient size to provide the necessary level of ionization to maintain a fixed discharge current. The possibility of the formation of nonmonotonic charge profiles in the case of increasing and falling nonmonotonic distributions of the dust grains is shown. [ABSTRACT FROM AUTHOR]

We present observations and modeling of argon gas at pressures of a few Torr that have been excited with high-voltage pulses (hundreds of volts) on the order of nanoseconds in duration. These tests are motivated by an effort to determine the feasibility of utilizing pulsed argon plasma as a conducting media in a novel antenna configuration. A vacuum chamber is constructed with plate electrodes inserted. An optical observation system is constructed to observe the temporal response. The rise time and fall time of the plasma’s optical emissions, taken as a proxy of the electron density, are measured as a function of pulse voltage and pressure using the captured optical light curve. In addition, spectroscopy measurements are made on a longer time scale. The maximum electron density of the plasma is then inferred through the use of PrismSPECT, a commercially available collisional radiative model, via the line ratio method. Measured pulsed plasmas reached their maximum ionization in as low as 5 ns and recombine in as low as 140 ns. Spectral measurements show that a 1-Torr plasma ionized with 5-ns long pulses had a maximum electron density of $5.2\times10\,\,^{\mathrm{ 20}}$ /m3 and maximum electron temperature of 1.28 eV. [ABSTRACT FROM AUTHOR]

This article describes the experimental results obtained for pulsed argon atmospheric plasma jets impinging on the grounded targets with a different conductivity. The values of the jet current and profiles of the integrated light emission of the plasma jets are presented. It was found that a propagation velocity and a length of the argon plasma jet in air depended on conductivity of the target. There were revealed differences in the jet propagating freely in air and the jet impinging on the target. [ABSTRACT FROM AUTHOR]

Far different from common plasma plumes, a regularly swelling hollow plume is observed in an argon plasma jet. The results indicate that the regularly swelling plume appears only at a low-frequency voltage (lower than 1 kHz) that is positively biased. Waveforms of applied voltage and light emissions reveal that there is a barrier discharge inside the nozzle, which initiates once every half voltage cycle. Outside the nozzle, it initiates once every positive half voltage cycle and never at the negative half cycle. By fast photography, it can be found that the positive discharge stems from the rod end of the powered electrode and bends down to hug the tube surface, which finally propagates to the outside as a cathode-directed streamer due to the charge overflow effect. The bifurcating streamer propagates along the periphery of the argon flow, which results in a hollow structure of the plasma plume. Due to abundant active species provided by the positive discharges inside the nozzle, the diameter of the plasma channel is comparatively larger in the swelling regions than in other regions, which induces the swells of the plume. Furthermore, the negative barrier discharge is diffuse, whose influence on the swells can be neglected. Finally, the contribution of active species generated upstream of the swells is verified by investigating the distance between two adjacent swells as a function of gas flow rate and driving frequency. [ABSTRACT FROM AUTHOR]

A plasma jet enhanced oil-based drug, named plasma-activated oil (PAO) is produced in sunflower oil by a single-step, room temperature, energy-efficient, and environment-friendly dry plasma jet enabled process. Plasma jets with two different working gas combinations, argon + air and argon + O2, were generated, namely PAO (air) and PAO (O2), respectively. Several hours of plasma jet treatment substantially increased the hydrogen peroxide and carboxylic acid concentrations in the PAO. Although the electrophilic fatty acid nitroalkenes produced by nitric oxide and nitrite of the argon + air plasma jet increased the acid value of PAO (air), similar sterilization and wound healing effect suggest that PAO (air) and PAO (O2) have similar concentrations of hydrogen peroxide and carboxylic acid. PAO killed the common Gram-positive bacteria [methicillin-resistant staphylococcus aureus (MRSA) and Micrococcus luteus] and Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli) efficiently. PAO accelerated the healing of infected wounds by 33%. [ABSTRACT FROM AUTHOR]

Cold atmospheric pressure plasma (CAP) is widely used in research for biomedical applications and is a promising therapy to selectively eradicate cancer cells. However, there is no unity for the species that cause this different effect. The aim of this article was to further determine the key reactive species causing differences in viability between melanoma cells (B16) and fibroblasts (L929). In this article, the cell viability of two cell lines exposed directly to the CAP was tested. The result shows CAP exhibit different cytotoxicity against the viability of two cell lines. The proliferation of B16 cells is significantly inhibited. By using superoxide anions scavengers and catalase, long-lived reactive oxygen species (ROS) generated by CAP, such as hydrogen peroxide (H2O2), were found to have stronger cytotoxicity to B16. Besides, the B16 cells were significantly inhibited after simultaneously scavenging free radicals and hydrogen peroxide, while it has the opposite effect on L929 cells. In order to explore whether there may be other long-lived species, such as protein oxides, which have important effects on cells, CAP-treated bovine serum albumin (BSA) was applied in cultured cells. We observed the inhibition effect of CAP-treated BSA on the growth of B16 but proliferation versus L929 cells. The content of peroxide in CAP-treated BSA was measured by xylenol orange method. The rate of peroxide reduction in B16 cells is faster than that of L929 cells. In addition, after adding certain enzymes to cells, the effects of CAP on intracellular ROS generation were examined by liquid chromatography $/$ mass spectrometry (LC/MS). There is a significant difference in the content of $\mathrm {O}_{{2}}^{ {\cdot -}}$ and H2O2 in the two cells. [ABSTRACT FROM AUTHOR]

Nonequilibrium plasma is an effective and one of versatile advanced oxidation process due to the formation of reactive species such as hydroxyl radicals, oxygen atom, and hydroperoxyl radicals. In pulsed discharge, free electrons gain energy from an imposed electric field and lose this energy through collisions with neutral gas/liquid molecules. The transfer of energy to the molecules leads to the formation of a variety of new species including atoms, free radicals, and ions. These products are all active chemically, and in our case, we measure the amount of hydroxyl radicals generated in the reactor and also the amount of escaped ozone generated in the reactor and decolorized indigo reagent in a graduated cylinder (GC). In this paper, we used oxygen and argon gases in various flow rate and mixed ratios to feed a gaseous phase in a water spraying droplet reactor. The experimental results indicated that the oxygen and O2/Ar mixture flow rates in spraying reactor have an effect on both hydroxyl radical generation and decolorization of indigo reagent solution. Argon gas discharge has less effect on hydroxyl radical production compared to the oxygen gas discharge with the same flow rates and no effect on the decolorization of indigo reagent solution in GC. We obtained remarkable results on both hydroxyl radical generation rate and decolorization efficiency of indigo reagent solution when we discharged with the mixture of O2/Ar “especially when the ratio has more oxygen than argon gas.” Hence, the presence of oxygen in the water spray plasma discharge is very important as it influence the generation of reactive species such as O atoms and ozone in the gas and liquid phase, which can react directly with organic contaminants and also contribute to more production of hydroxyl radicals in the aqueous phase. [ABSTRACT FROM AUTHOR]

To examine the effect of the radial electric field on the electron rotational motion under ${E}\times {B}$ field, particularly $E_{r} \times B_{z}$ geometry, for a plasma with magnetized electrons and nonmagnetized ions flowing through a uniform magnetic channel, an experimental study is conducted by applying a steady-state plasma flow along the uniform longitudinal magnetic field $B_{z}$. The argon plasma flow is generated by atmospheric-pressure dc arc discharge, followed by a continuous expansion into a rarefied gas-wind tunnel with a uniform magnetic field 0.15 T. Inside one of the magnets which is situated at rather a downstream position, a ring electrode is set to apply the radial electric field $E_{r}$. An up–down probe is employed for the analysis of the electron azimuthal rotational motion. The value of the radial electric field applied in the plasma is about ~150 V/m. The probe measurement indicates the ${E}\times {B}$ rotation of electrons, particularly when the radially inward electric field is externally applied, whose order is about ~1000 m/s. The inward electric field results in the electron rotational motion in the same direction as the diamagnetic current. On the other hand, when the outward electric field is applied, the electron rotational motion is not observed. The order of the observed electron drift velocity is consistent with the theoretical value. ${E}\times {B}$ rotation velocity is found to be almost equal to that by the electron diamagnetic current. Even without the external electric field, the observed electron saturation current indicates that there is a rotational motion of electrons, which is considered to be due to the electron diamagnetic current. [ABSTRACT FROM AUTHOR]

This paper presents the frequency- and power-dependent thermal and spectral properties of a microwave argon plasma jet in the gigahertz range. These properties are determined at 1.3 GHz, 2.4 GHz, and 3.5 GHz for input powers from 2 W to 15 W and gas-flows from 1 to 4 Lm−1, including the influence of an argon/nitrogen mixture. These investigations are performed to determine the specific influence of the excitation frequency on the spectral properties of the plasma. The gas temperature is determined via the hydroxyl radical (OH) rotational band around 310 nm by fitting the simulated spectrum to the measurements. It is shown that high temperatures above 1350 K are generated inside the plasma for an input power of 10 W. At the same time, selective discharge 2-D mapping is realized as a result of charge-coupled device (CCD) imaging through optical bandpass filters, corresponding to the OH, N2, Ar, and H spectral emission lines. It is found that all the investigated species change their size proportional to the size of the plasma. Influence of nitrogen is investigated by generating an argon/nitrogen gas mixture. The nitrogen admixtures up to 2% are examined. These investigations are based on measurements of the N2-band around 370 nm. A strong dependence of the discharge appearance on the nitrogen content is found. [ABSTRACT FROM AUTHOR]

In this paper, we characterize a Transparent Cathode Discharge (TCD), a type of Inertial Electrostatic Confinement (IEC) plasma, operated in helium and argon in the pressure range of 1–100 Pa. The discharge was investigated using a combination of electrical and optical diagnostic techniques. The imaging of the discharge indicated distinct operating regimes related to the background gas pressure, with each mode being characterized by different patterns of optical emission. The spectroscopic analysis of the optical emission showed that this mode structure represented an electron-driven discharge at higher pressures, and a discharge sustained by the activity of energetic heavy particles at lower pressures. The high-pressure discharge is shown to be assisted by the hollow cathode effect toward its low-pressure limit, and the visible color of emission from the discharge in helium is found to provide a convenient diagnosis of active species. The identification of a stable discharge mode in which energetic heavy particles are responsible for collisional processes has the potential to lead to new industrial applications based on this novel heavy particle-driven reactive plasma source. [ABSTRACT FROM AUTHOR]

A filamentary plasma jet was produced by a cylindrical dielectric-barrier discharge (DBD) equipped with a thin quartz tube. This plasma jet consists of many filaments, and the filaments bifurcate into thinner branches close to the ground electrode. Only a single filament is produced in each current pulse, and this filament is distorted in the long gas gap. The maximum electron density in the filament is on the order of $10^{15}$ cm $^{-3}$. Optical emission examination shows a decrease of optical emissions from OH and Ar but an increase of optical emissions from N2 along the plasma jet. The vapor in the working gas argon rather than in the ambient air dominates the optical emissions from the de-excitation of OH along the plasma jet. Near the ground electrode, the nitrogen emission spectra mainly resulted from the direct electron effect on the ground state or metastable nitrogen and the collisions between nitrogen metastables. The rotational temperature is lower than the vibrational temperature but much higher than the room temperature. This feature makes the filamentary plasma jet only suitable for processing samples bearing high temperature. [ABSTRACT FROM AUTHOR]

Numerical experiments are carried out on a low-energy (2.2 kJ) Mather-type Egyptian Atomic Energy Authority-Plasma Focus (EAEA-PF1) to investigate the optimum combination of all electrode system dimensions and gas pressure for maximum argon soft X-ray (SXR) yield, $Y_{\mathrm {SXR}}$ , using Lee Model RADPF5.15. This paper aims to finalize the first step prior to building an automated method of optimization that could be applied when a low-energy dense plasma focus is designed or need to be reconfigured, for this purpose, and to assist further research efforts in this field. The second part of the study deals with the investigation of the role of changing outer electrode radius “b” and the outer to inner radii ratio “c” on plasma focus (PF) parameters such as ion density, pinch duration, and column length and how are these, consequently, related to the maximum SXR yield. It is shown that lower radius ratio values (typically less than 2) are favored over higher ones, for argon SXR yield, and unlike most of the low-energy PF devices that are designed for this purpose. It is also shown that inductance and pinch current are only affected by the dimension of inner electrode radius, while the ion density, pinch duration, and focus volume are also affected by the change of outer electrode radius. [ABSTRACT FROM AUTHOR]

We found that steady-state paired-particle motion was often observed in a fine-particle cloud in the argon plasma produced by a 100-kHz high-frequency discharge. Monodispersed spherical silica particles with a diameter of $5.0~\mu \text{m}$ were trapped in the plasma. The 2-D motion of these charged particles was carefully recorded using a microscope camera, and their orbits and perturbation frequencies were analyzed. The loci and fast Fourier transform spectra of many paired particles were obtained. By moving the camera horizontally, 3-D images of the particles were recorded, and a 3-D map of the positions of charged particles was obtained. It is considered that the forces inducing the paired-particle motion were generated by the Debye shielding and the electric field surrounding the paired particles. [ABSTRACT FROM AUTHOR]

The so-called plasma window is a dc cascaded arc whose function, in this paper, is to greatly restrict gas flow from high pressure (upward of 40 kPa) chamber to a low-pressure side (order of 10 Pa). This is motivated by its potential to contain a gas charge stripper on a beamline of a high-intensity heavy-ion accelerator without the need for solid windows that would obstruct beam passage and not survive the beam’s intensity. At the National Superconducting Cyclotron Laboratory (NSCL), a test stand for this plasma window has been developed to study how this flow rate restriction is impacted by plasma physical properties and window geometry. Proposed mechanisms for this flow rate restriction are, first, a significant increase in temperature causing greatly enhanced viscosity in the plasma channel, and second, a choked flow condition being established through gas speed reaching supersonic conditions. The study in this paper is limited to pure Ar gas. Optical emission spectroscopy demonstrates the plasma that has an electron temperature of about 1.7 eV and an electron density of about 1016 cm–3. [ABSTRACT FROM AUTHOR]