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The plasma torch is the key component of the thermal plasma-assisted material processing system. Particularly, direct current (dc) nontransferred arc plasma torch is widely used in high-temperature material processing applications. The characteristics of the thermal plasma jet emanating from the plasma torch depend on many factors, including arc current, type of plasma forming gas, gas flow rates, gas injection configuration, torch geometry, and so on. This experimental study focuses on the comparison between the effects of CO2 and air on the arc voltage, electrothermal efficiency, and specific enthalpy of the plasma torch operated at the atmospheric pressure. For this purpose, a low-power dc plasma torch consisting of a rod-type thoriated tungsten cathode and the copper anode was customized. CO2 and air were used as the plasma forming gases along with a feeble amount of argon (15 lpm). The plasma torch was operated over a wide range of current (100–175 A) with fixed gas flow rates. The $I$ – $V$ characteristics and the electrothermal efficiency of the plasma torch were measured, and results were compared. The maximum electrothermal efficiency and specific enthalpy of the plasma torch when operated with CO2 were reported as 70% and 1900 KJ/Kg, respectively, which is higher than the same torch operated with air as the plasma forming gas. The electron number density and electron temperature of the air and CO2 plasma jet were measured by optical emission spectroscopy (OES). The calculated electron number density and electron temperature of the plasma jet with CO2 were $2.89\times 10\,\,^{\mathrm{ 16}}$ cm−3 and 8598 K, respectively, which is higher than air plasma jet. It was found that CO2 has a stronger influence than air on the arc voltage fluctuation, electrothermal efficiency, and operating regime of the plasma torch. [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]

A computational model for nucleation and growth of iron (II) oxide nanoparticle (IONP) in thermal plasma has been developed. A nondimensional form of the aerosol general dynamic equations (GDEs) along with a discrete volume sectional model assumption is used to numerically solve the coupled system of GDEs. The variation in supersaturation ratio and the mean particle diameter of IONPs with respect to temperature across the plasma reactor has been presented. The scatter plot showing the distribution of particle number density of certain size across the reactor chamber is shown. In silico molecular docking study was performed to reveal the putative interaction of the IONPs with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) virus. The results revealed significant binding affinity of IONPs with 6LZG (spike receptor-binding domain complexed with its receptor ACE2) and 5RH4 (main protease) of SARS-COV-2 by forming hydrogen and hydrophobic bonds with nearby amino acid residues. The interactions of IONPs are associated with the conformational changes in the protein which could be used to treat and control SARS-CoV-2 infection. [ABSTRACT FROM AUTHOR]

Novel features of arc plasma devices with thermionic and thermo-chemical cathodes and development of associated thermal plasma process reactors are investigated from device design and application point of view. Different types of plasma torches and open arcs, their fundamental differences in architecture, jet behavior, operational constraints, and evolution of interesting electromagnetic forces inside them have been probed. Investigation of instabilities in arcs through direct real-time imaging of arc path using fast photography and impact of powder loading on such instabilities are presented. Development of low power air plasma torches delivering large volume high-temperature plasma jet with long penetration depth has been investigated together with an estimation of hazardous NOx, produced from such devices during operation. Interesting attributes of various types of thermal plasma reactors including plasma spray chemical vapor deposition (CVD) reactors for thick and dense coating, reactors for generation of H-OH plasma, radio frequency (RF) thermal plasma reactors for the synthesis of nanostructures, and air plasma gasifier reactors for environment-friendly mitigation of municipal solid waste (MSW) and electronic wastes have been presented. Coke bed air plasma gasifiers are specially investigated for their important technological aspects. Experimental results are presented with simulation supports for enhanced understanding, wherever necessary. [ABSTRACT FROM AUTHOR]

This article proposes a numerical model to predict the abatement process of carbon tetrafluoride (CF4) in a reaction chamber with the assistance of nitrogen thermal plasma generated by a nontransferred and direct-current torch. The magneto-hydrodynamic equations, that is, the continuity, momentum, energy, and current continuity equations together with turbulence transport equations, are solved by an in-house parallelized finite volume code to obtain the thermal plasma flow jetting out the plasma torch. The thermal plasma is assumed in local thermal equilibrium, optically thin and electrically neutral. In the reaction chamber, a kinetics model is adopted to describe the transport phenomena as well as the chemical interactions among various species involving in the decomposition process. Fifty-six species and 235 chemical reactions are considered in the proposed full kinetic model. Three different models, namely a full kinetic one, a reduced one, and a simplified one, are compared for the prediction accuracy of the destruction and removal efficiency (DRE) along with the abatement products formed in the decomposition process. With the full kinetic model, the predicted DRE at three CF4 concentration conditions, that is, 7200, 12 600, and 16 000 ppm, has a good agreement with the experimental result indicating a nearly full decomposition except for a very small discrepancy less than 0.5% for the case of 16 000 ppm. The predicted abatement efficiency becomes saturated and approaches to a complete abatement provided the participated H2 O outnumbers CF4 in moles. A dry abatement process is forecast with a destruction rate decline from 97% to 92% as the CF4 concentration grows from 7200 to 16 000 ppm. Although the reduced kinetic model along the simplified model using a compact set of chemical reactions underpredicts the DRE for the investigated CF4 concentration in the range of 1%–2%, they practically deliver an incomplete group of abatement products that might mislead a proper design of the scrubber behind the reaction chamber. The validation with the experimental measurement justifies the employment of the proposed full kinetic model capable of delivering an accurate abatement prediction of the detoxifying process of CF4. [ABSTRACT FROM AUTHOR]

The atmospheric pressure radio frequency (RF) inductively coupled thermal plasma (ICTP) has been extensively used for many industrial processes. In order to understand the physical–chemical mechanism involved in the discharge process of ICTP, in situ optical emission spectroscopy (OES) was carried out to diagnose and determine the active particles and electron excitation temperature in this plasma. Several active particles such as Ar*, $\text{H}_{\alpha }$ , and $\text{H}_{\beta }$ were detected in the emission spectrum of Ar-H2 ICTP. Based on the Boltzmann plot method, the electron excitation temperature and thermal efficiency of ICTP were evaluated. It was obtained that the electron excitation temperatures in Ar-H2 ICTP varied from 9651.70 to 16691.91 K when the applied power was in the range of 8–15 kW, which was significantly higher than the electron excitation temperature in Ar ICTP at the same applied power. Besides, the thermal efficiency was enhanced from 17.19% for the Ar ICTP to 30.69% for the Ar-H2 ICTP. These results may be beneficial for understanding of the discharge process in atmospheric pressure Ar-H2 ICTP. [ABSTRACT FROM AUTHOR]

This study presents two 3-D atmospheric plasma spray models, namely, internal and external powder injections, by using the computational fluid dynamics technique to study the status of the melting of a particle and its in-flight velocity during a porous ceramic layer fabrication process. A bulk fluid model, which solves the time-dependent standard ${k}$ - $\varepsilon $ model, is used in combination with a Lagrangian to track the trajectories of alumina particles. The results of the fluid-analytical models are compared with experimental measurements, and it is seen that the spray angle increases as the flow rate of the carrier gas increases, which is more significant for an internal than for an external powder injector. Internal powder injection gives a particle a greater in-flight velocity and particle surface temperature because of the location of the powder injector. It is seen that the particle injection velocity and the particle penetration depth vary with the particle size and the flow rate of the carrier gas and that the dispersion for the internal type is more concentrated than that for the external type because of the momentum. The surrounding setup also plays an important role in the process of plasma spraying. [ABSTRACT FROM AUTHOR]

Recently, plasma activated water (PAW) has drawn huge attention because it is considered to be useful for biomedical and agricultural applications. Because the PAW contains several nitrogen compounds such as nitrate, it can be used as a natural fertilizer. In this article, we report the comparative test results of PAW production by combining nonthermal plasma, thermal plasma, and hybrid methods. As a thermal plasma source, gas-jet assisted pulsed discharge (GAPD) under water was used, and the coaxial cylindrical dielectric barrier discharge (DBD) was adopted as the nonthermal plasma source. The difference in the radical generation rate between the two methods was identified. Some synergy effects in the formation of nitrate ion by the hybrid system were also confirmed. It is considered that the surface discharge through the air channel in GAPD formed by the gas jet stabilized more rapidly by increasing the conductivity of water by relatively high power DBD. This combination can greatly improve the energy efficiency of nitric acid production at relatively low input energies. [ABSTRACT FROM AUTHOR]

For safe handling and transport, the exterior surfaces of a container used to collect microorganisms should be disinfected. Though conventional methods are highly reliable, they could damage the container or destroy the contents, rendering the collection of microorganisms pointless. In this paper, a pulsed subatmospheric pressure microsecond spark discharge plasma jet, referred to as a pin-to-hole discharge (PHD), was used as a source of ultraviolet (UV) radiation and reactive oxygen and nitrogen species (RONS) for the sterilization of inoculated surfaces with limited thermal impact. A device was created to generate an overlapped region of treatment on a cylindrical body from an array of these PHDs. The surface was inoculated with vegetative bacteria (Escherichia coli), sporulated bacteria (Bacillus atrophaeus), or a simulated dirt and spore solution and then treated with the plasma array. Gas composition effects on the bacterial load reduction were explored, and the combination of RONS from air was found to be an improvement of the effects from pure oxygen. Increasing treatment time caused an increase in bacterial load reduction, regardless of the distance or gas composition. Treatment of simulated soil inoculation showed suppressed sterilization results which asserted the fact that addition of UV radiation from the discharges improved bacterial inactivation from PHDs. The radial array of pulsed subatmospheric pressure microsecond spark discharges was shown to reduce the bacterial load on the inoculated surface by 5-log within 20 min of treatment from a discharge in air. [ABSTRACT FROM AUTHOR]

Triple dc plasma torch system was used for the synthesis of nanoparticles. Three thermal plasma jets are ejected from each plasma torch and they are merged into a strong single plasma plume. Since the feedstock is injected into the jet merging area, this system is suitable for refractory nanoparticle synthesis and enable to high production yield caused by the complete evaporation is possible. In this paper, numerical simulation was carried out to analyze thermal plasma characteristic inside a reactor according to the plasma-forming gas and carrier gas compositions: Ar, Ar–H2, and Ar–N2 plasma; Ar, He, and N2 carrier gas. Then, it was comparatively interpreted with the actually synthesized nanoparticle in order to understand the condensation process of nanoparticles. It was revealed that the thermal environment is able to control readily in the triple torch system by the operating condition depending on the target materials. [ABSTRACT FROM AUTHOR]

Argon–xenon laser-sustained plasma (LSP) was generated using a 1-kW class diode laser. At a total pressure of 1 MPa, the threshold laser power of the xenon–argon LSP was higher than that of the pure xenon LSP, whereas the former was lower than the latter at a total pressure of 0.1 MPa because of homonuclear associative ionization effect. The minimum xenon pressure ratio at which LSP could be generated was 7.67% at a total filled pressure of 3 MPa. The maximum value of fractional absorption was 37.7% at a total filled pressure of 0.5 MPa. [ABSTRACT FROM AUTHOR]

For modeling the carbon tetrafluoride disposal required in the semiconductor fabrication process, this paper proposes a numerical approach to predict the decomposition characteristics of carbon tetrafluoride in a reaction chamber via a nontransferred, direct-current torch, where the magnetohydrodynamic equations, such as the continuity, momentum, energy, and current continuity equations together with turbulence transport equations, are solved with a parallelized finite-volume approach. The thermal plasma is assumed in local thermal equilibrium, and a kinetics model is adopted to consider the transport phenomena as well as the chemical reactions of various species arising in the decomposition process. The proposed model is validated for a rod-type torch operating at 100 SLPM, 80 A, and 18 kW, whereas carbon tetrafluoride of various concentrations well premixed with the nitrogen of 300 SLPM is injected into the hollow torch with the possible presence of water vapor. The major products stemming from the decomposition mechanism of carbon fluoride with water are H2O, OH, H, O, H2, O2, HO2, H2O2, O3, H+, O+, F, HF, CF, CO, CH, F2, CHF, CF2, COF, CO2, CH2F, CF3, COF2, CH2F2, CF4, CHF3, and electron, where 28 species and 75 chemical reactions are considered in the proposed model. The measured destruction and removal efficiency of carbon tetrafluoride slightly decreases with the increase of the incoming concentration of CF4. The numerical model delivers a quantitative and qualitative agreement with the experimental measurement. The discrepancy can be explained by the secondary decomposition of the process gas after exiting the reaction chamber and before leaving the detoxifying system. [ABSTRACT FROM AUTHOR]

A quantitative interpretation of the schlieren technique applied to an atmospheric pressure, vortex-stabilized nitrogen thermal plasma jet generated in a direct-current nontransferred arc plasma torch (nitrogen gas flow rate of 25 NL/min, power level of 15 kW), discharging into ambient air is reported. A $Z$ -type, two-mirror schlieren system was used in the research. The technique allowed inferring the temporally averaged values of the temperatures and densities of different species present in the plasma jet in a wide range of radial and axial distances. Deviations from kinetic equilibrium in the calculation of the plasma refractive index were accounted for, but maintaining the assumption of the local chemistry equilibrium. The influence of several assumptions on the accuracy of the measurements was considered. The results have shown that for a distance of 3.5-mm downstream from the nozzle exit, the kinetic equilibrium is realized (being both electron and gas temperatures values around 11 000 K), but noticeable deviation from kinetic equilibrium appears toward the jet border. On the other hand, a marked deviation from the kinetic equilibrium was found in the whole far field of the plasma jet, where the electron temperature remains still quite high (about 10 000 K at 30-mm downstream of the nozzle exit), well decoupled from the gas temperature (about 7000 K at the same distance). The obtained results are in reasonable good agreement with those previously reported by some of the authors by using a double floating probe method in the same plasma torch. [ABSTRACT FROM AUTHOR]

Effects of the driving frequency on temperature in a multiphase ac arc were successfully clarified. A multiphase ac arc is one of the thermal plasmas, which is suitable for producing functional materials such as nanoparticles, in-flight glass melting, and waste treatment in terms of its large plasma volume, high-energy efficiency, and low flow velocity. The temperature and arc behavior in various driving frequencies were investigated by the observation system consisting of a high-speed video camera and bandpass filters for plasma spectroscopy. The temperature measurement was conducted on the basis of the Boltzmann plot method. The obtained results indicated that the arc behavior and its temperature field were strongly influenced by the driving frequency. An increase of the frequency led to concentrated arc region, higher arc temperature at the center of electrode region and lower arc fluctuation. The temperature and its distribution can be controlled depending on the material properties to be treated and the purpose of the process. [ABSTRACT FROM AUTHOR]

A numerical approach is proposed and demonstrated for efficient modeling of the thermal plasma behavior present during a lightning strike event. The approach focuses on events with timescales from microseconds to milliseconds and combines the finite element method, magnetohydrodynamics, and similitude theory. Similitude theory is used to scale the problem to require considerably less computing resource. To further reduce the computational burden and to resolve the numerical difficulty of simulating the nearly zero electrical conductivity of air at room temperature, an approach based on cold-field electron emissions is introduced. Simulations considering turbulent flow have been considered, modeling a test configuration from literature designed to inspect composite material performance and applying an aerospace standard test profile (Waveform-B). Predicted peak temperatures (of the order of ~40 000 K) and pressures (of the order of 0.1–0.2 MPa) suggest that the pressure loading during a Waveform-B event will have a minimal effect on composite material damage. [ABSTRACT FROM PUBLISHER]

Metal-supported solid oxide fuel cells (MS-SOFCs) are prepared by the high-temperature plasma spraying technique in this paper. The positive electrolyte and negative functional layers are deposited onto porous alloy substrate using thermal plasma in the air. The porous alloy supporting component is produced by molding ( $6 \times 6$ cm2), pressing (35 ton), and sintering (e.g., 1000 °C, 1100 °C, 1200 °C, and 1250 °C). The $5 \times 5$ -cm2 MS-SOFC with an effective electrode area of 16 cm2 shows that the open-circuit voltages are 0.95 V (Cell-1100), 1.09 V (cell-1200), and 1.08 V (Cell-1250) at 650 °C. In addition, the maximum power at a cell potential of 0.6 V is 5.7 W (Cell-1100), 11.5 W (Cell-1200), and 12.1 W (Cell-1250) at 650 °C. Thermal expansion coefficient of porous alloy supporting component is also measured in this paper. MS-SOFCs without cracking and deforming following thermal plasma spraying process have good electrical performance. Atmospheric plasma spraying method is revealed as a suitable deposition technique for manufacturing MS-SOFCs. [ABSTRACT FROM PUBLISHER]

The three-electrode plasma reactor for the treatment of polluted gases combines a dielectric-barrier discharge with a remote third electrode, designed to enhance streamer propagation in a relatively large region. In this paper, experimental studies of the electrical magnitudes of the discharge for different electrode bias voltage configurations are presented. Also, the Laplacian electric field distribution in the interelectrode gap is calculated for each configuration. The degradation efficiency of NO in an N2 atmosphere for the different configurations is also reported. It is found that the discharge is generated only for that electrode bias configuration for which the external electric field promotes the streamer propagation across the electrode gap. Also, for a triggered discharge, the reactor efficiency for the removal of NO changes with the different electrode bias configurations. This result can be explained in terms of the electric field intensity. The configuration with higher external electric field improves the number of streamers propagating in the interelectrode gap so that more reactive species generated in the streamers are effectively entrained in the gas flow to be treated. [ABSTRACT FROM AUTHOR]

This paper describes the application of a loop type of inductively coupled thermal plasmas (loop-ICTPs) to high-speed oxidation processing. We earlier developed a unique loop-ICTP for large-area thermal plasma materials processing. In this application of the loop-ICTP for oxidation, a part of the Ar/O2 loop-ICTP was formed directly lying in the longitudinal direction on the surface of a Si substrate located downstream of the plasma torch. Oxygen was supplied directly from the sides of the substrate. The uniformity and the stability of the thermal plasma formed on the substrate were measured using a high-speed video camera and spectroscopic observation. In addition, the uniformity of the oxidation processing was estimated from the fabricated oxide layer thickness. Finally, an almost uniform oxide layer could be obtained with 50 mm length and 100 nm depth after only 1 min of irradiation of Ar/O2 ICTP. [ABSTRACT FROM PUBLISHER]

The influence of gas pressure and electrical parameters on low-pressure plasma has been investigated in this paper. A fast intensified charge-coupled device (ICCD) imaging is utilized to examine the dynamics of plasma bullet and plasma plume length at different pressure and plasma parameters. The experimental results reveal that the gas pressure has great influence on both the length of the plasma and on the propagation velocity of the plasma bullet. By increasing the gas pressure from 15 to 15 000 Pa, both the length of the plasma jet and the velocity of the plasma bullet first increase and then decrease. The maximum value of plasma plume occurred at 100 Pa, in which the propagation velocity gets the maximum value of 5\times 10^6 m/s. Further increasing the gas pressure to 15 000 Pa results in decrease in both the plasma length and bullet velocity. Relative to voltage, the frequency of the applied pulse voltage has a different impact on the plasma propagation at different gas pressures. While a higher voltage induces a longer plasma plume and a faster propagation velocity at both 30 and 2000 Pa, increasing the frequency has little influence on plasma at 30 Pa but reduces the plasma length and propagation velocity observably at 2000 Pa. In addition, an exotic plasma plume structure is observed by ICCD. A possible hypothesis is discussed here to explain this phenomenon. These experiments may lead to a more precise control of the low-pressure plasma, warranted for advanced materials technologies. [ABSTRACT FROM AUTHOR]

In this paper, a plasma-assisted selective catalytic reduction (SCR) process was employed for the conversion of nitrogen oxides (NOx) from flue gas to nitrogen (N2) and water (H2O) using V2O5-WO3/TiO2 catalyst over a broad reaction temperature (125 °C–550 °C) range. Ammonia (NH3) was used as a reducing agent, and nonthermal plasma was generated in a multitooth wheel-cylinder corona discharge reactor driven by a dc power supply. In order to optimize the geometry of the corona discharge reactor, the discharge power and the NO oxidation efficiency were compared for different discharge gaps and sawtooth slice numbers of the multitooth wheel electrode, respectively. The effects of reaction temperature, water vapor, and SO2 concentration on the plasma facilitated SCR of NOx were also investigated. The experimental results showed that shorter discharge gap (11 mm) appeared to be more advantageous with respect to NO oxidation. NO oxidation efficiency was less affected by sawtooth slice number. The plasma-assisted SCR process enhanced the catalytic activity of SCR catalyst and exhibited a remarkable improvement in NOx removal efficiency at a temperature range of 125 °C–300 °C. The presence of water vapor in plasma-assisted SCR process significantly improved the NOx removal, especially at low temperature. The addition of SO2 suppressed the NOx removal in plasma-assisted SCR process; however, the NOx removal was greatly promoted by the presence of SO2 and H2O, indicating that water vapor can significantly ameliorate the SO2 inhibiting effect in the plasma-assisted SCR process. [ABSTRACT FROM AUTHOR]

An electrothermal (ET) plasma source has been used to produce intense transient high heat flux to evaluate surface erosion and melting of plasma-facing materials. The source produces high heat flux relevant to expected conditions during disruption event in future large fusion devices. Surface vaporization has been evaluated for selected fusion-relevant materials under radiant energy deposition. Additional simulation included the effect of melting and splattering. Vapor and droplet formation and their associated shielding effect have been investigated in this paper to assess the difference between a developed boundary layer from only vapor or melt layer or the mixed vapor-melt layer with possible ejection of molten droplets away from the surface. Fully self-consistent erosion models are developed and implemented in the ET ETFLOW code in a new version ETFLOW-boundary layer to model the response of plasma-facing materials and their erosive behavior under transient ET plasma high heat fluxes closely similar to expected ones in future fusion large tokamaks. [ABSTRACT FROM AUTHOR]

Nanocrystalline yttrium oxide has been synthesized by thermal plasma route using a dc plasma reactor. The phase composition of the product was analyzed by X-ray diffraction (XRD). The XRD patterns showed cubic and monoclinic phases in the synthesized product. The powder was characterized by scanning electron microscopy and transmission electron microscopy (TEM). The TEM images confirmed the nanometer size of the particles in the range of 3–47 nm. Surface area analysis [Brunauer–Emmett–Teller (BET)] and particle size analysis by laser scattering have also been used to characterize the particle size of plasma-synthesized yttria nanoparticles. The TEM images, BET, and particle size by laser scattering also reveal that particles are agglomerated. The results showed that the particle size decreased with an increase in plasma power and the fraction of nanosized powder increased with power. The amount of metastable monoclinic phase was found to increase as the fraction of particles below 20 nm increased. [ABSTRACT FROM AUTHOR]

Thermochemical assessment of the gasification of the biomass waste composed of sugarcane bagasse aiming for practical applications of an electric arc or radio frequency plasma reactors for the syngas production was carried out, considering different gasifying agents and their mixture (steam + air). The analysis of the calculations in the thermodynamic equilibrium shows that steam is the most efficient oxidant. In this case, the predicted optimum regime corresponds to the value of steam–biomass ratio of 0.4 at the temperature 1000 K (at ambient pressure), and for these conditions the maximum value of the energy efficiency is 0.91 and the value of the exergy efficiency is 0.84. [ABSTRACT FROM PUBLISHER]

Dual-channel thermal plasma torch can operate with air, argon, or combustible gases to produce high-temperature plasma flow. This plasma torch can be used in various important applications such as metal industry recycling, surface coating and hardening, space operations using controlled thrust, and macroparticle acceleration based on the electrothermal nature of thermal torches and electrical-to-thermal energy conversion. Power for this torch is supplied from the electric mains and the voltage is stepped up to 6 kV. However, the torch can also operate on dc or pulsed mode. The electrical operation is characterized by the voltampere relationship to determine the power rating of the torch as well as diagnosing the dynamic behavior of the plasma. Experiments on the torch using air and argon have shown plasma temperatures in the range of 0.4–0.6 eV with plasma number density in the range of 10^24 – 10^25/\textm^3 , indicating a dense plasma regime with the plasma tends to be weakly nonideal. Plasma kinetic temperature and electron number density were obtained from optical emission spectroscopy using the relative line method as the plasma is near local thermodynamic equilibrium condition. Plasma temperature has its peak for low flow rates and decreases for increased flow rates. The torch modeling was conducted using an electrothermal plasma code to simulate and predict the parameters for pulsed mode operation. Simulation was conducted on a single channel as the dual torch is symmetric. Code results for extended pulselength show a plasma temperature between 0.6 and 0.8 eV for nitrogen, oxygen, and helium; which are in good correlation with plasma temperatures obtained from optical emission spectra and measured plasma resistivity. A set of computational experiments using short pulses at higher discharge currents has shown temperature in the range of 2.0–2.5 eV for nitrogen and helium. [ABSTRACT FROM PUBLISHER]

This paper proposes a magnetohydrodynamic model that does not assume local thermal equilibrium (LTE) to predict the flow field and electron temperature and species density distributions inside a direct-current nontransferred-arc steam torch with a well-type cathode at atmospheric pressure. A steady, axisymmetric flow is assumed, and the azimuthal velocity component is not neglected. A finite volume method is adopted to solve the continuity equation, the current continuity equation, the momentum equation, and the energy equation according to a $k-\varepsilon $ turbulence model. Ohm’s law is used to calculate the induced magnetic field, and Ampere’s circuital law is adopted to compute the current distribution in space. Fifty-two chemical and plasma kinetic equations are employed to describe the interactions among the 12 main species of water plasma, H2O, OH, H, O, H2, O2, HO2, H2O2, O3, H+, O+, and electrons, considered in this paper. The electron temperature is predicted from the transport equation based on the electron energy balance, whereas the transport coefficients of the plasma are obtained from the Chapman-Enskog solution of the Boltzmann equation. The thermal plasma flow of steam inside the plasma torch, which measures 503 mm in length and 9 mm in radius, is predicted to have $I=180$ A and $Q=5$ g/s. The non-LTE simulation suggests that a plasma temperature of 11600 K and flow velocity of 3.8 km/s can be achieved at the center of the torch outlet. Compared with the LTE model, the non-LTE calculation yields lower plasma temperature and higher axial velocity at the torch outlet. The calculated electron temperature principally varies between 1 and 3 eV, and energetic electrons occur not only near the electrode surfaces but also within the axial electric arc. The model predictions suggest that the thermal plasma is well approximated as LTE in the hot plasma core, which is characterized by an isothermal contour of 10 kK, and in the vicinity of the electrodes. The deviation from the LTE condition predominantly grows with the radial coordinate, and the temperature ratio approaches unity at the electrode surfaces. The dominant species components of the water plasma in the inner region ( $r< 6$ mm) at the torch outlet are monoatomic and ionic species of H and O, whereas the diatomic species and water molecule become relatively important in the outer region ( $r>6$ mm) at the torch outlet. [ABSTRACT FROM PUBLISHER]

Gliding arc discharge systems have been used in various applications. However, the power of conventional gliding arc plasmas is relatively high and the system requires an additional discharge for its ignition and a resistor for current protection, which causes further total energy consumption. We have proposed ultraviolet (UV)-assisted gliding arc discharge systems supported by time-resolved understanding for electrical characteristics and dynamic behavior of serpentine plasmas. In this paper, we report on gas flow dependence on dynamic behavior of serpentine plasmas in a gliding arc discharge system with the irradiation of a low-pressure mercury lamp. Time-resolved evaluation was carried out using the results of synchronized measurement for serpentine plasmas with a high-speed camera, a high-voltage probe, and a current sensor. Waveforms and mean values of the applied voltage, current, power, impedance, and energy for serpentine plasmas in the UV-assisted gliding arc discharge system were studied. The power and impedance per unit plasma length were also evaluated. [ABSTRACT FROM PUBLISHER]

Thermal plasma melting is an efficient but energy intensive method for vitrifying municipal solid waste incineration (MSWI) fly ash. To reduce the energy cost and vitrification temperature, different biomass ashes were used as additives in this paper. The effects of the rice husks and wood waste combustion ashes on the MSWI fly ash melting behavior have been studied using a laboratory dc argon plasma torch. The melting heat for ash samples with different mass ratios of MSWI fly ash and biomass ash was predicted by an empirical mathematical model based on the major ash components and measured melting temperatures. The deduced melting heat was used to optimize the parameters of the plasma torch. Melting tests showed that the plasma firing time can be reduced to save energy cost, after biomass ash was added all samples were converted into dark blue glassy materials. When the molten slags were cooled with air, the slags from the rice husks ash mixed samples cracked into irregular pieces, while the slags from the wood ash mixed samples tended to form spherical pellets with a porous microstructure. The results indicate that wood combustion ash is a promising additive to MSWI fly ash for producing high quality construction materials through plasma vitrification with reduced melting energy. [ABSTRACT FROM PUBLISHER]

A gas-fed capillary plasma 2Please provide the full name for the author “A. Cuneyt Tas.” source has been developed to study plasma-surface interactions under pulsed high pressure arc conditions, without the use of an exploding fuse wire or ablative liner. A nonintrusive preionization source has been developed to break down relatively large interelectrode gaps at low charge voltages of 2–6 kV. The preionization source comprises a nonequilibrium surface streamer discharge that forms a conducting channel through which the main thermal arc discharge is initiated. The arc electron temperature and number density are estimated to be \(T_{e}\sim \) 1–2 eV and \(n_{e}\sim \) 1023m−3. Silicon and sapphire samples were exposed to the arc plasma and revealed deposition of electrode and wall materials. Substitution of Elkonite 50W3 for brass electrodes reduced plasma contamination to acceptable levels. The plasma-material interactions were examined and quantified using scanning electron microscopy and energy dispersive X-ray spectroscopy. [ABSTRACT FROM PUBLISHER]

Field theory is applied to analyze the behavior of the thermal plasma-loaded tape helix traveling-wave tube in the presence of a solid electron beam present inside the plasma. The plasma temperature effect on the phase velocity and the growth rate of the system are investigated. It is shown that, if plasma temperature increases in the system, its working frequency and growth rate will increase. The results indicate that the axial electric field and growth rate increase with plasma density. [ABSTRACT FROM PUBLISHER]

A helix-type slow-wave structure (SWS) filled with thermal plasma is immersed in an axial guide magnetic field. The sheath helix enclosed within a loss-free wall in which the gap between the helix and the outer wall is filled with a dielectric. Using the boundary condition of two regions, the dispersion relation of the SWS is derived. Solutions are found numerically, which correspond to both the extraordinary and ordinary solutions. The trend of change for the phase velocity and radial profile of the axial electric field is analyzed, respectively, in different plasma temperature. Some useful results are given. [ABSTRACT FROM PUBLISHER]

In this paper, the anisotropic model for the dc electric arc was expanded, which allows the obtaining of power function generalized expressions for calculating the characteristics of the electric discharge into the dc plasma torch channel without using a large number of experimental studies. The model is based on the power law approximation of temperature dependence of the plasma electrical conductivity \sigma with different exponents along the longitudinal and transversal coordinates. The approximation of the dependence for \sigma of steam plasma was obtained in simple linear forms \sigma=0.221\Delta S and as the power approximation \sigma=44.51\Delta S^0.484 [where \Delta S is increment of thermal conductivity function (TCF)]. The comparison of the obtained dependences with referenced data shows such moderate difference between the calculated approximations for \sigma of steam and the data of recent publications for this plasma as 15%–25% throughout the vast ranges of the plasma parameters T (temperature) and S (TCF). [ABSTRACT FROM PUBLISHER]

It is shown that high-voltage corona discharges in atmospheric air have significant potential for bacterial inactivation. Neutral reactive oxygen and nitrogen species and ions generated by the corona discharges act upon the target liquid or solid surfaces and produce chemical or biological effects. The concentration of ions and reactive species including ozone generated by these discharges defines the efficiency of the corona treatment. In this paper, the chemical (oxidation) effect of direct corona discharges (where ions act upon the target surface) and indirect corona discharges (where ions are screened by a grounded metallic mesh) in atmospheric air is studied by measuring the degree of decolorization of a blue dye dissolved in water. The biological effects of the direct and indirect discharges are studied by observing the degree of bacterial inactivation of gram-negative and gram-positive microorganisms, Escherichia coli and Staphylococcus aureus, seeded on agar plates. The relationship between the ozone concentration and biological efficiency of the corona treatment is evaluated. The obtained results can be used for optimization of cleaning and inactivation treatment processes based on the use of nonthermal plasma produced under dc energization conditions. [ABSTRACT FROM AUTHOR]

The accuracy of numerical simulation on plasma behavior depends strongly on the reliability of thermophysical property data. Large number of studies for thermal plasma properties in the local thermodynamic equilibrium (LTE) exist; however, the database for thermal nonequilibrium plasmas is still far from completeness. This paper derives a general expression of total reactive thermal conductivity (TRTC) with great applicability to monatomic, diatomic, and polyatomic gases in terms of a two-temperature model. The derived formula is applied to nitrogen plasmas under thermal equilibrium and nonequilibrium conditions, considering its wide use in plasma systems and switching devices. Typical calculated results of TRTC with two different Saha equations and Guldberg–Waage equations in the temperature range of 300 K–40 000 K under different degrees of nonequilibrium are given and compared with those computed according to Brokaw and Butler's derivation for the special case of LTE plasmas, which shows excellent agreement. The influence of different expressions for Saha equations and Guldberg–Waage equations, together with different pressures of 0.1, 1, 3, 5, and 10 atm, on the TRTC evaluated by this newly developed expression is presented as well. These provide reliable reference data for use in the simulation of plasmas. [ABSTRACT FROM AUTHOR]

The Asia–Pacific International Symposium on the Basics and Applications of Plasma Technology (APSPT) has been held in Taiwan or Japan every two to four years since 1997. It is an important annual event in the Asia–Pacific area and has been a great platform for scientists all around the world sharing novel and state-of-the-art research findings and exchanging innovative ideas in the field of plasma science and technology. The $11^{\mathrm{ th}}$ APSPT was held on December 11–14, 2019, at Kanazawa University, Kanazawa, Japan. The $11^{\mathrm{ th}}$ APSPT had a very strong program consisting of 13 sessions with 201 articles contributed by the 210 participants from nine countries. This Special Issue focuses on the following topics, which were also the focus topics in the $11^{\mathrm{ th}}$ APSPT. 1)Plasmas in semiconductor materials processing. 2)Plasmas in biomedical and agricultural applications. 3)Plasmas in nano-materials processing. 4)Plasma coating and surface modifications. 5)Plasmas in aerospace/space applications. 6)Plasmas in energy and environmental applications. 7)Plasmas-in-liquid. 8)Multiphase plasmas. 9)Thermal plasmas. 10)Cold plasmas. 11)Plasma diagnostics and modeling. 12)Advanced and novel plasma technologies and sources. As Guest Editors, we thank all the authors, the reviewers, the editors, and the IEEE staff to publish this Special Issue on time. Particularly, we would like to offer our special thanks to the Editor-in-Chief, Dr. S. Gitomer, and the Senior Editor, Prof. P. Chu, for their guidance and help throughout the review process. We hope this Special Issue will help to exchange our knowledge in plasma science and cultivate potential collaboration in the community. We look forward to see all participants again in the $12^{\mathrm{ th}}$ APSPT at Taiwan University of Science and Technology, Taipei, Taiwan, in December 2021. [ABSTRACT FROM AUTHOR]

The impact of the wire length on the large-scale diffuse discharge is investigated. The images and electrical measurements show that for a nanosecond pulse with a long tail, the decrease of the wire length can result in the transition from a diffuse mode to a spark discharge. [ABSTRACT FROM PUBLISHER]

High-speed and Schlieren imaging have been used to visualize ignition transients, discharge behavior and flow fields of a plasma device integrating a low-power inductively coupled plasma torch, generating a high temperature thermal plasma, with a quenching device, able to cool the gaseous effluent down to biocompatible temperatures for effective use in biomedical applications. [ABSTRACT FROM PUBLISHER]

This Special Issue on Atmospheric Pressure Plasmas and Their Applications in the IEEE Transactions on Plasma Science highlights topics from the 1st Sino-German Symposium on “Atmospheric Pressure Gas Discharges and Plasma Applications.” The symposium was jointly organized by Dr. Ping Yan from the Institute of Electrical Engineering of the Chinese Academy of Science and Dr. Juergen Kolb from the Leibniz Institute for Plasma Science and Technology. Financially supported by the Sino-German Center of the German Research Foundation and the Natural Science Foundation of China, the meeting was held in the Sino-German Science Center in Beijing from October 11–17, 2015. Invited talks were given by 25 researchers from China, 15 researchers from Germany, and 3 international researchers from the USA, the U.K., and Japan. In total, more than 80 attendees participated in the symposium. [ABSTRACT FROM AUTHOR]