Discharge In Mixture Research Articles

The influence of metastable molecular nitrogen N2(A3Σu+) on the electronic kinetics of CO molecules

The simulation of N2(A3Σu+) and CO(a3Π) vibrational populations at the altitudes of Titan’s upper atmosphere and for conditions of a laboratory discharge in the N2-CO mixture is made. The influence of metastable molecular nitrogen N2(A3Σu+) on the electronic excitation of CO molecules in inelastic collisions is studied. It is shown that the increase in the density of the Titan’s atmosphere and of the discharge mixture leads to more significant excitation of lowest vibrational levels of CO(a3Π) by intermolecular electron energy transfers from N2(A3Σu+) in comparison with direct excitation of the a3Π state by free electrons.

An investigation on optical properties of capacitive coupled radio-frequency mixture plasma with Langmuir probe

The properties of Capacitively Coupled Radio Frequency (CCRF) plasmas for mixture gases have not already been known. Therefore, our goal in this paper is to understand the characteristics of mixture gas discharges in the different ratio of capacitive coupled discharge at low pressure. For this aim, the single Langmuir probe can be used to estimate the electron temperature and the electron density of the mixture discharge in a capacitive coupled discharge plasma system at low pressure. The characteristics of helium (He) and electronegative oxygen (O2) mixture plasma is determined by the single Langmuir probe. The ratio of the ion saturation current to electron saturation current is investigated with obtaining values from this probe. The optical emission measurements have been taken to minimize the deficiency of the Langmuir probe diagnostics.

Emission characteristics of plasma based on xenon–rubidium bromide mixture

Luminescence spectra of a longitudinal pulse-periodic discharge in xenon mixture with rubidium bromide vapors (Xe–RbBr) are studied experimentally at low pressures. The conditions leading to the appearance of intense bands of ultraviolet radiation of exciplex XeBr* molecules in the spectral interval between 200 and 400 nm are found. The highest yield of UV radiation of XeBr* molecules is achieved when the temperature of discharge-tube walls is equal to 750°C. A maximum power of UV radiation from the entire plasma volume as high as 4.8 W is obtained.

Probing the conformational behavior of the doubly substituted methyl-ethyl Criegee intermediate by FTMW spectroscopy.

Four conformers of the doubly substituted methyl-ethyl Criegee intermediate, C2H5C(CH3)OO, have been observed by Fourier-transform microwave spectroscopy. The transient species was produced using a pulsed electric discharge of a gas mixture of 2,2-diiodobutane/O2. The conformational preferences differ from those observed previously for related alkyl-substituted Criegee intermediates. The observation of small splittings in the spectra due to the internal rotation of only one methyl group enabled us to determine the barrier heights of the hindered methyl rotation for the four conformers, which have been compared with those reported for other methyl-substituted Criegee intermediates.

A prototype of an electric-discharge gas flow oxygen−iodine laser: I. Modeling of the processes of singlet oxygen generation in a transverse cryogenic slab RF discharge

The existing kinetic model describing self-sustained and electroionization discharges in mixtures enriched with singlet oxygen has been modified to calculate the characteristics of a flow RF discharge in molecular oxygen and its mixtures with helium. The simulations were performed in the gas plug-flow approximation, i.e., the evolution of the plasma components during their motion along the channel was represented as their evolution in time. The calculations were carried out for the O2: He = 1: 0, 1: 1, 1: 2, and 1: 3 mixtures at an oxygen partial pressure of 7.5 Torr. It is shown that, under these conditions, volumetric gas heating in a discharge in pure molecular oxygen prevails over gas cooling via heat conduction even at an electrode temperature as low as ~100 K. When molecular oxygen is diluted with helium, the behavior of the gas temperature changes substantially: heat removal begins to prevail over volumetric gas heating, and the gas temperature at the outlet of the discharge zone drops to ~220–230 K at room gas temperature at the inlet, which is very important in the context of achieving the generation threshold in an electric-discharge oxygen−iodine laser based on a slab cryogenic RF discharge.

Revealing pMDI Spray Initial Conditions: Flashing, Atomisation and the Effect of Ethanol.

Sprays from pressurised metered-dose inhalers are produced by a transient discharge of a multiphase mixture. Small length and short time scales have made the investigation of the governing processes difficult. Consequently, a deep understanding of the physical processes that govern atomisation and drug particle formation has been elusive. X-ray phase contrast imaging and quantitative radiography were used to reveal the internal flow structure and measure the time-variant nozzle exit mass density of 50µL metered sprays of HFA134a, with and without ethanol cosolvent. Internal flow patterns were imaged at a magnification of 194pixels/mm and 7759 frames per second with 150ps temporal resolution. Spray projected mass was measured with temporal resolution of 1ms and spatial resolution 6µm × 5µm. The flow upstream of the nozzle comprised large volumes of vapour at all times throughout the injection. The inclusion of ethanol prevented bubble coalescence, altering the internal flow structure and discharge. Radiography measurements confirmed that the nozzle exit area is dominantly occupied by vapour, with a peak liquid volume fraction of 13%. Vapour generation in pMDIs occurs upstream of the sump, and the dominant volume component in the nozzle exit orifice is vapour at all times in the injection. The flow in ethanol-containing pMDIs has a bubbly structure resulting in a comparatively stable discharge, whereas the binary structure of propellant-only flows results in unsteady discharge and the production of unrespirable liquid masses.

A calculation of semi-empirical one-electron wave functions for multi-electron atoms used for elementary process simulation in nonlocal plasma

Subject of Research. The paper deals with development outcomes for creation method of one-electron wave functions of complex atoms, relatively simple, symmetrical for all atom electrons and free from hard computations. The accuracy and resource intensity of the approach are focused on systematic calculations of cross sections and rate constants of elementary processes of inelastic collisions of atoms or molecules with electrons (ionization, excitation, excitation transfer, and others). Method. The method is based on a set of two iterative processes. At the first iteration step the Schrödinger equation was solved numerically for the radial parts of the electron wave functions in the potential of the atomic core self-consistent field. At the second iteration step the new approximationfor the atomic core field is created that uses found solutions for all one-electron wave functions. The solution optimization for described multiparameter problem is achieved by the use of genetic algorithm. The suitability of the developed method was verified by comparing the calculation results with numerous data on the energies of atoms in the ground and excited states. Main Results. We have created the run-time version of the program for creation of sets of one-electron wave functions and calculation of the cross sections and constants of collisional transition rates in the first Born approximation. The priori available information about binding energies of the electrons for any many-particle system for creation of semi-empirical refined solutions for the one-electron wave functions can be considered at any step of this procedure. Practical Relevance. The proposed solution enables a simple and rapid preparation of input data for the numerical simulation of nonlocal gas discharge plasma. The approach is focused on the calculation of discharges in complex gas mixtures requiring inclusion in the model of a large number of elementary collisional and radiation processes involving heavy particles in different quantum states.

Redistribution of alloying elements in the surface region of titanium alloy VT-23 during glow discharge nitriding

VT-23 titanium alloy is processed in the plasma of abnormal glow discharge in a gas mixture of N2 and Ar under a total pressure of 4 mbar and a partial pressure ratio of N2 : Ar = 3 : 2 at 900°C. The phase composition of the alloy is determined, the cross-section structure is studied by electron microscopy, and maps of the elemental composition in the cross section are obtained. The distribution of alloying elements and nitrogen is found to be inhomogeneous in the surface region.

Diagnostics of Nitrogen-methane Atmospheric Glow Discharge Used for a Mimic of Prebiotic Atmosphere

The exploration of planetary atmosphere is being advanced by the exciting results of the Cassin-Huygens mission to Titan. The complex chemistry revealed in such atmospheres leading to the synthesis of bigger molecules is providing new insights into our understanding of how life on Earth developed. This work extends our previous investigation of nitrogen-methane (N<sub>2</sub>-CH<sub>4</sub>) atmospheric glow discharge for simulation chemical processes in prebiotic atmospheres. In presented experiments 2 % of water vapor were addet to nitrogen-methane gas mixture. Exhaust products of discharge in this gas mixture were in-situ analysed by Fourier Transform Infra Red spectroscopy (FTIR). The major products identified in spectra were: hydrogen cyanide, acetylene and acetonitrile.

Solution plasma synthesis of a boron-carbon-nitrogen catalyst with a controllable bond structure.

Synthesis of boron-carbon-nitrogen (BCN) nanocarbon with a controllable bond structure for enhanced oxygen reduction reaction (ORR) activity and durability was performed using a new method of discharge in organic solution mixtures named the 'Solution Plasma Process'. Using selected precursors a new strategy for the simultaneous synthesis of nanocarbon co-doped with heteroatoms was found. The synergistic effect of N and B in an uncoupling bond state improved the formation of new active sites for the ORR performance by changing the electronic structure of the base carbon. Meanwhile, when B and N are bonded together, the BCN catalyst contributes to a reduced ORR activity by forming a balanced electronic structure in carbon. The BCN nanocarbon with an uncoupling bond state exhibits an enhanced ORR activity under alkaline conditions, with an onset potential of -0.25 V versus -0.31 V for B/N coupling and 3.43 transferred electrons during the ORR. Although the ORR activity of the B/N uncoupling nanocarbon was not as good as the typical Pt/C, the durability of this synthesized material (15.1% current decrease after 20 000 s of operation) was significantly better than that of the Pt/C catalyst (61.5% current drop under the same conditions). After the durability test, the increase of the chemical states containing oxygen was higher for Pt/C than B/N uncoupling.

Effect of excitation frequency on characteristics of mixture discharge in fast-axial-flow radio frequency-excited carbon dioxide laser

A one-dimensional fluid model has been used to describe the effect of radio frequency (RF) on the characteristics of carbon dioxide (CO2), nitrogen (N2) and helium (He) mixture discharge at 120 mbar in fast-axial-flow RF-excited CO2 laser. A finite difference method was applied to solve the one-dimensional fluid model. The simulation results show that the spatial distributions of electron density and current density rely strongly on the modulating driven frequency. When the excitation frequency changes from 5 to 45 MHz, the plasma discharge is always in α mode. Moreover, as the excitation frequency increasing, the higher densities of CO2V001 and N2*Vib can be obtained, which is important to get higher excitation efficiency for the upper laser level.

Runaway electrons during subnanosecond breakdowns in high‐pressure gases

The parameters of runaway electrons produced in nanosecond high-voltage discharges in different gases (air, nitrogen, sulphur hexafluoride, krypton, argon, methane, neon, hydrogen, helium) at atmospheric and higher pressure were studied. An optical analysis was also performed to investigate the ionisation dynamics in diffuse discharges in nitrogen and nitrogen-containing mixtures. At breakdown of a point-to-plane gap by nanosecond (≃2 ns) high-voltage (≃200 kV) pulses of negative voltage polarity and gas pressure above 0.1 MPa, a supershort avalanche electron beam (SAEB) was detected by a collector behind the flat anode. For pressure >0.1 MPa of nitrogen and other gases it is shown that the maximum pressure for SAEB registration decreases with increasing the voltage pulse rise time. Therefore, to detect a SAEB at atmospheric and higher gas pressure, one should use voltage pulses with an amplitude of hundred kilovolts and rise time of ∼1 ns and shorter. The experimental research in the dynamics of optical radiation from the discharge plasma shows that the breakdown in which runaway electrons are produced develops as an ionisation wave.

Numerical study of nonequilibrium plasma assisted detonation initiation in detonation tube

Nonequilibrium plasma has shown great merits in ignition and combustion nowadays, which should be especially useful for hypersonic propulsion. A coaxial electrodes configuration was established to investigate the effect of alternating current (AC) dielectric barrier discharge nonequilibrium plasma on the detonation initiation process in a hydrogen-oxygen mixture. A discharge simulation-combustion simulation loosely coupled method was used to simulate plasma assisted detonation initiation. First, the dielectric barrier discharge in the hydrogen-oxygen mixture driven by an AC voltage was simulated, which takes 17 kinds of particles (including positively charged particles, negatively charged particles, and neutral particles) and 47 reactions into account. The temporal and spatial characteristics of the discharge products were obtained. Then, the discharge products were incorporated into the combustion model of a detonation combustor as the initial conditions for the later detonation initiation simulation. Results showed that the number density distributions of plasma species are different in space and time, and develop highly nonuniformly from high voltage electrode to grounded electrode at certain times. All the active species reach their highest concentration at approximately 0.6T (T denotes a discharge cycle). Compared with the no plasma case, the differences of flowfield shape mainly appear in the early stage of the deflagration to detonation transition process. None of the sub-processes (including the very slow combustion, deflagration, over-driven detonation, detonation decay, and propagation of a self-sustained stable detonation wave) have been removed by the plasma. After the formation of a C-J detonation wave, the whole flowfield remains unchanged. With the help of plasma, the deflagration to detonation transition (DDT) time and distance are reduced by about 11.6% and 12.9%, respectively, which should be attributed to the active particles effect of nonequilibrium plasma and the local turbulent enhancing effect by the spatial characteristics of discharge. In addition, as the duration of forming a shock wave in the combustor is shortened by approximately 8.1%, it can be inferred that the plasma accelerates the DDT process more significantly before the flow becomes supersonic.

High-power gas-discharge excimer ArF, KrCl, KrF, and XeCl lasers on buffer-gas free gas mixtures

Results of experimental studies of the gas mixture (laser active medium) effect on the lasing energy and overall efficiency of excimer discharge ArF (193 nm), KrCl (222 nm) KrF (248 nm), and XeCl (308 nm) lasers operating in buffer-free gas mixtures are presented. The optimal (in terms of maximum radiation energy) ratios of the gas components of the excimer laser active media are found, at which efficient operation is achieved with a sufficiently high power of the laser radiation. It is confirmed experimentally that for the rare gas halide discharge pumped excimer lasers the presence of a buffer gas in the active medium is not required for efficient laser operation. For example, in two-component excimer laser gas mixtures, containing working rare and halogen-containing gases, laser pulse energy of up to 170 mJ and high pulsed power of laser radiation of up to 24 MW have been attained for the first time for pulsed gas-discharge excimer lasers operating on electronic transitions at excimer ArF*, KrCl*, KrF*, and XeCl* molecules pumped by a transverse electric volume discharge of a low-pressure buffer-free gas mixture. A overall efficiency maximum of up to 0.8% was experimentally attained for binary gas mixture of KrF and XeCl lasers.

Comparative analysis of plasma-chemical models for computer simulation of glow discharges in air mixtures

Subject of Research. We present research results for numerical modeling possibility of discharges in gas mixtures within the modern model of nonlocal plasma by creation a sequence of plasma-chemical and numerical models and comparing the results with experimental data. Method. Creation method for series of models with gradually increasing complexity has been used. It is based on a step by step expansion of the range accounted for elementary processes in nonlocal glow discharge plasma in the air. The air is approximated by the mixture of nitrogen and oxygen at low pressures under conditions suitable for experimental verification. For each iteration of plasma chemical scheme, corresponding numerical models of gas-discharge were created. The graphs of the discharge gap electrical parameters on the pressure were obtained by this method. Theoretical data obtained at each step have been compared to the experimental data and the results of previous computer models. Main Results. The model has been created that provides a good agreement with the experimentally obtained dependencies of the voltage drop across the discharge gap on the gas pressure in the areas of normal and abnormal glow discharge. By the updated model the optimum value for the coefficient of secondary electron emission from the cathode was chosen. Additionally, we have obtained the spatial distribution of the internal parameters of nonlocal plasma (longitudinal and transverse profiles of the electric potential, electron and ion densities, the electron temperature) as a subject to further experimental verification. Practical Relevance. The created models are perspective to be used for diagnosis and the setting of parameters of micro-discharges in the air. They have different applications, including developing method of electronic collision spectroscopy (CES) gas mixtures.

Modeling of Single and Dual Frequency Capacitive Discharge in Argon Hydrogen Mixture − Dynamic Effects and Ion Energy Distribution Functions

Single (SF) and dual frequency capacitively coupled plasma (DF CCP) in (0–50%) H2/Ar mixtures was studied numerically with 1D hybrid (Particle‐in‐cell with Monte Carlo Collision + fluid) model. In SF (81 MHz) discharge the effect of hydrogen dilution is studied for the fixed discharge input power. Mechanisms of the plasma density decrease and variation of ions composition with H2 percentage are discussed. The effect of low‐frequency voltage on plasma density, ions composition, ions fluxes, and ions energy was studied in DF CCP (1.76–81 MHz) discharge in 5% H2/Ar gas mixture at low (20 mTorr) and high (100 mTorr) pressures.

Characterization of the large area plane-symmetric low-pressure DC glow discharge

Electron density and temperature as well as nitrogen dissociation degree in the low-pressure (10–50mTorr) large area plane–symmetric DC glow discharge in Ar-N2 mixtures are studied by probes and spectral methods. Electron density measured by a hairpin probe is in good agreement with that derived from the intensity ratio of the N2 2nd positive system bands IC,1−3/IC,0−2 and from the intensity ratio of argon ions and atom lines IArII/IArI, while Langmuir probe data provides slightly higher values of electron density. Electron density in the low-pressure DC glow discharge varies with the discharge conditions in the limits of ~108–1010cm−3. The concept of electron temperature can be used in low-pressure glow discharges with reservations. The intensity ratio of (0–0) vibrational bands of N2 1st negative and 2nd positive systems I391.4/I337.1 exhibits the electron temperature of 1.5–2.5eV when argon fraction in the mixture is higher than nitrogen fraction and this ratio quickly increases with nitrogen fraction up to 10eV in pure nitrogen. The electron temperature calculated from Langmuir probe I-V characteristics assuming a Maxwellian EEDF, gives Te~0.3–0.4eV. In-depth analysis of the EEDF using the second derivative of Langmuir probe I-V characteristics shows that in a low-pressure glow discharge the EEDF is non-Maxwellian. The EEDF has two populations of electrons: the main background non-Maxwellian population of “cold” electrons with the mean electron energy of ~0.3–0.4eV and the small Maxwellian population of “hot” electrons with the mean electron energy of ~1.0–2.5eV. Estimations show that with electron temperature lower than 1eV the rate of the direct electron impact ionization of N2 is low and the main mechanism of N2 ionization becomes most likely Penning and associative ionization. In this case, assumptions of the intensity ratio IN2+,391/IN2,337 method are violated.In the glow discharge, N2 dissociation degree reaches about 7% with the argon fraction in the Ar-N2 mixture<10% and decreases afterwards approaching to ~1–2% when the argon percentage becomes 90% and higher. The atomic nitrogen species is produced by electron-impact processes such as, collisions between electrons and nitrogen molecules or between electrons and N2+ ions. At small Ar fraction in Ar-N2 mixtures, the atomic nitrogen species is most likely produced by the collisions between electrons and N2+ ions.

Effects of Oxygen Concentration on Pulsed Dielectric Barrier Discharge in Helium-Oxygen Mixture at Atmospheric Pressure**supported by the Fundamental Research Funds of Shandong University, China (No. 2016JC016)

In this work the effects of O2 concentration on the pulsed dielectric barrier discharge in helium-oxygen mixture at atmospheric pressure have been numerically researched by using a one-dimensional fluid model in conjunction with the chosen key species and chemical reactions. The reliability of the used model has been examined by comparing the calculated discharge current with the reported experiments. The present work presents the following significant results. The dominative positive and negative particles are He2+ and O2−, respectively, the densities of the reactive oxygen species (ROS) get their maxima nearly at the central position of the gap, and the density of the ground state O is highest in the ROS. The increase of O2 concentration results in increasingly weak discharge and the time lag of the ignition. For O2 concentrations below 1.1%, the density of O is much higher than other species, the averaged dissipated power density presents an evident increase for small O2 concentration and then the increase becomes weak. In particular, the total density of the reactive oxygen species reaches its maximums at the O2 concentration of about 0.5%. This characteristic further convinces the experimental observation that the O2 concentration of 0.5% is an optimal O2/He ratio in the inactivation of bacteria and biomolecules when radiated by using the plasmas produced in a helium oxygen mixture.

A 3-D DNS and experimental study of the effect of the recirculating flow pattern inside a reactive kernel produced by nanosecond plasma discharges in a methane-air mixture

This paper presents 3-D DNS and experimental schlieren results used to study a non-equilibrium plasma discharge in a lean methane-air mixture. A detailed combustion mechanism and a plasma model, developed in our previous work, are used in the 3-D computations in order to study the impact of gas flow recirculation on the temporal evolution of species and gas temperature in the vicinity of the discharge zone. The results show that the formation of a fresh gas counterflow, with stagnation plane at the centre of the discharge and parallel to the electrodes, changes the topology of the hot kernel from an initial cylindrical shape to a toroidal one. This phenomenon leads to an increase of the area/volume ratio of the reactive kernel, that may result under certain conditions in kernel extinction. The results also show the importance of considering this 3-D gas flow recirculation to correctly predict the temporal evolution of the hot kernel. In particular, we show that the temperature and species concentrations in the central region of the discharge return to fresh gas conditions shortly after the end of the pulse. In the experimental case investigated here, this time is of the order of 150 µs. This result is particularly important for ignition by Nanosecond Repetitively Pulsed (NRP) discharges, because the gas conditions at the beginning of each successive pulse depend strongly on the time interval between pulses, thus on the pulse frequency

Pulsed radio-frequency discharge inductively coupled plasma mass spectrometry for oxide analysis

A direct solid sampling technique has been developed based on a pulsed radio-frequency discharge (RFD) in mixture of N2 and Ar environment at atmospheric pressure. With an averaged input power of 65W, a crater with the diameter of 80μm and depth of 50μm can be formed on sample surface after discharge for 1min, suggesting the feasibility of the pulsed RFD for sampling nonconductive solids. Combined with inductively coupled plasma mass spectrometry (ICPMS), this technique allows to measure elemental composition of solids directly with relative standard deviation (RSD) of ~20%. Capability of quantitative analysis was demonstrated by the use of soil standards and artificial standards. Good calibration linearity and limits of detection (LODs) in range of 10−8–10−9g/g were achieved for most elements.