In this study the applicability of the binary mixture model utilizing the first-order gas-kinetic Chapman–Enskog theory is substantiated for describing diffusion processes at different degrees of ionization of a single-temperature simple gas plasma consisting of three components: atoms, ions and electrons. On the same bases, the obtained expressions for a trinary mixture are applicable to a plasma with a fourth component that is difficult to ionize. The thermal diffusion relations of a trinary mixture are derived, whose peculiarity is the electronic component, which does not affect the diffusion flows of atoms and ions. It is shown that in a highly ionized He arc plasma with developed diffusion and ionization nonequilibrium, thermal diffusion is insignificant. It is noted that when thermodynamic equilibrium is violated, the diffusion coefficients may not change at all or decrease by half at most.

This article describes the study of low pressure helium plasma with magnetic confinement at the experimental test setup at the Moscow Power Engineering Institute: plasma linear multicusp (PLM). This facility is intended for testing refractory materials and prototypes of elements of the first wall within the framework of development of the national fusion reactor (DEMO–FNS) and the International Thermonuclear Experimental Reactor (ITER). The facility provides the conditions of plasma impact on the surface of tested sample close to the parameters and regime of operation of tokamak divertor plates. The facility is a magnetic trap with minimum magnetic field on the axis, where the plasma is created by the flow of electrons moving from the directly heated tantalum cathode toward the anode. It is possible to create stationary helium plasma in the facility and to maintain it for several hours under constant discharge parameters: helium pressure in the chamber of 10–3–10–1 Torr, discharge current of 4–30 A, plasma column diameter of 35–40 mm, voltage drop across the discharge gap of 100–200 V. The thermal load on the surface of target introduced into the axial region of plasma column has reached 5 MW/m2. Optical emission spectroscopy is the main diagnostic tool in this work. The procedure for determining atomic concentrations from the data on the relative intensities of atomic spectral lines of metallic impurities is proposed in this work.

The article demonstrates that the key link in the ionization and recombination kinetics of strongly ionized nonequilibrium He plasma at atmospheric pressure in a narrow water-cooled arc channel is the ionization–diffusion balance of atoms, which regulates the concentration of n and electrons ne and maintains close to isochoric conditions with a high concentration of neutrals n ne, exceeding the Saha equilibrium by two or three orders of magnitude. Using the measured radial dependences ne(r) and T(r), the problem of the diffusion of atoms in a binary mixture is solved approximately, taking into account the ambipolar diffusion of an electron–ion gas as one of the components of the binary mixture. The concentration of atoms at the center of the arc and its radial dependence, which strongly increases with distance from the center, is found, especially with powerful pulsed heating of a stationary arc. The pressure when the pulse is applied reaches its maximum and is twice the atmospheric pressure. Due to the high concentration of atoms and destruction of levels by plasma microfields, triple recombination is ten times weaker than ambipolar diffusion. One of the consequences of the predominant ambipolar diffusion in the kinetics of charged particles is the low density of double ions n++/n+ 10–3.

We studied the synthesis of composite Cu/graphene nanoparticles using the radiative characteristics of copper-containing plasma jets of a helium/hydrocarbon mixture, flowing from the nozzle of the output copper electrode of a DC plasmatron. A mixture of propane and butane was used as the hydrocarbon source. To determine the conditions for nanoparticle formation during the conversion of hydrocarbons in erosive jets, the concentration of copper was estimated by analyzing the optical emission spectra of Cu I lines observed in the spectrum. We found that the maximum saturation of graphene by copper (0.03 mass %) is reached at the copper concentration in plasma [Cu] = Nabs ≈ 3 × 1013 cm−3, which is sufficient to form a chemical bond of copper with sp2 carbon in a nanoparticle.

В работе с помощью газокинетической теории Чепмена‒Энскога первого порядка проведено обоснование применимости модели бинарной смеси для описания диффузионных процессов при разных степенях ионизации однотемпературной плазмы простого газа, состоящей из трех компонентов: атомов, ионов и электронов. На тех же основаниях полученные выражения для тринарной смеси применимы к плазме с трудноионизуемым четвертым компонентом. Выведены термодифузионные отношения тринарной смеси, особенностью которых является электронная составляющая, не влияющая на диффузионные потоки атомов и ионов. Показано, что в сильноионизованной дуговой плазме Не с развитой диффузией и ионизационной неравновесностью термодиффузия несущественна. Отмечено, что при нарушении термодинамического равновесия диффузионные коэффициенты могут не изменяться или уменьшаться в пределах двойки.

Methods for processing optical emission spectroscopy data in the study of the region of interaction between helium plasma with a density of the main gas [He] ≈ 10 12 –10 14 cm –3 and electrons n e ≈ 10 11 –10 13 cm –3 and a tungsten sample in a PLM facility designed for testing materials with a plasma load are presented. A method for measuring the electron temperature using the coronal approximation is proposed. For the calculation, it is necessary to choose the ratio of the intensities of spectral lines that is most sensitive to the electron temperature; in this case, this is the ratio of the intensity of ionic lines to atomic lines. Comparison of the ratio of the experimental intensities of the He II 468.5 nm ion line and a number of He I atomic lines with well-known electron excitation constants with the calculated dependence of this ratio on the mean electron energy is a reliable method for the spectral determination of the electron temperature of a magnetized rarefied helium plasma. In experiment, the concentration of atomic helium is [He] ≈ 10 14 cm –3 ; the discharge current is 2–10 A; the voltage drop is 160–180 V; the radius and length of the discharge are 16 and 370 mm, respectively. The electron temperature measured using two singlet and two triplet lines of He I is T e = 2.4 ± 0.2 eV. With consideration of the nonlocality of the electron energy distribution function (EEDF), the complex nature of the drift and diffusion of charges in crossed and inhomogeneous electric and magnetic fields, etc., the mean electron energy of ε^_ = (3/2) kT e ≈ 3.6 eV corresponding to this temperature can be considered a lower estimate for the energy of the Maxwellian section of the EEDF of the plasma.

A method to measure the velocity of subsonic submerged plasma jets with unstable flows based on an analysis of the motion of optical inhomogeneities introduced into the jet is considered. A source of these inhomogeneities in the form of a heat-resistant thin rod is placed in a diametrical direction of a chosen cross section of the jet flowing from the output channel of a high-current DC plasmatron into ambient air under atmospheric pressure. The plasma-forming gas is a mixture of argon and nitrogen, and the characteristic Reynolds numbers of the studied flows are ReD = 50–300. The perturbation effect of the body introduced into the plasma jet on the two most important characteristics (plasma temperature and velocity) was studied. Specific features of laminar and pulsating flows of submerged plasma jets were studied via two-site, high-speed, synchronous visualization. It is shown that the length of the continuity restoration part of the jet flowing around the rod at a temperature of 10–12 kK and a velocity of 100–500 m/s is very small (several millimeters) under these conditions. The plasma temperature in the region of the strongest thermal perturbation caused by the introduction of the rod was measured with spectral methods. The observed plasma cooling is compared with the calculated decrease in the enthalpy due to expenditures for the heating and ablation of the rod material.

We present the results of studying optical emission spectra of Ar:CH4 plasma produced on a DC plasmatron for graphene synthesis. We have identified the basic set of spectral lines and bands in the obtained spectra and shown that H lines and C2 bands appear due to direct excitation by an electron strike of corresponding neutral particles. C2 molecular bands were also identified in the spectra with intensity considerably lower compared to previous studies where He: C2H2 mixture was used as plasma-forming gas.

With the aim of studying nitrogen plasma flow impacting graphite surfaces, we investigated the evolution of a plasma jet moving from the nozzle of the plasma torch to the target. The motion is accompanied by a decrease in temperature from 10 to 7 kK with a loss of ≈ 60% of the deposited energy and an increase in the density of carbon-containing impurities with partial preservation of the local thermodynamic equilibrium. The main reactions are thermal processes of the formation and decomposition of molecules, dissociative recombination and recharging of nitrogen ions. In the presence of carbon impurities, this set is supplemented with the substitution reaction C + N 2 ↔ CN + N, electron-collision processes of stepwise ionization and recombination, and a whole ion-molecular cascades of reloads and substitutions. It has been established that a small admixture of carbon (∼ 0.1%) manifests itself only in ion-molecular kinetics, increasing the electron concentration, determining the ionic composition of the plasma, and thereby violating the equilibrium between its neutral and charged components. This leads, in particular, to the recombination nonequilibrium distribution of carbon atoms over electronic states. Other carbon-containing impurities (CN and C 2 ) are not significant.

The analysis of the current state of the technological process and equipment for plasma coating of various powder materials has been carried out. To increase the processing efficiency during the deposition of ceramic materials and refractory alloys a novel technological scheme of plasma spraying with a powder feed axially to the cathode was proposed and preliminarily tested. Basing the plasma torch with an expanding channel of the output electrode its plasma-spraying version has been developed in which the sprayed powder was supplied both to the cathode or anode arc striking zone and to the current-free plasma jet. The electrophysical parameters of the argon plasma torch and the speed, size and temperature of particles of sprayed powder were investigated. It was shown that the particle velocity of Al2O3 powder depending on the gas flow and arc current reaches up to 100 m/s. The temperature of the powder particles in the vicinity of substrate at a current of 300 A approximately equals to 2400–2500 K.

A method for estimating the gas-dynamic characteristics of supersonic plasma jets based on the minimum number of plasma parameters (electron number density and temperature) that are easily measured by spectral diagnostic methods is considered. The course of the most important parameters characterizing the gas dynamics of the nonequilibrium plasma flow in the shock-wave region of a supersonic plasma jet created by a pulsed capillary discharge is revealed, and their values are estimated. A significant difference between the electron and gas temperatures was found in the vicinity of the central shock wave.

The evolution of the kinetics of plasma moving from the outlet of a plasma torch to the object of impact is studied in order to study the effectiveness of action of a nitrogen plasma flow on graphite surfaces. The motion is accompanied by a decrease in temperature from 10 to 7 kK with a loss of ~60% of the input energy and an increase in the density of carbon-containing admixtures with partial conservation of the local thermodynamic equilibrium. The main reactions are the thermal processes of the formation and dissociation of molecules, the dissociative recombination and recharge of nitrogen ions, and, in the presence of carbon admixtures, the substitution reaction С + N 2 ↔ CN + N, the electron-collisional processes of stepwise ionization and recombination, and the entire ionic–molecular cascade of recharges and substitutions. It is found that a small amount of carbon impurity (~0.1%) manifests itself only in ionic–molecular kinetics. It increases the electron concentration, determines the ionic composition of the plasma, and thereby violates the equilibrium between its neutral and charged components. This leads, in particular, to a recombination nonequilibrium of distribution of carbon atoms over the electron states. Other carbon-containing impurities (CN and C 2 ) are insignificant.

The results of a spectroscopic study of the conversion of acetylene and methane in a helium plasma jet produced by a direct current plasma torch are presented. The operating mode of the plasma torch corresponds to conditions that provide a high yield of carbon nanostructures. In the emission spectra recorded during the transverse observation of a 20-mm jet section following the outlet of the anode channel of the plasma torch, high-intensity Swan bands of the С2 molecule are the dominant component in the visible wavelength range. The spectra show atomic hydrogen lines of the HI Balmer series from Hα to Hε, numerous CI carbon lines from ultraviolet 247.9 nm to infrared 962–966 nm, and a number of HeI helium lines. The axial temperature values of the plasma jet were spectrally determined by the observed ionized carbon CII lines 283.7 nm, 392.0 and 426.7 nm. A joint analysis of the emission spectra and the mixture composition calculated in the Saha–Boltzmann approximation revealed the nature of the spatial heterogeneity of the studied He : C : H plasma jet. It is manifested by the difference in the electron temperature of the axial region of the jet, which is measured with ionized carbon lines CII (Te(0) = 12 000–14 000 K) from the vibrational and rotational temperatures of C2 molecules (TV = TR ≅ 5000 K) that emit intensely at the jet periphery. The electron density measured along the Hβ and Hγ line widths, which varies in the range of the observed jet region of ne = (4–2) × 1016 cm–3, corresponds to the ionization equilibrium in a plasma He : C : H mixture with an electron temperature close to Te measured by carbon-ion lines.

We present results of spectroscopic measurement of electron temperature in submerged nitrogen and argon mixture plasma jet for cases of free flow and introduction of thin graphite rod into the jet. The observed cooling of plasma caused by rod introduction agrees with the calculated enthalpy decrease from graphite rod heating and ablation. In this experiment, a marker was used to create artificial optical inhomogeneities in the flow, which allowed us to determine flow velocity from the analysis of their movement. In this case, we aim to determine the degree of influence of rod introduction into the plasma on its parameters. Upon introduction into the plasma, the rod was heated and partially destroyed by the plasma flow, reducing its temperature by 8-20% depending on the flow rate of the plasma-forming gas. The observed plasma cooling was compared with the calculated decrease in enthalpy caused by the cost of heating and ablation of the rod material.