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We explore the plasma matter content in the innermost accretion disk/jet in M87* as relevant for an enthusiastic search for the signatures of anti-matter in the next generation of the Event Horizon Telescope (ngEHT). We model the impact of non-zero positron-to-electron ratio using different emission models, including a constant electron to magnetic pressure (constant β e model) with a population of non-thermal electrons as well as an R-beta model populated with thermal electrons. In the former case, we pick a semi-analytic fit to the force-free region of a general relativistic magnetohydrodynamic (GRMHD) simulation, while in the latter case, we analyze the GRMHD simulations directly. In both cases, positrons are being added at the post-processing level. We generate polarized images and spectra for some of these models and find out that at the radio frequencies, both of the linear and the circular polarizations are enhanced with every pair added. On the contrary, we show that, at higher frequencies, a substantial positron fraction washes out the circular polarization. We report strong degeneracies between different emission models and the positron fraction, though our non-thermal models show more sensitivities to the pair fraction than the thermal models. We conclude that a large theoretical image library is indeed required to fully understand the trends probed in this study, and to place them in the context of a large set of parameters which also affect polarimetric images, such as magnetic field strength, black hole spin, and detailed aspects of the electron temperature and the distribution function. [ABSTRACT FROM AUTHOR]

The spark plasma parameters with electrodes produced from the high-entropy CrMnFeCoNi alloy were studied by mathematical modeling and experimentally. The model describes the dependence of the spark discharge plasma composition and the intensity of spectral lines on the electrode erosion rate and discharge power. The concentrations of electrons, atoms, and ions of electrode components and molecular components of plasma were determined from conditions of local thermodynamic equilibrium at the discharge axis (quasi-equilibrium conditions), and temperature was calculated from the energy balance equations. The system of nonlinear equations is solved in iterative cycles until self-consistent values of concentrations and temperatures are received. Elements with a high second ionization potential in electrode materials (for instance, Al, Cu, Ag, B) essentially increase temperature at the discharge axis resulting from reduction in the cross-section of inelastic processes and associated energy losses. Increase in the evaporation rate leads to temperature decrease, but electron concentration reduces by less than 20%, other parameters being equal. This effect results from decrease in the effective ionization potential with higher metal vapor concentration in the discharge plasma. There are complex nonlinear relations between the erosion rate and the intensity of spectral lines of atoms and singly charged and doubly charged ions, which are associated with the dependence of plasma temperature at the discharge axis on the evaporation rate. The calculated temperature and electron concentrations agree with the experiment within the error, taking into account the simplifications accepted in the model. The developed method can be used for spectroscopic diagnostics of electric erosion of the high-entropy CrMnFeCoNi alloy in the production of nanopowders by electrospark method and for emission spectral analysis of its composition. [ABSTRACT FROM AUTHOR]

We explore the plasma matter content in the innermost accretion disk/jet in M87* as relevant for an enthusiastic search for the signatures of anti-matter in the next generation of the Event Horizon Telescope (ngEHT). We model the impact of non-zero positron-to-electron ratio using different emission models, including a constant electron to magnetic pressure (constant βe model) with a population of non-thermal electrons as well as an R-beta model populated with thermal electrons. In the former case, we pick a semi-analytic fit to the force-free region of a general relativistic magnetohydrodynamic (GRMHD) simulation, while in the latter case, we analyze the GRMHD simulations directly. In both cases, positrons are being added at the post-processing level. We generate polarized images and spectra for some of these models and find out that at the radio frequencies, both of the linear and the circular polarizations are enhanced with every pair added. On the contrary, we show that, at higher frequencies, a substantial positron fraction washes out the circular polarization. We report strong degeneracies between different emission models and the positron fraction, though our non-thermal models show more sensitivities to the pair fraction than the thermal models. We conclude that a large theoretical image library is indeed required to fully understand the trends probed in this study, and to place them in the context of a large set of parameters which also affect polarimetric images, such as magnetic field strength, black hole spin, and detailed aspects of the electron temperature and the distribution function.

In some polar coronal holes, previous studies have identified a coronal hole boundary layer (CHBL), which is different in composition from the coronal hole core region. However, compositionally distinct CHBL structure at low heliographic latitudes remains underexplored. Using solar wind composition measurements from the Advanced Composition Explorer (ACE), we study two particular low‐latitude coronal holes of 2003: a large polar hole extension with outward magnetic polarity and a smaller equatorial hole with inward magnetic polarity. For both of these coronal holes, we examine the distribution of two composition parameters, the O7+ to O6+ charge state density ratio (n(O7+)/n(O6+)) and the Fe to O abundance ratio (n(Fe)/n(O)), and find that each hole has an identifiable CHBL based on an anticorrelation of solar wind speed and n(O7+)/n(O6+). We also examine the FIP (first ionization potential) effect in the CHBL using n(Fe)/n(O), and find that there is no significant change from the CHBL to the core region for one of the coronal holes we study, while the other coronal hole has a noticeable decrease in n(Fe)/n(O) values in its core. Finally, we discuss our results in the context of previous work studying CHBL structure. Key Points: Advanced Composition Explorer composition measurements indicate that the largest coronal hole extension of 2003 has a thick coronal hole boundary layer (CHBL) distinct from its coreA CHBL is also observed in a small, inward‐polarity coronal hole in 2003; its speed range is not as broad as that of the largest extensionIn both coronal holes examined in this work, no change in the FIP effect is observed from the core to the CHBL [ABSTRACT FROM AUTHOR]

An algorithm for calculating the plasma composition based on the improved Raizer method is described in detail. The results of calculations by this method and by solving the system of the Saha equations, taking into account the degeneracy of electrons, are compared. A method of solution of scalar equation is proposed, which is just as reliable as the dichotomy method and is faster than the Brent method in calculating the composition of a multicomponent plasma. Formulas for calculation of thermodynamic functions of the plasma are given. [ABSTRACT FROM AUTHOR]

Wide spectrum of carbon nanostructures was synthesized by means of simple plasma chemistry using DC plasma torch: carbon nanotubes, nanowalls, graphene, hydrogenated graphene and a mixture of nanotubes with graphene. The synthesis was performed in the plasma-chemical reactor under the pressure varying in the close range 350–710 Torr with different types of hydrocarbon as an admixture to the helium plasma. Aliphatics (propane, butane methane and acetylene) were used providing a variation of C:H ratio. The plasma-chemical pyrolysis of hydrocarbons in the temperature range 1000–8000 K was analyzed using the thermodynamic and gas dynamic characteristics. It is determined that the main contribution to the formation of predecessors of solid carbon makes the composition of plasma jet in the temperature range 2500–3500 K. In this range the interrelation between atomic hydrogen H and hydrocarbon molecules CH varies dramatically, and the mole fraction of solid carbon Cgr goes upward. The C:H ratio in the carbon feedstock is shown to have an influence on the particularity of processes of formation of condensed carbon. [ABSTRACT FROM AUTHOR]

Orbiting Earth's dayside outer magnetosphere on 29 September 2015, the Magnetospheric Multiscale (MMS) satellites measured plasma composition, simultaneous electromagnetic ion cyclotron waves, and intermittent fast plasma flows consistent with ultralow frequency waves or convection. Such flows can accelerate typically unobservable low‐energy plasma into a measurable energy range of spacecraft plasma instrumentation. We exploit the flow occurrence to ensure measurement of cold ion species alongside the hot particles—consisting of ionospheric heavy ions and solar wind He++—during a subinterval of wave emissions with spectral properties previously described as peculiar. Through application of the composition and multisatellite wave vector data to linear theory, we demonstrate the emissions are in fact consistent with theory, growing naturally in the He++ band with sufficient free energy. Plain Language Summary: Electromagnetic ion cyclotron waves are a special class of plasma waves observed in space near Earth or in other magnetized plasmas. They emit electromagnetic energy near the local ion cyclotron frequencies, a relationship that has been studied extensively through theory. But investigations in space via satellite observations have been hindered by an observational problem. Spacecraft charge positive in sunlight due to interactions between sunlight and spacecraft surfaces. Because of this, positively charged ion species with very low energy are invisible to spacecraft plasma instruments. These invisible low‐energy ions are critical to measure to fully understand their effects on the wave emissions. Luckily, electric fields induced by sudden ambient magnetic field changes sometimes provide extra acceleration to these low‐energy ions, helping them enter plasma instrument apertures and be observed. We investigate the electromagnetic waves during one such acceleration interval and use comprehensive plasma instrument measurements to show waves thought to be peculiar are instead behaving consistent with theory. Exploring other times and regions of space under similar measurement conditions may improve our understanding of how the electromagnetic waves are generated and their evolution in space and time. Key Points: Convection flows enabled direct measurement of comprehensive plasma composition during observations of EMIC waves with peculiar propertiesSingle‐spacecraft and multispacecraft measurements were applied to modeling and tests of linear kinetic theoryThe multiple heavy ion populations, even with low abundances, help sustain wave growth and explain the wave properties [ABSTRACT FROM AUTHOR]

A tool based on the mass action law was developed to calculate plasma compositions and thermodynamic properties for pure gases and mixtures, assuming a local thermodynamic equilibrium for pressures of up to 300 bar. The collection of the data that was necessary for tool calculation was automated by another tool that was written using Python, and the formats for the model were adapted directly from the NIST and JANAF websites. In order to calculate the plasma compositions for high pressures, virial correction was introduced. The influences of the parameters that were chosen to calculate the Lennard–Jones (12-6) potential were studied. The results at high pressure show the importance of virial correction for low temperatures and the dependence of the dataset used. Experimental data are necessary to determine a good dataset, and to obtain interaction potential. However, the data available in the literature were not always provided, so they are not well-adapted to a large pressure range. Due to this lack, the formulation provided by L. I. Stiel and G. Thodos (Journal of Chemical and Engineering Data, vol. 7, 1962, p. 234–236) is a good alternative when the considered pressure is not close to the critical point. The results may depend strongly on the system studied: examples using SF6 and CH4 plasma compositions are given at high pressure. [ABSTRACT FROM AUTHOR]

For a thermal dusty plasma with metal particles, the relations of the particle charge to the temperature of the system and the particle size have been obtained using a two-plasma model and the approximation of a rectangular potential well. The number densities of electrons and ions in the plasma have been determined for various temperatures and particle sizes of the system. It has been shown that in the case of metal particles, the ionization of the buffer gas leads to underestimation of the charge in comparison with the case when the ionization of the gas is negligible. [ABSTRACT FROM AUTHOR]

A tool based on the mass action law was developed to calculate plasma compositions and thermodynamic properties for pure gases and mixtures, assuming a local thermodynamic equilibrium for pressures of up to 300 bar. The collection of the data that was necessary for tool calculation was automated by another tool that was written using Python, and the formats for the model were adapted directly from the NIST and JANAF websites. In order to calculate the plasma compositions for high pressures, virial correction was introduced. The influences of the parameters that were chosen to calculate the Lennard–Jones (12-6) potential were studied. The results at high pressure show the importance of virial correction for low temperatures and the dependence of the dataset used. Experimental data are necessary to determine a good dataset, and to obtain interaction potential. However, the data available in the literature were not always provided, so they are not well-adapted to a large pressure range. Due to this lack, the formulation provided by L. I. Stiel and G. Thodos (Journal of Chemical and Engineering Data, vol. 7, 1962, p. 234–236) is a good alternative when the considered pressure is not close to the critical point. The results may depend strongly on the system studied: examples using SF6 and CH4 plasma compositions are given at high pressure.

Knowledge of air-water vapor mixtures thermal plasmas thermodynamic properties is important to estimate the performances of electrical arc cutting in this gas by a circuit breaker. In this paper, air-water vapor mixtures thermal plasmas thermodynamic properties are calculated in a temperature range from 5000K to 30000K. The calculations are carried out by supposing local thermodynamic equilibrium at pressure of 1; 5 and 10 atm. The obtained results show the influence of the water vapor initial proportion but also that of the pressure on these plasmas thermodynamic properties. [ABSTRACT FROM AUTHOR]

Plasma spray-physical vapor deposition (PS-PVD) is an emerging coating technique that can produce columnar thermal barrier coatings from vapor phase. Feedstock treatment at the start of its trajectory in the plasma torch nozzle is important for such vapor-phase deposition. This study describes the effects of the plasma composition (Ar/He) on the plasma characteristics, plasma-particle interaction, and particle dynamics at different points spatially distributed inside the plasma torch nozzle. The results of calculations show that increasing the fraction of argon in the plasma gas mixture enhances the momentum and heat flow between the plasma and injected feedstock. For the plasma gas combination of 45Ar/45He, the total enthalpy transferred to a representative powder particle inside the plasma torch nozzle is highest (~9828 kJ/kg). Moreover, due to the properties of the plasma, the contribution of the cylindrical throat, i.e., from the feed injection point (FIP) to the start of divergence (SOD), to the total transferred energy is ~69%. The carrier gas flow for different plasma gas mixtures was also investigated by optical emission spectroscopy (OES) measurements of zirconium emissions. Yttria-stabilized zirconia (YSZ) coating microstructures were produced when using selected plasma gas compositions and corresponding carrier gas flows; structural morphologies were found to be in good agreement with OES and theoretical predictions. Quasicolumnar microstructure was obtained with porosity of ~15% when applying the plasma composition of 45Ar/45He. [ABSTRACT FROM AUTHOR]

Ionospheric heavy ions play an important role in the dynamics of Earth's magnetosphere. The greater mass and gyroradius of ionospheric oxygen differentiates its behavior from protons at the same energies. Oxygen may have an impact on tail reconnection processes, and it can at least temporarily dominate the energy content of the ring current during geomagnetic storms. At sub-keV energies, multispecies ion populations in the inner magnetosphere form the warm plasma cloak, occupying the energy range between the plasmasphere and the ring current. Lastly, cold lighter ions from the midlatitude ionosphere create the corotating plasmasphere whose outer regions can interact with the plasma cloak, plasma sheet, ring current, and outer electron belt. In this paper we present a statistical view of warm, cloak-like ion populations in the inner magnetosphere, contrasting, in particular, the warm plasma composition during quiet and active times. We study the relative abundances and absolute densities of warm plasma measured by the Van Allen Probes, whose two spacecraft cover the inner magnetosphere from plasmaspheric altitudes close to Earth to just inside geostationary orbit. We observe that warm (>30 eV) oxygen is most abundant closer to the plasmasphere boundary, whereas warm hydrogen dominates closer to geostationary orbit. Warm helium is usually a minor constituent but shows a noticeable enhancement in the near-Earth dusk sector. [ABSTRACT FROM AUTHOR]

The Inertial Electrostatic Confinement (IEC) method is a plasma confinement principle with different operation modes. The work presented investigates the jet mode, which occurs with a jet extraction relevant for space propulsion applications. Two different jet modes were observed, the tight jet mode and the spray jet mode. Depending on propellant, discharge pressure and power these modes occur at different operation conditions and characteristics. Emission spectroscopic investigations show a different plasma species composition of confinement and extraction plasma and the transition between those modes has been examined with a high-speed camera. Finally, the applicability of IEC plasma sources for space propulsion systems is discussed with respect to the experimental results. [ABSTRACT FROM AUTHOR]

Reflectance anisotropy spectroscopy (RAS) can be used to monitor (reactive) ion etching (RIE) of semiconductor samples. We present results on the influence of the Cl 2 content of the plasma gas on the RAS spectra during reactive ion etching. In a first step GaAs samples have been used and the RAS spectra are compared to results of secondary ion mass spectrometry (SIMS) on sample surfaces and depth profiles. In a second step a III–V semiconductor multilayer system has been investigated using the time-evolution of the average reflected intensity as an indication for the etch rate. In both cases usually even a high amount of Cl 2 does not disturb the surface-sensitivity of the RAS signal. [ABSTRACT FROM AUTHOR]

This paper reports the results of the experimental study and chemical composition modeling for a DC nitrogen discharge burning above water cathode in the pressure range of 0.1-1 bar and at discharge current of 40 mA. The gas temperature, vibrational temperatures, reduced electric field strength, cathode voltage drop, and emission intensities of some nitrogen bands were obtained from experiment. The modeling chemical composition of plasma was carried out on the basis of these data. At modeling, the combined solution of Boltzmann equation for electrons, equations of vibrational kinetics for ground states of N, O, HO and NO molecules, equations of chemical kinetics and plasma conductivity equation were used. The calculations agree with the measured bands intensities for the second positive system of N and vibrational temperatures of $${\text{N}}_{2} ( {\text{C}}^{3}\Pi _{\text{u}} )$$ . In the frame of the model proposed, the data of other studies were explained. The second kind collision of electrons with N vibration excited states was shown to affect strongly the electron gas parameters. The electron average energy and electron density are given. The difference between the properties of the discharges in N and air at the same conditions are discussed as well. [ABSTRACT FROM AUTHOR]

This paper reports the results of the experimental study and chemical composition modeling for a DC argon discharge burning above water cathode in the pressure range of 0.1-1 bar and at discharge current of 40 mA. The gas temperature, reduced electric field strength, and emission intensities of some argon lines were obtained. On the base of these data, the modeling chemical composition of plasma was carried out. At modeling, the combined solution of Boltzmann equation for electrons, equations of vibrational kinetics for ground states of N, O, HO and NO molecules, equations of chemical kinetics and plasma conductivity equation was used. The calculations agree well with the measured line intensities. It was shown that discharge burns in diffusion mode, at which the stepwise ionization rate of four lower excited states of argon is equal to the rate of charges diffusion losses. [ABSTRACT FROM AUTHOR]

Abstract: Reactive magnetron sputtering is a highly sensitive process because the working point depends on a large number of process parameters (power, pressure, reactive gas flow, pumping speed, magnetic field strength, resputtered material, …). Rotatable targets up to several meters long are used in large area coating tools due to their high productivity. Optimum film properties can only be obtained if the whole sputtered length of a tube target is operated in the same working point. Optical emission spectroscopy was used to monitor the local composition of species in the plasma during the deposition of ZnO:Al under standard deposition conditions. Differences in the plasma compositions and hence the working points of the two racetrack lines along the tube target were found. A special reactive gas channel set-up was used to influence the local racetrack plasma. The properties of the growing film can be much improved by balancing the plasma composition of the two racetrack lines. [Copyright &y& Elsevier]

Thrombin has multiple functions in blood coagulation and its regulation is central to maintaining the balance between hemorrhage and thrombosis. Empirical and computational methods that capture thrombin generation can provide advancements to current clinical screening of the hemostatic balance at the level of the individual. In any individual, procoagulant and anticoagulant factor levels together act to generate a unique coagulation phenotype (net balance) that is reflective of the sum of its developmental, environmental, genetic, nutritional and pharmacological influences. Defining such thrombin phenotypes may provide a means to track disease progression pre-crisis. In this review we briefly describe thrombin function, methods for assessing thrombin dynamics as a phenotypic marker, computationally derived thrombin phenotypes versus determined clinical phenotypes, the boundaries of normal range thrombin generation using plasma composition based approaches and the feasibility of these approaches for predicting risk. [ABSTRACT FROM AUTHOR]

In the present paper we determine the composition of dense beryllium, boron and carbon plasma by solving the Saha equations with corrections due to non-ideality. The lowering of the ionization potentials is calculated on the basis of effective potentials by taking into account screening and quantum diffraction effects. The considered range of density and temperature covers plasmas with a very low degree of ionization up to full ionization with ions having the maximum ionization state. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Abstract: The detection of O2 + and O+ ions over Saturn''s main rings by the Cassini INMS and CAPS instruments at Saturn orbit insertion (SOI) in 2004 confirmed the existence of the ring atmosphere and ionosphere. The source mechanism was suggested to be primarily photolytic decomposition of water ice producing neutral O2 and H2 (Johnson et al., 2006). Therefore, we predicted that there would be seasonal variations in the ring atmosphere and ionosphere due to the orientation of the ring plane to the sun (Tseng et al., 2010). The atoms and molecules scattered out of the ring atmosphere by ion–molecule collisions are an important source for the inner magnetosphere (Johnson et al., 2006; Martens et al., 2008; Tseng et al., 2010, 2011). This source competes with water products from the Enceladus'' plumes, which, although possibly variable, do not appear to have a seasonal variability (Smith et al., 2010). Recently, we found that the plasma density, composition and temperature in the region from 2.5 to 3.5 R S exhibited significant seasonal variation between 2004 and 2010 (Elrod et al., submitted for publication). Here we present a one-box ion chemistry model to explain the complex and highly variable plasma environment observed by the CAPS instrument on Cassini. We combine the water products from Enceladus with the molecules scattered from a corrected ring atmosphere, in order to describe the temporal changes in ion densities, composition and temperature detected by CAPS. We found that the observed temporal variations are primarily seasonal, due to the predicted seasonal variation in the ring atmosphere, and are consistent with a compressed magnetosphere at SOI. [Copyright &y& Elsevier]

This paper, divided into two parts, is devoted to the transport properties at local thermodynamic equilibrium: the first part shows the influences of partition functions through the plasma composition and the second part the influence of interaction potentials. In the first part, for complex chemical mixtures the determination of the partition functions of different species is considered: monatomic, diatomic and polyatomic. In the plasmas the monatomic species are important; we study thoroughly the partition functions of monatomic neutrals and ions. We introduce two cut-off criteria. We test the influence of the two criteria on the partition functions and consequently onto the plasma composition and transport properties. We applied the study to Ar-Cu mixtures. In the second part, an historic study shows that the collision integrals used in calculating the transport properties become more accurate leading to more reliable values of the transport coefficients: application to N plasma. Now we have to calculate transport properties of complex mixtures and in these cases, for numerous interactions, a lack of data means that model potentials have to be used to determine collision integrals. In this paper, we have used two potential models: the first, for neutral-neutral and ion-neutral interactions, is an improvement of the Lennard-Jones function and the second is developed, from Stockmayer potential, for polar gases. We compare, for the collision integrals, the results obtained by these two models with those determined with more accurate potentials: applications to CO plasma and H-N mixtures. [ABSTRACT FROM AUTHOR]

Investigations were carried out into the possibilities of obtaining special properties of the surface of a metal by a moving nitrogen-containing direct action plasma arc. Analysis of the calculated and experimental data indicates the effect of ‘freezing’ of nitrogen after implantation in the surface layer (up to 100 μm thick) as a result of a reduction of the rate of desorption from the surface and diffusion into the metal. At the same time, nitrogen dissolves to the concentration required for the formation of iron nitrides of different phase composition, and the metal with higher wear resistance of the surface layer can be produced. When carbon-containing gases are added to the mixture, the hardness and endurance limit of the surface of the metal increase. [ABSTRACT FROM AUTHOR]

We describe the response of the Solar Wind Around Pluto (SWAP) instrument (McComas et al. in Space Sci. Rev. 140:261, ) to 1-40 amu ions in order to assess whether it can be used to determine plasma composition. Our goal is to enhance the scientific return on the SWAP plasma measurements obtained during the New Horizons traversal down Jupiter's magnetotail in 2007. We present calibration data for the SWAP flight instrument and another largely flight-like SWAP sensor, dubbed 'SWAP-II'. SWAP's mass-dependent response was characterized by analyzing the count ratios from its two channel electron multipliers (CEMs). We observe significant differences in the instrument response between light (mass ≤ He) and heavy (mass > He) ions, especially for energies below ∼4 keV. We attribute these differences to the mass-dependent electron emission yield from SWAP's ultra-thin (∼1 μg/cm) carbon foil. Using these results, we develop a plasma composition analysis technique to statistically distinguish between light and heavy plasma ions measured by the instrument. [ABSTRACT FROM AUTHOR]

Abstract: Low-temperature plasma-enhanced diamond like carbon (DLC) film chemical deposition technique is developed. Emission spectra of plasma is digitized and processed for deposition process control. Electric field – transversely applied to plasma stream – permits to obtain coatings with predefined properties. The influence of this field on plasma characteristics and hence – on the properties of deposited coatings is studied. The specific resistance of nitrogen doped, hydrogenised DLC films could be varied from typically isolators down to ~10−4 Ohm cm. The coatings were of n-type. Mobility of major carriers approaches up to 40 cm2V−1s−1 depending on the technological parameters. Obtained films were durable, transparent and have high refractive index reaching up to 3.1. [Copyright &y& Elsevier]

Abstract: A collisional–radiative model (CRM) is developed to study nitrogen arc plasma. The model is based on solution of the rate equations of ν species chosen for the study. The species chosen are: electrons e, atomic ions N + , atoms N, diatomic molecules N2, and molecular ions , we have then ν=5 species. The CRM is applied to homogeneous and quasi-stationary state (HQSS) plasma for electron temperature Te upto 12000K. All heavy particles are assumed to have the same kinetic temperature Tg such that Tg =Te , this means the temperature of the all five species is identical and is called plasma temperature T. The total pressure of the plasma is considered between 1 and 4atm. The plasma composition is calculated taking into account all significant collisional and radiative mechanisms. The local effect of radiation absorption is described by the optical escape factors Λj and Λjk for free–bound and bound–bound transitions. Results show significant deviation from local thermodynamic equilibrium (LTE). It was also shown that the plasma pressure p has a strong influence on deviation from LTE. To assess the relative speeds of recombination reactions in nitrogen arc plasma we have calculated the relaxation time τ (or time constant) as a function of temperature. [Copyright &y& Elsevier]

The transformation of various carbonaceous substances into ordered carbon nanostructures is a fundamental process in nanotechnology. Since this structural transformation is a common property of various methods for producing CNTs, understanding the mechanism of this process in the bulk of a plasma jet will be extremely important, since no substrates are used here. We present an experimental and numerical study of the synthesis of CNTs with and without external catalysts for the pyrolysis of soot, acetylene, and ethanol in a DC argon plasma at a pressure of 350 Torr. By combining various physical methods, including simultaneous thermal analysis, diffraction analysis, electron microscopy, and energy dispersive analysis, we will show that the aggregation state of the precursor significantly affects the structural and morphological properties of CNTs. Theoretical calculations under the assumption of local thermodynamic equilibrium made it possible to study the gas phase composition of a plasma flow in which the CNT precursor is nucleated. It was found that during the pyrolysis of soot (C), the condensation temperature of solid carbon is 3672 K, with the hydrogen in precursor (C 2 H 2) it is lower and equals 3353 K, with the addition of oxygen (C 2 H 5 OH) its value becomes even <3141 K. At the lowest condensation temperature, the most thermally stable CNTs are formed. [Display omitted] • Carbon precursor in three states of aggregation was used for the synthesis of CNTs. • Synthesis was carried out in a stream of argon afterglow plasma at 350 Torr. • A DC plasma torch was used as a plasma jet generator. • CNTs synthesized from different precursors have different thermal stability. • The modeling revealed differences in the gas phase composition during the pyrolysis. [ABSTRACT FROM AUTHOR]