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Distribution of the potential and concentration of electrons in low-temperature plasma with hollow microparticles
Abstract
Using approximation of a uniform background (the jellium model) for a condensed dispersed phase, the analytical expressions describing a spatial distribution of the potential of the electric field and electron concentration in the low-temperature plasma at equilibrium which contains hollow spherical microparticles are obtained. The influence of heating temperature of plasma on the above distributions is studied, and the dependencies of the charge on microparticle radius, the size of the microparticle cavity and the absolute temperature of plasma are calculated. It is shown that electrons can be emitted not only into the surrounding plasma but also into the cavity of the particles.
... ВВЕДЕНИЕ Термическая плазма, содержащая частицы конденсированного вещества разных размеров, широко распространена в природе и используется во многих технологических процессах [1][2][3][4][5][6][7][8][9][10][11][12][13]. Например, синтез наночастиц различных веществ в термической плазме атмосферного давления позволяет эффективно получать необходимые по составу и размеру частицы [14][15][16][17][18][19][20]. ...
... Здесь необходимо отметить работы [22][23][24][25][26][27][28][29][30][31][32]. Для микронных частиц в плазме указанная модель была впервые применеwна в работах [9][10][11][12]. Преимуществом этой модели является то, что в ней могут учитываться особенности внутреннего строения частиц. ...
... Преимуществом этой модели является то, что в ней могут учитываться особенности внутреннего строения частиц. Так, в [12] рассмотрены полые частицы. В настоящей работе рассмотрены сферические наночастицы, состоящие из двух веществ с разной концентрацией свободных электронов. ...
Разработана простая аналитическая модель, описывающая эмиссию электронов с поверхности двухкомпонентных наночастиц в термической пылевой плазме. Рассчитаны концентрации свободных электронов в плазме в зависимости от состава наночастиц, их размеров и равновесной температуры системы. Установлен немонотонный характер зависимости концентрации эмитированных электронов от концентрации наночастиц.
... On the one hand, additives provide combustion quality improvement. On the other hand, the particles presence in flame contributes to the electric charge accumulation on their surface [1,2]. In [3], the effect of dispersed additives on the resulting change in the combustion rate under the electric field influence in a hybrid rocket engine (HRE) is investigated. ...
In the work, the influence of the electric force from the external electric field on the charged dispersed particles in the flame was evaluated. It is assumed that changes in the effect of the field on the combustion rate in the presence of dispersed additives in the gas phase take place due to the heat flux into the burning polymer condensed phase changes. However, as it turned out, the flame front moving towards the fuel under the action of field forces does not allow to fully explain the combustion rate increase.
... The dusty plasma with external fields interactions differ from the classical approaches describing combustion processes. The disperse admixtures introduction into the combustion zone makes it possible to control the dust plasma electrical properties in the flame [4], which affects the resulting combustion rate change under the influence of an electric field. ...
The paper presents experimental study results of the disperse admixtures in a flame plasma influence on the polymethylmethacrylate combustion rate change under the action of an electric field in a model hybrid rocket engine. It is shown that increase of disperse admixtures concentration in flame leads to the influence of the field on combustion intensification. An explanation of the results obtained on the basis of the ion-wind mechanism is proposed.
A simple analytical model has been developed that describes electron emission from the surface of two-component nanoparticles in a thermal dusty plasma. The concentrations of free electrons in the plasma are calculated depending on the composition of nanoparticles, their sizes, and equilibrium temperature of the system. The nonmonotonic nature of the dependence of the concentration of emitted electrons on the concentration of nanoparticles has been established.
On the basis of a statistical model describing the emission of electrons from the surface of dust particles in thermal plasma, a nonmonotonic character of the dependence of the concentration of emitted electrons on the concentration of grains has been established. The nature of the influence of the equilibrium temperature of the system and the size of dust particles on this effect is studied.
In this paper, it is shown that the choice of the reference point of the potential for the Poisson-Boltzmann equation can affect the accuracy of the solution in the linear approximation.
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.
The contradiction between the demands of employers and the insufficiently developed methodology for the formation of over-subject competencies of graduates of technical universities has been revealed. On the example of federal universities, the technology of forming “flexible skills” in mechanical engineering, allowing to be successful regardless of the specifics of a person’s professional activity, is considered.
The relevance of the study of the impact of the introduction of robotics to improve production efficiency is that it affects the level of development of domestic engineering. The article offers an economic justification of the use of the robot to automate the process of electrochemical machining of workpieces, in order to improve the quality of parts and improve production efficiency
This paper presents a step down converter with a high speed rectifier and filter for Argon plasma torches. Buck circuit with a high frequency pulse width modulation control and very fast MOSFET transistor were used for switching. For Argon (Ar) gas Plasma Torches, and by increasing the pulse width, the average output voltage has modified from 80 V up to 100 V. The frequency of the designed step down converter was steady at 20 KHz.
In this work investigate the chemical processes occurring during the manufacture of magnesium oxide-based mold and casting titanium products to prevent the formation of alpha case. When molten titanium is poured into the mold due to low thermal conductivity the mold is heated unevenly. The resulting carbon dioxide and active metal compounds migrate to the more heated regions adjacent to the surface of the casting. The increased concentration on the surface of the O, Si, Ca, Na forms promotes the reactions to form active metal titanates.
Calculations of the distribution of temperature in the mold based on magnesite oxide, when casting products from titanium alloys, are presented. It is shown that in the mold based on magnesite oxide it cools down exponentially to ambient temperature.
We obtained the equation, which describes electron density in an equilibrium dusty plasma taking into account parameters of the electron gas inside the dust particles. The inclusion of these parameters performed on the basis of the model of "solid-state plasma," considering the condensed particle system as the ion core and the free electron gas. The shape of potential barrier at the particle surface assumed as a rectangular.
We obtained the equation, which describes the distribution of electrical field in an equilibrium dust-electron plasma taking into account parameters of the electron gas inside the dust particles. The inclusion of these parameters performed on the basis of the model of "solid- state plasma," considering the condensed particle system as the ion core and the free electron gas. These calculations are performed for aluminum oxide particles.
Dust particulates immersed in a quasineutral plasma can emit electrons in several important applications.
Once electron emission becomes strong enough, the dust enters the positively charged regime where the
conventional orbital-motion-limited (OML) theory can break down due to potential-well effects on trapped
electrons. A minimal modification of the trapped-passing boundary approximation in the so-called OMLþ
approach is shown to accurately predict the dust charge and heat collection flux for a wide range of dust size
and temperature.
Dust production and its transport into the core plasma is an important issue for magnetic confinement fusion. Dust grains are charged by various processes, such as the collection of plasma particles and electron emissions, and their charge influences the dynamics of the dust. This paper presents the results of calculations of the surface potential of dust grains in a Maxwellian plasma. Our calculations include the charging balance of a secondary electron emission (SEE) from the dust. The numerical model that we have used accounts for the influence of backscattered electrons and takes into account the effects of grain size, material, and it is also able to handle both spherical and non-spherical grains. We discuss the role of the SEE under tokamak conditions and show that the SEE is a leading process for the grains crossing the scrape-off layer from the edge to core plasma. The results of our calculations are relevant for materials related to fusion experiments in ITER.
Present paper considers processes of production and treatment of hollow particles in plasma flows. Specifics of agglomerated powders treatment and expansion of hollow droplets are analyzed theoretically. Experimental results on production of hollow micro particles of ZrO2, Ni, CoNiCrAlY alloy, SiO2 are shown here.
It is shown that the presence of nano-sized and nano-structured erosion products not only affects the operation of thermonuclear devices but also, to a large extent, determines the safety and economy of future thermonuclear reactors. The formation mechanisms and the characteristics and properties of deposited films and nano-sized dust that form in tokamaks are reviewed.
This paper deals with a method for production of nanopowders of high-melting metal oxides by burning the starting metal powders in a laminar disperse flame. The method is called gas-dispersed synthesis. The combustion-zone structure for a laminar diffusion dispersed flame and for a laminar flame of premixed fuel and oxidizer was studied experimentally. Information was obtained on the temperature of combustion gases and its spatial distribution, the temperatures of the burning particles and of the condensed combustion products, and the combustion regimes of metal particles. The dependence of the properties of the resulting oxides on the flame and combustion-zone parameters and the mechanism of particle combustion is studied. Based on the results, an attempt is undertaken to reproduce the mechanisms of formation and growth of the condensed phase under conditions of laminar diffusion flames. The mass-averaged particle size of the oxide powders is estimated.
Thermal strongly collisional dusty plasma is studied. The electrical neutrality of the plasma suggests that the gas phase has some electrostatic energy when the plasma contains charged dust grains. The value of this energy determines the interphase interaction and ionization balance in the plasma. Proceeding from this, a new method of calculation of the dust grains' charges in plasmas with any number of ions (down to zero) has been proposed. The correspondence between the theory and the experimental data is demonstrated.
Dedicated experiments on melting of 2D plasma crystals were carried out. The
melting was always accompanied by spontaneous growth of the particle kinetic
energy, suggesting a universal plasma-driven mechanism underlying the process.
By measuring three principal dust-lattice (DL) wave modes simultaneously, it is
unambiguously demonstrated that the melting occurs due to the resonance
coupling between two of the DL modes. The variation of the wave modes with the
experimental conditions, including the emergence of the resonant (hybrid)
branch, reveals exceptionally good agreement with the theory of mode-coupling
instability.
The thermal complex plasma of atmospheric pressure, containing the grains of condensed phase, has been studied. It has been demonstrated that the existence of the space charge areas around the dust grains leads to the inhomogeneous ionization of the plasma and the occurrence of the fluxes of nonequilibrium charge carriers. These fluxes change the pressure of the gas on the grain surfaces and define the forces that force the grains to move towards the zone of maximum ionization perturbation of the plasma. It has been shown that the combined operation of the electrical forces and the forces of the interface pressure leads to the formation of the ordered structures, corresponding to the balance of forces. The results of computer simulation, corresponding to the experimental data, are given.
The Poisson-Boltzmann problem in spherical symmetry has been considered using the distribution of a self-consistent potential around a charged grain in a thermal collisional plasma as an example. The qualitative patterns of all possible solutions have been presented and a study of their asymptotics has been carried out. It has been demonstrated that for large potentials it is possible to neglect the curvature of the grain surface and to use the solution of the plane problem. It has also been demonstrated that the electrical interaction of the grains is possible only at distances smaller than eight screening lengths.
It is shown that the electrostatic interaction potential between a pair of positively charged particles embedded in a highly collisional plasma has a long-range attractive asymptote. The effect is due to continuous plasma absorption on the particles. The relevance of this result to experimental investigations of complex (dusty) plasmas is discussed.
At the frontiers of physics and chemistry lies the new and rapidly emerging area of complex plasma systems. The study of complex plasma systems that contain colloid nano/microscopic particles is now actively pursued in a diverse range of scientific fields — from plasma and gas discharge physics, to astrophysics, materials science and engineering. This book highlights, in a systematic, insightful, and perceptive way, the fundamental physics and industrial applications of complex plasmas, with emphasis on the conditions relevant to laboratory gas discharges and industrial plasma reactors. It provides a specialized and comprehensive description of the most recent theoretical, experimental, and modeling efforts to understand the unique properties of complex plasma systems involving the stability, dynamics, and self-organization of colloid particles and their associations. Special attention is focused on the physical understanding of up-to-date developments in major technological applications of micron and nano-sized particles. Each chapter is presented in a concise and comprehensive manner, with a categorized overview of the underlying physics followed by an in-depth description. The book will appeal to scientists and researchers as well as undergraduate and graduate students wishing to explore the flourishing interdisciplinary field of complex plasma systems.
Negatively charged dust particles immersed in 2-dimensional dusty plasma system are investigated by molecular dynamics simulations. The effects of the confinement potential and attraction interaction potential on dust particle self-organization are studied in detail and two typical dust particle distributions are obtained when the system reaches equilibrium. The average radial velocity (ARV), average radial force (ARF) and radial mean square displacement are employed to analyze the dust particles' dynamics. Both ARVs and ARFs exhibit oscillation behaviors when the simulation system reaches equilibrium state. The relationships between the oscillation and confinement potential and attraction potential are studied in this paper. The simulation results are qualitatively similar to experimental results.
The transport of dust particles in tokamak fusion devices is studied using computer simulations with the dust transport code, DUSTT. Recent developments in modelling with the DUSTT code are reported. The improved model of dust dynamics in edge plasmas takes into account several additional effects, including thermionic and secondary electron emission which affects dust charging and heating, dust grain size effect on thermal radiation, and the presence of impurities in the plasma. It is shown that thermionic emission leads to enhanced dust heating by the plasma that boosts destruction of dust particles. The zone structure of tokamak plasmas is introduced for a qualitative analysis of dust survivability conditions. It is shown that a dust particle can experience net deposition in relatively cold carbon-contaminated plasma regions. Trajectories of sample dust particles in the DIII-D tokamak are simulated and analysed using the zone plasma description. Statistical averaging over an ensemble of particle trajectories is used to obtain spatial distributions of dust characteristics in the edge plasma of tokamaks. It is shown that transport of dust in tokamaks can significantly enhance penetration of carbon impurities towards the core plasma.
This paper highlights some of the history of laboratory experiments in
dusty plasmas, beginning with an early unexpected discovery of Langmuir.
Although there was a great deal of theoretical work on dusty plasmas
long before dedicated laboratory experiments were initiated, the
experimental work is catching-up and new discoveries in the laboratory
are motivating further theoretical work.
Introduction -- Basics of plasma-dust particle interactions --
Production and diagnostics of complex plasmas -- Particle dynamics in a
complex plasma -- Structures and phase transitions in complex plasmas --
Waves and instabilities in complex plasmas -- Fine particles in
industrial applications.
An experimental study of the kinematic viscosity has been carried out for dust particles of size 0.95 and 3.92 μm, in weakly ionized plasma over a wide range of dust coupling parameters. Measurements of viscosity for weakly correlated dusty-plasma systems are presented for the first time. An approximation for the estimation of viscosity constants is proposed. The measured viscosity constants are compared with theoretical estimates and numerical data.
The work function of small metal particles is calculated with the use of the local-density approximation applied to the spherical jellium-background model. Large quantum-size effects are obtained in strict analogy to those obtained for thin metal films. Effective potentials and self-consistent charge densities are discussed in comparison to the semi-infinite half-space. The convergence of the various physical properties to their value of a semi-infinite half-space is investigated.
The physics of high-temperature plasmas are presented as a division of
contemporary physics for physicists dealing with plasma phenomena
outside characteristic plasma physics. Plasmas not in the presence of a
magnetic field are treated, with attention given to plasma oscillations,
particle collisions, transport phenomena, plasmas in high-frequency
fields, the propagation of electromagnetic waves in a plasma, kinetic
and hydrodynamic descriptions, parametric and beam instabilities,
wave-particle resonance interactions and Langmuir and stationary
nonlinear waves. The physics of plasmas in magnetic fields are also
examined, with discussions of the motion of charged particles in a
magnetic field, the kinetic and hydrodynamic theories of magnetized
plasmas, plasma waves and oscillations, wave-particle interactions,
plasma equilibrium, magnetohydrodynamic stability, tearing mode, drift
and micro-instabilities, the energy balance of tokamak plasmas,
anomalous diffusion and resistance, and collisionless shock waves.
The study of dusty plasmas in dc-generated plasmas is a broad topic because of the wide variety of experimental configurations that fall under the category of “dc plasma source”. Experimental configurations such as the hot filament discharge, anodic (anode/cathode) discharge, and Q-machine are all variations of the “dc plasma source” in which extensive studies of dusty plasmas have been performed. This paper will review dusty plasma investigations in these plasma sources. First, an introduction to each of these configurations and representative examples of each one will be given. This will be followed by a discussion of microparticle confinement in each of these configurations. Then, key results from dusty plasma investigations using these devices will be discussed. Specific emphasis will be placed on studies of: microparticle charging, particle cloud morphology, dust-driven and dust-modified waves, and strongly coupled effects. Some remarks on emerging research areas will be given at the end (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
The synthesis of nest-like silicon nanospheres and their highly reversible lithium storage and excellent high-rate capability has been demonstrated. Nest-like Si nanospheres were prepared through a solvothermal route from the reaction of sodium silicide and ammonium bromide with the mixture of pyridine and dimethoxyethane as the solvent. Experimental conditions were observed to have significant impact on the size and morphology of the products. The nest-like Si nanospheres could only be obtained with the addition of LaNi 5 alloys that were packed in the cotton-fiber bags to absorb the hydrogen generated during the reaction. The as-produced nest-like Si, coin-like Si or commercial Si were further constructed as the electrode materials of button-like Li-ion cells.
We develop a new model of a Thomas-Fermi cluster that describes the distribution of electrons in alkaline clusters with many
atoms. We examine the classical multiple ionization of such a cluster by a strong electromagnetic field. Finally, we calculate
the degree of ionization as a function of the field strength.
We report on the synthesis of a variety of sub-micron size carbon structures using RF, 13.6MHz, plasma enhanced CVD, without the use of any external heater or catalyzer precursor. The plasma is generated in an asymmetric capacitively coupled discharge operated at a low power of up to 30W, with a gas mixture of acetylene and hydrogen, at different mixing ratios. Carbon films are grown on mirror-like polished silicon (100) substrates, which are negatively biased using 4kV, 2μs pulses, at a 2kHz rate, with a characteristic exposure time of around 30min. The morphology, structure and atomic composition of the resulting carbon films are characterized using SEM, EDX, AFM and Raman spectroscopy. Carbon spheres of different diameters, of sub-micron range, are observed to grow in layers onto the Si surface. We present a detailed characterization of the resulting carbon films, in correlation with the plasma properties, as inferred from optical emission spectroscopy observations.
Particles generated in an argon plasma and suspended at the plasma/sheath boundary are localized by lateral trapping fields. In the commercial rf etching reactor used in this work, the particles and their motion in real time are observed by laser light scattering with the laser beam rapidly rastered in a plane parallel to the rf electrode. Repulsion between individual, relatively large particles is observed, verifying that there is significant negative charge on the particles. Two types of trapping regions are commonly seen: rings of particles around the outside edge of silicon wafers, and domes of particles over the centers of the wafers. It is shown that these effects are influenced by the topography of the electrode. In addition, particle densities ≫107 cm-3 for particles of diameter 0.2 μm are inferred from transmission studies for certain plasma conditions.
The trapping of dust particles has been observed in a dc abnormal glow discharge dominated by electron attachment. A dust cloud of several tens of positively charged particles was found to form in the anode sheath region. An analysis of the experimental conditions revealed that these particles were positively charged due to emission process, in contrast to most other experiments on the levitation of dust particles in gas-discharge plasmas where negatively charged particles are found. An estimate of the particle charge, taking into account the processes of photoelectron and secondary electron emission from the particle surface, is in agreement with the experimental measured values.
Voyager 2 photography has complemented that of Voyager I in revealing many additional characteristics of Saturn and its satellites and rings. Saturn's atmosphere contains persistent oval cloud features reminiscent of features on Jupiter. Smaller irregular features track out a pattern of zonal winds that is symmetric about Saturn's equator and appears to extend to great depth. Winds are predominantly eastward and reach 500 meters per second at the equator. Titan has several haze layers with significantly varying optical properties and a northern polar "collar" that is dark at short wavelengths. Several satellites have been photographed at substantially improved resolution. Enceladus' surface ranges from old, densely cratered terrain to relatively young, uncratered plains crossed by grooves and faults. Tethys has a crater 400 kilometers in diameter whose floor has domed to match Tethys' surface curvature and a deep trench that extends at least 270 degrees around Tethys' circumference. Hyperion is cratered and irregular in shape. Iapetus' bright, trailing hemisphere includes several dark-floored craters, and Phoebe has a very low albedo and rotates in the direction opposite to that of its orbital revolution with a period of 9 hours. Within Saturn's rings, the "birth" of a spoke has been observed, and surprising azimuthal and time variability is found in the ringlet structure of the outer B ring. These observations lead to speculations about Saturn's internal structure and about the collisional and thermal history of the rings and satellites.
Plasma physics for physicists
- L A Artsimovich
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Influence of electron emission on the charge and shielding of a microparticle in plasma in the regime of a continuous medium
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Emissivity of materials
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Physics of collisional plasma. Study guide
- Yv Fortov
- Ag Khrapak
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Synthesis of nanooxides in two-phase laminar flames
- A N Zolotko
- Y I Vovchuk
- N I Poletayev
- A V Florko
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