Mario J. Pinheiro

Self-consistent kinetic model of low-pressure - flowing discharges: I. Volume processes

This work is the first of two companion papers devoted to the kinetic modelling of low-pressure DC flowing discharges in - mixtures. While the present paper is mainly concerned with bulk discharge processes, the second one investigates surface processes involving dissociated N and H atoms, which are essential to understand the discharge properties. The global model combining bulk and surface processes as described in these two papers is self-contained in the sense that the sole input parameters it requires are those that can externally be chosen in experiments, namely: total gas pressure, radius and length of the discharge tube, discharge current, gas flow rate and initial gas temperature and composition (e.g., the relative hydrogen concentration X in the binary mixture at the discharge inlet). For a given set of input parameters, this model enables one to calculate the following bulk plasma properties as a function of the axial coordinate z: concentration of , , NH, , molecules and N, H atoms in the ground electronic state; population in the electronically excited states , (an effective high Rydberg state) and ; concentration of the ions , , , , , and ; vibrational level populations of and molecules; electron density , mean kinetic energy , characteristic energy and drift velocity ; discharge sustaining electric field E; average gas temperature across the tube T and wall temperature . The calculations are compared with data from different experiments in pure and discharges (measurements of electric field as a function of current and pressure) and in - discharges (measurements of relative changes in the electric field and the , concentrations as a function of the percentage). From the comparison to experiment, rate coefficients for associative ionization upon collisions between two excited molecules and deactivation of and by H atoms have been estimated from the model.

ELECTRON AND HEAVY-PARTICLE KINETICS IN THE LOW PRESSURE OXYGEN POSITIVE COLUMN

A kinetic model for the low-pressure oxygen positive column is presented and discussed. The model is based on the electron Boltzmann equation and the rate balance equations for the dominant heavy-particle species, which are solved simultaneously in order to take into account the coupling between the electron and the heavy-particle kinetics. The effects of vibrationally excited molecules, dissociated atoms and metastable states on the electron kinetics are analysed in detail. The predicted populations of O2(X3 Sigma ), O2(a1 Delta ), O(3P), and O- are shown to agree satisfactorily with previously reported measurements. A combination of this kinetic model with the continuity and transport equations for the charged species e, O-, and O2+ is shown to provide characteristics for the maintenance field that agree reasonably well with experiment.

Self-consistent kinetic model of low-pressure - flowing discharges: II. Surface processes and densities of N, H, species

This work is the second of two companion papers devoted to the kinetic modelling of low-pressure DC flowing discharges in mixtures. While the first paper was mainly concerned with bulk discharge processes, the present one investigates surface processes involving dissociated N and H atoms, which are essential to understand the discharge properties. The kinetic model for surface processes developed here takes into account: (a) physical adsorption and desorption of N and H atoms; (b) chemical adsorption and desorption of both types of atoms at vacant chemically active sites on the surface; (c) surface diffusion of physisorbed and atoms; (d) the reactions of chemisorbed and atoms with gas phase N and H atoms and with physisorbed and atoms, leading to the formation of gas phase , and chemisorbed (NH) molecules. The latter molecules can either be desorbed or react with H, , to produce gas phase NH, and molecules. The probability of wall losses for N, H, NH, and the rates for wall production of NH, , have been obtained for Pyrex glass as a function of the wall temperature and the relative concentrations of N, H, NH, , . A number of important parameters for surface processes have been estimated from detailed analysis of experimental data. Measurements of relative changes in N, H and concentrations in discharges as a function of the percentage have been interpreted in terms of the model.

Microwave air plasma source at atmospheric pressure: Experiment and theory

An experimental and theoretical investigation of the axial structure of a surface wave (2.45 GHz) driven atmospheric plasma source in air with a small admixture (1%) of water vapor has been performed. Measurements of the gas temperature and of the intensities of the O(777.4 nm), O(844.6 nm), and O(630 nm) atomic lines and the NO(γ) molecular band versus input power and axial position were carried out. Amplitude and phase sensitive measurements have also been performed to derive the surface wave dispersion characteristics. The experimental results are analyzed in terms of a one-dimensional theoretical model based on a self-consistent treatment of particle kinetics, gas dynamics, and wave electrodynamics. The predicted gas temperature and emission line intensities variations with power and axial position are shown to compare well with experiment. “Hot” excited O atoms (with kinetic energy ∼2 eV) have been detected.

Comparison of calculated and measured optical emission intensities in a direct current argon-copper glow discharge

q . Based on a collisional)radiative model for argon atoms and copper atoms and Cu ions, which was developed as a part of a comprehensive simulation network, optical emission intensities have been calculated for argon and copper lines in a direct current argon glow discharge with copper cathode. Comparison with experimental data has been made, both with respect to the optical emission spectra and to some selected emission lines as a function of axial position. From this study, information can be obtained about the importance of various plasma processes, like electron, fast ion and fast atom impact excitation, and reabsorption of resonant radiation. Q 2000 Elsevier Science B.V. All rights reserved.

A travelling wave sustained hydrogen discharge: modelling and experiment

A model has been developed for a surface wave sustained hydrogen discharge which, in a self-consistent way, accounts for the main plasma balances governing the discharge production, including bulk and surface processes. The approach used self-consistently describes the axial discharge structure, i.e. the axial distribution of charged particle concentrations, population densities of excited species and neutrals, taking into account inhomogeneous gas heating along the plasma column as well as plasma-wall interactions. A spatially resolved experimental investigation into the distribution of electron density, atomic line intensity and gas temperature confirms the main trends of the model predictions.

Modelling of low-pressure surface wave discharges in flowing oxygen: I. Electrical properties and species concentrations

This paper describes a self-consistent kinetic model of cylindrically symmetric surface wave discharges in flowing oxygen at low pressures consisting of: (i) the homogeneous electron Boltzmann equation; (ii) the radial continuity and transport equations for the electrons and the dominant ions, that is, and ; (iii) the axial equations of change of mass and momentum for the reacting gas mixture composed of the heavy species and . The model is solved using measured distributions of the electron density and gas temperature along the plasma column as inputs, and its predictions are compared to experiment. It is shown that the predicted discharge maintenance field, average absorbed power per electron-ion pair and populations of the main species along the column agree well with experimental data.

On the Electromagnetic Origin of Inertia and Inertial Mass

We address the problem of inertial property of matter through analysis of the motion of an extended charged particle. Our approach is based on the continuity equation for momentum (Newton’s second law) taking due account of the vector potential and its convective derivative. We obtain a development in terms of retarded potentials allowing an intuitive physical interpretation of its main terms. The inertial property of matter is then discussed in terms of a kind of induction law related to the extended charged particle’s own vector potential. Moreover, it is obtained a force term that represents a drag force acting on the charged particle when in motion relatively to its own vector potential field lines. The time rate of variation of the particle’s vector potential leads to the acceleration inertia reaction force, equivalent to the Schott term responsible for the source of the radiation field. We also show that the velocity dependent term of the particle’s vector potential is connected with the relativistic increase of mass with velocity and generates a longitudinal stress force that is the source of electric field lines deformation. In the framework of classical electrodynamics, we have shown that the electron mass has possibly a complete electromagnetic origin and the obtained covariant equation solves the “4/3 mass paradox” for a spherical charge distribution.

Comparison of kinetic calculation techniques for the analysis of electron swarm transport at low to moderate E/N values

We present a comparison between results for the electron velocity distribution function (evdf), and transport and rate coefficients of an electron swarm obtained under different assumptions for the space and angular dependence of the evdf. Several solution techniques for the Boltzmann equation as well as Monte Carlo simulations have been tested. The comparison is made in neon at a constant and homogeneous reduced electric field in the range 10 Td ≤ E/N ≤ 500 Td taking into account the production of electrons in ionizing collisions. The results show that to obtain an accurate description of the electron swarm we need to take into account the variation in space of the electron density in the representation of the evdf. In what regards the angular dependence on velocity we discuss criteria to estimate the importance of the anisotropy of the evdf for any gas. Depending on the solution technique and on the E/N value, we find good to excellent agreement between the Boltzmann results obtained with a half-range method, a multi-term Legendre expansion, an elliptic approximation and the Monte Carlo results. The accuracy of the transport and rate coefficients obtained with each approach is evaluated and it is found that although the two-term velocity expansion is not sufficiently accurate to be used for cross section fitting, the corresponding rate and transport coefficients can generally be used in discharge modelling.

Electrical and kinetic model of an atmospheric rf device for plasma aerodynamics applications

The asymmetrically mounted flat plasma actuator is investigated using a self-consistent two-dimensional fluid model at atmospheric pressure. The computational model assumes the drift-diffusion approximation and uses a simple plasma kinetic model. It investigated the electrical and kinetic properties of the plasma, calculated the charged species concentrations, surface charge density, electrohydrodynamic forces, and gas speed. The present computational model contributes to understand the main physical mechanisms, and suggests ways to improve its performance.