P. Segur

EXPERIMENTAL AND THEORETICAL STUDY OF A GLOW DISCHARGE AT ATMOSPHERIC PRESSURE CONTROLLED BY DIELECTRIC BARRIER

The aim of this paper is to confirm the existence of atmospheric pressure dielectric controlled glow discharge and to describe its main behavior. Electrical measurements, short time exposure photographs, and numerical modeling were used to achieve this task. Experimental observations and numerical simulation are in good agreement. Therefore, the analysis of the calculated space and time variations of the electric field together with the ion and electron densities helps to explain the discharge mechanisms involved, showing the main role played by the electron as well as helium metastable density just before the discharge is turned on.

The application of a modified form of theSN method to the calculation of swarm parameters of electrons in a weakly ionised equilibrium medium

A numerical method is developed for the solution of the Boltzmann equation in order to calculate the swarm parameters of a weakly ionised gas. A brief description is given of the three main types of swarm experiment in which the measurements of these parameters are usually carried out. Then it is shown how these experiments can be simulated by calculation in order to explain the discrepancies observed between the parameters measured under the same conditions but in different experiments. A description is given of the present method of solution which uses both Lesaints SN method and an iterative process based on the so-called Eddington factor. The efficiency and the accuracy of this treatment is shown in two model cases which have already been investigated by several authors. It is observed that the number of iterations is drastically reduced and that the results obtained are of high accuracy.

Boltzmann analysis of electron swarm parameters in CF4 using independently assessed electron-collision cross sections

Using independently assessed electron-collision cross sections, electron swarm parameters were calculated via the solution of the Boltzmann equation under the hydrodynamic regime. The cross sections used for the calculations were from a previously published assessment of electron–CF4-collision cross sections that was recently updated. All of the cross sections used are based on published measurements (except those for direct vibrational excitation), and were not modified during the calculations to improve agreement between the calculated swarm parameters and the experimental values. Agreement between calculated and measured values of the swarm parameters was good for the drift velocity in pure CF4 and in mixtures with argon, for the transverse diffusion coefficient in pure CF4, for the longitudinal diffusion coefficient in pure CF4 and in mixtures with argon, and for the electron attachment coefficient in pure CF4. Agreement is poor for the ionization coefficient in CF4 at most electric field-to-gas densi...

Numerical modelling of high-pressure glow discharges controlled by dielectric barrier

In this work, we carried out one-dimensional and self-consistent modeling of a high-pressure low-frequency helium discharge between insulated electrodes. We were able to obtain a stationary state which is qualitatively in agreement with the experimental results. We were also able to study the influence of the experimental parameters (gap length, frequency, etc.) on the numerical results. In the near future, we plan to fully include the Penning effect in our model. The calculations will also be extended to two-dimensional geometry.

Atmospheric pressure dielectric controlled glow discharges: diagnostics and modelling

The aim of this paper is to prove the existence of atmospheric pressure dielectric controlled glow discharge and to describe its main behavior. Electrical measurements, short time exposure photographs and numerical modelling were used to arrive at the conclusion. Experimental observations and numerical simulation agreed within a close range. Therefore, the analysis of the calculated space and time variations of the electric field together with the ion and electron densities helps to explain the discharge mechanisms involved.

A numerical method of solution of the Boltzmann equation in a weakly ionized heterogeneous gas

Abstract We give a numerical method of solution of the Boltzmann equation for a weakly ionized gas based on the study of the characteristic curves defined by the free motion of particles. First, we perform a systematic study of the topological properties of these characteristic lines when collisions are present. We show that their distribution not only gives us a method of attack for the numerical resolution but also allows us to predict, even before solving the Boltzmann equation, the complete behavior of the distribution function. Second, we define several discrete schemes and we prove that they are convergent and stable. We also give a brief proof of the convergence of the iterative process associated with the resolution of the discrete linear system of equations. Finally, we give the results obtained for helium gas, both the transmission factor of electrons and the isotropic part of the distribution function. The main feature to be emphasized is the existence of a distribution presenting a shape with a succession of “knobs” and “hollows” characteristic of a nonequilibrium state.

Inelastic collision integral approximation of the Boltzmann equation

A study is made of the inelastic collision integral of the Boltzmann equation using scattering probability formalism. The collision operators are expanded in a power series in the square root of the ratio of masses. Furthermore, a spherical harmonic expansion is made of all the operators so obtained. These developments are valid whatever the shape of the distribution function of the particles.

Theoretical and Experimental Analysis of a High Pressure Glow Discharge Controled by a Dielectric Barrier

Recently many experimental works have been devoted to the study of an atmospheric pressure glow discharge controled by a dielectric barrier1,2. There is a strong evidence that this type of discharge works well in pure helium. for other gases it seems to be necessary to introduce an additive (for example acetone in argon) in order to obtain a glow discharge or, in other situations (for example in air), small metallic mesh grids must be added inside the dielectric walls. Our experimental work, associated with our theoretical calculations3 showed that, in helium, a glow discharge can only be obtained if there is a small amount of impurity inside the gas. the main role of these impurities (N2 for example) is to allow, through the various metastable levels of helium, an increase of the ionization mainly in regions in which the electric field is so low that it cannot produce direct ionization of the molecules. It is clear then from these considerations that a glow discharge cannot occur in very pure helium in which the amount of impurities is too low.