Ismail Rafatov

On the accuracy and reliability of different fluid models of the direct current glow discharge

We developed and tested 2D “extended fluid model” of a dc glow discharge using COMSOL MULTIPHYSICS software and implemented two different approaches. First, assembling the model from COMSOL’s general form pde’s and, second, using COMSOL’s built-in Plasma Module. The discharge models are based on the fluid description of ions and excited neutral species and use drift-diffusion approximation for the particle fluxes. The electron transport as well as the rates of electron-induced plasma-chemical reactions are calculated using the Boltzmann equation for the EEDF and corresponding collision cross-sections. The self-consistent electric field is calculated from the Poisson equation. Basic discharge plasma properties such as current-voltage characteristics and electron and ion spatial density distributions as well as electron temperature and electric field profiles were studied. While the solutions obtained by two different COMSOL models are essentially identical, the discrepancy between COMSOL and CFD-ACE+ model...

Account of nonlocal ionization by fast electrons in the fluid models of a direct current glow discharge

We developed and tested a simple hybrid model for a glow discharge, which incorporates nonlocal ionization by fast electrons into the “simple” and “extended” fluid frameworks. Calculations have been performed for an argon gas. Comparison with the experimental data as well as with the hybrid (particle) and fluid modelling results demonstated good applicability of the proposed model.

Two-dimensional hybrid Monte Carlo–fluid modelling of dc glow discharges: Comparison with fluid models, reliability, and accuracy

Two-dimensional hybrid Monte Carlo–fluid numerical code is developed and applied to model the dc glow discharge. The model is based on the separation of electrons into two parts: the low energetic (slow) and high energetic (fast) electron groups. Ions and slow electrons are described within the fluid model using the drift-diffusion approximation for particle fluxes. Fast electrons, represented by suitable number of super particles emitted from the cathode, are responsible for ionization processes in the discharge volume, which are simulated by the Monte Carlo collision method. Electrostatic field is obtained from the solution of Poisson equation. The test calculations were carried out for an argon plasma. Main properties of the glow discharge are considered. Current-voltage curves, electric field reversal phenomenon, and the vortex current formation are developed and discussed. The results are compared to those obtained from the simple and extended fluid models. Contrary to reports in the literature, the analysis does not reveal significant advantages of existing hybrid methods over the extended fluid model.

Oscillations in DC driven "barrier" discharges: numerical solutions, stability analysis and phase diagram

A short gas-discharge layer sandwiched with a semiconductor layer between planar electrodes shows a variety of spatiotemporal patterns. We focus on the spontaneous temporal oscillations that occur while a dc voltage is applied and while the system stays spatially homogeneous; the results for these oscillations apply equally to a planar discharge in series with any resistor with capacitance. We define the minimal model, identify its independent dimensionless parameters, and then present the results of the full time-dependent numerical solutions of the model as well as of a linear stability analysis of the stationary state. Full numerical solutions and the results of the stability analysis agree very well. The stability analysis is then used for calculating bifurcation diagrams. We find semiquantitative agreement with experiment for the diagram of bifurcations from stationary to oscillating solutions as well as for amplitude and frequency of the developing limit cycle oscillations.

On modelling of microwave heating of a ceramic material

A simple model is proposed and tested for simulations of ceramic processing by microwave heating. The model is based on a piecewise constant approximation of the material properties and makes it possible to separate and analyse different effects caused by the sample shape and the dependence of the material properties on temperature. Specifically, the simulation results demonstrate that microwave heating of an alumina sample can be very sensitive to a variation of its dielectric constant with temperature. For different geometries, there is a similarity in the dependences of the thermal state characteristics (temperature drop across the sample, amount of dissipated power and electric field amplitude at the sample centre) on maximal temperature. It is shown also that a temperature drop between the sample centre and surface can be strongly enhanced in the case of a spherical sample irradiated symmetrically by microwaves.

An evidence of period doubling bifurcation in a dc driven semiconductor-gas discharge plasma

We present an experimental study of nonlinearity observed in a dc driven semiconductor-gas discharge system. The plasma glow is generated using planar electrodes in a vacuum chamber filled with nitrogen gas at partial atmospheric pressure. The discharge behaves oscillatory in time, showing single and sometimes multiple periodicities in plasma current and voltage measurements. Harmonic frequency generations and period doubling cascade are investigated experimentally by varying the applied voltage. To identify the stability condition, numerical simulations are conducted using COMSOL® Multiphysics software. The discharge is modeled as a one dimensional plasma slab. Numerical results are in good agreement with the experimental measurements.

Three-dimensional numerical modelling of temporal and spatial pattern formation in a dc-driven gas discharge-semiconductor system

A three-dimensional numerical model is developed and applied to study the temporal and spatial pattern formation in the planar layered system, consisting of a glow discharge layer, coupled to a high ohmic semiconductor layer. The whole system is sandwiched between two planar electrodes, to which a dc voltage is applied. In the case of temporal oscillations that occur in a transversely homogeneous mode, a bifurcation diagram as well as a Lorenz map are derived, demonstrating the transition of the system to chaos through a period-doubling bifurcation cascade. The results of the fully three-dimensional time-dependent calculations agree well with the linear stability analysis within its range of validity. Beyond the initial transient regime, the numerical solution reproduces the way in which the Turing–Hopf instability of the homogeneous stationary state develops into the running wave, which can be identified through the moving bands observed in the experiment.

Modelling of a continuous optical discharge stabilized by a gas flow in quasi-optical approximation

We consider a continuous optical discharge (COD) sustained by a weakly focused CO2 laser beam and stabilized by a cold gas flow incident in the direction of the laser radiation propagation. We develop and examine a two-dimensional radiative gas-dynamic model for COD which uses realistic quasi-optics and takes refraction of the laser radiation in the plasma properly into account in describing the laser beam propagation. The model is applied to calculate the parameters of COD in the air flow as functions of the laser power and inlet velocity of the incident flow.

Self-consistent model of thermal and ionization non-equilibrium spherical microwave discharge

A self-consistent model of a spherical microwave discharge is presented. The model takes into account thermal and ionization non-equilibrium of the discharge plasma. We adopt a partial local thermodynamic equilibrium model for the plasma in two-temperature approximation. Numerical experiments are carried out for the discharge in argon at atmospheric pressure. Results are presented for the characteristics of the discharge plasma against the external parameters (the power and frequency of the applied electromagnetic field and the size of the discharge chamber). Presented model results are compared with the results for the ionization equilibrium model of the spherical microwave discharge.

Particle in cell/Monte Carlo collision analysis of the problem of identification of impurities in the gas by the plasma electron spectroscopy method

The work deals with the Particle in Cell/Monte Carlo Collision (PIC/MCC) analysis of the problem of detection and identification of impurities in the nonlocal plasma of gas discharge using the Plasma Electron Spectroscopy (PLES) method. For this purpose, 1d3v PIC/MCC code for numerical simulation of glow discharge with nonlocal electron energy distribution function is developed. The elastic, excitation, and ionization collisions between electron-neutral pairs and isotropic scattering and charge exchange collisions between ion-neutral pairs and Penning ionizations are taken into account. Applicability of the numerical code is verified under the Radio-Frequency capacitively coupled discharge conditions. The efficiency of the code is increased by its parallelization using Open Message Passing Interface. As a demonstration of the PLES method, parallel PIC/MCC code is applied to the direct current glow discharge in helium doped with a small amount of argon. Numerical results are consistent with the theoretical...