Alexander S. Chirtsov

Different approaches to fluid simulation of the longitudinal structure of the atmospheric-pressure microdischarge in helium

Numerical results for different versions of the fluid model of an atmospheric-pressure glow discharge in helium are compared. It is shown that efforts to improve the fluid model are to a large extent prospectless and often even impair previous results. This is because the fluid model has fundamental limitations when describing heavily nonequilibrium media, such as the gas discharge. In such systems, the properties of an ensemble of electrons cannot be reduced to the behavior of an “averaged particle,” which is characterized by the averaged concentration, averaged directional velocity, and averaged energy (temperature). In particular, the values of the electron temperature in the near-cathode plasma obtained by fluid simulation far exceed both the available experimental data and physical estimates. It is therefore necessary to develop consistent kinetic techniques to correctly describe the behavior of electrons in the near-cathode plasma.

Transition to the obstructed discharge and a sharp change in the voltage-current characteristic as a result of gas heating in a short (positive-column-free) high-pressure glow discharge

The formation of a high-pressure glow discharge is studied under conditions when the discharge evolves from the normal glow to the abnormal glow. It is shown that the transition to the voltage-current characteristic of the obstructed discharge may take place as a result of heating the gas and a decrease in its density. The obstructed discharge follows the left-hand branch of the Paschen curve and features a sharp voltage rise and current density limitation.

Transition From Glow Microdischarge to Arc Discharge With Thermionic Cathode in Argon at Atmospheric Pressure

A 1-D model for the simulation of transition from glow microdischarge to arc discharge with a thermionic cathode was built using COMSOL Multiphysics. The extended fluid model was coupled with the gas heating equation for the self-consistent simulation of discharge at atmospheric pressure in a wide range of currents. Both the secondary electron emission and the thermionic emission were taken into account simultaneously to allow for the transition. In order to properly account for thermionic emission, cathode heating was considered-heat flux equation was solved in a 1-D solid domain with heat fluxes on the cathode surface from the discharge domain used as boundary conditions. A thorough set of plasma-chemical reactions with account of molecular ions of argon was used. Using the external circuit allowed for obtaining stable solutions in a wide range of currents. By changing ballast resistance, the classical current-voltage characteristic of direct current discharge with transition from glow to arc was obtained. The distributions of such discharge parameters as charged and excited particle densities and fluxes, electron mean energies and temperatures, gas temperature, and electric potential were obtained for microdischarge, arc discharge, and transitional state. Time-dependent simulations allowed for obtaining the dynamics of discharge formation. It is shown that after the breakdown, the cathode is heated by the discharge current for a time of tens of milliseconds, and then, transition to stable arc discharge with thermionic cathode takes place.

Electron energy spectra in helium observed in a microplasma collisional electron spectroscopy detector

The energy spectra of fast electrons resulting from pair collisions between metastable atoms and from collisions of the second kind with electrons are observed in the afterglow of a helium-filled microplasma collisional electron spectroscopy (CES) detector at a pressure of 5–40 Torr. It is demonstrated that impurities present in the main inert gas can be detected and their composition can be determined using a planar double-electrode detector in which the cathode simultaneously serves as an analyzer of electrons in the afterglow.

Nonlocal Behavior of Electron Fluxes and Excitation Rates for “Local” EEDF in Moderate and High Pressures DC Positive Column Plasmas

Kinetic simulations of a direct-current positive-column Ar plasma revealed that electron fluxes are sensitive to energy dependence of an elastic collision cross section. Paradoxical behavior of the electron flux in a coordinate-energy phase space is presented. The direction of the electron flux at the “elastic” energy region (5-10 eV) in whole volume, except the region near the wall, turned out to be oppositely directed to that conventionally assumed.

Fluxes of Charged Particles in Two-Chamber ICP Discharge in Oxygen

This article presents a nontrivial behavior of charged particles fluxes in electronegative 2-D plasmas. It is shown that in 2-D multicomponent plasmas, the ambipolarity of fluxes is violated, i.e., the algebraic sum of all fluxes turned out nonzero. It also turned out that the total current streamlines are closed circuit, which means that the current in plasma is a vortex.

Violation of the boltzmann distribution for plasma electron number density in two-chamber inductively coupled plasma discharges

It is found for inductively coupled plasma (ICP) discharges in two-chamber structures in which a strong electron temperature gradient can be produced, the classical Boltzmann distribution for the electron number density does not exist even at qualitative level; a more general (extended Boltzmann) distribution for the electron energy density holds with a satisfactory accuracy.

Genetic algorithm as a means of solving a radial schrödinger equations system

The aim of this work is to develop a fast practical method for calculating radial components of wave functions for multielectron atoms. Radial wave functions are used when cross-sections of atoms and speed of reaction in plasma should be known. We applied genetic algorithms to calculate eigenvalues of energy and difference methods for wave functions. As a result we have succeeded in creation a fast practical algorithm that is able to calculate wave functions for optical electron and for the inner ones in a multielectron atom.

Microplasma and VUV-photoionization gas analyzers based on collisional electron spectroscopy (CES)

Summary form only given. Traditional electron spectroscopy (ES) is one of the most informative means for chemical structure analysis of the matter1. According to ES, identification of atoms and molecules is carried out by the energy analysis of characteristic electrons formed in ionization process of atoms or molecules A during collisions with particles B* of definite energy (photons, excited atoms, etc.)