Stepan I. Eliseev

Spatial Distribution of Parameters in Normal Micro-DC Glow Discharge in Air

Design of devices based on glow microdischarges requires a detailed knowledge of spatial distribution of the main plasma parameters, which is almost impossible to obtain experimentally because of the small size of such discharges. This paper presents the results of simulation for flat microdischarge in air using an extended hydrodynamic model. Images of cathode spots for different discharge currents are presented, as well as current-voltage characteristics.

Longer Microwave Plasma Jet With Different Discharge Performances Originated by Plasma–Surface Interactions

With an input power of 50 W and a gas pressure of 100 Pa, 2.5 (without metal wire) and 10.5 cm (with a copper wire) long microwave air plasma jets are generated, respectively. When 95% Ar + 5% O2 is instead of air, the length of the plasma jet is stretched to 15 cm. Furthermore, the length of plasma plume is affected differently by adding the processed materials. These different discharge performances originate from the effect of plasma-surface interactions.

Gas Heating and Transition to Obstructed Mode in DC Glow Microdischarge in Air

Microdischarges have been the subject of numerous studies in the past decade. Numerical modeling has become a powerful tool to complement to the scarce experimental data on microdischarges, as their small size poses a great number of difficulties in implementing traditional experimental techniques. It has been shown that in atmospheric air discharges, gas heating becomes an important factor, greatly influencing plasma parameters and leading to transition from normal glow discharge to obstructed mode with abruptly growing current-voltage characteristic. Presented images of electron density distributions and volt-ampere characteristics confirm this interesting phenomenon.

Investigation of Low-Pressure Glow Discharge in a Coaxial Gridded Hollow Cathode

This paper contains results of numerical and experimental investigation of glow discharge plasma created in a chamber of a new-type large-volume coaxial gridded hollow cathode. The discharge is created in argon at 25 Pa by applying time-varying power with frequency 20 kHz on electrodes. A 2-D model of the discharge was built using COMSOL Multiphysics. Self-consistent description of the discharge was obtained using the extended fluid approach, which couples continuity equations for charged particles and electron energy balance with Poissons equation for electric potential. Electron transport coefficients and rates of electron-impact reactions were calculated using the electron energy distribution function. The spatial and radial distributions of plasma potential (Vp), electron density (ne), and electron temperature (Te) were obtained. It is shown that the plasma inside the chamber is similar to the negative glow of a dc glow discharge. Comparison of numerical results with the Langmuir probe measurements of electron density and electron temperature is presented and showed a good agreement.

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.

2-D Modeling of Orificed Hollow Cathodes of Stationary Plasma Thrusters SPT-100

In this paper, 2-D extended fluid model for the simulation of orificed hollow cathode (OHC) discharge in xenon flow of SPT-100 thruster was built using Comsol Multiphysics. Self-consistent discharge model is based on fluid description of ions and excited neutral species and uses drift-diffusion approximation for the particle fluxes. Electron transport and rates of electron-induced plasma-chemical reactions are calculated using Boltzmann equation for electron energy distribution function and corresponding collision cross sections. A reasonable set of plasma-chemical processes with electrons, ions, and excited and neutral particles were considered. The model accounts for gas flow and heating. Self-consistent electric field is calculated from the Poisson equation. The model geometry reproduces that of the experimental OHC for stationary plasma thruster SPT-100, which was studied in Harbin Institute of Technology. Simulations were carried out for different operational modes of the OHC. Distributions of key discharge parameters were obtained. A comparison between the simulation results and experimental data was conducted and showed good agreement.

Study on hairpin-shaped argon plasma jets resonantly excited by microwave pulses at atmospheric pressure

In the present study, atmospheric pressure argon plasma jets driven by lower-power pulsed microwaves have been proposed with a type of hairpin resonator. The plasma jet plume demonstrates distinctive characteristics, like arched plasma pattern and local plasma bullets. In order to understand how the hairpin resonator works, electromagnetic simulation of the electric field distribution and self-consistent fluid simulation of the interaction between the enhanced electric field and the pulse plasma plume are studied. Simulated spatio-temporal distributions of the electric field, the electron temperature, the electron density, and the absorbed power density have been sampled, respectively. The experimental and simulated results together suggest that the driving mechanism of the hairpin resonator works in the multiple electromagnetic modes of transmission line and microwave resonator, while the local plasma bullets are resonantly generated by local enhanced electric field of surface plasmon polaritons. Moreove...

Slow electron energy balance for hybrid models of direct-current glow discharges

In this paper, we present the formulation of slow electron energy balance for hybrid models of direct current (DC) glow discharge. Electrons originating from non-local ionization (secondary) contribute significantly to the energy balance of slow electrons. An approach towards calculating effective energy brought by a secondary electron to the group of slow electrons by means of Coulomb collisions is suggested. The value of effective energy shows a considerable dependence on external parameters of a discharge, such as gas pressure, type, and geometric parameters. The slow electron energy balance was implemented into a simple hybrid model that uses analytical formulation for the description of non-local ionization by fast electrons. Simulations of short (without positive column) DC glow discharge in argon are carried out for a range of gas pressures. Comparison with experimental data showed generally good agreement in terms of current-voltage characteristics, electron density, and electron temperature. Simu...

1D kinetic simulations of a short glow discharge in helium

This paper presents a 1D model of a direct current glow discharge based on the solution of the kinetic Boltzmann equation in the two-term approximation. The model takes into account electron-electron coulomb collisions, the corresponding collision integral is written in both detailed and simplified forms. The Boltzmann equation for electrons is coupled with continuity equations for ions and metastable atoms and the Poisson equation for electric potential. Simulations are carried out self-consistently for the whole length of discharge in helium (from cathode to anode) for cases p = 1 Torr, L = 3.6 cm and p = 20 Torr, L = 1.8 mm, so that pL = 3.6 cm·Torr in both cases. It is shown that simulations based on the kinetic approach give lower values of electron temperature in plasma than fluid simulations. Peaks in spatial differential flux corresponding to the electrons originating from superelastic collisions and Penning ionization were observed in simulations. Different approaches of taking coulomb collisions...

Numerical simulation and analysis of electromagnetic-wave absorption of a plasma slab created by a direct-current discharge with gridded anode

In this paper, we present investigation of a direct-current discharge with a gridded anode from the point of view of using it as a means of creating plasma coating that could efficiently absorb incident electromagnetic (EM) waves. A single discharge cell consists of two parallel plates, one of which (anode) is gridded. Electrons emitted from the cathode surface are accelerated in the short interelectrode gap and are injected into the post-anode space, where they lose acquired energy on ionization and create plasma. Numerical simulations were used to investigate the discharge structure and obtain spatial distributions of plasma density in the post-anode space. The numerical model of the discharge was based on a simple hybrid approach which takes into account non-local ionization by fast electrons streaming from the cathode sheath. Specially formulated transparency boundary conditions allowed performing simulations in 1D. Simulations were carried out in air at pressures of 10 Torr and higher. Analysis of the discharge structure and discharge formation is presented. It is shown that using cathode materials with lower secondary emission coefficients can allow increasing the thickness of plasma slabs for the same discharge current, which can potentially enhance EM wave absorption. Spatial distributions of electron density obtained during simulations were used to calculate attenuation of an incident EM wave propagating perpendicularly to the plasma slab boundary. It is shown that plasma created by means of a DC discharge with a gridded anode can efficiently absorb EM waves in the low frequency range (6–40 GHz). Increasing gas pressure results in a broader range of wave frequencies (up to 500 GHz) where a considerable attenuation is observed.In this paper, we present investigation of a direct-current discharge with a gridded anode from the point of view of using it as a means of creating plasma coating that could efficiently absorb incident electromagnetic (EM) waves. A single discharge cell consists of two parallel plates, one of which (anode) is gridded. Electrons emitted from the cathode surface are accelerated in the short interelectrode gap and are injected into the post-anode space, where they lose acquired energy on ionization and create plasma. Numerical simulations were used to investigate the discharge structure and obtain spatial distributions of plasma density in the post-anode space. The numerical model of the discharge was based on a simple hybrid approach which takes into account non-local ionization by fast electrons streaming from the cathode sheath. Specially formulated transparency boundary conditions allowed performing simulations in 1D. Simulations were carried out in air at pressures of 10 Torr and higher. Analysis of th...