Yuri Akishev

The influence of electrode geometry and gas flow on corona-to-glow and glow-to-spark threshold currents in air

In negative corona discharges in ambient air different discharge modes can be observed. In this paper the discharge current regions corresponding to these modes are determined. The influence of anode geometry, anode resistivity, inter-electrode distance and gas flow on the threshold currents that mark the corona-to-glow and glow-to-spark transitions is investigated. The experimental data are backed up by an analytical treatment of ionization instability development within a local current spot on metallic and resistive anodes.

Atmospheric-pressure, nonthermal plasma sterilization of microorganisms in liquids and on surfaces

Gas discharge plasma inactivation of microorganisms at low (close to ambient) temperature is a promising area of investigation that is attracting widespread interest. This paper describes atmospheric-pressure, nonthermal plasma (NTP) methods for cold sterilization of liquids and thermal sensitive surfaces. These methods are based on the use of direct current (DC) gas discharge plasma sources fed with steady-state high voltage. Parameters characterizing the plasma sources used (plasma-forming gas, gas flow rate, electric power consumed, etc.) are given. The results for plasma sterilization of different microorganisms (vegetative cells, spores, fungi, biofilms) are presented. An empirical mathematical approach is developed for describing NTP inactivation of microorganisms. This approach takes into account not only the destruction of different components of the cells, but their reparation as well.

Surface modification with a remote atmospheric pressure plasma: dc glow discharge and surface streamer regime

A remote atmospheric pressure discharge working with ambient air is used for the near room temperature treatment of polymer foils and textiles of varying thickness. The envisaged plasma effect is an increase in the surface energy of the treated material, leading, e.g., to a better wettability or adhesion. Changes in wettability are examined by measuring the contact angle or the liquid absorptive capacity. Two regimes of the remote atmospheric pressure discharge are investigated: the glow regime and the streamer regime. These regimes differ mainly in power density and in the details of the electrode design. The results show that this kind of discharge makes up a convenient non-thermal plasma source to be integrated into a treatment installation working at atmospheric pressure.

Novel AC and DC Non-Thermal Plasma Sources for Cold Surface Treatment of Polymer Films and Fabrics at Atmospheric Pressure

Novel types of non-thermal plasma sources at atmospheric pressure based on multi-pin DC (direct current) diffusive glow discharge and AC (alternative current) streamer barrier corona have been elaborated and tested successfully for cold surface treatment of polymer films [polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET),] and polyester fabric. Results on physical properties ofdischarges mentioned and output energy characteristics of new plasma sources as well as data on after-treatment changes in wettability of films and fabrics are presented. The main goal of this study was to find out the experimental conditions for gas discharge and surface processing to achieve a remarkable wettability change for a short treatment time.

The DC glow discharge at atmospheric pressure

The transition of a negative corona discharge into a glow discharge at atmospheric pressure is investigated. The volt-ampere characteristics of a pin-to-plate discharge configuration reveal the existence of three discharge regimes: corona, glow, and spark. The discharge luminosity is indicative of the differences in the electrical field distribution in the different regimes.

Numerical simulation and experimental study of the corona and glow regime of a negative pin-to-plate discharge in flowing ambient air

In a negative pin-to-plate discharge in ambient air, three different modes can be observed: corona, glow and spark. The experimental results of this paper reveal the effect of the anode geometry on the extent of the glow regime. A quasi-two-dimensional model is applied to reconstruct the experimental current–voltage characteristics of negative corona discharges with curved anode surfaces. For a sufficiently large discharge current, the model yields a discharge structure that is similar to that of a low-pressure glow discharge.

Instability wave control in turbulent jet by plasma actuators

Instability waves in the shear layer of turbulent jets are known to be a significant source of jet noise, which makes their suppression important for the aviation industry. In this study we apply plasma actuators in order to control instability waves in the shear layer of a turbulent air jet at atmospheric pressure. Three types of plasma actuators are studied: high-frequency dielectric barrier discharge, slipping surface discharge, and surface barrier corona discharge. Particle image velocimetry measurements of the shear layer demonstrate that the plasma actuators have control authority over instability waves and effectively suppress the instability waves artificially generated in the shear layer. It makes these actuators promising for application in active control systems for jet noise mitigation.

Generation of atmospheric pressure non-thermal plasma by diffusive and constricted discharges in air and nitrogen at the rest and flow

Main subject of this paper is low current atmospheric pressure gas discharges powering with DC power supplies. These discharges are widely used for generation of non-thermal or non-equilibrium plasma in air and nitrogen which are much cheaper compared to rare gases like He or Ar. Molecular nitrogen as plasma forming gas has a unique capability to accumulate huge energy in vibration, electron (metastables) and dissociated (atomic) states. Besides, all active species have a long life-time, and they can be therefore transported for a long distance away from the place of their generation. Different current modes (diffusive and constricted) of these discharges are discussed. Experimental and numerical results on generation of chemically active species in the diffusive and constricted mode are presented.

Determination of Local Ionic Wind Velocity in Corona by Laser Interferometer Taking Into Consideration the Charging–Discharging of Probe Particles

Experimental data on the probe-particle local velocity measured by laser interferometer in air gap of a negative pin-to-plane corona are presented. Small water droplets like mist were used as the probe particles, which can be charged by the corona. Experimental data are complemented with numerical calculations, allowing us to evaluate the drift velocity of the charged droplets and determine therefore a real local velocity of the ionic wind induced by the collisions of negative ions with the neutrals. It is shown the charging of probe particles impacts strongly on their total local velocity. To agree a calculated local velocity of the charged particle with the measured one, the discharging processes were introduced. It is assumed that the discharging processes occur due to emission of electrons from surface of the charged droplets. Proposed mechanism of the secondary emission is associated with the recombination of H atoms and OH radicals on the surface of the charged droplet.

Self-Pulsing Regime of DC Electric Discharge in Dielectric Tube Filled With Water Containing Gas Bubble

Effective generation of biochemically active species inside a liquid can be performed by an electric discharge in small gas bubbles admixed from outside into the liquid. In such a case, active species are produced by a gas discharge plasma inside bubbles and then transported due to diffusion into the liquid. This paper presents experimental data of electric discharges in small bubbles inserted into a thin dielectric tube filled with water. A low-frequency regime of periodic electrical breakdowns is revealed and described.