N. I. Trushkin

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.

Negative corona, glow and spark discharges in ambient air and transitions between them

Obtaining new information about different forms of self-sustained dc discharges that can be realized in pin-to-plane electrode geometry in ambient air is the goal of this paper. Experimental and numerical calculation data uncovering the physics of the temporal and spatial evolution of the negative corona and glow discharge (GD), with increase in current up to the transition to the spark, are presented. Special attention is paid to the properties of diffusive GD at atmospheric pressure, which is a necessary stage (steady-state or transient) preceding the spark and determining the threshold conditions of sparking.

A numerical simulation of Trichel-pulse formation in a negative corona

A new quasi-one-dimensional model for a negative corona in air is formulated allowing for the quantitative description of the mechanism of Trichel-pulse formation. Detailed analysis of the processes controlling pulse dynamics is made. Comparison with experiment for a short-gap corona demonstrates a reasonable agreement with the shape of the pulse and in the average characteristics of the negative corona.

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.

Studies on cold plasma-polymer surface interaction by example of PP- and PET-films

This paper presents the results of experimental and theoretical studies aimed at developing mathematical models for plasma–polymer interactions. Experiments on plasma treatment of polypropylene (PP) and poly(ethylene terephthalate) foils were carried out with the use of atmospheric pressure plasma sources operating with ambient air and purified nitrogen as plasma forming gases. Water contact angle was measured, and x-ray photoelectron spectroscopy characterization of the treated samples was done. A theoretical model based on a mechanism proposed by Kushner for plasma processing of PP foil is described. A comparison between experimental and theoretical results for oxygen enrichment of PP-polymer samples is presented.

Pulsed Regime of the Diffusive Mode of a Barrier Discharge in Helium

Periodic pulsations of the active current component are revealed experimentally in transversely homogeneous barrier discharges in helium at small values of the parameter Pd (below 500 torr mm) and moderate frequencies of the applied voltage (f < 100 kHz). The frequency of the current pulsations is higher than the frequency of the well-studied pulsations in a transversely inhomogeneous streamer barrier discharge in air by a factor of approximately 100. Numerical calculations show that the physical nature of the observed pulsations can be explained in terms of the negative differential resistance of the cathode fall region, which occupies essentially the entire interelectrode gap in each half-period of the applied voltage.

Transition of a Multipin Negative Corona in Atmospheric Air to a Glow Discharge

It is commonly accepted that, as the current increases, a diffuse negative corona inevitably goes over to a strongly nonuniform and nonsteady spark discharge. In this paper, a new effect—the transition of a negative corona to a diffuse glow discharge at atmospheric pressure—is studied experimentally and numerically. The evolution of the corona parameters during the transition to the regime of a glow discharge is traced.

Self-oscillations of a positive corona in nitrogen

The oscillatory behaviour of a glow positive corona in pure nitrogen is observed experimentally. The regular self-oscillations of the corona current and the light emission from the glow ionization region, as well as the averaged volt-ampere characteristics of this discharge, are studied comprehensively within gas pressure range 10-765 Torr. It is revealed that the positive glow corona generates a soft x-radiation. This radiation plays a crucial role in the photo-ionization of nitrogen. Furthermore, it provides a fast positive feedback for electron avalanches through the ionization region of the corona. The results of numerical modelling of the glow corona under free-running oscillations are also presented.

Non-equilibrium constricted dc glow discharge in N2 flow at atmospheric pressure: stable and unstable regimes

The experimental results from the study of a constricted glow discharge in turbulent flow of nitrogen at atmospheric pressure are presented. The discharge was induced by a dc high voltage superimposed between pin-to-plane electrodes inserted inside a glass tube of 1 cm diameter. At a low current I < 20 mA it is established that the properties of the constricted glow discharge in gas flow are strongly different from those in gas at rest: the discharge in gas flow exhibits four different current regimes instead of only a single one in gas at rest. One of these regimes corresponds to a spiral twisting of gas flow by the constricted glow discharge. This effect can be used properly in plasma actuators designed for atmospheric pressure flow control. Gas blowing also enables the constricted N2 plasma to be in a strong non-equilibrium state with vibration and gas temperatures of about 6000 K and 600 K, respectively. So, a constricted discharge in N2 flow can serve as a compact and effective non-thermal plasma source useful in the remote treatment of different surfaces.