The scientist described for the first time the different modes of plasma formation in atmospheric conditions – Search

09/21/2022

The Russian scientist for the first time described the mechanisms of formation of various forms of direct current gas discharges at atmospheric pressure. It was discovered that by changing the cooling conditions of the electrodes, the elements between which the electric current flows, it is possible to control the properties of the discharges. For example, the researcher received arc discharges that, near the negative cathode, had the form of a small point or point, and also quite voluminous, similar to a cloud. These data will make it possible to use plasma with certain properties in the synthesis of high-quality artificial nanodiamonds, which are used in devices to store large amounts of information. research results, supported grant from the Russian Science Foundation (RSF), published in Science and Technology of Plasma Sources.

An electric discharge is a special state of a gas when an electric current passes through it. In this case, an ionized medium is formed, that is, charged, made up of electrons, ions and neutral particles. This ionized matter is called plasma.

Depending on the strength of the current flowing through the medium, there are several types of electric shocks. The so-called dark discharge occurs at very low currents, down to tenths of a milliamp (mA), which is about ten thousand times less than the current in a phone charger. A glow discharge, which can be observed, for example, when lighting neon lamps, exists at currents from 1 mA to 1 A. Another type of discharge, the arc discharge, occurs at currents above 1 A.

All types of discharges and possible transitions from one to another at pressures several orders of magnitude lower than atmospheric have been studied in detail. At the same time, the properties of discharges in such conditions cannot always be projected under the conditions of an ordinary air environment. In connection with this, systematic investigations of a light discharge at atmospheric pressure began about twenty years ago. It was assumed that this type of discharge could exist under such conditions for a very short time due to the rapid heating of the electrode and the transition from the light discharge to a more powerful arc discharge.

employee National Technical Research University of Kazan named after AN Tupolev(Kazan) mathematically described the transition from a light discharge to an arc discharge in gases at atmospheric pressure. It was found that this process depends on the cooling conditions of the electrodes and their temperature. So, normally, during the flow of current and the formation of plasma under conditions of atmospheric pressure, the environment, in particular the gas, is strongly heated – up to several thousand degrees Celsius. This leads to the fact that the surfaces of the electrodes also heat up and begin to affect the discharge. For example, at the cathode, an additional mechanism for maintaining the discharge, thermionic emission, can be “turned on”.

The author of the paper showed that by artificially controlling the temperature of the electrodes, for example by cooling them in various ways, it is possible to achieve different discharge modes and, consequently, plasma properties. In particular, the researcher found the conditions under which an arc discharge was formed, which near the cathode had a diffuse form, that is, in the form of a sprayed spot or, on the contrary, a form compressed to a point. In fact, it has been shown that these two modes can be controlled. It should be noted that the results of the mathematical modeling were confirmed both by our own experimental measurements and by data available in the scientific literature. Thus, the presented model will be a reliable tool to predict plasma properties at atmospheric pressure.

“The study showed that in practice it is possible to create plasma with very controlled and unique properties. It will be useful in the creation of miniature detectors for the analysis of the chemical composition of a substance, in tasks related to the treatment of surfaces, including biological tissues. In addition, some plasma properties may be promising for the synthesis of nanometer diamonds used in photonics. We are now conducting investigations with various types of gaseous media, including inert gases containing hydrocarbon impurities. In addition, we are developing models that describe how the evaporation of the electrode material, in particular graphite, affects the plasma characteristics.”– says the head of the project, supported by a grant from the Russian Science Foundation, Almaz Saifutdinov, Candidate of Physical and Mathematical Sciences, Associate Professor of the General Physics Department of the Kazan National Research Technical University named after AN Tupolev.

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