RU2764165C1 - Device for obtaining a plasma jet - Google Patents

Abstract

FIELD: gas-discharge plasma technology.SUBSTANCE: invention relates to gas-discharge plasma technology and technology, in particular to sources of plasma jets of atmospheric pressure, where the source gas is air or its mixture with other gases. The device includes a high-voltage power source, the discharge gap is formed by coaxially located inner high-voltage hollow cylindrical electrode 1 with a sharpened outer edge 3 facing the discharge gap d, and free electrodes in an amount of at least two placed on the outer surface of the dielectric insert 6 in the form of plates 2 with tips 5, facing the discharge gap d, and distributed at equal distances from each other, not exceeding the interelectrode distance. The high-voltage hollow electrode 1 is a nozzle for supplying air with a flow rate of up to 1.5 l/min.EFFECT: increasing the plasma treatment zone, increasing the stability of the plasma jet to sharp fluctuations in the air in the environment and ensuring the arbitrary orientation of the plasma jets.3 cl, 4 dwg

Description

The proposed device relates to plasma technology, in particular to sources for obtaining and controlling the flow of atmospheric pressure plasma, the source gas for which is air or its mixtures with other gases. The device can be used to obtain plasma treatment zones in the processes of surface cleaning and modification, blood coagulation, biological disinfection of materials, and plasma-chemical synthesis of substances.

Known methods and devices for producing atmospheric pressure plasma jets (APJ) are based on the use of glow, arc, radio frequency, barrier discharges [1], etc. Due to the creation in the discharge zone of excess pressure exceeding atmospheric pressure, the plasma formed in the discharge enters through a nozzle (round or slotted in cross section), or several holes, or an interelectrode gap, forming the so-called. plasma jet. In particular, in devices based on radiofrequency excitation, a needle electrode is coaxially placed in a cylindrical dielectric cavity, to which a voltage is applied [2]. Here, the plasma is formed at the end of the electrode and is called a plasma needle ("plasma needle"). In a number of devices, a radio frequency field is applied to a dielectric capillary through which the excited gas enters, by means of two or more external electrodes located on the surface of the capillary [3]. The disadvantage of these devices is the high consumption of working gases required for the stability of the atmospheric pressure plasma jet. In addition, RF power supplies are complex and require additional protection measures during operation.

A device is known in which the formation of a plasma jet occurs by passing air at a speed of 30-70 m/s through the stationary glow discharge zone formed by plate anodes and pin cathodes [4]. The technical solution makes it possible to use cheap and available air for the formation of PSAD, but requires a large gas flow rate.

Devices are known that include a cylindrical tube made of a dielectric material through which the excited gas is passed. A pair of electrodes is located on the outer surface of the tube at a distance from each other. The grounded electrode is located at the outlet of the tube, i.e. at the nozzle. The electrodes are connected to a pulsed high-frequency power supply [5]. Often, a high-voltage electrode is made in the form of a rod with a pointed end and is located inside a cylindrical tube, coaxial with it [6]. The advantage of such devices is their constructive simplicity. To obtain plasma jets with a length from fractions to several centimeters, voltage pulses of positive and negative polarity are used here, with a duration of the order of 0.1–1 μs, an amplitude of up to 30 kV, a repetition rate of tens of kHz, and gas pumping rates from units to tens of l/min. The disadvantage of these devices is the complexity or impossibility of forming extended atmospheric pressure plasma jets in mixtures of inert gases He, Ar with an electronegative molecular gas, as well as in air or nitrogen. In these gaseous media, the greatest number of chemically active particles is formed, but in the presence of air, nitrogen, or an electronegative gas, the discharge quality decreases, and to maintain it, it is necessary to increase the gas flow rate (>10 l/min) and voltage (>20 kV). This increases the cost of operation and increases the requirements for the electrical safety of the installation. And in some cases, even this does not allow the formation of a plasma jet.

Of the known devices for producing an atmospheric pressure plasma jet, the closest in technical essence to the claimed invention is a method and device for producing a plasma jet, which contains two pointed electrodes forming a discharge gap of 5 to 20 mm, one electrode is free, a high-voltage power source , characterized by the fact that the electrodes are located at an angle of 0<a<160°, the second electrode is high voltage and has a positive voltage polarity with the specified rise front 0.1<τ<10 µs [7].

The advantage of the method is the simplicity of design and the possibility of obtaining an atmospheric pressure plasma jet, the source gas for which is air or its mixtures with other gases. The device has several drawbacks. The high temperature of the end of the plasma jet (about 100°C) does not allow biological and synthetic materials that are sensitive to overheating to be subjected to plasma treatment. A single plasma jet has a limited plasma treatment zone, which is inconvenient when processing extended objects. The sensitivity of the discharge to sharp fluctuations in the air in the environment can cause instability of the discharge burning up to its extinction. In addition, the orientation of the plasma jet should be close to vertical, propagating from bottom to top, which also limits the scope of the device.

Thus, among the existing devices for producing atmospheric pressure plasma jets, it is difficult to simultaneously ensure the formation of an extended plasma jet in media containing air, nitrogen, or an electronegative gas, and at the same time maintain the simplicity of the design and the power source used, or a moderate plasma jet temperature and discharge stability.

The technical result of the invention is to reduce the temperature of an extended plasma jet in air or in media containing mixtures of easily ionizable gases with electronegative gases, to increase the plasma treatment zone, to ensure the stability of the plasma jet to sharp fluctuations in the air in the environment, to provide arbitrary orientation of plasma jets.

The specified technical result is achieved by the fact that in a known device containing a high-voltage power source, pointed electrodes forming a discharge gap of 5 to 20 mm, one electrode is high-voltage and has a positive voltage polarity with a rising front from 0.1 to 10 μs, the other electrode is free , according to the invention, the discharge gap is formed by coaxially arranged internal high-voltage hollow cylindrical electrode with a pointed outer edge facing the discharge gap, and at least two free electrodes placed on the outer surface of the dielectric insert in the form of plates with tips facing the discharge gap , and distributed at equal distances from each other, not exceeding the interelectrode distance, while the hollow high-voltage electrode is a nozzle for supplying air with a flow rate of up to 1.5 l/min.

In addition, a feature of the device is that the air flow in the interelectrode gap is carried out through the gap between the dielectric insert and the high-voltage electrode at a flow rate of up to 1.5 l/min.

In addition, a feature of the device is that nitrogen, helium, argon or mixtures thereof are supplied between the dielectric cylinder and the high-voltage electrode, including additions of oxygen, hydrocarbons, and easily ionizable molecular gases.

In FIG. 1 and 2 shows a diagram of the proposed device - longitudinal and cross section, respectively. It contains pointed electrodes 1 and 2, forming a discharge gap of size d. A high-voltage hollow cylindrical electrode 1 with a pointed outer edge 3 is connected to a high-voltage power source 4. At least two free electrodes 2 are in the form of plates with points 5 facing the discharge gap. They are placed on the surface of the dielectric insert 6 at equal distances from each other x, and x≥d. The internal high-voltage hollow cylindrical electrode 1 is placed coaxially with the free electrodes 2.

The device works as follows. The hollow high-voltage electrode 1 simultaneously serves as a nozzle for supplying air with a flow rate of up to 1.5 l/min. Electrode 1 is supplied with voltage pulses of positive polarity from a high-voltage power source 4 with a front from 0.1 to 10 μs, electrode 2 is left at a floating potential, or connected to ground through a capacitance (this option is not shown in Fig. 1). As a result, spark discharges are ignited in the discharge gap between the pointed edge 3 of the electrode 1 and the tips 5 of the electrodes 2. In 1-3 seconds, the discharge channels heat up, bend, and luminous plasma jets are formed at the bends, the shape of which can be needle-shaped or conical. The number of jets depends on the number of free electrodes 5.

In FIG. 3 shows the result of the formation of atmospheric pressure plasma jets in air in a device having three free electrodes, which corresponds to the cross section of the device shown in FIG. 2.

The number of plasma jets is determined by the number of free electrodes. In FIG. 4 shows a version with four free electrodes.

Compared with the prototype device with the described design provides the formation of multiple plasma jets at the same time, which increases the area of plasma treatment. The number of plasma jets is limited by the condition x>d under which an electrical breakdown of the interelectrode gap d occurs.

Direct introduction into the area of formation of plasma jets of cold air (arrow I in Fig. 1) through the hollow electrode 1 provides several technical results at once.

First, there is a decrease in temperature at the ends of plasma jets in air or in media containing mixtures of easily ionizable gases with electronegative gases. The decrease in temperature is enhanced by the cold air drawn into the zone of ambient air plasma formation (arrows II in Fig. 1). This provides a total decrease in the air temperature at the ends of the plasma jets by 25–40%.

Secondly, blowing air through electrode 1 increases the resistance of plasma jets to sharp fluctuations of air in the environment: they do not go out even with a forced external blowing of the device.

Thirdly, the orientation of the plasma jets can be any (vertical and horizontal, including a 180-degree flip) (see, for example, Fig. 3).

Increasing the speed of blowing air through the hollow electrode 1 leads to a decrease in the temperature of the ends of the plasma jets only to a certain limit. It has been experimentally proven that with a power consumption of a high-voltage power source of 30 W, a discharge gap of 6 mm, in the electrode configuration shown in Fig. 2, turning on the purge and then increasing its speed to 1.5 l/min reduces the temperature by 25%, which makes the device suitable for plasma processing of fusible substances. A subsequent increase in the blowing rate does not reduce the temperature of the ends of the plasma jets, so a further increase in flow rate is impractical, it leads to unreasonable gas flow. Additional stabilization is also provided by the flow of air at a flow rate of up to 1.5 l/min into the gap between the dielectric insert 3 and the high-voltage electrode 1 (arrows III in Fig. 1). The supply of nitrogen, helium, argon, or mixtures thereof, including additives of oxygen, hydrocarbons, easily ionizable molecular gases, into the specified interval also allows expanding the scope of the device by expanding the composition of the formed atmospheric pressure plasma.

Thus, the proposed device expands the conditions for using the device for plasma processing, providing an increase in the plasma processing zone, the stability of the plasma jet to sharp fluctuations in the air in the environment, the arbitrary orientation of the plasma jets in space, and the decrease in the temperature of the plasma jets expands the range of low-melting substances subjected to processing .

Sources of information

1. Schutze A., Jeong J.Y., Babayan S.E., Park J., Selwyn G.S., Hicks R.F. The atmospheric-pressure plasma jet: a review and comparison to other plasma sources // IEEE Trans. Plasma Sci. 1998 Vol. 26, no. 6. P. 1685-1694.

2. Kieft I.E., v d Laan E.P., Stoffels E. Electrical and optical characterization of the plasma needle // New J Phys. 2004. Vol.6. 149.14 p.

3. Patelli A., Verga F.E., Scopece P., Pierobon R., Vezzu S. Patent WO 2015071746. Priority data: 11/14/2014. Published: 05/21/2015.

4. Akishev Yu.S., Grushin M.E., Trushkin N.I. Patent RU 2370924. Priority date: 10/26/2007. Published 10/20/2009. Bull. No. 25.

5. Uchida G., Takenaka K., Setsuhara Y. Effects of discharge voltage waveform on the discharge characteristics in a helium atmospheric plasma jet // J. Appl. Phys. 2015. Vol. 117.153301.6 p.

6. Ayan H., Yildirim E.D., Pappas D.D., Sun W. Development of a cold atmospheric pressure microplasma jet for freeform cell printing // Appl. Phys. Lett. 2011 Vol. 99.111502.3 p.

7. Sosnin E.A., Panarin V.A., Skakun B.C., Tarasenko V.F., Pechenitsin D.S. Patent RU No. 2633705. Priority date 20.06.2016. Published 10/17/2017. Bull. No. 29.

Claims (3)

1. A device for obtaining a plasma air jet at atmospheric pressure, containing a high-voltage power source, pointed electrodes forming a discharge gap from 5 to 20 mm, one electrode is high-voltage and has a positive voltage polarity with a rising front from 0.1 to 10 μs, the other electrode is free, characterized in that the discharge gap is formed by a coaxially located internal high-voltage hollow cylindrical electrode with a pointed outer edge facing the discharge gap, and at least two free electrodes placed on the outer surface of the dielectric insert in the form of plates with points facing the discharge gap, and distributed at equal distances from each other, not exceeding the interelectrode distance, while the hollow high-voltage electrode is a nozzle for supplying air with a flow rate of up to 1.5 l/min. 2. The device according to claim 1, characterized in that the air flow in the interelectrode gap is carried out through the gap between the dielectric insert and the high-voltage electrode at a flow rate of up to 1.5 l/min. 3. The device according to claim 1, characterized in that nitrogen, helium, argon or mixtures thereof are supplied between the dielectric cylinder and the high-voltage electrode, including additions of oxygen, hydrocarbons, easily ionizable molecular gases.

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