Device to produce stable microdischarge of atmospheric pressure

FIELD: electricity.

SUBSTANCE: discharge is ignited between a flat cathode and an anode, which is made in the form of a thin needle with a small radius of rounding. The proposed invention makes it possible to produce a stable microdischarge with a quite simple and inexpensive method, which does not require vacuum plants and does not require external injection of electrons, since the discharge burns in atmosphere and is independent. The invention may be used to create plasma-chemical reactors and gas analysers, and also in plasma sputtering and alloying of materials in sections of micron size.

EFFECT: increased stabilisation of a smouldering microdischarge under atmospheric pressure.

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The invention relates to plasma technology and plasma and can be used for plasma surface treatment, sterilization, spectroscopy, and also when creating a plasma-chemical reactors and gas analyzers.

Known gas discharge device of a high pressure to obtain a non-equilibrium plasma, which is based on different principles. Most often in these devices employ some additional source of ionization. As such a source may be either an auxiliary discharge, or an external ionization source.

One of the ways to obtain nonequilibrium plasma at high pressure is described in [1] and consists in the fact that the volume of non-equilibrium atmospheric pressure plasma generated in a three-electrode system, glow discharge, which includes a two-bit camera, three electrodes, a power source supply system and exhaust gas.

Known also realized in [2] a discharge device with a hollow cathode, consisting of a camera, in which are placed two flat electrodes, the anode and cathode, separated by a dielectric thickness of about 200 microns, with a hole diameter of the order of the thickness of the dielectric, and the third electrode is the anode, located at a distance of up to 1 inch from the first feed system and a gas outlet, a source of constant voltage. is between the first and the second electrode in the hole ignited the microdischarge hollow cathode with discharge current of a few milliamps. Non-self-maintained discharge occurs when connecting a voltage between the second and third electrodes. The disadvantages of these two known devices can be attributed to the presence of constantly working an additional source of ionization, which is necessary for stable combustion of the main discharge.

Known apparatus for producing fire resistant discharges in dense gases [3], which is the closest to the problem at hand and taken as a prototype. Common to the known device and the claimed invention is that the light discharge is independent.

A disadvantage of the known device is rather complicated system of pre-ionization discharge gap, which is necessary to stabilize the discharge, which prevents sparks and its stabilization. In addition, the known device is more expensive due to design complexity and time-consuming in operation.

The claimed invention free from the above disadvantages.

The technical result of the claimed invention is to improve the stabilization of glow microdischarge at atmospheric pressure in a simple way that does not require pre-ionization of the gas in the discharge gap and without the use of any system pumping gas. In addition, significant t is Henichesk result is the ability to conduct discharge and if the currents around units and less mA and interelectrode distances of the order of tens of µm and less [4].

This technical result is achieved in that a device for obtaining a stable microdischarge atmospheric pressure, containing a constant voltage source connected through a limiting current resistor with a bit of gap between the flat cathode located on the base, and an anode mounted on the lever, which is supplied with control the length of the discharge gap between the cathode and the anode, in accordance with the claimed invention, the anode is made in the form of a needle with a radius of not more than 20 μm and located above the flat cathode at a distance not exceeding the numerical value of the magnitude of the discharge gap between the anode and the cathode, which corresponds, according to the Paschen law the minimum breakdown voltage.

In addition, this technical result is achieved in that the anode is mounted on one end of the lever which is movably connected to the axle, fixed on the base and located at a distance from the anode is not more than 0.1 of its length, and the second end of the lever is located under its own gravity to control the length of the discharge gap, and the surface of the anode facing the cathode, has a spherical shape.

In addition, the technical result is achieved that control the length of the discharge gap is made in the form of a screw with the limb.

T is khnicheskie result in the claimed invention is achieved by the discharge is ignited between the planar cathode and anode, which is made in the form of a thin needle with a small radius. The spacing between the planar cathode and an acicular anode Lois selected less than the distance corresponding to the minimum of the Paschen curve Lmin. For this reason, the breakdown voltage of the gas U and binding discharge to the anode correspond to the minimum of the Paschen curve (U=UminL=Lmin)that occur above the tip of the needle at a distance of Lmin>Lo. A category like "chooses" its length so that when conditions change, it corresponded to stable burning near Lminthe minimum of the Paschen curve. Thus the voltage drop across the discharge gap has the same value (Umin), which weakly depends on the size of the gap and gas pressure.

In addition, the technical result is achieved in that the electrical capacity in this configuration of the electrodes is much less than if two flat electrodes.

All this allows to increase the stability and stabilization of discharge to sparks (failure mode of RC oscillation) when the currents around units and less mA and small bit intervals.

The essence of the invention illustrated by figure 1, Figure 2 and Figure 3, Figure 4, Figure 5 and 6

Figure 1 presents a diagram of the device to obtain a stable glow microdischarge atmosphere the th pressure.

Figure 2 presents an illustration of the behavior of the microdischarge when changing the discharge gap.

Figure 3 shows the form of the test monopulse and voltage pulses to the discharge.

Figure 4 presents the dependence of current and voltage discharge from a time when the gap between the needle-like anode and a flat cathode 6 µm and 1 µm.

Figure 5 presents the dependence of the voltage of combustion discharge from the gap between the planar cathode and a needle anode radius tip 25 microns at a current of about 4 mA.

Figure 6 presents the current-voltage characteristics of the discharge between the needle-like anode and a flat cathode at high currents and different bit intervals.

Figure 7 presents the dependence of the current and voltage of the discharge from the time when the gap between the planar anode and cathode in 10 µm.

The claimed invention (Figure 1) contains a constant voltage source (1)limiting the amount of current resistor (2)located on the base (5) is a flat cathode (3), the anode (4)made in the form of a thin needle and mounted on the end of lever (7), the controller (6) the length of the discharge gap between the cathode (3) and the anode (4) is made in the form of a screw with the limb and secured by a threaded connection on the basis of (5), the shaft (8), which provides a flexible connection between the lever (7) with base (5) and which RA is laid from the anode (4) at a distance of not more than 0.1 of the length of the lever (7).

Figure 2 presents an illustration of the behavior of the microdischarge when changing the discharge gap. This illustration shows that when the discharge gap is not less than the value corresponding to the minimum value of the breakdown voltage on the Paschen curve, the discharge parameters remain constant.

3 shows the waveforms of the input test monopulse and voltage pulses to the discharge. Shaper of monopulse consisted of high-voltage rectifier, charge storage capacity of 0.9 mF × 5 kV, and the discharge circuit. Applied to the input of the discharge device test monopulse voltage were of two types : symmetric and smoothly flowing back-to-back. To obtain pulse gradually falling back front (Fig.1 left) drive was discharged to the resistor 55Ω, the voltage which was applied to the investigated discharge through integrating the chain (1 kΩ, 4 μf) and a current limiting resistor R the value 364, 44, 6 or 2.74 kΩ. To obtain a pulse whose shape is close to symmetric (figure 1 right), the storage capacity of 0.3 mF discharged through the inductor L=0.2 H on the resistor 15 Ω, the voltage which was applied to the investigated discharge through a current limiting resistor.

Figure 4 presents as examples of specific implementations of the claimed invention according to the values of current and voltage is possible discharge from the time when the gap between the needle-like anode and a flat cathode 6 µm and 1 µm.

Figure 5 presents the dependence of the voltage of combustion discharge from the gap between the planar cathode and a needle anode radius tip 25 μm at a current of about 4 mA. This dependence clearly shows that the burning voltage of discharge is almost constant when we change the value of the discharge gap.

Figure 6 presents, as examples of specific implementations of the claimed invention, volt-ampere characteristics of the discharge between the needle-like anode and a flat cathode at high currents and different bit intervals.

Figure 7 presents the dependence of the current and voltage of the discharge from the time when the gap between the planar anode and cathode in 10 µm. The peculiarity of this case is that here the anode (4) not used a thin needle and a metal ball with a diameter of 11 mm. This anode with micron bit intervals can be considered as flat (quasiplastic).

The work of the claimed invention is as follows. Initially it is set up. For this you need to apply a small voltage to the input and turn the screw with the limb (6), slowly lower the lever (7) to the moment of occurrence of the current. Thus, between the anode (4) and the cathode (3) will be zero length. Then you need to raise the lever (7), setting the desired distance between the anode is m (4) and the cathode (3) (L~10 µm), and apply a high voltage (U~300 V) to the bit period through restrictive resistance (2). After the breakdown between an acicular anode and a flat cathode occurs stable glow discharge.

The claimed invention was tested in the laboratory, St. Petersburg state University in real-time.

The experiments confirmed the achievement of the technical result: improved stability glow microdischarge atmospheric pressure when the currents around units and less mA and interelectrode distances of the order of tens of µm and less.

Test modes the device to obtain a stable microdischarge atmospheric pressure are given in the specific examples.

Example 1.

The distance between the planar cathode (3) and needle electrodes (4) was 1 µm. According to the dependence of current and voltage discharge time (Figure 4) shows that the discharge is steadily lit when the currents around units mA or less (on the oscilloscope there are no abrupt changes of current and voltage).

Example 2.

The distance between the planar cathode (3) and needle electrodes (4) was 6 μm. According to the dependence of current and voltage discharge time (Figure 4) shows that the stable discharge is burning at a much higher currents than in the previous case, but the fall n the voltage on it almost has not changed. Example 3.

Discharges with currents up to 50 mA and different distances between the planar cathode (3) and needle electrodes (4). On presents the current-voltage characteristics (6) shows that at high currents the voltage drop across the discharge varies considerably, with an increase of the discharge gap (~100 µm) change in the voltage become larger.

It should be noted that when the currents of the order of several hundred mA pointed end of the anode for a period of approximately 1 s loses its shape due to erosion.

Example 4.

The discharge between the planar cathode (3) and a ball electrode (4) with a diameter of 11 mm (quasiplastic bit interval length of 10 µm). In quasilocal discharge gap dimension, as the burning glow discharge at the gap near the minimum of the Paschen curve and left its branches (10 µm or less) difficult as strongly influenced by the heterogeneity of the distribution of the gap and the surface roughness. There are multiple breakdowns already at voltages less than 330 V (Fig.7).

Breakdown and discharge with needle electrodes (4) near the minimum of the Paschen curve has a number of features. To the left of this minimum, as a breakdown and the discharge occur above the tip of the needle (Figure 2). The voltage drop has the same value in excess of 270 V (300-307 V), but weakly dependent on the gap and, accordingly, the gas pressure (Figure 5). If in weakly inhomogeneous gap when approaching the gap to 1 micron is a category of quite unstable, Yes even at low current, in this case due to the small interelectrode capacitance can be obtained relatively stable glow discharge with normal voltage drop at currents less than 1 mA (Figure 4). In addition, the sharp tip of the anode is not erodium at low currents.

The invention allows to obtain a stable microdischarge is quite simple and low-cost method that does not require vacuum installations, since the discharge burns in the atmosphere and does not require external injection of electrons, since the discharge is independent. The device can be used to create the plasma-chemical reactors and gas analyzers. It can also be applied in various methods of plasma spraying and alloying materials in areas of micron size. It is known, for example, that the alloying material surface under the action of the gas discharge is more intensive at higher pressures.

You can also use the claimed invention at the local plasma etching of materials in microelectronic technology. A device for the local plasma-chemical etching of the material [5] using high-frequency discharge. In contrast to the known device a claimed invention would allow the etching stable glow discharge DC ICRI is the R plots (of the order of units of microns) at atmospheric pressure.

Bibliography:

1. Simonchik L.V. V.I. Arkhipenko Safronov E.A. // Patent of Belarus BY 14068 C1 2011.02.28.

2. Robert N. Stark, Karl N. Schoenbach // United States Patent No.: US 6433480 B1, 2002.

3. Shalygina N.A. Sorokin A.P. // Patent of Russia RU 2297071 // Prototype.

4. Arkhipenko, V.I.; Kirillov, A.A.; Safronau, Y.A.; Simonchik, L.V. // DC atmospheric pressure glow microdischarges in the current range from microamps up to amperes // Eur. Phys. J. D 60, 455-463 (2010).

5. Abramov A.V., Dikarev SCI, Surovtsev I.S. // Russian Federation Patent RU 2091904, 27.09.1997.

1. Device to obtain a stable microdischarge atmospheric pressure, containing a constant voltage source connected through a limiting current resistor with a bit of gap between the flat cathode located on the base, and an anode mounted on the lever, which is supplied with control the length of the discharge gap between the cathode and the anode, wherein the anode is made in the form of needles with a corner radius of not more than 20 μm and located above the flat cathode at a distance not exceeding the numerical value of the magnitude of the discharge gap between the anode and the cathode, which corresponds to the Paschen law of the minimum breakdown voltage.

2. The device according to claim 1, characterized in that the anode is mounted on one end of the lever which is movably connected to the axle, fixed on the base and located at a distance from the anode, no more che is 0.1 of its length, and the second end of the lever is located under its own gravity to control the length of the discharge gap, and the surface of the anode facing the cathode, has a spherical shape.

3. The device according to claim 1, characterized in that the control the length of the discharge gap is made in the form of a screw with the limb.



 

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