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INVENTION
Patent of the Russian Federation RU2030849
HIGH-FREQUENCY PLASMA GENERATOR
Name of applicant: Tobolkin Alexander Savostyanovich
The name of the inventor: Tobolkin Alexander Savostyanovich
The name of the patent holder: Tobolkin Alexander Savostyanovich
Address for correspondence:
The effective date of the patent: 1992.03.31
Use: for obtaining plasma in low and high pressure gas media. SUMMARY OF THE INVENTION: The plasma generator comprises a generator lamp, for example a triode with an output capacitance not exceeding 7 pF, the anode of which is connected via a matching inductance of 2-4 μH and the capacitance is connected to a discharge electrode, and the grid of the lamp is connected to an earthed cathode through the RC circuit. The lamp anode is connected in parallel to a high-voltage DC power source. The capacitance and resistance of the RC circuit are adjustable in the range from 100 pF to 4 mF and from 1.5 MΩ to MΩ, respectively.
DESCRIPTION OF THE INVENTION
The invention relates to plasma technology and can be used to produce gas discharges with self-excitation in gaseous media of a complex chemical composition of low and high pressure.
A plasma generator is known, a plasma torch with an inductive coupling, intended for obtaining a plasma with a temperature 
9000 K for use in spectral analysis. In the mentioned patent, using an oscillator-type oscillator (LC-generator), providing sinusoidal oscillations of high frequency ( 40 MHz), create an inductive discharge in the dielectric chamber. The existence of such a discharge is determined by a narrow range of changes in the electro- and gas-dynamic characteristics of the system. To excite an independent discharge, an excitation system and adjustment means are provided, which complicates the design as a whole and reduces the service life of the plasma generator [1].
The closest of the known is a high-frequency plasma generator for obtaining a single-electrode (flare) discharge, described in [2] . This generator is built according to the scheme with a common cathode and autotransformer feedback. This circuit is characterized in that the cathode of the generator lamp is connected to the housing (grounded), a constant bias to the control grid is created by a constant resistor, and feedback to the grid is carried out through a serial CD circuit in which one end of the grid inductor is grounded together with one edge of the anode Inductance. The connection of the electrode with the other edge of the anode inductance is carried out by means of a matching inductor. The same edge of the anode inductance is connected to the anode of the generator lamp through the separation capacitance. In this scheme, the excitation of a single-electrode discharge is performed in a forced manner. In particular, with the help of a dielectric or metal rod, which is closed to the electrode at the time of discharge formation. Self-discharge burns in an open atmosphere. The power of the air discharge is (20-45) W. The change in power is realized through the control of the potential of the protective grid of the lamp.
The proposed high-frequency plasma generator, as well as known, contains a plasma-forming electrode connected to a generator lamp and a high-voltage DC source. The high-voltage source is connected via a choke to the anode of the generator lamp, and through a series-connected choke, capacitance and matching inductance with the electrode. In this case, the grid of the generator lamp is connected to the grounded cathode of the lamp by means of an RC circuit, which includes the resistance and capacitance connected in parallel.
Unlike the known one, in the proposed plasma generator, the electrode is electrically isolated from the RC circuit, the cathode and the lamp grid, the resistance and capacitance of the RC circuit being adjustable in magnitude. This RC circuit contains at least two parallel connected resistors connected via a switch to an adjustable resistance. In the proposed scheme, the generator lamp is made in the form of a triode with an output capacitance of not more than 7 pF, and the value of the matching inductance is chosen in the range from 2 to 4 μH. To obtain a variety of discharge generation regimes, the values of adjustable resistances and capacitances are selected in the range from 1.5 kOhm to 10 MΩ and from 100 pF to 4 mF, respectively.
The figure shows an equivalent circuit of the proposed plasma generator.
The circuit contains a VLI generator triode, cathode 1, which is connected directly to the body (ground). With a constant current source (not shown in the diagram), the anode 2 is connected through a reactor L dp 3. The choke 3 and the capacitance 4 are a filter for the high-frequency component of the anode voltage. The separation of the DC and AC currents in the anode and grid circuits is provided by the throttle L dr 3, the separating capacitors C p 5, C 1 6, the capacitor bank 7 and the variable resistor R 1 8. The single-electrode discharge 9 through the electrode 10, matching the inductance L 1 11 and The separation capacitance C p 5 is connected to the anode 2.
The capacitor bank 7 is assembled from parallel capacitances C 2 , C 3 ... C n-1 , C n with an arbitrary value in the range of 50 pF to 4 μF, one terminal of which is connected to the housing and the other via switch 12 - to the lamp grid 13, with the output of the variable capacitance C 1 6 and with one of the terminals of the resistor R 1 8. Another terminal of the resistor R 1 8 is connected via a switch 14 to a block of parallel connected resistors 15-R 2 , R 3 ... R n-1 , R n , one output of which is connected to the terminals of the switch, and the other - to the case. The resistance block 15 consists of constant resistances in the range from 1.5 kΩ to 10 MΩ. The change in resistance R 1 8 is carried out in the range (0.2-47) kOhm. The capacitance C 1 6 varies in the range of 50-2000 pF. The second terminal of the capacitor C 1 6 is connected to the housing. The free end of the electrode 10 is pointed with a radius of curvature (0.5-0.1) mm.
The plasma generator works as follows. The voltage is applied to the glow of the VLI lamp (not shown in the diagram). The VLI lamp is heated for (0.5-1) min. Then a constant anode voltage U a is applied in the range (1800-3500) V through the throttle 3 to the anode 2 of the lamp. Due to the auto-displacement created by the variable resistor and any resistance R n of the resistance block 15 (depending on the position of the switch 14) and due to the nonlinear active element - the VLI generator lamp, converting the DC voltage into an alternating voltage, the oscillator generates self-oscillations that lead to self-excitation Of the single-electrode discharge 9 from the rod electrode 10. By changing the resistance in the grid circuit with the variable resistance R 1 8 or by a discrete change with the switch 14, and by smoothly changing the capacitance C 1 6 or by a discrete change with the switch 12, the time constant of the parallel RC circuit (R RC), which controls the amplitude-frequency characteristics of the lamp. The operating mode of the plasma generator differs significantly from the known LC generators producing sinusoidal oscillations of constant amplitude. The proposed generator performs continuous operation in the self-modulation mode, when voltage impulses with a duration of (2-50) μs and a repetition rate of 0.2 to 10 5 Hz are superimposed on sinusoidal carrier waves with a frequency of (20-40) MHz. Moreover, in the interval between pulses, the amplitude of the carrier is not zero, but is (0.02-0.03) of the maximum amplitude in the pulse. Therefore, the term "Self-modulation" is introduced taking into account the specific features of the functioning of the plasma generator, which lacks a specially created modulator, which is necessary for creating modulated oscillations. The specific nature of the operation is characterized by the fact that it is in the range of the proposed parameters of the circuit that spontaneously arises (without external influence) and that modulation of high-frequency oscillations continuously results in self-excitation at low anode voltage (for self-excitation of a discharge in LC generators, voltages of at least 8 kV are required) of a single-electrode discharge And its steady burning. A wide range of control ensures the discharge in a variety of forms (single-channel, multi-cord, diffuse, branch-like, etc.) and different power (in the range 1-40 W). The discharge is excited from one or several tip electrodes. The increased stability of the discharge makes it possible to generate it in flue gases, flames, in vapor-gas mixtures, etc. There is a superficial distribution of the discharge along dielectric materials, self-compression when the second end of the discharge closes on the metal. In some modes, the discharge exists in dielectric capillaries with an internal diameter of 20 μm or more, while the discharge length is from 1 to 4 cm.
The specific features of the new discharge generation regimes consist in the fact that plasma with an extremely low temperature (500-1500) K always arises. At this temperature, there is a slight erosion of the electrode material or is completely absent. In the latter case, the service life of the plasma generator is determined by the life of the generator lamp.
CLAIM
1. A HIGH-FREQUENCY PLASMA GENERATOR , comprising a plasma-forming electrode connected to a generator lamp and a high-voltage DC source which is connected through a choke to the anode of the generator lamp, and through a series-connected choke, capacitance and matching inductance to the electrode, wherein the generator lamp grid is connected to Grounded cathode through an RC circuit including parallelly connected resistance and capacitance, characterized in that the electrode is electrically insulated from the RC circuit, the cathode and the lamp grid.
2. Generator according to claim 1, characterized in that the generator lamp is designed as a triode with an output capacitance of not more than 7nΦ, and the value of the matching inductance is selected in the range 2-4 μG.
3. The generator according to claims 1 and 2, characterized in that the resistance and capacitance of the RC circuit are adjustable in magnitude, and the resistance and capacitance values are selected in the ranges of 1.5 kΩ to 10 MΩ and 100 nF to 4 μF, respectively.
print version
Date of publication 18.12.2006гг
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