RU2695541C1 - Device for inputting energy into gas-discharge plasma - Google Patents

Abstract

FIELD: astronautics.SUBSTANCE: invention relates to devices for high-frequency excitation and maintenance of discharge of gas-discharge plasma in ion sources, ionic engines of spacecrafts with conversion of energy of direct-current source into radio-frequency electromagnetic energy of inductor field interacting with plasma volume through mutual inductance. Device for inputting energy into gas-discharge plasma includes at least one power supply connected to first input of amplifier, outputs of which are connected in parallel to at least one capacitor of LC-circuit, connected to inductor of this circuit, interacting through mutual inductance with plasma, at least one communication element with an LC circuit, the output of which is connected to the second input of the amplifier. Set of amplifier, LC-circuit, plasma, inductively interconnected with inductor of LC-circuit, coupling element of LC-circuit with amplifier together form self-oscillator.EFFECT: high rate of reaction of the energy input device into the gas-discharge plasma to change the resonant frequency of the circuit with the inductor, associated with the volume of plasma through mutual inductance, and stabilization of field intensity inside volume of inductor at variations of plasma density or changes in speed of working medium supply to plasma at high efficiency of energy input into plasma, with insignificant number of elements.4 cl, 4 dwg

Description

IPC H01J 27/16

Device for introducing energy into a gas discharge plasma

The invention relates to devices for high-frequency excitation and maintenance of a discharge of a gas discharge plasma in ion sources, ion engines of spacecraft with the conversion of the energy of a constant voltage source into radio frequency electromagnetic energy of an inductor field interacting with a plasma volume through mutual inductance.

The well-known "Control system of an electric rocket engine" (Patent for the invention of the Russian Federation No. 2564154 IPC F03H 1/00 (2006.01), publ. 09/27/2015 Bull. No. 27). The system contains a microcontroller, a power amplifier, a power source of the power amplifier. The microcontroller is made with an analog-to-digital converter of input control signals, a digital-to-analog converter of output signals and a clock signal generator with a tunable frequency. The outputs of the power amplifier are connected via a communication line with an energy input device, which is made in the form of an inductor. The device is installed on the outside of the walls of the gas discharge chamber. Current and voltage sensors are included in the communication line with the energy input device. The outputs of the sensors are connected to the inputs of the phase detector and to the signal inputs of the microcontroller. The output of the phase detector is connected to the signal input of the microcontroller.

This system has two significant drawbacks:

1) To ensure the adjustment of the clock signal generator integrated in the microcontroller with a tunable frequency into resonance with a serial circuit from the coupling capacitor and inductor, an analog-digital phase locked loop (PLL) is used, which includes current and voltage sensors, a phase detector, an analog-to-digital converter , internal microprocessor units, software-closing phase feedback loop between the inductor current and the voltage on the inductor circuit, a signal generator with a tunable frequency . It is known that any system with an analog or analog-to-digital PLL for the stability of its operation requires a loop filter with a certain delay in time and corresponding amplitude-frequency and phase-frequency characteristics. The specified delay leads to a delayed response of the frequency and phase of the clock generator from the phase mismatch signal between the current and voltage of the respective sensors connected to the inductor circuit. A random or functionally caused mismatch in frequency and phase, even short-term, can significantly change the amplitude of the current in the inductor circuit, as a rule, reducing it due to departure from the resonance frequency, leading to undesirable consequences in the form, for example, of plasma quenching.

2) To ensure "efficient energy input into the gas discharge chamber of the engine", to maximize the efficiency, in addition to "phase matching of the current and voltage in the resonant circuit", the condition for the ratio of the resistances: the output resistance of the power amplifier Rout and the equivalent plasma resistance and inductor loss Rpl + Ri given to the output of the amplifier. It is generally accepted that the ratio Rout << Rpl + Ri should be satisfied. On the other hand, due to a change in the plasma density, the value of Rpl + Ri can vary significantly, leading to a corresponding change in the current in the circuit of the series resonant circuit of the inductor and a proportional change in the power consumption from the power source, which is especially pronounced in the absence of a discharge in the plasma when the given value of Rpl is equal to zero. To prevent undesirable significant variations in the current consumption from the power source, “automatic programmed and calculated control of the RF signal power” was applied by changing the voltage of the power amplifier’s power source, which is a complication of the system and does not exclude sharp changes in the inductor current and current consumption during transients, as upwards , and downward.

The closest in technical essence to the claimed device is "High-frequency generator for ion and electronic sources" (patent for the invention of the Russian Federation No. 2461908 IPC H01J27 / 00, published. 09/20/2012 Bull. No. 26), adopted as a prototype.

The prototype device consists of a discharge chamber for ionizable gas, wound around the discharge chamber of a communication coil for supplying the high-frequency energy necessary to excite the plasma, a coupling capacitor electrically connected to the communication coil, and a high-frequency generator electrically connected to the communication coil and together at least with one coupling capacitor forming a resonant circuit, and the high-frequency generator is equipped with a phase-locked loop (PLL) for automatic matching impedance of the resonant circuit, which makes it possible to operate the resonant circuit with a resonant frequency. The coupling coil is connected to the high-frequency generator and forms a parallel or series resonant circuit with the coupling capacitor of the high-frequency generator.

The device corrects phase errors in current and voltage in the output power stage of a high-frequency generator by automatically tracking the frequency and phase of the resonant frequency of the load circuit. The principle of this regulation is based on the fact that the PLL control circuit continuously compares the phase position of the sinusoidal high-frequency output current and the phase position of the generator output voltage using a digital phase detector and corrects the resulting phase error by adjusting the generator frequency using a voltage-controlled generator (VCO) , to the frequency of the resonant circuit, until the phase error becomes zero.

The protopip device has three significant drawbacks:

в резонансном контуре в 4000 раз и более в соответствии с экспоненциальной зависимостью

, 1) A phase error feedback system in the form of a PLL loop has a known inertia of frequency and phase adjustment, which is stated in the patent description up to 100 μs. A sharp change in plasma density, which can be caused by various reasons, leads to a change in the resonant frequency of the circuit and its difference from a delayed change in the frequency of the master VCO. For a high-frequency generator with a frequency of the order of 1-2 MHz, a delay of 100 μs is equivalent to 100-200 periods of this frequency, which, taking into account the real practical Q factor of the loaded resonant circuit Q _L = 10 ... 20 in the presence of a plasma, means a decrease in the current amplitude

in the resonant circuit 4000 times or more in accordance with the exponential dependence

,

;Where

;

   t is the time from the beginning of the transition process.

Despite the increase in the quality factor of the circuit with a decrease in the amplitude of the current in the circuit due to the resulting decrease in plasma density, the resulting decrease in the amplitude of the current of the circuit remains significant over the indicated time interval and can be accompanied by the quenching of the plasma discharge. The disadvantage described in this paragraph occurs primarily for the variant with a serial resonant circuit, which is described in the patent most fully and has explanations in most figures.

2) For the embodiment of the generator loaded on a parallel oscillatory circuit, according to the description of the patent, there are several contradictions that impede the actual implementation of the invention. For example, mention is made of the "phase position of the sinusoidal high-frequency output current and the phase position of the output voltage of the generator by means of a digital phase detector and corrects the resulting phase error by adjusting the frequency." For a parallel oscillatory circuit onto which a generator can be loaded (in accordance with paragraph 5 of the claims of the prototype invention), for which a sine wave form on it is a prerequisite for resonance, this explanation also means a sinusoidal voltage at the generator output, however, at the same time sinusoidal current and sinusoidal voltage, the output stage of the generator can only work in classes A, AB and B (conductivity angle ≥ 180 °), which are not used in the patent and are not mentioned, but in any case ae efficiency of the generator output stage may not exceed the theoretical limit of 78.5%, which is not consistent with the values mentioned in the patent in the 90-95% efficiency. The classes C, E, F indicated in the patent (claim 17) do not work with the sinusoidal output currents of the amplifier element, the current spectrum of such high-efficiency stages contains a wide range of harmonics, which differs sharply from the voltage spectrum on the oscillatory circuit. In the time domain, a separation of the phases of current and voltage is required for classes C, E, F to fulfill the conditions defined for working in these classes (see Sokal, N. Class-E RF Power AmpLfiers // QEX. - 2001).

3) For a device containing a frequency and phase adjustment loop and adjustable energy sources for adjusting the power of the RF generator, there are no elements providing stability of the field strength inside the discharge chamber during transients, for example, when a discharge is ignited, even if the PLL circuit is conditionally perfect to maintain coordination of the impedance of the resonant circuit brought to the output of the high-frequency generator. It is known that the impedance of a series resonant circuit can change several times under conditions of perfect matching when varying the plasma density or at the moment of its ignition, causing a proportional change in the field strength, which is a drawback.

None of the known technical solutions makes it possible to really quickly real-time work out the change in the resonant frequency of the coupling circuit with the plasma volume in combination with maintaining a stable field strength inside the discharge chamber with variations in the plasma density or changes in the velocity of the working fluid into the plasma.

The technical result of the invention is to increase the reaction rate of the device for introducing energy into a gas-discharge plasma to a change in the resonant frequency of the circuit with the inductor associated with the plasma volume through mutual inductance and stabilization of the field strength inside the volume filled by the working gas covered by the inductor, with variations in the plasma density or changes in the feed rate working fluid in the plasma with high efficiency of energy input into the plasma, with a small number of elements.

To achieve the above technical result, a device for inputting energy into a gas-discharge plasma, containing at least one power source connected to the first input of the amplifier, the output of which is connected to a parallel LC circuit, an inductor of this circuit interacting through mutual inductance with the plasma inside the volume inductor LC circuit, according to the invention, the second input of the amplifier through at least one coupling element is connected to a parallel LC circuit, and the combination of amplifier, LC circuit, element connected The LC circuit with the amplifier together form a self-oscillator.

Embodiments of the invention are illustrated by equivalent circuits shown in FIG. 1-3, where indicated:

1 - power source;

2 - auto generator;

3 - amplifier;

4 - LC circuit;

5 - mutual inductance;

6 - plasma;

7 - communication element.

For example, a capacitor connected in series to the resonant circuit of a parallel LC circuit or a transformer connected in parallel to an LC inductor, or a tap from part of the turns of the LC circuit inductor, or inductive coupling is used with the powerful field of the inductor by arranging in its near field an inductive component with nonzero mutual inductance to the LC circuit inductor.

The gas plasma input device of the present invention, one embodiment of which is shown in FIG. 1, works as follows.

From the power source 1, the voltage 3 is supplied to the amplifier 3, the amplifier then smoothly switches from the off state to the active class A mode with a smooth increase in the transfer coefficient from input to output. Upon reaching the required minimum transfer coefficient required by the conditions of self-excitation, oscillations with increasing amplitude begin to appear in the LC circuit 4 due to the positive feedback from the LC circuit 4 through the communication element 7 to the second input of the amplifier 3. The growing amplitude of the oscillations sequentially transfers the amplifier 3 from mode A to mode AB, then B, then C (or E, or F, or DE). For the proposed device, the sequence of changing the classes of operation of the amplifier from A to B is insignificant, but the only thing that is important is that in the steady state oscillation mode the amplifier operates in classes C, DE, E, F. After the oscillation amplitude is established in LC circuit 4, one of known methods (for example, as described in the patent of the Russian Federation No. 2564154), a gas discharge (plasma 6) is initiated inside the volume filled with the working gas covered by the inductor L.

The method of initiating a discharge is not the subject of this invention. After ignition of plasma 6, it develops like an avalanche with a sufficient calculated field strength inside the volume enclosed by inductor L. At the same time, the density of plasma 6 increases and its conductivity increases, an electric current arises in the volume of plasma 6, and at the same time, this plasma current interacts with inductor L through mutual inductance 5, there is a process of transformer energy transfer from the LC circuit 4 through the inductor L into plasma 6 inside the volume enveloped by inductor L.

At the same time, being a single process that proceeds with the propagation speed of electromagnetic interaction, the energy loss in the plasma 6 together with the reaction from the mutual inductance 5, which leads to the growth of the reactive component of the inductor current, is transformed into the primary circuit of the inductor L  in the form of a sharp decrease in the reduced loss resistance of the parallel oscillating LC circuit 4 and some decrease in its inductance.

The oscillator 2 instantly responds to an increase in losses in the LC circuit 4, providing an increase in portions of energy from the source at least once during the period of the oscillator frequency for single-cycle amplifier circuits 3 or twice during the period of the oscillator frequency for push-pull amplifier circuits 3. Also quickly the oscillator 2 responds to a decrease in the inductance of the inductor L, ensuring that oscillations are maintained precisely at the resonant frequency of the circuit without delay.

Figure 4 shows the process of the effect of the resulting connection through the mutual inductance of the inductor L with the plasma 6 at the time of its formation. Graphic images of the current in the inductor and the current in the plasma, which are the result of mathematical SPICE modeling of the electrical processes of the oscillator, demonstrate the absence of delays during the transient frequency change at the moment of plasma formation 6. At 100 μs, a gas discharge is conditionally “ignited” in the model, plasma 6 and the frequency / period of the oscillator changes in a very short time, almost instantly, i.e. for less than one period of oscillation.

In the figure of FIG. 4. two examples of the effect on the frequency depending on the plasma density are shown 6. With a high density and a large plasma current, the frequency changes more strongly, and the plasma current in phase is closer to the current of the inductor L. At a low density and a small plasma current, the frequency practically does not change, and the plasma current in phase differs from the inductor current L by almost 90 degrees. Figure 4 also demonstrates the practical absence of the influence of plasma 6 on the amplitude of the inductor current L at substantially different values of the current in the plasma.

Thus, the quick reaction of the proposed technical solution to a change in the plasma density in the inductor L in frequency and the absence of a significant effect of the presence / absence of plasma 6 on the current amplitude of the inductor L show the obvious superiority of this solution over the known technical solutions. A drop in the current amplitude when changing the resonant frequency in analog devices using a relatively slow PLL to adjust the loop to resonance can provoke plasma quenching during the initiation of a gas discharge. The specified phenomenon of plasma quenching is completely excluded in the proposed technical solution.

In another embodiment of the invention represented by the simplified diagram in FIG. 2, the oscillator amplifier 3 is shown as a push-pull circuit on high-speed MOSFET field effect transistors with n and p conduction channels. Here, the coupling element 7 with the circuit is a capacitor C2. The capacitor C3, connected in series with the inductor L, can act as an isolation capacitor and have a larger capacitance value than the capacitor C1, thereby not significantly affect the tuning frequency of the LC circuit. Or, on the contrary, when choosing the capacitance of the capacitor C3, approximately equal to the capacitance C1 within the order, to act as an impedance transformation element from the side of the inductor L to the output of the amplifier 3.

The series connection of capacitors C1-C3 according to this embodiment form the resonant capacitance of the LC circuit 4. The capacitor C2 has a dual function - as a coupling element 7 and as an element of the LC circuit 4. Self-excitation of such a self-oscillator is not provided. The generation of undamped oscillations of a given oscillator can be started by the “shock method,” for example, by abruptly charging or discharging one or several capacitors C1-C3 or in another way, for example, connected between the coupling element 7 (capacitor C2) in the direction of the gates of the field-effect transistors by an auxiliary generator of the initial excitation .

In a third embodiment of the invention represented by the simplified diagram of FIG. 3, the oscillator amplifier 3 is shown as a push-pull circuit on high-speed MOSFET field effect transistors of the same conductivity type.

For some embodiments of the invention, single-ended circuits with additional power supply circuit elements can be used as amplifier 3.

As an amplifier, any circuit can be used on any components suitable for this task to amplify the oscillation power at the resonant frequency of the LC circuit, taking into account the influence of the plasma, but preferably the amplifier should operate in the energy-efficient amplification class C, DE, E, F during steady-state oscillations.

Description of classes C, DE, E, F as well as A, B, AB can be found in the following sources:

 - Titz U., Schenk K. Semiconductor circuitry. Volume II - 12th ed .. - M.: DMK-Press, 2007;

- Albulet, M. RF Power AmpLfiers. - Noble PubLshing, 2001;

- Livshits, I. I. Transistor amplifiers in the D. mode. - L .: Energy, 1973 .;

 - Sokal, N. Class-E RF Power AmpLfiers // QEX. - 2001.

in Russian https://ru.wikipedia.org/wiki/Classification of electronic amplifiers

and in the English version of Wikipedia https://en.wikipedia.org/wiki/Power_ampLfier_classes .

Implemented on the basis of the invention, variants of a device for introducing energy into a gas-discharge plasma always operate at the resonant frequency of the energy input circuit or close to it. High efficiency of energy input into the plasma is ensured by the fact that the main reactive current of the LC circuit, which is 10 times or more the active current of equivalent losses in the plasma, flows only inside this circuit and does not close through the active elements of the amplifier and the power source.

Thus, the achievement of the technical result in the claimed device is due to:

- instant response of the oscillator to the tuning frequency of its LC circuit when the plasma density changes due to the absence of any significant delays from communication elements with the LC circuit to the amplifier, commensurate with the period of oscillation;

- parallel connection of the output of an amplifier operating in classes C, DE, E, F to a parallel oscillating LC circuit or its equivalent with sectioned switching on of capacitors (English tapped capacitor);

- parametric specification of the frequency and amplitude of the voltage and current in the LC circuit, and the amplitude of the inductor current and the strength of the field created by it do not depend on the equivalent plasma loss resistance reduced to the parallel LC circuit, or the dependence is very weak.

In addition, a significant reduction in the number of elements of the proposed technical solution, due to its structural simplicity, allows to reduce the complexity of manufacturing, reduce the cost of the device and increase its reliability.

Claims (4)

1. A device for introducing energy into a gas-discharge plasma containing at least one power source connected to the first input of the amplifier, the output of which is connected to a parallel LC circuit, an inductor of this circuit interacting through mutual inductance with the plasma inside the volume of the LC circuit inductor, characterized the fact that the second input of the amplifier through at least one communication element is connected to a parallel LC circuit, and the combination of the amplifier, LC circuit, communication element of the LC circuit with the amplifier together form an oscillator . 2. The device according to claim 1, characterized in that the amplifier is configured to operate in classes C, DE, E, F during steady-state oscillations. 3. The device according to claim 1, characterized in that the parallel LC circuit contains more than one capacitor. 4. The device according to claim 1, characterized in that the parallel LC circuit contains more than one inductor.

Images