RU2784248C1 - Device for increasing thrust in an electric ion thruster - Google Patents

Abstract

FIELD: rocket technology.

SUBSTANCE: invention relates to rocket technology, in particular to electric ion engines equipped with a device for increasing the thrust force by accelerating ions in a constant electric field. The device contains an ionization system, a decelerating electrode and a multibeam ion-optical system of n sequentially installed flat accelerating electrodes with span holes connected to sources of constant accelerating voltage. The cathode of the previous pair is the anode of the next pair of electrodes. The distance between the first pair of electrodes is chosen to be as small as possible when focusing the ion beams, without electrical breakdown and deformations leading to contact of the accelerating electrodes. The distance between the electrodes of the i-th pair is selected from the condition of ensuring the maximum current density not lower than for the 1st pair.

EFFECT: calculations have shown that the proposed device makes it possible to increase the midship thrust from 2 to 500 times, depending on the value of the specific charge at an exhaust velocity of 50 to 500 km/s.

2 cl, 3 dwg, 1 tbl

Description

The invention relates to rocket technology, in particular to electric ion engines equipped with a device for increasing the thrust force by accelerating ions in a constant electric field.

A device is known for creating an adjustable thrust force in an electric rocket engine (patent for invention RU No. 2704523, IPC: F03H 1/00) and achieving ion flow velocities of more than 200 km/s due to additional acceleration of ions in a high-frequency field. In this device, to achieve a higher and continuously adjustable speed of the ion jet in the accelerating system, with a reduced, compared with the prototype (patent for utility model RU No. 73405, IPC: F03H 1/00, B64G 1/40), the value of the constant accelerating voltage , as well as in order to achieve greater durability of the device, additional, sequentially alternating, control and focusing electrodes with span holes were introduced into the IOS.

Device for creating adjustable thrust in an electric rocket engine operates as follows. The gas-discharge chamber is filled with working gas. After initiating a gas discharge, for example, using microwave energy, ions are extracted from the gas discharge chamber using the first two electrodes of the IOS (screen and input accelerating electrode). The final acceleration of the multipath ion flow by a constant electric field occurs in the gap between the accelerating electrode and the shielding electrode, which is at zero potential. Next, the ion beams pass through the holes of oppositely charged electrodes, forming a system of single lenses.

The regulation of the magnitude of the traction force is carried out due to their additional acceleration in a strong high-frequency electric field, the magnitude of which is smoothly changed. RF acceleration of ion bunches is carried out in the output section, the interaction space in which is formed by three consecutive double high-frequency gaps formed between the ends of the control and shielding electrodes. The phase of the signals in this line is controlled using an additional phase shifter so that the total RF voltage acting in the acceleration region is phase-synchronized with the phase of ion bunches formed in the input section of the device due to high-speed modulation and grouping of ions by a non-sinusoidal sinusoidal signal.

The disadvantage of the device is the need for phase synchronization of the total RF voltage with the phase of the ion bunches. Disruption of such synchronization will reduce the effectiveness of this device.

The device is known ) ion thruster, four-grid Dual-Stage (DS4G), which was successfully tested by the European Space Agency (ESA) at the Electric Propulsion Laboratory in the Netherlands. In terms of power, it is 10 times higher than the existing ion counterparts and 4 times the prototype ones, and develops specific thrust up to 210 km/s.

A typical ion thruster consists of three grids, each with a thousand millimeter holes. They are connected to a chamber containing charged particles. The first operates under a voltage of thousands of volts, and the second - under a low voltage. The difference creates an electric field that extracts ions from the fuel reservoir and accelerates them out. The third grid stops the electrons flying back into the ion beam. Ideally, the voltage difference between the two networks should be as large as possible to increase the speed of the ions as well as fuel efficiency. But when the difference approaches 5 thousand volts, the ions collide with the second grid and begin to destroy it. The new project has four grids. Ions are extracted from the reservoir using two grids placed side by side under a voltage of 3-5 thousand volts. Acceleration occurs in the second stage, when the extracted ions are transferred from the second grid to the third, which is under a very high voltage. And finally, the last stage - with low voltage - prevents electrons from getting back. The system allows creating a voltage difference of up to 30 thousand volts between two sets of grids and does not damage them.

The disadvantage of this device is that the ions are accelerated by one pair of electrodes (between the second and third grid). And the first and second grids are used to extract ions from the reservoir, but do not provide the maximum possible current density. As a result, the device realizes a low value of the product of the current density and the outflow velocity.

This device is the closest analogue to the claimed technical solution for increasing the thrust force in an electric ion engine.

The purpose of the proposed device is to increase the thrust force of the ion engine while maintaining high values of the specific impulse.

A device for increasing the thrust force in an electric ion engine, which contains an ionization system, a decelerating electrode, and a multibeam ion-optical system (IOS) consisting of n sequentially installed flat accelerating electrodes with span holes connected in series with constant accelerating voltage sources, and the cathode of the previous of the pair is the anode of the next pair of flat electrodes with span holes, and the distance between the first pair of electrodes is chosen as small as possible, when focusing ion beams, as well as the absence of electrical breakdown and deformations leading to contact of the accelerating electrodes in order to provide the maximum possible current density for a given ratio of specific charge is the ratio of the charge of an ion to its mass. In this case, the voltage between each pair of electrodes is limited by the magnitude of the electrostatic field strength, at which there is no breakdown between the electrodes. The current density of the charged jet is formed by the first pair of electrodes; between the ion emitting electrode (positive ion anode) and the first electrode. Given the limitations associated with the maximum allowable field strength, the voltage applied to the first pair of electrodes does not allow high charged jet velocities to be achieved. Achieving a high flow velocity is ensured by the acceleration of the charged jet by subsequent pairs of electrodes. In this case, the maximum possible current density between subsequent pairs of electrodes is not less than the current density of the first pair of electrodes, which is achieved by selecting the distance between the pairs of electrodes and the voltage applied to the pairs of electrodes. If there are technical restrictions on the maximum possible applied voltage, the distance between the pairs of electrodes is selected from the conditions of ensuring the maximum possible voltage applied to the pair of electrodes and ensuring the maximum possible current density not lower than the current density obtained on the first pair of electrodes.

When using the invention, a technical result is achieved, namely, a higher thrust force of the ion engine while providing high speeds of the charged jet.

In FIG. 1 shows the dependence of the maximum current density, related to the square root of the specific charge, on the distance between the electrodes and the initial speed of the charges w _a =100 ^m / _s .

In FIG. Figure 2 shows a schematic diagram of the acceleration of ions, including n series-installed flat accelerating electrodes with span holes, connected in series with sources of constant accelerating voltage. In this diagram, the cathode of the previous pair is the anode of the next pair of flat accelerating electrodes.

In FIG. Figure 3 shows a schematic diagram of the acceleration of ions, including n galvanically broken pairs of series-mounted flat accelerating electrodes with span holes.

The inventive device contains an ionization system, a neutralization system, and a decelerating electrode. A distinctive feature is the multi-beam IOS, which consists of n sequentially installed flat accelerating electrodes with span holes. The first pair of electrodes is used to create the maximum possible current density, the subsequent ones - to achieve the outflow rate.

The thrust of an ion engine, expressed in terms of current density and specific charge of ions, is equal to

where

- удельный заряд ионов;

- specific charge of ions;

q is the charge of the ion;

m is the mass of one charged particle;

S is the cross-sectional area of the jet;

W _ist - speed of expiration.

Dividing (1) by S, we obtain an expression for midship thrust (jet cross-sectional area thrust)

As can be seen from (2), the midship thrust is proportional to the current density and outflow velocity and inversely proportional to the specific charge.

The maximum current density that can be achieved between the anode and cathode is given in the book by O.N. Favorsky, V.V. Fishgoit, E.I. Yantovsky, Fundamentals of the theory of space electric propulsion systems. Under. ed. HE. Favorsky. Proc. allowance for universities. M., "Higher School", 1970. 488 p.:

here

ε ₀ =8.85×10 ^-12 - dielectric constant;

- относительная скорость среды у анода (в точке х=0);

- relative velocity of the medium at the anode (at the point x=0);

w _to - the speed of the medium at the cathode (at the point x=L);

L is the distance between the anode and the cathode;

- удельный заряд.

- specific charge.

The current density, expressed in terms of the ion velocity at the anode, the anode potential, or the field strength, will have the form

напряженность поля между анодом и катодом при отсутствии заряженной среды.here

field strength between anode and cathode in the absence of a charged medium.

From those shown in Fig. 1 data shows that the maximum possible density is higher, the smaller the distance between the electrodes. The influence of the distance between the electrodes on the value of the midship thrust is the same as on the value of the maximum current density.

From the above data, it is obvious that in order to increase the engine thrust, it is necessary to reduce the distance between the electrodes, which leads to an increase in the current density, but a decrease in the voltage accelerating the charges, which is associated with the need to provide a field strength value at which there is no electrical breakdown between the electrodes.

In the claimed device for accelerating charges, it is proposed to use a system of electrodes installed in series, the voltage and distance between which provide the maximum possible current density not lower than the first pair of electrodes (Fig. 2). The total ion acceleration voltage is determined by

here ΔU _i - the voltage applied to the i-th pair of electrodes, ΔU _Σ - the total voltage required to accelerate the ions with a given specific charge to the desired speed of expiration. The first pair of electrodes provides the maximum possible current density for the ions (or charges) used. For an ideal electrostatic motor, which has no leakage currents associated with the ingress of charges on the accelerating electrodes, the current density remains constant until the jet is neutralized. Subsequent pairs of electrodes provide acceleration of charged particles to the required speed. At the same time, on each next pair of electrodes, the condition for ensuring the electric field strength, in which there is no breakdown between the electrodes, must be met, as well as the distance between the electrodes, providing the maximum possible current density not less than for the first pair of accelerating electrodes.

The distance between the electrodes of the i-th pair, providing the maximum possible current density is not less than for the first pair of accelerating electrodes, is determined by the numerical solution of the inequality

Structurally, the multigrid scheme can be implemented as shown in Fig. 2, where the cathode of the previous pair is the anode of the next pair of accelerating electrodes, and in the form of galvanically broken pairs of FIG. 3.

In the first variant, the advantage is some reduction in the total length of the accelerating system. The disadvantage of the first scheme is the need to apply the total voltage ΔU _Σ between the first (leftmost) anode and the last (rightmost) cathode, as well as to use a voltage divider between the intermediate grids to provide the required voltage on the internal pairs of accelerating electrodes. The second variant, with some increase in the length of the accelerating system, makes it possible to apply independent voltage sources to pairs of accelerating electrodes. This removes the requirement to have a high voltage source ΔU _Σ .

The inventive device for increasing the thrust force in an electric ion engine operates as follows:

After ionization, the electrically charged medium enters the first pair of accelerating electrodes, which has a potential difference ΔU ₁ . An electrically charged medium is an uneven space charge that affects the potential distribution between the electrodes. The potential distribution function between the electrodes is a curve with a maximum. Thus, the charged medium first decelerates until it reaches the point of maximum potential, after which the medium accelerates. In the book of O.N. Favorsky and others (O.N. Favorsky, V.V. Fishgoyt, E.I. Yantovsky, Fundamentals of the theory of space electric propulsion systems. Edited by O.N. Favorsky. Textbook for universities. M., " Higher school", 1970. 488 p.) shows the dependence of the maximum possible current density on the potential difference between the accelerating electrodes, the distance between them, the magnitude of the specific charge and the initial velocity of the ions

как обеспечивающую отсутствие пробоя между электродами (согласно https://yandex.ru/search/?text=Напряженность+пробоя+электорческого+поля&lr=2&clid=1955454&win=2301, [https://studopedia.net/14_38080_probivnoe-napryazhenie-i-probivnaya-napryazhennost.html] величина пробоя в воздухе составляет

, для расстояния между ускоряющими электродами в 10 мм (ускоряющая разность потенциалов 10⁴ В) и начальной скорости

получаем:The calculations for cesium (k _q,Cs =7.25⋅10 ⁵ ) and lithium (k _q,Li =1.39⋅10 ⁷ ) ions are also given there. Setting the field strength between the electrodes in

as ensuring the absence of breakdown between the electrodes (according to https://yandex.ru/search/?text=Strength+breakdown+electric+field&lr=2&clid=1955454&win=2301, [https://studopedia.net/14_38080_probivnoe-napryazhenie-i- probivnaya-napryazhennost.html] the amount of breakdown in air is

, for a distance between the accelerating electrodes of 10 mm (accelerating potential difference of 10 ⁴ V) and an initial speed

we get:

скорость истечения

Р_мид=7.867 Па;for cesium

expiration rate

P _mid = 7.867 Pa;

скорость истечения

Р_мид=7.867 Па.for lithium

expiration rate

P _mid = 7.867 Pa.

When using the claimed acceleration scheme for the same ions and values of the expiration velocities, the following data were obtained:

скорость истечения

Р_мид=24.88 Па;for cesium

expiration rate

P _mid = 24.88 Pa;

скорость истечения

Р_мид=24.88 Па.for lithium

expiration rate

P _mid = 24.88 Pa.

Thus, the claimed overclocking scheme increases the midship thrust by 3.16 times compared to the classical overclocking scheme. This required 3 pairs of accelerating electrodes. The table below shows the parameters of the accelerating systems of the proposed scheme

The result is achieved due to the fact that conditions are created on the first pair of accelerating electrodes to achieve the maximum possible current density, i.e. charged medium density. In this case, the speed after passing the first pair of accelerating electrodes will be relatively small. And the achievement of a high velocity of the expiration is achieved due to acceleration by subsequent pairs of accelerating electrodes, the potential difference and the distance between which are chosen in such a way that the maximum possible current density would not be lower than for the first pair of accelerating electrodes. The current density in the entire accelerating system remains constant in the absence of leakage currents (no defocusing of ion beams), in the absence of pulsations, since constant supply of the working fluid - ions - and constant (not pulsating) voltages between the electrodes.

необходимо суммарное ускоряющее напряжение 158.63 кВ.It can be seen from the given data that the accelerating voltage applied to the next pair of accelerating electrodes is less than the total accelerating voltage required to achieve the same exhaust velocity as in the classical scheme. This allows you to significantly increase the rate of expiration in the proposed scheme. For example, for lithium ions, the outflow rate

a total accelerating voltage of 158.63 kV is required.

In this case, for the classical (two-electrode) overclocking scheme, we will have:

for the claimed overclocking scheme:

which is 12.6 times higher than for the classical scheme.

были оценены значения плотности тока, начальной скорости зарядов и расстояния между первой парой пластин (в описании аналога эти параметры не указаны). Были получены следующие значения:For comparison with the closest analogue, which used xenon ions, the specific charge of which is equal to

the values of the current density, the initial velocity of the charges, and the distance between the first pair of plates were estimated (these parameters are not indicated in the description of the analogue). The following values were obtained:

the distance between the first pair of plates - 5 mm;

initial speed of charges -

With these parameters, the increase in current density (and midship thrust) of the analog compared to the classic device is 2.75.

The inventive device, while maintaining the same expiration rate, makes it possible to achieve an increase in current density (middle thrust) 2.25-3.19 times higher than for the closest analogue. The midship thrust efficiency can be further increased compared to its counterpart by achieving a higher exhaust velocity. The current density in the proposed device remains unchanged, because the parameters of the first pair of accelerating electrodes do not change.

может быть достигнута скорость истечения в

при мидельной тяге 4334 Па, что в 551 раз выше, чем для классического устройства. При этом суммарное ускоряющее напряжение составляет 5 MB, но для заявляемого устройства за счет использования последовательно установленных ускоряющих пар электродов ускоряющее напряжение, подаваемое на эти пары может не превышать максимально технически возможного напряжения, обеспечиваемого энергоустановкой, например, 10 кВ.The proposed device provides even greater efficiency when accelerating charged particles having a relatively low specific charge. For example, for charged particles with a specific charge

flow rate can be reached

with a midship thrust of 4334 Pa, which is 551 times higher than for the classic device. In this case, the total accelerating voltage is 5 MB, but for the claimed device, due to the use of accelerating pairs of electrodes installed in series, the accelerating voltage applied to these pairs may not exceed the maximum technically possible voltage provided by the power plant, for example, 10 kV.

Calculations have shown that the proposed ion acceleration scheme makes it possible to obtain an increase in midship thrust compared to the classical acceleration scheme from 2 to 500 times, depending on the value of the specific charge at an exhaust velocity of 50 to 500 ^km / _s , which is approximately 2 times higher than the given value for closest analogue.

Claims (11)

1. A device for increasing the thrust force in an electric ion engine, which contains an ionization system, a slowing electrode and a multibeam ion-optical system (IOS) consisting of n sequentially installed flat accelerating electrodes with span holes connected in series with constant accelerating voltage sources, and the cathode of the previous pair is the anode of the next pair of flat electrodes with span holes, characterized in that the distance between the first pair of electrodes is chosen as small as possible for focusing ion beams, and also for the absence of electrical breakdown and deformations leading to contact of the accelerating electrodes, and the distance between the electrodes i - th pair is determined by the numerical solution of the system of inequalities

here

- maximum current density for the 1st pair;

- the maximum allowable field strength between the plates, ensuring the absence of breakdown between the electrodes;

- specific charge (the ratio of the charge to its mass);

is the absolute velocity of ions at the anode;

is the distance between the anode and cathode;

- dielectric constant;

- the maximum accelerating voltage of the device. 2. A device for increasing the thrust force in an electric ion engine according to claim 1, characterized in that the system of flat accelerating electrodes is a galvanically broken pair of electrodes.

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