RU2543103C2 - Ion engine - Google Patents

Abstract

FIELD: power industry.

SUBSTANCE: invention relates to power industry. An ion engine containing a housing, and a gas discharge chamber and an ion-optic system and a cathode-neutraliser installed on the housing, which are rigidly fixed on the outer surface of the housing, with that, the housing of the ion engine has a toroid shape, with that, the cathode-neutraliser is installed on the central axis of the housing, electrodes of the ion-optic system and the gas discharge chamber has an annular shape, with that, their internal surfaces are rigidly fixed along the perimeter on the internal surface of the housing of the ion engine.

EFFECT: invention allows considerable increase of vibration strength of electrodes, stability of inter-electrode gaps, as well as increase of efficiency.

1 dwg

Description

The invention relates to the field of electric rocket engines (ERE).

Among the various types of electric rocket engines (ERE) in ion engines (ID), the maximum specific thrust impulse can be achieved.

The operating principle of an ID is based on the extraction of ions from an ionized plasma and their further electrostatic acceleration. In such an engine, the processes of ionization and acceleration are completely separated. According to the method of transferring the working fluid (RT) to the ionized state, the IDs are divided into 3 groups: on the basis of a direct current discharge, an RF discharge, or a microwave discharge.

Medium power IDs are widely used abroad. To date, a wide range of such engines has been developed. In the USA, IDs with a direct current discharge are developed, manufactured, and operated [1].

A feature of German engines is that RT ionization occurs in an RF discharge.

In Japanese engines, xenon ionization occurs in a microwave discharge.

One of the main nodes of the ID is the ion-optical system (IOS).

Known ID [1 - p.240], containing a gas discharge chamber (GRK), having the shape of a cylinder with a conical rear wall. Anodes are attached to the walls of the GRK through insulators. The magnetic field is created using electromagnets located outside the GRK. The magnetic field configuration is set by three pole tips. Inside the cathode pole piece is a hollow cathode. The emitter is from lanthanum hexaboride. The working fluid (xenon) is supplied to the GRK through a collector located in the IOS region, which consists of a plasma, accelerating and slowing-down electrodes. The retarding electrode is made in the form of a ring covering the entire ion beam. Plasma and accelerating electrodes with a thickness of 0.5 and 1.0 mm have the shape of a sphere segment with a large radius and have an initial deflection directed outward of the GRK. Outside the IOS is a cathode-converter.

The disadvantage of an ID with a direct current discharge is that it has a high potential: anode, GRK wall, a cathode with power sources connected to it, an IOS screen grid and cables. It is technically difficult to provide reliable electrical isolation of these circuits from the case and in the power supply and control system (SPU). In addition, a DC motor is structurally more complex than the other two types. For its operation, the cathode of the GRK is required, the current of which should be 7-10 times higher than the current of the cathode-converter. For an engine with a power of (30-70) kW with an ion current (10-20) A, a discharge current cathode (70-150) A is required. Creating such a high-current cathode is a rather complicated engineering task. Cathodes and converters, especially high current ones, have a limited resource. So, the operating time of the cathodes-converters of the Design Bureau “Fakel” (for SPD-100 by 4.5 A) does not exceed 9000 hours [1 - p. 33]. Therefore, redundancy of both cathodes and neutralizing cathodes will be required, but it is practically impossible to place several cathodes in the gas distribution system, since the cathode should be located along the longitudinal axis of the engine.

The most powerful ion engine to date is the laboratory model of the NEXIS engine with power up to 25 kW. To increase its power by a factor of 2–3 (necessary for the marching tasks of deep space), it is necessary to proportionally increase the IOS area. As a result, at a power of 50 kW, the diameter of the model should be about 0.8 m, at 75 kW - 1 m. A membrane of this diameter, fixed on the periphery, has low vibration resistance.

The prototype is an ion engine with an RF discharge, for example, a RIT-ID with radio-frequency ionization [2]. In the general case, an ion engine, for example, RIT-22, contains: 2- or 3-grid IOS (circular cross-section); a cathode-converter installed outside the ID housing; GRK from a dielectric material with a small cosine of losses; an inductor in the form of a spiral made of copper wire; xenon supply unit, with gas-electric isolation; housing and radio frequency generator.

In a radio-frequency engine, the only element at high potential is the screen grid (with a wire connected to it), which is located inside the dielectric GRK, which, in addition, performs a protective function. Therefore, special measures to ensure the dielectric strength of the insulation of this mesh is not required. The remaining engine elements have relatively low potentials.

In the developed large-sized ID RIT-45 with a capacity of 35 kW, the diameter of the IOS will be about 500 mm, in the large-sized ID ERD-50 with a power of 30 kW, the characteristic size of the IOS (round section) is 700 mm [1]. Moreover, the IOS electrodes are traditionally made in the form of thin (0.4 ... 1.0 mm thick) plates perforated up to 35,000 holes. Moreover, the tolerance on the accuracy of the holes in the two electrodes is usually not more than 0.02 mm. The vibration strength of such electrodes, which is a thin-walled membrane of a large area, perforated by tens of thousands of holes embedded around a circumference, is quite small. In addition, the calculation of the thermal deformation of the IOS electrodes in a large ID taking into account the geometry, temperature fields and thermal properties of materials shows that providing acceptable thermal deformations of the grids is a rather complicated task. In this sense, it is preferable to make the grid of a homogeneous material - carbon, which has the lowest coefficient of linear expansion - minus 0.3 · 10 ^-6 ° C ^-1 . Since the electrodes are almost isothermal, they will repeat the shape of each other. When using dissimilar mesh materials, it is extremely difficult to achieve the stability of interelectrode gaps in the range of (0.5-1.0) mm.

The disadvantage of such a large ID is a significant decrease in the vibration resistance of the IOS, which is a huge perforated membrane. In addition, the asymmetric installation of the cathode-converter outside the IOS leads to a decrease in the efficiency of the ID by 5-7% [3].

The objective of the invention is to increase the vibration resistance and reliability of operation by ensuring the stability of the interelectrode gaps of the IOS, as well as increasing the efficiency of large-sized ID.

This problem is solved as follows.

In a large-sized ion engine containing a housing, a gas discharge chamber and an ion-optical system and a cathode-converter mounted rigidly on the outer surface of the casing are mounted on the casing, while the casing of the ionic motor has a mountain shape, with the cathode-neutralizer mounted on the central axis of the casing, electrodes the ion-optical system and the gas discharge chamber are made in the form of an annular shape, while their inner surfaces around the perimeter are rigidly fixed to the inner surface of the housing of the ion motor la.

Figure 1 presents a General view of the ID, which consists of enclosed in an annular body 6 of an annular 3-grid IOS 1 located along the central axis of the cathode-converter 2 and an annular GRK 3 made of a dielectric material with a small cosine of losses. The inductor 4 is made in the form of a spiral of copper wire and an annular xenon supply unit 5 with gas-electric isolation. In this case, the IOS 1 consists of a ring: a shield electrode 7 with a current lead 8, an accelerating electrode 9 with a current lead 10 and a slowdown electrode 11, electrically separated by insulators 12 and embedded in the housing from the outside and inside. The housing 6 is perforated with holes 13.

To start the engine, the xenon flow rate is fed to the cathode-converter 2 and the annular xenon supply unit 5 of the gas distribution unit 3. After starting the heating of the cathode-converter 2, a discharge is initiated in it and the RF generator supplying the inductor 4 is switched on. Electrons through the IOS 1 penetrate the cavity of the gas distribution station 3 where initiate the high-frequency discharge. Then, voltage is applied to the electrodes 7, 9, 11 of the IOS 1 and the engine goes into the nominal operating mode. A feature of the engine of such a scheme is that only the screen electrode 7 of the IOS 1 is at high potential, since the discharge in the GRK 3 is electrodeless.

Consider two membranes of the same material, of the same thickness, differing only in diameter.

The circular frequency of natural vibrations of the membrane is calculated by the formula

, $${\lambda }^2=35\frac{P}{m\cdot R^{\mathrm{four}}}$$

,

where λ is the circular frequency;

P is the cylindrical stiffness of the membrane;

m is the mass of a unit area of the membrane;

R is the radius of the membrane.

The cylindrical stiffness of the membrane is described as follows:

, $$P=\frac{E\cdot {\mathrm{<figure-callout\; id="3"\; label="h"\; filenames="00000004.png"\; state="\{\{state\}\}">h</figure-callout>}}^3}{12\left(l-{\mu }^2\right)}$$

,

where E is Young's modulus;

h is the thickness of the membrane;

µ is the Poisson's ratio.

. То есть собственная частота колебаний мембраны обратно пропорциональна ее площади. Сетки ИОС ионного двигателя в упрощенном виде можно представить в виде мембран. В ионном двигателе, в котором площадь оптики в два раза больше, чем у другого ИД, собственная частота сеток в два раза ниже. При одинаковом уровне перегрузок вдвое возрастет амплитуда перемещений, что увеличивает риск повреждения (поломок) сеток.As a result, we get: $$\lambda ~\frac{\mathrm{one}}{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="00000004.png"\; state="\{\{state\}\}">R</figure-callout>}}^2}$$

. That is, the natural frequency of membrane vibrations is inversely proportional to its area. IOS nets of the ion engine in a simplified form can be represented in the form of membranes. In an ion engine, in which the optics area is two times larger than that of another ID, the natural frequency of the grids is two times lower. With the same level of overloads, the amplitude of displacements doubles, which increases the risk of damage (breakdown) of the grids.

Thus, if it is necessary to significantly increase engine power (the area of its IOS), it is preferable to use the proposed ID. In it, the IOS electrodes are fixed on the outer and inner surfaces of the housing. This design of the ID will significantly increase the vibration resistance of the electrodes and ensure the stability of interelectrode gaps in the range (0.5-1.0) mm during their thermal expansion during operation of the ID.

In addition, the central location of the cathode-converter will provide an increase in efficiency by several (5-7) percent, especially with a significant increase in the diameter of the IOS.

Literature

1. Hall and ion plasma engines for spacecraft / OA Gorshkov, V.A. Muravlev, A.A. Shagayda; under the editorship of Acad. RAS A.S. Koroteva. - M.: Mechanical Engineering. - 2008.

2. H.W. Loeb, D. Feili, G.A. Popov, V.A. Obukhov, V.V. Balashov, A.I. Mogulkin, V.M. Murashko, A.N. Nesterenko, and S.A. Khartov: "Design of High-Power High-Specific Impulse RF-Ion Thruster", 32 nd IEPC, Wiesbaden, Sept. 11-15, 2011.

3. Research and development of a new generation of cathodes for stationary plasma engines. Arkhipov B.A. Abstract of dissertation for the degree of Doctor of Technical Sciences. Kaliningrad, 1998, p.21.

Claims (1)

An ion engine comprising a housing, a gas discharge chamber and an ion-optical system and a cathode-converter mounted rigidly on the outer surface of the casing, mounted on the casing, characterized in that the casing of the ionic engine has a toroidal shape, while the cathode-neutralizer is mounted on the central axis of the casing, the electrodes of the ion-optical system and the gas discharge chamber are ring-shaped, and their inner surfaces around the perimeter are rigidly fixed to the inner surface of the housing of the ion engine.

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