RU2612308C1 - Ion engine with device for protection against arc discharge in interelectrode gap of ion-optical system - Google Patents

Abstract

FIELD: aviation.

SUBSTANCE: ion engine is equipped with a device for protection against arc discharge caused by interelectrode arcing between emissive and accelerating electrodes of the ion-optical system. The device is a fast-operating normally-closed relay which input is connected to the accelerating electrode circuit and output is connected to the electromagnet circuit. The opening of the relay occurs when a current value is 3-5 times higher than the nominal current value in the accelerating electrode circuit. Permissible voltage between the input and the output of the relay is not less than 5000 V.

EFFECT: invention allows to automatically eliminate the arc discharge caused by the interelectrode arcing in the ion-optical system of the ion engine.

1 dwg

Description

The proposed technical solution relates to rocket and space technology and can be used in testing and operation of ion engines (ID).

Today, the issue of increasing the power capacity of spacecraft is becoming increasingly relevant, associated with the need to solve such problems as lengthy expeditions to the planets of the solar system, as well as correcting the orbit and maintaining the orientation of modern high-Earth near-Earth spacecraft.

To accomplish these tasks, one of the most important characteristics of the engines used on spacecraft of this class are high gas and electric efficiency, as well as resource characteristics. By the totality of these parameters, the most promising is the use of ion engines, which have the largest specific impulse among electric rocket engines and a resource of tens of thousands of hours.

Modern ion engines are built on the basis of ion sources with volumetric ionization of the atoms of the working fluid by electron impact. Xenon is traditionally used as a working substance. A typical DC discharge ion-displacement engine (GDK) engine is provided by Goebel D.M. and Katz I. “Fundamentals of Electric Propulsion: Ion and Hall Thrusters”, Wiley, 2008, 508 p.

The ionization of the atoms of the working fluid in such an engine is carried out in the gas distribution system due to the collision of atoms with electrons emitted by the cathode and gaining energy in a constant electric field. To exclude the departure of primary electrons to the anode, a longitudinal magnetic field is created in front of it in the GRK. All GRK walls have a cathodic potential, therefore, primary electrons, before reaching the anode, perform multiple oscillations, which increases the efficiency of ionization. An ion-optical system (IOS), which, as a rule, consists of emission and accelerating electrodes, is used to extract ions from GRC plasma, to form and accelerate an ion beam. A positive potential of several kilovolts is supplied to the emission electrode, which determines the energy of the beam ions, and a negative potential of several hundred volts is needed for the electron to be cut off from the beam plasma to the accelerating electrode. In order to prevent charged particles of the beam plasma from reaching high-potential surfaces, the GRK is closed externally by a thin-walled case. Behind a cut of the engine, a cathode-converter is installed on the side surface of the casing, which supplies electrons to the ion beam, which is necessary to neutralize the space charge. Thus, the ions create traction, moving from the plasma of the gas distribution system through the holes of the emission and accelerating electrodes and accelerating in the electric field applied in the gap between them.

When conducting bench tests and operating ion engines as part of a spacecraft, one of the most important problems is the occurrence of an arc discharge in the gap between the electrodes of the ion-optical system of the ion engine due to interelectrode breakdown. Such a discharge is a cause of significant degradation of the electrodes, since it leads to localization of the power released in the arc to a small portion of the electrode. Considering that the emission electrode has a thickness of less than 1 mm and is densely perforated with holes, even a short-term exposure to such power can lead to melting of the material and violation of the integrity of the electrode. Therefore, in the operation of ion engines, there is a need for an arc protection mechanism that will minimize the degradation of the electrodes of the ion-optical system.

Known US patent No. 7269940 (2007) "The electrical circuit for protecting the electrodes of the ion engine from breakdowns", selected as a prototype, in which to solve this problem, an electrical circuit is proposed that uses as a main element a high-resistance resistor installed in the accelerating electrode circuit . When a breakdown occurs, a large current flows through the resistor, creating a potential difference of more than kilovolt at its terminals and thereby increasing the potential of the accelerating electrode. This leads to a decrease in the potential difference between the electrodes and the extinction of the arc.

However, this device has the following disadvantages:

- taking into account that the potential of the accelerating electrode circuit during breakdown approaches the potential of the emission electrode, the insulation of this circuit should also be designed for a voltage of more than kilovolt;

- a current flows through the resistor even during normal engine operation, that is, stray power is released in it, which reduces the efficiency of the system;

- the current flowing through the resistor, in addition, leads to a voltage drop, that is, the potential arriving at the accelerating electrode is less than that set by the source and depending on the current value. In this regard, in order to stabilize the potential of the accelerating electrode, the considered circuit includes a system for measuring and adjusting the voltage at the power source of the accelerating electrode, which significantly complicates the circuit and reduces its reliability;

- when the engine is started on the accelerating electrode, a large current inevitably occurs, which is not connected with the interelectrode breakdown. In this regard, a relay is installed in the circuit parallel to the high-resistance resistor in the accelerating electrode circuit, which closes during engine start and opens when it reaches the specified parameters. This also complicates the circuit and leads to a decrease in system reliability.

The purpose of the invention is to ensure reliable operation of the ion engine in the event of an arc discharge caused by interelectrode breakdown.

The technical result of the invention consists in eliminating in an automatic mode an arc discharge in an ion engine caused by interelectrode breakdown, without reducing the efficiency of the system.

This goal and the technical result are achieved in that the ion engine is equipped with a device for protection against arc discharge caused by breakdown between the emission and accelerating electrodes of the ion-optical system, and is a fast-acting normally closed relay. The relay input is connected to the accelerating electrode circuit, and the output is connected to the electromagnet circuit. The relay opens when the current value is 3-5 times higher than the rated current in the accelerating electrode circuit. The permissible voltage between the input and output of the relay is at least 5000 V.

The potential of the emission electrode on the used ion engines reaches 4500 V, the accelerating electrode has a negative potential of up to minus 400 V, the gap between the electrodes is up to 2 mm. Under such conditions, breakdown does not occur in a vacuum.

However, it can occur in the presence of a stress concentrator in the form of a burr or an extraneous metal particle, which is unpredictable and is due solely to external factors.

At a high concentration of charge carriers near the ion-optical system, the arising breakdown causes an arc discharge to ignite between the electrodes, which leads to the local release of high power and significant degradation of the electrodes.

A necessary condition for maintaining an arc discharge is a high concentration of charge carriers near the ion-optical system, the role of which in the ion engine is played by charged particles of the plasma generated between the cathode and the anode of the GDK.

In the event of a breakdown, according to the invention, the concentration of charge carriers near the electrodes is sharply reduced due to the disconnection of the magnetic field in the GRK, which leads to the extinction of the arc discharge. For this, a relay is introduced into the electric circuit of the engine, the input of which is connected to the accelerating electrode circuit, and the output to the electromagnet circuit. When the relay opens, the discharge is localized in the cathode region, the plasma density near the IOS decreases sharply, and, thus, the arc discharge goes out.

Based on this idea, an ion engine was developed, equipped with a device for protection against arc discharge caused by interelectrode breakdown, schematically depicted in the figure.

The protection device is a normally closed high-speed relay, such as an electromagnetic or optical relay.

The relay input 3 is connected to the accelerating electrode circuit and is connected between the negative terminal of its power source 2 and the accelerating electrode 6 itself, and the relay output is connected to the electromagnet 4 circuit and connected between the negative terminal of its power source 1 and the electromagnet 4 itself.

The device operates as follows.

When a breakdown occurs, the current in the circuit of the accelerating electrode 6 increases. When the current value is 3-5 times higher than the rated current in the accelerating electrode circuit, a normally closed high-speed relay 3 opens, thus turning off the power of electromagnet 4. In this case, the concentration of charge carriers near the emission 5 and accelerating 6 electrodes drops sharply, the arc discharge goes out, the current in the accelerating electrode circuit decreases and relay 3 closes again. After that, the regular functioning of the engine continues. The dielectric strength of insulation, that is, the permissible voltage between the input and output circuits of the relay, is at least 5000 V.

Such a device allows in automatic mode to reliably eliminate the arc discharge caused by interelectrode breakdown in the ion-optical system of the ion engine and ensures its reliable operation.

Claims (1)

An ion engine equipped with a device for protection against arc discharge caused by interelectrode breakdown arising between the emission and accelerating electrodes of the ion-optical system, characterized in that the device is a fast-acting normally closed relay, the input of which is connected to the accelerating electrode circuit, and the output - an electromagnet circuit, and the relay opens when the current value is 3-5 times higher than the rated current in the accelerating electrode circuit, and the permissible voltage between the input output relay is not less than 5000 V.

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