EP2191699B1 - High-voltage insulator arrangement, and ion accelerator arrangement comprising such a high-voltage insulator arrangement - Google Patents

Description

The invention relates to a high voltage insulator assembly and an ion accelerator assembly having such a high voltage insulator assembly.

In electrostatic ion accelerator arrangements, as are particularly suitable for propulsion of spacecraft, a working gas is ionized in an ionization chamber and the ions are expelled under the influence of an electrostatic field through an opening in the chamber. The electrostatic field is formed between a cathode disposed outside the ionization chamber, typically laterally offset from the opening, and an anode disposed at the foot opposite the opening of the chamber and penetrating the chamber. Between anode and cathode is a high voltage for generating the electric field. Typically, the cathode is at least approximately at the ground potential of the spacecraft, on which are also other metallic components of the spacecraft, and the anode is located on an offset by the high voltage to ground anode potential. A particularly advantageous such ion accelerator is for example from WO03 / 000550 A known. Other designs are known as Hall thrusters.

The high voltage acts not only between anode and cathode, but also between the anode including the high voltage supply line and other conductive components at a different potential from the anode potential, in particular the ground potential. While separated components are generally sufficiently insulated against flashovers by the vacuum of the surrounding space, in areas in which the working gas occurs, in particular between the anode and a conductive component located upstream of the gas flow in the gas supply line, there is the risk of corona discharges through the corona working gas.

Corona discharges can also occur in vacuum applications in other areas and situations between two conductive components which are at potentials separated by a high voltage, wherein in an intermediate pressure region (Paschenbereich) a voltage flashover by existing gas is facilitated. In between the conductive components continuously open paths can then ignite discharges carrying high currents. A plasma arising in the discharges is able to penetrate into small cracks or gaps. By venting against a surrounding vacuum such areas can indeed be made coronafest by lowering the gas pressure below the critical pressure range, but again in areas with changing gas pressure discharges in the intermediate pressure region may occur, which then can pass through the continuously open paths forming vent openings. Furthermore, it can also come below the critical pressure range by free electrons to a shunt, which z. B. is disturbed by Stromwertverfälschungen or power consumption or can ignite a vacuum arc discharge.

A pressure-independent isolation between two components, in particular a high-voltage leading component to ground, can be achieved by completely gas-tight enclosing a component, so that there are no continuously open paths between the two components, eg. B. by potting or embedding a component in an insulator body, but this eliminates for releasable conductor connections as a component. It also shows that over such a long period damage also occurs in such potted high-voltage insulator arrangements, which, in particular when used in spacecraft without the possibility of exchanging components, can result in serious damage.

In the US 2 775 640 A is a method and an arrangement for isolating a high voltage electrode against a housing wall to indicate a wall bushing. In this case, a metallic electrode is surrounded by a ceramic tube whose porosity is adjusted so that a fluid, which is typically a transformer oil, but may also be formed by a gas that can pass through the porous tube walls and rinses out any metallic deposits.

The present invention has for its object to provide a high-voltage insulator arrangement and an ion accelerator arrangement with such a high-voltage insulator arrangement with improved high-voltage insulation.

Solutions according to the invention are described in the independent claims. The dependent claims contain advantageous refinements and developments of the invention.

In an electrostatic Ionenbeschleunigeranordnung with an ionization chamber and an arranged in the ionization chamber anode electrode and a gas supply for introducing working gas into the ionization chamber is during the introduction of working gas is typically a pressure range of the working gas, in which when in operation between the electrode and the ground voltage applied high voltage in the kilovolt range, a corona discharge from the anode electrode as the first component by the working gas could occur to a conductive second component, which is upstream in the gas supply, ie arranged in the flow direction of the supplied working gas in front of the ionization chamber. By inserting an insulator body in the gas supply, which contains a gas-permeable, open-porous (open-pored) dielectric, such a corona discharge is prevented and at the same time allows a supply of working gas into the ionization chamber. Electrically conductive, in particular metallic, second components of the gas supply, including an advantageously provided controllable valve, are arranged inside the gas flow path upstream of the insulator body, whereas the anode electrode and electrically conductive first components located in the flow path of the working gas are arranged downstream of the insulator body. In particular, the first components form the electrically conductive, in particular metallic, components located downstream of the insulator body downstream, and the second components form the conductive, in particular metallic, components located upstream of the insulator body. The gas flow is forced through the gas-permeable insulator body. Nebenstrompfade the working gas, bypassing the insulator body, which in turn would be possible high-voltage flashover, are not provided. The gas-permeable insulator body can advantageously be inserted into one or more gas-impermeable insulating dielectric bodies and enclosed laterally by them.

The insertion of the gas-permeable insulator body in the flow path of the gas stream in particular also allows a compact design of the gas supply in the ion accelerator, since only a small distance between the grounded gas supply and lying on high voltage anode assembly must be adhered to interposing the insulator body. Advantageously, the distance of the insulator body to conductive parts of the anode assembly and / or the gas supply may be less than the smallest dimension of the insulator body transverse to the main flow direction of the working gas through the insulator body, in particular smaller than the smallest dimension of the insulator body in the main flow direction of the working gas. The insulator body is preferably disk-shaped and aligned with the disk surface transversely to the main flow direction of the working gas. The insulator body is advantageously arranged on the side of the anode arrangement facing away from the ionization chamber.

A high voltage insulator assembly having a gas permeable, open porous insulator body between two conductive members on high voltage disconnected potentials, as particularly advantageous between an electrode of an ionization chamber and a conductive member upstream of a gas supply, is commonly used in vacuum applications High voltages and the occurrence of gas in a space between the conductive components, in turn, in an ion accelerator arrangement as a drive in a spacecraft advantageous. It is provided in general application that two conductive components, which are separated by a high voltage different Potentials are isolated by an insulating device against each other and at least part of the insulation device is formed by a gas-permeable, open-porous insulator body. The isolation device can in particular surround one of the conductive components on all sides. Such a high-voltage insulator arrangement is important if gas can occur in a space interspersed by the electrostatic field of the high voltage between the mutually insulated components. If certain pressure and high-voltage conditions exist, a current path, in particular a DC path, can arise via plasma in the gas. A gas flow is possible between the first subspace on the side of the first conductive component and the second subspace on the side of the second conductive component via the gas-permeable insulator body. Gas Nebenstrompfade over which flow gas bypassing the gas-permeable insulator body and a direct current path could occur, are not provided.

Such a Hochspannungsisolatoranordnung is particularly advantageous for a detachable plug connection between a high voltage source and a z in operation. B. an ion accelerator at high voltage against a ground potential electrode. The connector advantageously allows that from the separate production of a high voltage source and one or more drive modules on test measures to installation in a spacecraft, a conductor connection, especially via an insulated cable, between the high voltage source to an electrode of the drive module repeatedly solved and the overall device significantly can be handled easier than a one-time Isolatorverguss a conductor connection.

In addition, the gas-permeable, open-porous insulator body in the insulation device proves overall as a long-term resistant as encapsulated or other non-gas-permeable insulation sheaths of a conductive component. This is based on the finding that conventional plastic insulation materials, which are suitable for spacecraft and high voltage applications, often still gas inclusions, in particular between conductors and insulation, in which microplasmas can arise, which can damage the isolation device so far over time, that corona discharges can occur between conductive components. By the gas-permeable insulator body such possibly existing gas pockets are easier degraded by discharging the gas into the surrounding space.

Also in environments in which there is a gas in the intermediate pressure region or a high-pressure region around the insulation device, in particular also with changing gas pressure, the gas-permeable porous insulator body is of particular advantage. Although, in the presence of gas in an intermediate pressure region, a plasma can be ignited both inside and outside the cavity of the isolation device, but it is not possible to form a continuous DC path between the conductive components. If the intermediate pressure region left again, which is because of the gas permeability of the porous insulator body inside and outside the cavity of the isolation device takes place, extinguishes an existing plasma or ignites a new one.

The gas-permeable insulator body may, for. B. be formed by an open-cell foam or preferably by an open-cell ceramic material. The mean pore size of the open porous dielectric in the direction of the high voltage caused by the electric field between the components is advantageously less than 100 microns. The insulator body is particularly advantageous if the dimensions of the cavities in the gas-permeable insulator body in the direction of the electrical field built up by the high voltage are smaller than the Debye length. The flow paths of the gas through the insulator body are advantageously deflected in relation to a straight path between gas inlet side and gas outlet side. The gas-permeable insulator body can also be formed by a plurality of partial bodies.

Fig. 1

eine Gaszuführung mit einem Isolatorkörper,

Fig. 2

eine lösbare Leiterverbindung mit einem Isolatorkörper,

Fig. 3

eine Abwandlung der Anordnung nach Fig. 2.

The invention is illustrated below with reference to preferred embodiments in detail. Showing:

Fig. 1

a gas supply with an insulator body,

Fig. 2

a detachable conductor connection with an insulator body,

Fig. 3

a modification of the arrangement according to Fig. 2 ,

In Fig. 1 is schematically outlined a drive arrangement of an electrostatic ion accelerator for driving a spacecraft. The arrangement has, in a conventional and conventional manner, an ionization chamber IK which is open in one longitudinal direction LR to one side at a jet exit opening AO and in the longitudinal direction of the jet exit opening AO contains an anode arrangement AN at the foot of the ionization chamber. The ionization chamber is laterally through a chamber wall KW of preferably dielectric, z. B. ceramic material limited and may in particular have an annular cross-section. The anode arrangement AN consists in the example outlined of an anode electrode AE and an anode support body AT. In the region of the jet outlet opening, preferably laterally offset from the jet outlet opening, a cathode arrangement KA is arranged. Between anode electrode AE and cathode assembly KA there is a high voltage which generates in the ionization chamber an electric field pointing in the longitudinal direction LR, through which ions of a working gas ionized in the ionization chamber are accelerated and ejected as plasma jet PB in the longitudinal direction out of the chamber. Typically, the cathode is at ground potential of the spacecraft containing the drive assembly and the anode assembly is at a high voltage potential HV of a high voltage source. In the ionization chamber, a magnetic field is still present, the course of which depends on the design of the drive arrangement and, in a particularly advantageous manner, known per se in the longitudinal direction, contains a plurality of cusp structures with alternating polarity. The magnetic field generating magnet assemblies are known per se, for example from the aforementioned prior art, and in Fig. 1 for the sake of clarity not shown.

A working gas AG, such as xenon is stored in a Vörratsbehälter GQ as a gas source and fed via a gas supply line GL and a controllable valve GV of the ionization chamber IK, wherein in the example sketched the introduction of the working gas into the ionization chamber of the ionization chamber side facing away from the anode assembly and laterally takes place at this past, which is illustrated by the arrows indicating the flow directions.

The gas supply line GL and other components of the gas supply are typically at ground potential, so that between these components and the anode assembly AN, the high voltage is effective and during the supply of working gas from the gas source GQ in the Ionisationsquelle the risk of corona discharges between the anode assembly and on Ground potential M lying components by the present in an intermediate pressure range working gas. The intermediate pressure range is understood to be the pressure range in which a gas discharge can ignite through a gas. The intermediate pressure range is u. a. dependent on the high voltage.

In the flow path of the working gas is located between the components lying at ground potential of the gas supply, z. B. the gas supply line GL, and the anode assembly, a gas-permeable insulator body IS inserted from an open-porous dielectric, which preferably as open-cell ceramic Body is executed. The insulator body is in an advantageous embodiment, as sketched disk-shaped and aligned with the disk plane transverse to the main flow direction through the insulator body between a gas inlet surface EF and a gas outlet surface AF. The main flow direction through the insulator body extends in the example outlined parallel to the longitudinal direction LR. The disk plane of the insulator body is parallel to the advantageously also disk-shaped components anode electrode and anode support body of the anode assembly. Between the anode support body AT and the insulator body IS, a gas-conducting diaphragm arrangement GB is advantageously inserted, which is preferably metallic and is at anode potential with high voltage to ground.

The insulator body is resistant to breakdown for the high voltage occurring during operation of the drive assembly. During operation of the arrangement, the high potential potential HV of the anode arrangement and the gas inlet area EF essentially become ground potential M at the gas outlet area AF, so that the gas-filled volumes VM are connected between grounded gas supply line GL and the gas inlet area EF of the isolator. VA between the anode assembly and the gas outlet surface AF are substantially field-free and arise in these volumes VM, VA no corona discharges.

The insulator body advantageously has no open structures continuous in a straight line between the gas inlet surface EF and the gas outlet surface. The flow paths of the working gas between the gas inlet surface and gas outlet surface are deflected against a straight course and are formed in particular by interconnected, distributed within the insulator body pore cavities and usually branched. The mean dimension of such pore cavities in the direction perpendicular to the gas inlet surface and gas outlet surface is advantageously less than 100 μm. The pore size in the direction parallel to the gas inlet surface and gas outlet surface and thus substantially transversely to the direction of the high voltage resulting field is of less importance, so that insulator body of z. B. fibrous material with fiber direction transverse to the electric field direction can be used. The average dimension of such cavities in the direction perpendicular to the gas inlet surface and gas outlet surface is advantageously smaller than the Debye length, which at given operating parameters, in particular at known maximum pressure of the working gas, which on the side of the gas inlet surface EF typically in the order of 30-150 mbar and on the gas outlet side, for example, below 1 mbar results from known formulas.

The smallest transverse dimension of the insulator body in the disk plane is in an advantageous embodiment greater than the distance of the gas outlet surface of the anode assembly and / or the gas inlet surface of the gas supply line, so that can be realized in the flow direction of the working gas small overall length. The insulator body is arranged in an insulator assembly with one or more substantially gas-tight insulator KK, which are mechanically or directly mechanically connected in a schematically illustrated manner with the chamber wall. The insulator body IS fills the entire Cross-section of the gas supply in the arrangement of the insulator KK, so that no leading past the insulator body path is given, over which a corona discharge, a plasma propagation or other current-conducting path could arise.

In Fig. 2 an application of a high voltage insulator assembly with a gas permeable open porous insulator body is sketched on a plug connection as a high voltage leading component. In the connector SV, two line sections K1, K2 are energized connected to each other, for. B. electrical power from a high voltage source to high voltage potential HV to an electrode such. B. the anode assembly AN after Fig. 1 to lead. The two line sections K1, K2 each have an inner conductor L1 or L2 and an insulating jacket M1 or M2. In particular, the line section K1 may be a flexible cable coming from a high voltage source and the line section K2 may be a connection stub to an ion accelerator drive module. The insulating jacket M1 can then z. B. a flexible cable sheath, z. B. be made of PTFE, the insulating jacket M1 can, for. B. also be a tube of insulating material.

The plug connection (or other non-destructive releasable connection) advantageously allows the non-destructive release of the electrical connection of the two inner conductors, whereby z. B. for a trial phase of a drive assembly made the connection, during the installation of drive assembly and high voltage source in a spacecraft separated and then reassembled, wherein also during the Test phase, the high-voltage plug connection must be resistant to breakdown to ground potential M components.

The plug connection is surrounded by an insulation device IV, which extends in the longitudinal direction LL of the two conductors via their insulating jackets M1, M2 and surrounds the plug connection on all sides. When high voltage from the high voltage source is applied to the inner conductors, there is usually a vacuum outside of the isolation device. Inside the insulating device in the hollow space HO around the exposed plug connection, on the one hand, there may still be gas from the installation or even after a longer time, in particular from the boundary layer between inner conductors L1, L2 and insulating jackets M1, M2, entering the space around the plug connection. Gas in the cavity around the plug connection can lead to the formation of plasmas in the cavity, which can also damage the insulating device for a long time. The insulating device is sealed against the cable sheaths M1, M2 so far that at the junctions no plasma possibly arising in the hollow space HO can penetrate and cause a flashover to the ground potential M. At least part of the cavity HO surrounding the plug connection wall of the insulating device is formed by a gas-permeable open porous insulator body VK, which with comparable properties as the insulating body IS from the example according to Fig. 1 Gas from the cavity HO can escape into the surrounding vacuum, but prevents that a plasma possibly formed in the cavity to strike through to a ground potential lying outside the cavity conductive component. Meets in operation one in Fig. 2 sketched high voltage insulator arrangement containing device, for. B. a Ionenbeschleunigerantrieb a Raumflugkörpes in space a gas shock, z. Example, from a gas bubble between an inner conductor and an insulating jacket, in the cavity HO, so there can form a plasma, but which can not penetrate through the insulator body VK to the outside and because of the escaping through the open porous insulator body to the outside gas quickly goes out again. In contrast, in a gas-tight encapsulation of the connector with an insulating potting material in the presence of gas in the region of the plug connection, a plasma ignited therein could burn longer and / or ignite again and again and u. U. expose a path for plasma permeable path in the direction of a grounded component. The gas escaping through the insulator body does not reach the critical pressure required to form a plasma or a corona discharge outside of the insulation device IV.

With only very small amounts of gas entering the hollow space HO from the conductors K1, K2, no plasma is formed in the cavity from the outset, since a critical minimum pressure is not reached and because of the gas permeability of the insulator body, an accumulation of several very small amounts of gas does not take place.

Fig. 3 shows a high voltage insulator arrangement in a modification of the example Fig. 2 , A tubular insulator body IR here directly surrounds the inner conductor L32 of a non-flexible line section K32 and continues over the insulating jacket M1 of the line section K1, which is equal to Fig. 2 Let us suppose. The insulator body can again be surrounded by an outer tube AR, which can also be conductive and can be at ground potential. An end cap EK can be placed on the insulating jacket M11 encompassing the end of the insulator body IR and braced in the longitudinal direction against the outer tube AR, if it is ensured that a gas can escape through the insulator body in the surrounding vacuum VA from the cavity to the plug connection and on the other hand, there is no path for a plasma from the cavity to the outside in the vacuum or to a conductive component.

As in Hochspannungsisolatoranordnungen on the type of examples in Fig. 2 and Fig. 3 a short time in the cavity accumulating, sufficient for the formation of a plasma in the cavity sufficient gas pressure typically well below the pressure of the working gas and in the insulator body IS in the embodiment according to Fig. 1 and thus the electron density in such a plasma is lower, the Debye length is in arrangements Fig. 2 and Fig. 3 typically larger than in the example below Fig. 1 , so when aligned with the average pore size of the open porous dielectric for applications Fig. 2 or Fig. 3 a larger value is tolerable than in the example below Fig. 1 ,

In the event that outside the cavity of the Hochspannungsisolatoranordnungen after Fig. 2 or Fig. 3 If a gas pressure occurs in an intermediate pressure range, a plasma can ignite both inside and outside the cavity when the ignition conditions are met. The plasmas can but not penetrate the porous insulator body, so that no continuous DC path between the components can be constructed. After elimination of the intermediate pressure range, in particular setting a vacuum around the high-voltage insulator arrangement, the already described isolation function is given again.

The features indicated above and in the claims, as well as the features which can be seen in the figures, can be implemented advantageously both individually and in various combinations. The invention is not limited to the described embodiments but is defined in the appended claims.

Claims (9)

1. High-voltage insulator arrangement having a first (SV) and a second (M) conductive component, between which a high voltage can be applied and which are separated by means of a space through which the electrical field of the high voltage passes and which may contain gas, at least part of the time, and having in the space an insulation device (IV), which insulates the two conductive components from one another, wherein the insulation device is formed at least in part by an insulator body (VK, IR) composed of an open-porous, gas-permeable dielectric, characterized in that the first of the two components is formed by an anode electrode and conductive elements of an electrostatic ion accelerator arrangement connected thereto and the second of the two components is formed by parts of a gas feed system, by way of which a working gas can be introduced into an ionization chamber of the ion accelerator arrangement, and in that the insulator body is flowed through by the working gas and fills the cross section of the flow path.
2. Arrangement according to Claim 1, characterized by a porous ceramic as the open-porous dielectric.
3. Arrangement according to Claim 2, characterized in that gas-guiding paths through the insulator body are deflected with regard to a straight progression.
4. Arrangement according to one of Claims 1 to 3, characterized in that pore cavities in the insulator body are shorter than the Debye length in a direction parallel to the field direction of the electrical field brought about by the high voltage.
5. Arrangement according to one of Claims 1 to 4, characterized in that the average pore size of the open-porous dielectric lies below 100 µm.
6. Arrangement according to one of Claims 1 to 5, characterized in that the anode electrode (AE) is arranged at the foot of the ionization chamber (IK), opposite a beam exit opening (AO), and in that the insulator body (IS) is arranged on the side of the anode electrode that is facing away from the ionization chamber (IK).
7. Arrangement according to Claim 6, characterized in that a surface of the insulator body that is facing the anode electrode is away from a metallic surface that lies at the potential of the anode in the direction of the anode electrode by a distance that is less than the extent of the insulator body transversely to this direction.
8. Arrangement according to one of Claims 1 to 7, characterized in that the insulator body is configured in the form of a disc and the average direction of the gas flow through the insulator body runs perpendicularly to the surface of the disc.
9. Use of a high-voltage insulator arrangement according to one of Claims 1 to 8 in an electrostatic ion accelerator arrangement having an ionization chamber (IK) and an anode electrode (AE) arranged in the ionization chamber as a first conductive component, as well as a gas feed system (GV, GL, GQ) for introducing working gas (AG) into the ionization chamber and a field that passes through the ionization chamber and accelerates electrostatically positively charged ions in the direction of a beam exit opening, the anode electrode (AE) being at a high voltage (HV) with respect to a second conductive component (GL, GV, GQ) situated upstream in the gas feed system, a gas-permeable insulator body (IS) composed of an open-porous dielectric being arranged in the flow path of the gas feed system and the working gas (AG) flowing through the insulator body to the ionization chamber (IK) and the anode electrode and components that are at its potential lying completely downstream of the insulator body in the flow path of the working gas.

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