Hall-effect propulsion device with magnetic compensation

Abstract

The invention relates to a Hall-effect propulsion device (100) comprising: - a support body (110) extending between a first end (102) and a second end (103), the body comprising an annular outer wall (112) and an annular inner wall (113) arranged coaxially around a longitudinal axis AA' to form an annular channel (111), the first end (102) having an annular opening forming an ion outlet; - a magnetic circuit (120) arranged in the annular channel (111) and configured to generate a radial magnetic barrier in the annular channel close to the first end of the channel (102); - at least one magnetic compensation magnetic element (130) arranged in the magnetic circuit and configured to compensate for at least a fraction of an absolute value of the residual magnetic moment generated by the magnetic circuit (120).

Description

Description HALL EFFECT PROPULSION DEVICE WITH MAGNETIC COMPENSATION Technical field

[0001] The present disclosure relates to the field of ion ejection devices, in particular for forming plasma thrusters or electric thrusters.

[0002] The present disclosure relates more particularly to a Hall Effect plasma propulsion device with magnetic compensation. Prior art

[0003] In the field of space propulsion, it is well known to use electric or plasma thrusters to maintain a satellite in geostationary orbit, or to move a satellite between two orbits, or to compensate for drag forces on satellites placed in a so-called low orbit, or for missions requiring low thrusts over very long times during an interplanetary mission. Indeed, plasma thrusters can generate a specific impulse that is generally higher than chemical thrusters, which implies a reduction in fuel consumption (also called propellant) with the consequence of increasing the lifespan and / or payload of satellites.

[0004] There are several types of plasma thrusters depending on how they initiate the plasma and how they accelerate the plasma towards the exit of the ejection channel. Plasma thrusters can be classified into three main categories: electrothermal thrusters, electrostatic thrusters, and electromagnetic thrusters.

[0005] Electrothermal thrusters use the Joule effect to heat the gas, which is then accelerated. The so-called "arc-jet" thruster uses electric arcs formed between a central cathode and an external anode to heat the gas and create the plasma initiation. Another example is the Radio Frequency (RF) thruster, which belongs to this category.

[0006] Electromagnetic thrusters use the Lorentz force to accelerate plasma. Examples of this category include the so-called magnetoplasmadynamic thruster, which consists of a coaxial metallic discharge source whose central conductor is the cathode and the external conductor is the anode. The potential difference applied between the anode and the cathode initiates a plasma between these electrodes. At the same time, the strong current flowing through them induces an azimuthal magnetic field around each electrode. Thus, the coupling between the radial electric field and The azimuthal magnetic field in the cavity creates a Lorentz force that propels the plasma axially toward the exit.

[0007] In the family of electromagnetic thrusters, we can also mention cathodeless thrusters with magnetic nozzles. We can cite, for example, the "gyromagnetic resonance" thruster of magnetized free electrons in plasma or ECR ("Electron Cyclotron Resonance" according to the Anglo-Saxon term). In this family, the plasma is accelerated by the concept of a magnetic nozzle.

[0008] Electrostatic thrusters are based on accelerating plasma ions using an electric field gradient towards the exit of the ejection channel. So-called Hall effect plasma thrusters belong to this category.

[0009] All of these thrusters typically use coils and / or permanent magnets to produce a magnetic field that assists in the acceleration process by confining electrons to the cavity called the ionization chamber.

[0010] As an example and with reference to Figure 1, the operation and structure of a conventional Hall effect plasma thruster assembly 1 is described in more detail below.

[0011] The Hall effect thruster assembly 1 comprises a magnetic circuit 20 and a support body 10.

[0012] The support body 10 has a shape of revolution around a longitudinal axis AA'. The support body 10 comprises an annular channel 11 in which the magnetic circuit 20 is received. The propulsion assembly comprises a first end 2 having an annular opening and a second end 3. The inner surfaces of the annular channel 11 are provided with walls 26, 27 making it possible to physically delimit the ionization and acceleration zone. The walls are for example made of ceramic material.

[0013] The magnetic circuit 20 is formed by elements with high positive magnetic susceptibility 21 A, 21 B, 24A, 24B and permanent magnets generating a magnetic field 22, 23 arranged in the annular channel 11, around a longitudinal central axis AA' to form an annular ionization and acceleration chamber 40 in the annular channel 11.

[0014] A propellant gas supply circuit 4 is positioned in a lower portion of the body 10. The gas injection direction is represented by an arrow at the inlet of the circuit in Figure 1. The propellant assembly comprises one or more gas inlet holes formed in the bottom of the annular channel connected to the ionizable gas supply circuit 4. The gas is introduced into the annular ionization and acceleration chamber 40 through the gas supply holes. As an example, in FIG. 1, two supply holes 5 are shown.

[0015] The polarization of each permanent magnet is chosen so as to create magnetic field lines 6, ensuring the confinement of the electrons supplied by the cathode 8. Their geometric configuration is responsible for the “magnetic lens” effect at the first end 2 of the annular channel 11. This specific configuration of the magnetic field lines is designated by the term “magnetic lens” or “magnetic barrier” which is essential to the operating mode of a Hall effect thruster and is responsible for the ionization of neutral atoms and the acceleration of ions.

[0016] The propulsion unit further comprises an anode 9 positioned inside the annular channel 11, near the bottom of the channel. The anode 9 generally has a function of diffusing the propellant gas and may have a stepped structure as proposed in document US10723489B2. A hollow cathode 8 is located outside the annular channel 11, at the first open downstream end 2 of the channel 11. The cathode is oriented towards the first open end of the channel in order to eject electrons towards the main axis AA' and the area located downstream of the open end of the channel. When a voltage is applied between the cathode and the anode, the low axial conductivity of the electrons caused by their confinement in the "magnetic barrier", generates an electric field in the ionization chamber 40 which extends axially relative to the longitudinal axis AA'.

[0017] The operation of such a Hall effect plasma thruster is briefly described below.

[0018] The electrons ejected by the hollow cathode 8 are directed partly towards the anode 9 and they are first trapped and confined by the intense radial magnetic field in the vicinity of the first end 2 of the annular channel. The electrons then collide with the atoms or molecules constituting the propellant (injected in gaseous form from the bottom of the annular channel) and flowing from downstream to upstream of the channel to reach the anode 9. These electrons thus achieve a partial or total ionization of the gas, and the mixture of ions and electrons then constitutes the plasma state. On the other hand, the electrons trapped by the magnetic field create the axial electric field responsible for the acceleration of the ions between the anode and the outlet of the channel, so that these ions are ejected at high speed from the channel, in an ejection direction mainly parallel to the longitudinal axis AA', thus generating a thrust directed upstream. The direction of ion ejection is represented in Figure 1 by arrows.

[0019] The use of electromagnetic coils and / or permanent magnets to form the magnetic circuits 20 generates a residual magnetic moment in the propulsion device. When such a plasma thruster is implemented in satellites, the residual magnetic moment of the thruster contributes to the overall residual magnetic moment of the satellite. In the case where the thrusters are intended for satellites in low Earth orbit, the interaction between the Earth's magnetic field and the overall residual magnetic moment of the satellite is one of the main sources of disorientation and disturbance to the proper functioning of the satellite.

[0020] The first known solution is to use electromechanical stabilization devices such as reaction wheels or gyroscopic actuators to readjust the satellite's attitude. These devices allow the satellite's orientation to be maintained, but only temporarily, as it is necessary to dissipate the energy they only store temporarily. They are also a source of electrical consumption. Traditionally, a satellite always has a magnetic orientation device called a magnetocoupler, which consists of a coil associated with a power supply. This system is active only when the satellite is operational, consumes electricity, and contributes significantly to the satellite's mass. It is therefore necessary to reduce its size by limiting parasitic magnetic moments.

[0021] One solution is to use magnetic field generating coils that compensate for the thruster's magnetic field and thus minimize or even cancel out the residual magnetic moment. Examples of this solution are presented in WO2019229286A1 and US10752385. However, this solution involves greater complexity in the power supply as well as excess power consumption.

[0022] Generally speaking, canceling, or at least minimizing, the residual magnetic moment can be achieved by adding magnetic shielding devices and / or by adding magnetic compensation devices, which will be sized and placed to minimize the residual magnetic moment. Such solutions are described in the following documents: M de Soria-Santacruz et al., "An Approach to Magnetic Cleanliness for the Psyche Mission," (2020 IEEE Aerospace Conference, Big Sky, MT, USA, 2020, pp. 1-15), Noel Sebastian Janes, "Small Satellite Design for High Sensitivity Magnetic Measurements”, A. Lassakeur and C. Underwood, "Magnetic Cleanliness Program on CubeSats for Improved Attitude Stability," (2019 9th International Conference on Recent Advances in Space Technologies (RAST), Istanbul, Turkey, 2019, pp. 123-129).

[0023] W02021201871A1 describes a Hall thruster assembly that includes a Hall thruster and a mounting assembly coupled to one end of the Hall thruster. The mounting assembly is configured to support the Hall thruster and to secure the Hall thruster to a spacecraft. The mounting assembly includes a plurality of magnetic elements that may be electromagnetic coils or permanent magnets that are operable to produce a magnetic dipole moment to attenuate or reduce the magnetic moment of the Hall thruster. The magnetic elements are positioned away from the Hall thruster so as not to disturb the magnetic field generated by the magnetic circuit near the ion ejection end of the thruster.

[0024] Such a solution is not entirely satisfactory. The magnets that form the thruster's magnetic circuit are close to the ionization chamber and thus undergo significant heating. The walls forming the ionization chamber can generally reach more than 300°C, and the magnets more than 200°C. The magnetic properties of the magnets, in particular their remanence, can change with temperature. The remanence and therefore the residual magnetic moment is different depending on whether the thruster is on, therefore hot, or off, therefore cold. In addition, this remanence can decrease irreversibly over time. Having one or more compensation magnets at locations far from the ionization chamber, and therefore in a colder area, does not allow this temperature dependence of the remanence of the main magnets to be taken into account. The compensation produced by the compensation magnets is therefore not perfect.

[0025] Furthermore, the compactness of such a Hall effect thruster is not optimal because it requires a mounting assembly to support the compensation magnets.

[0026] An aim of the present disclosure is to propose a plasma thruster making it possible to overcome the drawbacks of the prior art and in particular offering a simple solution to implement to compensate for the residual magnetic moment resulting from the magnetic circuit of the thruster, while maintaining an optimal configuration of the magnetic field generated by the magnetic circuit in order to guarantee the performance of the thruster and its lifetime. Summary

[0027] This disclosure improves the situation.

[0028] A Hall effect propulsion device is proposed comprising: - a support body extending between a first end and a second end, said body comprising an annular outer wall and an annular inner wall arranged coaxially around a longitudinal axis AA' to form an annular channel, said first end having an annular opening forming an ion outlet; - a magnetic circuit arranged in the annular channel and configured to generate a radial magnetic barrier in the annular channel, near the first end of the channel; - at least one magnetic compensation magnetic element arranged in said magnetic circuit and configured to compensate at least a fraction of an absolute value of the residual magnetic moment generated by said magnetic circuit.

[0029] According to one embodiment, the magnetic circuit comprises at least one element with high positive magnetic susceptibility and at least one magnetic field generating magnetic element configured to generate said radial magnetic barrier, said at least one compensating magnetic element being positioned in the magnetic circuit so that it is further from the first end than said at least one magnetic field generating magnetic element.

[0030] According to one embodiment, said at least one magnetic compensation magnetic element has a continuous annular shape.

[0031] Alternatively, said at least one magnetic compensation magnetic element comprises a plurality of discrete magnetic elements positioned circumferentially with respect to the longitudinal axis AA'.

[0032] According to another embodiment, said at least one element with high positive magnetic susceptibility comprises a plurality of external elements with high positive magnetic susceptibility arranged against the annular external wall, said magnetic compensation magnetic element being held in position between two external elements with high positive magnetic susceptibility.

[0033] According to yet another embodiment, said at least one element with high positive magnetic susceptibility comprises a plurality of external elements with high positive magnetic susceptibility arranged against the annular external wall, at least one external element among the plurality of external elements with high positive magnetic susceptibility being provided with a housing adapted to receive said at least one compensating magnetic element.

[0034] The features set out in the following paragraphs may, optionally, be implemented, independently of each other or in combination with each other:

[0035] Said at least one magnetic compensation element is made of a material chosen from the following materials: neodymium-iron-boron, samarium-cobalt or hexaferrites.

[0036] Said at least one magnetic compensation element is in the form of a magnetic coil or a permanent magnet.

[0037] According to one embodiment, the device further comprises a gas supply circuit configured to inject an ionizable gas into the annular channel.

[0038] According to another embodiment, the device further comprises an electrical circuit configured to generate an electric field in a portion of the annular channel, said electrical circuit comprising an annular anode arranged inside the annular channel and at least one cathode arranged outside the annular channel, near the first end of the annular channel.

[0039] Preferably, said at least one magnetic compensation magnetic element is configured such that the absolute value of the residual magnetic moment of the circuit is at least less than 0.1 Am 2 over a temperature range between 50°C and 250°C. Brief description of the drawings

[0040] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analyzing the attached drawings, in which: Fig. 1

[0041] [Fig. 1] Figure 1 schematically represents a sectional view of a Hall effect plasma thruster according to the prior art. Fig. 2

[0042] [Fig. 2] Figure 2 schematically represents a sectional view of a Hall effect plasma thruster assembly according to one embodiment. Fig. 3

[0043] [Fig. 3] Figure 3 schematically represents a sectional view of the magnetic circuit of the Hall effect plasma propulsion device without the support body of Figure 2. Fig. 4

[0044] [Fig. 4] Figure 4 schematically represents a sectional view of the magnetic circuit of the Hall effect plasma propulsion device according to another embodiment without the support body of Figure 2. Description of the embodiments

[0045] A Hall effect ion ejection device according to an embodiment applied to a Hall effect plasma thruster will be described below.

[0046] With reference to Figure 2 and Figure 3, the Hall effect propulsion device 100 according to one embodiment is described below.

[0047] The propulsion device 100 comprises a support body 110 and a magnetic circuit 120.

[0048] The support body 110 has a shape of revolution about a longitudinal axis AA'. The body 110 comprises an annular outer wall 112, an annular inner wall 113 and a bottom 114 connecting the two walls. The outer wall 112 and the inner wall 113 are arranged coaxially about the longitudinal axis AA'. The outer and inner walls and the bottom form an annular channel 111. The magnetic circuit 120 is received in the annular channel 111.

[0049] The propellant assembly includes a first end 102 having an annular opening and a second end 103.

[0050] The propulsion device comprises a propellant gas supply circuit 104 positioned in a lower portion of the support body 110. The gas injection direction is represented by an arrow at the inlet of the circuit in FIG. 2. The propulsion device comprises one or more gas inlet holes 105 formed in the bottom of the annular channel connected to the ionizable gas supply circuit 4. The gas is introduced into the annular channel 111 through the gas supply holes. The propellant gas may be, for example, xenon, argon, krypton capable of being ionized. As an example, in FIG. 2, two supply holes 105 are shown.

[0051] An outer protective wall 126 and an inner protective wall 127 are arranged in the annular channel 111, respectively facing the annular outer wall 112 and the annular inner wall 113. These protective walls 126 and 127 are typically made of a ceramic material and protect the outer 112 and inner 113 annular walls from erosion.

[0052] According to another embodiment, a solid propellant source can be used instead of a gas. The gas supply circuit 4 is in this case replaced by a solid propellant placed in or upstream of the acceleration channel. The solid material is heated to directly pass into the vapor phase (by sublimation of the material) so that the particles are then ionized and accelerated in the channel.

[0053] For the purposes of this disclosure, the term "upstream" and "downstream" is defined relative to the normal flow direction of the gas which is in the same direction as the ejection of the ions, from upstream to downstream through the annular space 140 delimited by the outer 126 and inner 127 protective walls.

[0054] For the purposes of this disclosure, the term "internal" refers to a portion of the device close to the central longitudinal axis AA' while the term external refers to a portion of the device further from the central longitudinal axis AA'.

[0055] The Hall effect propulsion device also comprises a magnetic circuit 120 configured to generate a radial magnetic field in the annular channel 111, the intensity of which is maximum near the first end of the annular channel, namely at the annular opening of the device 102.

[0056] The magnetic circuit 120 is formed by a plurality of high positive magnetic susceptibility elements 121A, 12B, 121C, 124A, 124B and a plurality of magnetic field generating magnetic elements 122, 123 arranged in the annular channel 111 and configured to generate the radial magnetic barrier in the annular channel 111. The magnetic elements are arranged concentrically around the longitudinal central axis AA' to form an annular ionization and acceleration chamber 140 in the annular channel 111 of the support body 110.

[0057] The high positive magnetic susceptibility elements 121A, 12B, 121C, 124A, 124B and the magnetic field generating magnetic elements 22, 23 are designed to form a magnetic circuit capable of generating the radial magnetic field in the ionization chamber 140, the intensity of which in the axial direction (parallel to AA') is maximum near the first end 102, at the annular opening. The high positive magnetic susceptibility elements are selected and designed to guide and ensure the continuity of the magnetic field lines.

[0058] The propulsion device comprises one or more magnetic compensation magnetic elements 130 arranged in the magnetic circuit 120 and configured to compensate for at least a fraction of the residual magnetic moment generated by the magnetic circuit 120. The compensation magnetic elements 130 are positioned in the magnetic circuit 120 such that they are further from the first end 102 than the magnetic field generating magnetic elements 122, 123. They are positioned near the bottom of the annular channel so as not to affect the magnetic lenses formed at the first end of the device.

[0059] According to one embodiment, the magnetic field generating magnetic elements 122, 123 and the magnetic compensation elements 130 may have a continuous annular shape. This continuous annular shape is particularly suitable for a small propulsion device.

[0060] According to another embodiment, the magnetic field generating magnetic elements 122, 123 and the compensating magnetic elements 130 are formed by a plurality of discrete magnetic elements positioned circumferentially with respect to the longitudinal axis AA'. They are for example in the form of arc segments.

[0061] The use of discrete magnetic compensation elements makes it easier to adjust the volume of compensation magnets required to compensate for the residual magnetic moment. They are more suitable for a large propulsion device.

[0062] The magnetic field generating magnetic elements 122, 123 and the compensating magnetic elements 130 may be magnetic coils. Alternatively, they may be permanent magnets.

[0063] According to an exemplary embodiment as illustrated in FIG. 3, the magnetic circuit 120 comprises an external portion and an internal portion. The external portion comprises three external elements with high positive magnetic susceptibility 121A, 121B, 121C, an external magnetic field generating element 122, and a compensating magnetic element 130 arranged against the external wall of the annular channel 111 which is visible in FIG. 2. The internal portion comprises two internal elements with high positive magnetic susceptibility 124A, 124B and an internal magnetic field generating element 123 arranged against the internal wall of the annular channel 111.The compensating magnetic elements 130 are held in position between two external elements with high positive magnetic susceptibility 121A, 121C and arranged in the magnetic circuit so as to be further from the first end 102 forming the ion ejection outlet than the external magnetic field generating element 122. The elements with high positive magnetic susceptibility which are for example made of a soft iron material, are naturally attracted to the other elements of the magnetic circuit which are the permanent magnets.

[0064] The polarization of each permanent magnet is chosen so as to create magnetic field lines 106, ensuring the confinement of the electrons supplied by the cathode 108 in the magnetic barrier 106 or “magnetic lens” produced at the first end of the annular channel, as illustrated in Figure 3.

[0065] According to an exemplary embodiment, the thruster comprises an electrical circuit comprising an annular anode 109 located on the bottom of the annular channel and a hollow cathode 108 located at the open upstream end of the channel. The cathode 108 is oriented towards the first end 102 in order to eject electrons towards the main axis AA' and the area located downstream of the first end. When a voltage is applied between the cathode and the anode, an electric field is generated in the ionization chamber 140 and extends axially with respect to the longitudinal axis AA'.

[0066] According to another exemplary embodiment of the magnetic circuit and with reference to FIG. 4, the magnetic circuit 220 comprises an external part and an internal part. The external part comprises an upper external element with high positive magnetic susceptibility 221 B, a lower external element with high positive magnetic susceptibility 221 C and an external magnetic field generating element 222 arranged against the external wall of the annular channel 111 which is visible in FIG. 2. The external magnetic field generating element 222 is interposed between the two upper and lower external elements 221 B, 221 C and close to the first end 202 forming the ion ejection outlet.The inner portion comprises an upper internal element with strong positive magnetic susceptibility 224B, a lower internal element with strong positive magnetic susceptibility 224A and an internal magnetic field generating element 223 arranged against the inner wall of the annular channel 111. The internal magnetic field generating element 223 is interposed between the two upper and lower internal elements 224B, 224A and close to the first end 202 forming the ion ejection outlet. The lower external element with strong positive magnetic susceptibility 221C of the outer portion of the magnetic circuit comprises a housing adapted to receive a compensation magnetic element 230.

[0067] In the case where the magnetic compensation element 230 has a continuous annular shape around the longitudinal axis AA', the housing is formed by a continuous groove made in the thickness of the lower external element 221 C. The dimension and shape of the groove are adapted to receive the magnetic compensation element.

[0068] In the case where the magnetic compensation element 230 is formed from a plurality of discrete magnetic elements positioned circumferentially relative to the longitudinal axis AA', the housing is formed from a plurality of grooves made in the thickness of the lower external element 221 C to each receive a discrete magnetic element.

[0069] According to the present disclosure, the magnetic compensation element 130 is configured to compensate for the residual magnetic moment resulting from all of the magnetic elements forming the magnetic circuit 120 of the propulsion device.

[0070] The magnetic compensation element 130 is arranged in the magnetic circuit 120 so as not to disturb the magnetic field lines 106 formed by the magnetic circuit near the first end 102, at the channel outlet. Indeed, and in order to maintain the same performance between a compensated and uncompensated magnetic thruster, it is essential to maintain similar magnetic topologies with and without magnetic compensation 130.

[0071] The volume of the magnetic compensation element is determined so that the residual magnetic moment resulting from all the magnetic elements forming the magnetic circuit 120 of the thruster is at least less than 0.1 Am 2 .

[0072] The method of calculating the volume of all the compensation magnets is described below.

[0073] In a first step E1, the residual (total) magnetic moment is calculated as the integral of the magnetization (the volume density of magnetic moment) in the volume of all the magnetic elements, whether they are sources or conductors of the associated field.

[0074] In a second step E2, the residual magnetic moment is calculated for all the magnetic elements forming the initial magnetic circuit.

[0075] In a third step E3, the total volume of magnet(s) required to compensate for the magnetic moment is estimated.

[0076] In a fourth step E4, the residual (total) magnetic moment is calculated by integrating the magnetic compensation magnet(s) into the initial magnetic circuit.

[0077] In a fifth step E5, steps E2 to E4 are repeated so that the residual moment of the overall circuit of the propellant is at least less than 0.5 Am 2and ideally less than 0.1 Am 2 .

[0078] According to one embodiment, the compensation magnets can be made of a magnetic material such as neodymium-iron-boron, samarium-cobalt alloys or with hard ferrites called hexaferrites.

[0079] Directly integrating the magnetic compensation element into the magnetic circuit made it possible to improve the compactness of the Hall effect propulsion device compared to known solutions.

[0080] The magnetic compensation elements being placed close to the magnetic field generating magnetic elements, and in particular in thermal contact via a common part having good thermal conductivity, for example in figure 3, via the element with high external positive magnetic susceptibility 121A, they therefore undergo the same thermal operating conditions as the magnetic field generating magnetic elements and their remanence evolves in the same way as that of the magnetic field generating magnetic elements, thus making it possible to effectively compensate for the residual magnetic moment of the magnetic circuit, whatever the temperature of the magnetic field generating magnetic elements. As a result, the compensation of the residual magnetic moment remains optimal whatever the thermal state of the device.

[0081] As an example, residual magnetic moment (RMM) calculations were performed for two thermal conditions and in two magnetic situations (with magnetic compensation external or included in the magnetic circuit, as described previously).

[0082] In a first situation with external magnetic compensation (and therefore with different temperatures between the magnetic circuit and the compensation magnet(s)), the magnetic moment changes by -14 mA.m 2 (for a magnetic circuit and compensation magnets at 20°C), up to +126 mA.m 2 for a magnetic circuit at 200°C and compensation magnets at 20°C.

[0083] In a second situation with magnetic compensation included in the magnetic circuit (and therefore similar temperatures between the magnetic circuit and the compensation magnet(s)), the magnetic moment changes by -1 mA.m 2 (for all magnetic elements at 20°C) at -28 mA.m 2 (for all magnetic elements at 200°C).

[0084] Note that the positive or negative value of the MMR is not necessarily to be considered in the "magnetic compensation" because the sign of the MMR will correspond to the direction of rotation of the satellite (on which the Hall effect thruster is mounted) in orbit around the Earth. Generally speaking, the limiting value of the MMR depends on the type of mission for which the satellite is intended, but it is generally considered satisfactory to obtain an MMR of less than 100 mA.m 2 in order to limit the effects of the Earth's magnetic field. Comparing these two cases, we note that the compensation cannot be as optimal as if all the magnetic elements of the thruster are in the same thermal conditions.

[0085] If the magnetic compensation elements operate at different temperature conditions from the magnetic field generating magnetic elements, the calculation steps described above should ideally be carried out taking into account the properties of the materials, in particular their magnetic properties, at a temperature typical of thruster operation, so as to minimize the moment residual when the thruster is in operation. Alternatively, the calculation could aim to minimize the magnetic moment of the thruster when it is not in use, which may represent the largest part of its lifetime. It would also be possible to choose to minimize the residual moment for an intermediate temperature between the operating temperature and the off temperature, so as to minimize the overall disturbance during the life of the thruster, for example by weighting the temperature by the part of the lifetime spent at that temperature.

[0086] When implementing such a thruster in satellites, it is no longer necessary to calculate the residual magnetic moment by including the thruster's magnetic circuit, thus simplifying the process of implementing the thruster in the satellite. The thruster is self-compensated. The residual magnetic moment of the satellite can therefore be calculated and compensated independently of the choice and position of the thruster and before installing the propulsion device.

[0087] The technical solution proposed in the present disclosure is particularly suitable for compensating the residual magnetic moment resulting from the magnetic circuit of a Hall effect plasma thruster using permanent magnets. However, the proposed technical solution can be applied to other types of thrusters, including electrothermal thrusters such as Arc-jet thrusters, magnetoplasmadynamic thrusters, grid thrusters, ECR thrusters, vacuum arc thrusters, or Vacuum Arc Thrusters in English terminology which are part of solid storage propulsion systems.

Claims

CLAIMS

1. A Hall effect propulsion device (100) comprising: - a support body (110) extending between a first end (102) and a second end (103), said body comprising an annular outer wall (112) and an annular inner wall (113) arranged coaxially around a longitudinal axis AA' to form an annular channel (111), said first end (102) having an annular opening forming an ion outlet; - a magnetic circuit (120) arranged in the annular channel (111) and configured to generate a radial magnetic barrier in the annular channel, near the first end of the channel (102); - at least one magnetic compensation magnetic element (130) arranged in said magnetic circuit and configured to compensate at least a fraction of an absolute value of the residual magnetic moment generated by said magnetic circuit (120).

2. Device according to claim 1, wherein the magnetic circuit (120) comprises at least one element with high positive magnetic susceptibility (121 A, 121 B, 121 C, 124A, 124B) and at least one magnetic field generating magnetic element (122, 123) configured to generate said radial magnetic barrier, said at least one compensating magnetic element (130) being positioned in the magnetic circuit (120) so that it is further from the first end (102) than said at least one magnetic field generating magnetic element (122, 123).

3. Device according to claim 1 or 2, wherein said at least one magnetic compensation magnetic element (130) has a continuous annular shape.

4. A device according to claim 1 or 2, wherein said at least one magnetic compensation magnetic element (130) comprises a plurality of discrete magnetic elements positioned circumferentially relative to the longitudinal axis AA'.

5. Device according to one of claims 2 to 4, wherein said at least one element with high positive magnetic susceptibility comprises a plurality of external elements with high positive magnetic susceptibility (121 A, 121 B, 121 C) arranged against the annular external wall (112), said magnetic compensation magnetic element (130) being held in position between two external elements with high positive magnetic susceptibility (121 A, 121 C).

6. Device according to one of claims 2 to 4, wherein said at least one element with high positive magnetic susceptibility comprises a plurality of external elements with high positive magnetic susceptibility (221 C, 221 B) arranged against the annular external wall, at least one external element (221 C) among the plurality of external elements with high positive magnetic susceptibility being provided with a housing adapted to receive said at least one magnetic compensation element (230).

7. Device according to one of claims 1 to 6, in which said at least one magnetic compensation element is made of a material chosen from the following materials: neodymium-iron-boron, samarium-cobalt or hexaferrites.

8. Device according to one of claims 1 to 7, wherein said at least one magnetic compensation element (130) is in the form of a magnetic coil or a permanent magnet.

9. Device according to one of claims 1 to 8, further comprising a gas supply circuit (104) configured to inject an ionizable gas into the annular channel (111).

10. Device according to one of claims 1 to 9, further comprising an electrical circuit configured to generate an electric field in a portion of the annular channel (111), said electrical circuit comprising an annular anode (109) arranged inside the annular channel and at least one cathode (108) arranged outside the annular channel, near the first end of the annular channel (102).

11. Device according to one of claims 1 to 10, wherein said at least one magnetic compensation magnetic element (130) is configured so that the absolute value of the residual magnetic moment of the circuit is at least less than 0.1 Am 2 over a temperature range between 50°C and 250°C.

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