Cathode for hall effect ion thruster

Abstract

The invention relates to a cathode for an ion propulsion device, said cathode having a cylindrical shape extending along a main axis A-A' between a downstream end (10A) comprising an electron outlet (18) and an upstream end (10B) comprising a gas inlet (22). The cathode comprises a hollow cylindrical cathode body (14), an electron emitter (12) made of a thermionic emission material arranged inside the cathode body (14), a cylindrical inner electrode (21) coaxially surrounding the cathode body (14) and positioned at a distance from the cathode body (14), a hollow cylindrical dielectric carrier (17) coaxially surrounding the inner electrode (21) and positioned at a distance from the inner electrode (21), a heating wire (13) arranged in a spiral form on the inner face of the dielectric carrier (17), the inner electrode (21) comprising a plurality of through holes (25) configured to allow the passage of the thermal radiation emitted by the heating wire (13) in order to heat the cathode body (14).

Description

Technical Field

[0001] This disclosure relates to the field of ion jetting devices, particularly for forming plasma thrusters or electric thrusters.

[0002] This disclosure relates more particularly to a gas-supplied cathode for use in a Hall effect ion thruster suitable for propelling spacecraft. Background Technology

[0003] In the field of space propulsion, it is well known that electric or plasma thrusters are used to maintain satellites in geostationary orbit, move satellites between two orbits, compensate for drag on satellites placed in so-called low Earth orbit, or even for missions requiring extremely low thrust for extended periods during interplanetary missions. Specifically, plasma thrusters enable the generation of generally higher specific impulses than achievable with chemical thrusters, which translates to reduced fuel (also known as propellant) consumption and a corresponding increase in satellite lifespan and / or payload.

[0004] This Hall effect thruster is based on the acceleration of ions from plasma using an electric field induced by a magnetic barrier perpendicular to the exit direction of the jet channel. Typically, such a device includes: an annular main channel forming an ionization and acceleration chamber around a central axis; a magnetic circuit configured to generate magnetic field lines at the open end of the main channel; an anode positioned within the annular main channel near the bottom; and a cathode located outside the channel. The cathode is oriented toward the open end of the main channel to eject electrons toward the main axis. A portion of the electrons ejected from the cathode are directed to the anode and initially captured and confined by a strong radial magnetic field near the first end of the annular channel. The electrons then collide with the constituent atoms or molecules of the propellant (injected in gaseous form from the bottom of the annular channel) and flow from downstream to upstream to reach the anode. These electrons thus partially or completely ionize the gas, and the mixture of ions and electrons is thus in a plasma state. Furthermore, electrons trapped by the radial magnetic field (or barrier) have low conductivity in the vertical direction, which induces an axial electric field responsible for accelerating ions between the anode and the channel exit. These ions are thus ejected from the channel at high speeds, with the ejection direction substantially parallel to the longitudinal axis, thereby generating an upstream thrust.

[0005] When the temperature of the cathode rises, it emits electrons through a process called thermoemission. Therefore, the cathode is a key component in Hall effect thrusters responsible for electron emission and plasma generation.

[0006] Figure 1 A schematic diagram of the longitudinal cross-section of the prior art cathode 1 is shown.

[0007] The cathode 1 typically comprises a cylindrical hollow support 6 and a hollow cathode body 4 extending along the longitudinal main axis AA'. The hollow support and the cathode body are arranged coaxially around the longitudinal axis AA'. The cathode body 4 includes a downstream end equipped with an electron exit port 7 and an upstream end equipped with a gas inlet port. The cathode 14 also includes an electron emitter 2 made of a thermionic material capable of emitting electrons when heated to a certain operating temperature. Figure 1 In the example shown, the electron emitter 2 is in the form of a tube, which is inserted into and remains in contact with the inner wall of the cathode body 4. A heating wire 3 is located around the outer wall of the cathode body 4 and primarily faces the electron emitter 2. The end of the heating wire 3 is connected to a current source. The heating wire is designed to heat the cathode body and the emitter through heat conduction and emission when current passes through it. The power dissipation of the heating wire 3 causes the thermionic material 2 to heat up, which then induces electron emission. Simultaneously, a gas stream (typically xenon) is injected into the cathode ionization chamber 9, defined by the wall of the cathode body 4, via a gas injection port located upstream of the cathode.

[0008] A portion of the electrons emitted by emitter 2 are ejected through the outlet hole 7 of the hollow cathode 4 and then through the electron outlet hole 8 of the support 6 into a region downstream of the end of the Hall effect thruster anode discharge channel. Furthermore, some electrons present in the cathode ionization chamber collide with gas atoms or molecules flowing downstream in the cathode chamber, ionizing the gas and generating plasma. This plasma maintains a high temperature within the cathode ionization chamber, allowing the electron-emitting thermionic material to continue to be heated. To reduce heat loss, a heat shield 5 in the form of a hollow cylinder is inserted into the space defined by the wall of the support 6 and the cathode 4. During this self-sustaining operation phase of the cathode, where the high temperature is maintained by the plasma, the filament is then no longer powered.

[0009] This cathode has many advantages, making it particularly suitable for use in low-power Hall effect thrusters for small satellite propulsion.

[0010] However, the proposed cathodes do not have the optimal architecture in terms of lifetime, reliability, stability and power consumption.

[0011] Specifically, to initiate electron emission, the thermionic material forming the cathode electron emitter must be heated to a sufficiently high temperature using a heating element (i.e., a filament wound around the cathode tube wall) to initiate electron emission. Once plasma is generated within the cathode tube and a high temperature can be maintained, the heating filament 3 is no longer powered, and the cathode becomes self-heating. Therefore, the filament is only used for the initiation phase of the Hall effect actuator. However, due to the power of the current injected into the filament, it undergoes slight sublimation. Consequently, the filament diameter decreases with each use cycle, and the filament becomes increasingly resistant after each use cycle, exacerbating sublimation. Therefore, it is crucial to limit the power of the current injected into the filament to restrict its sublimation.

[0012] However, another factor contributing to its sublimation is directly related to its arrangement within the cathode and the heating process employed in currently used cathodes. Specifically, such as Figure 1 As shown, the filament 3 is wound around the outer wall of the cathode tube and in thermal contact with the cathode tube wall—it heats the cathode tube wall through thermal conduction and thus heats the thermionizer 2. Therefore, in self-sustaining mode, when it is no longer powered by current, it continues to be heated by the high temperature generated by the plasma in the cathode ionization chamber through thermal conduction. Thus, even when the filament is no longer supplied with current, it may sublimate during use due to the high temperature operation of the cathode. Therefore, effective thermal protection of the heating filament must be provided to prevent it from being heated by thermal conduction during cathode operation in self-sustaining mode, without hindering its function of heating the emitter to initiate the initial electron emission phase.

[0013] To improve cathode life and operational reliability, it is therefore crucial to limit filament degradation by reducing the power of the injected filament current and effectively protecting it from the high operating temperature of the cathode.

[0014] As mentioned above, to achieve a high-efficiency thruster with low power consumption, the cathode must operate in a self-sustaining or self-heating mode, where the heating power applied to the filament is zero during operation, and the emitter is heated only by plasma. In conventional cathodes, the emitter is not thermally constrained relative to the rest of the cathode because it is also in thermal contact with the inner wall of the cathode tube, resulting in heat dissipation via thermal conduction. Therefore, optimizing the thermal constraint of the emitter to limit heat dissipation from the cathode tube to the cathode periphery is also important. In other words, thermal decoupling of the emitter from the rest of the cathode is required while ensuring the mechanical robustness of the cathode to ensure it can withstand significant mechanical vibrations in its environment.

[0015] Therefore, one object of this disclosure is to provide an electron emission cathode with a novel architecture that allows for increased heating filament lifetime in order to improve cathode lifetime.

[0016] Another objective of this disclosure is to reduce heat dissipation to the outside of the cathode via radiation and thermal conduction in order to improve performance in maintaining the internal temperature of the cathode, thereby ensuring stable and reliable operation of the cathode, while improving its resistance to mechanical vibration. Summary of the Invention

[0017] This disclosure improves upon this situation.

[0018] It provides a cathode for an ion thruster, the cathode having a cylindrical shape extending along a main axis A-A' between a downstream end including an electron outlet and an upstream end including a gas inlet for gas intake, the upstream end of the cathode being coupled to a base, the cathode comprising: - A hollow cylindrical cathode body extends along the main axis A-A' between the downstream end and the upstream end, the wall of the cylindrical cathode body defining an ionization cavity; - An electron emitter made of thermionic material is arranged inside a cathode body, and the ionization cavity is located downstream of the electron emitter; - A cylindrical inner electrode, coaxially surrounding the cathode body and positioned at a certain distance from the cathode body, the inner electrode extending parallel to the main axis A-A' between the downstream end and the upstream end, a portion of the wall of the inner electrode facing the electron emitter; - A hollow cylindrical dielectric carrier, coaxially surrounding the inner electrode and positioned at a certain distance from the inner electrode; - A heating wire, arranged in a spiral shape on the inner surface of a dielectric carrier, at least a portion of which faces an electron emitter. The filament includes a downstream end connected to a downstream end of an inner electrode, which includes a plurality of through holes configured to allow thermal radiation emitted by the heating wire to pass through in order to heat the cathode body. - A cylindrical cathode holder extends along the main axis A-A' between the upstream and downstream ends and coaxially surrounds the dielectric carrier. The downstream end of the holder is provided with an aperture forming a cathode electron outlet.

[0019] According to one embodiment, the wall portion of the inner electrode that does not face the electron emitter includes a plurality of through holes configured to limit heat transfer to the base via thermal conduction.

[0020] According to another embodiment, the cathode further includes a cylindrical outer electrode that is coaxially surrounding the lower portion of the inner electrode and positioned at a distance from the inner electrode, and the heating wire includes an upstream end connected to the downstream end of the outer electrode.

[0021] Preferably, the external electrode includes a plurality of through holes configured to limit heat transfer to the base via thermal conduction.

[0022] According to one embodiment, the outer electrode is positioned between the inner electrode and the dielectric carrier such that its downstream end is on the extension line of the upstream end of the heating wire.

[0023] According to one example embodiment, the dielectric carrier includes at least one groove formed in a helical generatrix shape along the main axis A-A' on at least a portion of its inner surface, in which a heating wire is received and held.

[0024] The downstream end of the cathode is free and has an aperture facing the electron outlet of the holder.

[0025] According to one example embodiment, the electron emitter takes the form of a solid cylinder extending along the main axis A-A' and is held in the central region of the ionization cavity to form a channel for the flow of gas injected into the ionization cavity.

[0026] According to another example embodiment, the electron emitter takes the form of a tubular body extending along the main axis A-A' and is held in the central region of the ionization cavity to form a channel for the flow of gas injected into the ionization cavity.

[0027] The features described in the following paragraphs may be implemented either independently of each other or in combination with each other: According to an advantageous example embodiment, the wall of the hollow cathode body includes at least one radial deformation toward the interior of the ionization cavity in order to hold the electron emitter in place by crimping.

[0028] Preferably, the length of the electron emitter is shorter than the length of the cathode, and it is positioned closer to the downstream end of the cathode rather than the upstream end of the cathode.

[0029] Preferably, the internal electrode is positioned closer to the heating wire than to the cathode.

[0030] According to one example embodiment, the holes of the inner electrode and the holes of the outer electrode are regularly spaced apart from each other and thus form an array.

[0031] Preferably, the heating wire has a cross-section smaller than that of the inner electrode and / or the outer electrode, such that the heating wire is electrically more resistive than the inner and outer electrodes.

[0032] According to one embodiment, the cathode further includes a hollow cylindrical thermal shield that coaxially surrounds the dielectric carrier and is inserted between the cathode holder and the dielectric carrier.

[0033] According to another aspect of the invention, a Hall effect ion thruster comprising at least one cathode as described above is provided. Attached Figure Description

[0034] Other features, details, and advantages will become apparent after reading the following detailed description and analyzing the accompanying drawings, in which: Figure 1 A schematic cross-sectional view of a conventional cathode is shown.

[0035] Figure 2 A schematic cross-sectional view of a cathode according to one embodiment is shown.

[0036] Figure 3 Showing along Figure 2 A cross-sectional view taken by line B-B'.

[0037] Figure 4 Showing Figure 2An enlarged view of the radiative heat transfer region between the heating wire and the cathode body of the central cathode, wherein Figure (a) shows the radiative heat transfer from a portion of the heating wire through a hole in the inner electrode to the cathode body region, and Figure (b) shows the radiative heat transfer from the heated cathode body region to a portion of the heating wire.

[0038] Figure 5 In the left-hand figure, Figure (a) shows a schematic longitudinal cross-sectional view of a cathode body including an electron emitter according to one embodiment, and in the right-hand figure, Figure (b) shows a cross-sectional view taken along line C-C' in the left-hand figure.

[0039] Figure 6 The right-hand figure, Figure (a), shows the network of pores that form a honeycomb, while the left-hand figure, Figure (b), shows the network of pores with a rectangular geometry. Detailed Implementation

[0040] The accompanying drawings and the following description primarily contain elements of specific properties. Therefore, they not only serve to better understand the invention, but also contribute to its definition where appropriate.

[0041] First, it should be noted that the attached diagrams are not drawn to scale.

[0042] refer to Figure 2 and Figure 3 The cathode 10 according to an embodiment of the present invention will now be described. This electron-emitting cathode is particularly suitable for ion thrusters, such as Hall effect thrusters.

[0043] The cathode 10 has a cylindrical shape that extends along the main axis A-A' between the upstream end 10B and the downstream end 10A.

[0044] Figure 2 This is a longitudinal cross-sectional view taken along the axial direction of the cathode. The downstream end 10A of the cathode is configured to allow electrons to be emitted through the electron exit hole 18, and the upstream end 10B is configured to define a gas inlet 22 for gas intake.

[0045] Figure 3 It is along Figure 2 The cross-sectional view taken by line B-B' perpendicular to the main axis A-A'.

[0046] The cathode 10 includes: a hollow cylinder 14 defining an ionization cavity 19 into which an ionizable gas is injected; an electron emitter 12 disposed in the cavity 19 and capable of emitting electrons when heated to a certain temperature; a heating filament 13 capable of emitting thermal radiation to heat the emitter 12; an inner electrode 21 and an outer electrode 20 configured to connect the end of the heating filament 13 to a power source so that current flows through the filament; a thermal barrier 15 for limiting heat dissipation to the outside of the cathode; and a retainer 16 covering all elements of the cathode.

[0047] A hollow cylindrical cathode body 14 extends along the main axis A-A' between the upstream end 30 and the downstream end 29. According to one embodiment, the cylindrical cathode body 14 has a circular cross-section and thus forms a cathode tube.

[0048] The downstream end 29 of the cathode 14 includes an aperture 27 that allows electrons to exit. The aperture 27 faces the electron outlet 18 of the cathode. The upstream end 30 of the cathode 14 also includes an aperture 28 that allows gas to be injected into the ionization chamber 19. The upstream end 30 of the cathode 14 is closed by an injection system. The aperture 28 at the upstream end of the cathode is fluidly connected to a conduit 40 for conveying ionizable gas. The gas injection direction has been determined by… Figure 2 The arrow at the inlet of the central conduit 40 indicates this. The wall of the cathode 14 has an outer surface 14A and an inner surface 14B, which define the ionization chamber 19 into which gas is injected. The gas can be, for example, xenon, argon, krypton, or any other ionizable gas.

[0049] According to one example embodiment, the electron emitter 12 is preferably positioned closer to the downstream end 29 of the cathode body 14, i.e. closer to the aperture 27, in order to reduce heat conduction from the emitter 12 to the cathode body during its operation.

[0050] Typically, the cathode 14 is made of a material selected from the group consisting of tungsten (W), tantalum (Ta), molybdenum (Mo), and any mechanically robust, electrically conductive material with a melting point (or sublimation point) higher than the operating temperature of the emitter.

[0051] In the context of this invention, the terms “upstream” and “downstream” are defined relative to the normal flow direction of the injected gas, which is the same as the electron jet direction, flowing from upstream to downstream through the ionization chamber 19.

[0052] In the remainder of the description, the term “inner” refers to the portion closer to the main axis A-A’, while the term “outer” refers to the portion farther from the main axis A-A’.

[0053] The electron emitter 12 is made of a thermionic material that emits electrons when heated to a certain temperature. It is arranged inside the cathode 14 and within the ionization cavity 19.

[0054] Typically, emitters are made of ceramics, often lanthanum boride (LaB6), due to its robustness, high current density, and long lifetime. Electron emitters made of LaB6 can operate, for example, in a temperature range between 1000°C and 1700°C. Non-exhaustive, ceramic emitters based on C12A7 (also known as mayenite) can also be used, offering the advantage of operating at lower temperatures (between 900°C and 1200°C). Finally, these emitters can also be made of pure metals (e.g., tungsten (W), molybdenum (Mo), or tantalum (Ta), or exhibit enhanced thermionic emissivity when mixed with various oxides (e.g., barium oxide (BaO), scandium oxide (Sc2O3), strontium oxide (SRO), yttrium oxide (Y2O3), hafnium oxide (HfO2), and zirconium oxide (ZrO)).

[0055] The electron emitter 12 can have various geometric shapes. It can be formed from a hollow body or a solid body.

[0056] exist Figure 2 In this process, the electron emitter 12 takes the form of a solid body extending along the main axis A-A' and is fixed to the region of the inner surface 14B of the cathode body 14 by any suitable fastening device.

[0057] The electron emitter 12 may take the form of a solid cylinder extending along the main axis A-A' and be held in the central region of the ionization cavity of the cathode body 14 to form a channel for gas flow injected into the ionization cavity 19.

[0058] According to another example embodiment, the electron emitter 12 may take the form of a tubular body extending along the main axis A-A' and be held in the central region of the ionization cavity of the cathode body 14 to form a channel for gas flow injected into the ionization cavity 19.

[0059] According to one embodiment, the emitter 12 has a length less than that of the cathode 14 and is positioned closer to the downstream end 29 of the cathode than to the upstream end 30 of the cathode.

[0060] Preferably and with reference Figure 5 The emitter is positioned at the center of the ionization cavity 19 of the cathode body 140, and the walls of the hollow cathode body 140 include radial deformation toward the interior of the ionization cavity 19 to hold the emitter in place by crimping. The crimping ensures good mechanical grip and good electrical contact between the cathode body and the emitter, while allowing gas flow to pass around the emitter from upstream to downstream within the ionization cavity. The crimping also allows for limiting thermal contact between the cathode body and the emitter, thereby limiting heat dissipation from the emitter to the outside via heat conduction when the cathode is in self-sustaining mode.

[0061] Figure 5Figure (a) is a longitudinal cross-sectional view of the cathode body 140, showing four radial deformations 141, 142, 143, and 144 that hold the emitter 12 in the center of the cavity by pressing.

[0062] Figure 5 Figure (b) is a cross-sectional view taken along line C-C' of Figure (a), showing two (thermal and mechanical) contact points between the emitter 12 and the inner surface of the cathode body wall.

[0063] and Figure 1 Unlike existing cathodes, the heating wire 13 is maintained at a certain distance from the inner wall of the cathode body 14 by a dielectric carrier 17 positioned opposite the electron emitter 12. More precisely, as shown... Figure 2 As shown, the dielectric carrier 17 is in the form of a hollow cylinder, arranged coaxially around the cathode body 14 and at a certain distance from the cathode body. The dielectric carrier 17 is made of an electrically insulating material with a high melting point or sublimation point, such as alumina (Al2O3), boron nitride (BN), or zirconium dioxide (ZrO2). The heating wire is wound in a spiral shape around the main axis A-A' on the inner wall of the dielectric carrier 17. The heating wire 13 is held on the dielectric carrier 17 such that the turns are separated to avoid inter-turn short circuits.

[0064] According to one embodiment, the heating wire 13 is placed in a zigzag shape on the inner surface of the dielectric carrier 17.

[0065] According to another embodiment, the heating wire 13 is wound axially in a serpentine manner on the inner wall of the dielectric carrier 17.

[0066] Typically, the heating wire 13 can be wound into various geometric shapes on the inner wall of the dielectric carrier 17.

[0067] According to one embodiment, the dielectric carrier 17 includes a groove formed in a helical generatrix shape along a principal axis A-A' on a portion of its inner surface 17B. A filament 13 is received and held in the groove. The filament 13 includes a downstream end 13A connected to a downstream end 21A of the inner electrode 21 and an upstream end 13B connected to a downstream end 20A of the outer electrode 20.

[0068] It should be noted that, Figure 2 In the example embodiment, the length of the heating wire 13 substantially corresponds to the length of the emitter 12. The filament is preferably positioned closer to the downstream end 10A of the cathode than to the upstream end 10B of the cathode, such that the filament circumferentially surrounds the entire area occupied by the emitter.

[0069] The inner electrode 21 is in the form of a hollow cylinder. It is arranged coaxially around the cathode body 14. It is positioned between the cathode body 14 and the dielectric carrier 17. It does not contact the outer surface 14A of the wall of the cathode body 14, nor the inner surface 17B of the wall of the dielectric carrier 17 on which the filament 13 is wound. The inner electrode 21 extends parallel to the main axis A-A' between the downstream and upstream ends, occupying a portion that substantially corresponds to the length of the hollow cathode body 14.

[0070] According to a particularly advantageous technical feature, the inner electrode 21 is configured to form a hot wall that allows thermal radiation from the filament 13 to pass through to heat the emitter 12 via a radiative heating process, while restricting the passage of thermal radiation from the cathode 14 to the filament 13. For this purpose, the portion of the inner electrode facing the electron emitter 12 includes a plurality of through-holes 25 configured to allow thermal radiation to pass through, allowing them to heat both the cathode 14 and the electron emitter 12. When plasma is generated within the ionization cavity 19, allowing the temperature within the ionization cavity to be maintained to continue heating the emitter to a temperature sufficient for electron emission, the filament is no longer supplied with current. The thermal radiation emitted from the heated cathode 14 toward the filament 13 is partially blocked by the solid portion of the inner electrode 21 wall, thereby helping to maintain the temperature within the ionization cavity.

[0071] Therefore, the perforated wall of the inner electrode 21 allows the cathode body to be heated even when the filament and cathode body wall are not in physical contact. During the cathode heating phase, the cathode body 14 is primarily heated radiatively through the filament 13 via the orifice 25. This type of heating thus allows for better heat flow guidance, i.e., from the filament 13 to the emitter 12, and reduces the power that must be injected into the filament to heat the emitter. This reduction in power then allows for a lower operating temperature of the filament and the thermal stress that could thus cause degradation, deformation, or evaporation of its manufacturing materials. For this reason, it has a longer lifespan than filaments used in conventional cathodes, thereby allowing for increased cathode start-up cycles and reliability. When the cathode operates in self-sustaining mode, the heat transferred from the emitter 12 to the cathode body 14 is conducted along the cathode body 14 to the conduit 40 located upstream of the cathode, and radiated away from the cathode body 14 to the filament 13, where it is partially blocked by the inner electrode 21. Furthermore, since the filament is no longer in physical contact with the cathode body, heat dissipation to the outside is limited, thereby allowing for improved performance in maintaining high temperatures within the cavity.

[0072] refer to Figure 4 The process of radiative heat transfer through the hole 25 of the internal electrode will now be described.

[0073] Figure 4 Showing Figure 2 An enlarged view of the radiative heat transfer region between the heating wire 13 and the cathode body 14 of the central cathode.

[0074] A portion of the filament 13 is positioned opposite the outer surface 14A of the cathode. The wall of the inner electrode 21, equipped with a through-hole 25, is positioned between the outer surface 14A and the filament 13.

[0075] In Figure (a), when current flows through filament 13, thermal radiation emitted by filament 13 passes through hole 25 to heat region S1 on the outer surface 14A of cathode. The direction of radiation emission is indicated by arrows.

[0076] In Figure (b), when the cathode body 14 is heated to a certain temperature by means of the generated plasma, it also emits thermal radiation through the hole 25 to heat the filament region S2.

[0077] According to one example embodiment, in order to limit filament heating in region S2 and maximize cathode heating in region S1, the inner electrode 21 is positioned closer to the filament 13 than to the cathode 14. The distance L1 between the wall of the inner electrode 21 and the wall of the cathode is advantageously greater than the distance L2 between the wall of the inner electrode 21 and the filament 13.

[0078] The wall of the inner electrode 21 not only conducts electricity to supply power to the filament 13, but also forms a hot wall to allow direct radiation transfer from the heating filament 13 to the cathode body 14 containing the electron emitter, because it allows thermal radiation to pass through the through-hole to heat the cathode body and forms a thermal shield to block radiation emitted from the heated cathode body toward the heating filament which is no longer supplied with current.

[0079] According to another particularly advantageous feature, the lower portion of the wall of the inner electrode 21 that does not face the electron emitter 12 also includes a plurality of through holes 23. These holes 23 have a different function than the holes 25 on the upper portion of the electrode wall facing the emitter. These holes are configured to restrict heat transfer via thermal conduction to the base 32, which is thermally coupled to the upstream end 10B of the cathode 10.

[0080] The outer electrode 20 of the cathode 10 is in the form of a hollow cylinder extending along the main axis A-A'. It is arranged coaxially around the lower part of the inner electrode 21 and at a certain distance from the inner electrode. It is positioned between the inner electrode 21 and the dielectric carrier 17. The outer electrode 20 includes a downstream end 20A connected to the upstream end 13B of the filament 13 and an upstream end 20B connected to the base 32.

[0081] exist Figure 2 In an example embodiment, the outer electrode 20 is positioned between the inner electrode 21 and the dielectric carrier 17 such that its downstream end 20A is on the extension line of the upstream end 13B of the filament 13. In other words, the diameter of the outer electrode 20 is equal to the diameter of the turn formed by the filament 13, and the outer electrode 20 is positioned against the inner surface 17B of the lower portion of the dielectric carrier 17 wall, excluding the filament.

[0082] According to another particularly advantageous feature, the wall of the outer electrode 20 also includes a plurality of through holes 26 configured to limit heat transfer to the base 32 via thermal conduction.

[0083] The holes 25 on the upper part of the inner electrode 21 facing the emitter 12, the holes 23 on the lower part of the inner electrode 21, and the holes 26 on the outer electrode 20 can have different geometric shapes in the plane of the electrode wall.

[0084] According to one embodiment, the inner electrode 21 and the outer electrode 20 have a conductive cross-section larger than that of the heating wire 13. The thickness of each wall and the dimensions of the through holes 23, 25, 26 are configured such that the resistance along the inner electrode 21 and the outer electrode 20 is less than the resistance along the heating wire 13. As a result, energy will be primarily deposited in the filament during the heating phase.

[0085] Through holes can have the following characteristics: Figure 6 The hexagonal shape shown in Figure (a) forms a honeycomb, or as... Figure 6 The rectangular shape shown in Figure (b) on the left.

[0086] They can be spaced regularly apart from each other. Of course, the holes can be arranged alternately.

[0087] The densities of holes 23, 25, and 26 can be predetermined. Of course, the density of the formed holes can vary depending on their function in the cathode.

[0088] According to one embodiment, the through holes 23 at the lower part of the inner electrode 21 are staggered relative to the through holes 26 of the outer electrode 20. Therefore, the wall of the outer electrode 20 blocks the through holes of the inner electrode 21 to limit the thermal radiation of the cathode body to the outside.

[0089] According to one embodiment, the downstream end 29 of the cathode body is free and not connected to the cathode structure, thereby limiting heat dissipation.

[0090] According to one embodiment, the cathode 10 also includes a hollow cylindrical heat shield 15 surrounding the dielectric carrier 17. This shield is formed, for example, of one or more metal films, which allows for limiting heat dissipation to the outside of the cathode.

[0091] All components of the cathode are covered by a cylindrical cathode holder 16, which extends along the main axis A-A' between the upstream end 10B and the downstream end 10A. It is arranged to surround the heat shield 15. The downstream end of the holder is closed by a plate 31 with holes forming the cathode electron outlet 18, and the upstream end of the holder is connected to a base 32.

[0092] Advantageously, the retainer also forms a thermal barrier to limit heat dissipation to the outside of the cathode.

[0093] The cathode proposed in this invention is particularly suitable for ion thrusters, such as Hall effect ion thrusters. As an example, the proposed cathode can be arranged in the central cavity of the thruster head of the thruster.

[0094] However, the proposed technical solution can be applied to other types of thrusters.

[0095] This disclosure is not limited to the examples above, but includes any variations that a person skilled in the art can conceive of within the scope of the claims.

Claims

1. A cathode (10) for an ion thruster, the cathode having a cylindrical shape and extending along a main axis A-A' between a downstream end (10A) including an electron outlet (18) and an upstream end (10B) including a gas inlet (22) for gas intake, the upstream end (10B) of the cathode being coupled to a base (32), the cathode comprising: - A hollow cylindrical cathode (14) extends along the main axis A-A' between the downstream and upstream ends, the walls of the cylindrical cathode defining an ionization cavity (19). - An electron emitter (12) made of thermionic material is arranged inside the cathode body (14), and the ionization cavity is located downstream of the electron emitter; - A cylindrical inner electrode (21) is coaxially surrounding the cathode body (14) and positioned at a certain distance from the cathode body (14). The inner electrode (21) extends parallel to the main axis A-A' between the downstream end and the upstream end, and a portion of the wall of the inner electrode faces the electron emitter (12). - A hollow cylindrical dielectric carrier (17) is coaxially surrounding the inner electrode (21) and positioned at a certain distance from the inner electrode (21); - A heating filament (13) is placed in a spiral shape on the inner surface of a dielectric carrier (17), at least a portion of which faces an electron emitter (12). The filament (13) includes a downstream end (13A) connected to a downstream end (21A) of an inner electrode (21). The inner electrode (21) includes a plurality of through holes (25) configured to allow thermal radiation emitted by the heating filament (13) to pass through in order to heat the cathode body (14). - A cylindrical cathode holder (16) extends along the main axis A-A' between the upstream and downstream ends and coaxially surrounds the dielectric carrier (17), with an aperture forming an electron outlet (18) at the downstream end (31) of the holder.

2. The cathode according to claim 1, characterized in that, The wall portion of the inner electrode (21) that does not face the electron emitter (12) includes a plurality of through holes (23) configured to limit heat transfer to the base (32) via thermal conduction.

3. The cathode according to claim 1 or 2 further includes a cylindrical outer electrode (20) that is coaxially surrounding the lower part of the inner electrode (21) and positioned at a distance from the inner electrode, and the heating wire (13) includes an upstream end (13B) connected to the downstream end (20A) of the outer electrode.

4. The cathode according to claim 3, characterized in that, The external electrode (20) includes a plurality of through holes (26) configured to limit heat transfer to the base (32) via thermal conduction.

5. The cathode according to claim 3 or 4, characterized in that, The outer electrode (20) is positioned between the inner electrode (21) and the dielectric carrier (17) such that its downstream end (20A) is on the extension line of the upstream end (13B) of the heating wire (13).

6. The cathode according to any one of claims 1 to 5, characterized in that, The dielectric carrier (17) includes at least one groove formed in a helical generatrix shape along the main axis A-A' on at least a portion of its inner surface, in which the heating wire (13) is received and held.

7. The cathode according to any one of the preceding claims, characterized in that, The downstream end (29) of the cathode is free and has an aperture (27) for an electron outlet (18) facing the holder (16).

8. The cathode according to any one of the preceding claims, characterized in that, The electron emitter (12) takes the form of a solid cylinder extending along the main axis A-A' and is held in the central region of the ionization cavity to form a channel for the flow of gas injected into the ionization cavity (19).

9. The cathode according to any one of the preceding claims, characterized in that, The electron emitter (12) takes the form of a tubular body extending along the main axis A-A' and is held in the central region of the ionization cavity to form a channel for the flow of gas injected into the ionization cavity (19).

10. The cathode according to claim 8 or 9, characterized in that, The wall of the hollow cathode body (14) includes at least one radial deformation (141, 142, 143, 144) toward the interior of the ionization cavity (19) in order to hold the electron emitter (12) in place by crimping.

11. The cathode according to any one of claims 1 to 10, characterized in that, The electron emitter (12) has a length less than that of the cathode (14) and is positioned closer to the downstream end (29) of the cathode than to the upstream end (30) of the cathode.

12. The cathode according to any one of claims 1 to 11, characterized in that, The internal electrode (21) is positioned closer to the heating wire (13) rather than the cathode body (14).

13. The cathode according to any one of claims 1 to 12, in conjunction with claim 3, characterized in that, The holes (25, 23) of the inner electrode (21) and the holes (26) of the outer electrode (20) are regularly spaced apart from each other and thus form an array.

14. The cathode according to any one of claims 1 to 13, in conjunction with claim 3, characterized in that, The heating wire (13) has a cross-section smaller than that of the inner electrode (21) and / or the outer electrode (20), making the heating wire more resistive electrically than the inner and outer electrodes.

15. The cathode according to any one of claims 1 to 14 further comprises a hollow cylindrical heat shield (15) that coaxially surrounds the dielectric carrier (17) and is inserted between the cathode holder (16) and the dielectric carrier (17).

16. A Hall effect ion thruster comprising at least one cathode according to any one of claims 1 to 15.

Images