A lanthanum hexaboride emitter adapted to the hollow cathode erosion process

Abstract

The application provides a lanthanum hexaboride emitter adapted to the erosion process of a hollow cathode, which is made of lanthanum hexaboride and has an axial symmetric star-shaped column structure, and the cross section of the emitter is a regular star shape with n uniformly distributed star corners and n star grooves, the side edges of adjacent star corners form a star edge included angle θ, and the thickness of the emitter is e. A point H (i.e. a point where a straight line C-D segment disappears) divides the inner surface degradation into two stages, by designing the parameters n and θ, the emitter can realize constant surface, increasing surface or decreasing surface degradation before degrading to the point H. The design of the emitter as decreasing surface degradation can adapt to the actual working condition that the downstream degradation rate is faster in the working process of the hollow cathode, so that the electron emission surface area of the hollow cathode is basically maintained consistent in the whole life cycle. In addition, compared with the traditional emitter, the star-shaped emitter has a smaller outer diameter under the same emission area and thickness, which is beneficial to the design of the small size and low power consumption hollow cathode, and is suitable for long life space electric propulsion tasks.

Description

Technical Field

[0001] This invention relates to the field of low-temperature vacuum plasma technology, and in particular to a lanthanum hexaboride emitter adapted to the erosion process of a hollow cathode. Background Technology

[0002] Hollow cathodes, as a core electron emission device, have irreplaceable application value in key devices such as aerospace electric propulsion systems, plasma contactors, high-power lasers, and magnetrons. Their core function is to stably provide electron emission and continuously maintain the discharge plasma environment inside the device, ensuring the reliable operation of the entire system.

[0003] In the core components of a hollow cathode, the material properties of the emitter directly determine its operational stability and lifespan. Lanthanum hexaboride, with its excellent resistance to plasma poisoning, high electron emission current density, and long-term operating characteristics, has become the mainstream preferred material for hollow cathode emitters and is widely used in various scenarios with stringent requirements for reliability and long lifespan.

[0004] However, the lanthanum hexaboride emitter operates in an extremely harsh environment: on the one hand, it must withstand long-term high-temperature baking at temperatures exceeding 1500°C, and on the other hand, it is continuously bombarded by high-energy plasma throughout its entire operating cycle. These extreme conditions cause continuous high-temperature evaporation and loss of the emitter material, leading to continuous changes in the morphology and area of ​​the electron emission surface. This problem has become a key bottleneck restricting the performance stability of the hollow cathode.

[0005] In existing technologies, lanthanum hexaboride emitters generally employ a hollow cylindrical structure (such as...). Figure 1 (As shown). During operation, the electron emission surface area of ​​this structure irreversibly increases as the inner surface material continues to evaporate. In precision applications such as aerospace electric propulsion systems, this change in emission surface area directly affects the coupling voltage of the propulsion system, causing propulsion performance drift. The instability of propulsion performance further affects the accuracy of spacecraft orbit control, posing a significant challenge to the long-term mission reliability of the spacecraft. Summary of the Invention

[0006] This invention provides a lanthanum hexaboride emitter structure with a stable emission area. The star-shaped geometry enables self-compensation of the emission area during the erosion process, which can maintain a constant emission surface area during material evaporation and improve the working stability of the hollow cathode throughout its life cycle.

[0007] This invention provides a lanthanum hexaboride emitter adapted to the erosion process of a hollow cathode, wherein a centrally located inner hole penetrating both ends is provided, and the cross-section of the inner hole is star-shaped, the star shape comprising:

[0008] Multiple star-shaped points, circumferentially distributed along the center of the inner hole; and

[0009] Multiple star slots, wherein the star slots connect two star points;

[0010] The continuous profile segment of the cross-section of the combined half-star angle and half-star groove structure of the star-shaped emitter includes:

[0011] Section AB is the concave outline inside the star groove, and its length increases with the erosion depth.

[0012] Segment BC, which is the transition zone between the star angle and the star trough, varies in length as the star trough erodes and contracts; and

[0013] Segment CD is the sloping outline outside the star-shaped corner. It shrinks inward as erosion occurs, and its length decreases as the erosion depth increases.

[0014] During the operation of the launcher, the cross-sectional profile length s´ of the combined structure of the semi-star angle and semi-star slot is:

[0015] ;

[0016] in ;

[0017] ;

[0018] ;

[0019] Right now, ;

[0020] Where l is the characteristic dimension, ε is the star angle coefficient, n is the number of star angles, θ is the star edge angle, e is the combustion thickness, and r is the radius of the arc of the transition section between the star angle and the star groove;

[0021] When the emitter degrades uniformly along the axial direction, the geometric parameters satisfy the following formula:

[0022] To achieve constant surface degradation design;

[0023] When the axial temperature distribution of the emitter is uneven, the geometric parameters satisfy the following formula:

[0024] To achieve the design of increasing surface area and degrading,

[0025] or

[0026] This enables a reduced-surface degradation design, thereby achieving near-constant-surface degradation in practical applications.

[0027] In one embodiment of the present invention, the star-shaped angles are uniformly distributed circumferentially along the center of the inner hole; and / or

[0028] The number of star corners and star grooves is n, and n is a natural number and ≥ 2.

[0029] In an embodiment of the present application, the emitter is a symmetrical structure and is composed of lanthanum hexaboride.

[0030] In an embodiment of the present application, the two sides of the star corner are equal in length.

[0031] In an embodiment of the present application, the emitter region is uniformly distributed with plasma, the emitter is uniformly distributed in temperature along the axial direction, each point on the inner surface of the emitter is degraded at a uniform rate, and the electron emission area of the emitter is:

[0032] Ae = 2ns' L,

[0033] Wherein n is the number of star corners; s' is the cross-sectional profile length of the half star corner and half star groove combination structure; and L is the length of the emitter.

[0034] The present application has the following beneficial effects:

[0035] (1) The axial symmetrical star cross-sectional structure is adopted, the parameters of the number of star corners n and the star edge included angle θ are matched, the electron emission surface can realize “constant surface degradation” before the inner surface of the emitter is degraded to H point, the chain reaction of “inner surface evaporation of the traditional hollow cylindrical emitter → increase of the emission surface area → change of the coupling voltage” is avoided, the performance drift of the propulsion system is reduced, the frequency of the spacecraft thrust calibration is reduced, the orbit control accuracy is ensured, and the reliability requirement of long-life space missions (such as long-term on-orbit operation of satellites and deep space exploration) is especially adapted.

[0036] (2) The star type structure is distributed in space through “star corner-star groove”, under the premise of “constant emission surface area and constant minimum thickness e”, compared with the traditional hollow cylindrical structure, the outer diameter D of the emitter is greatly reduced (the occupied space of the invalid outer periphery is reduced). The reduction of the outer diameter of the emitter directly reduces the overall volume and heat dissipation area of the hollow cathode: on the one hand, it adapts to the installation space requirement of the spacecraft for “miniaturized equipment”; on the other hand, it reduces the heat dissipation loss and the energy consumption requirement of the cathode operation, which meets the development trend of “lightweight and low power consumption” of space equipment. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 A cross section of a hollow cylindrical emitter in the prior art is shown;

[0038] Figure 2 A comparison diagram of the loss form of the emitter in the prior art is shown;

[0039] Figure 3 A cross-sectional schematic diagram of a star type emitter in an embodiment of the present application is shown; and

[0040] Figure 4 Fig. 1 shows a cross-sectional view of a star-shaped emitter according to an embodiment of the present application. DETAILED DESCRIPTION

[0041] In the following description, reference is made to specific embodiments of the application. Those skilled in the art will recognize that the application can be practiced with one or more specific details, or that the application can be practiced without one or more of the specific details. In other instances, well-known structures, materials, or operations are not shown or described in detail in order to avoid obscuring the application. Similarly, like reference numerals refer to like elements throughout. Certain details are set forth for the purpose of explaining the embodiments of the application. However, the application is not limited to these details as aspects of the application can be practiced with or without one or more of the details. It is to be understood that other specific arrangements of parts and / or methods can be utilized, and that structural and operational changes can be made without departing from the scope of the present application.

[0042] In the present application, the embodiments are merely intended to illustrate the scheme of the present application, and should not be understood as limiting.

[0043] In this specification, reference to "one embodiment" or "the embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

[0044] The application will be further described with reference to the drawings.

[0045] Figure 2 Fig. 1 shows a cross-sectional view of a star-shaped emitter according to an embodiment of the present application.

[0046] In the operation of a hollow cathode, the temperature of the emitter is not uniformly distributed along the axial direction, with the temperature at the downstream being higher than that at the upstream. High-temperature evaporation is the main cause of emitter loss, and thus the emission surface at the downstream of the emitter degrades faster. The appearance of the degraded emitter is shown in Fig. 2. Figure 2

[0047] Figure 3 Fig. 1 shows a cross-sectional view of a star-shaped emitter according to an embodiment of the present application.

[0048] Figure 4 Fig. 1 shows a cross-sectional view of a star-shaped emitter according to an embodiment of the present application.

[0049] As shown in Figs. 3 and 4, in an embodiment of the present application, the emitter 100 serves as a carrier of propellant, and the thickness is a key dimension thereof. The star angle 110 and the star groove 120 are special structures. As shown in Fig. 3, the star angle 110 is a convex part, and the star groove 120 connects two star angles. Figure 3 Figure 4 As shown in Figs. 3 and 4, in an embodiment of the present application, the emitter 100 serves as a carrier of propellant, and the thickness is a key dimension thereof. The star angle 110 and the star groove 120 are special structures. As shown in Fig. 3, the star angle 110 is a convex part, and the star groove 120 connects two star angles. Figure 3

[0050] ​​​Taking a star-shaped emitter as an example, the emitter 100 has an inner hole running through both ends at its center. The inner hole is star-shaped, which is where the star angles 110 and star grooves 120 are located. The star angles 110 are evenly distributed around the inner hole, and multiple star angles 110 of the same shape are evenly distributed circumferentially along the center of the inner hole. The two sides of each star angle 110 are of equal length, and the radially extended ends on both sides are connected by a specific arc (such as the top arc of the star groove) to form the star groove 120.

[0051] like Figure 3 As shown, in one embodiment of the present invention, a star corner is set between every two star slots.

[0052] The thickness of the emitter, from its inner surface to its outer surface, is a crucial design parameter that determines its lifespan. It is generally believed that the emitter fails when its thickness reaches 2 / 3e1. To achieve control over the electron emission surface area throughout the entire lifespan of a hollow cathode, it is recommended to design the H-point to be around 2 / 3e1.

[0053] exist Figure 4 In the illustrated embodiment, the electron emitting surface of the emitter is not its entire inner surface, but rather a "specific cylindrical surface" extending along the emitter's axial direction (length L). The "cross-sectional boundary" of this cylindrical surface is the continuous ABCD contour segment in the cross-section of the star-shaped emitter, and s´ is precisely the "one-dimensional sum of lengths" of this contour segment (if it includes straight line segments, it is the sum of line segment lengths; if it includes the arc transition segment of the star slot, it is the sum of line segment lengths and arc lengths). s´ is the "projected length of the electron emitting surface on the cross-section," a key intermediate parameter for decomposing the three-dimensional emitting surface area (Ae) into the product of the "cross-sectional contour" and the "axial length."

[0054] Based on the cross-section of the star-shaped emitter (a regular star shape containing n star points and n star slots), the ABCD contour segment is a specific region defined according to the "area compensation requirements during the emitter erosion process". Its specific composition is directly bound to the core features of the star-shaped structure: AB segment: corresponds to the concave contour line inside the star slot, which expands outward as the emitter erodes (material evaporates), and its length increases with the erosion depth; BC segment: corresponds to the transition area between the star point and the star slot (the radius of the arc transition segment is r), and its length changes as the star slot erodes and contracts; CD segment: corresponds to the inclined contour line outside the star point, which contracts inward as erosion occurs, and its length decreases with the erosion depth.

[0055] In the working process of the star-shaped emitter, the degeneration process is divided into two stages by the point H (the point where the straight line C-D disappears). In the first stage before degenerating to the point H, when the inner surface of the emitter degenerates along the thickness direction (from inside to outside), the A-B-C segment (the inner profile of the star groove) in the cross section gradually increases, while the C-D segment (the outer profile of the star corner) gradually decreases. In the second stage after degenerating through the point H, as the degeneration continues, the C-D segment (the outer profile of the star corner) in the cross section completely disappears, and only the A-B-C segment (the inner profile of the star groove) continues to degenerate along the thickness direction.

[0056] The electron emission area Ae has Ae = 2ns´L;

[0057] Where n is the number of star corners; s´ is the cross-sectional profile length, that is, the length of the ABCD segment; and L is the length of the emitter.

[0058] In the working process of the hollow cathode, the electron emission area is only related to the length of A-B-C-D.

[0059] The degeneration of the inner surface of the emitter is divided into two stages by the point H. Before the degeneration of the inner surface of the emitter to the point H, the A-B-C segment increases, and the C-D segment decreases, and through the design of geometric parameters, this segment can present an area-increasing, area-decreasing or constant-area degeneration mode; after that, the C-D segment disappears, and the inner surface of the emitter inevitably degenerates in an area-increasing manner. It is generally believed that the emitter fails when it consumes 2 / 3 of the thickness, so the point H can be designed at 2 / 3e1 when designing the emitter.

[0060] Let the burning thickness be e, and the first stage of the designable analysis is as follows: in the working process of the emitter, the cross-sectional profile length s´ is:

[0061] ;

[0062] Where ;

[0063] ;

[0064] ;

[0065] That is, ;

[0066] Where l is the characteristic size, ε is the star corner coefficient, n is the number of star corners, θ is the star edge included angle, e is the burning thickness, and r is the radius of the circular arc transition segment.

[0067] When the emitter uniformly degenerates along the axial direction, the relationship between the change rule of the electron emission area and the geometric parameters is as follows:

[0068] .

[0069] The above degradation stage is based on the theoretical assumption of "axial uniform degradation", but in actual work in the prior art, the axial temperature distribution of the emitter is not uniform (downstream temperature > upstream temperature, because high temperature is the main factor of evaporation loss), which leads to a much faster degradation rate downstream than upstream, as shown in the experimental observation of "after 15kh of work, the downstream emitter profile erosion is more significant". In order to offset this actual deviation, the structural design of the star-shaped emitter needs to actively adopt "face reduction design": by adjusting n, θ and other parameters, the theoretical emission surface is "slightly reduced", which exactly offsets the "additional increase" caused by the rapid degradation of the downstream, and finally realizes "approximately constant surface" in actual work, ensuring stable performance. Figure 2

[0070] In an embodiment of the present application, assuming that the emitter degrades uniformly along the axis, when the star angle number n and θ as shown in the following table satisfy the following table, the emitter electron emission surface is a constant surface degradation. Figure 3

[0071]

[0072] Although the embodiments of the present application are described above, it should be understood that they are presented only as examples, not as limitations. It is obvious to those skilled in the relevant art that various combinations, modifications and changes can be made without departing from the spirit and scope of the present application. Therefore, the width and scope of the present application disclosed herein should not be limited by the above disclosed exemplary embodiments, but should be defined only according to the appended claims and their equivalent replacements.​​

Claims

1. A lanthanum hexaboride emitter adapted to the erosion process of a hollow cathode, characterized in that, It has an inner hole extending through both ends at its center, wherein the cross-section of the inner hole is star-shaped, and the star shape includes: Multiple star-shaped points, circumferentially distributed along the center of the inner hole; and Multiple star slots, wherein the star slots connect two star points; The continuous profile segment of the cross-section of the combined half-star angle and half-star groove structure of the star-shaped emitter includes: Section AB is the concave outline inside the star groove, and its length increases with the erosion depth. Segment BC, which is the transition zone between the star angle and the star trough, varies in length as the star trough erodes and contracts; and Segment CD is the sloping outline outside the star-shaped corner. It shrinks inward as erosion occurs, and its length decreases as the erosion depth increases. During the operation of the launcher, the cross-sectional profile length s´ of the combined structure of the semi-star angle and semi-star slot is: ； in ; ； ； Right now, ; Where l is the characteristic dimension, ε is the star angle coefficient, n is the number of star angles, θ is the star edge angle, e is the combustion thickness, and r is the radius of the arc of the transition section between the star angle and the star groove; When the emitter degrades uniformly along the axial direction, the geometric parameters satisfy the following formula: To achieve constant surface degradation design; When the axial temperature distribution of the emitter is uneven, the geometric parameters satisfy the following formula: To achieve the design of increasing surface area and degrading, or This enables a reduced-surface degradation design, thereby achieving near-constant-surface degradation in practical applications.

2. The lanthanum hexaboride emitter according to claim 1, characterized in that: The star-shaped points are evenly distributed circumferentially along the center of the inner hole; and / or The number of star slots and star angles is n, where n is a natural number and ≥2.

3. The lanthanum hexaboride emitter according to claim 1, characterized in that, The emitter has a symmetrical structure and is composed of lanthanum hexaboride.

4. The lanthanum hexaboride emitter according to claim 1, characterized in that, The two sides of the star angle are of equal length.

5. The lanthanum hexaboride emitter according to claim 1, characterized in that, Assuming a uniform plasma distribution in the emitter region, a uniform temperature distribution along the axial direction of the emitter, and uniform degradation at all points on the inner surface of the emitter, the electron emission surface area of ​​the emitter is: Ae=2ns´L, Where n is the number of star points; s´ is the cross-sectional profile length of the combined half-star point and half-star groove structure; and L is the length of the emitter.

Images