Large-aperture ion thruster under coupling of circumferential porous hollow cathode

Abstract

The invention discloses a large-caliber ion thruster under coupling of a circumferential porous hollow cathode. The large-caliber ion thruster comprises a discharge chamber, the circumferential porous hollow cathode, a cathode pole shoe, a grid electrode assembly and a grid electrode supporting rod. The circumferential porous hollow cathode is provided with a cathode emission end with a closed end surface, and n cathode emission holes are uniformly distributed in the circumferential direction of the cathode emission end; the cathode pole shoe coaxially sleeves the outer sides of the n cathode emission holes; the center of the grid assembly is connected with the closed end face of the cathode transmitting end through a grid supporting rod. The diameter of the gate assembly can be greater than 60 cm. According to the invention, the hollow cathode is changed into a peripheral opening, and an insulating rod-shaped grid electrode support rod extends from the closed end, so that the grid electrode support rod is connected with the center of the grid electrode and plays a role in supporting and fixing the grid electrode. Under the condition that the plasma generation environment in an original discharge chamber is not affected, the stability of the large-diameter thruster grid electrode is effectively improved, deformation caused by the too large diameter is reduced, and the primary electron generation efficiency of the large-diameter thruster grid electrode can be effectively improved.

Description

Technical Field

[0001] The invention relates to the field of spacecraft space propulsion technology, in particular to a large-caliber ion thruster under circumferential porous hollow cathode coupling. Background Art

[0002] Electric thrusters have advantages such as high specific impulse and good thrust control accuracy. Ion thrusters, as a more mature representative, have been widely used in various space propulsion missions. The main way for traditional ion thrusters to achieve high power is to increase the size of the discharge chamber and the size of the ion optical system. Therefore, large-size grid components become a key constraint on high power: the larger the size, the worse the mechanical resistance, the more difficult it is to control thermal deformation, the more likely the two grids will contact and short-circuit, and the difficulty of manufacturing and assembly will increase accordingly. If the above problems are prevented by increasing the grid thickness and increasing the grid spacing, it will inevitably affect the efficient extraction of ions. At present, the upper limit of the grid diameter that can be used for engineering applications of ion thrusters is 60cm, and the corresponding maximum power is 55kW.

[0003] At present, electric propulsion has been increasingly used in manned space flight and deep space exploration missions, which often require thrusters to operate in high-power modes above 60kW. Therefore, it is imperative to conduct research on high-power ion electric propulsion technology. In order to develop such high-power ion thrusters and not reduce the ion extraction efficiency, it is necessary to develop large-aperture ion thrusters with an aperture greater than 60cm. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a large-aperture ion thruster under circumferential porous hollow cathode coupling in view of the deficiencies of the above-mentioned prior art. The large-aperture ion thruster under circumferential porous hollow cathode coupling is mainly aimed at high-power and large-aperture ion thrusters with a power of 60kW to 120kW and an aperture greater than 60cm. By arranging a circumferentially open hollow cathode and arranging a grid support rod at the front end of the circumferentially open hollow cathode and connecting it to the center of the grid assembly, the stability of the grid assembly is improved, and structural support is provided for the stable operation of the grid with an aperture greater than 60cm.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A large-caliber ion thruster coupled with a circumferential porous hollow cathode comprises a discharge chamber, a circumferential porous hollow cathode, a cathode pole shoe, a grid assembly and a grid support rod.

[0007] The discharge chamber is a cylindrical structure with a front end and an open rear end.

[0008] The circumferential porous hollow cathode is coaxially inserted on the front end face of the discharge chamber and extends into the discharge chamber to form a cathode emission end with a closed end face; n cathode emission holes are evenly distributed circumferentially on the cathode emission end; wherein n≥2.

[0009] The cathode pole shoe is coaxially sleeved on the outer periphery of the cathode emission end outside the n cathode emission holes.

[0010] The grid assembly is arranged on the open tail end of the discharge chamber, and the center of the grid assembly is connected to the closed end surface of the cathode emission end through a grid support rod; the diameter of the grid assembly can be greater than 60 cm.

[0011] The circumferential porous hollow cathode includes an emitter, a cathode tube, a heater and a touch-holding electrode arranged in sequence from the inside to the outside; wherein the emitter, the cathode tube and the touch-holding electrode have the same structure, which are all end-face closed structures.

[0012] The emitter is provided with n emitting holes evenly distributed along the circumference, the cathode tube is provided with n cathode holes evenly distributed along the circumference, and the touch-holding electrode is provided with n touch-holding holes evenly distributed along the circumference; the n emitting holes, n cathode holes and n touch-holding holes correspond to each other in the circumferential position, and together form n cathode emitting holes.

[0013] The sum S of the areas of the n emitting holes is smaller than the newly added end surface area ΔS of the emitter.

[0014] Assuming that a conventional hollow cathode has an axial cathode emission hole along the axis and with an area of ​​S0, then S>S0.

[0015] The diameter d of each cathode emitting hole and the number n of the cathode emitting holes are adjusted so as to satisfy S0<S<ΔS.

[0016] d=(1 / 8~1 / 15)D, where D is the cathode tube diameter, that is, d is generally one eighth to one fifteenth of the cathode tube diameter; D is proportional to the power of the large-aperture ion thruster.

[0017] The power of large-caliber ion thrusters can reach 60 to 100 kW.

[0018] n=4,d=0.2~0.4cm.

[0019] Assuming the length of the cathode pole shoe is L, and the distance between the cathode pole shoe and the cathode emission end is W, by adjusting L and W, the trajectory of electrons in the discharge chamber can be adjusted and made the trajectory of electrons the same as or close to the trajectory of electrons in a conventional hollow cathode.

[0020] The grid assembly includes a screen grid and an accelerating grid arranged in parallel; wherein the hole spacing of the screen grid is smaller than the hole spacing of the accelerating grid; the grid support rods are respectively connected to the centers of the screen grid and the accelerating grid, and the diameter of the grid support rods is equal to the hole spacing of the screen grid.

[0021] The present invention has the following beneficial effects:

[0022] 1. The present invention closes the cathode hole originally located at the top of the hollow cathode and turns it into a circumferential opening, and extends an insulating rod-shaped grid support rod from the top of the closed hollow cathode, so that it is connected to the center of the grid and plays a supporting and fixing role for the grid. The configuration of this ion thruster does not affect the original plasma generation environment in the discharge chamber, and not only effectively increases the stability of the large-caliber thruster grid and reduces the deformation caused by the large diameter, but the circumferentially porous hollow cathode structure can also effectively improve its efficiency in generating primary electrons.

[0023] 2. The present invention proposes for the first time a "circumferential" hole-opening method for a hollow cathode. Under this hole-opening method, the emitter surface area for generating primary electrons in the hollow cathode is larger than that of a traditional cathode, making the generation efficiency of primary electrons higher and the plasma generation efficiency of the thruster higher.

[0024] 3. The present invention proposes a new type of structural ion thruster that solves the problem of easy deformation of the grid of a high-power ion thruster. A grid support rod for fixing is added in the discharge chamber, and its insulating properties prevent it from affecting the original ionization reaction in the discharge chamber. The support rod can better fix the grid at the center of the grid, solving the problem of large deformation caused by excessive grid diameter. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A half-section view of a large-aperture ion thruster coupled with a circumferentially porous hollow cathode according to the present invention is shown.

[0026] Figure 2 A cross-sectional schematic diagram of the circumferentially porous hollow cathode of the present invention is shown.

[0027] Figure 3 An exploded view of the circumferentially porous hollow cathode of the present invention is shown.

[0028] Figure 4 A schematic diagram showing the electron ejection direction of a large-aperture ion thruster coupled with a circumferentially porous hollow cathode of the present invention is shown.

[0029] Figure 5 The schematic diagram of the structure of a conventional hollow cathode in the prior art is shown.

[0030] Figure 6 A schematic diagram showing the additional area of ​​the emitter of the present invention compared to a conventional hollow cathode.

[0031] Among them are:

[0032] 10. Discharge chamber; 11. Cylindrical shell; 12. Front end surface; 13. Discharge chamber working fluid input pipeline; 14. Gas distribution ring;

[0033] 20. Anode;

[0034] 30. Circumferential porous hollow cathode; 31. Emitter; 311. Emitter hole; 32. Cathode tube; 321. Cathode hole; 33. Heater; 34. Holding electrode; 341. Holding hole; 35. Cathode working medium input pipeline; 36. Cathode emitting hole; 37. Axial cathode emitting hole;

[0035] 40. Cathode pole shoe;

[0036] 51. Screen grid; 52. Acceleration grid;

[0037] 60. Neutralizer; 61. Neutralizer working fluid input pipeline;

[0038] 70. Electromagnet;

[0039] 80. Grid support rod. DETAILED DESCRIPTION

[0040] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific preferred embodiments.

[0041] In the description of the present invention, it should be understood that the terms "left side", "right side", "upper part", "lower part" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. "First", "second" and the like do not indicate the importance of the components, and therefore cannot be understood as limiting the present invention. The specific dimensions used in this embodiment are only for illustrating the technical solution, and do not limit the scope of protection of the present invention.

[0042] like Figure 1 As shown, a large-aperture ion thruster with a circumferential porous hollow cathode coupling includes a discharge chamber 10, an anode 20, a circumferential porous hollow cathode 30, a cathode pole shoe 40, a grid assembly, a neutralizer 60, an electromagnet 70 and a grid support rod 80.

[0043] The discharge chamber is a cylindrical structure, including a cylindrical shell 11, which has a front end 12 and an open tail end. The front end is preferably provided with a discharge chamber working medium input pipeline 13 for inputting discharge working medium gas into the discharge chamber, preferably easily ionized mercury, cesium, xenon, etc.

[0044] The anode is coaxially sleeved in the discharge chamber adjacent to the inner wall of the cylindrical shell, and the anode wall can be made of high-temperature resistant nickel-based alloy sheet material.

[0045] A gas distribution ring 14 is preferably provided in the discharge chamber adjacent to the front end surface for uniformly distributing the discharge working medium gas input from the discharge chamber working medium input pipeline 13 in the discharge chamber.

[0046] The circumferentially porous hollow cathode is coaxially inserted on the front end face of the discharge chamber, and preferably extends into the discharge chamber after passing through the gas distribution ring to form a cathode emission end with a closed end face; n cathode emission holes 36 are evenly distributed circumferentially on the cathode emission end; wherein n≥2.

[0047] like Figure 2 and Figure 3 As shown, the circumferential porous hollow cathode includes an emitter 31, a cathode tube 32, a heater 33 and a touch-holding electrode 34 arranged in sequence from the inside to the outside; wherein the emitter, the cathode tube and the touch-holding electrode have the same structure, which are all end-face closed structures.

[0048] The emitter is provided with n emitting holes 311 evenly distributed along the circumference, the cathode tube is provided with n cathode holes 321 evenly distributed along the circumference, and the touch-holding electrode is provided with n touch-holding holes 341 evenly distributed along the circumference; the n emitting holes, n cathode holes and n touch-holding holes correspond to each other in the circumferential position, and together form n cathode emitting holes.

[0049] like Figure 6 As shown, the internal emitter is sealed on one end face on the basis of the original ring shape. In the present invention, the sum of the areas of the n emission holes S is less than the newly added end face area ΔS of the emitter. As a result, the area of ​​the emitter is effectively expanded. Since the electron current density emitted from the surface of the cathode emitter is proportional to the surface area of ​​the emitter, the new hollow cathode has a stronger electron emission capability than the traditional hollow cathode. Furthermore, the emitter material can be selected from barium tungsten, lanthanum hexaboride, etc., which have strong electron emission capability, good high temperature resistance and arc ablation resistance.

[0050] The contact electrode hole is slightly larger than the cathode hole, and the original top opening position is cancelled.

[0051] like Figure 5 and Figure 6 As shown, assuming that a conventional hollow cathode has an axial cathode emission hole along the axis and with an area of ​​S0, then S>S0.

[0052] The diameter d of each cathode emitting hole and the number n of the cathode emitting holes are adjusted so as to satisfy S0<S<ΔS.

[0053] The relationship between d and cathode tube diameter D is: d = (1 / 8 ~ 1 / 15) D. In this embodiment, d = 0.2 ~ 0.4 cm is preferred. D is proportional to the power of the large-caliber ion thruster. That is, n and d can be designed according to S1, S2 and D. When designing, first select a d based on D, then calculate an integer n based on S1 and S2, and finally fine-tune the roughly selected d value based on n.

[0054] The circumferentially porous hollow cathode of the present invention has n=4 holes correspondingly opened on the cathode hole and the holding electrode, so that the hollow cathode can generate electrons uniformly in the axial direction. If the number of holes is too small, it may lead to insufficient axial electron uniformity and affect the plasma generation efficiency in the thruster discharge chamber; if the number of holes is too large, the gas pressure inside the hollow cathode will be reduced, reducing the ability of the hollow cathode to generate electrons.

[0055] Although the circumferential porous hollow cathode of the present invention has three more holes than the traditional hollow cathode, its working background is a high-power ion thruster, which is usually in a high-flow, high-power mode when working. Therefore, the appropriate increase in the number of holes will not have a negative impact on the gas pressure inside the hollow cathode. Its electron generation ability will not be weakened, on the contrary, the above-mentioned gain will enhance its working ability to a certain extent.

[0056] The cathode pole shoe is coaxially sleeved on the outer periphery of the cathode emission end outside the n cathode emission holes, and the electromagnet is coaxially sleeved on the outer periphery of the cylindrical shell.

[0057] Assuming that the length of the cathode pole shoe is L, and the distance between the cathode pole shoe and the cathode emission end is W, by adjusting L and W, the trajectory of electrons in the discharge chamber can be adjusted and made the trajectory of electrons the same as or close to that of electrons in a conventional hollow cathode. Figure 4 shown.

[0058] The grid assembly is arranged on the open tail end of the discharge chamber, and the center of the grid assembly is connected to the closed end face of the cathode emission end through the grid support rod. The diameter of the grid assembly can be greater than 60cm, so that the power of the large-caliber ion thruster can reach 60-100kW. The grid is preferably made of precision alloy (4J33) or molybdenum.

[0059] The grid support rod can be made of a material with good hardness, no participation in ionization reaction and deformation resistance, one end of which is welded to the top of the hollow cathode shell, and the other end is supported at the center of the grid. The diameter of the grid support rod is preferably equal to the following screen grid hole spacing, so that the existence of the hard rod will not affect the grid operation.

[0060] The grid assembly comprises a screen grid and an accelerating grid arranged in parallel; wherein the hole spacing of the screen grid is smaller than the hole spacing of the accelerating grid; and the grid support rod is preferably connected to the center of the screen grid and the accelerating grid respectively.

[0061] When working, firstly, the heater is passed through the heating current until the emitter is heated to a certain emission temperature. After that, the working fluid (the working gas of the hollow cathode is usually xenon) flows into the hollow cathode tube. Under the current limiting effect of the small hole of the hollow cathode, the pressure inside the hollow cathode tube is usually several orders of magnitude higher than the pressure outside the small hole, generally up to 1-2 kPa. The emitter is slowly heated to about 2000K by the heater. After the cathode is ignited by the holding electrode and a voltage of about several hundred volts is applied to the cathode, a gas discharge is generated between the emitter and the ignition electrode. When the gas discharge is established, a high-density plasma is generated in the hollow cathode tube, and finally the hollow cathode is in a self-sustaining discharge state. A large number of primary electrons generated by the emitter will be emitted at high speed from the four cathode holes and participate in the formation of plasma in the discharge chamber. Finally, the ions are accelerated and extracted through the gate. At this time, the existence of the gate support rod can better reduce the degree of gate deformation under large diameter, so that the thruster can still work stably under large diameter.

[0062] Analysis of the impact on plasma generation: After the primary electrons are generated along the circumferential direction by touching the anode hole, the presence of the cathode pole shoe can further prevent the electrons from moving toward the anode, so that most of the primary electrons still have the same ejection direction as the traditional ion thruster, such as Figure 4 Therefore, the whole process of plasma generation will not be affected by the adjustment of the structure.

[0063] The preferred embodiments of the present invention are described in detail above; however, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all belong to the protection scope of the present invention.

Claims

1. A large-aperture ion thruster coupled with a circumferentially porous hollow cathode, characterized in that: It includes a discharge chamber, a circumferential porous hollow cathode, a cathode pole shoe, a grid assembly and a grid support rod; The discharge chamber is a cylindrical structure having a front end and an open rear end; The circumferentially porous hollow cathode is coaxially inserted on the front end surface of the discharge chamber and extends into the discharge chamber to form a cathode emission end with a closed end surface; n cathode emission holes are evenly arranged around the cathode emission end; wherein n≥2; The cathode pole shoe is coaxially sleeved on the outer periphery of the cathode emission end outside the n cathode emission holes; The grid assembly is arranged on the open tail end of the discharge chamber, and the center of the grid assembly is connected to the closed end surface of the cathode emission end through a grid support rod; the diameter of the grid assembly can be greater than 60 cm.

2. The large-aperture ion thruster with circumferentially porous hollow cathode coupling according to claim 1, characterized in that: The circumferential porous hollow cathode includes an emitter, a cathode tube, a heater and a touch-holding electrode arranged in sequence from the inside to the outside; wherein the emitter, the cathode tube and the touch-holding electrode have the same structure, which are all end-face closed structures; The emitter is provided with n emitting holes evenly distributed along the circumference, the cathode tube is provided with n cathode holes evenly distributed along the circumference, and the touch-holding electrode is provided with n touch-holding holes evenly distributed along the circumference; the n emitting holes, n cathode holes and n touch-holding holes correspond to each other in the circumferential position, and together form n cathode emitting holes.

3. The large-aperture ion thruster coupled with a circumferentially porous hollow cathode according to claim 2, characterized in that: The sum of the areas of the n emitting holes S is less than the newly added end surface area ΔS of the emitter.

4. The large-aperture ion thruster with circumferentially porous hollow cathode coupling according to claim 3, characterized in that: Assuming that a conventional hollow cathode has an axial cathode emission hole along the axis and with an area of ​​S0, then S>S0.

5. The large-aperture ion thruster with circumferentially porous hollow cathode coupling according to claim 4, characterized in that: The diameter d of each cathode emitting hole and the number n of the cathode emitting holes are adjusted so as to satisfy S0<S<ΔS.

6. The large-aperture ion thruster with circumferentially porous hollow cathode coupling according to claim 5, characterized in that: d = (1 / 8 ~ 1 / 15) D, where D is the cathode tube diameter, and D is proportional to the power of the large-aperture ion thruster.

7. The large-aperture ion thruster with circumferentially porous hollow cathode coupling according to claim 6, characterized in that: The power of large-caliber ion thrusters can reach 60 to 100 kW.

8. The large-aperture ion thruster with circumferentially porous hollow cathode coupling according to claim 5, characterized in that: n=4,d=0.2~0.4cm.

9. The large-aperture ion thruster with circumferentially porous hollow cathode coupling according to claim 1, characterized in that: Assuming the length of the cathode pole shoe is L, and the distance between the cathode pole shoe and the cathode emission end is W, by adjusting L and W, the trajectory of electrons in the discharge chamber can be adjusted and made the trajectory of electrons the same as or close to the trajectory of electrons in a conventional hollow cathode.

10. The large-aperture ion thruster with circumferentially porous hollow cathode coupling according to claim 1, characterized in that: The grid assembly includes a screen grid and an accelerating grid arranged in parallel; wherein the hole spacing of the screen grid is smaller than the hole spacing of the accelerating grid; the grid support rods are respectively connected to the centers of the screen grid and the accelerating grid, and the diameter of the grid support rods is equal to the hole spacing of the screen grid.

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