JP2020143581A - Ion thruster - Google Patents

Abstract

To provide an ion thruster having an electrostatic acceleration portion using a flat-plate grid capable of preventing ion beamlets from excessively diverging from through holes over the entire grid and taking a wide thrust range.SOLUTION: An ion thruster has a discharge chamber, a screen grid 40 disposed on its opening portion, and an acceleration grid 50 disposed in a manner that plane views of the screen grid 40, an acceleration grid through hole 51 and a screen grid through hole 41 are overlapped, and the acceleration grid 50 has a plurality of through holes 51 penetrating in a thickness direction from a central portion to a peripheral edge portion, and an enlarged diameter portion of at least one of (a) and (b). (a) An upstream-side enlarged diameter portion 52(b) in which a diameter of the through hole 51 is expanded to the screen grid 40 side at a surface of the screen grid 40 side, of the acceleration grid 50, and (b) a downstream-side enlarged diameter portion 53 in which the diameter of the through hole 51 is enlarged to a side opposite to the screen grid 40, at a surface of a side opposite to the screen grid 40, of the acceleration grid 50.SELECTED DRAWING: Figure 2

Description

The present invention relates to an ion thruster.

For example, ion thrusters are used for orbit control, north-south position maintenance, propulsion, etc. of space structures such as artificial satellites.
The ion thruster ionizes the propellant in the discharge chamber to generate plasma in the discharge chamber, and in the electrostatic acceleration unit, draws ions from the plasma and accelerates them to obtain thrust. At that time, in order to prevent the potential of the satellite or the like from dropping due to the emission of ions, the same amount of electrons as the ions are emitted from the neutralizing cathode.

The electrostatic acceleration unit of the DC discharge type ion thruster is a grid system composed of two or three grids. Each grid is called a screen grid, an accelerator grid, and a discel grid in order from the discharge chamber side. The discell grid may be omitted. Each grid has a thickness of about 1 mm and has a large number of through holes having a diameter of about 2 mm penetrating in the thickness direction. Further, each grid is fixed at an interval of about 1 mm. Further, each grid is applied with potentials such as + 1000V, −300V, and 0V depending on the power source. The cations drawn from the discharge chamber through the through holes of the screen grid are accelerated by the electric field between the screen grid and the accelerator grid and released into outer space (see, for example, Patent Documents 1 and 2).

There are two types of grids, dish-shaped and flat-shaped, and the flat-plate grid system is a grid system consisting of a flat-screen screen grid and an accelerator grid that do not have curvature, or an accelerator grid in addition to them. Is.
The flat grid system has an advantage that it is easy to design and can be manufactured at low cost, but there is a problem in the operating range. This problem is caused by the fact that the ion extraction state is different between the central portion and the peripheral portion of the grid. 6 to 8 are cross-sectional views showing an outline of a cation extraction state by a conventional flat plate grid system. 6 to 8, reference numeral 301 is a screen grid, reference numeral 302 is an accelerator grid, reference numeral 303 is a grid system generically referred to as a screen grid 301 and an accelerator grid 302, and reference numeral 400 is a plasma generated in a discharge chamber.

The extraction of cations in the grid system is affected by the plasma density in the discharge chamber, the spacing between the grids, and the potential difference between the grids. That is, in order to obtain the desired state of cation extraction, there is an optimum grid spacing corresponding to the plasma density and the potential difference. The desirable state is a state in which more ions are extracted in order to increase the thrust under an acceptable ion beam divergence angle, as shown in FIG. That is, the cations 500 are released to the outside without colliding with the accelerator grid 302.
More specifically, the shape of the ion extraction surface 400a is determined by the plasma density and the electric field between the screen grid 302 and the accelerator grid 301. The electric field between the grids is determined by the potential of each grid, the hole diameter of the through hole of each grid, and the grid spacing. When these are properly selected, the ion extraction surface 400a becomes concave, and the angle formed by the trajectory of the ion 500 accelerated from the screen grid through hole 301a through the accelerator grid through hole 302a and the central axis 600 of the hole is small. At this time, the ion beamlet 500a, which is a group of ions 500, is not excessively diverged.

When the density of the plasma 400 becomes low, as shown in FIG. 7, the ion extraction surface 400a of the cation 500 in the plasma 400 recedes. Then, the orbitals of the extracted cations 500 intersect, and the ion beamlet 500a diverges greatly. When the cation 500 diffuses significantly, the proportion of energy that contributes to thrust decreases. Further, the cation 500 collides with the through hole 302a of the accelerator grid 302, the accelerator grid 302 is worn, and if it continues for a long period of time, the ions cannot be drawn out.

On the other hand, when the density of the plasma 400 becomes high, as shown in FIG. 8, the ion extraction surface 400a of the cation 500 in the plasma 400 moves in the direction approaching the accelerator grid 302. Then, the angle formed by the central axis 600a of the through hole and the orbit of the cation 500 drawn out becomes large, and the ion beamlet 500a diffuses greatly. When the cation 500 diffuses significantly, the proportion of energy that contributes to thrust decreases. Further, the cation 500 collides with the through hole 302a of the accelerator grid 302, and the accelerator grid 302 is worn.

The plasma density in the discharge chamber is not uniform, and the extraction of ions may be undesirable at some points on the same grid. As an example, in a DC discharge type ion thruster, the plasma density is generally highest in the center of the grid and decreases toward the periphery of the grid. Therefore, in the portion between the central portion and the peripheral portion of the grid, as shown in FIG. 6, if the ion beamlet 500a is not excessively diffused, FIG. 7 is directed toward the peripheral portion of the grid 303. As shown in, the density of the plasma 400 becomes low. Then, since the distance between the screen grid 301 and the accelerator grid 302 is constant, the diffusion of the ion beamlet 500a becomes large in the holes at the peripheral edge of the grid 303, as shown in FIG.

That is, when the thrust is reduced, the plasma density of the entire discharge chamber is lowered, the plasma density is extremely lowered at the through hole at the peripheral edge of the grid, and as shown in FIG. 7, the ion beamlet 500a is greatly diffused. In the worst case, the cation 500 collides with the through hole 302a of the accelerator grid 302. The thrust corresponding to the plasma density distribution when the cation 500 collides with the through hole 302a of the accelerator grid 302 is set as the lower limit of the thrust. On the other hand, when an attempt is made to increase the thrust, the plasma density of the discharge chamber increases, and as shown in FIG. 8, the ion beamlet 500a diffuses greatly, and in the worst case, the cation 500 is a through hole of the accelerator grid 302. It collides with the opening of 302a or the like. The thrust corresponding to the plasma density distribution when the cation 500 collides with the opening of the through hole 302a of the accelerator grid 302 is set as the upper limit of the thrust. Conventionally, due to such lower and upper limits of thrust, the flat grid system has a significantly narrow operating range.

Further, when the orbit of the ion has a large angle with respect to the central axis 600 of the through hole 302a of the accelerator grid 302, the velocity component that does not contribute to the thrust increases, the momentum decreases, and the apparent effective thrust of the ion thruster increases. Decreases.
For example, when an ion thruster is applied to a geostationary satellite, if the orbit of the ion has a large angle with respect to the central axis 600 of the through hole 302a as shown in FIGS. 7 and 8, the ion will appear on the solar panel. There is a big restriction on the installation angle of the ion thruster so that they do not collide with each other. In addition, in order to obtain the thrust for performing the necessary attitude control within a certain period of time, the size of the ion thruster may be increased and a large amount of propellant may be consumed.

Japanese Unexamined Patent Publication No. 2003-139044 Japanese Unexamined Patent Publication No. 2003-201957

The present invention has been made in view of the above circumstances, and is a flat plate grid capable of preventing excessive emission of ion beamlets from through holes of the grid over the entire grid and widening the thrust range. It is an object of the present invention to provide an ion thruster having an electrostatic acceleration unit using the above.

In order to solve the above problems, the present invention proposes the following means.
The present invention is an ion thruster having a discharge chamber, a screen grid arranged at an opening of the discharge chamber, and an accelerator grid arranged so as to overlap the screen grid at a distance from the screen grid. The accelerator grid has a plurality of through holes penetrating in the thickness direction from the central portion to the peripheral portion of the access grid, and the through holes of the accelerator grid are at least one of the following (a) and (b). It is characterized by having one of the enlarged diameter portions.
(A) In the accelerator grid, the through hole is a first diameter-expanded portion (b) in the accelerator grid, which expands in diameter to the screen grid side surface of the accelerator grid. Is a second diameter-expanded portion that expands in diameter on the surface of the accelerator grid opposite to the screen grid and on the side opposite to the screen grid.

According to the ion thruster according to the present invention, it is possible to prevent the ion beamlet from the through hole of the grid from diverging excessively over the entire grid. As a result, the thrust range can be widened.

It is sectional drawing which shows the schematic structure of the ion thruster which concerns on embodiment of this invention. It is sectional drawing which shows the schematic structure of the grid of the ion thruster which concerns on embodiment of this invention. It is a front view which shows the schematic structure of the grid of the ion thruster which concerns on embodiment of this invention. It is a figure which shows the distribution of the plasma density in the discharge chamber of the ion thruster which concerns on embodiment of this invention. It is sectional drawing which shows the schematic structure of the modification of the grid of the ion thruster which concerns on embodiment of this invention. It is sectional drawing which shows the outline of the drawing state of the cation by the conventional flat plate grid system. It is sectional drawing which shows the outline of the drawing state of the cation by the conventional flat plate grid system. It is sectional drawing which shows the outline of the drawing state of the cation by the conventional flat plate grid system.

[Ion thruster]
Hereinafter, the ion thruster of the present embodiment will be described with reference to FIG.
FIG. 1 is a cross-sectional view showing a schematic configuration of the ion thruster of the present embodiment. FIG. 2 is a cross-sectional view showing a schematic configuration of the grid of the ion thruster of the present embodiment.
As shown in FIG. 1, the ion thruster 10 of the present embodiment has a discharge chamber 20, an anode 30, a screen grid 40, an accelerator grid 50, and a discel grid 60.

The discharge chamber 20 has an airtight structure including a non-magnetic metal cylinder 20a, an iron bottom plate 20b, and an iron downstream hole piece 20c. There are a plurality of bar magnets 21 on the outside of the metal cylinder 20a, and the bar magnets 21 are sandwiched between the bottom plate 20b and the downstream hole piece 20c. The bar magnet 21 may be a permanent magnet, an electromagnet, or a combination of a permanent magnet and an electromagnet. A magnetic circuit is composed of a bar magnet 21, a bottom plate 20b, an upstream pole piece 23, and a downstream hole piece 20c, and magnetic lines 80 are generated inside the discharge chamber 20. A hollow cathode 22 that emits electrons is provided at the center of the bottom plate 20b of the discharge chamber 20. Further, the bottom plate 20b of the discharge chamber 20 may be provided with a propellant supply port for supplying a propellant such as xenon to the inside of the discharge chamber 20. Further, a metal cylindrical anode 30 is provided inside the metal cylinder 20a. The anode 30 is held at a higher potential than the hollow cathode 22. Therefore, most of the electrons generated from the hollow cathode 22 finally reach the anode 30. In this process, electrons collide with propellant atoms and are ionized, producing ions. As a result, plasma is generated in the discharge chamber 20. The electrons are easy to move in the direction of the magnetic field lines, but are difficult to move in the direction across the magnetic field lines. By generating the magnetic field lines 80, the time for the electrons to stay in the discharge chamber 20 is increased. , Increasing the probability of ionization.
Although the ion thruster 10 according to the present embodiment uses a DC discharge type plasma generation mechanism, it may be an ion thruster adopting another method. For example, it may be a Radio Frequency (RF) type described in JP-A-4-86376, an Electron Cyclotron Resonance (ECR) type described in JP-A-3-145578, or the like.

The screen grid 40 has a disk shape in a plan view. As shown in FIG. 2, the screen grid 40 has a plurality of screen grid through holes 41 penetrating in the thickness direction.
The screen grid 40 is arranged in the opening 20c of the discharge chamber 20 so as to close the discharge chamber 20.

The accelerator grid 50 has a disk shape in a plan view. As shown in FIG. 2, the accelerator grid 50 has a plurality of accelerator grid through holes 51 penetrating in the thickness direction. The accelerator grid through hole 51 corresponds to the through hole according to the present invention.
As shown in FIG. 1, the accelerator grid 50 has a plan view of the screen grid 40, the accelerator grid through hole 51, and the screen grid through hole 41 at a distance from the screen grid 40 on the side opposite to the discharge chamber 20. They are arranged so that they overlap.

FIG. 3 is a schematic front view showing the screen grid 40.
In FIG. 3, the screen grid 40 has a plurality of screen grid through holes 41, mounting holes 42, and mounting holes 43 penetrating in the thickness direction thereof.
The mounting holes 42 and 43 are used for the purpose of fixing the screen grid 40 regardless of the extraction / acceleration of ions. In addition to the screen grid 40, the accelerator grid 50 and the discel grid 60, which will be described later, also have a plurality of accelerator grid through holes 51 and a plurality of discel grid through holes, respectively. For one screen grid through hole 41, there is one accelerator grid through hole 51 and one decel grid through hole through which ions drawn from the screen grid through hole accelerate and pass. These through holes are generally arranged so as to be coaxial with the central axis A direction.

Molybdenum, which has excellent spattering resistance, is often used as the grid material. Since metal materials such as molybdenum cause thermal expansion, each grid is made into a dish shape in advance in order to align the direction of deformation of each grid during thermal expansion to be convex or concave with respect to the discharge chamber. A method of appropriately designing the curvature is common. In addition, the distance between the grids can be controlled by appropriately designing the curvature for each grid. Examples of grid materials other than metal materials include carbon-based materials. Examples of the carbon-based material include graphite, carbon carbon (C / C), and the like. The carbon-based material has a sputtering resistance higher than that of molybdenum and has an extremely small coefficient of linear expansion. Therefore, the carbon-based material is superior to the dish-shaped grid in terms of cost because the grit can be produced on a flat plate without having to have a curvature, and it is easy to design and manufacture.

The discel grid 60 has a disk shape in a plan view. The discel grid 60 has a large number of discell grid through holes (not shown) penetrating in the thickness direction.
As shown in FIG. 1, the discel grid 60 is a plan view of the accelerator grid 50, the accelerator grid through hole 51, and the screen grid through hole 41 at a distance from the accelerator grid 50 on the side opposite to the discharge chamber 20. Are arranged so that they overlap.

That is, the screen grid 40, the accelerator grid 50, and the discel grid 60 are arranged in this order from the discharge chamber 20 side.
In the present embodiment, the shapes of the screen grid 40, the accelerator grid 50, and the discel grid 60 are all disk-shaped in a plan view, but they may be polygonal or any other shape.

As shown in FIG. 2, in the peripheral portion 50A of the accelerator grid 50, the accelerator grid through hole 51 has an upstream side diameter expansion in which the inner diameter is increased on the screen grid 40 side surface 50a of the accelerator grid 50 on the screen grid 40 side. It has a part 52. In FIG. 2, the number of holes in the outer edge portion-center portion-outer edge portion is set to 5, but the number is not limited to 5, and may be any number. The upstream side diameter-expanded portion 52 corresponds to the first diameter-expanded portion according to the present invention. Specifically, the upstream side enlarged diameter portion 52 is a recess in the accelerator grid 50 that is recessed from the surface 50a on the screen grid 40 side to the side opposite to the screen grid 40.
The peripheral portion 50A of the accelerator grid 50 is a portion of the accelerator grid 50 corresponding to a high plasma density near the central axis of the discharge chamber.

As shown in FIG. 2, in the central portion 50B of the accelerator grid 50, the accelerator grid through hole 51 is formed on the surface of the accelerator grid 50 opposite to the screen grid 40 (the surface on the discel grid 60 side) 50b. A downstream side diameter-expanding portion 53 whose inner diameter is expanded is provided on the opposite side (disel grid 60 side) from 40. The downstream side diameter-expanded portion 53 corresponds to the second diameter-expanded portion according to the present invention. Specifically, the downstream side enlarged diameter portion 53 is a recess in the accelerator grid 50 that is recessed from the surface 50b on the side opposite to the screen grid 40 to the screen grid 40 side.
The central portion 50B of the accelerator grid 50 is a portion of the accelerator grid 50 facing the hollow cathode 22 arranged in the central portion of the discharge chamber 20.

Further, as shown in FIG. 2, in the portion (intermediate portion) 50C between the peripheral portion 50A and the central portion 50B of the accelerator grid 50, the accelerator grid through hole 51 is formed on the upstream side enlarged diameter portion 52 and the downstream side. It does not have an enlarged diameter portion 53. That is, in the intermediate portion 50C of the accelerator grid 50, the inner diameters of the accelerator grid through holes 51 are equal over the entire length of the accelerator grid 50 in the thickness direction.

For example, in the DC discharge type, the density of the plasma 80 in the discharge chamber 20 is distributed so as to be high in the central portion and gradually decrease toward the peripheral portion, as shown in FIG. In this embodiment, the case where the density of the plasma 80 in the discharge chamber 20 shows the distribution as shown in FIG. 4 is illustrated, but the plasma density to which the ion thruster 10 of the present embodiment can be applied is not limited to this. .. The ion thruster 10 of the present embodiment can be applied to any plasma density, for example, a plasma density in which the central portion is low and gradually increases toward the peripheral portion.
In the ion thruster 10 of the present embodiment, in the peripheral portion 50A of the accelerator grid 50 facing the peripheral portion where the density of the plasma 80 is low in the discharge chamber 20, the accelerator grid through hole 51 is on the screen grid 40 side of the accelerator grid 50. The surface 50a has an upstream side diameter-expanding portion 52 that expands the diameter toward the screen grid 40 side. Further, in the central portion 50B of the accelerator grid 50 facing the central portion where the density of the plasma 80 is high in the discharge chamber 20, the accelerator grid through hole 51 is provided on the surface 50b of the accelerator grid 50 opposite to the screen grid 40. The downstream side diameter-expanding portion 53 that expands the diameter on the side opposite to the screen grid 40 is provided. Further, in the intermediate portion 50C of the accelerator grid 50 facing the intermediate portion between the central portion where the density of the plasma 80 is high and the peripheral portion where the density of the plasma 80 is low in the discharge chamber 20, the accelerator grid through hole 51 is formed. It does not have the upstream side enlarged diameter portion 52 and the downstream side enlarged diameter portion 53.

The depth of the upstream side enlarged diameter portion 52, that is, the length d1 of the accelerator grid 50 that is recessed from the surface 50a on the screen grid 40 side to the side opposite to the screen grid 40, is such that the position of the drawing surface 80a of the plasma 80 is the accelerator. It can be adjusted so as to be about the same as the pull-out surface 80a of the intermediate portion 50C of the grid 50.

The depth of the downstream side enlarged diameter portion 53, that is, the length d2 of the accelerator grid 50 that is recessed from the surface 50b opposite to the screen grid 40 toward the screen grid 40, is such that the position of the extraction surface 80a of the plasma 80 is the accelerator. It can be adjusted so as to be about the same as the pull-out surface 80a of the intermediate portion 50C of the grid 50.

The extraction surface 80a of the plasma 80 is a surface regarded as a starting point when the cation 90 in the discharge chamber 20 is drawn into the screen grid through hole 41 of the screen grid 40 or the accelerator grid through hole 51 of the accelerator grid 50. is there. In the ion thruster 10 of the present embodiment, the extraction surface 80a of the plasma 80 can be brought closer to the screen grid 40 side also in the peripheral portion 50A and the intermediate portion 50C of the accelerator grid 50.

According to the ion thruster 10 of the present embodiment, in the peripheral edge portion 50A of the accelerator grid 50, the through hole 51 has an upstream side diameter-expanding portion 52 that expands in diameter toward the screen grid 40 side on the surface 50a on the screen grid 40 side. , The ion beamlet 90a drawn out at the peripheral edge portion 50A can be prevented from diverging excessively. Specifically, in the peripheral edge portion 50A of the accelerator grid 50, the accelerator grid through hole 51 has an upstream-side enlarged diameter portion 52 that expands in diameter toward the screen grid 40 side on the surface 50a of the accelerator grid 50 on the screen grid 40 side. As a result, the electric field between the screen grid 40 and the accelerator grid 50 becomes smaller than in the case where the enlarged diameter portion 52 does not exist, so that the extraction surface 80a of the plasma 80 can be brought closer to the screen grid 40 side and accelerated. The angle formed by the orbit of the cation 90 and the central axis A of the grid (screen grid 40, accelerator grid 50, discel grid 60) is not excessive, and the divergence of the ion beamlet 90a formed by the assembly of the cation 90 Can be made smaller.
Further, in the central portion 50B of the accelerator grid 50, since the accelerator grid through hole 51 has a downstream diameter expanding portion 53 on the surface 50b on the side opposite to the screen grid 40, the diameter is expanded on the side opposite to the screen grid 40. It is possible to prevent the cation 90 from colliding with the accelerator grid 50. Specifically, in the central portion 50B of the accelerator grid 50, the accelerator grid through hole 51 expands on the surface 50a of the accelerator grid 50 on the side opposite to the screen grid 40 and on the downstream side expanding on the side opposite to the screen grid 40. By having the diameter portion 53, the extraction surface 80a of the plasma 80 is located closer to the screen grid 40, and even if the bundle of cation 90 (ion beamlet 90a) extracted from the discharge chamber 20 is thick, the ion beamlet ion It is possible to prevent the cation 90 on the outer edge side of the 90a from colliding with the opening of the accelerator grid through hole 51 of the accelerator grid 50.

According to the ion thruster 10 of the present embodiment, it is possible to prevent the ion beamlets drawn from the through holes from being excessively emitted over the entire grid. As a result, the thrust range can be widened.
Further, according to the ion thruster 10 of the present embodiment, since the downstream side enlarged diameter portion 53 is provided in addition to the upstream side enlarged diameter portion 52, the plasma density increases when the thrust of the ion thruster 10 is increased. Even if the divergence of the ion beamlet 90a drawn from the through hole becomes excessive, it is possible to reduce the collision of ions with the accelerator grid 50, and it is possible to widen the operating range in which thrust can be obtained.

<Other embodiments>
The present invention is not limited to the above embodiment.

For example, the accelerator grid 100 according to the modified example shown in FIG. 5 may be adopted. In the accelerator grid 100 according to the modified example, the same parts as the components in the embodiment are designated by the same reference numerals, the description thereof will be omitted, and only the different points will be described.

The accelerator grid 100 according to the modified example shown in FIG. 5 has a disk shape in a plan view. As shown in FIG. 5, the accelerator grid 100 has a plurality of accelerator grid through holes 101 penetrating in the thickness direction. The accelerator grid through hole 101 corresponds to the through hole according to the present invention.

As shown in FIG. 5, in the peripheral portion 100A of the accelerator grid 100, the accelerator grid through hole 101 has an upstream side diameter expansion in which the inner diameter is increased on the screen grid 40 side surface 100a of the accelerator grid 100 on the screen grid 40 side. It has a part 102. The upstream side diameter-expanded portion 102 corresponds to the first diameter-expanded portion according to the present invention. Specifically, the upstream side enlarged diameter portion 102 is a tapered portion that gradually reduces the diameter from the surface 100a on the screen grid 40 side of the accelerator grid 100 to the side opposite to the screen grid 40.
The peripheral edge portion 100A of the accelerator grid 100 is a portion of the accelerator grid 100 that faces the peripheral edge portion of the discharge chamber 20.

As shown in FIG. 5, in the central portion 100B of the accelerator grid 100, the accelerator grid through hole 101 is formed on the surface (the surface on the discel grid 60 side) 100b opposite to the screen grid 40 of the accelerator grid 100 and the screen grid. A downstream side diameter-expanding portion 103 whose inner diameter is expanded is provided on the opposite side (disel grid 60 side) from 40. The downstream diameter-expanded portion 103 corresponds to the second diameter-expanded portion according to the present invention. Specifically, the downstream side enlarged diameter portion 103 is a tapered portion of the accelerator grid 100 that gradually reduces in diameter from the surface 100b on the side opposite to the screen grid 40 to the screen grid 40 side.
The central portion 100B of the accelerator grid 100 is a portion of the accelerator grid 100 facing the hollow cathode 22 arranged in the central portion of the discharge chamber 20.

Further, as shown in FIG. 5, in the portion (intermediate portion) 100C between the peripheral portion 100A and the central portion 100B of the accelerator grid 100, the accelerator grid through hole 101 is formed on the upstream side enlarged diameter portion 102 and the downstream side. It does not have an enlarged diameter portion 103. That is, in the intermediate portion 100C of the accelerator grid 100, the inner diameters of the accelerator grid through holes 101 are equal over the entire length of the accelerator grid 100 in the thickness direction.

The depth of the upstream side enlarged diameter portion 102, that is, the length d3 in which the diameter is reduced from the surface 100a on the screen grid 40 side of the accelerator grid 100 to the side opposite to the screen grid 40, is such that the extraction surface 80a of the plasma 80 is the accelerator grid. It can be adjusted so as to be about the same as the pull-out surface 80a of the intermediate portion 50C of the above.

The depth of the downstream side enlarged diameter portion 103, that is, the length d4 of the accelerator grid 100 that is reduced in diameter from the surface 100b opposite to the screen grid 40 to the screen grid 40 side, is such that the extraction surface 80a of the plasma 80 is the accelerator grid. It can be adjusted so as to be about the same as the pull-out surface 80a of the intermediate portion 50C of the above.

According to the ion thruster of the present embodiment, in the peripheral portion 100A of the accelerator grid 100, the accelerator grid through hole 101 has an upstream side diameter-expanded portion 102 on the surface 100a on the screen grid 40 side to expand the diameter toward the screen grid 40 side. Therefore, the ion beamlet 90a drawn out at the peripheral edge portion 50A can be prevented from diverging excessively. As a result, the thrust range can be widened. Specifically, in the peripheral portion 100A of the accelerator grid 100, the accelerator grid through hole 101 has an upstream side diameter-expanded portion 102 that expands in diameter toward the screen grid 40 on the surface 100a of the accelerator grid 100 on the screen grid 40 side. As a result, the extraction surface 80a of the plasma 80 can be brought closer to the screen grid 40 side, and the orbit of the accelerated cation 90 and the central axis A of the grid (screen grid 40, accelerator grid 50, discel grid 60) form. The angle is not excessive and the divergence of the ion beamlet 90a formed by the assembly of cations 90 can be reduced.
Further, in the central portion 100B of the accelerator grid 100, since the accelerator grid through hole 101 has a downstream diameter expanding portion 103 on the surface 100b on the side opposite to the screen grid 40, the diameter is expanded on the side opposite to the screen grid 40. It is possible to prevent the cation 90 from colliding with the accelerator grid 50. Specifically, in the central portion 100B of the accelerator grid 100, the accelerator grid through hole 101 expands on the surface 100b on the side opposite to the screen grid 40 of the accelerator grid 100 and on the downstream side expanding on the side opposite to the screen grid 40. By having the diameter portion 103, the extraction surface 80a of the plasma 80 is located closer to the screen grid 40, and even if the bundle of cation 90 (ion beamlet 90a) extracted from the discharge chamber 20 is thick, the ion beamlet ion Prevents the cation 90 on the outer edge side of 90a from colliding with the opening of the accelerator grid through hole 101 of the accelerator grid 100, and prevents the ion beamlet 90a from the through hole from diverging excessively over the grid 100. be able to. As a result, the thrust range can be widened.

According to the ion thruster of this modification, even in the flat plate grid, the cation 90 drawn from the discharge chamber 20 is prevented from colliding with the accelerator grid through hole 101 of the accelerator grid 100 in the entire area of the accelerator grid 100, and the grid. It is possible to prevent the ion beamlet 90a from the through hole from diverging excessively throughout. As a result, the thrust range can be widened.

In the above embodiment, the case where the ion thruster 10 has the discell grid 60 is illustrated, but the present invention is not limited to this. The ion thruster of the present invention does not have to have a discell grid.
Further, in the above embodiment, the case where the accelerator grid 50 has the upstream side diameter expansion portion 52 and the downstream side diameter expansion portion 53, and the accelerator grid 100 has the upstream side diameter expansion portion 102 and the downstream side diameter expansion portion 103. Although exemplified, the present invention is not limited thereto. In the ion thruster of the present invention, if the accelerator grid has at least one of an upstream diameter expansion portion corresponding to the first diameter expansion portion and a downstream diameter expansion portion corresponding to the second diameter expansion portion. Good. Further, the upstream side diameter expansion portion 52, the downstream side diameter expansion portion 53, the upstream side diameter expansion portion 102, and the downstream side diameter expansion portion 103 may be mixed.

The ion thruster according to the present embodiment can be used for, for example, an artificial satellite. For example, when applied to a stationary orbital satellite, the orbits of ions accelerated and sent out from the ion thruster are aligned in a direction very close to the central axis of the through hole of the accelerator grid, so that the ions do not collide with the solar panel. It is possible to reduce the restrictions on the installation of ion thrusters for this purpose. In addition, it is possible to reduce the size of the ion thruster and save the amount of propellant used, which enables stable operation over a long period of time.

10 Ion thruster 20 Discharge chamber 30 Anode 40 Screen grid 41 Through hole 50, 100 Accelerator grid 50A, 101A Peripheral part 50B, 101B Central part 50C, 101C Intermediate part 51, 101 Through hole 52, 102 Upstream side diameter expansion part 53, 103 Downstream side diameter expansion part 60 discharge grid

Claims (8)

An ion thruster having a discharge chamber, a screen grid arranged at the opening of the discharge chamber, and an accelerator grid arranged so as to overlap the screen grid at a distance from the screen grid.
The accelerator grid has a plurality of through holes penetrating in the thickness direction from the central portion to the peripheral portion of the access grid.
An ion thruster characterized in that the through hole of the accelerator grid has an enlarged diameter portion of at least one of the following (a) and (b).
(A) In the accelerator grid, the through hole is a first diameter-expanded portion (b) in the accelerator grid, which expands in diameter to the screen grid side surface of the accelerator grid. Is a second diameter-expanded portion that expands in diameter on the surface of the accelerator grid opposite to the screen grid and on the side opposite to the screen grid. The ion according to claim 1, wherein in the accelerator grid, the through hole has a first diameter-expanded portion that expands in diameter toward the screen grid on the surface of the accelerator grid on the screen grid side. Thruster. A claim characterized in that, in the accelerator grid, the through hole has a second diameter-expanded portion that expands in diameter to the side opposite to the screen grid on a surface of the accelerator grid opposite to the screen grid. Item 2. The ion thruster according to item 2. The first one according to any one of claims 1 to 3, wherein the first diameter-expanded portion is a recess in the accelerator grid that is recessed from the surface on the screen grid side to the side opposite to the screen grid. Ion thruster. The ion according to any one of 1 to 4, wherein the second enlarged diameter portion is a recess in the accelerator grid that is recessed from a surface opposite to the screen grid to the screen grid side. Thruster. Any one of claims 1 to 3, wherein the first diameter-expanded portion is a tapered portion in the accelerator grid whose diameter gradually decreases from the surface on the screen grid side to the side opposite to the screen grid. The ion thruster described in the section. Item 1 to any one of 1 to 4, wherein the second diameter-expanded portion is a tapered portion of the accelerator grid that gradually reduces in diameter from a surface opposite to the screen grid to the screen grid side. The ion thruster described. The ion thruster according to any one of claims 1 to 7, wherein the accelerator grid and the screen grid are flat plate grids.

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