JP2014005799A - Ion beam generator - Google Patents

Abstract

An ion beam generator capable of performing plasma generation and neutralization using only one electron source installed outside a discharge chamber.
Ion acceleration is achieved by adjusting the acceleration grid voltage, arranging the ion passage holes 5a and 5b in the acceleration grid 4b and the screen grid 4a in a pattern different from the conventional one, and changing the area of the passage holes. The system 4 is used not only for emission of ion current but also for capturing electron current from the outside. As a result, an ion beam generator capable of operating with only one electron source is realized.
[Selection] Figure 1

Description

  The present invention relates to an ion engine mounted on an artificial satellite or the like, an ion beam generating apparatus used for material processing or the like.

  Ion engines are used for orbit control of artificial satellites, maintaining the north-south position, and main propulsion. Among such ion engines, an example of an ion beam generator that is a main part of a DC discharge ion engine is shown in FIG. 8 (partially cut out to show the internal structure).

  In the ion beam generator of FIG. 8, a shield case 1 made of a conductive material formed in a cylindrical shape has a plurality of small holes 2 on its peripheral wall. By providing the small holes 2, heat escapes from the discharge vessel 3 inside to the outside by radiation, and the weight of the ion beam generator is reduced. A cylindrical discharge vessel 3 made of a magnetic material is disposed in the shield case 1. The shield case 1 and the discharge vessel 3 are arranged so that their cylinders are coaxial. The opening of the discharge vessel 3 is covered with an ion acceleration system 4 composed of a screen grid 4a and an acceleration grid 4b.

  Each of the screen grid 4a and the acceleration grid 4b is a plate-like member made of a conductive material such as metal or carbon. The screen grid 4a has a plurality of ion passage holes 5a, and the acceleration grid 4b has a plurality of ion passage holes. 5b is formed. The ion passage holes 5a and 5b are concentric so that the center position of a certain ion passage hole 5a in the plane of the screen grid 4a and the center position of a certain ion passage hole 5b in the plane of the acceleration grid 4b coincide. Has been placed. However, even if this concentric relationship is not strict, normal operation is possible, and the strict concentric relationship may not be satisfied due to intentional, manufacturing restrictions or differences in the operating point of the ion engine. is there.

  FIG. 9 and FIG. 10 show two patterns conventionally known as formation patterns of the ion passage holes 5a and 5b. These drawings are schematic views drawn by partially cutting out the screen grid 4a or the acceleration grid 4b in the plane and showing the metal material portion by hatching. In FIG. 9, the ion passage holes 5 (ion passage holes 5a or 5b) are arranged in a close-packed manner with a uniform hole diameter in the plane of the screen grid 4a or the acceleration grid 4b in the ion acceleration system 4. On the other hand, in FIG. 10, the ion passage holes 53, 54, 55 have a hole diameter depending on the distance from the center of the screen grid 4 a or the acceleration grid 4 b to the center of each ion passage hole in the ion acceleration system 4. It is arranged in a close-packed manner while changing.

  The screen grid 4a and the acceleration grid 4b are each supported by a grid support mechanism 13, and are provided with a curvature for maintaining a grid interval of about 0.7 mm during rated operation (the screen grid 4a and the acceleration grid 4b are flat plates). Instead, they form curved surfaces such as spherical surfaces, etc. These grids have no curvature, that is, if they are configured as flat plates, the thermal strain of the grid becomes irregular and the grid spacing cannot be predicted or controlled. (For example, when these grids are formed as carbon grids, etc., the linear expansion coefficient is extremely small, so that a flat plate can be used.)

  A propellant distributor 6 is attached to the bottom wall of the discharge vessel 3, and small holes 7 are formed on the surface of the propellant distributor 6. The small hole 7 communicates with the gas introduction system 8 through the insulator 12 and discharges a propellant gas such as Xe (xenon) supplied from the gas introduction system 8 into the discharge vessel 3.

  Further, a hollow cathode 9 serving as a discharge cathode is disposed in the discharge vessel 3. A heater power supply (not shown) and a keeper power supply (not shown) are connected to the hollow cathode 9, and when the hollow cathode 9 is started, the heater power supply supplies a current to the heater (not shown), and a cathode insert (not shown) in the hollow cathode 9. Is heated above the temperature at which thermionic electrons can be emitted. The keeper power supply always supplies current to a keeper (not shown) during operation of the hollow cathode 9 to promote external emission of electrons in the hollow cathode 9.

  During operation of the ion engine, the discharge vessel 3 is kept at an anode potential with respect to the hollow cathode 9 by a power source (not shown). In this state, Xe gas passes through the insulator 12 from the gas introduction system 8 and is introduced into the discharge vessel 3 from the small hole 7 of the propellant distributor 6. Xe gas is also introduced into the discharge vessel 3 by passing through the insulator 12 from the gas introduction system 8 and then through the hollow cathode 9. Electrons are emitted from the hollow cathode 9 into the discharge chamber 3, and the electrons are accelerated by a potential difference between the hollow cathode 9 and the discharge vessel 3 and collide with Xe atoms, thereby ionizing Xe. As a result, plasma is generated in the discharge vessel 3. The plasma in the discharge vessel 3 is confined in a region away from the inner wall surface of the discharge vessel 3 by a cusp magnetic field created by the permanent magnet 10. Once a state in which plasma is generated in the discharge vessel 3 is reached, the state in which plasma is generated can be maintained without passing a current through the keeper.

During operation of the ion engine, the screen grid 4a is kept at a ground potential or a potential of about 1 kV with respect to the potential of the spacecraft on which the ion engine is mounted, and the acceleration grid 4b is kept at a potential of about -200V. . Usually, the screen grid 4a is connected to the hollow cathode 9 by an electric wire (not shown), and the hollow cathode 9 is also maintained at a potential of about 1 kV. The ion acceleration system 4 composed of the grids 4a and 4b extracts Xe ⁺ ions from the plasma in the discharge vessel 3, gives kinetic energy of about 1 keV to the ions, and discharges them into the space through the ion passage holes 5a and 5b. The reaction force accompanying this release becomes the thrust. In addition, the hollow cathode 11 used as a neutralizer performs electrical neutralization by discharging electrons e ⁻ having the same current value as the ion current of Xe ⁺ emitted from the ion accelerating system 4 into the outer space, and thereby performing artificial neutralization. Prevents satellites from being charged.

  FIG. 11 qualitatively represents the potential distribution in the space from the inside of the discharge vessel 3 through the ion passage holes 5a and 5b to the outer space along the central axis of the ion passage holes 5a and 5b. In this graph, the potential at the left end position is equal to the plasma potential in the discharge vessel 3, and the difference from the potential of the discharge vessel 3 is about several volts. The position of the screen grid 4a is affected by the potential of the screen grid 4a and is lower than that, and the position of the acceleration grid 4b is affected by the potential of the acceleration grid 4b and is higher than this. . Although the potential in the space takes a minimum value at the position of the acceleration grid 4b, during normal operation of the ion beam generator, the potential at this position is sufficiently lower than the potential outside the ion beam generator (right side in the graph). For this reason, electrons outside the ion beam generator cannot pass through the acceleration grid 4b and move inside the ion beam generator except for a very small number of electrons with extremely high energy.

However, if the density of Xe ⁺ ions passing through the ion passage hole 5b becomes too high, the minimum potential at this position increases due to the positive charge of the Xe ⁺ ions, and many electrons pass through the acceleration grid 4b. It becomes possible to move inside the ion beam generator. In FIG. 8, the electrons moved to the left side of the acceleration grid 4b move to the inside of the discharge vessel 3 and promote ionization of the Xe gas, so that the plasma density in the discharge vessel 3 increases. As a result, the ion current passing through the ion passage hole 5b increases, and the ion density at the minimum potential point further increases. When the ion current passing through the ion passage holes 5a and 5b rises and exceeds the upper limit value due to such a positive feedback relationship, an ion beamlet (an aggregate of ions passing through the individual ion passage holes 5a. Ion beamlet). ) Collides with the metal material portion of the acceleration grid 4b, an excessive current flows through a power source (not shown) connected to the acceleration grid 4b and the acceleration grid 4b is worn out. In order to avoid this, contrivances have been made such as adjusting the amount of ions generated in the discharge vessel 3, keeping the potential of the acceleration grid 4b sufficiently low, and preventing electrons from flowing in from the outside of the discharge vessel. .

Dan M. Goebel & Ira Katz, "Fundamentals of Electric Propulsion," (USA), Wiley, November 2008

  The conventional ion beam generator includes two electron sources (hollow cathodes 9 and 11). In order to operate these electron sources, a gas supply system and a power supply system associated with the electron sources are necessary. There has been a problem that the structure of the generator is complicated. Furthermore, since these electron sources are expensive and occupy a large proportion of the total cost of the ion engine, there is a problem that the cost of the ion engine is increased by requiring a plurality of electron sources.

  The conventional ion beam generator is configured to supply electrons used for plasma generation from an electron source in a discharge vessel. The electron source in the discharge vessel operates at a potential of about 1 kV from the ground potential or the like. Therefore, there has been a problem that a complicated and expensive power source having a sufficient ground insulation function is required to supply power to this. In this regard, since the conventional ion beam generator has a configuration that prevents electrons from flowing into the discharge vessel as described above, it is essential to provide an electron source inside the discharge chamber. .

  Conventional ion engines have these problems, and it has been difficult to adopt them in small satellites and the like that are required to be manufactured at low cost.

  Therefore, an object of the present invention is to provide an ion beam generator capable of performing plasma generation and neutralization using only one electron source installed outside the discharge chamber.

The present invention
(I) a discharge vessel;
(Ii) a gas introduction system for introducing a working gas into the discharge vessel;
(Iii) an insulator for preventing discharge inside the gas between the discharge vessel and the gas introduction system;
(Iv) an electron source installed outside the discharge vessel;
(V) Electrons emitted from the electron source are introduced into the discharge vessel as an electron current, and ions in the plasma generated by collision of the electrons introduced into the discharge vessel with the working gas particles are introduced. An ion beam generator comprising: a screen grid having a plurality of passage holes and an ion acceleration system including an acceleration grid, which is accelerated and sent to the outside of a discharge vessel as an ion current.

  In the ion beam generator of the present invention, electrons emitted from an electron source outside the discharge chamber are introduced into the discharge chamber, and plasma is generated using the electrons. Therefore, it is not necessary to install an electron source for plasma generation inside the discharge vessel. However, an arbitrary electron source may be installed in the discharge chamber as needed, such as when used as a backup electron source.

  In the ion beam generator of the present invention, it is preferable that a part of the plurality of through holes in the acceleration grid has a larger area than the surrounding through holes in the acceleration grid. By adopting such a configuration, a through hole having a large area is mainly used as an electron current path, while a surrounding through hole can be mainly used as an ion current path. However, it is not essential to provide a difference in the size of the passage holes.

  Among the plurality of through holes in the screen grid, the through holes at positions corresponding to the positions of the through holes having a larger area than the surrounding through holes in the acceleration grid are compared with the surrounding through holes in the screen grid. It is preferable to have a small area. A through-hole having a large area in the acceleration grid is inferior to the surrounding through-hole in terms of the ability to extract ions from the plasma. Therefore, a through-hole having a small area is provided at a corresponding position in the screen grid and directed toward the acceleration grid. It is effective to reduce the ion beamlet.

  The ion beam generator of the present invention preferably includes means for adjusting the magnitude of the ion current by changing the potential of the acceleration grid. Similarly, the magnitude of the ion current can be adjusted by changing the potential of the discharge vessel.

  In the ion engine of the present invention, plasma generation and neutralization can be performed using only one electron source. Therefore, of the two electron sources used in the conventional ion engine, the electron source in the discharge vessel. Can be removed to provide a low-cost ion engine. Further, since the hollow cathode, which is a heat source, can be removed from the discharge vessel, the amount of heat flowing into the artificial satellite or the like can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an internal structure of a part of an ion beam generator according to an embodiment of the present invention. It is the top view which partially cut out and showed the 1st example of the acceleration grid integrated in the ion beam generator of this invention in the surface. It is the top view which cut out partly and showed the 1st example of the screen grid integrated in the ion beam generator of this invention in the surface. It is the top view which partially cut out and showed the 2nd example of the acceleration grid integrated in the ion beam generator of this invention in the surface. It is the top view which partially cut out and showed the 2nd example of the screen grid integrated in the ion beam generator of this invention in the surface. It is the top view which partially cut out and showed the 3rd example of the acceleration grid integrated in the ion beam generator of this invention in the surface. It is the top view which partially cut out and showed the 3rd example of the screen grid integrated in the ion beam generator of this invention in the surface. It is the perspective view which cut off a part and showed the internal structure about the conventional ion beam generator. It is the top view which partially cut out and showed the 1st example of the acceleration grid incorporated in the conventional ion beam generator, or the screen grid. It is the top view which cut out partly and showed the 2nd example of the acceleration grid incorporated in the conventional ion beam generator, or the screen grid. It is the figure which expressed qualitatively the potential distribution in the space from the inside of a discharge vessel to the exterior through the ion passage hole of a screen grid and an acceleration grid along the central axis of an ion passage hole.

  The configuration and operation of the ion beam generator according to the present invention will now be described with reference to the drawings. However, the configuration and operation of the ion beam generator according to the present invention are not limited to the specific specific configuration and operation shown in the drawings and the related description. This will be described in detail later.

Configuration of Ion Beam Generating Device According to the Present Invention FIG. 1 shows the configuration of an ion beam generating device according to an embodiment of the present invention (partially cut out to show the internal structure). Elements similar to those of the conventional ion beam generator are denoted by the same reference numerals as those in FIG. The description of the same elements as those in the related art will be omitted.

  The ion beam generator of FIG. 1 differs from the ion beam generator of FIG. 8 in that the configuration of FIG. 1 is a hollow cathode 9 in a discharge vessel 3 and a gas introduction system for sending a working gas to this. 8. It is mentioned that the insulator 12 is not included. As will be described later, the ion beam apparatus of the present invention introduces electrons emitted from a hollow cathode 11 outside the discharge vessel 3 and conventionally used only as a neutralizer into the discharge vessel 3 to generate plasma. Is possible. Therefore, there is no need to provide an electron source inside the discharge vessel.

  When the hollow cathode is used for both the neutralizer and the plasma generating electron source, the formation patterns of the passage holes 5a and 5b in the screen grid 4a and the acceleration grid 4b are shown in FIGS. It is preferable to change from such a conventional pattern.

  An example of the acceleration grid 4b in which the passage holes 5b are formed in a preferable pattern is shown in FIG. 2, and an example of the screen grid 4a in which the passage holes 5a are formed in a pattern corresponding to this is shown in FIG. As shown in FIG. 2, some of the passage holes 52b in the acceleration grid 4b have a larger area than the surrounding passage holes 51b (if the passage holes are circular, they correspond to the hole diameter). .)have. As will be described in detail later, the large passage hole 52b mainly functions as a path for introducing electrons from the outside of the discharge vessel 3, and the small passage hole 51b mainly takes ions from plasma generated in the discharge vessel 3. It functions as a route to accelerate and release.

  Further, as shown in FIG. 3, in the acceleration grid 4b, at the position corresponding to the position of the large passage hole 52b (the position overlapping when viewed from the direction perpendicular to the grid surface), the passage hole 52a in the screen grid 4a It is formed as a passage hole having a smaller area than the passage hole 51a. As will be described in detail later, with such a configuration, it is possible to reduce the ion beamlet toward the passage hole 52b inferior in ion extraction capability and to flow an excessive current to a power source (not shown) connected to the acceleration grid 4b. In addition to preventing, it is possible to prevent the acceleration grid 4b from being worn.

Operation of Ion Beam Generating Device According to the Present Invention Hereinafter, an ion beam generating operation by the ion beam generating device of FIG. 1 will be described.

First, the hollow cathode 11 is operated to emit electrons, and then the working gas is supplied into the discharge vessel 3 through the propellant distributor 6. Here, the screen grid 4a and the acceleration grid 4b are set to predetermined potentials, for example, the screen grid 4a is set to 500V and the acceleration grid 4b is set to -50V. However, since the discharge starts, the potential of the acceleration grid 4b is temporarily close to 0V. Raise. At this time, as means for facilitating the start of discharge, the potential of the hollow cathode 11 is made negative, for example, −15 V by temporarily increasing the flow rate of the working gas and by a power source (not shown) connected to the hollow cathode 11. It is effective.

  Since the voltage of the acceleration grid 4b is in the vicinity of 0V, the emitted electrons flow into the discharge vessel 3 as an electron current. The electron current flows mainly through the passage hole 52b having a large area among the passage holes 51b and 52b in the acceleration grid 4b. The electrons are accelerated by the electric potential of the discharge vessel 3 and collide with Xe atoms, and plasma is generated by ionizing Xe.

  In the conventional ion engine, passage holes are provided in a pattern as shown in FIG. 9, the diameter of the passage hole 5a is set to 2 mm, for example, the diameter of the passage hole 5b is set to 1.5 mm, and the plate thickness of the screen grid 4a is set to, for example, The plate thickness of 0.3 mm and the acceleration grid 4b was 0.5 mm, for example. However, in such a configuration, no plasma is generated in the discharge vessel 3 even when the potential of the acceleration grid 4b is 0V. This is because the passage holes 5b are too small and the plate thickness of the accelerating grid 4b is too large, so that electrons are affected by space charge limitation due to their own negative charges, and most cannot pass through the passage holes 5b.

In the present embodiment, the diameter of the passage hole 52b having a large area is set to 5 mm, for example, so that an electronic current can flow into the discharge vessel 3. On the other hand, the passage hole 52b having a hole diameter of 5 mm is inferior to the surrounding passage hole 51b in terms of the ability to extract Xe ⁺ ions from the plasma, so that the passage hole 5a has a conventional pattern as shown in FIGS. Is used unless the plasma density in the discharge vessel 3 is significantly reduced as compared with the conventional ion beam generator by reducing the amount of Xe gas introduced from the gas introduction system 8 or the like. The ion beamlet spreads too much. If a part of the spread beamlet collides with the acceleration grid 4b, an excessive current flows through the power source connected to the acceleration grid 4b and the acceleration grid 4b is worn.

  By adjusting the Xe gas introduction amount according to the size of the passage hole 52b, the ion beam generator of the present invention can operate. However, as already described, in the present embodiment, the passage hole in the screen grid 4a. 52a is formed as a passage hole having a smaller area than the surrounding passage hole 51a (FIG. 3). Thereby, since the beamlet heading toward the through hole 52b having a large area among the ion beamlets becomes small, the ion beam generator of the present invention can operate while maintaining the same plasma density as the conventional one.

  As already described, in the conventional ion engine, the hole diameter of the passage hole 5 of the ion acceleration system 4 is uniform over the entire surfaces of the screen grid 4a and the acceleration grid 4b included in the ion acceleration system 4, or It was determined depending on the distance from the center to the center of the passage holes 5a and 5b. The present invention breaks this principle and makes part of the hole diameters of the passage holes 5a and 5b different from those of the surrounding passage holes 5a and 5b. Referring to FIG. 2, the hole diameter of the passage hole 51b is determined to be as small as possible within a range where the ion beamlet can pass without collision in order to minimize leakage of the working gas. The hole diameter of 52 b is determined to be larger than the hole diameter of the passage hole 51 b so that electrons emitted from the hollow cathode 11 can easily pass to the discharge vessel 3. Further, as shown in FIG. 3, the diameter of the passage hole 51a in the screen grid 4a is determined as large as possible within a range in which sufficient structural strength can be ensured even after wear due to long-time operation, while the passage hole 52a. 2 is determined to be smaller than the hole diameter of the passage hole 51a so as not to exceed the ion extraction capability of the passage hole 52b inferior to that of the passage hole 51b, corresponding to the hole diameter of the passage hole 52b in FIG. Although the ionic current flowing through the through holes 52a and 52b having different hole diameters from the surroundings is lower than the ionic current of the peripheral holes, the electron current flowing into the discharge vessel 3 through the through holes 52b and 52a is increased. It is possible to operate the ion beam generator while achieving both an electron current and a high plasma density.

As described above, the ion current, which is the flow of Xe ⁺ drawn from the plasma, is released into the outer space mainly through the passage holes 51a and 51b, and the thrust of the ion engine is generated. Further, the hollow cathode 11 also used as a neutralizer discharges electrons e ⁻ having the same current value as the ion current of Xe ⁺ emitted through the passage holes 51a and 51b to the electric space, thereby neutralizing electrically. To prevent the artificial satellites from being charged.

  2 and 3, the through holes are arranged in a close-packed manner, but such an arrangement is not essential. For example, the grid area is divided by orthogonal row lines and column lines, and the intersections of the lines are arranged. Passing holes may be arranged in (orthogonal arrangement). It is not essential that the passage holes 52a and 52b are periodically arranged. For example, they may be randomly arranged. The number of passage holes 52a and 52b is also arbitrary. Further, in FIG. 2 and FIG. 3, the passage holes are arranged so that the passage holes 51 a and 51 b always exist around the passage holes 52 a and 52 b, but such arrangement is not essential, for example, The passage holes 52a and 52b may be arranged at the outermost edge of the passage hole group.

  FIG. 4 and FIG. 5 show examples of modes that can be taken as arrangement modes of such passing holes. In the acceleration grid 4b of FIG. 4, the hole diameter of the passage hole 51b is determined so as to minimize the leakage of the propellant, while the hole diameter of the passage hole 52b is such that electrons emitted from the hollow cathode 11 are discharged from the discharge vessel. 3 is larger than the hole diameter of the passage hole 51b so as to easily flow into the inside. Similarly, in the screen grid 4a of FIG. 5, the hole diameter of the passage hole 51a is determined to be as large as possible within a range in which sufficient structural strength can be secured even after wear due to long-time operation. The hole diameter of 52a is determined corresponding to the hole diameter of the passage hole 52b in FIG. That is, the passage hole 52b is inferior to the surrounding passage hole 51b in terms of the ability to extract ions from the plasma. If the passage hole 52a has a hole diameter similar to that of the passage hole 51a, the ion beamlet spreads. Thus, an excessive current flows through the power source connected to the acceleration grid 4b and the acceleration grid 4b is worn by collision of ions, so that the diameter of the passage hole 52a is made smaller than that of the passage hole 51a.

  In FIGS. 4 and 5, the passage holes 52a are arranged so that the passage holes 51a are arranged in a close-packed manner, and three passage holes 51a arranged adjacently in a triangular shape are formed as one passage hole 52a. The passage holes 52b are also arranged by replacing the three passage holes 51b arranged adjacently in a triangular shape with one passage hole 52b. However, the present invention is not limited to such an arrangement. For example, as shown in FIGS. 6 and 7, the seven passage holes 51 a and the passage holes 51 b that are arranged adjacent to each other in a hexagonal shape are combined into one passage hole 52 a, It may be replaced by the passage hole 52b. Further, for example, if the above-described orthogonal arrangement is adopted, four, nine, or more adjacent passage holes 51a and 51b can be replaced by one passage hole 52a and passage hole 52b. is there. 4 to 7, the passage hole 52a and the passage hole 52b are arranged so as to be located at the same distance from the nearest three passage holes 51a and 51b, respectively. It is not essential. The number of passage holes 52a and passage holes 52b is not limited to a specific number, and may be one or more. Furthermore, in all aspects, it is not absolutely necessary to arrange the passage holes 51a and 51b around the passage holes 52a and 52b. For example, the passage holes 52a and 52b may be arranged at the outermost edge of the passage hole group.

In all of the above embodiments, if the potential of the screen grid 4a is lower by about 10 to 30V than the potential of the discharge vessel 3, Xe ⁺ ions are attracted from the discharge vessel 3 to the screen grid 4a. The ion current passing through 4 can be effectively increased. However, when the potential difference between the screen grid 4a and the discharge vessel 3 is excessively increased, the wear of the screen grid 4a is promoted by ion collision, and therefore the magnitude of the potential difference is determined by each embodiment. Depending on the theory, it should be determined theoretically, numerically or experimentally.

  The thrust of the ion engine can be controlled, for example, by controlling the potential of the discharge vessel 3, the potential of the screen grid 4a, the potential of the acceleration grid 4b, or a combination of both potentials with a power source (not shown). . Here, increasing the potential of the discharge vessel 3 or the screen grid 4a has the effect of increasing the speed of ions to be accelerated and the effect of increasing the ion current by slightly increasing the number of upstream electrons. Further, increasing the potential of the acceleration grid 4b has the effect of increasing the ion current by increasing the number of run-up electrons. It is also possible to control the thrust by controlling the supply amount of the propellant. Increasing the propellant increases the amount of ions produced, resulting in increased thrust.

Technical Significance of the Present Invention In the conventional ion engine, since only one electron source is provided in the central portion of the discharge vessel, the plasma density is high on the central axis and low in the peripheral portion. The higher the plasma density, the greater the wear of the ion acceleration system. Therefore, even if the peripheral portion of the ion acceleration system functions normally, the center portion is worn and becomes inoperable. In the ion engine of the present invention, the density of the plasma in contact with the ion acceleration system can be averaged by considering the distribution of the passage holes so as to promote the electron current, that is, the wear of the ion acceleration system can be averaged. , Can extend the life of the ion engine. In addition, regarding the phenomenon in which the electron current rises due to positive feedback, the resistance of the wire used and the current-voltage characteristics of the electron source play a role of stable resistance, so they may settle before the electron current becomes excessive. This characteristic is effective for simplifying the current control device. When the electron current becomes excessive, the spread of the ion beamlet becomes excessive, and continuous operation may be hindered.

Technical scope of the present invention The present invention is not limited to the above-described embodiments described as examples, and can be appropriately changed within the scope of the present invention described in the claims. As an example, the shape of the discharge vessel is arbitrary, and the propellant gas is not limited to Xe, and may be any gas such as oxygen or mercury that can generate plasma. In addition, the gas introduction system employs one system each for the discharge vessel and the electron source (not shown), but other numbers of systems may be employed. The insulator is not limited to the above example, and a sufficiently long non-conductive tube may be used, for example. Furthermore, although the shape of the through hole formed in the grid is circular in this embodiment, the through hole may be formed in an arbitrary shape. In FIG. 1, the ion acceleration system 4 is composed of two grids, a screen grid 4a and an acceleration grid 4b. However, the number of grids is not limited to two, and is arbitrary, for example, grounded or grounded to a spacecraft. An additional deceleration grid may be provided. In FIG. 1, the magnet 10 is a permanent magnet, and four rows of permanent magnets are arranged in the discharge vessel, but the number of rows can be arbitrarily changed. In this embodiment, the plasma is confined by the ring cusp magnetic field. However, what kind of magnetic field is generated is arbitrary, and confining the plasma by the magnetic field itself is not essential for the present invention. However, when there is no magnetic field, the plasma collides with the inner wall of the discharge vessel and is partially lost. Therefore, it is preferable to generate a magnetic field in order to effectively generate an ionic current. This magnetic field can also be generated by an electromagnet. The position and number of propellant distributors, and the number and distribution of gas discharge holes are not limited to the above-described embodiment. The electron source is not limited to the hollow cathode, and may be a direct heat type, an indirectly heated type, an oxide type, or a microwave type. The number of electron sources is not limited to one and may be any number.

  Furthermore, although the above-mentioned Example applies the ion beam generator of this invention especially to an ion engine, it is also possible to implement this invention as ion beam generators other than an ion engine. When an oxygen ion beam is generated by a conventional ion beam generator using a hollow cathode, if the oxygen is used as a working gas for the hollow cathode, the hollow cathode is damaged, and therefore argon or the like is used instead of oxygen. For this reason, in the past, a large amount of argon ions and the like were mixed in oxygen ions, but if the ion beam generator of the present invention is used, the working gas supplied into the discharge vessel can be oxygen only, Etc. can be a minute amount that goes up the passage hole, so that a highly pure oxygen ion beam can be generated.

  The ion beam generator of the present invention can be used as an ion engine mounted on a spacecraft such as an artificial satellite, or as an apparatus for generating an ion beam for material processing. In addition, an ion beam can be used. It is applicable to all industries that can

DESCRIPTION OF SYMBOLS 1 Shield case 2 Small hole 3 Discharge vessel 4 Ion acceleration system 4a Screen grid 4b Acceleration grid 5, 5a, 5b Passing hole 6 Propellant distributor 7 Small hole 8 Gas introduction system 9 Hollow cathode 10 Magnet 11 Hollow cathode 12 Insulator 13 Grid support mechanism 51a, 51b Passing hole 52a, 52b Passing hole (Promoting the passage of electrons)
53 Passing hole (large hole diameter)
54 Passing hole (medium hole diameter)
55 Passing hole (small hole diameter)

Claims (6)

A discharge vessel;
A gas introduction system for introducing a working gas into the discharge vessel;
An insulator for preventing discharge inside the gas between the discharge vessel and the gas introduction system;
An electron source installed outside the discharge vessel;
The electrons emitted from the electron source are introduced into the discharge vessel as an electron current, and ions in the plasma generated by the collision between the electrons introduced into the discharge vessel and the working gas are introduced. An ion beam generator comprising: a screen grid having a plurality of passage holes and an ion acceleration system including an acceleration grid that accelerates and sends out as an ion current to the outside of the discharge vessel.   The ion beam generator according to claim 1, wherein an electron source for generating plasma is not provided inside the discharge vessel.   3. The ion beam generating apparatus according to claim 1, wherein a part of the plurality of through holes in the acceleration grid has a larger area than a surrounding through hole in the acceleration grid. 4.   Among the plurality of through holes in the screen grid, a through hole located at a position corresponding to the position of the through hole having a larger area in the acceleration grid than that of the surrounding through holes is a peripheral passage in the screen grid. 4. The ion beam generator according to claim 3, wherein the ion beam generator has a smaller area than the hole.   5. The ion beam generator according to claim 1, further comprising a unit that adjusts the magnitude of the ion current by changing a potential of the acceleration grid. 6.   6. The ion beam generator according to claim 1, further comprising means for adjusting the magnitude of the ion current by changing a potential of the discharge vessel.

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