Patent Application
20240195037
The present invention relates to a DC block that transmits high-frequency power and cuts off direct-current power, and a plasma generator using the DC block.
Conventionally, a DC block is known as a device for preventing a direct current (DC) from flowing into a high-frequency signal, and is used in various technical fields. As an example, there is an application to spacecraft engines. Some types of spacecraft engines use electricity to discharge propellant, and are called electric propulsion rockets. A typical electric propulsion rocket has a discharge mechanism for ionizing a propellant to generate plasma and an acceleration mechanism for accelerating the plasma.
Here, it is necessary to send high-frequency power used in high-frequency discharge when plasma is generated, and high-voltage direct-current power necessary for acceleration of the generated plasma, to a plasma generation chamber which is a container for generating plasma. The device that interrupts the interference between the high-frequency power and the direct-current power is a DC block, is disposed on a transmission line of the high-frequency power, and transmits only the high-frequency power and interrupts the direct-current power. That is, a DC block is used as a device that separates high-frequency power for plasma generation and high-voltage direct-current power for plasma acceleration.
In addition, it is known that acceleration performance of plasma can be improved by applying a direct-current voltage to a plurality of wall surfaces in contact with plasma inside the plasma generation chamber (see, for example, Non Patent Literature 1). Non Patent Literature 1 discloses that particularly remarkable performance improvement is caused by applying a voltage to an antenna for oscillating high-frequency power inside a plasma generation chamber. As a method of applying a voltage to an antenna, a method is disclosed in which a T-shaped portion is provided in a microwave transmission path, only a core wire is taken out, and the voltage is applied.
Note that a high-frequency signal device is known in which two open ring-shaped resonators formed on different planes are disposed to face each other to enable direct-current power or a low-frequency signal to be transmitted, and the resonators are electromagnetically coupled to each other to enable a high-frequency signal to be transmitted (see, for example, Patent Literature 1). Patent Literature 1 also discloses that two resonators are disposed to face each other with a spacer plate made of an insulator interposed therebetween.
The DC block is often required for use of high-frequency power in technical fields on the ground other than spacecraft engines, but the application thereof is often limited to a combination of high-frequency low power (1 to 100 W) and a direct-current low voltage (1 to 100 V) or a combination of high-frequency high power (100 to 10000 W) and a direct-current high voltage (1 to 10 kV). In general, the latter DC block is a large device.
On the other hand, in a DC block used for an electric propulsion rocket that is space equipment, a combination of high-frequency low power (1 to 100 W) and a direct-current high voltage (1 to 10 kV) is required, and significant size reduction is required. In particular, in the case of application to a small spacecraft engine, significant size reduction is required. However, such high-frequency low power and a direct-current high voltage and ultra-small size has not been realized in a conventional DC block configured using a coaxial line shape or a waveguide shape.
In the case of a coaxial type DC block, the electrical coupling upstream and downstream of the coaxial line is capacitive. Therefore, it is necessary to overlap an outer conductor of an upstream-side coaxial line and an outer conductor of a downstream-side coaxial line with an insulator interposed therebetween, and also to overlap an upstream-side inner conductor and a downstream-side inner conductor with an insulator interposed therebetween. Furthermore, in order to efficiently transmit microwaves (electromagnetic waves), it is also necessary to adjust impedance to a predetermined value by designing the inner diameter of each conductor and the outer diameter of each conductor to have a predetermined ratio. In order to increase the withstand voltage under these restrictions, it is necessary to stack layers in a radial direction such as inner conductor upstream—insulation—inner conductor downstream—dielectric—outer conductor downstream—insulation—outer conductor upstream, and it is inevitable to increase the size of the device as the voltage increases.
On the other hand, in the case of a waveguide type DC block, since the electrical coupling is based on electromagnetic waves, it is not necessary to stack the layers as in the case of the coaxial type. Therefore, it can be said that insulation can be achieved by sandwiching one insulating sheet (or insulating plate) between the upstream and downstream waveguides, and it is suitable for a high withstand voltage. However, the minimum size of the waveguide is determined on the principle of passing microwaves inside. For example, when a microwave of 4 to 5 GHz is passed, the minimum size is 48 mm×22 mm. Therefore, there is a clear lower limit to size reduction.
The present invention has been made to solve such a problem, and an object of the present invention is to provide a reduced-size DC block compatible with a combination of high-frequency low power and a direct-current high voltage.
In order to solve the above problem, a DC block of the present invention has a configuration in which two high-frequency power transmission antennas formed on two microstrip lines, respectively, are disposed to face each other with an insulating sheet interposed between the two high-frequency power transmission antennas.
According to the present invention configured as described above, since the transmission of the high-frequency power is realized by forming the high-frequency power transmission antennas on the microstrip lines, it is not necessary to stack the layers as in the case of the coaxial type in order to increase the withstand voltage, and the minimum size is not limited on the principle of passing the microwaves as in the case of the waveguide type, and the size of the DC block can be reduced as compared with the conventional DC block using the coaxial line shape or the waveguide shape. In addition, it is possible to highly efficiently transmit only the high-frequency power while cutting off the high-voltage direct-current power by the insulating sheet sandwiched between the two high-frequency power transmission antennas. As a result, it is possible to provide the reduced-size DC block compatible with a combination of high-frequency low power and a direct-current high voltage.
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
The plasma generation chamber 1 is a container for generating plasma by discharge using high-frequency power and for accelerating the generated plasma by high-voltage direct-current power. The plasma generation chamber 1 includes a plasma generation antenna 11, a plurality of magnets 12 disposed on a wall surface 13, and an accelerator grid 14. In the plasma generation chamber 1, a magnetic field is formed by the plurality of magnets 12, and plasma discharge is performed by introducing high-frequency waves such as microwaves from the plasma generation antenna 11. The generated plasma is accelerated by a screen grid for plasma discharge installed on a surface of the wall surface 13 facing the accelerator grid, and the accelerator grid 14.
The high-frequency power source 2 supplies high-frequency power for plasma generation to the plasma generation chamber 1. The high-frequency power source 2 and the plasma generation chamber 1 are connected by two coaxial lines 5, 6 via the DC block 4. The coaxial line 5 on the upstream side includes an inner conductor 5a and an outer conductor 5b, and the coaxial line 6 on the downstream side includes an inner conductor 6a and an outer conductor 6b. The inner conductor 6a of the downstream-side coaxial line 6 is connected to the plasma generation antenna 11. The outer conductor 6b of the downstream-side coaxial line 6 is connected to the magnets 12 via the wall surface 13 of the plasma generation chamber 1.
The high-voltage direct-current power source 3 supplies high-voltage direct-current power for plasma generation to the plasma generation chamber 1. The high-voltage direct-current power source 3 is connected to the wall surface 13 of the plasma generation chamber 1 and the accelerator grid 14. A high voltage exceeding 1 kV is applied between the wall surface 13 and the accelerator grid 14, and the plasma is accelerated and discharged by the potential difference, and is discharged toward an infinite potential (0 V) of the space.
The DC block 4 is disposed on coaxial lines 5, 6 which are transmission lines for transmitting high-frequency power to the plasma generation chamber 1, and transmits only the high-frequency power and cuts off the direct-current power. The configuration of the DC block 4 will be described in detail with reference to
As illustrated in
The second microstrip line 102 similarly has a layer structure including a wiring conductor layer in which the second high-frequency power transmission antenna 121 is formed, a ground conductor layer 123 in which the second high-frequency power transmission antenna 121 is not formed, and a dielectric layer 122 sandwiched between the wiring conductor layer and the ground conductor layer 123. The ground conductor layer 123 is formed on one plane of the dielectric layer 122 and the second high-frequency power transmission antenna 121 is disposed on another plane, and the second high-frequency power transmission antenna 121 itself is a wiring conductor layer.
The two microstrip lines 101, 102 are disposed to face each other such that the wiring conductor layers (high-frequency power transmission antennas 111, 121) face each other with the insulating sheet 103 interposed therebetween, and the ground conductor layers 113, 123 of the two microstrip lines 101, 102 are separated from the insulating sheet 103.
In the first microstrip line 101, the first high-frequency power transmission antenna 111 is connected to the inner conductor 6a of the downstream-side coaxial line 6 via a terminal 107 illustrated in
In the second microstrip line 102, a through hole 124 penetrating the second high-frequency power transmission antenna 121, the dielectric layer 122, and the ground conductor layer 123 is formed. The second high-frequency power transmission antenna 121 is connected to the inner conductor 5a of the upstream-side coaxial line 5 via a terminal 108 in
The first high-frequency power transmission antenna 111 is an open ring-shaped antenna having a notch 111b in a part thereof. That is, the first high-frequency power transmission antenna 111 includes a ring antenna 111a having an open ring shape and a feeder line 111c connected to the inner conductor 6a of the downstream-side coaxial line 6. By connecting the terminal 107 illustrated in
The second high-frequency power transmission antenna 121 is a closed ring-shaped antenna without a notch. That is, the second high-frequency power transmission antenna 121 includes a ring antenna 121a having a closed ring shape, a feeder line 121c connected to the inner conductor 5a of the upstream-side coaxial line 5, and a hole 121d forming a part of the through hole 124. By connecting the terminal 108 illustrated in
When the first high-frequency power transmission antenna 111 and the second high-frequency power transmission antenna 121 are disposed to face each other with the insulating sheet 103 interposed therebetween, the central axes of the ring antennas 111a, 121a are disposed on the same line. This makes it possible to strengthen the electromagnetic coupling of the ring antennas 111a, 121a.
The feeder line 111c of the first high-frequency power transmission antenna 111 is formed to extend from the ring antenna 111a toward the outside of the ring to a position near the outer edge of the first microstrip line 101. On the other hand, the feeder line 121c of the second high-frequency power transmission antenna 121 is formed to extend from the ring antenna 121a toward the inside of the ring to the center position of the second microstrip line 102.
The terminals 107, 108 are connected to the high-frequency power transmission antennas 111, 121, respectively, and high-frequency power is input and output through the terminals 107, 108. The terminal 107 is provided with one pin 107a at the center and four legs 107b at the four corners, and the first microstrip line 101 is sandwiched by the four legs 107b. At this time, lower two legs 107b are connected to the ground conductor layer 113, and the pin 107a at the center is connected to the feeder line 111c of the first high-frequency power transmission antenna 111. In addition, the terminal 108 is provided with one pin 108a at the center, and this is connected to the feeder line 121c of the second high-frequency power transmission antenna 121 by being inserted into the through hole 124 from the hole 121d of the second microstrip line 102, and the bottom surface portion around the pin 108a is connected to the ground conductor layer 123.
As described above, in the DC block 4 of the present embodiment, since the high-frequency power transmission antenna 111, 121 are formed on the two microstrip lines 101, 102, respectively, to realize transmission of high-frequency power, it is possible to reduce the size of the DC block 4 as compared with a conventional DC block using a coaxial line shape or a waveguide shape. In addition, it is possible to highly efficiently transmit only the high-frequency power while cutting off the high-voltage direct-current power by the insulating sheet 103 sandwiched between the high-frequency power transmission antennas 111, 121, which are asymmetric.
As a result, it is possible to provide the reduced-size DC block 4 compatible with a combination of high-frequency low power and high-voltage direct-current power. Here, by appropriately designing at least one of the ring width, the ring diameter, the notch position, the notch width, the number of notches of each of the ring antennas 111a, 121a, and the line width of each of the feeder lines 111c, 121c, it is possible to highly efficiently transmit only high-frequency power of a desired frequency while blocking high-voltage direct-current power of several kV class by the insulating sheet 103.
As illustrated in
The wiring pattern 115 is electrically connected to the ring antenna 111a of the first high-frequency power transmission antenna 111. In addition, wiring 8a illustrated in
As a configuration for applying a voltage to the plasma generation antenna 11 of the plasma generation chamber 1, conventionally, as described in Non Patent Literature 1, a method in which a T-shaped connector and a stub tuner are disposed on the downstream-side coaxial line 6, only a core wire is taken out, and a voltage is applied has been common. However, the introduction of the T-shaped connector and the stub tuner has been a major obstacle to size reduction.
On the other hand, in the first modification, by using the wiring pattern 115 of the first microstrip line 101 and extracting a direct-current voltage from the first high-frequency power transmission antenna 111 without affecting the transmission of the high-frequency power, the application of the direct-current voltage to the plasma generation antenna 11 is realized without using the T-shaped connector and the stub tuner. Accordingly, the plasma generator can be reduced in size. This is equivalent to size reduction of the plasma generator by including the functions of the T-shaped connector and the stub tuner in the DC block 4′.
In the second modification, as a voltage application circuit for applying a direct-current voltage to the plasma generation antenna 11 connected to the inner conductor 6a of the downstream-side coaxial line 6, resistors 9a, 9b connected to a direct-current power supply (main power supply not illustrated) of the plasma generator are provided instead of the direct-current power supply 7 illustrated in
As described above, in the second modification, the wiring 8a connected from the first high-frequency power transmission antenna 111 via the wiring pattern 115, and the wiring 8b connected from the wall surface 13 of the plasma generation chamber 1 are connected to the main power supply of the plasma generator via the plurality of resistors 9a, 9b (including 0Ω). As a result, different potentials are applied to the plasma generation antenna 11 and the wall surface 13 of the plasma generation chamber 1 using the voltage drop in the resistors 9a, 9b without using the direct-current power supply 7 of a system different from the main power supply of the plasma generator as illustrated in
As a result, according to the second modification, the potential change of the plasma generation antenna 11 and the wall surface 13 of the plasma generation chamber 1 can be realized by resistance connection using the main power supply (plasma electromotive force) of the plasma generator. As a result, it is not necessary to provide the direct-current power supply 7 separately from the main power supply of the plasma generator, and the plasma generator can be reduced in size. That is, by using the resistors 9a, 9b instead of the direct-current power supply 7, it is possible to significantly reduce the size of the plasma generator and simplify the plasma generator.
In the above embodiment, the example in which only the first high-frequency power transmission antenna 111 has an open ring shape has been described. However, both of the two high-frequency power transmission antennas may have the closed ring shape, or both of the two high-frequency power transmission antennas 111, 121′ may have an open ring shape as illustrated in
Forming both of the two high-frequency power transmission antennas 111, 121′ in an open ring shape enables strengthening of electromagnetic coupling. At this time, by disposing the ring antennas 111a, 121a′ such that the central axes thereof are on the same line and the notches 111b, 121b′ are at symmetrical positions (positions shifted by 180 degrees) with respect to the central axes, it is possible to further strengthen the electromagnetic coupling of the ring antennas 111a, 121a′.
In addition, each of the above embodiments is merely an example of implementation in implementing the present invention, and the technical scope of the present invention should not be interpreted in a limited manner. That is, the present invention can be implemented in various forms without departing from the gist or main features thereof.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/010520 | 3/16/2021 | WO |
