Electromagnetic wave generator

Abstract

To increase an electric current of an electron beam as much as possible.SOLUTION: An electromagnetic wave generation apparatus includes a cathode electrode, an anode electrode that is arranged to face the cathode electrode, and through which electrons can penetrate, and a hollow cylindrical waveguide that is connected to an opposite side to the cathode electrode across the anode electrode, and guides an electromagnetic wave; generates an electron beam by applying a high voltage pulse between the cathode electrode and the anode electrode; and generates an electromagnetic wave by a virtual cathode that has been formed by electrons bunched in the waveguide. A surface shape of the cathode electrode includes: a flat surface that is located in a central part and faces the anode electrode; and a curve surface that is continuous to a periphery of the flat surface, has an annular shape surrounding the flat surface, and is bent away from the anode electrode. The curve surface is composed of a plurality of curve surfaces of which the radii of curvatures become smaller as the distances from the flat surface increase.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application relates to an electromagnetic wave generating device. [Background technology]

[0002] An electromagnetic wave generator using a virtual cathode generates microwave-band electromagnetic waves by using a virtual cathode formed by electrons being drawn from the surface of a cathode electrode through field emission using a high-voltage, high-speed pulse applied from a high-voltage, high-speed pulse generator. To generate microwave-band electromagnetic waves, it is important to place an anode electrode, such as a mesh-like electrode, through which electrons can physically pass, opposite the cathode electrode, and to have the electrons drawn from the cathode electrode form an electron beam that passes through the anode electrode and form a virtual cathode within a waveguide located behind the anode. The formed virtual cathode oscillates the electrons in time and space within the waveguide. A virtual cathode oscillator generates high-power pulsed electromagnetic waves (electromagnetic pulses) by oscillating these electrons (see, for example, Patent Document 1).

[0003] The creation of a virtual cathode is essential for generating electromagnetic waves, and for efficient electromagnetic wave generation, the magnitude of the electron beam current is one of the important parameters that affect the output of the generated electromagnetic waves. The current value is greatly influenced by the cathode structure. The cathode electrode structure can be, for example, spherical (see Patent Document 1), or in some cases, cylindrical (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 5-266810 [Patent Document 2] Special Publication No. 2005-505112 Summary of the Invention [Problem to be solved by the invention]

[0005] In the cathode structure of such an electromagnetic wave generator, in a spherical structure, the center is the largest electric field generation area, and although it depends on the distance to the anode electrode, only a small area in the center can generate an electron beam. In a cylindrical structure, the largest electric field generation area is located at the curvature of the edge of the disk facing the anode electrode, and electron emission is low in the center, resulting in a small electron generation area. To generate highly efficient microwaves in an electromagnetic wave generator in which the electron beam emitted from the cathode electrode forms a virtual cathode, it is necessary to maximize the current of the electron beam emitted from the cathode.

[0006] The present invention is intended to solve the above problems and has as its object to maximize the current of the electron beam. [Means for solving the problem]

[0007] The electromagnetic wave generator disclosed in the present application comprises a cathode electrode, an anode electrode opposite the cathode electrode and through which electrons can pass, and a hollow cylindrical waveguide connected to the anode electrode on the opposite side of the cathode electrode and guiding electromagnetic waves; the electromagnetic wave generator generates an electron beam by applying a high voltage pulse between the cathode electrode and the anode electrode, and the electrons gather in the waveguide to form a virtual cathode, thereby generating electromagnetic waves; the surface shape of the cathode electrode has a flat surface located in the center and facing the anode electrode, and a curved surface that is continuous with the periphery of the flat surface, is annular, surrounds the flat surface, and curves away from the anode electrode; the curved surface is made up of a plurality of curved surfaces whose radius of curvature decreases with increasing distance from the flat surface. [Effects of the Invention]

[0008] According to the electromagnetic wave generating device disclosed in the present application, electrons can be emitted from a wide area of ​​the cathode electrode and introduced into the waveguide, making it possible to increase the current of the electron beam. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing the configuration of an electromagnetic wave generating device according to a first embodiment. [Figure 2] 2 is a cross-sectional view showing the configuration of a cathode electrode of the electromagnetic wave generator according to the first embodiment. FIG. [Figure 3] 2A and 2B are a cross-sectional view showing the electric field distribution in a cathode electrode of the electromagnetic wave generator according to the first embodiment and a plan view showing the configuration of an anode electrode. [Figure 4] 10A and 10B are cross-sectional views showing examples of electric field distribution depending on the shape of the cathode electrode of the first comparative example. [Figure 5] 10A and 10B are cross-sectional views showing examples of electric field distribution depending on the shape of the cathode electrode of the second comparative example. [Figure 6] 10A and 10B are cross-sectional views showing examples of electric field distribution depending on the shape of the cathode electrode of the third comparative example. [Figure 7] FIG. 10 is a cross-sectional view showing the electric field distribution in the cathode electrode of the electromagnetic wave generator according to the second embodiment. [Figure 8] FIG. 10 is a cross-sectional view showing the configuration of a cathode electrode of an electromagnetic wave generator according to a fourth embodiment. [Figure 9] 10A and 10B are diagrams for explaining the effect of the cathode electrode of the electromagnetic wave generator according to the fourth embodiment. [Figure 10] FIG. 10 is a cross-sectional view showing the configuration of a cathode electrode of an electromagnetic wave generator according to a fifth embodiment. [Figure 11] FIG. 13 is a cross-sectional view showing the configuration of a cathode electrode of an electromagnetic wave generator according to a sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Embodiment 1 FIG. 1 is a cross-sectional view of an electromagnetic wave generator according to a first embodiment. In FIG. 1, a pulse generator 1 is provided that generates high-voltage pulses at high speed. When a Marx-type pulse generator 1 is used, it is composed of multiple stages of capacitors connected in series (not shown). Closing a switch between the stages releases the charge stored in the capacitors all at once, boosting the voltage in a cascade fashion until a high-voltage pulse is generated from the final stage. A metal conductor 3 is connected to a high-voltage generating section 2, which corresponds to the output section of the pulse generator 1, and a cathode electrode 4, which serves as the negative pole, is attached to the end of the metal conductor 3. A vacuum gap is provided around the radial periphery of the metal conductor 3 to insulate it from the vacuum vessel 6 housing. Furthermore, if the main insulation is not a vacuum, for example, to support the pulse generator 1 on the housing 6, insulation is ensured by an insulator 5. An anode electrode 7, which serves as the positive pole, is attached opposite the cathode electrode 4. A waveguide 8 is attached to the anode electrode 7 on the opposite side of the cathode electrode 4. The anode electrode 7 is a thin film or a perforated structure, such as a mesh electrode, to allow the electrons emitted from the cathode electrode 4 to pass through. The waveguide 8 is, for example, a hollow cylindrical circular waveguide. The anode electrode 7 and the waveguide 8 are electrically connected and have the same potential as the ground potential of the pulse generator 1.

[0011] Next, the generation of electromagnetic waves will be explained. When a high voltage pulse is applied from the pulse generator 1, electrons are emitted from the cathode electrode 4 toward the anode electrode 7 by field emission, forming an electron beam. The current I of the electron beam is CL is expressed by the following equation (1).

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[0012] Under a strong electric field, electrons move toward the anode electrode 7, jump over the anode electrode 7, which has a structure that allows electrons to physically pass through, and enter the waveguide 8 behind the anode electrode 7. As the number of electrons increases, they gather in the space of the waveguide 8 and form a potential group called a virtual cathode 9. The condition for the formation of the virtual cathode 9 is I CL is the spatially limited current I in the waveguide. C When the spatial limiting current I C is expressed by the following equation (2).

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[0013] The frequency of microwaves is expressed by the following equation (3).

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[0014] When the virtual cathode 9 is formed, electrons with energy lower than the potential of the virtual cathode 9 are repelled by the virtual cathode 9, reducing the supply of electrons to the virtual cathode 9 and lowering the potential of the virtual cathode 9. Then, electrons flow into the virtual cathode 9 again, causing the potential of the virtual cathode 9 to rise and repel the electrons again. This process is repeated, i.e., the temporal and spatial fluctuations of the virtual cathode 9 generate microwaves 10.

[0015] The microwave output is highly dependent on the electron beam current and the applied voltage. According to equation (3), the frequency is determined by the distance d between the cathode electrode 4 and the anode electrode 7. AK Since it depends on , if the frequency band is fixed, d AKIt is necessary to fix V. Also, the voltage between the anode electrode 7 and the cathode electrode 4 (between A and K) cannot be increased infinitely, so the voltage V that can be applied is limited. Therefore, the microwave output is highly dependent on the electron beam current. From equation (1) that expresses the electron beam current, in order to increase the current value, V and d AK It is necessary to increase the electrode area Sk, which is a parameter other than the above.

[0016] FIG. 2 is a cross-sectional view of the cathode electrode 4 in the electromagnetic wave generator according to the first embodiment, including the central axis. The cathode electrode 4 has an axially symmetrical structure, i.e., the cross-sectional shape perpendicular to the central axis (an axis including the center of the flat surface 11, described below, and perpendicular to the flat surface 11) is circular, with the flat surface 11 at the center. Furthermore, the cathode electrode 4 has a first curved surface 12 extending around the flat surface 11, and a second curved surface 13 extending from the first curved surface 12 and having a smaller radius of curvature than the first curved surface. The curved surface formed by the first curved surface 12 and the second curved surface 13 forms a ring that surrounds the flat surface 11. The cathode electrode is basically made of a metal electrode, and examples of such materials include aluminum, copper, and iron, as well as alloys thereof, brass, stainless steel, and duralumin. A low work function material is desirable for efficient electron beam extraction. Furthermore, to efficiently generate electron beams, a material with high electron generation, such as velvet, may be placed on the metal surface. This technique will be described in detail in the fourth through sixth embodiments.

[0017] Next, the function of the cathode electrode will be described. Figure 3 shows the electrostatic field distribution at the cathode electrode 4 of the electromagnetic wave generator according to embodiment 1. Figure 3 also shows a plan view of the anode electrode 7 as viewed from the axial direction of the waveguide. The anode electrode 7 is made of, for example, a mesh-like metal to allow electrons to pass through. The electrostatic field distribution at the cathode electrode 4 is shown by varying shades of color to indicate the strength of the electric field, with darker areas indicating areas where the electric field is concentrated. As comparative examples, Figure 4 shows the electrostatic field distribution at a spherical electrode 41, and Figure 5 shows the electrostatic field distribution at a cylindrical electrode 42. In the spherical electrode 41 of Figure 4, a high electric field is generated only near the center, while in the cylindrical electrode 42 of Figure 5, a high electric field is generated around the curved portion at the end of the central flat portion. On the other hand, in the case of the shape of the cathode electrode 4 according to embodiment 1 shown in Figure 3, a high electric field is generated across the entire flat surface of the central portion. That is, by forming the cathode electrode into a shape having a flat surface 11 in the center, a first curved surface 12 that is connected to the periphery of this flat surface 11, and a second curved surface 13 that is connected to the first curved surface 12 and has a radius of curvature smaller than that of the first curved surface, as in the present embodiment 1, a region where electrons can be generated from the cathode electrode exists over a wide range, and the current value of the electron beam is significantly increased, which is a remarkable effect not seen in the past.

[0018] Although the shape shown here has first curved surface 12 and second curved surface 13 extending around flat surface 11, the curved surface extending around flat surface 11 may have more curved surfaces with different radii of curvature. For example, a third curved surface may be provided between first curved surface 12 and second curved surface 13, the third curved surface having a radius of curvature smaller than that of first curved surface 12 and larger than that of second curved surface 13. In other words, the curved surface extending around flat surface 11 may be a curved surface that curves away from anode electrode 7, and may be composed of multiple curved surfaces whose radii of curvature decrease with increasing distance from flat surface 11.

[0019] Embodiment 2 The waveguide 8 has a cutoff frequency for transmitting microwaves, which depends on its diameter. The waveguide diameter must be determined so that the microwave frequency generated by equation (4) exceeds the lower limit of the desired frequency. As shown in Figure 1, the virtual cathode 9 is generated within the waveguide. Therefore, if the electron beam emitted from the cathode electrode does not travel within the waveguide, it becomes difficult for equation (1) to exceed equation (2), which is the condition for the virtual cathode 9 to form. Equation (1) does not include current loss. As loss increases, the value of equation (1) decreases, making it more difficult to form the virtual cathode 9. If the diameter of the flat surface of the cathode electrode is larger than the diameter of the waveguide 8, the electron beam will travel outside the diameter of the waveguide 8. Figure 6 simultaneously shows the electric field distribution and electric field vectors when the diameter D2 of the flat surface 111 of the cathode electrode 43 is larger than the diameter D of the waveguide 8. In the darkest region where the electron beam is generated, the electric field vector in the center points toward the waveguide, but the edge of the flat surface 111 faces outside the waveguide 8. Therefore, the electron beam emitted from the edge travels outside the waveguide 8, resulting in current loss. If the voltage is high, dielectric breakdown occurs in that path, and current flows only along that path, making it difficult to form a virtual cathode 9. On the other hand, if the diameter D1 of the flat surface 11 of the cathode electrode 4 is smaller than the diameter D of the waveguide 8, as shown in Figure 7, the electric field vector in the dark region with a high electric field points toward the waveguide 8. In other words, by designing the cathode electrode 4 so that the diameter D1 of the flat surface 11 is smaller than the diameter D of the waveguide, the electron beam travels entirely into the waveguide 8, resulting in a significant and unprecedented effect of significantly increasing the current value of the electron beam.

[0020] Embodiment 3 2, the curved surfaces extending around the flat surface 11 have a large radius of curvature for the first curved surface 12 extending around the flat surface 11 and a small radius of curvature for the second curved surface 13 extending from the first curved surface 12. This makes it possible to suppress electric field concentration in the curved surface portions near the edges of the flat surface, thereby enabling electron beams to be generated over a large-area flat surface. In addition, in a cross section including the central axis of the cathode shown in FIG. 2, i.e., a cross section including the center of flat surface 11 and perpendicular to flat surface 11, the apparent angle θ1 from the center of curvature O1 of first curved surface 12 to first curved surface 12 is made smaller than the apparent angle θ2 from the center of curvature O2 of second curved surface 13 to second curved surface 13. This reduces the overall diameter of the cathode electrode 4 and provides a significant, unprecedented effect of enabling the size of the vacuum vessel to be reduced.

[0021] Embodiment 4 As mentioned above, microwave output is highly dependent on the electron beam current. In the embodiments described above, we have described a technique for increasing the electrode area Sk to increase the current value based on equation (1) representing the electron beam current. However, the current can also be increased by increasing the constant a. The constant a is determined by various factors, one of which is the ease with which electrons are extracted from the cathode. Since field-emitted electrons account for the majority of the current, the material of the cathode electrode has a significant impact. As mentioned above, if the cathode electrode is made of a metal, it is effective to use a metal material with a small work function. It is also effective to provide the electrode surface with an electron-emitting material that generates electrons more easily than the cathode electrode material, i.e., has a higher electron-emitting ability.

[0022] Figure 8 is a cross-sectional view showing the configuration of the cathode electrode of an electromagnetic wave generator according to embodiment 4. As shown in Figure 8, a pile-like fabric is attached to the entire or partial surface of the cathode electrode 4, serving as electron-emitting material 14, which emits electrons more easily than a metal substrate. Figure 8 shows an example in which a pile-like fabric is attached to the entire surface. Fabrics with pile are commonly called velvet. Pile materials are often made from synthetic fibers such as rayon and polyester. Other materials include cotton and silk. Velvet has a large number of fine fibers extending in the thickness direction. When velvet is attached to the surface of the cathode electrode 4 as electron-emitting material 14, the fibers tend to align with the electric field. When an electric field is applied, the electric field is concentrated at the tips of the numerous fibers, promoting electron emission. Figure 9 compares the extracted current values ​​between a stainless steel (SUS) electrode and a velvet electrode with velvet attached to the SUS electrode. The electrode with velvet attached clearly exhibits a larger extracted current value. Therefore, by providing an electrode with a velvet-like pile on the surface as the electron emission material 14, a remarkable effect not seen in the past can be achieved, such as a significant increase in the current value of the electron beam.

[0023] Embodiment 5 As described in the second embodiment, if the diameter of the flat surface of the cathode electrode is larger than the diameter of the waveguide 8, the electron beam will travel outside the diameter of the waveguide 8, resulting in a corresponding current loss. Furthermore, if the voltage is high, insulation breakdown will occur in that path, and the current will flow only in that path, making it difficult to form the virtual cathode 9. On the other hand, as shown in Figure 10, if velvet is provided as the electron-emitting material 14 only on the flat surface 11 of the cathode electrode 4 so that the area where the electron-emitting material 14 is provided is smaller than the circular area whose diameter is the diameter D of the waveguide, all of the electron beam will travel into the waveguide 8, resulting in a significant and unprecedented effect of significantly increasing the current value of the electron beam.

[0024] Embodiment 6 If an electron-emitting material is simply attached to a cathode electrode optimized solely with a base metal electrode, as shown in Figure 10 described in the fifth embodiment, the edges of the electron-emitting material will have a corner structure, and depending on the thickness of the electron-emitting material, the electric field will concentrate at the edges. This may result in a biased electron beam generation area, which may affect the extraction current. Therefore, as shown in Figure 11, a recess 16 is formed in the portion of the underlying cathode electrode 4 where the electron-emitting material, velvet 14, will be provided. The depth of the recess 16 is the same as the thickness of the velvet, and by filling the recess 16 with the velvet 14, the edges of the velvet 14 do not protrude from the cathode electrode surface. The recess is preferably located in the area corresponding to the flat surface 11 shown in Figure 10. This structure suppresses the electric field concentration at the edges of the electron-emitting material, allowing the electric field to be generated uniformly on the velvet 14, thereby achieving a significant and unprecedented effect: the electron beam can be generated uniformly on the velvet.

[0025] Embodiment 7 1 to 8, 10, and 11 all have axially symmetric structures, with the cathode electrode 4 and the anode electrode 7 positioned so that their central axes coincide. If the cathode electrode 4 and the anode electrode 7 were not positioned coaxially, the positions of the flat surface 11 and the waveguide opening behind the anode electrode 7 would be misaligned, preventing all of the electron beam from entering the waveguide 8, resulting in a loss of current to form the virtual cathode 9 and making it difficult to establish the virtual cathode 9. Therefore, if the cathode electrode 4 and the anode electrode 7 are positioned so that their central axes coincide, as in each embodiment, the electron beam will all travel into the waveguide 8, resulting in a significant increase in the current value of the electron beam, an unprecedented and remarkable effect.

[0026] Although various exemplary embodiments and examples are described in this application, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless modifications not illustrated are contemplated within the scope of the technology disclosed in this specification. For example, this includes cases where at least one component is modified, added, or omitted, and even cases where at least one component is extracted and combined with components of other embodiments.

[0027] Various aspects of the present application will be summarized below as appendices. (Appendix 1) An electromagnetic wave generating device comprising: a cathode electrode; an anode electrode that is disposed opposite the cathode electrode and through which electrons can pass; and a hollow cylindrical waveguide that is connected to the anode electrode on the side opposite the cathode electrode and that guides electromagnetic waves; wherein a high voltage pulse is applied between the cathode electrode and the anode electrode to generate an electron beam, and the electrons are concentrated in the waveguide to form a virtual cathode, thereby generating electromagnetic waves; The surface shape of the cathode electrode has a flat surface located in the center facing the anode electrode, and a curved surface that is continuous with the periphery of the flat surface, is annular and surrounds the flat surface, and curves away from the anode electrode, and the curved surface is an electromagnetic wave generating device composed of multiple curved surfaces whose radius of curvature decreases as the curved surface moves away from the flat surface. (Appendix 2) 2. The electromagnetic wave generating device according to claim 1, wherein the cathode electrode has a circular cross section parallel to the flat surface. (Appendix 3) 3. The electromagnetic wave generating device according to claim 2, wherein the diameter of the flat surface is smaller than the diameter of the waveguide. (Appendix 4) 4. The electromagnetic wave generating device according to any one of claims 1 to 3, wherein the curved surface has a first curved surface that is continuous with the periphery of the flat surface, and a second curved surface that is continuous with the first curved surface and has a radius of curvature smaller than the radius of curvature of the first curved surface. (Appendix 5) 5. The electromagnetic wave generating device according to claim 4, wherein in a cross section including the center of the flat surface and perpendicular to the flat surface, the angle of view of the first curved surface from the center of curvature of the first curved surface is smaller than the angle of view of the second curved surface from the center of curvature of the second curved surface. (Appendix 6) An electromagnetic wave generating device according to any one of appendices 1 to 5, wherein the material of the cathode electrode is a metal, and an electron emitting material having a higher electron emission ability than the material of the cathode electrode is provided on the surface of the cathode electrode. (Appendix 7) 7. The electromagnetic wave generating device according to claim 6, wherein the electron emitting material is a pile-like woven material made of at least one fiber material selected from the group consisting of rayon, polyester, silk, and cotton. (Appendix 8) 8. The electromagnetic wave generating device according to claim 6, wherein the region where the electron emitting material is provided is smaller than a circular region having a diameter equal to the diameter of the waveguide. (Appendix 9) 9. The electromagnetic wave generator according to any one of claims 6 to 8, wherein a recess is provided on the surface of the metal cathode electrode, and the electron emitting material is provided in the recess. [Explanation of symbols]

[0028] 4 cathode electrode, 7 anode electrode, 8 waveguide, 9 virtual cathode, 11 flat surface, 12 first curved surface, 13 second curved surface, 14 electron emitting material, 16 recess

Claims

1. An electromagnetic wave generating device comprising: a cathode electrode; an anode electrode that is disposed opposite the cathode electrode and through which electrons can pass; and a hollow cylindrical waveguide that is connected to the anode electrode on the side opposite the cathode electrode and that guides electromagnetic waves; wherein a high voltage pulse is applied between the cathode electrode and the anode electrode to generate an electron beam, and the electrons are concentrated in the waveguide to form a virtual cathode, thereby generating electromagnetic waves; The surface shape of the cathode electrode has a flat surface located in the center facing the anode electrode, and a curved surface that is continuous with the periphery of the flat surface, is annular and surrounds the flat surface, and curves away from the anode electrode, and the curved surface is an electromagnetic wave generating device composed of multiple curved surfaces whose radius of curvature decreases as the curved surface moves away from the flat surface.

2. The electromagnetic wave generating device according to claim 1 , wherein the cathode electrode has a circular cross section parallel to the flat surface.

3. 3. The electromagnetic wave generating device according to claim 2, wherein the diameter of the flat surface is smaller than the diameter of the waveguide.

4. 4. The electromagnetic wave generating device according to claim 1, wherein the curved surface has a first curved surface that is continuous with the periphery of the flat surface, and a second curved surface that is continuous with the first curved surface and has a radius of curvature that is smaller than the radius of curvature of the first curved surface.

5. 5. The electromagnetic wave generating device according to claim 4, wherein in a cross section including the center of the flat surface and perpendicular to the flat surface, an angle of view of the first curved surface from the center of curvature of the first curved surface is smaller than an angle of view of the second curved surface from the center of curvature of the second curved surface.

6. 4. The electromagnetic wave generator according to claim 1, wherein the cathode electrode is made of a metal, and an electron-emitting material having a higher electron emission ability than the material of the cathode electrode is provided on the surface of the cathode electrode.

7. 7. The electromagnetic wave generating device according to claim 6, wherein the electron emitting material is a pile woven material made of at least one fiber material selected from the group consisting of rayon, polyester, silk, and cotton.

8. 7. The electromagnetic wave generating device according to claim 6, wherein the region where the electron emitting material is provided is smaller than a circular region having a diameter equal to the diameter of the waveguide.

9. 9. The electromagnetic wave generating device according to claim 8, wherein a recess is provided on the surface of the metal cathode electrode, and the electron emitting material is provided in the recess.

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