A permanent magnet packaged high current diode capable of suppressing electron beam backflow

Abstract

The invention belongs to the microwave source device in the field of high-power microwave technology, in particular to a permanent magnet packaged high-current diode capable of suppressing electron beam backflow, which is composed of a diode structure and a permanent magnet system: the diode structure comprises a cathode base, a cathode, and an anode outer cylinder; the permanent magnet system comprises a soft magnet, a first permanent magnet on the left, a second permanent magnet on the left, a third permanent magnet on the left, and a fourth permanent magnet on the left, a first permanent magnet on the right, a second permanent magnet on the right, a third permanent magnet on the right, and a fourth permanent magnet on the right, as well as an outer magnetic yoke; the entire structure is rotationally symmetric about a central axis; the invention designs a gradient matching permanent magnetic field, and changes the magnetic field distribution in a diode region by loading soft magnetic materials, so that the magnetic field lines originally pointing to the permanent magnet are bent downward at the cathode base position, thereby suppressing the return electron beam from moving toward the anode; the cathode base adopts a conical structure, further effectively reducing the electric field intensity on the surface of the cathode base, thereby suppressing abnormal electron emission of the cathode base.

Description

Technical Field

[0001] The invention belongs to the microwave source device in the technical field of high-power microwaves, in particular to a permanent magnet packaged high-current diode capable of suppressing electron beam backflow. Background Art

[0002] High-power microwave (HPM) is usually defined as electromagnetic waves with a frequency of 0.1-100 GHz and a peak power greater than 100 MW. HPM source refers to a device in the HPM system that converts the energy of a high-current relativistic electron beam into microwave field energy, usually an electric vacuum device. Since the first HPM source was produced in the 1970s, HPM source technology has developed rapidly due to its important military and civilian needs.

[0003] Since the 21st century, miniaturization and modularization have been the frontier research directions of HPM technology. The external guidance magnetic field of traditional high-power microwave devices is usually generated by an energized solenoid coil. However, the energized solenoid coil and its associated power supply and water cooling system will increase the size and energy consumption of the HPM system, which is not conducive to the miniaturization research of high-power microwave systems. In order to improve the energy utilization rate of the HPM system and reduce the system volume, researchers proposed a method of using permanent magnets to replace energized solenoid coils, which promoted the development of low-field permanent magnet packaged high-power microwave devices.

[0004] Suppressing the electron beam backflow problem in high-current diodes is an important focus of current research on permanent magnet packaging devices. For the cathode magnetic immersed coaxial diode commonly used in O-type high-power microwave devices, due to the external axial guide magnetic field and the radial electric field between the cathode and the cathode, a small part of the electrons emitted by the cathode and the cathode rod will move in the opposite direction to form a backflow electron beam. The backflow electron beam is an important factor affecting the power conversion efficiency of high-current diodes. In addition, it is very easy to damage the anode and shorten the life of the diode when bombarding the anode under the action of the guide magnetic field. The generation and transmission of electrons can be controlled by the cathode material and the permanent magnetic field. The design of the high-current diode needs to suppress the abnormal emission and backflow electron beam of the cathode base as much as possible to improve the efficient conversion of electric power to electron beam power.

[0005] In the research of high-current diodes that suppress the return electron beam, the following research institutions at home and abroad have carried out relevant work:

[0006] The patent scheme of the Chinese invention patent "A method for suppressing electron beam backflow in a foilless diode (patent number: ZL202011449225.7)" (hereinafter referred to as prior art 1, such as Figure 1(As shown in the figure) By applying a bevel cathode in a foilless diode, the reflux electron beam will be inhibited by the strong negative potential near the bevel cathode and the blocking and absorption effect of the bevel cathode, thereby inhibiting the reflux of the electron beam. However, the distance between the cathode and the cathode of the bevel cathode used in this scheme is further reduced, and the radial electric field at the diode is enhanced, making it easy for the cathode base to produce abnormal electron emission; and the bevel cathode can only inhibit the reflux of a small part of the electrons in the cathode and its cathode rod head, and cannot inhibit the abnormal electron emission of the cathode base from bombarding the anode.

[0007] The patent scheme of the Chinese invention patent application "A kind of anode electrostatic shielding groove structure to suppress backflow diode (application number: 202410538840.7, publication date: 2024-08-02)" (hereinafter referred to as prior art 2, such as Figure 2 As shown in the figure, an anode electrostatic shielding groove structure is used to reduce the electrostatic field strength on the surface of the reflux bombardment point. However, this solution can only delay the movement of ions or charged dust generated in the zero field area to the cathode base, and cannot suppress the abnormal emission of electrons from the cathode base and the cathode reflux electrons from bombarding the anode; and the anode electrostatic shielding groove structure also reduces the distance between the cathode and the cathode, so that the radial electric field at the diode is enhanced, which is easy to cause abnormal electron emission from the cathode base.

[0008] It is not difficult to see from the above research status that a lot of research has been done on the suppression of the reflux electron beam at the high-current diode. The publicly reported technical solutions are very likely to cause the radial electric field of the diode to be enhanced when suppressing the reflux electron beam, and it is impossible to take both into account. Therefore, an effective solution is needed that can suppress the reflux electron beam and reduce the radial electric field of the diode. However, there is no public report on the technical solution of suppressing the reflux of the electron beam by designing the permanent magnet and the structure of the cathode base. Summary of the invention

[0009] The technical problem to be solved by the present invention is: the present invention proposes a permanent magnet packaged high-current diode capable of suppressing electron beam reflux, and through the reasonable design of the permanent magnet magnetic field and the diode structure, the abnormal emission and reflux electron beam of the cathode base are suppressed, thereby improving the efficient conversion of the high-current diode electric power to the electron beam power.

[0010] The technical solution of the present invention is:

[0011] A permanent magnet packaged high-current diode capable of suppressing electron beam backflow consists of a diode structure and a permanent magnet system: the diode structure comprises a cathode base 301, a cathode 302, and an anode outer cylinder 303; the permanent magnet system comprises a soft magnet 304, a first permanent magnet 305a on the left, a second permanent magnet 305b on the left, a third permanent magnet 305c on the left, and a fourth permanent magnet 305d on the left, a first permanent magnet 306a on the right, a second permanent magnet 306b on the right, a third permanent magnet 306c on the right, and a fourth permanent magnet 306d on the right, and an outer yoke 307; the entire structure is rotationally symmetrical about a central axis.

[0012] The cathode base 301 consists of two parts: the left end is a R 1 thin-walled cylindrical cavity, the right end of which is a top base with a radius of R 1, the radius of the bottom base is R 2. High L 0 thin-walled truncated cone-shaped cavity, the wall thickness is 1 mm, satisfying R 2> R 1, L 0≤15 L 1. The cathode 302 is a thin-walled cylinder, which is sleeved on the right end of the cathode base 301. The wall thickness is only 2 mm and the outer radius is R 2 is equal to the radius of the outer electron beam, and the length is L 1, L 1≥10 mm. The anode outer cylinder 303 is composed of two integral cylindrical cylinders, and the inner radii are R 3 and R 4. Satisfaction R 3> R 4> R 2; The anode outer cylinder 303 can also be formed by connecting multiple cylinders through flanges with sealing grooves and positioning steps.

[0013] The soft magnetic body 304 is embedded in the cathode base 301, and the inner and outer radii are R 5 and R 6 circular ring structure, width L 2. Satisfaction R 5< R 6. L 2< L 0; The soft magnetic material used by the soft magnetic body 304 is usually low carbon steel, pure iron, iron-silicon alloy, iron-aluminum alloy, soft ferrite, etc. The left permanent magnet is composed of four permanent magnets with different magnetization directions: the first permanent magnet 305a on the left is a permanent magnet with an inner and outer radius of R 7 and R 11 The circular ring magnet meets R 11 > R 7>R 3, length is L 3. The magnetization direction is radial 0°. L 3> L 0; the second permanent magnet 305b on the left has an inner and outer radius of R 8 and R 11 The circular ring magnet meets R 11 > R 8≥ R 7> R 3, length is L 4. The magnetization direction is radial +45°. L 4≤ L 3; The third permanent magnet 305c on the left has an inner and outer radius of R 9 and R 11 The circular ring magnet meets R 11 > R 9> R 8≥ R 7, length is L 5. The magnetization direction is radial 0°, 0.5 L 4≤ L 5≤2 L 3; The fourth permanent magnet 305d on the left has an inner and outer radius of R 10 and R 11 The circular ring magnet meets R 11 > R 10 > R 9, length is L 6. The magnetization direction is radial 0°. L 6≥0.5 L 5. The longitudinal cross-sectional dimensions of the right permanent magnet and the left permanent magnet are symmetrical. The magnetization directions of the first right permanent magnet 306a, the third right permanent magnet 306c and the fourth right permanent magnet 306d are all 180° in the radial direction, and the magnetization direction of the second right permanent magnet 306b is -45° in the radial direction. The outer yoke 307 is a yoke with an inner and outer radius of R 11 and R 12 The circular structure, length L 7, R 12 > R 11 , L 7>2( L 3+ L 4+L 5+ L 6).

[0014] The present invention discloses a permanent magnet packaged high-current diode capable of suppressing electron beam backflow. A gradient matching permanent magnet magnetic field is designed. By loading soft magnetic materials, the magnetic field distribution in the diode area is changed, so that the magnetic field lines originally pointing to the permanent magnet are bent downward at the cathode base position, thereby suppressing the return electron beam from moving toward the anode. At the same time, the cathode base adopts a conical structure, which further effectively reduces the electric field strength on the cathode base surface, thereby suppressing abnormal electron emission from the cathode base.

[0015] Compared with the prior art, the present invention can achieve the following technical effects:

[0016] 1. The permanent magnet packaged high-current diode capable of suppressing electron beam backflow disclosed in the present invention, based on the traditional optimization of the permanent magnet structure size, changes the magnetic field distribution in the diode area by adding soft magnetic materials, so that the magnetic field lines bend downward at the cathode base position, generating a magnetic field pattern capable of suppressing the backflow electron beam, thereby effectively suppressing the backflow electrons.

[0017] 2. The permanent magnet packaged high-current diode capable of suppressing electron beam reflux disclosed in the present invention has a conical structure for the cathode base, a further reduced radius, an increased distance between the anode and cathode, and a further reduced surface electric field of the cathode base to 250-280 kV / cm, thereby effectively suppressing abnormal electron emission.

[0018] Please refer specifically to the following description of various embodiments of the permanent magnet packaged high current diode capable of suppressing electron backflow according to the present invention, which will make the above and other aspects of the present invention apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram of a method for suppressing electron beam backflow in a foil-free diode disclosed in the prior art 1 in the background introduction;

[0020] Figure 2 A schematic diagram of a diode for suppressing reflux with an anode electrostatic shielding groove structure disclosed in prior art 2 in the background introduction;

[0021] Figure 3 A schematic structural diagram of a preferred embodiment of a permanent magnet packaged high current diode capable of suppressing electron beam backflow provided by the present invention;

[0022] Figure 4 The electron beam trajectory of the high-current diode during full cathode emission without soft magnetic permanent magnet packaging in a preferred embodiment of the permanent magnet packaged high-current diode capable of suppressing electron beam backflow provided by the present invention;

[0023] Figure 5The preferred embodiment of the permanent magnet packaged high-current diode capable of suppressing electron beam backflow provided by the present invention is a motion trajectory of the backflow electron beam of the high-current diode when there is no soft magnetic permanent magnet package;

[0024] Figure 6 A permanent magnet magnetic field distribution curve diagram of a preferred embodiment of a permanent magnet packaged high current diode capable of suppressing electron beam backflow provided by the present invention;

[0025] Figure 7 A comparison diagram of the axial magnetic field intensity distribution with and without soft magnetic material of a preferred embodiment of a permanent magnet packaged high-current diode capable of suppressing electron beam backflow provided by the present invention;

[0026] Figure 8 A comparison diagram of radial magnetic field intensity distribution with and without soft magnetic material for a preferred embodiment of a permanent magnet packaged high-current diode capable of suppressing electron beam backflow provided by the present invention;

[0027] Fig. 9 The result of suppressing electron backflow of the permanent magnet packaged high current diode of the preferred embodiment of the permanent magnet packaged high current diode capable of suppressing electron beam backflow provided by the present invention;

[0028] Fig.10 The structure and field distribution of a permanent magnet packaged high current diode of a preferred embodiment of a permanent magnet packaged high current diode capable of suppressing electron beam backflow provided by the present invention; DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings.

[0030] The present invention is composed of a cathode base 301, a cathode 302, an anode outer cylinder 303, a soft magnet 304, left permanent magnets 305a, 305b, 305c and 305d, right permanent magnets 306a, 306b, 306c and 306d and an outer magnetic yoke 307; the entire structure is rotationally symmetrical about the central axis.

[0031] The cathode base 301 and the anode outer cylinder 303 are usually made of non-magnetic stainless steel, oxygen-free copper or titanium; the cathode 302 can be made of high-hardness graphite or heat-resistant glass cloth-epoxy resin copper-clad foil (FR-5) material; the left permanent magnet and the right permanent magnet are both made of neodymium iron boron and other materials; the soft magnet 304 is a soft magnetic material such as low-carbon steel, pure iron, iron-silicon alloy, iron-aluminum alloy or soft ferrite, and the outer yoke 307 can be made of stainless steel and other materials. The left end of the cathode base 301 is connected to the inner conductor of the pulse power drive source, and the left end of the anode outer cylinder 303 is connected to the outer conductor of the pulse power drive source.

[0032] The present invention discloses a permanent magnet packaged high-current diode capable of suppressing electron beam backflow. The cathode base adopts a conical structure, which effectively reduces the electric field strength on the surface of the cathode base, thereby suppressing abnormal electron emission from the cathode base. At the same time, a gradient matching permanent magnet magnetic field is designed, and the magnetic field distribution in the diode area is precisely controlled by loading soft magnetic materials. Under the guidance of the magnetic field, the backflow electrons generated at the high-current diode are effectively suppressed.

[0033] This solution realizes a permanent magnet packaged high current diode that can suppress electron backflow (the corresponding size is designed as: R 1 = 35 mm, R 2 = 45 mm, R 3 = 75 mm, R 4 = 52 mm, R 5=30 mm, R 6=40 mm, R 7=85 mm, R 8=85 mm, R 9=105 mm, R 10 =137 mm, R 11 =170 mm, R 12 =180 mm, L 0=60 mm, L 1=20 mm, L 2 = 40 mm, L 3 = 100 mm, L 4 = 40 mm, L 5=40 mm, L 6=50 mm, L 7=520 mm).

[0034] The main function of a high-current diode (mainly referring to the diode of the device) is to efficiently generate a high-quality high-current electron beam. For permanent magnet packaged HPM devices, the main problem is the efficient conversion of electrical power to electron beam power. The main reasons affecting the conversion efficiency include the generation of positive ions in the diode, abnormal emission of the cathode base, and reflux electron beams. Since the weight of positive ions is much greater than that of electrons, their generation and transmission are difficult to effectively suppress, while the mass of electrons is very light. The generation and transmission of electrons can be controlled by the cathode base material and the permanent magnetic field. The design of the high-current diode needs to suppress the abnormal emission of the cathode base and the reflux electron beam as much as possible to improve the efficient conversion of electrical power to electron beam power.

[0035] Figure 4The electron beam trajectory of the permanent magnet packaged high current diode during full cathode emission is shown. It can be seen that the abnormally emitted electrons and the return electron beam will bombard the diode anode under the guidance of the permanent magnetic field. The two types of electron beams cannot interact with each other and are invalid electrons. On the one hand, the invalid electron beam leads to the loss of electric power and reduces the power conversion efficiency from electric power to effective electron beam. On the other hand, it is very easy to damage the diode anode during heavy frequency operation, reducing the life of the device.

[0036] The present invention intends to effectively suppress the return electron beam and abnormal electron emission from the cathode base, first of all, the return electron beam. The entire high-current cathode is mainly composed of a cathode base and a graphite emitter. The cathode base material is usually titanium alloy or stainless steel. According to relevant literature reports, the emission thresholds of titanium alloy and stainless steel are ~300kV / cm and ~230kV / cm, and the emission threshold of graphite is less than 100kV / cm. Through structural optimization, the surface electric field of the cathode base can be controlled within the emission threshold, thereby suppressing the electron emission from the cathode base surface. However, for the graphite emitter, its emission threshold is low, and there is a dense plasma source near the emitter, so the return electrons are difficult to avoid (see Figure 5 ).

[0037] The preferred design of the present invention is a gradient matching permanent magnetic field, the permanent magnet structure and field distribution are as follows Figure 6 As shown, the permanent magnet is mainly composed of radially magnetized permanent magnets, ±45° obliquely magnetized permanent magnets and an outer magnetic yoke. The magnetic field uniformity area generated at the electron beam position is about 27 cm, the average magnetic field strength is about 0.42 T, and the total weight of the permanent magnet is about 250 kg. On the basis of the traditional optimization of the permanent magnet structure size, by loading soft magnetic materials, the magnetic field distribution in the diode area is precisely controlled, and a magnetic field configuration that can suppress the return flow of electrons is generated in the high-current diode. It can be seen that in the soft magnet loaded area, the magnetic field lines are adsorbed by the soft magnet and bent toward the soft magnet 304, while the magnetic field line distribution in the uniform area is not affected. The axial intensity distribution of the permanent magnet magnetic field is shown in Figure 7 As shown in the figure, compared with the magnetic field without soft magnets, due to the adsorption of soft magnets, the axial magnetic field strength of the magnetic field is significantly weakened in the soft magnet area, while the radial magnetic field strength towards the soft magnet direction is significantly enhanced (see Figure 8 ).

[0038] During the simulation, under the guidance of the gradient matching magnetic field, the diode voltage was set to 800 kV and the diode was immersed in Figure 6 In the permanent magnet magnetic field shown, the magnetic field lines of the cathode region are bent toward the soft magnetic body 304 , which inhibits the return electrons from moving toward the cathode base 301 or the anode outer cylinder 303 . Fig. 9The electron transfer trajectory of the high-current diode is shown. Even if a graphite emission end (about 20 mm in length, which is equivalent to the graphite length in the experiment) is set up for full emission, no reflux electron beam is found, indicating that the reflux electron beam is effectively suppressed.

[0039] In the simulation, the radial spacing between the anode and cathode was appropriately increased to reduce the electric field strength avoided by the cathode base. The emission threshold of the cathode base was set to 300 kV / cm. No obvious electron emission was generated, and the abnormal electron emission of the cathode base was initially suppressed (same Fig. 9 ). In order to further suppress the abnormal electron emission of the cathode base, the present invention further reduces the electric field amplitude on the surface of the cathode base by optimizing the diode structure. Fig.10 The structural schematic diagram and field distribution of the high-current diode are shown. The cathode base adopts a conical structure, and the radius is further reduced. The surface electric field of the cathode base is further reduced to ~250~280 kV / cm, thereby effectively suppressing abnormal electron emission.

Claims

1. A permanent magnet packaged high current diode capable of suppressing electron beam backflow, characterized in that: The permanent magnet packaged high current diode is composed of a diode structure and a permanent magnet system: the diode structure includes a cathode base (301), a cathode (302), and an anode outer cylinder (303); the permanent magnet system includes a soft magnet (304), a first permanent magnet (305a) on the left, a second permanent magnet (305b) on the left, a third permanent magnet (305c) on the left, and a fourth permanent magnet (305d) on the left, a first permanent magnet (306a) on the right, a second permanent magnet (306b) on the right, a third permanent magnet (306c) on the right, and a fourth permanent magnet (306d) on the right, and an outer magnetic yoke (307); the entire structure is rotationally symmetrical about the central axis; The cathode base (301) consists of two parts: the left end is a R 1 thin-walled cylindrical cavity, the right end of which is a top base with a radius of R 1, the radius of the bottom base is R 2. High L 0 thin-walled truncated cone-shaped cavity, the wall thickness is 1 mm, satisfying R 2> R 1, L 0≤15 L 1. The cathode (302) is a thin-walled cylinder, which is sleeved on the right end of the cathode base (301) and has an outer radius R 2 is equal to the radius of the outer electron beam, and the length is L 1, L 1≥10 mm; the anode outer cylinder (303) is composed of two integral cylindrical cylinders, and the inner radii are R 3 and R 4. Satisfaction R 3> R 4> R 2; The soft magnetic body (304) is embedded in the cathode base (301) and has inner and outer radii of R 5 and R 6 circular ring structure, width L 2. Satisfaction R 5< R 6. L 2< L 0; The left permanent magnet is composed of four permanent magnets with different magnetization directions: the first permanent magnet (305a) on the left is a permanent magnet with inner and outer radii of R 7 and R 11 The circular ring magnet meets R 11 > R 7> R 3, length is L 3. The magnetization direction is radial 0°. L 3> L 0; the second permanent magnet (305b) on the left is a magnet with inner and outer radii of R 8 and R 11 The circular ring magnet meets R 11 > R 8≥ R 7> R 3, length is L 4. The magnetization direction is radial +45°. L 4≤ L 3; The third permanent magnet (305c) on the left is a magnet with inner and outer radii of R 9 and R 11 The circular ring magnet meets R 11 > R 9> R 8≥ R 7, length is L 5. The magnetization direction is radial 0°, 0.5 L 4≤ L 5≤2 L 3; The fourth permanent magnet (305d) on the left is a magnet with inner and outer radii of R 10 and R 11 The circular ring magnet meets R 11 > R 10 > R 9, length is L 6. The magnetization direction is radial 0°. L 6≥0.5 L 5; the longitudinal cross-sectional dimensions of the right permanent magnet and the left permanent magnet are symmetrical, the magnetization directions of the first right permanent magnet (306a), the third right permanent magnet (306c) and the fourth right permanent magnet (306d) are all radially 180°, and the magnetization direction of the second right permanent magnet (306b) is radially -45°; the outer yoke (307) is a yoke with inner and outer radii of R 11 and R 12 The circular structure, length L 7, R 12 > R 11 , L 7>2( L 3+ L 4+ L 5+ L 6).

2. A permanent magnet packaged high current diode capable of suppressing electron beam backflow according to claim 1, characterized in that: The cathode (301) wall thickness is only 2 mm.

3. A permanent magnet packaged high current diode capable of suppressing electron beam backflow according to claim 1, characterized in that: The anode outer cylinder (303) is formed by connecting a plurality of cylinders through flanges with sealing grooves and positioning steps.

4. A permanent magnet packaged high current diode capable of suppressing electron beam backflow according to claim 1, characterized in that: The cathode base (301) and the anode outer cylinder (303) are made of non-magnetic stainless steel, oxygen-free copper or titanium; the cathode (302) is made of high-hardness graphite or heat-resistant glass cloth-epoxy resin copper-clad foil; the left permanent magnet and the right permanent magnet are both made of neodymium iron boron; the soft magnet (304) is low-carbon steel, pure iron, iron-silicon alloy, iron-aluminum alloy or soft magnetic ferrite, and the outer yoke (307) is made of stainless steel.

5. A permanent magnet packaged high current diode capable of suppressing electron beam backflow according to any one of claims 1 to 4, characterized in that: A permanent magnet packaged high current diode capable of suppressing electron backflow, the corresponding dimensions are designed as follows: R 1=35 mm, R 2 = 45 mm, R 3 = 75 mm, R 4 = 52 mm, R 5=30 mm, R 6=40 mm, R 7=85 mm, R 8=85 mm, R 9=105 mm, R 10 =137mm, R 11 =170 mm, R 12 =180 mm, L 0=60 mm, L 1=20 mm, L 2 = 40 mm, L 3 = 100 mm, L 4 = 40 mm, L 5=40mm, L 6=50 mm, L 7=520 mm.

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