Foilless diode suppressing undesirable electron emission and backflow electron beam and design method thereof

Abstract

The application discloses a foilless diode for inhibiting undesired electron emission and backflow electron beams and a design method thereof, and solves the technical problems that the methods for inhibiting undesired electron emission and backflow electron beams of permanent magnet guided foilless diodes are high in cost or poor in inhibition effect, wherein the foilless diode for inhibiting undesired electron emission and backflow electron beams comprises an insulating sub, an anode outer cylinder, a cathode lead, a cathode base, a permanent magnet and a magnetic steel; the cathode lead and the cathode base are both hollow structures; the magnetic steel is embedded in the interiors of the cathode lead and the cathode base, is used for attracting the surrounding electrons through the magnetism of the magnetic steel, and pulls back the undesired electrons to the cathode lead and the cathode base, so as to improve the electron emission threshold of the cathode lead and the cathode base; the magnetic steel cooperates with the magnetic field of the permanent magnet, so that the magnetic force lines around the backflow electron beams are distributed along the surface of the cathode lead and finally converge at the cathode base, and then the backflow electron beams are collected by the cathode lead and the cathode base.

Description

Technical Field

[0001] This invention relates to foil-free diodes and their design methods, specifically to a foil-free diode and its design method for suppressing unwanted electron emission and backflow electron beams. Background Technology

[0002] High-power microwave sources, as key devices for generating high-power microwaves using high-current relativistic electron beams, have broad application prospects. Currently, the high-current relativistic electron beam required for high-power microwave sources is mainly formed by plasma generation from an explosive emission cathode driven by a high-voltage pulse. The stability and beam current utilization rate of the electron beam generated by the explosive emission cathode directly determine the reliability and conversion efficiency of the high-power microwave source, which is also an important direction for current research in high-power microwave technology.

[0003] As high-power microwave sources evolve towards permanent magnets with higher output power and lower guiding magnetic fields, electron emission will inevitably occur in the strong electric field regions such as the cathode lead surface and the base of the explosive emission cathode. Furthermore, after generating a strong current relativistic electron beam, the explosive emission cathode will inevitably produce some backflow electron beam. Therefore, it is crucial to study how to suppress unwanted electron emission and backflow electron beam.

[0004] In the process of generating a high-current relativistic electron beam using a high-voltage pulse-driven explosive emission cathode, undesirable electron emission occurs due to the high field strength of the cathode leads and base in the foilless diode. The main electron beam propagates forward and undergoes beam transduction by a high-power microwave generator, converting its energy into microwave energy. However, the return electron beam propagates backward and cannot be converted into microwave energy. Both undesirable electron emission and the return electron beam negatively impact the stability and beam current utilization of the foilless diode.

[0005] Traditional superconducting or solenoid magnet-guided foilless diode structures and magnetic field distributions, such as Figure 1 As shown, its structure includes a dielectric-insulated side 1 of the pulsed power device, an insulator 2, an anode outer cylinder 3, a conventional superconducting or solenoid magnet 4, a cathode base 5, and a cathode lead 6, which generate and inject a high-current relativistic hollow electron beam into the high-power microwave generator 7. Its working mechanism has significant advantages: Firstly, from... Figure 1Looking at the distribution of magnetic field lines 8 in the cathode region and 9 in the anode region, the magnetic field lines 8 in the cathode region of a conventional superconducting or solenoid magnet 4 decrease slowly. The electron beam returning from the cathode moves along the magnetic field lines and can be completely collected by the base. Furthermore, the energy of the returning electron beam is extremely low, and it will not have an adverse effect on the diode insulation and structural materials. Secondly, due to the large magnetic field strength, electrons emitted from the cathode end face and side can be effectively confined by the magnetic field, so that both the forward main electron beam and the returning electron beam are well confined, thereby avoiding the risk of abnormal short circuits in the diode. Finally, the cathode base 5 is usually placed outside the conventional superconducting or solenoid magnet 4, and its surface electric field strength can be reduced to a low level, thereby eliminating the possibility of electron emission from the cathode base 5. However, the conventional superconducting or solenoid magnet 4 has a complex structure, requires strict confinement, and has high engineering and maintenance costs.

[0006] Permanent magnet-guided foil-less diodes, on the other hand, forgo extreme performance in favor of a simple, reliable, and low-cost technology. Their structure and magnetic field distribution are as follows: Figure 2 As shown, the structure includes a dielectric-insulated side 1 of the pulsed power device, an insulator 2, an anode outer cylinder 3, a cathode base 5, a permanent magnet 11, and a cathode lead rod 6. This structure generates and injects a high-current relativistic hollow electron beam into the high-power microwave generator 7. Its axial magnetic field is relatively weak, which significantly broadens the transmission of the main electron beam. From... Figure 2 Looking at the distribution of magnetic field lines 8 in the cathode region and 9 in the anode region, a more serious issue is that the magnetic field lines in the permanent magnet 11 always converge rapidly at the N and S poles of the permanent magnet 11 at the ends. This causes a rapid decrease in the axial magnetic field strength in areas such as the cathode lead 6 and cathode base 5 within the diode, while the radial magnetic field strength rapidly increases. For example... Figure 4As shown, the surface in these regions exhibits undesirable electron emission and insufficient electron beam confinement, leading to a significant increase in the electron distribution area. Therefore, electron emission and electron bombardment occur in multiple regions within the diode, accompanied by plasma generation. In some cases, electrons emitted from strong electric field regions such as the cathode lead 6 surface and cathode base 5 directly bombard the anode, posing risks such as structural damage and diode short circuits. These factors all affect the normal and stable operation of the foil-less diode guided by the permanent magnet. Currently, there are two main methods to suppress undesirable electron emission: First, by limiting the device's operating voltage and optimizing the diode radius and structure, the radial electric field strength at the diode can be controlled to ensure that electron emission in the diode's cathode region is minimized. For example, in 2011, Russian researchers used this method to ensure stable system operation (Gunin AV et al. 2011 IEEE Pulsed Power Conference, Chicago, USA, 2011:371-376). However, even with optimal diode radius and structure, the electric field strength of the cathode lead and cathode base may still be high, and undesirable electron emission cannot be completely suppressed. Second, the preferred emission-suppressing material is selected and surface treatment is performed. For example, research by Wu Xiaoling of Tsinghua University shows that TC18 material has unique advantages in suppressing electron emission and resisting electron bombardment (Wu Xiaoling, Tsinghua University Doctoral Dissertation, 2021). By using TC18 material to increase the electron emission threshold of the cathode lead and cathode base surface, unwanted electron emission can be effectively suppressed. In addition, the material surface can be further improved by mirror polishing and nano-sizing, but the production cost also increases accordingly.

[0007] There are two main methods to suppress the backflow electron beam: First, by improving the cathode lead structure, the backflow electron beam can be effectively collected under the low magnetic field conditions guided by permanent magnets. Specifically, a backflow collection ring is constructed using a local radius abrupt change or a tapered lead to block the cathode backflow electron beam, thereby completing the collection of the cathode backflow electron beam within a limited space (Related literature references: Xiang Fei et al., High Power Laser and Particle Beams, 2011, 23(3): 831-835; Yang Jianhua, Doctoral Dissertation of National University of Defense Technology, 2002; Liu Zhong et al., Journal of Microwave, 2012, 28(2): 79-82). However, the local field strength of this structure is significantly enhanced, which can easily lead to the breakdown of the backflow collection ring and cause a local short circuit in the diode, which has significant limitations and low practical application value. Secondly, Chinese invention patent CN119153289A discloses a permanent magnet packaged high-current diode that can suppress electron beam backflow. It uses soft magnets (i.e., non-magnetic ferroelectric materials) to optimize the magnetic field lines on the cathode end face of the diode region in order to block the backflow electron beam in the diode from bombarding the anode. However, the suppression effect of this method is poor. Summary of the Invention

[0008] The purpose of this invention is to address the technical problems of existing methods for suppressing unwanted electron emission and backflow electron beams using foilless diodes guided by permanent magnets. These methods suffer from the issues of complex structures, stringent constraints, high engineering and maintenance costs, or poor suppression effects of traditional superconducting or solenoid magnets. The invention provides a foilless diode for suppressing unwanted electron emission and backflow electron beams, along with its design method.

[0009] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0010] A foilless diode for suppressing unwanted electron emission and backflow electron beams includes an insulator, an anode outer cylinder, a cathode lead rod, a cathode base, and a permanent magnet; its special feature is that it also includes a magnet.

[0011] Both the cathode lead rod and the cathode base are hollow structures.

[0012] The magnet is embedded inside the cathode lead and cathode base to attract surrounding electrons through the magnetism of the magnet and pull unwanted electrons back to the cathode lead and cathode base, thereby increasing the electron emission threshold of the cathode lead and cathode base.

[0013] The magnetic field of the magnet and the permanent magnet work together to distribute the magnetic field lines around the return electron beam along the surface of the cathode lead rod and eventually converge at the cathode base, so that the return electron beam is collected by the cathode lead rod and the cathode base.

[0014] Furthermore, the axial distance between the end of the magnet embedded in the cathode and the cathode is greater than or equal to 1 / 10 of the axial length of the cathode lead, and the axial length of the magnet is greater than or equal to 1 / 2 of the axial length of the cathode lead.

[0015] Furthermore, the magnet inside the cathode base is adapted to the internal cavity size of the cathode base.

[0016] Meanwhile, the present invention also provides a design method for a foil-free diode to suppress unwanted electron emission and backflow electron beam, which is characterized by including the following steps:

[0017] Step 1: Model Establishment and Parameter Determination

[0018] A foilless diode explosion emission model was constructed using particle simulation software to determine the distribution of magnetic field lines in the cathode region, the trajectory of the electron beam in the cathode region, and the maximum envelope size of the cathode lead rod and the inner cavity of the cathode base.

[0019] Step 2: Determine the magnet material and envelope size

[0020] The material of the magnet is determined, and the envelope size of the magnet is determined based on the maximum envelope size of the cathode lead and the inner cavity of the cathode base. The maximum envelope size of the magnet is made smaller than the maximum envelope size of the inner cavity of the cathode lead and the cathode base, thus obtaining a foil-free diode model for primary suppression of unwanted electron emission and backflow electron beam.

[0021] Step 3: Magnetic field optimization design

[0022] The foilless diode model for suppressing unwanted electron emission and backflow of electron beams is imported into the magnetic field design software. Based on the distribution of magnetic field lines in the cathode region, the trajectory of the electron beam in the cathode region, and the material of the magnet, the size and / or magnetization direction of the magnet are adjusted until the magnetic field lines of the permanent magnet in the cathode region are distributed along the surface of the cathode lead and finally converge at the cathode base, thus completing the design of the foilless diode for suppressing unwanted electron emission and backflow of electron beams.

[0023] Furthermore, the design method for foil-free diodes that suppress unwanted electron emission and backflow electron beams also includes step S:

[0024] Cathode region electron beam trajectory verification

[0025] The electron beam trajectory in the cathode region was verified using particle simulation software to ensure that the returning electrons and unwanted emitted electrons were collected onto the cathode lead and cathode base.

[0026] Furthermore, in step 3, the magnetic field design software is ANSYS Maxwell electromagnetic simulation software.

[0027] Furthermore, step 3 specifically involves:

[0028] Step 3.1: Import the foil-free diode model for primary suppression of unwanted electron emission and backflow electron beam into the magnetic field design software;

[0029] Step 3.2: Using magnetic field design software, set the initial size structure of the magnet according to the material of the magnet, so as to be a cylindrical structure that does not exceed the maximum outer envelope of the cathode lead and the cathode base;

[0030] Step 3.3: Set the initial magnetization direction of the magnet to be the same as the main electron beam transmission direction;

[0031] Step 3.4: Make coarse adjustments to the diameter, length, and magnetization direction of the cylindrical magnet until the permanent magnets are distributed along the surface of the cathode lead rod within a preset range in the cathode region, and finally converge within the preset range of the cathode base.

[0032] Step 3.5: Finely adjust the irregular size and magnetization direction of the magnet until the magnetic lines of the permanent magnet in the cathode area are distributed along the surface of the cathode lead rod and finally converge at the cathode base.

[0033] Compared with the prior art, the present invention has the following beneficial technical effects:

[0034] 1. This invention provides a foilless diode for suppressing unwanted electron emission and backflow electron beams. By embedding magnets within the cathode lead and cathode base, the electron emission threshold of the cathode lead and cathode base can be further improved without altering the original structure of the foilless diode, effectively suppressing unwanted electron emission. Simultaneously, it optimizes the magnetic field distribution in the cathode region, thereby suppressing backflow electron beams and improving the stability and beam current utilization of the foilless diode.

[0035] 2. The present invention provides a foil-free diode for suppressing unwanted electron emission and backflow electron beam. Applying this technology to the research and development of permanent magnet packaged high-power microwave generators can significantly improve the working efficiency and reliability of high-power microwave generators.

[0036] 3. The present invention provides a foilless diode design method for suppressing unwanted electron emission and backflow electron beams, which can significantly improve the ability of permanent magnet packaged foilless diodes to restrain unwanted electron emission and backflow electron beams, improve the stability and beam current utilization of foilless diodes, and has universality. Attached Figure Description

[0037] Figure 1 A schematic diagram of the structure and magnetic field distribution of a foilless diode guided by a conventional superconducting or solenoid magnet (showing a high-power microwave generator).

[0038] Figure 2 A schematic diagram of the structure and magnetic field distribution of a foil-free diode guided by a permanent magnet (showing a high-power microwave generator).

[0039] Figure 3 This is a schematic diagram of the structure and magnetic field distribution of a foil-free diode embodiment of the present invention for suppressing unwanted electron emission and backflow electron beam (showing a high-power microwave generator).

[0040] Figure 4 A particle simulation effect diagram of a foil-free diode guided by a permanent magnet;

[0041] Figure 5 This is a particle simulation effect diagram of a foil-free diode for suppressing unwanted electron emission and backflow electron beam according to the present invention.

[0042] The annotations in the attached figures are explained as follows:

[0043] 1. Dielectric insulation side of pulse power device; 2. Insulator; 3. Anode outer cylinder; 4. Traditional superconducting or solenoid magnet; 5. Cathode base; 6. Cathode lead rod; 7. High-power microwave generator; 8. Cathode area magnetic field lines; 9. Anode area magnetic field lines; 10. Magnet; 11. Permanent magnet. Detailed Implementation

[0044] To make the objectives, advantages, and features of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0045] like Figure 3 As shown, this embodiment provides a foil-free diode for suppressing unwanted electron emission and backflow electron beams, including an insulator 2, a permanent magnet 11, a cathode base 5, a cathode lead 6, and a high-power microwave generator 7. One side of the insulator 2 is the dielectric insulation side 1 of the pulse power device, and the other side is the anode outer cylinder 3. The inner side of the insulator 2 is connected to the cathode base 5, and its outer side is connected to the anode outer cylinder 3. The anode outer cylinder 3 is connected to the permanent magnet 11 through a magnetic sleeve. The cathode base 5 is connected to one end of the cathode lead 6.

[0046] Both the cathode lead 6 and the cathode base 5 are hollow structures, with embedded magnets 10. The axial distance between the end of the embedded magnet 10 near the cathode and the cathode is greater than or equal to 1 / 10 of the axial length of the cathode lead 6, and the axial length of the magnet 10 is greater than or equal to 1 / 2 of the axial length of the cathode lead 6. The magnet 10 in the cathode base 5 is adapted to the internal cavity size of the cathode base 5. On the one hand, the attraction of the magnet 10 to the surrounding electrons is used to pull potentially unwanted electrons back to the cathode lead 6 and the cathode base 5, thereby indirectly increasing the electron emission threshold of the cathode lead 6 and the cathode base 5 and effectively suppressing the emission of unwanted electrons on the cathode lead 6 and the cathode base 5. On the other hand, through the coordinated magnetic field of the embedded magnet 10 and the permanent magnet 11, the distribution of magnetic field lines around the returning electron beam is adjusted, guiding it to distribute along the surface of the cathode lead 6 and finally converge near the cathode base 5. Under the influence of magnetic field lines, the returning electron beam moves along the surface of the cathode lead 6 and is collected by the cathode lead 6 and the cathode base 5, thereby preventing it from bombarding the anode of the foilless diode and thus improving the stability and beam current utilization of the foilless diode. The magnet 10 inside the cathode lead 6 is located in the cathode region, and the axial distance between its end closest to the cathode and the cathode is greater than or equal to 1 / 10 of the axial length of the cathode lead 6, and the axial length of the magnet 10 is greater than or equal to 1 / 2 of the axial length of the cathode lead 6. It has little impact on the magnetic field lines 9 in the anode region and does not affect the trajectory of the main electron beam entering the high-power microwave generator 7.

[0047] This invention can also effectively improve the original... Figure 2 The magnetic field lines 8 in the cathode region are shown. Figure 4The backflow electron beam is shown. The embedded magnet 10 optimizes the rapidly decreasing axial magnetic field and rapidly increasing radial magnetic field in these regions of the cathode, causing the magnetic field lines in the cathode region to distribute along the surface of the cathode lead 6 and ultimately converge onto the cathode base 5, as shown. Figure 3 As shown, when an external high-voltage electric pulse drives the explosive emission cathode to generate electrons, the binding ability of the electron emission and return electron beam on the inner surface of the cathode region is significantly enhanced. The return electron beam moves along the surface of the cathode lead 6 and is eventually collected on the cathode base 5.

[0048] Meanwhile, the present invention also provides a design method for a foil-free diode to suppress unwanted electron emission and backflow electron beam, comprising the following steps:

[0049] Step 1: Model Establishment and Parameter Determination

[0050] A foilless diode explosion emission model was constructed using particle simulation software to determine the distribution of magnetic field lines in the cathode region, the trajectory of the electron beam in the cathode region, and the maximum envelope size of the inner cavity of the cathode lead rod 6 and the cathode base 5.

[0051] Step 2: Determine the material and envelope size of magnet 10.

[0052] The material of magnet 10 is determined, and the envelope size of magnet 10 is determined based on the maximum envelope size of cathode lead 6 and cathode base 5. The maximum envelope size of magnet 10 is made smaller than the maximum envelope size of cathode lead 6 and cathode base 5, thus obtaining a foil-free diode model for primary suppression of unwanted electron emission and backflow electron beam.

[0053] Step 3: Magnetic field optimization design

[0054] The foil-free diode model for primary suppression of unwanted electron emission and backflow electron beam is imported into the magnetic field design software. Based on the distribution of magnetic field lines in the cathode region, the trajectory of the electron beam in the cathode region, and the material of the magnet 10, the size and / or magnetization direction of the magnet 10 are adjusted until the magnetic field lines of the permanent magnet 11 in the cathode region are distributed along the surface of the cathode lead rod 6 and finally converge at the cathode base 5. In this embodiment, the magnetic field design software is ANSYS Maxwell electromagnetic simulation software.

[0055] The specific optimization design steps include:

[0056] Step 3.1: Import the foil-free diode model for primary suppression of unwanted electron emission and backflow electron beam into the magnetic field design software;

[0057] Step 3.2: Using magnetic field design software, based on the material of magnet 10, set the initial size structure of magnet 10, so as to be a cylindrical structure that does not exceed the maximum outer envelope of cathode lead rod 6 and cathode base 5.

[0058] Step 3.3: Set the initial magnetization direction of magnet 10 to be the same as the main electron beam transmission direction;

[0059] Step 3.4: Roughly adjust the diameter, length and magnetization direction of the cylindrical magnet 10 so that the magnetic lines of force of the permanent magnet 11 are distributed along the surface of the cathode lead rod 6 within a preset range in the cathode region, and finally converge to the cathode base 5 within a preset range; the preset range is determined based on experience.

[0060] Step 3.5: Fine adjustment. Adjust the size and magnetization direction of the magnet 10 until the magnetic lines of the permanent magnet 11 in the cathode area are distributed along the surface of the cathode lead rod 6 and finally converge at the cathode base 5.

[0061] Step 4: Verification of electron beam trajectory in the cathode region

[0062] The electron beam trajectory in the cathode region was verified using particle simulation software to ensure that backflow electrons and unwanted emission electrons were collected onto the cathode lead 6 and cathode base 5. If the verification results did not meet the requirements, it could be determined that there was a deviation in the foil-less diode structure design for suppressing unwanted electron emission and backflow electron beam, requiring further adjustments.

[0063] In the design process of the embedded magnet 10, since the cathode lead 6 and cathode base 5 have hollow internal structures, to ensure that the introduction of the magnet 10 does not affect the original foil-free diode structure, it is necessary to make full use of the internal space of the cathode lead 6 and cathode base 5. The maximum envelope size of the embedded magnet 10 cannot exceed the maximum envelope size of the hollow internal structure of the cathode lead 6 and cathode base 5, ensuring that the magnet 10 can be embedded inside the cathode lead 6 and cathode base 5. Under the constraint of the maximum envelope size, the design of the embedded magnet 10 is optimized to determine the size and magnetization direction of the embedded magnet 10. To verify the effect achieved by the design, a particle simulation model of the foil-free diode needs to be established to simulate the electron beam trajectory. The electron beam trajectory is used to verify that the electron beam returning to the cathode region is collected by the cathode base.

[0064] The effectiveness of the embedded magnet 10 in suppressing unwanted electron emission and backflow electron beams in this embodiment of the invention is achieved through particle simulation methods, such as... Figure 4 , 5 As shown. Specifically, under the conditions of diode operating voltage of 600kV, beam current of 5kA, and guiding magnetic field strength of 0.5T in the uniform region of permanent magnet 11, comparing the particle simulation effect before and after the cathode lead rod 6 and the embedded magnet 10 in the cathode base 5, it can be seen that, as Figure 5 As shown, after embedding the magnet 10, it is not expected that electron emission will be effectively suppressed. All the returning electron beams are collected on the cathode base 5, and the stability and beam current utilization of the foilless diode are significantly improved.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. A foil-free diode for suppressing unwanted electron emission and backflow electron beam, comprising an insulator (2), an anode outer cylinder (3), a cathode lead (6), a cathode base (5), and a permanent magnet (11); characterized in that: It also includes magnets (10); Both the cathode lead rod (6) and the cathode base (5) are hollow structures; The magnet (10) is embedded inside the cathode lead (6) and the cathode base (5) to attract electrons around it through the magnetism of the magnet (10) and pull unwanted electrons back to the cathode lead (6) and the cathode base (5) to increase the electron emission threshold of the cathode lead (6) and the cathode base (5); The magnetic field of the magnet (10) and the permanent magnet (11) work together to distribute the magnetic field lines around the return electron beam along the surface of the cathode lead rod (6) and finally converge at the cathode base (5), so that the return electron beam is collected by the cathode lead rod (6) and the cathode base (5).

2. The foil-free diode for suppressing unwanted electron emission and backflow electron beam according to claim 1, characterized in that: The axial distance between the end of the magnet (10) embedded in the cathode and the cathode is greater than or equal to 1 / 10 times the axial length of the cathode lead rod (6), and the axial length of the magnet (10) is greater than or equal to 1 / 2 times the axial length of the cathode lead rod (6).

3. The foil-free diode for suppressing unwanted electron emission and backflow electron beam according to claim 2, characterized in that: The magnet (10) inside the cathode base (5) is adapted to the inner cavity size of the cathode base (5).

4. A design method for a foil-less diode that suppresses unwanted electron emission and backflow electron beam, characterized in that, Includes the following steps: Step 1: Model Establishment and Parameter Determination A foilless diode explosion emission model was constructed using particle simulation software to determine the distribution of magnetic field lines in the cathode region, the trajectory of the electron beam in the cathode region, and the maximum envelope size of the inner cavity of the cathode lead rod (6) and the cathode base (5). Step 2: Determine the material and envelope size of the magnet (10) The material of the magnet (10) is determined, and the envelope size of the magnet (10) is determined according to the maximum envelope size of the inner cavity of the cathode lead (6) and the cathode base (5). The maximum envelope size of the magnet (10) is made smaller than the maximum envelope size of the inner cavity of the cathode lead (6) and the cathode base (5) to obtain the foil-free diode model for primary suppression of unwanted electron emission and backflow electron beam. Step 3: Magnetic field optimization design The foilless diode model for suppressing unwanted electron emission and backflow of electron beams is imported into the magnetic field design software. Based on the distribution of magnetic field lines in the cathode region, the trajectory of the electron beam in the cathode region, and the material of the magnet (10), the size and / or magnetization direction of the magnet (10) are adjusted until the magnetic field lines of the permanent magnet (11) in the cathode region are distributed along the surface of the cathode lead rod (6) and finally converge at the cathode base (5), thus completing the design of the foilless diode for suppressing unwanted electron emission and backflow of electron beams.

5. The design method for a foil-less diode to suppress unwanted electron emission and backflow electron beam according to claim 4, characterized in that, It also includes step S: Cathode region electron beam trajectory verification The electron beam trajectory in the cathode region was verified using particle simulation software to ensure that the returning electrons and unwanted emitted electrons were collected onto the cathode lead rod (6) and the cathode base (5).

6. The design method for a foil-less diode to suppress unwanted electron emission and backflow electron beam according to claim 4, characterized in that: In step 3, the magnetic field design software is ANSYS Maxwell electromagnetic simulation software.

7. The design method for a foil-less diode to suppress unwanted electron emission and backflow electron beam according to claim 4, characterized in that, Step 3 specifically involves: Step 3.1: Import the foil-free diode model for primary suppression of unwanted electron emission and backflow electron beam into the magnetic field design software; Step 3.2: Using magnetic field design software, based on the material of the magnet (10), set the initial size structure of the magnet (10) to be a cylindrical structure that does not exceed the maximum outer envelope of the cathode lead rod (6) and the cathode base (5); Step 3.3: Set the initial magnetization direction of the magnet (10) to be the same as the transmission direction of the main electron beam; Step 3.4: Make rough adjustments to the diameter, length and magnetization direction of the cylindrical magnet (10) until the permanent magnet (11) is distributed along the surface of the cathode lead rod (6) within a preset range of the magnetic field lines in the cathode area, and finally converges within the preset range of the cathode base (5); Step 3.5: Finely adjust the irregular size and magnetization direction of the magnet (10) until the magnetic lines of the permanent magnet (11) in the cathode area are distributed along the surface of the cathode lead rod (6) and finally converge at the cathode base (5).

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