Design method of electron gun for circular single electron beam G-band extended interaction klystron

Abstract

This invention belongs to the field of vacuum electronic devices, specifically relating to an electron gun design method for a circular single-electron-beam G-band extended interaction klystron. The invention introduces an n (2≤n≤10) periodic structure on the electron gun focusing electrode surface to regulate the electrostatic field distribution, thereby increasing the total emission current of the electron gun cathode and enhancing the electron beam power. This method employs a circular single electron beam, ensuring simple design and fabrication of the magnetic focusing system and stable electron beam transmission. The electron gun focusing electrode uses an n-periodic corrugated control structure, guaranteeing that under G-band conditions and high electron beam voltage, the cathode emission current density is less than 12 A / (cm^2), the total cathode emission current is approximately 0.334 A, and its static flux density is 100%. This invention solves the problems of stable and efficient high-energy electron beam focusing and transmission in existing G-band extended interaction klystrons, while also considering the simplicity of electron gun fabrication and assembly, long cathode life, and a simple magnetic focusing system.

Description

Technical Field

[0001] This invention belongs to the field of vacuum electronic devices, specifically relating to an electron gun design method for a circular single-electron-beam G-band extended interaction klystron. Background Technology

[0002] Extended interaction klystrons are compact microwave devices characterized by high efficiency, high gain, high power, and wide bandwidth, and have broad application prospects in terahertz communication, radar, imaging, and other fields.

[0003] In the operation of an extended interaction klystron, the main physical processes include the generation, formation, and focusing of the electron beam; the interaction between the electron beam and the high-frequency interaction system; and the dissipation and cooling of the electron beam energy. Among these, the interaction process between the electron beam emitted by the electron gun and high-frequency electromagnetic waves in the high-frequency structure is the core. Therefore, a high-performance electron gun is a prerequisite for stable device operation, and its operating state directly affects the device's power, gain, efficiency, and other indicators.

[0004] Circular electron beams possess axisymmetric characteristics, with their rotation and twisting in space revolving around their center. This reduces the requirements for the focusing system and allows for stable long-distance transmission of the electron beam under relatively small magnetic fields. However, the current density of a circular electron beam is limited by the electron gun's conductivity, making it difficult to generate a large current and significantly restricting the device's power. Furthermore, as the operating frequency of the device gradually increases, the device size also decreases, leading to a reduction in the size of the electron beam. The limitation imposed by the electron gun's conductivity on the circular electron beam becomes increasingly pronounced.

[0005] To meet the needs of planar fabrication of terahertz microstructures and the future trend of integrated vacuum electronic devices, researchers often use novel electron beam channels with planar features, such as strip electron beams and multi-electron beams.

[0006] Due to its lateral expansion, a strip electron beam has a large aspect ratio, allowing it to withstand higher currents at the same current density and thus achieve higher output power. However, strip electron beams suffer from torsion, deformation, and instability during propagation, increasing the difficulty of confining and focusing them.

[0007] Multiple electron beams (MPBs) are developed from strip electron beams, inheriting their advantages and achieving a large operating current through the lateral arrangement of multiple circular electron beams. However, strong space charge effects exist among multiple electron beams, leading to mutual coupling and interference that affects stable electron beam propagation. This places stringent requirements on the design of the focusing system. Simultaneously, the cathode size is limited by space constraints, resulting in a small areal compression ratio of the electron gun and a significantly increased cathode emission current density, with a cathode load ranging from 10 to 40 A / cm². 2 Furthermore, when multiple electron beams enter the common collector, a virtual cathode can easily be generated, causing electron reversal and affecting the stability of the multi-beam klystron.

[0008] Therefore, it is of great significance to design a G-band extended interaction klystron electron gun that is easy to manufacture, has a long cathode life, and can stably and efficiently focus and transmit high-energy electron beams with a simple magnetic focusing system. Summary of the Invention

[0009] To address the aforementioned problems and shortcomings, and to meet the requirements of stable and efficient high-energy electron beam focusing and transmission in existing G-band extended interaction klystrons, while also considering the simplicity of electron gun fabrication and assembly, long cathode life, and convenient magnetic focusing system, this invention provides an electron gun design method for a circular single-electron-beam G-band extended interaction klystron. This invention introduces an n (2≤n≤10) periodic structure on the electron gun focusing electrode surface to regulate the electrostatic field distribution, thereby increasing the total emission current of the electron gun cathode and thus increasing the electron beam power. This method employs a circular single electron beam, ensuring simple design and fabrication of the magnetic focusing system and stable electron beam transmission. The electron gun focusing electrode uses an n-period corrugated control structure, ensuring that, in the G-band with an electron beam voltage of 17kV, the cathode emission current density is less than 12A / (cm^2), the total cathode emission current is approximately 0.334A, and its static flux is 100%.

[0010] A method for designing an electron gun in a circular single-electron-beam G-band extended interaction klystron includes the following steps:

[0011] S1. Based on the design requirements of the extended interaction klystron beam-wave interaction engineering, obtain the electron gun requirements parameters, including electron beam voltage U, total electron beam current I, electron emission model type, electron beam channel radius a, electron beam radius b, cathode emission current density Jc, and range Zw.

[0012] S2. Design an axisymmetric Pierce electron gun that satisfies the requirements of S1 as an initial scheme.

[0013] S3. Starting from the axisymmetric Pierce electron gun designed in step S2, use three-dimensional electromagnetic simulation software to perform trajectory tracking calculations and electrostatic field calculations.

[0014] The design is continuously adjusted and optimized based on the calculation results. The adjustment parameters are the structural parameters of each electrode of the electron gun, the electrode voltage, the longitudinal magnetic field strength of the focusing magnetic field, the length of the focusing magnetic field, and the distance between the rising and falling edges.

[0015] The optimization criteria for the optimization process are as follows: under the operating parameter requirements of the G-band extended interaction klystron, the electron gun trajectory tracking calculation iterative convergence, the electron beam static flux density of 100%, the cathode emission current density <12A / (cm^2), and the total cathode emission current greater than 0.3A. The cathode emission current density significantly affects the lifespan of the electron gun cathode. To maximize the cathode head lifespan while balancing the operation of the extended interaction klystron in the G-band, this invention limits the cathode emission current density to <12A / (cm^2).

[0016] The final design specifications for the G-band extended interaction klystron electron gun, which meet the optimization criteria, were obtained.

[0017] S4. Apply an n-period corrugated structure to the inner surface of the focusing electrode of the electron gun obtained in step S3 to control the electrostatic field distribution. The corrugated structure consists of pairs of positive and negative arcs. The radii of curvature of each positive and negative arc are equal, the directions of the positive and negative arcs are opposite, and the arc lengths are equal, with 2≤n≤10.

[0018] Then, by continuously optimizing the radius of curvature and arc length of the arcs in the corrugated structure, as well as the corrugation period, particle trajectory tracking calculations are performed, and the electrostatic field distribution is controlled to obtain the final electron gun specifications.

[0019] In summary, this invention provides an electron gun design method for a circular single-electron-beam G-band extended interaction klystron. The electrostatic field distribution is controlled by an n-period corrugated structure, which improves the total cathode emission current and electron beam power. At the same time, the electron beam is a circular single electron beam, which makes the magnetic focusing system easier to design, the electron beam easier to transmit stably, and the cathode has a long lifespan. Attached Figure Description

[0020] Figure 1 shows a typical Pierce electron gun;

[0021] Figure 2 is a flowchart of the Vaughan iterative synthesis method;

[0022] Figure 3 A cross-sectional view of the existing focusing electrode Pierce electron gun;

[0023] Figure 4 A 3D model of the existing focusing electrode Pierce electron gun;

[0024] Figure 5 A cross-sectional view of the Pierce electron gun with a focused electrode-loaded dual-period corrugated control structure in the embodiment;

[0025] Figure 6A three-dimensional model of the Pierce electron gun with a dual-period corrugated control structure with a focused electrode loading, as shown in the embodiment.

[0026] Figure 7 The projection of the electron beam envelope of the Pierce electron gun with an unloaded n-periodic corrugated structure onto the RZ plane;

[0027] Figure 8 The cathode emission current density of the Pierce electron gun with an unloaded n-period corrugated structure at the focusing electrode;

[0028] Figure 9 The projection of the electron trajectory of the Pierce electron gun with an unloaded n-period corrugated structure onto the YZ plane;

[0029] Figure 10 The static flow electron trajectory of the Pierce electron gun with an unloaded n-period corrugated structure at the focusing pole.

[0030] Figure 11 This is the projection of the electron beam envelope onto the RZ plane when the ripple curvature radius is 1 mm, as shown in the example.

[0031] Figure 12 The cathode emission current density is shown in the example when the corrugation radius is 1 mm.

[0032] Figure 13 The projection of the electron trajectory onto the YZ plane when the ripple curvature radius is 1 mm is shown in the example.

[0033] Figure 14 The static flow electron trajectory is shown in the example when the ripple curvature radius is 1 mm. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0035] A design method for an electron gun in a circular single-electron-beam G-band extended interaction klystron, comprising the following steps:

[0036] S1. Based on the research specifications of the G-band extended interaction klystron, the required parameters for the interaction between its electromagnetic waves and the high-energy electron beam are obtained, including the electron beam voltage U, the total electron beam current I, the electron emission model type, the electron beam channel radius a, the electron beam radius b, the cathode emission current density Jc, and the range Zw (i.e., the beam waist position). This design does not specify specific requirements; an industry-recommended value of 8mm is given. The initial parameters of the electron gun in this embodiment are shown in Table 1.

[0037] Table 1 Electron Gun Requirements

[0038] parameter numerical values Interaction requires electron beam voltage (kV) 16-20 Total electron beam current (A) 0.3-0.4 Electron emission model Space charge-limited thermal emission Electron beam channel radius (mm) 0.12 Interaction requires electron beam radius (mm) 0.072 Cathode emission current density (A / (cm^2)) <12 Electron injection range (mm) 8

[0039] S2. Based on Pierce's design principles and Figure 2 The Vaughan iterative synthesis method shown presents an axisymmetric Pierce electron gun that satisfies the S1 requirement as a preliminary design.

[0040] The specific design method is as follows: The performance of the Pierce electron gun is mainly described by the conductivity P and the area compression ratio C. The initial design is mainly determined by four parameters: U, I, injection waist radius rw, and cathode emission current density Jc. Several key values ​​need to be determined in the initial design of the electron gun: cathode semi-cone angle θ, cathode radius of curvature Rc and cathode radius rc, anode radius of curvature Ra and anode radius ra, anode head position za, electron injection range Zw, etc. A typical Pierce electron gun is shown below. Figure 1 As shown, in this embodiment, the initial values ​​of the electron gun structure are designed based on the Vaughan iterative synthesis method. The specific process is as follows: Figure 2 As shown.

[0041] S3. Starting from the axisymmetric Pierce electron gun designed in step S2, use the three-dimensional electromagnetic simulation software MTSS to perform trajectory tracking calculations and electrostatic field calculations.

[0042] Based on the calculation results, the design was continuously adjusted and optimized to obtain a high-throughput electron gun scheme for a G-band extended interaction klystron. The adjustment parameters were the structural parameters of each electrode of the electron gun, the electrode voltage, the longitudinal magnetic field strength of the focusing magnetic field, the length of the focusing magnetic field, and the distance between the rising and falling edges.

[0043] The optimization criteria are as follows:

[0044] (1) Maintain the required parameters for the interaction between the G-band extended interaction klystron electromagnetic wave and the high-energy electron beam;

[0045] (2) Iterative convergence of electron gun trajectory tracking calculation;

[0046] (3) The static flux of the electron beam is 100%;

[0047] (4) Cathode emission current density <12A / (cm^2);

[0048] (5) The total cathode emission current must be > 0.3A.

[0049] The final design specifications for the G-band extended interaction klystron electron gun, which meet the optimization criteria, are shown in Table 2.

[0050] Table 2 Electron gun structure and electrical parameters

[0051] parameter numerical values Cathode voltage (V) 0 Focusing electrode voltage (V) -6 Interaction requires electron beam voltage (V) 17000 Total electron beam current (A) 0.3111307 Electron emission model Space charge-limited thermal emission Electron beam channel radius (mm) 0.12 Cathode radius (mm) 1 Cathode curvature radius (mm) 3 Interaction requires electron beam radius (mm) ~0.072 Cathode emission current density <12A / (cm^2) Electron injection range (mm) 6.9500

[0052] For electron optical systems, the size parameters of the electron gun and the voltage of different electrons vary, resulting in different electrostatic field distributions and trajectory tracking calculations. These calculations are performed using numerical methods such as the finite element method or the method of moments. In other words, for any electron gun with a unique size, its electrostatic field distribution is also unique.

[0053] Figure 3 A cross-sectional view of the Pierce electron gun with an existing focusing electrode structure; Figure 4 A 3D model of the Pierce electron gun with an existing focusing electrode; Figure 7 The projection of the electron beam envelope of the Pierce electron gun with an unloaded n-periodic corrugated structure onto the RZ plane; Figure 8 The cathode emission current density of the Pierce electron gun with an unloaded n-period corrugated structure at the focusing electrode; Figure 9 The projection of the electron trajectory of the Pierce electron gun with an unloaded n-period corrugated structure onto the YZ plane; Figure 10 The static flow electron trajectory of the Pierce electron gun with an unloaded n-period corrugated structure at the focusing pole.

[0054] S4. Apply an n-period corrugated structure to the inner surface of the focusing electrode of the electron gun obtained in step S3 to optimize and improve its performance. In this embodiment, the period n=2, the corrugated structure is composed of pairs of positive and negative circular arcs, the radii of curvature of each positive and negative arc are equal, the directions of the positive and negative arcs are opposite, and the arc lengths are equal. Figure 5 This is a cross-sectional view of the Pierce electron gun with a focused electrode-loaded dual-period corrugated control structure in this embodiment. Figure 6 This is a three-dimensional model of the Pierce electron gun with a focused electrode loading dual-period corrugated control structure in this embodiment.

[0055] An n=2 periodic corrugated structure is introduced into the focusing electrode to regulate the electrostatic field distribution. The radius of curvature and the period of the corrugated structure are continuously optimized to further increase the total cathode emission current of a single cathode, thereby improving the electron beam power while maintaining stable transmission in a single circular beam. The optimization standard is to limit the total cathode emission current to above 330mA, while limiting the cathode emission current density to less than 12A / (cm^2) to ensure the lifespan of the cathode head.

[0056] Figure 3 This is a cross-sectional view of the existing focusing electrode Pierce electron gun. Figure 5 This is a cross-sectional view of the Pierce electron gun with a dual-period corrugated control structure loaded at the focusing electrode in this embodiment; the dual-period corrugated structure is loaded between points 14 and 18 in the figure. Figure 3 Rotate 360 ​​degrees, and the inner surface of the focusing electrode becomes a double-period corrugated surface.

[0057] Analysis and optimization criteria are given: For G-band strip-beam electron guns, the calculation results reported by the Chinese Academy of Sciences in the Journal of Microwave in 2014 show that the total cathode emission current is 580mA at 16.5kV. However, its focusing magnetic field is a uniform field focusing method with a focusing magnetic field of 8700GS, which results in high system complexity and cost. Furthermore, the strip-beam exhibits Diocotron instability, and the electron beam may even twist into individual separate filaments.

[0058] For multi-beam electron guns, the diameter of the electron beam channel in the electron gun pole piece is limited. In permanent magnet focusing, the magnetic field at the cathode surface is opposite in direction to the main magnetic field; in electromagnetic focusing, the magnetic field at the cathode surface is smaller. Therefore, the design of a multi-beam klystron focusing system differs significantly from that of a typical single-beam klystron. Furthermore, multiple electron beams entering the common collector can easily create a virtual cathode, causing electron reversal and affecting the stability of the multi-beam klystron.

[0059] Therefore, for the single-electron-beam electron gun with a single circular beam in this invention, in order to enable its use in G-band extended interaction klystron operation at 17kV, the optimization standard is to limit the total cathode emission current to above 330mA, while limiting the cathode emission current density to less than 12A / (cm^2) to ensure the lifespan of its cathode head. The emission current of the electron gun is compensated by adjusting the high-frequency structure of the extended interaction klystron to improve the coupling impedance and beam-wave interaction efficiency. According to industry knowledge and experience, when the high-frequency structure performance of the extended interaction klystron is good, a 330mA circular single-electron-beam electron gun is sufficient to enable the G-band extended interaction klystron to output power higher than 100W within a bandwidth of 400MHz. Simultaneously, the circular single-electron-beam electron gun uses a periodic magnetic field (PCM), which provides high focusing flexibility and can provide a magnetic field up to 15000GS, making the electron beam transmission more stable.

[0060] Figure 11 This is the projection of the electron beam envelope onto the RZ plane when the corrugation radius is 1 mm in this embodiment; Figure 12 This is the cathode emission current density when the corrugation radius is 1 mm in this embodiment; Figure 13 This is the projection of the electron trajectory onto the YZ plane when the ripple curvature radius is 1 mm in this embodiment; Figure 14 The table shows the static electron trajectory when the corrugation radius is 1 mm in this embodiment. Table 3 shows the electron gun trajectory tracking calculation results under different corrugation radii.

[0061] Table 3

[0062] radius of curvature Total cathode emission current (A) Injection waist radius Waist injection site Is the cathode emission current density <12A / (cm^2)? 0 0.3111307 0.0661 5.5250 yes 1 0.3347990 0.0652 16.6250 yes 1.5 0.3187944 0.0660 5.5250 yes 2 0.3157835 0.0659 5.5250 yes

[0063] Table 3 shows that when the corrugation radius is 1 mm, the total electron gun cathode emission current calculated by trajectory tracking is 0.3347990 A, which is higher than the 0.3111307 A calculated by trajectory tracking of a circular single-electron-beam electron gun without an n=2 periodic corrugated structure at the focusing electrode. Moreover, this data is sufficient to support the normal operation of the G-band extended interaction klystron. The compensation is that the injection waist position is relatively far, but compared with the complex magnetic focusing system of strip-beam and multi-beam electron guns, this compensation is acceptable.

[0064] As can be seen from the above embodiments, the electron gun design method of the circular single-electron-beam G-band extended interaction klystron provided by the present invention can greatly increase the total cathode emission current of the single circular electron gun, and the electron beam power is sufficient to support the normal operation of the G-band extended interaction klystron. At the same time, the magnetic focusing system is easy to design, the electron beam is easier to transmit stably, and the lifespan is long.

Claims

1. A method for designing an electron gun in a circular single-electron-beam G-band extended interaction klystron, characterized in that, Includes the following steps: S1. Based on the design requirements of the extended interaction klystron beam-wave interaction engineering, obtain the electron gun requirements parameters, including electron beam voltage U, total electron beam current I, electron emission model type, electron beam channel radius a, electron beam radius b, cathode emission current density Jc, and range Zw; S2. Design an axisymmetric Pierce electron gun that satisfies the requirements of S1 as an initial scheme; S3. Starting from the axisymmetric Pierce electron gun designed in step S2, use three-dimensional electromagnetic simulation software to perform trajectory tracking calculation and electrostatic field calculation; The design is continuously adjusted and optimized based on the calculation results. The adjustment parameters are the structural parameters of each electrode of the electron gun, the electrode voltage, the longitudinal magnetic field strength on the axis of the focusing magnetic field, the length of the focusing magnetic field, and the distance between the rising and falling edges. The optimization criteria for the optimization process are as follows: under the working parameter requirements of the G-band extended interaction klystron, the electron gun trajectory tracking calculation iterative convergence, the electron beam static flux density of 100%, the cathode emission current density <12A / (cm^2), and the total cathode emission current greater than 0.3A; The final design specifications for the G-band extended interaction klystron electron gun, which meet the optimization criteria, were obtained. S4. Load an n-period corrugated structure onto the inner surface of the focusing electrode of the electron gun obtained in step S3. The corrugated structure consists of pairs of positive and negative arcs. The radii of curvature of each positive and negative arc are equal, the directions of the positive and negative arcs are opposite, and the arc lengths are equal, with 2≤n≤10. By continuously optimizing the radius of curvature and arc length of the arcs in the corrugated structure, as well as the corrugation period, particle trajectory tracking calculations are performed, and the electrostatic field distribution is controlled to obtain the final electron gun specifications.

2. The electron gun design method of the circular single-electron-beam G-band extended interaction klystron as described in claim 1, characterized in that: The three-dimensional electromagnetic simulation software used in S3 is MTSS.

3. The electron gun design method of the circular single-electron-beam G-band extended interaction klystron as described in claim 1, characterized in that: The arc is a circular arc.

4. The electron gun design method of the circular single-electron-beam G-band extended interaction klystron as described in claim 1, characterized in that: The n=2.

5. The electron gun design method of the circular single-electron-beam G-band extended interaction klystron as described in claim 1, characterized in that: The Pierce electron gun was designed based on Pierce's design principles and Vaughan's iterative synthesis method.

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