Method for designing electron gun of circular single-electron-beam G-band extended interaction klystron

Abstract

The invention belongs to the field of vacuum electronic devices, and particularly relates to an electron gun design method of a circular single-electron-beam G-band extended interaction klystron. An n (n is greater than or equal to 2 and less than or equal to 10) periodic structure is introduced on the surface of the electron gun focusing electrode to regulate and control electrostatic field distribution, so that the total cathode emission current of the electron gun is improved, and electron beam power is increased; according to the method, a circular single electron beam is adopted, simple design and processing of a magnetic focusing system and stable transmission of the electron beam are ensured, an n-period ripple regulation and control structure is adopted by an electron gun focusing electrode, and it is ensured that under the conditions of G wave band and high electron beam voltage, the cathode emission current density is smaller than 12 A / (cm < 2 >), the total cathode emission current is about 0.334 A, and the static flow rate is 100%. According to the invention, stable and efficient bunching and transmission of high-energy electron beams in the existing G-band extended interaction klystron are realized, and the requirements of simple processing and assembling, long cathode service life, simple and convenient magnetic focusing system and the like of an electron gun scheme are met.

Description

Technical Field

[0001] The present invention belongs to the field of vacuum electronic devices, and particularly relates to a design method for an electron gun of a circular single electron beam G-band extended interaction klystron. Background Art

[0002] The extended interaction klystron is a compact microwave device with characteristics such as high efficiency, high gain, high power, and relatively wide bandwidth, and has broad application prospects in the fields of terahertz communication, radar, imaging, etc.

[0003] During the operation of the 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 them, the interaction process between the electron beam emitted by the electron gun and the high-frequency electromagnetic wave in the high-frequency structure is the core. Therefore, an electron gun with good performance is the premise for the stable operation of the device, and its working state directly affects the power, gain, efficiency and other indicators of the device.

[0004] The circular electron beam has the characteristic of axial symmetry. The rotation and distortion of the electron beam in space occur around the center of the electron beam, and the requirements for the focusing system are relatively low. The long-distance stable transmission of the electron beam can be achieved under a relatively small magnetic field. However, the current density of the circular electron beam is limited by the perveance of the electron gun, and it is difficult to generate a large current, resulting in a great limitation on the power of the device. And as the operating frequency of the device gradually increases, the size of the device is gradually reduced, and the size of the electron beam also decreases accordingly. The limitation of the perveance of the electron gun on the circular electron beam will become more obvious.

[0005] Current researchers, in order to adapt to the planar processing requirements of terahertz band microstructures and the future development trend of the integration of vacuum electronic devices, often adopt new electron beam channels with planar characteristics, such as strip electron beams and multi-electron beams.

[0006] Due to the expansion in the transverse space, the strip electron beam has a large aspect ratio. At the same current density, the strip electron beam can withstand a higher current, and thus can obtain a higher output power. However, the strip electron beam has problems such as distortion and instability during transmission, which increases the difficulty of constraining and focusing the strip electron beam.

[0007] The multi-electron beam is developed on the basis of the strip electron beam. It inherits the advantages of the strip electron beam and realizes a large operating current through the transverse arrangement of multiple circular electron beams. However, there is a strong space charge effect between the multi-electron beams, and they will be coupled with each other to generate interference, affecting the stable transmission of the electron beam. Therefore, strict requirements are put forward for the design of the focusing system. At the same time, the cathode size is limited by space, the surface compression ratio of the electron gun is small, the cathode emission current density increases greatly, and the cathode load is 10 - 40 A / cm 2 . And multiple electron beams enter the common collector, which is easy to generate a virtual cathode, causing electron inversion 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 process, has a long cathode life, and can stably and efficiently focus and transmit high-energy electron beams, and has a simple magnetic focusing system. Summary of the Invention

[0009] In view of the above existing problems or deficiencies, in order to solve the problems of stable, efficient bunching and transmission of high-energy electron beams in the existing G-band extended interaction klystron, and taking into account the requirements of simple processing and assembly of the electron gun scheme, long cathode life, and simple magnetic focusing system, etc., the present invention provides a design method for the electron gun of a circular single electron beam G-band extended interaction klystron. The present invention introduces an n (2 ≤ n ≤ 10) periodic structure on the surface of the focusing electrode of the electron gun to regulate the electrostatic field distribution, so as to increase the total cathode emission current of the electron gun and increase the electron beam power; this method uses a circular single electron beam to ensure the simplicity of the design and processing of the magnetic focusing system and the stable transmission of the electron beam. The focusing electrode of the electron gun adopts an n-period corrugated regulation structure to ensure that when the electron beam voltage is 17 kV in the G-band, the cathode emission current density is less than 12 A / (cm^2), the total cathode emission current is about 0.334 A, and its static circulation rate is 100%.

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

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

[0012] S2. Design an axisymmetric Pierce electron gun that meets the requirements of S1 as the 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] Continuously adjust and optimize the design according to the calculation results. The adjustment parameters are the structural parameters of each electrode of the electron gun, the electrode voltage, the axial longitudinal magnetic field intensity of the focusing magnetic field, the length of the focusing magnetic field, and the distance between the rising edge and the falling edge.

[0015] The optimization criteria for the optimization process are as follows: Under the working parameter requirements of the extended interaction klystron in the G band, the electron gun trajectory tracking calculation converges iteratively, the static transmission rate of the electron beam is 100%, the cathode emission current density < 12 A / (cm^2), and the total cathode emission current is greater than 0.3 A. The cathode emission current density seriously affects the service life of the cathode of the electron gun. In order to balance the service life of the cathode head as much as possible when the extended interaction klystron operates in the G band, the cathode emission current density is limited to < 12 A / (cm^2).

[0016] Finally, the design indexes of the electron gun of the extended interaction klystron in the G band that meet the optimization criteria are obtained.

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

[0018] Then continuously optimize the curvature radius and arc length of the arcs in the corrugated structure, as well as the corrugation period, perform particle trajectory tracking calculations, and regulate the electrostatic field distribution to obtain the final electron gun indexes.

[0019] In summary, the present invention provides a design method for the electron gun of a circular single electron beam extended interaction klystron in the G band, which uses an n-period corrugated structure to regulate the electrostatic field distribution, improves the total cathode emission current and the electron beam power, and at the same time the electron beam is a circular single electron beam, the magnetic focusing system is easy to design, the electron beam is more easily and stably transmitted, and the cathode has a long service life. Description of the Drawings

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

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

[0022] Figure 3 is a sectional view of a Pierce electron gun with an existing focusing electrode;

[0023] Figure 4 is a 3D model diagram of a Pierce electron gun with an existing focusing electrode;

[0024] Figure 5 is a sectional view of a Pierce electron gun with a double-period corrugation regulation structure loaded on the focusing electrode in the embodiment;

[0025] Figure 6 3D model diagram of a Pierce electron gun with a double-period corrugation regulation structure loaded on the focusing electrode for the embodiment;

[0026] Figure 7 Projection of the electron beam envelope of a Pierce electron gun without an n-period corrugation structure loaded on the focusing electrode on the RZ plane;

[0027] Figure 8 Cathode emission current density of a Pierce electron gun without an n-period corrugation structure loaded on the focusing electrode;

[0028] Figure 9 Projection of the electron trajectory of a Pierce electron gun without an n-period corrugation structure loaded on the focusing electrode on the YZ plane;

[0029] Figure 10 Static flow electron trajectory of a Pierce electron gun without an n-period corrugation structure loaded on the focusing electrode.

[0030] Figure 11 Projection of the electron beam envelope on the RZ plane when the corrugation radius of curvature is 1 mm for the embodiment;

[0031] Figure 12 Cathode emission current density when the corrugation radius of curvature is 1 mm for the embodiment;

[0032] Figure 13 Projection of the electron trajectory on the YZ plane when the corrugation radius of curvature is 1 mm for the embodiment;

[0033] Figure 14 Static flow electron trajectory when the corrugation radius of curvature is 1 mm for the embodiment. Specific implementation manner

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

[0035] A design method for the electron gun of a circular single electron beam G-band extended interaction klystron, the specific steps are as follows:

[0036] S1. According to the research indicators of the G-band extended interaction klystron, obtain the demand parameters for the interaction between electromagnetic waves and high-energy electron beams, including the electron beam voltage U, the total electron beam current I, the type of electron emission model, the electron beam channel radius a, the electron beam radius b, the cathode emission current density Jc. The range Zw (i.e., the position of the beam waist) is not specifically required in this design, and an industry experience value of 8 mm is given at this time. The initial parameters of the electron gun in this embodiment are shown in Table 1.

[0037] Table 1 Electron gun demand parameters

[0038]

[0039]

[0040] S2. According to Pierce's design principle and Figure 2 the iterative synthesis method of Vaughan shown in the figure, design an axisymmetric Pierce electron gun that meets the requirements of S1 as the preliminary scheme.

[0041] The specific design method is as follows: The performance of the Pierce electron gun is mainly described by the perveance P and the convergence ratio C. The initial value design is mainly determined by 4 parameters: U, I, the waist radius rw of the beam, and the cathode emission current density Jc. Several key values need to be determined for the initial value design of the electron gun: the cathode semi-cone angle θ, the cathode curvature radius Rc and the cathode radius rc, the anode curvature radius Ra and the anode radius ra, the anode head position za, the electron injection range Zw, etc. A typical Pierce electron gun is as Figure 1 shown in the figure. In this embodiment, the initial values of the electron gun structure are designed according to Vaughan's iterative synthesis method, and its process is specifically as Figure 2 shown in the figure.

[0042] 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.

[0043] According to the calculation results, continuously adjust and optimize the design to obtain an electron gun scheme with high throughput for the G-band extended interaction klystron; the adjusted parameters are the structural parameters of each electrode of the electron gun, the electrode voltage, the axial longitudinal magnetic field intensity of the focusing magnetic field, the length of the focusing magnetic field, and the distance of the rising and falling edges.

[0044] The optimization criteria are:

[0045] (1) Maintain the parameter requirements for the interaction between the electromagnetic wave and the high-energy electron beam of the G-band extended interaction klystron;

[0046] (2) The iterative convergence of the electron gun trajectory tracking calculation;

[0047] (3) The static throughput of the electron beam is 100%;

[0048] (4) The cathode emission current density < 12 A / (cm^2);

[0049] (5) The total cathode emission current needs to be > 0.3 A.

[0050] Finally, obtain the design indexes of the G-band extended interaction klystron electron gun that meet the optimization criteria, as shown in Table 2.

[0051] Table 2 Electron gun structure and electrical parameters

[0052]

[0053]

[0054] For an electron optical system, due to different size parameters of the electron gun and different voltages of different electrons, the electrostatic field distributions and the calculation results of trajectory tracking are different. The calculation methods are numerical calculation methods such as the finite element method or the method of moments. That is, for any electron gun with unique dimensions, its electrostatic field distribution is also unique.

[0055] Figure 3 It is a sectional view of a Pierce electron gun with an existing structure focusing electrode; Figure 4 It is a 3D model diagram of a Pierce electron gun with an existing structure focusing electrode; Figure 7 It is the projection of the electron beam envelope of a Pierce electron gun with an n-period corrugated structure not loaded on the focusing electrode in the RZ plane; Figure 8 It is the cathode emission current density of a Pierce electron gun with an n-period corrugated structure not loaded on the focusing electrode; Figure 9 It is the projection of the electron trajectory of a Pierce electron gun with an n-period corrugated structure not loaded on the focusing electrode in the YZ plane; Figure 10 It is the static circulating electron trajectory of a Pierce electron gun with an n-period corrugated structure not loaded on the focusing electrode.

[0056] S4. Load an n-period corrugated structure on the inner surface of the focusing electrode of the electron gun obtained in step S3 to optimize and improve the performance. In this embodiment, the period n = 2, and the corrugated structure is composed of pairs of positive and negative circular arcs. The curvature radii of each section of the positive and negative arcs are equal, the directions of the positive and negative arcs are opposite, and the arc lengths are equal. Figure 5 It is a sectional view of a Pierce electron gun with a double-period corrugated regulation structure loaded on the focusing electrode in this embodiment, Figure 6 It is a 3D model diagram of a Pierce electron gun with a double-period corrugated regulation structure loaded on the focusing electrode in this embodiment.

[0057] Introduce an n = 2 period corrugated structure to the focusing electrode to regulate the electrostatic field distribution, continuously optimize the curvature radius and the corrugated period of the corrugated structure, further increase the total cathode emission current of a single cathode, and improve the electron beam power on the basis of the stable transmission of a single circular beam. The optimization criterion is that the total cathode emission current is limited to more than 330 mA, and at the same time, to ensure the life of the cathode head, the cathode emission current density is limited to less than 12 A / (cm^2).

[0058] Figure 3 It is a sectional view of a Pierce electron gun with an existing focusing electrode, Figure 5 It is a sectional view of a Pierce electron gun with a double-period corrugated regulation structure loaded on the focusing electrode in this embodiment; the double-period corrugated structure is loaded between points 14 - 18 in the figure, Figure 3Rotate 360 degrees, and the inner surface of the focusing electrode is a double-period corrugated curved surface.

[0059] Analyze and give the optimization criteria: For the G-band sheet beam electron gun, the calculation results reported by the Chinese Academy of Sciences in the Journal of Microwaves in 2014 were that at 16.5 kV, the total cathode emission current was 580 mA, but its focusing magnetic field was a uniform field focusing method, the focusing magnetic field was 8700 GS, the system complexity and cost were relatively high, and there was Diocotron instability in the sheet beam, and the electron beam even twisted into separated filaments as a whole.

[0060] For a multi-beam electron gun, the diameter of the electron beam channel of its electron gun pole shoes is limited. In the case of permanent magnet focusing, the magnetic field on the cathode surface is opposite to the direction of the main magnetic field; in the case of electromagnetic focusing, the magnetic field on the cathode surface is small. Therefore, when designing the focusing system of a multi-beam klystron, there are significant differences from a general single-beam klystron. In addition, when multiple electron beams enter the common collector, a virtual cathode is likely to be generated, causing electron inversion and affecting the stability of the multi-beam klystron.

[0061] Therefore, for the single-circular-beam single-electron-beam electron gun in the present invention, in order for it to be used in a G-band extended interaction klystron at 17 kV, its optimization criteria are that the total cathode emission current is limited to more than 330 mA. At the same time, to ensure the life of its cathode head, the cathode emission current density is limited to less than 12 A / (cm^2). By adjusting the high-frequency structure of the extended interaction klystron, the coupling impedance and the beam-wave interaction efficiency are improved to compensate for the emission current of the electron gun. According to industry knowledge and experience, when the high-frequency structure performance of the extended interaction klystron is good, a 330 mA circular single-electron-beam electron gun is sufficient to make the G-band extended interaction klystron output a power higher than 100 W within a bandwidth of 400 MHz. At the same time, the circular single-electron-beam electron gun adopts a periodic magnetic field (PCM), which has high focusing flexibility, can provide a magnetic field up to 15000 GS, and the electron beam is more easily and stably transmitted.

[0062] Figure 11 This is the projection of the electron beam envelope on the RZ plane when the corrugation curvature radius in this embodiment is 1 mm; Figure 12 This is the cathode emission current density when the corrugation curvature radius in this embodiment is 1 mm; Figure 13 This is the projection of the electron trajectory on the YZ plane when the corrugation curvature radius in this embodiment is 1 mm; Figure 14 This is the static conduction electron trajectory when the corrugation curvature radius in this embodiment is 1 mm. Table 3 shows the calculation results of electron gun trajectory tracking under different corrugation curvature radii.

[0063] Table 3

[0064]

[0065] From Table 3, it can be found that when the corrugation radius of curvature is 1 mm, the total emission current of the electron gun cathode obtained by trajectory tracking is 0.3347990 A, which is higher than the result of 0.3111307 A obtained by trajectory tracking of a circular single electron beam electron gun without introducing an n = 2 periodic corrugation structure in the focusing electrode. And its data is sufficient to support the normal operation of the G-band extended interaction klystron. The compensation is that the position of the beam waist is relatively far away. However, compared with the complex magnetic focusing systems of strip beams and multi-beam electron guns, this part of the compensation is acceptable.

[0066] 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 emission current of the cathode of the single circular beam 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 more easily and stably transmitted, and has a long lifespan.

Claims

1. A design method for the electron gun of a circular single electron beam G-band extended interaction klystron, characterized in that The steps include: S1. According to the design requirements of the beam-wave interaction engineering of the extended interaction klystron, obtain the electron gun requirement parameters, including the electron beam voltage U, the total electron beam current I, the type of electron emission model, the radius a of the electron beam channel, the radius b of the electron beam, the cathode emission current density Jc, and the range Zw; S2. Design an axisymmetric Pierce electron gun that meets the requirements of S1 as the initial scheme; S3. Starting from the axisymmetric Pierce electron gun designed in step S2, use a three-dimensional electromagnetic simulation software to perform trajectory tracking calculations and electrostatic field calculations; Continuously adjust and optimize the design according to the calculation results. The adjusted parameters are the structural parameters of each electrode of the electron gun, the electrode voltage, the axial longitudinal magnetic field strength of the focusing magnetic field, the length of the focusing magnetic field, and the distance of the rising and falling edges; The optimization criteria for the optimization process are: under the working parameter requirements of the extended interaction klystron in the G band, the trajectory tracking calculation of the electron gun converges iteratively, the static throughput rate of the electron beam is 100%, the cathode emission current density < 12 A / (cm^2), and the total cathode emission current is greater than 0.3 A; Finally, obtain the design indexes of the electron gun of the extended interaction klystron in the G band that meet the optimization criteria; S4. Load an n-period corrugated structure on the inner surface of the focusing electrode of the electron gun obtained in step S3. The corrugated structure consists of positive and negative arc pairs. The curvature radii of each section of the positive and negative arcs are equal, the directions of the positive and negative arcs are opposite, the arc lengths are equal, and 2 ≤ n ≤ 10; Continuously optimize the curvature radius and arc length of the arcs in the corrugated structure, as well as the corrugation period, perform particle trajectory tracking calculations, and regulate the electrostatic field distribution to obtain the final electron gun indexes.

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

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

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

5. The design method of the electron gun of the circular single electron beam G-band extended interaction klystron according to claim 1, characterized in that: The Pierce electron gun is designed according to Pierce's design principle and Vaughan's iterative synthesis method.

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