High-frequency system for third harmonic klystron and design method

Abstract

The invention provides a high-frequency system for a third harmonic klystron and a design method. The high-frequency system comprises an electron beam channel for transmitting electron beams and a resonant cavity communicated with the electron beam channel. The resonant cavity is configured to work in a hybrid mode of a fundamental mode and a target high-order mode, so that when the electron beam moves in the electron beam channel and passes through the resonant cavity, the electron beam can interact with high-frequency electric fields of the fundamental mode and the target high-order mode at the same time; the range of the proportion of the resonant frequency of the target high-order mode to the resonant frequency of the fundamental mode is 2.9-3.1. Through the high-frequency system, the problems of insufficient harmonic current and low efficiency caused by the fact that a traditional harmonic klystron only extracts harmonic energy from an output cavity are fundamentally solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electric vacuum devices. More particularly, it relates to a high-frequency system for a third-harmonic velocity modulation tube and a design method. BACKGROUND

[0002] The existing harmonic velocity modulation tube is mainly a second-harmonic velocity modulation tube. This type of velocity modulation tube works at a fundamental frequency in the input cavity and the intermediate cavity, uses the fundamental wave to modulate the velocity of the electron beam and to group the electron beam, and uses a high-frequency cavity working at a second-harmonic frequency to extract energy in the output cavity. Based on the technical route of the above-mentioned second-harmonic velocity modulation tube, a third-harmonic velocity modulation tube can be obtained, that is, the input cavity and the intermediate cavity work at the fundamental frequency, the fundamental wave is used to modulate the velocity of the electron beam and to group the electron beam, and the high-frequency cavity working at the third-harmonic frequency is used to extract energy in the output cavity. However, research has found that the third-harmonic velocity modulation tube has the following limitations in performance: the efficiency is low, the root cause of which is that the harmonic current component is not effectively excited and extracted throughout the interaction; the output cavity is still a small-size resonant cavity working at a high frequency, and the difficulty and precision requirements of its processing and manufacturing have not been significantly reduced due to the use of harmonic technology; in addition, the small physical size of the output cavity fundamentally restricts the microwave power capacity of the whole tube. SUMMARY

[0003] The present application aims to provide a high-frequency system for a third-harmonic velocity modulation tube to solve at least one of the above technical problems.

[0004] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: The present application provides a high-frequency system for a third-harmonic velocity modulation tube, comprising: an electron beam channel for transmitting an electron beam and a resonant cavity in communication with the electron beam channel; the resonant cavity is configured to work in a hybrid mode of a fundamental mode and a target high-order mode, so that the electron beam can simultaneously interact with the high-frequency electric field of the fundamental mode and the target high-order mode when moving in the electron beam channel and passing through the resonant cavity; the resonant frequency of the target high-order mode and the resonant frequency of the fundamental mode are in the range of 2.9 to 3.1.

[0005] Preferably, the resonant cavity comprises an input cavity, at least one intermediate cavity and an output cavity arranged in sequence along the axis of the electron beam channel; the input cavity, the intermediate cavity and the output cavity each comprise a cavity body symmetrically arranged on both sides of the electron beam channel along its own radial direction, and the cavity body is in communication with the electron beam channel.

[0006] Preferably, the input cavity, the intermediate cavity and the output cavity all work in a hybrid mode of the TM020 mode and the fundamental mode TM010 mode; the frequency of the TM020 mode is the third-harmonic frequency of the fundamental mode TM010 mode.

[0007] Preferably, the input cavity, the intermediate cavity and the output cavity are cylindrical cavities; and a cross section of the cylindrical cavities perpendicular to the axis of the electron beam channel is circular.

[0008] Preferably, the input cavity, the intermediate cavity and the output cavity operate in a hybrid mode of a TM330 mode and a fundamental TM110 mode; and the frequency of the TM330 mode is three times the frequency of the fundamental TM110 mode.

[0009] Preferably, the input cavity, the intermediate cavity and the output cavity are rectangular cavities; and a cross section of the rectangular cavities perpendicular to the axis of the electron beam channel is rectangular.

[0010] Preferably, the high frequency system further comprises an input window connected to the input cavity and configured to transmit an excitation signal with a frequency equal to the fundamental resonant frequency to effectively excite the mode hybrid in each cavity; and an output window connected to the output cavity and configured to output a third harmonic microwave power signal dominated by the target high order mode.

[0011] The application further provides a third harmonic velocity modulation tube comprising an electron gun, a focusing system, a collector and the high frequency system as described above; the electron gun is used to emit an electron beam into the electron beam channel of the high frequency system; the focusing system is used to confine the electron beam in the electron beam channel; and the collector is used to recover the electron beam after energy exchange.

[0012] The application further provides a design method of the high frequency system as described above, comprising: determining a target third harmonic operating frequency of the high frequency system; setting a fundamental resonant frequency input into the resonant cavity as a value matched with the target third harmonic operating frequency, so that the ratio of the target third harmonic operating frequency to the fundamental frequency falls within the range of 2.9 to 3.1; and adjusting the geometric size of the resonant cavity through electromagnetic simulation so that the resonant frequency of the target high order mode is equal to the target third harmonic operating frequency.

[0013] Preferably, the adjusting the geometric size of the resonant cavity through electromagnetic simulation so that the resonant frequency of the target high order mode is equal to the target third harmonic operating frequency further comprises: when the resonant cavity is a cylindrical cavity with a circular cross section perpendicular to the axis of the electron beam channel, adjusting the cavity height of the cylindrical cavity in the axial direction of the electron beam channel and the diameter of the circular cross section so that the resonant frequency of the target high order mode of the resonant cavity is equal to the target third harmonic operating frequency. when the resonant cavity is a rectangular cavity with a rectangular cross section perpendicular to the axis of the electron beam channel, adjusting the length and width of the rectangular cross section of the rectangular cavity so that the resonant frequency of the target high order mode of the resonant cavity is equal to the target third harmonic operating frequency.

[0014] The application has the following beneficial effects: The application provides a high-frequency system for a third harmonic velocity modulation tube, comprising an electron beam channel for transmitting an electron beam and a resonant cavity in communication with the electron beam channel; the resonant cavity is configured to operate in a hybrid mode of a basic mode and a target high-order mode, so that the electron beam can simultaneously interact with high-frequency electric fields of the basic mode and the target high-order mode when the electron beam moves in the electron beam channel and passes through the resonant cavity; the resonant frequency of the target high-order mode is in a range of 2.9-3.1 times of the resonant frequency of the basic mode. The third harmonic component directly participates in energy interaction in the whole system of the input cavity, the intermediate cavity and the output cavity, and the electron beam is synergistically modulated by the hybrid mode of the basic mode and the high-order mode, so that the third harmonic current component in the electron beam is efficiently excited and continuously increased from the initial stage of group gathering. This fundamentally solves the problems of insufficient harmonic current and low efficiency caused by the fact that the traditional harmonic velocity modulation tube only extracts harmonic energy in the output cavity, so that the interaction efficiency of the application can approach the level of mature fundamental velocity modulation tubes. Since the output cavity operates in the high-order mode like the input cavity and the intermediate cavity, its physical size is multiplied compared with the basic mode cavity operating at the same frequency. The expansion of the size of the output cavity solves the problem of small microwave power capacity caused by the small size of the output cavity of the traditional high-frequency velocity modulation tube, so that the power capacity of the application is greatly improved. The resonant cavity of the application operates at a high frequency, but its physical size is significantly larger than the basic mode cavity at the same frequency due to the use of the high-order mode. The size amplification reduces the sensitivity of the frequency to the size change, widens the process error margin of the processing, welding and assembly links, and reduces the dependence on high-precision manufacturing. The resonant cavity structure is still a conventional cylindrical cavity or a rectangular cavity, and the original general processing methods such as turning and milling are completely applicable, which greatly simplifies the manufacturing process, improves the production yield, and effectively controls the manufacturing cost. BRIEF DESCRIPTION OF DRAWINGS

[0015] The specific embodiments of the application will be further described in detail below with reference to the accompanying drawings.

[0016] Figure 1 is a schematic diagram of the overall structure of the high-frequency system of the application.

[0017] Reference signs: 1, electron beam channel, 2, input cavity, 3, intermediate cavity, 4, output cavity, 5, input window, 6, output window, 7, drift head, 8, cavity body. DETAILED DESCRIPTION

[0018] Various exemplary embodiments of the application will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement, numerical expressions and values of the components and steps set forth in these embodiments do not limit the scope of the application unless otherwise specifically stated.

[0019] The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the application or its application and uses.

[0020] Techniques and equipment known to those of ordinary skill in the relevant art can not be discussed in detail, but where appropriate, such techniques and equipment should be considered as part of the specification.

[0021] In all examples shown and discussed herein, any specific values should be interpreted as merely exemplary and not as a limitation. Thus, other examples of the exemplary embodiments can have different values.

[0022] It should be noted that like reference numerals and letters refer to like items in the following drawings, and thus, once an item is defined in one drawing, it need not be discussed further in subsequent drawings.

[0023] The present application provides a high frequency system for a third harmonic velocity tube, which combines Figure 1 As shown, in particular, the high frequency system comprises an electron beam channel 1 for transmitting an electron beam and a resonant cavity in communication with the electron beam channel 1; the resonant cavity is configured to operate in a hybrid mode of a fundamental mode and a target high-order mode, so that the electron beam can simultaneously interact with high frequency electric fields of the fundamental mode and the target high-order mode when the electron beam moves in the electron beam channel 1 and passes through the resonant cavity; the ratio of the resonant frequency of the target high-order mode to the resonant frequency of the fundamental mode ranges from 2.9 to 3.1. The existing third harmonic velocity tube has a far lower efficiency than the fundamental mode because the high-order harmonic component does not directly participate in the bunching of the input cavity and the intermediate cavity, and the growth of the harmonic component in the cathode current is far lower than that of the fundamental component. The third harmonic velocity tube of the present application has a third harmonic component directly participating in the interaction of the whole high frequency system and accompanying the fundamental mode, and the interaction efficiency is close to that of the fundamental mode.

[0024] The output cavity of the existing third harmonic velocity modulation tube returns to the basic mode working at the corresponding harmonic frequency, which causes the output cavity size to decrease, although the input cavity and intermediate cavity size is enlarged, but the structural size of the output cavity restricts the power capacity. Further, the resonant cavity of the present application comprises an input cavity 2, at least one intermediate cavity 3 and an output cavity 4 arranged along the electron beam channel axis in sequence; the input cavity 2, intermediate cavity 3 and output cavity 4 all comprise two cavities 8 symmetrically arranged on both sides of the electron beam channel along its radial direction, and the two cavities 8 are communicated with the electron beam channel 1 through the drift head 7. The space between the two symmetrically arranged cavities 8 is called cavity gap. The arrangement interval distance of the above-mentioned input cavity 2, intermediate cavity 3 and output cavity 4 and the specific number of intermediate cavities 3, frequency distribution, quality factor and other parameters are selected according to the technical parameter requirements of the velocity modulation tube. The working mode of the output cavity 4 of the present application is the same as that of the input cavity 2 and the intermediate cavity 3, and its size is more than twice the size of the basic mode resonant cavity working at the third harmonic frequency, and the volume is increased by more than four times, and the power capacity is greatly improved. The resonant cavity structure of the third harmonic velocity modulation tube of the present application adopts a simple cylindrical cavity or rectangular cavity structure, which is completely compatible with the turning and milling machining process; and the resonant cavity size is enlarged by more than twice, so that the sensitivity of the frequency to the size is reduced. For high frequency applications, the resonant cavity size is enlarged by more than twice, which provides more error margin for high-precision processes such as welding and mounting.

[0025] In an optional embodiment, the input cavity 2, intermediate cavity 3 and output cavity 4 all work in the hybrid mode of TM020 mode and basic mode TM010 mode; the frequency of the TM020 mode is the third harmonic frequency of the basic mode TM010 mode. The input cavity 2, intermediate cavity 3 and output cavity 4 are all cylindrical cavities; the cross section of the cylindrical cavity perpendicular to the axis of the electron beam channel is circular. The working mode of the existing velocity modulation tube is mainly cylindrical cavity TM010 mode or rectangular cavity TM110 mode. In order to utilize high-order modes, the height and circular cross-sectional diameter of each cylindrical cavity are adjusted in the present application. The size of the cylindrical cavity is selected by considering the diameter of the electron beam channel, the cavity gap and other factors, so that the frequency of the cylindrical cavity TM020 mode = the frequency of the TM010 mode x (2.9~3.1), so that the frequency of the cylindrical cavity TM020 mode is the third harmonic frequency of the basic mode TM010 mode, and thus the third harmonic component in the cathode current rapidly increases during the bunching process, and can even exceed the fundamental current component. The different cavity sizes of all resonant cavities in the same high frequency system are generally different. Although the size is the same, the gain is high, but this will reduce the efficiency, bandwidth and other indicators, so the different cavity sizes of the resonant cavities need to be simulated and designed according to the specific indicator requirements.

[0026] In another alternative embodiment, the input cavity 2, the intermediate cavity 3 and the output cavity 4 all work in a hybrid mode of TM330 mode and fundamental mode TM110 mode; the frequency of the TM330 mode is the third harmonic frequency of the fundamental mode TM110 mode. The input cavity 2, the intermediate cavity 3 and the output cavity 4 are all rectangular cavities; the cross section of the rectangular cavities perpendicular to the axis of the electron beam channel is rectangular. By adjusting the cross section height and the length-width size of the rectangular cavities, the frequency of the TM330 mode of the rectangular cavities is equal to the frequency of the TM110 mode x (2.9~3.1), so that the frequency of the TM330 mode of the rectangular cavities is the third harmonic frequency of the fundamental mode TM110 mode. The electric field distribution of the TM330 mode of the rectangular cavities is close to that of the TM020 mode of the cylindrical cavity. In the bunching process, the third harmonic component in the cathode current rapidly increases, and can even exceed the fundamental current component.

[0027] In a conventional klystron design, the resonant cavity is usually designed to work in a single mode. This is due to a common technical concern that if there are two modes in a resonant cavity, and their frequencies are very close, or the frequency of one mode is close to the high harmonic frequency of another mode, the working state of the cavity is easy to jump back and forth between the two modes, resulting in unstable output power of the klystron. However, the present application successfully utilizes this multi-mode working state, and changes it from a technical risk that needs to be avoided to a technical means to achieve high performance. Specifically, the present application actively sets the ratio range of the fundamental mode frequency (such as TM010) of the resonant cavity to the high mode frequency (such as TM020) to 2.9~3.1 through precise electromagnetic design, and uses the nonlinear bunching effect of the electron beam as the link of energy coupling, so that the two form a stable and cooperative mode hybrid working state. This design makes the energy conversion between modes controllable, rather than random jumping. The electron beam exchanges energy with the electric field of the fundamental mode and the high mode at the same time when passing through the cavity gap, so that the third harmonic component is efficiently established and amplified from the beginning of modulation. Therefore, the present application not only completely eliminates the power instability caused by mode competition in traditional design, but also realizes efficient third harmonic energy exchange throughout the entire interaction process through this stable mode hybrid, and finally achieves the technical effects of high frequency, high efficiency and high power capacity.

[0028] More specifically, when the TM020 mode frequency of each resonant cavity of the high-frequency system of the present application is close to about 3 times the fundamental mode TM010 mode frequency (the TM020 mode frequency of each cavity is 170MHz~420MHz lower than 3 times the fundamental mode TM010 mode frequency), the third harmonic component of the output microwave of the klystron is significantly increased, and the higher the operating voltage, the higher the third harmonic component. The operating frequency of the output window is set to the third harmonic, and the standing wave ratio is 1.07. In this case, the fundamental wave signal is cut off. The test waveguide system also uses the third harmonic as the operating frequency, and the load standing wave ratio is 1.16. The specific test results are as follows:

[0029] As can be seen from the data in the above table, as the operating voltage and current increase, the third harmonic efficiency of the klystron of the present application gradually increases. When the operating voltage reaches 145kV and the cathode peak current reaches 144A, this is the limit of the normal working parameters of the electron gun, and at this time the best third harmonic efficiency of the present application is 19.8%. However, based on the traditional design idea, the third harmonic klystron, i.e. all resonant cavities work in the fundamental mode - cylindrical cavity TM010 mode, the input cavity and the intermediate cavity work at the fundamental frequency, and the output cavity works at the third harmonic (three times the fundamental frequency), when the operating voltage reaches 145kV and the cathode peak current reaches 144A, the simulation results show that the third harmonic efficiency is only 8.6%, which is much lower than the third harmonic klystron of the present application of 19.8%. Moreover, due to the small size of the resonant cavity, the output power of the traditional third harmonic klystron is only 1.3MW when the high-frequency electric field is relatively high, which affects the stability of the work. Moreover, due to the fact that the size of the output cavity of the traditional klystron is much smaller than that of the other cavities, the machining precision requirement is higher, the welding yield is lower, the power capacity and thermal capacity are small, which affects the output power, working ratio and other parameters of the klystron.

[0030] The present application creates a stable state of mode cooperation by designing the frequency of two modes in the resonant cavity to satisfy a specific proportional relationship, and using the electron beam as a link to form a stable cooperative working relationship (hybrid mode). In short, the present application does not passively avoid mode competition, but actively creates a stable state of mode cooperation, which is the key to achieving high efficiency and stability. Specifically, when the resonant frequency of the target high-order mode TM020 mode and the resonant frequency of the fundamental mode TM010 mode are in the proportional range of 2.9~3.1, the fundamental wave microwave electric field is excited in each resonant cavity, and the third harmonic microwave electric field is also excited at the same time. The third harmonic component of the cathode current is high, and the power fed out of the output cavity can exceed the fundamental wave power. When the resonant cavity TM020 mode frequency is lower than 2.9 times the TM010 mode frequency or higher than 3.1 times the TM010 mode frequency, the output power of the third harmonic is at least 10dB lower than the fundamental wave, which has no application value.

[0031] In a specific embodiment, the high frequency system further comprises an input window 5 connected with the input cavity 2, configured to transmit an excitation signal with a frequency equal to the fundamental mode resonance frequency, to effectively excite the mode mixing in each cavity; and an output window 6 connected with the output cavity 4, configured to output a third harmonic microwave power signal dominated by the target high order mode. The input window 5 transmits a fundamental frequency signal, and the mode mixing in the cavity is excited by a low-loss fundamental signal. The third harmonic power dominated by the high order mode is directly output through the output window 6, avoiding the interference of the fundamental frequency and other modes, ensuring the spectral purity of the output microwave signal, which is crucial for applications requiring high frequency and high stability signals. The input window 5 transmits a fundamental excitation signal, and the working frequency is a low-frequency fundamental wave; the output window 6 transmits a third harmonic signal, and the working frequency is 2.9-3.1 times the fundamental wave.

[0032] The application also provides a design method of the high frequency system as described above, which comprises: determining the target third harmonic working frequency of the high frequency system; setting the fundamental mode resonance frequency input into the resonant cavity as a value matched with the target third harmonic working frequency, so that the ratio of the target third harmonic working frequency to the fundamental mode frequency falls within the range of 2.9 to 3.1; and adjusting the geometric size of the resonant cavity through electromagnetic simulation, so that the resonance frequency of the target high order mode is equal to the target third harmonic working frequency. Further, adjusting the geometric size of the resonant cavity through electromagnetic simulation, so that the resonance frequency of the target high order mode is equal to the target third harmonic working frequency further comprises: when the resonant cavity is a cylindrical cavity with a circular cross section perpendicular to the electron beam channel axis, adjusting the cavity height and the circular cross section diameter of the cylindrical cavity in the axial direction of the electron beam channel, so that the resonance frequency of the target high order mode of the resonant cavity is equal to the target third harmonic working frequency; and when the resonant cavity is a rectangular cavity with a rectangular cross section perpendicular to the electron beam channel axis, adjusting the length and width of the rectangular cross section of the rectangular cavity, so that the resonance frequency of the target high order mode of the resonant cavity is equal to the target third harmonic working frequency.

[0033] The application also provides a third harmonic klystron, comprising an electron gun, a focusing system, a collector and a high frequency system as described above; the electron gun is used to emit an electron beam into the electron beam channel of the high frequency system; the focusing system is used to constrain the electron beam in the electron beam channel; and the collector is used to recover the electron beam after energy exchange. The electron gun emits an electron beam into the electron beam channel of the high frequency system, and the focusing system constrains the electron beam in the electron beam channel to maintain its shape. The electron beam exchanges energy with the high frequency field in the high frequency system, and the electron beam after energy exchange is recovered by the collector. The electron beam channel 1 is correspondingly matched with the collector at one end close to the output cavity 4, and correspondingly matched with the electron gun at one end close to the input cavity 2.

[0034] Further, the third harmonic velocity modulation tube provided by the present application can be manufactured and verified by the following steps. Step one: overall interaction design of the velocity modulation tube is performed, the electron beam parameters required to achieve the target performance are determined, and the target resonance frequency of the resonant cavity in the high frequency system is determined accordingly. The core purpose of this step is to determine the target third harmonic operating frequency of the resonant cavity. Step two: based on the target frequency determined in step one, the resonant cavity is electromagnetically designed. Through electromagnetic simulation software, the geometric size of the resonant cavity (mainly the diameter and height for a cylindrical cavity; the length and width for a rectangular cavity) is accurately calculated and adjusted. The core design goal of this step is to adjust the size so that the resonance frequency of the TM020 mode (or TM330 mode) of the resonant cavity is equal to 2.9 to 3.1 times the fundamental mode resonance frequency of the TM010 mode (or TM110 mode). The simulation verification is performed until the electric field distribution and mode spectrum of each cavity meet the above proportion relationship, and the mode mixing state is stable. Step three: use conventional machining methods (such as turning and milling) to process the resonant cavities and electron beam channels of the high frequency system. Perform cold state parameter test on the processed high frequency system, verify whether the actual resonance frequency and mode of each resonant cavity are consistent with the design target, and perform necessary fine tuning. Assemble, seal, exhaust and age the cold test qualified high frequency system with the electron gun, focusing system, collector and the like. Test the completed tube, and finally obtain a third harmonic velocity modulation tube with performance up to standard.

[0035] In summary, the application provides a high frequency system for a third harmonic velocity modulation tube, comprising an electron beam channel for transmitting an electron beam and a resonant cavity in communication with the electron beam channel; the resonant cavity is configured to operate in a hybrid mode of a basic mode and a target high order mode, so that the electron beam can interact with the high frequency electric field of the basic mode and the target high order mode at the same time when the electron beam moves in the electron beam channel and passes through the resonant cavity; the resonant frequency of the target high order mode is in the range of 2.9-3.1 times the resonant frequency of the basic mode. The third harmonic component directly participates in energy interaction in the whole system of the input cavity, the intermediate cavity and the output cavity, and the hybrid mode of the basic mode and the high order mode is used to cooperatively modulate the electron beam, so that the third harmonic current component in the electron beam is efficiently excited and continuously increased from the initial stage of group gathering. This fundamentally solves the problems of insufficient harmonic current and low efficiency caused by the fact that the traditional harmonic velocity modulation tube only extracts harmonic energy in the output cavity, so that the interaction efficiency of the application can approach the level of mature fundamental velocity modulation tubes. Since the output cavity works in the high order mode (TM020 / TM330) like the input cavity and the intermediate cavity, its physical size is doubled compared with the basic mode cavity working at the same frequency. The expansion of the size of the output cavity solves the problem of small microwave power capacity caused by the small size of the output cavity in the traditional high frequency velocity modulation tube, so that the power capacity of the application is greatly improved. The resonant cavity of the application works at a high frequency, but because it uses a high order mode, its physical size is significantly larger than that of the basic mode cavity at the same frequency. The size amplification reduces the sensitivity of the frequency to the size change, widens the process error margin of the processing, welding and assembly links, and reduces the dependence on high-precision manufacturing. The resonant cavity structure is still a conventional cylindrical cavity or a rectangular cavity, and the original general machining methods such as turning and milling are fully applicable, greatly simplifying the manufacturing process, improving the production yield, and effectively controlling the manufacturing cost.

[0036] Obviously, the above embodiments of the application are only examples for clearly illustrating the application, and are not intended to limit the embodiments of the application. For those skilled in the art, other different forms of changes or modifications can be made on the basis of the above description, and it is impossible to enumerate all the embodiments here. Any obvious changes or modifications derived from the technical solutions of the application are still within the protection scope of the application.

Claims

1. A high-frequency system for a third harmonic klystron, characterized in that, include: An electron beam channel for transmitting electron beams and a resonant cavity connected to the electron beam channel; The resonant cavity is configured to operate in a hybrid mode of the fundamental mode and the target higher-order mode, so that when the electron beam moves in the electron beam channel and passes through the resonant cavity, it can simultaneously interact with the high-frequency electric fields of the fundamental mode and the target higher-order mode; the ratio of the resonant frequency of the target higher-order mode to the resonant frequency of the fundamental mode is in the range of 2.9 to 3.

1.

2. The high-frequency system according to claim 1, characterized in that, The resonant cavity includes an input cavity, at least one intermediate cavity, and an output cavity arranged sequentially along the axial direction of the electron beam channel; the input cavity, intermediate cavity, and output cavity each include cavities symmetrically arranged on both sides of the electron beam channel along its own radial direction, and the cavities are connected to the electron beam channel.

3. The high-frequency system according to claim 2, characterized in that, The input cavity, intermediate cavity, and output cavity all operate in a hybrid mode of TM020 mode and fundamental mode TM010 mode; the frequency of the TM020 mode is the third harmonic frequency of the fundamental mode TM010 mode.

4. The high-frequency system according to claim 3, characterized in that, The input cavity, intermediate cavity, and output cavity are all cylindrical cavities; the cross-section of the cylindrical cavity perpendicular to the electron injection channel axis is circular.

5. The high-frequency system according to claim 2, characterized in that, The input cavity, intermediate cavity, and output cavity all operate in a hybrid mode of TM330 mode and fundamental mode TM110 mode; the frequency of the TM330 mode is the third harmonic frequency of the fundamental mode TM110 mode.

6. The high-frequency system according to claim 5, characterized in that, The input cavity, intermediate cavity, and output cavity are all rectangular cavities; the cross-section of the rectangular cavity perpendicular to the electron injection channel axis is rectangular.

7. The high-frequency system according to claim 2, characterized in that, The high-frequency system also includes an input window connected to the input cavity, which is configured to transmit an excitation signal with a frequency equal to the fundamental mode resonant frequency to effectively excite mode mixing in each cavity; and an output window connected to the output cavity, which is configured to output a third harmonic microwave power signal dominated by the target higher-order mode.

8. A third harmonic klystron, characterized in that, The system includes an electron gun, a focusing system, a collecting electrode, and a high-frequency system as described in any one of claims 1 to 7; the electron gun is used to emit an electron beam into the electron beam channel of the high-frequency system; the focusing system is used to constrain the electron beam in the electron beam channel; and the collecting electrode is used to recover the electron beam after energy exchange.

9. A design method for a high-frequency system as described in claim 1, characterized in that, include: Determine the target third harmonic operating frequency of the high-frequency system; set the fundamental mode resonant frequency of the input resonant cavity to a value that matches the target third harmonic operating frequency, so that the ratio of the target third harmonic operating frequency to the fundamental mode frequency falls within the range of 2.9 to 3.1; adjust the geometric dimensions of the resonant cavity through electromagnetic simulation so that the resonant frequency of its target higher-order modes is equal to the target third harmonic operating frequency.

10. The design method according to claim 9, characterized in that, Adjusting the geometric dimensions of the resonant cavity through electromagnetic simulation to make the resonant frequency of the target higher-order mode equal to the target third harmonic operating frequency further includes: when the resonant cavity is a cylindrical cavity with a circular cross-section perpendicular to the electron beam channel axis, adjusting the cavity height and circular cross-section diameter of the cylindrical cavity in the electron beam channel axis to make the resonant frequency of the target higher-order mode equal to the target third harmonic operating frequency. When the resonant cavity is a rectangular cavity with a rectangular cross-section perpendicular to the electron beam channel axis, the length and width of the rectangular cross-section of the cavity are adjusted so that the resonant frequency of the target higher-order mode of the resonant cavity is equal to the target third harmonic operating frequency.

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