Microwave input high frequency modulation grid-controlled electron gun

Abstract

The application discloses a microwave input high-frequency modulation grid-controlled electron gun, discards the modulation means of the traditional density emission electron gun using alternating voltage, adopts a quarter wavelength resonant cavity with a double coaxial structure as an input cavity, and positions a cathode and a grid in the input cavity, so that the microwave input can be used to establish a radio frequency standing wave electric field between the cathode and the grid to modulate the emission of the electron beam, and the amplitude of the radio frequency standing wave electric field remains stable under high-frequency microwave. Simulation results show that the application can still emit a high-power electron beam with density modulation under 915 MHz microwave input, and realizes the emission of a megawatt-level electron beam.

Description

Technical Field

[0001] This invention belongs to the field of microwave technology, and more specifically, relates to a microwave input high-frequency modulation grid-controlled electron gun. Background Technology

[0002] High-power vacuum electronic microwave sources have broad application prospects in fields such as industrial detection, medical diagnosis and treatment, particle accelerators, and controlled thermonuclear fusion. The core component of a vacuum electronic microwave source is the electron gun, which emits an electron beam. The electron gun's function is to emit an electron beam that meets the operating conditions of the vacuum electronic device, and then the high-frequency structure of the vacuum electronic device converts the kinetic or potential energy of the electron beam into microwave energy.

[0003] There are two types of electron guns in vacuum electronic microwave sources: one type emits a DC electron beam under the action of an electrostatic field, such as the Pierce electron gun; the other type emits a specific frequency electron beam under the combined action of an electrostatic field and an alternating electric field, such as the electron gun in a vacuum tetrode, which is also called a density emission electron gun.

[0004] Electron guns that emit DC electron beams, exemplified by the Pierce electron gun, have the advantage of higher emitted electron beam power. However, their disadvantage is limited efficiency in the interaction between the emitted electron beam and the microwave, as the emitted electron beam needs to be modulated to meet operating conditions before energy exchange with the microwave. Density emission electron guns, on the other hand, have the advantage of high efficiency in the interaction between the emitted electron beam and the microwave, but their disadvantage is that they can only operate at lower frequencies, such as below 10 MHz.

[0005] Figure 1 This is a schematic diagram of a conventional density-emission electron gun.

[0006] like Figure 1 As shown, a conventional density emission electron gun includes a cathode, a control electrode, and an anode located in a vacuum environment. In low-frequency scenarios below 10 MHz, the density emission electron gun directly applies an alternating voltage to the control electrode to control the electron beam emitted from the cathode. However, as the frequency increases, the amplitude of the alternating voltage provided by the modulator cannot meet the requirements of the density emission electron gun. This is because the microwave period shortens with increasing frequency, while the modulator output voltage requires sufficient rise and fall times, causing the amplitude of the modulator output voltage to decrease with increasing frequency. The difficulty of emitting high-power electron beams at high frequencies is a problem that urgently needs to be solved. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a microwave input high-frequency modulated grid-controlled electron gun to realize the emission of high-power electron beams with density modulation at high frequencies.

[0008] To achieve the above-mentioned objective, the present invention provides a microwave-input high-frequency modulated gate-controlled electron gun, comprising: a cathode and a gate, characterized in that it further comprises:

[0009] The cathode support cylinder is made of metal, with the cathode on its right end face, which closes the right end face of the cathode support cylinder.

[0010] The gate support cylinder is made of metal, and its right end face is the gate. The outer edge of the gate is connected to the right end face of the gate support cylinder, thus sealing the right end face of the gate support cylinder.

[0011] The gate support sleeve fits the cathode support sleeve from the right side. The cathode support sleeve and the gate support sleeve are coaxial. The distance between the cathode and the gate is determined by the transit time effect. The higher the operating frequency, the smaller the distance between the cathode and the gate.

[0012] The grounding shell is a cylindrical structure made of metal material. Its right end face is closed with a circular metal plate. A circular electron injection conduit is installed in the center of the circular metal plate. The circular electron injection conduit passes through the center of the circular metal plate and communicates with the inside of the grounding shell. The circular electron injection conduit serves as the anode.

[0013] The grounded housing fits the gate support cylinder from the right side. The gate support cylinder is coaxial with the grounded housing. The space between the anode and the gate is a DC acceleration space for electron beam.

[0014] The gate support cylinder is fitted into the cathode support cylinder, and the grounding shell is fitted into the gate support cylinder, forming a double coaxial structure. The left ends of the grounding shell, the gate support cylinder, and the cathode support cylinder are sealed with metal ring plates to form the inner and outer cavities of the double coaxial structure. The inner cavity of the double coaxial structure is the space between the cathode support cylinder and the gate support cylinder, and its function is to obtain microwave energy from the coupling structure to establish a radio frequency standing wave electric field. The outer cavity is the space between the gate support cylinder and the grounding shell, and its function is to prevent electromagnetic leakage, prevent high-voltage arcs, and prevent the external electromagnetic environment from affecting the electron gun.

[0015] Both the cathode support cylinder and the grid support cylinder are divided into two sections, connected by insulating ceramic in the middle to isolate DC voltage;

[0016] The inner cavity of the dual coaxial structure serves as the input cavity. A coupling structure is installed on its left end face to couple microwaves into the input cavity. The length of the input cavity from left to right is one-quarter of the microwave wavelength. The microwave energy establishes a radio frequency standing wave electric field between the cathode and the grid. The amplitude of the radio frequency standing wave electric field is [value missing]. Apply negative high voltage to the cathode A negative high voltage is applied to the gate. ,and The cathode operates under space charge confinement, while the anode and the grounded casing are at ground voltage.

[0017] Before the input microwaves establish the radio frequency standing wave electric field, the cathode emits a weak leakage current under the action of the grid and the anode. After the radio frequency standing wave electric field is established, the cathode emits an electron beam, i.e., an electron bead, under the combined action of the DC electric field and the radio frequency standing wave electric field within half a cycle of the radio frequency standing wave electric field. During the adjacent half cycle, the cathode is in the cutoff state, and the cathode conduction angle is 180 degrees. After the electron bead passes through the grid, it is accelerated under the DC voltage between the grid and the anode, and then output from the circular electron bead conduit.

[0018] The objective of this invention is achieved as follows.

[0019] This invention relates to a microwave-input high-frequency modulated grid-controlled electron gun, which abandons the traditional method of alternating voltage modulation used in density-emission electron guns. Instead, it employs a quarter-wavelength resonant cavity with a dual coaxial structure as the input cavity, with the cathode and grid located within the input cavity. This allows the use of microwave input to establish a radio frequency standing wave electric field between the cathode and grid to modulate the emission of the electron beam. The amplitude of the radio frequency standing wave electric field remains stable under high-frequency microwave conditions. Simulation results show that this invention can still emit high-power density-modulated electron beams under a 915 MHz microwave input, achieving megawatt-level electron beam emission. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a traditional density-emission electron gun;

[0021] Figure 2 This is a cross-sectional view of a specific embodiment of the microwave input high-frequency modulation grid-controlled electron gun of the present invention;

[0022] Figure 3 yes Figure 2 A magnified view of a portion A of the cathode-gate cross-section shown;

[0023] Figure 4 yes Figure 2 The diagram shows the structure of the gate.

[0024] Figure 5 It is the input power, i.e., microwave energy diagram, of the microwaves coupled into the input cavity by the coupling structure;

[0025] Figure 6 A voltage diagram of the radio frequency standing wave electric field established between the cathode and the gate;

[0026] Figure 7 It is the Fourier spectrum of the radio frequency voltage between the cathode and the gate;

[0027] Figure 8 It shows the waveforms of the gate intercept current and the current through the anode hole;

[0028] Figure 9 It is the Fourier spectrum of the high-frequency components of the current passing through the anode hole. Detailed Implementation

[0029] The specific embodiments of the present invention will now be described with reference to the accompanying drawings to enable those skilled in the art to better understand the invention. It should be particularly noted that in the following description, detailed descriptions of known functions and designs that might obscure the main content of the invention will be omitted here.

[0030] Figure 2 This is a cross-sectional view of a specific embodiment of the microwave input high-frequency modulation grid-controlled electron gun of the present invention.

[0031] In this embodiment, as Figure 2 As shown, the microwave input high-frequency modulation grid-controlled electron gun of the present invention includes: cathode 1, grid 2, anode 3, cathode support cylinder 4, grid support cylinder 5, grounded shell 6, metal circular sheet 7, metal circular plate 8, insulating ceramic 9, and coupling structure 10. The overall structure presents a dual coaxial structure.

[0032] The function of cathode 1 is to provide electrons, the function of grid 2 is to control the emission of electron beam from cathode 1, the outer diameter of grid 2 is slightly larger than that of cathode 1, and the function of anode 3 is to accelerate the electron beam by DC.

[0033] The cathode support cylinder 4 is made of metal, and its right end face is the cathode 1, which closes the right end face of the cathode support cylinder 4. The gate support cylinder 5 is made of metal, and its right end face is the gate 2. The outer edge of the gate 2 is connected to the right end face of the gate support cylinder 5, thus closing the right end face of the gate support cylinder 5.

[0034] The gate support cylinder 5 is inserted into the cathode support cylinder 4 from the right side. The cathode support cylinder 4 and the gate support cylinder 5 are coaxial. The distance between the cathode 1 and the gate 2 is determined by the transit time effect. The higher the operating frequency, the smaller the distance between the cathode 1 and the gate 2.

[0035] The grounding shell 6 is a cylindrical structure made of metal material. Its right end face is closed by a metal circular plate 7. A circular electron injection conduit is installed in the center of the metal circular plate 7. The circular electron injection conduit passes through the center of the metal circular plate 7 and communicates with the inside of the grounding shell. The circular electron injection conduit serves as the anode 3.

[0036] The grounded housing 6 inserts the gate support cylinder 5 from the right side. The gate support cylinder 5 is coaxial with the grounded housing 6. The space between the anode 3 and the gate 2 is the DC acceleration space for electron injection.

[0037] The gate support cylinder 5 is fitted into the cathode support cylinder 4, and the grounding shell 6 is fitted into the gate support cylinder 5, forming a double coaxial structure. The left end of the grounding shell 6, the left end of the gate support cylinder, and the left end of the cathode support cylinder are sealed with a metal ring plate 8, forming the inner cavity and outer cavity of the double coaxial structure. The inner cavity of the double coaxial structure is the space between the cathode support cylinder 4 and the gate support cylinder 5, which is used to obtain microwave energy from the coupling structure 10 to establish a radio frequency standing wave electric field. The outer cavity is the space between the gate support cylinder 5 and the grounding shell 6, which is used to prevent electromagnetic leakage, prevent high-voltage arcs, and prevent the external electromagnetic environment from affecting the electron gun.

[0038] Both the cathode support cylinder 4 and the gate support cylinder 5 are divided into two sections, connected by an insulating ceramic 9 in the middle to isolate DC voltage. Specifically, the insulating ceramic 9 is connected to the cathode support cylinder 4 and the gate support cylinder 5 using ceramic metallization welding to ensure structural strength and maintain vacuum tightness. In this embodiment, as... Figure 2 As shown, the insulating ceramic 9 on the gate support cylinder 5 has a circular ring structure. The inner diameter edge divides the gate support cylinder 5 into two equal sections for connection, and the outer diameter edge is welded to the inner wall of the grounded outer shell 6. There is also a circular ring structure of insulating ceramic 9 on the right end edge of the gate support cylinder 5. The inner diameter edge is ceramic-metallized and welded to the right end edge of the gate support cylinder 5, and the outer diameter edge is welded to the inner wall of the grounded outer shell 6. This makes the microwave input high-frequency modulation gate-controlled electron gun structure stable.

[0039] The inner cavity of the dual coaxial structure serves as the input cavity. A coupling structure 10 is installed on its left end face to couple microwaves into the input cavity. The length of the input cavity from left to right is one-quarter of the microwave wavelength. The microwave energy establishes a radio frequency standing wave electric field between the cathode 1 and the gate 2. The amplitude of the radio frequency standing wave electric field is [value missing]. A negative high voltage is applied to cathode 1. A negative high voltage is applied to gate 2. ,and The cathode 1 operates under space charge confinement, while the anode 1 and the grounded casing 6 are at ground voltage.

[0040] Before the input microwave is used to establish the radio frequency standing wave electric field, cathode 1 emits a weak leakage current under the action of grid 2 and anode 3. After the radio frequency standing wave electric field is established, cathode 1 emits an electron beam, i.e., an electron bead, under the combined action of the DC electric field and the radio frequency standing wave electric field within half a cycle of the radio frequency standing wave electric field. During the adjacent half cycle, the cathode is in the cutoff state, and the conduction angle of cathode 1 is 180 degrees. After the electron bead passes through grid 2, it is accelerated under the DC voltage between grid 2 and anode 3, and then output from the circular electron bead conduit.

[0041] Figure 3 yes Figure 2The image shows a magnified view of a portion A of the cathode-gate cross-section. In this embodiment, the frequency of the input microwave is 915 MHz. The energy of the radio frequency standing wave electric field in the input cavity is mainly concentrated between cathode 1 and gate 2, achieving density-modulated emission of the electron beam.

[0042] In this invention, the electron beam emitted by the electron gun contains the fundamental frequency of the input frequency and numerous higher harmonic components, with the fundamental frequency component accounting for more than 60%. This invention's microwave-input high-frequency modulation grid-controlled electron gun abandons the traditional method of alternating voltage modulation used in density-emission electron guns, instead employing a microwave-input radio frequency standing wave electric field to modulate the emission of the electron beam, resulting in a simple structure that is easy to manufacture.

[0043] This invention relates to a microwave-input high-frequency modulated gate-controlled electron gun, which achieves microwave frequency alteration by changing the cavity length of the input cavity and the distance between the cathode 1 and the gate 2. Simultaneously, the input microwave energy and the negative high voltage of the cathode 1 can be varied. By altering the electron beam, the emission energy can reach the megawatt level.

[0044] Figure 4 yes Figure 2 The diagram shows the structure of the gate. In this embodiment, as shown... Figure 4 As shown, gate 2 adopts a strip gate structure, which ensures mechanical strength while reducing gate interception current. Specifically, the region of equal radius corresponding to cathode 1 adopts a strip structure, while the remaining supporting parts use a thicker all-metal plate to ensure the mechanical strength of the electron gun at high temperatures and improve the bombardment resistance of gate 2.

[0045] Figure 5 This is the input power, or microwave energy diagram, of the microwaves coupled into the input cavity by the coupling structure. For example... Figure 5 As shown, a 915MHz single-frequency microwave signal is input into the input cavity of the microwave input high-frequency modulation grid-controlled electron gun, with an input peak power of 5kW.

[0046] Figure 6 A voltage diagram of the radio frequency standing wave electric field established between the cathode and the gate. Figure 6 This demonstrates that when radio frequency (RF) energy is input into the electron gun, an RF standing wave electric field is established between the cathode and the grid. The amplitude of this RF standing wave electric field increases to a saturation point over time and then remains stable, limited by the power capacity of the input cavity. After reaching its maximum value, the amplitude of the RF standing wave electric field does not change over time under continuous microwave energy input.

[0047] Figure 7 This is the Fourier spectrum of the radio frequency voltage between the cathode and the gate. For example... Figure 7As shown, the Fourier spectrum of the radio frequency standing wave electric field established between the cathode and the gate contains only a single-frequency component of 915 MHz, which is the same as the input power.

[0048] Figure 8 It shows the waveforms of the gate trap current and the current through the anode hole. For example... Figure 8 As shown, the current emitted by the microwave-input high-frequency modulated gate-controlled electron gun varies with time. Under the conditions of an operating voltage of 65 kV, a gate bias voltage of 300V, and an input microwave power of 5 kW, it can emit a peak current of 23.5 A, and the peak power emitted by the electron gun is 1.5 MW. The gate interception current is 6 A, and the electron interception rate of the gate is 25%.

[0049] Figure 9 This is the Fourier spectrum of the high-frequency components of the current passing through the anode hole. For example... Figure 9 As shown, the Fourier spectrum of the electron beam current from the anode hole, after removing the DC component, is 0-2 GHz. The fundamental frequency component accounts for the highest proportion in the Fourier spectrum of the current. The frequency of the fundamental frequency component is the same as the input microwave frequency of 915 MHz, and only harmonics of the fundamental frequency exist; there are no difference frequency components. The spectrum of the electron beam current emitted by the microwave-input high-frequency modulated grid-controlled electron gun mainly contains the second harmonic component of the fundamental frequency component. Third and higher harmonic components are negligible, and the proportion of the fundamental frequency component is over 60%.

[0050] The microwave-input high-frequency modulation grating electron gun of this invention is applicable to P-band, L-band, and S-band. In this embodiment, a 915 MHz microwave-input high-frequency modulation grating electron gun is used for illustration and performance analysis.

[0051] Structurally, the microwave input high-frequency modulation gate-controlled electron gun and its variants based on the present invention include, but are not limited to: changes in the shape of the cathode and gate, changes in the coupling method of the input cavity, and changes in the shape of the insulating ceramic.

[0052] In terms of scheme optimization, the working mode optimization based on the present invention includes, but is not limited to: other working modes of the resonant cavity and the use of other types of resonant cavities.

[0053] In terms of material selection, an iron-cobalt-nickel alloy can be used as the metal cavity of the electron gun, a molybdenum-rhenium alloy can be used for the gate, and alumina ceramic can be used as the ceramic part of the electron gun. The protection range also includes: changing the metal or ceramic material.

[0054] In terms of processing, high-precision CNC milling, grinding and ceramic metallization welding are used, and the protection range also includes advanced processing and manufacturing technologies such as 3D printing, ion etching and photolithography.

[0055] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A microwave-input high-frequency modulated grid-controlled electron gun, comprising: The cathode and gate are characterized in that they further include: The cathode support cylinder is made of metal, with the cathode on its right end face, which closes the right end face of the cathode support cylinder. The gate support cylinder is made of metal, and its right end face is the gate. The outer edge of the gate is connected to the right end face of the gate support cylinder, thus sealing the right end face of the gate support cylinder. The gate support sleeve fits the cathode support sleeve from the right side. The cathode support sleeve and the gate support sleeve are coaxial. The distance between the cathode and the gate is determined by the transit time effect. The higher the operating frequency, the smaller the distance between the cathode and the gate. The grounding shell is a cylindrical structure made of metal material. Its right end face is closed with a circular metal plate. A circular electron injection conduit is installed in the center of the circular metal plate. The circular electron injection conduit passes through the center of the circular metal plate and communicates with the inside of the grounding shell. The circular electron injection conduit serves as the anode. The grounded housing fits the gate support cylinder from the right side. The gate support cylinder is coaxial with the grounded housing. The space between the anode and the gate is a DC acceleration space for electron beam. The gate support cylinder is fitted into the cathode support cylinder, and the grounding shell is fitted into the gate support cylinder, forming a double coaxial structure. The left ends of the grounding shell, the gate support cylinder, and the cathode support cylinder are sealed with metal ring plates to form the inner and outer cavities of the double coaxial structure. The inner cavity of the double coaxial structure is the space between the cathode support cylinder and the gate support cylinder, and its function is to obtain microwave energy from the coupling structure to establish a radio frequency standing wave electric field. The outer cavity is the space between the gate support cylinder and the grounding shell, and its function is to prevent electromagnetic leakage, prevent high-voltage arcs, and prevent the external electromagnetic environment from affecting the electron gun. Both the cathode support cylinder and the grid support cylinder are divided into two sections, connected by insulating ceramic in the middle to isolate DC voltage; The inner cavity of the dual coaxial structure serves as the input cavity. A coupling structure is installed on its left end face to couple microwaves into the input cavity. The length of the input cavity from left to right is one-quarter of the microwave wavelength. The microwave energy establishes a radio frequency standing wave electric field between the cathode and the grid. The amplitude of the radio frequency standing wave electric field is [value missing]. Apply negative high voltage to the cathode A negative high voltage is applied to the gate. ,and The cathode operates under space charge confinement, while the anode and the grounded casing are at ground voltage. Before the input microwaves establish the radio frequency standing wave electric field, the cathode emits a weak leakage current under the action of the grid and the anode. After the radio frequency standing wave electric field is established, the cathode emits an electron beam, i.e., an electron bead, under the combined action of the DC electric field and the radio frequency standing wave electric field within half a cycle of the radio frequency standing wave electric field. During the adjacent half cycle, the cathode is in the cutoff state, and the cathode conduction angle is 180 degrees. After the electron bead passes through the grid, it is accelerated under the DC voltage between the grid and the anode, and then output from the circular electron bead conduit.

2. The microwave input high-frequency modulation grid-controlled electron gun according to claim 1, characterized in that, The gate adopts a strip gate structure, the area with the same radius corresponding to the cathode adopts a strip structure, and the remaining support parts use a thicker all-metal plate.

3. The microwave input high-frequency modulation grid-controlled electron gun according to claim 1, characterized in that, The insulating ceramic on the gate support cylinder has a circular ring structure. The inner diameter edge divides the gate support cylinder into two equal sections for connection, and the outer diameter edge is welded to the inner wall of the grounded outer shell. There is also an insulating ceramic ring structure on the right edge of the gate support cylinder. The inner diameter edge is ceramic metallized and welded to the right edge of the gate support cylinder, and the outer diameter edge is welded to the inner wall of the grounded shell.

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