Miniaturized permanent magnet focusing system for cold cathode electron guns

Abstract

The application belongs to the technical field of vacuum electron devices, and relates to a magnetic focusing system, and particularly provides a miniaturized permanent magnetic focusing system of a cold cathode electron gun, to solve the problems of the oversized size, difficult heat dissipation, complex structure, and difficult processing of a traditional permanent magnetic system and an electromagnetic focusing system under the increasingly miniaturized trend of a terahertz band vacuum electron device. The permanent magnetic focusing system is designed by using a magnetic material, the peak strength of the magnetic field in the electron channel is ensured by a main magnet, the magnetic field strength on the surface of the frustum-shaped cold cathode carrier is enhanced by combining two pole shoes and a guide magnet, and the length of the uniform region of the magnetic field in the electron channel is prolonged, so that a long enough strong magnetic field region is ensured to meet the condition that the electron beam enters the collecting cavity after fully interacting with the high-frequency field. In summary, the application provides the miniaturized permanent magnetic focusing system of the cold cathode electron gun, which has the advantages of compact structure, stable performance, easy assembly, low cost, and the like, and is beneficial to batch processing and manufacturing.

Description

Technical Field

[0001] This invention belongs to the field of vacuum electronic device technology, and relates to magnetic focusing systems, specifically providing a miniaturized permanent magnet focusing system for a cold cathode electron gun. Background Technology

[0002] Terahertz waves refer to electromagnetic waves with frequencies ranging from 0.1 THz to 10 THz, corresponding to wavelengths from 3 mm to 30 μm. Located in the transition region between microwaves and infrared light in the electromagnetic spectrum, this band was long referred to as the "terahertz gap" due to the lack of effective generation and detection technologies. In recent years, with the development of ultrafast laser technology and vacuum electronics technology, the research and application of terahertz technology have developed rapidly. The extended interaction oscillator (EDO) is a terahertz source based on the principles of vacuum electronics. It achieves the excitation and amplification of electromagnetic waves through the interaction between the electron beam and the standing waves in a multi-gap slow-wave structure. Compared with traditional microwave vacuum devices, the EDO has advantages such as high power, high efficiency, high reliability, low voltage, and miniaturization, making it a current research hotspot for terahertz radiation sources. With the continuous expansion of application scenarios, higher requirements are placed on the miniaturization, integration, and portability of terahertz EDOs. Correspondingly, its magnetic focusing system also needs miniaturization design and research. Therefore, in-depth research on the magnetic focusing system of terahertz EDO oscillators is particularly important.

[0003] Traditional thermionic electron guns, limited by their operating conditions and temperatures, are unsuitable for the miniaturization of vacuum electronic devices. The operating temperature of thermionic electron guns is generally above 1000℃, which is highly detrimental to device miniaturization. In contrast, cold cathode devices, with their room-temperature and instantaneous operation characteristics, are very suitable for application in the miniaturization of vacuum electronic devices. Among them, carbon nanotube cold cathodes, with their advantages of high emission current density, instantaneous operation, stability, and room-temperature operation, have considerable application prospects in high-power microwave and millimeter-wave vacuum electronic devices. The field emission theory of nanocold cathodes includes local electric field enhancement mechanisms, defect emission mechanisms, localized state band emission mechanisms, and surface adsorption state emission mechanisms. Nanocold cathodes have a hollow tubular structure. When placed in an electric field, the electric field strength experienced at their tip is significantly enhanced; this phenomenon is called local electric field enhancement. The strong surface electric field leads to a high initial electron velocity, making the trajectory difficult to control and causing the electron beam to easily bombard the anode. Strong magnetic beam focusing is needed to solve this technical challenge. In addition, for high-frequency vacuum electronic devices based on cold cathodes, due to their high operating frequency and relatively small operating current, their high-frequency structure will also become longer. At this time, a sufficiently long uniform magnetic field region is needed to satisfy the wave-beam interaction and realize effective radiation to generate millimeter-wave terahertz signals.

[0004] For the electron beam emitted from the cathode of the electron gun, the electrons repel each other due to the same charge (negative charge) and the electrons themselves also have a small lateral velocity. Therefore, without any control, the electron beam will quickly diverge and thicken as it moves forward, eventually colliding with the tube wall of the device. Therefore, when the current generated by the electron gun interacts in the slow-wave structure, an additional magnetic field needs to be applied to focus it and prevent the electrons from diverging and being intercepted by the inner wall, etc. After the magnetic field is introduced, when charged particles (such as electrons) move in the magnetic field, the magnetic field will exert a "lateral force (Lorentz force)" on them, the direction of which is always perpendicular to the direction of electron movement. As a result, when electrons try to escape the axis laterally, they will be subjected to a continuous force that pulls them back to the central axis, so that the electron beam does not fly in a straight line, but moves in a tight spiral motion along the direction of the magnetic field lines.

[0005] A permanent magnet focusing system can be seen as a permanent, self-sustaining provider of the aforementioned invisible magnetic conduit. Utilizing the inherent magnetism of high-performance permanent magnet materials (specifically including AlNiCo, NdFeB, SMA, ferrite permanent magnet materials, etc.), it continuously generates a stable and powerful axial magnetic field without any external power supply. The significant advantage of a permanent magnet focusing system compared to an electromagnetic focusing system is that it eliminates the need for an external excitation power supply and cooling device, thereby greatly reducing system complexity and energy consumption, while also possessing higher reliability and stability, and generating a permanent and uniform magnetic field. However, its inherent disadvantage is that because the magnetic field strength decays rapidly with axial distance, obtaining a longer and more uniform strong magnetic field region often requires a significant increase in the size and weight of the permanent magnet, leading to a bulky system and increased cost, which is particularly prominent in applications with limited space or requiring compact designs. Therefore, this invention proposes a miniaturized permanent magnet focusing system for a cold cathode electron gun by introducing pole shoes and guide magnets, extending the length of the uniform magnetic field region and enhancing the peak magnetic field strength while maintaining a small permanent magnet focusing system size. Summary of the Invention

[0006] The purpose of this invention is to provide a miniaturized permanent magnet focusing system for a cold cathode electron gun, addressing the problems of excessive size, heat dissipation difficulties, complex structure, and difficult fabrication inherent in traditional magnetic focusing systems in the context of the increasing miniaturization trend of vacuum electronic devices in the terahertz band. This invention utilizes two main magnets, two guiding magnets, and two pole shoes to ensure a higher magnetic field strength in the initial section of the electron beam channel and significantly increases the length of the magnetic field uniformity region, ensuring that cold cathode field emission electrons are not intercepted by the anode and the inner wall of the channel. Compared to the traditional two main magnets, the peak magnetic field strength can be increased by more than 100%, the length of the magnetic field uniformity region is increased by more than 75%, and the magnetic field peak is located on the surface of the cold cathode, ensuring strong focusing of field emission electrons.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A miniaturized permanent magnet focusing system for a cold cathode electron gun is characterized by comprising a cathode region 1, a focusing region 2, and a collecting region 3 connected sequentially to form an internally sealed structure; wherein:

[0009] The cathode region includes: a cylindrical guiding magnet 1-1 and a cathode pole piece 1-2, with a cold cathode disposed at the top of the cathode pole piece 1-2, and the cylindrical guiding magnet disposed on the back of the cathode pole piece and located directly below the cold cathode.

[0010] The focusing area includes: an integrated electronic channel 2-1, an annular anode 2-2 and a main magnet 2-3. The annular anode is welded into the integrated electronic channel, and the main magnet 2-3 is arranged around the outer wall of the electronic channel.

[0011] The collection area includes: an annular pole piece 3-1, an annular guide magnet 3-2, and a collection cavity 3-3. The annular guide magnet is stacked on the annular pole piece, and the annular pole piece is correspondingly disposed at the end of the integrated electronic channel. The electronic channel of the collection cavity passes through the central hole of the annular guide magnet and the annular pole piece and is inserted into the integrated electronic channel.

[0012] Furthermore, the cathode shoe 1-2 adopts an irregular structure, including: a disc-shaped main body, an annular lower limiting protrusion, and a frustum-shaped cold cathode platform. The annular limiting protrusion and the frustum-shaped cold cathode platform are respectively disposed on the front and back sides of the disc-shaped main body, and both are located at the center position. The cylindrical guiding magnet 1-1 is disposed in the annular limiting protrusion of the cathode shoe 1-2 and is magnetically attracted to the back side of the disc-shaped main body. A cold cathode is disposed on the bottom surface of the frustum-shaped cold cathode platform.

[0013] Furthermore, the integrated electronic channel 2-1 consists of an electronic channel, a lower chassis, and an upper chassis. The electronic channel is vertically positioned between the lower chassis and the upper chassis and is located at the center of the lower chassis and the upper chassis. The main magnet adopts a semi-circular ring structure, and two main magnets are engaged and positioned between the lower chassis and the upper chassis, surrounding the outer wall of the electronic channel.

[0014] Furthermore, the two main magnets are fixed by an annular fixing device 2-4, which is a circular ring structure and is fitted around the outer ends of the two main magnets for fixation.

[0015] Furthermore, the upper chassis of the integrated electronic channel is provided with annular upper limit protrusions corresponding to the annular guide magnet and the annular pole shoe, so that the annular guide magnet and the annular pole shoe are overlapped in the annular upper limit protrusions.

[0016] Furthermore, the integrated electronic channel has rectangular output ports 2-5, and the main magnet has a window corresponding to the rectangular output port.

[0017] Furthermore, the cathode shoe is sealed and welded to the focusing area via the cathode ceramic ring 1-3, and the collection chamber is sealed and welded to the focusing area via the collection ceramic ring 3-4.

[0018] Furthermore, the cathode shoe, integrated electron channel, and collection chamber together constitute the internal vacuum structure.

[0019] Furthermore, during operation, the cathode shoe is connected to a negative high voltage, and the electron channel is grounded; electrons are emitted through the cathode area and enter the integrated electron channel in the focusing area, where they are focused by the longitudinal magnetic field and finally enter the collection area and are received by the collection cavity.

[0020] Based on the above technical solution, the beneficial effects of the present invention are as follows:

[0021] This invention provides a miniaturized permanent magnet focusing system for terahertz cold cathodes. During operation, the cathode region is responsible for emitting electrons. Through the guiding magnet and pole shoes, a strong magnetic field is formed at the emitting end to strongly focus the newly emitted electrons, allowing them to pass smoothly through the anode. After entering the focusing region, the electrons are kept in a relatively compact state within the channel by the main magnet, preventing them from being intercepted by the inner wall. At the same time, due to the action of the pole shoes and guiding magnet at both ends, the length of the uniform magnetic field region is effectively extended, allowing the electron beam to fully interact and exchange energy with the high-frequency field over a longer region before smoothly passing through the electron channel into the collecting cavity without premature divergence. As the magnetic field strength in the collecting cavity decreases, the electrons are eventually intercepted by the inner wall of the collecting cavity.

[0022] In the aforementioned terahertz miniaturized permanent magnet focusing system for cold cathodes, firstly, the longitudinal electric field within the channel is optimized using four permanent magnets and two pole shoes of different shapes, extending the longitudinal length of the uniform magnetic field region within the channel. Particularly noteworthy is the frustum-shaped cathode pole shoes, which concentrate the magnetic field at the apex of the frustum, significantly enhancing the magnetic field strength at the upper surface of the frustum. Through the design of the cathode pole shoes, the magnetic field strength on the surface of the cathode frustum can reach 1.8T. Furthermore, due to the small size of the nano-cold cathode, its height typically does not exceed 1mm. The high-intensity magnetic field on the surface of the cathode frustum has a very good effect on focusing the current of the nano-cold cathode. Simultaneously, the design of the annular pole shoes and annular guiding magnet in the collection area, while reserving an electron channel, further extends the length of the uniform magnetic field region. Specific details can be obtained through… Figure 3 and Figure 4The comparison shows that the peak magnetic field strength increased from 0.89T to 1.8T, and the length of the uniform magnetic field region (magnetic field strength ±5% at the center of the main magnetic field) increased from 12mm to 21mm. Furthermore, the magnetic field strength at the front end of the channel is always higher than 0.85T, making full use of the space at the front end of the channel. Compared with electromagnetic focusing systems and traditional permanent magnet focusing systems, the permanent magnet focusing system proposed in this invention has the characteristics of miniaturization, no heat source, stable performance and simple assembly. It also significantly enhances the magnetic field strength at the nano cold cathode emission point, making it very suitable for electron beam focusing in terahertz vacuum electronic devices.

[0023] In summary, this invention provides a miniaturized permanent magnet focusing system for a cold cathode electron gun, which has the advantages of compact structure, stable performance, easy assembly, and low cost, and is conducive to mass production. Attached Figure Description

[0024] Figure 1 This is a cross-sectional schematic diagram of the miniaturized permanent magnet focusing system of the cold cathode electron gun in this invention.

[0025] Wherein: 1 is the cathode region, 1-1 is the cylindrical guiding magnet, 1-2 is the cathode pole piece, and 1-3 is the cathode region ceramic ring; 2 is the focusing region, 2-1 is the integrated electronic channel, 2-2 is the anode inside the channel, 2-3 is the main magnet, 2-4 is the annular fixing device, and 2-5 is the rectangular output port; 3 is the collection region, 3-1 is the annular pole piece, 3-2 is the annular guiding magnet, 3-3 is the collection cavity, and 3-4 is the collection region ceramic ring.

[0026] Figure 2 This is a three-dimensional structural diagram of the miniaturized permanent magnet focusing system of the cold cathode electron gun in this invention.

[0027] Figure 3 This is a graph showing the magnetic field strength curve on the central axis of the miniaturized permanent magnet focusing system of the cold cathode electron gun in this invention.

[0028] Figure 4 This is a graph showing the magnetic field strength along the central axis when only the main magnet is retained in this invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and technical effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0030] This embodiment provides a miniaturized permanent magnet focusing system for a cold cathode electron gun, the structure of which is as follows: Figure 1 , Figure 2As shown, it specifically consists of a cathode region 1, a focusing region 2, and a collecting region 3. The cathode region 1 includes a cylindrical guiding magnet 1-1, a cathode pole piece 1-2, and a cathode ceramic ring 1-3. The focusing region 2 includes an integrated electron channel 2-1, an annular anode 2-2, a main magnet 2-3, an annular fixing device 2-4, and a rectangular output port 2-5. The collecting region 3 includes an annular pole piece 3-1, an annular guiding magnet 3-2, a collecting ceramic ring 3-4, and a collecting cavity 3-3. The cathode region 1, the integrated electron channel 2-1, and the collecting region 3 are sequentially sealed by welding to form an internal sealed structure, which is in a vacuum environment. Electrons are emitted from the cathode region 1 and enter the integrated electron channel 2-1 of the focusing region 2. They are focused by the longitudinal magnetic field inside the channel and finally enter the collecting electrode 3, where they are received by the inner wall of the collecting cavity 3-3.

[0031] Specifically:

[0032] In the cathode region 1, the cathode shoe 1-2 adopts an irregular structure, specifically composed of a disc-shaped main body, an annular lower limiting protrusion, and a frustum-shaped cold cathode platform. The annular limiting protrusion and the frustum-shaped cold cathode platform are respectively located on the front and back of the disc-shaped main body, and both are located at the center. The cylindrical guiding magnet 1-1 is located in the annular limiting protrusion of the cathode shoe 1-2 and is magnetically attracted to the back of the disc-shaped main body. The bottom surface of the frustum-shaped cold cathode platform is the top of the cathode shoe 1-2, where the cold cathode is placed. Due to the magnetic field gathering effect of the shoe, there will be a high-intensity magnetic field on the top surface of the shoe. When electrons are emitted from the cold cathode, they will be focused by the strong magnetic field. The cathode region ceramic ring 1-3 has a ring structure. The disc-shaped main body of the cathode shoe 1-2 is sealed and welded to the focusing region 2 through the cathode region ceramic ring, thereby connecting the cathode region 1 and the focusing region 2.

[0033] In the focusing area 2, the integrated electronic channel 2-1 consists of an electronic channel, a lower chassis, and an upper chassis. The electronic channel is vertically positioned between the lower and upper chassis and is located at the center of the two chassis. The annular anode 2-2 is welded into the electronic channel of the integrated electronic channel 2-1. The main magnet 2-3 adopts a semi-circular ring structure. Two main magnets are engaged between the lower and upper chassis, surrounding the outer wall of the electronic channel, and the two main magnets are fixed by an annular fixing device 2-4. The annular fixing device is a circular ring structure and is fitted around the outer ends of the two main magnets for fixation. The rectangular output port 2-5 is opened at a preset position in the electronic channel, and correspondingly, the main magnets have windows.

[0034] In the collection area 3, an annular guide magnet 3-2 is stacked on an annular pole piece 3-1, which is mounted on the upper chassis of the integrated electronic channel 2-1. A circular upper limit protrusion is provided on the upper chassis of the integrated electronic channel 2-1 corresponding to the annular guide magnet 3-2 and the annular pole piece 3-1. The electronic channel of the collection cavity 3-3 passes through the central hole of the annular guide magnet 3-2 and the annular pole piece 3-1 and is inserted into the electronic channel of the integrated electronic channel 2-1. The collection cavity 3-3 is sealed and welded to the focusing area 2 via a ceramic ring 3-4, thereby connecting the collection area 3 and the focusing area 2.

[0035] Furthermore, in this embodiment, the cylindrical guiding magnet 1-1 has a bottom radius of 5mm and a thickness of 10mm; the cathode shoe 1-2 is divided into three parts: the middle disk has a radius of 30mm and a thickness of 2mm; the lower annular protrusion has a thickness of 5mm, an outer radius of 10mm, and an inner radius of 5.1mm; the upper end is a frustum structure with a lower radius of 3mm, an upper radius of 0.5mm, and a height of 6mm; the ceramic ring has an outer radius of 30mm, an inner radius of 25mm, and a thickness of 4mm.

[0036] Furthermore, in this embodiment, the integrated electronic channel 2-1 has an inner radius of 5mm, a channel length of 35mm (excluding the thickness of the upper and lower chassis), and an outer radius of 6mm; the upper and lower chassis both have an outer radius of 30mm, an inner radius of 5mm, and a thickness of 2mm; the annular protrusion on the upper chassis has an outer radius of 20mm, an inner radius of 15.1mm, and a protrusion thickness of 8mm; a rectangular output port 2-5 with a length of 2.54mm and a width of 1.27mm is reserved inside the channel; the rectangular output port is spaced from... The distance from the lower chassis surface is 30mm; the outer radius of anode 2-2 is 5mm and the inner radius is 1mm, and it is welded to the electronic channel. In this embodiment, the vertical distance from the lower surface of the anode to the lowest horizontal plane of the chassis is 4mm; the main magnet 2-3 is a semi-circular hollow cylinder with an outer radius of 50mm, an inner radius of 6.1mm, and a thickness of 35mm. The two main magnets 2-3 are respectively embedded in the middle of the upper and lower chassis of the integrated electronic channel 2-1, and then the annular fixing device 2-4 is fitted around the two main magnets, such as... Figure 1 and Figure 2 As shown, the ring-shaped fixing device has a thickness of 10mm, an outer radius of 60mm, and an inner radius of 50.1mm.

[0037] Furthermore, in this embodiment, the annular pole shoe 3-1 has an outer radius of 15mm, an inner radius of 3mm, and a thickness of 3mm; the annular guiding magnet 3-2 has a thickness of 7mm, an outer radius of 15mm, and an inner radius of 3mm; the collecting cavity 3-3 is divided into two parts, one being an electron channel and the other a cylindrical collecting cavity. The electron channel has a length of 12mm, an outer radius of 3mm, and an inner radius of 2mm. The cylindrical collecting cavity has a total length of 25mm and an internal frustum-shaped groove. The lower surface of the frustum (near the electron channel end) has a radius of 2mm, the upper surface radius is 27mm, and the groove depth is 20mm. Figure 1 As shown; the outer radius of the ceramic ring 3-4 in the collection area is 30mm, the inner radius is 25mm, and the thickness is 10mm.

[0038] Furthermore, in this embodiment, the magnets used are all magnetic materials (specifically including AlNiCo, NdFeB, SMAFeNi, ferrite permanent magnets, etc.), and the pole piece material is pure iron with a purity greater than 99%. The curves showing the variation of magnetic field lines and magnetic field strength in the system channel with the distance from the cathode pole pieces 1-4 are as follows: Figure 3 As shown in the figure, the main magnet and the guiding magnet create a strong uniform region inside the electron channel. In the uniform region, the magnetic field strength is maintained at a considerable level, and the electron beam always moves towards the collection area in a relatively compact state within the channel.

[0039] Furthermore, for the rectangular output port reserved in the integrated electronic channel and main magnet, different types of signal receivers need to be installed and sealed according to actual needs. In this embodiment, it is assumed that this rectangular output port has been connected to the receiver and is well sealed. Cold cathodes of different shapes and sizes can be welded to the upper surface of the cone on the cathode shoe. The upper radius of the cone can also be adjusted according to the shape and size of the cathode. In this embodiment, the cold cathode at the upper part of the cone is not shown. The focus is on the magnetic field performance of this permanent magnet focusing system.

[0040] Furthermore, the various parts of the permanent magnet system are welded together to form a whole using microwave vacuum device technology, and vacuum exhaust is performed to create an absolute vacuum environment inside the entire device. During operation, the cathode chassis is connected to a negative voltage, and since the anode is connected inside the integrated electronic channel, the integrated electronic channel is grounded.

[0041] In addition, an external cooling device is added to the entire system to maintain the normal temperature of the entire system. Common cooling methods include water cooling, oil cooling, and air cooling. Among them, water cooling is a relatively simple cooling method. It is relatively easy to operate and does not affect the installation of the system. At the same time, it achieves a good cooling effect and maintains the normal operation of the system.

[0042] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A miniaturized permanent magnet focusing system for a cold cathode electron gun, characterized in that, It is composed of a cathode region (1), a focusing region (2), and a collecting region (3) connected in sequence, forming an internal sealed structure; wherein: The cathode region includes: a cylindrical guiding magnet (1-1) and a cathode pole piece (1-2), with a cold cathode disposed at the top of the cathode pole piece (1-2) and the cylindrical guiding magnet disposed on the back of the cathode pole piece and located directly below the cold cathode; The focusing area includes: an integrated electronic channel (2-1), an annular anode (2-2), and a main magnet (2-3). The annular anode is welded inside the integrated electronic channel, and the main magnet (2-3) is arranged around the outer wall of the electronic channel. The collection area includes: an annular pole piece (3-1), an annular guide magnet (3-2), and a collection cavity (3-3). The annular guide magnet is stacked on the annular pole piece, and the annular pole piece is correspondingly disposed at the end of the integrated electronic channel. The electronic channel of the collection cavity passes through the central hole of the annular guide magnet and the annular pole piece and is inserted into the integrated electronic channel.

2. The miniaturized permanent magnet focusing system of the cold cathode electron gun according to claim 1, characterized in that, The cathode shoe (1-2) adopts an irregular structure, including: a disc-shaped main body, an annular lower limiting protrusion, and a frustum-shaped cold cathode stage. The annular limiting protrusion and the frustum-shaped cold cathode stage are respectively located on the front and back of the disc-shaped main body, and both are located in the center position. A cylindrical guiding magnet is set in the annular limiting protrusion of the cathode shoe and is magnetically attracted to the back of the disc-shaped main body. The upper bottom surface of the frustum-shaped cold cathode stage serves as the top of the cathode shoe, where the cold cathode is set.

3. The miniaturized permanent magnet focusing system of the cold cathode electron gun according to claim 1, characterized in that, The integrated electronic channel (2-1) consists of an electronic channel, a lower chassis and an upper chassis. The electronic channel is vertically positioned between the lower chassis and the upper chassis and is located at the center of the lower chassis and the upper chassis. The main magnet adopts a semi-circular ring structure, and two main magnets are engaged between the lower chassis and the upper chassis, surrounding the outer wall of the electronic channel.

4. The miniaturized permanent magnet focusing system of the cold cathode electron gun according to claim 3, characterized in that, The two main magnets are fixed by a ring-shaped fixing device (2-4). The ring-shaped fixing device is a circular ring structure and is fitted around the outer ends of the two main magnets for fixation.

5. The miniaturized permanent magnet focusing system of the cold cathode electron gun according to claim 3, characterized in that, On the upper chassis of the integrated electronic channel, a circular upper limit protrusion is provided corresponding to the annular guide magnet and the annular pole shoe, so that the annular guide magnet and the annular pole shoe are overlapped in the circular upper limit protrusion.

6. The miniaturized permanent magnet focusing system of the cold cathode electron gun according to claim 1, characterized in that, The integrated electronic channel has a rectangular output port (2-5), and the main magnet has a window corresponding to the rectangular output port. The output window can be connected externally and then sealed.

7. The miniaturized permanent magnet focusing system of the cold cathode electron gun according to claim 1, characterized in that, The cathode shoe is sealed and welded to the focusing area via a cathode ceramic ring (1-3), and the collection chamber is sealed and welded to the focusing area via a collection ceramic ring (3-4).

8. The miniaturized permanent magnet focusing system of the cold cathode electron gun according to claim 1, characterized in that, The cathode shoe, integrated electron channel, and collection chamber together constitute the internal vacuum structure.

9. The miniaturized permanent magnet focusing system of the cold cathode electron gun according to claim 1, characterized in that, During operation, the cathode shoe is connected to a negative high voltage, and the electron channel is grounded. Electrons are emitted through the cathode area and enter the integrated electron channel in the focusing area. They are focused by the longitudinal magnetic field in the electron channel and finally enter the collection area and are received by the collection cavity.

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