Multi-channel pole piece, multi-channel periodic permanent magnet focusing system and design method

Abstract

The application provides a multi-channel pole shoe, a multi-channel periodic permanent magnet focusing system and a design method. The multi-channel pole shoe comprises a pole shoe head and a pole shoe ring surface surrounding the outside of the pole shoe head, and the pole shoe head and the pole shoe ring surface are coaxially arranged. A plurality of pole shoe through holes are formed on the pole shoe head and arranged along the circumference of the pole shoe head. The pole shoe through hole comprises an assembly channel in a rectangular structure for assembling a slow wave structure and two grooves respectively outwardly extending from two opposite edge sides of the assembly channel along the radial direction of the pole shoe head. The extension direction of the assembly channel is perpendicular to the extension direction of the groove. In the extension direction of the assembly channel, the length of the assembly channel is greater than the length of the groove. The multi-channel pole shoe can improve the axial magnetic field strength on the channel axis and reduce the angular magnetic field strength, thereby effectively improving the confinement ability of the magnetic focusing system to the electron beam.

Description

Technical Field

[0001] This invention relates to the field of microwave vacuum electronics technology. More specifically, it relates to a multi-channel pole piece, a multi-channel periodic permanent magnet focusing system, and its design method. Background Technology

[0002] A traveling wave tube (TWT) is a vacuum amplification device, serving as the final power amplifier stage in radar systems, and its application in numerous weapon systems has been clearly defined. The focusing system is one of the core components of a TWT, its function being to constrain the radial divergence of the electron beam, allowing it to propagate stably along the axial direction. The periodic permanent magnet focusing system is one of the commonly used focusing systems in TWTs. Its principle is to constrain the electron beam by the Lorentz force received by the electron beam in a periodically changing magnetic field. The constraining ability of the focusing system is positively correlated with the axial magnetic field strength within the electron beam channel and negatively correlated with the angular magnetic field strength.

[0003] By integrating multiple RF amplification channels into a single traveling wave tube (TWT) and sharing a single focusing system to form an array integration, the cross-sectional size of individual channels can be effectively reduced, adapting to the application requirements of arrayed systems, such as active phased arrays. Existing array arrangements involve circular amplification channels arranged in a ring along the angular direction on a cross-section perpendicular to the TWT axis. In this case, for a periodic permanent magnet focusing system, the inner diameter of the magnet needs to be larger than the outer edge of the amplification channel, leading to an increase in the magnet's inner diameter and a decrease in magnetic field strength, thus reducing the constraint on the electron beam. Furthermore, for multi-channel periodic permanent magnet focusing systems with channels arranged in a ring centered on the system axis, the amplification channels deviate from the system axis, generating angular field components within the amplification channels, further reducing the constraint on the electron beam. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a multi-channel pole shoe that can increase the axial magnetic field strength along the channel axis while reducing the angular magnetic field strength, thereby effectively improving the magnetic focusing system's ability to constrain the electron beam.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a multi-channel pole shoe, comprising:

[0007] The pole shoe head and the pole shoe annular surface surrounding the outside of the pole shoe head are coaxially arranged; the pole shoe head has a plurality of pole shoe through holes arranged circumferentially along the pole shoe head.

[0008] The pole shoe through-hole includes a rectangular assembly channel for assembling the slow wave structure and two channels formed by extending outward from two opposite sides of the assembly channel along the radial direction of the pole shoe head; the extension direction of the assembly channel is perpendicular to the extension direction of the channels; in the extension direction of the assembly channel, the length of the assembly channel is greater than the length of the channels.

[0009] The preferred arrangement is that the two channels are symmetrically arranged about the assembly channel.

[0010] A preferred embodiment is that the assembly channel includes a central channel and two side channels located on opposite sides of the central channel along the extension direction of the assembly channel; the two channels are respectively located on opposite sides of the central channel along the radial direction of the pole shoe head.

[0011] The preferred embodiment is that the two side channels are symmetrically arranged about the middle channel; the side channels and the channel have the same structural dimensions.

[0012] A preferred embodiment is that the cross-section of the central channel is square, and the width of the side channels along the radial direction of the pole shoe head is equal to the side length of the central channel.

[0013] The preferred embodiment is that the radius corresponding to the pole shoe annular surface is r1, and the distance between the center of the assembly channel and the center of the pole shoe head is r3; 0 < r3 < r1;

[0014] The assembly channel has a length of a2 and a width of b2; the length and width of the assembly channel satisfy the following relationships: 0 < b2 < 2r3, 0 < a2 < 2r1, and

[0015] A preferred embodiment is that the channel includes an inner channel near the center of the pole shoe head and an outer channel away from the center of the pole shoe head; the length of the inner channel is a3 and the width is b3, and the length and width of the inner channel satisfy the following relationship: 0 < a3 <a2,

[0016] The length of the outer channel is a1, and the width is b1. The length and width of the outer channel satisfy the following relationship: 0 < a1 <a2,

[0017] The present invention also provides a multi-channel periodic permanent magnet focusing system, comprising the multi-channel pole shoes and magnets as described above; a plurality of multi-channel pole shoes and a plurality of magnets are periodically alternately arranged along the axial direction of the multi-channel pole shoes; the magnetic field directions of adjacent magnets are opposite.

[0018] This invention also provides a design method for a multi-channel periodic permanent magnet focusing system, comprising the following steps:

[0019] Several pole shoes and several magnets are periodically and alternately arranged along the axial direction of the magnetic focusing system;

[0020] The pole shoe includes a pole shoe head and a pole shoe annular surface surrounding the outside of the pole shoe head, with the pole shoe head and the pole shoe annular surface being coaxially arranged.

[0021] A plurality of pole shoe through holes are designed on the pole shoe head, arranged circumferentially along the pole shoe head. The pole shoe through holes include a rectangular assembly channel for assembling the slow wave structure and two channels formed by extending outward from the two opposite sides of the assembly channel along the radial direction of the pole shoe head. The extension direction of the assembly channel is perpendicular to the extension direction of the channel. In the extension direction of the assembly channel, the length of the assembly channel is greater than the length of the channel.

[0022] A preferred embodiment is that the channel includes an inner channel close to the center of the pole shoe head and an outer channel far from the center of the pole shoe head; the magnetic field distribution of the magnetic focusing system can be adjusted by adjusting the length and width of the outer channel and the length and width of the inner channel.

[0023] The beneficial effects of this invention are as follows:

[0024] This invention, through the coordination of assembly channels and slots, solves the problem in existing multi-channel periodic permanent magnet focusing systems where angular field components are generated in the amplification channel due to the deviation of the amplification channel from the magnetic focusing system axis, reducing the constraint capability of the electron beam. It effectively increases the axial magnetic field strength within the through-hole while significantly reducing the angular magnetic field strength, resulting in better electron beam focusing performance. Furthermore, this invention allows adjustment of the focusing magnetic field distribution by changing the size of the two slots, ensuring the uniformity of the focusing magnetic field. Compared to periodic permanent magnet focusing systems based on traditional circular inner-hole pole shoe structures, the shape of the pole shoe through-hole is more suitable for rectangular cross-section slow-wave structures, and the through-hole opening area is smaller, improving the utilization rate of the pole shoe through-hole cross-section and further enhancing the focusing magnetic field strength. The traveling wave tube of the multi-channel periodic permanent magnet focusing system using this invention can integrate multiple RF amplification channels, achieving an arrayed arrangement of multiple slow-wave structures, and can be widely used in next-generation mobile communication, radar, and other equipment. Attached Figure Description

[0025] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0026] Figure 1 This is a schematic diagram of the cross-section of an existing rectangular outer boundary folded waveguide slow wave structure.

[0027] Figure 2 This is a schematic diagram of an existing four-channel periodic permanent magnet focusing system based on a circular channel pole shoe structure.

[0028] Figure 3 This is a schematic diagram of the structure of the four-channel periodic permanent magnet focusing system of the present invention.

[0029] Figure 4 This is one of the cross-sectional schematic diagrams of the four-channel periodic permanent magnet focusing system of the present invention.

[0030] Figure 5A This is the second cross-sectional schematic diagram of the four-channel periodic permanent magnet focusing system of the present invention.

[0031] Figure 5B yes Figure 5A A schematic diagram of the structure of the bottommost pole shoe through hole.

[0032] Figure 6 This is a BH characteristic curve of the pole shoe material during the simulation process of this invention.

[0033] Figure 7 This is a comparison diagram of the axial magnetic field strength on the channel axis of the existing four-channel periodic permanent magnet focusing system based on a circular channel pole shoe structure and the four-channel periodic permanent magnet focusing system of the present invention.

[0034] Figure 8 The diagrams show the angular magnetic field intensity distribution at a distance d / 2 from the channel axis at different angular positions of the existing four-channel periodic permanent magnet focusing system based on a circular channel pole shoe structure and the four-channel periodic permanent magnet focusing system of the present invention. Detailed Implementation

[0035] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention.

[0036] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use.

[0037] Technologies and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such technologies and equipment should be considered part of the specification.

[0038] In all the examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0039] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0040] The amplification channel in a periodic permanent magnet focusing system typically has a circular cross-sectional shape. This circular cross-section structure is compatible with traditional helical slow-wave structures, which also have a circular cross-section. However, for folded waveguides and staggered double-grid slow-wave structures with rectangular cross-sections, the circular channel results in an opening area larger than the actual cross-sectional size, wasting some area and thus reducing the focusing magnetic field strength. Furthermore, in existing multi-channel periodic permanent magnet focusing systems, because the axis of the circular amplification channel is not coaxial with the axis of the magnetic focusing system, angular field components are generated in the amplification channel, causing electron beam divergence and reducing the focusing system's ability to constrain the electron beam.

[0041] To address the problems existing in the prior art, this invention provides a multi-channel pole shoe, combined with... Figures 1 to 8 As shown, the multi-channel pole shoe specifically includes: a pole shoe head 1 and a pole shoe annular surface 2 surrounding the outside of the pole shoe head 1, with the pole shoe head 1 and the pole shoe annular surface 2 coaxially arranged. The pole shoe head 1 has a plurality of pole shoe through holes 3 arranged circumferentially along its surface. Each pole shoe through hole 3 includes a rectangular assembly channel 31 for assembling a slow-wave structure and two channels formed by the assembly channel 31 extending outward from two opposite sides radially along the pole shoe head 1; the extension direction of the assembly channel 31 is perpendicular to the extension direction of the channels; in the extension direction of the assembly channel, the length of the assembly channel 31 is greater than the length of the channels.

[0042] This invention, while ensuring multiple assembly channels, effectively increases the axial magnetic field strength within the pole shoe through-hole 3, while significantly reducing the angular magnetic field strength. This results in better electron beam focusing performance of the magnetic focusing system and effectively improves its ability to constrain the electron beam. It solves the problem in existing multi-channel periodic permanent magnet focusing systems where the axes of each amplification channel are not coaxial with the focusing system axis, leading to angular field components in the amplification channels, causing electron beam divergence and poor constraint of the electron beam by the magnetic focusing system.

[0043] In the millimeter-wave and terahertz bands, the electron beam channels of traveling wave tubes are typically small, resulting in stronger Coulomb forces between electrons. This places higher demands on the strength of the focusing magnetic field. Reducing the cross-sectional size of the circular channel in the pole shoe of the focusing system can effectively increase the strength of the focusing magnetic field. However, due to the physical size limitations of the slow-wave structure, the cross-sectional size of the circular amplification channel in existing magnetic focusing systems cannot be reduced indefinitely, limiting the increase in the focusing magnetic field strength. This invention improves the strength of the focusing magnetic field by rationally modifying the shape of the pole shoe through-hole in the focusing system, thereby increasing the utilization rate of the pole shoe through-hole cross-section. To accommodate the rectangular cross-section of the slow-wave structure, the cross-section of the assembly channel 31 is also set to rectangular, achieving compatibility with rectangular cross-section folded waveguides and staggered double-grid slow-wave structures, thus effectively reducing the opening area on the pole shoe and improving the cross-sectional utilization rate.

[0044] In the above embodiment, the assembly channel 31 and the groove are connected. The pole shoe through holes 3 are rotationally symmetrical about the center of the pole shoe head. That is, the pole shoe through holes 3 are evenly distributed on the same circle with the center of the pole shoe head 1 as the center, and all the pole shoe through holes 3 are evenly arranged around the circumference of the pole shoe head 1. The groove extends radially along the pole shoe head, and the assembly channel 31 extends in a direction perpendicular to the extension direction of the groove. That is, in the plane where the end face of the pole shoe head 1 is located, the groove extends radially along the pole shoe head, and the extension direction of the assembly channel 31 is perpendicular to the extension direction of the groove. For example, Figure 3 The uppermost pole shoe through hole has a horizontal extension direction for the assembly channel and a vertical extension direction for the slot. Figure 3 The leftmost pole shoe through hole has a vertical extension direction for the assembly channel and a horizontal extension direction for the slot.

[0045] To ensure the uniformity of the magnetic field, the two channels are symmetrically arranged about the assembly channel 31.

[0046] Combination Figure 5A and Figure 5B As shown, to further improve the uniformity of the magnetic field and facilitate processing, the assembly channel 31 includes a central channel 311 and two side channels 312 on opposite sides along the extension direction of the assembly channel 31. The two channels are located on opposite sides of the central channel 311 along the radial direction of the pole shoe head 1. The two side channels 312 are symmetrically arranged about the central channel 311, and have the same structural dimensions as the channels. The central channel 311 has a square cross-section, and the width of the side channels 312 along the radial direction of the pole shoe head is equal to the side length of the central channel 311. This arrangement simplifies and facilitates the processing, reducing processing difficulty.

[0047] More specifically, when the cross-section of the intermediate channel 311 is square, and a slow-wave structure with a square cross-section is assembled inside the pole shoe through-hole 3, the slow-wave structure is assembled inside the intermediate channel 311, and the four corners of the slow-wave structure are fixed at the intersection of the side channel 312 and the slot. In this case, the magnetic field distribution of the magnetic focusing system can be adjusted by adjusting the dimensions of the side channel 312 and the slot. When a slow-wave structure with a rectangular cross-section is assembled, the slow-wave structure is assembled inside the intermediate channel 311 and the side channel 312, and the four corners of the slow-wave structure are respectively fitted and fixed to the corners of the side channel 312. In this case, the magnetic field distribution of the magnetic focusing system can be adjusted by adjusting the dimensions of the slot. Compared with the existing circular inner hole, the cross-shaped pole shoe through-hole 3 of the present invention can better adapt to the rectangular cross-section of the folded waveguide and the staggered double-grid type slow-wave structure, which can effectively reduce the opening area, improve the utilization rate of the through-hole cross-section, and thus improve the focusing magnetic field strength and the confinement ability of the electron beam.

[0048] In one specific embodiment, the radius corresponding to the pole shoe annular surface 2 is r1, and the distance between the center of the assembly channel 31 and the center of the pole shoe head 1 is r3; 0 < r3 < r1; the length of the assembly channel 31 is a2, and the width is b2; the length and width of the assembly channel 31 satisfy the following relationship: 0 < b2 < 2r3, 0 < a2 < 2r1, and The above settings ensure that the assembly channel 31 and the groove are all located inside the pole shoe, avoiding discontinuities on the outer circle of the pole shoe annular surface 2.

[0049] Furthermore, the channel includes an inner channel 32 near the center of the pole shoe head 1 and an outer channel 33 away from the center of the pole shoe head 1. (Refer to...) Figure 5A As shown in the figure, the dashed lines are the boundary lines between the assembly channel 31 and the inner channel 32 and the outer channel 33. The assembly channel 31, the inner channel 32, and the outer channel 33 all have rectangular cross-sections. The inner channel 32 has a length of a3 and a width of b3, and the length and width of the inner channel 32 satisfy the following relationship: 0 < a3. <a2, The outer channel 33 has a length of a1 and a width of b1. The length and width of the outer channel 33 satisfy the following relationship: 0 < a1 <a2, The above settings ensure that the assembly channel 31 and the groove are all located inside the pole shoe, avoiding discontinuities on the outer circle of the pole shoe annular surface 2.

[0050] In the axial direction of the pole shoe, the thickness of the pole shoe head 1 is greater than or equal to the thickness of the pole shoe annular surface 2. Increasing the thickness of the pole shoe head 1 helps to reduce pole shoe saturation and improve magnetic field distribution. Furthermore, the step formed at the junction of the pole shoe head 1 and the pole shoe annular surface 2 is beneficial to the structural strength and airtightness during subsequent welding with the spacer ring.

[0051] This invention also provides a multi-channel periodic permanent magnet focusing system, comprising multi-channel pole shoes and magnets 4 as described above; a plurality of multi-channel pole shoes and a plurality of magnets 4 are periodically alternating along the axial direction of the multi-channel pole shoes. A slow-wave structure is inserted within a row of coaxially arranged pole shoe through-holes 3. This multi-channel periodic permanent magnet focusing system can increase the axial magnetic field strength along the channel axis while reducing the angular magnetic field strength, thereby effectively improving the confinement capability of the electron beam. More specifically, the magnetic field directions of two adjacent magnets 4 are opposite, the magnets 4 are in a ring structure, and the multi-channel pole shoes and magnets 4 are coaxially arranged.

[0052] Reference Figure 1 As shown, a0 is the wide side of the waveguide outer boundary, b0 is the narrow side of the waveguide outer boundary, and d0 is the diameter of the electron beam channel. Its specific structural dimensions are as follows (unit: mm): a0 = 1.980, b0 = 1.270, d0 = 0.240.

[0053] Reference Figure 4and Figure 5A The diagram shown is a cross-sectional schematic of a four-channel periodic permanent magnet focusing system provided by the present invention. The radius corresponding to the pole shoe annulus is r1, the distance between the center of the assembly channel and the center of the pole shoe head is r3, the radius corresponding to the pole shoe head is r2, L1 is the thickness of the pole shoe annulus, and L2 is the thickness of the pole shoe head; the length of the outer channel is a1, and the width is b1; the length of the assembly channel is a2, and the width is b2; the length of the inner channel is a3, and the width is b3; R1 is the outer radius of the magnet, R2 is the inner radius of the magnet, L is the thickness of the magnet, and p / 2 is the half-cycle length of the magnetic field transformation, p / 2 = L1 + L. Figure 6 The figure shows the BH characteristic curve of the pole shoe material during the simulation process, with the remanence Br of the magnet set to 10000 Gs.

[0054] The specific structural dimensions of a four-channel periodic permanent magnet focusing system of the present invention are as follows (unit: mm): r1 = 6.900, r2 = 4.400, r3 = 2.500, a1 = 1.270, a2 = 1.980, a3 = 1.270, b1 = 1.006, b2 = 1.270, b3 = 0.934, L1 = 0.900, L2 = 1.200, R1 = 8.000, R2 = 5.000, L = 2.000, p = 2.900.

[0055] Reference Figure 2 As shown, 1 is the pole shoe head, 2 is the pole shoe annular surface, 4 is the magnet, and 5 is the circular through hole. This comparative four-channel periodic permanent magnet focusing system based on a circular channel pole shoe structure is identical to the four-channel periodic permanent magnet focusing system provided by this invention, except that the cross-sectional shape of the through hole is circular and the radius of the circular through hole is 1.176 mm.

[0056] Reference Figure 7 As shown, the peak value of the axial magnetic field strength on the amplification channel axis of the four-channel periodic permanent magnet focusing system based on the circular channel pole shoe structure is 3129 Gs. The peak value of the axial magnetic field strength on the amplification channel axis of the four-channel periodic permanent magnet focusing system provided by the present invention is 3454 Gs, which is 10.4% higher than that of the four-channel periodic permanent magnet focusing system based on the circular channel pole shoe structure.

[0057] Reference Figure 8 As shown, the peak value of the angular magnetic field strength of the amplified channel in the four-channel periodic permanent magnet focusing system based on the circular channel pole shoe structure is 60.29 Gs, while the peak value of the angular magnetic field strength of the amplified channel in the four-channel periodic permanent magnet focusing system provided by the present invention is 1.61 Gs, which is 97.3% lower than that of the four-channel periodic permanent magnet focusing system based on the circular channel pole shoe structure.

[0058] This invention also provides a design method for a multi-channel periodic permanent magnet focusing system, specifically including the following steps: periodically and alternately assembling a plurality of pole shoes and a plurality of magnets along the axial direction of the magnetic focusing system; the pole shoe includes a pole shoe head 1 and a pole shoe annular surface 2 surrounding the outside of the pole shoe head 1, the pole shoe head 1 and the pole shoe annular surface 2 being coaxially arranged; a plurality of pole shoe through holes 3 arranged circumferentially on the pole shoe head 1 are designed, the pole shoe through holes 3 including a rectangular assembly channel 31 for assembling a slow wave structure and two channels formed by the assembly channel 31 extending outward from two opposite sides of the pole shoe head 1 radially; the extension direction of the assembly channel 31 is perpendicular to the extension direction of the channel; in the extension direction of the assembly channel, the length of the assembly channel 31 is greater than the length of the channel.

[0059] Furthermore, the channel includes an inner channel 32 near the center of the pole shoe head 1 and an outer channel 33 away from the center of the pole shoe head 1; by adjusting the length a1 and width b1 of the outer channel 33 and the length a3 and width b3 of the inner channel 32, the magnetic field distribution state of the magnetic focusing system is adjusted.

[0060] In summary, this invention, through the coordination of assembly channels and slots, solves the problem in existing multi-channel periodic permanent magnet focusing systems where angular field components are generated in the amplification channel due to the deviation of the amplification channel from the magnetic focusing system axis, reducing the constraint capability of the electron beam. It effectively enhances the axial magnetic field strength within the through-hole while significantly reducing the angular magnetic field strength, resulting in better electron beam focusing performance. Furthermore, this invention allows adjustment of the focusing magnetic field distribution by changing the size of the two slots, ensuring the uniformity of the focusing magnetic field. Compared to periodic permanent magnet focusing systems based on traditional circular inner-hole pole shoe structures, the shape of the pole shoe through-hole is more suitable for rectangular cross-section slow-wave structures, and the through-hole opening area is smaller, improving the utilization rate of the pole shoe through-hole cross-section and further enhancing the focusing magnetic field strength. The traveling wave tube of the multi-channel periodic permanent magnet focusing system using this invention can integrate multiple RF amplification channels, achieving an arrayed arrangement of multiple slow-wave structures, and can be widely used in next-generation mobile communication, radar, and other equipment.

[0061] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A multi-channel pole shoe, characterized in that, include: The pole shoe head and the pole shoe annular surface surrounding the outside of the pole shoe head are coaxially arranged; the pole shoe head has a plurality of pole shoe through holes arranged circumferentially along the pole shoe head. The pole shoe through-hole includes a rectangular assembly channel for assembling the slow wave structure and two channels extending outward from two opposite sides of the assembly channel along the radial direction of the pole shoe head; the extension direction of the assembly channel is perpendicular to the extension direction of the channels; in the plane containing the end face of the pole shoe head, the channels extend radially along the pole shoe head, and the extension direction of the assembly channel is perpendicular to the extension direction of the channels; in the direction perpendicular to the radial extension direction of the pole shoe head, the length of the assembly channel is greater than the length of the channels.

2. The multi-channel pole shoe according to claim 1, characterized in that, The two channels are symmetrically arranged about the assembly channel.

3. The multi-channel pole shoe according to claim 1, characterized in that, The assembly channel includes a central channel and two side channels located on opposite sides of the central channel along the extension direction of the assembly channel; the two channels are located on opposite sides of the central channel along the radial direction of the pole shoe head.

4. The multi-channel pole shoe according to claim 3, characterized in that, The two side channels are symmetrically arranged about the middle channel; the side channels and the channel have the same structural dimensions.

5. The multi-channel pole shoe according to claim 4, characterized in that, The cross-section of the central channel is square, and the width of the side channels along the radial direction of the pole shoe head is equal to the side length of the central channel.

6. The multi-channel pole shoe according to claim 1, characterized in that, The radius corresponding to the toroidal surface of the pole shoe is r1, and the distance between the center of the assembly channel and the center of the pole shoe head is r3; 0 < r3 < r1; The assembly channel has a length of a2 and a width of b2; the length and width of the assembly channel satisfy the following relationships: 0 < b2 < 2r3, 0 < a2 < 2r1, and .

7. The multi-channel pole shoe according to claim 6, characterized in that, The channel includes an inner channel near the center of the pole shoe head and an outer channel away from the center of the pole shoe head; the length of the inner channel is a3 and the width is b3, and the length and width of the inner channel satisfy the following relationship: 0 < a3 <a2, ; The length of the outer channel is a1, and the width is b1. The length and width of the outer channel satisfy the following relationship: 0 < a1 <a2, .

8. A multi-channel periodic permanent magnet focusing system, characterized in that, It includes the multi-channel pole piece and magnet as described in any one of claims 1-7; a plurality of multi-channel pole pieces and a plurality of magnets are arranged alternately and periodically along the axial direction of the multi-channel pole piece; the magnetic field directions of two adjacent magnets are opposite.

9. A design method for a multi-channel periodic permanent magnet focusing system, characterized in that, Includes the following steps: Several pole shoes and several magnets are periodically and alternately arranged along the axial direction of the magnetic focusing system; The pole shoe includes a pole shoe head and a pole shoe annular surface surrounding the outside of the pole shoe head, with the pole shoe head and the pole shoe annular surface being coaxially arranged. A plurality of pole shoe through holes are designed on the pole shoe head, arranged circumferentially along the pole shoe head. The pole shoe through holes include a rectangular assembly channel for assembling the slow wave structure and two channels formed by extending outward from the two opposite sides of the assembly channel along the radial direction of the pole shoe head. The extension direction of the assembly channel is perpendicular to the extension direction of the channel. In the plane containing the end face of the pole shoe head, the channel extends radially along the pole shoe head, and the extension direction of the assembly channel is perpendicular to the extension direction of the channel. In the direction perpendicular to the radial extension direction of the pole shoe head, the length of the assembly channel is greater than the length of the channel.

10. The design method according to claim 9, characterized in that, The channel includes an inner channel near the center of the pole shoe and an outer channel away from the center of the pole shoe; by adjusting the length and width of the outer channel and the length and width of the inner channel, the magnetic field distribution of the magnetic focusing system can be adjusted.

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