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

Abstract

The invention 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 outer side 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 arranged in the circumferential direction of the pole shoe head are formed in the pole shoe head; the pole shoe through hole comprises an assembling channel which is of a rectangular structure and is used for assembling the slow wave structure and two channels which are formed by outwards extending the assembling channel along two opposite sides in the radial direction of the pole shoe head; the extending direction of the assembling channel is perpendicular to the extending direction of the channel. In the extending direction of the assembling channel, the length of the assembling channel is larger than that of the groove channel. According to the multi-channel pole shoe, the axial magnetic field intensity on the channel axis can be improved, and the angular magnetic field intensity can be reduced, so that the constraint capability of a magnetic focusing system on electron beams can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of microwave vacuum electronic technology, and more specifically, to a multi-channel pole shoe, a multi-channel periodic permanent magnet focusing system and a design method thereof. Background Art

[0002] The traveling wave tube is a vacuum amplifier device. As the final power amplifier of the radar, it has now put forward clear application requirements in many weapons and equipment. The focusing system is one of the core components of the traveling wave tube. Its function is to constrain the radial divergence of the electron beam so that the electron beam can be transmitted stably along the axial direction. The periodic permanent magnet focusing system is one of the commonly used focusing systems in the traveling wave tube. The principle is to constrain the electron beam through the Lorentz force received by the electron beam in the periodically changing magnetic field. Its ability to constrain the electron beam is positively correlated with the axial magnetic field strength of the focusing system in the electron beam channel, and negatively correlated with the angular magnetic field strength.

[0003] By integrating multiple RF amplification channels in the same traveling wave tube, sharing a set of focusing systems, and forming an array integration, the cross-sectional size of a single channel can be effectively reduced to meet the application requirements of array systems represented by active phased arrays. The existing array arrangement is that the circular amplification channels are arranged in a circular ring shape along the angular direction with the axis of the traveling wave tube as the axis on the cross section perpendicular to the axis of the traveling wave tube. At this time, for the periodic permanent magnet focusing system, the inner diameter of the magnetic steel needs to be larger than the outer edge of the amplification channel, resulting in an increase in the inner diameter of the magnetic steel and a decrease in the magnetic field strength, thereby reducing the ability to constrain the electron beam. In addition, for a multi-channel periodic permanent magnet focusing system in which the channels are arranged along a circular ring with the system axis as the center, since the amplification channel deviates from the system axis, an angular field component will be generated in the amplification channel, further reducing the ability to constrain the electron beam. Summary of the invention

[0004] In view of the above problems, the present invention provides a multi-channel pole shoe that can improve the axial magnetic field strength on the channel axis and reduce the angular magnetic field strength, thereby effectively improving the electron beam confinement capability of the magnetic focusing system.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

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

[0007] A pole shoe head and a pole shoe annular surface surrounding the pole shoe head, wherein the pole shoe head and the pole shoe annular surface are coaxially arranged; a plurality of pole shoe through holes arranged along the circumference of the pole shoe head are formed on the pole shoe head;

[0008] The pole shoe through hole includes a rectangular assembly channel for assembling a slow-wave structure and two grooves formed by extending outward from two opposite radial sides of the assembly channel along 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.

[0009] Preferably, the two grooves are arranged symmetrically with respect to the assembly channel.

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

[0011] A preferred solution is that the two side channels are symmetrically arranged with respect to the middle channel; and the side channels and the channel have the same structural dimensions.

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

[0013] The preferred solution 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 length of the assembly channel is a2, and the width is b2; the length and width of the assembly channel satisfy the following relationship: 0<b2<2r3, 0<a2<2r1, and

[0015] The preferred solution is that the groove includes an inner groove close to the center of the pole shoe head and an outer groove away from the center of the pole shoe head; the length of the inner groove is a3 and the width is b3, and the length and width of the inner groove satisfy the following relationship: 0<a3 <a2,

[0016] The length of the outer groove is a1, and the width is b1. The length and width of the outer groove 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 and alternately arranged along the axial direction of the multi-channel pole shoes; and the magnetic fields of two adjacent magnets are in opposite directions.

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

[0019] A plurality of pole shoes and a plurality of magnetic steels are periodically and alternately arranged along the axial direction of the magnetic focusing system;

[0020] The pole shoe comprises a pole shoe head and a pole shoe annular surface surrounding the outer side of the pole shoe head, and the pole shoe head and the pole shoe annular surface are coaxially arranged;

[0021] A plurality of pole shoe through holes arranged along the circumference of the pole shoe head are designed on the pole shoe head, and the pole shoe through holes include an assembly channel with a rectangular structure for assembling a slow-wave structure and two grooves 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 groove; in the extension direction of the assembly channel, the length of the assembly channel is greater than the length of the groove.

[0022] The preferred solution is that the groove includes an inner groove close to the center of the pole shoe head and an outer groove away from the center of the pole shoe head; the magnetic field distribution state of the magnetic focusing system is adjusted by adjusting the length and width of the outer groove and the length and width of the inner groove.

[0023] The beneficial effects of the present invention are:

[0024] The present invention solves the problem of the existing multi-channel periodic permanent magnetic focusing system that the amplifying channel deviates from the axis of the magnetic focusing system, resulting in an angular field component in the amplifying channel, which reduces the restraining ability of the electron beam, by assembling the channel and the groove, and effectively improves the axial magnetic field strength in the through hole, while greatly reducing the angular magnetic field strength, so that the magnetic focusing system has better electron beam focusing performance. In addition, the present invention can adjust the distribution state of the focusing magnetic field by changing the size of the two grooves to ensure the uniformity of the focusing magnetic field. Compared with the periodic permanent magnetic focusing system based on the traditional circular inner hole pole shoe structure, the shape of the pole shoe through hole is more suitable for the rectangular cross-section slow wave structure, the pole shoe through hole opening area is smaller, the utilization rate of the pole shoe through hole cross section is improved, and the focusing magnetic field strength is further improved. The traveling wave tube using the multi-channel periodic permanent magnetic focusing system of the present invention can integrate multiple radio frequency amplification channels together to realize the array arrangement of multiple slow wave structures, and can be widely used in new generation mobile communications, radar and other equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0026] Figure 1 It is a schematic cross-sectional view of an existing rectangular outer boundary folded waveguide slow-wave structure.

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

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

[0029] Figure 4 It 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 Schematic diagram of the structure of the pole shoe through hole located at the bottom.

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

[0033] Figure 7 It is a comparison diagram of the axial magnetic field intensity on the channel axis of an 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 diagram is a distribution diagram of the angular magnetic field intensity at a distance d / 2 from the channel axis at different angular positions of an 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 DESCRIPTION

[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 the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless otherwise specifically stated.

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

[0037] Techniques and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the techniques and equipment should be considered part of the specification.

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

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

[0040] The cross-sectional shape of the amplifying channel commonly used in the periodic permanent magnet focusing system is circular. This circular cross-sectional structure can adapt to the traditional spiral slow-wave structure with a circular cross-sectional shape. However, for the folded waveguide and staggered double-grid slow-wave structures with a rectangular cross-sectional shape, the circular channel will cause the opening area to be larger than the actual cross-sectional size, and part of the area will be wasted, thereby reducing the focusing magnetic field strength. In addition, in the existing multi-channel periodic permanent magnet focusing system, since the axis of the circular amplifying channel is not coaxial with the axis of the magnetic focusing system, an angular field component will be generated in the amplifying channel, causing the electron beam to diverge, reducing the focusing system's ability to constrain the electron beam.

[0041] In order to solve the problems existing in the prior art. The present invention provides a multi-channel pole shoe, combined with Figures 1 to 8 As shown, specifically, the multi-channel pole shoe comprises: a pole shoe head 1 and a pole shoe annular surface 2 surrounding the outer side of the pole shoe head 1, and the pole shoe head 1 is coaxially arranged with the pole shoe annular surface 2. The pole shoe head 1 is formed with a plurality of pole shoe through holes 3 arranged along the circumference of the pole shoe head 1. The pole shoe through hole 3 comprises an assembly channel 31 of a rectangular structure for assembling a slow-wave structure and two grooves formed by the assembly channel 31 extending outwardly along two opposite sides of the radial direction of the pole shoe head 1; the extension direction of the assembly channel 31 is perpendicular to the extension direction of the groove; in the extension direction of the assembly channel, the length of the assembly channel 31 is greater than the length of the groove.

[0042] Under the premise of ensuring multiple assembly channels, the present invention effectively improves the axial magnetic field strength in the pole shoe through hole 3, and at the same time greatly reduces the angular magnetic field strength, so that the magnetic focusing system has better electron beam focusing performance, and effectively improves the magnetic focusing system's ability to constrain the electron beam. The problem that the existing multi-channel periodic permanent magnetic focusing system generates angular field components in the amplifying channels, resulting in electron beam divergence, and the magnetic focusing system has poor ability to constrain the electron beam due to the fact that the axes of each amplifying channel and the axis of the focusing system are not coaxial, which solves the problem.

[0043] In the millimeter wave terahertz band, the electron injection channel of the traveling wave tube is usually small, and the Coulomb force between electrons is larger, which puts higher requirements on the strength of the focusing magnetic field. By reducing the cross-sectional size of the circular channel of the pole shoe in the focusing system, the strength of the focusing magnetic field can be effectively improved. However, due to the physical size limitation of the slow-wave structure, the cross-sectional size of the circular amplification channel in the existing magnetic focusing system cannot be infinitely reduced, and the strength of the focusing magnetic field that can be improved is limited. The present invention improves the utilization rate of the cross-sectional area of ​​the pole shoe through hole by reasonably improving the shape of the pole shoe through hole in the focusing system, thereby improving the strength of the focusing magnetic field. In order to assemble a slow-wave structure with a rectangular cross-section, the cross-section of the assembly channel 31 is also set to a rectangular shape to achieve adaptation with a folded waveguide with a rectangular cross-section and an interlaced double-grid type slow-wave structure, thereby 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 is connected to the groove. The pole shoe through holes 3 are rotationally symmetrically arranged about the center of the pole shoe head. That is to say, 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 along 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 pole shoe through hole located at the top has the assembly channel extending in the horizontal direction and the groove extending in the vertical direction; Figure 3 For the pole shoe through hole located on the far left, the extending direction of the assembly channel is the vertical direction, and the extending direction of the groove is the horizontal direction.

[0045] In order to ensure the uniformity of the magnetic field, the two grooves are symmetrically arranged with respect to the assembly channel 31 .

[0046] Combination Figure 5A and Figure 5B As shown, in order to further improve the uniformity of the magnetic field and facilitate processing, the assembly channel 31 includes a middle channel 311 and two side channels 312 on two opposite sides along the extension direction of the assembly channel 31, and the two grooves are respectively located on two opposite sides of the middle channel 311 along the radial direction of the pole shoe head 1. The two side channels 312 are symmetrically arranged with respect to the middle channel 311, and the side channels 312 have the same structural dimensions as the grooves. The cross-section of the middle channel 311 is square, 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 middle channel 311. Through the above arrangement, it is possible to ensure that the processing process is simpler and more convenient, and reduce the difficulty of processing.

[0047] More specifically, when the cross-section of the middle channel 311 is square and a slow-wave structure with a square cross-section is assembled in the pole shoe through hole 3, the slow-wave structure is assembled in the middle channel 311, and the four corners of the slow-wave structure are fixed at the intersection of the side channel 312 and the groove. At this time, the magnetic field distribution state of the magnetic focusing system can be adjusted by adjusting the size of the side channel 312 and the groove. When the slow-wave structure with a rectangular cross-section is assembled, the slow-wave structure is assembled in the middle channel 311 and the side channel 312, and the four corners of the slow-wave structure are respectively fitted and fixed with the corners of the side channel 312. At this time, the magnetic field distribution state of the magnetic focusing system is adjusted by adjusting the size of the groove. Compared with the existing circular inner hole, the pole shoe through hole 3 with a cross-section of the present invention can better adapt to the folded waveguide and staggered double-grid slow-wave structures with a rectangular cross-section shape, 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 improve the ability to restrain the electron beam.

[0048] In a 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 arrangement can ensure that the assembly channel 31 and the groove are all located inside the pole shoe, thus avoiding discontinuities on the outer circle of the pole shoe annular surface 2.

[0049] Further, the groove includes an inner groove 32 close to the center of the pole shoe head 1 and an outer groove 33 away from the center of the pole shoe head 1. Figure 5A As shown in the figure, the dotted line is the boundary between the assembly channel 31 and the inner groove 32 and the outer groove 33. The cross-sections of the assembly channel 31, the inner groove 32 and the outer groove 33 are all rectangular. The length of the inner groove 32 is a3 and the width is b3. The length and width of the inner groove 32 satisfy the following relationship: 0<a3 <a2, The length of the outer groove 33 is a1, and the width is b1. The length and width of the outer groove 33 satisfy the following relationship: 0<a1 <a2, The above arrangement can ensure that the assembly channel 31 and the groove are all located inside the pole shoe, thus 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. The increase in the thickness of the pole shoe head 1 is conducive to reducing the saturation of the pole shoe and improving the magnetic field distribution. In addition, a step is formed at the junction of the pole shoe head 1 and the pole shoe annular surface 2, which is conducive to the structural strength and air tightness when welding with the spacer ring in the subsequent process.

[0051] The present invention also provides a multi-channel periodic permanent magnet focusing system, comprising the multi-channel pole shoes and magnetic steel 4 as described above; a plurality of multi-channel pole shoes and a plurality of magnetic steels 4 are periodically arranged alternately along the axial direction of the multi-channel pole shoes. A slow wave structure is arranged in a row of coaxially arranged pole shoe through holes 3. The multi-channel periodic permanent magnet focusing system can improve the axial magnetic field strength on the channel axis while reducing the angular magnetic field strength, thereby effectively improving the confinement capability of the electron beam. More specifically, the magnetic fields of two adjacent magnetic steels 4 are in opposite directions, the magnetic steel 4 is in an annular structure, and the multi-channel pole shoes and the magnetic steel 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 injection channel. The specific structural dimensions are as follows (unit: mm): a0 = 1.980, b0 = 1.270, d0 = 0.240.

[0053] Reference Figure 4and Figure 5A As shown, it is a cross-sectional schematic diagram 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 groove 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 groove is a3, and the width is b3; R1 is the outer radius of the magnetic steel, R2 is the inner radius of the magnetic steel, L is the thickness of the magnetic steel, p / 2 is the length of the half-cycle of the magnetic field transformation, and p / 2=L1+L. As shown Figure 6 As shown, it is the BH characteristic curve of the pole shoe material during the simulation process, and the remanent magnetism Br of the magnetic steel is set to 10000Gs.

[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 magnetic steel, and 5 is the circular through hole. The four-channel periodic permanent magnet focusing system based on the circular channel pole shoe structure for comparison is the same as the four-channel periodic permanent magnet focusing system provided by the present invention except that the cross-sectional shape of the through hole is circular and the radius corresponding to the circular through hole is 1.176 mm.

[0056] Reference Figure 7 As shown, the peak axial magnetic field intensity on the axis of the amplified channel of the four-channel periodic permanent magnet focusing system based on the circular channel pole shoe structure is 3129Gs, and the peak axial magnetic field intensity on the axis of the amplified channel of the four-channel periodic permanent magnet focusing system provided by the present invention is 3454Gs, which is 10.4% higher than the axial magnetic field intensity 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 angular magnetic field strength of the amplified channel of the four-channel periodic permanent magnet focusing system based on the circular channel pole shoe structure is 60.29 Gs, and the peak angular magnetic field strength of the amplified channel of the four-channel periodic permanent magnet focusing system provided by the present invention is 1.61 Gs, which is 97.3% lower than the angular magnetic field strength of the four-channel periodic permanent magnet focusing system based on the circular channel pole shoe structure.

[0058] The present invention also provides a design method for a multi-channel periodic permanent magnet focusing system, which specifically includes the following steps: arranging a plurality of pole shoes and a plurality of magnetic steels in an alternating periodic manner 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 outer side of the pole shoe head 1, and the pole shoe head 1 and the pole shoe annular surface 2 are coaxially arranged; a plurality of pole shoe through holes 3 arranged circumferentially along the pole shoe head 1 are designed on the pole shoe head 1, and the pole shoe through hole 3 includes an assembly channel 31 with a rectangular structure for assembling a slow-wave structure and two grooves formed by the assembly channel 31 extending outwardly along two opposite radial sides of the pole shoe head 1; the extension direction of the assembly channel 31 is perpendicular to the extension direction of the groove; in the extension direction of the assembly channel, the length of the assembly channel 31 is greater than the length of the groove.

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

[0060] In summary, the present invention solves the problem of the existing multi-channel periodic permanent magnetic focusing system generating angular field components in the amplifying channel due to the deviation of the amplifying channel from the axis of the magnetic focusing system, thereby reducing the constraint ability of the electron beam, and effectively improves the axial magnetic field strength in the through hole, while greatly reducing the angular magnetic field strength, so that the magnetic focusing system has better electron beam focusing performance. And the present invention can adjust the distribution state of the focusing magnetic field by changing the size of the two grooves to ensure the uniformity of the focusing magnetic field. Compared with the periodic permanent magnetic focusing system based on the traditional circular inner hole pole shoe structure, the shape of the pole shoe through hole of the present invention is more suitable for the rectangular cross-section slow wave structure, and the pole shoe through hole opening area is smaller, which improves the utilization rate of the pole shoe through hole cross section, and further improves the focusing magnetic field strength. The traveling wave tube using the multi-channel periodic permanent magnetic focusing system of the present invention can integrate multiple radio frequency amplification channels together to realize the array arrangement of multiple slow wave structures, and can be widely used in new generation mobile communications, 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 limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution 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: A pole shoe head and a pole shoe annular surface surrounding the pole shoe head, wherein the pole shoe head and the pole shoe annular surface are coaxially arranged; a plurality of pole shoe through holes arranged along the circumference of the pole shoe head are formed on the pole shoe head; The pole shoe through hole includes a rectangular assembly channel for assembling a slow-wave structure and two grooves formed by extending outward from two opposite radial sides of the assembly channel along 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.

2. The multi-channel pole piece according to claim 1, characterized in that: The two grooves are symmetrically arranged with respect to the assembly channel.

3. The multi-channel pole piece according to claim 1, characterized in that: The assembly channel comprises a middle channel and two side channels located at two opposite sides of the middle channel along the extension direction of the assembly channel; the two grooves are respectively located at two opposite sides of the middle channel along the radial direction of the pole shoe head.

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

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

6. The multi-channel pole piece according to claim 1, characterized in 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; The length of the assembly channel is a2, and the width is b2; the length and width of the assembly channel satisfy the following relationship: 0<b2<2r3, 0<a2<2r1, and 7. The multi-channel pole piece according to claim 6, characterized in that: The groove includes an inner groove close to the center of the pole shoe head and an outer groove far from the center of the pole shoe head; the length of the inner groove is a3 and the width is b3, and the length and width of the inner groove satisfy the following relationship: 0<a3 <a2, The length of the outer groove is a1, and the width is b1. The length and width of the outer groove satisfy the following relationship: 0<a1 <a2, 8. A multi-channel periodic permanent magnet focusing system, characterized in that: It comprises the multi-channel pole shoes and magnetic steel as described in any one of claims 1 to 7; a plurality of multi-channel pole shoes and a plurality of magnetic steels are periodically and alternately arranged along the axial direction of the multi-channel pole shoes; and the magnetic fields of two adjacent magnetic steels are in opposite directions.

9. A design method for a multi-channel periodic permanent magnet focusing system, characterized in that: The following steps are involved: A plurality of pole shoes and a plurality of magnetic steels are periodically and alternately arranged along the axial direction of the magnetic focusing system; The pole shoe comprises a pole shoe head and a pole shoe annular surface surrounding the outer side of the pole shoe head, and the pole shoe head and the pole shoe annular surface are coaxially arranged; A plurality of pole shoe through holes arranged along the circumference of the pole shoe head are designed on the pole shoe head, and the pole shoe through holes include an assembly channel with a rectangular structure for assembling a slow-wave structure and two grooves 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 groove; in the extension direction of the assembly channel, the length of the assembly channel is greater than the length of the groove.

10. The design method according to claim 9, characterized in that: The grooves include an inner groove close to the center of the pole shoe head and an outer groove far from the center of the pole shoe head; the magnetic field distribution state of the magnetic focusing system is adjusted by adjusting the length and width of the outer groove and the length and width of the inner groove.

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