Two-dimensional planar array multi-channel periodic permanent magnet focusing system and design method thereof

Abstract

The application provides a two-dimensional planar array multi-channel periodic permanent magnet focusing system and a design method thereof. The periodic permanent magnet focusing system comprises pole shoes and magnetic groups which are arranged at intervals along a first direction. The pole shoes and the magnetic groups are periodically and alternately arranged along the first direction to form a plurality of periodic permanent magnet structures. The magnetic group comprises a plurality of magnetic steels which are arranged at intervals along a second direction. The magnetic steels are arranged along a third direction. A plurality of through holes are formed on the pole shoes in an array. The through holes are used to assemble a slow wave structure. A plurality of through holes constitute a through hole unit. The through hole unit comprises transverse through hole units arranged along the second direction and longitudinal through hole units arranged along the third direction. The transverse through hole units are located between two adjacent magnetic steels arranged along the second direction. A plurality of amplification channels are integrated in a set of magnetic focusing system, the distance between the amplification channels is reduced, the unit density is improved, and the focusing performance of the magnetic focusing system on the electron beam is not affected.

Description

Technical Field

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

[0002] A traveling wave tube (TWT) is a vacuum amplification device. As the final power amplifier stage in radar, it has been explicitly required for application in communication radar information warfare. The focusing system is one of the core components of the TWT, and its function is to constrain the radial divergence of the electron beam, allowing the electron beam to propagate stably along the axial direction.

[0003] Periodic permanent magnet focusing systems are one of the commonly used focusing systems in traveling wave tubes (TWTs). Their principle is to constrain the electron beam by the Lorentz force experienced by the electron beam in a periodically changing magnetic field. Typically, a single periodic permanent magnet focusing system can only focus the electron beam within one amplification channel. When TWTs using this single-channel periodic permanent magnet focusing system are used in arrays, the presence of the magnet fixing structure and magnetic shielding structure, along with the need to prevent mutual interference between elements, usually requires the array element spacing to be larger than the cross-sectional size of the periodic permanent magnet focusing system. This limits the element density during TWT array formation, restricting its application in array systems such as active phased array radars. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a two-dimensional planar array multi-channel periodic permanent magnet focusing system and its design method, which integrates multiple amplification channels into a single magnetic focusing system, reduces the distance between amplification channels, increases unit density, and does not affect the focusing performance of the magnetic focusing system on the electron beam.

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

[0006] This invention provides a two-dimensional planar array multi-channel periodic permanent magnet focusing system, comprising:

[0007] The pole shoes and magnetic groups are spaced apart along a first direction; the pole shoes and magnetic groups are periodically alternated along the first direction to form multiple periodic permanent magnet structures;

[0008] The magnetic assembly includes a plurality of magnets arranged at intervals along a second direction; the magnets extend along a third direction.

[0009] The pole shoe has a plurality of through holes arranged in an array for mounting a slow wave structure; the plurality of through holes constitute a through hole unit, the through hole unit including transverse through hole units arranged along a second direction and longitudinal through hole units arranged along a third direction; the transverse through hole units are located between two adjacent magnets arranged along the second direction.

[0010] A preferred embodiment is that the pole shoe includes m×n through holes arranged in a rectangular array, where m is the number of columns of the through holes in the third direction and n is the number of rows of the through holes in the second direction, m>1 and n>1.

[0011] The preferred solution is that the width of the extreme boot in the third direction is w. p The height of the pole shoe in the second direction is h. p The diameter of the through hole is D0;

[0012] In a preferred embodiment, the spacing between two adjacent through holes in the transverse through-hole unit in the third direction is d. x ,

[0013] The spacing between two adjacent through holes in the longitudinal through-hole unit in the second direction is d. y ,

[0014] In a preferred embodiment, the magnetic assembly includes at least three magnets, with the two magnets located at both ends of the magnetic assembly along the second direction being the outer magnets, and the magnet located between the two outer magnets being the inner magnet; the outer magnets are located outside the through-hole units, and the inner magnets are located between two adjacent transverse through-hole units; the width of the outer magnets and the inner magnets in the third direction and their thickness in the first direction are equal; the height of the outer magnets and the inner magnets in the second direction may be equal or unequal.

[0015] The preferred solution is that the width of the magnet in the third direction is w. m ;w m ≥d x ×(n-1)+D0;

[0016] The height of the internal magnet in the second direction is h1; 0 < h1 ≤ d y -D0.

[0017] The preferred approach is that the magnets in the same magnetic group are magnetized in the same direction, while the magnets in two adjacent magnetic groups are magnetized in opposite directions.

[0018] This invention also provides a design method for a two-dimensional planar array multi-channel periodic permanent magnet focusing system, the design method comprising:

[0019] The design includes pole shoes and magnetic groups arranged periodically along a first direction to form multiple periodic permanent magnet structures. The magnetic groups include several magnets arranged at intervals along a second direction, and the magnets extend along a third direction.

[0020] Several through holes arranged in an array on the pole shoe are designed for assembling the slow wave structure. Several through holes constitute a through hole unit. The through hole unit includes transverse through hole units arranged along the second direction and longitudinal through hole units arranged along the third direction. The transverse through hole units are located between two adjacent magnets arranged along the second direction.

[0021] In a preferred embodiment, the magnetic assembly comprises at least three magnets, with the two magnets located at both ends of the magnetic assembly along the second direction being the outer magnets, and the magnet located between the two outer magnets being the inner magnets; the outer magnets are located outside the through-hole units, and the inner magnets are located between two adjacent transverse through-hole units; the width of the outer magnets and the inner magnets in the third direction and their thickness in the first direction are equal; the height of the outer magnets and the inner magnets in the second direction may be equal or unequal.

[0022] The preferred approach is to adjust the axial magnetic field strength and angular magnetic field intensity of the periodic permanent magnet focusing system by changing the width of the magnet in the third direction and the height of the outer magnet in the second direction, thereby optimizing the focusing performance of the periodic permanent magnet focusing system.

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

[0024] This invention integrates multiple channels with assembled slow-wave structures into a single focusing system, enabling the integration of traveling-wave tube amplification channel arrays. This effectively reduces the element spacing and increases element density, meeting the application requirements of arrayed systems such as active phased arrays. Furthermore, this invention ensures that the ratio of the angular magnetic field peak value to the axial magnetic field peak value within the channel of the periodic permanent magnet focusing system is less than 0.5%, thus not affecting the focusing performance of the electron beam. By changing the width of the magnet in the third direction and the height of the outer magnet in the second direction, this invention adjusts the axial and angular magnetic field strength of the periodic permanent magnet focusing system, optimizing its focusing performance. 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 one of the structural schematic diagrams of the two-dimensional planar array multi-channel periodic permanent magnet focusing system of the present invention.

[0027] Figure 2 This is the second schematic diagram of the structure of the two-dimensional planar array multi-channel periodic permanent magnet focusing system of the present invention.

[0028] Figure 3 This is the third schematic diagram of the structure of the two-dimensional planar array multi-channel periodic permanent magnet focusing system of the present invention.

[0029] Figure 4This is a BH characteristic curve of the pole shoe material during the simulation process of this invention.

[0030] Figure 5 This is a diagram showing the magnetic field intensity distribution at the center of the pole shoe of the two-dimensional planar array multi-channel periodic permanent magnet focusing system of the present invention.

[0031] Figure 6 This is a diagram showing the magnetic field intensity distribution of the central cross-section of the magnet in the two-dimensional planar array multi-channel periodic permanent magnet focusing system of the present invention.

[0032] Figure 7 This is a diagram showing the axial magnetic field intensity distribution along the axial direction of each channel in the two-dimensional planar array multi-channel periodic permanent magnet focusing system of the present invention.

[0033] Figure 8 This is a diagram showing the angular magnetic field distribution along the angular direction at a distance rc from the channel axis on the cross-section of the pole shoe center of the two-dimensional planar array multi-channel periodic permanent magnet focusing system of the present invention.

[0034] Figure 9 This is a diagram showing the axial magnetic field strength distribution along the axis of channel 3-3 under different magnet widths in the two-dimensional planar array multi-channel periodic permanent magnet focusing system of the present invention.

[0035] Figure 10 This is a diagram showing the angular magnetic field distribution along the angular direction at a distance rc from the channel axis of channel 3-3 on the cross-section of the pole shoe center of the two-dimensional planar array multi-channel periodic permanent magnet focusing system of the present invention, with different magnet widths.

[0036] Figure 11 This is a diagram showing the axial magnetic field strength distribution along the axis of channel 3-3 at different external magnet heights in the two-dimensional planar array multi-channel periodic permanent magnet focusing system of the present invention.

[0037] Figure 12 This is a diagram showing the angular magnetic field distribution along the angular direction at a distance rc from the channel axis of channel 3-3 on the cross-section of the pole shoe center of the two-dimensional planar array multi-channel periodic permanent magnet focusing system of the present invention, under different heights of the outer magnets.

[0038] Reference numerals: 1. Pole shoe, 21. Outer magnet, 22. Inner magnet, 3. Through hole. Detailed Implementation

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] Periodic permanent magnet focusing systems are among the most commonly used electron beam focusing systems for traveling wave tubes (TWTs). Compared to electron beam focusing systems such as single permanent magnet focusing and solenoid magnetic field focusing, periodic permanent magnet focusing systems are smaller in size. Typically, a single periodic permanent magnet focusing system can only focus one electron beam, meaning a single TWT can only have one amplification channel. Therefore, when TWTs are used in array systems, such as active phased array radars, the spacing between the amplification channels is usually not less than the cross-sectional size of the TWT. This limits the element density when TWTs are arrayed, restricting their application in array systems like active phased array radars. Furthermore, in current manufacturing processes, due to the inhomogeneity of the magnetic material, if the spacing between the amplification channels is smaller than the cross-sectional size of the TWT, interference between different amplification channels will occur, leading to a deterioration in the focusing performance of the magnetic focusing system.

[0045] To address the aforementioned problems, this invention provides a two-dimensional planar array multi-channel periodic permanent magnet focusing system, combined with... Figures 1 to 12As shown, the two-dimensional planar array multi-channel periodic permanent magnet focusing system specifically includes: pole shoes 1 and magnetic groups spaced apart along a first direction z, wherein the pole shoes 1 and magnetic groups are periodically alternately arranged along the first direction z to form multiple periodic permanent magnet structures. The magnetic groups include several magnets spaced apart along a second direction y, and the magnets extend along a third direction x. Several through holes 3 are formed on the pole shoes in an array, and the through holes 3 are used to assemble slow-wave structures. The several through holes 3 constitute through-hole units, and the through-hole units include transverse through-hole units arranged along the second direction y and longitudinal through-hole units arranged along the third direction x. The transverse through-hole units are located between two adjacent magnets arranged along the second direction y. For example, when the number of transverse through-hole units is five, the number of magnets is six, and each pair of adjacent magnets includes one transverse through-hole unit. Furthermore, the aforementioned through-hole 3 is used to form a channel for assembling the slow-wave structure. The axis of the channel is arranged along a first direction, that is, the through-holes 3 coaxially arranged on each pole piece 1 along the first direction are connected in the first direction to form a channel, and the slow-wave structure is assembled in this channel. (Refer to...) Figure 1 and Figure 2 As shown, the z-direction is the first direction, the y-direction is the second direction, and the x-direction is the third direction. The x-direction is perpendicular to the y-direction, and the z-direction is perpendicular to both the x-direction and the y-direction. This invention can integrate multiple channels in the same magnetic focusing system, reducing the distance between channels and increasing the unit density. The traveling wave tube of the two-dimensional planar array multi-channel periodic permanent magnet focusing system based on this invention can be widely used in arrayed systems represented by active phased arrays.

[0046] In one embodiment, the pole shoe 1 includes m×n through holes 3 arranged in a rectangular array, where m is the number of columns of the through holes 3 in the third direction and n is the number of rows of the through holes 3 in the second direction, m>1, n>1. That is, the periodic permanent magnet focusing system contains m×n channels for assembling slow-wave structures. The number of magnets in the same magnetic group is n+1.

[0047] More specifically, pole shoe 1 has a flat plate structure, and the width of pole shoe 1 in the third direction is w. p The height of the pole shoe 1 in the second direction is h. p The thickness of the pole shoe 1 in the first direction is L. p Value range: w p >0; h p >0; L p >0. The diameter of through hole 3 is D0; The spacing d between two adjacent through holes 3 in the third direction of the transverse through hole unit is d. x , The spacing d between two adjacent through holes 3 in the longitudinal through hole unit in the second direction is y ,

[0048] In one specific embodiment, the magnetic assembly includes at least three magnets. Two magnets located at both ends of the magnetic assembly along the second direction are outer magnets 21, and the magnet between the two outer magnets 21 is an inner magnet 22. The outer magnets 21 are located outside the through-hole units, and the inner magnets 22 are located between two adjacent transverse through-hole units. The width of the outer magnets 21 and the inner magnets 22 in the third direction and their thickness in the first direction are equal. The height of the outer magnets 21 and the inner magnets 22 in the second direction may be equal or unequal. In the two-dimensional planar array multi-channel periodic permanent magnet focusing system of the present invention, the inner magnets 22 mainly function to control the magnetic field strength of the system, while the outer magnets 21 mainly function to adjust the magnetic field shape distribution and the transverse field size within the channel. Further, the width of the magnets in the third direction is w. m ;w m ≥d x ×(n-1)+D0; The height of the inner magnet 22 in the second direction is h1, with a value range of: 0 y -D0. Specifically, the width of the outer magnet 21 is w. m Value range: w m ≥d x ×(n-1)+D0; Height is h2, value range: h2>0; Thickness is L m Value range: L m >0. The inner n-1 magnets are inner magnets 22, and their width is w. m The height is h1, and its value range is 0 < h1 ≤ d. y -D0; Thickness is L m Furthermore, the distance between two adjacent magnets is d. m d m =d y -h1.

[0049] In one specific embodiment, the magnets in the same magnetic group are magnetized in the same direction, while the magnets in adjacent magnetic groups are magnetized in opposite directions. The half-cycle length of the periodic permanent magnet focusing system is L, with a value ranging from L to L. p +L m Within the same half-cycle, the magnetic field of the magnet is in the same direction, while within adjacent half-cycles, the magnetic field of the magnet is in the opposite direction.

[0050] Reference Figure 1 and Figure 2 As shown, this invention illustrates a 5×5 channel two-dimensional planar array multi-channel periodic permanent magnet focusing system, whose specific structural dimensions are as follows (unit: mm): w p =41,h p =29, L p =1, D0=3, d y =6,d​x =6, w m =45, h1=3, h2=2, L m =2,d m =3, L=3.

[0051] Reference Figure 3 The diagram shown illustrates the main aperture numbering of the aforementioned 5×5 channel two-dimensional planar array multi-channel periodic permanent magnet focusing system. Due to the symmetrical shape of the rectangular array, only in... Figure 3 Nine through holes are marked 1-1, 1-2, 1-3, 2-1, 2-2, 2-3, 3-1, 3-2, and 3-3. The electron beam channel of the preset slow-wave structure has a radius of rc, which is set to rc = 0.12 mm. The electron beam will be confined within the electron beam channel with a radius of rc.

[0052] The 5×5 channel two-dimensional planar array multi-channel periodic permanent magnet focusing system of the present invention was simulated using three-dimensional electromagnetic software, and the relevant magnetic field strength and field distribution characteristics were calculated.

[0053] Reference Figure 4 The figure shows the BH characteristic curve of the pole shoe material during the simulation. In addition, the remanence Br of the magnet is set to 10000Gs.

[0054] Reference Figure 5 As shown, the magnetic field intensity distribution at the center sectional area of ​​the pole shoe of a 5×5 two-dimensional planar array multi-channel periodic permanent magnet focusing system is shown. The magnetic field distribution pattern within the channel is concentric circles, which meets the requirements of cylindrical electron beam focusing for magnetic field shape.

[0055] Reference Figure 6 The figure shows the magnetic field intensity distribution of the polar magnetic steel core cross section of a 5×5 two-dimensional planar array multi-channel periodic permanent magnet focusing system. The magnetic field distribution pattern in the channel is concentric circles, which meets the requirements of cylindrical electron beam focusing for magnetic field shape.

[0056] Reference Figure 7 The figure shows the axial magnetic field intensity distribution along the axial direction of each channel in a 5×5 two-dimensional planar array multi-channel periodic permanent magnet focusing system. The axial magnetic field is strongest on channel 3-1, with a maximum value of 3083.2 Gs, while the axial magnetic field is weakest on channels 1-3, with a maximum value of 3080.6 Gs. The difference in the maximum value of the axial magnetic field on each channel axis does not exceed 0.084%, which has no impact on the focusing performance.

[0057] Reference Figure 8The figure shows the angular magnetic field distribution along the angular direction at a distance rc from the channel axis of each channel on the cross-section of the pole shoe center of a 5×5 two-dimensional planar array multi-channel periodic permanent magnet focusing system. Among them, the angular magnetic field at a distance rc from the channel axis of channel 3-3 is the strongest, with a maximum value of 1.67 Gs, accounting for 0.054% of the peak value of the axial magnetic field on the channel axis, and has no impact on the electron beam focusing performance.

[0058] The present invention also provides a design method for a two-dimensional planar array multi-channel periodic permanent magnet focusing system. The design method includes: designing pole shoes 1 and magnetic groups that are periodically arranged along a first direction to form multiple periodic permanent magnet structures. The magnetic groups include several magnets that are spaced apart along a second direction and extend along a third direction. The pole shoes 1 are designed with several through holes 3 arranged in an array for mounting slow-wave structures. The several through holes 3 constitute a through hole unit. The through hole unit includes transverse through hole units arranged along the second direction and longitudinal through hole units arranged along the third direction. The transverse through hole units are located between two adjacent magnets arranged along the second direction.

[0059] Furthermore, the magnetic assembly includes at least three magnets. Two magnets located at both ends of the magnetic assembly along the second direction are called outer magnets 21, and the magnet located between the two outer magnets 21 is called an inner magnet 22. The outer magnets 21 are located outside the through-hole units, and the inner magnets 22 are located between two adjacent transverse through-hole units. The width of the outer magnets 21 and the thickness of the inner magnets 22 in the third direction are equal, and their heights in the second direction are equal or unequal.

[0060] Reference Figure 9 It can be seen that the width of the magnet in the third direction has little effect on the axial magnetic field strength along the channel axis. (Refer to...) Figure 10 It can be seen that the width of the magnet in the third direction has a greater impact on the angular magnetic field. (Refer to...) Figure 11 It can be seen that the height of the outer magnet 21 in the second direction has a significant impact on the axial magnetic field strength along the channel axis. (Refer to...) Figure 12 It can be seen that the height of the external magnet 21 in the second direction has a greater impact on the angular magnetic field.

[0061] Combination Figures 9-12 As shown, more specifically, by changing the width of the magnet in the third direction and the height of the outer magnet 21 in the second direction, the axial magnetic field strength and angular magnetic field intensity of the periodic permanent magnet focusing system are adjusted, thereby optimizing the focusing performance of the periodic permanent magnet focusing system. This avoids the angular magnetic field from having an excessively large proportion of the axial magnetic field, which would affect the electron beam focusing effect. The smaller the proportion of the angular magnetic field to the axial magnetic field, the smaller the impact on electron beam focusing. When the peak value of the angular magnetic field is less than 0.5% of the peak value of the axial magnetic field, it has virtually no impact on the electron beam focusing performance.

[0062] In summary, this invention integrates multiple channels with assembled slow-wave structures into a single focusing system, enabling the integration of traveling wave tube amplification channel arrays. This effectively reduces the unit spacing and increases unit density, meeting the application requirements of arrayed systems such as active phased arrays. Furthermore, this invention ensures that the ratio of the angular magnetic field peak value to the axial magnetic field peak value within the channel of the periodic permanent magnet focusing system is less than 0.5%, thus not affecting the focusing performance of the electron beam. By changing the width of the magnet in the third direction and the height of the outer magnet in the second direction, this invention adjusts the axial and angular magnetic field strength of the periodic permanent magnet focusing system, optimizing its focusing performance.

[0063] 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 two-dimensional planar array multi-channel periodic permanent magnet focusing system, characterized in that, include: The pole shoes and magnetic groups are spaced apart along a first direction; the pole shoes and magnetic groups are periodically alternated along the first direction to form multiple periodic permanent magnet structures; The magnetic assembly includes a plurality of magnets arranged at intervals along a second direction; the magnets extend along a third direction. The pole shoe has a plurality of through holes arranged in an array, which are used to assemble the slow wave structure; the plurality of through holes constitute a through hole unit, which includes transverse through hole units arranged along the second direction and longitudinal through hole units arranged along the third direction; the transverse through hole units are located between two adjacent magnets arranged along the second direction. The first direction is perpendicular to both the second and third directions, and the second direction is perpendicular to the third direction. The magnetic assembly includes at least three magnets. The two magnets located at both ends of the magnetic assembly along the second direction are the outer magnets, and the magnet located between the two outer magnets is the inner magnet. The outer magnets are located outside the through-hole unit, and the inner magnets are located between two adjacent transverse through-hole units.

2. The two-dimensional planar array multi-channel periodic permanent magnet focusing system according to claim 1, characterized in that, The pole shoe includes m×n through holes arranged in a rectangular array, where m is the number of columns of the through holes in the third direction and n is the number of rows of the through holes in the second direction, m>1 and n>1.

3. The two-dimensional planar array multi-channel periodic permanent magnet focusing system according to claim 2, characterized in that, The width of the extreme boot in the third direction is w. p The height of the pole shoe in the second direction is h. p The diameter of the through hole is D0; 0 < D0 < min[ , ].

4. The two-dimensional planar array multi-channel periodic permanent magnet focusing system according to claim 3, characterized in that, The spacing between two adjacent through holes in the transverse through-hole unit in the third direction is d. x D0 < d x < ; The spacing between two adjacent through holes in the longitudinal through-hole unit in the second direction is d. y D0 < d y < .

5. The two-dimensional planar array multi-channel periodic permanent magnet focusing system according to claim 3, characterized in that, The outer magnet and the inner magnet have the same width in the third direction and the same thickness in the first direction; the outer magnet and the inner magnet have the same or different heights in the second direction.

6. The two-dimensional planar array multi-channel periodic permanent magnet focusing system according to claim 5, characterized in that, The width of the magnet in the third direction is w. m ;w m ≥d x ×(n-1)+D0; The height of the internal magnet in the second direction is h1; 0 < h1 ≤ d y -D0.

7. The two-dimensional planar array multi-channel periodic permanent magnet focusing system according to claim 1, characterized in that, The magnets in the same magnetic group are magnetized in the same direction, while the magnets in two adjacent magnetic groups are magnetized in opposite directions.

8. A design method for a two-dimensional planar array multi-channel periodic permanent magnet focusing system, characterized in that, This design methodology includes: The design includes pole shoes and magnetic groups arranged periodically along a first direction to form multiple periodic permanent magnet structures. The magnetic groups include several magnets arranged at intervals along a second direction, and the magnets extend along a third direction. Several through holes arranged in an array on the pole shoe are designed for assembling the slow wave structure. Several through holes constitute a through hole unit. The through hole unit includes a transverse through hole unit arranged along the second direction and a longitudinal through hole unit arranged along the third direction. The transverse through hole unit is located between two adjacent magnets arranged along the second direction. The first direction is perpendicular to both the second and third directions, and the second direction is perpendicular to the third direction. The magnetic assembly includes at least three magnets. The two magnets located at both ends of the magnetic assembly along the second direction are the outer magnets, and the magnet located between the two outer magnets is the inner magnet. The outer magnets are located outside the through-hole unit, and the inner magnets are located between two adjacent transverse through-hole units.

9. The design method according to claim 8, characterized in that, The outer magnet and the inner magnet have the same width in the third direction and the same thickness in the first direction; the outer magnet and the inner magnet have the same or different heights in the second direction.

10. The design method according to claim 9, characterized in that, By changing the width of the outer magnet in the third direction and the height of the outer magnet in the second direction, the axial magnetic field strength and angular magnetic field intensity of the periodic permanent magnet focusing system can be adjusted, thereby optimizing the focusing performance of the periodic permanent magnet focusing system.

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