Multipole magnet

Abstract

The application provides a multipole magnet. The multipole magnet comprises a magnetic yoke, M pole heads, permanent magnets and field coils. The M pole heads are arranged inside the magnetic yoke, and M is an even number greater than or equal to 2. The permanent magnets are arranged on the M pole heads, and each of the M pole heads is sleeved with a field coil. The permanent magnets are used to generate a fixed magnetic field, the M pole heads generate an adjustable magnetic field under the condition that the M field coils are energized, adjacent pole heads have opposite polarities, the polarization direction of the permanent magnets matches the polarity of the adjacent pole heads, the fixed magnetic field and the adjustable magnetic field are superimposed to form a composite magnetic field for deflecting or focusing a charged particle beam, and a magnetic circuit formed by the magnetic yoke is used to constrain the composite magnetic field.

Description

Technical Field

[0001] This application relates to the fields of nuclear science and accelerator magnet technology, and specifically to a multipole magnet. Background Technology

[0002] Multipole magnets, as one of the core components of particle accelerators, are used to control the trajectory of charged particles. The ability of multipole magnets to control particle trajectories depends on the strength of the magnetic field they generate. However, the inherent magnetic field saturation problem of the excitation materials themselves has become a technical bottleneck limiting the improvement of the magnetic field strength of multipole magnets. Summary of the Invention

[0003] In view of the above problems, this application provides a multipole magnet.

[0004] According to a first aspect of the embodiments of this application, a multipole magnet is provided. The multipole magnet includes a yoke, M pole heads, a permanent magnet, and excitation coils. The M pole heads are disposed inside the yoke, where M is an even number greater than or equal to 2. The permanent magnets are disposed on the M pole heads, and each of the M pole heads is fitted with an excitation coil. The permanent magnets generate a fixed magnetic field, and the M pole heads generate an adjustable magnetic field when the M excitation coils are energized. Adjacent pole heads have opposite polarities, and the polarization direction of the permanent magnets matches the polarity of the adjacent pole heads. The fixed magnetic field and the adjustable magnetic field are superimposed to form a composite magnetic field for deflecting or focusing a beam of charged particles. The magnetically conductive circuit formed by the yoke is used to confine the composite magnetic field.

[0005] According to an embodiment of this application, permanent magnets are disposed between the ends of adjacent poles that are away from the yoke, and the M permanent magnets and the M poles form a closed pattern.

[0006] According to an embodiment of this application, adjacent poles include a first pole and a second pole, and the polarization direction of the permanent magnet points towards the first pole and away from the second pole.

[0007] According to an embodiment of this application, the permanent magnets have the same length in a preset direction, which is perpendicular to the plane containing the M pole heads.

[0008] According to an embodiment of this application, permanent magnets are disposed on opposite sides of the end of the pole head away from the yoke in a preset direction, and the preset direction is perpendicular to the plane where the M pole heads are located.

[0009] According to an embodiment of this application, adjacent poles include a third pole and a fourth pole. The polarization direction of the permanent magnet on the third pole points towards the third pole, and the polarization direction of the permanent magnet on the fourth pole points away from the fourth pole.

[0010] According to an embodiment of this application, the shape of the permanent magnet is the same as the shape of the end of the pole head.

[0011] According to embodiments of this application, the permanent magnets on opposite sides of the end of the pole head have the same length in a preset direction; and / or the magnetic field saturation value of the composite magnetic field is determined based on the length of the permanent magnets in the preset direction.

[0012] According to an embodiment of this application, the ends of the M poles furthest from the yoke are arc-shaped to increase the convergence of magnetic lines of force at the ends.

[0013] According to an embodiment of this application, the diameter of the magnet formed by the M pole heads is greater than or equal to 10 mm.

[0014] According to an embodiment of this application, a multipole magnet is provided. This multipole magnet has permanent magnets disposed on multiple poles located inside the yoke, the polarization direction of which matches the poles to which they are connected. The permanent magnets can generate a fixed magnetic field inside the yoke, and this fixed magnetic field, combined with the adjustable magnetic field generated by the multiple poles, forms a composite magnetic field. This composite magnetic field can improve the magnetic field saturation value of the adjustable magnetic field, alleviating the magnetic field saturation problem of the multiple poles. Attached Figure Description

[0015] The above-mentioned contents, other objects, features and advantages of this application will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0016] Figure 1 A schematic diagram of the structure of a multipole magnet according to an embodiment of this application is shown. Figure 2 A schematic diagram of the structure of a quadrupole magnet according to an embodiment of this application is shown.

[0017] Figure 3 A partial schematic diagram of the structure of a quadrupole magnet according to an embodiment of this application is shown;

[0018] Figure 4 A schematic diagram illustrating the magnetic field lines distribution of a quadrupole magnet in a relevant example is shown.

[0019] Figure 5 A schematic diagram illustrating the magnetic field lines distribution of a quadrupole magnet according to an embodiment of this application is shown.

[0020] Figure 6 The diagram illustrates the trend of the magnetic field gradient of a quadrupole magnet as a function of excitation current according to embodiments of this application and related examples.

[0021] Figure 7 A schematic diagram of the structure of a hexagonal magnet according to an embodiment of this application is shown.

[0022] Figure 8 A partial schematic diagram of the structure of a hexapole magnet according to an embodiment of this application is shown;

[0023] Figure 9 A schematic diagram of the structure of an octagonal magnet according to an embodiment of this application is shown.

[0024] Figure 10 A partial schematic diagram of the structure of an octagonal magnet according to an embodiment of this application is shown;

[0025] Figure 11 The diagram schematically illustrates the magnetic field strength distribution of a hexapole magnet according to embodiments and related examples of this application;

[0026] Figure 12 The diagram schematically illustrates the magnetic field strength distribution of an octagonal magnet according to embodiments and related examples of this application;

[0027] Figure 13 A schematic diagram of the structure of a multipole magnet according to another embodiment of this application is shown.

[0028] Figure 14 A schematic diagram illustrating the structure of the pole head of a multipole magnet according to another embodiment of this application is shown.

[0029] Figure 15 The diagram schematically illustrates the magnetic field strength distribution of a multipole magnet according to another embodiment and related examples of this application. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0031] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this application.

[0032] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0033] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0034] In the description of this application, it should be understood that the terms "longitudinal", "length", "circumferential", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the subsystem or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0035] Similarly, to simplify this application and aid in understanding one or more of the various disclosed aspects, in the above description of exemplary embodiments of this application, various features of this application are sometimes grouped together into a single embodiment, figure, or description thereof. The use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicates that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0036] Multipole magnets are one of the core components of particle accelerators, which are part of synchrotron radiation sources, colliders, or free-electron laser devices. Multipole magnets can be used to generate strong magnetic fields to deflect or focus beams of charged particles to maintain their trajectories and thus control beam quality (e.g., beam size).

[0037] For example, multipole magnets can be configured with different numbers of poles to create different corresponding gradient magnetic fields, causing charged particles to produce different trajectories.

[0038] However, the ability of a multipole magnet to control particle trajectories depends on the strength of the magnetic field it generates. Limited by the excitation efficiency of the pole head and the magnet aperture in the beam region, the maximum magnetic field gradient that a multipole magnet can provide is constrained; that is, a saturation magnetic field gradient exists. Beyond the saturation gradient, even a significant increase in the excitation current yields only a negligible increase in the magnetic field gradient, thus limiting the improvement in magnetic field strength. Therefore, the inherent magnetic field saturation problem of the excitation material itself is one of the factors limiting the upper limit of the magnetic field strength provided by a multipole magnet.

[0039] In view of this, embodiments of this application provide a multipole magnet. By incorporating permanent magnets at the pole heads, this multipole magnet can alleviate the magnetic field saturation problem at the pole heads, thereby achieving the goal of increasing the magnetic field strength in the central region of the multipole magnet.

[0040] Figure 1A schematic diagram of a multipole magnet according to an embodiment of this application is shown. It should be noted that... Figure 1 Characterized the multipole magnet in the direction of the particle beam (e.g. Figure 4 A schematic diagram of the structure on a cross-section perpendicular to the plane of the paper. Figure 1 In the diagram, the x-axis represents the horizontal direction on the cross-section of the multipole magnet, the y-axis represents the vertical direction on the cross-section of the multipole magnet, and the intersection of the x-axis and y-axis represents the beam center of the magnetic field formed by the multipole magnet.

[0041] like Figure 1 As shown, the multipole magnet of this embodiment may include a yoke 1, M pole heads 2, a permanent magnet 4, and an excitation coil 3. The yoke 1 is a magnetically conductive component that forms a closed magnetic circuit. The pole heads 2 and the yoke 1 may be integrated. In this embodiment, the yoke 1 and the pole heads 2 may be iron cores, such as electromagnetic pure iron DT4 of grade 4 or ferromagnetic material J23, etc. In specific embodiments, the shape of the yoke 1 may include any one of a circle or a polygon. For example, a polygon may include a quadrilateral, pentagon, or hexagon, etc. The shape of the yoke 1 can be designed according to specific practical application requirements, and this application does not impose specific limitations.

[0042] M pole heads 2 can be arranged on the inner side of the magnetic yoke 1, where M can be an even number greater than or equal to 2. The pole heads 2 can be evenly distributed on the inner wall of the magnetic yoke 1 and arranged facing each other. Each pole head 2 can be fitted with an excitation coil 3, which provides excitation current to the pole head 2 when energized. The excitation coils 3 can generate excitation current using a single power supply, group power supply, or independent power supply. The excitation coils 3 can be coils made of metal wire, such as copper wire. Adjacent pole heads 2 have opposite polarities under the action of the excitation current; that is, adjacent pole heads 2 can be N poles and S poles, respectively. Multiple pole heads 2 can generate an adjustable magnetic field within the beam region.

[0043] A permanent magnet 4 can be mounted on the pole head 2 to generate a fixed magnetic field. The polarization direction of the permanent magnet 4 matches the polarity of the connected pole head 2. The fixed magnetic field generated by the permanent magnet 4 and the adjustable magnetic fields generated by multiple pole heads 2 can be superimposed to form a composite magnetic field. The composite magnetic field can be used to deflect or focus a charged particle beam. The magnetic circuit formed by the magnetic yoke 1 can be used to confine this composite magnetic field.

[0044] According to an embodiment of this application, the multipole magnet has permanent magnets disposed on multiple poles located inside the yoke, and the polarization direction of the permanent magnets matches that of the poles they are connected to. The permanent magnets can generate a fixed magnetic field inside the yoke, and the fixed magnetic field is superimposed with the adjustable magnetic field generated by the multiple poles to form a composite magnetic field. This composite magnetic field can increase the magnetic field saturation value of the adjustable magnetic field, thereby alleviating the magnetic field saturation problem of the multiple poles.

[0045] For ease of description, the multipole magnet of this application will be further described below with reference to specific embodiments.

[0046] Figure 2 A schematic diagram of the structure of a quadrupole magnet according to an embodiment of this application is shown. Figure 3 A partial schematic diagram of the structure of a quadrupole magnet according to an embodiment of this application is shown. It should be noted that... Figure 3 The conical arrow in the figure represents the polarization direction of the permanent magnet.

[0047] In some embodiments, such as Figure 2 and Figure 3 As shown, the permanent magnet 4 can be disposed between adjacent pole heads 2. For example, Figure 2 and Figure 3 In the example quadrupole magnet, a permanent magnet 4 can be disposed between every two pole heads 2. The permanent magnet 4 can be disposed at the end of the pole head 2, i.e., the end furthest from the yoke 1, where an excitation coil 3 can be wound around the exposed area of ​​each pole head 2. Thus, multiple permanent magnets 4 and multiple pole heads 2 can form a closed shape, for example... Figure 2 and Figure 3 The example is a ring, or any of the other polygons.

[0048] Continue to refer to Figure 2 and Figure 3 The permanent magnets 4 can have the same length in a preset direction, which can be perpendicular to the plane where the multiple poles are located, i.e., the preset direction can be perpendicular to the plane of the paper. In addition, the permanent magnets 4 located between adjacent poles 2 can have the same shape and size, so that the multiple permanent magnets 4 can form a uniform fixed magnetic field.

[0049] Continue to refer to Figure 3 Adjacent poles 2 may include a first pole 21 and a second pole 22. The first pole 21 may be the N pole, and the second pole 22 may be the S pole. The polarization direction of the permanent magnet 4 may point towards the first pole 21 and away from the second pole 22, such as... Figure 3 The conical arrow indicates the meaning.

[0050] In relevant examples, multi-pole magnets with different numbers of poles can construct uniform magnetic fields with corresponding gradients that cause ions to produce different trajectories. For example, a diode magnet (without a permanent magnet) in a relevant example can form a uniform zero-order gradient magnetic field; this magnetic field can cause the particle's trajectory to bend into an arc, with the radius of curvature being directly proportional to the particle's energy and inversely proportional to the magnetic field strength of the diode magnet. Additionally, a quadrupole magnet (without a permanent magnet) in a relevant example can form a uniform first-order gradient magnetic field in the beam region, i.e., a magnetic field whose magnetic field strength changes at a constant rate with spatial displacement; this magnetic field can focus the particle's trajectory around the central orbit, with the focusing force proportional to the magnetic field gradient of the quadrupole magnet. The following will combine... Figure 4 and Figure 5 The differences in the magnetic field lines distribution between the quadrupole magnets in the relevant examples and the quadrupole magnet of this application are further described.

[0051] Figure 4 A schematic diagram illustrating the magnetic field lines distribution of a quadrupole magnet in a relevant example is shown. Figure 5 A schematic diagram illustrating the magnetic field lines distribution of a quadrupole magnet according to an embodiment of this application is provided. It should be noted that... Figure 4 The magnetic field line distribution of a quadrupole magnet without permanent magnets under magnetic field saturation conditions is characterized. Figure 5 The magnetic field lines distribution of a quadrupole magnet equipped with permanent magnets is characterized under magnetic field saturation conditions.

[0052] like Figure 4 and Figure 5 As shown, the quadrupole magnet (without a permanent magnet) in the related examples has relatively uniform magnetic field lines distributed within its beam region. In this embodiment, the quadrupole magnet (with a permanent magnet) has more concentrated magnetic field lines at the pole tip end, creating a magnetic field convergence effect. This indicates that the permanent magnet significantly affects the magnetic flux at the pole tip end, making the magnetic flux more concentrated in a specific region, which is beneficial for improving the magnetic field gradient of the quadrupole magnet. Furthermore, the density of magnetic field lines can also characterize the magnetic field saturation within the beam region. Compared to the quadrupole magnet in the related examples, the magnetic field line density near the permanent magnet is lower, indicating that the permanent magnet also has a positive effect on alleviating the magnetic field saturation problem at the pole tip.

[0053] Figure 6 The diagram schematically illustrates the trend of the magnetic field gradient of a quadrupole magnet as a function of excitation current, according to embodiments of this application and related examples. It should be noted that the ideal case represents a trend without considering magnetic field saturation.

[0054] like Figure 6As shown, compared to the quadrupole magnet (without a permanent magnet) in related examples, the saturation magnetic field gradient of the quadrupole magnet (with a permanent magnet) in this embodiment can be increased by nearly 25%. The addition of a permanent magnet widens the linear space of the magnetic field gradient as a function of the excitation current, resulting in a relatively higher plateau for magnetic field gradient saturation, thus increasing the saturation magnetic field gradient. Therefore, the addition of a permanent magnet can improve the magnetic field strength under the same excitation current within a certain range.

[0055] The effect of increasing the magnetic field gradient by setting permanent magnets is also applicable to higher-order multipole magnets. The following will describe this further using hexapole magnets and octapole magnets as examples. Figure 7 A schematic diagram of the structure of a hexagonal magnet according to an embodiment of this application is shown. Figure 8 A partial schematic diagram of the structure of a hexapole magnet according to an embodiment of this application is shown; Figure 9 A schematic diagram of the structure of an octagonal magnet according to an embodiment of this application is shown. Figure 10 A partial schematic diagram of the structure of an octagonal magnet according to an embodiment of this application is shown. Figure 8 and Figure 10 The conical arrow in the figure represents the polarization direction of the permanent magnet.

[0056] like Figures 7-10 As shown, both the hexapole and octagonal magnets in this embodiment may include a yoke 1, multiple pole pieces 2, an excitation coil 3, and a permanent magnet 4. The polarization direction of the permanent magnet 4 matches the polarity of the adjacent pole piece 2. Adjacent pole pieces 2 may include a first pole piece 21 and a second pole piece 22. The first pole piece 21 may be an N pole, and the second pole piece 22 may be an S pole. The polarization direction of the permanent magnet 4 may point towards the first pole piece 21 and away from the second pole piece 22. Other structures of the hexapole and octagonal magnets in this embodiment are similar to the structure of the aforementioned quadrupole magnet, and will not be described in detail here.

[0057] In the relevant examples, a hexapole magnet (without a permanent magnet) can generate a uniform second-order gradient magnetic field, meaning the magnetic field strength is distributed as a quadratic function along spatial displacement, with a constant second-order gradient. This magnetic field can correct the chromaticity of particle motion, and its ability to correct chromaticity is proportional to the second-order gradient. Similarly, an octapole magnet (without a permanent magnet) in the relevant examples can generate a uniform third-order gradient magnetic field, meaning the magnetic field strength is distributed as a cubic function along spatial displacement, with a constant third-order gradient. This magnetic field can be used for Landau damping in particle accelerators, thereby stabilizing particle motion and suppressing instabilities. The following will combine... Figure 11 and Figure 12 The effects of the multipole magnets in this application are further described.

[0058] Figure 11The diagram schematically illustrates the magnetic field strength distribution of a hexapole magnet according to embodiments and related examples of this application; Figure 12 The diagram illustrates the magnetic field strength distribution of an octagonal magnet according to embodiments and related examples of this application. Figure 11 and Figure 12 The horizontal axis represents the distance from the center of the beam on the horizontal axis inside the magnetic field, and the vertical axis represents the magnetic field strength at different distances on the horizontal axis. It should be noted that the aperture of the magnets housed in both the hexapole and octagonal magnets in this embodiment is 75mm.

[0059] like Figure 11 As shown, for a hexapole magnet with a 75mm aperture, the saturation magnetic field strength of the hexapole magnet in the related example (without a permanent magnet) can be 0.5T, while the saturation magnetic field strength of the hexapole magnet in this embodiment (with a permanent magnet) can be 0.8T, achieving an improvement of 60%. In addition, the second-order magnetic field gradient of the hexapole magnet in this embodiment is also significantly improved.

[0060] like Figure 12 As shown, for an octagonal magnet with a 75mm aperture, the saturation magnetic field strength of the octagonal magnet in the related example (without a permanent magnet) can be 0.4T, while the saturation magnetic field strength of the octagonal magnet in this embodiment (with a permanent magnet) can be 0.8T, achieving a 100% improvement. Furthermore, the third-order magnetic field gradient of the octagonal magnet in this embodiment is also significantly improved.

[0061] Figure 13 A schematic diagram of the structure of a multipole magnet according to another embodiment of this application is shown. Figure 14 A schematic diagram of the structure of the pole head of a multipole magnet according to another embodiment of this application is shown. Figure 13 Using a quadrupole magnet as an example, this principle also applies to other types of multipole magnets. Figure 14 The horizontal direction of the middle paper is perpendicular to Figure 15 The orientation of the middle paper, Figure 14 The conical arrow in the diagram can represent the polarization direction of the permanent magnet.

[0062] like Figure 13 and Figure 14 As shown, the permanent magnet 4 can also be disposed on opposite sides of the end of the pole head 2 in a preset direction. The preset direction can be perpendicular to the plane where the multiple pole heads 2 are located, that is, the permanent magnet 4 is disposed in the longitudinal direction of the multi-pole magnet. In some embodiments, the lengths of the permanent magnets 4 on opposite sides of the end of the pole head 2 in the preset direction can be the same. The shape of the permanent magnet 4 can be the same as the shape of the end of the pole head 2.

[0063] According to embodiments of this application, placing the permanent magnet in the longitudinal direction of the multipole magnet not only increases the magnetic field strength by enhancing the magnetic field gradient, but more importantly, it allows for compatibility with the vacuum chamber structure in particle accelerators, avoiding structural conflicts. In complex devices involving vacuum chamber structures, the spatial layout and structural compatibility between components are crucial considerations. The longitudinal permanent magnet design avoids mutual interference with the vacuum chamber structure, ensuring the structural and functional stability and coordination of the entire device. This structural advantage not only simplifies the overall device design and reduces potential failures and performance degradation caused by structural conflicts, but also facilitates the installation, commissioning, and maintenance of the device, thereby improving the overall operating efficiency and reliability of the device.

[0064] Continue to refer to Figure 14 Adjacent pole heads 2 may include a third pole head 23 and a fourth pole head 24. The third pole head 23 can be an N pole, and the fourth pole head 24 can be an S pole. The polarization direction of the permanent magnet 4 on the third pole head 23 can point towards the third pole head 23, and the polarization direction of the permanent magnet 4 on the fourth pole head 24 can point away from the fourth pole head 24, such as... Figure 14 The conical arrow indicates the meaning.

[0065] In some embodiments, the magnetic field saturation value of the composite magnetic field can be determined based on the length of the permanent magnet in a predetermined direction. The magnetic field saturation value may include the magnetic field gradient, magnetic field strength, etc.

[0066] Figure 15 The schematic diagram illustrates the magnetic field strength distribution of a multipole magnet according to another embodiment and related examples of this application. It should be noted that... Figure 15 The example multipole magnet is a quadrupole magnet. The horizontal axis represents the distance from the center of the beam on the horizontal axis inside the magnetic field, and the vertical axis represents the magnetic field strength at different distances on the horizontal axis. It should be noted that the quadrupole magnet in this embodiment has a magnet aperture of 75mm, a pole length of 0.3m in the preset direction, and a permanent magnet length of 40mm in the preset direction.

[0067] like Figure 15 As shown, for a quadrupole magnet with a 75mm aperture, the saturation magnetic field strength of the quadrupole magnet (with a permanent magnet) in this embodiment is slightly higher than that of the quadrupole magnet (without a permanent magnet) in the related examples. Furthermore, the magnetic field gradient of the quadrupole magnet in the related examples is 22.28 T / m, while the magnetic field gradient of the quadrupole magnet in this embodiment can be 23.94 T / m, representing an improvement of 7.5%.

[0068] Continue to refer to Figure 1 , Figure 2 , Figure 7 , Figure 8 and Figure 13 The ends of the multiple pole tips 2 furthest from the yoke 1 can be rounded to increase the convergence of magnetic lines of force at the ends. The rounded shape of the pole tips 2 can be formed by chamfering. The excitation coil 3 exposes the ends of the pole tips 2.

[0069] According to embodiments of this application, the chamfered pole tip is arc-shaped, which can reduce stress concentration at the pole tip end, optimize magnetic field distribution, and improve the uniformity and continuity of magnetic field quality. Exposing the pole tip end with the excitation coil can reduce magnetic field distortion at the pole tip end and improve the control accuracy of beam extraction.

[0070] In some embodiments, the magnet aperture within the beam region formed by the multiple pole heads can be greater than or equal to 10 mm, such as 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 75 mm, 80 mm, etc., which are not listed here. The multipole magnet can generate a strong magnetic field within this magnet aperture to deflect or focus the charged particle beam to maintain particle orbits, thereby controlling the beam size and quality. According to embodiments of this application, the permanent magnet structure can alleviate the magnetic field saturation problem of the multipole magnet, thereby achieving the purpose of increasing the magnetic field strength in the central region of the multipole magnet.

[0071] Those skilled in the art will understand that the features described in the various embodiments of this application can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in this application. In particular, the features described in the various embodiments of this application can be combined and / or combined in various ways without departing from the spirit and teachings of this application. All such combinations and / or combinations fall within the scope of this application.

[0072] The embodiments of this application have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of this application. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Without departing from the scope of this application, those skilled in the art can make various substitutions and modifications, all of which should fall within the scope of this application.

Claims

1. A multipole magnet, characterized in that, include: Magnetic yoke; M poles are disposed on the inner side of the magnetic yoke, wherein M is an even number greater than or equal to 2; Permanent magnets are disposed on the M pole heads; The excitation coils of each of the M poles are fitted together; The permanent magnet is used to generate a fixed magnetic field. The M poles generate an adjustable magnetic field when the M excitation coils are energized. Adjacent poles have opposite polarities. The permanent magnets are disposed between the ends of the adjacent poles that are away from the magnetic yoke. The M permanent magnets and the M poles form a closed shape. The adjacent poles include a first pole and a second pole. The polarization direction of the permanent magnets points to the first pole and away from the second pole. The fixed magnetic field and the adjustable magnetic field are superimposed to form a composite magnetic field for deflecting or focusing a charged particle beam. The magnetic circuit formed by the magnetic yoke is used to confine the composite magnetic field.

2. The multipole magnet according to claim 1, characterized in that, The permanent magnets have the same length in a preset direction, which is perpendicular to the plane where the M poles are located.

3. The multipole magnet according to claim 1 or 2, characterized in that, The ends of the M poles furthest from the yoke are rounded to increase the convergence of magnetic field lines at the ends.

4. The multipole magnet according to claim 1 or 2, characterized in that, The diameter of the magnet formed by the M poles is greater than or equal to 10 mm.

5. A multipole magnet, characterized in that, include: Magnetic yoke; M poles are disposed on the inner side of the magnetic yoke, wherein M is an even number greater than or equal to 2; Permanent magnets are disposed on the M pole heads; The excitation coils of each of the M poles are fitted together; The permanent magnet is used to generate a fixed magnetic field. The M poles generate an adjustable magnetic field when the M excitation coils are energized. Adjacent poles have opposite polarities. The permanent magnet is disposed on opposite sides of the end of the pole away from the magnetic yoke in a preset direction. The preset direction is perpendicular to the plane in which the M poles are located. The adjacent poles include a third pole and a fourth pole. The polarization direction of the permanent magnet on the third pole points towards the third pole, and the polarization direction of the permanent magnet on the fourth pole points away from the fourth pole. The fixed magnetic field and the adjustable magnetic field are superimposed to form a composite magnetic field for deflecting or focusing a charged particle beam. The magnetic circuit formed by the magnetic yoke is used to confine the composite magnetic field.

6. The multipole magnet according to claim 5, characterized in that, The permanent magnet has the same shape as the end of the pole head.

7. The multipole magnet according to claim 6, characterized in that, The permanent magnets on opposite sides of the end of the pole head have the same length in the predetermined direction; and / or The magnetic field saturation value of the composite magnetic field is determined based on the length of the permanent magnet in the preset direction.

8. The multipole magnet according to any one of claims 5 to 7, characterized in that, The ends of the M poles furthest from the yoke are rounded to increase the convergence of magnetic field lines at the ends.

9. The multipole magnet according to any one of claims 5 to 7, characterized in that, The diameter of the magnet formed by the M poles is greater than or equal to 10 mm.

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