Antisymmetric hexapole magnet

Abstract

This invention provides an antisymmetric hexapole magnet, comprising an outer pole ring, pole heads, and an excitation coil. The pole heads are integral with the outer pole ring and include three pairs of sub-pole head groups uniformly distributed and facing each other on the inner wall of the outer pole ring. Two pairs of sub-pole head groups each include two facing main pole heads, and each of the other pair of sub-pole head groups includes two auxiliary pole heads with a predetermined interval. The facing main pole heads have the same polarity, while the auxiliary pole heads with the predetermined interval have opposite polarities, and adjacent main and auxiliary pole heads have opposite polarities. Each main pole head has the same geometric dimensions, and the sum of the volumes of the auxiliary pole heads with the predetermined interval is less than the volume of each main pole head. The excitation coil is wound around the pole heads to provide excitation current. The auxiliary pole heads are used to reduce the coupling effect between the main pole heads to improve the magnetic field quality of the antisymmetric hexapole magnetic field within the outer pole ring.

Description

Technical Field

[0001] This invention relates to the fields of nuclear science, resonant slow extraction of particle accelerators, and nonlinear beam collimation, and specifically to an antisymmetric hexapole magnet. Background Technology

[0002] Compared to hexapole magnets, antisymmetric hexapole magnets exhibit stronger resistance to magnet power supply ripple jitter and higher beam intensity in terms of slow beam resonant extraction and nonlinear beam collimation. This improves beam extraction stability and achieves higher beam collimation efficiency. Common antisymmetric hexapole magnets form their magnetic field by placing a pair of shielding plates between two pairs of magnetic poles. However, this structure has limitations. For example, when the beam extraction tube aperture is large, a larger magnet structure is often required to meet the requirement that the spacing of the shielding plates be greater than the beam extraction tube aperture, leading to a decrease in magnetic field quality. Summary of the Invention

[0003] In view of the above problems, embodiments of the present invention provide an antisymmetric hexapole magnet.

[0004] According to a first aspect of the present invention, an antisymmetric hexapole magnet is provided, comprising an outer pole ring, pole heads, and an excitation coil. The pole heads are integral with the outer pole ring and include three pairs of sub-pole head groups uniformly distributed and arranged opposite to each other on the inner wall of the outer pole ring. Two pairs of sub-pole head groups each include two main pole heads arranged opposite to each other, and each of the other pair of sub-pole head groups includes two auxiliary pole heads with a predetermined interval. The main pole heads arranged opposite to each other have the same polarity, and the auxiliary pole heads with the predetermined interval have opposite polarities. Adjacent main pole heads and auxiliary pole heads have opposite polarities. Each main pole head has the same geometric dimensions, and the sum of the volumes of the auxiliary pole heads with the predetermined interval is less than the volume of each main pole head. The excitation coil is wound around the pole head to provide an excitation current to the pole head. The auxiliary pole heads are used to reduce the coupling effect between the main pole heads to improve the magnetic field quality of the antisymmetric hexapole magnetic field within the outer pole ring.

[0005] According to an embodiment of the present invention, the excitation coil includes a first excitation coil wound around each main pole and a second excitation coil wound around each secondary pole. The first excitation coil and the second excitation coil are controlled by a first power supply and a second power supply that are independent of each other, so as to generate a first excitation current and a second excitation current.

[0006] According to an embodiment of the present invention, the magnetic field distribution of the preset region of the antisymmetric hexapole magnet is controlled by adjusting the first excitation current and the second excitation current. The preset region is the particle distribution region to be extracted in the beam extraction tube within the outer ring of the magnetic poles.

[0007] According to an embodiment of the present invention, the excitation coil further includes a third excitation coil. The third excitation coil is wound around the first excitation coil and located at the root of each main pole near the end of the outer ring of the magnetic pole. The third excitation coil is controlled by a third power supply to generate a third excitation current to regulate the magnetic field distribution of the antisymmetric hexapole magnetic field. The third power supply is independent of the first power supply and the second power supply.

[0008] According to an embodiment of the present invention, the secondary pole heads with a predetermined interval have the same geometric dimensions and are symmetrical to each other radially along the outer ring of the magnetic pole. The predetermined interval is determined based on the accommodating space of the excitation coil wound on each secondary pole head.

[0009] According to an embodiment of the invention, the ends of the main pole and the secondary pole away from the outer ring of the magnetic pole are arc-shaped to reduce magnetic field concentration at the ends. The excitation coil exposes the ends of the main pole and the secondary pole.

[0010] According to an embodiment of the present invention, the radial length of the outer ring of the magnetic pole is less than or equal to 700 mm, and the radius of the beam extraction tube in the antisymmetric hexapole magnet is less than or equal to 55 mm.

[0011] According to an embodiment of the present invention, the preset interval between the secondary electrodes is less than or equal to 32 mm.

[0012] According to an embodiment of the present invention, the distance between the top of the end of the pole head away from the outer ring of the magnetic pole and the beam outlet tube in the radial direction of the outer ring of the magnetic pole is greater than or equal to 5 mm.

[0013] According to an embodiment of the present invention, the shortest distance between the main electrode head and the cross-section of the beam outlet tube is greater than or equal to 12 mm.

[0014] According to an embodiment of the present invention, an antisymmetric hexapole magnet is provided. This magnet has three pairs of opposing sub-pole head groups disposed inside the outer ring of the magnetic poles, and the sub-pole head groups are uniformly distributed on the inner wall of the outer ring. Each sub-pole head group includes two pairs of opposing main pole heads with identical geometric dimensions and one pair of opposing secondary pole heads with a predetermined interval. The sum of the volumes of the secondary pole heads with the predetermined interval is less than the volume of each main pole head. The opposing main pole heads have the same polarity, while the secondary pole heads with the predetermined interval have opposite polarities, and adjacent main and secondary pole heads also have opposite polarities. Under the control of the excitation current, the main and secondary pole heads can form an antisymmetric hexapole magnetic field inside the outer ring of the magnetic poles. The secondary pole heads can reduce the coupling effect between the main pole heads, thereby improving the magnetic field quality of the antisymmetric hexapole magnetic field. Furthermore, this structure avoids the need to add a shielding plate to form an antisymmetric hexapole magnetic field, alleviating the contradiction between increasing the aperture of the current extraction tube and improving the magnetic field quality. Attached Figure Description

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

[0016] Figure 1 A schematic diagram of a hexapole magnet is shown.

[0017] Figure 2 A schematic diagram of the structure of an antisymmetric hexapole magnet in a relevant example is shown.

[0018] Figure 3 A schematic diagram of the antisymmetric hexapole magnetic field formed by an antisymmetric hexapole magnet in a relevant example is shown.

[0019] Figure 4 A schematic diagram of the structure of an antisymmetric hexapole magnet according to an embodiment of the present invention is shown.

[0020] Figure 5 A magnetic flux structure diagram of an antisymmetric hexapole magnet according to an embodiment of the present invention is shown.

[0021] Figure 6 The diagram shows the magnetic field strength of an antisymmetric hexapole magnet under different excitation currents according to an embodiment of the present invention.

[0022] Figures 7(a) to 7(d) show the fitting diagrams of the magnetic field strength of the antisymmetric hexapole magnet of the present invention under different excitation currents.

[0023] Figure 8 The diagram shows a comparison of the magnetic field strength of the antisymmetric hexapole magnetic field under the control of the third excitation current and the ideal antisymmetric hexapole magnetic field according to an embodiment of the present invention.

[0024] Figure 9 The diagram shows the first derivative of the magnetic field strength of the antisymmetric hexapolar magnetic field formed according to an embodiment of the present invention.

[0025] Figure 10 A comparison diagram of the linearity of the magnetic field strength of the antisymmetric hexapole magnet according to an embodiment of the present invention is shown. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0027] The endpoints and any values ​​of the ranges disclosed in this invention 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 invention.

[0028] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. 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.

[0029] 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.

[0030] In the description of this invention, 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 invention 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 invention.

[0031] Similarly, to simplify the invention and aid in understanding one or more aspects, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof in the above description of exemplary embodiments of the invention. The use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples" 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 the invention. 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.

[0032] As an important nonlinear element in particle accelerators, hexapole magnets are widely used in particle accelerators for chromaticity correction, third-order resonant slow extraction, and nonlinear beam collimation.

[0033] Figure 1 A schematic diagram of a hexapole magnet is shown. Figure 1 Characterized the direction of the hexapole magnet and the beam (e.g.) Figure 1 A schematic diagram of 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 hexapole magnet, the y-axis represents the vertical direction on the cross-section of the hexapole magnet, and the intersection of the x-axis and y-axis represents the beam center of the hexapole magnetic field formed by the hexapole magnet.

[0034] like Figure 1 As shown, a hexapole magnet may include an outer pole ring 1, pole heads 2, and an excitation coil 3. Three pairs of pole heads 2 are evenly distributed and arranged opposite to each other on the inner wall of the outer pole ring 1. Adjacent pole heads 2 have opposite polarities. The excitation coil 3 is wound around the pole heads 2 and uses a single power supply to generate the same excitation current on the pole heads 2.

[0035] A hexapole magnet can form a hexapole magnetic field that is symmetrically distributed horizontally about the center of the beam inside the outer ring 1 of the magnetic poles. The magnetic field strength of the hexapole magnetic field can be expressed as shown in formula (1).

[0036] (1)

[0037] In formula (1), B x B y The x and y axes can represent the magnetic field strength of the hexagonal magnetic field, respectively. x and y can represent the horizontal and vertical distances of the particle to be extracted relative to the beam center on the x and y axes, respectively.

[0038] Compared to a hexapole magnetic field, the antisymmetric hexapole magnetic field exhibits an antisymmetric field pattern about the beam center, only aligning with the hexapole magnetic field on the horizontal side of the beam center. Regarding slow beam resonant extraction, the antisymmetric hexapole magnetic field, due to the greater distance between the operating point and the resonant point of the extracted particles, possesses stronger resistance to magnet power supply ripple jitter, thus improving beam extraction stability. In terms of nonlinear beam collimation, because it can collimate halo particles (unstable particles deviating from the beam particle trajectory) on both sides of the collimator, theoretically, within the range where the collimator can collimate halo particles, the beam intensity can be nearly doubled, thereby achieving higher beam collimation efficiency.

[0039] To achieve the aforementioned antisymmetric hexapolar magnetic field, the relevant examples designed as follows: Figure 2 The antisymmetric hexapole magnet structure shown. Figure 2 A schematic diagram of the structure of an antisymmetric hexapole magnet in a relevant example is shown. Figure 3 A schematic diagram of the antisymmetric hexapole magnetic field formed by an antisymmetric hexapole magnet in a relevant example is shown. It should be noted that... Figure 2 The x-axis and y-axis in Figure 1 The coordinate axes in the text have the same meaning, so they will not be repeated here. Figure 3 In the diagram, the x and y coordinates of the antisymmetric hexapole magnet represent the distances from the beam center, with the unit of distance being cm.

[0040] like Figure 2As shown, the antisymmetric hexapole magnet in the relevant example may include an outer pole ring 1, pole heads 2, an excitation coil 3, and a shielding plate 4. This structure may include two pairs of pole heads 2 arranged opposite each other, with the pole heads 2 having an antisymmetric polarity distribution; for example, pole heads 2 arranged opposite each other have opposite polarities, and pole heads 2 on the same side of the x-axis have opposite polarities. Opposing shielding plates 4 can be placed in the middle region of the two pairs of pole heads 2. The shielding plate 4 functions similarly to the iron spacer or air gap in a magnet, thereby forming a structure such as... Figure 3 The antisymmetric hexapole magnetic field is shown. The magnetic field strength of the antisymmetric hexapole magnetic field can be expressed as shown in formula (2).

[0041] (2)

[0042] In formula (2), B x B y These can represent the magnetic field strength of the antisymmetric hexagonal magnetic field on the x-axis and y-axis, respectively. x and y can represent the horizontal and vertical distances of the particle to be extracted relative to the beam center on the x-axis and y-axis, respectively.

[0043] However, the antisymmetric hexapole magnets in the relevant examples have certain limitations. To obtain better magnetic field quality, the spacing between the shielding plates is generally set to be relatively small. For example... Figure 3 As shown, the radial dimension of the outer ring of the magnetic poles is approximately 70 cm, while the spacing between the shielding plates is less than 10 cm. Generally, the beam extraction tubes used for resonant slow extraction are relatively large. To meet the requirement that the spacing of the shielding plates is larger than the aperture of the beam extraction tube, it is often necessary to design an antisymmetric hexapole magnet much larger than the aperture of the beam extraction tube. Because the antisymmetric hexapole magnet is short in the longitudinal direction (e.g., perpendicular to the plane of the paper), the increased size in the transverse direction (e.g., in the plane of the paper) will produce a strong edge field effect, resulting in a significant decrease in magnetic field quality. Furthermore, the positions of the pole heads and shielding plates of the antisymmetric hexapole magnet in the above structure are relatively fixed, and the field shape of the resulting antisymmetric hexapole magnetic field is also fixed, making significant adjustments difficult. This also reduces the operational flexibility of the resonant slow extraction process.

[0044] In view of this, embodiments of the present invention provide an antisymmetric hexapole magnet. This magnet structure employs two pairs of main pole heads and four secondary pole heads arranged inside the outer ring of the magnetic poles. By designing the polarity of each pole head, an antisymmetric hexapole magnetic field is formed. This not only reduces the coupling effect between the main pole heads and improves the magnetic field quality of the antisymmetric hexapole magnetic field, but also avoids the contradiction between increasing the overall size of the magnet and improving the magnetic field quality caused by setting a shielding plate.

[0045] Figure 4 A schematic diagram of the structure of an antisymmetric hexapole magnet according to an embodiment of the present invention is shown.

[0046] like Figure 4 As shown, the antisymmetric hexapole magnet of this embodiment may include an outer pole ring 1, a pole head 2, and an excitation coil 3. The pole head 2 and the outer pole ring 1 may be integral. In this embodiment, the outer pole ring 1 and the pole head 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 outer pole ring 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 outer pole ring 1 can be designed according to specific practical application requirements, and this invention does not impose specific limitations.

[0047] The pole head 2 may include three pairs of sub-pole head groups. These sub-pole head groups can be uniformly distributed on the inner wall of the outer magnetic ring 1 and arranged opposite each other. Two pairs of sub-pole head groups may each include two main pole heads 21 arranged opposite each other. Each sub-pole head group in the other pair may include two auxiliary pole heads 22 with a predetermined interval d. The main pole heads 21 arranged opposite each other have the same polarity; for example, both main pole heads arranged opposite each other may be N poles or both may be S poles. The auxiliary pole heads 22 with the predetermined interval have opposite polarities. Adjacent main pole heads 21 and auxiliary pole heads 22 have opposite polarities. Thus, each adjacent pole head 2 (including main pole head 21 and auxiliary pole head 22) inside the outer magnetic ring 1 has opposite polarities. The auxiliary pole heads 22 can be used to reduce the coupling effect between the main pole heads 21 to improve the magnetic field quality of the antisymmetric hexapole magnetic field within the outer magnetic ring 1. The magnetic field quality can be characterized by magnetic field strength, etc.

[0048] Each main pole head 21 has the same geometric dimensions, and the sum of the volumes of the secondary pole heads 22 with a preset interval d can be less than the volume of each main pole head 21. In the process of manufacturing the antisymmetric hexapole magnet of this embodiment, six uniformly distributed pole heads 2 can be formed inside the outer ring 1 of the magnetic poles, each pole head 2 having the same geometric dimensions; then, the middle part of one pair of opposing pole heads 2 is cut to form two secondary pole heads 22 with a preset interval d, thereby forming the structure of the antisymmetric hexapole magnet of this embodiment.

[0049] The excitation coil 3 can be wound around the pole 2 to provide excitation current to the pole 2. The excitation coil 3 can be a coil made of metal wire, such as copper wire.

[0050] According to an embodiment of the present invention, an antisymmetric hexapole magnet is provided. This magnet has three pairs of opposing sub-pole head groups disposed inside the outer ring of the magnetic poles, and the sub-pole head groups are uniformly distributed on the inner wall of the outer ring. Each sub-pole head group includes two pairs of opposing main pole heads with identical geometric dimensions and one pair of opposing auxiliary pole heads with a predetermined interval. The sum of the volumes of the auxiliary pole heads with the predetermined interval is less than the volume of each main pole head. Each adjacent pole head has opposite polarities. Under the control of the excitation current, the main pole heads and auxiliary pole heads can form an antisymmetric hexapole magnetic field inside the outer ring of the magnetic poles. The auxiliary pole heads can reduce the coupling effect between the main pole heads, thereby improving the magnetic field quality of the antisymmetric hexapole magnetic field. Furthermore, this structure avoids the need to add a shielding plate to form an antisymmetric hexapole magnetic field, alleviating the contradiction between increasing the size of the beam extraction tube and improving the magnetic field quality.

[0051] Continue to refer to Figure 4 The excitation coil 3 is wound around each pole head 2 on the inner wall of the outer ring 1 of the magnetic poles. The excitation coil 3 may include a first excitation coil 31 wound around each main pole head 21 and a second excitation coil 32 wound around each auxiliary pole head 22. The first excitation coil 31 and the second excitation coil 32 may be controlled by a first power supply and a second power supply, respectively, to generate a first excitation current and a second excitation current. That is, the first excitation current in the four main pole heads 21 is controlled by the first power supply, and the second excitation current in the four auxiliary pole heads 22 is controlled by the second power supply.

[0052] According to an embodiment of the present invention, the four main poles in this embodiment regulate the excitation current through a first power supply, and the four auxiliary poles regulate the excitation current through a second power supply independent of the first power supply. The independent regulation of the first and second excitation currents can adjust the field shape of the antisymmetric hexapole magnet according to actual application requirements, making up for the shortcomings of the original magnetic field shape and distribution range being unadjustable after adding a shielding plate, and enhancing the flexibility of magnetic field regulation.

[0053] Figure 5 A magnetic flux structure diagram of an antisymmetric hexapole magnet according to an embodiment of the present invention is shown. Figure 5 The magnetic flux structure in the simulation is generated by calculation and can characterize the magnetic field distribution of the antisymmetric hexapolar magnetic field.

[0054] like Figure 5 As shown, the antisymmetric hexapole magnet of this embodiment can generate a magnetic field antisymmetric to the hexapole magnetic field, and the distribution within the central flat region (i.e., the good field region) is very close to that of an ideal antisymmetric hexapole magnetic field. In a particle accelerator, the beam extraction tube can be placed in the space formed by the pole head within the outer ring of the magnetic poles. By adjusting the first excitation current and the second excitation current, an antisymmetric hexapole magnetic field can be formed in a preset region of the antisymmetric hexapole magnet, and the particles to be extracted in the beam extraction tube can be distributed within the preset region.

[0055] In specific embodiments, the radial length of the outer ring of the magnetic poles can be less than or equal to 700 mm, such as 700 mm, 650 mm, 600 mm, 550 mm, 500 mm, etc. In this case, the radius of the beam extraction tube in the antisymmetric hexapole magnet can be less than or equal to 55 mm, such as 55 mm, 50 mm, 45 mm, 40 mm, 35 mm, 30 mm, etc. The minimum size of the beam extraction tube aperture can be determined based on the magnetic field strength required for beam extraction. It can be observed that, compared to the antisymmetric hexapole magnets in related examples, the aperture of the beam extraction tube accommodated by the magnet structure of this embodiment is much larger.

[0056] In a specific embodiment, the distance between the top of the end of the pole head furthest from the outer ring of the magnetic poles and the beam extraction tube in the radial direction of the outer ring of the magnetic poles can be greater than or equal to 5 mm, such as 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 7.5 mm, 8 mm, etc. The maximum distance between the pole head and the beam extraction tube can be set according to the aperture size of the beam extraction tube, which will not be listed here. The shortest distance between the main pole heads and the cross-section of the beam extraction tube can be greater than or equal to 12 mm, such as 12 mm, 13 mm, 14 mm, 15 mm, etc. The maximum distance between the main pole heads can be determined according to the magnetic field strength required for beam extraction.

[0057] Figure 6 The diagram shows the magnetic field strength of the antisymmetric hexapole magnet of the present invention under different excitation currents. Figures 7(a) to 7(d) show the fitted diagrams of the magnetic field strength of the antisymmetric hexapole magnet of the present invention under different excitation currents. Figure 6 In Figures 7(a) to 7(d), the horizontal axis represents the distance from the beam center along the horizontal axis inside the magnetic field, and the vertical axis represents the magnetic field strength at different distances along the horizontal axis. It should be noted that the aperture of the beam extraction tube housed in the antisymmetric hexapole magnet of this embodiment is 110 mm. Figure 6 Curves S1 to S4 correspond to the application of a current density of 0.4 A / mm² on the main electrode. 2 0.8A / mm 2 1.2A / mm 2 and 1.6A / mm 2 The magnetic field strength curves obtained from the first excitation current; Figures 7(a) to 7(d) correspond to the applied current density of 0.4 A / mm². 2 0.8A / mm 2 1.2A / mm 2 and 1.6A / mm 2 The fitting graph of the magnetic field strength under the excitation current.

[0058] like Figure 6 As shown, by adjusting the magnitude of the excitation current, the field shape distribution and magnetic field mass of the antisymmetric hexapole magnetic field can be controlled. The magnetic field strength in the magnetic field region of the antisymmetric hexapole magnet can be less than or equal to 0.06T. As shown in Figures 7(a) to 7(d), under different excitation currents, the fitting results of the antisymmetric hexapole magnetic field formed by the embodiments of the present invention are very close to those of the theoretical antisymmetric hexapole magnetic field. The fitting results in Figures 7(a) to 7(d) can be obtained using a 19th-order fitting algorithm, for example, with 0.4A / mm 2 0.8A / mm 2 1.2A / mm 2 and 1.6A / mm 2 The determination system R in the corresponding fitting results 2 As shown in Figures 7(a) to 7(d) respectively.

[0059] According to an embodiment of the present invention, since the antisymmetric hexagonal magnet is mainly used for the resonant slow extraction of particles in the horizontal direction (such as the paper direction in this embodiment), the magnetic field distribution in the good field region and the ideal antisymmetric hexagonal magnetic field match the requirements for particle extraction. This structure can also reduce the limitation on the aperture of the beam extraction tube.

[0060] Continue to refer to Figure 4 The excitation coil 3 may also include a third excitation coil 33. Since there is still additional space around the main pole head 21, the third excitation coil 33 can be wound around the first excitation coil 31. The third excitation coil 33 is located at the root of each main pole head 21 near the end of the outer ring 1 of the magnetic pole. The third excitation coil 33 can be controlled by a third power supply to generate a third excitation current to regulate the magnetic field distribution of the antisymmetric hexapole magnetic field. The third power supply can be independent of the first and second power supplies.

[0061] Figure 8 The diagram illustrates the difference in magnetic field strength between the antisymmetric hexapole magnetic field and the ideal antisymmetric hexapole magnetic field under the control of the third excitation current, according to an embodiment of the present invention. Curve S5 represents the difference in magnetic field strength between the antisymmetric hexapole magnet and the ideal antisymmetric hexapole magnet in the absence of a third excitation current. Curves S6 and S7 represent the difference in magnetic field strength between the antisymmetric hexapole magnet and the ideal antisymmetric hexapole magnet in the embodiment under different current directions of the third excitation current, respectively. Figure 8 The horizontal axis represents the distance from the beam center in the horizontal direction, and the vertical axis represents the difference between the magnetic field strength of the antisymmetric hexapole magnetic field in this embodiment and the magnetic field strength of the ideal antisymmetric hexapole magnetic field.

[0062] like Figure 8 As shown, the current density of the first excitation current at the main pole head is maintained at 1.2 A / mm. 2Without a third excitation current, a difference diagram of the magnetic field strength between the magnet and an ideal antisymmetric hexapole magnet, as shown in curve S5, can be formed in the good field region. By adjusting the current direction of the third excitation current in this embodiment, a difference diagram of the magnetic field strength between the magnet and an ideal antisymmetric hexapole magnet, as shown in curves S6 or S7, can be formed in the good field region. It can be observed that when the first excitation current of the main pole head remains unchanged, adjusting the current direction of the third excitation current changes the field distribution in the good field region. It can be observed that changing the current direction of the third excitation current can purposefully adjust the magnetic field quality of a certain region to be closer to the magnetic field of an ideal antisymmetric hexapole magnet, which is very beneficial for beam extraction.

[0063] According to an embodiment of the present invention, by adjusting the third excitation current in the third excitation coil, the magnetic field shape distribution and magnetic field quality in different regions of the field area can be adjusted. Since the particles at the edge of the beam are generally extracted first, and then the particles inside the beam are gradually extracted from the outside to the inside, adjusting the third excitation current can facilitate the gradual extraction of particles from the outside to the inside.

[0064] In addition, adjusting the magnitude of the second excitation current to regulate the magnetic field quality can further meet the application requirements of beam extraction.

[0065] Continue to refer to Figure 4 The secondary pole heads 22 with a preset interval d can have identical geometric dimensions. Two secondary pole heads 22 located on one side can be symmetrical to each other radially along the outer ring 1 of the magnetic poles. The size of the preset interval d can be determined based on the accommodating space of the excitation coil (second excitation coil) wound on each secondary pole head 22. In a specific embodiment of the invention, the preset interval d between the secondary pole heads 22 can be less than or equal to 32 mm, for example, it can be 16 mm, 20 mm, 24 mm, 28 mm, 32 mm, etc. The minimum distance of the preset interval between the secondary pole heads can be determined according to the magnetic field strength required for beam extraction.

[0066] According to embodiments of the present invention, by designing secondary poles with a preset interval, the coupling effect between primary poles can be reduced, thereby improving the magnetic field quality. The secondary poles are controlled by an independent second power supply, enhancing the flexibility of magnetic field regulation.

[0067] Continue to refer to Figure 4 The ends of the main pole head 21 and the auxiliary pole head 22 away from the outer ring 1 of the magnetic pole can be rounded to reduce magnetic field concentration at the ends. The rounded pole head shape can be formed by chamfering. The excitation coil 3 exposes the ends of the main pole head 21 and the auxiliary pole head 22.

[0068] According to an embodiment of the present invention, 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.

[0069] In addition, the magnetic field formed by the antisymmetric hexapole magnet in this embodiment can be evaluated from other perspectives.

[0070] Figure 9 The diagram shows the first derivative of the magnetic field strength of the antisymmetric hexapolar magnetic field formed according to an embodiment of the present invention. Figure 9 In equation (2), the horizontal axis represents the distance from the beam center in the horizontal direction, and the vertical axis represents the first derivative of the magnetic field strength. It can be seen from equation (2) that the change of the first derivative of the magnetic field strength of the antisymmetric hexapolar magnetic field with respect to the horizontal position on the horizontal axis should be two straight lines that are symmetrical about the vertical axis.

[0071] like Figure 9 As shown, the first derivative of the magnetic field formed by the antisymmetric hexapole magnet in this embodiment is approximately a linear straight line when the horizontal distance is greater than 10 mm, which is very close to that of an ideal antisymmetric hexapole magnetic field. When the horizontal distance is less than 10 mm, its first derivative exhibits an arc-shaped transition. Although the magnetic field strength of an ideal antisymmetric hexapole magnetic field is continuously non-differentiable near the beam center, the magnetic field strength near the beam center is relatively small and will not have a significant substantial impact on the beam process. Therefore, an error within a range of less than 10 mm is acceptable.

[0072] Figure 10 A comparison diagram of the linearity of the magnetic field strength of the antisymmetric hexapole magnet according to an embodiment of the present invention is shown. Figure 10 With a current density of 0.4 A / mm 2 (by Figure 10 Using the magnetic field generated by the excitation current (shown in S8) as a reference, it is compared with a current density of 0.8 A / mm². 2 1.2A / mm 2 and 1.6A / mm 2 (in the following words) Figure 10 The magnetic field generated by the excitation current (shown in S9, S10, and S11) is compared. It should be noted that... Figure 10 0.8A / mm 2 1.2A / mm 2 and 1.6A / mm 2 The magnetic field strength generated under the excitation current has been scaled proportionally. The horizontal axis represents the distance from the beam center in the horizontal direction, and the vertical axis represents the difference between the magnetic field strength and the reference magnetic field strength under different current densities.

[0073] like Figure 10 As shown, under different excitation currents, the difference in magnetic field strength of the antisymmetric hexapole magnetic field is less than or equal to 0.5 Gs across the entire horizontal axis range (i.e., the aperture range of the beam extraction tube). The small difference in magnetic field strength indicates a high linearity of the magnetic field strength and good stability of the beam extraction.

[0074] Those skilled in the art will understand that the features described in the various embodiments of the present invention can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in the present invention. In particular, the features described in the various embodiments of the present invention can be combined and / or combined in various ways without departing from the spirit and teachings of the present invention. All such combinations and / or combinations fall within the scope of the present invention.

[0075] The embodiments of the present invention have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of the invention. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the invention, and all such substitutions and modifications should fall within the scope of the invention.

Claims

1. An antisymmetric hexapole magnet, characterized in that, include: Magnetic pole outer ring; The pole head is integrated with the outer ring of the magnetic poles. The pole head includes three pairs of sub-pole head groups evenly distributed and facing each other on the inner wall of the outer ring of the magnetic poles. Two pairs of sub-pole head groups each include two main pole heads facing each other. Each sub-pole head group in the other pair of sub-pole head groups includes two auxiliary pole heads with a preset interval. The main pole heads facing each other have the same polarity, and the auxiliary pole heads with the preset interval have opposite polarities. Adjacent main pole heads and auxiliary pole heads have opposite polarities. Each main pole head has the same geometric dimensions, and the sum of the volumes of the auxiliary pole heads with the preset interval is less than the volume of each main pole head. An excitation coil, wound around the pole head, is used to provide excitation current to the pole head; The secondary pole head is used to reduce the coupling effect between the primary pole heads in order to improve the magnetic field quality of the antisymmetric hexapolar magnetic field within the outer ring of the magnetic poles.

2. The antisymmetric hexapole magnet according to claim 1, characterized in that, The excitation coil includes a first excitation coil wound on each main pole and a second excitation coil wound on each auxiliary pole. The first excitation coil and the second excitation coil are controlled by a first power supply and a second power supply, which are independent of each other, to generate a first excitation current and a second excitation current.

3. The antisymmetric hexapole magnet according to claim 2, characterized in that, The magnetic field distribution of the preset region of the antisymmetric hexapole magnet is controlled by adjusting the first excitation current and the second excitation current. The preset region is the particle distribution region to be extracted in the beam extraction tube within the outer ring of the magnetic pole.

4. The antisymmetric hexapole magnet according to claim 3, characterized in that, The excitation coil also includes: The third excitation coil is wound around the first excitation coil and located at the root of each main pole head near the end of the outer ring of the magnetic pole. The third excitation coil is controlled by a third power source to generate a third excitation current to regulate the magnetic field distribution of the antisymmetric hexagonal magnetic field. The third power source is independent of the first power source and the second power source.

5. The antisymmetric hexapole magnet according to any one of claims 1 to 4, characterized in that, The secondary pole heads with the preset interval have the same geometric dimensions and are symmetrical to each other radially along the outer ring of the magnetic pole. The preset interval is determined based on the accommodating space of the excitation coil wound on each of the secondary pole heads.

6. The antisymmetric hexapole magnet according to any one of claims 1 to 4, characterized in that, The ends of the main pole head and the secondary pole head away from the outer ring of the magnetic pole are arc-shaped to reduce the concentration of the magnetic field at the ends; The excitation coil exposes the ends of the main pole and the secondary pole.

7. The antisymmetric hexapole magnet according to any one of claims 1 to 4, characterized in that, The radial length of the outer ring of the magnetic pole is less than or equal to 700 mm, and the radius of the beam outlet tube in the antisymmetric hexapole magnet is less than or equal to 55 mm.

8. The antisymmetric hexapole magnet according to any one of claims 1 to 4, characterized in that, The preset interval between the secondary electrodes is less than or equal to 32mm.

9. The antisymmetric hexapole magnet according to any one of claims 1 to 4, characterized in that, The distance between the top of the end of the pole head away from the outer ring of the magnetic pole and the beam outlet tube in the radial direction of the outer ring of the magnetic pole is greater than or equal to 5 mm.

10. The antisymmetric hexapole magnet according to any one of claims 1 to 4, characterized in that, The shortest distance between the main electrode head and the cross-section of the beam outlet tube is greater than or equal to 12 mm.

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