Permanent magnet type axial uniform magnetic field generating device and design method thereof

Abstract

The invention belongs to the technical field of uniform magnetic field device design, and particularly relates to a permanent magnet type axial uniform magnetic field generating device and a design method thereof. The device comprises two conical permanent magnets, the vertexes of the two conical permanent magnets are oppositely arranged, the two conical permanent magnets are magnetized in the radial direction, and the magnetizing directions of the two conical permanent magnets are opposite. The problems that a traditional permanent magnet type axial uniform magnetic field generating device is large in size and low in magnetic field utilization rate are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of uniform magnetic field device design, and in particular relates to a permanent magnet type axial uniform magnetic field generating device and a design method thereof. Background Art

[0002] In a uniform magnetic field, the charged particles in the particle beam are subjected to the Lorentz force, which can cause their trajectory to be deflected. Therefore, by adjusting the appropriate magnetic field amplitude and direction, the trajectory of the particle beam can be precisely controlled, so that the particle beam can be converged and focused, the collimation of the particle beam can be improved, and the requirements of different application scenarios can be met. An axial uniform magnetic field can be easily generated by a solenoid coil. However, the solenoid coil requires an additional power supply, and even a matching cooling device is required in situations where the magnetic field amplitude is required to be large, resulting in a significant increase in the cost and volume of the system. Permanent magnets have strong magnetic properties and do not require additional power supplies and cooling devices. Therefore, the permanent magnet magnetic field generating device has a simple structure and a small size.

[0003] The traditional permanent magnet axial uniform magnetic field generator adopts a long circular ring structure and axially magnetizes, thereby generating a uniform axial magnetic field at its axis. However, most of the magnetic field generated by this structure spreads outward, and only a small part enters the axis. Therefore, there are disadvantages such as large device size and low magnetic field utilization. Summary of the invention

[0004] The invention provides a permanent magnet type axial uniform magnetic field generating device and a design method thereof, aiming at the problems that the conventional permanent magnet type axial uniform magnetic field generating device has a large volume and a low magnetic field utilization rate.

[0005] The present invention is achieved through the following technical solutions:

[0006] A permanent magnet axial uniform magnetic field generating device for particle beam transmission comprises two conical permanent magnets, the apexes of the two conical permanent magnets are arranged oppositely, the two conical permanent magnets are radially magnetized, and the magnetization directions of the two conical permanent magnets are opposite.

[0007] A design method for a permanent magnet axial uniform magnetic field generating device for particle beam transmission, the design method comprising: obtaining an integral formula for magnetic field intensity generated by the permanent magnet axial uniform magnetic field generating device based on Ampere's circuit theorem and Stokes' theorem; obtaining an expression for magnetic field intensity generated by the permanent magnet axial uniform magnetic field generating device based on the symmetry of the structure, taking into account the material constitutive relationship and assuming the axial air gap magnetic field intensity and the core magnetic permeability.

[0008] Furthermore, according to Ampere's circuit theorem, the following formula can be listed:

[0009] ▽×H=J (1) In the formula, H is the magnetic field intensity and J is the current density;

[0010] Since there is no current in the device, the right side is equal to zero. Integrating equation (1) yields

[0011]

[0012] Where Ω is the area surrounded by the red border, and dS is the differential unit that constitutes the area;

[0013] By using Stokes' theorem, the above formula can be transformed into

[0014]

[0015] Where Γ is the closed path formed by the red border, and dl is the differential unit that constitutes the path;

[0016] Formula (3) means that the integral of the magnetic field intensity along the magnetic field line path is zero, which can be written as follows:

[0017]

[0018] In the formula, H a , H b , H iron and H pm Respectively represent the path l a The magnetic field strength on the path l b Magnetic field on

[0019] The magnetic field strength, the magnetic field strength on the core path and the magnetic field strength inside the permanent magnet.

[0020] Furthermore, due to the symmetry of the device, l b The magnetic field strength H on the path b is 0; considering the material constitutive

[0021] Relationship and assuming that the air gap flux density in the axial direction is uniform, equation (4) can be written as follows:

[0022]

[0023] In the formula, B δ is the air gap flux density, μ 0 is the magnetic permeability of air, B iron Magnetic flux density inside the core, μ iron is the core permeability.

[0024] Since the magnetic permeability of the iron core is much larger than that of the air, the second term in equation (5) can be ignored, so we have

[0025]

[0026] In a permanent magnet, the magnetic induction intensity (magnetic flux density) is generated by the external magnetic field and the magnetization of the permanent magnet itself, that is,

[0027] B δ =μ 0 (H pm +M) (7)

[0028] Where, M is the residual magnetization of the permanent magnet;

[0029] Through (6) and (7), the expression of air gap flux density can be obtained:

[0030]

[0031] make

[0032]

[0033] Then formula (8) becomes,

[0034]

[0035] From formula (10), we can know that as long as α remains unchanged, the air gap flux density will remain unchanged.

[0036] Furthermore, it can be seen from formula (10) that the air gap magnetic field amplitude is related to α; therefore, a permanent magnet pole face can be designed so that α at the center is larger and gradually decreases as it moves away from the center point, so that the magnetic field generated by the device at the axis is more uniform, and the changing relationship between α and the z coordinate is obtained. Through the changing relationship between α and the z coordinate, straight line segments can be used to transition at the end and the center line respectively. The permanent magnet pole face curve drawn through the changing relationship between α and the z coordinate can shear the original conical surface to the intersection of the curve and the original oblique line.

[0037] Furthermore, to ensure that the axial length and outer diameter of the device are consistent, a curve is intercepted between a symmetry line passing through the center point of the device and a distance of 40% of the axial length of the device from the center symmetry line. At the center point of the device z = 0.1, l a and l b are close to infinitesimal, so we can define an initial ratio α 0 =0.4, then, 0 / (α 0 +1) and the magnetic field amplitude at z = 0.1 as the base, divided by Figure 5 The magnetic field at other positions in the curve is used to obtain the relationship curve between α / (α+1) and the z coordinate.

[0038] Furthermore, based on the relationship curve, let

[0039]

[0040] therefore,

[0041]

[0042] Through equation (12), the changing relationship between α and the z coordinate can be obtained.

[0043] Furthermore, when the axial length of the device is relatively small compared to the outer diameter, that is, the axial length / diameter <2.5, straight line segments are used for transition at the end and the center line respectively; the permanent magnet pole surface curve drawn by the changing relationship between the α and z coordinates shears the original conical surface to the intersection of the curve and the original oblique line.

[0044] Furthermore, when the axial length of the device is relatively large compared to the outer diameter, that is, the axial length / diameter ≥ 2.5, a conical pole surface permanent magnet solution is adopted.

[0045] A permanent magnet type axial uniform magnetic field generating device, the device adopts the above structure and is used for particle beam transmission.

[0046] The beneficial effects of the present invention are:

[0047] of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a structural schematic diagram of the present invention.

[0049] Figure 2 It is a traditional permanent magnet axial uniform magnetic field generating device.

[0050] Figure 3 This is a comparison chart of the magnetic fields generated by the traditional solution and the new solution.

[0051] Figure 4 This is a magnetic field distribution diagram of a new solution of the present invention when the aspect ratio is 0.66.

[0052] Figure 5 It is the magnetic field distribution diagram on the interception line segment of the present invention.

[0053] Figure 6 This is a variation curve diagram of α / (α+1) of the present invention.

[0054] Figure 7 It is a curve diagram of the change of α with the z coordinate of the present invention.

[0055] Figure 8 It is a curve diagram of the change of α with the z coordinate of the present invention.

[0056] Figure 9 This is a diagram of the permanent magnet axial uniform magnetic field generating device after the pole surface is changed according to the present invention.

[0057] Figure 10 It is a comparison diagram between the conical pole surface of the present invention and the novel pole surface. DETAILED DESCRIPTION

[0058] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0059] It should be understood that when used in this specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0060] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in the present specification and the appended claims, the singular forms "a", "an" and "the" are intended to be used in the present invention unless the context clearly indicates otherwise.

[0061] Including plural forms.

[0062] The following is attached to this application specification Figures 1-10 , clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, ordinary technicians in this field can

[0063] All other embodiments obtained under this premise belong to the scope of protection of this application.

[0064] In the following description, many specific details are set forth to facilitate a full understanding of the present application, but the present application may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0065] Implementation Method 1

[0066] This embodiment provides a permanent magnet axial uniform magnetic field generating device for particle beam transmission, the device includes two conical permanent magnets, the vertices of the two conical permanent magnets are arranged opposite to each other, the two conical permanent magnets are radially magnetized, and the magnetization directions of the two conical permanent magnets are opposite, such asFigure 1 As shown, Figure 1 Zhongxian

[0067] A circular section is shown, which is rotated 360 degrees through the axis to form the complete device.

[0068] Implementation Method 2

[0069] The present embodiment provides a design method for a permanent magnet axial uniform magnetic field generator for particle beam transmission. The design method is to obtain the integral formula of the magnetic field intensity generated by the permanent magnet axial uniform magnetic field generator based on the Ampere loop theorem and the Stokes theorem, and obtain the permanent magnet axial uniform magnetic field generator based on the symmetry of the structure and the material constitutive relationship and assuming the axial air gap magnetic density and the core magnetic permeability.

[0070] Generates a magnetically dense expression.

[0071] Furthermore, according to Ampere's circuit theorem, the following formula can be listed:

[0072] ▽ × H = J (1) Where H is the magnetic field intensity and J is the current density;

[0073] Since there is no current in the device, the right side is equal to zero. Integrating equation (1) yields

[0074]

[0075] Where Ω is the area surrounded by the red border, and dS is the differential unit that constitutes the area;

[0076] By using Stokes' theorem, the above formula can be transformed into

[0077]

[0078] Where Γ is the closed path formed by the red border, and dl is the differential unit that constitutes the path;

[0079] Formula (3) means that the integral of the magnetic field intensity along the magnetic field line path is zero, which can be written as follows:

[0080]

[0081] In the formula, H a , H b , H iron and H pm Respectively represent the path l a The magnetic field strength on the path l b Magnetic field on

[0082] The magnetic field strength, the magnetic field strength on the core path and the magnetic field strength inside the permanent magnet.

[0083] Furthermore, due to the symmetry of the device, l b The magnetic field strength H on the path b is 0; considering the material constitutive

[0084] Relationship and assuming that the air gap flux density in the axial direction is uniform, equation (4) can be written as follows:

[0085]

[0086] In the formula, B δ is the air gap flux density, μ 0 is the magnetic permeability of air, B iron Magnetic flux density inside the core, μ iron is the core permeability.

[0087] Since the magnetic permeability of the iron core is much larger than that of the air, the second term in equation (5) can be ignored, so we have

[0088]

[0089] In a permanent magnet, the magnetic induction intensity (magnetic flux density) is generated by the external magnetic field and the magnetization of the permanent magnet itself, that is,

[0090] B δ =μ 0 (H pm +M) (7)

[0091] Where, M is the residual magnetization of the permanent magnet;

[0092] Through (6) and (7), the expression of air gap flux density can be obtained:

[0093]

[0094] make

[0095]

[0096] Then formula (8) becomes,

[0097]

[0098] From formula (10), we can know that as long as α remains unchanged, the air gap flux density will remain unchanged.

[0099] Furthermore, by comparing the magnetic field distribution generated by the two structural schemes at their axes (ensuring that the axial length and outer diameter of the device are consistent), it can be seen that the new structural scheme generates a larger magnetic field amplitude and a larger uniform area while using less permanent magnets, such as Figure 3 shown.

[0100] However, when the aspect ratio (ratio of axial length to outer diameter) of the device is low, the magnetic field uniformity zone at its axis will be distorted, such as Figure 4 As shown in Figure 2, it can be seen that the magnetic field distribution at the center of the axis is a curve with poor uniformity.

[0101] It can be seen from equation (10) that the air gap magnetic field amplitude is related to α. Therefore, a permanent magnet pole face can be designed so that α is larger at the center and gradually decreases as it moves away from the center point, so that the magnetic field generated by the device at the axis is more uniform.

[0102] The next question is how to obtain the changing relationship between α and z coordinates. Draw two auxiliary lines in the figure, one symmetry line passing through the center point of the device, and the other auxiliary line 40% of the axial length of the device from the center symmetry line. Intercept the magnetic field curve between the two auxiliary lines, such as Figure 5 shown.

[0103] At the center point z = 0.1, l a and l b are close to infinitesimal, so we can define an initial ratio α 0 =0.4. Then, α 0 / (α 0 +1) and the magnetic field amplitude at z = 0.1 as the base, divided by Figure 5 The magnetic field at other positions in the image is obtained, and the relationship curve between α / (α+1) and the z coordinate is obtained, such as Figure 6 shown.

[0104] Furthermore, based on the relationship curve, let

[0105]

[0106] therefore,

[0107]

[0108] Through equation (12), the relationship between α and z coordinate can be obtained, as Figure 7 shown.

[0109] At this point, through the changing relationship between α and z coordinates, the permanent magnet pole surface curve can be drawn on the conical permanent magnet base section, such as Figure 8 shown.

[0110] Furthermore, Figure 8In the figure, considering the actual processing technology, the permanent magnet does not adopt a completely triangular cross-section. When the axial length of the device is relatively small compared to the outer diameter, that is, the axial length / diameter <2.5, straight line segments are used for transition at the end and the center line respectively; the permanent magnet pole surface curve drawn by the changing relationship between α and the z coordinate shears the original conical surface to the intersection of the curve and the original oblique line.

[0111] Furthermore, when the axial length of the device is relatively large compared to the outer diameter, that is, the axial length / diameter ≥ 2.5, a conical pole surface permanent magnet solution is adopted.

[0112] Implementation Method 3

[0113] This embodiment provides a permanent magnet axial uniform magnetic field generating device, which adopts the structure described in the first embodiment and is used for particle beam transmission.

Claims

1. A permanent magnet axial uniform magnetic field generating device, characterized in that: The device comprises two conical permanent magnets, the vertices of the two conical permanent magnets are arranged opposite to each other, and the two conical permanent magnets are magnetized radially. The magnetization directions of the two conical permanent magnets are opposite.

2. A design method for a permanent magnet axial uniform magnetic field generating device, characterized in that: The design method is to obtain an integral formula for the magnetic field intensity generated by a permanent magnet axial uniform magnetic field generating device based on Ampere's circuit theorem and Stokes' theorem, and to obtain an expression for the magnetic field density generated by the permanent magnet axial uniform magnetic field generating device based on the symmetry of the structure, considering the material constitutive relationship and assuming the axial air gap magnetic field density and the core magnetic permeability.

3. The design method according to claim 2, characterized in that: According to Ampere's circuit theorem, the following formula can be listed: ▽ × H = J (1) Where H is the magnetic field intensity and J is the current density; Since there is no current in the device, the right side is equal to zero; integrating equation (1) yields Where Ω is the area surrounded by the red border, and dS is the differential unit that constitutes the area; By using Stokes' theorem, the above formula can be transformed into Where Γ is the closed path formed by the red border, and dl is the differential unit that constitutes the path; Formula (3) means that the integral of the magnetic field intensity along the magnetic field line path is zero, which can be written as follows: In the formula, H a , H b , H iron and H pm Respectively represent the path l a The magnetic field strength on the path l b The magnetic field strength on the core, the magnetic field strength on the iron core path and the magnetic field strength inside the permanent magnet.

4. The design method according to claim 3, characterized in that: Due to the symmetry of the device, l b The magnetic field strength H on the path b is 0; considering the material constitutive relationship and assuming that the air gap flux density in the axial direction is uniform, Formula (4) can be written as follows: In the formula, B δ is the air gap flux density, μ0 is the air permeability, B iron Magnetic flux density inside the core, μ iron is the core permeability; Since the magnetic permeability of the iron core is much larger than that of the air, the second term in equation (5) can be ignored. Therefore, there is In a permanent magnet, the magnetic induction intensity is generated by the external magnetic field and the magnetization of the permanent magnet itself, that is, B δ =μ0(H pm +M) (7) Where, M is the residual magnetization of the permanent magnet; Through (6) and (7), the expression of air gap flux density can be obtained: make Then formula (8) becomes, From formula (10), we can know that as long as α remains unchanged, the air gap flux density will remain unchanged.

5. The design method according to claim 4, characterized in that: It can be seen from equation (10) that the air gap magnetic field amplitude is related to α; therefore, a permanent magnet pole face can be designed so that α is larger at the center and gradually decreases as it moves away from the center point, so that the magnetic field generated by the device at the axis is more uniform, and the relationship between α and z is obtained. The changing relationship between the coordinates and the changing relationship between the α and z coordinates can be used to transition with straight line segments at the end and the center line respectively. The permanent magnet pole surface curve drawn by the changing relationship between the α and z coordinates can shear the original conical surface to the intersection of the curve and the original oblique line.

6. The design method according to claim 5, characterized in that: Ensure that the axial length and outer diameter of the device are consistent, intercept the symmetry line passing through the center point of the device and the curve that is 40% of the axial length of the device from the center symmetry line. At the center point z = 0.1, l a and l b They are all close to infinitesimal, so an initial ratio α0=0.4 can be defined. Then, the product of α0 / (α0+1) and the magnetic field amplitude at z=0.1 is taken as the base and divided by the magnetic field at other positions in the curve of Figure 5 to obtain the relationship curve between α / (α+1) and the z coordinate.

7. The design method according to claim 6, characterized in that: Based on the relationship curve, let therefore, Through equation (12), the changing relationship between α and the z coordinate can be obtained.

8. The design method according to claim 7, characterized in that: When the axial length of the device is relatively small compared to the outer diameter, that is, the axial length / diameter <2.5, straight line segments are used for transition at the end and the center line respectively; the permanent magnet pole surface curve drawn by the changing relationship between the α and z coordinates shears the original conical surface to the intersection of the curve and the original oblique line.

9. The design method according to claim 7, characterized in that: When the axial length of the device is relatively large compared to the outer diameter, that is, the axial length / diameter ≥ 2.5, the conical pole surface permanent magnet solution is adopted.

10. A permanent magnet axial uniform magnetic field generating device, characterized in that: The device adopts the structure as claimed in claim 1 and is used for particle beam transmission.

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