A four / eight-pole complex iron system for beam homogenization

Abstract

The application discloses a four / eight-pole composite iron system for beam homogenization, which comprises a composite magnet current control device, a composite magnet main power supply and a four / eight-pole composite iron, wherein the composite magnet current control device is used for controlling the four-pole field coil current output and the eight-pole field coil current output of the four / eight-pole composite iron by the composite magnet main power supply; the four / eight-pole composite iron is used for simultaneously generating a dominant four-pole magnetic field and an eight-pole magnetic field, so that the functions of the four-pole iron and the eight-pole iron can be realized simultaneously by installing only one transmission element; the four-pole magnetic field and the eight-pole magnetic field are generated in the aperture of the composite iron, the functions of focusing and homogenizing the beam envelope are realized simultaneously, the number of transmission elements can be reduced, the length of the transmission line can be shortened, and the engineering cost of the beam transport line is reduced. The problem that the traditional four-pole iron and the eight-pole iron cannot be simultaneously installed at the maximum position of the beam envelope due to the space problem and cannot play a large role of the magnet is solved.

Description

Technical Field

[0001] This invention belongs to the field of cyclotron technology, and particularly relates to a four / octet composite iron system for beam homogenization. Background Technology

[0002] For a charged particle beam generated in an accelerator to be utilized, it must be transmitted to the experimental terminal or a designated location using beam transport lines composed of beam transport elements. Common beam transport elements include dipolar, tetrapolar, hexapolar, and octapole iron. The function of the beam transport elements is to control the envelope shape of the beam during transmission, ensuring that the envelope does not diverge and thus preventing collisions between particles and the transport channel, which would cause beam loss. Simultaneously, the experimental terminal imposes a series of requirements on beam quality, such as beam uniformity. Only beams that meet these conditions can be used effectively. Good beam quality is achieved through beam modulation by the transport elements.

[0003] The beam transmission elements currently used generally function independently. The quadrupole field that controls beam focusing or divergence is generated by a quadrupole iron, while the octupole field that controls beam uniformity is generated by an octupole magnet.

[0004] The beam distribution from an accelerator typically approximates a Gaussian distribution, with the highest particle density at the center of the beam cluster. However, this also results in excessively high local power and temperature on the neutron target, potentially causing damage. To address the issue of uneven particle distribution, octagonal magnets have been used on the beam transmission line to homogenize the Gaussian beam distribution and reduce the peak power density on the neutron target.

[0005] One of the challenges in homogenizing a Gaussian-distributed beam using octagonal magnets lies in the fact that the same octagonal magnet, when installed at different positions on the beam transmission line, will have different effects. Only when the octagonal magnet is installed at a location with a large beam envelope can it provide the strongest homogenization effect. However, in existing technologies, the areas with the largest beam envelope are usually occupied by quadrupole magnetic fields: such as... Figure 14bAs shown, the transmission line in the prior art is arranged in the order of quadrupole 1, octupole 1, quadrupole 2, and octupole 2. Since the octupole must be focused before homogenization (the purpose of focusing is to allow the beam to pass through the circular hole in the center of the octupole without hitting the octupole), in order to ensure focusing, the positions of octupole 1 and octupole 2 must first be selected at the waist position of the X-direction envelope and the waist position of the Y-direction envelope. However, since the Y-direction envelope of quadrupole 1 at the waist position of the X-direction envelope is small, and the X-direction envelope of quadrupole 2 at the waist position of the Y-direction envelope is small, at octupole 1, although the position of octupole 1 at the waist position of the X-direction is guaranteed, the Y-direction envelope at that position is small. Similarly, at octupole 2, although the position of octupole 2 at the waist position of the Y-direction is guaranteed, the X-direction envelope at that position is small. In summary, according to the traditional method, the beam envelope is significantly reduced after the particles pass through quadrupole 1 and quadrupole 2, so the full effect of octupole 1 and octupole 2 cannot be achieved.

[0006] The second difficulty in homogenizing a Gaussian-distributed beam using an octagonal magnet lies in the fact that the beam envelope at the locations of octagonal magnet 1 and octagonal magnet 2 is small, resulting in a very large field strength K value for the octagonal magnet. Excessively high magnetic field strength is not only difficult to achieve in engineering, but also too costly and difficult to implement.

[0007] The third challenge in homogenizing a Gaussian-distributed beam using octagonal magnets lies in the fact that each type of transmission element on the beam transmission line performs only one function, and each element has a fixed size. The number of transmission elements on the transmission line directly determines its length. In certain situations, due to limited axial space for arranging the beam transmission line, too many transmission elements cannot be accommodated, necessitating some omissions along the axial direction, resulting in suboptimal beam quality. To achieve good beam homogenization using octagonal magnets, the placement and phase of the octagonal magnets are subject to strict requirements. To meet these requirements, the transmission line length often needs to be over ten meters. A cyclotron accelerator with a diameter of no more than 2 meters would be rendered pointless by dragging a beamline over ten meters long; miniaturizing the accelerator would be futile, and the longer the beamline, the more expensive the surrounding shielding infrastructure becomes. In short, the large footprint and high cost of excessively long transmission lines significantly limit the application of beam homogenization technology. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention proposes a four / octet composite iron system for beam homogenization. The first objective is to solve the problem that the largest envelope area in the prior art is usually occupied by the four-pole magnetic field, and the octet iron cannot provide the strongest homogenization effect. The second objective is to solve the problem that the small envelope at the location of the octet iron on the transmission line in the prior art results in a very large field strength K value for the octet magnet, which is not only difficult to implement in engineering but also too costly. The third objective is to solve the problem that in order to achieve good beam homogenization using the octet iron, the transmission line length often needs to be tens of meters, resulting in a large footprint and high cost, which greatly limits the application of beam homogenization technology.

[0009] To solve its technical problems, the present invention proposes the following technical solutions:

[0010] A four / octagonal composite iron system for beam homogenization includes a composite magnet current control device, a composite magnet main power supply, and a four / octagonal composite iron. The composite magnet current control device controls the current output of the four-pole field coil and the octagonal field coil of the composite magnet from the main power supply. The four / octagonal composite iron is used to simultaneously generate a dominant four-pole magnetic field and an octagonal magnetic field, so that the functions of both a four-pole and an octagonal iron can be achieved by installing only transmission elements.

[0011] The composite magnet current control device includes: a module for establishing two-dimensional sampling points for coil current, a module for experimentally measuring and initially establishing a three-dimensional surface sample library of magnetic field gradient, a module for refining the three-dimensional surface sample library of magnetic field gradient using interpolation, a module for inputting field gradient and solving the corresponding field gradient current curve, a module for solving the intersection point of four / octagonal field gradient current curves, and a module for outputting four / octagonal coil current.

[0012] The module for establishing two-dimensional sampling points for coil current is used to establish a two-dimensional data comparison table of coil current for quadrupole and octupole iron.

[0013] The experimental measurement initially establishes a three-dimensional surface sample library module for magnetic field gradients. This module uses the current values ​​from a two-dimensional data lookup table of coil currents to perform magnetic field experimental measurements on composite iron, thereby obtaining four-pole and octole magnetic field gradient measurement values ​​that correspond one-to-one with the two-dimensional current data lookup table, thus obtaining a three-dimensional surface sample database of magnetic field gradients. The aforementioned three-dimensional surface sample database of magnetic field gradients includes a four-pole field magnetic field gradient three-dimensional surface sample database and an octole field magnetic field gradient three-dimensional surface sample database.

[0014] The module for refining the magnetic field gradient three-dimensional surface sample library using interpolation is used to perform two-dimensional interpolation on the quadrupole magnetic field gradient three-dimensional surface sample database and the octupole magnetic field gradient three-dimensional surface sample database using cubic spline functions, thereby increasing the density of grid points.

[0015] The module for solving the input field gradient corresponding to the current curve is used to intersect the input quadrupole field gradient and octupole field gradient with the magnetic field gradient surface of the three-dimensional sample database, and obtain two corresponding current curves after the intersection; specifically: a quadrupole field magnetic field gradient plane is selected, and this plane intersects with the surface of the quadrupole field magnetic field gradient three-dimensional surface sample database to obtain the current curve that satisfies the fourth-order field gradient; an octupole field magnetic field gradient plane is selected, and this plane intersects with the surface of the octupole field magnetic field gradient three-dimensional surface sample database to obtain the current curve that satisfies the eighth-order field gradient.

[0016] The module for solving the intersection point of the four / octet field gradient current curves is used to obtain the intersection point of the current curve that satisfies the fourth-order field gradient and the current curve that satisfies the eighth-order field gradient, and uses the intersection point as the solution of the composite iron excitation current.

[0017] The output four-pole / octole coil current module outputs four-pole field coil current and octole field coil current to the four-pole / octole composite iron according to the solution of the excitation current of the composite iron.

[0018] Furthermore, this novel four / eight-pole composite iron model has a total of eight poles. Each pole has two layers of current coils along the radial direction near the large radius. The inner layer coil is an eight-pole magnetic field excitation coil, and the outer layer coil is a four-pole magnetic field excitation coil.

[0019] Furthermore, the inner layer of the octagonal magnetic field excitation coil has adjacent poles with opposite current directions, that is, the octagonal field coil is divided into two groups: poles 1, 3, 5, 7 and poles 2, 4, 6, 8. The excitation currents of the two groups are equal in magnitude but opposite in direction, thereby generating an octagonal magnetic field.

[0020] Furthermore, the outer quadrupole magnetic field excitation coil has four groups, namely, poles 1 and 2, poles 3 and 4, poles 5 and 6, and poles 7 and 8. Among them, the excitation current of the quadrupole magnetic field coils of poles 1 and 2 and the symmetrically arranged poles 5 and 6 is in the same direction and magnitude. The excitation current of the coils of poles 3 and 4 and the symmetrically arranged poles 7 and 8 is in the same direction and magnitude. The current direction of the coils of poles 1 and 2 is opposite to that of the coils of poles 3 and 4. The current direction of the coils of poles 5 and 6 is opposite to that of the coils of poles 7 and 8, thereby generating a quadrupole magnetic field.

[0021] Advantages and effects of the present invention

[0022] 1. This invention generates a quadrupole magnetic field and an octupole magnetic field within the aperture of the composite iron, which can simultaneously achieve the focusing and homogenization of the beam envelope, solving the problem that the largest area of ​​the envelope in the prior art is usually occupied by the quadrupole magnetic field and the octupole iron cannot provide the strongest homogenization effect.

[0023] 2. This invention generates a quadrupole magnetic field and an octupole magnetic field within the aperture of the composite iron, which can simultaneously achieve the focusing and homogenization of the beam envelope, providing the strongest homogenization effect. It solves the problem in the transmission line of the prior art that, due to the small envelope of the octupole iron, the field strength K value of the octupole magnet is very large. The excessively high magnetic field strength is not only difficult to implement in engineering, but also too costly.

[0024] 3. This invention generates both quadrupole and octupole magnetic fields within the aperture of the composite iron, enabling simultaneous focusing and homogenization of the beam envelope. Installing it on the beam transmission line reduces the number of transmission elements, shortens the transmission line length, and lowers the engineering cost of the beam transmission line. For the transmission line, the quadrupole and octupole composite iron can simultaneously exert the maximum effect of the magnets because it is installed at the maximum position of the beam envelope, where the focusing and homogenization effects are strongest. This solves the problem that traditional quadrupole and octupole irons cannot be simultaneously installed at the maximum position of the beam envelope due to space constraints, thus limiting their magnetic effectiveness.

[0025] 4. The four-eight-pole iron scheme proposed in this paper can be used flexibly. When the current of any type of coil is turned off, it can be used as a four-pole iron or an eight-pole iron. This also means that the current of the two types of coils can be flexibly adjusted to generate a variety of four / eight-pole composite fields for different applications. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the four / octet composite iron system for beam control according to the present invention;

[0027] Figure 2 Application effects of beam transmission elements: (left) quadrupole; (right) octupole.

[0028] Figure 3 The distribution and focusing principle of quadrupole magnetic fields;

[0029] Figure 4 Octapole magnetic field and beam homogenization process;

[0030] Figure 5 This invention provides a novel four / octet composite iron model.

[0031] Figure 6 for Figure 5 Enlarged view of a partial view of a four / octet composite iron model;

[0032] Figure 7 The arrangement and current direction of the four / octet composite magnet coil.

[0033] Figure 8 This is a schematic diagram showing the current values ​​of the two sets of coils during magnetic field measurement in this invention;

[0034] Figure 9 This is a schematic diagram showing the quadrupole / octapole magnetic field gradients corresponding to different currents measured in the present invention.

[0035] Figure 10 This is a schematic diagram illustrating the use of cubic spline functions for two-dimensional interpolation to refine the grid point density in this invention.

[0036] Figure 11 This is a schematic diagram showing the intersection of the magnetic field gradient plane selected in this invention with the magnetic field gradient surface of the three-dimensional sample database;

[0037] Figure 12 This is a schematic diagram of the current curve corresponding to the four / octet field selected in this invention;

[0038] Figure 13 This is a schematic diagram illustrating the solution for the composite iron excitation current of the present invention;

[0039] Figure 14a This is a schematic diagram illustrating the application of the four / octet composite iron of the present invention to an ultrashort beam homogenization transmission line.

[0040] Figure 14b A schematic diagram of an existing octet iron at the small envelope position;

[0041] Figure 15 This is a flowchart of the excitation current adjustment method for four / eight pole composite iron according to the present invention. Detailed Implementation

[0042] Design principle of the invention

[0043] 1. Problems with laying transmission lines based on discrete components of quadrupole and octupole iron.

[0044] 1) Conventional methods of combining two quadrupole magnets cannot meet the requirements of limited axial space in the transmission line. The magnetic field lines distribution of a quadrupole field generated by a quadrupole magnet are as follows: Figure 3As shown, when the beam passes through the central aperture of a quadrupole magnet, the beam experiences an inward lateral focusing force in the X direction, causing the beam envelope to contract and focus in that direction. Conversely, the beam experiences an outward lateral focusing force in the Z direction, causing the beam envelope to diverge and defocus in that direction. Therefore, a quadrupole magnet focuses the beam in one direction and defocuses it in the other. To ensure the beam experiences an inward lateral focusing force in both the Y and X directions, two quadrupole magnets are typically used. When using two quadrupole magnets, the excitation currents of their coils are in opposite directions; one magnet focuses in the X direction, and the other defocuses it. Combining the two quadrupole magnets in this case, according to the alternating focusing principle, ensures that the beam is focused in both the X and Z directions, thus preventing divergence during transmission. The same quadrupole will have different effects depending on the position it is installed on the beam transmission line. When it is installed at the position with the largest beam envelope, it can provide the strongest focusing effect. Generally, the quadrupole is installed at the position with the largest beam envelope.

[0045] 2) When octagonal and quadrature magnets are deployed independently, the octagonal magnet cannot fully exert its function. For example... Figure 4 As shown, the first principle of how an octagonal magnet achieves a uniform particle distribution is as follows: An octagonal magnet generates an eight-pole magnetic field, which ensures a uniform distribution of particles in the beam within space. Before passing through the octagonal magnet, the particles exhibit a Gaussian distribution, primarily concentrated in the central region of the envelope. After passing through the octagonal magnet, they become uniformly distributed within the envelope. In the octagonal magnet, the N and S poles are arranged alternately. The effect of the octagonal magnet on the beam is as follows: Figure 4 As shown, adjacent magnetic poles have opposite effects on the beam: one compresses inward, and the other stretches outward, gradually transforming the beam envelope from a circle to a square, and finally to a four-pointed star envelope. Because the proportions of the four inward-facing beams and the four outward-facing beams are similar, the four-pointed star envelope shape results in a more uniform particle distribution. Therefore, by adjusting the strength of the octagonal magnetic field, a square beam spot can be initially obtained, and over time, the square envelope shape gradually changes to the final four-pointed star envelope shape. Secondly, when octagonal and quadrupole magnets are deployed independently, the octagonal magnet cannot fully exert its function. The same octagonal magnet installed at different positions on the beam transmission line will have different effects. When installed at the position with the largest beam envelope, it provides the strongest homogenization effect. However, quadrupole magnets are generally installed where the envelope is largest, so octagonal magnets can only be installed where the envelope is not very large, and their function cannot be fully utilized.

[0046] 2. Design Challenges of this Invention: The multipole magnetic fields generated by the two sets of coils in a four-pole / octole composite magnet are coupled. This coupling means that changing the current in either the four-pole or octole coil will simultaneously alter both the original four-pole and octole magnetic field gradients of the magnet. Therefore, the one-to-one adjustment strategy for the current-magnetic field gradient of a single type of magnet is no longer applicable. In a composite magnet, if the current in the four-pole coil is adjusted first to meet the usage requirements, and then the current in the octole coil is adjusted, any change in the octole coil current will alter the previously adjusted four-pole magnetic field gradient, causing it to no longer meet the usage requirements.

[0047] 3. Innovation points of this invention:

[0048] One of the innovations lies in the invention of a four-octet composite iron. For example... Figure 5 , 6 As shown in Figure 7, tetra / octet composite iron was used instead of the type shown in Figure 7. Figure 14b The existing technology uses discrete components of tetrapole and octapole iron. After composite formation, tetrapole and octapole magnetic fields are generated within the aperture of the tetrapole / octapole composite iron, such as... Figure 14a As shown, for transmission lines, the four / octet composite iron can simultaneously exert the maximum effect of a magnet because it is installed at the maximum position of the beam envelope, where the focusing and homogenization effects are strongest. This solves the problem that traditional four-pole and eight-pole irons cannot be simultaneously installed at the maximum position of the beam envelope due to space constraints, thus failing to maximize their magnetic effect. Specifically, as shown... Figure 14a As shown, the quadrupole in quadrupole / octupole composite iron 1 and the quadrupole in front of it share the position of the large envelope in the Y direction, while the quadrupole in quadrupole / octupole composite iron 2 and the quadrupole in front of quadrupole / octupole composite iron 1 share the position of the large envelope in the X direction. Because the octupoles in quadrupole / octupole composite iron 1 and quadrupole / octupole composite iron 2 are positioned within the large envelope, a better beam homogenization effect can be achieved; that is, it can simultaneously achieve the functions of focusing and homogenizing the beam envelope. Compared to... Figure 14b The existing technology, due to the separate arrangement of quadrupole and octupole magnets, cannot change its envelope like the quadrupole magnet, meaning it cannot coexist with the quadrupole magnet to form a large envelope. Therefore, the envelopes in both the Y and X directions of the separately arranged octupole magnets are relatively small, resulting in poor homogenization. Secondly, installing composite magnets on the beam transmission line can reduce the number of transmission elements, shorten the transmission line length, and reduce the engineering cost of the beam transmission line. This reduction in the number of transmission elements not only saves on quadrupole magnets but also saves on the multiple additional components required to achieve the same homogenization effect on the transmission line.

[0049] The second innovation lies in the establishment of a three-dimensional surface sample database of magnetic field gradients. This database uses the current values ​​from a two-dimensional data lookup table of coil currents to conduct magnetic field experiments on composite iron, obtaining four- and eight-pole magnetic field gradient measurement values ​​that correspond one-to-one with the two-dimensional current data lookup table, thus obtaining a three-dimensional surface sample database of magnetic field gradients.

[0050] The third innovation lies in establishing the relationship between the intersection of the magnetic field gradient plane and the three-dimensional surface of the magnetic field gradient, thereby obtaining the current curve at the intersection. The magnetic field gradient is equal at any point on the curve, but the values ​​of the four-pole magnetic field current and the eight-pole magnetic field current at any point on the curve are not equal or equal. This lays the foundation for solving the problem of the intersection of the two curves as the excitation current of the composite iron.

[0051] The fourth innovation lies in utilizing the independence between the current curve and the magnetic field gradient to project the current curves on different magnetic field gradients onto the same coordinate plane, and to obtain the intersection point and the solution of the composite iron excitation current using the intersection point.

[0052] Based on the above principles, this invention designs a four / octet composite iron system for beam homogenization, such as... Figure 1 As shown, the composite iron system includes a composite magnet current control device, a composite magnet main power supply, and a four-pole / eight-pole composite iron. The composite magnet current control device is used to control the current output of the four-pole field coil and the eight-pole field coil of the four-pole / eight-pole composite iron from the composite magnet main power supply. The four-pole / eight-pole composite iron is used to simultaneously generate the dominant four-pole magnetic field and the eight-pole magnetic field, so that the functions of a four-pole iron and an eight-pole iron can be realized simultaneously by installing only one transmission element.

[0053] like Figure 1 As shown, the composite magnet current control device includes: a module for establishing two-dimensional sampling points for coil current, a module for experimentally establishing a three-dimensional surface sample library of magnetic field gradient, a module for refining the three-dimensional surface sample library of magnetic field gradient using interpolation, a module for inputting field gradient and solving the corresponding field gradient current curve, a module for solving the intersection point of four / octagonal field gradient current curves, and a module for outputting four / octagonal coil current.

[0054] like Figure 8 As shown, the module for establishing two-dimensional sampling points for coil current is used to establish a two-dimensional data comparison table of coil current for quadrupole and octupole iron.

[0055] like Figure 9As shown, the experimental measurement initially establishes a three-dimensional surface sample library module for magnetic field gradients. This is achieved by using the current values ​​from a two-dimensional data lookup table of coil currents to perform magnetic field experimental measurements on composite iron, thereby obtaining four-pole and octole magnetic field gradient measurement values ​​that correspond one-to-one with the two-dimensional current data lookup table, thus obtaining a three-dimensional surface sample database of magnetic field gradients. The aforementioned three-dimensional surface sample database of magnetic field gradients includes a four-pole field magnetic field gradient three-dimensional surface sample database and an octole field magnetic field gradient three-dimensional surface sample database.

[0056] like Figure 10 As shown, the module for refining the three-dimensional surface sample library of magnetic field gradient using interpolation is used to perform two-dimensional interpolation on the three-dimensional surface sample database of quadrupole magnetic field gradient and the three-dimensional surface sample database of octupole magnetic field gradient using cubic spline functions, thereby increasing the density of grid points.

[0057] like Figure 11 , 12 As shown, the module for solving the input field gradient corresponding to the field gradient current curve is used to intersect the input quadrupole field gradient and octupole field gradient with the magnetic field gradient surface of the three-dimensional sample database, and obtain two corresponding current curves after the intersection; specifically: a quadrupole field magnetic field gradient plane is selected, and this plane intersects with the surface of the quadrupole field magnetic field gradient three-dimensional surface sample database to obtain the current curve that satisfies the fourth-order field gradient; an octupole field magnetic field gradient plane is selected, and this plane intersects with the surface of the octupole field magnetic field gradient three-dimensional surface sample database to obtain the current curve that satisfies the eighth-order field gradient.

[0058] like Figure 13 As shown, the module for solving the intersection point of the four / octet field gradient current curves is used to obtain the intersection point of the current curve that satisfies the fourth-order field gradient and the current curve that satisfies the eighth-order field gradient, and uses the intersection point as the solution of the composite iron excitation current.

[0059] The output four-pole / octole coil current module outputs four-pole field coil current and octole field coil current to the four-pole / octole composite iron according to the solution of the excitation current of the composite iron.

[0060] like Figure 5 , Figure 6 , Figure 7 As shown, the inner layer of the octagonal magnetic field excitation coil has two adjacent poles with opposite current directions, that is, the octagonal field coil is divided into two groups: poles 1, 3, 5, 7 and poles 2, 4, 6, 8. The excitation currents of the two groups are equal in magnitude but opposite in direction, thereby generating an octagonal magnetic field.

[0061] like Figure 5 , Figure 6 , Figure 7As shown, the outer quadrupole magnetic field excitation coil has four groups, consisting of coils on adjacent poles: poles 1 and 2, poles 3 and 4, poles 5 and 6, and poles 7 and 8. The excitation current of poles 1 and 2, and the symmetrically arranged poles 5 and 6, has the same magnitude and direction. The excitation current of poles 3 and 4, and the symmetrically arranged poles 7 and 8, also has the same magnitude and direction. The current direction of poles 1 and 2 is opposite to that of poles 3 and 4, and the current direction of poles 5 and 6 is opposite to that of poles 7 and 8, thus generating a quadrupole magnetic field.

[0062] Supplementary Note 1

[0063] Figure 7 for Figure 5 Cross-sectional view, Figure 7 The coils tightly attached to the poles on both sides of the middle pole head are octagonal iron coils, and the coils on the outside of the octagonal iron coils are quadrature iron coils. The current direction of the octagonal iron coil is indicated by "O", and the current direction of the quadrature iron coil is indicated by "Q". The octagonal iron coil is divided into two groups: pole heads 1, 3, 5, and 7, and pole heads 2, 4, 6, and 8. The excitation current of the two groups is equal in magnitude but opposite in direction. For example, in an octagonal coil, the current direction of each pole (1, 3, 5, 7) is O+ (entering from the left) and O- (exiting from the right); in an octagonal field coil, the current direction of each pole (2, 4, 6, 8) is O+ (entering from the right) and O- (exiting from the left); in a quadrupole field coil, adjacent poles are grouped together with the same current direction. For example, poles 1 and 2 are grouped together with the same current direction. For example, the current direction on both sides of poles 1 and 2 is right-in (Q+) and left-out (Q-); poles 3 and 4 are grouped together, and the current direction of poles 3 and 4 is opposite to that of poles 1 and 2. The current direction on both sides of poles 3 is left-in (Q+) and right-out (Q-).

[0064] Example 1

[0065] Based on the above-mentioned four / octet composite iron structure for beam control, this invention also relates to a method for adjusting the excitation current of the four / octet composite iron, such as... Figure 14a As shown, the method for adjusting the excitation current of this four / octet composite iron includes the following steps:

[0066] Step 1: Establish a two-dimensional data comparison table for coil current of four-pole iron and eight-pole iron; this two-dimensional data comparison table for coil current is based on the two-dimensional data comparison table for coil current of four / eight-pole composite iron.

[0067] The above two-dimensional data comparison table of coil current is as follows: Figure 8 As shown, the horizontal axis represents the current of the fourth-stage coil, and the vertical axis represents the current of the fourth-stage coil.

[0068] Step 2: Experimental measurement to obtain the four-pole and octole magnetic field gradient measurement values ​​that correspond one-to-one with the two-dimensional current data comparison table, thereby obtaining a three-dimensional surface sample database of magnetic field gradients; the above three-dimensional surface sample database of magnetic field gradients includes a three-dimensional surface sample database of four-pole field magnetic field gradients and a three-dimensional surface sample database of octole field magnetic field gradients.

[0069] The above-mentioned three-dimensional surface sample database, such as Figure 9 As shown, the current of the four-stage coil is used as the X-axis coordinate, the current of the eight-stage coil is used as the Y-axis coordinate, and the magnetic field gradient is used as the Z-axis coordinate.

[0070] Step 3: Use cubic spline functions to perform two-dimensional interpolation on the three-dimensional surface sample database of the quadrupole magnetic field gradient and the octupole magnetic field gradient to refine the grid point density.

[0071] The effect of the above-mentioned encrypted grid point density is as follows: Figure 10 As shown, the grid density on the X, Y, and Z axes has increased.

[0072] Step 4: Select a quadrupole magnetic field gradient plane. This plane intersects with the surface of the quadrupole magnetic field gradient three-dimensional surface sample database to obtain a current curve that satisfies the four-level field gradient. Select an octupole magnetic field gradient plane. This plane intersects with the surface of the octupole magnetic field gradient three-dimensional surface sample database to obtain a current curve that satisfies the eight-level field gradient.

[0073] like Figure 11 , Figure 12 The diagram shown is a schematic of the intersection of the plane and the curved surface, where the current curve is obtained.

[0074] Step 5: Obtain the current curves that satisfy the fourth-order field gradient and the current curves that satisfy the eighth-order field gradient in the two-dimensional data grid plane of the coil current, and finally find the intersection point of the two current curves.

[0075] like Figure 12 The figure shows the current curve obtained after projection. Projection can be used because the current values ​​of the four-pole coil and the octole coil are current values ​​on a two-dimensional plane and are independent of the magnetic field gradient. Therefore, the projection method is used. The projection method projects the current values ​​on two different magnetic field gradients onto the same plane, which makes it easier to calculate the intersection of the two current curves.

[0076] Step 6: Use the intersection point as the solution for the composite iron excitation current.

[0077] like Figure 13 As shown, the current value at this intersection satisfies both the quadrupole gradient and the octupole gradient.

[0078] Furthermore, the establishment of a two-dimensional data comparison table for the coil current of the four-pole and eight-pole iron in step one is as follows:

[0079] 1) Use Gq to maximize the gradient requirement of the quadrupole field. max This indicates that the maximum demand for the octagonal field gradient is expressed using Go. max express;

[0080] 2) When the current in the four-pole field coil is zero, the eight-pole field coil generates Go. max The current at that time is the maximum operating current I of the octagonal field coil. o When the current in the octagonal field coil is zero, the quadrupole field coil generates Gq. max The current at that time is the maximum operating current I of the four-pole field coil. q ;

[0081] 3) Using the maximum operating current I of the four-pole field coil q and the maximum operating current I of the octagonal field coil o The current data covers the boundary of the two-dimensional data lookup table for coil current, and is measured with equal-interval current changes.

[0082] Supplementary Note 2 :

[0083] The "current data coverage boundary" is as follows: Figure 8 As shown, the boundary on the horizontal axis represents the maximum operating current of the four-pole field coil (3600A), and the boundary on the vertical axis represents the maximum operating current of the eight-pole field coil (3600A).

[0084] like Figure 11 As shown, the current curve that satisfies the fourth-order field gradient or the eighth-order field gradient in step four means that the magnetic field gradient is equal at all points on the curve, and the current value at all points on the curve corresponds to a four-pole field coil current and an eight-pole field coil current, respectively.

[0085] Furthermore, in step five, the current curves that satisfy the fourth-order field gradient and the current curves that satisfy the eighth-order field gradient are obtained in the two-dimensional data grid plane of the coil current, and the intersection point of the two current curves is finally determined. Specifically, the two current curves that satisfy the requirements of the four-pole field gradient and the eight-pole field gradient respectively are projected onto the same coordinate plane and the intersection point between them is obtained.

[0086] Supplementary Note 3 :

[0087] The significance of the intersection point is that when the user simultaneously proposes a four-pole field gradient requirement and an eight-level field gradient requirement, if the current intersection point corresponding to the four-pole field gradient requirement and the eight-level field gradient is found, the current value at the intersection point is used to adjust the current values ​​of the four-pole field coil and the eight-level field coil. When the requirements are met, the magnetic field generated at the intersection point meets both the four-pole field gradient requirement and the eight-level field gradient requirement proposed by the user.

[0088] Furthermore, step six uses this intersection point as the solution for the composite ferromagnetic current, specifically as follows:

[0089] 1) Obtain the current curves that satisfy all fourth-order field gradients in the three-dimensional surface sample database of the four-pole field magnetic field gradient, and obtain the current curves that satisfy all eighth-order field gradients in the three-dimensional surface sample database of the eight-pole field magnetic field gradient.

[0090] Supplementary Note 4 :

[0091] The aforementioned "obtaining current curves that satisfy all four-level field gradients in the three-dimensional surface sample database of the quadrupole field magnetic field gradient" involves gradually increasing the value of the quadrupole field gradient plane along the "quadrupole field gradient coordinate axis" from the minimum to the maximum value to obtain multiple quadrupole field gradient planes. Intersecting each quadrupole field gradient plane with the surface will produce a series of intersection lines, which are the current curves of all four-level field gradients.

[0092] The above-mentioned "obtaining current curves that satisfy all eight-level field gradients in the three-dimensional surface sample database of the octagonal field magnetic field gradient" involves gradually increasing the value of the octagonal field gradient plane from the minimum to the maximum value along the "octagonal field gradient coordinate axis" to obtain multiple octagonal field gradient planes. Intersecting each octagonal field gradient plane with the surface will produce a series of intersection lines, which are the current curves of all eight-level field gradients.

[0093] 2) Obtain all intersection points of the current curve satisfying the fourth-order field gradient and the current curve satisfying the eighth-order field gradient;

[0094] Supplementary Note 5 :

[0095] Only two curves on the same plane can intersect. Therefore, these two current curves must be projected onto the same coordinate plane. Although the two current curves have different heights, that is, they lie on different magnetic field gradient planes, each point on the current curve is independent of height and magnetic field gradient, and is only related to the current of the four-pole coil and the eight-pole coil. Therefore, it is entirely possible to project two curves with different spatial heights onto the same coordinate plane.

[0096] 3) Save the current values ​​of the four-pole and eight-pole field coils at all intersection points;

[0097] 4) Input the current gradient requirements for the quadrupole field and the octupole field;

[0098] 5) Based on the current input requirements for the quadrupole gradient and the octupole gradient, find the corresponding intersection point;

[0099] 6) Adjust the current of the four-pole field coil and the octole field coil according to the current value at the intersection point.

[0100] It should be emphasized that the above specific embodiments are merely explanations of the present invention and are not intended to limit the present invention. After reading this specification, those skilled in the art can make modifications to the above embodiments without contributing any inventive step, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A quad / octupole compound iron system for beam homogenization, characterized by: The composite iron system comprises a composite magnet current control device, a composite magnet main power supply and a four-pole / eight-pole composite iron; the composite magnet current control device is used for controlling the four-pole field coil current output and the eight-pole field coil current output of the composite magnet main power supply to the four-pole / eight-pole composite iron; and the four-pole / eight-pole composite iron is used for simultaneously generating a dominant four-pole magnetic field and an eight-pole magnetic field, so that the functions of the four-pole iron and the eight-pole iron can be realized simultaneously by installing only one transmission element; The four-pole / eight-pole composite iron has a total of eight pole heads, and each pole head is provided with inner and outer two layers of current coils in the radial direction close to the major radius; the inner layer coil is an eight-pole magnetic field excitation coil, and the outer layer coil is a four-pole magnetic field excitation coil; The eight-pole magnetic field excitation coil has opposite current directions of adjacent two pole heads, and divides the eight-pole field coil into two groups of 1, 3, 5, 7 pole heads and 2, 4, 6, 8 pole heads; the excitation currents of the two groups are equal in size but opposite in direction, thereby generating an eight-pole magnetic field; The four-pole magnetic field excitation coil has coils on adjacent two pole heads as a group, and is divided into four groups, i.e., 1, 2 pole heads, 3, 4 pole heads, 5, 6 pole heads and 7, 8 pole heads; among them, 1, 2 pole heads and symmetrically arranged 5, 6 pole heads have the same excitation current size and direction of the two groups of four-pole magnetic field coils, 3, 4 pole heads and symmetrically arranged 7, 8 pole heads have the same excitation current size and direction of the two groups of coils, and the current directions of 1, 2 pole heads and 3, 4 pole heads are opposite, and the current directions of 5, 6 pole heads and 7, 8 pole heads are opposite, thereby generating a four-pole magnetic field.

2. A quadrupole / octupole compound iron system for beam homogenization according to claim 1, characterized in that: The composite magnet current control device comprises a two-dimensional sampling point module of coil current, an experimental measurement preliminary establishment of a three-dimensional curved surface sample library of magnetic field gradient module, an interpolation refinement of a three-dimensional curved surface sample library of magnetic field gradient module, an input field gradient solving corresponding field gradient current curve module, a four / eight-pole field gradient current curve intersection point solving module and an output four-pole / eight-pole coil current module; The two-dimensional sampling point module of coil current is used for establishing a two-dimensional data reference table of coil current of the four-pole iron and the eight-pole iron; The experimental measurement preliminary establishment of a three-dimensional curved surface sample library of magnetic field gradient module is used for performing magnetic field experimental measurement on the composite iron by using the current values of the two-dimensional data reference table of coil current, thereby obtaining four / eight-pole magnetic field gradient measurement values corresponding to the two-dimensional current data reference table one by one, and thereby obtaining a three-dimensional curved surface sample database of magnetic field gradient; the three-dimensional curved surface sample database of magnetic field gradient comprises a four-pole field magnetic field gradient three-dimensional curved surface sample database and an eight-pole field magnetic field gradient three-dimensional curved surface sample database; The interpolation refinement of a three-dimensional curved surface sample library of magnetic field gradient module is used for performing two-dimensional interpolation on the four-pole field magnetic field gradient three-dimensional curved surface sample database and the eight-pole field magnetic field gradient three-dimensional curved surface sample database by using a cubic spline function to encrypt the grid point density. The input field gradient solving corresponding field gradient current curve module is configured to intersect the input quadrupole field gradient and octupole field gradient with the magnetic field gradient surface of the three-dimensional sample database, and obtain two corresponding current curves after the intersection; specifically, a quadrupole field magnetic field gradient plane is selected, the plane intersects the surface of the three-dimensional surface sample database of the quadrupole field magnetic field gradient, and a current curve satisfying the quadrupole field gradient is obtained; an octupole field magnetic field gradient plane is selected, the plane intersects the surface of the three-dimensional surface sample database of the octupole field magnetic field gradient, and a current curve satisfying the octupole field gradient is obtained; The solving quadrupole / octupole field gradient current curve intersection point module is configured to obtain the intersection point of the current curve satisfying the quadrupole field gradient and the current curve satisfying the octupole field gradient, and use the intersection point as the solution of the composite iron excitation current; The output quadrupole / octupole coil current module is configured to output the quadrupole field coil current and the octupole field coil current to the quadrupole / octupole composite iron according to the solution of the composite iron excitation current.

Images