Ultra-short bending type beam homogenization structure

Abstract

The application discloses a kind of ultra-short bending type beam uniformization structures, the ultra-short bending type strong current uniformization structure is realized bending type strong current uniformization substructure and symmetric bending type strong current uniformization substructure by using a piece of two-stage iron and multiple pieces of four-eight-stage composite iron on beam line;The bending type strong current uniformization substructure is used to realize bending type strong current uniformization beam line;The symmetric bending type strong current uniformization substructure is used to realize symmetric bending type strong current uniformization beam line;The application solves the problem that the maximum envelope is usually occupied by four-pole magnetic field when using discrete quadrupole iron and eight-stage in the prior art, which cannot fully play the role of octupole iron;Solve the problem that the beam envelope is small at the position of existing octupole iron 1 and octupole iron 2, which requires very high field strength of eight-stage magnet, and is too high in engineering cost and difficult to implement;Solve the problem that the length of the beam line is too long, which leads to more expensive surrounding shielding construction, large area and high cost.

Description

Technical Field

[0001] This invention belongs to the field of accelerator transmission line technology, and particularly relates to an ultra-short bending beam homogenization structure. Background Technology

[0002] The secondary particles produced when the beam from an accelerator strikes a target are important radiation sources for many nuclear technology research and applications. For example, in nuclear technology applications such as neutron imaging and boron neutron capture therapy based on high-current proton accelerators, the accelerator generates a high-energy, high-current proton beam, which, after passing through a transmission line, strikes a neutron target, producing high-flux neutrons.

[0003] The distribution of the accelerator beam is generally similar to a Gaussian distribution, with the highest particle density at the center of the beam cluster. This also causes excessive local power and temperature on the neutron target, leading to damage to the neutron target.

[0004] To address the issue of uneven particle distribution, an octagonal magnet was attempted on the beam transmission line to homogenize the Gaussian-distributed beam and reduce the peak power density on the neutron target.

[0005] One of the challenges in using octagonal magnets to homogenize a Gaussian-distributed beam is that the same octagonal magnet will have different effects depending on the position it is installed on the beam transmission line. Only when the octagonal magnet is installed at a position with a larger beam envelope can it provide the strongest homogenization effect. However, the largest envelope area in existing technologies is usually occupied by quadrupole magnetic fields: the transmission lines in existing technologies are arranged in the order of quadrupole 1, octupole 1, quadrupole 2, and octupole 2. Since the octupoles 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 achieving good beam homogenization requires strict control over the placement and phase of the octagonal magnets. To meet these requirements, transmission lines often need to be over ten meters long. Cyclotrons have a diameter of no more than two meters; dragging a beamline over ten meters long would render miniaturizing the accelerator pointless. Furthermore, 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] This invention addresses the problems existing in the prior art by proposing an ultra-short bending beam homogenization structure. The first objective is to solve the problem that, in existing technologies using discrete quadrupole magnets or octagons, the area with the largest envelope is usually occupied by the quadrupole magnetic field, preventing the octagon from fully utilizing its function. The second objective is to solve the problem that, when using discrete quadrupole magnets or octagons, the smaller beam envelope at the locations of octagon 1 and octagon 2 necessitates extremely high field strength requirements for the octagon magnets, which is too costly and difficult to achieve in engineering. The third objective is to solve the problem that, when using discrete quadrupole magnets or octagons, the excessively long transmission line length leads to increasingly expensive surrounding shielding structures, larger footprints, and higher costs.

[0009] To solve its technical problem, the present invention adopts the following technical solution:

[0010] An ultra-short bend-type beam homogenization structure is characterized by the following: This ultra-short bend-type beam homogenization structure utilizes a single secondary iron plate and multiple 4 / 8 composite iron plates on the transmission line to realize both a bend-type beam homogenization substructure and a symmetrical bend-type beam homogenization substructure; the bend-type beam homogenization substructure is used to realize a bend-type beam homogenization transmission line; the symmetrical bend-type beam homogenization substructure is used to realize an ultra-short symmetrical bend-type beam homogenization transmission line.

[0011] The ultra-short bending beam homogenization structure is arranged along the beam direction as follows: a quadrupole-octupole composite iron 1, a secondary iron, a quadrupole-octupole composite iron 2, and / or a quadrupole-octupole composite iron 3; the secondary iron is used to change the beam direction of the transmission line from a straight line to a bending line; the quadrupole-octupole composite iron 1, the quadrupole-octupole composite iron 2, and / or the quadrupole-octupole composite iron 3 are used to generate quadrupole magnetic fields and octupole magnetic fields simultaneously, so that only one transmission element is installed to achieve the functions of quadrupole iron and octupole iron simultaneously;

[0012] When using a bend-type beam homogenization substructure or a symmetrical first bend-type beam homogenization structure, the beam envelope function in the Y or X direction reaches a large value at the 4 / 8 composite iron 1, and the beam envelope function in the X or Y direction reaches a large value at the 4 / 8 composite iron 2; the phase shift of the particle between the 4 / 8 composite iron 1 and 4 / 8 composite iron 2 and the target. These values ​​are approximately integer multiples of 180 degrees (0, 1, 2, 3…); the transmission matrix between the two octagonal magnetic fields is approximately an identity matrix; when using a bending-type beam homogenization substructure or a symmetrical second bending-type beam homogenization structure, the beam envelope function in the Y or X direction reaches a large value at the 4 / 8-pole composite iron 1, and the beam envelope function in the X or Y direction reaches a large value at the 4 / 8-pole composite iron 3; the phase shift of the particle between the 4 / 8-pole composite iron 1 and 4 / 8-pole composite iron 3 and the target. They are respectively close to integer multiples of 180 degrees (0, 1, 2, 3...); the transmission matrix between the two octagonal magnetic fields is close to the identity matrix;

[0013] The four-eight-pole composite iron 1 and / or four-eight-pole composite iron 3 are based on a four-eight-pole composite magnet system, which includes a composite magnet current control device, a composite magnet main power supply, and a four-eight-pole composite magnet; 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-eight-pole composite magnet by the main power supply of the composite magnet.

[0014] The curved beam homogenization substructure has a 4 / 8 composite iron 1 upstream of the secondary iron and a 4 / 8 composite iron 2 or 4 / 8 composite iron 3 downstream of the secondary iron.

[0015] Based on the bending beam homogenization substructure, the bending beam homogenization transmission line utilizes the combined focusing effect of the quadrupole-octupole composite iron 1 and the dipole iron to generate the beam waist in the Y direction near the quadrupole-octupole composite iron 2; and utilizes the quadrupole field superposition of the dipole iron and the quadrupole-octupole composite iron 2 to generate the envelope size in the X direction on the target, so that the envelope sizes in the X and Y directions are consistent.

[0016] The symmetrical bend-type beam homogenization substructure includes a symmetrical first bend-type beam homogenization structure and a symmetrical second bend-type beam homogenization structure. The symmetrical first bend-type beam homogenization structure has a 4 / 8 composite iron 1 upstream of the secondary iron and a 4 / 8 composite iron 2 downstream of the secondary iron. The symmetrical second bend-type beam homogenization structure has a 4 / 8 composite iron 1 upstream of the secondary iron and a 4 / 8 composite iron 3 downstream of the secondary iron. The symmetrical first bend-type beam homogenization structure and the symmetrical second bend-type beam homogenization structure operate in a time-sharing manner.

[0017] The diode on the symmetrical bending beam homogenization transmission line based on this ultrashort symmetrical bending beam homogenization substructure is a shared diode on the ultrashort symmetrical bending beam homogenization transmission line. This shared diode has an exit edge with symmetrical upper and lower edge angles. Specifically, its beam inlet edge is a straight line, and its beam outlet edge is a pair of symmetrical upper and lower oblique lines. The inclination direction of these symmetrical oblique lines is the direction in which the beam bends at the exit edge. The line connecting the center of the beam bending trajectory and the beam at the diode outlet forms the diode outlet edge angle. By changing the size of the diode outlet edge angle, the edge field focusing effect of the diode is adjusted, and in conjunction with the envelopes of the four-eight-level composite iron on both sides of the diode in the Y direction and the X direction, an ideal phase shift that meets the homogenization requirements is obtained.

[0018] Furthermore, the phase shift of the particle between the two octet composite magnets and the target is close to an integer multiple of 180 degrees, meaning close to but not equal to an integer multiple of 180 degrees: it is set as the remainder of 180 degrees, and the value is generally less than ±15 degrees.

[0019] Furthermore, the transmission matrix between the two octagonal magnetic fields is close to the identity matrix, that is, the phase shift between the two four-octagonal composite magnets is controlled within a range of 30 degrees. This 30-degree range can greatly avoid the high-order nonlinear effects caused by the coupling of the two octagonal magnets and can achieve a better homogenization effect.

[0020] Furthermore, the expression for the magnet strength k at the 48-grade composite iron 1 and 48-grade composite iron 2, or at the 48-grade composite iron 1 and 48-grade composite iron 3, is as follows:

[0021]

[0022] Let: the starting point of the transport line be 0, the position of the first quadrupole magnet be 1, the position of the second quadrupole magnet be 2, and the position of the endpoint, which is the position of the target, be 3; the above formula (1) represents the phase shift of the particle in the x direction between positions 0 and 2, ux23 represents the phase shift of the particle in the x direction between positions 2 and 3; βx2 represents the envelope function in the x direction at position 2; the above formula (2) uy01 represents the phase shift of the particle in the y direction between 0 and 1; uy13 represents the phase shift of the particle in the y direction between 1 and 3; and represents the envelope function in the y direction at position 1.

[0023] Furthermore, 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] The output four-pole / eight-pole coil current module outputs four-pole field coil current and eight-pole field coil current to the four-pole / eight-pole composite iron according to the solution of the excitation current of the composite iron.

[0030] Furthermore, this four-eight-pole composite magnet has a total of eight poles. Each pole has two layers of current coils along the radial direction near the large radius. The inner coil is an eight-pole magnetic field excitation coil, and the outer coil is a four-pole magnetic field excitation coil.

[0031] 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.

[0032] The outer quadrupole magnetic field excitation coil has four groups, consisting of coils on two adjacent poles: poles 1 and 2, poles 3 and 4, poles 5 and 6, and poles 7 and 8. The excitation current of the quadrupole magnetic field coils on poles 1 and 2, and symmetrically arranged on poles 5 and 6, is in the same direction and magnitude. The excitation current of the coils on poles 3 and 4, and symmetrically arranged on poles 7 and 8, is in the same direction and magnitude. The current direction of the coils on poles 1 and 2 is opposite to that of the coils on poles 3 and 4, and the current direction of the coils on poles 5 and 6 is opposite to that of the coils on poles 7 and 8, thus generating a quadrupole magnetic field.

[0033] Advantages and effects of the present invention

[0034] 1. The bending beam homogenization substructure and the symmetrical bending beam homogenization substructure of the present invention adopt the method of generating a large envelope by using four-eight-pole composite iron and four-pole iron together, which solves the problem that when the existing technology uses discrete four-pole iron and eight-pole iron, the largest part of the envelope is usually occupied by the four-pole magnetic field, and the role of the eight-pole iron cannot be fully utilized.

[0035] 2. The bending beam homogenization substructure and the symmetrical bending beam homogenization substructure of the present invention adopt a large envelope to achieve homogenization. Due to the large envelope, the requirement for the magnetic field strength K value of the four-octet composite iron is reduced. This solves the problem that when using discrete four-pole iron and eight-pole iron in the prior art, the beam envelope at the location of octet iron 1 and octet iron 2 is small, which makes the field strength requirement of the octet magnet very high. Excessive magnetic field strength is too costly and difficult to achieve in engineering.

[0036] 3. The bending beam homogenization substructure and the symmetrical bending beam homogenization substructure of the present invention simultaneously generate quadrupole magnetic fields and octupole magnetic fields within the aperture of the quadrupole-octupole composite iron, thereby achieving the focusing and homogenization of the beam envelope. The composite iron installed on the beam transmission line can reduce the number of transmission elements and shorten the length of the transmission line, solving the problem that when using discrete quadrupole irons and octupoles, the excessively long transmission line length leads to increasingly expensive civil engineering for surrounding shielding, large footprint, and high cost.

[0037] 4. The present invention provides a bending beam homogenization substructure and a symmetrical bending beam homogenization substructure that limit the phase shift of particles between two quadrupole composite magnets and the target. The values ​​of the magnetic field strengths k1 and k2 at the first and second four-eight-pole composite magnets are close to integer multiples of 180 degrees (0, 1, 2, 3...), but not equal to integer multiples of 180 degrees (0, 1, 2, 3...), which makes the required magnetic field strengths k1 and k2 at the first and second four-eight-pole composite magnets smaller, which helps to reduce the difficulty and cost of magnet manufacturing.

[0038] 5. The bending beam homogenization substructure and the symmetrical bending beam homogenization substructure of the present invention limit the transmission matrix between the two octagonal magnetic fields to be close to the identity matrix, that is, the phase shift between the two four-octagonal composite magnets is controlled within a range of 30 degrees. This 30-degree range can greatly avoid the high-order nonlinear effects caused by the coupling of the two octagonal magnets and can obtain a better homogenization effect. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of an ultra-short bending beam homogenization structure according to the present invention;

[0040] Figure 2a This is a schematic diagram of the ultra-short symmetrical bending beam homogenization substructure of the present invention;

[0041] Figure 2b This is a schematic diagram of the ultra-short bending beam homogenization substructure A of the present invention. Figure 1 ;

[0042] Figure 2c This is a schematic diagram of the ultra-short bending beam homogenization substructure B of the present invention;

[0043] Figure 3a This is a schematic diagram of the ultra-short symmetrical bending beam homogenization transmission line of the present invention;

[0044] Figure 3b This is a schematic diagram of the ultra-short bending beam homogenization transmission line of the present invention. Figure 1 ;

[0045] Figure 3c This is a schematic diagram of the ultra-short curved beam homogenization transmission line of the present invention (Figure 2).

[0046] Figure 4a This is a schematic diagram showing the maximum envelope positions of the four-octet composite iron 1 and 2 in the ultra-short bending beam homogenization transmission line of the present invention.

[0047] Figure 4b This is a schematic diagram showing the maximum envelope positions of the four-octet composite iron 1 and 2 in the ultra-short symmetrical bending beam homogenization transmission line of the present invention.

[0048] Figure 4c This is a schematic diagram of the secondary iron of the ultra-short symmetrical bending beam homogenization transmission line of the present invention.

[0049] Figure 5 This is a schematic diagram showing the phase difference between the two octet composite iron pieces and the target point (target) and the phase difference between the two octet composite iron pieces;

[0050] Figure 6a This is a schematic diagram of the four / octet composite iron system for beam control according to the present invention;

[0051] Figure 6b This invention provides a novel four / octet composite iron model.

[0052] Figure 6c Four / eight-pole composite magnet coil arrangement and current direction;

[0053] Figure 6d This is a schematic diagram showing the current values ​​of the two sets of coils during magnetic field measurement in this invention;

[0054] Figure 6e This is a schematic diagram showing the quadrupole / octapole magnetic field gradients corresponding to different currents measured in the present invention.

[0055] Figure 6f 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.

[0056] Figure 6g 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;

[0057] Figure 6h This is a schematic diagram of the current curve corresponding to the four / octet field selected in this invention;

[0058] Figure 6i This is a schematic diagram illustrating the solution for the composite iron excitation current of the present invention;

[0059] Figure 7 This is a schematic diagram of an existing octet iron in the small envelope position.

[0060] Figure 8 This is a schematic diagram of an embodiment of the ultra-short curved beam homogenization transmission line of the present invention;

[0061] Figure 9 This is a schematic diagram of an embodiment of the ultra-short symmetrical bending beam homogenization transmission line of the present invention;

[0062] Figure 10a This invention provides a comparison of the states of the curved beam homogenization transmission line before and after homogenization.

[0063] Figure 10b This is a comparison of the states of the symmetrical bending beam homogenization transmission line before and after homogenization in this invention. Detailed Implementation

[0064] Design principle of the invention

[0065] 1. Innovation of this invention

[0066] One of the innovations lies in the invention of a four-octet composite iron. (The text abruptly ends here, seemingly mid-sentence.) Figure 6a , 6b The four-octet composite iron shown in 6c replaces, for example, Figure 7The discrete components shown are tetrapole and octapole iron. One effect is that after being combined, the tetrapole and octapole magnetic fields are generated within the aperture of the tetrapole-octapole composite iron, with the following effect: Figure 4a As shown: the quadrupole and octupole share the positions of the large envelopes in the Y and X directions. The reason they can share the positions of the large envelopes in the Y or X directions is that the quadrupole-octupole composite iron 1 and the quadrupole preceding it coexist in the large envelope in the Y direction; the quadrupole-octupole composite iron 2 and the quadrupole of the quadrupole-octupole composite iron 1 preceding it coexist in the large envelope in the X direction. Because the octupoles in the quadrupole-octupole composite iron 1 and 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 7 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.

[0067] The second innovation lies in the invention of a four / octagonal composite magnet current control system and a four / octagonal composite iron excitation current design method. Firstly, the design challenge of the four / octagonal composite iron excitation current lies in the coupling relationship between the multipole magnetic fields generated by the two sets of coils in the four / octagonal composite iron. This coupling relationship means that changing the current magnitude of the four-pole or octagonal field coil will simultaneously change the original four-pole and octagonal magnetic field gradients of the magnet. Therefore, the one-to-one adjustment strategy of the current magnetic field gradient for a single type of magnet is no longer applicable. In a composite magnet, if the current magnitude of the four-pole field coil is adjusted first to meet the usage requirements, and then the current magnitude of the octagonal field coil is adjusted, once the octagonal field coil current begins to change, it will alter the previously adjusted four-pole magnetic field gradient, causing it to no longer meet the usage requirements. Secondly, an innovative four / octagonal composite magnet current control system and a four / octagonal composite iron excitation current design method were designed. This system and method solved the problem of coupling relationship between the multipole magnetic fields generated by the two sets of coils of the four / octagonal composite iron, and found the current intersection point that simultaneously satisfies the four-pole field gradient and the octagonal field gradient.

[0068] The system is like Figure 6aAs shown, it includes: a two-dimensional sampling point module based on coil current, a three-dimensional surface sample library module based on experimentally measured initial magnetic field gradient, a three-dimensional surface sample library module based on interpolation algorithm for refined magnetic field gradient, a current curve module for solving the corresponding field gradient based on field gradient input, a current curve intersection module based on field gradient solution, and a module for outputting four-pole / eight-pole coil current.

[0069] The design method for the excitation current of a four / octet composite iron is as follows:

[0070] Step 1, such as Figure 6d As shown, a two-dimensional data comparison table for coil currents of four-pole and eight-pole composite iron is established; this two-dimensional data comparison table is based on the two-dimensional data comparison table for coil currents of four / eight-pole composite iron; the above two-dimensional data comparison table for coil currents is as follows. Figure 6d 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.

[0071] Step 2, as follows Figure 6e As shown, experimental measurements were performed 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.

[0072] The above three-dimensional surface sample database Figure 6e 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.

[0073] Step 3, as follows Figure 6f As shown, cubic spline functions are used to perform two-dimensional interpolation on the three-dimensional surface sample database of the quadrupole magnetic field gradient and the octupole magnetic field gradient, thereby increasing the density of the grid points.

[0074] The effect of the above-mentioned encrypted grid point density is as follows: Figure 6f As shown, the grid density on the X, Y, and Z axes has increased.

[0075] Step 4, as follows Figure 6g As shown, a quadrupole magnetic field gradient plane is selected, which 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; an octupole magnetic field gradient plane is selected, which 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.

[0076] Step 5, as follows Figure 6hAs shown, the current curves satisfying the fourth-order field gradient and 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.

[0077] Step Six, as Figure 6i As shown, the intersection point is used as the solution for the excitation current of the composite iron.

[0078] The third innovation lies in finding a balance between transmission line homogenization, avoiding nonlinear effects caused by coupling, and shortening the transmission line. For example... Figure 4a , 4b As shown, the homogenization effect of the ultra-short bend transition beam homogenization transmission line is significant, stemming from innovations in three aspects. All three are indispensable and must support each other to achieve the desired homogenization effect:

[0079] The first aspect is to ensure uniformity as a premise. Specifically, two octet composite irons are used on the transmission line. The octet in front of octet composite iron 1 and its own octet are used to generate a large envelope in the Y direction at octet composite iron 1. The octet in front of octet composite iron 1 and its own octet are used to generate a large envelope in the X direction at octet composite iron 2.

[0080] The second aspect: Solving the problem of optimizing the homogenization effect: specifically as follows Figure 5 As shown, this is achieved through the phase shift between the four-octet composite magnet 1 and the target. The phase shift between the four-octet composite magnet 2 and the target is close to an integer multiple of 180 degrees (0, 1, 2, 3…). It is achieved by applying multiples of 0 degrees. The homogenization effect is best when the angle is close to 180 degrees and close to 0 degrees.

[0081] The third aspect is to avoid nonlinear effects caused by coupling while ensuring homogenization. These nonlinear effects occur when two octet composite iron pieces are used together; improper handling can lead to nonlinear coupling. When nonlinear coupling occurs, the particle amplitude increases, causing particle loss, which reduces the homogenization effect. Therefore, to avoid nonlinear coupling, this invention approximates the transmission matrix between the two octet magnetic fields of the two octet composite iron pieces to a unit matrix. This approximation to a unit matrix is ​​as follows: Figure 1 , Figure 5As shown, the phase difference between the first octagonal composite iron (point 1) and the second octagonal composite iron (point 2) is close to 0 degrees and less than 30 degrees. At this point, the required magnetic field strength of the octagonal magnet is relatively small, and the nonlinear effect caused by coupling is smaller, resulting in better homogenization. The difference between this invention and the prior art is that the transmission matrix between the two octagonal magnetic fields in the prior art is "equal to the identity matrix" rather than "close to the identity matrix," while the transmission matrix between the two octagonal magnetic fields in this invention is "close to the identity matrix" rather than "equal to the identity matrix." That is, the phase difference between the first octagonal composite iron (point 1) and the second octagonal composite iron (point 2) is close to 0 degrees rather than equal to 0 degrees, and less than 30 degrees rather than equal to 30 degrees. The significance of using "close to" rather than "equal to" in this invention is to shorten the transmission line. If the method of "equal to the identity matrix" were used, many more components would need to be added to the transmission line, resulting in a very long transmission line. This invention adopts a "sufficient" approach to address the issue of "avoiding nonlinear effects caused by coupling": when the phase difference between the first 4x8 composite iron (point 1) and the second 4x8 composite iron (point 2) is close to 0 degrees and less than 30 degrees, it can effectively shorten the transmission line length and meet the requirement of "avoiding nonlinear effects caused by coupling". A balance point is found between transmission line homogenization, avoiding nonlinear effects caused by coupling, and shortening the transmission line.

[0082] The fourth innovation lies in the invention of a curved beam homogenization structure and a secondary iron for an ultra-short symmetrical curved beam homogenization transmission line.

[0083] like Figure 4a , Figure 4b As shown, the bending beam homogenization structure employs two quadrupole-octupole composite iron pieces and a diode in between on the transmission line. The diode is used to bend the direction of the beam. The innovation lies in the fact that, based on this bending beam homogenization substructure, the bending beam homogenization transmission line utilizes the combined focusing effect of the quadrupole-octupole composite iron 1 and the diode to generate a beam waist in the Y direction near the quadrupole-octupole composite iron 2. The quadrupole fields of the diode and the quadrupole-octupole composite iron 2 are superimposed to generate the envelope size in the X direction on the target, making the envelope sizes in the X and Y directions consistent.

[0084] First, second, such as Figure 4cAs shown, the secondary electrode used for the ultra-short symmetrical bending beam homogenization transmission line is a common electrode on the ultra-short symmetrical bending beam homogenization transmission line. This common electrode has an exit edge with symmetrical upper and lower edge angles. Specifically, its beam inlet edge is a straight line, and its beam outlet edge is a pair of symmetrical upper and lower oblique lines. The inclination direction of these symmetrical oblique lines is the direction in which the beam bends at the exit edge. The line connecting the center of the beam bending trajectory and the beam at the electrode outlet forms the electrode outlet edge angle. By changing the size of the electrode outlet edge angle, the edge field focusing effect of the electrode is adjusted, and in conjunction with the envelopes of the four-eight-stage composite electrodes on both sides of the electrode in the Y direction and the X direction, an ideal phase shift that meets the homogenization requirements is obtained.

[0085] Based on the above-mentioned inventive principles, this invention designs an ultra-short bending beam homogenization structure, such as... Figure 1 As shown, its characteristics are: this ultra-short bending beam homogenization structure achieves bending beam homogenization substructure and symmetrical bending beam homogenization substructure by using a single secondary iron and multiple 4 / 8 composite iron on the transmission line; as shown... Figure 2b , 2c As shown, this curved beam homogenization substructure is used to realize a curved beam homogenization transmission line; as Figure 2a As shown, this symmetrical bending beam homogenization substructure is used to realize a symmetrical bending beam homogenization transmission line.

[0086] like Figure 1 As shown, the ultra-short bending beam homogenization structure is arranged along the beam direction with: a quadrupole-octupole composite iron 1, a secondary iron, a quadrupole-octupole composite iron 2, and / or a quadrupole-octupole composite iron 3; the secondary iron is used to change the beam direction of the transmission line from a straight line to a bending line; the quadrupole-octupole composite iron 1, quadrupole-octupole composite iron 2, and / or quadrupole-octupole composite iron 3 are used to simultaneously generate a quadrupole magnetic field and an octupole magnetic field, respectively, so that only one transmission element is installed to achieve the functions of both quadrupole and octupole irons; as shown Figure 6a As shown, the four-eight-pole composite iron 1 and / or four-eight-pole composite iron 3 are based on a four-eight-pole composite magnet system. The four-eight-pole composite magnet system includes a composite magnet current control device, a composite magnet main power supply, and a four-eight-pole composite magnet. 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-eight-pole composite magnet by the composite magnet main power supply.

[0087] like Figure 2b , 2c As shown, the curved beam homogenization substructure has a 4 / 8 composite iron 1 upstream of the secondary iron and a 4 / 8 composite iron 2 or 4 / 8 composite iron 3 downstream of the secondary iron.

[0088] Based on the bending beam homogenization substructure, the bending beam homogenization transmission line utilizes the combined focusing effect of the quadrupole-octupole composite iron 1 and the dipole iron to generate the beam waist in the Y direction near the quadrupole-octupole composite iron 2; and utilizes the quadrupole field superposition of the dipole iron and the quadrupole-octupole composite iron 2 to generate the envelope size in the X direction on the target, so that the envelope sizes in the X and Y directions are consistent.

[0089] like Figure 2a As shown, the symmetrical bending beam homogenization substructure includes a symmetrical first bending beam homogenization structure and a symmetrical second bending beam homogenization structure. The symmetrical first bending beam homogenization structure has a 4 / 8 composite iron 1 upstream of the secondary iron and a 4 / 8 composite iron 2 downstream of the secondary iron. The symmetrical second bending beam homogenization structure has a 4 / 8 composite iron 1 upstream of the secondary iron and a 4 / 8 composite iron 3 downstream of the secondary iron. The symmetrical first bending beam homogenization structure and the symmetrical second bending beam homogenization structure operate in a time-sharing manner.

[0090] Based on the bending beam homogenization substructure, the bending beam homogenization transmission line utilizes the combined focusing effect of the quadrupole-octupole composite iron 1 and the dipole iron to generate the beam waist in the Y direction near the quadrupole-octupole composite iron 2; and utilizes the quadrupole field superposition of the dipole iron and the quadrupole-octupole composite iron 2 to generate the envelope size in the X direction on the target, so that the envelope sizes in the X and Y directions are consistent.

[0091] The beam waist in the Y direction near the four-eight-pole composite iron 1 and the dipole iron is generated by superimposing the combined focusing effect of the four-eight-pole composite iron 2. The envelope size in the X direction on the target is generated by superimposing the quadrupole fields of the dipole iron and the four-eight-pole composite iron 2. Specifically: at the current intersection point of the four-eight-pole composite iron 1, the quadrupole current of the four-eight-pole composite iron 1 is appropriately reduced, and the edge field focusing effect of the dipole iron inlet behind the four-eight-pole composite iron 1 and the quadrupole focusing effect of the four-eight-pole composite iron 1 itself are superimposed to generate the waist in the Y direction at the four-eight-pole composite iron 2. At the current intersection point of the four-eight-pole composite iron 2, the quadrupole current of the four-eight-pole composite iron 2 is appropriately reduced, and the edge field focusing effect of the dipole iron outlet behind the four-eight-pole composite iron 1 and the quadrupole focusing effect of the four-eight-pole composite iron 2 itself are superimposed to generate the envelope size in the X direction on the target, making the envelope sizes in the X and Y directions consistent.

[0092] like Figure 2a , 2bAs shown, when using the bending beam homogenization substructure A or the symmetrical first bending beam homogenization structure, the beam envelope function in the Y or X direction reaches a large value at the 4-8 pole composite iron 1, and the beam envelope function in the X or Y direction reaches a large value at the 4-8 pole composite iron 2; the phase shift of the particle between the target and the 4-8 pole composite iron 1 and 4-8 pole composite iron 2 is close to an integer multiple of 180 degrees (0, 1, 2, 3…); the transmission matrix between the two octagonal magnetic fields is close to the identity matrix;

[0093] like Figure 2a , 2c As shown, when using the bending beam homogenization substructure B or the symmetrical second bending beam homogenization structure, the beam envelope function in the Y or X direction reaches a large value at the 48-pole composite iron 1, and the beam envelope function in the X or Y direction reaches a large value at the 48-pole composite iron 3; the phase shift of the particle between the target and the 48-pole composite iron 1 and 48-pole composite iron 3 is close to an integer multiple of 180 degrees (0, 1, 2, 3...); the transmission matrix between the two octagonal magnetic fields is close to the identity matrix.

[0094] Supplementary Note 1

[0095] The aforementioned "phase shift of the particle between the two octet composite magnets and the target" The values ​​are "approaching integer multiples of 180 degrees (0, 1, 2, 3...)" but not equal to 180 degrees. The principle behind this is as follows:

[0096] In formula (1), since the molecule's Csc[ux23] = 1 / sin[ux23], when ux23 approaches 180°, sin[ux23] tends to 0, and Csc[ux23] tends to infinity; similarly, in formula (2), the molecule's Csc[uy13] = 1 / sin[uy13], when ux13 approaches 180°, sin[ux13] tends to 0, and Csc[uy13] tends to infinity; therefore, the phase shift of the particle between the two quadrupole composite magnets and the target... Each is a multiple of 180 degrees (0, 1, 2, 3...) but not equal to 180 degrees.

[0097] The phase shift of the particle between the two octet composite magnets and the target is close to an integer multiple of 180 degrees, meaning close to but not equal to an integer multiple of 180 degrees: it is set as the remainder of 180 degrees, and the value is generally less than ±15 degrees.

[0098] The transmission matrix between the two octagonal magnetic fields is close to the identity matrix, that is, the phase shift between the two four-octagonal composite magnets is controlled within a range of 30 degrees. This 30-degree range can greatly avoid the high-order nonlinear effects caused by the coupling of the two octagonal magnets and can achieve a better homogenization effect.

[0099] The expression for the magnet strength k at points 1 and 2 of the 48-grade composite iron, or points 3 of the 48-grade composite iron, is:

[0100]

[0101] Let: the starting point of the transport line be 0, the position of the first quadrupole magnet be 1, the position of the second quadrupole magnet be 2, and the position of the endpoint, which is the position of the target, be 3; the above formula (1) represents the phase shift of the particle in the x direction between positions 0 and 2, ux23 represents the phase shift of the particle in the x direction between positions 2 and 3; βx2 represents the envelope function in the x direction at position 2; the above formula (2) uy01 represents the phase shift of the particle in the y direction between 0 and 1; uy13 represents the phase shift of the particle in the y direction between 1 and 3; and represents the envelope function in the y direction at position 1.

[0102] Supplementary Note 2

[0103] The derivation process of the above formulas (1) and (2) is briefly described as follows: In the reference "Yosuke Yuri, Uniformization of the transverse beam profile by means of nonlinear focusing method[J]. Physical Review Special Topics-Accelerators and Beams,2007.DOI:10.1103 / physrevstab.10.104001.", the formula for the octagonal magnetic field strength in a single direction is given. This formula only considers an octagonal magnet and the subsequent transmission section. In order to more accurately describe the relationship between the octagonal magnetic field strength and the transmission line design, we extend the formula to consider the influence of the matching section from the accelerator exit to the octagonal magnet on the beam homogenization. The parameters involved are ux02 (phase shift in the x direction between positions 0 and 2), ux23 (phase shift in the x direction between positions 2 and 3), uy01 (phase shift in the x direction between positions 0 and 2), and uy13 (phase shift in the x direction between positions 2 and 3). Using the same "higher-order transport mapping" derivation method as in the references, we obtain the expressions (1) and (2) for the magnetic strength k at the first four-octet composite magnet and the second four-octet composite magnet.

[0104] like Figure 6aAs 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.

[0105] like Figure 6d 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.

[0106] like Figure 6e As 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.

[0107] like Figure 6f 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.

[0108] like Figure 6g , 6h 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.

[0109] like Figure 6i 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.

[0110] The output four-pole / eight-pole coil current module outputs four-pole field coil current and eight-pole field coil current to the four-pole / eight-pole composite iron according to the solution of the excitation current of the composite iron.

[0111] like Figure 6b , Figure 6c As shown, this four-eight-pole composite magnet has a total of eight poles. Each pole has two layers of current coils along the radial direction near the large radius. The inner coil is an eight-pole magnetic field excitation coil, and the outer coil is a four-pole magnetic field excitation coil.

[0112] like Figure 6b , Figure 6c 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.

[0113] like Figure 6b , Figure 6c As shown, the outer quadrupole magnetic field excitation coil has four groups, with the coils on two adjacent poles forming a group: poles 1 and 2, poles 3 and 4, poles 5 and 6, and poles 7 and 8. The excitation current of the quadrupole magnetic field coils in the groups of poles 1 and 2 and symmetrically arranged poles 5 and 6 is in the same magnitude and direction. The excitation current of the coils in the groups of poles 3 and 4 and symmetrically arranged poles 7 and 8 is in the same magnitude and direction. The current direction of the coils in the groups of poles 1 and 2 is opposite to that of the coils in the groups of poles 3 and 4. The current direction of the coils in the groups of poles 5 and 6 is opposite to that of the coils in the groups of poles 7 and 8. This generates a quadrupole magnetic field.

[0114] Example 1

[0115] like Figure 8 As shown, based on the above ultra-short bendable beam homogenization structure, this invention designs an ultra-short bendable beam homogenization transmission line. When the total length of the ultra-short bendable beamline is 6, the initial placement positions of the components that enable the beamline to achieve a better homogenization effect are as follows: the initial position of the fluorescent target 1 is 100mm, the initial position of the quadrupole magnet (Q0) is 1300mm; the initial position of the guide magnet 1 is 1650mm; the initial position of the quadrupole-octupole composite iron (Q1) is 2100mm, the initial position of the dipole iron is 2700mm, the initial position of the quadrupole-octupole composite iron (Q2) is 3850mm; the initial position of the guide magnet 2 is 4250mm; the initial position of the Faraday cylinder is 4700mm; the initial position of the fluorescent target 2 is 5350mm, the initial position of the dual wire is 5750mm; and the initial position of the terminal is 6000mm.

[0116] The magnetic field component of the tetrapole iron (Q0) is 6.8 (T / m); the tetrapole magnetic field component of the tetrapole-octapole composite iron (Q1) is 2.25 (T / m), and the octapole magnetic field component is 1e4 (T / m). 3The quadrupole magnetic field component of the four-octupole composite iron (Q2) is 0.6 (T / m), and the octupole magnetic field component is 6.25e3 (T / m). 3 The beam is deflected by 90°, with both the incident and exit angles at 45° and a deflection radius of 0.55m.

[0117] like Figure 10a The image shows a comparison of the ultra-short bend beam homogenization transmission line before and after homogenization according to the present invention. Figure 10a The left figure is a cross-section of the beam with a Gaussian distribution before homogenization, which is the beam cross-section of the fluorescent target 1 at the position of 100mm of the transmission line. Figure 10a The right figure shows the beam cross-section after homogenization, which is the beam cross-section of fluorescent target 2 at the transmission line position of 5350 mm. As can be seen from the figure, before homogenization, the particle distribution on the beam cross-section is dense in the middle and sparse around the edges. After homogenization, the particle distribution on the beam cross-section is uniform in both the middle and around the edges.

[0118] Example 2

[0119] like Figure 9 As shown, based on the ultra-short curved beam homogenization structure, this invention designs an ultra-short symmetrical curved beam homogenization transmission line. When the total length of the ultra-short symmetrical curved beam homogenization transmission line is 6.5 meters, the initial placement positions of the components that enable the streamline to achieve a better homogenization effect are as follows: the initial position of the fluorescent target 1 is 100 mm; the initial position of the quadrupole magnet (Q0) is 700 mm; the initial position of the guide magnet 1 is 1100 mm; the initial position of the quadrupole-octupole composite iron (Q1) is 1600 mm; the initial position of the dipole iron is 2200 mm; the initial position of the quadrupole-octupole composite iron (Q2 / Q3) is 3500 mm; the initial position of the guide magnet 2 / 3 is 4200 mm; the initial position of the Faraday cylinder 1 / 2 is 4800 mm; the initial position of the fluorescent target 2 / 3 is 5500 mm; the initial position of the dual wire 1 / 2 is 6000 mm; and the initial position of the terminal 1 / 2 is 6500 mm.

[0120] The magnetic field component of the tetrapole iron (Q0) is 6 (T / m); the tetrapole magnetic field component of the tetrapole-octapole composite iron (Q1) is 2.6 (T / m), and the octapole magnetic field component is 3.5e3 (T / m). 3 The quadrupole magnetic field component of the four-pole / octupole composite iron (Q2 / Q3) is 0.55 (T / m), and the octupole magnetic field component is 3e3 (T / m). 3 The inlet edge angle of the diode is 0°, the outlet edge angle is 32°, and the beam bends at 45°.

[0121] like Figure 10b The image shows a comparison of the ultra-short symmetrical bending beam homogenization transmission line before and after homogenization according to the present invention. Figure 10bThe left figure is a cross-section of the beam with a Gaussian distribution before homogenization, which is the beam cross-section of the fluorescent target 1 at the position of 100mm of the transmission line. Figure 10b The right figure shows the beam cross-section after homogenization, that is, the beam cross-section with 2 / 3 of the fluorescent target placed at the 5500mm position of the transmission line. As can be seen from the figure, before homogenization, the particle distribution on the beam cross-section was dense in the middle and sparse around the edges. After homogenization, the particle distribution on the beam cross-section is uniform in both the middle and around the edges.

[0122] 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. An ultrashort bending-type beam homogenization structure, characterized by: The super-short bending-type beam homogenization structure realizes the bending-type beam homogenization substructure and the symmetric bending-type beam homogenization substructure by using a two-stage iron and multiple four-octupole composite irons on the transmission line; the bending-type beam homogenization substructure is used to realize the bending-type beam homogenization transmission line; and the symmetric bending-type beam homogenization substructure is used to realize the super-short symmetric bending-type beam homogenization transmission line; The super-short bending-type beam homogenization structure is sequentially arranged along the beam direction with the four-octupole composite iron 1, the two-stage iron, the four-octupole composite iron 2 and / or the four-octupole composite iron 3; the two-stage iron is used to change the beam direction of the transmission line from a straight line type to a bending type; and the four-octupole composite iron 1, the four-octupole composite iron 2 and / or the four-octupole composite iron 3 are used to simultaneously generate a quadrupole magnetic field and an octupole magnetic field, so that the functions of the quadrupole iron and the octupole iron can be realized simultaneously by installing only one transmission element; When using the bending type beam homogenization substructure or the symmetric first bending type beam homogenization structure, the Y direction or X direction beam envelope function reaches a large value at the four-octupole composite iron 1, and the X direction or Y direction beam envelope function reaches a large value at the four-octupole composite iron 2; the phase shift of particles between the four-octupole composite iron 1 and the four-octupole composite iron 2 and the target respectively close to integer multiples of 180 degrees (0, 1, 2, 3…); the transmission matrix between the two octupole magnetic fields is close to the unit matrix; when using the bending type beam homogenization substructure or the symmetric second bending type beam homogenization structure, the Y direction or X direction beam envelope function reaches a large value at the four-octupole composite iron 1, and the X direction or Y direction beam envelope function reaches a large value at the four-octupole composite iron 3; the phase shift of particles between the four-octupole composite iron 1 and the four-octupole composite iron 3 and the target respectively close to integer multiples of 180 degrees (0, 1, 2, 3…); the transmission matrix between the two octupole magnetic fields is close to the unit matrix; The four-octupole composite iron 1 and / or the four-octupole composite iron 3 are based on a four-octupole composite magnet system, which includes a composite magnet current control device, a composite magnet main power supply and a four-octupole composite magnet; the composite magnet current control device is used to control the quadrupole field coil current output and the octupole field coil current output of the four-octupole composite magnet by the composite magnet main power supply; The bending-type beam homogenization substructure is provided with the four-octupole composite iron 1 upstream of the two-stage iron and the four-octupole composite iron 2 or the four-octupole composite iron 3 downstream of the two-stage iron; Based on the bending-type beam homogenization transmission line of the bending-type beam homogenization substructure, the focusing effect of the four-octupole composite iron 1 and the two-stage iron is superimposed to generate the Y-direction beam waist near the four-octupole composite iron 2; and the quadrupole field of the two-stage iron and the four-octupole composite iron 2 is superimposed to generate the X-direction envelope size on the target, so that the envelope sizes in the X direction and the Y direction are consistent; The symmetric bending-type beam homogenization substructure includes a symmetric first bending-type beam homogenization structure and a symmetric second bending-type beam homogenization structure; the symmetric first bending-type beam homogenization structure is provided with the four-octupole composite iron 1 upstream of the two-stage iron and the four-octupole composite iron 2 downstream of the two-stage iron; the symmetric second bending-type beam homogenization structure is provided with the four-octupole composite iron 1 upstream of the two-stage iron and the four-octupole composite iron 3 downstream of the two-stage iron; and the symmetric first bending-type beam homogenization structure and the symmetric second bending-type beam homogenization structure work at different times. The shared dipole iron is a dipole iron with upper and lower symmetric edge angles on the outlet side, specifically: the beam inlet side is a straight line, the beam outlet side is a pair of upper and lower symmetric oblique lines, the inclination direction of the upper and lower symmetric oblique lines is the direction of beam bending at the outlet side; the upper and lower symmetric oblique lines and the line from the center of the beam bending track to the beam at the outlet of the dipole iron form the dipole iron outlet edge angle; the edge field focusing effect of the dipole iron is adjusted by changing the size of the dipole iron outlet edge angle, and the Y-direction envelope and X-direction envelope of the four-octupole composite iron on both sides of the dipole iron are matched, so that the ideal phase shift meeting the uniformization requirement is obtained.

2. The ultra-short bending type beam homogenization structure according to claim 1, characterized in that: Phase shift of the particles between two four-pole compound magnets and the target An integer multiple close to 180 degrees means an integer multiple close to but not equal to 180 degrees: let For example, an integer multiple close to 180 degrees is an integer multiple of 180 degrees ± 15 degrees. The remainder of 180 degrees, The value is generally less than ± 15 degrees.

3. The ultra-short bending type beam homogenization structure according to claim 2, characterized in that: The transmission matrix between the two octupole magnetic fields is close to a unit matrix, that is, the phase shift between the front and rear four-octupole composite magnets is controlled within 30 degrees, which can greatly avoid the high-order nonlinear effect caused by the coupling of the two octupole magnets, and better uniformization effect can be obtained.

4. The ultra-short bending type beam homogenization structure according to claim 1, characterized in that: The expression of the magnet strength k at the four-octupole composite iron 1, the four-octupole composite iron 2, or the four-octupole composite iron 3 is: Suppose that the starting point of the transport line is 0, the position of the first four-octupole magnet is 1, the position of the second four-octupole magnet is 2, and the position of the terminal, that is, the position of the target, is 3; ux02 in the above formula (1) represents the x-direction phase shift of the particle between positions 0 and 2, and ux23 represents the x-direction phase shift of the particle between positions 2 and 3; βx2 represents the x-direction envelope function at position 2; uy01 in the above formula (2) represents the y-direction phase shift of the particle between 0 and 1; uy13 represents the y-direction phase shift of the particle between 1 and 3; and βy1 represents the y-direction envelope function at position 1.

5. The ultra-short bending-type beam homogenization structure according to claim 1, characterized in that: The composite magnet current control device comprises: a coil current two-dimensional sampling point establishment module, an experimental measurement preliminary magnetic field gradient three-dimensional curved surface sample library establishment module, an interpolated magnetic field gradient three-dimensional curved surface sample library using module, an input field gradient corresponding field gradient current curve solving module, a four-octupole / eight-octupole coil current output module, and a four-octupole / eight-octupole coil current output module; The coil current two-dimensional sampling point establishment module is used to establish a four-octupole and eight-octupole coil current two-dimensional data comparison table; The experimental measurement preliminary magnetic field gradient three-dimensional curved surface sample library establishment module uses the current value of the coil current two-dimensional data comparison table to perform magnetic field experimental measurement on the composite iron, so as to obtain four-octupole and eight-octupole magnetic field gradient measurement values corresponding to the two-dimensional current data comparison table, thereby obtaining a magnetic field gradient three-dimensional curved surface sample database; the magnetic field gradient three-dimensional curved surface sample database comprises a four-octupole field magnetic field gradient three-dimensional curved surface sample database and an eight-octupole field magnetic field gradient three-dimensional curved surface sample database; The interpolation and refinement of the magnetic field gradient three-dimensional curved surface sample library module is configured to use a cubic spline function to perform two-dimensional interpolation on the quadrupole field magnetic field gradient three-dimensional curved surface sample database and the octupole field magnetic field gradient three-dimensional curved surface sample database, and to encrypt the grid point density. The input field gradient and corresponding field gradient current curve solving module is configured to intersect the input quadrupole field gradient and octupole field gradient with the magnetic field gradient curved surface of the three-dimensional sample database, and to obtain two corresponding current curves after the intersection. Specifically, a quadrupole field magnetic field gradient plane is selected, the plane intersects the curved surface of the quadrupole field magnetic field gradient three-dimensional curved surface sample database, and a current curve satisfying the quadrupole field gradient is obtained. An octupole field magnetic field gradient plane is selected, the plane intersects the curved surface of the octupole field magnetic field gradient three-dimensional curved surface sample database, and a current curve satisfying the octupole field gradient is obtained. The quadrupole / octupole field gradient current curve intersection point solving 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 to use the intersection point as the solution of the composite iron excitation current. The quadrupole / octupole coil current output module outputs 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.

6. The ultrashort bending beam uniformization structure of claim 1, wherein: The quadrupole / octupole composite magnet has eight pole heads in total, and each pole head is provided with inner and outer current coils in the radial direction near the major radius. The inner coil is an octupole magnetic field excitation coil, and the outer coil is a quadrupole magnetic field excitation coil. The adjacent two pole heads of the inner octupole magnetic field excitation coil have opposite current directions, i.e., the octupole field coils are divided 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 octupole magnetic field. The adjacent two pole heads of the outer quadrupole magnetic field excitation coil have coils that form a group, which are 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 excitation currents of the two groups of quadrupole magnetic field coils that are consistent in size and direction, 3, 4 pole heads and symmetrically arranged 7, 8 pole heads have excitation currents of the two groups of coils that are consistent in size and direction, 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 quadrupole magnetic field.

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