Ultra-short straight beam homogenization transmission line

Abstract

The application discloses a kind of ultra-short linear beam homogenization transmission line, the linear type high-current homogenization beam line is sequentially provided with: accelerator exit, beam matching mechanism, four eight-pole composite iron 1, four eight-pole composite iron 2, beam homogenization effect observation mechanism, terminal along the beam direction;The four eight-pole composite iron 1 and four eight-pole composite iron 2 are used to generate four-pole magnetic field and octupole magnetic field respectively, so that only one transmission element can realize the role of four-pole iron and eight-pole iron simultaneously;The four eight-pole composite iron 1 and four eight-pole composite iron 2 are based on a four eight-pole composite magnet system.The application solves the problem that the place where the envelope of the prior art is maximum is usually occupied by four-pole magnetic field, and the role of eight-pole iron cannot be fully played;Solve the problem that the beam envelope is small at the position of the existing eight-pole iron, which makes the field intensity requirement of eight-level magnet very high and difficult to realize in engineering;Solve the problem that the length of beam line is too long, resulting in large floor area and high cost.

Description

Technical Field

[0001] This invention belongs to the field of accelerator transmission line technology, and particularly relates to an ultrashort straight beam homogenization transmission line. 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 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 6 As 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 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 of existing technologies by proposing an ultrashort, straight beam homogenization transmission line. The first objective is to solve the problem that existing technologies using discrete quadrupole magnets or octagons often fail to fully utilize the octagon's function because the area with the largest envelope is usually occupied by the quadrupole magnetic field. The second objective is to solve the problem that using discrete quadrupole magnets or octagons results in a smaller beam envelope at the locations of octagon 1 and octagon 2, requiring extremely high field strength from the octagon magnets, which is prohibitively expensive and difficult to achieve in engineering. The third objective is to solve the problem that using discrete quadrupole magnets or octagons leads to excessively long transmission lines, resulting in 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 ultrashort linear beam homogenization transmission line is characterized by the following: the transmission line is a linear beam homogenization transmission line containing two quadrupole-octupole composite iron pieces; the linear beam homogenization transmission line is provided with the following in sequence along the beam direction: accelerator outlet, beam matching mechanism, quadrupole-octupole composite iron 1, quadrupole-octupole composite iron 2, beam homogenization effect observation mechanism, and terminal.

[0011] The four-pole / octole composite iron 1 and 2 are used to simultaneously generate a quadrupole magnetic field and an octole magnetic field, respectively, thus achieving the functions of both quadrupole and octole iron with only one transmission element. At the four-pole / octole composite iron 1, the beam envelope function in the Y or X direction reaches a large value; at the four-pole / octole composite iron 2, the beam envelope function in the X or Y direction reaches a large value. The phase shift of the particle between the two four-pole / octole composite magnets and the target... They are all 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;

[0012] The four-eight-pole composite iron 1 and four-eight-pole composite iron 2 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 composite magnet main power supply.

[0013] The beam matching mechanism is used to observe the initial state of the beam extracted from the accelerator, adjust the size of the beam envelope in the X or Y direction according to the initial state, and align the beam center with the mechanical center of the beam tube.

[0014] This beam homogenization effect observation device is used to observe the beam intensity, weak beam shape, and strong beam cross-section after homogenization by four-octet composite iron 1 and four-octet composite iron 2.

[0015] Furthermore, the beam matching mechanism includes a fluorescent target 1, a quadrupole magnet, and a guide magnet; the fluorescent target 1 provides the tester with the initial beam state; the quadrupole magnet is used to form a large beam envelope in the Y or X direction at the position of the quadrupole-octupole composite iron 1; and the guide magnet is used to align the beam center with the mechanical center of the beam channel.

[0016] Furthermore, the beam homogenization effect observation mechanism includes a Faraday tube, a fluorescent target 2, and a dual-wire structure. The Faraday tube is used to measure the beam intensity after homogenization, the fluorescent target 2 is used to observe the shape of the weak beam after homogenization, and the dual-wire structure is used to observe the shape of the strong beam after homogenization.

[0017] Furthermore, the phase shift of the particle between the two quadrupole composite magnets and the target Multiples close to 180 degrees refer to multiples that are close to but not equal to 180 degrees: Let... for The remainder after 180 degrees, The value is generally less than ±15 degrees.

[0018] 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.

[0019] Furthermore, the expression for the magnet strength k at the four-eight-pole composite iron 1 and the four-eight-pole composite iron 2 is as follows:

[0020]

[0021] 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; in the above formula (1), ux02 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; in 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; βy1 represents the envelope function in the y direction at position 1.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] Advantages and effects of the present invention

[0033] 1. This invention comprises a linear beam homogenization transmission line consisting of two quadrupole-octupole composite irons. It employs a method of generating a large envelope using both quadrupole-octupole composite irons and quadrupole irons, which solves the problem in existing technologies where, when using discrete quadrupole irons and octupoles, the largest area of ​​the envelope is usually occupied by the quadrupole magnetic field, thus failing to fully utilize the function of the octupole iron.

[0034] 2. This invention includes a linear beam homogenization transmission line consisting of two quadrupole-octupole composite irons. Since the quadrupole-octupole composite irons are located at the large envelope, the requirement for the magnetic field strength K value of the quadrupole-octupole composite irons is reduced. This solves the problem that when using discrete quadrupole irons and octupoles in the prior art, the beam envelope at the locations of octupole iron 1 and octupole iron 2 is small, which makes the field strength requirement of the octupole magnet very high. Excessive magnetic field strength is too costly and difficult to achieve in engineering.

[0035] 3. This invention comprises a linear beam homogenization transmission line consisting of two quadrupole and octupole composite irons. Within the aperture of the quadrupole and octupole composite irons, quadrupole and octupole magnetic fields are generated simultaneously, achieving both focusing and homogenization of the beam envelope. Installing the composite irons on the beam transmission line reduces the number of transmission elements and shortens the transmission line length. This solves the problem that when using discrete quadrupole and octupole irons, the excessively long transmission line length leads to increasingly expensive civil engineering for surrounding shielding, a large footprint, and high costs.

[0036] 4. This invention comprises a linear beam homogenization transmission line consisting of two quadrature-octet composite magnets, which limits the phase shift of particles between the two quadrature-octet 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...). This makes the required magnetic field strengths k1 and k2 at the first and second four-eight-pole composite magnets smaller. While ensuring the homogenization effect, it is beneficial to reduce the difficulty and cost of magnet manufacturing.

[0037] 5. The present invention comprises a linear beam homogenization transmission line of two octagonal composite irons, which limits the transmission matrix between the two octagonal magnetic fields to be close to the identity matrix. That is, the phase shift between the two octagonal composite magnets is controlled within 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. Attached Figure Description

[0038] Figure 1a This is a schematic diagram of the linear beam homogenization transmission line of the present invention;

[0039] Figure 1b This is a schematic diagram of the linear beam homogenization transmission line-beam matching mechanism of the present invention;

[0040] Figure 1c This is a schematic diagram of the linear beam homogenization transmission line and beam homogenization effect observation mechanism of the present invention.

[0041] Figure 1d This is a schematic diagram comparing the particle distribution state before and after the transmission line homogenization in this invention.

[0042] Figure 2 This is a schematic diagram showing the maximum envelope positions of the four-octet composite iron 1 and 2 of the present invention;

[0043] Figure 3 This is a schematic diagram illustrating the representative meanings of the four points 0, 1, 2, and 3 involved in formulas (1) and (2) of this invention.

[0044] Figure 4This 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;

[0045] Figure 5a This is a schematic diagram of the four-eight-pole composite magnet current control device of the present invention;

[0046] Figure 5b This invention provides a novel four / octet composite iron model.

[0047] Figure 5c The arrangement and current direction of the four-eight-pole composite magnet coils of this invention;

[0048] Figure 5d This is a schematic diagram showing the current values ​​of the two sets of coils during magnetic field measurement in this invention;

[0049] Figure 5e This is a schematic diagram illustrating the quadrupole magnetic field gradient under different currents in the experimental measurement of this invention.

[0050] Figure 5f 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.

[0051] Figure 5g 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;

[0052] Figure 5h This is a schematic diagram of the current curve corresponding to the four / octet field selected in this invention;

[0053] Figure 5i This is a schematic diagram illustrating the solution for the composite iron excitation current of the present invention;

[0054] Figure 6 A schematic diagram of an existing octet iron at the small envelope position;

[0055] Figure 7 This is a schematic diagram of an embodiment of an ultra-short linear beam homogenization transmission line according to the present invention. Detailed Implementation

[0056] Design principle of the invention

[0057] 1. Innovation of this invention

[0058] One of the innovations lies in the invention of a four-octet composite iron. (The text abruptly ends here, seemingly mid-sentence.) Figure 5a , 5b The four-octet composite iron shown in 5c replaces, for example, Figure 6 The 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 2As 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 6 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.

[0059] 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.

[0060] The system is like Figure 5a As 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.

[0061] The design method for the excitation current of a four / octet composite iron is as follows:

[0062] Step 1, such as Figure 5d 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 5d 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.

[0063] Step Two, as follows Figure 5e 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.

[0064] The above three-dimensional surface sample database Figure 5e 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.

[0065] Step 3, as follows Figure 5f 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.

[0066] The effect of the above-mentioned encrypted grid point density is as follows: Figure 5f As shown, the grid density on the X, Y, and Z axes has increased.

[0067] Step 4, as follows Figure 5g 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.

[0068] Step 5, as follows Figure 5h As 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.

[0069] Step Six, as Figure 5i As shown, the intersection point is used as the solution for the excitation current of the composite iron.

[0070] 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 2 As shown, the homogenization effect of the ultra-short linear beam homogenization transmission line is significant, which stems from three innovations. All three are indispensable and must support each other to achieve the ideal homogenization effect:

[0071] 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.

[0072] The second aspect: Solving the problem of optimizing the homogenization effect: specifically as follows Figure 4 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.

[0073] 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 3 , Figure 4As 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.

[0074] The fourth innovation lies in the invention of an ultra-short, straight beam homogenization transmission line. As shown in Figure 1, the ultrashort straight beam homogenization transmission line uses two octet composite iron pieces. The octet composite iron piece 1 and the preceding octet together generate a large envelope in the Y direction. This large envelope is generated because the preceding octet defocuses, causing the beam to gradually diverge in the Y direction, while the octet field of the following octet composite iron piece 1 focuses the beam, causing it to gradually converge in the Y direction, thus generating a large envelope in the Y direction at the octet composite iron piece 1. Similarly, the octet composite iron piece 2 and the preceding octet composite iron piece 1 together generate a large envelope in the X direction. This large envelope is generated because the preceding octet focuses the beam, the octet field of the octet composite iron piece 1 defocuses the beam, causing it to gradually diverge in the X direction, while the octet field of the following octet composite iron piece 2 focuses the beam, thus generating a large envelope in the X direction at the octet composite iron piece 2. The use of two octet composite iron pieces in the ultrashort straight beam homogenization transmission line can achieve a good beam homogenization effect, that is, it can simultaneously achieve the functions of focusing and homogenizing the beam envelope. The four-octet composite iron and its large envelope are two complementary aspects. A large envelope results in a relatively small magnetic field strength (k-value) for the four-octet composite iron. A relatively small k-value means a relatively low requirement for the magnetic field strength of the four-octet magnet. A relatively low magnetic field strength requirement makes it easier to achieve in engineering. Ease of engineering achievement makes it easier for four-octet composite iron to be widely used. If beam homogenization requires a very high magnetic field strength for the four-octet composite iron, it is not easy to achieve in engineering. If it is not easy to achieve, then the use of four-octet composite iron is out of the question.

[0075] Based on the above-mentioned inventive principles, this invention designs an ultra-short, straight beam homogenization transmission line, such as... Figure 1a , 1b As shown in 1c and 1d, the characteristics are: the transmission line is a linear beam homogenization transmission line containing two quadrupole composite irons; the linear beam homogenization transmission line is provided with the following in sequence along the beam direction: accelerator outlet, beam matching mechanism, quadrupole composite iron 1, quadrupole composite iron 2, beam homogenization effect observation mechanism, and terminal.

[0076] like Figure 2 As shown, the four-eight-pole composite iron 1 and the four-eight-pole composite iron 2 are used to simultaneously generate a four-pole magnetic field and an octagonal magnetic field, respectively, so that the functions of a four-pole iron and an octagonal iron can be realized simultaneously with only one transmission element; at the four-eight-pole composite iron 1, the beam envelope function in the Y or X direction reaches a large value, and at the four-eight-pole composite iron 2, the beam envelope function in the X or Y direction reaches a large value; the phase shift of the particle between the two four-eight-pole composite magnets and the target. They are all 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;

[0077] Supplementary Note 1:

[0078] The aforementioned "phase shift of the particle between the two octet composite magnets and the target" The degrees are respectively close to integer multiples of 180 degrees (0, 1, 2, 3...) but not equal to 180 degrees. The principle is explained in formulas (1) and (2) below:

[0079]

[0080] 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 an integer multiple of 180 degrees (0, 1, 2, 3...).

[0081] like Figure 5aAs shown, the four-eight-pole composite iron 1 and four-eight-pole composite iron 2 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.

[0082] The beam matching mechanism is used to observe the initial state of the beam extracted from the accelerator, adjust the size of the beam envelope in the X or Y direction according to the initial state, and align the beam center with the mechanical center of the beam tube.

[0083] This beam homogenization effect observation device is used to observe the beam intensity, weak beam shape, and strong beam cross-section after homogenization by four-octet composite iron 1 and four-octet composite iron 2.

[0084] like Figure 1b As shown, the beam matching mechanism includes a fluorescent target 1, a quadrupole magnet, and a guide magnet; the fluorescent target 1 provides the tester with the initial beam state; the quadrupole magnet is used to form a large beam envelope in the Y or X direction at the position of the quadrupole-octupole composite iron 1; and the guide magnet is used to align the beam center with the mechanical center of the beam channel.

[0085] like Figure 1c As shown, the beam homogenization effect observation mechanism includes a Faraday tube, a fluorescent target 2, and a double wire. The Faraday tube is used to measure the beam intensity after homogenization, the fluorescent target 2 is used to observe the shape of the weak beam after homogenization, and the double wire is used to observe the shape of the strong beam after homogenization.

[0086] The phase shift of the particle between the two octapole composite magnets and the target Multiples close to 180 degrees refer to multiples that are close to but not equal to 180 degrees: Let... for The remainder after 180 degrees, The value is generally less than ±15 degrees.

[0087] Supplementary Note 2

[0088] The aforementioned "phase shift of the particle between the two quadrupole composite magnets and the target" The explanation for "approaching an integer multiple of 180 degrees" is as follows: Assuming the phase of the four-octet composite iron 1 is 170 degrees, the remainder when 170 degrees is divided by 180 degrees is 10 degrees; assuming the phase of the four-octet composite iron 2 is 168 degrees, the remainder when 168 degrees is divided by 180 degrees is 12 degrees. Both the remainders of 10 and 12 are within the range of less than ±15 degrees, which is permissible.

[0089] 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.

[0090] The expression for the magnetic strength k at the four-octet composite iron 1 and four-octet composite iron 2 is:

[0091]

[0092] like Figure 3 As shown, 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; in the above formula (1), ux02 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; in 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; βy1 represents the envelope function in the y direction at position 1.

[0093] Supplementary Note 3

[0094] 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.

[0095] like Figure 5a 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.

[0096] like Figure 5d 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.

[0097] like Figure 5e 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.

[0098] like Figure 5f 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.

[0099] like Figure 5g , 5h 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.

[0100] like Figure 5i 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] like Figure 5c 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 on poles 1 and 2, and symmetrically arranged on poles 5 and 6, is in the same magnitude and direction. The excitation current of the coils on poles 3 and 4, and symmetrically arranged on poles 7 and 8, is in the same magnitude and direction. 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.

[0105] Example 1

[0106] like Figure 7 As shown, this invention designs an ultrashort linear beam homogenization transmission line. When the total length of the ultrashort linear beam homogenization transmission line is 6 meters, the initial placement positions of the components that enable the transmission line 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 900 mm; the initial position of the guide magnet is 1300 mm; the initial position of the quadrupole-octupole composite iron (Q1) is 1900 mm; the initial position of the quadrupole-octupole composite iron (Q2) is 3050 mm; the initial position of the Faraday cylinder is 4200 mm; the initial position of the fluorescent target 2 is 5200 mm; the initial position of the dual wire is 5600 mm; and the initial position of the terminal is 6000 mm. The magnetic field component of the tetrapole iron (Q0) is 2.9 (T / m); the tetrapole magnetic field component of the tetrapole-octapole composite iron (Q1) is 3.05 (T / m), and the octapole magnetic field component is 2.5e3 (T / m). 3 The quadrupole magnetic field component of the four-pole octupole composite iron (Q2) is 0.45 (T / m), and the octupole magnetic field component is 3.82e3 (T / m). 3 ).

[0107] like Figure 1d The image shows a comparison of the transmission line before and after homogenization according to the present invention. Figure 1dThe 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 1d 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 5200 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.

[0108] 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 linear beam homogenization transmission line, characterized in that: The beam homogenization transmission line is a linear beam homogenization transmission line containing two quadrupole-octupole composite iron pieces; the linear beam homogenization transmission line is provided with the following components along the beam direction: accelerator outlet, beam matching mechanism, quadrupole-octupole composite iron 1, quadrupole-octupole composite iron 2, beam homogenization effect observation mechanism, and terminal. The four-pole / octole composite iron 1 and 2 are used to simultaneously generate a quadrupole magnetic field and an octole magnetic field, respectively, thus achieving the functions of both quadrupole and octole iron with only one transmission element. At the four-pole / octole composite iron 1, the beam envelope function in the Y or X direction reaches a large value; at the four-pole / octole composite iron 2, the beam envelope function in the X or Y direction reaches a large value. The phase shift of the particle between the two four-pole / octole composite magnets and the target... They are all 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; The phase shift of the particle between the two octapole composite magnets and the target Multiples close to 180 degrees refer to multiples that are close to but not equal to 180 degrees: Let... for The remainder after 180 degrees, The value should be less than ±15 degrees; 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 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. Both the four-eight-pole composite iron 1 and the four-eight-pole composite iron 2 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. The beam matching mechanism is used to observe the initial state of the beam extracted from the accelerator, adjust the size of the beam envelope in the X or Y direction according to the initial state, and align the beam center with the mechanical center of the beam tube. This beam homogenization effect observation device is used to observe the beam intensity, weak beam shape, and strong beam cross-section after homogenization by four-octet composite iron 1 and four-octet composite iron 2.

2. The ultrashort linear beam homogenization transmission line according to claim 1, characterized in that: The beam matching mechanism includes a fluorescent target 1, a quadrupole magnet, and a guide magnet; the fluorescent target 1 provides the tester with the initial beam state; the quadrupole magnet is used to form a large beam envelope in the Y or X direction at the position of the quadrupole composite iron 1; and the guide magnet is used to align the beam center with the mechanical center of the beam channel.

3. The ultrashort linear beam homogenization transmission line according to claim 1, characterized in that: The beam homogenization effect observation mechanism includes a Faraday tube, a fluorescent target 2, and a double wire. The Faraday tube is used to measure the beam intensity after homogenization, the fluorescent target 2 is used to observe the shape of the weak beam after homogenization, and the double wire is used to observe the shape of the strong beam after homogenization.

4. The ultrashort linear beam homogenization transmission line according to claim 1, characterized in that: The expression for the magnetic strength k at the four-octet composite iron 1 and four-octet composite iron 2 is: 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; in the above formula (1), ux02 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; in 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; βy1 represents the envelope function in the y direction at position 1.

5. The ultrashort linear beam homogenization transmission line according to claim 1, characterized in that: The composite magnet current control device includes: a module for establishing two-dimensional sampling points of 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. 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. 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. 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. The module for solving the input field gradient corresponding to the current curve is used to intersect the input quadrupole magnetic field gradient and octupole magnetic 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 magnetic field gradient plane is selected, and this plane intersects with the surface of the quadrupole magnetic field gradient three-dimensional surface sample database to obtain the current curve that satisfies the quadrupole magnetic field gradient; an octupole magnetic field gradient plane is selected, and this plane intersects with the surface of the octupole magnetic field gradient three-dimensional surface sample database to obtain the current curve that satisfies the octupole magnetic field gradient. The module for solving the intersection point of the four / octapole field gradient current curves is used to obtain the intersection point of the current curve that satisfies the magnetic field gradient of the four-pole field and the current curve that satisfies the magnetic field gradient of the octapole field, and uses the intersection point as the solution of the composite iron excitation current. 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.

6. The ultrashort linear beam homogenization transmission line according to claim 1, characterized in that: 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. 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. 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.

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