Ultra-short bending type beam homogenization transmission line

Abstract

The invention discloses an ultrashort bending type beam homogenization transmission line. The ultrashort bending type beam homogenization transmission line is characterized in that the transmission line is an ultrashort bending type high-current homogenization transmission line comprising two pieces of four-eight-level composite iron and one piece of second-level iron; the ultra-short bending type high-current homogenized transmission line is an ultra-short bending type high-current homogenized transmission line A which is arranged along a beam current direction; or the ultra-short bending type high-current homogenization transmission line B is arranged along the beam direction; the ultra-short bending type high-current homogenization transmission line A is sequentially provided with an accelerator leading-out port, a beam matching mechanism, fourth and eight-stage composite iron 1, second-stage iron, fourth and eight-stage composite iron 2, a beam matching and homogenization effect observation mechanism 1 and a terminal 1 along the beam leading-out direction; the tetra-octupole composite iron of the beam line can simultaneously realize focusing and homogenization effects on beam envelope, the composite iron is installed on a beam transmission line, the number of transmission elements can be reduced, the length of the transmission line is shortened, and the construction cost of the beam transmission line is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of accelerator transmission lines, and particularly relates to an ultrashort bending type beam current homogenization transmission line. Background Art

[0002] The secondary particles generated after the accelerator extracts the beam current and hits the target are important radiation sources required 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-intensity proton accelerators, the accelerator generates a high-energy and high-intensity proton beam, which hits the neutron target after passing through the transmission line to generate a high-flux neutron.

[0003] The distribution of the accelerator-extracted beam current is generally approximately Gaussian, with the highest particle density at the center of the bunch, which also causes excessive local power and temperature on the neutron target, resulting in damage to the neutron target.

[0004] In order to solve the problem of uneven particle distribution, octupole magnets are tried on the beam current transmission line to homogenize the Gaussian-distributed beam current and reduce the peak power density on the neutron target.

[0005] One of the difficulties in using octupole magnets to homogenize the Gaussian-distributed beam current is that: when the same octupole iron is installed at different positions on the beam current transmission line, the functions it plays will be different. Only when the octupole iron is installed at a position with a larger beam envelope can it provide the strongest homogenization effect. However, the place with the largest envelope in the prior art is usually occupied by the quadrupole magnetic field: as Figure 6 shown, the transmission line of the prior art is arranged in the order of quadrupole iron 1, octupole iron 1, quadrupole iron 2, and octupole iron 2. Since the octupole iron must first focus before homogenization (the function of focusing is to allow the beam current to pass through the circular hole in the center of the octupole iron without hitting the octupole iron), in order to ensure focusing, the positions of octupole iron 1 and octupole iron 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 iron 1 at the waist position of the X-direction envelope is small, and the X-direction envelope of quadrupole iron 2 at the waist position of the Y-direction envelope is small, at octupole iron 1, although the waist position of octupole iron 1 in the X direction is ensured, the Y-direction envelope at this place is small. Similarly, at octupole iron 2, although the waist position of octupole iron 2 in the Y direction is ensured, the X-direction envelope at this place is small. In short, according to the traditional method, the beam envelope has significantly decreased after the particles pass through quadrupole iron 1 and quadrupole iron 2, so the functions of octupole iron 1 and octupole iron 2 cannot be fully exerted.

[0006] The second difficulty in using octupole magnets to homogenize a Gaussian beam lies in that: since the beam envelopes at the positions of octupole magnet 1 and octupole magnet 2 are small, the field strength K value of the octupole magnet is very large. Such a high magnetic field strength is not only difficult to achieve in engineering, but also too costly and hard to implement.

[0007] The third difficulty in using octupole magnets to homogenize a Gaussian beam is that: if octupole magnets are to be used to achieve a good beam homogenization effect, there are relatively strict requirements for the positions where the octupole magnets are placed and their phases. To meet these requirements, the length of the transmission line often needs to be more than ten meters. The diameter of the cyclotron does not exceed 2 meters. Dragging a beam line of more than ten meters is equivalent to making the accelerator smaller, which is meaningless. The longer the beam line, the more expensive the civil engineering for the surrounding shielding becomes. In short, the disadvantages of a too-long transmission line, such as large floor area and high cost, greatly limit the use of the beam homogenization technology. Summary of the Invention

[0008] In view of the problems existing in the prior art, the present invention provides an ultra-short bending type beam homogenization transmission line. The first object is to solve the problem that when discrete quadrupole magnets and octupole magnets are used in the prior art, since the place with the largest envelope is usually occupied by the quadrupole magnetic field, the octupole magnets cannot fully play their roles. The second object is to solve the problem that when discrete quadrupole magnets and octupole magnets are used, due to the small beam envelopes at the positions of octupole magnet 1 and octupole magnet 2, the requirements for the field strength of the octupole magnet are very high, and such a high magnetic field strength is too costly and hard to implement in engineering. The third object is to solve the problem that when discrete quadrupole magnets and octupole magnets are used, the too-long transmission line leads to more expensive civil engineering for the surrounding shielding, large floor area and high cost.

[0009] To solve the technical problems thereof, the present invention provides the following technical solutions:

[0010] An ultra-short bending type beam homogenization transmission line, characterized in that: the transmission line is an ultra-short bending type beam homogenization transmission line including two quadrupole-octupole composite irons and one dipole iron; the ultra-short bending type beam homogenization transmission line is an ultra-short bending type beam homogenization transmission line A arranged along the beam direction, or an ultra-short bending type beam homogenization transmission line B arranged along the beam direction: the ultra-short bending type beam homogenization transmission line A is successively provided with, along the beam extraction direction: an accelerator extraction port, a beam matching mechanism, a quadrupole-octupole composite iron 1, a dipole iron, a quadrupole-octupole composite iron 2, a beam matching and homogenization effect observation mechanism 1, and a terminal 1; the ultra-short bending type beam homogenization transmission line B is successively provided with, along the beam extraction direction: an accelerator extraction port, a beam matching mechanism, a quadrupole-octupole composite iron 1, a dipole iron, a quadrupole-octupole composite iron 3, a beam matching and homogenization effect observation mechanism 2, and a terminal 2;

[0011] The four-eight-pole composite iron 1, four-eight-pole composite iron 2, or four-eight-pole composite iron 1 and four-eight-pole composite iron 3 respectively generate a quadrupole magnetic field and an octupole magnetic field simultaneously, so that the functions of a quadrupole iron and an octupole iron can be realized simultaneously by installing only one transmission element; at the four-eight-pole composite iron 1, the beam envelope function in the Y direction or X direction reaches a maximum value, and at the four-eight-pole composite iron 2 or four-eight-pole composite iron 3, the beam envelope function in the X direction or Y direction reaches a maximum value; the phase shift of the particles between the four-eight-pole composite iron 1 and four-eight-pole composite iron 2 and the target, or between the four-eight-pole composite iron 1 and four-eight-pole composite iron 3 and the target is respectively close to an integer multiple of 180 degrees (0, 1, 2, 3...); the transfer matrix between the two octupole magnetic fields is close to the unit matrix.

[0012] This ultra-short bending type beam homogenization transmission line uses the combined focusing effect of the four-eight-pole composite iron 1 and the dipole iron to generate a beam waist in the Y direction near the four-eight-pole composite iron 2; uses the superposition of the quadrupole field of the dipole iron and the four-eight-pole composite iron 2 to generate the envelope size in the X direction on the target, so that the envelope sizes in the X direction and Y direction are the same.

[0013] The four-eight-pole composite iron 1, four-eight-pole composite iron 2, or four-eight-pole composite iron 3 is 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 output of the quadrupole field coil current and octupole field coil current of the composite magnet main power supply to the four-eight-pole composite magnet;

[0014] This beam matching mechanism is used to observe the initial state of the beam extracted from the accelerator, and adjust the envelope size of the beam in the X or Y direction according to this initial state, and align the beam center with the mechanical center of the beam pipe;

[0015] This beam matching and homogenization effect observation mechanism 1 or beam matching and homogenization effect observation mechanism 2 is used to adjust the eccentricity of the beam after passing through the dipole iron, and observe the beam intensity, weak beam shape, and strong beam shape of the beam homogenized by the four-eight-pole composite iron 1 and four-eight-pole composite iron 2.

[0016] Furthermore, the beam matching mechanism includes a fluorescent target 1, a quadrupole magnet, and a steering magnet; the fluorescent target 1 provides the initial position of the beam for the tester; the quadrupole magnet is used to provide an anti-direction beam envelope for the four-eight-pole composite iron 1; the steering magnet is used to adjust the eccentricity of the beam.

[0017] Further, the beam matching and homogenization effect observation mechanism 1 includes a guiding magnet 2, a Faraday cup 1, a fluorescent target 2, and a double wire 1; the guiding magnet 2 is used to align the beam center with the mechanical center of the beam pipe; the Faraday cup 1 is used to measure the beam current intensity after homogenization, the fluorescent target 2 is used to observe the shape of the weak beam after homogenization; the double wire 1 is used to observe the shape of the strong beam after homogenization; the beam matching and homogenization effect observation mechanism 2 includes a guiding magnet 3, a Faraday cup 3, a fluorescent target 3, and a double wire 2; the guiding magnet 3 is used to align the beam center with the mechanical center of the beam pipe; the Faraday cup 2 is used to measure the beam current intensity after homogenization, the fluorescent target 3 is used to observe the shape of the weak beam after homogenization; the double wire 2 is used to observe the shape of the strong beam after homogenization.

[0018] Further, the phase shift of the particles between the four-eight-stage composite iron 1 and the four-eight-stage composite iron 2 and the target or the phase shift of the particles between the four-eight-stage composite iron 1 and the four-eight-stage composite iron 3 and the target being close to an integer multiple of 180 degrees means being close to but not equal to an integer multiple of 180 degrees: Let be the remainder of with 180 degrees, and the value generally is less than ±15 degrees.

[0019] Further, the transfer matrix between the two octupole magnetic fields is close to the identity matrix, that is, the phase shift between the front and rear four-eight-stage 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 octupole magnets and can achieve a good homogenization effect.

[0020] Further, the expression of the magnet strength k at the four-eight-stage composite iron 1 and the four-eight-stage composite iron 2, or the magnet strength k at the four-eight-stage composite iron 1 and the four-eight-stage composite iron 3 is:

[0021]

[0022] Let: The starting point of the transport line is denoted as 0, the position of the first four-eight-pole magnet is denoted as 1, the position of the second four-eight-pole magnet is denoted as 2, and the position at the end, which is the position of the target, is denoted as 3; ux02 in the above formula (1) represents the phase shift in the x direction between positions 0 and 2 of the particles, ux23 represents the phase shift in the x direction between positions 2 and 3 of the particles; βx2 represents the envelope function in the x direction at position 2; uy01 in the above formula (2) represents the phase shift in the y direction between 0 and 1 of the particles; uy13 represents the phase shift in the y direction between 1 and 3 of the particles; βy1 represents the envelope function in the y direction at position 1.

[0023] Furthermore, the composite magnet current control device includes: a coil current two-dimensional sampling point establishing module, an experimental measurement and preliminary establishment of a magnetic field gradient three-dimensional surface sample library module, a module for using interpolation to refine the magnetic field gradient three-dimensional surface sample library, an input field gradient to solve the corresponding field gradient current curve module, a module for solving the intersection point of the quadrupole / octupole field gradient current curves, and an output quadrupole / octupole coil current module;

[0024] The coil current two-dimensional sampling point establishing module is used to establish a two-dimensional data comparison table of the coil currents of the quadrupole iron and the octupole iron;

[0025] The experimental measurement and preliminary establishment of a magnetic field gradient three-dimensional surface sample library module uses the current values in the two-dimensional data comparison table of the coil currents to conduct magnetic field experiments on the composite iron, so as to obtain the quadrupole and octupole magnetic field gradient measurement values corresponding one-to-one to the two-dimensional current data comparison table, thereby obtaining a three-dimensional surface sample database of the magnetic field gradient; the above three-dimensional surface sample database of the magnetic field gradient includes a three-dimensional surface sample database of the quadrupole field magnetic field gradient and a three-dimensional surface sample database of the octupole field magnetic field gradient;

[0026] The module for using interpolation to refine the magnetic field gradient three-dimensional surface sample library is used to perform two-dimensional interpolation on the three-dimensional surface sample database of the quadrupole field magnetic field gradient and the three-dimensional surface sample database of the octupole field magnetic field gradient using a cubic spline function to increase the grid point density;

[0027] The input field gradient to solve the corresponding field gradient current curve module 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 two corresponding current curves are obtained after the intersection; specifically: select the quadrupole field magnetic field gradient plane, and this plane intersects with the surface of the three-dimensional surface sample database of the quadrupole field magnetic field gradient to obtain a current curve that satisfies this quadrupole field gradient; select the octupole field magnetic field gradient plane, and this plane intersects with the surface of the three-dimensional surface sample database of the octupole field magnetic field gradient to obtain a current curve that satisfies this octupole field gradient;

[0028] The module for solving the intersection point of the quadrupole / octupole field gradient current curves is used to obtain the intersection point of the current curve that satisfies the quadrupole field gradient and the current curve that satisfies this octupole field gradient, and use this intersection point as the solution of the excitation current of the composite iron;

[0029] The output quadrupole / octupole coil current 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 excitation current of the composite iron.

[0030] Furthermore, this quadrupole-octupole composite magnet has a total of eight pole heads, and each pole head is provided with two inner and outer current coils along the radial direction near the large radius. The inner coil is an octupole magnetic field excitation coil, and the outer coil is a quadrupole magnetic field excitation coil;

[0031] For the octupole magnetic field excitation coil of the inner layer, the current directions of two adjacent pole tips are opposite. That is, the octupole field coil is divided into two groups: pole tips 1, 3, 5, 7 and pole tips 2, 4, 6, 8. The magnitudes of the exciting currents of the two groups are equal, but the current directions are opposite, thereby generating an octupole magnetic field;

[0032] For the quadrupole magnetic field excitation coil of the outer layer, the coils on two adjacent pole tips form a group, and are divided into four groups, namely pole tips 1, 2; pole tips 3, 4; pole tips 5, 6; pole tips 7, 8 respectively. Among them, for the two groups of quadrupole magnetic field coils of pole tips 1, 2 and symmetrically arranged pole tips 5, 6, the magnitudes and directions of the exciting currents are the same; for the two groups of coils of pole tips 3, 4 and symmetrically arranged pole tips 7, 8, the magnitudes and directions of the exciting currents are the same; the current directions of the coils of pole tips 1, 2 and pole tips 3, 4 are opposite, and the directions of the coils of pole tips 5, 6 and pole tips 7, 8 are opposite, thereby generating a quadrupole magnetic field.

[0033] Advantages and effects of the present invention

[0034] 1. The present invention includes an ultra-short bending type beam uniformity transmission line with two pieces of quadrupole-octupole composite iron and one piece of dipole iron. By using the method of jointly generating a large envelope by the quadrupole-octupole composite iron and the quadrupole iron, it solves the problem in the prior art that when discrete quadrupole iron and octupole iron are used, since the place with the largest envelope is usually occupied by the quadrupole magnetic field, the function of the octupole iron cannot be fully exerted;

[0035] 2. The present invention includes an ultra-short bending type beam uniformity transmission line with two pieces of quadrupole-octupole composite iron and one piece of dipole iron. Since the quadrupole-octupole composite iron is located at the large envelope, the requirement for the magnetic field strength K value of the quadrupole-octupole composite iron is reduced, solving the problem in the prior art that when discrete quadrupole iron and octupole iron are used, since the beam envelope at the positions of octupole iron 1 and octupole iron 2 is small, the requirement for the field strength of the octupole magnet is very high, and the too high magnetic field strength is too costly and difficult to achieve in engineering;

[0036] 3. The present invention includes an ultra-short bending type beam uniformity transmission line with two pieces of quadrupole-octupole composite iron and one piece of dipole iron. A quadrupole magnetic field and an octupole magnetic field are simultaneously generated within the aperture of the quadrupole-octupole composite iron, and the functions of focusing and uniformizing the beam envelope are simultaneously achieved. Installing the composite iron 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 discrete quadrupole iron and octupole iron are used, the overly long transmission line leads to more expensive civil engineering for the surrounding shielding, large floor area and high cost;

[0037] 4. The present invention includes an ultra-short bending type beam uniformity transmission line with two pieces of quadrupole-octupole composite iron and one piece of dipole iron, which limits the phase shift of particles between the two quadrupole-octupole composite magnets and the target Are respectively close to integer multiples of 180 degrees (0, 1, 2, 3...), but not equal to integer multiples of 180 degrees (0, 1, 2, 3...), so that the required magnetic field strength values k1 and k2 at the first and second four-eight-pole composite magnets are small, which is beneficial to reducing the manufacturing difficulty and cost of the magnets.

[0038] 5. The present invention includes an ultra-short bending type beam homogenization transmission line composed of two four-eight-pole composite irons and one two-pole iron, and defines that the transmission matrix between two octupole magnetic fields is close to the unit matrix, that is, the phase shift between the front and rear four-eight-pole 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 two octupole magnets and can obtain a better homogenization effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1a Schematic diagram of the ultra-short bending type beam homogenization transmission line A of the present invention;

[0040] Figure 1b Schematic diagram of the ultra-short bending type beam homogenization transmission line B of the present invention;

[0041] Figure 1c Schematic diagram of the beam matching mechanism of the transmission line of the present invention;

[0042] Figure 1d Schematic diagram for comparing the particle distribution states before and after homogenization of the transmission line of the present invention;

[0043] Figure 1e Schematic diagram of the beam matching and homogenization effect observation mechanism 1 of the transmission line of the present invention;

[0044] Figure 1f Schematic diagram of the beam matching and homogenization effect observation mechanism 2 of the transmission line of the present invention;

[0045] Figure 2 Schematic diagram of the maximum envelope positions of the first and second four-eight-pole composite irons of the present invention;

[0046] Figure 3 Schematic diagram of the phase difference between two four-eight-pole composite irons of the present invention and the phase differences from the two four-eight-pole composite irons to the target point respectively;

[0047] Figure 4 Schematic diagram of the representative meanings of the four points 0, 1, 2, and 3 involved in formula (1) and formula (2) of the present invention;

[0048] Figure 5a Schematic diagram of the four / octupole composite iron system for beam control of the present invention;

[0049] Figure 5b New four / octupole composite iron model of the present invention;

[0050] Figure 5c Arrangement of four / eight-pole composite magnet coils and current directions.

[0051] Figure 5d Schematic diagram of current values of two groups of coils during magnetic field measurement of the present invention;

[0052] Figure 5e Schematic diagram of corresponding four / eight-pole magnetic field gradients measured experimentally under different currents of the present invention;

[0053] Figure 5f Schematic diagram of using cubic spline function for two-dimensional interpolation to encrypt grid point density of the present invention;

[0054] Figure 5g Schematic diagram of the intersection of the selected magnetic field gradient plane and the magnetic field gradient surface of the three-dimensional sample database of the present invention;

[0055] Figure 5h Schematic diagram of the selected current curve corresponding to the four / eight-pole field of the present invention;

[0056] Figure 5i Schematic diagram of the solution of the composite iron excitation current of the present invention;

[0057] Figure 6 Schematic diagram of the octupole iron in the small envelope position of the prior art.

[0058] Figure 7 Embodiment of the ultra-short bending type beam homogenization transmission line of the present invention. Detailed implementation mode

[0059] Design principle of the present invention

[0060] 1. Innovation points of the present invention

[0061] One of the innovation points is: inventing a four-eight-pole composite iron. Using the four-eight-pole composite iron shown in Figure 5a , 5b , 5c to replace the quadrupole iron and octupole iron of discrete components shown in Figure 6 . One of the effects: after combination, a quadrupole magnetic field and an octupole magnetic field are generated inside the aperture of the four-eight-pole composite iron, and its effect is as shown in Figure 2 : The quadrupole iron and the octupole iron share the positions of the large envelopes in the Y direction and the X direction. The reason why they can share the positions of the large envelopes in the Y direction or the X direction is that the four-eight-pole composite iron 1 and the quadrupole iron in front of it share the large envelope in the Y direction; the four-eight-pole composite iron 2 and the quadrupole iron of the four-eight-pole composite iron 1 in front of it share the large envelope in the X direction. Since the octupole irons in the four-eight-pole composite iron 1 and the four-eight-pole composite iron 2 are arranged at the positions of the large envelopes, a better beam homogenization effect can be achieved, that is: the functions of focusing and homogenizing the beam envelope can be achieved simultaneously. Compared withFigure 6 In the prior art, since the quadrupole magnet and octupole magnet are arranged separately in the prior art, the octupole magnet itself cannot change the envelope like the quadrupole magnet, that is, it cannot form a large common envelope with the previous quadrupole magnet. Therefore, the envelopes in the Y and X directions of the position of the separately arranged octupole magnet are relatively small, so its homogenization effect is not good. The second effect: Installing the composite magnet on the beam transmission line can reduce the number of transmission elements, shorten the length of the transmission line, and reduce the project cost of the beam transport line; the reduction of the number of transmission elements not only saves the quadrupole magnets, but also saves multiple components that need to be added on the transmission line to achieve the same homogenization effect.

[0062] The second innovation point lies in: inventing a four / octupole composite magnet current control system as Figure 5a shown, and a four / octupole composite magnet excitation current design method. First, the design difficulty of the four / octupole composite magnet excitation current lies in: there is a coupling relationship between the multipole magnetic fields generated by the two groups of coils of the four / octupole composite magnet. This coupling relationship means that changing the current magnitude of the quadrupole field or octupole field coil will simultaneously change the original quadrupole magnetic field gradient and octupole magnetic field gradient of the magnet. Therefore, the one-to-one adjustment strategy for the magnetic field gradient of a single type of magnet current will no longer apply. In the composite magnet, if the current magnitude of the quadrupole field coil of the magnet is first adjusted and the quadrupole magnetic field gradient is adjusted to meet the usage requirements, and then the current magnitude of the octupole field coil is adjusted, once the current of the octupole field coil starts to change, it will change the previously adjusted quadrupole magnetic field gradient, making it no longer meet the usage requirements. Second, a four / octupole composite magnet current control system and a four / octupole composite magnet excitation current design method are innovatively designed. This system and method solve the problem of the coupling relationship between the multipole magnetic fields generated by the two groups of coils of the four / octupole composite magnet, and find the current intersection point that simultaneously satisfies the quadrupole field gradient and the octupole field gradient. This system is as Figure 5a shown, and includes: a two-dimensional sampling point module based on coil current, an initial magnetic field gradient three-dimensional surface sample library module based on experimental measurement, a refined magnetic field gradient three-dimensional surface sample library module based on interpolation algorithm, a current curve module for solving the corresponding field gradient based on field gradient input, a current curve intersection point module based on field gradient solution, and an output four / octupole coil current module.

[0063] The design method of the four / octupole composite magnet excitation current is as follows:

[0064] Step 1: As Figure 5d shown, establish a two-dimensional data comparison table of the coil currents of the quadrupole magnet and the octupole magnet; this two-dimensional data comparison table of the coil currents is based on the two-dimensional data comparison table of the coil currents of the four / octupole composite magnet; the above two-dimensional data comparison table of the coil currents is as Figure 5d shown, the abscissa is the quadrupole coil current, and the ordinate is the quadrupole coil current.

[0065] Step 2: As shown in Figure 5e , through experimental measurement, obtain the four- and eight-pole magnetic field gradient measurement values corresponding one by one to the two-dimensional current data comparison table, so as to obtain a three-dimensional surface sample database of the magnetic field gradient; the above three-dimensional surface sample database of the magnetic field gradient includes a three-dimensional surface sample database of the quadrupole field magnetic field gradient and a three-dimensional surface sample database of the octupole field magnetic field gradient;

[0066] For the above three-dimensional surface sample database Figure 5e , as shown, the current of the quadrupole coil is used as the X-axis coordinate, the current of the octupole coil is the Y-axis coordinate, and the magnetic field gradient is the Z-axis coordinate.

[0067] Step 3: As shown in Figure 5f , use the cubic spline function to perform two-dimensional interpolation on the three-dimensional surface sample database of the quadrupole field magnetic field gradient and the three-dimensional surface sample database of the octupole field magnetic field gradient to increase the density of grid points;

[0068] The effect of the above increased density of grid points is as shown in Figure 5f , and the grid densities on the X-axis, Y-axis, and Z-axis are all increased.

[0069] Step 4: As shown in Figure 5g , select the quadrupole field magnetic field gradient plane, which intersects with the surface of the three-dimensional surface sample database of the quadrupole field magnetic field gradient to obtain a current curve that meets the quadrupole field gradient; select the octupole field magnetic field gradient plane, which intersects with the surface of the three-dimensional surface sample database of the octupole field magnetic field gradient to obtain a current curve that meets the octupole field gradient;

[0070] Step 5: As shown in Figure 5h , obtain the current curve that meets the quadrupole field gradient and the current curve that meets the octupole field gradient in the two-dimensional data grid plane of the coil current, and finally find the intersection point of the above two current curves;

[0071] Step 6: As shown in Figure 5i , use this intersection point to solve for the composite iron excitation current.

[0072] The third innovation point lies in: inventing an ultra-short bent beam current homogenization transmission line. As shown in Figure 1a , 1b , the ultra-short bent beam current homogenization transmission line uses two four-eight-pole composite irons and a dipole iron in the middle on the transmission line, and the dipole iron is used to bend the direction of the beam; as shown in Figure 2As shown in the figure, the innovation lies in that for this ultra-short bent beam current homogenization transmission line, the combined focusing effect of the quadrupole-octupole composite magnet 1 and the dipole magnet is utilized to generate a beam waist in the Y direction near the quadrupole-octupole composite magnet 2; the superposition of the quadrupole field of the dipole magnet and the quadrupole-octupole composite magnet 2 is used to generate the envelope size in the X direction on the target, so that the envelope sizes in the X and Y directions are the same. Specifically: at the current intersection point of the quadrupole-octupole composite magnet 1, appropriately reduce the quadrupole current of the quadrupole-octupole composite magnet 1, and use the edge field focusing effect at the entrance of the dipole magnet behind the quadrupole-octupole composite magnet 1 and the quadrupole focusing effect of the quadrupole-octupole composite magnet 1 itself to generate a waist in the Y direction at the quadrupole-octupole composite magnet 2. At the current intersection point of the quadrupole-octupole composite magnet 2, appropriately reduce the quadrupole current of the quadrupole-octupole composite magnet 2, and use the edge field focusing effect at the exit of the dipole magnet behind the quadrupole-octupole composite magnet 1 and the quadrupole focusing effect of the quadrupole-octupole composite magnet 2 itself to generate the envelope size in the X direction on the target (terminal 1 or the terminal), so that the envelope sizes in the X and Y directions are the same.

[0073] The fourth innovation point is that: a balance point has been found among the homogenization of the transmission line, avoiding the non-linear effects caused by coupling, and shortening the transmission line. As Figure 2 shown, the homogenization effect of the ultra-short bent beam current homogenization transmission line is obvious. There are three aspects of innovation, and none of them can be absent. They support each other to achieve the ideal homogenization effect:

[0074] The first aspect: with ensuring homogenization as the premise, specifically, two quadrupole-octupole composite magnets are used on the transmission line. The quadrupole magnet in front of the quadrupole-octupole composite magnet 1 and its own quadrupole magnet are used to generate a large envelope in the Y direction at the quadrupole-octupole composite magnet 1, and the quadrupole magnet of the quadrupole-octupole composite magnet 1 in front of the quadrupole-octupole composite magnet 2 and the quadrupole magnet of the quadrupole-octupole composite magnet itself are used to generate a large envelope in the X direction at the quadrupole-octupole composite magnet 2;

[0075] The second aspect: solving the problem of optimizing the homogenization effect: specifically as Figure 3 shown, it is achieved by the phase shift between the quadrupole-octupole composite magnet 1 and the target close to an integer multiple of 180 degrees (0, 1, 2, 3...), and the phase shift between the quadrupole-octupole composite magnet 2 and the target close to an integer multiple of 0 degrees. When it is close to the said 180 degrees and close to the said 0 degrees, the homogenization effect is the best;

[0076] The third aspect: On the premise of ensuring homogenization, it is also necessary to avoid the non-linear effect caused by coupling. The non-linear effect is as follows: When two four-eight-pole composite irons are used together, if not properly processed, a non-linear effect coupling effect will occur. When the non-linear effect coupling occurs, the amplitude of the particles increases, resulting in particle loss, and the particle loss reduces the homogenization effect. Therefore, in order to avoid the non-linear effect coupling effect, the present invention also makes the transfer matrix between the two octupole magnetic fields of the two four-eight-pole composite irons close to the unit matrix. The so-called close to the unit matrix, as Figure 3 , Figure 4 shown, means that the phase difference between the first four-eight-pole composite iron (point 1) and the second four-eight-pole composite iron (point 2) is close to 0 degrees and less than 30 degrees. At this time, the magnetic field strength of the required octupole magnet is small, and due to the small non-linear effect caused by coupling, the homogenization degree is better. The difference between the present invention and the prior art is that: the transfer matrix between the two octupole magnetic fields in the prior art "equals the unit matrix" rather than "is close to the unit matrix", and the transfer matrix between the two octupole magnetic fields in the present invention "is close to the unit matrix" rather than "equals the unit matrix", that is, the phase difference between the first four-eight-pole composite iron (point 1) and the second four-eight-pole 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 the present invention using "close to" rather than "equal to" is to shorten the transmission line. If the method of "equal to the unit matrix" is adopted, many components need to be added to the transmission line, and the increase in components makes the transmission line very long. The present invention adopts the method of "enough is enough" in the problem of "avoiding the non-linear effect caused by coupling": when the phase difference between the first four-eight-pole composite iron (point 1) and the second four-eight-pole composite iron (point 2) is close to 0 degrees and less than 30 degrees, it can not only effectively shorten the length of the transmission line, but also meet the requirement of "avoiding the non-linear effect caused by coupling", and find a balance point among the homogenization of the transmission line, avoiding the non-linear effect caused by coupling, and shortening the transmission line.

[0077] Based on the above invention principle, the present invention designs an ultra-short bending type beam homogenization transmission line, as Figure 1a , 1bAs shown in the figure, it is characterized in that: the transmission line is an ultra-short bent beam current homogenization transmission line including two four-eight-stage composite irons and one two-stage iron; the ultra-short bent beam current homogenization transmission line is an ultra-short bent beam current homogenization transmission line A arranged along the beam current direction, or an ultra-short bent beam current homogenization transmission line B arranged along the beam current direction: the ultra-short bent beam current homogenization transmission line A is successively provided with: an accelerator beam extraction port, a beam current matching mechanism, a four-eight-stage composite iron 1, a two-stage iron, a four-eight-stage composite iron 2, a beam current matching and homogenization effect observation mechanism 1, and a terminal 1 along the beam current extraction direction; the ultra-short bent beam current homogenization transmission line B is successively provided with: an accelerator beam extraction port, a beam current matching mechanism, a four-eight-stage composite iron 1, a two-stage iron, a four-eight-stage composite iron 3, a beam current matching and homogenization effect observation mechanism 2, and a terminal 2 along the beam current extraction direction;

[0078] As Figure 1a , 1b shown, the four-eight-stage composite iron 1, the four-eight-stage composite iron 2, or the four-eight-stage composite iron 1 and the four-eight-stage composite iron 3 respectively generate a quadrupole magnetic field and an octupole magnetic field at the same time, so that the functions of a quadrupole iron and an octupole iron can be realized simultaneously by installing only one transmission element;

[0079] As Figure 2 shown, at the four-eight-stage composite iron 1, the beam current envelope function in the Y direction or the X direction reaches a maximum value, and at the four-eight-stage composite iron 2 or the four-eight-stage composite iron 3, the beam current envelope function in the X direction or the Y direction reaches a maximum value; the phase shift of the particles between the four-eight-stage composite iron 1 and the four-eight-stage composite iron 2 and the target, or between the four-eight-stage composite iron 1 and the four-eight-stage composite iron 3 and the target is respectively close to an integer multiple of 180 degrees (0, 1, 2, 3...); the transfer matrix between the two octupole magnetic fields is close to the unit matrix.

[0080] Supplementary Note 1:

[0081] The above-mentioned "phase shift of the particles between the two four-eight-pole composite magnets and the target is respectively close to an integer multiple of 180 degrees (0, 1, 2, 3...)" but not equal to 180 degrees, and its principle is shown in the following formulas (1) and (2):

[0082]

[0083] In Equation (1), since Csc[ux23] in the numerator is equal to 1 / sin[ux23], when ux23 approaches 180, sin[ux23] approaches 0 and Csc[ux23] approaches infinity. Similarly, for Csc[uy13] in the numerator of Equation (2), which is equal to 1 / sin[uy13], when ux13 approaches 180, sin[ux13] approaches 0 and Csc[uy13] approaches infinity. Therefore, the phase shift of the particle between the two combined quadrupole and octupole magnets and the target respectively approaches but is not equal to an integer multiple of 180 degrees (0, 1, 2, 3…).

[0084] This ultra-short bending type beam homogenization transmission line utilizes the combined focusing effect of the combined quadrupole and octupole magnet 1 and the dipole magnet to generate a beam waist in the Y direction near the combined quadrupole and octupole magnet 2; and utilizes the superposition of the quadrupole field of the dipole magnet and the combined quadrupole and octupole magnet 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 the same.

[0085] As Figure 5a shown, the combined quadrupole and octupole magnet 1, the combined quadrupole and octupole magnet 2, or the combined quadrupole and octupole magnet 3 is based on a combined quadrupole and octupole magnet system, which includes a combined magnet current control device, a combined magnet main power supply, and a combined quadrupole and octupole magnet; the combined magnet current control device is used to control the output of the quadrupole field coil current and the octupole field coil current of the combined quadrupole and octupole magnet by the combined magnet main power supply;

[0086] As Figure 1c shown, the beam matching mechanism is used to observe the initial state of the beam extracted from the accelerator, and adjust the envelope size of the beam in the X or Y direction according to the initial state, and align the beam center with the mechanical center of the beam pipe;

[0087] As Figure 1e , 1f shown, the beam matching and homogenization effect observation mechanism 1 or the beam matching and homogenization effect observation mechanism 2 is used to adjust the eccentricity of the beam after passing through the dipole magnet, and observe the beam intensity, the shape of the weak beam, and the shape of the strong beam of the beam homogenized by the combined quadrupole and octupole magnet 1 and the combined quadrupole and octupole magnet 2.

[0088] As Figure 1c , 1d shown, the beam matching mechanism includes a fluorescent target 1, a quadrupole magnet, and a steering magnet; the fluorescent target 1 provides the initial position of the beam for the tester; the quadrupole magnet is used to provide a beam envelope in the opposite direction for the combined quadrupole and octupole magnet 1; the steering magnet is used to adjust the eccentricity of the beam.

[0089] As Figure 1e , 1fAs shown, the beam matching and homogenization effect observation mechanism 1 includes a guiding magnet 2, a Faraday cup 1, a fluorescent target 2, and a double wire 1; the guiding magnet 2 is used to align the beam center with the mechanical center of the beam pipe; the Faraday cup 1 is used to measure the beam current intensity after homogenization, the fluorescent target 2 is used to observe the shape of the weak beam after homogenization; the double wire 1 is used to observe the shape of the strong beam after homogenization; the beam matching and homogenization effect observation mechanism 2 includes a guiding magnet 3, a Faraday cup 3, a fluorescent target 3, and a double wire 2; the guiding magnet 3 is used to align the beam center with the mechanical center of the beam pipe; the Faraday cup 2 is used to measure the beam current intensity after homogenization, the fluorescent target 3 is used to observe the shape of the weak beam after homogenization; the double wire 2 is used to observe the shape of the strong beam after homogenization.

[0090] As Figure 3 shown, the phase shift of the particles between the quadruple-octupole magnet 1 and the quadruple-octupole magnet 2 and the target or the phase shift of the particles between the quadruple-octupole magnet 1 and the quadruple-octupole magnet 3 and the target being close to an integer multiple of 180 degrees means close but not equal to an integer multiple of 180 degrees: Let be the remainder of divided by 180 degrees, and the value generally is less than ±15 degrees.

[0091] As Figure 3 shown, the transfer matrix between the two octupole magnetic fields is close to the identity matrix, that is, the phase shift between the front and rear quadruple-octupole 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 octupole magnets and can achieve a better homogenization effect.

[0092] The expression for the magnet strength k at the quadruple-octupole magnet 1 and the quadruple-octupole magnet 2, or the magnet strength k at the quadruple-octupole magnet 1 and the quadruple-octupole magnet 3 is:

[0093] [[ID=2⑧]]

[0094] Let: The starting point of the transport line is denoted as 0, the position of the first quadruple-octupole magnet is denoted as 1, the position of the second quadruple-octupole magnet is denoted as 2, and the position at the end, which is the position of the target, is denoted as 3; ux02 in the above formula (1) represents the phase shift in the x direction between positions 0 and 2 of the particle, ux23 represents the phase shift in the x direction between positions 2 and 3 of the particle; βx2 represents the envelope function in the x direction at position 2; uy01 in the above formula (2) represents the phase shift in the y direction between 0 and 1 of the particle; uy13 represents the phase shift in the y direction between 1 and 3 of the particle; βy1 represents the envelope function in the y direction at position 1.

[0095] Supplementary Note 2

[0096] The derivation process of the above formulas (1) and (2) is briefly introduced 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 octupole magnetic field strength in a single direction is given. This formula only considers one octupole magnet and the subsequent transport section. To more accurately describe the relationship between the octupole magnetic field strength and the transport line design, we expand this formula and consider the influence of the matching section from the accelerator exit to the octupole magnet on 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 1), and uy13 (phase shift in the x direction between positions 1 and 3). Using the same "higher-order transport mapping" derivation method as in the reference, the expressions for the magnet strength k at the first and second quadrupole-octupole composite magnets, formulas (1) and (2), are obtained.

[0097] As Figure 5a shown, 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 gradients, a module for refining the three-dimensional surface sample library of magnetic field gradients using interpolation, a module for solving the corresponding field gradient current curve for the input field gradient, a module for solving the intersection points of the quadrupole / octupole field gradient current curves, and a module for outputting the quadrupole / octupole coil current.

[0098] As Figure 5d shown, the module for establishing two-dimensional sampling points of coil current is used to establish a two-dimensional data comparison table of the coil currents of the quadrupole magnet and the octupole magnet.

[0099] As Figure 5e shown, the module for experimentally measuring and initially establishing a three-dimensional surface sample library of magnetic field gradients uses the current values in the two-dimensional data comparison table of coil current to conduct magnetic field experiments on the composite iron, thereby obtaining the measured values of the quadrupole and octupole magnetic field gradients corresponding one-to-one to the two-dimensional current data comparison table, and thus 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 the quadrupole field magnetic field gradient and a three-dimensional surface sample database of the octupole field magnetic field gradient.

[0100] As Figure 5fAs shown, the interpolation and refinement of the magnetic field gradient three-dimensional surface sample library module is used to perform two-dimensional interpolation on the three-dimensional surface sample database of the quadrupole field magnetic field gradient and the three-dimensional surface sample database of the octupole field magnetic field gradient using cubic spline functions to encrypt the grid point density.

[0101] As Figure 5g , 5h As shown, the input field gradient solving the corresponding field gradient current curve module 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 two corresponding current curves are obtained after the intersection. Specifically: select the quadrupole field magnetic field gradient plane, and this plane intersects with the surface of the three-dimensional surface sample database of the quadrupole field magnetic field gradient to obtain the current curve that satisfies this quadrupole field gradient; select the octupole field magnetic field gradient plane, and this plane intersects with the surface of the three-dimensional surface sample database of the octupole field magnetic field gradient to obtain the current curve that satisfies this octupole field gradient.

[0102] As Figure 5i As shown, the solving the intersection point of the quadrupole / octupole field gradient current curve module is used to obtain the intersection point of the current curve that satisfies the quadrupole field gradient and the current curve that satisfies this octupole field gradient, and use this intersection point as the solution of the composite iron excitation current.

[0103] The output quadrupole / octupole coil current 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.

[0104] As Figure 5b , 5c As shown, this quadrupole-octupole composite magnet has a total of eight pole heads, and each pole head is provided with two layers of current coils along the radial direction near the large radius. The inner layer coil is the octupole magnetic field excitation coil, and the outer layer coil is the quadrupole magnetic field excitation coil.

[0105] As Figure 5b , 5c As shown, for the inner layer octupole magnetic field excitation coil, the current directions of its adjacent two pole heads are opposite, that is, the octupole field coils are divided into two groups: the 1st, 3rd, 5th, and 7th pole heads and the 2nd, 4th, 6th, and 8th pole heads. The excitation currents of the two are equal in magnitude but opposite in direction, thereby generating an octupole magnetic field.

[0106] As Figure 5b , 5cAs shown in the figure, the quadrupole magnetic field excitation coils of the outer layer are grouped with the coils on two adjacent pole heads as a group, divided into four groups, namely, pole heads 1 and 2, pole heads 3 and 4, pole heads 5 and 6, and pole heads 7 and 8. Among them, for pole heads 1 and 2 and symmetrically arranged pole heads 5 and 6, the magnitudes and directions of the excitation currents of these two groups of quadrupole magnetic field coils are the same; for pole heads 3 and 4 and symmetrically arranged pole heads 7 and 8, the magnitudes and directions of the excitation currents of these two groups of coils are the same; the current directions of the coils of pole heads 1 and 2 are opposite to those of the coils of pole heads 3 and 4, and the directions of the coils of pole heads 5 and 6 are opposite to those of the coils of pole heads 7 and 8, thus generating a quadrupole magnetic field.

[0107] Embodiment 1

[0108] As Figure 7 shown, the present invention designs an ultra-short bent beam current homogenization transmission line. When the total length of the ultra-short bent beam current beam line is 6, the initial layout positions of the components that can achieve a better homogenization effect for the streamline are as follows: the initial position of the fluorescent target 1 is 100 mm, the initial position of the quadrupole magnet (Q0) is 1300 mm; the initial position of the guiding magnet 1 is 1650 mm; the initial position of the quadruple-octupole composite magnet (Q1) is 2100 mm, the initial position of the dipole magnet is 2700 mm, and the initial position of the quadruple-octupole composite magnet (Q2) is 3850 mm; the initial position of the guiding magnet 2 is 4250 mm; the initial position of the Faraday cylinder is 4700 mm; the initial position of the fluorescent target 2 is 5350 mm, the initial position of the double wire is 5750 mm; the initial position of the terminal is 6000 mm.

[0109] Among them, the magnetic field component of the quadrupole magnet (Q0) is 6.8 (T / m); the quadrupole magnetic field component of the quadruple-octupole composite magnet (Q1) is 2.25 (T / m), and the octupole magnetic field component is 1e4 (T / m 3 ), the quadrupole magnetic field component of the quadruple-octupole composite magnet (Q2) is 0.6 (T / m), and the octupole magnetic field component is 6.25e3 (T / m 3 ). The beam current deflects 90°, the incident and exit angles are both 45°, and the deflection radius is 0.55 m.

[0110] As Figure 1d shown, for the comparison before and after the homogenization of the transmission line of the present invention, Figure 1d the left figure of is the screenshot of the beam current showing a Gaussian distribution before homogenization, that is, the beam current cross-section diagram when the fluorescent target 1 is at the 100 mm position of the transmission line; Figure 1d the right figure of is the beam current cross-section diagram after homogenization, that is, the beam current cross-section diagram when the fluorescent target 2 is at the 5350 mm position of the transmission line. It can be seen from the figure that before homogenization, the distribution of particles on the beam current cross-section is dense in the middle and sparse around; after homogenization, the distribution of particles on the beam current cross-section is uniform in the middle and around.

[0111] It should be emphasized that the above specific embodiments are merely explanations of the present invention and not limitations thereof. After reading this specification, those skilled in the art may make modifications to the above embodiments that do not involve creative contributions as needed, but as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

Claims

1. A ultra-short bent beam homogenization transmission line, characterized in that: The transmission line is an ultra-short bending type beam homogenization transmission line including two pieces of four-eight stage composite iron and one piece of two-stage iron; the ultra-short bending type beam homogenization transmission line is the ultra-short bending type beam homogenization transmission line A arranged along the beam direction, or the ultra-short bending type beam homogenization transmission line B arranged along the beam direction: The ultra-short bending type beam homogenization transmission line A is successively provided with: an accelerator beam extraction port, a beam matching mechanism, four-eight stage composite iron 1, two-stage iron, four-eight stage composite iron 2, a beam matching and homogenization effect observation mechanism 1, and a terminal 1 along the beam extraction direction; the ultra-short bending type beam homogenization transmission line B is successively provided with: an accelerator beam extraction port, a beam matching mechanism, four-eight stage composite iron 1, two-stage iron, four-eight stage composite iron 3, a beam matching and homogenization effect observation mechanism 2, and a terminal 2 along the beam extraction direction; The four-eight-pole composite iron 1, four-eight-pole composite iron 2, or four-eight-pole composite iron 1 and four-eight-pole composite iron 3 respectively generate a quadrupole magnetic field and an octupole magnetic field simultaneously, so that the functions of the quadrupole iron and the octupole iron can be realized simultaneously by installing only one transmission element; at the four-eight-pole composite iron 1, the beam envelope function in the Y direction or the X direction reaches a maximum value, and at the four-eight-pole composite iron 2 or the four-eight-pole composite iron 3, the beam envelope function in the X direction or the Y direction reaches a maximum value; the phase shift of the particles between the four-eight-pole composite iron 1 and the four-eight-pole composite iron 2 and the target, or between the four-eight-pole composite iron 1 and the four-eight-pole composite iron 3 and the target are respectively close to integer multiples of 180 degrees (0, 1, 2, 3...); the transfer matrix between the two octupole magnetic fields is close to the unit matrix; Based on the bending type beam homogenization substructure of the bending type beam homogenization transmission line, the focusing effects of the four-eight pole composite iron 1 and the two-pole iron are superimposed to generate a beam waist in the Y direction near the four-eight stage composite iron 2; the quadrupole fields of the two-pole iron and the four-eight stage composite iron 2 are superimposed to generate the envelope size in the X direction on the target, so that the envelope sizes in the X direction and the Y direction are consistent; The four-eight stage composite iron 1, the four-eight stage composite iron 2 or the four-eight stage composite iron 3 is based on a four-eight pole composite magnet system, and 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 output of the quadrupole field coil current and the octupole field coil current 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, and adjust the envelope size of the beam in the X or Y direction according to the initial state, and align the beam center with the mechanical center of the beam pipe; The beam matching and homogenization effect observation mechanism 1 or the beam matching and homogenization effect observation mechanism 2 is used to adjust the eccentricity of the beam after passing through the two-stage iron, and observe the beam intensity, the shape of the weak beam and the shape of the strong beam after homogenization by the four-eight stage composite iron 1 and the four-eight stage composite iron 2.

2. The ultra-short bent beam current homogenizing transmission line according to claim 1, wherein: The beam matching mechanism includes a fluorescent target 1, a quadrupole magnet and a guiding magnet; the fluorescent target 1 provides the initial position of the beam for the tester; the quadrupole magnet is used to provide an anti-direction beam envelope for the four-eight stage composite iron 1; the guiding magnet is used to adjust the eccentricity of the beam.

3. The ultra-short bending type beam current homogenizing transmission line according to claim 1, wherein: The beam matching and homogenization effect observation mechanism 1 includes a guiding magnet 2, a Faraday cup 1, a fluorescent target 2, and a double wire 1; the guiding magnet 2 is used to align the beam center with the mechanical center of the beam pipe; the Faraday cup 1 is used to measure the beam current intensity after homogenization, the fluorescent target 2 is used to observe the shape of the weak beam after homogenization; the double wire 1 is used to observe the shape of the strong beam after homogenization; the beam matching and homogenization effect observation mechanism 2 includes a guiding magnet 3, a Faraday cup 3, a fluorescent target 3, and a double wire 2; the guiding magnet 3 is used to align the beam center with the mechanical center of the beam pipe; the Faraday cup 2 is used to measure the beam current intensity after homogenization, the fluorescent target 3 is used to observe the shape of the weak beam after homogenization; the double wire 2 is used to observe the shape of the strong beam after homogenization.

4. The ultra-short bending type beam current homogenizing transmission line according to claim 1, characterized in that: The phase shift of the particles between the quadruple-octuple combined iron 1 and the quadruple-octuple combined iron 2 and the target or the phase shift of the particles between the quadruple-octuple combined iron 1 and the quadruple-octuple combined iron 3 and the target being close to an integer multiple of 180 degrees means being close to but not equal to an integer multiple of 180 degrees: Let be the remainder with respect to 180 degrees, and its value is generally less than ±15 degrees.

5. The ultra-short bent beam current homogenization transmission line according to claim 1, wherein: The transfer matrix between the two octupole magnets is close to the identity matrix, that is, the phase shift between the front and rear quadruple-octupole 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 octupole magnets and can achieve a better homogenization effect.

6. The ultra-short bending type beam current homogenization transmission line according to claim 1, wherein: The expression for the magnet strength k at the quadruple-octupole composite magnet 1 and quadruple-octupole composite magnet 2, or the magnet strength k at the quadruple-octupole composite magnet 1 and quadruple-octupole composite magnet 3 is: Let: the starting point of the transport line be denoted as 0, the position of the first quadruple-octupole magnet be denoted as 1, the position of the second quadruple-octupole magnet be denoted as 2, and the position at the end, which is the position of the target, be denoted as 3; ux02 in 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; uy01 in the above formula (2) 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.

7. The ultra-short bending type beam current homogenizing transmission line according to claim 1, wherein: 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 gradients, a module for using interpolation to refine the three-dimensional surface sample library of magnetic field gradients, a module for solving the corresponding field gradient current curve for the input field gradient, a module for solving the intersection point of the quadruple / octupole field gradient current curves, and a module for outputting the quadruple / octupole coil current; The module for establishing two-dimensional sampling points of coil current is used to establish a two-dimensional data comparison table of the coil currents of the quadrupole iron and octupole iron; The module for experimentally measuring and initially establishing a three-dimensional surface sample library of magnetic field gradients uses the current values in the two-dimensional data comparison table of coil current to conduct magnetic field experiments on the composite iron, so as to obtain the measured values of the quadruple and octupole magnetic field gradients corresponding one-to-one to 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 quadrupole field magnetic field gradients and a three-dimensional surface sample database of octupole field magnetic field gradients; The interpolation and refinement of the magnetic field gradient three-dimensional surface sample library module is used to perform two-dimensional interpolation on the three-dimensional surface sample database of the quadrupole field magnetic field gradient and the three-dimensional surface sample database of the octupole field magnetic field gradient using the cubic spline function to encrypt the grid point density; The input field gradient solving the corresponding field gradient current curve module 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 two corresponding current curves are obtained after the intersection; specifically: select the quadrupole field magnetic field gradient plane, and this plane intersects with the surface of the three-dimensional surface sample database of the quadrupole field magnetic field gradient to obtain the current curve that satisfies the quadrupole field gradient; select the octupole field magnetic field gradient plane, and this plane intersects with the surface of the three-dimensional surface sample database of the octupole field magnetic field gradient to obtain the current curve that satisfies the octupole field gradient; The module for solving the intersection point of the quadrupole / octupole field gradient current curve is used to obtain the intersection point of the current curve that satisfies the quadrupole field gradient and the current curve that satisfies the octupole field gradient, and use this intersection point as the solution of the composite iron excitation current; The output quadrupole / octupole coil current 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.

8. The ultra-short bent beam current homogenization transmission line according to claim 1, characterized in that: This quadrupole-octupole composite magnet has a total of eight pole tips. Each pole tip is provided with two layers of current coils along the radial direction near the large radius. The inner layer coil is an octupole magnetic field excitation coil, and the outer layer coil is a quadrupole magnetic field excitation coil; For the inner layer octupole magnetic field excitation coil, the current directions of its adjacent two pole tips are opposite, that is, the octupole field coils are divided into two groups: the 1st, 3rd, 5th, and 7th pole tips and the 2nd, 4th, 6th, and 8th pole tips. The magnitudes of their excitation currents are equal, but the current directions are opposite, thereby generating an octupole magnetic field; For the outer layer quadrupole magnetic field excitation coil, the coils on its adjacent two pole tips are in a group, divided into four groups, namely the 1st and 2nd pole tips, the 3rd and 4th pole tips, the 5th and 6th pole tips, and the 7th and 8th pole tips; among them, the 1st and 2nd pole tips and the symmetrically arranged 5th and 6th pole tips, the magnitudes and directions of the excitation currents of these two groups of quadrupole magnetic field coils are the same, the 3rd and 4th pole tips and the symmetrically arranged 7th and 8th pole tips, the magnitudes and directions of the excitation currents of these two groups of coils are the same, the current directions of the 1st and 2nd pole tip coils are opposite to those of the 3rd and 4th pole tip coils, and the directions of the 5th and 6th pole tip coils are opposite to those of the 7th and 8th pole tip coils, thereby generating a quadrupole magnetic field.

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