Ultra-short symmetrical bending type beam homogenization transmission line

Abstract

The invention relates to an ultra-short symmetrical bending type beam homogenization transmission line. A beam line is a symmetrical bending type high-current homogenization beam line which comprises two pieces of four-eight-level composite iron and a piece of shared two-level iron. The symmetrical bending type high-current homogenization beam line is composed of a common beam line and two branch beam lines. The common beam line is provided with an accelerator leading-out port, a beam matching mechanism, four-level and eight-level composite iron 1 and second-level iron in the beam direction. The first branch beam line is sequentially provided with four-eight-level composite iron 2, a beam matching and homogenization effect observation mechanism 1 and a terminal 1; the second branch beam line is sequentially provided with four-eight-level composite iron 3, a beam matching and homogenizing effect observation mechanism 2 and a terminal 2; 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 symmetric 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 passes through the transmission line and then hits the neutron target 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 to be used 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: the same octupole magnet installed at different positions on the beam current transmission line will have different effects. Only when the octupole magnet is installed at a position with a larger beam envelope can it provide the strongest homogenization effect. However, in the prior art, the place with the largest envelope is usually occupied by the quadrupole magnetic field: 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 has to focus first before homogenization (the role of focusing is to enable 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 position 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 position is small. In short, according to the traditional method, the beam envelope has been significantly reduced 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] Another difficulty in using octupole magnets to homogenize the Gaussian-distributed beam current is that: since the beam envelopes at the positions of octupole iron 1 and octupole iron 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 in engineering, but also too costly and difficult to achieve.

[0007] The third difficulty in using octupole magnets to homogenize a Gaussian beam lies in that: if an octupole magnet is to be used to achieve a better beam homogenization effect, there are relatively strict requirements for the position where the octupole magnet is placed and the phase it is in. 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 more than ten meters long is equivalent to making the accelerator smaller, which has no meaning. The longer the beam line, the more expensive the civil engineering for 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 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 symmetrically bent beam homogenization transmission line. The first objective 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 magnet cannot fully play its role. The second objective is to solve the problem that when discrete quadrupole magnets and octupole magnets are used, since the beam envelope is small at the positions where the octupole magnet 1 and the octupole magnet 2 are located, the requirement for the field intensity of the octupole magnet is very high, and too high a magnetic field intensity is too costly and difficult to achieve in engineering. The third objective 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 surrounding shielding, large floor area and high cost.

[0009] The present invention adopts the following technical solutions to solve its technical problems:

[0010] An ultra-short symmetrically bent beam homogenization transmission line, characterized in that: the transmission line is a symmetrically bent beam homogenization transmission line respectively including two quadrupole-octupole composite irons and one common secondary iron; the symmetrically bent beam homogenization transmission line respectively including two quadrupole-octupole composite irons and one common secondary iron is composed of one common transmission line and two branch transmission lines;

[0011] The quadrupole-octupole composite iron 1, the quadrupole-octupole composite iron 2, and the quadrupole-octupole composite iron 3 of the first bent beam homogenization transmission line and the second bent beam homogenization transmission line respectively generate quadrupole magnetic fields and octupole magnetic fields at the same time, so that the functions of quadrupole magnets and octupole magnets can be realized simultaneously by installing only one transmission element;

[0012] At the quadrupole-octupole composite iron 1 of the first bent beam homogenization transmission line, the beam envelope function in the Y direction or the X direction reaches a larger value, and at the quadrupole-octupole composite iron 2, the beam envelope function in the X direction or the Y direction reaches a larger value; the phase shift of the particles between the quadrupole-octupole composite iron 1 and the quadrupole-octupole composite iron 2 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;

[0013] The secondary iron on the ultra-short symmetrically bent beam homogenization transmission line is a shared diode on the ultra-short symmetrically bent beam homogenization transmission line. The shared diode has an exit edge with upper and lower symmetrical edge angles. Specifically, the beam entrance edge is a straight line, and the beam exit edge is a pair of upper and lower symmetrical oblique lines. The inclination direction of the upper and lower symmetrical oblique lines is the direction in which the beam bends at the exit edge. The upper and lower symmetrical oblique lines and the line connecting the center of the beam bending track to the beam at the diode exit constitute the diode exit edge angle. By changing the size of the diode exit edge angle, the fringe field focusing effect of the diode is adjusted, and the envelope of the four-eighth grade composite iron on both sides of the diode in the Y direction and the X direction is coordinated to obtain an ideal phase shift that meets the homogenization requirements.

[0014] The second bending beam uniformization transmission line has a maximum value of the beam envelope function in the Y direction or X direction at the 48-level composite iron 1, and a maximum value of the beam envelope function in the X direction or Y direction at the 48-level composite iron 3. The phase shift of the particles between the 48-level composite iron 1 and the 48-level composite iron 3 and the target are respectively close to integer multiples of 180 degrees (0, 1, 2, 3...); the transmission matrix between the two octupole magnetic fields is close to the unit matrix;

[0015] The four-eighth-level composite iron 1, four-eighth-level composite iron 2, and four-eighth-level composite iron 3 of the first bend-type beam uniformization transmission line and the second bend-type beam uniformization transmission line are based on a four-eighth-level composite magnet system, and the four-eighth-level composite magnet system includes a composite magnet current control device, a composite magnet main power supply, and a four-eighth-level composite magnet; the composite magnet current control device is used to control the composite magnet main power supply to output the quadrupole field coil current and the octupole field coil current of the four-eighth-level composite magnet;

[0016] The shared transmission line is provided with: an accelerator outlet, a beam matching mechanism, a four-eighth level composite iron 1, and a secondary iron in sequence along the beam direction; the two branch transmission lines are a first branch transmission line and a second branch transmission line; the first branch transmission line is provided with a four-eighth level composite iron 2, a beam matching and homogenization effect observation mechanism 1, and a terminal 1 in sequence; the second branch transmission line is provided with a four-eighth level composite iron 3, a beam matching and homogenization effect observation mechanism 2, and a terminal 2 in sequence; the shared transmission line and the first branch transmission line constitute a first bending type beam homogenization transmission line; the shared transmission line and the second branch transmission line constitute a second bending type beam homogenization transmission line; the first bending type beam homogenization transmission line and the second bending type beam homogenization transmission line work in a time-sharing manner;

[0017] The beam matching mechanism on the shared transmission line is used to observe the initial state of the beam drawn 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 pipeline;

[0018] The beam matching and homogenization effect observation mechanism 1 on the first branch transmission line is used to align the beam center with the mechanical center of the beam pipe, measure the beam current intensity after homogenization by the quadruple-octupole iron 1 and the quadruple-octupole iron 2, and observe the shapes of the weak beam and the strong beam after homogenization;

[0019] The beam matching and homogenization effect observation mechanism 2 on the second branch transmission line is used to align the beam center with the mechanical center of the beam pipe, measure the beam current intensity after homogenization by the quadruple-octupole iron 1 and the quadruple-octupole iron 3, and observe the shapes of the weak beam and the strong beam after homogenization;

[0020] The entrance side of the dipole magnet for the symmetrically bent beam is a straight edge that is symmetric up and down, and the exit side of the symmetrically bent beam is a bevel edge that is symmetric up and down. The inclination direction of the symmetric bevel edge is the direction of beam bending.

[0021] Furthermore, the beam matching mechanism includes a fluorescent target 1, a quadrupole magnet, and a guiding magnet; the fluorescent target 1 provides the initial state of the beam for the tester; the quadrupole magnet is used to form a large beam envelope in the Y direction or the X direction at the position of the quadruple-octupole iron 1, and the guiding magnet is used to align the beam center with the mechanical center of the beam pipe.

[0022] Furthermore, the beam matching and homogenization effect observation mechanism 1 on the first branch transmission line 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 on the second branch transmission line includes a guiding magnet 3, a Faraday cup 2, 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.

[0023] Furthermore, the phase shift of the particles between the quadruple-octupole iron 1 and the quadruple-octupole iron 2 and the target or the phase shift of the particles between the quadruple-octupole iron 1 and the quadruple-octupole iron 3 and the target is close to an integer multiple of 180 degrees, which means close to but not equal to an integer multiple of 180 degrees: Let be the remainder of divided by 180 degrees, and

[0024] Furthermore, 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 a range of 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.

[0025] Furthermore, the expression of the magnet strength k at the quadruple-octupole composite iron 1 and quadruple-octupole composite iron 2, or the magnet strength k at the quadruple-octupole composite iron 1 and quadruple-octupole composite iron 3 is as follows:

[0026]

[0027] 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 point, 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, and 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.

[0028] Furthermore, the composite magnet current control device includes: 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 inputting the field gradient to solve the corresponding field gradient current curve, a module for solving the intersection points of the quadruple / octupole field gradient current curves, and a module for outputting the quadruple / octupole coil current;

[0029] The module for establishing two-dimensional sampling points of coil current is used to establish a two-dimensional data comparison table of the coil current of the quadrupole iron and the octupole iron;

[0030] 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 to the two-dimensional current data comparison table one by one, 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 the quadrupole field magnetic field gradient and a three-dimensional surface sample database of the octupole field magnetic field gradient;

[0031] The module for using interpolation to refine the three-dimensional surface sample library of magnetic field gradients 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 density of grid points;

[0032] The input field gradient solving 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 gradient plane, which intersects with the surface of the quadrupole field magnetic gradient three-dimensional surface sample database to obtain the current curve that meets the quadrupole field gradient; select the octupole field magnetic gradient plane, which intersects with the surface of the octupole field magnetic gradient three-dimensional surface sample database to obtain the current curve that meets the octupole field gradient.

[0033] The solving quadrupole / octupole field gradient current curve intersection point module is used to obtain the intersection point of the current curve that meets the quadrupole field gradient and the current curve that meets the octupole field gradient, and use this intersection point as the solution of the composite iron excitation current.

[0034] The output quadrupole / octupole coil current module outputs the quadrupole field coil current and octupole field coil current to the quadrupole / octupole composite iron according to the solution of the composite iron excitation current.

[0035] Furthermore, this quadrupole-octupole composite magnet has a total of eight pole heads. Each pole head is provided with two inner and outer current coils along the radial direction near the large radius. The inner coil is the octupole magnetic field excitation coil, and the outer coil is the quadrupole magnetic field excitation coil.

[0036] For the inner octupole magnetic field excitation coil, the current directions of two adjacent pole heads are opposite, that is, the octupole field coils are divided into two groups: pole heads 1, 3, 5, 7 and pole heads 2, 4, 6, 8. The excitation current magnitudes of the two are equal, but the current directions are opposite, thus generating an octupole magnetic field.

[0037] For the outer quadrupole magnetic field excitation coil, the coils on two adjacent pole heads are in a group, divided into four groups, namely pole heads 1, 2; pole heads 3, 4; pole heads 5, 6; pole heads 7, 8 respectively. Among them, for pole heads 1, 2 and symmetrically arranged pole heads 5, 6, the excitation current magnitudes and directions of these two groups of quadrupole magnetic field coils are the same; for pole heads 3, 4 and symmetrically arranged pole heads 7, 8, the excitation current magnitudes and directions of these two groups of coils are the same; the current directions of the coils of pole heads 1, 2 and pole heads 3, 4 are opposite, and the directions of the coils of pole heads 5, 6 and pole heads 7, 8 are opposite, thus generating a quadrupole magnetic field.

[0038] Advantages and effects of the present invention

[0039] 1. The present invention respectively includes two quadrupole-octupole composite irons and a symmetrically bent beam uniformization transmission line with a common secondary 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 using discrete quadrupole irons and octupole irons, since the place with the largest envelope is usually occupied by the quadrupole magnetic field, the octupole iron cannot fully play its role.

[0040] 2. The symmetrically bent beam current homogenization transmission line of the present invention respectively includes two four - eight - pole composite irons and one shared two - pole iron. Since the four - eight - pole composite iron is located at the large envelope, the requirement for the magnetic field strength K value of the four - eight - pole composite iron is reduced. It solves the problem that in the prior art, when discrete quadrupole irons and octupole irons are used, due to the smaller beam current envelope at the positions where octupole iron 1 and octupole iron 2 are located, 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.

[0041] 3. The symmetrically bent beam current homogenization transmission line of the present invention respectively includes two four - eight - pole composite irons and one shared two - pole iron. A quadrupole magnetic field and an octupole magnetic field are simultaneously generated within the aperture of the four - eight - pole composite iron, and at the same time, the functions of focusing and homogenizing the beam current envelope are realized. Installing the composite iron on the beam current transmission line can reduce the number of transmission elements and shorten the length of the transmission line. It solves the problem that when discrete quadrupole irons and octupole irons are used, the overly long transmission line leads to more expensive civil engineering for the surrounding shielding, large floor area and high cost.

[0042] 4. The symmetrically bent beam current homogenization transmission line of the present invention respectively includes two four - eight - pole composite irons and one shared two - pole iron, which limits the phase shift of particles between the two four - eight - pole composite magnets and the target to be respectively close to an integer multiple of 180 degrees (0, 1, 2, 3...), but not equal to an integer multiple of 180 degrees (0, 1, 2, 3...), so that the required magnetic field strength k1 and k2 values at the first four - eight - pole composite magnet and the second four - eight - pole composite magnet are smaller, which is beneficial to reducing the manufacturing difficulty and cost of the magnet.

[0043] 5. The symmetrically bent beam current homogenization transmission line of the present invention respectively includes two four - eight - pole composite irons and one shared two - pole iron, which limits the transfer matrix between the two octupole magnetic fields to be close to the unit matrix, that is, the phase shift between the front and rear four - eight - pole 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 obtain a better homogenization effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1a It is a schematic diagram of the ultra - short symmetrically bent beam current homogenization transmission line of the present invention;

[0045] Figure 1b It is a schematic diagram of the beam current matching mechanism of the transmission line of the present invention;

[0046] Figure 1c It is a schematic diagram for comparing the particle distribution states before and after the homogenization of the transmission line of the present invention;

[0047] Figure 1d It is a schematic diagram of the beam current matching and homogenization effect observation mechanism 1 of the present invention;

[0048] Figure 1e Schematic diagram of the beam matching and homogenization effect observation mechanism 2 of the present invention;

[0049] Figure 1f Usage method of the secondary iron of the symmetric bending transfer line based on shape change of the present invention;

[0050] Figure 1g Usage method of the secondary iron of the single bending transfer line based on attitude change in the prior art;

[0051] Figure 2 Schematic diagram of the maximum envelope positions of the four-octupole composite irons 1 and 2 of the present invention;

[0052] Figure 3 Schematic diagram of the representative meanings of the four points 0, 1, 2, and 3 involved in formulas (1) and (2) of the present invention;

[0053] Figure 4 Schematic diagram of the phase difference between two four-octupole composite irons and the phase differences from the two four-octupole composite irons to the target point respectively of the present invention;

[0054] Figure 5a Schematic diagram of the four / octupole composite iron system for beam control of the present invention;

[0055] Figure 5b New four / octupole composite iron model of the present invention;

[0056] Figure 5c Arrangement of coils and current directions of the four / octupole composite magnet.

[0057] Figure 5d Schematic diagram of the current values of two groups of coils during magnetic field measurement of the present invention;

[0058] Figure 5e Schematic diagram of the corresponding four / octupole magnetic field gradients measured experimentally at different currents of the present invention;

[0059] Figure 5f Schematic diagram of using cubic spline function to perform two-dimensional interpolation to encrypt grid point density of the present invention;

[0060] 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;

[0061] Figure 5h Schematic diagram of the selected current curve corresponding to the four / octupole field of the present invention;

[0062] Figure 5i Schematic diagram of the solution of the excitation current of the composite iron of the present invention;

[0063] Figure 6 It is a schematic diagram of the octupole magnet in the prior art at the small envelope position.

[0064] Figure 7 It is a schematic diagram of an embodiment of the ultra-short symmetric bending type beam homogenization transmission line of the present invention; Detailed implementation manners

[0065] Design principle of the present invention

[0066] One of the innovation points lies in: inventing a quadruple-octupole composite magnet. Using the quadruple-octupole composite magnet as shown in Figure 5b , 5c to replace the quadrupole magnet and octupole magnet of discrete components as 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 quadruple-octupole composite magnet, and its effect is as shown in Figure 2 : The quadrupole magnet and the octupole magnet 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 quadruple-octupole composite magnet 1 and the quadrupole magnet in front of it generate the large envelope in the Y direction symbiotically; the quadruple-octupole composite magnet 2 and the quadrupole magnet of the quadruple-octupole composite magnet 1 in front of it generate the large envelope in the X direction symbiotically. Since the octupole magnets in the quadruple-octupole composite magnet 1 and the quadruple-octupole composite magnet 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 realized simultaneously. Compared with the prior art in Figure 6 , since the prior art arranges the quadrupole magnet and the octupole magnet discretely, the octupole magnet itself cannot change the envelope like the quadrupole magnet, that is, it cannot generate the large envelope symbiotically with the quadrupole magnet in front. Therefore, the envelopes in the Y direction and the X direction of the discretely arranged octupole magnet are relatively small, so its homogenization effect is not good. Another effect: installing the composite magnet on the beam transmission line can reduce the number of transmission components, shorten the length of the transmission line, and reduce the project cost of the beam transport line; the reduction of the number of transmission components not only saves the quadrupole magnet, but also saves multiple components that need to be added on the homogenization transmission line to achieve the same effect.

[0067] The second innovation lies in: inventing a four / eight-pole composite magnet current control system and a four / eight-pole composite iron excitation current design method. First, the design difficulty of the four / eight-pole composite iron excitation current is that there is a coupling relationship between the multi-pole magnetic fields generated by the two sets of coils of the four / eight-pole composite iron. 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 a 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 / eight-pole composite magnet current control system and a four / eight-pole composite iron excitation current design method are innovatively designed. This system and method solve the problem of the coupling relationship between the multi-pole magnetic fields generated by the two sets of coils of the four / eight-pole composite iron, and find the current intersection point that simultaneously satisfies the quadrupole field gradient and 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 quadrupole / octupole coil current module.

[0068] The design method of the four / eight-pole composite iron excitation current is as follows:

[0069] Step 1: As Figure 5d shown, establish a two-dimensional data comparison table of the coil currents of the quadrupole iron and octupole iron; 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 / eight-pole composite iron; the above two-dimensional data comparison table of the coil currents is as Figure 5d shown, with the abscissa being the quadrupole coil current and the ordinate being the quadrupole coil current.

[0070] Step 2: As Figure 5e shown, through experimental measurement, obtain the measured values of the quadrupole and octupole magnetic field gradients 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;

[0071] The above three-dimensional surface sample database Figure 5e is shown with the quadrupole coil current as the X-axis coordinate, the octupole coil current as the Y-axis coordinate, and the magnetic field gradient as the Z-axis coordinate.

[0072] Step 3: AsFigure 5f As shown, using a cubic spline function, two-dimensional interpolation is performed 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;

[0073] The effect of the above-mentioned increased grid point density is as Figure 5f shown, and the grid densities on the X-axis, Y-axis, and Z-axis have all increased.

[0074] Step Four: As Figure 5g shown, select the quadrupole field magnetic field gradient plane. 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 the quadrupole field gradient; select the octupole field magnetic field gradient plane. 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 the octupole field gradient;

[0075] Step Five: As Figure 5h shown, obtain the current curve that satisfies the quadrupole field gradient and the current curve that satisfies 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;

[0076] Step Six: As Figure 5i shown, use this intersection point as the solution for the composite iron excitation current.

[0077] The third innovation point lies in: inventing an ultra-short symmetric bent beam current uniform transmission line and a secondary iron for the ultra-short symmetric bent beam current uniform transmission line.

[0078] First, as Figure 2 shown, two quadrupole-octupole composite irons are used on the ultra-short symmetric bent beam current uniform transmission line. The quadrupole-octupole composite iron 1 and the quadrupole iron in front of it coexist to generate a large envelope in the Y direction. The generation of the large envelope is due to the defocusing of the quadrupole iron in front and the dotted line pointing upward, and the focusing of the quadrupole iron behind and the dotted line pointing downward. The large envelope in the Y direction is generated at the intersection of the two dotted lines; the quadrupole-octupole composite iron 2 and the quadrupole iron of the quadrupole-octupole composite iron 1 in front of it coexist to generate a large envelope in the X direction. The generation of the large envelope is due to the defocusing of the quadrupole iron in front and the solid line pointing upward, and the focusing of the quadrupole iron behind and the solid line pointing downward. The large envelope in the X direction is generated at the intersection of the two solid lines;

[0079] As Figure 2As shown in the figure, the ultra-short symmetric bending type beam homogenization transmission line uses two four-octupole 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; the innovation lies in that the ultra-short symmetric bending type beam homogenization transmission line uses the combined focusing effect of the four-octupole composite iron 1 and the dipole iron to generate a beam waist in the Y direction near the four-octupole composite iron 2; uses the superposition of the dipole iron and the quadrupole field of the four-octupole 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 the Y direction are the same; specifically: at the current intersection point of the four-octupole composite iron 1, appropriately reduce the quadrupole iron current of the four-octupole composite iron 1, and use the edge field focusing effect at the entrance of the dipole iron behind the four-octupole composite iron 1 and the quadrupole iron focusing effect of the four-octupole composite iron 1 itself to generate a waist in the Y direction at the four-octupole composite iron 2. At the current intersection point of the four-octupole composite iron 2, appropriately reduce the quadrupole iron current of the four-octupole composite iron 2, and use the edge field focusing effect at the exit of the dipole iron behind the four-octupole composite iron 1 and the quadrupole iron focusing effect of the four-octupole composite iron 2 itself 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 the same.

[0080] Thirdly, as Figure 1f shown, the dipole iron for the ultra-short symmetric bending type beam homogenization transmission line is a common dipole iron on the ultra-short symmetric bending type beam homogenization transmission line. The common dipole iron is a dipole iron with upper and lower symmetric edge angles at the exit side. Specifically: its beam entrance side is a straight line, and its beam exit side is a pair of upper and lower symmetric oblique lines. The inclination direction of the upper and lower symmetric oblique lines is the direction in which the beam bends at the exit side respectively; the upper and lower symmetric oblique lines and the connection line from the center of the beam bending orbit to the beam at the exit of the dipole iron form the dipole iron exit edge angle; by changing the size of the dipole iron exit edge angle, the edge field focusing effect of the dipole iron is adjusted, and the envelopes in the Y direction and the X direction of the four-eight-pole composite irons on both sides of the dipole iron are coordinated to obtain an ideal phase shift that meets the homogenization requirements.

[0081] The fourth innovation point lies in: finding a balance among the homogenization of the transmission line, avoiding the non-linear effects formed by coupling, and shortening the transmission line. As Figure 2 shown, the homogenization effect of the ultra-short bending type beam homogenization transmission line is obvious. It comes from three aspects of innovation, and none of them can be missing. Only by supporting each other can an ideal homogenization effect be achieved:

[0082] The first aspect: taking ensuring homogenization as the premise. Specifically, two four-octupole composite irons are used on the transmission line. The quadrupole iron in front of the four-octupole composite iron 1 and its own quadrupole iron are used to generate a large envelope in the Y direction at the four-octupole composite iron 1, and the quadrupole iron of the four-octupole composite iron 1 in front of the four-octupole composite iron 2 and the quadrupole iron of the four-octupole composite iron itself are used to generate a large envelope in the X direction at the four-octupole composite iron 2;

[0083] The second aspect: Solving the problem of optimizing the homogenization effect: Specifically, as Figure 4 shown, it is achieved by the phase shift between the quadrupole-octupole combined magnet 1 and the target being close to an integer multiple of 180 degrees (0, 1, 2, 3...), and the phase shift between the quadrupole-octupole combined magnet 2 and the target being 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;

[0084] The third aspect: On the premise of ensuring homogenization, it is also necessary to avoid the non-linear effect formed by coupling. The said non-linear effect is: When two quadrupole-octupole combined irons are used together, if not properly processed, a non-linear effect coupling effect will be generated. 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 in the present invention, the transfer matrix between the two octupole magnetic fields of the two quadrupole-octupole combined irons is also close to the unit matrix. Specifically, as Figure 3 、 Figure 4 shown, the said being close to the unit matrix means that the phase difference between the first quadrupole-octupole combined iron (point 1) and the second quadrupole-octupole combined 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 smaller, and due to the smaller non-linear effect formed by coupling, the homogenization degree is better.

[0085] 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 quadrupole-octupole combined iron (point 1) and the second quadrupole-octupole combined 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 "equals the unit matrix" is adopted, many components need to be added to the transmission line, and the transmission line will be very long with the increase of components. The present invention adopts the method of "enough is enough" in the problem of "avoiding the non-linear effect formed by coupling": when the phase difference between the first quadrupole-octupole combined iron (point 1) and the second quadrupole-octupole combined 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 formed by coupling", and find a balance among the transmission line homogenization, avoiding the non-linear effect formed by coupling, and shortening the transmission line.

[0086] Based on the above principles involved in the present invention, the present invention designs an ultra-short symmetric bending type beam homogenization transmission line as Figure 1a 、 Figure 1b 、Figure 1c , Figure 1d , 1e As shown in 1e , its characteristics are: the transmission line is a symmetrically bent beam homogenization transmission line that respectively includes two four-eight-stage composite irons and one common second-stage iron; the symmetrically bent beam homogenization transmission line that respectively includes two four-eight-stage composite irons and one common second-stage iron is composed of one common transmission line and two branch transmission lines;

[0087] As Figure 1a shown in Figure 1a , the following are successively provided on the common transmission line along the beam direction: an accelerator beam outlet, a beam matching mechanism, four-eight-stage composite iron 1, and second-stage iron; the two branch transmission lines are the first branch transmission line and the second branch transmission line; the first branch transmission line successively has four-eight-stage composite iron 2, a beam matching and homogenization effect observation mechanism 1, and terminal 1; the second branch transmission line successively has four-eight-stage composite iron 3, a beam matching and homogenization effect observation mechanism 2, and terminal 2; the common transmission line and the first branch transmission line form a first bent beam homogenization transmission line; the common transmission line and the second branch transmission line form a second bent beam homogenization transmission line; the first bent beam homogenization transmission line and the second bent beam homogenization transmission line work at different times;

[0088] The four-eight-stage composite iron 1, four-eight-stage composite iron 2, and four-eight-stage composite iron 3 of the first bent beam homogenization transmission line and the second bent beam homogenization transmission line respectively generate quadrupole magnetic fields and octupole magnetic fields at the same time, so that the functions of quadrupole iron and octupole iron can be realized simultaneously by installing only one transmission element;

[0089] As Figure 2 shown in Figure 2 , at four-eight-stage composite iron 1 of the first bent beam homogenization transmission line, the beam envelope function in the Y direction or X direction reaches a large value, and at four-eight-stage composite iron 2, the beam envelope function in the X direction or Y direction reaches a large value; the phase shift of the particles between four-eight-stage composite iron 1 and four-eight-stage composite iron 2 and the target respectively approaches an integer multiple of 180 degrees (0, 1, 2, 3...); the transfer matrix between the two octupole magnetic fields approaches the unit matrix;

[0090] The secondary iron on the ultra-short symmetrically bent beam homogenization transmission line is a shared diode on the ultra-short symmetrically bent beam homogenization transmission line. The shared diode has an exit edge with upper and lower symmetrical edge angles. Specifically, the beam entrance edge is a straight line, and the beam exit edge is a pair of upper and lower symmetrical oblique lines. The inclination direction of the upper and lower symmetrical oblique lines is the direction in which the beam bends at the exit edge. The upper and lower symmetrical oblique lines and the line connecting the center of the beam bending track to the beam at the diode exit constitute the diode exit edge angle. By changing the size of the diode exit edge angle, the fringe field focusing effect of the diode is adjusted, and the envelope of the four-eighth grade composite iron on both sides of the diode in the Y direction and the X direction is coordinated to obtain an ideal phase shift that meets the homogenization requirements.

[0091] like Figure 2 As shown, the second bending beam uniformization transmission line reaches a maximum value in the Y direction or X direction at the four-eighth level composite iron 1, and a maximum value in the X direction or Y direction at the four-eighth level composite iron 3. The phase shift of the particles between the four-eighth level composite iron 1 and the four-eighth level composite iron 3 and the target is are respectively close to integer multiples of 180 degrees (0, 1, 2, 3...); the transmission matrix between the two octupole magnetic fields is close to the unit matrix;

[0092] like Figure 5a As shown, the four-eighth-level composite iron 1, the four-eighth-level composite iron 2, and the four-eighth-level composite iron 3 of the first bend-type beam uniformization transmission line and the second bend-type beam uniformization transmission line are based on a four-eighth-pole composite magnet system, and the four-eighth-pole composite magnet system includes a composite magnet current control device, a composite magnet main power supply, and a four-eighth-pole composite magnet; the composite magnet current control device is used to control the composite magnet main power supply to output the quadrupole field coil current and the octupole field coil current of the four-eighth-pole composite magnet;

[0093] like Figure 1b 、 1c As shown, the beam matching mechanism on the shared transmission line is used to observe the initial state of the beam drawn out by 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 pipeline;

[0094] like Figure 1d As shown, the beam matching and homogenization effect observation mechanism 1 on the first branch transmission line is used to align the beam center and the mechanical center of the beam pipeline, measure the beam intensity after being homogenized by the four-eighth grade composite iron 1 and the four-eighth grade composite iron 2, and observe the weak beam shape and strong beam shape after homogenization;

[0095] like Figure 1eAs shown, the beam current matching and homogenization effect observation mechanism 2 on the second branch transmission line is used to align the beam center with the mechanical center of the beam pipe, measure the beam current intensity after homogenization by the first and third quadruple-octupole irons 1 and 3, and observe the shapes of weak and strong beams after homogenization;

[0096] As Figure 1f shown, on the entrance side of the beam with symmetric bending, the dipole iron has straight edges that are symmetric up and down, and on the exit side of the beam with symmetric bending, it has bevel edges that are symmetric up and down. The inclination direction of the symmetric bevel edges is the direction of beam bending.

[0097] Supplementary Note 1:

[0098] As Figure 1f shown, the function of the above-mentioned dipole iron is to bend the beam. At the same time, as Figure 2 shown, when the beam passes through the dipole iron, beam focusing in the X and Y directions will also occur. In the design of an ultra-short bent beam beamline, in order to shorten the length of the transmission line, it is necessary to adjust the arrangement of beam elements so that the first quadrupole iron is close to the dipole iron, making full use of the edge field focusing effect of the dipole iron and obtaining an ideal phase shift that meets the homogenization requirements.

[0099] Traditional methods, such as Figure 1g shown, use a dipole iron for single-direction beam deflection. When designing a symmetric bent beam beamline in this embodiment, it is required that the beam can be led out from two symmetric directions after entering the dipole iron. Therefore, a new type of dipole iron is adopted. As Figure 1f shown, the beam enters the dipole iron vertically. By adjusting the magnetic field direction, it is possible to control the direction in which the beam deflects. And in order to achieve a better homogenization effect, when designing a symmetric bent beam beamline, the exit edge angle E2 can be modified to control the focusing strength of the dipole iron edge field in the X and Y directions. E2 is the angle between the beam direction at the beam exit side and the exit side of the dipole iron. Adjusting the angle E2 can only change the shape of the beam exit side of the dipole iron, that is, Figure 1g a pair of diagonal lines in the symmetric direction of the beam exit side of the dipole iron in. The inclination directions of the pair of diagonal lines in the symmetric direction are the respective bending directions of the beam at the exit side.

[0100] As Figure 1b shown, the beam matching mechanism includes a fluorescent target 1, a quadrupole magnet, and a guiding magnet; the fluorescent target 1 provides the initial state of the beam for the tester; the quadrupole magnet is used to form a large beam envelope in the Y or X direction at the position of the first quadruple-octupole iron 1, and the guiding magnet is used to align the beam center with the mechanical center of the beam pipe.

[0101] As Figure 1d 、 1eAs shown in the figure, the beam current matching and uniformity observation mechanism 1 on the first branch transmission line 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 uniformity. The fluorescent target 2 is used to observe the shape of the weak beam after uniformity. The double wire 1 is used to observe the shape of the strong beam after uniformity. The beam current matching and uniformity observation mechanism 2 on the second branch transmission line includes a guiding magnet 3, a Faraday cup 2, 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 uniformity. The fluorescent target 3 is used to observe the shape of the weak beam after uniformity. The double wire 2 is used to observe the shape of the strong beam after uniformity.

[0102] As Figure 4 shown, 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 the phase shift of the particles between the four-eight-pole composite iron 1 and the four-eight-pole composite iron 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

[0103] Supplementary Note 2:

[0104] The above-mentioned "phase shift of the particles between two four-eight-pole composite magnets and the target being respectively close to an integer multiple of 180 degrees (0, 1, 2, 3...)" but not equal to 180 degrees. The principle is shown in the following formula (1) and formula (2):

[0105]

[0106] In formula (1), since Csc[ux23] in the numerator = 1 / sin[ux23], when ux23 is close to 180, sin[ux23] tends to 0 and Csc[ux23] tends to infinity. Similarly, Csc[uy13] in the numerator of formula (2) = 1 / sin[uy13], when ux13 is close to 180, sin[ux13] tends to 0 and Csc[uy13] tends to infinity. Therefore, the phase shift of the particles between two four-eight-pole composite magnets and the target is respectively close but not equal to an integer multiple of 180 degrees (0, 1, 2, 3...).

[0107] As Figure 4As 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 good homogenization effect.

[0108] Furthermore, the expression of the magnet strength k at the quadruple-octupole composite magnet 1 and the quadruple-octupole composite magnet 2, or the magnet strength k at the quadruple-octupole composite magnet 1 and the quadruple-octupole composite magnet 3 is:

[0109]

[0110] 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 of the particle in the x direction between positions 0 and 2, and 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.

[0111] Supplementary Note 3

[0112] The derivation process of the above formula (1) and formula (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 iron on the beam homogenization. The parameters involved are ux02 (the phase shift of the particle in the x direction between positions 0 and 2), ux23 (the phase shift of the particle in the x direction between positions 2 and 3), uy01 (the phase shift of the particle in the x direction between positions 0 and 2), and uy13 (the phase shift of the particle in the x direction between positions 2 and 3). Using the same "high-order transport mapping" derivation method as in the reference, the expressions of the magnet strength k at the first quadruple-octupole composite magnet and the second quadruple-octupole composite magnet, namely formula (1) and formula (2), are obtained.

[0113] As Figure 5a shown, the composite magnet current control device includes: a coil current two-dimensional sampling point establishing module, an experimental measurement-based initial magnetic field gradient three-dimensional surface sample library establishing module, an interpolation-using magnetic field gradient three-dimensional surface sample library refinement module, an input field gradient corresponding field gradient current curve solving module, a four / eight-pole field gradient current curve intersection point solving module, and a four-pole / eight-pole coil current output module;

[0114] As Figure 5d shown, 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;

[0115] As Figure 5e shown, the experimental measurement-based initial magnetic field gradient three-dimensional surface sample library establishing module uses the current values in the two-dimensional data comparison table of the coil currents to perform magnetic field experimental measurements on the composite iron, so as to obtain the four- and eight-pole magnetic field gradient measurement values corresponding one-to-one to the two-dimensional current data comparison table, and thus 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;

[0116] As Figure 5f shown, the interpolation-using magnetic field gradient three-dimensional surface sample library refinement 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 a cubic spline function to increase the grid point density;

[0117] As Figure 5g 、 5h shown, the input field gradient corresponding field gradient current curve solving 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 after intersection, obtain two corresponding current curves; 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;

[0118] As Figure 5i shown, the four / eight-pole field gradient current curve intersection point solving 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 excitation current of the composite iron;

[0119] 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.

[0120] As Figure 5b , 5c shown, this quadrupole / octupole composite magnet has a total of eight pole heads. 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;

[0121] As Figure 5b , 5c shown, for the inner octupole magnetic field excitation coil, the current directions of two adjacent pole heads are opposite, that is, the octupole field coils are divided into two groups: pole heads 1, 3, 5, 7 and pole heads 2, 4, 6, 8. The excitation currents of the two groups are equal in magnitude but opposite in direction, thereby generating an octupole magnetic field;

[0122] As Figure 5b , 5c shown, for the outer quadrupole magnetic field excitation coil, the coils on two adjacent pole heads are in a group, divided into four groups, namely pole heads 1, 2; pole heads 3, 4; pole heads 5, 6; pole heads 7, 8; among them, the excitation currents of the two groups of quadrupole magnetic field coils of pole heads 1, 2 and symmetrically arranged pole heads 5, 6 are equal in magnitude and the same in direction, and the excitation currents of the two groups of coils of pole heads 3, 4 and symmetrically arranged pole heads 7, 8 are equal in magnitude and the same in direction. The current directions of the coils of pole heads 1, 2 and pole heads 3, 4 are opposite, and the directions of the coils of pole heads 5, 6 and pole heads 7, 8 are opposite, thereby generating a quadrupole magnetic field;

[0123] Embodiment 1

[0124] As Figure 7 shown, the present invention designs an ultra-short symmetric bending type beam homogenization transmission line. When the total length of the ultra-short symmetric bending type beam homogenization transmission line is 6.5 meters, the initial layout positions of the components that can achieve a better homogenization effect of 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 700 mm; the initial position of the guiding magnet 1 is 1100 mm; the initial position of the quadrupole / octupole composite iron (Q1) is 1600 mm, the initial position of the dipole iron is 2200 mm, and the initial positions of the quadrupole / octupole composite irons (Q2 / Q3) are 3500 mm; the initial positions of the guiding magnets 2 / 3 are 4200 mm; the initial positions of the Faraday cylinders 1 / 2 are 4800 mm; the initial positions of the fluorescent targets 2 / 3 are 5500 mm, and the initial positions of the double wires 1 / 2 are 6000 mm; the initial positions of the terminals 1 / 2 are 6500 mm.

[0125] Among them, the magnetic field component of the quadrupole magnet (Q0) is 6 (T / m); the quadrupole magnetic field component of the quadrupole-octupole combined magnet (Q1) is 2.6 (T / m), and the octupole magnetic field component is 3.5e3 (T / m 3 ), the quadrupole magnetic field component of the quadrupole-octupole combined magnet (Q2 / Q3) is 0.55 (T / m), and the octupole magnetic field component is 3e3 (T / m 3 ). The entrance edge angle of the dipole magnet is 0, the exit edge angle is 32°, and the beam is bent by 45°.

[0126] As Figure 1c shown, it is the comparison before and after the homogenization of the transmission line of the present invention. Figure 1c The left figure of is the screenshot of the beam with a Gaussian distribution before homogenization, that is, the beam cross-section diagram when the fluorescent target 1 is at the 100 mm position of the transmission line; Figure 1c The right figure of is the beam cross-section diagram after homogenization, that is, the beam cross-section diagram when the fluorescent target 2 / 3 is placed at the 5500 mm position of the transmission line. It can be seen from the figure that before homogenization, the distribution of particles on the beam cross-section is dense in the middle and sparse around, and after homogenization, the distribution of particles on the beam cross-section is uniform in the middle and around.

[0127] It should be emphasized that the above specific embodiments are only explanations of the present invention, and they are not limitations on the present invention. Those skilled in the art can make modifications to the above embodiments without creative contributions according to needs after reading this specification, 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 symmetric bending and transforming type beam current homogenization transmission line, characterized in that: The transmission line is a symmetrically bent beam homogenization transmission line that respectively includes two four-eight-stage composite irons and one common two-stage iron; the symmetrically bent beam homogenization transmission line that respectively includes two four-eight-stage composite irons and one common two-stage iron is composed of one common beam line and two branch beam lines; The following are successively arranged on the common beam line along the beam direction: an accelerator extraction port, a beam matching mechanism, a four-eight-stage composite iron 1, and a two-stage iron; the two branch beam lines are the first branch beam line and the second branch beam line; the following are successively arranged on the first branch beam line: a four-eight-stage composite iron 2, a beam matching and homogenization effect observation mechanism 1, and a terminal 1; the following are successively arranged on the second branch beam line: a four-eight-stage composite iron 3, a beam matching and homogenization effect observation mechanism 2, and a terminal 2; the common beam line and the first branch beam line form a first bent beam homogenization transmission line; the common beam line and the second branch beam line form a second bent beam homogenization transmission line; the first bent beam homogenization transmission line and the second bent beam homogenization transmission line operate at different times; The four-eight-stage composite irons 1, 2, and 3 of the first bent beam homogenization transmission line and the second bent beam homogenization transmission line 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 first bending and beam shaping beam homogenization transmission line at the quadruple-octupole magnet 1, the beam envelope function in the Y or X direction reaches a large value. At the quadruple-octupole magnet 2, the beam envelope function in the X or Y direction reaches a large value; the phase shift of the particles between the quadruple-octupole magnet 1 and the quadruple-octupole magnet 2 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; At the quadruple-octupole magnet 1 of the second bending and beam flattening transmission line, the beam envelope function in the Y or X direction reaches a maximum value. At the quadruple-octupole magnet 3, the beam envelope function in the X or Y direction reaches a maximum value. The phase shift of the particles between the quadruple-octupole magnet 1 and the quadruple-octupole magnet 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 magnets is close to the unit matrix; The bent beam homogenization transmission line based on this bent beam homogenization substructure uses the combined focusing effect of the four-eight-pole composite iron 1 and the two-pole iron to generate a beam waist in the Y direction near the four-eight-pole composite iron 2; the quadrupole fields of the two-pole iron and the four-eight-pole 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 the same; The four-eight-stage composite irons 1, 2, and 3 of the first bent beam homogenization transmission line and the second bent beam homogenization transmission line are 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 composite magnet main power supply to the four-eight-pole composite magnet; The beam matching mechanism on the common beam line is used to observe the initial state of the beam extracted from the accelerator, 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; The beam matching and homogenization effect observation mechanism 1 on the first branch beam line is used to align the beam center with the mechanical center of the beam pipe, measure the beam current intensity after being homogenized by the four-eight-stage composite irons 1 and 2, and observe the shapes of the weak beam and the strong beam after homogenization; The beam matching and homogenization effect observation mechanism 2 on the second branch beam line is used to align the beam center with the mechanical center of the beam pipe, measure the beam current intensity after being homogenized by the four-eight-stage composite irons 1 and 3, and observe the shapes of the weak beam and the strong beam after homogenization; The dipole magnet is a dipole magnet that satisfies the beam homogenization of symmetric bending type. The entrance side of the beam with symmetric bending of this dipole magnet is a straight edge that is symmetric up and down, and the exit side of the beam with symmetric bending is a bevel edge that is symmetric up and down. The inclination direction of the symmetric bevel edge is the direction of beam bending; the symmetric oblique lines up and down and the connection line from the center of the beam bending orbit to the beam at the exit of the dipole magnet form the dipole magnet exit edge angle; by changing the size of the dipole magnet exit edge angle, the focusing effect of the edge field of the dipole magnet is adjusted, and it is coordinated with the envelopes in the Y direction and the X direction of the quadrupole-octupole composite magnets on both sides of the dipole magnet, so as to obtain an ideal phase shift that meets the homogenization requirements.

2. The ultra-short symmetric bending and transforming beam current homogenization transmission line according to claim 1, wherein: The beam matching mechanism includes a fluorescent target 1, quadrupole magnets, and steering magnets; the fluorescent target 1 provides the initial state of the beam for the tester; the quadrupole magnets are used to form a large beam envelope in the Y direction or the X direction at the position of the quadrupole-octupole composite magnet 1, and the steering magnets are used to align the beam center and the mechanical center of the beam pipe.

3. The ultra-short symmetric bending type beam current homogenization transmission line according to claim 1, wherein: The beam matching and homogenization effect observation mechanism 1 on the first branch beam line includes a steering magnet 2, a Faraday cup 1, a fluorescent target 2, and a double wire 1. The steering magnet 2 is used to align the beam center and the mechanical center of the beam pipe; the Faraday cup 1 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; 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 on the second branch beam line includes a steering magnet 3, a Faraday cup 2, a fluorescent target 3, and a double wire 2. The steering magnet 3 is used to align the beam center and the mechanical center of the beam pipe; the Faraday cup 2 is used to measure the beam 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 symmetric bending type beam current homogenization 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 180 degrees, and the value generally is less than ±15 degrees.

5. The ultra-short symmetric bending type beam current homogenization transmission line according to claim 1, characterized in that: The transfer matrix between the two octupole magnetic fields is close to the unit matrix, that is, the phase shift between the front and rear quadrupole-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 obtain a better homogenization effect.

6. The ultra-short symmetric bending type beam current homogenization transmission line according to claim 1, characterized in that: The expression of the magnet strength k at the quadrupole-octupole composite magnet 1 and the quadrupole-octupole composite magnet 2, or the magnet strength k at the quadrupole-octupole composite magnet 1 and the quadrupole-octupole composite magnet 3 is: Let: The starting point of the transport line is denoted as 0, the position of the first quadrupole-octupole magnet is denoted as 1, the position of the second quadrupole-octupole magnet is denoted as 2, and the position at the end, that is, the position of the target, is 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, and 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; uy 7. The ultra-short symmetric bending type beam current 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 preliminarily 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 four / eight-pole field gradient current curves, and a module for outputting the four-pole / eight-pole 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 the octupole iron; The module for experimentally measuring and preliminarily 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 four- and eight-pole magnetic field gradient measurement values corresponding one-to-one to the two-dimensional current data comparison table, and thus obtain 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; The module for using interpolation to refine the three-dimensional surface sample library of magnetic field gradients 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; The module for solving the corresponding field gradient current curve for the input field gradient 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 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; The module for solving the intersection point of the four / eight-pole 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; The module for outputting the four-pole / eight-pole coil current outputs the four-pole field coil current and the 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.

8. The ultra-short symmetric bending type beam current homogenization transmission line according to claim 1, wherein: This four-octupole composite magnet has a total of eight pole heads. Each pole head 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 heads are opposite, that is, the octupole field coils are divided into two groups: pole heads 1, 3, 5, 7 and pole heads 2, 4, 6, 8. The excitation currents of the two are equal in magnitude but opposite in direction, thereby generating an octupole magnetic field; For the quadrupole magnetic field excitation coil of the outer layer, the coils on two adjacent pole heads form a group, and there are 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, and 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 pole heads 3 and 4, and the directions of the coils of pole heads 5 and 6 are opposite to those of pole heads 7 and 8, thereby generating a quadrupole magnetic field.

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