Ultra-short bending type beam homogenization transmission line

Abstract

The application discloses a kind of ultra-short bending type beam homogenization transmission lines, its characteristics are: the transmission line is the ultra-short bending type strong current homogenization transmission line containing two four-eight level composite iron and a two level iron;The ultra-short bending type strong current homogenization transmission line is the ultra-short bending type strong current homogenization transmission line A arranged along the beam direction, or the ultra-short bending type strong current homogenization transmission line B arranged along the beam direction: the ultra-short bending type strong current homogenization transmission line A is sequentially provided with: accelerator exit, beam matching mechanism, four-eight level composite iron 1, two level iron, four-eight level composite iron 2, beam matching and homogenization effect observation mechanism 1, terminal 1 along the beam extraction direction;The four-eight pole composite iron of the beam line can simultaneously realize the focusing and homogenization effect to beam envelope, and the composite iron is installed on the beam transmission line, which can reduce the number of transmission elements, shorten the length of transmission line, and reduce the engineering cost of beam transport line.

Description

Technical Field

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

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

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

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

[0005] One of the challenges in homogenizing a Gaussian-distributed beam using octagonal magnets lies in the fact that the same octagonal magnet, when installed at different positions on the beam transmission line, will have different effects. Only when the octagonal magnet is installed at a location with a large beam envelope can it provide the strongest homogenization effect. However, in existing technologies, the areas with the largest beam envelope are usually occupied by quadrupole magnetic fields: such as... Figure 6 As shown, the transmission line in the prior art is arranged in the order of quadrupole 1, octupole 1, quadrupole 2, and octupole 2. Since the octupole must be focused before homogenization (the purpose of focusing is to allow the beam to pass through the circular hole in the center of the octupole without hitting the octupole), in order to ensure focusing, the positions of octupole 1 and octupole 2 must first be selected at the waist position of the X-direction envelope and the waist position of the Y-direction envelope. However, since the Y-direction envelope of quadrupole 1 at the waist position of the X-direction envelope is small, and the X-direction envelope of quadrupole 2 at the waist position of the Y-direction envelope is small, at octupole 1, although the position of octupole 1 at the waist position of the X-direction is guaranteed, the Y-direction envelope at that position is small. Similarly, at octupole 2, although the position of octupole 2 at the waist position of the Y-direction is guaranteed, the X-direction envelope at that position is small. In summary, according to the traditional method, the beam envelope is significantly reduced after the particles pass through quadrupole 1 and quadrupole 2, so the full effect of octupole 1 and octupole 2 cannot be achieved.

[0006] The second difficulty of using octupole magnets to homogenize the Gaussian distribution of the beam is that the field strength K of the octupole magnet is very high because the beam envelope at the positions of the octupole magnet 1 and the octupole magnet 2 is small, and the excessively high magnetic field strength is difficult to realize in engineering and has a high cost.

[0007] The third difficulty of using octupole magnets to homogenize the Gaussian distribution of the beam is that the positions and phases of the octupole magnets have strict requirements if the octupole magnets are used to achieve a better beam homogenization effect, and the length of the transmission line often needs to be tens of meters to meet the requirements. If the transmission line is too long, the surrounding shielding civil engineering is more expensive, the land occupation is large, and the cost is high. SUMMARY

[0008] The present application aims at the problems existing in the prior art, and provides an ultra-short bending type beam homogenization transmission line. The first purpose is to solve the problem that the eight-pole magnet cannot fully play a role because the place with the largest envelope is usually occupied by the quadrupole magnetic field in the prior art. The second purpose is to solve the problem that the field strength of the eight-pole magnet is very high because the beam envelope at the positions of the octupole magnet 1 and the octupole magnet 2 is small, and the excessively high magnetic field strength is difficult to realize in engineering and has a high cost. The third purpose is to solve the problem that the length of the transmission line is too long, the surrounding shielding civil engineering is more expensive, the land occupation is large, and the cost is high.

[0009] The present application aims at the problems existing in the prior art, and provides an ultra-short bending type beam homogenization transmission line. The first purpose is to solve the problem that the eight-pole magnet cannot fully play a role because the place with the largest envelope is usually occupied by the quadrupole magnetic field in the prior art. The second purpose is to solve the problem that the field strength of the eight-pole magnet is very high because the beam envelope at the positions of the octupole magnet 1 and the octupole magnet 2 is small, and the excessively high magnetic field strength is difficult to realize in engineering and has a high cost. The third purpose is to solve the problem that the length of the transmission line is too long, the surrounding shielding civil engineering is more expensive, the land occupation is large, and the cost is high.

[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 comprising two four-eight-level composite magnets and one two-level magnet; 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 sequentially provided with an accelerator exit, a beam matching mechanism, a four-eight-level composite magnet 1, a two-level magnet, a four-eight-level composite magnet 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 sequentially provided with an accelerator exit, a beam matching mechanism, a four-eight-level composite magnet 1, a two-level magnet, a four-eight-level composite magnet 3, a beam matching and homogenization effect observation mechanism 2, and a terminal 2 along the beam extraction direction.

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

[0012] The super-short bending type beam homogenization transmission line uses the focusing effect of the four-octupole composite iron 1 and the dipole iron to superimpose to generate the Y direction beam waist near the four-octupole composite iron 2; the quadrupole field of the dipole iron and the four-octupole composite iron 2 is superimposed to generate the X direction envelope size on the target, so that the X direction and the Y direction envelope size are consistent.

[0013] The four-octupole composite iron 1, the four-octupole composite iron 2 or the four-octupole composite iron 3 is based on a four-octupole composite magnet system, which includes a composite magnet current control device, a composite magnet main power supply and a four-octupole composite magnet; the composite magnet current control device is used to control the quadrupole field coil current output and the octupole field coil current output of the four-octupole composite magnet of the composite magnet main power supply;

[0014] The beam matching mechanism is used to observe the initial state of the beam extracted from the accelerator, and adjust the X or Y direction envelope size of the beam according to the initial state, and make the beam center and the mechanical center of the beam pipe centered;

[0015] 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 weak beam shape and the strong beam shape after homogenization by the four-octupole composite iron 1 and the four-octupole composite iron 2.

[0016] Further, the beam matching mechanism includes a fluorescent target 1, a quadrupole magnet and a guide magnet; the fluorescent target 1 provides the initial position of the beam for the tester; the quadrupole magnet is used to provide the beam envelope in the opposite direction for the four-octupole composite iron 1; the guide magnet is used to adjust the eccentricity of the beam.

[0017] Further, the beam matching and uniformity effect observation mechanism 1 comprises a guiding magnet 2, a Faraday cylinder 1, a fluorescent target 2, and a double wire 1; the guiding magnet 2 is used to center the beam center and the mechanical center of the beam pipe; the Faraday cylinder 1 is used to measure the beam current after uniformization; the fluorescent target 2 is used to observe the shape of the weak beam after uniformization; and the double wire 1 is used to observe the shape of the strong beam after uniformization; the beam matching and uniformity effect observation mechanism 2 comprises a guiding magnet 3, a Faraday cylinder 3, a fluorescent target 3, and a double wire 2; the guiding magnet 3 is used to center the beam center and the mechanical center of the beam pipe; the Faraday cylinder 2 is used to measure the beam current after uniformization; the fluorescent target 3 is used to observe the shape of the weak beam after uniformization; and the double wire 2 is used to observe the shape of the strong beam after uniformization.

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

[0019] Further, the transmission matrix between the two octupole magnetic fields is close to the unit matrix, that is, the phase shift between the front and rear four-octupole composite magnets is controlled within 30 degrees, which can greatly avoid the high-order nonlinear effects caused by the coupling of the two octupole magnets, and better uniformization effect can be obtained.

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

[0021]

[0022] Let the starting point of the transport line be 0, the position of the first four-octupole magnet be 1, the position of the second four-octupole magnet be 2, and the position of the terminal, that is, the position of the target, be 3; ux02 in the above formula (1) represents the phase shift of the particles in the x direction between positions 0 and 2, and ux23 represents the phase shift of the particles 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 particles in the y direction between 0 and 1; uy13 represents the phase shift of the particles in the y direction between 1 and 3; and βy1 represents the envelope function in the y direction at position 1.

[0023] Further, the composite magnet current control device comprises: a coil current two-dimensional sampling point establishing module, an experimental measurement preliminary magnetic field gradient three-dimensional curved surface sample library establishing module, an interpolation fine magnetic field gradient three-dimensional curved surface sample library using 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 an output four / eight pole coil current module.

[0024] The coil current two-dimensional sampling point establishing module is used to establish a four-pole iron and eight-pole iron coil current two-dimensional data reference table.

[0025] The experimental measurement preliminary magnetic field gradient three-dimensional curved surface sample library establishing module is used to perform magnetic field experimental measurement on the composite iron by using the current value of the coil current two-dimensional data reference table, so as to obtain four / eight pole magnetic field gradient measurement values corresponding to the two-dimensional current data reference table, thereby obtaining a magnetic field gradient three-dimensional curved surface sample database; the magnetic field gradient three-dimensional curved surface sample database comprises a four-pole field magnetic field gradient three-dimensional curved surface sample database and an eight-pole field magnetic field gradient three-dimensional curved surface sample database.

[0026] The interpolation fine magnetic field gradient three-dimensional curved surface sample library using module is used to perform two-dimensional interpolation on the four-pole field magnetic field gradient three-dimensional curved surface sample database and the eight-pole field magnetic field gradient three-dimensional curved surface sample database by using a cubic spline function, and to encrypt the grid point density.

[0027] The input field gradient corresponding field gradient current curve solving module is used to intersect the input four-pole field gradient and eight-pole field gradient with the magnetic field gradient curved surface of the three-dimensional sample database, and to obtain two corresponding current curves after the intersection; specifically, a four-pole field magnetic field gradient plane is selected, the plane intersects the curved surface of the four-pole field magnetic field gradient three-dimensional curved surface sample database, and a current curve satisfying the four-pole field gradient is obtained; an eight-pole field magnetic field gradient plane is selected, the plane intersects the curved surface of the eight-pole field magnetic field gradient three-dimensional curved surface sample database, and a current curve satisfying the eight-pole field gradient is obtained.

[0028] The four / eight pole field gradient current curve intersection point solving module is used to obtain the intersection point of the current curve satisfying the four-pole field gradient and the current curve satisfying the eight-pole field gradient, and to use the intersection point as the solution of the composite iron excitation current.

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

[0030] Further, the four / eight pole composite magnet has a total of eight pole heads, and each pole head is provided with inner and outer two layers of current coils along the radial direction near the large radius; the inner layer coil is an eight-pole magnetic field excitation coil, and the outer layer coil is a four-pole magnetic field excitation coil.

[0031] The octupole magnetic field excitation coil of the inner layer, adjacent two pole heads have opposite current directions, that is, the octupole field coil is divided into two groups of 1, 3, 5, 7 pole heads and 2, 4, 6, 8 pole heads, the excitation currents of the two groups are equal in size but opposite in direction, thereby generating an octupole magnetic field;

[0032] The quadrupole magnetic field excitation coil of the outer layer, the coils on the adjacent two pole heads form a group and are divided into four groups, that is, 1, 2 pole heads, 3, 4 pole heads, 5, 6 pole heads and 7, 8 pole heads; wherein, the excitation currents of the two groups of quadrupole magnetic field coils of 1, 2 pole heads and symmetrically arranged 5, 6 pole heads are consistent in size and direction, the excitation currents of the two groups of 3, 4 pole heads and symmetrically arranged 7, 8 pole heads are consistent in size and direction, the current directions of the 1, 2 pole heads and the 3, 4 pole heads are opposite, and the current directions of the 5, 6 pole heads and the 7, 8 pole heads are opposite, thereby generating a quadrupole magnetic field.

[0033] Advantages and effects of the present application

[0034] 1. The super-short bending type beam homogenization transmission line comprising two four-octupole composite iron blocks and one two-level iron block adopts the method of generating a large envelope by four-octupole composite iron and four-level iron, thereby solving the problem that in the prior art, when separate four-pole iron and eight-level iron are used, the place with the largest envelope is usually occupied by the four-pole magnetic field, and the eight-pole iron cannot fully play its role.

[0035] 2. The super-short bending type beam homogenization transmission line comprising two four-octupole composite iron blocks and one two-level iron block, since the four-octupole composite iron is located at the place with the largest envelope, the requirement for the field strength K value of the four-octupole composite iron is reduced, thereby solving the problem that in the prior art, when separate four-pole iron and eight-level iron are used, the field strength requirement for the eight-level magnet is very high due to the small beam envelope at the positions of the eight-pole iron 1 and the eight-pole iron 2, and the excessively high magnetic field strength is too high in cost and difficult to realize in engineering.

[0036] 3. The super-short bending type beam homogenization transmission line comprising two four-octupole composite iron blocks and one two-level iron block simultaneously generates a quadrupole magnetic field and an octupole magnetic field in the aperture of the four-octupole composite iron, simultaneously realizes the focusing and homogenization of the beam envelope, and the composite iron installed on the beam transmission line can reduce the number of transmission elements and shorten the length of the transmission line, thereby solving the problem that in the prior art, when separate four-pole iron and eight-level iron are used, the excessively long length of the transmission line leads to the increasing cost of the surrounding shielding civil engineering, large occupied area and high cost.

[0037] 4. The super-short bending type beam homogenization transmission line comprising two four-octupole composite iron blocks and one two-level iron block limits the phase movement of particles between the two four-octupole composite magnets and the target Respectively close to 180 degrees integer multiple (0, 1, 2, 3…), but not equal to 180 degrees integer multiple (0, 1, 2, 3…), so that the required magnetic field strength k1, k2 value at the first block four eight pole composite magnet, the second block four eight pole composite magnet is smaller, which is conducive to reducing the difficulty and cost of magnet manufacturing.

[0038] 5, the present application contains two blocks of four eight level composite iron and a block of two level iron, the transmission matrix between the two eight pole magnetic field is close to the unit matrix, namely the phase shift between the front and rear two four eight pole composite magnets is controlled within 30 degrees, which can greatly avoid the high-order nonlinear effect caused by the coupling of the two eight pole magnets, and better uniformization effect can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1a It is a schematic diagram of the super short bending type beam current homogenization transmission line A of the present application;

[0040] Figure 1b It is a schematic diagram of the super short bending type beam current homogenization transmission line B of the present application;

[0041] Figure 1c It is a schematic diagram of the transmission line beam matching mechanism of the present application;

[0042] Figure 1d It is a schematic diagram of the particle distribution state before and after the transmission line homogenization of the present application;

[0043] Figure 1e It is a schematic diagram of the transmission line beam matching and homogenization effect observation mechanism 1 of the present application;

[0044] Figure 1f It is a schematic diagram of the transmission line beam matching and homogenization effect observation mechanism 2 of the present application;

[0045] Figure 2 It is a schematic diagram of the maximum envelope position of four eight pole composite iron 1 and 2 respectively;

[0046] Figure 3 It is a schematic diagram of the phase difference between the two four eight pole composite iron and the phase difference between the two four eight pole composite iron and the target point respectively;

[0047] Figure 4 It is a schematic diagram of the representative meaning of 0, 1, 2, 3 four points involved in formula (1) and formula (2);

[0048] Figure 5a It is a schematic diagram of the four / eight pole composite iron system for beam control of the present application;

[0049] Figure 5b It is a new four / eight pole composite iron model of the present application.

[0050] Figure 5c Four / eight-pole composite magnet coil arrangement and current direction.

[0051] Figure 5d Current value diagram of two groups of coils in the magnetic field measurement of the application;

[0052] Figure 5e Four / eight-pole magnetic field gradient diagram corresponding to different currents in the experimental measurement of the application;

[0053] Figure 5f Grid point density diagram of two-dimensional interpolation using cubic spline function in the application;

[0054] Figure 5g Magnetic field gradient plane selected in the application intersects with the magnetic field gradient surface of the three-dimensional sample database;

[0055] Figure 5h Current curve diagram corresponding to the four / eight-pole field selected in the application;

[0056] Figure 5i Solution diagram of composite iron excitation current in the application;

[0057] Figure 6 Existing eight-pole iron in a small envelope position diagram.

[0058] Figure 7 An embodiment of the application for the uniformization transmission line of the ultra-short bending beam. DETAILED DESCRIPTION

[0059] Design principle of the application

[0060] 1. Innovation of the application

[0061] One of the innovations is to invent a four / eight-pole composite iron. Figure 5a 、 5b , the four / eight-pole composite iron shown in 5c replaces the four-pole iron and eight-pole iron of discrete elements shown in 5b. Figure 6 One of the effects is that the four / eight-pole composite iron generates a four-pole magnetic field and an eight-pole magnetic field in the aperture, and the effect is shown in 5d: the four-pole iron and the eight-pole iron share the Y direction and the X direction large envelope position. Figure 2 The reason why the Y direction or X direction large envelope position can be shared is that the four / eight-pole composite iron 1 and the four-pole iron in front of it share the Y direction large envelope; the four / eight-pole composite iron 2 and the four-pole iron in front of the four / eight-pole composite iron 1 share the X direction large envelope. Because the eight-pole iron in the four / eight-pole composite iron 1 and the four / eight-pole composite iron 2 is arranged at the large envelope position, a better beam uniformization effect can be achieved, that is, the focusing and uniformization of the beam envelope can be realized at the same time. Compared withFigure 6 The prior art of the present application, because the prior art is four-pole iron, eight-pole iron is arranged separately, the eight-pole iron itself cannot change the envelope like the four-pole iron, that is, it cannot coexist with the previous four-pole iron to form a large envelope, therefore, the envelope of the eight-pole iron arranged separately in the Y direction and the X direction is relatively small, so the homogenization effect is not good. Effect two: the installation of the composite iron on the beam transport line can reduce the number of transmission elements, shorten the length of the transmission line, and reduce the engineering cost of the beam transport line; the reduction of the number of transmission elements not only saves the four-pole iron, but also saves the multiple components needed to achieve the same effect of homogenization on the transmission line.

[0062] The second innovation is that a four / eight-pole composite magnet current control system as shown in Figure 5a and a four / eight-pole composite iron excitation current design method are invented. 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 groups of coils of the four / eight-pole composite iron. This coupling relationship means that changing the current size of the four-pole field or eight-pole field coil will simultaneously change the original four-pole magnetic field gradient and eight-pole magnetic field gradient of the magnet. Therefore, the one-to-one adjustment strategy of a single type of magnet current magnetic field gradient will no longer be applicable. In the composite magnet, if the four-pole field coil current size is adjusted first to adjust the four-pole magnetic field gradient to meet the use requirements, and then the eight-pole field coil current size is adjusted, the eight-pole field coil current will change the previously adjusted four-pole magnetic field gradient, making it no longer meet the use requirements. Second, the four / eight-pole composite magnet current control system and the four / eight-pole composite iron excitation current design method are innovatively designed, which solves the problem of the coupling relationship between the multi-pole magnetic fields generated by the two groups of coils of the four / eight-pole composite iron, and finds the intersection point of the current that simultaneously satisfies the four-pole field gradient and the eight-pole field gradient. The system is as shown in Figure 5a , which 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 corresponding field gradient based on field gradient input, a current curve intersection point module based on field gradient solving, and an output four-pole / eight-pole coil current module.

[0063] The four / eight-pole composite iron excitation current design method is as follows:

[0064] Step one, as shown in Figure 5d , a four-pole iron and eight-pole iron coil current two-dimensional data comparison table is established; the coil current two-dimensional data comparison table is based on the coil current two-dimensional data comparison table of the four / eight-pole composite iron; the above-mentioned coil current two-dimensional data comparison table is as shown in Figure 5d , the abscissa is the four-pole coil current, and the ordinate is the four-pole coil current.

[0065] Step Two, as follows Figure 5e As shown, experimental measurements were performed to obtain the four-pole and octole magnetic field gradient measurement values ​​that correspond one-to-one with the two-dimensional current data comparison table, thereby obtaining a three-dimensional surface sample database of magnetic field gradients; the above three-dimensional surface sample database of magnetic field gradients includes a three-dimensional surface sample database of four-pole field magnetic field gradients and a three-dimensional surface sample database of octole field magnetic field gradients.

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

[0067] Step 3, as follows Figure 5f As shown, cubic spline functions are used to perform two-dimensional interpolation on the three-dimensional surface sample database of the quadrupole magnetic field gradient and the octupole magnetic field gradient, thereby increasing the density of the grid points.

[0068] The effect of the above-mentioned encrypted grid point density is as follows: Figure 5f As shown, the grid density on the X, Y, and Z axes has increased.

[0069] Step 4, as follows Figure 5g As shown, a quadrupole magnetic field gradient plane is selected, which intersects with the surface of the quadrupole magnetic field gradient three-dimensional surface sample database to obtain a current curve that satisfies the four-level field gradient; an octupole magnetic field gradient plane is selected, which intersects with the surface of the octupole magnetic field gradient three-dimensional surface sample database to obtain a current curve that satisfies the eight-level field gradient.

[0070] Step 5, as follows Figure 5h As shown, the current curves satisfying the fourth-order field gradient and the eighth-order field gradient are obtained in the two-dimensional data grid plane of the coil current, and the intersection point of the two current curves is finally determined.

[0071] Step Six, as Figure 5i As shown, the intersection point is used as the solution for the excitation current of the composite iron.

[0072] The third innovation lies in the invention of an ultra-short, curved beam homogenization transmission line. For example... Figure 1a , 1b As shown, the ultra-short bending beam homogenization transmission line uses two octet composite iron pieces and a diode in between on the transmission line. The diode is used to bend the direction of the beam; as... Figure 2As shown, the innovation lies in that the super-short bending type beam homogenization transmission line uses the focusing effect of the four-octupole composite iron 1 and the dipole iron to superimpose the Y direction beam waist near the four-octupole composite iron 2; and uses the four-pole field superposition of the dipole iron and the four-octupole composite iron 2 to generate the X direction envelope size on the target, so that the envelope sizes in the X direction and the Y direction are consistent. Specifically, at the current intersection point of the four-octupole composite iron 1, the four-pole iron current of the four-octupole composite iron 1 is appropriately reduced, and the edge field focusing effect of the entrance of the dipole iron behind the four-octupole composite iron 1 and the four-pole iron focusing effect of the four-octupole composite iron 1 itself are superimposed to generate the Y direction waist at the four-octupole composite iron 2. At the current intersection point of the four-octupole composite iron 2, the four-pole iron current of the four-octupole composite iron 2 is appropriately reduced, and the edge field focusing effect of the exit of the dipole iron behind the four-octupole composite iron 1 and the four-pole iron focusing effect of the four-octupole composite iron 2 itself are superimposed to generate the X direction envelope size on the target (terminal 1 or terminal), so that the envelope sizes in the X direction and the Y direction are consistent.

[0073] The fourth innovation lies in that a balance point is found among the transmission line homogenization, the avoidance of the nonlinear effects caused by coupling, and the shortening of the transmission line. As shown in Figure 2 The homogenization effect of the super-short bending type beam homogenization transmission line is obvious, and the three innovations are indispensable and support each other to achieve the ideal homogenization effect.

[0074] The first aspect is to use the guarantee of homogenization as a premise, specifically, two four-octupole composite irons are used on the transmission line, the four-pole iron in front of the four-octupole composite iron 1 and the four-pole iron of the four-octupole composite iron 1 itself generate the large envelope in the Y direction at the four-octupole composite iron 1, and the four-pole iron of the four-octupole composite iron 1 in front of the four-octupole composite iron 2 and the four-pole iron of the four-octupole composite iron 2 itself generate the large envelope in the X direction at the four-octupole composite iron 2;

[0075] The second aspect is to solve the problem of optimizing the homogenization effect, specifically as shown in Figure 3 The phase shift between the four-octupole composite magnet 1 and the target is close to an integer multiple (0, 1, 2, 3…) of 180 degrees, and the phase shift between the four-octupole composite magnet 2 and the target is close to an integer multiple of 0 degrees. When close to the 180 degrees and close to the 0 degrees, the homogenization effect is the best.

[0076] ​Third aspect: to avoid the nonlinear effect caused by coupling under the premise of ensuring homogenization. The nonlinear effect caused by coupling occurs when the two four-octupole compound iron are used together and not handled properly. When the nonlinear effect caused by coupling occurs, the amplitude of the particles increases, causing particle loss, which reduces the homogenization effect. Therefore, to avoid the nonlinear effect caused by coupling, the transmission matrix between the two octupole magnetic fields of the two four-octupole compound iron is close to the unit matrix. As shown in Figure 3 、 Figure 4 , the phase difference between the first four-octupole compound iron (1) and the second four-octupole compound iron (2) is close to 0 degrees and less than 30 degrees. At this time, the required octupole magnet magnetic field strength is smaller, and the nonlinear effect caused by coupling is smaller, making the homogenization better. The difference between the present application and the prior art is that the transmission matrix between the two octupole magnetic fields of the prior art is "equal to the unit matrix" rather than "close to the unit matrix", and the transmission matrix between the two octupole magnetic fields of the present application is "close to the unit matrix" rather than "equal to the unit matrix", that is, the phase difference between the first four-octupole compound iron (1) and the second four-octupole compound iron (2) is close to 0 degrees rather than equal to 0 degrees, less than 30 degrees rather than equal to 30 degrees. The meaning of "close to" rather than "equal to" in the present application is to shorten the transmission line. If the method of "equal to the unit matrix" is used, many components need to be added to the transmission line, and the transmission line is very long with the increase of components. The present application adopts the method of "enough for the time being" in the problem of "avoiding the nonlinear effect caused by coupling": when the phase difference between the first four-octupole compound iron (1) and the second four-octupole compound iron (2) is close to 0 degrees and less than 30 degrees, the length of the transmission line can be effectively shortened, and the requirement of "avoiding the nonlinear effect caused by coupling" can be met. A balance point is found among the transmission line homogenization, the avoidance of the nonlinear effect caused by coupling, and the shortening of the transmission line.

[0077] Based on the above invention principle, the present application designs an ultra-short bending type beam homogenization transmission line, as shown in Figure 1a 、 1bAs shown, the transmission line is characterized in that: the transmission line is an ultra-short bending transmission line for beam homogenization containing two four-eight-level composite iron and one two-level iron; the ultra-short bending transmission line for beam homogenization is an ultra-short bending transmission line for beam homogenization A arranged along the beam direction, or an ultra-short bending transmission line for beam homogenization B arranged along the beam direction; the ultra-short bending transmission line for beam homogenization A is sequentially provided with: an accelerator exit, a beam matching mechanism, four-eight-level composite iron 1, two-level iron, four-eight-level 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 transmission line for beam homogenization B is sequentially provided with: an accelerator exit, a beam matching mechanism, four-eight-level composite iron 1, two-level iron, four-eight-level composite iron 3, a beam matching and homogenization effect observation mechanism 2, and a terminal 2 along the beam extraction direction;

[0078] As shown in Figure 1a , 1b , the four-eight-level composite iron 1 and the four-eight-level composite iron 2, or the four-eight-level composite iron 1 and the four-eight-level composite iron 3 simultaneously generate a four-pole magnetic field and an eight-pole magnetic field, so that the functions of four-pole iron and eight-pole iron can be realized simultaneously by installing only one transmission element;

[0079] As shown in Figure 2 , at the four-eight-level composite iron 1, the Y-direction or X-direction beam envelope function reaches a large value, at the four-eight-level composite iron 2 or the four-eight-level composite iron 3, the X-direction or Y-direction beam envelope function reaches a large value; the phase shift of the particles between the four-eight-level composite iron 1 and the four-eight-level composite iron 2 and the target, or between the four-eight-level composite iron 1 and the four-eight-level composite iron 3 and the target is close to an integer multiple (0, 1, 2, 3…) of 180 degrees, respectively; the transmission matrix between the two eight-pole 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 close to an integer multiple (0, 1, 2, 3…) of 180 degrees, respectively" but is not equal to 180 degrees, and the principle is shown in the following formula (1) and formula (2):

[0082]

[0083] In formula (1), because of the molecule Csc[ux23]=1 / sin[ux23], when ux23 approaches 180, sin[ux23] tends to 0, Csc[ux23] tends to infinity; similarly, the molecule Csc[uy13]=1 / sin[uy13] of formula (2), when ux13 approaches 180, sin[ux13] tends to 0, Csc[uy13] tends to infinity; therefore, the phase shift of the particle between the two four-octupole composite magnets and the target Respectively close to but not equal to 180 degrees integer multiples (0, 1, 2, 3…).

[0084] The super-short bending beam current homogenization transmission line uses the focusing effect of the four-octupole composite iron 1 and the dipole iron to superimpose to generate the Y-direction beam waist near the four-octupole composite iron 2; the four-pole field of the dipole iron and the four-octupole composite iron 2 is superimposed to generate the X-direction envelope size on the target, so that the X-direction and Y-direction envelope sizes are consistent.

[0085] As shown in Figure 5a , the four-octupole composite iron 1, the four-octupole composite iron 2 or the four-octupole composite iron 3 are based on a four-octupole composite magnet system, which includes a composite magnet current control device, a composite magnet main power supply and a four-octupole composite magnet; the composite magnet current control device is used to control the four-pole field coil current output and the eight-pole field coil current output of the four-octupole composite magnet by the composite magnet main power supply;

[0086] As shown in Figure 1c , 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 X or Y direction of the beam according to the initial state, and make the beam center and the mechanical center of the beam pipe centered;

[0087] As shown in Figure 1e , 1f , 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, weak beam shape and strong beam shape after homogenization by the four-octupole composite iron 1 and the four-octupole composite iron 2.

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

[0089] As shown in Figure 1e , 1fAs shown, the beam matching and homogenization effect observation mechanism 1 includes a guide magnet 2, a Faraday cylinder 1, a fluorescent target 2, and a dual-wire 1. The guide magnet 2 is used to align the beam center with the mechanical center of the beam channel. The Faraday cylinder 1 is used to measure the beam intensity after homogenization, and the fluorescent target 2 is used to observe the shape of the weak beam after homogenization. The dual-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 guide magnet 3, a Faraday cylinder 3, a fluorescent target 3, and a dual-wire 2. The guide magnet 3 is used to align the beam center with the mechanical center of the beam channel. The Faraday cylinder 2 is used to measure the beam intensity after homogenization, and the fluorescent target 3 is used to observe the shape of the weak beam after homogenization. The dual-wire 2 is used to observe the shape of the strong beam after homogenization.

[0090] like Figure 3 As shown, the phase shift of the particle between the target and the 4 / 8 composite iron 1 and 4 / 8 composite iron 2. Or the phase shift of particles between the target and the 4 / 8 composite iron 1 and 4 / 8 composite iron 3. Multiples close to 180 degrees refer to multiples that are close to but not equal to 180 degrees: Let... for The remainder after 180 degrees, The value is generally less than ±15 degrees.

[0091] like Figure 3 As shown, the transmission matrix between the two octagonal magnetic fields is close to the identity matrix, that is, the phase shift between the two four-octagonal composite magnets is controlled within a range of 30 degrees. This 30-degree range can greatly avoid the high-order nonlinear effects caused by the coupling of the two octagonal magnets and can achieve a better homogenization effect.

[0092] The expression for the magnetic strength k at points 1 and 2 of the 48-grade composite iron, or at points 3 of the 48-grade composite iron, is as follows:

[0093]

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

[0095] Supplementary note 2

[0096] The derivation process of the above formula (1) 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 of octupole magnetic field strength in a single direction is given. The formula only considers a block of octupole magnet and the transmission section after it. In order to more accurately describe the relationship between the octupole magnetic field strength and the transmission line design, we extend the formula to consider the influence of the matching section from the accelerator outlet to the octupole iron on the beam homogenization, involving the parameters ux02 (the phase shift in the x direction between positions 0 and 2), ux23 (the phase shift in the x direction between positions 2 and 3), uy01 (the phase shift in the x direction between positions 0 and 2), and uy13 (the phase shift in the x direction between positions 2 and 3). Using the same "high-order transmission mapping" derivation method as the reference, the expressions of the magnetic field strength k at the first and second four-octupole composite magnets are obtained as formula (1) and formula (2).

[0097] As shown in Figure 5a , the composite magnet current control device comprises: a two-dimensional sampling point module for establishing coil current, an experimental measurement preliminary establishment of magnetic field gradient three-dimensional curved surface sample library module, an interpolation refinement of magnetic field gradient three-dimensional curved surface sample library module, an input field gradient solving corresponding field gradient current curve module, a four / eight-pole field gradient current curve intersection point solving module, and an output four-pole / eight-pole coil current module.

[0098] As shown in Figure 5d , the two-dimensional sampling point module for establishing coil current is used to establish a two-dimensional data table of coil current for four-pole iron and eight-pole iron.

[0099] As shown in Figure 5e , the experimental measurement preliminary establishment of magnetic field gradient three-dimensional curved surface sample library module is used to perform magnetic field experimental measurement on the composite iron using the current values of the two-dimensional data table of coil current, so as to obtain four / eight-pole magnetic field gradient measurement values corresponding to the two-dimensional current data table one by one, thereby obtaining a three-dimensional curved surface sample database of magnetic field gradient; the three-dimensional curved surface sample database of magnetic field gradient comprises a four-pole field magnetic field gradient three-dimensional curved surface sample database and an eight-pole field magnetic field gradient three-dimensional curved surface sample database.

[0100] As shown in Figure 5fAs shown in the figure, the interpolation refinement magnetic field gradient three-dimensional curved surface sample library module is configured to use a cubic spline function to perform two-dimensional interpolation on the quadrupole field magnetic field gradient three-dimensional curved surface sample database and the octupole field magnetic field gradient three-dimensional curved surface sample database, and to encrypt the grid point density.

[0101] As shown in the figure, Figure 5g , 5h As shown in the figure, the input field gradient corresponding field gradient current curve solving module is configured to intersect the input quadrupole field gradient and octupole field gradient with the magnetic field gradient curved surface of the three-dimensional sample database, and to obtain two corresponding current curves after the intersection. Specifically, a quadrupole field magnetic field gradient plane is selected, the plane intersects the curved surface of the quadrupole field magnetic field gradient three-dimensional curved surface sample database, and a current curve satisfying the quadrupole field gradient is obtained. An octupole field magnetic field gradient plane is selected, the plane intersects the curved surface of the octupole field magnetic field gradient three-dimensional curved surface sample database, and a current curve satisfying the octupole field gradient is obtained.

[0102] As shown in the figure, Figure 5i The quadrupole / octupole field gradient current curve intersection point solving module is configured to obtain the intersection point of the current curve satisfying the quadrupole field gradient and the current curve satisfying the octupole field gradient, and to use the intersection point as the solution of the composite iron excitation current.

[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 shown in the figure, Figure 5b , 5c The quadrupole / octupole composite magnet has a total of eight pole heads, and each pole head is provided with inner and outer current coil layers in the radial direction near the major radius. The inner layer coil is an octupole magnetic field excitation coil, and the outer layer coil is a quadrupole magnetic field excitation coil.

[0105] As shown in the figure, Figure 5b , 5c The adjacent two pole heads of the inner layer octupole magnetic field excitation coil have opposite current directions, i.e., the octupole field coil is divided into two groups of 1, 3, 5, 7 pole heads and 2, 4, 6, 8 pole heads. The excitation currents of the two groups are equal in size but opposite in direction, thereby generating an octupole magnetic field.

[0106] As shown in the figure, Figure 5b , 5cAs shown, the outer quadrupole magnetic field excitation coil has four groups, with the coils on two adjacent poles forming a group: poles 1 and 2, poles 3 and 4, poles 5 and 6, and poles 7 and 8. The excitation current of the quadrupole magnetic field coils on poles 1 and 2, and symmetrically arranged on poles 5 and 6, is in the same magnitude and direction. The excitation current of the coils on poles 3 and 4, and symmetrically arranged on poles 7 and 8, is in the same magnitude and direction. The current direction of the coils on poles 1 and 2 is opposite to that of the coils on poles 3 and 4, and the current direction of the coils on poles 5 and 6 is opposite to that of the coils on poles 7 and 8, thus generating a quadrupole magnetic field.

[0107] Example 1

[0108] like Figure 7 As shown, this invention designs an ultra-short bendable beam homogenization transmission line. When the total length of the ultra-short bendable beamline is 6, the initial placement positions of the components that enable the beamline to achieve a better homogenization effect are as follows: the initial position of the fluorescent target 1 is 100mm, the initial position of the quadrupole magnet (Q0) is 1300mm; the initial position of the guide magnet 1 is 1650mm; the initial position of the quadrupole-octupole composite iron (Q1) is 2100mm, the initial position of the dipole iron is 2700mm, the initial position of the quadrupole-octupole composite iron (Q2) is 3850mm; the initial position of the guide magnet 2 is 4250mm; the initial position of the Faraday cylinder is 4700mm; the initial position of the fluorescent target 2 is 5350mm, the initial position of the dual wire is 5750mm; and the initial position of the terminal is 6000mm.

[0109] The magnetic field component of the tetrapole iron (Q0) is 6.8 (T / m); the tetrapole magnetic field component of the tetrapole-octapole composite iron (Q1) is 2.25 (T / m), and the octapole magnetic field component is 1e4 (T / m). 3 The quadrupole magnetic field component of the four-octupole composite iron (Q2) is 0.6 (T / m), and the octupole magnetic field component is 6.25e3 (T / m). 3 The beam is deflected by 90°, with both the incident and exit angles at 45° and a deflection radius of 0.55m.

[0110] like Figure 1d The image shows a comparison of the transmission line before and after homogenization according to the present invention. Figure 1d The left figure is a cross-section of the beam with a Gaussian distribution before homogenization, which is the beam cross-section of the fluorescent target 1 at the position of 100mm of the transmission line. Figure 1d The right figure shows the beam cross-section after homogenization, which is the beam cross-section of fluorescent target 2 at the transmission line position of 5350 mm. As can be seen from the figure, before homogenization, the particle distribution on the beam cross-section is dense in the middle and sparse around the edges. After homogenization, the particle distribution on the beam cross-section is uniform in both the middle and around the edges.

[0111] It should be noted that the above specific embodiments are only an explanation of the present application, and are not a limitation of the present application, and those skilled in the art can make modifications to the above embodiments without creative contribution after reading the specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. An ultra-short, curved beam homogenization transmission line, characterized in that: The transmission line is an ultra-short bend beam homogenization transmission line comprising two quadrupole-octupole composite iron pieces and one dipole iron piece; the ultra-short bend beam homogenization transmission line is either ultra-short bend beam homogenization transmission line A or ultra-short bend beam homogenization transmission line B arranged along the beam direction; ultra-short bend beam homogenization transmission line A is provided with the following components in sequence along the beam exit direction: accelerator exit, beam matching mechanism, quadrupole-octupole composite iron 1, dipole iron, quadrupole-octupole composite iron 2, beam matching and homogenization effect observation mechanism 1, and terminal 1; ultra-short bend beam homogenization transmission line B is provided with the following components in sequence along the beam exit direction: accelerator exit, beam matching mechanism, quadrupole-octupole composite iron 1, dipole iron, quadrupole-octupole composite iron 3, beam matching and homogenization effect observation mechanism 2, and terminal 2. The four-eight-pole composite iron 1, four-eight-pole composite iron 2, or four-eight-pole composite iron 1, four-eight-pole composite iron 3 simultaneously generate a quadrupole magnetic field and an octupole magnetic field, respectively, thus achieving the functions of both quadrupole and octupole iron with only one transmission element. At the four-eight-pole composite iron 1, the beam envelope function in the Y or X direction reaches a large value; at the four-eight-pole composite iron 2 or four-eight-pole composite iron 3, the beam envelope function in the X or Y direction reaches a large 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... They are respectively close to integer multiples of 180 degrees, where integer multiples refer to 0 and positive integer multiples; the transmission matrix between the two octagonal magnetic fields is close to the identity matrix; The phase shift of the particles between the target and the octapsotron composite iron 1 and octapsotron composite iron 2. Or the phase shift of particles between the target and the octapole composite iron 1 and octapole composite iron 3. Multiples close to 180 degrees refer to multiples that are close to but not equal to 180 degrees: Let... for The remainder after 180 degrees, The value should be less than ±15 degrees; The transmission matrix between the two octagonal magnetic fields is close to the identity matrix, that is, the phase shift between the two four-octagonal composite magnets is controlled within 30 degrees. This 30-degree range can greatly avoid the high-order nonlinear effects caused by the coupling of the two octagonal magnets and can achieve a better homogenization effect. Based on the bending beam homogenization substructure, the bending beam homogenization transmission line utilizes the combined focusing effect of the quadrupole-octupole composite iron 1 and the dipole to generate the beam waist in the Y direction near the quadrupole-octupole composite iron 2; and utilizes the quadrupole field superposition of the dipole and the quadrupole-octupole composite iron 2 to generate the envelope size in the X direction on the target, so that the envelope sizes in the X and Y directions are consistent. 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 current output of the four-pole field coil and the eight-pole field coil of the four-eight-pole composite magnet by the composite magnet main power supply. The beam matching mechanism is used to observe the initial state of the beam extracted from the accelerator, adjust the size of the beam envelope in the X or Y direction according to the initial state, and align the beam center with the mechanical center of the beam tube. 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 iron, and to observe the beam intensity, weak beam shape and strong beam shape after homogenization by the four-octapole composite iron 1 and the four-octapole composite iron 2.

2. The ultra-short bending beam homogenization transmission line according to claim 1, characterized in that: The beam matching mechanism includes a fluorescent target 1, a quadrupole magnet, and a guide magnet; the fluorescent target 1 provides the tester with the initial beam position; the quadrupole magnet is used to provide a beam envelope in the opposite direction for the quadrupole-octupole composite iron 1; and the guide magnet is used to adjust the beam eccentricity.

3. The ultra-short bending beam homogenization transmission line according to claim 1, characterized in that: The beam matching and homogenization effect observation mechanism 1 includes a guide magnet 2, a Faraday cylinder 1, a fluorescent target 2, and a dual-wire 1. The guide magnet 2 is used to align the beam center with the mechanical center of the beam channel. The Faraday cylinder 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 dual-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 guide magnet 3, a Faraday cylinder 2, a fluorescent target 3, and a dual-wire 2. The guide magnet 3 is used to align the beam center with the mechanical center of the beam channel. The Faraday cylinder 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 dual-wire 2 is used to observe the shape of the strong beam after homogenization.

4. The ultra-short bending beam homogenization transmission line according to claim 1, characterized in that: The expression for the magnetic strength k at points 1 and 2 of the four-eight-pole composite iron, or at point 3 of the four-eight-pole composite iron, is as follows: Let: the starting point of the transport line be 0, the position of the first quadrupole magnet be 1, the position of the second quadrupole magnet be 2, and the position of the endpoint, which is the position of the target, be 3; in the above formula (1), ux02 represents the phase shift of the particle in the x direction between positions 0 and 2, ux23 represents the phase shift of the particle in the x direction between positions 2 and 3; βx2 represents the envelope function in the x direction at position 2; in the above formula (2), uy01 represents the phase shift of the particle in the y direction between 0 and 1; uy13 represents the phase shift of the particle in the y direction between 1 and 3; βy1 represents the envelope function in the y direction at position 1.

5. The ultra-short curved beam homogenization transmission line according to claim 1, characterized in that: The composite magnet current control device includes: a module for establishing two-dimensional sampling points for coil current, a module for experimentally measuring and initially establishing a three-dimensional surface sample library of magnetic field gradient, a module for refining the three-dimensional surface sample library of magnetic field gradient using interpolation, a module for inputting field gradient and solving the corresponding field gradient current curve, a module for solving the intersection point of four / octagonal field gradient current curves, and a module for outputting four / octagonal coil current. The module for establishing two-dimensional sampling points for coil current is used to establish a two-dimensional data comparison table of coil current for quadrupole and octupole iron. The experimental measurement initially establishes a three-dimensional surface sample library module for magnetic field gradients. This module uses the current values ​​from a two-dimensional data lookup table of coil currents to perform magnetic field experimental measurements on composite iron, thereby obtaining four-pole and octole magnetic field gradient measurement values ​​that correspond one-to-one with the two-dimensional current data lookup table, thus obtaining a three-dimensional surface sample database of magnetic field gradients. The aforementioned three-dimensional surface sample database of magnetic field gradients includes a four-pole field magnetic field gradient three-dimensional surface sample database and an octole field magnetic field gradient three-dimensional surface sample database. The module for refining the magnetic field gradient three-dimensional surface sample library using interpolation is used to perform two-dimensional interpolation on the quadrupole magnetic field gradient three-dimensional surface sample database and the octupole magnetic field gradient three-dimensional surface sample database using cubic spline functions, thereby increasing the density of grid points. The module for solving the input field gradient corresponding to the current curve is used to intersect the input quadrupole field gradient and octupole field gradient with the magnetic field gradient surface of the three-dimensional sample database, and obtain two corresponding current curves after the intersection; specifically: a quadrupole field magnetic field gradient plane is selected, and this plane intersects with the surface of the quadrupole field magnetic field gradient three-dimensional surface sample database to obtain the current curve that satisfies the quadrupole field gradient; an octupole field magnetic field gradient plane is selected, and this plane intersects with the surface of the octupole field magnetic field gradient three-dimensional surface sample database to obtain the current curve that satisfies the octupole field gradient. The module for solving the intersection point of the four / octet field gradient current curves is used to obtain the intersection point of the current curve that satisfies the four-pole field gradient and the current curve that satisfies the octet field gradient, and uses the intersection point as the solution of the composite iron excitation current. The output four-pole / eight-pole coil current module outputs four-pole field coil current and eight-pole field coil current to the four-pole / eight-pole composite iron according to the solution of the excitation current of the composite iron.

6. The ultra-short curved beam homogenization transmission line according to claim 1, characterized in that: This four-eight-pole composite magnet has a total of eight poles. Each pole has two layers of current coils along the radial direction near the large radius. The inner coil is an eight-pole magnetic field excitation coil, and the outer coil is a four-pole magnetic field excitation coil. The inner layer of the octagonal magnetic field excitation coil has two adjacent poles with opposite current directions, that is, the octagonal field coil is divided into two groups: poles 1, 3, 5, 7 and poles 2, 4, 6, 8. The excitation currents of the two groups are equal in magnitude but opposite in direction, thereby generating an octagonal magnetic field. The outer quadrupole magnetic field excitation coil has four groups, consisting of coils on two adjacent poles: poles 1 and 2, poles 3 and 4, poles 5 and 6, and poles 7 and 8. The excitation current of the quadrupole magnetic field coils on poles 1 and 2, and symmetrically arranged on poles 5 and 6, is in the same direction and magnitude. The excitation current of the coils on poles 3 and 4, and symmetrically arranged on poles 7 and 8, is in the same direction and magnitude. The current direction of the coils on poles 1 and 2 is opposite to that of the coils on poles 3 and 4, and the current direction of the coils on poles 5 and 6 is opposite to that of the coils on poles 7 and 8, thus generating a quadrupole magnetic field.

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