Four-pole / eight-pole composite iron system for beam homogenization

Abstract

The invention discloses a quadrupole / octupole composite iron system for beam homogenization. The composite iron system comprises a composite magnet current control device, a composite magnet main power supply and quadrupole / octupole composite iron, the composite magnet current control device is used for controlling a composite magnet main power supply to output quadrupole field coil current and octupole field coil current of quadrupole / octupole composite iron. The quadrupole / octupole composite iron is used for simultaneously generating a dominant quadrupole magnetic field and an octupole magnetic field, so that the effects of quadrupole iron and octupole iron can be simultaneously realized by only installing one transmission element; according to the invention, a quadrupole magnetic field and an octupole magnetic field are generated in the aperture of the composite iron, focusing and homogenization of beam envelope are realized at the same time, the number of transmission elements can be reduced, the length of a transmission line can be shortened, and the construction cost of the beam transport line is reduced. The problem that traditional quadrupole iron and octupole iron cannot be simultaneously installed at the maximum beam envelope position due to the space problem and cannot play a great role of a magnet is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of cyclotrons, and particularly relates to a quadrupole / octupole composite iron system for beam current homogenization. Background Art

[0002] In order to utilize the charged particle beam generated in an accelerator, it is necessary to use a beam transport line composed of beam transport elements to transport the beam to the experimental terminal or a specified position. Common beam transport elements include dipoles, quadrupoles, sextupoles, and octupoles. The function of the beam transport element is to control the envelope shape of the beam during transmission, ensure that its envelope does not diverge during transmission, and thus avoid the collision of particles with the transmission pipeline and cause beam loss. At the same time, the experimental terminal will put forward a series of requirements for the beam quality, such as beam uniformity, etc. Only the beam that meets these conditions can meet the usage requirements. Good beam quality needs to be achieved through the modulation of the beam by the transport element.

[0003] At present, the functions of the beam transport elements used are generally independent. The quadrupole field that controls the focusing or divergence of the beam is generated by a quadrupole iron, and the octupole field that controls the beam uniformity is generated by an octupole magnet.

[0004] The distribution of the beam extracted from the accelerator generally approximates a Gaussian distribution, with the highest particle density at the center of the bunch, which also causes excessive local power and high temperature on the neutron target, resulting in damage to the neutron target. In order to solve the problem of uneven particle distribution, an octupole magnet is tried on the beam transport line to homogenize the Gaussian-distributed beam and reduce the peak power density on the neutron target.

[0005] One of the difficulties in using an octupole magnet to homogenize the Gaussian-distributed beam is that: the same octupole iron installed at different positions on the beam transport line will have different effects. Only when the octupole iron 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: such as Figure 14bAs shown, the transmission lines of the prior art are arranged in the order of quadrupole magnet 1, octupole magnet 1, quadrupole magnet 2, and octupole magnet 2. Since the octupole magnet needs to be focused first before homogenization (the function of focusing is to enable the beam to pass through the circular hole in the center of the octupole magnet without hitting the octupole magnet), in order to ensure focusing, the positions of octupole magnet 1 and octupole magnet 2 must first be selected at the waist positions of the X-direction envelope and the waist positions of the Y-direction envelope. However, since the Y-direction envelope of quadrupole magnet 1 at the waist position of the X-direction envelope is small, and the X-direction envelope of quadrupole magnet 2 at the waist position of the Y-direction envelope is small, at octupole magnet 1, although the waist position in the X direction of octupole magnet 1 is ensured, the Y-direction envelope at this position is small. Similarly, at octupole magnet 2, although the waist position in the Y direction of octupole magnet 2 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 magnet 1 and quadrupole magnet 2, so the functions of octupole magnet 1 and octupole magnet 2 cannot be fully exerted.

[0006] The second difficulty in using an octupole magnet to homogenize a Gaussian-distributed beam is that: due to the small beam envelope at the positions where octupole magnet 1 and octupole magnet 2 are located, 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 an octupole magnet to homogenize a Gaussian-distributed beam is that: in a beam transmission line, one type of transmission element only realizes one function, and each element has a fixed size. The number of transmission elements on the transmission line directly determines the length of the transmission line. For some specific occasions, due to the limited axial space for arranging the beam transmission line, not too many transmission elements can be placed, so some sacrifices have to be made axially, resulting in an unsatisfactory beam quality. 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 its phase. 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, and 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 surrounding shielding civil engineering will be. In short, the disadvantages of a too-long transmission line, such as large floor area and high cost, have greatly limited the use of beam homogenization technology. Summary of the Invention

[0008] To solve the problems existing in the prior art, the present invention proposes a quadrupole / octupole composite iron system for beam current homogenization. The first object is to solve the problem that the place with the largest envelope in the prior art is usually occupied by the quadrupole magnetic field, and the octupole iron cannot provide the strongest homogenization effect. The second object is to solve the problem that the envelope at the position of the octupole iron on the transmission line in the prior art is small, so that 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 implement. The third object is to solve the problem that if the octupole iron is used in the prior art to achieve a better beam current homogenization effect, the length of the transmission line often needs to be more than ten meters. The too long transmission line has a large floor area and high costs, which greatly limits the use of the beam current homogenization technology.

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

[0010] A quadrupole / octupole composite iron system for beam current homogenization, which includes a composite magnet current control device, a composite magnet main power supply, and a quadrupole / octupole composite iron. The composite magnet current control device is used to control the quadrupole field coil current output and octupole field coil current output of the composite magnet main power supply to the quadrupole / octupole composite iron. The quadrupole / octupole composite iron is used to simultaneously generate a dominant quadrupole magnetic field and an octupole magnetic field, so that the functions of the quadrupole iron and the octupole iron can be realized only by installing transmission elements.

[0011] The composite magnet current control device includes: a module for establishing a two-dimensional sampling point of coil current, a module for experimentally measuring and initially establishing a three-dimensional surface sample library of magnetic field gradients, a module for using interpolation to refine the three-dimensional surface sample library of magnetic field gradients, a module for solving the corresponding field gradient current curve according to the input field gradient, a module for solving the intersection point of the quadrupole / octupole field gradient current curves, and a module for outputting the quadrupole / octupole coil current;

[0012] The module for establishing a two-dimensional sampling point 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;

[0013] 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 currents to conduct magnetic field experiments on the composite iron, so as to obtain the measured values of the quadrupole and octupole magnetic field gradients corresponding to the two-dimensional current data comparison table one by one, 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;

[0014] 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 by using a cubic spline function to increase the grid point density;

[0015] 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 satisfies 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 satisfies the octupole field gradient.

[0016] The solving quadrupole / octupole field gradient current curve intersection point module is used to obtain the intersection point of the current curve that satisfies the quadrupole field gradient and the current curve that satisfies the octupole field gradient, and use this intersection point as the solution of the composite iron excitation current.

[0017] 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.

[0018] Furthermore, this new type of quadrupole / octupole composite iron model 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.

[0019] Furthermore, 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.

[0020] Furthermore, for the outer quadrupole magnetic field excitation coil, the coils on two adjacent pole heads are in a group, and are divided into four groups, namely pole heads 1, 2; pole heads 3, 4; pole heads 5, 6; pole heads 7, 8. Among them, for pole heads 1, 2 and symmetrically arranged pole heads 5, 6, the excitation currents of these two groups of quadrupole magnetic field coils are equal in magnitude and direction. For pole heads 3, 4 and symmetrically arranged pole heads 7, 8, the excitation currents of these two groups of coils are equal in magnitude and 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.

[0021] Advantages and effects of the present invention

[0022] 1. The present invention generates a quadrupole magnetic field and an octupole magnetic field within the aperture of the composite iron, which can simultaneously achieve the functions of focusing and homogenizing the beam envelope, and solves the problems that the place with the largest envelope in the prior art is usually occupied by the quadrupole magnetic field and the octupole iron cannot provide the strongest homogenizing effect.

[0023] 2. The present invention generates a quadrupole magnetic field and an octupole magnetic field within the aperture of the composite iron, which can simultaneously achieve the functions of focusing and homogenizing the beam envelope, providing the strongest homogenization effect, and solving the problems in the prior art transmission line that due to the relatively small envelope at the position where the octupole iron is located, the field strength K value of the octupole magnet is very large, and the excessively high magnetic field strength is not only difficult in engineering, but also too costly and difficult to implement.

[0024] 3. The present invention generates a quadrupole magnetic field and an octupole magnetic field within the aperture of the composite iron, which can simultaneously achieve the functions of focusing and homogenizing the beam envelope. Installing it on the beam transmission line can reduce the number of transmission elements, shorten the length of the transmission line, and reduce the project cost of the beam transport line. For the transmission line, the quadrupole-octupole composite iron can simultaneously exert the maximum effect of the magnet because it is installed at the position where the beam envelope is the largest, and at this time the focusing effect and the homogenization effect are the strongest, solving the problem that the traditional quadrupole iron and octupole iron cannot be installed at the position where the beam envelope is the largest due to space problems and thus cannot exert the maximum effect of the magnet.

[0025] 4. The proposed quadrupole-octupole iron solution in this paper can be used flexibly. When the current of any type of coil is turned off, it can be used as a quadrupole iron or an octupole iron. At the same time, it also means that the currents of the two coils can be adjusted flexibly to generate a variety of quadrupole / octupole composite fields for application in different scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the quadrupole / octupole composite iron system for beam control of the present invention;

[0027] Figure 2 Beam transmission element: (left) quadrupole iron; (right) application effect diagram of octupole iron;

[0028] Figure 3 Quadrupole magnetic field distribution and focusing principle;

[0029] Figure 4 Octupole magnetic field and beam homogenization process;

[0030] Figure 5 New quadrupole / octupole composite iron model of the present invention;

[0031] Figure 6 is Figure 5 Partial enlarged view of the quadrupole / octupole composite iron model;

[0032] Figure 7 Quadrupole / octupole composite magnet coil arrangement and current direction.

[0033] Figure 8 Schematic diagram of the current values of two groups of coils during the magnetic field measurement of the present invention;

[0034] Figure 9 Schematic diagram of experimental measurement of the corresponding four / octupole magnetic field gradients at different currents for the present invention;

[0035] Figure 10 Schematic diagram of using cubic spline function for two-dimensional interpolation to encrypt grid point density for the present invention;

[0036] Figure 11 Schematic diagram of the intersection of the magnetic field gradient plane selected for the present invention and the magnetic field gradient surface of the three-dimensional sample database;

[0037] Figure 12 Schematic diagram of the current curve corresponding to the four / octupole field selected for the present invention;

[0038] Figure 13 Schematic diagram of the solution of the excitation current of the composite iron for the present invention;

[0039] Figure 14a Schematic diagram of applying the four / octupole composite iron of the present invention to the ultra-short beam current homogenization transmission line;

[0040] Figure 14b Schematic diagram of the octupole iron in the small envelope position in the prior art;

[0041] Figure 15 Flowchart of the excitation current adjustment method for the four / octupole composite iron of the present invention. Detailed implementation manners

[0042] Design principle of the present invention

[0043] 1. Problems existing in the layout of the transmission line based on discrete elements of quadrupole iron and octupole iron

[0044] 1) The conventional method of combining two quadrupole magnets cannot meet the requirement of limited axial space of the transmission line. The magnetic field line distribution of the quadrupole field generated by the quadrupole magnet is as Figure 3As shown, when the beam passes through the middle aperture of the quadrupole magnet, the beam is subjected to an inward transverse focusing force in the X direction, whose function is to contract the beam envelope in this direction, i.e., to focus it. While the beam is subjected to an outward transverse focusing force in the Z direction, whose function is to diverge the beam envelope in this direction, i.e., to defocus it. Therefore, a quadrupole magnet focuses the beam in one direction and defocuses it in another direction. To make the beam be subjected to an inward transverse focusing force in both the Y direction and the X direction, two quadrupole magnets are usually used. When two quadrupole magnets are used, the excitation current directions of the two quadrupole magnet coils are opposite, i.e., one quadrupole magnet focuses in the X direction and the other quadrupole magnet defocuses in the X direction. In this case, the two quadrupole magnets are used in combination. According to the principle of alternating focusing, their combined action is that the beam is focused in both the X direction and the Z direction, thus ensuring that the beam does not diverge during transmission. Among them, the same quadrupole magnet installed at different positions on the beam transmission line will play different roles. When it is installed at the position where the beam envelope is the largest, it can provide the strongest focusing effect. Generally, the quadrupole magnet is installed at the position where the beam envelope is the largest.

[0045] 2) When the octupole magnet and the quadrupole magnet are arranged independently, the octupole magnet cannot fully play its role. As Figure 4 shown, first, the principle of the octupole magnet making the particles evenly distributed. The octupole magnet generates an octupole magnetic field, whose function is to make the particles in the beam be evenly distributed in space. Before the beam passes through the octupole magnet, its particles are in a Gaussian distribution, mainly concentrated in the central region of the envelope. After passing through the octupole magnet, they are evenly distributed in the envelope. Among the 8 magnetic poles of the octupole magnet, the N and S poles are arranged alternately. The influence of the octupole magnet on the beam is as Figure 4 shown. The adjacent magnetic poles have opposite effects on the beam, one compresses inward and the other stretches outward, gradually changing the beam envelope from a circle to a square and finally to the envelope shape of a four-pointed star. Since the proportion of the four inward beams and the four outward beams in the envelope shape of the four-pointed star is similar, the envelope shape of the four-pointed star makes the particle distribution more uniform. Therefore, a square beam spot can be obtained first by adjusting the intensity of the octupole magnetic field. As time goes by, the envelope shape of the square gradually changes to the final envelope shape of the four-pointed star. Second, when the octupole magnet and the quadrupole magnet are arranged independently, the octupole magnet cannot fully play its role. The same octupole magnet installed at different positions on the beam transmission line will play different roles. When it is installed at the position where the beam envelope is the largest, it can provide the strongest homogenization effect. However, the quadrupole magnet is generally installed at the place where the envelope is the largest. Therefore, the octupole magnet can only be installed at the place where the envelope is not very large and cannot fully play its role.

[0046] 2. Design Difficulties of the Invention: There is a coupling relationship between the multi-pole magnetic fields generated by the two sets of coils of the quadrupole / octupole composite iron. This coupling relationship means that changing the current magnitude of the quadrupole field or octupole field coils 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 coils 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 coils is adjusted, once the current of the octupole field coils starts to change, it will change the previously adjusted quadrupole magnetic field gradient, making it no longer meet the usage requirements.

[0047] 3. Innovation Points of the Invention:

[0048] One of the innovation points lies in: inventing a quadrupole / octupole composite iron. As shown in Figure 5 、 6 、7, the quadrupole / octupole composite iron is used to replace the discrete-element quadrupole iron and octupole iron in the prior art as shown in Figure 14b . After combination, a quadrupole magnetic field and an octupole magnetic field are generated inside the aperture of the quadrupole / octupole composite iron. As shown in Figure 14a , for the transmission line, the quadrupole / octupole composite iron can simultaneously exert the maximum effect of the magnet because the quadrupole / octupole composite iron is installed at the position with the largest beam envelope. At this time, the focusing effect and homogenization effect are the strongest, solving the problem that the traditional quadrupole iron and octupole iron cannot be installed at the position with the largest beam envelope due to space problems and thus cannot exert the maximum effect of the magnet. Specifically, as shown in Figure 14a , the quadrupole iron of the quadrupole / octupole composite iron 1 shares the position of the large envelope in the Y direction with the quadrupole iron in front of it, and the quadrupole iron of the quadrupole / octupole composite iron 2 shares the position of the large envelope in the X direction with the quadrupole iron of the quadrupole / octupole composite iron 1 in front of it. Since the octupole iron in the quadrupole / octupole composite iron 1 and the quadrupole / octupole composite iron 2 is arranged at the position of the large envelope, a better beam homogenization effect can be achieved, that is: the functions of focusing and homogenizing the beam envelope can be simultaneously realized. Compared with Figure 14b in the prior art, since the prior art is that the quadrupole iron and octupole iron are discretely arranged, the octupole iron itself cannot change the envelope like the quadrupole iron, that is, it cannot share the large envelope with the quadrupole iron in front. Therefore, the envelopes in the Y direction and X direction of the discretely arranged octupole iron are relatively small, so its homogenization effect is not good. The second effect: Installing the composite iron 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 in the number of transmission components not only saves the quadrupole iron, but also saves multiple components that need to be added on the transmission line to achieve the same homogenization effect.

[0049] The second innovation lies in: establishing a three-dimensional surface sample database of magnetic field gradient. This three-dimensional surface sample database of magnetic field gradient uses the current values in the two-dimensional data comparison table of coil current to conduct magnetic field experimental measurements on composite iron, obtaining the four-pole and eight-pole magnetic field gradient measurement values corresponding one-to-one with the two-dimensional current data comparison table, thereby obtaining the three-dimensional surface sample database of magnetic field gradient;

[0050] The third innovation lies in establishing the relationship between the magnetic field gradient plane and the intersection of the three-dimensional surface of the magnetic field gradient, thereby obtaining the current curve at the intersection. The magnetic field gradient at any point on this curve is equal, but the four-pole magnetic field current and the eight-pole magnetic field current values at any point on this curve are not equal or are equal, which lays the foundation for solving the excitation current of the composite iron at the intersection point of the two curves.

[0051] The fourth innovation lies in using the irrelevance between the current curve and the magnetic field gradient, projecting the current curves on different magnetic field gradients onto the same coordinate plane, and obtaining the intersection point and using the intersection point as the solution of the excitation current of the composite iron.

[0052] Based on the above principles, the present invention designs a four / eight-pole composite iron system for beam current homogenization, as Figure 1 shown. This composite iron system includes a composite magnet current control device, a composite magnet main power supply, and a four-pole / eight-pole composite iron; the composite magnet current control device is used to control the output of the four-pole field coil current and the eight-pole field coil current of the composite magnet main power supply to the four-pole / eight-pole composite iron; the four-pole / eight-pole composite iron is used to simultaneously generate a dominant four-pole magnetic field and an eight-pole magnetic field, so that the functions of a four-pole iron and an eight-pole iron can be simultaneously realized by only installing one transmission element.

[0053] As Figure 1 shown, the composite magnet current control device includes: a module for establishing two-dimensional sampling points of coil current, a module for experimentally measuring and initially establishing a three-dimensional surface sample library of magnetic field gradient, a module for using interpolation to refine the three-dimensional surface sample library of magnetic field gradient, a module for inputting the field gradient to solve the corresponding field gradient current curve, 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;

[0054] As Figure 8 shown, the module for establishing two-dimensional sampling points of coil current is used to establish a two-dimensional data comparison table of the coil current of the four-pole iron and the eight-pole iron;

[0055] As Figure 9As shown, the module for preliminarily establishing a three-dimensional surface sample library of magnetic field gradients in the experimental measurement uses the current values in the two-dimensional data comparison table of coil currents to conduct magnetic field experiments on the composite iron, thereby obtaining the measurement values of the four-pole and eight-pole magnetic field gradients corresponding one-to-one with the two-dimensional current data comparison table, and thus obtaining a three-dimensional surface sample database of magnetic field gradients; the above three-dimensional surface sample database of magnetic field gradients includes a three-dimensional surface sample database of four-pole field magnetic field gradients and a three-dimensional surface sample database of eight-pole field magnetic field gradients;

[0056] As Figure 10 shown, the module for refining the three-dimensional surface sample library of magnetic field gradients using interpolation is used to perform two-dimensional interpolation on the three-dimensional surface sample database of four-pole field magnetic field gradients and the three-dimensional surface sample database of eight-pole field magnetic field gradients using a cubic spline function to increase the density of grid points;

[0057] As Figure 11 、 12 shown, the module for solving the corresponding field gradient current curve of the input field gradient is used to intersect the input four-pole field gradient and eight-pole 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 four-pole field magnetic field gradient plane, which intersects with the surface of the three-dimensional surface sample database of four-pole field magnetic field gradients to obtain a current curve that satisfies this four-pole field gradient; select the eight-pole field magnetic field gradient plane, which intersects with the surface of the three-dimensional surface sample database of eight-pole field magnetic field gradients to obtain a current curve that satisfies this eight-pole field gradient;

[0058] As Figure 13 shown, 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 four-pole field gradient and the current curve that satisfies the eight-pole field gradient, and use this intersection point as the solution of the excitation current of the composite iron;

[0059] 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;

[0060] As Figure 5 、 Figure 6 、 Figure 7 shown, for the inner eight-pole magnetic field excitation coil, the current directions of its adjacent two pole heads are opposite, that is, the eight-pole field coil is divided into two groups of pole heads 1, 3, 5, 7 and 2, 4, 6, 8. The excitation currents of the two are equal in magnitude but opposite in direction, thereby generating an eight-pole magnetic field.

[0061] As Figure 5 、 Figure 6 、 Figure 7As shown, for the quadrupole magnetic field excitation coils of the outer layer, the coils on two adjacent pole heads form a group, and are divided into four groups, namely, pole heads 1 and 2, pole heads 3 and 4, pole heads 5 and 6, and pole heads 7 and 8. Among them, for pole heads 1 and 2 and symmetrically arranged pole heads 5 and 6, the magnitudes and directions of the excitation currents of these two groups of quadrupole magnetic field coils are the same; for pole heads 3 and 4 and symmetrically arranged pole heads 7 and 8, the magnitudes and directions of the excitation currents of these two groups of coils are the same; the current directions of the coils of pole heads 1 and 2 are opposite to those of 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.

[0062] Supplementary Note 1

[0063] Figure 7 is Figure 5 a sectional view of Figure 7 in which, on both sides of the pole head and close to the pole head are octupole iron coils, and outside the octupole iron coils are quadrupole iron coils; the current direction of the octupole iron coils is indicated by "O", and the current direction of the quadrupole iron coils is indicated by "Q"; the octupole iron coils are divided into two groups of pole heads 1, 3, 5, 7 and pole heads 2, 4, 6, 8, and the magnitudes of their excitation currents are equal, but the current directions are opposite. For example, for each of the pole heads 1, 3, 5, 7 of the octupole coils, the current direction is O+ entering from the left and O- flowing out from the right; for each of the pole heads 2, 4, 6, 8 of the octupole field coils, the current direction is O+ entering from the right and O- flowing out from the left; for the quadrupole field coils, every two adjacent pole heads form a group and the current directions are the same. For example, pole heads 1 and 2 form a group and the current directions are the same. For example, the current directions on both sides of pole head 1 and pole head 2 are both Q+ entering from the right and Q- flowing out from the left; pole heads 3 and 4 form a group, and the current directions of pole heads 3 and 4 are opposite to those of pole heads 1 and 2. The current directions on both sides of pole head 3 and pole head 3 are both Q+ entering from the left and Q- flowing out from the right.

[0064] Embodiment 1

[0065] Based on the above quadrupole / octupole composite iron structure for beam control, the present invention also relates to a method for adjusting the excitation current of the quadrupole / octupole composite iron, as Figure 14a shown, and its feature is that the method for adjusting the excitation current of the quadrupole / octupole composite iron includes the following steps:

[0066] Step 1: Establish a two-dimensional data comparison table of the coil currents of the quadrupole iron and the 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 quadrupole / octupole composite iron;

[0067] The above two-dimensional data comparison table of the coil currents is as Figure 8 shown, with the abscissa being the coil current of the quadrupole coil and the ordinate being the coil current of the quadrupole coil.

[0068] Step 2: Experimental measurement to obtain the measurement values of the quadrupole and octupole magnetic field gradients corresponding one by one to the two-dimensional current data comparison table, thereby obtaining a three-dimensional surface sample database of the magnetic field gradient; the above-mentioned 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;

[0069] The above three-dimensional surface sample database is as Figure 9 shown. The current of the quadrupole coil is used as the X-axis coordinate, the current of the octupole coil is the Y-axis coordinate, and the magnetic field gradient is the Z-axis coordinate.

[0070] Step 3: Use the cubic spline function to perform two-dimensional interpolation on the three-dimensional surface sample database of the quadrupole field magnetic field gradient and the three-dimensional surface sample database of the octupole field magnetic field gradient to increase the density of grid points;

[0071] The effect of the above increased density of grid points is as Figure 10 shown. The grid densities on the X-axis, Y-axis, and Z-axis have all increased.

[0072] Step 4: Select the quadrupole field magnetic field gradient plane, which intersects with the surface of the three-dimensional surface sample database of the quadrupole field magnetic field gradient to obtain a current curve that satisfies the quadrupole field gradient; select the octupole field magnetic field gradient plane, which intersects with the surface of the three-dimensional surface sample database of the octupole field magnetic field gradient to obtain a current curve that satisfies the octupole field gradient;

[0073] As Figure 11 、 Figure 12 shown, it is a schematic diagram of the intersection of the above plane and the surface, and a current curve is obtained at the intersection.

[0074] Step 5: 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;

[0075] As Figure 12 shown, it is the current curve obtained after projection. The reason for being able to use projection is that the current values of the quadrupole field coil and the octupole field coil are current values on a two-dimensional plane and have nothing to do with the magnetic field gradient, so the method of projection is adopted. The method of projection is to project the current values on two different magnetic field gradients onto the same plane to facilitate the calculation of the intersection point of the two current curves.

[0076] Step 6: Use this intersection point as the solution of the composite iron excitation current.

[0077] As Figure 13 shown, the current value of this intersection point satisfies both the quadrupole field gradient and the octupole field gradient.

[0078] Further, the establishment of the two-dimensional data comparison table of the coil currents of the quadrupole magnet and the octupole magnet in Step 1 is as follows:

[0079] 1) Represent the maximum required quadrupole field gradient by Gq max and the maximum required octupole field gradient by Go max ;

[0080] 2) When the quadrupole field coil current is zero, the current when the octupole field coil generates Go max is the maximum working current I o of the octupole field coil; when the octupole field coil current is zero, the current when the quadrupole field coil generates Gq max is the maximum working current I q of the quadrupole field coil;

[0081] 3) Use the maximum working current I q of the quadrupole field coil and the maximum working current I o of the octupole field coil as the current data coverage boundaries of the two-dimensional data comparison table of the coil currents, and measure with equally spaced current changes.

[0082] Supplementary Note 2 :

[0083] The "current data coverage boundaries" are as Figure 8 shown. The boundary on the abscissa is the maximum working current 360 A of the quadrupole field coil, and the boundary on the ordinate is the maximum working current 360 A of the octupole field coil

[0084] As Figure 11 shown, the current curve that satisfies the quadrupole field gradient or the current curve that satisfies the octupole field gradient in Step 4, that is: the magnetic field gradients of all points on the curve are equal, and the current values of all points on the curve respectively correspond to a quadrupole field coil current and an octupole field coil current.

[0085] Further, in Step 5, 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 currents, and finally find the intersection point of the above two current curves; specifically: project the two current curves that respectively satisfy the requirements of the quadrupole field gradient and the octupole field gradient onto the same coordinate system plane and obtain the intersection point between them.

[0086] Supplementary Note 3 :

[0087] The significance of the intersection point is as follows: When the user simultaneously puts forward requirements for the quadrupole field gradient and the octupole field gradient, if the current intersection point corresponding to the quadrupole field gradient requirement and the octupole field gradient is found, the current values at the intersection point are used to adjust the currents of the quadrupole field coil and the octupole field coil. When the requirements are met, the magnetic field generated at the intersection point reaches both the quadrupole field gradient requirement put forward by the user and the octupole field gradient requirement put forward by the user.

[0088] Further, step six uses this intersection point as the solution for the composite iron excitation current, specifically as follows:

[0089] 1) Obtain the current curves that satisfy all the quadrupole field gradients in the three-dimensional surface sample database of the quadrupole field magnetic gradient, and obtain the current curves that satisfy all the octupole field gradients in the three-dimensional surface sample database of the octupole field magnetic gradient;

[0090] Supplementary Note 4 :

[0091] The above-mentioned "obtain the current curves that satisfy all the quadrupole field gradients in the three-dimensional surface sample database of the quadrupole field magnetic gradient" means incrementing the quadrupole field gradient plane gradually from the minimum value to the maximum value along the "quadrupole field gradient coordinate axis" to obtain multiple quadrupole field gradient planes. Intersecting each quadrupole field gradient plane with the surface will generate a series of intersection lines, and this series of intersection lines is the current curves that satisfy all the quadrupole field gradients.

[0092] The above-mentioned "obtain the current curves that satisfy all the octupole field gradients in the three-dimensional surface sample database of the octupole field magnetic gradient" means incrementing the octupole field gradient plane gradually from the minimum value to the maximum value along the "octupole field gradient coordinate axis" to obtain multiple octupole field gradient planes. Intersecting each octupole field gradient plane with the surface will generate a series of intersection lines, and this series of intersection lines is the current curves that satisfy all the octupole field gradients.

[0093] 2) Obtain all the intersection points of the current curve that satisfies the quadrupole field gradient and the current curve that satisfies the octupole field gradient;

[0094] Supplementary Note 5 :

[0095] Only two curves on the same plane will have an intersection point. Therefore, these two current curves must be projected onto the same coordinate plane. Although the heights of the two current curves are different, that is, the magnetic field gradient planes they are on are different, but because each point on the current curve is independent of the height and the magnetic field gradient, and only related to the currents of the quadrupole field coil and the octupole field coil, it is completely possible to project two curves with different spatial heights onto the same coordinate plane.

[0096] 3) Save the current values of the quadrupole field coil and the octupole field coil at all the intersection points;

[0097] 4) Input the current quadrupole field gradient requirement and octupole field gradient requirement;

[0098] 5) Find the corresponding intersection point according to the current input quadrupole field gradient requirement and octupole field gradient requirement;

[0099] 6) Adjust the quadrupole field coil current and octupole field coil current according to the current value of the intersection point.

[0100] It should be emphasized that the above specific embodiments are only explanations of the present invention, and they are not limitations of the present invention. Those skilled in the art can make modifications without creative contributions to the above embodiments 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 quadrupole / octupole composite iron system for beam current homogenization, the composite iron system comprising a composite magnet current control device, a composite magnet main power supply, and a quadrupole / octupole composite iron; the composite magnet current control device is used to control the quadrupole field coil current output and octupole field coil current output of the composite magnet main power supply to the quadrupole / octupole composite iron; the quadrupole / octupole composite iron is used to simultaneously generate a dominant quadrupole magnetic field and an octupole magnetic field, so that the functions of a quadrupole iron and an octupole iron can be simultaneously realized by installing only one transmission element.

2. The quadrupole / octupole composite iron system for beam current homogenization according to claim 1, characterized in that: The composite iron system comprises a composite magnet current control device, a composite magnet main power supply, and a quadrupole / octupole composite iron; the composite magnet current control device is used to control the quadrupole field coil current output and octupole field coil current output of the composite magnet main power supply to the quadrupole / octupole composite iron; the quadrupole / octupole composite iron is used to simultaneously generate a dominant quadrupole magnetic field and an octupole magnetic field, so that the functions of a quadrupole iron and an octupole iron can be simultaneously realized by installing only one transmission element; The composite magnet current control device includes: a module for establishing two-dimensional sampling points of coil current, a module for experimentally measuring and initially establishing a three-dimensional surface sample library of magnetic field gradients, a module for using interpolation to refine the three-dimensional surface sample library of magnetic field gradients, a module for solving the corresponding field gradient current curve for the input field gradient, a module for solving the intersection point of the quadrupole / octupole field gradient current curves, and a module for outputting the quadrupole / octupole coil current; The module for establishing two-dimensional sampling points of coil current is used to establish a two-dimensional data comparison table of the coil currents of the quadrupole iron and the octupole iron; The module for experimentally measuring and initially establishing a three-dimensional surface sample library of magnetic field gradients uses the current values in the two-dimensional data comparison table of coil current to 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, 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; 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 encrypt 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 two corresponding current curves are obtained after the intersection; specifically: select a 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 an 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 quadrupole / octupole field gradient current curves is used to obtain the intersection point of the current curve that satisfies the quadrupole field gradient and the current curve that satisfies this octupole field gradient, and use this intersection point as the solution of the excitation current of the composite iron; 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.

3. The quadrupole / octupole composite iron system for beam current homogenization according to claim 1, characterized in that: The quadrupole / octupole composite iron 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.

4. The quadrupole / octupole composite iron system for beam current homogenization according to claim 3, wherein: For the octupole magnetic field excitation coil in the inner layer, the current directions of two adjacent pole heads are opposite. That is, the octupole field coils are divided into two groups: the 1st, 3rd, 5th, and 7th pole heads and the 2nd, 4th, 6th, and 8th pole heads. The excitation currents of the two groups are equal in magnitude but opposite in direction, thus generating an octupole magnetic field.

5. The four / eight-pole composite iron system for beam current homogenization according to claim 1, characterized in that: For the quadrupole magnetic field excitation coil in the outer layer, the coils on two adjacent pole heads form a group, and there are four groups in total, namely the 1st and 2nd pole heads, the 3rd and 4th pole heads, the 5th and 6th pole heads, and the 7th and 8th pole heads. Among them, the 1st and 2nd pole heads and the symmetrically arranged 5th and 6th pole heads have the same magnitude and direction of the excitation current for the two groups of quadrupole magnetic field coils. The 3rd and 4th pole heads and the symmetrically arranged 7th and 8th pole heads also have the same magnitude and direction of the excitation current for the two groups of coils. The current directions of the coils on the 1st and 2nd pole heads are opposite to those on the 3rd and 4th pole heads, and the directions of the coils on the 5th and 6th pole heads are opposite to those on the 7th and 8th pole heads, thus generating a quadrupole magnetic field.

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