Bending type beam homogenization transmission line debugging method based on four-pole and eight-pole composite magnet

Abstract

The invention discloses a bent beam homogenization transmission line debugging method based on a four-eight-pole composite magnet, and the method comprises the steps: appropriately reducing the quadrupole iron current of the four-eight-pole composite iron 1 at a current intersection point of the four-eight-pole composite iron 1, a fringe field focusing effect of an inlet of two-pole iron behind the four-eight-pole composite iron 1 and a four-pole iron focusing effect of the four-eight-pole composite iron 1 are superposed to generate a waist part of the four-eight-pole composite iron 2 in the Y direction. At the intersection point of the four-eight-pole composite iron 2, the quadrupole iron current of the four-eight-pole composite iron 2 is properly reduced, and the envelope size in the X direction on the target is generated through superposition of the two-pole iron outlet edge focusing effect behind the four-eight-pole composite iron 1 and the quadrupole iron focusing effect of the four-eight-pole composite iron 2, so that the envelope size in the X direction is consistent with the envelope size in the Y direction. According to the invention, the fringing field effect of the secondary iron is utilized, and the problem of using the secondary iron on the ultra-short beam line is solved by a method of generating a superimposed effect on the fringing field effect of the secondary iron and the front and rear quadrupole iron of the secondary iron.

Description

Technical Field

[0001] The present invention belongs to the technical field of accelerator transmission lines, and in particular relates to a debugging method for a bending-type beam uniformization transmission line based on a quad-octupole composite magnet. Background Art

[0002] The distribution of the accelerator's extracted beam generally resembles a Gaussian distribution, with the highest particle density at the center of the bunch. This distribution also results in localized overpower and overtemperature on the neutron target, leading to target damage. To address this uneven particle distribution, attempts were made to use octopole magnets in the beam transmission line to homogenize the Gaussian beam. This led to the commissioning of a curved beam homogenization transmission line based on octopole magnets.

[0003] The reason why it is difficult to homogenize the Gaussian distribution beam when debugging the bent beam uniformization transmission line based on the octopole is that the same octopole installed at different positions on the beam transmission line will play different roles. Only when the octopole is installed at a position with a larger beam envelope can it provide the strongest homogenization effect. However, the place with the largest envelope in the existing technology is usually occupied by the quadrupole magnetic field: Figure 6 As shown, the transmission line of the prior art is arranged in the order of quadrupole 1, octupole 1, quadrupole 2, and octupole 2. Since the octupole must first be focused before being homogenized (the function 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 the octupole 1 and the 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 the quadrupole 1 at the waist position of the X-direction envelope is smaller, the X-direction envelope of the quadrupole 2 at the waist position of the Y-direction envelope is smaller. Therefore, at the octupole 1, although the waist position of the octupole 1 in the X-direction is guaranteed, the Y-direction envelope at this location is smaller. Similarly, at the octupole 2, although the waist position of the octupole 2 in the Y-direction is guaranteed, the X-direction envelope at this location is smaller.

[0004] The commissioning of an octopole-based curved beam homogenization transmission line presents difficulties in achieving an ultra-short, strong homogenization transmission line. One reason for this difficulty is that a curved transmission line requires a diode between the quadrupole and octopole to bend the beam. Because the diode exhibits entrance and exit edge focusing effects, to minimize these edge effects from affecting the beam envelope, the quadrupole, diode, and octopole must be spaced apart, resulting in a long transmission line. A second reason is that achieving optimal beam homogenization requires stringent requirements for the placement and phase of the octopole magnets. To meet these requirements, the transmission line often requires lengths exceeding several meters. Cyclotrons typically have diameters of no more than two meters, and a beam line several dozen meters long renders the accelerator significantly less efficient. Furthermore, the longer the beam line, the more expensive the shielding work becomes. In short, the drawbacks of excessively long transmission lines, such as the large footprint and high cost, significantly limit the use of beam homogenization technology. Summary of the Invention

[0005] This invention addresses the problems of the prior art by proposing a method for debugging a curved beam uniformization transmission line based on a quad-octupole composite magnet. The first objective is to address the difficulty in homogenizing a Gaussian-distributed beam using octupole-based beam uniformization. The second objective is to address the difficulty in achieving an ultrashort, strong-retention uniformization transmission line using octupole-based beam uniformization.

[0006] The present invention adopts the following technical solutions to solve the technical problems:

[0007] A method for debugging a bent-type beam uniformization transmission line based on a quad-octupole composite magnet, the method being based on a quad-octupole composite iron, a quad-octupole composite iron system, a quad-octupole composite iron excitation current adjustment method, and an ultra-short bent-type beam uniformization transmission line;

[0008] Its characteristic is that the debugging method includes the following steps:

[0009] Step 1: set the quadrupole field and octupole field current of the quadrupole iron and the two quadrupole-octupole composite irons to zero;

[0010] Step 2: Adjust the diode current so that the center of the beam spot is roughly aligned with the center of the fluorescent target;

[0011] Step 3: Observe the changes in the beam envelope on the fluorescent target and adjust the quadrupole iron current in front of the quad-octupole iron complex 1 so that the beam forms a waist in the X direction near the quad-octupole iron complex 1.

[0012] Step 4: Observe the changes in the beam envelope on the fluorescent target and adjust the quadrupole field current of the quadruple-octupole composite iron 1 in front of the dipole iron. Under the combined action of the fringe field of the dipole iron and the quadrupole field of the quadruple-octupole composite iron 1, the beam is waisted in the Y direction near the quadruple-octupole composite iron 2, while retaining the quadrupole field gradient of the quadruple-octupole composite iron 1 at this time.

[0013] Step 5: Adjust the quadrupole iron current of the quadrupole iron composite 2 so that the X-direction envelope of the beam on the fluorescent target is consistent with the Y-direction envelope to obtain a circular beam, and adjust the dipole iron current again so that the center of the beam spot is aligned with the center of the target, retaining the quadrupole field gradient of the quadrupole iron composite 2 at this time;

[0014] Step 6: Adjust the octopole field of the quadruple-octupole composite iron 1 to adjust the uniformity of the beam in the Y direction. According to the quadruple field gradient of the quadruple-octupole composite iron 1 and the current octopole field gradient of the quadruple-octupole composite iron 1 recorded in step 4, calculate the intersection current that satisfies both the quadruple field gradient and the octopole field gradient of the quadruple-octupole composite iron 1, and retain the octopole field gradient of the quadruple-octupole composite iron 1 at this time.

[0015] Step 7: If the uniformity of the beam current does not change significantly when the octopole field current of the quad-octopole composite iron 1 is adjusted, it is necessary to modify the quadrupole field gradient of the quad-octopole composite iron 1 for phase shift matching so that the Y-direction phase shift from the quad-octopole composite iron 1 to the target is close to 180°, that is, based on the adjusted quadrupole field gradient of the quad-octopole composite iron 1 and the octopole field gradient retained in step 6, calculate the current at the intersection that simultaneously satisfies the quadrupole field gradient and the octopole field gradient of the quad-octopole composite iron 1;

[0016] Step 8: Adjust the octopole field of the quadruple-octupole composite iron 2 to adjust the uniformity of the beam in the X direction. According to the quadruple field gradient of the quadruple-octupole composite iron 2 and the current octopole field gradient of the quadruple-octupole composite iron 2 recorded in step 5, calculate the intersection current that satisfies both the quadruple field gradient and the octopole field gradient of the quadruple-octupole composite iron 2, and retain the octopole field gradient of the quadruple-octupole composite iron 2 at this time.

[0017] Step 9: If the beam current uniformity does not change significantly when adjusting the octupole field current of the quad-octupole composite iron 2, it is necessary to increase the X-direction beam envelope at the quad-octupole composite iron 2;

[0018] Furthermore, the specific process of step 2 is as follows:

[0019] To protect the components on the transmission line, calculate and set the initial current value of the diode based on the current beam parameters and the number of turns of the diode coil. Observe whether a beam appears on the fluorescent target. If not, adjust the diode current value around the initial current value until a beam appears on the fluorescent target. At this point, the quadrupole field currents of the quadrupole and the two quad-octupole composite irons are both zero, and the beam envelope is large. Align the beam roughly with the center of the target before proceeding to the next step.

[0020] Furthermore, the specific process of step three is as follows:

[0021] 1) Starting from zero, gradually increase the quadrupole iron current in front of the quadruple-octupole composite magnet 1. Observe that the X-direction envelope size of the beam on the fluorescent target gradually decreases. Continue to increase the quadrupole iron current until the X-direction envelope size on the target increases, indicating that the X-direction beam waist is formed somewhere between the quadrupole iron and the target (near the target).

[0022] 2) To make the X-direction beam waist near the quadrupole iron compound 1, it is necessary to continue increasing the quadrupole iron current to shift the X-direction beam waist to the left. Stop increasing the current until the following condition is reached: increasing the quadrupole field current of the quadrupole iron compound 1 and observing that the X-direction beam envelope size on the fluorescent target hardly changes, at which point the X-direction beam waist is near the quadrupole iron compound 1;

[0023] Furthermore, the specific process of step 4 is as follows:

[0024] 1) Gradually increase the quadrupole field current of the quadrupole-octupole composite magnet 1 from zero. Observe that the Y-direction envelope size of the beam on the fluorescent target gradually decreases. Continue to increase the quadrupole field current of the quadrupole-octupole composite magnet 1 until the Y-direction envelope size on the target increases. This indicates that the Y-direction beam waist is formed somewhere between the quadrupole-octupole composite magnet 1 and the target (near the target).

[0025] 2) To make the Y-direction beam waist near the quadrupole iron composite 2, it is necessary to continue increasing the quadrupole field current of the quadrupole iron composite 1 to shift the Y-direction beam waist to the left. Stop increasing the quadrupole field current when the following condition is reached: when the quadrupole field current of the quadrupole iron composite 2 is increased and the Y-direction beam envelope size on the fluorescent target is observed to be almost unchanged, the Y-direction beam waist is now near the quadrupole iron composite 2.

[0026] Furthermore, the specific process of step five is as follows:

[0027] After steps 1 to 4, ideally, the beam envelope size in the X direction should be larger than the Y direction envelope size. Starting from zero, gradually increase the quadrupole field current of the quadruple-octupole composite magnet 2. Observe on the fluorescent target that the beam envelope size in the X direction gradually decreases. Continue to increase the quadrupole field current of the quadruple-octupole composite magnet 2 until the beam envelope size in the X direction is consistent with the Y direction envelope size on the target.

[0028] If the envelope dimensions in the X and Y directions do not meet expectations after steps 1 to 4, the following adjustments should be made:

[0029] 1) If the X-direction size of the fluorescent target beam is larger than the target size, reduce the quadrupole iron current in front of the quadruple-octupole composite magnet 1 or increase the quadrupole field current of the quadruple-octupole composite magnet 2; if the X-direction size of the beam is smaller than the target size, increase the quadrupole iron current in front of the quadruple-octupole composite magnet 1 or reduce the quadruple field current of the quadruple-octupole composite magnet 2.

[0030] 2) If the Y-direction envelope size of the beam on the fluorescent target is larger than the target size, reduce the quadrupole field current of the quadruple-octupole composite magnet 1; if the Y-direction size of the beam is smaller than the target size, increase the quadrupole field current of the quadruple-octupole composite magnet 1.

[0031] The target size mentioned above is specifically: a square target is usually set at the end of the transmission line. If the side length of the target is L, the target size is That is, the diameter of the circular beam is

[0032] After the above operation, the beam spot can be clearly observed on the target. The diode iron current is adjusted again to align the center of the beam spot with the center of the target. After the adjustment, it is necessary to reconfirm that the X-direction beam waist is near the quad-octupole composite iron 1 and the Y-direction beam waist is near the quad-octupole composite iron 2 according to the methods described in claims 2 and 3.

[0033] Furthermore, the step 6 of adjusting the Y-direction uniformity effect on the fluorescent target by the octupole field of the quad-octupole composite magnet 1 is specifically as follows:

[0034] The brightness of the beam spot on the fluorescent target in the Y direction is uneven. If the brightness of the beam spot on the fluorescent target is bright in the middle and dark on both sides in the Y direction, increase the eight-pole field current of the four-octupole composite magnet 1 until the brightness of the beam spot on the fluorescent target in the Y direction is evenly distributed and the shape of the beam spot changes from a circle to a rectangle. If the brightness of the beam spot on the fluorescent target is bright on both sides and dark in the Y direction, reduce the eight-pole field current of the four-octupole composite magnet 1 until the brightness of the beam spot on the fluorescent target in the Y direction is evenly distributed and the shape of the beam spot changes from a circle to a rectangle.

[0035] Furthermore, the step seven of fine-tuning the phase of the quad-eightpole composite magnet 1 to be close to 180 degrees is specifically as follows:

[0036] 1) Increase the octupole field current of the quad-octupole composite iron 1 and observe whether the brightness change in the Y direction of the beam spot on the fluorescent target is significant; if the brightness in the middle and both sides of the Y direction of the beam spot on the fluorescent target is almost unchanged, it means that the Y-direction phase shift of the quad-octupole composite magnet 1 to the target is significantly different from 180°. If the Y-direction of the beam spot on the fluorescent target changes from bright to dark in the middle and from dark to bright on both sides, or from dark to bright in the middle and from bright to dark on both sides, it means that the Y-direction phase shift of the quad-octupole composite magnet 1 to the target is close to 180°. The bright color indicates that there are many particles, and the dark color indicates that there are few particles.

[0037] 2) When the brightness of the beam spot in the Y direction on the fluorescent target does not change significantly, it proves that the difference between the Y phase shift of the beam between the quad-octupole composite magnet 1 and the target is large and 180 degrees. Assuming that the current phase shift is less than 180 degrees, reduce the quadrupole iron current in front of the quad-octupole composite magnet 1, or increase the quadrupole iron current of the quad-octupole composite magnet 1. After completing the operation, observe again according to the method in 1). If the brightness of the beam spot in the Y direction on the fluorescent target changes significantly when the octupole field current of the quad-octupole composite magnet 1 is increased, it means that the assumption is correct. If the brightness of the beam spot in the Y direction on the fluorescent target remains almost unchanged, it means that the current phase shift is greater than 180 degrees. Increase the quadrupole iron current in front of the quad-octupole composite magnet 1, or reduce the quadrupole iron current of the quad-octupole composite magnet 1. After completing the operation, observe again according to the method in 1) until the brightness of the beam spot in the Y direction on the fluorescent target changes significantly when the octupole field current of the quad-octupole composite magnet 1 is increased. After completing the operation, observe again according to the method in 1) until the brightness of the beam spot in the Y direction on the fluorescent target changes significantly when the octupole field current of the quad-octupole composite magnet 1 is increased.

[0038] Furthermore, the step eight of adjusting the X-direction uniformity effect on the fluorescent target by the octupole field of the quad-octupole composite magnet 2 is specifically as follows:

[0039] The brightness of the beam spot on the fluorescent target in the X direction is uneven. If the beam spot on the fluorescent target is bright in the middle and dark on both sides in the X direction, increase the octapole field current of the quad-octapole composite magnet 2 until the brightness distribution of the beam spot on the fluorescent target in the X direction is uniform and the shape of the beam spot changes from a rectangle to a square. If the beam spot on the fluorescent target is bright on both sides and dark in the X direction, reduce the octapole field current of the quad-octapole composite magnet 2 until the brightness distribution of the beam spot on the fluorescent target in the X direction is uniform and the shape of the beam spot changes from a rectangle to a square.

[0040] Furthermore, the step nine of increasing the X-direction beam envelope at the quad-octupole composite magnet 2 is specifically as follows:

[0041] 1) Increase the octupole field current of the quad-octupole composite iron 2 and observe whether the brightness of the beam spot in the X direction on the fluorescent target changes significantly. If the brightness of the center and both sides of the beam spot in the X direction on the fluorescent target remains almost unchanged, it indicates that the X-direction beam envelope at the quad-octupole composite magnet 2 is small. If the center of the beam spot in the X direction on the fluorescent target changes from bright to dark and both sides change from dark to bright, or the center changes from dark to bright and both sides change from bright to dark, it indicates that the X-direction beam envelope size at the quad-octupole composite magnet 2 meets the uniformity requirement. Bright indicates more particles, and dark indicates fewer particles.

[0042] 2) When the brightness of the beam spot in the X direction on the fluorescent target does not change significantly, increase the quadrupole iron current and observe again according to the method in 1) whether the brightness of the beam spot in the X direction on the fluorescent target changes significantly when the octupole field current of the quad-octupole composite iron 2 is increased. If the brightness of the beam spot does not change significantly, continue to increase the quadrupole iron current. If the brightness of the beam spot changes significantly, the size of the beam envelope in the X direction at the quad-octupole composite magnet 2 meets the uniformity requirements and the adjustment is complete.

[0043] Advantages and effects of the present invention

[0044] 1. The present invention solves the problem of using a secondary iron on an ultra-short transmission line. Since the secondary iron is very close to the front quad-octapole composite iron 1 and the rear quad-octapole composite iron 2 on the ultra-short transmission line, the fringe field focusing effect at the entrance and exit edges of the secondary iron will affect them. Therefore, the present invention utilizes the fringe field effect of the secondary iron and creates a superposition effect with the front and rear quadrupole irons, thus solving the problem of using a secondary iron on an ultra-short transmission line.

[0045] 2. The present invention replaces the prior art method of separately adjusting the quadrupole iron 1 and the octupole iron 1 by adjusting whether the quadrupole iron 1 is at the waist in the X direction (at the large envelope in the Y direction); replaces the prior art method of separately adjusting the quadrupole iron 2 and the octupole iron 2 by adjusting whether the quadrupole iron 2 is at the large envelope in the X direction (at the waist in the Y direction); further ensures a better homogenization effect at the quadrupole iron 1 by adjusting whether the phase of the quadrupole iron 1 is close to 180 degrees; and further ensures a better homogenization effect at the quadrupole iron 2 by adjusting whether the phase of the quadrupole iron 2 is close to 0 degrees. This solves the problem that the beam homogenization adjustment based on the octupole iron is difficult to homogenize the Gaussian distribution beam.

[0046] 3. The present invention adopts a method of solving the coupling between the quadrupole field and the octupole field of the four-octupole composite iron by solving the intersection point current multiple times. The quadrupole field and the octupole field of the four-octupole composite iron are coupled: the coupling relationship is: first adjust the current size of the four-octupole composite iron quadrupole field coil, and then adjust the current size of the octupole field coil. Adjusting the octupole field coil current will change the quadrupole magnetic field gradient adjusted before; first adjust the current size of the four-octupole composite iron octupole field coil, and then adjust the current size of the quadrupole field coil. The quadrupole field coil current will change the octupole magnetic field gradient adjusted before. The solution is that each time the current gradient value is modified, the modified gradient value (quadrupole field or octupole field) and the previously retained gradient value (octupole field or quadrupole field) are used to intersect with the magnetic field gradient surface of the three-dimensional sample database. After the intersection, Figure 5h As shown, two corresponding current curves are obtained. The intersection point of these two current curves is shown as Figure 5i As shown, the current value at the intersection point meets the requirements of both the current octupole field gradient and the quadrupole field gradient. In this way, the problem of coupling relationship when the four-octupole composite iron is combined is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1a This is a flow chart of a method for debugging a bending beam homogenization based on a quad-octupole composite magnet according to the present invention;

[0048] Figure 1bSchematic diagram of the ultra-short bend beam uniformization transmission line A of the present invention;

[0049] Figure 1c Schematic diagram of the ultra-short bend beam uniformization transmission line B of the present invention;

[0050] Figure 1d Schematic diagram of the linear beam uniformization transmission line and beam uniformization effect observation mechanism of the present invention;

[0051] Figure 1e Schematic diagram comparing the particle distribution states before and after the transmission line is homogenized according to the present invention;

[0052] Figure 1f Schematic diagram of the transmission line beam matching and uniformity effect observation mechanism 1 of the present invention;

[0053] Figure 1g Schematic diagram of the transmission line beam matching and uniformity effect observation mechanism 2 of the present invention;

[0054] Figure 2 Schematic diagram of the maximum envelope position of each of the four-octupole composite iron 1 and 2 of the present invention;

[0055] Figure 3 This is a schematic diagram showing the representative meanings of the four points 0, 1, 2, and 3 involved in formulas (1) and (2) of the present invention.

[0056] Figure 4 Schematic diagram of the phase difference between two pieces of quad-octapole composite iron to the target point (target) and the phase difference between the two pieces of quad-octapole composite iron;

[0057] Figure 5a Schematic diagram of the quad-octapole composite magnet current control device of the present invention;

[0058] Figure 5b This is the new quadrupole / octupole composite iron model of the present invention;

[0059] Figure 5c The arrangement of the coils and the current direction of the four-eight-pole composite magnet of the present invention;

[0060] Figure 5d This is a schematic diagram of the current values of the two sets of coils during magnetic field measurement of the present invention;

[0061] Figure 5e This is a schematic diagram of the quadrupole magnetic field gradient corresponding to different currents measured in the experiment of the present invention;

[0062] Figure 5f This is a schematic diagram of the density of two-dimensional interpolation encrypted grid points using a cubic spline function in the present invention;

[0063] Figure 5gA schematic diagram of the intersection of the magnetic field gradient plane selected for the present invention and the magnetic field gradient curved surface of the three-dimensional sample database;

[0064] Figure 5h The current curve corresponding to the quadrupole / octupole field is selected for the present invention;

[0065] Figure 5i Schematic diagram for solving the composite iron excitation current of the present invention;

[0066] Figure 6 Schematic diagram of the prior art octupole iron in a small envelope position;

[0067] Figure 7 This is a schematic diagram of an embodiment of an ultra-short straight beam uniformization transmission line according to the present invention. DETAILED DESCRIPTION

[0068] Design principle of the present invention

[0069] 1. Innovation of the present invention

[0070] One of the innovations is that the combination debugging based on quadrupole iron, quad-octupole composite iron 1, secondary iron, quad-octupole composite iron 2 replaces the combination debugging based on quadrupole iron 1, octupole 1, secondary iron, quadrupole iron 2, octupole 2, thereby solving the problem of beam uniformity and the problem of establishing an ultra-short transmission line; the difference between the present invention and the prior art is that: ① Since the quad-octupole composite iron 1 and the quad-octupole composite iron 2 replace the octupole iron 1 and octupole iron 2 on the traditional transmission line, the quad-octupole composite iron 1 and the quad-octupole composite iron 2 are respectively located at Y The invention solves the problem of beam uniformity by adjusting the large envelope in the X direction (waist in the X direction) and the large envelope in the X direction (waist in the Y direction). Specifically, the method of adjusting whether the quad-octupole composite iron 1 is at the waist in the X direction (large envelope in the Y direction) and whether the quad-octupole composite iron 2 is at the waist in the Y direction (large envelope in the X direction) is used instead of the method of separately adjusting the quadrupole composite iron 1 and the octupole composite iron 1, and the quadrupole composite iron 2 and the octupole composite iron 2 in the prior art. After the adjustment, the quad-octupole composite iron 1 and the quad-octupole composite iron 2 are both located in the large envelope in the Y direction and the X direction, thereby solving the problem of beam uniformity.

[0071] The second innovation is that it solves the problem of using a secondary iron in ultra-short transmission lines. Because the secondary iron is very close to the front quad-octapole composite iron 1 and the rear quad-octapole composite iron 2 on the ultra-short transmission line, the fringe field focusing effect at the entrance and exit edges of the secondary iron will affect them. Therefore, the present invention takes advantage of the fringe field effect of the secondary iron and creates a superposition effect with the front and rear quadrupole irons, thus solving the problem of using a secondary iron in ultra-short transmission lines. Specifically, at the current intersection point of the quadruple-octupole composite iron 1, the quadruple iron current of the quadruple-octupole composite iron 1 is appropriately reduced, and the edge field focusing effect of the dipole iron entrance behind the quadruple-octupole composite iron 1 and the quadruple iron focusing effect of the quadruple-octupole composite iron 1 itself are superimposed to generate the Y-direction waist of the quadruple-octupole composite iron 2; at the current intersection point of the quadruple-octupole composite iron 2, the quadruple iron current of the quadruple-octupole composite iron 2 is appropriately reduced, and the edge field focusing effect of the dipole iron exit behind the quadruple-octupole composite iron 1 and the quadruple iron focusing effect of the quadruple-octupole composite iron 2 itself are superimposed to generate the X-direction envelope size on the target, so that the envelope sizes in the X and Y directions are consistent.

[0072] The third innovation is to solve the beam uniformity problem from the debugging method. The debugging method is to solve the problem of how to adjust. Since there is a coupling relationship when the quadrupole iron and the octupole iron are combined together, each time the current gradient value is modified, the modified gradient value (quadrupole field or octupole field) and the previously retained gradient value (octupole field or quadrupole field) are intersected with the magnetic field gradient surface of the three-dimensional sample database. Figure 5h As shown, two corresponding current curves are obtained. The intersection point of these two current curves is shown as Figure 5i As shown, the current value at the intersection point meets the requirements of both the current octupole field gradient and the quadrupole field gradient. In this way, the problem of coupling relationship when the four-octupole composite iron is combined is solved.

[0073] 2. Design principle of quadrupole / octupole composite iron

[0074] This debugging method is based on a quadrupole / octupole composite iron, which is as follows Figure 5b 、 5cAs shown, there are eight pole heads in total. Each pole head is provided with an inner and outer layer of current coils along the radial direction near the large radius. The inner coil is an octapole magnetic field excitation coil, and the outer coil is a quadrupole magnetic field excitation coil. The inner octapole magnetic field excitation coil has currents in opposite directions between the two adjacent pole heads, that is, the octapole field coil is divided into two groups: 1, 3, 5, 7 pole heads and 2, 4, 6, 8 pole heads. The excitation currents of the two groups are equal in magnitude but opposite in direction, thereby generating an octapole magnetic field. The outer quadrupole magnetic field excitation coil has adjacent currents in opposite directions. The coils on the two poles form a group, which is divided into four groups, namely poles 1 and 2, poles 3 and 4, poles 5 and 6, and poles 7 and 8. Among them, the excitation currents of the poles 1 and 2 and the symmetrically arranged poles 5 and 6, the two groups of quadrupole magnetic field coils, are consistent in magnitude and direction, the excitation currents of the poles 3 and 4 and the symmetrically arranged poles 7 and 8, the two groups of coils are consistent in magnitude and direction, the current directions of the poles 1 and 2 and the coils of the poles 3 and 4 are opposite, and the directions of the poles 5 and 6 and the coils of the poles 7 and 8 are opposite, thereby generating a quadrupole magnetic field;

[0075] 3. Design principle of four / octapole composite iron system

[0076] This debugging method is based on a four / octapole composite iron system, such as Figure 5a As shown, the composite magnet current control device includes: a module for establishing two-dimensional sampling points of coil current, a module for preliminarily establishing a three-dimensional surface sample library of magnetic field gradients through experimental measurement, a module for refining the three-dimensional surface sample library of magnetic field gradients using interpolation, a module for inputting field gradients to solve corresponding field gradient current curves, a module for solving intersection points of quadrupole / octupole field gradient current curves, and a module for outputting quadrupole / octupole coil currents;

[0077] like Figure 5d As shown, the module for establishing coil current two-dimensional sampling points is used to establish a two-dimensional data comparison table of coil current of quadrupole iron and octupole iron;

[0078] like Figure 5e As shown, the experimental measurement preliminarily establishes a magnetic field gradient three-dimensional surface sample library module, which uses the current value of the coil current two-dimensional data comparison table to perform magnetic field experimental measurement on the composite iron, thereby obtaining quadrupole and octupole magnetic field gradient measurement values that correspond one-to-one to the two-dimensional current data comparison table, thereby obtaining a three-dimensional surface sample database of the magnetic field gradient; the above-mentioned three-dimensional surface sample database of the magnetic field gradient includes a quadrupole field magnetic field gradient three-dimensional surface sample database and an octupole field magnetic field gradient three-dimensional surface sample database;

[0079] like Figure 5f As shown, the module for refining the magnetic field gradient three-dimensional surface sample library by interpolation is used to perform two-dimensional interpolation on the quadrupole field magnetic field gradient three-dimensional surface sample database and the octopole field magnetic field gradient three-dimensional surface sample database using a cubic spline function to encrypt the grid point density;

[0080] like Figure 5g As shown, the input field gradient solution corresponding field gradient current curve module is used to select a quadrupole field magnetic field gradient plane, which intersects with the surface of the quadrupole field magnetic field gradient three-dimensional surface sample database to obtain a current curve that satisfies the four-level field gradient; select an octopole field magnetic field gradient plane, which intersects with the surface of the octopole field magnetic field gradient three-dimensional surface sample database to obtain a current curve that satisfies the eight-level field gradient;

[0081] like Figure 5h As shown, the input field gradient solution corresponding field gradient current curve module is also 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;

[0082] like Figure 5i As shown, the module for solving the intersection of the quadrupole / octupole field gradient current curve is used to obtain the intersection of the current curve that satisfies the quadrupole field gradient and the current curve that satisfies the octupole field gradient, and use the intersection as the solution of the composite iron excitation current;

[0083] The output quadrupole / octupole coil current module outputs quadrupole field coil current and octupole field coil current to the quadrupole / octupole composite iron according to the solution of the composite iron excitation current.

[0084] 4. Design principle of the four-pole / octapole composite iron excitation current adjustment method

[0085] This debugging method is based on a four-pole / eight-pole composite iron excitation current adjustment method, including the following steps:

[0086] 1) If Figure 5d As shown, a two-dimensional data comparison table of coil currents of quadrupole iron and octupole iron is established; the two-dimensional data comparison table of coil currents is based on a two-dimensional data comparison table of coil currents of quadrupole / octupole composite iron;

[0087] 2) If Figure 5e As shown, the experimental measurement obtains the quadrupole and octupole magnetic field gradient measurement values corresponding 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 magnetic field gradient and a three-dimensional surface sample database of the octupole magnetic field gradient;

[0088] 3) If Figure 5f As shown, a cubic spline function is used to perform two-dimensional interpolation on the quadrupole magnetic field gradient three-dimensional surface sample database and the octopole magnetic field gradient three-dimensional surface sample database to encrypt the grid point density;

[0089] 4) If Figure 5gAs shown, a quadrupole magnetic field gradient plane is selected, and the plane intersects with the surface of the quadrupole magnetic field gradient three-dimensional curved surface sample database to obtain a current curve that satisfies the four-level field gradient; an octopole magnetic field gradient plane is selected, and the plane intersects with the surface of the octopole magnetic field gradient three-dimensional curved surface sample database to obtain a current curve that satisfies the eight-level field gradient;

[0090] 5) If Figure 5h As shown, a current curve satisfying a fourth-order field gradient and a current curve satisfying an eighth-order field gradient are obtained in the two-dimensional data grid plane of the coil current, and finally the intersection point of the above two current curves is obtained;

[0091] 6) If Figure 5i As shown, the intersection point is used as the solution for the composite iron excitation current;

[0092] 5. Design principle of ultra-short bend beam uniformization transmission line

[0093] This debugging method is based on an ultra-short bend-type beam uniformization transmission line. Figure 1b 、 1c , 1d, 1e, 1f, 1g, based on the above invention principles, the present invention designs an ultra-short bend-type beam uniformization transmission line, such as Figure 1b 、 1c As shown, its characteristics are: the transmission line is an ultra-short bend-type beam homogenization transmission line comprising two pieces of 4-8 grade composite iron and one piece of secondary iron; the ultra-short bend-type beam homogenization transmission line is an ultra-short bend-type beam homogenization transmission line A arranged along the beam direction, or an ultra-short bend-type beam homogenization transmission line B arranged along the beam direction: the ultra-short bend-type beam homogenization transmission line A is provided with: an accelerator outlet, a beam matching mechanism, 4-8 grade composite iron 1, secondary iron, 4-8 grade composite iron 2, a beam matching and homogenization effect observation mechanism 1, and a terminal 1 in sequence along the beam extraction direction; the ultra-short bend-type beam homogenization transmission line B is provided with: an accelerator outlet, a beam matching mechanism, 4-8 grade composite iron 1, secondary iron, 4-8 grade composite iron 3, a beam matching and homogenization effect observation mechanism 2, and a terminal 2 in sequence along the beam extraction direction;

[0094] like Figure 1b 、 1c As shown, the four-eighth grade composite iron 1, the four-eighth grade composite iron 2, or the four-eighth grade composite iron 1, the four-eighth grade composite iron 3 respectively generate a quadrupole magnetic field and an octupole magnetic field at the same time, so that only one transmission element is installed to realize the functions of the quadrupole iron and the octupole iron at the same time;

[0095] like Figure 2As shown, at the 48-level composite iron 1, the beam envelope function in the Y direction or X direction reaches a maximum value, and at the 48-level composite iron 2 or the 48-level composite iron 3, the beam envelope function in the X direction or Y direction reaches a maximum value; the phase shift of the particles between the 48-level composite iron 1 and the 48-level composite iron 2 and the target, or between the 48-level composite iron 1 and the 48-level composite iron 3 and the target They are close to integer multiples of 180 degrees (0, 1, 2, 3...); the transmission matrix between the two octupole magnetic fields is close to the unit matrix.

[0096] Supplementary Note 1:

[0097] The above-mentioned "phase shift of particles between two four-eight-pole composite magnets and the target They are respectively close to integer multiples of 180 degrees (0, 1, 2, 3...) but not equal to 180 degrees. The principle is shown in the following formulas (1) and (2):

[0098]

[0099] In formula (1), since the molecule Csc[ux23]=1 / sin[ux23], when ux23 approaches 180, sin[ux23] tends to 0 and Csc[ux23] tends to infinity; similarly, the molecule Csc[uy13]=1 / sin[uy13] in formula (2) tends to 0 and Csc[uy13] tends to infinity when ux13 approaches 180; therefore, the phase shift of the particle between the two four-eightpole composite magnets and the target is They are close to but not equal to integer multiples of 180 degrees (0, 1, 2, 3...).

[0100] like Figure 5a As shown, the four-eight-level composite iron 1, the four-eight-level composite iron 2 or the four-eight-level composite iron 3 is based on a four-eight-pole composite magnet system, and the four-eight-pole composite magnet system includes a composite magnet current control device, a composite magnet main power supply and a four-eight-pole composite magnet; the composite magnet current control device is used to control the composite magnet main power supply to output the quadrupole field coil current and the octapole field coil current of the four-eight-pole composite magnet;

[0101] like Figure 1d As shown, the beam matching mechanism is used to observe the initial state of the beam drawn out by the accelerator, and adjust the envelope size of the beam in the X or Y direction according to the initial state, and align the beam center with the mechanical center of the beam pipe;

[0102] like Figure 1f 、 1gAs shown, the beam matching and homogenization effect observation mechanism 1 or the beam matching and homogenization effect observation mechanism 2 is used to adjust the eccentricity of the beam after passing through the secondary iron, and observe the beam intensity, weak beam shape and strong beam shape after being homogenized by the four-eighth grade composite iron 1 and the four-eighth grade composite iron 2.

[0103] like Figure 1d 、 1e As shown, the beam matching mechanism includes a fluorescent target 1, a quadrupole magnet, and a guide magnet; the fluorescent target 1 provides the tester with an initial beam position; the quadrupole magnet is used to provide a beam envelope in the opposite direction for the quadrupole-eighth composite iron 1; and the guide magnet is used to adjust the eccentricity of the beam.

[0104] like Figure 1f 、 1g As shown, the beam matching and homogenization effect observation mechanism 1 includes a guide magnet 2, a Faraday cup 1, a fluorescent target 2, and a double wire 1; the guide magnet 2 is used to align the beam center with the mechanical center of the beam tube; the Faraday cup 1 is used to measure the beam intensity after homogenization, the fluorescent target 2 is used to observe the shape of the weak beam after homogenization; the double wire 1 is used to observe the shape of the strong beam after homogenization; the beam matching and homogenization effect observation mechanism 2 includes a guide magnet 3, a Faraday cup 3, a fluorescent target 3, and a double wire 2; the guide magnet 3 is used to align the beam center with the mechanical center of the beam tube; the Faraday cup 2 is used to measure the beam intensity after homogenization, the fluorescent target 3 is used to observe the shape of the weak beam after homogenization; the double wire 2 is used to observe the shape of the strong beam after homogenization.

[0105] like Figure 3 As shown, 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 is Or the phase shift of particles between the four-eighth grade composite iron 1 and the four-eighth grade composite iron 3 and the target Close to an integer multiple of 180 degrees, means close to but not equal to an integer multiple of 180 degrees: Let for The remainder of 180 degrees, The value is generally less than ±15 degrees.

[0106] like Figure 3 As shown, 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 a range of 30 degrees. This 30-degree range can greatly avoid the high-order nonlinear effects caused by the coupling of the two octupole magnets and can achieve a better homogenization effect.

[0107] The expression of the magnetic strength k at the 48-grade composite iron 1 and the 48-grade composite iron 2, or the magnetic strength k at the 48-grade composite iron 1 and the 48-grade composite iron 3 is:

[0108]

[0109] Assume that the starting point of the transport line is 0, the position of the first quadruple-octapole magnet is 1, the position of the second quadruple-octapole magnet is 2, and the end point, i.e., the position of the target, is 3; ux02 in the above formula (1) represents the phase shift of the particle in the x direction between positions 0 and 2, ux23 represents the phase shift of the particle in the x direction between positions 2 and 3; βx2 represents the envelope function in the x direction at position 2; uy01 in the above formula (2) represents the phase shift of the particle in the y direction between 0 and 1; uy13 represents the phase shift of the particle in the y direction between 1 and 3; βy1 represents the envelope function in the y direction at position 1.

[0110] Supplementary Note 2

[0111] The derivation process of the above formulas (1) and (2) is briefly described as follows: In the reference "Yosuke Yuri, Uniformization of the transverse beam profile by means of nonlinear focusing method [J]. Physical Review Special Topics-Accelerators and Beams, 2007. DOI: 10.1103 / physrevstab.10.104001.", a formula for the octopole magnetic field strength in a single direction is given. This formula only considers one octopole magnet and the subsequent transmission section. To more accurately describe the relationship between the octopole magnetic field strength and the transmission line design, we expand this formula to consider the effect of the matching section from the accelerator exit to the octopole iron on beam uniformity. The parameters involved are 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 in the reference, the expressions of the magnet strength k at the first quadruple-octapole composite magnet and the second quadruple-octapole composite magnet are obtained: Formula (1) and Formula (2).

[0112] Based on the above principles, the present invention designs a method for debugging a bending-type beam uniformization transmission line based on a quad-octupole composite magnet, as shown in Figure 1. The debugging method is based on a quad-octupole composite iron, a quad-octupole composite iron system, a quad-octupole composite iron excitation current adjustment method, and an ultra-short bending-type beam uniformization transmission line;

[0113] Its characteristic is that the debugging method includes the following steps:

[0114] Step 1: set the quadrupole field and octupole field current of the quadrupole iron and the two quadrupole-octupole composite irons to zero;

[0115] Step 2: Adjust the diode current so that the center of the beam spot is roughly aligned with the center of the fluorescent target;

[0116] The specific process is as follows:

[0117] To protect the components on the transmission line, calculate and set the initial current value of the diode based on the current beam parameters and the number of turns of the diode coil. Observe whether a beam appears on the fluorescent target. If not, adjust the diode current value around the initial current value until a beam appears on the fluorescent target. At this point, the quadrupole field currents of the quadrupole and the two quad-octupole composite irons are both zero, and the beam envelope is large. Align the beam roughly with the center of the target before proceeding to the next step.

[0118] Step 3: Observe the changes in the beam envelope on the fluorescent target and adjust the quadrupole iron current in front of the quad-octupole iron complex 1 so that the beam forms a waist in the X direction near the quad-octupole iron complex 1.

[0119] The specific process is as follows:

[0120] 1) Starting from zero, gradually increase the quadrupole iron current in front of the quadruple-octupole composite magnet 1. Observe that the X-direction envelope size of the beam on the fluorescent target gradually decreases. Continue to increase the quadrupole iron current until the X-direction envelope size on the target increases, indicating that the X-direction beam waist is formed somewhere between the quadrupole iron and the target (near the target).

[0121] 2) To make the X-direction beam waist near the quadrupole iron compound 1, it is necessary to continue increasing the quadrupole iron current to shift the X-direction beam waist to the left. Stop increasing the current until the following condition is reached: increasing the quadrupole field current of the quadrupole iron compound 1 and observing that the X-direction beam envelope size on the fluorescent target hardly changes, at which point the X-direction beam waist is near the quadrupole iron compound 1;

[0122] Supplementary Note A:

[0123] ① If the beam is waisted in the X direction near the quad-octopole composite iron 1, then the Y direction near the quad-octopole composite iron 1 is large. Observing the change in beam spot size on the target cannot accurately determine whether the beam has a large Y direction envelope. For example, a large Y direction envelope is considered when the Y direction envelope is close to 2.5 cm. By varying the quadrupole field current of the quad-octopole composite iron 1, significant changes in the Y direction of the beam on the target can be observed. However, even when the Y direction envelope is less than 2.5 cm, such as 1 cm, significant changes in the Y direction of the beam on the target can still be observed when varying the quadrupole field current of the quad-octopole composite iron 1. Therefore, the change in the beam envelope on the target cannot be used to determine whether the Y direction envelope at the quad-octopole composite iron 1 is large. The quadrupole iron in front of the quad-octopole composite iron 1 is focused in the X direction but defocused in the Y direction. When the beam envelope at the quad-octopole composite iron 1 is waisted in the X direction, the Y direction envelope is considered large.

[0124] ② Use the current of the quadrupole iron in front of the quadruple-octupole iron 1 to adjust the large envelope (waisted in the X direction) at the quadruple-octupole iron 1. The stronger the current of the front quadrupole iron, the higher the Y-direction beam envelope (dashed line) at the quadruple-octupole iron 1 will be. The dotted line and the quadrupole iron of the quadruple-octupole iron 1 itself (the quadruple iron of the quadruple-octupole iron 1 itself is in a focused state with the dotted line tilted downward) together form a large envelope.

[0125] Step 4: Observe the changes in the beam envelope on the fluorescent target and adjust the quadrupole field current of the quadruple-octupole composite iron 1 in front of the dipole iron. Under the combined action of the fringe field of the dipole iron and the quadrupole field of the quadruple-octupole composite iron 1, the beam is waisted in the Y direction near the quadruple-octupole composite iron 2, while retaining the quadrupole field gradient of the quadruple-octupole composite iron 1 at this time.

[0126] The specific process is as follows:

[0127] 1) Gradually increase the quadrupole field current of the quadrupole-octupole composite magnet 1 from zero. Observe that the Y-direction envelope size of the beam on the fluorescent target gradually decreases. Continue to increase the quadrupole field current of the quadrupole-octupole composite magnet 1 until the Y-direction envelope size on the target increases. This indicates that the Y-direction beam waist is formed somewhere between the quadrupole-octupole composite magnet 1 and the target (near the target).

[0128] 2) To make the Y-direction beam waist near the quadrupole iron composite 2, it is necessary to continue increasing the quadrupole field current of the quadrupole iron composite 1 to shift the Y-direction beam waist to the left. Stop increasing the quadrupole field current when the following condition is reached: when the quadrupole field current of the quadrupole iron composite 2 is increased and the Y-direction beam envelope size on the fluorescent target is observed to be almost unchanged, the Y-direction beam waist is now near the quadrupole iron composite 2.

[0129] Supplementary Note B:

[0130] like Figure 5gAs shown, the quadrupole field gradient is retained in order to intersect with the subsequent octopole field gradient and the magnetic field gradient surface of the three-dimensional sample database. Figure 5h As shown, two corresponding current curves are obtained. The intersection point of these two current curves is shown as Figure 5i As shown, the current value at the intersection point meets the requirements of the quadrupole field gradient and the octupole field gradient at the same time; thus solving the coupling relationship when the four-octupole composite iron is combined together, first adjust the current size of the magnet quadrupole field coil, adjust the quadrupole magnetic field gradient to meet the use requirements, and then adjust the current size of the octupole field coil. Once the octupole field coil current starts to change, it will change the problem of the quadrupole magnetic field gradient adjusted before, solving the bottleneck problem of beam uniformity debugging based on the four-octupole composite iron.

[0131] Step 5: Adjust the quadrupole iron current of the quadrupole iron composite 2 so that the X-direction envelope of the beam on the fluorescent target is consistent with the Y-direction envelope to obtain a circular beam, and adjust the dipole iron current again so that the center of the beam spot is aligned with the center of the target, retaining the quadrupole field gradient of the quadrupole iron composite 2 at this time;

[0132] Supplementary Note C:

[0133] The fluorescent target of the present invention is as follows Figure 1d As shown, it refers to the fluorescent target 2, which is arranged behind the quad-octapole composite iron 2, approximately at the 5.4-meter position of the 6-meter-long transmission line.

[0134] The specific process is as follows:

[0135] After steps 1 to 4, ideally, the beam envelope size in the X direction should be larger than the Y direction envelope size. Starting from zero, gradually increase the quadrupole field current of the quadruple-octupole composite magnet 2. Observe on the fluorescent target that the beam envelope size in the X direction gradually decreases. Continue to increase the quadrupole field current of the quadruple-octupole composite magnet 2 until the beam envelope size in the X direction is consistent with the Y direction envelope size on the target.

[0136] If the envelope dimensions in the X and Y directions do not meet expectations after steps 1 to 4, the following adjustments should be made:

[0137] 1) If the X-direction size of the fluorescent target beam is larger than the target size, reduce the quadrupole iron current in front of the quadruple-octupole composite magnet 1 or increase the quadrupole field current of the quadruple-octupole composite magnet 2; if the X-direction size of the beam is smaller than the target size, increase the quadrupole iron current in front of the quadruple-octupole composite magnet 1 or reduce the quadruple field current of the quadruple-octupole composite magnet 2.

[0138] 2) If the Y-direction envelope size of the beam on the fluorescent target is larger than the target size, reduce the quadrupole field current of the quadruple-octupole composite magnet 1; if the Y-direction size of the beam is smaller than the target size, increase the quadrupole field current of the quadruple-octupole composite magnet 1.

[0139] The target size mentioned above is specifically: a square target is usually set at the end of the transmission line. If the side length of the target is L, the target size is That is, the diameter of the circular beam is

[0140] After the above operation, the beam spot can be clearly observed on the target. The diode iron current is adjusted again to align the center of the beam spot with the center of the target. After the adjustment, it is necessary to reconfirm that the X-direction beam waist is near the quad-octupole composite iron 1 and the Y-direction beam waist is near the quad-octupole composite iron 2 according to the methods described in claims 2 and 3.

[0141] Step 6: Adjust the octopole field of the quadruple-octupole composite iron 1 to adjust the uniformity of the beam in the Y direction. According to the quadruple field gradient of the quadruple-octupole composite iron 1 and the current octopole field gradient of the quadruple-octupole composite iron 1 recorded in step 4, calculate the intersection current that satisfies both the quadruple field gradient and the octopole field gradient of the quadruple-octupole composite iron 1, and retain the octopole field gradient of the quadruple-octupole composite iron 1 at this time.

[0142] The specific process is:

[0143] The brightness of the beam spot on the fluorescent target in the Y direction is uneven. If the brightness of the beam spot on the fluorescent target is bright in the middle and dark on both sides in the Y direction, increase the eight-pole field current of the four-octupole composite magnet 1 until the brightness of the beam spot on the fluorescent target in the Y direction is evenly distributed and the shape of the beam spot changes from a circle to a rectangle. If the brightness of the beam spot on the fluorescent target is bright on both sides and dark in the Y direction, reduce the eight-pole field current of the four-octupole composite magnet 1 until the brightness of the beam spot on the fluorescent target in the Y direction is evenly distributed and the shape of the beam spot changes from a circle to a rectangle.

[0144] Supplementary Note D:

[0145] The intersection current is calculated for the first time in step 6. The reason for calculating the intersection current is that when the octopole field beam is adjusted in step 6, the quadrupole field current adjusted previously will also change. In order to solve the problem that the quadrupole field current will also change, it is necessary to find their intersection current (this is the first time to obtain the intersection current), that is, to intersect the current and octopole field gradients and the previously retained quadrupole field gradients with the magnetic field gradient surface of the three-dimensional sample database (here the plane and the surface intersect for the first time), and after the intersection, Figure 5h As shown, two corresponding current curves are obtained. The intersection point of these two current curves is shown as Figure 5i As shown, the current value at the intersection point meets the requirements of both the current octupole field gradient and the quadrupole field gradient. In this way, the problem of coupling relationship when the four-octupole composite iron is combined is solved.

[0146] Step 7: If the uniformity of the beam current does not change significantly when the octopole field current of the quad-octopole composite iron 1 is adjusted, it is necessary to modify the quadrupole field gradient of the quad-octopole composite iron 1 for phase shift matching so that the Y-direction phase shift from the quad-octopole composite iron 1 to the target is close to 180°, that is, based on the adjusted quadrupole field gradient of the quad-octopole composite iron 1 and the octopole field gradient retained in step 6, calculate the current at the intersection that simultaneously satisfies the quadrupole field gradient and the octopole field gradient of the quad-octopole composite iron 1;

[0147] Supplementary Note E:

[0148] The intersection current is calculated for the second time in step seven. The first time the intersection current is obtained is when the octopole field of the quad-octupole composite iron 1 is adjusted to adjust the uniformity of the beam in the Y direction. The second time the intersection current is obtained is because the uniformity of the beam is not changed significantly when the octopole field current of the quad-octupole composite iron 1 is adjusted. At this time, the quadrupole field gradient of the quad-octupole composite iron 1 needs to be modified for phase shift matching. Since the quadrupole field gradient has changed, the new quadrupole field gradient and the octopole field gradient retained in step five are intersected with the magnetic field gradient surface of the three-dimensional sample database (the plane and the surface intersect for the second time here). After the intersection, Figure 5h As shown, two corresponding current curves are obtained. The intersection point of these two current curves is shown as Figure 5i As shown, the current value at the intersection point meets the requirements of both the current octupole field gradient and the quadrupole field gradient. In this way, the problem of coupling relationship when the four-octupole composite iron is combined is solved.

[0149] Specifically:

[0150] 1) Increase the octupole field current of the quad-octupole composite iron 1 and observe whether the brightness change in the Y direction of the beam spot on the fluorescent target is significant; if the brightness in the middle and both sides of the Y direction of the beam spot on the fluorescent target is almost unchanged, it means that the Y-direction phase shift of the quad-octupole composite magnet 1 to the target is significantly different from 180°. If the Y-direction of the beam spot on the fluorescent target changes from bright to dark in the middle and from dark to bright on both sides, or from dark to bright in the middle and from bright to dark on both sides, it means that the Y-direction phase shift of the quad-octupole composite magnet 1 to the target is close to 180°. The bright color indicates that there are many particles, and the dark color indicates that there are few particles.

[0151] 2) When the brightness of the beam spot in the Y direction on the fluorescent target does not change significantly, it proves that the difference between the Y phase shift of the beam between the quad-octupole composite magnet 1 and the target is large and 180 degrees. Assuming that the current phase shift is less than 180 degrees, reduce the quadrupole iron current in front of the quad-octupole composite magnet 1, or increase the quadrupole iron current of the quad-octupole composite magnet 1. After completing the operation, observe again according to the method in 1). If the brightness of the beam spot in the Y direction on the fluorescent target changes significantly when the octupole field current of the quad-octupole composite magnet 1 is increased, it means that the assumption is correct. If the brightness of the beam spot in the Y direction on the fluorescent target remains almost unchanged, it means that the current phase shift is greater than 180 degrees. Increase the quadrupole iron current in front of the quad-octupole composite magnet 1, or reduce the quadrupole iron current of the quad-octupole composite magnet 1. After completing the operation, observe again according to the method in 1) until the brightness of the beam spot in the Y direction on the fluorescent target changes significantly when the octupole field current of the quad-octupole composite magnet 1 is increased. After completing the operation, observe again according to the method in 1) until the brightness of the beam spot in the Y direction on the fluorescent target changes significantly when the octupole field current of the quad-octupole composite magnet 1 is increased.

[0152] Step 8: Adjust the octopole field of the quadruple-octupole composite iron 2 to adjust the uniformity of the beam in the X direction. According to the quadruple field gradient of the quadruple-octupole composite iron 2 and the current octopole field gradient of the quadruple-octupole composite iron 2 recorded in step 5, calculate the intersection current that satisfies both the quadruple field gradient and the octopole field gradient of the quadruple-octupole composite iron 2, and retain the octopole field gradient of the quadruple-octupole composite iron 2 at this time.

[0153] Specifically:

[0154] The brightness of the beam spot on the fluorescent target in the X direction is uneven. If the beam spot on the fluorescent target is bright in the middle and dark on both sides in the X direction, increase the octapole field current of the quad-octapole composite magnet 2 until the brightness distribution of the beam spot on the fluorescent target in the X direction is uniform and the shape of the beam spot changes from a rectangle to a square. If the beam spot on the fluorescent target is bright on both sides and dark in the X direction, reduce the octapole field current of the quad-octapole composite magnet 2 until the brightness distribution of the beam spot on the fluorescent target in the X direction is uniform and the shape of the beam spot changes from a rectangle to a square.

[0155] Supplementary Note F:

[0156] In step 8, the intersection point current is calculated for the third time. The third intersection point current is different from the first two times. The first two times the intersection point current is calculated by adjusting the octapole field of the quad-octapole composite iron 1, and the third time is calculated by adjusting the octapole field of the quad-octapole composite iron 2.

[0157] Step 9: If the beam current uniformity does not change significantly when adjusting the octupole field current of the quad-octupole composite iron 2, it is necessary to increase the X-direction beam current envelope at the quad-octupole composite iron 2. The specific process is:

[0158] 1) Increase the octupole field current of the quad-octupole composite iron 2 and observe whether the brightness of the beam spot in the X direction on the fluorescent target changes significantly. If the brightness of the center and both sides of the beam spot in the X direction on the fluorescent target remains almost unchanged, it indicates that the X-direction beam envelope at the quad-octupole composite magnet 2 is small. If the center of the beam spot in the X direction on the fluorescent target changes from bright to dark and both sides change from dark to bright, or the center changes from dark to bright and both sides change from bright to dark, it indicates that the X-direction beam envelope size at the quad-octupole composite magnet 2 meets the uniformity requirement. Bright indicates more particles, and dark indicates fewer particles.

[0159] 2) When the brightness of the beam spot in the X direction on the fluorescent target does not change significantly, increase the quadrupole iron current and observe again according to the method in 1) whether the brightness of the beam spot in the X direction on the fluorescent target changes significantly when the octupole field current of the quad-octupole composite iron 2 is increased. If the brightness of the beam spot does not change significantly, continue to increase the quadrupole iron current. If the brightness of the beam spot changes significantly, the size of the beam envelope in the X direction at the quad-octupole composite magnet 2 meets the uniformity requirements and the adjustment is complete.

[0160] Supplementary Note G:

[0161] In step nine, the intersection current is not obtained. The reason is that the X-direction phase shift of the beam from the quad-octupole composite iron 2 to the target is close to 0 degrees. The phase shift method can no longer solve the problem of increasing the X-direction envelope of the beam at the quad-octupole composite iron 2. It is necessary to increase the quadrupole iron current in front of the quad-octupole composite iron 1. Figure 2 It can be seen that when the quadrupole iron current is increased, the beam envelope in the X direction at the octupole composite iron 2 will be increased, until the octupole field current of the quadrupole octupole composite iron 2 is changed and the beam uniformity in the X direction on the target changes significantly.

[0162] Example 1

[0163] like Figure 7 As shown, the debugging method of the present invention is based on an ultra-short bend-type beam homogenization transmission line. When the total length of the ultra-short bend-type beam line is 6, the initial layout positions of the components that can achieve a good homogenization effect on the streamline are as follows: the initial position of the fluorescent target 1 is 100 mm, the initial position of the quadrupole magnet (Q0) is 1300 mm; the initial position of the guide magnet 1 is 1650 mm; the initial position of the quad-octupole composite iron (Q1) is 2100 mm, the initial position of the dipole iron is 2700 mm, and the initial position of the quad-octupole composite iron (Q2) is 3850 mm; the initial position of the guide magnet 2 is 4250 mm; the initial position of the Faraday cage is 4700 mm; the initial position of the fluorescent target 2 is 5350 mm, the initial position of the double wire is 5750 mm; and the initial position of the terminal is 6000 mm.

[0164] Among them, the magnetic field component of the quadrupole iron (Q0) is 6.8 (T / m); the quadrupole magnetic field component of the quadrupole-octupole composite iron (Q1) is 2.25 (T / m), and the octupole magnetic field component is 1e4 (T / m 3 ), the quadrupole magnetic field component of the quadruple-octupole composite 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.

[0165] like Figure 1d As shown, it is a comparison of the transmission line before and after homogenization of the present invention. Figure 1d The left figure is a cross-sectional view of the beam with Gaussian distribution before homogenization, that is, the cross-sectional view of the beam when the fluorescent target 1 is at the position 100mm of the transmission line; Figure 1d The right figure shows the beam cross-section after homogenization, i.e., the beam cross-section at fluorescent target 2 at position 5350 mm along the transmission line. As can be seen from the figure, before homogenization, the particle distribution in the beam cross-section was dense in the center and sparse around the edges. After homogenization, the particle distribution in the beam cross-section is uniform both in the center and around the edges.

[0166] As can be seen from the figure, adjusting the large Y-direction envelope of the quadrupole iron (Q1) relies primarily on the action of the preceding quadrupole iron, whose magnetic field gradient is 6.8 (T / m). Due to the use of secondary iron, the quadrupole magnetic field component of the quadrupole iron (Q1) is appropriately reduced near the current intersection point of the quadrupole iron (Q1), to a value of only 2.25 (T / m). The quadrupole magnetic field component of the quadrupole iron (Q2) is also appropriately reduced, to a value of only 0.6 (T / m).

[0167] It should be emphasized that the above specific embodiments are merely explanations of the present invention and are not limitations of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the above embodiments as needed, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A method for debugging a curved beam uniformization transmission line based on a quad-octupole composite magnet, the method being based on a quad-octupole composite iron, a quad-octupole composite iron system, a method for adjusting the excitation current of the quad-octupole composite iron, and an ultra-short curved beam uniformization transmission line; It is characterized by: The debugging method includes the following steps: Step 1: set the quadrupole field and octupole field current of the quadrupole iron and the two quadrupole-octupole composite irons to zero; Step 2: Adjust the diode current so that the center of the beam spot is roughly aligned with the center of the fluorescent target; Step 3: Observe the changes in the beam envelope on the fluorescent target and adjust the quadrupole iron current in front of the quad-octupole iron complex 1 so that the beam forms a waist in the X direction near the quad-octupole iron complex 1. Step 4: Observe the changes in the beam envelope on the fluorescent target and adjust the quadrupole field current of the quadruple-octupole composite iron 1 in front of the dipole iron. Under the combined action of the fringe field of the dipole iron and the quadrupole field of the quadruple-octupole composite iron 1, the beam is waisted in the Y direction near the quadruple-octupole composite iron 2, while retaining the quadrupole field gradient of the quadruple-octupole composite iron 1 at this time. Step 5: Adjust the quadrupole iron current of the quadrupole iron composite 2 so that the X-direction envelope of the beam on the fluorescent target is consistent with the Y-direction envelope to obtain a circular beam, and adjust the dipole iron current again so that the center of the beam spot is aligned with the center of the target, retaining the quadrupole field gradient of the quadrupole iron composite 2 at this time; Step 6: Adjust the octopole field of the quadruple-octupole composite iron 1 to adjust the uniformity of the beam in the Y direction. According to the quadruple field gradient of the quadruple-octupole composite iron 1 and the current octopole field gradient of the quadruple-octupole composite iron 1 recorded in step 4, calculate the intersection current that satisfies both the quadruple field gradient and the octopole field gradient of the quadruple-octupole composite iron 1, and retain the octopole field gradient of the quadruple-octupole composite iron 1 at this time. Step 7: If the uniformity of the beam current does not change significantly when the octopole field current of the quad-octopole composite iron 1 is adjusted, it is necessary to modify the quadrupole field gradient of the quad-octopole composite iron 1 for phase shift matching so that the Y-direction phase shift from the quad-octopole composite iron 1 to the target is close to 180°, that is, based on the adjusted quadrupole field gradient of the quad-octopole composite iron 1 and the octopole field gradient retained in step 6, calculate the current at the intersection that simultaneously satisfies the quadrupole field gradient and the octopole field gradient of the quad-octopole composite iron 1; Step 8: Adjust the octopole field of the quadruple-octupole composite iron 2 to adjust the uniformity of the beam in the X direction. According to the quadruple field gradient of the quadruple-octupole composite iron 2 and the current octopole field gradient of the quadruple-octupole composite iron 2 recorded in step 5, calculate the intersection current that satisfies both the quadruple field gradient and the octopole field gradient of the quadruple-octupole composite iron 2, and retain the octopole field gradient of the quadruple-octupole composite iron 2 at this time. Step 9: If the beam uniformity does not change significantly when adjusting the octupole field current of the quad-octupole composite iron 2, it is necessary to increase the X-direction beam envelope at the quad-octupole composite iron 2.

2. The method for debugging a bending-type beam uniformization transmission line based on a quad-octupole composite magnet according to claim 1, characterized in that: The specific process of step 2 is as follows: To protect the components on the transmission line, the initial current value of the diode is calculated and set based on the current beam parameters and the number of turns of the diode coil. Observe whether a beam appears on the fluorescent target. If not, adjust the current value of the diode near the initial current value until a beam appears on the fluorescent target. At this point, the quadrupole field currents of the quadrupole and the two quad-octupole composite irons are both zero, and the beam envelope is large. Align the beam roughly with the center of the target before proceeding to the next step.

3. The method for debugging a bending-type beam uniformization transmission line based on a quad-octupole composite magnet according to claim 1, characterized in that: The specific process of step three is as follows: 1) Starting from zero, gradually increase the quadrupole iron current in front of the quadruple-octupole composite magnet 1. Observe that the X-direction envelope size of the beam on the fluorescent target gradually decreases. Continue to increase the quadrupole iron current until the X-direction envelope size on the target increases, indicating that the X-direction beam waist is formed somewhere between the quadrupole iron and the target (near the target). 2) To make the X-direction beam waist near the quadrupole iron compound 1, it is necessary to continue increasing the quadrupole iron current to shift the X-direction beam waist to the left. Stop increasing the current until the following situation is reached: Increase the quadrupole field current of the quadrupole iron compound 1 and observe that the X-direction beam envelope size on the fluorescent target hardly changes. At this time, the X-direction beam waist is near the quadrupole iron compound 1.

4. The method for debugging a bending-type beam uniformization transmission line based on a quad-octupole composite magnet according to claim 1, characterized in that: The specific process of step 4 is as follows: 1) Gradually increase the quadrupole field current of the quadrupole-octupole composite magnet 1 from zero. Observe that the Y-direction envelope size of the beam on the fluorescent target gradually decreases. Continue to increase the quadrupole field current of the quadrupole-octupole composite magnet 1 until the Y-direction envelope size on the target increases. This indicates that the Y-direction beam waist is formed somewhere between the quadrupole-octupole composite magnet 1 and the target (near the target). 2) To make the Y-direction beam waist near the quadruple-octupole composite iron 2, it is necessary to continue to increase the quadrupole field current of the quadruple-octupole composite magnet 1 to shift the Y-direction beam waist to the left. Stop increasing the current to the following point: Increase the quadrupole field current of the quadruple-octupole composite iron 2 and observe that the Y-direction beam envelope size on the fluorescent target hardly changes. At this time, the Y-direction beam waist is near the quadruple-octupole composite iron 2.

5. The method for debugging a bending-type beam uniformization transmission line based on a quad-octupole composite magnet according to claim 1, characterized in that: The specific process of step five is as follows: After steps 1 to 4, ideally, the beam envelope size in the X direction should be larger than the Y direction envelope size. Starting from zero, gradually increase the quadrupole field current of the quadruple-octupole composite magnet 2. Observe on the fluorescent target that the beam envelope size in the X direction gradually decreases. Continue to increase the quadrupole field current of the quadruple-octupole composite magnet 2 until the beam envelope size in the X direction is consistent with the Y direction envelope size on the target. If the envelope dimensions in the X and Y directions do not meet expectations after steps 1 to 4, the following adjustments should be made: 1) If the X-direction size of the fluorescent target beam is larger than the target size, reduce the quadrupole iron current in front of the quadruple-octupole composite magnet 1 or increase the quadrupole field current of the quadruple-octupole composite magnet 2; if the X-direction size of the beam is smaller than the target size, increase the quadrupole iron current in front of the quadruple-octupole composite magnet 1 or reduce the quadruple field current of the quadruple-octupole composite magnet 2; 2) If the Y-direction envelope size of the beam on the fluorescent target is larger than the target size, reduce the quadrupole field current of the quadrupole-octupole composite magnet 1; if the Y-direction size of the beam is smaller than the target size, increase the quadrupole field current of the quadrupole-octupole composite magnet 1; The target size mentioned above is specifically: a square target is usually set at the end of the transmission line. If the side length of the target is L, the target size is That is, the diameter of the circular beam is After the above operation, the beam spot can be clearly observed on the target, and the diode iron current is adjusted again so that the center of the beam spot is aligned with the center of the target; after the adjustment, it is necessary to reconfirm that the X-direction beam waist is near the quad-octupole composite iron 1 and the Y-direction beam waist is near the quad-octupole composite iron 2 according to the method described in claims 2 and 3.

6. The method for debugging a bending-type beam uniformization transmission line based on a quad-octupole composite magnet according to claim 1, characterized in that: The step six of adjusting the Y-direction uniformity effect on the fluorescent target by the octupole field of the quad-octupole composite magnet 1 is specifically as follows: The brightness of the beam spot on the fluorescent target in the Y direction is uneven. If the brightness of the beam spot on the fluorescent target is bright in the middle and dark on both sides in the Y direction, increase the eight-pole field current of the four-octupole composite magnet 1 until the brightness of the beam spot on the fluorescent target in the Y direction is evenly distributed and the shape of the beam spot changes from a circle to a rectangle. If the brightness of the beam spot on the fluorescent target is bright on both sides and dark in the Y direction, reduce the eight-pole field current of the four-octupole composite magnet 1 until the brightness of the beam spot on the fluorescent target in the Y direction is evenly distributed and the shape of the beam spot changes from a circle to a rectangle.

7. The method for debugging a bending-type beam uniformization transmission line based on a quad-octupole composite magnet according to claim 1, characterized in that: The step 7 of fine-tuning the phase of the four-eight-pole composite magnet 1 to be close to 180 degrees is specifically as follows: 1) Increase the octupole field current of the quad-octupole composite iron 1 and observe whether the brightness change in the Y direction of the beam spot on the fluorescent target is significant; if the brightness in the middle and both sides of the Y direction of the beam spot on the fluorescent target is almost unchanged, it means that the Y-direction phase shift of the quad-octupole composite magnet 1 to the target is significantly different from 180°. If the Y-direction of the beam spot on the fluorescent target changes from bright to dark in the middle and from dark to bright on both sides, or from dark to bright in the middle and from bright to dark on both sides, it means that the Y-direction phase shift of the quad-octupole composite magnet 1 to the target is close to 180°. The bright color indicates that there are many particles, and the dark color indicates that there are few particles. 2) When the brightness of the beam spot in the Y direction on the fluorescent target does not change significantly, it proves that the difference between the Y phase shift of the beam between the quad-octupole composite magnet 1 and the target is large and 180 degrees. Assuming that the current phase shift is less than 180 degrees, reduce the quadrupole iron current in front of the quad-octupole composite magnet 1, or increase the quadrupole iron current of the quad-octupole composite magnet 1. After completing the operation, observe again according to the method in 1). If the brightness of the beam spot in the Y direction on the fluorescent target changes significantly when the octupole field current of the quad-octupole composite magnet 1 is increased, it means that the assumption is correct. If the brightness of the beam spot in the Y direction on the fluorescent target remains almost unchanged, it means that the current phase shift is greater than 180 degrees. Increase the quadrupole iron current in front of the quad-octupole composite magnet 1, or reduce the quadrupole iron current of the quad-octupole composite magnet 1. After completing the operation, observe again according to the method in 1) until the brightness of the beam spot in the Y direction on the fluorescent target changes significantly when the octupole field current of the quad-octupole composite magnet 1 is increased. After completing the operation, observe again according to the method in 1) until the brightness of the beam spot in the Y direction on the fluorescent target changes significantly when the octupole field current of the quad-octupole composite magnet 1 is increased.

8. The method for debugging a bending-type beam uniformization transmission line based on a quad-octupole composite magnet according to claim 1, characterized in that: The eighth step of adjusting the X-direction uniformity effect on the fluorescent target by the octupole field of the quad-octupole composite magnet 2 is specifically as follows: The brightness of the beam spot on the fluorescent target in the X direction is uneven. If the beam spot on the fluorescent target is bright in the middle and dark on both sides in the X direction, increase the octapole field current of the quad-octapole composite magnet 2 until the brightness distribution of the beam spot on the fluorescent target in the X direction is uniform and the shape of the beam spot changes from a rectangle to a square. If the beam spot on the fluorescent target is bright on both sides and dark in the X direction, reduce the octapole field current of the quad-octapole composite magnet 2 until the brightness distribution of the beam spot on the fluorescent target in the X direction is uniform and the shape of the beam spot changes from a rectangle to a square.

9. The method for debugging a bending-type beam uniformization transmission line based on a quad-octupole composite magnet according to claim 1, characterized in that: The step nine of increasing the X-direction beam envelope at the quad-octupole composite magnet 2 is specifically as follows: 1) Increase the octupole field current of the quad-octupole composite iron 2 and observe whether the brightness of the beam spot in the X direction on the fluorescent target changes significantly. If the brightness of the center and both sides of the beam spot in the X direction on the fluorescent target remains almost unchanged, it indicates that the X-direction beam envelope at the quad-octupole composite magnet 2 is small. If the center of the beam spot in the X direction on the fluorescent target changes from bright to dark and both sides change from dark to bright, or the center changes from dark to bright and both sides change from bright to dark, it indicates that the X-direction beam envelope size at the quad-octupole composite magnet 2 meets the uniformity requirement. Bright indicates more particles, and dark indicates fewer particles. 2) When the brightness of the beam spot in the X direction on the fluorescent target does not change significantly, increase the quadrupole iron current and observe again according to the method in 1) whether the brightness of the beam spot in the X direction on the fluorescent target changes significantly when the octupole field current of the quad-octupole composite iron 2 is increased. If the brightness of the beam spot does not change significantly, continue to increase the quadrupole iron current. If the brightness of the beam spot changes significantly, the size of the beam envelope in the X direction at the quad-octupole composite magnet 2 meets the uniformity requirements and the adjustment is complete.

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