A method to improve the efficiency of slow extraction beam with large emittance

Abstract

The present invention relates to a method for improving the efficiency of a large emittance slow extraction beam, comprising: setting an initial working point Q of a synchrotron slow extraction platform; 1 and the total strength S of the hexapole iron n , so that the area of ​​the stable region is larger than the maximum emittance of the circulating beam; adjust the initial working point Q 1 To Q 2 Closer to the resonance line Q res , that is, reduce Δq and maintain the total strength S of the hexapole iron n No change, or keep Q 1 Unchanged, increasing the total strength S of the hexapole iron n ; Adjust the initial working point Q 1 To Q 2 Closer to the resonance line Q res Or increase the total strength S of the hexapole iron n , so that the area of ​​the stable zone gradually decreases, and the extraction pitch and angular divergence gradually increase; modulate the amplitude and angle of the extraction boundary track, select a suitable pitch, reduce the angular divergence, and thus obtain a high extraction efficiency after the large emittance slow extraction beam is contracted. The present invention dynamically shrinks the area of ​​the triangular stable zone and modulates the angle of the entrance at the electrostatic deflection plate (or modulates the angle and amplitude in parallel) to obtain a slow extraction beam with high extraction efficiency.

Description

Technical Field

[0001] The invention relates to a method for improving the efficiency of a large-emittance slow-extraction beam, and belongs to the technical field of synchrotron accelerators. Background Art

[0002] The slow extraction beam of synchrotron accelerator is widely used in aerospace, materials, medicine, agriculture, biology and other fields. For example, it can be used to carry out single particle effect irradiation research on aerospace electronic components, especially electronic device complete machines; study the laws of irradiation effects of particles in organisms and semiconductor materials; it can be used in the production of nuclear pore membranes and particle cancer treatment, which is of great significance to promoting the development of relevant social and economic fields in my country.

[0003] At present, the main method for synchrotrons to provide slow extraction beams is third-order integer resonance extraction, that is, the working point is adjusted to the vicinity of the third-order integer on the extraction platform, and the nonlinear sextupole magnetic field is used to transform the elliptical phase space into a triangle. The area of ​​the triangle should be larger than the emittance of the circulating beam, otherwise it will lead to serious beam loss. However, for miniaturized synchrotrons, such as the study of single particle effects and displacement damage effects of aerospace components, it is necessary to extract low-energy heavy ions and protons. Since the injection and extraction energies are very close, the emittance of the beam shrinks little during the acceleration process, and the emittance of the circulating beam is very large during extraction, resulting in an extremely large area of ​​the stable zone required, making the extraction pitch at the ES entrance very small. Particles will accumulate in large quantities at the ES entrance and the density will increase, resulting in serious beam loss and very low extraction efficiency. Summary of the invention

[0004] In view of the above technical problems, the present invention provides a method for improving the efficiency of a large emittance slow extraction beam, which obtains high extraction efficiency by increasing the pitch to reduce the density of the extraction beam at ES or reducing the angular divergence of the extraction beam at ES.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for improving the efficiency of a large emittance slow extraction beam, comprising:

[0007] Set the initial working point Q1 of the synchrotron slow extraction platform and the total strength S of the hexapole iron n , so that the area of ​​the stable region is larger than the maximum emittance of the circulating beam;

[0008] Adjust the initial operating point Q1 to Q2 closer to the resonance line Q res , that is, reduce Δq and maintain the total strength S of the hexapole iron n Keep Q1 unchanged, or increase the total strength S of the hexapole iron n ;

[0009] Adjust the initial operating point Q1 to Q2 closer to the resonance line Qres Or increase the total strength S of the hexapole iron n , which makes the stable area gradually shrink, and the lead-out pitch and angular divergence gradually increase;

[0010] By modulating the amplitude and angle of the extraction boundary track and selecting a suitable pitch, the angular divergence can be reduced to obtain a high extraction efficiency of a large emittance slow extraction beam.

[0011] The method for improving the efficiency of a large emittance slow extraction beam is preferably such that the area of ​​the stable region The calculation formula is as follows:

[0012]

[0013] In the formula, is the working point deviation between the particle and the resonance line particle; S n is the total strength of the resonant hexapole iron.

[0014] The method for improving the efficiency of the large emittance slow extraction beam is preferably such that the working point difference between the particle and the resonance line particle is The calculation formula is as follows:

[0015] Δq=(Q1-Q res )+ξ x,n Δp / p or Δq=(Q2-Q res )+ξ x,n ·Δp / p

[0016] In the formula, Q res =N±1 / 3 or N±2 / 3 is the third-order integer resonance line, N is an integer; ξ x,n is the chromaticity value; Δp / p is the momentum dispersion.

[0017] In the method for improving the efficiency of a large-emittance slow extraction beam, preferably, the hexapole iron includes a resonant hexapole iron and a chromaticity hexapole iron, and the chromaticity is adjusted by changing the total intensity of the chromaticity hexapole iron or by changing the momentum dispersion Δp / p of the circulating beam through longitudinal high-frequency voltage modulation, thereby achieving the purpose of reducing Δq, thereby allowing the extraction platform to dynamically reduce the area of ​​the stable zone.

[0018] In the method for improving the efficiency of a large-emittance slow extraction beam, preferably, the synchrotron slow extraction platform increases the total intensity of the resonant hexapole iron from S1 to S2, and a linear function or an arbitrary function with a similar trend is used from S1 to S2, so that the extraction platform dynamically reduces the area of ​​the stable zone.

[0019] The method for improving the efficiency of the slow extraction beam with large emittance preferably adjusts the initial working point Q1 to Q2 closer to the resonance line Q resThe method is to change the strength k1→k2 of conventional quadrupole iron or fast quadrupole iron on the extraction platform, so as to bring the working point closer to the resonance line and reduce Δq, so that the extraction platform can dynamically reduce the area of ​​the stable zone.

[0020] The method for improving the efficiency of the large emittance slow extraction beam preferably modulates the amplitude and angle of the extraction boundary track, selects a suitable pitch, and reduces the angular divergence, thereby obtaining a high extraction efficiency of the large emittance slow extraction beam after the area is shrunk, and includes the following steps:

[0021] If the stable region area is reduced, resulting in an increase in the pitch, and the extraction limit track is within the ES channel, the extraction angle can be modulated at the ES entrance by the convex track magnet to obtain a small extraction angle divergence, which is beneficial to improving the efficiency of the slow extraction beam.

[0022] The method for improving the efficiency of the large emittance slow extraction beam preferably modulates the amplitude and angle of the extraction boundary track, selects a suitable pitch, and reduces the angular divergence, thereby obtaining a high extraction efficiency of the large emittance slow extraction beam after the area is shrunk, and includes the following steps:

[0023] If the pitch increases significantly due to the reduction in the area of ​​the stable zone, and the lead-out boundary track exceeds the range of the ES channel, it is necessary to simultaneously modulate the amplitude and angle of the lead-out boundary track at the ES through the convex rail magnet, modulate the pitch of the lead-out boundary track into the ES lead-out channel, and reduce the lead-out angular dispersion at the ES, thereby obtaining high lead-out efficiency.

[0024] The present invention adopts the above technical solution, which has the following advantages:

[0025] 1. The present invention dynamically shrinks the area of ​​the triangular stable region and simultaneously modulates the angle of the entrance at the electrostatic deflection plate (or modulates the angle and amplitude in parallel) to obtain a slow extraction beam method with high extraction efficiency.

[0026] 2. The present invention proposes a new technical solution to the low efficiency of large-emittance slow extraction through innovative beam dynamics control, especially for the extraction of low-energy ion beams from synchrotrons. This solution is based on the existing slow extraction components, and does not require additional component types and quantities to achieve high-efficiency extraction of large-emittance beams. The solution is simple to implement, and only requires modification and modulation of the working waveforms of existing components on the extraction platform, which effectively solves the problems encountered in the project, enriches the diversity and flexibility of the slow extraction system for beam control, and reduces the difficulty of extraction system design. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1A flow chart of a method for improving the efficiency of a large-emittance slow extraction beam provided in one embodiment of the present invention; in the figure: Q1 and Q2 are the initial working point and the terminal working point of the extraction platform, respectively, S1 and S2 are the total intensities of the resonant hexapole iron before and after adjustment, respectively, and the curve of the change of the quadrupole iron intensity from Q1 to Q2 (or from S1 to S2) adopts a linear or other function.

[0028] Figure 2 The solid line in the figure is the linear (other arbitrary function waveforms with similar trends are also acceptable) function working diagram of the main components on the extraction platform, and the dotted line represents the existing commonly used scheme. Among them, Figure (a) keeps the total strength of the resonant sextupole iron unchanged on the extraction platform, changes the strength of the quadrupole iron (which can be a conventional quadrupole iron or a fast quadrupole iron, usually a group of quadrupole iron) to move the working point close to the resonance line, reduce Δq, reduce the area of ​​the stable zone, and the convex rail magnet dynamically modulates the angle and position of the extraction boundary rail at the entrance of the ES to improve the extraction efficiency. Figure (b) keeps the total strength of the resonant sextupole iron unchanged on the extraction platform, changes the chromaticity or momentum dispersion to move the working point close to the resonance line, reduce Δq, reduce the area of ​​the stable zone, and the convex rail magnet dynamically modulates the angle and position of the extraction boundary rail at the entrance of the ES to improve the extraction efficiency. However, adjusting the chromaticity will affect the Hardt condition, which will also affect the extraction efficiency. Therefore, this scheme is not commonly used. Figure (c) shows that the working point is kept unchanged on the extraction platform, the total strength of the resonant sextupole iron is increased and the area of ​​the stable zone is reduced. The convex rail magnet dynamically modulates the angle and position of the extraction boundary rail at the ES entrance, thereby improving the extraction efficiency.

[0029] Figure 3 A1 represents the stable zone area corresponding to the initial large emittance beam, A2 represents the stable zone area after contraction caused by the working point approaching the resonance line or the increase in the total intensity of the resonant hexapole iron, R1 and R2 are the pitches before and after the contraction of the stable zone area, respectively. It can be seen that the pitch and angular divergence of the extracted beam are increased, and the ES channel is the extraction channel of the slow extraction beam.

[0030] Figure 4 The amplitude and angle of the ES entrance are modulated by the bump magnet to reduce the extraction angular dispersion, thereby obtaining a high slow extraction beam efficiency. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work are within the scope of protection of the present invention.

[0032] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the usual meanings understood by persons with ordinary skills in the field to which the present invention belongs. The words "first", "second", "third", "fourth" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" and the like mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" and the like are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect.

[0033] For ease of description, spatially relative terms may be used herein to describe the relationship of one element or feature relative to another element or feature as shown in the figures, such as "inside", "outside", "inner side", "outer side", "below", "above", etc. Such spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation depicted in the figures.

[0034] When the synchrotron extracts a low-energy beam, the emittance shrinks during the acceleration process from injected energy to extracted energy. The emittance of the circulating beam during extraction is very large. At this time, the required stabilization zone area is extremely large, resulting in a small pitch of the particles at the electrostatic deflection plate and a large particle density at the ES entrance, which can easily cause beam loss and low extracted beam efficiency.

[0035] Based on the above technical problems, the present invention proposes a method for improving the efficiency of a large-emittance slow extraction beam, which provides a method for dynamically reducing the area of ​​a stable triangle, increasing the pitch at ES (Electrostatic Septum, abbreviated as ES), and reducing the particle density at the entrance of ES. However, during the shrinkage of the triangle area, the angular dispersion at ES will also increase. At this time, it is necessary to dynamically modulate the angle at ES through a convex track magnet on the extraction platform to reduce the angular dispersion. Therefore, by increasing the pitch to reduce the particle density and modulating the angle at ES to reduce the angular dispersion, the efficiency of the slow extraction beam can be greatly improved. This method provides a new technical means for the high-efficiency extraction of low-energy particle beams from synchrotrons, and has important engineering value in proton and heavy ion synchrotrons in the fields of biological and material irradiation, aerospace and industrial irradiation.

[0036] like Figure 1 , 2 As shown, the method for improving the efficiency of a large emittance slow extraction beam according to the present invention comprises the following steps:

[0037] Set the initial working point Q1 of the synchrotron slow extraction platform and the total strength S of the hexapole iron n, so that the area of ​​the stable region is larger than the maximum emittance of the circulating beam;

[0038] Adjust the initial operating point Q1 to Q2 closer to the resonance line Q res , that is, reduce Δq and keep the total strength of the hexapole iron unchanged S n , or keep Q1 unchanged and increase the total strength S of the hexapole iron n ;

[0039] Adjust the initial operating point Q1 to Q2 close to the resonance line Q res Or increase the total strength S of the hexapole iron n , which makes the stable area gradually shrink, and the lead-out pitch and angular divergence gradually increase;

[0040] By modulating the amplitude and angle of the extraction boundary track, selecting a suitable pitch, and reducing the angular divergence, a high extraction efficiency of a large emittance slow extraction beam can be obtained after the area is reduced.

[0041] The synchrotron slow extraction platform adjusts the working point Q1 to extract the third-order integer resonance line Q res Nearby, taking into account the different momentum dispersion particles Δp / p due to chromaticity ξ x，n The existence of the particle leads to different working points. The difference between the working points of the particle and the resonance line particle is Δq=|Q1-Q res ∣+ξ x,n ·Δp / p; If the working point is adjusted from Q1 to Q2 on the lead-out platform, it is closer to the resonance line Q res , then Δq=|Q2-Q res ∣+ξ x,n ·Δp / p. The total strength S of the loaded nonlinear resonant hexapole iron n , so that the phase space changes from an ellipse to a triangle, and the area A of the triangular stable region is:

[0042]

[0043] Where: Q res =N±1 / 3 or N±2 / 3 is the third-order integer resonance line, N is an integer; ξ x,n is the chromaticity value,

[0044] Δp / p is the momentum dispersion.

[0045] By dynamically reducing the area of ​​the stable zone on the extraction platform, the working point can be adjusted to be close to the resonance line to reduce Δq or increase the total strength S of the resonant hexapole iron. n The pitch and angular dispersion of the particles at the ES will increase. The working curves of the main components on the extraction platform are as follows: Figure 2As shown. Among them, Figure (a) shows that the total strength of the resonant sextupole iron is kept unchanged on the extraction platform, the strength of the quadrupole iron (which can be a conventional quadrupole iron or a fast quadrupole iron, usually a plurality of quadrupole irons) is changed to move the working point close to the resonance line, reduce Δq, reduce the area of ​​the stable zone, and the convex track magnet dynamically modulates the angle and position of the extraction boundary track at the entrance of the ES to improve the extraction efficiency. Figure (b) shows that the total strength of the resonant sextupole iron is kept unchanged on the extraction platform, the chromaticity or momentum dispersion is changed to move the working point close to the resonance line, reduce Δq, reduce the area of ​​the stable zone, and the convex track magnet dynamically modulates the angle and position of the extraction boundary track at the entrance of the ES to improve the extraction efficiency. However, adjusting the chromaticity in scheme 2 will affect the Hardt condition, thereby also affecting the extraction efficiency. Therefore, this scheme is not commonly used. Figure (c) shows that the working point is kept unchanged on the extraction platform, the total strength of the resonant sextupole iron is increased and the area of ​​the stable zone is reduced, and the convex track magnet dynamically modulates the angle and position of the extraction boundary track at the entrance of the ES to improve the extraction efficiency.

[0046] The technical solutions for reducing the area of ​​the stable zone of the present invention include the following three:

[0047] Reduce the working point Solution 1 is to adjust the working point Q1 to Q2 closer to the resonance line Q by changing the strength k1→k2 of the conventional quadrupole iron or fast quadrupole iron on the lead-out platform (k1 to k2 can use a linear function or any other function with similar trends), res Solution 2 is to adjust the chromaticity by changing the total intensity of the chromaticity hexapole iron or to change the momentum dispersion Δp / p of the circulating beam by longitudinal high-frequency voltage modulation, thereby achieving the purpose of reducing Δq. However, adjusting the chromaticity in Solution 2 will affect the Hardt condition, thereby also affecting the extraction efficiency. Therefore, Solution 1 is usually used to reduce the working point Δq.

[0048] Increase the total strength S of the resonant hexapole iron n : Scheme 3 is to increase the total intensity of the resonant hexapole iron S1→S2 on the extraction platform, and S1 to S2 can adopt a linear function or any function with a similar trend.

[0049] Of course, the area of ​​the stable zone can also be adjusted by freely combining the three schemes.

[0050] After the area of ​​the stable zone shrinks, the pitch and angular dispersion of the particles at the ES increase, resulting in the following two situations:

[0051] Case 1: If the extraction boundary track is within the ES channel after the pitch is increased, the extraction angle can be modulated at the ES entrance by the convex track magnet to obtain a small extraction angular divergence. Therefore, an appropriate increase in the extraction boundary track amplitude and a reduction in the angular divergence will help improve the efficiency of the slow extraction beam.

[0052] Case 2: If the lead-out boundary track exceeds the range of the ES channel after the pitch is greatly increased, it is necessary to simultaneously modulate the amplitude and angle of the lead-out boundary track at the ES through the convex track magnet, modulate the lead-out boundary track into the lead-out channel, and reduce the lead-out angular dispersion at the ES, thereby obtaining high lead-out efficiency.

[0053] The present invention proposes a new technical solution to solve the low efficiency of large-emittance slow extraction through innovative beam dynamics control, especially for the extraction of low-energy ion beams from synchrotrons. This solution is based on the existing slow extraction components, and does not require additional component types and quantities to achieve high-efficiency extraction of large-emittance beams. The solution is simple to implement, and only requires modification and modulation of the working waveforms of existing components on the extraction platform, which effectively solves the problems encountered in the project, enriches the diversity and flexibility of the slow extraction system for beam control, and reduces the difficulty of extraction system design.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the efficiency of a large emittance slow extraction beam, characterized in that: include: Set the initial working point Q1 of the synchrotron slow extraction platform and the total strength S of the hexapole iron n , so that the area of ​​the stable region is larger than the maximum emittance of the circulating beam; Adjust the initial operating point Q1 to Q2 closer to the resonance line Q res , that is, reduce Δq and keep the total strength of the hexapole iron unchanged, or keep Q1 unchanged and increase the total strength of the hexapole iron S n ; Adjust the initial operating point Q1 to Q2 closer to the resonance line Q res Or increase the total strength of the hexapole iron, so that the stable area gradually decreases, and the lead-out pitch and angular divergence gradually increase; Modulate the amplitude and angle of the extraction boundary track, select the appropriate pitch, and reduce the angular divergence, so as to obtain high extraction efficiency after the large emittance slow extraction beam is contracted; The calculation formula of the stable zone area A is as follows: Where Δq is the working point deviation between the particle and the resonance line particle; S n is the total strength of the resonant sextupole; The calculation formula for the working point deviation Δq between the particle and the resonance line particle is as follows: Δq = (Q1 - Q res ) + ξ x,n ·Δp / p or Δq = (Q2 - Q res ) + ξ x,n ·Δp / p In the formula, Q res =N±1 / 3 or N±2 / 3 is the third-order integer resonance line, N is an integer; ξ x,n is the chromaticity value; Δp / p is the momentum dispersion; Modulate the amplitude and angle of the extraction boundary track, select the appropriate pitch, reduce the angular divergence, and thus obtain a high extraction efficiency after the area of ​​the large emittance slow extraction beam is contracted, including the following steps: If the stable region area is reduced, resulting in an increase in the pitch, and the extraction limit track is within the ES channel, the extraction angle can be modulated at the ES entrance by the convex track magnet to obtain a small extraction angle divergence, which is beneficial to improving the efficiency of the slow extraction beam; If the pitch increases significantly due to the reduction in the area of ​​the stable zone, and the lead-out boundary track exceeds the range of the ES channel, it is necessary to simultaneously modulate the amplitude and angle of the lead-out boundary track at the ES through the convex rail magnet, modulate the pitch of the lead-out boundary track into the ES lead-out channel, and reduce the lead-out angular dispersion at the ES, thereby obtaining high lead-out efficiency.

2. The method for improving the efficiency of a large emittance slow extraction beam according to claim 1, characterized in that: The hexapole includes resonant hexapole and chromaticity hexapole. The chromaticity is adjusted by changing the total intensity of the chromaticity hexapole or by changing the momentum dispersion Δp / p of the circulating beam through longitudinal high-frequency voltage modulation, so as to achieve the purpose of reducing Δq, thereby making the extraction platform dynamically reduce the area of ​​the stable zone.

3. The method for improving the efficiency of a large emittance slow extraction beam according to claim 2, characterized in that: The synchrotron slow extraction platform increases the total intensity of the resonant hexapole iron from S1 to S2, and a linear function or an arbitrary function with a similar trend is used from S1 to S2, so that the extraction platform dynamically reduces the area of ​​the stable zone.

4. The method for improving the efficiency of a large emittance slow extraction beam according to claim 1, characterized in that: Adjust the initial operating point Q1 to Q2 closer to the resonance line Q res The method is to change the strength k1→k2 of conventional quadrupole iron or fast quadrupole iron on the extraction platform, so as to bring the working point closer to the resonance line and reduce Δq, so that the extraction platform can dynamically reduce the area of ​​the stable zone.

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