Method for rapid and uniform scanning of high-current and high-power particle beams using radio frequency cavity

Abstract

The present invention relates to a method for quickly and uniformly scanning a high-current, high-power particle beam using a radio frequency cavity. The method comprises the following steps: converging the high-current, high-power particle beam into a beam spot size required by a target surface by a focusing element group; controlling the phase shift between the radio frequency cavity and the target surface by the focusing element group; deflecting the beam so that the beam hits the target in a required direction; selecting an appropriate radio frequency cavity fundamental frequency so that there is a frequency difference between the beam bunch and the radio frequency cavity, thereby achieving angular phase sliding scanning with the beam spot distributed at different angular positions with the target surface as the center; selecting an appropriate radio frequency cavity harmonic order, harmonic frequency and harmonic component amplitude so that adjacent beam bunch centers experience different effects of the radio frequency cavity's transverse field, thereby achieving radial variation of the beam spot center at the target surface; and utilizing an orthogonal tristable radio frequency cavity transverse electromagnetic field to perform transverse kicking on the beam so that the beam spot is evenly distributed to a circular area of the target surface.

Description

Technical Field

[0001] The invention relates to a method for quickly and evenly scanning a high-current and high-power particle beam by utilizing a radio frequency cavity, and relates to the technical field of accelerator high-current particle beams. Background Art

[0002] The beam at the exit of a high-current, high-power accelerator has a Gaussian distribution in the transverse direction. Considering the transverse utilization of the beam, the target often requires a uniformly distributed beam spot.

[0003] For rectangular targets represented by the European Spallation Source (ESS), Lissajous scanning can achieve uniform distribution of the beam spot. The scanning magnet frequency is about 40 kHz, but the duty cycle is only 4%. For circular targets represented by the China Accelerator Driven Transmutation Research Device (CiADS), due to the current power supply technology bottleneck, the use of scanning magnets cannot achieve uniform scanning at frequencies above kHz, especially scanning magnets operating in continuous wave mode. Summary of the Invention

[0004] In view of the above problems, the purpose of the present invention is to provide a method for quickly and uniformly scanning an intense and high-power particle beam using a three-stable (frequency, amplitude, phase) radio frequency cavity, which can meet the needs of quickly and uniformly scanning an intense and high-power particle beam.

[0005] In order to achieve the above-mentioned purpose of the invention, the technical solution adopted by the present invention is: a method for quickly and uniformly scanning a high-current, high-power particle beam using a radio frequency cavity, comprising: converging the high-current, high-power particle beam into a beam spot size required by the target surface through a focusing element group; controlling the phase shift between the radio frequency cavity and the target surface through the focusing element group; deflecting the beam so that the beam hits the target in the required direction; selecting the radio frequency cavity fundamental frequency so that there is a frequency difference between the bunch and the radio frequency cavity, ensuring that the centers of adjacent bunches feel different transverse fields of the radio frequency cavity, thereby realizing that the beam spots are distributed in different angular positions with the target surface as the center, that is, angular phase sliding scanning; selecting the radio frequency cavity harmonic order, harmonic frequency and harmonic component amplitude so that the centers of adjacent bunches feel different total effects of the transverse field of the radio frequency cavity, thereby realizing radial changes in the center of the beam spot at the target surface; using the orthogonal tristable radio frequency cavity transverse electromagnetic field to perform transverse kicking on the beam so that the beam spot is evenly distributed to a circular area of the target surface.

[0006] Furthermore, radial changes in the center of the beam spot at the target surface are achieved. The process is as follows: the RF cavity harmonic order, harmonic frequency tuning and harmonic component amplitude are selected according to the beam spot distribution requirements at the target surface. After the radial modulation function is expanded to a high order, the different frequency terms are separated by the product and difference method to ensure that the amplitudes of different harmonic components are constant. The fundamental wave and harmonics need to be realized by frequency modulation of the tuner.

[0007] Furthermore, appropriate RF cavity harmonic order, harmonic frequency tuning, and harmonic component amplitude are selected according to the beam spot distribution requirements at the target surface, including:

[0008] Select appropriate RF cavity harmonic order, harmonic frequency tuning, and harmonic component amplitude based on the beam spot distribution requirements at the target surface, including:

[0009] The change of the position of the beam spot center on the target surface over time can be described as:

[0010]

[0011] in, is the angular frequency, x(t) and y(t) are the coordinates of the beam spot on the target surface, and t is the time;

[0012] The amplitude modulation term A(t) can be expanded into higher harmonic form:

[0013] A(t)=m0+m1cos(ω r t)+m2cos(2ω r t)+m3cos(3ω r t)+m4cos(4ω r t)+…,

[0014] Among them, ω r is the radial frequency related term, m0, m1… are the harmonic coefficients;

[0015] Substitute the expanded amplitude modulation term into the center position of the beam spot:

[0016]

[0017] By using the product-sum-difference formula, different frequency terms can be separated, thus ensuring the constant amplitude of different harmonic components and the tristable operation of the cavity:

[0018]

[0019] Determine the harmonic frequency that the RF cavity needs to provide Higher-order harmonics, h is the order;

[0020] In order to form a strictly uniform distribution within the circular area, the radial position of the beam spot on the target surface must change with time to meet The waveform is expanded according to Fourier, and the amplitude of the harmonic components can be determined based on the harmonic frequency and the selected order.

[0021] Furthermore, the average current intensity of the high-current and high-power particle beam is in the mA level or above, and it operates in a continuous wave mode or a quasi-continuous wave mode, with an average power of more than several hundred kW.

[0022] Furthermore, the focusing element group includes a number of quadrupole magnets or solenoids arranged at intervals along the beam transmission line between the radio frequency cavity and the target surface, which constrain the distribution size of the cross-sectional direction of the high-current and high-power particle beam by alternating focusing in the horizontal and vertical directions, and converge it into the beam spot size required by the target surface.

[0023] Furthermore, the focusing element group adopts a plurality of 11 quadrupole magnets or solenoids arranged at intervals along the beam transmission line.

[0024] Furthermore, the focusing element group is also used to realize phase shift control between the RF cavity and the target surface. By optimizing the quadrupole magnet gradient or solenoid magnetic field, the phase shift between the RF cavity and the target surface is achieved to be (k+1 / 2)π, thereby maximizing the lateral kicking effect of the RF cavity.

[0025] Furthermore, several dipole magnets are used to deflect the beam. The required magnetic field is determined based on the magnetic stiffness of the beam and the designed deflection radius of the dipole magnet. The current is then set according to the current-magnetic field curve to achieve beam deflection to the desired angle.

[0026] Furthermore, three dipole magnets are used, and the three dipole magnets are respectively arranged at preset beam deflection positions of the beam transmission line, so that the beam is deflected to a desired angle.

[0027] Furthermore, the fundamental frequency of the RF cavity is determined according to the beam micropulse frequency f0, the annular scanning radius R on the target surface, and the root mean square RMS size σ of the beam spot on the target surface. After scanning, the number of beam spots distributed on the target surface N≥2πR / 2σ, f c =(nm / N)f0, where n is a positive integer, m is an integer less than N, and m and N are relatively prime.

[0028] The present invention adopts the above technical solution, which has the following characteristics:

[0029] 1. The present invention provides a method for quickly and evenly scanning a high-current, high-power particle beam using a tristable radio frequency cavity, which can quickly and evenly distribute the particle beam to a circular area on the target surface.

[0030] 2. The present invention can increase the scanning frequency of continuous wave operation to above MHz level by manipulating beam micropulses.

[0031] 3. The present invention distributes a high-current, high-power particle beam quickly and evenly to a circular area on the target surface at a frequency above the MHz level. By selecting appropriate RF cavity fundamental frequency, harmonic order, harmonic frequency tuning, and harmonic component amplitude, the amplitude modulation of the cavity during the beam spot scanning process is eliminated, and three-stable operation can be put into operation, which is convenient for monitoring and has high system stability.

[0032] In summary, the beam spot distribution in the circular area achieved by the present invention is more uniform and the peak power density is lower, and it can be widely used in accelerator high-current particle beam scanning. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. Throughout the drawings, the same reference numerals are used to denote the same components. In the drawings:

[0034] Figure 1 Schematic diagram of the beam transmission line and elements along the line in an embodiment of the present invention.

[0035] Figure 2 Schematic diagram of the distribution of beam spot centers on the target surface in an embodiment of the present invention.

[0036] Figure 3 Schematic diagram of beam spot distribution on the target surface after scanning in an embodiment of the present invention (intuitive three-dimensional diagram).

[0037] Figure 4 Schematic diagram of beam spot distribution on the target surface after scanning (radial cross section) in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] It should be understood that the terms used herein are for the purpose of describing specific example embodiments only and are not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "one", "an" and "said" as used herein may also be meant to include plural forms. The terms "comprise", "include", "contain" and "have" are inclusive and therefore specify the presence of stated features, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, steps, operations, elements, parts, and / or combinations thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring them to be performed in the specific order described or illustrated, unless the order of execution is clearly indicated. It should also be understood that additional or alternative steps may be used.

[0039] Although the terms first, second, third, etc. can be used in the text to describe multiple elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms can only be used to distinguish an element, component, region, layer or section from another region, layer or section. Unless the context clearly indicates otherwise, terms such as "first", "second" and other numerical terms do not imply order or sequence when used in the text. Therefore, the first element, component, region, layer or section discussed below can be referred to as the second element, component, region, layer or section without departing from the teaching of the example embodiments.

[0040] 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," "lower," "upper," etc. Such spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures.

[0041] The present invention proposes a method for rapidly and uniformly scanning an intense, high-power particle beam using a radio frequency cavity, comprising: controlling the beam spot size at the target surface and the phase shift between the radio frequency cavity and the target surface through a focusing element group; selecting an appropriate radio frequency cavity fundamental frequency based on the beam micropulse frequency, target surface size, and beam spot size at the target surface, ensuring a frequency difference between the radio frequency cavity and the bunch, achieving angular phase-sliding scanning, and radially distributing the beam spot center on the target surface; selecting appropriate radio frequency cavity harmonic orders, harmonic frequency tuning, and harmonic component amplitudes based on the beam spot distribution requirements at the target surface, achieving radial variation of the beam spot center; and utilizing an orthogonal tristable radio frequency cavity transverse electromagnetic field to perform a transverse kick on the beam, resulting in a quasi-uniform distribution of the beam spot on the target surface. Therefore, the present invention can evenly distribute an intense, high-power particle beam at frequencies above the MHz level within a circular region of the target surface.

[0042] Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0043] The method provided in this embodiment for rapidly and uniformly scanning a high-current particle beam with a radio frequency cavity includes:

[0044] S1, through the focusing element group, the high-current and high-power particle beam is focused into the beam spot size required by the target surface;

[0045] Specifically, the high-current, high-power particle beam of this embodiment has an average current intensity of mA or above, operates in continuous wave mode (duty cycle 100%) or quasi-continuous wave mode (duty cycle close to 100%), and has an average power of more than 100 kW.

[0046] like Figure 1 As shown, the focusing element group is used to focus the size of the cross-sectional distribution of the high-current high-power particle beam. The focusing element group of this embodiment includes a plurality of quadrupole magnets 3 or solenoids arranged between the radio frequency cavity 1 and the target surface 2. For example, this embodiment adopts 11 quadrupole magnets 3 (taking this as an example, not limited thereto, and the number can be set as needed). The 11 quadrupole magnets 3 are arranged at intervals along the beam transmission line, and the distribution size of the cross-sectional distribution of the high-current high-power particle beam is constrained by alternating focusing in the horizontal and vertical directions, and converged into the beam spot size required by the target surface. Among them, the beam spot size is determined by the scanning mode, and the scanning mode is related to boundary conditions such as the target surface size, the instantaneous peak power density limit during scanning, and the peak power density limit after scanning. It can be controlled according to specific usage requirements and is not specifically limited here.

[0047] S2, controlling the phase shift between the RF cavity and the target surface through the focusing element group;

[0048] In addition to the focusing function of the high-current, high-power particle beam in the cross-sectional direction, the 11 quadrupole magnets 3 in this embodiment also take into account the phase shift control between the RF cavity 1 and the target surface 2. Since the kicking effect is related to the sine value of the phase shift, and the phase shift is related to the beam spot envelope, the gradient of the focusing element group will affect the beam spot envelope. Therefore, the kicking effect can be controlled by adjusting the gradient of the quadrupole magnet 3. By optimizing the gradient of the quadrupole magnet 3, the phase shift between the RF cavity 1 and the target surface 2 can be achieved to be (k+1 / 2)π, thereby maximizing the lateral kicking effect of the RF cavity 1.

[0049] S3. Deflect the beam so that it hits the target in the required direction;

[0050] Specifically, in order to achieve beam irradiation in a specific target direction, a dipole magnet can be used to deflect the beam so that the beam hits the target in the required direction. The dipole magnet 4 of this embodiment can be a room temperature dipole magnet or a superconducting dipole coil. The beam needs to be irradiated in a specific direction according to the needs of the target. The required magnetic field is determined based on the beam magnetic stiffness and the designed deflection radius of the dipole magnet, and then the current is set according to the current-magnetic field curve to achieve beam deflection to the desired angle. For example, this embodiment is provided with three dipole magnets 4, and the three dipole magnets 4 are respectively set at the preset beam deflection positions of the beam transmission line to achieve beam deflection to the desired angle.

[0051] S4. Select an appropriate RF cavity fundamental frequency so that there is a frequency difference between the beam bunch and the RF cavity, ensuring that the centers of adjacent beam bunches feel different transverse fields of the RF cavity, and realizing that the beam spots are distributed in different angular positions with the target surface as the center, i.e., angular sliding phase scanning;

[0052] Specifically, an appropriate RF cavity fundamental frequency is selected based on the beam micropulse frequency, target surface size, and beam spot size at the target surface; the RF cavity fundamental frequency is determined based on the beam micropulse frequency f0, target surface radius R, and beam spot root mean square (RMS) size σ at the target surface. After scanning, the number of beam spots distributed on the target surface N ≥ 2πR / 2σ, so f c =(nm / N)f0, where n is a positive integer, m is an integer less than N, and m and N are relatively prime.

[0053] S5. Select appropriate RF cavity harmonic order, harmonic frequency, and harmonic component amplitude so that adjacent bunch centers experience different total effects of the RF cavity transverse field, thereby achieving radial variation of the beam spot center at the target surface.

[0054] Specifically, in the annular scan, the center of the beam spot is distributed in an annular linear shape, and the total effect of the kicking effect in the horizontal and vertical directions is constant, that is, is a fixed value. Unlike circular scanning, uniform scanning requires the beam spot center to be distributed planarly on the target surface, and A needs to be variable. Select the appropriate RF cavity harmonic frequency, harmonic order, and harmonic component amplitude based on the beam spot distribution requirements on the target surface.

[0055] The change of the position of the beam spot center on the target surface over time can be described as:

[0056]

[0057] in, is the angular frequency, x(t) and y(t) are the coordinates of the beam spot on the target surface, and t is the time.

[0058] The amplitude modulation term A(t) can be expanded into higher harmonic form:

[0059] A(t)=m0+m1cos(ω r t)+m2cos(2ω r t)+m3cos(3ω r t)+m4cos(4ω r t)+…, where ω r is the radial frequency related term, and m0, m1… are the harmonic coefficients.

[0060] Substitute the expanded amplitude modulation term into the center position of the beam spot:

[0061]

[0062] By using the product-sum-difference formula, different frequency terms can be separated, thus ensuring the constant amplitude of different harmonic components and the tristable operation of the cavity:

[0063]

[0064] Thus, it is determined that the RF cavity needs to provide a harmonic frequency of The harmonic order is a compromise between post-scan uniformity and system complexity, and can be determined based on actual needs.

[0065] Harmonic frequency tuning is related to the fundamental frequency selection. After the radial modulation function is expanded to a high order, the fundamental and harmonic waves need to be tuned by a tuner (several MHz). Tuning is achieved by applying pressure to the cavity through remote control of the mechanical structure, causing the cavity resonant frequency to change.

[0066] In order to form a strictly uniform distribution within the circular area, the radial position of the beam spot on the target surface must change with time to meet The waveform is expanded according to Fourier, and the amplitude of the harmonic component can be determined based on the harmonic frequency and order.

[0067] S6. Use the transverse electromagnetic field of the orthogonal tristable RF cavity to kick the beam laterally, so that the beam spot forms a quasi-uniform distribution on the target surface. Because the harmonic order cannot be taken to infinity, the strictly uniform distribution within the circular area will degenerate into a quasi-uniform distribution.

[0068] Specifically, the cavity is put into operation in a three-stable manner. During the scanning process, the amplitude of the RF cavity is not modulated, and the two RF cavities kick the beam in the horizontal and vertical directions respectively, with a phase difference of 90°.

[0069] The method for rapidly and uniformly scanning a high-current particle beam using a radio frequency cavity of the present invention is further described in detail below through specific embodiments.

[0070] This embodiment uses a 500 MeV proton beam, a micropulse frequency of 162.5 MHz, a beam current of 5 mA, a duty cycle of 100%, and a total beam power of 2.5 MW. The specific process is as follows:

[0071] S1. The high-current, high-power particle beam is converged into a beam spot with an RMS size of σ = 12 mm through a focusing element group.

[0072] The focusing element group includes several quadrupole magnets 3, which constrain the cross-sectional direction of the high-current, high-power particle beam. At the same time, in order to increase the scanning capability, the phase shift between the cavity and the target surface is controlled to be close to 270° through the focusing element group. In addition, in order to aim the beam downward at the target, multiple vertical deflection dipole magnets 4 are used to deflect the beam and perform a dispersion elimination design.

[0073] S2. In order to make the center of the beam spot distributed on N=25 radial lines in the circular area of R=150mm on the target surface, the RF cavity frequency is selected as f c =(nm / N)f0=(1-17 / 25)f0=52MHz, that is: It is 52MHz.

[0074] S3. Determine radial frequency ω r = 200MHZ, expand the radial modulation function to h = 4th order, and calculate the amplitude of each harmonic component. It should be noted that the harmonic frequency needs to be tuned based on the and ω r To fine tune (a few MHz).

[0075] S4, the RF cavity operates in a tristable state, and uses the transverse electromagnetic field of the fundamental wave and harmonic superposition to kick the beam bunch, so that the position of the beam spot center on the target surface changes, such as Figure 2 shown.

[0076] S5, the beam spot distribution after scanning at the target surface is as follows Figure 3 As shown, the radial cross-section is as follows Figure 4 shown.

[0077] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In the description of this specification, the reference terms "one embodiment", "some implementations", etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiments of this specification. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in an appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples, unless they are contradictory.

[0078] 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 various embodiments of the present invention.

Claims

1. A method for rapidly and uniformly scanning a high-current, high-power particle beam using a radio frequency cavity, characterized in that include: The high-current and high-power particle beam is focused into the beam spot size required by the target surface through the focusing element group; The phase shift between the RF cavity and the target is controlled by a focusing element group. The focusing element group uses 11 quadrupole magnets spaced along the beam transmission line. The focusing element group is also used to achieve phase shift control between the RF cavity and the target. By optimizing the quadrupole magnet gradient, the phase shift between the RF cavity and the target is (k+1 / 2)π, thereby maximizing the lateral kicking effect of the RF cavity. Deflect the beam so that it hits the target in the required direction; The fundamental frequency of the RF cavity is selected so that there is a frequency difference between the beam bunch and the RF cavity, so that the beam spot is distributed in different angular positions with the target surface as the center, that is, angular sliding phase scanning; the fundamental frequency of the RF cavity f c According to the beam micropulse frequency f0, the annular scanning radius R on the target surface, and the root mean square RMS size σ of the beam spot on the target surface, the number of beam spots distributed on the target surface after scanning N≥2πR / 2σ, f c =(nm / N)f0, where n is a positive integer, m is an integer less than N, and m and N are relatively prime; The harmonic order, harmonic frequency, and harmonic component amplitude of the RF cavity are selected so that the centers of adjacent bunches experience different total effects of the transverse field of the RF cavity, thereby achieving radial variation of the beam spot center at the target surface. The process is as follows: the harmonic order, harmonic frequency tuning, and harmonic component amplitude of the RF cavity are selected according to the beam spot distribution requirements at the target surface. After the radial modulation function is expanded to a high order, the different frequency terms are separated by the product and difference method to ensure that the amplitudes of different harmonic components are constant. The frequencies of the fundamental wave and harmonics are achieved by frequency modulation of the tuner. Select appropriate RF cavity harmonic order, harmonic frequency tuning, and harmonic component amplitude based on the beam spot distribution requirements at the target surface, including: The change of the position of the beam spot center on the target surface over time is described as: in, is the angular frequency, and is the coordinate of the beam spot on the target surface, and t is the time; Amplitude modulation term It can be expanded into higher harmonic form: ,in, is the radial frequency related term, m 0 、m 1… is the harmonic coefficient; Substitute the expanded amplitude modulation term into the center position of the beam spot: The product-sum-difference formula is used to separate different frequency terms, thereby ensuring that the amplitudes of different harmonic components are constant and the cavity operates in a three-stable manner: Determine the harmonic frequency that the RF cavity needs to provide The higher-order harmonics of , h is the order; In order to form a strictly uniform distribution within the circular area, the radial position of the beam spot on the target surface must change with time to meet , expand the waveform according to Fourier, and determine the harmonic component amplitude based on the harmonic frequency and the selected order; The transverse electromagnetic field of the orthogonal tristable radio frequency cavity is used to kick the beam laterally, so that the beam spot is evenly distributed to the circular area of the target surface.

2. The method for rapidly and uniformly scanning a high-current, high-power particle beam using a radio frequency cavity according to claim 1, wherein: The average current intensity of the high-current and high-power particle beam is above the mA level, operating in continuous wave mode or quasi-continuous wave mode, with an average power of more than 100 kW.

3. The method for rapidly and uniformly scanning a high-current, high-power particle beam using a radio frequency cavity according to claim 1, characterized in that: The focusing element group includes several quadrupole magnets arranged at intervals along the beam transmission line between the radio frequency cavity and the target surface. It constrains the distribution size of the cross-sectional direction of the high-current and high-power particle beam by alternating focusing in the horizontal and vertical directions, and converges it into the beam spot size required by the target surface.

4. The method for rapidly and uniformly scanning a high-current, high-power particle beam using a radio frequency cavity according to any one of claims 1 to 3, characterized in that: Several dipole magnets are used to deflect the beam. The required magnetic field is determined based on the magnetic stiffness of the beam and the designed deflection radius of the dipole magnet. The current is then set according to the current-magnetic field curve to achieve beam deflection to the desired angle.

5. The method for rapidly and uniformly scanning a high-current, high-power particle beam using a radio frequency cavity according to claim 4, characterized in that: Three dipole magnets are used, and the three dipole magnets are respectively arranged at preset beam deflection positions on the beam transmission line to deflect the beam to a desired angle.

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