Method for performing phase-sliding annular scanning of high-current and high-power particle beams using radio frequency cavity

Abstract

The present invention relates to a method for performing phase-sliding annular scanning on an intense, high-power particle beam using a radio frequency cavity, comprising: converging the intense, high-power particle beam into a beam spot size required by a 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 an appropriate radio frequency cavity frequency based on the beam micropulse frequency, the target surface size, and the beam spot size at the target surface, ensuring a frequency difference Δf between the radio frequency cavity and the bunch, so that the centers of adjacent bunches experience inconsistent transverse field phases, thereby being scanned to different positions on the target surface, thereby achieving phase-sliding scanning; and utilizing the transverse electromagnetic field of an orthogonal three-stable radio frequency cavity to perform a transverse kick on the beam, so that the center of the beam spot forms an annular distribution on the target surface. The present invention's method for performing phase-sliding annular scanning on an intense, high-power particle beam using a three-stable radio frequency cavity can meet the needs of annular scanning of an intense, high-power particle beam.

Description

Technical Field

[0001] The invention relates to a method for performing phase-sliding annular scanning on 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] High-intensity particle beams have broad application prospects in areas such as isotope production (IPF), spallation neutron sources (SNS), and accelerator-driven subcritical systems (ADS). Taking into account the varying demands of end users, beam energies range from hundreds of MeV in isotope production to GeV in SNS and ADS. Consequently, high-intensity particle beams with average intensities above the mA level typically have powers ranging from hundreds of kW to MW. For example, the China Accelerator-Driven Transmutation Research Facility (CiADS) boasts a beam power of 10 MW (beam energy 1 GeV, average intensity 10 mA), and the European Spallation Source (ESS) boasts a beam power of 5 MW (beam energy 2 GeV, average intensity 2.5 mA). Consequently, practical applications of high-intensity particle beams often present the problem of excessively high beam power density at the target surface.

[0003] To reduce the peak power density of the intense, high-power beam at the target, the ESS uses Lissajous scanning to create a uniform distribution within a rectangular area. The scanning magnet frequency is approximately 40 kHz, but the duty cycle is only 4%. The scanning magnet frequency in the Isotope Production Terminal (BLIP) at Brookhaven National Laboratory and the Isotope Production Facility (IPF) at Los Alamos National Laboratory is 5 kHz, with beam duty cycles of only 0.3% and 1.5%, respectively. On continuous-wave (CW) machines, such as the TRIUMF, the scanning magnet frequency reaches only 400 Hz.

[0004] Taking the requirements for liquid lead-bismuth targets in CiADS as an example, considering factors such as peak power density, target temperature rise, and target window irradiation damage, a circular scanning method is proposed to reduce peak power density, requiring a scanning frequency above kHz. However, due to current technical bottlenecks in scanning power supplies, there are currently no publicly available kHz-range scanning magnets operating in continuous wave mode. Summary of the Invention

[0005] In view of the above problems, the purpose of the present invention is to provide a phase-sliding annular scanning method that can use a radio frequency cavity to quickly and evenly distribute a high-current, high-power particle beam to an annular area on the target surface at a frequency above the MHz level.

[0006] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is: a method for performing phase-sliding annular scanning of a high-current, high-power particle beam using a radio frequency cavity, comprising:

[0007] 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;

[0008] The phase shift between the radio frequency cavity and the target surface is controlled by a focusing element group;

[0009] Deflect the beam so that it hits the target in the required direction;

[0010] Select an appropriate RF cavity frequency based on the beam micropulse frequency, target surface size, and beam spot size on the target surface to ensure a frequency difference △f between the RF cavity and the bunches. This ensures that adjacent bunch centers experience inconsistent transverse field phases and are scanned to different locations on the target surface, achieving phase-sliding scanning.

[0011] The transverse electromagnetic field of the orthogonal tristable radio frequency cavity is used to kick the beam laterally, so that the center of the beam spot forms a ring distribution on the target surface.

[0012] 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.

[0013] 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. The distribution size of the high-current and high-power particle beam in the cross-sectional direction is constrained by alternating focusing in the horizontal and vertical directions, and is converged into the beam spot size required by the target surface.

[0014] Furthermore, the focusing element group uses 11 quadrupole magnets, and the 11 quadrupole magnets are arranged at intervals along the beam transmission line.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] Furthermore, the RF cavity frequency 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 spacing between adjacent scanning points on the target surface is less than 2σ, thereby ensuring that the beam spot is evenly distributed on the annular ring after scanning. 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.

[0019] Furthermore, the amplitudes of the two RF cavities of the orthogonal tristable RF cavity are determined according to the annular scanning radius R on the target, the phase shift Φ between the RF cavity and the target surface, the type of beam, and the energy of the beam. The amplitude of the RF cavity is determined by the kicking effect and the required kicking angle.

[0020] Furthermore, the two RF cavities kick the beam in the horizontal and vertical directions respectively, with a phase difference of 90°, thereby ensuring that the beam spot is distributed in a ring shape on the target surface.

[0021] The present invention adopts the above technical solution, which has the following characteristics:

[0022] 1. The present invention utilizes a radio frequency cavity to perform a phase-sliding annular scanning method for a high-current, high-power particle beam, which can quickly and evenly distribute the particle beam to an annular area of the target surface, thus meeting the needs of annular scanning of a high-current, high-power particle beam.

[0023] 2. The RF cavity amplitude in the present invention is constant. By selecting an appropriate RF cavity frequency, amplitude modulation during the beam spot scanning process is eliminated, and three-stable (frequency, amplitude, phase) operation can be put into operation, which is convenient for monitoring and has high system stability.

[0024] 3. The present invention can increase the scanning frequency of a continuous wave scanning device from hundreds of Hz to above MHz by manipulating the beam micropulse.

[0025] 4. The present invention distributes a high-current, high-power particle beam quickly and evenly to an annular area of the target surface at a frequency above the MHz level.

[0026] In summary, the present invention can be widely used in high-current and high-power particle beam scanning. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] 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:

[0028] Figure 1 Schematic diagram of the beam transmission line and elements along the line in an embodiment of the present invention.

[0029] Figure 2 Schematic diagram of the relationship between the beam bunch and the RF cavity waveform in an embodiment of the present invention. The horizontal axis is the RF cavity period, and the black dots are the horizontal and vertical coordinates of the beam spot center on the target surface after the RF cavity acts on it.

[0030] Figure 3 Schematic diagram of the distribution of beam spot centers on the target surface in an embodiment of the present invention.

[0031] Figure 4 Schematic diagram of beam spot distribution on the target surface after scanning in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] 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.

[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," "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.

[0034] The present invention provides a method for performing phase-sliding annular scanning of 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 frequency based on the beam micropulse frequency, the target surface size, and the beam spot size at the target surface to ensure a frequency difference between the radio frequency cavity and the beam bunch, thereby achieving phase-sliding scanning; and utilizing the transverse electromagnetic field of the orthogonal tristable radio frequency cavity to perform a transverse kick on the beam, such that the beam spot center forms an annular distribution on the target surface. Therefore, the present invention can evenly distribute an intense, high-power particle beam at frequencies above the MHz level onto an annular region of the target surface.

[0035] 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.

[0036] The method provided in this embodiment for performing phase-sliding annular scanning on an intense, high-power particle beam using a radio frequency cavity includes:

[0037] S1. Control the beam spot size at the target surface through the focusing element group, that is, use the focusing element group to converge the high-current and high-power particle beam into the beam spot size required by the target surface.

[0038] 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 several hundred kW.

[0039] The focusing element group 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 uses 11 quadrupole magnets 3 (this is an example, not limited to this, and the number can be set as needed), such as Figure 1 As shown, eleven quadrupole magnets 3 are spaced along the beam transmission line. By alternating horizontal and vertical focusing, they constrain the cross-sectional distribution of the intense, high-power particle beam and converge it to the desired beam spot size on the target. The beam spot size is determined by the scanning mode, which in turn is dependent on boundary conditions such as the target size, the instantaneous peak power density limit during scanning, and the peak power density limit after scanning. This can be controlled based on specific usage requirements and is not specifically limited here.

[0040] S2. Control the phase shift between the RF cavity 1 and the target surface 2 through the focusing element group.

[0041] In addition to the focusing function of the cross-sectional direction of the high-current, high-power particle beam, 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 quadrupole magnet 3 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.

[0042] S3. In order to achieve beam irradiation in a specific target direction, the beam can be deflected by using a dipole magnet 4 so that the beam hits the target in the required direction.

[0043] Specifically, the dipole magnet 4 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 target's requirements. The required magnetic field is determined based on the beam's magnetic stiffness 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. For example, in this embodiment, three dipole magnets 4 are provided, each positioned at a predetermined beam deflection position on the beam transmission line to achieve beam deflection to the desired angle.

[0044] S4. Select an appropriate RF cavity frequency according to the beam micropulse frequency, target surface size, and beam spot size on the target surface to ensure that there is a frequency difference △f between the RF cavity 1 and the bunch (i.e., the RF cavity frequency and the bunch frequency are different values. If the two values are the same, or the RF cavity frequency is an integer multiple of the bunch frequency, the transverse fields felt by the centers of adjacent bunches are the same, and scanning cannot be achieved). Phase sliding scanning is achieved, that is, the transverse fields felt by the centers of adjacent bunches are inconsistent in phase, and thus are scanned to different positions on the target surface, such as Figure 2 shown.

[0045] Specifically, the RF cavity frequency f c The beam spot distribution on the target surface is determined by 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, so that the distance between adjacent scanning points on the target surface is less than 2σ, thereby ensuring that the beam spot distribution on the annular surface after scanning is uniform. 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.

[0046] The cavity is put into operation with three stability (frequency, amplitude and phase remain unchanged). Due to the use of phase sliding scanning, the RF cavity amplitude is not modulated during the scanning process.

[0047] S5. Use the transverse electromagnetic field of the orthogonal tristable RF cavity to kick the beam laterally so that the center of the beam spot forms a ring distribution on the target surface.

[0048] Specifically, the amplitudes of the two RF cavities in the orthogonal tristable RF cavity are determined by the circular scanning radius R on the target, the phase shift Φ between the RF cavity and the target surface, the beam type, and the beam energy. The kicking effect of the RF cavity's transverse electromagnetic field depends on the beam type and energy, while the scanning radius R and the phase shift Φ determine the required kicking angle. Therefore, the amplitude of the RF cavity can be determined by the kicking effect and the required kicking angle. Furthermore, the two RF cavities kick the beam horizontally and vertically, respectively, with a phase difference of 90°, to ensure a circular distribution of the beam spot on the target surface.

[0049] The following further describes in detail the implementation process of the method for performing phase-sliding annular scanning of an intense and high-power particle beam using a radio frequency cavity according to the present invention through specific embodiments.

[0050] 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 implementation process is as follows:

[0051] 1. The high-current, high-power particle beam is focused into a beam spot with an RMS size of σ = 19 mm through a focusing element group.

[0052] The focusing element group of this embodiment includes 11 quadrupole magnets 3, which constrain the cross-sectional direction of the high-current, high-power particle beam. At the same time, to improve scanning capability, the focusing element group controls the phase shift between the RF cavity 1 and the target surface 2 to approach 270°. In addition, to direct the beam downward to the target, three vertical deflection dipole magnets 4 are used to deflect the beam and implement a dispersion-eliminating design.

[0053] 2. In order to make the center of the beam spot distributed on the target surface R = 50mm annular area N = 25 points, the RF cavity frequency is selected as f c =(nm / N)f0=(2-1 / 25)f0=318.5MHz.

[0054] 3. The RF cavity operates in a tristable state, using its transverse electromagnetic field to kick the beam bunch, causing the position of the beam spot center on the target surface to change with time, such as Figure 2 shown.

[0055] 4. The distribution of beam spot center points on the target surface is as follows Figure 3 As shown, the beam spot distribution after scanning is as follows Figure 4 shown.

[0056] 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.

[0057] 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 performing phase sliding annular scanning on 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 includes a number of quadrupole magnets or solenoids arranged at intervals along the beam transmission line between the RF cavity and the target. The focusing element group constrains the distribution size of the high-current, high-power particle beam in the cross-sectional direction by alternating horizontal and vertical focusing, and converges it to the beam spot size required by the target surface. The focusing element group is also used to achieve 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 (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; According to the beam micropulse frequency, target surface size and beam spot size on the target surface, an appropriate RF cavity frequency is selected to ensure that there is a frequency difference △f between the RF cavity and the bunch, so that the centers of adjacent bunches feel inconsistent lateral field phases and are scanned to different positions on the target surface to achieve phase sliding scanning. The RF cavity frequency 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 spacing between adjacent scanning points on the target surface is less than 2σ, thereby ensuring that the beam spot is evenly distributed on the annular ring after scanning. 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 transverse electromagnetic field of the orthogonal tristable RF cavity is used to kick the beam laterally, so that the center of the beam spot forms a ring distribution on the target surface. The two RF cavities kick the beam in the horizontal and vertical directions respectively, with a phase difference of 90°, thus ensuring that the beam spot is distributed in a ring on the target surface.

2. The method for performing phase-sliding annular scanning of a high-current, high-power particle beam using a radio frequency cavity according to claim 1, characterized in that: 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 performing phase-sliding annular scanning of a high-current, high-power particle beam using a radio frequency cavity according to claim 1, characterized in that: The focusing element group uses 11 quadrupole magnets, and the 11 quadrupole magnets are arranged at intervals along the beam transmission line.

4. The method for performing phase-sliding annular scanning of 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 performing phase-sliding annular scanning of 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, so that the beam is deflected to a desired angle.

6. The method for performing phase-sliding annular scanning of a high-current, high-power particle beam using a radio frequency cavity according to claim 1, wherein: The amplitudes of the two RF cavities of the orthogonal tristable RF cavity are determined according to the annular scanning radius R on the target, the phase shift Φ between the RF cavity and the target surface, the type of beam, and the energy of the beam. The amplitude of the RF cavity is determined by the kicking effect and the required kicking angle.

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