CN115003002A - A method of phase-slip ring scanning of high-current and high-power particle beams by using a radio frequency cavity - Google Patents

Abstract

The invention relates to a method for performing phase-slip annular scanning on a high-power particle beam by using a radio frequency cavity, which comprises the following steps: converging the high-power particle beams with strong current into 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 current to enable the beam current to target according to the required direction; selecting proper radio frequency cavity frequency according to beam micro-pulse frequency, target surface size and beam spot size at the target surface, ensuring that the radio frequency cavity and the beam cluster have frequency difference delta f, and enabling the centers of adjacent beam clusters to feel the inconsistency of transverse field phases, thereby scanning to different positions of the target surface and realizing sliding phase scanning; and transverse kicking tracks are carried out on the beam current by utilizing a transverse electromagnetic field of the orthogonal three-stable radio frequency cavity, so that the centers of the beam spots form annular distribution on the target surface. The invention utilizes the three-stable radio frequency cavity to carry out the sliding phase annular scanning method on the strong current high-power particle beam, and can meet the requirement of annular scanning of the strong current high-power particle beam.

Description

A method for phase-slip ring scanning of high-current and high-power particle beams by using a radio frequency cavity

technical field

The invention relates to a method for using a radio frequency cavity to perform phase-slip ring scanning on a high-current high-power particle beam, and relates to the technical field of accelerator high-current particle beams.

Background technique

Intense particle beams have broad application prospects in isotope production (IPF), spallation neutron sources (SNS), accelerator-driven subcritical systems (ADS) and other fields. Considering the different needs of the terminal, the beam energy is in the order of hundreds of MeV in isotope production, and in the order of GeV in SNS and ADS. Therefore, the power of high-current particle beams with an average current intensity above the mA level is in the order of 100 kW to MW. For example, the beam power of the China Accelerator-Driven Transmutation Research Device (CiADS) is 10MW (beam energy 1GeV, average current intensity 10mA), The beam power of the European Spallation Neutron Source (ESS) is 5MW (beam energy 2GeV, average current intensity 2.5mA), so high-current particle beams are often accompanied by high beam power density at the target surface in practical applications.

In order to reduce the peak power density of the high-current high-power beam at the target surface, ESS uses Lissajous scanning to form a uniform distribution in a rectangular area. The frequency of the scanning magnet is about 40kHz, but the duty cycle is only 4%; Brookhaven experiment in the United States The scanning magnets in the chamber's Isotope Production Terminal (BLIP) and Los Alamos Laboratory's Isotope Production Facility (IPF) have a frequency of 5 kHz with beam duty cycles of only 0.3% and 1.5%. On a continuous wave (CW) operating machine represented by TRIUMF, the frequency of scanning the magnet only reaches 400Hz.

Taking the demand of CiADS liquid lead-bismuth target as an example, considering factors such as peak power density, target temperature rise, target window irradiation damage, etc., a circular scanning method is proposed to reduce the peak power density, and the scanning frequency needs to be above kHz. However, due to the technical bottleneck of the current scanning power supply, so far, there is no kHz-level scanning magnet that works in the continuous wave mode.

SUMMARY OF THE INVENTION

In view of the above problems, the purpose of the present invention is to provide a phase-sliding annular scanning method that can quickly and evenly distribute a high-current high-power particle beam to the annular area of the target surface by using a radio frequency cavity with a frequency above MHz.

In order to achieve the above purpose of the invention, the technical solution adopted in the present invention is: a method for performing phase-slip annular scanning on a high-current high-power particle beam by using a radio frequency cavity, comprising:

The beam spot size required to focus the high-current high-power particle beam into the target surface through the focusing element group;

Control the phase shift between the radio frequency cavity and the target surface through the focusing element group;

Deflect the beam so that the beam hits the target in the required direction;

According to the beam micro-pulse frequency, the size of the target surface and the size of the beam spot at the target surface, the appropriate RF cavity frequency is selected to ensure that there is a frequency difference Δf between the RF cavity and the beam cluster, so that the center of the adjacent beam clusters feels the phase of the transverse field is inconsistent, so that Scanned to different positions on the target surface to achieve phase-slip scanning;

The beam is laterally kicked by the transverse electromagnetic field of the orthogonal tristable radio frequency cavity, so that the center of the beam spot forms a circular distribution on the target surface.

Further, the average current intensity of high-current high-power particle beams is in the order of mA and above, operating in continuous wave mode or quasi-continuous wave mode, and the average power is above several hundred kW.

Further, the focusing element group includes several quadrupole magnets or solenoids that are arranged between the radio frequency cavity and the target surface and are spaced along the beam transmission line. The distribution size in the cross-sectional direction is constrained and converged to the beam spot size required by the target surface.

Further, the focusing element group adopts 11 quadrupole magnets, and the 11 quadrupole magnets are arranged at intervals along the beam transmission line.

Further, the focusing element group is also used to realize the phase shift control between the radio frequency cavity and the target surface. After optimizing the gradient of the quadrupole magnet or the solenoid magnetic field, the phase shift between the radio frequency cavity and the target surface is (k+1/2) π, so that the lateral kick-rail effect of the RF cavity is maximized.

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

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

Further, the RF cavity frequency f _c is determined according to the beam micro-pulse frequency f ₀ , the annular scanning radius R on the target surface, and the RMS size σ of the beam spot at the target surface, so that the distance between adjacent scanning points on the target surface is less than 2σ, Further ensure that the beam spot distribution on the ring after scanning is uniform, and the distribution number of beam spots on the target surface after scanning is N≥2πR/2σ, f _c =(nm/N)f ₀ , where n is a positive integer, m is less than N integers, and m is relatively prime to N.

Further, the amplitudes of the two RF cavities of the orthogonal three-stable 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 magnitude of is determined by the kick effect and the desired kick angle.

Further, the two radio frequency cavities kick the beams in the horizontal and vertical directions respectively, with a phase difference of 90°, so as to ensure that the beam spot is distributed in an annular shape on the target surface.

The present invention has the following characteristics due to adopting the above technical solutions:

1. The present invention utilizes the phase-sliding annular scanning method of the high-current high-power particle beam by the radio frequency cavity, which can quickly and evenly distribute the particle beam to the annular area of the target surface, which can meet the needs of the annular scanning of the high-current and high-power particle beam.

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

3. The present invention can increase the scanning frequency of the continuous wave scanning device from the order of 100 Hz to the order of MHz or more by manipulating the beam micro-pulse.

4. The present invention quickly and evenly distributes the high-current high-power particle beam to the annular area of the target surface at a frequency above the MHz order.

In conclusion, the present invention can be widely used in high-current high-power particle beam scanning.

Description of drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are for the purpose of illustrating preferred embodiments only and are not to be considered limiting of the invention. The same reference numerals are used to refer to the same parts throughout the drawings. In the attached image:

FIG. 1 is a schematic diagram of a beam transmission line and elements along the line in an embodiment of the present invention.

2 is a schematic diagram of the relationship between the beam cluster and the radio frequency cavity waveform in the embodiment of the present invention, the horizontal axis is the radio frequency cavity period, and the black dots are the horizontal and vertical coordinates of the beam spot center on the target surface after being acted by the radio frequency cavity.

FIG. 3 is a schematic diagram of the distribution of the center point of the beam spot on the target surface in the embodiment of the present invention.

FIG. 4 is a schematic diagram of beam spot distribution on the target surface after scanning in an embodiment of the present invention.

Detailed ways

It is to be understood that the terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a," "an," and "the" can also be intended to include the plural forms unless the context clearly dictates otherwise. The terms "comprising", "comprising", "containing" and "having" are inclusive and thus indicate the presence of stated features, steps, operations, elements and/or components, but do not preclude the presence or addition of one or Various other features, steps, operations, elements, components, and/or combinations thereof. Method steps, procedures, and operations described herein are not to be construed as requiring that they be performed in the particular order described or illustrated, unless an order of performance is explicitly indicated. It should also be understood that additional or alternative steps may be used.

For ease of description, spatially relative terms may be used herein to describe the relationship of one element or feature to another element or feature as shown in the figures, such as "inner", "outer", "inner" ", "outside", "below", "above", etc. This spatially relative term is intended to include different orientations of the device in use or operation other than the orientation depicted in the figures.

The method of using a radio frequency cavity to perform phase-slip ring scanning on a high-current high-power particle beam provided by the present invention includes: 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; The pulse frequency, the size of the target surface and the size of the beam spot at the target surface select the appropriate RF cavity frequency to ensure that there is a frequency difference between the RF cavity and the beam cluster to achieve phase-slip scanning; the transverse electromagnetic field of the orthogonal three-stable RF cavity is used to laterally kick the beam. track, so that the center of the beam spot forms an annular distribution on the target surface. Therefore, the present invention can evenly distribute the high-current high-power particle beam to the annular area of the target surface at a frequency of the order of MHz or higher.

Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that the present invention will be more thoroughly understood, and will fully convey the scope of the present invention to those skilled in the art.

The method for performing phase-slip ring scanning on a high-current high-power particle beam by using a radio frequency cavity provided in this embodiment includes:

S1. The beam spot size at the target surface is controlled by the focusing element group, that is, the beam spot size required by the focusing element group to converge the high-current high-power particle beam into the target surface.

Specifically, the average current intensity of the high-current high-power particle beam in this embodiment is in the order of mA and above, and it operates in a continuous wave mode (duty ratio of 100%) or a quasi-continuous wave mode (duty ratio is close to 100%), The average power is above several hundred kW.

The focusing element group includes several quadrupole magnets 3 or solenoids arranged between the radio frequency cavity 1 and the target surface 2, for example, 11 quadrupole magnets 3 are used in this embodiment (this is an example, not limited to this, can be based on Quantity setting is required), as shown in Figure 1, 11 quadrupole magnets 3 are arranged at intervals along the beam transmission line, and the distribution size of the cross-sectional direction of the high-current high-power particle beam is constrained by alternating focusing in the horizontal and vertical directions. And converge 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 the target surface size, the instantaneous peak power density limit during scanning, the peak power density limit after scanning and other boundary conditions, which can be controlled according to specific application requirements. Make specific restrictions.

S2. Control the phase shift between the radio frequency cavity 1 and the target surface 2 through the focusing element group.

The 11 quadrupole magnets 3 in this embodiment not only undertake the focusing function in the cross-sectional direction of the high-current high-power particle beam, but also take into account the phase shift control between the radio frequency 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, so the kicking effect can be achieved by adjusting the gradient of the quadrupole magnet 3. control. By optimizing the gradient of the quadrupole magnet 3, the phase shift between the radio frequency cavity 1 and the target surface 2 can be (k+1/2)π, so that the lateral kick rail effect of the radio frequency cavity 1 is maximized.

S3. In order to realize the beam current irradiation for a specific target surface direction, the beam current can be deflected by using the dipole magnet 4, so that the beam current can hit the target according to the required direction.

Specifically, the dipole magnet 4 can be a normal temperature dipole magnet or a superconducting dipole coil. The beam current needs to be irradiated in a specific direction according to the needs of the target. The required magnetic field is determined according to the beam magnetic stiffness and the design deflection radius of the dipole magnet, and then the current is set according to the current-magnetic field curve to achieve the beam deflection to the desired angle. . For example, in this embodiment, three dipole magnets 4 are provided, and the three dipole magnets 4 are respectively arranged at preset beam deflection positions of the beam transmission line, so as to realize beam deflection to a desired angle.

S4. Select the appropriate RF cavity frequency according to the beam current micro-pulse frequency, the size of the target surface and the size of the beam spot at the target surface to ensure that the RF cavity 1 and the beam cluster have a frequency difference Δf (that is, the frequency of the RF cavity and the cluster frequency are taken to be different If the two values are the same, or the frequency of the radio frequency cavity is an integer multiple of the cluster frequency, the lateral field felt by the center of the adjacent cluster is the same, and the scanning cannot be realized), and phase-slip scanning is realized, that is, the center of the adjacent cluster is The perceived lateral field is out of phase and thus scanned to different locations on the target surface, as shown in Figure 2.

Specifically, the RF cavity frequency f _c is determined according to the beam micro-pulse frequency f ₀ , 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 uniform beam spot distribution on the ring after scanning. The distribution number of the beam spot on the target surface after scanning is N≥2πR/2σ, f _c =(nm/N)f ₀ , where n is a positive integer, m is an integer smaller than N, and m and N are relatively prime.

The cavity tri-stable (frequency, amplitude, and phase remain unchanged) are put into operation. Due to the use of phase-slip scanning, the RF cavity amplitude is not modulated during the scanning process.

S5, using the transverse electromagnetic field of the orthogonal three-stable radio frequency cavity to laterally kick the beam, so that the center of the beam spot forms an annular distribution on the target surface.

Specifically, the amplitudes of the two RF cavities in the orthogonal three-stable 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 kicking effect of the transverse electromagnetic field of the RF cavity depends on the type and energy of the beam. 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. to make sure. Further, the two radio frequency cavities kick the beams in the horizontal and vertical directions respectively, with a phase difference of 90°, so as to ensure that the beam spot is distributed in an annular shape on the target surface.

The implementation process of the method for performing phase-slip annular scanning on a high-current high-power particle beam by using a radio frequency cavity of the present invention is further described in detail below through specific embodiments.

This embodiment uses a 500MeV proton beam, the micro-pulse frequency is 162.5MHz, the beam current intensity is 5mA, the duty cycle is 100%, and the total beam power is 2.5MW. The specific implementation process is as follows:

1. Focus the high-current high-power particle beam into a beam spot with RMS size σ=19mm through the focusing element group.

The focusing element group in this embodiment includes 11 quadrupole magnets 3 to constrain the cross-sectional direction of the high-current high-power particle beam; at the same time, in order to improve the scanning capability, the focusing element group is used to control the phase between the radio frequency cavity 1 and the target surface 2 The shift is close to 270°; in addition, in order to target the beam downward, three vertical deflection dipole magnets 4 are used to deflect the beam and carry out an achromatic design.

2. In order to distribute the center of the beam spot on the target surface R=50mm annular area N=25 points, the frequency of the radio frequency cavity is selected as f _c =(nm/N)f ₀ =(2-1/25)f ₀ =318.5 MHz.

3. The radio frequency cavity operates in a tri-stable state, and uses its transverse electromagnetic field to kick the beam cluster, so that the position of the center of the beam spot on the target surface changes with time, as shown in Figure 2.

4. The distribution of the center point of the beam spot at the target surface is shown in Figure 3, and the distribution of the beam spot after scanning is shown in Figure 4.

Each embodiment in this specification is described in a progressive manner, and the same and similar parts between the various embodiments may be referred to each other, and each embodiment focuses on the differences from other embodiments. In the description of this specification, reference to the description of the terms "one embodiment", "some implementations", etc. means that a particular feature, structure, material or characteristic described in connection with the embodiment or example is included in at least one implementation of the embodiment of this specification example or example. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, those skilled in the art may combine and combine the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples, without conflicting each other.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that it can still be The technical solutions described in the foregoing embodiments are modified, or some technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. A method for performing a slip-phase annular scan on a high-power particle beam with a high current by using a radio frequency cavity is characterized by comprising the following steps:

converging the high-power particle beams with strong current into 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 flow to enable the beam flow to target according to the required direction;

selecting proper radio frequency cavity frequency according to beam micro-pulse frequency, target surface size and beam spot size at the target surface, ensuring that the radio frequency cavity and the beam cluster have frequency difference delta f, and enabling the centers of adjacent beam clusters to feel the inconsistency of transverse field phases, thereby scanning to different positions of the target surface and realizing sliding phase scanning;

and transverse kicking tracks are carried out on the beam current by utilizing a transverse electromagnetic field of the orthogonal three-stable radio frequency cavity, so that the centers of the beam spots form annular distribution on the target surface.

2. The method of claim 1 in which the high power particle beam has an average power of mA or more, operates in continuous wave mode or quasi-continuous wave mode, and has an average power of hundreds kW or more.

3. The method of claim 1, wherein the focusing element set comprises a plurality of quadrupole magnets or solenoids arranged between the rf cavity and the target surface at intervals along the beam transport line, and the distribution size of the high-power particle beam in the cross-sectional direction is constrained by alternately focusing horizontally and vertically and converged to the beam spot size required by the target surface.

4. The method of claim 3 in which 11 quadrupole magnets are used in the focusing element group, the 11 quadrupole magnets being spaced along the beam transmission line.

5. The method of claim 3, wherein the focusing element set is further used to control the phase shift between the RF cavity and the target surface, and the phase shift between the RF cavity and the target surface is (k +1/2) pi by optimizing the quadrupole magnet gradient or the solenoid magnetic field, so as to maximize the lateral kicking effect of the RF cavity.

6. The method according to any of claims 1 to 5, wherein a plurality of dipole magnets are used for deflecting the beam, the required magnetic field is determined according to the beam magnetic stiffness and the designed deflection radius of the dipole magnets, and the current is set according to the current-magnetic field curve to deflect the beam to a desired angle.

7. The method according to claim 6, wherein 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.

8. The method of claim 1, wherein the high-power particle beam is scanned in a slip-phase ring by an RF cavityMethod, characterized in that the radio-frequency cavity frequency f _c According to the micro-pulse frequency f of the beam ₀ Determining the annular scanning radius R on the target surface and the root mean square RMS (root mean square) size sigma of the beam spots at the target surface to ensure that the distance between adjacent scanning points of the target surface is less than 2 sigma and further ensure that the beam spots on the scanned ring are uniformly distributed, wherein the distribution quantity N of the scanned beam spots on the target surface is more than or equal to 2 pi R/2 sigma, f _c ＝(n-m/N)f ₀ Wherein N is a positive integer, m is an integer less than N, and m and N are relatively prime.

9. The method of claim 1, wherein the amplitudes of two orthogonal tristable rf cavities are determined according to the scanning radius R of the ring on the target, the phase shift Φ between the rf cavity and the target surface, the type of the beam, and the energy of the beam, and the amplitudes of the rf cavities are determined by the kicking effect and the required kicking angle.

10. The method of claim 9 in which two rf cavities are used to kick the beam in the horizontal and vertical directions with a 90 ° phase difference, so as to ensure the beam spots are distributed annularly on the target surface.

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