A radio frequency quadrupole accelerator and charged particle accelerator system

Abstract

This application discloses a radio frequency quadrupole accelerator and charged particle accelerator system, relating to the field of particle acceleration equipment and its application technology. The quadrupole accelerator includes an accelerator housing containing four elongated accelerating electrodes symmetrically mounted around the accelerator's central axis. Near the accelerator's central axis, an accelerating zone is formed by the four accelerating electrodes facing each other. A vacuum isolation pipe composed of a non-metallic material is installed around the accelerating zone to enclose the accelerating zone and form a vacuum accelerating cavity. The non-accelerating zone of this application operates under atmospheric pressure, eliminating the need for vacuum sealing requirements for the accelerator housing, allowing for lightweight and simplified structure.

Description

Technical Field

[0001] The present application relates to the field of particle acceleration equipment and its application technology, and specifically to a radio frequency quadrupole accelerator and a charged particle accelerator system, which can be used as a linear injection accelerator for a proton or heavy ion tumor treatment device or a device for manufacturing radioactive nuclides. Background Art

[0002] Boron neutron capture heavy tumor therapy devices typically used for tumor treatment require proton beams with energies above 2.5 MeV and beam powers of tens of kilowatts. Proton beams with kinetic energies above 2.8 MeV typically require radio frequency linear accelerators, cyclotrons, or electrostatic accelerators, with radio frequency quadrupole accelerators (RFQ accelerators) and cyclotrons being the most commonly used methods.

[0003] Among them, the radio frequency quadrupole accelerator generally includes an accelerator shell, accelerating electrodes, a high-frequency power source, a high-frequency power transmission line, a high-frequency power coupler, a frequency and field distribution tuner, a vacuum system, a support system and a control system. When the RFQ accelerator is in operation, it is necessary to maintain a high vacuum state in the accelerator cavity (also called the accelerator shell) to avoid discharge and to prevent the charged particle beam from colliding with gas molecules and being lost.

[0004] The existing invention patent 202211722381.5, patent name "A superconducting quadrupole field accelerator device" and invention patent 202211193177.9, patent name "Quadrupole accelerator and method for manufacturing a quadrupole accelerator", disclose an accelerator structure in which the entire inner cavity of the accelerator is an acceleration cavity with a large volume. When evacuating the cavity, work needs to be performed on the entire cavity, resulting in long evacuation time, low efficiency, high energy consumption, and complex structure. At the same time, the high-frequency power coupler installed on the accelerator, the tuner for adjusting the resonant frequency and electric field distribution, and the signal pickup and other components all need to have both vacuum sealing and high-frequency sealing structures to maintain a high vacuum state in the accelerator cavity and prevent the electromagnetic field in the cavity from leaking outside the acceleration cavity. In particular, the vacuum sealing structure of the high-frequency power coupler is particularly complex, requiring ceramic-metal welding technology and a variable diameter structure to maintain impedance matching during manufacturing. At the same time, in order to maintain the vacuum inside the accelerator cavity, the accelerator shell usually requires a metal shell several centimeters thick to offset the pressure generated by the pressure difference between the inside and outside, which makes the accelerator cavity bulky and increases the manufacturing cost. Summary of the Invention

[0005] The main purpose of the present application is to provide a radio frequency quadrupole accelerator and a charged particle accelerator system. By maintaining a high vacuum in a limited range of space in the accelerator cavity where the accelerating electric field through which the beam passes is located, the rest of the accelerator cavity can operate at atmospheric pressure. The system has the advantages of simple structure, light weight, reliability, simple maintenance, and low manufacturing cost.

[0006] The technical solutions adopted in this application are as follows:

[0007] First aspect:

[0008] A radio frequency quadrupole accelerator includes an accelerator housing containing four elongated accelerating electrodes symmetrically mounted around the central axis of the accelerator. An accelerating zone is formed near the central axis by the four accelerating electrodes facing each other. A vacuum isolation pipe made of non-metallic material is mounted around the accelerating zone to enclose the accelerating zone and form a vacuum accelerating cavity area.

[0009] Optionally, the vacuum isolation pipe is made of a ceramic material with aluminum oxide or boron nitride as the main component.

[0010] Optionally, the four accelerating electrodes consist of a central electrode located inside the vacuum isolation pipe and a peripheral electrode located outside the hollow isolation pipe. The central electrode and the vacuum isolation pipe form a vacuum sealing structure through welding or a rubber ring structure. The central electrode and the peripheral electrode are in close contact to form a surface current conductive loop.

[0011] Optionally, the portion of the central electrode inside the vacuum isolation pipe is respectively equipped with electrode compensation blocks at the inlet and outlet ends of the accelerator.

[0012] Optionally, the electrode compensation block is installed in the acceleration zone after the accelerating electrode is inserted into the vacuum isolation pipe, and is welded and fixed to both ends of the central electrode.

[0013] Optionally, the electrode compensation block is installed in the acceleration zone after the accelerating electrode is inserted into the vacuum isolation pipe, and is fixed to both ends of the central electrode by bolts.

[0014] Optionally, four electrode mounting openings are provided on the wall surface of the vacuum isolation pipe and are opened along the central axis direction of the accelerator, and the accelerating electrodes are mounted in the electrode mounting openings in a one-to-one correspondence.

[0015] Optionally, the radio frequency quadrupole accelerator further includes at least one high-frequency power coupler, and a through coupler mounting opening is provided on the accelerator housing.

[0016] Optionally, the high-frequency power coupler includes a power coupler outer conductor, a power coupler inner conductor and a power coupler coupler ring. The power coupler inner conductor is coaxially installed in the inner cavity of the power coupler outer conductor. The power coupler coupler ring is connected to the power coupler inner conductor. The inner diameter of the power coupler outer conductor and the outer diameter of the power coupler inner conductor are coaxial structures with uniform impedance. The inner surface of the power coupler inner conductor and the outer surface of the power coupler outer conductor are tightly connected.

[0017] Optionally, the accelerator housing is further provided with a plurality of high-frequency signal pickup installation openings and field distribution and frequency tuner installation openings.

[0018] A charged particle accelerator system includes the above-mentioned radio frequency quadrupole accelerator and an ion source, wherein the ion source and the radio frequency quadrupole accelerator are connected via a low-energy transmission line pipeline, and the radio frequency quadrupole accelerator is connected to a radio frequency power source.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] The embodiment of the present application proposes a radio frequency quadrupole accelerator and a charged particle accelerator system. In the cavity of the radio frequency quadrupole accelerator, due to the presence of the accelerating tube, the interior of the accelerator shell is divided into a vacuum zone corresponding to the internal space of the accelerating tube and a non-vacuum zone corresponding to the external space of the accelerating tube. The vacuum zone is the area where the charged particles are accelerated and focused, and the non-vacuum zone is the cavity space area between the accelerating tube and the accelerating shell. When the accelerator is working, it is only necessary to use a vacuum pump to vacuum exhaust the accelerating zone of the internal space of the accelerating tube from the accelerating tube end components on both sides of the accelerating tube and maintain the high vacuum required for the normal operation of the accelerator to ensure that the charged particles in the accelerating zone are smoothly accelerated by the accelerating and focusing alternating electromagnetic field generated by the space between the four accelerating electrodes; because the quadrupole field accelerator works in TE210 mode, in this mode, the area near the central axis in the accelerating cavity is the acceleration area where the electric field is concentrated, while other areas far from the central axis belong to the magnetic field area. The electric field in the magnetic field area is very weak, and the magnetic field area is a non-acceleration area. The accelerator shell does not need to consider the mechanical deformation caused by the pressure difference, eliminating the vacuum sealing requirements and vacuum exhaust requirements. Only electrical contact or high-frequency sealing is required between the accelerator shell and the accelerating tube, and no vacuum is required. Vacuum sealing and high-frequency sealing can generally be achieved using silver coil spring washers, a common sealing technology in the field of particle accelerators. Therefore, the radio frequency quadrupole accelerator according to the present invention can significantly reduce the wall thickness of the accelerator housing and simplify the accelerator housing manufacturing process, achieving lightweight and simplified structure. The high-frequency power coupler and operating frequency and electric field distribution tuner required to be installed on the accelerator housing no longer need to be vacuum sealed, and only high-frequency sealing is required. This significantly simplifies the structure and processing costs, as well as the manufacturing cycle, and also facilitates the maintenance and repair of the accelerator. This solves the problems faced by conventional linear accelerators and provides a radio frequency quadrupole accelerator (i.e., RFQ accelerator) that is lightweight, simple in structure, reliable in performance, easy to maintain, easy to manufacture, and low-cost. At the same time, the positional relationship between the four accelerating electrodes and the accelerating tube end components of the quadrupole accelerating tube, including alignment, concentricity, and parallelism, can be simply achieved independently of the accelerator housing, allowing for quick and simple assembly. This significantly simplifies the alignment and installation process of the RFQ accelerator, which is very beneficial for medical applications. In particular, the vacuum exhaust equipment normally required for the accelerator housing is eliminated, and a low-noise and low-vibration RFQ accelerator can be realized, which is of great significance for operation and environmental protection, as well as for improving the reliability and stability of the RFQ accelerator. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the three-dimensional structure of the radio frequency quadrupole accelerator of the present invention;

[0022] Figure 2 It is a schematic diagram of the cross-sectional three-dimensional structure of the radio frequency quadrupole accelerator of the present invention;

[0023] Figure 3 A simplified longitudinal cross-sectional view of the radio frequency quadrupole accelerator of the present invention;

[0024] Figure 4 is a simplified cross-sectional view of the radio frequency quadrupole accelerator of the present invention;

[0025] Figure 5 Schematic cross-sectional view of the high frequency power coupler of the present invention;

[0026] Figure 6 It is a longitudinal cross-sectional view of the accelerator housing in the present invention;

[0027] Figure 7 Schematic diagram of the sealing surfaces of the radio frequency quadrupole accelerator of the present invention;

[0028] Figure 8 Schematic diagram of the structure of the charged particle accelerator system of the present invention;

[0029] Figure 9 This is a schematic diagram of the radial distribution of the electric field inside the accelerator obtained by the present invention using three-dimensional electromagnetic field simulation software;

[0030] Figure 10 This is a schematic diagram of the magnetic field size and direction inside the accelerator at time t1 obtained using three-dimensional electromagnetic field simulation software;

[0031] Figure 11 This is a schematic diagram of the magnetic field size and direction inside the accelerator at time t2 obtained using three-dimensional electromagnetic field simulation software;

[0032] Figure 12 This is a schematic diagram of the welding and fixing of the accelerating electrode and the electrode compensation block;

[0033] Figure 13 Schematic diagram of bolt fixing of accelerating electrode and electrode compensation block Figure 1 ;

[0034] Figure 14 Schematic diagram of bolt fixing of accelerating electrode and electrode compensation block Figure 2 ;

[0035] Figure 15 for Figure 13 Enlarged view of point A in the middle.

[0036] Description of the reference numerals in the accompanying drawings:

[0037] 1-Accelerator housing, 2-Vacuum isolation pipe, 3-Accelerating electrode A, 4-Accelerating electrode B, 5-Accelerating electrode C, 6-Accelerating electrode D, 7-Accelerating electrode connecting component A, 8-Accelerating electrode connecting component B, 9-Accelerating electrode connecting component C, 10-Accelerating electrode connecting component D, 11-Coupler mounting port, 12-High-frequency signal pickup mounting port, 13-Field distribution and frequency tuner mounting port, 14-Accelerating tube end component A, 15-Accelerating tube end component B, 16-High-frequency signal pickup, 17-Field distribution and frequency tuner, 18-High-frequency power coupler, 181-Power coupler outer conductor, 182-Power coupler inner conductor, 183-Power coupler coupler ring, 19-Contact surface between the accelerating electrode and the mounting hole, 20-Contact surface between the accelerating electrode and the accelerating electrode connecting component, 21-Contact surface between the electrode connecting component and the accelerator housing, 22-Electrode compensation block, 23-Bolt, 24-Bolt connection hole, 25-Weld. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0039] It should be noted that all directional indications in the embodiments of the present application (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0040] In this application, unless otherwise specified or limited, the terms "connection" and "fixation" should be understood in a broad sense. For example, "fixation" can mean fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. For those skilled in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0041] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present application, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the meaning of "and / or" appearing throughout the text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme in which A and B are satisfied at the same time. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement it. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0042] As an explanation, a traditional radio frequency quadrupole accelerator (RFQ accelerator) designs the interior of the accelerator shell to be a high vacuum, and designs four accelerating electrodes inside the accelerator shell. A high-frequency power coupler is used to form a standing wave electromagnetic field with a specific resonant frequency in the RFQ accelerator cavity. When the periodic modulation changes in the shape of the four electrode heads are not considered, the four electrodes of the RFQ accelerator can be regarded as an electric quadrupole lens whose electric field intensity vibrates sinusoidally with time. It has a focusing or defocusing effect on charged particles entering between the four accelerating electrodes. The focusing or defocusing depends on the speed of the charged particles along the central axis of the RFQ accelerator and the vibration phase of the standing wave electromagnetic field when they reach a given z-direction position. Therefore, during the entire movement process, the charged particles can be affected by the focusing and defocusing effects of the electric quadrupole lens, just like the charged particles passing through a transport line composed of quadrupole electromagnets. At the same time, since the geometric shapes of the electrode heads of the four electrodes have wavy periodic modulation changes along the z direction, the period length of the wave increases with the increase of the speed of the charged particles. At the same time, since the electrode wave modulation positions of the opposite electrodes are completely consistent along the z direction, the wave positions between adjacent electrodes differ by half a wave period. Therefore, in addition to the above-mentioned focusing and defocusing effects on the charged particles, there is also the Ez electric field component that accelerates the charged particles, which can realize the speed modulation, longitudinal bunching, acceleration and other effects of the charged particles. This is the principle of accelerating charged particles by the RFQ accelerator.

[0043] Example 1

[0044] Refer to the attached Figures 1 to 7 As shown, the embodiment of the present application provides a radio frequency quadrupole accelerator, including an accelerator housing 1, which is made of metal material and has end covers with holes at both ends of the accelerator housing 1. The interior of the accelerator housing 1 contains four long strip accelerating electrodes symmetrically installed around the central axis of the accelerator, such as Figure 1 and Figure 2The four accelerating electrodes shown are accelerating electrode A3, accelerating electrode B4, accelerating electrode C5, and accelerating electrode D6. Near the central axis of the accelerator, an accelerating region 26 is formed by the four accelerating electrodes facing each other. A vacuum isolation pipe 2 made of a non-metallic material is installed around accelerating region 26 to enclose accelerating region 26 and form a vacuum accelerating chamber.

[0045] Based on the above structural design, due to the presence of the vacuum isolation pipe 2, the interior of the accelerator shell is divided into a vacuum area corresponding to the internal space of the vacuum isolation pipe 2 and a non-vacuum area corresponding to the external space of the vacuum isolation pipe 2, so that the non-acceleration area inside the acceleration shell of the RFQ accelerator operates in a non-high vacuum or non-vacuum state. Such a design can achieve many benefits, for example: when the accelerator is working, it is only necessary to use a vacuum pump to vacuum-exhaust the acceleration zone in the internal space of the vacuum isolation pipe 2 from both sides of the acceleration tube and maintain the high vacuum required for the normal operation of the accelerator, ensuring that the charged particles in the acceleration zone are smoothly accelerated by the accelerating and focusing alternating electromagnetic field generated in the space between the four accelerating electrodes; because the quadrupole field accelerator operates in TE210 mode, in this mode, the area near the central axis in the acceleration cavity is an acceleration area with a concentrated electric field, while other areas far from the central axis belong to the magnetic field area, the electric field in the magnetic field area is very weak, and the magnetic field area is a non-acceleration area. The accelerator shell does not need to consider the mechanical deformation caused by the pressure difference, eliminating the vacuum sealing requirements and vacuum exhaust requirements. Only electrical contact or high-frequency sealing is required between the accelerator shell and the acceleration tube, and no vacuum sealing is required. High-frequency sealing can generally be achieved using a coil spring washer, which is a commonly used sealing technology in the field of particle accelerators. Therefore, the radio frequency quadrupole accelerator according to the present invention can significantly reduce the wall thickness of the accelerator shell and simplify the accelerator shell manufacturing process, achieving lightweight and simple structure.

[0046] The above design mainly focuses on the location of the vacuum isolation pipe 2 and the location of the peripheral electrodes in the acceleration region, which are characterized by a large magnetic field intensity and a small electric field intensity, so that the device can operate under non-high vacuum conditions. Meanwhile, although the vacuum isolation pipe 2 isolates the vacuum inside and outside the pipe, the ceramic material has good high-frequency electromagnetic wave transmission characteristics, so it does not substantially affect the formation and distribution of the accelerating electric field in the acceleration region. This can cause a change in the accelerator's resonant frequency. Therefore, a frequency tuner can be installed on the accelerator housing or the inner diameter of the housing can be adjusted to easily adjust the operating frequency back to the designed operating frequency. Simultaneously, since the non-acceleration region does not require a high vacuum state, the installation of the tuner no longer requires consideration of vacuum sealing, and high-frequency sealing can be achieved. This significantly simplifies the structure and processing cost, as well as the manufacturing cycle, and facilitates the maintenance and repair of the accelerator. This solves the problems faced by linear accelerators in the prior art, and can provide a radio frequency quadrupole accelerator (i.e., an RFQ accelerator) that is lightweight, simple in structure, reliable in performance, easy to maintain, easy to manufacture, and low in cost. In particular, the vacuum exhaust equipment normally required for the accelerator housing is eliminated, and a low-noise and low-vibration RFQ accelerator can be realized, which is of great significance for operation and environmental protection, as well as for improving the reliability and stability of the RFQ accelerator.

[0047] In the above description, the vacuum isolation pipe 2 is composed of a ceramic material with aluminum oxide or boron nitride as the main component. Since aluminum oxide or boron nitride has good high-frequency electromagnetic wave penetration properties, the vacuum isolation pipe can reduce the absorption of electromagnetic waves, ensuring that the high-frequency electromagnetic wave energy fed into the accelerator is fully utilized and reducing heat generation.

[0048] In this embodiment, if Figure 1 As shown, the four accelerating electrodes consist of a central electrode 110 located inside the vacuum isolation tube 2 and a peripheral electrode 111 located outside the hollow isolation tube. The central electrode 110 and the vacuum isolation tube 2 form a vacuum seal structure through welding or a rubber ring structure. The central electrode 110 and the peripheral electrode 111 are in close contact to form a surface current conductive loop. Through this design, the four accelerating electrodes are each divided into a central electrode 110 and a peripheral electrode 111. The central electrode portion, which determines the electric field distribution and accuracy of the acceleration zone and requires submillimeter machining and installation precision, can be separately machined and aligned and installed. This makes it easier to achieve high-precision acceleration electrode tips 112 in the acceleration zone. Machining and installation precision of approximately 0.05 mm is generally required to ensure accelerator performance, as smaller components are easier to achieve higher machining precision. The peripheral electrodes, which have a relatively small impact on the electric field distribution in the acceleration zone, have relatively low machining and installation precision requirements and can be made of less expensive oxygen-free copper. The RFQ accelerator tube, which is composed of the central electrode 110 and the vacuum isolation pipe 2, can independently implement electrode precision and vacuum tests, thereby improving the manufacturing efficiency of the RFQ accelerator, increasing the yield rate, and reducing the processing and manufacturing costs.

[0049] Another example Figure 3 As shown, the portion of the central electrode 110 located within the vacuum isolation tube 2 is equipped with an electrode compensation block 22 at both the entrance and exit ends of the accelerator. The design of the electrode compensation block 22 can improve the uniformity of the electric field intensity distribution in the acceleration region. For example, if a rubber ring is used to seal the central electrode 110 and the vacuum isolation tube 2, the portion of the central electrode located outside the vacuum isolation tube needs to have smaller geometric dimensions than the portion of the electrode located inside the vacuum isolation tube. This is to achieve vacuum sealing using the rubber O-ring. However, this change in geometric dimensions can cause variations in the accelerating electric field distribution at the end regions of the accelerator's entrance and exit zones. Adding the electrode compensation block 22 at these ends can reduce the unevenness of the electric field.

[0050] In the above description, the four accelerating electrodes form a symmetrical electric quadrupole structure within the interior space of the vacuum isolation tube 2. One end of the accelerating electrode is located within the vacuum isolation tube 2, forming a central electrode 110, while the other end is located outside the vacuum isolation tube 2, forming a peripheral electrode 111. Electrode compensation blocks 22 are provided at both ends of the central electrode 110. After the accelerating electrodes are inserted into the vacuum isolation tube 2, the electrode compensation blocks 22 are fixedly mounted to both ends of the central electrode 110. After installation, the cross-section of the electrode compensation blocks 22 is substantially consistent with that of the central electrode 110. Furthermore, the spacing between the outer end surface of the electrode compensation blocks 22 and the accelerating tube end components is equal to the spacing between the outer end surfaces of the peripheral electrodes and the accelerating tube end components, preferably ranging from a few millimeters to 1 cm.

[0051] In the above-mentioned process of assembling the accelerating electrode, the accelerating electrode is first inserted into the vacuum isolation pipe 2 from the electrode installation port. After the accelerating electrode is installed, the electrode compensation block 22 can be welded to both ends of the central electrode 110, such as Figure 12 As shown, the weld 25 must be kept smooth and burr-free after welding. In addition, the electrode compensation block 22 can also be fixed to both ends of the center electrode 110 by bolts, as shown in FIG. Figures 13 to 15 As shown, bolt connection holes 24 are provided on the end faces of both ends of the center electrode 110, and threaded through holes are provided through the electrode compensation block 22, in which bolts 23 are provided. After the acceleration electrode is installed, the electrode compensation block 22 is attached to the two ends of the center electrode 110, and the bolts 23 are screwed into the bolt connection holes 24, thereby fixing the electrode compensation block 22 to the two ends of the center electrode 110, so that the acceleration electrode can be smoothly assembled.

[0052] Among the above, Figures 1 to 7As shown, a quadrupole accelerating tube is disposed within the accelerator housing 1. The quadrupole accelerating tube includes a vacuum isolation tube 2, which is formed of a tubular body made of a non-metallic material, preferably a ceramic material containing aluminum oxide or boron nitride. Accelerator tube end components, namely accelerating tube end component A14 and accelerating tube end component B15, are disposed at both ends of the vacuum isolation tube 2. These accelerating tube end components are also made of a metal material. The two ends of the vacuum isolation tube 2 and the metallic accelerating tube end components are in a sealed connection to prevent gaps at the connection between the vacuum isolation tube 2 and the accelerating tube end components, ensuring that a high vacuum state can be achieved within the vacuum isolation tube 2 during operation. Since the accelerator housing 1 is composed of a metal material, the accelerator housing 1 has an end cover structure with holes at both ends. The shape and size of the holes in the end cover plates on both sides are exactly matched with the metal-structured accelerator tube end components at both ends of the vacuum isolation pipe 2, thereby forming a high-frequency sealed state, so that a hollow inner cavity is formed between the vacuum isolation pipe 2 and the accelerator housing 1 to prevent the leakage of high-frequency electromagnetic waves, thereby preventing the radio frequency electromagnetic waves in the internal space of the accelerator housing 1 from escaping to the external space of the accelerator housing 1. It should be noted here that the so-called high-frequency sealed state means that the accelerator housing 1 and the accelerator tube end components can form discontinuous point or surface contacts through the metal material. The two do not need to form a completely sealed state, but the gap between the two should be small enough to ensure that the radio frequency signal or high-frequency electromagnetic waves do not leak through the gap.

[0053] In the above, the interior of the vacuum isolation pipe 2 is an acceleration chamber, and the vacuum degree inside the acceleration chamber is higher than 10 -3 Pa, at the same time, there are channels of conductive materials at both ends of the accelerating cavity for the charged particle beam to enter and emit. Since the size of the channel is short relative to the wavelength of the high-frequency signal and the length of the channel is much longer than the wavelength, the high-frequency signal will not leak, so it is ensured that the accelerating cavity is a complete resonant cavity. At the same time, vacuum pipes and vacuum flanges (not shown in the figure) for connecting to external vacuum pipes are connected on either side of the accelerating cavity to realize vacuuming inside the accelerating cavity.

[0054] In this embodiment, the wall of the vacuum isolation pipe 2 is provided with four electrode mounting openings in a circumferential array. The electrode mounting openings are arranged along the length of the vacuum isolation pipe 2, and the distances between the two ends of the four electrode mounting openings and the two ends of the vacuum isolation pipe 2 components are not less than zero. The quadrupole accelerator tube also includes four long strip-shaped accelerating electrodes, such as Figure 1 and Figure 2 The accelerating electrodes A3, B4, C5 and D6 are shown as follows. The four accelerating electrodes are inserted into the four electrode mounting openings one by one, and the contact surfaces 19 between the four strip-shaped accelerating electrodes and the mounting holes are in close contact (as shown in FIG. Figure 7As shown, a specific sealing method is used to isolate the inner and outer spaces of the tubular vacuum isolation pipe 2 to achieve vacuum sealing. The specific sealing method may be a sealing ring between the vacuum isolation pipe 2 and the accelerating electrode. Alternatively, the sealing between the vacuum isolation pipe 2 and the accelerating electrode may be achieved by metal-ceramic welding.

[0055] At the same time, the quadrupole accelerator tube also includes four accelerating electrode connecting components, such as Figure 1 and Figure 2 Shown are accelerating electrode connecting component A7, accelerating electrode connecting component B8, accelerating electrode connecting component C9, and accelerating electrode connecting component D10. The four accelerating electrodes are fixed to the accelerator housing 1 by the peripheral electrodes through the corresponding accelerating electrode connecting components.

[0056] Each accelerating electrode is located in the hollow cavity at one end and is integrated with an accelerating electrode connecting component. The contact surface 20 (eg, Figure 7 As shown in FIG2 , the high frequency sealing state is also maintained. The wall surface of the accelerator housing 1 is also provided with four mounting slots. The accelerating electrode connecting components are correspondingly mounted in the mounting slots. The contact surface 21 (as shown in FIG2 ) between the electrode connecting component and the accelerator housing is Figure 7 A high-frequency sealing state is formed between them).

[0057] At the same time, the four accelerating electrodes do not contact each other in the accelerating cavity. One end of the four accelerating electrodes located in the accelerating cavity is the wingtip or pole head of each accelerating electrode. The closest distance between two symmetrically facing electrodes is represented by 2r0(z). r0(z) represents the vertical distance from the wingtip of any accelerating electrode to the direction of the central axis of the vacuum isolation pipe 2. The wingtip distance 2r0(z) of the accelerating electrode changes periodically along the z direction. The ratio between the maximum and minimum values ​​of r0(z) in each change period is called the modulation coefficient m(k). k is the period number, and the maximum number of k is n. The size change of the wingtip of each accelerating electrode is called pole head modulation (vanetip modulation). The number of pole head modulation cycles of the four accelerating electrodes is equal, which is n. Part of the four accelerating electrodes is located in the internal space of the vacuum isolation pipe 2, and the other part is located outside the vacuum isolation pipe 2.

[0058] Furthermore, the radio frequency quadrupole accelerator also includes at least one high-frequency power coupler 18. A through coupler mounting port 11 is provided on the accelerator housing 1. The high-frequency power coupler 18 is high-frequency sealed and mounted at the coupler mounting port 11, communicating with the hollow inner cavity. The high-frequency power coupler 18 is made of metal material and includes a power coupler outer conductor 181, a power coupler inner conductor 182, and a power coupler coupler ring 183. The power coupler inner conductor 182 is coaxially mounted in the inner cavity of the power coupler outer conductor 181. The power coupler coupler ring 183 connects the power coupler inner conductor 182. The inner diameter of the power coupler outer conductor 181 and the outer diameter of the power coupler inner conductor 182 form a coaxial structure with uniform impedance from the inlet end to the outlet end. The inner surface of the power coupler inner conductor 182 and the outer surface of the power coupler outer conductor 181 are tightly connected. At the same time, in the present invention, the high-frequency power coupler 18 does not have a vacuum-sealed ceramic component, that is, no vacuum-sealed structure is required between the power coupler inner conductor 182 and the power coupler outer conductor 181.

[0059] In addition, the accelerator housing 1 is provided with a plurality of high-frequency signal pickup installation openings 12 and field distribution and frequency tuner installation openings 13 for installing high-frequency signal pickups 16 and field distribution and frequency tuners 17 respectively.

[0060] Based on the above structure, the radio frequency quadrupole accelerator of the present invention is composed of a quadrupole accelerating tube in a high vacuum state and an accelerating shell in a non-vacuum state. Therefore, the accelerator shell 1 can be made of any metal material, and the accelerator shell 1 does not need to maintain a high vacuum state, so that the accelerator shell 1 can be made of a very thin metal cavity, which can greatly reduce the weight of the accelerator. The accelerator shell 1 only needs high-frequency sealing and no longer needs vacuum sealing, which can greatly reduce the manufacturing difficulty and manufacturing cost. Since the need for vacuuming is eliminated, not only the cost associated with maintaining a high vacuum in the accelerator shell is saved, but also the operating cost of the radio frequency quadrupole accelerator can be greatly reduced and the reliability and stability can be increased. At the same time, compared with the traditional radio frequency quadrupole accelerator, since the present application adopts the arrangement of a quadrupole accelerating tube inside the accelerator shell 1, an accelerator similar to a "double-layer shell" structure is formed. The traditional "one-layer shell" structure uses vacuum sealing of the entire accelerating electrode, so that the outer diameter of the traditional accelerator shell 1 is above 30cm-80cm (depending on the operating frequency, the higher the frequency, the smaller the diameter), requiring a larger vacuum container. The present invention adopts a vacuum isolation pipe 2 set inside the accelerator shell 1, and uses the vacuum isolation pipe 2 to vacuum-seal the wingtip acceleration area of ​​the accelerating electrode, so that the vacuum volume required by the vacuum isolation pipe 2 is greatly reduced. For example, when the operating frequency is 180 MHz, the size of the vacuum isolation pipe 2 of the present invention only needs to be in the range of 7 cm to 8 cm. Since the surface area of ​​the vacuum container part is proportional to the square of the diameter, it can be seen that based on the "double-layer shell" structure of the present invention, at the same operating frequency, the vacuum pressure difference of the vacuum isolation pipe 2 of the present invention can be significantly reduced.

[0061] Example 2

[0062] This embodiment discloses a charged particle linear accelerator system, such as Figure 8 As shown, in addition to the aforementioned RF quadrupole accelerator, the linear accelerator system also includes an ion source, a charged particle generator. The ion source and RF quadrupole accelerator are connected via a low-energy transport line pipeline, and the RF quadrupole accelerator is connected to an RF power source. During operation, the rear end of the linear accelerator system of this embodiment is connected to a beam monitor, which is connected to other accelerators or a beam application terminal.

[0063] The use process of the present invention is:

[0064] When using, Figure 8As shown, the low-energy transport line between the ion source and the radio frequency quadrupole accelerator is connected by a pipeline, and the acceleration chamber in the radio frequency quadrupole accelerator is evacuated by a vacuum pump, and the vacuum degree is maintained within the working range of the linear accelerator system. The radio frequency power source and the high-power coupler of the radio frequency quadrupole accelerator are connected by a coaxial microwave feeder. The coaxial microwave inner conductor and the power coupler inner conductor 182 are directly connected, and all operate under the same pressure (atmospheric pressure) until the coupling ring of the power coupler. The field distribution and frequency tuner 17 installed on the accelerator housing 1 also only need high-frequency sealing, not vacuum sealing, so the insertion depth of the accelerator in the acceleration chamber can be easily adjusted to adjust or stabilize the resonant frequency of the accelerator. The heat generated by the accelerator cavity itself can also be easily taken away by the cooling water pipeline laid in the accelerator housing 1, keeping the resonant frequency of the accelerator stable at the operating frequency. Because only the acceleration zone is in a high vacuum state, the accelerator housing 1 will not be deformed by evacuation. The accelerator housing 1 can be made of thinner oxygen-free copper (OFCu), using less shell material, low cost, and light weight.

[0065] Then, the various control systems and power supply systems are activated, and the charged particles are accelerated by the radio frequency quadrupole accelerator. Because the isolation tube is constructed of ceramic materials with excellent high-frequency electromagnetic wave transmission properties, such as alumina ceramic, which has a dielectric constant (ε) as high as 9, high-frequency electromagnetic waves can easily penetrate the walls of the vacuum isolation tube 2 and enter the acceleration zone, forming the high-frequency electric field inside the vacuum isolation tube 2 required to accelerate the charged particles.

[0066] In the present invention, see Figures 9 to 11Figure 2 shows the electric and magnetic field distributions within the RFQ accelerator housing 1, calculated using three-dimensional electromagnetic field simulation software. Since the quadrupole field accelerator operates in TE210 mode, the region near the central axis of the accelerating cavity is the accelerating region, where the electric field is concentrated. Other regions farther from the central axis are magnetic fields, where the electric field is very weak, and are non-accelerating regions. The figure shows that the electric field in the non-accelerating region is an order of magnitude lower than that in the accelerating region. According to the electronic version of the third edition of the textbook "Fundamentals of High Voltage Insulation Technology" (Yan Zhang), the breakdown field strength of air in a uniform electric field under standard atmospheric conditions is approximately 3 kV / mm. The electric field in the non-accelerating region of a typical RFQ accelerator is approximately 1 MV / m, or 1 kV / mm, and is a high-frequency electric field. According to the Kilpatric equation for high-frequency electric field discharge, the breakdown field of a high-frequency electric field is generally much greater than the DC breakdown field. Therefore, from a discharge perspective, the non-accelerating region of the RFQ does not need to operate in a high vacuum. At the same time, when designing RFQ, the inter-electrode voltage can be reduced so that the maximum electric field in the non-acceleration zone can be reduced as needed. Therefore, the non-acceleration zone does not need to work in a high vacuum environment, so the accelerator shell 1 does not need to consider the mechanical deformation caused by the pressure difference, eliminating the vacuum sealing requirement and the vacuum exhaust requirement, which can greatly reduce the wall thickness of the accelerator shell 1 and simplify the manufacturing process of the accelerator shell 1, so as to achieve lightweight and simple structure; the vacuum exhaust pump system can be simplified, and the time for gas cleaning and vacuum pumping before the accelerator is used can be reduced, thereby reducing energy consumption; the high-frequency power coupler 18 and the operating frequency and electric field distribution tuner that must be installed on the accelerator shell 1 no longer need to consider vacuum sealing, and only high-frequency sealing is required, thereby greatly simplifying the structure and processing cost, as well as the manufacturing cycle, and also facilitating the maintenance and repair of the accelerator, solving the problems faced by the RFQ accelerator of the prior art, and providing an RFQ accelerator with light weight, simple structure, reliable performance, easy maintenance, easy manufacturing and low cost.

[0067] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A radio frequency quadrupole accelerator, characterized in that: The accelerator shell includes four long accelerating electrodes symmetrically installed around the central axis of the accelerator. Near the central axis of the accelerator, there is an accelerating zone formed by the four accelerating electrodes facing each other. A vacuum isolation pipe made of non-metallic material is installed around the accelerating zone to surround the accelerating zone and form a vacuum accelerating cavity area. The four accelerating electrodes are composed of a central electrode located on the inside of the vacuum isolation pipe and a peripheral electrode located on the outside of the vacuum isolation pipe. The part of the central electrode inside the vacuum isolation pipe is respectively equipped with electrode compensation blocks at the inlet and outlet ends of the accelerator.

2. The radio frequency quadrupole accelerator according to claim 1, characterized in that The vacuum isolation pipe is made of a ceramic material with aluminum oxide or boron nitride as the main component.

3. The radio frequency quadrupole accelerator according to claim 1 or 2, characterized in that: The central electrode and the vacuum isolation pipe form a vacuum sealing structure through welding or a rubber ring structure, and the central electrode and the peripheral electrode are in close contact to form a surface current conductive loop.

4. The radio frequency quadrupole accelerator according to claim 1, characterized in that The electrode compensation block is installed in the acceleration zone after the accelerating electrode is inserted into the vacuum isolation pipe, and is welded and fixed to both ends of the central electrode.

5. The radio frequency quadrupole accelerator according to claim 1, characterized in that: The electrode compensation block is installed in the acceleration zone after the accelerating electrode is inserted into the vacuum isolation pipe, and is fixed to both ends of the central electrode by bolts.

6. The radio frequency quadrupole accelerator according to claim 1, characterized in that: Four electrode installation openings are provided on the wall surface of the vacuum isolation pipe and are opened along the central axis direction of the accelerator. The accelerating electrodes are installed in the electrode installation openings in a one-to-one correspondence.

7. The radio frequency quadrupole accelerator according to claim 1, characterized in that: It also includes at least one high-frequency power coupler, and the accelerator housing is provided with a through coupler installation opening.

8. The radio frequency quadrupole accelerator according to claim 7, characterized in that: The high-frequency power coupler includes a power coupler outer conductor, a power coupler inner conductor and a power coupler coupler ring. The power coupler inner conductor is coaxially installed in the inner cavity of the power coupler outer conductor. The power coupler coupler ring is connected to the power coupler inner conductor. The inner diameter of the power coupler outer conductor and the outer diameter of the power coupler inner conductor form a coaxial structure with uniform impedance. The inner surface of the power coupler inner conductor and the outer surface of the power coupler outer conductor are tightly connected.

9. The radio frequency quadrupole accelerator according to claim 1, characterized in that: The accelerator housing is also provided with a plurality of high-frequency signal pickup installation openings and field distribution and frequency tuner installation openings.

10. A charged particle accelerator system, characterized in that: The invention comprises the radio frequency quadrupole accelerator and an ion source according to any one of claims 1 to 9, wherein the ion source and the radio frequency quadrupole accelerator are connected via a low-energy transport line pipeline, and the radio frequency quadrupole accelerator is connected to a radio frequency power source.

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