Radio frequency quadrupole accelerator and charged particle accelerator system

Abstract

The present application relates to the technical field of particle acceleration apparatuses and applications thereof. Disclosed are a radio frequency quadrupole accelerator and a charged particle accelerator system. The quadrupole accelerator comprises an accelerator housing, wherein four long-strip-shaped acceleration electrodes which are symmetrically mounted around a central axis of the accelerator are arranged in the accelerator housing, an acceleration area formed by arranging the four acceleration electrodes opposite each other is provided near the center axis of the accelerator, and a vacuum isolation pipe which is made of a non-metal material and configured to surround the acceleration area to form a vacuum acceleration cavity area is mounted around the acceleration area. In the present application, a non-acceleration area operates under the atmospheric pressure condition, and there is no need to consider the vacuum sealing requirements of the accelerator housing, thereby enabling a light weight and a simplified structure.

Description

A radio frequency quadrupole accelerator and charged particle accelerator system Technical Field

[0001] This application relates to the field of particle acceleration equipment and its application technology, specifically to a radio frequency quadrupole accelerator and a charged particle accelerator system, which can be used as a linear injection accelerator for proton or heavy ion tumor therapy devices or as a device for manufacturing radionuclides. Background Technology

[0002] Boron neutron capture therapy devices for tumor treatment typically require proton beams with energies above 2.5 MeV and beam power of tens of kilowatts. Obtaining proton beams with kinetic energies above 2.8 MeV usually requires the use of radio frequency linear accelerators, cyclotron accelerators, or electrostatic accelerators, with radio frequency quadrupole accelerators (RFQ accelerators) and cyclotron accelerators being the more commonly used methods.

[0003] A typical radio frequency quadrupole accelerator includes an accelerator housing, 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 running, it is necessary to maintain a high vacuum state inside the accelerator cavity (also known as the accelerator housing) to avoid discharge and to prevent the charged particle beam from colliding with gas molecules and being lost.

[0004] Existing invention patents 202211722381.5, entitled "A Superconducting Quadrupole Accelerator Device," and 202211193177.9, entitled "A Quadrupole Accelerator and a Method for Manufacturing a Quadrupole Accelerator," disclose accelerator structures in which the entire inner cavity of the accelerator is an acceleration chamber. The acceleration chamber has a large volume, and when evacuating, work needs to be done on the entire cavity, resulting in problems such as long evacuation time, low efficiency, high energy consumption, and complex structure. At the same time, components such as the high-frequency power coupler, the tuner for adjusting the resonant frequency and electric field distribution, and the signal pickup installed on the accelerator all need to have both vacuum sealing and high-frequency sealing structures to maintain the high vacuum state inside the accelerator cavity and prevent the electromagnetic field inside 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. Meanwhile, in order to maintain the vacuum inside the accelerator chamber, the accelerator shell usually needs a metal shell several centimeters thick to counteract the pressure generated by the pressure difference between the inside and outside, which makes the accelerator chamber bulky and increases manufacturing costs. Summary of the Invention

[0005] The main objective of this application is to provide a radio frequency quadrupole accelerator and a charged particle accelerator system that maintains a high vacuum in a limited area of ​​the accelerator cavity where the accelerating electric field through which the beam passes, while the rest of the accelerator cavity can operate at atmospheric pressure. This system has the advantages of simple structure, light weight, reliability, simple maintenance, and low manufacturing cost.

[0006] The technical solution adopted in this application is as follows:

[0007] First aspect:

[0008] A radio frequency 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, there is an acceleration zone formed by the four accelerating electrodes facing each other. A vacuum isolation pipe made of non-metallic material is installed around the acceleration zone to surround the acceleration zone and form a vacuum acceleration cavity region.

[0009] Optionally, the vacuum isolation pipe is composed of ceramic materials with alumina or boron nitride as the main components.

[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-sealed 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.

[0011] Optionally, the portion of the central electrode located inside the vacuum isolation pipe may have electrode compensation blocks installed at both the inlet and outlet ends of the accelerator.

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

[0014] Optionally, the vacuum isolation pipe has four electrode mounting openings on its wall surface, which are opened along the central axis of the accelerator, and the acceleration electrodes are installed in the electrode mounting openings one by one.

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

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

[0017] Optionally, the accelerator housing is also provided with multiple high-frequency signal pickup mounting ports and field distribution and frequency tuner mounting ports.

[0018] A charged particle accelerator system includes the aforementioned radio frequency quadrupole accelerator and an ion source. The ion source and the radio frequency quadrupole accelerator are connected via a low-energy transport line. The radio frequency quadrupole accelerator is connected to a radio frequency power source.

[0019] Compared with the prior art, the beneficial effects of this application are:

[0020] This application proposes a radio frequency quadrupole accelerator and charged particle accelerator system. Within the accelerator cavity, the presence of the accelerating tube divides the accelerator housing into a vacuum region corresponding to the space inside the accelerating tube and a non-vacuum region corresponding to the space outside the accelerating tube. The vacuum region is where charged particles are accelerated and focused, while the non-vacuum region is the cavity space between the accelerating tube and the accelerator housing. During accelerator operation, only a vacuum pump is needed to exhaust the internal space of the accelerating tube from the two ends of the accelerating tube, maintaining the high vacuum required for normal accelerator operation. This ensures that charged particles within the accelerating region are smoothly accelerated and focused by the alternating electromagnetic field generated between the four accelerating electrodes. Since the quadrupole accelerator operates in TE210 mode, the area near the central axis within the accelerating cavity is an electric field-concentrated acceleration region, while other areas far from the central axis are magnetic field regions. The electric field in the magnetic field regions is very weak, making them non-accelerating regions. Therefore, the accelerator housing does not need to consider mechanical deformation caused by pressure differences, eliminating the requirements for vacuum sealing and vacuum exhaust. Only electrical contact or high-frequency sealing is needed between the accelerator housing and the accelerating tube; a vacuum seal is not required. Vacuum sealing and high-frequency sealing are generally achieved using silver helical spring washers, a common sealing technology in particle accelerators. Therefore, the radio frequency quadrupole accelerator based on this invention can significantly reduce the wall thickness of the accelerator housing and simplify the manufacturing process, achieving lightweight and structurally simple design. The high-frequency power coupler and the tuner for operating frequency and electric field distribution, which must be installed on the accelerator housing, no longer need to consider vacuum sealing; high-frequency sealing is sufficient. This significantly simplifies the structure, processing costs, and manufacturing cycle, and also facilitates accelerator maintenance and repair. It solves the problems faced by existing linear accelerators and provides a lightweight, simple, reliable, easy-to-maintain, easy-to-manufacture, and low-cost radio frequency quadrupole accelerator (i.e., RFQ accelerator). Furthermore, the positional relationships of the four accelerating electrodes and the terminal components of the quadrupole tube, including collimation, concentricity, and parallelism, can be easily achieved independently of the accelerator housing, allowing for quick and simple assembly. This significantly simplifies the collimation and installation process of the RFQ accelerator, which is highly beneficial for applications in the medical field. In particular, it eliminates the need for the vacuum exhaust equipment that is usually required for accelerator housings, enabling low-noise and low-vibration RFQ accelerators, which is of great significance for operation, environmental protection, and improving the reliability and stability of RFQ accelerators. Attached Figure Description

[0021] Figure 1 is a three-dimensional structural schematic diagram of the radio frequency quadrupole accelerator of the present invention;

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

[0023] Figure 3 is 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 is a cross-sectional schematic diagram of the high-frequency power coupler in this invention;

[0026] Figure 6 is a longitudinal sectional view of the accelerator housing in this invention;

[0027] Figure 7 is a schematic diagram of the sealing surfaces of the radio frequency quadrupole accelerator in this invention;

[0028] Figure 8 is a schematic diagram of the charged particle accelerator system of the present invention;

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

[0030] Figure 10 is a schematic diagram of the magnitude and direction of the magnetic field inside the accelerator at time t1 obtained by the present invention under the three-dimensional electromagnetic field simulation software.

[0031] Figure 11 is a schematic diagram of the magnitude and direction of the magnetic field inside the accelerator at time t2 obtained by the present invention under the three-dimensional electromagnetic field simulation software.

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

[0033] Figure 13 is a schematic diagram of the bolt fixing between the accelerating electrode and the electrode compensation block;

[0034] Figure 14 is a schematic diagram of the bolt fixing between the accelerating electrode and the electrode compensation block (II).

[0035] Figure 15 is an enlarged view of point A in Figure 13.

[0036] Explanation of the labels in the attached 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 accelerating electrode and mounting hole, 20-Contact surface between accelerating electrode and accelerating electrode connecting component, 21-Contact surface between electrode connecting component and accelerator housing, 22-Electrode compensation block, 23-Bolt, 24-Bolt connection hole, 25-Weld. Detailed Implementation

[0038] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0039] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0040] In this application, unless otherwise expressly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0041] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0042] As an explanation, a traditional radio frequency quadrupole accelerator (RFQ accelerator) is designed with a high vacuum inside the accelerator housing and four accelerating electrodes inside the housing. A standing wave electromagnetic field with a specific resonant frequency is formed in the RFQ accelerator cavity using a high-frequency power coupler. Without considering the periodic modulation changes in the shape of the four electrode tips, the four electrodes of the RFQ accelerator can be regarded as electric quadrupole lenses whose electric field intensity oscillates sinusoidally with time. They have a focusing or defocusing effect on charged particles entering between the four accelerating electrodes. The focusing or defocusing depends on the velocity 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 motion process, the charged particles can be focused and defocused by the electric quadrupole lenses, just like charged particles passing through a transport line composed of quadrupole electromagnets. Meanwhile, since the geometry of the electrode heads of the four electrodes has a wave-like periodic modulation change along the z-direction, the period length of the wave increases with the increase of the charged particle velocity. At the same time, since the electrode wave modulation positions of the opposing 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 charged particles, there is also an Ez electric field component that accelerates charged particles. This can achieve velocity modulation, longitudinal focusing, and acceleration of charged particles. This is the principle of the RFQ accelerator for accelerating charged particles. Example 1

[0043] Referring to Figures 1 to 7, this application provides a radio frequency quadrupole accelerator, including an accelerator housing 1 made of metal, with perforated end caps at both ends. The accelerator housing 1 contains four elongated accelerating electrodes symmetrically mounted around the accelerator's central axis, as shown in Figures 1 and 2, namely accelerating electrode A3, accelerating electrode B4, accelerating electrode C5, and accelerating electrode D6. Near the accelerator's central axis is an acceleration region 26 formed by the four accelerating electrodes facing each other. A vacuum isolation pipe 2, made of non-metallic material, surrounds the acceleration region 26 to form a vacuum acceleration cavity region.

[0044] Based on the above structural design, due to the presence of the vacuum isolation pipe 2, the interior of the accelerator housing is divided into a vacuum region corresponding to the space inside the vacuum isolation pipe 2 and a non-vacuum region corresponding to the space outside the vacuum isolation pipe 2, so that the non-acceleration region inside the acceleration housing of the RFQ accelerator operates in a non-high vacuum or non-vacuum state. This design offers numerous advantages. For instance, during accelerator operation, only the internal space of the vacuum isolation pipe 2 needs to be evacuated from both sides of the acceleration tube using a vacuum pump to maintain the high vacuum required for normal accelerator operation. This ensures that charged particles within the acceleration zone are smoothly accelerated and focused by the alternating electromagnetic field generated between the four accelerating electrodes. Since the quadrupole accelerator operates in TE210 mode, the area near the central axis within the acceleration chamber is an acceleration region with concentrated electric field, while other areas far from the central axis belong to the magnetic field region. The electric field in the magnetic field region is very weak, making it a non-acceleration region. The accelerator housing does not need to consider mechanical deformation caused by pressure differences, eliminating the requirements for vacuum sealing and vacuum evacuation. Only electrical contact or high-frequency sealing is required between the accelerator housing and the acceleration tube; vacuum sealing is not necessary. High-frequency sealing can generally be achieved using helical spring washers, a commonly used sealing technology in the particle accelerator field. Therefore, the radio frequency quadrupole accelerator based on this invention can significantly reduce the wall thickness of the accelerator housing and simplify the manufacturing process, achieving lightweight and structural simplification.

[0045] Through the above design, the location of the vacuum isolation pipe 2 and the location of the peripheral electrodes in the acceleration region are characterized by high magnetic field strength and low electric field strength, thus allowing operation under non-high vacuum conditions. Simultaneously, although the vacuum isolation pipe 2 isolates the vacuum inside and outside the pipe, the excellent high-frequency electromagnetic wave transmission characteristics of the ceramic material mean it has minimal impact on the formation and distribution of the accelerating electric field in the acceleration region. This will cause changes in the accelerator's resonant frequency. Therefore, by installing a frequency tuner on the accelerator housing or adjusting the inner diameter of the housing, the operating frequency can be easily adjusted back to the designed operating frequency. Furthermore, since a high vacuum state is not required in the non-acceleration region, the tuner installation no longer needs to consider vacuum sealing; high-frequency sealing is sufficient. This significantly simplifies the structure, reduces processing costs and manufacturing cycle, and facilitates accelerator maintenance and repair. It solves the problems faced by existing linear accelerators and provides a lightweight, simple, reliable, easy-to-maintain, easy-to-manufacture, and low-cost radio frequency quadrupole accelerator (i.e., RFQ accelerator). In particular, it eliminates the need for the vacuum exhaust equipment that is usually required for accelerator housings, enabling low-noise and low-vibration RFQ accelerators, which is of great significance for operation, environmental protection, and improving the reliability and stability of RFQ accelerators.

[0046] In the above, the vacuum isolation pipe 2 is composed of ceramic materials with aluminum oxide or boron nitride as the main components. Since aluminum oxide or boron nitride has good high-frequency electromagnetic wave penetration characteristics, it can reduce the absorption of electromagnetic waves by the vacuum isolation pipe, ensure that the high-frequency electromagnetic wave energy fed into the accelerator is fully utilized, and also reduce heat generation.

[0047] In this embodiment, as shown in Figure 1, the four accelerating electrodes consist of a central electrode 110 located inside the vacuum isolation pipe 2 and peripheral electrodes 111 located outside the hollow isolation pipe. The central electrode 110 and the vacuum isolation pipe 2 form a vacuum-sealed structure through welding or a rubber ring structure. The central electrode 110 and the peripheral electrodes 111 are in close contact to form a surface current conduction circuit. This design divides the four accelerating electrodes into a central electrode 110 and a peripheral electrode 111. This allows for the separate machining and collimation of the central electrode portion, which requires sub-millimeter machining precision and is crucial for determining the electric field distribution and accuracy in the acceleration zone. This makes it easier to achieve high precision in the accelerating electrode tip 112, typically requiring a machining and installation accuracy of around 0.05 mm to ensure accelerator performance, as smaller components are easier to achieve higher machining precision. The peripheral electrodes, which have a relatively smaller impact on the electric field distribution in the acceleration zone, have lower machining and installation precision requirements and can utilize less expensive oxygen-free copper materials. The RFQ accelerator tube, consisting of the central electrode 110 and the vacuum isolation channel 2, can perform electrode precision and vacuum testing independently, which can improve the manufacturing efficiency of the RFQ accelerator, increase the yield, and reduce the processing and manufacturing cost.

[0048] As shown in Figure 3, the portion of the central electrode 110 inside the vacuum isolation pipe 2 has electrode compensation blocks 22 installed at both the inlet and outlet ends of the accelerator. The design of the electrode compensation blocks 22 improves the uniformity of the electric field distribution in the acceleration zone. For example, if the vacuum seal between the central electrode 110 and the vacuum isolation pipe 2 uses a rubber ring, the portion of the central electrode outside the vacuum isolation pipe needs to have a smaller geometric dimension than the portion inside the pipe. This is to achieve vacuum sealing using the rubber O-ring. However, this change in geometry causes variations in the electric field distribution at the end regions of the accelerator inlet and outlet. Adding electrode compensation blocks 22 at the ends reduces the non-uniformity of the electric field.

[0049] In the above description, four accelerating electrodes form a symmetrical quadrupole structure within the vacuum isolation pipe 2. One end of each accelerating electrode is located inside the vacuum isolation pipe 2, forming a central electrode 110, while the other end is located outside the vacuum isolation pipe 2, forming a peripheral electrode 111. Electrode compensation blocks 22 are installed at both ends of the central electrode 110. These blocks are fixedly installed at both ends of the central electrode 110 after the accelerating electrodes are inserted into the vacuum isolation pipe 2. After installation, the cross-section of the electrode compensation block 22 is substantially consistent with that of the central electrode 110, and the distance between the outer end face of the electrode compensation block 22 and the end component of the accelerating pipe is equal to the distance between the outer end face of the peripheral electrode and the end component of the accelerating pipe. This distance is preferably within the range of a few millimeters to 1 cm.

[0050] In the aforementioned assembly process of the accelerating electrode, the accelerating electrode is first inserted into the vacuum isolation pipe 2 through the electrode mounting port. After the accelerating electrode is installed, the electrode compensation block 22 can be welded to both ends of the central electrode 110, as shown in Figure 12. After welding, the weld 25 must be kept smooth and burr-free. Alternatively, the electrode compensation block 22 can be fixed to both ends of the central electrode 110 with bolts, as shown in Figures 13 to 15. Bolt connection holes 24 are provided on the end faces of both ends of the central electrode 110, and the electrode compensation block 22 has a through threaded hole with a bolt 23 installed in the through threaded hole. After the accelerating electrode is installed, the electrode compensation block 22 is fitted to both ends of the central electrode 110, and the bolts 23 are screwed into the bolt connection holes 24, thereby fixing the electrode compensation block 22 to both ends of the central electrode 110, enabling the accelerating electrode to be assembled smoothly.

[0051] As shown in Figures 1 to 7, the accelerator housing 1 contains a quadrupole accelerator tube, which includes a vacuum isolation pipe 2. The vacuum isolation pipe 2 is a tube-shaped structure made of non-metallic material, preferably a ceramic material containing alumina or boron nitride. Accelerator tube end components, A14 and B15, are located at both ends of the vacuum isolation pipe 2. These components are made of metallic material, and the two ends of the vacuum isolation pipe 2 and the metallic acceleration tube end components are in a sealed connection to prevent gaps at the connection point and ensure a high vacuum is formed inside the vacuum isolation pipe 2 during operation. Because the accelerator housing 1 is made of metal, it has end caps with holes at both ends. The shape and size of the holes in the end caps perfectly match the metal end components of the vacuum isolation pipe 2, thus forming a high-frequency seal. This creates a hollow cavity between the vacuum isolation pipe 2 and the accelerator housing 1, preventing the leakage of high-frequency electromagnetic waves and thus preventing radio frequency electromagnetic waves from escaping from the interior of the accelerator housing 1 to the exterior. It should be noted that the high-frequency seal means that the accelerator housing 1 and the accelerator tube end components can form discontinuous point or surface contact through the metal material. A complete seal is not required, but the gap between them should be small enough to ensure that radio frequency signals or high-frequency electromagnetic waves do not leak through the gap.

[0052] In the above description, the interior of the vacuum isolation pipe 2 is an acceleration chamber, and the vacuum level inside the acceleration chamber is higher than 10 during operation. -3 Pa, at the same time, there are conductive material channels at both ends of the accelerating cavity for the entry and exit of charged particle beams. Since the size of the channel is relatively short compared to the wavelength of the high-frequency signal, and the length of the channel is much greater than the wavelength, the high-frequency signal will not leak, thus ensuring that the accelerating cavity is a complete resonant cavity. At the same time, a vacuum pipe and a vacuum flange (not shown in the figure) are connected to either side of the accelerating cavity for connection with an external vacuum pipe to achieve vacuuming inside the accelerating cavity.

[0053] In this embodiment, the vacuum isolation pipe 2 has four electrode mounting openings arranged circumferentially on its wall surface. These openings extend along the length of the vacuum isolation pipe 2, and the distance between the two ends of each opening and the two ends of the vacuum isolation pipe 2 component is not less than zero. The quadrupole accelerator tube also includes four elongated accelerating electrodes, as shown in Figures 1 and 2: accelerating electrode A3, accelerating electrode B4, accelerating electrode C5, and accelerating electrode D6. These four electrodes are inserted one-to-one into the four mounting openings, and the contact surfaces 19 between the four elongated accelerating electrodes and the mounting holes are in close contact (as shown in Figure 7). A specific sealing method is used to isolate the inner and outer spaces of the tubular vacuum isolation pipe 2, achieving a vacuum seal. This specific sealing method can be a sealing connection between the vacuum isolation pipe 2 and the accelerating electrodes via a sealing ring, or a sealing connection between the vacuum isolation pipe 2 and the accelerating electrodes via metal-ceramic welding.

[0054] Meanwhile, the quadrupole accelerator tube also includes four accelerating electrode connection components, as shown in Figures 1 and 2, namely accelerating electrode connection component A7, accelerating electrode connection component B8, accelerating electrode connection component C9 and accelerating electrode connection component D10. The four accelerating electrodes are installed and fixed to the accelerator housing 1 by the peripheral electrodes through the corresponding accelerating electrode connection components.

[0055] Each accelerating electrode is integrated with an accelerating electrode connecting component at one end of the hollow cavity. The contact surface 20 between the accelerating electrode and the accelerating electrode connecting component (as shown in Figure 7) also maintains a high-frequency sealed state. The wall of the accelerator housing 1 is also provided with four mounting elongated holes. The accelerating electrode connecting component is installed in the mounting elongated holes, and a high-frequency sealed state is formed between the electrode connecting component and the contact surface 21 between the accelerator housing and the connecting component (as shown in Figure 7).

[0056] Meanwhile, the four accelerating electrodes do not contact each other within the accelerating cavity. The end of each of the four accelerating electrodes located within the accelerating cavity is its wingtip or tip. The distance between the closest points of two symmetrically facing electrodes is denoted by 2r0(z), where 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 distance from the wingtip of the accelerating electrode to 2r0(z) varies periodically along the z-direction. The ratio between the maximum and minimum values ​​of r0(z) in each variation period is called the modulation coefficient m(k), where k is the period number, and k has a maximum of n. The size change of the wingtip of each accelerating electrode is called vane tip modulation. The number of vane tip modulation periods for the four accelerating electrodes is equal, all being n. Part of the four accelerating electrodes is located inside the vacuum isolation pipe 2, and the other part is located outside the vacuum isolation pipe 2.

[0057] Furthermore, the radio frequency quadrupole accelerator also includes at least one high-frequency power coupler 18. The accelerator housing 1 has a through-hole coupler mounting port 11. The high-frequency power coupler 18 is high-frequency sealed and installed at the coupler mounting port 11, communicating with the hollow inner cavity. The high-frequency power coupler 18 is made of metallic material and includes an outer conductor 181, an inner conductor 182, and a coupler ring 183. The inner conductor 182 is coaxially mounted within the inner cavity of the outer conductor 181. The coupler ring 183 connects to the inner conductor 182. The inner diameter of the outer conductor 181 and the outer diameter of the inner conductor 182 form a coaxial structure with uniform impedance from the inlet to the outlet. The inner surface of the inner conductor 182 and the outer surface of the outer conductor 181 are tightly connected. Additionally, the high-frequency power coupler 18 in this invention does not have a vacuum-sealed ceramic component; that is, no vacuum sealing structure is required between the inner conductor 182 and the outer conductor 181.

[0058] In addition, the accelerator housing 1 is provided with multiple high-frequency signal pickup ports 12 and field distribution and frequency tuner ports 13, which are used to install high-frequency signal pickups 16 and field distribution and frequency tuners 17, respectively.

[0059] Based on the above structure, the radio frequency quadrupole accelerator of this invention consists of a quadrupole accelerating tube under high vacuum and an accelerating shell under non-vacuum conditions. Therefore, the accelerator shell 1 can be made of any metallic material, and it does not need to maintain a high vacuum. This allows the accelerator shell 1 to be manufactured using a very thin metal cavity, significantly reducing the weight of the accelerator. The accelerator shell 1 only requires high-frequency sealing, eliminating the need for vacuum sealing, thus greatly reducing manufacturing difficulty and cost. By eliminating the need for vacuuming, not only are the costs associated with maintaining a high vacuum inside the accelerator shell saved, but the operating costs of the radio frequency quadrupole accelerator are also significantly reduced, and reliability and stability are increased. Furthermore, compared to traditional radio frequency quadrupole accelerators, this application uses a quadrupole accelerating tube inside the accelerator shell 1, forming an accelerator with a structure similar to a "double-shell" structure. Traditional "single-shell" structures, due to the vacuum sealing of the entire accelerating electrode, require a conventional accelerator shell 1 with an outer diameter of 30cm-80cm (depending on the operating frequency; the higher the frequency, the smaller the diameter), necessitating a larger vacuum container. The present invention employs a vacuum isolation pipe 2 inside the accelerator housing 1, which vacuum seals the wingtip acceleration region of the acceleration electrode. This greatly reduces the vacuum volume required for the vacuum isolation pipe 2. For example, at a working frequency of 180MHz, the size of the vacuum isolation pipe 2 of the present invention only needs to be in the range of 7cm to 8cm. Since the surface area of ​​the vacuum container is proportional to the square of the diameter, it can be seen that based on the "double-layer housing" structure of the present invention, the vacuum pressure difference experienced by the vacuum isolation pipe 2 of the present invention can be significantly reduced at the same working frequency. Example 2

[0060] This embodiment discloses a charged particle linear accelerator system, as shown in Figure 8. In addition to the aforementioned radio frequency quadrupole accelerator, it also includes an ion source, which is a charged particle generator. The ion source and the radio frequency quadrupole accelerator are connected via a low-energy transport line. The radio frequency quadrupole accelerator is connected to a radio frequency power source. In application, the linear accelerator system of this embodiment is connected to a beam monitor at its rear end, which is connected to other accelerators or beam application terminals.

[0061] The process of using this invention is as follows:

[0062] In use, as shown in Figure 8, the low-energy transport line pipe between the ion source and the radio frequency quadrupole accelerator is connected. A vacuum pump is used to evacuate the acceleration chamber inside the radio frequency quadrupole accelerator and maintain the vacuum level within the operating 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 feed tube. The inner conductor of the coaxial microwave and the inner conductor 182 of the power coupler are directly connected all the way to the coupling ring of the power coupler, all operating under the same pressure (atmospheric pressure). The field distribution and frequency tuner 17 installed on the accelerator housing 1 only requires high-frequency sealing and does not require vacuum sealing. Therefore, its insertion depth in the acceleration chamber can be easily adjusted to adjust or stabilize the resonant frequency of the accelerator. The heat generated by the accelerator chamber itself can also be easily carried away by the cooling water pipes 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 deform due to vacuuming. The accelerator housing 1 can be made of thinner oxygen-free copper (OFCu), which uses less shell material, has lower cost, and is lighter in weight.

[0063] Then, the various control systems and power source systems are activated, and the charged particles are accelerated by the radio frequency quadrupole accelerator. Because the isolation tube is made of ceramic materials with good high-frequency electromagnetic wave transmission characteristics, such as alumina ceramic with an electrolyte constant (ε) as high as 9, high-frequency electromagnetic waves can easily pass through the tube wall of the vacuum isolation tube 2 and enter the acceleration zone, forming the high-frequency electric field required to accelerate charged particles inside the vacuum isolation tube 2.

[0064] In this invention, referring to Figures 9 to 11, the electric field distribution and magnetic field distribution inside the RFQ accelerator housing 1 are calculated using three-dimensional electromagnetic field simulation software. Since the quadrupole accelerator operates in TE210 mode, the region near the central axis within the acceleration cavity in this mode is the acceleration region where the electric field is concentrated, while other regions far from the central axis belong to the magnetic field region. The electric field in the magnetic field region is very weak, and the magnetic field region is the non-acceleration region. As can be seen from the figures, the electric field value in the non-acceleration region is less than one order of magnitude that in the acceleration region. According to the electronic version of the textbook "Fundamentals of High Voltage Insulation Technology" (3rd edition, Yan Zhang), the breakdown field strength of air in a uniform electric field under standard atmospheric conditions is approximately 3 kV / mm. Generally, the electric field value in the non-acceleration region of an RFQ accelerator is approximately 1 MV / m, which is 1 kV / mm, and it is a high-frequency electric field. According to the Kilpatric formula for high-frequency electric field discharge, the breakdown electric field of a high-frequency electric field is generally much greater than that of a DC breakdown electric field. Therefore, from the perspective of discharge, the non-acceleration region of the RFQ does not need to operate in a high vacuum state. Simultaneously, when designing the RFQ, the inter-electrode voltage can be reduced to decrease the maximum electric field value in the non-accelerating region as needed. Therefore, the non-accelerating region does not need to operate in a high vacuum environment. Thus, the accelerator housing 1 does not need to consider the mechanical deformation caused by the pressure difference, eliminating the requirements for vacuum sealing and vacuum exhaust. This significantly reduces the wall thickness of the accelerator housing 1 and simplifies its manufacturing process, achieving lightweight and structural simplicity. It also simplifies the vacuum exhaust pump system, reducing the time for gas cleaning and vacuuming before accelerator use, and lowering energy consumption. The high-frequency power coupler 18 and the tuner for operating frequency and electric field distribution that must be installed on the accelerator housing 1 no longer need to consider vacuum sealing; high-frequency sealing is sufficient. This significantly simplifies the structure, reduces processing costs and manufacturing cycle, and facilitates accelerator maintenance and repair. It solves the problems faced by existing RFQ accelerators and can provide a lightweight, simple, reliable, easy-to-maintain, easy-to-manufacture, and low-cost RFQ accelerator.

[0065] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A radio frequency quadrupole accelerator, characterized in that, The accelerator includes an accelerator housing containing four elongated accelerating electrodes symmetrically mounted around the central axis of the accelerator. Near the central axis of the accelerator, there is an acceleration zone formed by the four accelerating electrodes facing each other. A vacuum isolation pipe made of non-metallic material is installed around the acceleration zone to surround the acceleration zone and form a vacuum acceleration cavity region.

2. The radio frequency quadrupole accelerator according to claim 1, characterized in that, The vacuum isolation pipe is composed of ceramic materials with alumina or boron nitride as the main components.

3. The radio frequency quadrupole accelerator according to claim 1 or 2, characterized in that, The four accelerating electrodes consist of a central electrode located inside the vacuum isolation pipe and an outer electrode located outside the hollow isolation pipe. The central electrode and the vacuum isolation pipe form a vacuum-sealed structure through welding or a rubber ring structure. The central electrode and the outer electrode are in close contact to form a surface current conductive loop.

4. The radio frequency quadrupole accelerator according to claim 3, characterized in that, The portion of the central electrode located inside the vacuum isolation pipe has electrode compensation blocks installed at both the inlet and outlet ends of the accelerator.

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

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

7. The radio frequency quadrupole accelerator according to claim 1, characterized in that, The vacuum isolation pipe has four electrode mounting openings on its wall surface, which are opened along the central axis of the accelerator. The accelerating electrodes are installed in the electrode mounting openings one by one.

8. 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 has a through-hole coupler mounting port.

9. The radio frequency quadrupole accelerator according to claim 8, characterized in that, The high-frequency power coupler includes an outer conductor, an inner conductor, and a coupler ring. The inner conductor is coaxially mounted inside the outer conductor. The coupler ring is connected to the inner conductor. The inner diameter of the outer conductor and the outer diameter of the inner conductor are coaxial with uniform impedance. The inner surface of the inner conductor and the outer surface of the outer conductor are tightly connected.

10. The radio frequency quadrupole accelerator according to claim 1, characterized in that, The accelerator housing is also equipped with multiple high-frequency signal pickup mounting ports and field distribution and frequency tuner mounting ports.

11. A charged particle accelerator system, characterized in that, The invention includes the radio frequency quadrupole accelerator and ion source as described in any one of claims 1-10, wherein the ion source and the radio frequency quadrupole accelerator are connected via a low-energy transport line, and the radio frequency quadrupole accelerator is connected to a radio frequency power source.

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