CN117580239A - Ultrahigh frequency linear accelerator for medical isotope production and parameter design method - Google Patents

Ultrahigh frequency linear accelerator for medical isotope production and parameter design method Download PDF

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Publication number
CN117580239A
CN117580239A CN202311770468.4A CN202311770468A CN117580239A CN 117580239 A CN117580239 A CN 117580239A CN 202311770468 A CN202311770468 A CN 202311770468A CN 117580239 A CN117580239 A CN 117580239A
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accelerator
low
energy
rfq
dtl
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何源
王志军
窦为平
黄玉璐
李晨星
金晓凤
陈伟龙
施龙波
黎晓晓
黄燃
张斌
胡正国
徐瑚珊
赵红卫
高郑
邱丰
黄贵荣
张鹏
张军辉
薛纵横
王锋锋
秦元帅
贾欢
蔡汉杰
杨锋
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Institute of Modern Physics of CAS
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H9/00—Linear accelerators
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00
    • H05H7/22—Details of linear accelerators, e.g. drift tubes
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K7/00—Constructional details common to different types of electric apparatus
    • H05K7/20—Modifications to facilitate cooling, ventilating, or heating
    • H05K7/20218—Modifications to facilitate cooling, ventilating, or heating using a liquid coolant without phase change in electronic enclosures
    • H05K7/20272—Accessories for moving fluid, for expanding fluid, for connecting fluid conduits, for distributing fluid, for removing gas or for preventing leakage, e.g. pumps, tanks or manifolds
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K7/00—Constructional details common to different types of electric apparatus
    • H05K7/20—Modifications to facilitate cooling, ventilating, or heating
    • H05K7/20218—Modifications to facilitate cooling, ventilating, or heating using a liquid coolant without phase change in electronic enclosures
    • H05K7/20281—Thermal management, e.g. liquid flow control
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H2277/00—Applications of particle accelerators
    • H05H2277/10—Medical devices
    • H05H2277/11—Radiotherapy
    • H05H2277/116—Isotope production
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00—Energy generation of nuclear origin
    • Y02E30/10—Nuclear fusion reactors

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Plasma & Fusion (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Thermal Sciences (AREA)
  • Particle Accelerators (AREA)

Abstract

The invention relates to an ultrahigh frequency linear accelerator for medical isotope production and a parameter design method, which comprises the following steps: the low-energy accelerating device comprises an ion source system, a vacuum pump chamber and an RFQ accelerator which are sequentially connected through a low-energy transmission line, wherein the ion source system is used for outputting low-emissivity high-peak-current-intensity plasma beam, and the RFQ accelerator is used for low-energy acceleration of the low-emissivity high-peak-current-intensity plasma beam to obtain ultrahigh-frequency high-peak-current-intensity low-energy plasma beam; the high-energy accelerating device comprises an IH-DTL accelerator and is used for accelerating the high-energy of the ultrahigh-frequency high-peak-current low-energy plasma beam output by the RFQ accelerator; and cooling flow channels are arranged in the RFQ accelerator and the IH-DTL accelerator, so that stable operation of the RFQ accelerator and the IH-DTL accelerator is realized, and high-energy plasma beam with high peak flow intensity and high average flow intensity is obtained. The invention can be widely applied to the field of accelerators.

Description

Ultrahigh frequency linear accelerator for medical isotope production and parameter design method
Technical Field
The invention relates to an ultrahigh frequency linear accelerator for medical isotope production and a parameter design method, in particular to an ultrahigh frequency linear accelerator for medical isotope germanium-68/gallium-68 production and a parameter design method, belonging to the field of accelerators.
Background
Positron emission computed tomography (PET) is one of the advanced imaging techniques in the clinical field of nuclear medicine. Currently, the radionuclide fluorine-18 has been widely used in PET examinations, and fluorine-18 can be produced on a small cyclotron in hospitals. Recently, various radiopharmaceuticals of the positron nuclide gallium-68 have been approved by the U.S. FDA for the diagnosis of various tumors and cancers. Gallium-68 may be produced by a germanium-68/gallium-68 generator and may be available for long periods of time due to its relatively long half-life (about 271 days) of the parent nuclide germanium-68.
Based on the existing large accelerator, scientific researchers bombard a large-area gallium-nickel alloy target for 10 hours by using proton beam with average flow of about 100uA, and after cooling, the germanium-68 is separated and purified by using a double chromatographic column automatic separation device, so that a 5 millicurie SnO 2-based germanium-68/gallium-68 generator is successfully prepared. Scientific researchers establish a double chromatographic column separation process route for preparing germanium-68 by accelerator irradiation, grasp the preparation technology of a gallium-nickel alloy target and a germanium-68/gallium-68 generator, and lay a good foundation for the future autonomous and large-scale production and preparation of the generator in China.
However, the linacs of the existing isotope production apparatus are largely classified into superconducting linacs and normal temperature linacs. For a superconducting linear accelerator, the acceleration gradient is high, the average flow intensity can reach tens mA level, the energy is continuously adjustable, but the superconducting linear accelerator is long as a whole and accelerates proton beam to 20MeV because of the superconducting state, the linear accelerator is about 15-18m in length, and the economic cost of the cryostat and a refrigerating system is huge. For a normal temperature low frequency linear accelerator, although the average flow is strong and can reach a plurality of mA levels, the acceleration gradient is low, usually 2-3MV/m, the acceleration beam reaches 20-30MeV, the length of the linear accelerator is usually 12-18m, the low working frequency can lead the transverse size of the acceleration cavity to be large, and the cavity is manufactured to be high.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide an ultra-high frequency linear accelerator and a parameter design method suitable for the production of medical isotope germanium-68/gallium-68, which can provide a proton beam of about 20MeV, reduce the size of the equipment and improve the efficiency of isotope production.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
in a first aspect, the present invention provides an ultra-high frequency linac for medical isotope production comprising: the low-energy accelerating device comprises an ion source system, a vacuum pump chamber and an RFQ accelerator, which are sequentially connected through a low-energy transmission line, wherein the ion source system is used for outputting low-emittance high-peak-current-intensity plasma beam, the RFQ accelerator is used for carrying out low-energy acceleration on the low-emittance high-peak-current-intensity plasma beam to obtain ultrahigh-frequency high-peak-current-intensity low-energy plasma beam, and the vacuum pump chamber is used for ensuring that the low-energy accelerating device is in a vacuum state;
the high-energy accelerating device comprises an IH-DTL accelerator and is used for accelerating the high energy of the ultrahigh-frequency high-peak-current low-energy plasma beam output by the RFQ accelerator;
and cooling flow channels are arranged in the RFQ accelerator and the IH-DTL accelerator, and are used for realizing stable operation of the RFQ accelerator and the IH-DTL accelerator and obtaining high-energy plasma beam current with high peak current intensity and high average current intensity.
Further, the ion source system includes an upstream arc chamber and a downstream chamber connected by a ceramic window;
the inlet end of the upstream arc cavity is used for receiving the plasma beam excited by the gyrotron, the outlet end of the upstream arc cavity is provided with an arc cavity electrode which is used for matching with the extraction electrode arranged in the downstream cavity to optimally debug the electric field distribution of the plasma extraction outlet, so that a radial mirror surface potential zone is formed at a position close to the axial direction;
the extraction electrode is used for outputting a plasma beam with low emittance and high peak current.
Further, a permanent magnet restraining magnet is sleeved outside the upstream arc cavity, and the permanent magnet restraining magnet is used for realizing that the central area of the upstream arc cavity is a magnetic field trap, so that plasma beam current can be restrained in the magnetic field trap area.
Further, the average aperture of the pole head of the RFQ accelerator is 1.5-1.7mm, a first cooling flow channel and a second cooling flow channel are formed between the electrodes on the pole head and close to the outer edge of the pole head, one side of each of the first cooling flow channel and one side of each of the second cooling flow channel are brazed with plugs to complete closing of a water channel, and the aperture of each of the first cooling flow channels is larger than that of each of the second cooling flow channels.
Further, a third cooling flow passage is arranged on a drift tube girder of the IH-DTL accelerator, a plug is brazed at the inlet end of the third cooling flow passage, the middle section is in an inverted trapezoid shape, and the outlet end is a blind hole; a fourth cooling flow passage is arranged on a cavity barrel of the IH-DTL accelerator, and one end of the fourth cooling flow passage is brazed with a plug to finish closing of a water passage.
In a second aspect, the present invention provides a method for designing parameters of an ultra-high frequency linac for medical isotope production, comprising the steps of:
optimizing and simulating design parameters of an ion source system, a low-energy transmission line and an RFQ accelerator;
optimizing and simulating design parameters of cooling runners in the RFQ accelerator and the IH-DTL accelerator;
and configuring structural components in the low-energy accelerating device and the high-energy accelerating device based on the obtained optimized simulation parameters to obtain the ultrahigh-frequency linear accelerator for medical isotope production.
Further, the optimizing simulation of the design parameters of the ion source system, the low-energy transmission line and the RFQ accelerator comprises the following steps:
determining key factors influencing the output beam quality of the ion source system, and optimally designing structural parameters of the ion source system based on the key factors;
determining key factors influencing the increase of the beam emittance, and optimally designing design parameters of the low-energy transmission line based on the key factors;
and determining key factors influencing the transverse focusing of the RFQ accelerator, and optimally designing structural parameters of the RFQ accelerator based on the key factors.
Further, determining key factors affecting the output beam quality of the ion source, and optimally designing structural parameters of the ion source system based on the key factors, including:
based on preset frequency requirements, performing simulation calculation on working frequency and working voltage parameters of the cyclotron resonance tube to obtain optimal output frequency and power range;
the method comprises the steps of optimally designing a constraint magnetic field pattern to enable an upstream arc cavity central area to be a magnetic field trap, so that plasma beam current can be constrained in the magnetic field trap area;
and simulating structural parameters of the arc chamber electrode in the upstream arc chamber and the extraction electrode in the downstream chamber to obtain aperture ranges of the arc chamber electrode and the extraction electrode.
Further, the determining the key factor affecting the increase of the beam emittance, and optimizing design parameters of the low-energy transmission line based on the key factor includes:
determining the material type of the low-energy transmission line;
performing compact beam flow mechanical simulation on the low-energy transmission lines, and determining the relation between the drift distance between the low-energy transmission lines and the effective length of the magnets;
and configuring a beam limiting diaphragm and a beam limiting cone for the low-energy transmission line to realize beam space beam scraping.
Further, the optimizing simulation of the design parameters of the cooling flow channels in the RFQ accelerator and the IH-DTL accelerator comprises the following steps:
electromagnetic simulation calculation is carried out on the RFQ accelerator and the IH-DTL accelerator, and main parts affecting heating of cavities of the RFQ accelerator and the IH-DTL accelerator are determined;
based on the determined main parts of the RFQ accelerator and the IH-DTL accelerator cavity, the cooling flow channels in the RFQ accelerator and the IH-DTL accelerator cavity are designed on the premise of ensuring the mechanical strength and the stability of the RFQ accelerator and the IH-DTL accelerator.
Due to the adoption of the technical scheme, the invention has the following advantages:
1. the invention reasonably optimizes the range of the extraction electrode in the ion source system in the low-energy accelerating device, the low-energy transmission line and the average aperture in the pole head in the RFQ accelerator, so that the accelerator can provide peak intensity of 5-10mA, the transmission efficiency is more than 80%, and the requirement of high isotope generation efficiency can be met.
2. According to the invention, through the reasonable design of the cooling flow channels in the RFQ accelerator and the IH-DTL accelerator, the cavities of the RFQ accelerator and the IH-DTL accelerator can be rapidly cooled, and under the condition of ensuring the stable operation of the system, the beam current with the average current strength of 50-100uA can be provided, the duty ratio reaches 1%, which is 100-200 times of the average strength of the existing ultra-high linear accelerator, and the average current strength of the ion beam current output by the accelerator is effectively improved.
3. The RFQ cooling scheme provided by the invention realizes the layout of the cooling water path on a compact structure, ensures that the maximum temperature rise, the maximum deformation, the maximum stress and the generated frequency drift of the RFQ cavity are in reasonable ranges in the working state, has small disturbance on an electromagnetic field, and has simple implementation mode, low cost and good effect.
4. According to the cooling scheme of the IH-DTL accelerator, through coupling simulation analysis such as high frequency, heat, deformation and the like, a calculation result shows that the ultrahigh frequency IH-DTL accelerator can work at a 1% duty ratio under the cooling flow channel with the optimal design, and the integral temperature rise of the cavity is less than 20 ℃ at the moment, so that the high frequency IH-DTL accelerator can stably operate.
5. The high-frequency linear accelerator accelerates beam current to about 20MeV, and the length is about 8-10m, and is shortened by 30-50% compared with the existing normal-temperature accelerator.
6. According to the invention, the working frequency of the RFQ and IH-DTL accelerator is improved, so that the transverse dimension of the accelerator is reduced to 50%, and the processing and manufacturing cost of the accelerator is reduced.
Therefore, the invention can be widely applied to the field of accelerators.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Like parts are designated with like reference numerals throughout the drawings. In the drawings:
FIG. 1 is a schematic diagram of an ultra-high frequency linac for medical isotope production provided by an embodiment of the present invention;
fig. 2 is a schematic structural diagram of an ion source system according to an embodiment of the present invention;
FIG. 3 is a transverse cross-section of an RFQ accelerator provided by an embodiment of the present invention;
fig. 4 is a cooling flow path layout design diagram of the RFQ accelerator provided in the present embodiment;
FIG. 5 is an external focus solenoid design for an RFQ accelerator provided in an embodiment of the present invention;
fig. 6 is a schematic diagram showing a cooling flow path layout of the IH-DTL accelerator according to the present embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. It will be apparent that the described embodiments are some, but not all, embodiments of the invention. All other embodiments, which are obtained by a person skilled in the art based on the described embodiments of the invention, fall within the scope of protection of the invention.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
In order to realize that the ultrahigh frequency linear accelerator accelerates the beam with high average current intensity so as to meet the requirement of the SnO 2-based germanium-68/gallium-68 generator on the high average current intensity, two technical problems need to be solved, namely, how to improve the peak intensity of the beam, and how to improve the average intensity of the beam. In order to improve the peak intensity of the beam, optimization can be performed in terms of the output beam quality of the ion source, the transmission characteristics of the low-energy transmission line, the transverse focusing of the RFQ accelerator, and the like. In order to increase the average intensity of the beam, i.e. to increase the duty cycle of the accelerator, it is most critical to increase the duty cycle of the RFQ accelerator and the IH-DTL accelerator, since both the ion source and the low energy transmission line are continuous waves. When the duty cycle needs to be greatly increased, local heating will have a great influence on the operation of the accelerator, possibly causing field emission and ignition, and finally affecting the stable operation of the RFQ accelerator and the IH-DTL accelerator, so that the cooling problem of the two needs to be solved.
Based on the analysis, in some embodiments of the present invention, an ultrahigh-frequency linear accelerator for medical isotope production with high peak current intensity and high average current intensity is provided, where the linear accelerator realizes the high peak current intensity by optimizing the structures of an ion source system, a low-energy transmission line and an RFQ accelerator in a low-energy acceleration section, and realizes the high average current intensity by optimizing the cooling structures of the RFQ accelerator and an IH-DTL accelerator in the high-energy acceleration section. The invention can integrate the advantages of high average flow, high transmission efficiency and low cost, and is applied to the field of medical isotope germanium-68/gallium-68 generators.
Accordingly, in other embodiments of the present invention, a method of designing parameters for an ultra-high frequency linac for medical isotope production is provided.
Example 1
As shown in fig. 1, the present embodiment provides an ultra-high frequency linac for medical isotope production, which includes: low energy accelerating device and high energy accelerating device. The low-energy accelerating device comprises an ion source system 1, a vacuum pump chamber 2 and an RFQ accelerator 3 which are sequentially connected through a low-energy transmission line, wherein the ion source system 1 is used for outputting low-emittance high-peak-current-intensity plasma beam, the RFQ accelerator 3 is used for carrying out low-energy acceleration on the low-emittance high-peak-current-intensity plasma beam to obtain ultrahigh-frequency high-peak-current-intensity low-energy plasma beam, and the vacuum pump chamber 2 is used for ensuring that the vacuum degree of the low-energy accelerating device is in a preset range; the high-energy accelerating device comprises an IH-DTL accelerator 4 and is used for accelerating the high energy of the ultrahigh-frequency high-peak-current low-energy plasma beam output by the RFQ accelerator 3; meanwhile, cooling flow channels are arranged in the RFQ accelerator 3 and the IH-DTL accelerator 4 and used for realizing stable operation of the RFQ accelerator 3 and the IH-DTL accelerator 4, and high-energy plasma beam with high peak current intensity and high average current intensity is obtained.
Preferably, as shown in fig. 2, the ion source system 1 includes an upstream arc chamber 11 and a downstream chamber 12, which are connected by a ceramic window 13. The inlet end of the upstream arc cavity 11 is used for receiving plasma beam excited by the gyrotron, the outlet end of the upstream arc cavity 11 is provided with an arc cavity electrode 14, and the arc cavity electrode is used for matching with an extraction electrode 15 arranged in the downstream cavity 12 to optimally debug the electric field distribution of the plasma extraction outlet, so that a radial mirror surface potential zone is formed at a position close to the axial direction; the structure of the extraction electrode 15 is optimized to reduce the effect of the radial nonlinear field on the plasma beam, and output the plasma beam with low emittance and high peak current.
More preferably, a permanent magnet restraining magnet 16 is further sleeved outside the upstream arc cavity 11, and the permanent magnet restraining magnet 16 is used for realizing that the central area of the upstream arc cavity 11 is a magnetic field trap, so that the plasma beam can be restrained in the magnetic field trap area.
More preferably, the arc chamber electrode 14 adopts a horn-shaped structure, and the wide-mouth end of the horn-shaped structure is connected with the outlet end of the upstream arc chamber 11 through threads, and the narrow-mouth end of the horn-shaped structure is spaced from the extraction electrode 15 by a preset distance, so that a mirror surface trap area is formed at a position close to the axial direction.
When in use, on one hand, the arc chamber electrode 14 can isolate the downstream chamber 12 from the upstream arc chamber 11, ensure that the upstream arc chamber 11 becomes an independent chamber, and electrons in the upstream arc chamber are circularly operated in a resonance electromagnetic field, so as to realize ionization of electrons and hydrogen, finally form plasma in a hydrogen ionization state, and the plasma comprises H + /H 2 + /H 3 + /e - The method comprises the steps of carrying out a first treatment on the surface of the On the other hand, the arc chamber electrode 1 is used as a window for leading out plasma, and is at high voltage potential through the high voltage power supply mounted on the outer wall of the upstream arc chamber, and forms potential difference with the zero potential leading-out electrode 15 grounded in the downstream chamber, and the electric field can lead the plasma beam (H + ) Sucking out and accelerating.
More preferably, the extraction electrode 15 adopts a spherical extraction electrode head, one end of the spherical extraction electrode head is provided with a spherical groove, the other end of the spherical extraction electrode head is provided with a rectangular groove, the rectangular groove is sequentially connected with the chamber connecting rod, the outlet flange and the vacuum pipeline through a built-in threaded structure, and the other end of the vacuum pipeline is connected with the low-energy transmission line.
More preferably, the upstream arc chamber 11 and the downstream chamber 12 are filled with polytetrafluoroethylene vacuum isolated, and are matched with a vacuum pump arranged in the vacuum chamber 2, so that the whole inside of the ion source system 1 is in a vacuum state.
More preferably, the ion source system 1 further comprises an air inlet system, and a gas outlet of the air inlet system is communicated with an air inlet hole 17 reserved at the inlet end of the upstream arc chamber 11, so as to provide the injected hydrogen for the ion source system 1.
More preferably, the ion source system further comprises a high-precision mass flowmeter for controlling and monitoring the air pressure state of the downstream chamber 12 of the ion source system 1, and sending the monitoring data to a control feedback system, and the control feedback system performs feedback control on the air pressure state of the ion source system 1 to ensure the quasi-steady air pressure of the ion source system 1. In the embodiment, the high-precision mass flowmeter can realize the adjustment quantity of 3sccm (standard milliliters per minute), the adjustment precision is +/-1%, and compared with a needle valve system adopted by the traditional ion source at present, the adjustment precision is improved by one order of magnitude.
When in operation, the ion source system 1 adopts 28GHz resonance cyclotron frequency to be matched with a tens of kilowatts cyclotron resonance tube for exciting plasma to generate; in order to ensure enough plasma restraint, an external electromagnet is utilized to optimize and debug a magnetic field, and an arc cavity electrode is matched with an extraction electrode so as to form mirror surface potential at a position close to the axial direction; the extraction electrode is designed into a sphere, so that the effect of a radial nonlinear field on beam current can be reduced; by the scheme, the beam with low emittance and high peak current intensity is obtained, the peak current intensity is 15-20 mA, and the emittance is 0.04-0.08 mm.
Preferably, the low energy transmission line adopts a double electromagnetic solenoid, and the drift distance between the two low energy transmission lines is 1-2 times of the effective length of the magnet.
Preferably, the front and rear ends of the two low-energy transmission lines are respectively provided with a limited beam diaphragm, and the end of the low-energy transmission line between the vacuum pump chamber 2 and the RFQ accelerator 3 is also provided with a limited beam cone. The beam limiting diaphragm is used for leading the ion current into the beam current to obtain the beam current RMS envelope with the aperture of 2.8-3.2 times; the beam limiting cone is used for scraping and limiting H < 2+ > beam; the beam limiting diaphragms and the beam limiting cones jointly realize the matching of the ion beam output by the ion source and the strong beam of the RFQ accelerator, the peak beam intensity is between 6 and 12mA, and the emittance is increased by less than 20%.
Preferably, as shown in fig. 3 and 4, the average pore diameter R of the pole head portion of the RFQ accelerator 3 0 A first cooling flow passage 31 and a second cooling flow passage 32 are formed between the electrodes on the pole head and near the outer edge of the pole head, which are 1.5-1.7mm, the same asWhen the plug is soldered on one side to complete the closing of the water path, and the aperture of the first cooling flow channel 31 is larger than that of the second cooling flow channel 32.
More preferably, as shown in fig. 5, a solenoid 33 for increasing transverse focusing is further sleeved at the position 350-500 mm of the inlet end of the RFQ accelerator 3, so that the transmission efficiency of the RFQ accelerator 3 can be effectively improved. Wherein the solenoid 33 has an inner diameter of about 120 to 150mm.
Preferably, as shown in fig. 6, a third cooling flow channel 41 is arranged on a drift tube girder of the IH-DTL accelerator 4, an inlet end of the third cooling flow channel 41 is brazed with a plug, a middle section is in an inverted trapezoid shape, and an outlet end is a blind hole; a fourth cooling flow passage (not shown in the figure) is provided on the cavity of the IH-DTL accelerator 4, and a plug is soldered on one side to complete the closing of the water path.
Preferably, the operating frequencies of the RFQ accelerator 3 and the IH-DT accelerator 4 are 714MHz-1000MHz.
Preferably, the high-energy accelerator may employ any one of SCDTL accelerator, BTW accelerator, or CCL accelerator, in addition to the IH-DTL accelerator 4. The working frequency of the SCDTL accelerator, the BTW accelerator or the CCL accelerator is preferably 2856MHz-3000MHz.
Example 2
Based on the ultra-high frequency linear accelerator for medical isotope production provided in embodiment 1, the embodiment provides a parameter design method of the ultra-high frequency linear accelerator for medical isotope production, comprising the following steps:
1) Optimizing and simulating design parameters of an ion source system 1, a low-energy transmission line and an RFQ accelerator 3 in the low-energy accelerating device;
2) Optimizing and simulating design parameters of cooling runners in an RFQ accelerator 3 in a low-energy accelerator and an IH-DTL accelerator 4 in a high-energy accelerator;
3) And configuring structural components of each device in the low-energy accelerating device and the high-energy accelerating device based on the obtained optimized simulation parameters to obtain the ultra-high frequency linear accelerator for medical isotope production.
Preferably, in the step 1), the method includes the steps of:
1.1 Determining key factors influencing the output beam quality of the ion source system, and optimally designing the field type of the constrained magnetic field, the distribution of the extracted electric field, the resonance frequency, the air pressure of the arc cavity and the like based on the key factors;
1.2 Determining a key factor influencing the increase of the beam emittance, and optimally designing design parameters of the low-energy transmission line based on the key factor;
1.3 A key factor affecting the lateral focusing of the RFQ accelerator 3 is determined, and the structural parameters of the RFQ accelerator 5 are optimally designed based on the key factor.
Preferably, in the step 1.1), the method includes the steps of:
1.1.1 Based on the preset frequency requirement, performing simulation calculation on the working frequency and the working voltage parameters of the cyclotron resonance tube to obtain the optimal output frequency and the power range;
1.1.2 Optimally designing the constraint magnetic field pattern to ensure that the central area of the arc cavity of the ion source is a magnetic field trap, so that the plasma beam can be constrained in the magnetic field trap area;
1.1.3 The structural parameters of the arc chamber electrode in the upstream arc chamber and the extraction electrode in the downstream chamber are simulated, and the aperture ranges of the arc chamber electrode and the extraction electrode are obtained.
Preferably, in the step 1.1.1), a gyrotron with an output resonance frequency of 28GHz and an output power range of 5 to 15kW is selected in this embodiment.
Preferably, in the step 1.1.2), the confining magnetic field is reasonably designed in the embodiment, so that the end magnetic field is 1.5T and the central well region is 0.25T, and the ion beam can be effectively confined in the magnetic field well region.
Preferably, in the step 1.1.3), the diameter of the horn-shaped narrow mouth end of the arc chamber electrode in the embodiment ranges from 2.5mm to 6.5mm; the spherical aperture of the extraction electrode is between 1.5 and 2.5 mm.
Preferably, in the step 1.2), the method includes the steps of:
1.2.1 Determining the material type of the low-energy transmission line, and reducing the beam emittance increase caused by space charge force by using space charge compensation of the low-energy transmission line.
1.2.2 Compact beam flow mechanics simulation is performed on the low-energy transmission lines, and the relation between the drift distance between the low-energy transmission lines and the effective length of the magnets is determined.
1.2.3 A beam limiting diaphragm and a beam limiting cone are configured on the low-energy transmission line, so that beam space beam scraping is realized, and the beam quality is further improved.
On the one hand, the compact beam hydrodynamic design of the double electromagnetic solenoids is adopted, through simulation, the effective length of the magnet with the drift distance of 1-2 times between the two solenoids can be compressed, the necessary space for assembling a vacuum pump chamber is ensured, and an ion source can also be in a pulse operation mode, so that a chopper which is usually used for generating a pulse time structure is saved, the distance from a second low-energy transmission line to an inlet matching section of the RFQ accelerator is shortened by about 33%, the distance has serious influence on the increase of the emittance and the matching of the beam current, and the shorter the distance is, the smaller the increase of the emittance is, and the more favorable for the matching of the inlet of the RFQ accelerator is. On the other hand, the space charge effect compensation is fully utilized, and can be realized by optimally configuring a vacuum pump, and the vacuum degree of the front end of the low-energy transmission line (namely, the connecting section between the ion source outlet and the vacuum pump chamber inlet) is controlled to be 5E-3 to 5E-4Pa so as to improve the space charge compensation capability; the vacuum at the outlet of the low-energy transmission line (namely, the connection section between the second low-energy transmission line 4 and the inlet of the RFQ accelerator) is controlled to be 5E-4 to 5E-5Pa so as to reduce the probability of striking fire at the inlet end of the RFQ accelerator.
Preferably, in the above step 1.3), based on the dynamic simulation calculation, the present embodiment finds that by narrowing the electrode average radius R 0 And a solenoid is sleeved on the outer wall of the RFQ accelerator, so that the transverse focusing effect of the RFQ accelerator can be effectively improved.
As shown in FIG. 3, it was found through dynamics simulation that when the average radius R of the electrode of the RFQ accelerator is 0 Is reduced to
When the firing coefficient is not more than 2, the high-efficiency transmission of the RFQ accelerator to the peak beam intensity of 5-10mA can be satisfied only when the firing coefficient is 1.5-1.7 mm.
However, the RFQ accelerator has a large number of electrode-related dimensions, high precision requirements, and great processing difficulty. In particular the average pore diameter of the pole head partR O And the thickness dimension R of the polar head V These two dimensional changes directly affect the processing of the electrode tip. When the average radius R of the electrode O When getting smaller, the corresponding wall thickness R V The size of the electrode head is reduced, and the electrode head is easy to deform in the processing process. In order to solve the problems, a CNC numerical control machining center with high precision and high rotating speed is adopted in electrode machining, a small ball head cutter is adopted in order to ensure the machining precision of a pole head position modulation wave line, a plurality of pole head test pieces are machined in a small number of times, corresponding data are detected, the fact that the actual contour of the machined pole head is consistent with the theoretical contour is ensured, an optimal pole head machining process route is determined, and the machining size and the machining precision of the pole head are ensured to the greatest extent. In the later transportation and assembly processes, special protection is needed to be carried out on the pole head part, thereby avoiding the pole head from being scratched or bumped.
As shown in fig. 5, by sleeving a solenoid on the outer wall of the RFQ accelerator, the lateral focusing can be increased. Although the transverse dimension of the RFQ accelerator is about 85-100 mm, the transverse dimension of the RFQ accelerator is 300-400 mm because of the auxiliary equipment such as cooling and the like, and the solenoid with the large radius is difficult to process and has high cost. In this embodiment, it is found through simulation calculation that the length of the external focusing needs to be increased by only 350-500 mm at the inlet end of the RFQ accelerator, so in this embodiment, the external wall auxiliary device originally disposed at 350-500 mm at the inlet end of the RFQ accelerator is replaced by a solenoid, so as to reduce the transverse dimension of the solenoid, and ensure that the inner diameter of the solenoid is about 120-150 mm and the length is about 300-500 mm.
In this embodiment, the working frequency of the RFQ accelerator is set to 714MHz-1000MHz, the average radius of the electrode is reduced to 1.5-1.7mm, and meanwhile, the inlet end of the RFQ accelerator is sleeved with the solenoid, so that the beam with the peak intensity of 5-10mA can be obtained at the outlet end of the RFQ accelerator 5, and the RFQ transmission efficiency can reach 90%.
Preferably, in the step 2), the method includes the steps of:
2.1 Electromagnetic simulation calculation is carried out on the RFQ accelerator and the IH-DTL accelerator, and main parts affecting heating of cavities of the RFQ accelerator and the IH-DTL accelerator are determined;
2.2 Based on the determined main parts of the RFQ accelerator and the IH-DTL accelerator cavity, the cooling flow passage in the cavity is designed on the premise of ensuring the mechanical strength and the stability of the RFQ accelerator and the IH-DTL accelerator.
Preferably, in the step 2.1), when the radio frequency cavity (RFQ accelerator and IH-DTL accelerator cavity) is operated, the electromagnetic wave propagates in the radio frequency cavity, and the metal surface of the cavity has a strong reflection effect on the electromagnetic wave, but a small part of the electromagnetic wave still penetrates into the conductor, and the part of the electromagnetic wave is attenuated quickly, and the energy of the electromagnetic wave is converted into joule heat. Heating of the cavity is the primary cause of deformation of the cavity, thereby creating a frequency drift of the radio frequency cavity. A cooling channel of the radio frequency cavity needs to be designed to ensure that the frequency is stable at the working frequency in the running process of the cavity. The running process of the radio frequency cavity involves multi-physical field coupling calculation of an electromagnetic-thermal-structure, and the purpose of the calculation is to check whether the current cooling condition in the running state can ensure that the cavity frequency drift caused by the multi-physical field is within the bandwidth of a transmitter.
Through electromagnetic calculation, the embodiment finds that the heat of the cavity of the RFQ accelerator is mainly distributed on four electrodes, and then the cavity wall is arranged, and the tuner and the end plate are smaller. And the heat of the IH-DTL cavity is mainly distributed on the supporting rod and the girder of the drift tube, and the cavity wall is the second cavity wall, and the tuner, the coupler and the end plate are smaller.
Preferably, in the above step 2.2), the cooling flow path is determined based on the determined main part of the heat generation.
For RFQ accelerator, unlike RFQ accelerator with low operating frequency, the ultra-high frequency RFQ accelerator electrode tip wall thickness dimension R V Smaller, no cooling flow path is machined in order to ensure mechanical strength and stability.
As shown in fig. 4, in order to accomplish the cooling of the ultra-high frequency RFQ accelerator based on the understanding of the surface thermal power density distribution, the cooling channels are further away from the RFQ pole head to design the first cooling channel and the second cooling channel on each electrode of the RFQ, so as to ensure mechanical strength and stability. Through coupling simulation analysis of high frequency, heat, deformation and the like, the calculation result shows that the ultrahigh frequency RFQ accelerator can work at a 1% duty ratio under the cooling flow channel with the optimal design, and the temperature rise of the cavity is smaller than 5.7 ℃ at the moment, and the maximum deformation is about 0.7 mu m, so that the ultrahigh frequency RFQ accelerator can stably operate.
For IH-DTL accelerator, when the ultra-high frequency IH-DTL works at 0.1% duty cycle, water cooling is usually only needed to be conducted in the cavity cylinder. However, unlike the IH-DTL accelerator with low operating frequency, the dimensions of the drift tube and the support rod of the ultra-high frequency IH-DTL accelerator are small, and it is difficult to process the cooling flow channel in order to ensure mechanical strength and stability.
As shown in fig. 6, in order to complete cooling of the ultra-high frequency IH-DTL accelerator under high duty ratio, and also in order to ensure mechanical strength and stability, the cooling flow channels are optimally designed on the drift tube girder and the cavity cylinder, respectively, and the area at the middle point of the drawing is the cooling flow channel on the drift tube girder. Through coupling simulation analysis of high frequency, heat, deformation and the like, the calculation result shows that the ultra-high frequency IH-DTL accelerator can work at 1% duty ratio under the cooling flow channel with optimal design, and the integral temperature rise of the cavity is less than 20 ℃ at the moment, so that the ultra-high frequency IH-DTL accelerator can stably operate.
Finally, it should be noted that: the above embodiments are only for illustrating the technical aspects of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the above embodiments, it should be understood by those of ordinary skill in the art that: modifications and equivalents may be made to the specific embodiments of the invention without departing from the spirit and scope of the invention, which is intended to be covered by the claims.

Claims (10)

1. An ultra-high frequency linac for medical isotope production comprising: the low-energy accelerating device is characterized by comprising an ion source system, a vacuum pump chamber and an RFQ accelerator, wherein the ion source system, the vacuum pump chamber and the RFQ accelerator are sequentially connected through a low-energy transmission line, the ion source system is used for outputting low-emissivity high-peak-current-intensity plasma beam, the RFQ accelerator is used for low-energy accelerating the low-emissivity high-peak-current-intensity plasma beam to obtain ultrahigh-frequency high-peak-current-intensity low-energy plasma beam, and the vacuum pump chamber is used for ensuring that the low-energy accelerating device is in a vacuum state;
the high-energy accelerating device comprises an IH-DTL accelerator and is used for accelerating the high energy of the ultrahigh-frequency high-peak-current low-energy plasma beam output by the RFQ accelerator;
and cooling flow channels are arranged in the RFQ accelerator and the IH-DTL accelerator, and are used for realizing stable operation of the RFQ accelerator and the IH-DTL accelerator and obtaining high-energy plasma beam current with high peak current intensity and high average current intensity.
2. An ultra-high frequency linac for medical isotope production according to claim 1 wherein said ion source system includes upstream and downstream arc chambers connected by a ceramic window;
the inlet end of the upstream arc cavity is used for receiving the plasma beam excited by the gyrotron, the outlet end of the upstream arc cavity is provided with an arc cavity electrode which is used for matching with the extraction electrode arranged in the downstream cavity to optimally debug the electric field distribution of the plasma extraction outlet, so that a radial mirror surface potential zone is formed at a position close to the axial direction;
the extraction electrode is used for outputting a plasma beam with low emittance and high peak current.
3. The ultra-high frequency linear accelerator for medical isotope production according to claim 2, wherein a permanent magnet restraint magnet is sleeved outside the upstream arc cavity, and the permanent magnet restraint magnet is used for realizing that the central area of the upstream arc cavity is a magnetic field trap, so that plasma beam current can be restrained in the magnetic field trap area.
4. The ultra-high frequency linear accelerator for medical isotope production of claim 1, wherein the average pore diameter of the polar head of the RFQ accelerator is 1.5-1.7mm, a first cooling flow passage and a second cooling flow passage are formed between the electrodes on the polar head and near the outer edge of the polar head, a plug is soldered on one side of the first cooling flow passage and one side of the second cooling flow passage to complete the closure of a water path, and the pore diameter of the first cooling flow passage is larger than that of the second cooling flow passage.
5. The ultra-high frequency linear accelerator for medical isotope production according to claim 1, wherein a third cooling flow passage is arranged on a drift tube girder of the IH-DTL accelerator, an inlet end of the third cooling flow passage is brazed with a plug, a middle section is in an inverted trapezoid shape, and an outlet end is a blind hole; a fourth cooling flow passage is arranged on a cavity barrel of the IH-DTL accelerator, and one end of the fourth cooling flow passage is brazed with a plug to finish closing of a water passage.
6. A method for designing parameters of an ultra-high frequency linac for medical isotope production according to any one of claims 1 to 5, comprising the steps of:
optimizing and simulating design parameters of an ion source system, a low-energy transmission line and an RFQ accelerator;
optimizing and simulating design parameters of cooling runners in the RFQ accelerator and the IH-DTL accelerator;
and configuring structural components in the low-energy accelerating device and the high-energy accelerating device based on the obtained optimized simulation parameters to obtain the ultrahigh-frequency linear accelerator for medical isotope production.
7. The method of claim 6, wherein optimizing the design parameters of the ion source system, the low energy transmission line, and the RFQ accelerator comprises:
determining key factors influencing the output beam quality of the ion source system, and optimally designing structural parameters of the ion source system based on the key factors;
determining key factors influencing the increase of the beam emittance, and optimally designing design parameters of the low-energy transmission line based on the key factors;
and determining key factors influencing the transverse focusing of the RFQ accelerator, and optimally designing structural parameters of the RFQ accelerator based on the key factors.
8. The method of claim 7, wherein determining key factors that affect the output beam quality of the ion source and optimizing structural parameters of the ion source system based on the key factors comprises:
based on preset frequency requirements, performing simulation calculation on working frequency and working voltage parameters of the cyclotron resonance tube to obtain optimal output frequency and power range;
the method comprises the steps of optimally designing a constraint magnetic field pattern to enable an upstream arc cavity central area to be a magnetic field trap, so that plasma beam current can be constrained in the magnetic field trap area;
and simulating structural parameters of the arc chamber electrode in the upstream arc chamber and the extraction electrode in the downstream chamber to obtain aperture ranges of the arc chamber electrode and the extraction electrode.
9. The method of claim 7, wherein determining the key factor that affects the increase in the emittance of the beam, and optimizing the design parameters of the low-energy transmission line based on the key factor, comprises:
determining the material type of the low-energy transmission line;
performing compact beam flow mechanical simulation on the low-energy transmission lines, and determining the relation between the drift distance between the low-energy transmission lines and the effective length of the magnets;
and configuring a beam limiting diaphragm and a beam limiting cone for the low-energy transmission line to realize beam space beam scraping.
10. The method of claim 7, wherein optimizing the design parameters of the cooling channels in the RFQ accelerator and the IH-DTL accelerator comprises:
electromagnetic simulation calculation is carried out on the RFQ accelerator and the IH-DTL accelerator, and main parts affecting heating of cavities of the RFQ accelerator and the IH-DTL accelerator are determined;
based on the determined main parts of the RFQ accelerator and the IH-DTL accelerator cavity, the cooling flow channels in the RFQ accelerator and the IH-DTL accelerator cavity are designed on the premise of ensuring the mechanical strength and the stability of the RFQ accelerator and the IH-DTL accelerator.
CN202311770468.4A 2023-12-21 2023-12-21 Ultrahigh frequency linear accelerator for medical isotope production and parameter design method Pending CN117580239A (en)

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