WO2023226245A1

WO2023226245A1 - CYCLOTRON CAPABLE OF ACCELERATING α PARTICLES AND H2 + PARTICLES, AND HIGH-GAIN METHOD AND HIGH-PRECISION METHOD

Info

Publication number: WO2023226245A1
Application number: PCT/CN2022/118851
Authority: WO
Inventors: 张天爵; 付伟; 王飞; 储智超; 殷治国; 王川; 张素平; 赵博涵; 魏素敏; 刘景源; 靳昭军
Original assignee: 中国原子能科学研究院
Priority date: 2022-05-23
Filing date: 2022-09-15
Publication date: 2023-11-30
Also published as: CN114916118B; EP4319493A1; EP4319493A4; CN114916118A

Abstract

Disclosed in the present invention are a cyclotron capable of accelerating α particles and H2 + particles, and a high-gain method and a high-precision method. The cyclotron comprises: a dual-ECR ion source system; a dual-beam injection line transmission system based on a magnetic analyzer; a main magnet system; a high-frequency system based on eighth-order harmonics; and a dual-beam extraction system based on a deflection plate for accurate control of extracted α beam energy. The high-gain method comprises: doubling the frequency of an eighth-order harmonic cavity; respectively reducing the height of the cavity and an opening angle of a D plate by half compared with those of a fourth-order harmonic high-frequency cavity; and adaptively adjusting the diameter of an inner rod, the corner width of the outer radius of the cavity, and the thickness of the D plate. The high-precision method comprises: setting the position of a beam extraction point; and performing beam debugging, so as to observe radial target particle distribution, and adjusting the position of the deflection plate in real time. The present invention develops, for the first time in the world, a cyclotron capable of accelerating α particles and H2 + particles, realizes dual-beam high-brightness combined injection of α particles and H2 + particles for the first time, and implements, for the first time in China, a compact cyclotron in which an eighth-order harmonic high-frequency cavity is used for acceleration.

Description

Can accelerate alpha particles and H 2 +Particle cyclotron and high gain and high precision method

Technical field

The invention belongs to the field of cyclotrons, and specifically relates to a cyclotron that can accelerate alpha particles and H2+ particles and a high-gain and high-precision method.

Background technique

Multi-purpose, high-yield, high-energy gain, and precise energy extraction accelerators have important applications in nuclear physics, public health, advanced energy, national defense and security and other fields.

At this stage, the bottleneck issues that restrict multi-purpose, high-yield, high-energy-gain, and precise energy extraction accelerators include:

First, the accelerator has a single purpose. The alpha particle accelerator is an accelerator specially used to produce alpha nuclide for integrated diagnosis and treatment. The typical nuclide is 211At. The physical properties of 211At nuclide determine that it can be used as a good carrier for integrated diagnosis and treatment, and can combine radioimmunoassay and alpha nuclide. The targeted radiation therapy is organically combined, and the dosage is determined based on the uptake of the imaging agent in the tumor and other organs throughout the body, which not only achieves effective tumor treatment, but also ensures that important organs are not damaged. Due to the single use of alpha particle accelerators, alpha particle accelerators can only produce alpha particles and cannot meet the diverse isotope production needs. The reason why the accelerator has a single purpose is that different particle accelerators have different requirements for high-frequency cavity parameters for accelerating particles. If the accelerator is changed to produce another type of particle acceleration, the high-frequency cavity parameters and the magnetic field parameters that match the high-frequency cavity need to be readjusted. High-frequency cavity parameters and magnetic field parameters are the main technical parameters of accelerator parameters. The workload of adjusting these two types of parameters is no less than that of rebuilding an accelerator. Precisely because it is too difficult to implement and the workload is too large, for a long time, the vast majority of cyclotrons have been single-purpose accelerators.

Second, it is difficult to achieve peak acceleration with existing fourth-harmonic high-frequency cavity designs. Because the high-frequency cavity is a fourth-harmonic high-frequency cavity, in order for the fourth-harmonic high-frequency cavity to achieve peak acceleration, the opening angle of the high-frequency cavity must be 45 degrees, so that particles can enter and leave the high-frequency gap respectively. The accelerated high-frequency voltage is the peak voltage. However, the 45-degree high-frequency cavity opening angle is only an ideal value. The actual physical space in the magnetic field valley area of the accelerator must leave less than 45 degrees for the high-frequency cavity opening angle (the accelerator has two layers of eight magnetic poles, each layer is evenly distributed with four magnetic poles. Block magnetic poles, between the magnetic poles is the magnetic field valley area, and the upper and lower high-frequency cavities are installed symmetrically at 180 degrees in the magnetic field valley area). The reason why the space left for the opening angle of the high-frequency cavity is less than 45 degrees is: the magnetic pole opening angle The opening angle will be greater than 45 degrees: In order to meet the isochronic needs, magnetic pole padding strips are installed on both sides of each magnetic pole. The magnetic pole padding strips occupy the space originally reserved for the high-frequency cavity, causing the actual magnetic field valley area to remain. The opening angle for the high-frequency cavity is less than 45 degrees.

Third, the α particles and H2+ particles injected from the ion source into the accelerator are not all expected particles, and there are relatively many impurities. For conventional H- ions, since there are very few impurities, the treatment of impurities is basically not considered. When alpha particles and H2+ particles share a transmission system, the difficulty lies in taking into account both the requirements of the two ion sources for impurity separation and the need for engineering costs.

Fourth, the energy of the particle near the extraction point is not necessarily the desired energy. This is manifested in the fact that the radial position of the particles at the lead-out point is different. The energy is greater when the radial position is closer to the larger radius, and the energy is relatively smaller when the radial position is closer to the smaller radius. The different radial positions at the extraction point are related to the different initial phases. Particles with different initial phases lead to different energies at the extraction point.

To sum up, the existing bottleneck problems of accelerators include: the accelerator has a single purpose, the high-frequency cavity design makes it difficult to achieve peak acceleration, there are impurities in the injected particles, and the particle energy near the extraction point is not necessarily the desired energy.

Contents of the invention

In view of the problems raised by the prior art, the present invention proposes a cyclotron that can accelerate α particles and H2+ particles and a high-gain and high-precision method. The purpose is to solve the problem that the existing accelerator has a single purpose and the high-frequency cavity design is difficult to achieve peak acceleration. There are problems with the presence of impurities in the injected particles, and the particle energy near the extraction point may not necessarily be the desired energy.

The present invention proposes the following technical solutions to solve its technical problems:

A cyclotron that can accelerate alpha particles and H2+ particles. It is characterized by: including a dual Electron cyclotron resonance ion source system 1, a dual-beam injection line transmission system based on a magnetic analyzer 2, a main magnet system 3, and an eight-axis cyclotron resonance ion source system. Sub-harmonic high-frequency system 4. Double-beam extraction system 5 based on precise control of deflection plates to extract α-beam energy;

The dual-beam injection line transmission system 2 is arranged between the dual-particle outlet of the dual-ECR ion source system 1 and the lower surface of the cyclotron main magnet system 3; the main magnet system 3 is arranged in two layers at the center of the cyclotron. On the upper and lower sides of the plane, the main magnet system 3 on each side is composed of four magnetic poles evenly distributed in the circumferential direction, and the main magnet cover plate outside the magnetic poles. Each magnetic pole on each layer and between the magnetic poles is a magnetic field valley area; The above-mentioned high-frequency system 4 based on the eighth harmonic is divided into two layers, which are arranged on the upper and lower sides of the cyclotron center plane, and each layer is symmetrically arranged at 180 degrees in the magnetic field valley area; the double-beam extraction system 5 includes separately arranged The alpha particle extraction port and the H2+ particle extraction port in the outermost circle of the accelerator beam trajectory;

The cyclotron that accelerates α particles and H2+ particles shares the magnet parameters and high-frequency parameters of the dual-beam injection line transmission system 2 to achieve isochronous acceleration of α particles and H2+ particles;

The dual ECR ion source system 1 includes a time-sharing α particle ion source injection system and a H2+ particle source injection system; the dual extraction system 5 includes a time-sharing α particle extraction port and an H2+ particle extraction port. , the double extraction system 5 extracts α particles through electrostatic deflection and extracts strong proton beams through H2+ stripping;

The double-beam injection line transmission system 2 based on the magnetic analyzer is shown in Figure 2. It is a system in which α particles and H2+ particles use the same set of transmission lines: the beam passes through the 30-degree analysis magnet 2- of the double-beam injection line transmission system 2. 2's ±30-degree dipolar magnet separates alpha particles and H2+ particles with a normalized emissivity of 0.2πmm mrad. The normalized alpha particles and H2+ particles are analyzed through the front-end solenoid 2-1 and 30 degrees. Magnet 2-2, rear stage solenoid 2-3, x-y guide magnet 2-4, and buncher 2-5 are injected into the central area of the accelerator for acceleration; the 30-degree analysis magnet 2-2 is used for the impurity ion analyzer;

The dual-beam extraction system 5 based on the precise control of the deflection plate to extract α-beam energy, in the accelerator design stage, strictly limits the phase width of the particles injected into the central area through the phase selector to control the energy dispersion of the extracted α-particles and reduce the extraction area The beam loss; during the accelerator debugging stage, the deflection plate position and voltage are adjusted in real time through the host computer control system. By adjusting the deflection plate position and voltage, the position of the beam extraction point is accurately controlled;

The high-frequency system 4 based on the eighth harmonic is shown in Figures 5-1 and 5-2. When the same type of λ/2 double-gap coaxial cavity is selected, the cavity height is reduced by less than half, and the D plate The opening angle was reduced by half, and the diameter of the inner rod, the width of the outer radius of the cavity, and the thickness of the D plate were adjusted accordingly.

Further, the implementation of isochronous acceleration of α particles and H2+ particles is specifically: based on the principle of isochronic acceleration, the gyration frequency of the particles is calculated as:

Among them, B is the magnetic field strength in Tesla, q is the particle charge number, and A is the particle mass number.

Further, the separation of α particles and H2+ particles with a normalized emissivity of 0.2πmm mrad includes: analyzing the magnet 2-2 at 30 degrees, according to the deflection radius and deflection of the impurity particles and non-impurity particles in the secondary magnet. The angles are different, and the deflection angle and radius of α particles and H2+ are calculated to filter out impurity particles that are not α particles and H2+.

Further, the method of filtering out impurity particles that are not α particles and H2+ is specifically: calculating the deflection angle and radius of α particles and H2+ particles at the bipolar deflection magnet according to the mass resolution m/Δm, and the mass resolution m/Δm Expressed as:

where m is the mass of the required particle, Δm is the mass deviation, M _x is the transmission matrix of the two-pole magnet,

_In formula (2) _, _Y Knowing _the conditions _, we can calculate the transmission matrix _M Particles with a deflection angle of ₀ and θ are filtered out as impurities; the mass resolution m/Δm of the formula (2) is shared by α particles and H2+ particles: the relatively high mass resolution m/Δm of the two particles is taken as the common The mass resolution is m/Δm.

Further, the H2+ particles peel off two protons through the peeling film, and the beam current intensity is twice that before peeling off.

Further, after the α particles and H2+ particles pass through the 30-degree analysis magnet 2-2, the α particles and H2+ particles enter the double-beam injection line transmission system 2 because they use the same set of double-beam injection lines for transmission. System 2, the injected energy ratio is 2:1 to ensure consistent magnetic stiffness.

Further, the height of the cavity dropped from 2.4m to 0.9m, and the opening angle of the D plate was reduced from 45 degrees to 22.5 degrees; the adaptive adjustment of the inner rod diameter, the outer radius angle width of the cavity, and the thickness of the D plate includes: The lower limit of the inner rod diameter is adjusted to 40mm, the cavity angular width is adjusted to 40 degrees, and the D plate thickness is adjusted to 12mm to 14mm; the cavity angular width of 40 degrees is: the last 85% from the center of the cyclotron outward The angular width of the cavity is increased in the radius range.

Further, the phase width of the small phase width injection is 5 to 10 degrees.

Further, the method of extracting a strong proton beam by stripping H2+ includes: after passing through the stripping membrane, the particles become H+ particles, the gyration radius of the orbit becomes smaller, and then are deflected in the accelerator for one or more turns before being extracted from the accelerator; the deflected The number of turns is determined by the extraction energy and the size of the beam envelope.

A method for achieving peak acceleration in an eighth harmonic high-frequency system 4 includes the following steps:

Step 1. Set the cavity height of the eighth harmonic high-frequency cavity to 0.9m, and the D plate opening angle to 22.5 degrees;

Step 2: Set the lower limit of the inner rod diameter to 40mm;

Step 3: Increase the angular width of the cavity to 40 degrees, leaving only space for water-cooling wiring between the magnetic pole strips of the main magnet system (3) of the cyclotron and the side of the cavity to increase the size of the cavity. Internal vacuum zone; increasing the angular width of the cavity to 40 degrees means that the angular width of the cavity is increased in the last 85% radius range from the center of the cyclotron outward.

Step 4. Set the thickness of D plate to 12mm to 14mm to increase the distributed capacitance;

Step 5: Use a nose cone-shaped accelerating electrode design to reduce useless electric field distribution and reduce losses.

A method for accurately controlling the beam extraction point, which includes the following steps:

Step 1: Design the first harmonic amplitude phase, use resonance precession to expand the circle spacing of the beam orbit, and determine the preset position of the deflection plate; the preset position of the deflection plate is to place the deflection plate on the outermost ring and the second outer ring. between the circle beam orbits;

Step 2: Obtain the designed first harmonic distribution through magnetic field padding;

Step 3: Debug the beam and observe the radial target particle distribution;

Step 4: Check whether the beam reaches the lead-out point. If it does not reach the lead-out point, continue to step 5; if it reaches the lead-out point, go to step 6; the lead-out point is the preset position of the deflection plate;

Step 5: Adjust the deflection plate position and voltage in real time, and return to step 3;

Step 6: Extract the beam.

Advantages and effects of the present invention

1. For the first time in the world, a cyclotron is developed based on the injection of an external strong current ion source that can accelerate α particles and H2+ particles. It can realize the equalization of α particles and H2+ particles without adjusting any main technical parameters of the accelerator such as magnets and high frequencies. Temporal acceleration.

2. For the first time, dual-beam high-brightness combined injection of α particles and H2+ particles was achieved. Using a dual ECR ion source, the beam passes through a ±30-degree dipolar magnet to separate alpha particles and H2+ particles with a normalized emissivity of 0.2πmm mrad. A transmission system composed of wire tubes injects beams into the central area of the accelerator. Dual beams use the same transmission system, which can further reduce construction costs.

3. Alpha particles and H2+ particles can be extracted through a double extraction system. The double extraction system extracts alpha particles through electrostatic deflection and extracts strong proton beams through H2+ stripping. The core technology lies in electrostatic deflection extraction, which can accurately control the energy of the α beam and reduce the energy dispersion, so as to strictly control the production of toxic nuclide 210At during the production of 211At; the H2+ stripping method can extract proton beam intensity up to H2+ particle beam intensity Twice that, achieving high-yield medical nuclide production based on solid targets.

4. The first compact cyclotron in China uses eighth-order harmonic high-frequency cavity acceleration, which successfully solves the problem of the traditional fourth-order harmonic acceleration high-frequency cavity resonant frequency being difficult to adapt to the lower cyclotron frequency of particles and the compact spatial structure of the main magnet valley area. High-efficiency isochronous acceleration with maximum energy gain is achieved.

Description of the drawings

Figure 1 is an overall layout diagram of an accelerator capable of accelerating α particles and H2+ particles according to the present invention;

Figure 2 is a schematic diagram of the dual-beam injection system of the present invention;

Figure 3 shows the integral slip phase in the isochronous acceleration of α particles and H2+ particles;

Figure 4 is a flow chart of the deflection plate position adjustable process according to the present invention;

Figure 5-1 is a schematic diagram of a fourth harmonic cavity with an opening angle of 45 degrees;

Figure 5-2 is a schematic diagram of the eighth harmonic cavity with an opening angle of 22.5 degrees;

In the figure, 1: Dual ECR ion source system; 1-1: α ion source injection system; 1-2: H2+ ion source injection system; 2: Double beam injection line transmission system based on magnetic analyzer; 2-1: Front Stage solenoid; 2-2: 30 degree analysis magnet; 2-3: rear stage solenoid; 2-4: x-y guide magnet; 2-5: buncher; 3: main magnet system; 4: based on eight Subharmonic high-frequency system; 5: Double-beam extraction system based on precise control of deflection plates to extract α-beam energy; 5-1: α-particle extraction port; 5-2: H2+ particle extraction port;

Detailed ways

Design principle of the present invention

1. The design principle of the high energy gain of the eighth harmonic cavity: First, due to the limitations of the accelerator magnetic field design, the physical space in the valley area of the existing accelerator magnetic field is not enough to support the fourth harmonic cavity to reach an opening angle of 45 degrees. Due to the opening angle It cannot reach 45 degrees, so that the particles cannot be accelerated by the peak voltage when entering and leaving the acceleration slit, resulting in a not high enough circle energy gain. In order to solve the problem of insufficient physical space at the 45-degree opening angle in the magnetic field valley area, when selecting the same type of λ/2 (λ here is the wavelength) double-gap coaxial cavity, the frequency is doubled and the cavity height is reduced by half. The following, as well as the method of reducing the D plate opening angle by half compared to the fourth harmonic acceleration: the cavity height is reduced from 2.4m to 0.9m, the D plate opening angle is reduced from 45 degrees to 22.5 degrees; the second and eighth harmonics The design basis of the wave cavity is that the height is 0.9m and the opening angle is 22.5 degrees. When this height and opening angle can be guaranteed, the voltage when the particles pass through the accelerating slit is guaranteed to be the peak voltage. However, the simulation experiment results show that when the cavity height is 0.9m, the frequency is still too high. Although the frequency is too high, the frequency cannot be reduced by raising the cavity height, because there are still cables left between the upper and lower covers of the high-frequency cavity. space, thirdly, the method of reducing frequency can be determined by the formula of resonant frequency f:

It can be seen from the above frequency relationship that the frequency can be reduced by increasing the capacitance and inductance. If the relationship between the cavity shell and the inner rod is approximated to a coaxial line, the inductance per unit length of the coaxial line is calculated according to the formula

see:

1) Reducing the diameter of the inner rod is equivalent to reducing a, so the inductance increases and the frequency decreases. This is the first way to reduce the cavity frequency. Here a and b are the equivalent inner and outer conductor radii. However, the smaller diameter of the inner rod will cause the mechanical strength of the cavity to decrease and the surface current to increase, which will increase the power loss. The solution is to first determine a lower limit of the inner rod diameter that ensures mechanical strength. In this embodiment, the lower limit of the inner rod diameter is 40mm;

2) Increasing the outer radius angular width of the cavity to 40 degrees is the second method to reduce the cavity frequency. Increase the angular width of the outer radius of the cavity to 40 degrees, so that it is as close as possible to the magnetic pole strips and the side of the cavity to increase the vacuum layer of the cavity. The maximum contact means that only the distance between the magnetic pole strips and the side of the cavity is left In the space for water-cooled wiring, the increase in the angular width of the outer radius of the cavity is 40 degrees, which means that the angular width of the cavity is increased in the last 85% radius range from the center of the cyclotron outward. Under certain assumptions, the calculation formula for the side capacitance of the coaxial cavity is:

Increasing the outer radius angle width is equivalent to increasing b, and can also have the effect of increasing capacitance;

3) Slightly increase the thickness of the D plate from 12mm to 14mm to increase the distributed capacitance (analogous to the parallel plate capacitance calculation formula). This is the third method to reduce the cavity frequency. Finally, the purpose of ensuring sufficient inner rod diameter is achieved while reducing the cavity frequency to the target value. Finally, the nose cone-shaped accelerating electrode design is adopted. The smooth electrode surface can effectively reduce the excessive concentration of the gap electric field, avoid the risk of discharge, and achieve the purpose of reducing useless electric field distribution and reducing losses.

The combination of the above points allows the cavity to consume less than 7kW of power under a small acceleration gap angle width. It also ensures that the time transit factor is around 0.987, achieving the best of both worlds. Assuming that the electric field in the gap is uniformly distributed, the energy gain of a particle passing through the gap once is as follows:

here

is the transition factor, q is the particle charge number, V _D is the peak acceleration voltage, h is the harmonic number, θ is the acceleration gap angular width, and the phase when the particle reaches the gap center line is

Therefore, the larger the transition factor, the higher the energy gain.

Summary: The fourth harmonic is changed to the eighth harmonic. Although the opening angle of the eighth harmonic is 22.5 degrees, the cavity frequency is still too high when the height is 0.9m. In order to reduce the frequency, the method of reducing the diameter of the inner rod, increasing the width of the outer radius of the cavity, and increasing the thickness of the D plate is used to find a balance point: excessively reducing the diameter of the inner rod will reduce the frequency, but it will also reduce the mechanical Strength; although increasing the outer radius angular width of the cavity can expand the capacitance, the outer radius angular width is also limited by the physical space of the magnetic field valley area and cannot be increased excessively; increasing the thickness of the D plate can also increase the capacitance and reduce the frequency, but increasing the thickness will This leads to an increase in the total height of the cavity. Therefore, a balance point must be found: the balance point is that the cavity height decreases from 2.4m to 0.9m, the D plate opening angle decreases from 45 degrees to 22.5 degrees, and the lower limit of the inner rod diameter is 40mm. The cavity angular width is 40 degrees, and the D-plate thickness is 12mm to 14mm.

2. The design principle of accurately controlling the energy of particles at the extraction point: The difficulty is that the energy of particles near the extraction point is not necessarily the desired energy. There is always a gap between the actual energy and what we want. The present invention adopts a method of combining small phase width injection and adjusting the position of the deflection plate. Since the radial position difference of particles at the lead-out point is related to the phase width of particle injection, the role of a small phase width is to reduce the phase gap of a group of particles within the phase width range of the injection point, which also reduces the diameter of the particles at the lead-out point. The gap to the position (can be dispersed and reduced). The difficulty of extracting a small phase width is how to select the required phase extraction, because not any phase can be extracted, only a few phases can be extracted, and at the same time, the range of the small phase width must also take into account that the intensity of the extracted beam will not be reduced. If the small phase width is too narrow, the intensity of the extracted beam will decrease. Therefore, in the present invention, the phase width of the small phase width injection is set to 5 to 10 degrees. The effect of small phase width extraction is also directly related to adjusting the position of the deflection plate: during design, there is a matching relationship between which phase particles are at which extraction point, but in actual debugging, although the simulation calculation can be as much as possible Accurate, but the actual position of the particle is not the position calculated theoretically. Various error factors lead to always a gap between theory and reality. Therefore, relying solely on the small phase width still cannot get the desired position of the particle at the lead-out point. Conventional methods, due to The position of the deflection plate (where the beam is extracted) cannot be adjusted. You can only start with the phase width of the injection port. When adjusting the phase width still cannot make the particles reach the expected extraction point, you will continue to debug. This debugging process is very time-consuming and difficult. . The present invention adopts goal-oriented reverse thinking, changing the position of the deflection plate from unadjustable to adjustable, and using the adjustable position of the deflection plate to compensate for theoretical and actual errors. In short, the small phase width injection and the adjustable position of the deflection plate can solve the problem of accurately controlling the particle energy at the extraction point.

3. The design principle of α particles and H2+ particles sharing a transmission system: The first key point of dual ion sources sharing a transmission system is how to get the number and take into account the needs of the two ion sources to separate impurities. In formula (2), the relatively high mass resolution m/Δm of the two particles is taken as the common mass resolution m/Δm. For example, the mass m of α particles is 4 and Δm is 1. The mass m of H2+ particles is 2 and Δm is 1. A relatively high mass resolution is 4/1=4 instead of 2/1=2. However, the mass resolution cannot be too high, which will increase the project cost. Another key point of dual ion sources sharing a transmission system is to ensure consistent magnetic stiffness. In the present invention, the energy ratio injected is 2:1 to ensure consistent magnetic stiffness. Magnetic stiffness is related to the magnetic field and the deflection radius of the deflection magnet. When the magnetic stiffness of the two types of particles is inconsistent, even if the deflection radius of the deflection magnet for non-impurity particles is calculated by formula (2), the α particles and α particles will be caused by the inconsistent magnetic stiffness. The deflection radii of H2+ particles are different. When the deflection radius of one of them does not reach the predetermined standard, it will also affect the filtration of impurities. Therefore, the injected energy ratio is 2:1 to ensure consistent magnetic stiffness, and the two technologies of formula (2) are complementary and interdependent.

Based on the above invention principle, the present invention designs a cyclotron that can accelerate alpha particles and H2+ particles.

A cyclotron that can accelerate alpha particles and H2+ particles is shown in Figures 1 and 2. Its characteristics are: including a dual ECR ion source system 1, a dual-beam injection line transmission system 2 based on a magnetic analyzer, and a main magnet system 3 , High-frequency system based on the eighth harmonic 4. Double-beam extraction system based on precise control of deflection plates to extract α-beam energy 5;

Additional instructions:

For H2+ particles, the extraction design should be carried out and the location of the peeling film should be selected. After the particles pass through the peeling film, they become H+ particles. The radius of gyration of the orbit becomes smaller, and then they are deflected in the accelerator for one or more turns before being extracted from the accelerator. The specific number of turns depends on the extraction energy and the requirements for the beam envelope size.

The dual-beam extraction system (5) based on the precise control of the deflection plate to extract the alpha beam energy, during the accelerator design stage, strictly limits the phase width of the particles injected into the central area through the phase selector to control and reduce the energy dispersion of the extracted alpha particles. Beam loss in the extraction area; during the accelerator debugging stage, the position and voltage of the deflection plate are adjusted in real time through the host computer control system. By adjusting the position and voltage of the deflection plate, the position of the beam extraction point is accurately controlled;

Supplementary explanation: Since the nuclear-to-mass ratio q/A of α particles and H2+ particles in formula (1) is the same, the cyclotron frequencies f are nearly equal. This accelerator can realize α particles and H2+ particles without adjusting magnets and high-frequency parameters. isochronous acceleration.

Further, the H2+ particles peel off two protons through the peeling film, and the beam current intensity is twice that before peeling off, achieving high-yield production of commonly used medical isotopes;

The α particles are extracted through an electrostatic deflection plate, and the electric field of the electrostatic deflection plate can be calculated by the following formula:

Among them, q and E _k are the charge and kinetic energy of the particle respectively, ρ and η are the radius of curvature and angular width of the deflection plate respectively, and Δs is the radial deviation at the exit of the deflection plate.

Further, after the α particles and H2+ particles pass through the 30-degree analysis magnet (2-2), the α particles and H2+ particles enter the double-beam injection line transmission system (2), because they use the same set of double-beam injection lines. The beam is injected into the line transmission system (2), and the injected energy ratio is 2:1 to ensure consistent magnetic stiffness.

Additional instructions:

The high-frequency cavity opening angle of the eighth-harmonic high-frequency system (4) is θ, and the harmonic number of the accelerator is h. When using two high-frequency cavities, the energy gain obtained by the particles per revolution is Δw= 4qeV _a |sin(hθ)/2|, maximum energy gain acceleration can be achieved when the opening angle θ is 22.5 degrees, ensuring acceleration efficiency.

Further, the phase width of the small phase width injection is 5 to 10 degrees.

Further, the method of extracting a strong proton beam by stripping off H2+ includes: after passing through the stripping membrane, the particles become H+ particles, and the radius of gyration of the orbit becomes smaller, and then are deflected in the accelerator for one or more turns before being led out of the accelerator; The number of turns is determined by the extraction energy and the size of the beam envelope.

A method for achieving peak acceleration in an eighth-order harmonic high-frequency system 4, which is characterized by including the following steps:

Step 2: Set the lower limit of the inner rod diameter to 40mm;

A method for accurately controlling the beam extraction point is shown in Figure 4. It is characterized in that the method includes the following steps:

Additional explanation: Because the particles are continuously accelerated, under normal circumstances they will definitely reach the lead-out point, that is, the preset position of the deflection plate. If they cannot reach the lead-out point or the preset position of the deflection plate, it means that due to the influence of errors, before the lead-out point The beam current has been lost.

Step 3: Debug the beam and observe the radial target particle distribution;

Step 6: Extract the beam.

Example 1: Alpha particles and H ₂ ⁺ particles share a transmission system

In a cyclotron that accelerates 9 MeV/A alpha particles and 9 MeV/A H2+ particles, since the particles extracted from the ECR ion source are not all expected alpha particles or H2+ particles, a pre-analysis system is required as an impurity ion analyzer. For example, for the H2+ ion source, the particles drawn out of the outlet include H2+, H+, etc., as shown in Figure 2. H+ is deflected through the 30-degree deflection magnet into the beam collector. The angle and radius of the two-pole deflection magnet can be designed according to the mass resolution requirements, and the mass resolution can be expressed as

_Among _them _, _M After determining the energy resolution, the matrix element M _x (1,3) can be obtained, and then the specific magnetic field intensity can be obtained.

After passing through the analysis system, α particles and H2+ particles enter the double-beam merged injection line. Since they use the same injection line system, the injected energy ratio is 2:1 to ensure consistent magnetic stiffness; for example, for 40keV α particles , its magnetic stiffness is 0.02888T·m, and for 20keV H2+ particles, its magnetic stiffness is also 0.02888T·m. For a quadrupole lens, its transmission matrix can be written as:

Among them, K ² =μ ₀ G/Bρ. Under the same magnetic stiffness, the focusing characteristics of the quadrupole lens for different particles are consistent, which also achieves the effect of using the same injection line system for different particles.

Example 2: Testing the integral slip phase of α particles and H ₂ ⁺

As shown in Figure 3, after entering the central area, since the charge-to-mass ratios of α particles and H2+ particles are the same, isochronous acceleration can be achieved without changing any high-frequency parameters. The main magnet system uses a four-blade structure with a magnetic pole opening angle of 22.5 degrees. The peak magnetic field and the valley magnetic field are 1.7T and 0.4T respectively. An 8th harmonic high-frequency cavity is used for acceleration. For 9MeV/A alpha particles and The integral slip phase during acceleration of 9MeV/A H2+ particles is shown in Figure 3. It can be seen that the integral slip phase of both is less than ±10 degrees, thus completing the high-efficiency acceleration process and entering the lead-out area.

Embodiment 3: Design of the circle spacing of the lead-out area of the alpha particle deflection plate

Different types of particles enter the double extraction system for extraction. During the design process, α particles are kept at a certain distance between circles. The distance between circles can be expressed by the following formula

Δr＝Δr ₀ +Δx sin[2πn(v _r -1)+θ ₀ ]+2π(v _r -1)x cos[2πn(v _r -1)+θ ₀ ]

The first term is the natural circle spacing brought by energy gain, the second term is the circle spacing brought by resonance, and the third term is the circle spacing brought by orbital precession. Taking the 36MeVα particle as an example, the extraction radius is ~0.8m. The acceleration voltage in the lead-out area is 0.08MeV, and the estimated highest single-turn energy gain is 0.32MeV. Extract energy ~36MeV. The radial oscillation frequency of the lead-out area is ~1. Enter the formula to get the circle distance separation obtained by acceleration ~3.2mm. The circle pitch separation produced by the energy gain is slightly smaller than the radial size of the beam flow in the extraction area. In order to further increase the lead-out circle distance, the first harmonic magnetic field error can be introduced, and the resonance of v _r =1 in the lead-out area can be used to further increase the circle distance. It is estimated that a first harmonic magnetic field of 1Gs can produce about 3mm of additional ring separation, which is very easy to achieve for magnetic field padding. Through a certain circle spacing, the alpha particles enter the cutting plate and deviate from the original orbit through electrostatic high voltage. Then, the beam envelope is controlled through a series of magnetic channels and led out of the accelerator.

It should be emphasized that the above-mentioned specific embodiments are only explanations of the present invention and are not limitations of the present invention. Those skilled in the art can make modifications to the above-mentioned embodiments without creative contribution as needed after reading this specification. However, As long as the invention is within the scope of the claims, it is protected by patent law.

Claims

A cyclotron that can accelerate alpha particles and H 2 + particles, which is characterized by: including a dual ECR ion source system (1), a dual-beam injection line transmission system (2) based on a magnetic analyzer, and a main magnet system (3) , a high-frequency system based on the eighth harmonic (4), a dual-beam extraction system based on precise control of the deflection plate to extract α-beam energy (5);

The dual-beam injection line transmission system (2) is arranged between the dual-particle extraction port of the dual-ECR ion source system (1) and the lower surface of the cyclotron main magnet system (3); the main magnet system (3) is The upper and lower layers are arranged on the upper and lower sides of the cyclotron center plane. The main magnet system (3) on each side consists of four magnetic poles evenly distributed in the circumferential direction and the main magnet cover plate outside the magnetic poles. Each magnetic pole on each layer Between the magnetic pole and the magnetic pole is the magnetic field valley area; the high-frequency system (4) based on the eighth harmonic is divided into two layers and is arranged on the upper and lower sides of the cyclotron center plane, and each layer is symmetrically arranged at 180 degrees in the magnetic field valley area. Inside; the dual-beam extraction system (5) includes an α particle extraction port and an H 2 + particle extraction port respectively arranged at the outermost circle of the accelerator beam trajectory;

The cyclotron for accelerating α particles and H2+ particles shares the magnet parameters and high-frequency parameters of the double-beam injection line transmission system (2) to achieve isochronous acceleration of α particles and H2+ particles;

The dual ECR ion source system (1) includes a time-sharing α particle ion source injection system and an H 2 + particle source injection system; the double extraction system (5) includes a time-sharing α particle extraction port. , and an H2+ particle extraction port. The double extraction system (5) extracts α particles through electrostatic deflection and extracts strong proton beams through H2+ stripping;

The double-beam injection line transmission system (2) based on the magnetic analyzer is a system in which α particles and H 2 + particles use the same set of transmission lines: the beam passes through the 30-degree analysis magnet (2) of the double-beam injection line transmission system (2) 2-2) The ±30-degree dipolar magnet separates α particles and H 2 + particles with a normalized emissivity of 0.2πmm mrad. The normalized α particles and H 2 + particles pass through the front-end solenoid. (2-1), 30-degree analysis magnet (2-2), rear-stage solenoid (2-3), xy guide magnet (2-4), and buncher (2-5) are injected into the center area of the accelerator for acceleration ;The 30-degree analysis magnet (2-2) is used in the impurity ion analyzer;

The dual-beam extraction system (5) based on the precise control of the deflection plate to extract the alpha beam energy, during the accelerator design stage, strictly limits the phase width of the particles injected into the central area through the phase selector to control and reduce the energy dispersion of the extracted alpha particles. Beam loss in the extraction area; during the accelerator debugging stage, the position and voltage of the deflection plate are adjusted in real time through the host computer control system. By adjusting the position and voltage of the deflection plate, the position of the beam extraction point is accurately controlled;

In the high-frequency system (4) based on the eighth harmonic, when the same type of λ/2 double-gap coaxial cavity is selected, the cavity height is reduced by less than half, the D plate opening angle is reduced by half, and the internal The diameter of the rod, the width of the outer radius of the cavity, and the thickness of the D plate are adjusted accordingly.
A cyclotron capable of accelerating α particles and H2 + particles according to claim 1, characterized in that: realizing isochronous acceleration of α particles and H2+ particles, specifically: according to the principle of isochronic acceleration, calculate The gyration frequency of the particle is:

Among them, B is the magnetic field strength in Tesla, q is the particle charge number, and A is the particle mass number.
A cyclotron that can accelerate α particles and H2+ particles according to claim 1, characterized in that: said separation of α particles and H2+ particles with a normalized emissivity of 0.2πmm mrad includes: passing a 30-degree analysis magnet (2 -2), according to the different deflection radii and deflection angles of impurity particles and non-impurity particles in the secondary magnet, calculate the deflection angle and radius of α particles and H2+ to filter out non-α particles and H2+ impurity particles.
A cyclotron capable of accelerating α particles and H 2 + particles according to claim 3, characterized in that: filtering out non-α particles and H 2 + impurity particles, specifically: according to the mass resolution m/Δm , calculate the deflection angle and radius of α particles and H 2 + particles at the two-pole deflection magnet, and the mass resolution m/Δm is expressed as:

where m is the mass of the required particle, Δm is the mass deviation, M x is the transmission matrix of the two-pole magnet, in formula (2), Y x is the known radial amplification, and δW/W is the known beam current Energy dispersion, s 1 and s 2 are the known object slit width and image slit width respectively. The transmission matrix M The motion behind the magnet includes the deflection radius ρ 0 and the deflection angle θ, and the particles that do not belong to the deflection radius ρ 0 and the deflection angle θ are filtered out as impurities; the mass resolution of the formula (2) is m/ Δm is shared by α particles and H 2 + particles: the relatively high mass resolution m/Δm of the two particles is taken as the common mass resolution m/Δm.
A cyclotron capable of accelerating α particles and H 2 + particles according to claim 1, characterized in that: the H 2 + particles peel off two protons through a peeling film, and the beam intensity is twice that before peeling off.
A cyclotron capable of accelerating α particles and H2+ particles according to claim 5, characterized in that: after the α particles and H2+ particles pass through the 30-degree analysis magnet (2-2), the α particles and H2+ particles enter the Since the two use the same double-beam injection line transmission system (2), the injected energy ratio is 2:1 to ensure consistent magnetic stiffness.
A cyclotron capable of accelerating α particles and H 2 + particles according to claim 6, characterized in that: the height of the cavity decreases from 2.4m to 0.9m, and the D plate angle decreases from 45 degrees to 22.5 degrees; so The adaptive adjustments to the inner rod diameter, cavity outer radius angular width, and D plate thickness include: adjusting the lower limit of the inner rod diameter to 40mm, adjusting the cavity angular width to 40 degrees, and adjusting the D plate thickness to 12mm to 14mm. ; The cavity angular width of 40 degrees means that the cavity angular width increases in the last 85% radius range from the center of the cyclotron outward.
A cyclotron capable of accelerating α particles and H 2 + particles according to claim 1, characterized in that the phase width of the small phase width injection is 5 to 10 degrees.
A cyclotron capable of accelerating α particles and H 2 + particles according to claim 1, characterized in that: said eliciting a strong proton beam by stripping off H 2 + includes: after the particles pass through the stripping membrane, they become H + The radius of gyration of the particle's orbit becomes smaller, and then it is deflected in the accelerator for one or more turns before being extracted from the accelerator; the number of deflections is determined by the extraction energy and the size of the beam envelope.
A method for achieving peak acceleration based on the eighth harmonic high-frequency system (4) of a cyclotron capable of accelerating α particles and H 2 + particles according to any one of claims 1 to 9, characterized in that it includes the following step:

Step 1. Set the cavity height of the eighth harmonic high-frequency cavity to 0.9m, and the D plate opening angle to 22.5 degrees;

Step 2: Set the lower limit of the inner rod diameter to 40mm;

Step 3: Increase the angular width of the cavity to 40 degrees, leaving only space for water-cooling wiring between the magnetic pole strips of the main magnet system (3) of the cyclotron and the side of the cavity to increase the size of the cavity. Internal vacuum zone; increasing the angular width of the cavity to 40 degrees means that the angular width of the cavity is increased in the last 85% radius range from the center of the cyclotron outward;

Step 4. Set the thickness of D plate to 12mm to 14mm to increase the distributed capacitance;

Step 5: Use a nose cone-shaped accelerating electrode design to reduce useless electric field distribution and reduce losses.
A method for accurately controlling the beam extraction point based on a cyclotron capable of accelerating α particles and H 2 + particles according to any one of claims 1 to 9, characterized in that the method includes the following steps:

Step 1: Design the first harmonic amplitude phase, use resonance precession to expand the circle spacing of the beam orbit, and determine the preset position of the deflection plate; the preset position of the deflection plate is to place the deflection plate on the outermost ring and the second outer ring. between the circle beam orbits;

Step 2: Obtain the designed first harmonic distribution through magnetic field padding;

Step 3: Debug the beam and observe the radial target particle distribution;

Step 4. Check whether the beam reaches the lead-out point. If it does not reach the lead-out point, continue to step 5; if it reaches the lead-out point, go to step 6; the lead-out point is the preset position of the deflection plate;

Step 5: Adjust the deflection plate position and voltage in real time, and return to step 3;

Step 6: Extract the beam.