Particle accelerator radio frequency cavity frequency tuning system and method

Abstract

The application provides a particle accelerator RF cavity frequency tuning system and method. The system comprises an RF cavity, a D-shaped plate electrode arranged in the cavity, and at least one set of radial capacitance tuning components, which are arranged on one side of the tail of the D-shaped plate electrode, and comprise a tail coupling disc, a tuning rod with a head coupling plate, and a driving assembly. The distance between the two coupling discs is changed by driving the axial movement of the tuning rod, the distributed capacitance is adjusted, and frequency tuning is realized. The tuning components are arranged on one side of the tail of the D-shaped plate, which has high space adaptability, simple and reliable structure, low cost, and is suitable for compact accelerators with limited ESD structure, and can realize high-precision frequency locking in cooperation with a closed loop.

Description

Technical Field

[0001] This invention relates to the field of particle accelerator technology, and more specifically to a frequency tuning system and method for a particle accelerator radio frequency cavity. Background Technology

[0002] Particle accelerators are crucial equipment in modern scientific research and industrial applications, particularly in medical treatment (such as proton / heavy ion cancer therapy). Their core component—the radio frequency (RF) cavity—is used to generate a high-frequency electric field to accelerate charged particles. The RF cavity is essentially a resonant cavity, and its resonant frequency is determined by the cavity's geometry, dimensions, and internal dielectric material. To achieve efficient microwave power feeding and stable particle beam acceleration, the excitation frequency of the RF power supply must be precisely matched to the cavity's intrinsic resonant frequency and remain highly stable.

[0003] However, during actual accelerator operation, the radio frequency cavity faces various factors that cause resonant frequency drift, including but not limited to: thermal deformation of the cavity conductor due to radio frequency power loss, power supply voltage fluctuations, and beam load variations. Therefore, a frequency tuning device must be equipped to precisely lock the cavity frequency to the preset operating frequency in real time.

[0004] Various radio frequency cavity tuning schemes have been developed in the existing technology, mainly including: Dual-sided mechanical tuning: This method changes the equivalent inductance or capacitance of the cavity by symmetrically placing tuning mechanisms (such as moving short-circuit plates or tuning rods) on both sides of the cavity. This type of solution has a complex structure, requires a large amount of space on both sides of the cavity, and has many moving parts, increasing the number of potential failure points.

[0005] Airbag tuning: This method uses an inflated and deflated airbag to drive the movement of tuning elements. However, this method has a slow response time, the airbag material is prone to fatigue and leakage, and its long-term reliability is insufficient.

[0006] Piezoelectric ceramic tuning: This method utilizes the inverse piezoelectric effect of piezoelectric ceramics to achieve micro-displacement adjustment, offering fast response and high precision. However, its adjustment stroke is typically very small (micrometer level), resulting in high cost and susceptibility to radiation.

[0007] Temperature control system tuning: This method compensates for thermally induced frequency drift by precisely controlling the temperature of the coolant in the cavity. However, it suffers from significant response hysteresis and can only compensate for slow temperature drifts, failing to address transient or wide-range frequency deviations.

[0008] Capacitor plate spacing tuning: In recent years, researchers have adjusted the distributed capacitance by changing the spacing between the tuning capacitor plate and the cavity D-shaped plate, thereby achieving frequency tuning (e.g., Chinese patent application CN202311106758.X). This type of solution has a simpler structure than the above-mentioned methods. However, this type of solution places the tuning capacitor plate on the side of the D-shaped plate, which results in insufficient side space in compact structures with electrostatic deflectors (ESDs); moreover, it does not disclose or imply a technical concept of placing the tuning component on only one side of the tail of the D-shaped plate to utilize the narrow axial space.

[0009] In summary, existing RF cavity frequency tuning technologies struggle to achieve a good balance between structural simplicity, spatial adaptability, dynamic response, and cost-effectiveness, and in particular, lack a solution that can achieve reliable and efficient tuning within the extremely limited space of a single tail section. Summary of the Invention

[0010] The present invention aims to provide a particle accelerator radio frequency cavity frequency tuning system and method that can achieve reliable and efficient tuning in an extremely limited single-sided tail space, in order to solve the problem that existing radio frequency cavity frequency tuning technology is difficult to achieve a good balance between structural simplicity, spatial adaptability, dynamic response and cost-effectiveness.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a frequency tuning system for a particle accelerator radio frequency cavity, comprising: The radio frequency cavity has D-shaped plate electrodes inside. At least one set of radial capacitor tuning components, wherein the radial capacitor tuning components are only disposed on one side of the tail of the D-shaped plate electrode; The radial capacitance tuning assembly includes: a tail coupling disk, which is fixedly disposed relative to the tail of the D-shaped plate electrode; a tuning rod, the end of which is provided with a head coupling plate, the head coupling plate and the tail coupling disk being disposed opposite to each other and spaced apart, forming a capacitive coupling gap between them; and a driving assembly, which is used to drive the tuning rod to move along its axial direction to change the distance between the head coupling plate and the tail coupling disk, thereby changing the distributed capacitance between them and realizing the adjustment of the resonant frequency of the radio frequency cavity.

[0012] Furthermore, both the tail coupling disk and the head coupling plate are annular disk structures and are coaxially arranged to optimize capacitive coupling efficiency and the uniformity of electromagnetic field distribution.

[0013] Furthermore, the drive component is a linear stepper motor, a servo motor, or an electric push cylinder to achieve precise axial displacement control.

[0014] Furthermore, the system also includes: a displacement sensor for real-time detection of the distance between the head coupling plate and the tail coupling disk; a capacitance detection unit for real-time detection of the equivalent capacitance value corresponding to the capacitive coupling gap; and a controller connected to the displacement sensor, the capacitance detection unit, and the drive assembly, respectively, for closed-loop control of the drive assembly's operation based on the deviation between the detected distance and the equivalent capacitance value and the target value.

[0015] Furthermore, the tail coupling plate and the head coupling plate are provided with cooling channels to remove the heat generated by radio frequency loss and improve the thermal stability of the system.

[0016] Furthermore, the tail end of the D-shaped plate electrode is provided with two or more sets of radial capacitor tuning components connected in parallel to expand the tuning range or achieve redundancy backup.

[0017] The present invention also provides a method for tuning the radio frequency cavity frequency of a particle accelerator based on the above system, comprising the following steps: S1. Obtain the actual resonant frequency of the current radio frequency cavity and calculate the frequency error between it and the target resonant frequency. S2. Determine the target distance between the head coupling plate and the tail coupling disk based on the frequency error; S3. Drive the tuning rod to move axially through the driving component, adjust the actual distance between the head coupling plate and the tail coupling disk to the target distance, thereby changing the distributed capacitance between them, so that the actual resonant frequency of the radio frequency cavity approaches the target resonant frequency.

[0018] Further, in step S2, the target spacing is calculated according to a preset frequency-spacing mapping model or empirical formula.

[0019] Furthermore, after step S3, a closed-loop fine-tuning step is also included: real-time monitoring of the actual resonant frequency after tuning; if a frequency error still exists, steps S2 and S3 are repeated until the frequency error falls within the allowable range.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention places the radial capacitor tuning component only on one side of the tail of the D-shaped plate electrode, making full use of the narrow space in the axial direction and effectively avoiding the space limitations of structures such as side electrostatic deflectors (ESD). It is particularly suitable for scenarios with extremely limited space, such as the 30A accelerator, and solves the problem that conventional tuning components cannot be installed in the prior art.

[0021] 2. The present invention has a simple and reliable structure. Compared with dual-sided mechanical tuning or airbag / fluid tuning schemes, the number of moving parts is significantly reduced, which reduces the complexity of design, manufacturing and assembly, reduces potential failure points, and improves the long-term operational reliability of the system. Moreover, the required materials, processing technology and control system complexity are reduced, and the initial investment and long-term maintenance costs are significantly reduced, providing an economical and efficient engineering solution.

[0022] 3. This invention directly adjusts the spacing between the coupling disks through the driving component, which provides a rapid response to frequency drift (especially thermal drift); at the same time, the structure of this solution is clear and easy to integrate, and with closed-loop control, it can achieve high-precision frequency locking, and has a high degree of engineering feasibility. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the radio frequency cavity tuning component of the particle accelerator of the present invention; Figure 2 This is a schematic diagram of the structure of the D-shaped plate electrode (pseudo-Dee plate) of the present invention; Figure 3 This is a schematic diagram of the curve showing the change of the resonant frequency of the present invention with the distance between the head coupling plate and the tail coupling disk. In the diagram: 1. D-shaped plate electrode; 2. Tail coupling plate; 3. Tuning rod; 4. Head coupling plate; 5. Drive assembly; 6. Vacuum bellows; 7. Cavity sealing plate; 8. Tuning fixed guide shaft; 9. Tuning limit rod; 10. Displacement sensor; Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The illustrative embodiments and descriptions of this invention are for illustrative purposes only and are not intended to limit the invention.

[0025] Example 1: Particle accelerator radio frequency cavity frequency tuning system This embodiment provides a frequency tuning system for a particle accelerator radio frequency cavity. The system includes: a radio frequency cavity, a D-shaped plate electrode 1 (a dummy Dee plate) disposed inside the radio frequency cavity, and at least one set of radial capacitor tuning components. The radial capacitor tuning components are only disposed on one side of the tail end of the D-shaped plate electrode 1 to fully utilize the axial space and avoid interference with structures such as electrostatic deflectors (ESDs) on the side. Figure 2 As shown, the tail of the D-shaped plate electrode 1 is provided with a tail coupling disk 2 opposite to it; preferably, the tail coupling disk 2 and the D-shaped plate electrode 1 are made of the same metal material (such as oxygen-free copper) and are fixed by screws or welding to ensure good electrical connection.

[0026] Furthermore, such as Figure 1As shown, the radial capacitor tuning assembly specifically includes: Tuning lever 3: Its end is provided with a head coupling plate 4. In specific operation, the head coupling plate 4 is positioned opposite and spaced apart from the tail coupling disk 2, forming a capacitive coupling gap between them. The width of this gap is denoted as... (Unit: mm)

[0027] Drive assembly 5: Used to drive the tuning lever 3 along its axial direction ( Figure 1 The horizontal movement changes the spacing between the coupling disks. The drive component 5 is preferably a linear stepper motor, a servo motor, or an electric push cylinder, and is equipped with a high-precision ball screw to achieve micron-level displacement control.

[0028] To prevent vacuum leakage, a vacuum bellows 6 is provided where the tuning rod 3 passes through the wall panel of the radio frequency cavity. One end of the bellows 6 is connected to the cavity sealing plate 7, and the other end is connected to the moving part of the tuning rod 3 or the drive assembly 5, to ensure that the cavity is always kept in a high vacuum state when the tuning rod 3 moves axially.

[0029] As a further optimization, the head coupling plates 4 are all designed with an arc-shaped structure and are coaxially arranged with the tail coupling disk. This arc-shaped structure can form an arc-shaped distributed capacitance, making the electric field distribution more uniform and avoiding the risk of arcing caused by local electric field concentration.

[0030] When the drive component pushes the tuning lever 3 to move, the spacing... When the capacitance C decreases, the distributed capacitance C between the tail coupling plate 2 and the head coupling plate 4 increases, and the resonant frequency of the RF cavity decreases. The corresponding reduction; conversely, when the spacing As the capacitance C increases, the distributed capacitance C decreases, and the resonant frequency decreases. The relationship between the frequency change and the spacing change is non-linear, but it can be approximated as linear within a small range.

[0031] To further improve the guiding accuracy and reliability of the axial movement of the tuning rod 3, this embodiment also includes a guiding and limiting structure; specifically, it includes a tuning fixed guide shaft 8 and a tuning limiting rod 9.

[0032] The tuning guide shaft 8 is located at the moving end of the drive assembly 5 and is connected to the tuning rod 3 via a coupling. The outer wall of the tuning guide shaft 8 mates with a guide sleeve, which is fixedly mounted on an inner mounting plate of the RF cavity. The guide shaft and the guide sleeve employ a precision sliding fit, which effectively constrains the radial wobble of the tuning rod 3 during axial movement, ensuring that the tail coupling plate 2 and the head coupling plate 4 remain coaxially aligned, thus preventing unstable capacitive coupling or localized arcing due to eccentricity.

[0033] The tuning limit rod 9 is fixedly installed on the cavity sealing plate 7. The tuning limit rod 9 is arranged along the axial direction of the tuning rod 3, and its end is provided with a mechanical stop or buffer pad. At the same time, a limiting fitting part (such as a limiting block or limiting ring) is provided at a corresponding position on the mounting support plate. When the tuning rod 3 moves to the preset maximum stroke endpoint, the limiting fitting part abuts against the end of the tuning limit rod 9, thereby limiting the further movement of the tuning rod 3 and preventing the head coupling plate 4 and the tail coupling disk 2 from getting too close and colliding or being damaged. In addition, the position of the tuning limit rod 9 can be finely adjusted according to the actual tuning range (for example, by adjusting and locking with threads) to adapt to the tuning stroke requirements of different accelerators.

[0034] Furthermore, to further improve the system's tuning accuracy and automation level, this embodiment also includes a closed-loop control module. Specifically: Displacement sensor 10: Mounted on the drive assembly, used to detect the actual distance between the head coupling plate 4 and the tail coupling disk 2 in real time. The displacement sensor can be a laser displacement sensor, a grating ruler, or a magnetostrictive displacement sensor, with a resolution better than 1 μm.

[0035] Capacitance detection unit (not shown in the figure): can be connected in parallel across the capacitor coupling gap for real-time detection of the equivalent capacitance value C. This unit can employ a high-frequency capacitance measurement circuit with an operating frequency between 1MHz and 10MHz to improve anti-interference capability.

[0036] The controller is electrically connected to the displacement sensor, capacitance detection unit, and drive assembly. It contains a pre-stored frequency-spacing mapping model or empirical formula, and calculates the target spacing based on the deviation between the current cavity frequency and the target frequency. Then, a drive signal is output through a PID control algorithm to control the movement of the drive component until the actual distance is reached. equal (or within the allowable error range).

[0037] Optionally, cooling channels are provided inside the tail coupling plate 2 and the head coupling plate 4. The cooling channels are connected to an external water chiller, through which deionized water is introduced at a flow rate controlled at 1–5 L / min, and the inlet water temperature is set at 25 ± 0.5 °C. Since RF loss generates heat on the surface of the coupling plate, the cooling channels can effectively remove heat, reduce thermal deformation and frequency drift, and improve the long-term stability of the system.

[0038] To extend the tuning range or achieve redundancy, two or more sets of radial capacitance tuning components connected in parallel can be provided at the tail of the D-shaped plate electrode 1. For example, the main tuning component is used for coarse tuning over a large range, and the auxiliary tuning component is used for fine tuning over a small range; or both sets can operate simultaneously to increase the total capacitance change.

[0039] Example 2: Frequency Tuning Method for Particle Accelerator Radio Frequency Cavity This embodiment provides a method for tuning the radio frequency cavity of a particle accelerator based on the above system, including the following steps: S1. Obtaining Frequency Error: The electric field signal inside the RF cavity is sampled in real time using a coupling loop or probe, and the actual resonant frequency is measured by a frequency meter or phase-locked loop circuit. The controller reads the preset target frequency. (Typically the operating frequency of the accelerator, such as 91.5MHz for the 30A accelerator), calculate the frequency error. (Unit: Hz).

[0040] S2. Determine the target spacing: based on frequency error. The target spacing between the head coupling plate and the tail coupling disk is calculated using a preset frequency-spacing mapping model. This mapping model can be obtained through theoretical simulation or calibration experiments. A simplified approximation formula is: (1); In formula (1): The initial spacing (mm) corresponds to Nominal position at time; The tuning sensitivity coefficient (mm / Hz) has a sign determined by the system design: when When the actual frequency is too high, the distributed capacitance needs to be increased to lower the frequency; therefore, the spacing should be reduced. ,at this time It is negative; otherwise It is a positive value. In practical applications, It is usually a negative constant, and its absolute value is usually in the range of 1000-1000. ~ The speed is on the order of mm / Hz, and the specific value is determined by the electromagnetic design parameters of the cavity.

[0041] For greater accuracy, piecewise linear interpolation models or high-order polynomial models based on electromagnetic field simulation data can be used. For example: (2); In formula (2): , , The fitting coefficients are obtained by scanning the cavity frequencies at different spacings using finite element simulation (such as CST Microwave Studio).

[0042] S3. Execute Spacing Adjustment: The controller issues a control command, and the drive component moves the tuning lever axially to adjust the actual spacing. Adjust to During the driving process, the displacement sensor provides real-time feedback of the actual position, forming a position closed loop. When the actual distance is... When the deviation is less than ±1μm, the drive stops.

[0043] S4. Closed-loop fine-tuning (optional step): After completing one coarse adjustment, remeasure the actual resonant frequency. .like If the error is still greater than the allowable error (e.g., ±1kHz), repeat steps S2 and S3 for iterative fine-tuning until the frequency error falls within the allowable range. This iterative process can usually be completed within 1 to 3 cycles, with each cycle taking less than 0.5 seconds.

[0044] This method is particularly suitable for particle accelerators with space constraints due to electrostatic deflector (ESD) structures, such as the 30A medical superconducting cyclotron. In these accelerators, the single-sided tail of the D-shaped plate electrode is the only available space for mounting the tuning components. This invention arranges the radial capacitor tuning assembly only on this single-sided tail, eliminating the need for space on both sides and avoiding the occupation of side areas, thus possessing irreplaceable engineering value.

[0045] Example 3: A specific engineering case (tuning parameters of the 30A accelerator) Taking the 30A medical superconducting cyclotron accelerator as an example, its main parameters are as follows: operating frequency: 91.5 MHz; tuning range requirement: ±150 kHz; tail coupling disk outer diameter: 80 mm, inner diameter: 50 mm, thickness: 5 mm; head coupling plate outer diameter: 78 mm, inner diameter: 52 mm, thickness: 4 mm; initial spacing 2.0 mm; Tuning sensitivity The simulation calibration result is -0.008 mm / kHz (meaning the spacing needs to be reduced by 0.008 mm for every 1 kHz increase in frequency); the drive component is a linear stepper motor with a step angle of 0.9°, a lead screw of 2 mm, and a minimum displacement step of 0.5 μm; the displacement sensor is a magnetostrictive type with a resolution of 0.1 μm; and the vacuum bellows is a single-layer 316L stainless steel bellows with a compression of ±5 mm and a lifespan greater than 10 years. 6 Second-rate.

[0046] In actual operation, when the cavity frequency drifts down by 80 kHz due to radio frequency heating, the controller... The target distance was calculated at -80 kHz. = 2.0mm + (-0.008 mm / kHz)×(-80 kHz) = 2.0 +0.64 = 2.64 mm. The drive assembly pushes the tuning lever to the right by 0.64 mm, and the actual frequency rises back to around 91.5 MHz, with an error of less than ±2 kHz, which meets the accelerator operation requirements.

[0047] like Figure 3 As shown, the particle accelerator radio frequency cavity frequency tuning system and method provided by this invention has a simple structure and excellent spatial adaptability, making it particularly suitable for replacing traditional dual-sided or gasbag tuning schemes in compact superconducting cyclotron accelerators. It has low manufacturing costs, is easy to maintain, and can be combined with closed-loop control to achieve high-precision, high-reliability automatic frequency locking, demonstrating significant industrial practical value and economic benefits.

[0048] The above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A frequency tuning system for a particle accelerator radio frequency cavity, characterized in that, include: The radio frequency cavity has D-shaped plate electrodes inside. At least one set of radial capacitor tuning components, wherein the radial capacitor tuning components are only disposed on one side of the tail of the D-shaped plate electrode; The radial capacitance tuning assembly includes: The tail coupling disk is fixedly disposed relative to the tail of the D-shaped plate electrode; The tuning rod has a head coupling plate at its end. The head coupling plate is opposite to and spaced apart from the tail coupling plate, and a capacitive coupling gap is formed between them. A driving component is used to drive the tuning rod to move along its axial direction to change the distance between the head coupling plate and the tail coupling disk, thereby changing the distributed capacitance between them and adjusting the resonant frequency of the radio frequency cavity.

2. The particle accelerator radio frequency cavity frequency tuning system according to claim 1, characterized in that, Both the tail coupling disk and the head coupling plate are annular disk structures and are coaxially arranged.

3. The particle accelerator radio frequency cavity frequency tuning system according to claim 1, characterized in that, The drive component is a linear stepper motor, a servo motor, or an electric push cylinder.

4. The particle accelerator radio frequency cavity frequency tuning system according to claim 1, characterized in that, Also includes: A displacement sensor is used to detect the distance between the head coupling plate and the tail coupling disk in real time. The capacitance detection unit is used to detect the equivalent capacitance value corresponding to the capacitive coupling gap in real time. The controller is connected to the displacement sensor, the capacitance detection unit, and the drive assembly, respectively, and is used to perform closed-loop control of the drive assembly based on the deviation between the detected spacing and the equivalent capacitance value and the target value.

5. The particle accelerator radio frequency cavity frequency tuning system according to claim 1, characterized in that, The tail coupling plate and the head coupling plate are provided with cooling channels inside.

6. The particle accelerator radio frequency cavity frequency tuning system according to claim 1, characterized in that, The tail end of the D-shaped plate electrode is provided with two or more sets of radial capacitor tuning components connected in parallel.

7. A method for tuning the radio frequency cavity frequency of a particle accelerator based on the system according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Obtain the actual resonant frequency of the current radio frequency cavity and calculate the frequency error between it and the target resonant frequency. S2. Determine the target distance between the head coupling plate and the tail coupling disk based on the frequency error; S3. Drive the tuning rod to move axially through the driving component, adjust the actual distance between the head coupling plate and the tail coupling disk to the target distance, thereby changing the distributed capacitance between them, so that the actual resonant frequency of the radio frequency cavity approaches the target resonant frequency.

8. The particle accelerator radio frequency cavity frequency tuning method according to claim 7, characterized in that, In step S2, the target spacing is calculated according to a preset frequency-spacing mapping model or empirical formula.

9. The particle accelerator radio frequency cavity frequency tuning method according to claim 7, characterized in that, Step S3 is followed by a closed-loop fine-tuning step: The actual resonant frequency after tuning is monitored in real time. If a frequency error still exists, steps S2 and S3 are repeated until the frequency error falls within the allowable range.

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