Pi / 2 mode standing wave accelerator tube with beam position probe and beam monitoring method

Abstract

The application provides a π / 2 mode standing wave accelerating tube containing a beam position detector and a beam monitoring method. The π / 2 mode standing wave accelerating tube containing the beam position detector comprises a plurality of radio frequency period units arranged in sequence along an axial direction, each radio frequency period unit comprises four cavities, and the four cavities are a first accelerating cavity, a first coupling cavity, a second accelerating cavity and a second coupling cavity in sequence along the axial direction; the first accelerating cavity and the second accelerating cavity are internally provided with an axial accelerating electromagnetic field for accelerating an electron beam; the first coupling cavity and the second coupling cavity are internally free of the axial accelerating electromagnetic field and are used for coupling the power of adjacent accelerating cavities; the cavity wall of the first coupling cavity and / or the second coupling cavity is embedded with the beam position detector; at least one coupling cavity in each radio frequency period unit is provided with the beam position detector; the beam pipeline of the beam position detector is collinear with a main axis of the π / 2 mode standing wave accelerating tube and is used for monitoring the beam inside the π / 2 mode standing wave accelerating tube.

Description

Technical Field

[0001] This application relates to the field of accelerator tube technology, and in particular to a π / 2 mode standing wave accelerator tube with a beam position detector and a beam monitoring method. Background Technology

[0002] In the field of industrial CT inspection, the stable transmission of the electron beam within the standing-wave accelerator tube is a core prerequisite for ensuring high dose rate and high-quality output of the X-ray source. If the beam deviates from the main axis of the accelerator tube, it will lead to energy spectrum broadening, dose loss, and X-ray quality degradation, directly affecting the resolution and detection accuracy of CT imaging. Therefore, real-time monitoring of the beam position and intensity is a key link to ensure the long-term stable operation of the system.

[0003] Currently, beam position monitoring mainly relies on external detectors or non-in-situ measurement devices, which has significant limitations: On the one hand, external detectors require additional space, which conflicts with the compactness requirements of industrial CT equipment, and the beam may be deflected twice during transmission to the external detector, resulting in deviations between the monitoring results and the actual beam state inside the accelerating tube; on the other hand, existing built-in solutions are often poorly designed (such as detector interference with the electromagnetic field of the accelerating cavity, asymmetrical electrode layout), making it difficult to achieve multi-point synchronous monitoring, and signal acquisition is affected by noise and circuit delay, resulting in insufficient peak voltage extraction accuracy, which cannot accurately reflect the real-time deflection and intensity changes of the beam.

[0004] Therefore, this invention integrates a beam position detector in the acceleration tube coupling cavity to achieve in-situ, multi-point monitoring of the beam, thus solving problems such as low monitoring accuracy, poor structural compatibility, and interference with the acceleration process in the prior art. Summary of the Invention

[0005] In view of this, this application provides a π / 2 mode standing wave accelerator tube with a beam position detector and a beam monitoring method, which can realize in-situ, multi-point monitoring of the beam by integrating the beam position detector in the coupling cavity of the accelerator tube, and solve the problems of low monitoring accuracy, poor structural compatibility and interference with the acceleration process in the prior art.

[0006] Specifically, this application is implemented through the following technical solution:

[0007] The first aspect of this application provides a π / 2 mode standing wave accelerator tube with a beam position detector. The π / 2 mode standing wave accelerator tube includes a plurality of radio frequency periodic units arranged sequentially along the axial direction. Each radio frequency periodic unit includes four cavities, which are arranged sequentially along the axial direction as a first accelerating cavity, a first coupling cavity, a second accelerating cavity, and a second coupling cavity.

[0008] The first and second acceleration cavities are equipped with axial accelerating electromagnetic fields to accelerate the electron beam.

[0009] The first and second coupling cavities have no axial accelerating electromagnetic field inside, and are used to couple the power of adjacent accelerating cavities;

[0010] A beam position detector is embedded in the cavity wall of the first coupling cavity and / or the second coupling cavity. At least one coupling cavity in each radio frequency cycle unit is provided with the beam position detector. The beam channel of the beam position detector is collinear with the main axis of the π / 2 mode standing wave accelerator tube and is used to monitor the beam inside the π / 2 mode standing wave accelerator tube.

[0011] The beam position detector of the first coupling cavity is used to measure the lateral position and current intensity of the electron beam after acceleration by the first accelerating cavity, and the beam position detector of the second coupling cavity is used to measure the lateral position and current intensity of the electron beam after acceleration by the second accelerating cavity. The beam position detectors in multiple radio frequency periodic units are combined to form a multi-point monitoring array distributed along the axial direction of the π / 2 mode standing wave accelerating tube, so as to track the entire trajectory of the electron beam from the inlet to the outlet of the π / 2 mode standing wave accelerating tube and monitor the changes in current intensity.

[0012] A second aspect of this application provides a beam monitoring method, the method being applied to any of the π / 2 mode standing wave accelerator tubes provided in the first aspect of this application, the method comprising:

[0013] When the electron beam passes through the coupling cavity of each radio frequency periodic unit sequentially along the main axis of the π / 2 mode standing wave accelerator tube, the button electrodes of the beam position detector embedded in the coupling cavity sense the electric field generated by the beam charge and generate four original voltage signals.

[0014] The four original voltage signals are filtered, pre-amplified, and converted from analog to digital to obtain four digitized voltage signal waveforms.

[0015] The voltage signal waveform is subjected to noise suppression, the maximum amplitude point in each waveform is identified, and the voltage value corresponding to the maximum amplitude point is determined as the peak voltage of each electrode.

[0016] The lateral bias position and current intensity of the beam are calculated based on the peak voltage.

[0017] Based on the calculated lateral offset position and current intensity, the beam guiding component or accelerating electromagnetic field parameters of the π / 2 mode standing wave accelerator tube are adjusted to control the beam to return to the main axis and maintain the preset current intensity.

[0018] The π / 2 mode standing wave accelerator tube and beam monitoring method with beam position detector provided in this application integrate a beam position detector in a coupling cavity without acceleration function, based on each radio frequency cycle unit as a basic module. This achieves both precise control of the local beam state and full-process tracking of the global beam path. Using the radio frequency cycle unit as the smallest monitoring unit, the beam position detector is embedded in the first and / or second coupling cavities without axial accelerating electromagnetic fields. This avoids mutual interference between the beam position detector and the electromagnetic fields of the acceleration cavities, ensuring that the core acceleration function of the accelerator tube remains unaffected. Furthermore, it allows the beam position detector to directly monitor the beam accelerated by the previous acceleration cavity. Since the beam position detector's beam channel is collinear with the main axis of the accelerator tube, measurement deviations caused by channel offset are eliminated, enabling precise capture of the lateral position and current intensity of the beam after each acceleration segment. This allows for timely detection of beam offset caused by parameter anomalies (such as electromagnetic field distortion) in a single acceleration cavity, preventing local problems from accumulating into overall failures. Simultaneously, at least one coupling cavity in each radio frequency cycle unit is equipped with a beam position detector. Multiple periodic units of detectors are sequentially distributed along the axial direction of the accelerating tube, forming a multi-point monitoring array covering the inlet to the outlet. This breaks through the limitations of traditional external or single-point monitoring, which can only acquire the state at the beginning and end of the beam. It enables full-path trajectory tracking and current intensity fluctuation monitoring of the beam from entering the accelerating tube, through multiple cycles of acceleration, to the outlet. This can quickly locate which specific RF cycle or accelerating cavity in the overall acceleration link has a problem. Furthermore, because the beam position detector has a built-in coupling cavity, no additional space is needed, which is suitable for the compactness requirements of industrial CT equipment. The in-situ monitoring mode eliminates the secondary offset error in the beam transmission process of external detectors, further ensuring the continuity and accuracy of the overall monitoring data. Ultimately, it provides full-dimensional and high-precision data support for real-time beam adjustment and accelerating tube fault diagnosis. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the π / 2 mode standing wave accelerator tube with a beam position detector provided in Embodiment 1 of this application;

[0020] Figure 2 A schematic diagram of the beam position detector provided in this application;

[0021] Figure 3 A flowchart of the beam monitoring method provided in Embodiment 2 of this application;

[0022] Figure 4 A schematic diagram of the equivalent circuit of the beam position detector provided in this application;

[0023] Figure 5 The actual pulse voltage waveform of the beam position detector provided in this application. Detailed Implementation

[0024] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application.

[0025] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used herein are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0026] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0027] The following specific embodiments are given to illustrate the technical solution of this application in detail.

[0028] Figure 1 This is a schematic diagram of the π / 2 mode standing wave accelerator tube with a beam position detector provided in Embodiment 1 of this application. Please refer to... Figure 1 The π / 2 mode standing wave accelerator tube with beam position detector provided in this embodiment includes a plurality of radio frequency periodic units arranged sequentially along the axial direction. Each radio frequency periodic unit includes four cavities, which are arranged sequentially along the axial direction as a first accelerating cavity, a first coupling cavity, a second accelerating cavity, and a second coupling cavity.

[0029] The first and second acceleration cavities are equipped with axial accelerating electromagnetic fields to accelerate the electron beam.

[0030] The first and second coupling cavities have no axial accelerating electromagnetic field inside, and are used to couple the power of adjacent accelerating cavities;

[0031] A beam position detector is embedded in the cavity wall of the first coupling cavity and / or the second coupling cavity. At least one coupling cavity in each radio frequency cycle unit is provided with the beam position detector. The beam channel of the beam position detector is collinear with the main axis of the π / 2 mode standing wave accelerator tube and is used to monitor the beam inside the π / 2 mode standing wave accelerator tube.

[0032] The beam position detector of the first coupling cavity is used to measure the lateral position and current intensity of the electron beam after acceleration by the first accelerating cavity, and the beam position detector of the second coupling cavity is used to measure the lateral position and current intensity of the electron beam after acceleration by the second accelerating cavity. The beam position detectors in multiple radio frequency periodic units are combined to form a multi-point monitoring array distributed along the axial direction of the π / 2 mode standing wave accelerating tube, so as to track the entire trajectory of the electron beam from the inlet to the outlet of the π / 2 mode standing wave accelerating tube and monitor the changes in current intensity.

[0033] For details, please refer to Figure 1 The core function of the π / 2 mode standing wave accelerator tube is to accelerate an electron beam by establishing a standing wave electromagnetic field. This allows the electrons to gain sufficient energy to bombard a target material, generating high-energy X-rays, providing a key radiation source for non-destructive testing of the internal structure of workpieces in industrial CT. The π / 2 mode refers to its characteristic radio frequency (RF) operating mode. Based on an RF cycle composed of multiple cavities, the total phase change of the standing wave electromagnetic field within each RF cycle is 2π. Through a specific cavity layout and electromagnetic field distribution, it ensures that the electron beam is accelerated synchronously with the electromagnetic field, efficiently acquiring energy.

[0034] Furthermore, the π / 2 mode standing wave accelerator tube is not a single-cavity structure, but rather composed of multiple identical radio frequency (RF) cycle units connected in series along the axial direction (the direction of electron beam movement). Through continuous acceleration over multiple cycles, the electron beam gradually reaches the high-energy state required for industrial CT. Each RF cycle unit is the basic functional unit of the accelerator tube, containing four cavities arranged sequentially along the axial direction: first accelerating cavity → first coupling cavity → second accelerating cavity → second coupling cavity. The four cavities together constitute one complete RF cycle (phase change of 2π), and the functions of each cavity are strictly divided.

[0035] Acceleration cavities (first acceleration cavity and second acceleration cavity): As the core region for beam acceleration, each cavity contains an axially distributed standing wave electromagnetic field. When the electron beam passes along the main axis of the accelerating tube, the electromagnetic field exerts an axial thrust on the electrons, accelerating them by energizing them. The phase of the electromagnetic fields in the two acceleration cavities is synchronized with the electron velocity, ensuring that the electrons can continuously gain energy in both cavities.

[0036] Coupled cavities (first coupled cavity, second coupled cavity): There is no axial accelerating electromagnetic field inside the cavity, and its core function is power coupling. That is, it transfers radio frequency energy from one accelerating cavity to another adjacent accelerating cavity through its own structure, ensuring that the standing wave electromagnetic field strength and phase of multiple accelerating cavities are consistent, and maintaining the stability of the acceleration process.

[0037] It should be noted that the integration of the beam position detector must meet three core conditions: First, it must not interfere with the core acceleration function of the accelerating tube, meaning that the beam position detector and its mounting structure must not disrupt the axial acceleration electromagnetic field distribution of the accelerating cavity to avoid affecting the synchronous acceleration of the electron beam; second, it must be compatible with the high vacuum working environment of the accelerating tube, and the connection between the beam position detector and the cavity must achieve a reliable vacuum seal to prevent leakage and beam loss; third, it must ensure monitoring accuracy, the beam channel of the detector must be strictly collinear with the main axis of the accelerating tube, and the sensing components (such as electrodes) must be close to the beam movement path to avoid data distortion due to monitoring position deviation, while not occupying too much extra space to meet the compact requirements of industrial CT equipment. This application chooses to integrate the beam position detector onto the coupling cavity, with core considerations revolving around functional compatibility and monitoring optimization: On the one hand, there is no axial accelerating electromagnetic field inside the coupling cavity, so integrating the beam position detector will not cause acceleration field distortion, fundamentally avoiding interference with beam acceleration and ensuring that the core performance of the accelerating tube is not affected; on the other hand, the coupling cavity itself has independent installation space, without the need for additional structures, which can achieve close contact between the beam position detector and the beam path while maintaining the overall compactness of the accelerating tube, and the coupling cavity is located precisely between adjacent accelerating cavities, which can directly monitor the beam state after acceleration by the previous accelerating cavity, realizing in-situ connection between acceleration and monitoring. In the future, detectors can be integrated on coupling cavities of multiple radio frequency cycles to form a multi-point monitoring array distributed along the axis, achieving full beam tracking and further improving the comprehensiveness and accuracy of monitoring.

[0038] Based on the above description, the beam position detector functions in two layers: precise local measurement and overall full-process tracking, and is deeply matched with the acceleration logic of the accelerating tube. From the perspective of a single beam position detector, its core function is to specifically measure beam parameters after a particular acceleration stage. The beam position detector in the first coupling cavity specifically measures the lateral position (i.e., the horizontal and vertical distance of the beam from the main axis of the accelerating tube) and current intensity (the beam's current strength) of the electron beam after acceleration in the first accelerating cavity. The beam position detector in the second coupling cavity specifically measures the lateral position and current intensity of the beam after acceleration in the second accelerating cavity, and can capture the beam's state changes in real time after each acceleration stage. From the perspective of the synergistic effect of multiple beam position detectors, the beam position detectors in each coupling cavity of the multiple RF cycle units distributed along the axial direction of the accelerating tube combine to form a multi-point monitoring array. Its function is to achieve full-process tracking of the electron beam, covering the complete path of the beam from the accelerating tube inlet, through multiple acceleration cycles, to the outlet. It tracks both the dynamic offset of the beam trajectory and monitors the real-time fluctuations in current intensity, providing full-link data support for subsequent beam adjustments.

[0039] Furthermore, the beam position detector is installed in the coupling cavity of the accelerating tube, specifically the cavity wall of the first coupling cavity and / or the cavity wall of the second coupling cavity. The detector can be installed only in the first coupling cavity, only in the second coupling cavity, or in both coupling cavities. Simultaneously, at least one coupling cavity in each RF cycle unit is equipped with a beam position detector, ensuring at least one monitoring node in each acceleration cycle (including both accelerating cavities), avoiding monitoring blind spots, and guaranteeing coverage of the beam state after each acceleration segment. Moreover, the beam channel of the beam position detector is collinear with the main axis of the π / 2 mode standing wave accelerating tube to eliminate monitoring errors. Since the beam channel is the path for the beam to pass through the beam position detector, its collinearity with the main axis of the accelerating tube ensures that the beam passes smoothly along the original axis of the accelerating tube, avoiding premature beam deflection due to channel offset. This ensures that the lateral position measured by the detector is the true offset state of the beam within the accelerating tube, rather than a false deviation caused by channel offset, ultimately ensuring the accuracy of the monitoring data.

[0040] The π / 2 mode standing wave accelerator tube with beam position detector provided in this embodiment has two main aspects. First, the beam position detector is embedded in the coupling cavity after each acceleration process (the first coupling cavity measures the beam accelerated by the first acceleration cavity, and the second coupling cavity measures the beam accelerated by the second acceleration cavity). The coupling cavity is free of axial accelerating electromagnetic fields, and the detector beam channel is collinear with the main axis of the accelerator tube. This fundamentally avoids electromagnetic interference from the accelerating field to the beam and beam position detector, while ensuring that the beam passes through the beam position detector along the original axis, eliminating measurement deviations caused by channel offset. Ultimately, it achieves accurate capture of the lateral position and current intensity of the beam after each acceleration process, and can promptly detect beam offset caused by parameter anomalies (such as electromagnetic field distortion) in a single acceleration cavity, preventing local problems from accumulating into overall failures. Second, the coupling cavity beam position detectors of multiple RF periodic units are sequentially distributed along the axial direction of the accelerator tube, forming a multi-point monitoring array covering the inlet to outlet, breaking away from traditional external or single-point methods. This approach overcomes the limitations of monitoring which only captures the initial and final states. It enables full-path tracking of the beam from its entry into the accelerating tube to the completion of multiple acceleration cycles and final output. It allows for real-time monitoring of the dynamic changes in the beam trajectory and the trend of current intensity fluctuations after each acceleration segment, quickly pinpointing which specific RF cycle or accelerating cavity in the overall acceleration link is experiencing a problem. Furthermore, the built-in coupling cavity of the beam position detector eliminates the need for additional space, accommodating the compact requirements of industrial CT equipment. The in-situ monitoring mode also eliminates secondary offset errors during beam transmission in external detectors, further ensuring the continuity and accuracy of the overall monitoring data. In summary, this setup, with its core approach of coupling cavity structure adaptation, corresponding acceleration segment measurement, and axial array layout, achieves both precise control of beam parameters after each acceleration segment and dynamic tracking of the overall beam state throughout the entire path. It balances measurement accuracy, monitoring completeness, and equipment compatibility, providing comprehensive data support for subsequent real-time beam adjustment and accelerating tube fault diagnosis.

[0041] Optionally, the beam position detector is a four-electrode button-type beam position detector, which includes four button electrodes, an insulating sealing assembly, and a signal extraction assembly. The four button electrodes are symmetrically distributed at 90° to the inner wall of the beam pipe with the center of the beam pipe as the reference, and the electrode surface is flush with the inner wall of the beam pipe. The insulating sealing assembly is disposed between the button electrodes and the cavity wall of the coupling cavity for vacuum sealing and electrical insulation. One end of the signal extraction assembly is connected to the button electrodes, and the other end extends to the outside of the coupling cavity for outputting electrode sensing signals.

[0042] Specifically, Figure 2 This is a schematic diagram of the beam position detector provided in this application. Please refer to... Figure 2The beam position detector is used to monitor the lateral position and current intensity of the electron beam inside a π / 2 mode standing wave accelerator tube in real time. This application specifically employs a four-electrode button-type structure, designed to adapt to the installation environment of the coupling cavity. It can accurately sense the electric field generated by the beam charge and output a characteristic signal. The four-electrode button-type beam position detector consists of four button electrodes, an insulating sealing assembly, and a signal extraction assembly. These three components work together: the button electrodes sense the beam electric field to generate a signal; the insulating sealing assembly ensures stable operation of the electrodes in a vacuum and insulating environment; and the signal extraction assembly outputs the sensed signal, collectively achieving accurate monitoring of the beam's lateral position and current intensity.

[0043] Four button-shaped electrodes serve as the core sensing components, symmetrically distributed at 90° angles (i.e., orthogonally distributed along the horizontal and vertical directions) on the inner wall of the beam channel, with the electrode surfaces flush with the inner wall. This arrangement ensures that the electrodes can uniformly sense beam deviations in different directions. When the beam deviates from the center, the induced voltage of the electrodes at different locations will differ, providing a basis for calculating the lateral position. The flush surface design avoids electrode protrusions interfering with the normal beam transmission, while ensuring a consistent distance between the beam and the electrodes, thus improving the stability of the sensed signal.

[0044] An insulating sealing assembly is positioned between the button electrode and the coupling cavity wall, with one end connected to the button electrode and the other end connected to the coupling cavity wall. Its core function is dual: firstly, it achieves vacuum sealing, preventing leakage from the high-vacuum environment inside the accelerator tube due to electrode installation (leakage would lead to beam scattering and energy loss); secondly, it provides electrical insulation, preventing electrical conduction between the button electrode and the metallic coupling cavity wall, ensuring that the electrode can independently sense and output the beam electric field signal without interference from the charged cavity wall.

[0045] One end of the signal extraction component is directly connected to the button electrode (e.g., by soldering), while the other end extends through the coupling cavity wall to the outside. Its function is to stably transmit the voltage signal sensed by the button electrode to the external acquisition system. Because the electrode signal is weak and susceptible to interference, this component must ensure the integrity of the signal transmission process to provide reliable raw data for subsequent signal processing (such as peak extraction and position calculation).

[0046] The π / 2 mode standing wave accelerator tube with beam position detector provided in this embodiment uses a four-electrode button-type detector. The four button electrodes are symmetrically distributed at 90° with respect to the center of the beam tube. This orthogonal layout can sense the beam's deviation in the horizontal and vertical directions. When the beam deviates from the center, the electrodes in the corresponding directions generate voltage differences due to their different distances from the beam, providing bidirectional data support for accurate calculation of the lateral position. This avoids the limitation of asymmetrical electrodes that can only monitor a single direction. At the same time, the electrode surface is flush with the inner wall of the beam tube, which prevents protrusions from interfering with the normal beam transmission (preventing beam scattering or energy loss) and ensures that the distance from each electrode to the beam is consistent, eliminating the induction signal deviation caused by uneven distance and improving measurement stability. An insulating sealing assembly is connected between the button electrodes and the coupling cavity wall. On the one hand, it can adapt to the high vacuum working environment of the accelerator tube and achieve reliable vacuum sealing (preventing leakage and beam loss). On the other hand, it electrically isolates the electrodes from the metal cavity wall, avoiding signal interference caused by the two conducting through electrical insulation, ensuring electrical... It can independently output pure beam sensing signals; one end of the signal extraction component is directly connected to the button electrode, and the other end extends to the outside of the coupling cavity, which can effectively extract the weak voltage signal generated by the electrode, avoiding signal attenuation or electromagnetic interference during transmission inside the accelerating tube, and providing high-quality raw data for the external acquisition system; In summary, this design of four-electrode symmetrical layout + insulated and sealed connection + external signal extraction not only utilizes the compact button structure to adapt to the limited installation space of the coupling cavity, but also takes into account the needs of accurate multi-directional beam measurement, high vacuum environment adaptation and effective signal transmission through the coordinated connection of various components. It solves the problems of beam interference, signal distortion or poor adaptability when traditional detectors are built-in, and provides reliable hardware support for in-situ monitoring of beams inside the accelerating tube.

[0047] Optionally, the button electrode is made of oxygen-free copper and the electrode surface is polished.

[0048] For details, please continue to refer to... Figure 2 Four button electrodes made of oxygen-free copper are embedded in the mounting holes to collect beam-induced signals. Oxygen-free copper has excellent conductivity, which helps to obtain stronger signal strength. The electrodes are processed into small discs (button-shaped), with their surfaces flush with the inner wall of the tube and precision polished to minimize beam impedance and vacuum disturbance.

[0049] Optionally, the insulating sealing assembly is a high-purity alumina ceramic ring, which is connected to the button electrode and the cavity wall of the coupling cavity respectively by a high-temperature active metal brazing process.

[0050] For details, please continue to refer to... Figure 2Electrical insulation and vacuum sealing are achieved between the button electrode and the grounded vacuum pipe wall through a high-purity alumina ceramic ring. The ceramic ring is connected to the electrode at one end and to the pipe wall at the other end through a high-temperature active metal brazing process, forming a robust, high-vacuum compatible, and high-insulation-resistance sealed structure.

[0051] Optionally, the signal output assembly is a coaxial feedthrough structure, including a metal inner conductor, a ceramic dielectric ring, and a stainless steel housing; one end of the metal inner conductor is welded to a button electrode, and the other end is insulated from the stainless steel housing through the ceramic dielectric ring; the stainless steel housing is sealed to the cavity wall of the coupling cavity, and the output end of the signal output assembly is provided with an SMA connector for transmitting signals.

[0052] Specifically, the signal output section employs a coaxial feedthrough design. When a charged particle beam passes through, its electromagnetic field induces a high-frequency mirror current signal on the four button electrodes. This signal is guided to the outside of the vacuum chamber through the vacuum feedthrough assembly. At the heart of the feedthrough is a metal inner conductor (typically Kovar alloy or stainless steel), whose vacuum-insulated end is reliably connected to the back of the button electrodes via micro-welding. The inner conductor is encased in a high-purity alumina ceramic dielectric ring, insulating it from the outer stainless steel casing. This casing is welded to the vacuum pipe wall and grounded. Finally, the atmospheric output of the vacuum feedthrough transmits the signal to a remote preamplifier and data acquisition system via a standard SMA coaxial connector.

[0053] Optionally, the axes of the four cavities in each radio frequency cycle unit are collinear, and the inner diameter of the cavity is adapted to the inner diameter of the beam channel.

[0054] Specifically, the four cavities refer to the first accelerating cavity, the first coupling cavity, the second accelerating cavity, and the second coupling cavity arranged sequentially along the axial direction within a single radio frequency cycle unit. The axis refers to the central axis of each cavity; collinearity means that the central axes of these four cavities completely coincide and are consistent with the main axis of the π / 2 mode standing wave accelerator tube (the preset propagation path of the beam). This ensures that the electron beam propagates in a straight line throughout the entire radio frequency cycle unit, avoiding beam collisions with cavity walls (causing energy loss and beam scattering) or deviations from the preset path (affecting subsequent acceleration and monitoring accuracy) due to misalignment of the cavity axes.

[0055] Furthermore, the beam tube is the core channel component of the beam position detector (the beam must pass through this tube to be sensed by the electrodes); adaptation refers to the inner diameter of the accelerating cavity and coupling cavity being close to or the same as the inner diameter of the beam tube, without obvious steps or abrupt changes in size. Adapting the inner diameter of the cavity to the inner diameter of the beam tube eliminates structural obstacles during beam transmission. If the difference between the inner diameter of the cavity and the beam tube is too large (e.g., the cavity is larger than the tube, or vice versa), the beam is prone to diffusion, contraction, or airflow disturbance when entering the tube from the cavity (or vice versa) (the accelerating tube is a high-vacuum environment, and abrupt changes in size may cause vacuum fluctuations). This will interfere with the stable shape of the beam and affect the uniform sensing of the beam electric field by the detector electrodes, thereby reducing the accuracy of position and current intensity measurements.

[0056] Corresponding to the aforementioned embodiment of a π / 2 mode standing wave accelerator tube with a beam position detector, this application also provides an embodiment of a beam monitoring method.

[0057] Figure 3 This is a flowchart of the beam monitoring method provided in Embodiment 2 of this application. Please refer to... Figure 3 The beam monitoring method provided in this embodiment is applied to any of the π / 2 mode standing wave accelerator tubes provided in the first aspect of this application, and the method includes:

[0058] S301. When the electron beam passes through the coupling cavity of each radio frequency periodic unit sequentially along the main axis of the π / 2 mode standing wave accelerating tube, the button electrodes of the beam position detector embedded in the coupling cavity respectively sense the electric field generated by the beam charge, generating four original voltage signals.

[0059] Specifically, when the electron beam moves along the main axis of the π / 2 mode standing wave accelerating tube and enters and passes through the first and second coupling cavities of each radio frequency periodic unit in sequence, the four button electrodes in the beam position detector embedded on the cavity wall of the coupling cavity are symmetrically distributed at 90° with the center of the beam tube as the reference. They are within the electric field range generated by the beam charge. Each button electrode senses the electric field and generates its own original voltage signal, thus forming four original voltage signals.

[0060] S302. The four original voltage signals are filtered, pre-amplified, and converted from analog to digital to obtain four digitized voltage signal waveforms.

[0061] Specifically, the four raw voltage signals (typically in the microvolt range and containing high-frequency electromagnetic interference) output from the beam position detector signal extraction component are each connected to an independent RC low-pass filter circuit. This circuit consists of a resistor (1kΩ-10kΩ) and a capacitor (1nF-10nF) connected in series, with a cutoff frequency set to 10kHz-100kHz (matching the signal characteristics of a 4.0μs beam pulse duration). The circuit attenuates high-frequency interference above the cutoff frequency (such as accelerator tube RF noise and external electromagnetic radiation), retaining the effective low-frequency signal related to the beam. The filtered four signals are then input into a non-inverting amplifier circuit composed of a low-noise operational amplifier (such as an OPA277). The amplifier is powered by a ±5V dual power supply, and the amplification factor is set to 100-1000 times based on the raw signal amplitude. The signal amplitude is boosted to the millivolt level (e.g., 0-5V). Simultaneously, the low input offset voltage and low noise characteristics of the operational amplifier are used to avoid introducing additional noise or signal distortion during amplification. The four pre-amplified analog voltage signals are then connected to a 12-bit or 16-bit resolution analog-to-digital converter (ADC, such as the ADS1115). The ADC's sampling rate is set to 1MHz (higher than the beam repetition frequency to ensure complete acquisition of a single beam pulse waveform). The amplified signal is discretely sampled through the ADC's analog input, converting the analog voltage value at each sampling moment into a corresponding binary digital value. This digital value is then transmitted to the data acquisition card via an SPI or I2C communication interface. Finally, the data acquisition card integrates these digital voltage signal waveforms according to the time sequence, generating four digital voltage signal waveforms containing voltage amplitude and time information, which are then stored in the buffer of the subsequent signal processing module.

[0062] S303. Perform noise suppression on the voltage signal waveform, identify the maximum amplitude point in each waveform, and determine the voltage value corresponding to the maximum amplitude point as the peak voltage of each electrode.

[0063] Specifically, peak voltage refers to the voltage value corresponding to the maximum amplitude point of each signal in the digital voltage signal waveform. Since the lateral offset position and current intensity of the beam are directly related to the electric field strength induced by the button electrodes, and peak voltage is a direct quantitative representation of the electric field strength, the following applies: For lateral offset position: When the beam deviates from the detector center, the distance between the button electrodes and the beam varies depending on their orientation; the closer the electrode, the higher the peak voltage induced. By comparing the differences in peak voltage between different electrodes (such as the difference in electrode combinations in the horizontal and vertical directions), the degree of beam deviation in the horizontal and vertical directions can be quantified. For current intensity: The sum of the peak voltages of the four button electrodes is linearly positively correlated with the total charge of the beam (i.e., current intensity). The stronger the beam and the greater the total charge, the larger the sum of the peak voltages induced by the electrodes; therefore, the current intensity can be accurately calculated using the sum of the peak voltages.

[0064] In specific implementation, the linear charge density distribution of the electron beam along the axial direction is determined; based on the linear charge density, the normal electric field generated on the surface of the four button electrodes when the beam passes through the beam channel of the beam position detector is calculated. The intensity of the normal electric field is related to the distance of the beam from the center of the channel, the radial angle of the electrodes, and the radius of the beam channel; according to Gauss's law, the normal electric field is integrated over the cylindrical enclosed space containing the button electrodes to convert the normal electric field into the charge induced on a single button electrode; the induced charge is converted through an RC equivalent circuit composed of the electrode and an external load resistor to obtain the induced voltage output by the electrode; based on the induced voltage, a measurable pulse voltage waveform is obtained; a moving average filtering algorithm is used to suppress noise in the pulse voltage waveform; in the noise-suppressed pulse voltage waveform, the point with the largest voltage amplitude is identified, and the voltage value corresponding to the point is determined as the peak voltage of the button electrode.

[0065] Specifically, the electron beam current intensity I and bundle length σ are measured using beam diagnostic equipment. Combined with the beam velocity v along the axial direction, a Gaussian distribution model is used to calculate the linear charge density distribution ρ(z) along the axial direction z. The horizontal offset x and vertical offset y of the beam channel center of the beam position detector are measured to determine the radial angles of the four button electrodes (0°, 90°, 180°, and 270°, with the channel center as the origin) and the channel radius R. Based on the linear charge density ρ(z), the normal electric field intensity E_n on the surface of each electrode is calculated using the electric field calculation formula. According to Gauss's law, a cylindrical enclosed space containing a single button electrode is considered, and the normal electric field E_n is integrated over the electrode surface area A to obtain the integral result, which is then used to calculate the induced charge Q on the electrode. The button electrode, external load resistor R_L, and the electrode's own parasitic capacitance C form an RC equivalent circuit. When the induced charge Q discharges through this circuit, the output voltage is obtained. The time series u(t) of this induced voltage is obtained through circuit simulation or actual measurement. Furthermore, a data acquisition card is used to continuously sample the induced voltage u(t), with the sampling duration covering the complete time the cluster passes through the electrode, obtaining pulse voltage waveform data containing time point t and the corresponding voltage value u. A moving average filtering algorithm is used to process the pulse voltage waveform, setting the sliding window size to 5 sampling points. The average voltage within the window is calculated point by point for the waveform data, replacing the original voltage value at the center of the window. This process is repeated until all data has been traversed, resulting in a smoothed waveform. The noise-suppressed pulse voltage waveform data is then traversed, and the voltage values ​​of all sampling points are compared. The point with the largest voltage amplitude is selected, and the voltage value corresponding to that point is read; this is the peak voltage of the button electrode.

[0066] For example, assuming the charge distribution of the bundle along the longitudinal direction of motion is a Gaussian distribution, its linear charge density is:

[0067] ;

[0068] in, It is the linear charge density; It is the average beam intensity. It is the RMS length of the bundle. It is the repetition frequency. It is the speed of movement of the bundle; These are the spatial coordinates along the longitudinal direction of the beam; It's time.

[0069] The beam will not pass through the center of the beam position detector; the deviation from the center position is denoted as... The normal electric field generated on the electrode surface is:

[0070] ;

[0071] in, It is the normal electric field; It is the linear charge density; It is the vacuum permittivity; It is the probe radius; It is off-center; It is the radial angle of the electrode.

[0072] Assuming the normal electric field magnitudes on the electrodes are equal, then according to Gauss's law, integrating over the closed cylindrical space containing the electrodes, we can obtain:

[0073] ;

[0074] in, It is the electric field intensity vector; It is an area element vector; It is the normal electric field; It is the electrode diameter; It is the amount of charge induced on an electrode; It is the vacuum permittivity.

[0075] Combining the above equations, we can obtain the expression for the induced charge as follows:

[0076] ;

[0077] Among them, the It is the amount of induced charge; It is the electrode diameter; It is the probe radius; It is the average beam intensity; It is the RMS length of the bundle; It is the repetition frequency; It is off-center; It is the radial angle of the electrode; It is the speed of movement of the bundle; It's time.

[0078] Figure 4 This is a schematic diagram of the equivalent circuit of the beam position detector provided in this application. C represents the electrode capacitance, and R represents the external load resistance, i.e., 50Ω for the coaxial line.

[0079] The induced voltage can be written as:

[0080] ;

[0081] in, It is induced voltage; It is an external load resistor; It is electrode capacitance; It is the imaginary unit; It is angular frequency; It is the amount of induced charge; It is time; It is the electrode diameter; It is the speed of movement of the bundle; It is the average beam intensity; It is the probe radius; It is the RMS length of the bundle; It is the repetition frequency; It is off-center; It is the radial angle of the electrode.

[0082] The measured pulse voltage is:

[0083] ;

[0084] in, It is a pulse voltage; It is an external load resistor; It is angular frequency; It is electrode capacitance; It is the electrode diameter; It is the speed of movement of the bundle; It is the average beam intensity; It is the probe radius; It is the RMS length of the bundle; It is the repetition frequency; It is off-center; It is the radial angle of the electrode; It's time.

[0085] Figure 5 The actual pulse voltage waveform of the beam position detector provided in this application is shown. Please refer to... Figure 5 The maximum value is At that location, the maximum value is:

[0086] ;

[0087] in, Peak voltage; It is an external load resistor; It is angular frequency; It is electrode capacitance; It is the electrode diameter; It is the speed of movement of the bundle; It is the average beam intensity; It is the probe radius; It is the RMS length of the bundle; It is a constant; It is the repetition frequency; It is off-center; It is the radial angle of the electrode.

[0088] S304. Calculate the lateral offset position and current intensity of the beam based on the peak voltage.

[0089] Specifically, the lateral offset position refers to the actual trajectory of the electron beam within the π / 2 mode standing wave accelerator tube, and its deviation from the main axis of the accelerator tube (the ideal propagation path preset by the beam) in a direction perpendicular to the beam's motion (axial direction). It is divided into two dimensions: horizontal and vertical. The reference point is the main axis of the accelerator tube, and its magnitude reflects the degree to which the beam deviates from the ideal path. Beam intensity, also known as current intensity, is the core parameter describing the strength of the electron beam, specifically referring to the total electron charge passing through a cross-section of the accelerator tube (such as the cross-section of the detector beam channel) per unit time.

[0090] In specific implementation, the step of calculating the lateral offset position of the beam based on the peak voltage includes: calculating the sum of the peak voltages of the first and fourth electrodes among the four button electrodes, and subtracting the sum of the peak voltages of the third and second electrodes to obtain a horizontal voltage difference; dividing the horizontal voltage difference by the sum of the peak voltages of the four electrodes to obtain a horizontal voltage ratio; multiplying the horizontal voltage ratio by a horizontal position calibration coefficient to obtain the horizontal offset position of the beam; calculating the sum of the peak voltages of the first and second electrodes among the four button electrodes, and subtracting the sum of the peak voltages of the third and fourth electrodes to obtain a vertical voltage difference; dividing the vertical voltage difference by the sum of the peak voltages of the four electrodes to obtain a vertical voltage ratio; multiplying the vertical voltage ratio by a vertical position calibration coefficient to obtain the vertical offset position of the beam; the horizontal and vertical position calibration coefficients are determined by the structural parameters of the beam position detector.

[0091] Specifically, for the horizontal direction: take the peak voltage of the first electrode and the peak voltage of the fourth electrode among the four button electrodes, and calculate their sum; take the peak voltage of the third electrode and the peak voltage of the second electrode, and calculate their sum; subtract the sum of the peak voltages of the third and second electrodes from the sum of the peak voltages of the first and fourth electrodes to obtain the horizontal voltage difference; calculate the total peak voltage of the four button electrodes (peak voltage of the first + second + third + fourth electrodes); divide the horizontal voltage difference by the total peak voltage of the four electrodes to obtain the horizontal voltage ratio; multiply the horizontal voltage ratio by the horizontal position calibration coefficient, and the result is the horizontal bias position of the beam. For the vertical direction: take the peak voltage of the first electrode and the peak voltage of the second electrode, and calculate their sum; take the peak voltage of the third electrode and the peak voltage of the fourth electrode, and calculate their sum; subtract the sum of the peak voltages of the third and fourth electrodes from the sum of the peak voltages of the first and second electrodes to obtain the vertical voltage difference; divide the vertical voltage difference by the sum of the peak voltages of the four electrodes to obtain the vertical voltage ratio; multiply the vertical voltage ratio by the vertical position calibration coefficient, and the result is the vertical offset position of the beam.

[0092] For example, the lateral offset position of the beam can be represented as:

[0093] ;

[0094] ;

[0095] Among them, the The horizontal bias position of the beam; The vertical offset position of the beam; , These are the horizontal position calibration coefficient and the vertical position calibration coefficient, respectively; , , , These are the first, second, third, and fourth electrodes, which are four button electrodes.

[0096] Optionally, the step of calculating the beam current intensity based on the peak voltage includes: calculating the sum of the peak voltages of the four button electrodes; and multiplying the sum of the peak voltages by a current intensity calibration coefficient to obtain the beam current intensity.

[0097] Specifically, the peak voltage of each of the four button electrodes is taken, the sum of these four peak voltages is calculated, and the sum of the peak voltages is multiplied by the current intensity calibration coefficient. The result is the current intensity of the beam.

[0098] For example, the current intensity of a beam can be expressed as:

[0099] ;

[0100] Among them, the The current intensity; the stated The current intensity calibration coefficient; , , , These are the first, second, third, and fourth electrodes, which are four button electrodes.

[0101] The method provided in this embodiment employs differential electrode voltage calculation (e.g., the voltage difference between the first + fourth electrodes and the second + third electrodes in the horizontal direction, and the voltage difference between the first + second electrodes and the third + fourth electrodes in the vertical direction). This effectively cancels common-mode interference such as environmental electromagnetic interference and beam position detector circuit noise (these types of interference have similar effects on the four symmetrical electrodes, and can be significantly reduced after differential calculation). Simultaneously, by normalizing the voltage difference by dividing by the sum of the total voltages, the interference of overall beam intensity fluctuations on position calculation can be eliminated (e.g., when the current intensity temporarily increases, the voltages of each electrode rise synchronously, but the voltage ratio remains stable). Furthermore, combined with calibration coefficients determined by the beam position detector structural parameters (e.g., electrode spacing, beam pipe radius), the abstract voltage signal can be correlated with the actual physical position. The system achieves precise alignment (e.g., millimeter-level offset) to realize high-precision calculation of the two-dimensional lateral offset position. When calculating the current intensity, it directly utilizes the sum of the peak voltages of the four electrodes. Since the sum of the total voltages is linearly positively correlated with the total charge of the beam per unit time (i.e., current intensity), the result can be quickly obtained through simple multiplication, avoiding the calculation delay caused by complex physical models. Furthermore, since the sum integrates the sensing signals of the four electrodes, it can average the local errors of individual electrodes (such as signal deviation caused by slight poor contact of a certain electrode), improving the stability of the current intensity calculation. At the same time, the current intensity calibration coefficient can also match the sensing sensitivity characteristics of the detector, ensuring the consistency between the calculation results and the actual beam intensity. Overall, it achieves anti-interference, accuracy, stability, and efficiency in the calculation of lateral offset position and current intensity.

[0102] S305. Based on the calculated lateral offset position and current intensity, adjust the beam guiding component or accelerating electromagnetic field parameters of the π / 2 mode standing wave accelerating tube to control the beam to return to the main axis and maintain the preset current intensity.

[0103] Specifically, the calculated horizontal and vertical beam offset positions are input into the control system of the beam guiding component. The control system outputs adjustment signals to the beam guiding component (such as deflection coils or correction electrodes) based on the offset direction (horizontal or vertical) and the magnitude of the offset. By changing the current or voltage parameters of the guiding component, a corresponding lateral correction force is generated, pushing the beam towards the main axis of the accelerating tube until the horizontal and vertical offset positions approach zero (the beam returns to the main axis). The calculated actual beam current is compared with the preset current to obtain the current deviation value. This deviation value is input into the accelerating electromagnetic field parameter adjustment system. Based on the deviation direction (actual current higher or lower than the preset value), the system adjusts the radio frequency power or electromagnetic field phase input to the first and second accelerating cavities, changing the amount of electron charge passing per unit time by enhancing or weakening the acceleration effect until the actual current stabilizes within the preset current range. The specific implementation process of the internal adjustment of the accelerating tube can be found in relevant technical descriptions and will not be elaborated here.

[0104] The method provided in this embodiment firstly uses a button electrode inside the coupling cavity to directly sense the beam electric field, ensuring that the source signal can reflect the current state of the beam in real time, providing real raw data for subsequent processing. Secondly, the four raw signals are filtered, pre-amplified, and converted from analog to digital. The processed digital waveform avoids distortion caused by noise and weak signals, laying the foundation for accurate peak identification in the third step. Thirdly, the waveform is further optimized through noise suppression, and the peak voltage is determined by locating the maximum amplitude point of each waveform, ensuring that the core data used for calculation is accurate and reliable. Fourthly, based on the peak voltage, the precise lateral offset position and current intensity are obtained by calculating using differential, normalization, and calibration coefficients, providing a clear basis for the adjustment process. Fifthly, based on the calculated beam parameters, the beam guiding components or accelerating electromagnetic field parameters are adjusted in a targeted manner, forming a closed loop of monitoring-calculation-adjustment. This close collaboration enables real-time monitoring and dynamic correction of the beam state, avoiding the lag (such as untimely signal processing affecting adjustment speed) or error accumulation (such as interference in the original signal causing calculation deviation, leading to inaccurate adjustment) caused by isolated operation of a single step. At the same time, the anti-interference design (filtering, noise suppression) and accurate calculation (application of calibration coefficients) of each step jointly improve the beam control accuracy, which can quickly pull the beam that deviates from the main axis back to the correct track and maintain the preset flow intensity, ensuring that the π / 2 mode standing wave accelerator tube stably outputs a high-quality electron beam, meeting the requirements of industrial CT for X-ray source dose rate and stability.

[0105] The method in this embodiment can be used to execute Figure 1 The steps of the device embodiment shown are similar in principle and process, and will not be repeated here.

[0106] The specific implementation process of the functions and roles of each unit in the above device can be found in the implementation process of the corresponding steps in the above method, and will not be repeated here.

[0107] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can be referred to in the description of the method embodiments. The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this application according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0108] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A π / 2 mode standing wave accelerator tube with a beam position detector, characterized in that, The π / 2 mode standing wave accelerator tube includes multiple radio frequency periodic units arranged sequentially along the axial direction. Each radio frequency periodic unit contains four cavities, which are arranged sequentially along the axial direction as a first accelerating cavity, a first coupling cavity, a second accelerating cavity, and a second coupling cavity. The first and second acceleration cavities are equipped with axial accelerating electromagnetic fields to accelerate the electron beam. The first and second coupling cavities have no axial accelerating electromagnetic field inside, and are used to couple the power of adjacent accelerating cavities; A beam position detector is embedded in the cavity wall of the first coupling cavity and / or the second coupling cavity. At least one coupling cavity in each radio frequency cycle unit is provided with the beam position detector. The beam channel of the beam position detector is collinear with the main axis of the π / 2 mode standing wave accelerator tube and is used to monitor the beam inside the π / 2 mode standing wave accelerator tube. The beam position detector of the first coupling cavity is used to measure the lateral position and current intensity of the electron beam after acceleration by the first accelerating cavity, and the beam position detector of the second coupling cavity is used to measure the lateral position and current intensity of the electron beam after acceleration by the second accelerating cavity. The beam position detectors in multiple radio frequency periodic units are combined to form a multi-point monitoring array distributed along the axial direction of the π / 2 mode standing wave accelerating tube, so as to track the entire trajectory of the electron beam from the inlet to the outlet of the π / 2 mode standing wave accelerating tube and monitor the changes in current intensity.

2. The π / 2 mode standing wave accelerator tube according to claim 1, characterized in that, The beam position detector is a four-electrode button-type beam position detector, which includes four button electrodes, an insulating sealing assembly, and a signal extraction assembly. The four button electrodes are symmetrically distributed at 90° to the inner wall of the beam channel with the center as the reference, and the electrode surfaces are flush with the inner wall of the beam channel. The insulating sealing assembly is disposed between the button electrodes and the cavity wall of the coupling cavity for vacuum sealing and electrical insulation. One end of the signal extraction assembly is connected to the button electrodes, and the other end extends to the outside of the coupling cavity for outputting electrode sensing signals.

3. The π / 2 mode standing wave accelerator tube according to claim 1, characterized in that, The button electrodes are made of oxygen-free copper, and the electrode surface is polished.

4. The π / 2 mode standing wave accelerator tube according to claim 1, characterized in that, The insulating and sealing assembly is a high-purity alumina ceramic ring, which is connected to the button electrode and the cavity wall of the coupling cavity respectively by a high-temperature active metal brazing process.

5. The π / 2 mode standing wave accelerator tube according to claim 1, characterized in that, The signal output assembly is a coaxial feedthrough structure, including a metal inner conductor, a ceramic dielectric ring, and a stainless steel shell; one end of the metal inner conductor is welded to a button electrode, and the other end is insulated from the stainless steel shell through the ceramic dielectric ring; the stainless steel shell is sealed to the cavity wall of the coupling cavity, and the output end of the signal output assembly is equipped with an SMA connector for signal transmission.

6. The π / 2 mode standing wave accelerator tube according to claim 1, characterized in that, The axes of the four cavities in each radio frequency cycle unit are collinear, and the inner diameter of the cavity is adapted to the inner diameter of the beam channel.

7. A beam monitoring method, characterized in that, The method is applied to the π / 2 mode standing wave accelerator tube according to any one of claims 1-6, and the method includes: When the electron beam passes through the coupling cavity of each radio frequency periodic unit sequentially along the main axis of the π / 2 mode standing wave accelerator tube, the button electrodes of the beam position detector embedded in the coupling cavity sense the electric field generated by the beam charge and generate four original voltage signals. The four original voltage signals are filtered, pre-amplified, and converted from analog to digital to obtain four digitized voltage signal waveforms. The voltage signal waveform is subjected to noise suppression, the maximum amplitude point in each waveform is identified, and the voltage value corresponding to the maximum amplitude point is determined as the peak voltage of each electrode. The lateral bias position and current intensity of the beam are calculated based on the peak voltage. Based on the calculated lateral offset position and current intensity, the beam guiding component or accelerating electromagnetic field parameters of the π / 2 mode standing wave accelerator tube are adjusted to control the beam to return to the main axis and maintain the preset current intensity.

8. The method according to claim 7, characterized in that, The calculation of the beam lateral offset position based on the peak voltage includes: Calculate the sum of the peak voltages of the first and fourth electrodes among the four button electrodes, and subtract the sum of the peak voltages of the third and second electrodes to obtain the voltage difference in the horizontal direction. Divide the horizontal voltage difference by the sum of the peak voltages of the four electrodes to obtain the horizontal voltage ratio. Multiplying the horizontal voltage ratio by the horizontal position calibration coefficient yields the horizontal bias position of the beam. Calculate the sum of the peak voltages of the first and second electrodes among the four button electrodes, and subtract the sum of the peak voltages of the third and fourth electrodes to obtain the voltage difference in the vertical direction. Divide the vertical voltage difference by the sum of the peak voltages of the four electrodes to obtain the vertical voltage ratio. The vertical voltage ratio is multiplied by the vertical position calibration coefficient to obtain the vertical offset position of the beam; the horizontal and vertical position calibration coefficients are determined by the structural parameters of the beam position detector.

9. The method according to claim 7, characterized in that, The calculation of the beam current intensity based on the peak voltage includes: Calculate the sum of the peak voltages of the four button electrodes; The beam current intensity is obtained by multiplying the sum of the peak voltages by the current intensity calibration coefficient.

10. The method according to claim 7, characterized in that, The step of noise suppression of the voltage signal waveform, identifying the maximum amplitude point in each waveform, and determining the voltage value corresponding to the maximum amplitude point as the peak voltage of each electrode includes: Determine the linear charge density distribution when the electron beam moves along the axial direction; Based on the linear charge density, the normal electric field generated on the surface of the four button electrodes when the beam passes through the beam channel of the beam position detector is calculated. The strength of the normal electric field is related to the distance of the beam from the center of the channel, the radial angle of the electrodes, and the radius of the beam channel. According to Gauss's theorem, integrating over the cylindrical enclosed space containing the button electrodes converts the normal electric field into the amount of charge induced on a single button electrode. The induced charge is converted through an RC equivalent circuit consisting of the electrode and an external load resistor to obtain the induced voltage output by the electrode. Based on the induced voltage, a measurable pulse voltage waveform is obtained; The pulse voltage waveform is noise suppressed by a moving average filtering algorithm. In the noise-suppressed pulse voltage waveform, the point with the largest voltage amplitude is identified, and the voltage value corresponding to the point is determined as the peak voltage of the button electrode.

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