Micro-focus CT bulb tube based on laser trigger cathode and quadrupole magnetic focusing and working method of micro-focus CT bulb tube

Abstract

The invention relates to a micro-focus CT bulb tube based on a laser trigger cathode and quadrupole magnetic focusing and a working method of the micro-focus CT bulb tube, which are applied to the technical field of CT bulb tubes and comprise a vacuum tube shell, a gallium nitride cathode system arranged in the vacuum tube shell, a laser trigger system, a quadrupole magnetic focusing system, a rotating target structure and a ray window, by adopting the gallium nitride annular cathode film and the laser trigger system, an electron emission mechanism with low power consumption and high response rate is realized; by arranging a quadrupole magnetic focusing structure, the focus position and size of the electron beam are effectively controlled; the rotary tungsten-rhenium target disc is used for enhancing the thermal load bearing capacity and improving the X-ray yield; the high vacuum environment and the dynamic thermal modeling feedback strategy are combined, the technical problems of a traditional micro-focus CT bulb tube in response speed, focus stability and thermal management are solved, the imaging resolution and the system reliability are remarkably improved, and the method is suitable for the field of high-precision medical and industrial nondestructive testing.

Description

Technical Field

[0001] The present application relates to the technical field of CT tubes, and in particular to a microfocus CT tube based on a laser-triggered cathode and quadrupole magnetic focusing and a working method thereof. Background Art

[0002] Microfocus CT tubes are widely used in high-resolution imaging, particularly in medical diagnosis and industrial nondestructive testing, offering the technical advantage of high-precision imaging. Conventional microfocus CT tubes typically rely on a thermal emission cathode to generate electrons, which are then focused onto the target using an electrostatic focusing system to produce X-rays. However, existing technology has significant limitations in several key areas, hindering its development in high-performance applications.

[0003] First, in terms of electron emission performance, traditional thermal emission cathodes suffer from long startup delays, high operating temperatures, low emission efficiency, and short lifespans, making them difficult to meet the demands of high-frequency, high-precision imaging. Second, in terms of power carrying capacity, due to irrational heat dissipation structure design, traditional tubes are prone to heat accumulation under long-term high-power operating conditions, resulting in unstable X-ray output and even damage to key components. Furthermore, to maintain focal spot size stability and image resolution, the tube requires a high level of stability in the focusing system, but existing electrostatic focusing designs struggle to meet the dual demands of high precision and compactness.

[0004] In order to solve the above technical difficulties, some studies have attempted to introduce improved launch materials, rotating target designs and more efficient heat dissipation structures. However, there are common problems such as complex structure, high cost and difficulty in system integration, and a mature engineering solution has not yet been formed.

[0005] Therefore, there is an urgent need for a new type of microfocus CT tube with optimized design in terms of electron emission mechanism, heat dissipation capacity and focusing system, so as to achieve higher power density, more stable electron emission and better X-ray quality, thereby improving the overall imaging quality and system adaptability, and expanding its application in high-end fields such as medical and industrial testing. Summary of the Invention

[0006] The object of the present invention is to provide a microfocus CT tube based on laser-triggered cathode and quadrupole magnetic focusing and its operating method, so as to solve the above-mentioned technical problems.

[0007] Technical solution: A microfocus CT tube based on laser-triggered cathode and quadrupole magnetic focusing is provided, comprising: a vacuum tube shell, a cathode system arranged inside the vacuum tube shell, a laser triggering system, a quadrupole magnetic focusing system, a rotating target structure, a ray window, and a control system electrically or mechanically connected to the above components; the cathode system comprises an annular cathode film arranged on the inner surface of a quartz shell, and the quartz shell is fixedly mounted on the inner wall of one end of the vacuum tube shell; the laser triggering system is located outside the cathode system, and the laser emits a laser beam toward the cathode film; the quadrupole magnetic focusing system is arranged on the cathode The laser trigger system is arranged between the laser trigger system and the rotating target structure, and is arranged around the electron beam propagation path, and is used to focus the electron beam before it enters the rotating target structure; the rotating target structure includes a target disk arranged at the other end of the vacuum tube shell, and the target disk is horizontally installed on a rotating shaft, and the rotating shaft is connected to a motor to drive it to rotate; the ray window is arranged in front of the electron beam bombardment area of the target disk on the side wall of the vacuum tube shell, which is corresponding to the target disk, and is used to output the generated X-rays; the control system is respectively connected to the laser trigger system, the quadrupole magnetic focusing system and the rotating target structure by signal or electrical connection, and is used to coordinately control the electron emission, focusing and target disk rotation processes.

[0008] In one possible embodiment, the cathode film in the cathode system is made of gallium nitride material and is plated on the inner wall of a hollow quartz cylindrical shell. The quartz shell is mounted on one end of the vacuum tube shell and fixed and sealed by high-temperature glass sealing or metal welding.

[0009] In one possible implementation, the laser triggering system includes a laser, a laser guide mirror assembly, and an optical fiber output end. The laser is externally mounted outside the vacuum tube shell, and the laser is guided into the location of the cathode system through an optical guide assembly.

[0010] In one possible embodiment, the quadrupole magnetic focusing system includes four groups of magnetic coils symmetrically distributed around the electron beam channel. Each magnetic coil is mounted on a magnetic pole frame and connected to a control system via a powered cable to form a magnetic field distribution perpendicular to the direction of the electron beam.

[0011] In a possible embodiment, the target disk in the rotating target structure is made of a tungsten-rhenium alloy and is fixed on a rotating shaft. The rotating shaft is supported by a bearing device and is driven to rotate by a motor disposed outside the vacuum tube shell.

[0012] In a possible implementation, the rotating shaft passes through a rotating sealing component at the bottom of the vacuum tube shell and is connected to an external motor, and the sealing component is a ceramic-based or magnetic fluid sealing structure.

[0013] In a possible implementation, the ray window is made of beryllium material and welded to the side wall of the vacuum tube shell where the window is located, with its center aligned with the emission direction of the electron beam bombardment area of the target disk.

[0014] In one possible embodiment, the interior of the vacuum tube is evacuated to 10⁻ by a molecular pump or an ion pump. 6 Pa and maintain a stable high vacuum during operation.

[0015] In one possible embodiment, a method for operating the microfocus CT tube is provided, comprising the following steps: Step 1: a control system activates a laser trigger system to emit a laser pulse toward a gallium nitride cathode on the inner wall of a quartz shell, thereby inducing electron emission; Step 2: During the electron emission process, the control system models and optimizes the emission performance based on the following algorithm; Step 3: The electron beam is focused to a micro-spot area on the target disk when passing through the quadrupole magnetic focusing system, and the magnetic field strength and the degree of electron beam deviation are simultaneously evaluated to ensure focusing accuracy; Step 4: The electron beam bombards the surface of the rotating target disk to generate rays; Step 5: The rays are emitted through the ray window to achieve imaging or detection functions.

[0016] In a possible implementation, step 2 includes the following steps: Step 2.1, collecting laser wavelength, power density, pulse width and cathode material parameters; Step 2.2, calculate the single photon energy, determine the minimum absorption number in the multi-photon absorption mode, and calculate the electron kinetic energy; Step 2.3, calculate the electron emission efficiency based on the fitting model; Step 2.4: Build a heat conduction model to simulate the cathode temperature distribution and output the cathode temperature; Step 2.5: Feedback the results to the control system for dynamic update of laser energy regulation and thermal management strategy.

[0017] In summary, the present application has the following beneficial technical effects: the microfocus CT tube based on laser-triggered cathode and quadrupole magnetic focusing and the working method thereof of the present invention realize a low-power, high-response-rate electron emission mechanism by adopting a gallium nitride annular cathode film and a laser triggering system; effectively control the focus position and size of the electron beam by deploying a quadrupole magnetic focusing structure; utilize a rotating tungsten-rhenium target disk to enhance the heat load carrying capacity and improve the X-ray yield; combine a high vacuum environment and a dynamic thermal modeling feedback strategy to solve the technical difficulties of traditional microfocus CT tubes in response speed, focus stability and thermal management, significantly improve imaging resolution and system reliability, and are suitable for high-precision medical and industrial non-destructive testing fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a working principle diagram of the bulb of the present invention; Figure 2 This is the magnetic field distribution diagram of the quadrupole magnetic focusing coil of the present invention.

[0019] Figure numerals: 1. vacuum tube shell; 2. cathode system; 3. laser triggering system; 4. quadrupole magnetic focusing system; 5. rotating target structure; 6. ray window; 8. laser head; 9. laser beam; 10. anti-reflection coating; 11. gallium nitride target layer; 12. electron focusing groove; 13. emission electron beam; 14. focusing electromagnetic coil; 15. target disk; 16. ray window; 17. X-ray; 18. motor; 19. vacuum layer structure; 20. exhaust pipe; 21. rotating axis. DETAILED DESCRIPTION

[0020] In the following description, numerous specific details are provided to provide a more thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without one or more of these details. In other instances, certain technical features well known in the art are not described to avoid confusion with the present invention.

[0021] according to Figure 1The microfocus CT tube based on laser-triggered cathode and quadrupole magnetic focusing is shown, comprising: a vacuum tube shell 1, a cathode system 2 disposed inside the vacuum tube shell, a laser triggering system 3, a quadrupole magnetic focusing system 4, a rotating target structure 5, a ray window 6, and a control system 7 electrically or mechanically connected to the above components; the cathode system 2 comprises an annular cathode film disposed on the inner surface of a quartz shell, and the quartz shell is fixedly mounted on the inner wall of one end of the vacuum tube shell 1; the laser triggering system 3 is located outside the cathode system 2, and the laser emits a laser beam toward the cathode film; the quadrupole magnetic focusing system 4 is disposed on the cathode The system 2 is arranged around the electron beam propagation path between the system 2 and the rotating target structure 5, and is used to focus the electron beam before it enters the rotating target structure 5; the rotating target structure 5 includes a target disk located at the other end of the vacuum tube shell, and the target disk is horizontally mounted on a rotating shaft, and the rotating shaft is connected to a motor to drive its rotation; a ray window 6 is arranged on the side wall of the vacuum tube shell, in front of the electron beam bombardment area corresponding to the target disk, and is used to output X-rays; the control system 7 is respectively connected to the laser trigger system 3, the quadrupole magnetic focusing system 4 and the rotating target structure 5 by signal or electrical connection, and is used to coordinate the control of electron emission, focusing and target disk rotation processes. An external laser is used to emit a laser beam through a laser triggering system to irradiate an annular cathode film located in a vacuum chamber. Under the action of the laser energy, the surface material of the cathode film realizes photoelectric emission to generate an electron beam. The electron beam propagates along a preset path. When it propagates to the quadrupole magnetic focusing system area, it is focused and adjusted by the vertical magnetic field generated by the magnetic coils distributed around the path to ensure that the electron beam is converged to a microfocus before reaching the target disk. The focused high-energy electron beam hits the surface of the target disk, and X-rays are generated due to the interaction between the target material and the electrons. The X-rays are emitted from the direction of the target disk through a ray window set on the side wall of the vacuum shell. The rotating target disk rotates under the drive of an electric motor to disperse heat accumulation and optimize the direction of X-ray emission. The control system coordinates the timing and power adjustment of each subsystem according to preset parameters to achieve stable X-ray output.

[0022] like Figure 1 As shown in the figure, the laser trigger system: the laser head is fixedly installed on the top of the vacuum shell, and the laser is directed to the cathode system below through the laser beam hole. The laser beam passes through the anti-reflection coating and is incident on the cathode target layer made of gallium nitride material.

[0023] Cathode system: The gallium nitride target layer is fixed to the inner wall of the electron focusing groove and combined with the quartz window to form a photoelectric emission structure. Electrons are emitted from this area.

[0024] Quadrupole magnetic focusing system: The focusing electromagnetic coil is installed between the electron source and the target disk in a quadrupole symmetrical manner around the electron beam channel. The coil is fixed on the magnetic pole support frame and connected to the external control system through a wire to form a vertical magnetic field to focus the electron beam.

[0025] Rotating target structure: The target disc is horizontally set at the front end of the rotating shaft and is driven to rotate by the motor located at the bottom of the tube. The rotating shaft passes through the vacuum layer and is fixedly connected to the target disc. The bearing and sealing structure ensure mobility and sealing in a high vacuum environment.

[0026] X-ray output system: A ray window is opened on the side wall of the vacuum tube shell corresponding to the target disk electron bombardment area. The window is made of high X-ray transmittance material (such as beryllium) and is installed in the direction of X-ray emission.

[0027] Vacuum and exhaust system: The internal space of the whole tube forms a closed vacuum chamber, which is connected to the molecular pump or ion pump system through the exhaust pipe to maintain 10⁻ 6 A high vacuum state below Pa ensures the free propagation of the electron beam. When the system is activated, the laser trigger system first activates the laser head, emitting a laser beam of a specific wavelength and power density. This laser beam passes through the anti-reflection coating and irradiates the gallium nitride cathode layer mounted on the inner wall of the electron focusing tank. The laser photons interact with the cathode surface, inducing electron emission through a multiphoton absorption mechanism.

[0028] Electron beam edge Figure 2 The electron beam accelerates in the indicated direction and passes through the area where the focusing electromagnetic coils are located. Four sets of symmetrical magnetic coils are arranged here. When energized, they form a magnetic field perpendicular to the propagation direction of the electron beam. Under the action of the magnetic field, the electron beam trajectory is compressed and focused to a tiny spatial point, ultimately bombarding the target area on the target disk surface with high density.

[0029] The target disk is driven by a motor and rotates continuously. Bombarded by focused electrons, it generates X-rays, which are emitted from the X-ray window in a fan-shaped pattern. The X-ray window material ensures a vacuum seal while also possessing excellent X-ray transmittance. The rays are directed to an external detection device for image acquisition. During operation, the control system dynamically adjusts the laser output power, coil current, rotation speed, and vacuum state to ensure electron beam emission accuracy, focus stability, and target disk temperature balance. This results in an X-ray source output with high spatial resolution, high brightness, and low drift, meeting the high-performance requirements of microfocus CT imaging.

[0030] Specifically, the cathode film in the cathode system is made of gallium nitride (GaN) and coated on the inner wall of a hollow quartz cylindrical shell. The quartz shell is fitted over one end of the vacuum tube and sealed securely by high-temperature glass sealing or metal welding. The GaN film, used as the cathode material, leverages its excellent photoemission properties, enabling rapid response and efficient electron release under laser irradiation. This material is uniformly coated onto the inner wall of the quartz shell using physical vapor deposition or magnetron sputtering to form an annular thin film layer. The quartz shell, serving as the cathode support substrate, exhibits excellent thermal stability and insulation properties. It is hermetically sealed to the vacuum tube via high-temperature glass sealing or metal welding, ensuring the system maintains a high vacuum environment for a long time. The GaN cathode film features low work function, high thermal conductivity, and high-temperature resistance, improving electron emission efficiency and extending cathode life. Furthermore, the quartz shell's reliable sealing ensures long-term stable operation, preventing leakage and contamination, and enhancing overall system reliability and performance consistency.

[0031] As a preferred case, the laser triggering system includes a laser, a laser guide mirror group and an optical fiber output end. The laser is externally mounted on the outside of the vacuum tube shell, and the laser is guided into the location of the cathode system through the optical fiber component. The laser is mounted outside the vacuum system, and the laser is collimated by the laser guide mirror group and guided to the laser irradiation position inside the cathode system through the optical fiber output end. The laser beam irradiates the cathode film to generate photoelectric emission. The optical fiber component design can adjust the focal length and angle of the beam to ensure that the laser is focused on the cathode active area and improve the excitation efficiency. The external laser design reduces the interference of high temperature on the laser source and improves its stability and service life. The laser is transmitted through the mirror group and optical fiber guidance. The system layout is flexible, easy to adjust and maintain, and ensures the accuracy and repeatability of electron emission.

[0032] Specifically, the quadrupole magnetic focusing system includes four groups of magnetic coils symmetrically distributed around the electron beam channel. Each magnetic coil is mounted on a magnetic pole frame and connected to the control system via a powered cable, forming a magnetic field distribution perpendicular to the direction of the electron beam. The four groups of magnetic coils are equidistantly distributed around the electron beam path. When energized, a uniform magnetic field is formed inside the coil, and the direction of the magnetic field is perpendicular to the propagation direction of the electron beam. The control system adjusts the power intensity and controls the strength of the magnetic field to achieve focusing and convergence of the electron beam trajectory and improve the positioning accuracy of the electron beam entering the target. This structure realizes precise magnetic control of high-energy electron beams, significantly improving focusing ability and imaging resolution; it can automatically adjust the magnetic field parameters according to the electron beam intensity, flexibly adapt to different working modes, and improve the imaging stability of the system.

[0033] As shown in Figure 2, the quadrupole magnetic focusing system consists of four sets of magnetic coils, located in the upper, lower, left, and right quadrants of the electron beam propagation path, arranged symmetrically around the electron beam path. These coils are mounted on a magnetic pole frame and powered by a control system to produce a symmetrical, alternating magnetic field distribution.

[0034] The electron beam enters the magnetic focusing region from the left side of the diagram. When the coils are energized, each pair of opposing magnetic coils establishes a magnetic field with opposite flux densities in its respective quadrant, forming a quadrupole magnetic field distribution. The direction and gradient of the magnetic field exhibit spatially non-uniform characteristics, with low flux density at the center and high flux density at the edges. Electrons in this field are subject to the radial Lorentz force, pushing back any electrons that stray from the center, thus achieving automatic focusing and correction of the electron beam.

[0035] This quadrupole magnetic field not only suppresses the radial divergence of the electron beam but also improves the precision of controlling the beam spot size at the focal point. After magnetic focusing, the electron beam is focused onto a specific rotational point on the target disk, resulting in high-density bombardment and enabling microfocus bombardment imaging. The continuous rotation of the target disk causes the electron beam impact area to continuously shift, creating a "dynamic incident-distributed energy" thermal management effect.

[0036] Example The microfocus CT tube described in this application includes a feedback control algorithm module for controlling the quadrupole magnetic focusing system. This control algorithm is used to achieve high-precision focusing adjustment of the electron beam trajectory, ensuring that the electron beam forms a stable and controllable microfocus before entering the rotating target surface, thereby improving the spatial resolution and imaging consistency of the X-ray emission.

[0037] The quadrupole magnetic focusing system comprises four sets of magnetic coils, symmetrically arranged around the electron beam path, located in the upper, lower, left, and right quadrants. These coils are secured to the center of the vacuum chamber by a magnetic pole frame. These four sets of magnetic coils are connected to a control system via wires, forming independent, adjustable current loops. The control system acquires real-time electron beam deflection information, calculates the deflection, and outputs current adjustment commands to drive the magnetic coils to form an adaptive magnetic field.

[0038] To achieve the above functions, the control system adopts a control algorithm based on the proportional-integral-differential (PID) regulation structure. Assume that the ideal focus point of the electron beam is the center of the target disk, and the actual displacement coordinate is , then the system defines the focusing error as:

[0039] The control system uses the offset in each direction As input, the current of the four coils is Perform independent adjustment, the specific adjustment formula is:

[0040] in, is the basic current setting value, They are proportional, integral and differential adjustment coefficients, respectively, which are used to adjust the focusing current response speed, steady-state accuracy and anti-interference ability.

[0041] In addition, in order to improve the focusing stability of the electron beam, the system further constructed a mathematical model based on the Lorentz force to deduce the dynamic behavior of the electron beam in the magnetic field. According to the principle of electron dynamics, it is assumed that the electron moves in the propagation direction (Z axis) and is affected by the quadrupole magnetic field. The lateral force after the action is

[0042] From this we can see that electrons move laterally The differential equation of motion in the direction is:

[0043] This equation shows that the quadrupole magnetic field has a focusing effect in one direction and a diverging effect in the other direction. The two are coupled to form a spatially confined saddle point field. The electron beam can be effectively confined near the axis in this magnetic field structure.

[0044] Based on this model and incorporating real-time electron beam displacement detection results, the control system continuously corrects the magnetic field gradient through a feedback current regulation mechanism, ensuring that the electron beam trajectory continues to converge to the target focus. To improve thermal management capabilities and focus uniformity, the control system also periodically adjusts the coil current phase offset based on the target disk rotation angle signal, enabling dynamic flying focus control within the rotating target disk. The control algorithm described in this embodiment features fast adjustment response, high focusing accuracy, and strong robustness, making it suitable for a variety of microfocus X-ray applications, particularly those in high-resolution CT imaging systems that require high electron focusing consistency and stability.

[0045] Specifically, the target disc in the rotating target structure is made of a tungsten-rhenium alloy and fixed to a rotating shaft. The rotating shaft is supported by a bearing assembly and driven by a motor mounted outside the vacuum tube shell. When a high-energy electron beam strikes the tungsten-rhenium alloy target disc, X-rays are generated. The rotating shaft rotates the target disc at a constant speed, dispersing the bombardment heat source and preventing local overheating. The motor drives the rotating shaft through bearings, and operational stability is achieved through optimized bearing design. Tungsten-rhenium alloy has a high melting point and good thermal conductivity, capable of withstanding continuous bombardment by high-energy electron beams. The rotating structure extends the service life of the target disc and improves the stability of X-ray output, facilitating continuous imaging or detection.

[0046] Specifically, the rotating shaft passes through a rotating seal at the bottom of the vacuum tube housing and connects to the external motor. This seal is either ceramic-based or employs a magnetic fluid seal structure. As the rotating shaft passes through the vacuum chamber, a rotating seal isolates the pressure differential between inside and outside. The ceramic seal provides rigid support, while the magnetic fluid seal utilizes magnetic fluid to form a sealing layer, preventing gas leakage and ensuring a stable vacuum environment. This sealing solution maintains a high vacuum environment for extended periods, ensuring airtightness during operation. This improves system stability and service life, and facilitates continuous, high-speed rotation.

[0047] Specifically, the X-ray window is made of beryllium and welded to the sidewall of the vacuum tube where the window is located. Its center is aligned with the emission direction of the electron beam bombardment area of the target disk. Beryllium material has high X-ray transmittance, which can effectively output X-rays without significantly absorbing radiation. The welding process ensures its airtightness and structural stability. The window is directly opposite the X-ray emission point of the target disk, maximizing signal utilization. The use of beryllium windows can reduce signal attenuation and improve detection sensitivity; its high strength and corrosion resistance extend component life; and the center alignment design improves emission efficiency and image focusing.

[0048] Specifically, the interior of the vacuum tube is evacuated to 10⁻ by a molecular pump or an ion pump. 6 Pa and maintain a stable high vacuum during operation. Use a high-performance molecular pump or ion pump to remove the gas inside the vacuum tube cavity to reach 10⁻ 6 The ultra-high vacuum of Pa prevents electrons from colliding with gas molecules during propagation, thereby improving imaging stability and electron emission efficiency.

[0049] The high vacuum environment suppresses interference from stray electrons and photons, prolongs component life, and enhances imaging accuracy; the molecular pump operates with low noise and has a long life, which is conducive to the long-term operation of the precision system.

[0050] Specifically, a method for operating the microfocus CT tube includes the following steps: Step 1: a control system activates a laser trigger system to emit laser pulses toward a gallium nitride cathode on the inner wall of a quartz shell, thereby inducing electron emission; Step 2: during the electron emission process, the control system models and optimizes the emission performance based on the following algorithm; Step 2.1. Collect laser wavelength, power density, pulse width and cathode material parameters; Step 2.2. Calculate single-photon energy, determine the minimum absorption number in multi-photon absorption mode, and calculate electron kinetic energy; Step 2.3. Calculate electron emission efficiency based on the fitting model; Step 2.4. Construct a heat conduction model, simulate the cathode temperature distribution, and output the cathode temperature; Step 2.5. Feedback the above parameters to the control system for dynamic update of laser energy regulation and thermal management strategy; Step 3. When the electron beam passes through the quadrupole magnetic focusing system, it is focused to the micro-point area of the target disk, and the magnetic field strength and the degree of electron beam deviation are simultaneously evaluated; Step 4. The electron beam bombards the surface of the rotating target disk to generate rays; Step 5. The rays are emitted through the ray window to realize imaging or detection functions.

[0051] This application proposes a working method for a microfocus CT tube based on a laser-triggered cathode and quadrupole magnetic focusing. The core principle is to use laser pulses to induce electron emission, accurately focus the electron beam through a quadrupole magnetic field, and bombard the target disk to generate X-rays. At the same time, a modeling algorithm is introduced to dynamically optimize and control electron emission and thermal behavior, thereby achieving a high-precision and high-efficiency X-ray output process.

[0052] The entire system's operation is coordinated by a control system and includes the following steps: First, driven by a control signal, the laser trigger system fires a laser pulse at the GaN cathode thin film within the vacuum chamber. The laser beam is focused onto the cathode's emission region via a light guide mirror or fiber optic guidance system. The laser photon energy meets or exceeds the work function of the GaN material. Through multiphoton absorption, the laser excites the material's surface to release free electrons, forming a high-energy electron beam.

[0053] The electron beam then accelerates along a pre-set path in a vacuum environment and enters the quadrupole magnetic focusing system. This system uses four sets of symmetrically distributed magnetic coils to form a perpendicular magnetic field around the electron beam path. The control system adjusts the coil current intensity and phase in real time based on the current electron beam characteristics, thereby achieving spatial focusing of the electron beam and fine-tuning its trajectory, ensuring that the electron beam accurately strikes a micro-point area on the target disk.

[0054] The electron beam strikes the surface of a rotating tungsten-rhenium alloy target disk, generating X-rays through the interaction of the high-energy particles with the high-Z target material. The target disk is driven by a motor, rotating at high speed, dissipating heat buildup to prevent localized damage and improving the consistency and thermal stability of the X-ray output. The X-rays are ultimately emitted through a beryllium radiation window for high-resolution imaging or microstructure material inspection.

[0055] To improve overall system performance and reliability, this invention incorporates a modeling algorithm into the electron emission control process. The control system first collects laser wavelength, power density, pulse width, and cathode material parameters, calculates the laser single-photon energy, and determines the minimum absorption number and electron kinetic energy under multi-photon absorption. Furthermore, based on material properties and input laser parameters, the electron emission efficiency is derived using empirical fitting or mathematical models to quantify the conversion rate of laser energy into electron beam kinetic energy.

[0056] Furthermore, to prevent heat accumulation during electron emission from affecting cathode lifespan and emission efficiency, the system constructs a mathematical heat conduction model to simulate the temperature distribution and heat flux density on the cathode surface. The model calculates the instantaneous and steady-state cathode temperature distribution based on the heat source power density, material thermal conductivity, and heat dissipation structure parameters. All model output parameters are fed back to the control system, which dynamically adjusts the laser pulse frequency, energy density, and thermal management strategy, thereby achieving thermal stability control and protection for the system while maintaining efficient electron emission.

[0057] Through the above-mentioned collaborative mechanism, this application realizes closed-loop intelligent control of the entire process of electron emission-focusing-bombardment-imaging, which not only improves the X-ray output efficiency and image quality, but also significantly extends the service life of key components (such as cathodes and target plates), providing a stable, controllable, high-performance radiation source core technology platform for high-end imaging equipment such as microfocus CT.

[0058] Working principle: Laser pulses are used to excite the gallium nitride cathode material to achieve electron emission, and the electron beam is focused with high precision through a quadrupole magnetic field, thereby forming a stable micro-focus electron bombardment area on the rotating target disk, generating high-resolution X-rays for precision CT scanning imaging.

[0059] The system consists of a vacuum-sealed cavity structure, housing a cathode system, a quadrupole magnetic focusing system, a rotating target structure, and a laser trigger and control system for laser drive and process control. The cathode system utilizes a hollow quartz shell coated with a thin film of gallium nitride as a photocathode. When an external laser emits a laser pulse of a specific wavelength and power density through a light guide toward the film, the photon energy triggers the cathode material to release electrons. Due to the low work function of gallium nitride, the electron emission response time is short and efficiency is high.

[0060] The emitted electron beam passes through a quadrupole magnetic focusing system positioned between the cathode and target disk. The quadrupole magnetic field is generated by four sets of symmetrically spaced magnetic coils. Adjusting the magnetic field intensity controls the electron beam's focal position and beam diameter. The electron beam is ultimately focused onto a micro-spot on the rotating target disk, where it strikes the tungsten-rhenium alloy target disk at high speed, inducing the generation of X-rays.

[0061] The rotating target structure is supported by bearings and driven by an external motor to achieve continuous rotation of the target disk, thereby alleviating the heat accumulation caused by electron bombardment, maintaining a stable target surface temperature, and extending the target life. The generated X-rays are output through a ray window located in the emission direction of the target disk. The ray window is made of a material with high X-ray transmittance, such as beryllium, and is airtightly welded to the vacuum shell. The entire system operates in a high vacuum environment, and the vacuum is maintained to 10⁻ by a molecular pump or an ion pump. 6 Pa or less to reduce the scattering and energy loss of electrons during propagation.

[0062] The control system realizes the coordinated management of processes such as laser excitation, electron focusing, and target disk rotation, and introduces thermal modeling and electron emission efficiency prediction algorithms. By adjusting laser parameters and magnetic field current through feedback, it realizes dynamic optimization of electron beam quality and thermal management, thereby ensuring the long-term stable output of high-quality X-rays by the system and achieving high-resolution CT imaging goals.

[0063] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to it in form and detail without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A microfocus CT tube based on laser-triggered cathode and quadrupole magnetic focusing, characterized in that: include: A vacuum tube shell (1), a cathode system (2) arranged inside the vacuum tube shell, a laser triggering system (3), a quadrupole magnetic focusing system (4), a rotating target structure (5), a ray window (6), and a control system (7) electrically or mechanically connected to the above components; the cathode system (2) includes an annular cathode film arranged on the inner surface of a quartz shell, and the quartz shell is fixedly mounted on the inner wall of one end of the vacuum tube shell (1); the laser triggering system (3) is located outside the cathode system (2), and the laser emits a laser beam toward the cathode film; the quadrupole magnetic focusing system (4) is arranged between the cathode system (2) and the rotating target structure ( 5) and arranged around the electron beam propagation path, for focusing the electron beam before it enters the rotating target structure (5); the rotating target structure (5) includes a target disk arranged at the other end of the vacuum tube shell, the target disk is horizontally mounted on a rotating shaft, and the rotating shaft is connected to a motor to drive it to rotate; the ray window (6) is arranged in front of the electron beam bombardment area of the target disk on the side wall of the vacuum tube shell, and is used to output the generated X-rays; the control system is respectively connected to the laser trigger system (3), the quadrupole magnetic focusing system (4) and the rotating target structure (5) by signal or electrical connection, for collaboratively controlling the electron emission, focusing and target disk rotation processes.

2. The microfocus CT tube according to claim 1, characterized in that: The cathode film in the cathode system is made of gallium nitride material and is plated on the inner wall of a hollow quartz cylindrical shell. The quartz shell is sleeved on one end of the vacuum tube shell and fixed and sealed by high-temperature glass sealing or metal welding.

3. The microfocus CT tube according to claim 1, characterized in that: The laser triggering system includes a laser, a laser guide mirror assembly and an optical fiber output end. The laser is externally installed outside the vacuum tube shell, and the laser is guided into the position of the cathode system through the optical guide assembly.

4. The microfocus CT tube according to claim 1, characterized in that: The quadrupole magnetic focusing system includes four groups of magnetic coils symmetrically distributed around the electron beam channel. Each magnetic coil is mounted on a magnetic pole frame and connected to a control system through a powered cable to form a magnetic field distribution perpendicular to the direction of the electron beam.

5. The microfocus CT tube according to claim 1, characterized in that: The target disk in the rotating target structure is made of tungsten-rhenium alloy and is fixed on a rotating shaft. The rotating shaft is supported by a bearing device and is driven to rotate by a motor arranged outside the vacuum tube shell.

6. The microfocus CT tube according to claim 5, characterized in that: The rotating shaft passes through a rotating sealing component at the bottom of the vacuum tube shell and is connected to an external motor. The sealing component is a ceramic-based or magnetic fluid sealing structure.

7. The microfocus CT tube according to claim 1, characterized in that: The ray window is made of beryllium material and is welded to the side wall of the vacuum tube shell where the window is located, with its center aligned with the emission direction of the target disk electron beam bombardment area.

8. The microfocus CT tube according to claim 1, characterized in that: The interior of the vacuum shell is evacuated to 10⁻ by a molecular pump or an ion pump 6 Pa and maintain a stable high vacuum during operation.

9. A method for operating a microfocus CT tube according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step 1: The control system starts the laser trigger system to emit laser pulses to the gallium nitride cathode on the inner wall of the quartz shell, triggering electron emission: Step 2: During the electron emission process, the control system models and optimizes the emission performance based on the algorithm: Step 3: The electron beam is focused to the target micro-spot area when passing through the quadrupole magnetic focusing system, and the magnetic field strength and the degree of electron beam deviation are simultaneously evaluated to ensure the focusing accuracy: Step 4: The electron beam bombards the surface of the rotating target disk to produce ray; Step 5 The rays are emitted through the ray window to achieve imaging or detection functions.

10. A method for operating the microfocus CT tube according to claim 9, characterized in that: The step 2 includes the following steps: Step 2.1: Collect laser wavelength Power density 1, pulse accuracy and cathode material parameters ; Step 2.2: Calculate single photon energy , and determine the minimum absorption number in the multiphoton absorption mode , calculate the electron kinetic energy ； Where: is Planck's constant, which represents the energy constant per unit frequency. is the frequency of the photon, is the laser wavelength, represents the energy of a single photon; is the kinetic energy of electron emission; the number of photons absorbed by the electron; is the work function of the cathode material, that is, the minimum energy required for electrons to escape from the surface of the material; Step 2.3: Based on the fitted model ;Calculate electron emission efficiency ; Where: is the electron emission efficiency, that is, the ratio of input laser energy converted into electron emission energy; is the laser power density; is the laser pulse width; is the conductivity of the cathode material; Step 2.4: Build a heat conduction model Simulate cathode temperature and output cathode temperature ; Where: is the thermal conductivity of the cathode material, is the temperature distribution function, is the heat source power density per unit volume, is the divergence operator, which represents the spatial variation of heat flux density, temperature gradient; Step 2.5, and Feedback is sent to the control system for dynamic update of laser energy regulation and thermal management strategy.

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