Permanent-magnetic-electromagnetic composite regulation focusing lens structure and control method thereof

Abstract

The application discloses a permanent magnet-electromagnetic composite regulation and control focusing lens structure and a control method thereof, and relates to the technical field of electron beam focusing control. The structure comprises a permanent magnet main focusing module, an electromagnetic dynamic compensation module, a magnetic circuit structure, a thermal management and stable control structure and a control driving structure which are coaxially arranged along the electron beam propagation direction. The permanent magnet main focusing module is used for forming a stable axisymmetric permanent magnet main field. The electromagnetic dynamic compensation module is used for superimposing an electromagnetic compensation field through forward and reverse compensation currents. The magnetic circuit structure is used for forming a closed magnetic circuit and restraining magnetic flux. The control driving structure calculates compensation currents based on the focal spot size, position deviation, electron beam current and acceleration voltage variation, and realizes dynamic closed-loop adjustment of the electron beam focal spot size and position. The structure and method have magnetic field stability and dynamic adjustability, reduce the influence of energy consumption and temperature rise, and improve the electron beam focusing stability, response speed and anti-interference ability.

Description

Technical Field

[0001] This invention relates to the field of electron beam focusing control technology, and in particular to a permanent magnet-electromagnetic composite control focusing lens structure and its control method. Background Technology

[0002] Electron beam focusing lenses are widely used in X-ray sources, electron microscopes, electron beam processing equipment, and other electron optical systems. The focusing performance of the electron beam directly affects the spatial resolution, energy distribution, imaging quality, and processing accuracy of the system. With the development of high-resolution imaging technology and micro-nano scale processing technology, related equipment has placed higher demands on the electron beam focal spot size, focal spot position stability, and dynamic adjustment capability. Especially in long-term continuous operation and high-precision working scenarios, the electron beam needs to maintain a stable focused state and be able to respond quickly to external disturbances.

[0003] Existing electron beam focusing methods mainly include electromagnetic lens focusing and permanent magnet lens focusing. Electromagnetic lenses typically generate a magnetic field through an energized coil to adjust the focusing intensity of the electron beam. This method features adjustable magnetic field strength, adapting to different beam current conditions. However, electromagnetic lenses require continuous current drive, resulting in high energy consumption. Furthermore, the coil generates heat during prolonged energization, and this temperature rise causes changes in coil resistance, leading to fluctuations in the drive current and magnetic field strength, affecting the stability of electron beam focusing. Simultaneously, electromagnetic lenses are highly sensitive to power supply stability and are susceptible to voltage fluctuations and electromagnetic noise, limiting their application in high-precision electro-optical systems.

[0004] Furthermore, the electron beam is affected by factors such as space charge effect, high-voltage power supply fluctuations, structural thermal deformation, and external electromagnetic interference during propagation. These factors can cause changes in the electron beam divergence angle, increase the focal spot size, and cause the focal spot position to drift, thereby reducing imaging quality or processing accuracy. Traditional single electromagnetic focusing methods struggle to balance low energy consumption and long-term stability, while single permanent magnet focusing methods struggle to balance dynamic adjustability and disturbance compensation capabilities. Existing focusing systems also suffer from insufficient anti-interference capabilities, limited response speed, and inadequate long-term stable control.

[0005] Chinese patent application CN114999765A discloses a multimodal magnetic therapy device combining permanent magnets and electromagnetics. This solution applies rotating permanent magnets and alternating electromagnetic fields to the sample through electromagnetic and permanent magnet mechanisms, causing the magnetic material to undergo jumping, rotating, and flipping motions, thereby achieving multimodal magnetic therapy. The core of this solution lies in controlling the permanent magnet motion, electromagnetic wave frequency, current magnitude, and current direction in the biomagnetic therapy scenario. It does not address the focal spot size, positional drift, and focusing magnetic field stability of the electron beam in the electron optics system. Furthermore, its permanent magnet and electromagnetic mechanisms interact with the magnetic material at the sample stage, rather than constructing a composite focusing lens coaxially along the electron beam propagation direction to form the permanent magnet main field and the electromagnetic compensation field. It lacks a dynamic compensation mechanism for electron beam disturbances caused by space charge effects, high-voltage fluctuations, and thermal deformation, making it difficult to use for high-precision, stable electron beam focusing control. Invention patent CN119673731B discloses a stacked magnetic lens. This scheme generates a basic adjustable magnetic field through multiple ring permanent magnets coaxially arranged along the central axis, and adjusts the magnetic field distribution and magnitude by the relative displacement of at least one ring permanent magnet. In some embodiments, an electromagnetic coil is also provided to generate an additional adjustable magnetic field. This scheme focuses on achieving magnetic field adjustment through the mechanical displacement of stacked ring permanent magnets. Although it can improve stray fields and reduce the thermal management problems caused by traditional electromagnetic lenses, its adjustment mainly depends on the relative position changes between the ring permanent magnets. The response speed is limited by the mechanical displacement mechanism, making it difficult to compensate for rapid changes in disturbances such as space charge effect, high voltage power supply fluctuations, and thermal deformation in real time. At the same time, this scheme does not form a dynamic focusing control structure that integrates permanent magnet main focusing, electromagnetic forward and reverse compensation, closed magnetic circuit shielding, and temperature feedback correction, resulting in insufficient closed-loop stable control of the electron beam focal spot size and position under long-term operation. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of the prior art by providing a permanent magnet-electromagnetic composite control focusing lens structure and its control method, which has the advantages of stabilizing the main focusing magnetic field, dynamically compensating for focusing intensity, reducing the influence of coil energy consumption and temperature rise, suppressing external electromagnetic interference, and improving the size and position stability of the electron beam focal spot.

[0007] The technical solution to achieve the purpose of this invention is as follows:

[0008] A permanent magnet-electromagnetic composite control focusing lens structure, comprising:

[0009] The permanent magnet main focusing module is used to achieve initial focusing of the electron beam by forming a stable and axisymmetric permanent magnet main field in the direction of electron beam propagation through a multi-ring combined permanent magnet.

[0010] The electromagnetic dynamic compensation module is used to generate an adjustable electromagnetic compensation field coupled with the main field of the permanent magnet by means of an electromagnetic coil assembly wound around the outside of the permanent magnet, so as to adjust the magnetic flux density and magnetic field distribution of the main field of the permanent magnet.

[0011] The magnetic circuit structure is used to form a closed magnetic circuit by a magnetic yoke located outside the permanent magnet and the electromagnetic coil assembly to achieve magnetic flux constraint, leakage magnetic field reduction and suppression of external electromagnetic interference;

[0012] A thermal management and stability control structure is used to obtain the coil temperature through a cooling structure and a temperature sensor, and to feed back the temperature signal to reduce the impact of temperature rise on the electromagnetic coil assembly.

[0013] The control drive structure is used to calculate the compensation current based on the electron beam focal spot size, position deviation information, electron beam current and acceleration voltage changes, and drive the electromagnetic coil assembly to achieve dynamic closed-loop control of the electron beam focal spot size and position. Each module is arranged coaxially along the electron beam propagation direction to form an axisymmetric composite magnetic field environment.

[0014] Furthermore, the permanent magnet main focusing module includes a ring-shaped permanent magnet assembly made of neodymium iron boron material. The ring-shaped permanent magnet assembly is magnetized along a preset magnetization direction to form a stable magnetic field distribution in the electron beam propagation direction and reduce the initial divergence angle of the electron beam.

[0015] The multi-segment permanent magnet assembly includes multiple permanent magnet rings spaced apart along the direction of electron beam propagation. The multiple permanent magnet rings form an axial gradient magnetic field distribution through different sizes and spacings, which is used to compress the electron beam step by step and provide the pre-focused electron beam input to the electromagnetic dynamic compensation module.

[0016] Furthermore, the electromagnetic dynamic compensation module includes a low-inductance electromagnetic coil assembly, which is made of multi-strand insulated stranded wire wound around the outside of the permanent magnet, in order to reduce AC loss and improve the response speed of the electromagnetic compensation field to changes in compensation current.

[0017] Furthermore, the low-inductance electromagnetic coil assembly includes a multi-layer coil structure, which is divided into a coarse adjustment coil and a fine adjustment coil. The coarse adjustment coil is used to adjust the focusing intensity range based on the compensation current, and the fine adjustment coil is used to continuously adjust the electron beam focusing state based on the feedback correction current.

[0018] Furthermore, the specific configuration of the magnetic circuit structure is as follows:

[0019] A magnetic yoke made of high-permeability soft magnetic material is used to surround the permanent magnet and the electromagnetic coil assembly.

[0020] A closed magnetic circuit is formed by the magnetic yoke in conjunction with the permanent magnet main focusing module and the electromagnetic dynamic compensation module to concentrate and confine the magnetic flux to the electron beam propagation region.

[0021] External electromagnetic interference is shielded by a closed magnetic circuit to maintain a stable composite magnetic field distribution within the electron beam propagation area.

[0022] Furthermore, the specific configuration of the thermal management and stability control structure is as follows:

[0023] A heat exchange and cooling structure thermally coupled to the electromagnetic coil assembly is provided inside the coil frame of the electromagnetic coil assembly, and the heat exchange and cooling structure forms a heat conduction path from the electromagnetic coil assembly to the external heat dissipation medium.

[0024] Temperature sensors are placed at key locations in the electromagnetic coil assembly and its surrounding environment to collect coil temperature signals and ambient temperature signals;

[0025] The coil temperature signal and the ambient temperature signal are fed back to the control drive structure to correct the compensation current and reduce the impact of temperature rise on the magnetic field distribution.

[0026] Furthermore, the dynamic focusing control process of the control drive structure is as follows:

[0027] The electron beam focal spot size and position deviation information are obtained by the electron beam state detection component to obtain the electron beam focusing state detection result;

[0028] Based on the preset model, the detection results of the electron beam focusing state, and the changes in electron beam current and accelerating voltage, the required compensation current is calculated to obtain the current magnitude and current direction of the electromagnetic coil assembly.

[0029] The adjustment command, which includes the magnitude and direction of the current, is sent to the electromagnetic coil drive circuit to drive the electromagnetic coil assembly to generate an electromagnetic compensation field and achieve closed-loop adjustment of the size and position of the electron beam focal spot.

[0030] Furthermore, the calculation process for the required compensation current is as follows:

[0031] The changes in electron beam current and accelerating voltage are input into the feedforward compensation channel to calculate the pre-compensation current.

[0032] Input the focal spot size deviation and position deviation into the proportional-integral-derivative feedback channel to calculate the feedback correction current;

[0033] The pre-compensation current is superimposed with the feedback correction current to obtain the required compensation current.

[0034] Furthermore, the adjustment process of the electromagnetic compensation field is as follows:

[0035] When the current direction of the electromagnetic coil assembly is consistent with the direction of the permanent magnet main field, the electron beam focusing effect is enhanced by superimposing a co-directional electromagnetic compensation field.

[0036] When the current direction of the electromagnetic coil assembly is opposite to the direction of the permanent magnet main field, the electron beam focusing intensity is weakened by superimposing a reverse electromagnetic compensation field.

[0037] Dynamic compensation is achieved by adjusting the forward and reverse currents to compensate for electron beam disturbances caused by space charge effect, high voltage fluctuations, and thermal deformation, so that the electron beam bombards the target area with a stable focal spot size and position.

[0038] A method for controlling a permanent magnet-electromagnetic composite focusing lens includes the following steps:

[0039] Step S1: Based on the electron beam energy, current density and target focal spot size, perform permanent magnet structure parameter matching, electromagnetic coil initial current setting and control system calibration to complete the initialization setting of the electron beam focusing lens structure;

[0040] Step S2: A stable and axially symmetrical permanent magnet main field is formed in the direction of electron beam propagation by the permanent magnet main focusing module to initially focus the electron beam emitted from the cathode and entering the compound lens region;

[0041] Step S3: A compensation current of a set magnitude and direction is supplied to the electromagnetic coil assembly through the electromagnetic dynamic compensation module to superimpose an electromagnetic compensation field on the permanent magnet main field and to finely focus the electron beam.

[0042] Step S4: Obtain the electron beam focal spot size and position deviation information through the electron beam state detection component, and calculate the required compensation current based on the electron beam current change, acceleration voltage change, focal spot size deviation and position deviation.

[0043] Step S5: By controlling the drive structure, the adjustment command including the magnitude and direction of the current is sent to the electromagnetic coil drive circuit to drive the electromagnetic coil assembly to generate an adjustable electromagnetic compensation field coupled with the permanent magnet main field.

[0044] Step S6: When the direction of the electromagnetic compensation field is consistent with the direction of the permanent magnet main field, the electron beam focusing effect is enhanced; when the direction of the electromagnetic compensation field is opposite to the direction of the permanent magnet main field, the electron beam focusing intensity is weakened. This is to dynamically compensate for the electron beam disturbance caused by space charge effect, high voltage fluctuation and thermal deformation, and to make the electron beam bombard the target area with a stable focal spot size and position.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] (1) The present invention provides a permanent magnet-electromagnetic composite control focusing lens structure and its control method, which forms a stable and axisymmetric permanent magnet main field through a permanent magnet main focusing module, and superimposes a positive or negative electromagnetic compensation field through an electromagnetic dynamic compensation module, so that the focusing lens has both stable main focusing capability and dynamic adjustment capability, solving the problems of high energy consumption, large temperature rise and insufficient adjustment capability of a single electromagnetic lens and a single permanent magnet lens.

[0047] (2) The present invention provides a permanent magnet-electromagnetic composite control focusing lens structure and its control method, which realizes rapid calculation and fine adjustment of compensation current through low inductance electromagnetic coil assembly, double or multi-layer coil structure, feedforward compensation and proportional-integral-derivative feedback control, thereby dynamically compensating for electron beam disturbances caused by space charge effect, high voltage fluctuation and thermal deformation, and improving the stability of electron beam focal spot size and position.

[0048] (3) The present invention provides a permanent magnet-electromagnetic composite control focusing lens structure and its control method, which forms a closed magnetic circuit through a magnetic yoke to constrain the magnetic flux and suppress external electromagnetic interference, and reduces the temperature rise of the electromagnetic coil assembly through a microchannel cooling structure, water cooling device or air cooling device combined with a temperature sensor, thereby improving the magnetic field utilization efficiency, anti-interference ability and long-term operation stability of the focusing lens. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of a permanent magnet-electromagnetic composite focusing lens structure;

[0050] Figure 2 This is a schematic diagram of the overall structure of a permanent magnet-electromagnetic composite focusing lens;

[0051] Figure 3 A schematic diagram of the structure of a permanent magnet-electromagnetic composite focusing lens applied to an X-ray generation system. Detailed Implementation

[0052] To more clearly describe the ideas, technical solutions, and advantages of the present invention, specific embodiments are illustrated through examples and accompanying drawings. Obviously, the described embodiments are only a portion, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0053] A permanent magnet-electromagnetic composite control focusing lens structure, the schematic diagram of which is shown below. Figure 1 As shown, it includes:

[0054] The permanent magnet main focusing module is used to achieve initial focusing of the electron beam by forming a stable and axisymmetric permanent magnet main field in the direction of electron beam propagation through a multi-ring combined permanent magnet.

[0055] The electromagnetic dynamic compensation module is used to generate an adjustable electromagnetic compensation field coupled with the main field of the permanent magnet by means of an electromagnetic coil assembly wound around the outside of the permanent magnet, so as to adjust the magnetic flux density and magnetic field distribution of the main field of the permanent magnet.

[0056] The magnetic circuit structure is used to form a closed magnetic circuit by a magnetic yoke located outside the permanent magnet and the electromagnetic coil assembly to achieve magnetic flux constraint, leakage magnetic field reduction and suppression of external electromagnetic interference;

[0057] A thermal management and stability control structure is used to obtain the coil temperature through a cooling structure and a temperature sensor, and to feed back the temperature signal to reduce the impact of temperature rise on the electromagnetic coil assembly.

[0058] The control drive structure is used to calculate the compensation current based on the electron beam focal spot size, position deviation information, electron beam current and acceleration voltage changes, and drive the electromagnetic coil assembly to achieve dynamic closed-loop control of the electron beam focal spot size and position. Each module is arranged coaxially along the electron beam propagation direction to form an axisymmetric composite magnetic field environment.

[0059] Furthermore, the permanent magnet main focusing module includes a ring-shaped permanent magnet assembly made of neodymium iron boron material. The ring-shaped permanent magnet assembly is magnetized along a preset magnetization direction to form a stable magnetic field distribution in the electron beam propagation direction and reduce the initial divergence angle of the electron beam.

[0060] The multi-segment permanent magnet assembly includes multiple permanent magnet rings spaced apart along the direction of electron beam propagation. The multiple permanent magnet rings form an axial gradient magnetic field distribution through different sizes and spacings, which is used to compress the electron beam step by step and provide the pre-focused electron beam input to the electromagnetic dynamic compensation module.

[0061] Furthermore, the electromagnetic dynamic compensation module includes a low-inductance electromagnetic coil assembly, which is made of multi-strand insulated stranded wire wound around the outside of the permanent magnet, in order to reduce AC loss and improve the response speed of the electromagnetic compensation field to changes in compensation current.

[0062] Furthermore, the low-inductance electromagnetic coil assembly includes a multi-layer coil structure, which is divided into a coarse adjustment coil and a fine adjustment coil. The coarse adjustment coil is used to adjust the focusing intensity range based on the compensation current, and the fine adjustment coil is used to continuously adjust the electron beam focusing state based on the feedback correction current.

[0063] Furthermore, the specific configuration of the magnetic circuit structure is as follows:

[0064] A magnetic yoke made of high-permeability soft magnetic material is used to surround the permanent magnet and the electromagnetic coil assembly.

[0065] A closed magnetic circuit is formed by the magnetic yoke in conjunction with the permanent magnet main focusing module and the electromagnetic dynamic compensation module to concentrate and confine the magnetic flux to the electron beam propagation region.

[0066] External electromagnetic interference is shielded by a closed magnetic circuit to maintain a stable composite magnetic field distribution within the electron beam propagation area.

[0067] Furthermore, the specific configuration of the thermal management and stability control structure is as follows:

[0068] A heat exchange and cooling structure thermally coupled to the electromagnetic coil assembly is provided inside the coil frame of the electromagnetic coil assembly, and the heat exchange and cooling structure forms a heat conduction path from the electromagnetic coil assembly to the external heat dissipation medium.

[0069] Temperature sensors are placed at key locations in the electromagnetic coil assembly and its surrounding environment to collect coil temperature signals and ambient temperature signals;

[0070] The coil temperature signal and the ambient temperature signal are fed back to the control drive structure to correct the compensation current and reduce the impact of temperature rise on the magnetic field distribution.

[0071] Furthermore, the dynamic focusing control process of the control drive structure is as follows:

[0072] The electron beam focal spot size and position deviation information are obtained by the electron beam state detection component to obtain the electron beam focusing state detection result;

[0073] Based on the preset model, the detection results of the electron beam focusing state, and the changes in electron beam current and accelerating voltage, the required compensation current is calculated to obtain the current magnitude and current direction of the electromagnetic coil assembly.

[0074] The adjustment command, which includes the magnitude and direction of the current, is sent to the electromagnetic coil drive circuit to drive the electromagnetic coil assembly to generate an electromagnetic compensation field and achieve closed-loop adjustment of the size and position of the electron beam focal spot.

[0075] Furthermore, the calculation process for the required compensation current is as follows:

[0076] The changes in electron beam current and accelerating voltage are input into the feedforward compensation channel to calculate the pre-compensation current.

[0077] Input the focal spot size deviation and position deviation into the proportional-integral-derivative feedback channel to calculate the feedback correction current;

[0078] The pre-compensation current is superimposed with the feedback correction current to obtain the required compensation current.

[0079] Furthermore, the adjustment process of the electromagnetic compensation field is as follows:

[0080] When the current direction of the electromagnetic coil assembly is consistent with the direction of the permanent magnet main field, the electron beam focusing effect is enhanced by superimposing a co-directional electromagnetic compensation field.

[0081] When the current direction of the electromagnetic coil assembly is opposite to the direction of the permanent magnet main field, the electron beam focusing intensity is weakened by superimposing a reverse electromagnetic compensation field.

[0082] Dynamic compensation is achieved by adjusting the forward and reverse currents to compensate for electron beam disturbances caused by space charge effect, high voltage fluctuations, and thermal deformation, so that the electron beam bombards the target area with a stable focal spot size and position.

[0083] A method for controlling a permanent magnet-electromagnetic composite focusing lens includes the following steps:

[0084] Step S1: Based on the electron beam energy, current density and target focal spot size, perform permanent magnet structure parameter matching, electromagnetic coil initial current setting and control system calibration to complete the initialization setting of the electron beam focusing lens structure;

[0085] Step S2: A stable and axially symmetrical permanent magnet main field is formed in the direction of electron beam propagation by the permanent magnet main focusing module to initially focus the electron beam emitted from the cathode and entering the compound lens region;

[0086] Step S3: A compensation current of a set magnitude and direction is supplied to the electromagnetic coil assembly through the electromagnetic dynamic compensation module to superimpose an electromagnetic compensation field on the permanent magnet main field and to finely focus the electron beam.

[0087] Step S4: Obtain the electron beam focal spot size and position deviation information through the electron beam state detection component, and calculate the required compensation current based on the electron beam current change, acceleration voltage change, focal spot size deviation and position deviation.

[0088] Step S5: By controlling the drive structure, the adjustment command including the magnitude and direction of the current is sent to the electromagnetic coil drive circuit to drive the electromagnetic coil assembly to generate an adjustable electromagnetic compensation field coupled with the permanent magnet main field.

[0089] Step S6: When the direction of the electromagnetic compensation field is consistent with the direction of the permanent magnet main field, the electron beam focusing effect is enhanced; when the direction of the electromagnetic compensation field is opposite to the direction of the permanent magnet main field, the electron beam focusing intensity is weakened. This is to dynamically compensate for the electron beam disturbance caused by space charge effect, high voltage fluctuation and thermal deformation, and to make the electron beam bombard the target area with a stable focal spot size and position.

[0090] Example 1:

[0091] In this embodiment, the permanent magnet-electromagnetic composite controlled electron beam focusing lens is applied to a microfocus X-ray source, and its structural diagram is shown below. Figure 2As shown, the electron beam emitted by the electron gun is accelerated by the accelerating electrode and then enters the compound focusing lens region. The lens is set coaxially with the direction of electron beam propagation.

[0092] A schematic diagram of the X-ray generating system is shown below. Figure 3 As shown, before system startup, the permanent magnet spacing, initial coil current, and control parameters are calibrated based on the electron beam accelerating voltage, beam current intensity, and target focal spot size. During operation, the permanent magnets provide a stable main focusing magnetic field, enabling the electron beam to achieve initial convergence; the electromagnetic coils, under the control system, output positive or negative compensation currents to enhance or weaken the total focusing magnetic field. The beam spot detection device acquires real-time information on the electron beam focal spot size or focal point position deviation, and the controller adjusts the compensation current based on the detection results to ensure stable bombardment of the anode target by the electron beam.

[0093] This embodiment can reduce the temperature rise caused by continuous high current driving of the coil during long-term operation of the X-ray source, and improve the stability of the focal spot size and focal position.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A permanent magnet-electromagnetic composite control focusing lens structure, characterized in that, include: The permanent magnet main focusing module is used to achieve initial focusing of the electron beam by forming a stable and axisymmetric permanent magnet main field in the direction of electron beam propagation through a multi-ring combined permanent magnet. The electromagnetic dynamic compensation module is used to generate an adjustable electromagnetic compensation field coupled with the main field of the permanent magnet by means of an electromagnetic coil assembly wound around the outside of the permanent magnet, so as to adjust the magnetic flux density and magnetic field distribution of the main field of the permanent magnet. The magnetic circuit structure is used to form a closed magnetic circuit by a magnetic yoke located outside the permanent magnet and the electromagnetic coil assembly to achieve magnetic flux constraint, leakage magnetic field reduction and suppression of external electromagnetic interference; A thermal management and stability control structure is used to obtain the coil temperature through a cooling structure and a temperature sensor, and to feed back the temperature signal to reduce the impact of temperature rise on the electromagnetic coil assembly. The control drive structure is used to calculate the compensation current based on the electron beam focal spot size, position deviation information, electron beam current and acceleration voltage changes, and drive the electromagnetic coil assembly to achieve dynamic closed-loop control of the electron beam focal spot size and position. Each module is arranged coaxially along the electron beam propagation direction to form an axisymmetric composite magnetic field environment.

2. The permanent magnet-electromagnetic composite control focusing lens structure according to claim 1, characterized in that, The permanent magnet main focusing module includes a ring-shaped permanent magnet assembly made of neodymium iron boron material. The ring-shaped permanent magnet assembly is magnetized along a preset magnetization direction to form a stable magnetic field distribution in the electron beam propagation direction and reduce the initial divergence angle of the electron beam. The multi-segment permanent magnet assembly includes multiple permanent magnet rings spaced apart along the direction of electron beam propagation. The multiple permanent magnet rings form an axial gradient magnetic field distribution through different sizes and spacings, which is used to compress the electron beam step by step and provide the pre-focused electron beam input to the electromagnetic dynamic compensation module.

3. The permanent magnet-electromagnetic composite control focusing lens structure according to claim 1, characterized in that, The electromagnetic dynamic compensation module includes a low-inductance electromagnetic coil assembly, which uses multi-strand insulated stranded wire wound around the outside of a permanent magnet to reduce AC losses and improve the response speed of the electromagnetic compensation field to changes in the compensation current.

4. The permanent magnet-electromagnetic composite control focusing lens structure according to claim 3, characterized in that, The low-inductance electromagnetic coil assembly includes a multi-layer coil structure, which is divided into a coarse adjustment coil and a fine adjustment coil. The coarse adjustment coil is used to adjust the focusing intensity range based on the compensation current, and the fine adjustment coil is used to continuously adjust the electron beam focusing state based on the feedback correction current.

5. The permanent magnet-electromagnetic composite control focusing lens structure according to claim 1, characterized in that, The specific configuration of the magnetic circuit structure is as follows: A magnetic yoke made of high-permeability soft magnetic material is used to surround the permanent magnet and the electromagnetic coil assembly. A closed magnetic circuit is formed by the magnetic yoke in conjunction with the permanent magnet main focusing module and the electromagnetic dynamic compensation module to concentrate and confine the magnetic flux to the electron beam propagation region. External electromagnetic interference is shielded by a closed magnetic circuit to maintain a stable composite magnetic field distribution within the electron beam propagation area.

6. The permanent magnet-electromagnetic composite control focusing lens structure according to claim 1, characterized in that, The specific structure of the thermal management and stability control system is as follows: A heat exchange and cooling structure thermally coupled to the electromagnetic coil assembly is provided inside the coil frame of the electromagnetic coil assembly, and the heat exchange and cooling structure forms a heat conduction path from the electromagnetic coil assembly to the external heat dissipation medium. Temperature sensors are placed at key locations in the electromagnetic coil assembly and its surrounding environment to collect coil temperature signals and ambient temperature signals; The coil temperature signal and the ambient temperature signal are fed back to the control drive structure to correct the compensation current and reduce the impact of temperature rise on the magnetic field distribution.

7. The permanent magnet-electromagnetic composite control focusing lens structure according to claim 1, characterized in that, The dynamic focusing control process of the control drive structure is as follows: The electron beam focal spot size and position deviation information are obtained by the electron beam state detection component to obtain the electron beam focusing state detection result; Based on the preset model, the detection results of the electron beam focusing state, and the changes in electron beam current and accelerating voltage, the required compensation current is calculated to obtain the current magnitude and current direction of the electromagnetic coil assembly. The adjustment command, which includes the magnitude and direction of the current, is sent to the electromagnetic coil drive circuit to drive the electromagnetic coil assembly to generate an electromagnetic compensation field and achieve closed-loop adjustment of the size and position of the electron beam focal spot.

8. The permanent magnet-electromagnetic composite control focusing lens structure according to claim 7, characterized in that, The calculation process for the required compensation current is as follows: The changes in electron beam current and accelerating voltage are input into the feedforward compensation channel to calculate the pre-compensation current. Input the focal spot size deviation and position deviation into the proportional-integral-derivative feedback channel to calculate the feedback correction current; The pre-compensation current is superimposed with the feedback correction current to obtain the required compensation current.

9. The permanent magnet-electromagnetic composite control focusing lens structure according to claim 7, characterized in that, The adjustment process of the electromagnetic compensation field is as follows: When the current direction of the electromagnetic coil assembly is consistent with the direction of the permanent magnet main field, the electron beam focusing effect is enhanced by superimposing a co-directional electromagnetic compensation field. When the current direction of the electromagnetic coil assembly is opposite to the direction of the permanent magnet main field, the electron beam focusing intensity is weakened by superimposing a reverse electromagnetic compensation field. Dynamic compensation is achieved by adjusting the forward and reverse currents to compensate for electron beam disturbances caused by space charge effect, high voltage fluctuations, and thermal deformation, so that the electron beam bombards the target area with a stable focal spot size and position.

10. A method for controlling a permanent magnet-electromagnetic composite focusing lens, characterized in that, The permanent magnet-electromagnetic composite control focusing lens structure according to claims 1-9, wherein the permanent magnet-electromagnetic composite control focusing lens control method includes the following steps: Step S1: Based on the electron beam energy, current density and target focal spot size, perform permanent magnet structure parameter matching, electromagnetic coil initial current setting and control system calibration to complete the initialization setting of the electron beam focusing lens structure; Step S2: A stable and axially symmetrical permanent magnet main field is formed in the direction of electron beam propagation by the permanent magnet main focusing module to initially focus the electron beam emitted from the cathode and entering the compound lens region; Step S3: A compensation current of a set magnitude and direction is supplied to the electromagnetic coil assembly through the electromagnetic dynamic compensation module to superimpose an electromagnetic compensation field on the permanent magnet main field and to finely focus the electron beam. Step S4: Obtain the electron beam focal spot size and position deviation information through the electron beam state detection component, and calculate the required compensation current based on the electron beam current change, acceleration voltage change, focal spot size deviation and position deviation. Step S5: By controlling the drive structure, the adjustment command including the magnitude and direction of the current is sent to the electromagnetic coil drive circuit to drive the electromagnetic coil assembly to generate an adjustable electromagnetic compensation field coupled with the permanent magnet main field. Step S6: When the direction of the electromagnetic compensation field is consistent with the direction of the permanent magnet main field, the electron beam focusing effect is enhanced; when the direction of the electromagnetic compensation field is opposite to the direction of the permanent magnet main field, the electron beam focusing intensity is weakened. This is to dynamically compensate for the electron beam disturbance caused by space charge effect, high voltage fluctuation and thermal deformation, and to make the electron beam bombard the target area with a stable focal spot size and position.

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