An X-ray conversion target device for an electron linear accelerator

Abstract

This invention discloses an X-ray conversion target device for an electron linear accelerator, comprising: a tungsten target, serving as the core component for converting a high-energy electron beam into X-rays; a layered composite water-cooling system disposed on the back of the tungsten target for heat dissipation; an integrated encapsulation and thermal stress buffer structure for accommodating and fixing the tungsten target and the layered composite water-cooling system, and alleviating internal thermal stress; and an X-ray extraction window and shielding structure disposed on the integrated encapsulation and thermal stress buffer structure, opposite to the tungsten target, for extracting the generated X-rays and shielding stray radiation. This invention achieves efficient heat dissipation and temperature control, employing an oxygen-free copper substrate with a cooling layer to control the maximum temperature of the tungsten target under 10MeV / 20kW electron beam bombardment to below 800°C, significantly extending its service life to over 2000 hours; and improving thermal stress relief, structural reliability, real-time safety monitoring, and overall performance.

Description

Technical Field

[0001] This invention relates to the field of electron linear accelerators and X-ray generation technology, and more specifically to an X-ray conversion target device for electron linear accelerators. Background Technology

[0002] High-energy electron linear accelerators have wide applications in industrial irradiation, non-destructive testing, materials modification, and medicine. The X-ray conversion target is the core component that converts the high-energy electron beam generated by the accelerator into high-dose-rate X-rays. For high-power electron beams in the range of 10 MeV / 20 kW, the conversion target must withstand extremely high thermal loads (power densities can reach tens of kW / cm²) and continuous irradiation damage. Existing conversion target structures have significant shortcomings in terms of heat dissipation efficiency, target lifetime, and X-ray output stability.

[0003] Currently, common methods for cooling conversion targets mostly involve natural cooling or simple water-cooled pipe bonding. These solutions have the following problems:

[0004] First, the cooling channel is in contact with the target. The heat conduction path of the contact connection is long and the thermal resistance is large, making it difficult to effectively remove the deposited heat. This causes the target temperature to rise sharply (often exceeding 1500°C), resulting in the target material evaporating, cracking, or even melting.

[0005] Secondly, the large difference in thermal expansion coefficients between the target and the cooling structure makes it prone to thermal stress fatigue under long-term thermal cycling, leading to failure of the connection interface.

[0006] Third, the lack of real-time monitoring of the target's operating status makes it impossible to prevent overheating failures. While existing technologies employ microchannel cooling or composite target materials, these are mostly designed for low-power (<5kW) or pulsed electron beams, failing to meet the demands of high-power continuous wave operation (10MeV / 20kW). Therefore, developing an X-ray conversion target device capable of withstanding high-power electron beams, possessing efficient heat dissipation, and long-term stable operation is of great significance. Summary of the Invention

[0007] This invention addresses the problems existing in the prior art by proposing an X-ray conversion target device for electron linear accelerators. The aim is to achieve the design goal of a highly reliable, long-life X-ray conversion target that can adapt to 10MeV / 20kW-level high-power continuous electron beam irradiation, has efficient and uniform heat dissipation capabilities, can effectively alleviate thermal stress damage, and integrates real-time status monitoring functions.

[0008] To solve its technical problem, the present invention adopts the following technical solution:

[0009] An X-ray conversion target device for an electron linear accelerator includes: a tungsten target, serving as the core component for converting a high-energy electron beam into X-rays; a layered composite water-cooling system disposed on the back of the tungsten target for heat dissipation; an integrated encapsulation and thermal stress buffer structure for accommodating and fixing the tungsten target and the layered composite water-cooling system, and for alleviating thermal stress within the structure; and an X-ray extraction window and shielding structure disposed on the integrated encapsulation and thermal stress buffer structure, opposite to the tungsten target, for extracting the generated X-rays and shielding stray radiation; the oxygen-free copper thermally conductive substrate (3) has an integrated water-cooling channel (3-1), and the layered composite water-cooling system includes the oxygen-free copper thermally conductive substrate (3), which contains the water-cooling channel (3-1).

[0010] Its features are as follows: the layered composite water cooling system is composed of a graphite pad brazing layer (2), an oxygen-free copper thermal conductive substrate (3), and an aerogel insulation layer (5); the front side of the oxygen-free copper thermal conductive substrate (3) is connected to the back side of the tungsten target (1) through the brazing layer (2-1) to form a low thermal resistance and high strength connection interface; an aerogel insulation layer (5) is set on the back side of the cooling layer (3-1) to prevent the heat from the cooling channel from radiating outward; the integrated packaging and thermal stress buffer structure includes: a packaging shell (8) and a thermal stress buffer. The heat stress buffer layer is set at the edge of the connection layer between the tungsten target (1) and the oxygen-free copper thermal conductive substrate (3), and at the edge of the connection layer between the oxygen-free copper thermal conductive substrate (3) and the encapsulation shell (8); a K-type armored thermocouple (4) is embedded in the oxygen-free copper thermal conductive substrate (3) near the tungsten target (1) to measure the temperature of the oxygen-free copper thermal conductive substrate (3); the encapsulation shell (8) is made of stainless steel, has a cavity inside, and has an inlet and an outlet connected to the layered composite water cooling system.

[0011] Furthermore, the tungsten target is made of tungsten material with a purity of ≥99.95% and a density of ≥19.2 g / cm³. It is a rectangular sheet with a mechanically polished electron beam incident surface and a chemically etched X-ray exit surface to form a micro-uneven structure. The target thickness of 2 mm matches the range of the 10 MeV electron beam, balancing complete electron beam blocking with low self-absorption of X-rays.

[0012] Furthermore, the target size is matched with the titanium window size of the scanning box, leaving sufficient heat diffusion area.

[0013] Furthermore, the oxygen-free copper thermal conductive substrate (3) is made of oxygen-free copper material with a purity of ≥99.99% and a thermal conductivity of up to 390 W / (m·K); the oxygen-free copper thermal conductive substrate (3) has a thickness of 8mm and a rectangular cross-section, which plays a role in the lateral expansion and uniform transfer of heat.

[0014] Furthermore, the water-cooling channel (3-1) has a rectangular cross-section, 2 mm wide and 3 mm thick; the cooling medium is deionized water with a conductivity ≤0.1 μS / cm, which is forced to circulate by an external water chiller with a rated flow rate of 12 L / min and an inlet water temperature controlled at 20±1°C; according to thermal simulation calculations, this cooling system can control the maximum operating temperature of the tungsten target to below 800°C and the average temperature to below 600°C, meeting the requirements for long-term stable operation.

[0015] Furthermore, the aerogel insulation layer (5) has a thickness of 2 mm and a thermal conductivity of ≤0.02 W / (m·K).

[0016] Furthermore, the thermal stress buffer layer is disposed at the edge of the connection layer between the tungsten target (1) and the oxygen-free copper thermal conductive substrate (3), and at the edge of the connection layer between the oxygen-free copper thermal conductive substrate (3) and the encapsulation shell (8); that is: the thermal stress buffer layer is provided with a brazing layer graphite sheet (2-2) and an oxygen-free copper layer graphite sheet (3-2), the brazing layer graphite sheet (2-2) is filled in the same layer as the brazing layer (2-1) and is located at the outer edge of the layer; the oxygen-free copper layer graphite sheet (3-2) is filled in the same layer as the oxygen-free copper thermal conductive substrate (3) and is located at the outer edge of the layer; the graphite sheet is a highly thermally conductive flexible graphite sheet, which has excellent compression resilience, can absorb the expansion difference generated during thermal cycling, and maintain good thermal conductivity, avoiding stress concentration and interface cracking caused by rigid connection.

[0017] Furthermore, the high thermal conductivity flexible graphite sheet has a thickness of 0.5 mm and a thermal conductivity of 150 W / (m·K).

[0018] Furthermore, the temperature measuring point of the K-type armored thermocouple (4) is 1 mm away from the back of the target. At the same time, a flow sensor and a temperature sensor are installed in the external cooling water outlet pipe. The flow sensor is used to measure the water flow rate, and the temperature sensor is used to measure the water temperature. All sensor signals are connected to an external controller. When the temperature of the oxygen-free copper thermal conductive substrate (3) exceeds 850°C or the cooling water flow rate is lower than 8 L / min, the electron beam cut-off protection is automatically triggered to ensure the safety of the device.

[0019] Advantages and effects of the present invention

[0020] 1. High-efficiency heat dissipation and temperature control: This invention achieves a transformation from "extensive cooling" to "directional heat conduction" through the brazing connection between the target and the oxygen-free copper cooling layer. This significantly shortens the heat transfer path from the tungsten target to the oxygen-free copper thermally conductive substrate, thereby significantly reducing thermal resistance. Combined with the oxygen-free copper thermally conductive substrate containing cooling channels and forced convection cooling with deionized water, the maximum temperature of the tungsten target can be controlled below 800℃ under 10MeV / 20kW electron beam bombardment, which is far below the melting point (3422℃) and recrystallization temperature (approximately 1200℃) of tungsten. This effectively prevents the target from melting, evaporating, and undergoing thermal deformation, and the service life is expected to exceed 2000 hours.

[0021] 2. Thermal Stress Relief and Structural Reliability: Addressing the issue of significant differences in thermal expansion coefficients between the target and cooling structure, which can easily lead to thermal stress fatigue, this invention introduces an oxygen-free copper-layer graphite sheet (3-2) and a brazed graphite sheet (2-2). The highly thermally conductive flexible graphite sheet acts as a "buffer," utilizing its excellent compressive resilience and thermal conductivity to absorb dimensional changes caused by thermal expansion, release interfacial stress, and avoid stress concentration and interfacial cracking caused by rigid connections. This significantly improves the reliability and fatigue life of the structure under thermal cycling.

[0022] 3. Real-time safety monitoring and fault prevention: This invention integrates a K-type armored thermocouple (4) inside the oxygen-free copper thermal conductive substrate (3) near the tungsten target (1) to monitor the temperature of key areas in real time; at the same time, flow and temperature sensors are set in the cooling water outlet pipeline to comprehensively monitor the cooling status. The sensor signals are connected to an external controller to form a closed-loop intelligent interlocking protection mechanism: when the temperature of the oxygen-free copper thermal conductive substrate exceeds 850℃ or the cooling water flow rate is lower than 8L / min, the system automatically cuts off the electron beam to achieve early warning and active protection against faults, ensuring the safe operation of the device.

[0023] 4. Parameter Matching Optimization: The target thickness (2mm) is matched with the 10MeV electron beam range, balancing the requirements of complete electron beam blocking and low X-ray self-absorption; the target size is coordinated with the titanium window size of the scanning box, reserving sufficient thermal diffusion area. The above parameters are specifically optimized for the 10MeV / 20kW power combination, and are not simple conventional selections.

[0024] 5. High X-ray output efficiency: High-purity tungsten target and high-transmittance beryllium window (6) are used to minimize the attenuation of X-rays during generation and extraction. The X-ray conversion efficiency is not less than 80% (relative to the calculated value of an ideal thin target). The output dose rate fully meets the requirements of industrial irradiation and detection.

[0025] 6. Improved overall performance: Compared with existing technologies, this invention extends the maintenance cycle from several days to several months under the same 10MeV / 20kW operating conditions, achieving significant improvements in reliability, service life and operating economy, with outstanding economic and social benefits. Attached Figure Description

[0026] Figure 1 Convert the target top view to existing technology;

[0027] Figure 2 Convert the target HH cross-sectional view to the existing technology;

[0028] Figure 3 A cross-sectional view of a tungsten target using existing technology;

[0029] Figure 4 This is a cross-sectional view of an existing oxygen-free copper thermally conductive substrate.

[0030] Figure 5 This is a cross-sectional view of a beryllium window in the prior art;

[0031] Figure 6 This is a cross-sectional view of a lead shielding layer in the prior art.

[0032] Figure 7 This is a top view of the target converted according to the present invention;

[0033] Figure 8 This is a cross-sectional view of the conversion target AA of the present invention;

[0034] Figure 9a For the present invention Figure 8 BB brazing layer plan view;

[0035] Figure 9b For the present invention Figure 8 A cross-sectional view of the CC layer of the brazing layer;

[0036] Figure 10 For the present invention Figure 8 DD plan view of oxygen-free copper thermally conductive substrate;

[0037] Figure 11 For the present invention Figure 8 A plan view of the aerogel insulation layer EE;

[0038] Figure 12 For the present invention Figure 8 FF plan view of beryllium window;

[0039] Figure 13 For the present invention Figure 8 A plan view of the lead shielding layer GG.

[0040] In the figure, 1: Tungsten target; 2-1: Brazing layer; 2-2: Brazing layer graphite sheet; 3: Oxygen-free copper thermal conductive substrate; 3-1: Water tank; 3-2: Oxygen-free copper layer graphite sheet; 4: Thermocouple; 5: Aerogel insulation layer; 6: Beryllium window; 7: Lead shielding layer; 8: Stainless steel shell; 9: Tungsten target; 10: Oxygen-free copper thermal conductive substrate; 11: Beryllium window; 12: Lead shielding layer; 13: Stainless steel shell. Detailed Implementation

[0041] Design principle of the invention

[0042] 1. High-Efficiency Thermal Management: From "Extensive Cooling" to "Directional Heat Conduction." This approach transforms traditional contact-based "extensive cooling" into "directional heat conduction" based on metallurgical bonding. It abandons mechanical contact connections that easily generate high interfacial thermal resistance and innovatively employs brazing metallurgical bonding technology. Through brazing layer 2-1, a robust metallurgical connection is achieved between the back side of the heat-generating tungsten target 1 and the front side of the oxygen-free copper thermally conductive substrate 3. This significantly shortens the heat transfer path from the target to the cooling substrate, greatly reduces interfacial thermal resistance, and achieves efficient, low-resistance heat conduction along a predetermined path, fundamentally improving heat dissipation efficiency.

[0043] 2. Stress Management: From "Rigid Connection" to "Flexible Buffer". This addresses the stress problem caused by the mismatch in thermal expansion coefficients between tungsten and oxygen-free copper, transforming the "rigid connection" into a "flexible buffer". A highly thermally conductive flexible graphite sheet is creatively introduced as a stress buffer layer. Specifically, a brazing layer graphite sheet 2-2 is placed on the outer edge of the brazing layer 2-1, and an oxygen-free copper layer graphite sheet 3-2 is placed on the outer edge of the oxygen-free copper thermally conductive substrate 3. The graphite sheet utilizes its excellent compressive resilience and thermal conductivity to effectively absorb the deformation and stress caused by the difference in material expansion during thermal cycling, alleviating interface stress concentration, preventing interface cracking caused by rigid connections, and significantly improving the reliability and lifespan of the structure under thermal fatigue.

[0044] 3. Status Monitoring and Safety: From "Passive Protection" to "Proactive Intelligence". The safety mode is upgraded from passive protection of "post-fault handling" to proactive intelligent monitoring of "pre-fault intervention". K-type armored thermocouples 4 are integrated into key locations within the oxygen-free copper thermal conductive substrate 3 to monitor the temperature near the target in real time. Combined with flow and temperature sensors on the cooling water circuit, a dual-dimensional real-time monitoring system of temperature and flow is constructed. All sensor signals are connected to an external controller, forming a closed-loop interlocking protection mechanism. When the temperature of the oxygen-free copper thermal conductive substrate exceeds 850°C or the cooling water flow rate falls below 8 L / min, the system automatically triggers electron beam cutoff, achieving early warning and proactive protection against faults, ensuring operational safety.

[0045] In summary, this invention systematically overcomes the key challenges of existing technologies by synergistically implementing three core principles: directional heat conduction, flexible buffering, and intelligent monitoring. It provides a high-performance, long-life, and highly reliable X-ray conversion target device solution for electron linear accelerators.

[0046] Innovation of this invention

[0047] 1. The use of brazing metallurgical bonding significantly improves thermal conductivity. Addressing the problem of long heat conduction paths and high thermal resistance caused by contact connections between the target and cooling layer in existing technologies, this invention innovatively uses a brazing layer (2-1) to connect the tungsten target (1) to the oxygen-free copper thermally conductive substrate (3). This metallurgical bonding method replaces traditional mechanical contact, reduces interfacial thermal resistance, and shortens the heat transfer path to the cooling medium, thereby achieving efficient and low-resistance heat conduction.

[0048] 2. Introducing a flexible graphite sheet buffer layer effectively alleviates thermal stress fatigue. To address the risk of thermal stress fatigue and interface cracking caused by the mismatch in thermal expansion coefficients between the target and the thermally conductive substrate, this invention creatively introduces a highly thermally conductive flexible graphite sheet as a buffer structure. Specifically, a brazed graphite sheet 2-2 is placed on the outer edge of the brazed layer 2-1, and an oxygen-free copper graphite sheet 3-2 is placed on the outer edge of the oxygen-free copper thermally conductive substrate 3. This design utilizes the excellent compressive resilience and thermal conductivity of the graphite sheet to effectively absorb dimensional changes and expansion differences during thermal cycling, alleviate interface stress concentration, and significantly enhance structural reliability and service life.

[0049] 3. Integrated Real-time Temperature Monitoring and Closed-Loop Interlocking Protection System: To overcome the shortcomings of existing technologies in monitoring the target's operating status, this invention embeds a K-type armored thermocouple 4 near the target inside the oxygen-free copper thermally conductive substrate 3 to monitor the substrate temperature in real time. Combined with flow and temperature sensors at the cooling water outlet, a multi-dimensional real-time monitoring system is constructed. When key parameters such as temperature or flow exceed safety thresholds, the system automatically triggers electron beam cutoff protection, forming a closed-loop interlocking protection mechanism, thereby proactively preventing overheating faults and significantly improving operational safety.

[0050] Based on the above principles, this invention designs an X-ray conversion target device for an electron linear accelerator, such as... Figure 1-13As shown, it includes: a tungsten target, serving as the core component for converting a high-energy electron beam into X-rays; a layered composite water-cooling system disposed on the back of the tungsten target for heat dissipation; an integrated package and thermal stress buffer structure for accommodating and fixing the tungsten target and the layered composite water-cooling system, and for alleviating internal thermal stress; and an X-ray extraction window and shielding structure disposed on the integrated package and thermal stress buffer structure, opposite to the tungsten target, for extracting the generated X-rays and shielding stray radiation; the oxygen-free copper thermally conductive substrate 3 integrates a water-cooling channel 3-1, and the layered composite water-cooling system includes the oxygen-free copper thermally conductive substrate 3, which in turn includes the water-cooling channel 3-1.

[0051] Its features include: the layered composite water cooling system comprises a graphite pad brazing layer 2, an oxygen-free copper thermally conductive substrate 3, and an aerogel insulation layer 5; the front side of the oxygen-free copper thermally conductive substrate 3 is connected to the back side of the tungsten target 1 through the brazing layer 2-1, forming a low thermal resistance and high strength connection interface; an aerogel insulation layer 5 is provided on the back side of the cooling layer 3-1 to prevent heat from radiating outward from the cooling channel; the integrated encapsulation and thermal stress buffer structure includes: an encapsulation shell 8 and a thermal stress buffer layer, which is located at the edge of the connection layer between the tungsten target 1 and the oxygen-free copper thermally conductive substrate 3, and at the edge of the connection layer between the oxygen-free copper thermally conductive substrate 3 and the encapsulation shell 8; a K-type armored thermocouple 4 is embedded inside the oxygen-free copper thermally conductive substrate 3 near the tungsten target 1 to measure the temperature of the oxygen-free copper thermally conductive substrate 3; the encapsulation shell 8 is made of stainless steel, has an internal cavity, and is provided with an inlet and an outlet that communicate with the layered composite water cooling system.

[0052] The tungsten target is made of tungsten material with a purity of ≥99.95% and a density of ≥19.2 g / cm³. It is a rectangular thin sheet. The electron beam incident surface is mechanically polished, and the X-ray exit surface is chemically etched to form a micro-uneven structure. The target thickness of 2 mm matches the range of the 10 MeV electron beam, taking into account both complete electron beam blocking and low self-absorption of X-rays.

[0053] The target size is matched with the titanium window size of the scanning box, leaving sufficient heat diffusion area.

[0054] The oxygen-free copper thermal conductive substrate 3 is made of oxygen-free copper material with a purity of ≥99.99% and a thermal conductivity of up to 390 W / (m·K). The oxygen-free copper thermal conductive substrate 3 has a thickness of 8mm and a rectangular cross-section, which plays a role in the lateral expansion and uniform transfer of heat.

[0055] The water-cooling channel 3-1 has a rectangular cross-section, 2mm wide and 3mm thick; the cooling medium is deionized water with a conductivity ≤0.1 μS / cm, which is forced to circulate by an external water chiller with a rated flow rate of 12 L / min and an inlet water temperature controlled at 20±1°C; according to thermal simulation calculations, this cooling system can control the maximum operating temperature of the tungsten target below 800°C and the average temperature below 600°C, meeting the requirements for long-term stable operation.

[0056] The aerogel insulation layer 5 has a thickness of 2 mm and a thermal conductivity of ≤0.02 W / (m·K).

[0057] The thermal stress buffer layer is disposed at the edge of the connection layer between the tungsten target 1 and the oxygen-free copper thermally conductive substrate 3, and at the edge of the connection layer between the oxygen-free copper thermally conductive substrate 3 and the encapsulation shell 8; that is: the thermal stress buffer layer is provided with a brazed graphite sheet 2-2 and an oxygen-free copper graphite sheet 3-2. The brazed graphite sheet 2-2 is filled in the same layer as the brazed layer 2-1 and is located at the outer edge of the layer; the oxygen-free copper graphite sheet 3-2 is filled in the same layer as the oxygen-free copper thermally conductive substrate 3 and is located at the outer edge of the layer; the graphite sheet is a highly thermally conductive flexible graphite sheet, which has excellent compressive resilience, can absorb the expansion difference generated during thermal cycling, and maintain good thermal conductivity, avoiding stress concentration and interface cracking caused by rigid connection.

[0058] Supplementary Note 1:

[0059] like Figure 9a , Figure 9b As shown, the outer ring of the brazing layer 2-1 in the vacuum region of the brazing layer is a rectangular frame of brazing layer 2-1, and the outer ring of the rectangular frame of brazing layer 2-1 is a graphite sheet 2-2 of the brazing layer. The rectangular frame 2-1 and the graphite sheet 2-2 of the brazing layer are in the same layer. The outer ring of the graphite sheet 2-2 of the brazing layer is a stainless steel shell 8.

[0060] like Figure 10 As shown, the oxygen-free copper layer graphite sheet 3-2 is on the outer ring of the oxygen-free copper thermal conductive substrate 3, and is in the same layer as the oxygen-free copper thermal conductive substrate 3. The oxygen-free copper thermal conductive substrate 3 is on the outer ring of the vacuum region of the oxygen-free copper layer. The outer ring of the oxygen-free copper layer graphite sheet 3-2 is a stainless steel shell 8.

[0061] The water-cooling channel is located inside the oxygen-free copper heat-conducting substrate, between the oxygen-free copper layer graphite sheet 3-2 and the oxygen-free copper layer vacuum region.

[0062] The brazing layer 2-1 faces upwards onto the back or lower surface of the tungsten target 1 (e.g., the back or lower surface). Figure 9aThe side that penetrates the paper is the back side), and the oxygen-free copper heat-conducting substrate 3-1 is welded to the front or upper surface of the substrate downwards, changing the contact connection between the tungsten target and the oxygen-free copper heat-conducting substrate in the existing technology to a metallurgical connection, thus shortening the heat conduction path.

[0063] Supplementary Note 2:

[0064] Figures 8 to 11 Each has a rectangular vacuum area located in the center. Figure 12 Instead of a rectangular vacuum region, a vacuum-sealed region was used. Figure 13 Instead of a rectangular vacuum seal area, a rectangular atmospheric area is used.

[0065] The highly thermally conductive flexible graphite sheet is 0.5 mm thick and has a thermal conductivity of 150 W / (m·K).

[0066] The K-type armored thermocouple 4 has a temperature measuring point 1 mm away from the back of the target. At the same time, a flow sensor and a temperature sensor are installed in the external cooling water outlet pipe. The flow sensor is used to measure the water flow rate, and the temperature sensor is used to measure the water temperature. All sensor signals are connected to an external controller. When the temperature of the oxygen-free copper thermal conductive substrate 3 exceeds 850°C or the cooling water flow rate is lower than 8 L / min, the electron beam cut-off protection is automatically triggered to ensure the safety of the device.

[0067] Example 1

[0068] 1. Tungsten target structure design

[0069] The conversion target of this invention uses high-purity (≥99.95%), high-density (≥19.2 g / cm³) tungsten material as the target body. Tungsten has a high atomic number (Z=74), a high melting point (3422°C), a high thermal conductivity (173 W / (m·K)), and good radiation resistance, which can effectively convert a 10MeV electron beam into continuous spectrum X-rays, while withstanding high-power electron beam bombardment.

[0070] The target is designed as a rectangular thin sheet structure, 1000 mm long, 200 mm wide, and 2 mm thick. This thickness was optimized based on the continuously moderated approximate range (CSDA range of approximately 1.8 mm) of a 10 MeV electron beam in tungsten material, ensuring that most of the electron beam energy is deposited within the target while avoiding X-ray self-absorption caused by excessive thickness. The front side of the target is the electron beam incident surface, which is precision mechanically polished (surface roughness Ra ≤ 0.4 μm) to reduce local overheating and surface evaporation. The back side of the target is the X-ray exit surface, which is chemically etched to form a micro-uneven structure, increasing the contact area with the subsequent heat-conducting substrate and reducing interfacial thermal resistance.

[0071] 2. Design of a layered composite water cooling system

[0072] To address the high heat load (average heat flux density of approximately 1.02 kW / cm², with even higher peak values) resulting from a 20 kW electron beam power, this invention incorporates a layered composite water-cooling system on the back of the tungsten target. This system comprises an oxygen-free copper thermally conductive substrate, a cooling layer, and a thermal insulation layer.

[0073] 1) Oxygen-free copper thermally conductive substrate: Oxygen-free copper material (purity ≥99.99%) is used, with a thermal conductivity as high as 390 W / (m·K), far exceeding that of ordinary copper materials. The front side of the substrate is connected to the back side of the tungsten target through a vacuum brazing process, forming a low thermal resistance and high strength connection interface. The substrate thickness is 8mm, which plays a role in the lateral expansion and uniform transfer of heat.

[0074] 2) Cooling Layer: Water-cooling channels are machined inside the oxygen-free copper thermally conductive substrate. The channel cross-section is rectangular (2mm wide, 3mm deep). The cooling medium is deionized water (conductivity ≤0.1 μS / cm), which is forcibly circulated by an external water chiller with a rated flow rate of 12L / min and an inlet water temperature controlled at 20±1°C. Thermal simulation calculations show that this cooling system can control the maximum operating temperature of the tungsten target below 800°C and the average temperature below 600°C, meeting the requirements for long-term stable operation.

[0075] 3) Insulation layer: An aerogel insulation layer (2mm thick) with a thermal conductivity ≤0.02 W / (m·K) is installed on the back of the cooling layer to prevent heat from the cooling channel from radiating outward, improve cooling efficiency and protect external equipment.

[0076] 3. Integrated packaging and thermal stress buffer structure

[0077] To eliminate the tungsten target (thermal expansion coefficient 4.5 × 10⁻) 6 / K), oxygen-free copper thermally conductive substrate (thermal expansion coefficient 16.5×10⁻ 6 / K) and encapsulation housing (stainless steel, coefficient of thermal expansion 17.3×10⁻ 6 To address the thermal mismatch issue between / K), this invention employs an integrated packaging structure with a built-in thermal stress buffer layer.

[0078] 1) Encapsulation housing: Made of 304L stainless steel, rectangular in shape, 1200mm in length, 300mm in width, and 12mm in height. The housing has an internal cavity to accommodate the target, substrate, and cooling channels, and is equipped with water inlet and outlet, both of which use quick-connect fittings for easy on-site installation.

[0079] 2) Thermal stress buffer layer: High thermal conductivity flexible graphite sheets (0.5 mm thick, thermal conductivity 150 W / (m·K)) are filled at the edges of the brazed connection layer between the tungsten target and the oxygen-free copper thermally conductive substrate, and between the substrate and the shell. This graphite sheet has excellent compressive resilience, which can absorb the expansion difference generated during thermal cycling, while maintaining good thermal conductivity and avoiding stress concentration and interface cracking caused by rigid connection.

[0080] 3) Sensor Integration: A type K-type armored thermocouple (temperature measurement point 1mm from the back of the target) is embedded inside the oxygen-free copper thermally conductive substrate near the tungsten target. Simultaneously, a flow sensor and a temperature sensor are installed in the cooling water outlet pipe. All sensor signals are connected to an external controller. When the target temperature exceeds 850°C or the cooling water flow rate falls below 8 L / min, the electron beam cutoff protection is automatically triggered to ensure device safety.

[0081] 4. X-ray extraction window and shielding structure

[0082] An X-ray extraction window is positioned on the back of the encapsulation housing, facing the tungsten target. The window is made of beryllium (0.5 mm thick, purity ≥99.5%), which has a low atomic number (Z=4), a high melting point (1287°C), and high X-ray transmittance, with an absorption rate of less than 5% for 10 MeV bremsstrahlung X-rays. The window is sealed to the housing using argon arc welding, ensuring a vacuum level better than 1×10⁻⁻⁻⁶. 4 Pa. A lead shielding layer, 12 mm thick, is installed around the window to absorb scattered electrons and stray radiation. The shielding layer is lined internally.

[0083] It should be emphasized that the above specific embodiments are merely explanations of the present invention and are not intended to limit the present invention. After reading this specification, those skilled in the art can make modifications to the above embodiments without contributing any inventive step, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. An X-ray conversion target device for an electron linear accelerator, comprising: Tungsten target, as the core component for converting high-energy electron beams into X-rays; A layered composite water cooling system is disposed on the back of the tungsten target to dissipate heat from the tungsten target; an integrated package and thermal stress buffer structure is used to accommodate and fix the tungsten target and the layered composite water cooling system, and to alleviate the thermal stress inside the structure; and an X-ray extraction window and shielding structure are disposed on the integrated package and thermal stress buffer structure, opposite to the tungsten target, to extract the generated X-rays and shield stray radiation; the oxygen-free copper thermal conductive substrate (3) has an integrated water cooling channel (3-1), the layered composite water cooling system includes the oxygen-free copper thermal conductive substrate (3), and the oxygen-free copper thermal conductive substrate (3) includes the water cooling channel (3-1). The layered composite water cooling system is characterized by comprising a graphite pad brazing layer (2), an oxygen-free copper thermal conductive substrate (3), and an aerogel insulation layer (5); the front side of the oxygen-free copper thermal conductive substrate (3) is connected to the back side of the tungsten target (1) through a brazing layer (2-1) to form a low thermal resistance and high strength connection interface; an aerogel insulation layer (5) is provided on the back side of the cooling layer (3-1) to prevent heat from the cooling channel from radiating outwards; the integrated packaging and thermal stress buffer structure includes: a packaging shell (8) and a thermal stress buffer. The heat stress buffer layer is set at the edge of the connection layer between the tungsten target (1) and the oxygen-free copper thermal conductive substrate (3), and at the edge of the connection layer between the oxygen-free copper thermal conductive substrate (3) and the encapsulation shell (8); a K-type armored thermocouple (4) is embedded in the oxygen-free copper thermal conductive substrate (3) near the tungsten target (1) to measure the temperature of the oxygen-free copper thermal conductive substrate (3); the encapsulation shell (8) is made of stainless steel, has a cavity inside, and has an inlet and an outlet connected to the layered composite water cooling system.

2. The X-ray conversion target device for an electron linear accelerator according to claim 1, characterized in that, The tungsten target is made of tungsten material with a purity of ≥99.95% and a density of ≥19.2 g / cm³. It is a rectangular thin sheet. The electron beam incident surface is mechanically polished, and the X-ray exit surface is chemically etched to form a micro-uneven structure. The target thickness of 2 mm matches the range of the 10 MeV electron beam, taking into account both complete electron beam blocking and low self-absorption of X-rays.

3. The X-ray conversion target device for an electron linear accelerator according to claim 1, characterized in that, The target size is matched with the titanium window size of the scanning box, leaving sufficient heat diffusion area.

4. The X-ray conversion target device for an electron linear accelerator according to claim 1, characterized in that, The oxygen-free copper thermal conductive substrate (3) is made of oxygen-free copper material with a purity of ≥99.99% and a thermal conductivity of up to 390 W / (m·K). The oxygen-free copper thermal conductive substrate (3) has a thickness of 8mm and a rectangular cross-section, which plays a role in the lateral expansion and uniform transfer of heat.

5. An X-ray conversion target device for an electron linear accelerator according to claim 1, characterized in that, The water-cooling channel (3-1) has a rectangular cross-section, 2 mm wide and 3 mm thick; the cooling medium is deionized water with a conductivity ≤0.1 μS / cm, which is forced to circulate by an external water chiller with a rated flow rate of 12 L / min and an inlet water temperature controlled at 20±1°C; according to thermal simulation calculations, the cooling system can control the maximum operating temperature of the tungsten target below 800°C and the average temperature below 600°C, meeting the requirements for long-term stable operation.

6. An X-ray conversion target device for an electron linear accelerator according to claim 1, characterized in that, The aerogel insulation layer (5) has a thickness of 2 mm and a thermal conductivity of ≤0.02 W / (m·K).

7. The X-ray conversion target device for an electron linear accelerator according to claim 1, characterized in that, The thermal stress buffer layer is disposed at the edge of the connection layer between the tungsten target (1) and the oxygen-free copper thermal conductive substrate (3), and at the edge of the connection layer between the oxygen-free copper thermal conductive substrate (3) and the encapsulation shell (8); that is: the thermal stress buffer layer is provided with a brazing layer graphite sheet (2-2) and an oxygen-free copper layer graphite sheet (3-2). The brazing layer graphite sheet (2-2) is filled in the same layer as the brazing layer (2-1) and is located at the outer edge of the layer; the oxygen-free copper layer graphite sheet (3-2) is filled in the same layer as the oxygen-free copper thermal conductive substrate (3) and is located at the outer edge of the layer; the graphite sheet is a highly thermally conductive flexible graphite sheet. The graphite sheet has excellent compression resilience and can absorb the expansion difference generated during the thermal cycle, while maintaining good thermal conductivity and avoiding stress concentration and interface cracking caused by rigid connection.

8. An X-ray conversion target device for an electron linear accelerator according to claim 8, characterized in that, The highly thermally conductive flexible graphite sheet is 0.5 mm thick and has a thermal conductivity of 150 W / (m·K).

9. An X-ray conversion target device for an electron linear accelerator according to claim 1, characterized in that, The temperature measuring point of the K-type armored thermocouple (4) is 1 mm away from the back of the target. At the same time, a flow sensor and a temperature sensor are installed in the external cooling water outlet pipe. The flow sensor is used to measure the water flow rate, and the temperature sensor is used to measure the water temperature. All sensor signals are connected to an external controller. When the temperature of the oxygen-free copper thermal conductive substrate (3) exceeds 850°C or the cooling water flow rate is lower than 8 L / min, the electron beam cut-off protection is automatically triggered to ensure the safety of the device.

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