Hot cathode for micro-focus X-ray tube and X-ray tube

Abstract

The invention provides a hot cathode for a micro-focus X-ray tube and the X-ray tube, the hot cathode comprises a cathode body, a cathode cylinder, potting ceramic, a heater, a sealing cover, a heat insulation straight cylinder, a heat insulation conical cylinder and heat insulation ceramic, the outer side wall of the cathode cylinder is sequentially provided with a first step part and a second step part, the heat insulation straight cylinder is connected with the cathode cylinder through the first step part, and the heat insulation conical cylinder is connected with the cathode cylinder through the second step part; the heat-insulating conical cylinder is located on the periphery of the heat-insulating straight cylinder, the bottom of the heat-insulating conical cylinder is connected with the heat-insulating straight cylinder, and the heat-insulating ceramic is connected to the top of the heat-insulating conical cylinder. Through the structural cooperation of the heat insulation straight cylinder, the heat insulation conical cylinder and the heat insulation ceramic, the heat flow path is prolonged and bent, and the radial heat resistance is effectively improved; through the design of the conical heat insulation cylinder, the heat flow sectional area changes in the axial direction, the heat flow density redistribution effect is generated, the heat flow density of the high-temperature end is reduced, the conical cylinder is matched with the straight cylinder to form a heat flow impedance matching structure, and heat reflection loss is reduced.

Description

Technical Field

[0001] The present invention relates to the field of X-ray technology, and in particular to a hot cathode for a microfocus X-ray tube and an X-ray tube. Background Art

[0002] As an important component in the field of industrial inspection, microfocus X-ray tubes have been widely used in many application scenarios, including semiconductors, casting, welding, and new energy. Microfocus X-ray tubes typically use a hot cathode as their electron emission source. Heat is obtained indirectly through heating by the heater behind the cathode body, reaching its emission temperature point and achieving normal electron emission from the cathode body. As the core component of a microfocus X-ray tube, changes in the emission characteristics of the hot cathode during its life cycle will limit the stability and life of the tube during long-term use. The life of the hot cathode largely depends on the life and stability of the heater, and the heater characteristics are directly related to the power size. Generally, the smaller the heater power, the better its life and stability.

[0003] However, existing hot cathodes for microfocus X-ray tubes still present several technical challenges. First, the structural design between the heater and the cathode tube is irrational, which can easily lead to heater short circuits, a failure to provide proper heating power, and consequently, failure of the cathode to properly emit electrons. Furthermore, the hot cathode's thermal insulation design is suboptimal, and excessively high heater power can result in a short lifespan and poor stability.

[0004] Therefore, there is an urgent need for a hot cathode for microfocus X-ray tubes with reasonable structural design, excellent thermal insulation performance and long service life to solve the problems existing in the existing technology such as short circuit of the heater, short life and poor stability caused by excessive power. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a hot cathode for a microfocus X-ray tube, which solves the problems of short life and poor stability caused by excessively high heater power in the prior art by increasing the thermal resistance between the cathode and the outside world and improving the thermal contact between the insulation tube and the cathode body. At the same time, the present invention will also provide a microfocus X-ray tube.

[0006] To achieve the above-mentioned and other related purposes, the present invention provides the following technical solutions:

[0007] A first aspect of the present invention provides a hot cathode for a microfocus X-ray tube, the hot cathode comprising a cathode body, a cathode cylinder, a potting ceramic, a heater, a cover, a heat-insulating straight cylinder, a heat-insulating conical cylinder, and heat-insulating ceramic; wherein:

[0008] The cathode tube is a cylindrical structure with a cathode tube opening at the bottom, the sealing cover is connected to the cathode tube through the cathode tube opening, and the potting ceramic and the heater are placed inside the cathode tube;

[0009] The outer side wall of the cathode tube is provided with a first step portion and a second step portion in sequence, the first step portion is located at the upper position of the side of the cathode tube, the second step portion is located in the middle position of the side of the cathode tube, the thermal insulation straight tube is connected to the cathode tube through the first step portion, and a gap is formed between the thermal insulation straight tube and the cathode tube through the second step portion, the thermal insulation cone is located at the periphery of the thermal insulation straight tube, the thermal insulation cone is connected to the thermal insulation straight tube at the bottom, and the thermal insulation ceramic is connected to the top of the thermal insulation cone.

[0010] The present invention reduces the external heat radiation of the entire hot cathode by adding a cover; through the structural coordination of the insulating straight cylinder, the insulating conical cylinder, and the insulating ceramic, the heat flow path is extended and the heat flow path is tortuous, thereby effectively improving the radial thermal resistance; and the design of the conical insulating cylinder causes the heat flow cross-sectional area to change along the axial direction, resulting in a heat flux density redistribution effect, thereby reducing the heat flux density at the high-temperature end, and the conical cylinder cooperates with the straight cylinder to form a "heat flow impedance matching" structure, thereby reducing heat reflection loss.

[0011] As a preferred technical solution, both the insulating straight cylinder and the insulating conical cylinder are thin-walled structures, and the side walls of the insulating straight cylinder and the insulating conical cylinder are provided with square groove structures. The square grooves are arranged in a staggered array; the ratio of the groove depth to the side wall thickness is controlled at 0.3-0.5:1; and the groove spacing is 1-3 times the groove width.

[0012] The heat flow must bypass the edge of the square groove. The design of the square groove can further increase the length of the heat flow path and improve the radial thermal resistance; combined with the thin-wall structure of the insulating straight cylinder and the insulating cone cylinder, the contact thermal resistance between the hot cathode and the external connection is increased. The simultaneous implementation of the two can effectively reduce the power of the heater, thereby improving the working stability and life of the entire cathode.

[0013] As a preferred technical solution, the thermal insulation ceramic is provided with a groove, and the groove is arranged on the upper surface and / or lower surface of the thermal insulation ceramic.

[0014] As a preferred technical solution, the heater includes a filament and pins. The filament and the potting ceramic are encapsulated inside the cathode tube, and the heat is transferred to the cathode body after being powered on and heated. The cover is provided with a through-hole for leading out the pins, and the two through-holes are located in the middle of the cover.

[0015] As a preferred technical solution, a cathode bowl is provided on the top of the cathode cylinder, and the cathode body is connected to the cathode cylinder through the cathode bowl.

[0016] As a preferred technical solution, the material of the cathode cylinder includes but is not limited to stainless steel, tantalum, Kovar alloy, Monel alloy, molybdenum alloy, tungsten alloy, etc.; the material of the insulating straight cylinder and / or the insulating cone cylinder includes but is not limited to tantalum, stainless steel, Kovar alloy, Monel alloy, etc.; the material of the cover includes but is not limited to tantalum, stainless steel, Kovar alloy, Monel alloy, etc.; the material of the insulating ceramic includes but is not limited to alumina, zirconia, forsterite, etc.

[0017] As a preferred technical solution, the cathode body and the cathode bowl of the cathode tube are connected by high-temperature brazing at 1200-1500°C; the thermally insulating straight tube and the cathode tube are connected by laser welding or resistance welding; the thermally insulating straight tube and the thermally insulating conical tube are connected by laser welding or resistance welding; the thermally insulating ceramic and the thermally insulating conical tube are connected by high-temperature brazing at 500-900°C; and the cover and the cathode tube are connected by laser welding or resistance welding.

[0018] As a preferred technical solution, the insulating straight tube has a multi-layer structure, and the insulating straight tube includes an inner surface layer, a main body layer and an outer surface layer from the inside to the outside. The thermal expansion coefficients of the inner surface layer and the outer surface layer are greater than the thermal expansion coefficient of the main body layer.

[0019] Furthermore, the inner surface layer is selected from Mo-30Cu alloy, tantalum or Kovar alloy;

[0020] The main body layer is selected from silicon nitride porous ceramics or aluminum nitride porous ceramics;

[0021] The outer layer is selected from stainless steel, nickel-based alloy, monel alloy, Y2O3-ZrO2 composite ceramic or Al2O3-MgO composite ceramic.

[0022] The present invention uses a three-layer structure of an insulating straight tube, in which the inner surface layer directly contacts the cathode tube (high-temperature heat source). A material with a larger thermal expansion coefficient is selected, which can match the thermal expansion of the cathode tube material, thereby forming a reasonable transition and avoiding interface cracking; the main layer undertakes the main insulation and support functions, so a material with low thermal conductivity and low expansion coefficient is selected to reduce the thermal deformation of the insulating straight tube, and the main layer of porous material can also absorb strain energy through the pores, thereby improving the thermal shock resistance of the insulating straight tube; the outer layer is connected to the insulating cone tube, and the higher thermal expansion coefficient can achieve thermal expansion transition with the insulating cone tube, compensating for the thermal deformation of the insulating cone tube.

[0023] Furthermore, the thermal expansion coefficient of the outer surface layer is greater than the thermal expansion coefficient of the inner surface layer.

[0024] Furthermore, the thickness of the main body layer accounts for 50%-80% of the total thickness of the heat-insulating straight tube.

[0025] A second aspect of the present invention provides a microfocus X-ray tube, wherein the microfocus X-ray tube uses the hot cathode for the microfocus X-ray tube.

[0026] As described above, the hot cathode for microfocus X-ray tube and the X-ray tube of the present invention have the following beneficial effects:

[0027] 1. The present invention effectively reduces the external heat radiation of the entire hot cathode and reduces heat loss through the design of the sealing cover; through the structural coordination of the insulating straight cylinder, the insulating conical cylinder, and the insulating ceramic, the heat flow path is extended and the heat flow path is tortuous, effectively improving the radial thermal resistance; the design of the conical insulating cylinder causes the heat flow cross-sectional area to change along the axial direction, resulting in a heat flux density redistribution effect, reducing the heat flux density at the high-temperature end, and the conical cylinder and the straight cylinder form a "heat flow impedance matching" structure, reducing heat reflection loss.

[0028] 2. The present invention can further increase the length of the heat flow path and improve the radial thermal resistance through the design of the square groove; combined with the thin-wall structure of the insulating straight cylinder and the insulating cone cylinder, the contact thermal resistance between the hot cathode and the external connection is increased, effectively reducing the power required by the heater, thereby improving the working stability and life of the entire cathode.

[0029] 3. The present invention adopts a three-layer composite structure of an insulating straight tube, and utilizes the differences in thermal expansion coefficients and thermal conductivity characteristics of different materials to achieve efficient thermal insulation and thermal management, which can be widely used in high-resolution industrial CT, medical imaging equipment, scientific research instruments and other fields; the inner surface layer is in direct contact with the cathode tube (high-temperature heat source), and a material with a larger thermal expansion coefficient is selected to match the thermal expansion of the cathode tube material, thereby forming a reasonable transition and avoiding interface cracking; the main layer bears the main insulation and support functions, so the material with low thermal conductivity and low expansion coefficient is selected to reduce the thermal deformation of the insulating straight tube, and the main layer of porous material can also absorb strain energy through the pores, thereby improving the thermal shock resistance of the insulating straight tube; the outer surface layer is connected to the insulating cone tube, and the higher thermal expansion coefficient can achieve thermal expansion transition with the insulating cone tube, compensating for the thermal deformation of the insulating cone tube.

[0030] 4. Compared with the prior art, the hot cathode structure design of the microfocus X-ray tube of the present invention is reasonable, which effectively solves the technical problems such as poor stability and short life caused by short circuit of the heater and excessive power. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic cross-sectional view of a hot cathode for a microfocus X-ray tube disclosed in Example 1 of the present invention.

[0032] Figure 2 It shows a schematic structural diagram of the end cover disclosed in Example 1 of the present invention.

[0033] Figure 3It shows a schematic diagram of the side square groove of the heat-insulating straight cylinder or heat-insulating conical cylinder disclosed in Example 1 of the present invention.

[0034] Figure 4 It shows a schematic cross-sectional view of the heat-insulating straight cylinder disclosed in Example 2 of the present invention.

[0035] Component number description

[0036] 1. Cathode body; 2. Cathode tube; 2a. Cathode bowl; 2b. First step; 2c. Second step; 2d. Cathode tube opening; 3. Potting ceramic; 4. Heater; 4a. Filament; 4b. Pin; 5. Cover; 5a. Round end face; 5b. Perforation; 6. Insulating straight tube; 6a. Square groove; 6b. Inner surface; 6c. Main body; 6d. Outer surface; 7. Insulating cone; 8. Insulating ceramic; 8a. Groove. DETAILED DESCRIPTION

[0037] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless there is a conflict.

[0038] Example 1

[0039] See also Figure 1 This embodiment provides a hot cathode for a microfocus X-ray tube, which includes a cathode body 1, a cathode tube 2, a potting ceramic 3, a heater 4, a cover 5, an insulating straight tube 6, an insulating cone 7 and an insulating ceramic 8.

[0040] The cathode tube 2 is a cylindrical structure with a cathode tube opening at the bottom. The cover 5 is connected to the cathode tube 2 through the cathode tube opening. The potting ceramic 3 and the heater 4 are placed inside the cathode tube 2. The outer wall of the cathode tube 2 is sequentially provided with a first step 2b and a second step 2c. The first step 2b is located at the upper side of the cathode tube 2, and the second step 2c is located in the middle of the side of the cathode tube 2. The thermal insulation straight tube 6 is connected to the cathode tube 2 through the first step 2b. A gap is formed between the thermal insulation straight tube 6 and the cathode tube 2 through the second step 2c. The thermal insulation cone 7 is located outside the thermal insulation straight tube 6 and is connected to the thermal insulation straight tube 6 at the bottom. The thermal insulation ceramic 8 is connected to the top of the thermal insulation cone 7.

[0041] refer to Figure 2 The heater 4 includes a filament 4a and a lead 4b. The filament 4a and the potting ceramic 3 are encapsulated within the cathode tube 2. The cover 5 includes a circular end surface 5a, which is located at the outermost periphery of the cover 5 and has a through-hole 5b for the lead 4b to be led out. The cathode tube 2 is topped with a cathode bowl 2a, through which the cathode body 1 is connected to the cathode tube 2.

[0042] refer to Figure 3 The heat-insulating straight cylinder 6 and the heat-insulating cone cylinder 7 are both thin-walled structures, and square grooves 6a are provided on the side walls of the heat-insulating straight cylinder 6 and the heat-insulating cone cylinder 7. The square grooves 6a are arranged in an array and staggered.

[0043] In this embodiment, the operating principle of the hot cathode used in a microfocus X-ray tube is as follows: When energized, the filament 4a in the heater 4 generates thermal electrons. These electrons are emitted from the cathode body 1 under the action of the electric field and focused into a beam by the focusing electrode, bombarding the anode target surface to produce X-rays. During this process, the heat generated by the filament 4a diffuses to the surrounding area through thermal conduction, thermal radiation, and other methods, causing the temperature of the cathode tube 2 to rise.

[0044] The double-layer insulation structure formed by the insulating straight tube 6 and the insulating cone 7 can effectively block the heat from being transferred outward from the cathode tube 2. The insulating straight tube 6 is connected to the cathode tube 2 through the first step 2b, and a gap is formed at the second step 2c. This design reduces the heat conduction contact area, and the gap layer provides additional thermal resistance. The insulating cone 7 is located outside the insulating straight tube 6 and is connected to the insulating straight tube 6 at the bottom to form a second thermal barrier, further reducing heat loss. The insulating ceramic 8 is connected to the top of the insulating cone 7. Due to the low thermal conductivity of the ceramic material, it can effectively block the upward transfer of heat. The square groove 6a structure designed on the side walls of the insulating straight tube 6 and the insulating cone 7 further increases the length of the heat transfer path and reduces heat conduction.

[0045] Example 2

[0046] This embodiment provides a hot cathode for a microfocus X-ray tube. Compared with the first embodiment, the only difference is that in order to reduce heat loss and maintain a stable operating temperature of the cathode body, the present invention adopts a multi-layer heat insulation structure design. Figure 4 The thermal insulation straight tube 6 has a multi-layer structure, and the thermal insulation straight tube 6 includes an inner surface layer 6b, a main body layer 6c and an outer surface layer 6d from the inside to the outside. The thermal expansion coefficients of the inner surface layer 6b and the outer surface layer 6d are greater than the thermal expansion coefficient of the main body layer 6c, and the thermal expansion coefficient of the outer surface layer 6d is greater than the thermal expansion coefficient of the inner surface layer 6b.

[0047] The inner surface layer 6b is selected from Mo-30Cu alloy, the main body layer 6c is selected from silicon nitride porous ceramics, and the outer surface layer 6d is selected from stainless steel. The thickness of the main body layer 6c accounts for 65% of the total thickness of the heat-insulating straight tube 6.

[0048] The multi-layered design of the insulating cylinder 6 fully considers thermal stress matching. The inner surface layer 6b is made of Mo-30Cu alloy, which has excellent conductivity and a high thermal expansion coefficient, close to that of the cathode cylinder 2 material, reducing stress concentration during thermal cycling. The main body layer 6c is made of porous silicon nitride ceramic, which has a low thermal expansion coefficient and low thermal conductivity. It serves as the primary thermal insulation layer, accounting for 65% of the total thickness of the insulating cylinder 6. The outer surface layer 6d is made of stainless steel, with a higher thermal expansion coefficient than the inner surface layer 6b. This layer generates appropriate compressive stress during thermal cycling, enhancing structural stability.

[0049] This multi-layer thermal insulation structure design enables the hot cathode used in microfocus X-ray tubes to maintain a stable temperature distribution during operation, reduce heat loss, extend the life of the filament, and improve the stability and reliability of the X-ray tube.

[0050] Furthermore, both the insulating straight cylinder 6 and the insulating conical cylinder 7 are thin-walled structures, and square grooves 6a are provided on the side walls of the insulating straight cylinder 6 and the insulating conical cylinder 7. The square grooves 6a are arranged in a staggered array, with the ratio of the groove depth to the side wall thickness being controlled at 0.4:1, and the groove spacing of the square grooves 6a being twice the groove width.

[0051] The square grooves 6a designed on the sidewalls of the insulating straight tube 6 and insulating conical tube 7 further increase the heat transfer path length and reduce heat conduction. The square grooves 6a are arranged in a staggered array, with a groove depth to sidewall thickness ratio of 0.4:1 and a groove spacing of twice the groove width. This design maximizes thermal insulation while ensuring structural strength.

[0052] Example 3

[0053] This embodiment provides a hot cathode for a microfocus X-ray tube. Compared with Example 1, the only difference is that the insulating straight tube 6 has a multi-layer structure, and the insulating straight tube 6 includes, from the inside to the outside, an inner surface layer 6b, a main body layer 6c and an outer surface layer 6d. The thermal expansion coefficients of the inner surface layer 6b and the outer surface layer 6d are greater than the thermal expansion coefficient of the main body layer 6c, and the thermal expansion coefficient of the outer surface layer 6d is greater than the thermal expansion coefficient of the inner surface layer 6b.

[0054] The inner surface layer 6b is selected from tantalum, the main body layer 6c is selected from aluminum nitride porous ceramics, and the outer surface layer 6d is selected from nickel-based alloy. The thickness of the main body layer 6c accounts for 50% of the total thickness of the heat-insulating straight tube 6.

[0055] Both the insulating straight cylinder 6 and the insulating conical cylinder 7 are thin-walled structures, and the side walls of the insulating straight cylinder 6 and the insulating conical cylinder 7 are provided with square grooves 6a. The square grooves 6a are arranged in a staggered array, with the ratio of the groove depth to the side wall thickness controlled at 0.3:1, and the groove spacing of the square grooves 6a is 1 times the groove width.

[0056] In this embodiment, the structure of the hot cathode for a microfocus X-ray tube is essentially the same as that of Example 2, but differs in material selection and some structural parameters. The inner surface layer 6b of the insulating cylinder 6 of this embodiment is made of tantalum, which has a high melting point and good electrical conductivity, enabling stability in high-temperature environments. The main body layer 6c is made of porous aluminum nitride ceramic, which offers improved thermal conductivity and mechanical strength compared to porous silicon nitride ceramic while still maintaining good thermal insulation properties. The outer surface layer 6d is made of a nickel-based alloy, which offers excellent high-temperature resistance and strong oxidation resistance.

[0057] In this embodiment, the ratio of the groove depth to the sidewall thickness of the square grooves 6a is 0.3:1, and the groove spacing is 1 times the groove width. This design increases the structural strength of the insulating straight tube 6 and the insulating cone 7, making it suitable for applications requiring high mechanical strength. The thickness of the main layer 6c accounts for 50% of the total thickness of the insulating straight tube 6, a decrease from 65% in Example 2. This design improves the overall strength and stability of the structure while maintaining thermal insulation performance.

[0058] Example 4

[0059] This embodiment provides a hot cathode for a microfocus X-ray tube. Compared with Example 1, the only difference is that the insulating straight tube 6 has a multi-layer structure, and the insulating straight tube 6 includes, from the inside to the outside, an inner surface layer 6b, a main body layer 6c and an outer surface layer 6d. The thermal expansion coefficients of the inner surface layer 6b and the outer surface layer 6d are greater than the thermal expansion coefficient of the main body layer 6c, and the thermal expansion coefficient of the outer surface layer 6d is greater than the thermal expansion coefficient of the inner surface layer 6b.

[0060] The inner surface layer 6b is selected from Kovar alloy, the main body layer 6c is selected from silicon nitride porous ceramics, and the outer surface layer 6d is selected from Y2O3-ZrO2 composite ceramics. The thickness of the main body layer 6c accounts for 80% of the total thickness of the heat-insulating straight tube 6.

[0061] Both the insulating straight cylinder 6 and the insulating conical cylinder 7 are thin-walled structures, and the side walls of the insulating straight cylinder 6 and the insulating conical cylinder 7 are provided with square grooves 6a. The square grooves 6a are arranged in a staggered array, with the ratio of the groove depth to the side wall thickness controlled at 0.5:1, and the groove spacing of the square grooves 6a is three times the groove width.

[0062] In this embodiment, the basic structure of the hot cathode for a microfocus X-ray tube is the same as in the previous two embodiments, but there are significant differences in material selection and structural parameters. The inner surface layer 6b of the insulating cylinder 6 in this embodiment utilizes Kovar alloy, which has a thermal expansion coefficient similar to that of glass and ceramics, reducing thermal stress during thermal cycling. The main body layer 6c is still constructed of porous silicon nitride ceramic, but its thickness accounts for 80% of the total thickness of the insulating cylinder 6, significantly enhancing the thermal insulation effect. The outer surface layer 6d utilizes a Y2O3-ZrO2 composite ceramic, which exhibits excellent high-temperature stability and thermal shock resistance.

[0063] In this embodiment, the ratio of the groove depth to the sidewall thickness of the square groove 6a reaches 0.5:1, approaching the upper limit of structural safety and maximizing thermal insulation. The groove spacing is three times the groove width, increasing the overall strength of the structure and reducing stress concentration points. This design is suitable for applications requiring extremely high thermal insulation performance, such as high-power X-ray tubes.

[0064] Example 5

[0065] A microfocus X-ray tube adopts the hot cathode for the microfocus X-ray tube described in Example 2.

[0066] The microfocus X-ray tube comprises a vacuum housing, an anode assembly, and a hot cathode assembly. The vacuum housing is evacuated to a high vacuum, providing a collision-free environment for electrons. The anode assembly includes an anode target and an anode support structure. The anode target is made of a high-melting-point metal material, such as tungsten, molybdenum, or an alloy thereof. The hot cathode assembly is the hot cathode for the microfocus X-ray tube described in Example 2.

[0067] In this microfocus X-ray tube, the cathode body 1 of the hot cathode is positioned opposite the anode target. When the filament 4a in the heater 4 is energized and heated, thermal electrons are generated on the surface of the cathode body 1. A high voltage is applied between the cathode body 1 and the anode target. The thermal electrons are accelerated toward the anode target by the electric field and formed into a fine electron beam by the focusing electrode. When the electron beam strikes the anode target surface, most of its kinetic energy is converted into heat, generating X-rays.

[0068] Due to the adoption of the hot cathode structure described in Example 2, the microfocus X-ray tube has the following advantages:

[0069] The hot cathode's multi-layer insulation structure effectively reduces heat loss, improves energy efficiency, and reduces X-ray tube power consumption. The square grooves 6a on the insulating straight tube 6 and insulating conical tube 7 further enhance the insulation effect, allowing the hot cathode to maintain a stable temperature distribution even under high-temperature operating conditions.

[0070] The multi-layer material structure design of the heat-insulating straight tube 6 reasonably matches the thermal expansion coefficient of each layer, reduces the thermal stress during the thermal cycle, and improves the service life and reliability of the hot cathode.

[0071] The gap design between the cathode tube 2 and the heat-insulating straight tube 6 reduces the heat conduction path and further improves the heat insulation effect. The use of the heat-insulating ceramic 8 blocks the upward transfer of heat and protects other components of the X-ray tube.

[0072] These advantages make the microfocus X-ray tube have the characteristics of small focus, good stability and long life, and are suitable for high-precision non-destructive testing, medical imaging and other fields.

[0073] Example 6

[0074] A microfocus X-ray tube adopts the hot cathode for the microfocus X-ray tube described in Example 3.

[0075] The basic structure of the microfocus X-ray tube is the same as that of Example 5, including a vacuum housing, an anode assembly, and a hot cathode assembly. The difference is that the hot cathode assembly adopts the hot cathode structure described in Example 3.

[0076] Due to the differences in material selection and structural parameters of the hot cathode in Example 3, the microfocus X-ray tube has the following characteristics:

[0077] The hot cathode inner surface layer 6b is made of tantalum, which has a higher melting point and better high-temperature stability, making it suitable for operation at higher power densities. The main body layer 6c is made of porous aluminum nitride ceramic, which provides better mechanical strength, allowing the X-ray tube to withstand greater mechanical vibration and shock.

[0078] Adjustment of the structural parameters of the square slot 6a (the ratio of slot depth to side wall thickness is 0.3:1, and the slot spacing is 1 times the slot width) enhances the structural strength, making the X-ray tube suitable for scenarios that require frequent transportation, such as mobile devices.

[0079] The thickness of the main body layer 6c accounts for 50% of the total thickness of the heat-insulating straight tube 6. While ensuring the heat-insulating performance, it improves the overall strength and stability of the structure, making the X-ray tube have better shock resistance.

[0080] These features make the microfocus X-ray tube particularly suitable for application scenarios such as portable X-ray detection equipment and mobile medical equipment that require frequent movement and have high requirements for mechanical stability.

[0081] Example 7

[0082] A microfocus X-ray tube adopts the hot cathode for the microfocus X-ray tube described in Example 4.

[0083] The basic structure of the microfocus X-ray tube is the same as that of the previous two embodiments, including a vacuum housing, an anode assembly, and a hot cathode assembly. The difference is that the hot cathode assembly adopts the hot cathode structure described in embodiment 4.

[0084] Due to the significant differences in material selection and structural parameters of the hot cathode of Example 4, the microfocus X-ray tube has the following characteristics:

[0085] The hot cathode's inner surface layer 6b is made of Kovar alloy, which matches the thermal expansion coefficient of the ceramic material well. This reduces interfacial stress during thermal cycling and increases the hot cathode's service life. The main body layer 6c, which accounts for 80% of the total thickness of the insulating tube 6, significantly improves thermal insulation and enables stable operation of the X-ray tube at higher powers.

[0086] The outer layer 6d is made of Y2O3-ZrO2 composite ceramic, which has excellent high-temperature stability and thermal shock resistance, enabling the X-ray tube to withstand more frequent switching cycles and larger temperature fluctuations.

[0087] Adjustment of the structural parameters of square slot 6a (the ratio of slot depth to side wall thickness is 0.5:1, and the slot spacing is three times the slot width) maximizes the thermal insulation effect while maintaining sufficient structural strength, enabling the X-ray tube to remain stable under high-power, long-term continuous working conditions.

[0088] These features make the microfocus X-ray tube particularly suitable for application scenarios such as industrial CT and high-precision non-destructive testing, which require long-term continuous operation and extremely high requirements for focus stability.

[0089] In summary, the present invention extends the heat flow path and tortuously makes it effective in improving radial thermal resistance by combining the structures of an insulating straight tube, an insulating conical tube, and insulating ceramics. The design of the conical insulating tube causes the cross-sectional area of ​​the heat flow to vary along the axial direction, resulting in a heat flux density redistribution effect, which reduces the heat flux density at the high-temperature end. The conical tube cooperates with the straight tube to form a "heat flux impedance matching" structure, reducing heat reflection losses. The present invention uses an insulating straight tube with a three-layer composite structure, utilizing the differences in thermal expansion coefficients and thermal conductivity characteristics of different materials to achieve efficient thermal insulation and thermal management. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has a high industrial utilization value.

[0090] Among them, the terms such as "upper", "lower", "left", "right", "front", "back", "middle" and "one" quoted in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships should be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0091] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any equivalent modifications or variations made by persons skilled in the art without departing from the spirit and technical concepts disclosed herein shall be encompassed by the claims of the present invention.

Claims

1. A hot cathode for a microfocus X-ray tube, characterized in that: The hot cathode comprises a cathode body, a cathode cylinder, a potting ceramic, a heater, a cover, a heat-insulating straight cylinder, a heat-insulating cone cylinder and heat-insulating ceramic; wherein: The cathode tube is a cylindrical structure with a cathode tube opening at the bottom, the sealing cover is connected to the cathode tube through the cathode tube opening, and the potting ceramic and the heater are placed inside the cathode tube; The outer side wall of the cathode tube is provided with a first step portion and a second step portion in sequence, the first step portion is located at the upper position of the side of the cathode tube, the second step portion is located in the middle position of the side of the cathode tube, the thermal insulation straight tube is connected to the cathode tube through the first step portion, and a gap is formed between the thermal insulation straight tube and the cathode tube through the second step portion, the thermal insulation cone is located at the periphery of the thermal insulation straight tube, the thermal insulation cone is connected to the thermal insulation straight tube at the bottom, and the thermal insulation ceramic is connected to the top of the thermal insulation cone.

2. The hot cathode for a microfocus X-ray tube according to claim 1, wherein: The heat-insulating straight cylinder and the heat-insulating conical cylinder are both thin-walled structures, and square groove structures are provided on the side walls of the heat-insulating straight cylinder and the heat-insulating conical cylinder.

3. The hot cathode for a microfocus X-ray tube according to claim 2, characterized in that: The square grooves are arranged in an array and staggered; the ratio of the groove depth to the side wall thickness of the square grooves is controlled at (0.3-0.5):1; the groove spacing of the square grooves is 1-3 times the groove width.

4. The hot cathode for a microfocus X-ray tube according to claim 1, wherein: The heater includes a filament and pins. The filament and the potting ceramic are packaged inside the cathode tube. The cover is provided with a through hole for leading out the pins.

5. The hot cathode for a microfocus X-ray tube according to claim 1, wherein: A cathode bowl is provided on the top of the cathode cylinder, and the cathode body is connected to the cathode cylinder through the cathode bowl.

6. The hot cathode for a microfocus X-ray tube according to claim 1, wherein: The heat-insulating straight tube has a multi-layer structure, and includes an inner surface layer, a main body layer and an outer surface layer from the inside to the outside. The thermal expansion coefficients of the inner surface layer and the outer surface layer are greater than the thermal expansion coefficient of the main body layer.

7. The hot cathode for a microfocus X-ray tube according to claim 6, characterized in that: The thermal expansion coefficient of the outer surface layer is greater than the thermal expansion coefficient of the inner surface layer.

8. The hot cathode for a microfocus X-ray tube according to claim 6, characterized in that: The inner surface layer is selected from Mo-30Cu alloy, tantalum or Kovar alloy; The main body layer is selected from silicon nitride porous ceramics or aluminum nitride porous ceramics; The outer layer is selected from stainless steel, nickel-based alloy, monel alloy, Y2O3-ZrO2 composite ceramic or Al2O3-MgO composite ceramic.

9. The hot cathode for a microfocus X-ray tube according to claim 6, characterized in that: The thickness of the main body layer accounts for 50%-80% of the total thickness of the heat-insulating straight tube.

10. A microfocus X-ray tube, characterized in that: The microfocus X-ray tube adopts the hot cathode for the microfocus X-ray tube according to any one of claims 1 to 9.

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