A method for preparing silica for coaxial cables, a superconducting cryogenic coaxial cable, and a connector.

Abstract

This invention belongs to the field of accelerator beam diagnostics technology, and relates to a method for preparing silica for coaxial cables, a superconducting cryogenic coaxial cable, and a connector. The coaxial cable includes an inner conductor layer and an outer conductor layer, with a silica layer disposed between the inner and outer conductor layers. The silica in the silica layer is prepared by the following method: first, silica and a mixture are loaded into an extruder, and the mixture is extruded under controlled pressure by a pusher to generate a mixed gel state of organic and inorganic substances; the mixed gel state of organic and inorganic substances is chemically foamed; the chemically foamed mixed gel is sintered at high temperature to remove the organic additives; the outer conductor layer is fitted onto the high-temperature sintered silica layer and drawn to form a tubular silica insulation layer. The cable of this invention can meet the signal transmission requirements of equipment such as the cryogenic beam measurement (BPM) and superconducting cavity in the accelerator cryostat.

Description

Technical Field

[0001] This invention relates to a method for preparing silica for coaxial cables, a superconducting cryogenic coaxial cable, and a connector, belonging to the field of accelerator beam diagnostic technology. Background Technology

[0002] Beam diagnostics is a crucial subsystem in proton and heavy ion accelerators. It involves measuring and monitoring various parameters such as beam position, phase energy, current intensity, and emittance, ensuring parameter matching and stable operation of the beam before and after the accelerator. In the cryogenic superconducting section of a superconducting linear accelerator, the beam position detector (BPM) is one of the only beam diagnostic devices within the cryostat. The accurate and stable operation of the cryogenic BPM system is essential for measuring the beam centroid, scanning the superconducting cavity, and monitoring regional energy in the superconducting section.

[0003] Cryogenic BPM systems require the long-term, reliable transmission of the mirror current signal generated by the beam across an extremely low temperature range of 2K / 4K within the cryostat. This signal is then transmitted to the ambient temperature feedthrough flange on the cryostat housing, where it is ultimately acquired by the BPM electronics within the cabinet to obtain the beam position and phase information. As a component of the cryogenic BPM system, the extremely low temperature and wide temperature range pose significant challenges to the coaxial cable used for signal transmission. It must possess excellent long-term stability at 2K / 4K, preventing material cracking or damage that could lead to cable breakage and disconnection. Furthermore, it must maintain good high-frequency phase stability across an ultra-wide temperature range approaching 300°C, ensuring that drastic temperature changes do not significantly affect the accuracy of the BPM probe's beam phase measurement due to variations in cable phase velocity. Finally, the cable must also have low thermal conductivity and a small heat transfer cross-section while transmitting high-frequency signals across temperature ranges. A single cryostat may contain dozens of coaxial cables for the BPM and its chamber; large-scale cable heat leakage would significantly increase the liquid helium cooling power and workload of the cryostat.

[0004] As a replacement device for vacuum pipelines, the cryogenic BPM probe will operate in a high-dose environment for a long time and at close range, especially inside the thermostat, which is difficult to access and maintain. Therefore, the coaxial cable that transmits signals from the BPM plate to the thermostat housing must have a high radiation resistance of at least 1E9 rad to meet the cable lifespan requirements of the accelerator's strong radiation zone.

[0005] Extensive research shows that most commonly used coaxial cables use foamed PE or PTFE engineering plastics as insulation. These materials are essentially high-molecular organic compounds, and their radiation resistance is generally weak. They are prone to material deformation or damage due to radiation displacement damage (DPA) after the cumulative dose reaches the standard. For example, PTFE's tolerance dose is approximately 1E5 rad, and based on an average online dose of 500 mSv / h, its lifespan is only about 83 days, which cannot meet the application requirements of the high-radiation areas of accelerators. Furthermore, these cables are usually equipped with plastic shielding layers or sheaths, which have a higher probability of deformation or damage at extremely low temperatures, making them unsuitable for use in superconducting accelerators operating in extremely low temperature environments of 2K / 4K. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide a method for preparing silica for coaxial cables, a superconducting cryogenic coaxial cable, and a connector, which can meet the signal transmission requirements of equipment such as beam measurement cryogenic BPM in accelerator thermostats and superconducting cavities.

[0007] To achieve the above objectives, the present invention proposes the following technical solution: a method for preparing silica for coaxial cables, the coaxial cable comprising: an inner conductor layer and an outer conductor layer, wherein a silica layer is disposed between the inner conductor layer and the outer conductor layer, and the silica in the silica layer is prepared by the following method: firstly, silica and a mixture are loaded into an extruder, and the mixture is extruded by controlling the extrusion of the mixture through a pusher to generate a mixed gel state of organic and inorganic substances; the mixed gel state of organic and inorganic substances is chemically foamed; the mixed gel state after chemical foaming is sintered at high temperature to remove the organic additives therein; the outer conductor layer is sleeved on the silica layer after high temperature sintering and drawn to form a tubular silica insulation layer.

[0008] Furthermore, the chemically foamed particle units are encapsulated to coat the particle units with a dense silicon dioxide film.

[0009] Furthermore, the packaging process is a non-moisture-sensitive packaging process.

[0010] The present invention also discloses a coaxial cable, comprising: an inner conductor layer and an outer conductor layer, wherein a silicon dioxide layer is disposed between the inner conductor layer and the outer conductor layer, and the silicon dioxide layer is prepared by any of the above-described silicon dioxide preparation methods for coaxial cables.

[0011] Furthermore, the inner conductor layer includes an iron core and an inner conductor copper layer, the inner conductor copper layer being plated on the iron core; the outer conductor layer includes an outer conductor copper layer and a metal sheath layer, the metal sheath layer being sleeved on the outer conductor copper layer.

[0012] Furthermore, the coaxial cable is a 090 type coaxial cable, and the metal sheath layer is a 304L stainless steel sheath layer.

[0013] The present invention also discloses a coaxial cable connector for use in any of the coaxial cables described above, comprising: a nut, a front housing, a pin, a glass insulator, a rear housing, an inner guide sleeve, a rear top cover, and a bushing. The front housing is fixedly connected to the nut. The glass insulator is fixed in the rear housing. One end of the rear housing is connected to the front housing. One end of the glass insulator is connected to the pin. The other end of the glass insulator is connected to the inner conductor layer. The inner guide sleeve is disposed in the rear housing for fixing the inner conductor layer. The other end of the rear housing is connected to the rear top cover. The bushing is disposed on the rear top cover for fixing the outer conductor layer.

[0014] Furthermore, the connector includes N-type and SMA-type male connectors.

[0015] Furthermore, the connector also includes a retaining ring and a rear insulating sheet. The retaining ring is disposed between the nut and the front housing and is fixed in the annular groove of the central column of the front housing for connecting the front housing and the nut. The rear insulating sheet is disposed inside the rear housing, behind the inner guide sleeve, for isolating the inner guide sleeve from the outer conductor layer.

[0016] Furthermore, the glass insulator includes a glass insulating column and a Kovar alloy needle core. The main body of the glass insulating column is insulating glass, and a metal ring is provided on its outer wall for laser welding to the front shell. The needle core is fixed in the center of the glass insulating column, one end of the needle core is connected to the insertion pin, and the other end of the needle core is connected to the inner guide sleeve.

[0017] The technical solution of the present invention has at least the following technical effects or advantages:

[0018] 1. Obtain cryogenic coaxial cables that can meet the signal transmission requirements of equipment such as the cryogenic beam measurement BPM and superconducting cavity in the accelerator thermostat.

[0019] 2. By generating a mixed gel state of organic and inorganic matter, stable extrusion and size control of silica particles are achieved. In subsequent processes, a unique transformation from organic to inorganic powder is achieved to ensure a stable high foaming rate, uniform powder, and regular cell size.

[0020] 3. In addition to the foaming process and chemical treatment, the present invention also encapsulates the foamed particle units by coating them with a dense SiO2 film, giving them excellent hydrophobic properties and realizing the key and practical non-moisture-sensitive characteristics of the cable assembly.

[0021] 4. The solution in this invention comprehensively utilizes the low thermal conductivity and support strength of the inner iron core layer, as well as the excellent electrical conductivity and skin effect mechanism of the outer copper layer when transmitting BPM high-frequency signals. This achieves efficient signal transmission while reducing the heat conduction and heat leakage effects of conventional pure copper inner conductors, thereby reducing the cooling load in the thermostat caused by the cable operating across temperature zones. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a silicon dioxide dielectric coaxial cable in one embodiment of the present invention;

[0023] Figure 2 This is a flowchart of chemical foaming in one embodiment of the present invention;

[0024] Figure 3 This is a microstructure diagram of a non-humidity-sensitive silica foaming unit in one embodiment of the present invention;

[0025] Figure 4 This is a cross-sectional view of a silicon dioxide dielectric coaxial cable according to an embodiment of the present invention;

[0026] Figure 5 This is a TDR impedance diagram of a silicon dioxide dielectric coaxial cable in one embodiment of the present invention;

[0027] Figure 6 This is a loss attenuation diagram of a silicon dioxide dielectric coaxial cable in one embodiment of the present invention;

[0028] Figure 7 This is a schematic diagram of an N-type connector according to an embodiment of the present invention;

[0029] Figure 8 This is a schematic diagram of an SMA type connector according to an embodiment of the present invention.

[0030] Figure label:

[0031] 1-Coaxial cable; 2-N-type male connector; 3-SMA-type male connector; 4-Iron core; 5-Inner conductor copper layer; 6-Silica layer; 7-Outer conductor copper tube; 8-Metal sheath layer; 9-Nut; 10-Front shell; 11-Snap ring; 12-Pin; 13-Glass insulator; 14-Rear shell; 15-Inner conductor sleeve; 16-Rear insulating sheet; 17-Rear top cover; 18-Bushing. Detailed Implementation

[0032] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention is described in detail through specific embodiments. However, it should be understood that the specific embodiments are provided only for a better understanding of the present invention and should not be construed as limiting the present invention. In the description of the present invention, it should be understood that the terminology used is for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] To address the problems in existing technologies, where commonly used coaxial cables 1 are mostly made of foamed PE or PTFE engineering plastics as the insulating medium, their radiation resistance is generally weak, and they are prone to material deformation or damage due to radiation displacement damage (DPA) after the cumulative dose reaches the standard, failing to meet the application requirements of the high radiation area of ​​accelerators. Furthermore, their probability of deformation or damage at extremely low temperatures is relatively high, making it difficult to meet the usage requirements of superconducting accelerators in the 2K / 4K extremely low temperature environment, this invention proposes a method for preparing silica for coaxial cables 1, a superconducting cryogenic coaxial cable 1, and a connector. The production process of the silica dielectric cable... The production process can be summarized as follows: Raw material SiO2 undergoes a series of processes including mixing, extrusion, core wire shaping, tubing, foaming and treatment, precision shaping of the outer conductor, post-treatment, and sheath drawing. A key feature is that the SiO2 material is in a mixed gel state of organic and inorganic substances during mixing and extrusion to achieve stable extrusion and dimensional control. In subsequent processes, a unique transformation from organic to inorganic powder is achieved to ensure a stable high foaming rate, uniform powder, and regular cell size. Finally, an outer conductor copper tube 7 is fitted and subjected to multiple drawing processes, forming a foamed SiO2 insulating medium with a low dielectric constant between the inner and outer conductors of the cable. The following detailed description of the invention is based on specific embodiments.

[0034] Example 1

[0035] This embodiment discloses a method for preparing silicon dioxide for a coaxial cable 1, such as... Figure 1 As shown, the coaxial cable 1 includes an inner conductor layer and an outer conductor layer, with a silicon dioxide layer 6 disposed between the inner conductor layer and the outer conductor layer. The silicon dioxide in the silicon dioxide layer 6 is prepared by the following method:

[0036] S1 first loads silica and a mixture into an extruder. The mixture is extruded using a pusher, generating a mixed gel state of organic and inorganic matter. This ensures stable extrusion and controlled silica particle size. In subsequent processes, a unique transformation from organic to inorganic powder is achieved, guaranteeing a stable high foaming rate, uniform powder, and regular cell size. The main components of the mixture are silica sol, Freon-11, purified water, sodium dodecyl sulfate, and methanol, but these are not limited to these; other auxiliary materials can be added as needed. Silica and the mixture are processed using methods such as the sol-gel method to generate a mixed gel state of organic and inorganic matter. After treatment, high-purity, low-loss silica is produced.

[0037] S2 chemically foams a mixed gel state of organic and inorganic substances;

[0038] Existing silica foaming methods involve mixing silica raw materials, foaming agents, and co-solvents, followed by heating and foaming. This special method utilizes the sol-gel process, specifically using a mixture of silica sol, Freon-11, purified water, and sodium dodecyl sulfate for chemical foaming. The process is completed through temperature adjustments, stirring, and heating. The specific chemical foaming process is as follows: Figure 2 As shown, liquid Freon was vaporized into bubbles by different stirring methods and then maintained at 30°C for 12 hours and 70°C for 12 hours. After tube insertion, a heating and foaming process was performed at 100-500°C to remove impurities and obtain the desired high-purity, low-loss silica insulating medium.

[0039] The chemically foamed particle units are encapsulated to coat them with a dense silica film. In this embodiment, the encapsulation process is non-humidity-sensitive. Unlike earlier moisture-sensitive powders such as MgO2 and third-generation SiO2, this embodiment encapsulates the foamed particle units simultaneously with the foaming and chemical treatment, coating them with a dense SiO2 film to impart excellent hydrophobic properties, thus achieving the crucial and practical non-humidity-sensitive characteristic of the cable assembly. Figure 3 As shown, its non-moisture-sensitive encapsulation process, under the same foaming rate, only slightly affects the dielectric constant of the insulation material, yet it gives the cable assembly a crucial moisture-proof function. Even in situations where the cable joint seal fails or bare cable is used, it can still maintain low loss attenuation and a stable 50Ω characteristic impedance for a long time, thereby significantly improving the yield rate during cable processing and the long-term reliability and lifespan. Conventional third-generation SiO2 and other oxide materials are all moisture-sensitive. Their nanoscale foamed micropores easily trap H2O molecules in the air or combine to form SiO2·H2O, affecting the insulation layer resistance, increasing dielectric loss, and causing a sharp deterioration in impedance, standing wave, phase, and other indicators. In this embodiment, the SiO2 film effectively prevents H2O molecules in the air from entering the pores, alleviating the moisture absorption problem of the insulation material from the production process, retaining high foaming and low loss characteristics, and significantly improving the yield rate during cable production and transportation, as well as the service life under harsh environments.

[0040] S3 removes organic additives by high-temperature sintering of the chemically foamed mixed gel;

[0041] S4 involves placing the outer conductor layer onto the high-temperature sintered silicon dioxide layer 6 and drawing it to form a tubular silicon dioxide insulating layer. Finally, it undergoes high-temperature treatment to obtain an ultra-high purity inorganic material with a SiO2 content of 99.99%, easily achieving radiation resistance on the order of 1E9 rad or higher. Due to the foaming process and low-density treatment, the insulating medium of this invention also possesses a relatively low relative permittivity of approximately 2.0, enabling low-loss characteristics during high-frequency signal transmission.

[0042] Example 2

[0043] Based on the same inventive concept, this embodiment discloses a coaxial cable 1, such as... Figure 4 As shown, it includes an inner conductor layer and an outer conductor layer, with the inner conductor serving as a signal transmission carrier. A silicon dioxide layer 6 is disposed between the inner conductor layer and the outer conductor layer, and the silicon dioxide layer 6 is prepared using any of the aforementioned silicon dioxide preparation methods for coaxial cable 1.

[0044] The inner conductor layer comprises an iron core 4 and an inner conductor copper layer 5, with the copper layer 5 plated on the iron core 4. Together, they form the copper-iron composite inner conductor of the coaxial cable 1, serving as the transmission medium for high-frequency signals. Due to the skin effect, high-frequency signals are transmitted within the thin copper outer layer. Utilizing the extremely high conductivity of high-purity copper, transmission losses caused by metal conductors in high-frequency cables are reduced. The iron core 4, with its low thermal conductivity and high strength, serves as the inner conductor skeleton and support, as well as reducing heat transfer in the cable. By comprehensively utilizing the low thermal conductivity and supporting strength of the iron core 4, the excellent conductivity of the outer copper layer, and the skin effect mechanism during BPM high-frequency signal transmission, efficient signal transmission is achieved while reducing heat conduction and leakage effects of conventional pure copper inner conductors, thus lowering the cooling load on the thermostat caused by the cable operating across temperature zones.

[0045] The inner conductor layer is not limited to the iron core 4 and the inner conductor copper layer 5. If cost is not a concern, copper plated with nickel or copper plated with silver can be used.

[0046] The outer conductor layer includes an outer conductor copper layer and a metal sheath layer 8 fitted onto the outer conductor copper layer. In this embodiment, the metal sheath layer 8 is preferably a 304L stainless steel sheath layer. It has high purity, good surface quality and formability, excellent electromagnetic shielding performance, and good corrosion resistance, heat resistance, low-temperature strength, and machinability. The 304L stainless steel sheath is drawn and formed onto the outer conductor copper tube 7 using a tube drawing device. This drawing process requires six steps. Since the 304L stainless steel will generate a large internal stress after each drawing, or exhibit brittleness enhancement, it needs to be annealed under vacuum or a specific gas protection. The 304L stainless steel sheath layer can be replaced with pure niobium, niobium-titanium alloy, or other materials more suitable for superconducting low-temperature environments. That is, in this embodiment, the coaxial cable 1 consists of, from the inside out: iron core 4, inner conductor copper layer 5, SiO2 insulating medium, outer conductor copper tube 7, and stainless steel 304L sheath.

[0047] Both the inner conductor copper layer 5 and the outer conductor copper layer are made of 99.9% oxygen-free copper, which has extremely high electrical conductivity and is easy to weld and pressure process. Due to the superior toughness of oxygen-free copper, the copper conductor can be shaped using drawing dies, allowing for precise control of conductor dimensions. Furthermore, the drawing fluid used in the copper tube drawing process must be thoroughly cleaned after shaping to prevent corrosion in subsequent high-temperature processes and to reduce the release of undesirable gases in the processing workshop.

[0048] In this embodiment, the coaxial cable 1 is preferably a 090 type coaxial cable 1, that is, the outermost sheath diameter is 0.09 inches, approximately 2.29 mm. A small cross-section helps reduce heat conduction when the cable operates across temperature zones, thus reducing the load on the liquid helium refrigerator of the superconducting accelerator. In this embodiment, the type of coaxial cable 1 is not limited to this; if low heat leakage requirements are not considered, it can also be designed in larger sizes such as "141" and "270", with sheath outer diameters of 3.58 mm (approximately 0.141 inches) and 6.86 mm (approximately 0.27 inches), respectively.

[0049] In the design process of the cable in this embodiment, the relevant industry standards for coaxial cable 1 mentioned above must also be followed. Prioritize the cutoff frequency f. c It is an important parameter, which is determined by the following formula (1), where c is the speed of light in vacuum, ∈ r This is the relative permittivity, where d and D represent the outer diameter of the inner conductor and the inner diameter of the outer conductor, respectively. The cable's operating frequency must be less than f. c This ensures that unnecessary higher-order modes outside the TEM are not excited. Substituting the parameters of the cable in this embodiment, its f is calculated. c At approximately 55.62 GHz, it meets the project's requirements. With a smaller cross-sectional size, f c The frequency will be higher.

[0050]

[0051] During high-frequency signal transmission, the transmission thin layer on the outer surface of the inner conductor of the cable caused by the skin effect is the penetration depth δ, which can be expressed by formula (2), where σ is the conductivity of the metal, taken as m / (Ωmm). 2 ), where f is the operating frequency in kHz, and this parameter affects the selection of the thickness of the inner conductor of the cable. Substituting the cable parameters of this embodiment, the calculated skin depths are 66.02 μm and 1.21 μm when the frequencies are 1 MHz and 3 GHz, respectively. The copper layer thickness of the inner conductor of the cable in this embodiment is 100 μm, taking into account the transmission requirements of both low and high frequency signals.

[0052]

[0053] Characteristic impedance Z is a key indicator in coaxial cable design. It is actually a frequency-dependent complex number, which tends to be a constant in the radio frequency field, as shown in formula (3). It is determined by the outer diameter d of the inner conductor, the inner diameter D of the outer conductor, and the relative permittivity ∈ Z. r The decision is made. In this embodiment, the cable is used for low-temperature BPM signal transmission, with a bandwidth requirement of approximately 3 GHz and a design value and tolerance of 50 ± 3 Ω for the characteristic impedance. Figure 5 The 1.66-meter cable assembly sample of this embodiment is shown. The time-domain TDR impedance measured using a vector network analyzer shows that its average impedance is 49.93Ω and the maximum deviation is 4.66Ω.

[0054]

[0055] Attenuation α is a core indicator affecting cable performance. As shown in formula (4), it is defined as the ratio of the cable input power P1 to the far-end output power P2. This is determined by resistive attenuation α. R and dielectric attenuation α ∈ It consists of two parts. As can be seen from formulas (5) and (6), the resistive attenuation α R It is proportional to the square of the frequency f, and is determined by the relative permittivity ∈ r The outer diameter d of the inner conductor, the inner diameter D of the outer conductor, and the conductivity σ1 and σ2 of the inner and outer conductor metals determine the dielectric attenuation α as the frequency gradually increases. ∈ The contribution of the relative permittivity increases, and it is proportional to the frequency f, which is determined by the relative permittivity ∈ r The attenuation is determined by the loss tangent tanδ of the dielectric. In this embodiment, the cable is used in low-temperature BPM applications, requiring an attenuation α ≤ 0.35 dB / m @ 162.5 MHz at room temperature (20°C). At even lower temperatures, the attenuation will be relatively lower.

[0056]

[0057] In this embodiment, the attenuation of a 1.66-meter sample of the cable assembly was measured. Figure 6 As shown, the voltage levels at 162.5MHz and 3GHz are -0.50dB and -2.14dB respectively, which translates to lengths of 0.30dB / m at 165.28MHz and 1.29dB / m at 3GHz. The measured values ​​both meet the design specifications and usage requirements. Note that the "@" followed by the frequency indicates the parameter specifications at a specific frequency; many parameters vary with frequency.

[0058] Example 3

[0059] Based on the same inventive concept, this embodiment discloses a connector for a coaxial cable 1, used for any of the aforementioned coaxial cables 1. The connector includes an N-type male connector 2 and an SMA-type male connector 3. Both adopt a modular component design, with various components of the connector being specially designed and modularly detachable. For example, an additional bushing is designed to reduce shear stress at the laser welding point, increasing the connector's strength and lifespan. This facilitates internal component adjustment or dimensional optimization to better meet the 50-ohm impedance matching requirement, and also facilitates the connector's maintenance and replacement.

[0060] like Figure 7 and 8 As shown, it includes: nut 9, front housing 10, retaining ring 11, pin 12, glass insulator 13, rear housing 14, inner guide sleeve 15, rear insulating sheet 16, rear top cover 17, and bushing 18. The front housing 10 is fixedly connected to the nut 9. The glass insulator 13 is fixed in the rear housing 14. One end of the rear housing 14 is connected to the front housing 10. One end of the glass insulator 13 is connected to the pin 12. The other end of the glass insulator 13 is connected to the inner conductor layer. The inner guide sleeve 15 is set in the rear housing 14 to fix the inner conductor layer. The other end of the rear housing 14 is connected to the rear top cover 17. The bushing 18 is set on the rear top cover 17 to fix the outer conductor layer.

[0061] The outer diameter of nut 9, which represents the size of N-type male connector 2, is 21.5 mm. The outer diameter of nut 9, which represents the size of SMA-type male connector 3, is 9 mm.

[0062] The front housing 10 has a smaller diameter at the end near the nut 9, with an annular groove in the middle section for accommodating the retaining ring 11. The other end of the front housing 10 has a larger diameter, with an M10*1.25 internal thread on the inner surface of the larger diameter end, 5.50mm deep, for a detachable tightening connection with the rear housing 14. The front housing 10 has a through hole inside. The retaining ring 11 is located between the nut 9 and the front housing 10, fixed in the annular groove of the central columnar portion of the front housing 10, for connecting the front housing 10 and the nut 9.

[0063] The rear housing 14 has a smaller diameter at one end that connects to the front housing 10, and its surface has an M10*1.25mm external thread with a length of 5.50mm, used for tightening with the internal thread of the columnar part on the upper right end of the front housing 10; its middle section is a hexagonal nut 9. The columnar part at the other end of the rear housing 14 also has an external thread, used for tightening with the bushing 18 at the rear end. The rear housing 14 also has a through hole inside for the cable sheath to pass through and be welded and fixed.

[0064] The rear insulating sheet 16 is disposed inside the rear housing 14, behind the inner guide sleeve 15, and is used to isolate the inner guide sleeve 15 from the outer conductor layer.

[0065] The glass insulator 13 includes a glass insulating column and a Kovar alloy needle core. The main body of the glass insulating column is insulating glass, with a metal ring on its outer wall for laser welding to the front outer shell 10. The needle core has a diameter of 0.9 mm and a length of 3 mm, and is fixed to the glass column by high-temperature sintering. The needle core is fixed at the center of the glass insulating column, with one end connected to the pin 12 and the other end connected to the inner guide sleeve 15. After the needle core on the glass insulator 13 is connected to the pin 12 and the inner guide sleeve 15 respectively through interlocking, laser welding is performed to reinforce them through the reserved holes on the pin 12 and the inner guide sleeve 15. The front outer shell 10 and the rear outer shell 14 are connected by their own threads. The glass insulator 13 is connected and reinforced to the front outer shell 10, and the rear outer shell 14 is connected to the cable metal sheath through laser welding, ensuring the vacuum seal of the dielectric powder and the entire cable.

[0066] The tip of the pin 12 is tapered, and the bottom is a hollow post with an inner diameter of 3.5 mm. The surface has a single-end groove with a diameter of 1 mm. The bottom of the hollow post is connected to the Kovar alloy needle core. The pin 12 and the needle core at the left end of the glass insulator 13 are reinforced by laser welding.

[0067] The inner guide sleeve 15 has an inner hole. The inner hole near the front outer shell 10 has an inner diameter of 0.92 mm, which is inserted and connected to the rear pin core of the glass insulator 13. The inner hole at the other end has an inner diameter of 0.60 mm, which is inserted and connected to the inner conductor of the SiO2 cable. The inner guide sleeve 15 has two single holes on the side for better laser welding and reinforcement.

[0068] The bushing 18 includes a cylindrical left end and an open right end. The left end has an internal thread of M7*0.5mm with a depth of 6.50mm, used for tightening with the thread on the right end of the rear housing 14. The rear top cover 17 is a six-lobed elastic cone structure with a through hole in the middle for the SiO2 cable sheath to pass through. The rear top cover 17 is located between the rear housing 14 and the bushing 18. As the bushing 18 and the rear housing 14 are tightened together by the threads, the six-lobed elastic rear top cover 17 and the cable sheath will also be continuously compressed and fixed.

[0069] In this embodiment, the welding points are as follows: W1—welding point between pin 12 and the front core of glass insulator 13, used for connecting and fixing the coaxial inner conductor; W2—welding point between the metal wall of glass insulator 13 and the front outer shell 10, used for fixing the coaxial outer conductor and vacuum sealing; W3—welding point between inner guide sleeve 15 and the rear core of glass insulator 13, used for connecting and fixing the coaxial inner conductor; W4—welding point between inner guide sleeve 15 and the copper-iron inner core of cable, used for connecting and fixing the coaxial inner conductor; W5—welding point between rear outer shell 14 and stainless steel sheath of cable, used for fixing the coaxial outer conductor and vacuum sealing.

[0070] The characteristics of laser welding are that a high-power laser bombards the joint of the metals to be welded, generating local high temperature in a short time and forming a fused metal layer. After cooling, the weld is fixed and vacuum sealed. It is suitable for welding small-sized and thin-layer metals. The laser welding process parameters used in this embodiment are: power density of 600W, pulse width of 12ms, and frequency of 1Hz.

[0071] It should be noted that the product of this invention uses component laser welding technology, pure inorganic materials and production processes for cables, inorganic materials for connectors and glass sintering processes, etc., all of which can withstand operating conditions of up to about 1000℃. Optionally, in addition to the extremely low temperature application of 2K / 4K in the thermostat, the SiO2 cable assembly of this invention can also be used in high temperature scenarios such as aerospace and industry.

[0072] It should be noted that in this invention, the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the system or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed.

[0073] Furthermore, in the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0074] 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 it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific embodiments of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention. The above content is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims

1. A method for preparing silica for coaxial cables, characterized in that, The coaxial cable includes an inner conductor layer and an outer conductor layer, with a silicon dioxide layer disposed between the inner conductor layer and the outer conductor layer. The silicon dioxide in the silicon dioxide layer is prepared by the following method: First, silica and the mixture are loaded into an extruder, and the mixture is extruded by controlling the extrusion of the extruder to generate a mixed gel state of organic and inorganic substances; Silica and the mixture are used to generate a mixed gel state of organic and inorganic substances through the sol-gel method; The mixed gel state of the organic and inorganic substances is chemically foamed; Chemical foaming is performed by mixing silica sol, Freon-11, pure water, and sodium dodecyl sulfate. The liquid Freon is vaporized into bubbles by different stirring methods and then kept at 30°C for 12 hours and 70°C for 12 hours. After the tube is threaded, the heating foaming process is completed at 100-500°C to remove impurities and obtain the required high-purity, low-loss silica insulating medium. The chemically foamed mixed gel is then subjected to high-temperature sintering to remove the organic additives. The outer conductor layer is placed on a silicon dioxide layer that has been sintered at high temperature, and then drawn to form a tubular silicon dioxide insulating layer.

2. The method for preparing silica for coaxial cables as described in claim 1, characterized in that, The chemically foamed particle units are encapsulated to coat the particle units with a dense silicon dioxide film.

3. The method for preparing silica for coaxial cables as described in claim 2, characterized in that, The packaging process is a non-moisture-sensitive packaging process.

4. A coaxial cable, characterized in that, include: An inner conductor layer and an outer conductor layer are provided, wherein a silicon dioxide layer is disposed between the inner conductor layer and the outer conductor layer, and the silicon dioxide layer is prepared by the silicon dioxide preparation method for coaxial cables as described in any one of claims 1-3.

5. The coaxial cable as described in claim 4, characterized in that, The inner conductor layer includes an iron core and an inner conductor copper layer, the inner conductor copper layer being plated on the iron core; the outer conductor layer includes an outer conductor copper layer and a metal sheath layer, the metal sheath layer being sleeved on the outer conductor copper layer.

6. The coaxial cable as described in claim 5, characterized in that, The coaxial cable is a 090 type coaxial cable, and the metal sheath layer is a 304L stainless steel sheath layer.

7. A connector for a coaxial cable, characterized in that, A coaxial cable as described in any one of claims 4-6, comprising: a nut, a front outer shell, a pin, a glass insulator, a rear outer shell, an inner conductor sleeve, a rear top cover, and a bushing, wherein the front outer shell is fixedly connected to the nut, the glass insulator is fixed in the rear outer shell, one end of the rear outer shell is connected to the front outer shell, one end of the glass insulator is connected to the pin, the other end of the glass insulator is connected to the inner conductor layer, the inner conductor sleeve is disposed in the rear outer shell for fixing the inner conductor layer, the other end of the rear outer shell is connected to the rear top cover, and the bushing is disposed on the rear top cover for fixing the outer conductor layer.

8. The coaxial cable connector as described in claim 7, characterized in that, The connectors include N-type and SMA-type male connectors.

9. The coaxial cable connector as described in claim 7, characterized in that, The connector further includes a retaining ring and a rear insulating plate. The retaining ring is disposed between the nut and the front housing and is fixed in the annular groove of the central column of the front housing for connecting the front housing and the nut. The rear insulating plate is disposed inside the rear housing, behind the inner guide sleeve, for isolating the inner guide sleeve from the outer conductor layer.

10. The coaxial cable connector as described in claim 7, characterized in that, The glass insulator includes a glass insulating column and a Kovar alloy needle core. The main body of the glass insulating column is insulating glass, and a metal ring is provided on its outer wall for laser welding to the front shell. The needle core is fixed in the center of the glass insulating column, one end of the needle core is connected to the insertion pin, and the other end of the needle core is connected to the inner guide sleeve.

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