Preparation method of silicon dioxide for coaxial cable, superconducting low-temperature coaxial cable and joint connector

Abstract

The invention belongs to the technical field of accelerator beam diagnosis, and relates to a silicon dioxide preparation method for a coaxial cable, a superconducting low-temperature coaxial cable and a joint connector, the coaxial cable comprises an inner conductor layer and an outer conductor layer, and a silicon dioxide layer is arranged between the inner conductor layer and the outer conductor layer. The silicon dioxide in the silicon dioxide layer is prepared by the following steps: filling silicon dioxide and a mixture into an extruder, and controlling the mixture to be extruded through a pushing machine to generate a mixed gel state of an organic matter and an inorganic matter; performing chemical foaming on the mixed gel state of the organic matter and the inorganic matter; carrying out high-temperature sintering on the mixed gel subjected to chemical foaming to remove the organic auxiliary agent in the mixed gel; and sleeving the outer conductor layer on the silicon dioxide layer subjected to high-temperature sintering, and drawing the outer conductor layer to form a tubular silicon dioxide insulating layer. The cable provided by the invention can meet the signal transmission requirements of equipment such as beam measurement low-temperature BPM and a superconducting cavity in an accelerator thermostat.

Description

Technical Field

[0001] The invention relates to a method for preparing silicon dioxide for a coaxial cable, a superconducting low-temperature coaxial cable and a joint connector, and belongs to the technical field of accelerator beam diagnosis. Background Art

[0002] The beam diagnostic system is one of the most important subsystems in proton and heavy ion accelerators. The beam diagnostic content includes the measurement and monitoring of various parameters such as beam position, phase energy, flux, emittance, etc., which ensures the parameter matching and stable operation of the beam in each section before and after the accelerator. Among them, in the low-temperature superconducting section of the superconducting linear accelerator, the beam position detector (BPM) is one of the only beam diagnostic equipment in the thermostat of this area. The accurate and stable operation of the low-temperature BPM system is crucial for the beam centroid measurement, superconducting cavity phase scanning and regional energy monitoring of the superconducting section.

[0003] The cryogenic BPM system needs to reliably guide the image current signal generated by the beam in the extremely low temperature environment of 2K / 4K in the thermostat for a long time, transmit it across an extremely wide temperature range to the normal temperature feed-through flange on the thermostat shell, and finally obtain the beam position and phase information by the BPM electronics in the cabinet. As a part of the cryogenic BPM equipment system, the extremely low temperature and wide temperature range pose great challenges to the coaxial cable of the signal transmission medium. It is required to have good long-term stability at the extremely low temperature of 2K / 4k, and the material cannot be cracked or damaged due to low temperature, causing the cable to break and lose connection; in addition, the product is required to have good high-frequency phase stability performance when crossing the ultra-wide temperature range of nearly 300℃, and the cable phase velocity difference caused by the drastic temperature change cannot greatly affect the accuracy of the BPM probe's beam phase measurement; finally, the cable is also required to have low thermal conductivity and heat transfer cross-section while transmitting high-frequency signals across the temperature range. There are dozens of coaxial cables for BPM and cavity in a single thermostat. Large-scale cable heat leakage will significantly increase the liquid helium refrigeration power and burden of the thermostat.

[0004] As a low-temperature BPM probe that replaces the vacuum pipe, it will work in a high-dose environment for a long time and at close range, especially in a thermostat that is difficult to access and replace during maintenance. Therefore, the coaxial cable that transmits the signal from the BPM plate to the thermostat housing feedthrough is required to have a high radiation resistance of at least 1E9 rad to meet the cable service life in the strong radiation area of ​​the accelerator.

[0005] Extensive research shows that most commonly used coaxial cables are made of foamed PE or PTFE engineering plastics as insulating media. The material is essentially a high-molecular organic substance, and its radiation resistance is generally not strong. It is easy to cause material degeneration or damage due to radiation displacement damage (DPA) after the cumulative dose reaches the standard. For example, the tolerance dose of PTFE is about 1E5 rad. According to the average online dose of 500mSv / h, the life span is only about 83 days, which cannot meet the application requirements of the accelerator's strong radiation area. In addition, this type of cable is usually equipped with a plastic shielding layer or sheath, which has a high probability of deformation or damage at extremely low temperatures, making it difficult to meet the use requirements of superconducting accelerators in 2K / 4K extremely low temperature environments. Summary of the invention

[0006] In view of the above problems, the purpose of the present invention is to provide a method for preparing silica for coaxial cable, a superconducting low-temperature coaxial cable and a joint connector, which can meet the signal transmission requirements of equipment such as beam measurement low-temperature BPM and superconducting cavity in accelerator thermostat.

[0007] To achieve the above-mentioned purpose, the present invention proposes the following technical scheme: a method for preparing silica for a coaxial cable, the coaxial cable comprising: an inner conductor layer and an outer conductor layer, a silica layer is arranged between the inner conductor layer and the outer conductor layer, and the silica in the silica layer is prepared by the following method, including: firstly loading silica and a mixed material into an extruder, and controlling the extrusion of the mixture by a pusher to generate a mixed gel state of organic and inorganic substances; chemically foaming the mixed gel state of the organic and inorganic substances; high-temperature sintering the chemically foamed mixed gel to remove the organic additive therein; and sleeve the outer conductor layer on the high-temperature sintered silica layer, and drawing it to form a tubular silica insulation layer.

[0008] Furthermore, the particle units after chemical foaming are packaged so that the particle units are wrapped with a layer of 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 arranged between the inner conductor layer and the outer conductor layer, and the silicon dioxide layer is prepared by any of the above-mentioned silicon dioxide preparation methods for coaxial cables.

[0011] Furthermore, the inner conductor layer includes an iron core and an inner conductor copper layer, and the inner conductor copper layer is plated on the iron core; the outer conductor layer includes an outer conductor copper layer and a metal sheath layer, and the metal sheath layer is 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 stainless steel 304L sheath layer.

[0013] The present invention also discloses a joint connector for a coaxial cable, which is used for the coaxial cable described in any of the above items, and comprises: a nut, a front shell, a pin, a glass insulator, a rear shell, an inner guide sleeve, a rear top cover and a bushing, wherein the front shell is fixedly connected to the nut, the glass insulator is fixed in the rear shell, one end of the rear shell is connected to the front shell, one end of the glass insulator is connected to the pin, and the other end of the glass insulator is connected to the inner conductor layer, the inner guide sleeve is arranged in the rear shell for fixing the inner conductor layer, the other end of the rear shell is connected to the rear top cover, the bushing is arranged on the rear top cover, and the bushing is used to fix the outer conductor layer.

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

[0015] Furthermore, the joint connector also includes a snap ring and a rear insulating sheet. The snap ring is arranged between the nut and the front shell, and is fixed in an annular groove of the middle columnar portion of the front shell to connect the front shell and the nut. The rear insulating sheet is arranged in the rear shell, behind the inner guide sleeve, to isolate 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 circle of metal is arranged on its outer wall for laser welding with the front outer shell; the needle core is fixed at the center of the glass insulating column, one end of the needle core is connected to the 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 low-temperature coaxial cables that can meet the signal transmission requirements of equipment such as low-temperature BPM and superconducting cavity in the accelerator thermostat.

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

[0020] 3. While carrying out the foaming process and chemical treatment, the present invention also performs packaging treatment on the foamed particle units. By wrapping them with a dense SiO2 film, they have excellent hydrophobic properties, thereby achieving the key and practical non-moisture-sensitive characteristics of the cable assembly.

[0021] 4. The solution of the present invention comprehensively utilizes the low thermal conductivity and supporting strength of the inner core layer, the excellent electrical conductivity of the outer copper layer and the skin effect mechanism when transmitting BPM high-frequency signals, thereby achieving efficient signal transmission while reducing the thermal conduction and heat leakage effects of the conventional pure copper inner conductor, thereby reducing the refrigeration load in the thermostat caused by the cable working across temperature zones. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of a silicon dioxide dielectric coaxial cable according to an embodiment of the present invention;

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

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

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

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

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

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

[0029] Figure 8 Schematic diagram of an SMA type connector according to an embodiment of the present invention.

[0030] Reference numerals:

[0031] 1-coaxial cable; 2-N-type male connector; 3-SMA-type male connector; 4-iron core; 5-inner conductor copper layer; 6-silicon dioxide layer; 7-outer conductor copper tube; 8-metal sheath layer; 9-nut; 10-front shell; 11-clamp ring; 12-pin; 13-glass insulator; 14-rear shell; 15-inner guide sleeve; 16-rear insulation sheet; 17-rear top cover; 18-bushing. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is described in detail through specific embodiments. However, it should be understood that the provision of specific embodiments is only for a better understanding of the present invention, and they should not be understood as limitations of the present invention. In the description of the present invention, it should be understood that the terms used are only for the purpose of description and cannot be understood as indicating or implying relative importance.

[0033] In order to solve the problems in the prior art that the commonly used coaxial cables 1 are mostly made of foamed PE or PTFE engineering plastics as insulating media, and their radiation resistance is generally not strong, and they are prone to material degeneration or damage due to radiation displacement damage (DPA) after the cumulative dose reaches the standard, and cannot meet the application requirements of the accelerator's strong radiation area, and the probability of deformation or damage at extremely low temperatures is relatively high, and it is difficult to meet the use requirements of superconducting accelerators in 2K / 4K extremely low temperature environments. The present invention proposes a method for preparing silicon dioxide for coaxial cable 1, a superconducting low-temperature coaxial cable 1 and a joint connector, and a production method for silicon dioxide dielectric cable. The production process is summarized as follows: the raw material SiO2 is subjected to a series of processes such as mixing, extrusion, core wire shaping, pipe threading, foaming and processing, precision shaping of the outer conductor, post-processing, and sheath drawing. The characteristic is that the SiO2 material is a mixed gel state of organic and inorganic substances after mixing and extrusion to achieve stable extrusion and size control, and then realizes a unique transformation from organic to inorganic powder in the subsequent process to ensure a stable high foaming rate, uniform powder, regular pore size, etc. Finally, the outer conductor copper tube 7 is put on and after multiple drawing, a foamed SiO2 insulating medium with a small dielectric constant is formed between the inner and outer conductors of the cable. The scheme of the present invention is described in detail in conjunction with the embodiments below.

[0034] Embodiment 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 comprises: an inner conductor layer and an outer conductor layer, a silicon dioxide layer 6 is arranged between the inner conductor layer and the outer conductor layer, and the silicon dioxide in the silicon dioxide layer 6 is prepared by the following method, including:

[0036] S1 first loads silica and mixed materials into the extruder, and controls the extrusion of the mixture through a pusher to generate a mixed gel state of organic and inorganic substances, so as to achieve stable extrusion and size control of silica particles, and then realize the unique transformation from organic to inorganic powder in the subsequent process to ensure a stable high foaming rate, uniform powder, and regular pore size; wherein, the main components of the mixed materials are silica sol, Freon-11, pure water, sodium dodecyl sulfate and methanol, etc., but not limited to this, and other auxiliary materials can also be added as needed. Silica and mixed materials are generated into a mixed gel state of organic and inorganic substances through methods such as sol-gel method, and the mixed gel state is treated to generate high-purity, low-loss silica.

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

[0038] The existing silica foaming method uses silica raw material + foaming agent + co-solvent to mix and heat for foaming. This special method uses the sol-gel method to synthesize, specifically using silica sol + Freon-11 + pure water + sodium dodecyl sulfate mixed chemical foaming, and is completed through different temperatures, stirring, and heating. Specifically, the chemical foaming process is as follows Figure 2 As shown, the liquid Freon is gasified into bubbles by different stirring and then kept at 30°C for 12 hours and 70°C for 12 hours. After the pipe is inserted, the heating and foaming treatment is completed at 100-500°C to remove impurities and obtain the required high-purity and low-loss silica insulating medium.

[0039] The particle units after chemical foaming are packaged so that a dense silicon dioxide film is wrapped around the particle units. The packaging process in this embodiment is a non-moisture-sensitive packaging process. Different from the early moisture-sensitive powders such as MgO2 and third-generation SiO2, this embodiment not only performs the foaming process and chemical treatment, but also packages the foamed particle units. By wrapping them with a dense SiO2 film, they have excellent hydrophobic properties, thus achieving the key and practical non-moisture-sensitive characteristics of the cable assembly. Figure 3 As shown, its non-humidity-sensitive packaging process, at the same foaming rate, only slightly affects the dielectric constant of the insulating material, but enables the cable assembly to obtain a very critical moisture-proof function. Even if the cable joint seal fails or the bare cable is used, it can still maintain a low loss attenuation and a stable 50Ω characteristic impedance for a long time, thereby greatly improving the yield rate in the cable processing process, as well as the reliability and life of long-term use. Conventional third-generation SiO2 and other oxide materials are all moisture-sensitive. Their nano-scale foaming micropores are very easy to collect H2O molecules in the air, or combine to form SiO2·H2O, affecting the body resistance of the insulation layer, increasing the dielectric loss, and causing the impedance, standing wave, phase and other indicators to deteriorate sharply. The SiO2 film in this embodiment effectively prevents H2O molecules in the air from entering the holes, alleviates the moisture absorption problem of the insulating material from the production process, retains the high foaming and low loss characteristics, and greatly improves the yield rate in the cable production and transportation process, as well as the service life in harsh environments.

[0040] S3 sintering the chemically foamed mixed gel at high temperature to remove the organic additives therein;

[0041] S4 sets the outer conductor layer on the high-temperature sintered silicon dioxide layer 6, and draws it to form a tubular silicon dioxide insulation layer, and finally treats it at high temperature to become an ultra-high purity inorganic material with a SiO2 content of 99.99%, which can easily achieve radiation resistance of more than 1E9 rad. Due to the use of foaming technology and light density treatment, the insulating medium of the present invention also has a relatively low relative dielectric constant of about 2.0 to achieve low loss characteristics during high-frequency signal transmission.

[0042] Embodiment 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, the inner conductor is used as a signal transmission carrier. A silicon dioxide layer 6 is arranged between the inner conductor layer and the outer conductor layer, and the silicon dioxide layer 6 adopts any of the above-mentioned silicon dioxide preparation methods for coaxial cable 1.

[0044] The inner conductor layer includes an iron core 4 and an inner conductor copper layer 5, and the inner conductor copper layer 5 is plated on the iron core 4. The copper-iron composite inner conductor that together constitutes the coaxial cable 1 is used as a transmission medium for high-frequency signals. The high-frequency signal will be transmitted in the thin layer on the outer surface of the copper due to the skin effect. The extremely high electrical conductivity of the high-purity copper material is utilized to reduce the transmission loss of the high-frequency cable caused by the metal conductor. The iron core 4 has low thermal conductivity and high strength, and is used as the inner conductor skeleton and support, as well as to reduce the heat transfer performance of the cable. It comprehensively utilizes the low thermal conductivity and support strength of the iron core 4, the excellent electrical conductivity of the outer copper layer, and the skin effect mechanism when transmitting the BPM high-frequency signal, so as to achieve efficient signal transmission while reducing the heat conduction and heat leakage effect of the conventional pure copper inner conductor, and reducing the refrigeration load caused by the cable working across the temperature zone in the thermostat.

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

[0046] The outer conductor layer includes an outer conductor copper layer and a metal sheath layer 8 sleeved on the outer conductor copper layer. In this embodiment, the metal sheath layer 8 is preferably a stainless steel 304L 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 mechanical processing performance. The 304L stainless steel sheath is drawn and formed on the outer conductor copper tube 7 by a tube drawing device. The drawing process needs to be performed six times in total. Since each time the 304L stainless steel is drawn, it will produce a large internal stress after deformation, or show enhanced brittleness, so it needs to be annealed under vacuum or specific gas protection. The stainless steel 304L sheath layer can be replaced with pure niobium, niobium-titanium alloy and other materials that are more suitable for superconducting low-temperature environments. That is, the coaxial cable 1 in this embodiment is from the inside to the outside: iron core 4, inner conductor copper layer 5, SiO2 insulating medium, outer conductor copper tube 7 and stainless steel 304L sheath.

[0047] 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 press process. Due to the superior toughness of oxygen-free copper, the copper conductor can be shaped using a drawing die to accurately control the conductor size. In addition, the drawing liquid used in the copper tube drawing process must be cleaned after the shaping is completed to avoid corrosion in subsequent high-temperature processes and 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, about 2.29 mm. The small cross-section is beneficial to reduce heat conduction when the cable works across the temperature range, and reduce the load of the liquid helium refrigerator of the thermostat on the superconducting accelerator. The model of the coaxial cable 1 in this embodiment is not limited to this. If the low heat leakage requirement is not considered, it can also be designed to a larger size specification of "141" and "270", and the outer diameter of the sheath is 3.58 mm (about 0.141 inches) and 6.86 mm (about 0.27 inches) respectively.

[0049] In the design process of the cable of this embodiment, the relevant industry standards of the above-mentioned coaxial cable 1 must also be followed. Preferably, the cut-off frequency f c is an important parameter, which is determined by the following formula (1), where c is the speed of light in vacuum, ∈ r is the relative dielectric constant, d and D represent the outer diameter of the inner conductor and the inner diameter of the outer conductor of the cable respectively. The operating frequency of the cable must be less than f c , ensuring that no unnecessary higher-order modes other than TEM are excited. Substituting various parameters of the cable of this embodiment into the calculation of its f c About 55.62GHz, which can meet the needs of the project. With a smaller cross-sectional size, f c The frequency will be higher.

[0050]

[0051] When high-frequency signals are transmitted, the thin transmission 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 metal conductivity in m / (Ωmm 2 ), f is the operating frequency in kHz, which affects the thickness of the cable inner conductor. Substituting the cable parameters of this embodiment into the frequency points of 1MHz and 3GHz, the skin depths are calculated to be 66.02μm and 1.21μm respectively. The copper layer thickness of the inner conductor of the cable in this embodiment is 100μm, which comprehensively considers the transmission requirements of low and high frequency signals.

[0052]

[0053] Characteristic impedance Z is a key indicator in the design of coaxial cable 1. It is actually a complex number related to frequency. In the RF field, it tends to be a constant, as shown in formula (3), which is determined by the outer diameter d of the inner conductor of the cable, the inner diameter D of the outer conductor, and the relative dielectric constant ∈ r When the cable of this embodiment is used for beam diagnosis low temperature BPM signal transmission, its bandwidth requirement is about 3 GHz, and the design value and error of characteristic impedance is 50±3Ω. Figure 5 The 1.66-meter cable assembly sample of this embodiment is displayed. The time domain TDR impedance measured by a vector network analyzer shows that its average impedance is 49.93Ω and the maximum deviation value is 4.66Ω.

[0054]

[0055] Attenuation α is a core indicator that affects cable performance. As shown in formula (4), it is defined as the ratio of the cable input power P1 to the remote output power P2. R and dielectric attenuation α ∈ It consists of two parts. From formulas (5) and (6), it can be seen that the resistive attenuation α R Proportional to the square of the frequency f, given by the relative dielectric constant ∈ r , the cable's inner conductor outer diameter d, outer conductor inner diameter D, and the conductivity σ1 and σ2 of the inner and outer conductor metals; as the frequency gradually increases, the dielectric attenuation α ∈ The contribution of the proportion increases, which is proportional to the frequency f, given by the relative dielectric constant ∈ r , and the loss tangent tanδ of the medium. When the cable of this embodiment is used in a beam diagnosis low-temperature BPM, it is required that at room temperature 20°C, the attenuation α≤0.35dB / m@162.5MHz, and at a lower temperature, the attenuation will be relatively lower.

[0056]

[0057] The attenuation of the 1.66-meter sample of the cable assembly of this embodiment is measured. Figure 6 As shown in the figure, at 162.5MHz and 3GHz, the values ​​are -0.50dB and -2.14dB respectively. After length conversion, they are 0.30dB / m@165.28MHz and 1.29dB / m@3GHz respectively. The actual measurement meets the design indicators and usage requirements. The @ followed by the frequency refers to the parameter indicators at a specific frequency. Many parameters change with frequency.

[0058] Embodiment 3

[0059] Based on the same inventive concept, this embodiment discloses a connector for a coaxial cable 1, which is used for any of the above coaxial cables 1, and the connector includes an N-type male connector 2 and an SMA-type male connector 3. A modular component design is adopted, and various parts of the connector are specially designed and modularly detachable. For example, an additional bushing is designed to reduce the shear force at the laser welding point and increase the strength and life of the connector. It is convenient for internal parts to be adjusted or optimized in size to better meet the impedance matching requirements of 50 ohms, and it is also convenient for the inspection and replacement of the connector itself.

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

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

[0062] The end of the front housing 10 near the nut 9 has a smaller diameter, and an annular groove is provided in the middle section for placing the snap ring 11. The other end of the front housing 10 has a larger diameter, and the inner hole surface of the end with the larger diameter is an M10*1.25 internal thread with a depth of 5.50mm, which is used for detachable tightening connection with the rear housing 14. A through hole is provided inside the front housing 10. The snap ring 11 is provided between the nut 9 and the front housing 10, and is fixed in the annular groove of the middle columnar part of the front housing 10, and is used to connect the front housing 10 and the nut 9.

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

[0064] The rear insulating sheet 16 is disposed in the rear housing 14 and behind the inner guide sleeve 15 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, and a circle of metal is set on its outer wall for laser welding with the front shell 10; the needle core has a diameter of 0.9 mm and a length of 3 mm. It is fixed on the glass column by high-temperature sintering. The needle core is fixed at the center of the glass insulating column. One end of the needle core is connected to the plug pin 12, and the other end of the needle core is connected to the inner guide sleeve 15. After the needle core on the glass insulator 13 is connected with the plug pin 12 and the inner guide sleeve 15 respectively, laser welding is performed to reinforce it through the reserved holes on the plug pin 12 and the inner guide sleeve 15. The front shell 10 and the rear shell 14 are tightened and connected through their own threads. The glass insulator 13 and the front shell 10, as well as the rear shell 14 and the cable metal sheath, are connected and reinforced by laser welding, and the vacuum sealing of the dielectric powder and the cable as a whole is guaranteed.

[0066] The tip of the pin 12 is a cone, and the bottom is a hollow column with an inner diameter of 3.5 mm and a single-ended groove with a diameter of 1 mm on the surface. The bottom end of the hollow column is connected to the Kovar alloy needle core, and 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 is provided with an inner hole, the inner hole near the front shell 10 is 0.92mm in inner diameter, and the inner diameter is connected with the rear end needle core of the glass insulator 13, and the inner hole at the other end is 0.60mm in inner diameter, and is connected with the inner conductor of the SiO2 cable. The inner guide sleeve 15 is provided with two side single holes for better laser welding and reinforcement.

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

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

[0070] The process characteristic of laser welding is that high-power laser bombards the joint of the metal to be welded, generates local high temperature in a short time, and forms a fused metal layer. After cooling, welding fixation and vacuum sealing are achieved. It is suitable for welding of small size and thin layer metal. The process parameters of laser welding 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 the present invention uses component laser welding technology, pure inorganic materials and production technology for cables, inorganic materials and glass sintering technology for connectors, etc., all of which can withstand operating conditions up to about 1000°C. Optionally, in addition to the extremely low temperature application of 2K / 4K in the thermostat, the SiO2 cable assembly of the present invention can also be used in high temperature scenarios such as aerospace and industry.

[0072] It should be noted that, in the present invention, the orientation or position relationship indicated by the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the system or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present 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 that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed.

[0073] In addition, in the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation of the present invention can still be modified or replaced by equivalents, and any modification or equivalent replacement that does not deviate from the spirit and scope of the present invention should be included in the protection scope of the claims of the present invention. The above content is only a specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for preparing silicon dioxide for coaxial cable, characterized in that: The coaxial cable comprises: an inner conductor layer and an outer conductor layer, a silicon dioxide layer is arranged between the inner conductor layer and the outer conductor layer, and the silicon dioxide in the silicon dioxide layer is prepared by the following method, including: First, silica and mixed materials are loaded into an extruder, and the mixture is extruded by a pusher to generate a mixed gel state of organic and inorganic substances; Chemically foaming the mixed gel state of the organic and inorganic substances; The mixed gel after chemical foaming is subjected to high temperature sintering to remove the organic additives therein; The outer conductor layer is sleeved on the silicon dioxide layer sintered at high temperature and drawn to form a tubular silicon dioxide insulation layer.

2. The method for preparing silicon dioxide for coaxial cable according to claim 1, characterized in that: The particle units after chemical foaming are packaged so that the particle units are wrapped with a layer of dense silicon dioxide film.

3. The method for preparing silicon dioxide for coaxial cable according to 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, a silicon dioxide layer is arranged 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 cable according to any one of claims 1 to 3.

5. The coaxial cable according to claim 4, characterized in that The inner conductor layer comprises an iron core and an inner conductor copper layer, and the inner conductor copper layer is plated on the iron core; the outer conductor layer comprises an outer conductor copper layer and a metal sheath layer, and the metal sheath layer is sleeved on the outer conductor copper layer.

6. The coaxial cable according to claim 4, characterized in that The coaxial cable is a 090 type coaxial cable, and the metal sheath layer is a stainless steel 304L sheath layer.

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

8. The coaxial cable connector according to claim 7, wherein: The joint connectors include N-type and SMA-type male connectors.

9. The coaxial cable connector according to claim 7, wherein: The joint connector also includes a snap ring and a rear insulating sheet. The snap ring is arranged between the nut and the front shell, and is fixed in an annular groove of the middle columnar portion of the front shell for connecting the front shell and the nut. The rear insulating sheet is arranged in the rear shell, behind the inner guide sleeve, for isolating the inner guide sleeve from the outer conductor layer.

10. The coaxial cable connector according to claim 7, wherein: 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 circle of metal is arranged on the outer wall thereof for laser welding with the front outer shell. The needle core is fixed at the center of the glass insulating column, one end of the needle core is connected to the pin, and the other end of the needle core is connected to the inner guide sleeve.

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