Production method of low-temperature superconductive low-heat-leakage superfine coaxial cable

Abstract

The invention relates to the technical field of cables, in particular to a production method of a low-temperature superconductive low-heat-leakage superfine coaxial cable, the outer diameter of the coaxial cable is smaller than or equal to 1.5 mm, and the cable is provided with a core material, a first superconductive layer, a PTFE dielectric layer, a second superconductive layer and a stainless steel pipe from inside to outside; the production method comprises the following steps: coating the periphery of the core material with the first superconducting layer to prepare the inner conductor; coating the periphery of the inner conductor with a PTFE layer to form a medium wire core; longitudinally penetrating the strip-shaped second superconducting layer through a round hole mold with the inner diameter gradually reduced, and rolling into a hollow pipe with the outer diameter slightly smaller than the inner diameter of the stainless steel pipe; and synchronously pulling the hollow pipe into the stainless steel pipe, pulling the medium wire core into the hollow pipe in the stainless steel pipe, and completing cable assembly. Pulling the cable through a round hole die with the inner diameter smaller than the outer diameter of the stainless steel pipe for reducing extrusion; in inert gas or high vacuum, the internal stress of the cable is released through heating. The second superconducting layer lining is longitudinally covered in the stainless steel tube, so that the problem that the inner wall of the extremely long and thin tube is difficult to uniformly plate the superconducting layer is solved.

Description

Technical Field

[0001] This invention relates to the field of cable manufacturing technology, specifically to a method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable, and more particularly to a manufacturing process for a coaxial cable with an extremely fine inner diameter. Background Technology

[0002] Coaxial cable, also known as a coaxial line or common axis cable, is a transmission medium composed of an inner conductor, a dielectric layer, an outer conductor, and a sheath. Its name derives from the unique structure where the inner and outer conductors are aligned on the same axis. This configuration allows coaxial cables to exhibit lower losses and higher interference immunity when transmitting high-frequency signals.

[0003] When the inner conductor transmits a signal, it generates an alternating electromagnetic field around it. This electromagnetic field is confined within the coaxial space formed by the inner and outer conductors. Its electric field lines are radially distributed between the inner and outer conductors, while its magnetic field lines form a closed loop around the inner conductor. The dielectric layer not only provides mechanical support but also determines the propagation speed of electromagnetic waves and the characteristic impedance of the cable through its dielectric constant. The outer conductor, acting as an electromagnetic shielding layer, effectively suppresses the outward radiation of the internal electromagnetic field according to the Faraday cage principle, while also blocking the coupling of external electromagnetic interference. Therefore, coaxial cables can maintain stable signal transmission quality in complex electromagnetic environments.

[0004] Superconducting coaxial cables are core components of low-temperature superconducting quantum computer signal transmission systems, and their performance directly affects the computational accuracy and stability of the entire system. To achieve superconducting transmission, the conductive layer of the cable must use a temperature-superconducting material (such as niobium and its alloys). Current manufacturing processes mostly use pure niobium or niobium-titanium alloys, which undergo complex, high-precision metal processing to form a tubular shape, serving as the inner and outer conductors. Pure niobium is used in some applications due to its ease of processing and low cost, but it has higher heat leakage. Niobium-titanium alloys are also used in some cases because they are difficult to process but have lower heat leakage. Another method involves electroplating a niobium compound layer onto the inner wall of a stainless steel tube to form the outer conductor, which has the advantages of low cost and ease of processing, but it cannot produce extremely thin cables to reduce heat leakage in a single cable.

[0005] For example, Chinese patent CN119560230B discloses a superconducting coaxial cable for quantum computers and its manufacturing method. The method involves covering an inner conductor with an inner insulating layer to form an inner conductor layer, electroplating a niobium compound coating on the inner wall of a stainless steel tube to form an outer conductor, and then inserting a single inner conductor layer into a single outer conductor to form the cable's conductive layer. During the outer conductor electroplating process, the surface of the stainless steel tube, except for the inner wall, needs to be coated with silicone resin insulating varnish. The stainless steel tube and the niobium rod serve as the positive and negative electrodes for electroplating. The stainless steel tube is vertically immersed in the electrolyte, and the electroplating stirring rod moves vertically inside the stainless steel tube.

[0006] However, electroplating inside pipes requires inserting an electrode (anode) into the bore, ensuring it remains insulated from the inner wall and never contacts it throughout the process. For extremely long and thin pipes (inner diameter less than 10mm, length several meters, length-to-diameter ratio over 1000), the pressure of gravity, liquid flow impact, and vibration places near-limiting demands on the equipment's machining precision, rigidity, and control system to maintain precise centering within such a confined space. In actual production, current technology can hardly reliably prevent the electrode from contacting the inner wall for extremely long and thin pipes. A short circuit can not only cause plating ablation and defects but also directly lead to product scrap.

[0007] Meanwhile, uniform electroplating requires the plating solution to flow fully and evenly within the cathode cavity to replenish consumed metal ions and eliminate generated bubbles in a timely manner. However, in extremely long and narrow tubes, fluid resistance is extremely high, making it difficult for existing technologies to create good, controllable laminar or turbulent flow of the plating solution within such a small space. Poor flow can lead to untimely ion replenishment (concentration polarization), easily resulting in thin coating areas in the middle or deeper parts of the pipe. At the same time, the generated hydrogen bubbles are difficult to expel, adhering to the pipe wall and forming defects such as pinholes and pits, severely compromising the density, uniformity, and conductivity of the coating.

[0008] In summary, this method cannot be directly used to manufacture low-temperature superconducting outer conductors for extremely thin coaxial cables, and has significant limitations. Summary of the Invention

[0009] This invention provides a method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable. The new process replaces the traditional electroplating process to solve the technical problem of the difficulty in uniformly depositing a superconducting layer on the inner wall of an ultra-fine, long tube.

[0010] To address the aforementioned problems, this invention provides a method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable, employing the following technical solution: A method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable, wherein the coaxial cable has an outer diameter of no more than 1.5 mm, and the coaxial cable is composed of a core material, a first superconducting layer, a PTFE dielectric layer, a second superconducting layer, and a stainless steel tube tightly arranged from the inside out; the method for producing the coaxial cable includes the following steps: The first superconducting layer is wrapped around the outer periphery of the core material in a concentric overlapping wrapping manner to form an inner conductor; The PTFE dielectric layer is wrapped around the outer periphery of the inner conductor to form a dielectric core. A strip-shaped second superconducting layer with a width slightly larger than the circumference of the inner diameter of the stainless steel tube is longitudinally passed through a first circular hole mold with a gradually decreasing inner diameter and rolled up to form a hollow tube with an outer diameter slightly smaller than the inner diameter of the stainless steel tube. Simultaneously, the second superconducting layer hollow tube is pulled into the stainless steel tube. The shape of the hollow tube is freed from the mold constraint and naturally spreads out and thickens, closely adhering to the inner wall of the stainless steel tube. Then, the dielectric core is pulled into the interior of the second superconducting layer hollow tube inside the stainless steel tube, and the cable assembly is completed. The assembled cable is pulled through a second circular hole mold with an inner diameter smaller than the outer diameter of the stainless steel tube, so that the outer diameter of the stainless steel tube is continuously reduced to the target value, so that the stainless steel tube, the second superconducting layer and the dielectric core are squeezed tightly together. Under inert gas protection or high vacuum environment, place the cable in an oven at 200℃~220℃ and heat for 12~60 hours to release the internal stress of the cable.

[0011] The cable has an extremely small outer diameter (no more than 1.5 mm), which not only means that its heat conduction cross-sectional area is smaller, which can fundamentally reduce axial heat leakage and meet the stringent low heat leakage requirements of cryogenic systems; at the same time, under the same performance requirements, the smaller size directly reduces the consumption of expensive superconducting materials and metal materials, laying the foundation for cost reduction.

[0012] This invention employs a physical inner liner longitudinal cladding method to form the superconducting layer of the outer conductor, allowing for precise control of material thickness and overlap width. This ensures the continuity, density, and uniformity of the superconducting layer along the cable's length. Compared to defects easily encountered in electroplating processes, such as "thin center," "pinholes," "pockmarks," inability to perform ultra-fine tube electroplating, and easy cracking of the plating layer, this significantly improves the surface quality and conductivity of the conductor, providing a solid foundation for low-loss, high-fidelity transmission of quantum computer signals.

[0013] The assembled cable is subjected to a diameter-reducing extrusion rolling process using a second circular die with an inner diameter smaller than the outer diameter of the stainless steel tube. This causes the stainless steel tube to undergo plastic deformation under external force, uniformly shrinking inward. This process forces the outer conductor (composed of the stainless steel tube and the second superconducting layer) to fit tightly and seamlessly with the dielectric core, greatly reducing the gaps between layers and the contact resistance of the contact gaps in the longitudinally clad niobium foil inside the steel tube. This effectively improves the continuity of the second superconducting layer; the further reduction in cross-sectional area due to the reduced outer diameter results in a smaller thermal conductivity cross-sectional area for the cable. Based on the ultra-low thermal conductivity properties of the austenitic stainless steel inner conductor core and the austenitic stainless steel outer conductor substrate (i.e., the stainless steel tube), low heat leakage is ensured in extremely low-temperature environments.

[0014] Prolonged (12-60 hours) and medium-temperature (200℃-220℃) heat treatment under inert gas protection or high vacuum effectively releases the internal residual stress generated during cable wrapping, extrusion, and other processing. The stress-released cable structure is more stable, less prone to deformation or delamination, improving the product's mechanical strength at ultra-low temperatures and its long-term reliability, while also helping to maintain stable electrical performance.

[0015] As a preferred embodiment of the present invention, the core material is austenitic stainless steel wire with a magnetic permeability of not more than 1.05.

[0016] Austenitic stainless steel not only possesses excellent non-magnetic properties but also exhibits good low-temperature toughness, corrosion resistance, and a coefficient of thermal expansion that matches that of superconducting materials such as niobium. During cycling from room temperature to extremely low temperatures (such as the 4K liquid helium temperature range), this core material is less prone to brittle fracture, and its thermal deformation difference with the outer layer material is small, reducing the risk of structural delamination or cracking caused by thermal stress. This further enhances the long-term reliability and service life of the cable under extreme conditions.

[0017] As a preferred embodiment of the present invention, the first superconducting layer is a pure niobium foil or a niobium-titanium alloy foil, and the thickness of the first superconducting layer is 2 μm to 50 μm.

[0018] As a preferred embodiment of the present invention, the wrapping overlap rate of the first superconducting layer is 0.5% to 80%.

[0019] As a preferred embodiment of the present invention, the density of the PTFE dielectric layer is between 0.5 g / cm³. 3 ~2.2g / cm 3 between.

[0020] As a preferred embodiment of the present invention, the PTFE dielectric layer is disposed on the outer periphery of the inner conductor by concentric wrapping or extrusion covering.

[0021] As another preferred technical solution of the present invention, the PTFE dielectric layer is replaced with an ultra-high purity silicon-based glass fiber layer with lower thermal conductivity. The glass fiber layer is wrapped around the outer periphery of the inner conductor by weaving or winding, and the number of weaving or winding layers is 1 to 12.

[0022] As a preferred embodiment of the present invention, the second superconducting layer is a pure niobium foil or a niobium-titanium alloy foil, and the thickness of the second superconducting layer is 2 μm to 50 μm.

[0023] The outer conductor uses the same superconducting material (pure niobium or niobium-titanium alloy) as the inner conductor, which not only simplifies material supply but, more importantly, ensures a high degree of matching between the thermal expansion coefficients, mechanical properties, and superconducting transition behavior of the inner and outer conductors at low temperatures. This avoids the risk of interfacial stress concentration, delamination, or cracking caused by material differences, ensuring the structural integrity and long-term reliability of the cable during room temperature-low temperature cycling.

[0024] As a preferred embodiment of the present invention, the overlap rate of the second superconducting layer is 0.5% to 90%.

[0025] During the cold extrusion molding process, the second superconducting layer, which has a certain initial overlap ratio, will increase its overlap ratio under radial pressure. The inner overlap area will automatically roll up and compact with the outer layer, forming a "reinforcing rib" structure that is thicker than a single layer. This not only enhances the mechanical strength and crush resistance of the overlap, but also further consolidates the contact between the two superconducting materials, making the electrical connection more robust and reliable.

[0026] As a preferred embodiment of the present invention, the stainless steel tube is an austenitic stainless steel tube, and the inner diameter of the stainless steel tube is not greater than 1.3 mm and the wall thickness is not greater than 0.2 mm.

[0027] This coaxial cable utilizes the skin effect principle, employing a composite structure of a low thermal conductivity stainless steel core and an ultra-thin superconducting layer for both inner and outer conductors, rather than a single pure niobium or niobium-titanium alloy. This significantly reduces heat conduction while maintaining superconducting performance, thus lowering material costs. The main body of the inner and outer conductors is made of weldable stainless steel, overcoming the limitation of pure superconducting materials being "unweldable." By using expensive superconducting materials (niobium or niobium-titanium alloy) only in the most performance-critical areas, while using low-cost stainless steel for the main structure, it achieves an optimal balance between performance and cost.

[0028] As a preferred embodiment of the present invention, the first circular hole mold for the second superconducting niobium foil winding tube is a series of circular hole molds with an inner diameter gradient ratio of 1.25 to 5 times.

[0029] By employing a gradient die design, the feasibility and uniformity of cold extrusion molding are ensured. This avoids shrinking to the target size in one step, as excessive deformation can lead to a sharp increase in material stress, easily causing niobium foil rupture, internal structural damage, or excessive extrusion tearing at the overlap. Multi-stage gradient dies distribute the total deformation across multiple processes, with the deformation at each stage controlled within a safe range, ensuring the stability of the molding process and high yield. Simultaneously, a reasonable gradient ratio (1.25-5 times) ensures the smoothness of metal yielding, effectively preventing flattening, wrinkling, or localized damage caused by uneven yielding deformation, guaranteeing the roundness of the second superconducting layer and the concentricity of each layer in the final cable size.

[0030] During the single-stage diameter reduction process of the outermost stainless steel tube, the pressure exerted by the stainless steel tube on the internal structure (second superconducting outer conductor, PTFE dielectric layer, and inner conductor) is achieved in one step. Utilizing the ample space for movement between the layers within the steel tube before diameter reduction, their relative positions are determined in one continuous motion. This one-step pressurization method ensures the simultaneous positioning of the internal multi-layered structure, avoiding the drawbacks of "multiple diameter reduction forming," which leads to repeated friction, displacement, and increasing frictional forces between internal layers, resulting in damage. This achieves a seamless and damage-free perfect fit between the stainless steel tube, the second superconducting outer conductor, and the PTFE dielectric layer, minimizing contact thermal resistance and contact resistance.

[0031] The beneficial effects are: 1. This invention provides a method for producing low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cables. It replaces traditional methods of rolling niobium tubes, rolling niobium-titanium alloy tubes, and electroplating niobium with a new process to solve the technical problems of difficult processing, high heat leakage, and difficulty in uniformly plating a superconducting layer on the inner wall of ultra-fine, long tubes. The production method of this invention does not rely on complex electroplating equipment, electrolyte circulation systems, or precise electrode positioning devices. The main processes are wrapping, longitudinal lining, extrusion, and heat treatment, all of which are mature and easily automated industrial technologies. This not only significantly simplifies the production process and reduces equipment investment but also makes continuous, large-scale production easier to achieve.

[0032] 2. This invention abandons the complex traditional process of electroplating the inner wall of a stainless steel tube to form an outer conductor. Instead, it uses a method of longitudinally bonding a second superconducting layer to the inner wall of the stainless steel tube as an inner lining, and then extruding it through subsequent diameter reduction processing to ensure a tight fit between the stainless steel tube and the internal structure. This method completely avoids the difficulties of inserting and precisely controlling the anode electrode to prevent it from touching the inner wall of an extremely thin and long tube while ensuring smooth flow of the electroplating solution. It fundamentally solves the risks of short circuits, ablation, and product scrap caused by electrode contact with the wall, enabling large-scale, high-yield production of extremely thin and long coaxial cables with an inner diameter of no more than 1.5 mm.

[0033] 3. The outer diameter of the final product can be precisely controlled by extrusion through the second round hole mold (not greater than 1.5mm), with small dimensional tolerances and high batch-to-batch consistency, meeting the stringent requirements of high-end electronic equipment for precision cables. Attached Figure Description

[0034] Figure 1 A schematic diagram of the structure of a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable; Figure 2 This is a cross-sectional view of the coaxial cable and coaxial connector after welding according to the present invention; Figure 3 This is a schematic diagram of the structure of the second superconducting layer wrapped in the first circular hole mold.

[0035] Explanation of reference numerals in the attached figures: 1. Core material; 2. First superconducting layer; 3. PTFE dielectric layer; 4. Second superconducting layer; 5. Stainless steel tube; 6. Connector center conductor; 7. Connector outer tube; 8. Solder; 9. Solder hole; 10. First round hole mold. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0037] In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more. The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and do not limit the number of objects; for example, a first object can be one or more.

[0038] Table 1 shows the structural materials and characteristics of low-temperature superconducting radio frequency coaxial cables used in the low-temperature superconducting quantum computing and nuclear magnetic resonance markets.

[0039] Table 1. Existing materials and properties of low-temperature superconducting radio frequency coaxial cables on the market.

[0040] As shown in the table above, the market currently needs a low-temperature superconducting coaxial cable product that combines low heat leakage at low temperatures (low thermal conductivity at 4K), excellent superconducting performance, moderate cost, and good solderability to replace the current superconducting coaxial cable products on the market and promote industry development.

[0041] Therefore, the inventors selected austenitic stainless steel, the metal with the lowest thermal conductivity, as the main material for the inner and outer conductors, niobium or niobium-titanium alloy as the superconducting layer, and silica glass or PTFE (expanded polytetrafluoroethylene), which has extremely low thermal conductivity, as the dielectric material. They plan to use the above materials to produce a low-temperature superconducting cable with low heat leakage, moderate cost, and good weldability.

[0042] However, during the production process, the inventors discovered that using existing electroplating technology to achieve the plating of the outer conductor faces insurmountable technical bottlenecks for electroplating micropores with an inner diameter of less than 1.5 mm: 1. The Challenge of Electrode Positioning and Insulation in Micro-orifices: Electroplating processes require inserting an electrode (anode) into the inner bore of pipes, ensuring that the electrode remains insulated from the bore wall and never comes into contact with it throughout the entire plating process. For slender pipes with an inner diameter of less than 1.5 mm (reaching lengths of several meters and length-to-diameter ratios exceeding 1000), ensuring that an extremely thin electrode remains precisely centered within such a confined space without touching the wall under the influence of gravity, liquid flow impact, and vibration places near-limiting demands on the processing precision, rigidity, and control system of the equipment. In actual production, for pipes with an inner diameter of less than 1.5 mm, current technology can hardly reliably guarantee that the electrode will not touch the inner wall. A short circuit can not only cause plating ablation and defects but also directly lead to product scrap.

[0043] 2. Challenges in Controlling the Flow Field of Electroplating Solution in Micro-orifices: Uniform electroplating requires the electroplating solution to flow fully and uniformly within the cathode tube (i.e., the outer conductor) cavity to replenish consumed metal ions and eliminate generated bubbles in a timely manner. However, in micro-orifices with an inner diameter of less than 1.5 mm, fluid resistance is extremely high, making it difficult for existing technologies to create good, controllable laminar or turbulent flow of the electroplating solution within such a small space. Poor flow can lead to untimely ion replenishment (concentration polarization), easily resulting in thin coating areas in the middle or deeper parts of the pipe. Simultaneously, the generated hydrogen bubbles are difficult to expel, adhering to the pipe wall and forming pinholes, pitting, and other defects, severely compromising the density, uniformity, and conductivity of the coating.

[0044] In summary, existing electroplating processes are still limited by traditional electrode insertion and forced flow methods, and cannot overcome the two major physical limits of "micro-hole electrode centering" and "micro-hole flow control", thus restricting the development of superconducting coaxial cables in terms of smaller size and higher performance.

[0045] Therefore, developing a manufacturing method that can fundamentally circumvent or solve the aforementioned bottlenecks in microporous electroplating has become an urgent technical problem to be solved in this field.

[0046] To address the aforementioned problems, this invention provides a method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable. This method utilizes austenitic stainless steel, a metal with the lowest thermal conductivity and lowest cost, as the main material for both the inner and outer conductors; niobium or niobium-titanium alloy as the superconducting layer; and silica glass or PTFE (expanded polytetrafluoroethylene), a material with extremely low thermal conductivity, as the dielectric material. Through an innovative production process, this method produces a low-temperature superconducting cable with low heat leakage, moderate cost, and good weldability.

[0047] After introducing the basic principles of the present invention, various non-limiting embodiments of the present invention are described in detail below. Any number of elements in the accompanying drawings is for illustrative purposes only and not for limitation, and any naming is for distinction only and has no limiting meaning.

[0048] The principles and essence of the present invention will be explained in detail below with reference to several representative embodiments.

[0049] Example 1: like Figure 1 As shown, a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable comprises, from the inside out, a core material 1, a first superconducting layer 2, a PTFE dielectric layer 3, a second superconducting layer 4, and a stainless steel tube 5. The core material 1 and the first superconducting layer 2 surrounding it constitute the inner conductor. The core material 1 is made of austenitic stainless steel wire, used to provide mechanical strength and suppress axial heat conduction. The PTFE dielectric layer 3, a low-loss dielectric material, covers the inner conductor. The second superconducting layer 4 is longitudinally bonded to the inner wall of the stainless steel tube 5. The first superconducting layer 2 and the second superconducting layer 4 (hereinafter referred to as superconducting layers) are made of pure niobium foil. This coaxial cable has the advantages of low-temperature superconductivity, low heat leakage, moderate cost, and good solderability.

[0050] The magnetic permeability of austenitic stainless steel is no greater than 1.05. Austenitic stainless steel possesses extremely strong non-magnetic (weakly magnetic) properties, with a magnetic permeability close to that of vacuum. It exhibits almost no magnetization response under extremely low temperatures and alternating electromagnetic fields. This effectively avoids the additional energy loss (i.e., magnetic loss) caused by hysteresis and eddy current effects in traditional magnetic materials, effectively preventing the core material itself from becoming a source of interference, and ensuring high fidelity and high stability of weak quantum signals during transmission.

[0051] The niobium foil superconducting layer is 5 μm thick, and the inner conductor diameter is 0.21 mm; the PTFE material density is 1 g / cm³. 3 Stainless steel pipe 5 has a wall thickness of 0.08mm and an inner diameter of 0.8mm.

[0052] A method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable includes the following steps: S1. The first superconducting layer 2 is wrapped around the outer periphery of the core material 1 in a concentric overlapping wrapping manner (the wrapping overlap rate is 50%) to form an inner conductor; S2. Wrap a PTFE dielectric layer 3 around the outer periphery of the first superconducting layer 2 (with a wrapping overlap rate of 50%) to form a dielectric wire core; S3, longitudinal lining (such as...) Figure 3 As shown): A strip-shaped second superconducting layer 4, with a width slightly larger than the inner diameter circumference of the stainless steel tube 5 by 0.15 mm, is longitudinally passed through a first circular hole mold 10 with a gradually decreasing inner diameter (the inner diameter of the mold hole decreases from 2.25 mm to 0.7 mm), and rolled up to form a niobium foil tube with an outer diameter slightly smaller than the inner diameter of the stainless steel tube 5. At this time, the overlap rate of the second superconducting layer 4 is approximately 17%. S4. Simultaneously, the niobium foil tube is pulled into the stainless steel tube 5 to form a steel-niobium composite tube; then the dielectric core is pulled into the steel-niobium composite tube, and the cable assembly is completed. S5. Pull the assembled cable through the second round hole mold with an inner diameter of 0.79mm to reduce the outer diameter of the stainless steel tube 5 to the target value of 0.79mm, so that the stainless steel tube 5, the niobium foil tube and the dielectric core are squeezed tightly. S6. Under the protection of high-purity nitrogen inert gas or in a high vacuum environment, place the cable in an oven at 210°C and heat for 48 hours to release the internal stress of the cable.

[0053] The production method involves first longitudinally covering the inside of a stainless steel tube 5 with a niobium foil liner, then pulling in a low-temperature resistant PTFE dielectric core with a self-lubricating, soft, and smooth surface; next, the steel-niobium composite tube with the niobium foil liner on the inner wall is reduced in diameter to ensure close contact between the niobium foil and the steel tube, and the smooth inner surface of the stainless steel tube 5 is used to flatten and shape the longitudinally liner niobium foil, thereby ensuring that the second superconducting layer 4 (i.e., the niobium foil layer) of the cable's outer conductor is smooth and continuous, improving transmission performance.

[0054] The niobium foil tube is bonded to the inner wall of the stainless steel tube 5 using a longitudinal lining method. Because the niobium foil is very thin, the cross-sectional area of ​​the niobium is small, and very little niobium foil is used. This achieves extremely low heat leakage while ensuring top-level superconducting radio frequency performance. At the same time, it significantly reduces costs.

[0055] like Figure 2 As shown, when the cable is soldered to the coaxial connector, the first superconducting layer 2 is removed from the end of the inner conductor of the cable. 1. The outer tube 7 of the coaxial connector is directly welded to the outer surface of the stainless steel tube 5 to avoid welding to the second superconducting layer 4 of the outer conductor, which cannot be welded. The stepped surface of the outer tube 7 of the connector is flush with the second superconducting layer 4. 2. A solder hole 9 is opened on the center conductor 6 of the coaxial connector at the position corresponding to the end of the inner conductor. The solder 8 flows through the solder hole 9 to the surface of the stainless steel wire, and the center conductor 6 of the connector is directly welded to the surface of the inner conductor core material 1 (i.e. the surface of the stainless steel wire), avoiding welding with the first superconducting layer 2. At the same time, the sleeve end of the center conductor 6 of the connector is sleeved with the first superconducting layer 2 to prevent the first superconducting layer 2 from loosening.

[0056] This embodiment employs the aforementioned innovative process to replace traditional electroplating, perfectly solving the global challenge of uniformly depositing a superconducting layer on the inner wall of extremely thin tubes. The quality of the niobium foil layer (i.e., the superconducting layer) far surpasses that of electroplating. Utilizing the skin effect principle, the inner and outer conductors adopt a composite structure of "low thermal conductivity stainless steel core + ultra-thin layer superconducting niobium," rather than a monolithic pure niobium or niobium-titanium alloy. This significantly reduces heat conduction while ensuring superconducting performance, and also lowers material costs. The outer conductor uses weldable stainless steel, solving the pain point of pure superconducting materials being "unweldable." By using expensive superconducting materials (niobium) only in the most performance-critical parts, while using low-cost stainless steel for the main structure, an optimal balance between performance and cost is achieved. Thermal stress release ensures the product's dimensional and performance stability under extreme low-temperature environments.

[0057] Example 2: Its main difference from Example 1 is: In this embodiment, the superconducting layer thickness is 20 μm, the inner conductor diameter is 0.3 mm, and the PTFE material density is 1.5 g / cm³. 3 The stainless steel pipe 5 has a wall thickness of 0.12mm and an inner diameter of 1.3mm.

[0058] A method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable includes the following steps: S1. The first superconducting layer 2 is wrapped around the outer periphery of the core material 1 in a concentric overlapping wrapping manner (the wrapping overlap rate is 30%) to form an inner conductor; S2. PTFE is pushed around the outer periphery of the first superconducting layer 2 to form a dielectric core; S3. Longitudinal lining: A strip-shaped second superconducting layer 4, with a width slightly larger than the inner diameter circumference of the stainless steel tube 5 by 0.3 mm, is longitudinally passed through a first circular hole mold 10 with a gradually decreasing inner diameter (the inner diameter of the mold hole decreases from 4 mm to 1.1 mm), and rolled up to form a niobium foil tube with an outer diameter slightly smaller than the inner diameter of the stainless steel tube 5. At this time, the overlap rate of the second superconducting layer 4 is approximately 21%. S4. Simultaneously, the niobium foil tube is pulled into the stainless steel tube 5 to form a steel-niobium composite tube; then the dielectric core is pulled into the steel-niobium composite tube, and the cable assembly is completed. S5. Pull the assembled cable through the second round hole mold with an inner diameter of 1.19mm to reduce the outer diameter of the stainless steel tube 5 to the target value of 1.19mm, so that the stainless steel tube 5, the niobium foil tube and the dielectric core are squeezed tightly. S6. Under the protection of high-purity argon inert gas or in a high vacuum environment, place the cable in an oven at 205°C and heat for 50 hours to release the internal stress of the cable.

[0059] Example 3: Its main difference from Example 1 is: In this embodiment, the superconducting layer has a thickness of 7 μm and the inner conductor diameter is 0.15 mm; the PTFE dielectric layer is replaced with an ultra-high purity quartz glass fiber layer with lower thermal conductivity; the stainless steel tube 5 has a wall thickness of 0.05 mm and an inner diameter of 0.7 mm.

[0060] A method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable includes the following steps: S1. The first superconducting layer 2 is wrapped around the outer periphery of the core material 1 in a concentric overlapping wrapping manner (the wrapping overlap rate is 10%) to form an inner conductor; S2. A layer of high-purity quartz glass fiber is woven around the outer periphery of the first superconducting layer 2 to form a dielectric wire core; S3. Longitudinal lining: A strip-shaped second superconducting layer 4, with a width slightly larger than the inner diameter circumference of the stainless steel tube 5 by 0.1 mm, is longitudinally passed through a first circular hole mold 10 with a gradually decreasing inner diameter (the inner diameter of the mold hole decreases from 1.95 mm to 0.55 mm), and rolled up to form a niobium foil tube with an outer diameter slightly smaller than the inner diameter of the stainless steel tube 5. At this time, the overlap rate of the second superconducting layer 4 is approximately 25%. S4. Insert the niobium foil tube into the stainless steel tube 5 to form a steel-niobium composite tube; then insert the dielectric core into the steel-niobium composite tube to complete the cable assembly. S5. Pull the assembled cable through the second round hole mold with an inner diameter of 0.54mm to reduce the outer diameter of the stainless steel tube 5 to the target value of 0.54mm, so that the stainless steel tube 5, the niobium foil tube and the dielectric core are squeezed tightly. S6. Under the protection of high-purity helium inert gas or in a high vacuum environment, place the cable in an oven at 215°C and heat for 35 hours to release the internal stress of the cable.

[0061] Of course, in other embodiments, step S2 may also be: weaving or winding multiple layers of high-purity quartz glass fiber around the outer periphery of the first superconducting layer 2 to form a dielectric core; such as 2 layers, 4 layers, 6 layers, 8 layers, etc.

Claims

1. A method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable, characterized in that, The coaxial cable has an outer diameter of no more than 1.5 mm, and is composed of a core material, a first superconducting layer, a PTFE dielectric layer, a second superconducting layer, and a stainless steel tube, tightly arranged from the inside out. The production method of the coaxial cable includes the following steps: The first superconducting layer is wrapped around the outer periphery of the core material in a concentric overlapping wrapping manner to form an inner conductor; The PTFE dielectric layer is wrapped around the outer periphery of the inner conductor to form a dielectric core. A strip-shaped second superconducting layer with a width slightly larger than the circumference of the inner diameter of the stainless steel tube is longitudinally passed through a first circular hole mold with a gradually decreasing inner diameter and rolled up to form a hollow tube with an outer diameter slightly smaller than the inner diameter of the stainless steel tube. The second superconducting layer hollow tube is simultaneously pulled into the stainless steel tube, and then the dielectric core is pulled into the second superconducting layer hollow tube inside the stainless steel tube, thus completing the cable assembly. The assembled cable is pulled through a second circular hole mold with an inner diameter smaller than the outer diameter of the stainless steel tube, so that the outer diameter of the stainless steel tube is reduced to the target value, so that the stainless steel tube, the second superconducting layer and the dielectric core are squeezed tightly together. Under inert gas protection or high vacuum environment, place the cable in an oven at 200℃~220℃ and heat for 12~60 hours to release the internal stress of the cable.

2. The method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable according to claim 1, characterized in that, The core material is austenitic stainless steel wire with a magnetic permeability of no more than 1.

05.

3. The method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable according to claim 1, characterized in that, The first superconducting layer is a pure niobium foil or a niobium-titanium alloy foil, and the thickness of the first superconducting layer is 2 μm to 50 μm.

4. The method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable according to claim 1, characterized in that, The overlap rate of the first superconducting layer is 0.5% to 80%.

5. The method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable according to claim 1, characterized in that, The density of the PTFE dielectric layer is 0.5 g / cm³. 3 ~2.2g / cm 3 .

6. The method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable according to claim 1, characterized in that, The PTFE dielectric layer is wrapped around the outer periphery of the inner conductor by concentric wrapping or pushing.

7. The method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable according to claim 1, characterized in that, The second superconducting layer is a pure niobium foil or a niobium-titanium alloy foil, and the thickness of the second superconducting layer is 2 μm to 50 μm.

8. The method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable according to claim 1, wherein the overlap rate of the second superconducting layer is 0.5% to 90%.

9. The method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable according to claim 1, characterized in that, The stainless steel pipe is an austenitic stainless steel pipe, with an inner diameter not exceeding 1.3 mm and a wall thickness not exceeding 0.2 mm.

10. The method for producing a low-temperature superconducting, low-heat-leakage, ultra-fine coaxial cable according to claim 1, characterized in that, The first circular hole mold for the second superconducting layer niobium foil winding tube is a plurality of circular hole molds with an inner diameter gradient ratio of 1.25 to 5 times.

Images