Coaxial superconducting joint structure suitable for CICC conductor and preparation method thereof

Abstract

The invention discloses a coaxial superconducting joint structure suitable for a CICC conductor and a preparation method, and belongs to the technical field of superconducting magnet joint design and manufacturing. The two stainless steel tubes are respectively arranged at the tail end core parts of the two CICC conductors, the tail end axes of the two stainless steel tubes are aligned, and the end parts are tightly attached; the two copper pipes sleeve the peripheries of the two CICC conductor tail end superconducting cables, the tail end axes of the two copper pipes are aligned, and the end parts of the two copper pipes are tightly attached; the indium conducting layer is wound on the peripheries of the two copper pipes; the four fan-shaped copper sheets jointly wrap the periphery of the indium conducting layer; the two stainless steel shells wrap the peripheries of the four fan-shaped copper sheets, and the two ends of the two stainless steel shells are connected with the stainless steel armors at the tail ends of the two CICC conductors respectively. The CICC coaxial connector has the advantages that coaxial connection between the two CICC conductors is achieved, the occupied radial space is small, and the arrangement requirement of a narrow space is met. The superconducting joint structure has excellent resistance characteristics and low alternating current loss.

Description

Technical Field

[0001] The invention relates to the technical field of superconducting magnet joint design and manufacturing, and in particular to a coaxial superconducting joint structure suitable for CICC conductors and a preparation method thereof. Background Art

[0002] All-superconducting magnetic confinement nuclear fusion power generation technology is one of the important technical means to solve human energy problems and achieve sustainable development of human society. With the continuous advancement of the construction of the International Thermonuclear Experimental Reactor (ITER) project, nuclear fusion energy has taken another step towards commercial power generation. High-temperature superconducting materials have excellent current-carrying performance in a strong magnetic field environment of more than 20T, and are expected to further improve the magnetic field of the fusion reactor, thereby reducing the size of the host and effectively reducing the manufacturing and operating costs. Therefore, the high-temperature superconducting cable conductor (CICC) made of high-temperature superconducting materials has become the core component for manufacturing future fusion reactor magnets.

[0003] Different sub-coil units are connected in series into a whole through superconducting joints; on the one hand, the conductor length of superconducting magnets is getting longer and longer. Due to physical properties, the length of a single CICC conductor is limited to 1000 meters, and superconducting magnets can only be manufactured by connecting multiple CICC conductors in series; in order to ensure the safe operation of superconducting magnets, armored cable conductors with absolute advantages in mechanical structure, insulation performance, magnet winding process and operation safety are preferred when manufacturing superconducting magnets. Superconducting magnets are installed in a confined space (inner circle of a toroidal vacuum chamber). In order to generate a stronger magnetic field and obtain a better fusion confinement effect, it is preferred to arrange as many coil magnets as possible in a limited space.

[0004] The traditional staggered handshake type superconducting joint has a large radial dimension, an irregular outer contour, is not easy to wrap around the insulating structure, and is not suitable for arranging as many coil magnets as possible in a limited space. Summary of the invention

[0005] The purpose of the present invention is to provide a coaxial superconducting joint structure and preparation method suitable for CICC conductors, aiming to solve at least one of the technical problems existing in the above-mentioned prior art. To achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A coaxial superconducting joint structure suitable for a CICC conductor, comprising:

[0008] Two stainless steel tubes, the two stainless steel tubes are respectively arranged at the end cores of the two CICC conductors, and the axes of the two stainless steel tubes are aligned and the ends are tightly attached;

[0009] Two copper tubes, the two copper tubes are sleeved on the outer circumference of the superconducting cables at the ends of the two CICC conductors, and the axes of the ends of the two copper tubes are aligned and the ends are tightly attached;

[0010] An indium conductive layer, the indium conductive layer is wound around the outer circumferences of the two copper tubes;

[0011] Four fan-shaped copper sheets, the four fan-shaped copper sheets are wrapped together around the outer periphery of the indium conductive layer;

[0012] Two halves of the stainless steel shell are wrapped around the outer periphery of the four fan-shaped copper sheets, and two ends of the two halves of the stainless steel shell are respectively connected to the stainless steel armors at the ends of the two CICC conductors.

[0013] As a further solution of the present invention: a silver coating is electroplated on the outer periphery of the superconducting cable at the ends of the two CICC conductors, and the porosity of the superconducting cable is in the range of 18%-22%.

[0014] As a further solution of the present invention: the inner and outer surfaces of the two copper tubes are plated with silver layers, and a plurality of holes are opened on the surfaces.

[0015] As a further solution of the present invention: the thickness of the indium conductive layer is 0.2 mm.

[0016] As a further solution of the present invention: the inner surfaces of the four fan-shaped copper sheets are plated with silver, and the side surfaces of the four fan-shaped copper sheets are plated with chrome.

[0017] As a further solution of the present invention: a plurality of holes are opened on the surface of the stainless steel tube.

[0018] And a method for preparing a coaxial superconducting joint structure suitable for a CICC conductor, comprising:

[0019] S1, the stainless steel armor at the ends of the two CICC conductors is machined away to expose the superconducting cables inside;

[0020] S2, remove the central solenoid of the superconducting cable core and replace it with a stainless steel tube, and drill several holes on the surface of the stainless steel tube;

[0021] S3, removing the metal coating on the outer surface of the superconducting cable and re-electroplating the silver coating;

[0022] S4, silver-plating the inner and outer surfaces of the copper tube, and opening a plurality of holes on the surface of the copper tube;

[0023] S5, putting the silver-plated copper tube on the superconducting cable to ensure that the porosity of the superconducting cable is within the range of 18%-22%;

[0024] S6, after the adjacent subunits of the superconducting magnet are precisely assembled, the axes of the ends of the two CICC conductors are aligned and the ends are in close contact;

[0025] S7, spirally winding indium wires at a set interval on the outer surfaces of the copper tubes outside the two CICC superconducting cables until the outer surfaces of the two copper tubes are completely wound with indium wires;

[0026] S8, a silver layer is plated on the inner surface of the fan-shaped copper sheet, and a chrome layer is plated on the side surface of the fan-shaped copper sheet;

[0027] S9, four copper sheets are simultaneously installed on the outer surface of the copper tube wrapped with the indium wire, and a dedicated radial shrinking device is used to shrink the copper sheets toward the axis at different positions along the length direction at the same time, so that the indium wire is flattened and spread out into an indium conductive layer;

[0028] S10, install and weld the two-piece stainless steel shell on the outer periphery of the four sector-shaped copper sheets.

[0029] As a further solution of the present invention: in step S5, after the silver-plated copper tube is sleeved on the superconducting cable, it is squeezed and compressed by radial tube shrinking equipment so that the copper tube clamps the superconducting cable and the porosity of the superconducting cable is within the range of 18%-22%.

[0030] As a further solution of the present invention: the diameter of the indium wire is 1.2 mm, and the thickness of the indium conductive layer is 0.2 mm.

[0031] Beneficial effects of the present invention:

[0032] The present invention discloses a coaxial superconducting joint structure suitable for CICC conductors, which realizes the coaxial connection between two CICC conductors and occupies a small radial space, meeting the layout requirements of narrow spaces. The excellent DC resistance characteristics, fan-shaped copper sheet partition design and high-resistance coating effectively reduce internal AC losses, and have good thermal stability and cooling characteristics. It is a superconducting joint structure with excellent resistance characteristics and low AC losses. A joint resistance of less than 5nΩ can be obtained under typical working conditions of 70kA transmission current. The joint structure uses a split-flange fan-shaped copper sheet combined with an indium conductive layer to realize the coaxial connection of the ends of the two CICC conductors. Compared with the traditional staggered handshake superconducting joint, it has the significant advantages of small radial size, regular outline, and easy to wrap insulation structure, and is particularly suitable for CICC conductors of NbTi and Nb3Sn. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will be further described below in conjunction with the accompanying drawings.

[0034] Figure 1 It is an overall schematic diagram of a coaxial superconducting joint structure suitable for CICC conductors of the present invention;

[0035] Figure 2 It is a schematic cross-sectional view of a coaxial superconducting joint structure suitable for a CICC conductor according to the present invention;

[0036] Figure 3 It is an exploded schematic diagram of a coaxial superconducting joint structure suitable for CICC conductors of the present invention;

[0037] Figure 4 The present invention is a flow chart of a method for preparing a coaxial superconducting joint structure suitable for a CICC conductor.

[0038] In the figure: 1. Stainless steel tube; 2. Superconducting cable; 3. Copper tube; 4. Indium conductive layer; 5. Fan-shaped copper sheet; 6. Stainless steel shell; 7. Stainless steel armor. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] In the description of the present invention, it should be understood that terms such as "up", "down", "left", "right", "front" and "back" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, and a specific direction structure and operation. Therefore, they should not be understood as limitations on the present invention.

[0041] In addition, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", etc. 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 an indirect connection 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.

[0042] See also Figure 1-3As shown, the present invention provides a coaxial superconducting joint structure suitable for CICC conductors, including two stainless steel tubes 1, two copper tubes 3, an indium conductive layer 4, four fan-shaped copper sheets 5 and two stainless steel shells 6. The two stainless steel tubes 1 are respectively arranged at the end cores of the two CICC conductors to be connected, and a plurality of holes are opened on the surface of the stainless steel tubes 1. When connected, the axes of the ends of the two stainless steel tubes 1 are aligned and the ends are tightly attached. The two copper tubes 3 are sleeved on the outer periphery of the superconducting cable 2 at the end of the two CICC conductors, and the inner and outer surfaces of the two copper tubes 3 are silver-plated, and a plurality of holes are opened on the surface. When connected, the axes of the ends of the two copper tubes 3 are aligned and the ends are tightly attached. The superconducting cable 2 is exposed by removing the stainless steel armor 7 at the end of the CICC conductor by machining, and the outer periphery of the superconducting cable 2 at the end of the two CICC conductors is electroplated with a silver coating, and the porosity of the superconducting cable 2 is in the range of 18%-22%. The indium conductive layer 4 is wrapped around the outer periphery of the two copper tubes 3, and the thickness of the indium conductive layer 4 is 0.2 mm. The fan-shaped copper sheets 5 are wrapped around the outer periphery of the indium conductive layer 4, the inner surfaces of the four fan-shaped copper sheets 5 are plated with a silver layer, and the sides of the four fan-shaped copper sheets 5 are plated with a chrome layer. The two halves of the stainless steel shell 6 are wrapped around the outer periphery of the four fan-shaped copper sheets 5, and the two ends of the two halves of the stainless steel shell 6 are respectively connected to the stainless steel armor 7 at the ends of the two CICC conductors.

[0043] The advantages of the present invention are that it realizes the coaxial connection between two CICC conductors, occupies a small radial space, meets the layout requirements of narrow space, has excellent DC resistance characteristics, the fan-shaped copper sheet 5 partition design and the high resistance coating effectively reduce the internal AC loss, good thermal stability and cooling characteristics, and is a superconducting joint structure with excellent resistance characteristics and low AC loss. A joint resistance of less than 5nΩ can be obtained under the typical working condition of 70kA transmission current. The joint structure uses a split fan-shaped copper sheet 5 combined with an indium conductive layer 4 to realize the coaxial connection of the ends of the two CICC conductors. Compared with the traditional staggered handshake superconducting joint, it has the significant advantages of small radial size, regular outline, and easy to wrap around the insulating structure, and is particularly suitable for CICC conductors of NbTi and Nb3Sn.

[0044] See also Figure 4 As shown, the preparation process of the superconducting joint structure is described in detail below:

[0045] The stainless steel armor 7 at the ends of the two CICC conductors is machined away to expose the internal superconducting cable 2, and the high-resistance metal plating on the cylindrical outer surface of the superconducting cable 2 is removed and a new low-resistance, anti-oxidation silver plating is electroplated; the solenoids at the cores of the two CICC conductors are removed and replaced with a 316L stainless steel tube 1 with a suitable diameter and wall thickness, a plurality of holes are drilled on the surface of the stainless steel tube 1, and the stainless steel tube 1 is used to replace the central solenoid at the core of the superconducting cable 2 as a support for the core of the subsequent radially contracted superconducting cable 2.

[0046] A thin-walled copper tube 3 of suitable diameter and wall thickness is selected, and its inner and outer surfaces are silver-plated. A plurality of holes are opened on the surface of the copper tube 3. A plurality of holes are opened on the surface of the stainless steel tube 1 and the thin-walled copper tube 3 as the liquid helium flow channel cooling contact resistance generation area. The thin-walled copper tube 3 is sleeved on the outer surface of the superconducting cable 2 of the two CICC conductors, and a radial tube shrinking machine is used to squeeze the thin copper tube 3 inward to reduce the diameter of the thin-walled copper tube 3 and tighten the superconducting cable 2 at the core of the CICC conductor, so that the porosity of the superconducting cable 2 becomes 18%-22%. The thickness of the thin-walled copper tube 3 is strictly selected through calculation and testing: on the one hand, it is ensured that the superconducting cable 2 at the core can be firmly, stably and tightly tightened to ensure good electrical conductivity; on the other hand, the surface of the copper tube 3 after radial tube shrinking should be smooth, flat and wrinkle-free; in addition, a smaller wall thickness is conducive to reducing the circular induced current and Joule heat power.

[0047] After the subunits of the superconducting magnet are precisely assembled and positioned, the ends of the two CICC conductors should be in a state where the end faces are facing each other and the axes are aligned; then, an indium wire with a diameter of 1.2 mm is used to spirally wind from the thin-walled copper tube 3 of one CICC superconducting cable 2 to the end of the thin-walled copper tube 3 of another CICC conductor according to the calculated design spiral pitch, until the outer surfaces of the two copper tubes 3 are completely wound with indium wire. The diameter selection and winding pitch / interval of the indium wire are strictly selected through calculation and experiment. The flattened indium wire must fill the gap between the two contacting copper tubes 3 to ensure that the two are fully and tightly fitted, and an indium conductive layer 4 is formed on the outer periphery of the two thin-walled copper tubes 3. The thickness of the indium conductive layer 4 is 0.2 mm.

[0048] A thick-walled copper tube is selected and divided into four identical fan-shaped copper sheets 5 along the axial direction, and the cut surface is chrome-plated and the inner surface is plated; the four fan-shaped copper sheets 5 are installed on the outside of the thin-walled copper tube 3 wound with indium wire, and multiple shrinking devices are used simultaneously to ensure that the four fan-shaped copper sheets 5 are synchronously and evenly squeezed toward the axis and closed; the indium wire wound with a fixed pitch will be flattened and extended and spread along the radial direction, and the pitch gap between two adjacent turns of indium wire will be just filled with indium wire after reaching the designed extrusion value. The chrome plating of the cut surface is used to increase the lateral resistance between the four copper sheets, greatly reduce the circular induced current, reduce the heating power of the induced current, reduce the consumption of liquid helium, and improve the stability margin of the superconducting joint; the four-petal fan-shaped copper sheet 5 has a larger wall thickness than the thin-walled copper tube 3, ensuring that the superconducting joint has excellent thermal stability under thermal disturbance.

[0049] Finally, two halves of the stainless steel shell 6 are assembled and welded to the outside of the coaxial connector and connected to the stainless steel armors 7 of the two CICC conductors.

[0050] When in use, the transmission current passes through the input end CICC superconducting cable 2, through the thin-walled copper tube 3 (input end) → indium conductive layer 4 (input end) → four-petal fan-shaped copper sheet 5 → indium conductive layer 4 (output end) and thin-walled copper tube 3 (output end) to reach the output end CICC superconducting cable 2. The use of low RRR (4.2K residual resistivity) copper material is one of the keys to ensure the DC resistance performance of the superconducting joint; the layout and extrusion flattening of the indium wire, and the silver plating of the current transmission interface (the inner surface of the four-petal fan-shaped copper sheet 5, the inner and outer surfaces of the thin-walled copper tube 3, and the outer surface of the superconducting cable 2) are all key steps to reduce the contact resistance.

[0051] The above is a detailed description of the preferred embodiments of the present invention, which cannot be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A coaxial superconducting joint structure suitable for CICC conductors, characterized in that: include: Two stainless steel tubes, the two stainless steel tubes are respectively arranged at the end cores of the two CICC conductors, and the axes of the two stainless steel tubes are aligned and the ends are tightly attached; Two copper tubes, the two copper tubes are sleeved on the outer circumference of the superconducting cables at the ends of the two CICC conductors, and the axes of the ends of the two copper tubes are aligned and the ends are tightly attached; An indium conductive layer, the indium conductive layer is wound around the outer circumferences of the two copper tubes; Four fan-shaped copper sheets, the four fan-shaped copper sheets are wrapped together around the outer periphery of the indium conductive layer; Two halves of the stainless steel shell are wrapped around the outer periphery of the four fan-shaped copper sheets, and two ends of the two halves of the stainless steel shell are respectively connected to the stainless steel armors at the ends of the two CICC conductors.

2. A coaxial superconducting joint structure suitable for CICC conductors according to claim 1, characterized in that: The outer periphery of the superconducting cable at the ends of the two CICC conductors is electroplated with a silver coating, and the porosity of the superconducting cable is in the range of 18%-22%.

3. A coaxial superconducting joint structure suitable for CICC conductors according to claim 1, characterized in that: The inner and outer surfaces of the two copper tubes are plated with silver layers, and a plurality of holes are opened on the surfaces.

4. A coaxial superconducting joint structure suitable for CICC conductors according to claim 1, characterized in that: The thickness of the indium conductive layer is 0.2 mm.

5. A coaxial superconducting joint structure suitable for CICC conductors according to claim 1, characterized in that: The inner surfaces of the four fan-shaped copper sheets are plated with a silver layer, and the side surfaces of the four fan-shaped copper sheets are plated with a chrome layer.

6. A coaxial superconducting joint structure suitable for CICC conductors according to claim 1, characterized in that: A plurality of holes are opened on the surface of the stainless steel tube.

7. The method for preparing a coaxial superconducting joint structure suitable for a CICC conductor according to claim 1, characterized in that: include: S1, the stainless steel armor at the ends of the two CICC conductors is machined away to expose the superconducting cables inside; S2, remove the central solenoid of the superconducting cable core and replace it with a stainless steel tube, and drill several holes on the surface of the stainless steel tube; S3, removing the metal coating on the outer surface of the superconducting cable and re-electroplating the silver coating; S4, silver-plating the inner and outer surfaces of the copper tube, and opening a plurality of holes on the surface of the copper tube; S5, putting the silver-plated copper tube on the superconducting cable to ensure that the porosity of the superconducting cable is within the range of 18%-22%; S6, after the adjacent subunits of the superconducting magnet are precisely assembled, the axes of the ends of the two CICC conductors are aligned and the ends are in close contact; S7, spirally winding indium wires at a set interval on the outer surfaces of the copper tubes outside the two CICC superconducting cables until the outer surfaces of the two copper tubes are completely wound with indium wires; S8, a silver layer is plated on the inner surface of the fan-shaped copper sheet, and a chrome layer is plated on the side surface of the fan-shaped copper sheet; S9, four copper sheets are simultaneously installed on the outer surface of the copper tube wrapped with the indium wire, and a dedicated radial shrinking device is used to shrink the copper sheets toward the axis at different positions along the length direction at the same time, so that the indium wire is flattened and spread out into an indium conductive layer; S10, install and weld the two-piece stainless steel shell on the outer periphery of the four sector-shaped copper sheets.

8. The method for preparing a coaxial superconducting joint structure suitable for a CICC conductor according to claim 7, characterized in that: In step S5, after the silver-plated copper tube is sleeved on the superconducting cable, it is squeezed and compressed by radial tube shrinking equipment, so that the copper tube clamps the superconducting cable tightly and the porosity of the superconducting cable is within the range of 18%-22%.

9. The method for preparing a coaxial superconducting joint structure suitable for a CICC conductor according to claim 7, characterized in that: The diameter of the indium wire is 1.2 mm, and the thickness of the indium conductive layer is 0.2 mm.

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