Joint structure of multi-band stacked superconductor

Abstract

The utility model provides a joint structure of a multi-strip stacked superconductor, which comprises two end parts of REBCO multi-strip conductors welded together, each of the two REBCO multi-strip conductors comprises N stacked superconductive strips with the same structure, N is an integer and is greater than or equal to 2, and the directions of the two REBCO multi-strip conductors from the front side to the back side are opposite; the lengths of the stacked superconducting strips at the end parts of the two REBCO multi-strip conductors are sequentially reduced one by one according to the opposite orientations; the i superconducting strip at the end part of one REBCO multi-strip conductor is in butt welding with the (N-i) superconducting strip at the end part of the other REBCO multi-strip conductor; and the front surface of the ith superconducting strip at the end part of one REBCO multi-strip conductor is in contact welding with the front surface of the (N-i + 1) th superconducting strip at the end part of the other REBCO multi-strip conductor. The joint resistance of the joint structure under 77K is less than 10 nanoohms.

Description

Technical Field

[0001] The utility model belongs to the technical field of high-temperature superconducting conductors, and particularly relates to a joint structure of multi-band stacked superconducting conductors. Background Art

[0002] The working current density of superconducting magnets can be increased by dozens of times or even higher than that of traditional electromagnets and permanent magnets. Therefore, superconducting magnets can obtain extremely high magnetic field strength and more stable and controllable magnetic field configuration distribution with a more compact volume and lower energy consumption. Existing superconducting magnets are mainly wound with low-temperature superconducting materials such as NbTi alloys and Nb3Sn compounds and high-temperature superconducting materials such as Bi-2223 and ReBCO. Among them, high-temperature superconducting materials themselves have mechanical brittleness and are very easy to be damaged. At present, they are mostly prepared into superconducting thin strips by powder sleeve method or thin film deposition technology. For example, ReBCO high-temperature superconducting tape is mainly grown by depositing a superconducting layer on a base tape, and Bi-2223 high-temperature superconducting tape is mainly prepared by superconducting powder sleeve method. Due to the limitations of process technology, the single length of high-temperature superconducting tape can only be several hundred meters long at present. Taking into account the single-length limit, cross-sectional shape, brittleness and other factors of the high-temperature superconducting tape, most of the current methods are to first wind a single high-temperature superconducting tape into a double-pancake coil, and then stack the double-pancake coils on each other and prepare joints to connect them to meet the design requirements.

[0003] The quality stability and reliability of the joints of high-temperature superconducting tapes directly affect the performance of high-temperature superconducting coils. The most basic performance requirement for high-temperature superconducting tape joints is that the joints must have a low resistance value while meeting the operating current value of the magnet. The working current of a superconducting magnet generally reaches hundreds of amperes. Too much resistance will cause serious Joule heat loss and may cause the magnet to quench. For superconducting magnets operating in a closed loop, the joint resistance causes the attenuation of the magnetic field. Similarly, superconducting joints need to be installed at the edge of the magnet, and the joints will be affected by strong electromagnetic forces. Since the joints may be subjected to bending stress during the magnet winding process, electromagnetic stress under working conditions, and contraction stress during cooling, the superconducting joints must also have certain mechanical strength and toughness.

[0004] The joint resistance of existing superconducting magnets is usually 100 nanoohms, which can easily cause heating of the superconducting magnet during operation and is not conducive to improving the stability of the superconducting magnet. In addition, a high-temperature superconducting magnet can be composed of multiple high-temperature superconducting double-pancake windings connected in series. However, due to the mechanical brittleness of the high-temperature superconducting tape itself, the current high-temperature superconducting tape joint technology mainly uses soldering to directly connect. The disadvantage of the joint made in this way is that since the high-temperature superconducting tape joint will become hard after welding, the bending radius will increase significantly, and it is very difficult to bend the joint again, and it is very easy to be damaged.

[0005] In summary, there is currently no ideal high-temperature superconducting tape joint suitable for high-temperature superconducting double-pancake coils. Utility Model Content

[0006] In view of the above problems, the utility model provides a joint structure of multi-strip stacked superconducting conductors.

[0007] The joint structure of a multi-strip stacked superconducting conductor provided by the utility model comprises: ends of two REBCO multi-strip conductors welded together,

[0008] The two REBCO multi-strip conductors each contain N stacked superconducting tapes of the same structure, N is an integer and N≥2, and the two REBCO multi-strip conductors are oriented in opposite directions from the front side to the back side;

[0009] The stacked superconducting tapes at the ends of the two REBCO multi-strip conductors decrease in length one by one in the opposite directions, and the length of the i-th superconducting tape from the back side of the two REBCO multi-strip conductors decreases by (i-1)×L centimeters, where L is a real number and 12≥L≥8;

[0010] The i-th superconducting tape at the end of one REBCO multi-strip conductor is butt-welded to the Ni-th superconducting tape at the end of another REBCO multi-strip conductor;

[0011] The front side of the i-th superconducting tape at the end of one REBCO multi-strip conductor is contact-welded with the front side of the (N-i+1)-th superconducting tape at the end of another REBCO multi-strip conductor.

[0012] further,

[0013] The front side refers to a surface of the superconducting tape, and a distance between the surface and a superconducting film in the superconducting tape is less than half of the thickness of the superconducting tape.

[0014] further,

[0015] The L is 10.

[0016] further,

[0017] The welding is performed by soldering tin.

[0018] further,

[0019] The two multi-strip conductors are respectively a multi-strip conductor of a first double-pancake winding and a multi-strip conductor of a second double-pancake winding.

[0020] The resistance of the joint structure of the multi-band stacked superconducting conductor provided by the utility model is much lower than the resistance of the existing joint, which improves the stability of the superconducting magnet. In addition, the joint structure avoids the problem that the existing joint is difficult to bend and is prone to damage.

[0021] Other features and advantages of the utility model will be described in the following description, and partly become apparent from the description, or understood by implementing the utility model. The purpose and other advantages of the utility model can be realized and obtained by the structures indicated in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 A schematic cross-sectional view of a superconducting tape in a joint structure of a multi-tape stacked superconducting conductor according to an embodiment of the present invention is shown;

[0024] Figure 2 A schematic cross-sectional view of a high-temperature superconducting tape double-tape stacked superconducting conductor in a joint structure of a multi-tape stacked superconducting conductor according to an embodiment of the present invention is shown;

[0025] Figure 3 A schematic diagram of a cross section of a high-temperature superconducting stacked conductor with a stepped structure prepared in a method for preparing a joint structure of a multi-tape stacked superconducting conductor according to an embodiment of the present invention is shown. Figure 1 ;

[0026] Figure 4 A schematic diagram of a cross section of a high-temperature superconducting stacked conductor with a stepped structure prepared in a method for preparing a joint structure of a multi-tape stacked superconducting conductor according to an embodiment of the present invention is shown. Figure 2 ;

[0027] Figure 5 A schematic diagram of a high-temperature superconducting stacked conductor joint structure prepared by a method for preparing a joint structure of a multi-tape stacked superconducting conductor according to an embodiment of the utility model is shown;

[0028] Figure 6 The simplified process and structural schematic diagram of the joint of high-temperature superconducting stacked conductors according to the method for preparing the joint structure of multi-tape stacked superconducting conductors according to the embodiment of the utility model are shown;

[0029] Figure 7The voltage-current test curve of a high-temperature superconducting stacked conductor joint prepared by the method for preparing a joint structure of a multi-tape stacked superconducting conductor according to an embodiment of the utility model is shown. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the embodiment of the utility model clearer, the technical solution in the embodiment of the utility model will be clearly and completely described below in conjunction with the drawings in the embodiment of the utility model. Obviously, the described embodiment is a part of the embodiment of the utility model, not all of the embodiments. Based on the embodiment of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used in the specification of the application herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions. The terms "first", "second", "third", etc. in the specification and claims of this application or the above-mentioned figures are used to distinguish different objects, not to describe a specific order or a primary and secondary relationship. "Multiple" appearing in this application refers to more than two (including two).

[0032] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0033] Figure 1 It is a cross-sectional schematic diagram of a superconducting tape such as a ReBCO high-temperature superconducting tape in a joint structure of a multi-tape stacked superconducting conductor (abbreviated as a multi-tape conductor) provided by the utility model, wherein "multi" means that the number is more than 1. In the utility model, the front side of a superconducting tape used for winding a high-temperature superconducting magnet refers to a surface of the superconducting tape, which is closer to the superconducting film in the superconducting tape, that is, the distance between the surface and the superconducting film in the superconducting tape is less than half the thickness of the superconducting tape; the other surface of the superconducting tape is the back side, which is also the surface of the superconducting tape that is farther away from the superconducting film, such as Figure 1As shown, from the front side to the back side of the superconducting tape are a first metal layer such as a copper layer, a superconducting film such as a ReBCO film, an alloy substrate such as a nickel-based alloy substrate, and a second metal layer such as a copper layer. At this time, the superconducting tape is recorded as a ReBCO high-temperature superconducting tape or a ReBCO superconducting tape, wherein the upper surface of the superconducting tape is the front side, the distance between the superconducting film and the upper surface of the superconducting tape is less than half the thickness of the superconducting tape, and the lower surface of the superconducting tape is the front side.

[0034] Figure 2 A schematic cross-sectional view of a high-temperature superconducting tape double-tape stacked superconducting conductor in a joint structure of a multi-tape stacked superconducting conductor provided by the utility model. A plurality of ReBCO high-temperature superconducting tapes are stacked in a consistent front direction and soldered with a solder such as tin to prepare a multi-tape stacked superconducting conductor (abbreviated as REBCO multi-tape conductor, if the specific number of the plurality of tapes is N, N is an integer and N≥2, it can also be recorded as REBCON tape conductor), such as Figure 2 As shown, the front and back sides of the multi-tape stacked superconducting conductor are consistent with the superconducting tape.

[0035] The joint area of ​​the joint structure of the multi-tape stacked superconducting conductor provided by the utility model can be located outside the winding, and a section of stainless steel belt is pasted and fixed in the joint welding area on the surface of the winding, and a polyimide film is pasted on the surface of the stainless steel belt to insulate its surface.

[0036] The method for manufacturing a joint structure of a multi-tape stacked superconducting conductor provided by the utility model may include the following steps:

[0037] 1. Set the temperature of the hot air gun to 120-180°C, preferably 150°C, heat the REBCO multi-strip conductor of the first double-pancake winding and the REBCO multi-strip conductor of the second double-pancake winding to be welded for 1.5-5 minutes, preferably 3 minutes, respectively, and then carefully separate the adjacent superconducting tapes of the two REBCO multi-strip conductors at the joint, and assume that the two REBCO multi-strip conductors each contain N superconducting tapes.

[0038] Second, the two REBCO multi-strip conductors are oriented in opposite directions from the front to the back, and the two separated REBCO multi-strip conductors are cut off at the joint of the i-th superconducting tape from the back by a length of (i-1)×L cm (centimeter), where L is a real number and 12≥L≥8, preferably 10. Figure 3 and 4 The diagrams are schematic cross-sectional views of two REBCO double-strip conductors after being cut. It should be noted that the length of the portion of the ith superconducting tape separated in step 1 is not shorter than the portion cut off in this step.

[0039] 3. Use an electric soldering iron heated to 220-300°C, preferably 260°C, to evenly apply solder Sn to the welding area at the joint of the two REBCO multi-strip conductors. 63 Pb 37 . The two REBCO multi-strip conductors coated with solder are fixed at the joint position between the cakes with polyimide tape. The welding area is the contact area of ​​the two REBCO multi-strip conductors when the two cut REBCO multi-strip conductors are parallel to each other and when the i-th superconducting tape of one REBCO multi-strip conductor is butted against the Ni-th superconducting tape of another REBCO multi-strip conductor. The role of the tape fixation is to ensure that the manufactured joint is close to the surface of the winding, there is no gap between the joint and the surface of the winding, and no movement occurs. After the following welding, the joint has the same bending curvature as the surface of the winding, and no bending is required, which avoids the problem that it is difficult to bend the existing joint and it is very easy to be damaged.

[0040] Fourth, heat the temperature of the electric soldering iron to 240-320° C., preferably 280° C., and weld the two REBCO multi-strip conductors together in a tightly fitting manner at the welding area of ​​the joint. Figure 5 The figure shows a REBCO double-strip conductor high-temperature superconducting stacked conductor joint structure manufactured by the method for manufacturing a joint structure of a multi-strip stacked superconducting conductor provided by the utility model. Figure 6 The figure shows a simplified process and a schematic diagram of the structure of a REBCO three-strip conductor high-temperature superconducting stacked conductor joint made by the method for preparing the joint structure of a multi-strip stacked superconducting conductor provided by the utility model, wherein the REBCO three-strip conductor high-temperature superconducting stacked conductor joint structure made by the method for preparing the joint structure of a multi-strip stacked superconducting conductor provided by the utility model is shown. When welding, the electric soldering iron head is flat against the joint welding area and dragged back and forth to heat and melt the middle solder and pressurize to make the excess solder overflow until the solder between the superconducting tape layers is melted and the superconducting tape is not delaminated. Finally, the welded REBCO multi-strip conductor is wiped with alcohol to make its surface smooth and free of tin spots.

[0041] The joint structure of the multi-strip stacked superconducting conductor prepared by the above method comprises: ends of two REBCO multi-strip conductors welded together by soldering,

[0042] The two REBCO multi-strip conductors each contain N stacked superconducting tapes of the same structure, N is an integer and N≥2, and the two REBCO multi-strip conductors are oriented in opposite directions from the front side to the back side;

[0043] The stacked superconducting tapes at the ends of the two REBCO multi-strip conductors decrease in length one by one in the opposite directions, and the length of the i-th superconducting tape from the back side of the two REBCO multi-strip conductors decreases by (i-1)×L centimeters, where L is a real number and 12≥L≥8, preferably 10;

[0044] The i-th superconducting tape at the end of one REBCO multi-strip conductor is butt-welded to the Ni-th superconducting tape at the end of another REBCO multi-strip conductor;

[0045] The front side of the i-th superconducting tape at the end of one REBCO multi-strip conductor is contact-welded with the front side of the (N-i+1)-th superconducting tape at the end of another REBCO multi-strip conductor.

[0046] in,

[0047] The front side refers to a surface of the superconducting tape, the distance between the front side and the superconducting film in the superconducting tape is less than half of the thickness of the superconducting tape.

[0048] The two multi-strip conductors are respectively multi-strip conductors of a first double-pancake winding and a second double-pancake winding.

[0049] The joint of the utility model is actually to stagger a superconducting tape for docking, because: the resistance of superconducting tapes overlapped front to front is very small, while the resistance of overlapped in other overlap directions (i.e., front to back, or back to back) is very large. The structure of welding each layer at a position staggered by about 10 cm adopted by the utility model ensures that each layer of superconducting tape in the first multi-tape stacked superconducting conductor forms a lap joint of about 10 cm in length with the corresponding superconducting tape in the second conductor, so that the superconducting current in each layer of superconducting tape of the first conductor can flow into the second conductor through this low-resistance front-to-front overlap area. In the above step 2, the two REBCO multi-tape conductors are oriented in opposite directions from front to back, ensuring that the two REBCO multi-tape conductors form a joint in a front-to-front overlap manner.

[0050] The joint resistance of the superconducting magnet pancake joints welded by the joint structure of the multi-strip stacked superconducting conductor provided by the utility model is less than 10 nanoohms when tested at 77K. Figure 7 The figure shows a voltage-current test curve of a high-temperature superconducting stacked conductor joint made using the joint structure of the multi-strip stacked superconducting conductor of the present invention. Specifically, the curve is a voltage (volt)-current (ampere) test curve of a joint sample of two double-strip stacked conductors (N=2, L=10). Figure 7It can be seen that within the range of 0-550A, the voltage and current are linearly related, and according to the slope of the curve, the joint resistance is 4.4 nanoohms (nΩ).

[0051] In summary, the resistance of the joint structure of the multi-band stacked superconducting conductor provided by the utility model is much lower than the resistance of the existing joints, which improves the stability of the superconducting magnet. In addition, the joint structure avoids the problem that the existing joints are difficult to bend and are prone to damage.

[0052] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A joint structure of a multi-tape stacked superconducting conductor, characterized in that: include: The ends of two REBCO multi-strip conductors welded together, The two REBCO multi-strip conductors each contain N stacked superconducting tapes with the same structure, N is an integer and N≥2, and the two REBCO multi-strip conductors are oriented in opposite directions from the front side to the back side; The stacked superconducting tapes at the ends of the two REBCO multi-strip conductors decrease in length one by one in the opposite directions, and the length of the i-th superconducting tape from the back side of the two REBCO multi-strip conductors decreases by (i-1)×L centimeters, where L is a real number and 12≥L≥8; The i-th superconducting tape at the end of one REBCO multi-strip conductor is butt-welded to the Ni-th superconducting tape at the end of another REBCO multi-strip conductor; The front side of the i-th superconducting tape at the end of one REBCO multi-strip conductor is contact-welded with the front side of the (N-i+1)-th superconducting tape at the end of another REBCO multi-strip conductor.

2. The joint structure of a multi-tape stacked superconducting conductor according to claim 1, characterized in that: The front side refers to a surface of the superconducting tape, and a distance between the surface and a superconducting film in the superconducting tape is less than half of the thickness of the superconducting tape.

3. The joint structure of a multi-tape stacked superconducting conductor according to claim 1 or 2, characterized in that: The L is 10.

4. The joint structure of a multi-tape stacked superconducting conductor according to claim 1 or 2, characterized in that: The welding is performed by soldering tin.

5. The joint structure of a multi-tape stacked superconducting conductor according to claim 1 or 2, characterized in that: The two multi-strip conductors are respectively a multi-strip conductor of a first double-pancake winding and a multi-strip conductor of a second double-pancake winding.

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