Preparation method of second-generation high-temperature superconducting tape closed coil and closed magnet

Abstract

The application discloses a preparation method of a second-generation high-temperature superconducting tape closed coil and a closed magnet, and belongs to the technical field of high-temperature superconducting applications. The preparation method comprises the following steps: winding the superconducting tape into a superconducting coil, and reserving two ends of the superconducting tape as two to-be-connected joints; removing a protective layer of the joint to expose a superconducting layer; coating a precursor liquid on the superconducting layer; performing heat treatment on the superconducting coil at a first set temperature, so that the coated precursor liquid becomes a gel; preparing a channel between concave-convex phases on the gel; overlapping the two to-be-connected joints through the channel, and performing heat treatment on the superconducting coil at a second set temperature, so that the gel becomes a tetragonal phase crystal; performing annealing treatment on the superconducting coil in an oxygen atmosphere, so that the tetragonal phase crystal becomes an orthorhombic phase crystal; and bridging the two to-be-connected joints with the orthorhombic phase crystal to obtain the closed coil. The closed magnet obtained based on the preparation method can realize closed-loop operation without attenuation.

Description

Technical Field

[0001] This invention relates to the field of high-temperature superconducting application technology, and in particular to a method for preparing a second-generation high-temperature superconducting tape closed coil and a closed magnet. Background Technology

[0002] Magnetic Resonance Imaging (MRI) is a technique that utilizes the principle of nuclear magnetic resonance. Based on the varying attenuation of emitted energy in different structural environments within a substance, and by detecting the emitted electromagnetic waves through an applied gradient magnetic field, the location and type of atomic nuclei that make up the object can be determined, allowing for the creation of an image of the object's internal structure. It does not require electron beams or X-rays, nor does it require contrast agents, and no harmful effects of strong magnetic fields on the human body have been found, thus it is considered a safe and efficient biomedical diagnostic technique. The clarity of an MRI is significantly related to the strength, homogeneity, and stability of the magnetic field; higher magnetic field strength, better homogeneity, and better stability result in higher MRI clarity.

[0003] Currently, the vast majority of MRI devices worldwide use NbTi superconducting alloys. NbTi is a low-temperature superconductor (LTS) material, discovered by J.K. Hulm et al. at Westinghouse National Laboratory. Its superconducting critical temperature (Tc) is 9.7 K, and its upper critical magnetic field at 4.2 K is approximately 11 T. NbTi wires are typically prepared using a high-temperature melting method, then drawn multiple times into multi-core wires (hundreds to tens of thousands of cores), and finally heat-treated to become an (α+β) dual-phase alloy. NbTi superconducting alloys possess excellent superconductivity, good plasticity and strength under medium to low magnetic fields, and their processing technology is relatively simple, making them the most widely used superconducting material. However, NbTi can only be used in liquid helium environments, making it very expensive, and its upper critical field also limits the magnetic field strength of the magnets developed.

[0004] REBa2Cu3O 7-x Second-generation high-temperature superconducting materials, represented by REBCO (Resilient Biotic Carbon), have enormous application potential in superconducting magnets and other fields due to their advantages of low anisotropy, high irreversible field, and strong current-carrying capacity. However, the biggest problem currently limiting the application of second-generation high-temperature superconducting tapes in nuclear magnetic resonance imaging is their inability to operate in a closed loop. This is because the REBCO superconducting layer in second-generation high-temperature superconducting tapes is a ceramic oxide, which is very brittle, and REBCO superconducting materials have weak connections; they cannot conduct electricity when the angle between grains is greater than 7 degrees. These two factors make it very difficult to connect the face-to-face REBCO superconducting layers. Therefore, no patents have been reported for closed magnets based on REBCO superconducting tapes. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a second-generation high-temperature superconducting tape closed coil and a closed magnet, so as to achieve attenuation-free closed-loop operation of the closed magnet.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] A method for fabricating a second-generation high-temperature superconducting tape closed coil includes:

[0008] The second-generation high-temperature superconducting tape is wound into a superconducting coil, and the two ends of the superconducting coil are reserved as two connectors to be connected.

[0009] Remove the protective layer of the connector to be connected, exposing the superconducting layer of the connector;

[0010] A precursor solution is coated onto the superconducting layer of the connector to be connected; the precursor solution is a solution containing components of the superconducting layer.

[0011] The superconducting coil is heat-treated at a first set temperature to turn the precursor liquid coated on the connector to be connected into a gel.

[0012] Alternating grooves are formed on the gel;

[0013] The two connectors to be connected are overlapped through the channel, and the superconducting coil is heat-treated at a second set temperature to transform the gel on the connectors to be connected into a tetragonal phase crystal; the second set temperature is greater than the first set temperature.

[0014] The superconducting coil is annealed in an oxygen atmosphere to transform the tetragonal crystal into an orthorhombic crystal.

[0015] Two connectors with the orthogonal phase crystals are bridged to obtain a closed coil.

[0016] Optionally, the second-generation high-temperature superconducting tape comprises, from bottom to top: a metal substrate layer, a buffer layer, a superconducting layer, and a protective layer; the superconducting layer is composed of REBa2Cu3O. 7-x , where RE is a rare earth element, and x = 0 to 1.

[0017] Optionally, the protective layer of the connector to be connected can be removed by etching.

[0018] Optionally, a precursor liquid may be coated onto the superconducting layer of the connector to be connected by drop coating or dip coating.

[0019] Optionally, the precursor solution is a fluorine-free acetate solution containing rare earth elements, barium elements, and copper elements; the rare earth elements are yttrium or gadolinium.

[0020] Optionally, the first set temperature is 300-650°C, and the heating time for heat treatment of the superconducting coil at the first set temperature is 60-180 minutes.

[0021] Optionally, the second set temperature is 800-900°C, and the heat treatment time of the superconducting coil at the second set temperature is 60-300 min.

[0022] Optionally, the width of the channel is 5 to 10 μm.

[0023] Optionally, the oxygen atmosphere is oxygen with a purity of 99.9% and an oxygen pressure of 15-100 MPa.

[0024] A second-generation high-temperature superconducting tape closed magnet includes:

[0025] The Dewar, current leads, voltage leads, and closed coil prepared using the above-described method for preparing second-generation high-temperature superconducting tape closed coils;

[0026] The closed coil is located in the Dewar; both the current lead and the voltage lead are connected to the closed coil, and both the current lead and the voltage lead are led out from the Dewar.

[0027] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0028] This invention winds second-generation high-temperature superconducting tape into a superconducting coil. At the connection points of the superconducting coil, etching is used to expose the superconducting layer. The superconducting layers at the connection points are then connected through steps including coating with a precursor solution, low-temperature heat treatment, high-temperature heat treatment, and oxygen-filled annealing. Finally, bridging is performed to obtain a closed coil. During the heat treatment process, oxygen filling of the superconducting layer increases its oxygen content, transforming its molecular structure from a tetragonal phase to an orthorhombic phase, achieving superconductivity and thus realizing a superconducting connection at both ends of the coil, reducing magnetic field attenuation at the connection points. Bridging the two connection points strengthens the mechanical properties at the connection points, preventing breakage due to the brittleness of the superconducting layer. Therefore, the closed magnet obtained based on the preparation method provided by this invention can achieve attenuation-free closed-loop operation. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 A flowchart illustrating the fabrication method of the second-generation high-temperature superconducting tape closed coil provided by this invention;

[0031] Figure 2 This is a schematic diagram of the structure of the second-generation high-temperature superconducting tape provided by the present invention;

[0032] Figure 3 This is a schematic diagram of the winding of the superconducting coil provided by the present invention;

[0033] Figure 4 A bridging schematic diagram of the connector to be connected provided by the present invention;

[0034] Figure 5 This is a structural diagram of the second-generation high-temperature superconducting tape closed magnet provided by the present invention;

[0035] Figure 6 This is a schematic diagram of the operation of the YBCO closed magnet prepared according to an embodiment of the present invention;

[0036] Figure 7 The voltage-current (VI) curve of the superconducting connector of the closed coil prepared for an embodiment of the present invention was measured at 77K zero field using the four-lead method.

[0037] Figure 8 X-ray diffraction pattern of the YBCO strip joint;

[0038] Figure 9 The voltage-current (VI) curves of the welded joint of the closed coil prepared for comparison were obtained by measuring the four-lead method at 77K zero field.

[0039] Symbol explanation:

[0040] Superconducting connector—1, superconducting coil—2, current lead—3, voltage lead—4, cold head hole of refrigerator—5, room temperature hole—6, superconducting switch—7, Dewar—8, first connector to be connected—9, coil frame—10, second connector to be connected—11, metal base layer—12, buffer layer—13, superconducting layer—14, protective layer—15. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] The purpose of this invention is to provide a method for preparing a second-generation high-temperature superconducting tape closed coil and a closed magnet, so as to achieve attenuation-free closed-loop operation of the closed magnet.

[0043] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0044] This invention provides a method for preparing a second-generation high-temperature superconducting tape closed coil. Figure 1 A flowchart illustrating the fabrication method of a second-generation high-temperature superconducting tape closed coil provided in an embodiment of the present invention. Figure 1 As shown, the preparation method includes:

[0045] Step S1: Wind the second-generation high-temperature superconducting tape into a superconducting coil, and leave the two ends of the superconducting coil as two connectors to be connected.

[0046] Specifically, see the structural schematic diagram of the second-generation high-temperature superconducting tape. Figure 2 It comprises, from bottom to top: a metal substrate layer 12, a buffer layer 13, a superconducting layer 14, and a protective layer 15; the superconducting layer 14 is composed of REBa2Cu3O. 7-x In this context, RE represents rare earth elements, Ba represents barium, Cu represents copper, O represents oxygen, and x = 0 to 1.

[0047] Figure 3 This is a schematic diagram of the winding of the superconducting coil provided by the present invention. Figure 3 As shown, with the protective layer 15 inside and the metal base layer 12 outside, the second-generation high-temperature superconducting tape is wound on the coil frame 10 to form a superconducting coil 2. At the same time, in order to achieve closed-loop operation of the superconducting coil 2, a length of not less than 5 cm is reserved at both ends as two connectors to be connected, namely the first connector 9 and the second connector 11, for subsequent connection.

[0048] Step S2: Remove the protective layer of the connector to be connected, exposing the superconducting layer of the connector. Specifically, the protective layer of the connector to be connected is removed by etching.

[0049] Step S3: Coat the superconducting layer of the connector to be connected with a precursor solution; the precursor solution is a solution containing the components of the superconducting layer.

[0050] Specifically, a precursor solution is coated onto the superconducting layer of the connector to be connected using a drop-coating or dip-coating method. The precursor solution is a fluorine-free acetate solution containing rare earth elements, barium, and copper; the rare earth (RE) elements are yttrium (Y) or gadolinium (Gd). That is, the precursor solution is used to prepare YBa₂Cu₃O₃. 7-x (or GdBa2Cu3O) 7-x A fluorine-free acetate solution containing Y (or Gd), Ba and Cu.

[0051] Step S4: Heat-treat the superconducting coil at a first set temperature to turn the precursor liquid coated on the connector to be connected into a gel.

[0052] Specifically, the first set temperature is 300-650°C, and the heating time for heat treatment of the superconducting coil at the first set temperature is 60-180 minutes.

[0053] Step S5: Prepare grooves with alternating concave and convex surfaces on the gel.

[0054] Preferably, the width of the channel is 5 to 10 μm.

[0055] Step S6: The two connectors to be connected are overlapped through the channel, and the superconducting coil is heat-treated at a second set temperature to transform the gel on the connectors to be connected into a tetragonal phase crystal. The second set temperature is higher than the first set temperature.

[0056] Specifically, the second set temperature is 800-900°C, and the heat treatment time of the superconducting coil at the second set temperature is 60-300 minutes.

[0057] Step S7: Anneal the superconducting coil in an oxygen atmosphere to transform the tetragonal phase crystal into an orthorhombic phase crystal; the orthorhombic phase crystal has superconductivity.

[0058] Specifically, the oxygen atmosphere is oxygen with a purity of 99.9% and an oxygen pressure of 15-100 MPa.

[0059] Step S8: Bridge the two connectors containing the orthogonal phase crystals to obtain a closed coil. Preferably, the bridging material is a strip with the same composition as the superconducting layer, thus improving the strength at the connector and providing quench protection.

[0060] Figure 4This is a bridging diagram of the connector to be connected according to the present invention. Figure 4 As shown, both the first connector 9 and the second connector 11 have alternating grooves (i.e. channels) with a length of about 5 cm. The channels on the first connector 9 and the second connector 11 match, so that the first connector 9 and the second connector 11 can fit together tightly and serve as a superconducting connector.

[0061] This invention also provides a second-generation high-temperature superconducting tape closed magnet. Figure 5 This is a structural diagram of the second-generation high-temperature superconducting tape closed magnet provided by the present invention. Figure 5 As shown, the closed magnet includes: a Dewar 8, a current lead 3, a voltage lead 4, and a closed coil (i.e., a superconducting coil 2 with a superconducting connector 1) prepared using the above-described method for preparing a second-generation high-temperature superconducting tape closed coil. The closed coil is located in the Dewar 8; both the current lead 3 and the voltage lead 4 are connected to the closed coil, and both the current lead 3 and the voltage lead 4 are led out from the Dewar 8.

[0062] Specifically, the Dewar 8 is a cryogenic Dewar with a sealed structure, which prevents liquid nitrogen from evaporating when liquid nitrogen is used for cooling. The current lead 3 is used to apply excitation current to the superconducting coil 2. The voltage lead 4 is used to monitor voltage changes during the excitation process to prevent the magnet from losing its supercharger.

[0063] Furthermore, the closed magnet also includes a superconducting switch 7. The current lead 3 is connected to the superconducting coil 2 through the superconducting switch 7; the superconducting switch 7 is used to close when an excitation current needs to be applied, and to open after the excitation current application is completed.

[0064] Furthermore, the Dewar 8 is also provided with a refrigerator cold head hole 5. The refrigerator cold head hole 5 is used to connect the Dewar 8 to a refrigerator, so that the internal temperature of the Dewar 8 can be lowered. The refrigerator is a device for cooling in order to achieve a lower temperature (below 77K).

[0065] Furthermore, the Dewar 8 is also provided with a room temperature aperture 6. The room temperature aperture 6 is used to control the connection and closure of the Dewar 8 with the outside world. Moreover, the room temperature aperture 6 can serve as a location for experiments conducted under strong magnetic fields using the magnetic field generated by the magnet, and can also be used to place a magnetic field detection sensor to measure changes in magnetic field strength. Preferably, the direction of the room temperature aperture is parallel to the axis of the closed coil (i.e., parallel to the length direction of the closed coil).

[0066] Taking the fabrication of a closed coil using YBCO superconducting tape as an example, several specific embodiments and comparative examples are provided below to illustrate in detail the method of the present invention for fabricating a second-generation high-temperature superconducting tape closed coil and a closed magnet.

[0067] Example 1

[0068] A method for preparing a second-generation high-temperature superconducting tape closed magnet includes the following steps:

[0069] (1) The second-generation high-temperature superconducting tape (YBCO tape is used in this embodiment) is wound into a coil, leaving both ends of the tape as connectors to be connected.

[0070] (2) Use etching to remove the metal protective layer (i.e., protective layer) of the YBCO strip in the joint to be connected.

[0071] (3) YBCO precursor liquid is coated on the YBCO superconducting layer by drop coating.

[0072] (4) The superconducting coil is placed in a heat treatment furnace and heated from room temperature to 300°C at a heating rate of 5°C / min. The coated YBCO precursor solution becomes YBCO gel.

[0073] (5) A channel with a width of 5 μm was prepared on YBCO gel by etching.

[0074] (6) After the superconducting tape with gel at both ends of the YBCO superconducting layer is overlapped, it is placed in a heat treatment furnace for heat treatment at 800℃ and held for 60 minutes to generate tetragonal YBCO.

[0075] (7) The above coil is placed in a heat treatment furnace with an oxygen atmosphere and an oxygen pressure of 15 MPa to generate a YBCO superconductor with an orthogonal phase.

[0076] (8) YBCO tape is used to connect the superconducting joint in a bridging manner to enhance the mechanical strength of the joint and obtain a closed coil.

[0077] (9) Design the low-temperature Dewar, current lead, voltage lead, refrigerator, etc. according to the closed coil, and make the direction of the room temperature hole of the low-temperature Dewar parallel to the length direction of the closed coil.

[0078] (10) Place the closed coil into the Dewar and connect the current lead and voltage lead to form a second-generation high-temperature superconducting tape closed magnet.

[0079] Furthermore, a current lead and a superconducting switch are applied to the closed coil, that is, the current lead is connected to the closed coil through the superconducting switch. The structural schematic diagram of the resulting closed magnet is shown below. Figure 5 As shown.

[0080] Figure 6 This is a schematic diagram of the operation of the YBCO closed magnet prepared in this embodiment, where the horizontal axis represents time in hours (h), and the vertical axis represents the ratio of the current magnetic field strength to the initial magnetic field strength. Figure 6 As can be seen from this embodiment, the YBCO closed magnet prepared has almost no attenuation and can meet the requirements of closed-loop operation.

[0081] Example 2

[0082] A method for preparing a second-generation high-temperature superconducting tape closed magnet includes the following steps:

[0083] (1) The second-generation high-temperature superconducting tape (YBCO tape is used in this embodiment) is wound into a coil, leaving both ends of the tape as connectors to be connected.

[0084] (2) Use etching to remove the metal protective layer of the YBCO strip in the joint to be connected.

[0085] (3) YBCO precursor liquid is coated on the YBCO superconducting layer by drop coating.

[0086] (4) The superconducting coil is placed in a heat treatment furnace and heated from room temperature to 450°C at a heating rate of 5°C / min. The coated YBCO precursor solution becomes YBCO gel.

[0087] (5) A 7 μm channel was prepared on the YBCO gel by etching.

[0088] (6) After overlapping the superconducting tapes with YBCO superconducting layers at both ends, they were placed in a heat treatment furnace for heat treatment at 850℃ and held for 180 min. Tetragonal YBCO was generated.

[0089] (7) The above coil is placed in an oxygen atmosphere heat treatment furnace for annealing at an oxygen pressure of 55 MPa to generate a YBCO superconductor with orthogonal phase.

[0090] (8) YBCO tape is used to connect the superconducting joint in a bridging manner to enhance the mechanical strength of the joint and obtain a closed coil.

[0091] (9) Based on the design of the closed coil, the low temperature Dewar, current lead, voltage lead, refrigerator, etc., the direction of the room temperature hole is parallel to the length direction.

[0092] (10) Place the closed coil into the Dewar and connect the current lead and voltage lead to form a second-generation high-temperature superconducting tape closed magnet.

[0093] Figure 7The voltage-current (VI) curve of the superconducting junction of the closed coil prepared for this embodiment was measured at 77K zero field using the four-lead method, where the horizontal axis represents the current value in A and the vertical axis represents the voltage value in μV. Figure 7 As shown, the critical current of the superconducting junction is 33A, determined by the 1μV / cm criterion.

[0094] Example 3

[0095] A method for preparing a second-generation high-temperature superconducting tape closed magnet includes the following steps:

[0096] (1) The second-generation high-temperature superconducting tape (YBCO tape is used in this embodiment) is wound into a coil, leaving both ends of the tape as connectors to be connected.

[0097] (2) Use etching to remove the metal protective layer of the YBCO strip in the joint to be connected.

[0098] (3) YBCO precursor liquid is coated on the YBCO superconducting layer by drop coating.

[0099] (4) The superconducting coil is placed in a heat treatment furnace and heated from room temperature to 600°C at a heating rate of 5°C / min. The coated YBCO precursor solution becomes YBCO gel.

[0100] (5) A 10 μm channel was prepared on the YBCO gel by etching.

[0101] (6) After overlapping the superconducting tapes with YBCO superconducting layers at both ends, they were placed in a heat treatment furnace for heat treatment at 900℃ for 300 min. Tetragonal YBCO was generated.

[0102] (7) The above coil is placed in a heat treatment furnace with an oxygen atmosphere and an oxygen pressure of 100 MPa to generate a YBCO superconductor with an orthogonal phase.

[0103] (8) YBCO tape is used to connect the superconducting joint in a bridging manner to enhance the mechanical strength of the joint and obtain a closed coil.

[0104] (9) Based on the design of the closed coil, the low temperature Dewar, current lead, voltage lead, refrigerator, etc., the direction of the room temperature hole is parallel to the length direction.

[0105] (10) Place the closed coil into the Dewar and connect the current lead and voltage lead to form a second-generation high-temperature superconducting tape closed magnet.

[0106] Figure 8 This is an X-ray diffraction pattern of the YBCO strip joint, where the horizontal axis represents the diffraction angle and the vertical axis represents the diffraction peak intensity. From Figure 8 It can be seen that the YBCO at the joint is completely c-axis oriented.

[0107] Comparative Example

[0108] Compared to Example 1, the two ends of the YBCO strip are connected using a traditional brazing method. The resulting welded joint has resistance; after the power supply is removed, the energy in the magnet is quickly dissipated due to heat generation at the joint, causing the magnetic field to decay rapidly and preventing closed-loop operation.

[0109] Figure 9 The voltage-current (VI) curves of the welded joint of the closed coil prepared for comparison were measured at 77K zero field using the four-lead method, where the horizontal axis represents the current value in A and the vertical axis represents the voltage value in μV. Figure 9 As shown, the connector resistance R is obtained by fitting the linear portion of the VI curve. j It is 36nΩ.

[0110] This invention provides a method for fabricating a closed coil from second-generation high-temperature superconducting tape and a closed magnet, belonging to the field of high-temperature superconducting application technology. After winding the second-generation high-temperature superconducting tape into a coil, the YBCO superconducting layer of the superconducting tape is exposed by etching at the connection points. The superconducting layer is connected using a chemical solution method, mainly including steps such as preparing a precursor solution, drop coating, low-temperature heat treatment, high-temperature sintering, and oxygen annealing. Then, the mechanical properties at the joint are strengthened by bridging the YBCO tape to obtain the closed coil. Finally, a low-temperature Dewar is designed based on the fabricated closed coil to form a superconducting magnet operating in a closed loop. Because this invention reserves a sufficient radius during the coil winding process, ensuring that the bending radius is not less than the minimum bending radius, it can prevent problems such as non-conductivity. After the gel is formed by low-temperature heat treatment, the channel is formed by etching. Then, high-temperature sintering is performed to form the tetragonal YBCO phase. Following this, the superconducting coil with a joint is heat-treated in an oxygen atmosphere. During heat treatment, the superconducting layer is oxygenated, increasing the oxygen content of the superconducting layer composition. The YBCO phase transforms from tetragonal to orthorhombic, achieving superconductivity, thus realizing the connection of the second-generation high-temperature superconducting tape at both ends of the coil in a superconducting state. Furthermore, this invention designs a Dewar based on the dimensions of the closed coil, introducing devices such as a refrigerator, current leads, voltage leads, and a superconducting switch to realize the operation of the closed magnet. The results of the embodiments show that the second-generation high-temperature superconducting tape closed magnet provided by this invention has a magnetic field strength of 0.5T at 77K zero field, and its initial magnetic field decay rate after 72 hours is less than 0.01%, achieving the standard of no-attenuation closed-loop operation.

[0111] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0112] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for fabricating a second-generation high-temperature superconducting tape closed coil, characterized in that, include: The second-generation high-temperature superconducting tape is wound into a superconducting coil, and the two ends of the superconducting coil are reserved as two connectors to be connected. The second-generation high-temperature superconducting tape comprises, from bottom to top: a metal substrate layer, a buffer layer, a superconducting layer, and a protective layer; the composition of the superconducting layer is... , where RE is a rare earth element, and x = 0 to 1; Remove the protective layer of the connector to be connected, exposing the superconducting layer of the connector; A precursor solution is coated on the superconducting layer of the connector to be connected; the precursor solution is a solution containing the components of the superconducting layer; the precursor solution is a fluorine-free acetate solution containing rare earth elements, barium elements and copper elements; the rare earth elements are yttrium or gadolinium. The superconducting coil is heat-treated at a first set temperature to turn the precursor liquid coated on the connector to be connected into a gel. Alternating grooves are formed on the gel; The two connectors to be connected are overlapped through the channel, and the superconducting coil is heat-treated at a second set temperature to transform the gel on the connectors to be connected into a tetragonal phase crystal; the second set temperature is greater than the first set temperature. The superconducting coil is annealed in an oxygen atmosphere to transform the tetragonal crystal into an orthorhombic crystal. Two connectors with the orthogonal phase crystals are bridged to obtain a closed coil.

2. The method for preparing a second-generation high-temperature superconducting tape closed coil according to claim 1, characterized in that, The protective layer of the connector to be connected is removed by etching.

3. The method for preparing a second-generation high-temperature superconducting tape closed coil according to claim 1, characterized in that, The precursor liquid is coated onto the superconducting layer of the joint to be connected by drop coating or dip coating.

4. The method for preparing a second-generation high-temperature superconducting tape closed coil according to claim 1, characterized in that, The first set temperature is 300-650°C, and the heating time for heat treatment of the superconducting coil at the first set temperature is 60-180 minutes.

5. The method for preparing a second-generation high-temperature superconducting tape closed coil according to claim 1, characterized in that, The second set temperature is 800-900℃, and the heat treatment time of the superconducting coil at the second set temperature is 60-300 min.

6. The method for preparing a second-generation high-temperature superconducting tape closed coil according to claim 1, characterized in that, The width of the channel is 5–10 μm.

7. The method for preparing a second-generation high-temperature superconducting tape closed coil according to claim 1, characterized in that, The oxygen atmosphere is 99.9% pure oxygen, and the oxygen pressure is 15-100 MPa.

8. A second-generation high-temperature superconducting tape closed magnet, characterized in that, include: The Dewar, current leads, voltage leads, and closed coil prepared by the preparation method of the second-generation high-temperature superconducting tape closed coil as described in any one of claims 1-7; The closed coil is located in the Dewar; both the current lead and the voltage lead are connected to the closed coil, and both the current lead and the voltage lead are led out from the Dewar.

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