Superconducting composite wire and method for producing the same

Abstract

The application belongs to the technical field of superconducting materials, and particularly relates to a superconducting composite wire and a preparation method thereof. The application provides a superconducting composite wire, which comprises, from inside to outside, an inner tin method Nb3Sn sub-element, a thermal sensitive phase change barrier layer, a Cu-Mn-Ni high-damping copper alloy stabilizing layer, a thermochromic warning coating and an outer insulating sheath. The application can be widely applied to high-field magnets in fusion reactors, high-energy accelerators and advanced MRI systems, and can significantly improve the operation safety and state monitoring capability.

Description

Technical Field

[0001] This invention belongs to the field of superconducting materials technology, and particularly relates to a superconducting composite wire and its preparation method. Background Technology

[0002] Nb3Sn superconducting wires possess high critical current densities, making them a crucial raw material for manufacturing high-field magnets. Nb3Sn has become a core material for manufacturing high-field magnets (such as nuclear fusion devices, high-energy physics accelerators, and advanced nuclear magnetic resonance equipment). However, traditional Nb3Sn wires only possess electrical and magnetic properties, lacking the ability to respond to external physical fields (such as light, heat, and stress).

[0003] With the development of smart materials and integrated devices, the demand for multifunctional integrated materials is becoming increasingly urgent. Currently, the highest-performing and most widely used Nb3Sn superconducting wires internationally are all prepared using the internal tin method. This method typically involves inserting a SnTi alloy rod into an internal tin method Nb3Sn CuNb composite rod to assemble internal tin method Nb3Sn sub-components. Subsequently, the sub-components are bundled and assembled into Ta tubes and oxygen-free copper tubes for multiple drawing passes to obtain Nb3Sn composite wires. In the existing technology, there is no technology that directly integrates thermal response functionality into the superconducting wire body. Summary of the Invention

[0004] The purpose of this invention is to provide a superconducting composite wire and its preparation method to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] On one hand, the present invention provides a superconducting composite wire, which includes, from the inside out, an inner tin-based Nb3Sn subunit, a thermosensitive phase change barrier layer, a Cu-Mn-Ni high-damping copper alloy stabilizing layer, a thermochromic warning coating, and an outer insulating sheath.

[0007] On the other hand, a method for preparing the superconducting composite wire according to the present invention is provided, the method comprising the following steps: S1. After surface polishing and cleaning, Fe-Cr-Al alloy rods are deposited sequentially in a vacuum sputtering system with an adhesion layer, an Al2O3 insulating layer, and a Pt temperature-sensing layer. The Pt temperature-sensing layer is photolithographically etched to form a spiral resistance structure, and then annealed and passivated to obtain a Pt resistance temperature-sensing structure. Two Ag-coated Ni-Cr alloy wires are led out as signal leads to obtain a central thermal response core unit (3). The central thermal response core unit is installed in a SnTi alloy tube (2) to obtain a SnTi / central thermal response core unit alloy rod. The SnTi / central thermal response core unit alloy rod is inserted into an inner tin method Nb3Sn CuNb composite tube (1) and drawn in multiple passes to obtain inner tin method Nb3Sn subunits (4) of different shapes. S2. After cleaning the Nb3Sn subunits (4) obtained in S1, the bundles are sequentially loaded into the cleaned Ta tube (5) and oxygen-free copper tube (6) to obtain ITER type Nb3Sn superconducting wire; the ITER type Nb3Sn superconducting wire is cold-drawn to the target diameter to obtain ITER type Nb3Sn superconducting basic wire. S3. The ITER type Nb3Sn superconducting base wire obtained in S2 is coated with VO2-W / ZrO2 composite powder on the surface of the ITER type Nb3Sn superconducting base wire using plasma spraying technology to obtain a thermosensitive phase change barrier layer with uniform thickness (7). Then, after curing, the density and adhesion of the thermosensitive phase change barrier layer are improved to obtain the ITER type Nb3Sn superconducting base wire with thermosensitive phase change barrier layer. S4. Insert the ITER-type Nb3Sn superconducting base wire with a thermosensitive phase change barrier layer obtained in S3 into a Cu-3Mn-2Ni alloy tube, and then perform hot isostatic pressing (HIP) to obtain a Cu-Mn-Ni high-damping copper alloy stabilizing layer (8). S5. The Cu-Mn-Ni high-damping copper alloy stabilizing layer obtained in S4 is electrostatically sprayed with thermochromic microcapsule suspension. After curing, a thermochromic warning coating is obtained (9). The surface of the wire is wrapped with biaxially stretched polyimide film at a 50% overlap rate to form an outer insulating sheath (10), and the final finished wire is obtained. S6. The final finished wire obtained in S5 is cured to ensure that the materials of each layer are fully cross-linked and stable, and the final blank of Nb3Sn obtained by the inner tin method is obtained. Then, it is stretched multiple times to obtain Nb3Sn composite wire with both high field superconductivity and thermal response functions.

[0008] Preferably, in S1, The surface cleaning process involves sequentially ultrasonically cleaning the Fe-Cr-Al alloy rod with acetone, ethanol, and deionized water (each cleaning time is 15-30 min), followed by oxygen plasma treatment for 10-20 min to enhance the surface energy. The adhesive layer is made of Ti or Cr and has a thickness of 5~10 nm; The thickness of the Al2O3 insulating layer is 30~50 nm; The thickness of the Pt temperature-sensing layer is 40~100 nm; The conditions for the vacuum sputtering system are: sputtering power of 150~200 W, working pressure of Ar atmosphere protection (0.4~1.0 Pa), and substrate temperature of 200~300℃; During the deposition process, a trace amount of N2 (2-5%) is introduced to form a Pt-N solid solution, which reduces the internal stress of the film. The photolithography conditions are as follows: spin-coating positive photoresist onto the Pt temperature-sensitive layer, pre-baking at 90 °C for 90 s, ultraviolet exposure using a mask, and development to form a serpentine or spiral pattern with a linewidth of 5~10 μm. The etching conditions are as follows: reactive ion etching (RIE) is used, the gas is Cl2 / Ar (3:1), the power is 100 W, and the etching time is 60~90 s to achieve anisotropic etching; The annealing conditions are as follows: step annealing is carried out in an N2 atmosphere, with the step annealing process being 200℃ / 1 h → 300℃ / 1 h → 400℃ / 2 h. A SiO2 passivation layer with a thickness of 200~300 nm is grown on the Pt temperature-sensitive layer structure using plasma-enhanced chemical vapor deposition (PECVD).

[0009] Preferably, in step S2, the target diameter is φ1.0mm~φ15mm.

[0010] Preferably, in S3, The conditions for the plasma spraying technology are: plasma spraying power of 30~50 kW and argon flow rate of 40~60 L / min; The curing conditions are: temperature 700~800℃, time 2~4h, carried out in an Ar protective atmosphere; The preparation method of the VO2-W / ZrO2 composite powder is as follows: 0.5~2 at% W-doped VO2 nanopowder is synthesized by sol-gel method, and mixed with ZrO2 nanopowder by ball milling at a mass ratio of 80~90:10~20, and spray dried and granulated to obtain VO2-W / ZrO2 composite powder with a particle size of 40~50μm. The thickness of the thermosensitive phase change barrier layer is 50~80 μm.

[0011] Preferably, in S4, The specifications of the Cu-3Mn-2Ni alloy tube are φ2.5~16.5 / φ1.5~15.5 mm. The Cu-3Mn-2Ni alloy tube also contains 0.1~0.3 wt% Ce element to refine the grains and improve low-temperature strength and fatigue resistance. The conditions for hot isostatic pressing (HIP) are: temperature 700~800℃, pressure 150~200 MPa, and time 2~4h.

[0012] Preferably, in S5, The thermochromic microcapsule suspension is composed of thermochromic microcapsules dispersed in an epoxy-silica hybrid matrix. The core of the thermochromic microcapsules is a crystal violet lactone / bisphenol A / tetradecyl alcohol reversible thermosensitive system. The particle size of the thermochromic microcapsules is 1~5 μm, the wall material is urea-formaldehyde resin, and the encapsulation rate is ≥95%. The conditions for spraying are: voltage of 50~70 kV and distance of 10~20 cm; The curing conditions are: temperature 110~130℃, time 30~60 min; The thickness of the thermochromic warning coating is 100~200 μm.

[0013] Preferably, in S5, The polyimide film has a thickness of 50~150 μm and has 2~5 wrapping layers. The polyimide film is doped with 1~3 wt% boron nitride nanosheets to improve its axial thermal conductivity, enabling rapid heat diffusion along the longitudinal direction of the wire and preventing local hot spot accumulation.

[0014] Preferably, in S6, The final curing conditions are: nitrogen protection atmosphere, heating rate of 5~7 ℃ / min, temperature of 180~220℃, and time of 1~3 h; The stretching pass rate is 2%~30%, and the stretching speed is 1~100 m / min.

[0015] On the other hand, the present invention provides the application of the preparation method described herein in the preparation of Nb3Sn composite wires that combine high-field superconductivity and thermal response.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: The superconducting composite wire of this invention adopts a multi-layer functional integrated structural design, which includes, from the inside out: a central thermal response core unit, an ITER-type Nb3Sn superconducting base wire, a thermosensitive phase change barrier layer, a Cu-Mn-Ni high-damping copper alloy stabilizing layer, a thermochromic warning coating, and an outer insulating sheath, realizing three major functions: temperature self-sensing, thermal stress buffering, and early warning of quench failure.

[0017] First, a central thermal response core unit is obtained by depositing an adhesion layer, an Al2O3 layer, and a Pt thin film (Pt temperature-sensitive layer) on the surface of an Fe-Cr-Al rod using magnetron sputtering technology. The obtained central thermal response core unit is then sequentially inserted into a SnTi alloy tube and an inner-tin Nb3SnCuNb composite tube. After multiple drawing processes, inner-tin Nb3Sn sub-components of different shapes are obtained. Finally, the sub-component bundles are sequentially loaded into a Ta tube and an oxygen-free copper tube and cold-drawn to the target diameter to obtain an ITER-type Nb3Sn superconducting base wire. On the ITER-type Nb3Sn superconducting base wire, a thermosensitive phase change barrier layer, a Cu-Mn-Ni high-damping copper alloy stabilizing layer, and a thermochromic warning coating are obtained through plasma spraying, hot isostatic pressing, and electrostatic spraying processes. Finally, a polyimide film is wrapped around the surface of the wire. Through the above steps, an inner-tin Nb3Sn superconducting composite wire with integrated thermal response function can be obtained.

[0018] In this method, the assembly of the inner-tin Nb3SnCuNb composite rod by inserting a SnTi alloy rod into the inner-tin Nb3Sn subunit is changed to first drilling a hole in the SnTi alloy rod and inserting the central thermal response core unit, followed by assembly with the inner-tin Nb3SnCuNb composite tube. A thermosensitive phase change barrier layer, a Cu-Mn-Ni high-damping copper alloy stabilizing layer, a thermochromic warning coating, and an outer insulating sheath are designed on the surface of the composite line. The central thermal response core unit contains a resistance temperature sensing layer, enabling real-time, in-situ monitoring of the superconducting core temperature with a response time of less than 1 second and a temperature measurement accuracy of ±0.1 K. The thermosensitive phase change barrier layer undergoes lattice reconstruction at a specific temperature threshold (e.g., 15~25K), causing a step change in resistivity, which can be used to locate thermal disturbance sources. Cu-Mn-Ni alloy has high internal friction and excellent thermal expansion matching, which effectively relieves thermal cycling stress; the outermost thermochromic warning coating undergoes a reversible color change (e.g., blue → red) when the local temperature rise exceeds the safety threshold (e.g., 20K), realizing a visual warning of overrun.

[0019] This invention can be widely applied to high-field magnets in fusion reactors, high-energy accelerators, and advanced MRI systems, significantly improving operational safety and condition monitoring capabilities. Attached Figure Description

[0020] Figure 1A schematic diagram of the cross-sectional structure of the Nb3Sn subcomponent using the internal tin method in an Nb3Sn composite wire that combines high-field superconductivity and thermal response, provided for an embodiment of the present invention; In the figure: 1-Inner tin method Nb3Sn CuNb composite tube; 2-SnTi alloy tube; 3-Central thermal response core unit.

[0021] Figure 2 This invention provides a schematic diagram of the cross-sectional structure of an Nb3Sn composite wire with both high-field superconductivity and thermal response capabilities, using the inner tin method. In the figure: 4-Inner tin-process Nb3Sn subcomponent; 5-Ta tube; 6-Oxygen-free copper tube; 7-Thermosensitive phase change barrier layer; 8-Cu-Mn-Ni high-damping copper alloy stabilizing layer; 9-Thermochromic warning coating; 10-Outer insulating sheath. Detailed Implementation

[0022] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental methods and detection methods described in each embodiment are conventional methods; unless otherwise specified, the reagents and materials can be purchased commercially.

[0023] like Figure 1 , Figure 2 As shown, this embodiment of the invention provides a method for preparing Nb3Sn composite wires that combine high-field superconductivity and thermal response, comprising the following steps: S1. First, select an Fe-Cr-Al alloy rod and ultrasonically clean it sequentially with acetone, ethanol, and deionized water (each cleaning time is 15~30 min). Then, treat the surface with oxygen plasma (10~20 min) to increase the surface energy. Next, in a vacuum sputtering system, sequentially deposit an adhesion layer (material Ti or Cr) with a thickness of 5~10 nm, an Al2O3 insulating layer with a thickness of 30~50 nm, and a Pt temperature-sensitive layer with a thickness of 40~100 nm. The sputtering power is 150~200 W, the working pressure is Ar atmosphere protection (0.4~1.0 Pa), and the substrate temperature is 200~300℃. During the deposition process, a trace amount of N2 (2~5%) is introduced to form a Pt-N solid solution, reducing the internal stress of the film. The Pt temperature-sensitive layer is then photolithographically etched and etched. The photolithography conditions are: spin-coating positive photoresist onto the surface of the Pt temperature-sensitive layer, followed by pre-baking at 90℃ / 90°C. The process involves UV exposure using a mask to develop a serpentine or spiral-shaped resistance structure with a linewidth of 5–10 μm. Reactive ion etching (RIE) is then performed using a Cl2 / Ar gas (volume ratio 3:1) at 100 W for 60–90 s to achieve anisotropic etching. This structure is then subjected to step-annealing in an N2 atmosphere: 200℃ / 1 h → 300℃ / 1 h → 400℃ / 2 h. Plasma-enhanced chemical vapor deposition (PECVD) is used to grow a 200–300 nm thick SiO2 passivation layer on the Pt temperature-sensing layer structure, obtaining the Pt resistance temperature-sensing structure. Two Ag-coated Ni-Cr alloy wires are then led out as signal leads to obtain the central thermal response core unit 3. This core unit is then inserted into a SnTi alloy tube 2 to obtain a SnTi / central thermal response core unit alloy rod. The obtained SnTi / central thermal response core unit alloy rod is then inserted into an inner tin-grown Nb3Sn alloy tube. In CuNb composite tube 1, Nb3Sn subcomponents 4 with different shapes are obtained by multiple drawing processes; S2. After cleaning the Nb3Sn subunit 4 obtained in step S1, the bundle is sequentially loaded into the cleaned Ta tube 5 and the oxygen-free copper tube 6 to obtain the ITER type Nb3Sn superconducting wire; the ITER type Nb3Sn superconducting wire is cold-drawn to the target diameter (φ1.0mm~φ15mm) to obtain the ITER type Nb3Sn superconducting base wire. S3. First, W-doped VO2 nanopowder (0.5-2 at%) was synthesized using the sol-gel method. It was then ball-milled with ZrO2 nanopowder at a mass ratio of (80-90):(10-20), followed by spray drying and granulation to a particle size of (40-50 μm). The ITER-type Nb3Sn superconducting base wire obtained in step S2 was then coated with VO2-W / ZrO2 composite powder using plasma spraying technology at a power of (30-50 kW) and an argon flow rate of (40-60 L / min), resulting in a thermosensitive phase change barrier layer 7 with a uniform thickness of (50-80 μm). Subsequently, the layer was subjected to a temperature of (700-800℃) and a time of (2-4 hours). h) The curing process is carried out in an Ar gas protective atmosphere to improve the density and adhesion of the thermosensitive phase change barrier layer, and to obtain an ITER-type Nb3Sn superconducting base wire with a thermosensitive phase change barrier layer. S4. The ITER-type Nb3Sn superconducting base wire with a thermosensitive phase change barrier layer obtained in step S3 is inserted into a Cu-3Mn-2Ni alloy tube with a specification of (φ2.5~16.5 / φ1.5~15.5 mm). The Cu-3Mn-2Ni alloy tube also contains (0.1~0.3 wt%) Ce element to refine the grains and improve low-temperature strength and fatigue resistance. After hot isostatic pressing (HIP) treatment, the alloy layer is densely coated to obtain a Cu-Mn-Ni high-damping copper alloy stabilizing layer (Cu-3Mn-2Ni stabilizing layer) 8. The hot isostatic pressing (HIP) treatment process is as follows: temperature (700~800℃), pressure (150~200 MPa), and time (2~4 h). S5. First, thermochromic microcapsules are dispersed in an epoxy-silica hybrid matrix to obtain a thermochromic microcapsule suspension. The core of the thermochromic microcapsules is a crystal violet lactone / bisphenol A / tetradecyl alcohol reversible thermosensitive system. The particle size of the thermochromic microcapsules is (1~5 μm), the wall material is urea-formaldehyde resin, and the encapsulation rate is ≥95%. On the surface of the Cu-3Mn-2Ni stabilizing layer obtained in step S4, an electrostatic spraying process is used. The spraying voltage is (50~70 kV), the distance is (10~20 cm), and the thermochromic microcapsule suspension is uniformly sprayed on the surface of the stabilizing layer. After curing, a thermochromic warning coating 9 with a thickness of (100~200 μm) is obtained. The curing temperature is (110~130℃), and the curing time is (30~60 min). A biaxially stretched coating with a thickness of (50~150 μm) is then applied. A polyimide film (μm) is wrapped around the surface of the wire at a 50% overlap rate (2-5 layers) to form an outer insulating sheath 10, and finally the finished wire is obtained; the polyimide is doped with boron nitride nanosheets (1-3 wt%) to improve its axial thermal conductivity, so as to realize the rapid diffusion of heat along the longitudinal direction of the wire and prevent the accumulation of local hot spots. S6. The final finished wire obtained in step 5 is subjected to final curing under nitrogen protection, with a heating rate of 5~7 ℃ / min, a curing temperature of 180~220℃, and a curing time of 1~3 h, so that the materials of each layer are fully cross-linked and stable, and the final blank of Nb3Sn by internal tin method is obtained. Then, multiple stretching is performed (the processing rate of stretching passes is 2%~30%, and the stretching speed is 1~100 m / min) to obtain Nb3Sn composite wire with both high field superconductivity and thermal response function.

[0024] Example 1 This example provides a method for preparing superconducting composite wires. First, an Fe-Cr-Al alloy rod was selected and ultrasonically cleaned sequentially with acetone, ethanol, and deionized water (each cleaning time was 15 min). Then, the surface was treated with oxygen plasma for 10 min to increase the surface energy. Next, a 5 nm thick Ti adhesion layer, a 30 nm thick Al2O3 insulating layer, and a 40 nm thick Pt temperature-sensitive layer were sequentially deposited in a vacuum sputtering system. The sputtering power was 150 W, the working pressure was 0.4 Pa, and the Ar atmosphere was used for protection. The substrate temperature was 200℃. During the deposition process, a trace amount of N2 (2% flow rate) was introduced to form a Pt-N solid solution, reducing the internal stress of the film. The Pt temperature-sensitive layer was then photolithographically and etched. The photolithography conditions were: spin-coating a positive photoresist onto the Pt temperature-sensitive layer surface, pre-baking at 90℃ for 90 s, UV exposure using a mask, and development to form a serpentine or spiral resistive structure with a linewidth of 5 μm. Reactive ion etching (RIE) was used with a Cl2 / Ar (3:1) gas, a power of 100 W, and an etching time of 60-90 seconds. Anisotropic etching was achieved; then, it was subjected to step annealing in an N2 atmosphere: 200℃ / 1h → 300℃ / 1h → 400℃ / 2h; a 200 nm thick SiO2 passivation layer was grown on the Pt temperature-sensing layer structure using plasma-enhanced chemical vapor deposition (PECVD) to obtain the Pt resistance temperature-sensing structure, and two Ag-coated Ni-Cr alloy wires were led out as signal leads to obtain the central thermal response core unit 3; it was installed into the SnTi alloy tube 2 to obtain the SnTi / central thermal response core unit alloy rod, and the obtained SnTi / central thermal response core unit alloy rod was inserted into the inner tin method Nb3Sn CuNb composite tube 1, and the inner tin method Nb3Sn sub-components 4 of different shapes were obtained through multiple drawing processes; After cleaning the obtained Nb3Sn subunit 4 obtained by the internal tin method, the bundle is sequentially loaded into the cleaned Ta tube 5 and the oxygen-free copper tube 6 to obtain the ITER type Nb3Sn superconducting wire; the assembled ITER type Nb3Sn superconducting wire is cold-drawn to the target diameter φ1.0 mm to obtain the ITER type Nb3Sn superconducting basic wire. First, 0.5 at% W-doped VO2 nanopowder was synthesized using the sol-gel method. This VO2 nanopowder was then ball-milled and mixed with ZrO2 nanopowder at a mass ratio of 80:10, followed by spray drying and granulation to achieve a particle size of 40 μm. The obtained ITER-type Nb3Sn superconducting base wire was then coated with VO2-W / ZrO2 composite powder using plasma spraying technology at a power of 30 kW and an argon flow rate of 40 L / min. This resulted in a uniform 50 μm thickness of thermosensitive phase change barrier layer 7. Subsequently, the layer was cured at 700℃ for 2 h in an Ar atmosphere to improve the density and adhesion of the thermosensitive phase change barrier layer, thus obtaining an ITER-type Nb3Sn superconducting base wire with a thermosensitive phase change barrier layer. The obtained ITER-type Nb3Sn superconducting base wire with a thermosensitive phase change barrier layer was inserted into a Cu-3Mn-2Ni alloy tube with a specification of φ2.5 / φ1.5 mm. The Cu-3Mn-2Ni alloy tube also contains 0.1 wt% Ce element to refine the grains and improve low-temperature strength and fatigue resistance. After hot isostatic pressing (HIP) treatment, the alloy layer is densely coated to obtain a Cu-Mn-Ni high-damping copper alloy stabilizing layer (Cu-3Mn-2Ni stabilizing layer) 8. The hot isostatic pressing (HIP) treatment process is as follows: temperature 700℃, pressure 150 MPa, time 2 h. First, thermochromic microcapsules were dispersed in an epoxy-silica hybrid matrix to obtain a thermochromic microcapsule suspension. The core of the thermochromic microcapsules was a crystal violet lactone / bisphenol A / tetradecyl alcohol reversible thermosensitive system. The microcapsule particle size was 1 μm, the wall material was urea-formaldehyde resin, and the encapsulation efficiency was ≥95%. On the surface of the obtained Cu-3Mn-2Ni stable layer, an electrostatic spraying process was used with a spraying voltage of 50 kV and a distance of 10 cm to uniformly spray the thermochromic microcapsule suspension onto the surface of the stable layer. After curing, a 100 μm thick thermochromic warning coating 9 was obtained. The curing temperature was 110℃, and the curing time was 30 min. A 50 μm thick biaxially stretched polyimide film was used to wrap the wire surface with two layers at a 50% overlap rate to form an outer insulating sheath 10, resulting in the final finished wire. The polyimide was doped with 1... wt% boron nitride nanosheets are used to improve the axial thermal conductivity, enabling rapid heat diffusion along the longitudinal direction of the wire and preventing the accumulation of local hot spots. The final finished wire was then cured under nitrogen protection, with a heating rate of 5 °C / min, a curing temperature of 180 °C, and a curing time of 1 h to ensure that each layer of material was fully cross-linked and stable. The final blank of Nb3Sn obtained by the inner tin method was then subjected to multiple stretching processes to produce Nb3Sn composite wire with both high-field superconductivity and thermal response.

[0025] The Nb3Sn composite wire prepared in this embodiment, possessing both high-field superconductivity and thermal response capabilities, can be used as the innermost winding of a superconducting magnet. Two Ag-coated Ni-Cr alloy wires are led out as signal lines connected to the central control unit. The central control unit converts the internal thermal signal of the wire into digital temperature readings, displaying the real-time temperature inside the magnet and achieving millisecond-level sampling of the temperature of each coil turn. Under conditions of a 15 T magnetic field and 4.2 K liquid helium immersion, the magnet system wound with this wire successfully completed over 500 charge-discharge cycles. When a coil turn generates minor frictional heat due to mechanical loosening, the central thermal response core unit detects a temperature rise of 0.6 K within 0.8 seconds and triggers an early warning system to automatically reduce the current slope, preventing excessively high current from causing localized overheating inside the wire and leading to quench failure at the superconducting critical temperature. Compared to traditional coils without integrated sensing capabilities, this magnet system exhibits a 92% reduction in quench failure rate, significantly improving the operational reliability of the device.

[0026] Example 2 This example provides another method for preparing superconducting composite wires. First, an Fe-Cr-Al alloy rod was selected and ultrasonically cleaned sequentially with acetone, ethanol, and deionized water (each cleaning time was 30 min). Then, the surface was treated with oxygen plasma for 20 min to increase the surface energy. Next, a 10 nm thick Cr adhesion layer, a 50 nm thick Al2O3 insulating layer, and a 100 nm thick Pt temperature-sensitive layer were sequentially deposited in a vacuum sputtering system. The sputtering power was 200 W, the working pressure was 1.0 Pa, and an Ar atmosphere was used for protection. The substrate temperature was 300℃. During the deposition process, a trace amount of N2 (5% flow rate) was introduced to form a Pt-N solid solution, reducing the internal stress of the film. The Pt temperature-sensitive layer was then photolithographically etched and etched. The photolithography conditions were: spin-coating of positive photoresist onto the Pt film surface, pre-baking at 90℃ / 90 s, UV exposure using a mask, and development to form a serpentine or spiral-shaped resistor structure with a linewidth of 10 nm. μm; Reactive ion etching (RIE) was used with Cl2 / Ar (3:1) gas, power 100W, and etching time 60~90 s to achieve anisotropic etching; then it was subjected to step annealing in N2 atmosphere: 200℃ / 1 h→300℃ / 1 h→400℃ / 2 h; a 300 nm thick SiO2 passivation layer was grown on the Pt temperature sensing layer structure by plasma enhanced chemical vapor deposition (PECVD) to obtain the Pt resistance temperature sensing structure, and two Ag-coated Ni-Cr alloy wires were led out as signal leads to obtain the central thermal response core unit 3; it was installed into SnTi alloy tube 2 to obtain SnTi / central thermal response core unit alloy rod, and the obtained SnTi / central thermal response core unit alloy rod was inserted into the inner tin method Nb3Sn CuNb composite tube 1, and the inner tin method Nb3Sn sub-components 4 of different shapes were obtained by multi-pass drawing. After cleaning the obtained Nb3Sn subunit 4 obtained by the internal tin method, the bundle is sequentially loaded into the cleaned Ta tube 5 and the oxygen-free copper tube 6 to obtain the ITER type Nb3Sn superconducting wire; the assembled ITER type Nb3Sn superconducting wire is cold-drawn to the target diameter φ15mm to obtain the ITER type Nb3Sn superconducting basic wire. First, 2 at% W-doped VO2 nanopowder was synthesized using the sol-gel method. This VO2 nanopowder was then ball-milled with ZrO2 nanopowder at a mass ratio of 90:20, followed by spray drying and granulation to achieve a particle size of 50 μm. The obtained ITER-type Nb3Sn superconducting base wire was then coated with VO2-W / ZrO2 composite powder using plasma spraying technology at a power of 50 kW and an argon flow rate of 60 L / min. This resulted in a uniformly thick thermosensitive phase change barrier layer 7 of 80 μm. Subsequently, the layer was cured at 800℃ for 4 h in an Ar atmosphere to improve the density and adhesion of the thermosensitive phase change barrier layer 7, thus obtaining an ITER-type Nb3Sn superconducting base wire with the thermosensitive phase change barrier layer 7. The obtained ITER-type Nb3Sn superconducting base wire with a thermosensitive phase change barrier layer 7 was threaded into a Cu-3Mn-2Ni alloy tube with a specification of φ16.5 / φ15.5 mm. The Cu-3Mn-2Ni alloy tube also contains 0.3 wt% Ce element to refine the grains and improve low-temperature strength and fatigue resistance. After hot isostatic pressing (HIP) treatment, the alloy layer is densely coated to obtain a Cu-Mn-Ni high-damping copper alloy stabilizing layer (Cu-3Mn-2Ni stabilizing layer) 8. The hot isostatic pressing (HIP) treatment process is as follows: temperature 800℃, pressure 200 MPa, time 4 h. First, thermochromic microcapsules were dispersed in an epoxy-silica hybrid matrix to obtain a thermochromic microcapsule suspension. The microcapsule core was a crystal violet lactone / bisphenol A / tetradecyl alcohol reversible thermosensitive system. The thermochromic microcapsule particle size was 5 μm, and the wall material was urea-formaldehyde resin with an encapsulation efficiency of ≥95%. On the surface of the obtained Cu-3Mn-2Ni stable layer, an electrostatic spraying process was used with a spraying voltage of 70 kV and a distance of 20 cm to uniformly spray the thermochromic microcapsule suspension onto the surface of the stable layer. After curing, a 200 μm thick thermochromic warning coating 9 was obtained. The curing temperature was 130℃, and the curing time was 60 min. A 150 μm thick biaxially stretched polyimide film was used to wrap the wire surface with 5 layers at a 50% overlap rate to form an outer insulating sheath 10, resulting in the final finished wire. The polyimide was doped with 3... wt% boron nitride nanosheets are used to improve the axial thermal conductivity, enabling rapid heat diffusion along the longitudinal direction of the wire and preventing the accumulation of local hot spots. The final finished wire was then cured under nitrogen protection, with a heating rate of 7 °C / min, a curing temperature of 220 °C, and a curing time of 3 h to ensure full cross-linking and stability of each layer of material. The final blank of Nb3Sn obtained by the inner tin method was then subjected to multiple stretching operations to produce Nb3Sn composite wire with both high-field superconductivity and thermal response.

[0027] In this embodiment, the Pt thermistor unit (i.e., the central thermal response core unit 3) in the Nb3Sn composite wire, which combines high-field superconductivity and thermal response, is positioned and numbered during the magnet winding stage, forming a space-temperature mapping array. Ag-coated Ni-Cr alloy wire is connected to the central control unit as a signal line. The central control unit detects the local resistance data inside the wire. After cooling to 4.2 K, the magnet system wound with this wire automatically collects the reference resistance values ​​at each point and establishes a thermal response reference database. In actual operation, the control system scans all sensor data every 5 minutes. Once the system detects an abnormal temperature increase of 0.35 K in a certain area of ​​the upper part of the magnet, the wire resistance will increase with the temperature rise, allowing for timely fault diagnosis (by monitoring resistance changes to provide feedback on wire fault conditions), thus preventing magnet demagnetization accidents. This ensures continuous and stable magnet operation and reduces magnetic field drift.

[0028] Example 3 This example provides another method for preparing superconducting composite wires. First, an Fe-Cr-Al alloy rod was selected and ultrasonically cleaned sequentially with acetone, ethanol, and deionized water (each cleaning time was 20 min). Then, the surface was treated with oxygen plasma for 15 min to increase the surface energy. Next, an 8 nm thick Ti adhesion layer, a 35 nm thick Al2O3 insulating layer, and a 60 nm thick Pt temperature-sensitive layer were sequentially deposited in a vacuum sputtering system. The sputtering power was 170 W, the working pressure was 0.6 Pa, and the Ar atmosphere was used for protection. The substrate temperature was 240℃. During the deposition process, a trace amount of N2 (4% flow rate) was introduced to form a Pt-N solid solution, reducing the internal stress of the film. The Pt temperature-sensitive layer was then photolithographically and etched. The photolithography conditions were: spin-coating positive photoresist onto the Pt film (i.e., the Pt temperature-sensitive layer), pre-baking at 90℃ / 90 s, UV exposure using a mask, and development to form a serpentine or spiral-shaped resistive structure with a linewidth of 8 μm. Reactive ion etching (RIE) was used with a Cl2 / Ar (3:1) gas and a power of 100 W. W, etching time 60-90 s, to achieve anisotropic etching; then it is subjected to step annealing in N2 atmosphere: 200℃ / 1 h→300℃ / 1 h→400℃ / 2 h; a 240 nm thick SiO2 passivation layer is grown on the Pt temperature sensing layer structure by plasma enhanced chemical vapor deposition (PECVD) to obtain the Pt resistance temperature sensing structure, and two Ag-coated Ni-Cr alloy wires are led out as signal leads to obtain the central thermal response core unit 3; it is installed into SnTi alloy tube 2 to obtain SnTi / central thermal response core unit alloy rod, and the obtained SnTi / central thermal response core unit alloy rod is inserted into the inner tin method Nb3SnCuNb composite tube 1, and obtained inner tin method Nb3Sn sub-components 4 of different shapes through multiple drawing. After cleaning the obtained Nb3Sn subunit 4 obtained by the internal tin method, the bundle is sequentially loaded into the cleaned Ta tube 5 and the oxygen-free copper tube 6 to obtain the ITER type Nb3Sn superconducting wire; the assembled ITER type Nb3Sn superconducting wire is cold-drawn to the target diameter φ2.0 mm to obtain the ITER type Nb3Sn superconducting base wire. First, 1.0 at% W-doped VO2 nanopowder was synthesized using the sol-gel method. This VO2 nanopowder was then ball-milled with ZrO2 nanopowder at a mass ratio of 85:10, followed by spray drying and granulation to achieve a particle size of 45 μm. The obtained ITER-type Nb3Sn superconducting base wire was then coated with VO2-W / ZrO2 composite powder using plasma spraying technology at a power of 40 kW and an argon flow rate of 50 L / min. This resulted in a uniformly thick thermosensitive phase change barrier layer 7 of 70 μm. Subsequently, the layer was cured at 750℃ for 3 h in an Ar atmosphere to improve the density and adhesion of the thermosensitive phase change barrier layer 7, thus obtaining an ITER-type Nb3Sn superconducting base wire with the thermosensitive phase change barrier layer 7. The obtained ITER-type Nb3Sn superconducting base wire with a thermosensitive phase change barrier layer 7 was inserted into a Cu-3Mn-2Ni alloy tube with a specification of φ3.5 / φ2.5 mm. The Cu-3Mn-2Ni alloy tube also contains 0.2wt% Ce element to refine the grains and improve low-temperature strength and fatigue resistance. After hot isostatic pressing (HIP) treatment, the alloy layer is densely coated to obtain a Cu-Mn-Ni high-damping copper alloy stabilizing layer (Cu-3Mn-2Ni stabilizing layer) 8. The hot isostatic pressing (HIP) treatment process is as follows: temperature 750℃, pressure 170 MPa, time 3 h. First, thermochromic microcapsules were dispersed in an epoxy-silica hybrid matrix to obtain a thermochromic microcapsule suspension. The microcapsule core was a crystal violet lactone / bisphenol A / tetradecyl alcohol reversible thermosensitive system. The thermochromic microcapsule particle size was 3 μm, and the wall material was urea-formaldehyde resin with an encapsulation efficiency of ≥95%. On the surface of the obtained Cu-3Mn-2Ni stable layer, an electrostatic spraying process was used with a spraying voltage of 60 kV and a distance of 15 cm to uniformly spray the thermochromic microcapsule suspension onto the stable layer surface. After curing, a thermochromic warning coating with a thickness of 150 μm was obtained. The curing temperature was 120℃, and the curing time was 45 min. A biaxially stretched coating with a thickness of 100 μm was then applied. A 10-layer outer insulating sheath is formed by wrapping 3 layers of a 10 μm polyimide film around the surface of the wire at a 50% overlap rate, resulting in the final finished wire. 2 wt% boron nitride nanosheets are doped into the polyimide to improve its axial thermal conductivity, enabling rapid heat diffusion along the longitudinal direction of the wire and preventing the accumulation of local hot spots. The final finished wire was then cured under nitrogen protection, with a heating rate of 5 °C / min, a curing temperature of 200 °C, and a curing time of 2 h to ensure full cross-linking and stability of each layer of material. The final blank of Nb3Sn obtained by the internal tin method was then subjected to multiple stretching processes to produce Nb3Sn composite wire with both high-field superconductivity and thermal response.

[0029] In this embodiment, the Nb3Sn composite wire, which combines high-field superconductivity and thermal response, incorporates a thermal response system (i.e., the central thermal response core unit 3). An Ag-coated Ni-Cr alloy wire serves as the signal line connected to the central control unit. This central control unit collects data from the wire's internal thermal response system, enabling real-time monitoring of local temperature fluctuations (maximum ΔT = 0.42 K) caused by micro-vibrations in the cooling head. It also coordinates with the active cooling system for compensation and adjustment, ensuring the magnet remains in a superconducting state. Disassembly and inspection after testing revealed no microcracks or performance degradation.

[0030] In summary, the Nb3Sn composite wire prepared in this embodiment, which combines high-field superconductivity and thermal response, has great potential in dynamic thermal management, intelligent early warning, and system adaptive control, providing a reliable technical path for future cutting-edge fields such as electric aircraft and space propulsion.

[0031] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but rather to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art through related deductions and substitutions based on the inventive concept, without inventive effort, are within the scope of protection of the present invention.

Claims

1. A superconducting composite wire, characterized in that, The superconducting composite wire comprises, from the inside out, an inner tin-based Nb3Sn subunit, a thermosensitive phase change barrier layer, a Cu-Mn-Ni high-damping copper alloy stabilizing layer, a thermochromic warning coating, and an outer insulating sheath.

2. The method for preparing the superconducting composite wire according to claim 1, characterized in that, The preparation method includes the following steps: S1. After surface polishing and cleaning, Fe-Cr-Al alloy rods are deposited sequentially in a vacuum sputtering system with an adhesion layer, an Al2O3 insulating layer, and a Pt temperature-sensing layer. The Pt temperature-sensing layer is photolithographically etched to form a spiral resistance structure, and then annealed and passivated to obtain a Pt resistance temperature-sensing structure. Two Ag-coated Ni-Cr alloy wires are led out as signal leads to obtain a central thermal response core unit (3). The central thermal response core unit is installed in a SnTi alloy tube (2) to obtain a SnTi / central thermal response core unit alloy rod. The SnTi / central thermal response core unit alloy rod is inserted into an inner tin method Nb3Sn CuNb composite tube (1) and drawn in multiple passes to obtain inner tin method Nb3Sn subunits (4) of different shapes. S2. After cleaning the Nb3Sn subunits (4) obtained in S1, the bundles are sequentially loaded into the cleaned Ta tube (5) and oxygen-free copper tube (6) to obtain ITER type Nb3Sn superconducting wire; the ITER type Nb3Sn superconducting wire is cold-drawn to the target diameter to obtain ITER type Nb3Sn superconducting basic wire. S3. The ITER type Nb3Sn superconducting base wire obtained in S2 is coated with VO2-W / ZrO2 composite powder by plasma spraying technology to obtain a uniformly thick thermosensitive phase change barrier layer (7); then cured to obtain the ITER type Nb3Sn superconducting base wire with thermosensitive phase change barrier layer. S4. Insert the ITER-type Nb3Sn superconducting base wire with a thermosensitive phase change barrier layer obtained in S3 into a Cu-3Mn-2Ni alloy tube, and after hot isostatic pressing, obtain a Cu-Mn-Ni high-damping copper alloy stabilizing layer (8). S5. The Cu-Mn-Ni high-damping copper alloy stabilizing layer obtained in S4 is electrostatically sprayed with thermochromic microcapsule suspension. After curing, a thermochromic warning coating is obtained (9). The surface of the wire is wrapped with biaxially stretched polyimide film at a 50% overlap rate to form an outer insulating sheath (10), and the final finished wire is obtained. S6. The final finished wire obtained in S5 is cured to ensure that the materials of each layer are fully cross-linked and stable, and the final blank of Nb3Sn obtained by the inner tin method is obtained. Then, it is stretched multiple times to obtain Nb3Sn composite wire with both high field superconductivity and thermal response functions.

3. The preparation method according to claim 2, characterized in that, In S1, The surface cleaning process involves sequentially ultrasonically cleaning the Fe-Cr-Al alloy rod with acetone, ethanol, and deionized water, followed by surface treatment with oxygen plasma for 10-20 minutes. The adhesive layer is made of Ti or Cr and has a thickness of 5~10 nm; The thickness of the Al2O3 insulating layer is 30~50 nm; The thickness of the Pt temperature-sensing layer is 40~100 nm; The conditions for the vacuum sputtering system are: sputtering power of 150~200W, working pressure of Ar atmosphere protection, and substrate temperature of 200~300℃. During the deposition process, a trace amount of N2 (2-5%) is introduced to form a Pt-N solid solution. The photolithography conditions are as follows: spin-coating positive photoresist onto the Pt temperature-sensitive layer, pre-baking at 90 °C for 90 s, ultraviolet exposure using a mask, and development to form a serpentine or spiral pattern with a linewidth of 5~10 μm. The etching conditions are as follows: reactive ion etching is used, the gas is Cl2 / Ar, the power is 100 W, and the etching time is 60~90s to achieve anisotropic etching. The annealing conditions are as follows: step annealing is performed in an N2 atmosphere, and a SiO2 passivation layer with a thickness of 200~300 nm is grown on the Pt temperature-sensitive layer structure by plasma-enhanced chemical vapor deposition.

4. The preparation method according to claim 2, characterized in that, In S2, the target diameter is φ1.0mm~φ15mm.

5. The preparation method according to claim 2, characterized in that, In S3, The conditions for the plasma spraying technology are: plasma spraying power of 30~50 kW and argon flow rate of 40~60 L / min; The curing conditions are: temperature of 700~800℃, time of 2~4 h, carried out in an Ar protective atmosphere; The preparation method of the VO2-W / ZrO2 composite powder is as follows: 0.5~2 at% W-doped VO2 nanopowder is synthesized by sol-gel method, and mixed with ZrO2 nanopowder by ball milling at a mass ratio of 80~90:10~20, and spray dried and granulated to obtain VO2-W / ZrO2 composite powder with a particle size of 40~50 μm. The thickness of the thermosensitive phase change barrier layer is 50~80 μm.

6. The preparation method according to claim 2, characterized in that, In S4, The specifications of the Cu-3Mn-2Ni alloy tube are φ2.5~16.5 / φ1.5~15.5 mm, and the Cu-3Mn-2Ni alloy tube also contains 0.1~0.3 wt% Ce element; The conditions for hot isostatic pressing are: temperature 700~800℃, pressure 150~200 MPa, and time 2~4 h.

7. The preparation method according to claim 2, characterized in that, In S5, The thermochromic microcapsule suspension is composed of thermochromic microcapsules dispersed in an epoxy-silica hybrid matrix. The core of the thermochromic microcapsule is a crystal violet lactone / bisphenol A / tetradecyl alcohol reversible thermosensitive system. The particle size of the thermochromic microcapsule is 1~5 μm, and the wall material is urea-formaldehyde resin. The conditions for spraying are: voltage of 50~70 kV and distance of 10~20 cm; The curing conditions are: temperature 110~130℃, time 30~60 min; The thickness of the thermochromic warning coating is 100~200 μm.

8. The preparation method according to claim 2, characterized in that, In S5, The polyimide film has a thickness of 50~150 μm and has 2~5 wrapping layers. The polyimide film is doped with 1~3 wt% boron nitride nanosheets.

9. The preparation method according to claim 2, characterized in that, In S6, The final curing conditions are: nitrogen protection atmosphere, heating rate of 5~7℃ / min, temperature of 180~220℃, and time of 1~3 h; The stretching pass rate is 2%~30%, and the stretching speed is 1~100 m / min.

10. The application of the preparation method according to any one of claims 2-9 in the preparation of Nb3Sn composite wires with both high-field superconductivity and thermal response functions.

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