A multi-core round cable type Nb3Sn magnet low resistance connector and its preparation method

Abstract

The application discloses a multi-core round cable type Nb3Sn magnet low-resistance joint and a preparation method thereof, and belongs to the technical field of key component manufacturing of superconducting magnets. The joint comprises a conductive sleeve, a multi-core round cable type Nb3Sn superconducting cable arranged in a slot of the conductive sleeve, an auxiliary superconducting conductor layer arranged along the circumference of the superconducting cable, and a continuous conductive filling body formed by remelting a first conductive filling material and a second conductive filling material; and further comprises a conductive support seat with a joint slot, an insulating structure and a connecting piece. During preparation, a main cable channel is reserved by using a removable placeholder, the first conductive filling material is introduced to position the auxiliary superconducting conductor layer, the multi-core round cable type Nb3Sn superconducting cable is placed, and the second conductive filling material is introduced, so that the two kinds of conductive filling materials are remelted and combined. The application can increase the equivalent conductive cross section of the joint, reduce the joint resistance, and improve the electrical connection stability and shunt protection capacity of the joint.

Description

Technical Field

[0001] This invention belongs to the field of manufacturing technology of key components of superconducting magnets, specifically relating to a low-resistance connector for multi-core round cable type Nb3Sn magnets and its preparation method. Background Technology

[0002] During the high-current steady-state operation of Nb3Sn high-field superconducting magnet devices, the termination connections of their superconducting cables generally rely on electrical connectors with extremely low contact resistance. Traditional connector structures often suffer from problems such as excessively high local contact resistance and excessively high local current density at the cable connection interface. Therefore, there is an urgent need for a multi-core round cable type low-resistance connector structure for Nb3Sn magnets that can both reduce contact resistance and solve the problem of excessively high local current density by increasing the equivalent cross-section, along with its stepwise fabrication process. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a multi-core round cable type Nb3Sn magnet low-resistance joint and its preparation method. Under the condition that the magnetic field and temperature in the joint area meet the operating margin of the NbTi superconducting wire, this joint increases the equivalent conductive cross-sectional area and reduces the local current density by arranging multiple peripheral auxiliary superconducting conductor units circumferentially along the outside of the multi-core round cable type Nb3Sn superconducting cable, thus forming an auxiliary current shunt channel. Combined with stepwise conductive filler material injection filling, the contact resistance of the joint can be reduced.

[0004] The joint includes a conductive sleeve, a multi-core round cable-type Nb3Sn superconducting cable with a groove inside the conductive sleeve, an auxiliary superconducting conductor layer arranged circumferentially along the superconducting cable, and a continuous conductive filler formed by remelting a first conductive filler material and a second conductive filler material; it also includes a conductive support with a joint groove, an insulation structure, and connectors. During fabrication, a removable spacer is used to reserve a main cable channel. First, the first conductive filler material is introduced to position the auxiliary superconducting conductor layer. Then, the multi-core round cable-type Nb3Sn superconducting cable is placed in, and the second conductive filler material is introduced, allowing the two conductive filler materials to remelt and bond together. This invention can increase the equivalent conductive cross-section of the joint, reduce the joint resistance, and improve the electrical connection stability and shunt protection capability of the joint.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A multi-core round cable type Nb3Sn magnet low resistance connector includes:

[0007] A magnet connector includes: a conductive sleeve, a multi-core round cable type Nb3Sn superconducting cable located in a slot inside the conductive sleeve, auxiliary superconducting conductor layers arranged circumferentially along the multi-core round cable type Nb3Sn superconducting cable, and a continuous conductive filler formed by remelting and bonding a first conductive filler material and a second conductive filler material.

[0008] A magnet connector support assembly includes: a conductive support base having a connector slot and connection holes at both ends; an insulating gasket disposed outside the conductive support base; an insulating sleeve disposed within the connection holes; and a connector; an auxiliary superconducting conductor layer is arranged around at least a portion of the circumference of the multi-core round cable type Nb3Sn superconducting cable, forming a concentrically encased auxiliary conductive and shunt structure around the multi-core round cable type Nb3Sn superconducting cable; and a continuous conductive filler is filled and disposed inside the conductive sleeve, in the outer peripheral gap of the multi-core round cable type Nb3Sn superconducting cable, and between the outer side of the conductive sleeve and the conductive support base.

[0009] Beneficial effects:

[0010] 1. The auxiliary superconducting conductor layer provided in this invention increases the equivalent cross-sectional area of ​​the conductor at the key connection of the magnet connector and reduces the local current density at the electrical connection interface.

[0011] 2. The auxiliary superconducting conductor layer of the present invention is arranged at least partially circumferentially along the multi-core round cable type Nb3Sn superconducting cable; in one embodiment, the auxiliary superconducting conductor layer is composed of multiple NbTi superconducting wires and arranged concentrically around it in 360°. Under the condition of satisfying the working magnetic field and temperature margin, the addition of the peripheral auxiliary superconducting conductor layer provides additional current carrying space for the core area of ​​the joint, thereby expanding the steady-state current carrying margin of the joint assembly itself.

[0012] 3. The present invention causes the first conductive filler material to undergo controlled remelting at least in the interface region by the heat input of the second conductive filler material. While forming a continuous conductive bonding interface, it limits the temperature-time history experienced by the Nb3Sn superconducting cable and reduces the risk of irreversible critical current degradation caused by the secondary injection thermal process.

[0013] 4. The auxiliary superconducting conductor layer of the present invention provides an additional current-carrying path for the joint area; before the multi-core round cable type Nb3Sn superconducting cable is inserted, the first conductive filler material fixes the auxiliary superconducting conductor layer to a predetermined circumferential position within the conductive sleeve; after the main cable is inserted, the second conductive filler material fills the remaining gap and remelts with the first conductive filler material at the interface region; the conductive sleeve provides radial boundary constraints for the auxiliary superconducting conductor layer and the continuous conductive filler. The above structure and process work together to reduce the risk of relative displacement, interface separation, or interface discontinuity of each conductive unit during injection, cooling, and assembly, which is beneficial to maintaining the continuity and stability of the multi-path current transfer structure between the main cable, the auxiliary superconducting conductor layer, and the conductive sleeve. Attached Figure Description

[0014] Figure 1 This is a three-dimensional structural diagram of the overall support for the connector, the conductive sleeve, and the connector groove.

[0015] Figure 2 This is a radial front view of the assembly structure at the bottom of the connector.

[0016] Figure 3 This is a cross-sectional topological diagram showing the distribution of internal components of the magnet connector.

[0017] Figure 4 This is a flowchart illustrating the preparation method of a multi-core round cable type Nb3Sn magnet low-resistance connector according to the present invention.

[0018] Figure 5 This diagram illustrates the process of removing and inserting a multi-core round cable-type Nb3Sn superconducting cable using a removable insert.

[0019] Figure 6 The figure shows the voltage-current measurement and linear fitting resistance test curves of the connector under low temperature and high magnetic field conditions.

[0020] The reference numerals in the attached drawings are as follows: 101-conductive sleeve; 1011-first material introduction section; 1012-second material introduction section; 1013-third material introduction section; 1014-fourth material introduction section; 102-multi-core round cable type Nb3Sn superconducting cable; 103-auxiliary superconducting conductor layer; 10301-first NbTi superconducting wire; 10312-twelfth NbTi superconducting wire; 104-first conductive filler material; 105-second conductive filler material; 106-removable occupant; 107-continuous conductive filler; 201-conductive support; 202-insulating gasket; 203-insulating sleeve; 204-connector; 205-joint slot; 206-connection hole. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0022] like Figures 1-3 As shown, a multi-core round cable type Nb3Sn magnet low-resistance connector of the present invention includes:

[0023] The conductive sleeve 101, the multi-core round cable type Nb3Sn superconducting cable 102 located in the internal slot of the conductive sleeve 101, the auxiliary superconducting conductor layer 103 arranged at least partially circumferentially along the multi-core round cable type Nb3Sn superconducting cable 102, and the continuous conductive filler 107 formed by remelting and bonding the first conductive filler material 104 and the second conductive filler material 105.

[0024] The magnet connector support assembly includes: a conductive support base 201 having a connector slot 205 and connection holes 206 at both ends, an insulating gasket 202 disposed outside the conductive support base 201, an insulating sleeve 203 disposed inside the connection holes 206, and a connector 204.

[0025] The auxiliary superconducting conductor layer 103 is arranged at least partially circumferentially along the multi-core round cable type Nb3Sn superconducting cable 102, and together with the continuous conductive filler 107, it forms an auxiliary conductive and shunt solidification structure around the multi-core round cable type Nb3Sn superconducting cable 102.

[0026] The continuous conductive filler 107 is filled and disposed inside the conductive sleeve 101, in the outer peripheral gap of the multi-core round cable type Nb3Sn superconducting cable 102, and between the outer side of the conductive sleeve 101 and the conductive support 201.

[0027] Furthermore, the multi-core round cable type Nb3Sn superconducting cable 102 is located within the concentric accommodating area of ​​the main cable enclosed by the auxiliary superconducting conductor layer 103, and is located inside the continuous conductive filler 107.

[0028] Preferably, the auxiliary superconducting conductor layer 103 is composed of multiple NbTi superconducting wires, the specific number of which can be adjusted according to the working conditions. They are arranged at least part of the circumferential spacing along the multi-core round cable type Nb3Sn superconducting cable 102. At the same time, the first NbTi superconducting wires 10301-10312 are all located inside the continuous conductive filler 107 and are closely attached to the inner surface of the conductive sleeve 101.

[0029] When the auxiliary superconducting conductor layer is arranged along part of the circumferential direction of the multi-core round cable type Nb3Sn superconducting cable 102, as long as it forms an auxiliary current shunting path electrically connected to the multi-core round cable type Nb3Sn superconducting cable 102 and meets the predetermined current carrying conditions, it can still achieve the corresponding current shunting and reduction of local current density.

[0030] Furthermore, the conductive support base 201 has a connector slot 205 on one side and a connection hole 206 at the bottom. An insulating gasket 202 for electrical insulation is arranged at the connection between the bottom of the conductive support base 201 and the external bearing structure. The connector 204 passes through the insulating sleeve 203 and the connection hole 206 at the bottom of the conductive support base 201 to connect the magnet connector support assembly to the external bearing structure. The connector slot 205 and the conductive sleeve 101 are joined by continuous conductive filler 107.

[0031] Furthermore, the conductive sleeve 101 has a circular internal slot at its center that is slightly larger than the combination of the multi-core circular cable type Nb3Sn superconducting cable 102 and the auxiliary superconducting conductor layer 103; the conductive sleeve 101 has one or more material introduction portions on its outer side, and the multiple material introduction portions may be a first material introduction portion 1011, a second material introduction portion 1012, a third material introduction portion 1013, and a fourth material introduction portion 1014.

[0032] Furthermore, the connector slot 205 on the conductive support 201 is a rectangular or U-shaped slot, and the edge of the connector slot 205 is chamfered or rounded; the bottom of the conductive support 201 is chamfered or rounded; the bottom of the conductive support 201 has a reinforcing rib or reinforcing block; the connector slot 205 is opened on the conductive support 201, the opening direction of the connector slot 205 is consistent with the magnet wire exit direction, and the opening size of the connector slot 205 is flush with the conductive sleeve 101.

[0033] Furthermore, the first conductive filler material 104 and the second conductive filler material 105 are low-melting-point solders or other compatible conductive filler materials; they can be the same or have similar melting temperatures. The continuous conductive filler 107 refers to a filling structure in which the first conductive filler material 104 and the second conductive filler material 105 are remelted and bonded together in the interface region to form a continuous conductive path.

[0034] like Figure 4 As shown, the present invention also discloses a method for preparing the above-mentioned multi-core round cable type Nb3Sn magnet low resistance connector, comprising the following steps:

[0035] S1, the insulating pad 202 is placed at the connection of the external bearing structure to provide electrical insulation for the bottom of the overall connector; the connector 204 passes through the insulating sleeve 203 and is locked in the connection hole 206 at the bottom of the conductive support base 201 to rigidly fix the magnet connector support assembly on the external bearing structure, thus completing the construction of the peripheral limiting support frame.

[0036] S2, the removable occupier 106 is axially placed inside the center of the conductive sleeve 101. The spatial dimensions of the removable occupier 106 match the outer envelope of the multi-core round cable type Nb3Sn superconducting cable 102 to reserve a main cable channel. The auxiliary superconducting conductor layer 103 is placed on the circumferential outer side of the removable occupier 106, and the first conductive filler material 104 in a molten state is poured in through one or more material introduction portions opened on the outside of the conductive sleeve 101 to solidify and lock the relative spatial position between the auxiliary superconducting conductor layers 103. After the first conductive filler material 104 has solidified, the removable occupier 106 is pulled out axially to leave a hollow central channel in the center of the conductive sleeve 101.

[0037] S3, the multi-core round cable type Nb3Sn superconducting cable 102 is axially inserted into the hollow central channel formed by removing the removable occupier 106 inside the conductive sleeve 101, so that the multi-core round cable type Nb3Sn superconducting cable 102 is confined to the surrounding center of the auxiliary superconducting conductor layer 103; then the entire assembly is moved into the joint slot 205 of the conductive support 201, and the second conductive filler material 105 in a molten state is injected again into the installation gap between the conductive sleeve 101 and the conductive support 201, and into the cable gaps of the hollow central channel; during injection, the high temperature heat of the second conductive filler material 105 guides the cold solidified first conductive filler material 104 to remelt and integrate, so as to achieve electrical and mechanical filling and solidification, and complete the assembly of the entire joint.

[0038] Furthermore, in S2, the removable spacer 106 is a metal, ceramic, graphite, or composite material mandrel that is resistant to solder pouring temperature, and the outer surface of the removable spacer 106 is provided with a release layer, an anti-sticking structure layer, or a low surface energy isolation layer to reduce the interfacial frictional resistance when the removable spacer 106 is pulled out axially, and to prevent the removable spacer 106 from physically adhering to the first conductive filler material 104 after it has been cooled and solidified.

[0039] Further, in step S3, the injection temperature and holding time of the second conductive filler material 105 are configured to cause the first conductive filler material 104 to remelt in the interface region without causing irreversible degradation of the critical current of the multi-core round cable type Nb3Sn superconducting cable 102, thereby limiting the multi-core round cable type Nb3Sn superconducting cable 102 from suffering abnormal temperature rise thermal damage. The injection temperature of the second conductive filler material is higher than the solidus temperature of the first conductive filler material, causing the first conductive filler material to undergo local remelting at least in the interface region adjacent to the second conductive filler material; at the same time, by limiting the heat source temperature, holding time, and cumulative heat input in the joint region, the temperature-time history of the Nb3Sn superconducting cable is kept below the thermal damage conditions that would cause irreversible degradation of its critical current. The degree of remelting is evaluated based on the interface continuity between the first and second conductive filler materials and whether there is a penetrating unbonded region in the interface region; the degree of thermal damage is judged by the fact that the critical current reduction rate of the Nb3Sn superconducting cable before and after treatment does not exceed a preset allowable value.

[0040] Example 1:

[0041] like Figure 1 , Figure 2 , Figure 3 and Figure 5 As shown, a multi-core round cable type Nb3Sn magnet low-resistance connector of this embodiment includes: a magnet connector, including a conductive sleeve 101, a multi-core round cable type Nb3Sn superconducting cable 102 located in the internal slot of the conductive sleeve 101, an auxiliary superconducting conductor layer 103 arranged circumferentially around the entire outer periphery of the multi-core round cable type Nb3Sn superconducting cable 102, and a continuous conductive filler 107 formed by remelting and bonding a first conductive filler material 104 and a second conductive filler material 105; before assembly, the connector also includes a removable placeholder 106 housed in the center of the conductive sleeve 101 to reserve a main cable channel. The magnet connector support assembly includes a conductive support base 201 having a connector slot 205 and connection holes 206 at both ends, an insulating gasket 202 disposed outside the conductive support base 201, an insulating sleeve 203 disposed in the connection hole 206, and a connector 204. In this embodiment, the conductive sleeve 101 is a copper sleeve, the auxiliary superconducting conductor layer 103 is an NbTi superconducting conductor layer, the first material introduction part 1011-the fourth material introduction part 1014 are solder filling grooves, the conductive support base 201 is a connector support copper base, the connector 204 is a fastening screw, and the connecting hole 206 is a bolt hole.

[0042] In this embodiment, the first conductive filler material and the second conductive filler material are soldered and remelted to form a continuous conductive filler; the auxiliary superconducting conductor layer 103 is arranged at intervals along the circumference of the multi-core round cable type Nb3Sn superconducting cable 102, forming an auxiliary conductive and current shunting structure around the multi-core round cable type Nb3Sn superconducting cable 102. The continuous conductive filler 107 is formed by step-by-step injection and remelting. The first conductive filler material 104 is injected into the gap between the inner surface of the conductive sleeve 101 and the outer superconducting wires to rigidly lock the initial spatial position of the wires. The second conductive filler material 105 is injected into the remaining space inside the conductive sleeve 101, the internal strand gap of the multi-core round cable type Nb3Sn superconducting cable 102, and between the outer wall of the conductive sleeve 101 and the inner groove wall of the conductive support 201. The second conductive filler material 105 and the first conductive filler material 104 are in a remelted integrated state at the interface to provide mechanical rigidity and reduce interlayer contact thermal resistance.

[0043] like Figure 3 As shown, the multi-core round cable type Nb3Sn superconducting cable 102 is concentrically arranged within the central main cable concentric accommodating area surrounded by the auxiliary superconducting conductor layer 103, and is completely wrapped and confined inside the continuous conductive filler 107.

[0044] In a preferred embodiment of the present invention, the auxiliary superconducting conductor layer 103 is composed of multiple NbTi superconducting wires with the same or similar geometric dimensions, the specific number of which can be adjusted according to the working conditions. These NbTi superconducting wires are arranged in a uniform angular displacement span, spaced apart and forming a complete circle around the outer wall of the multi-core circular cable-type Nb3Sn superconducting cable 102, and are all located within the inner filling layer of the continuous conductive filler 107. The outer cylindrical surface of each NbTi superconducting wire is in close contact with the inner surface of the conductive sleeve 101.

[0045] Combination Figure 1 and Figure 2 As shown, the conductive support base 201 has an axially formed connector slot 205 on one side, and the conductive support base 201 has symmetrically formed connecting holes 206 on the outer ear of its bottom. Insulating gaskets 202 for blocking conventional circulating current and leakage current are fitted onto the outer surface of the bottom and side of the conductive support base 201 where it connects to the external magnet frame. During peripheral assembly, the connector 204 passes sequentially through the insulating sleeve 203 and the connecting hole 206 at the bottom of the conductive support base 201 to securely and rigidly thread the magnet connector support assembly onto the magnet frame, providing a rated pre-tightening constraint force. The connector slot 205 and the conductive sleeve 101 are joined by a continuous conductive filler 107.

[0046] like Figure 1 As shown, the conductive sleeve 101 has a circular internal slot at its center, with a geometric dimension slightly larger than the outer envelope of each internal conductive composite wire, for concentrically accommodating the multi-core round cable type Nb3Sn superconducting cable 102 and the auxiliary superconducting conductor layer 103 surrounding it. One or more material inlet portions are evenly spaced along the axial direction on the outer side of the conductive sleeve 101. These material inlet portions connect the inner and outer walls of the sleeve and serve as channels for the inflow of external molten solder material during the manufacturing process.

[0047] In this embodiment, the connector slot 205 on the conductive support 201 is a rectangular slot or a U-shaped slot, and the edge of the connector slot 205 is provided with a chamfer or rounded structure to eliminate shear stress concentration. The side edges of the bottom of the conductive support 201 are also symmetrically provided with the same chamfer or rounded structure. Furthermore, in order to resist extreme excitation stress fluctuations, an integrally extended reinforcing rib or reinforcing block is provided on the outer side wall of the bottom of the conductive support 201. The slotting direction of the connector slot 205 is completely consistent with the end wire exit direction of the superconducting magnet, and the slotting size of the connector slot 205 is configured so that the upper surface of the assembled slot is completely flush with the outer edge of the conductive sleeve 101.

[0048] Example 2:

[0049] The preparation method of the above-mentioned multi-core round cable type Nb3Sn magnet low resistance connector includes:

[0050] S1, Rigid erection of the outer support frame: The insulating pad 202 is placed at the connection of the magnet frame to provide electrical insulation for the bottom of the overall connector; the connector 204 passes through the insulating sleeve 203 and is locked in the connection hole 206 at the bottom of the conductive support base 201 to rigidly fix the magnet connector support assembly on the magnet frame, thus completing the erection of the outer limiting support frame.

[0051] S2, Initial Soldering and Channel Reservation of the Sleeve: The removable occupant 106 is axially placed inside the center of the conductive sleeve 101. The spatial dimensions of the removable occupant 106 match the outer envelope of the multi-core round cable type Nb3Sn superconducting cable 102 to reserve a main cable channel. The auxiliary superconducting conductor layer 103 is placed on the circumferential outer side of the removable occupant 106, and the first conductive filler material 104 in a molten state is poured in through several material introduction parts opened on the outside of the conductive sleeve 101 to solidify and lock the relative spatial position between the auxiliary superconducting conductor layers 103. After the first conductive filler material 104 has solidified, the removable occupant 106 is pulled out axially to leave a hollow central channel in the center of the conductive sleeve 101.

[0052] S3, Main cable insertion and secondary remelting and filling assembly: The multi-core round cable type Nb3Sn superconducting cable 102 is inserted axially into the hollow central channel formed by removing the removable occupier 106 inside the conductive sleeve 101, so that the multi-core round cable type Nb3Sn superconducting cable 102 is confined to the surrounding center of the auxiliary superconducting conductor layer 103; then the entire assembly is moved into the joint slot 205 of the conductive support 201, and the second conductive filler material 105 in a molten state is injected again into the installation gap between the conductive sleeve 101 and the conductive support 201, and into the cable strand gaps of the hollow central channel; during injection, the high temperature heat of the second conductive filler material 105 guides the cold solidified first conductive filler material 104 to remelt and integrate, so as to achieve filling and solidification at the electrical and mechanical levels, and complete the filling, solidification and assembly of the entire multi-core round cable type Nb3Sn magnet low resistance joint.

[0053] Using the aforementioned step-by-step injection method, the first injection is completed before the multi-core round cable-type Nb3Sn superconducting cable is inserted. This fills the gap between the inner side of the conductive sleeve and the auxiliary superconducting conductor layer, and fixes the circumferential position of each auxiliary superconducting conductor. The second injection is performed after the placeholder is removed and the multi-core round cable-type Nb3Sn superconducting cable is inserted. This fills the gaps between the main cable strands, the gap between the main cable and the auxiliary superconducting conductor layer, and the installation gap on the outer side of the conductive sleeve. The heat input generated by the second injection causes the first conductive filler material to undergo local remelting, at least in the interface region adjacent to the second conductive filler material. This reduces the risk of forming a through-hole unbonded area in the interface region and facilitates the formation of a continuous conductive path between the first and second conductive filler materials. The aforementioned step-by-step grouting does not involve repeated welding of the same connection part. The first grouting is used to fix the auxiliary superconducting conductor layer and reserve the main cable channel before the main cable is inserted. The second grouting is used to fill the remaining gap after the main cable is inserted, and the conductive filling materials formed before and after are connected into a continuous conductive filling body through local remelting of the junction area.

[0054] In a preferred embodiment of this invention, the first conductive filler material 104 and the second conductive filler material 105 are low-melting-point solders, and the two are the same solder or solders with similar melting points.

[0055] In a preferred embodiment of this example, in step S2, the removable spacer 106 is a metal, ceramic, graphite, or composite material mandrel that is resistant to solder pouring temperature, and the outer surface of the removable spacer 106 is provided with a release layer, an anti-sticking structure layer, or a low surface energy isolation layer to reduce the interfacial frictional resistance when the removable spacer 106 is pulled out axially, and to prevent the removable spacer 106 from physically adhering to the first conductive filler material 104 after it has been cooled and solidified.

[0056] In a preferred embodiment of this invention, in step S3, the injection temperature and holding time of the second conductive filler material 105 are configured to cause the first conductive filler material 104 to remelt in the interface region without causing irreversible degradation of the critical current of the multi-core round cable type Nb3Sn superconducting cable 102, thereby limiting the multi-core round cable type Nb3Sn superconducting cable 102 from suffering abnormal temperature rise thermal damage. In this embodiment, the injection temperature of the second conductive filler material 105 is higher than the solidus temperature of the first conductive filler material 104, causing the already solidified first conductive filler material 104 to undergo local remelting at least in the interface region adjacent to the second conductive filler material 105. Simultaneously, by limiting the introduction temperature, holding time, and cumulative heat input of the second conductive filler material 105, the temperature-time history experienced by the multi-core round cable type Nb3Sn superconducting cable 102 is lower than the thermal damage conditions that would cause irreversible degradation of its critical current. The degree of remelting is evaluated based on the interfacial continuity between the first and second conductive filler materials and the presence of unbonded areas at the interface. The degree of thermal damage is judged by the critical current reduction rate of the multi-core round cable type Nb3Sn superconducting cable 102 before and after treatment not exceeding a preset allowable value. The above criteria are used to determine the allowable process window for the injection temperature, holding time, and cumulative heat input of the second conductive filler material (105).

[0057] Excitation tests were conducted at a liquid helium temperature of 4.2 K and a background magnetic field of 8 T. The equivalent contact resistances of the two channels were measured to be 5.82 nΩ and 5.48 nΩ, respectively, indicating that the connector has low resistance conductivity.

[0058] like Figure 6 As shown, the voltage-current characteristics of the multi-core circular cable type Nb3Sn magnet low resistance connector prepared according to this embodiment were tested at a liquid helium temperature of 4.2 K and a steady-state background magnetic field of 8 T, with the excitation current ranging from 100 A to 600 A. Figure 6The horizontal axis represents the excitation current in A; the vertical axis represents the measured voltage in μV. The gray square data points and red circular data points represent the measured results of the two measurement channels, Signal 1 and Signal 2, respectively, and the red and blue straight lines represent the corresponding linear fitting results.

[0059] Figure 6 In the diagram, "Model Line" indicates the use of a linear fitting model with the fitting equation y = A + B × x, where x represents the excitation current, y represents the measured voltage, A represents the y-intercept of the fitted line in μV, and B represents the slope of the fitted line in μV / A. B and C in the "Plotting" section are identifiers for the fitted data sequences, and their meanings differ from the fitting parameter B. The fitting intercepts for signal 1 and signal 2 are -2.4784411247 μV and -3.8595716301 μV, respectively, with fitting slopes of 0.0058240495 μV / A and 0.0054771572 μV / A, respectively. The fitting intercept characterizes the constant bias in the measured voltage, which does not affect the fitting slope. Based on the conversion of 1 μV / A = 1000 nΩ, the equivalent contact resistances of the connectors for the two measurement channels are approximately 5.82 nΩ and 5.48 nΩ, respectively.

[0060] Figure 6 In the figure, "R-squared (COD)" is the coefficient of determination, used to evaluate the degree of explanation of the linear model for the measurement data. The values ​​for the two measurement channels are 0.9940883402 and 0.9912414993, respectively. "Adjusted R-squared" is the coefficient of determination after considering the sample size and the number of fitting parameters, with values ​​of 0.9926104252 and 0.9890518741, respectively. "Reduced Chi-Sqr" is the reduced chi-square statistic, whose calculation is related to the weights and degrees of freedom used in the fitting. The values ​​for the two measurement channels are 0.0087549033 and 0.0115047582, respectively. The above fitting results show that under the test conditions of this embodiment, the voltage and current of the two measurement channels have a good linear relationship, and the multi-core round cable type Nb3Sn magnet low-resistance connector exhibits a nano-ohm equivalent contact resistance.

[0061] Matters not covered in this invention are common knowledge.

[0062] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multi-core round cable type Nb3Sn magnet low-resistance connector, characterized in that, include: A magnet connector includes: a conductive sleeve, a multi-core round cable type Nb3Sn superconducting cable located in a slot inside the conductive sleeve, auxiliary superconducting conductor layers arranged circumferentially along the multi-core round cable type Nb3Sn superconducting cable, and a continuous conductive filler formed by remelting and bonding a first conductive filler material and a second conductive filler material. A magnet connector support assembly includes: a conductive support base having a connector slot and connection holes at both ends; an insulating gasket disposed outside the conductive support base; an insulating sleeve disposed within the connection holes; and a connector; an auxiliary superconducting conductor layer is arranged around at least a portion of the circumference of the multi-core round cable type Nb3Sn superconducting cable, forming a concentrically encased auxiliary conductive and shunt structure around the multi-core round cable type Nb3Sn superconducting cable; and a continuous conductive filler is filled and disposed inside the conductive sleeve, in the outer peripheral gap of the multi-core round cable type Nb3Sn superconducting cable, and between the outer side of the conductive sleeve and the conductive support base.

2. The multi-core round cable type Nb3Sn magnet low resistance connector according to claim 1, characterized in that: The multi-core round cable type Nb3Sn superconducting cable is located within the concentric containment area of ​​the main cable enclosed by the auxiliary superconducting conductor layer and is located inside the continuous conductive filler. The auxiliary superconducting conductor layer is composed of several NbTi superconducting wires of the same size, which are arranged around the outer periphery of the multi-core round cable type Nb3Sn superconducting cable in at least part of the circumference, and each of the NbTi superconducting wires is located inside the continuous conductive filler and is closely attached to the inner surface of the conductive sleeve.

3. The multi-core round cable type Nb3Sn magnet low resistance connector according to claim 1, characterized in that: The conductive support base has a connector slot on one side and a connection hole at the bottom. An insulating pad for electrical insulation is provided at the connection between the bottom of the conductive support base and the external bearing structure. The connector passes through the insulating sleeve and the connection hole at the bottom of the conductive support base to connect the magnet connector support assembly and the external bearing structure. The connector slot and the conductive sleeve are joined by continuous conductive filler.

4. The multi-core round cable type Nb3Sn magnet low resistance connector according to claim 1, characterized in that: The first conductive filler material and the second conductive filler material are both low-melting-point solders, and they are the same solder.

5. A multi-core round cable type Nb3Sn magnet low resistance connector according to claim 2, characterized in that: The conductive sleeve has an internal slot at its center that is larger than the combination of the multi-core round cable type Nb3Sn superconducting cable and the auxiliary superconducting conductor layer; one or more material introduction portions are provided on the outer side of the conductive sleeve.

6. A multi-core round cable type Nb3Sn magnet low resistance connector according to claim 3, characterized in that: The connector slot on the conductive support base is a rectangular or U-shaped slot, and the edge of the connector slot is chamfered or rounded; the bottom of the conductive support base is chamfered or rounded; the bottom of the conductive support base has a reinforcing rib or reinforcing block; the connector slot is opened on the conductive support base, the slot opening direction is consistent with the magnet outlet direction, and the slot opening size is flush with the conductive sleeve.

7. A method for preparing a multi-core round cable type Nb3Sn magnet low-resistance connector according to any one of claims 1-6, characterized in that, Includes the following steps: S1. The insulating pad is placed at the connection of the external bearing structure to provide electrical insulation for the bottom of the overall connector; the connector passes through the insulating sleeve and is locked in the connection hole at the bottom of the conductive support base to rigidly fix the magnet connector support assembly on the external bearing structure, thus completing the construction of the peripheral limiting support frame. S2. A removable spacer is placed axially inside the center of the conductive sleeve. The spatial dimensions of the removable spacer are matched with the outer envelope of the multi-core round cable type Nb3Sn superconducting cable to reserve a main cable channel. The auxiliary superconducting conductor layer is placed on the circumferential outside of the removable spacer, and the first conductive filler material in a molten state is poured in through one or more material introduction parts opened on the outside of the conductive sleeve to solidify and lock the relative spatial position between the auxiliary superconducting conductor layers. After the first conductive filler material has cooled and solidified, the removable spacer is pulled out axially to leave a hollow central channel in the center of the conductive sleeve. S3. The multi-core round cable type Nb3Sn superconducting cable is axially inserted into the hollow central channel formed by removing the removable spacer in the conductive sleeve, so that the multi-core round cable type Nb3Sn superconducting cable is confined to the center of the auxiliary superconducting conductor layer; then the entire assembly is moved into the joint slot of the conductive support, and the second conductive filler material in a molten state is injected again into the installation gap between the conductive sleeve and the conductive support, and into the cable gap of the hollow central channel; during injection, the high temperature heat of the second conductive filler material guides the cold solidified first conductive filler material to remelt and bond together to form the continuous conductive filler body, so as to achieve filling and solidification at the electrical and mechanical levels, and complete the assembly of the entire multi-core round cable type Nb3Sn magnet low resistance connector.

8. The preparation method according to claim 7, characterized in that: In step S2, the removable spacer is a metal, ceramic, graphite, or composite material mandrel that is resistant to solder pouring temperature, and the outer surface of the removable spacer is provided with a release layer, an anti-sticking structure layer, or a low surface energy isolation layer to reduce the interfacial frictional resistance when the removable spacer is pulled out axially and to prevent the removable spacer from physically adhering to the first conductive filler material after it has been cooled and solidified.

9. The method for preparing a multi-core round cable type Nb3Sn magnet low-resistance connector according to claim 7, characterized in that: In step S3, the injection temperature of the second conductive filler material is higher than the solidus temperature of the first conductive filler material, causing the first conductive filler material to undergo local remelting at least in the interface region adjacent to the second conductive filler material.

10. The method for preparing a multi-core round cable type Nb3Sn magnet low-resistance connector according to claim 9, characterized in that: The injection temperature, heat preservation time, and cumulative heat input of the joint area of ​​the second conductive filler material are limited to ensure that the temperature-time history of the multi-core round cable type Nb3Sn superconducting cable is below the thermal damage conditions that cause irreversible degradation of its critical current.

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