A device for continuous application of large stress loads at low temperatures using superconducting coils

Abstract

The application discloses a device for continuously applying large stress load at low temperature by using a superconducting coil, which is connected with a shell, and a circular boss in the middle of the base is used for limiting a lower circular disc coil; a pressing plate is placed above an upper circular disc coil, a circular boss in the middle of the lower part of the pressing plate is used for limiting the upper circular disc coil, the pressing plate is connected with a piston, and a top block is placed above the piston, contacts with a sample and applies pressure. The upper and lower circular disc coils are wound on a stainless steel framework by using wet winding or dry winding impregnation of NbTi superconducting wire. When the upper and lower circular disc coils pass through opposite currents to generate electromagnetic repulsion, the upper circular disc coil is pushed upward, and the pressure is transmitted to the top block through the pressing plate and the piston, so that the pressure is applied to the sample. The electromagnetic repulsion generated by the superconducting coil can continuously apply large stress load to the test sample at low temperature, the device principle is simple, the operation is simple, the applied load range is large, the stability is good, the uniformity is high, and the device provides a new type of low-temperature stress continuous loading device for critical performance stress dependence measurement of various types of superconducting cables.

Description

Technical Field

[0001] This invention relates to the field of stress dependence measurement of critical properties of low-temperature superconducting conductors, specifically a device that uses a superconducting coil to continuously apply large stress loads at low temperatures. Background Technology

[0002] In recent years, with the development of superconducting technology, particle accelerators and fusion magnets require stable superconducting materials to obtain higher magnetic fields. Critical current (Ic) c The critical current is one of the important properties for evaluating the performance of superconducting materials, and temperature and magnetic field have a certain influence on the critical current. Currently, NbTi and Nb3Sn are still the main superconducting materials for large-scale superconducting applications. NbTi is a tough material that is easy to process, and many magnets in the past were made of NbTi, but its critical current is poor, making it difficult to obtain higher magnetic fields. The critical current of Nb3Sn is significantly higher than that of NbTi. Therefore, to obtain higher magnetic fields, brittle Nb3Sn or new practical high-temperature superconducting materials (MgB2, Bi-2212, YBCO, etc.) must be selected. However, due to technical and commercial reasons, new practical high-temperature superconducting materials have not yet been widely used. Therefore, Nb3Sn must be selected for superconducting applications with higher fields.

[0003] Nb3Sn superconducting wires are not monolithic structures but need to be embedded in ordinary metal structures to achieve higher mechanical properties and thermal stability. With technological advancements, different wire manufacturing techniques have been used in production. Currently, the main manufacturing techniques used for producing commercial Nb3Sn superconducting wires include the bronze process, PIT, and RRP. All Nb3Sn must undergo heat treatment to induce an internal material reaction and generate a superconducting phase. To avoid excessive self-inductance, multi-strand superconducting wires are typically used to create superconducting cables for the development of large superconducting magnets. For example, accelerator magnets mostly use Rutherford cables, which have a twisted structure that allows for complete superconductor transposition. Rutherford cables offer advantages such as high current density, good mechanical strength, compact winding structure, and low coil circulating current loss. The critical performance of heat-treated Nb3Sn is highly sensitive to stress and strain. Under high fields, it is subject to electromagnetic, mechanical, and thermal stresses, typically resulting in performance degradation. Therefore, it is necessary to experimentally apply continuous stress to Nb3Sn materials / conductors to simulate their operational stress state and evaluate the stress dependence of their critical performance.

[0004] Currently, various measurement technologies are developing rapidly, resulting in numerous methods for applying loads to Nb3Sn Rutherford cables. However, these methods are limited by structural dimensions, making continuous stress loading at low temperatures impossible, and the load application process is cumbersome and difficult to operate. This invention develops a device that utilizes the electromagnetic repulsion of superconducting coils to achieve continuous application of large stress loads at low temperatures. This device can apply continuous, large-range loads to Nb3Sn Rutherford cable test samples in an extremely low temperature environment (4.2K), and can accurately measure the load magnitude. This simplifies the load application procedure, shortens the testing time, and increases the load loading range. Simultaneously, by using extensometers and strain gauges to jointly measure the applied load magnitude, the accuracy of load measurement is improved, providing key infrastructure for the study of critical performance degradation of Nb3Sn Rutherford cables under transverse stress loads. Summary of the Invention

[0005] The purpose of this invention is to provide a device for continuously applying large stress loads at low temperatures using the electromagnetic repulsion of superconducting coils. This low-temperature electromagnetic continuous pressurization device can continuously apply loads to Nb3Sn Rutherford cable test samples in an extremely low temperature (4.2K) environment and can accurately measure the load magnitude.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A device for continuously applying high-stress loads at low temperatures using superconducting coils:

[0008] The device includes a base, an upper disc coil, a lower disc coil, a pressure plate, a housing, a piston, a top block, an extensometer, and a strain gauge;

[0009] The upper and lower circular coils are superconducting coils; the base is bolted to the outer shell, and a circular boss is provided in the middle of the base to limit the lower circular coil; the pressure plate is placed above the upper circular coil, and a circular boss is also provided in the middle of the lower part of the pressure plate to limit the upper circular coil; the pressure plate is bolted to the piston, and the top block is placed above the piston, in contact with the sample and applying pressure.

[0010] When reverse currents are applied to the upper and lower disc coils, electromagnetic repulsion is generated. The upper disc coil is pushed upwards and transmitted to the top block through the pressure plate and piston, thereby continuously applying pressure to the sample. The displacement change of the pressure plate is detected by an extensometer, and the strain at both ends of the top block is detected by a strain gauge. The stress value applied to the sample is calculated by combining the input current of the lower disc coil and the self-weight of the upper disc coil, pressure plate, piston, and top block, and the uniformity of the applied stress is monitored in real time.

[0011] Furthermore, the base, pressure plate, outer shell, and top block are made of stainless steel.

[0012] Furthermore, the base, pressure plate, outer shell, and top block are made of 304 stainless steel.

[0013] Furthermore, the piston material is carbon fiber. Compared to stainless steel, carbon fiber has a lower density and higher strength, while also maintaining good strength even at extremely low temperatures.

[0014] Furthermore, the upper and lower disc coils are constructed by winding NbTi superconducting wire onto a stainless steel frame using wet or dry winding impregnation. The NbTi superconducting wire is in a superconducting state at an extremely low temperature of 4.2K, exhibiting no heat loss and higher current-carrying capacity compared to conventional resistance coils. When a reverse current is applied to the upper and lower disc coils at this temperature, electromagnetic repulsion is generated, causing the upper disc coil to be lifted. The pressure is then transmitted upwards to the top block via the pressure plate and piston.

[0015] Furthermore, the top block is made of 316 stainless steel and has rounded corners to avoid stress concentration during the application of pressure to the test sample.

[0016] Furthermore, the extensometer is mounted on the pin passing through the upper disc coil to measure the relative displacement caused by electromagnetic repulsion when the upper and lower disc coils are energized. The electromagnetic repulsion generated by the upper and lower disc coils after energization is calculated in combination with the energizing current. The weight of the pressure plate, piston, and top block is subtracted to obtain the pressure value applied to the sample surface.

[0017] Furthermore, two strain gauges are installed on both sides of the top block. When the upper and lower disc coils are energized with opposite currents to generate electromagnetic repulsion, the force is transmitted to the top block through the pressure plate and piston, and then applied to the surface of the test sample. When the top block is subjected to force, it will produce a small deformation. The strain gauges calculate the magnitude of the force on the top block by measuring the small deformation produced by the top block, that is, the magnitude of the load applied to the test sample, and at the same time determine the uniformity of the pressure.

[0018] Furthermore, the load applied to the test sample is obtained by measuring and calculating the load using strain gauges and extensometers respectively, thus providing load measurement accuracy and precision.

[0019] The beneficial effects of this invention are as follows: This invention utilizes the electromagnetic repulsion generated by a superconducting coil to continuously apply large stress loads to test samples at low temperatures. The device has a simple principle, is easy to operate, and has a large applied load range, good stability, and high uniformity. It provides a novel low-temperature continuous stress loading device for measuring the stress dependence of critical performance of various types of superconducting cables. Attached Figure Description

[0020] Figure 1 This is a structural diagram of a device that utilizes the electromagnetic repulsion of superconducting coils to continuously apply high stress loads at low temperatures.

[0021] In the diagram: 1-Strain gauge, 2-Top block, 3-Outer shell, 4-Piston, 5-Extensometer, 6-Pressure plate, 7-Upper disc coil, 8-Lower disc coil, 9-Base. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] like Figure 1 As shown, a device for continuously applying high stress loads at low temperatures using the electromagnetic repulsion of superconducting coils includes a base 9, an upper circular coil 7, a lower circular coil 8, a pressure plate 6, a housing 3, a piston 4, a top block 2, an extensometer 5, and a strain gauge 1. The base 9, pressure plate 6, housing 3, and top block 2 are made of stainless steel. The base 9 is bolted to the housing 3. A circular boss in the middle of the base 9 limits the movement of the lower circular coil 8. The pressure plate 6 is placed above the upper circular coil 7, and a circular boss in the middle of the lower part of the pressure plate 6 limits the movement of the upper circular coil 7. The pressure plate 6 is bolted to the piston 4. The top block 2 is placed above the piston 4, contacting the sample and applying pressure. The upper and lower circular coils 7 and 8 are made of NbTi superconducting wire wound onto a stainless steel frame using wet or dry winding impregnation. When a reverse current is applied to the upper and lower circular coils 7 and 8, electromagnetic repulsion is generated. The upper circular coil 7 is pushed upwards, and this force is transmitted through the pressure plate 6 and piston 4 to the top block 2, thereby continuously applying pressure to the sample. The displacement change z of the pressure plate 6 is detected by extensometer 5, and the deformation ∈ at both ends of the top block 2 is detected by strain gauge 1. Combined with the input current of the superconducting coil and the self-weight of the upper circular coil 7, pressure plate 6, piston 4, and top block 2, the stress value applied to the sample can be calculated according to the formula:

[0024] σ=∈×E

[0025] Where σ represents the internal stress of the top block 2 under the repulsive force transmitted upward by the piston 4, ∈ represents the strain of the top block 2 as measured by the strain gauge, and E is the elastic modulus of the top block 2 under this condition. This formula allows for the calculation of the internal stress of the top block 2 under load. Furthermore, since the top block 2 is only subjected to an upward force, the internal stress of the top block 2 is equal to the pressure generated by the thrust of the piston 4. Based on the area of ​​the top block 2, the magnitude of the upward force can then be calculated. Strain gauges on both sides of the top block 2 can monitor the uniformity of the applied stress in real time.

[0026] Then, according to the formula:

[0027]

[0028] Where F is the electromagnetic repulsive force generated by the upper circular coil 7 and the lower circular coil 8 being energized, I is the magnitude of the current flowing through the upper circular coil 7 and the lower circular coil 8, and M... 12Let z be the mutual inductance between the upper circular coil 7 and the lower circular coil 8, z be the displacement measured by the extensometer, m be the mass of the pressure plate 6 and the piston 4, and g be the acceleration due to gravity. The magnitude of the electromagnetic repulsion can be calculated using this formula.

[0029] The base 9, pressure plate 6, outer shell 3, and top block 2 are made of 304 stainless steel.

[0030] The piston 4 is made of carbon fiber, which has a lower density and higher strength than stainless steel, and can maintain good strength even in extremely low temperature environments.

[0031] The upper and lower circular coils 7 and 8 are made of NbTi superconducting wire wound on a stainless steel frame using wet or dry winding impregnation. The NbTi superconducting wire is in a superconducting state at an extremely low temperature of 4.2K. Compared with conventional resistance coils, it has no heat loss and a higher current carrying capacity. When a reverse current is applied to the upper and lower circular coils 7 and 8, an electromagnetic repulsion force is generated, and the upper circular coil 7 is lifted up. The pressure is transmitted upward to the top block 2 through the pressure plate 6 and the piston 4.

[0032] The top block 2 is made of 316 stainless steel and has rounded corners to avoid stress concentration during the application of pressure to the test sample.

[0033] The extensometer 5 is installed on the pin that passes through the upper disc coil 7. It is used to measure the relative displacement of the upper and lower disc coils 7 and 8 after they are energized due to electromagnetic repulsion. The electromagnetic repulsion generated by the upper and lower disc coils 7 and 8 after energization is calculated by combining the energizing current. The weight of the pressure plate 6, piston 4 and top block 2 is subtracted to obtain the pressure value applied to the sample surface.

[0034] Two strain gauges 1 are installed on both sides of the top block 2. When reverse currents are applied to the upper and lower circular coils 7 and 8, generating electromagnetic repulsion, the force is transmitted to the top block 2 through the pressure plate 6 and piston 4, and then applied to the surface of the test sample. When the top block 2 is subjected to force, it will produce a small deformation. The strain gauges 1 calculate the magnitude of the force on the top block 2 by measuring the small deformation produced by the top block, that is, the magnitude of the load applied to the test sample, and at the same time determine the uniformity of the pressure application. The calculation formula is as follows:

[0035] σ=∈×E

[0036] Where σ represents the internal stress of the top block 2 under the repulsive force transmitted upward by the piston 4, ∈ represents the strain of the top block 2 as measured by the strain gauge, and E represents the elastic modulus of the top block 2 under this condition. The internal stress of the top block 2 under stress can be calculated using this formula. Furthermore, since the top block is only subjected to a vertically upward force, the internal stress of the top block 2 is equal to the pressure generated by the thrust of the piston 4. The magnitude of the upward force can then be calculated based on the area of ​​the top block 2. Strain gauges on both sides of the top block can monitor the uniformity of the applied stress in real time.

[0037] This invention combines two methods to obtain the load applied to the test sample: measuring the electromagnetic repulsion force F generated by the energization of the upper and lower circular coils 7 and 8, using strain gauge 1 to measure the strain of the top block 2 under pressure and calculating the force on the top block 2, and using extensometer 5 to measure the small upward displacement of the upper circular coil 7 under the electromagnetic repulsion force F and calculating the force on the top block 2. This method can mutually verify the accuracy of the measurements and improve the precision and accuracy of load measurement.

Claims

1. A device for continuously applying high-stress loads at low temperatures using a superconducting coil, characterized in that: The device includes a base, an upper disc coil, a lower disc coil, a pressure plate, a housing, a piston, a top block, an extensometer, and a strain gauge; The upper and lower circular coils are superconducting coils; the base is bolted to the outer shell, and a circular boss is provided in the middle of the base to limit the lower circular coil; the pressure plate is placed above the upper circular coil, and a circular boss is also provided in the middle of the lower part of the pressure plate to limit the upper circular coil; the pressure plate is bolted to the piston, and the top block is placed above the piston, in contact with the sample and applying pressure. When reverse currents are applied to the upper and lower disc coils, electromagnetic repulsion is generated. The upper disc coil is pushed upwards and transmitted to the top block through the pressure plate and piston, thereby continuously applying pressure to the sample. The displacement change of the pressure plate is detected by an extensometer, and the strain at both ends of the top block is detected by a strain gauge. The stress value applied to the sample is calculated by combining the input current of the lower disc coil and the self-weight of the upper disc coil, pressure plate, piston, and top block, and the uniformity of the applied stress is monitored in real time. The extensometer is installed on the pin that passes through the upper disc coil to measure the relative displacement of the upper and lower disc coils due to electromagnetic repulsion after they are energized. The electromagnetic repulsion generated by the upper and lower disc coils after they are energized is calculated by combining the energizing current. The weight of the pressure plate, piston and top block is subtracted to obtain the pressure value applied to the sample surface. Two strain gauges are installed on both sides of the top block. When the upper and lower disc coils are energized with opposite currents to generate electromagnetic repulsion, the force is transmitted to the top block through the pressure plate and piston, and then applied to the surface of the test sample. When the top block is subjected to force, it will produce a small deformation. The strain gauges calculate the magnitude of the force on the top block by measuring the small deformation produced by the top block, that is, the magnitude of the load applied to the test sample, and at the same time determine the uniformity of the pressure.

2. The device for continuously applying high stress loads at low temperatures using a superconducting coil according to claim 1, characterized in that: The base, pressure plate, outer shell, and top block are made of stainless steel.

3. The device for continuously applying high stress loads at low temperatures using a superconducting coil according to claim 2, characterized in that: The base, pressure plate, outer shell, and top block are made of 304 stainless steel.

4. The device for continuously applying high stress loads at low temperatures using a superconducting coil according to claim 1, characterized in that: The piston material is carbon fiber.

5. The device for continuously applying high stress loads at low temperatures using a superconducting coil according to claim 1, characterized in that: The upper and lower circular coils are constructed by winding NbTi superconducting wire onto a stainless steel frame using wet or dry winding impregnation.

6. The device for continuously applying high stress loads at low temperatures using a superconducting coil according to claim 1, characterized in that: The top block is made of 316 stainless steel and has rounded corners.

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