Liquid helium immersion type high field large current superconducting tape / wire critical current testing device and method

Abstract

The application provides a liquid helium immersion type high-field large-current superconducting tape / wire critical current testing device and method, which comprises a substrate, a first electrode, a second electrode and a third electrode; a plurality of limiting grooves are formed on at least one side of the substrate, the limiting grooves comprise narrow grooves and wide grooves; the first electrode, the second electrode and the third electrode are fixed with the substrate, and the first electrode, the second electrode and the third electrode are provided with first electrode grooves, second electrode grooves and third electrode grooves which are the same as the structure of the limiting grooves and are in communication. According to the application, a plurality of test samples can be welded simultaneously by forming a plurality of wide and narrow grooves on multiple sides of the substrate, and the different test samples can be tested in sequence by switching the lines of the first electrode, the second electrode and the third electrode with the external power supply, so that the number of current lead lines is reduced, and the consumption of liquid helium caused by the cooling of the current lead lines is reduced. Simultaneously welding a plurality of to-be-tested samples reduces the number of times of opening the Dewar, and reduces the leakage of liquid helium. The to-be-tested samples are welded in the limiting grooves, the disturbance of the samples caused by the electromagnetic force is reduced, and the measurement signal is more accurate.

Description

Technical Field

[0001] This invention relates to the field of critical performance testing technology for superconducting strips / wires, and in particular to a superconducting strip / wire testing device and method that allows for the introduction of a large current in a high background magnetic field through liquid helium immersion and can measure multiple samples at once. Background Technology

[0002] High magnetic fields are crucial scientific infrastructure platforms for research in physics, materials science, chemistry, and life sciences, as well as interdisciplinary research. Matter can exhibit new properties under these extreme conditions, and the application research of high magnetic field devices catalyzes and promotes high-tech industries. Currently, devices capable of generating the highest steady-state strong magnetic fields are made of internally water-cooled magnets and externally superconducting magnets. High-field water-cooled magnets consume enormous amounts of electricity, and due to cooling system limitations, continuous operation cannot exceed 6 hours. Compared to water-cooled magnetic fields, superconducting magnets, due to their high stability, good uniformity, low energy consumption, and small size, are widely used in high-field magnets, accelerator magnets, magnetic confinement fusion devices, and experimental devices related to medicine, materials science, and biology.

[0003] In large scientific facilities, the magnetic field strength, magnetic field homogeneity, and field resistance of superconducting magnets directly determine the performance of the device. In future large scientific facilities such as those for strong magnetic fields and magnetic confinement fusion, superconducting magnets should possess large apertures and high field strengths. However, limited by the upper critical magnetic field, the low-temperature superconducting materials NbTi and Nb3Sn can only be used in the manufacture of superconducting magnets below 23T. To achieve even higher field strengths, it is necessary to find superconducting materials that can maintain high critical current densities under high fields. Ceramic oxide high-temperature superconducting materials possess extremely high irreversible field strengths in the liquid helium temperature range and still exhibit excellent current-carrying capacity in background magnetic fields above 20T, making them ideal materials for manufacturing high-field magnets.

[0004] Among all high-temperature superconducting materials, Bi₂Sr₂Ca₁Cu₂OX (Bi₂₁₂) is the only one that can be fabricated into isotropic circular wires. Its superconducting electrical properties are independent of the magnetic field angle, making it easy to wind into superconducting magnets of various structures. Furthermore, its multi-core structure effectively avoids magnetic shielding effects. Bi₂₁₂ possesses the circular wire structure of Nb-based superconducting materials, exhibits low hysteresis loss, high RRR value, mature cable fabrication technology, and excellent performance under high fields, making it the most promising high-temperature superconducting material for future applications in high-field magnets.

[0005] Before using Bi2212 superconducting wire to wind coils or manufacture CICC conductors, a detailed study of the wire's properties is necessary, especially its critical performance under high fields. Currently, the experimental Bi2212 superconducting wire is produced by powder in-tube (PIT) heat treatment under high pressure and oxygen. The mechanical properties of the core wire material after heat treatment are close to those of ceramics, making it prone to breakage under external disturbances, severely reducing its critical performance. Superconducting wires experience significant electromagnetic forces under high fields, so disturbances caused by electromagnetic forces must be minimized during testing.

[0006] In the critical performance testing of superconducting wires, the four-lead method is used for measurement.

[0007] The experiment mainly included the testing of the critical current and n value of the superconducting wire at 4.2K under different magnetic fields.

[0008] The test sample is immersed in liquid helium for an electric current test. A reliable and liquid helium-saving test sample plate needs to be designed to fix the test sample, pass DC current through the sample in a certain background magnetic field, test the critical current of the sample, and at the same time reduce the influence of electromagnetic force on sample disturbance. Summary of the Invention

[0009] The technical problem to be solved by this invention is how to save liquid helium when testing samples, speed up the experimental process, and obtain accurate results.

[0010] The present invention solves the above-mentioned technical problems through the following technical means:

[0011] A liquid helium immersion-type high-field, high-current superconducting strip / wire critical current testing device includes a Dewar flask, a flange for sealing the Dewar flask, and a test sample plate. The test sample plate is located inside the Dewar flask. The test sample plate includes a substrate, a first electrode, and a second electrode. Multiple limiting grooves are formed on at least one side of the substrate, including narrow grooves and wide grooves. The first electrode and the second electrode are both fixed to the substrate. The first electrode and the second electrode have first electrode grooves and second electrode grooves with the same structure as the limiting grooves and are connected to each other. After the sample to be tested is placed in the limiting groove, it can form a circuit with the first electrode and the second electrode. The first electrode and the second electrode are connected to an external power source through a current lead passing through the flange. The flange has a liquid helium inlet and a liquid helium return port.

[0012] This invention utilizes multiple slots of varying widths on a substrate to simultaneously weld multiple test samples. By switching the circuitry between the first and second electrodes and an external power supply, different test samples can be tested sequentially. This reduces the number of current leads and minimizes liquid helium consumption caused by lead cooling. Simultaneous welding of multiple test samples also reduces the frequency of inserting and removing the test sample board, thus reducing liquid helium leakage. The test samples are welded within limiting slots, minimizing sample disturbance caused by electromagnetic forces and resulting in more accurate measurement signals.

[0013] Furthermore, the substrate has multiple limiting grooves on both its upper and lower surfaces; it also includes a third electrode; the third electrode is fixed to the substrate and has the same number of third electrode grooves as the limiting groove structure; the first electrode has two first electrode grooves that are connected to the limiting grooves on both sides of the substrate; the second electrode groove and the third electrode groove are respectively connected to the limiting grooves on both sides of the substrate.

[0014] Furthermore, the number of limiting grooves on both sides of the substrate is the same; the number of the first electrodes is the same as the number of limiting grooves on one side of the substrate.

[0015] Furthermore, the first electrode includes a terminal block and a transverse portion fixed to the terminal block. The transverse portion is bolted to the substrate, and first electrode grooves are respectively formed on the upper and lower surfaces of the transverse portion.

[0016] Furthermore, the second and third electrodes have the same structure and are fixed on the upper and lower surfaces of the substrate, respectively. The second / third electrode includes a terminal block and a fixing part. The fixing part is fixed on the upper / lower surface of the substrate and has the same number of second / third electrode slots as the limiting slots on one side of the substrate.

[0017] Furthermore, the narrow slot is located within the wide slot.

[0018] Furthermore, it also includes a transverse groove that penetrates the limiting groove and is deeper than the narrow groove.

[0019] Furthermore, it also includes multiple support plates, which are fixed together by support rods; the support plates have holes for current leads to pass through; one end of the current lead is electrically connected to the first electrode, the second electrode, and the third electrode, and the other end passes through a flange and is connected to an external power source.

[0020] Furthermore, it includes multiple test sample plates, which are stacked and fixed together.

[0021] Corresponding to the above-mentioned device, the present invention also provides a liquid helium immersion method for testing the critical current of high-current superconducting strips / wires under high field conditions, comprising the following steps:

[0022] Step 1. Using the four-lead method for measurement, first place the superconducting tape in the wide slot, or place the superconducting wire in the narrow slot, and electrically connect it to the electrodes at both ends. Pass the voltage signal line through the horizontal slot, wrap it around the sample to be tested, and fix it with solder. Then electrically connect the electrodes to the current lead. Then insert the sample rod into the Dewar.

[0023] Step 2. Connect the flange to the Dewar with bolts and seal it, and then lead the current lead out of the flange and electrically connect it to the external power supply;

[0024] Step 3. Introduce liquid nitrogen into the Dewar to achieve pre-cooling; when the sample temperature drops to 77K, use nitrogen gas to expel the liquid nitrogen inside the Dewar through the hollow stainless steel tube inserted into the bottom of the Dewar; after expelling the liquid nitrogen, introduce liquid helium into the Dewar to lower the sample temperature to 4.2K.

[0025] Step 4. By switching the current lead to connect to the terminals of different first electrodes, the purpose of testing different samples can be achieved.

[0026] The advantages of this invention are:

[0027] This invention utilizes multiple slots of varying widths on a substrate to simultaneously weld multiple test samples. Furthermore, by switching the circuitry between the first and second electrodes and the external power supply, different samples can be tested sequentially. This reduces the number of current leads and minimizes liquid helium consumption due to lead cooling. Simultaneous welding of multiple test samples also reduces the frequency of sample insertion and removal, thus minimizing liquid helium leakage. The test samples are welded within limiting slots, reducing sample disturbance caused by electromagnetic forces and resulting in more accurate measurement signals.

[0028] Because the Dewar is cylindrical, the closer to the Dewar wall, the shorter the sample that can be placed. Therefore, this device saves liquid helium while allowing for double-sided, three-dimensional placement of the sample plate. Samples placed on one side are not placed too close to the substrate edge in pursuit of quantity, resulting in a longer measurable sample length. The longer sample allows for a greater spacing between voltage signal lines and a greater distance between the signal lines and the welding position between the sample and the electrode, leading to more accurate measurements. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall structure of the testing device in Embodiment 1 of the present invention;

[0030] Figure 2 This is a schematic diagram of the sample rod inside the Dewar in Embodiment 1 of the present invention;

[0031] Figure 3 This is a schematic diagram of the lead wire structure between the sample rod and the flange plate in Embodiment 1 of the present invention;

[0032] Figure 4This is a schematic diagram of the test sample plate in Embodiment 1 of the present invention;

[0033] Figure 5 for Figure 4 Schematic diagram of the enlarged structure of A in the middle;

[0034] Figure 6 This is a bottom view of the test sample plate in Embodiment 1 of the present invention.

[0035] Figure 7 This is a schematic cross-sectional view of the first electrode in Embodiment 1 of the present invention;

[0036] Figure 8 This is a schematic diagram of the stacked test sample plates in Embodiment 2 of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Example 1

[0039] like Figures 1 to 4 As shown, a superconducting strip / wire testing device that allows for the transmission of a large current in a high background magnetic field through liquid helium immersion and can measure multiple samples simultaneously includes a Dewar 1', a flange plate 1, a room temperature terminal block 2, a liquid helium inlet 3, an aviation plug 4, a liquid helium return port 5, a current lead 6, an epoxy support plate 7, an epoxy support rod 8, a copper lug 9, a stainless steel support rod 10, an epoxy resin substrate 12, a first electrode 15, a second electrode 14, a third electrode 13, and a level gauge 16. In this embodiment, the first electrode 15, the second electrode 14, and the third electrode 13 are copper electrodes.

[0040] The Dewar flange 1 is made of 304 stainless steel and is equipped with an aviation connector and a liquid helium return port. The liquid helium inlet is detachable and can be replaced with different sized liquid helium tubing.

[0041] The room temperature terminal 2 is divided into upper and lower parts, which are connected by threads and fixed to the Dewar flange plate 1. A polytetrafluoroethylene T-type gasket is fitted at the threaded connection to serve as insulation material. Both the upper and lower parts have circular through holes. The upper end of the current lead 6 is crimped with a copper lug and connected to the lower part of the room temperature terminal 2 by bolts.

[0042] The epoxy support plate 7 is circular with a central through-hole through which the stainless steel support rod 10 passes. The epoxy support plate 7 is fixed to the stainless steel support rod 10 with nuts, and its position on the rod can be adjusted by changing the thread position. The epoxy support plate 7 has evenly distributed through-holes slightly larger than the diameter of the current lead 6. The current lead 6 first passes through the holes in the first epoxy support plate 7, then passes through the next epoxy support plate 7 in a staggered manner, spiraling downwards to form a cable-like structure. Through-holes are located around the perimeter of the epoxy support plate 7, through which the epoxy support rod 8 passes sequentially from top to bottom and is connected to the epoxy support plate 7 with nuts. A notch is located on one side of the epoxy support plate 8 to facilitate the insertion of the liquid helium rod.

[0043] like Figure 4 As shown, the specific structure of the test sample plate 100 in this embodiment is as follows: the substrate 12 can have multiple limiting grooves 200 on one side, or multiple limiting grooves 200 on both the top and bottom sides. If it is a single-sided limiting groove, only the first electrode 15 and the second electrode 14 are needed. The specific structure is as follows: multiple limiting grooves 200 are opened on one side of the substrate 12, and three are shown in the figure. Each limiting groove 200 includes a wide groove 201 and a narrow groove 202. The narrow groove 202 is located inside the wide groove 201 and is elongated in shape. Figure 5 As shown, the narrow groove 202 is lower than the wide groove 201. The wide groove 201 is used to limit the superconducting tape, and the narrow groove 202 is used to limit the superconducting wire. By setting the narrow groove 202 inside the wide groove 201, the utilization rate of the substrate can be improved and the volume of the substrate can be reduced. If there are 3 limiting grooves 200, there are also 3 corresponding first electrodes 15. Each first electrode 15 is L-shaped, with the vertical part being a terminal and the horizontal part being fixed to the substrate 12 by bolts. One side of the horizontal part has a first electrode groove 151 with the same width and depth as the limiting groove 200. The second electrode 14 is also roughly L-shaped, with the vertical part being a terminal. The three limiting grooves 200 that cross the substrate 12 are fixed to the substrate. The horizontal part of the second electrode 14 can have 3 second electrode grooves 141 with the same width and depth as the limiting groove 200. In this way, the first electrode groove 151, the limiting groove 200, and the second electrode groove 141 are connected as one unit. Superconducting tape (placed in the wide slot 201) or superconducting wire (placed in the narrow slot 202) is placed in the three limiting slots 200. The two ends of the superconducting tape / wire are electrically connected to the first electrode slot 151 and the second electrode slot 141 by soldering. Then, the terminals of the three first electrodes and the second electrodes are respectively connected to the current lead 6 to form a circuit.

[0044] like Figure 6As shown, when the substrate 12 is slotted on both sides, a third electrode 13 needs to be set. The third electrode 13 has a similar structure to the second electrode 14, with one terminal and three third electrode slots 131. At this time, the upper and lower surfaces of the horizontal portion of the first electrode 15 are respectively provided with corresponding first electrode slots 151. The first electrode slots 151, the limiting groove 200 on the lower surface of the substrate, and the third electrode slots 131 are connected. At this time, six superconducting strips / wires can be welded to the test sample plate. The terminals of the three first electrodes, second electrodes, and third electrodes are respectively connected to the power supply through the room temperature terminal on the flange plate 1. Different test samples can be tested by switching different room temperature terminal. This embodiment realizes the three-dimensional placement of the sample, makes full use of the small space of the liquid helium Dewar, eliminates the need to frequently open the Dewar, and reduces liquid helium leakage. In this embodiment, because the superconducting wire is very thin and difficult to weld, a transverse groove 203 is also provided on the limiting groove 200 of the substrate. The voltage signal line passes through the transverse groove 203 and is bound to the superconducting wire. Then, the voltage signal line is soldered to the surface of the superconducting wire. After the superconducting tape / wire is welded and fixed, liquid paraffin is poured into the limiting groove 200 for further overall fixation.

[0045] In this embodiment, the third electrode 13, the second electrode 14, and the first electrode 15 are bolted to the epoxy plate 12 via a transverse portion. Taking the first electrode 15 as an example, as follows... Figure 7 The cross-sectional view of the first electrode 15 shown has small screw holes in its horizontal portion for bolting to the substrate 12. First electrode grooves 151 are respectively formed on the upper and lower surfaces of the horizontal portion.

[0046] The terminals of the third electrode 13, the second electrode 14, and the first electrode 15 are all provided with through holes and are connected to the lower end of the current lead 6 by bolts.

[0047] The level gauge 16 is placed on the lowest epoxy support rod 8 and is used to detect the liquid helium level.

[0048] During the experiment, the superconducting tape / wire was placed in a rectangular groove. The two ends of the superconducting sample were sequentially soldered to the grooves of the copper electrode. The larger rectangular groove held the superconducting tape, and the smaller rectangular groove held the superconducting wire. Superconducting samples of uniform length could be mounted on both the upper and lower surfaces of the test plate, achieving three-dimensional placement and fully utilizing the limited space of the liquid helium Dewar. The symmetrical small grooves in the middle were used to solder voltage signal lines. The voltage signal lines were passed through the small grooves and wound around the surface of the superconducting sample, then soldered to the surface. Finally, liquid paraffin was poured into the grooves. After the paraffin solidified, the epoxy test plate with the soldered sample was bolted to the stainless steel connecting frame 11. The stainless steel support rod 10 was a stainless steel threaded rod, with its upper end directly connected to the Dewar flange plate 1 via threads, and its lower end connected to the stainless steel connecting frame 11 via nuts, thus fixing the entire test sample plate inside the Dewar.

[0049] Replacing a sample with the sample rod requires recooling, which consumes liquid helium and is time-consuming. This embodiment's device can hold multiple samples at once, saving liquid helium and speeding up the measurement process. If only a small number of samples can be measured at once, experiments with a large number of samples require multiple insertions and removals of the sample rod for sample replacement, which is time-consuming and labor-intensive.

[0050] Example 2

[0051] Based on Example 1, such as Figure 8 As shown, the test sample plates can also be stacked to weld more test samples. This reduces the number of current leads while fully utilizing the axial space of the liquid helium Dewar. Specifically, the upper and lower test sample plates can be fixed using a connecting frame 11. The connecting frame is roughly U-shaped, with screw holes on the U-shaped sides and on the sides of the upper and lower plates. The two test sample plates are fixed within the U-shaped cavity of the connecting frame 11 using bolts. Figure 8 (Middle connecting frame 11 not shown). Figure 8 The device can weld a total of 12 samples to be tested, further reducing the number of times the sample rods need to be inserted and removed, and reducing liquid helium leakage.

[0052] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A liquid helium immersion type high-field high-current superconducting strip / wire critical current testing device, comprising a Dewar, a Dewar flange, and a test sample plate; wherein the test sample plate is located inside the Dewar; characterized in that, The test sample plate includes a substrate, a first electrode, and a second electrode. Multiple limiting grooves are formed on both sides of the substrate, with the same number of grooves on both sides. The limiting grooves include narrow grooves and wide grooves. Both the first and second electrodes are fixed to the substrate. The first and second electrodes have first electrode grooves and second electrode grooves with the same structure as the limiting grooves and that are connected to each other. When the sample to be tested is placed in the limiting groove, it can form a circuit with the first and second electrodes. The first and second electrodes are connected to an external power source via current leads passing through a flange. The flange has a liquid helium inlet and a liquid helium return port. The number of first electrodes is the same as the number of limiting grooves on one side of the substrate. It also includes a third electrode; the third electrode is fixed to the substrate and has a third electrode groove with the same structure and number as the limiting groove. Each first electrode is provided with two first electrode grooves that are connected to the limiting grooves on both sides of the substrate. The second electrode groove and the third electrode groove are respectively connected to the limiting grooves on both sides of the substrate. The second electrode and the third electrode are respectively fixed on the upper and lower sides of the substrate.

2. The liquid helium immersion type high-field high-current superconducting strip / wire critical current testing device according to claim 1, characterized in that, The first electrode includes a terminal block and a transverse portion fixed to the terminal block. The transverse portion is bolted to the substrate, and first electrode grooves are respectively formed on the upper and lower surfaces of the transverse portion.

3. The liquid helium immersion type high-field high-current superconducting strip / wire critical current testing device according to claim 1 or 2, characterized in that, The second electrode and the third electrode have the same structure. The second electrode / third electrode includes a terminal block and a fixing part. The fixing part is fixed on the upper / lower surface of the substrate. The fixing part has the same number of second electrode slots / third electrode slots as the limiting slots on one side of the substrate.

4. The liquid helium immersion type high-field high-current superconducting strip / wire critical current testing device according to claim 1 or 2, characterized in that, The narrow slot is located within the wide slot.

5. The liquid helium immersion type high-field high-current superconducting strip / wire critical current testing device according to claim 1 or 2, characterized in that, It also includes a transverse groove that penetrates the limiting groove and is deeper than the narrow groove.

6. The liquid helium immersion type high-field high-current superconducting strip / wire critical current testing device according to claim 5, characterized in that, It also includes multiple support plates, which are fixed together by support rods; the support plates have holes for current leads to pass through; one end of the current lead is electrically connected to the first electrode, the second electrode, and the third electrode, and the other end passes through a flange and is connected to an external power source.

7. The liquid helium immersion type high-field high-current superconducting strip / wire critical current testing device according to claim 5, characterized in that, It includes multiple test sample plates, which are stacked and fixed together.

8. A test method for a liquid helium immersion type high-field high-current superconducting strip / wire critical current testing device as described in any one of claims 5 to 7, characterized in that, Includes the following steps: Step 1. Using the four-lead method for measurement, first place the superconducting tape in the wide slot, or place the superconducting wire in the narrow slot, and electrically connect it to the electrodes at both ends. Pass the voltage signal line through the horizontal slot, wrap it around the sample to be tested, and fix it with solder. Then electrically connect the electrodes to the current lead. Then insert the sample rod into the Dewar. Step 2. Connect the flange to the Dewar with bolts and seal it, and then lead the current lead out of the flange and electrically connect it to the external power supply; Step 3. Introduce liquid nitrogen into the Dewar to achieve pre-cooling; when the sample temperature drops to 77K, use nitrogen gas to expel the liquid nitrogen inside the Dewar through the hollow stainless steel tube inserted into the bottom of the Dewar; after expelling the liquid nitrogen, introduce liquid helium into the Dewar to lower the sample temperature to 4.2K. Step 4. By switching the current lead to connect to the terminals of different first electrodes, the purpose of testing different samples can be achieved.

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