A system and method for non-destructive testing of superconducting material defects based on thermoelectric power

Abstract

This invention discloses a non-destructive testing system and method for defects in superconducting materials based on thermoelectric electromotive force (TEMF), belonging to the field of non-destructive testing technology for superconducting materials. This method introduces a controllable temperature gradient along the length of a practical superconducting material and monitors the changes in thermoelectric electromotive force generated at both ends or in localized areas of the superconducting material in real time. Utilizing the anomalous response of the electrical transport characteristics of the defect region near the critical temperature, it achieves rapid and non-destructive identification and location of internal defects in the superconducting material. This method does not require disassembly of the superconducting material or application of large currents, and is applicable to various practical superconducting materials such as tapes, wires, and armored cables. It has advantages such as high detection sensitivity, low implementation cost, simple operation, and scalability to online detection.

Description

Technical Field

[0001] This invention belongs to the field of nondestructive testing technology for superconducting materials, specifically relating to a nondestructive testing system and method for defects in superconducting materials based on thermoelectric potential. Background Technology

[0002] Superconducting technology has been widely applied in engineering fields such as energy, medicine, nuclear fusion, high-energy physics, and power transmission and storage, serving as a crucial support for high-performance magnets and advanced electrical equipment. Superconducting materials possess zero resistance and perfect diamagnetism, enabling them to maintain excellent current-carrying capacity even under high current and high magnetic field conditions, making them suitable for magnets, superconducting cables, and energy storage systems. However, as engineering scale continues to expand, the impact of internal material defects on system reliability becomes increasingly prominent. In tokamak nuclear fusion, high-field magnets, and superconducting power transmission and storage systems, even minute defects can induce local thermal instability, abnormal currents, and even lead to system quenching and structural damage, posing significant safety risks. Low temperatures, high magnetic fields, and complex structural conditions further increase the difficulty of defect monitoring; traditional detection methods struggle to achieve online assessment and early warning, becoming a technical bottleneck for engineering applications.

[0003] Superconducting materials mainly include low-temperature superconductors (LTS) and high-temperature superconductors (HTS, such as REBCO, Bi-2212, and Bi-2223). LTS technology is mature and has good ductility, but some low-temperature superconducting materials, such as Nb3Sn (a low-temperature high-magnetic-field superconducting material, an intermetallic compound superconductor composed of niobium (Nb) and tin (Sn) in a 3:1 atomic ratio), are brittle and sensitive to heat treatment, limiting their application in complex structures. High-temperature superconducting materials still have high current density in the liquid nitrogen temperature range, making them candidate systems for high-field magnets and high-current transmission. However, REBCO (rare earth barium copper oxide) tapes are significantly brittle, and delamination and microcracks are prone to occur during winding and armoring. The heat treatment and oxygen partial pressure control of Bi-2212 (bismuth strontium calcium copper oxide (2212 phase)) / Bi-2223 (bismuth strontium calcium copper oxide (2223 phase)) wires are complex, and even small process deviations can cause performance degradation. Overall, the mechanical brittleness and structural coupling characteristics of high-temperature superconducting materials make conductor performance evaluation and defect monitoring a core challenge for engineering applications.

[0004] Defects in superconducting materials exhibit multi-scale and multi-factor characteristics: lattice defects, impurities, and residual stress may occur during the fabrication stage; microcracks and interface weakening may occur during processing; and structural degradation may result from mechanical loads, thermal cycling, electromagnetic forces, and environmental factors during operation. These defects easily evolve into localized heat sources and electrically anomalous regions under high magnetic fields and high currents, reducing system stability. Defect evolution is highly nonlinear and localized, making it difficult for a single detection technique to cover all defect types and development stages.

[0005] Existing nondestructive testing (NDT) technologies have significant limitations. Optical and surface imaging can only detect surface defects; ultrasonic and X-ray inspections are limited in low-temperature and liquid environments, making online monitoring difficult; eddy current and electromagnetic induction are insufficiently sensitive to internal defects in composite conductors, failing to accurately locate microcracks or interface delamination; detection methods based on electrical transport and magnetic properties typically require large currents or complex magnetic fields, making rapid, online detection difficult in armored cable conductors and large superconducting magnets; magnetic imaging and flux measurement are susceptible to background magnetic field interference, resulting in limited positioning accuracy; acoustic emission and vibration monitoring data analysis is complex and easily affected by environmental noise. Therefore, achieving highly sensitive, real-time, and online defect detection in multi-strand cable structures and low-temperature, high-magnetic environments remains a critical problem that urgently needs to be solved in engineering.

[0006] In summary, microscopic defects (such as lattice defects, microcracks, and grain boundary impurities) and macroscopic defects (such as interlayer delamination, wire slippage, and poor contact) are prevalent in the preparation, processing, and operation of superconducting materials, and can easily evolve into localized thermal instability or abnormal current regions under extreme conditions. Current technologies cannot achieve highly sensitive, rapid, and online detection of internal defects, and practical engineering methods are lacking. There is an urgent need for a highly sensitive, easy-to-operate, and online defect detection method applicable to superconducting conductors such as strips, wires, and armored cables to ensure the safe operation of superconducting systems and support material performance evaluation and process optimization. Summary of the Invention

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A non-destructive testing system for defects in superconducting materials based on thermoelectric potential, comprising:

[0009] A cryogenic medium container is used to hold cryogenic media; the superconducting material sample to be tested is placed vertically inside the cryogenic medium container.

[0010] The sample heater, located on top of the cryogenic medium container and attached to one end of the superconducting material sample, is used to provide controllable thermal power input and establish a controllable temperature gradient along the axial direction of the superconducting material sample.

[0011] Multiple temperature sensors are arranged at equal intervals along the axial direction of the superconducting material sample for real-time multi-point temperature acquisition along the axial direction of the superconducting material sample.

[0012] The voltage and temperature acquisition system is connected to the voltage leads and local voltage taps at both ends of the superconducting material sample, as well as each temperature sensor. It is used to acquire the terminal voltage and local voltage signals of the superconducting material sample and send them to the data acquisition and control system. At the same time, it receives the temperature data from each temperature sensor and forwards it to the data acquisition and control system.

[0013] The data acquisition and control system is used to receive voltage signals and temperature data sent by the voltage and temperature acquisition system, display and generate temperature change curves and voltage change curves in real time, and determine the distribution location and type of defects accordingly.

[0014] The non-destructive testing system for defects in superconducting materials based on thermoelectric potential utilizes the influence of defects in superconducting materials on thermoelectric potential to identify and locate defects.

[0015] A non-destructive testing method for defects in superconducting materials based on thermoelectric potential, used in the aforementioned non-destructive testing system for defects in superconducting materials based on thermoelectric potential, comprising:

[0016] S1, The cryogenic medium container holds the cryogenic medium, the superconducting material sample is vertically immersed in the cryogenic medium, and the temperature of the superconducting material sample is controlled below its critical temperature;

[0017] S2, monitor the overall terminal voltage and local voltage signals of the superconducting material sample; the voltage and temperature acquisition system acquires the overall terminal voltage and local voltage signals of the superconducting material sample and sends them to the data acquisition and control system to check the stability and accuracy of the output of each temperature sensor;

[0018] S3, the sample heater starts to heat one end of the superconducting material sample, introducing a temperature gradient within the superconducting material sample; the voltage and temperature acquisition system acquires the overall terminal voltage and local voltage signals of the superconducting material sample and sends them to the data acquisition and control system, and the voltage and temperature acquisition system acquires the corresponding temperature data and sends it to the data acquisition and control system.

[0019] S4, the data acquisition and control system receives the terminal voltage and local voltage signals and temperature data sent by the voltage and temperature acquisition system, displays and generates temperature change curves and voltage change curves in real time, and determines the distribution location and type of defects accordingly.

[0020] The present invention has the following beneficial effects:

[0021] This invention enables online detection of defects in large superconducting magnets, is low-cost, easy to operate, and effectively solves engineering application problems existing in the prior art.

[0022] (1) Detection method based on thermoelectric potential: This invention achieves highly sensitive identification of microcracks, interface peeling and interlayer defects by applying a controllable temperature gradient and monitoring the thermoelectric potential change of superconducting materials in real time, which solves the problem that existing detection technologies are difficult to obtain internal defect signals online and in real time.

[0023] (2) No need for high current or complex magnetic field conditions: This invention can realize defect detection in low temperature environment, avoiding the limitation of traditional methods based on electrical transport or magnetic properties that require the application of high current and complex magnetic field, reducing the difficulty of operation and equipment cost, and solving the problem that it is difficult to quickly implement the detection of large armored cables and superconducting magnets.

[0024] (3) Applicable to a variety of superconducting structures: The method of the present invention can be applied to a variety of superconducting conductor structures such as tape, wire and armored cable, and can cover the entire process of preparation, transportation and operation, realize online monitoring of defects, and solve the problem of inaccurate defect location in multi-strand cable and complex structure conductors in the existing technology.

[0025] (4) Rapid spatial positioning and online monitoring: Through multi-point temperature acquisition and data analysis, the present invention can locate the defect area in real time, realize online monitoring and early warning, and solve the problems of low positioning accuracy and difficulty in implementing early defect warning in traditional detection methods.

[0026] (5) Strong engineering scalability: Combining automated data acquisition and model analysis, this invention can evaluate the performance stability of large-size conductors and provide a basis for defect evolution prediction and material improvement, reduce operating costs, improve system reliability, and solve the problem that existing technologies cannot perform engineering online monitoring of large-scale superconducting systems. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the non-destructive testing system for defects in superconducting materials based on thermoelectric potential according to the present invention, wherein 1-low temperature medium container, 2-sample, 3-sample heater, 4-temperature sensor, 5-voltage and temperature acquisition system, and 6-data acquisition and control system. Detailed Implementation

[0028] 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.

[0029] This invention provides a non-destructive testing system for defects in superconducting materials based on thermoelectric potential, comprising:

[0030] Cryogenic medium container 1 is used to hold cryogenic medium; the superconducting material sample 2 to be tested is placed vertically inside the cryogenic medium container 1.

[0031] The sample heater 3 is located on the top of the cryogenic medium container 1 and attached to one end of the superconducting material sample 2. It is used to provide controllable thermal power input, and the heat output is precisely controlled by current adjustment. A controllable temperature gradient is established along the axial direction of the superconducting material sample 2.

[0032] Multiple temperature sensors 4 are arranged at equal intervals along the axial direction of the superconducting material sample 2 for real-time multi-point temperature acquisition along the axial direction of the superconducting material sample 2.

[0033] The voltage and temperature acquisition system 5 is connected to the voltage leads and local voltage taps at both ends of the superconducting material sample 2, as well as each temperature sensor 4. It is used to acquire the terminal voltage and local voltage signals of the superconducting material sample 2 and send them to the data acquisition and control system 6. At the same time, it receives the temperature data of each temperature sensor 4 and forwards it to the data acquisition and control system 6.

[0034] The data acquisition and control system 6 receives voltage signals and temperature data sent by the voltage and temperature acquisition system 5, displays and generates temperature change curves and voltage change curves in real time, and determines the distribution location and type of defects accordingly. This invention utilizes the influence of defects in superconducting materials on thermoelectric potential to achieve the identification and location of defects in superconducting materials.

[0035] The present invention further provides a non-destructive testing method for defects in superconducting materials based on thermoelectric potential. This method establishes a controllable temperature gradient along the length (axial direction) of the superconducting material sample 2 and simultaneously monitors the terminal voltage and local voltage signal of the superconducting material sample 2. Based on the abnormal response of the local voltage signal to temperature change, the location and type of defects in the superconducting material sample 2 are identified.

[0036] To achieve the above objectives, the present invention is implemented through the following specific steps:

[0037] A practical non-destructive testing method for defects in superconducting materials based on thermoelectric potential includes the following steps:

[0038] S1, the low-temperature medium container 1 contains the low-temperature medium, the superconducting material sample 2 is vertically immersed in the low-temperature medium, and the temperature of the superconducting material sample 2 is controlled below its critical temperature;

[0039] S2, monitor the overall terminal voltage and local voltage signals of the superconducting material sample 2; the voltage and temperature acquisition system 5 acquires the corresponding voltage signals and sends them to the data acquisition and control system 6, and checks the stability and accuracy of the output of each temperature sensor 4;

[0040] S3, the sample heater 3 starts to heat one end of the superconducting material sample 2, introducing a temperature gradient in the superconducting material sample 2 (the temperature at each position is different as the liquid level drops); the voltage and temperature acquisition system 5 acquires the overall terminal voltage and local voltage signals of the superconducting material sample 2 and sends them to the data acquisition and control system 6; the voltage and temperature acquisition system 5 acquires the corresponding temperature data and sends it to the data acquisition and control system 6.

[0041] S4, the data acquisition and control system 6 receives the terminal voltage and local voltage signals and temperature data sent by the voltage and temperature acquisition system 5, displays and generates temperature change curves and voltage change curves in real time, and determines the distribution location and type of defects accordingly.

[0042] As a preferred option, the superconducting material sample 2 is elongated, and a nanovoltmeter is used to monitor the voltage signal across the two ends of the elongated superconducting material sample 2 in real time.

[0043] As a preferred option, a temperature monitoring instrument is used to select and set the parameters of the thermometers used at various locations of the superconducting material sample 2, and to monitor and display the temperature data in real time, and to control the temperature of the superconducting material sample 2 below its critical temperature.

[0044] As a preferred embodiment, in step S1, the superconducting material sample 2 is vertically immersed in a cryogenic medium container 1. The boiling point of the cryogenic medium in the container 1 is lower than the critical current-carrying temperature of the superconducting material sample 2. As the cryogenic medium evaporates, a temperature gradient is formed from the surface of the cryogenic medium to the upper end of the superconducting material sample 2. When the temperature at the defect location rises or falls to the critical temperature, the thermoelectric potential across the two ends of the superconducting material sample 2 will fluctuate significantly. By combining the characteristics of the thermoelectric potential variation and the temperature change pattern of the superconducting material sample 2, the type and distribution of defects in the superconducting material sample 2 can be determined. Specifically, the type of defect can be determined based on the characteristics of the thermoelectric potential variation, and the location of the defects can be determined based on the positions of the multiple temperature sensors 4.

[0045] The working principle of this invention: Practical superconducting materials are typically composite materials, meaning superconducting materials are incorporated into a metal matrix. Below the critical temperature of a practical superconducting material, the entire material exhibits superconductivity, with equal voltage across the entire material. Above the critical temperature, the superconducting material exhibits metallic properties, generating a thermoelectric potential due to temperature differences. Defects within the superconducting material cause it to lose its superconductivity below the critical temperature, exhibiting a thermoelectric potential. Therefore, by heating / cooling the superconducting material, the distribution of defects within it can be clearly identified.

[0046] Example 1:

[0047] The specific implementation of the present invention is based on, for example, Figure 1The diagram shows the overall layout of a non-destructive testing system for defects in superconducting materials based on thermoelectric potential. Specifically, a cryogenic medium container 1 holds liquid nitrogen (the cryogenic medium), which is constructed using low thermal conductivity engineering materials, particularly a multi-layered vacuum insulation structure, to minimize the impact of external thermal disturbances on temperature gradient stability. The liquid level of the cryogenic medium inside the cryogenic medium container 1 is higher than the effective detection area of ​​the superconducting material sample 2, ensuring that the entire sample is in a stable cryogenic environment. Simultaneously, an venting and pressure relief structure is installed at the top of the cryogenic medium container 1 to prevent pressure fluctuations caused by the evaporation of the cryogenic medium from affecting system stability.

[0048] Superconducting material sample 2 is a Bi-2212 elongated superconducting wire formed after heat treatment phase transformation. Superconducting material sample 2 is placed vertically inside a cryogenic medium container 1.

[0049] The sample heater 3, located at the top of the cryogenic medium container 1, applies a controlled heat flow to one end of the superconducting material sample 2. Precise control of the heat output is achieved through current regulation, thereby establishing a controllable temperature gradient along the axial direction of the superconducting material sample 2. In this example, the preferred temperature gradient is 0.1-2 K / cm. This temperature gradient range is sufficient to excite a measurable thermoelectric potential while avoiding overheating that could cause the sample to lose its superconductivity.

[0050] Multiple temperature sensors 4 are arranged at equal intervals along the axial direction of the superconducting material sample 2 for multi-point real-time temperature acquisition. Preferably, in this example, a PT-100 (platinum resistance thermometer 100) is used to monitor temperatures from 77K to room temperature. Each temperature sensor 4 is thermally coupled to the surface of the superconducting material sample 2 through thermally conductive silicone grease or a thin metal foil to ensure that the temperature measurement error is controlled within ≤0.01K and to reduce the impact of contact thermal resistance on data accuracy.

[0051] The voltage and temperature acquisition system 5 has a nanovolt-level voltage resolution (≤10nV) and a sampling frequency of not less than 10Hz, which can realize synchronous sampling of voltage and temperature signals.

[0052] The implementation of the non-destructive testing method for defects in superconducting materials based on thermoelectric potential of the present invention is as follows: Figure 1 Based on the superconducting material defect nondestructive testing system shown, its process is divided into four consecutive steps according to time and operation sequence: system initialization, zero-point calibration, gradient loading, data acquisition and defect judgment.

[0053] S1: System initialization. Liquid nitrogen (77K) is injected into the cryogenic medium container 1, and the superconducting material sample 2 connected to the voltage and temperature acquisition system 5 is immersed in the cryogenic medium. Because the critical temperature of the superconducting material sample 2, Bi-2212, is greater than 77K, the Bi-2212 elongated superconducting wire is in a superconducting state at this time.

[0054] S2: Zero-point calibration. After the system reaches thermal equilibrium, start the voltage and temperature acquisition system 5 and check the stability and accuracy of the outputs from each temperature sensor 4.

[0055] S3: Gradient loading. The sample heater 3 is activated, introducing an axial temperature gradient into the superconducting material sample 2. Simultaneously, due to heat leakage from the superconducting material sample 2, the cryogenic medium, liquid nitrogen, is consumed at a slow rate. The liquid level of the cryogenic medium in the cryogenic medium container 1 decreases slowly.

[0056] S4: Data Acquisition and Defect Judgment. Each temperature sensor 4 synchronously acquires T(x,t), where T is the temperature, x is the position coordinate along the sample axis, and t is the liquid level drop time. The location and characteristics of defects on the superconducting material sample 2 are determined based on the temperature changes and voltage signal changes on the sample.

[0057] Example 2:

[0058] The cryogenic medium container 1 contains liquid nitrogen, and the height of the liquid nitrogen is higher than the axial length of the sample 2.

[0059] Superconducting material sample 2 is a Bi-2212 armored cable conductor with a length of 2.7m.

[0060] Multiple temperature sensors 4 are evenly arranged on the conductor of the Bi-2212 armored cable. Each temperature sensor 4 is a PT-100 thermometer. Potential lines are fixed at both ends of the superconducting material sample 2 and at the locations where defects need to be evaluated.

[0061] A PT-100 thermometer and a potential line were connected to the voltage and temperature acquisition system 5 to monitor the voltage and temperature distribution of the superconducting material sample 2 in real time. The voltage and temperature acquisition system 5 was configured to include a Lake Shore 350 temperature controller and a Lake Shore 2182 nanovoltmeter.

[0062] Using a hoisting device, the conductor of the Bi-2212 armored cable was slowly immersed into a low-temperature medium at a speed of 1 cm / min and placed vertically. A temperature gradient along the length of the Bi-2212 armored cable conductor was introduced, and the thermoelectric potential generated by the temperature gradient was monitored.

[0063] The defect distribution of the Bi-2212 armored cable conductor was determined based on the changes in thermoelectric electromotive force and the temperature of the Bi-2212 armored cable conductor over time.

[0064] The above description is merely an embodiment of the present invention and does not limit the scope of the invention. Any equivalent structural or procedural transformations made based on the description and drawings of this invention, or direct or indirect applications in other related system fields, are similarly included within the protection scope of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A non-destructive testing system for defects in superconducting materials based on thermoelectric potential, characterized in that, include: A cryogenic medium container is used to hold cryogenic media; the superconducting material sample to be tested is placed vertically inside the cryogenic medium container. The sample heater, located on top of the cryogenic medium container and attached to one end of the superconducting material sample, is used to provide controllable thermal power input and establish a controllable temperature gradient along the axial direction of the superconducting material sample. Multiple temperature sensors are arranged at equal intervals along the axial direction of the superconducting material sample for real-time multi-point temperature acquisition along the axial direction of the superconducting material sample. The voltage and temperature acquisition system is connected to the voltage leads and local voltage taps at both ends of the superconducting material sample, as well as each temperature sensor. It is used to acquire the terminal voltage and local voltage signals of the superconducting material sample and send them to the data acquisition and control system. At the same time, it receives the temperature data from each temperature sensor and forwards it to the data acquisition and control system. The data acquisition and control system is used to receive voltage signals and temperature data sent by the voltage and temperature acquisition system, display and generate temperature change curves and voltage change curves in real time, and determine the distribution location and type of defects accordingly. The non-destructive testing system for defects in superconducting materials based on thermoelectric potential utilizes the influence of defects in superconducting materials on thermoelectric potential to identify and locate defects.

2. The non-destructive testing system for defects in superconducting materials based on thermoelectric potential according to claim 1, characterized in that, The cryogenic medium container is made of low thermal conductivity engineering materials.

3. The non-destructive testing system for defects in superconducting materials based on thermoelectric potential according to claim 2, characterized in that, The low thermal conductivity engineering material is a multi-layer vacuum insulation structure.

4. The non-destructive testing system for defects in superconducting materials based on thermoelectric potential according to claim 1, characterized in that, The multiple temperature sensors are PT-100 resistance thermometers.

5. The non-destructive testing system for defects in superconducting materials based on thermoelectric potential according to claim 1, characterized in that, Each temperature sensor is thermally coupled to the surface of the superconducting material sample via thermally conductive silicone grease or a thin metal foil.

6. The non-destructive testing system for defects in superconducting materials based on thermoelectric potential according to claim 1, characterized in that, The cryogenic medium container is equipped with an exhaust and pressure relief structure at the top.

7. The non-destructive testing system for defects in superconducting materials based on thermoelectric potential according to claim 1, characterized in that, The superconducting material sample is a Bi-2212 elongated superconducting wire formed after heat treatment phase transformation.

8. A non-destructive testing method for defects in superconducting materials based on thermoelectric potential, used in the non-destructive testing system for defects in superconducting materials based on thermoelectric potential as described in any one of claims 1 to 7, characterized in that, include: S1, The cryogenic medium container holds the cryogenic medium, the superconducting material sample is vertically immersed in the cryogenic medium, and the temperature of the superconducting material sample is controlled below its critical temperature; S2, monitor the overall terminal voltage and local voltage signals of the superconducting material sample; the voltage and temperature acquisition system acquires the overall terminal voltage and local voltage signals of the superconducting material sample and sends them to the data acquisition and control system to check the stability and accuracy of the output of each temperature sensor; S3, the sample heater starts to heat one end of the superconducting material sample, introducing a temperature gradient within the superconducting material sample; the voltage and temperature acquisition system acquires the overall terminal voltage and local voltage signals of the superconducting material sample and sends them to the data acquisition and control system, and the voltage and temperature acquisition system acquires the corresponding temperature data and sends it to the data acquisition and control system. S4, the data acquisition and control system receives the terminal voltage and local voltage signals and temperature data sent by the voltage and temperature acquisition system, displays and generates temperature change curves and voltage change curves in real time, and determines the distribution location and type of defects accordingly.

9. The non-destructive testing method for defects in superconducting materials based on thermoelectric potential according to claim 8, characterized in that, In S1, a temperature monitoring instrument is used to monitor the temperature values ​​at various locations of the superconducting material sample in real time, and the temperature of the superconducting material sample is controlled below its critical temperature.

10. The non-destructive testing method for defects in superconducting materials based on thermoelectric potential according to claim 8, characterized in that, In S1, the superconducting material sample is in the shape of a long strip, and a nanovoltmeter is used to monitor the voltage signal at both ends of the long strip of superconducting material sample in real time.

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