A device and method for detecting internal damage of superconducting thin film materials in a liquid nitrogen environment

Abstract

The present invention discloses a device and method for detecting internal damage of superconducting thin film materials in a liquid nitrogen environment, and relates to the field of magneto-optical observation technology. In order to solve the problem that the existing detection equipment needs to be evacuated, heat-shielded, and cooled by heat conduction, and the experimental device is too complicated and cannot meet the observation requirements, the following technical scheme is proposed: it includes a liquid nitrogen container, a sample stage, liquid nitrogen, an observation medium, a spectroscopic prism, an observation component, and a light source component; the light generated by the light source component passes through the spectroscopic prism and the observation medium to the top of the magneto-optical film, and is reflected by the magneto-optical film to the observation medium and the spectroscopic prism to enter the observation component; the superconducting film to be tested is arranged on the top of the sample stage, and the magneto-optical film is arranged on the top of the superconducting film. The present invention adopts PMMA as the observation medium, realizes the clear observation of the surface magnetic field of the superconducting thin film material in a liquid nitrogen environment, does not need evacuation and heat-shielding, greatly reduces the complexity of the experimental device and the test cost, and improves the test efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of magneto-optical observation systems, and in particular to a device and method for detecting internal damage of a superconducting thin film material in a liquid nitrogen environment. Background Art

[0002] The magneto-optical method based on the Faraday effect has the advantages of full-field measurement, real-time and high resolution, and is widely used in the magnetic research of superconducting materials. However, since the surface of low-temperature cooling media such as liquid nitrogen and liquid helium is usually in a boiling state, it is impossible to directly perform clear optical observations on samples immersed in them for cooling. Therefore, the traditional magneto-optical imaging (MOI) technology mainly includes a vacuum system and a temperature control refrigeration system. During the experiment, it is necessary to first evacuate the vacuum system to avoid ice and frost during cooling, and then use the refrigerator to achieve refrigeration and temperature control by heat conduction. Finally, the optical observation window above the vacuum low-temperature refrigeration cavity is used for visual observation. The main disadvantage is that it requires vacuuming, heat shielding and cooling by heat conduction, and the experimental equipment is complex and costly. During the experiment, the superconducting sample and magneto-optical film are placed in a high vacuum Dewar device, and then cooled by a refrigerator. After the experiment, the sample temperature rises to room temperature and the vacuum system is turned off before the device can be opened for the next set of experiments. It usually takes several hours to complete a set of tests.

[0003] For visualization technology in liquid nitrogen, visualization research in liquid nitrogen is generally achieved by arranging an observation window on the side of the Dewar flask. The Dewar flask is generally a double-layer design, and the air in the middle layer needs to be evacuated to form a vacuum, and observation is performed from the side, which cannot meet the top-down observation requirements of magneto-optical imaging. More importantly, the internal observation window of the Dewar jar is in contact with liquid nitrogen, so its material selection and sealing require special selection and design; another method is to half-immerse 2cm thick acrylic glass in liquid nitrogen, and to prevent freezing, the entire device is covered with acrylic glass. Using acrylic glass to cover the device can meet the top-down observation requirements, but the presence of two layers of acrylic glass will change the optical path, making it impossible to conduct accurate quantitative research, and will increase the complexity of the device. Therefore, the above two types of liquid nitrogen observations are both costly and complex. Summary of the invention

[0004] The purpose of the present invention is to provide a device and method for detecting internal damage of superconducting thin film materials in a liquid nitrogen environment, so as to solve the problem that the existing detection equipment requires vacuuming, heat shielding and cooling by heat conduction, and the experimental device is too complicated to meet the observation requirements.

[0005] The technical solution of the present invention to solve the above technical problems is as follows:

[0006] A device for detecting internal damage of superconducting thin film materials in a liquid nitrogen environment comprises: a sample stage is arranged at the bottom of a liquid nitrogen container, and liquid nitrogen is contained in the liquid nitrogen container; an observation medium is arranged above the sample stage, the lower end of the observation medium is immersed in the liquid nitrogen, the upper end of the observation medium is arranged outside the liquid nitrogen, the observation medium undergoes convective heat exchange in the liquid nitrogen and the air; a beam splitter prism is arranged above the observation medium, an observation assembly is arranged above the beam splitter prism, and a light source assembly is arranged at the side end of the beam splitter prism; a superconducting thin film is arranged on the top of the sample stage, a magneto-optical film is arranged on the top of the superconducting thin film, and light generated by the light source assembly passes through the beam splitter prism and the observation medium to the top of the magneto-optical film respectively, and is reflected by the magneto-optical film to the observation medium and the beam splitter prism to enter the observation assembly.

[0007] Preferably, the liquid nitrogen container is a polylactic acid cylindrical barrel, and an insulation barrel is arranged outside the polylactic acid cylindrical barrel.

[0008] Preferably, the observation medium is a polymethyl methacrylate rectangular column.

[0009] Preferably, the observation assembly includes a polarizer arranged above the beam splitter prism and a camera arranged above the polarizer.

[0010] Preferably, the light source assembly includes a polarizer arranged at a side end of the beam splitter prism and a light source arranged at a side end of the polarizer.

[0011] A method for detecting internal damage of a superconducting thin film material in a liquid nitrogen environment, applied to the above-mentioned device for detecting internal damage of a superconducting thin film material in a liquid nitrogen environment, comprises the following steps:

[0012] S1. Prepare and cool a liquid nitrogen container: Use 3D printing technology to prepare a polylactic acid cylindrical barrel as a liquid nitrogen container, and embed the container into a foam barrel for heat insulation treatment; then, introduce liquid nitrogen into the liquid nitrogen container as a cooling medium and keep it in a cooling state;

[0013] S2. Optimize and place the observation medium: Use polymethyl methacrylate material to make a rectangular column of a specific size as the observation medium, and optimize its shape through finite element heat transfer analysis to ensure thermal conductivity; half-immerse the observation medium in a liquid nitrogen container and place it above the superconducting thin film material to be observed, while ensuring that the lower surface of the observation medium is continuously immersed in liquid nitrogen to maintain a low temperature state;

[0014] S3, assemble and cool the sample stage: cover the magneto-optical film on the superconducting film material, and use bolts, springs and clips to fix the two on a specially designed sample stage; then, put the assembled sample stage into a cooled liquid nitrogen container and keep it cooled for a period of time to ensure thermal equilibrium;

[0015] S4. Configure the observation system: install a bracket on the polymethyl methacrylate rectangular column half immersed in liquid nitrogen to support the observation path of the magneto-optical imaging system (MOI); ensure that the light emitted by the light source of the magneto-optical imaging system can penetrate the polymethyl methacrylate medium and reach the magneto-optical film on the surface of the superconducting thin film material;

[0016] S5. Adjust and collect magneto-optical images: adjust the magneto-optical imaging system so that the light emitted by the light source becomes linearly polarized light after passing through the filter and the polarizer. The polarized light passes through the beam splitter prism and the polymethyl methacrylate medium, reaches the magneto-optical film and is reflected, passes through the medium and the beam splitter prism again, and forms a light and dark distribution image after passing through the analyzer; use a camera to capture and record this image;

[0017] S6. Analyze and extract magnetic field information: apply a post-processing program to the collected magneto-optical image to extract the magnetic field distribution information; based on the magnetic field distribution information, inversely calculate the current density distribution, and determine the defect size and location information of the superconducting thin film material according to the attenuation of the current density.

[0018] The present invention has the following beneficial effects:

[0019] The present invention adopts polymethyl methacrylate as the observation medium, realizes clear observation of superconducting thin film materials in a liquid nitrogen environment, does not require vacuuming and heat shielding, and greatly reduces the complexity and cost of the experimental device.

[0020] The present invention utilizes magneto-optical imaging technology to realize quantitative detection of internal damage of superconducting thin film materials in liquid nitrogen, and the observation result can directly reflect the quality of the superconducting thin film materials.

[0021] The invention has the advantages of high testing efficiency, simple operation, etc. and is suitable for superconducting thin film material performance evaluation and production quality control in large-scale industrial production.

[0022] The magneto-optical imaging system is very sensitive to the penetrating magnetic field caused by damage and defects in superconducting thin film materials, and the observation results can directly reflect the quality of superconducting thin film materials. The emergence of high-temperature superconductors with critical transition temperatures exceeding 77K has greatly promoted the development of superconducting research with low cryogenic costs. Experiments in liquid nitrogen can meet the requirements of many applications.

[0023] Therefore, the present invention does not require heat conduction, heat shielding and vacuum, and realizes in-situ magneto-optical imaging observation in liquid nitrogen by semi-immersing the observation medium in liquid nitrogen as a visualization medium, which greatly reduces the test cost of the magneto-optical imaging system, improves the test efficiency and has stronger practicality. As my country's rare earth barium copper oxide superconducting tape enters mass production, it is expected that this technology can be further developed into an effective tool for industrial defect detection of rare earth barium copper oxide tapes, serving the performance evaluation and production quality control of superconducting materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic structural diagram of the internal damage detection device of the superconducting thin film material in a liquid nitrogen environment of the present invention;

[0025] Figure 2 This is a magneto-optical principle diagram of the internal damage detection device for superconducting thin film materials in a liquid nitrogen environment of the present invention;

[0026] Figure 3 This is a schematic diagram of the liquid nitrogen immersion visualization structure of the internal damage detection device for superconducting thin film materials in a liquid nitrogen environment of the present invention.

[0027] Figures 1 to 3 The reference numerals shown in the figure represent respectively: liquid nitrogen container 1, sample stage 2, observation medium 3, dichroic prism 4, superconducting film 5, analyzer 6, camera 7, polarizer 8, light source 9, magneto-optical film 10. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0029] Please refer to Figure 1 The present invention provides a device for detecting internal damage of superconducting thin film materials in a liquid nitrogen environment. The specific implementation of the present invention will be described in detail below to better understand the technical solution of the present invention and its beneficial effects.

[0030] The liquid nitrogen environment superconducting thin film internal damage detection device of this embodiment is mainly composed of a liquid nitrogen container 1, a sample stage 2, an observation medium 3, a superconducting thin film 5, a magneto-optical imaging system and necessary accessories.

[0031] The liquid nitrogen container 1 is one of the core components of this embodiment, which is used to contain liquid nitrogen and provide a stable low-temperature environment. In this embodiment, the liquid nitrogen container 1 is a polylactic acid (PLA) cylindrical barrel manufactured by 3D printing technology. The polylactic acid material has good biocompatibility and degradability, and has certain strength and toughness, which can meet the use requirements of the liquid nitrogen container 1. In addition, the cost of the polylactic acid material is relatively low, which is conducive to reducing the cost of the entire device.

[0032] The liquid nitrogen container 1 needs to be fully cleaned and dried before use to ensure that there are no impurities and moisture inside. Then, pour the liquid nitrogen into the container until the liquid level reaches a predetermined height. In order to maintain the low temperature state of the liquid nitrogen container 1, a layer of foam barrel is also wrapped around the outside of the liquid nitrogen container 1 for heat insulation. The foam barrel has good heat insulation performance, which can effectively reduce the evaporation of liquid nitrogen and the increase in temperature, thereby extending the use time of liquid nitrogen.

[0033] The observation medium 3 is another key component in this embodiment, which is used to achieve clear observation of the superconducting film 5 in a liquid nitrogen environment. In this embodiment, the observation medium 3 is made of polymethyl methacrylate (PMMA). The observation medium 3 has excellent transparency, weather resistance and processing performance, and can meet the use requirements of the observation medium.

[0034] In order to achieve clear observation of the superconducting film 5, the shape and size of the observation medium 3 are specially designed in this embodiment. Specifically, the observation medium 3 is designed to be in the shape of a rectangular column and is half immersed in the liquid nitrogen container 1. When the observation medium 3 is half immersed in liquid nitrogen, its lower surface is always immersed in liquid nitrogen to maintain a low temperature state of 77K, while the upper surface is exposed to the air to maintain room temperature. Due to the low thermal conductivity of the observation medium 3 itself, after the shape of the observation medium 3 is optimized through finite element heat transfer analysis, a stable temperature gradient can be formed in its axial direction (height direction). The existence of this temperature gradient prevents the liquid nitrogen from boiling on the lower surface of the observation medium 3, and the upper surface from frosting or fogging, thereby ensuring the clarity of the observation.

[0035] Please refer to Figure 2-3 The sample stage 2 is a component used to fix the superconducting film 5 in this embodiment. The sample stage 2 is made of metal material and has sufficient strength and stability. The sample stage 2 is provided with bolts, springs, clips and other accessories used to fix the magneto-optical film 10 to ensure the stability and reliability of the superconducting film 5 during the test.

[0036] When preparing the sample stage 2, the superconducting film 5 and the magneto-optical film 10 need to be pre-processed. Specifically, the superconducting film 5 needs to be cut into appropriate sizes and shapes, and cleaned to remove impurities and oil stains on the surface. The surface of the magneto-optical film 10 is cleaned to ensure the imaging quality, and the cleaned magneto-optical film 10 is placed on top of the superconducting film 5, and the magneto-optical film 10 is fixed to the sample stage 2 by bolts, springs and clips.

[0037] The fixed sample stage 2 needs to be placed in the liquid nitrogen container 1 and fully cooled. In this embodiment, the cooling time is usually 1-2 minutes to ensure that the superconducting film 5 and the magneto-optical film 10 can fully adapt to the liquid nitrogen environment and reach a stable low temperature state.

[0038] The magneto-optical imaging system is the core component used to realize the internal damage detection of the superconducting film 5 in this embodiment. Specifically, the magneto-optical imaging system is mainly composed of a filter, a beam splitter 4, an observation component and a light source component. The observation component includes a polarizer 6 arranged above the beam splitter 4 and a camera 7 arranged above the polarizer 6. The light source component includes a polarizer 8 arranged at the side end of the beam splitter 4 and a light source 9 arranged at the side end of the polarizer 8. The light source 9 emits light as the initial light source for imaging, and adjusts its luminous intensity and direction to ensure that the light can be evenly irradiated on the magneto-optical film 10. The filter is placed between the light source 9 and the superconducting film 5, and the light emitted by the light source 9 is converted into a single wavelength of 532nm green light to meet the needs of magneto-optical imaging. The polarizer 8 is arranged between the filter and the superconducting film 5 to convert the green light into linearly polarized light, which is one of the key steps in the magneto-optical imaging process. The beam splitter 4 is used to guide the linearly polarized light to the observation medium 3 and make the linearly polarized light reach the magneto-optical film 10. The analyzer 6 is placed orthogonally to the polarizer 8, and is used to detect the change in the polarization state of the light after passing through the magneto-optical film 10, thereby forming an image of light and dark distribution. The camera 7 is used to collect the image formed by the analyzer 6, and extract the magnetic field distribution information through a post-processing program, and then invert the obtained current density distribution and defect information of the superconducting film 5.

[0039] After the magneto-optical imaging system is built, it needs to be debugged to ensure that it can work properly. Specifically, it is necessary to adjust the luminous intensity of the light source 9, the polarization directions of the polarizer 8 and the analyzer 6, and the exposure time and focal length of the camera 7.

[0040] In order to ensure that the observation medium 3 and the magneto-optical imaging system can work stably, this embodiment also includes a set of brackets and fixing devices (not clearly marked in the figure, but implicit components). The bracket is used to support the observation medium 3 and various components of the magneto-optical imaging system to ensure that they can be accurately positioned above the liquid nitrogen container 1. The fixing device is used to firmly fix the bracket on the experimental table to prevent shaking or displacement during the experiment.

[0041] The present invention also provides a method for detecting internal damage of a superconducting thin film material in a liquid nitrogen environment, which is applied to a device for detecting internal damage of a superconducting thin film material in a liquid nitrogen environment, and specifically comprises the following steps:

[0042] S1. Prepare and cool a liquid nitrogen container: Use 3D printing technology to prepare a polylactic acid cylindrical barrel as a liquid nitrogen container 1, and put the liquid nitrogen container 1 into a foam barrel for heat insulation treatment; then, introduce liquid nitrogen into the liquid nitrogen container 1 as a cooling medium, and keep it in a cooling state;

[0043] S2. Optimize and place the observation medium: Use a rectangular column made of polymethyl methacrylate as the observation medium 3, and optimize its shape through finite element heat transfer analysis to ensure thermal conductivity; half-immerse the observation medium 3 in the liquid nitrogen container 1 and place it above the superconducting film 5 to be observed, while ensuring that the lower surface of the observation medium 3 is continuously immersed in liquid nitrogen to maintain a low temperature state;

[0044] S3, assembling and cooling the sample stage: covering the magneto-optical film 10 on the superconducting film 5 material, and fixing the two on the sample stage 2 with bolts, springs and clips; placing the assembled sample stage 2 in the cooled liquid nitrogen container 1, and keeping it in a cooling state to ensure thermal equilibrium;

[0045] S4, configure the observation system: install a bracket above the semi-immersed polymethyl methacrylate rectangular column, and the light source emits light that can penetrate the polymethyl methacrylate medium and reach the magneto-optical film 10 on the surface of the superconducting film 5;

[0046] S5, adjusting and collecting magneto-optical images: the single wavelength green light emitted by the light source 9 is made to become linearly polarized light after passing through the filter and the polarizer 8, and the polarized light passes through the beam splitter 4 and the polymethyl methacrylate medium, reaches the magneto-optical film 10 and is reflected, and passes through the polymethyl methacrylate medium and the beam splitter 4 again, and forms a light and dark distribution image after passing through the analyzer 6; the image is captured and recorded by the camera 7;

[0047] S6. Analyze and extract magnetic field information: apply a post-processing program to the collected magneto-optical image to extract magnetic field distribution information; based on the magnetic field distribution information, inversely calculate the current density distribution, and determine the defect size and position information of the superconducting film 5 according to the attenuation of the current density.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A device for detecting internal damage of superconducting thin film materials in a liquid nitrogen environment, characterized in that: include: A liquid nitrogen container (1), wherein a sample stage (2) is provided at the bottom of the liquid nitrogen container (1), and the liquid nitrogen container (1) is filled with liquid nitrogen; an observation medium (3) is provided above the sample stage (2); the lower end of the observation medium (3) is immersed in the liquid nitrogen, and the upper end of the observation medium (3) is arranged outside the liquid nitrogen; the observation medium (3) undergoes convective heat exchange between the liquid nitrogen and the air; a beam splitter prism (4) is provided above the observation medium (3); an observation component is provided above the beam splitter prism (4); and a light source component is provided at the side end of the beam splitter prism (4); A superconducting film (5) is arranged on the top of the sample stage (2), a magneto-optical film (10) is arranged on the top of the superconducting film (5), and the light generated by the light source assembly passes through the beam splitter prism (4) and the observation medium (3) to the top of the magneto-optical film (10), and is reflected by the magneto-optical film (10) to the observation medium (3) and the beam splitter prism (4) to enter the observation assembly; The liquid nitrogen container (1) is a polylactic acid cylindrical barrel, and a heat preservation barrel is arranged outside the polylactic acid cylindrical barrel; The observation medium (3) is a polymethyl methacrylate rectangular column.

2. The device for detecting internal damage of superconducting thin film materials in liquid nitrogen environment according to claim 1, characterized in that: The observation component comprises a polarizer (6) arranged above the beam splitter prism (4) and a camera (7) arranged above the polarizer (6).

3. The internal damage detection device for superconducting thin film materials in liquid nitrogen environment according to claim 1, characterized in that: The light source assembly comprises a polarizer (8) arranged at the side end of the beam splitter prism (4) and a light source (9) arranged at the side end of the polarizer (8).

4. A method for detecting internal damage of superconducting thin film materials in a liquid nitrogen environment, characterized in that: The internal damage detection device for superconducting thin film materials in a liquid nitrogen environment as claimed in any one of claims 1 to 3 comprises the following steps: S1. preparing and cooling a liquid nitrogen container (1): using 3D printing technology to prepare a polylactic acid cylindrical barrel as a liquid nitrogen container (1), placing the liquid nitrogen container (1) in a foam barrel for heat insulation treatment; then, introducing liquid nitrogen as a cooling medium into the liquid nitrogen container (1), and maintaining the liquid nitrogen container (1) in a cooling state; S2. Optimize and place the observation medium (3): use a rectangular column made of polymethyl methacrylate as the observation medium (3), and optimize its shape through finite element heat transfer analysis to ensure thermal conductivity; half-immerse the observation medium (3) in a liquid nitrogen container (1) and place it above the superconducting film (5) to be observed, while ensuring that the lower surface of the observation medium (3) is continuously immersed in liquid nitrogen to maintain a low temperature state; S3, assembling and cooling the sample stage (2): covering the magneto-optical film (10) on the superconducting film (5) material, and fixing the two on the sample stage (2) using bolts, springs and clips; placing the assembled sample stage (2) in a cooled liquid nitrogen container (1), and keeping it in a cooled state to ensure that thermal equilibrium is achieved; S4, configuring an observation system: installing a bracket above the semi-immersed polymethyl methacrylate rectangular column, and emitting light from a light source capable of penetrating the polymethyl methacrylate medium and reaching the magneto-optical film (10) on the surface of the superconducting film (5); S5, adjusting and collecting magneto-optical images: the single wavelength green light emitted by the light source (9) is converted into linear polarized light after passing through the filter and the polarizer (8); the polarized light passes through the beam splitter (4) and the polymethyl methacrylate medium, reaches the magneto-optical film (10) and is reflected, passes through the polymethyl methacrylate medium and the beam splitter (4) again, and forms a light and dark distribution image after passing through the analyzer (6); the image is captured and recorded using a camera (7); S6. Analyze and extract magnetic field information: apply a post-processing program to the collected magneto-optical image to extract magnetic field distribution information; based on the magnetic field distribution information, inversely calculate the current density distribution, and determine the defect size and position information of the superconducting film (5) according to the attenuation of the current density.

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