Device and method for detecting critical current density of high temperature superconducting film

Abstract

The present application relates to the field of high-temperature superconductivity, and in particular to a device and method for detecting the critical current density of a high-temperature superconducting film, comprising a vector network analyzer, a waveguide, a coil unit, and a low-temperature sample stage arranged in sequence along the direction of microwave propagation, and also comprising a data acquisition and analysis system connected to the vector network analyzer in communication, the high-temperature superconducting film to be tested is placed on the low-temperature sample stage, and the coil unit is used to generate an alternating magnetic field according to different currents to stimulate the internal part of the high-temperature superconducting film to be tested to generate a superconducting current, so that the high-temperature superconducting film to be tested changes from a superconducting state to a non-superconducting state, and the reflection coefficient of microwaves is detected by the vector network analyzer to monitor the change of the critical state of the high-temperature superconducting film, thereby detecting the critical current density. The device can solve the technical problems faced by the prior art, such as low resolution and unreliable measurement.

Description

Technical Field

[0001] The present application relates to the field of high-temperature superconductivity, and in particular to a device and method for detecting critical current density of a high-temperature superconducting film. Background Art

[0002] Due to its unique physical properties and superior performance in a tiny size, high-temperature superconducting thin films have shown broad application prospects in power transmission, magnetic levitation, electronic communications, medical treatment and other fields. As one of the basic properties of superconducting materials, critical current density determines the stability of the working characteristics and power load capacity of superconducting devices. Rapid, accurate, high-resolution and non-destructive critical current density evaluation methods are extremely important for the successful application of high-temperature superconducting thin films.

[0003] There are currently two main methods for measuring critical current density: the four-terminal method and the inductance method. The four-terminal method of applying current to a high-temperature superconducting film is very reliable in its measurement results. However, since it is necessary to apply a current greater than the critical current of the sample, when the critical current density of the high-temperature superconducting film is large, it is difficult to measure without a power supply capable of outputting a large current. At the same time, this method is damaging to superconducting materials, especially the etching process will have a certain impact on the properties of the superconducting material, the electrode preparation process is also very complicated, and the use of large current measurements may also pose the risk of burning out the high-temperature superconducting film to be tested.

[0004] The electromagnetic induction method evaluates the critical current density by measuring the third harmonic voltage. This method allows non-contact measurement of high-temperature superconducting films, thereby avoiding damage to the sample or reduction of critical current characteristics due to heating. This method allows a more detailed evaluation of electromagnetic characteristics by measuring the AC penetration flux value in the high-temperature superconducting film when a small AC magnetic field is superimposed on a DC magnetic field and applied in parallel. However, the current common problems faced by the electromagnetic induction method based on third harmonic measurement to detect critical current density are: ① The coil volume is too large, resulting in a large spatial resolution of the system, which is difficult to meet the detection requirements of small areas of high-temperature superconducting films; ② The system uses a coil to detect the third harmonic voltage, which is easily affected by external factors (such as magnetic field, temperature, frequency of coil excitation current, etc.), resulting in uncertainty in the detection results. Summary of the invention

[0005] Based on this, it is necessary to provide a device and method for detecting the critical current density of a high-temperature superconducting film in order to solve the above-mentioned technical problems.

[0006] In a first aspect, an embodiment of the present application provides a device for detecting critical current density of a high-temperature superconducting film, comprising a vector network analyzer, a waveguide, a coil unit, and a low-temperature sample stage arranged in sequence along the direction of microwave propagation, and also comprising a data acquisition and analysis system connected to the vector network analyzer in communication, wherein the high-temperature superconducting film to be tested is placed on the low-temperature sample stage; wherein,

[0007] The vector network analyzer is used to generate continuous microwaves, which pass through the waveguide and the coil unit and are vertically focused on the surface of the high-temperature superconducting film to be tested. The reflected microwaves return to the vector network analyzer through the waveguide along the original path. The vector network analyzer detects the reflection coefficient of the microwaves and transmits it to the data acquisition and analysis system.

[0008] The coil unit is used to generate an alternating magnetic field according to different currents, to stimulate the inside of the high-temperature superconducting film to be tested to generate a superconducting current, so that the high-temperature superconducting film to be tested changes from a superconducting state to a non-superconducting state;

[0009] The data acquisition and analysis system detects the critical current density of the high-temperature superconducting film to be tested in a critical state based on the reflection coefficient under different currents.

[0010] In some embodiments, the data acquisition and analysis system generates a relationship curve between reflection coefficient and current according to the reflection coefficient under different currents, obtains a critical current by fitting the relationship curve, and obtains the critical current density based on the critical current.

[0011] In some embodiments, the data acquisition and analysis system includes a data acquisition card and an intelligent terminal that are communicatively connected. The data acquisition card is communicatively connected to the vector network analyzer and is used to collect the reflection coefficient under different currents. The intelligent terminal is used to calculate the critical current density based on the reflection coefficient under different currents.

[0012] In some embodiments, the coil unit includes a coil bracket in the shape of a trapezoidal cylinder with an inner diameter gradually decreasing from top to bottom, and a multi-turn coil wound around the coil bracket. The coil bracket is hollow, and a light-through hole is provided on the lower surface of the multi-turn coil. When the coil unit is energized, a magnetic field is formed from top to bottom.

[0013] In some embodiments, the height of the coil support is 5 mm, the diameter of the upper surface is 4 mm, the diameter of the lower surface is 2 mm, and the number of turns of the coil is 500.

[0014] In some embodiments, a translation stage is further included below the low-temperature sample stage for adjusting the position of the high-temperature superconducting film to be tested and focusing the microwave on the surface of the high-temperature superconducting film to be tested.

[0015] In some embodiments, a vacuum chamber is further included, and the high-temperature superconducting film to be tested, the low-temperature sample stage, and the translation stage are arranged in the vacuum chamber.

[0016] In some embodiments, a liquid nitrogen pump connected to the low-temperature sample stage through a liquid nitrogen circulation pipeline is also included to control the temperature of the low-temperature sample stage.

[0017] In some embodiments, a current source meter connected to the coil unit is further included to provide different currents.

[0018] In a second aspect, an embodiment of the present application provides a startup control method for a high-temperature superconducting film critical current density detection device, which is applied to the high-temperature superconducting film critical current density detection device as described in the first aspect, and the method includes:

[0019] Controlling the vector network analyzer to generate microwaves, and adjusting the position of the high-temperature superconducting film to be tested through the displacement stage so that the microwaves are focused on the surface of the high-temperature superconducting film to be tested;

[0020] Control the low temperature sample stage to keep its temperature below the critical temperature of the high temperature superconducting film to be tested; control the vacuum degree in the vacuum chamber to be 10 -4 Below Pa;

[0021] Controlling the current source to provide different currents to the coil unit so that it generates an alternating magnetic field, thereby stimulating the inside of the high-temperature superconducting film to be tested to generate a superconducting current, so that the high-temperature superconducting film to be tested changes from a superconducting state to a non-superconducting state;

[0022] Controlling the vector network analyzer to detect the reflection coefficient of microwaves and transmit the result to the data acquisition and analysis system;

[0023] The control data acquisition and analysis system detects the critical current density of the high-temperature superconducting film to be tested in a critical state based on the reflection coefficient under different currents.

[0024] The present application has the following technical effects: the coil unit is used to generate an alternating magnetic field according to different currents, and the superconducting current is stimulated inside the high-temperature superconducting film to be tested, so that the high-temperature superconducting film to be tested changes from a superconducting state to a non-superconducting state, and the reflection coefficient of microwaves is detected by a vector network analyzer to monitor the change of the critical state of the high-temperature superconducting film, thereby detecting the critical current density. The device can solve the technical problems of low resolution and unreliable measurement faced by the prior art, and has the advantages of high resolution, rapid detection, high sensitivity and reliable results, and the device has a compact structure, is easy to operate, and is easier to miniaturize, practical and commercialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of the structure of a device for detecting critical current density of a high-temperature superconducting film provided in one embodiment of the present application;

[0026] Figure 2 This is a schematic diagram of the structure of the coil unit in the embodiment of the present application;

[0027] Figure 3A schematic diagram of a process for detecting critical current density of a high-temperature superconducting film provided in one embodiment of the present application;

[0028] Figure 4 A schematic diagram of the structure of a computer device provided in one embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is described and illustrated below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Based on the embodiments provided in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application. In addition, it can also be understood that although the efforts made in this development process may be complex and lengthy, for ordinary technicians in the field related to the contents disclosed in the present application, some changes such as design, manufacturing or production based on the technical contents disclosed in the present application are only conventional technical means, and should not be understood as insufficient contents disclosed in the present application.

[0030] Reference to "embodiments" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those of ordinary skill in the art that the embodiments described in this application may be combined with other embodiments without conflict.

[0031] Unless otherwise defined, the technical terms or scientific terms involved in this application should be understood by people with ordinary skills in the technical field to which this application belongs. The words "one", "a", "a", "the" and the like involved in this application do not indicate a quantitative limitation, and may represent the singular or plural. The terms "include", "comprise", "have" and any of their variations involved in this application are intended to cover non-exclusive inclusions; for example, a process, method, system, product or device that includes a series of steps or modules (units) is not limited to the listed steps or units, but may also include steps or units that are not listed, or may also include other steps or units inherent to these processes, methods, products or devices. The words "connect", "connected", "coupled" and the like involved in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The "multiple" involved in this application refers to greater than or equal to two. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships, for example, "A and / or B" can represent: A exists alone, A and B exist at the same time, and B exists alone. The terms "first", "second", "third" and the like involved in the present application are merely used to distinguish similar objects and do not represent a specific ordering of the objects.

[0032] Figure 1 This is a schematic diagram of the structure of the critical current density detection device for high-temperature superconducting thin films provided in the embodiment of the present application. Figure 1 As shown, the detection device includes a vector network analyzer 1, a waveguide 2, a coil unit 3, and a low-temperature sample stage 6 which are arranged in sequence along the direction of microwave propagation, and also includes a data acquisition and analysis system which is communicatively connected to the vector network analyzer 1. The high-temperature superconducting film 4 to be tested is placed on the low-temperature sample stage 6 through a film substrate 5.

[0033] The detection device further comprises a displacement stage 7 disposed below the low temperature sample stage 6. The high temperature superconducting film 4 to be tested, the low temperature sample stage 6 and the displacement stage 7 are disposed in a vacuum chamber 8.

[0034] The detection device also includes a liquid nitrogen pump 9 connected to the low-temperature sample stage 6 through a liquid nitrogen circulation pipeline.

[0035] The detection device further includes a current source meter 12 connected to the coil unit 3 .

[0036] The low temperature sample stage 6 is used to control the temperature of the high temperature superconducting film 4 to be tested. It has a liquid nitrogen circulation pipeline connected to the liquid nitrogen pump 9 and has a real-time temperature monitoring function. Generally speaking, the temperature should reach 77 K. The surface of the low temperature sample stage 6 is completely horizontal, so that the surface of the high temperature superconducting film 4 to be tested is horizontal and perpendicular to the microwave, ensuring that the reflected microwave can return along the original path.

[0037] The low temperature sample stage 6 is fixed on the displacement stage 7, and a temperature detection probe is installed inside to detect the temperature of the high temperature superconducting film 4 to be tested in real time. Generally speaking, the temperature should be below the critical temperature of the high temperature superconducting film during the test and remain unchanged to ensure that the temperature drift does not exceed 0.5°C.

[0038] The translation stage 7 is fixed at the bottom of the vacuum chamber, and its XY stroke is 100 mm and Z axis stroke is 60 mm. The translation stage 7 is connected to the data acquisition and analysis system through a data cable, and is moved and controlled by the operating rod 11 through the developed labview program to achieve automatic focusing and scanning imaging, and is used to control the position of the high-temperature superconducting film 4 to be tested.

[0039] The vacuum chamber 8 is connected to the vacuum pump through a pipeline. During the actual operation, the vacuum degree in the vacuum chamber 8 should be maintained at 10 -4 Below Pa.

[0040] The air and moisture inside the vacuum chamber 8 are pumped out by a vacuum pump to prevent water droplets from condensing on the surface when the temperature of the high-temperature superconducting film to be measured drops below zero degrees Celsius, thereby damaging the high-temperature superconducting film to be measured and affecting the measurement results.

[0041] The coil unit is connected to the current source meter 12 wire, and the current source meter 12 provides the coil unit with an alternating current of no more than 100mA. The current size can be continuously adjusted from 0.1-100mA, and the frequency is adjustable from 500-1000Hz. In actual testing, 800Hz or 1000Hz can be selected. The current size changes continuously from 0.01-0.5A, with an interval of 0.01A.

[0042] The vector network analyzer 1 is fixed above the coil unit 3 and is used to generate continuous microwaves, which pass through the waveguide 2 and the light-through hole of the coil unit 3 and are vertically focused on the surface of the high-temperature superconducting film 4 to be tested. The reflected microwaves return to the vector network analyzer 1 through the waveguide 2 along the original path.

[0043] The high temperature superconducting film 4 to be tested completely reflects microwaves when in a superconducting state, and has a certain absorption and transmission of microwaves when in a non-superconducting state. The coil unit 3 is used to generate an alternating magnetic field according to different currents, and to stimulate the inside of the high temperature superconducting film 4 to be tested to generate a superconducting current, so that the high temperature superconducting film 4 to be tested changes from a superconducting state to a non-superconducting state.

[0044] The microwave reflected by the surface returns along the original path, passes through the waveguide and is injected into the vector network analyzer 1. The vector network analyzer 1 analyzes the change of the microwave reflection coefficient with the current applied by the coil unit 3, so as to judge the state change of the high-temperature superconducting film 4 to be tested, and transmits the reflection coefficient to the data acquisition and analysis system. This step is also automated using the developed labview program.

[0045] The data acquisition and analysis system includes a data acquisition card 10 and an intelligent terminal 13 which are communicatively connected. The data acquisition card 10 is communicatively connected to the vector network analyzer 1 for collecting the reflection coefficient under different currents. The intelligent terminal 13 is used for calculating the critical current density according to the reflection coefficient under different currents.

[0046] Specifically, the intelligent terminal 13 generates a curve of the relationship between the reflection coefficient and the current according to the reflection coefficient under different currents, and fits the nonlinear part of the curve drawn in the previous step to obtain the intersection point of the horizontal coordinate of the fitting curve, that is, the critical current Ic.

[0047] The fitted current is converted into the critical current density Jc using the formula:

[0048] Jc=KIc / d

[0049] Where K is a constant coefficient that needs to be determined through experimental calibration, Ic is the critical current, and d is the high-temperature superconducting film to be tested, in Å.

[0050] The detection device can realize rapid, non-destructive and accurate detection of the critical current density of high-temperature superconducting thin films. Compared with the traditional detection method of the critical current density of high-temperature superconducting thin films, this method can meet the detection requirements of higher resolution and more reliable.

[0051] Figure 2 Schematic diagram of the structure of the coil unit in the embodiment of the present application. The coil unit 3 includes a coil support 301 with a trapezoidal cylinder and an inner diameter that gradually decreases from top to bottom, and a multi-turn coil 302 wound on the coil support 301. The coil support 301 is hollow, and a light hole is provided on the lower surface of the multi-turn coil 302 for unimpeded transmission of microwaves. When the coil unit 3 is powered on, a magnetic field 14 is formed from top to bottom.

[0052] The height of the coil support 301 is 5 mm, the diameter of the upper surface is 4 mm, the diameter of the lower surface is 2 mm, and the number of turns of the coil 302 is 500.

[0053] The lower side of the coil is parallel to the surface of the high-temperature superconducting film 4 to be tested, with a spacing of 0.2 mm, and the light hole is perpendicular to the surface of the high-temperature superconducting film 4 to be tested. After the coil unit 3 is powered on, the generated alternating magnetic field is shown by the dotted line in the figure. The magnetic field below the coil is parallel to the surface of the high-temperature superconducting film 4 to be tested. Due to the complete anti-magnetism of the high-temperature superconducting film 4 to be tested, a superconducting shielding current will be generated on the surface, hindering the passage of the magnetic field. When the current in the coil increases to a certain value, the magnetic field reaches the critical magnetic field of the high-temperature superconducting film 4 to be tested, and the high-temperature superconducting film 4 to be tested changes from a superconducting state to a non-superconducting state, and the terahertz reflectivity changes at this time.

[0054] In this embodiment, the light-transmitting coil allows microwaves to pass through the coil and irradiate the surface of the high-temperature superconducting film 4 to be tested, thereby detecting the state change of the high-temperature superconducting film 4 to be tested. A new detection method is provided for non-destructive detection of the critical current density of the high-temperature superconducting film 4 to be tested, making the result more reliable and accurate.

[0055] The present application embodiment provides a startup control method for a high-temperature superconducting film critical current density detection device, such as Figure 3 As shown, the method comprises the following steps:

[0056] S101, controlling the vector network analyzer to generate microwaves, and adjusting the position of the high-temperature superconducting film to be tested by the displacement stage so that the microwaves are focused on the surface of the high-temperature superconducting film to be tested.

[0057] Specifically, the developed Labview program is used to set the specified coordinate value and control the distance between the high-temperature superconducting film to be tested and the lower surface of the coil to be 0.2 mm. The microwave focus is on the surface of the high-temperature superconducting film, which specifically means that the microwave is focused by a lens, and the spot size after focusing is ≤1 mm.

[0058] S102, controlling the low temperature sample stage to keep its temperature at a value below the critical temperature of the high temperature superconducting film to be tested; controlling the vacuum degree in the vacuum chamber to be at 10 -4 Below Pa.

[0059] Control the flow and flow rate of liquid nitrogen inside the cryogenic sample stage to first ensure that the temperature of the cryogenic sample stage is at 77K, and then transfer the temperature to the high-temperature superconducting film to be tested, with the temperature drifting up and down not exceeding 0.5℃.

[0060] S103, controlling the current source to provide different currents to the coil unit to generate an alternating magnetic field, thereby stimulating the inside of the high-temperature superconducting film to be tested to generate a superconducting current, so that the high-temperature superconducting film to be tested changes from a superconducting state to a non-superconducting state.

[0061] Specifically, the frequency and current magnitude of the sinusoidal current output by the current source meter are controlled by the LabVIEW program. The frequency is a fixed value, generally 800Hz. The current magnitude changes continuously from 0.01-0.5A, with an interval of 0.01A.

[0062] S104, controlling the vector network analyzer to detect the reflection coefficient of the microwave and transmit it to the data acquisition and analysis system.

[0063] S105, controlling the data acquisition and analysis system to detect the critical current density of the high-temperature superconducting film to be tested in a critical state based on the reflection coefficient under different currents.

[0064] In one embodiment, the present invention provides a computer device, which may be a server, and its internal structure diagram may be as follows: Figure 4 As shown. The computer device includes a processor, a memory and a network interface connected via a system bus. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store motion detection data. The network interface of the computer device is used to communicate with an external terminal via a network connection. When the computer program is executed by the processor, the steps in any one of the above detection method embodiments are implemented.

[0065] Those skilled in the art will understand that Figure 4 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components.

[0066] In one embodiment, an embodiment of the present invention provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps in any one of the above detection method embodiments are implemented.

[0067] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0068] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A device for detecting critical current density of a high-temperature superconducting film, characterized in that: It includes a vector network analyzer, a waveguide, a coil unit, and a low-temperature sample stage which are sequentially arranged along the direction of microwave propagation, and also includes a data acquisition and analysis system which is communicatively connected to the vector network analyzer, and the high-temperature superconducting film to be tested is placed on the low-temperature sample stage; wherein, The vector network analyzer is used to generate continuous microwaves, which pass through the waveguide and the coil unit and are vertically focused on the surface of the high-temperature superconducting film to be tested. The reflected microwaves return to the vector network analyzer through the waveguide along the original path. The vector network analyzer detects the reflection coefficient of the microwaves and transmits it to the data acquisition and analysis system. The coil unit is used to generate an alternating magnetic field according to different currents, to stimulate the inside of the high-temperature superconducting film to be tested to generate a superconducting current, so that the high-temperature superconducting film to be tested changes from a superconducting state to a non-superconducting state; The data acquisition and analysis system detects the critical current density of the high-temperature superconducting film to be tested in a critical state based on the reflection coefficient under different currents.

2. The device for detecting critical current density of a high-temperature superconducting thin film according to claim 1, characterized in that: The data acquisition and analysis system generates a relationship curve between the reflection coefficient and the current according to the reflection coefficient under different currents, obtains the critical current by fitting the relationship curve, and obtains the critical current density based on the critical current.

3. The device for detecting critical current density of a high-temperature superconducting thin film according to claim 2, characterized in that: The data acquisition and analysis system includes a data acquisition card and an intelligent terminal that are communicatively connected. The data acquisition card is communicatively connected to the vector network analyzer and is used to collect the reflection coefficient under different currents. The intelligent terminal is used to calculate the critical current density based on the reflection coefficient under different currents.

4. The device for detecting critical current density of a high-temperature superconducting thin film according to claim 1, characterized in that: The coil unit includes a coil bracket in the shape of a trapezoidal cylinder with an inner diameter gradually decreasing from top to bottom and a multi-turn coil wound on the coil bracket. The coil bracket is hollow, and a light-through hole is provided on the lower surface of the multi-turn coil. When the coil unit is energized, a magnetic field from top to bottom is formed.

5. The device for detecting critical current density of a high-temperature superconducting thin film according to claim 4, characterized in that: The coil support has a height of 5 mm, an upper surface diameter of 4 mm, a lower surface diameter of 2 mm, and the number of turns of the coil is 500.

6. The device for detecting critical current density of a high-temperature superconducting thin film according to claim 1, characterized in that: It also includes a translation stage arranged below the low-temperature sample stage, which is used to adjust the position of the high-temperature superconducting film to be tested and focus the microwave on the surface of the high-temperature superconducting film to be tested.

7. The device for detecting critical current density of a high-temperature superconducting thin film according to claim 6, characterized in that: It also includes a vacuum chamber, in which the high-temperature superconducting film to be tested, the low-temperature sample stage, and the displacement stage are arranged.

8. The device for detecting critical current density of a high temperature superconducting thin film according to claim 7, characterized in that: It also includes a liquid nitrogen pump connected to the low-temperature sample stage through a liquid nitrogen circulation pipeline, which is used to control the temperature of the low-temperature sample stage.

9. The device for detecting critical current density of a high temperature superconducting thin film according to claim 1, characterized in that: Also included is a current source meter connected to the coil unit for providing different currents.

10. A method for detecting critical current density of a high-temperature superconducting film, applied to the detection device according to any one of claims 1 to 9, characterized in that: The method comprises: Controlling the vector network analyzer to generate microwaves, and adjusting the position of the high-temperature superconducting film to be tested through the displacement stage so that the microwaves are focused on the surface of the high-temperature superconducting film to be tested; Control the low temperature sample stage to keep its temperature below the critical temperature of the high temperature superconducting film to be tested; control the vacuum degree in the vacuum chamber to be 10 -4 Below Pa; Controlling the current source to provide different currents to the coil unit so that it generates an alternating magnetic field, thereby stimulating the inside of the high-temperature superconducting film to be tested to generate a superconducting current, so that the high-temperature superconducting film to be tested changes from a superconducting state to a non-superconducting state; Controlling the vector network analyzer to detect the reflection coefficient of microwaves and transmit the result to the data acquisition and analysis system; The control data acquisition and analysis system detects the critical current density of the high-temperature superconducting film to be tested in a critical state based on the reflection coefficient under different currents.

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