Method for measuring critical current of superconducting material by using additional power supply preloading current

Abstract

The invention relates to the technical field of superconducting materials, and discloses a method for measuring the critical current of a superconducting material by using an additional power supply preloading current, which comprises the following steps of: setting the output voltage of a high-precision safety power supply to be recognizable minimum resolution voltage, and setting the current output to be close to or reach the upper limit; gradually increasing the current output of the main direct-current power supply, and measuring and recording the output current of the main power supply and the high-precision safety power supply and the voltage on the superconducting sample; and repeating the steps until the voltage on the superconducting sample reaches the specified criterion voltage, and at the moment, the total current on the superconducting sample is the critical current of the sample. According to the invention, the total number of test steps is reduced through the large-step test, the overall test time is remarkably shortened, and when the voltage on the superconducting sample is close to the identification voltage, the circuit can automatically reduce the current output to ensure that the voltage on the sample does not exceed a safety limit value, so that the sample is prevented from being damaged due to overhigh voltage.

Description

Technical Field

[0001] The invention relates to the technical field of superconducting materials, and in particular to a method for measuring the critical current of a superconducting material by using an additional power supply to preload a current. Background Art

[0002] Superconducting materials are widely used in science and technology and daily life. For example, they can be used to manufacture energy-efficient maglev trains and power transmission lines, as well as high-tech equipment such as high-energy particle accelerators and MRI scanners. In superconductors, when the strength of the external magnetic field exceeds a certain value, the conductivity suddenly changes, the resistance suddenly drops, and the current suddenly increases. This phenomenon is called the critical current of the superconductor. At a certain temperature, a superconductor has a critical current value. Only when the strength of the external magnetic field exceeds this value can the superconductor be called a superconductor. The value of the critical current is different for different materials and different temperatures. The critical current is an important parameter of superconducting materials, which is related to the properties and temperature of the material.

[0003] After searching, the Chinese patent number CN110426661B discloses a critical current measurement method, system and medium for superconducting materials, including: a time-varying current loading step: passing a time-varying current through a sample; a magnetic field measurement step: setting a sensor including an inductive coil at a preset position, measuring the magnetic field distribution around the sample through the sensor, and obtaining measurement information; a critical current judgment step: judging whether the sample has reached a critical current state and at which moment the sample has reached the critical current in the time-varying current loading step according to the obtained measurement information, and obtaining the critical current of the sample. The present invention has been tested with a short sample, and the sample has been repeatedly tested for many times under the condition that the current is much larger than the critical current of the sample (a current of 550A is passed through a sample with a critical current of 300A), thereby avoiding the burning of the sample.

[0004] However, the above measurement method is to gradually increase the output current until the voltage exceeds the critical value, so as to determine whether the critical current has been reached. However, this test method has two problems. The first problem is that each cycle of current flow and voltage measurement takes time, so the entire test process is relatively slow, and a curve measurement takes about tens of seconds; the second problem is that the voltage of superconducting materials is nonlinear, and the change of current is difficult to estimate under voltages in different regions. The sudden increase in current value is enough to burn the sample, which poses a certain threat to the safety of the sample and the entire experiment. Based on this, the present invention designs a method for measuring the critical current of superconducting materials by using an additional power supply to preload current to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to provide a method for measuring the critical current of a superconducting material by using an additional power supply to preload current, thereby solving the problems of low test efficiency and difficulty in estimating current changes in the background technology.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A test device for preloading current by using an additional power supply comprises the following structures:

[0008] Main DC power supply (PS1): used to provide step-up current;

[0009] High-precision safety power supply (PS2): connected in parallel with the main DC power supply for preloading current;

[0010] Superconducting sample (Rsc): acts as a variable resistor;

[0011] Voltmeter (V): used to measure the voltage change across the superconducting sample;

[0012] Line resistance (R1): represents the line resistance in the test circuit;

[0013] Feedback wires (s2+ and s2-): connect the safety power supply and the measurement circuit.

[0014] Preferably, the main DC power supply (PS1) and the high-precision safety power supply (PS2) are designed in parallel, so that the total current during the test process is provided by both.

[0015] Preferably, the dual (multi) power supply structure in the above technical solution includes the following steps:

[0016] Step S1: setting the output voltage of the high-precision safety power supply to the minimum recognizable resolution voltage, and the current output approaches or reaches its upper limit (I2M);

[0017] Step S2: gradually increasing the current output of the main DC power supply, with each step being at least (I2M) or slightly less than (I2M), while measuring and recording the output currents (I1) and (I2) of the main power supply and the high-precision safety power supply, as well as the voltage on the superconducting sample;

[0018] Step S3: Repeat step S2 until the voltage on the superconducting sample reaches the specified criterion voltage. At this time, the total current (I1+I2) on the superconducting sample is the critical current of the sample.

[0019] Preferably, the voltage output of the high-precision safety power supply (PS2) is set to the minimum recognizable resolution voltage, and the current output is set to the output upper limit (I2M) of the high-precision safety power supply (PS2) itself or a value close to this value.

[0020] Preferably, the feedback lines (s2+ and s2-) feed back the voltage on the superconducting sample (Rsc) to the high-precision safety power supply (PS2), so that the high-precision safety power supply (PS2) can automatically adjust its current output mode according to the feedback voltage, that is, switch between constant current mode and constant voltage mode to ensure sample safety.

[0021] Preferably, the safe and fast testing device for measuring the critical current of superconducting materials also includes an optional voltage upper limit protection mechanism, which adds feedback compensation to the main DC power supply (PS1) and sets a voltage upper limit to further protect the superconducting sample (Rsc) from the influence of excessively high voltage.

[0022] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0023] 1. The present invention, due to the introduction of the high-precision safety power supply PS2, the test step size can be set to its output upper limit I2M, which is much larger than the 2A or 5A step size commonly used in traditional methods. The large step size test reduces the total number of test steps and significantly shortens the overall test time; when the superconducting sample Rsc approaches the critical current, the voltage will increase rapidly. The traditional method requires more steps to detect significant changes in voltage due to the small step size. The present invention, through the large step size test, can approach and determine the critical current more quickly, thereby accelerating the test process.

[0024] 2. In the present invention, the high-precision safety power supply PS2 has the ability to automatically adjust the output current. When the voltage on the superconducting sample Rsc is close to its identification voltage, PS2 will automatically reduce the current output to ensure that the voltage on the sample does not exceed the safety limit, thereby avoiding damage to the sample due to excessive voltage. In the traditional method, due to the slow increase of current and the small step size, when the superconducting sample suddenly changes to a resistive state, the voltage may rise sharply, and there is a risk of burning the sample. The present invention effectively reduces this risk through large step size testing and the automatic adjustment function of PS2.

[0025] 3. The present invention designs an optional voltage upper limit protection mechanism, which increases the voltage upper limit through feedback compensation of the main DC power supply PS1, further ensuring voltage safety during the test. This dual protection mechanism greatly improves the safety of the test. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a flow chart of the method of the present invention;

[0027] Figure 2 The traditional test circuit diagram for the critical current of superconducting materials;

[0028] Figure 3 A test circuit diagram of the present invention;

[0029] Figure 4 A test circuit diagram for increasing the main circuit feedback voltage limit of the present invention;

[0030] Figure 5 It is a working principle diagram of the safety power supply of the present invention. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Embodiment 1;

[0033] See also Figure 1-Figure 5 In an embodiment of the present invention, a method for measuring the critical current of a superconducting material by using an additional power source to preload a current needs to provide a safe and fast testing device for measuring the critical current of a superconducting material, including the following structure:

[0034] Main DC power supply PS1: used to provide step-up current;

[0035] High-precision safety power supply PS2: connected in parallel with the main DC power supply, used for preloading current;

[0036] Superconducting sample Rsc: acts as a variable resistor;

[0037] Voltmeter V: used to measure the voltage change across the superconducting sample;

[0038] Line resistance R1: represents the line resistance in the test circuit;

[0039] Feedback lines s2+ and s2-: connect the safety power supply and the measurement circuit;

[0040] The method for measuring the critical current of a superconducting material by using an additional power source to preload the current comprises the following steps:

[0041] Step S1: Set the output voltage of the high-precision safety power supply to the minimum recognizable resolution voltage, and the current output is close to or reaches its upper limit I 2M ;

[0042] Step S2: gradually increase the current output of the main DC power supply, with each increase step being at least I 2M Or slightly less than I 2M , simultaneously measure and record the output current I of the main power supply and high-precision safety power supply 1 and I 2 , and the voltage across the superconducting sample;

[0043] Step S3: Repeat step 2 until the voltage on the superconducting sample reaches the specified criterion voltage. At this time, the total current I 1 +I 2 This is the critical current of the sample.

[0044] The working principle of the embodiment of the present invention is: the characteristic of the prior art is to use the transmission method of measuring voltage by passing current, and its circuit diagram is as follows Figure 2 As shown. The superconducting sample is a variable resistor Rsc. During the test, the output current in the power supply PS is gradually increased, and the voltage change is observed through the voltmeter V until the voltage exceeds the critical value, so as to determine whether the critical current is reached. There are two problems with this test method. The first problem is that each current-measurement cycle takes time, so the whole test process is slow and the test efficiency is low. The second problem is that since the voltage of the superconducting material is nonlinear, the voltage at a certain moment in the measurement is still very small, even less than 1μV, and the slow increase in current will cause a sharp increase in voltage. When the current is hundreds of amperes or even thousands of amperes, the sharp increase in voltage will damage the entire sample.

[0045] Compared with the conventional test method, in this application, in addition to the conventional main DC power supply PS1, an additional high-precision safety power supply PS2 is introduced. The two power supplies are connected in parallel to jointly provide current for the superconducting tape, and the safety power supply is in feedback mode through the feeders s2+ and s2-, such as Figure 3 shown.

[0046] The test steps are as follows:

[0047] The testing process is as follows:

[0048] First, set the high-precision safety power supply PS2 as follows and keep it during the test: the voltage output is the minimum recognizable resolution voltage, and the current should be as large as possible. Preferably, it is set to the output upper limit I of the high-precision safety power supply PS2 itself. 2M According to the working principle of DC power supply, the actual output of high-precision safety power supply PS2, that is, the preload current is I 2 , 0 2 2M ;

[0049] Gradually increase the current of the main DC power supply PS1, and the step size is I 2M or slightly smaller, and measure the output I of the current source at each step 1 and I 2 , the current on the sample is I 1 +I 2 , while measuring the voltage drop V on the sample;

[0050] ​​Repeat the above steps until V reaches the specified criterion voltage. At this time, the current I 1 +I 2 That is the critical current of the sample.

[0051] Embodiment 2;

[0052] See also Figure 1-Figure 5 In the embodiment of the present invention, the voltage output of the high-precision safety power supply PS2 is set to the minimum recognizable resolution voltage, and the current output is set to the output upper limit I of the high-precision safety power supply PS2 itself. 2M Or a value close to this value; the superconducting sample acts as a variable resistor Rsc, whose resistance changes with the current, and the resistance increases significantly when the critical current is reached.

[0053] Feedback lines s2+ and s2- feed back the voltage on the superconducting sample Rsc to the high-precision safety power supply PS2, so that the high-precision safety power supply PS2 can automatically adjust its current output mode according to the feedback voltage, that is, switch between constant current mode and constant voltage mode to ensure sample safety.

[0054] When the voltage on the superconducting sample is close to 0, the high-precision safety power supply PS2 outputs the set current I in constant current mode. 2M When the feedback voltage reaches the set value, it automatically switches to constant voltage mode and adjusts the output current to maintain the voltage not exceeding the minimum identification voltage. The main DC power supply PS1 and the high-precision safety power supply PS2 are designed in parallel so that the total current during the test is provided by both.

[0055] The safe and fast test device for measuring critical current of superconducting materials also includes an optional voltage upper limit protection mechanism, which adds feedback compensation to the main DC power supply PS1 and sets a voltage upper limit to further protect the superconducting sample Rsc from excessive voltage.

[0056] The working principle of the safety power supply is as follows:

[0057] Step 1: If the voltage on the superconductor is close to 0, the safety power supply will enter the constant current control mode and output the set current I 2M If the feedback voltage of the safety power supply through the compensation line reaches the set value during the measurement, the safety power supply works in the constant voltage mode, and the current is less than the set value I 2M .

[0058] Step 2: Assume that at the nth step of the test, the sample is still in a state of no resistance. At this time, the safety power supply output is I 2M , the total current on the sample is I 1n +I 2M , which is the sum of the main power current and the preload current.

[0059] Step 3: In the test step n+1, the main power output increases by one step, the step length is I 2M Or slightly smaller, that is, the main power output is I 1n+1 ≤I 1n +I 2M At this time, if the sample is still in a state of no resistance, the total current becomes I 1n+1 +I 2M There is no voltage on the sample, the power is 0, the sample is safe, and the test continues.

[0060] Step 4: In the n+1th step of the test, if the sample reaches the critical current, resistance will appear near the critical current, and the voltage can reach the minimum identification voltage of the safety power supply, then the safety power supply will automatically adjust the current output to ensure that the voltage does not exceed the minimum identification voltage. At this time, the total current of the sample is near the critical current, and the voltage is the identification voltage of the safety power supply. The critical current of conventional high-temperature superconducting tape is below 1000A. The safety power supply can choose a high-precision power supply with an output voltage resolution of 1mV.

[0061] Step 5: In principle, the heating power of the superconducting tape is less than 1W, so the sample is safe and the test is over. Since the main power supply current in this step has been verified by preloading in the previous step, this step of measurement will not burn the sample. No matter how much the critical current of the sample increases, the safety power supply will control the current to reach the critical current, because if the voltage reaches the set value, the safety power supply can adjust its current to 0, and when the safety power supply output is 0, the total current is I 1n+1 ≤I 1n +I 2M , which is less than or equal to the current that has been preloaded and verified in the previous step.

[0062] The working principle of the embodiment of the present invention is: by introducing a safe power supply, the rapid and safe sample testing is guaranteed. The step size in the above measurement can be set to the output upper limit of the safe power supply. The actual power supply can reach tens of amperes. In the conventional method, the reasonable test step size is 2A or 5A. Although a larger step size can increase the speed, it increases the test risk. However, the present invention does not have this problem. The safe power supply has high voltage recognition accuracy and fast response, but the current is often small and cannot reach the typical value of the critical current of the superconducting material alone. According to the above calculation, the existing power supply accuracy combined with the critical current of the superconducting material can ensure an input power of less than 1W, which is not enough to burn the superconducting material. The above steps rely on hardware implementation, and the speed and reliability of protection far exceed ordinary test procedures.

[0063] Embodiment 3;

[0064] See also Figure 1-Figure 5In the embodiment of the present invention, if the superconducting sample Rsc reaches the critical current and resistance appears during the test, the high-precision safety power supply PS2 automatically adjusts the output current to ensure that the superconducting sample Rsc voltage does not exceed the identification voltage of the high-precision safety power supply PS2, thereby protecting the safety of the sample.

[0065] The main DC power supply PS1 increases the voltage upper limit through feedback compensation to further protect the superconducting sample Rsc.

[0066] The working principle of the embodiment of the present invention is as follows: the feedback compensation system is mainly used to further protect the superconducting sample Rsc from being damaged due to excessive voltage during the test process. The system monitors the voltage across the superconducting sample and adjusts the output of the power supply when necessary to ensure that the voltage does not exceed the set safety upper limit.

[0067] First, voltage monitoring. The voltmeter V continuously monitors the voltage changes across the superconducting sample Rsc. When the voltage approaches the preset safety upper limit, the system triggers the feedback compensation mechanism. Once the voltage approaches the safety upper limit, the voltmeter V transmits this information to the control units of the main DC power supply PS1 and the high-precision safety power supply PS2 through the feedback line (which may be s2+ and s2- or other dedicated lines). According to the feedback signal, the main DC power supply PS1 may reduce its current output step or suspend increasing the current to prevent the voltage from rising further. If it is in constant voltage mode and the voltage is close to its set minimum identification voltage, the high-precision safety power supply PS2 will automatically adjust its current output to maintain the voltage within a safe range.

[0068] In some specific cases, an additional voltage upper limit protection mechanism can be added to the main DC power supply PS1, such as setting a voltage upper limit threshold, and automatically cutting off or limiting the current output when the threshold is reached. The main DC power supply PS1 and the high-precision safety power supply PS2 work together to ensure that the current and voltage during the test are within a safe range, while accelerating the test process. Through the above-mentioned feedback compensation system, the test device of the present invention can achieve fast and accurate critical current measurement while ensuring the safety of superconducting samples. This design not only improves the test efficiency, but also reduces the risk during the test process.

[0069] Working principle: The present invention uses an additional power supply, i.e., a high-precision safety power supply PS2, to preload the current to quickly and safely measure the critical current of superconducting materials. The device includes a main DC power supply PS1, a high-precision safety power supply PS2, a superconducting sample Rsc, a voltmeter V, a line resistor R1, and feedback lines s2+ and s2-. The method connects two power supplies in parallel, so that the main DC power supply PS1 gradually increases the current, while the high-precision safety power supply PS2 is preloaded with a current close to its output upper limit, thereby speeding up the test process and ensuring the safety of the superconducting sample when it is close to the critical current.

[0070] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and alterations may be made to the embodiments without departing from the principles and spirit thereof, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A test device using an additional power supply to preload current, characterized in that: Includes the following structures: Main DC power supply (PS1): used to provide step-up current; High-precision safety power supply (PS2): connected in parallel with the main DC power supply for preloading current; Superconducting sample (Rsc): acts as a variable resistor; Voltmeter (V): used to measure the voltage change across the superconducting sample; Line resistance (R1): represents the line resistance in the test circuit; Feedback wires (s2+ and s2-): connect the safety power supply and the measurement circuit.

2. The method for measuring the critical current of a superconducting material by using an additional power source to preload current according to claim 1, characterized in that: The main DC power supply (PS1) and the high-precision safety power supply (PS2) are designed in parallel, so that the total current during the test process is provided by both.

3. A method for safe and rapid testing of critical current measurement of superconducting materials, characterized in that: Utilizing the dual (multi) power supply structure in claim 1 comprises the following steps: Step S1: Set the output voltage of the high-precision safety power supply to the minimum recognizable resolution voltage, and the current output is close to or reaches its upper limit (I 2M ); Step S2: gradually increase the current output of the main DC power supply, with each increase step being at least (I 2M ) or slightly less than (I 2M ), and simultaneously measure and record the output currents (I1) and (I2) of the main power supply and the high-precision safety power supply, as well as the voltage on the superconducting sample; Step S3: Repeat step S2 until the voltage on the superconducting sample reaches the specified criterion voltage. At this time, the total current (I1+I2) on the superconducting sample is the critical current of the sample.

4. The method for measuring the critical current of a superconducting material by using an additional power source to preload current according to claim 1, characterized in that: The voltage output of the high-precision safety power supply (PS2) is set to the minimum recognizable resolution voltage, and the current output is set to the output upper limit (I 2M ) or a value close to it.

5. The method for measuring the critical current of a superconducting material by using an additional power source to preload current according to claim 1, characterized in that: The feedback lines (s2+ and s2-) feed back the voltage on the superconducting sample (Rsc) to the high-precision safety power supply (PS2), so that the high-precision safety power supply (PS2) can automatically adjust its current output mode according to the feedback voltage, that is, switch between constant current mode and constant voltage mode to ensure sample safety.

6. The method for measuring the critical current of a superconducting material by using an additional power source to preload current according to claim 1, characterized in that: The safe and fast testing device for measuring critical current of superconducting materials also includes an optional voltage upper limit protection mechanism, which adds feedback compensation to the main DC power supply (PS1) and sets a voltage upper limit to further protect the superconducting sample (Rsc) from the influence of excessively high voltage.

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