High-temperature superconducting magnet temperature detection and quench detection method based on Michelson optical fiber interference system

Abstract

The invention relates to a high-temperature superconducting magnet temperature detection and quench detection method based on a Michelson optical fiber interference system. According to the method, the characteristic that the refractive index of an optical fiber changes along with the change of external temperature is utilized, high-precision detection is achieved by arranging two optical fibers with the same length, one optical fiber serves as a measuring optical fiber to be wound along with a superconducting strip to form a superconducting magnet, and the other optical fiber is wound into the same structure to serve as a reference optical fiber. Light emitted by the light source is refracted by the two optical fibers and reflected by the reflecting end face to form Michelson optical fiber interference in the optical fiber coupler, a corresponding optical path difference is obtained by analyzing an interference image, and then the temperature change of the superconducting magnet is accurately calculated. According to the invention, the Michelson optical fiber interference system is adopted to measure the temperature of the superconducting magnet, so that the precision and sensitivity of temperature detection are remarkably improved, the anti-interference capability is excellent, and an innovative and efficient solution is provided for temperature detection and quench detection of the high-temperature superconducting magnet.

Description

Technical Field

[0001] The invention belongs to the field of superconducting magnet applications, and in particular relates to a high-temperature superconducting magnet temperature detection and quench detection method based on a Michelson optical fiber interference system. Background Art

[0002] Superconducting magnets have extensive application potential in cutting-edge fields such as efficient power transmission, magnetic levitation technology, and magnetic resonance imaging due to their excellent electromagnetic properties and low energy consumption. However, the operating stability of high-temperature superconducting magnets is related to their own temperature. Even a small temperature change may significantly affect their performance. In extreme cases, it may even cause quenching, which will generate a lot of heat and damage the equipment. Therefore, accurate temperature detection of high-temperature superconducting magnets during operation is the key to ensuring their efficient and stable operation.

[0003] Traditional high-temperature superconducting magnet temperature measurement methods, such as thermocouple method and infrared temperature measurement method, often face limitations such as reduced measurement accuracy, insufficient sensitivity, slow response or susceptibility to interference from external factors under extreme conditions such as strong magnetic fields and extremely low temperatures.

[0004] Given the slow propagation speed of quench in high-temperature superconducting magnets, this undoubtedly poses a huge challenge to quench detection. Therefore, developing a superconducting magnet temperature detection technology with high precision, high sensitivity and fast response is of great significance for maintaining the long-term stable operation of high-temperature superconducting magnets. The realization of this technology will provide more solid technical support and safety guarantee for the application of high-temperature superconducting magnets in various fields. Summary of the invention

[0005] The purpose of the present invention is to provide a high-temperature superconducting magnet temperature detection and quench detection method based on a Michelson fiber interferometer system. The temperature of the superconducting magnet can be measured during the operation of the high-temperature superconducting magnet, and has the advantages of high detection accuracy, high sensitivity, and strong anti-interference ability.

[0006] The core idea of ​​the present invention is that the refractive index of optical fiber is affected by temperature. In the Michelson fiber interference system, when the temperature of the magnet changes, the refractive index of the measuring optical fiber will change, resulting in an optical path difference between the two optical fibers. The change in the optical path difference is obtained by detecting the change in the number of light and dark fringes in the interference image, thereby obtaining the temperature of the magnet after the change. A 2×2 type fiber coupler with a splitting ratio of 1:1 is used to split the incident light into two beams and enter the measuring optical fiber and the reference optical fiber. When the magnet starts to run or fails, the heat generated by the magnet itself will cause the temperature of the measuring optical fiber to change, resulting in different refractive indices of the two optical fibers. Therefore, the temperature change of the magnet can be accurately obtained by simply detecting the change in the number of light and dark fringes in the interference image of the two optical fibers to obtain the optical path difference.

[0007] The technical solution of the present invention is as follows:

[0008] A method for detecting temperature and quenching of a high-temperature superconducting magnet based on a Michelson fiber interferometer system is characterized in that the structure includes a light source, the output end of the light source is connected to the input end of a fiber coupler, the two output ends of the fiber coupler are respectively connected to the input ends of two equal-length optical fibers, a metal reflective film is plated on the output end of a measuring optical fiber to form a reflective end, the output end of the other reference optical fiber is connected to a rod-shaped self-focusing collimating lens, and a reflective scanning mirror is placed vertically to the rod-shaped lens as a reflective end, the other output end of the optical coupler is connected to a photodetector, and is sequentially connected to a microwave amplifier, a data acquisition card and a data processor.

[0009] Among them, the two optical fibers have the same length. One optical fiber is used as a measurement optical fiber and is wound together with the superconducting tape to form a superconducting magnet. The other optical fiber is wound into a reference optical fiber with the same shape as the optical fiber inside the superconducting magnet and is in the same environment as the superconducting magnet.

[0010] Among them, the incident light emitted by the light source is split by the optical coupler and then enters the two optical fibers respectively. It is reflected at the reflection end of each optical fiber and meets in the interference device to cause Michelson interference, forming an interference image. The corresponding optical path difference is obtained by analyzing the interference image. There is a definite relationship between the optical path difference and the temperature change of the superconducting magnet, so the temperature of the superconducting magnet is calculated.

[0011] The light source is a fiber laser, a distributed feedback laser or other types of light-emitting devices in the 1550 nm band, such as a light emitting diode.

[0012] The optical fiber coupler is a standard 2×2 type, and its splitting ratio is 1:1.

[0013] Wherein, the measuring optical fiber is made of low-temperature resistant and easily bendable material.

[0014] The superconducting magnet is wound from superconducting tape and has a solenoid shape, a racetrack shape, a D shape, etc.

[0015] Wherein, the superconducting magnet is cooled by liquid nitrogen immersion cooling, liquid helium immersion cooling, or other cooling medium cooling, or conduction cooling.

[0016] The method for detecting the temperature of a high-temperature superconducting magnet and detecting a quench using the above-mentioned Michelson fiber interferometer system comprises the following steps:

[0017] ① Start the light source, so that the incident light is divided into two beams by the fiber coupler and enters two measuring optical fibers respectively to be refracted, and then reflected back to the fiber coupler through the reflection ends at their respective ends and interferes. The optical signal is converted into an electrical signal by the photodetector and input into the data processor. The reflective scanning mirror at the output end of the reference optical fiber is adjusted to make the interference image bright fringes, and the optical path difference at this time is recorded as 0.

[0018] ② Start the superconducting magnet and keep it running in the superconducting state for a long time. At this time, the heat generated by the superconducting magnet itself will cause the temperature of the environment where the measuring fiber and the reference fiber are located to be different. Therefore, the optical path of the light in them also changes, resulting in a change in the number of light and dark fringes in the interference image. The specific principle is as follows:

[0019] In the Michelson fiber interference system, if the optical path difference △l = mλ, the interference image is bright fringes; if the optical path difference △l = (m+1 / 2)λ, the interference image is dark fringes; where m is a positive integer and λ is the wavelength of the refracted light.

[0020] In the interference system, △l=l1-l2=n1(T1)L1-n2(T2)L2, wherein n1(T1) represents the refractive index of the measurement optical fiber at temperature T1, n2(T2) represents the refractive index of the reference optical fiber at temperature T2, L1 represents the length of the measurement optical fiber, and L2 represents the length of the reference optical fiber.

[0021] At the beginning, the temperature of the measuring fiber and the reference fiber are equal, T1 = T2, and the lengths of the two light rays are the same, L1 = L2, so △l = 0. When the superconducting magnet is in operation, the heat generated causes the temperature T1 of the measuring fiber to change, thereby causing the refractive index n1 to change. At this time, the increase in the optical path difference causes the change of light and dark fringes in the interference image. By recording the number of changes in light and dark fringes to obtain the value of m, the corresponding optical path difference △l can be obtained and input into the data processor.

[0022] ③ The data processor performs data processing and uses the following formula to obtain the temperature change △T and then the magnet temperature T:

[0023]

[0024] Where: L represents the length of the optical fiber measured at temperature T0, n(λ,T0) represents the refractive index of the optical fiber measured at wavelength λ and temperature T0, α T Indicates the thermal expansion coefficient of the measured optical fiber, C T It indicates the temperature coefficient of the measured optical fiber. The above data can be obtained through calibration measurement or from the manufacturer. T0 indicates the initial cooling temperature of the environment where the superconducting magnet is located.

[0025] The beneficial effects of the present invention are:

[0026] The present invention proposes a method for detecting the temperature and quenching of a high-temperature superconducting magnet based on the Michelson fiber interference system, and realizes the accurate measurement of the temperature of a superconducting magnet. Compared with the traditional temperature detection method, this method utilizes the characteristic that the refractive index of the optical fiber changes with temperature, and uses one optical fiber as a measuring optical fiber to be wound with a superconducting tape to form a superconducting magnet, and another optical fiber as a reference optical fiber. The interference image of the two beams of light is detected to obtain the optical path difference to reflect the temperature change of the magnet. The temperature of the superconducting magnet can be measured during the operation of the high-temperature superconducting magnet, and has the advantages of simple operation, high detection accuracy, high sensitivity, and strong anti-interference ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Attached Figure 1 Schematic diagram of the superconducting magnet structure prepared by winding optical fiber and superconducting tape together for measurement;

[0028] Description of reference numerals: 101 - superconducting tape; 102 - measuring optical fiber;

[0029] Attached Figure 2 is a schematic diagram of the reference optical fiber structure;

[0030] Description of reference numerals: 201 - reference optical fiber; 202 - rod-shaped self-focusing collimating lens; 203 - reflective scanning mirror;

[0031] Attached Figure 3 A system connection block diagram of a high-temperature superconducting magnet temperature detection and quench detection method based on a Michelson fiber interferometer system;

[0032] Description of reference numerals: 301-light source; 302-fiber coupler; 303-measurement fiber; 304-reference fiber; 305-metal reflective film; 306-rod-shaped self-focusing collimating lens; 307-reflective scanning mirror; 308-photodetector; 309-microwave amplifier; 310-data acquisition card; 311-data processor; 312-high-temperature superconducting magnet; DETAILED DESCRIPTION

[0033] The following will be combined with the accompanying drawings in the examples of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. It is obvious that 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.

[0034] The present invention provides a high-temperature superconducting magnet temperature detection and quench detection method based on a Michelson fiber interferometer system. The present invention is further described below in conjunction with embodiments and drawings.

[0035] 1. As attached Figure 1, the measuring optical fiber and the superconducting tape are wound together to prepare the superconducting magnet 1, and the specific process is as follows:

[0036] The measuring optical fiber is fixed to the middle of the superconducting tape using a low-temperature adhesive, and then the superconducting tape and the measuring optical fiber are wound together into a solenoid shape to obtain the following Figure 1 The solenoid-shaped high-temperature superconducting magnet 1 is shown.

[0037] 2. As attached Figure 2 , prepare reference fiber 2: wind the reference fiber into the same spiral shape as the measurement fiber, connect a rod-shaped self-focusing collimating lens to its output end, and place a reflective scanning mirror perpendicular to the rod-shaped lens as the reflective end, and obtain the following Figure 2 Reference fiber 2 is shown.

[0038] 3. As attached Figure 3 , is a connection block diagram of the Michelson fiber interferometer system of the present invention, which comprises a light source 301, the output end of the light source 301 is connected to the input end of a fiber coupler 302, the two output ends of the fiber coupler are respectively connected to the input ends of a measuring fiber 303 and a reference fiber 304, the output end of the measuring fiber is plated with a metal reflective film to form a reflective end 305, the output end of the reference fiber is connected to a rod-shaped self-focusing collimating lens 306, and a reflective scanning mirror 307 is placed vertically to the rod-shaped lens as a reflective end, the other output end of the optical coupler is connected to a photodetector 308 to convert the optical signal into an electrical signal, and is connected to a data processor 311 via a microwave amplifier 309 and a data acquisition card 310.

[0039] The two optical fibers have the same length. One optical fiber is wound together with the superconducting tape as the measuring optical fiber 303 to form the high-temperature superconducting magnet 312, and the other optical fiber is wound into a reference optical fiber 304 of the same shape as the optical fiber inside the superconducting magnet and is in the same environment as the superconducting magnet.

[0040] The light source 301 is a fiber laser, a distributed feedback laser or other type of light emitting device in the 1550 nm band, such as a light emitting diode.

[0041] The fiber coupler 302 is of a standard 2×2 type, and its splitting ratio is 1:1.

[0042] The following are the relevant devices and parameters in the embodiment

[0043] The light source 301 is a self-made 1550nm band fiber laser with an output light intensity of 50mw and a line width of 8KHz. Other distributed feedback lasers or other light-emitting devices may also be used.

[0044] The optical fiber coupler 302 is a 2x2 type common single-mode optical fiber coupler with a splitting ratio of 1:1.

[0045] The photodetector 308 is a high-speed detector that converts optical signals into electrical signals. The photodetector used in the example of the present invention is a detector model 1617-AC-FC produced by Newport Company. The bandwidth of this detector is 800MHz, which can realize high-speed optical pulse signal detection. Other types of high-speed photodetectors can also be used.

[0046] The microwave amplifier 309 is a device for amplifying electrical signals. The present invention uses a gain adjustable amplifier from ALPHALAS, and other types of microwave amplifying components can also be used.

[0047] The data acquisition card 310 is a device for triggering data acquisition. The data acquisition card used in the present invention is a digitizer of model CS82G from Gage Company, with a sampling rate of 3GS / s. A PCI-5152 digitizer from NI Company or a high-speed acquisition card from other companies can also be used.

[0048] The data processor 311 is mainly used to process and display the data collected by the data acquisition card 310 in real time. The system processing software written in the example of the present invention is programmed based on the data acquisition card and MATLAB.

[0049] The method for detecting the temperature of a high-temperature superconducting magnet and detecting a quench using the above-mentioned Michelson fiber interferometer system comprises the following steps:

[0050] ① Start the light source, so that the incident light is divided into two beams by the fiber coupler and enters two measuring optical fibers respectively to be refracted, and then reflected back to the fiber coupler through the reflection ends at their respective ends and interferes. The optical signal is converted into an electrical signal by the photodetector and input into the data processor. The reflective scanning mirror at the output end of the reference optical fiber is adjusted to make the interference image bright fringes, and the optical path difference at this time is recorded as 0.

[0051] ② Start the superconducting magnet and keep it running in the superconducting state for a long time. At this time, the heat generated by the superconducting magnet itself will cause the temperature of the environment where the measuring fiber and the reference fiber are located to be different. Therefore, the optical path of the light in them also changes, resulting in a change in the number of light and dark fringes in the interference image. The specific principle is as follows:

[0052] In the Michelson fiber interference system, if the optical path difference △l = mλ, the interference image is bright fringes; if the optical path difference △l = (m+1 / 2)λ, the interference image is dark fringes; where m is a positive integer and λ is the wavelength of the refracted light.

[0053] In the interference system, △l=l1-l2=n1(T1)L1-n2(T2)L2, wherein n1(T1) represents the refractive index of the measurement optical fiber at temperature T1, n2(T2) represents the refractive index of the reference optical fiber at temperature T2, L1 represents the length of the measurement optical fiber, and L2 represents the length of the reference optical fiber.

[0054] At the beginning, the temperature of the measuring fiber and the reference fiber are equal, T1 = T2, and the lengths of the two light rays are the same, L1 = L2, so △l = 0. When the superconducting magnet is in operation, the heat generated causes the temperature T1 of the measuring fiber to change, thereby causing the refractive index n1 to change. At this time, the increase in the optical path difference causes the change of light and dark fringes in the interference image. By recording the number of changes in light and dark fringes to obtain the value of m, the corresponding optical path difference △l can be obtained and input into the data processor.

[0055] ③ The data processor performs data processing and uses the following formula to obtain the temperature change △T and then the magnet temperature T:

[0056]

[0057] Where: L represents the length of the optical fiber measured at temperature T0, n(λ,T0) represents the refractive index of the optical fiber measured at wavelength λ and temperature T0, α T Indicates the thermal expansion coefficient of the measured optical fiber, C T It indicates the temperature coefficient of the measured optical fiber. The above data can be obtained through calibration measurement or from the manufacturer. T0 indicates the initial cooling temperature of the environment where the superconducting magnet is located.

Claims

1. A method for detecting temperature and quenching of a high-temperature superconducting magnet based on a Michelson fiber interferometer system, characterized in that the structure includes a light source, the output end of the light source is connected to the input end of a fiber coupler, the two output ends of the fiber coupler are respectively connected to the input ends of two equal-length optical fibers, a metal reflective film is plated on the output end of a measuring optical fiber to form a reflective end, the output end of another reference optical fiber is connected to a rod-shaped self-focusing collimating lens, and a reflective scanning mirror is placed vertically to the rod-shaped lens as a reflective end, the other output end of the optical coupler is connected to a photodetector, and is sequentially connected to a microwave amplifier, a data acquisition card and a data processor. The two optical fibers are of the same length. One optical fiber is used as a measurement optical fiber and is wound together with the superconducting tape to form a superconducting magnet. The other optical fiber is wound into a reference optical fiber with the same shape as the optical fiber inside the superconducting magnet and is in the same environment as the superconducting magnet. The incident light from the light source is split by the optical coupler and then enters two optical fibers respectively. It is reflected at the reflection end of each optical fiber and meets in the interference device to cause Michelson interference, forming an interference image. The corresponding optical path difference is obtained by analyzing the interference image. There is a definite relationship between the optical path difference and the temperature change of the superconducting magnet, so the temperature of the superconducting magnet can be calculated.

2. The method according to claim 1, characterized in that The light source is a fiber laser, a distributed feedback laser or other types of light emitting devices in the 1550 nm band, such as a light emitting diode.

3. The method according to claim 1, characterized in that The fiber coupler is a standard 2×2 type with a splitting ratio of 1:

1.

4. The method according to claim 1, characterized in that: The optical fiber is made of low-temperature-resistant and easily bendable material.

5. The method according to claim 1, characterized in that The superconducting magnet is formed by winding a superconducting tape, and its shape is a solenoid type, a racetrack type, a D type, etc.

6. The method according to claim 1, characterized in that The superconducting magnet is cooled by immersion cooling using liquid nitrogen, immersion cooling using liquid helium, or other cooling media, or by conduction cooling.

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