A cryogenic temperature calibration system in the superfluid helium temperature range under a magnetic field environment

Abstract

A low-temperature temperature calibration system in a superfluid helium temperature range under a magnetic field environment, which is used to calibrate a thermometer in the 1.8K liquid helium temperature range. The system includes a cryogenic dewar, a cryogenic constant temperature system, a sample chamber, a superconducting magnet system, and cryogenic measurement and control equipment. The cryogenic dewar consists of an outer vacuum chamber assembly and a radiation shield assembly located in the vacuum chamber. Among them, the vacuum chamber consists of a top cover and a cylinder body, and a vacuum unit that provides negative pressure. The cold screen is hoisted in the cylinder body; the sample chamber consists of a cavity and a sample rod. The sample chamber is installed at the center of the top cover, extends downward to the center of the vacuum chamber, and a heater is provided at the bottom. The sample rod is inserted into the sample chamber, and a sample rack is provided at the bottom; the cryogenic constant temperature system consists of two GM refrigerators, which are respectively installed on both sides of the sample chamber, and the main part extends into the vacuum chamber; the superconducting magnet system is hoisted around the sample rack. The low-temperature temperature calibration system of the present invention can reduce the consumption and waste of liquid helium and significantly reduce costs.

Description

Technical Field

[0001] The present invention belongs to the fields of nuclear fusion technology and superconducting cryogenic technology, and particularly relates to a cryogenic temperature calibration system in the superfluid helium temperature range under a magnetic field environment. Background Art

[0002] In the field of metrology and measurement science, temperature measurement is a basic physical quantity. With the rapid development of many scientific and technological fields such as high-energy physics, superconducting technology, aerospace engineering, atomic energy science, and medicine, new requirements for temperature measurement at extremely low temperatures have been put forward, such as high accuracy, good reproducibility, easy use, low cost, and little influence by magnetic fields. Precise temperature measurement and calibration in a cryogenic magnetic field environment are important issues that directly affect the development of related research fields.

[0003] Large superconducting magnets in large scientific engineering projects such as domestic nuclear fusion devices, high-energy physics accelerators, and advanced light sources need to be equipped with large helium cryogenic systems for cooling. The entire device and its cryogenic system require a large number of cryogenic temperature measurements. Currently, the most commonly used cryogenic thermometer in the cryogenic field is the Cernox carbon resistance thermometer of LakeShore Company in the United States. It is necessary to consider suitable alternative products for thermometers for cryogenic temperature measurement in a magnetic field environment, and conduct measurement and test research on different types of cryogenic thermometers in the ultra-low temperature range under a magnetic field environment. It is of great significance to develop theoretical research and engineering technology related to cryogenic measurement and testing.

[0004] Constructing a research and calibration platform for precise cryogenic temperature measurement in the superfluid helium temperature range under a magnetic field environment is of great significance for carrying out precise cryogenic measurement and testing research under cryogenic, vacuum, and magnetic field environments, mastering the precise measurement methods and fast response testing technologies for cryogenic physical parameters under extreme environments, and ensuring the safe and stable operation of large scientific engineering experimental devices such as Tokamak fusion devices, high-energy physics accelerators, and advanced light sources.

[0005] This research and calibration platform for precise cryogenic temperature measurement in the superfluid helium temperature range under a magnetic field environment is planned to be constructed into a cryogenic public service platform. In addition to meeting the cryogenic-related research in the fusion field, it can also be open to and shared with all sectors of society, providing long-term and efficient cryogenic measurement and testing services for industries related to cryogenic applications in China, such as power electronics, aerospace, chemical engineering, semiconductor industry, and biopharmaceuticals. In recent years, a number of major achievements have been made in nuclear fusion technology, and the progress of nuclear fusion project experiments is inseparable from the ultra-low temperature environment created by liquid helium. In order to achieve the goal of more stable control of ultra-low temperature experimental conditions, the temperature calibration of ultra-low temperature liquid helium plays an important role.

[0006] Currently, there is no cryogenic calibration system in the superfluid helium temperature range under small-scale magnetic field conditions in China. Summary of the Invention

[0007] Aiming at the existing technical problems, the purpose of the present invention is to provide a low-temperature temperature calibration system in the superfluid helium temperature range under a magnetic field environment.

[0008] The technical solution of the present invention is as follows:

[0009] A low-temperature temperature calibration system in the superfluid helium temperature range under a magnetic field environment, which is used to calibrate the thermometer in the liquid helium temperature range. The calibration system includes a cryogenic dewar, a cryogenic constant temperature system, a sample chamber, a superconducting magnet system, and cryogenic measurement and control equipment;

[0010] Among them, the cryogenic dewar consists of an outer vacuum chamber and a radiation shield located in the vacuum chamber. The vacuum chamber consists of a top cover, a cylinder, and a vacuum unit that provides negative pressure. The radiation shield is hoisted inside the cylinder;

[0011] The sample chamber consists of a cavity and a sample rod. The cavity is installed at the center of the top cover and is connected to the radiation shield through a heat sink. The cavity extends downward to a heater. The sample rod is inserted into the cavity, and a sample rack is installed at the bottom;

[0012] The cryogenic constant temperature system consists of two GM refrigerators. The two GM refrigerators are respectively installed on both sides of the sample chamber, and the main parts of the two GM refrigerators extend into the vacuum chamber;

[0013] The superconducting magnet system is hoisted around the sample rack;

[0014] The cryogenic measurement and control equipment includes a cryogenic temperature sensor, a pressure transmitter, a temperature controller, and acquisition and control equipment.

[0015] Furthermore, the vacuum unit constitutes a vacuum loop, which includes 2 sets of vacuum pump groups: 1 set of roots pumps is used for helium gas circulation and decompression to obtain the 1.8K superfluid helium temperature range, and 1 set of molecular pumps is used for vacuum extraction and maintenance of the vacuum chamber and the sample chamber.

[0016] Furthermore, the sample chamber isolates the vacuum environment of the background field generated by the superconducting magnet system, provides an independent vacuum space for the calibration of sensor samples, and enables the replacement of samples without affecting the normal operation of the superconducting magnet system.

[0017] Furthermore, the calibration system also includes a helium gas circulation loop, which is respectively composed of a high-temperature intake loop and a low-temperature intake loop. The main parts of the high-temperature intake loop and the low-temperature intake loop are centered around the sample rack for circulation. Among them, the cooling and heating parts in the high-temperature intake loop and the low-temperature intake loop are installed inside the vacuum chamber, and the circulation and intake parts in the high-temperature intake loop and the low-temperature intake loop are installed outside the cryogenic dewar. The cryogenic constant temperature system cooperates with the vacuum pump group to maintain the low temperature and vacuum environment required by the calibration system.

[0018] Further, the two GM refrigerators include a first refrigerator and a second refrigerator. The first refrigerator provides cooling capacity for the magnet of the superconducting magnet system, and the second refrigerator provides cooling capacity for the helium circulation loop.

[0019] Further, the superconducting magnet system provides a stable magnetic field environment for the cryogenic measurement and control equipment.

[0020] Further, the cryogenic measurement and control equipment is used for the measurement, acquisition, testing, analysis and control of parameters such as temperature, pressure, flow rate, and magnetic field strength in the cryogenic process.

[0021] Further, the cryogenic temperature sensor is installed at the bottom of the sample rack, and leads are drawn through holes in each baffle. Further, the cavity includes two corrugated pipe sections.

[0022] The cryogenic temperature calibration system in a magnetic field environment according to the present invention can be used to calibrate thermometers in the 1.8K liquid helium temperature range; the superconducting magnet system can provide a stable magnetic field environment for the cryogenic measurement and control equipment to meet the experimental test requirements for the magnetic field, including magnetic field strength, magnetic field direction, magnetic field center uniformity, the diameter of the space for accommodating test samples, etc.

[0023] It can be seen from the technical solutions provided by the present invention described above that the beneficial effects of the present invention are as follows:

[0024] Compared with the wet system, the cryogenic temperature calibration system of the present invention reduces the consumption and waste of liquid helium and significantly reduces the test cost.

[0025] The helium gas provided by the cryogenic temperature calibration system of the present invention has a stable and continuous flow, small temperature fluctuations, a more uniform sample temperature distribution, high temperature control sensitivity, and a good linearity of the heating curve.

[0026] The cryogenic temperature calibration system of the present invention obtains extremely low temperature superfluid helium of 1.8K or lower, and the heat leakage of the system is extremely low, meeting the test requirements in the temperature range from 1.8K to 325K.

[0027] The cryogenic temperature calibration system of the present invention adopts a sample cavity with a multi-stage structure, increases the solid travel of the sample cavity, reduces the solid heat leakage, conducts a thermal insulation design, and reduces the heat leakage of the sample cavity. The cryogenic temperature calibration system of the present invention is designed with two-way air intake to achieve rapid cooling from room temperature to 4.2K, and can significantly reduce the cooling waiting time of the system. Description of the Drawings

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings required for the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0029] Figure 1 It is a schematic structural diagram of a low-temperature temperature calibration system in the superfluid helium temperature range under a magnetic field environment provided by the embodiments of the present invention.

[0030] In the figure: 1 - 1# GM refrigerator, 2 - pre-cooling pipeline, 3 - sample rod, 4 - 2# GM refrigerator, 5 - vacuum chamber, 6 - cold shield, 7 - superconducting magnet, 8 - sample holder, 9 - heater, 10 - condenser, 11 - regenerator, 12 - circulation pipeline, 13 - 1# manual ball valve, 14 - 2# manual ball valve, 15 - 3# manual needle valve, 16 - 4# manual ball valve, 17 - 5# manual ball valve, 18 - sample chamber molecular pump, 19 - circulation pump, 20 - gas cylinder, 21 - 6# manual ball valve, 22 - buffer tank, 23 - flowmeter, 24 - 7# manual ball valve, 25 - 8# manual ball valve, 26 - top cover, 27 - rewarming heater, 28 - vacuum chamber molecular pump, 29 - gate valve. Specific embodiments

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0032] The following will describe in detail the low-temperature temperature calibration system in the superfluid helium temperature range under a magnetic field environment provided by the present invention.

[0033] As Figure 1 shown, a low-temperature temperature calibration system in the superfluid helium temperature range under a magnetic field environment is used to calibrate a thermometer in the 1.8K liquid helium temperature range. The calibration system includes a cryogenic dewar, a cryogenic constant temperature system, a sample chamber, a superconducting magnet system, and cryogenic measurement and control equipment. The cryogenic dewar consists of an outer vacuum chamber 5 and a radiation shielding cold shield 6 located inside the vacuum chamber 5. Among them, the vacuum chamber 5 consists of a top cover 26 and a cylinder body, as well as a vacuum unit that provides negative pressure, and the cold shield 6 is hoisted inside the cylinder body;

[0034] The sample chamber consists of a cavity and a sample rod 3. The sample chamber is installed at the center of the top cover and extends downward to the center bottom of the vacuum chamber 5. The sample rod 3 is inserted into the sample chamber, and a sample holder 8 is installed at the bottom. The cryogenic temperature control system consists of two GM cryocoolers 1 and 4, which are respectively installed on both sides of the sample chamber, and the main part extends into the vacuum chamber 5. The superconducting magnet system is hoisted around the sample holder 8. The cryogenic measurement and control equipment is configured with measuring instruments such as cryogenic temperature sensors and pressure transmitters, as well as a temperature controller and a acquisition and control device.

[0035] An embodiment of the present invention provides a cryogenic temperature calibration system. This temperature calibration system is a closed-loop system with a cryocooler as the cold source, and the medium is high-purity helium gas. When operating stably, no helium gas needs to be supplemented. Compared with the wet system, the consumption and waste of liquid helium are reduced, and the test cost is significantly reduced. The helium gas flow in the provided temperature calibration system is stable and continuous, with small temperature fluctuations, a more uniform sample temperature distribution, high temperature control sensitivity, and a good linearity of the heating curve. This temperature calibration system adopts a dual method of throttling cooling and evacuating and decompressing to obtain extremely low temperature superfluid helium of 1.8K or lower. The heat leakage of the system is extremely low, meeting the test requirements in the temperature range from 1.8K to 325K.

[0036] The cryogenic temperature calibration system of the embodiment of the present invention utilizes the cooling capacity of the first-stage cold head, second-stage cylinder, and second-stage cold head of the 1# GM cryocooler 1 and the 2# GM cryocooler 4 to liquefy the helium gas in the copper coiled tube of the winding heat exchanger, making full use of the cooling capacity of the cryocooler. Among them, the condensers of the GM cryocoolers 1 and 4 are installed at the bottom of the second-stage cold head and are made of oxygen-free copper. Numerous 1mm×1mm copper bars are obtained inside by wire cutting. Helium gas is blown into the condenser at a 45-degree angle to increase the contact area between the helium gas and the copper bars, maximizing the liquefaction rate of the helium gas and increasing the cooling capacity of the temperature calibration system.

[0037] The sample chamber of the cryogenic temperature calibration system of the embodiment of the present invention adopts a multi-section structure, connecting two welded bellows to increase the solid travel of the sample chamber and reduce the solid heat leakage. A copper heat sink seat is welded on the outer surface of the middle of the sample chamber, and the cold screen top cover is connected by copper braiding for heat insulation design to reduce the heat leakage of the sample chamber. The suction return gas pipeline is the gas outlet section of the sample chamber in the helium gas circulation loop, and it also adopts welded bellows and heat insulation to reduce the heat leakage of this temperature calibration system to the sample chamber. Openings are made on the sample holder at the bottom of the sample rod located in the sample chamber for installing multiple temperature sensors, enabling the calibration of more than 30 temperature sensors at one time. The sample holder is made of oxygen-free copper, providing a stable and uniform temperature field for sample testing. Both the sample rod and the sample holder can be replaced, with a compact structure and convenient operation.

[0038] The low-temperature temperature calibration system of the embodiment of the present invention is designed with two air inlets. When cooling from room temperature to 4.2K, a pre-cooling pipeline 2 with a larger inner diameter is adopted, with a large air flow and small resistance, realizing rapid cooling of the sample area and significantly reducing the cooling waiting time of the system. From 4.2K to 1.8K, a circulation pipeline 12 with a smaller inner diameter is adopted, with a small air flow and large flow resistance, and the 1.8K superfluid helium temperature region is achieved through throttling and additional pressure evacuation.

[0039] The low-temperature temperature calibration system of the embodiment of the present invention is provided with a regenerator 11 in the circulation pipeline 12, using the low-temperature reflux helium gas to pre-cool the helium gas in the circulation pipeline, realizing the heat exchange between the inlet gas and the return gas, so that the temperature of the helium gas entering the sample area is lower and it is easier to obtain a low temperature of 1.8K.

[0040] The low-temperature temperature calibration system of the embodiment of the present invention is provided with a heater 9 below the bottom of the sample cavity. The heater 9 is a closed chamber, processed with oxygen-free copper with a high RRR value, and its internal structure is a fin structure with a path in the shape of a several, greatly increasing the heat exchange area and realizing precise temperature control of the helium gas.

[0041] Specifically, the working process of the low-temperature temperature calibration system in the superfluid helium temperature region under this magnetic field environment is as follows:

[0042] 1. Evacuate the vacuum chamber and the sample chamber

[0043] Turn on the vacuum chamber molecular pump 28 and the gate valve 29, first evacuate the vacuum chamber 5. When the vacuum degree of the vacuum chamber 5 reaches 0.5 (at room temperature), close the gate valve 29 to maintain the vacuum degree of the vacuum chamber 5. Stop the circulation pump 19, turn on the sample chamber molecular pump 18, open the 8# manual ball valve 25, 7# manual ball valve 24, 2# manual ball valve 14, 1# manual ball valve 13, 3# manual needle valve 15, 5# manual ball valve 17, and then evacuate the sample chamber, the external pipeline, and the buffer tank 22 of the internal pipeline. When the vacuum degree of the sample chamber reaches 0.1Pa (at room temperature), close the valves of the 7# manual ball valve 24, 1# manual ball valve 13, 3# manual needle valve 15, 4# manual ball valve 16, and 5# manual ball valve 17. Fill helium gas into the buffer tank 22 through the high-pressure helium gas cylinder, and then close the 6# manual ball valve 21. Turn on the sample chamber molecular pump 18 again, open the 8# manual ball valve 25, 7# manual ball valve 24, 2# manual ball valve 14, 1# manual ball valve 13, 3# manual needle valve 15, 5# manual ball valve 17, and then evacuate the sample chamber, the external pipeline, and the buffer tank 22 of the internal pipeline. When the vacuum degree of the sample chamber reaches 0.1Pa (at room temperature), close the valves of the 7# manual ball valve 24, 1# manual ball valve 13, 3# manual needle valve 15, 4# manual ball valve 16, and 5# manual ball valve 17.

[0044] 2. Helium gas filling and circulation

[0045] Fill a slightly positive pressure of helium gas (1.1 bara) into the buffer tank 22 through a high-pressure helium gas cylinder, and then close the 6# manual ball valve 21. Turn on the dry pump, and the helium gas circulates through the 8# manual ball valve 25 in the high-temperature loop. When the temperature of the sample chamber reaches 4.2K, close the 8# manual ball valve 25 and open the 7# manual ball valve 24 for low-temperature loop circulation.

[0046] 3. Cooling and circulating pre-cooling of the GM cryocooler

[0047] Turn on two GM cryocoolers 1 and 4 simultaneously for cooling, and keep the dry pump circulating. Eventually, the temperature of the superconducting magnet system drops to about 4K; the temperature of the sample chamber is 1.8K, and the readings of the low-temperature temperature sensors arranged under the sample holder 8 are all 1.8K.

[0048] 4. Heating and temperature control 1 (1.8K - 4.2K)

[0049] After the temperature drops to the lowest, the temperature of the sample chamber is 1.8K. After the temperature stabilizes, calibrate the sensor to be calibrated. Then, heat the outlet helium gas through the heater 9 to calibrate the sensor to be calibrated in the temperature range of 1.8K - 4.2K.

[0050] 5. Heating and temperature control 2 (4.4K - 300K)

[0051] Close the 2# manual ball valve 14, open the 1# manual ball valve 13, and the 3# manual needle valve 15. The circulation pipeline is changed to a small diameter to ensure a positive pressure circulation in the sample chamber. Then, heat the outlet helium gas through the heater 9 to calibrate the sensor to be calibrated in the temperature range of 4.4K - 300K.

[0052] As described above, it is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A low-temperature temperature calibration system in the superfluid helium temperature range under a magnetic field environment, which is used to calibrate thermometers in the liquid helium temperature range. Characterized in that, The calibration system includes a cryogenic dewar, a cryogenic constant temperature system, a sample chamber, a superconducting magnet system and cryogenic measurement and control equipment; Among them, the cryogenic dewar consists of an outer vacuum chamber and a radiation shield located in the vacuum chamber. The vacuum chamber consists of a top cover, a cylinder body and a vacuum pump unit that provides negative pressure. The radiation shield is hoisted inside the cylinder body; The sample chamber consists of a cavity and a sample rod. The cavity is installed at the center of the top cover and is connected to the radiation shield through a heat sink. The cavity extends downward to a heater. The sample rod is inserted into the cavity, and a sample rack is installed at the bottom; The cryogenic constant temperature system consists of two GM cryocoolers. The two GM cryocoolers are respectively installed on both sides of the sample chamber, and the main parts of the two GM cryocoolers extend into the vacuum chamber; The superconducting magnet system is hoisted around the sample rack; The cryogenic measurement and control equipment includes a cryogenic temperature sensor, a pressure transmitter, a temperature controller and acquisition and control equipment; The calibration system also includes a helium circulation loop, which is respectively composed of a high-temperature intake loop and a low-temperature intake loop. The main bodies of the high-temperature intake loop and the low-temperature intake loop are centered around the sample rack for circulation. Among them, the cooling and heating parts in the high-temperature intake loop and the low-temperature intake loop are installed inside the vacuum chamber, and the circulation and intake parts in the high-temperature intake loop and the low-temperature intake loop are installed outside the cryogenic dewar. The cryogenic constant temperature system cooperates with the vacuum pump unit to maintain the low temperature and vacuum environment required by the calibration system; The two GM cryocoolers include a first cryocooler and a second cryocooler. The first cryocooler provides cooling for the magnet of the superconducting magnet system, and the second cryocooler provides cooling for the helium circulation loop; The cavity includes two bellows sections.

2. A low-temperature temperature calibration system in the superfluid helium temperature range under a magnetic field environment according to claim 1, Characterized in that: The vacuum pump unit constitutes a vacuum loop, which includes 2 sets of vacuum pump units: 1 set of circulation pumps is used for helium circulation and decompression to obtain the 1.8K superfluid helium temperature range, and 1 set of molecular pumps is used for extracting and maintaining the vacuum degree of the vacuum chamber and the sample chamber.

3. A low-temperature temperature calibration system in the superfluid helium temperature range under a magnetic field environment according to claim 1 or 2, Characterized in that: The sample chamber isolates the vacuum environment of the background field generated by the superconducting magnet system, provides an independent vacuum space for the calibration of sensor samples, and enables the replacement of samples without affecting the normal operation of the superconducting magnet system.

4. A low-temperature temperature calibration system in the superfluid helium temperature range under a magnetic field environment according to claim 1, Characterized in that: The superconducting magnet system provides a stable magnetic field environment for the cryogenic measurement and control equipment.

5. A low-temperature temperature calibration system in the superfluid helium temperature range under a magnetic field environment according to claim 1, Characterized in that: The cryogenic measurement and control equipment is used for the measurement, acquisition, testing, analysis and control of temperature, pressure, flow rate and magnetic field strength parameters in the cryogenic process.

6. A cryogenic temperature calibration system in the superfluid helium temperature region under a magnetic field environment according to claim 1, characterized in that: the sample rod is provided with a plurality of baffles, and the cryogenic temperature sensor is installed at the bottom of the sample holder, and the lead is led through the openings on each baffle.

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