Low-temperature measuring device and low-temperature measuring method based on thermal molecule pressure difference

Abstract

The invention relates to the technical field of low-temperature measurement, in particular to a low-temperature measurement device and a low-temperature measurement method based on thermal molecule pressure difference. The low temperature measuring device comprises a reference part which is arranged to be a metal shell with a first cavity; the measuring part is arranged to be a metal shell with a second cavity; the connecting capillary tube is arranged between the reference part and the measuring part; the pressure gauge is arranged on the reference part; the thermometer is arranged on the reference part; wherein one end of the connecting capillary tube is communicated with the first cavity, the other end of the connecting capillary tube is communicated with the second cavity to form a closed system, and helium is filled in the closed system to serve as a working medium freely flowing between the first cavity and the second cavity. In the invention, the measuring part is set as a passive metal cavity, so that the interference of self-heating on the temperature of the to-be-measured target can be avoided, and the reference end is far away from the to-be-measured target, so that the interference of a magnetic field on a measured value can be avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of low-temperature measurement, and in particular to a low-temperature temperature measuring device based on thermal molecular pressure difference and a low-temperature temperature measuring method. BACKGROUND

[0002] In the fields of quantum computing, cryogenics, aerospace, etc., accurate measurement of extremely low-temperature environments (e.g., mK-level temperature zones) is of great importance.

[0003] At present, the most commonly used low-temperature thermometer is a resistance thermometer, such as Cernox, RuO2 (ruthenium dioxide), etc. However, the existing resistance temperature measurement technology has two inherent defects that are difficult to overcome when applied to extreme conditions such as extremely low temperatures and strong magnetic fields: One is the self-heating effect. The resistance thermometer needs to apply an excitation current to measure its resistance value, and this current will inevitably generate Joule heat on the sensor. Although this power is extremely small (usually in the order of pW to nW), in an extremely low-temperature environment of mK level, this amount of heat is enough to cause significant temperature disturbance to the measurement object (such as a quantum bit chip), resulting in measurement distortion.

[0004] Two is the magnetoresistance effect. The resistance value of most resistance thermometers will change with the strength of the applied magnetic field, i.e., the magnetoresistance effect. This makes their readings in strong magnetic field research equipment (such as a dilution refrigerator) severely inaccurate, and a complex and time-consuming magnetic field correction must be performed.

[0005] Traditional gas thermometers, although based on the basic laws of thermodynamics, have complex error sources such as "dead volume" in low-temperature applications, which are extremely difficult to correct and make it difficult to achieve precise measurement. SUMMARY

[0006] The present application aims to solve the technical problems in the related art. To this end, the present application provides a low-temperature temperature measuring device based on thermal molecular pressure difference and a low-temperature temperature measuring method to solve the problem that the existing low-temperature thermometer cannot accurately measure the low-temperature target due to self-heating effect and magnetic field interference.

[0007] In a first aspect, the present application provides a low-temperature temperature measuring device based on thermal molecular pressure difference, comprising: a reference part, which is a metal shell provided with a first cavity; a measuring part, which is a metal shell provided with a second cavity; a connecting capillary arranged between the reference part and the measuring part; a pressure gauge installed in the reference part; a thermometer installed in the reference part; One end of the connecting capillary is in communication with the first chamber, and the other end of the connecting capillary is in communication with the second chamber to form a closed system, and helium gas is filled in the closed system as a working medium flowing freely between the first chamber and the second chamber.

[0008] According to the low-temperature temperature measuring device based on thermal molecular pressure difference provided by the application, the equivalent channel diameter of the connecting capillary is much smaller than the average free path of helium molecules, so that the connecting capillary becomes a free molecular flow area of helium.

[0009] According to the low-temperature temperature measuring device based on thermal molecular pressure difference provided by the application, the connecting capillary adopts a structure of multiple micro-channel arrays. Alternatively, the connecting capillary adopts a pore structure.

[0010] According to the low-temperature temperature measuring device based on thermal molecular pressure difference provided by the application, the material of the connecting capillary has heat insulation characteristics, which is used to avoid heat transfer between the reference part and the measuring part.

[0011] According to the low-temperature temperature measuring device based on thermal molecular pressure difference provided by the application, the material of the connecting capillary has heat insulation characteristics, which is used to avoid heat transfer between the reference part and the measuring part. A vacuum pump group connected with the reference part is used to vacuumize the sealed system. A helium tank connected with the reference part is used to supply helium to the sealed system.

[0012] According to the low-temperature temperature measuring device based on thermal molecular pressure difference provided by the application, the material of the connecting capillary has heat insulation characteristics, which is used to avoid heat transfer between the reference part and the measuring part.

[0013] In the second aspect, the application further provides a low-temperature temperature measuring method, which uses the low-temperature temperature measuring device based on thermal molecular pressure difference described above, and the low-temperature temperature measuring method comprises the following steps. S1, calibrating the low-temperature temperature measuring device to obtain the volume V1 of the first chamber, the volume V2 of the second chamber, and the total number N of helium molecules in the sealed system total Or the equivalent characteristic constant C=N total ×k B ; S2, installing the calibrated low-temperature temperature measuring device on a low-temperature target to be measured, so that the measuring part is in contact with the low-temperature target to keep the temperature consistent, and the reference part is placed in a high-temperature environment, and waiting for the helium in the first chamber to reach thermodynamic equilibrium with the helium in the second chamber. S3, obtaining the first pressure P1 and the first temperature T1 in the first chamber by using a pressure gauge and a thermometer, and then using a mass conservation model and a thermal molecular pressure difference model to calculate the temperature T2 of the second chamber.

[0014] According to the low-temperature temperature measuring method, the calibration of the low-temperature temperature measuring device comprises: The closed system composed of the first chamber, the connecting capillary and the second chamber is vacuumized by using a vacuum pump set; The measuring part is placed at a known and stable standard temperature point, a helium bottle is used to fill helium into the closed system, and after waiting for the helium to reach a thermodynamic equilibrium in the closed system, the pressure P 1,cal and the temperature T 1,cal of the first chamber in the calibration state are collected. Firstly, the pressure P 2,cal of the second chamber in the calibration state is calculated according to a free molecule flow model: Secondly, the characteristic constant C of the closed system is calculated according to a mass conservation model:

[0015] According to the low-temperature temperature measuring method, the placing of the measuring part at a known and stable standard temperature point comprises: immersing the measuring part into liquid nitrogen contained in a low-temperature Dewar to ensure that the temperature T 2,cal of the second chamber in the calibration state is stable.

[0016] According to the low-temperature temperature measuring method, the calculation of the temperature T2 of the second chamber by using the mass conservation model and the thermal molecular pressure difference model comprises: The first pressure P1 and the first temperature T1 are substituted into formula one: and formula two: to obtain the temperature T2 of the second chamber.

[0017] The above one or more technical solutions in the application have at least one of the following technical effects: The measuring part is set as a passive metal cavity, which can make the temperature of the gas in the second chamber the same as the temperature of the target to be measured after contacting the target to be measured, and the temperature of the gas in the second chamber can be obtained by measuring the gas pressure and temperature in the first chamber and using the thermodynamic and kinetic principles of the gas, so that the measurement error caused by the self-heating interference of the excitation current on the target to be measured is avoided. Meanwhile, the thermometer and the pressure gauge are arranged in the reference part, which can be away from the target to be measured to prevent the magnetic field near the target to be measured from interfering with the thermometer and the pressure gauge.

[0018] In addition to the technical problems solved by the application, the technical features of the technical solutions and the advantages brought by the technical features, other technical features of the application and the advantages brought by the technical features will be further described with reference to the drawings or understood through the practice of the application. BRIEF DESCRIPTION OF DRAWINGS ​

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the following will briefly introduce the drawings needed to be used in the embodiments or the related art description. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0020] Figure 1 The schematic diagram of the low-temperature temperature measuring device provided by the embodiment of the present application during calibration.

[0021] Reference signs: 1, reference part; 2, helium; 3, connecting capillary; 4, low-temperature dewar; 5, liquid nitrogen; 6, measuring part; 7, pressure gauge; 8, thermometer; 9, three-way valve; 10, vacuum pump set; 11, gas connecting pipeline; 12, helium bottle. DETAILED DESCRIPTION

[0022] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly below in combination with the drawings in the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0023] In the embodiment of the present application, a low-temperature temperature measuring device based on thermal molecular pressure difference is introduced.

[0024] As shown in Figure 1 The low-temperature temperature measuring device mainly includes a reference part 1, a measuring part 6 and a connecting capillary 3.

[0025] The reference part 1 is arranged as a metal shell with a first chamber. The measuring part 6 is arranged as a metal shell with a second chamber. The connecting capillary 3 is arranged between the reference part 1 and the measuring part 6.

[0026] The pressure gauge 7 is installed on the reference part 1. The thermometer 8 is installed on the reference part 1.

[0027] The one end of the connecting capillary 3 is in communication with the first chamber, and the other end of the connecting capillary 3 is in communication with the second chamber to form a closed system. The closed system is filled with helium 2 as a working medium which freely flows between the first chamber and the second chamber.

[0028] Specifically, the reference part 1 is made of a high-thermal-conductivity material to improve the heat exchange efficiency between the gas in the first chamber and the external environment, so that the temperature of the gas is the same as that of the external environment. Preferably, the material of the reference part 1 is oxygen-free copper, The reference part 1 is made of a high-thermal-conductivity material to ensure that the temperature of the gas in the second chamber is the same as that of the target to be measured. Preferably, the material of the measurement part 6 is oxygen-free copper.

[0029] The thermometer 8 is installed above the reference part 1 and communicates with the first chamber, and is used to measure the first temperature T1 in the first chamber.

[0030] The pressure gauge 7 is installed above the reference part 1 and communicates with the first chamber, and is used to measure the first pressure P1 in the first chamber.

[0031] Further, the low-temperature temperature measuring device further comprises a data processor. The data processor is electrically connected with the thermometer 8 and the pressure gauge 7 respectively, and is used to collect the first pressure P1 and the first temperature T1 in the first chamber, and calculate the temperature T2 of the second chamber according to an internal model.

[0032] When the low-temperature temperature measuring device is used to measure a low-temperature target, the reference part 1 is placed in a high-temperature environment, and the measurement part 6 is in thermal contact with the low-temperature target to be measured. Then, after the closed system reaches a thermodynamic equilibrium, the first pressure P1 and the first temperature T1 in the first chamber are obtained, and the temperature value T2 of the target to be measured can be obtained through the data processor.

[0033] Further, for the measurement of extremely low temperature in the mK level, helium 3 is preferably used as the working medium, because it can still maintain a high enough vapor pressure at a lower temperature and will not condense. For the measurement of the K-level temperature region, helium 4 can be used to reduce the cost.

[0034] In the embodiment, the measurement part 6 is a passive metal cavity, which can make the temperature of the gas in the second chamber the same as that of the target to be measured after contacting the target to be measured. The temperature of the gas in the second chamber can be obtained by measuring the gas pressure and temperature in the first chamber and using the thermodynamic and kinetic principles of the gas, thereby avoiding the measurement error caused by the self-heating interference of the excitation current on the target to be measured. Meanwhile, the thermometer 8 and the pressure gauge 7 are arranged on the reference part 1, which can be away from the target to be measured to prevent the magnetic field near the target to be measured from interfering with the thermometer 8 and the pressure gauge 7.

[0035] On the basis of the above embodiment, another embodiment of the present application introduces a low-temperature temperature measuring device based on thermal molecular pressure difference.

[0036] The low-temperature temperature measuring device calculates the second temperature T2 based on the mass conservation relationship and the thermomolecular pressure difference relationship, using the collected first temperature T1 and first pressure P1.

[0037] The equivalent channel diameter of the connecting capillary 3 is much smaller than the mean free path of helium 2 molecules, so that the connecting capillary 3 becomes a free molecular flow region of helium 2.

[0038] Specifically, the inner diameter d of the connecting capillary 3 is designed to be sufficiently small, such that within the target working pressure and temperature range, the mean free path λ of helium 2 molecules is much greater than the inner diameter d, i.e., the Knudsen number Kn = λ / d is much greater than 1. This results in the collision frequency of gas molecules with the channel wall within the connecting capillary 3 being much higher than the collision frequency between them.

[0039] In this region, the thermomolecular pressure difference relationship has a definite physical form, namely: .

[0040] Meanwhile, the mass conservation relationship of the low-temperature temperature measuring device can be expressed (when the capillary volume is ignored) as follows: The data processor can obtain the second temperature T2 by simultaneously solving these two equations.

[0041] Furthermore, the connecting capillary 3 adopts a structure of multiple microchannel arrays; or, the connecting capillary 3 adopts a porous structure.

[0042] The material used to make the connecting capillary tube 3 has heat insulation properties, which is used to avoid heat transfer between the reference part 1 and the measuring part 6, thereby establishing and maintaining a significant and stable temperature difference at both ends of the connecting capillary tube 3.

[0043] The housing connecting the capillary tube 3 is made of a material with low thermal conductivity to minimize heat leakage from the reference section 1 to the measuring section 6. Preferably, the housing connecting the capillary tube 3 is made of stainless steel or a copper-nickel alloy.

[0044] Furthermore, the cryogenic temperature measuring device also includes a vacuum pump assembly 10 and two helium cylinders.

[0045] Vacuum pump assembly 10 is connected to the reference unit 1 and is used to evacuate the sealing system. Helium cylinder 2 is connected to the reference unit 1 and is used to supply helium gas 2 to the sealing system.

[0046] Specifically, the vacuum pump unit 10 is connected to the reference unit 1 via a three-way valve 9, and is used to evacuate the closed system consisting of the reference unit 1, the connecting capillary tube 3 and the measuring unit 6.

[0047] Helium cylinder 2 is connected to reference unit 1 via gas connection pipe 11 and three-way valve 9, and is used to fill the closed system consisting of reference unit 1, connecting capillary tube 3 and measuring unit 6 with helium gas 2.

[0048] The low-temperature measuring device in this embodiment measures the low-temperature target based on the thermodynamics and kinetics of the gas. Since the measuring unit 6 has the same temperature as the low-temperature target, any tiny temperature change of the low-temperature target will cause the helium gas 2 to redistribute between the first chamber and the second chamber, thereby causing a significant change in the first pressure in the first chamber, making the low-temperature measuring device extremely sensitive.

[0049] Furthermore, by placing the active electrical measuring components (pressure gauge 7 and thermometer 8) on the high-temperature reference part 1, the low-temperature temperature measuring device can eliminate the need for complex low-temperature wiring and a precision low-temperature resistance bridge, simplifying the structure of the measuring device, and can provide accurate temperature readings in a strong magnetic field environment, thus solving the magnetoresistive effect problem.

[0050] Furthermore, in another embodiment of the present invention, a low-temperature temperature measurement method is described. This measurement method is applied to the low-temperature temperature measurement device in any of the above embodiments.

[0051] Low-temperature measurement methods include: S1. Calibrate the cryogenic temperature measuring device and obtain the volume V1 of the first chamber, the volume V2 of the second chamber, and the total number N of helium 2 molecules in the sealed system. total Or the equivalent characteristic constant C=N total ×k B ; S2. Install the calibrated low-temperature measuring device onto the low-temperature target to be measured, so that the measuring part 6 is in contact with the low-temperature target to maintain a consistent temperature, and place the reference part 1 in a high-temperature environment, waiting for the helium 2 in the first chamber and the helium 2 in the second chamber to reach thermodynamic equilibrium. S3. Obtain the first pressure P1 and the first temperature T1 in the first chamber through pressure gauge 7 and thermometer 8, and then use the mass conservation model and the thermomolecular pressure difference model to calculate the temperature T2 of the second chamber.

[0052] Specifically, the calibration of the low-temperature measuring device includes: The vacuum pump assembly 10 is used to evacuate the closed system consisting of the first chamber, the connecting capillary tube 3, and the second chamber. The measuring unit 6 is placed at a known and stable standard temperature point. Helium 2 is introduced into the closed system using helium cylinder 2. After the helium 2 reaches thermodynamic equilibrium within the closed system, the pressure P of the first chamber under the calibration condition is collected. 1,cal and temperature T 1,cal ; First, based on the free molecular flow model: Calculate the pressure P in the second chamber under calibration conditions. 2,cal Then, according to the mass conservation model: Calculate the characteristic constant C of the closed system.

[0053] Preferably, to improve the sensitivity of the low-temperature measuring device, the ratio of the volume V1 of the first chamber to the volume V2 of the second chamber can be optimized according to the low-temperature measurement range. The larger the V1 / V2 ratio, the higher the sensitivity of the low-temperature measuring device to the extremely low-temperature region.

[0054] Furthermore, placing the measuring unit 6 at a known and stable standard temperature point includes immersing the measuring unit 6 in liquid nitrogen 5 contained in a cryogenic Dewar 4 to ensure that the second chamber is at the calibrated temperature T. 2,cal Stablize.

[0055] The calculation of the temperature T2 of the second chamber using the mass conservation model and the thermomolecular pressure difference model includes: Substituting the first pressure P1 and the first temperature T1 into Equation 1: And Formula 2: The temperature T2 of the second chamber was calculated.

[0056] Specifically, the process of measuring the temperature of mK-level cryogenic targets using a cryogenic temperature measuring device is as follows: Step 1, System Preparation and Calibration: Charge the system with a known total number of molecules N. total Helium 2, or calibrating the equivalent system characteristic constant C=N total ×k B .

[0057] Vacuuming the sealed system: Open the three-way valve 9, start the vacuum pump group 10, and perform high-vacuum exhaust on the sealed system consisting of the reference part 1, the connecting capillary tube 3 and the measuring part 6.

[0058] Establish a calibration point: Place the measuring unit 6 at a known and stable standard temperature point. For example, immerse the measuring unit 6 in liquid helium of a cryogenic Dewar 4 until its temperature stabilizes at T. cal =4.20K.

[0059] Gas filling and equilibration: Turn off vacuum pump unit 10, open the valve of helium cylinder 2, and slowly fill the closed system with helium 2 through three-way valve 9 until pressure gauge 7 shows a suitable pressure (e.g., P1 = 20.0 Pa). Wait for the closed system to reach complete thermodynamic equilibrium.

[0060] Sealing: Close the three-way valve 9 to disconnect the sealed system from the vacuum pump group 10 and the helium cylinder 2, forming a permanently sealed system containing a known total number of molecules.

[0061] Data collection and calibration: After the closed system stabilizes, simultaneously read the readings of thermometer 8 and pressure gauge 7, and record the high-temperature parameter under calibration conditions: T 1,cal =295.0K and P 1,cal =20.0Pa.

[0062] Calculate the characteristic constant C: First, calculate the low-temperature pressure P under the calibration state according to the thermomolecular pressure difference formula. 2,cal : Then, the characteristic constant C=N of the system is calculated according to the mass conservation formula. total ×k B : .

[0063] Step Two: System Installation and Balancing Installation: Remove the calibrated measuring unit 6 from the calibration environment (such as liquid helium) and install it onto the cryogenic target to be measured. For example, the mK sample stage of a dilution refrigerator.

[0064] Cooling and Equilibrium: The refrigeration unit is activated, causing the measuring unit 6 to cool down along with the low-temperature target. The reference unit 1 remains in a high-temperature environment, waiting for the entire closed system to reach a new thermodynamic equilibrium.

[0065] Step 3: Data Collection Real-time monitoring: Once the system stabilizes at the unknown low temperature T2, the data processor begins to monitor the high-temperature end T1 and P1 in real time using thermometer 8 and pressure gauge 7.

[0066] Record instantaneous values: Suppose that the instantaneous values ​​collected at this moment are T1=296.0K and P1=8.50Pa.

[0067] Step 4: Temperature Calculation Substituting into the equations: The data processor calls the characteristic constant C stored in step one and the P1 and T1 values ​​collected in step three, and substitutes them into the system of equations: Solve for T2: Solve simultaneously using the data processor.

[0068] Output result: The data processor finally outputs the measured temperature T2 = 12.2mK.

[0069] Cycle: Steps three and four are continuously repeated to achieve real-time, self-heating-free, and magnetic field-resistant temperature monitoring of the low-temperature target. The temperature can also be compared and verified with the calibrated low-temperature thermometer mounted on the measurement unit.

[0070] Furthermore, the characteristic constant C of the closed system can also be determined by weighing. Specifically, the vacuum state mass of the thermomolecular pressure difference cryogenic temperature measuring device is... m 0 and the mass after filling with working gas m p Change Δ m = m p - m The ratio of 0 to molar mass is determined. C = N A ×Δ m / M ,in N A is Avogadro's constant.

[0071] In the description of the embodiments of the present invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0072] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0073] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0074] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms are not limited to the same embodiments or examples. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-temperature temperature measuring device based on thermomolecular pressure difference, characterized in that, include: The reference part (1) is configured as a metal housing having a first chamber; The measuring unit (6) is configured as a metal housing with a second chamber; A capillary tube (3) is connected and disposed between the reference part (1) and the measuring part (6); Pressure gauge (7) is installed on the reference unit (1); Thermometer (8) is installed on the reference unit (1); One end of the connecting capillary tube (3) is connected to the first chamber, and the other end of the connecting capillary tube (3) is connected to the second chamber to form a closed system. The closed system is filled with helium gas (2) as a working medium that flows freely between the first chamber and the second chamber.

2. The low-temperature temperature measuring device based on thermomolecular pressure difference according to claim 1, characterized in that, The equivalent channel diameter of the connecting capillary (3) is much smaller than the mean free path of the helium (2) molecules, so that the connecting capillary (3) becomes a free molecular flow region of helium (2).

3. The low-temperature temperature measuring device based on thermomolecular pressure difference according to claim 2, characterized in that, The connecting capillary (3) adopts a structure of multiple microchannel arrays; Alternatively, the connecting capillary (3) may have a porous structure.

4. The low-temperature temperature measuring device based on thermomolecular pressure difference according to claim 3, characterized in that, The material used to make the connecting capillary (3) has heat insulation properties to prevent heat transfer between the reference part (1) and the measuring part (6).

5. The low-temperature temperature measuring device based on thermomolecular pressure difference according to claim 4, characterized in that, Also includes: A vacuum pump assembly (10) is connected to the reference unit (1) and is used to evacuate the sealing system; A helium (2) bottle, connected to the reference part (1), is used to supply helium (2) to the sealing system.

6. The low-temperature temperature measuring device based on thermomolecular pressure difference according to any one of claims 1 to 5, characterized in that, The reference part (1) is made of oxygen-free copper, and the measuring part (6) is made of oxygen-free copper.

7. A low-temperature temperature measurement method, characterized in that, The cryogenic temperature measurement method, applied to the cryogenic temperature measuring device based on thermomolecular pressure difference as described in any one of claims 1 to 6, comprises: S1. Calibrate the low-temperature measuring device to obtain the volume V1 of the first chamber, the volume V2 of the second chamber, and the total number N of helium (2) molecules in the sealed system. total Or the equivalent characteristic constant C=N total ×k B ; S2. Install the calibrated low-temperature measuring device onto the low-temperature target to be measured, so that the measuring part (6) is in contact with the low-temperature target to maintain a consistent temperature, and place the reference part (1) in a high-temperature environment, waiting for the helium (2) in the first chamber and the helium (2) in the second chamber to reach thermodynamic equilibrium. S3. Obtain the first pressure P1 and the first temperature T1 in the first chamber through the pressure gauge (7) and the thermometer (8), and then use the mass conservation model and the thermomolecular pressure difference model to calculate the temperature T2 of the second chamber.

8. The low-temperature temperature measurement method according to claim 7, characterized in that, The calibration of the low-temperature measuring device includes: The vacuum pump assembly (10) is used to evacuate the closed system consisting of the first chamber, the connecting capillary tube (3), and the second chamber; The measuring unit (6) is placed at a known and stable standard temperature point. Helium (2) is introduced into the closed system using a helium (2) cylinder. After the helium (2) reaches thermodynamic equilibrium in the closed system, the pressure P of the first chamber under the calibration condition is collected. 1,cal and temperature T 1,cal ; First, based on the free molecular flow model: Calculate the pressure P in the second chamber under calibration conditions. 2,cal Then, according to the mass conservation model: Calculate the characteristic constant C of the closed system.

9. The low-temperature temperature measurement method according to claim 8, characterized in that, The step of placing the measuring unit (6) at a known and stable standard temperature point includes immersing the measuring unit (6) in liquid nitrogen (5) contained in a cryogenic Dewar (4) to ensure that the second chamber is at the calibrated temperature T. 2,cal Stablize.

10. The low-temperature temperature measurement method according to any one of claims 7 to 9, characterized in that, The calculation of the temperature T2 of the second chamber using the mass conservation model and the thermomolecular pressure difference model includes: Substituting the first pressure P1 and the first temperature T1 into Equation 1: And Formula 2: The temperature T2 of the second chamber was calculated.

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