An optimization device and method based on a diamond anvil cell high pressure and low temperature system

Abstract

The present invention provides an optimization device and method based on a diamond anvil high-pressure and low-temperature system. The structure includes a cold source, a low-temperature thermostat, a molecular pump, a liquid nitrogen recovery device, a temperature measurement system, and a host computer for monitoring temperature. By improving the traditional cold source pressurization method, the structure of the pressure pump is simplified, and a liquid nitrogen recovery device is added to collect excess liquid nitrogen. It also ensures multiple choices of linear pressure changes and temperature changes. By placing a heating rod and a thermal resistor on the sample clamp, they are used to increase the temperature and measure the temperature at different positions of the sample clamp respectively. At the same time, for experiments with high requirements for temperature distribution, a heating resistor wire is wrapped around the low-temperature thermostat sample clamp for uniform heating. By arranging a self-made thermocouple in the high-pressure device, it can adapt to the temperature difference of high-pressure devices of different materials and sizes, meet the needs of various experiments, and provide a clearer temperature change for the influence of different degrees of experimental temperature differences brought by various high-pressure devices.

Description

Technical Field

[0001] The present invention relates to a diamond anvil cell high pressure and low temperature system, and in particular to an optimization device and an optimization method based on the diamond anvil cell high pressure and low temperature system. Background Art

[0002] The Diamond Anvil Cell (DAC) is currently the only device that can generate pressures exceeding 100 GPa, and is an indispensable and important scientific instrument in the field of high-pressure science and technology. As early as the 1930s, high-pressure devices were used to study the physical properties of substances under high-pressure environments. Over the past few decades, with the continuous advancement of technology, the limits of high-pressure technology have been continuously improved. With the emergence of beveled anvil technology, the limit has increased from tens of GPa to the current 500 GPa. During the development of DAC, research has also been conducted under extreme temperature conditions, using electricity, magnetism, spectroscopy, etc. to study the properties of materials under high-pressure and low-temperature conditions.

[0003] When conducting high-pressure, low-temperature physics experiments, it is usually necessary to place the high-pressure device in a cryostat and use it with precision cryogenic equipment for measurement. A cold source, typically consisting of a liquid nitrogen tank and a pressure pump, continuously delivers liquid nitrogen to the cryostat. A molecular pump ensures that the cryostat cavity remains in a vacuum state. The temperature monitoring system consists of a temperature measurement system and computer control. While the aforementioned equipment essentially addresses the requirements for high-pressure, low-temperature experiments under specific conditions, it still suffers from the following drawbacks:

[0004] 1. Cold source delivery is difficult to control: There are two traditional ways to deliver liquid nitrogen to the cryostat: one is to set a fixed pressure value for the pressure pump, that is, to fill the liquid nitrogen tank with gas within a certain period of time; this method is often not conducive to fine-grained control of the liquid nitrogen flow rate because the pressure value of the pressure pump is fixed or the pressure value step is too large; the other method is to connect the liquid nitrogen tank to a nitrogen cylinder and use nitrogen to increase the pressure of the liquid nitrogen tank; this method requires a special inflatable liquid nitrogen tank for the selection of nitrogen cylinders, which is not universal, and the replacement and use of nitrogen cylinders is cumbersome. At the same time, the pressure of the nitrogen cylinder changes over time during the experiment, making it difficult to maintain pressure stability.

[0005] 2. Liquid nitrogen waste: In experiments, the pursuit of the maximum cooling rate usually requires excessive liquid nitrogen delivery to achieve it. The problem this brings is that excess liquid nitrogen will flow out from the outlet, causing waste.

[0006] 3. For experiments requiring high temperature uniformity, the built-in heating rods in the cryostat cannot meet these requirements. Existing cryostats use heating rods during the heating process, heating the entire sample holder by point diffusion. This approach offers the advantages of simplicity and direct control by the temperature measurement system, resulting in good controllability. However, it poses a challenge for experiments requiring high temperature uniformity. For example, when measuring high-pressure thermal conductivity, this approach results in a chaotic, non-unidirectional heat conduction pattern, which can easily lead to large errors.

[0007] 4. Temperature measurement results vary due to the size and material of high-pressure devices. Extreme high-pressure, low-temperature experiments require devices of varying materials and sizes to meet specific experimental requirements. These various high-pressure devices exhibit varying temperature conduction, yet this issue is often overlooked. Currently, a RTD is often placed at a specific location within the cryostat sample holder to measure the sample chamber temperature. This approach can significantly deviate from the desired sample chamber temperature and is unstable. Furthermore, because extreme high pressure conditions result in very small sample sizes, typically less than 0.5 mm, measuring temperature differences within components within the high-pressure device requires extremely small temperature sensors with excellent low-temperature stability and high accuracy. While current commercial RTD temperature measurement methods offer high accuracy, their primary drawback is that they are often too large to fit within the high-pressure device. Summary of the Invention

[0008] In order to solve the above technical problems, the present invention provides an optimization device based on a diamond anvil high-pressure and low-temperature system, the structure of which includes a cold source, a low-temperature thermostat, a molecular pump, a liquid nitrogen recovery device, a temperature measurement system and a host computer for monitoring the temperature;

[0009] The cold source includes a liquid nitrogen tank and a pressure pump. The pressure pump includes a pump body, a connecting pipe, a liquid nitrogen delivery pipe and an exhaust pipe. The connecting pipe is arranged at the lower part of the pump body, and the air outlet at the lower end of the pump body is located in the connecting pipe. The pressure pump is inserted into the liquid nitrogen tank through the connecting pipe and is connected; the liquid nitrogen delivery pipe and the exhaust pipe are respectively arranged in the connecting pipe, the upper port of the liquid nitrogen delivery pipe passes through the pipe wall of the connecting pipe and is connected to the liquid nitrogen inlet of the low-temperature thermostat, and the lower port of the liquid nitrogen delivery pipe penetrates into the bottom of the liquid nitrogen tank; the upper port of the exhaust pipe passes through the pipe wall of the connecting pipe, and the lower port of the exhaust pipe is located in the connecting pipe and is higher than the liquid surface of the liquid nitrogen tank; the upper ports of the liquid nitrogen delivery pipe and the exhaust pipe are both provided with knob flow control valves.

[0010] The liquid nitrogen recovery device includes a collecting tank and a liquid nitrogen tank. A liquid nitrogen recovery port is provided on the upper part of one side of the collecting tank, and the liquid nitrogen recovery port is connected to the liquid nitrogen outlet of the low-temperature thermostat. A liquid nitrogen outlet is provided on the lower part of the other side of the collecting tank, and the liquid nitrogen outlet is no higher than 1 / 3 of the collecting tank; the liquid nitrogen outlet is connected to the liquid inlet provided on the upper part of the liquid nitrogen tank through a Z-shaped tube; a knob-type pressure valve is provided on a section of the Z-shaped tube close to the liquid nitrogen tank; a vertical observation tube is provided on the upper part of the collecting tank, a float is provided in the collecting tank, a benchmark is provided on the upper part of the float, and the benchmark extends into the observation tube; a valve is provided on the top of the observation tube.

[0011] The length of the benchmark rod shall not be less than the length of the observation tube; the length of the benchmark rod shall be greater than the height from the observation tube to the bottom surface of the collecting tube.

[0012] The lower part of the collecting tank is provided with a structure recessed into the tank.

[0013] The molecular pump is connected to the air extraction interface of the low-temperature thermostat.

[0014] The temperature measurement system includes at least two thermal resistors, a heating rod and at least two thermocouples; the thermal resistors and heating rod are respectively arranged at different positions of the sample clamp, and the thermal resistors and heating rod are connected to an electrical interface of the low-temperature thermostat; the thermocouples are arranged on the diamond anvil high-pressure device, including between the diamond and the gasket, between the diamond and the pad, or between the pad and the press, and the thermocouples are connected to another electrical interface of the low-temperature thermostat; the temperature measurement system is connected to the host computer.

[0015] The thermocouple is a T-type thin film thermocouple, which is made of a 0.1mm diameter copper wire and a 0.1mm diameter constantan wire, which are stacked under a press, with the two positioned in the same position and extruded into a thin sheet with a thickness of 0.04-0.05mm and a diameter of 1-1.2mm.

[0016] A nickel-chromium heating resistance wire is evenly wound around the outside of the sample holder, and the heating resistance wire is connected to a heating controller.

[0017] The present invention provides an optimization method based on a diamond anvil cell high pressure and low temperature system for the above-mentioned optimization device:

[0018] (1) Connect the components:

[0019] Connect the pressure pump to the liquid nitrogen tank through the connecting pipe, and connect the upper port of the liquid nitrogen delivery pipe to the liquid nitrogen inlet of the cryostat; connect the liquid nitrogen recovery port of the collection tank to the liquid nitrogen outlet of the cryostat; close the knob-type pressure valve on the Z-shaped pipe between the collection tank and the liquid nitrogen tank;

[0020] Connect the molecular pump to the cryostat exhaust port and seal the port with a snap to prevent air leakage.

[0021] Arrange the thermal resistor, heating rod and thermocouple and connect them to the sockets of the low temperature thermostat. The connection sockets of the thermal resistor and heating rod are different from the connection sockets of the thermocouple to keep the socket functions independent;

[0022] Connect the nickel-chromium heating resistor wire wrapped around the outside of the sample holder to the heating controller; select the appropriate size, number of bundles, number of layers of the heating resistor wire and the power of the heating controller to provide the best uniform temperature distribution.

[0023] (2) Vacuuming:

[0024] Only start the molecular pump and do not start other instruments to ensure the vacuum state of the low-temperature thermostat cavity. Only when a vacuum layer is formed in the low-temperature thermostat cavity can the temperature stability be maintained and the instrument be protected at the same time. When the vacuum degree reaches the requirement, proceed to the next step.

[0025] (3) Adjust the temperature change rate of the cryostat:

[0026] When the molecular pump power reaches 100% and the vacuum degree meets the requirements, first open the knob flow control valve of the liquid nitrogen delivery pipe to the maximum opening, and then start the pressure pump of the cold source. The pressure pump applies constant pressure to the liquid nitrogen tank, so that the liquid nitrogen in the liquid nitrogen tank is input into the low-temperature thermostat through the liquid nitrogen delivery pipe; during the liquid nitrogen delivery process, the knob flow control valve of the exhaust pipe is adjusted to adjust the outlet volume, and then the pressure value in the liquid nitrogen tank is adjusted. By observing the temperature display, the temperature change rate is obtained, and then the knob flow control valve of the exhaust pipe is adjusted to control the appropriate temperature change rate; if the opening is increased, the pressure value in the liquid nitrogen tank decreases, the amount of liquid nitrogen delivered to the low-temperature thermostat is reduced, and the cooling rate is reduced; conversely, the cooling rate increases; if the knob flow control valve of the exhaust pipe is opened to the maximum, the temperature change rate needs to be reduced, and then the opening of the knob flow control valve of the liquid nitrogen delivery pipe of the pressure pump is further reduced.

[0027] (4) Monitoring the temperature change of the cryostat:

[0028] After starting the pressure pump, monitor the temperatures of the two thermal resistors on the cryostat sample clamp and the temperature of the thermocouple on the high-pressure device, and observe the temperature difference between the thermal resistors on the sample clamp and the temperature difference between the thermocouples; if one or both of the temperature differences between the thermal resistors on the cryostat sample clamp and the temperature difference between the thermocouples on the high-pressure device are unstable, continue to adjust the temperature change rate of the cryostat until it stabilizes before proceeding to the next step.

[0029] (5) Change external conditions:

[0030] If the temperature difference between the RTDs on the cryostat sample holder and the temperature difference between the thermocouples on the high-voltage device are stable, end the current operation and proceed to the next step to change the external temperature conditions:

[0031] If the temperature uniformity requirement is not high, you can choose heating rod heating;

[0032] If high temperature uniformity is required, choose heating resistance wire heating, and choose different resistance wire diameters, number of layers, and number of turns in each layer to increase the temperature; when heating is in progress, change the current through the heating controller to change the heating rate.

[0033] If cooling is required, the pressure value in the liquid nitrogen tank is changed, that is, the gas outlet is adjusted by adjusting the knob flow control valve of the pressure pump exhaust pipe. If the opening is reduced, the pressure value in the liquid nitrogen tank increases, the amount of liquid nitrogen delivered to the low-temperature thermostat increases, and the cooling rate increases.

[0034] (6) Liquid nitrogen recovery:

[0035] During the cooling process of transporting liquid nitrogen to the cryostat through the liquid nitrogen tank, the liquid nitrogen that has not had time to liquefy will flow through the liquid nitrogen outlet of the cryostat to the liquid nitrogen recovery port of the collection tank and enter the collection tank; as the amount of liquid nitrogen in the collection tank increases, the liquid level rises and the float rises; when the float mark is observed through the observation tube above the collection tank, it means that the amount of liquid nitrogen in the collection tank has reached the threshold, close the valve on the top of the observation tube, open the knob-type pressure valve on the Z-shaped tube, and transport the liquid nitrogen in the collection tank to the liquid nitrogen tank.

[0036] (7) Calibrate the temperature of the sample chamber of the high-pressure device:

[0037] Usually, when doing the same set of experiments, after each installation of the main cryostat of the high-pressure low-temperature temperature measurement system, the above steps are repeated in sequence until the cooling rate or temperature is stable. When a new measurement experiment is required, including a new high-pressure device or new material, the temperature measurement system of the cryostat is needed to measure the new temperature difference and accurately calibrate the temperature of the sample chamber of the high-pressure device.

[0038] First, calibrate the thermocouple temperature curve, and then determine the relative error of the thermocouple under certain conditions, as well as the temperature difference with the reference thermal resistor:

[0039] Use a calibrated thermal resistor as a reference thermal resistor, place thermocouples at the same point, and measure the temperature difference between the thermocouple and the reference thermal resistor and the relative temperature difference between the thermocouples.

[0040] (8) Replacement of high-pressure device components:

[0041] (8.1) Diamond replacement: Place the thermocouple between the diamond and the gasket and secure it with low-temperature varnish. Similarly, place another thermocouple between the diamond and the gasket and secure it with low-temperature varnish.

[0042] (8.2) Replace the spacer: Place the thermocouple between the diamond and the spacer and secure it with low-temperature varnish. Similarly, place another thermocouple between the spacer and the press and secure it with low-temperature varnish. For materials with poor thermal conductivity, place the thermocouple on the outer wall of the cryostat for measurement.

[0043] (8.3) Replace the press: Place the thermocouple between the pad and the press and stick it with low-temperature varnish to fix the position; similarly, place another thermocouple on the outer wall of the press and fix it with low-temperature varnish.

[0044] (8.4) Replace the gasket: Place the thermocouple on both sides of the gasket, clamp it with diamonds, and fix it with low-temperature varnish.

[0045] (8.5) If two or more accessories are replaced, first determine whether the previous temperature measurement data can be reused based on the size and material, and then arrange the thermocouples; if the diamond and gasket are replaced, only thermocouples need to be placed at the bottom of the diamond on both sides to basically determine their impact; if the gasket and diamond are replaced, the temperature difference impact needs to be re-measured from the outer wall of the press.

[0046] Beneficial effects of the present invention:

[0047] The present invention provides an optimization device and an optimization method based on a diamond anvil high-pressure and low-temperature system. By improving the traditional cold source pressurization method, the structure of the pressure pump is simplified, a liquid nitrogen recovery device is added, and the collection tank and the liquid nitrogen tank are connected. It is ensured that the collection tank and the liquid nitrogen tank remain independent during working time to collect excess liquid nitrogen; it also ensures the linear change of pressure value and multiple choices of temperature change. By placing a heating rod and a thermal resistor on the sample clamp, they are used to heat up and measure the temperature at different positions of the sample clamp respectively; at the same time, for experiments with high temperature distribution requirements, a heating resistor wire is wrapped around the low-temperature thermostat sample clamp for uniform heating. By arranging a self-made thermocouple in the high-pressure device, it adapts to the temperature difference of high-pressure devices of different materials and sizes, meets the needs of various experiments, and provides a clearer temperature change for the influence of different degrees of experimental temperature differences brought by various high-pressure devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a structural schematic diagram of the pressure pump of the present invention;

[0049] Figure 2 This is a schematic structural diagram of the liquid nitrogen recovery device of the present invention;

[0050] Figure 3 Schematic diagram of the arrangement of the sample holder heating rod and thermal resistor of the cryostat of the present invention;

[0051] Figure 4 Schematic diagram of the arrangement of thermocouples of the high-voltage device of the present invention;

[0052] Figure 5 This is a schematic diagram of the manufacturing principle of the thermocouple of the present invention;

[0053] Figure 6 This is a schematic diagram of a sample holder wrapped with a heating resistance wire according to the present invention;

[0054] Figure 7 Schematic diagram of the calibration temperature difference between the thermocouple and the reference thermal resistor according to an embodiment of the present invention;

[0055] Figure 8 This is a diagram of the actual temperature difference measured between the thermocouple and the reference thermal resistor implemented in the present invention.

[0056] 1. Cold source 2. Cryostat 3. Liquid nitrogen tank 4. Pressure pump 5. Pump body 6. Connecting pipe 7. Liquid nitrogen delivery pipe 8. Exhaust pipe 9. Knob flow control valve 10. Sealing ring 11. Collection tank 12. Liquid nitrogen recovery port 13. Z-shaped tube 14. Knob-type pressure valve 15. Observation tube 16. Float 17. Marking rod 18. Depression 19. Heating rod 20. Heating resistance wire 21. Diamond 22. Gasket 23. Spacer block 24. Press 25. Liquid nitrogen outlet. DETAILED DESCRIPTION

[0057] The present invention provides an optimization device based on a diamond anvil high-pressure and low-temperature system, the structure of which includes a cold source 1, a low-temperature thermostat 2, a molecular pump, a liquid nitrogen recovery device, a temperature measurement system and a host computer for monitoring the temperature;

[0058] like Figure 1As shown, the cold source 1 includes a liquid nitrogen tank 3 and a pressure pump 4, the pressure pump 4 includes a pump body 5, a connecting pipe 6, a liquid nitrogen delivery pipe 7 and an exhaust pipe 8, the connecting pipe 6 is provided at the lower part of the pump body 5, and the air outlet at the lower end of the pump body 5 is located in the connecting pipe 6, and the pressure pump 4 is inserted into the liquid nitrogen tank 3 through the connecting pipe 6 to be connected; the liquid nitrogen delivery pipe 7 and the exhaust pipe 8 are respectively arranged in the connecting pipe 6, the upper port of the liquid nitrogen delivery pipe 7 passes through the pipe wall of the connecting pipe 6 and is connected to the liquid nitrogen inlet of the low-temperature thermostat 2, and the lower port of the liquid nitrogen delivery pipe 7 goes deep into the bottom of the liquid nitrogen tank 3; the upper port of the exhaust pipe 8 passes through the pipe wall of the connecting pipe 6, and the lower port of the exhaust pipe 8 is located in the connecting pipe 6, which is higher than the liquid surface of the liquid nitrogen tank 3; the upper ports of the liquid nitrogen delivery pipe 7 and the exhaust pipe 8 are both provided with a knob flow control valve 9. When the pump body 5 pressurizes the liquid nitrogen tank 3, the pressure value in the tank rises, and the liquid nitrogen flows from the liquid nitrogen delivery pipe 7 to the low-temperature thermostat 2 according to the direction of the arrow, and the liquid nitrogen delivery amount is controlled by the knob flow control valve 9 of the liquid nitrogen delivery pipe 7; the exhaust pipe 8 releases the air pressure in the tank by exhausting, and is also designed with the knob flow control valve 9 like the liquid nitrogen delivery pipe 7 to control the air output, change the pressure value in the tank, and control the flow rate of liquid nitrogen; and the knob flow control valve 9 in the form of a twisting bolt can not only refine the liquid nitrogen flow rate, but also make the change of the pressure value in the tank present a quasi-linear change, so that the temperature change and the cooling rate are also quasi-linear.

[0059] A sealing ring 10 is provided on the outer ring of the connecting pipe 6 to seal and prevent gas leakage when connected to the liquid nitrogen tank 3 .

[0060] like Figure 2 As shown, the liquid nitrogen recovery device includes a collecting tank 11 and a liquid nitrogen tank 3. A liquid nitrogen recovery port 12 is provided on the upper portion of one side of the collecting tank 11. The liquid nitrogen recovery port 12 is connected to the liquid nitrogen outlet 25 of the cryostat 2. A liquid nitrogen outlet is provided on the lower portion of the other side of the collecting tank 11. The liquid nitrogen outlet is not higher than 1 / 3 of the collecting tank 11. This design is because more liquid nitrogen in the collecting tank 11 can be transferred to the liquid nitrogen tank 3; the liquid nitrogen outlet is connected to the liquid inlet provided on the upper portion of the liquid nitrogen tank 3 through a Z-shaped tube 13; the Z-shaped tube 13 is close to the liquid A knob-type pressure valve 14 is provided on one section of the nitrogen tank 3; a vertical observation tube 15 is provided on the upper part of the collecting tank 11; a float 16 is provided in the collecting tank 11, and the float 16 floats on the surface of the liquid nitrogen. A mark 17 is provided on the upper part of the float 16, and the mark 17 extends into the observation tube 15. When the top of the mark 17 extends out of the top of the observation tube 15, it indicates that the amount of liquid nitrogen in the collecting tank 11 has reached the threshold and can be transported to the liquid nitrogen tank 3; a valve is provided on the top of the observation tube 15, and the observation tube 15 also serves to discharge vaporized nitrogen and waste gas.

[0061] The length of the marking rod 17 is not less than the length of the observation tube 15; the length of the marking rod 17 is greater than the height from the observation tube 15 to the bottom surface of the collecting cylinder.

[0062] The lower portion of the collection tank 11 is provided with a recessed structure 18 extending into the tank. This design is based on two main considerations: first, to keep the float 16 at a relatively high position, so that the rod 17 of the float 16 is always inside the observation tube 15 to prevent it from falling off; second, to increase the efficiency of recycling. In order to transport more liquid nitrogen to the liquid nitrogen tank 3, the bottom of the collection tank 11 does not need to store too much liquid nitrogen, but only needs to retain the amount of liquid nitrogen that keeps the collection tank 11 in a cold tank.

[0063] The molecular pump is connected to the air extraction interface of the low-temperature thermostat 2.

[0064] The place where the high-pressure device is placed in the cryostat 2 is referred to as the sample holder; the temperature measurement system includes two thermal resistors b and c, a heating rod 19 and two thermocouples m and n; the thermal resistors b and c and the heating rod 19 are respectively arranged at different positions of the sample holder, such as Figure 3 As shown, the heating rod 19 is used to heat the sample holder; the thermal resistors b and c are used to measure the temperature at different positions of the sample holder; the thermal resistors b, c and the heating rod 19 are connected to a 19-core socket of the low-temperature thermostat 2; the thermocouples m and n are arranged on the diamond anvil high-pressure device, including between the diamond and the gasket, between the diamond and the pad, or between the pad and the press, and the thermocouples m and n are connected to another 19-core socket of the low-temperature thermostat 2; the temperature measurement system is connected to the host computer.

[0065] The thermocouple is a T-type thin film thermocouple, which is made of a 0.1mm diameter copper wire and a 0.1mm diameter constantan wire, which are stacked under a press, and the two are placed in the same position, and squeezed into a thin sheet with a thickness of 0.04-0.05mm and a diameter of 1-1.2mm. Figure 6 As shown, A is copper wire, B is constantan wire, c is temperature measuring point, d is the same plane of the component to measure the average temperature, so as to accurately measure the temperature; using parallel circuits, the positive poles of multiple thermocouple wires of the same type are connected to the positive poles and the negative poles to the negative poles.

[0066] According to calculations, if it is proved that the thermoelectric potential of each thermocouple is not much different and the resistance between the wires is equal, then the following formula can be obtained:

[0067]

[0068] Among them, Ev represents the average value, E1, E2, E3…E n It represents the value of each thermocouple. The total potential of the parallel measurement circuit is equal to the average value of the thermoelectric potentials of n thermocouples.

[0069] Moreover, the parallel circuit is very practical in low temperature applications. It can measure low temperature specific heat, thermal conductivity and thermal expansion with very high accuracy. Although the thermoelectric potential of the parallel circuit is small, the relative error is also very small, which is only a fraction of that of a single thermocouple. Another advantage of parallel thermocouples is that even if one of the thermocouples is broken, the entire system can still operate without affecting the temperature measurement. This is a great advantage for strictly closed experiments.

[0070] To ensure uniform heating, a nickel-chromium heating resistor 20 is evenly wound around the outside of the sample holder. This resistor is connected to a heating controller. The advantage of this nickel-chromium resistor is that it cools down after extended use without becoming brittle. Furthermore, nickel-chromium is non-magnetic, meeting the requirement for non-magnetic materials around high-voltage devices in magnetic experiments. The heating rate is controlled based on the precise requirements of the experiment. Variable factors include the material and size of the resistor, as well as the number of strands and layers wound around the sample holder.

[0071] The present invention provides an optimization method based on a diamond anvil cell high pressure and low temperature system for the above-mentioned optimization device:

[0072] (1) Connect the components:

[0073] Connect the pressure pump 4 to the liquid nitrogen tank 3 via the connecting pipe 6. Connect the upper end of the liquid nitrogen delivery pipe 7 to the liquid nitrogen inlet of the cryostat 2. Connect the liquid nitrogen recovery port 12 of the collection tank 11 to the liquid nitrogen outlet of the cryostat 2 via a steel wire tube that does not become brittle at low temperatures. Close the knob-type pressure valve 14 on the Z-shaped pipe 13 between the collection tank 11 and the liquid nitrogen tank 3.

[0074] Connect the molecular pump to the exhaust port of cryostat 2 and seal the port with a snap to prevent air leakage;

[0075] Arrange the thermal resistor, heating rod 19 and thermocouple and connect them to the sockets of the low temperature thermostat 2. The connection sockets of the thermal resistor and heating rod 19 are different from the connection sockets of the thermocouple to keep the socket functions independent;

[0076] like Figure 6 As shown, the nickel-chromium heating resistance wire 20 wrapped around the outside of the sample holder is connected to the heating controller; the size, number of bundles, number of layers of the heating resistance wire 20 and the power of the heating controller are appropriately selected to provide the best uniform temperature distribution.

[0077] (2) Vacuuming:

[0078] Only the molecular pump is started, and other instruments are not started, to ensure the vacuum state of the cryostat 2 cavity. Only when the vacuum layer is formed in the cryostat 2 cavity can the temperature stability be maintained and the instrument be protected. The degree of vacuum directly determines the experimental temperature holding time and the stability of the measured temperature. If the vacuum degree is low, moisture will form in the cavity, and the welding points in the cavity, including the low-temperature components and high-voltage devices, will be exposed to moisture, thus damaging the components. When the vacuum degree reaches 7.7×10 -4 When p, proceed to the next step.

[0079] (3) Adjust the temperature change rate of cryostat 2:

[0080] After the molecular pump power reaches 100% and the vacuum degree meets the requirement, the knob flow control valve 9 of the liquid nitrogen delivery pipe 7 is first opened to the maximum opening, and then the pressure pump 4 of the cold source 1 is started. The pressure pump 4 applies a constant pressure to the liquid nitrogen tank 3, so that the liquid nitrogen in the liquid nitrogen tank 3 is input into the cryostat 2 through the liquid nitrogen delivery pipe 7; the liquid nitrogen vaporizes after contacting the sample holder of the cryostat 2, thereby cooling the sample holder. During the process of transporting liquid nitrogen, the knob flow control valve 9 of the exhaust pipe 8 is adjusted at the same time to adjust the gas outlet, thereby adjusting the pressure value in the liquid nitrogen tank 3. By observing the temperature display, the temperature change rate is obtained, and then the knob flow control valve 9 of the exhaust pipe 8 is adjusted to control the appropriate temperature change rate; if the opening is increased, the pressure value in the liquid nitrogen tank 3 decreases, the amount of liquid nitrogen transported to the low-temperature thermostat 2 decreases, and the cooling rate decreases; conversely, the cooling rate increases; if the knob flow control valve 9 of the exhaust pipe 8 is opened to the maximum, the temperature change rate needs to be reduced, and then the opening of the knob flow control valve 9 of the liquid nitrogen delivery pipe 7 of the pressure pump 4 is further reduced.

[0081] (4) Monitoring the temperature change of cryostat 2:

[0082] After starting the pressure pump 4, monitor the temperatures of the two thermal resistors on the sample clamp of the low-temperature thermostat 2 and the temperatures of the two thermocouples on the high-pressure device, and at the same time observe the temperature difference between the thermal resistors b and c on the sample clamp, and the temperature difference between the thermocouples m and n; if one or both of the temperature difference between the two thermal resistors b and c on the sample clamp of the low-temperature thermostat 2 and the temperature difference between the two thermocouples m and n on the high-pressure device are unstable at the same time, continue to adjust the temperature change rate of the low-temperature thermostat 2 until it stabilizes before proceeding to the next step.

[0083] (5) Change external conditions:

[0084] If the temperature difference between the two thermal resistors b and c on the sample holder of cryostat 2 is stable, and the temperature difference between the two thermocouples m and n on the high-voltage device is stable, then the current operation ends and the next step is to change the external temperature conditions. The purpose of changing the external temperature is to proceed to the next experimental operation, adjust to the target temperature, and observe the experimental phenomena. In the optimization method, when the temperature difference between the two thermocouples is stable, it can be determined that the temperature reading is accurate and the next operation can be carried out.

[0085] Methods for changing external temperature conditions include:

[0086] If the temperature uniformity requirement is not high, the heating rod 19 can be selected for heating. The methods include: 1. changing the current output of the heating rod 19; 2. changing the power range of the heating rod 19; 3. changing the output range, that is, the output at the current power, which can be divided into three levels: high, med, and low.

[0087] If the temperature uniformity requirement is high, the heating resistance wire 20 is selected for heating, and different resistance wire diameters, number of layers, and number of turns of each layer are selected to increase the temperature. When heating is in progress, the heating controller changes the current to change the heating rate.

[0088] If cooling is required, the pressure value in the liquid nitrogen tank 3 is changed, that is, the gas outlet is adjusted by adjusting the knob flow control valve 9 of the exhaust pipe 8 of the pressure pump 4. When the opening is reduced, the pressure value in the liquid nitrogen tank 3 increases, the amount of liquid nitrogen delivered to the cryostat 2 increases, and the cooling rate increases.

[0089] (6) Liquid nitrogen recovery:

[0090] During the process of transporting liquid nitrogen to the low-temperature thermostat 2 for cooling through the liquid nitrogen tank 3, the liquid nitrogen that has not had time to liquefy will flow to the liquid nitrogen recovery port 12 of the collection tank 11 through the liquid nitrogen outlet of the low-temperature thermostat 2 and enter the collection tank 11; as the amount of liquid nitrogen in the collection tank 11 increases, the liquid level rises and the float 16 rises; when the mark 17 of the float 16 is observed through the observation tube 15 above the collection tank 11, it means that the amount of liquid nitrogen in the collection tank 11 has reached the threshold, the valve on the top of the observation tube 15 is closed, and the knob-type pressure valve 14 on the Z-shaped tube 13 is opened to transport the liquid nitrogen in the collection tank 11 to the liquid nitrogen tank 3.

[0091] (7) Calibrate the temperature of the sample chamber of the high-pressure device:

[0092] Usually, when doing the same set of experiments, after each installation of the main cryostat 2 of the high-pressure low-temperature temperature measurement system, the above steps are repeated in sequence until the cooling rate or temperature is stable. When a new measurement experiment is required, including a new high-pressure device or new material, the temperature measurement system of the cryostat 2 is needed to measure the new temperature difference and accurately calibrate the temperature of the sample chamber of the high-pressure device.

[0093] First, calibrate the thermocouple temperature curve, and then determine the relative error of the thermocouple under certain conditions, as well as the temperature difference with the reference thermal resistor:

[0094] Using a calibrated DT thermal resistor as a reference thermal resistor, placing two T-shaped thin film thermocouples of the present invention at the same point, and measuring the temperature difference between the thermocouple and the reference thermal resistor and the relative temperature difference between the two thermocouples;

[0095] like Figure 7 The figure shows the temperature difference when a thermocouple is placed at a point. Point B is the reference RTD, and points C and D are the thermocouples. BC and BD are the temperature differences of the thermocouple relative to the reference RTD, and CD is the relative temperature difference between the two thermocouples. This method confirms that the temperature difference between the two thermocouples is stable, and the temperature difference is approximately 1.5K when placed at a point.

[0096] (8) Replacement of high-pressure device components:

[0097] (8.1) Change diamond: Figure 3 As shown, if switching from a Type I diamond to a Type II diamond, thermocouple m needs to be placed between diamond 21 and spacer 22 and secured with low-temperature varnish. Similarly, thermocouple n needs to be sandwiched between diamond 21 and spacer 23 and secured with low-temperature varnish. Experimental results show that there is virtually no temperature difference (relative to the measurement error of thermocouples) between Type I and Type II diamonds. Therefore, if only the diamond is replaced, while other components of the high-voltage device remain unchanged, the temperature difference data can be reused without the need for recalibration.

[0098] like Figure 8 As shown, it can be seen from the temperature rise and fall that the temperature difference between the above two places is about 1.5k. At the same time, according to Figure 7 As shown, after subtracting the relative temperature difference between points C and D, the temperature difference between the two is almost negligible, indicating that diamond has little effect on the temperature difference. The improvement in the manufacturing and method of the thin film thermocouple of the present invention has a good temperature measurement effect during the replacement of the measuring component.

[0099] (8.2) Replace the pad: If Figure 3 As shown, if the copper spacer is replaced with an alloy spacer, thermocouple m needs to be placed between diamond 21 and spacer 23 and fixed with low-temperature varnish. Similarly, thermocouple n needs to be clamped between spacer 23 and press 24 and fixed with low-temperature varnish. In experiments, it was found that the temperature difference between thermocouples m and n cannot be ignored in materials with poor thermal conductivity. In this case, thermocouple n needs to be placed on the outer wall of cryostat 2 for measurement.

[0100] (8.3) Replace the compressor: Figure 3As shown, just like changing the pad, if the copper press is replaced with an alloy press, the thermocouple m needs to be placed between the pad 23 and the press 24, and glued with low-temperature varnish to fix the position; similarly, the thermocouple n needs to be placed on the outer wall of the press 24 and fixed with low-temperature varnish.

[0101] (8.4) Replace gasket: If Figure 3 As shown, similar to replacing a diamond, if a rhenium gasket is replaced with a steel gasket, thermocouples m and n need to be placed on either side of gasket 22, clamped with diamonds, and secured with low-temperature varnish. The temperature difference between the rhenium gasket and the steel gasket is very small (relative to the measurement error of the thermocouple). Therefore, if other components of the high-voltage device remain unchanged and experimental accuracy is not required, replacing only the gasket allows the temperature difference data to be reused without recalibration.

[0102] (8.5) Based on the previous four individual components, we can conclude that if two or more components are replaced, first determine whether the previous temperature measurement data can be reused based on the size and material, and then determine the placement of thermocouples. For example, if the diamond and gasket are replaced, only thermocouples need to be placed at the bottom of the diamond on both sides to basically determine their impact. If the gasket and diamond are replaced, the temperature difference impact needs to be remeasured from the outer wall of the press.

Claims

1. An optimization device based on a diamond anvil cell high pressure and low temperature system, characterized by: It includes a cold source, a cryostat, a molecular pump, a liquid nitrogen recovery device, a temperature measurement system and a host computer for monitoring temperature; The cold source includes a liquid nitrogen tank and a pressure pump. The pressure pump includes a pump body, a connecting pipe, a liquid nitrogen delivery pipe and an exhaust pipe. The connecting pipe is arranged at the lower part of the pump body, and the air outlet at the lower end of the pump body is located in the connecting pipe. The pressure pump is inserted into the liquid nitrogen tank through the connecting pipe and connected; the liquid nitrogen delivery pipe and the exhaust pipe are respectively arranged in the connecting pipe. The upper port of the liquid nitrogen delivery pipe passes through the pipe wall of the connecting pipe and is connected to the liquid nitrogen inlet of the low-temperature thermostat, and the lower port of the liquid nitrogen delivery pipe penetrates into the bottom of the liquid nitrogen tank; the upper port of the exhaust pipe passes through the pipe wall of the connecting pipe, and the lower port of the exhaust pipe is located in the connecting pipe and is higher than the liquid surface of the liquid nitrogen tank; the upper ports of the liquid nitrogen delivery pipe and the exhaust pipe are both provided with knob flow control valves; The liquid nitrogen recovery device includes a collection tank and a liquid nitrogen tank. A liquid nitrogen recovery port is provided on the upper part of one side of the collection tank, and the liquid nitrogen recovery port is connected to the liquid nitrogen outlet of the cryostat. A liquid nitrogen outlet is provided on the lower part of the other side of the collection tank, and the liquid nitrogen outlet is no higher than 1 / 3 of the collection tank; the liquid nitrogen outlet is connected to the liquid inlet provided on the upper part of the liquid nitrogen tank through a Z-shaped tube; a knob-type pressure valve is provided on a section of the Z-shaped tube close to the liquid nitrogen tank; a vertical observation tube is provided on the upper part of the collection tank, a float is provided in the collection tank, a benchmark is provided on the upper part of the float, and the benchmark extends into the observation tube; a valve is provided on the top of the observation tube; The molecular pump is connected to the exhaust interface of the cryostat; The temperature measurement system includes at least two thermal resistors, a heating rod, and at least two thermocouples; the thermal resistors and heating rods are respectively arranged at different positions of the sample holder, and the thermal resistors and heating rods are connected to an electrical interface of the low-temperature thermostat; the thermocouples are arranged on the diamond anvil high-pressure device, including between the diamond and the gasket, between the diamond and the pad, or between the pad and the press, and the thermocouples are connected to another electrical interface of the low-temperature thermostat; the temperature measurement system is connected to the host computer; A nickel-chromium heating resistance wire is evenly wound around the outside of the sample holder, and the heating resistance wire is connected to a heating controller.

2. The optimization device based on a diamond anvil cell high pressure and low temperature system according to claim 1, characterized in that: The length of the benchmark rod shall not be less than the length of the observation tube; the length of the benchmark rod shall be greater than the height from the observation tube to the bottom surface of the collecting tube.

3. The optimization device based on a diamond anvil cell high pressure and low temperature system according to claim 1, characterized in that: The lower part of the collecting tank is provided with a structure recessed into the tank.

4. The optimization device based on a diamond anvil cell high pressure and low temperature system according to claim 1, characterized in that: The thermocouple is a T-type thin film thermocouple, which is made of a 0.1mm diameter copper wire and a 0.1mm diameter constantan wire, which are stacked under a press, with the two positioned in the same position and extruded into a thin sheet with a thickness of 0.04-0.05mm and a diameter of 1-1.2mm.

5. An optimization method based on a diamond anvil cell high pressure and low temperature system, characterized in that: An optimization device based on a diamond anvil cell high pressure and low temperature system according to any one of claims 1 to 4 comprises the following steps: (1) Connect the components: Connect the pressure pump to the liquid nitrogen tank through the connecting pipe, and connect the upper port of the liquid nitrogen delivery pipe to the liquid nitrogen inlet of the cryostat; connect the liquid nitrogen recovery port of the collection tank to the liquid nitrogen outlet of the cryostat; close the knob-type pressure valve on the Z-shaped pipe between the collection tank and the liquid nitrogen tank; Connect the molecular pump to the cryostat exhaust port and seal the port with a snap to prevent air leakage. Arrange the thermal resistor, heating rod and thermocouple and connect them to the sockets of the low temperature thermostat. The connection sockets of the thermal resistor and heating rod are different from the connection sockets of the thermocouple to keep the socket functions independent; Connect the nickel-chromium heating resistance wire wrapped around the outside of the sample holder to the heating controller; select the appropriate size, number of bundles, number of layers of the heating resistance wire and the power of the heating controller; (2) Vacuuming: Only start the molecular pump and do not start other instruments to ensure the vacuum state of the cryostat cavity. Only when the vacuum layer is formed in the cryostat cavity can the temperature stability be maintained and the instrument be protected. When the vacuum degree reaches the requirement, proceed to the next step. (3) Adjust the temperature change rate of the cryostat: Wait until the molecular pump power reaches 100% and the vacuum degree meets the requirements, first open the knob flow control valve of the liquid nitrogen delivery pipe to the maximum opening, then start the pressure pump of the cold source. The pressure pump applies constant pressure to the liquid nitrogen tank, so that the liquid nitrogen in the liquid nitrogen tank is input into the cryostat through the liquid nitrogen delivery pipe; During the liquid nitrogen delivery process, the knob flow control valve of the exhaust pipe is adjusted to adjust the gas output, thereby adjusting the pressure value in the liquid nitrogen tank. By observing the temperature display, the temperature change rate is obtained, and then the knob flow control valve of the exhaust pipe is adjusted to control the appropriate temperature change rate. If the opening is increased, the pressure value in the liquid nitrogen tank decreases, the amount of liquid nitrogen delivered to the cryostat decreases, and the cooling rate decreases; conversely, the cooling rate increases. If the knob flow control valve of the exhaust pipe is opened to the maximum, the temperature change rate needs to be reduced, and then the opening of the knob flow control valve of the pressure pump liquid nitrogen delivery pipe is further reduced. (4) Monitoring the temperature changes of the cryostat: After starting the pressure pump, monitor the temperature of the two thermal resistors on the cryostat sample clamp and the temperature of the thermocouple on the high-pressure device. At the same time, observe the temperature difference between the thermal resistors on the sample clamp and the temperature difference between the thermocouples. If one or both of the temperature difference between the RTD on the cryostat sample holder and the temperature difference between the thermocouple on the high-pressure device are unstable, continue to adjust the temperature change rate of the cryostat until it stabilizes before proceeding to the next step; (5) Change external conditions: If the temperature difference between the RTDs on the cryostat sample holder and the temperature difference between the thermocouples on the high-voltage device are stable, end the current operation and proceed to the next step to change the external temperature conditions: If the temperature uniformity requirement is not high, you can choose heating rod heating; If the temperature uniformity is high, choose heating resistance wire heating, and choose different resistance wire diameters, number of layers, and number of turns in each layer to increase the temperature; when heating, change the current through the heating controller to change the heating rate; If cooling is required, the pressure value in the liquid nitrogen tank is changed, that is, the gas outlet is adjusted by adjusting the knob flow control valve of the pressure pump exhaust pipe. If the opening is reduced, the pressure value in the liquid nitrogen tank increases, the amount of liquid nitrogen delivered to the cryostat increases, and the cooling rate increases; (6) Liquid nitrogen recovery: During the cooling process of transferring liquid nitrogen from the liquid nitrogen tank to the cryostat, the liquid nitrogen that has not yet liquefied will flow through the liquid nitrogen outlet of the cryostat to the liquid nitrogen recovery port of the collection tank and enter the collection tank; as the amount of liquid nitrogen in the collection tank increases, the liquid level rises and the float rises; when the float mark is observed through the observation tube above the collection tank, it means that the amount of liquid nitrogen in the collection tank has reached the threshold, the valve on the top of the observation tube is closed, and the knob-type pressure valve on the Z-shaped tube is opened to transfer the liquid nitrogen in the collection tank to the liquid nitrogen tank; (7) Calibrate the temperature of the sample chamber of the high-pressure device: Usually, when doing the same set of experiments, after each installation of the main cryostat of the high-pressure low-temperature temperature measurement system, the above steps are repeated in sequence until the cooling rate or temperature is stable. When a new measurement experiment is required, including a new high-pressure device or new material, the temperature measurement system of the cryostat is needed to measure the new temperature difference and accurately calibrate the temperature of the sample chamber of the high-pressure device. First, calibrate the thermocouple temperature curve, and then determine the relative error of the thermocouple under certain conditions, as well as the temperature difference with the reference thermal resistor: Use a calibrated thermal resistor as a reference thermal resistor, place thermocouples at the same point, and measure the temperature difference between the thermocouple and the reference thermal resistor and the relative temperature difference between the thermocouples. (8) Replacement of high-voltage device components: (8.1) Diamond replacement: Place the thermocouple between the diamond and the gasket and secure it with low-temperature varnish. Place another thermocouple between the diamond and the gasket and secure it with low-temperature varnish. (8.2) Replace the spacer: Place the thermocouple between the diamond and the spacer and secure it with low-temperature varnish. Place another thermocouple between the spacer and the press and secure it with low-temperature varnish. For materials with poor thermal conductivity, place the thermocouple on the outer wall of the cryostat for measurement. (8.3) Replace the press: Place the thermocouple between the pad and the press and stick it with low-temperature varnish to fix the position; place the other thermocouple on the outer wall of the press and fix it with low-temperature varnish; (8.4) Replace the gasket: Place the thermocouple on both sides of the gasket, clamp it with diamonds, and fix it with low-temperature varnish; (8.5) If two or more accessories are replaced, first determine whether the previous temperature measurement data can be reused based on the size and material, and then arrange the thermocouples; if the diamond and gasket are replaced, only thermocouples need to be placed at the bottom of the diamond on both sides; if the gasket and diamond are replaced, the temperature difference effect needs to be re-measured from the outer wall of the press.

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