An automated method for preparing supercooled superfluid helium

Abstract

This invention discloses an automated method for preparing supercooled superfluid helium, comprising: injecting liquid helium from a liquid helium source into a storage tank, and splitting the liquid helium into a first portion and a second portion in the storage tank; injecting the first portion of liquid helium into a subcooling cavity to cool the magnet coil therein; throttling and cooling the second portion of liquid helium through a negative pressure regenerator pipeline to obtain saturated superfluid helium; controlling the saturated superfluid helium to exchange heat with the first portion of liquid helium in an evaporator to obtain supercooled superfluid helium in the subcooling cavity; sending the low-temperature saturated helium gas formed by the heat exchange and evaporation of the saturated superfluid helium into a regenerator to recover the cold energy, and then sending it to a liquefaction unit to be reliquefied into liquid nitrogen, and returning the liquid nitrogen to the liquid helium source. This invention achieves fully automated adjustment of the entire process, including liquid helium injection, throttling and cooling, helium heating, and safe venting, through multi-sensor collaborative control, realizing automated preparation of supercooled superfluid helium, reducing the need for manual intervention, and improving system response speed and operational stability.

Description

Technical Field

[0001] This invention relates to the field of supercooled superfluid helium preparation technology, and in particular to an automated method for preparing supercooled superfluid helium. Background Technology

[0002] Superfluid helium (HeII), as an ultra-low temperature working fluid, possesses superior properties compared to conventional liquid helium (HeI), including extremely low viscosity, high specific heat capacity, and ultra-high thermal conductivity. Therefore, it is widely used in cooling high-field superconducting magnets, superconducting cavities, particle accelerators, and other cutting-edge cryogenic physics experimental devices. Particularly in superconducting magnet systems, reducing its operating temperature from the conventional 4.2 K to 1.8 K can significantly increase the magnetic field strength by approximately 20% to 30%, while also greatly enhancing the magnet's thermal stability and operational reliability. Supercooled superfluid helium (HeIIp), as a metastable superfluid helium state, has a critical heat flux density far exceeding that of saturated superfluid helium (HeIIs) and conventional liquid helium, thus showing significant application potential in superconducting systems with high heat loads or high magnetic field gradients.

[0003] Currently, significant progress has been made both domestically and internationally in superfluid helium refrigeration technology, particularly in the stable production of saturated superfluid helium in large-scale scientific facilities. A common technique involves using negative pressure suction to transform liquid helium into saturated superfluid helium (HeIIs). However, the preparation technology of supercooled superfluid helium is still in its early stages in China, and a mature, stable, and engineering-applicable system solution has not yet been developed. Existing technologies largely rely on open-loop or semi-open-loop designs, with liquid helium directly vaporized and discharged during use. This not only results in a significant waste of expensive liquid helium resources but also limits the system's ability to operate stably over the long term.

[0004] Furthermore, existing devices are often structurally complex and bulky, with low temperature control accuracy and insufficient automation. They also suffer from problems such as pipe icing or frosting and incomplete helium recovery during the cooling process. In particular, when dealing with sudden high heat load events such as superconducting magnet quench failure, the system's rapid response and safe discharge capabilities are insufficient, which may lead to equipment damage or even safety accidents. Summary of the Invention

[0005] To address the technical problems existing in the background art, this invention proposes an automated method for preparing supercooled superfluid helium.

[0006] This invention proposes an automated method for preparing supercooled superfluid helium, comprising: S1. Liquid helium from the liquid helium source is injected into the storage tank, and the liquid helium is split into a first part of liquid helium and a second part of liquid helium through the storage tank; S2. Inject the first portion of liquid helium into the supercooled cavity to cool the magnet coil inside; S3. Throttling and cooling the second part of liquid helium after it flows through the negative pressure regenerator pipeline to obtain saturated superfluid helium; S4. Control the saturated superfluid helium to exchange heat with the first part of liquid helium in the evaporator so that the subcooled superfluid helium is obtained in the subcooled cavity. S5. The low-temperature saturated helium gas formed by the heat exchange and evaporation of saturated superfluid helium is sent to the regenerator to recover the cold energy, and then sent to the liquefaction unit to be liquefied again into liquid nitrogen. The liquid nitrogen is then returned to the liquid helium source.

[0007] Preferably, step S1 specifically involves: monitoring the liquid level of the liquid helium storage tank in real time using a first liquid level sensor installed in the tank; automatically adjusting the opening of a regulating valve installed on the liquid helium injection pipeline based on the first liquid level signal fed back by the first liquid level sensor to control the flow rate of the liquid helium injected into the storage tank; causing the injected liquid helium to flow through a phase separator installed in the storage tank for gas-liquid separation; splitting the separated liquid helium into a first portion of liquid nitrogen and a second portion of liquid nitrogen; and heating the separated cryogenic helium gas to room temperature via a first heater on a first tube before releasing it into a gasbag for collection.

[0008] Preferably, step S4 further includes: heating the low-temperature helium gas formed by evaporation in the supercooled cavity to room temperature via a second heater on the second tube and then discharging it into the airbag; a safety valve and a large-diameter valve are connected in parallel on the second tube; monitoring the gas pressure in the tube in real time via a pressure sensor on the second tube; opening the safety valve to discharge the helium gas generated by natural heat accumulation when the gas pressure exceeds a first threshold; opening the large-diameter valve to quickly release the high-pressure helium gas when the gas pressure exceeds a second threshold higher than the first threshold; passing the room-temperature helium gas recovered in the airbag into a liquefier to reliquefy it into liquid helium; and returning the liquid nitrogen to the liquid helium source.

[0009] Preferably, the first part of the liquid helium diversion process is as follows: the liquid level is monitored in real time by a second liquid level sensor installed in the subcooling chamber; when the second liquid level signal fed back by the second liquid level sensor is lower than the set value, the flow rate of the first part of the liquid helium flowing into the subcooling chamber is increased; the first liquid level signal of the liquid level height in the reaction tank is acquired simultaneously; when the first liquid level signal is lower than the set range due to the increase in the flow rate of the first part of the liquid helium, the opening of the regulating valve is increased to increase the liquid helium injection amount.

[0010] Preferably, step S3 specifically involves: allowing the second portion of liquid helium to flow through the tube side of the regenerator and exchange heat with the low-temperature saturated helium flowing through the shell side of the regenerator to pre-cool the second portion of liquid helium; delivering the pre-cooled second portion of liquid helium to a throttling valve; and adjusting the opening of the throttling valve to induce a throttling expansion effect in the flowing liquid helium to obtain low-temperature saturated superfluid helium.

[0011] Preferably, adjusting the opening of the throttle valve specifically involves: using a first temperature sensor located downstream of the throttle valve to monitor the temperature of the cryogenic saturated superfluid helium in real time, generating a temperature signal; and automatically adjusting the opening of the throttle valve based on the temperature signal fed back by the first temperature sensor to maintain the temperature of the cryogenic saturated superfluid helium within a set range.

[0012] Preferably, step S5 specifically involves: sending the low-temperature saturated helium gas formed by the evaporation of the first portion of liquid helium after heat exchange into the shell side of the regenerator; outputting the low-temperature saturated helium gas through the third tube connected to the shell side of the regenerator; heating the low-temperature saturated helium gas to room temperature helium gas by the third heater on the third tube; sending the room temperature helium gas to the liquefier for reliquefaction into liquid helium gas by the circulation pump on the third tube; and then transporting the liquid helium gas to the liquid helium source.

[0013] Preferably, the control process of the first heater, the second heater, and the third heater is as follows: the exhaust temperature in the first tube, the second tube, and the third tube is monitored in real time by a second temperature sensor at the outlet of the first heater / second heater / third heater; the exhaust temperature is compared with the room temperature; and the heating power of the first heater / second heater / third heater is adjusted according to the comparison result until the exhaust temperature of the first tube / second tube / third tube is at room temperature.

[0014] Preferably, the control steps of the large-diameter valve further include: acquiring the monitoring temperature of a third temperature sensor installed on the magnet coil; when the monitoring temperature exceeds a safety threshold, determining it as a failure event, and immediately outputting a control signal to fully open the large-diameter valve installed on the second pipe for emergency pressure relief.

[0015] Preferably, the monitored temperature obtained by the third temperature sensor can also be used to adjust the temperature of the magnet coil. Specifically, the monitored temperature is compared with the target temperature, and an adjustment signal is generated based on the comparison result. The adjustment signal is used to adjust at least one of the throttle valve opening, the circulating pump speed, and / or the regulating valve opening, so that the temperature of the magnet coil approaches the target temperature.

[0016] In this invention, by precisely controlling the opening of the throttling valve and the heat exchange process of the regenerator, subcooled superfluid helium below 1.8K can be stably obtained, meeting the requirements of high-field superconducting magnets for extremely low-temperature cooling media. A closed-loop recovery process is formed by the liquefier and circulating pump, allowing the evaporated helium to be reliquefied and returned to the liquid helium source for reuse, essentially achieving zero liquid helium loss. This overcomes the shortcomings of traditional open systems where large amounts of liquid helium evaporate, significantly improving economic efficiency and sustainable operation. This invention utilizes multi-sensor collaborative control (liquid level, temperature, pressure, etc.) to achieve fully automated adjustment of the entire process, including liquid helium injection, throttling cooling, helium heating, and safe venting, reducing the need for manual intervention and improving system response speed and operational stability. In particular, the large-diameter valve can quickly depressurize in extreme situations such as magnet quench failure, preventing equipment damage and safety accidents. Attached Figure Description

[0017] Figure 1 This is a flowchart of an automated method for preparing supercooled superfluid helium proposed in this invention; Figure 2 This is a schematic diagram of the system composition of the supercooled superfluid helium preparation apparatus used in this invention. Detailed Implementation

[0018] To address the problems existing in the preparation of superfluid helium using existing open-loop systems and the "forced flow subcooling method" for preparing supercooled superfluid helium, this invention proposes a method based on... Figure 2 The supercooled superfluid helium preparation apparatus shown is vertical and includes a tank 15 with a top cover 151 and a vacuum-sealed and isolated first and second chambers. An electromagnetic valve and a molecular pump are connected to the outside of the tank 15. This setup is primarily used to evacuate the first chamber to a vacuum state. Simultaneously, a vacuum gauge is installed inside the tank 15 to monitor the vacuum level of the first chamber. The vacuum gauge is linked to the molecular pump and the electromagnetic valve to ensure that the inside of the tank 15 is in a vacuum environment, thereby reducing heat conduction.

[0019] A subcooling chamber 3 is provided inside the tank 15, dividing its internal cavity into a first chamber and a second chamber. The first chamber is specifically the portion of the tank 15's internal cavity outside the subcooling chamber 3, and the second chamber is specifically the internal cavity of the subcooling chamber 3. A storage tank 2 is installed in the first chamber of the tank 15, and the storage tank 2 is connected to the liquid helium source 1. This arrangement allows liquid helium to be introduced into the storage tank 2. During the pipeline transportation process, due to heat loss in the pipeline, the portion of liquid helium in contact with the pipeline wall will experience a temperature increase and vaporize into helium gas. Therefore, the substance introduced into the storage tank 2 will be a gas-liquid mixture. If the gas in this mixture enters the downstream pipeline, it will not only occupy pipeline space and reduce the actual flow rate of liquid helium, but may also become a source of thermal disturbance during superfluid helium preparation, potentially causing malfunctions. Therefore, a phase separator 21 is also installed in the storage tank 2. The inlet of the phase separator 21 is connected to the outlet of the liquid helium source 1, and the outlet of the phase separator 21 is connected to the inner cavity of the storage tank 2. The phase separator 21 can use gravity or special internal structures (such as baffles or wire mesh) to reduce the flow rate and change the flow direction of the mixture, so that the denser liquid helium settles to the bottom of the storage tank 2, while the less dense helium gas gathers at the top of the storage tank 2, thus achieving gas-liquid separation.

[0020] In this embodiment, a capillary tube is used to connect the storage tank 2 and the subcooling chamber 3. Due to the "creeping film" effect of superfluid helium—superfluid helium can crawl along a solid surface in an extremely thin film (tens of atoms thick) with no viscous resistance—the slender inner wall of the capillary tube provides a large surface area for this effect. This allows the liquid helium in the storage tank 2 to be slowly but continuously replenished through the capillary tube (especially the superfluid film on the tube wall) when the liquid helium level in the subcooling chamber 3 drops due to evaporation or consumption. This helps maintain the pressure balance within both the subcooling chamber 3 and the storage tank 2.

[0021] The storage tank 2 is also equipped with a first liquid level sensor. During the process of liquid helium being input into the storage tank 2, it will pass through the regulating valve installed on the pipeline. The system can automatically set the valve opening of the regulating valve according to the liquid level in the storage tank 2 as reflected by the first liquid level sensor, so that it can maintain the opening degree for liquid injection when the liquid level is low and stop the injection operation when the liquid level is close to full. Then, it will replenish the liquid in time according to the liquid level change, so as to realize the automatic liquid injection operation.

[0022] The separated liquid helium flows out in two parts. One part flows into the subcooling chamber 3 through the first outlet of the storage tank 2, where the magnet coil 10 is installed and immersed in the liquid environment. The other part flows to the regenerator 4, which is connected to the second outlet of the storage tank 2, and then through the regenerator 4 to the throttling valve 5. Finally, it expands through the throttling valve 5, causing a sudden drop in pressure. According to the Joule-Thomson effect, the temperature of helium will further decrease after throttling below its reversal temperature (about 40K). This process produces saturated superfluid helium in both gas and liquid phases, with the temperature dropping to about 1.8K (corresponding to its saturated vapor pressure).

[0023] Since the outlet of the throttle valve 5 is connected to the inlet of the evaporator 7, the 1.8K saturated superfluid helium flowing out of the throttle valve 5 will flow to the evaporator 7. A storage tank 9 for containing saturated superfluid helium is also installed on the pipe section between the throttle valve 5 and the evaporator 7. This storage tank 9 can act as a melting pool to ensure that enough liquid is evacuated into gas to meet the requirements of uninterrupted system circulation. The saturated superfluid helium in the storage tank 9 continues to flow and flows into the evaporator 7, which is arranged in the subcooling chamber 3. The saturated superfluid helium exchanges heat with the low-temperature liquid helium in the subcooling chamber 3 through the evaporator 7, so that the liquid helium in the subcooling chamber 3 is converted into subcooled superfluid helium with a temperature of about 1.8K. Thus, the 1.8K subcooled superfluid helium can be used to cool and dissipate heat for the magnet coil 10. The evaporator 7 has a finned copper tube structure, which can increase the heat exchange area and improve the heat exchange efficiency. The supercooled superfluid helium prepared by the above methods has advantages such as lower viscosity, high specific heat, and high thermal conductivity, and is widely used in the cooling of high magnetic field strength superconducting magnets and superconducting cavities.

[0024] In this embodiment, by immersing the magnet coil 10 in supercooled superfluid helium, the magnet coil 10 can be cooled and maintained below the superconducting transition temperature (usually 1.8K). When the magnet coil 10 at this temperature is energized, it will enter the superconducting state, thereby being able to carry a very large current without generating resistance loss and generating a strong magnetic field. This allows it to be widely used in application scenarios where the stability and uniformity of the magnetic field in time and space are required.

[0025] The aforementioned saturated superfluid helium will vaporize into low-temperature saturated helium gas after heat exchange in evaporator 7. In order to utilize the cooling capacity of this portion of saturated helium gas, a heat exchange tube 41 is provided in the regenerator 4. The inlet of the heat exchange tube 41 is connected to the second outlet of the storage tank 2. This arrangement allows liquid nitrogen to flow directly into the heat exchange tube 41 of the regenerator 4. The outlet of the heat exchange tube 41 is connected to the inlet of the throttling valve 5, and the inlet of the regenerator 4 is connected to the outlet of the evaporator 7. This arrangement allows the low-temperature saturated helium gas formed during the preparation of supercooled superfluid helium to flow into the inner cavity of the regenerator 4, so that it can exchange heat with the liquid helium in the heat exchange tube 41 to reduce the temperature of the liquid helium and obtain low-temperature liquid helium with a temperature below 4.2K.

[0026] The separated helium gas flows out through the third outlet of storage tank 2, which is connected to airbag 9. This arrangement allows the airbag 9 to collect the helium in the system for reuse, thus helping to achieve zero loss of liquid helium. During the heating process of magnet coil 10, the supercooled helium in supercooled cavity 3 will also be converted into helium gas. To collect this portion of helium gas, the outlet of supercooled cavity 3 is also connected to the inlet of airbag 9.

[0027] Because the helium gas formed by vaporization is at a low temperature, to prevent the pipeline from freezing and frosting due to the direct discharge of this part of the helium gas, the storage tank 2 and the gas bag 9 are connected by a first pipe 11, and the subcooling chamber 3 and the gas bag 9 are connected by a second pipe 12. A first heater, a second temperature sensor and a one-way valve are installed on the first pipe 11 in the direction of airflow, and a second heater, another second temperature sensor and a one-way valve are installed on the second pipe 12 in the direction of airflow. By heating the low-temperature helium gas to room temperature helium gas, the pipeline freezing phenomenon can be effectively avoided, and the one-way valve can also prevent blockage caused by gas backflow.

[0028] For system safety considerations, a pressure sensor is also installed on the second pipe 12. The second pipe 12 has a main pipe section and a first branch and a second branch formed by branching. A safety valve 121 is adapted to be installed on the first branch. The safety valve 121 is mainly used for the discharge of helium gas that has been naturally vaporized for a long time with low heat under non-quench conditions. A large-diameter valve 122 is adapted to be installed on the second branch. The large-diameter valve 122 is an electric valve. When a large amount of vaporized helium gas is rapidly generated due to a large amount of heat generated by the magnet coil 10 in a short time, the pressure sensor on the main pipe section detects the ultra-high pressure. After the helium gas pressure reaches the set value, the large-diameter valve 122 opens to quickly release a large amount of high-pressure helium gas into the gasbag 9 to ensure system safety.

[0029] Furthermore, a third temperature sensor is installed on the magnet coil 10 to monitor the surface temperature of the magnet coil 10 in real time. The system can also determine whether an overrun has occurred or is about to occur based on the monitored temperature value. This temperature signal is also linked to the pressure sensor signal on the second pipe 12, triggering the highest level of safety response. For example, the large-diameter valve 122 is immediately fully opened to release high-pressure helium gas as quickly as possible, protecting the magnet and piping system. This is the final active line of defense in the system's safety design.

[0030] The supercooled superfluid helium prepared above has a low temperature. To avoid radiative heat leakage, a first cylinder 16 and a second cylinder 17 are connected inside the tank 15. The first chamber is specifically the part of the inner cavity of the tank 15 outside the supercooled chamber 3, and the second chamber is specifically the inner cavity of the supercooled chamber 3. The supercooled chamber 3 is adapted to be installed inside the second cylinder 17, and part of the supercooled chamber 3 extends through the second cylinder 17 into the first cylinder 16. The regenerator 4 and the throttling valve 5 are both located in the inner cavity of the first cylinder 16 outside the first cylinder 44. Both the first cylinder 16 and the second cylinder 17 are made of thermally conductive materials (such as oxygen-free copper). The first cylinder 16 has an inner cylinder 161 and an outer cylinder 162, which are connected by an annular flange. The annular flange at the connection is also made of oxygen-free copper. The inner cylinder 161, the outer cylinder 162, and the connecting annular flange are connected by silver brazing, forming a jacketed area filled with liquid nitrogen. The inlet of this jacketed area is connected to the outlet of the liquid nitrogen Dewar 14, which stores liquid nitrogen. Compared with the coil structure, this significantly reduces the temperature of the first cylinder 16, improves the temperature uniformity of the first cylinder 16, and reduces the radiative heat leakage of the system. This is because, compared to the radiative heat input of the tank 15 to the internal 4.2K liquid helium, the jacketed area filled with liquid nitrogen can change the radiative heat to the radiative heat of 77K liquid nitrogen to 4.2K liquid helium, thereby greatly reducing the radiative heat leakage inside the tank 15.

[0031] In addition, the interlayer region of the first cylinder 16 is also connected to an exhaust pipe 15, through which the vaporized nitrogen in the interlayer region can be discharged.

[0032] To achieve zero loss of liquid helium, a liquefier 8 is installed outside the tank 15. The outlet of the regenerator 4 is connected to the inlet of the liquefier 8. By connecting the regenerator 4 and the liquefier 8, the low-temperature saturated helium formed after heat exchange with the saturated superfluid helium can flow to the liquefier 8. However, since the temperature of the saturated helium is low, in order to avoid pipe freezing, a third heater and a second temperature sensor are installed sequentially in the direction of airflow on the third pipe 13 connecting the regenerator 4 and the liquefier 8. By activating the third heater, the low-temperature saturated helium flowing into the third pipe 13 can be heated to room temperature helium. The first, second, and third heaters and the second temperature sensor are all arranged inside the tank 15. The temperature sensor on this pipe section monitors the low-temperature gas in the pipeline in real time and sends it as an input signal to the heater. The heater matches the heating power according to the temperature, so that the outlet temperature is room temperature, ensuring that the helium discharged from the tank 15 is room temperature helium. A circulation pump is also installed on the third pipe 13. The circulation pump is arranged between the liquefier 8 and the second temperature sensor on the pipe. It can continuously draw room temperature helium into the liquefier 8, and then use the liquefier 8 to liquefy the gaseous helium back into liquid helium. The outlet of the liquefier 8 is connected to the inlet of the liquid helium source 1. The liquefied liquid helium can be directly returned to the liquid helium source 1 (the liquid helium source 1 is a Dewar containing liquid helium), realizing the recycling of liquid helium, eliminating the loss of liquid helium, and greatly improving economic efficiency.

[0033] The automated control process of the above-mentioned device, such as Figure 1 As shown, it includes the following steps: S1. Liquid helium from liquid helium source 1 is injected into storage tank 2, and the liquid helium is split into a first portion and a second portion in storage tank 2. This process specifically includes the following sub-processes: (1) Liquid helium injection and automatic flow rate regulation process Liquid helium from liquid helium source 1 is injected into storage tank 2, which is in a vacuum environment, through a liquid helium injection pipe. During the injection process, a first liquid level sensor installed in storage tank 2 monitors the liquid level in real time and generates a first liquid level signal. The first liquid level signal is fed back to the control system and compared with a preset liquid level range, thereby driving the regulating valve to automatically adjust its opening to control the liquid helium flow rate injected into storage tank 2, realizing closed-loop control of liquid helium injection and ensuring that the liquid level in storage tank 2 remains stable within the set range.

[0034] (2) Gas-liquid separation process in storage tank 2 Liquid helium injected into storage tank 2 via the liquid helium injection pipe flows into a phase separator located within storage tank 2. In the phase separator, the liquid helium, due to its higher density, sinks downwards, while the gaseous helium rises and collects in the upper space of storage tank 2. This design prevents air bubbles from entering downstream pipelines with the liquid helium, avoiding interference from the two-phase flow on the throttling and heat exchange processes, and improving the system's operational stability.

[0035] (3) Liquid helium splitting process A portion of the separated liquid helium enters the capillary tube at the bottom of the storage tank 2 as the first part of liquid nitrogen. The capillary tube is connected to the subcooling chamber 3. This portion of liquid helium is mainly used as a cooling medium to cool the magnet coil 10 installed in the subcooling chamber 3. The other portion flows to the pipeline connected to the tube side of the regenerator 4 as the second part of liquid helium.

[0036] (4) Helium recovery process The separated helium is cryogenic helium with a temperature of around 4.2K. If this cryogenic helium is directly discharged through the first pipe 11, the pipe is prone to freezing or frosting. Therefore, before being discharged to room temperature, it needs to be heated to room temperature by the first heater on the first pipe 11 before it can be discharged into the gasbag 9 for collection.

[0037] A second temperature sensor is installed at the outlet of the first heater to monitor the exhaust temperature of the first tube 11 in real time. By comparing the exhaust temperature with the room temperature at that time, the heating power of the first heater is adjusted according to the comparison result to ensure that the exhaust temperature of the first tube 11 is at room temperature.

[0038] For adjusting the heating power of the first heater, an industrial-grade analog temperature controller (such as a temperature controller with PID function) can be used as the driver for the first heater. The signal from the second temperature sensor is connected to the measurement input terminal of the controller; on the controller panel, the target temperature value (e.g., 293K) is directly set via knobs or buttons; the controller internally uses analog circuitry (such as a PID circuit composed of operational amplifiers) to automatically calculate the deviation and output a continuous current or voltage signal (e.g., 4-20mA) to control the heater power. It is worth noting that this is only one method of adjusting the heater power; other methods for adjusting the heating power of the first heater can also be applied to this invention, and no further limitations are imposed here.

[0039] S2. The first portion of liquid helium that is diverted is injected into the supercooled cavity 3 through the capillary connecting tube between the storage tank 2 and the supercooled cavity 3. A second liquid level sensor is installed in the supercooled cavity 3. The liquid level height in the supercooled cavity 3 can be monitored in real time through the second liquid level sensor to ensure that the magnet coil 10 can be submerged below the liquid surface.

[0040] It is worth emphasizing that the flow rate of the first portion of liquid helium in step S1 above is also affected by the change in the liquid level in the supercooled cavity 3, as follows: Step 1): The second liquid level sensor in the subcooling chamber 3 collects the second liquid level signal that reflects the liquid level height in the subcooling chamber 3 in real time. The system compares the second liquid level signal with the preset minimum safe liquid level and target liquid level: if the second liquid level signal is ≥ the target liquid level, it means that the liquid level is sufficient and the current flow rate is maintained; if the second liquid level signal is < the target liquid level, a "liquid demand signal" is generated and the process proceeds to Step 2).

[0041] Step 2): By adjusting the system back pressure or the exhaust valve of the subcooled chamber 3, more liquid helium is allowed to flow naturally into the subcooled chamber 3 through the capillary tube under the action of pressure difference.

[0042] Step 3): While increasing the first portion of liquid helium flow rate, the system continuously monitors the first liquid level signal from the first liquid level sensor in storage tank 2. Due to the increase in the first portion of liquid helium flow rate, the amount of liquid helium extracted from storage tank 2 increases, which usually leads to a decrease in the liquid level in storage tank 2. At this time, it is necessary to compare the first liquid level signal with the preset minimum safe liquid level of storage tank 2: If the first liquid level signal is greater than the minimum safe liquid level of storage tank 2 and is within the normal range, it indicates that storage tank 2 has sufficient inventory, and the system only records the change, and the total liquid helium injection volume can be temporarily not adjusted; If the first liquid level signal is close to or lower than the minimum safe liquid level of storage tank 2, the controller sends a command to the regulating valve on the liquid helium injection pipe to increase its opening, thereby increasing the liquid helium flow rate injected from the liquid helium source into storage tank 2, so as to increase the total liquid helium injection volume, until the second liquid level signal is stabilized back within the set range.

[0043] This setup ensures that the magnet coil 10 remains continuously immersed in liquid helium, maintaining its stable temperature. It also automatically coordinates the demand of the subcooling chamber 3 with the total system supply, maintaining a global balance of the working fluid. This reduces manual intervention and prevents cooling failure or idling of the storage tank 2 due to liquid level imbalance. Furthermore, it avoids ineffective liquid helium overflow or excessive injection, achieving economical operation.

[0044] S3. The second portion of liquid helium is throttled and cooled after flowing through the negative pressure regenerator 4 pipe to obtain saturated superfluid helium; the specific process is as follows: Step 1: The second portion of liquid helium is drawn from storage tank 2 through pipelines and enters the tube side (i.e., internal pipelines) of regenerator 4. Regenerator 4 is a shell-and-tube heat exchanger. Its shell side carries low-temperature saturated helium gas (approximately 1.8K) from the outlet of evaporator 7, while its tube side carries the second portion of liquid helium to be cooled (approximately 4.2K). The two undergo counter-current heat exchange within regenerator 4: the higher-temperature liquid helium transfers its cooling energy to the lower-temperature return gas, pre-cooling itself to near the saturated superfluid helium temperature (e.g., 2.0-2.2K), while the return gas is slightly heated. This process recovers and utilizes the system's cooling energy, improving energy efficiency.

[0045] Step 2: After precooling, the second portion of liquid helium flows out of the fourth tube of the regenerator and enters the JT throttling valve 5. By adjusting the opening of the JT throttling valve 5, the high-pressure liquid helium undergoes adiabatic throttling expansion (Joule-Thomson effect) as it passes through the narrow flow channel. The enthalpy remains unchanged, but the temperature drops significantly. The throttled liquid helium becomes a gas-liquid two-phase mixture, in which the liquid portion is the desired low-temperature saturated superfluid helium (HeIIs), and the temperature can be reduced to approximately 1.8 K.

[0046] In the above process, a first temperature sensor is installed on the pipeline downstream of the JT throttle valve 5 to monitor the generated saturated superfluid helium temperature in real time. The first temperature sensor transmits the monitored saturated superfluid helium temperature signal to the control system. The system compares the saturated superfluid helium temperature with the set target temperature (e.g., 1.8K). Based on the magnitude of the deviation between the two, the system automatically adjusts the opening of the throttle valve 5: if the saturated superfluid helium temperature is higher than the set target temperature, the opening of the throttle valve 5 is reduced to enhance the throttling effect and further reduce the temperature; if the saturated superfluid helium temperature is lower than the set target temperature, the opening of the throttle valve 5 is increased to weaken the throttling effect and cause the temperature to rise slightly.

[0047] Through the closed-loop feedback described above, the saturated superfluid helium temperature can be stably maintained within the set range (e.g., 1.8K ± 0.1K).

[0048] Step 3: The throttled gas-liquid mixture enters storage tank 6. Storage tank 6 serves as a buffer and gas-liquid separation container: the liquid (HeIIs) accumulates at the bottom of storage tank 6, forming a stable liquid pool; the gas portion is located at the top of storage tank 6 and can be pumped away through connecting pipelines. The storage tank 6 ensures a constant supply of liquid working fluid to the downstream evaporator 7, preventing heat exchange interruptions due to flow fluctuations.

[0049] Step 4: Saturated superfluid helium flows out from the bottom of storage tank 6 and enters the pipeline of evaporator 7, ready to perform the heat exchange task of step S4.

[0050] S4. Saturated superfluid helium flowing from storage tank 6 enters the piping of evaporator 7 located in subcooling chamber 3. The saturated superfluid helium and the first portion of liquid helium in subcooling chamber 3 undergo indirect heat exchange at evaporator 7, which is typically a copper tube with fins or enhanced heat exchange surfaces, immersed in the liquid helium within the subcooled superfluid helium chamber. The temperature of the saturated superfluid helium flowing within evaporator 7 (approximately 1.8 K) is lower than the temperature of the first portion of liquid helium within the chamber (approximately 4.2 K). Driven by the temperature difference, heat is transferred from the liquid helium within the chamber to the saturated superfluid helium through the wall of evaporator 7. After absorbing heat, part of the saturated superfluid helium within evaporator 7 evaporates, becoming low-temperature saturated helium gas; simultaneously, the first portion of liquid helium within subcooling chamber 3 is cooled, transforming into subcooled superfluid helium when its temperature drops below the saturation temperature corresponding to the current pressure.

[0051] Ultimately, stable supercooled helium is obtained in the supercooled cavity 3, with a temperature as low as below 1.8K, thereby achieving efficient and highly stable cooling of the magnet coil 10.

[0052] During operation, the supercooled overfluid helium in the supercooled cavity 3 may generate cryogenic helium due to thermal load. The release of this cryogenic helium requires safe handling, as follows: The generated cryogenic helium gas is led out through a second pipe 12, which has a larger diameter (e.g., an inner diameter of 89 mm) to meet the requirements of instantaneous high-flow-rate discharge. A second heater on the second pipe 12 heats this portion of cryogenic helium gas to room temperature before discharging it into the gas bag 9, preventing the direct discharge of cryogenic gas from causing icing of the pipeline or cold damage to the equipment. A second temperature sensor is installed at the outlet of the second heater to monitor the outlet temperature of the second pipe 12. The heating power of the second heater can be adjusted based on the monitoring results of the second temperature sensor (the adjustment method for the heating power of the second heater is the same as that for the first heater in step S1, and will not be elaborated further here), ensuring that the outlet gas is at room temperature.

[0053] Synchronously, the pressure sensor on the second tube 12 monitors the gas pressure in real time. When the gas pressure exceeds the first threshold (e.g., slightly higher than the system operating pressure, such as 1.2 bar), it indicates gas accumulation due to continuous small heat load (such as conventional heat leakage). At this time, the system automatically opens the safety valve for slow and controllable venting, discharging the gas into the helium recovery bladder 9. When the gas pressure rises sharply and exceeds the second threshold (significantly higher than the first threshold, such as 2.5 bar, usually corresponding to sudden high-temperature events such as the "quenching" of the magnet coil 10), it indicates that a large amount of gas is instantaneously generated. The system immediately fully opens the large-diameter valve (e.g., DN150) to achieve rapid pressure relief and protect system safety. The released gas also enters the recovery bladder 9.

[0054] The above settings can automatically distinguish between normal heat loads and emergency quench events based on gas pressure, and take corresponding venting strategies, ensuring both the smoothness of daily system operation and safety under extreme conditions. This process, through feedback from pressure and temperature sensors, achieves fully automated control from heat exchange and gas treatment to safe venting, ensuring reliable system operation and minimizing manual intervention.

[0055] In addition, a third temperature sensor is installed on the surface of the magnet coil 10 to monitor the temperature of the magnet coil 10 and obtain a monitored temperature. The system usually presets a temperature safety threshold, which is usually set slightly higher than the stable operating temperature of supercooled superfluid helium, but much lower than the dangerous temperature that may cause superconducting quenching and lead to catastrophic heating (for example, set at 2.5K-3.0K, with the specific value determined according to the magnet characteristics).

[0056] The system compares the monitored temperature measured by the third temperature sensor with the temperature safety threshold in real time. When the monitored temperature is less than the temperature safety threshold, the magnet coil 10 is considered to be operating normally, and the large-diameter valve remains closed. When the monitored temperature is greater than or equal to the temperature safety threshold, the system determines that the magnet coil 10 is starting to quench or is about to quench, that is, the coil is partially or entirely transitioning from a superconducting state to a normally conducting state, accompanied by intense heating. At this time, the signal from the third temperature sensor is transmitted to the control system in real time, and the system identifies this signal as the highest priority "emergency event". The control system immediately (the response time is usually in the millisecond range) outputs a fully open (100% opening) control signal to the drive mechanism of the large-diameter valve (such as an electric actuator or a solenoid valve). After receiving the signal, the large-diameter valve switches from the normally closed state to the fully open state as quickly as possible (such as within 1-2 seconds). After the valve is fully opened, the large amount of high-pressure helium gas generated in the subcooling chamber 3 due to quench can be released quickly to the gasbag 9 with almost no resistance through the second pipe 12 and the fully opened large-diameter valve, thereby avoiding structural damage caused by a sudden increase in pressure inside the chamber.

[0057] This temperature-triggered mechanism coexists with the aforementioned pressure-triggered mechanism (gas pressure ≥ second threshold), and has a higher or equal priority. This is because, in some implementations, the temperature criterion can be set to be more sensitive. Even if the pipeline pressure has not yet risen to the second threshold due to response delay, the large-diameter valve can be preemptively triggered as long as the temperature of the magnet coil 10 exceeds the temperature safety threshold. This achieves predictive venting based on the heat source itself, which is more proactive and direct than waiting for the pressure to rise. In terms of control logic, it can be set so that either "temperature over-limit" or "pressure over-limit" condition is met, triggering the large-diameter valve to fully open. This constitutes a double safety measure, greatly improving the reliability of the safety response.

[0058] S5. The low-temperature saturated helium gas formed by the evaporation of the first portion of liquid helium after heat exchange is sent into the shell side of the regenerator 4. This gas absorbs heat in the evaporator 7 and undergoes a phase change of saturated superfluid helium (HeIIs), resulting in an extremely low temperature (approximately 1.8K) and carrying a large amount of "cold energy". The low-temperature saturated helium gas flowing into the shell side of the regenerator 4 undergoes countercurrent heat exchange with the second portion of liquid helium (approximately 4.2K) flowing through the tube side from the storage tank 2. The low-temperature saturated helium gas transfers its "cold energy" to the second portion of liquid helium in the tube side, pre-cooling it (corresponding to step S3), while the temperature of the low-temperature saturated helium gas itself is increased (e.g., to the range of 4K-10K). This process efficiently recovers the cold energy of the low-temperature saturated helium gas, significantly reducing the energy consumption of subsequent liquefaction.

[0059] After heat exchange, the low-temperature saturated helium gas flows out from the third tube 13, which is connected to the shell side of the regenerator 4. The temperature of this gas is still far below room temperature. If it directly enters the subsequent pipelines, it may cause low-temperature damage to the equipment, icing of the pipelines, or solidification of the lubricating oil. Therefore, before being discharged, this gas needs to be heated to room temperature by the third heater on the third tube 13. A second temperature sensor is installed at the outlet of the third heater to monitor the exhaust temperature of the third tube 13 in real time and compare it with the room temperature. Based on the comparison result, the heating power of the third heater is adjusted (this adjustment method is the same as the heating power adjustment method of the first and second heaters mentioned above, and will not be described further here), thereby ensuring that the output helium gas meets the requirements of the inlet of the subsequent equipment.

[0060] The third pipe 13 is equipped with a circulation pump and a liquefaction unit 8. The ambient temperature helium discharged from the third pipe 13, as well as the helium recovered from the gasbag 9, are both fed into the liquefaction unit 8. The liquefaction unit 8 typically uses a small refrigeration unit (such as a GM refrigeration unit) for pre-cooling combined with the JT throttling principle to re-condense the helium into liquid helium. This process consumes electrical energy, but it is extremely economical compared to directly discharging and purchasing new liquid helium. The liquid helium produced by the liquefaction unit 8 is transported back to the liquid helium source 1 (i.e., the liquid helium Dewar) for storage. Thus, the liquid helium Dewar becomes the "source" and "destination" of liquid helium within the system, completing a full closed-loop cycle of "liquid helium → cooling / heat exchange → gaseous helium → recovery / heating → liquefaction → liquid helium." This allows for nearly 100% recovery and conversion of used helium into reusable liquid helium, essentially achieving zero liquid helium loss and solving the core pain points of high cost and significant liquid helium loss in open systems.

[0061] In addition, the monitored temperature obtained by the third temperature sensor can also be used to adjust the temperature of the magnet coil 10, as follows: First, the system calculates the deviation between the monitored temperature and the target temperature of the magnet coil 10 set by the system in real time. Based on the magnitude and sign of the deviation, the system status is determined: when the deviation is greater than 0, it indicates that the temperature of the magnet coil 10 is too high and cooling needs to be enhanced; when the deviation is less than 0, it indicates that the temperature of the magnet coil 10 is too low and cooling needs to be reduced or overcooling needs to be prevented; when the absolute value of the deviation is very small, it indicates that the magnet coil is in a steady state and can be finely adjusted to maintain it.

[0062] Secondly, based on the deviation value, the control system generates adjustment commands for one or more of the aforementioned actuators according to a preset multivariable collaborative control strategy. These adjustment commands can assign different adjustment weights and timing sequences to each actuator for different deviation value ranges, as detailed below: The first method: When the absolute value of the deviation is in the range of large deviation values ​​(for example, the absolute value of the deviation is > 0.5K), the throttle valve 5 is adjusted first, and the circulation pump is adjusted simultaneously.

[0063] When adjusting throttle valve 5: if the deviation value > 0, significantly reduce the opening to produce cooler saturated superfluid helium; if the deviation value < 0, increase the opening to raise the saturated superfluid helium temperature. This is the most direct method of temperature regulation.

[0064] When adjusting the circulating pump, if the deviation value is >0, increase the speed to accelerate evaporation and heat exchange circulation; if the deviation value is <0, decrease the speed to slow down the circulation.

[0065] The second approach: When the absolute value of the deviation is within a small deviation range (e.g., 0.1K < absolute value of deviation ≤ 0.5K), the throttle valve 5 and the circulating pump are adjusted in tandem. The controller calculates the adjustment amount for both, achieving a new balance between cooling intensity and flow rate. For example, to reduce the deviation by 0.2K, the opening of the throttle valve 5 may be slightly reduced and the pump speed slightly increased simultaneously.

[0066] The third method: When the absolute value of the deviation is within the steady-state micro-disturbance range (e.g., absolute value ≤ 0.1K), compensation is mainly achieved through small fluctuations in the rotational speed of the circulating pump. Because adjusting the pump speed affects the "flow rate," the response is relatively mild, suitable for offsetting high-frequency small disturbances. Throttling valve 5 remains essentially stationary to avoid frequent operation affecting its lifespan and system pressure stability. The regulating valve can be adjusted according to the long-term, slow changes in the liquid level of storage tank 2 to maintain the total balance of the working fluid in the system, providing a stable basis for temperature control.

[0067] Finally, each actuator receives the instruction and takes action. The system continuously monitors the changes in the monitored temperature, recalculates the deviation value, and enters the next control cycle, forming a closed-loop feedback.

[0068] During the above adjustment process, when the overrun protection is triggered (monitored temperature ≥ temperature safety threshold), the temperature control loop is immediately overrun, the system prioritizes safety relief, and temperature control is suspended. When the liquid level is too low, the opening adjustment of the regulating valve will prioritize liquid level safety, and its command may temporarily conflict with the command issued by the temperature control loop. In this case, liquid level safety takes priority.

[0069] Based on the above design, the present invention achieves high-precision temperature control and rapid dynamic response, which can stabilize the temperature of the magnet coil 10 within the target value ±0.05K or even narrower range; in the face of changes in thermal load, the system can quickly restore temperature balance through the linkage of multiple actuators, thereby improving the automation level of the system.

[0070] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An automated method for preparing supercooled superfluid helium, characterized in that, include: S1. Liquid helium from the liquid helium source is injected into the storage tank, and the liquid helium is split into a first part of liquid helium and a second part of liquid helium through the storage tank; S2. Inject the first portion of liquid helium into the supercooled cavity to cool the magnet coil inside; S3. Throttling and cooling the second part of liquid helium after it flows through the negative pressure regenerator pipeline to obtain saturated superfluid helium; S4. Control the saturated superfluid helium to exchange heat with the first part of liquid helium in the evaporator so that the subcooled superfluid helium is obtained in the subcooled cavity. S5. The low-temperature saturated helium gas formed by the heat exchange and evaporation of saturated superfluid helium is sent to the regenerator to recover the cold energy, and then sent to the liquefaction unit to be liquefied again into liquid nitrogen. The liquid nitrogen is then returned to the liquid helium source.

2. The automated preparation method of supercooled superfluid helium according to claim 1, characterized in that, S1 specifically involves: monitoring the liquid level of the liquid helium storage tank in real time using a first liquid level sensor installed in the tank; automatically adjusting the opening of a regulating valve installed on the liquid helium injection pipeline based on the first liquid level signal fed back by the first liquid level sensor to control the flow rate of the liquid helium injected into the storage tank; causing the injected liquid helium to flow through a phase separator installed in the storage tank for gas-liquid separation; splitting the separated liquid helium into a first portion of liquid nitrogen and a second portion of liquid nitrogen; and heating the separated cryogenic helium gas to room temperature via a first heater on a first tube before releasing it into a gasbag for collection.

3. The automated preparation method of supercooled superfluid helium according to claim 2, characterized in that, The S4 further includes: heating the low-temperature helium gas formed by evaporation in the supercooled cavity to room temperature via a second heater on the second tube and then discharging it into the airbag; a safety valve and a large-diameter valve are connected in parallel on the second tube; monitoring the gas pressure in the tube in real time via a pressure sensor on the second tube; opening the safety valve to discharge the helium gas generated by natural heat accumulation when the gas pressure exceeds a first threshold; opening the large-diameter valve to quickly release the high-pressure helium gas when the gas pressure exceeds a second threshold higher than the first threshold; passing the room-temperature helium gas recovered in the airbag into a liquefier to reliquefy it into liquid helium; and returning the liquid nitrogen to the liquid helium source.

4. The automated preparation method of supercooled superfluid helium according to claim 2, characterized in that, The first part of the liquid helium diversion process is as follows: the liquid level is monitored in real time by a second liquid level sensor installed in the supercooled cavity; When the second liquid level signal fed back by the second liquid level sensor is lower than the set value, the flow rate of the first part of liquid helium flowing into the subcooling chamber is increased; the first liquid level signal of the liquid level height in the reaction tank is acquired simultaneously. When the first liquid level signal is lower than the set range due to the increase in the flow rate of the first part of liquid helium, the opening of the regulating valve is increased to increase the liquid helium injection volume.

5. The automated preparation method of supercooled superfluid helium according to claim 3, characterized in that, S3 specifically involves: allowing the second portion of liquid helium to flow through the tube side of the regenerator and exchange heat with the low-temperature saturated helium flowing through the shell side of the regenerator to pre-cool the second portion of liquid helium; delivering the pre-cooled second portion of liquid helium to a throttle valve; and adjusting the opening of the throttle valve to cause the flowing liquid helium to produce a throttling expansion effect to obtain low-temperature saturated superfluid helium.

6. The automated preparation method of supercooled superfluid helium according to claim 5, characterized in that, The adjustment of the throttle valve opening is specifically achieved by: real-time monitoring of the temperature of the cryogenic saturated superfluid helium obtained by a first temperature sensor installed after the throttle valve, generating a temperature signal; and automatically adjusting the opening of the throttle valve according to the temperature signal fed back by the first temperature sensor so that the temperature of the cryogenic saturated superfluid helium is maintained within a set range.

7. The automated preparation method of supercooled superfluid helium according to claim 5, characterized in that, Specifically, S5 involves sending the low-temperature saturated helium gas, formed by the evaporation of the first portion of liquid helium after heat exchange, into the shell side of the regenerator. The low-temperature saturated helium gas is then output through the third tube connected to the shell side of the regenerator. The low-temperature saturated helium gas is heated to room temperature helium gas by the third heater on the third tube. The room temperature helium gas is then sent to the liquefier to be reliquefied into liquid helium by the circulation pump on the third tube. Finally, the liquid helium gas is transported to the liquid helium source.

8. The automated preparation method of supercooled superfluid helium according to claim 7, characterized in that, The control process of the first heater, the second heater, and the third heater is as follows: the exhaust temperature in the first tube, the second tube, and the third tube is monitored in real time by the second temperature sensor at the outlet of the first heater / second heater / third heater, the exhaust temperature is compared with the room temperature, and the heating power of the first heater / second heater / third heater is adjusted according to the comparison result until the exhaust temperature of the first tube / second tube / third tube is room temperature.

9. The automated preparation method of supercooled superfluid helium according to claim 7, characterized in that, The control steps of the large-diameter valve further include: acquiring the monitoring temperature of the third temperature sensor installed on the magnet coil; when the monitoring temperature exceeds the safety threshold, it is determined to be a failure event, and a control signal is immediately output to fully open the large-diameter valve installed on the second pipe for emergency pressure relief.

10. The automated preparation method of supercooled superfluid helium according to claim 9, characterized in that, The monitored temperature obtained by the third temperature sensor can also be used to adjust the temperature of the magnet coil. Specifically, the monitored temperature is compared with the target temperature, and an adjustment signal is generated based on the comparison result. The adjustment signal is used to adjust at least one of the throttle valve opening, the circulating pump speed, and / or the regulating valve opening, so that the temperature of the magnet coil approaches the target temperature.

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