Supercooled superfluid helium preparation device with zero liquid helium loss

Abstract

The invention discloses a supercooled superfluid helium preparation device with zero liquid helium loss, which comprises a first Dewar, a first tank body, a second tank body, a throttle valve, a heat exchanger and a liquefier, the first tank body is provided with a first chamber and a second chamber which are vacuum and separated, and an outlet of the first Dewar is communicated with the second tank body to input liquid helium into the second tank body; the liquid helium is discharged through the second tank body and then shunted to the second cavity and the throttle valve, the throttle valve is arranged in the first cavity to throttle the liquid helium flowing through the inside of the throttle valve into saturated superfluid helium, and an inlet of the heat exchanger is communicated with an outlet of the throttle valve to enable the liquid helium in the second cavity to exchange heat with the saturated superfluid helium flowing into the heat exchanger to form supercooled superfluid helium. The heat regenerator, the throttling valve and the heat exchanger are integrated in the first cavity of the first tank body, continuous and stable preparation from 4.2 K conventional liquid helium to 1.8 K supercooled superfluid helium is achieved, the preparation method is simple, the initial investment cost is low, zero loss of liquid helium is achieved, and the problem of liquid helium consumption cost in the traditional superfluid helium preparation process is solved.

Description

Technical Field

[0001] This invention relates to the field of supercooled superfluid helium preparation technology, and in particular to a supercooled superfluid helium preparation apparatus with zero liquid helium loss. Background Technology

[0002] Compared to conventional liquid helium (HeI), superfluid helium (HeII) has advantages such as lower viscosity, higher specific heat, and higher thermal conductivity, and is widely used in cooling high-field-strength superconducting magnets and superconducting cavities. Typically, superconducting magnets operate at 4.2 K; if the operating temperature is lowered to 1.8 K, the magnetic field strength will increase by 20% to 30%. Supercooled superfluid helium refrigeration technology has been successfully applied to large-scale superconducting magnet devices and engineering projects abroad. The critical heat flux density of supercooled superfluid helium (HeIIp) is approximately twice that of saturated superfluid helium (HeIIs) and 20 times that of conventional liquid helium (HeI). Besides enhancing magnetic field strength, it also significantly improves the stability of the magnet. Using HeIIp to cool high-field magnets and superconducting cavities is of great significance.

[0003] Currently, saturated superfluid helium (HeIIs) is commonly obtained in China using negative pressure evacuation. Methods for obtaining supercooled superfluid helium (HeIIp) are still immature. In open-loop systems, a large amount of helium is directly released into the atmosphere during the preparation of saturated superfluid helium, resulting in significant waste of liquid helium and poor economic efficiency. Furthermore, traditional open-loop systems can only prepare saturated superfluid helium, while the testing and operation of modern high-performance superconducting magnets and superconducting cavities often require the superior performance of supercooled superfluid helium. Therefore, superfluid helium prepared by traditional open-loop systems is insufficient to meet the needs of superconducting testing. Although the forced-flow supercooling method can be used to prepare supercooled superfluid helium, this method is only suitable for large-scale equipment (such as large particle accelerators), has high technical complexity, and requires substantial initial investment. Summary of the Invention

[0004] To address the technical problems existing in the background art, the present invention proposes a supercooled superfluid helium preparation device with zero liquid helium loss.

[0005] This invention proposes a zero-liquid-helium-loss subcooled superfluid helium preparation apparatus, comprising a first Dewar, a first tank, a second tank, a throttling valve, a heat exchanger, and a liquefier. The first tank has a vacuum-sealed, isolated first chamber and a second chamber. The second tank is located within the first chamber. The outlet of the first Dewar is connected to the second tank to input liquid helium into the second tank. After being discharged from the second tank, the liquid helium is diverted to the second chamber and the throttling valve. The throttling valve is arranged within the first chamber to throttle the liquid helium flowing through it into saturated superfluid helium. The inlet of the heat exchanger is connected to the outlet of the throttling valve, allowing the liquid helium in the second chamber to exchange heat with the saturated superfluid helium flowing into the heat exchanger to form subcooled superfluid helium. The outlet of the heat exchanger is connected to the inlet of the liquefier, allowing the low-temperature saturated helium formed after heat exchange with the saturated superfluid helium to flow towards the liquefier. The outlet of the liquefier is connected to the inlet of the first Dewar, allowing the liquefied liquid helium to return to the first Dewar.

[0006] Preferably, the first tank body has a first cylinder that divides its internal cavity into a first chamber and a second chamber, and a second cylinder and a third cylinder that are connected to each other. The first chamber is specifically the part of the first tank body cavity outside the first cylinder, and the second chamber is specifically the cavity inside the first cylinder. The second cylinder and the third cylinder are both made of thermally conductive material. The second cylinder has an inner cylinder and an outer cylinder, and a sandwich area is formed between the inner cylinder and the outer cylinder. The first cylinder is adapted to be installed inside the third cylinder, and part of the first cylinder extends through the third cylinder into the second cylinder. The throttling valve is located in the cavity inside the second cylinder outside the first cylinder. The heat exchanger is arranged inside the first cylinder, and the inlet of the first cylinder is connected to the first outlet of the second tank body.

[0007] Preferably, it also includes a load, which is arranged inside the first cylinder and immersed in supercooled superfluid helium inside the first cylinder.

[0008] Preferably, it also includes a regenerator arranged in the first chamber, the regenerator having heat exchange tubes, the inlet of the heat exchange tubes being connected to the second outlet of the second tank to allow liquid helium to flow in, the outlet of the heat exchange tubes being connected to the inlet of the throttle valve, and the inlet of the regenerator being connected to the outlet of the heat exchange tubes to allow the low-temperature saturated helium gas formed after heat exchange to flow into the regenerator and exchange heat with the liquid helium in the heat exchange tubes to reduce the temperature of the liquid helium and obtain low-temperature liquid helium below 4.2K.

[0009] Preferably, the outlet of the regenerator is connected to the inlet of the liquefier, and the outlet of the regenerator and the inlet of the liquefier are connected by a first pipe. A first heater and a first temperature sensor are installed on the first pipe in sequence according to the airflow direction. By activating the first heater, the low-temperature saturated helium flowing into the first pipe is heated to room temperature helium. A circulation pump is also installed on the first pipe. The circulation pump is arranged between the liquefier and the first temperature sensor to draw room temperature helium into the liquefier.

[0010] Preferably, a phase separator is installed inside the second tank, with the inlet of the phase separator connected to the outlet of the first Dewar and the outlet of the phase separator connected to the inner cavity of the second tank.

[0011] Preferably, it also includes an airbag, and the second tank also has a third outlet. The third outlet of the second tank is connected to the airbag inlet so that the helium separated by the phase separator flows into the airbag. The outlet of the first cylinder is connected to the airbag inlet so that the helium in the first cylinder flows into the airbag. The second tank and the airbag are connected by a second pipe, and the first cylinder and the airbag are connected by a third pipe. A second heater, a second temperature sensor and a one-way valve are installed on the second pipe and the third pipe in sequence according to the airflow direction to heat the low-temperature helium into room temperature helium.

[0012] Preferably, a pressure sensor is also installed on the third pipe. The third pipe has a main pipe section and a first branch and a second branch formed by branching. A safety valve is adapted to be installed on the first branch and an electric valve is adapted to be installed on the second branch. The electric valve opens when the pressure sensor detects that the air pressure value in the main pipe section is greater than the set value.

[0013] Preferably, it also includes a second Dewar, the outlet of which is connected to the inlet of the interlayer region to introduce liquid nitrogen into the interlayer region, and the outlet of the second Dewar is connected to a fourth pipe, which extends from the first tank body and connects to the outside.

[0014] Preferably, the first heater, the first temperature sensor, the second heater, and the second temperature sensor are all arranged inside the first tank.

[0015] This invention integrates a regenerator, a throttling valve, and a heat exchanger into a vacuum chamber within the first tank. By employing throttling cooling, the temperature of the cryogenic liquid helium is further reduced to obtain saturated superfluid helium at 1.8K. Then, the efficient heat exchange of the heat exchanger is used to obtain subcooled superfluid helium at 1.8K. This process achieves continuous and stable preparation from 4.2K conventional liquid helium to 1.8K subcooled superfluid helium. The subcooled superfluid helium preparation process in this invention is simple, enabling micro-circulation at the single-unit level, serving individual users, and offering greater flexibility in application. Furthermore, the cost per unit is controllable, significantly reducing the initial investment cost of subcooled superfluid helium. In addition, by introducing a liquefier and a circulation pump, this invention allows the vaporized helium within the system to be recovered and reliquefied for reuse. Compared to open systems, this completely solves the problem of liquid helium loss, achieving zero liquid helium loss and completely eliminating the cost of liquid helium consumption during operation. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of a supercooled superfluid helium preparation device with zero liquid helium loss proposed in this invention. Detailed Implementation

[0017] To address the problems existing in the preparation of superfluid helium using existing open-loop systems and the "forced flow subcooling method" for preparing subcooled superfluid helium, this paper refers to... Figure 1This invention proposes a zero-liquid-helium-loss supercooled superfluid helium preparation apparatus. The apparatus is vertical and includes a first tank 2, which has a top cover 21 and a vacuum-sealed and isolated first and second chambers. The first tank 2 is externally connected to an electromagnetic valve and a molecular pump. This setup is mainly used to evacuate the first chamber to a vacuum state. At the same time, a vacuum gauge is installed inside the first tank 2 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 first tank 2 is in a vacuum environment to reduce heat conduction.

[0018] A first cylinder 22 is provided inside the first tank 2, dividing its internal cavity into a first chamber and a second chamber. Specifically, the first chamber is the portion of the first tank 2's internal cavity outside the first cylinder 22, and the second chamber is the portion of the first cylinder 22's internal cavity. A second tank 3 is installed inside the first chamber of the first tank 2, and the second tank 3 is connected to the first Dewar 1. This arrangement allows liquid helium to be introduced into the second tank 3. During the pipeline transport process, due to heat loss in the pipeline, the portion of liquid helium in contact with the pipeline wall will heat up and vaporize into helium gas. Therefore, the substance introduced into the second tank 3 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 131 is also provided in the second tank 3. The inlet of the phase separator 131 is connected to the outlet of the first Dewar 1, and the outlet of the phase separator 131 is connected to the inner cavity of the second tank 3. The phase separator 131 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 second tank 3, while the less dense helium gas gathers at the top of the second tank 3, thus achieving gas-liquid separation.

[0019] In this embodiment, the pipe connecting the second tank 3 and the first cylinder 22 is a capillary tube. Due to the "creeping film" effect of superfluid helium—superfluid helium can crawl along the 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 second tank 3 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 first cylinder 22 drops due to evaporation or consumption, which helps maintain the pressure balance between the inner cavities of the first cylinder 22 and the second tank 3.

[0020] The second tank 3 is also equipped with a first liquid level sensor. During the process of liquid helium being input into the second tank 3, 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 second tank 3 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.

[0021] The separated liquid—liquid helium—flows out in two parts. One part flows into the first cylinder 22 through the first outlet of the second tank 3, where the load 10 is installed and immersed in the liquid environment. The other part flows to the regenerator 15, which is connected to the second outlet of the second tank 3, and then through the regenerator 15 to the throttling valve 4. Finally, it expands through the throttling valve 4, causing a sudden drop in pressure. During this process, 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).

[0022] Since the outlet of throttle valve 4 is connected to the inlet of heat exchanger 5, the 1.8K saturated superfluid helium flowing out of throttle valve 4 will flow to heat exchanger 5. A storage tank 9 for containing saturated superfluid helium is also installed on the pipe section between throttle valve 4 and heat exchanger 5. 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 storage tank 9 continues to flow and flows into heat exchanger 5, which is arranged inside the first cylinder 22. The saturated superfluid helium exchanges heat with the cryogenic liquid helium in the first cylinder 22 through heat exchanger 5, so that the liquid helium in the first cylinder 22 is converted into supercooled superfluid helium with a temperature of about 1.8K. Thus, the 1.8K supercooled superfluid helium can be used to cool and dissipate heat from the load 10. The structure of heat exchanger 5 is a copper tube with fins. This design 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.

[0023] In this embodiment, the load 10 can be a magnet coil. By immersing the magnet coil in supercooled superfluid helium, the magnet coil can be cooled and maintained below the superconducting transition temperature (usually 1.8K). When the magnet coil 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.

[0024] The aforementioned saturated superfluid helium will vaporize into low-temperature saturated helium gas after heat exchange in heat exchanger 5. In order to utilize the cooling capacity of this portion of saturated helium gas, a heat exchange tube 151 is provided in the regenerator 15. The inlet of the heat exchange tube 151 is connected to the second outlet of the second tank 3. This arrangement allows liquid nitrogen to flow directly into the heat exchange tube 151 of the regenerator 15. The outlet of the heat exchange tube 151 is connected to the inlet of the throttle valve 4, and the inlet of the regenerator 15 is connected to the outlet of the heat exchanger 5. 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 15, so that it can exchange heat with the liquid helium in the heat exchange tube 151 to reduce the temperature of the liquid helium and obtain low-temperature liquid helium with a temperature below 4.2K.

[0025] The separated helium gas flows out through the third outlet of the second tank 3, which is connected to the gasbag 11. This arrangement allows the gasbag 11 to collect the helium in the system for reuse, thus helping to achieve zero loss of liquid helium. During the heating process of the load 10, the supercooled overfluid helium in the first cylinder 22 will also be converted into helium gas. To collect this portion of helium gas, the outlet of the first cylinder 22 is also connected to the inlet of the gasbag 11.

[0026] Because the helium gas formed by vaporization is at a low temperature, in order to prevent the pipeline from freezing or frosting due to the discharge of this part of the helium gas, a second tank 3 is connected to the gas bag 11 through a second pipe 13, and a first cylinder 22 is connected to the gas bag 11 through a third pipe 14. A second heater 141, a second temperature sensor 142, and a one-way valve 146 are installed sequentially on the second pipe 13 and the third pipe 14 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.

[0027] For system safety considerations, a pressure sensor 145 is also installed on the third pipe 14. The third pipe 14 has a main pipe section and a first branch and a second branch formed by branching. A safety valve 143 is adapted to be installed on the first branch. The safety valve 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. An electric valve 144 is adapted to be installed on the second branch. The electric valve 144 is an electric valve 144 gate. When a large amount of vaporized helium gas is rapidly generated due to a large amount of heat generated by the load 10 in a short period of time, the pressure sensor 145 on the main pipe section detects the ultra-high pressure. After the helium gas pressure reaches the set value, the electric valve 144 opens to quickly release a large amount of high-pressure helium gas into the gasbag 11 to ensure system safety.

[0028] Furthermore, a third temperature sensor 101 is installed on load 10 to monitor the surface temperature of load 10 in real time. The system can also determine whether an overrun or impending overrun has occurred based on the monitored temperature value. This temperature signal is linked to the signal from the pressure sensor 145 on the third pipe 14, triggering the highest level of safety response, such as immediately opening the electric valve 114 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.

[0029] The supercooled superfluid helium prepared above has a low temperature. To avoid radiative heat leakage, a second cylinder 23 and a third cylinder 24 are connected inside the first tank 2. The first chamber is specifically the part of the inner cavity of the first tank 2 outside the first cylinder 22, and the second chamber is specifically the inner cavity of the first cylinder 22. The first cylinder 22 is adapted to be installed inside the third cylinder 24, and part of the first cylinder 22 passes through the third cylinder 24 and extends into the second cylinder 23. The regenerator 15 and the throttling valve 4 are both located in the inner cavity of the second cylinder 23 outside the first cylinder 44. Both the second cylinder 23 and the third cylinder 24 are made of thermally conductive materials (such as oxygen-free copper). The second cylinder 23 has an inner cylinder 232 and an outer cylinder 231, which are connected by an annular flange. The annular flange at the connection is also made of oxygen-free copper. The inner cylinder 232, the outer cylinder 231, and the connecting annular flange are connected by silver brazing, forming a jacketed region 233 filled with liquid nitrogen. The inlet of this jacketed region 233 is connected to the outlet of the second Dewar 8, which stores liquid nitrogen. Compared with the coil structure, this significantly reduces the temperature of the second cylinder 23, improves the temperature uniformity of the second cylinder 23, and reduces the radiative heat leakage of the system. This is because, compared to the radiative heat input of the first tank 2 to the internal 4.2K liquid helium, the jacketed region 233 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 first tank 2.

[0030] In addition, the interlayer region 233 of the second cylinder 23 is also connected to an exhaust pipe 15, through which the vaporized nitrogen in the interlayer region 233 can be discharged.

[0031] To achieve zero loss of liquid helium, the present invention also installs a liquefier 7 outside the first tank 2, connecting the outlet of the regenerator 15 to the inlet of the liquefier 7. By connecting the regenerator 15 and the liquefier 7, the low-temperature saturated helium formed after heat exchange with the saturated superfluid helium can flow to the liquefier 7. However, since the temperature of the saturated helium is low, in order to avoid pipe freezing, a first heater 122 and a first temperature sensor 121 are installed sequentially on the first pipe 12 connecting the regenerator 15 and the liquefier 7 in the direction of airflow. By activating the first heater 122, the low-temperature saturated helium flowing into the first pipe 12 can be heated to room temperature helium. The first heater 122, the first temperature sensor 121, the second heater 141, and the second temperature sensor 142 are all arranged inside the first tank 2. 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 second heater 141 matches the heating power according to the temperature, so that the outlet temperature is room temperature, ensuring that the helium discharged from the first tank 2 is room temperature helium. A circulation pump 123 is also installed on the first pipe 12. The circulation pump 123 is arranged between the liquefier 7 and the first temperature sensor 121. It can continuously draw room temperature helium into the liquefier 7, and then use the liquefier 7 to liquefy the gaseous helium back into liquid helium. The outlet of the liquefier 7 is connected to the inlet of the first Dewar 1. The liquefied liquid helium can be directly returned to the first Dewar 1, realizing the recycling of liquid helium, eliminating the loss of liquid helium, and greatly improving economic efficiency.

[0032] The above-mentioned zero-liquid-helium-loss supercooled superfluid helium preparation apparatus operates automatically and cyclically according to the control steps shown below: S1. Liquid helium from the first Dewar 1 is injected into the second tank 3, and the liquid helium is split into a first portion and a second portion in the second tank 3. This step specifically includes the following sub-processes: (1) Liquid helium injection and automatic flow rate regulation process Liquid helium from the first Dewar 1 is injected into the second tank 3, which is in a vacuum environment, through a liquid helium injection tube. During the injection process, the liquid level in the second tank 3 is monitored in real time by a first liquid level sensor installed in the second tank 3, generating a first liquid level signal. The first liquid level signal is fed back to the control system and compared with the preset liquid level range, thereby driving the regulating valve to automatically adjust its opening to control the flow rate of liquid helium injected into the second tank 3, realizing closed-loop control of liquid helium injection and ensuring that the liquid level in the second tank 3 remains stable within the set range.

[0033] (2) Gas-liquid separation process in the second tank 3 Liquid helium injected into the second tank 3 via the liquid helium injection pipe flows into a phase separator located within the second tank 3. In the phase separator, the liquid helium, due to its higher density, sinks and accumulates, while the gaseous helium rises and gathers in the upper space of the second tank 3. This design prevents air bubbles from entering the downstream pipeline 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.

[0034] (3) Liquid helium splitting process A portion of the separated liquid helium enters the capillary tube at the bottom of the second tank 3 as the first part of liquid nitrogen. The capillary tube is connected to the first cylinder 22. This portion of liquid helium is mainly used as a cooling medium to cool the load 10 set in the first cylinder 22. The other portion flows to the pipeline connected to the tube side of the regenerator 6 as the second part of liquid helium.

[0035] (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 second pipe 13, 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 second heater 141 on the second pipe 13 before it can be discharged into the gasbag 11 for collection.

[0036] A second temperature sensor 142 is installed at the outlet of the second heater 141 to monitor the exhaust temperature of the second tube 13 in real time. By comparing the exhaust temperature with the room temperature at that time, the heating power of the second heater 141 is adjusted according to the comparison result to ensure that the exhaust temperature of the second tube 13 is at room temperature.

[0037] For adjusting the heating power of the second heater 141, 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 142 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 a knob or button; 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 second heater 141 can also be applied to this invention, and no further limitations are imposed here.

[0038] S2. The first portion of liquid helium that is diverted is injected into the first cylinder 22 through the capillary connecting tube between the second tank 3 and the first cylinder 22. A second liquid level sensor is installed in the first cylinder 22. The liquid level height in the first cylinder 22 can be monitored in real time through the second liquid level sensor to ensure that the load 10 can be submerged below the liquid surface.

[0039] 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 inside the first cylinder 22, as follows: Step 1): The second liquid level sensor in the first cylinder 22 collects the second liquid level signal in real time, which can reflect the liquid level height in the first cylinder 22. 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 proceeds to step 2).

[0040] Step 2): By adjusting the system back pressure or the exhaust valve of the first cylinder 22, more liquid helium is allowed to flow naturally into the first cylinder 22 through the capillary tube under the action of pressure difference.

[0041] 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 the second tank 3. Due to the increase in the first portion of liquid helium flow rate, the amount of liquid helium extracted from the second tank 3 increases, which usually leads to a drop in the liquid level in the second tank 3. At this time, it is necessary to compare the first liquid level signal with the preset minimum safe liquid level of the second tank 3: If the first liquid level signal is greater than the minimum safe liquid level of the second tank 3 and is within the normal range, it indicates that the inventory in the second tank 3 is sufficient, 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 the second tank 3, the controller sends a command to the regulating valve on the liquid helium injection pipe to increase its opening, thereby increasing the flow rate of liquid helium injected into the second tank 3 from the first Dewar 1, so as to increase the total liquid helium injection volume until the second liquid level signal is stabilized back within the set range.

[0042] This setup ensures that the load 10 remains continuously immersed in liquid helium, maintaining a stable temperature. It also automatically coordinates the demand of the first tank 22 with the total system supply, maintaining a global balance of the working fluid. This reduces manual intervention and prevents cooling failures or idling of the second tank 3 due to liquid level imbalances. Furthermore, it avoids ineffective liquid helium overflow or excessive injection, achieving economical operation.

[0043] S3. The second part of the liquid helium flows through the pipeline where the regenerator 6 is located and is throttled and cooled to obtain saturated superfluid helium; the specific process is as follows: Step 1: The second portion of liquid helium is drawn from the second tank 3 through pipelines and enters the tube side (i.e., the internal pipelines) of the regenerator 6. The regenerator 6 is a shell-and-tube heat exchanger. Its shell side carries low-temperature saturated helium gas (approximately 1.8K) from the outlet of heat exchanger 5, 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 the regenerator 6: 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.

[0044] Step 2: After pre-cooling, the second portion of liquid helium flows out of the 6th tube of the regenerator and enters the throttling valve 4. By adjusting the opening of the throttling valve 4, 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.

[0045] In the above process, a temperature sensor is installed on the pipeline downstream of throttle valve 4 to monitor the generated saturated superfluid helium temperature in real time. The 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 throttle valve 4: if the saturated superfluid helium temperature is higher than the set target temperature, the opening of throttle valve 4 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 throttle valve 4 is increased to weaken the throttling effect and cause the temperature to rise slightly.

[0046] 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).

[0047] Step 3: The throttled gas-liquid mixture enters storage tank 9. This storage tank 9 serves as a buffer and gas-liquid separation container: the liquid (HeIIs) accumulates at the bottom of storage tank 9, forming a stable liquid pool; the gas portion is located at the top of storage tank 9 and can be pumped away through connecting pipelines. The storage tank 9 ensures that the downstream heat exchanger 5 always has a sufficient supply of liquid working fluid, avoiding heat exchange interruptions due to flow fluctuations.

[0048] Step 4: Saturated superfluid helium flows out from the bottom of storage tank 9 and enters the pipeline of heat exchanger 5, ready to perform the heat exchange task of step S4.

[0049] S4. Saturated superfluid helium flowing from storage tank 9 enters the pipeline of heat exchanger 5 located in the first cylinder 22. The saturated superfluid helium and the first portion of liquid helium in the first cylinder 22 undergo indirect heat exchange at heat exchanger 5, which is typically a copper tube with fins or a reinforced heat exchange surface, immersed in the liquid helium within the subcooled superfluid helium cavity. The temperature of the saturated superfluid helium flowing within heat exchanger 5 (approximately 1.8 K) is lower than the temperature of the first portion of liquid helium within the cavity (approximately 4.2 K). Driven by the temperature difference, heat is transferred from the liquid helium within the cavity to the saturated superfluid helium through the wall of heat exchanger 5. After absorbing heat, part of the saturated superfluid helium within heat exchanger 5 evaporates, becoming low-temperature saturated helium gas; simultaneously, the first portion of liquid helium within the first cylinder 22 is cooled, transforming into subcooled superfluid helium when its temperature drops below the saturation temperature corresponding to the current pressure.

[0050] Ultimately, stable supercooled helium is obtained in the first cylinder 22, with a temperature as low as below 1.8K, thereby achieving efficient and highly stable cooling of the load 10.

[0051] During the operation of load 10, the supercooled overfluid helium in the first cylinder 22 may generate cryogenic helium due to the thermal load. The release of this cryogenic helium requires safe handling, as follows: The generated cryogenic helium gas is led out through a third pipe 14, which has a relatively large diameter (e.g., an inner diameter of 89 mm) to meet the requirements of instantaneous high-flow-rate discharge. A second heater 141 on the third pipe 14 heats this portion of cryogenic helium gas to room temperature before discharging it into the gasbag 11, preventing direct discharge of cryogenic gas from causing icing in the pipeline or cold damage to the equipment. A second temperature sensor 142 is installed at the outlet of the second heater 141 to monitor the outlet temperature of the third pipe 14. The heating power of the second heater 142 can be adjusted based on the monitoring results of the second temperature sensor 142 (the method of adjusting the heating power of the second heater 142 has been explained in step S1 and will not be elaborated further here) to ensure that the outlet gas is at room temperature.

[0052] Synchronously, the pressure sensor 145 on the third tube 14 monitors the gas pressure in the tube 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 143 for slow and controlled venting, discharging the gas into the helium recovery bladder 11. 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 "overload failure" of load 10), it indicates that a large amount of gas is generated instantaneously. The system immediately fully opens the electric valve 144 (e.g., DN150) to achieve rapid pressure relief and protect system safety. The released gas also enters the recovery bladder 11.

[0053] 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.

[0054] In addition, a third temperature sensor 101 is installed on the surface of the load 10 to monitor the temperature of the load 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).

[0055] The system compares the monitored temperature measured by the third temperature sensor 101 with the temperature safety threshold in real time. When the monitored temperature is less than the temperature safety threshold, the system considers the load 10 to be operating normally and the electric valve 144 remains closed. When the monitored temperature is greater than or equal to the temperature safety threshold, the system determines that the load 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 101 is transmitted to the control system in real time. The system identifies this signal as a "highest priority emergency event". The control system immediately (response time is usually in milliseconds) outputs a fully open (100% opening) control signal to the drive mechanism of the electric valve 144 (such as an electric actuator or solenoid valve). After receiving the signal, the electric valve 144 switches from the normally closed state to the fully open state as quickly as possible (e.g., within 1-2 seconds). After the valve is fully opened, the large amount of high-pressure helium gas generated in the first cylinder 22 due to the quench can be released quickly to the airbag 11 with almost no resistance through the third pipe 14 and the fully open electric valve 144, thereby avoiding structural damage caused by a sudden increase in internal pressure.

[0056] 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, as long as the temperature of load 10 exceeds the temperature safety threshold, the electric valve 144 can be preemptively triggered. 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 if either the "temperature over-limit" or "pressure over-limit" condition is met, the electric valve 144 is triggered to fully open. This constitutes a double safety measure, greatly improving the reliability of the safety response.

[0057] S5. The low-temperature saturated helium gas, formed by the evaporation of the first portion of liquid helium after heat exchange, is fed into the shell side of the regenerator 6. This gas absorbs heat within the heat exchanger 5 and undergoes a phase change with saturated superfluid helium (HeIIs), resulting in an extremely low temperature (approximately 1.8 K) and carrying a large amount of "cold energy." The low-temperature saturated helium gas flowing into the shell side of the regenerator 6 undergoes countercurrent heat exchange with the second portion of liquid helium (approximately 4.2 K) flowing through the tube side from the second tank 3. 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 its own temperature is increased (e.g., to the range of 4 K-10 K). This process efficiently recovers the cold energy of the low-temperature saturated helium gas, significantly reducing the energy consumption for subsequent liquefaction.

[0058] After heat exchange, the low-temperature saturated helium gas flows out from the first tube 12, which is connected to the shell side of the regenerator 6. This gas temperature is still far below room temperature. If it directly enters subsequent pipelines, it may cause low-temperature damage to the equipment, icing of the pipelines, or solidification of the lubricating oil. Therefore, before discharge, this gas needs to be heated to room temperature by the first heater 122 on the first tube 12. A first temperature sensor 121 is installed at the outlet of the first heater 122 to monitor the exhaust temperature of the first tube 12 in real time and compare it with room temperature. Based on the comparison result, the heating power of the first heater 122 is adjusted (this adjustment method is the same as the heating power adjustment method of the second heater 141 mentioned above, and will not be further elaborated here), thereby ensuring that the output helium gas meets the requirements of the subsequent equipment inlet.

[0059] A circulation pump and a liquefaction unit 7 are installed on the first pipe 12. The room-temperature helium gas discharged from the first pipe 12, as well as the helium gas recovered from the gasbag 11, are both fed into the liquefaction unit 7. The liquefaction unit 7 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 gas 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 7 is transported back to the first Dewar 1 for storage. Thus, the first Dewar 1 becomes the "source" and "destination" of liquid helium in the system, completing a complete closed-loop cycle of "liquid helium → cooling / heat exchange → gaseous helium → recovery / heating → liquefaction → liquid helium". It can recover almost 100% of the used helium gas and convert it into reusable liquid helium, basically achieving zero liquid helium loss and solving the core pain points of high cost and high liquid helium loss in open systems.

[0060] In addition, the monitored temperature obtained by the third temperature sensor 101 can also be used to adjust the temperature of the load 10, as follows: First, the system calculates the deviation between the monitored temperature and the target temperature of load 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 means that the temperature of load 10 is too high and cooling needs to be enhanced; when the deviation is less than 0, it means that the temperature of load 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 means that the magnet coil is in a steady state and can be finely adjusted to maintain it.

[0061] 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 large deviation range (for example, the absolute value of the deviation is > 0.5K), the throttle valve 4 is adjusted first, and the circulation pump is adjusted simultaneously.

[0062] When adjusting throttle valve 4: 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.

[0063] 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.

[0064] 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 4 and the circulation pump 123 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 4 may be slightly reduced, and the speed of the circulation pump 123 may be slightly increased simultaneously.

[0065] 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 minor fluctuations in the rotational speed of circulating pumps 123. Because adjusting the pump speed affects the "flow rate," the response is relatively mild, suitable for offsetting high-frequency small disturbances. Throttling valve 4 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 the second tank 3 to maintain the total balance of the working fluid in the system, providing a stable basis for temperature control.

[0066] 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.

[0067] 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.

[0068] Based on the above design, the present invention achieves high-precision temperature control and rapid dynamic response, which can stabilize the temperature of load 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.

[0069] 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. A supercooled superfluid helium preparation apparatus with zero liquid helium loss, characterized in that, The system includes a first Dewar, a first tank, a second tank, a throttling valve, a heat exchanger, and a liquefier. The first tank has a vacuum and two isolated chambers. The second tank is located within the first chamber. The outlet of the first Dewar is connected to the second tank to allow liquid helium to be introduced into the second tank. After being discharged from the second tank, the liquid helium is diverted to the second chamber and the throttling valve. The throttling valve is located within the first chamber to throttle the liquid helium flowing through it into saturated superfluid helium. The inlet of the heat exchanger is connected to the outlet of the throttling valve, allowing the liquid helium in the second chamber to exchange heat with the saturated superfluid helium flowing into the heat exchanger to form subcooled superfluid helium. The outlet of the heat exchanger is connected to the inlet of the liquefier, allowing the low-temperature saturated helium formed after the saturated superfluid helium heat exchange to flow to the liquefier. The outlet of the liquefier is connected to the inlet of the first Dewar, allowing the liquefied liquid helium to return to the first Dewar.

2. The zero-liquid-helium-loss supercooled superfluid helium preparation apparatus according to claim 1, characterized in that, The first tank body has a first cylinder that divides its internal cavity into a first chamber and a second chamber, as well as a second cylinder and a third cylinder that are connected to each other. The first chamber is specifically the part of the first tank body cavity outside the first cylinder, and the second chamber is specifically the cavity inside the first cylinder. The second cylinder and the third cylinder are both made of thermally conductive material. The second cylinder has an inner cylinder and an outer cylinder, and a sandwich area is formed between the inner cylinder and the outer cylinder. The first cylinder is adapted to be installed inside the third cylinder, and part of the first cylinder extends through the third cylinder into the second cylinder. The throttling valve is located in the cavity inside the second cylinder outside the first cylinder. The heat exchanger is arranged inside the first cylinder, and the inlet of the first cylinder is connected to the first outlet of the second tank body.

3. The zero-liquid-helium-loss supercooled superfluid helium preparation apparatus according to claim 2, characterized in that, It also includes a load, which is arranged inside the first cylinder and immersed in supercooled superfluid helium inside the first cylinder.

4. The zero-liquid-helium-loss supercooled superfluid helium preparation apparatus according to claim 2, characterized in that, It also includes a regenerator arranged in the first chamber, which has heat exchange tubes. The inlet of the heat exchange tubes is connected to the second outlet of the second tank to allow liquid helium to flow in, and the outlet of the heat exchange tubes is connected to the inlet of the throttle valve. The inlet of the regenerator is connected to the outlet of the heat exchange tubes so that the low-temperature saturated helium gas formed after heat exchange flows into the regenerator to exchange heat with the liquid helium in the heat exchange tubes to reduce the temperature of the liquid helium and obtain low-temperature liquid helium below 4.2K.

5. The zero-liquid-helium-loss supercooled superfluid helium preparation apparatus according to claim 4, characterized in that, The outlet of the regenerator is connected to the inlet of the liquefier. The outlet of the regenerator and the inlet of the liquefier are connected by a first pipe. A first heater and a first temperature sensor are installed on the first pipe in sequence according to the airflow direction. By starting the first heater, the low-temperature saturated helium flowing into the first pipe is heated to room temperature helium. A circulation pump is also installed on the first pipe. The circulation pump is arranged between the liquefier and the first temperature sensor to draw room temperature helium into the liquefier.

6. The zero-liquid-helium-loss supercooled superfluid helium preparation apparatus according to claim 4, characterized in that, The second tank is equipped with a phase separator. The inlet of the phase separator is connected to the outlet of the first Dewar tank, and the outlet of the phase separator is connected to the inner cavity of the second tank.

7. The zero-liquid-helium-loss supercooled superfluid helium preparation apparatus according to claim 6, characterized in that, It also includes an airbag. The second tank also has a third outlet. The third outlet of the second tank is connected to the airbag inlet so that the helium separated by the phase separator flows into the airbag. The outlet of the first cylinder is connected to the airbag inlet so that the helium in the first cylinder flows into the airbag. The second tank and the airbag are connected by a second pipe, and the first cylinder and the airbag are connected by a third pipe. A second heater, a second temperature sensor and a one-way valve are installed on the second pipe and the third pipe in sequence according to the airflow direction to heat the low-temperature helium into room-temperature helium.

8. The zero-liquid-helium-loss supercooled superfluid helium preparation apparatus according to claim 7, characterized in that, The third pipe is also equipped with a pressure sensor. The third pipe has a main pipe section and a first branch and a second branch formed by branching. A safety valve is adapted to be installed on the first branch and an electric valve is adapted to be installed on the second branch. The electric valve opens when the pressure sensor detects that the air pressure in the main pipe section is greater than the set value.

9. The zero-liquid-helium-loss supercooled superfluid helium preparation apparatus according to claim 2, characterized in that, It also includes a second Dewar, the outlet of which is connected to the inlet of the interlayer area to introduce liquid nitrogen into the interlayer area. The outlet of the second Dewar is connected to a fourth pipe, which extends from the first tank and connects to the outside.

10. The zero-liquid-helium-loss supercooled superfluid helium preparation apparatus according to claim 7, characterized in that, The first heater, the first temperature sensor, the second heater, and the second temperature sensor are all arranged inside the first tank.

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