Supercritical helium low-temperature system and method for nuclear fusion strong field magnet

Abstract

The invention discloses a supercritical helium low-temperature system and method for a nuclear fusion strong field magnet, and relates to the technical field of refrigeration systems and temperature control, and the method comprises the steps: employing a refrigeration and magnet test double independent loop, and transmitting the cooling capacity through an intermediate heat exchanger. The distribution valve box is arranged to support simultaneous testing of multiple samples, the double low-temperature fans are connected in series to adapt to different flow resistance requirements, and the built-in purifier ensures that the loop is clean. An independent circulation loop for refrigeration and magnet testing is achieved, the problem that a helium compressor cannot achieve the high-pressure operation condition of a magnet circulation path is solved, and the high-field magnet operates under the working conditions of high pressure, low circulation flow resistance, uniform temperature and small thermal stress. The adjustable temperature supply of 4.5-30K can be realized according to different working temperatures of different to-be-tested magnets, the adjustable temperature supply device can be matched with the thermal load of the to-be-tested magnets to realize 0-100% elastic adjustable cooling capacity in a 0-2000W range, and the test conditions that the temperature difference between the inlet and the outlet of the to-be-tested magnets is less than 1K and the working pressure is greater than or equal to 20bara can be realized.

Description

Technical Field

[0001] This invention relates to the field of refrigeration systems and temperature control technology, and more specifically to a supercritical helium cryogenic system and method for nuclear fusion strong field magnets. Background Technology

[0002] Nuclear fusion energy, as a clean, efficient, and sustainable new energy source, is considered one of the important directions for solving the global energy crisis. The TF high-field magnet is a core component of a nuclear fusion device, its main function being to confine high-temperature plasma and ensure the stable conduct of the nuclear fusion reaction. The TF high-field magnet approaches the limits of materials, making it extremely difficult and costly; moreover, the normal operation of the high-field magnet depends on an extremely low temperature environment, typically requiring operation in ultra-low temperature conditions of 4.5K to 20K, which places stringent requirements on the performance of the cryogenic cooling system.

[0003] Due to its excellent thermophysical properties, supercritical helium has become an ideal working fluid for cryogenic cooling systems of strong-field magnets in nuclear fusion reactors, and the corresponding supercritical helium cryogenic systems have become important supporting equipment for nuclear fusion devices. Currently, most existing supercritical helium cryogenic systems employ the Brayton refrigeration cycle based on a turbine expander, achieving cryogenic preparation through processes such as helium compression, cooling, and expansion, thereby providing a stable cooling environment for the strong-field magnet.

[0004] However, existing technologies still face several unresolved issues in practical applications: First, most cryogenic systems use an integrated design between the refrigeration cycle loop and the test loop of the magnet sample, causing pressure and temperature fluctuations during the refrigeration cycle to be directly transmitted to the magnet, which can easily damage delicate, high-field magnet samples, affecting the accuracy of test results and the safety of the samples; the operating pressure and pressure ratio of existing large-scale cryogenic system compressors cannot meet the high-pressure operation requirements of magnets; second, existing systems have poor adaptability to the magnets under test, making it difficult to simultaneously meet the testing needs of multiple magnet samples of different specifications, and the flow distribution accuracy is insufficient, making it impossible to adjust according to... The system needs to achieve precise matching of cooling capacity to meet the heat load requirements of different samples. However, the system's operational stability needs improvement. During the switching between loading and unloading conditions, the loop pressure fluctuates significantly, which can easily lead to equipment failure. As a scarce and expensive working fluid, helium has a generally low helium recovery efficiency in existing systems, and the waste of a large amount of helium significantly increases the system's operating costs. After the sample test, the rewarming process of the system and test loop is slow and time-consuming, which seriously affects the testing efficiency. In addition, impurities in the circulation loop are prone to accumulate, making it difficult to achieve efficient cleaning of the loop. Long-term operation will reduce the heat exchanger's heat exchange efficiency and affect the system's cooling performance.

[0005] Therefore, how to propose a supercritical helium cryogenic system and method for nuclear fusion strong field magnets and overcome the defects in the existing technology is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a supercritical helium cryogenic system and method for nuclear fusion strong-field magnets, which features independent operation of dual loops, multi-sample adaptability, high stability, high helium recovery rate, rapid rewarming, and loop cleaning functions, thereby improving the safety, accuracy, and efficiency of nuclear fusion strong-field magnet testing. To achieve the above objectives, the present invention adopts the following technical solution: A supercritical helium cryogenic system for a nuclear fusion strong field magnet includes: a refrigeration cycle loop and a magnet under test cycle loop; The refrigeration cycle includes: a helium compressor, a high-pressure helium pipeline, a low-pressure helium pipeline, a loading / unloading pipeline, and a bypass pipeline; the outlet of the helium compressor is sequentially connected to the high-pressure helium pipeline, the low-pressure helium pipeline, and the inlet of the helium compressor to form a loop; one end of the loading / unloading pipeline is connected to the high-pressure helium pipeline, and the other end of the loading / unloading pipeline is connected to the low-pressure helium pipeline; one end of the bypass pipeline is connected to the high-pressure helium pipeline, and the other end of the bypass pipeline is connected to the low-pressure helium pipeline; the loading / unloading pipeline is connected to a first helium storage tank; an unloading valve and a loading valve are sequentially installed on the loading / unloading pipeline; and a bypass valve is installed on the bypass pipeline. The refrigeration cycle circuit and the test magnet cycle circuit are connected through an intermediate heat exchanger; The circulating loop of the magnet under test includes: the hot side outlet of the intermediate heat exchanger is connected to the inlet of the distribution valve box; an inlet main valve is installed in the distribution valve box; the inlet main valve is connected to the first inlet branch pipeline; a first regulating valve is installed on the first inlet branch pipeline; the first inlet branch pipeline is connected to the inlet of the magnet under test; the outlet of the magnet under test is connected to the first return branch pipeline; a first return regulating valve is installed on the first return branch pipeline; the first return branch pipeline is connected to the return main valve installed in the distribution valve box; the return main valve is connected to the outlet of the distribution valve box; the first branch pipeline of the outlet of the distribution valve box is connected to the inlet of the first low-temperature fan; the outlet of the first low-temperature fan is connected to the inlet of the second low-temperature fan; and the outlet of the second low-temperature fan is connected to the hot side inlet of the intermediate heat exchanger. The circulating loop of the magnet under test is equipped with a distribution valve box, which contains an inlet main valve and a return main valve. The inlet main valve is connected to multiple branches, each of which is equipped with a regulating valve. The return main valve is also connected to multiple branches, each of which is equipped with a regulating valve. Pressure sensors, temperature sensors, flow meters, and differential pressure transmitters are installed on the inlet and outlet branches. The flow meter is located at the outlet of the magnet under test, and the differential pressure transmitter is connected in parallel at the inlet and outlet of the magnet under test. The test magnet circulation loop also includes electronic pressure regulating valves connected in parallel on both sides of the second shut-off valve of the sample loop; it includes a first fan bypass valve located before the inlet of the first cryogenic fan and a fourth fan bypass valve located before the inlet of the second cryogenic fan; a third fan bypass valve connected in parallel before the inlet of the first fan bypass valve and the outlet of the first cryogenic fan; and a second fan bypass valve connected in parallel at the inlet of the fourth fan bypass valve and the outlet of the second cryogenic fan.

[0007] Optionally, the refrigeration cycle loop specifically includes: The inlet and outlet of the water-oil heat exchanger inside the helium compressor are connected to the inlet and outlet of the chiller. The high-pressure helium pipeline includes: a helium compressor outlet, an oil filter, a cold trap, hot-side inlet and outlet of a first heat exchanger, hot-side inlet and outlet of a second heat exchanger, hot-side inlet and outlet of a third heat exchanger, and a turbine expander inlet; the low-pressure helium pipeline includes: an electric heater inlet and outlet, cold-side inlet and outlet of an intermediate heat exchanger, cold-side inlet and outlet of a third heat exchanger, cold-side inlet and outlet of a second heat exchanger, cold-side inlet and outlet of a first heat exchanger, and a helium compressor inlet; the helium compressor outlet is connected to the oil filter inlet, the oil filter outlet is connected to the cold trap inlet, and the cold trap outlet is connected to the hot-side inlet of the first heat exchanger. The hot-side outlet of the first heat exchanger is connected to the hot-side inlet of the second heat exchanger; the hot-side outlet of the second heat exchanger is connected to the hot-side inlet of the third heat exchanger; the hot-side outlet of the third heat exchanger is connected to the inlet of the turbine expander; the outlet of the turbine expander is connected to the inlet of the electric heater; the outlet of the electric heater is connected to the cold-side inlet of the intermediate heat exchanger; the cold-side outlet of the intermediate heat exchanger is connected to the cold-side inlet of the third heat exchanger; the cold-side outlet of the third heat exchanger is connected to the cold-side inlet of the second heat exchanger; the cold-side outlet of the second heat exchanger is connected to the cold-side inlet of the first heat exchanger; and the cold-side outlet of the first heat exchanger is connected to the inlet of the helium compressor. It also includes a throttling expansion valve connected in parallel at the turbine expander outlet and the electric heater outlet.

[0008] Optionally, it also includes: a first air compressor, a first solenoid directional valve, a second air compressor, and a second solenoid directional valve; the first air compressor is connected to the first solenoid directional valve, the first outlet of the first solenoid directional valve is connected to the pneumatic actuator of the unloading valve in the loading and unloading pipeline, the second outlet of the first solenoid directional valve is connected to the pneumatic actuator of the loading valve in the loading and unloading pipeline, and the third outlet of the first solenoid directional valve is connected to the pneumatic actuator of the bypass valve in the bypass pipeline; The second air compressor is connected to the second solenoid directional valve. The first outlet of the second solenoid directional valve is connected to the pneumatic actuator of the inlet main valve. The inlet main valve is connected to the inlet first regulating valve. The second outlet of the second solenoid directional valve is connected to the pneumatic actuator of the inlet first regulating valve. The third outlet of the second solenoid directional valve is connected to the pneumatic actuator of the return main valve. The return main valve is connected to the return first regulating valve. The fourth outlet of the second solenoid directional valve is connected to the pneumatic actuator of the return first regulating valve.

[0009] Optionally, it also includes: a purification system, The purification system includes: a built-in purifier, a purity analyzer, a first shut-off valve for the purification pipeline, and a second shut-off valve for the purification pipeline. The built-in purifier is connected in parallel to both a high-pressure helium pipeline and a low-pressure helium pipeline. The inlet of the built-in purifier is connected to the high-pressure helium pipeline, and the inlet and outlet of the built-in purifier are connected in parallel to the purity analyzer. The inlet of the purity analyzer is connected to the inlet of the built-in purifier, and the outlet of the purity analyzer is connected to the outlet of the built-in purifier. A first shut-off valve for the purification pipeline is installed on the pipeline preceding the inlet of the built-in purifier, and a second shut-off valve for the purification pipeline is installed on the pipeline preceding the inlet of the purity analyzer.

[0010] Optionally, it also includes a hot gas bypass pipeline, which includes a hot gas bypass main pipeline and a hot gas bypass loop pipeline. The connection point between the hot gas bypass main pipeline and the high-pressure helium pipeline is located at the cold trap outlet. The hot gas bypass main pipeline is divided into a first hot gas bypass branch pipeline and a second hot gas bypass branch pipeline. The first hot gas bypass branch pipeline is connected to the low-pressure helium pipeline, and the interface between the first hot gas bypass branch pipeline and the low-pressure helium pipeline is located at the outlet of the intermediate heat exchanger. The second hot gas bypass branch pipeline is connected to the hot side outlet of the intermediate heat exchanger. One end of the hot gas bypass loop pipeline is connected to the second branch pipeline at the outlet of the distribution valve box, and the other end of the hot gas bypass loop pipeline is connected to the low-pressure helium pipeline. The connection point between the other end of the hot gas bypass loop pipeline and the low-pressure helium pipeline is located at the inlet of the helium compressor.

[0011] Optionally, a helium recovery and storage system may also be included; The helium recovery and storage system includes: a booster pump, a pressure reducing pump, a first shut-off valve, a second shut-off valve, a first check valve, a second check valve, an external purifier, an ambient air vaporizer, a storage tank manual valve, and a second helium storage tank. The booster pump and the pressure reducing pump are connected in parallel, with their inlets connected to the second branch pipeline of the distribution valve box outlet. The booster pump is equipped with a first shut-off valve at its inlet and a first check valve at its outlet. The pressure reducing pump is equipped with a second shut-off valve at its inlet and a second check valve at its outlet. The outlets of the booster pump and the pressure reducing pump are connected to the first inlet and outlet of the external purifier. The second inlet and outlet of the external purifier are connected to the inlet of the ambient air vaporizer. The outlet of the ambient air vaporizer is connected to the inlet of the storage tank manual valve, and the outlet of the storage tank manual valve is connected to the interface of the second helium storage tank.

[0012] Optionally, pressure sensors and temperature sensors may also be included; The pressure and temperature sensors include: a first pressure sensor and a first temperature sensor located at the outlet of the helium compressor; a second temperature sensor located at the hot-side outlet of the first heat exchanger; a third temperature sensor located at the hot-side outlet of the second heat exchanger; a second pressure sensor and a fourth temperature sensor located at the hot-side outlet of the third heat exchanger; a third pressure sensor and a fifth temperature sensor located at the cold-side inlet of the intermediate heat exchanger; a fourth pressure sensor and a sixth temperature sensor located at the cold-side outlet of the intermediate heat exchanger; a seventh temperature sensor located at the cold-side outlet of the third heat exchanger; an eighth temperature sensor located at the cold-side outlet of the second heat exchanger; and a pressure sensor located at the outlet of the helium compressor. The fifth pressure sensor and the ninth temperature sensor are located at the machine inlet; the sixth pressure sensor and the tenth pressure sensor are located at the hot side outlet of the intermediate heat exchanger; the seventh pressure sensor and the eleventh temperature sensor are located on the first branch pipeline inside the distribution valve box; the eighth pressure sensor and the twelfth temperature sensor are located on the first branch pipeline at the return port; the ninth pressure sensor and the thirteenth temperature sensor are located at the outlet of the distribution valve box; the tenth pressure sensor is located at the outlet of the first low-temperature fan; the eleventh pressure sensor and the fourteenth temperature sensor are located at the outlet of the second low-temperature fan; and the twelfth pressure sensor and the fifteenth temperature sensor are located at the outlet of the ambient air vaporizer.

[0013] Optionally, a supercritical helium cryogenic method for nuclear fusion strong-field magnets, comprising a refrigeration cycle process, including: In the refrigeration cycle, the helium compressor draws in helium from the low-pressure helium pipeline, pressurizes it to obtain high-temperature, high-pressure gas, cools it down by the cooling water provided by the chiller, and then passes through a cold trap to remove impurities. After exiting the cold trap, the helium enters the hot-side inlet of the first heat exchanger, where it is cooled by the helium returning from the cold side. It then passes through the hot-side inlet of the second heat exchanger, where it is cooled by the helium returning from the cold side, and then through the hot-side inlet of the third heat exchanger, where it is cooled by the returning helium. It then undergoes adiabatic expansion through a turbine expander, at which point the throttling expansion valve closes. Subsequently, it enters the intermediate heat exchanger to exchange heat with the helium that has been cooled and reheated by the magnet under test. It then enters the cold-side inlet of the third heat exchanger to exchange heat with the hot-side helium, and then enters the cold-side inlet of the second heat exchanger to exchange heat with the high-pressure side helium. Finally, it enters the cold-side inlet of the first heat exchanger to exchange heat with the high-pressure side helium, and is then drawn in and pressurized again by the helium compressor to enter the next cycle. In the refrigeration cycle, the electronic expansion valve is opened, and the low-temperature, low-pressure helium gas from the turbine expander outlet directly enters the throttling expansion valve. The throttling expansion valve performs adiabatic expansion on the helium gas to obtain even lower-temperature helium gas, which then enters the cold side inlet of the intermediate heat exchanger to cool the helium gas in the test magnet circulation loop, thereby providing a lower-temperature testing environment for the test magnet. In the test magnet circulation loop, the series-connected cryogenic fans sequentially draw in helium gas after heat exchange with the test magnet, pressurize it, and enter the intermediate heat exchanger to exchange heat with the cryogenic helium gas in the refrigeration cycle and be cooled. The gas then enters the test magnet inlet through the distribution valve box, cools the test magnet, and is drawn in again by the series-connected cryogenic fans to enter the next cycle. The refrigeration cycle and the test magnet cycle are independent of each other. The cooling capacity is transferred through an intermediate heat exchanger. The refrigeration cycle drives the test magnet cycle to cool down simultaneously. During the cooling process, the maximum temperature difference between the two cycles is kept less than a preset value. The temperatures measured by the sixth temperature sensor at the cold side outlet and the tenth temperature sensor at the hot side outlet of the intermediate heat exchanger are converted into electrical signals and transmitted to the control system. By calculating the difference between the sixth and tenth temperature sensors, the helium mass flow rate of the two cycles is controlled to ensure that the temperature difference between the two cycles in the intermediate heat exchanger is less than the preset value. Set a set value for the eleventh temperature sensor at the inlet of the magnet under test, set a set value for the twelfth temperature sensor at the outlet, and set the difference between the two as a preset value. When the measured temperature of the helium gas at the outlet is higher than the set value, the electrical signal of the eleventh temperature sensor is transmitted to the control system to adjust the speed of the helium compressor and the turbine expander to control the temperature of the magnet under test.

[0014] Optional, series-connected operation control of cryogenic fans includes: The series-connected cryogenic fans include a first cryogenic fan and a second cryogenic fan. These fans drive the flow of helium gas in the circuit of the magnet under test. When the pressure drop inside the magnet under test is large, the series-connected cryogenic fans sequentially draw in helium gas after heat exchange with the magnet under test, pressurize it, and then allow it to enter the intermediate heat exchanger to exchange heat with the cryogenic helium gas in the refrigeration cycle for cooling. The gas then enters the magnet under test inlet through the distribution valve box, cooling the magnet before being drawn in again by the series-connected cryogenic fans for the next cycle. Notably, when the pressure drop inside the magnet under test is small, the control system switches to a single-fan operation mode to match the internal pressure drop, ensuring the cryogenic fan operates within its optimal range. The system switches between cryogenic fans according to a set operating time. The PLC control system converts the pressure signals from the seventh and eighth pressure sensors and the differential pressure transmitter at the inlet and outlet of the magnet under test into electrical signals. These signals are transmitted to the control system, which in turn adjusts the start / stop status and speed of the cryogenic fans. The system controls the cryogenic fan speed based on the internal pressure drop of the sample, switching between single-fan and dual-fan drive modes.

[0015] Optionally, helium can be recovered using a helium recovery and storage system, including: The second helium storage tank is pre-filled with helium. The storage tank manual valve, the second shut-off valve, the helium recovery shut-off valve, and the pressure reducing pump are opened. The high-pressure helium in the second helium storage tank flows towards the magnet under test. After passing through the pressure reducing pump, the pressure reducing pump outlet pressure setpoint is set to the working pressure inside the magnet under test to avoid the impact of high-pressure helium on the magnet under test. The helium is continuously output at a stable pressure. As the temperature of the circuit of the magnet under test decreases, the second helium storage tank continues to replenish it until it stabilizes within the working pressure range required by the magnet under test. Then, the filling is stopped, and the storage tank manual valve and the helium recovery shut-off valve are closed. After the magnet under test is completed, the helium gas expands when heated. At this time, the helium gas recovery shut-off valve and the storage tank manual valve remain open. The booster pump and the first shut-off valve are opened, and the expanded helium gas enters the booster pump through the helium gas recovery pipeline. The outlet pressure setting value of the booster pump is set to the working pressure of the second helium gas storage tank. After being boosted, the helium gas passes through an external purifier to remove impurities, and then passes through an ambient temperature vaporizer to return to room temperature before entering the second helium gas storage tank for storage, in order to avoid low temperature shock to the second helium gas storage tank. Once the pressure inside the magnet under test returns to normal, shut off the manual valve of the storage tank and the helium recovery shut-off valve. After the system returns to normal temperature, shut off the helium compressor, close the inlet main valve and return main valve in the distribution valve box, and remove the magnet under test.

[0016] Optionally, the distribution valve box is further equipped with an inlet / outlet main valve and inlet / outlet branch valves for simultaneous testing of multiple samples. The inlet / outlet main valve and inlet / outlet branch valves are pneumatic valves, powered by a second air compressor to drive the valves to adjust their opening, thereby adjusting the cooling capacity allocated to each sample. A cold shield branch pipeline is led out from the outlet of the second heat exchanger and connected to the interlayer of the distribution valve box to form a cold shield, which is used to reduce heat loss caused by heat conduction and heat radiation between the low-temperature helium gas inside the distribution valve box and the ambient temperature air.

[0017] Optionally, it also includes high and low pressure control of the refrigeration cycle loop: The first air compressor provides compressed air to the unloading valve, loading valve, and bypass valve to drive the valve actuators and regulate the high and low pressure of the system. The loading valve, unloading valve, bypass valve, inlet main valve, inlet first regulating valve, return first regulating valve, and return main valve are all pneumatic valves and are equipped with pneumatic actuators. The electrical signal output by the control system is the control command, which opens and closes the air path and reverses the direction through the first and second solenoid directional valves, thereby driving the cylinder piston of the pneumatic actuator to move. The piston links the valve stem to complete the opening and closing action or continuous adjustment of the opening degree. The unloading valve connects the high-pressure outlet of the helium compressor to the first helium storage tank. When the high-pressure pressure is higher than the set pressure, the unloading valve opens, and the helium in the high-pressure helium pipeline returns to the first helium storage tank. The loading valve connects the low-pressure inlet of the helium compressor to the first helium storage tank. When the outlet pressure of the helium compressor is lower than the set pressure, the loading valve opens, and the helium in the first helium storage tank enters the low-pressure helium pipeline. The bypass valve connects the high-pressure helium pipeline and the low-pressure helium pipeline and is used to regulate the pressure of the low-pressure helium pipeline. When the low pressure is lower than the set value, the opening of the bypass valve increases; when the low pressure is higher than the set value, the opening of the bypass valve decreases.

[0018] Optionally, rapid reheating via a hot gas bypass line is also included: Open the first hot gas bypass valve, the second hot gas bypass valve, and the third hot gas bypass valve, and turn on the electric heater. High-temperature and high-pressure helium gas enters the cold side of the third heat exchanger, the cold side of the second heat exchanger, and the cold side of the first heat exchanger through the first branch pipeline of the hot gas bypass, so as to quickly reheat the helium gas in the refrigeration cycle system. Another part of the helium gas enters the circulation loop of the magnet under test through the second branch pipeline of the hot gas bypass, so as to heat the circulation loop of the magnet under test and the helium gas in the magnet under test.

[0019] Optionally, it also includes cleaning via a purification system: Before testing the magnet to be tested, turn on the helium compressor to drive helium, open the main high-pressure valve and the main low-pressure valve, and the helium will circulate in the refrigeration cycle loop. The built-in purifier is connected in parallel at the inlet and outlet of the helium compressor. Open the first shut-off valve of the purification pipeline to adsorb non-condensable gases and impurities in the system. Open the second shut-off valve of the purification pipeline and the purity analyzer to detect the cleanliness of the helium in the system. When cleaning the circuit of the magnet under test, close the main high-pressure valve and the main low-pressure valve, close the first hot gas bypass valve, and open the second hot gas bypass valve and the third hot gas bypass valve. At this time, the helium compressor is connected to the circuit of the magnet under test, forming a circulation loop.

[0020] Optionally, the startup procedure of the supercritical helium cryogenic system includes: Before the experiment, the gas in the pipeline was purified. The chiller unit was turned on while the compressor was running to check its normal operation and ensure the cooling water flow rate met requirements. The inlet and outlet valves of the built-in purifier and the first and second shut-off valves of the purification pipeline were opened. The purity analyzer was started, and the helium compressor was started at the lowest pressure holding speed, driving the helium to circulate in a closed loop within the refrigeration cycle. Impurities were adsorbed by the built-in purifier until the purity analyzer detected that the helium purity met requirements. The purification pipeline valves were then closed, completing the system pre-purification. The helium compressor was temporarily stopped. The first and second air compressors were then turned on. The gas pressure required by the pneumatic valve is brought to the required level, the chiller continues to work, the cooling water flow rate is brought to the required level, the compressor is started, and the inlet and outlet valves, main high-pressure valve, main low-pressure valve, bypass valve, loading valve, and unloading valve of the helium compressor itself are opened. The unloading valve is kept at the preset opening degree to connect the refrigeration cycle loop. The gas in the first helium storage tank enters the compressor for circulation. Automatic control is activated during the process to control the outlet pressure of the helium compressor. At the beginning, the compressor runs at a low frequency. After the compressor runs stably, the set pressure is gradually increased until the outlet pressure and inlet pressure are stable at the preset values. The turbine expander is started and kept running at the preset speed. The sample circuit first shut-off valve, sample circuit second shut-off valve, helium recovery shut-off valve, inlet main valve, inlet first regulating valve, return first regulating valve, and return main valve of the magnet under test circuit are controlled. The first cryogenic fan is turned on and runs at a preset speed, while the second cryogenic fan is kept off. The pressure reducing pump and the first shut-off valve are turned on to connect the magnet under test circulation circuit and the helium charging and recovery system. The high-pressure helium in the second helium storage tank flows into the magnet under test circulation circuit and is charged into the circulation circuit after the pressure is stabilized by the pressure reducing pump. By adjusting the opening of the first regulating valve at the inlet and outlet of the magnet under test, the internal pressure of the magnet under test is gradually increased to a preset value at a preset rate. Then, the working intensity of the turbine expander is increased by a preset step size. After the helium gas is cooled by the three-stage heat exchanger and the temperature decreases after the turbine expander expands adiabatically, the cold-side inlet temperature of the intermediate heat exchanger steadily decreases to the target range at a preset rate. The sixth and tenth temperature sensors at the cold-side outlet of the intermediate heat exchanger collect the temperature difference between the two loops and control the cooling rate of the two loops to keep the temperature difference between the two loops less than the preset value. The operating mode and speed of the cryogenic fan are controlled according to the actual pressure drop of the magnet under test detected by the differential pressure transmitter. The control system collects the sample inlet and outlet temperature, pressure, pressure drop, and flow rate data in real time through sensors, and adjusts the speed of the turbine expander, the speed of the cryogenic fan, and the opening of each regulating valve in a coordinated manner to stabilize the sample temperature, inlet and outlet temperature difference, working pressure inside the magnet under test, and pressure drop at preset values. After the parameters stabilize, the system enters the fully automatic closed-loop control mode and begins the testing of the magnet under test.

[0021] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a supercritical helium cryogenic system and method for nuclear fusion strong field magnets, which has the following beneficial effects: The system described in this invention has a low temperature range of 4.5K to 30K, and can achieve an adjustable temperature supply of 4.5K to 30K according to the different operating temperatures of different magnets under test. The system matches the heat load of the magnet under test to achieve a flexible and adjustable cooling supply of 0% to 100% in the range of 0W to 2000W.

[0022] This invention sets up a distribution valve box and its corresponding internal measuring points. The distribution valve box reserves multiple sets of valve interfaces and measuring points such as temperature, pressure, differential pressure, and flow rate as expansion interfaces to prepare for the connection of multiple magnets to be tested, thereby improving the utilization rate of this helium cryogenic system and realizing the purpose of testing multiple magnets to be tested simultaneously. Furthermore, the electrical signals transmitted through the above measuring points are sent to the control system to achieve dynamic matching of cooling capacity and temperature control for the thermal load changes of each magnet to be tested.

[0023] The system of this invention can provide a test condition with a sample inlet and outlet temperature difference of <1K for the magnet under test. The temperature measurement point of the system adopts a Cernox™ sensor, which can achieve a temperature control accuracy of ±10mK within the temperature range of 4.5K~30K. A sample inlet and outlet temperature difference of <1K means that the supercritical helium temperature distribution flowing through the magnet is uniform, which can keep all parts of the magnet in a consistent low temperature environment, eliminate thermal stress caused by local temperature differences, avoid irreversible structural or performance damage to the superconducting cable, and greatly improve the reliability of the magnet testing process.

[0024] The cooling cycle circuit and the test magnet cycle circuit of this invention are independent of each other. The advantage of this is that it effectively avoids damage to the test magnet caused by pressure and temperature fluctuations in the cooling cycle circuit. The working pressure of the test magnet cycle circuit can be adjusted separately according to the different working conditions required by the test magnet, without being affected by the cooling cycle circuit. At the same time, the system adopts a cooling method in which the cooling system circuit cools the test magnet at the same time. During the cooling process, the temperature difference between the two is kept ≤50K to avoid thermal shock to the test magnet caused by excessive temperature difference.

[0025] The sample testing circuit of this invention uses two cryogenic fans connected in series to drive the flow of helium gas, providing a high driving capacity of >100kPa. Its advantages include the ability to select between a single-fan timed switching drive mode or a dual-fan drive mode based on the pressure drop of the magnet under test and the required volumetric flow rate. This reduces the operating energy consumption of the cryogenic fans, adapts to the resistance requirements of complex internal channels in multiple magnets under test, and improves the system's adaptability to different magnets. The single-fan timed switching drive mode allows the fans to alternately bear the workload and rotate into standby mode, avoiding excessive wear of local components caused by long-term continuous high-load operation of a single fan. This ensures that the wear rates of the two fans are consistent, significantly reducing the probability of premature failure of a single fan, extending the overall service life of the fan unit, and reducing the replacement cost of core equipment.

[0026] This system can provide a working pressure of ≥20 bara for the magnet under test. Its advantages are that, within the low temperature range of 4.5K to 30K, the higher working pressure can keep helium in a stable supercritical state and avoid gas-liquid phase transition; at the same time, it can improve the thermal conductivity and density of helium, allowing helium to more efficiently carry away the Joule heat generated by the operation of the magnet under test when flowing through the magnet sample, ensuring that the magnet under test is in a stable low temperature condition; the high working pressure of the test circuit has a stronger tolerance to external operating condition fluctuations, effectively absorbing small pressure fluctuations in the circuit and improving the reliability of the system's stable operation.

[0027] The helium recovery system of this invention utilizes the pressure difference between the second helium storage tank and the magnet under test as a driving force to charge the magnet under test with helium, and replenishes or recovers helium into the magnet under test according to the internal pressure of the magnet under test; after the sample test is completed, the helium in the sample test circuit can be recovered, with a recovery mass of about 17 kg per test, and a recovery rate of 90%, saving system operating costs; the second helium storage tank can serve as a pressure buffer area to avoid the impact of internal pressure fluctuations on the magnet under test.

[0028] The helium recovery system of this invention is further equipped with a booster pump and a depressurizer pump connected in parallel. The depressurizer pump reduces the high-pressure helium in the second helium storage tank to the working pressure required by the magnet under test and injects it into the magnet. The booster pump increases the low-pressure helium in the magnet under test to the design pressure of the helium storage tank and injects it into the tank. The setup of the booster pump and the depressurizer pump reduces the volume of the second helium storage tank to 4m³. Correspondingly, the installation area of ​​the second helium storage tank is greatly reduced, saving space for the overall layout of the system.

[0029] This invention adds a hot gas bypass pipeline, regulating valve, and electric heater. High-pressure helium enters the low-pressure, low-temperature helium pipeline and heats it, effectively utilizing the waste heat of the helium compressor, reducing system operating energy consumption, achieving rapid system rewarming, and significantly reducing the duration of a single test.

[0030] This invention also includes a built-in purifier and a purity analyzer. Before testing, the corresponding valves are opened, and helium is driven by a helium compressor to circulate in the system. The built-in purifier absorbs gaseous impurities in the system, ensuring the cleanliness of the system, improving refrigeration efficiency, and ensuring the normal operation of the system. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0032] Figure 1 This invention provides a flowchart of a supercritical helium cryogenic system for a nuclear fusion strong field magnet.

[0033] Figure 2 This invention provides a monitoring point diagram for a supercritical helium cryogenic system used in a nuclear fusion strong field magnet.

[0034] Among them, 1-Helium compressor; 2-Oil filter; 3-Cold trap; 4-First heat exchanger; 5-Second heat exchanger; 6-Third heat exchanger; 7-Turbine expander; 8-Electric heater; 9-Intermediate heat exchanger; 10-Distribution valve box; 11-First cryogenic fan; 12-Second cryogenic fan; 13-Built-in purifier; 14-Purity analyzer; 15-First helium storage tank; 16-Chiller; 17-First air compressor; 18-First electromagnetic reversing valve; 19-Unloading valve; 20-Loading valve; 21-Bypass valve; 22-Test magnet; 23-External purifier; 24-Ambient vaporizer; 25-Second helium storage tank; 26-Throttle expansion valve; 27-Storage tank manual valve; 28-Second air compressor; 29-Second electromagnetic reversing valve. Valves; 30-Boost pump; 31-Pressure reducing pump; 32-First shut-off valve; 33-Second shut-off valve; 34-First check valve; 35-Second check valve; 101-Main line high-pressure valve; 102-Main line low-pressure valve; 103-Purification pipeline first shut-off valve; 104-Purification pipeline second shut-off valve; 105-First hot gas bypass valve; 106-Second hot gas bypass valve; 107-Third hot gas bypass valve; 108-Sample circuit first shut-off valve; 109-Sample circuit second shut-off valve; 110-Helium recovery shut-off valve; 111-Inlet main valve; 112-Inlet first regulating valve; 113-Return port first regulating valve; 114-Return port main valve; 115-Electronic pressure regulating valve; 116-First fan bypass valve; 117-Second fan bypass valve Valves; 118-Third fan bypass valve; 119-Fourth fan bypass valve; 201-High-pressure helium pipeline; 202-Low-pressure helium pipeline; 203-Loading / unloading pipeline; 204-Bypass pipeline; 205-Hot gas bypass main pipeline; 206-Hot gas bypass first branch pipeline; 207-Hot gas bypass second branch pipeline; 208-Hot gas bypass loop pipeline; 209-Distribution valve box outlet first branch pipeline; 210-Distribution valve box outlet second branch pipeline; 211-Cold shield branch pipeline; 212-Inlet first branch pipeline; 213-Return outlet first branch pipeline; 301-First pressure sensor; 302-Second pressure sensor; 303-Third pressure sensor; 304-Fourth pressure sensor; 305-Fifth pressure sensor Sensors; 306 - Sixth pressure sensor; 307 - Seventh pressure sensor; 308 - Eighth pressure sensor; 309 - Ninth pressure sensor; 310 - Tenth pressure sensor; 311 - Eleventh pressure sensor; 312 - Twelfth pressure sensor; 401 - First temperature sensor; 402 - Second temperature sensor; 403 - Third temperature sensor; 404 - Fourth temperature sensor; 405 - Fifth temperature sensor; 406 - Sixth temperature sensor; 407 - Seventh temperature sensor; 408 - Eighth temperature sensor; 409 - Ninth temperature sensor; 410 - Tenth temperature sensor; 411 - Eleventh temperature sensor; 412 - Twelfth temperature sensor; 413 - Thirteenth temperature sensor;414 - Fourteenth temperature sensor; 415 - Fifteenth temperature sensor; 501 - Flow meter; 502 - Differential pressure transmitter. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] To address the problems of existing technologies, such as the significant impact of pressure fluctuations on the operating conditions of the magnet under test due to a single circulation loop, low efficiency, poor scalability, and inability to recover helium, this invention aims to provide a supercritical helium cryogenic system for nuclear fusion high-field magnets. This system can achieve dynamic matching of temperature and cooling capacity according to the load of the magnet under test. The system employs a dual helium circulation loop with independent cooling and magnet under test circulation loops. Compared to existing single circulation loops, this effectively avoids damage to the magnet under test caused by pressure and temperature fluctuations in the cooling circulation loop; the working pressure of the magnet under test circulation loop can be adjusted independently according to the different operating conditions required by the magnet under test, unaffected by the cooling circulation loop; and the magnet under test circulation loop uses two cryogenic fans connected in series. The driving method offers the advantage of allowing selection of either a single or dual cryogenic fan based on the pressure drop of the magnet under test and the required volumetric flow rate. A helium purification and recovery system is included to recover helium from the sample testing circuit, saving on sample testing costs. A second helium storage tank serves as a pressure buffer zone, preventing internal pressure fluctuations from impacting the magnet under test. A distribution valve box and its control system are added to expand testing to multiple magnets under test, enabling simultaneous testing of multiple magnets and achieving cooling capacity matching and temperature regulation based on the different heat loads of the magnets under test. A hot gas bypass and electric heater are added to effectively utilize the waste heat from the helium compressor, reducing system energy consumption and achieving rapid system rewarming, significantly reducing the duration of a single test.

[0037] This invention discloses a supercritical helium cryogenic system for strong-field magnets in nuclear fusion, such as... Figure 1 As shown, the specific structure includes: The outlet of helium compressor 1 is connected to the inlet of oil filter 2; the outlet of oil filter 2 is connected to the inlet of cold trap 3; the outlet of cold trap 3 is connected to the hot-side inlet of the first heat exchanger 4; the hot-side outlet of the first heat exchanger 4 is connected to the hot-side inlet of the second heat exchanger 5; the hot-side outlet of the second heat exchanger 5 is connected to the hot-side inlet of the third heat exchanger 6; the hot-side outlet of the third heat exchanger 6 is connected to the inlet of turbine expander 7; the outlet of turbine expander 7 is connected to the inlet of electric heater 8; the outlet of electric heater 8 is connected to the cold-side inlet of intermediate heat exchanger 9; the cold-side outlet of intermediate heat exchanger 9 is connected to the cold-side inlet of the third heat exchanger 6; and the cold-side outlet of the third heat exchanger 6 is connected to the inlet of the second heat exchanger 4. The cold-side inlet of the second heat exchanger 5 is connected to the cold-side inlet of the first heat exchanger 4, and the cold-side outlet of the first heat exchanger 4 is connected to the inlet of the helium compressor 1. The hot-side outlet of the intermediate heat exchanger 9 is connected to the inlet of the distribution valve box 10, the first outlet of the distribution valve box 10 is connected to the inlet of the magnet under test 22, the outlet of the magnet under test 22 is connected to the first return port of the distribution valve box 10, the first branch pipeline 209 of the distribution valve box outlet is connected to the inlet of the first cryogenic fan 11, the outlet of the first cryogenic fan 11 is connected to the inlet of the second cryogenic fan 12, and the outlet of the second cryogenic fan 12 is connected to the hot-side inlet of the intermediate heat exchanger 9.

[0038] Electronic pressure regulating valve 115 is connected in parallel to the inlet and outlet of the second shut-off valve 109 in the sample circuit. First fan bypass valve 116 is connected to the inlet of the first cryogenic fan 11. Fourth fan bypass valve 119 is connected to the inlet of the second cryogenic fan 12. Third fan bypass valve 118 is connected in parallel before the inlet of the first fan bypass valve 116 and at the outlet of the first cryogenic fan 11. Second fan bypass valve 117 is connected in parallel at the inlet of the fourth fan bypass valve 119 and at the outlet of the second cryogenic fan 12.

[0039] The inlet and outlet of the chiller 16 are connected to the inlet and outlet of the water-oil heat exchanger inside the helium compressor 1.

[0040] The first air compressor 17 is connected to the first solenoid directional valve 18. The first outlet of the first solenoid directional valve 18 is connected to the pneumatic actuator of the unloading valve 19. The second outlet of the first solenoid directional valve 18 is connected to the pneumatic actuator of the loading valve 20. The third outlet of the first solenoid directional valve 18 is connected to the pneumatic actuator of the bypass valve 21.

[0041] The second air compressor 28 is connected to the second solenoid directional valve 29. The first outlet of the second solenoid directional valve 29 is connected to the pneumatic actuator of the inlet main valve 111. The second outlet of the second solenoid directional valve 29 is connected to the pneumatic actuator of the inlet first regulating valve 112. The third outlet of the second solenoid directional valve 29 is connected to the pneumatic actuator of the return main valve 114. The fourth outlet of the second solenoid directional valve 29 is connected to the pneumatic actuator of the return first regulating valve 113.

[0042] It also includes pressure sensors and temperature sensors installed in the refrigeration cycle loop, the magnet under test cycle loop, and the helium charging and recovery pipeline, specifically including: The following sensors are installed: a first pressure sensor 301 and a first temperature sensor 401 at the outlet of helium compressor 1; a second temperature sensor 402 at the hot-side outlet of the first heat exchanger 4; a third temperature sensor 403 at the hot-side outlet 5 of the second heat exchanger; a second pressure sensor 302 and a fourth temperature sensor 404 at the hot-side outlet of the third heat exchanger; a third pressure sensor 303 and a fifth temperature sensor 405 at the cold-side inlet of the intermediate heat exchanger 9; a fourth pressure sensor 304 and a sixth temperature sensor 406 at the cold-side outlet of the intermediate heat exchanger 9; a seventh temperature sensor 407 at the cold-side outlet of the third heat exchanger 6; an eighth temperature sensor 408 at the cold-side outlet of the second heat exchanger 5; and a fifth pressure sensor 305 and a ninth temperature sensor 406 at the inlet of helium compressor 1. Temperature sensor 409; sixth pressure sensor 306 and tenth temperature sensor 410 installed at the hot side outlet of intermediate heat exchanger 9; seventh pressure sensor 307 and eleventh temperature sensor 411 installed at the inlet first branch pipeline 212 inside the distribution valve box 10; eighth pressure sensor 308 and twelfth temperature sensor 412 installed on the return first branch pipeline 213; ninth pressure sensor 309 and thirteenth temperature sensor 413 installed at the outlet of distribution valve box 10; tenth pressure sensor 310 installed at the outlet of first low temperature fan 11; eleventh pressure sensor 311 and fourteenth temperature sensor 414 installed at the outlet of second low temperature fan 12; twelfth pressure sensor 312 and fifteenth temperature sensor 415 installed at the outlet of ambient temperature vaporizer 24.

[0043] The supercritical helium cryogenic system also includes a flow meter 501 installed at the outlet of the magnet under test 22, and a differential pressure transmitter 502 connected in parallel to the inlet and outlet of the magnet under test 22.

[0044] Furthermore, the values ​​of the measuring points located at the seventh pressure sensor 307, the eighth pressure sensor 308, the eleventh temperature sensor 411, the twelfth temperature sensor 412, the flow meter 501, and the differential pressure transmitter 502 are transmitted to the control system via electrical signals, thereby realizing the control of the helium compressor 1, the turbine expander 7, the first cryogenic fan 11, the second cryogenic fan 12, the inlet first regulating valve 112, and the return first regulating valve 113.

[0045] In Example 1, taking a single magnet under test and the rated operating conditions of the superfluid helium refrigeration system (operating temperature 20K, operating pressure 20bar, and cooling capacity 1050W) as an example, the process and characteristics are described as follows: After the helium compressor 1 is turned on, it draws in helium from the low-pressure helium pipeline 202, pressurizes it to form a high-temperature, high-pressure gas of 1.5 MPa and 800 K. After being cooled to 310 K by the cooling water supplied by the chiller 16, the high-temperature, high-pressure helium passes through the cold trap 3 to remove impurities from the helium, preventing impurities from entering the turbine expander 7 and causing damage or reducing refrigeration efficiency. After exiting the cold trap 3, it enters the hot-side inlet of the first heat exchanger 4, where the helium being returned from the cold side is cooled from 310 K to 150 K. After passing through the hot-side inlet of the second heat exchanger 5, the helium being returned from the cold side is cooled to 80 K. After passing through the hot-side inlet of the third heat exchanger 6, the helium is cooled from 310 K to 150 K. The inlet helium gas is cooled to 23K by the recirculated helium gas, and then adiabatically expanded to 0.2MPa and 14.55K by the turbine expander 7. At this point, the throttling expansion valve 26 closes, and the gas then enters the intermediate heat exchanger 9 to exchange heat with the helium gas that has been cooled and reheated by the magnet 22 under test. Next, it enters the cold-side inlet of the third heat exchanger 6 to exchange heat with the hot-side helium gas, reaching a temperature of 80K. Then, it enters the cold-side inlet of the second heat exchanger 5 to exchange heat with the high-pressure side helium gas, reaching a temperature of 150K. Finally, it enters the cold-side inlet of the first heat exchanger 4 to exchange heat with the high-pressure side helium gas, reaching a temperature of 310K. It is then drawn back into the helium compressor 1 for pressurization, entering the next cycle. The first helium storage tank 15, along with the loading valve 20, unloading valve 19, and bypass valve 21, maintains stable inlet and outlet pressures of the helium compressor 1.

[0046] Specifically, in this embodiment: The outlet pressure of helium compressor 1 should be maintained at 1.5 MPa, and the inlet pressure should be maintained at 0.2 MPa. Unloading valve 19 connects the high-pressure outlet of helium compressor 1 to the first helium storage tank 15. When the high-pressure is higher than the set pressure, unloading valve 19 opens, and helium in the high-pressure helium pipeline 201 returns to the first helium storage tank 15. Loading valve 20 connects the low-pressure inlet of helium compressor 1 to the first helium storage tank 15. When the outlet pressure of helium compressor 1 is lower than the set pressure, loading valve 20 opens, and helium in the first helium storage tank 15 enters the low-pressure helium pipeline 202. Bypass valve 21 connects the high-pressure helium pipeline 201 and the low-pressure helium pipeline 202 to regulate the pressure of the low-pressure helium pipeline 202. When the low pressure is lower than the set value, the opening of bypass valve 21 increases; when the low pressure is higher than the set value, the opening of bypass valve 21 decreases. The specific control algorithm is as follows: the actual outlet pressure of helium compressor 1 is represented by P... 出 The outlet pressure setpoint is represented by P, which is measured by the first pressure sensor 301. 出sp This indicates that P is set. 出sp =1.5 MPa, when P 出 >P 出sp When P is open, unloading valve 19 opens and loading valve 20 closes. 出 <P 出sp At that time, loading valve 20 opens and unloading valve 19 closes; the actual inlet pressure of helium compressor 1 is represented by P. 进This indicates that the inlet pressure setpoint is measured by the fifth pressure sensor 305. 进sp This indicates that P is set. 进sp =0.2 MPa, when P 进 >P 进sp When P 进 <P 进sp At that time, the bypass valve 21 increases its opening degree.

[0047] The first cryogenic fan 11 and the second cryogenic fan 12 drive the flow of helium in the circuit of the magnet under test 22. The series-connected cryogenic fans sequentially draw in helium gas at 20K and 0.2MPa after heat exchange with the magnet under test 22, pressurize it to 0.21MPa, and enter the intermediate heat exchanger 9 to exchange heat with the cryogenic helium gas in the refrigeration cycle and cool it to 18.92K. Then, it enters the inlet of the magnet under test 22 through the distribution valve box 10. At this time, the temperature of the helium gas is 19K and the pressure is 0.21MPa, which cools the magnet under test 22, raises the temperature to 20K and reduces the pressure to 0.2MPa, and is drawn in again by the series-connected cryogenic fans to start the next cycle.

[0048] In the above process, the first air compressor 17 provides compressed air to the unloading valve 19, loading valve 20, and bypass valve 21 to drive the valve actuators and adjust the high and low pressure of the system. The second air compressor 28 provides air to the inlet main valve 111, inlet first regulating valve 112, return first regulating valve 113, and return main valve 114 to drive the valves to adjust their opening. The aforementioned loading valve 20, unloading valve 19, bypass valve 21, inlet main valve 111, inlet first regulating valve 112, return first regulating valve 113, and return main valve 114 are all pneumatic valves and are equipped with pneumatic actuators. This mechanism is the core of the valve's operation. The 0.6~0.8MPa high-pressure compressed air generated by the first air compressor 17 is its power source. The electrical signal output by the PLC control system is the control command. The air circuit is opened and closed and reversed through the first solenoid directional valve 18 and the second solenoid directional valve 29, which in turn drives the cylinder piston of the pneumatic actuator to move. The piston links the valve stem of the valve to complete the opening and closing action or continuous adjustment of the opening degree.

[0049] In the control system, the eleventh temperature sensor 411 at the inlet of the magnet under test 22 is set to 19K, and the twelfth temperature sensor 412 at the outlet is set to 20K. The difference between the two is set to 1K. When the actual measured temperature of the helium gas at the outlet is higher than the set value of 20K, the electrical signal of the eleventh temperature sensor 411 is transmitted to the control system to adjust the speed of the helium compressor 1 and the turbine expander 7, so as to achieve temperature control of the magnet under test 22.

[0050] The specific control process is as follows: The target inlet temperature T of the magnet to be tested 22 is preset in the control system. 磁进sp =19K, Target outlet temperature T磁出sp =20K, and the inlet and outlet temperature difference setpoint ΔT sp <1K; Set the temperature deviation threshold ΔT0 = ±10mK, and the temperature overshoot warning value ΔT1 = 0.5K. The actual inlet temperature T is collected at a frequency of 100ms / time through the eleventh temperature sensor 411 at the sample inlet and the twelfth temperature sensor 412 at the outlet. 磁进 Actual outlet temperature T 磁出 Set the inlet temperature deviation ΔT1'=T 磁进 -T 磁进sp , Outlet temperature deviation ΔT2'=T 磁出 -T 磁出sp The actual temperature difference between the inlet and outlet is ΔT'=T 磁出 -T 磁进 If |ΔT1'|≤ΔT0 and |ΔT2'|≤ΔT0, then keep the current speed of the turbine expander 7 unchanged; if ΔT1'>ΔT0 (inlet temperature is too high), increase the speed of the turbine expander 7 in steps of 50 rpm / cycle until ΔT1' returns to the range of ΔT; if ΔT1'<-ΔT0 (inlet temperature is too low), decrease the speed of the turbine expander 7 in the same step; if ΔT'>ΔT sp If the temperature difference between the inlet and outlet exceeds the threshold, the speed of the low-temperature fan will be adjusted accordingly, and the helium flow rate will be reduced to prolong the heat exchange time.

[0051] The required helium mass flow rate m is calculated based on the actual heat load Q of the magnet under test 22 and the set inlet and outlet temperature difference ΔT'. The electrical signal from the flow meter 501 is transmitted to the control system, which adjusts the speed of the helium compressor 1 to regulate the helium mass flow rate in the refrigeration cycle, thereby adjusting the supplied refrigeration capacity. The target refrigeration capacity of the magnet under test 22 is preset in the control system, corresponding to the mass flow rate m. sp The actual mass flow rate measured by flow meter 501 is m. If m = m sp If m < m sp At that time, increase the speed of helium compressor 1 by 2% per cycle, and simultaneously increase the opening of the inlet first regulating valve 112 and the return first regulating valve 113; if m > m sp At the same time, the speed of helium compressor 1 is reduced by the same percentage, and the opening of the inlet first regulating valve 112 and the return first regulating valve 113 is reduced.

[0052] Pressure and temperature sensors installed in the refrigeration cycle loop, the test magnet cycle loop, and the helium charging and recovery pipeline detect the temperature and pressure at the inlet and outlet of key equipment, reflecting the state of helium in the flow channels at each stage of the system in real time.

[0053] In summary, by controlling the rotational speeds of the helium compressor 1 and the turbine expander 7, this implementation method allows for the dynamic matching of the superfluid helium refrigeration system with the heat load of the magnet under test 22 (0W~2000W) and temperature (15K~30K), thereby achieving stable system operation. This ensures that the magnet under test 22 remains under stable operating conditions, preventing damage from thermal shock and ensuring the effectiveness of the test.

[0054] In Example 2, based on Example 1, as follows: Figure 2 As shown, it also includes: A throttling expansion valve 26, connected in parallel to the outlet of the turbine expander 7 and the outlet of the electric heater 8, is opened. Low-temperature, low-pressure helium gas from the outlet of the turbine expander 7 enters the throttling expansion valve 26, which further adiabatically expands the helium gas to obtain 4K low-temperature helium gas. This helium gas is used to cool the helium gas in the circulation loop of the magnet under test 22, thus providing a 4.5K low-temperature testing environment for the magnet under test 22. The control and adjustment method in this example is the same as in Example 1, enabling the magnet under test 22 to receive 0W~650W of cooling capacity and operate at 4.5K~15K.

[0055] In Example 3, based on Examples 1 and 2, a helium recovery shut-off valve 110, an external purifier 23, a second helium storage tank 25, a storage tank manual valve 27, a twelfth pressure sensor 312, and a fifteenth temperature sensor 415 are also provided.

[0056] Specifically, the external purifier 23 is connected to the second branch pipeline 210 at the outlet of the inlet distribution valve box, the outlet of the external purifier 23 is connected to the inlet of the ambient air vaporizer 24, and the outlet of the ambient air vaporizer 24 is connected to the interface of the second helium storage tank 25.

[0057] In summary, the helium filling and recovery process of this system is described as follows: The second helium storage tank 25 is pre-filled with helium at a pressure of 25 MPa. The storage tank manual valve 27 is opened, the second shut-off valve 33 is opened, the helium recovery shut-off valve 110 is opened, and the pressure reducing pump 31 is started. At this time, the high-pressure helium in the second helium storage tank 25 flows to the magnet under test 22. After passing through the pressure reducing pump 31, the outlet pressure setting value of the pressure reducing pump 31 is set to the working pressure inside the magnet under test 22 to avoid the impact of high-pressure helium on the magnet under test 22. The helium is continuously output at a stable pressure. As the temperature of the circuit of the magnet under test 22 decreases, the second helium storage tank 25 continues to replenish it until it stabilizes within the working pressure range required by the magnet under test 22. Then, the filling is stopped, and the storage tank manual valve 27 and the helium recovery shut-off valve 110 are closed. After the test of the magnet 22 is completed, the helium expands due to heating. At this time, the helium recovery shut-off valve 110 and the storage tank manual valve 27 remain open. The booster pump 30 is turned on, and the first shut-off valve 32 is opened. The expanded helium enters the booster pump 30 through the helium recovery pipeline. The outlet pressure setpoint of the booster pump 30 is set to the working pressure of the second helium storage tank 25. After being pressurized, the helium passes through the external purifier 23 to remove impurities, and then passes through the ambient temperature vaporizer 24 to be restored to room temperature (300K) before entering the second helium storage tank 25 for storage. This avoids low-temperature shock to the second helium storage tank 25 and reduces damage to the helium storage tank. When the pressure inside the magnet 22 returns to atmospheric pressure, the storage tank manual valve 27 and the helium recovery shut-off valve 110 are turned off. After the system returns to room temperature, the helium compressor 1 is turned off, and the inlet main valve 111 and return main valve 114 in the distribution valve box 10 are closed. The magnet 22 is then removed. The recovered helium can be reused after purification and reheating. Under the nominal operating conditions of 20K / 1050W, each test recovers approximately 17kg of helium, achieving a recovery rate of 90.85%, which saves on system operating costs. The addition of booster and depressurizer pumps effectively converts helium into storage methods with different pressures, effectively reducing the volume of the second helium storage tank 25, thereby reducing the footprint of the second helium storage tank.

[0058] The above embodiment is illustrated using the example of the magnet under test 22 requiring 20 bara. If the working pressure required by the magnet under test 22 is greater than 20 bara, a higher working pressure can be obtained by simply setting the outlet pressure of the pressure reducing pump 31 and filling the magnet under test 22 with helium.

[0059] In Example 4, based on Examples 1 and 2, a distribution valve box 10 is also provided, which contains inlet and outlet main valves and inlet and outlet branch valves. An interface is reserved for expanding the testing of the magnets under test, allowing for simultaneous testing of multiple samples and adjustment of the cooling capacity allocated to each sample. Similar to Example 1, all inlet and outlet of the receiving magnets 22 are equipped with pressure sensors, temperature sensors, and flow meters. The control method is the same as in Example 1 and will not be described in detail here. A cold shield branch pipeline 211, led from the outlet of the second heat exchanger 5, connects to the interlayer of the distribution valve box 10 to form an 80K cold shield, effectively reducing heat loss caused by heat conduction and radiation between the 4.5K~30K low-temperature helium gas inside the distribution valve box 10 and the ambient temperature air.

[0060] In Example 5, based on Examples 1 and 2, the first cryogenic fan 11 and the second cryogenic fan 12 are connected in series. The cryogenic fans are of the same model, and the single-unit speed adjustment range of the cryogenic fan is 9000rpm / min~18000rpm / min. The maximum pressure boost of a single fan can reach 85kPa, thereby enabling the test magnet circulation loop to have a driving capability of ≥100kPa. The seventh pressure sensor 307, the eighth pressure sensor 308, and the differential pressure transmitter 502 set at the inlet and outlet of the test magnet 22 are converted into electrical signals. The electrical signals are transmitted to the control system, which reversely adjusts the operating mode and speed of the cryogenic fan to achieve the control of the cryogenic fan speed, single-unit switching drive, and dual-unit drive modes according to the internal pressure drop and load of the sample, dynamically matching the test requirements.

[0061] Since the optimal boosting capacity range for a single fan is 25kPa to 85kPa, the following control modes are set according to different pressure drops corresponding to the boosting capacity range: Mode 1: When the actual pressure drop ΔP of the magnet under test 22 is greater than 50 kPa, the first low-temperature fan 11 and the second low-temperature fan 12 operate simultaneously. The two fans overcome half of the total pressure drop respectively. At this time, the second shut-off valve 109 of the sample circuit is opened, and the low-temperature helium gas does not pass through the electronic pressure regulating valve. Mode 2: When the actual pressure drop of the magnet under test 22 is 25 kPa < ΔP ≤ 50 kPa, the start and stop of the fans are controlled according to the running time of a single fan, and the switching is based on the running time of a single fan T = 200 hours. When the first low-temperature fan 11 is running, the first fan bypass valve 116 and the second fan bypass valve 117 remain open, while the third fan bypass valve 118 and the fourth fan bypass valve 119 remain closed. The low-temperature helium gas from the distribution valve box 10 exits through the second shut-off valve 109 of the sample circuit, passes through the first fan bypass valve 116, enters the inlet of the first low-temperature fan 11, is pressurized by the first low-temperature fan 11, exits through the outlet, and then enters the hot side inlet of the intermediate heat exchanger 9 through the second fan bypass valve 117. When the first low-temperature fan is running... After 200 hours, the second cryogenic fan 12 starts running. At this time, the third fan bypass valve 118 and the fourth fan bypass valve 119 remain open, while the first fan bypass valve 116 and the second fan bypass valve 117 remain closed. The cryogenic helium gas from the distribution valve box 10 exits through the second shut-off valve 109 of the sample circuit, passes through the third fan bypass valve 118, and then through the fourth fan bypass valve 119 before entering the second cryogenic fan 12. After being pressurized, the gas is ejected from the outlet of the second cryogenic fan 12 and enters the hot side inlet of the intermediate heat exchanger 9. Mode 3: When the actual pressure drop of the magnet under test 22 is 0 kPa < ΔP ≤ 25 kPa, the second shut-off valve 109 of the sample circuit is closed, and the outlet pressure of the electronic pressure regulating valve 115 is set to stabilize at 25 kPa. The cryogenic helium gas coming out of the distribution valve box 10 passes through the electronic pressure regulating valve 115 and is pressurized to 25 kPa. As in Mode 2, it enters the running cryogenic fan according to the running time of the cryogenic fan.

[0062] The specific control algorithm is as follows: Taking the working pressure of the magnet under test 22 as 20 bar and the actual pressure drop inside the magnet as 1 bar as an example: The control system selects different fan operating modes based on the actual pressure drop of the magnet under test. Under the corresponding pressure drop fan operating mode, the seventh pressure sensor 307 and the eighth pressure sensor 308 collect the actual inlet pressure Pmagnetic in and the actual outlet pressure Pmagnetic out of the magnet under test 22 at a frequency of 100ms / time. The differential pressure transmitter 502 detects the actual pressure drop ΔP of the magnet under test 22. If the actual pressure drop ΔP < the target pressure drop, the control system reduces the fan speed by a phase length of 500rpm / time until the actual pressure drop returns to the target range, while ensuring that the magnet outlet pressure is not lower than 20bar. If the actual pressure drop ΔP > the target pressure drop, the control system increases the fan speed by a phase length of 500rpm / time until the pressure drop reaches the target. If the magnet inlet pressure > the target inlet pressure, the fan speed is immediately reduced. If the outlet pressure < the target outlet pressure, the fan speed is immediately increased to ensure that the magnet is always under the set working pressure, and the pressure deviation is controlled within ±0.1bar.

[0063] The difference between Mode 2 and Mode 3 is the switching control of a single fan: If the currently running fan has reached a 200-hour rotation cycle, the fan switching process maintains a synchronous and gradual change in speed and pressure fluctuation ≤ ±0.2 bar: The standby fan is pre-started at 30% of the base speed, the standby bypass valve group is in the ready-to-open state, the currently running fan decreases speed by 500 rpm / time, and the standby fan increases speed by 500 rpm / time until the speeds of the two fans are the same, the bypass valve group of the current fan is closed and the bypass valve group of the standby fan is opened to complete the air path switching. After the switching, the PLC makes precise fine adjustments to the standby fan within ±500 rpm based on the real-time pressure drop, and quickly returns to steady state.

[0064] In Example 6, based on Examples 1 and 2, the refrigeration cycle system consists of a refrigeration cycle loop and a test magnet cycle loop. The two loops are independent of each other and transfer cold energy through the intermediate heat exchanger 9. In this invention, the refrigeration cycle loop drives the test magnet cycle loop to cool down simultaneously. During the cooling process, the maximum temperature difference between the two loops is kept ≤50K. The temperatures measured by the sixth temperature sensor 406 located at the cold side outlet of the intermediate heat exchanger 9 and the tenth temperature sensor 410 located at the hot side outlet of the intermediate heat exchanger 9 are converted into electrical signals and transmitted to the control system. By calculating the difference between the sixth temperature sensor 406 and the tenth temperature sensor 410, the helium mass flow rate of the two loops is controlled, so that the temperature difference between the two loops in the intermediate heat exchanger 9 is ≤50K.

[0065] The specific control algorithm is as follows: the actual temperature T of the refrigeration circuit is collected by the sixth temperature sensor 406 at the cold side outlet of the intermediate heat exchanger 9. a The actual temperature T of the sample circuit is collected by the tenth temperature sensor 410 at the hot side outlet of the intermediate heat exchanger 9. b The sampling frequency is 200ms / time, and the actual temperature difference ΔT between the two loops is calculated. 双 =|T a -T b |. If ΔT 双 ≤50K, keep the helium flow rate in the dual-loop system constant; if ΔT 双 >50K, adjust the helium mass flow rate of the cooling circuit and the sample circuit. The flow rate of the cooling circuit is achieved by adjusting the speed of the helium compressor 1, and the flow rate of the sample circuit is achieved by adjusting the opening of the first regulating valve 112 at the inlet, until ΔT 双 ≤50K.

[0066] In Example 7, based on Example 1, as follows: Figure 1 and Figure 2 As shown, it also includes: The system includes a built-in purifier 13, a purity analyzer 14, a first shut-off valve 103 for the purification pipeline, and a second shut-off valve 104 for the purification pipeline. Specifically, the built-in purifier 13 is connected in parallel to the high-pressure helium pipeline 201 and the low-pressure helium pipeline 202. The inlet of the built-in purifier 13 is connected to the high-pressure helium pipeline 201. The inlet and outlet of the built-in purifier 13 are connected in parallel to the purity analyzer 14. The inlet of the purity analyzer 14 is connected to the inlet of the built-in purifier 13, and the outlet of the purity analyzer 14 is connected to the outlet of the built-in purifier 13. The first shut-off valve 103 for the purification pipeline is installed on the pipeline before the inlet of the built-in purifier 13, and the second shut-off valve 104 for the purification pipeline is installed before the inlet of the purity analyzer 14.

[0067] In summary, the system cleaning process of this invention is described as follows: Before sample testing, helium compressor 1 is turned on to drive helium, and main high-pressure valve 101 and main low-pressure valve 102 are opened. Helium circulates in the refrigeration loop. Built-in purifier 13 is connected in parallel to the inlet and outlet of helium compressor 1. First shut-off valve 103 of the purification pipeline is opened to adsorb non-condensable gases and impurities in the system. Second shut-off valve 104 of the purification pipeline and purity analyzer 14 are opened to detect the cleanliness of helium in the system. When cleaning the circuit of magnet 22 under test, main high-pressure valve 101 and main low-pressure valve 102 are closed, first hot gas bypass valve 105 is closed, and second hot gas bypass valve 106 and third hot gas bypass valve 107 are opened. At this time, helium compressor 1 is connected to the circuit of magnet 22 under test, forming a circulation loop.

[0068] The aforementioned circulation loop includes: the outlet of helium compressor 1 is connected to high-pressure helium pipeline 201; high-pressure helium pipeline 201 is connected in series with oil filter 2 and cold trap 3 and is connected to hot gas bypass main pipeline; at this time, main high-pressure valve 101 and first hot gas bypass valve 105 are closed; helium passes through hot gas bypass second branch pipeline 207; hot gas bypass second branch pipeline 207 is connected to the inlet of distribution valve box 10; distribution valve box 10 is equipped with inlet main valve 111; inlet main valve 111 is connected to inlet first branch pipeline 212; inlet first branch pipeline 212... Line 12 is connected to the inlet of the magnet under test 22. The outlet of the magnet under test 22 is connected to the first branch line 213 of the return port. The first branch line 213 of the return port is connected to the main return valve 114 installed in the distribution valve box. The main return valve 114 is connected to the outlet of the distribution valve box. The second branch line 210 of the outlet of the distribution valve box is connected to the hot gas bypass loop line 208. The hot gas bypass loop line 208 is connected to the low-pressure helium line 202. At this time, the main low-pressure valve 102 is closed, and helium enters the inlet of the helium compressor 1 through the low-pressure helium line 202. The built-in purifier 13 and purity analyzer 14 have the same function as described above.

[0069] Once the cleaning process is complete, the formal cooling mode can be turned on.

[0070] In Example 8, based on Example 1, a hot gas bypass main pipeline 205, a hot gas bypass first branch pipeline 206, a hot gas bypass second branch pipeline 207, a hot gas bypass loop pipeline 208, a first hot gas bypass valve 105, a second hot gas bypass valve 106, and a third hot gas bypass valve 107 are also provided.

[0071] Specifically, the hot gas bypass main line 205 is connected to the high-pressure helium pipeline 201. The connection point between the hot gas bypass main line 205 and the high-pressure helium pipeline 201 is located at the outlet of the cold trap 3. The hot gas bypass main line 205 is divided into a first hot gas bypass branch line 206 and a second hot gas bypass branch line 207. The first hot gas bypass branch line 206 is connected to the low-pressure helium pipeline 202. The interface is located at the outlet of the intermediate heat exchanger 9. The hot gas bypass second branch pipeline 207 is connected to the hot side outlet of the intermediate heat exchanger 9 of the circuit of the magnet under test 22. One end of the hot gas bypass loop pipeline 208 is connected to the outlet second branch pipeline of the distribution valve box 10. The other end of the hot gas bypass loop pipeline 208 is connected to the low-pressure helium pipeline 202. The connection between the other end of the hot gas bypass loop pipeline 208 and the low-pressure helium pipeline 202 is located at the inlet of the helium compressor 1.

[0072] In summary, the rapid rewarming process of this system is described as follows: Open the first hot gas bypass valve 105, the second hot gas bypass valve 106, and the third hot gas bypass valve 107, and turn on the electric heater 8. High-temperature and high-pressure helium gas enters the cold side of the third heat exchanger 6, the cold side of the second heat exchanger 5, and the cold side of the first heat exchanger 4 through the first branch pipeline 206 of the hot gas bypass, so as to quickly reheat the helium gas in the refrigeration cycle system. Another part of the helium gas enters the circulation loop of the magnet under test 22 through the second branch pipeline 207 of the hot gas bypass, so as to heat the helium gas in the loop and the magnet under test 22.

[0073] In this embodiment, the high-temperature and high-pressure helium gas discharged from the helium compressor 1 is used to heat and rewarm the refrigeration cycle circuit and the test magnet cycle circuit, which reduces the energy consumption of the system, significantly reduces the system rewarming time, and improves the efficiency of sample testing.

[0074] Example 9 details the startup procedure of the supercritical helium cryogenic system: Before the system is first started, the pipeline must contain high-purity helium. Therefore, before the experiment begins, the gas in the pipeline needs to be purified. Turn on the chiller unit while the compressor is running, check if the chiller unit is working properly, and ensure that the cooling water flow rate reaches 32 m³ / h. Open the inlet and outlet valves of the built-in purifier 13, as well as the first and second shut-off valves of the purification pipeline 103 and 104. Start the purity analyzer 14, and control the helium compressor 1 to start at the minimum pressure holding speed, driving the helium to circulate in a closed loop within the refrigeration cycle. Impurities are adsorbed by the built-in purifier until the purity analyzer detects a helium purity ≥99.999%. Close the purification pipeline valves to complete the system pre-purification, and temporarily stop the helium compressor 1. The system includes multiple pneumatic valves; therefore, the first air compressor 17 and the second air compressor 28 need to be opened to ensure that the gas pressure required by the pneumatic valves reaches 7 bar. The chiller operates continuously, ensuring a cooling water flow rate of 32 m³ / h. The compressor is started, and the inlet and outlet valves of helium compressor 1, main high-pressure valve 101, main low-pressure valve 102, bypass valve 21, and loading valve 20 are opened. The unloading valve 19 is kept at 10% opening to connect the refrigeration cycle loop. Gas from the first helium storage tank 15 enters the compressor for circulation. Automatic control is activated during the process to regulate the outlet pressure of the helium compressor. Initially, the compressor operates at a low frequency. After the compressor stabilizes, the set pressure is gradually increased until the outlet pressure stabilizes at 12-13 bar and the inlet pressure stabilizes at approximately 2 bar. The turbine expander 7 is started and maintained at 30% speed.

[0075] The sample circuit first shut-off valve 108, sample circuit second shut-off valve 109, helium recovery shut-off valve 110, inlet main valve 111, inlet first regulating valve 112, return first regulating valve 113, and return main valve 114 of the magnet under test circuit are controlled. The first cryogenic fan 11 is turned on and runs at 30% speed, while the second cryogenic fan 12 remains off. The pressure reducing pump 31 and its inlet second shut-off valve 33 are turned on, thus connecting the magnet under test circulation circuit and the helium charging and recovery system. The 25 MPa high-pressure helium in the second helium storage tank 25 flows into the magnet under test circulation circuit, and after being stabilized to 2 MPa by the pressure reducing pump 31, it charges the magnet under test circulation circuit. By adjusting the opening of the first regulating valve 112 at the inlet and the first regulating valve 113 at the outlet of the magnet under test 22, the internal pressure of the magnet under test is gradually increased to 20 bara at a rate of 0.5 bara / min. Then, the turboexpander 7 is controlled to steadily increase in steps of 500 rpm / min. After the helium gas is cooled by the three-stage heat exchanger and adiabatically expanded by the turboexpander 7, its temperature drops rapidly, causing the cold-side inlet temperature of the intermediate heat exchanger 9 to steadily decrease to the target range at a rate of 5 K / min. The sixth temperature sensor 406 and the tenth temperature sensor 410 at the cold-side outlet of the intermediate heat exchanger 9 collect the temperature difference between the two loops, control the cooling rate of the dual loops, keep the temperature difference between the two loops ≤ 50 K, and control the operating mode and speed of the cryogenic fan based on the actual pressure drop of the magnet under test detected by the differential pressure transmitter 502. The PLC collects real-time data on sample inlet and outlet temperature, pressure, pressure drop, and flow rate through sensors, and adjusts the speed of the turbine expander 7, the speed of the low-temperature fan, and the opening of each regulating valve in a coordinated manner to stabilize the sample temperature at 20K±10mK, the inlet and outlet temperature difference at <1K, the working pressure inside the magnet under test 22 at 20bara, and the pressure drop at around 100kPa. Once the above parameters are stable, the system enters a fully automatic closed-loop control mode and the testing of the magnet under test 22 can begin.

[0076] This invention uses helium as the working fluid and comprises a refrigeration loop consisting of a helium compressor, a multi-stage heat exchanger, a throttling expansion valve, and other core components and valve assembly pipelines. The refrigeration loop is independent of the test magnet's loop, isolating the sample from fluctuations in the refrigeration side's operating conditions. The sample loop pressure is independently adjustable, and a synchronous cooling mode maintains a temperature difference of ≤50K between the two loops, preventing thermal shock damage. It can be used for testing typical nuclear fusion high-field magnets (such as TF and CS magnets), achieving adjustable helium temperatures from 4.5K to 30K, matching and continuously adjusting sample heat loads from 0W to 2000W, with a magnet inlet-outlet temperature difference of <1K and a circulation pressure >100kPa. The system uses a Cernox™ temperature sensor, achieving a temperature control accuracy of ±10mK within the 4.5K~30K temperature range, improving magnet testing performance and operational reliability. It is suitable for testing samples under low-temperature conditions such as nuclear fusion high-field magnets and for ensuring the low-temperature operation of equipment. The helium recovery system utilizes the pressure difference between the storage tank and the sample to drive helium charging, replenishment, and recovery. Approximately 17 kg of helium can be recovered in a single test, achieving a recovery rate of 90%, significantly reducing design and operating costs. The added hot gas bypass line utilizes waste heat from the helium compressor for rapid system rewarming, shortening testing time and reducing energy consumption. The system also integrates a built-in purifier and purity analyzer, enabling helium circulation purification before testing to adsorb impurities, ensuring loop cleanliness, and improving cooling efficiency and long-term system stability. This invention significantly improves the adaptability, accuracy, and safety of nuclear fusion strong-field magnet testing, reduces operating costs, and is suitable for cryogenic testing scenarios of various strong-field magnets, possessing significant engineering application value.

[0077] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0078] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A supercritical helium cryogenic system for nuclear fusion strong-field magnets, characterized in that, include: Cooling cycle circuit and magnet under test cycle circuit; The refrigeration cycle includes: a helium compressor, a high-pressure helium pipeline, a low-pressure helium pipeline, a loading / unloading pipeline, and a bypass pipeline; the outlet of the helium compressor is sequentially connected to the high-pressure helium pipeline, the low-pressure helium pipeline, and the inlet of the helium compressor to form a loop; one end of the loading / unloading pipeline is connected to the high-pressure helium pipeline, and the other end of the loading / unloading pipeline is connected to the low-pressure helium pipeline; one end of the bypass pipeline is connected to the high-pressure helium pipeline, and the other end of the bypass pipeline is connected to the low-pressure helium pipeline; the loading / unloading pipeline is connected to a first helium storage tank; an unloading valve and a loading valve are sequentially installed on the loading / unloading pipeline; and a bypass valve is installed on the bypass pipeline. The refrigeration cycle circuit and the test magnet cycle circuit are connected through an intermediate heat exchanger; The circulating loop of the magnet under test includes: the hot side outlet of the intermediate heat exchanger is connected to the inlet of the distribution valve box; an inlet main valve is installed in the distribution valve box; the inlet main valve is connected to the first inlet branch pipeline; a first regulating valve is installed on the first inlet branch pipeline; the first inlet branch pipeline is connected to the inlet of the magnet under test; the outlet of the magnet under test is connected to the first return branch pipeline; a first return regulating valve is installed on the first return branch pipeline; the first return branch pipeline is connected to the return main valve installed in the distribution valve box; the return main valve is connected to the outlet of the distribution valve box; the first branch pipeline of the outlet of the distribution valve box is connected to the inlet of the first low-temperature fan; the outlet of the first low-temperature fan is connected to the inlet of the second low-temperature fan; and the outlet of the second low-temperature fan is connected to the hot side inlet of the intermediate heat exchanger. The circulating loop of the magnet under test is equipped with a distribution valve box, which contains an inlet main valve and a return main valve. The inlet main valve is connected to multiple branches, each of which is equipped with a regulating valve. The return main valve is also connected to multiple branches, each of which is equipped with a regulating valve. Pressure sensors, temperature sensors, flow meters, and differential pressure transmitters are installed on the inlet and outlet branches. The flow meter is located at the outlet of the magnet under test, and the differential pressure transmitter is connected in parallel at the inlet and outlet of the magnet under test. The test magnet circulation loop also includes electronic pressure regulating valves connected in parallel on both sides of the second shut-off valve of the sample loop; it includes a first fan bypass valve located before the inlet of the first cryogenic fan and a fourth fan bypass valve located before the inlet of the second cryogenic fan; a third fan bypass valve connected in parallel before the inlet of the first fan bypass valve and the outlet of the first cryogenic fan; and a second fan bypass valve connected in parallel at the inlet of the fourth fan bypass valve and the outlet of the second cryogenic fan.

2. The supercritical helium cryogenic system for a nuclear fusion strong-field magnet according to claim 1, characterized in that, The refrigeration cycle circuit specifically includes: The inlet and outlet of the water-oil heat exchanger inside the helium compressor are connected to the inlet and outlet of the chiller. The high-pressure helium pipeline includes: a helium compressor outlet, an oil filter, a cold trap, hot-side inlet and outlet of a first heat exchanger, hot-side inlet and outlet of a second heat exchanger, hot-side inlet and outlet of a third heat exchanger, and a turbine expander inlet; the low-pressure helium pipeline includes: an electric heater inlet and outlet, cold-side inlet and outlet of an intermediate heat exchanger, cold-side inlet and outlet of a third heat exchanger, cold-side inlet and outlet of a second heat exchanger, cold-side inlet and outlet of a first heat exchanger, and a helium compressor inlet; the helium compressor outlet is connected to the oil filter inlet, the oil filter outlet is connected to the cold trap inlet, and the cold trap outlet is connected to the hot-side inlet of the first heat exchanger. The hot-side outlet of the first heat exchanger is connected to the hot-side inlet of the second heat exchanger; the hot-side outlet of the second heat exchanger is connected to the hot-side inlet of the third heat exchanger; the hot-side outlet of the third heat exchanger is connected to the inlet of the turbine expander; the outlet of the turbine expander is connected to the inlet of the electric heater; the outlet of the electric heater is connected to the cold-side inlet of the intermediate heat exchanger; the cold-side outlet of the intermediate heat exchanger is connected to the cold-side inlet of the third heat exchanger; the cold-side outlet of the third heat exchanger is connected to the cold-side inlet of the second heat exchanger; the cold-side outlet of the second heat exchanger is connected to the cold-side inlet of the first heat exchanger; and the cold-side outlet of the first heat exchanger is connected to the inlet of the helium compressor. It also includes a throttling expansion valve connected in parallel at the turbine expander outlet and the electric heater outlet.

3. A supercritical helium cryogenic system for a nuclear fusion strong-field magnet according to claim 2, characterized in that, Also includes: First air compressor, first solenoid reversing valve, second air compressor and second solenoid reversing valve; The first air compressor is connected to the first solenoid directional valve. The first outlet of the first solenoid directional valve is connected to the pneumatic actuator of the unloading valve in the loading and unloading pipeline. The second outlet of the first solenoid directional valve is connected to the pneumatic actuator of the loading valve in the loading and unloading pipeline. The third outlet of the first solenoid directional valve is connected to the pneumatic actuator of the bypass valve in the bypass pipeline. The second air compressor is connected to the second solenoid directional valve. The first outlet of the second solenoid directional valve is connected to the pneumatic actuator of the inlet main valve. The inlet main valve is connected to the inlet first regulating valve. The second outlet of the second solenoid directional valve is connected to the pneumatic actuator of the inlet first regulating valve. The third outlet of the second solenoid directional valve is connected to the pneumatic actuator of the return main valve. The return main valve is connected to the return first regulating valve. The fourth outlet of the second solenoid directional valve is connected to the pneumatic actuator of the return first regulating valve.

4. A supercritical helium cryogenic system for a nuclear fusion strong-field magnet according to claim 1, characterized in that, Also includes: Purification system, The purification system includes: a built-in purifier, a purity analyzer, a first shut-off valve for the purification pipeline, and a second shut-off valve for the purification pipeline. The built-in purifier is connected in parallel to the high-pressure helium pipeline and the low-pressure helium pipeline. The inlet of the built-in purifier is connected to the high-pressure helium pipeline, and a purity analyzer is connected in parallel to the inlet and outlet of the built-in purifier. The inlet of the purity analyzer is connected to the inlet of the built-in purifier, and the outlet of the purity analyzer is connected to the outlet of the built-in purifier. A first shut-off valve for the purification pipeline is provided on the pipeline before the inlet of the built-in purifier, and a second shut-off valve for the purification pipeline is provided on the pipeline before the inlet of the purity analyzer.

5. A supercritical helium cryogenic system for a nuclear fusion strong-field magnet according to claim 2, characterized in that, It also includes a hot gas bypass pipeline, which includes a hot gas bypass main pipeline and a hot gas bypass loop pipeline. The connection point between the hot gas bypass main pipeline and the high-pressure helium pipeline is located at the cold trap outlet. The hot gas bypass main pipeline is divided into a first hot gas bypass branch pipeline and a second hot gas bypass branch pipeline. The first hot gas bypass branch pipeline is connected to the low-pressure helium pipeline, and the interface between the first hot gas bypass branch pipeline and the low-pressure helium pipeline is located at the outlet of the intermediate heat exchanger. The second hot gas bypass branch pipeline is connected to the hot side outlet of the intermediate heat exchanger. One end of the hot gas bypass loop pipeline is connected to the second branch pipeline at the outlet of the distribution valve box, and the other end of the hot gas bypass loop pipeline is connected to the low-pressure helium pipeline. The connection point between the other end of the hot gas bypass loop pipeline and the low-pressure helium pipeline is located at the inlet of the helium compressor.

6. A supercritical helium cryogenic system for a nuclear fusion strong-field magnet according to claim 1, characterized in that, It also includes a helium recovery and storage system; The helium recovery and storage system includes: a booster pump, a pressure reducing pump, a first shut-off valve, a second shut-off valve, a first check valve, a second check valve, an external purifier, an ambient air vaporizer, a storage tank manual valve, and a second helium storage tank. The booster pump and the pressure reducing pump are connected in parallel, with their inlets connected to the second branch pipeline of the distribution valve box outlet. The booster pump is equipped with a first shut-off valve at its inlet and a first check valve at its outlet. The pressure reducing pump is equipped with a second shut-off valve at its inlet and a second check valve at its outlet. The outlets of the booster pump and the pressure reducing pump are connected to the first inlet and outlet of the external purifier. The second inlet and outlet of the external purifier are connected to the inlet of the ambient air vaporizer. The outlet of the ambient air vaporizer is connected to the inlet of the storage tank manual valve, and the outlet of the storage tank manual valve is connected to the interface of the second helium storage tank.

7. A supercritical helium cryogenic system for a nuclear fusion strong-field magnet according to claim 1, characterized in that, It also includes pressure sensors and temperature sensors; The pressure and temperature sensors include: a first pressure sensor and a first temperature sensor located at the outlet of the helium compressor; a second temperature sensor located at the hot-side outlet of the first heat exchanger; a third temperature sensor located at the hot-side outlet of the second heat exchanger; a second pressure sensor and a fourth temperature sensor located at the hot-side outlet of the third heat exchanger; a third pressure sensor and a fifth temperature sensor located at the cold-side inlet of the intermediate heat exchanger; a fourth pressure sensor and a sixth temperature sensor located at the cold-side outlet of the intermediate heat exchanger; a seventh temperature sensor located at the cold-side outlet of the third heat exchanger; an eighth temperature sensor located at the cold-side outlet of the second heat exchanger; and a pressure sensor located at the outlet of the helium compressor. The fifth pressure sensor and the ninth temperature sensor are located at the machine inlet; the sixth pressure sensor and the tenth pressure sensor are located at the hot side outlet of the intermediate heat exchanger; the seventh pressure sensor and the eleventh temperature sensor are located on the first branch pipeline inside the distribution valve box; the eighth pressure sensor and the twelfth temperature sensor are located on the first branch pipeline at the return port; the ninth pressure sensor and the thirteenth temperature sensor are located at the outlet of the distribution valve box; the tenth pressure sensor is located at the outlet of the first low-temperature fan; the eleventh pressure sensor and the fourteenth temperature sensor are located at the outlet of the second low-temperature fan; and the twelfth pressure sensor and the fifteenth temperature sensor are located at the outlet of the ambient air vaporizer.

8. A supercritical helium cryogenic method for a nuclear fusion strong-field magnet, applicable to the supercritical helium cryogenic system for a nuclear fusion strong-field magnet as described in any one of claims 1-7, characterized in that, The refrigeration cycle process includes: In the refrigeration cycle, the helium compressor draws in helium from the low-pressure helium pipeline, pressurizes it to obtain high-temperature, high-pressure gas, cools it down by the cooling water provided by the chiller, and then passes through a cold trap to remove impurities. After exiting the cold trap, the helium enters the hot-side inlet of the first heat exchanger, where it is cooled by the helium returning from the cold side. It then passes through the hot-side inlet of the second heat exchanger, where it is cooled by the helium returning from the cold side, and then through the hot-side inlet of the third heat exchanger, where it is cooled by the returning helium. It then undergoes adiabatic expansion through a turbine expander, at which point the throttling expansion valve closes. Subsequently, it enters the intermediate heat exchanger to exchange heat with the helium that has been cooled and reheated by the magnet under test. It then enters the cold-side inlet of the third heat exchanger to exchange heat with the hot-side helium, and then enters the cold-side inlet of the second heat exchanger to exchange heat with the high-pressure side helium. Finally, it enters the cold-side inlet of the first heat exchanger to exchange heat with the high-pressure side helium, and is then drawn in and pressurized again by the helium compressor to enter the next cycle. In the refrigeration cycle, the electronic expansion valve is opened, and the low-temperature, low-pressure helium gas from the turbine expander outlet directly enters the throttling expansion valve. The throttling expansion valve performs adiabatic expansion on the helium gas to obtain even lower-temperature helium gas, which then enters the cold side inlet of the intermediate heat exchanger to cool the helium gas in the test magnet circulation loop, thereby providing a lower-temperature testing environment for the test magnet. In the test magnet circulation loop, the series-connected cryogenic fans sequentially draw in helium gas after heat exchange with the test magnet, pressurize it, and enter the intermediate heat exchanger to exchange heat with the cryogenic helium gas in the refrigeration cycle and be cooled. The gas then enters the test magnet inlet through the distribution valve box, cools the test magnet, and is drawn in again by the series-connected cryogenic fans to enter the next cycle. The refrigeration cycle and the test magnet cycle are independent of each other. The cooling capacity is transferred through an intermediate heat exchanger. The refrigeration cycle drives the test magnet cycle to cool down simultaneously. During the cooling process, the maximum temperature difference between the two cycles is kept less than a preset value. The temperatures measured by the sixth temperature sensor at the cold side outlet and the tenth temperature sensor at the hot side outlet of the intermediate heat exchanger are converted into electrical signals and transmitted to the control system. By calculating the difference between the sixth and tenth temperature sensors, the helium mass flow rate of the two cycles is controlled to ensure that the temperature difference between the two cycles in the intermediate heat exchanger is less than the preset value. Set a set value for the eleventh temperature sensor at the inlet of the magnet under test, set a set value for the twelfth temperature sensor at the outlet, and set the difference between the two as a preset value. When the measured temperature of the helium gas at the outlet is higher than the set value, the electrical signal of the eleventh temperature sensor is transmitted to the control system to adjust the speed of the helium compressor and the turbine expander to control the temperature of the magnet under test.

9. A supercritical helium cryogenic method for a nuclear fusion strong-field magnet according to claim 8, characterized in that, The operation control of series-connected cryogenic fans includes: The series-connected cryogenic fans include a first cryogenic fan and a second cryogenic fan. These fans drive the flow of helium gas in the circuit of the magnet under test. When the pressure drop inside the magnet under test is large, the series-connected cryogenic fans sequentially draw in helium gas after heat exchange with the magnet under test, pressurize it, and then allow it to enter the intermediate heat exchanger to exchange heat with the cryogenic helium gas in the refrigeration cycle for cooling. The gas then enters the magnet under test inlet through the distribution valve box, cooling the magnet before being drawn in again by the series-connected cryogenic fans for the next cycle. Notably, when the pressure drop inside the magnet under test is small, the control system switches to a single-fan operation mode to match the internal pressure drop, ensuring the cryogenic fan operates within its optimal range. The system switches between cryogenic fans according to a set operating time. The PLC control system converts the pressure signals from the seventh and eighth pressure sensors and the differential pressure transmitter at the inlet and outlet of the magnet under test into electrical signals. These signals are transmitted to the control system, which in turn adjusts the start / stop status and speed of the cryogenic fans. The system controls the cryogenic fan speed based on the internal pressure drop of the sample, switching between single-fan and dual-fan drive modes.

10. A supercritical helium cryogenic method for a nuclear fusion strong-field magnet according to claim 8, characterized in that, Helium recovery through a helium recovery and storage system includes: The second helium storage tank is pre-filled with helium. The storage tank manual valve, the second shut-off valve, the helium recovery shut-off valve, and the pressure reducing pump are opened. The high-pressure helium in the second helium storage tank flows towards the magnet under test. After passing through the pressure reducing pump, the pressure reducing pump outlet pressure setpoint is set to the working pressure inside the magnet under test to avoid the impact of high-pressure helium on the magnet under test. The helium is continuously output at a stable pressure. As the temperature of the circuit of the magnet under test decreases, the second helium storage tank continues to replenish it until it stabilizes within the working pressure range required by the magnet under test. Then, the filling is stopped, and the storage tank manual valve and the helium recovery shut-off valve are closed. After the magnet under test is completed, the helium gas expands when heated. At this time, the helium gas recovery shut-off valve and the storage tank manual valve remain open. The booster pump and the first shut-off valve are opened, and the expanded helium gas enters the booster pump through the helium gas recovery pipeline. The outlet pressure setting value of the booster pump is set to the working pressure of the second helium gas storage tank. After being boosted, the helium gas passes through an external purifier to remove impurities, and then passes through an ambient temperature vaporizer to return to room temperature before entering the second helium gas storage tank for storage, in order to avoid low temperature shock to the second helium gas storage tank. Once the pressure inside the magnet under test returns to normal, shut off the manual valve of the storage tank and the helium recovery shut-off valve. After the system returns to normal temperature, shut off the helium compressor, close the inlet main valve and return main valve in the distribution valve box, and remove the magnet under test.

11. A supercritical helium cryogenic method for a nuclear fusion strong-field magnet according to claim 8, characterized in that, It also includes an inlet / outlet main valve and inlet / outlet branch valves installed in the distribution valve box for simultaneous testing of multiple samples; the inlet / outlet main valve and inlet / outlet branch valves are pneumatic valves, with air supplied by a second air compressor to drive the valves to adjust their opening, thereby adjusting the cooling capacity distributed to each sample; a cold shield branch pipeline is led out from the outlet of the second heat exchanger and connected to the interlayer of the distribution valve box to form a cold shield, which is used to reduce heat loss caused by heat conduction and heat radiation between the low-temperature helium gas inside the distribution valve box and the ambient temperature air.

12. The supercritical helium cryogenic method for a nuclear fusion strong-field magnet according to claim 8, characterized in that, This also includes high and low pressure control of the refrigeration cycle loop: The first air compressor provides compressed air to the unloading valve, loading valve, and bypass valve to drive the valve actuators and regulate the high and low pressure of the system. The loading valve, unloading valve, bypass valve, inlet main valve, inlet first regulating valve, return first regulating valve, and return main valve are all pneumatic valves and are equipped with pneumatic actuators. The electrical signal output by the control system is the control command, which opens and closes the air path and reverses the direction through the first and second solenoid directional valves, thereby driving the cylinder piston of the pneumatic actuator to move. The piston links the valve stem to complete the opening and closing action or continuous adjustment of the opening degree. The unloading valve connects the high-pressure outlet of the helium compressor to the first helium storage tank. When the high-pressure pressure is higher than the set pressure, the unloading valve opens, and the helium in the high-pressure helium pipeline returns to the first helium storage tank. The loading valve connects the low-pressure inlet of the helium compressor to the first helium storage tank. When the outlet pressure of the helium compressor is lower than the set pressure, the loading valve opens, and the helium in the first helium storage tank enters the low-pressure helium pipeline. The bypass valve connects the high-pressure helium pipeline and the low-pressure helium pipeline and is used to regulate the pressure of the low-pressure helium pipeline. When the low pressure is lower than the set value, the opening of the bypass valve increases; when the low pressure is higher than the set value, the opening of the bypass valve decreases.

13. The supercritical helium cryogenic method for a nuclear fusion strong-field magnet according to claim 8, characterized in that, This also includes rapid reheating via hot gas bypass lines: Open the first hot gas bypass valve, the second hot gas bypass valve, and the third hot gas bypass valve, and turn on the electric heater. High-temperature and high-pressure helium gas enters the cold side of the third heat exchanger, the cold side of the second heat exchanger, and the cold side of the first heat exchanger through the first branch pipeline of the hot gas bypass, so as to quickly reheat the helium gas in the refrigeration cycle system. Another part of the helium gas enters the circulation loop of the magnet under test through the second branch pipeline of the hot gas bypass, so as to heat the circulation loop of the magnet under test and the helium gas in the magnet under test.

14. The supercritical helium cryogenic method for a nuclear fusion strong-field magnet according to claim 8, characterized in that, This also includes cleaning via a purification system: Before testing the magnet to be tested, turn on the helium compressor to drive helium, open the main high-pressure valve and the main low-pressure valve, and the helium will circulate in the refrigeration cycle loop. The built-in purifier is connected in parallel at the inlet and outlet of the helium compressor. Open the first shut-off valve of the purification pipeline to adsorb non-condensable gases and impurities in the system. Open the second shut-off valve of the purification pipeline and the purity analyzer to detect the cleanliness of the helium in the system. When cleaning the circuit of the magnet under test, close the main high-pressure valve and the main low-pressure valve, close the first hot gas bypass valve, and open the second hot gas bypass valve and the third hot gas bypass valve. At this time, the helium compressor is connected to the circuit of the magnet under test, forming a circulation loop.

15. A supercritical helium cryogenic method for a nuclear fusion strong-field magnet according to claim 8, characterized in that, The startup procedure for the supercritical helium cryogenic system includes: Before the experiment, the gas in the pipeline was purified. The chiller unit was turned on while the compressor was running to check its normal operation and ensure the cooling water flow rate met requirements. The inlet and outlet valves of the built-in purifier and the first and second shut-off valves of the purification pipeline were opened. The purity analyzer was started, and the helium compressor was started at the lowest pressure holding speed, driving the helium to circulate in a closed loop within the refrigeration cycle. Impurities were adsorbed by the built-in purifier until the purity analyzer detected that the helium purity met requirements. The purification pipeline valves were then closed, completing the system pre-purification. The helium compressor was temporarily stopped. The first and second air compressors were then turned on. The gas pressure required by the pneumatic valve is brought to the required level, the chiller continues to work, the cooling water flow rate is brought to the required level, the compressor is started, and the inlet and outlet valves, main high-pressure valve, main low-pressure valve, bypass valve, loading valve, and unloading valve of the helium compressor itself are opened. The unloading valve is kept at the preset opening degree to connect the refrigeration cycle loop. The gas in the first helium storage tank enters the compressor for circulation. Automatic control is activated during the process to control the outlet pressure of the helium compressor. At the beginning, the compressor runs at a low frequency. After the compressor runs stably, the set pressure is gradually increased until the outlet pressure and inlet pressure are stable at the preset values. The turbine expander is started and kept running at the preset speed. The sample circuit first shut-off valve, sample circuit second shut-off valve, helium recovery shut-off valve, inlet main valve, inlet first regulating valve, return first regulating valve, and return main valve of the magnet under test circuit are controlled. The first cryogenic fan is turned on and runs at a preset speed, while the second cryogenic fan is kept off. The pressure reducing pump and the first shut-off valve are turned on to connect the magnet under test circulation circuit and the helium charging and recovery system. The high-pressure helium in the second helium storage tank flows into the magnet under test circulation circuit and is charged into the circulation circuit after the pressure is stabilized by the pressure reducing pump. By adjusting the opening of the first regulating valve at the inlet and outlet of the magnet under test, the internal pressure of the magnet under test is gradually increased to a preset value at a preset rate. Then, the working intensity of the turbine expander is increased by a preset step size. After the helium gas is cooled by the three-stage heat exchanger and the temperature decreases after the turbine expander expands adiabatically, the cold-side inlet temperature of the intermediate heat exchanger steadily decreases to the target range at a preset rate. The sixth and tenth temperature sensors at the cold-side outlet of the intermediate heat exchanger collect the temperature difference between the two loops and control the cooling rate of the two loops to keep the temperature difference between the two loops less than the preset value. The operating mode and speed of the cryogenic fan are controlled according to the actual pressure drop of the magnet under test detected by the differential pressure transmitter. The control system collects the sample inlet and outlet temperature, pressure, pressure drop, and flow rate data in real time through sensors, and adjusts the speed of the turbine expander, the speed of the cryogenic fan, and the opening of each regulating valve in a coordinated manner to stabilize the sample temperature, inlet and outlet temperature difference, working pressure inside the magnet under test, and pressure drop at preset values. After the parameters stabilize, the system enters the fully automatic closed-loop control mode and begins the testing of the magnet under test.

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