Superconducting magnet system based on superfluid helium cooling

Abstract

The application provides a superconducting magnet system based on superfluid helium cooling, which can be applied to the technical fields of strong magnetic field construction, nuclear magnetic resonance spectrometer and the like. The system comprises a superconducting coil, a superfluid helium cooler, a superconducting magnet cavity, a liquid helium storage cavity and a vacuum container; the liquid helium storage cavity, the superconducting magnet cavity and the superfluid helium cooler are arranged inside the vacuum container, and the superconducting coil is arranged in the superconducting magnet cavity; the liquid helium storage cavity is communicated with the superfluid helium cooler, and the superfluid helium cooler is communicated with the superconducting magnet cavity; wherein the superfluid helium cooler comprises a liquid helium precooling heat exchanger, a negative pressure heat exchanger and a superfluid heat exchanger, the liquid helium storage cavity is communicated with the liquid helium precooling heat exchanger, the liquid helium precooling heat exchanger is communicated with the negative pressure heat exchanger, the negative pressure heat exchanger is communicated with the superfluid heat exchanger, and the superfluid heat exchanger is arranged in the superconducting magnet cavity.

Description

Technical Field

[0001] This application relates to the technical fields of strong magnetic field construction and nuclear magnetic resonance spectrometers, and specifically to a superconducting magnet system based on superfluid helium cooling. Background Technology

[0002] The superconducting magnet system is one of the most complex components in a nuclear magnetic resonance spectrometer, used to provide the magnetic field required to generate nuclear magnetic resonance.

[0003] The magnetic field strength generated by a superconducting magnet system is closely related to the temperature of its operating environment. Currently, the cryogenic system structure of superconducting magnet systems is relatively simple. Most superconducting magnet systems operate under saturated liquid helium immersion conditions at 4.2K, which results in limited magnetic field strength and a limited range of magnetic field strength adjustment, failing to meet the requirements of high magnetic field nuclear magnetic resonance spectrometers. Summary of the Invention

[0004] In view of the above problems, this application provides a superconducting magnet system based on superfluid helium cooling that can stably meet the high magnetic field strength requirements of nuclear magnetic resonance spectrometers.

[0005] According to a first aspect of this application, a superconducting magnet system based on superfluid helium cooling is provided. The system includes a superconducting coil, a superfluid helium cooler, a superconducting magnet cavity, a liquid helium storage cavity, and a vacuum container. The liquid helium storage cavity, the superconducting magnet cavity, and the superfluid helium cooler are respectively disposed inside the vacuum container, and the superconducting coil is disposed inside the superconducting magnet cavity. The superfluid helium cooler includes a liquid helium precooling heat exchanger, a negative pressure heat exchanger, and a superfluid heat exchanger. The liquid helium storage cavity is connected to the liquid helium precooling heat exchanger, the liquid helium precooling heat exchanger is connected to the negative pressure heat exchanger, the negative pressure heat exchanger is connected to the superfluid heat exchanger, and the superfluid heat exchanger is disposed inside the superconducting magnet cavity. According to an embodiment of this application, the superconducting coil includes a first coil structure and a second coil structure sleeved outside the first coil structure, and the first coil structure and the second coil structure are coaxially arranged.

[0006] According to an embodiment of this application, the first coil structure includes a first coil group, a second coil group, and a third coil group arranged radially from the inside out; the first coil group includes a plurality of first coils arranged radially from the inside out, the plurality of first coils having equal lengths; the second coil group includes a plurality of second coils, the plurality of second coils being symmetrically arranged along the centerline of the first coil group, the second coil including a first sub-coil and a second sub-coil, the first sub-coil and the second sub-coil located at the upper part of the first coil group being arranged from top to bottom; the third coil group includes a third coil and a fourth coil arranged radially from the inside out, the length of the third coil being less than the length of the fourth coil.

[0007] According to an embodiment of this application, the second coil structure includes a plurality of fifth coils and a plurality of sixth coils arranged radially from the inside out. The plurality of fifth coils are of equal length, and the plurality of sixth coils are arranged symmetrically along the centerline of the plurality of fifth coils.

[0008] According to an embodiment of this application, the first coil structure is wound with niobium-tin superconducting wire, and the second coil structure is wound with niobium-titanium superconducting wire.

[0009] According to an embodiment of this application, the first coil structure is impregnated with paraffin wax, and the second coil structure is impregnated with epoxy resin.

[0010] According to embodiments of this application, the operating modes of the system include a 4.2K saturated liquid helium cooling mode and a 1.8K-2.2K supercooled superfluid helium cooling mode.

[0011] According to an embodiment of this application, the system further includes a metal ring, which is fitted around the superconducting coil by an interference fit.

[0012] According to an embodiment of this application, a helium-cooled screen and a liquid helium-cooled screen are also provided inside the vacuum container; the helium-cooled screen is located inside the vacuum container, and the liquid helium-cooled screen is located inside the helium-cooled screen, between the helium-cooled screen and the superconducting magnet cavity.

[0013] According to an embodiment of this application, the system further includes a pressure reducing pump and a condenser, wherein the superfluid helium cooler is connected to the pressure reducing pump and the pressure reducing pump is connected to the condenser.

[0014] The above one or more embodiments have the following beneficial effects:

[0015] (1) A highly uniform central magnetic field is generated through a multi-layered combination structure composed of internal and external coils.

[0016] (2) Two optional immersion cooling modes are provided: 4.2K saturated liquid helium and 1.8-2.2K superfluid helium. This allows the magnet to operate stably at 18.8T under normal conditions (4.2K) and at 21.15T under ultra-low temperature conditions (2.1K), which significantly expands the stable operating range of the magnet, ensures sufficient current operating margin, and improves the reliability and operational flexibility of the system; thus meeting the usage requirements of high magnetic field nuclear magnetic resonance spectrometer.

[0017] (3) Based on the different characteristics of Nb3Sn and NbTi superconducting materials, different processes such as frameless paraffin impregnation and epoxy vacuum impregnation were adopted to maximize the performance potential of their respective conductors; combined with the metal ring to provide external support for the coil structure, the mechanical stability and safety of the entire magnet under extremely high electromagnetic stress were jointly guaranteed. Attached Figure Description

[0018] The above-mentioned contents, other objects, features and advantages of this application will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0019] Figure 1 A schematic diagram of a superconducting magnet system based on superfluid helium cooling according to an embodiment of this application is shown.

[0020] Figure 2 A schematic diagram illustrating the arrangement of coils according to an embodiment of this application is shown.

[0021] Figure 3 A schematic diagram of the structure of an ultrafluid helium cooler according to an embodiment of this application is shown.

[0022] The above figures include the following reference numerals:

[0023] 101. Vacuum container; 102. Helium cooling shield; 103. Liquid helium storage chamber; 104. Superconducting magnet chamber; 105. Second coil structure; 106. First coil structure; 107. Superfluid helium cooler; 108. Pressure reducing pump; 109. Liquid helium cooling shield; 201. Coil 1; 202. Coil 2; 203. Coil 3; 204. Coil 4; 205. Coil 5; 206. Coil 6; 207. Coil 7; 2 08, No. 8 coil; 209, No. 9 coil; 210, No. 10 coil; 2011, No. 11 coil; 2012, No. 12 coil; 2013, No. 13 coil; 2014, No. 14 coil; 2015, No. 15 coil; 301, liquid helium precooling heat exchanger; 302, liquid helium replenishment valve; 303, negative pressure heat exchanger; 304, liquid helium replenishment port; 305, superfluid heat exchanger; 306, liquid helium inlet; 307, throttle valve. Detailed Implementation

[0024] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of this application. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this application for ease of explanation. However, it will be apparent that one or more embodiments may be implemented without these specific details. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0025] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0026] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0027] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0028] The embodiments of this application provide a superconducting magnet system based on superfluid helium cooling. The superfluid helium cooler is designed to provide different immersion cooling modes for the superconducting magnet system, which significantly expands the stable operating range of the superconducting magnet, ensures sufficient current operating margin, and improves the reliability and operational flexibility of the superconducting magnet system.

[0029] The following will be through Figures 1-3 A superconducting magnet system based on superfluid helium cooling according to embodiments of this application will be described in detail.

[0030] Figure 1 The schematic diagram illustrates the structure of a superconducting magnet system based on superfluid helium cooling according to an embodiment of this application. Figure 2 A schematic diagram illustrating the arrangement of coils according to an embodiment of this application is shown. Figure 3 A schematic diagram of the structure of an ultrafluid helium cooler according to an embodiment of this application is shown.

[0031] Combination Figures 1-3 The system includes a superconducting coil (superconducting magnet), a superfluid helium cooler 107, a superconducting magnet cavity 104, a liquid helium storage cavity 103, and a vacuum container 101. The liquid helium storage cavity 103, the superconducting magnet cavity 104, and the superfluid helium cooler 107 are respectively installed inside the vacuum container 101, and the superconducting coil is installed inside the superconducting magnet cavity 104. The liquid helium storage cavity 103 is connected to the superfluid helium cooler 107, and the superfluid helium cooler 107 is connected to the superconducting magnet cavity 104. The superfluid helium cooler 107 includes a liquid helium precooling heat exchanger 301, a negative pressure heat exchanger 303, and a superfluid heat exchanger 305. The liquid helium storage chamber 103 is connected to the liquid helium precooling heat exchanger 301, the liquid helium precooling heat exchanger 301 is connected to the negative pressure heat exchanger 303, the negative pressure heat exchanger 303 is connected to the superfluid heat exchanger 305, and the superfluid heat exchanger 305 is installed inside the superconducting magnet chamber 104.

[0032] According to an embodiment of this application, the vacuum container 101 is the outermost sealed container of the superconducting magnet system, and its interior is evacuated to a high vacuum state to minimize heat leakage caused by heat conduction and convection of gas molecules; the liquid helium storage cavity 103 stores liquid helium to replenish the superfluid helium cooler 107 and the superconducting magnet cavity 104; the superconducting magnet cavity 104 stores liquid helium to serve as a liquid helium pool for the superconducting coil; the superfluid helium cooler 107 reduces the temperature of the liquid helium from the liquid helium storage cavity 103 through heat exchange, and transports the generated cryogenic liquid helium to the superfluid heat exchanger 305 to reduce the temperature of the liquid helium in the superconducting magnet cavity 104, providing a long-lasting and stable cryogenic environment for the superconducting coil.

[0033] Furthermore, the superfluid helium cooler 107 also includes a throttle valve 307, the outlet of the negative pressure heat exchanger 303 is connected to the inlet of the throttle valve 307, and the outlet of the throttle valve 307 is connected to the superfluid heat exchanger 305.

[0034] According to an embodiment of this application, the pre-cooled subcooled liquid helium undergoes adiabatic expansion through the throttle valve 307, further reducing the temperature and pressure of the liquid helium.

[0035] Combination Figure 3 Specifically, the superfluid helium cooler 107 also includes a liquid helium buffer chamber, which has a liquid helium inlet 306 and a liquid helium outlet. The liquid helium storage chamber 103 is connected to the liquid helium inlet 306 of the liquid helium buffer chamber, and the liquid helium outlet is connected to the inlet of the liquid helium precooling heat exchanger 301. The outlet of the liquid helium precooling heat exchanger 301 is connected to the inlet of the negative pressure heat exchanger 303, the outlet of the negative pressure heat exchanger 303 is connected to the inlet of the throttle valve 307, and the outlet of the throttle valve 307 is connected to the inlet of the superfluid heat exchanger 305.

[0036] The liquid helium precooling heat exchanger 301 is connected to a pipeline with a liquid helium replenishment port 304, and a liquid helium replenishment valve 302 is connected between the liquid helium replenishment port 304 and the liquid helium precooling heat exchanger 301.

[0037] Here, the aforementioned outlet and inlet can be connected by a pipeline. The specific pipeline material, location, and structure can be flexibly set according to the spacing and location between the aforementioned components. This embodiment does not limit this.

[0038] For example, the operation of the superfluid helium cooler 107 is as follows:

[0039] The 4.2K saturated liquid helium in the liquid helium storage chamber 103 flows through the liquid helium buffer chamber to the pre-cooling heat exchanger 301, where it exchanges heat with the returning cryogenic helium gas to initially lower the temperature of the 4.2K saturated liquid helium to 2.2K. Subsequently, the initially cooled liquid helium flows through the negative pressure heat exchanger 303 into the throttling valve 307, where it undergoes adiabatic expansion to further reduce the pressure and temperature to below the λ point (2.17K), i.e., superfluid helium. Finally, the generated superfluid helium exchanges sufficient heat with the liquid helium in the superconducting magnet cavity 104 through the superfluid heat exchanger 305, allowing the liquid helium in the superconducting magnet cavity 104 to be continuously cooled, thereby stably obtaining and maintaining a supercooled superfluid helium state within the range of 1.8K to 2.2K.

[0040] Here, the refluxed cryogenic helium gas refers to the gaseous fluid resulting from the evaporation of cryogenic liquid after passing through downstream equipment such as the negative pressure heat exchanger 303 and the superfluid heat exchanger 305.

[0041] In some embodiments, the system operates in two modes: a 4.2K saturated liquid helium cooling mode and a 1.8K-2.2K supercooled superfluid helium cooling mode.

[0042] According to embodiments of this application, the design of the superfluid helium cooler 107 enables the superconducting magnet system to have two switchable cooling modes, providing great flexibility for the operation of the superconducting magnet.

[0043] In the following detailed description, the 4.2K saturated liquid helium cooling mode will be referred to as Mode 1, and the 1.8K-2.2K supercooled superfluid helium cooling mode will be referred to as Mode 2.

[0044] For example, Mode 1 could refer to maintaining the boiling point temperature of liquid helium in the superconducting magnet cavity 104 at approximately 4.2 K by controlling the decompression and cooling power. For instance, this could be achieved by activating the decompression pump while simultaneously adjusting the throttle valve opening to enable superfluid helium cooling mode operation.

[0045] At this point, the superconducting coil is in a state of saturated liquid helium immersion cooling.

[0046] Mode 2 could refer to starting the superfluid helium final stage cycle, that is, starting the superfluid helium cooler 107 to reduce the liquid helium temperature in the superfluid heat exchanger 305 to below 2.2K, thereby achieving supercooled superfluid helium cooling of the superconducting coil.

[0047] To improve the quality of the magnetic field generated by the superconducting magnet system, a coil structure combining inner and outer multilayer coils is designed to effectively counteract the axial attenuation of the magnetic field, thereby achieving extremely high uniformity in the central region. In some embodiments, the superconducting coil includes a first coil structure 106 and a second coil structure 105 sleeved on the first coil structure 106, with the first coil structure 106 and the second coil structure 105 coaxially arranged.

[0048] According to an embodiment of this application, the second coil structure 105 is an outer coil and the first coil structure 106 is an inner coil. Through the cooperation of the outer coil and the inner coil, a highly uniform central strong magnetic field is generated.

[0049] Furthermore, the first coil structure 106 includes a first coil group, a second coil group, and a third coil group arranged radially from the inside out. The first coil group includes multiple first coils arranged radially from the inside out, and the multiple first coils are of equal length. The second coil group includes multiple second coils, which are symmetrically arranged along the centerline of the first coil group. The second coil includes a first sub-coil and a second sub-coil, with the first sub-coil and the second sub-coil located at the upper part of the first coil group arranged from top to bottom. The third coil group includes a third coil and a fourth coil arranged radially from the inside out, with the length of the third coil being less than the length of the fourth coil.

[0050] According to an embodiment of this application, the first coil group is located in the innermost layer, the second coil group is symmetrically arranged about the Z=0 coordinate axis, and the third coil group has the most turns and contributes significantly to the generation of the main magnetic field.

[0051] Combination Figure 2 For example, the first coil group includes three first coils: coil 1 (201), coil 2 (202), and coil 3 (203). The second coil group includes two second coils: two first sub-coils and two second sub-coils: coil 4 (204), coil 5 (205), coil 6 (206), and coil 7 (207). The third coil group includes a third coil and a fourth coil: coil 8 (208) and coil 9 (209). Coils 1 through 9 are arranged coaxially, sequentially from the inside out. Coils 1 through 3 have equal lengths and are located in the innermost layer; coils 4 and 5, and coils 6 and 7 are symmetrically arranged about the Z=0 coordinate axis; coils 8 and 9 have the most turns and contribute significantly to the generation of the main magnetic field.

[0052] Furthermore, the second coil structure 105 includes a plurality of fifth coils and a plurality of sixth coils arranged radially from the inside out. The plurality of fifth coils are of equal length, and the plurality of sixth coils are arranged symmetrically along the center line of the plurality of sixth coils.

[0053] According to embodiments of this application, a plurality of fifth coils and a plurality of sixth coils are arranged coaxially.

[0054] Combination Figure 2For example, the second coil structure 105 includes four fifth coils and two sixth coils. The four fifth coils are coil 2010 (10), coil 2011 (11), coil 202 (12), and coil 203 (13). Coil 2010, coil 2011, coil 2012, and coil 2013 are of equal length and are used to generate the main magnetic field. The two sixth coils are coil 2014 (14) and coil 2015 (15), which are shielded coils and are symmetrical about the Z=0 coordinate axis.

[0055] All of the above coils are formed using high-precision winding technology and are symmetrically distributed along the central axis.

[0056] Furthermore, the first coil structure 106 is wound with niobium-tin superconducting wire, and the second coil structure 105 is wound with niobium-titanium superconducting wire.

[0057] For example, niobium-tin superconducting wires can be Nb3Sn conductors, and niobium-titanium superconducting wires can be NbTi conductors.

[0058] According to embodiments of this application, the Nb3Sn conductor possesses high critical magnetic field characteristics, and the first coil structure 106 is internal, allowing the Nb3Sn conductor to fully utilize its high critical magnetic field characteristics. The NbTi conductor exhibits mature and stable performance advantages in the low-field region, and the second coil structure 105 is external, allowing its performance advantages to be fully utilized.

[0059] Considering the different mechanical and thermal properties of Nb3Sn and NbTi conductors, in order to avoid damaging the conductors, in some embodiments, the first coil structure 106 is impregnated with paraffin wax and the second coil structure 105 is impregnated with epoxy resin.

[0060] According to embodiments of this application, after curing, paraffin wax provides uniform support for coils made of Nb3Sn conductors, effectively absorbing mechanical stress. Simultaneously, its low thermal shrinkage helps reduce thermal stress and prevent damage to the conductor. Epoxy resin can improve the mechanical properties of coils made of NbTi conductors.

[0061] According to an embodiment of this application, a frameless paraffin impregnation process is used when preparing the first coil structure 106.

[0062] Specifically, after the coil winding of the first coil structure 106 is completed and the Nb3Sn superconducting phase is formed by reaction heat treatment, the first coil structure 106 is placed in a vacuum impregnation tank, and the paraffin wax is completely impregnated through the coil winding gap under heating conditions.

[0063] The second coil structure 105 was treated with an epoxy vacuum impregnation process.

[0064] Specifically, after completing the coil winding and reaction heat treatment of the second coil structure 105, the second coil structure 105 is placed in a vacuum impregnation tank, and the paraffin wax is completely impregnated into the coil winding gap under heating conditions.

[0065] Based on the above coil structure, when the superconducting magnet system operates in the 4.2K liquid helium temperature range, its key performance parameters are shown in Tables 1 and 2 below.

[0066] Table 1

[0067]

[0068] Table 2

[0069]

[0070] As shown in the table above, based on the coil structure and materials described, the performance of the superconducting magnet system at a liquid helium temperature of 4.2K is as follows:

[0071] Central magnetic field strength: The superconducting magnet system successfully generated and stably maintained a central magnetic field of 18.8T, which meets the field strength requirements of the 800MHz nuclear magnetic resonance spectrometer;

[0072] Magnetic field uniformity: The superconducting magnet system achieves extremely high magnetic field uniformity in the central region; specifically, the magnetic field non-uniformity (peak-to-peak value) is better than 0.1944 ppm within a spherical volume with a diameter of 20 mm.

[0073] Electromagnetic and energy storage parameters: In this operating mode, the superconducting magnet operates stably with a current of 119 A, the total inductance of the entire magnet system is 1945.12 H, and the stored magnetic energy is as high as 13.77 MJ.

[0074] Based on the above coil structure, when the superconducting magnet system operates in the 1.8K liquid helium temperature range, its key performance parameters are shown in Tables 3 and 4 below.

[0075] Table 3

[0076]

[0077] Table 4

[0078]

[0079] As shown in the table above, based on the coil structure and materials described, the critical current of the superconducting magnet is significantly improved in the 1.8K liquid helium temperature range. The superconducting magnet system can achieve stable operation with a higher central magnetic field strength of 21.15T (corresponding to 900MHz), while also possessing extremely high magnetic field uniformity. The performance of the superconducting magnet system is as follows:

[0080] Magnetic field uniformity: The superconducting magnet system achieves extremely high magnetic field uniformity in the central region, specifically: within a spherical volume with a diameter of 20 mm, the magnetic field non-uniformity (peak-to-peak value) is better than 0.1944 ppm.

[0081] Electromagnetic and energy storage parameters: In this operating mode, the superconducting magnet operates stably with a current of 133.88A; the total inductance of the entire superconducting magnet system is 1945.12H, and the stored magnetic energy reaches 17.43MJ.

[0082] To constrain and protect the aforementioned frameless coil assembly and to withstand the enormous electromagnetic stress from the inside out, in some embodiments, the system further includes a metal ring, which is fitted around the superconducting coil by an interference fit.

[0083] For example, a metal ring with a shrinkage rate similar to or higher than that of the superconducting material can be used to reinforce the superconducting magnet coil through an interference fit (thermal expansion and contraction) process. The metal ring can be made of aluminum alloy or stainless steel.

[0084] Stainless steel has high strength and high modulus, while aluminum alloy has a thermal shrinkage coefficient that is more compatible with superconductors, which can ensure structural integrity and dimensional stability throughout the entire process from room temperature assembly to ultra-low temperature operation.

[0085] According to an embodiment of this application, the metal ring is installed as follows:

[0086] During the assembly stage of the superconducting coil, a metal ring is expanded by controlling the temperature and then assembled onto the superconducting coil. After returning to room temperature, a strong radial preload is applied to the internal superconducting coil. When the magnet is energized, the outward expansion tendency of the superconducting coil due to the Lorentz force is counteracted by the inward pressure pre-applied by the metal ring, thus keeping the superconducting coil under pressure at all times. This greatly improves the mechanical stability and quench resistance of the magnet. The magnet structure, uniformity, and support strength simultaneously meet the requirements of 800MHz, 900MHz, and higher NMR spectrometers for superconducting magnets.

[0087] In some embodiments, a liquid helium cooling screen 109 and a helium cooling screen 102 are also installed inside the vacuum container 101; the helium cooling screen 102 is installed inside the vacuum container 101, and the liquid helium cooling screen 109 is installed inside the helium cooling screen 102, located between the helium cooling screen 102 and the superconducting magnet cavity 104.

[0088] For example, the helium-cooled shield 102 includes a first helium-cooled shield and a second helium-cooled shield. The second helium-cooled shield includes a first pipe and a second pipe. The first helium-cooled shield is installed inside the vacuum container 101. The first pipe is coiled around the first helium-cooled shield from top to bottom, and the second pipe is coiled around the first helium-cooled shield from bottom to top. These pipes are used to connect the liquid helium storage cavity 103 and the superconducting magnet cavity 104, respectively. Their surfaces are typically covered with multiple layers of heat-insulating material, which can effectively shield thermal radiation from the room temperature environment (approximately 300K). The liquid helium-cooled shield 109 is fitted onto the superconducting magnet cavity 104, located between the helium-cooled shield 102 and the superconducting magnet cavity 104.

[0089] According to an embodiment of this application, the helium cooling screen 102 utilizes the cooling capacity of cryogenic helium from the evaporation of saturated liquid helium and saturated superfluid helium, while the liquid helium cooling screen 109 is cooled by liquid helium in the liquid helium storage chamber 103 and is typically maintained in a temperature range of around 5K, further blocking residual radiant heat and significantly reducing the heat load reaching the innermost layer.

[0090] For example, vacuum container 101 is a vacuum Dewar.

[0091] Based on the above-mentioned multi-layer thermal insulation design, together with the superfluid helium cooler 107, the liquid helium in the superconducting magnet cavity 104 can be stably maintained at 4.2K (saturated state) or 1.8-2.2K (supercooled superfluid state) for a long time, thereby creating the necessary ultra-low temperature operating conditions for the superconducting magnet.

[0092] In order to recover and reuse the helium gas evaporated during the use of the system, in some embodiments, the system also includes a pressure reducing pump 108 and a condenser, with an overflow helium cooler 107 connected to the pressure reducing pump 108 and the pressure reducing pump 108 connected to the condenser to form a closed-loop helium cryogenic system.

[0093] For example, the pressure reducing pump 108 is connected to the superfluid helium cooler 107 via a pipeline.

[0094] Therefore, the evaporated helium gas is recovered through a condenser.

[0095] Those skilled in the art will understand that the features described in the various embodiments of this application can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in this application. In particular, the features described in the various embodiments of this application can be combined and / or combined in various ways without departing from the spirit and teachings of this application. All such combinations and / or combinations fall within the scope of this application.

Claims

1. A superconducting magnet system based on superfluid helium cooling, characterized in that, The system includes a superconducting coil, a superfluid helium cooler, a superconducting magnet cavity, a liquid helium storage cavity, and a vacuum container; The liquid helium storage chamber, the superconducting magnet chamber, and the superfluid helium cooler are respectively disposed inside the vacuum container, and the superconducting coil is disposed inside the superconducting magnet chamber; The superfluid helium cooler includes a liquid helium precooling heat exchanger, a negative pressure heat exchanger, and a superfluid heat exchanger. The liquid helium storage chamber is connected to the liquid helium precooling heat exchanger, the liquid helium precooling heat exchanger is connected to the negative pressure heat exchanger, the negative pressure heat exchanger is connected to the superfluid heat exchanger, and the superfluid heat exchanger is disposed inside the superconducting magnet cavity.

2. The system according to claim 1, characterized in that, The superconducting coil includes a first coil structure and a second coil structure sleeved outside the first coil structure, wherein the first coil structure and the second coil structure are coaxially arranged.

3. The system according to claim 2, characterized in that, The first coil structure includes a first coil group, a second coil group, and a third coil group arranged radially from the inside out; The first coil group includes a plurality of first coils arranged radially from the inside to the outside, and the plurality of first coils are of equal length; The second coil group includes a plurality of second coils, which are symmetrically arranged along the centerline of the first coil group. Each second coil includes a first sub-coil and a second sub-coil, which are arranged sequentially from top to bottom in the upper part of the first coil group. The third coil group includes a third coil and a fourth coil arranged radially from the inside out, with the length of the third coil being less than the length of the fourth coil.

4. The system according to claim 2, characterized in that, The second coil structure includes a plurality of fifth coils and a plurality of sixth coils arranged radially from the inside out. The plurality of fifth coils are of equal length, and the plurality of sixth coils are arranged symmetrically along the center line of the plurality of fifth coils.

5. The system according to claim 2, characterized in that, The first coil structure is wound with niobium-tin superconducting wire, and the second coil structure is wound with niobium-titanium superconducting wire.

6. The system according to claim 2, characterized in that, The first coil structure is impregnated with paraffin wax, and the second coil structure is impregnated with epoxy resin.

7. The system according to claim 1, characterized in that, The system operates in two modes: a 4.2K saturated liquid helium cooling mode and a 1.8K-2.2K supercooled superfluid helium cooling mode.

8. The system according to claim 1, characterized in that, The system also includes a metal ring, which is fitted around the superconducting coil by an interference fit.

9. The system according to claim 1, characterized in that, The vacuum container is also equipped with a helium cooling screen and a liquid helium cooling screen. The helium-cooled shield is disposed inside the vacuum container, and the liquid helium-cooled shield is disposed inside the helium-cooled shield, located between the helium-cooled shield and the superconducting magnet cavity.

10. The system according to claim 1, characterized in that, The system also includes a pressure reducing pump and a condenser, the superfluid helium cooler being connected to the pressure reducing pump, and the pressure reducing pump being connected to the condenser.

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