A eddy current-free liquid helium cryostat for use in a pulsed high magnetic field environment

Abstract

The present invention belongs to the technical field related to refrigeration and cryogenic containers, and discloses a eddy-current-free liquid helium cryostat for use in a pulsed high-magnetic field environment. The cryostat comprises a sample rod, a helium chamber, a liquid nitrogen layer, a vacuum chamber, and a tail pipe. The tail pipe is composed of an inner epoxy tail pipe and an outer epoxy tail pipe, each of which is mounted via metal flanges. The epoxy tail pipe and the metal flanges are bonded together with epoxy sealant. The vacuum interlayer between the helium chamber and the vacuum chamber is interconnected with the vacuum interlayer between the inner epoxy tail pipe and the outer epoxy tail pipe. In addition, the metal flange of the inner tail pipe is precisely mounted concentrically from top to bottom, and a removable metal seal is achieved between the metal flange of the inner tail pipe and the bottom flange of the helium chamber. The present invention effectively solves the problem of liquid helium loss caused by Joule heat generated by induced eddy currents in a pulsed high-magnetic field environment in the prior art, while significantly improving the measurement accuracy of scientific experiments in a high-field pulsed high-magnetic field environment.

Description

Technical Field

[0001] The present invention belongs to the technical field related to refrigeration and cryogenic containers, and more specifically, relates to an eddy current-free liquid helium cryostat for use in a pulsed strong magnetic field environment. Background Art

[0002] Currently, cryostats used for scientific research in pulsed high magnetic fields are generally helium-immersed cryostats. Limited by the aperture size of the pulsed magnet and the space required for measuring samples, the available space for the tail of the cryostat inserted into the magnet is very limited. To ensure mechanical strength and vacuum insulation, the tail tube of a typical cryostat is constructed with a double-layer, thin-walled stainless steel structure, with a vacuum layer of only about 1-2 mm between the two layers. However, due to the high dB / dt characteristics of the pulsed magnet's discharge process, the eddy current effect generated by electromagnetic induction during the discharge of conductors in a pulsed high magnetic field environment cannot be ignored. For liquid helium cryostats, the Joule heating caused by eddy currents causes liquid helium loss, reducing the time it can be maintained, especially the time it can maintain the superfluid state of liquid helium at around 1.5 K.

[0003] More specifically, the inventors of this application discovered that the tail tube of a liquid helium cryostat used in a pulsed high-magnetic field environment typically utilizes a double-layer, thin-walled stainless steel structure. However, this structure, when subjected to high-field discharges from a pulsed magnet, produces significant eddy currents on the stainless steel sample chamber. Furthermore, the structure is also subject to certain electromagnetic forces, causing the stainless steel sample chamber to undergo a certain degree of elastic deformation. This phenomenon results in significant measurement noise during experiments conducted in pulsed magnetic fields, particularly those at high intensities of 60 T or higher, directly impacting the accuracy of scientific experiments. Furthermore, for ultra-strong pulsed magnetic fields exceeding 80 T, the magnetic field generated by the eddy currents induced in the stainless steel tail tube can even affect the internal structure of the magnet, thereby compromising its structural strength and hindering experimental performance.

[0004] Accordingly, there is an urgent need in this field to make further improvements so as to better meet the experimental use of high-performance liquid helium cryostats in pulsed strong magnetic field environments. Summary of the Invention

[0005] In response to the above-mentioned defects or needs of the prior art, the purpose of the present invention is to provide an eddy-current-free liquid helium cryostat for use in a pulsed high magnetic field environment, wherein the structural composition and spatial layout of the entire device are redesigned, and targeted improvements are made to the specific structures and settings of some key modules. This can effectively solve the problems of liquid helium loss caused by Joule heat generated by induced eddy currents in the prior art in a pulsed high magnetic field environment, and at the same time significantly improve the measurement accuracy of scientific experiments in a high-field pulsed high magnetic field environment in a compact structure, easy to install and well-sealed manner.

[0006] To achieve the above objectives, according to the present invention, there is provided an eddy-free liquid helium cryostat for use in a pulsed high magnetic field environment. The eddy-free liquid helium cryostat comprises a sample holder, a helium chamber, a liquid nitrogen layer, a vacuum chamber, and a tail pipe, and is characterized in that:

[0007] The helium chamber and the vacuum chamber are coaxially arranged from the inside to the outside, and the liquid nitrogen layer is provided between them; the sample rod and the tail pipe are respectively provided at the head and tail ends of the helium chamber;

[0008] The tail pipe adopts a double-layer epoxy structure, that is, it consists of an inner epoxy tail pipe and an outer epoxy tail pipe, and is installed through the inner tail pipe metal flange and the outer tail pipe metal flange respectively. Each epoxy tail pipe is bonded to its corresponding metal flange with sealant, and a plug is bonded and sealed at the bottom of each epoxy tail pipe.

[0009] The vacuum interlayer between the helium cavity and the vacuum cavity is connected to the vacuum interlayer between the inner epoxy tail tube and the outer epoxy tail tube;

[0010] The inner tail pipe metal flange includes a guide groove, a limiting boss, a guide groove, and a metal sealing groove. The guide groove is used to insert the inner epoxy tail pipe and maintain the engagement. The limiting boss is located at the upper end of the guide groove and serves as a limiter. The guide groove is further arranged on the upper portion of the limiting boss. Its interior is an inverted trapezoidal structure for guiding liquid helium. At the same time, a boss structure is formed on its outer side to serve as a concentric positioning. The metal sealing groove is arranged on the side of the inner tail pipe metal flange facing the bottom flange of the helium chamber and is used to be filled with a metal wire to achieve a detachable metal seal.

[0011] Based on the above ideas, on the one hand, by designing a double-layer epoxy tail pipe structure, the vacuum layer between them can effectively reduce the heat load on the liquid helium inside the thermostat. On the other hand, the overall epoxy tail pipe structure can eliminate the influence of eddy currents induced by stainless steel materials in the pulsed magnetic field, reduce the loss of liquid helium during the experiment, reduce the measurement interference of scientific experiments under pulsed strong magnetic fields, and eliminate the influence of the metal tail pipe on the structural strength of the high-field pulsed magnet.

[0012] On the other hand, by improving the specific structure and setting method of the tail pipe flange structure, metal such as indium wire can be used to directly perform a detachable seal between the tail pipe flange and the bottom flange of the helium chamber, which is convenient for replacing tail pipes of different apertures to adapt to pulse magnets of different sizes; this type of metal sealing structure is compact and easy to install and operate. Only an indium wire groove of appropriate depth is left on one side of the flange, and the other side flange is a smooth plane. The tooling structure is used to make the upper and lower parts concentric. Accordingly, while ensuring the sealing performance of the low-temperature thermostat, it also greatly reduces the difficulty of processing, manufacturing and disassembly of the indium wire sealing surface.

[0013] As a further preference, the inner tail pipe metal flange and the outer tail pipe metal flange are preferably made of stainless steel.

[0014] As a further preference, for the above tail pipes, each epoxy tail pipe and its corresponding metal flange are preferably bonded with epoxy sealant, and a plug made of epoxy material is bonded and sealed at the bottom of each tail pipe.

[0015] As a further preference, for the above-mentioned tail pipes, the outer wall of each epoxy tail pipe is preferably coated with epoxy glue, thereby further increasing its structural strength and sealing performance.

[0016] As a further preferred embodiment, the inner tail pipe metal flange further comprises a glue filling groove, which is located at the lower end of the guide groove and is used to further increase the glue filling space between the inner tail pipe metal flange and the inner epoxy tail pipe.

[0017] As a further preferred embodiment, the inner tail pipe metal flange further comprises bolt holes, which are used to install a plurality of bolts between the inner tail pipe metal flange and the bottom flange of the helium chamber, thereby achieving fixation between the two.

[0018] As a further preference, the metal sealing groove is preferably used to fill indium wire to achieve a detachable metal seal.

[0019] As a further preferred embodiment, the metal sealing groove preferably has a depth of 0.6 mm to 1.0 mm and is filled with an indium wire with a diameter of about 2 mm.

[0020] As a further preference, each component of the above device is designed and manufactured using a modular structure.

[0021] In general, the above technical solutions conceived by the present invention have the following technical advantages compared with the existing technology:

[0022] (1) The present invention redesigns the structural composition and spatial layout of the entire eddy-free liquid helium cryostat. With the cooperation of the double-layer epoxy tail pipe and its supporting components, it can effectively reduce the heat load on the liquid helium inside the cryostat, and at the same time significantly eliminate the influence of eddy currents induced by stainless steel materials in the pulsed magnetic field, reduce the loss of liquid helium during the experiment, reduce the measurement interference of scientific experiments under pulsed strong magnetic fields, and eliminate the adverse effects of the metal tail pipe on the structural strength of the high-field pulsed magnet.

[0023] (2) The present invention further improves the specific structure and setting method of multiple key components such as the inner tail pipe metal flange, and accordingly can use the tooling structure to ensure the concentricity of the upper and lower parts. While ensuring the sealing performance of the low-temperature thermostat, it greatly reduces the difficulty of processing, manufacturing and disassembly of the indium wire sealing surface, improves the assembly efficiency, and further effectively meets the high performance requirements of the tail pipe flange sealing design;

[0024] (3) The eddy-free liquid helium cryostat according to the present invention has a compact structure, is easy to install and maintain, and significantly improves the measurement accuracy of scientific experiments. Therefore, it is particularly suitable for high-precision measurement applications such as pulsed strong magnetic field environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a cross-sectional view of the overall structure of the eddy-free liquid helium cryostat according to the present invention;

[0026] Figure 2 is a cross-sectional view showing the structure of the inner tail pipe flange in more detail according to a preferred embodiment of the present invention;

[0027] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0028] 1-sample rod interface, 2-helium chamber, 3-liquid nitrogen layer, 4-vacuum chamber, 5-inner tail pipe metal flange, 6-outer tail pipe metal flange, 7-inner epoxy tail pipe, 8-outer epoxy tail pipe, 101-guide groove, 102-glue filling groove, 103-limiting boss, 104-guide groove, 105-metal sealing groove, 106-bolt hole. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0030] Figure 1 FIG. 1 is a cross-sectional view of the overall structure of the eddy-free liquid helium cryostat according to the present invention. Figure 1 As shown, the device is used for scientific experimental measurements in a pulsed strong magnetic field environment, and mainly includes components such as a sample rod 1, a helium chamber 2, a liquid nitrogen layer 3, a vacuum chamber 4 and a tail pipe, which will be explained in detail one by one below.

[0031] See Figure 1The helium chamber 2 and the vacuum chamber 4 are coaxially arranged from the inside to the outside, and a liquid nitrogen layer 3 is provided between the two; the sample rod 1 and the tail tube are respectively provided at the head and tail ends of the helium chamber 2.

[0032] As one of the key structures of the present invention, the tail pipe adopts a double-layer epoxy structure, that is, it is composed of an inner epoxy tail pipe 7 and an outer epoxy tail pipe 8, and is installed through an inner tail pipe metal flange 5 and an outer tail pipe metal flange 6 respectively. In addition, the vacuum interlayer between the helium chamber 2 and the vacuum chamber 4 is interconnected with the vacuum interlayer between the inner epoxy tail pipe 7 and the outer epoxy tail pipe 8.

[0033] More specifically, each epoxy tail pipe can be bonded to its corresponding metal flange using a sealant such as STYCAST 2850 epoxy adhesive. At the same time, an epoxy plug can be used to seal the bottom of each epoxy tail pipe. A thin layer of epoxy adhesive can also be applied to the outer surface of the epoxy tail pipe to further enhance its structural strength and sealing properties.

[0034] As another key structure of the present invention, the inner tail pipe metal flange 5 includes a guide groove 101, a limiting boss 103, a guide groove 104, and a metal sealing groove 105. The guide groove 101 is used to insert the inner epoxy tail pipe 7 and maintain the engagement. The limiting boss 103 is located at the upper end of the guide groove and serves as a limiter. The guide groove 104 is further provided on the upper portion of the limiting boss 103. Its interior is an inverted trapezoidal structure for guiding liquid helium, and a boss structure is formed on its outer side for concentric positioning. The metal sealing groove 105 is provided on the side of the inner tail pipe metal flange 5 facing the bottom flange of the helium chamber 2 and is used to fill a metal wire to achieve a detachable metal seal.

[0035] More specifically, see Figure 2 The inner tail pipe metal flange is key to connecting the epoxy tail pipe to the main structure of the helium chamber. In this invention, it provides both an adhesive seal with the epoxy tail pipe and a metal seal with the helium chamber. Guide groove 1 is inserted into the epoxy tail pipe and fits tightly against it. Glue filling groove 2, located at the end of guide groove 1, further increases the glue filling space between the epoxy pipe and the stainless steel flange. The internal structure of guide groove 4 can also be depicted as a slope, used to guide liquid helium and the sample rod. The outer diameter of this slope forms a boss structure and serves to concentrically position the epoxy tail pipe and the helium chamber. Metal sealing groove 5 is located between the tail pipe flange and the helium chamber and can be used to fill metal wire, such as indium wire, for sealing. 6 is the bolt hole connecting the tail pipe flange to the helium chamber.

[0036] Accordingly, the above low-temperature metal sealing structure provided by the present invention makes targeted improvements to the conventional low-temperature metal sealing structure based on the reference to the O-ring sealing groove used at ordinary room temperature. Only an indium wire groove of appropriate depth is left on the tail pipe flange (for example, if a 2mm diameter indium wire is used, a sealing groove depth of 0.8mm is sufficient). The bottom flange of the helium chamber on the other side is a smooth plane. The tooling structure is used to make the upper and lower parts concentric, and it is fixed by bolts, which can ensure the sealing effect of the commonly used low-temperature thermostat at the low temperature of liquid helium (the internal and external pressure difference is within 0.2MPa).

[0037] According to a preferred embodiment of the present invention, the inner tail pipe metal flange 5 and the outer tail pipe metal flange 6 are preferably made of stainless steel. For the tail pipes, each epoxy tail pipe is preferably bonded to its corresponding metal flange using epoxy sealant, and a plug made of epoxy material is bonded and sealed at the bottom of each tail pipe.

[0038] According to another preferred embodiment of the present invention, the inner tail pipe metal flange may further include a glue filling groove 102 , which is located at the lower end of the guide groove 102 and is used to further increase the glue filling space between the inner tail pipe metal flange 5 and the inner epoxy tail pipe 7 .

[0039] In addition, the inner tail pipe metal flange 5 may further include bolt holes 106 , which are used to install multiple bolts between the inner tail pipe metal flange 5 and the bottom flange of the helium chamber 2 , thereby achieving fixation between the two.

[0040] In summary, the eddy current-free liquid helium cryostat according to the present invention can effectively eliminate the influence of eddy currents induced by stainless steel materials in a pulsed magnetic field in a compact structure, easy to install and maintain, and reduce the loss of liquid helium during the experiment. At the same time, it can also significantly reduce the difficulty of processing, manufacturing and disassembly of the indium wire sealing surface while ensuring the sealing performance of the cryostat. Therefore, it is particularly suitable for high-precision measurement applications such as pulsed strong magnetic field environments, and has broad application prospects.

[0041] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A vortex-free liquid helium cryostat for use in a pulsed strong magnetic field environment, the vortex-free liquid helium cryostat comprising a sample rod (1), a helium chamber (2), a liquid nitrogen layer (3), a vacuum chamber (4) and a tail pipe, characterized in that: The helium chamber (2) and the vacuum chamber (4) are coaxially arranged from the inside out, and the liquid nitrogen layer (3) is provided between the two; the sample rod (1) and the tail tube are respectively provided at the head and tail ends of the helium chamber (2); The tail pipe adopts a double-layer epoxy structure, i.e., it is composed of an inner epoxy tail pipe (7) and an outer epoxy tail pipe (8), and is installed through an inner tail pipe metal flange (5) and an outer tail pipe metal flange (6) respectively; each epoxy tail pipe is bonded to its corresponding metal flange using a sealant, and a plug is bonded and sealed at the bottom of each epoxy tail pipe; The vacuum interlayer between the helium cavity (2) and the vacuum cavity (4) is in communication with the vacuum interlayer between the inner epoxy tail tube (7) and the outer epoxy tail tube (8); The inner tail pipe metal flange (5) comprises a guide groove (101), a limiting boss (103), a guide groove (104) and a metal sealing groove (105), wherein the guide groove (101) is used to insert the inner epoxy tail pipe (7) and maintain the engagement, and the limiting boss (103) is located at the upper end of the guide groove (101) and plays a limiting role; the guide groove (104) is further arranged on the upper part of the limiting boss (103), and its interior is an inverted trapezoidal structure for guiding liquid helium, while a boss structure is formed on its outer side to play a concentric positioning role; the metal sealing groove (105) is arranged on the side of the inner tail pipe metal flange (5) facing the bottom flange of the helium chamber (2), and is used to fill a metal wire to achieve a detachable metal seal.

2. The eddy-free liquid helium cryostat according to claim 1, wherein: The inner tail pipe metal flange (5) and the outer tail pipe metal flange (6) are made of stainless steel.

3. The eddy-free liquid helium cryostat according to claim 2, wherein: For the above tail pipes, each epoxy tail pipe and its corresponding metal flange are bonded with epoxy sealant, and a plug made of epoxy material is bonded and sealed at the bottom of each tail pipe.

4. The eddy-free liquid helium cryostat according to claim 3, wherein: For the above tail pipes, the outer wall of each epoxy tail pipe is coated with epoxy glue, thereby further increasing its structural strength and sealing performance.

5. The eddy-free liquid helium cryostat according to any one of claims 1 to 4, characterized in that: The inner tail pipe metal flange (5) further comprises a glue filling groove (102), which is located at the lower end of the guide groove (101) and is used to further increase the glue filling space between the inner tail pipe metal flange (5) and the inner epoxy tail pipe (7).

6. The vortex-free liquid helium cryostat according to claim 5, wherein: The inner tail pipe metal flange (5) further comprises a bolt hole (106), wherein the bolt hole (106) is used to install a plurality of bolts between the inner tail pipe metal flange (5) and the bottom flange of the helium chamber (2), thereby achieving a connection and fixation between the two.

7. The eddy-free liquid helium cryostat according to claim 6, wherein: As for the metal sealing groove (105), it is used to fill indium wire to achieve a detachable metal seal.

8. The vortex-free liquid helium cryostat according to claim 7, wherein: The metal sealing groove (105) has a depth of 0.6 mm to 1.0 mm and is filled with an indium wire with a diameter of 2 mm.

9. The vortex-free liquid helium cryostat according to any one of claims 1 to 4, characterized in that: Each component of the eddy-free liquid helium cryostat is designed and manufactured using a modular structure.

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