Dilution refrigeration probe with sample transfer channel and method of sample transfer

Abstract

The present application relates to dilution refrigeration heat exchange technical field, especially to a kind of dilution refrigeration insertion rod with sample transmission channel and sample transmission method.Dilution refrigeration insertion rod includes dilution refrigeration insertion rod structure and top connecting pipeline.Dilution refrigeration insertion rod structure includes: vacuum cavity, precooling device with through hole in middle part is sequentially arranged in vacuum cavity from top to bottom, distillation device, double-pipe heat exchanger, sintered heat exchanger and mixing chamber;Through hole is coaxially aligned, and is connected to form sample transmission channel from the top of vacuum cavity to the bottom of mixing chamber;First heat insulation plug and second heat insulation plug, first heat insulation plug is detachably arranged in the through hole on distillation device;Second heat insulation plug is detachably arranged in the through hole on mixing chamber.By reserving sample transmission channel through upper and lower in middle part, sample can be transmitted to the test area below mixing chamber cold plate along axial direction.It has the capability of providing central sample transmission while ensuring the performance of dilution refrigeration.

Description

Technical Field

[0001] This invention relates to the field of dilution refrigeration heat exchange technology, and in particular to a dilution refrigeration insert with a sample transfer channel and a sample transfer method. Background Technology

[0002] Dilution refrigerators are core experimental devices for obtaining ultra-low temperature environments at the milliKelvin (mK) level, and are widely used in cutting-edge fields such as scanning tunneling microscopy (STM), quantum transport measurement, superconducting quantum bit characterization, and topological materials research. A typical wet dilution refrigerator system consists of a liquid helium Dewar and a dilution refrigerator plug.

[0003] In cryogenic experiments, sample loading and replacement is a high-frequency and critical operation. The existing dilution cooling plug's internal space is occupied by circulation pipelines, support structures, and various levels of thermal shielding, lacking a sample transfer channel running axially through the plug. Whenever a sample needs to be replaced, the operator must remove the entire vacuum chamber from the liquid helium Dewar, break the vacuum, heat it to room temperature, remove the old sample, load the new sample, and then re-evacuate and cool it down. This process is time-consuming, and repeated thermal cycling negatively impacts the lifespan and temperature stability of the cryogenic components.

[0004] Some existing technologies employ a dedicated transfer tube or robotic arm within the vacuum chamber for sample transfer. However, these additional transfer tubes and robotic arms increase the complexity of the internal structure of the vacuum chamber, encroach on radial space, and interfere with existing components such as circulation pipelines and thermal shielding. For equipment like scanning tunneling microscopes, which require coaxial arrangement of the probe and sample and have extremely high demands for mechanical stability and temperature uniformity, the space congestion and vibration interference caused by the additional transfer structure are particularly pronounced. Furthermore, the additional heat mass and heat conduction path introduced by the transfer structure also increase the heat load on the dilution cooling unit, prolonging the cooling time and affecting the final achievable steady-state temperature.

[0005] Therefore, the existing technology still needs further development and improvement. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a dilution cooling insert with a sample transfer channel and a sample transfer method, aiming to solve the problem of complex insert structure caused by lateral sample transfer in the prior art.

[0007] To achieve the above objectives, the core inventive concept of this invention lies in designing the functional components arranged axially in the dilution refrigeration plug structure—the precooling device, distillation device, shell-and-tube heat exchanger, sintering heat exchanger, and mixing chamber—as hollow structures with centrally located through-holes. This allows each component to perform its respective refrigeration function while its central through-holes are naturally coaxially aligned, forming a sample transfer channel extending from the top of the vacuum chamber to the bottom of the mixing chamber. This sample transfer channel is integrated with the functional bodies of each component, without occupying additional radial space. Furthermore, removable heat insulation plugs are installed in the through-holes of the precooling device and the mixing chamber, respectively. In the non-sample transfer state, the channel is sealed to ensure that the refrigeration performance is not affected; in the sample transfer state, the heat insulation plugs are removed to allow the sample to pass smoothly along the channel.

[0008] Specifically, in the first aspect, a dilution cooling insert with a sample transfer channel includes: Top connection pipes; A dilution cooling plug structure with a sample transfer channel includes: a vacuum chamber, in which a precooling device, a distillation device, a shell-and-tube heat exchanger, a sintering heat exchanger, and a mixing chamber are arranged sequentially from top to bottom; each of the precooling device, distillation device, shell-and-tube heat exchanger, sintering heat exchanger, and mixing chamber has a through hole in its middle; wherein the through holes are coaxially aligned and interconnect to form a sample transfer channel extending from the top of the vacuum chamber to the bottom of the mixing chamber; a first heat insulation plug and a second heat insulation plug are used to seal the sample transfer channel when not transferring samples; the first heat insulation plug is detachably disposed in the through hole of the distillation device; the second heat insulation plug is detachably disposed in the through hole of the mixing chamber. The top connecting pipe includes a pipe for sample transfer and a third heat insulation plug. The pipe for sample transfer is coaxially aligned with and connected to the through hole. The third heat insulation plug is used to close the pipe for sample transfer when not transferring samples. The sintered heat exchanger is a circular metal powder sintered heat exchanger, comprising: A circular sintered substrate, wherein a metal powder layer is disposed on both the upper and lower surfaces of the circular sintered substrate; A hot fluid inflow pipe is welded to the upper surface edge region of the circular sintered substrate and extends axially through the circular sintered substrate to guide the hot fluid to the region where the lower surface of the circular sintered substrate is located. A cold fluid inflow pipe is welded to the lower surface edge region of the circular sintered substrate and extends axially through the circular sintered substrate to guide the cold fluid to the region where the upper surface of the circular sintered substrate is located. A cold fluid encapsulation shell is disposed above the circular sintered substrate, and together with the circular sintered substrate, they form a cold fluid chamber. The cold fluid encapsulation shell is provided with a cold fluid outflow pipe. A hot fluid encapsulation shell is disposed below the circular sintered substrate, and together with the circular sintered substrate, they form a hot fluid chamber. The hot fluid encapsulation shell is provided with a hot fluid outflow pipe. The cold fluid encapsulation shell, the circular sintered substrate, and the hot fluid encapsulation shell are stacked and assembled sequentially along the axial direction and sealed together as a single unit through an annular welded sealing port. In this structure, the through hole in the middle of the circular metal powder sintered heat exchanger is completely independent of the cold fluid encapsulation shell and the hot fluid encapsulation shell, and the through sample transfer channel and the heat exchange area do not interfere with each other spatially.

[0009] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0010] As a preferred technical solution, in the dilution cooling insert with a sample transfer channel, the thickness of the metal powder layer is 0.5 mm to 4 mm.

[0011] As a preferred technical solution, the dilution cooling insert with sample transfer channel is wherein the annular welded sealing port is a continuous annular weld formed by argon arc welding or laser welding.

[0012] As a preferred technical solution, the dilution cooling plug with sample transfer channel is wherein the cold fluid outflow pipe is welded to the top surface of the cold fluid encapsulation shell, the hot fluid outflow pipe is welded to the bottom surface of the hot fluid encapsulation shell, and both the hot fluid inflow pipe and the cold fluid inflow pipe are led out from the side of the circular sintered substrate and penetrate the corresponding encapsulation shell sidewall.

[0013] As a preferred technical solution, in the dilution cooling insert with sample transfer channel, the metal powder in the metal powder layer is silver powder or copper powder.

[0014] As a preferred technical solution, the dilution cooling plug with sample transfer channel is wherein the sintering heat exchanger is a multi-stage circular metal powder sintering heat exchanger, including 2 to 5 stages of circular metal powder sintering heat exchangers as described above. The circular metal powder sintered heat exchangers of each level are arranged in series along the axial direction, and the diameter of the circular metal powder sintered heat exchangers increases progressively along the flow direction of the cold or hot fluid.

[0015] As a preferred technical solution, the dilution cooling plug with a sample transfer channel is wherein adjacent two stages of the circular metal powder sintering heat exchanger are connected by welding a cold fluid connecting pipe and a hot fluid connecting pipe. The cold fluid connecting pipe connects the cold fluid outlet pipe of the previous stage and the cold fluid inlet pipe of the next stage, and the hot fluid connecting pipe connects the hot fluid outlet pipe of the previous stage and the hot fluid inlet pipe of the next stage.

[0016] As a preferred technical solution, the dilution cooling insert with a sample transfer channel is wherein the multi-stage circular metal powder sintering heat exchanger has four stages. The central through holes of each stage are coaxially aligned and connected, collectively forming a continuous and unobstructed sample transfer channel in the sintering heat exchanger section.

[0017] Secondly, a sample transfer method based on the above-described dilution cooling insert, comprising: The vacuum chamber is evacuated to a vacuum, and the dilution cooling plug is placed in a liquid helium environment; The third heat insulation plug, the first heat insulation plug, and the second heat insulation plug are removed in sequence, and the sample to be tested is sent to the bottom of the mixing chamber; The second heat insulation plug, the first heat insulation plug, and the third heat insulation plug are placed back in their original positions in sequence. The pre-cooling device is then turned on to cool the temperature down to 1K. The refrigeration cycle is then started until the temperature drops to the minimum.

[0018] Beneficial effects: Compared with the prior art, the present invention uses a hollow configuration design with through holes in the center of each component, which integrates the sample transfer channel with the functional body of each component, and realizes the axial sample transfer function without adding additional structural components, resulting in a compact overall structure. The first and second heat insulation plugs are respectively located in the through holes of the precooling device and the mixing chamber, and are simultaneously sealed from both ends of the channel, the high-temperature end close to room temperature and the mK end close to extremely low temperature, effectively blocking heat radiation and gas heat conduction along the channel. The opening and closing of the refrigerant delivery pipeline is linked to the sample transfer operation, eliminating the need for additional valve mechanisms, making the system simple and reliable. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a perspective view of the dilution cooling insert with a sample transfer channel provided in an embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram of the internal structure of the dilution cooling plug structure with a sample transfer channel provided in an embodiment of the present invention.

[0022] Figure 3 This is a perspective view of a circular metal powder sintered heat exchanger provided in an embodiment of the present invention.

[0023] Figure 4 This is a perspective view of the multi-stage circular metal powder sintering heat exchanger provided in an embodiment of the present invention. Detailed Implementation

[0024] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0025] In the description of the embodiments of the present invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0026] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0027] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0028] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0029] like Figure 1 and Figure 2 As shown, this embodiment provides a dilution cooling insert with a sample transfer channel, including a lower dilution cooling insert structure 100 with a sample transfer channel and a top connecting pipe 40 connected to the dilution cooling insert structure 100. The dilution cooling insert structure 100 with a sample transfer channel includes: a precooling device 110 with through holes in the center of a vacuum chamber (not shown separately), a distillation device 120, a shell-and-tube heat exchanger 130, a sintering heat exchanger 140, and a mixing chamber 150. The through holes are coaxially aligned and interconnect to form a sample transfer channel extending from the top of the vacuum chamber to the bottom of the mixing chamber. A first heat insulation plug 121 is provided in the through hole of the distillation device, and a second heat insulation plug 151 is provided in the through hole of the mixing chamber. The heat insulation plugs are used to seal the sample transfer channel when not transferring samples.

[0030] In this embodiment, the top connecting pipe 40 is equipped with a pipe for sample transfer and a third heat insulation plug (not shown). The pipe for sample transfer is coaxially aligned with and connected to the through hole; the third heat insulation plug is used to seal the pipe for sample transfer when not transferring samples. By adding heat insulation plugs, heat can be reflected back step by step, preventing excessive radiant heat from being received. It should be noted that the heat insulation plug can be made of magnetic material. The structure and fitting method of the heat insulation plug are existing technologies and will not be described in detail here.

[0031] In one implementation of this embodiment, the precooling device 110 is a liquid helium circulation 1K pool. Its operation is as follows: an external liquid helium supply system introduces liquid helium into the precooling device 110 through an inlet pipe. The liquid helium evaporates under reduced pressure within the chamber of the precooling device 110, utilizing the latent heat of vaporization to lower the temperature of the precooling device 110 to approximately 1K. Simultaneously, it provides initial low temperatures to the distillation device 120 and sintering heat exchanger 140 below through contact heat conduction. The precooling device 110 adopts a hollow annular configuration arranged around a central axis. Its annular cavity contains liquid helium and achieves reduced pressure evaporation cooling, while the central through-hole remains open. The precooling device 110 is connected to a 1K pool inlet pipe and a 1K pool return pipe, both integrated into the refrigerant delivery pipeline, introduced along the radial sidewall of the vacuum chamber, without passing through the axial path of the sample transfer channel.

[0032] The distillation apparatus 120 is located below the precooling apparatus 110 and includes a distillation chamber, a distillation apparatus return gas pipeline, and a helium-3 inlet pipe. The distillation apparatus 120 also has a hollow annular configuration with a central through-hole. The distillation chamber contains a 3He / 4He mixed liquid. Under the temperature of approximately 1K provided by the precooling apparatus 110, utilizing the vapor pressure difference between 3He and 4He (the saturated vapor pressure of 3He is much higher than that of 4He), 3He preferentially evaporates from the mixture and is discharged through the distillation apparatus return gas pipeline to the external circulation system for purification and recompression. The remaining 4He-rich liquid flows downwards into the sintering heat exchanger 140 and the mixing chamber 150 under gravity. The 3He inlet pipe introduces the 3He gas, processed by the external circulation system, into the distillation apparatus 120, where it undergoes initial condensation.

[0033] A shell-and-tube heat exchanger 130 is located between the distillation unit 120 and the sintering heat exchanger 140, and also has a central through-hole aligned with the central through-holes of the upper and lower components. The shell-and-tube heat exchanger 130 performs preliminary heat exchange between the downward-flowing 3He liquid from the distillation unit 120 and the upward-flowing dilute-phase reflux vapor from the mixing chamber 150. The downward-flowing liquid receives first-stage precooling here, reducing the heat load when entering the sintering heat exchanger 140; simultaneously, the upward-flowing vapor receives preliminary preheating here, reducing temperature fluctuations when entering the distillation unit 120, which is beneficial for the stable operation of the distillation unit 120. The shell-and-tube heat exchanger 130 typically adopts a thin-tube bundle or coaxial shell-and-tube structure, with the 3He liquid flowing inside the tubes and the dilute-phase vapor flowing counter-currently outside the tubes, exchanging heat through the tube walls. Its heat exchange area and tube diameter are determined based on the design refrigeration capacity of the dilution refrigeration unit. If the heat exchange area is too small, precooling will be insufficient and the heat load of the sintering heat exchanger will be too high; if the heat exchange area is too large, additional flow resistance will be introduced. The central through-hole of the shell-and-tube heat exchanger 130 runs through it, and the sample transfer channel remains continuous and unobstructed in this section.

[0034] In one implementation of this embodiment, the sintered heat exchanger 140 is a circular metal powder sintered heat exchanger with a through hole 203 in the middle, such as... Figure 3As shown, the circular metal powder sintered heat exchanger includes: a circular sintered substrate 10, a cold fluid inlet pipe 301, a hot fluid inlet pipe 201, a cold fluid encapsulation shell 20, and a hot fluid encapsulation shell 30. The cold fluid encapsulation shell 20 covers the circular sintered substrate 10, forming a cold fluid chamber together with the circular sintered substrate 10; the hot fluid encapsulation shell 30 covers the circular sintered substrate 10, forming a hot fluid chamber together with the circular sintered substrate 10. The circular sintered substrate 10 is a circular metal plate made of oxygen-free copper, possessing good low-temperature thermal conductivity and processing performance, and will not become embrittled at extremely low temperatures. A layer of metal powder (not shown) is sintered on the upper and lower surfaces of the circular sintered substrate 10. The metal powder is silver powder, and the thickness of the powder layer can be 2 mm. The sintered silver powder layer forms a large number of interconnected micropores, constituting a porous structure that provides a heat exchange interface for the cold and hot fluids. The large specific surface area of ​​the porous structure of silver powder effectively increases the heat transfer area, compensating for the high thermal resistance of Carpicar at extremely low temperatures. Compared to direct heat transfer on a smooth surface, the effective heat transfer area of ​​the porous structure is increased by tens of times. It should be noted that the metal powder material is not limited to silver or copper powder; other metal powders suitable for extremely low-temperature sintering can also be used, as long as the metal powder can be sintered at high temperatures and maintain a stable porous structure at extremely low temperatures. In practical applications, the technical solution of this invention can be adjusted according to the specific operating parameters of the dilution refrigerator. When the operating temperature range of the dilution refrigerator is wide, the thickness of the metal powder layer can be selected as 3 mm to provide a larger heat transfer area; when the operating temperature range is narrow and the heat transfer load is low, the thickness of the metal powder layer can be selected as 1.5 mm to reduce flow resistance and decrease the flow pressure drop of the fluid.

[0035] A hot fluid inlet pipe 201 is welded to the upper surface edge region of the circular sintered substrate 10, axially penetrates the circular sintered substrate 10, and communicates with the lower metal powder layer. It is used to introduce the dense-phase hot fluid into the lower hot fluid chamber. A cold fluid inlet pipe 301 is welded to the lower surface edge region of the circular sintered substrate 10, axially penetrates the circular sintered substrate 10, and communicates with the upper metal powder layer. It is used to introduce the dilute-phase cold helium fluid into the upper cold fluid chamber. The welded seal between the two pipes and the substrate ensures that no fluid leakage occurs at the interface. It is easy to understand that the cold fluid flows from the bottom to the top of the circular metal powder sintered heat exchanger, while the hot fluid flows from the top to the bottom.

[0036] The cold fluid encapsulation shell 20 is a circular cover structure, made of the same or compatible metal material as the circular sintered substrate 10, and is placed over the circular sintered substrate 10. The opening edge of the cold fluid encapsulation shell 20 matches the outer edge shape of the circular sintered substrate 10, and after assembly, it together with the upper surface of the circular sintered substrate 10 to form a sealed cold fluid chamber. A mounting hole is provided on the top of the cold fluid encapsulation shell 20, and the cold fluid outflow pipe 202 is welded to the mounting hole, communicating with the cold fluid chamber. On one side of the cold fluid outflow pipe 202, a through hole is also provided for the passage of the hot fluid inflow pipe 201, which passes through the through hole and is exposed above the cold fluid encapsulation shell 20.

[0037] The hot fluid encapsulation shell 30 is a circular cover structure, positioned beneath the circular sintered substrate 10. The opening edge of the hot fluid encapsulation shell 30 matches the outer edge shape of the circular sintered substrate 10, and together with the lower surface of the circular sintered substrate 10, they form a sealed hot fluid chamber. A mounting hole is provided at the bottom of the hot fluid encapsulation shell 30, and a hot fluid outlet pipe 302 is welded to this mounting hole, communicating with the hot fluid chamber. A through hole is also provided on one side of the hot fluid outlet pipe 302 for a cold fluid inlet pipe 301 to pass through, with the cold fluid inlet pipe 301 exposed beneath the hot fluid encapsulation shell 30.

[0038] Along the axial direction from top to bottom, the assembly sequence of the three main components is as follows: the cold fluid encapsulation shell 20 is at the top, the circular sintered substrate 10 is in the middle, and the hot fluid encapsulation shell 30 is at the bottom. After the three components are stacked in sequence, a continuous annular weld seal is formed along the outer edge by laser welding, encapsulating the three components into a single, non-removable integrated structure. This single annular weld simultaneously completes the sealing connection between the cold fluid encapsulation shell and the substrate, as well as between the hot fluid encapsulation shell and the substrate, eliminating the need for separate welding operations. This significantly reduces the number of weld seams and lowers the risk of incomplete or faulty welds.

[0039] The heat exchanger operates as follows in this embodiment: The hot fluid (dense phase) enters through the hot fluid inlet pipe 201 from the edge of the upper surface of the circular sintered substrate 10, axially penetrates the circular sintered substrate 10, and enters the lower hot fluid chamber. It flows through the porous structure of silver powder on the lower surface for heat exchange, and then exits through the hot fluid outlet pipe 302. The cold fluid (dilute phase) enters through the cold fluid inlet pipe 301 from the edge of the lower surface of the circular sintered substrate 10, axially penetrates the circular sintered substrate 10, and enters the upper cold fluid chamber. It flows through the porous structure of silver powder on the upper surface for heat exchange, and then exits through the cold fluid outlet pipe 202. The heat from the hot fluid is transferred to the circular sintered substrate 10 through the lower silver powder layer, and then to the upper silver powder layer via the circular sintered substrate 10, ultimately being carried away by the cold fluid, thus achieving counter-current heat exchange. In this process, the large specific surface area of ​​the porous structure of silver powder allows heat to be fully exchanged within a shorter flow path, effectively overcoming the adverse effects of the Carpicar thermal resistance in the millikel temperature range.

[0040] like Figure 4 As shown, this embodiment provides a multi-stage circular metal powder sintered heat exchanger. This multi-stage heat exchanger consists of three single-stage heat exchangers arranged in series along the axial direction, from top to bottom: stage 101, stage 102, and stage 103. From the first stage to the third stage, the diameter of each heat exchanger increases progressively to accommodate the changes in the thermodynamic properties of the fluid at different temperature stages. In practical applications, the number of stages can be flexibly adjusted according to cooling requirements. For applications with high target temperatures and stringent compactness requirements, a 2-stage or 3-stage configuration can be used; for applications requiring extremely low temperatures, up to 5 stages can be added. More stages result in a larger total heat exchange area and a lower achievable mixing chamber temperature, but the axial length of the insert also increases. A 4-stage configuration achieves a good balance between cooling power, heat exchange efficiency, axial space occupation, and assembly complexity.

[0041] During the dilution refrigeration process, the temperature of the hot and cold fluids gradually decreases from a higher inlet temperature to an outlet temperature in the milliKelvin range. In the first few stages with higher temperatures, the fluid volumetric flow rate is large, requiring a large heat exchange area to ensure sufficient heat exchange. As the fluid cools down stage by stage, its thermodynamic parameters change continuously, and its specific volume and thermal conductivity also change accordingly. The design of gradually increasing diameter allows the fluid at different temperature stages to exchange heat under the conditions of a matching heat exchange area, achieving tiered heat exchange and optimizing the overall heat exchange efficiency.

[0042] Adjacent heat exchangers are directly welded together via cold fluid connecting pipes and hot fluid connecting pipes. Specifically (taking four stages as an example): the cold fluid inlet pipe of the previous stage is welded to the cold fluid outlet pipe of the next stage via a cold fluid connecting pipe, and the hot fluid outlet pipe of the previous stage is welded to the hot fluid inlet pipe of the next stage via a hot fluid connecting pipe. With each stage of heat exchangers connected in series, the cold and hot fluids flow sequentially within each stage. The cold fluid flows in from the fourth stage, passes through the third, second, and first stages, and then flows out; the hot fluid flows in from the first stage, passes through the second, third, and fourth stages, and then flows out. In each stage of the heat exchanger, the cold and hot fluids form a counter-current heat exchange, gradually completing a multi-stage heat exchange process from high temperature to low temperature.

[0043] Based on the dilution cooling insert with a sample transfer channel in the above embodiments, the present invention provides a sample transfer operation, as follows: Step 1, Pre-cooling stage: After evacuating the vacuum chamber, immerse the dilution cooling plug into the liquid helium Dewar, and cool the components inside the vacuum chamber to the liquid helium temperature of about 4.2K.

[0044] Step 2, Sample Loading Stage: Using the magnetic transfer rod in the sample transfer channel, the third heat insulation plug (located in the refrigerant delivery pipeline), the first heat insulation plug, and the second heat insulation plug are removed respectively, and the sample to be tested is installed at the measurement position at the bottom of the mixing chamber 150. The transfer rod is inserted from the sample transfer channel inlet at the top of the vacuum chamber, and passes sequentially through the central through holes of the precooling device 110, the distillation device 120, the shell-and-tube heat exchanger 130, and the sintering heat exchanger 140, finally delivering the sample to the bottom of the mixing chamber 150.

[0045] Step 3, Cooling Measurement Stage: After sample installation, use a magnetic transfer rod to return the second, first, and third heat insulation plugs to their respective positions step by step through the sample transfer channel, restoring the channel to a closed state. The order of heat insulation plug return is as follows: first return the second heat insulation plug (mixing chamber through-hole), then return the first heat insulation plug (pre-cooling device through-hole), and finally return the third heat insulation plug (refrigerant delivery pipeline). This sequence ensures that during the placement of the upper heat insulation plug, the lower layer is already sealed by the heat insulation plugs in place, preventing heat leakage windows caused by simultaneous opening at both ends of the channel. Then, first activate the 1K cell circulation to lower the temperature of the 1K cell to approximately 1K; then activate the dilution cooling cycle to gradually cool the mixing chamber 150. After the mixing chamber 150 is cooled to 5-100mK, sample measurements begin. Throughout the cooling process, the sample transfer channel remains sealed by the heat insulation plug, and heat leakage along the channel is controlled within permissible levels. The cooling rate and steady-state temperature of the dilution cooling unit are not substantially affected by the presence of the sample transfer channel.

[0046] In summary, this invention provides a dilution refrigeration insert structure with a sample transfer channel and a dilution refrigeration insert. The dilution refrigeration insert structure includes: a vacuum chamber, within which, from top to bottom, are arranged a precooling device, a distillation device, a shell-and-tube heat exchanger, a multi-stage circular metal powder sintering heat exchanger, and a mixing chamber; each of the precooling device, distillation device, shell-and-tube heat exchanger, sintering heat exchanger, and mixing chamber has a through hole in its center; wherein the through holes are coaxially aligned and interconnect to form a sample transfer channel extending from the top of the vacuum chamber to the bottom of the mixing chamber; a first heat insulation plug and a second heat insulation plug, used to seal the sample transfer channel in a non-sample transfer state; the first heat insulation plug is detachably disposed within the through hole of the distillation device; the second heat insulation plug is detachably disposed within the through hole of the mixing chamber. The hollow configuration design with through holes in the center of each component integrates the sample transfer channel with the functional body of each component, achieving axial sample transfer without adding extra structural parts, resulting in a compact overall structure. The circular powder sintering heat exchanger uses an upper and lower annular wall to form a dense phase downward flow channel and a dilute phase upward flow channel, respectively, with the central through hole independent of the heat exchange channel. While maintaining efficient countercurrent heat exchange, the central through hole remains unobstructed, achieving synergistic coexistence of sample transfer and heat exchange functions. The first and second heat insulation plugs are respectively located in the through holes of the precooling device and the mixing chamber, sealing both ends of the channel simultaneously from the high-temperature end close to room temperature and the mK end close to extremely low temperature, effectively blocking heat radiation and gas conduction along the channel. The multi-stage sintering heat exchanger scheme allows for flexible selection of the number of stages according to the target temperature and cooling power, adapting to different application scenarios. The on / off state of the refrigerant delivery pipeline is linked to the sample transfer operation, eliminating the need for additional valve mechanisms, making the system simple and reliable.

[0047] Finally, it should be noted that the above embodiments are only for illustrating the present invention and not for limiting the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications, or equivalent substitutions of the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and should be covered within the scope of the claims of the present invention.

Claims

1. A dilution cooling insert with a sample transfer channel, characterized in that, include: Top connection pipes; A dilution cooling plug structure with a sample transfer channel includes: a vacuum chamber, in which a precooling device, a distillation device, a shell-and-tube heat exchanger, a sintering heat exchanger, and a mixing chamber are arranged sequentially from top to bottom; each of the precooling device, distillation device, shell-and-tube heat exchanger, sintering heat exchanger, and mixing chamber has a through hole in its middle; wherein the through holes are coaxially aligned and interconnect to form a sample transfer channel extending from the top of the vacuum chamber to the bottom of the mixing chamber; a first heat insulation plug and a second heat insulation plug are used to seal the sample transfer channel when not transferring samples; the first heat insulation plug is detachably disposed in the through hole of the distillation device; the second heat insulation plug is detachably disposed in the through hole of the mixing chamber. The top connecting pipe includes a pipe for sample transfer and a third heat insulation plug. The pipe for sample transfer is coaxially aligned with and connected to the through hole. The third heat insulation plug is used to close the pipe for sample transfer when not transferring samples. The sintered heat exchanger is a circular metal powder sintered heat exchanger, comprising: A circular sintered substrate, wherein a metal powder layer is disposed on both the upper and lower surfaces of the circular sintered substrate; A hot fluid inflow pipe is welded to the upper surface edge region of the circular sintered substrate and extends axially through the circular sintered substrate to guide the hot fluid to the region where the lower surface of the circular sintered substrate is located. A cold fluid inflow pipe is welded to the lower surface edge region of the circular sintered substrate and extends axially through the circular sintered substrate to guide the cold fluid to the region where the upper surface of the circular sintered substrate is located. A cold fluid encapsulation shell is disposed above the circular sintered substrate, and together with the circular sintered substrate, they form a cold fluid chamber. The cold fluid encapsulation shell is provided with a cold fluid outflow pipe. A hot fluid encapsulation shell is disposed below the circular sintered substrate, and together with the circular sintered substrate, they form a hot fluid chamber. The hot fluid encapsulation shell is provided with a hot fluid outflow pipe. The cold fluid encapsulation shell, the circular sintered substrate, and the hot fluid encapsulation shell are stacked and assembled sequentially along the axial direction, and are sealed together as one unit by an annular welded sealing port; The thickness of the metal powder layer is 0.5 mm to 4 mm; The annular welded seal is a continuous annular weld bead formed by argon arc welding or laser welding.

2. The dilution cooling insert with sample transfer channel according to claim 1, characterized in that, The cold fluid outflow pipe is welded to the top surface of the cold fluid encapsulation shell, and the hot fluid outflow pipe is welded to the bottom surface of the hot fluid encapsulation shell. Both the hot fluid inflow pipe and the cold fluid inflow pipe are led out from the side of the circular sintered substrate and penetrate the corresponding sidewall of the encapsulation shell.

3. The dilution cooling insert with sample transfer channel according to claim 1, characterized in that, The metal powder in the metal powder layer is silver powder or copper powder.

4. The dilution cooling insert with sample transfer channel according to claim 1, characterized in that, The sintering heat exchanger is a multi-stage circular metal powder sintering heat exchanger, and the number of stages in the multi-stage circular metal powder sintering heat exchanger is 2 to 5. The circular metal powder sintered heat exchangers of each level are arranged in series along the axial direction, and the diameter of the circular metal powder sintered heat exchangers increases progressively along the flow direction of the cold or hot fluid.

5. The dilution cooling insert with sample transfer channel according to claim 4, characterized in that, The two adjacent circular metal powder sintered heat exchangers are connected by welding cold fluid connecting pipes and hot fluid connecting pipes. The cold fluid connecting pipes connect the cold fluid outlet pipe of the previous stage to the cold fluid inlet pipe of the next stage, and the hot fluid connecting pipes connect the hot fluid outlet pipe of the previous stage to the hot fluid inlet pipe of the next stage.

6. The dilution cooling insert with sample transfer channel according to claim 4, characterized in that, The multi-stage circular metal powder sintering heat exchanger has four stages.

7. A sample transfer method based on the dilution cooling insert as described in any one of claims 1-6, characterized in that, include: The vacuum chamber is evacuated to a vacuum, and the dilution cooling plug is placed in a liquid helium environment; The third heat insulation plug, the first heat insulation plug, and the second heat insulation plug are removed in sequence, and the sample to be tested is sent to the bottom of the mixing chamber; The second heat insulation plug, the first heat insulation plug, and the third heat insulation plug are placed back in their original positions in sequence. The pre-cooling device is then turned on to cool the temperature down to 1K. The refrigeration cycle is then started until the temperature drops to the minimum.

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