Cryogenic cooling apparatus and cryogenic cooling method for samples

Abstract

The cryogenic cooling device includes a container (101) configured to contain a working fluid (102) during operation, and at least one solid micro-refrigerator (103) having a heat receiving end and a heat dissipation end. The cryogenic cooling device includes a sample attachment (704) configured to receive and mechanically and thermally connect to a sample (104) for cooling the sample (104) during operation of the cryogenic cooling device. The at least one solid micro-refrigerator (103) is located in a heat conduction path between the sample attachment and the working fluid (102) contained by the container (101), such that the heat receiving end faces the sample (104) and the heat dissipation end faces the working fluid (102).

Description

Technical Field

[0001] The present invention generally relates to cooling a sample to a temperature in the millikelvin range. In particular, the present invention relates to the structure and operation of a cooling device capable of obtaining a high cooling capacity at low temperatures.

Background Art

[0002] In cryogenic cooling technology, a dilution refrigerator is typically used to cool a sample to a temperature in the millikelvin range, that is, a temperature of several millikelvins to several tens of millikelvins. There are other cooling technologies such as an adiabatic demagnetization refrigerator, but this requires the use of a magnetic field, and when the sample uses a magnetic sensitive component such as a SQUID and / or a quantum bit, in many cases, the use of a magnetic field is impossible.

[0003] The main parts of a dilution refrigerator are a mixing chamber, a fractionator, and a helium circulation system. The mixing chamber is the coldest part where a layer of liquid helium 3 (more precisely, , 4 , 3 , 2 , 3 , 3 ,

[0004] , , the He rich phase or concentrated phase) floats on a liquid helium mixture ( 3 the He dilute phase or diluted phase). The helium circulation system sucks the mixture from the lower part of the mixing chamber and sends it to the fractionator, circulates gaseous helium 3 in the fractionator, and after purification and condensation, returns it to the 3 He rich phase in the mixing chamber. Since the process of moving helium 3 across the phase boundary in the mixing chamber is endothermic, when the conditions and the helium circulation are appropriate, the mixing chamber is cooled to an extremely low temperature of only a few millikelvins. In a cryostat, the mixing chamber is attached to a mechanical structure that constitutes a working area to which a payload to be cooled is attached. The payload is usually called a sample and may include, for example, a scientific experiment or one or more quantum processing circuits.

[0004] The cooling capacity of an operating dilution refrigerator is from the second to the fourth power of the temperature, that is, ~T 2 …T 4It scales almost to that extent. As an unfortunate consequence, the cooling capacity decreases significantly as you approach the lowest temperature. For example, in many applications such as practical quantum computers, there would be great advantages to combining high cooling capacity with very low achievable temperatures. This requires a large amount of helium-3 and a large infrastructure of helium circulation system in dilution refrigerators, and simply increasing the helium circulation rate without changing the dimensions inevitably sacrifices some of the achievable temperature. Since helium-3 is a scarce and extremely valuable resource, increasing the amount of helium-3 to increase cooling capacity is an expensive solution. [Overview of the project] [Problems that the invention aims to solve]

[0005] The objective is to provide hardware means and methods that are inexpensive, eliminate technical complexity, and provide high cooling capacity at low temperatures. Furthermore, the objective is to provide a cryogenic cooling system that can operate over a wide range of parameter values ​​to find the optimal combination of cooling capacity, temperature, and cost. Finally, the objective is to provide a cryogenic cooling system and method that is scalable to meet cryogenic cooling needs of various capacities. [Means for solving the problem]

[0006] These objectives, and many more beneficial ones, are achieved by utilizing a solid micro-refrigerator between the coldest part of the helium circulation and the sample.

[0007] According to one embodiment, a cryogenic cooling device is provided, comprising a container configured to contain an operating fluid during operation, and at least one solid-state microrefrigerator having a heat-receiving end and a heat-dissipating end. The cryogenic cooling device includes a sample attachment configured to receive and mechanically and thermally connect to a sample for cooling the sample during operation of the cryogenic cooling device. The at least one solid-state microrefrigerator is located in a heat conduction path between the sample attachment and the operating fluid contained by the container, such that the heat-receiving end faces the sample and the heat-dissipating end faces the operating fluid.

[0008] According to one embodiment, the container includes a cover portion attached to the base portion by a sealed mounting portion. This provides at least the advantage of facilitating the manufacture of the container and the assembly of the container as part of a cryogenic cooling system.

[0009] According to one embodiment, at least one of the at least one solid micro-refrigerator is located inside the container within the space defined by the cover and the base. This provides at least the advantage of enabling efficient heat transfer from the solid micro-refrigerator to the working fluid.

[0010] According to one embodiment, the base portion is an integrated structure between the sealed mounting portion and the sample mounting portion. This provides at least the advantage of a simple and robust base portion structure.

[0011] According to one embodiment, the base portion includes at least a first part manufactured from a first material and a second part manufactured from a second material different from the first material, wherein the first part and the second part are fixedly attached to each other. The first part may be involved in the sealed mounting portion, and the second part may be involved in the sample mounting portion. This provides at least the advantage that the base portion can be precisely adjusted to various requirements regarding its mechanical and thermal properties.

[0012] According to one embodiment, the first portion is manufactured from the same material as the cover portion, and the second material has a higher thermal conductivity than the first material at sub-Kelvin temperatures. This provides at least the advantage that the second portion can efficiently conduct heat as part of the heat conduction path of the sample, and the first portion can be mechanically fitted very well with the cover portion.

[0013] According to one embodiment, the cryogenic cooling device includes a thermal interface enhancer attached to the heat dissipation end of a solid micro-refrigerator. This provides at least the advantage of efficiently transferring heat from the solid micro-refrigerator to the working fluid and avoiding inefficient thermal coupling between other nearby parts.

[0014] According to one embodiment, the heat transfer facilitator includes a sintered thermally conductive material. This provides at least the advantage that the heat transfer facilitator can be manufactured by a well-known method to have well-known properties.

[0015] According to one embodiment, the heat transfer facilitator includes an array of thermally conductive posts protruding from the heat dissipation end of the solid microrefrigerator. This provides at least the advantage that multiple options are available for manufacturing at least a portion of the heat transfer facilitator.

[0016] According to one embodiment, the at least one solid micro-refrigerator includes at least one NIS refrigerator or SINIS refrigerator, in the order from the heat receiving end to the heat dissipation end, a first contact layer, a layer of normal metal-insulator-superconductor tunnel junctions or superconductor-insulator-normal metal-insulator-superconductor tunnel junctions, and a second contact layer. This provides at least the advantage of achieving efficient cooling at cryogenic temperatures with minimal additional losses.

[0017] According to one embodiment, the cryogenic cooling device includes a dilution refrigerator, and the container is the mixing chamber of the dilution refrigerator. This provides at least the advantage that a reference temperature in the millikelvin range can be used as the starting point for the solid microrefrigeration device.

[0018] A second embodiment provides a method for cryogenically cooling a sample. The method includes the steps of supplying a cooled working fluid into a container, using at least one solid microrefrigerator to absorb heat from the sample to the low-temperature end of the solid microrefrigerator, and releasing heat from the high-temperature end of the solid microrefrigerator toward the working fluid.

[0019] According to one embodiment, the step of releasing heat from the high-temperature end of the solid microrefrigerator toward the working fluid includes the step of directly releasing the heat from the high-temperature end of the solid microrefrigerator toward the working fluid. This provides at least the advantage of a relatively simple and efficient heat conduction path.

[0020] According to one embodiment, the step of releasing heat from the high-temperature end of the solid micro-refrigerator toward the working fluid includes the step of releasing the heat from the high-temperature end of the solid micro-refrigerator toward the low-temperature end of another solid micro-refrigerator. This provides at least the advantage of being able to reach a lower temperature than when using only a single solid micro-refrigerator.

[0021] According to one embodiment, the step of supplying the cooled working fluid into the container includes the step of circulating a helium mixture in a mixing chamber of a dilution refrigerator, and the method includes the step of operating the dilution refrigerator at a level such that the temperature of the mixing chamber becomes less than 600 mK and higher than 50 mK. Thereby, at least the advantage can be obtained that the dilution refrigerator can provide a higher cooling capacity than when it has to be operated near the absolute lowest achievable reference temperature.

Brief Description of the Drawings

[0022] The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

[0023] [Figure 1] Shows a cryogenic cooling arrangement according to one embodiment. [Figure 2] Shows a cryogenic cooling arrangement according to one embodiment. [Figure 3] Shows a cryogenic cooling arrangement according to one embodiment. [Figure 4] Shows a cryogenic cooling arrangement according to one embodiment. [Figure 5] Shows a cryogenic cooling arrangement according to one embodiment. [Figure 6] Shows a cryogenic cooling arrangement according to one embodiment. [Figure 7] Shows a cryogenic cooling arrangement according to one embodiment. [Figure 8] Is an exploded view of a solid micro-refrigerator. [Figure 9] Shows a cryogenic cooling arrangement according to one embodiment. [Figure 10] Shows details of a cryogenic cooling arrangement according to one embodiment. [Figure 11] Shows details of a cryogenic cooling arrangement according to one embodiment. [Figure 12] Shows a cryogenic cooling arrangement according to one embodiment. [Modes for carrying out the invention]

[0024] The following description refers to the accompanying drawings, which constitute part of this disclosure and illustrate specific embodiments to which this disclosure may apply. It should be understood that other embodiments or structural or logical modifications may be used without departing from the scope of this disclosure. Therefore, the following detailed description should not be construed as restrictive, and the scope of this disclosure shall be defined by the accompanying claims.

[0025] For example, it should be understood that disclosures relating to a method described also apply to corresponding devices or systems configured to perform that method, and vice versa. For instance, when describing steps of a particular method, the corresponding device may include units that perform the steps of the described method, even if such units are not explicitly described or illustrated. Conversely, when describing a particular device based on a functional unit, the corresponding method may include steps that perform the function described, even if such steps are not explicitly described or illustrated. Furthermore, unless otherwise specified, it should be understood that features of the various exemplary embodiments described herein can be combined with each other.

[0026] In this specification, the concept of temperature primarily refers to so-called macroscopic temperature. Macroscopic temperature is intuitively understandable because it is the quantity indicated on the scale of a thermometer used in everyday life, but in a strict physical sense, it should only be understood as the sum of the average kinetic energies of the atomic or molecular particles that make up a substance, and this is a statistical measure, not an accurate physical quantity. In solid conductive (or superconducting) materials, phonon temperature is a measure of the kinetic energy of nucleons, and electron temperature is the kinetic energy stored in the conduction electrons of the material. Since atoms have both electrons and nucleons, electron-phonon coupling exists. The way the concept of temperature is used in this specification is closely related to the flow of thermal energy on a macroscopic scale between different objects and / or substances.

[0027] In the following explanation, the solid micro-refrigerator plays a crucial role. This term refers to a type of device that transfers heat from a heat-receiving end to a heat-dissipating end in response to power supplied from a power source. In other words, a solid micro-refrigerator is a solid-state device that can lower the macroscopic temperature of a first object (and / or first substance) thermally coupled to the heat-receiving end of the solid micro-refrigerator, and accordingly raise the macroscopic temperature of a second object (and / or second substance) thermally coupled to the heat-dissipating end of the solid micro-refrigerator.

[0028] One possible form of a solid microrefrigerator is based on the use of electrons in a standard transistor structure as a gas-equivalent refrigerant that induces cooling by alternately expanding and compressing in a Carnot cycle. Such a solid microrefrigerator is described, for example, in U.S. Patent Application Publication No. 20220208644A1, which is incorporated herein by reference.

[0029] Another possible form of solid microrefrigeration is an electrocaloric cooler. Such solid microrefrigeration is described, for example, in the scientific publication Adriana Greco, Claudia Masselli, "Electrocaloric Cooling: A Review of the Thermodynamic Cycles, Materials, Models, and Devices," Magnetochemistry 2020, 6, 67, doi:10.3390 / magnetochemistry 6040067, which is incorporated herein by reference.

[0030] Other possible forms of solid micro-refrigerators are those based on a normal-conducting metal-insulator-superconductor tunnel junction, a superconductor-insulator-normal-conducting metal-insulator-superconductor tunnel junction, or a semiconductor-superconductor tunnel junction. Such solid micro-refrigerators are often referred to as NIS refrigerators, SINIS refrigerators, or Sm-S refrigerators, respectively. An example of an NIS refrigerator is described, for example, in U.S. Patent Publication No. 6,581,387B1, incorporated herein by reference. An example of an Sm-S refrigerator is described, for example, in the scientific publication Emma Mykkanen et al., “Thermionic junction devices utilizing phonon blocking,” Sci.Adv. 2020;6:eaax9191, April 10, 2020, incorporated herein by reference.

[0031] Figure 1 schematically shows a part of a cryogenic cooling system. The cryogenic cooling system includes a container 101 configured to contain a working fluid 102 during operation. In a non-limiting example, the cryogenic cooling system may include a dilution refrigerator, in which case the container 101 may be the mixing chamber of the dilution refrigerator, as indicated by the text labels in Figure 1. In such a case, the working fluid 102 in the container 101 consists of a mixture of helium isotopes, helium-3 and helium-4. In another example, the container 101 may be part of a cooling system based on the evaporation of liquid helium, in which case the working fluid 102 is liquid helium.

[0032] The cryogenic cooling apparatus in Figure 1 includes at least one solid micro-refrigerator 103 having a heat receiving end (low temperature end) and a heat dissipation end (high temperature end). When operational, the solid micro-refrigerator 103 can maintain a temperature gradient between its low temperature end and high temperature end. The solid micro-refrigerator 103 absorbs heat from anything thermally coupled to its low temperature end, transfers the absorbed heat to its high temperature end, and at this high temperature end, releases heat to any other object or substance thermally coupled to the high temperature end. In Figure 1 and subsequent drawings, the low temperature end of the solid micro-refrigerator 101 faces downward, and the high temperature end faces upward.

[0033] For the sake of simplicity in the drawings, Figure 1 includes only one block labeled solid micro-refrigerator 103. In practical embodiments of the principle shown in Figure 1 and the subsequent drawings, there may be multiple solid micro-refrigerators configured in parallel and / or in series. In a parallel configuration of two solid micro-refrigerators, the cold ends of the solid micro-refrigerators are coupled together, and the hot ends of the solid micro-refrigerators are coupled together. In a series configuration of two solid micro-refrigerators, the hot end of one solid micro-refrigerator is coupled to the cold end of the other solid micro-refrigerator.

[0034] The cryogenic cooler in Figure 1 includes a sample mounting section configured to receive and mechanically and thermally connect a sample 104. Its purpose is to cool the sample 104 during operation of the cryogenic cooler. The sample 104 may alternatively be called a payload. The sample 104 may be, for example, part of a scientific experiment and / or quantum processing circuit. The sample mounting section is configured to allow the sample (more generally, one or more samples) to be mounted, replaced, and removed without requiring the removal of other components provided in the work area. In particular, the sample mounting section allows the solid micro-refrigerator 103 to be part of the work area (structure provided in it), so that the sample can be mounted, replaced, and removed independently of the solid micro-refrigerator.

[0035] At least one solid micro-refrigerator 103 is located in the heat conduction path between the sample mounting section and the working fluid 102 contained in the container 101. The heat receiving end (low temperature end) of the solid micro-refrigerator 103 faces the sample 104, and the heat dissipation end (high temperature end) of the solid micro-refrigerator 103 faces the working fluid 102. Thus, the solid micro-refrigerator 103 is configured to transfer heat from the sample 104 to the working fluid 102 during operation. This allows the sample 104 to be cooled to a lower temperature than the working fluid 102 in the container 101 during operation.

[0036] In Figure 1, the cryogenic cooler includes a support structure 105 that mechanically supports the container 101. The support structure 105 may be, for example, a flange of a cryostat. Considering its position in the heat conduction path between the sample mounting portion and the working fluid 102 contained in the container 101, the solid micro-refrigerator 103 is located between the sample 104 and the support structure 105. The solid micro-refrigerator 103 may include (at least a portion of) the sample mounting portion, thereby allowing the sample 104 to be (at least partially) attached to the solid micro-refrigerator 103. From a mechanical attachment point of view, the solid micro-refrigerator 103 may be a mechanical element that attaches the sample 104 to the support structure 105. The heat absorbed from the sample 104 by the low-temperature end of the solid micro-refrigerator 103 is transferred through the solid micro-refrigerator 103, released from the high-temperature end of the solid micro-refrigerator 103 to the support structure 105, further conducted from the support structure 105 to the structure of the container 101, and finally conducted to the working fluid 102.

[0037] Figure 2 shows a part of a cryogenic cooling apparatus similar to the one in Figure 1, except that the position of the solid micro-refrigerator 103 in the heat conduction path between the sample mounting section and the working fluid 102 contained in the container 101 is slightly different. In Figure 2, the solid micro-refrigerator 103 is located between the support structure 105 and the container 101. Heat from the sample 104 is conducted to the support structure 105 and absorbed from the support structure 105 by the low-temperature end of the solid micro-refrigerator 103. The absorbed heat is transferred through the solid micro-refrigerator 103, released from the high-temperature end of the solid micro-refrigerator 103 to the structure of the container 101, and conducted from the structure of the container 101 to the working fluid 102.

[0038] In the embodiment shown in Figure 2, the solid micro-refrigerator 103 may constitute at least a portion of the mechanical mounting section between the container 101 and the support structure 105. Furthermore, the solid micro-refrigerator 103 may constitute the sole mechanical element for attaching the container 101 to the support structure 105.

[0039] Figure 3 shows a portion of a cryogenic cooling apparatus similar to those in Figures 1 and 2, except that the position of the solid micro-refrigerator 103 in the heat conduction path between the sample mounting section and the working fluid 102 contained in the container 101 is slightly different. In Figure 3, the solid micro-refrigerator 103 is positioned between the structure of the container 101 and the working fluid 102 contained within the container 101. Heat from the sample 104 is conducted to the support structure 105, and further conducted from the support structure 105 to the structure of the container 101. The low-temperature end of the solid micro-refrigerator 103 absorbs heat from the structure of the container 101. The absorbed heat is transferred through the solid micro-refrigerator 103 and released into the working fluid 102 from the high-temperature end of the solid micro-refrigerator 103. In the embodiment of Figure 3, the solid micro-refrigerator 103 may be characterized by facilitating heat transfer from the solid structure of the container 101 to the working fluid 102 contained within the container 101.

[0040] Figure 4 shows a portion of a cryogenic cooling apparatus similar to those in Figures 1-3, except that the position of the solid micro-refrigerator 103 in the heat conduction path between the sample mounting section and the working fluid 102 contained in the container 101 is slightly different. In Figure 4, the solid micro-refrigerator 103 is located between the sample 104 and the structure of the container 101. Heat from the sample 104 is absorbed by the low-temperature end of the solid micro-refrigerator 103, transferred through the solid micro-refrigerator 103, and released from the high-temperature end of the solid micro-refrigerator 103 to the structure of the container 101, where the heat is further coupled to the working fluid 102. In a sense, at least considering thermal coupling, in the embodiment of Figure 4, the solid micro-refrigerator 103 bridges the support structure 105.

[0041] It should be noted that the graphical representations in Figures 1 to 6 are only schematic and should not be interpreted as teaching a specific mechanical structure. For example, in Figure 4, one possibility is that the support structure 105 supports the container 101 only by its sides or top edge, so that the solid micro-refrigerator 103 is the only element mechanically connecting the sample 104 to the container 101 (the lower part). Furthermore, it is never taught that in any embodiment the sample 104 must be located below the container 101. The principle shown in Figure 4 is, for example, that the support structure 105 supports the container 101 from below, but the solid micro-refrigerator 103 can be implemented to attach the sample 104 to the side and / or top surface of the container 101. However, it is possible that the support structure 105 may also provide some direct mechanical support to the solid micro-refrigerator 103 and / or the sample 104.

[0042] Figure 5 shows a part of a cryogenic cooling apparatus similar to those in Figures 1 to 4, except that the position of the solid micro-refrigerator 103 in the heat conduction path between the sample mounting section and the working fluid 102 contained in the container 101 is slightly different. In Figure 5, the solid micro-refrigerator 103 is located between the support structure 105 and the working fluid 102 contained in the container 101. Heat from the sample 104 is conducted to the support structure 105, absorbed from the support structure 105 by the low-temperature end of the solid micro-refrigerator 103, transmitted through the solid micro-refrigerator 103, and released into the working fluid 102 from the high-temperature end of the solid micro-refrigerator 103.

[0043] In Figure 5, the solid micro-refrigerator 103 may enclose a space for the working fluid 102 and constitute part of the solid structure of the container 101 that holds the working fluid 102 inside the container 101. At the same time, the solid micro-refrigerator 103 may form at least part of the attachment portion of the container 101 to the support structure 105. From the viewpoint of heat conduction, it bridges the other mechanical structure of the container 101 by directly transferring heat between the support structure 105 and the working fluid 102.

[0044] In Figure 6, the solid micro-refrigerator 103 is positioned between the sample 104 and the working fluid 102. The solid micro-refrigerator 103 can directly transfer heat from the sample 104 to the working fluid 102 and can bridge the structure of both the support structure 105 and the container 101. Heat from the sample 104 is absorbed by the low-temperature end of the solid micro-refrigerator 103, transferred through the solid micro-refrigerator 103, and released into the working fluid 102 from the high-temperature end of the solid micro-refrigerator 103.

[0045] Mechanically, in Figure 6, the solid micro-refrigerator 103 may form part of the support structure 105 and / or part of the structure of the container 101. Alternatively, since the support structure 105 may be located on the side or above the container 101, although it is primarily used as shown in the figure, the solid micro-refrigerator 103 does not need to pass through any part of the support structure 105 in a mechanical sense. If the solid micro-refrigerator 103 forms part of the mechanical structure of the container 101 (i.e., a wall), the solid micro-refrigerator 103 (and its attachment to other parts of the container structure) must be sufficiently airtight to prevent the working fluid 102 from leaking out of the container 101.

[0046] A feature common to all embodiments described herein is the order of the cooling mechanisms. Since the purpose of cooling a sample in a cryostat is to bring the sample to a low temperature, from the standpoint of heat transfer pathways, the cooling mechanism closest to the sample must be the one that can achieve the lowest temperature. In the embodiments described herein, a solid micro-refrigerator is used to achieve a temperature lower than that of the vessel containing the working fluid. Therefore, the vessel configured to contain the working fluid does not need to be designed to achieve a temperature as low as that of the solid micro-refrigerator (or its cryogenic head).

[0047] This can be considered in conjunction with the fact that, for example, the cooling capacity achievable with a dilution refrigerator scales from the square to the fourth power of the temperature. On the other hand, the cooling capacity of many types of solid micro-refrigeration is approximately T 1.5It simply scales to the desired temperature. For example, if the goal is to cool a sample to 10 mK, but the solid micro-refrigerator handles the final cooling step from 100 mK to 10 mK, then the dilution refrigerator does not need to reach temperatures below 100 mK. Because the cooling capacity of the dilution refrigerator is much higher at 100 mK than at 10 mK, the system can handle a much larger heat load in the sample than conventional systems where the dilution refrigerator needs to reach 10 mK, provided the solid micro-refrigerator has sufficient cooling capacity. According to the physical laws of dilution refrigeration, the mixing chamber needs to be below approximately 600 mK during operation, but the principle as interpreted herein does not require the mixing chamber to reach temperatures of a few millikelvin or tens of millikelvin. Operating this type of cryogenic cooling system with a dilution refrigerator may include operating the dilution refrigerator at a level that keeps the temperature of the mixing chamber below 600 mK and above 50 mK.

[0048] Figure 7 is a cross-sectional view of a portion of the cryogenic cooling apparatus. In this figure, the vessel mentioned in the descriptions of Figures 1-6 is assumed to be the mixing chamber of the dilution refrigerator. At the top of Figure 7, arrows indicate the possible directions in which the helium mixture may enter and exit the vessel.

[0049] In the embodiment shown in Figure 7, the container includes a cover portion 701 attached to a base portion 702 by a sealed mounting portion. A seal 703 is schematically shown between the edge of the cover portion 701 and the corresponding receiving surface of the base portion 702. As shown by the dashed line extending outward, the base portion 702 may also constitute the cryogenic flange of the cryostat, although this is not a mandatory requirement. Viewed from Figures 1 to 6, the base portion 702 in Figure 7 may be considered to constitute (at least part of) the support structure of the container. Alternatively, the base portion 702 may be considered to constitute part of the mixing chamber structure, as it also defines the space in which the working fluid is contained.

[0050] The cryogenic cooler in Figure 7 includes a sample mounting section, which in this exemplary embodiment is represented in the lower surface of the base 702 as three screw holes indicated by reference numeral 704. This allows the sample to be bolted to the lower surface of the base 702. This method of mounting the sample is merely one example, and other possible methods can be used instead of or in addition to the screw holes. Examples of such other possibilities include, but are not limited to, one or more threaded extruded parts and clamps configured to press the sample against the base or other support.

[0051] The solid micro-refrigerator 103 is positioned according to the principle shown in Figure 3 or Figure 5, depending on whether the base portion 702 is considered part of the container structure or part of the support structure. Thermally, the solid micro-refrigerator 103 is located in the heat conduction path between the working fluid, which is contained within a sealed cavity defined by the cover portion 701 and the base portion 702, and the sample mounting portion 704. As in Figures 1 to 6, the heat-receiving end (low-temperature end) of the solid micro-refrigerator 103 is the lower end in Figure 7, i.e., the end attached to the base portion 702. Therefore, the heat-receiving end of the solid micro-refrigerator 103 faces the sample attached to the sample mounting portion 704. The heat-dissipating end (high-temperature end) of the solid micro-refrigerator 103 is the upper end in Figure 7.

[0052] Mechanically, in the embodiment shown in Figure 7, the solid micro-refrigerator 103 is located inside a container or space defined by the cover portion 701 and the base portion 702.

[0053] The heat transfer enhancer 705 is attached to the heat dissipation end of the solid microrefrigerator 103. When using the heat transfer enhancer 705, the objective is to improve the thermal coupling between the high-temperature end of the solid microrefrigerator 103 and what it is thermally coupled to. In the embodiment shown in Figure 7, the heat transfer enhancer 705 is thermally coupled to the working fluid contained in the mixing chamber during operation. In such cases, the heat transfer enhancer 705 may include, for example, a sintered thermal conductive material. Additionally or alternatively, the heat transfer enhancer 705 may include an array of thermal conductive posts protruding from the heat dissipation end of the solid microrefrigerator 103. Such thermal conductive posts can be manufactured, for example, by electroplating. Additionally or alternatively, the heat transfer enhancer 705 may include a solid material formed into a final shape in an additive manufacturing process, such material having at least 10 5 It has a surface area-to-volume ratio of 1 / m. In this case, the material includes a plurality of extended heat conduction paths formed as regularly shaped portions of the solid material, these paths extending over most of the thickness of the material and forming a repeating pattern throughout the entire layer of the material.

[0054] Figure 8 is an exploded cross-sectional view of the most important layer of one possible type of solid microrefrigerator 103. Here, the solid microrefrigerator 103 is an NIS refrigerator or a SINIS refrigerator. The solid microrefrigerator 103 includes, in order from the heat receiving end to the heat dissipation end, a first contact layer 801, a layer 802 of a normal-conducting metal-insulator-superconductor tunnel junction or a superconductor-insulator-normal-conducting metal-insulator-superconductor tunnel junction, and a second contact layer 803. A bias voltage coupling section 804 is connected to the upper and lower halves of the normal-conducting metal-insulator-superconductor tunnel junction or superconductor-insulator-normal-conducting metal-insulator-superconductor tunnel junction layer 802. The geometric shape of the layer 802 may include a constriction to optimize performance against heat leakage due to undesirable phonon transport in the reverse direction.

[0055] In the embodiment shown in Figure 7, the layer shown as the first contact layer 801 in Figure 8 connects the NIS refrigerator or SINIS refrigerator 103 to the base 702. The layer shown as the second contact layer 803 in Figure 8 connects the NIS refrigerator or SINIS refrigerator 103 to the heat transfer facilitator 705. The first contact layer 801 and the second contact layer 803 may include several materials that are thermally conductive but electrically insulating, such as aluminum oxide. Electrical insulation by the first contact layer 801 and the second contact layer 803 is not essential, but may help optimize the performance of the solid micro-refrigerator and electrically protect it. For graphical clarity, the wiring of the bias voltage coupling is not shown in Figure 7. This is because the exact wiring method of the bias voltage coupling is not important in this specification.

[0056] Figure 9 is a cross-sectional view of a part of the cryogenic cooling apparatus. Here again, the container referred to in the description of Figures 1 to 6 is assumed to be the mixing chamber of the dilution refrigerator. In the embodiment of Figure 9, the container also includes a cover portion 701 attached to the base portion. However, in the embodiment of Figure 7, the base portion (702) is an integrated structure between the sealed mounting portion (703) and the sample mounting portion (704), whereas this is not the case in the embodiment of Figure 9. In Figure 9, the base portion includes a first portion 901 manufactured from a first material and a second portion 902 manufactured from a second material different from the first material. The first portion 901 and the second portion 902 are fixedly mounted at the position indicated by reference numeral 903. The first portion 901 is accompanied by the sealed mounting portion 703 together with the cover portion 701. The second portion 902 is accompanied by the sample mounting portion 704. In the exemplary embodiment shown in Figure 9, the sample mounting portion 704 includes a screw hole on the surface of a second portion 902 that is accessible from outside the container for the working fluid.

[0057] The first part 901 and the second part 902 are manufactured from different materials in order to optimize their properties for their respective intended uses. The first part 901 may be manufactured from the same material as the cover part 701, for example. This provides at least the advantage of reducing the mechanical stress on the sealed mounting part 703 during cooling compared to when the cover part 701 and the first part 901 are manufactured from materials with different coefficients of thermal expansion. The first material may be, for example, stainless steel.

[0058] The second material, i.e., the material of the second part 902, may have a higher thermal conductivity at sub-Kelvin temperatures than the first material. This provides at least the advantage that the second part 902 constitutes an effective heat conduction path between the sample attached to the sample mounting section 704 and the low-temperature end of the solid micro-refrigerator 103. The second material may be, for example, a type of copper particularly suitable for cryogenic applications.

[0059] The fixed mounting portion 903 between the first portion 901 and the second portion 902 can be manufactured in any preferred method that is robust enough to securely mount two solid pieces of different materials in cryogenic applications. One example of a preferred mounting method is brazing. In any case, it is advantageous to configure the mounting portion 903 such that the thermal conductivity between the first portion 901 and the second portion 902 is low. One way to achieve this objective is to ensure that the cross-sectional area of ​​the mounting portion is small. In the embodiment of Figure 9, the edges of the opening of the first portion 901 are much thinner than the majority of the first portion. This is because they provide only a relatively small surface area to contact the second portion 902.

[0060] As indicated by the continuous dashed lines extending outward, the first part 901 may also simultaneously constitute the cryogenic flange of the cryostat, although this is not a mandatory requirement.

[0061] Similar to the embodiment in Figure 7, in the embodiment in Figure 9, the solid micro-refrigerator 103 is located inside a container within the space defined by the cover portion 701 and the base portion. Also, similar to the embodiment in Figure 9, a heat transfer promoter 705 is attached to the heat dissipation end of the solid micro-refrigerator 103.

[0062] At first glance, it might appear that the working fluid contained within the space defined by the cover and base portions would thermally short-circuit the solid micro-refrigerator 103 in the embodiments shown in Figures 7 and 9. In other words, the working fluid (which maintains a nearly constant temperature throughout) is in contact with both the high-temperature end (upper end) and at least the edge of the low-temperature end (lower end) of the solid micro-refrigerator 103, as well as with the solid portion (base portion 702 in Figure 7, second portion 902 in Figure 9) that transfers heat from the sample to the low-temperature end of the solid micro-refrigerator 103.

[0063] However, at least the specific surface area should be considered. Even without using a heat transfer enhancer, the cross-sectional area available for heat exchange between the high-temperature end of the solid micro-refrigerator 103 and the working fluid is far greater than the cross-sectional area available for heat exchange between the low-temperature end of the solid micro-refrigerator 103 and the working fluid. Secondly, the effect of the heat transfer enhancer 705 is to reduce the Kapitza resistance between the high-temperature end (upper end) of the solid micro-refrigerator 103 and the working fluid. By using sintered blocks, 3D-printed labyrinth structures, etc., as the heat transfer enhancer, this effect can be significant enough to essentially mitigate any effects of the (much weaker) thermal coupling between the working fluid and the low-temperature end of the solid micro-refrigerator 103.

[0064] Figures 10 and 11 are partially enlarged views showing examples of the structure of a heat transfer enhancer. In both Figures 10 and 11, layers 801, 802, and 803 of the solid microrefrigerator are visible at the bottom. In Figure 10, the heat transfer enhancer includes an array of thermally conductive posts 1001 protruding from the hot end (heat dissipation end) of the solid microrefrigerator. These thermally conductive posts 1001 are embedded in a sintered block 705. In Figure 11, the heat transfer enhancer also includes an array of thermally conductive posts 1101 protruding from the hot end (heat dissipation end) of the solid microrefrigerator. These thermally conductive posts 1101 are longer than the posts 1001 in Figure 10 and are effective in sufficiently reducing the Kapitza resistance without requiring additional sintering.

[0065] Figure 12 is a cross-sectional view of a part of the cryogenic cooling apparatus. Here again, the container referred to in the description of Figures 1 to 6 is assumed to be the mixing chamber of the dilution refrigerator. Similar to the embodiment in Figure 9, the base portion constituting the lower part of the container includes a first portion 901 and a second portion 902. The first solid micro-refrigerator 103 is located inside the container in the space defined by the cover portion 701 and the base portion. The sealed mounting portion 703 and the fixed mounting portion 903 may be the same as those with the same reference numerals above, and the materials of the cover portion 701, the first portion 901 and the second portion 902 may also be the same as those with the same reference numerals above. However, the high-temperature end of the second solid micro-refrigerator 1201 is attached to the underside of the second portion 902. Another portion 1202 having a sample mounting portion 704 is attached to the low-temperature end of the second solid micro-refrigerator 1201.

[0066] Figure 12 shows an example of cascaded solid micro-refrigerators, where the low-temperature end of one solid micro-refrigerator 103 is positioned to absorb heat from the high-temperature end of the other solid micro-refrigerator 1201. In addition to (or instead of) cascading, two or more solid micro-refrigerators can be arranged in parallel at any point in the cryogenic cooling system compliant with the foregoing. For example, since key components of NIS, SINIS, and SmS refrigerators are typically manufactured on wafers in the same way as those used in the manufacture of integrated circuits, the size of the solid micro-refrigerator that can be manufactured may be limited by the size of the wafers available. In such cases, two or more solid micro-refrigerators may be connected in parallel and used instead of any of the individual solid micro-refrigerators described above.

[0067] As technology advances, it will be apparent to those skilled in the art that the basic concept of the present invention can be implemented in various ways. Therefore, the present invention and its embodiments are not limited to the examples described above and can be modified within the scope of the claims.

Claims

1. A container (101) configured to contain the working fluid (102) during operation, A solid micro-refrigerator (103) having a heat receiving end and a heat dissipation end A cryogenic cooling device including, To cool the sample (104) during operation of the cryogenic cooling apparatus, it includes a sample mounting section (704) configured to receive and mechanically and thermally connect to the sample, A cryogenic cooling device wherein at least one solid micro-refrigerator (103) is located in a heat conduction path between the sample mounting portion and the working fluid (102) contained in the container (101), such that the heat receiving end faces the sample (104) and the heat dissipating end faces the working fluid (102).

2. The cryogenic cooling apparatus according to claim 1, wherein the container includes a cover portion (701) attached to the base portion (702, 901, 902) by a sealed mounting portion (703).

3. The cryogenic cooling apparatus according to claim 2, wherein at least one of the at least one solid microrefrigerator (103) is located inside the container (101) in the space defined by the cover portion (701) and the base portion (702).

4. The cryogenic cooling apparatus according to claim 2 or 3, wherein the base portion (702) is integrated between the sealed mounting portion (703) and the sample mounting portion (704).

5. The base portion includes at least a first part (901) manufactured from a first material and a second part (902) manufactured from a second material different from the first material, and the first part (901) and the second part (902) are fixedly attached to each other. The first portion (901) is accompanied by the sealed mounting portion (703), The cryogenic cooling apparatus according to claim 2 or 3, wherein the second portion (902) is accompanied by the sample mounting portion (704).

6. The first portion (901) is manufactured from the same material as the cover portion (701), The cryogenic cooling apparatus according to claim 5, wherein the second material has a higher thermal conductivity than the first material at a sub-Kelvin temperature.

7. The cryogenic cooling apparatus according to any one of claims 3 to 6, comprising heat transfer facilitators (705, 1001, 1101) attached to the heat dissipation end of the solid microrefrigerator.

8. The cryogenic cooling apparatus according to claim 7, wherein the heat transfer promoting material (705) includes a sintered thermally conductive material.

9. The cryogenic cooling apparatus according to claim 7 or 8, wherein the heat transfer promoting material includes an arrangement of thermally conductive posts (1001, 1101) protruding from the heat dissipation end of the solid micro-refrigerator.

10. The at least one solid micro-refrigerator has, in order from the heat receiving end to the heat dissipation end, The first contact layer (801), A layer (802) of a normal-conducting metal-insulator-superconductor tunnel junction or a superconductor-insulator-normal-conducting metal-insulator-superconductor tunnel junction, A cryogenic cooling apparatus according to any one of claims 1 to 9, comprising at least one NIS refrigerator or SINIS refrigerator including a second contact layer (803).

11. The cryogenic cooling device includes a dilution refrigerator, The cryogenic cooling apparatus according to any one of claims 1 to 10, wherein the container (101) is the mixing chamber of the dilution refrigerator.

12. A method for cryogenically cooling a sample, The steps include supplying cooled working fluid into a container, The steps include using at least one solid micro-refrigerator (103) to absorb heat from the sample to the low-temperature end of the solid micro-refrigerator (103, 1201), The steps include releasing heat from the high-temperature end of the solid micro-refrigerator (103, 1201) toward the working fluid, and Methods that include...

13. The method according to claim 12, wherein the step of releasing heat from the high-temperature end of the solid micro-refrigerator (103) toward the working fluid includes the step of directly releasing the heat from the high-temperature end of the solid micro-refrigerator (103) toward the working fluid.

14. The method according to claim 12, wherein the step of releasing heat from the high-temperature end of the solid micro-refrigerator (1201) toward the working fluid includes the step of releasing the heat from the high-temperature end of the solid micro-refrigerator (1201) toward the low-temperature end of another solid micro-refrigerator (103).

15. The method according to any one of claims 12 to 14, wherein the step of supplying the cooled working fluid into a container includes the step of circulating a helium mixture in the mixing chamber of a dilution refrigerator, the method comprising the step of operating the dilution refrigerator at a level such that the temperature of the mixing chamber is less than 600 mK and greater than 50 mK.

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