Cryogenic cooling system and insert therefor

Abstract

A cryogenic cooling system is provided that includes a primary insert 118 and a removable secondary insert 128. The primary insert 118 includes a plurality of primary plates 111, 112, each having a primary contact surface, and one or more primary connecting members 117 arranged to connect the plurality of primary plates 111, 112. The removable secondary insert 128 includes a plurality of secondary plates 121, 122, each having a secondary contact surface, and one or more secondary connecting members 127 arranged to connect the plurality of secondary plates 121, 122 such that the secondary insert 128 is self-supporting. The one or more adjustment members are configured such that when the secondary insert 128 is attached to the primary insert 118, the adjustment members place the primary and secondary contact surfaces of the respective primary plates 111, 112 and secondary plates 121, 122 in thermally conductive contact.

Description

[Technical field]

[0001] CRYOGENIC COOLING SYSTEM FIELD OF THEINVENTION The present invention relates to a cryogenic cooling system, and more particularly to a cryogenic cooling system with a free-standing removable insert. [Background technology]

[0002] Cryogenic cooling systems are commonly used to perform experiments at temperatures below 100 Kelvin. Systems are typically customized for a particular experiment by installing the experimental equipment in a specific configuration. Installation of the experimental equipment is difficult and time consuming, typically requiring the use of a crane or elevated platform to access the system. Furthermore, after installation of the experimental equipment, testing is typically required to ensure it is functioning adequately, which can take a significant amount of time. Time spent on installation and troubleshooting leaves less time available for collecting experimental data.

[0003] Cryogenic cooling systems are typically capable of reaching milliKelvin temperatures during use by including multiple platforms held at intermediate temperatures between room temperature and milliKelvin temperatures. In this manner, cooling can be staged such that the final platform in the system can provide successive cooling to milliKelvin temperatures. Installed experimental equipment and other components of the system can provide a path from room temperature to the final platform. To prevent unintended heating by these parts, each platform provides a thermal sink to remove additional heat.

[0004] It is possible to incorporate the experimental services into the module outside the system and install it in a pre-assembled state. This method is generally faster than direct installation of the experimental services. However, it is important that the module is fully thermally equilibrated so that milli-Kelvin temperatures are obtained. In the prior art, thermal equilibration is achieved using clamps and / or complex and extensive adjustment processes.

[0005] A small offset can result in poor thermal balancing in the system.

[0006] Low temperature physics experiments are becoming increasingly complex, with a consequent increase in the experimental services required to perform the experiments. For example, quantum information processing (QIP) experiments use radio frequency (RF) wiring to accommodate devices with a large number of qubits. As the number of qubits increases, the amount of RF wiring required increases accordingly. Cryogenic cooling systems are expected to accommodate the growing volume of experimental services. One way to accommodate the increasing demand is to provide modular improvements for the core system. However, cumulative manufacturing tolerances result in mismatched joints and poorly thermally equilibrated platforms within the cryogenic cooling systems, thus necessitating extensive fine-tuning to improve performance.

[0007] There is a need for a method to more easily introduce experimental services into cryogenic cooling systems. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] "Pressed copper and gold-plated copper contacts at low temperature - A review of thermal contact resistance", RCDhuley, Cryogenics 101 (2019)111-124 Summary of the Invention

[0009] A first aspect of the present invention provides a cryogenic cooling system comprising: a primary insert comprising: a plurality of primary plates, each having a primary contact surface, and one or more primary connecting members arranged to connect the plurality of primary plates; a removable secondary insert comprising a plurality of secondary plates, each having a secondary contact surface, and one or more secondary connecting members arranged to connect the plurality of secondary plates such that the secondary insert is self-supporting; and one or more adjustment members, the one or more adjustment members configured such that, in use, when the secondary insert is attached to the primary insert, the adjustment members bring the primary and secondary contact surfaces of the primary and secondary plates, respectively, into thermally conductive contact.

[0010] Advantageously, the system includes an adjustment member that brings the primary and secondary contact surfaces of the respective primary and secondary plates into thermally conductive contact with one another. This eliminates the need for numerous fine adjustments to overcome misalignments between the two portions of the cryogenic cooling system so that they are in effective thermal communication. When unmounted, the secondary insert can also be moved relative to the primary insert as a free-standing body, further simplifying installation and removal operations. For example, each plate of the secondary insert can be aligned with a corresponding plate of the primary insert in a single step.

[0011] One or more adjustment members may form part of the primary insert. In this case, the adjustment members may form part of a plurality of primary plates, one or more primary connecting members, or both the plates and the connecting members. Similarly, one or more adjustment members may form part of the secondary insert. In this case, the adjustment members may form part of a plurality of secondary plates, one or more secondary connecting members, or both the plates and the connecting members. It is also possible for the adjustment members to form part of the primary insert and the secondary insert. Alternatively, the adjustment members may take the form of fastening members configured to couple corresponding plates of the primary and secondary inserts. The choice of the location of the adjustment members may depend on the particular implementation. For example, if the secondary insert is designed to accommodate rigid laboratory equipment, the location and type of adjustment members will be selected accordingly.

[0012] The primary and secondary plates typically extend generally planar and, in use, are joined along adjacent peripheral surfaces of the plates, which may have a step. Preferably, thermally conductive contact between the primary and corresponding secondary plates is provided by surface contact between conformal planar areas of the respective primary and secondary contact surfaces. Each of the primary and secondary plates may include a flange. When the primary plate contacts the corresponding secondary plate, the lower surface of the flange of the primary plate matches the upper surface of the flange of the secondary plate to form a continuous structure. Typically, the primary and secondary plates are formed from a highly conductive material, so that the joint where the plates are closely joined over a large area provides a good thermal connection throughout the joint.

[0013] The adjustment member typically adjusts the misalignment between each of the plurality of secondary plates of the removable secondary insert and a corresponding primary plate of the primary insert, thereby providing thermally conductive contact between the primary and secondary contact surfaces of the respective primary and secondary plates. As a result of manufacturing tolerances, misalignment between the primary and secondary plates may occur. If left unadjusted, the misalignment between the plates reduces the thermal conductance between the plates.

[0014] Although the cryogenic cooling system includes both a primary insert and a secondary insert, the secondary insert (or, alternatively, the primary insert) is detachable and therefore removable from the system. When the secondary insert is in an unmounted state, the secondary plates are typically spatially positioned relative to one another in a secondary configuration. The secondary insert is freestanding in its unmounted state, and spacing between adjacent plates in the secondary insert may be determined by secondary connecting members. Similarly, when the secondary insert is in an unmounted state, the primary plates are typically spatially positioned relative to one another in a primary configuration. Spacing between adjacent plates in the primary insert may be determined by primary connecting members.

[0015] During the mounting process, the secondary insert can be attached to the primary insert. The plates of the secondary insert are preferably configured to be brought into contact with the corresponding plates of the primary insert. However, there may be misalignment between said plates. The misalignment may be an offset between the plane of the secondary plate and the plane of the corresponding primary plate in each primary and secondary configuration. Each pair of plates may have a different misalignment, which may be positive or negative. As a result, each adjustment member provides a different level of adjustment, typically providing a range of motion of at least 2 millimeters, preferably at least 4 millimeters, to adjust the misalignment.

[0016] The secondary insert is removable from the cryogenic cooling system. The secondary insert can be completely removable, i.e. all plates of the secondary insert can be separated and removed from the primary insert. Optionally, the secondary insert can be only partially removable. When the secondary insert is partially removed, some of the plates of the secondary insert remain attached to the primary insert, while the remaining plates of the secondary insert are removed from the primary insert. Preferably, one or more secondary connecting members are removable such that two or more of the plurality of secondary plates can be removed from the removable secondary insert as a unitary free-standing body or assembly.

[0017] The secondary insert comprises a first secondary plate, a second secondary plate, and a third secondary plate connected with secondary connecting members, the second secondary plate being disposed between the first and third secondary plates. Upon removal of the secondary connecting members connecting the second and third secondary plates, the second and first secondary plates may be removed as a unitary structure. The partially removed secondary insert (first and second secondary plates) is preferably free-standing, similar to the free-standing characteristics of a completely unattached secondary insert.

[0018] The removable nature of the secondary insert advantageously allows the secondary insert to be modified away from the cryogenic cooling system. However, in cases where it is not necessary to remove the entire secondary insert, it may be beneficial to leave a portion of the secondary insert attached to the primary insert. For example, cryogenic experiments are usually performed in a vacuum, so one of the joints between the primary and secondary inserts may form part of the barrier between atmospheric and low pressure. Therefore, additional sealing may be required, such as using an O-ring or other vacuum seal, to reduce the possibility of gas leakage. Leaving the plate forming said barrier in place can be beneficial, avoiding repeated reformation of the seal.

[0019] The advantage of the secondary insert being removable from the cryogenic cooling system is the ability to assemble, modify and test experimental devices attached to the secondary insert away from the cryogenic cooling system. Furthermore, modifications can be made only to two or any number of plates of the secondary insert. It is simpler and therefore preferred to partially remove the secondary insert, removing only the plates required.

[0020] Typically, experimental services or equipment are placed in the cryogenic cooling system and used to perform experiments at low temperatures. Preferably, one or more of the plurality of secondary plates are configured to accommodate the experimental equipment. This is particularly advantageous when the experimental equipment to be mounted on the secondary insert is complex and time consuming to assemble. Thus, the experimental services can be assembled and tested at a location remote from the cryogenic cooling system before being attached to the primary insert.

[0021] Cryogenic cooling systems can be used for low temperature experimental procedures, and cooling can be achieved using a number of refrigeration devices. It is particularly desired for such systems to achieve millikelvin temperatures. For this purpose, a dilution unit preferably forms part of the cryogenic cooling system, for example the primary insert can comprise a dilution refrigerator or a component thereof. The dilution refrigerator can be thermally coupled to one or more plates of the primary insert. Alternatively, the primary insert can comprise a Helium 3 refrigerator or a 1 Kelvin pot. In this way one or more plates of the primary insert can achieve millikelvin temperatures. The thermally conductive contact between the primary insert and the secondary insert ensures that the secondary insert reaches similarly low temperatures during operation.

[0022] One or more of the primary or secondary plates may comprise a rigid portion and one or more deformable portions. Preferably, the deformable portion is deformable relative to the rigid portion to adjust the misalignment. Thus, the one or more adjustment members may comprise one or more deformable portions. During attachment of the removable secondary insert to the primary insert, the one or more deformable portions may be locally deformed to cause a thermally conductive contact. The deformable portions of the plates may be provided at the edges of the plates, for example in the form of flanges. One advantage of this mode of adjustment is the ability to maintain the primary and / or secondary configurations within the respective inserts. For example, the manipulation of the adjustment members does not change the spacing between adjacent primary plates of the primary insert or adjacent secondary plates of the secondary insert. This means that in practice, the primary or secondary inserts, respectively, remain fixed and thus can accommodate rigid experimental devices that are attached to two or more plates. Similarly, the spacing between the corresponding plates of the primary and secondary inserts, respectively, may also be maintained fixed. The deformation may be configured to occur locally in a predefined area of ​​the plate such that the experimental device is not damaged, but nevertheless a thermally conductive contact is achieved. The deformable portion may form part of the primary plate. Alternatively, the deformable portion may form part of the secondary plate. The deformable portion may optionally form part of both the primary and secondary plates.

[0023] When the secondary insert is in an unmounted state, the primary and secondary inserts may have respective primary and secondary configurations as described above. If the adjustment is achieved by local deformation, it is possible to maintain the primary and secondary configurations even when the removable secondary insert is in the mounted state. The one or more adjustment members may alternatively make one or both of the primary or secondary configurations adjustable to cause thermally conductive contact. For example, the one or more adjustment members are configured to change the spacing between adjacent primary plates or adjacent secondary plates. This may be achieved by configuring each of the one or more primary or secondary connecting members to deform to adjust the misalignment between the plates.

[0024] The one or more adjustment members may form at least a portion of one or more primary or secondary connecting members. For example, the one or more adjustment members may form a flexible portion of the primary or secondary connecting members, respectively. By placing the secondary connecting members under a compressive or tensile load during attachment of the secondary insert to the primary insert, the misalignment can be adjusted. In response to the load, the secondary connecting members can deform, thereby aligning the secondary plate with the corresponding primary plate, thereby causing thermally conductive contact. Similarly, deformation of the flexible primary connecting members can adjust the misalignment.

[0025] Alternatively, one or more adjustment members may be configured to allow movement of one or more primary plates relative to one or more of said primary connecting members, or one or more adjustment members may be configured to allow movement of one or more secondary plates relative to one or more of said secondary connecting members. For example, one or more adjustment members may be used to rotate a primary or secondary connecting member to change the spacing between adjacent primary or adjacent secondary plates. This adjustment is typically achieved when an end of a primary or secondary connecting member comprises a thread or tap. In this case, the adjustment member may comprise a combination of the thread or tap of a connecting member and a receiving member configured to engage the thread or tap to adjust the spacing between adjacent plates of a primary or secondary insert.

[0026] Preferably, the primary and secondary connecting members are thermally balanced at the respective primary and secondary plates. In general, there is a thermal load that is transferred from room temperature along the primary and / or secondary connecting members to a cold stage of the system. Thermal balancing at the plates advantageously blocks this thermal load, thereby forming a thermal sink that allows a distal stage of the primary or secondary insert to obtain a lower temperature during operation of the system. Effective thermal balancing of the primary connecting members may be achieved by the use of one or more primary shims, each configured to thermally couple the primary plate to one or more primary connecting members and allow movement of the primary plate relative to one or more primary connecting members. Similarly, effective thermal balancing of the secondary connecting members may be achieved by the use of one or more secondary shims, each configured to thermally couple the secondary plate to one or more secondary connecting members and allow movement of the secondary plate relative to one or more secondary connecting members.

[0027] Further aspects of the invention will now be described, with the features described in relation to one aspect being equally applicable to the remaining features, and each aspect sharing similar advantages.

[0028] A second aspect of the invention provides a removable secondary insert for use in a cryogenic cooling system according to the first aspect.

[0029] A third aspect of the invention provides a method of operating the system according to the first aspect, wherein the secondary insert comprises a first secondary plate, a second secondary plate, a third secondary plate, a first secondary connecting member connecting the first secondary plate to the second secondary plate, and a second secondary connecting member connecting the second secondary plate to the third secondary plate, the primary insert comprises three primary plates, each primary plate corresponding to a respective secondary plate of the secondary insert, the method comprising: mounting the secondary insert to the primary insert such that the secondary plates are thermally coupled to corresponding primary plates using one or more adjustment members; and partially removing the secondary insert from the primary insert, wherein partially removing the secondary insert comprises removing the first secondary connecting member from the secondary insert, and removing the second secondary plate, the third secondary plate, and the second secondary connecting member from the primary insert as an integrated, freestanding assembly without removing the first secondary plate from the corresponding plate of the primary insert.

[0030] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. [Brief description of the drawings]

[0031] [Figure 1] 1 is a schematic diagram of a cryogenic cooling system according to a first embodiment of the present invention. [Diagram 2] 1 is a perspective view of a cryogenic cooling device according to a first embodiment of the present invention. [Diagram 3] FIG. 1 is an exploded side view of a cryogenic cooling system according to a first embodiment of the present invention. [Figure 4] FIG. 1 is a first exploded perspective view of a cryogenic cooling system according to a first embodiment of the present invention. [Diagram 5] FIG. 2 is a second exploded perspective view of the cryogenic cooling system according to the first embodiment of the present invention. [Figure 6] FIG. 2 is an exploded perspective view showing a state in which an experimental service of the cryogenic cooling system according to the first embodiment of the present invention is installed. [Figure 7] FIG. 2 is a schematic diagram of a secondary plate from a cryogenic cooling system according to a first embodiment of the present invention. [Figure 8(a)] FIG. 2 is a schematic diagram showing a portion of a cryogenic cooling system according to a first embodiment of the present invention before thermal connection. [Figure 8(b)] FIG. 2 is a schematic diagram of a portion of a cryogenic cooling system according to a first embodiment of the present invention after thermal connection. [Figure 9(a)] FIG. 11 is a first schematic diagram showing a part of a cryogenic cooling system according to a second embodiment of the present invention. [Figure 9(b)] FIG. 2 is a second schematic diagram showing a part of a cryogenic cooling system according to a second embodiment of the present invention. [Figure 10(a)] FIG. 13 is a schematic diagram showing a portion of a cryogenic cooling system according to a third embodiment of the present invention before thermal connection. [Figure 10(b)] FIG. 13 is a schematic diagram of a portion of a cryogenic cooling system according to a third embodiment of the present invention after thermal connection. [Figure 11] FIG. 11 is a first cross-sectional view of a portion of a cryogenic cooling system according to a third embodiment of the present invention. [Figure 12] FIG. 11 is a perspective view of a portion of a cryogenic cooling system according to a third embodiment of the present invention. [Figure 13] FIG. 11 is a second cross-sectional view of a portion of a cryogenic cooling system according to a third embodiment of the present invention. [Figure 14] 1A-1D are perspective views of three exemplary secondary inserts for use in a cryogenic cooling system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] FIG. 1 is a cross-sectional view showing the inside of a cryogenic cooling system according to a first embodiment. The system comprises a number of thermal stages 1-5 and an outer stage 6. The thermal stages 1-5 and the outer stage 6 are connected by primary and secondary rods 17, 27, thus forming a spatially distributed hierarchical assembly in which the stages are aligned along a central axis extending parallel to the rods. The primary rods 17 are not shown in FIG. 1 for clarity. The primary and secondary rods 17, 27 are formed from a low thermal conductivity material, such as stainless steel. In use, the thermal stages 1-5 are housed within a cryostat 36, which is typically evacuated to eliminate convective and conductive heat paths through any gases in the cryostat 36 to improve thermal performance. The cryostat 36 is attached to the outer stage 6, the outer surface 7 of which is exposed to room temperature and pressure and is formed from a low conductivity material.

[0033] The cryogenic cooling system includes a cooling device. The cooling device cools the cryogenic cooling system from room temperature to an operating base temperature. The cryogenic cooling system in the first embodiment is substantially cryogen-free (also referred to in the art as "dry") in that it is not primarily cooled by contact with a reservoir of cryogenic fluid. However, despite being substantially cryogen-free, as will become apparent, some cryogenic fluid includes a liquid phase and is typically present within the cryostat in use. In this embodiment, cooling is achieved through the use of a mechanical refrigerator and a dilution unit. The mechanical refrigerator may be a pulse tube refrigerator (PTR), a Stirling refrigerator, or a Gifford-McMahon (GM) refrigerator.

[0034] In this embodiment, the mechanical refrigerator is a PTR 40 and is thermally coupled to a first thermal stage 1 and a second thermal stage 2. Each thermal stage 1-5 is formed from a highly conductive material, such as copper, and has a different operating base temperature. The first thermal stage 1 is thermally coupled to a first PTR stage 41 and achieves an operating base temperature of approximately 50-70 Kelvin. The second thermal stage 2 is thermally coupled to a second PTR stage 42 and achieves an operating base temperature of approximately 3-5 Kelvin. In this embodiment, the second PTR stage 42 forms the lowest temperature stage of the PTR 40.

[0035] The third thermal stage 3, the fourth thermal stage 4 and the fifth thermal stage 5 are thermally coupled to the dilution unit 8. Cooling of the third, fourth and fifth thermal stages 3, 4 and 5 is achieved by operation of the dilution unit 8, whereby a working fluid is circulated around the cooling circuit 60. The working fluid is typically a mixture of helium-3 and helium-4. The working fluid is pumped around the cooling circuit 60, which comprises a condensate line 61 and a still pump line 62, using a compressor pump 63 and a turbomolecular pump 64. It should be noted that the working fluid can be stored in a storage vessel 65 and fed to the cooling circuit 60 using a feed line 66. The third thermal stage 3 is thermally coupled to a still 10 which constitutes part of the dilution unit 8. The operating base temperature of the third thermal stage 3 is typically 0.5 to 2 Kelvin. The fifth thermal stage 5 is thermally coupled to a mixing chamber 9 of the dilution unit 8. The fifth thermal stage 5 typically has an operating base temperature of 3-30 milliKelvin. The fourth thermal stage 4 forms an intermediate stage between the third and fifth thermal stages 3,5 and has an operating base temperature of about 50-200 milliKelvin.

[0036] In use, a number of thermal radiation shields 56-58 are attached to thermal stages 1-5, each shield surrounding a respective one of the remaining lower base temperature components. A first thermal radiation shield 56, a second thermal radiation shield 57 and a third thermal radiation shield 58 are attached to first thermal stage 1, second thermal stage 2 and third thermal stage 3, respectively. This reduces any unwanted thermal communication between thermal stages 1-5 and allows each stage to achieve a different operating base temperature.

[0037] The cryogenic cooling system of Figure 1 may be controlled using a control system 50. The control system 50 is typically a suitable computer system, although control of the system may be performed manually. The operation of each part of the system may be controlled using the control system 50, including operation of the PTR 40, dilution unit 8, pumps 63, 64 and associated valves, monitoring of temperature and pressure sensors, and operation of other ancillary equipment to carry out the desired procedure.

[0038] Cryogenic cooling systems as described can be used to perform experiments at temperatures generally below 100 Kelvin. Although not shown in FIG. 1, experimental services can be installed in the cryostat 36. The selection of experimental services and their specific equipment in the cryostat 36 can be customized. One such example of experimental services is described with reference to FIG. 6. Typically, the specific equipment of the experimental services is installed, tested, and left fixed for a period of time. Modifying the equipment in the system to perform different types of experiments requires numerous adjustments and troubleshooting procedures before the experiment can be performed, and is typically very time-consuming. An embodiment of the present invention provides a primary insert 18 and a secondary insert 28, which is detachable from the primary insert 18. Thus, experimental services can be installed in the primary insert 18, or in the secondary insert 28, which is easily detachable and reattachable, or in both the primary and secondary inserts 18, 28. The primary insert 18 comprises a plurality of primary plates and the secondary insert 28 comprises a plurality of secondary plates 21-26, each primary plate configured for attachment to a corresponding secondary plate to form a respective thermal stage 1-5 of the system, as further described.

[0039] The advantage of mounting the experimental services on the secondary insert 28 arises from the ability to remove the secondary insert 28 from the cryogenic cooling system. Assembly and preliminary testing can be performed "at the bench" outside the cryogenic cooling system where the experiments are performed. In this way, modifications or updates of the experimental services to perform different experiments can be performed relatively quickly and easily. Cryogenic experiments using a cryogenic cooling system such as a dilution refrigerator typically take days, weeks, or months to perform. Changing the experimental services in the system typically requires making the changes at room temperature, resulting in experimental downtime, i.e., time when the cryogenic cooling system is not at its base temperature at which it can operate. The ability to operate the experimental services on a removed secondary insert 28 on the bench (away from the system itself) reduces experimental downtime. For example, multiple secondary inserts can be provided for use with a given cryogenic cooling system. A cryogenic environment is maintained within the system to perform experiments on a second secondary insert while conditioning the experimental services on a first secondary insert under atmospheric pressure conditions.

[0040] An embodiment of the present invention also provides a conditioning member that places the primary insert 18 and the secondary insert 28 in thermally conductive contact. Good thermal contact is important when performing cryogenic measurements. In the presence of a heat flux, such as that generated by the operation of a cooling source, a temperature gradient will naturally develop between the primary insert 18 and the secondary insert 28. The temperature difference between these components is proportional to the heat flux and inversely proportional to the thermal conductance. In any practical experiment, there is a limit to the heat flux that can be applied to the system (due to the finite cooling power available from either the PTR stages 41, 42 or the dilution refrigerator 8). The thermal conductance of the junction varies with a number of factors, including its temperature and the contact pressure. The conditioning member is typically configured to limit the temperature difference between corresponding stages of the primary and secondary inserts 18, 28 to within 2%, preferably 1%, of the absolute temperature of the higher temperature stage, for example. This is achieved by making the thermal conductance between these stages sufficiently high. For example, if the second thermal stage 2 is cooled by the second PTR stage 42 to 4 Kelvin (with 1 Watt of cooling power), the adjustment member for the second thermal stage 2 can ensure that the temperature difference between the corresponding primary and secondary plates of the second thermal stage 2 does not exceed 40 milliKelvin. Thus, the thermal conductance between the primary and secondary plates of the second thermal stage 2 is about 25 W / K at 4 Kelvin. Similarly, if the fifth thermal stage 5 is cooled by the mixing chamber 9 to 100 milliKelvin (with 400 microWatts of cooling power), the adjustment member for the fifth thermal stage 5 can ensure that the temperature difference between the corresponding primary and secondary plates of the fifth thermal stage 5 does not exceed 1 milliKelvin. Thus, the thermal conductance between the primary and secondary plates of the fifth thermal stage 5 is about 0.4 W / K at 0.1 Kelvin.

[0041] The difference in expected thermal conductance between the second thermal stage 2 and the fifth thermal stage 5 is due to the temperature dependence of the joints, as further discussed in "Pressed copper and gold-plated copper contacts at low temperature - A review of thermal contact resistance" by R.C.D. Huley, published in Cryogenics 101 (2019) 111-124. The thermal conductance of a given joint decreases with temperature. However, the practical heat flux that can be applied between each primary and secondary plate of the respective primary and secondary inserts 18, 28 also decreases with temperature, so that all mounting arrangements between the primary and secondary plates can be designed and mounted in the same manner to provide acceptable performance in each thermal stage 1-5.

[0042] A variety of adjustment members are contemplated and embodiments are described that facilitate different adjustment methods.

[0043] FIG. 2 shows the primary and secondary inserts 18, 28 of FIG. 1 in more detail. As shown, each thermal stage 1-5 includes an inner primary plate 11-15, an inner secondary plate 21-25, and edge pieces 31-35. The outer stage 6 includes an outer primary plate 16 and an outer secondary plate 26. Each of the inner and outer secondary plates 21-25, 26 is connected to a corresponding inner and outer primary plate 11-15, 16 along the periphery of the secondary plate. Each of the edge pieces 31-35 is connected to a corresponding inner primary plate 11-15 and a corresponding inner secondary plate 21-25 along the periphery of the respective inner primary and secondary plate. The inner and outer primary plates 11-15, 16 are connected by a primary rod 17, and the inner and outer secondary plates 21-25, 26 are connected by a secondary rod 27. The primary and secondary rods 17, 27 extend between the plates in a direction perpendicular to the plates. In this embodiment, the edge pieces 31-35 are not connected, however, in alternative embodiments, the edge pieces 31-35 may be connected by edge rods extending between the edge pieces.

[0044] The inner and outer primary plates 11-15, 16 and the primary rod 17 form part of the primary insert 18. The inner and outer secondary plates 21-25, 26 and the secondary rod 27 form part of the secondary insert 28. The secondary insert 28 is removable from the cryogenic cooling system, and in particular from the primary insert 18. When the secondary insert 28 is in an unmounted state, it forms a free-standing assembly and does not require additional support structure to maintain its original configuration, but can be removed from the primary insert 18 as an integral body.

[0045] The design of the secondary inserts 28 and primary inserts 18 is such that when the secondary inserts 28 are in the installed condition, good thermal contact is achieved between any secondary insert 28 and the primary insert 18. It is important to ensure effective thermal balancing between the corresponding plates of the primary inserts 18 and secondary inserts 28 so that cooling applied to one of the primary or secondary plates is effectively applied to the other of the secondary or primary plates.

[0046] Achieving good thermal contact between any secondary insert 28 and the primary insert 18 when the secondary insert 28 is in the installed state is not trivial. During manufacture of the primary insert 18 or secondary insert 28, the relative positional relationship of the inner and outer primary plates 11-15, 16 and the inner and outer secondary plates 21-25, 26 in the respective inserts 18, 28 may vary within certain manufacturing tolerances even if made to the same specifications. Small differences may result in misalignment, i.e., offset between the plane of the secondary plates and the plane of the corresponding primary plates, when the secondary insert 28 is brought into the installed position. Such deviations, even if small, may lead to poor thermal contact. This is particularly important at low temperatures, such as the operating base temperatures of the third, fourth and fifth thermal stages 3, 4, 5.

[0047] To achieve good thermal contact between the corresponding plates of the primary insert 18 and the secondary insert 28, the cryogenic cooling system may also include adjustment members (examples of which are described in more detail below) that bring the inner primary plates 11-15 and the inner secondary plates 21-25 into thermally conductive contact when the secondary insert 28 is in the installed state, thereby accommodating any misalignment. The adjustment members may form part of the primary insert 18, part of the secondary insert 28, or both.

[0048] In Figure 2, the components of the cryogenic cooling system are shown installed. Figure 3 provides an exploded view of the cryogenic cooling system according to the first embodiment with the secondary insert 28 and edge pieces 31-35 removed from the primary insert 18 to more clearly show the components of the system. Figure 3 shows the edge pieces 31-35, the secondary insert 28 including a plurality of inner secondary plates 21-25 and an outer secondary plate 26 connected by secondary rods 27, and the primary insert 18 including a plurality of inner primary plates 11-15 and an outer primary plate 16 connected by primary rods 17.

[0049] In this embodiment, the cooling device is mounted to the primary insert 18. The cooling device includes a PTR 40 and comprises a first PTR stage 41 thermally coupled to the first inner primary plate 11 of the first thermal stage 1 and a second PTR stage 42 thermally coupled to the second inner primary plate 12 of the second thermal stage 2. The cooling device further comprises a dilution unit 8, the still 10 of the dilution unit 8 being thermally coupled to the primary plate 13 of the third thermal stage 3 and the mixing chamber 9 of the dilution unit 8 being thermally coupled to the primary plate 15 of the fifth thermal stage 5. In an alternative embodiment, the cooling device is mounted to the secondary insert. For example, the dilution units could alternatively be mounted to the inner secondary plates 23, 24, 25 of the third, fourth and fifth thermal stages 3, 4, 5.

[0050] The inner and outer plates 11-15, 16 of the primary insert 18 are aligned along an axis 39 extending in a direction perpendicular to the inner and outer primary plates 11-15, 16 in the primary configuration. Similarly, the inner and outer plates 21-25, 26 of the secondary insert 28 are aligned along a central axis perpendicular to the inner and outer plates 21-25, 26 of the secondary insert 28 in the secondary configuration and are spatially distributed. In each primary and secondary configuration, there may be an offset, referred to as a misalignment, between the plane of the secondary plate and the plane of the corresponding primary plate. Each of the inner secondary plates 21-25 is configured to be in thermally conductive contact with its corresponding inner primary plate 11-15 when the secondary insert 28 is mounted in the primary insert 18, and thus accommodates any misalignment. Such thermally conductive contact is provided by an adjustment member. The outer secondary plate 26 forms a vacuum seal with the outer primary plate 16, for example by use of an O-ring, although any suitable sealing mechanism is possible.

[0051] The mounting of the secondary insert 28 to the cryogenic cooling system will now be described with reference to FIG. 3. First, the secondary insert 28 is aligned in two dimensions with the primary insert 18, with each of the inner and outer secondary plates 21-25, 26 being positioned slightly below the corresponding inner and outer primary plates 11-15, 16. Second, the secondary insert 28 is aligned in a third dimension, with the third dimension being parallel to the major axis 39 of the primary insert 18. Alignment in the third dimension with the primary insert 18 is achieved by raising the secondary insert 28 so that each of the inner and outer secondary plates 21-25, 26 faces the corresponding inner and outer primary plates 11-15, 16, so as to form a thermally conductive contact between each pair of primary and secondary plates. The outer secondary plate 26 of the outer stage 6 forms a seal with the outer primary plate 16. The inner secondary plates 21-25 can then be fixed in place. In this embodiment, they are fixed using fasteners, here in the form of screws. Adjustment members (not shown) bring the inner primary plates 11-15 into thermally conductive contact with the inner secondary plates 21-25 in the mounted state. Finally, the edge pieces 31-35 are fixed in place using screws.

[0052] Each edge piece 31-35 is formed to shield the lower base temperature components from excess radiation. As can be seen in FIG. 3, the shape of each edge piece 31-35 is designed to match the shape of each inner secondary plate 21-25 and each inner primary plate 11-15 to complete each thermal stage 1-5. In an alternative embodiment, the edge pieces 31-35 can be attached to the inner primary plates 11-15 without placing the secondary insert 28. In another embodiment, the edge pieces are not required. Instead, each inner secondary plate 21-25 can be formed to complete each thermal stage 1-5 and act as a heat shield to block radiation between adjacent stages.

[0053] The secondary insert 28 of the cryogenic cooling system is removable from the primary insert 18. Figure 4 shows the cryogenic cooling system according to the first embodiment with the secondary insert 28 in a removed position and the edge pieces 31-35 attached to the corresponding inner primary plates 11-15.

[0054] While the secondary insert 28 is in the unloaded position, modifications can be made to the secondary insert 28, and in particular to the experimental services attached to the secondary insert 28. This is practically easier for the user to accomplish in the unloaded position. Modification of the secondary insert 28 can include, for example, updating or testing the experimental services attached to the secondary insert 28. If desired, the updated secondary insert 28 can then be mounted on the primary insert 18. Furthermore, it is advantageous to have multiple secondary inserts 28, so that one secondary insert 28 is in operation, i.e., mounted, and used experimentally, and one or more secondary inserts 28 are on the bench, i.e., unloaded. While in the unloaded state, the experimental services on the secondary insert 28 can be more easily modified or updated. The experimental services on the detached secondary insert 28 can be tested at room temperature, or the secondary insert 28 can be mounted in a donor cryostat to test the experimental services at low temperature. The above-mentioned testing, assembly, modifications and updates can be performed in parallel with the experiments being performed on the cryogenic cooling system.

[0055] As mentioned above, the secondary inserts 28 form a hierarchical assembly. The spatial distribution of the inner and outer secondary plates 21-25, 26 within the assembly defines five interplate spaces 51-55, as shown in FIG. 4: a first interplate space 51 between the outer secondary plate 26 and the first inner secondary plate 21, a second interplate space 52 between the first inner secondary plate 21 and the second inner secondary plate 22, a third interplate space 53 between the second inner secondary plate 22 and the third inner secondary plate 23, a fourth interplate space 54 between the third inner secondary plate 23 and the fourth inner secondary plate 24, and a fifth interplate space 55 between the fourth inner secondary plate 24 and the fifth inner secondary plate 25.

[0056] In FIG. 4, a group of four secondary rods 27 extends across each interplate space 51-55 and connects each pair of adjacent secondary plates 21-26. The location of each group of secondary rods 27 is offset with respect to adjacent groups so that each rod can be independently adjusted or removed from each interplate space 51-55. Removal of all of the secondary rods 27 in one of the interplate spaces 51-55 can split the secondary insert 28 into two parts. Thus, two or more plates of the secondary insert 28 can be removed from the remaining plates as a unitary structure. FIG. 5 shows a cryogenic cooling system according to the first embodiment with the secondary insert 28 partially removed.

[0057] In FIG. 5, the secondary rod 27 in the fourth interplate space 54 has been removed. The fourth interplate space 54 is between the third inner secondary plate 23 and the fourth inner secondary plate 24, and therefore removal of said secondary rod 27 allows the fourth inner secondary plate 24 and the fifth inner secondary plate 25 to be removed from the cryogenic cooling system while leaving the remaining inner and outer secondary plates 21-23, 26 attached. The fourth and fifth inner secondary plates 24, 25 remain held together by the connecting secondary rod 27, and therefore the assembly is self-supporting after removal from the cryogenic cooling system. In alternative embodiments, any number of the inner and outer secondary plates 21-25, 26 can be removed.

[0058] In some experimental situations, it may be necessary to test or modify only a subset of the secondary plates 21-26 of the secondary insert 28. Thus, partial removal of the secondary insert 28 is advantageous as it allows for more flexible preparation and testing of experimental services. Furthermore, re-installation of a portion of the secondary insert 28, as opposed to the entire secondary insert 28, is less complex for the user to perform. The cryogenic cooling system can be operated with the inner secondary plates 21-25 removed. However, if the inner secondary plates 21-24 of any of the first to fourth thermal stages 1-4 are removed, they are typically replaced with blanks to reduce radiation transfer between the thermal stages.

[0059] Experimental services can be mounted on the cryogenic cooling system. Figure 6 shows a cryogenic cooling system according to a first embodiment with experimental services attached to the secondary insert 28. Examples of experimental services can include wiring, which can be RF wiring, ultra-high vacuum components, electrical devices (attenuators, filters, circulators or other microwave components, amplifiers, resistors, transistors, thermometers, capacitors, inductors, etc.), or other experimental services required for the selected experiment. The experimental service shown in Figure 6 is a coaxial line.

[0060] As mentioned above, the secondary insert may be fully or partially removed from the cryogenic cooling system and inserted into another cryogenic cooling system. If misalignment occurs between each inner secondary plate 21-25 and the corresponding inner primary plate 11-15 when the secondary insert 28 is brought into position, this may result in poor thermal contact. To ensure good thermal contact, the cryogenic cooling system is provided with adjustment members. Possible adjustment members will now be described with reference to Figures 7 to 12.

[0061] FIG. 7 is a schematic front view of an inner secondary plate according to a first embodiment. The following description will be given with respect to the first inner secondary plate 21, but the description is applicable to any one or more of the inner secondary plates 21-25 of the secondary insert 28. The first inner secondary plate 21 has a rigid central portion 43. Along each side of the rigid central portion 43 there is a flange 44 located in the plane of the first secondary plate 21. In this embodiment, each flange 44 is provided with secondary holes 59 evenly distributed along the length of the flange 44. These holes may be tapped or untapped. A matching series of holes is arranged on the corresponding primary plate so that the first inner secondary plate 21 can be attached to the first inner primary plate 11 using screws or any suitable attachment mechanism (see FIGS. 8(a) and 8(b)).

[0062] The flange 44 is separated from the rigid central portion 43 by a link or connecting portion 45. The link portion 45 is a relatively thin strip of the first inner secondary plate 21 that extends along the length of the flange 44 and forms a pivot about which the flange 44 is movable. The first inner secondary plate 21 further contains four receiving holes 46 for positioning the secondary rods 27, although of course the number of receiving holes 46 may vary depending on the number of secondary rods 27 used.

[0063] In the first embodiment, the flange 44 is configured to deform when a load is applied to bring the first inner primary plate 11 and the first inner secondary plate 21 into thermally conductive contact. The localized deformation allows a rigid laboratory device, such as an ultra-high vacuum port, to be attached to the secondary insert 28. Such a rigid device, once attached, can effectively determine the spacing between two or more of the inner or outer secondary plates 21-25, 26. In this embodiment, the rigid device is attached to a rigid central portion 43 of the first inner secondary plate 21, with the flange 44 providing a deformable portion thus forming an adjustment member. The localized deformation of the flange 44 adjusts for any misalignment between the first inner primary plate 11 and the first inner secondary plate 21. The inclusion of the rigid central portion 43 of the inner secondary plate advantageously ensures effective thermal equilibration between the secondary insert 28 and the primary insert 18 while still keeping the rigid laboratory device unaffected by any required adjustments.

[0064] Figures 8(a) and 8(b) are schematic side views of a portion of a cryogenic cooling system according to a first embodiment during an installation process. Figure 8(a) shows a portion of a secondary insert 28 in an uninstalled state, and Figure 8(b) shows a portion of the secondary insert 28 in an installed state using an adjustment member. Figures 8(a) and 8(b) show portions of a first inner secondary plate 21, a second inner secondary plate 22, a first inner primary plate 11, and a second inner primary plate 12. However, the present description applies to any adjacent inner plate of the secondary insert 28 and the corresponding plate of the primary insert 18.

[0065] The first inner secondary plate 21 includes a rigid central portion 43, a flange 44, and a link portion 45. The second secondary plate 22 includes a rigid central portion 43', a flange 44', and a link portion 45'. Prime-marked (') reference numerals are used to designate similar device features between the second inner secondary plate 22 and the first inner secondary plate 21. The first and second inner secondary plates 21, 22 both have the shape shown in FIG. 7. The first inner primary plate 11 is connected to the second inner primary plate 12 by a primary rod 17. Typically, a plurality of primary rods 17 are used to connect adjacent plates of the primary insert 18, but only one is shown here for clarity.

[0066] FIG. 8(a) schematically shows a part of the secondary insert 28 and the corresponding part of the primary insert 18 when the secondary insert 28 is in the non-mounted state. In the non-mounted state, the separation between the first inner secondary plate 21 and the second inner secondary plate 22 is d2. The separation between the first inner primary plate 11 and the second inner primary plate 12 is d1, and d1 > d2. In different embodiments, the deviation may be in the opposite direction, i.e., d1 < d2. The relative lateral positional relationship in FIG. 8(a) is exemplary and is for clearly showing vertical deviation or misalignment. This deviation is between the first inner secondary plate 21 and the first inner primary plate 11. The first and second inner primary plates 11, 12 include stepped portions along the periphery through which the primary holes 69, 69' extend. The secondary holes 59, 59' of the first and second inner secondary plates 21, 22 are configured to be aligned with the primary holes 69, 69' of the first and second inner primary plates 11, 12, respectively.

[0067] In an alternative embodiment, the flange may be located on the plate of the primary insert 18 instead of the secondary insert 28. This is particularly advantageous when there are multiple replaceable secondary inserts 28 for a cryogenic cooling system, some of which may not include adjustment members. In another alternative embodiment, the flange 44 may be located on the plate of the primary insert 18 and the secondary insert 28. This may advantageously allow for a larger possible misalignment, since deformations may occur on both sides.

[0068] FIG. 8(b) shows a schematic of the portion of the secondary insert 28 of FIG. 8(a) and the corresponding portion of the primary insert 18 when the secondary insert 28 is in an installed state. In FIG. 8(b), the secondary holes 59, 59' are aligned with the primary holes 69, 69'. The flange 44 and the link portion 45 are in a deformed position and are deformed to bring the first inner primary plate 11 and the first inner secondary plate 21 into thermally conductive contact. Thus, the flange 44 is in face contact with the first inner primary plate 11 along the stepped portion of the first inner primary plate 11. The planar area of ​​the stepped portion of the first inner primary plate 11 conforms or is geometrically consistent with the flange 44 of the first inner secondary plate 21.

[0069] In this embodiment, deformation of the flanges 44, 44' is able to accommodate or adjust for the misalignment between d1 and d2 while the rigid central portions 43, 43' of the first 21 and second 22 inner secondary plates remain in fixed positions relative to each other. The first 11 and second 12 inner primary plates also remain in fixed positions relative to each other before and after the attachment process.

[0070] 9(a) and 9(b) are schematic side views of a portion of a cryogenic cooling system according to a second embodiment, showing a portion of a secondary insert 128 in a mounted state using an adjustment member. This cryogenic cooling system has a similar form to that described in the first embodiment, but with a different adjustment member. Each of FIGS. 9(a) and 9(b) shows a first inner secondary plate 121 connected to a second inner secondary plate 122 by a secondary rod 127, and a first inner primary plate 111 connected to a second inner primary plate 112 by a primary rod 117. Typically, further primary rods 117 and further secondary rods 127 are used, but only one is shown in FIGS. 9(a) and 9(b) for clarity. With the secondary insert 128 shown in the mounted position, the secondary holes 159, 159' are aligned with the primary holes 169, 169'.

[0071] In a second embodiment, the secondary rod 127 is configured to deform upon application of a compressive or tensile load to adjust the spacing between adjacent inner secondary plates 121, 122. This movement adjusts for any misalignment between corresponding plates of the primary and secondary inserts 118, 128. In this embodiment, the primary rod 117 is rigid, and therefore the spacing between adjacent plates of the primary insert 118 is fixed. The secondary rod 127 is formed from stainless steel and is curved to allow deformation as described. Deformation of the secondary rod 127 brings each of the inner secondary plates 121-125 into thermally conductive contact with the corresponding inner primary plate 111-115.

[0072] In Fig. 9(a), the distance d2 between the first inner secondary plate 121 and the second inner secondary plate 122 in the non-attached state is smaller than the distance d1 between the first inner primary plate 111 and the second inner primary plate 112, that is, d2 < d1. When the secondary insert 128 is in the non-attached state, the secondary rod 127 is at the first position 147 shown by the dashed line in Fig. 9(a). The secondary rod 127 is configured to extend to the second position 148 shown by the solid line in Fig. 9(a) in response to a tensile load. At this position, the first and second inner secondary plates 121, 122 are further separated, and good thermal contact can be achieved between the first and second inner primary plates 111, 112 along the contact surfaces, respectively.

[0073] In Fig. 9(b), the distance d2 between the first inner secondary plate 121 and the second inner secondary plate 122 in the non-attached state is larger than the distance d1 between the first inner primary plate 111 and the second inner primary plate 112, that is, d2 > d1. When the secondary insert 128 is in the non-attached state, the secondary rod 127 is at the first position 147 shown by the dashed line in Fig. 9(b). The secondary rod 127 is configured to compress to the third position 149 shown by the solid line in Fig. 9(b) in response to a compressive load. At this position, the first and second inner secondary plates 121, 122 are brought into good thermal contact states with the first and second inner primary plates 111, 112, respectively.

[0074] In a second embodiment as described above with reference to Figures 9(a) and 9(b), the secondary rods 127 can adjust the misalignment between the primary insert 118 and the corresponding inner plates of the secondary insert 128 of the cryogenic cooling system. The secondary rods 127 are configured to adjust the distance between adjacent secondary plates to align each plate of the secondary insert 128 with each plate of the primary insert 118. In an alternative embodiment, the primary rods may be configured to deform when a compressive or tensile load is applied, as described above with respect to the secondary rods 127, and the secondary rods can be rigid to thus fix the positions of the inner and outer secondary plates relative to each other. This can make the secondary insert more rigidly fixed in the unmounted state.

[0075] Figures 10(a) and 10(b) are schematic side views of a portion of a cryogenic cooling system according to a third embodiment. Similar to the second embodiment (Figures 9(a) and 9(b)) and unlike the first embodiment (Figures 8(a) and 8(b)), the third embodiment includes an adjustment member configured to adjust the spacing between adjacent plates of the insert. Figure 10(a) shows a portion of the secondary insert 228 in an unmounted state, while Figure 10(b) shows a portion of the secondary insert 228 in an mounted state with the adjustment member in use. Figures 10(a) and 10(b) show the first inner secondary plate 221, the second inner secondary plate 222, the first inner primary plate 211, and the second inner primary plate 212.

[0076] In Figures 10(a) and 10(b), the first inner secondary plate 221 is connected to the second inner secondary plate 222 by secondary rods 227. The upper secondary rod 227' connects the first inner secondary plate 221 to the outer secondary plate (not shown). The lower secondary rod 227" connects the second inner secondary plate 222 to the third inner secondary plate (not shown). Each of the secondary rods 227, 227', 227" includes a shoulder 229, 229" at the proximal end of each rod 227, 227', 227" adapted to receive a grub screw 230, 230'. The first inner primary plate 211 is connected to the second inner primary plate 212 by primary rods 217. The upper primary rod 217' connects the first inner primary plate 211 to the outer primary plate 216 (not shown). A lower primary rod 217'' connects the second inner primary plate 212 to a third inner primary plate 213 (not shown).

[0077] FIG. 10(a) is a schematic diagram of a portion of the secondary insert 228 and a corresponding portion of the primary insert 218 when the secondary insert 228 is in an uninstalled state. The secondary holes 259, 259' are configured to align with the primary holes 269, 269' when the secondary insert 228 is in an installed state, with fasteners extending therebetween. The primary holes 269, 269' and / or the secondary holes 259, 259' may be threaded or may form clearance or clearance holes, for example when the fasteners are used in combination with back nuts. In FIG. 10(a), the spacing d2 between the first inner secondary plate 221 and the second inner secondary plate 222 in the uninstalled state is greater than the spacing d1 between the first inner primary plate 211 and the second inner primary plate 212, i.e. d2>d1. The relative horizontal positions in FIG. 10(a) are exemplary and are intended to clearly illustrate the vertical positions. The offset is between the second inner secondary plate 222 and the second inner primary plate 212 .

[0078] In the unmounted state, the first inner secondary plate 221 and the second inner secondary plate 222 rest on the shoulders 229, 229" of the secondary rod 227 and the lower secondary rod 227", respectively. A first grub screw 230 is located between the secondary rod 227 and the upper secondary rod 227'. The upper portion of the secondary rod 227 and the lower portion of the upper secondary rod 227' are tapped or internally threaded to engage the first grub screw 230. A second grub screw 230' is disposed between the secondary rod 227 and the lower secondary rod 227". An upper portion of the lower secondary rod 227' and a lower portion of the secondary rod 227 are tapped to receive the second grub screw 230'. It is the combination of the tapped portion of the secondary rod and the corresponding grub screw it engages that forms the adjustment member in this embodiment. In alternative embodiments, the primary rod may include an adjustment mechanism as described for the secondary rod, or both the primary and secondary rods may include such adjustment mechanisms.

[0079] FIG. 10(b) is a schematic diagram of the portion of the secondary insert 228 shown in FIG. 10(a) and the corresponding portion of the primary insert 218 when the secondary insert 228 is in an installed state. The secondary holes 259, 259' and the primary holes 269, 269' are aligned and the corresponding plates are thermally coupled with high thermal conductance. The spacing between the first inner secondary plate 221 and the second inner secondary plate 222 is adjusted to match the spacing between the first inner primary plate 211 and the second inner primary plate 212. In this embodiment, the offset is adjusted by moving the second inner secondary plate 222 away from the shoulder 229". In some embodiments, this may be accomplished by rotating the secondary rod 227. In this embodiment, the act of adjusting the fastener extending through the primary hole 269' and into the corresponding secondary hole 259' lifts the second inner secondary plate 222 away from the shoulder 229". It should therefore be appreciated that unlike the first and second embodiments, the adjustment member of the third embodiment facilitates movement of the second inner secondary plate 222 relative to the secondary rod 227 along the direction of the secondary rod 227. Accordingly, a thermal balancing shim 238 is disposed between the secondary rod 227 and the second inner secondary plate 222. The thermal balancing shim 238 provides mechanical support and thermal connection between the secondary rod 227 and the second inner secondary plate 222 and will be described in further detail with reference to FIG.

[0080] FIG. 11 is a cross-sectional view of a portion of the secondary insert plate according to the third embodiment shown in FIGS. 10(a) and 10(b). The second inner secondary plate 222 is described below, but the description can be applied to either inner secondary plate. FIG. 11 shows the second inner secondary plate 222, a secondary rod 227, and a lower secondary rod 227″. A first threaded insert 219 is disposed between the secondary rod 227 and the second inner secondary plate 222. The first threaded insert 219 extends into the hollow secondary rod 227 at a proximal end and into the second inner secondary plate 222 at a distal end. A second threaded insert 220 is disposed between the lower secondary rod 227″ and the second inner secondary plate 222. The second threaded insert 220 has a shoulder 229" portion at its proximal end which extends into the second inner secondary plate 222. At its distal end, the second threaded insert 222 extends into a hollow lower secondary rod 227".

[0081] In this embodiment, the first threaded insert 219 and the second threaded insert 220 are threaded or tapped to receive the second grub screw 230'. In an alternative embodiment, the grub screw can be a set screw or any screw suitable for adjusting the distance between the secondary rod 227 and the lower secondary rod 227". The first threaded insert 219 and the second threaded insert 220 are formed from a material that has a high thermal conductance at the operating base temperature of the associated thermal stage, such as brass or copper. Again, a thermal balancing shim 238 is placed between the secondary rod 227 and the second inner secondary plate 222. This can also be seen in FIG. 12, which provides a perspective view of a portion of the detached secondary insert 228 according to the third embodiment. In FIG. 12, a laboratory service is attached to the secondary insert 228. In particular, the laboratory service shown is a coaxial wire connected to the second inner secondary plate 222 and the first inner secondary plate 221.

[0082] FIG. 13 is a schematic cross-sectional view of a portion of a cryogenic cooling system according to a third embodiment, showing the deformation of the thermal balancing shim 238 when the secondary insert 228 is in the installed state. The inner secondary plate is movable in the secondary insert 228 towards the secondary rods to accommodate the misalignment. In FIG. 13, the first inner secondary plate 221 is shown together with the two secondary rods 227 and the two upper secondary rods 227'. The corresponding primary plate is not shown for clarity.

[0083] The thermal balancing shim 238 connects the secondary rods 227, 227' to the first inner secondary plate 221 and provides mechanical stability to the device as the first inner secondary plate 221 moves along the secondary rods 227, 227'. In this embodiment, the thermal balancing shim 238 is formed from a material that has a high thermal conductance at the operating base temperature of the associated thermal stage, such as brass or copper, and further provides effective thermal balancing of the secondary rods 227, 227'. The thermal balancing shim 238 is configured to thermally couple the ends of the secondary rods 227' to the inner secondary plate 221. Advantageously, the thermal balancing of the secondary rods 227 and the primary rods 217 in each thermal stage 201-205 reduces the time required to cool the cryogenic cooling system from room temperature to the operating base temperature. It also reduces any unwanted heat transfer between the warm and cold ends of the secondary inserts along the secondary rods 227. This is accomplished by increasing the thermal conductance between the secondary rod 227 and the secondary plate, especially when relative movement between these components is permitted.

[0084] The grub screw 230 has a radial projection around which the thermal balancing shim 238 is positioned. The outer hole of the thermal balancing shim 238 is slotted to allow movement of the shim perpendicular to the secondary rods 227, 227' as shown by the arrows. Once positioned, the thermal balancing shim 238 is held in place between the first and second threaded inserts 219, 220 by a clamping force. The thermal balancing shim is also fixed firmly to the first inner secondary plate 221 using the shim screws 267. The thermal balancing shim 238 is flexible to maintain physical contact between the first inner secondary plate 221 and the secondary rods 227, 227', ensuring effective thermal balancing of the secondary rods 227, 227' as the first inner secondary plate 221 moves relative to the secondary rods 227, 227'. This deformation of the thermal balancing shim 238 can be seen in FIG. 13.

[0085] FIG. 14 illustrates exemplary secondary inserts 28', 28", 28''' for use with primary inserts according to the previous embodiments. In each case, a number of ports are shown axially aligned between the plates. However, as shown, the secondary inserts can take a variety of forms. It may be advantageous for one of the secondary inserts to have two or more secondary inserts with different arrangements of ports. In this case, the same cryogenic cooling system can be used for multiple types of experiments by replacing a secondary insert configured in a first arrangement with another secondary insert configured in a second arrangement.

[0086] In further embodiments, any combination of the adjustment members described above may be used alone or in combination.

[0087] Thus, as can be seen, there is provided a cryogenic cooling system that allows for the secondary insert to be removed from the system while still achieving effective thermal equilibration while installed. Removal of the secondary insert allows for remote assembly, testing, and setup. Additionally, the system provides additional flexibility due to the ability to provide modular upgrades in the form of updated secondary inserts. Effective thermal equilibration, which is critical for cryogenic experiments, is achieved using dedicated conditioning members as described.

Claims

1. 1. A cryogenic cooling system comprising: a primary insert comprising a plurality of primary plates, each having a primary contact surface, and one or more primary connecting members arranged to connect the plurality of primary plates; a removable secondary insert comprising a plurality of secondary plates, each having a secondary contact surface, and one or more secondary connecting members arranged to connect the plurality of secondary plates such that the secondary insert is self-supporting; one or more adjustment members, the one or more adjustment members are configured such that when the secondary insert is attached to the primary insert, the adjustment members place the primary and secondary contact surfaces of the primary and secondary plates in thermally conductive contact; The one or more adjustment members form part of the secondary insert and are configured to vary a spacing between adjacent secondary plates.

2. The system of claim 1 , wherein the one or more adjustment members form at least a portion of one or more secondary connection members.

3. The system of claim 1 or 2, wherein the one or more adjustment members form a flexible portion of each of the secondary connection members.

4. A cryogenic cooling system comprising: a primary insert comprising a plurality of primary plates, each having a primary contact surface, and one or more primary connecting members arranged to connect the plurality of primary plates; a removable secondary insert comprising a plurality of secondary plates, each having a secondary contact surface, and one or more secondary connecting members arranged to connect the plurality of secondary plates such that the secondary insert is self-supporting; one or more adjustment members, the one or more adjustment members are configured such that when the secondary insert is attached to the primary insert, the adjustment members place the primary and secondary contact surfaces of the primary and secondary plates in thermally conductive contact; the one or more adjustment members are configured to vary the spacing between adjacent primary plates; The system, wherein the one or more adjustment members further comprise one or more primary shims, each primary shim configured to thermally couple the primary plate to one or more primary connection members and enable movement of the primary plate relative to the one or more primary connection members.

5. A cryogenic cooling system comprising: a primary insert comprising a plurality of primary plates, each having a primary contact surface, and one or more primary connecting members arranged to connect the plurality of primary plates; a removable secondary insert comprising a plurality of secondary plates, each having a secondary contact surface, and one or more secondary connecting members arranged to connect the plurality of secondary plates such that the secondary insert is self-supporting; one or more adjustment members, the one or more adjustment members are configured such that when the secondary insert is attached to the primary insert, the adjustment members place the primary and secondary contact surfaces of the primary and secondary plates in thermally conductive contact; the one or more adjustment members are configured to vary a spacing between adjacent secondary plates; The one or more adjustment members are configured to allow movement of one or more secondary plates relative to the one or more secondary connection members.

6. 6. The system of claim 5, further comprising one or more secondary shims, each secondary shim configured to thermally couple the secondary plate to one or more secondary connection members and enable movement of the secondary plate relative to the one or more secondary connection members.

7. A cryogenic cooling system comprising: a primary insert comprising a plurality of primary plates, each having a primary contact surface, and one or more primary connecting members arranged to connect the plurality of primary plates; a removable secondary insert comprising a plurality of secondary plates, each having a secondary contact surface, and one or more secondary connecting members arranged to connect the plurality of secondary plates such that the secondary insert is self-supporting; one or more adjustment members, the one or more adjustment members are configured such that when the secondary insert is attached to the primary insert, the adjustment members place the primary and secondary contact surfaces of the primary and secondary plates in thermally conductive contact; the one or more adjustment members are configured to vary a spacing between adjacent primary plates or adjacent secondary plates; The system wherein the primary linkage members or the secondary linkage members are rotatable such that the one or more adjustment members are used to vary the spacing between adjacent primary plates or adjacent secondary plates.

8. 1. A cryogenic cooling system comprising: a primary insert comprising a plurality of primary plates, each having a primary contact surface, and one or more primary connecting members arranged to connect the plurality of primary plates; a removable secondary insert comprising a plurality of secondary plates, each having a secondary contact surface, and one or more secondary connecting members arranged to connect the plurality of secondary plates such that the secondary insert is self-supporting; one or more adjustment members; the one or more adjustment members are configured such that when the secondary insert is attached to the primary insert, the adjustment members place the primary and secondary contact surfaces of the primary and secondary plates in thermally conductive contact; A cryogenic cooling system, wherein the one or more adjustment members comprise one or more deformable members forming part of the primary plate or secondary plate, respectively.

9. The system of claim 8 , wherein actuation of the adjustment member does not change the spacing between adjacent primary plates of the primary insert or the spacing between adjacent secondary plates of the secondary insert.

10. The system of any preceding claim, wherein the primary insert comprises a dilution refrigerator, a Helium-3 refrigerator, or a 1 Kelvin pot.

11. The system of any one of claims 1 to 10, wherein the one or more secondary connection members are removable such that two or more of the plurality of secondary plates are removable from the removable secondary insert as a unitary, self-supporting assembly.

12. A method for operating a system according to any one of claims 1 to 11, comprising the steps of: the removable secondary insert comprises a first secondary plate, a second secondary plate, a third secondary plate, a first secondary connecting member connecting the first secondary plate to the second secondary plate, and a second secondary connecting member connecting the second secondary plate to the third secondary plate, the primary insert comprises three primary plates, each primary plate corresponding to a respective secondary plate of the secondary insert, and the method comprises: mounting the secondary insert to the primary insert such that the secondary plate is conductively and thermally coupled to the corresponding primary plate with the one or more adjustment members; partially removing the secondary insert from the primary insert; The step of partially removing the secondary insert comprises: removing the first secondary connection member from the secondary insert; and removing the second secondary plate, the third secondary plate, and the second secondary connecting member as an integrated, free-standing assembly from the primary insert without removing the first secondary plate from the corresponding plate of the primary insert.

Images