Cryogenic cooling system and insert therefor

Abstract

To provide a cryogenic cooling system.SOLUTION: A primary insert 118 comprises a plurality of primary plates 111, 112 each of which has a primary contact surface, and one or more primary connection members 117 arranged to connect the plurality of primary plates 111, 112. A demountable secondary insert 128 comprises a plurality of secondary plates 121, 122 each of which has a secondary contact surface, and one or more secondary connection members 127 arranged to connect the plurality of secondary plates 121, 122 such that the secondary insert 128 is self-supporting. One or more adjustment members are configured such that, when the secondary insert 128 is mounted to the primary insert 118, the adjustment members bring the primary and secondary contact surfaces of the respective primary plates 111, 112 and secondary plates 121, 122 into a conductive thermal contact condition.SELECTED DRAWING: Figure 9(a)

Description

Technical Field

[0001] The present invention relates to cryogenic cooling systems, particularly cryogenic cooling systems with self - contained detachable inserts.

Background Art

[0002] Cryogenic cooling systems are commonly used for conducting experiments at low temperatures below 100 Kelvin. The systems are generally customized for specific experiments by installing experimental equipment in a particular arrangement. Installation of the experimental equipment usually requires the use of a crane or an elevated platform to access the system, which is difficult and time - consuming. Further, after installation of the experimental equipment, a test is usually required to confirm that its function is sufficient, which also takes a significant amount of time. Spending time on installation and troubleshooting leaves less time for collecting experimental data.

[0003] Cryogenic cooling systems can typically reach millikelvin temperatures during use by including a plurality of platforms maintained at intermediate temperatures between room temperature and millikelvin temperature. In this way, cooling can be staged so that the final platform of the system can provide continuous cooling to the millikelvin temperature. The installed experimental equipment and other components of the system can provide a path from room temperature to the final platform. To prevent unintentional heating by these components, each platform provides a thermal sink for removing additional heat.

[0004] It is possible to incorporate experimental services into modules outside the system and install them in a pre - assembled state. This method is generally faster than direct installation of experimental services. However, it is important that the modules are sufficiently thermally equilibrated to obtain millikelvin temperatures. In the prior art, thermal equilibration is achieved using clamps and / or complex and large - scale adjustment processes.

[0005] A slight offset may cause poor thermal equilibration within the system.

[0006] Cryogenic physics experiments are becoming increasingly complex, and the experimental services required to conduct the experiments have consequently increased. For example, in quantum information processing (QIP) experiments, high-frequency (RF) wiring is used to accommodate devices with a large number of qubits. As the number of qubits increases, the amount of RF wiring required also increases accordingly. Cryogenic cooling systems are expected to accommodate the increasing amount of experimental services. One way to meet the increasing demand is to provide improvements to the modules for the core system. However, as manufacturing tolerances accumulate, inconsistent joints and insufficient thermal equilibration platforms occur within the cryogenic cooling system, thus requiring extensive fine-tuning to improve performance.

[0007] In cryogenic cooling systems, a method for more easily introducing experimental services is desired.

Prior Art Documents

Non-Patent Documents

[0008]

Non-Patent Document 1

Summary of the Invention

[0009] A first aspect of the present invention provides, in use: 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 detachable 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 so that the secondary insert is self-standing; and one or more adjustment members, wherein the one or more adjustment members are configured, in use, to bring the primary contact surface and the secondary contact surface of the primary plate and the secondary plate into thermally conductive contact when the secondary insert is attached to the primary insert, and is characterized by a cryogenic cooling system.

[0010] Advantageously, the system comprises adjustment members that bring the primary and secondary contact surfaces of the respective primary and secondary plates into thermally conductive contact with each other. This eliminates the need for a number of fine adjustments to overcome misalignment between the two parts so that the two parts of the cryogenic cooling system are effectively in thermal communication. When not attached, the secondary insert can also be moved relative to the primary insert as a self-standing body, thereby further simplifying the attachment and detachment operations. For example, each plate of the secondary insert can be aligned with the 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 member may form part of a plurality of primary plates, part of one or more primary connecting members, or part of both the plate and the connecting member. Similarly, one or more adjustment members may form part of the secondary insert. In this case, the adjustment member may form part of a plurality of secondary plates, part of one or more secondary connecting members, or part of both the plate and the connecting member. Also, the adjustment member may form part of both the primary insert and the secondary insert. Alternatively, the adjustment member may take the form of a fastening member configured to join corresponding plates of the primary insert and the secondary insert. The selection of the position of the adjustment member can depend on a particular implementation. For example, if the secondary insert is designed to accommodate a rigid experimental device, the position and type of the adjustment member are selected accordingly.

[0012] The primary plate and the secondary plate typically generally extend planar and are connected along the adjacent peripheral surfaces of the plates in use, and these may have a step. Preferably, the thermally conductive contact between the primary plate and the corresponding secondary plate is provided by surface contact between conformal planar regions of the respective primary and secondary contact surfaces. Each of the primary plate and the secondary plate may include a flange. When the primary plate contacts the corresponding secondary plate, the lower surface of the flange of the primary plate coincides with the upper surface of the flange of the secondary plate, forming a continuous structure. Generally, since the primary plate and the secondary plate are formed from a highly conductive material, a joint where the plates are closely connected over a large area provides a good thermal connection throughout the joint.

[0013] The adjustment member typically thermally conducts the respective primary and secondary contact surfaces of the primary plate and the secondary plates by adjusting the displacement between each of the plurality of secondary plates of the detachable secondary insert and the corresponding primary plate of the primary insert. As a result of manufacturing tolerances, a misalignment may occur between the primary plate and the secondary plate. If the misalignment between the plates remains unadjusted, it will reduce the thermal conductance between the plates.

[0014] The cryogenic cooling system includes both a primary insert and a secondary insert. However, the secondary insert (alternatively, the primary insert) is detachable and thus removable from the system. When the secondary insert is in the non-mounted state, the secondary plates are typically spatially positioned in a secondary configuration relative to each other. The secondary insert is self-standing in its non-mounted state, and the spacing between adjacent plates within the secondary insert may be determined by secondary connecting members. Similarly, when the secondary insert is in the non-mounted state, the primary plates are typically spatially positioned in a primary configuration relative to each other. The spacing between adjacent plates within 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 a misalignment between the above-mentioned plates. The misalignment may be an offset between the plane of the secondary plate and the plane of the corresponding primary plate in each of the respective primary and secondary configurations. Each pair of plates may have a different misalignment, and the misalignment can be positive or negative. As a result, each adjustment member provides a different level of adjustment and can typically provide a movable range 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 removed, i.e., all plates of the secondary insert can be separated from and removed from the primary insert. Optionally, the secondary insert can only be partially removed. 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 so that two or more of the plurality of secondary plates can be removed from the removable secondary insert as an integral self - standing body or assembly.

[0017] The secondary insert includes a first secondary plate, a second secondary plate, and a third secondary plate connected using a secondary connecting member, and the second secondary plate is disposed between the first secondary plate and the third secondary plate. When the secondary connecting member connecting the second secondary plate and the third secondary plate is removed, the second secondary plate and the first secondary plate can be removed as an integral structure. The partially removed secondary insert (the first and second secondary plates) preferably stands on its own, similar to the self - standing characteristics of a completely non - attached secondary insert.

[0018] The detachable nature of the secondary insert advantageously allows the secondary insert to be removed from the cryogenic cooling system for modification. However, when it is not necessary to remove the entire secondary insert, it may be beneficial to leave a part of the secondary insert attached to the primary insert. For example, since cryogenic experiments are usually conducted in a vacuum, one of the joints between the primary insert and the secondary insert may form part of a barrier between atmospheric pressure and low pressure. Therefore, additional sealing may be required, such as using an O - ring or other vacuum seals, to reduce the possibility of gas leakage. Leaving the plate forming the above - mentioned barrier in place can avoid repeating the re - formation of the seal and is beneficial.

[0019] The advantage that the secondary insert can be removed 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 only be made to two or any number of plates of the secondary insert. It is easier and thus preferable to remove only the necessary plates and partially remove the secondary insert.

[0020] Typically, experimental services or experimental devices are placed within the cryogenic cooling system and used to conduct experiments at low temperatures. Preferably, one or more of the plurality of secondary plates are configured to accommodate experimental instruments. This is particularly advantageous when the experimental devices attached to the secondary insert are complex and time-consuming to assemble. Thus, experimental services can be assembled and tested away from the cryogenic cooling system before being attached to the primary insert.

[0021] The cryogenic cooling system can be used for cryogenic experimental procedures, and cooling can be achieved using a number of refrigerators. Such a system is particularly desired 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 its components. 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 a similar low temperature during operation.

[0022] One or more of the primary plate or the secondary plate can comprise a rigid portion and one or more deformable portions. Preferably, the deformable portion is deformable relative to the rigid portion to adjust for misalignment. Thus, one or more adjustment members can comprise one or more deformable portions. During attachment of a detachable secondary insert to the primary insert, the one or more deformable portions can be deformed locally to cause thermally conductive contact. The deformable portion of the plate can be provided at the edge of the plate, for example, in the form of a flange. One advantage of this mode of adjustment is the ability to maintain the primary and / or secondary configuration within each insert. For example, operation of the adjustment member does not change the spacing between adjacent primary plates of the primary insert or between adjacent secondary plates of the secondary insert. This effectively means that the primary insert or the secondary insert each maintain a fixed state and, thus, can accommodate a rigid experimental device attached to two or more plates. Similarly, the spacing between corresponding plates of each of the primary and secondary inserts can also be maintained in a fixed state. The deformation can be configured to occur locally in a predetermined region of the plate such that the experimental device is not damaged, but nevertheless thermally conductive contact is achieved. The deformable portion can form part of the primary plate. Alternatively, the deformable portion can form part of the secondary plate. Optionally, the deformable portion can form part of both the primary plate and the secondary plate.

[0023] When the secondary insert is in the non-mounted state, the primary and secondary inserts may each have their 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 detachable secondary insert is in the mounted state. One or more adjustment members can alternatively be configured to adjust one or both of the primary and secondary configurations so as to cause thermally conductive contact. For example, one or more adjustment members are configured to change the spacing between adjacent primary plates or adjacent secondary plates. This can be achieved by configuring each of the one or more primary connecting members or secondary connecting members to deform so as to adjust the displacement between the plates.

[0024] One or more adjustment members may form at least a part of one or more primary connecting members or secondary connecting members. For example, one or more adjustment members may form the respective flexible portions of the primary or secondary connecting members. During the attachment of the secondary insert to the primary insert, the displacement can be adjusted by placing the secondary connecting member under a compressive or tensile load. In response to the load, the secondary connecting member deforms, thereby causing thermally conductive contact by aligning the secondary plate with the corresponding primary plate. Similarly, the displacement can be adjusted by the deformation of the flexible primary connecting member.

[0025] Alternatively, one or more adjustment members may be configured to allow movement of one or more of the primary plates relative to one or more of the primary connecting members, or one or more adjustment members may be configured to allow movement of one or more of the secondary plates relative to one or more of the secondary connecting members. For example, the primary or secondary connecting members may be rotatable to change the spacing between adjacent primary plates or adjacent secondary plates using one or more adjustment members. This adjustment is generally achieved when the ends of the primary or secondary connecting members comprise threads or tapped portions. In this case, the adjustment member can comprise a combination of the thread or tapped portion of the connecting member and a receiving member configured to engage the thread or tapped portion to adjust the spacing between adjacent plates of the primary or secondary insert.

[0026] Preferably, the primary and secondary connecting members are thermally equilibrated with their respective primary and secondary plates. Generally, there is a heat load transmitted along the primary and / or secondary connecting members from room temperature to the cryogenic stage of the system. Thermal equilibration at the plates advantageously blocks this heat load, thereby forming a heat sink that allows the distal stage of the primary or secondary insert to obtain a lower temperature during operation of the system. Effective thermal equilibration of the primary connecting member can be achieved by use of one or more primary shims, each primary shim thermally coupling a primary plate to one or more primary connecting members and being configured to allow movement of the primary plate relative to one or more primary connecting members. Similarly, effective thermal equilibration of the secondary connecting member can be achieved by use of one or more secondary shims, each secondary shim thermally coupling a secondary plate to one or more secondary connecting members and being configured to allow movement of the secondary plate relative to one or more secondary connecting members.

[0027] Next, a further aspect of the present invention will be described. Features described in relation to one aspect are equally applicable in relation to the remaining features, and each aspect shares similar advantages.

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

[0029] A third aspect of the present invention provides a method for operating the system according to the first aspect, wherein the secondary insert includes 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 includes three primary plates, each primary plate corresponding to a respective secondary plate of the secondary insert, the method comprising mounting the secondary insert on the primary insert such that the secondary plates are thermally coupled to the 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 as an integral self-standing assembly from the primary insert 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

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8(a)

Figure 8(b)

Figure 9(a)

Figure 9(b)

Figure 10(a)

Figure 10(b)

Figure 11

Figure 12

Figure 13

Figure 14

Embodiments for Carrying Out the Invention

[0032] FIG. 1 is a cross-sectional view showing the interior of a cryogenic cooling system according to the first embodiment. This system includes a plurality 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, and thus form a hierarchical assembly that is aligned along a central axis with the stages extending parallel to the rods and spatially distributed. The primary rod 17 is 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 typically evacuated and housed within a cryostat 36 to remove convective and conductive heat paths via any gas within the cryostat 36 to improve thermal performance. The cryostat 36 is attached to the outer stage 6, and the outer surface 7 of the outer stage 6 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 refrigerant-free (also referred to as "dry" in the art) in that it is not primarily cooled by contact with a cryogenic fluid reservoir. However, although substantially refrigerant-free, as will become apparent, some cryogenic fluids contain a liquid phase and are typically present within the cryostat during use. In this embodiment, cooling is achieved by 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 PTR40, which is thermally coupled to the first thermal stage 1 and the second thermal stage 2. Each of the thermal stages 1 - 5 is formed of a highly conductive material such as copper and has different operating base temperatures. The first thermal stage 1 is thermally coupled to the first PTR stage 41 and achieves an operating base temperature of about 50 - 70 Kelvin. The second thermal stage 2 is thermally coupled to the second PTR stage 42 and achieves an operating base temperature of about 3 - 5 Kelvin. In this embodiment, the second PTR stage 42 forms the lowest temperature stage of PTR40.

[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. The cooling of the third, fourth, and fifth thermal stages 3, 4, 5 is achieved by the operation of the dilution unit 8, during which the 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 having a condensation line 61 and a still pump line 62 using a compressor pump 63 and a turbo molecular pump 64. Incidentally, the working fluid can be stored in a storage container 65 and supplied to the cooling circuit 60 using a supply line 66. The third thermal stage 3 is thermally coupled to a still 10 that forms part of the dilution unit 8. The operating base temperature of the third thermal stage 3 is typically 0.5 - 2 Kelvin. The fifth thermal stage 5 is thermally coupled to the mixing chamber 9 of the dilution unit 8. The operating base temperature of the fifth thermal stage 5 is typically 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 the thermal stages 1 - 5, each shield surrounding each of the remaining lower base temperature components. The first thermal radiation shield 56, the second thermal radiation shield 57, and the third thermal radiation shield 58 are attached to the first thermal stage 1, the second thermal stage 2, and the third thermal radiation stage 3, respectively. This reduces any unwanted thermal communication between the thermal stages 1 - 5 and allows different operating base temperatures to be achieved for each stage.

[0037] The cryogenic cooling system of FIG. 1 can be controlled using a control system 50. The control system 50 is typically a suitable computer system, although manual control of the system is also possible. The operation of each part of the system includes the operation of the PTR 40, the dilution unit 8, the pumps 63, 64 and associated valves, the monitoring of temperature and pressure sensors, and the operation of other auxiliary equipment for performing desired procedures, etc., and can be controlled using the control system 50.

[0038] The cryogenic cooling system as described can generally be used to conduct experiments at low temperatures below 100 Kelvin. Although not shown in FIG. 1, the experimental services can be installed within the cryostat 36. The selection of the experimental services and their specific devices within the cryostat 36 can be customized. An example of such experimental services will be described with reference to FIG. 6. Typically, the specific devices of the experimental services are installed, tested, and left fixed for a certain period. Modifying the devices within the system to perform different types of experiments requires a number of adjustment and troubleshooting procedures before the experiment is executed and is typically very time-consuming. Embodiments of the present invention provide a primary insert 18 and a secondary insert 28, and the secondary insert 28 is detachable from the primary insert 18. Thus, the experimental services can be attached to the primary insert 18, or to the secondary insert 28 that is easy to remove and reattach, or to both the primary and secondary inserts 18, 28. The primary insert 18 consists of a plurality of primary plates, and the secondary insert 28 consists of a plurality of secondary plates 21-26. Each primary plate is configured to be attached to the corresponding secondary plate to form each of the thermal stages 1-5 of the system, as will be further described.

[0039] The advantage of attaching the experimental service to the secondary insert 28 results from the ability to remove the secondary insert 28 from the cryogenic cooling system. Assembly and preliminary testing can be done "on the bench" outside the cryogenic cooling system where the experiment is to be conducted. Thus, modifications or updates to the experimental service to perform different experiments can be carried out relatively quickly and easily. Cryogenic experiments using cryogenic cooling systems such as dilution refrigerators typically take days, weeks, or months to execute. Changes to the experimental service within the system usually require the changes to be made at room temperature, resulting in experiment downtime, i.e., the time when the cryogenic cooling system is not at its operable base temperature. The ability to manipulate the experimental service on the removed secondary insert 28 on the bench (away from the system itself) reduces the experiment downtime. For example, multiple secondary inserts can be provided for use with a given cryogenic cooling system. While adjusting the experimental service on the first secondary insert under atmospheric pressure conditions, a cryogenic environment is maintained within the system for conducting experiments on the second secondary insert.

[0040] Embodiments of the present invention also provide an adjustment member that brings the primary insert 18 and the secondary insert 28 into thermally conductive contact. Good thermal contact is important when performing low-temperature measurements. For example, in the presence of a heat flux such as generated by the operation of a cooling source, a temperature gradient will naturally occur 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 (because the cooling power available from either the PTR stages 41, 42 or the dilution refrigerator 8 is finite). The thermal conductance of the joint varies depending on a number of factors including its temperature and contact pressure. The adjustment member is typically configured to limit the temperature difference between the corresponding stages of the primary and secondary inserts 18, 28, for example, within 2% of the absolute temperature of the higher-temperature stage, preferably within 1%. This is achieved by making the thermal conductance between these stages sufficiently high. For example, when the second thermal stage 2 is cooled to 4 Kelvin by the second PTR stage 42 (with a cooling power of 1 watt), 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 approximately 25 W / K at 4 Kelvin. Similarly, when the fifth thermal stage 5 is cooled to 100 millikelvin by the mixing chamber 9 (with a cooling power of 400 microwatts), 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 approximately 0.4 W / K at 0.1 Kelvin.

[0041] The difference in the predicted thermal conductances 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. Dhuley published in Cryogenics 101 (2019) 111-124. The thermal conductance of a given joint decreases with temperature. However, since the practical heat fluxes applicable between the primary and secondary plates of each of the primary and secondary inserts 18, 28 also decrease with temperature, all of the mounting devices between the primary and secondary plates can be designed and mounted in the same way to provide acceptable performance at each of the thermal stages 1-5.

[0042] Various adjustment members are envisioned and embodiments facilitating different adjustment methods are described.

[0043] Figure 2 shows the primary and secondary inserts 18, 28 of Figure 1 in further detail. As shown, each of the thermal stages 1-5 includes inner primary plates 11-15, inner secondary plates 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 the corresponding inner and outer primary plates 11-15, 16 along the peripheral edge of the secondary plate. Each of the edge pieces 31-35 is connected to the corresponding inner primary plate 11-15 and the corresponding inner secondary plate 21-25 along the peripheral portions of the respective inner primary and secondary plates. 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 in a direction perpendicular to the plates between the plates. In this embodiment, the edge pieces 31-35 are not connected, but in an alternative embodiment, the edge pieces 31-35 can be connected by an edge rod 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 detachable from the primary insert 18, particularly in a cryogenic cooling system. When the secondary insert 28 is in the non-attached state, it forms a self-supporting assembly and does not require an additional support structure to maintain its original configuration and can be removed from the primary insert 18 as an integral body.

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

[0046] When the secondary insert 28 is in the mounted state, achieving good thermal contact between any secondary insert 28 and the primary insert 18 is no small matter. During the manufacture of the primary insert 18 or the secondary insert 28, the relative positional relationships of the inner and outer primary plates 11-15, 16 and the inner and outer secondary plates 21-25, 26 within each insert 18, 28 may differ within a certain manufacturing tolerance even if made to the same specifications. Small differences can result in misalignment, i.e., an offset between the plane of the secondary plate and the plane of the corresponding primary plate, when the secondary insert 28 is brought into the mounting position. Such a deviation, even if small, can 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 can also include an adjustment member (examples of which are described in more detail below) that thermally conducts the inner primary plates 11-15 and the inner secondary plates 21-25 when the secondary insert 28 is in the mounted state, thereby accommodating the deviation. The adjustment member can form part of the primary insert 18, part of the secondary insert 28, or part of both.

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

[0049] In this embodiment, the cooling device is attached 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, where the still 10 of the dilution unit 8 is thermally coupled to the primary plate 13 of the third thermal stage 3, and the mixing chamber 9 of the dilution unit 8 is thermally coupled to the primary plate 15 of the fifth thermal stage 5. In an alternative embodiment, the cooling device is attached to the secondary insert. For example, the dilution unit can alternatively be attached 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 and are spatially distributed in the secondary configuration. In each of the respective primary and secondary configurations, there may be an offset, called 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 on the primary insert 18, thus accommodating any misalignment. Such thermally conductive contact is provided by adjustment members. The outer secondary plate 26 forms a vacuum seal with the outer primary plate 16, for example, by the use of an O-ring, although any suitable sealing mechanism is possible.

[0051] Next, the attachment of the cryogenic cooling system to the secondary insert 28 will be described with reference to FIG. 3. First, the secondary insert 28 is two-dimensionally aligned with the primary insert 18, and each of the inner and outer secondary plates 21-25, 26 is disposed slightly below the corresponding inner and outer primary plates 11-15, 16. Second, the secondary insert 28 is aligned in the third dimension, and the third dimension is parallel to the main 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 such 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. And the inner secondary plates 21-25 can be fixed in place. In this embodiment, they are here fixed using fastening members in the form of screws. Adjusting 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 of the edge pieces 31-35 is formed to shield the components at the lower base temperature from excess radiation. As can be seen from FIG. 3, the shape of each of the edge pieces 31-35 is designed to conform to the shape of each of the inner secondary plates 21-25 and each of the inner primary plates 11-15 in order to complete each of the thermal stages 1-5. In an alternative embodiment, the edge pieces 31-35 can be attached to the inner primary plates 11-15 without disposing the secondary insert 28. In another embodiment, the edge pieces are not necessary. Instead, each of the inner secondary plates 21-25 can be formed to function as a thermal shield that completes each of the thermal stages 1-5 and blocks radiation between adjacent stages.

[0053] The secondary insert 28 of the cryogenic cooling system is detachable from the primary insert 18. FIG. 4 shows the cryogenic cooling system according to the first embodiment, in a position where the secondary insert 28 has been removed, and the edge pieces 31 to 35 are attached to the corresponding inner primary plates 11 to 15.

[0054] While the secondary insert 28 is in the non-mounted position, modifications can be made to the secondary insert 28, particularly to the experimental services attached to the secondary insert 28. This is practically easy for the user to achieve as it is done in the non-mounted position. Modifications to 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. Further, it is advantageous to have a plurality of secondary inserts 28 so that one secondary insert 28 can be used experimentally while in operation, i.e., in the mounted state, and one or more secondary inserts 28 can be on the bench, i.e., in the non-mounted state. While in the non-mounted 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 on a donor cryostat to test the experimental services at low temperature. The above tests, assembly, modifications, and updates can be carried out in parallel with the experiments being conducted in the cryogenic cooling system.

[0055] As described above, the secondary insert 28 forms a hierarchical assembly. The spatial distribution of the inner and outer secondary plates 21-25, 26 within the assembly defines five inter-plate spaces 51-55, as shown in FIG. 4. The first inter-plate space 51 between the outer secondary plate 26 and the first inner secondary plate 21, the second inter-plate space 52 between the first inner secondary plate 21 and the second inner secondary plate 22, the third inter-plate space 53 between the second inner secondary plate 22 and the third inner secondary plate 23, the fourth inter-plate space 54 between the third inner secondary plate 23 and the fourth inner secondary plate 24, and the fifth inter-plate 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 the respective inter-plate spaces 51-55, connecting each pair of adjacent secondary plates 21-26. The arrangement of each group of secondary rods 27 is offset with respect to adjacent groups so that each rod can be adjusted or removed independently from its respective inter-plate space 51-55. Removing all of the secondary rods 27 in one of the inter-plate spaces 51-55 allows the secondary insert 28 to be split into two parts. Therefore, two or more plates of the secondary insert 28 can be removed as an integral structure from the remaining plates. FIG. 5 shows a cryogenic cooling system according to a first embodiment in which the secondary insert 28 is partially removed.

[0057] In FIG. 5, the secondary rod 27 in the fourth plate space 54 is removed. The fourth plate space 54 is between the third inner secondary plate 23 and the fourth inner secondary plate 24. Thus, by removing the secondary rod 27, the fourth inner secondary plate 24 and the fifth inner secondary plate 25 can be detached 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. Thus, this assembly remains self-supporting even after being removed from the cryogenic cooling system. In an alternative embodiment, any number of the inner and outer secondary plates 21-25, 26 can be removed.

[0058] Depending on the experimental situation, 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 to allow for more flexible preparation and testing of experimental services. Further, in contrast to the entire secondary insert 28, reattachment of a part of the 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, when any of the inner secondary plates 21-24 of the first to fourth thermal stages 1-4 are removed, they are generally replaced with blanks to reduce radiative heat transfer between the thermal stages.

[0059] Experimental services can be mounted on the cryogenic cooling system. FIG. 6 shows a cryogenic cooling system according to a first embodiment with an experimental service attached to the secondary insert 28. Examples of experimental services can include wiring that 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 a selected experiment. The experimental service shown in FIG. 6 is coaxial.

[0060] As described above, the secondary insert may be wholly or partially removed from the cryogenic cooling system and inserted into another cryogenic cooling system. When the secondary insert 28 is brought to the mounting position, if a shift occurs between each of the inner secondary plates 21-25 and the corresponding inner primary plates 11-15, this may result in poor thermal contact. To ensure good thermal contact, the cryogenic cooling system is provided with adjustment members. Here, possible adjustment members will be described with reference to FIGS. 7-12.

[0061] FIG. 7 is a schematic front view of the inner secondary plate according to the first embodiment. Hereinafter, the first inner secondary plate 21 will be described, but this 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, a flange 44 is provided which is disposed in the plane of the first secondary plate 21. In the present embodiment, each flange 44 is provided with secondary holes 59 which are evenly distributed along the length of the flange 44. These holes may or may not be tapped. A series of holes which coincide are arranged on the corresponding primary plate so that the first inner secondary plate 21 is 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 portion or connecting portion 45. The link portion 45 is a relatively thin strip of the first inner secondary plate 21 which extends along the length of the flange 44 and forms a pivot about which the flange 44 can move. The first inner secondary plate 21 further houses four receiving holes 46 for positioning the secondary rod 27. 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 so as to bring the first inner primary plate 11 and the first inner secondary plate 21 into thermally conductive contact. Due to the local deformation, a rigid experimental apparatus such as an ultra-high vacuum port can be attached to the secondary insert 28. Once such a rigid apparatus is attached, it can effectively determine the spacing between two or more of the inner or outer secondary plates 21-25, 26. In this embodiment, the rigid apparatus is attached to the rigid central portion 43 of the first inner secondary plate 21, and the flange 44 thus provides a deformable portion that forms an adjustment member. The local deformation of the flange 44 adjusts any misalignment between the first inner primary plate 11 and the first inner secondary plate 21. Including the rigid central portion 43 of the inner secondary plate advantageously allows the rigid experimental apparatus to be maintained unaffected by any necessary adjustments while ensuring effective thermal equilibration between the secondary insert 28 and the primary insert 18.

[0064] FIGS. 8(a) and 8(b) are side views schematically showing a part of the cryogenic cooling system according to the first embodiment during the mounting process. FIG. 8(a) shows a part of the secondary insert 28 in the non-mounted state, and FIG. 8(b) shows a part of the secondary insert 28 in the mounted state using an adjustment member. FIGS. 8(a) and 8(b) show a part of the first inner secondary plate 21, the second inner secondary plate 22, the first inner primary plate 11, and the second inner primary plate 12. However, this 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 take 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 a 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 a stepped portion 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 align 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 disposed 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 the cryogenic cooling system, some of which may not include adjustment members. In another alternative embodiment, the flange 44 may be disposed on the plates of the primary insert 18 and the secondary insert 28. This advantageously allows for a greater possible displacement since deformation can occur on both sides.

[0068] FIG. 8(b) schematically shows 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 the mounted 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 the 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 surface contact with the first inner primary plate 11 along the stepped portion of the first inner primary plate 11. The planar region of the stepped portion of the first inner primary plate 11 is shaped to match or conform to the flange 44 of the first inner secondary plate 21.

[0069] In this embodiment, the deformation of the flanges 44, 44' can adapt or adjust to the displacement between d1 and d2 while the central portions 43, 43' of the rigid bodies of the first inner secondary plate 21 and the second inner secondary plate 22 remain in fixed positions relative to each other. The first inner primary plate 11 and the second inner primary plate 12 also remain in fixed positions relative to each other before and after the mounting process.

[0070] Figs. 9(a) and 9(b) are side views schematically showing a part of the cryogenic cooling system according to the second embodiment, and showing a part of the secondary insert 128 in a mounted state using an adjustment member. This cryogenic cooling system has the same form as that described in the first embodiment, but the provided adjustment member is different. 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, additional primary rods 117 and additional 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 the second embodiment, the secondary rod 127 is configured to deform when a compressive or tensile load is applied to adjust the distance between adjacent inner secondary plates 121, 122. This movement adjusts any misalignment between the corresponding plates of the primary and secondary inserts 118, 128. In this embodiment, the primary rod 117 is a rigid body, and thus the distance between adjacent plates of the primary insert 118 is fixed. The secondary rod 127 is formed of stainless steel and is curved so as to be deformable as described. The deformation of the secondary rod 127 brings each of the inner secondary plates 121 - 125 into thermally conductive contact with the corresponding inner primary plates 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 the second embodiment as described above with reference to FIGS. 9(a) and 9(b), the secondary rod 127 can adjust the displacement between the corresponding inner plates of the primary insert 118 and the secondary insert 128 of the cryogenic cooling system. The secondary rod 127 is configured to adjust the distance between adjacent secondary plates in order to align each plate of the secondary insert 128 with each plate of the primary insert 118. In an alternative embodiment, the primary rod may be configured to deform when a compressive or tensile load is applied, as described above in relation to the secondary rod 127, and the secondary rod can be rigid so as to fix the positions of the inner and outer secondary plates relative to each other in this way. Thereby, the secondary insert can be made more firmly fixed in the non-attached state.

[0075] FIGS. 10(a) and 10(b) are side views schematically showing a part of the cryogenic cooling system according to the third embodiment. Similar to the second embodiment (FIGS. 9(a) and 9(b)) and different from the first embodiment (FIGS. 8(a) and 8(b)), the third embodiment includes an adjustment member configured to adjust the interval between adjacent plates of the insert. FIG. 10(a) shows a part of the secondary insert 228 in the non-attached state, while FIG. 10(b) shows a part of the secondary insert 228 in the attached state in which the adjustment member is used. FIGS. 10(a) and 10(b) illustrate 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 FIGS. 10(a) and 10(b), the first inner secondary plate 221 is connected to the second inner secondary plate 222 by a secondary rod 227. The upper secondary rod 227' connects the first inner secondary plate 221 to an outer secondary plate (not shown). The lower secondary rod 227'' connects the second inner secondary plate 222 to a third inner secondary plate (not shown). Each of the secondary rods 227, 227', 227'' is provided at the proximal end of each rod 227, 227', 227'' and has shoulders 229, 229'' adapted to receive grub screws 230, 230'. The first inner primary plate 211 is connected to the second inner primary plate 212 by a primary rod 217. The upper primary rod 217' connects the first inner primary plate 211 to an outer primary plate 216 (not shown). The lower primary rod 217'' connects the second inner primary plate 212 to a third inner primary plate 213 (not shown).

[0077] FIG. 10(a) schematically shows a part of the secondary insert 228 and a corresponding part of the primary insert 218 when the secondary insert 228 is in the non-mounted state. The secondary holes 259, 259' are configured to align with the primary holes 269, 269' when the secondary insert 228 is in the mounted state, and a fastening member extends therebetween. The primary holes 269, 269' and / or the secondary holes 259, 259' may be threaded, or may form clearance holes or clearance slots, for example, when the fastening member is used in combination with a back nut. In FIG. 10(a), the distance d2 between the first inner secondary plate 221 and the second inner secondary plate 222 in the non-mounted state is greater than the distance d1 between the first inner primary plate 211 and the second inner primary plate 212, that is, d2 > d1. The relative lateral positional relationship in FIG. 10(a) is exemplary and is for clearly showing the vertical positional relationship. This shift is between the second inner secondary plate 222 and the second inner primary plate 212.

[0078] In the non-mounted state, the first inner secondary plate 221 and the second inner secondary plate 222 are respectively disposed on the shoulders 229, 229" of the secondary rod 227 and the lower secondary rod 227". The first grab screw 230 is disposed 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 so as to engage with the first grab screw 230. The second grab screw 230' is disposed between the secondary rod 227 and the lower secondary rod 227". The upper portion of the lower secondary rod 227' and the lower portion of the secondary rod 227 are tapped so as to accommodate the second grab screw 230'. In this embodiment, the adjustment member is formed by the combination of the tapped portion of the secondary rod and the corresponding grab screw with which it engages. In an alternative embodiment, the primary rod may be provided with an adjustment mechanism as described for the secondary rod, or both the primary rod and the secondary rod may be provided with such an adjustment mechanism.

[0079] FIG. 10(b) is a diagram schematically showing a portion of the secondary insert 228 shown in FIG. 10(a) and a corresponding portion of the primary insert 218 when the secondary insert 228 is in the mounted state. The secondary holes 259, 259' and the primary holes 269, 269' are aligned, and the corresponding plates are thermally connected with high thermal conductivity. The distance between the first inner secondary plate 221 and the second inner secondary plate 222 is adjusted to match the distance between the first inner primary plate 211 and the second inner primary plate 212. In this embodiment, the misalignment is adjusted by separating the second inner secondary plate 222 from the shoulder 229". In some embodiments, this can be achieved by rotation of the secondary rod 227. In this embodiment, the act of adjusting the fastening member extending through the primary hole 269' into the corresponding secondary hole 259' lifts the second inner secondary plate 222 from the shoulder 229". Thus, unlike the first and second embodiments, it should be understood that the adjustment member of the third embodiment facilitates movement of the second inner secondary plate 222 along the direction of the secondary rod 227 with respect to 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 more detail with reference to FIG. 13.

[0080] FIG. 11 is a cross-sectional view showing a part of the secondary insert plate according to the third embodiment shown in FIGS. 10(a) and 10(b). Hereinafter, the second inner secondary plate 222 will be described, but this description can be applied to any inner secondary plate. FIG. 11 shows the second inner secondary plate 222, the secondary rod 227, and the 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 its proximal end and into the second inner secondary plate 222 at its 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 the 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 accommodate 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 having a high thermal conductivity at the operating base temperature of the associated thermal stage, such as brass or copper. Again, the thermal equilibration shim 238 is disposed 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 part of the detached secondary insert 228 according to the third embodiment. In FIG. 12, an experimental service is attached to the secondary insert 228. In particular, the experimental 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 cross-sectional view schematically showing a part of the cryogenic cooling system according to the third embodiment, and shows a deformation of the thermal equilibration shim 238 when the secondary insert 228 is in the mounted state. The inner secondary plate is movable in the direction of the secondary rod within the secondary insert 228 so as to adjust the displacement. In FIG. 13, the first inner secondary plate 221 is shown together with two secondary rods 227 and two upper secondary rods 227'. The corresponding primary plate is not shown for clarity.

[0083] The thermal equilibration shim 238 connects the secondary rods 227, 227' to the first inner secondary plate 221 and provides mechanical stability to the device when the first inner secondary plate 221 moves along the secondary rods 227, 227'. In this embodiment, the thermal equilibration shim 238 is formed from a material having a high thermal conductivity at the operating base temperature of the associated thermal stage, such as brass or copper, and further provides effective thermal equilibration of the secondary rods 227, 227'. The thermal equilibration shim 238 is configured to thermally couple the end of the secondary rod 227' to the inner secondary plate 221. Advantageously, the thermal equilibration of the secondary rods 227 and the primary rods 217 in each thermal stage 201-205 shortens 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 insert along the secondary rod 227. This is achieved by increasing the thermal conductivity between the secondary rod 227 and the secondary plate, especially when relative movement between these components is possible.

[0084] The grab screw 230 has a radial protrusion around which the thermal equilibration shim 238 is disposed. The holes on the outside of the thermal equilibration shim 238 are slotted to allow movement of the shim perpendicular to the secondary rods 227, 227’ as indicated by the arrows. When positioned, the thermal equilibration shim 238 is held in a predetermined position between the first and second threaded inserts 219, 220 by a clamping force. Also, the thermal equilibration shim is firmly fixed to the first inner secondary plate 221 using the shim screw 267. The thermal equilibration shim 238 is flexible to maintain physical contact between the first inner secondary plate 221 and the secondary rods 227, 227’ and to ensure effective thermal equilibration of the secondary rods 227, 227’ when the first inner secondary plate 221 moves relative to the secondary rods 227, 227’. The deformation of this thermal equilibration shim 238 can be seen in FIG. 13.

[0085] FIG. 14 illustrates exemplary secondary inserts 28’, 28”, 28’’’ for use with the primary insert according to the previous embodiment. In each case, a number of axially aligned ports are shown between the plates. However, as shown, the secondary insert can take various 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, by exchanging the secondary insert configured in the first arrangement for another secondary insert configured in the second arrangement, the same cryogenic cooling system can be used for multiple types of experiments.

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

[0087] Accordingly, as will be understood, there is provided a cryogenic cooling system that can remove the secondary insert from the system while achieving effective thermal equilibration in the mounted state. Removal of the secondary insert allows for remote assembly, testing, and setup. Further, this system has additional flexibility due to its ability to provide module upgrades in the form of updated secondary inserts. Effective thermal equilibration, which is important for cryogenic experiments, is achieved using dedicated adjustment components as described.

Claims

1. A cryogenic cooling system comprising: a primary insert having 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 detachable secondary insert having 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 so that the secondary insert is self-supporting; one or more adjustment members; wherein the one or more adjustment members are configured such that when the secondary insert is attached to the primary insert, the adjustment members bring the primary contact surface and the secondary contact surface of each of the primary plate and the secondary plate into thermally conductive contact.

2. The system according to claim 1, wherein the one or more adjustment members form part of one or both of the primary insert and the secondary insert.

3. The system according to claim 1 or 2, wherein the thermally conductive contact is provided by surface contact between conformal planar regions of the respective primary contact surface and secondary contact surface.

4. The system according to any one of claims 1 to 3, wherein the one or more adjustment members are configured to adjust a displacement between each of the plurality of secondary plates of the detachable secondary insert and a corresponding primary plate of the primary insert.

5. The system according to claim 4, wherein the displacement is less than 2 millimeters, preferably less than 1 millimeter.

6. When the detachable secondary insert is in a non-attached state, the secondary plates are spatially arranged in a secondary configuration relative to each other, the primary plates of the primary insert are spatially arranged in a primary configuration relative to each other, and the displacement is the displacement between the plane of the secondary plate and the plane of the corresponding primary plate in the primary configuration and the secondary configuration, respectively.

7. The system according to claim 6, wherein the primary configuration and the secondary configuration are each maintained when the detachable secondary insert is in an attached state.

8. The system according to any one of claims 1 to 7, wherein the operation 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.

9. The system according to any one of claims 1 to 8, wherein the one or more adjustment members comprise one or more deformable members forming part of each of the primary plate and the secondary plate.

10. The system according to claim 6, wherein the one or more adjustment members are configured to adjust one or both of the primary configuration and the secondary configuration so as to provide the thermally conductive contact.

11. The system according to any one of claims 1 to 6 and 10, wherein the one or more adjustment members are configured to change the spacing between adjacent primary plates or adjacent secondary plates.

12. The system according to claim 11, wherein the one or more adjustment members form at least part of one or more primary connecting members or secondary connecting members.

13. The system according to claim 11 or 12, wherein the one or more adjustment members are configured to enable movement of the one or more primary plates relative to the one or more primary connecting members.

14. The system according to claim 13, further comprising one or more primary shims, each primary shim thermally coupling the primary plate to one or more primary connecting members and being configured to enable movement of the primary plate relative to the one or more primary connecting members.

15. The system according to any one of claims 11 to 14, wherein the one or more adjustment members are configured to enable movement of the one or more secondary plates relative to the one or more secondary connecting members.

16. The system according to claim 15, further comprising one or more secondary shims, each secondary shim thermally coupling the secondary plate to one or more secondary connecting members and being configured to enable movement of the secondary plate relative to the one or more secondary connecting members.

17. The system according to any one of claims 11 to 16, wherein the primary connecting member or the secondary connecting member is rotatable so as to change the spacing between adjacent primary plates or adjacent secondary plates using the one or more adjustment members.

18. The system according to claim 11 or 12, wherein the one or more adjustment members form respective flexible portions of the primary connecting member or the secondary connecting member.

19. The system according to any one of claims 1 to 18, wherein one or more of the plurality of secondary plates are configured to house an experimental device.

20. The system according to any one of claims 1 to 19, wherein the primary insert includes a dilution refrigerator, a helium-3 refrigerator, or a 1 Kelvin pot.

21. The system according to any one of claims 1 to 20, wherein the one or more secondary connecting members are removable so that two or more of the plurality of secondary plates can be removed from the detachable secondary insert as an integral self-standing assembly.

22. A detachable secondary insert for use in a cryogenic cooling system according to any one of claims 1 to 21.

23. A method of operating a system according to any one of claims 1 to 21, wherein the detachable secondary insert includes 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 includes three primary plates, each primary plate corresponding to a respective secondary plate of the secondary insert, and the method includes: mounting the secondary insert on the primary insert such that the secondary plate is conductively and thermally coupled to the corresponding primary plate using the one or more adjustment members; partially removing the secondary insert from the primary insert, wherein the step of partially removing the secondary insert includes: removing the first secondary connecting member from the secondary insert; removing the second secondary plate, the third secondary plate, and the second secondary connecting member as an integral self-standing assembly from the primary insert without removing the first secondary plate from the corresponding plate of the primary insert.

Images