Cryogenic cooling module and cryogenic cooling system

Abstract

A cryogenic cooling module comprises a vacuum chamber mmoodduullee (501) and, sup¬ ported therein, thermal stages (301, 302, 303) spatially displaced from each other in a first direction (310) and one or more heat radiation shields (304, 305, 306) corresponding to at least a subset of said thermal stages (301, 302, 303). A shape of said vacuum chamber module (501) is at least partly defined by one or more planar sides extending in said first direction (310). The vvaaccuuuumm chamber module (501) has an opening on one planar side, with a vacuum finish arrangement on edges (502) of said opening for enabling gastight closing. The thermal stages (301, 302, 303) reach, in a second direction (311) perpendicular to said first direction (310), to a first common interface plane (503) at or close to a plane defined by the edges (502) of the opening. Each of said one or more heat radiation shields has a respective second opening, edges of which reach to said first ccoommmmoonn inter- face plane (503).

Description

[0001] 14 MAR 2025

[0002] 1

[0003] CRYOGENIC COOLING MODULE AND CRYOGENIC COOLING SYSTEM

[0004] FIELD OF THE INVENTION

[0005] The invention is related to the technical field of cryogenic cooling systems . In particular the invention is related to structural and functional solutions that enable easier building, operating, maintenance , and later modi fication of a large cryogenic cooling system or a cryogenic platform .

[0006] BACKGROUND OF THE INVENTION

[0007] Cryogenic cooling systems are intricate pieces of machinery designed to cool a target region or payload volume down to very low temperatures and maintain such conditions for des ired periods o f time . The payload to be cooled may contain e . g . a scienti fic experiment , a quantum computer, a measurement setup, and / or something else , the correct operation of which requires temperatures in the order of only some kelvins or even well below one kelvin . A cryogenic cooling system may also be cal led a cryostat . In some sources , the designation cryogenic cooling system is used for j ust that subsystem of a cryostat that produces the low temperatures , while the cryostat is additionally said to comprise other subsystems like mechanical support , vacuum pumping, radiation shielding, cabling, and the like . In this text the terms cryostat and cryogenic cooling system are used as synonyms of each other, possibly including an interpretation that a cryostat may be somewhat simpler, like a vacuum can with a single cold source (mechanical cooler or bath of liquid cryogen) , while a cryogenic cooling system may be more elaborate with one or more outer cold sources for pre-cooling and one or more inner cold sources ( such as dilution refrigerators for example ) to reach the coldest temperatures . 14 MAR 2025

[0008] 2

[0009] Fig . 1 is a simpli fied schematic illustration of a cryogenic cooling system equipped with a dilution refrigerator and a mechanical pre-cooler . The outermost structure is a vacuum can 101 , which is shown with dashed lines in fig . 1 . The topmost f lange 102 is the lid o f the vacuum can . The room temperature stage 103 of the mechanical pre-cooler is attached thereto . The first stage 104 of the mechanical pre-cooler is attached to a first flange 105 and the second stage 106 of the mechanical pre-cooler is attached to a second flange 107 . The first and second flanges may be called the 50 K flange and the 4 K flange for example , reflecting their temperatures during operation .

[0010] Further below there are more flanges , like the still flange 108 to which the still 109 of the dilution refrigerator is attached . In fig . 1 the mixing chamber 110 of the dilution refrigerator i s attached to the base temperature flange 111 . Reference designator 112 illustrates the payload that is to be refrigerated, frequently referred to as the sample . It is firmly attached to the base temperature f lange 111 in order to ensure as good thermal conductance as possible . As the base temperature flange 111 is made of a material that conducts heat as well as possible at cryogenic temperatures , the sample ( or other forms of payload) may be attached to any part o f it . There may be extending structures called cold fingers thermally coupled to the mixing chamber 110 , with which more suitable attachment places for payloads may be provided .

[0011] Cylindrical , flat-bottomed radiation shields , which are not shown in fig . 1 for graphical clarity, are typically attached to the flanges in a nested configuration, in order to keep radiated heat from surrounding, higher-temperature parts from reaching the colder parts inside . The structure may comprise other, intermediate flanges like a so-called 100 mK flange between the sti ll flange 108 and the base temperature flange 111 . Aligned 14 MAR 2025

[0012] 3 apertures 113, 114, and 115 may exist in the flanges to provide, together with a cover 116 at the top, a so- called line-of-sight port to the sample 112.

[0013] Fig. 2 illustrates a cryogenic cooling system that is otherwise the same as in fig. 1 but comprises the possibility of loading samples with a fast sample exchanging mechanism, often called a sample changer for short. It comprises a load lock 201 that can be attached to a gate valve 202. The system depicted in fig. 2 is of the top-loading type, so the gate valve 202 is in the lid 102 of the vacuum can 101. The sample holder 203 is at the lower end of an elongate probe 204, which can be moved in its longitudinal direction (vertical direction in fig. 1) to eventually attach the sample holder 203 in place at the target region 205 on the base temperature flange. Systems of bottom-loading type have the gate valve in the bottom of the vacuum can, so that the sample is loaded in from below. Systems of side-loading type are also known, in which the sample loader connects to a gate valve in a side surface of the vacuum can.

[0014] Conventional cryogenic cooling systems of the kind schematically shown in figs. 1 and 2 have been roughly of the size of a standalone cupboard, with the diameter of the base temperature flange in the order of some tens of centimetres. In the framework of certain applications, in particular quantum computing, larger and larger payload volumes and payload footprints are required. A straightforward approach for providing larger payload volumes and / or footprints is simply to scale up the dimensions of the conventional structure. An example of a large cryogenic cooling system is presented in M. Hollister, R. Dhuley, G. Tatkowski: "A large millikelvin platform at Fermilab for quantum computing applications", available at https: / / arxiv.org / abs / 2108.10816vl. The payload volume of the cryostat described therein is 2 metres in diameter and 1.5 metres in height. 14 MAR 2025

[0015] 4

[0016] Another approach of scaling up the payload volume and footprint of a cryostat is known from the internet publication available at https : / / www . cry- oworld . com / proj ects / proj ect- l / . In said approach, the cylindrical main vacuum chamber is placed hori zontally and provided with a liquid-helium-cooled 4 kelvin base plate 4 metres in length and 60 centimetres in width . Rectangular doors in the sides of the vacuum chamber make the inside accessible for servicing .

[0017] Further known approaches of scaling up the payload volume and footprint of a cryostat are known from patent publications EP 4 184 081 and WO 2023 / 156801 . In both of these , the cryogenic cooling system consists of modules that can be attached to each other side by side . Lateral extension structures are used to couple thermal stages of adj acent modules mechanically and, i f desired, also thermally to each other .

[0018] Despite said known attempts , it is not trivial to provide a cryogenic cooling system with a large payload volume . In particular, it would be desirable to present solutions that enable providing large-scale cryogenic cooling systems in a flexible way that can be adapted to various and changing needs concerning cooling capacity, cooling technology, and base temperature , as well as payload size and shape . More advanced solutions would also be welcome in the sense of easier manufacturing of large-scale cryogenic systems and their transporting between manufacturing and installing locations .

[0019] SUMMARY

[0020] An obj ective is to present a cryogenic cool ing system that has a large and flexibly adaptable payload volume ; allows for large payload footprints at desired temperature stages ; has easy access to the payload area and parts that need servicing; i s easy to operate and maintain; and is capable of reaching temperatures in the millikelvin range or lower i f needed . Another obj ective 14 MAR 2025

[0021] 5 is that the cryogenic cooling system can be flexibly adapted to di f ferent kinds of needs . Yet another obj ective i s to ensure that the cryogenic cool ing system is reliable in operation, yet possible to manufacture , assemble , and operate at a reasonable cost .

[0022] These and further advantageous obj ectives are achieved by constructing the cryogenic cooling system of modules that have a constant structure of their mutual interfaces , where at least some o f the structural elements that should continue to the next module reach to the interface plane defined by the edges of the module .

[0023] According to a first aspect , there is provided a cryogenic cooling module that comprises a vacuum chamber module . Supported inside said vacuum chamber module are a plurality of thermal stages spatially displaced from each other at least in a first direction, and one or more heat radiation shields . A shape of said vacuum chamber module is at least partly defined by one or more planar sides extending in said first direction . The vacuum chamber module has at least a first opening on a first one of said one or more planar sides , with a vacuum finish arrangement on edges of said first opening for enabling gastight closing of said first opening . Said thermal stages reach, in a second direction perpendicular to said first direction to a f irst common interface plane at or close to a plane de fined by the edges of said first opening . Each of said one or more heat radiation shields has a respective second opening, edges of which reach to said first common interface plane .

[0024] According to an embodiment , each of said one or more heat radiation shields is mechanically supported by a corresponding one of said plurality of thermal stages . This involves at least the advantage of relative simplicity in mechanical structure , as no dedicated support arrangement is separately needed for the one or more heat radiation shields . 14 MAR 2025

[0025] 6

[0026] According to an embodiment , the cryogenic cooling module comprising a dedicated support structure attached to an inside o f said vacuum chamber module and configured to mechanically support said one or more heat radiation shields independently of said plurality of thermal stages . This involves at least the advantage that a separate cooling system may be used to cool at least some of the heat radiation shields independently of said thermal stages , which may have advantageous consequences in dimensioning the cooling systems .

[0027] According to an embodiment , the vacuum chamber module has at least two planar sides extending in said first direction and a third opening on a second one of said planar sides . The cryogenic cooling module may then comprise an openable closing member gastightly attached to cover said third opening . This involves at least the advantage that it is relatively simple to arrange access to the inside of the module also in a complete , assembled cryogenic cooling system .

[0028] According to an embodiment , at least a subset of said one or more heat radiation shields consi sts of modular heat radiation shields , each such modular heat radiation shield having a respective detachable shield part on a side facing said second one of said planar sides . This involves at least the advantage that access to a space inside each such modular heat shield can be arranged relatively simply .

[0029] According to an embodiment, the vacuum chamber module has at least three planar s ides extending in said first direction and a fourth opening on a third one of said planar sides , with a vacuum finish arrangement on edges of said third opening for enabling gastight closing of said fourth opening . Said thermal stages may then reach to a second common interface plane at or close to a plane defined by the edges of said fourth opening . Each of said one or more heat radiation shields may have a respective fi fth opening, edges of which reach to said 14 MAR 2025

[0030] 7 second common interface plane . This involves at least the advantage that the module can be used as a part of a large variety of di f ferently assembled modular cryogenic cooling systems .

[0031] According to an embodiment , the cryogenic cooling module comprises a shield ring conf igured to block radiated heat from passing through any slit at the edges of the second opening . This involves at least the advantage that heat radiation shields can be allowed to freely shrink during cooling, and radiated heat from outer parts may still be kept from penetrating inside radiation shields that consist of portions located in adj acent modules .

[0032] According to an embodiment , the shield ring is movable between a retracted position and an extended position, of which in the retracted position said shield ring does not reach further than the respective edges of the respective heat radiation shield and in the extended position said shield ring reaches further than the respective edges of the respective heat radiation shield . This involves at least the advantage that the shield ring can be kept from making the removal and inserting of modules too di f ficult in a modular cryogenic cooling system .

[0033] According to a second aspect , there is provided a cryogenic cooling system that comprises at least one cryogenic cooling module of the kind described above and a f irst vacuum chamber end part gastightly attached to cover the first opening in the vacuum chamber module of said at least one cryogenic cooling module . The cryogenic cooling system comprises a cryogenic refrigerator configured to establish and maintain cryogenically cooled conditions inside the at least one cryogenic cooling module , and, inside said first vacuum chamber end part , as many heat radiation shield end parts as there are heat radiation shields edges of the respective second openings of which reach to said first common 14 MAR 2025

[0034] 8 interface plane . Each of said heat radiation shield end parts connects to a respective at least one heat radiation shield to cover the respective second opening in said respective at least one heat radiation shield .

[0035] According to an embodiment , the cryogenic cooling system comprises two or more cryogenic cooling modules , each being a cryogenic cooling module of the kind described above , attached to each other by the edges of such openings on their sides where the respective thermal stages and heat radiation shields reach to a respective common interface plane . The cryogenic cooling system may then comprise as many end modules , each compri sing the respective vacuum chamber end part and respective heat radiation shield end parts of the kind described above , as there are further openings on the sides of said two or more cryogenic cooling modules where the respective thermal stages and heat radiation shields reach to a respective common interface plane . Said end modules may be gastightly attached to cover the respective further openings in the assembly of said two or more cryogenic cooling modules . This involves at least the advantage that gastight systems can be assembled in a large variety of configurations .

[0036] According to an embodiment , said two or more cryogenic cooling modules di f fer from each other with respect to cryogenic refrigerator capacity built therein . This involves at least the advantage that in a modular, assembled cryogenic cooling system one may dedicate particular modules for essentially j ust cooling, while other modules may be dedicated for example as payload modules .

[0037] According to an embodiment , said two or more cryogenic cooling modules may di f fer from each other with respect to a configuration of refrigerated payload built therein . This involves at least the advantage that in a modular, assembled cryogenic cooling system one may dedicate particular modules for essentially j ust 14 MAR 2025

[0038] 9 cooling, while other modules may be dedicated for example as payload modules .

[0039] According to an embodiment, thermal stages inside said two or more cryogenic cooling modules form at least two subsets . Thermal stages of one subset may be thermally coupled forming a common thermal stage that reaches across at least two adj acent ones of said two or more cryogenic cooling modules . Thermal stages of another subset may be thermally isolated of each other . Thi s involves at least the advantage that one may construct dedicated cooled payload areas inside the cryogenic cooling system, with the cool ing power of cooler devices distributed in a sensible manner among the various spaces and structures inside the system .

[0040] According to an embodiment , the cryogenic cooling system comprises a thermal and mechanical coupling between two coplanar thermal stages inside respective two adj acent ones of said at least two or more cryogenic cooling modules . Such a thermal and mechanical coupling may comprise a slot or gap between two layers of a first material of said two coplanar thermal stages , said first material having a first coef ficient of thermal expansion at cryogenic temperatures . Within said slot or gap there may be at least one layer of a second material , said second material having a second coef ficient of thermal expansion at cryogenic temperatures that is smaller than said first coef ficient of thermal expansion . Either said two layers are then part of one of said two coplanar thermal stages with a part of the other coplanar thermal stage therebetween, or said two layers are parts of di f ferent ones of said two coplanar thermal stages . This involves at least the advantage that contraction due to decreasing temperature can be utili zed as a factor in maintaining good connections between the structural parts inside the cryogenic cooling system .

[0041] According to an embodiment , the cryogenic cooling modules of the cryogenic cooling system are located 14 MAR 2025

[0042] 10 on more than one level with respect to each other, wherein said more than one level are levels perpendicular to said first direction . The cryogenic cooling system may then comprise at least one interface between cryogenic cooling modules adj acent to each other in the first direction, wherein at such an at least one interface a shielded space inside the cryogenic cooling system continues through a plane at which these two cryogenic cool ing modules are attached to each other . This involves at least the advantage that payload spaces of various si zes and shapes can be provided in a very flexible way .

[0043] According to an embodiment , the cryogenic cooling system comprises support structures for supporting the cryogenic cooling modules in their assembled configuration . This involves at least the advantage that the cryogenic cooling modules themselves do not need to carry all structural loads .

[0044] According to an embodiment , said support structures comprise rails that support one or more of the cryogenic cooling modules so that it is possible to move such one or more of the cryogenic cooling modules along the rails in relation to other cryogenic cooling modules between a disassembled configuration and an assembled configuration . This involves at least the advantage that easier assembling and disassembling the cryogenic cooling system is facilitated .

[0045] BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The accompanying drawings , which are included to provide a further understanding of the invention and constitute a part of this speci fication, illustrate embodiments of the invention and together with the description help to explain the principles of the invention . In the drawings :

[0047] Figure 1 is a schematic illustration of a cryostat equipped with a dilution refrigerator, 14 MAR 2025

[0048] 11 figure 2 is a schematic illustration of a cryostat equipped with a dilution refrigerator and a sample changer, figure 3 illustrates schematically an arrangement of nested cold stages and radiation shields , figure 4 illustrates schematically an arrangement of nested cold stages and radiation shields , figure 5 illustrates schematically an assembly with a central module and two end modules , figure 6 illustrates the assembly of fig . 5 in assembled configuration, figure 7 illustrates schematically an assembly with two central modules and two end modules , figure 8 illustrates schematically an assembly of the kind of fig . 7 in axonometric view, figure 9 illustrates schematically an assembly with a plurality of central modules and a plural ity of end modules , figures 10a to lOe illustrate examples of modular configurations , figure 11 illustrates one possible way of supporting heat radiation shields inside a module , figure 12 illustrates one possible way of dividing the cryogenically cooled domain into subdomains , figure 13 illustrates one possible way of coupling the edges of sections of cold plates and / or radiation shields , figure 14 illustrates one possible way of coupling the edges of sections of cold plates and / or radiation shields , figure 15 illustrates one possible way of coupling the edges of sections of cold plates and / or radiation shields , figure 16 illustrates one possible way of coupling the edges of sections of cold plates and / or radiation shields , 14 MAR 2025

[0049] 12 figure 17 illustrates schematically an assembly with modules in more than one hori zontal layer, figure 18 illustrates a cross section of an assembly of the kind shown in fig . 17 , figure 19 illustrates schematically an assembly with modules in more than one hori zontal layer, figure 20 illustrates schematically an assembly with modules in more than one hori zontal layer, figure 21 illustrates schematically an assembly with two central modules and an example end module , figure 22 illustrates two heat radiation shields before and after cooling, figure 23 illustrates two heat radiation shields and a shield ring before and after cooling, figure 24 illustrates a heat radiation shield and a movable shield ring, figure 25 illustrates a detail of a shield ring, figure 26 illustrates a heat radiation shield and a movable shield ring, figure 27 illustrates two heat radiation shields and a movable shield ring, and figure 28 illustrates two heat radiation shields , a shield ring, and a coupling plate before and after cooling .

[0050] DETAILED DESCRIPTION

[0051] In the following description, reference is made to the accompanying drawings , which form part of the disclosure , and in which are shown, by way of illustration, speci fic aspects in which the present disclosure may be placed . I t i s understood that other aspects may be utilised, and structural or logical changes may be made without departing from the scope of the present disclosure . The following detailed description, therefore , is not to be taken in a limiting sense , as the 14 MAR 2025

[0052] 13 scope of the present disclosure is defined by the appended claims.

[0053] For instance, it is understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if a specific method step is described, a corresponding device may include a unit to perform the described method step, even if such unit is not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on functional units, a corresponding method may include a step performing the described functionality, even if such step is not explicitly described or illustrated in the figures. Further, it is understood that the features of the various example aspects described herein may be combined with each other, unless specifically noted otherwise .

[0054] Fig. 3 illustrates an example of a way in which a plurality of thermal stages and nested heat radiation shields can be arranged. Shown in fig. 3 are a plurality of thermal stage plates 301, 302, and 303 spatially displaced from each other in a first direction 310. For simplicity of description, the first direction 310 may be called the vertical direction. This is, however, not meant to limit the ways or orientations in which systems of the kind shown in fig. 3 can be built and / or used. According to the same non-limiting convention, each of the thermal stage plates 301, 302, and 303 may be said to be oriented horizontally in fig. 3. The thermal stage plates 301, 302, and 303 are each shown to consist of a respective uniform piece, but this is also not limiting as one or more of them could consist of an arrangement of coplanar or essentially coplanar thermal stage plate portions. As their designation indicates, each of the thermal stage plates 301, 302, and 303 (as well as each coplanar thermal stage plate portion, if such are 14 MAR 2025

[0055] 14 included in the arrangement) is preferably made of a material that is a good thermal conductor at cryogenic temperatures. In cryogenic technology, a good thermal conductivity may be for example at least 100 W / (m*K) at or above 10 K, at least 10 W / (m*K) at 1 K, at least 1 W / (m*K) at 0.1 K, or at least 0.1 W / (m*K) at 0.01 K.

[0056] A support system of some kind is used to maintain this configuration of the plurality of thermal stage plates 301, 302, and 303. The support system may comprise, for example, sets of rods made of a material of low thermal conductivity at cryogenic temperatures. Such rods, if used, may be oriented vertically, i.e. in the first direction 310, and / or obliquely between neighbouring thermal stage plates. In cryogenic technology, low thermal conductivity may be for example less than 50 W / (m*K) at 100 K, less than 5 W / (m*K) at 10 K, less than 0.75 W / (m*K) at 1 K, less than 0.075 W / (m*K) at 0.1 K, and less than 0.0075 W / (m*K) at 0.01 K. Additionally, one may choose structural forms like long, thin-walled tubes for parts of the support system to minimize the thermally conductive cross-section at each part where low thermal conductivity is aimed at. Some or all the supporting structures may comprise heat switches for selectively coupling selected thermal stage plates to each other for thermal conduction and for, likewise selectively, thermally insulating them from each other.

[0057] Also shown in fig. 3 are one or more heat radiation shields 304, 305, and 306 corresponding to at least a subset of the thermal stage plates 301, 302, and 303. In fig. 3, there is a corresponding heat radiation shield for each of the three thermal stage plates 301, 302, and 303. A support structure for mechanically supporting the heat radiation shields 304, 305, and 306 is omitted in fig. 3 for graphical clarity. One possibility is that each heat radiation shield is mechanically supported by a corresponding one of the plurality of thermal stage plates. Another possibility is that there is 14 MAR 2025

[0058] 15 a dedicated support structure configured to mechanically support the one or more heat radiation shields 304, 305, and 306 independently of the thermal stage plates 301, 302, and 303. Also a mixed embodiment is possible, in which one or more heat radiation shields are mechanically supported by a corresponding thermal stage plate while one or more other heat radiation shields are mechanically supported by a dedicated support structure.

[0059] In the embodiment shown in fig. 3, at least a subset of the heat radiation shields 304, 305, and 306 consists of modular heat radiation shields. Each such modular heat radiation shield has a respective detachable shield part 307, 308, or 309 on one side of the arrangement. Any modular heat radiation shield, or even all modular heat radiation shields, could have more than one respective detachable shield part. In such a case, the more than one respective detachable shield parts could be located all on the same side of the arrangement and / or on different sides.

[0060] If the first direction 310 is named the vertical direction, two other directions 311 and 312 may be considered. These may be perpendicular to each other and to the first direction 310, so that the directions 310, 311, and 312 define the three axes of a three-dimensional Cartesian coordinate system. Being perpendicular to the first or "vertical" direction 310 makes said two other directions 311 and 312 "horizontal". For unambiguous reference, they may be called the second direction 311 and the third direction 312.

[0061] In the second direction 311, the thermal stage plates 301, 302, and 303 reach to a common interface plane. In other words, those visible edges of the thermal stage plates 301, 302, and 303 to which no detachable shield parts will be attached are all on the level of a same, imaginary vertical plane.

[0062] A peculiar feature in fig. 3, compared to most cryostats of prior art, is that even when the detachable 14 MAR 2025

[0063] 16 shield parts 307, 308, and 309 are attached to their respective places as shown with the dashed lines, no combination of a thermal stage plate and its respective heat radiation shield will constitute a completely closed structure. Rather, each of the heat radiation shields 304, 305, and 306 has a respective opening, edges of which reach to the same common interface plane to which also the thermal stage plates 301, 302, and 303 reach. The situation is the same on the opposite side of the structure, so that each thermal stage plate and its respective heat radiation shield constitutes a structural element in the form of a three-dimensional (here also: rectangular) ring. Considered in the second direction 311, there are similar openings and common interface planes at both extremities of the structure shown in fig. 3.

[0064] In the foreground of fig. 4 is the arrangement of thermal stage plates and heat radiation shields from fig. 3 with the detachable shield parts in place. In the background of fig. 4 is a set of heat radiation shield end parts 401, 402, and 403. There are as many heat radiation shield end parts 401, 402, and 403 as there are heat radiation shields 304, 305, and 306. As such, the set of heat radiation shield end parts 401, 402, and 403 is closely similar to the assembly of thermal stage plates 301, 302, and 303 and heat radiation shields 304, 305, and 306, however with one important difference. Each heat radiation shield end part 401, 402, and 403 is concave and not ring-shaped in form. This means that while each heat radiation shield end part 401, 402, and 403 has an opening on the side that is visible in fig. 4, it is closed on its other side. The edges of each visible opening in fig. 4 reach to a common interface plane, but the dimensions of the heat radiation shield end parts 401, 402, and 403 in the second direction 311 are different: the innermost heat radiation shield part 403 is the shallowest and the outermost heat radiation 14 MAR 2025

[0065] 17 shield part 401 is the deepest , so that the set of heat radiation shield end parts 401 , 402 , and 403 is like a set of nested, open boxes or bins that do not touch each other .

[0066] Figs . 5 and 6 are cross-section views of a cryogenic cooling system that comprises three cryogenic cooling modules . In fig . 5 the three modules are shown displaced from each other in the hori zontal direction, while in fig . 6 the same modules are attached together .

[0067] The largest , central module comprises a vacuum chamber module 501 as its outermost structural element in figs . 5 and 6 . Supported inside the vacuum chamber module 501 are a plurality of thermal stage plates 301 , 302 , and 303 spatially displaced from each other in a first direction 310 . Also supported inside the vacuum chamber module 501 are one or more heat radiation shields 304 , 305 , and 306 corresponding to at least a subset of the thermal stage plates 301 , 302 , and 303 . As the same reference designators indicate , the thermal stage plates 301 , 302 , and 303 as well as the heat radiation shields 304 , 305 , and 306 may follow the same structural principles as in figs . 3 and 4 above . Their support structures are not shown in figs . 5 and 6 for reasons of graphical clarity, but similar principles as those already explained above may be followed in order to have them supported inside the vacuum chamber module 501 .

[0068] A polyhedral shape of the vacuum chamber module 501 is at least partly defined by planar sides extending in the first direction 310 , which is the vertical direction also in figs . 5 and 6 . As such, the vacuum chamber module does not need to have a polyhedral shape , as for the purposes explained next it would suf fice for it to have at least one planar side extending in the first direction 310 . The vacuum chamber module 501 has a first opening on a first one of said planar sides . In fig . 5 this is the opening to the left of the central 14 MAR 2025

[0069] 18 module . A vacuum finish arrangement is provided on edges 502 of the f irst opening for enabling gastight clos ing of the first opening . The vacuum finish arrangement may be as simple as a solid, suitably designed edge surface to which a closing member can be gastightly attached, possibly with a sealing member such as an 0-ring or a layer of indium therebetween . More elaborate forms of vacuum finish arrangements may comprise for example multiple sealing surfaces and / or integrally attached sealing members .

[0070] The second direction 311 is a hori zontal direction also in figs . 5 and 6 and thus perpendicular to the first (vertical ) direction 310 . In the second direction 311 , the thermal stage plates 301 , 302 , and 303 inside the vacuum chamber module 501 reach to a first common interface plane 503 at or close to a plane defined by the edges 502 of the first opening in the vacuum chamber module 501 . Each o f the one or more heat radiation shields 304 , 305 , and 306 has a respective second opening, edges o f which reach al so to the first common interface plane 503 .

[0071] To the left of the central module in figs . 5 and 6 is another cryogenic cooling module , the basic structure of which corresponds to that explained of the central module above . For ease of unambiguous reference , the outermost structural element of said other cryogenic cool ing module is cal led a vacuum chamber end part 504 in the following . It could, however, be called also a vacuum chamber module as it i s a part of a modular vacuum chamber, as will become clear from the following description .

[0072] The leftmost module in figs . 5 and 6 comprises , inside the first vacuum chamber end part 504 , as many heat radiation shield end parts 401 , 402 , and 403 as there are heat radiation shields 304 , 305 , and 306 in the central module . When the central and le ftmost modules are attached together at the first common interface 14 MAR 2025

[0073] 19 plane 503, each of the heat radiation shield end parts 401, 402, and 403 connects to a respective at least one heat radiation shield 304, 305, or 306 to cover the respective ("second") opening in such a respective at least one heat radiation shield 304, 305, or 306.

[0074] The cryogenic cooling system shown in figs. 5 and 6 is symmetrical with respect to its vertical centre line. Thus, to the right of the central module is a further cryogenic cooling module, the parts and structure of which are essentially mirror images of those of the module on the left. In the second direction 311, the thermal stage plates 301, 302, and 303 reach to a second common interface plane 506 at or close to the plane defined by the edges 505 of the opening that the vacuum chamber module 501 has on this side. Similar to the edges 502 on the left side, also the edges 505 to the right side of the vacuum chamber module 501 comprise a vacuum finish arrangement for enabling gastight closing of the respective opening.

[0075] The vacuum chamber end part in the rightmost module is marked with the reference designator 507. There are as many heat radiation shield end parts 508, 509, and 510 as there are heat radiation shields 304, 305, and 306, edges of the respective openings of which reach to the second common interface plane 506. Each of said heat radiation shield end parts 508, 509, and 510 connects to a respective at least one heat radiation shield 304, 305, or 306 to cover the respective opening in said respective at least one heat radiation shield 304, 305, or 306.

[0076] A thing to note in figs. 5 and 6 is that taken alone, each of the three modules corresponds to the definition of a cryogenic cooling module. Each of them has a respective vacuum chamber module, and - supported therein - a plurality of thermal stage plates and one or more heat radiation shields. The shape of each such vacuum chamber module is at least partly defined by one 14 MAR 2025

[0077] 20 or more planar side extending in the first (vertical ) direction, and each such vacuum chamber module has at least a first opening on a first one of said one or more planar sides , with a vacuum finish arrangement on edges of said f irst opening for enabling gastight clos ing of the first opening . The respective thermal stage plates reach, in a second direction perpendicular to said first direction, to a first common interface plane at or close to a plane defined by the edges of the first opening . Also each of said one or more heat radiation shields has a respective second opening, edges of which reach to the first common interface plane .

[0078] It would be possible , though, to construct the end modules in a slightly di f ferent way . As the heat radiation shield end parts 401 , 402 , 403 , 508 , 509 , and 510 have essentially the role of closing a respective side o f the respective heat radiation shield, it would not be necessary to have a section of a thermal stage plate at the top of each o f them . In other words , each heat radiation shield end part could be s imply a suitably formed open box or bin of a material used for j ust heat radiation shields , such as a thin sheet of aluminium, copper, brass , or other material that is a good thermal conductor at cryogenically cooled temperatures .

[0079] Another thing to note is that the cryogenic cooling system of figs . 5 and 6 does not need to be symmetrical with respect to its central vertical axis , or indeed with respect to any axis . For example , instead of being parts of a detachable module like in figs . 5 and 6 , one vacuum chamber end part and the heat radiation shield end parts inside it in f igs . 5 and 6 could be integral parts with the central module , so that there would be only one common interface plane at which the two remaining modules would be attached to each other .

[0080] Fig . 7 illustrates an example o f how the modular approach explained above can be applied to construct a cryogenic cooling system . The cryogenic cooling 14 MAR 2025

[0081] 21 system comprises at least one cryogenic cooling module of the inner type , meaning a module like the central module in figs . 5 and 6 . In the embodiment of fig . 7 there are two cryogenic cooling modules of inner type 701 and 702 , attached together at the respective common interface plane . Additionally, as the presence of at least one cryogenic cooling module of the inner type implies at least one opening of the first type with a vacuum finish arrangement on edges thereof , the cryogenic cooling system comprises a first vacuum chamber end part ( see vacuum chamber end parts 504 and 507 in fig . 5 ) gastightly attached to cover the opening of first type in the vacuum chamber module of said at least one cryogenic cooling module o f inner type . In the embodiment of fig . 7 there are two modules 703 and 704 of the outer type , each attached to cover the respective remaining opening in the respective one of the cryogenic cooling modules of inner type 701 and 702 .

[0082] Configured to establish and maintain cryogenically cooled conditions inside the at least cryogenic cooling module of inner type , the cryogenic cooling system comprises at least one cryogenic refrigerator . In the embodiment o f f ig . 7 such a cryogenic re frigerator is compri sed in the schematically shown block 705 that forms a part of the leftmost cryogenic cooling module of inner type 701 .

[0083] One advantage of the modular approach is that the modules of the cryogenic cooling system do not need to be similar to each other regarding cryogenic refrigerator capacity and / or real estate available for payloads on the cryogenically cooled thermal stage plates . According to the principle shown in fig . 7 , there may be one or more dedicated modules for refrigeration, gas handling, and general housekeeping . This is the role of the leftmost cryogenic cooling module of inner type 701 in fig . 7 . The modules 701 and 702 di f fer from each other with respect to cryogenic capacity built therein, 14 MAR 2025

[0084] 22 as the other cryogenic cooling module of inner type 702 does not comprise any cryogenic refrigerators of its own . Thermal couplings between the respective thermal plate stages and the respective heat radiation shields take care of keeping also the thermal plate stages and heat radiation shields in the other cryogenic cooling module of inner type 702 cold enough . Similarly, thermal couplings ensure that also the heat radiation shield end parts in the outermost modules 703 and 704 remain at their desired low temperatures during operation .

[0085] Various types of cooling mechanisms and cooler devices may be used within the schematically shown block 705 to re frigerate parts o f the cryogenic cooling system . This applies equally to all cryogenic cooling systems meant and described in this text . As an example , of the three nested heat radiation shields shown in fig . 7 , the two outer heat radiation shields could be refrigerated with one or more mechanical coolers such as pulse tubes , Gi f ford-McMahon cryocoolers , or the like . Additionally or alternatively, particularly i f there is an outermost heat radiation shield that only needs to be cooled somewhat colder than zero degrees Cels ius , a compressor-type mechanical refrigerator may be used . One or more inner heat radiation shields , i f present , may be cooled with one or more di lution refrigerators , for example . Yet another possible way of cooling some dedicated part within the cryogenic cooling system is to circulate refrigerated operating fluid such as liquid hel ium through some suitably located tubing that has a thermally conductive coupling to one or more parts to be cooled .

[0086] The cryogenic cooling modules need not be equal with respect to the configuration of refrigerated payload either . The rightmost cryogenic cooling module of inner type 702 in fig . 7 is a payload module in the sense that it of fers largest poss ible space for experiments and signal lines , represented by the block 706 14 MAR 2025

[0087] 23 in fig . 7 . The concept of re frigerated payload means al l such parts and components that should be intentionally exposed to arranged refrigeration to keep them at a temperature lower than room temperature during operation . Examples of refrigerated payload include but are not limited to refrigerated electric circuits ( such as circuits of quantum computers ) and signal lines to and from such electric circuits . Further examples are scienti fic experiments that require refrigeration of at least some o f the materials and components involved to cryogenic temperatures . Yet further examples are stored samples that must be maintained at extremely low temperatures to prevent unwanted changes in their constitution and / or characteristics . Yet further examples are electromagnets in which the current-carrying parts are made of superconductor materials .

[0088] Fig . 8 is an axonometric exploded view of an example of a cryogenic cooling system consisting of two cryogenic cooling modules of inner type 701 and 702 and two modules of the outer type 703 and 704 like in fig . 7 . The outermost structural element of each module is the respective vacuum chamber module , so that in assembled configuration the cryogenic cooling system will look basically like one large vacuum chamber . Each vacuum chamber module has a shape defined by one or more generally vertical planar sides as wel l as a top and a bottom .

[0089] A closer look can be taken of the second cryogenic cooling module of inner type 702 . The vacuum chamber module 501 that serves as its outermost structural element has an opening, called here the third opening for unambiguous reference , on one of the planar sides that define its polyhedral shape . The cryogenic cooling module comprises an openable closing member 801 that in the assembled configuration is gastightly attached to cover said third opening . Said third opening in the vacuum chamber module 501 coincides with the 14 MAR 2025

[0090] 24 location of the respective detachable shield parts 307 , 308 , and 309 on the respective s ides o f the heat radiation shields 304 , 305 , and 306 facing that side of the vacuum chamber module 501 .

[0091] The openable closing member 801 and the correspondingly located detachable shield parts 307 , 308 , and 309 may be useful in allowing access to the inside of at least the second cryogenic cooling module of inner type 702 . Such access may come handy both in the assembling stage in which the modules 701 , 702 , 703 , and 704 of the cryogenic cooling system are assembled together and during use , enabling users to access the inner parts without having to disassemble the modules 701 , 702 , 703 , and 704 from each other .

[0092] In the embodiment of fig . 8 , also the first cryogenic cooling module of inner type 701 includes a similar solution, with similar advantages , although the openable closing member 802 as well as the detachable shield parts inside it are shown in their respective attached positions in fig . 8 .

[0093] Another advantageous possibility shown in fig . 8 is the one where the cryogenic cooling modules of inner type 701 and 702 have the " see-through" conf iguration already known from f ig . 5 : both have two distinct sides on which it is possible to attach either a further cryogenic cooling module o f the inner type or a module of the outer type . For example , in the assembled configuration, the first cryogenic cooling module of inner type 701 wi ll have the second cryogenic cool ing module of inner type 702 attached on one side and the module of outer type 703 attached on the opposite side . Both these sides may be characteri zed more exactly so that the vacuum chamber has an opening on the respective planar side , with a vacuum fini sh arrangement on edges of said third opening for enabling gastight closing of said fourth opening . Inside the respective vacuum chamber module , the thermal stage plates reach to a common 14 MAR 2025

[0094] 25 interface plane at or close to a plane defined by the edges of said opening . Each of the one or more heat radiation shields has a respective opening, edges of which reach to said common interface plane .

[0095] I f all modules of the cryogenic cooling system are either cryogenic cooling modules of inner type like modules 701 and 702 or modules of the outer type like modules 703 and 704 in fig . 4 , the assembled cryogenic cooling system may be described as follows . There are two or more cryogenic cooling modules of inner type 701 and 702 , attached to each other by the edges of such openings on their sides where the respective thermal stage plates and heat radiation shields reach to a respective common interface plane . Also, there are as many modules of outer type 703 and 704 , each compris ing the respective vacuum chamber end part and respective heat radiation shield end parts , as there are further openings on the sides of said two or more cryogenic cooling modules of inner type 701 and 702 where the respective thermal stage plates and heat radiation shields reach to a respective common interface plane . Said modules of outer type 703 and 704 are gastightly attached to cover the respective further openings in the assembly of said two or more cryogenic cooling modules of inner type 701 and 702 .

[0096] There being as many modules of outer type as there are further openings on the s ides o f the modules of inner type means that also such an embodiment is possible where there are no modules of outer type at all . Namely, there may be two modules of inner type , each of them having only one opening on only one planar side , with a vacuum finish arrangement on edges of such an opening for enabling gastight closing . Thermal stages inside the modules may then reach to a common interface plane at or close to the plane defined by the edges of such an opening . Simi larly, each o f the heat radiation shields inside the modules may have a respective second 14 MAR 2025

[0097] 26 opening, edges of which reach to said common interface plane . The modularly assembled cryogenic cooling system would then consist of such two modules of inner type attached to each other by the edges of their respective openings .

[0098] In all embodiments where there are two or more cryogenic cooling modules of inner type , such modules may di f fer from each other with respect to cryogenic refrigerator capacity built therein . Similarly, such modules may di f fer from each other with respect to a configuration of refrigerated payload space built therein . As already explained earlier, there may be for example one or more dedicated cooling modules that primarily contain cryogenic refrigerators and one or more dedicated payload modules that primarily contain space for payloads to be refrigerated .

[0099] Fig . 9 and figs . 10a to l Oe illustrate examples of various possible module configurations of cryogenic cooling systems that follow the basic principles explained above . The cryogenic cooling system in fig . 9 has two similar cryogenic cooling modules of inner type 701 and 702 as in figs . 7 and 8 as wel l as a module o f outer type 703 attached to a further opening of one of them . Additionally, the cryogenic cooling system in fig . 9 has a further, hexagonal cryogenic cooling module o f inner type 901 attached to where the other module of outer type 704 was attached in f igs . 7 and 8 . The hexagonal module 901 has two further openings on its vertical sides , to which there are attached two further modules of outer type 704 and 902 . A more spacious module like the hexagonal module 901 in fig . 9 may be particularly advantageous by o f fering more real estate on which payload to be refrigerated can be attached .

[0100] Figs . 10a to l Oe are schematic footprints of various modular cryogenic cooling systems assembled from modules . In each of these schematic footprints , a dashed line marks a common interface plane where thermal stage 14 MAR 2025

[0101] 27 plates and heat radiation shields may continue from one module to the adjacent module without requiring any extension plates, due to said thermal stage plates and heat radiation shields advantageously reaching to the respective common interface plane from both sides. A flat side panel on slightly protruding edges, like the side panels 1001 and 1002 in fig. 10a, illustrates an openable closing member that can be gastightly attached to cover an opening on a side of a module. Most advantageously at the corresponding location inside the respective module there are detachable shield parts in at least some of the heat radiation shields, allowing access to the inside of the respective module as was described above with reference to fig. 8.

[0102] Fig. 10a is a footprint of a cryogenic cooling system like that in figs. 5 and 6, with one cryogenic cooling module of inner type 701 and two modules of outer type 703 and 704. Fig. 10b is a footprint of a cryogenic cooling system like that in figs. 7 and 8, with two cryogenic cooling modules of inner type 701 and 702 and two modules of outer type 703 and 704, all linearly arranged in a line. Fig. 10c is a footprint of a cryogenic cooling system that is otherwise like that of figs. 7, 8, and 10b, but there is a further cryogenic cooling module of inner type 1003, albeit somewhat narrower in one dimension, in the middle of the linear arrangement of modules. This serves as a reminder that not all cryogenic cooling modules in the cryogenic cooling system need to be of the same size.

[0103] Fig. lOd is a footprint of a cryogenic cooling system like that in fig. 9, with three cryogenic cooling modules of inner type 701, 702, and 901, one of which is larger than the two others and has also a different shape (hexagonal vs. rectangular) . There are three modules of outer type 703, 704, and 902 attached to such openings where, alternatively, the modular cryogenic cooling system could continue with further modules. This 14 MAR 2025

[0104] 28 serves as a reminder that not all cryogenic cooling modules in the cryogenic cooling system need to be o f the same si ze or shape .

[0105] Fig . l Oe is a footprint of a cryogenic cooling system in which one cryogenic cooling module of inner type 1004 has three sides with openings where further modules of the cryogenic cooling system may be attached . Together, the three cryogenic cooling modules of inner type 701 , 702 , and 1004 have an L-shaped footprint in fig . l Oe . This serves as a reminder of two things . First , a cryogenic cooling module may have one , two , or more such sides on which further modules of the cryogenic cooling system may be attached . Second, in the assembled configuration, the modules of the cryogenic cooling system need not be linearly arranged one after the other .

[0106] Fig . 11 illustrates an example of a dedicated support structure 1101 that can be attached to the inside o f a vacuum chamber module . The dedicated support structure 1101 may then mechanically support at least some of the heat radiation shields inside that vacuum chamber module independently of the thermal stage plates . In this example , the dedicated support structure 1101 comprises an array of support bars to which one may attach shield parts 304 , 305 , and 306 of respective modular heat radiation shields . In thi s example , it is possible to assemble each heat radiation shield inside the module from two s imilar halves , each of which includes a bottom hal f that reaches to the imaginary centre line of the structure extending from left to right in fig . 11 . Only those halves that face the viewer are shown in fig . 11 .

[0107] Fig . 12 is a schematic cross section of a cryogenic cooling system in which not all thermal stage plates extend across the whole length of the system through all modules . A system that had the principal structure of fig . 12 could be as sembled for example by placing five cryogenic cooling modules of inner type in 14 MAR 2025

[0108] 29 a line, with a respective module of outer type at each end of the line. Of the five cryogenic cooling modules of inner type, the first, third, and fifth modules are of a full size, while the second and fourth modules are of a smaller size in the linear direction through the assembled modules. Inside the second and fourth modules, at least some of the heat radiation shields do not extend through the whole module. Rather, inside the second and fourth modules, some heat radiation shield modules resemble those that also appear inside the modules of outer type, but placed back-to-back so that they close the respective heat radiation shields in the adjacent modules rather than extending them across.

[0109] This way, the thermal stages inside the cryogenic cooling modules may be made to form at least two subsets with respect to their thermal couplings to each other or thermal isolation from each other. In the example shown in fig. 12, the thermal stage plates 1201, 1204, and 1207 are thermally coupled and form a common thermal stage that reaches across at least two (here: five) adjacent modules. Thermal stages 1203, 1206, and 1209 form another subset by being thermally isolated of each other.

[0110] Concerning coplanar thermal stage plates inside adjacent cryogenic cooling modules that should be thermally coupled to each other, it is advantageous to use some suitable kind of combined thermal and mechanical coupling therebetween. The coupling should take into account the changes in physical dimensions of objects caused by the relatively large change in temperature when an assembled cryogenic cooling system is put into operation. Some advantageous forms of thermal and mechanical coupling are shown in cross section in figs. 13 to 16.

[0111] In fig. 13, the edge of a first coplanar thermal stage plate 1301 is thinned and formed into an arch, the distal end of which is bolted to the edge of the 14 MAR 2025

[0112] 30 second coplanar thermal stage plate 1302. In fig. 14, a strip-formed piece 1401 pliable material joins the two coplanar thermal stage plates 1301 and 1302. The pliable material may be a copper braid or a piece of a good thermal conductor material bent to a shape of arcuate or meandering cross section, for example.

[0113] Figs. 15 and 16 show examples in which the mechanical and thermal coupling comprises a slot or gap between two layers 1501, 1502, 1601, and 1602 of a first material of the two coplanar thermal stage plates 1301 and 1302. This first material having a first coefficient of thermal expansion at cryogenic temperatures. Within the slot or gap, there is at least one layer 1503, 1603, or 1604 of a second material. The second material is chosen so that it has a second coefficient of thermal expansion at cryogenic temperatures, smaller than said first coefficient of thermal expansion. In other words, the relative effect of a temperature change on the dimensions of the second material is smaller than the corresponding change in the dimensions of the first material. When refrigerated, the second material does not shrink as much as the first material.

[0114] In the example shown in fig. 15 the two layers 1501 and 1502 are part of one of said two coplanar thermal stage plates (here: the thermal stage plate 1301 on the right) . A part 1504 of the other coplanar thermal stage plate (the thermal stage plate 1302 on the left) reaches therebetween. The layer 1503 of the second material is there in the same gap, stacked with the part 1504 of the other thermal stage plate 1302 that reaches in the gap. Now when the layers marked as 1501, 1502, and 1504 shrink in thickness because of the dropping temperature, the layer marked as 1503 does not shrink as much in relation, which causes the gap to squeeze tightly around the part 1504 and the layer 1503. This way, the colder it gets, the firmer is the mechanical support offered by the joint. 14 MAR 2025

[0115] 31

[0116] In the example shown in fig . 16 the two layers 1601 and 1602 are parts of di f ferent ones of said two coplanar thermal stage plates 1301 and 1302 . As shown in the partial enlargement , the layers 1603 and 1604 of the second material are therebetween . Thermal shrinking reduces all dimensions of the structure relatively as much, except the dimensions of the layer 1603 and 1604 , which again causes a squeeze . Further, the matching patterns of sawtooth- formed ridges and grooves in the mutually engaging surfaces of the layers 1603 and 1604 are formed so that any tendency of the coplanar thermal stage plates 1301 and 1302 to draw away from each other in the hori zontal direction would increase the total thickness of the two-layer stack, adding to the squeezing ef fect .

[0117] The examples shown in f igs . 13 to 16 al so illustrate the meaning of the definition "a common interface plane at or close to a plane defined by the edges of a first opening" . Thermal stages reaching to such a common interface plane must reach close enough to the plane at which two adj acent vacuum chamber modules are attached to each other , so that the thermal stages inside the adj acent vacuum chamber modules can be coupled together without having to resort to additional intermediate extensions . In each of figs . 13 to 16 , the vertical dashed line in the middle illustrates one possible location of a plane at which two adj acent vacuum chamber modules are attached to each other . In many of the examples , at least one edge of a thermal stage does not reach quite as far as the dashed line . There are also examples in which at least one edge of a thermal stage reaches further than the dashed l ine . The selected approach of j oining those thermal stages ( and other structures to be j oined) to each other that should continue from module to module then defines , how close is close enough . 14 MAR 2025

[0118] 32

[0119] Modules may be on one or more horizontal levels with respect to each other in a cryogenic cooling system, and the interfaces between adjacent modules may open also in other directions that would be considered horizontal directions in the examples discussed above. Fig. 17 is a schematic axonometric view of a cryogenic cooling system that comprises five cryogenic cooling modules of the inner type. Of these, modules 1701, 1702, 1703, and 1704 are on the same horizontal level, together forming a footprint with the shape of a letter T in this example. The fifth cryogenic cooling module of the inner type 1705 is directly above the module 1701.

[0120] The cryogenic cooling system of fig. 17 comprises a total of eight modules of the outer type, shown with reference designators 1711 to 1718 in fig. 17. On the lower horizontal level, modules of the outer type 1711, 1712, 1713, and 1714 are attached to selected free sides of the modules 1701, 1702, 1703, and 1704 respectively. On the upper horizontal plane, there is a respective module of outer type 1715, 1716, 1717, or 1718 attached to each side of the fifth cryogenic cooling module of inner type 1705.

[0121] Fig. 18 is a schematic cross section of the cryogenic cooling system of fig. 17 in an imaginary plane that would cut the system along the dashed line shown in fig. 17. Fig. 18 shows how each of the modules of outer type, of which modules 1711, 1712, 1715, and 1716 are seen in fig. 18, has the arrangement of nested, concave parts of heat radiation shields that closes the shielded spaces inside the cryogenic cooling system at its respective extremity. The first cryogenic cooling module of inner type 1701 on the left, as well as the fifth cryogenic cooling module of inner type 1705 on top of it, have special arrangements of their inner structures as well as their respective upper and lower surfaces, so that the shielded spaces inside the cryogenic cooling system continue through the horizontal plane at 14 MAR 2025

[0122] 33 which these two cryogenic cooling modules of inner type are attached to each other.

[0123] Arrangements in which cryogenic cooling modules are in located in more than one horizontal level can be used for example if there is some payload that would require an exceptionally high spatial region inside the cryogenic cooling system.

[0124] Regardless of whether the modules are in one or more horizontal planes, it is advantageous (although not mandatory) to assemble the system so that each module of inner type is reasonably easily accessible from at least one side also in the completed system, either by removing a respective module of outer type on that side or - more favourably - by opening an openable closing member like that shown with reference designator 801 in fig. 8. It is even more advantageous to design the system so that as many sides as possible of each module of inner type remains accessible.

[0125] Examples of such assemblies are shown in figs. 19 and 20. In the embodiment of fig. 19 the modules of inner type form a kind of a wall, columns of which may have the same number of stacked modules or different numbers of stacked modules. In the first column of the example system shown in fig. 19, there are three stacked modules 1901, 1902, and 1903. In the next column, there is only one module 1904, and so on.

[0126] Fig. 19 also illustrates a principle according to which support functions such as gas handling subsystems, electric power, communications, telemetry, and the like may come as additions to the assembly of modules. In the embodiment of fig. 19, support function subassemblies 1905 and 1906 are placed at appropriate locations adjacent to the wall consisting of the modules of inner type. Connections between each support function sub-assembly and a respective one (or respective ones) of the modules of inner type are shown schematically with reference designators 1907 and 1908. Such 14 MAR 2025

[0127] 34 connections may contain for example cables, gas conduits, mechanical support entities, and / or the like. As an advantageous detail, the support function sub-assemblies 1905 and 1906 are built in the form of carriages on lockable wheels so that it is easier to find suitable locations for them adjacent to the modules of inner type and then fix them in place.

[0128] In the embodiment of fig. 20 the modules of inner type form a number of parallel walls; three such walls are shown in fig. 20. Bridging modules may be used to connect selected modules in such walls; see bridging modules 2001, 2002, and 2003 in fig. 20. Notable in fig. 20 is that while for example bridging modules 2001 and 2002 are between the same two walls of modules, they are on different horizontal levels: the bridging module 2001 in the front is on the lower level and the bridging module 2002 in the back is on the upper level. In the next gap between adjacent walls of modules, bridging module 2003 is on the upper level; there may be a further bridging module in the same gap but on the lower level at the back so that the bridging modules alternate between levels in both orthogonal directions across the grid of modules. Such an alternating strategy of placing the bridging modules helps to keep as many sides of the modules of inner type accessible.

[0129] Which sides of the modules of inner type have openable closing members built therein and which of them are covered by a respective module of outer type is not important to the considerations above concerning figs. 19 and 20. The spatial arrangements of modules shown in figs. 19 and 20 are shown solely as examples, as they could be varied regarding how many modules of inner type are placed where in a completed assembly.

[0130] Fig. 21 shows a part of a cryogenic cooling system that has two modules 2101 and 2102 of the inner type. An example of a module 2103 of outer type is shown on the right in fig. 21. In the system of fig. 21, each 14 MAR 2025

[0131] 35 module of inner type has the general shape of a round cylinder, however with two planar sides extending in the vertical direction . On each of the planar sides , there are two openings with a vacuum finish arrangement on edges of the openings so that one can connect thereto another module of inner type or a module of outer type , which in this embodiment consists of two sub-modules .

[0132] In the embodiment o f fig . 21 , not all thermal stages inside each module of inner type are necessarily planar . Instead, at least some of the thermal stages may have three-dimensional forms that allow their edges to reach to the common interface plane between modules through the openings . This way the roles of a thermal stage and an associated radiation shield may become intertwined, so that a three-dimensional entity made of one or more thermally conductive materials may constitute simultaneously a thermal stage and the associated radiation shield .

[0133] The lower part o f f ig . 21 shows how there may be openable clos ing members on the round side portions of the vacuum chamber modules . In fig . 21 , one such openable closing member is the curved door 2104 that has been opened and remains supported by hinges 2105 on one edge thereof . Radiation shields inside the vacuum chamber modules may then have correspondingly formed openable portions through which one can gain access to the innermost parts of the system .

[0134] As a notable detail , it is not necessary to always attach two adj acent modules of inner type to each other so that there would be thermally conductive connections between them . According to an embodiment , any subset of mutually matching mechanical features in two adj acent modules of inner type ( or even all mutually matching mechanical features in two adj acent modules of inner type ) may have mechanically supporting but thermally insulating connections between each other . 14 MAR 2025

[0135] 36

[0136] The cryogenic cooling system may comprise various support structures for supporting the modules in their assembled configuration, but possibly also before they are finally assembled . One example of such support structures comprises rail s that support one or more of the modules so that it is possible to move such one or more of the modules along the rails in relation to other modules between a disassembled and assembled configuration . Rails , i f provided, may be located under the module ( s ) in question, on sides of the module ( s ) in question, and / or above the module ( s ) in question .

[0137] In all embodiments described above, thermal shrinkage of structural parts should be addressed appropriately . In the following, some aspects related to the thermal shrinkage of heat radiation shields are considered .

[0138] The left part of f ig . 22 shows two heat radiation shields 304 and 2201 . According to the principles described above , each of them is assumed to be a heat radiation shield inside a respective vacuum chamber module . Compared to fig . 8 , heat radiation shield 304 may be the correspondingly marked heat radiation shield inside module 702 , and heat radiation shield 2201 may be that heat radiation shield inside module 701 that is to be cooled to the same temperature . The mutual ly facing openings of the heat radiation shields 304 and 2201 come against each other in the assembled configuration .

[0139] Whether or not an assembly described here as a heat radiation shield includes the respective thermal stage or flange in the cryostat , i s immaterial to thi s description . Conventionally, a flange of a cryostat and the heat radiation shield attached to its edges formed an enclosure . The present description applies also to solutions where heat radiation shields are structurally independent of the thermal stages or flanges .

[0140] The outer walls of each vacuum chamber module face the room temperature environment , so they may 14 MAR 2025

[0141] 37 remain at room temperature during operation . Hence , the outer walls do not exhibit any signi ficant thermal shrinkage during cooling . To the contrary, the cooled parts inside each vacuum chamber module will shrink in proportion to the dropping temperature . Aluminium, which is a frequently used material for heat radiation shields , may shrink by several millimetres per metre . Thermal shrinkage may result in a slit 2202 developing between adj acent heat radiation shields , as shown in the right part of fig . 22 and the partial enlargement .

[0142] Any slit in a heat radiation shield exposes the cold parts inside the heat radiation shield to radiated heat from warmer parts outside the heat radiation shield . I f there are aligned slits in nested heat radiation shields , like in such heat radiation shields the edges of which reach to a common interface plane between modules , some of the radiated heat may penetrate through two or more heat radiation shields and cause a signi ficant heat load to the cryogenic ref rigerator ( s ) that should keep the innermost parts of the cryostat as cold as possible .

[0143] Fig . 23 illustrates a solution to the possible problem of shrinkage-based slits . As shown in fig . 23 , a shield ring 2301 may be provided that blocks any direct line-of-sight path through a pos sible slit . In f ig . 23 and elsewhere in this description, an embodiment is considered where the shield ring encircles the assembly of two adj acent heat radiation shields on the outside . It should be noted, however, that the description is equally applicable to any shield ring that would be placed inside the two heat radiation shields , as long as it ef fectively blocks direct line-of-sight paths through any slit that may develop between the heat radiation shields due to thermal shrinkage . In some embodiments , shield rings could be provided both on the outside and on the ins ide . In some embodiments , one or more parts of a shield ring can be on the outside and 14 MAR 2025

[0144] 38 one or more further parts of the shield ring can be on the inside , so that together the parts form a conceptual shield ring even i f there is no complete shield ring on the outside or the inside as such .

[0145] In figs . 22 and 23 , only heat radiation shields of a single thermal stage are shown for graphical clarity . It should be noted, however, that this description applies equally to solutions with two or more nested heat radiation shields , as in systems like that of fig . 8 , for example . Shield rings may be used on one or more of the heat radiation shields of di f ferent temperatures .

[0146] A shield ring, i f provided, may be a structural part that is independent of the two heat radiation shields . However, certain advantages may be gained by making it constitute an additional part of the corresponding heat radiation shield . On the other hand, the provision of a shield ring should not make it overly di f ficult to remove a module from a modular cryogenic cooling system . It would be advantageous i f a module could be removed even from the middle of an array of adj acent modules , possibly even without having to move the further modules that in the assembled configuration are attached to the module to be removed .

[0147] A solution that meets such needs is schematical ly shown in fig . 24 . Two shield rings 2301 and 2401 are slidably mounted on a heat radiation shield 304 so that they can be moved, in a direction essentially perpendicular to the respective common interface planes mentioned earlier, between at least two positions . In the retracted position shown on the left in fig . 24 , the shield rings 2301 and 2401 do not reach further in said direction than the respective edges of the heat radiation shield 304 . I f the heat radiation shield 304 i s a part of a vacuum module installed in a hori zontal row of modules , and i f the vacuum module should be movable into and out of its place in the row in a direction 14 MAR 2025

[0148] 39 perpendicular to the row, shield ring ( s ) in their retracted position will not prevent such a movement .

[0149] The short black arrows in the left part of fig . 24 show how the shield rings 2301 and 2401 may be moved into the extended position shown on the right in fig . 24 . In its extended position, a shield ring reaches further in the direction perpendicular to the common interface plane than the respective edges of the heat radiation shield . This is , in any case , the fact that makes it possible for the shield ring to block radiated heat from passing through any slit that may develop at the interface between two adj acent heat shields due to thermal shrinkage .

[0150] Two shield rings 2301 and 2401 are shown in fig . 24 in relation to a single heat radiation shield 304 . Such a solution could be used for example so that in a modular cryogenic cooling system with a plural ity of vacuum modules in a direct hori zontal row, the heat shields of every second module are equipped with shield rings . It is , however, possible to design the system also so that each heat radiation shield has a respective slidably mounted shield ring at only one edge , so that in a row of adj acent vacuum modules , each shield ring is moved in the same direction from its retracted position to its extended position . I t is also possible to apply di f ferent principles of the kind above at di f ferent nested levels of heat radiation shields , and / or in di f ferent modules of a modular cryogenic cooling system .

[0151] For a shield ring to achieve optimal results in blocking radiated heat through the slit it covers , the shield ring should acquire at least roughly the same temperature as the respective heat radiation shield . This is most straightforward to ensure by establishing a thermally conductive coupling between the shield ring and the heat radiation shield . Notable is that even i f the shield ring would not achieve exactly the same low temperature as the main components of the heat radiation 14 MAR 2025

[0152] 40 shield, this is probably not a big disadvantage , especially i f the shield ring covers the slit between adj acent heat radiation shields on the outside . Namely, any additional heat radiated by a sl ightly warmer shield ring will only have a very narrow slit available to pass through to the inside of the heat radiation shield . Also , as the shield ring itsel f is relatively narrow at its outer surface, the amount of radiated heat from outer, warmer parts of the system that becomes absorbed to the shield ring is relatively small compared to the amount of radiated heat that becomes absorbed in the heat radiation shield .

[0153] Figs . 25 , 26 , and 27 illustrate an example of providing at least one of slidable support and thermally conductive coupling to a shield ring . In fig . 25 , a part of the corner of a shield ring 2301 is shown . The ins ide of the shield ring 2301 comprises thermally conductive springs 2501 arranged in two rows that extend in the longitudinal direction of the sections of the shield ring 2301 . Fig . 26 shows a part o f a shield ring 2301 in its retracted position, mounted on a heat radiation shield 304 . The common interface plane defined by the edges of the opening at one end of the heat radiation shield 304 is on the right in fig . 26 . It is easy to see how, in its retracted position, the shield ring 2301 has no part thereof reaching further to the right in fig . 26 than the edges of the heat radiation shield 304 . Rather, i f the retracted position of the shield ring 2301 is as far back as in fig . 26 , the shield ring 2301 does not reach even the common interface plane . The thermally conductive springs of both rows are against the same heat radiation shield 304 in fig . 26 .

[0154] Fig . 27 shows the part of a shield ring 2301 in its extended pos ition, where it covers any possible slit between the heat radiation shield 304 it was initially mounted on and the adj acent heat radiation shield 2201 . I f the extended pos ition o f the shield ring 2301 14 MAR 2025

[0155] 41 is symmetric with respect to the interface between adj acent heat radiation shields , as in fig . 27 , the middle of the shield ring 2301 coincides with said interface in the extended position like in fig . 27 . The thermally conductive springs of one row are against the heat radiation shield 304 on which the shield ring 2301 was initially mounted, while the thermally conductive springs o f the other row are against the ad acent heat radiation shield 2201 . Thus , irrespective of whether the cooling o f the heat radiation shield parts takes place on the left or on the right in the orientation shown in fig . 27 , the shield ring 2301 will acquire a temperature that is either the same as or at least suf ficiently close to the temperature of the heat radiation shields 304 and 2201 .

[0156] The use of a slidable mounting, with the slidable thermally conductive springs of figs . 25 to 27 for example , is also advantageous because it allows for various relative changes in dimensions . As described earlier with re ference to f ig . 22 , when the modular cryogenic cooling system is in its assembling stage and all parts are thus essentially at room temperature , the adj acent heat radiation shields may come very close to each other, or even directly against each other . Thermal shrinkage during cooling makes both of them retract towards the centre of their respective vacuum modules . Any such movement of the adj acent heat radiation shields into opposite directions with the zone covered by the shield ring can be readily allowed, as the thermally conductive springs j ust slide on the surface of each respective heat radiation shield . I f some reason, like the use o f di f ferent materials for example , causes the shortest perpendicular distance between the shield ring and the heat radiation shield surface to increase or decrease during cooling, the thermally conductive springs will j ust adapt to the changed width of the gap by bending or straightening more as needed . 14 MAR 2025

[0157] 42

[0158] An integral shield ring does not necessarily encircle the whole seam between two adj acent heat radiation shields . It is possible to make a shield ring consist of separate sections . I f slidable or otherwise movable shield rings are considered, such sections can be movable independently of each other .

[0159] Fig . 28 shows an embodiment in which two adj acent heat radiation shields 304 and 2201 both have a U- formed shape so that in each case , a respective thermal stage connects the top ends of the branches of the U . A U-shaped, s lidably mounted shield ring 2801 i s used to cover any slit that would develop between the two adj acent heat radiation shields due to thermal shrinkage . A coupling plate 2802 is used to connect the two adj acent thermal stages together . The coupling plate 2802 may comprise means for absorbing any ef fect caused by the thermal shrinkage of the thermal stages . Additionally, or alternatively, it i s possible to utili ze any of the principles of figs . 13 to 16 , for example .

[0160] Using a connection plate for the thermal stages and a (partial ) shield ring for the heat radiation shields may involve the advantage that a stronger thermal coupl ing can be formed between the thermal stages . As described above , the thermal coupling to and from a shield ring does not need to be that strong because it is sufficient to ensure that the shield ring reaches at least approximately the same temperature as the respective heat radiation shield . On the other hand, it may be very important to ensure that adj acent thermal stages can reach and remain at the same temperature , which then advocates the use of as strong a thermal coupling as possible .

[0161] In fig . 28 the connection plate 2802 is a separate piece that can be e . g . bolted onto the two adj acent thermal stages when the modular cryogenic cooling system is assembled . It is also possible to use some extendable 14 MAR 2025

[0162] 43 portion of any of the thermal stages as a coupling plate for the same purpose .

[0163] It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways . The invention and its embodiments are thus not limited to the examples described above , instead they may vary within the scope of the claims .

Claims

14 MAR 202544CLAIMS1. A cryogenic cooling module, comprising:- a vacuum chamber module (501) ,- supported inside said vacuum chamber module (501) , a plurality of thermal stages (301, 302, 303) spatially displaced from each other at least in a first direction (310) , and- supported inside said vacuum chamber module (501) , one or more heat radiation shields (304, 305, 306) corresponding to at least a subset of said thermal stages (301, 302, 303) ; wherein a shape of said vacuum chamber module (501) is at least partly defined by one or more planar sides extending in said first direction (310) , and wherein the vacuum chamber module (501) has at least a first opening on a first one of said one or more planar sides, with a vacuum finish arrangement on edges (502) of said first opening for enabling gastight closing of said first opening; characterized in that:- said thermal stages (301, 302, 303) reach, in a second direction (311) perpendicular to said first direction (310) , to a first common interface plane (503) at or close to a plane defined by the edges (502) of said first opening, and- at least one of said one or more heat radiation shields (304, 305, 306) has a respective second opening, edges of which reach to said first common interface plane (503) .

2. A cryogenic cooling module according to claim 1, wherein each of said one or more heat radiation shields (304, 305, 306) is mechanically supported by a corresponding one of said plurality of thermal stages (301, 302, 303) .14 MAR 2025453. A cryogenic cooling module according to claim 1, comprising a dedicated support structure (1101) attached to an inside of said vacuum chamber module (501) and configured to mechanically support said one or more heat radiation shields (304, 305, 306) independently of said plurality of thermal stages (301, 302, 303) .

4. A cryogenic cooling module according to any of the preceding claims, wherein:- said one or more planar sides comprise at least two planar sides extending in said first direction (310) ,- the vacuum chamber module (501) has a third opening on a second one of said planar sides and- the cryogenic cooling module comprises an openable closing member (801) gastightly attached to cover said third opening.

5. A cryogenic cooling module according to claim 4, wherein at least a subset of said one or more heat radiation shields (304, 305, 306) consists of modular heat radiation shields, each such modular heat radiation shield having a respective detachable shield part (307, 308, 309) on a side facing said second one of said planar sides.

6. A cryogenic cooling module according to any of the preceding claims, wherein:- said one or more planar sides comprise at least three planar sides extending in said first direction (310) ,- the vacuum chamber module has a fourth opening on a third one of said planar sides, with a vacuum finish arrangement on edges (505) of said third opening for enabling gastight closing of said fourth opening,- said thermal stages (301, 302, 303) reach to a second common interface plane (506) at or close to a plane defined by the edges (505) of said fourth14 MAR 202546 opening, and- each of said one or more heat radiation shields (304, 305, 306) has a respective fifth opening, edges of which reach to said second common interface plane (506) .

7. A cryogenic cooling module according to any of the preceding claims, comprising a shield ring (2301, 2401, 2801) configured to block radiated heat from passing through any slit (2202) at said edges of said second opening.

8. A cryogenic cooling module according to claim 7, wherein said shield ring (2301, 2401, 2801) is movable between a retracted position and an extended position, of which in the retracted position said shield ring (2301, 2401, 2801) does not reach further than the respective edges of the respective heat radiation shield (304) and in the extended position said shield ring (2301, 2401, 2801) reaches further than the respective edges of the respective heat radiation shield (304) .

9. A cryogenic cooling system, characterized in that:- the cryogenic cooling system comprises at least one cryogenic cooling module (701, 702) according to any of the preceding claims and a first vacuum chamber end part (504) gastightly attached to cover the first opening in the vacuum chamber module (501) of said at least one cryogenic cooling module (701, 702) ,- the cryogenic cooling system comprises a cryogenic refrigerator configured to establish and maintain cryogenically cooled conditions inside the at least one cryogenic cooling module (701, 702) , and- the cryogenic cooling system comprises, inside said first vacuum chamber end part (504) , as many heat radiation shield end parts (401, 402, 403) as there are14 MAR 202547 heat radiation shields (304, 305, 306) edges of the respective second openings of which reach to said first common interface plane (503) ; wherein each of said heat radiation shield end parts (401, 402, 403) connects to a respective at least one heat radiation shield (304, 305, 306) to cover the respective second opening in said respective at least one heat radiation shield (304, 305, 306) .

10. A cryogenic cooling system according to claim 9, comprising:- two or more cryogenic cooling modules (701, 702) , each being a cryogenic cooling module according to any of claims 1 to 6, attached to each other by the edges of such openings on their sides where the respective thermal stages and heat radiation shields reach to a respective common interface plane, and- as many end modules (703, 704) , each comprising the respective vacuum chamber end part (504, 507) and respective heat radiation shield end parts (401, 402, 403, 508, 509, 510) of the kind defined in claim 7, as there are further openings on the sides of said two or more cryogenic cooling modules (701, 702) where the respective thermal stages and heat radiation shields reach to a respective common interface plane; wherein said end modules (703, 704) are gastightly attached to cover the respective further openings in the assembly of said two or more cryogenic cooling modules (501) .

11. A cryogenic cooling system according to claim 10, wherein said two or more cryogenic cooling modules (701, 702) differ from each other with respect to cryogenic refrigerator capacity (705) built therein .

12. A cryogenic cooling system according to any of claims 10 or 11, wherein said two or more14 MAR 202548 cryogenic cooling modules (701, 702) differ from each other with respect to a configuration of refrigerated payload (706) built therein.

13. A cryogenic cooling system according to any of claims 10 to 12, wherein thermal stages inside said two or more cryogenic cooling modules (701, 702) form at least two subsets, wherein:- thermal stages of one subset (1201, 1204, 1207) are thermally coupled forming a common thermal stage that reaches across at least two adjacent ones of said two or more cryogenic cooling modules (701, 702) , and- thermal stages of another subset (1203, 1206, 1209) are thermally isolated of each other.

14. A cryogenic cooling system according to any of claims 10 to 13, comprising a thermal and mechanical coupling between two coplanar thermal stages inside respective two adjacent ones of said at least two or more cryogenic cooling modules, wherein said thermal and mechanical coupling comprises:- a slot or gap between two layers (1501, 1502, 1601, 1602) of a first material of said two coplanar thermal stages, said first material having a first coefficient of thermal expansion at cryogenic temperatures, and- within said slot or gap, at least one layer (1503, 1603, 1604) of a second material, said second material having a second coefficient of thermal expansion at cryogenic temperatures that is smaller than said first coefficient of thermal expansion; wherein either said two layers (1501, 1502) are part of one of said two coplanar thermal stages with a part of the other coplanar thermal stage therebetween, or said two layers (1601, 1602) are parts of different ones of said two coplanar thermal stages.

15. A cryogenic cooling system according to any of claims 10 to 14, wherein:14 MAR 202549- the cryogenic cooling modules ( 1701 , 1702 , 1703 , 1704 , 1705 ) of the cryogenic cooling system are located on more than one level with respect to each other, wherein said more than one level are levels perpendicular to said first direction, and- the cryogenic cooling system comprises at least one interface between cryogenic cooling modules ( 1701 , 1705 ) adj acent to each other in the first direction, wherein at such an at least one interface a shielded space inside the cryogenic cooling system continues through a plane at which these two cryogenic cooling modules ( 1701 , 1705 ) are attached to each other .16 . A cryogenic cooling system according to any of claims 10 to 15 , comprising support structures for supporting the cryogenic cooling modules in their assembled configuration .17 . A cryogenic cooling system according to claim 16 , wherein said support structures comprise rails that support one or more of the cryogenic cooling modules so that it is possible to move such one or more of the cryogenic cooling modules along the rails in relation to other cryogenic cooling modules between a disassembled configuration and an assembled configuration .

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