Cryogenic cooling system with multiple dilution units

Abstract

Within the vacuum enclosure of the cryostat, multiple temperature stages form an ordered row in the main direction. These are cooled to their respective cryogenic cooling temperatures by stages of a stepwise cooling system. The first dilution refrigerator comprises a first distiller and a first mixing chamber, the first distiller being positioned on the first distiller flange and the first mixing chamber being positioned on the first mixing chamber flange. The second dilution refrigerator comprises a second distiller and a second mixing chamber, the second distiller being positioned on the second distiller flange and the second mixing chamber being positioned on the second mixing chamber flange. The first distiller flange is thermally isolated from the second distiller flange, and the first mixing chamber flange is thermally isolated from the second mixing chamber flange. The second dilution refrigerator is configured for a greater cooling capacity than the first dilution refrigerator.

Description

[Technical Field]

[0001] This invention generally relates to the cooling of cryostats. In particular, it relates to structural solutions and refrigeration mechanisms that enable the efficient cooling of cryostats with reasonable consequences for structural complexity. [Background technology]

[0002] Early cryostats were cooled with liquid coolants such as liquid nitrogen and liquid helium. Subsequently, mechanical cooling devices such as Stirling cryocoolers, Gifford-McMahon condensers, pulse tube refrigerators (PTRs), and Joule-Thomson condensers were introduced to achieve so-called coolant-free cooling. If the core of the cryostat has a further cooling system, such as a dilution refrigerator that operates only at temperatures below approximately 4K, the necessary pre-cooling can be performed, for example, using a PTR. Typically, a PTR has two cooling stages, the first of which is used to achieve a temperature of approximately 50-70K, and the second stage pre-cools the dilution refrigerator's fractional distiller (still) to the required 4K level.

[0003] According to the stepped structure of the refrigeration system, the entire cryostat typically comprises temperature stages constructed as flanges that are parallel to each other and displaced from each other in the vertical direction. Often, this vertical direction is the vertical direction. The upper plate of the cryostat may constitute a room temperature flange, below which are flanges that progressively decrease in temperature, starting with a 50K flange cooled by the first stage of the PTR, a 4K flange cooled by the second stage of the PTR, and further cooled to the target region by the mixing chamber of the dilution refrigerator. Each temperature stage and the radiation shield each thermally coupled to it form a nested structure in which the lower temperature stage may be surrounded by the radiation shield of the preceding higher temperature stage. The purpose of the radiation shield is to reduce the heat load on the lower temperature parts inside by blocking radiant heat from the hotter parts outside and conducting it to the respective parts of the refrigeration system.

[0004] Figure 1 is a simplified schematic diagram of a cryostat equipped with a dilution refrigerator and a mechanical precooler. The outermost structure of the cryostat is a vacuum enclosure 101, shown as a dashed line in Figure 1. The uppermost flange 102 is the lid of the vacuum enclosure. The room temperature stage 103 of the mechanical precooler is attached to it. The first stage 104 of the mechanical precooler is attached to the first flange 105, and the second stage 106 of the mechanical precooler is attached to the second flange 107. The first and second flanges can be referred to as, for example, 50K flanges and 4K flanges, respectively, reflecting their operating temperatures.

[0005] Further down, there are more flanges, such as the distiller flange 108 to which the distiller 109 of the dilution refrigerator is attached. In Figure 1, the mixing chamber 110 of the dilution refrigerator is attached to the reference temperature flange 111. Reference numeral 112 indicates the target region of the payload to be cooled. The payload, often referred to as the sample, should be firmly attached to the reference temperature flange 111 to ensure the best possible heat conduction.

[0006] To clarify the diagram, radiation shields not shown in Figure 1 are typically cylindrical and mounted on flanges in a nested configuration. This structure may include other intermediate flanges, such as a so-called 100mK flange, between the distiller flange 108 and the reference temperature flange 111. Aligned openings may be present in the flanges to provide a so-called line-of-sight port to the target area 112, along with the cover 113 at the top.

[0007] Dilution refrigerators have a certain cooling capacity, thereby cooling a target region. In many technological fields requiring cryogenic cooling, such as quantum computing, there is a clear trend toward increasingly larger settings, which can consume more power in or near the target region and in the higher temperature stages of the cryostat, consequently requiring greater cooling capacity. Essentially, it is possible to increase the cooling capacity of a dilution refrigerator by enhancing the circulation of 3He. However, unavoidable physical facts such as the (inherently relatively large) flow resistance of liquid 3He mean that the achievable baseline temperature also rises. In short, improving cooling capacity and achieving the lowest possible baseline temperature tend to be conflicting goals. [Overview of the project]

[0008] The objective is to present a cryostat and a method for cooling a cryostat that solves the problem of larger thermal loads in a beneficial and technically simple manner. Another objective is to ensure that this solution is scalable to even larger cryostats. A further objective is to solve the problem of increasing thermal loads without compromising reliability during operation. Yet another objective is to combine effective cooling while increasing structural complexity only within a reasonable range.

[0009] These and further beneficial objectives are achieved by equipping the cryostat with two dilution refrigerators of different dimensions or configurations, and by appropriately separating their operations so that they can serve different purposes with respect to cooling capacity and reference temperature.

[0010] According to one embodiment, a cryostat comprising a vacuum enclosure is provided. Inside the vacuum enclosure, there are a plurality of temperature stages arranged as an ordered series of flanges in the principal direction of the cryostat, each cooled to its respective cryogenic cooling temperature. The stages of the stepwise cooling system are thermally coupled to each of the plurality of temperature stages and configured to cool each of the plurality of temperature stages. The cryostat comprises a first dilution refrigerator comprising a first fractionator and a first mixing chamber, wherein the first fractionator is located on the first fractionator flange and the first mixing chamber is located on the first mixing chamber flange. The first fractionator flange and the first mixing chamber flange are in an ordered series of flanges included in the plurality of temperature stages. The cryostat comprises a second dilution refrigerator comprising a second fractionator and a second mixing chamber, wherein the second fractionator is located on the second fractionator flange and the second mixing chamber is located on the second mixing chamber flange. The second fractionator flange and the second mixing chamber flange are located in an ordered row of flanges included in the plurality of temperature stages. The first fractionator flange is thermally isolated from the second fractionator flange. The first mixing chamber flange is thermally isolated from the second mixing chamber flange. The second dilution refrigerator is configured for a greater cooling capacity than the first dilution refrigerator.

[0011] According to one embodiment, in the ordered row, the first distiller flange is displaced in the principal direction from the second distiller flange. This has the advantage that there may be many spaces available for at least one or both of the first and second distiller flanges.

[0012] According to one embodiment, in the ordered row, the first mixing chamber flange is displaced in the principal direction from the second mixing chamber flange. This has the advantage that there may be more space available for at least one or both of the first and second mixing chamber flanges.

[0013] According to one embodiment, the second mixing chamber flange defines a first toroidal spatial region having a first bore, and the first mixing chamber flange is at least partially located within the first bore or within its spatial extension in the axial direction. This has the advantage that at least the second mixing chamber flange or a portion thereof can be used as a radiation shield to shield the first mixing chamber flange or a portion thereof.

[0014] According to one embodiment, the second fractionator flange defines a second toroidal spatial region having a second bore, and the first fractionator flange is at least partially located within the second bore or within its spatial extension in the axial direction of the second bore. This has the advantage of at least a relatively simple structure.

[0015] According to one embodiment, the cryostat comprises one or more signal lines for facilitating communication with one or more samples located in one or both of the first and second mixing chamber flanges. There may then be one or more thermal equilibrium points for thermally equilibriumizing at least a subset of the one or more signal lines. The one or more thermal equilibrium points may be located in at least one of the first fractionator flange, the second fractionator flange, the first mixing chamber flange, and the second mixing chamber flange. This has the advantage of at least reducing the thermal load imposed on the lowest temperature stage(s) by the signal lines.

[0016] According to one embodiment, the cryostat is provided with a signal connector on at least one of the first mixing chamber flange and the second mixing chamber flange to facilitate coupling of the one or more samples with the one or more signal lines. This has the advantage of at least simplifying the wiring of samples for experiments and other types of operations.

[0017] According to one embodiment, the cryostat comprises a first gas processing subsystem for a first dilution refrigerator and a second gas processing subsystem for a second dilution refrigerator. The second gas processing subsystem may then comprise at least one functional component that is not part of the first gas processing subsystem. This has the advantage that the first and second dilution refrigerators can be operated relatively independently of each other.

[0018] According to one embodiment, the first gas processing subsystem comprises a first circulation pump configured to circulate a working fluid through a first dilution refrigerator. The second gas processing subsystem may then comprise a second circulation pump, different from the first circulation pump, configured to circulate a working fluid through a second dilution refrigerator. This has the advantage of being able to maintain different flow rates through at least the first and second dilution refrigerators.

[0019] According to a second embodiment, a method for cooling a cryostat is provided. This method includes cooling a plurality of temperature stages, arranged as an ordered row of flanges in the principal direction of the cryostat inside a vacuum enclosure, to their respective cryogenic cooling temperatures using a stepwise cooling system. The stages are thermally coupled to each of the plurality of temperature stages and configured to cool each of the plurality of temperature stages. This method includes cooling a first mixing chamber flange, in which the first mixing chamber is located, using a first dilution refrigerator comprising a first fractionator and a first mixing chamber. The first mixing chamber flange is in an ordered row of flanges included in the plurality of temperature stages. This method includes cooling a second mixing chamber flange, in which the second mixing chamber is located, using a second dilution refrigerator comprising a second fractionator and a second mixing chamber. The second mixing chamber stage is in an ordered row of flanges included in the plurality of temperature stages. The method includes the step of thermally separating the first distiller flange, on which the first distiller is located, from the second distiller flange, on which the second distiller is located. The method also includes the step of thermally separating the first mixing chamber flange from the second mixing chamber flange, and operating the second dilution refrigerator with a greater cooling capacity than the first dilution refrigerator, thereby raising the temperature of the second mixing chamber above the temperature of the first mixing chamber. [Brief explanation of the drawing]

[0020] Included to provide a further understanding of the present invention, the accompanying drawings, which form a part of this specification, illustrate embodiments of the present invention and together with the description serve to explain the principles of the present invention.

[0021] [Figure 1] A cryostat using coolant-free cooling according to known techniques is shown. [Figure 2] It is a schematic diagram of the cryostat of FIG. 1. [Figure 3] A cryostat equipped with two dilution refrigerators is schematically shown. [Figure 4] A cryostat equipped with two dilution refrigerators is schematically shown. [Figure 5] A cryostat equipped with two dilution refrigerators is schematically shown. [Figure 6] A cryostat equipped with two dilution refrigerators is schematically shown. [Figure 7] A cryostat equipped with two dilution refrigerators is schematically shown. [Figure 8] A cryostat equipped with two dilution refrigerators is schematically shown. [Figure 9] A cryostat equipped with two dilution refrigerators is schematically shown. [Figure 10] A part of a cryostat according to an embodiment is shown.

Embodiments of the Invention

[0022] In the following description, reference is made to the accompanying drawings, which form a part of this disclosure and illustrate, by way of example, specific aspects to which the present disclosure may be applied. It should be understood that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. Therefore, since the scope of the present disclosure is defined by the appended claims, the following detailed description should not be construed in a limiting sense.

[0023] For example, please understand that disclosures relating to a described method may also apply to a corresponding device or system configured to perform that method, and vice versa. For instance, if a particular method step is described, a corresponding device may include a unit that performs the described method step, even if the unit is not explicitly shown or illustrated in the drawings. Conversely, if a particular device is described based on a functional unit, a corresponding method may include steps that perform the described function, even if the steps are not explicitly shown or illustrated in the drawings. Furthermore, unless otherwise specified, please understand that the features of the various embodiments described herein can be combined with each other.

[0024] To facilitate a more direct comparison, Figure 2 provides a further simplified schematic diagram of a previously known cryostat with a dilution refrigerator. The parts corresponding to the parts shown in Figure 1 are the vacuum enclosure 101; the upper (room temperature) flange 102; the room temperature portion 103 of the mechanical precooler, the first stage 104, and the second stage 106; the 50K flange 105; the 4K flange 107; the fractionator flange 108; the mixing chamber flange 111; and the fractionator 109 and mixing chamber 110 of the dilution refrigerator. Also schematically shown in Figure 2 are the two outermost radiation shields 201 and 202, as well as the 100mK flange 203, and examples of heat exchangers 204 and 205 that may appear at various levels as part of the dilution refrigerator. Above the upper flange 102 in Figure 2 is the gas processing subsystem of the dilution refrigerator, of which the circulation pump 206 and mixture dump 207 are shown separately in Figure 2.

[0025] For systematic reference, flanges 105, 107, 108, 203, and 111 within the vacuum enclosure 101 can be characterized as a plurality of temperature stages arranged in an ordered column in the principal direction of the cryostat, each cooled to a cryogenic temperature. In this case, the principal direction is vertical, but generally, in both the prior art and the solutions described herein, the principal direction may also refer to the direction toward the lowest temperature portion of the cryostat, regardless of shape or orientation. A mechanical precooler can be characterized as a stepwise cooling system, whose stages are configured to be thermally coupled to each of the plurality of temperature stages and to cool those stages. The fractionator flange 108 and the mixing chamber flange 111 are also referred to as the fractionator stage and the mixing chamber stage, respectively.

[0026] A cryostat may have more components than those shown in the schematic diagram of Figure 2. For example, thermal switches are required between different stages to control the thermal conductivity between them. When this type of high-temperature cryostat is started for the first time, the thermal switches between temperature stages 107, 108, 203, and 111 must be thermally conductive, because stages 104 and 106 of the stepwise cooling system are initially the only means available to cool the low-temperature stages as well. After reaching the dilution refrigerator start temperature (approximately 4K), the thermal switches must be insulated so that the lowest temperature stages can reach and maintain their desired temperatures through the operation of the dilution refrigerator.

[0027] Furthermore, the routing of the helium circulation lines for the dilution refrigerator is typically more complex than that schematically shown in Figure 2. For example, the inflow (condensation) line may be interconnected with the components and stages of a mechanical precooler so that the mechanical precooler cools the inflow helium mixture. In the description of this embodiment and subsequent embodiments, such details of structures that are of little importance to the invention are omitted for clarity.

[0028] Figure 3 shows a vacuum enclosure 101 and a cryostat comprising a plurality of temperature stages 105, 107, 108, 203, and 111 arranged in a column ordered in the principal direction of the cryostat within the vacuum enclosure. The temperature stages are cooled to their respective cryogenic cooling temperatures during the normal operation of the cryostat. In the upper center of Figure 3, there is a stepwise cooling system in which stages 104 and 106 are configured to be thermally coupled to the plurality of temperature stages, i.e., stages 105 and 107, respectively, and to cool those stages. In this schematic example, the stepwise cooling system is depicted with some similarity to a pulse tube known at the time of writing this specification. However, it should be noted that in this embodiment and in subsequent embodiments, the disclosure is not limited to a pulse tube as a stepwise cooling system. Other alternatives include, but are not limited to, Joule-Thomson condensers, Gifford-McMahon condensers, and "wet" cooling systems based on liquid coolants. Examples of cooling systems based on liquid coolants include, but are not limited to, a liquid coolant bath and the circulation of cooled gas or liquid coolant through piping.

[0029] The cryostat in Figure 3 comprises two dilution refrigerators. The one on the right may be called the first dilution refrigerator for ease of clear reference. It comprises a first fractionator 109 and a first mixing chamber 110, of which the first fractionator 109 is located on an intermediate temperature stage 108, also referred to herein as the fractionator stage. The first mixing chamber 110 is located on the lowest temperature stage 111, also referred to herein as the mixing chamber stage.

[0030] The dilution refrigerator on the left side of Figure 3 may be called the second dilution refrigerator. It comprises a second fractionator 301 and a second mixing chamber 302. They are located on the same temperature stage as the respective parts of the first dilution refrigerator on the right side. The second fractionator 301 is located on the fractionator stage (temperature stage 108), and the second mixing chamber 302 is located on the mixing chamber stage (temperature stage 111).

[0031] The purpose of each temperature stage in a cryostat is to establish a temperature point during the operation of the cryostat; therefore, they are composed of materials(s) with high thermal conductivity. In cryogenic technology, high thermal conductivity is, for example, at least 100 W / (m²) above 10K. * (k), at least 10W / (m) at 1K * At 0.1K, at least 1W / (m * (K), or at least 0.1 W / (m³) at 0.01 K * It can be K). Thus, in the cryostat of Figure 3, the first distiller 109 is kept at essentially the same temperature as the second distiller 301, and the first mixing chamber 110 is kept at essentially the same temperature as the second mixing chamber 302. As a difference from the cryostat of Figure 2, the cooling capacity in each of the distiller stage 108 and the mixing chamber stage 111 can be higher in either case, because both of these temperature stages have two parallel-operating cooling means of the type shown in the previous Figure 2, which are connected to them respectively.

[0032] Figure 4 shows a vacuum enclosure 101 and a cryostat comprising several temperature stages 105, 107, 108, 203, and 111 arranged in a sequence in the principal direction of the cryostat inside the vacuum enclosure. The temperature stages are cooled to their respective cryogenic cooling temperatures during the normal operation of the cryostat. Similar to Figure 3, a stepwise cooling system is present, of which stages 104 and 106 are configured to be thermally coupled to the respective temperature stages, i.e., stages 105 and 107, in order to cool those stages.

[0033] The cryostat in Figure 4 comprises two dilution refrigerators. The first dilution refrigerator on the right may be similar to the first dilution refrigerator in Figure 3. It comprises a first fractionator 109 and a first mixing chamber 110, of which the first fractionator 109 is located on an intermediate temperature stage 108, also referred to herein as the fractionator stage. The first mixing chamber 110 is located on the lowest temperature stage 111, also referred to herein as the mixing chamber stage.

[0034] The dilution refrigerator on the left side of Figure 4 may be called the second dilution refrigerator. It comprises a second fractionator 301 and a second mixing chamber 402. The second fractionator 301 is located on the fractionator stage (temperature stage 108), i.e., the same temperature stage as the first fractionator 109. The second mixing chamber 402 is not located on the mixing chamber stage (temperature stage 111), but is located on an intermediate stage 203 between the fractionator stage 108 and the mixing chamber stage 111. Figure 4 shows only one(s)(sets) of heat exchangers 403 between the second fractionator 301 and the second mixing chamber 402, but as with all accompanying drawings, this is merely a schematic representation and does not limit the number or location of heat exchangers or other unshown components of the cryostat.

[0035] An intermediate stage 203, sometimes also referred to as a 100 mK stage, functions as a second mixing chamber stage in FIG. 4. It is thermally separated from the (first) mixing chamber stage 111, meaning that these two can have different temperatures. Being thermally separated means that the two stages are thermally insulated from each other or, at least in the design of the cryostat, active measures are taken to reduce the exchange of thermal energy between the two. Two parts of a cryostat that are thermally separated from each other do not reach thermal equilibrium during any typical operating time of the cryostat and are not configured to reach thermal equilibrium. For example, they can be structurally connected to each other only through materials with low thermal conductivity, or they can be connected to each other only through some third part of the cryostat such that at least a part of such an indirect connection consists of a material with low thermal conductivity. In cryogenic technology, low thermal conductivity can 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.

[0036] In such a configuration, if not all parts of the payload cooled within the cryostat require the lowest possible temperature, it may be possible to place the "warmer" parts of the payload on the second mixing chamber stage 203 and the "cooler" parts of the payload on the first mixing chamber stage 111. Then, the heat dissipated by the "warmer" parts is not thermally loaded onto the first mixing chamber stage 111, so the latter can reach a lower temperature during operation than if the two mixing chamber stages were thermally coupled.

[0037] In the embodiment shown in Figure 4, similar to the embodiments in Figures 3 and 5-10, the first and second dilution refrigerators each have their own gas treatment subsystem. The gas treatment subsystem of the first dilution refrigerator comprises a circulation pump 206 and a mixture dump 207. The gas treatment subsystem of the second dilution refrigerator comprises a circulation pump 305 and a mixture dump 306. Some components, such as the mixture dump, may be shared between, for example, two or more gas treatment subsystems. However, for the purposes described in more detail below, it is beneficial to have at least a dedicated circulation pump in each dilution refrigerator.

[0038] Figure 5 shows a vacuum enclosure 101 and a cryostat comprising several temperature stages 105, 107, 501, 502, 503, 504, 505, and 506 arranged in an ordered column in the principal direction of the cryostat within the vacuum enclosure. Some of the temperature stages may coincide with each other in the principal direction of the cryostat, in which case such temperature stages can be said to occupy a common level in the ordered column. The temperature stages are cooled to their respective cryogenic cooling temperatures during the normal operation of the cryostat. Similar to Figures 3 and 4, a stepwise cooling system exists, of which stages 104 and 106 are configured to be thermally coupled to the respective stages of the multiple temperature stages, namely stages 105 and 107, to cool those stages.

[0039] The cryostat in Figure 5 comprises two dilution refrigerators. The first dilution refrigerator on the right may be similar to the first dilution refrigerator in Figure 3. It comprises a first fractionator 109 and a first mixing chamber 110, of which the first fractionator 109 is located on the first fractionator stage 501. The first mixing chamber 110 is located on the first mixing chamber stage 502.

[0040] The dilution refrigerator on the left side of Figure 5 may be called the second dilution refrigerator. It comprises a second fractionator 301 and a second mixing chamber 302. The second fractionator 301 is located on a second fractionator stage 504, which is thermally separated from the first fractionator stage 501. The second mixing chamber 302 is located on a second mixing chamber stage 505, which is thermally separated from the first mixing chamber stage 502.

[0041] For illustrative purposes, Figure 5 shows a first 100 mK stage 503 between the first fractionator stage 501 and the first mixing chamber stage 502, and a second 100 mK stage 506 between the second fractionator stage 504 and the second mixing chamber stage 505. Also for illustrative purposes, Figure 5 shows two heat exchangers (sets) in both the first dilution refrigerator (reference numerals 204 and 205) and the second dilution refrigerator (reference numerals 303 and 304). Furthermore, radiation shielding, thermal switches, and other components not shown may also be included in the cryostat.

[0042] The fractionator stages 501 and 504 are thermally separated from each other, allowing them to have different temperatures during the operation of the cryostat. Similarly, the mixing chamber stages 502 and 505 are thermally separated from each other, allowing them to have different temperatures during the operation of the cryostat. Functionally, the cryostat of Figure 5 can be characterized by the fact that, during operation, the fractionator stages 501 and 504 have intentionally different temperatures, and / or the mixing chamber stages 502 and 505 have intentionally different temperatures.

[0043] In terms of structure, the cryostat in Figure 5 can be characterized as a second dilution refrigerator configured for a greater cooling capacity than the first dilution refrigerator. This characterization is consistent with the functional definition above, given that greater cooling capacity typically involves higher temperatures.

[0044] Configuring a dilution refrigerator for a specific cooling capacity can be done through dimensional setting, a predetermined flow rate in the circulation of helium-3, or both, as is known to those skilled in the art. As a basic rule, the cooling capacity of a dilution refrigerator is proportional to the circulation rate of 3He. Basically, the cooling capacity can be increased by increasing the flow rate. However, at the lowest temperatures, viscous heating and incomplete heat exchange adversely affect the reference temperature that can be achieved at a sufficient circulation rate.

[0045] Dilution refrigerators with high cooling capacity can be dimensionally designed to have large flow paths and large heat exchange surfaces. This means that a large amount of rare and expensive 3He is required for operation. On the other hand, if an increase in the achievable reference temperature is tolerable, a dilution refrigerator not specifically dimensionally designed for a fast circulation rate can be configured for high cooling capacity at (relatively) high temperatures simply by increasing the flow rate through additional heat added to the fractional distiller, in which case viscous heating and heat exchange surfaces have less impact.

[0046] Two dilution refrigerators configured for different cooling capacities may be the same type of unit, but operating differently (i.e., configured to operate at different flow rates), or they may be different types of units. If such two dilution refrigerators are configured to operate at different flow rates, it is advantageous to have their gas processing subsystems separated from each other, at least insofar as each has its own circulation pump, because the circulation pump is the component responsible for setting and maintaining the flow rate.

[0047] Figure 6 shows a vacuum enclosure 101 and a cryostat comprising several temperature stages 105, 107, 501, 502, 503, 504, 505, and 506 arranged in an ordered column in the principal direction of the cryostat within the vacuum enclosure. Similar to Figure 5, some of the temperature stages may coincide with each other in the principal direction of the cryostat, in which case such temperature stages can be said to occupy a common level in the ordered column. The temperature stages are cooled to their respective cryogenic cooling temperatures during the normal operation of the cryostat. Similar to Figures 3 to 5, a stepwise cooling system exists, of which stages 104 and 106 are configured to be thermally coupled to the respective stages of the multiple temperature stages, namely stages 105 and 107, to cool those stages.

[0048] The cryostat in Figure 6 comprises two dilution refrigerators. The first dilution refrigerator on the right may be similar to the first dilution refrigerators in Figures 3 to 5. It comprises a first fractionator 109 and a first mixing chamber 110, of which the first fractionator 109 is located on the first fractionator stage 501. The first mixing chamber 110 is located on the first mixing chamber stage 502.

[0049] The second dilution refrigerator on the left side of Figure 6 comprises a second distiller 301 and a second mixing chamber 302. The second distiller 301 is located on a second distiller stage 504, which is thermally separated from the first distiller stage 501. The second mixing chamber 302 is located on a second mixing chamber stage 505, which is thermally separated from the first mixing chamber stage 502. In difference from Figure 5, the first distiller stage 501 is displaced from the second distiller stage 504 in the main direction. In Figure 6, the first distiller stage 501 is closer to the lowest temperature portion of the cryostat in the main direction than the second distiller stage 504.

[0050] For illustrative purposes, Figure 6 shows a first 100 mK stage 503 between the first fractionator stage 501 and the first mixing chamber stage 502, and a second 100 mK stage 506 between the second fractionator stage 504 and the second mixing chamber stage 505. Also for illustrative purposes, Figure 6 shows two heat exchangers (sets) in both the first dilution refrigerator (reference numerals 204 and 205) and the second dilution refrigerator (reference numerals 303 and 304). Furthermore, radiation shielding, thermal switches, and other components not shown may also be included in the cryostat.

[0051] As described above with reference to Figure 5, in Figure 6 as well, the fractionator stages 501 and 504 may have different temperatures during the operation of the cryostat, and the mixing chamber stages 502 and 505 may have different temperatures during the operation of the cryostat. Functionally, the cryostat of Figure 6 may be characterized by the fact that, during operation, the fractionator stages 501 and 504 have intentionally different temperatures, and / or the mixing chamber stages 502 and 505 have intentionally different temperatures. In terms of structure, the cryostat of Figure 6 may be characterized as a second dilution refrigerator configured for a greater cooling capacity than the first dilution refrigerator.

[0052] Figure 7 shows a cryostat very similar to those in Figures 5 and 6 above. The difference from Figure 6 is that the first fractionator stage 501 and the second fractionator stage 504 are not displaced from each other in the principal direction of the cryostat and are on the same level. The difference from both Figures 5 and 6 is that the first mixing chamber stage 502 is displaced from the second mixing chamber stage 505 in the principal direction. In this example, the first mixing chamber stage 502 is further vertically below the second mixing chamber stage 505. Considering that the first mixing chamber stage 502 is the coldest part of the cryostat, it is also possible to position the first mixing chamber stage 502 above the second mixing chamber stage 505 if this helps reduce the amount of radiant heat received by the first mixing chamber stage 502. This may be the case when, in the vertical direction, there are, for example, radiation shields or other structural components below both mixing chamber stages 502 and 505, and it is anticipated that they will reach a higher temperature than the second mixing chamber stage 505 during operation. Similar to Figures 5 and 6, the second dilution refrigerator in Figure 7 is configured for a greater cooling capacity than the first dilution refrigerator.

[0053] Figure 8 shows a cryostat very similar to those in Figures 5 through 7 above. The difference is that the first fractionator stage 501 and the second fractionator stage 504 are displaced from each other in the main direction, and the first mixing chamber stage 502 and the second mixing chamber stage 505 are displaced from each other in the main direction. Similar to Figures 5 through 7, the second dilution refrigerator in Figure 8 is configured for a greater cooling capacity than the first dilution refrigerator.

[0054] Figure 9 shows a vacuum enclosure 101 and a cryostat comprising several temperature stages inside the vacuum enclosure, of which stages 105, 107, 501, 502, 504, and 505 are shown. The temperature stages are arranged in an ordered column in the principal direction of the cryostat. Some of the temperature stages may coincide with each other in the principal direction of the cryostat, in which case such temperature stages can be said to occupy a common level in the ordered column. The temperature stages are cooled to their respective cryogenic cooling temperatures during the normal operation of the cryostat. As in embodiments previously described, a stepwise cooling system exists, of which stages 104 and 106 are configured to be thermally coupled to the respective stages of the multiple temperature stages, namely stages 105 and 107, to cool those stages. Cryostat components of less importance in this description, such as thermal shields, thermal switches, structural supports, and additional temperature stages, are not shown in Figure 9.

[0055] The cryostat in Figure 9 comprises two dilution refrigerators. The central first dilution refrigerator includes a first fractionator 109 and a first mixing chamber 110, of which the first fractionator 109 is located on the first fractionator stage 501. The first mixing chamber 110 is located on the first mixing chamber stage 502. Between the first fractionator 109 and the first mixing chamber 110, a heat exchanger 205 is shown as an example. For example, one or more further temperature stages, such as a 100 mK stage, may exist between the first fractionator stage 501 and the first mixing chamber stage 502, but none are shown in Figure 9 for clarity of the drawing.

[0056] The dilution refrigerator on the left side of Figure 9 may be called the second dilution refrigerator. It comprises a second fractionator 301 and a second mixing chamber 302. The second fractionator 301 is located on the second fractionator stage 504, which is thermally separated from the first fractionator stage 501. The second mixing chamber 302 is located on the second mixing chamber stage 505, which is thermally separated from the first mixing chamber stage 502. Between the second fractionator 301 and the second mixing chamber 302, a heat exchanger 304 is shown as an example. Between the second fractionator stage 504 and the second mixing chamber stage 505, there may be one or more further temperature stages, such as a 100 mK stage, but none are shown in Figure 9 for clarity of the figure.

[0057] The second mixing chamber stage 505 is generally ring-shaped. It can be said that it defines a (first) toroidal space region having a (first) bore. Any reference to toroidal or bore-like should not be interpreted as requiring any kind of symmetry, but rather as encompassing any three-dimensional shape enclosing an empty space. A bore means a hole that penetrates the empty space, i.e., such a three-dimensional shape. A bore may be centrally located with respect to the three-dimensional shape, or off-center. There may be one, two, or more such bores penetrating the three-dimensional shape. In such cases, a singular reference to a bore in this specification should be interpreted as meaning any individual bore, all such bores, or a subset of all such bores.

[0058] The first mixing chamber stage 502 is positioned at least partially within the (first) inner bore. That is, the first mixing chamber stage 502 fills most of the void inside the annular second mixing chamber stage 505. In this way, the second mixing chamber stage 505 can be used as a partial radiation shield partially surrounding the (lower temperature) first mixing chamber stage 502, thus reducing the thermal load on the first mixing chamber 110 and allowing the first mixing chamber 110 to reach a lower temperature than would be possible without the shielding effect of the (partially) surrounding second mixing chamber stage 505.

[0059] If there are two or more bores defined by the second mixing chamber stage 505, the first mixing chamber stage 502 may be present in only one of them, or two or more of them may have separate first mixing chamber stages.

[0060] The two distiller stages shown in Figure 9 follow similar geometric shapes. The second distiller stage 504 defines a (second) toroidal spatial region having a (second) bore, and the first distiller stage 501 is located at least partially within the (second) bore. The above-mentioned toroidal shape and bore also apply here. While some advantageous shielding effects may arise here as well, a major advantage of making the distiller stages similar in shape to the mixing chamber stages is that the mechanical design becomes relatively simpler. The two distillers may operate at different temperatures, in particular, so that the second distiller 301 may be configured to operate at a higher temperature than the first distiller 109. This may reflect differences in dimensional settings and / or flow rates, for example, the flow rate of 3He through the second distiller 301 may be greater than the flow rate of 3He through the first distiller 109.

[0061] The second dilution refrigerator is configured for greater cooling capacity than the first dilution refrigerator in Figure 9. An advantageous method for utilizing this difference will be described next with reference to Figure 10.

[0062] Figure 10 schematically shows two fractionator stages 501 and 504, two mixing chamber stages 502 and 505, and two dilution refrigerators 1001 and 1002 of the cryostat. The second mixing chamber stage 505 defines a first toroidal spatial region having a first bore, thereby positioning the first mixing chamber stage 502 at least partially within the first bore or within its spatial extension in the axial direction of the first bore. In this figure, the axial direction of the bore is vertical, and since the first mixing chamber stage 502 is not on the same level as the second mixing chamber stage 505, it is positioned "within the spatial extension in the axial direction of the first bore". Similarly, in the exemplary embodiment of Figure 10, the second fractionator stage 504 defines a second toroidal spatial region having a second bore, and the first fractionator stage 501 is at least partially located within the second bore or within its spatial extension in the axial direction of the second bore.

[0063] The first dilution refrigerator 1001 is configured for a cooling capacity P1, and the second dilution refrigerator 1002 is configured for a cooling capacity P2 that is greater than P1. As a result, during the operation of the cryostat, T MXCI <T MXC2 To that end, the first mixing chamber stage 502 is set to temperature T MXCI The second mixing chamber stage 505 then reaches a temperature of T MXC2 It will become.

[0064] A further possible feature schematically shown in Figure 10 is to provide one or more samples to be placed on either or both of the first mixing chamber stage 502 and the second mixing chamber stage 505. In Figure 10, the first sample 1003 is placed on and thermally coupled to the first mixing chamber stage 502, and the second sample 1004 is placed on and thermally coupled to the second mixing chamber stage 505. Given that the installation of two dilution refrigerators with relative differences in the structural geometry and cooling capacity of the cryostats will result in the first mixing chamber stage 502 being at a lower temperature than the second mixing chamber stage 505 during operation, it is desirable that the first sample 1003 contain a payload that benefits from the lowest absolutely achievable temperature. Furthermore, considering the relative differences in the cooling capacity of the dilution refrigerators, it is desirable that the second sample 1004 include payloads or payload support components and functionalities that do not require the lowest possible temperature during operation and / or cause significant heat dissipation during operation.

[0065] Figure 10 illustrates how a cryostat may have one or more signal lines for configuring communication with one or more samples. Signal lines 1005, 1006, 1007, 1008, 1009, and 1010 are shown as examples. Furthermore, the cryostat may have one or more thermal equilibration points for thermally equilibrating at least a subset of the one or more signal lines. Examples of thermal equilibration points are shown in Figure 10 and are located on the first fractionator stage (thermal equilibration point 1011), the second fractionator stage (thermal equilibration points 1012 and 1013), the first mixing chamber stage (thermal equilibration point 1014), and the second mixing chamber stage (thermal equilibration point 1015). The purpose of thermal equilibration is to conduct heat that may be generated in the signal lines, and / or heat conducted along the signal lines from the hotter parts of the cryostat, to the actively cooled parts of the cryostat so as to block and absorb it.

[0066] Although not specifically shown in Figure 10, one possibility that could facilitate the construction of experimental or operational setups is to provide signal connectors on the first mixing chamber stage 502 and / or the second mixing chamber stage 505. Such signal connectors can facilitate the connection of one or more samples to one or more signal lines.

[0067] Like many of the previous drawings, Figure 10 is a simplified diagram, omitting possible further components that may be present in an actual cryostat, such as structural supports, thermal switches, and radiation shields, which are surrounding components in and / or near the operating area.

[0068] As technology advances, it will be apparent to those skilled in the art that the basic idea of ​​the present invention can be implemented in a variety of ways. For example, although the above description consistently refers to two dilution refrigerators for brevity and clarity, a cryostat may have more than two dilution refrigerators, and either or both of the first and second dilution refrigerators may be doubled or added to two or more similar, similarly operating and arranged units, and / or there may be a cascade of three or more dilution refrigerator stages, each sized and configured for different cooling capacities and achievable temperatures. Thus, the present invention and its embodiments are not limited to the examples described above, but rather can be modified within the scope of the claims.

Claims

1. It is a cryostat, - Vacuum enclosure (101), - Inside the vacuum enclosure, in the main direction of the cryostat, a plurality of temperature stages are arranged as an ordered row of flanges (105, 107, 108, 111, 203, 501, 502, 503, 504, 505, 506), each cooled to its respective cryogenic cooling temperature. - A stepwise cooling system in which the stages (104, 106) are thermally coupled to each of the stages (105, 107) of the plurality of temperature stages and configured to cool each of the stages (105, 107) of the plurality of temperature stages, - A first dilution refrigerator (1001) comprising a first fractionator (109) and a first mixing chamber (110), wherein the first fractionator (109) is positioned on a first fractionator flange (501), and the first mixing chamber (110) is positioned on a first mixing chamber flange (502), and the first fractionator flange (501) and the first mixing chamber flange (502) are in the ordered row of flanges included in the plurality of temperature stages, Equipped with, - The cryostat comprises a second dilution refrigerator (1002) having a second fractionator (301) and a second mixing chamber (302), wherein the second fractionator (301) is positioned on a second fractionator flange (504), and the second mixing chamber is positioned on a second mixing chamber flange (505), and the second fractionator flange (504) and the second mixing chamber flange (505) are in the ordered row of flanges included in the plurality of temperature stages. - The first fractionator flange (501) is thermally separated from the second fractionator flange (504), - The first mixing chamber flange (502) is thermally separated from the second mixing chamber flange (505), A cryostat characterized in that the second dilution refrigerator (1002) is configured for a greater cooling capacity than the first dilution refrigerator (1001).

2. - The cryostat according to claim 1, wherein in the ordered row, the first distiller flange (501) is displaced in the principal direction from the second distiller flange (504).

3. - In the ordered row, the first mixing chamber flange (502) is displaced in the principal direction from the second mixing chamber flange (505), A cryostat according to claim 1 or 2.

4. - The second mixing chamber flange (505) defines a first toroidal space region having a first internal bore, - The first mixing chamber flange (502) is at least partially located within the first bore or within its spatial extension in the axial direction of the first bore. A cryostat according to any one of claims 1 to 3.

5. - The second fractionator flange (504) defines a second toroidal space region having a second internal bore, - The first fractionator flange (501) is at least partially located within the second bore, or within its spatial extension in the axial direction of the second bore. A cryostat according to any one of claims 1 to 4.

6. One or more signal lines (1005, 1006, 1007, 1008, 1009, 1010) for facilitating communication with one or more samples (1003, 1004) located in one or both of the first mixing chamber flange (502) and the second mixing chamber flange (505), - One or more thermal equilibrium points (1011, 1012, 1013, 1014, 1015) for thermally equilibriuming at least a subset of the one or more signal lines (1005, 1006, 1007, 1008, 1009, 1010), Equipped with, The one or more thermal equilibrium points (1011, 1012, 1013, 1014, 1015) are located on at least one of the first fractionator flange (501), the second fractionator flange (504), the first mixing chamber flange (502), and the second mixing chamber flange (505). A cryostat according to any one of claims 1 to 5.

7. To facilitate the coupling of one or more samples (1003, 1004) with one or more signal lines (1005, 1006, 1007, 1008, 1009, 1010), a signal connector is provided on at least one of the first mixing chamber flange (502) and the second mixing chamber flange (505). The cryostat according to claim 6.

8. - The cryostat comprises a first gas processing subsystem (206, 207) for the first dilution refrigerator (1001) and a second gas processing subsystem (305, 306) for the second dilution refrigerator (1002), - The cryostat according to any one of claims 1 to 7, wherein the second gas processing subsystem (305, 306) comprises at least one functional component that is not part of the first gas processing subsystem (206, 207).

9. - The first gas processing subsystem (206, 207) includes a first circulation pump (206) configured to circulate the working fluid through the first dilution refrigerator (1001), - The cryostat according to claim 8, wherein the second gas processing subsystem (305, 306) comprises a second circulation pump (305), which is different from the first circulation pump (206), configured to circulate the working fluid through the second dilution refrigerator (1002).

10. A method for cooling a cryostat, wherein the method is - A step of cooling a plurality of temperature stages, arranged as an ordered row of flanges (105, 107, 108, 111, 203, 501, 502, 503, 504, 505, 506) in the main direction of the cryostat inside a vacuum enclosure (101), to their respective cryogenic cooling temperatures using a stepwise cooling system, wherein the stages (104, 106) of the stepwise cooling system are thermally coupled to each of the stages (105, 107) of the plurality of temperature stages and configured to cool each of the stages (105, 107) of the plurality of temperature stages, - A step of cooling a first mixing chamber flange (502) on which the first mixing chamber (110) is located, using a first dilution refrigerator (1001) comprising a first fractionator (109) and a first mixing chamber (110), wherein the first mixing chamber flange (502) is located in the ordered row of flanges included in the plurality of temperature stages, Includes, - The method includes the step of cooling a second mixing chamber flange (505) on which the second mixing chamber (302) is located, using a second dilution refrigerator (1002) comprising a second fractionator (301) and a second mixing chamber (302), wherein the second mixing chamber flange (505) is located in the ordered row of flanges included in the plurality of temperature stages, - The method includes the step of thermally separating and maintaining the first distiller flange (501) on which the first distiller (109) is located from the second distiller flange (504) on which the second distiller (301) is located. - The method includes the step of thermally separating and maintaining the first mixing chamber flange (502) from the second mixing chamber flange (505), - A method characterized in that the second dilution refrigerator (1002) operates with a greater cooling capacity than the first dilution refrigerator (1001), and as a result, the temperature of the second mixing chamber (302) is higher than the temperature of the first mixing chamber (110).

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