Cryogenic cooling system

Abstract

To provide a cryogenic cooling system.SOLUTION: Wherein the cryogenic cooling system comprises a working area, a first cryocooler having a first cooling stage, a first conduit for passing a flow of a fluid cooling medium towards the working area, at least one thermal coupling of the first conduit and the first cooling stage for cooling the fluid cooling medium on its way to the working area, a second cryocooler having a second cooling stage, a first cold stage, at least one thermal coupling of the second cooling stage and the first cold stage for cooling the first cold stage, and a first thermal coupling of the first cooling stage and the first cold stage provided by a coupling element for cooling the first cold stage, the coupling element comprises a controlled thermal coupling for reducing the first thermal coupling when an associated temperature of the cryogenic cooling system is below a threshold temperature.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to cryogenic cooling, and more particularly to cryogenic cooling systems. [Background technology]

[0002] In a cryogenic cooling system, multiple cryocoolers, such as pulse tubes, can be used to increase cooling power and thereby reduce the system's cool-down time. For example, multiple pulse tubes can be used to cool the 4 Kelvin stage and the high-temperature stage of a cryogenic cooling system. Other means, such as a dilution refrigerator, can be used to cool the low-temperature stage of the system, for example, to millikelvin temperatures. If all cryocoolers are used to cool the 4 Kelvin stage and other parts of the system as well as the helium in the dilution refrigerator, the temperature of the helium may increase, which may affect the performance of the dilution refrigerator and cause it to become unstable. On the other hand, if some of the cryocoolers are dedicated to cooling helium, the cryogenic cooling system may take longer to cool. Summary of the Invention [Problem to be solved by the invention]

[0003] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0004] It is an object of the present invention to provide a cryogenic cooling system. These and other objects are achieved by the features of the independent claims. Further embodiment forms become apparent from the dependent claims, the description and the drawings. [Means for solving the problem]

[0005] According to a first aspect, a cryogenic cooling system includes a vacuum enclosure and a working area within the vacuum enclosure; a first cryocooler having a first cooling stage, the first cooling stage being disposed within the vacuum enclosure; a first conduit for passing a flow of a fluid cooling medium toward the working area; at least one thermal coupling between the first conduit and the first cooling stage for cooling the fluid cooling medium on its way to the working area; and a second cryocooler having a second cooling stage, the second cooling stage being disposed within the vacuum enclosure. The system includes a second cryocooler disposed within the enclosure, a first cold stage disposed within the vacuum enclosure, at least one thermal coupling between the second cooling stage and the first cold stage for cooling the first cold stage, and a first thermal coupling between the first cooling stage and the first cold stage provided by a coupling element for cooling the first cold stage, the coupling element having a controlled thermal coupling for reducing the first thermal coupling when an associated temperature of the cryogenic cooling system is below a threshold temperature.

[0006] In an embodiment of the first aspect, the work area is arranged to receive an object to be cooled.

[0007] In another embodiment of the first aspect, the first cold stage is thermally coupled to or is part of a thermal radiation shield surrounding the working area.

[0008] In another embodiment of the first aspect, the first cold stage is a 4K stage of a cryogenic cooling system.

[0009] In another embodiment of the first aspect, the first cryocooler comprises a first pulse tube, the second cryocooler comprises a second pulse tube, the first cooling stage is a low temperature stage of the first pulse tube, and the second cooling stage is a low temperature stage of the second pulse tube.

[0010] In another embodiment of the first aspect, the coupling element comprises a thermal conductor, the controlled thermal coupling portion comprises an actuator and a controller for controlling the actuator, the thermal conductor being arranged to be moved between a contact state and a non-contact state by the actuator and the controller, wherein in the contact state the thermal conductor is in thermal contact with the first cold stage and the first cooling stage, and in the non-contact state the thermal conductor is not in thermal contact with the first cooling stage and / or the first cold stage.

[0011] In another embodiment form of the first aspect, the actuator comprises a piezoelectric actuator.

[0012] In another embodiment of the first aspect, the controlled thermal coupling portion comprises a first material, the thermal conductivity of which is higher at a higher reference temperature above the threshold temperature than at a lower reference temperature below the threshold temperature.

[0013] In another embodiment of the first aspect, the first material comprises a superconducting material, the critical temperature of the superconducting material being greater than the threshold temperature.

[0014] In another embodiment of the first aspect, the superconducting material is niobium.

[0015] In another embodiment of the first aspect, the controlled thermal coupling further comprises a second material, the second material being in thermal contact with the first cooling stage, the first material being in thermal contact with the first cold stage, and the first material and the second material being thermally coupled.

[0016] In another embodiment of the first aspect, the second material is a thermal conductor at all temperatures.

[0017] In another embodiment of the first aspect, the second material comprises copper or silver and the first material comprises stainless steel, graphite, and / or niobium.

[0018] In another embodiment of the first aspect, the controlled thermal coupling comprises a heat exchange fluid.

[0019] In another embodiment form of the first aspect, the cryogenic cooling system further comprises an airtight sleeve surrounding the first cooling stage, the sleeve comprising a thermally conductive interface coupled to the first cold stage, and the cryogenic cooling system further comprises a pump for pumping a heat exchange fluid into and out of the sleeve.

[0020] In another embodiment of the first aspect, the controlled thermal coupling has a first thermal conductance above a threshold temperature and a second thermal conductance below the threshold temperature, the first thermal conductance being greater than the second thermal conductance.

[0021] In another embodiment of the first aspect, the ratio of the second thermal conductance to the first thermal conductance is less than or equal to 0.1.

[0022] In another embodiment of the first aspect, the fluid coolant is helium 3, helium 4, or a mixture of helium 3 and helium 4.

[0023] In another embodiment form of the first aspect, the fluid cooling medium is helium in a dilution refrigerator.

[0024] Many of the attendant features will be more readily appreciated as the same becomes better understood by reference to the following detailed description considered in connection with the accompanying drawings. [Brief explanation of the drawings]

[0025] In the following, exemplary embodiments are explained in more detail with reference to the accompanying drawings.

[0026] [Figure 1] 1 shows a schematic diagram of a cryogenic cooling system according to one embodiment.

[0027] [Figure 2]1 shows a schematic diagram of a cryogenic cooling system according to another embodiment.

[0028] [Figure 3] 1 shows a schematic diagram of a controlled thermal coupling implemented using an actuator, according to one embodiment.

[0029] [Figure 4] 1 shows a schematic diagram of a controlled thermal bond implemented using a first material, according to one embodiment.

[0030] [Figure 5] 1 shows a schematic diagram of a controlled thermal coupling implemented using a first material and a second material, according to one embodiment.

[0031] [Figure 6] 1 shows a plot of the thermal conductivity of various materials as a function of temperature.

[0032] [Figure 7] 1 shows a schematic diagram of a controlled thermal coupling implemented using a heat exchange fluid, according to one embodiment.

[0033] [Figure 8] 1 shows a schematic diagram of a controller according to one embodiment.

[0034] In the following, like reference numerals are used to denote like parts in the accompanying drawings. DETAILED DESCRIPTION OF THE INVENTION

[0035] In the following description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific aspects to which the present disclosure may be applied. It is understood that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. Accordingly, the following detailed description is not to be taken in a limiting sense, as the scope of the present disclosure is defined by the appended claims.

[0036] For example, it is understood that disclosure related to a described method may also apply to a corresponding device or system configured to perform that method, and vice versa. For example, if particular method steps are described, a corresponding device may include units that perform the described method steps, even if such units are not explicitly described or illustrated in the drawings. Conversely, for example, if a particular apparatus is described based on functional units, a corresponding method may include steps that perform the described functions, even if such steps are not explicitly described or illustrated in the drawings. Furthermore, it is understood that features of various exemplary aspects described herein may be combined with each other, unless otherwise noted.

[0037] FIG. 1 shows a schematic diagram of a cryogenic cooling system according to one embodiment.

[0038] According to one embodiment, the cryogenic cooling system 100 comprises a vacuum enclosure and a working area 101 within the vacuum enclosure.

[0039] In the embodiment of FIG. 1, the vacuum enclosure is not shown for clarity of illustration.

[0040] The working area 101 can include, for example, a mixing chamber stage / flange 130 of the cryogenic cooling system 100. The mixing chamber stage / flange 130 may also be referred to as a base temperature stage / flange, a mixing plate, etc. A mixing chamber of a dilution refrigerator can be thermally coupled to the mixing chamber stage / flange 130 to cool the working area 101 to millikelvin temperatures.

[0041] The cryogenic cooling system 100 may further comprise a first cryocooler 102 having a first cooling stage 103, the first cooling stage 103 being disposed within the vacuum enclosure.

[0042] In this specification, the attribute "first" and consecutively corresponding attributes "second," "third," etc. are used for clarity of reference only, without indicating any limitation to any numerical order.

[0043] The first cryocooler 102 may include any number of cooling stages, and the first cooling stage 103 may be any cooling stage of the first cryocooler 102 .

[0044] In this specification, a cryocooler may also be referred to as a mechanical precooler, a mechanical refrigerator, or the like.

[0045] The cryogenic cooling system 100 may further comprise a first conduit 104 for passing a flow of fluid cooling medium towards the working region 101 .

[0046] For example, in some embodiments, the working area 101 may be cooled by the mixing chamber 131 of a dilution refrigerator, in which case the fluid cooling medium may be helium-3 or a mixture of helium-3 and helium-4, and the first conduit 104 may be part of the circulation required for proper operation of the dilution refrigerator. The working area may be a surface of the mixing chamber 131 or a thermally conductive object in thermal contact with the mixing chamber 131. In other embodiments, the fluid cooling medium may cool the working area by absorbing heat from the working area and / or a payload connected to the working area. The absorbed heat may evaporate condensed cooling fluid or may be transferred away from the working area by a flow of cooling fluid.

[0047] The cryogenic cooling system 100 may further comprise at least one thermal coupling 105 of the first conduit 104 and the first cooling stage 103 for cooling the fluid cooling medium on its way to the working region 101 .

[0048] As used herein, a thermal coupling between two objects may refer to any coupling that can be used to transfer heat between the two objects sufficiently efficiently. For example, the two objects may be in mechanical contact, a heat exchange gas may be arranged to transfer heat between the two objects, some other material may be arranged to transfer heat between the two objects, or the thermal coupling may be implemented in some other manner.

[0049] The thermal coupling 105 between the first conduit 104 and the first cooling stage 103 may be implemented in various ways. For example, at least a portion of the first conduit 104 may be in mechanical contact with the first cooling stage 103. Additionally, the first conduit 104 may be thermally coupled to other components, such as other cooling stages of the first cryocooler 102. For example, in some embodiments, other cooling stages of the first cryocooler 102 may be used to cool the fluid cooling medium before further cooling the fluid cooling medium via the first cooling stage 103.

[0050] The cryogenic cooling system 100 may further include a second cryocooler 106 having a second cooling stage 107, the second cooling stage 107 being disposed within the vacuum enclosure.

[0051] The second cryocooler 106 may have any number of cooling stages, and the second cooling stage 107 may be any cooling stage of the second cryocooler 106 .

[0052] The cryogenic cooling system 100 may further include a first cold stage 108 disposed within the vacuum enclosure.

[0053] The first cold stage 108 may comprise, for example, a four Kelvin (4K) flange / stage of the cryogenic cooling system 100 .

[0054] The cryogenic cooling system 100 may further comprise at least one thermal coupling 110 of the second cooling stage 107 and the first cold stage 108 for cooling the first cold stage 108 .

[0055] The second cryocooler 106 may be configured to cool the first cold stage 108 via at least one thermal coupling 110 between the second cooling stage 107 and the first cold stage 108 .

[0056] The cryogenic cooling system 100 may further include a first thermal coupling 111 between the first cooling stage 103 and the first cold stage 108 provided by a coupling element 109 for cooling the first cold stage 108.

[0057] The coupling element 109 may comprise a controlled thermal coupling for reducing the first thermal coupling when an associated temperature of the cryogenic cooling system 100 is below a threshold temperature.

[0058] The coupling element 109 may, for example, substantially thermally decouple the first cooling stage 103 and the first cold stage 108 when the associated temperature of the cryogenic cooling system 100 is below a threshold temperature.

[0059] The relevant temperature of the cryogenic cooling system 100 may include any temperature based on which the coupling element 109 may be operated to reduce the first thermal coupling.

[0060] The relevant temperature of the cryogenic cooling system 100 may include, for example, the temperature of the mixing chamber stage / flange 130, the temperature of the first cold stage 108, the temperature of the still stage / flange of the cryogenic cooling system 100, the temperature of the first cooling stage 103, or the temperature of the coupling element 109. In some embodiments, the relevant temperature may be an estimated relevant temperature, for example, estimated based on the cool-down time of the cryogenic cooling system 100. The cool-down time may be measured, for example, from when the cryogenic cooling system 100 begins to cool down from room temperature.

[0061] The threshold temperature is a predefined / preset temperature. For example, in some embodiments, the threshold temperature may be defined by characteristics such as material selection and geometry of the coupling element 109. In other embodiments, the threshold temperature may be a temperature set by an operator of the cryogenic cooling system 100. In other embodiments, the threshold temperature may be an estimate of the temperature of the system after a certain time has elapsed since cooling began.

[0062] According to one embodiment, the relevant temperature of the cryogenic cooling system 100 is the temperature of the mixing chamber stage / flange 130, with the threshold temperature being 100 mK. Thus, the coupling element 109 can reduce the first thermal coupling 111 to substantially decouple the first cooling stage 103 and the first cold stage 108 when the temperature of the mixing chamber stage / flange 130 is below 100 mK.

[0063] According to one embodiment, the relevant temperature of the cryogenic cooling system 100 is the temperature of the first cold stage 108, and the threshold temperature is 2.2 K, 4 K, 6 K, 10 K, or 15 K. Thus, the coupling element 109 can reduce the first thermal coupling 111 to substantially decouple the first cooling stage 103 and the first cold stage 108 when the temperature of the first cold stage 108 is below 10 K.

[0064] According to one embodiment, the relevant temperature of the cryogenic cooling system 100 is the temperature of the still stage of the cryogenic cooling system 100, and the threshold temperature is 1 K, 2.2 K, 4 K, 6 K, 10 K, or 15 K. Thus, the coupling element 109 can reduce the first thermal coupling 111 to substantially decouple the first cooling stage 103 and the first cold stage 108 when the temperature of the still stage is below 15 K.

[0065] According to one embodiment, the first cold stage 108 is a 4K stage of the cryogenic cooling system 100 .

[0066] According to one embodiment, the controlled thermal coupling has a first thermal conductance above a threshold temperature and a second thermal conductance below the threshold temperature, the first thermal conductance being greater than the second thermal conductance.

[0067] According to one embodiment, the ratio of the second thermal conductance to the first thermal conductance is less than or equal to 0.1.

[0068] In any embodiment, the cryogenic cooling system 100 may include any number of cryocoolers in addition to the first cryocooler 102 and the second cryocooler 106. Additional cryocoolers may be used, for example, to further cool the first cold stage 108.

[0069] In the cryogenic cooling system 100, when the relevant temperature of the cryogenic cooling system 100 is above a threshold temperature, both the first cryocooler 102 and the second cryocooler 106 can be used to cool the first cold stage 108. When the relevant temperature of the cryogenic cooling system 100 is below the threshold temperature, the coupling element 109 can be used to reduce the first thermal coupling 111 between the first cooling stage 103 and the first cold stage 108, and the first cooling stage 103 can be used to cool, for example, only the fluid cooling medium. In this manner, by using both the first cryocooler 102 and the second cryocooler 106 to cool the first cold stage 108, the cooling time of the first cold stage 108 can be reduced and the fluid cooling medium can be used to cool the working area to a lower temperature.

[0070] In some embodiments, the cryogenic cooling system 100 can be cooled in two phases. For example, during a first phase, the first cryocooler 102 and the second cryocooler 106 can be used to cool the first cold stage 108 to or near a threshold temperature. The cooling power of the first cryocooler 102 and the second cryocooler 106 can be used to cool the first cold stage 108 during the first phase, thereby shortening the system cool-down time. Then, during a second phase, the first cryocooler 102 can be substantially thermally decoupled from the first cold stage 108 and used to cool a fluid cooling medium. The fluid cooling medium can be used to cool the working region 101, for example, to millikelvin temperatures. If the first cooling stage 103 is substantially thermally decoupled from the first cold stage 108, the first cold stage 108 can be warmed, for example, to 10 K, where the cooling power of the cryocooler is higher, without affecting the cryogenic cooling of the working region 100.

[0071] If the first thermal coupling 111 is not reduced, the temperature of the first cold stage 108 can become a limiting factor in the cryogenic cooling system 100. If the temperature of the fluid cooling medium increases too much after being cooled by the first cooling stage 103, the dilution refrigerator may become unstable and its performance may be degraded. This can occur, for example, if the temperature of the first cooling stage 103 exceeds 3.2 K and / or if the temperature of the first cold stage 108 exceeds 3.6 K. In many use cases, this 3.6 K limit is unnecessary for other components of the cryogenic cooling system 100. For example, many components thermally coupled to the first cold stage 108 can operate at temperatures ranging from 4 to 10 K. For example, the first cold stage 108 can be used to thermalize wiring leading to the working area 101. Various experimental devices can also be placed on the first cold stage 108.

[0072] FIG. 2 shows a schematic diagram of a cryogenic cooling system according to another embodiment.

[0073] The outermost structure of the cryogenic cooling system 100 may be a vacuum enclosure 121, shown in dashed lines in Figure 2. A top flange 122 is the lid of the vacuum enclosure. The room temperature stages 123, 124 of the first cryocooler 102 and second cryocooler 106 may be attached to the top flange 122.

[0074] According to one embodiment, the first cryocooler 102 comprises a first pulse tube, the second cryocooler 106 comprises a second pulse tube, the first cooling stage 103 is a low temperature stage of the first pulse tube, and the second cooling stage 107 is a low temperature stage of the second pulse tube.

[0075] For example, in the embodiment of Figure 2, the first cryocooler 102 comprises a first pulse tube, and the second cryocooler 106 comprises a second pulse tube. The first pulse tube and the second pulse tube further comprise high temperature stages 125, 126 attached to a second cold stage 127. It should be understood that the naming of the cold stages herein does not reflect the order of the cold stages, but may merely represent the order in which the cold stages are introduced herein. For example, in the embodiment of Figure 2, the second cold stage 127 is a higher temperature stage than the first cold stage 108.

[0076] In other embodiments, the first cryocooler 102 and / or the second cryocooler 106 may comprise any other type of cryocooler, such as a Gifford-McMahon cryocooler, a Joule-Thomson cryocooler, a Stirling cryocooler, a regenerative heat exchanger, or a recuperator heat exchanger.

[0077] During operation of the cryogenic cooling system 100, the hot stages 125, 126 may reach a temperature of, for example, about 30-50 K. The cold stages 103, 107 may reach a temperature of, for example, about 2-10 K, such as 2.2 K, 4 K, 6 K, or 10 K.

[0078] The second cold stage 127 and the first cold stage 108 are also sometimes referred to as the 50K stage / flange and the 4K stage / flange, respectively, reflecting their approximate temperatures during operation of the cryogenic cooling system 100.

[0079] The cryogenic cooling system 100 may further include a still stage / flange 128 to which a dilution refrigerator still 129 may be attached.

[0080] According to one embodiment, the fluid coolant is Helium 3, Helium 4, or a mixture of Helium 3 and Helium 4.

[0081] According to one embodiment, the fluid cooling medium is helium in a dilution refrigerator.

[0082] The cryogenic cooling system 100 may further include a base temperature stage / flange 130. The mixing chamber of the dilution refrigerator may be attached to the base temperature stage / flange 130. The base temperature stage / flange 130 may include a target area 132 for the payload to be refrigerated. The payload may also be referred to as the sample.

[0083] According to one embodiment, the first cold stage 108 is thermally coupled to or is part of a thermal radiation shield that surrounds the working area 101 .

[0084] For example, the cryogenic cooling system 100 may further include a cylindrical radiation shield, which is not shown in Figure 2 for clarity of illustration. The cylindrical radiation shield may be attached to a stage / flange in a nested configuration.

[0085] The cryogenic cooling system 100 may further include other intermediate stages / flanges between the still stage / flange 128 and the base temperature stage / flange 130, such as a so-called 100 mK stage / flange.

[0086] According to one embodiment, the work area 101 is positioned to receive an object to be cooled.

[0087] For example, the stage / flange of the cryogenic cooling system 100 may be provided with aligned openings to provide a so-called line-of-sight port into the target area 132 where an object to be cooled may be inserted.

[0088] FIG. 3 shows a schematic diagram of a controlled thermal coupling implemented using an actuator, according to one embodiment.

[0089] According to one embodiment, the coupling element 109 comprises a thermal conductor, the controlled thermal coupling portion comprises an actuator and a controller for controlling the actuator, and the thermal conductor is arranged to be moved between a contact state and a non-contact state by the actuator and the controller, in the contact state the thermal conductor is in thermal contact with the first cold stage and the first cooling stage, and in the non-contact state the thermal conductor is not in thermal contact with the first cooling stage and / or the first cold stage.

[0090] According to one embodiment, the actuator comprises a piezoelectric actuator.

[0091] For example, in the embodiment of FIG. 3 , the coupling element 109 includes a first thermal conductor 202 and a second thermal conductor 203, and the controlled thermal coupling includes a piezoelectric actuator 201. The piezoelectric actuator 201 can be electrically coupled to a controller for controlling the piezoelectric actuator 201. The first thermal conductor 202 and the second thermal conductor 203 are arranged to be moved by the piezoelectric actuator 201 and the controller between a contact state shown on the right side of FIG. 3 and a non-contact state shown on the left side of FIG. 3. In the contact state, the first thermal conductor 202 is in thermal contact with the first cold stage 108 via the second thermal conductor 203, and the second thermal conductor 203 is in thermal contact with the first cooling stage 103 via the first thermal conductor 202. In the non-contact state, the first thermal conductor 202 is not in thermal contact with the first cold stage 108, and the second thermal conductor 203 is not in thermal contact with the first cooling stage 103. In the contact and non-contact states, the first heat conductor 202 is in contact with the first cooling stage 103 and the second heat conductor 203 is in contact with the first cold stage 108 .

[0092] In other embodiments, the piezoelectric actuator 201 can be replaced with any other type of actuator.

[0093] The thermal conductor may include, for example, copper.

[0094] The piezoelectric actuator 201 is capable of providing mechanical motion and force induced by a voltage applied to the piezoelectric actuator 201 without imparting a significant amount of heat to the cryogenic cooling system 100 .

[0095] The controller may be configured to monitor an associated temperature of the cryogenic cooling system 100 and, in response to the associated temperature of the cryogenic cooling system 100 being below a threshold temperature, control the actuator to move the coupling element 109 from a contact state to a non-contact state.

[0096] In some embodiments, the controller can monitor the relevant temperature of the cryogenic cooling system 100 by estimating the relevant temperature of the cryogenic cooling system 100 based on a cooling time. For example, based on previous measurements, an operator of the cryogenic cooling system 100 can determine that it will take a certain amount of time for the relevant temperature of the cryogenic cooling system 100 to reach a threshold temperature. Based on this, the operator can configure the controller to control the actuator to move the coupling element 109 from a contacting state to a non-contacting state after this amount of time has elapsed.

[0097] In other embodiments, an operator can manually perform the actions of the controller. For example, the operator can monitor the relevant temperature of the cryogenic cooling system 100 by estimating the relevant temperature of the cryogenic cooling system 100 based on the cooling time, and control the actuator to move the coupling element 109 from a contact state to a non-contact state based on the estimated relevant temperature of the cryogenic cooling system.

[0098] In some embodiments, the piezoelectric actuator 201 can comprise multiple layers of piezoelectric material. Cryogenic, long-travel piezoelectric actuators can generate forces up to about 1 Newton. Piezoelectric actuators with multiple layers of piezoelectric material, also called piezoelectric stacks, can generate up to several thousand Newtons. In some embodiments, leverage can be used to increase the force generated by the piezoelectric actuator 201.

[0099] Long-range stepping piezoelectric actuators can produce a range of motion up to several centimeters. Piezoelectric actuators with multiple layers of piezoelectric material typically produce a range of motion of less than a millimeter.

[0100] The piezoelectric actuator 201 may include, for example, lead zirconate titanate (PZT) and / or zinc oxide (ZnO).

[0101] When the coupling element 109 is implemented using an actuator, the controlled thermal coupling can be controlled with a high degree of customization. For example, the controller can be configured to control the actuator based on various relevant temperatures of the cryogenic cooling system 100, and / or the relevant temperatures need not be measured directly but can be estimated based on cooling time. Furthermore, because the thermal conductors 202, 203 can be moved out of contact, good thermal isolation can be achieved between the first cooling stage 103 and the first cold stage 108.

[0102] It should be understood that the embodiment of Figure 3 is merely a simplified illustration of the operating principle of coupling element 109 with piezoelectric actuator 201. Various aspects of coupling element 109, such as its shape, can be modified to better suit a particular application.

[0103] FIG. 4 shows a schematic diagram of a controlled thermal coupling implemented using a first material, according to one embodiment.

[0104] According to one embodiment, the controlled thermal coupling comprises a first material 301, the thermal conductivity of which is higher at a higher reference temperature above a threshold temperature than at a lower reference temperature below the threshold temperature.

[0105] The high reference temperature may refer to any temperature above the threshold temperature but below room temperature.

[0106] A low reference temperature may refer to any temperature below a threshold temperature.

[0107] In some embodiments, the thermal conductivity of the first material may be higher at all temperatures above a threshold temperature than at temperatures below the threshold temperature.

[0108] In some embodiments, the threshold temperature may be 10K and the high reference temperature may be a temperature above 100K.

[0109] In some embodiments, the high reference temperature may be any temperature above 10 K, such as, for example, 50 K or 100 K, and the low reference temperature may be any temperature below 10 K, such as, for example, 4 K or 2 K.

[0110] According to one embodiment, the thermal conductivity of the first material 301 is 20 times higher at a high reference temperature above the threshold temperature than at a low reference temperature below the threshold temperature.

[0111] According to one embodiment, the first material 301 comprises a superconducting material, the critical temperature of which is greater than the threshold temperature.

[0112] According to one embodiment, the superconducting material is niobium.

[0113] Niobium undergoes a superconducting transition at 9.3 K, below which its thermal conductivity decreases exponentially. Thus, when the first cold stage 108 reaches a temperature of, for example, 3-6 K due to cooling of the first cooling stage 103 and the second cooling stage 107, the residual thermal conductivity of niobium may become so small that the first cooling stage 103 and the first cold stage 108 become effectively thermally isolated.

[0114] In some embodiments, the first material 301 may be single crystal niobium, which may provide enhanced thermal conductivity above a threshold temperature.

[0115] When the coupling element 109 is implemented using the first material 301, the controlled thermal coupling can be controlled in a passive manner, and therefore the structure of the coupling element 109 can be simplified because no other components are required to control the controlled thermal coupling.

[0116] It should be understood that the embodiment of Figure 4 merely illustrates in a simplified manner a coupling element 109 comprising a first material 301. Various aspects of the coupling element 109, such as the shape, can be modified to better suit a particular application.

[0117] FIG. 5 shows a schematic diagram of a controlled thermal coupling implemented using a first material and a second material, according to one embodiment.

[0118] According to one embodiment, the controlled thermal coupling portion further comprises a second material 401, the second material 401 being in thermal contact with the first cooling stage 103, the first material 301 being in thermal contact with the first cold stage 108, and the first material 301 and the second material 401 being thermally coupled.

[0119] Alternatively, the second material 401 may be in thermal contact with the first cold stage 108, and the first material 301 may be in thermal contact with the first cooling stage 103, and the first material 301 and the second material 401 are thermally coupled.

[0120] According to one embodiment, the second material 401 is a thermal conductor at all temperatures.

[0121] In cryogenics, high thermal conductivity is, for example, at least 100 W / (m) above 10 K. * K), at least 10W / (m at 1K * K), at least 1 W / (m at 0.1 K * K), or at least 0.1 W / (m * If a material has a high thermal conductivity, it can be considered a thermal conductor.

[0122] In cryogenics, low thermal conductivity is, for example, 50 W / (m) at 100 K. * K), 5W / (m at 10K * K), 0.75W / (m at 1K * K), 0.075W / (m at 0.1K * K), and 0.0075W / (m at 0.01K * K).

[0123] According to one embodiment, the second material 401 comprises copper or silver, and the first material 301 comprises stainless steel, graphite, and / or niobium.

[0124] According to one embodiment, the second material 401 comprises copper and the first material 301 comprises stainless steel.

[0125] According to one embodiment, the second material 401 comprises copper and the first material 301 comprises graphite.

[0126] According to one embodiment, the second material 401 comprises copper and the first material 301 comprises niobium.

[0127] According to one embodiment, the second material 401 comprises silver and the first material 301 comprises stainless steel.

[0128] According to one embodiment, the second material 401 comprises silver and the first material 301 comprises graphite.

[0129] According to one embodiment, the second material 401 comprises silver and the first material 301 comprises niobium.

[0130] The thermal conductivity of the first material 301 below the threshold temperature may be lower than the thermal conductivity of the second material 401 below the threshold temperature.

[0131] The thermal conductivity of the first material 301 above the threshold temperature may be lower than the thermal conductivity of the second material 401 above the threshold temperature.

[0132] The first material 301 may comprise, for example, a material whose thermal conductivity drops off sharply between 50K and 4K, and the second material 401 may comprise a material with high thermal conductivity, such as copper or silver.

[0133] By using the first material 301 and the second material 401, the threshold temperature and thermal conductivity of the first thermal coupling portion 111 can be fine-tuned, for example, by changing the dimensions of the first material 301 and the second material 401 and / or the shape of the first material 301 and the second material 401.

[0134] The thermal composite conductance K of the first material 301 and the second material 401 S teeth,

number

[0135] If the coupling element 109 is implemented using the first material 301 or a combination of the first material 301 and the second material 401, the relevant temperature may be the temperature of the first material 301 and / or the second material 401. Thus, the first material 301 or a combination of the first material 301 and the second material 401 may be used to passively implement a controlled thermal coupling to reduce the first thermal coupling when the relevant temperature of the cryogenic cooling system 100 is below a threshold temperature.

[0136] The controlled thermal coupling can be passively controlled when coupling element 109 is implemented using a combination of first material 301 and second material 401. In this manner, the structure of coupling element 109 can be simplified because no other components are required to control the controlled thermal coupling. Furthermore, by selecting the materials of first material 301 and second material 401 and / or the dimensions of first material 301 and second material 401, the controlled thermal coupling can be controlled with a high degree of customization.

[0137] FIG. 6 shows a plot of the thermal conductivity of various materials as a function of temperature.

[0138] Curve 501 corresponds to copper, curve 502 corresponds to pure aluminum, curve 503 corresponds to niobium, curve 504 corresponds to 6061 aluminum alloy, curve 505 corresponds to titanium, curve 506 corresponds to 304 stainless steel, curve 507 corresponds to Invar, and curve 508 corresponds to G10, i.e., gallolite.

[0139] FIG. 7 shows a schematic diagram of a controlled thermal coupling implemented using a heat exchange fluid, according to one embodiment.

[0140] According to one embodiment, the controlled thermal coupling includes a heat exchange fluid.

[0141] The heat exchange fluid may include, for example, a heat exchange gas and / or a heat exchange liquid, such as gaseous or liquid helium.

[0142] According to one embodiment, the cryogenic cooling system 100 further comprises an airtight sleeve 601 surrounding the first cooling stage 103, the sleeve 601 comprising a thermally conductive interface 602 coupled to the first cold stage 108, and the cryogenic cooling system 100 further comprises a pump for pumping heat exchange fluid into and out of the sleeve 601.

[0143] 7, the first cryocooler 102 comprises a first pulse tube, and the first cooling stage 103 is the cold stage of the first pulse tube. A gas-tight sleeve 601 surrounds the first cooling stage 103, and the sleeve 601 comprises a thermally conductive interface 602 coupled to the first cold stage 108.

[0144] The pulse tube does not have to be mechanically coupled to the first cold stage 108. Rather, the thermal coupling between the first cold stage 103 and the first cold stage 108 can be achieved via gas or liquid helium, for example, by filling the sleeve 601 with gas or liquid helium using a pump 603.

[0145] In some embodiments, the cryogenic cooling system 100 can further include a heater for evacuating the heat exchange fluid from the sleeve 601. The heater can make evacuating the sleeve 601 more efficient.

[0146] The fluid cooling medium should be cooled even when the heat exchange fluid is exhausted from the gas-tight sleeve 601. Therefore, at least one thermal coupling 105 between the first conduit 104 and the first cooling stage 103 should still exist even when the heat exchange fluid is exhausted from the gas-tight sleeve 601. This can be achieved, for example, by locating the first conduit 104 inside the gas-tight sleeve 601 and making thermal contact with the first cooling stage 103 even when no heat exchange fluid is present.

[0147] 7, the pulse tube further comprises a hot stage 125, and the cryogenic cooling system 100 further comprises a second hermetic sleeve 604 surrounding the hot stage 125. The second hermetic sleeve 604 may be used, for example, to control the thermal coupling between the hot stage 125 and the second cold stage 127.

[0148] The use of gas-tight sleeves 601, 604 reduces the number of interfaces between the pulse tube cooling stages 103, 125 and the cold stage / flanges 108, 127.

[0149] The use of gas-tight sleeves 601, 604 allows for easy replacement of the pulse tubes.

[0150] The use of gas-tight sleeves 601, 604 can provide good vibration isolation between the pulse tube cooling stages 103, 125 and the cold stage / flanges 108, 127.

[0151] In other embodiments, the gas-tight sleeve 601 can be replaced with a different type of container for heat exchange fluid having a different type of shape. The container can include a thermally conductive interface coupled to the first cold stage 108, and the pump 603 can be positioned to pump the heat exchange fluid into and out of the container.

[0152] When the coupling element 109 is implemented using the gas-tight sleeve 106 and heat exchange fluid, the controlled thermal coupling can be controlled with a high degree of customization. For example, the controller can be configured to control the pumping of the heat exchange fluid based on various relevant temperatures of the cryogenic cooling system 100, and / or the relevant temperatures need not be directly measured but can be estimated based on cooling time. Furthermore, since there may be no mechanical contact between the first cooling stage 103 and the first cold stage 108, good thermal isolation can be achieved. Furthermore, the use of the gas-tight sleeve 106 and heat exchange fluid can facilitate removal / replacement of the first cryocooler 102.

[0153] FIG. 8 shows a schematic diagram of a controller according to one embodiment.

[0154] The controller 800 may comprise at least one processor 801. The at least one processor 801 may comprise one or more of a variety of processing devices, such as, for example, a coprocessor, a microprocessor, a digital signal processor (DSP), processing circuitry with or without an associated DSP, or a variety of other processing devices including integrated circuits, such as, for example, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a microprocessor unit (MCU), a hardware accelerator, a special purpose computer chip, or the like.

[0155] The controller 800 may further include a memory 802. The memory 802 may be configured to store, for example, a computer program. The memory 802 may include one or more volatile memory devices, one or more non-volatile memory devices, and / or a combination of one or more volatile and non-volatile memory devices. For example, the memory 802 may be embodied as a magnetic storage device (such as a hard disk drive, a floppy disk, or a magnetic tape), a magneto-optical storage device, or a semiconductor memory (such as a mask ROM, a programmable ROM (PROM), an erasable PROM (EPROM), a flash ROM, or a random access memory (RAM)).

[0156] The controller 800 may further include other components not shown in the embodiment of FIG. 8 . The controller 800 may include, for example, an input / output bus for connecting the controller 800 to the coupling element 109 and / or other components, such as one or more temperature sensors for measuring relevant temperatures of the cryogenic cooling system 100. Furthermore, a user may control the controller 800 via the input / output bus. The user may, for example, use the controller 800 to control the operation of the coupling element 109. For example, an operator of the cryogenic cooling system 100 may store a threshold temperature in the memory 802 of the controller 800, which may include program code configured to control the coupling element 109 according to the threshold temperature.

[0157] If the controller 800 is configured to implement several functions, several components and / or multiple components of the controller 800 may be configured to implement the functions, such as the at least one processor 801 and / or the memory 802. Furthermore, if the at least one processor 801 is configured to implement several functions, the functions may be implemented using program code contained in the memory 802, for example.

[0158] The controller 800 may be implemented using, for example, a computer, some other computing device, or the like.

[0159] In some embodiments, the controller 800 may be electrically coupled to the piezoelectric actuator 201. The electrical coupling may comprise, for example, a boost converter. The controller 800 may be configured to control the boost converter, which may be configured to provide the high voltage necessary to drive the piezoelectric actuator 201. The controller 800 may be configured to use the piezoelectric actuator 201 to move the thermal conductors 202, 203 from a contacting state to a non-contacting state in response to an associated temperature of the cryogenic cooling system 100 being below a threshold temperature.

[0160] In some embodiments, the piezoelectric actuator 201 may be replaced with any other type of actuator, and the controller 800 may be electrically coupled to the actuator.

[0161] In some embodiments, the controller 800 may be electrically coupled to the pump 603. The controller 800 may be configured to control the pump 603 to pump the heat exchange fluid out of the sleeve 601 in response to an associated temperature of the cryogenic cooling system 100 being below a threshold temperature.

[0162] Any range or device value given herein can be expanded or modified without losing the desired effect, and any embodiment can be combined with another embodiment unless expressly prohibited.

[0163] Although the present subject matter has been described in terms of particular structural features and / or acts, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the particular features or acts described above. Rather, the particular features and acts described above are disclosed as example ways of implementing the claims, and other equivalent features and acts are intended to be encompassed within the scope of the claims.

[0164] It will be understood that the benefits and advantages described above may relate to one embodiment or to multiple embodiments. Embodiments are not limited to those that solve any or all of the stated problems or that have any or all of the stated benefits and advantages. Furthermore, it will be understood that reference to "an" item may refer to one or more of those items.

[0165] The steps of the methods described herein may be performed in any suitable order, or simultaneously where appropriate. Additionally, individual blocks may be deleted from any of the methods without departing from the spirit and scope of the subject matter described herein. Aspects of any of the above-described embodiments may be combined with aspects of any of the other described embodiments to form further embodiments without losing the desired effect.

[0166] The term "comprising" is used herein to mean including specified methods, blocks, or elements, but such blocks or elements do not comprise an exclusive list and methods or apparatus may include additional blocks or elements.

[0167] It will be understood that the above description is provided by way of example only, and that various modifications may be made by those skilled in the art. The above specification, examples, and data provide a complete description of the structure and use of the exemplary embodiments. While various embodiments have been described above with a certain degree of particularity, or with reference to one or more specific embodiments, those skilled in the art can make numerous modifications to the disclosed embodiments without departing from the spirit or scope of the specification.

Claims

1. a vacuum enclosure and a working area within said vacuum enclosure; a first cryocooler having a first cooling stage, the first cooling stage being disposed within the vacuum enclosure; and a first conduit for passing a flow of fluid cooling medium toward said working area; at least one thermal coupling of the first conduit and the first cooling stage for cooling the fluid cooling medium en route to the working area; a second cryocooler having a second cooling stage, the second cooling stage being disposed within the vacuum enclosure; and a first cold stage disposed within the vacuum enclosure; - at least one thermal coupling of the second cold stage and the first cold stage for cooling the first cold stage; a first thermal coupling of the first cooling stage and the first cold stage provided by a coupling element for cooling the first cold stage; A cryogenic cooling system comprising: A cryogenic cooling system, wherein the coupling element comprises a controlled thermal coupling for reducing the first thermal coupling when an associated temperature of the cryogenic cooling system is below a threshold temperature.

2. The cryogenic cooling system of claim 1 , wherein the work area is arranged to receive an object to be cooled.

3. 3. The cryogenic cooling system of claim 1 or claim 2, wherein the first cold stage is thermally coupled to or is part of a thermal radiation shield surrounding the working area.

4. 3. The cryogenic cooling system of claim 1, wherein the first cold stage is a 4K stage of the cryogenic cooling system.

5. 3. The cryogenic cooling system of claim 1, wherein the first cryocooler comprises a first pulse tube, the second cryocooler comprises a second pulse tube, the first cooling stage is a low temperature stage of the first pulse tube, and the second cooling stage is a low temperature stage of the second pulse tube.

6. 2. The cryogenic cooling system of claim 1, wherein the coupling element comprises a thermal conductor, the controlled thermal coupling portion comprises an actuator and a controller for controlling the actuator, the thermal conductor being arranged to be moved between a contact state and a non-contact state by the actuator and the controller, wherein in the contact state the thermal conductor is in thermal contact with the first cold stage and the first cooling stage, and in the non-contact state the thermal conductor is not in thermal contact with the first cooling stage and / or the first cold stage.

7. The cryogenic cooling system of claim 6 , wherein the actuator comprises a piezoelectric actuator.

8. 2. The cryogenic cooling system of claim 1, wherein the controlled thermal coupling comprises a first material, the first material having a higher thermal conductivity at an upper reference temperature above the threshold temperature than at a lower reference temperature below the threshold temperature.

9. The cryogenic cooling system of claim 8 , wherein the first material comprises a superconducting material, the superconducting material having a critical temperature greater than the threshold temperature.

10. 10. The cryogenic cooling system of claim 9, wherein the superconducting material is niobium.

11. 9. The cryogenic cooling system of claim 8, wherein the controlled thermal coupling further comprises a second material, the second material in thermal contact with the first cooling stage, the first material in thermal contact with the first cold stage, and the first material and the second material being thermally coupled.

12. The cryogenic cooling system of claim 11 , wherein the second material is a thermal conductor at all temperatures.

13. 13. The cryogenic cooling system of claim 11 or claim 12, wherein the second material comprises copper or silver and the first material comprises stainless steel, graphite, and / or niobium.

14. The cryogenic cooling system of claim 1 , wherein the controlled thermal coupling comprises a heat exchange fluid.

15. 15. The cryogenic cooling system of claim 14, further comprising an airtight sleeve surrounding the first cooling stage, the sleeve comprising a thermally conductive interface coupled to the first cold stage, and the cryogenic cooling system further comprising a pump for pumping the heat exchange fluid into and out of the sleeve.

16. 2. The cryogenic cooling system of claim 1, wherein the controlled thermal junction has a first thermal conductance above the threshold temperature and a second thermal conductance below the threshold temperature, the first thermal conductance being greater than the second thermal conductance.

17. 17. The cryogenic cooling system of claim 16, wherein a ratio of the second thermal conductance to the first thermal conductance is less than or equal to 0.

1.

18. 3. The cryogenic cooling system of claim 1 or claim 2, wherein the fluid cooling medium is helium 3, helium 4, or a mixture of helium 3 and helium 4.

19. 3. The cryogenic cooling system of claim 1 or claim 2, wherein the fluid cooling medium is helium in a dilution refrigerator.

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