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] This disclosure relates to cryogenic cooling, and more particularly to cryogenic cooling systems. [Background technology]

[0002] In cryogenic cooling systems, multiple cryocoolers, such as pulse tubes, may be used to increase cooling capacity and thereby shorten the system's cooling time. For example, multiple pulse tubes may 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, may be used to cool the low-temperature stage of the system to, for example, a millikelvin temperature. 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 helium temperature may rise, which may affect the performance of the dilution refrigerator and could destabilize it. On the other hand, if some of the cryocoolers are specialized for cooling helium, the cooling of the cryogenic cooling system may take longer. [Overview of the project] [Problems that the invention aims to solve]

[0003] This summary is provided to introduce a selection of concepts in a simplified form, which will be further described below in the detailed explanation. This summary is not intended to identify any major 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] The objective is to provide a cryogenic cooling system. The aforementioned and other objectives are achieved by the features of the independent claims. Further embodiments will become apparent from the dependent claims, description and drawings. [Means for solving the problem]

[0005] According to a first embodiment, the cryogenic cooling system includes a vacuum enclosure, a working area within the vacuum enclosure, and a first cryocooler having a first cooling stage, wherein the first cooling stage is located within the vacuum enclosure, and a second cryocooler having a first cryocooler, a first conduit for passing a flow of a fluid cooling medium toward the working area, and at least one thermal coupling between the first conduit and the first cooling stage for cooling the fluid cooling medium on its way toward the working area, wherein the second cooling stage is vacuum The system comprises a second cryocooler located within an enclosure, a first cold stage located within a 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, wherein the coupling element includes a controlled thermal coupling for reducing the first thermal coupling when the 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 the 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 work 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, and the controlled thermal coupling comprises an actuator and a controller for controlling the actuator, wherein the thermal conductor is arranged to move 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.

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

[0012] In another embodiment of the first aspect, the controlled thermal coupling comprises a first material, the thermal conductivity of the first material is higher at a 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, wherein the critical temperature of the superconducting material is higher 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 which is in thermal contact with the first cooling stage and the first material which is in thermal contact with the first cold stage, and the first material and the second material are thermally bonded.

[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 portion includes a heat exchange fluid.

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

[0020] In another embodiment of the first aspect, the controlled thermal coupling portion has a first thermal conductance above a threshold temperature and a second thermal conductance below the threshold temperature, the first thermal conductance being higher 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 0.1 or less.

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

[0023] In another embodiment 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 by reference to the following detailed description, which is to be considered in connection with the accompanying drawings.

Brief Description of the Drawings

[0025] In the following, exemplary embodiments will be described in more detail with reference to the accompanying drawings.

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

[0027] [Figure 2]A schematic diagram of a cryogenic cooling system according to another embodiment is shown.

[0028] [Figure 3] A schematic diagram of a controlled thermal coupling section implemented using an actuator, according to one embodiment, is shown.

[0029] [Figure 4] A schematic diagram of a controlled thermal coupling portion implemented using the first material according to one embodiment is shown.

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

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

[0032] [Figure 7] A schematic diagram of a controlled thermal coupling section implemented using a heat exchange fluid, according to one embodiment, is shown.

[0033] [Figure 8] A schematic diagram of a controller according to one embodiment is shown.

[0034] In the following, similar reference figures in the attached drawings are used to indicate the same parts. [Modes for carrying out the invention]

[0035] In the following description, reference is made to the accompanying drawings, which constitute part of this disclosure and illustrate specific embodiments to which this disclosure may apply. It is understood that other embodiments may be utilized and structural or logical modifications may be made without departing from the scope of this disclosure. Therefore, since the scope of this disclosure is defined by the accompanying claims, the following detailed description should not be constrained.

[0036] For example, 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 steps of a particular method are described, a corresponding device may include a unit that performs the steps of the described method, even if such a unit is not explicitly shown or illustrated in the drawings. On the other hand, if a particular device is described based on a functional unit, a corresponding method may include steps that perform the described function, even if such steps are not explicitly shown or illustrated in the drawings. Furthermore, it is understood that the features of the various exemplary embodiments described herein may be combined with each other unless otherwise specified.

[0037] Figure 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 work area 101 within the vacuum enclosure.

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

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

[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 located within a vacuum enclosure.

[0042] In this specification, the attribute "1st," and the corresponding attributes "2nd," "3rd," etc., are used solely for the purpose of clear reference and do not imply any limitation on the order of any numbers.

[0043] The first cryocooler 102 may have 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, mechanical refrigerator, or the like.

[0045] The cryogenic cooling system 100 may further include a first conduit 104 for passing a flow of a fluid cooling medium toward the work area 101.

[0046] For example, in some embodiments, the work area 101 may be cooled by a 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 necessary for the proper operation of the dilution refrigerator. The work area may be the 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 can cool the work area by absorbing heat from the work area and / or a payload connected to the work area. The absorbed heat can evaporate the condensed cooling fluid or transfer heat away from the work area by the flow of the cooling fluid.

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

[0048] In this specification, a thermal coupling between two objects may refer to any connection that can be used to transfer heat between 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 way.

[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. Furthermore, the first conduit 104 may also be thermally coupled to other components, such as other cooling stages of the first cryocooler 102. For example, in some embodiments, the fluid cooling medium can be cooled using other cooling stages of the first cryocooler 102 before being further cooled through the first cooling stage 103.

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

[0051] The second cryocooler 106 may have any number of cooling states, 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 located within a vacuum enclosure.

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

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

[0056] The cryogenic cooling system 100 may further comprise a first thermal coupling portion 111 of 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 include a controlled thermal coupling portion for reducing (shrinking) the first thermal coupling portion when the relevant temperature of the cryogenic cooling system 100 is below a threshold temperature.

[0058] The coupling element 109 can substantially thermally separate the first cooling stage 103 and the first cold stage 108, for example, when the relevant 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, and based on that temperature, the coupling element 109 can 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 cooling time of the cryogenic cooling system 100. The cooling time can be measured, for example, from when the cryogenic cooling system 100 begins to cool from room temperature.

[0061] The threshold temperature is a predefined / pre-set temperature. For example, in some embodiments, the threshold temperature can be defined by characteristics such as the material selection and shape of the bonding element 109. In other embodiments, the threshold temperature may be a temperature set by the operator of the cryogenic cooling system 100. In other embodiments, the threshold temperature may be an estimate of the system temperature after a certain amount of 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, and the threshold temperature is 100 mK. Therefore, the coupling element 109 can reduce the first thermal coupling portion 111 so as to substantially separate the first cooling stage 103 and the first cold stage 108 when the temperature of the mixing chamber stage / flange 130 is less than 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 2.2K, 4K, 6K, 10K, or 15K. Therefore, the coupling element 109 can reduce the first thermal coupling portion 111 so as to substantially separate the first cooling stage 103 and the first cold stage 108 when the temperature of the first cold stage 108 is less than 10K.

[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 1K, 2.2K, 4K, 6K, 10K, or 15K. Therefore, the coupling element 109 can reduce the first thermal coupling portion 111 so as to substantially separate the first cooling stage 103 and the first cold stage 108 when the temperature of the still stage is less than 15K.

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

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

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

[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 exceeds the 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 falls 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, for example, to cool only the fluid cooling medium. In this way, 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 working area can be cooled to a lower temperature using the fluid cooling medium.

[0070] In some embodiments, the cryogenic cooling system 100 may be cooled in two phases. For example, during the first phase, the first cryocooler 102 and the second cryocooler 106 may 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 reducing the system's cooling time. Then, during the second phase, the first cryocooler 102 may be substantially thermally isolated from the first cold stage 108 and used to cool a fluid cooling medium. The fluid cooling medium may be used to cool the working area 101 to, for example, a millikelvin temperature. If the first cooling stage 103 is substantially thermally isolated from the first cold stage 108, the first cold stage 108 can be heated to a higher temperature, for example, 10K, without affecting the cryogenic cooling of the work area 100.

[0071] If the first thermal coupling 111 is not reduced, the temperature of the first cold stage 108 can become one limiting factor for the cryogenic cooling system 100. If the temperature of the fluid coolant after it has been cooled by the first cooling stage 103 rises too high, the dilution refrigerator may become unstable and its performance may deteriorate. This can happen, for example, if the temperature of the first cooling stage 103 exceeds 3.2K and / or if the temperature of the first cold stage 108 exceeds 3.6K. In many use cases, this 3.6K limit is an unnecessary limitation 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, for example, 4 to 10K. For example, the first cold stage 108 could be used to heat wiring leading to the work area 101. Various experimental apparatuses could also be placed on the first cold stage 108.

[0072] Figure 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 by a dashed line in Figure 2. The uppermost flange 122 is the lid of the vacuum enclosure. The room temperature stages 123 and 124 of the first cryocooler 102 and the second cryocooler 106 can be attached to the uppermost flange 122.

[0074] According to one embodiment, the first cryocooler 102 includes a first pulse tube, the second cryocooler 106 includes a second pulse tube, the first cooling stage 103 is the low-temperature stage of the first pulse tube, and the second cooling stage 107 is the 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 and second pulse tubes further comprise high-temperature stages 125 and 126 attached to the second cold stage 127. It should be understood that the naming of the cold stages in this specification does not reflect the order of the cold stages, but rather may simply be 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 stage with a higher temperature 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 recovery heat exchanger.

[0077] During operation of the cryogenic cooling system 100, the high-temperature stages 125 and 126 may reach temperatures of approximately 30-50K, for example. The low-temperature stages 103 and 107 may reach temperatures of approximately 2-10K, for example, 2.2K, 4K, 6K, or 10K.

[0078] Additionally, the second cold stage 127 and the first cold stage 108 may also be referred to as the 50K stage / flange and the 4K stage / flange, respectively, to reflect the approximate temperatures of the cryogenic cooling system 100 during operation.

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

[0080] According to one embodiment, the fluid cooling medium 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 comprise a base temperature stage / flange 130. A mixing chamber for a dilution refrigerator may be mounted on the base temperature stage / flange 130. The base temperature stage / flange 130 may comprise a target region 132 for the payload to be refrigerated. The payload may also be called a sample.

[0083] According to one embodiment, the first cold stage 108 is thermally coupled to or part of a thermal radiation shield surrounding the work 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. The cylindrical radiation shield can be mounted on a nested stage / flange.

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

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

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

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

[0089] According to one embodiment, the coupling element 109 comprises a heat conductor, and the controlled thermal coupling portion comprises an actuator and a controller for controlling the actuator, wherein the heat conductor is arranged to move between a contact state and a non-contact state by the actuator and the controller, in the contact state the heat conductor is in thermal contact with the first cold stage and the first cooling stage, and in the non-contact state the heat 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 shown in Figure 3, the coupling element 109 comprises a first heat conductor 202 and a second heat conductor 203, and the controlled thermal coupling portion comprises a piezoelectric actuator 201. The piezoelectric actuator 201 may be electrically coupled to a controller for controlling the piezoelectric actuator 201. The first heat conductor 202 and the second heat conductor 203 are arranged by the piezoelectric actuator 201 and the controller to move between a contact state shown on the right side of Figure 3 and a non-contact state shown on the left side of Figure 3. In the contact state, the first heat conductor 202 is in thermal contact with the first cold stage 108 via the second heat conductor 203, and the second heat conductor 203 is in thermal contact with the first cooling stage 103 via the first heat conductor 202. In the non-contact state, the first heat conductor 202 is not in thermal contact with the first cold stage 108, and the second heat 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 can provide mechanical motion and force induced by the voltage applied to it without generating a considerable amount of heat in the cryogenic cooling system 100.

[0095] The controller may be configured to monitor the relevant temperature of the cryogenic cooling system 100 and, in response to the relevant temperature of the cryogenic cooling system 100 being below a threshold temperature, to 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 associated temperature of the cryogenic cooling system 100 by estimating the associated temperature of the cryogenic cooling system 100 based on the cooling time. For example, based on previous measurements, the operator of the cryogenic cooling system 100 may determine that a certain amount of time will pass before the associated temperature of the cryogenic cooling system 100 reaches a threshold temperature. Based on this, the operator can configure the controller to control the actuator to move the coupling element 109 from a contact state to a non-contact state after this time has elapsed.

[0097] In other embodiments, the operator can manually perform the operation of the controller. For example, the operator can monitor the associated temperature of the cryogenic cooling system 100 by estimating the associated 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 associated temperature of the cryogenic cooling system.

[0098] In some embodiments, the piezoelectric actuator 201 may comprise multiple layers of piezoelectric material. Cryogenic long-range piezoelectric actuators can generate forces up to approximately 1 Newton. Piezoelectric actuators comprising multiple layers of piezoelectric material, also known as piezoelectric stacks, can generate forces up to several thousand Newtons. In some embodiments, lever action can be used to increase the force generated by the piezoelectric actuator 201.

[0099] Long-range stepping piezoelectric actuators can create a travel range of up to several centimeters. Piezoelectric actuators with multiple layers of piezoelectric material typically create a travel range of less than one 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 customizability. 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 temperature does not need to be measured directly but can be estimated based on the cooling time. Furthermore, since the heat conductors 202, 203 can be moved to a non-contact state, good thermal isolation can be achieved between the first cooling stage 103 and the first cold stage 108.

[0102] Please understand that the embodiment in Figure 3 merely illustrates a simplified operating principle of the coupling element 109 equipped with the piezoelectric actuator 201. Various aspects of the coupling element 109, such as its shape, can be modified to better suit specific applications.

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

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

[0105] A high reference temperature can sometimes refer to any temperature that is above the threshold temperature but below room temperature.

[0106] A low reference temperature can refer to any temperature that falls below the threshold temperature.

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

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

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

[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 includes a superconducting material, and the critical temperature of the superconducting material is higher than the threshold temperature.

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

[0113] Niobium undergoes a superconducting transition at 9.3K, and below that temperature, its thermal conductivity decreases exponentially. Therefore, when the first cold stage 108 reaches a temperature of, for example, 3-6K due to the cooling of the first cooling stage 103 and the second cooling stage 107, the residual thermal conductivity of niobium can become very small, and 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 can improve 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. Therefore, since no other components are required to control the controlled thermal coupling, the structure of the coupling element 109 can be simplified.

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

[0117] Figure 5 shows a schematic diagram of a controlled thermal coupling section implemented using the first and second materials according to one embodiment.

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

[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 bonded.

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

[0121] In cryogenic technology, a high thermal conductivity can be, for example, at least 100 W / (m * K) at 10 K or higher, at least 10 W / (m * K) at 1 K, at least 1 W / (m * K) at 0.1 K, or at least 0.1 W / (m * K) at 0.01 K. When the thermal conductivity of a material is high, the material can be regarded as a heat conductor.

[0122] In cryogenic technology, a low thermal conductivity is, 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.

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

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

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

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

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

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

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

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

[0132] The first material 301 may be, for example, a material whose thermal conductivity decreases sharply between 50K and 4K, and the second material 401 may be a material having 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 bond 111 can be fine-tuned, for example, by changing the dimensions of the first material 301 and the second material 401 and / or the shapes of the first material 301 and the second material 401.

[0134] 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. Therefore, 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] When the coupling element 109 is implemented using a combination of the first material 301 and the second material 401, the controlled thermal coupling can be passively controlled. In this way, the structure of the coupling element 109 can be simplified because no other components are required to control the controlled thermal coupling. Furthermore, by selecting the materials of the first material 301 and the second material 401, and / or the dimensions of the first material 301 and the second material 401, the controlled thermal coupling can be controlled with a high degree of customizability.

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

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

[0139] Figure 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 portion 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 gas or liquid helium.

[0142] According to one embodiment, the cryogenic cooling system 100 further comprises an airtight sleeve 601 surrounding a 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 supplying heat exchange fluid into the sleeve 601 and supplying it out of the sleeve 601.

[0143] For example, in the embodiment shown in Figure 7, the first cryocooler 102 comprises a first pulse tube, and the first cooling stage 103 is the low-temperature stage of the first pulse tube. An airtight 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 necessarily have to be mechanically coupled to the first cold stage 108. Rather, the thermal coupling between the first cooling 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 the pump 603.

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

[0146] Even if the heat exchange fluid is discharged from the airtight sleeve 601, the fluid cooling medium should still be cooled. Therefore, even if the heat exchange fluid is discharged from the airtight sleeve 601, at least one thermal coupling 105 between the first conduit 104 and the first cooling stage 103 should still exist. This can be achieved, for example, by placing the first conduit 104 inside the airtight sleeve 601 and ensuring thermal contact with the first cooling stage 103 even when the heat exchange fluid is absent.

[0147] In the embodiment shown in Figure 7, the pulse tube further comprises a high-temperature stage 125, and the cryogenic cooling system 100 further comprises a second airtight sleeve 604 surrounding the high-temperature stage 125. The second airtight sleeve 604 may be used, for example, to control the thermal coupling between the high-temperature stage 125 and the second cold stage 127.

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

[0149] The use of airtight sleeves 601 and 604 makes it easy to replace pulse tubes.

[0150] The use of airtight sleeves 601 and 604 provides good vibration isolation between the cooling stages 103 and 125 of the pulse tube and the cold stages / flanges 108 and 127.

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

[0152] When the coupling element 109 is implemented using an airtight sleeve 106 and a heat exchange fluid, the controlled thermal coupling can be controlled with a high degree of customizability. For example, the controller can be configured to control the pump operation of the heat exchange fluid based on various relevant temperatures of the cryogenic cooling system 100, and / or the relevant temperature can be estimated based on the cooling time, although it does not need to be measured directly. Furthermore, good thermal isolation can be achieved since there may be no mechanical contact between the first cooling stage 103 and the first cold stage 108. In addition, the use of an airtight sleeve 106 and a heat exchange fluid makes it easy to remove / replace the first cryocooler 102.

[0153] Figure 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 various processing devices, such as a coprocessor, a microprocessor, a digital signal processor (DSP), a processing circuit with or without an associated DSP, or a variety of other processing devices, such as an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a microprocessor unit (MCU), a hardware accelerator, or a special-purpose computer chip.

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

[0156] The controller 800 may further comprise other components not shown in the embodiment of Figure 8. The controller 800 may, for example, have an input / output bus for connecting to the coupling element 109 and / or other components, such as one or more temperature sensors for measuring the relevant temperature of the cryogenic cooling system 100. Furthermore, the user can control the controller 800 via the input / output bus. The user can, for example, use the controller 800 to control the operation of the coupling element 109. For example, the operator of the cryogenic cooling system 100 may store a threshold temperature in the controller 800's memory 802, which may contain 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, then several components of the controller 800, such as at least one processor 801 and / or memory 802, may be configured to implement these functions. Furthermore, if at least one processor 801 is configured to implement several functions, these functions may be implemented, for example, using program code contained within memory 802.

[0158] The controller 800 can be implemented using, for example, a computer, several other computing devices, or similar.

[0159] In some embodiments, the controller 800 may be electrically coupled to the piezoelectric actuator 201. The electrical coupling may include, for example, a boost converter. The controller 800 may be configured to control the boost converter, which may be configured to supply the high voltage required to drive the piezoelectric actuator 201. The controller 800 may be configured to use the piezoelectric actuator 201 to move the heat conductors 202, 203 from a contact state to a non-contact state in response to the relevant 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 deliver the heat exchange fluid out of the sleeve 601 in response to the relevant temperature of the cryogenic cooling system 100 being below a threshold temperature.

[0162] Any range or device value given herein can be extended or modified without loss of the desired effect. Furthermore, any embodiment can be combined with another embodiment unless expressly prohibited.

[0163] While this subject matter has been described using expressions specific to structural features and / or functions, it should be understood that the subject matter defined in the attached claims is not necessarily limited to the specific features or functions described above. Rather, the specific features and functions described above are disclosed as examples of implementing the claims, and other equivalent features and functions are also intended to be included in 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 described problems, or that possess any or all of the described benefits and advantages. Furthermore, it will be understood that a reference to an item “one” 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, where appropriate, simultaneously. In addition, individual blocks may be removed from any of the methods without departing from the spirit and scope of the subject matter described herein. Any aspect of the embodiments described above may be combined with any aspect of any of the other embodiments described herein to form further embodiments without losing the desired effect.

[0166] The term “comprising” is used herein to mean including a specified method, block, or element, but such block or element does not constitute an exclusive list, and the method or apparatus may include additional blocks or elements.

[0167] The above description is provided for illustrative purposes only, and it will be understood 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 exemplary embodiments. Various embodiments have been described above with some degree of specificity or by reference to one or more individual embodiments, but those skilled in the art can make numerous modifications to the disclosed embodiments without departing from the spirit or scope of this specification.

Claims

1. - Vacuum enclosure, and the work area inside the vacuum enclosure, - A first cryocooler having a first cooling stage, wherein the first cooling stage is located within the vacuum enclosure, - A first conduit for allowing the flow of a fluid cooling medium to pass towards the work area, - At least one thermally coupled portion of the first conduit and the first cooling stage for cooling the fluid cooling medium on its way to the work area, A second cryocooler having a second cooling stage, wherein the second cooling stage is located within the vacuum enclosure, - A first cold stage located inside the vacuum enclosure, - A second cooling stage and at least one thermal coupling portion of the first cold stage for cooling the first cold stage, - A coupling element provided for cooling the first cold stage, the first cooling stage and the first thermal coupling portion of the first cold stage A cryogenic cooling system comprising, A cryogenic cooling system comprising a controlled thermal coupling portion for reducing the thermal coupling of the first thermal coupling portion when the associated temperature of the cryogenic cooling system is below a threshold temperature.

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

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

4. The cryogenic cooling system according to claim 1 or claim 2, wherein the first cold stage is the 4K stage of the cryogenic cooling system.

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

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

8. The cryogenic cooling system according to claim 1, wherein the controlled thermal coupling portion comprises a first material, and the thermal conductivity of the first material is higher at a reference temperature above the threshold temperature than at a lower reference temperature below the threshold temperature.

9. The cryogenic cooling system according to claim 8, wherein the first material comprises a superconducting material, and the critical temperature of the superconducting material is higher than the threshold temperature.

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

11. The cryogenic cooling system according to claim 8, wherein the controlled thermally coupled portion further comprises a second material, the second material is in thermal contact with the first cooling stage, the first material is in thermal contact with the first cold stage, and the first material and the second material are thermally bonded.

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

13. The cryogenic cooling system according to 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 according to claim 1, wherein the controlled thermal coupling portion includes a heat exchange fluid.

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

16. The cryogenic cooling system according to claim 1, wherein the controlled thermal coupling portion has a first thermal conductance above the threshold temperature and a second thermal conductance below the threshold temperature, and the first thermal conductance is higher than the second thermal conductance.

17. The cryogenic cooling system according to claim 16, wherein the ratio of the second thermal conductance to the first thermal conductance is 0.1 or less.

18. The cryogenic cooling system according to 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. The cryogenic cooling system according to claim 1 or claim 2, wherein the fluid cooling medium is helium in a dilution refrigerator.

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