Dilution refrigerator capable of continuous operation during filter regeneration, and related methods

Abstract

There is described herein a dilution refrigerator and a method of operation thereof. The dilution refrigerator has a dilution unit inside a cryostat and a pumping arrangement operable for circulating a fluid mixture through the dilution unit. A fluid mixture is directed through the dilution unit via a fluid circulation path having a first contaminant filter and a second contaminant filter connected in series and disposed inside the cryostat. The first contaminant filter is removed from the fluid circu- lation path without interrupting operation of the dilution refrigerator. A cleaning procedure is per- formed on the first contaminant filter while the fluid mixture is concurrently directed in the fluid circulation path through the second contaminant filter. When the cleaning procedure is completed, the first contaminant filter is reintegrated into the fluid circulation path.

Description

SYSTEMS AND METHODS FOR REMOVING CONTAMINANTS FROM THE FLUID CIRCULATION SYSTEM OF A DILUTION REFRIGERATORCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of United States Patent Application No. 63 / 494,319 filed on April 5, 2023, the contents of which are hereby incorporated by referenced in their entirety.TECHNICAL FIELD

[0002] The present disclosure generally relates to dilution refrigerators and, more particularly, to regenerable contaminant filters in dilution refrigerators.BACKGROUND OF THE ART

[0003] Dilution refrigerators, which comprise a cryostat and a gas handling system, provide cooling down to millikelvin temperatures. The cryostat is designed to host at least one device and cool down the device to cryogenic temperatures.

[0004] There are significant costs associated with the operation of a dilution refrigerator, and many scaling challenges to provide additional cooling for larger devices. Therefore, improvements are needed.SUMMARY

[0005] In accordance with a first broad aspect, there is provided a dilution refrigerator comprising a cryostat having a plurality of temperature-controlled flanges inside a vacuum chamber, the temperature-controlled flanges operable to be cooled to progressively lower temperatures. A dilution unit having an inlet and an outlet is disposed inside the cryostat and operable to cool at least a subset of the flanges. A pumping arrangement is operatively coupled to the cryostat for circulation of a fluid mixture through the dilution unit along a fluid circulation path. A first contaminant filter having a first inlet and a first outlet is disposed inside the cryostat, in the fluid circulation path. A second contaminant filter having a second inlet and a second outlet is disposed inside the cryostat and connected in series with the first contaminant filter. The first and second contaminant filters are operably connected to the inlet of the dilution unit. A plurality of flow control devices are operable between a first flow position directing the fluid mixture from the pumping arrangement throughthe first and second contaminant filters and the dilution unit, and a second flow position bypassing the first contaminant filter and directing the fluid mixture from the pumping arrangement through the second contaminant filter and the dilution unit.

[0006] The dilution refrigerator as defined above and described herein may further include one or more of the following additional features, in whole or in part, and in any combination.

[0007] In some embodiments, the first contaminant filter is upstream from the second contaminant filter in a direction of flow of the fluid mixture in the first flow position of the flow control devices.

[0008] In some embodiments, at least a first one of the flow control devices is arranged in a fluid recovery path between the first contaminant filter and the pumping arrangement, and is operable to recover fluid mixture from the first contaminant filter when the plurality of flow control devices are in the second flow position.

[0009] In some embodiments, the at least first one of the flow control devices is a tunable flow control device to control flow resistance therethrough.

[0010] In some embodiments, the pumping arrangement comprises circulating pumps to circulate the fluid mixture inside the cryostat, and the fluid recovery path connects the first contaminant filter to the circulating pumps.

[0011] In some embodiments, at least a second one of the flow control devices is arranged in a contaminant removal path between the first contaminant filter and the pumping arrangement, and is operable to remove contaminants from the first contaminant filter when the plurality of flow control devices are in the second flow position.

[0012] In some embodiments, the pumping arrangement comprises vacuum pumps to apply a vacuum to the cryostat, and the contaminant removal path connects the first contaminant filter to the vacuum pumps.

[0013] In some embodiments, the dilution refrigerator further comprises a thermal coupling device between the first contaminant filter and one of the temperature-controlled flanges, the thermal coupling device operable in a conductive mode and a non-conductive mode for selective cooling of the first contaminant filter.

[0014] In some embodiments, the thermal coupling device is disposed on a first side of the temperature-controlled flange and the first contaminant filter extends on a second and opposite side of the temperature-controlled flange.

[0015] In some embodiments, the thermal coupling device is a gas gap heat switch.

[0016] In some embodiments, the dilution refrigerator further comprises a first heat exchanger inside the cryostat thermally coupling the first outlet of the first contaminant filter to the second inlet of the second contaminant filter.

[0017] In some embodiments, the dilution refrigerator further comprises a second heat exchanger inside the cryostat thermally coupling the first outlet of the first contaminant filter to the first inlet of the first contaminant filter.

[0018] In some embodiments, the dilution refrigerator further comprises a third heat exchanger inside the cryostat thermally coupling the outlet of the dilution unit to the first inlet of the first contaminant filter.

[0019] In some embodiments, the third heat exchanger further couples the outlet of the dilution unit to the second inlet of the second contaminant filter.

[0020] In accordance with another broad aspect, there is provided a method for operating a dilution refrigerator having a dilution unit inside a cryostat and a pumping arrangement operable for circulating a fluid mixture through the dilution unit. A fluid mixture is directed through the dilution unit via a fluid circulation path having a first contaminant filter and a second contaminant filter connected in series and disposed inside the cryostat upstream from the dilution unit. The first contaminant filter is removed from the fluid circulation path without interrupting operation of the dilution refrigerator. A cleaning procedure is performed on the first contaminant filter while the fluid mixture is concurrently directed in the fluid circulation path through the second contaminant filter. When the cleaning procedure is completed, the first contaminant filter is reintegrated into the fluid circulation path.

[0021] The method as defined above and described herein may further include one or more of the following additional features, in whole or in part, and in any combination.

[0022] In some embodiments, directing the fluid mixture through the circulation path comprises flowing the mixture through the first contaminant filter prior to flowing the mixture through the second contaminant filter.

[0023] In some embodiments, removing the first contaminant filter from the fluid circulation path comprises closing at least one first flow control device provided between the pumping arrangement and the first contaminant filter and at least one second flow control device provided between the first contaminant filter and the second contaminant filter, and opening at least one third flow control device between the pumping arrangement and the second contaminant filter.

[0024] In some embodiments, performing the cleaning procedure comprises recovering fluid mixture remaining in the first contaminant filter through a fluid recovery path; and extracting contaminants from the first contaminant filter through a contaminant removal path.

[0025] In some embodiments, recovering fluid mixture remaining in the first contaminant filter comprises opening at least one fourth flow control device between the first contaminant filter and the pumping arrangement.

[0026] In some embodiments, extracting contaminants from the first contaminant filter comprises opening at least one fifth flow control device between the first contaminant filter and the pumping arrangement.

[0027] In some embodiments, performing the cleaning procedure comprises uncoupling the first contaminant filter from a temperature-controlled flange inside the cryostat, the temperature-controlled flange acting as a cooling source for the first contaminant filter.

[0028] In some embodiments, the method further comprises cooling the fluid mixture flowing into the second contaminant filter with the fluid mixture flowing out of the first contaminant filter.

[0029] In some embodiments, the method further comprises cooling the fluid mixture flowing into the first contaminant filter with the fluid mixture flowing out of the first contaminant filter.

[0030] In some embodiments, the method further comprises cooling the fluid mixture entering the first contaminant filter with the fluid mixture flowing out of the dilution unit.

[0031] In some embodiments, the method further comprises cooling the fluid mixture entering the second contaminant filter with the fluid mixture flowing out of the dilution unit.

[0032] In some embodiments, the method further comprises using a flow of the fluid mixture exiting at least one of the first contaminant filter and the dilution unit to cool a flow of the fluid mixture entering at least one of the first contaminant filter and the second contaminant filter.

[0033] In accordance with another broad aspect, there is provided a method for cleaning a contaminant filter in a dilution refrigerator having a dilution unit inside a cryostat and a pumping arrangement operable for circulating a fluid mixture through the dilution unit. The method comprises removing, from a fluid circulation path and without interrupting operation of the dilution refrigerator, a first contaminant filter connected in series with a second contaminant filter upstream from the dilution unit. A cleaning procedure is performed on the first contaminant filter while concurrently directing the fluid mixture in the fluid circulation path through the second contaminant filter. The first contaminant filter is reintegrated into the fluid circulation path after the cleaning procedure, andthe fluid mixture is directed in the fluid circulation path through the first contaminant filter and the second contaminant filter.

[0034] The method as defined above and described herein may further include one or more of the additional features recited herein, in whole or in part, in any combination.BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Reference is now made to the drawings, in which:

[0036] FIGS. 1A-1 B are examples of a dilution refrigerator;

[0037] FIG. 2 is a cross-sectional view of an example upstream contaminant filter and thermal coupling device;

[0038] FIGS. 3A-3B show other examples of a dilution refrigerator;

[0039] FIG. 4 is another example of a dilution refrigerator;

[0040] FIG. 5 is another example of a dilution refrigerator;

[0041] FIG. 6 is a flowchart of an example method for operating a dilution refrigerator;

[0042] FIGS 7A-7D are diagrams showing various paths for the fluid mixture and contaminants; and

[0043] FIG. 8 is a block diagram of an example computing device.DETAILED DESCRIPTION

[0044] A dilution refrigerator is a cryogenic system that provides continuous cooling from ambient temperature all the way down to millikelvin temperature. Dilution refrigerators are used in various applications, including low temperature detectors, superconductivity research, low temperature solid state physics, and quantum computing. A fluid circulation system circulates a mixture throughout a cryostat at a pressure that remains below atmospheric pressure. As a result, contaminants leak into the fluid circulation system and must be removed to prevent small passages from getting clogged by frozen contaminants.

[0045] The present disclosure is directed to systems and methods for removing contaminants from the fluid circulation system of a dilution refrigerator. The contaminants are captured by two contaminant filters inside a cryostat of the dilution refrigerator, within a circulation path defined for steady-state operation of the dilution refrigerator. The contaminant filters are provided in a serial configuration, where an upstream contaminant filter performs a first filtering on the fluid mixtureand thus captures a first portion of the contaminants. The fluid mixture then flows through a downstream contaminant filter where a second filtering of the fluid mixture occurs, further removing from the fluid mixture contaminants not captured by the upstream contaminant filter.

[0046] At least one of the two contaminant filters is a filter that can be cleaned without interrupting the operation of the dilution refrigerator. As used herein, a filter that can be cleaned without interrupting operation of the dilution refrigerator is referred to as a regenerable filter. A plurality of flow control devices are provided and coupled to a pumping arrangement. The flow control devices are operable between a first flow position directing the fluid mixture through the two contaminant filters, and a second position bypassing one of the contaminant filters that is regenerable and directing the fluid mixture only through the other contaminant filter.

[0047] When the regenerable filter is bypassed, fluid mixture remaining in the regenerable contaminant filter is recovered by the pumping arrangement, after which contaminants held by the regenerable filter are removed. During the fluid mixture recovery and contaminant removal operations, fluid mixture can continue circulating in the dilution refrigerator and be filtered by the other contaminant filter. After the regenerable filter is cleaned, the regenerable filter may be reintegrated into the flow path of the fluid mixture.

[0048] With reference to Fig. 1A, there is illustrated an example embodiment of a dilution refrigerator 100. A cryostat 102 comprises temperature-controlled flanges, illustratively five flanges 104A, 104B, 104C,104D and 104E defining five temperature stages of decreasing temperature from top to bottom. When the cryostat 102 is in steady-state operation, the flange 104A, also called an outer vacuum chamber, is at room temperature (e.g. 300 K) while flanges 104B, 104C,104D and 104E can, for example, be at 50 K, 4 K, 800 mK, and 8 mK, respectively. These temperatures are exemplary, and other temperature stages may be used. The flanges may serve for supporting radiation shields as well as for thermal anchoring of other components of the cryostat 102. The flanges 104A, 104B, 104C,104D and 104E can be made of plates (where components can be affixed). In some embodiments, the plates also act as radiation shields. Additional thermal anchoring stages which may not take the form of a flange may also be present, for example at the 100 mK stage. Other embodiments may have a different number of flanges at different temperatures. At least one device 108 resides inside a holder 106 thermally anchored to the coldest flange 104E. The device 108 can, for example, be a quantum processor. Note that some of the temperature stages illustrated as flanges in FIG. 1 could also take the shape of an open structure. In some cases, the flanges 104A-104E may take the form of nested enclosures, where the innermost flange is at a lowest temperature and the outermost flange is at a highest temperature, with intermediateflanges being maintained at progressively lower temperatures from the outermost flange towards the innermost flange.

[0049] In some embodiments, the cryostat 102 is a dry cryostat in which cooling of upper stages (e.g. 50 K, 10 K, and 4 K stages) is provided by one or more pulse tube cryocooler 105. Other embodiments for cooling of upper stages may also apply, such as those described in U.S. Patent Application No. 18 / 051 ,992. In some embodiments, the pulse tube cryocooler 105 comprises a first pulse tube 107A providing cooling to a first flange, for example flange 104B, and a second pulse tube 107B providing cooling to a second flange, for example flange 104C. The pulse tubes 107A and 107B are connected to regenerators 109A and 109B (i.e. periodic flow heat exchangers), respectively, through heat exchangers 111 A and 1 11 B, respectively. Note that the heat exchangers 1 11A and 11 1 B are illustrated as if in direct contact with the flanges 104B and 104C, but they could also be in indirect contact with the flanges through thermally conductive elements such as heat straps. Other embodiments, for example having more or less than two pulse tubes 107A, 107B, may also apply.

[0050] Cooling of the lower temperature stages, such as those defined by flanges 104D, 104E, is provided by a dilution unit 110, which is schematically represented by a rectangle in Fig. 1A. The dilution unit 1 10 may comprise a mixing chamber, liquid counter flow (recuperative) heat exchangers, a still and a condenser, which can be a vapor counter flow (recuperative) heat exchanger or a liquid 4He heat exchanger coupled to a liquid 4He bath supplied via a separate circulation circuit. The dilution unit 110 is supplied with fluid mixture through a supply line 125, which is thermally anchored at different temperature stages. A pumping line 130 is used to extract fluid mixture from the dilution unit 110.

[0051] The dilution unit 110 provides cooling power by the energy required to mix two isotopes of helium, liquid 3He and 4He. At low temperature, the mixture of both isotopes separates into two phases: a 3He rich phase and a 4He rich phase. When liquid 3He is circulated into a mixing chamber containing 4He, it mixes with the 4He rich phase which requires energy and thus removes heat from the mixing chamber’s environment.

[0052] Continuous cooling power is produced by circulating 3He, for example using various pumps located in a pumping arrangement 1 18 outside the cryostat 102, such that 3He evaporated from the 3He / 4He mixture is returned to the dilution unit 1 10 to be condensed before entering the mixing chamber again. The dilution unit 110 comprises a condenser to turn the gaseous 3He supply to liquid 3He. The condenser can be a recuperative heat exchanger cooled by the enthalpy of the 3He evaporated from the still. Alternatively, the condenser can be a heat exchanger cooled by a liquid 4He bath at a temperature of about 1 K.

[0053] In operation, the dilution unit 110 and the 3He supply are first cooled from room temperature, and then maintained at temperatures close to liquid Helium temperature (4.2 K) to allow for the liquefaction of the incoming 3He supply in the condenser.

[0054] In cases where the device 108 employs electronic control from outside the cryostat 102, as is the case for quantum processors, the cryostat 102 can be wired with control cables thermally anchored at each temperature stage through various heat exchangers.

[0055] During steady-state operation, the pumping arrangement 118 circulates the fluid mixture into the cryostat through the supply line 125. The fluid mixture circulates through an upstream contaminant filter 114 followed by a downstream contaminant filter 112. The fluid mixture then flows into the dilution unit 110 through inlet 126 and back out of the dilution unit 110 through outlet 128 to return to the pumping arrangement 118 through the pumping line 130. Flow control devices 124A, 124B are in an open position to allow the fluid mixture to flow therethrough. Flow control device 124C is in a closed position to prevent the fluid mixture from flowing therethrough. In response to a trigger, which may be a manual trigger or an automated trigger such as a timing signal or a sensor signal (e.g., temperature sensor or others), flow control devices 124A, 124B are changed to a closed position to prevent the fluid mixture from flowing therethrough. Flow control device 124C is set to an open position to allow the fluid mixture in the supply line 125 to flow through the downstream contaminant filter 112 and bypass the upstream contaminant filter 114.

[0056] When the upstream contaminant filter 114 is removed from the fluid circulation path, it may be desirable to recover fluid mixture contained in the upstream contaminant filter 114 and its piping before cleaning the upstream contaminant filter 114. The remaining fluid mixture is mainly 3He, a valuable gas that can be recovered and reinjected into the fluid circulation path. A fluid recovery path is provided between the upstream contaminant filter 114 and the pumping arrangement 118 for recovery of the remaining fluid mixture. Flow control device 124D controls flow of the remaining fluid mixture from the upstream contaminant filter 114 to the pumping arrangement 118 in the fluid recovery path.

[0057] In some embodiments, the pumping line 130 is used for recovery of the remaining fluid mixture, and flow control device 124D comprises an on / off valve 127A and a modulated valve 127B. The modulated valve 127B is used to ensure minimal disruption to the flow of fluid mixture through the pumping arrangement 118 by gradually decreasing the flow resistance from the upstream contaminant filter 114 to the pumping arrangement 118 as the upstream containment filter 114 is evacuated. Thus, the modulated valve 127B minimizes the change in pressure within the inlet line 130 and outlet line 125 of the pumping arrangement 118 during mixture recovery. In someembodiments, the modulated valve 127B is maintained at its initial flow resistance (instead of being gradually decreased) and the fluid recovery operation takes longer.

[0058] Alternatively, the fluid recovery path may be provided separately from the pumping line 130 and only require a standard on / off type valve to control the flow of fluid mixture in the fluid recovery path. However, by integrating the pumping line 130 into the fluid recovery path, this allows circulating pumps 120A used in the pumping arrangement 118 for circulating the fluid mixture through the dilution unit 110 during steady-state operation to also be used for recovery of the remaining fluid mixture in the upstream contaminant filter 114. The arrangement also allows the recovered fluid mixture to be reinjected into the fluid circulation path more easily via the pumping arrangement 118.

[0059] A contaminant removal path is provided between the upstream contaminant filter 114 and the pumping arrangement 118 for removal of the contaminants from the upstream contaminant filter 1 14. Flow control device 124E controls flow of the collected contaminants in the contaminant removal path. In some embodiments, the contaminants are pumped out of the upstream contaminant filter 114 by cryostat vacuum pumps 120B and released externally to the dilution refrigerator 100 through an outlet 122. Cryostat vacuum pumps 120B are used during the initial cool down of the dilution refrigerator 100 to evacuate the cryostat 102.

[0060] In some embodiments, the upstream contaminant filter 1 14 is a cold trap comprising an adsorbent filtering material to which contaminants adhere when the fluid mixture flowing therethrough is sufficiently cold. The upstream contaminant filter 1 14 is thus cooled by a cooling source for operation thereof. A thermal coupling device 116 may be provided between the upstream contaminant filter 1 14 and a flange of the cryostat 102, for example flange 104B, whereby the flange acts as the cooling source. The thermal coupling device 116 is operable in a conductive mode to establish a thermal path from the flange 104B to the upstream contaminant filter 114. The thermal coupling device 116 is also operable in a non-conductive mode to remove the thermal path from the flange 104B to the upstream contaminant filter 1 14. In this manner, the upstream contaminant filter 114 may be cooled by the flange 104B for operation thereof, and cooling is interrupted when the upstream contaminant filter 114 is cleaned for removal of contaminants therefrom.

[0061] Referring back to Fig. 1A, the downstream contaminant filter 1 12 may be a filter of any known design capable of filtering the targeted contaminants in the cryogenic environment, including a cold trap as described herein with regards to the upstream contaminant filter 1 14. It may be cooled using, for example, the 50K flange 104B of the cryostat 102. In some embodiments, the downstream contaminant filter 112 is composed of a series of vessels mounted at increasingly lower temperatures (e.g. 50K, 35K, 20K) and connected by tubing in series. This may be done, forexample, to more effectively trap contaminants that are harder to target due to their lower boiling point, such as Hydrogen.

[0062] In some embodiments, the downstream contaminant filter 112 is cleaned prior to each cooldown of the dilution refrigerator 100 and / or after each warmup of the dilution refrigerator 100, and thus does not need any mechanism to break the thermal path with the cooling source. Given the position of the downstream filter 112 as a secondary filter when the upstream filter 114 is in use, its cleaning frequency may be reduced compared to the upstream filter 114, thus reducing downtime for the dilution refrigerator 100. The downstream contaminant filter 112 may also have a filtering capacity that is greater than the upstream contaminant filter 114, to ensure proper filtering when the upstream contaminant filter 1 14 is offline and a less frequent need for cleaning.

[0063] In some embodiments, and as shown in the example of Fig. 1A, the upstream contaminant filter 114 is regenerable and the downstream contaminant filter 1 12 is not regenerable. In some embodiments, the downstream contaminant filter 112 is regenerable, such that it may be cleaned without interrupting operation of the dilution refrigerator, and the upstream contaminant filter 114 is not regenerable. One such example is illustrated in Fig. 1 B. The fluid mixture circulates through the upstream contaminant filter 114 and the downstream contaminant filter 1 12 when flow control devices 124A, 124B, and 124F are open, and flow control devices 124G, 124D, and 124E are closed. The downstream contaminant filter 1 12 may be removed from the fluid circulation path by closing flow control devices 124B and 124F, and opening flow control device 124G. Fluid mixture remaining in the downstream contaminant filter 112 may be recovered by opening flow control device 124D. Contaminants may be extracted from the downstream contaminant filter 112 by opening flow control device 124E. The downstream contaminant filter 112 may be thermally uncoupled from the flange 104B using thermal coupling device 116 for cleaning.

[0064] In some embodiments, both the upstream and downstream contaminant filters 112, 114 are regenerable, and the flow control devices are arranged to allow each filter 112, 1 14 to be selectively taken out of the circulation path for mixture recovery and / or cleaning thereof. The upstream contaminant filter 1 14 may be cleaned at first intervals and the downstream contaminant filter 1 12 may be cleaned at second intervals greater than the first intervals, due to the second contaminant filter 112 being exposed to an already partially filtered fluid mixture. Alternatively, the cleaning intervals for the upstream contaminant filter 114 and the downstream contaminant filter 1 12 are the same.

[0065] An example embodiment of a regenerable contaminant filter, for example the upstream contaminant filter 1 14, is shown in Fig. 2. An outer housing 200 defines a cavity 202 filled with the adsorbent filtering material, which may be activated charcoal, mesh cloth, or any other materialeffective to trap the specific contaminant targeted herein. In some embodiments, the fluid mixture flows into the cavity 202 through a flow channel 204. The fluid mixture is received in the flow channel 204 through an inlet 206. The flow channel 204 may be made of a conductive material to act as a heat exchanger. The flow channel 204 may also be filled with a high surface area material, such as mesh, to enhance heat extraction from the fluid mixture as it enters the upstream contaminant filter 114 and is drawn into the cavity 202. Contaminants are adsorbed on the surface of the heat exchange material inside the flow channel 204 as well as on the adsorbent material in cavity 202 before the fluid mixture exits the filter 114 through an outlet 208.

[0066] The thermal coupling device 116 is used to ensure that the upstream contaminant filter 114 is cold enough to capture the contaminants on the surface of the adsorbent material during operation of the upstream contaminant filter 114. The thermal coupling device 116 is coupled to the upstream contaminant filter 114, for example, through the flange 104B. In some embodiments, the thermal coupling device 116 is a gas gap heat switch. A body 210 comprises two conductive blocks separated by a small gas layer which can be selectively injected or removed. The presence of the gas between the conductive blocks allows heat to flow freely therebetween. One part of the body 210 is connected to the element to be cooled, namely the filter 114. The other part of the body 210 is connected to the cooling source. In the present example, the cooling source is the 50K flange 104B of the cryostat 102 but other cooling sources may be used.

[0067] In some embodiments, the upstream contaminant filter 114 is mounted above the flange 104B and the thermal coupling device 116 extends below the flange 104B. In other embodiments, the upstream contaminant filter 114 is mounted below the flange 104B and the thermal coupling device 116 extends above the flange 104B. Alternatively, both the upstream contaminant filter 114 and the thermal coupling device 116 may be on a same side of the flange 104B, with the thermal coupling device 116 in contact with the flange 104B and coupled to the upstream contaminant filter 114.

[0068] The thermal coupling device 116 may comprise a substance held by an adsorbent in a cavity 216 defined in a base 212. A heater 218 is used to release the adsorbed substance into gaseous form, thus causing the gas to flow through a passage 220 into the space between the two conductive blocks in the base 210. In some embodiments, passage 220 acts to thermally anchor the cavity 216 to the portion of the body 210 that is connected to the cooling source. When the heater 218 is turned off, the cavity 216 is cooled by the cooling source and the substance is once again adsorbed inside the cavity 216, thus retreating from the space between the two conductive blocks. In some embodiments, the cavity 216 can be thermally coupled to another cooling source, such as the first or second stage of the pulse tube cryocooler. The adsorbent and substance arechosen to ensure nearly complete adsorption at a temperature that is above, but not too far above, the operating point of the cooling source. In the present example, the cooling source is the 50K flange 104B. The substance is selected to be Neon and the adsorbent is selected to be activated charcoal. Other embodiments for the substance, adsorbent and cooling source may also apply.

[0069] In some embodiments, the presence of the gas in the body 210 is controlled using a cryopump inside the cavity 216. Heating of the cryopump by the heater 218 causes the gas to be released. When the heater 218 is turned off, the cryopump is in the off state, allowing the gas to be adsorbed by charcoal inside the cryopump. Other embodiments for controlling the gas gap heat switch are also considered.

[0070] A heater 222 may be provided on the upstream contaminant filter 114 in order to allow the upstream contaminant filter 1 14 to increase its temperature, thus causing frozen or adsorbed contaminants to unfreeze and be free to extract therefrom. A temperature sensor 224 may also be used to monitor the temperature of the upstream contaminant filter 1 14 during operation as well as during cleaning. Piping 226 used to bring the fluid mixture into the upstream contaminant filter 114 may have an end thermally integrated into the housing 200 of the upstream contaminant filter 114 to ensure proper cleaning of the piping 226 and remove any frozen contaminants therefrom, since the piping 226 will get heated when the upstream contaminant filter 114 is heated by the heater 222.

[0071] With reference to the pumping arrangement 118 shown in Figs. 1A, 1 B, it may comprise one or more pump(s) 120A, 120B. The vacuum pump(s) 120B may comprise rotary vane vacuum pump(s), diaphragm vacuum pump(s), liquid ring vacuum pump(s), scroll vacuum pump(s), and turbomolecular vacuum pump(s). The circulating pumps 120A may comprise a high vacuum pump, such as a turbomolecular pump, and an appropriately sized backing pump, for example a scroll pump. Other embodiments may also apply based on a desired vacuum level and other specifications of the dilution refrigerator 100. The pumping arrangement 1 18 is coupled to a controller 150 that is configured for operating the flow control devices, and thus opening and closing various flow paths for the fluid mixture.

[0072] The flow control devices may be provided entirely externally from the cryostat 102. Any flow control device outside of the cryostat 102 may be any type of on-off or modulated valve, operable to allow and prevent the flow of fluid therethrough. In some embodiments, the valves are actuated valves, such as linear valves, rotary valves, and self-actuated valves, and may be manual or automated. In some embodiments, the valves are fast acting on / off valves with built-in actuators, such as but not limited to solenoid valves, coaxial valves, and angle seat valves. Alternatively, one or more of the flow control devices may be disposed inside the cryostat 102. Any flow control deviceinside the cryostat 102 may be a cryogenic valve designed to be used at very low temperatures. In some embodiments, the cryogenic valves are cryogenic ball valves, cryogenic butterfly valves, cryogenic gate valves, cryogenic globe valves, cryogenic check valves or cryogenic relief valves, which may be manual or automatic.

[0073] Figs. 3A and 3B show example arrangements where cryogenic valve 124B has been replaced with non-cryogenic valve 324B, disposed outside of the cryostat 102. As such, the fluid mixture is effectively cooled twice, once as it enters the upstream contaminant filter 114 and then once more as it enters the downstream contaminant filter 112. This can increase the thermal loading on the first stage of the pulse tube cryocooler 105. In some embodiments, this effect is countered by using the flow of fluid mixture exiting the upstream contaminant filter 114 to cool the flow of fluid mixture entering the downstream contaminant filter 112 through a heat exchanger 304, as shown in Fig. 3A. Although cooling through heat exchanger 304 is not available when the upstream contaminant filter 1 14 is offline for cleaning and / or mixture recovery, the increased load on the pulse tube cryocooler 105 has been removed in this case, as the fluid mixture flows from the pumping arrangement 1 18 directly to the downstream contaminant filter 112 through flow control device 124C in supply line 125. Furthermore, since heat exchanger 304 is coupled to the outlet line of the upstream contaminant filter 114 and not to the body of the upstream contaminant filter 114, the heat exchanger 304 will not become a source of heat for the fluid mixture entering the downstream contaminant filter 112 when the upstream contaminant filter 114 is offline for cleaning and / or mixture recovery. In another example embodiment shown in Fig. 3B, the inlet and outlet of the upstream contaminant filter 114 are coupled with a heat exchanger 305, such that the fluid mixture in the inlet of the first contaminant filter 1 14 is cooled by fluid mixture in the outlet of the first contaminant filter 114. In some embodiments, heat exchangers 304, 305 are used concurrently.

[0074] Various configurations may be used for the flow circulation path of the fluid mixture, with heat exchangers provided at various positions for targeted cooling of the fluid mixture. For example, a heat exchanger 300 anchored at flange 104B may further cool the fluid mixture as it enters the downstream contaminant filter 112. The fluid mixture may then flow through another heat exchanger 302 wrapped around the regenerator 109B of the pulse tube 107B and then through another heat exchanger 1 11 B anchored to flange 104C. Additional heat exchangers may be provided in the dilution unit 100, for example a recuperative heat exchanger above the still of the dilution unit, one or more recuperative heat exchanger between the still and the mixing chamber.

[0075] Another example embodiment for cooling the fluid mixture is shown in Fig. 4. The inputs and outputs to the upstream contaminant filter 114 have been simplified such that there is a single input and a single output. When the upstream contaminant filter 114 is online, flow control devices124A, 324B are open, flow control devices 124C, 124E, 124D are closed. The fluid mixture flows from the pumping arrangement 118 into the upstream contaminant filter 114 through flow control device 124A. The fluid mixture flows from the upstream contaminant filter 114 to the downstream contaminant filter 112 through flow control device 324B. Heat exchanger 304 is used to recover some of the cold lost when the fluid mixture exits the cryostat to flow through flow control device 324B and into the path 403. When the upstream contaminant filter 114 is taken offline for fluid mixture recovery and / or cleaning, flow control devices 124A, 324B are closed and flow control device 124C is opened. The flow to the dilution unit 110 is uninterrupted.

[0076] In a fluid mixture recovery mode, flow control device 124D is opened and the fluid mixture remaining in the upstream contaminant filter 114 flows through the fluid mixture recovery path into the pumping arrangement 118. In a filter cleaning mode, flow control device 124D is closed and flow control device 124E is opened and the contaminants are pumped out of the upstream contaminant filter 114 by the pumping arrangement 118, for release externally to the dilution refrigerator 100.

[0077] A heat exchanger 402 uses the flow exiting the dilution unit 110 to cool down the flow entering the upstream contaminant filter 114. The cooling power available from the flow exiting the dilution unit 110 is much greater than that required to cool the flow entering the upstream contaminant filter 114, such that the flow may be pre-cooled prior to reaching the upstream contaminant filter 114. When heat exchanger 402 is used concurrently with heat exchanger 304, the cooling power required by the first stage of the pulse tube cryocooler 105 may be reduced significantly.

[0078] Another embodiment, shown in Fig. 5, further uses the cooling power available from the flow exiting the dilution unit 110. A heat exchanger 502 may be used to cool the flow entering the downstream contaminant filter 112 and to cool the flow entering the upstream contaminant filter 114. In this scenario, heat exchanger 304 may or may not be used. Although illustrated as a single component, heat exchanger 502 may be composed of separate components, with one component coupling the outlet 128 of the dilution unit 110 to the input of the upstream contaminant filter 114, and another separate component coupling the outlet 128 of the dilution unit 110 to the input of the downstream contaminant filter 112. In some embodiments, only the component coupling the outlet 128 of the dilution unit 110 to the input of the downstream contaminant filter 112 is used.

[0079] Operating and maintaining dilution refrigerators is complex, and it is desirable to move towards increasingly more user-friendly, automated, ergonomic, and low-maintenance systems. In the embodiments described herein, the two filters 112, 114 inside the cryostat 102 remove the need for additional filtering performed externally from the cryostat 102. The series configuration of having an upstream and a downstream filter avoids an architecture where only one filter is ever inuse, as would be for two filters connected in parallel. The parallel configuration is inefficient, takes up space in the cryostat, and requires additional parts. The series configuration also allows an architecture where one of the two filters is regenerable and can be taken out of the fluid circulation path for cleaning without interrupting operation of the system. It also simplifies cleaning and mixture recovery operations for the regenerable filter. It will be understood that more than two filters may be provided inside the cryostat 102 to perform the filtering of the fluid mixture as it circulates therethrough. Additional regenerable and / or non-regenerable filters may be provided throughout the fluid circulation path.

[0080] With reference to Fig. 6, there is illustrated a method 600 for operating a dilution refrigerator as described herein. The method 600 may be performed, for example by the controller 150 via operation of the pumping arrangement 1 18 and the flow control devices. At step 602, fluid mixture is directed through the dilution unit inside the cryostat. The dilution unit sits in a fluid circulation path and is coupled to the pumping arrangement operable to circulate the fluid mixture in the fluid circulation path. Upstream from the dilution unit and downstream from the pumping arrangement are first and second contaminant filters connected together in series. An example fluid circulation path 700 is shown in Fig. 7A. In this simplified diagram, the fluid mixture flows along the fluid circulation path 700 from a pumping arrangement 702 to the upstream contaminant filter 704, the downstream contaminant filter 706, the dilution unit 708, and back to the pumping arrangement 702.

[0081] Referring back to Fig. 6, at step 604 the first contaminant filters is removed from the circulation path. An example is shown in Fig. 7B, where the upstream contaminant filter 704 is removed from the circulation path 700. It will be understood that the first contaminant filter may be the upstream 704 orthe downstream 706 filter of the series connection. In some embodiments, the first contaminant filter is removed from the fluid circulation path 700 by closing at least one flow control device provided between the pumping arrangement and the first contaminant filter, and closing at least one other flow control device provided between the first contaminant filter and the second contaminant filter. Flow of the fluid mixture through the fluid circulation path is maintained by opening at least one flow control device provided between the pumping arrangement and the second contaminant filter, which may be for example along a supply line of the dilution refrigerator.

[0082] Referring back to Fig. 6, a cleaning procedure is performed on the first contaminant filter at step 606, and the fluid mixture is concurrently directed though the fluid circulation path through the second contaminant filter at step 608. In some embodiments, the cleaning procedure comprises recovering fluid mixture remaining in the first contaminant filter through a fluid recovery path. For example, one or more flow control device may be opened between the first contaminant filter andthe pumping arrangement to allow remaining fluid mixture to circulate from the first contaminant filter to the pumping arrangement in the fluid recovery path. An example is shown Fig. 7C, where a fluid recovery path 710 is provided between the upstream contaminant filter 704 and the pumping arrangement 702. Fluid mixture still flows through the fluid circulation path 700.

[0083] In some embodiments, the cleaning procedure comprises extracting contaminants from the first contaminant filter through a contaminant removal path. For example, one or more flow control device may be opened between the first contaminant filter and the pumping arrangement to allow contaminants to flow from the first contaminant filter to the pumping arrangement in the contaminant removal path. An example is shown in Fig. 7D, where a contaminant removal path 712 is provided between the upstream contaminant filter 704 and the pumping arrangement 702. In some embodiments, the fluid recovery path 710 and the contaminant removal path 712 are separate and comprise different flow control devices. This allows, for example, the remaining fluid mixture to be pumped by circulating pumps of the pumping arrangement and returned into the circulating path, and the contaminants to be pumped by cryostat vacuum pumps and released externally to the dilution refrigerator.

[0084] In some embodiments, the first contaminant filter is uncoupled from a cold source as part of the cleaning procedure. The first contaminant filter may further be heated to further assist in removing the contaminant therefrom.

[0085] Referring back to Fig. 6, the first contaminant filter is reintegrated into the fluid circulation path at step 610 once the cleaning procedure is completed. This may be done, for example, by closing any flow control device outside the fluid circulation path, closing the flow control devices between the pumping arrangement and the second contaminant filter, and opening flow control devices between the pumping arrangement and the first contaminant filter and between the first contaminant filter and the second contaminant filter. After step 610, the dilution refrigerator may continue operating in steady-state.

[0086] In accordance with some embodiments of the method 600, no fluid mixture is lost during the cleaning procedure due to the ability to recover remaining fluid mixture from the first contaminant filter. Furthermore, no additional pumps are required for fluid mixture recovery or for contaminant removal as the existing pumps of the dilution refrigerator may be used to perform both operations.

[0087] In some embodiments, it may be desirable to recover cooling power inside the cryostat using various heat exchangers. This can reduce the thermal load on the pulse tube or any other mechanism used to cool the upper stages of the cryostat. In one exemplary embodiment, the fluidmixture flowing into the second contaminant filter is cooled by the fluid mixture flowing out of the first contaminant filter using a heat exchanger. In another exemplary embodiment, the fluid mixture entering the first contaminant filter is cooled by the fluid mixture flowing out of the first contaminant filter. In yet another exemplary embodiment, the fluid mixture entering the first contaminant filter is cooled by the fluid mixture exiting the dilution unit using another heat exchanger. In yet another embodiment the fluid mixture entering the second contaminant filter is cooled by the fluid mixture exiting the dilution unit using yet another heat exchanger. In some embodiments, multiple ones of these heat exchangers are used.

[0088] FIG. 8 is an example computing device 800 for implementing the controller 150 in accordance with various embodiments. The controller 150 can be provided as a computing unit of the dilution refrigerator 100, either separately therefrom or integrated therewith. As depicted, the computing device 800 includes at least one processor 802, one or more memory 804, at least one I / O interface 806, and at least one network interface 808. Processor 802 may be an Intel or AMD x86 or x64, PowerPC, ARM processor, or the like. Memory 804 may include a suitable combination of computer memory that is located either internally or externally such as, for example, random-access memory (RAM), read-only memory (ROM), integrated memory, compact disc read-only memory (CDROM).

[0089] One or more I / O interface 806 enables the computing device 800 to interconnect with one or more input devices, such as a keyboard, mouse, camera, touch screen and a microphone, or with one or more output devices such as a display screen and a speaker. This interface can be used, for example, for receiving command controls from an operator of the dilution refrigerator 100.

[0090] One or more network interface 808 enables the computing device 800 to communicate with other components, for example, through an API to exchange data with other components, to access and connect to network resources, to serve applications, and perform other computing applications by connecting to a network (or multiple networks) capable of carrying data including the Internet, Ethernet, plain old telephone service (POTS) line, public switch telephone network (PSTN), integrated services digital network (ISDN), digital subscriber line (DSL), coaxial cable, fiber optics, satellite, mobile, wireless (e.g., Wi-Fi, WiMAX), SS7 signaling network, fixed line, local area network, wide area network, and others.

[0091] In some embodiments, the computing device 800 is a Programmable Logic Controller (PLC) which has the capacity for sending and receiving digital signals and analog signals, as well as communicating with devices using Ethernet and serial communication. In some embodiments, the computing device 800 contains relay modules capable of switching low power DC components,such as heaters, on and off. The processor 802 may be a PLC Central Processing Unit (CPU). The inputs to the PLC may be, for example, pressure readings, temperature readings, status of devices (pumps, pulse tubes, valves, etc.), critical parameters (pump speed, pulse tube oil temperature, etc.), pneumatic switch status, and valve position. The PLC may be used to control, for example, valves, pumps, heaters, and pulse tube compressor.

[0092] The described embodiments and examples are illustrative and non-limiting. Practical implementation of the features may incorporate a combination of some or all of the aspects, and features described herein should not be taken as indications of future or existing product plans. Applicant partakes in both foundational and applied research, and in some cases, the features described are developed on an exploratory basis.

[0093] The term "connected" or "coupled to" may include both direct coupling (in which two elements that are coupled to each other contact each other) and indirect coupling (in which at least one additional element is located between the two elements).

[0094] Although the embodiments have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the scope. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification.

[0095] As one of ordinary skill in the art will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

[0096] As can be understood, the examples described above and illustrated are intended to be exemplary only.

Claims

CLAIMS1 . A dilution refrigerator comprising: a cryostat having a plurality of temperature-controlled flanges inside a vacuum chamber, the temperature-controlled flanges operable to be cooled to progressively lower temperatures; a dilution unit disposed inside the cryostat and operable to cool at least a subset of the temperature-controlled flanges, the dilution unit having an inlet and an outlet; a pumping arrangement operatively coupled to the cryostat for circulation of a fluid mixture through the dilution unit along a fluid circulation path; a first contaminant filter, having a first inlet and a first outlet, disposed inside the cryostat in the fluid circulation path; a second contaminant filter, having a second inlet and a second outlet, disposed inside the cryostat, the second contaminant filter connected in series with the first contaminant filter, the first and second contaminant filters operably connected to the inlet of the dilution unit; and a plurality of flow control devices operable between a first flow position directing the fluid mixture from the pumping arrangement through the first and second contaminant filters and the dilution unit, and a second flow position bypassing the first contaminant filter and directing the fluid mixture from the pumping arrangement through the second contaminant filter and the dilution unit.

2. The dilution refrigerator of claim 1 , wherein the first contaminant filter is upstream from the second contaminant filter in a direction of flow of the fluid mixture in the first flow position of the flow control devices.

3. The dilution refrigerator of claims 1 or 2, wherein at least a first one of the flow control devices is arranged in a fluid recovery path between the first contaminant filter and the pumping arrangement, and is operable to recover the fluid mixture from the first contaminant filter when the plurality of flow control devices are in the second flow position.

4. The dilution refrigerator of claim 3, wherein the pumping arrangement comprises circulating pumps to circulate the fluid mixture inside the cryostat, and the fluid recovery path connects the first contaminant filter to the circulating pumps.

5. The dilution refrigerator of any one of claims 1 to 4, wherein at least a second one of the flow control devices is arranged in a contaminant removal path between the first contaminant filter andthe pumping arrangement, and is operable to remove contaminants from the first contaminant filter when the plurality of flow control devices are in the second flow position.

6. The dilution refrigerator of claim 5, wherein the pumping arrangement comprises vacuum pumps to apply a vacuum to the cryostat, and the contaminant removal path connects the first contaminant filter to the vacuum pumps.

7. The dilution refrigerator of any one of claims 1 to 6, further comprising a thermal coupling device between the first contaminant filter and one of the temperature-controlled flanges, the thermal coupling device operable in a conductive mode and a non-conductive mode for selective cooling of the first contaminant filter.

8. The dilution refrigerator of any one of claims 1 to 7, further comprising a first heat exchanger inside the cryostat thermally coupling the first outlet of the first contaminant filter to the second inlet of the second contaminant filter.

9. The dilution refrigerator of any one of claims 1 to 8, further comprising a second heat exchanger inside the cryostat thermally coupling the first inlet of the first contaminant filter to the first outlet of the first contaminant filter.

10. The dilution refrigerator of any one of claims 1 to 9, further comprising a third heat exchanger inside the cryostat thermally coupling the outlet of the dilution unit to the first inlet of the first contaminant filter.1 1 . The dilution refrigerator of claim 10, wherein the third heat exchanger further couples the outlet of the dilution unit to the second inlet of the second contaminant filter.

12. A method for operating a dilution refrigerator having a dilution unit inside a cryostat and a pumping arrangement operable for circulating a fluid mixture through the dilution unit, the method comprising: directing the fluid mixture through the dilution unit via a fluid circulation path having a first contaminant filter and a second contaminant filter connected in series and disposed inside the cryostat upstream from the dilution unit; removing the first contaminant filter from the fluid circulation path without interrupting operation of the dilution refrigerator;performing a cleaning procedure on the first contaminant filter while concurrently directing the fluid mixture in the fluid circulation path through the second contaminant filter; and reintegrating the first contaminant filter into the fluid circulation path when the cleaning procedure is completed.

13. The method of claim 12, wherein directing the fluid mixture through the fluid circulation path comprises flowing the mixture through the first contaminant filter prior to flowing the mixture through the second contaminant filter.

14. The method of claims 12 or 13, wherein removing the first contaminant filter from the fluid circulation path comprises closing at least one first flow control device provided between the pumping arrangement and the first contaminant filter and at least one second flow control device provided between the first contaminant filter and the second contaminant filter, and opening at least one third flow control device between the pumping arrangement and the second contaminant filter.

15. The method of any one of claims 12 to 14, wherein performing the cleaning procedure comprises: recovering fluid mixture remaining in the first contaminant filter through a fluid recovery path; and extracting contaminants from the first contaminant filter through a contaminant removal path.

16. The method of claim 15, wherein recovering fluid mixture remaining in the first contaminant filter comprises opening at least one fourth flow control device between the first contaminant filter and the pumping arrangement.

17. The method of claims 15 or 16, wherein extracting the contaminants from the first contaminant filter comprises opening at least one fifth flow control device between the first contaminant filter and the pumping arrangement.

18. The method of any one of claims 12 to 17, wherein performing the cleaning procedure comprises uncoupling the first contaminant filter from a temperature-controlled flange inside the cryostat, the temperature-controlled flange acting as a cooling source for the first contaminant filter.

19. The method of any one of claims 12 to 18, further comprising using a flow of the fluid mixture exiting at least one of the first contaminant filter and the dilution unit to cool a flow of the fluid mixture entering at least one of the first contaminant filter and the second contaminant filter.

20. A method for cleaning a contaminant filter in a dilution refrigerator having a dilution unit inside a cryostat and a pumping arrangement operable for circulating a fluid mixture through the dilution unit, the method comprising: removing, from a fluid circulation path and without interrupting operation of the dilution refrigerator, a first contaminant filter connected in series with a second contaminant filter upstream from the dilution unit; performing a cleaning procedure on the first contaminant filter while concurrently directing the fluid mixture in the fluid circulation path through the second contaminant filter; and reintegrating the first contaminant filter into the fluid circulation path after the cleaning procedure and directing the fluid mixture in the fluid circulation path through the first contaminant filter and the second contaminant filter.

Images