JP2006046896A - Lossless cryogen cooling device for cryostat configuration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To permit operation with no or little cryogen loss, without (or with minimum) adjustment, even if several cryogens are used, by enabling easy retrofitting into existing cryostat configurations, in particular, those containing superconducting magnets. <P>SOLUTION: A cooling device 7 for reliquefying cryogenic gases, comprising an outer jacket 8 which delimits a vacuum chamber 9, and a cryocooler cold head 10 installed therein, which has at least two cold stages 11 and 12 and is at least partially surrounded by a radiation shield 13, is characterized in that at least two cold stages of the cold head are separately individually connected in a heat conducting manner to heat transferring devices 14a and 14b which can be inserted into neck or suspension tubes 3a and 3b of a cryostat 1 for keeping at least two different cryogenic liquids 18a and 18b. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an apparatus for cooling a reliquefied refrigerant gas, the apparatus comprising an outer jacket defining a vacuum chamber and a cryogenic refrigerator cold head installed in the jacket, the cold head comprising at least two cold stages. And at least partially surrounded by a radiation shield.

  Patent Documents 1-10 describe cooling a superconducting magnet system with little or no refrigerant loss by using a low-temperature refrigerator.

  For example, the cold head of a two-stage cryogenic refrigerator has its first cold stage firmly connected to the radiation shield and allows the second cold stage to conduct heat directly to the helium vessel or via a fixed thermal bridge. To be connected, it is usually installed in a separate sleeve assembly under vacuum (e.g. as described in U.S. Pat. No. 6,057,049) or in a cryostat vacuum chamber (e.g. as described in U.S. Pat. The helium container holds the superconducting magnet in liquid helium. Helium evaporates due to external heat input, but helium can be recondensed at the low temperature contact surface in the helium container to compensate for the overall heat input to the helium container, resulting in almost no loss of system refrigerant. Driving is done without doing. Instead, for example, as described in Patent Document 9, a cold head can be inserted into a neck tube. This neck tube connects an outer vacuum sleeve of a cryostat to a helium vessel, and helium gas is used. be satisfied. The first cold stage of the two-stage cold head is in fixed and thermal contact with the radiation shield, and the second cold stage is suspended freely in a helium atmosphere to directly liquefy evaporated helium.

  These have some drawbacks. That is, the design and construction of the cryostat requires labor and the design and construction are complicated, and further heat input to the cold head is generated by the installation of a further sleeve that accommodates the cold head of the low-temperature refrigerator. When an additional neck tube is used for the cold head, additional heat is transferred to the helium vessel and the cold head of the refrigerator by heat conduction and helium gas convection in the helium gas column and tube wall. Furthermore, a fixed, rigid or flexible thermal element is connected between the cold head and the cryostat, and the vibration of the cold head is transmitted to the cryostat by this thermal element. Furthermore, in the temperature range lower than 10K, the magnetic regenerator material is usually used in the second stage regenerator of the cold head of a low-temperature refrigerator such as a pulse tube refrigerator or a Gibbe-McMaan refrigerator, It may be relatively close to the magnetic center of the NMR magnet system. As a result, the regenerator must generally be shielded in order to prevent magnetic field disturbances at the location of the NMR sample and to prevent the regenerator from functioning. Finally, when a low-temperature refrigerator fails, an unstable state occurs, and the temperature of a cryostat component such as a radiation shield changes continuously until a new equilibrium state is reached. For example, in a magnet system for high resolution nuclear magnetic resonance (NMR) spectroscopy, the shim state of the magnet constantly changes, and in the worst case, the magnet is demagnetized and quenches, thus preventing NMR measurements.

  One way to achieve a semi-lossless refrigerant system while solving these problems requires the use of a device cooled by a low-temperature refrigerator. This device can be used to reliquefy a single evaporative refrigerant. For example, in a cryostat device that is conventionally used in a superconducting magnet system, the magnet is usually installed in a container filled with 4.2 K of liquid helium. To minimize external heat input to the helium vessel, the helium vessel is generally surrounded by a radiation shield that is cooled with boil-off gas and another shield that is cooled with liquid nitrogen. In addition, liquid helium and nitrogen must be refilled at regular intervals for passive cooling with evaporative refrigerant.

  In Patent Documents 11 and 12, a heat transfer device of a heat tube type is inserted into a neck tube or a suspension tube of a nitrogen vessel having an existing cryostat structure, and this heat tube is connected to a cold head of a low-temperature refrigerator to recycle evaporated nitrogen. It is proposed to liquefy (see also Non-Patent Document 1). The liquefaction device is directly flanged to the cold head of the single-stage pulse tube refrigerator and is composed of a thin tube. Nitrogen vapor rises in this tube and is liquefied on the cold surface in contact with the cold head, It flows down along the tube wall. This very thin tube is surrounded by a vacuum sleeve in its upper region and can be inserted directly into a nitrogen neck tube or suspension tube to prevent or reduce nitrogen evaporation and nitrogen loss. Here, only nitrogen is reliquefied, and therefore helium loss is not a problem.

  Similarly, reliquefaction of only helium is performed in a helium storage vessel using a cold head of a two-stage cryogenic refrigerator.

  In either case (nitrogen liquefaction device or helium liquefaction device), the cold head of the cryocooler is in the outer jacket that defines the vacuum chamber. When a multi-stage cryocooler is used, the cold head part is usually surrounded by a radiation shield, which is in contact with the cold stage (not the coldest cold stage), and the cold head is protected from thermal radiation in the low temperature region. Good insulation.

As described above, various cryostat structures conventionally used in magnet systems, particularly in high resolution nuclear magnetic resonance (NMR) spectroscopy, have two or more refrigerants. In addition to a container filled with liquid helium and holding a magnet, an additional radiation shield is provided, which is cooled with liquid nitrogen. Thus, in order to reduce both helium loss and nitrogen loss or to realize lossless operation, a separate helium liquefier and a separate nitrogen liquefier must be used. This will significantly increase the number of equipment, capital investment and operating costs.
European Patent Application No. 0905436 European Patent Application No. 0905524 International Publication No. 03/036207 Pamphlet International Publication No. 03/036190 Pamphlet US Pat. No. 5,966,944 US Pat. No. 5,563,566 US Pat. No. 5,613,367 US Pat. No. 5,782,095 US Patent Application Publication No. 2002/0002830 US Patent Application Publication No. 2003/230089 JP 11-257770 A JP 2000-283578 A Advances of Cryogenic Engineering, Vol. 45, p. 41-45

  Accordingly, an object of the present invention is a cooling device that can be advantageously and easily retrofitted to an existing cryostat structure including at least two refrigerants, particularly a cryostat structure including a superconducting magnet device. It is an object of the present invention to provide a cooling device that can eliminate part or all of the loss or can significantly reduce the loss compared to conventional devices.

  Unlike the prior art, according to the present invention, this object is achieved with a heat transfer device that can be inserted into a neck tube or suspension tube of a cryostat that holds at least two different refrigerant liquids. This is achieved by connecting the cold stages separately so that they can conduct heat.

  This type of cooling device has the following advantages. That is, it can be retrofitted without adjustment (or only with slight adjustment) to an existing cryostat structure, particularly a cryostat structure including a superconducting magnet, and even when several refrigerants are used, no special hardware is required and Operation can be performed with little or no refrigerant loss. There is no need to redesign the cryostat. Further heat input to the cryostat generated by the apparatus is small, and when correctly designed, further heat input can be accurately predicted. In the heat transfer device, the refrigerant is liquefied, but this heat transfer device is designed so that it can be introduced into the neck tube or suspension tube of the cryostat structure without contact. Since the evaporative gas is not overheated and it is not necessary to cool the evaporative gas to the liquefaction temperature, the evaporative gas is liquefied effectively thermodynamically. The cold head of the cryocooler is such that the disturbance from the magnetic regenerator on the magnet device is less serious than the distance from the magnetic center of the superconducting magnet device in the cryostat when the cold head is directly incorporated into the cryostat. It arranges so that it may become a distance. On the other hand, the function of the low-temperature refrigerator is not significantly impaired by the magnetic field of the magnet device. Even if the cryocooler fails or is turned off for maintenance work, the cryostat structure can still function to cool the superconducting magnet device, for example. This ensures driving reliability. Further, the user can freely select an operation mode (conventional mode or no refrigerant loss mode).

  In a particularly preferred embodiment of the cooling device according to the invention, the at least one heat transfer device has a cavity, which is connected to an open line, in particular a conduit. The refrigerant evaporated from the liquid tank of the cryostat passes through the conduit to the cavity in the cold stage and is liquefied at the cold stage. The condensed refrigerant flows back through the conduit to the cryostat liquid tank. This heat transfer device functions like a conventional thermal engineering heat pipe.

  In another preferred embodiment of the invention, the at least one heat transfer device comprises a metal connection with excellent heat transfer characteristics, the refrigerant evaporating from the cryostat liquid tank is liquefied at the end of the metal connection and thereafter It flows back to the liquid tank of the cryostat liquid tank. The other end of this connection is flange-connected to the cold stage of the cold head of the low-temperature refrigerator. The heat transfer device can be combined in various ways. For example, a metal connection having excellent heat transfer characteristics can be flanged to the first cold stage of the two-stage cold head, and the second cold stage can be connected to the conduit.

  Particularly in the high-resolution NMR method, it is advantageous that the low-temperature refrigerator is a pulse tube refrigerator. This is because the pulse tube refrigerator can be operated with extremely low vibration. In addition, pulse tube refrigerators are reliable in operation and require little maintenance.

  The cooling device can also be operated by a Gibaud-McMaan refrigerator. When compared with pulse tube refrigerators, the disadvantage of this low-temperature refrigerator is that it has a large vibration. This disadvantage can be solved by providing a soft sealing element between the cryocooler and the cryostat structure, as will be explained below.

  Particularly advantageously, at least one connecting line open at both ends is provided, and the cold head of the cryogenic refrigerator is connected to at least one neck tube or suspension tube of the liquid tank containing the refrigerant having the lowest boiling point. The heat transfer device is not inserted into the liquid tank. The connecting line is in thermal contact with at least two cold stages of the cold head and is also in contact with the regenerator tube on the coldest cold stage. The connecting line terminates in a cavity attached to the cold head after thermal contact with the coldest cold stage or is guided to a liquid tank along a metal connection. The gas in this pipeline is cooled by the cold head of the low-temperature refrigerator and liquefied by the coldest cold stage, and the resulting suction causes the flow through the neck tube or suspension tube to the cooling device to enter the pipeline. appear. The gas flow cools the neck tube or suspension tube, ideally completely compensating for heat input through the neck tube or suspension tube. This circulating flow for the neck tube or suspension tube further reduces the heat input to the cryostat.

  In a further development of this embodiment, a valve and / or pump is provided in the connecting line between the neck tube or suspension tube and the cold head to control the gas flow. For example, if the suction effect at the cold head is large and the gas flow is larger than what is required for optimal cooling of the suspension tube or neck tube, the gas flow can be reduced or the optimal gas flow adjusted as needed can do.

  Advantageously, helium can be liquefied at temperatures below 4.2K on the coldest cold stage of the cold head, providing a plurality of viable applications in the low temperature region. If the cooling capacity of the cryocooler is sufficiently large, helium loss and refilling processes can be reduced or lossless operation can be achieved.

  In another advantageous embodiment, nitrogen can be liquefied at 77K or lower in the cold stage of a low-temperature refrigerator. By using a heat transfer device in a cryostat structure having a liquid nitrogen container, if the cooling capacity of the low-temperature refrigerator is sufficiently large, nitrogen loss during operation can be reduced or eliminated.

  In an advantageous embodiment, a cold stage, not the coldest cold stage, of the cold head is connected in a thermally conductive manner to a radiation shield that at least partially surrounds the cold head. In this way, radiant heat input to the colder parts of the cold head is substantially reduced.

  More advantageously, the heat transfer device is at least partially placed in the outer jacket of the cooling device, i.e. in the vacuum chamber. This is especially true for the heat transfer device portion connected to the cold head of the cryocooler. This heat transfer device part is thereby well insulated against heat conduction to the outside.

  It is also very advantageous to at least partly surround the heat transfer device by the first tube in the region outside the outer jacket. This tube insulates the heat transfer device. However, the tube must not have a constant diameter over its entire length. It may be more constructive to choose the smallest possible diameter for some of the tubes and the larger diameter for the other parts.

  In a preferred embodiment, the first tube surrounding the heat transfer device is open at one end, which is connected to the vacuum chamber of the outer jacket and the other end is airtight to the conduit or the metal connection of the heat transfer device. Connected to. When the vacuum chamber of the cooling device of this embodiment is evacuated, the heat transfer device portion surrounded by the first tube is also evacuated. The heat transfer device is well insulated against heat conduction outside in this region.

  In another advantageous embodiment, the first tube surrounding the heat transfer device is hermetically connected at both ends to a conduit or metal connection of the heat transfer device and evacuated via another connection. As a result, the inside of the tube is evacuated and the heat transfer device portion surrounded by the tube is well insulated against heat conduction to the outside.

  Advantageously, the metal connection of the conduit or heat transfer device at least partly surrounds another second tube that is connected to the radiation shield in a heat conducting manner. This tube is disposed within the first tube and provides vacuum insulation as described above. In this way, the heat transfer device part surrounded by the second tube is well insulated against the outward heat radiation.

  The tube surrounding the above-mentioned heat transfer device is particularly preferably at least partially flexible and is preferably designed as a bellows.

  Further advantageously, the heat transfer device is at least partially flexible and is designed in particular as a bellows or knitted in the form of a wire strand. In this embodiment of the cooling device of the present invention, the heat transfer device and the surrounding tubes are flexible, making installation on a cryostat neck tube or suspension tube much easier.

  In this connection, it is also advantageous for the neck tube or suspension tube and the surrounding tube to be able to contact and separate from each other using an airtight joint in at least one place. This joint is designed so that the functions of the heat transfer device and the surrounding tube are not impaired. This substantially facilitates the attachment of the cooling device to the cryostat structure.

  In another embodiment of the present invention, a cooling device can be attached at the neck tube or suspension tube to the cryostat holding the refrigerant liquid, or it can be attached on the outer jacket of the cryostat structure.

  In another preferred embodiment, the cooling device is attached to the outside of the cryostat, such as the room ceiling or a separate stand. In this case, the cryostat structure does not need to support the weight of the cooling device, thereby increasing the mechanical stability of the cryostat structure.

  In this connection, it is advantageous to provide a soft connecting element that does not transmit vibrations as a seal between the cooling device and the cryostat. Thereby, especially in the high-resolution NMR method, the disturbing vibration of the cooling device is hardly transmitted to the cryostat structure.

  Another possibility is to attach an electric heater to the cold stage of the cold head of the cryocooler. When the cooling capacity of the low-temperature refrigerator has a margin, the heater can be adjusted so that the low-temperature refrigerator accurately compensates the heat input to the various containers of the cryostat structure.

  The advantages of the cooling device of the present invention are particularly well utilized when the cooling device forms part of a cryostat structure.

  Particularly advantageously, the cooling device cools a superconducting magnet, in particular a superconducting magnet that is part of a nuclear magnetic resonance apparatus, in particular a magnetic resonance imaging (MRI) apparatus or a nuclear magnetic resonance (NMR) spectroscopic apparatus. Used for.

  The electric heater can also be introduced into a cryostat-structured liquid tank equipped with the cooling device of the present invention via the neck tube or suspension tube of at least one liquid tank. If the cooling capacity of the low-temperature refrigerator cold head integrated in the cooling device is sufficient, this allows the pressure in the liquid container to be kept at a constant level higher than the surrounding pressure. However, the output of the low-temperature refrigerator can be controlled by the operating frequency of the low-temperature refrigerator and / or the working gas filling amount of the low-temperature refrigerator.

  Other advantages of the present invention will become apparent from the following description and drawings. The features described above and below can be used individually or in any combination. It is to be understood that the illustrated and described embodiments are not exhaustive and are exemplary in nature to illustrate the invention.

  FIG. 1 is a schematic view of a cryostat 1 including a magnet device 5 that is normally used in MR applications. The cryostat 1 includes a liquid tank 2a filled with helium. The liquid tank 2a is connected to the outer jacket 4 of the cryostat 1 by a suspension tube 3a and accommodates a magnet device 5. Around the liquid tank 2a, another liquid tank 2b is disposed. This liquid tank 2b contains nitrogen and is connected to the outer jacket 4 of the cryostat 1 by a suspension tube 3b. The liquid tank 2b containing nitrogen is in thermal contact with the suspension tube 3a. A radiation shield 6 cooled by boil-off gas is disposed between the two liquid tanks 2a and 2b, and the radiation shield 6 is in thermal contact with the suspension tube 3a.

  FIG. 2a shows an embodiment of the cooling device 7 according to the invention. The cooling device includes an outer jacket 8 defining a vacuum chamber 9 and a cold head 10 disposed in the jacket, the cold head 10 comprising at least two cold stages 11, 12, at least by a radiation shield 13. Partially surrounded. The cold stages 11 and 12 of the cold head 10 are connected to the heat transfer devices 14a and 14b, respectively, so as to be able to conduct heat. The heat transfer devices 14a and 14b have cavities 15a and 15b, respectively, and the cavities 15a and 15b are connected to the conduits 16a and 16b, respectively.

  FIG. 2b shows another embodiment of the cooling device 7 according to the present invention. The heat transfer devices 14a and 14b are provided with connections 17a and 17b having excellent heat conduction characteristics. These connections can be, for example, in the form of cold fingers, which are generally designed as metal rods. The metal rod must have the largest cross section so that the temperature difference along the rod is minimized.

  The conduits 16a and 16b can be inserted into the suspension tubes 3a and 3b of the liquid tanks 2a and 2b of the cryostat 1. FIG. 3 shows the cooling device 7 of the present invention in an installed state. The conduits 16a and 16b are positioned in the refrigerant vapor above the liquid level of the refrigerants 18a and 18b arranged in the liquid tanks 2a and 2b. The heat transfer devices 14a and 14b are connected to the cold stages 11 and 12 of the low-temperature refrigerator so as to be able to conduct heat (FIGS. 2a, 2b and 3). The refrigerants 18a and 18b evaporated from the liquid tanks 2a and 2b of the cryostat 1 are guided to the cavities 15a and 15b on the cold stages 12 and 11 through the conduits 16a and 16b, respectively. The refrigerants 18a and 18b are condensed and liquefied in the cold stages 12 and 11, and then flow back to the liquid tanks 2a and 2b of the cryostat 1 through the conduits 16a and 16b. Helium vapor can also be liquefied at the ends of the metal connections 17a, 17b that are in contact with the cold head 10 and have excellent thermal conductivity (FIG. 2b).

  The refrigerant 18b having a higher boiling point from the liquid tank 2b is liquefied in the first cold stage 11 of the cold head 10, while the refrigerant 18a having a lower boiling point is the second cold of the cold head 10 having a lower temperature. It is liquefied at stage 12. The present invention includes a cooling device having a multi-stage cold head 10 and can in principle liquefy any number of refrigerants corresponding to the number of cold stages of the cold head 10.

  In order to isolate the heat transfer devices 14a, 14b from heat input, the heat transfer devices are surrounded by the first tubes 19a, 19b. The first tube is connected to the vacuum chamber 9 of the outer jacket 8 of the cooling device 7 and can be evacuated together with the vacuum chamber 9 (FIGS. 2a and 2b). In order to enhance heat insulation from external heat radiation, the second tube 20 is disposed in the first tube 19a and is connected to the radiation shield 13 so as to be capable of conducting heat. The diameter of the first tube 19a changes in the length direction of the tube in FIGS. 2a, 2b and 3. The tube diameter may have to be reduced at the closed end so that the first tube can be inserted into the suspension tube 3b of the liquid tank 2b without contact. The bellows provides a flexible connection between the first tube 19b and the outer jacket 8 of the cooling device 7. Further, bellows can be interposed between the first tube 19 a and the outer jacket 8 and in the section of the second tube 20. The metal connections 17a, 17b shown in FIG. 2b can be made flexible by flexible connection elements 21a, 21b (for example, wires knitted in a string). When the cooling capacity of the low-temperature refrigerator is sufficient, an additional heater (not shown) can be attached to the cold stages 11 and 12 of the cold head 10 of the low-temperature refrigerator. Alternatively or in addition to this, when the cooling capacity of the low-temperature refrigerator has a margin, the pressures in the liquid tanks 2a and 2b of the refrigerants 18a and 18b can be kept constant using the heaters 22a and 22b. The heaters 22a and 22b are disposed in the liquid tanks 2a and 2b, and are inserted through, for example, free neck tubes or free suspension tubes 3c and 3d.

  FIG. 4 shows an advantageous variant of the cooling device according to the invention, in which the free neck tube or free suspension tube 3c of the cryostat 1 is connected to the cold stages 11, 12 of the cold head 10 via lines 23 open on both sides. After being in thermal contact, it is connected to the cavity 15a, that is, connected to the liquid tank 2a. This type of connection can also be realized by several free neck tubes or free suspension tubes 3c. The pipelines from the suspension tube 3 c are first combined into one pipeline 23. The pipe line 23 is guided through the outer jacket 8 of the cooling device 7 including the cold head 10 and is in thermal contact with at least two cold stages 11 and 12 of the cold head by heat exchangers 24b and 24a. In some cases, for example, the pipe line 23 is wound around the regenerator tube 25, and the pipe line 23 is also brought into thermal contact with the regenerator tube 25 of the coldest cold stage 12. After contact with the coldest cold stage 12, the pipe line 23 terminates in a cavity 15a provided in the cold head 10, or is led to the liquid tank 2a of the refrigerant 18a (helium) along the metal connection 17a. . The gas in the pipe line 23 is cooled by the cold head 10, liquefied by the coldest cold stage 12, and the resulting suction generates a flow in the pipe line 23 through the suspension tube 3 c toward the cooling device 7. The heated gas stream cools the suspension tube 3c so that ideally the heat input through the suspension tube 3c is completely compensated or at least reduced. The overall cooling power of the cryocooler is slightly reduced due to the additional load. The benefit from reduced heat input is greater than the decrease in cooling power. Particularly in the case of a system using a large neck tube or suspension tube 3c, a low-power low-temperature refrigerator can be used. The heat transfer devices 14a, 14b (heat tubes or cold fingers) can be made from two or three parts so that the heat transfer device parts can be separated using an airtight joint (not shown). This facilitates installation and disassembly. The pipe line 23 has a valve 26 and a pump 27, and can control the gas flow through the pipe line 23 to adjust the optimum gas flow. These devices (valve 26 or pump 27) can be provided in the conduit 23, or these devices can be omitted completely. In the embodiment of FIG. 4 and the embodiment of FIG. 3, heaters 22a and 22b are provided in the liquid tanks 2a and 2b. For clarity, the connections are omitted in FIG.

  Figures 5a to 5c show various possibilities for fixing the cooling device 7. The vacuum vessel that houses the cold head 10 of the cryocooler can be attached directly to the outer jacket 4 of the cryostat 1 as shown in FIG. 5a, or it can be externally mounted, for example, the room ceiling 28 (FIG. 5b) or a separate stand. 29 (FIG. 5c). A seal 30 must be used to attach to the cryostat 1. When suspended externally, only another sealing element 31a, 31b is used between the vacuum chamber 9 and the outer jacket 4 of the cryostat 1, and as a result, the vibration of the cryocooler is not transmitted to the cryostat 1 at all or minimal. Only the vibration of is transmitted. When the cooling device 7 is used for cooling the cryostat structure containing the superconducting magnet device 5, the superconducting magnet device 5 is a part of the nuclear magnetic resonance device, particularly a magnetic resonance imaging device (MRI) or magnetic resonance spectroscopy (nuclear magnetic resonance). , NMR), this is particularly advantageous. Therefore, according to the cooling device of the present invention, a high-resolution NMR method becomes possible.

  In summary, existing cryostat structures, particularly those containing superconducting magnets, can be retrofitted without adjustment (or with only minor adjustments), with some or no refrigerant loss even with some refrigerants. There is provided a cooling device that can be operated without any problems.

A cryostat structure provided with two liquid tanks for refrigerant liquid is shown. 1 shows a cooling device of the present invention comprising a heat transfer device having a cavity. The cooling device of the present invention provided with the heat transfer device provided with the metal connection excellent in the heat transfer characteristic is shown. 2b shows the cooling device according to FIG. 2a installed in a cryostat. 1 shows a cooling device according to the invention installed in a cryostat, together with a connecting line connecting a cold head of a cryogenic refrigerator to a suspension tube of a liquid tank. 1 shows a cooling device according to the invention attached to a cryostat. Fig. 2 shows a cooling device according to the invention mounted on a room ceiling. 1 shows a cooling device according to the invention attached to a stand.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cryostat 2a, 2b Liquid tank 3a, 3b, 3c, 3d Suspension tube 4 Outer jacket 5 Magnet device 6 Radiation shield of cryostat 7 Cooling device 8 Outer jacket of cooling device 9 Vacuum chamber 10 Cold head 11 First cold stage 12 Second Cold stage 13 Radiation shield of cooling device 14a, 14b Heat transfer device 15a, 15b Cavity 16a, 16b Conduit 17a, 17b Connection 18a, 18b Refrigerant 19a, 19b First tube 20 Second tube 21a, 21b Connecting element 22a, 22b Heater 23 Open pipes 24a, 24b Heat exchanger 25 Regenerator tube 26 Valve 27 Pump 28 Room ceiling 29 Stand 30 Seal 31a, 31b Seal element

Claims (19)

  An outer jacket (10) containing a cold head (10) of a cryocooler comprising at least two cold stages (11, 12) and at least partially surrounded by a radiation shield (13) and defining a vacuum chamber (9) 8) and a cooling device (7) for reliquefying the refrigerant gas, the neck tube or suspension tube (3a, 3b) of the cryostat (1) holding at least two different refrigerant liquids (18a, 18b). At least two cold stages (11, 12) of the cold head (10) are separately connected to each insertable heat transfer device (14a, 14b) so as to be capable of conducting heat. 7).   At least one of the heat transfer devices (14a, 14b) has a cavity (15a, 15b) connected to an open conduit, particularly a conduit (16a, 16b), and the open conduit, particularly the conduit, is a cryostat (1 ) Of the refrigerant (18a, 18b) evaporated from the liquid tank (2a, 2b) is led to a cavity on the cold stage where the refrigerant liquefies, and then the refrigerant passes through the conduits (16a, 16b). The cooling device (7) according to claim 1, wherein the cooling device (7) flows back to the liquid tank (2a, 2b) of the cryostat (1).   At least one of the heat transfer devices (14a, 14b) has a metal connection (17a, 17b) excellent in heat conduction characteristics, and refrigerant evaporated from the liquid tank (2a, 2b) of the cryostat (1). (18a, 18b) is liquefied at the end of the metal connection and then returned to the liquid tank (18a, 18b) of the liquid tank (2a, 2b) of the cryostat (1). Or the cooling device (7) of 2.   The cooling device (7) according to any one of claims 1 to 3, wherein the low-temperature refrigerator is a pulse tube refrigerator or a Gibéd McMean refrigerator.   A liquid tank having at least one connecting line (23) that is open at both ends and into which a valve and / or a pump can be inserted, contains the refrigerant (18a) having the lowest boiling point, and is not introduced with a heat transfer device (14a) The cold head (10) of a low-temperature refrigerator can be connected to at least one neck tube or suspension tube (3c) of (2a) via the connection pipe, and the connection pipe (23) In thermal contact with at least two cold stages (11, 12) of the head (10) and optionally a regenerator tube (25) on the coldest cold stage (12), said connecting line (23) being After thermal contact with the coldest cold stage (12), it terminates in the cavity (15a) attached to the cold head (10) or made of the metal Nekushon cooling device according to any one of claims 1, characterized in that it is guided to the liquid tank (2a) inside along (17a) 4 (7).   The cooling device (7) according to any one of claims 1 to 5, characterized in that helium can be liquefied at a temperature of 4.2K or lower in the coldest cold stage (12) of the low-temperature refrigerator.   The cooling device (7) according to any one of claims 1 to 6, characterized in that liquid nitrogen can be generated at a temperature of 77K or less in the cold stage (11) of a low-temperature refrigerator.   The cold stage (11) of the cold head of the low-temperature refrigerator, which is not the coldest cold head, is connected to a radiation shield (13) that at least partially surrounds the cold head (10) in a heat conductive manner. The cooling device (7) according to any one of claims 1 to 7.   9. Cooling device (7) according to any one of the preceding claims, characterized in that the heat transfer device (14a, 14b) is at least partly arranged in the outer jacket (8).   The heat transfer device (14a, 14b) is at least partially surrounded by a first tube (19a, 19b) in a region outside the outer jacket (8). The cooling device (7) according to claim 1.   The first tube (19a, 19b) surrounding the heat transfer device (14a, 14b) is open at one end, and the open end is connected to the vacuum chamber (9) of the outer jacket (8), 11. Cooling device (7) according to claim 10, characterized in that the other end is hermetically connected to a conduit (16a, 16b) or a metal connection (17a, 17b) of the heat transfer device (14a, 14b). .   The first tube (19a, 19b) surrounding the heat transfer device (14a, 14b) is airtight at both ends, and the metal connection (17a) of the conduit (16a, 16b) or the heat transfer device (14a, 14b). 17b), the cooling device (7) according to claim 10, characterized in that another connection for evacuation is provided.   The metal connection (17a) of the conduit (16a) or the heat transfer device (14a) is at least partially surrounded by a second tube (20) connected to the radiation shield (13) in a heat conductive manner. The cooling device (7) according to any one of claims 1 to 12, wherein the second tube (20) is arranged in the first tube (19a).   The conduit (16a, 16b) or the metal connection (17a, 17b) having excellent heat conduction characteristics is flexible at least in sections, including a tube surrounding the heat transfer device (14a, 14b), 14. Cooling device (7) according to any one of claims 1 to 13, characterized in particular as a bellows or in the form of a braided wire.   The cooling device (1) according to any one of claims 1 to 14, characterized in that the cooling device (7) can be hermetically attached to a cryostat (1) holding a refrigerant liquid (18a, 18b). 7).   15. The cooling device (7) according to any one of claims 1 to 14, characterized in that it can be attached to the outside of the cryostat (1) by means of soft connecting elements (31a, 31b) that do not transmit vibrations. Cooling device (7).   A cryostat structure comprising the cooling device (7) according to any one of claims 1 to 16.   The cooling device (7) plays a role of cooling a superconducting magnet device (5), particularly a cryostat structure, and the superconducting magnet device (5) is a part of a device for nuclear magnetic resonance, particularly a magnetic resonance imaging (MRI) device. Alternatively, the cryostat structure according to claim 17, which is a part of a magnetic resonance spectrometer (nuclear magnetic resonance, NMR).   The electric heater (22a, 22b) can be inserted into the liquid tank (2a, 2b) via a suspension or neck tube (3c) of at least one liquid tank (2a, 2b). The cryostat structure described in 1.

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