Cryocontainer assembly and method with liquid helium transfer device with reduced transfer losses

Abstract

To provide a liquid helium transfer device capable of easily reducing transfer loss.SOLUTION: A device for transferring liquid helium to a practical helium container of a practical cryostat, includes: a reservoir cryostat having a vacuum-insulated reservoir helium container for storing liquid helium that can be used for charging the practical helium container; and a liquid helium supply line extending from the reservoir helium container to be connected to the practical helium container. The device further includes: a gas helium return line leading into the reservoir helium container for connecting the device to the practical helium container; and a transfer device capable of transferring the liquid helium from the reservoir helium container to the practical helium container via the supply line and transferring the gas helium from the practical helium container to the reservoir helium container via the return line.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The invention relates to a device for transferring liquid helium into a practical helium container of a practical cryostat, comprising: a reservoir cryostat having a vacuum insulated reservoir helium vessel for storing liquid helium available for filling a working helium vessel; a liquid helium supply line extending from the reservoir helium container for connection to a working helium container; The present invention relates to an apparatus comprising: [Background technology]

[0002] Such a transfer device has become known, for example, from the publication "NMR Magnet System UltraShield Magnets (English version) User Manual Version 006" of Bruker Biospin AG, Faellanden, Switzerland, dated October 12, 2004, in particular Chapter 12 thereof (pp. 26-30).

[0003] Liquid helium is required for cooling in a variety of applications, such as the cooling of superconducting magnets in NMR spectrometers (NMR = nuclear magnetic resonance) and MRI systems (MRI = magnetic resonance imaging). In this case, liquid helium is stored in a vacuum-insulated practical helium vessel formed in a practical cryostat. An object placed in the liquid helium, such as a magnetic coil, is cooled by the liquid helium.

[0004] Liquid helium must be replenished in a working cryostat, typically after two to three months, as it is slowly consumed during cooling applications. Liquid helium is a rare and relatively expensive substance.

[0005] The usual procedure for refilling liquid helium is often as follows, see the above-mentioned Bruker Biospin AG publication, "NMR Magnet System UltraShield Magnets...": 1) A reservoir cryostat (also called a transport dewar) equipped with a vacuum-insulated reservoir helium vessel containing liquid helium for replenishing the operational cryostat is transported near the operational cryostat. 2) A room temperature supply line (also called a transfer line) is inserted into the reservoir cryostat until one end of the supply line protrudes into the liquid helium. 3) This causes the helium in the reservoir cryostat to warm slightly, increasing helium gas pressure in the reservoir cryostat and forcing liquid helium into the supply line, where it initially flows out as gaseous helium into the ambient environment at the other end. The supply line gradually cools, and eventually liquid helium leaks out the other end of the supply line. 4) The other end of the supply line is then inserted into the working cryostat. 5) Liquid helium then flows into the working cryostat, and simultaneously gaseous helium is forced out of the working cryostat, which is maintained at near atmospheric pressure. The forced gaseous helium usually escapes into the surrounding environment, or the working cryostat is connected to a recovery system that captures the gaseous helium. 6) To ensure sufficient pressure in the reservoir cryostat to transport liquid helium to the working cryostat, the reservoir cryostat is connected to a helium compressed gas cylinder (Druckgasflache) and the overpressure in the reservoir cryostat is set to approximately 50-100 mbar, which is sufficient for helium transfer.

[0006] This process can be performed successfully with relatively simple equipment. However, the process results in a relatively large loss of helium to the surrounding environment both as the supply lines cool and during the actual filling of the working cryostat with liquid helium. Additionally, it is energetically unfavorable to introduce warm, room-temperature helium from a compressed helium gas cylinder into the reservoir cryostat in order to pump the liquid helium out of the reservoir cryostat.

[0007] Recovery systems capable of capturing the gaseous helium escaping from a practical cryostat when liquid helium is being filled into it are relatively complex and expensive. The cryogenic helium escaping from a practical cryostat during transport exhibits a significant volume increase of more than ten times as it warms to room temperature on its way to the recovery system. Because recovery system components (compressors, balloon reservoirs, etc.) cannot be economically designed to operate with cryogenic gas, it is often even necessary to actively heat the helium escaping from a practical cryostat.

[0008] Recovery systems typically include either a large, low-pressure accumulator (e.g., a large, space-consuming balloon reservoir) for intermediate storage of gaseous helium before liquefying or compressing it for space-saving storage, or a high-pressure accumulator connected upstream to a very high-performance, and therefore expensive, compressor that must be designed directly for the helium flow expelled from the practical cryostat when it is refilled with liquid helium. Theoretically, it might be possible to directly cool and liquefy the helium leaking from the practical cryostat using a refrigerator appropriately sized for space-saving storage in the liquid state. However, in that case, the recovery system's refrigerator must be designed directly for the very high flow rates of helium gas expelled from the practical cryostat when it is refilled with liquid helium. In the latter case, the refrigerator becomes very expensive and is rarely utilized to its full potential during normal operation of the application.

[0009] US Patent Publication No. 20110312502 proposes controlling the transfer of liquid helium from a container to a magnet via gas pressure within the container.

[0010] U.S. Patent Application Publication No. 2019 / 0211970 describes a system for automatically replenishing cryogenic helium. The system includes an automated valve device that can introduce liquid helium from a compressed gas source into an LHe dewar, which is connected to an LHe cryostat via a liquid helium transfer line. Sensors monitor the liquid levels in the LHe dewar and the LHe cryostat.

[0011] US Pat. No. 3,399,691 proposes using a cryogenic pump to pump liquid helium from a reservoir into a vessel.

[0012] Japanese Patent Application Laid-Open No. 54-161109 proposes providing an outlet valve in the supply line between the liquid helium storage container and the cryostat, and first cooling the front of the supply line to prepare for the transfer of liquid helium, with gaseous helium being collected in a balloon reservoir by the outlet valve.

[0013] French Patent Application Publication No. 2,752,037, A1 proposes that when filling the cryostat with liquid helium, the gaseous helium escaping from the cryostat passes alongside the liquid helium supply line, and the escaping helium can be collected and, in particular, compressed.

[0014] From J.G. Weisend II (ed.), Cryostat Design, International Cryogenics Monograph Series, Springer International Publishing Switzerland 2016, Chapter 9, various types of cryogenic transfer lines, especially those with vacuum insulation, have become known.

[0015] U.S. Patent No. 6,442,948 describes a liquid helium recondenser in which gaseous helium is introduced from a liquid helium reservoir through a line into a freezer, where it is liquefied, and the reliquefied helium is returned to the reservoir through another line, with the first line and the second line extending through a common vacuum insulator.

[0016] From the company publication "Heliosmart Recovery Technical Specifications" dated 03 / 2022 of Bruker BioSpin, it is known to capture helium evaporating from an NMR magnet in continuous operation and store it in a compressed gas cylinder. The Bruker Heliosmart Recovery is equipped with an internal balloon reservoir and a three-stage high-pressure compressor. It is not designed to capture and store the helium produced at high flow rates that are forced out of a practical cryostat when liquid helium is replenished therein.

[0017] D. Kramer, “Helium is again short in supply,” Physics Today, April 4, 2022, states that liquid helium is currently in short supply, which has caused the price of helium to double over the past two years. Summary of the Invention [Problem to be solved by the invention]

[0018] The object of the present invention is to provide a liquid helium transfer device that can easily reduce transfer losses. Cryocontainer assembly and method comprising: The purpose is to provide [Means for solving the problem]

[0019] According to the present invention, the above problem is solved as follows: a gaseous helium return line leading into the reservoir helium container for connection to a working helium container;

[0020] The problem is solved by an apparatus of the type mentioned at the outset, characterized in that it further comprises a conveying device which is able to convey liquid helium from the reservoir helium vessel through a supply line to the working helium vessel and gaseous helium from the working helium vessel through a return line to the reservoir helium vessel.

[0021] Within the scope of the present invention, the supply and return lines may form a closed system when filling a working cryostat or its working helium vessel with liquid helium from a reservoir cryostat or its reservoir helium vessel.

[0022] When filling a working helium container with new liquid helium, the gaseous helium expelled from this working helium container is returned to the reservoir helium container via the return line without intermediate storage and with little heat input, and is therefore not lost. Within the scope of the present invention, complex intermediate storage of the gaseous helium before it is compressed or liquefied (e.g., at atmospheric pressure and ambient temperature in a balloon reservoir) is neither necessary nor contemplated. The gaseous helium introduced into the reservoir helium container in this way can contribute to the pumping, in particular the pushing, of liquid helium from the reservoir helium container into the supply line.

[0023] In the absence of significant heat input, the volume of gaseous helium expelled from the working helium tank corresponds to the volume of liquid helium pumped out of the reservoir helium tank and the volume of gaseous helium returned to the reservoir helium vessel. In practice, some heating is unavoidable, so under pressure buildup in the reservoir helium vessel, at least temporarily, a slightly larger amount of gaseous helium (volume-wise) is pumped into the reservoir helium vessel than the liquid helium pumped out of the reservoir helium vessel. This may be useful when pumping liquid helium through a supply line, but is not critical (as long as the pressure buildup is not too great). If the temperature of the liquid helium in the reservoir helium vessel is slightly below its boiling point (4.2 K at atmospheric pressure), the gaseous helium pumped into the reservoir helium vessel is cooled again by the liquid helium, specifically to 4.2 K, thereby limiting the pressure buildup in the reservoir helium vessel. For example, the temperature of the liquid helium in the reservoir helium vessel (at the start of the liquid helium transfer) may be 3.6 K or less, or even 3.0 K or less. In case of excessive pressure buildup, gaseous helium can exceptionally be released from the system, e.g., from the reservoir helium vessel, into the ambient environment, in particular via a safety valve (overpressure valve). However, this is usually not necessary, and it is preferred that the cryostat assembly, comprising the transfer device and the connected working cryostat, be configured in a closed state for the liquid helium when transferring it.

[0024] A transfer device transfers liquid helium from the reservoir helium vessel to the working helium vessel, and gaseous helium from the working helium vessel to the reservoir helium vessel. Typically, one flow is transferred directly (usually the gaseous helium flow) and the other gas flow is transferred indirectly (usually the liquid helium flow). The transfer device typically includes a transfer pump. The pressure (gas pressure) in the reservoir helium vessel and the working helium vessel, particularly the pressure difference between the reservoir helium vessel and the working helium vessel, can be influenced via the transfer device. During transfer, the pressure in the reservoir helium vessel is typically slightly higher than the pressure in the working helium vessel. Typically, the entire system is maintained at a slight excess pressure above atmospheric pressure in the surrounding environment to minimize contamination of the helium circuit with air or air components.

[0025] The reservoir helium vessel and the working helium vessel typically each have a storage capacity of at least 50 liters, preferably at least 100 liters.

[0026] Preferred Embodiments of the Invention In a preferred embodiment of the apparatus according to the invention, the supply and return lines are vacuum insulated, which minimizes heating of the liquid and gaseous helium during transport between helium vessels.

[0027] In one preferred development of this embodiment, the supply and return lines are at least partially formed into a common transport line, which has a vacuum chamber within a common vacuum boundary through which both the supply and return lines extend. This is space-saving, material-saving, easy to handle, and energy-efficient. In particular, the return line allows the supply lines to be at least partially thermally isolated from the ambient environment or minimizes thermal coupling between the supply lines and the ambient environment. The supply and return lines typically extend to a section close to the operational cryostat as a common transport line and are connected to the operational cryostat by the common transport line via a common helium tower of the operational cryostat. Preferably, the entire cross section of at least one other helium tower can be utilized for emergency release of gaseous helium from the operational helium vessel, especially in the event of a quench of the superconducting magnet coils in the operational cryostat. A magnet coil quench is a sudden loss of superconductivity that can result in the sudden release of stored electromagnetic energy as heat and the sudden evaporation of large amounts of helium.

[0028] In this case, a particularly advantageous development is one in which the supply line and the return line run coaxially within a common vacuum boundary, the supply line being located radially inside the return line, whereby the return line thermally shields the supply line, i.e. the return line acts as a radiation shield.

[0029] A further development is also preferred in which the supply line and the return line run parallel to one another and next to one another within a common vacuum boundary, which can be constructed in a particularly simple and cost-effective manner.

[0030] In another development, it is provided that the return line is suspended in the common vacuum boundary by means of one or more spacers, and that the supply line is suspended in the return line by means of one or more spacers but not in the common vacuum boundary, whereby the supply line is separated from the vacuum boundary as far as heat conduction via the spacers is concerned, and the heat input from the ambient environment into the supply line conducting the liquid helium is particularly low.

[0031] The line cross section QZ of the supply line and the line cross section QR of the return line QR>QZ, Preferably, QR≧3*QZ, Particularly preferably, QR≧5*QZ In this case, the device can operate very reliably even if the gaseous helium flow warms up somewhat, and the pressure loss in the return line is minimized.

[0032] Furthermore, embodiments in which the supply and return lines are made flexible are preferred, as this makes handling and installation of the supply and return lines easier, especially when they are only temporarily installed for a one-time filling of a working cryostat with liquid helium.

[0033] In an advantageous embodiment, the delivery device includes a circulation pump for the liquid helium in the supply line. This allows for a very efficient transfer of the liquid helium and direct control of the delivery rate of the liquid helium. Since no (gas) pressure is required to pump the liquid helium, a relatively low pressure can be set in the reservoir helium container.

[0034] An embodiment in which the conveying device includes a circulation pump for gaseous helium in the return line is particularly preferred. This is structurally simple, and helium circulation pumps are inexpensive, simple, and safe to operate. The formation of gas bubbles and cavitation effects that must be taken into account with pumps in the supply line are not important here.

[0035] In a preferred development of this embodiment, the return line comprises a line loop including an inlet region and an outlet region, the outlet region being thermally coupled to the inlet region via a heat exchanger; the line loop includes a circulation pump; In particular, the circulation pump must be at room temperature. In this manner, the circulation pump does not have to be configured for cryogenic operation, which is particularly simple in construction and also particularly cost-effective.

[0036] the transfer device includes a piston within the reservoir helium vessel, the piston being movable within the reservoir helium vessel and separating a first portion of the reservoir helium vessel for gaseous helium from a second portion of the reservoir helium vessel for liquid helium; An advantageous embodiment is also contemplated in which the supply line extends to the second section and the return line leads to the first section. A piston (also called a slider) can simply pump the liquid helium from the reservoir. In that case, no circulation pump is required. Additionally, the supply and return lines between the working cryostat and the reservoir cryostat can simply run as a completely common transport line.

[0037] Additionally, the apparatus further comprises a controller for controlling the helium pressure within the apparatus and / or the working helium vessel; In particular, an embodiment in which the control device is configured to control the transfer device is preferred. Typically, to minimize air infiltration, the helium pressure is adjusted to be higher than atmospheric pressure everywhere in the device (particularly in the reservoir helium vessel) and the practical helium vessel. Via the control device, a pressure difference between the reservoir helium vessel and the practical helium vessel, particularly sufficient to pump out liquid helium, can be controlled and set, particularly in the transfer device. Even if high pressure occurs in the system, for example in the practical helium vessel, the control device can trigger the opening of at least one discharge valve. Alternatively or additionally, one or more overpressure valves independent of the control device (e.g., passively, spring-loaded only) can also be provided. The control device is typically connected to a gas pressure sensor in the practical helium vessel. Typically, the control device also includes a gas pressure sensor in the reservoir helium vessel.

[0038] In this embodiment, the device a heating device, particularly arranged within the reservoir helium vessel, and / or A preferred development further comprises a helium compressed gas reservoir, in particular having a control valve for connection to a practical helium container, and in particular the control device is configured to control the heating device and / or the control valve. The heating device or the helium compressed gas reservoir makes it easy to increase the amount of gas in the system, and thus the pressure, in order to ensure a slight overpressure in the system that minimizes the ingress of air from the ambient environment. The heating device can be arranged, for example, at the lower end of the supply line that protrudes into the liquid helium in the reservoir helium container. The heating device is typically electric. The helium compressed gas reservoir ("compressed gas cylinder") is typically at room temperature.

[0039] Advantageously, in one embodiment, the device comprises a laboratory liquefier for helium, the laboratory liquefier comprising: a reservoir cryostat having a reservoir helium vessel; and a cryocooler for liquefying gaseous helium. The laboratory liquefier makes available to the reservoir cryostat. The liquefaction capacity of the laboratory liquefier is relatively low, typically 40 L / day or less, often 25 L / day or less, and often about 20 L / day. During normal operation, the laboratory liquefier can store liquid helium that is evaporated as gaseous helium during normal operation of the practical cryostat (e.g., NMR instrument) and liquefied by the cryocooler. The cryocooler can cool the stored liquid helium to the boiling point of liquid helium at atmospheric pressure (about 1 bar), i.e., 4.2 K, thereby providing a cold reserve for transferring liquid helium when refilling the practical cryostat. This cold reserve ("cold energy") compensates for heat input to the system during liquid helium transfer, thereby reducing or avoiding undesirably high pressure buildup in the system. The cryocooler can build up a cold reserve over an extended period of time (such as several weeks), thereby requiring the cryocooler to be only slightly larger than required for normal operation.

[0040] Cryocontainer assembly according to the present invention Within the scope of the present invention there is also provided a cryogenic vessel assembly comprising an apparatus according to the invention as described above and a practical cryostat having a practical helium vessel, the supply line is connected to and leads into the utility helium vessel; The cryocontainer assembly also includes a return line connected to and extending from the practical helium vessel. The practical helium vessel can be filled with liquid helium from the device, minimizing helium, particularly liquid helium, transfer losses. The connection between the device for transferring liquid helium (the "transfer device") and the practical cryostat with the practical helium vessel is typically releasable (or reversible), allowing the transfer device to be removed from the practical cryostat during normal operation and, in some cases, to be used alternately even when multiple practical cryostats are used.

[0041] Advantageously, the cryocontainer assembly according to the invention further comprises at least one pressure sensor in the region of the working helium vessel, in particular the pressure sensor being connected to a control device of the device, which pressure sensor can monitor the gas pressure in the working helium vessel, in order to keep the gas pressure above ambient (atmospheric) pressure using the control device, in particular to minimize air ingress into the system.

[0042] Method for transferring liquid helium according to the present invention Within the scope of the present invention is a method for transferring liquid helium from a reservoir helium vessel of a reservoir cryostat to a working helium vessel of a working cryostat, comprising the steps of: A method in which liquid helium stored in a reservoir helium vessel is transferred from the reservoir helium vessel to a working helium vessel through a liquid helium supply line extending from the reservoir helium vessel and connected to the working helium vessel, The method also includes returning gaseous helium from the practical helium vessel to the reservoir helium vessel through a gaseous helium return line connected to the practical helium vessel and leading into the reservoir helium vessel. This method minimizes helium, particularly liquid helium, transfer losses when refilling the practical cryostat with liquid helium from the reservoir cryostat. The helium returned to the reservoir helium vessel via the return line is not lost and does not need to be stored intermediately, and can thereby help pump, particularly push, the liquid helium from the reservoir helium vessel. Typically, when transferring liquid helium, the transfer capacity is at least 8 kg / h, and in most cases at least 12 kg / h. Within this method, the above-described apparatus according to the present invention, or further the above-described cryocontainer assembly according to the present invention, can also be used. The practical cryostat can, in particular, be the cryostat of an NMR magnet.

[0043] A preferred variant of the method according to the invention provides for the volumetric flow rates of liquid helium through the supply line and gaseous helium through the return line to be approximately the same. In other words, the transfer of liquid helium takes place in a closed circuit between the reservoir helium container and the working helium container (without an outlet to the ambient environment or additional intermediate storage of helium outside the reservoir helium container and the working helium container). The transfer is highly efficient, minimizing transfer losses. Typically, the volumetric flow rates of liquid helium through the supply line and gaseous helium through the return line differ by no more than 10%, often no more than 5%, and preferably no more than 1% of the smaller volumetric flow rate (for helium transfer under stable conditions).

[0044] The temperature of the liquid helium in the reservoir helium vessel, TLHe, is at least at the start of the transfer of the liquid helium. TLHe<4.2K, Preferably, TLHe≦3.6K, Particularly preferably, TLHe≦3.0K and In particular, a variant is advantageous in which the temperature TLHe of the liquid helium in the reservoir helium container is set using a cryocooler of a laboratory liquefier integrated into a reservoir cryostat with the reservoir helium container before the start of the liquid helium transfer. Liquid helium at a temperature significantly lower than its boiling point (4.2 K at atmospheric pressure) provides a cold supply that can compensate for the heat input to the system during the transfer of the liquid helium to the operational cryostat, thereby limiting the pressure increase in the system. In particular, the cold supply can be used to recool and possibly reliquefy the helium gas returned from the operational cryostat to the reservoir cryostat. When the liquid helium in the reservoir helium container is cooled below the temperature of the phase transition to superfluid helium (2.17 K at atmospheric pressure), a particularly large cold supply is available due to the high specific heat in the phase transition region.

[0045] Other advantages of the present invention will become apparent from the following description and drawings. According to the present invention, the above and following features may be used either alone or in any combination. The illustrated and described embodiments should not be considered as an exhaustive list, but rather have an exemplary character for explaining the present invention. [Brief explanation of the drawings]

[0046] [Figure 1] 1 is a schematic diagram of a first embodiment of a cryocontainer assembly according to the invention, comprising a device for transferring liquid helium, with a cryogenic circulation pump in the return line; FIG. [Figure 2] 2 is a schematic diagram of a second embodiment of a cryocontainer assembly according to the invention, comprising a device for transferring liquid helium, with a circulation pump in the supply line; FIG. [Figure 3] 10 is a schematic diagram of a third embodiment of a cryogenic vessel assembly according to the invention, comprising a device for transferring liquid helium, with a room temperature circulation pump in the line loop of the return line. FIG. [Figure 4]FIG. 10 is a schematic partial view of a fourth embodiment of a cryocontainer assembly according to the present invention, with a common transport line having a common vacuum boundary. [Figure 5] 1 is a schematic cross-sectional view of a first type of common transport line of the present invention, with coaxial supply and return lines; FIG. [Figure 6] FIG. 1 is a schematic cross-sectional view of a second type of common transport line of the present invention, with parallel supply and return lines. [Figure 7] 10 is a schematic diagram of a fifth embodiment of a cryocontainer assembly according to the invention with a device for transferring liquid helium, in which a reservoir cryostat is integrated into a laboratory liquefier; FIG. [Figure 8] 10 is a schematic diagram of a sixth embodiment of a cryogenic vessel assembly according to the present invention, comprising an apparatus for transferring liquid helium having a piston vertically movable within a reservoir helium vessel including a rigid wall. FIG. [Figure 9] 10 is a schematic diagram of a seventh embodiment of a cryogenic vessel assembly according to the present invention, comprising a device for transferring liquid helium, the device having a piston vertically movable within a reservoir helium vessel having a wall formed in part as a bellows; [Figure 10] FIG. 10 shows a schematic partial view of an eighth embodiment of a cryogenic vessel assembly according to the present invention, comprising a device for transferring liquid helium, the device having a piston movable horizontally within a reservoir helium vessel including a rigid wall, the piston defining a subspace within the reservoir helium vessel together with a bellows. DETAILED DESCRIPTION OF THE INVENTION

[0047] Background of the Invention Within the scope of the present invention, liquid helium should be used as sustainably as possible. Superconducting magnets, e.g., in NMR and MRI, are usually cooled with liquid helium. Helium is usually obtained as a by-product of natural gas extraction or extracted from so-called "helium wells" (gas wells with an exceptionally high helium content). Helium is a scarce resource, and the amount available on the world market is decreasing. This trend will become even more pronounced in the future.

[0048] Helium shortages constantly drive up prices, which makes helium-requiring equipment (e.g., superconducting magnets) increasingly expensive to operate. Furthermore, there can be considerable uncertainty as to whether liquid helium will even be available at a particular time, which can lead to the need to shut down operations of equipment requiring liquid helium.

[0049] Liquid helium is transported from a supplier to a consumer (e.g., operating an NMR magnet) using a so-called "transport dewar" (also referred to herein as a reservoir cryostat). This is a vacuum-insulated container, typically equipped with casters. The liquid helium then needs to be transferred from the transport dewar to an NMR magnet or another working cryostat using vacuum-insulated transfer lines. The invention described herein helps make this transfer more efficient.

[0050] Many consumers also invest in helium recovery equipment in which helium gas evaporated from equipment (e.g., NMR magnets) or pushed out of the equipment during transport is captured and then fed to an accumulator or helium liquefier, where it can then be re-liquefied and fed back into the NMR magnet to cool the superconducting coils.

[0051] Recovery systems typically include either a large, low-pressure accumulator (e.g., a large balloon reservoir, requiring a relatively large amount of space) for intermediate storage of gaseous helium before liquefying or compressing it for space-saving storage, or a high-pressure accumulator connected upstream to a very high-performance, and therefore expensive, compressor that must be designed directly for the helium flow expelled from the practical cryostat when it is refilled with liquid helium. Theoretically, it might be possible to directly cool and liquefy helium leaking from the practical cryostat using a refrigerator appropriately sized for space-saving storage in a liquid state. In that case, the recovery system's refrigerator would have to be designed directly for the very high flow rate of helium gas expelled from the practical cryostat when it is refilled with liquid helium. In the latter case, the refrigerator would be very expensive and would rarely be fully utilized during normal operation of the application. The invention described herein makes it possible to omit the large balloon reservoir, the oversized compressor, or the oversized refrigerator.

[0052] Helium transfer typically proceeds as follows (see also the company publication of Bruker Biospin AG mentioned at the beginning, "NMR Magnet System UltraShield Magnets (English version) User Manual Version 006").

[0053] The transport dewar is brought close to the NMR magnet (a few meters away).

[0054] ·The warm transfer line is inserted into the transfer dewar so that the end of the transfer line is below the liquid level.

[0055] Heat input in the warm transfer line causes helium in the transfer dewar to evaporate, which increases pressure in the transfer dewar and forces liquid helium into the transfer line, thereby cooling it. Helium that leaks out the end of the line during the cooling process is typically not captured and is lost to the atmosphere. For a typical transfer line several meters long, several liters of liquid helium are required for cooling.

[0056] As soon as the helium leaking out the end of the line opposite the transfer dewar is sufficiently cold (i.e., the transfer line is sufficiently cooled), the transfer line is connected to the NMR magnet (or the end of the transfer line is inserted into the cryostat of the NMR magnet).

[0057] After connecting the transfer line to the NMR magnet, liquid helium flows from the transfer dewar to the NMR magnet. The mass flow rate is driven by the pressure difference that exists between the transfer dewar and the NMR magnet. As mentioned above, an overpressure is created in the transfer dewar due to the insertion of the transfer line. The magnet outlet (the connection through which the helium escapes from the NMR magnet) is either directly connected to the atmosphere or to a recovery system that always has approximately atmospheric pressure at the outlet.

[0058] Normally, the pressure increase in the transport dewar caused by the heat input during the insertion of the transfer line is not sufficient to transfer the desired amount of helium. Therefore, the pressure in the transport dewar is kept artificially high by keeping the transport dewar at a constant height via a pressure regulator using helium gas from a compressed cylinder. Typically, the overpressure set in the transport dewar is about 50-100 mbar.

[0059] Before helium transfer begins, the NMR magnet's helium tank is not empty; the tank is mostly filled with gaseous helium at a temperature of about 4.2 K. As transfer progresses and liquid helium slowly fills the helium tank, the cold gaseous helium that was in the helium tank before transfer began is gradually pushed out of the helium tank and leaks out the magnet's outlet.

[0060] At 4.2 K and atmospheric pressure, gaseous helium has a density of 16.5 g / L. At 4.2 K and atmospheric pressure, liquid helium has a density of 125 g / L. Therefore, for example, if 100 liters of liquid helium, or 12.5 kg of helium, are transferred, 100 liters of gaseous helium, or 1.65 kg, will be forced out of the magnet. This corresponds to 13.2 liters of liquid helium, or 13.2 percent of the amount transferred.

[0061] In the worst case scenario, this amount of helium will leak into the atmosphere through the magnet outlet. Because this is not sustainable, many users decide to install a gas balloon reservoir large enough to capture the helium generated during helium transfer ("transfer losses") and to supply the high-pressure accumulator and / or liquefier. In the line system leading to the gas balloon, or in the balloon itself, the gaseous helium warms to room temperature. Because gas balloons are typically not compatible with low temperatures (e.g., due to ice formation, condensed water, or material embrittlement), the gas balloon may be intentionally heated in a heat exchanger connected upstream of the gas balloon. Heating helium gas significantly increases the volume of the gas. 100 liters of gaseous helium at atmospheric pressure and 4.2 K will expand to approximately 10,000 liters (i.e., 10 m 3 ) is equivalent to

[0062] When transferring helium to an NMR magnet, typically 100-400 liters of liquid helium are transferred, depending on the type of magnet. The transfer takes approximately one hour. During this time, 10-40 cubic meters of gaseous helium are generated at room temperature, which must be stored in gas balloons or processed in a recovery system (e.g., compressed in a pressure accumulator). These transfer losses equate to 13 l / h-50 l / h of liquid helium (or approximately 1.6-6.6 kg of helium per hour).

[0063] For comparison, the helium consumption of several typical NMR magnets during normal operation is shown. 400MHz: 0.013l / h 500MHz: 0.013l / h 600MHz: 0.016l / h 700MHz: 0.026l / h 800MHz: 0.05l / h 1.2GHz: 0.25l / h

[0064] It is clear that the transfer losses per unit time during liquid helium transfer are much greater than the helium consumption during normal operation, and therefore the recovery system (if it is also able to handle helium transfer) must be designed for large peak loads that occur relatively infrequently (typically for only 1-2 hours at intervals of several months). In particular, gas storage balloons with a volume of several cubic meters are difficult to accommodate in an NMR laboratory, taking up valuable space within the building. Furthermore, gas balloons have other drawbacks: for example, helium can leak due to diffusion through the balloon's surface, and impurities (moisture, air components) can enter the helium circuit.

[0065] Recently, small recovery systems sized to match evaporation rates during normal operation have been introduced to the market (see the Bruker BioSpin company publication, "Heliosmart Recovery Technical Specifications," mentioned at the beginning). These systems, which are very inexpensive, compact, and therefore easy to install, do not capture transport losses, which are therefore accepted as lost.

[0066] Furthermore, the typical practice of introducing warm, room temperature gaseous helium from a gas cylinder into the transport dewar at the start of the process, or dissipating heat within the transport dewar to evaporate the liquid helium and thus increase the pressure within the transport dewar, is energetically unfavorable, essentially wasting the liquid helium that was liquefied at the expense of significant energy.

[0067] Various concepts exist for circulating helium for cooling in a closed circuit during normal operation of an application, as described, for example, in the aforementioned U.S. Patent No. 6,442,948. Such circulation does not require the processing of large amounts of gaseous helium in a short time. However, the procurement and operation of the corresponding equipment is often expensive and complex, and various operational disturbances may occur. Furthermore, these equipments are prone to introducing vibrations into the working cryostat through the cryocooler operating during normal operation, which may impair the desired application (e.g., NMR measurements). Solutions based on closed-circuit cooling cannot be easily retrofitted to existing systems and are therefore not of interest to all current operators.

[0068] In contrast, the present invention relates to a system in which large volumes of liquid helium are transferred occasionally over short periods of time, allowing long periods of time for cooling in a cryostat (a practical cryostat). The advantage of such "batch transfer" is that the cryostat can operate independently without relying on continuously circulating helium for cooling. This leads to particularly high reliability and low vibration, which is important for many applications, such as NMR. However, with such batch transfer, as described above, large volumes of cold helium gas must be pumped and handled, which can be achieved with the present invention. The vast majority (estimated >99%) of all existing NMR spectrometers with superconducting magnets worldwide operate using the batch transfer method.

[0069] Overview of the Invention Within the scope of the present invention, helium transfer can be carried out using suitable devices in such a way that no significant amounts of helium gas are generated at room temperature. This is achieved in particular by deriving cryogenic helium gas from the NMR magnet (or more generally from the working cryostat) during transfer through insulated lines and storing it in the free volume of a transfer dewar (also called reservoir cryostat), where it is also used partially for pressure buildup. The pressure difference required for circulation can be set using a pump specially adapted for the cryogenic fluid.

[0070] The circulation pump can be located either in the liquid helium line leading to the NMR magnet or in the gaseous helium line leading from the magnet. The latter is advantageous as it avoids the need to pump a boiling liquid (helium at 4.2 K and atmospheric pressure), which is difficult to pump due to the risk of e.g. bubble / cavitation formation.

[0071] For reasons primarily related to safety and reliability aspects of operation, care must be taken to avoid, as far as possible, subatmospheric pressure anywhere in the helium circuit, especially in the NMR magnet. Any leaks in the system would allow air or other impurities to be sucked into the NMR magnet and freeze there, leading to icing and clogging there. Pressure in the NMR magnet can be achieved by a pressure control valve and a connection to a gas reservoir (via a pressure regulator).

[0072] It is also advantageous to provide an electric heater that can increase the amount of gas in the circuit so that a pressure increase can be created if necessary. This heating device can be located at the end of the transfer line that protrudes into the liquid helium in the transfer dewar. This has the advantage that the heater is part of the transfer system and no modifications are required to either the NMR magnet or the transfer dewar.

[0073] The pressure difference between the transport dewar (or reservoir cryostat) and the NMR magnet (or working cryostat) required for helium transfer can be achieved by using a speed-regulated pump, whose pumping capacity is controlled depending on the pressure measured by a sensor. The pressure sensor can also be part of the transfer device. Two-point control is also possible, switching the pump on and off at variable intervals.

[0074] Instead of a pump suitable for cryogenic fluids, a room temperature pump can also be used in combination with a heat exchanger, particularly preferably a tube-in-tube countercurrent heat exchanger.

[0075] Presentation of a Preferred Embodiment A first preferred embodiment of a cryostat assembly 1 according to the present invention is shown in FIG.

[0076] The cryostat assembly 1, which here belongs to an NMR magnet, comprises a working cryostat 2 with a vacuum-insulated working helium vessel 3 for liquid helium 6 / 6a and a device 5 for transferring liquid helium 6. This device 5 comprises a reservoir cryostat 7 (also called a transport dewar) with a vacuum-insulated reservoir helium vessel 8 for liquid helium 6 / 6b, a vacuum-insulated supply line 9 for liquid helium 6, and a vacuum-insulated return line 10 for gaseous helium 11. A circulation pump 12a for the cold gaseous helium is arranged in the return line 10 as a conveying device 49.

[0077] To transfer liquid helium 6 / 6b from reservoir helium vessel 8 through supply line 9 to working helium vessel 3, cryogenic gaseous helium 11a is pumped out of working helium vessel 3 by circulation pump 12a and introduced into reservoir helium vessel 8 ("direct flow"). This increases the gas pressure of gaseous helium 11 / 11b in reservoir helium vessel 8, forcing liquid helium 6 / 6b from reservoir helium vessel 8 into supply line 9 at reservoir cryostat end 13 of supply line 9, and liquid helium 6 / 6c exits working cryostat end 14 of supply line 9 and flows into working cryostat 2 ("indirect flow").

[0078] The circulation pump 12a is controlled by an electronic control device 17, which also monitors a pressure sensor 18 in the reservoir helium vessel 8 and a pressure sensor 19 in the working helium vessel 3. Furthermore, an electric heating device 20 is attached in the region of the end 13 of the supply line 9, immersed in the liquid helium 6 / 6b in the reservoir helium vessel 8, and this heating device 20 is also controlled by the control device 17. Arranging the heating device 20 in the liquid phase ensures a particularly fast response behavior of the pressure control (or pressure difference control). Alternatively, the heating device can be arranged in the gas phase, which may be energetically advantageous (a constant pressure increase can be achieved with less loss of liquid helium 6), but in that case the response of the pressure control will be slower. Via the circulation pump 12a, the control device 17 can ensure that the pressure in the reservoir helium vessel 8 is slightly higher than the pressure in the working helium vessel 3, so that the liquid helium 6 / 6b flows at the desired flow rate through the supply line 9 to the working helium vessel 3. A pressure difference of 50-100 mbar is usually sufficient for this. If the overall system pressure becomes too low, especially if the pressure in the working helium vessel 3 or in the reservoir helium vessel 8 falls below ambient pressure (atmospheric pressure of about 1 bar), then as an emergency measure the control device 17 can evaporate a small amount of helium 6b in the reservoir helium vessel 8 by means of the heating device 20. Adding helium gas increases the gas pressure in the system.

[0079] In the illustrated embodiment, the supply line 9 and return line 10 are formed separately, and each of the lines 9, 10 is connected to a magnet tower (helium tower) 15, 16 specific to the practical cryostat 2. The reservoir helium vessel 8 within the reservoir cryocooler 7 typically has a storage capacity of 100 to 400 liters.

[0080] A second embodiment of a cryostat assembly 1 according to the invention is shown in FIG. 2 and is largely similar to the version of FIG. 1, so only the important differences will be described here.

[0081] In the illustrated embodiment, the conveying device 49 is configured as a circulation pump 12b disposed in the supply line 9 and pumping the liquid helium 6 / 6b from the reservoir helium vessel 8 through the supply line 9 to the working helium vessel 3 ("direct flow"). The liquid helium 6 / 6c entering the working helium vessel 3 pushes a corresponding volume of gaseous helium 11 / 11a through the return line 10 to the reservoir helium vessel 8 ("indirect flow"). In the reservoir helium vessel 8, gaseous helium 11 / 11b can accumulate above the liquid helium 6 / 6b and help pump the liquid helium 6 / 6b into the supply line 9.

[0082] In the illustrated embodiment, a room temperature helium compressed gas reservoir 21 is provided, which is connected to the practical helium vessel 3 via a control valve 22. If the overall system pressure becomes too low, particularly if the pressure in the practical helium vessel 3 or in the reservoir helium vessel 8 falls below ambient pressure (which is approximately atmospheric pressure = 1 bar), the controller 17 can inject small amounts of helium gas into the practical helium vessel 3 via the control valve 22. Adding helium gas increases the gas pressure in the system.

[0083] A third embodiment of a cryostat assembly 1 according to the present invention is shown in Figure 3 and is largely similar to the form of Figure 1, so only the significant differences will be described here. For simplicity, the illustration of Figure 3 omits the control equipment and components connected thereto.

[0084] In this embodiment, the conveying device 49 is formed by including a circulation pump 12c in the line loop 23 of the return line 10. The line loop 23 is provided with a heat exchanger 24. In the illustrated embodiment, the inlet region 23a of the line loop 23 is formed with an outer tube, and the outlet region 23b of the line loop 23 is formed with an inner tube passing through the outer tube ("tube-in-tube"). Initially cold gaseous helium 11 / 11b flowing from the utility helium vessel 3 flows through the outer tube and then enters the room-temperature warm loop portion 25, where it warms. In the room-temperature warm loop portion 25, the circulation pump 12c pumps room-temperature (approximately 20°C) gaseous helium. The room-temperature warm gaseous helium then flows from the circulation pump 12c into the inner tube, where it is cooled by the cold gaseous helium surrounding it in the outer tube. The gaseous helium thus cooled again by the heat exchanger 24 then flows into the reservoir helium vessel 8 .

[0085] Note that the heat exchanger 24, including the outer and inner tubes, is vacuum insulated, see vacuum boundary 26.

[0086] Common Transportation Line NMR magnets typically have two or three towers leading to the helium vessel. In the embodiments shown so far, helium is extracted from one magnet tower and supplied from another. This simplifies the installation and connection of supply and return lines, especially when an NMR magnet has three towers, as is sometimes the case. Alternatively, it is possible and advantageous to configure the transfer device so that helium extraction and supply occur in the same tower. In this way, in a two-tower system, it is possible to ensure that at least one tower remains free to ensure a sufficiently large outflow cross-section is available, even in the event of a quench of the NMR magnet during helium transfer. The two lines (gas extraction and liquid helium supply) can be arranged coaxially, but at least in a common vacuum chamber.

[0087] Figure 4 shows diagrammatically a fourth embodiment of a cryocontainer assembly 1 according to the invention in the region of a practical cryostat 2. Only the important differences from the version of Figure 1 will be described.

[0088] In the embodiment shown, the supply line 9 and the return line 10 extend within a common vacuum boundary 27, thereby forming a common transport line 28. The common transport line 28 leads to the working helium vessel 3 via a single magnet tower (helium tower) 15. The other magnet tower 16 is not required for helium transfer, and in particular its entire cross section is available for releasing helium gas in the event of a quench of the superconducting magnet coils (not shown) cooled by liquid helium 6 / 6a in the working helium vessel 3. For this purpose, an overpressure valve or rupture disk can be provided in the magnet tower 16 (not shown in detail).

[0089] Transfer lines (common transport lines) are usually made flexible rather than rigid to facilitate their handling (e.g., insertion into a transport dewar or NMR magnet). Therefore, flexible metal bellows are preferably used instead of rigid tubes. Fluid-conducting lines are often wrapped with a super-insulating film (or tape) for thermal insulation. To prevent the warm fluid-conducting lines from coming into direct contact with the boundary line (also called the vacuum boundary) enclosing the vacuum-insulated volume, which would lead to unacceptable heat input, the fluid-conducting lines are separated from the boundary line by spacers. These spacers (also called spacers) are made of materials with low thermal conductivity and therefore insulating properties (e.g., nylon or G10). Furthermore, the spacers preferably have a geometric shape that ensures the heat-flow bridge is as long as possible and therefore has the smallest possible cross-section. Furthermore, the two lines can be made coaxial, i.e., the gaseous helium line (with a circular cross-section) surrounds the liquid helium line, and these lines are insulated from each other by a vacuum.

[0090] To keep the manufacturing costs of the transfer line (common transport line) low, it is also possible to form both lines with a circular cross section. Here, to avoid direct mechanical contact between the warm vacuum boundary and the cold liquid helium line, it is advantageous to mechanically attach the liquid helium line to the gaseous helium line via a thermally insulating structure.

[0091] FIG. 5 shows a schematic cross-sectional view of a first exemplary type of common transport line 28 of the present invention. The common transport line 28 has a circular cross-section. The common transport line has a vacuum boundary 27 on the radially outer side, and a plurality of spacers 29 protruding radially inward are disposed on the vacuum boundary. A circular return line 10 is attached radially inward of the spacers, and gaseous helium 11 / 11c is conducted through this return line. Note that the return line 10 has a radially outer outer wall 10a and a radially inner inner wall 10b, which are mutually supported by auxiliary spacers (not shown in detail). Another spacer 30 protruding radially inward is attached to the return line 10. A circular supply line 9 conducting liquid helium 6 / 6c is attached radially inward to this other spacer. A vacuum exists in the space between the vacuum boundary 27 and the outer wall 10a of the return line, and a vacuum exists in the space between the inner wall 10b of the return line 10 and the supply line 9. The line cross section QR of the return line 10 is here about 12 times larger than the line cross section QZ of the supply line 9.

[0092] FIG. 6 shows a schematic cross-sectional view of a second exemplary type of common transport line 28, also having a circular cross-section. A spacer 29, again projecting inward, is disposed at the vacuum boundary 27. A circular return line 10 carrying gaseous helium 11 / 11c is attached to the inner end of the spacer. Another spacer 30, projecting from the return line 10, is attached to the side of the return line 10. A circular supply line 9 carrying liquid helium 6 / 6c is attached to the opposite end of this spacer. The supply line 9 and the return line 10 are spaced apart from the vacuum boundary 27. A vacuum exists in the space between the vacuum boundary 27 and the lines 9 and 10. The line cross-section QR of the return line 10 is approximately six times larger than the line cross-section QZ of the supply line 9.

[0093] In both the FIG. 5 and FIG. 6 configurations, the supply line 9 is mechanically connected to the vacuum boundary 27 only via the return line 10 .

[0094] Calculation examples and integration in laboratory liquefiers In a typical transfer device, the liquid helium line is several meters long and about 4 mm in diameter. At a flow rate of 12.5 kg / h, the flow velocity in this line is about 2.2 m / s, and the flow is turbulent (Reynolds number is about 350,000). If the surface of the line can be considered technically smooth, the pressure loss can be calculated to be about 10 mbar per meter of line length. This closely matches practical considerations: for lines several meters long, an overpressure of about 50 mbar is typically required to transfer liquid helium.

[0095] In the transfer device described herein, the gaseous helium line (return line) must be configured so that the pressure loss is not unacceptably high. It should be noted that the mass flow rate through the gaseous helium line (return line) is much smaller than the mass flow rate through the liquid helium line (supply line). Specifically, to a first approximation (i.e., assuming a gaseous helium temperature of 4.2 K), the mass flow rate through the gaseous helium line is only 13.2 percent of the mass flow rate through the liquid helium line. To a first approximation, the volumetric flow rates through the two lines are the same. Therefore, because the flow velocities are the same for the same cross section and the density of gaseous helium is lower than that of liquid helium, the Reynolds number is also smaller (118,000), and the pressure loss is on the order of 1.7 mbar per meter (for a 4 mm diameter). Therefore, the pressure loss in the gaseous helium line can be neglected.

[0096] In reality, heat input into the helium circuit due to imperfect insulation of the transfer lines, pumps, friction, limited efficiency of heat exchangers, etc. causes the gaseous helium to warm slightly on its path from the NMR magnet to the transfer Dewar. Exemplary calculations show that this heat input is kept small.

[0097] Cryogenic gaseous helium is assumed to flow from the NMR magnet to the transfer dewar at a flow rate of 1.6 kg / h. Note that this value is at the lower end of a typical range; i.e., it is a "best-case" calculation for a relatively slow helium transfer. Assuming that 1.6 kg of gaseous helium warms from 4.2 K to 10 K on its way from the magnet to the transfer dewar, cooling the helium gas back to 4.2 K (the enthalpy of helium gas at 1 bar and 4.2 K is 20.6 kJ / kg, and the enthalpy of helium gas at 1 bar and 10 K is 55.4 kJ / kg) requires 55.68 kJ of "cold energy" or 15 W of cooling power (for the duration of the hourly transfer). This is about an order of magnitude more than a typical cryocooler, for example, can achieve in this temperature range.

[0098] As the temperature of the cold gaseous helium returning from the NMR magnet to the transport dewar increases, so does the specific volume of the gas and the pressure loss in the line. Helium gas at 1 bar and a temperature of 10 K has a pressure loss of, for example, 6.6 mbar for a line diameter of 4 mm, which is much higher than the 1.7 mbar calculated for a gas temperature of 4.2 K. Therefore, it is advantageous to oversize the cross section of the return gas line by some margin to ensure that the transport device functions reliably even at higher gas temperatures.

[0099] The helium transfer apparatus described herein can also be integrated into a "laboratory-scale" helium liquefier (also referred to herein as a laboratory liquefier). Such helium liquefiers often use a cryocooler-pulse tube or Gifford-McMahon refrigerator to liquefy gaseous helium at a relatively low rate, e.g., 20 l / d. The liquefier typically has an integrated storage capacity of several hundred liters (the volume of the helium vessel in the cryostat of the laboratory liquefier) ​​and is mounted on casters. As soon as helium is to be transferred to the NMR magnet, the entire liquefier is moved close to the magnet, and transfer to the magnet occurs directly from the liquefier's integrated storage capacity.

[0100] When the transfer apparatus described herein is combined with such a "laboratory-scale" or "laboratory liquefier," it is conceivable to use a cryocooler to pre-cool the liquid helium to a temperature below 4.2 K within the integrated storage capacity. If the liquid helium is cooled to, for example, 2.8 K, 4.63 kJ / kg of "cold energy" is stored in the helium tank (the enthalpy of liquid helium at 1 bar and 4.2 K is -0.12 kJ / kg, and the enthalpy of liquid helium at 1 bar and 2.8 K is -4.75 kJ / kg). That is, if the liquefier is ready (at 2.8 K) to transfer 100 liters of liquid helium (i.e., 12.5 kg) at the start of the transfer, 57.8 kJ of cold energy is available. This is more than would be required to cool 1.6 kg of helium gas (which is the amount of gas produced when transferring 100 liters of liquid helium) from the 10 K assumed above back down to 4.2 K. Cooling of the helium in the storage volume can be done hours or days before the planned helium transfer, and the cryocooler used in the liquefier does not need to be oversized for the proposed method.

[0101] A fifth embodiment of a cryostat assembly 1 according to the present invention is shown in Figure 7 and is largely similar to the form of Figure 1, so only the significant differences will be described here. For simplicity, the illustration of Figure 7 omits the control device and its connected components.

[0102] In this embodiment, a laboratory liquefier 31 is integrated into the device 5 for transferring liquid helium 6. The laboratory liquefier 31 comprises a reservoir cryostat 7 having a reservoir helium vessel 8 containing liquid helium 6 / 6b, and a cryocooler 32. Gaseous helium 11 / 11b can be liquefied by the cryocooler 32. In this case, the coldest cooling stage of the cryocooler 32 can reach temperatures well below 4.2 K. This allows the liquid helium 6 / 6b in the reservoir helium vessel 8 to be cooled to a temperature TLHe much lower than 4.2 K, e.g., about TLHe = 2.8 K here. The reservoir helium vessel 8 in the reservoir cryostat 7 typically has a storage capacity of 100 to 400 liters.

[0103] If the liquid helium 6 / 6b in the reservoir helium vessel 8 is cooled below the phase transition temperature to superfluid helium (2.17 K at atmospheric pressure), a particularly high cold supply is available due to the high specific heat in the region of the phase transition.

[0104] Slidable Piston Embodiment In Figures 8, 9 and 10, further embodiments of a cryostat assembly 1 according to the invention are shown in schematic form, in which the transfer device is formed with a movable piston in a reservoir cryostat 7. These embodiments correspond largely to the embodiment of Figure 1, so only the important differences will be described. For simplicity, the control device and its connected components have been omitted from the illustrations of Figures 8 to 10.

[0105] In the sixth embodiment shown in FIG. 8, a horizontally oriented piston 40 of a transport device 49 is disposed in a rigidly formed vacuum-insulated reservoir helium vessel 8. The piston is movable vertically within the reservoir helium vessel 8 by a motor-driven mechanism (not shown in detail). The piston 40 divides the reservoir helium vessel 8 into an upper first section 41 for gaseous helium 11 / 11b and a lower second section 42 for liquid helium 6 / 6b. The piston 40, which abuts against and can slide along the inner wall of the reservoir helium vessel 8, separates the two sections 41, 42 from each other in an airtight and liquid-tight manner. The reservoir cryostat-side end 13 of the supply line 9 extends from the second section 42. The return line 10 leads to the first section 41.

[0106] By moving the piston 40 downward, the second portion 42 contracts and the liquid helium 6 / 6b is forced into the supply line 9, thereby delivering the liquid helium 6 / 6c to the working helium vessel 3 in the working cryostat 2. At the same time, the first portion 41 expands and helium gas 11 is drawn from the return line 10 into the reservoir helium vessel 8, thereby delivering the liquid helium 6 / 6c from the working helium vessel 3 to the reservoir helium vessel 8.

[0107] The piston 40 is preferably thermally insulated, in particular vacuum insulated. To this end, the piston 40 can be made entirely or partly of a material with low thermal conductivity, such as plastic, preferably foamed plastic. The piston 40 can also comprise two plates facing each other, between which a vacuum space is formed (not shown in detail).

[0108] It should be noted that the presence of some liquid helium in the first portion 41 and / or some gaseous helium in the second portion does not harm the function of the transfer device 49 or the piston 40 (this applies to all embodiments of FIGS. 8, 9, and 10). If desired, a switchable valve 50 can be placed on the piston 40 via the control device, and this valve can be used to temporarily open a passage in the piston 40. To transfer liquid helium 6 / 6b (as described above), the switchable valve 50 is closed, i.e., the piston 40 is "sealed." If an undesirable amount of gaseous helium forms in the lower second portion 42 and an undesirable amount of liquid helium forms in the upper first portion 41 (e.g., due to significant heat conduction through the piston 40), the transfer can be paused and the switchable valve 50 can be opened. Liquid helium from the upper first portion 41 can then be allowed to flow into the lower second portion 42, and the piston 40 can be lowered to minimize the proportion of space in the lower second portion 42 filled with gaseous helium, after which the switchable valve 50 is closed again and the transfer operation continues. To allow for a fill "from above", the switchable valve 50 can also be opened during the initial filling of the reservoir cryostat 7 with liquid helium 6 / 6b (e.g., at the helium transfer site).

[0109] In the seventh embodiment of Fig. 9, which corresponds substantially to the embodiment of Fig. 8 and in which only the essential differences will be described, the walls of the vacuum-insulated reservoir helium vessel 8 in the upper section 43 and the lower section 44 are formed by flexible bellows 45, 46, respectively. In the central section 47 and the remaining parts, the walls of the reservoir helium vessel 8 are formed rigidly. A piston 40 of a conveying device 49 is rigidly attached to the central section 47 in an airtight and liquid-tight manner. In addition, the bellows 45, 46 are airtight and liquid-tight. This separates the reservoir helium vessel 8 into an upper first section 41 for gaseous helium 11 / 11b and a lower second section 42 for liquid helium 6 / 6b. The piston 40, here oriented horizontally, is movable, here vertically, within the reservoir helium vessel 8 by a motor-driven mechanism, again not shown in detail, so that the descent of the piston 40 causes liquid helium 6 / 6b to be pumped from the reservoir helium vessel 8 into the supply line 9 and gaseous helium 11 to be sucked into the reservoir helium vessel 8 from the return line 10.

[0110] For simplicity, FIG. 10 shows only a partial view from the eighth embodiment in the region of the reservoir cryostat 7 of the cryostat assembly 1. The reservoir helium vessel 8, vacuum insulated toward the outside, is again rigidly formed. In the interior space of the reservoir helium vessel 8, a first portion 41 for gaseous helium 11 / 11b is gas-tightly and liquid-tightly separated by a vertically oriented piston 40 here and a flexible bellows 48 attached to the inner surface of the vertical side wall of the reservoir helium vessel 8, while the remaining interior space of the reservoir helium vessel 8 forms a second portion 42 for liquid helium 6 / 6b. The piston 40 can be moved horizontally here using a motor-driven mechanism, not shown in detail. When the piston 42 is moved to the left in FIG. 10, i.e., the second portion 42 contracts and the first portion 41 expands, liquid helium 6 / 6b is pumped out of the second portion into the supply line 9, and gaseous helium 11 is sucked into the first portion 41 in the return line 10.

[0111] To improve the thermal insulation between the first part 41 and the second part 42, the bellows 48 can also be formed to provide thermal insulation, for example by means of a double wall with a vacuum space therebetween (not shown in detail). [Explanation of symbols]

[0112] 1. Cryostat Assembly 2 Practical cryostat 3 Practical helium container 5. Device for transferring liquid helium 6 Liquid helium (general) 6a Liquid helium (in a practical helium container) 6b Liquid helium (in reservoir helium container) 6c Liquid helium (transported through supply lines) 7 Reservoir Cryostat (Transport Dewar) 8 Reservoir helium container 9 Supply Line 10 Return Line 10a Return line outer wall 10b Inner wall of return line 11 Gaseous helium (general) 11a Gaseous helium (in a practical helium container) 11b Gaseous helium (in reservoir helium container) 11c Gaseous helium (carried by return line) 12a Circulation pump (return line, low temperature) 12b Circulation pump (in the supply line) 12c Circulation pump (return line, line loop) 13 Reservoir cryostat end of supply line 14 Working cryostat end of supply line 15 Helium Tower (Magnetic Tower) 16 Helium Tower (Magnetic Tower) 17 Control device 18 Pressure sensor (inside the reservoir helium container) 19 Pressure sensor (inside practical helium vessel) 20 Heating device 21 Helium compressed gas reservoir 22 Control valve 23 Line Loop 23a Line Loop Entrance Area 23b Line loop exit area 24 Heat exchanger 25 Room temperature warmth loop 26 Vacuum boundary 27 Vacuum Boundary (Common Transportation Line) 28 Common Transportation Line 29 Spacer (vacuum boundary to return line) 30 Spacer (return and supply lines) 31 Laboratory Liquefaction Machine 32 Cryocooler 40 pistons 41 First Part 42 Second Part 43 Upper division 44 Lower Division 45 Upper Bellows 46 Lower Bellows 47 Central section 48 Bellows 49 Conveyor equipment 50 Switchable valve (inside piston) QR return line cross section QZ supply line cross section

Claims

1. 1. A cryogenic vessel assembly (1) comprising a working cryostat (2) having a working helium vessel (3) and a device (5) for transferring liquid helium (6) to the working helium vessel (3) of the working cryostat (2), The device (5) a reservoir cryostat (7) having a vacuum insulated reservoir helium vessel (8) for storing liquid helium (6, 6b) available for filling said working helium vessel (3); a liquid helium (6, 6c) supply line (9) extending from said reservoir helium vessel (8) for connection to said working helium vessel (3); a return line (10) for gaseous helium (11, 11c) leading into said reservoir helium vessel (8) for connection to said working helium vessel (3); a transfer device (49) capable of transferring the liquid helium (6, 6b) from the reservoir helium vessel (8) through the supply line (9) to the working helium vessel (3) and of transferring gaseous helium (11, 11a) from the working helium vessel (3) to the reservoir helium vessel (8) through the return line (10); Equipped with the conveying device (49) comprises a circulation pump (12a; 12c) provided for the gaseous helium (11, 11c) in the return line (10), The supply line (9) is connected to the practical helium vessel (3) and leads into the practical helium vessel (3); the return line (10) is connected to and extends from the utility helium vessel (3); the practical cryostat is an NMR magnet cryostat, the return line (10) comprises a line loop (23) including an inlet region (23a) and an outlet region (23b), the outlet region (23b) being thermally coupled to the inlet region (23a) via a heat exchanger (24); the line loop (23) includes the circulation pump (12c), and the circulation pump (12c) is at room temperature; A cryogenic vessel assembly (1) characterized in that:

2. Cryocontainer assembly (1) according to claim 1, characterized in that the supply line (9) and the return line (10) are vacuum insulated.

3. 3. A cryogenic vessel assembly (1) according to claim 2, characterized in that the supply line (9) and the return line (10) are at least partially formed in a common transport line (28), the common transport line having within a common vacuum boundary (27) a vacuum chamber through which both the supply line (9) and the return line (10) extend.

4. 4. The cryogenic vessel assembly (1) according to claim 3, characterized in that the supply line (9) and the return line (10) extend coaxially within the common vacuum boundary (27), the supply line (9) being located radially inside the return line (10).

5. 4. A cryocontainer assembly (1) according to claim 3, characterized in that the supply line (9) and the return line (10) run parallel and side by side with each other within the common vacuum boundary (27).

6. 6. The cryogenic vessel assembly (1) according to any one of claims 3 to 5, characterized in that the return line (10) is suspended in the common vacuum boundary (27) by means of one or more spacers (29), and the supply line (9) is suspended in the return line (10) but not in the common vacuum boundary (27) by means of one or more spacers (30).

7. The line cross section QZ of the supply line (9) and the line cross section QR of the return line (10) are QR>QZ, 2. The cryocontainer assembly (1) according to claim 1, characterized in that:

8. 2. The cryocontainer assembly (1) according to claim 1, characterized in that the supply line (9) and the return line (10) are made flexible.

9. A cryogenic container assembly (1) as described in claim 1, characterized in that the device (5) further comprises a control device (17) for controlling the helium pressure within the device (5) and / or within the practical helium container (3).

10. The device (5) a heating device (20) placed inside said reservoir helium vessel (8), and / or 10. The cryogenic vessel assembly (1) according to claim 9, further comprising a helium compressed gas reservoir (21) having a control valve (22) for connection to the utility helium vessel (3), wherein the control device (17) is configured to control the heating device (20) and / or the control valve (22).

11. The device (5) comprises a laboratory liquefier (31) for helium, The laboratory liquefier (31) - said reservoir cryostat (7) with said reservoir helium vessel (8); A cryocontainer assembly (1) according to claim 1, characterized in that it comprises a cryocooler (32) for liquefying gaseous helium (11).

12. The cryogenic vessel assembly (1) further comprises at least one pressure sensor (19) in the region of the working helium vessel (3); 2. The cryocontainer assembly (1) according to claim 1, characterized in that the pressure sensor (19) is connected to a control device (17) of the device (5).

13. A method for transferring liquid helium from a reservoir helium vessel (8) of a reservoir cryostat (7) to a working helium vessel (3) of a working cryostat (2) using the cryogenic vessel assembly (1) of claim 1, comprising: the liquid helium (6, 6b) stored in the reservoir helium vessel (8) is transferred from the reservoir helium vessel (8) to the practical helium vessel (3) through a liquid helium (6, 6c) supply line (9) extending from the reservoir helium vessel (8) and connected to the practical helium vessel (3); At the same time, gaseous helium (11, 11a) is returned from the practical helium vessel (3) to the reservoir helium vessel (8) through a gaseous helium (11, 11c) return line (10) connected to the practical helium vessel (3) and leading into the reservoir helium vessel (8).

14. The method according to claim 13, characterized in that the volumetric flow rate of liquid helium (6, 6c) passing through the supply line (9) and the volumetric flow rate of gaseous helium (11, 11c) passing through the return line (10) are approximately the same.

15. The temperature TLHe of the liquid helium (6, 6b) in the reservoir helium vessel (8) is at least at the start of transfer of the liquid helium (6, 6b): TLHe<4.2K, 15. The method according to claim 13 or 14, wherein

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