Liquid helium storage cryostat comprising a vertically extended convection-suppression system

Abstract

The invention relates to a storage cryostat (2) for liquid helium (7), suitable for transferring liquid helium (7) from the storage cryostat (2) into an application cryostat (3), wherein the storage cryostat (2) comprises: - a vacuum-insulated helium vessel (6) for liquid helium (7), the helium vessel (6) having a vertical height HHB that can be filled with liquid helium (7), - a transfer line (4) for liquid helium (7), having an inlet opening (20) which opens into a lower region of the helium vessel (6), in particular into a lower fifth of the helium vessel (6), and - a convection-suppression system (9) which is arranged within the helium vessel (6) and impedes vertical convection of liquid helium (7) in the helium vessel (6), characterised in that the convection-suppression system (9) is formed in the helium vessel (6) over a height interval (IKS) with a vertical height HKS, where HKS ≥ 0.50 × HHB, and in that the convection-suppression system (9) impedes the vertical convection of liquid helium (7) in the helium vessel (6) over the region of the height interval (IKS) of the convection-suppression system (9). The invention provides a storage cryostat that enables simple and rapid transfer of liquid helium from the storage cryostat into the application cryostat, with minimised helium losses.

Description

[0001] Storage cryostat for liquid helium, with vertically extended convection inhibition system

[0002] The invention relates to a storage cryostat for liquid helium, suitable for transferring liquid helium from the storage cryostat to an application cryostat, wherein the storage cryostat comprises a vacuum-insulated helium container for liquid helium, the helium container having a vertical height HHB that can be filled with liquid helium, a transfer line for liquid helium with an inlet opening that opens into a lower region of the helium container, in particular into a lower fifth of the helium container, and a convection inhibition system which is arranged in the helium container and hinders vertical convection of liquid helium in the helium container.

[0003] Such a storage cryostat is described in the published German patent application 10 2023 212 894.2. Superconducting magnets, for example for NMR spectroscopy (NMR = nuclear magnetic resonance) or magnetic resonance imaging (MRI), require cooling to maintain their superconducting state. In many cases, the superconducting magnet is housed in an application cryostat containing liquid helium, typically at a temperature of approximately 4.2 K, which corresponds to the boiling point of liquid helium at atmospheric pressure. Cooling with liquid helium in an application cryostat is also known from other applications.

[0004] Since the application cryostat cannot provide perfect thermal insulation, or because heat is introduced into the application cryostat by the application itself, the liquid helium evaporates during operation. If the liquid helium level in the application cryostat drops too low for continued operation, liquid helium is added to the application cryostat.

[0005] It should be noted that helium is a scarce resource. Helium is a byproduct of natural gas production. Its availability on the world market is decreasing, and its price is rising; see D. Kramer, “Helium is again short in supply”, Physics Today, April 4, 2022, American Institute of Physics, https: / / doi.org / 10.1063 / PT.6.2.20220404a.

[0006] Therefore, efforts are being made to minimize helium consumption for the operation of application cryostats. Many users are investing in helium recovery systems that capture and reliquefy evaporating helium.

[0007] A significant loss of helium occurs during the standard procedure for refilling the application cryostat with liquid helium from a storage dewar ("storage cryostat"). This standard procedure is described, for example, in the company publication "NMR Magnet System UltraShield Magnets (English Version) User Manual" Version 006 (October 12, 2004), chapter 12, from Bruker BioSpin AG, Fällanden, Switzerland. This standard procedure can be summarized as follows:

[0008] Step a) The storage dewar (also called "storage cryostat" or "transport dewar") is moved to the vicinity of the application cryostat, in the aforementioned company publication an NMR magnet, to within a few meters.

[0009] Step b) The warm transfer line is inserted into the transport dewar so that its (first) end lies below the liquid surface of the contained liquid helium.

[0010] Step c) The heat input from the warm transfer line causes helium in the transport dewar to evaporate. This increases the pressure in the transport dewar, forcing liquid helium into the transfer line, which is thereby cooled. The helium that escapes from the end of the transfer line during the cooling process is usually not collected and is lost to the atmosphere. For a typical transfer line of just a few meters in length, several liters of liquid helium are required for cooling.

[0011] Step d) Once the helium escaping from the (second) end of the transfer line, which is facing away from the transport dewar, is sufficiently cold (i.e., the transfer line has cooled sufficiently), the transfer line is connected to the application cryostat (e.g., an NMR magnet), i.e., the second end is inserted into the application cryostat.

[0012] Step e) After the transfer line is connected to the application cryostat, liquid helium flows from the transport dewar into the application cryostat. The mass flow is driven by the pressure difference between the transport dewar and the application cryostat. As mentioned above, an overpressure has built up in the transport dewar due to the insertion of the transfer line. However, the pressure increase in the transport dewar, caused by the heat input when the transfer line is inserted, is usually insufficient to transfer the desired amount of liquid helium. Therefore, helium gas from a pressurized gas cylinder is introduced into the transport dewar via a pressure regulator to maintain a constant, high pressure. Typically, the overpressure set in the transport dewar is approximately 50–100 mbar.

[0013] During the transfer of liquid helium, gaseous helium is forced out of the application cryostat at an outlet, corresponding to the volume of inflowing liquid helium.

[0014] To clarify: At the start of the liquid helium transfer to the application cryostat, the application cryostat, or rather its helium tank ("application helium container"), is typically not empty, but still contains a small amount of liquid helium, and is otherwise filled with gaseous helium at a temperature of 4.2 K and a pressure of approximately 1 bar. As the helium tank slowly fills with liquid helium during the transfer, the cold gaseous helium that was in the helium tank before the start of the transfer is gradually forced out of the helium tank and escapes through the outlet of the application cryostat.

[0015] Gaseous helium at 4.2 K and atmospheric pressure has a density of 16.5 g / l. Liquid helium at 4.2 K and atmospheric pressure has a density of 125 g / l. Therefore, if 100 liters of liquid helium – i.e., 12.5 kg of helium – are transferred, 100 liters of gaseous helium – i.e., 1.65 kg – will be forced out of the cryostat. This corresponds to 13.2 liters of liquid helium, or 13.2% of the transferred amount.

[0016] In most cases, this amount of helium simply escapes into the atmosphere through the outlet of the application cryostat, which is unsustainable and also increases the operating costs of the application cryostat. Alternatively, it is possible, for example, to install a gas balloon storage system that is sufficiently large to capture the gaseous helium produced during the helium transfer (the "transfer losses") at the outlet and feed it to a high-pressure storage tank or liquefier. In the piping system leading to the gas balloon and in the gas balloon itself, the gaseous helium warms up to room temperature, resulting in a significant increase in the gas's volume. 100 liters of gaseous helium at atmospheric pressure and 4.2 K correspond to approximately 10,000 liters (i.e., 10 m³). 3) at atmospheric pressure and room temperature. The collection system for the gaseous helium must also be designed in such a way that the heating of the gaseous helium (to room temperature) is ensured with the expected gas flow, so that damage to the gas balloon due to excessive subcooling is avoided.

[0017] In a typical helium transfer into an NMR magnet, between 100 and 400 liters of liquid helium are transferred, depending on the magnet type. A typical transfer takes about an hour. During this time, between 10 and 40 cubic meters of gaseous helium at room temperature are produced, which must be stored in a gas balloon or processed by a recovery system (e.g., compressed in a pressure tank). This corresponds to 13 to 50 liters of liquid helium per hour (or between approximately 1.6 and 6.6 kg of helium per hour). Correspondingly large gas balloons or high-performance recovery systems are very space-consuming and also very expensive. Furthermore, it should be noted that reliquefying the room-temperature, gaseous helium from the gas balloon is quite energy-intensive.

[0018] German patent application DE 10 2022 209 941 A proposes that during the transfer of liquid helium from the storage dewar to the application dewar, the gaseous helium expelled from the application cryostat is returned to the storage dewar via a return line. A feed line extends into the stored liquid helium within the storage dewar. In one embodiment, the liquid helium in the storage dewar has a temperature of less than 4.2 K. However, the proposed return line is quite complex to install. The subsequently published German patent application DE 10 2023 212 894.2 proposes inserting a condensation heat exchanger into the application cryostat for the duration of the transfer. During the transfer of the liquid helium, the condensation heat exchanger liquefies the gaseous helium into liquid helium.The cooling capacity of the condensation heat exchanger is controlled such that the volume of liquid helium transferred per unit of time through the transfer line is approximately equal to the volume change of the helium that condenses from helium gas to liquid helium per unit of time at the condensation heat exchanger. This approach completely avoids helium loss during the transfer of the liquid helium; however, the additional condensation heat exchanger required in the application cryostat is comparatively complex to install and expensive.

[0019] It should also be noted that it is possible to actively cool application cryostats (e.g., containing superconducting magnets for NMR applications) in continuous operation using a cryocooler; see, for example, US 2002 / 0002830 Al. In this case, it is not necessary to refill with liquid helium, and the problem of helium loss during refilling is eliminated.

[0020] Active cooling has several disadvantages compared to passive operation with a liquid helium bath, particularly the introduction of vibrations into the application cryostat by the cryogenic cooler, high energy consumption (approximately 8 kW in continuous operation), relatively high maintenance costs, and relatively long downtimes during maintenance activities. In the case of cryogen-free, actively cooled superconducting magnets (i.e., superconducting magnets that do not have a buffer volume of liquid helium), the very short time between a potential power failure and the breakdown of superconductivity in the superconducting magnet ("time-to-quench") is an additional factor.

[0021] US Patent 8,671,698 describes a helium reliquefier with a pulse tube cooler that is separate from the application cryostat. US Patent 2007 / 0107445 Al discloses a retrofittable helium reliquefier. Installing such a device is quite complex. Furthermore, vibrations can be introduced into the application cryostat, resulting in high energy and maintenance costs.

[0022] DE 40 39 365 Al describes an NMR magnet with a cryostat in which supercooled liquid helium is arranged in a first, lower chamber and liquid helium at atmospheric pressure at 4.2 K is arranged in an upper, second chamber, with a heat-insulating but pressure-permeable barrier arranged between the chambers.

[0023] In NASA's SHOOT experiment in June 1993 (SHOOT = superfluid helium on orbit transfer), superfluid helium was transferred from one container to another in microgravity, utilizing the so-called "fountain effect." An overview of this experiment can be found online at https: / / cryo.gsfc.nasa.gov / SHOOT / SHOOT.html (downloaded on May 8, 2024).

[0024] German patent application 10 2023 212 894.2 describes the process of transferring liquid helium from the storage cryostat to the application cryostat by liquefying gaseous helium within the application cryostat using a condensation heat exchanger. One variant proposes transferring subcooled liquid helium from the storage cryostat to the application cryostat. When the subcooled liquid helium warms to 4.2 K within the application cryostat, heat is extracted from the application cryostat. This reduces the cooling capacity required at the condensation heat exchanger. In this variant, the storage cryostat incorporates a substantially plate-shaped, horizontally oriented thermal barrier in its upper section. This barrier allows liquid helium to flow through but is thermally insulating. The transfer line terminates near the bottom of the storage cryostat's helium reservoir.A cold head extends from above through the thermal barrier and cools the liquid helium below the thermal barrier to approximately 3.7 K with its lowest cooling stage. Saturated helium is located above the thermal barrier at a temperature of approximately 4.2 K. The storage cryostat is connected to a pressurized gas storage system.

[0025] When helium gas is introduced from the pressurized gas storage unit into the storage cryostat in this setup, the helium gas pressure in the storage cryostat is initially increased. The gaseous helium exerts pressure on the saturated liquid helium at 4.2 K, which in turn exerts pressure through the thermal barrier onto the supercooled liquid helium at 3.7 K. The supercooled liquid helium is then conveyed from the storage cryostat to the application cryostat via the transfer line. With a sufficiently high flow rate of the supercooled liquid helium, the helium level in the storage cryostat drops. Once the helium level falls below the thermal barrier, the supercooled liquid helium mixes with the saturated liquid helium below the thermal barrier through convection. This causes the surface temperature of the liquid helium to drop below 4.2 K.Helium gas above the liquid level, which initially has a gas pressure of approximately 1 bar or slightly higher, then rapidly condenses on the surface of the liquid helium, and the gas pressure drops rapidly. Consequently, no further gas pressure can be built up in the storage cryostat, even if more helium gas were added from the pressurized gas storage tank. Therefore, when transferring the supercooled liquid helium, care must be taken to ensure that the liquid helium level does not fall below the thermal barrier. This could be achieved by continuously introducing sufficient gaseous helium from the pressurized gas storage tank into the storage cryostat and immediately liquefying it using the cold head in the storage cryostat. However, this would result in a comparatively slow transfer of the supercooled liquid helium.

[0026] From JP 2012 49 413 A, a cooling device for a superconducting component is known, comprising a first tank for liquid nitrogen with a feed pump and a second tank for liquid nitrogen containing the superconducting component. The two tanks are connected to each other via a feed line and a return line. The feed line extends into the area of ​​the liquid component in the first tank.

[0027] Note of the invention

[0028] The object of the invention is to provide a storage cryostat with which a transfer of liquid helium from the storage cryostat to an application cryostat can be carried out simply, quickly and with minimized helium losses.

[0029] This problem is solved according to the invention by a device of the type mentioned at the outset, which is characterized in that the convection inhibition system in the helium container is designed in a height interval (IKS) with a vertical height HKS, with HKS > 0.50*HHB, and that the convection inhibition system hinders the vertical convection of liquid helium in the helium container over the area of ​​the height interval (IKS) of the convection inhibition system.

[0030] With the storage cryostat according to the invention, it is possible to transfer stored supercooled liquid helium to an application cryostat in a short time. For this purpose, a corresponding gas pressure of gaseous helium can be set above a liquid helium level in the helium reservoir of the storage cryostat and used to pump out the supercooled liquid helium.

[0031] According to the invention, a convection inhibition system is provided in the helium reservoir of the storage cryostat, which extends in the vertical direction. The convection inhibition system extends vertically over a height interval (IKS) that has a height HKS in the vertical direction. This height HKS is at least as great as half the height HHB of the helium reservoir of the storage cryostat (the maximum usable height for filling with liquid helium). Within the entire height interval (IKS), the convection inhibition system prevents vertical convection in the liquid helium.

[0032] The convection barrier system is (sufficiently) permeable to liquid helium in the vertical direction over the area of ​​the height interval (IKS), e.g. at bores in a plate, but is (largely) thermally insulating in the vertical direction.

[0033] The convection inhibition system according to the invention makes it possible to prevent the mixing of layers of liquid helium with different densities or temperatures across the height interval (ICS) in the helium container. Instead, the existing stratification of liquid helium with different densities or temperatures can be maintained. In particular, existing layers of liquid helium can traverse the convection inhibition system together in the vertical direction without altering the relative arrangement of the existing layers.

[0034] In particular, it is possible to arrange liquid helium in the helium reservoir of the storage cryostat, with saturated liquid helium at 4.2 K or higher present in an upper section, supercooled liquid helium at a desired limit temperature GT or lower (e.g., GT = 3.39 K) present in a lower section, and the temperature of the liquid helium transitioning from 4.2 K to GT in a middle section. Gaseous liquid helium can be arranged above the upper section containing the liquid helium.

[0035] By applying a suitable pressure (typically a slight overpressure compared to the application cryostat) of gaseous helium in the storage cryostat, supercooled liquid helium from the lower part of the storage cryostat can be transferred through the transfer line (with an inlet opening in the lower part of the helium container) into the application cryostat. The gaseous helium at 4.2 K (or higher) borders the upper part of the liquid helium at 4.2 K (or higher), so that the gas and liquid phases are in equilibrium, and gas pressure can therefore be easily built up in the storage cryostat.

[0036] During the removal of supercooled helium from the lower section, the liquid helium level can drop without any problems. As long as the middle section of liquid helium (where the transition between 4.2 K and the limit temperature GT occurs) remains above the lower edge of the convection damping system or within the altitude interval (IKS), the stratification of the liquid helium in the middle section is maintained. Accordingly, the upper section of liquid helium retains its temperature of 4.2 K (or higher), and there are no problems with pressure build-up in the helium gas. The lower section of liquid helium also retains its temperature of GT or lower. However, the amount of liquid helium in the helium reservoir of the storage cryostat, which belongs to the lower section, gradually decreases due to the removal process.

[0037] Due to the large extension of the convection inhibition system over at least half the height of the helium container of the storage cryostat, a correspondingly large proportion of the helium container can be used for the provision and rapid delivery of supercooled liquid helium.

[0038] The subcooling of the subcooled, liquid helium, which is pumped into the application cryostat, can be used to condense any gaseous helium present in the application cryostat or its application helium container.

[0039] When a volume of liquid helium is introduced into the application cryostat, a corresponding volume is no longer available for the gaseous helium previously present in the application cryostat. In the prior art, this volume ("displaced volume") of gaseous helium is, in the worst case, simply lost to the environment, or complex measures are taken to prevent helium loss (e.g., collection with a balloon storage system, or return to the storage cryostat, or an additional condensation heat exchanger in the application cryostat for liquefaction of helium gas). By using the storage cryostat according to the invention, supercooled liquid helium can be introduced into the application cryostat simply and quickly, whereby the supercooling of the introduced, supercooled helium allows any gaseous helium present in the application cryostat to condense.This makes it easy to create space in the application cryostat for the injected liquid helium.

[0040] The storage cryostat according to the invention, or the introduced subcooled liquid helium, can reduce helium losses (e.g., the amount of helium gas released into the environment can be reduced because further measures would be too expensive and complex), or other measures can be made less complex (e.g., the cooling capacity of a condensing heat exchanger in the application cryostat can be reduced). It is also possible to create enough space in the application cryostat simply by sufficiently subcooling (i.e., a sufficiently low temperature) the introduced subcooled helium that no gaseous helium would be displaced from the application helium container (see below).

[0041] Note that the convection inhibition system according to the invention can be set up very cost-effectively, for example by filling the helium reservoir of the storage cryostat with perforated hollow spheres (see below). The storage cryostat can also be equipped with wheels for easier transport.

[0042] The vertical interval (IKS) denotes a vertical zone in which the convection inhibition system is formed within the helium container. HKS corresponds to the length (in the vertical direction) of this vertical zone. The vertical direction corresponds to the direction of gravity. In a horizontal cross-section, the convection inhibition system typically occupies a construction area BFL, at least locally and preferably over the entire area of ​​the vertical interval IKS, which corresponds to at least 60%, preferably at least 80%, and particularly preferably at least 95%, of the cross-sectional area QFL of the helium container. Furthermore, the convection system typically occupies a construction space BAU within the helium container, which corresponds to at least 40%, preferably at least 60%, and particularly preferably at least 72%, of the internal volume INV of the helium container.

[0043] Preferred embodiments of the inventive device

[0044] In a preferred embodiment of the storage cryostats according to the invention, it is provided that HKS>0.75*HHB, preferably HKS>0.90*HHB. This allows an even larger proportion of the container to be used for a rapid transfer of supercooled liquid helium.

[0045] A preferred embodiment further includes a cooling device in the storage cryostat. The cooling device can comprise a cold head or a cooling stage thereof as a heat sink and can, in particular, be configured with a Gifford-McMahon condenser or a pulse tube condenser. Alternatively, the cooling device can comprise a refrigerator as a heat sink, the operation of which is based on the expansion of helium in a closed circuit. With the cooling device, the storage cryostat can be used as a helium liquefier (reliquefier). The gaseous helium to be liquefied can, for example, be stored in a local storage tank (which is connected to the application cryostat during normal operation, also called an intermediate storage tank) and can be reliquefied over the course of several days before the transfer of the liquid helium into the storage cryostat.The storage reservoir can comprise a gas balloon and / or a pressurized gas reservoir (with an upstream compressor). A preferred embodiment features a heat sink of the cooling device located in a lower region of the helium reservoir, particularly in the lower fifth. The heat sink is typically situated below the convection damping system or in the lower region, particularly in the lower third, of the convection damping system. The cooling device allows for the simple provision of supercooled liquid helium in the lower part of the cryostat, particularly at a temperature of 3.39 K or less.

[0046] An advantageous embodiment involves the convection inhibition system being fixed in place within the storage cryostat. This makes the storage cryostat particularly robust and simple in design. Turbulence of liquid helium is avoided.

[0047] In a preferred embodiment, the convection inhibition system comprises a plurality of vertically stacked, horizontally or approximately horizontally extending barrier structures, wherein the barrier structures are liquid-tight except for a few interruptions, and wherein, in projection onto a horizontal plane, each barrier structure occupies an area FHS, and the associated interruptions of this barrier structure collectively occupy an area FUN, with FHS > 10 * FUN, preferably FHS > 50 * FUN. With this design, a robust and highly efficient convection inhibition system can be easily constructed. Note that in this design, the convection inhibition system is typically installed in the storage cryostat before it is welded shut.

[0048] An advantageous further development of this embodiment involves the barrier structures being designed as flat plates, and the openings being formed as bores in the plates. This design is cost-effective and has proven its worth in practice. The plates are typically made of plastic or thin sheet metal.

[0049] In another advantageous embodiment, the interruptions of vertically adjacent barrier structures are offset from one another in at least one horizontal direction. This ensures that a vertical liquid flow must be deflected horizontally by the interruption of a first barrier structure before it can continue flowing vertically through an interruption at the next barrier structure. Accordingly, the formation of vertical flows (especially within a circular flow) of liquid helium in the helium container is made more difficult.

[0050] A further preferred embodiment provides that the convection inhibition system has a plurality of vertically or approximately vertically oriented divider structures, through which a plurality of top and bottom open, but horizontally liquid-tight chambers are formed in the helium container, and that for a respective maximum inner diameter IDK of the chambers and a maximum container diameter BDM of the helium container, each measured in the horizontal plane, the following applies:

[0051] BDM > 10*IDK, preferably BDM > 20*IDK. The divider structures prevent the formation of large circular flows of liquid helium within the helium container. Convection vortices cannot form within the very narrow chambers (compared to the maximum container diameter). The divider structures generally extend over the entire height interval IKS.

[0052] An advantageous further development of this embodiment is one in which the divider structures are formed by vertically or approximately vertically oriented tubes, particularly where the tubes are bundled. This design is particularly easy to manufacture. A further preferred embodiment is one in which the convection barrier system comprises a bed of hollow bodies, particularly hollow spheres, wherein the walls of the hollow bodies each have a plurality of holes. This design of the convection barrier system is very simple and cost-effective to implement and can, in particular, be easily retrofitted. Typically, for a hole diameter DL of the holes and a maximum diameter DHK of the hollow bodies, DL < 0.2 * DHK applies.

[0053] A particularly preferred embodiment comprises at least one accumulation of open-pore filling material. In other words, the filling material is impregnable with liquid helium. This allows for the simple and cost-effective installation of a convection-inhibiting system in the helium container. Preferably, the pore area comprises at least 80% of the volume of the open-pore filling material. Usually, a single accumulation is provided for the entire helium container (open-pore filling material arranged in a single fabric bag, or open-pore filling material arranged directly in the helium container, e.g., as a loose fill). However, several separate accumulations can also be installed in the helium container (e.g., in several fabric sleeves / bags).

[0054] In an advantageous further development of this embodiment, the filling material comprises a fibrous material, in particular glass wool. Fiber material, especially glass wool, is readily available at low cost, allows for the absorption of a large proportion of liquid helium, and, due to its flexibility at room temperature, can be easily packed into the helium container through a neck tube.

[0055] An equally advantageous embodiment includes a filling material comprising an open-cell foam, particularly one made of a plastic material. Open-cell foams are comparatively mechanically stable and readily available at low cost. The open-cell foam can, in particular, be a polyurethane foam. A further advantageous embodiment provides that a filter, in particular a sintered filter, is arranged at the inlet opening of the transfer line. The filter is permeable to liquid helium but retains fragments and / or abrasion of the filling material. This minimizes the introduction of fragments or abrasion of the filling material into the application cryostat and prevents blockages of the transfer line.

[0056] Equally advantageous is a further development in which a respective accumulation of filling material is arranged in a fabric sheath, the fabric sheath being permeable to liquid helium but retaining fragments and / or abrasion of the filling material. This also minimizes the introduction of fragments or abrasion of the filling material into the application cryostat and prevents blockages of the transfer line.

[0057] A particularly preferred embodiment provides that the storage cryostat has a neck tube through which the interior of the helium container is accessible, and that the convection inhibition system is designed to be inserted into the helium container through this neck tube, particularly wherein the convection inhibition system comprises a plurality of unconnected individual elements, each of which is small enough to be passed through the neck tube, and / or the convection inhibition system is wholly or partially flexible at room temperature. This allows an existing helium container of a storage cryostat to be easily retrofitted with a convection inhibition system, and / or the convection inhibition system can be easily replaced during maintenance work on the storage cryostat. In particular, the convection inhibition system does not need to be installed before the helium container is welded shut.Depending on the material, the convection dampening system can be stuffed or poured through the neck tube, either as a whole or in individual parts. Alternatively, the convection dampening system can be inserted through the neck tube in a folded state, either as a whole or in individual parts, and then unfolded inside the helium cylinder.

[0058] A particularly preferred embodiment is one in which the following applies to the installation space BAU occupied by the convection inhibition system in the helium container and the maximum volume MW of liquid helium displaced by the convection inhibition system in the helium container: BAU > 5 * MVV, preferably BAU > 20 * MVV. With these ratios of BAU and MW, a large proportion of the helium container can be used for storing liquid helium. Accordingly, for a given desired volume of stored (supercooled) liquid helium, a comparatively small storage cryostat is possible. The specified ratios can be achieved with minimal effort, for example, using horizontal barrier structures / plates or open-pore filling material.

[0059] In an advantageous embodiment, the convection inhibition system is at least partially, preferably completely, made of a material or materials with a specific thermal conductivity X measured at 4.2 K, with X < 0.1 W / (cm*K), preferably X < 0.01 W / (cm*K), particularly wherein the convection inhibition system is at least partially made of plastic, preferably nylon. Due to the overall low thermal conductivity of the convection inhibition system, heat conduction in the vertical direction can be minimized, and a vertical temperature stratification of liquid helium in the helium container can be easily established and maintained.

[0060] An embodiment is also advantageous in which the convection inhibition system is designed such that, on average, for a horizontal thermal conductivity HWL of the convection inhibition system and a vertical thermal conductivity VWL of the convection inhibition system, VWL < 0.33 * HWL, preferably VWL < 0.2 * HWL. In other words, the average thermal conductivity of the convection inhibition system is significantly lower in the vertical direction than in the horizontal direction. This helps to minimize heat conduction in the vertical direction, so that a vertical temperature stratification of liquid helium in the helium tank can be easily established and maintained. Furthermore, horizontal temperature equalization can be achieved via the significant horizontal heat conduction.

[0061] In an advantageous embodiment, one or more horizontal heat-conducting elements are provided in the area of ​​the vertical interval (ICS) of the convection damping system and / or below the convection damping system. These elements are horizontally or substantially horizontally oriented, and in particular, one or more of the horizontal heat-conducting elements are connected to a heat sink of a cooling device. The heat-conducting elements can promote horizontal temperature equalization. The heat-conducting elements can be made of metal, perforated metal sheets, or metal mesh, for example, copper. The horizontal heat-conducting elements ensure that the (liquid) helium has a temperature as uniform as possible throughout a given horizontal plane (and is, for example, not significantly colder on the side near a cold head than on the side facing away from the cold head).If a sensor device for determining the current fill level of liquid helium (also called a helium level sensor or fill level sensor) and / or a heating system with one or more heating elements are present, it is typically intended that the helium level sensor and the heating elements protrude through one or more heat-conducting elements. In this case, a small gap (typically a few centimeters) should be maintained between the heat-conducting element and the helium level sensor or the heating element to prevent the heat-conducting element from dissipating the heat emanating from the helium level sensor and the heating element horizontally. Preferably, there is no direct contact between the helium level sensor / heating element and the heat-conducting element.

[0062] A particularly preferred embodiment provides that a heating system is arranged in the helium container, that the heating system comprises a plurality of heating sections distributed vertically within the helium container over a height interval (IHZ) of the heating sections, wherein the height interval (IHZ) of the heating sections has a vertical height HHZ, where HHZ > 0.5 * HHB, preferably HHZ > 0.75 * HHB, and particularly preferably HHZ > 0.9 * HHB, and that the heating system is configured to vary the distribution of a relative heating power to the heating sections along the vertical direction. The heating system makes it possible to vaporize liquid helium in the helium container of the storage cryostat, thereby increasing the gas pressure PVOR in the helium container. This facilitates the transfer of the liquid (supercooled) helium from the storage cryostat to the application cryostat.The design allows the heat input to be adjusted and varied along the vertical direction. Preferably, heating power is directed into the upper part of the liquid helium, which has a temperature of 4.2 K or slightly above, or into the gas space above the liquid helium, in order to avoid reducing the available amount of supercooled liquid helium.

[0063] A particularly preferred embodiment is one in which the heating system is configured to change the distribution of the relative heating power depending on the fill level of liquid helium in the helium container. This allows the heating power to be optimally applied with regard to the current fill level, especially in the upper part of the liquid helium or in the gas space above it.

[0064] A further development is advantageous if it stipulates that the heating output at the heating sections is temperature-dependent and reaches its maximum at 4.2 K. This makes it possible to operate the heating system "passively" (without active control) while still concentrating the heating output in the upper part of the liquid helium. The heating output is reduced both in the colder (i.e., deeper) layers of the liquid helium and in the gas phase, where the heating element heats up rapidly to more than 4.2 K due to reduced thermal contact with the helium. The heating system can have one or more continuous heating elements in the vertical direction, with sections of these elements being considered heating sections.

[0065] A further preferred design includes a heating system with a control device that allows for variable control of the distribution of the relative heating power across the heating sections, particularly where the heating power of each individual heating section can be set using the control device. This design allows for particularly targeted application of the heating power and minimizes energy input into undesired areas, especially into supercooled liquid helium at 3.39 K or less.

[0066] A particularly advantageous variant of this improved design includes a storage cryostat with a sensor for determining the current liquid helium level in the helium tank, and a control unit configured to distribute the heating power so that it is concentrated on the heating section(s) currently located below the liquid helium level in the tank. This allows the gas pressure in the helium tank to be increased very quickly and efficiently when needed. This minimizes the energetically unfavorable heat input into the supercooled liquid helium; likewise, it minimizes the heat input into the gaseous helium, which would only lead to the evaporation of further liquid helium after a considerable time delay.

[0067] A preferred embodiment is one in which the helium container is at least partially filled with liquid helium, wherein at least a lower portion of the liquid helium is present as supercooled liquid helium, particularly with a temperature <3.39 K. The supercooled liquid helium can be easily drawn from the storage cryostat according to the invention by means of helium gas pressure above the liquid helium. If the supercooled liquid helium is at a temperature of 3.39 K or less, the supercooling of the supercooled gaseous helium is generally sufficient to liquefy enough gaseous helium in the application cryostat that, when drawing the liquid helium into the application cryostat, no gaseous helium needs to be vented from the application cryostat or liquefied by other means (without prejudice to any additional cooling capacity required due to incomplete thermal insulation).

[0068] Application systems according to the invention

[0069] The scope of the present invention also includes an application system comprising

[0070] - a storage cryostat according to the invention, described above, and

[0071] - an application cryostat, wherein the application cryostat comprises a vacuum-insulated application helium reservoir, and wherein an outlet opening of the transfer line opens into the application helium reservoir. The application cryostat can be easily and quickly filled with liquid helium from the storage cryostat with minimized helium loss.

[0072] A particularly preferred embodiment of the application system according to the invention includes a heating device with which helium in the transfer line and / or in the application helium container can be heated. The heating device makes it possible to increase the gas pressure PANW in the application cryostat as needed, particularly to prevent the intake of ambient air into the application cryostat. For this purpose, PANW can be maintained at a desired target pressure that is above the ambient pressure (if necessary, the target pressure can be adjusted depending on the current ambient pressure, e.g., with a predetermined fixed overpressure value relative to the current ambient pressure). Preferably, a pressure sensor is provided with which the current gas pressure PANW in the application helium container is monitored, and advantageously, the heating power of the heating device is regulated so that the desired target pressure is maintained in the application helium container.Furthermore, a pressure sensor can be provided to monitor the ambient pressure.

[0073] Advantageously, one embodiment provides for a pressurized gas storage tank for gaseous helium, and a helium gas line connects the pressurized gas storage tank to the helium reservoir of the storage cryostat. The pressurized gas storage tank allows the gas pressure PVOR in the storage cryostat, or in its helium reservoir, to be increased in order to transfer supercooled liquid helium from the storage cryostat to the application cryostat. Optionally, prior to transferring liquid helium, helium gas can first be pumped from the pressurized gas storage tank into the storage cryostat to be liquefied and brought to a supercooled state by a local cooling device of the storage cryostat.

[0074] Inventive methods for transferring liquid helium

[0075] The present invention further encompasses a method for transferring liquid helium from a storage cryostat to an application cryostat, in particular wherein the storage cryostat and the application cryostat are configured in an application system according to the invention as described above, wherein the storage cryostat comprises a vacuum-insulated helium container for liquid helium, the helium container having a vertical height HHB that can be filled with liquid helium, and a transfer line for liquid helium, with an inlet opening that opens into a lower region of the helium container, in particular into a lower fifth of the helium container, wherein the application cryostat comprises a vacuum-insulated application helium container, and wherein an outlet opening of the transfer line opens into the application helium container, comprising the following steps:

[0076] In step a, liquid helium is provided in the helium container of the storage cryostat, wherein at least a lower part of the liquid helium in the helium container is supercooled liquid helium and has a temperature of <3.39 K throughout the lower part. The supercooled liquid helium from the lower part is transferred through the transfer line into the application cryostat, the supercooling of the transferred liquid helium alone being sufficient to liquefy a gas volume (GV) of gaseous helium in the application helium container, which corresponds to a liquid volume (FVtrans) that the supercooled liquid helium fills after transfer into the application helium container and heating to the saturation temperature at the desired final pressure in the application helium container, plus a liquid volume (FVkond) that is obtained from the gas volume of gaseous helium after its liquefaction.

[0077] In the process according to the invention, supercooled liquid helium is transferred from the storage cryostat to the application cryostat. The supercooling of the transferred liquid helium liquefies any gaseous helium already present in the application cryostat. This creates space in the application cryostat for the incoming liquid helium. According to the invention, the supercooling is sufficient to liquefy as much gas volume (GV) of gaseous helium as corresponds to the volume of liquid helium FVtrans plus the volume of liquid helium FVkond that results from the condensation (liquefaction) of said gaseous helium volume. In other words, GV > FVtrans + FVkond.Then neither gaseous helium needs to be released into the environment, nor are other measures (such as an additional condensation heat exchanger in the application cryostat or a gas balloon) necessary to prevent helium loss. According to the invention, the gaseous helium in the application cryostat can be replenished in a particularly simple manner and with minimized helium losses.

[0078] Note that the above condition GV>FVtrans+FVkond is met taking into account the existing heat inputs, particularly into the transfer line. If there are no significant heat inputs due to incomplete thermal insulation, a temperature of 3.39 K or less is sufficient to meet the condition (see also below for a calculation). If there are significant heat inputs, the temperature of the supercooled liquid helium in the helium reservoir of the storage cryostat can be set correspondingly lower to compensate for these heat inputs. Typically, the temperature of the supercooled liquid helium in the helium reservoir of the storage cryostat is set so that even slightly more gas volume GV of helium gas can be liquefied in the application helium reservoir than corresponds to the sum FVtrans+FVkond.A drop in the gas pressure of the helium gas in the application helium container can then be counteracted by introducing some heating power with a heating device in the transfer line or in the application helium container, and the helium gas pressure in the application helium container can then be kept very precisely at a desired pressure value.

[0079] A particularly preferred variant of the method according to the invention provides that, at least during step b), an upper part of the liquid helium in the helium reservoir of the storage cryostat has a temperature > 4.2 K, and that helium gas with a temperature > 4.2 K is present in a gas space of the helium reservoir of the storage cryostat above a liquid level of the liquid helium, and that, for the transfer of the supercooled liquid helium in the gas space of the helium reservoir of the storage cryostat, a gas pressure PVOR of the helium gas is set which is sufficient to convey the liquid helium of the lower part through the transfer line into the application helium reservoir. Driving the transfer of the supercooled liquid helium via the gas pressure PVOR in the helium reservoir is particularly simple. In particular, no pump for supercooled liquid helium is required in the transfer line.Note that for this variant, a convection inhibition system is typically installed in the storage cryostat according to the invention (see above). Typically, the gas pressure PVOR in the helium container for transfer is greater than the gas pressure PANW of helium gas in the application helium container of the application cryostat by a differential pressure Ap of 0.05 bar. <Ap<0,30bar und AP= PVOR- PANW. Typischerweise gilt auch PvoR> lbar and pANw>lbar. Note that depending on the placement of the storage cryostat, application cryostat, inlet and outlet openings of the transfer line, and the fill level in the storage cryostat, the required pressure differential Ap or the required gas pressure PVOR in the storage container can vary. Alternatively, the transfer of liquid helium can be driven, for example, by pumping the liquid helium in the transfer line.

[0080] A preferred further development of this variant provides that the storage cryostat comprises a convection inhibition system arranged in the helium container and hinders vertical convection of liquid helium in the helium container, wherein the convection inhibition system in the helium container is configured in a height interval (IKS) with a vertical height HKS, with HKS > 0.50*HHB, and the convection inhibition system hinders the vertical convection of liquid helium in the helium container over the area of ​​the height interval (IKS) of the convection inhibition system, such that between the upper part and the lower part of the liquid helium in the helium container of the storage cryostat there is a middle part of the liquid helium in which the temperature of the liquid helium varies with a vertical temperature gradient from a first temperature > 4.2 K to a second temperature < 3.39 K.and that during the transfer of supercooled liquid helium in step b), the liquid level of the liquid helium in the helium container gradually decreases, with the middle portion of the liquid helium always remaining above and / or within the height interval (ICE) of the convection damping system. The convection damping system allows the stratification of the liquid helium in the cryostat to be maintained during the transfer of the supercooled liquid helium (taken from the lower portion). In particular, the upper portion of the liquid helium, which is at a temperature of 4.2 K or higher, can be maintained, so that liquid helium and gaseous helium can be essentially in equilibrium at the surface. This makes it possible to build up a (slight) gas pressure in the gas space above the liquid helium without the gaseous helium immediately condensing.

[0081] During step b), the liquid level of the liquid helium typically migrates from top to bottom through the vertical interval (VSI) of the convection inhibition system, but does not reach its lower end.

[0082] A preferred variant of this further development involves at least occasionally introducing helium gas from a pressurized gas storage unit into the helium reservoir of the storage cryostat to adjust the gas pressure. This approach is structurally simple and, in particular, does not require a heating system in the storage cryostat.

[0083] In an advantageous sub-variant of the above further development, it is provided that, to adjust the gas pressure PVOR, the helium in the helium chamber of the storage cryostat is heated at least occasionally by a heating system, and that the heating power of the heating system is introduced exclusively or at least predominantly directly into the upper part of the liquid helium, which has a temperature T > 4.2 K, and / or the gas space of the helium chamber, preferably wherein the heating power of the heating system is introduced exclusively or at least predominantly directly into the upper part of the liquid helium, which has a temperature T > 4.2 K. Heating with the heating system can cause some liquid helium in the helium chamber of the storage cryostat to evaporate, thereby increasing the gas pressure in the helium chamber.Heating of the supercooled liquid helium is minimized by directing the heating power primarily into the upper part of the liquid helium or the gas space. Preferably, the heating power is directed primarily into the liquid helium of the upper part. This allows the gas pressure in the storage cryostat to be increased particularly quickly and efficiently.

[0084] It is particularly preferred that the heating system comprises a plurality of heating sections arranged vertically distributed in the helium container over a height interval (IHZ) of the heating sections, wherein the height interval (IHZ) of the heating sections has a vertical height HHZ, where HHZ > 0.5 * HHB, preferably HHZ > 0.75 * HHB, and particularly preferably HHZ > 0.9 * HHB, and that the distribution of a relative heating power to the heating sections along the vertical direction is changed during step b), in particular wherein the change in the distribution of the heating power depends on repeated level measurements of liquid helium in the helium container of the storage cryostat. By changing the distribution of the heating power to the heating sections during the transfer of the liquid helium, an optimized introduction of the heating power into the storage cryostat can be achieved at any time with regard to a fast response and energy efficiency.By measuring the fill level, the currently optimal zone for introducing the heating power (which is basically just below the liquid level in the liquid helium) can be easily determined, and the heating power can be concentrated there.

[0085] Further advantages of the invention will become apparent from the description and the drawing. Likewise, the features mentioned above and those described in more detail can each be used individually or in any combination according to the invention. The embodiments shown and described are not to be understood as an exhaustive list, but rather serve as examples for illustrating the invention. Detailed the and

[0086] Fig. 1 shows a schematic view of an embodiment of an application system according to the invention, wherein a convection inhibition system comprising drilled plates is arranged in the storage cryostat n, and with a cold head in the lower region of the helium container;

[0087] Fig. 2 shows a schematic top view of a drilling scheme of the drilled plates of Fig. 1;

[0088] Fig. 3 shows a schematic view of an embodiment of an application system according to the invention similar to Fig. 1, with a refrigerator;

[0089] Fig. 4 shows a schematic view of an embodiment of an application system according to the invention similar to Fig. 1, with a heating system comprising a continuous heating element with temperature-dependent heating power distribution;

[0090] Fig. 5 shows a schematic view of an embodiment of a storage cryostat according to the invention, with vertically oriented divider structures which are designed as tubes;

[0091] Fig. 6 shows a schematic top view of an arrangement scheme of the pipes from Fig. 5;

[0092] Fig. 7 shows a schematic view of an embodiment of a storage cryostat according to the invention, with a bed of perforated hollow spheres;

[0093] Fig. 8 shows a schematic view of an embodiment of a storage cryostat according to the invention, with an accumulation of fiber material directly in the helium container; Fig. 9 shows a schematic view of an embodiment of a storage cryostat according to the invention, with several accumulations of fiber material each contained in a fabric sheath in the helium container;

[0094] Fig. 10 shows a schematic view of an embodiment of an application system according to the invention similar to Fig. 1, with a heating system comprising several discrete heating sections and a level sensor;

[0095] Fig. 11 shows a schematic view of the application system of Fig. 1, at the beginning of a filling of liquid helium in the application cryostat;

[0096] Fig. 12 shows the application system of Fig. 11, in the middle of the filling of liquid helium in the application cryostat;

[0097] Fig. 13 shows the application system of Fig. 11, at the end of a filling of liquid helium in the application cryostat;

[0098] Fig. 14 shows an exemplary storage cryostat with convection inhibition system for the invention in a schematic side view;

[0099] Fig. 15 shows an exemplary storage cryostat with convection inhibition system for the invention in a schematic cross-sectional view.

[0100] Fig. 1 shows in a schematic view (from the side, partially cut away) an exemplary embodiment of an application system 1 according to the invention. The application system 1 comprises a storage cryostat 2, an application cryostat 3, a transfer line 4, and in the embodiment shown also a pressurized gas storage tank 5 for gaseous helium.

[0101] The storage cryostat 2 comprises a helium reservoir 6. The helium reservoir 6 can be filled with liquid helium 7 to a height HHB. In the state shown, the helium reservoir is filled to approximately 2 / 3 with liquid helium 7 and to approximately 1 / 3 with gaseous helium 8. A convection dampening system 9 is also arranged in the helium reservoir 6. In the state shown, a liquid level 10 of the liquid helium 7 lies vertically slightly above the convection dampening system 9.

[0102] The gaseous helium-8 in the gas space 15 above the liquid level 10 has a pressure PVOR of slightly over 1 bar. The gaseous helium-8 has a temperature of 4.2 K.

[0103] The helium container 6 is arranged inside an evacuated storage vacuum tank 11; in other words, the helium container 6 is vacuum-insulated. A radiation shield 12 is arranged between the helium container 6 and the storage vacuum tank 11.

[0104] The storage cryostat 2 has a cooling device 13, which here includes a cold head 14. The cold head 14 has a first (warmer) heat sink 15a, which is thermally coupled to the radiation shield 12 and is located at a temperature of approximately 50 K. The cold head 14 also has a second heat sink 15b, which is thermally coupled to the helium container 6 from the outside. The second heat sink 15b contacts the helium container 6 in one-fifth of its height HHB. The second heat sink 15b is located at a temperature of approximately 3.2 K.

[0105] Accordingly, the liquid helium 7 exists in a lower part UT as supercooled helium, with a temperature equal to or below a limit temperature GT, where GT = 3.39 K. In an upper part OT, the liquid helium 7 exists as saturated helium with a temperature of 4.2 K. In a vertically intervening, middle part MT, the liquid helium 7 has a temperature gradient between 4.2 K and 3.39 K. In other words, the liquid helium 7 in the helium tank 6 is vertically stratified according to its density and temperature. The convection inhibition system 9 supports the formation and maintenance of this stratification of the liquid helium 7 by impeding the vertical convection of the liquid helium 7 in the helium tank.

[0106] The convection inhibition system 9 extends over a height interval IKS, which has a height HKS in the vertical direction (i.e., along the direction of gravity). In the configuration shown, HKS = 0.5 * HHB. Note that generally HKS > 0.5 * HHB, preferably HKS > 0.75 * HHB, and most preferably HKS > 0.9 * HHB. Within the height interval IKS, the vertical convection of the liquid helium 7 is inhibited. In particular, no large circular flows of liquid helium 7 can form.

[0107] In the illustrated embodiment of the cryostat n 2, the convection barrier system 9 comprises a plurality of vertically stacked, horizontally extending barrier structures; barrier structures 16 and 17 are marked as examples in Fig. 1. The barrier structures 16, 17 are designed here as flat plates 18, 19. The barrier structures 16, 17 are liquid-tight (i.e., also watertight to liquid helium 7), with the exception of a few openings 16a, 17a, which are designed here as bores 18a, 19a in the plates 18, 19. Liquid helium 7 can pass through the barrier structures 16, 17 in a vertical direction at the openings 16a, 17a.

[0108] Figure 2 shows a top view (along the vertical direction) of the barrier structures 16 (top) and 17 (bottom / hidden, associated contours shown as dotted lines). The interruptions 16a of the upper barrier structure 16 are horizontally offset from the interruptions 17a of the lower barrier structure 17. Note that in the vertical sequence of barrier structures in the convection barrier system, the barrier structures of types 16 and 17 alternate, which prevents continuous (straight-line) vertical convection through the interruptions 16a, 17a; rather, vertical convection through two (or more) barrier structures 16, 17 requires a horizontal offset of the flow (or several horizontal offsets of the flow). The area ratio FUN / FHS of the areas FUN of the respective interruptions 16a, 17a to the area FHS of the associated horizontal barrier structure 16, 17, in the horizontal plane, is approximately 1 / 50.It is readily apparent that the convection damping system, which is composed of the alternating and vertically spaced plates 16, 17, has a mean vertical thermal conductivity VWL (“perpendicular to the plates 18, 19”) that is small compared to a mean horizontal thermal conductivity HWL (“in the plates 18, 19”), here with VWL <l / 10*HWL. Zudem sind typischerweise die vertikalen Plattenabstände benachbarter Platten 18, 19 typischerweise sehr viel größer, zB wenigstens 20 mal größer, als die vertikalen Plattendicken. Dann kann beim Konvektionshemmsystem ein eingenommener Bauraum BAU im Vergleich zum maximal verdrängten Volumen MW an Helium sehr viel größer sein, hier mit BAU> 10*MVV.

[0109] As can be seen again in Fig. 1, the vacuum-insulated transfer line 4 leads from an inlet opening 20 in a lower fifth of the helium container 6 to an outlet opening 21 in an upper region of an application helium container 22 of the application cryostat 3. The application cryostat 3 is the cryostat of an NMR measuring arrangement, wherein the liquid helium 23 (and optionally also the gaseous helium 24) in the application cryostat 3 serves to cool a superconducting magnet coil of the NMR measuring arrangement (magnet coil not shown in detail). Above the liquid helium 23, gaseous helium 24 is arranged in a gas chamber 25. The liquid helium 23 has a temperature of 4.2 K, and the gaseous helium 24 also has a temperature of 4.2 K. The gas pressure PANW in the gas chamber 25 is slightly above 1 bar.The application helium container 22 is arranged in an evacuated application vacuum tank 26; in other words, the application helium container 22 is vacuum-insulated. A radiation shield (not shown) may be arranged between the application vacuum tank 26 and the application helium container 22.

[0110] During normal operation of the application cryostat 3, liquid helium 23 is gradually vaporized to keep the superconducting magnetic coil cold. Typically, helium gas slowly escaping from the application cryostat 3 is collected and temporarily stored (not shown in detail). The liquid helium 23 in the application cryostat 3 must be replenished occasionally (typically after a few months). In preparation for this, supercooled liquid helium is provided in the storage cryostat 2. For this purpose, purified helium gas from an intermediate storage tank 27 can be fed into the storage cryostat 2, or rather its helium reservoir 6, via a feed line 28. There, it is liquefied by the cooling device 13 and partially (in the lower part UT and middle part MT) brought to a supercooled state.

[0111] When enough supercooled liquid helium is stored in the helium container 6, the transfer of the liquid helium 7 can begin. In the illustrated configuration, some helium gas is introduced from the pressurized gas container 5 into the helium gas line 29 of the storage cryostat 2 via the helium gas line; the gas pressure PVOR in the helium container 6 can be monitored by the gas pressure sensor 59a.

[0112] This causes the gas pressure PVOR in the gas space 15 to increase slightly. Note that the upper part OT of the liquid helium 7, which is stable due to the convection barrier 9, is at 4.2 K, so that a helium gas pressure can build up in the gas space 15 without immediately collapsing again due to condensation on the liquid surface 10.

[0113] Due to the gas pressure PVOR of the gaseous helium 8 in the gas space 15, supercooled, liquid helium from the lower part UT is forced from the helium container 6 through the transfer line 4 into the application helium container 22 of the application cryostat 3.

[0114] The subcooling of the transferred subcooled, gaseous helium 31 is sufficient to liquefy helium gas 24 in the gas chamber 25 of the application cryostat 3. This creates space in the application cryostat 3 for the inflowing, subcooled liquid helium 31. The liquefied gas volume GV of gaseous helium 24 is at least as large as the liquid volume FVtrans of the transferred liquid helium 31 (measured after the transfer and after heating to the saturation temperature of 4.2 K at the desired final pressure PANW of just over 1 bar) plus the liquid volume FVkond, which is obtained from the gas volume GV of gaseous helium 24 after liquefaction. In other words, GV > FVtrans + FVkond. This procedure ensures that no gaseous helium 24 is displaced from the application cryostat 3 during the transfer of liquid helium 7, which would otherwise have to be collected and / or processed in a costly manner.

[0115] If the gas pressure PANW in the application helium container 22, measured with the pressure sensor 59b, should drop too much, especially below ambient pressure, the application helium container 22 can be heated with an electric heating device 32.

[0116] The following is a brief estimate of the required subcooling of the transferred, subcooled liquid helium in order to meet the above condition GV>FVtrans+FVkond.

[0117] For the sake of simplicity, let us assume that the fill level of liquid helium in the application cryostat is to be increased by 100 liters of liquid helium during the transfer.

[0118] Initially, as relevant here, 100 liters of gaseous helium (i.e., GV = 100 liters) are present in the application cryostat at 4.2 K and 1 bar, which will later be replaced by liquid helium. With a density of 16.5 g / L for gaseous helium (at 4.2 K and 1 bar), these 100 liters correspond to approximately 1.65 kg of helium. This 100 liters (or 1.65 kg) of gaseous helium is liquefied to prevent displacement. With a latent heat of 20.6 kJ / kg for helium, approximately 34.0 kJ of cooling energy is therefore required for liquefaction.

[0119] With a density of 125 g / L for liquid helium at 4.2 K and 1 bar, the 1.65 kg of the formerly gaseous helium correspond to 13.2 L of liquid helium (i.e., FVcond = 13.2 L). Accordingly, another 86.8 L of liquid helium (measured at 4.2 K and 1 bar) must be transferred (FVtrans = 86.8 L) to reach a total of 100 L of liquid helium (at 4.2 K and 1 bar). These 86.8 L of liquid helium, at a density of 125 g / L, then correspond to 10.85 kg of helium.

[0120] In these 10.85 kg of liquid helium, subcooling must be provided sufficient to supply the liquefaction enthalpy for gaseous helium of 34.0 kJ. Accordingly, the subcooled liquid helium must create a specific enthalpy difference AH between the enthalpies Hstart (when the liquid helium flows into the application cryostat) and Hstart. EThe liquid helium at 4.2 K and 1 bar is provided with AH = H end“ H start — “ 34 kJ / 10.85kg=-3.13 kJ / kg.

[0121] The specific enthalpy of liquid helium at 4.2 K and 1 bar is 0.07 kJ / kg (i.e., H). En (de = 0.07 kJ / kg). Accordingly, the initial enthalpy Hstart must be 3.20 kJ / kg. This initial enthalpy Hstart is found in liquid helium at a temperature of approximately 3.39 K, as can be seen in the literature.

[0122] If the liquid helium is transferred using a short, thermally well-insulated transfer line, the above condition GV>FVtrans+FVkond can be met with supercooled liquid helium at 3.39 K (temperature in the storage cryostat). If the transfer line introduces a significant heat load, the temperature of the supercooled helium in the storage cryostat must be chosen accordingly, somewhat lower. For example, if the transfer is carried out with a 1.5 m long transfer line at a heat load of 1.2 W / m for a period of 30 minutes, the temperature in the storage cryostat must be approximately 3.31 K.

[0123] The process of transferring liquid helium, with particular consideration of the different parts OT, NMT, and UT of the liquid helium 7 in the storage cryostat 2, is explained in more detail below in Figures 11 to 13. Further embodiments of the application system 1 and the storage cryostat 2 according to the invention are presented below. These largely correspond to the respective design shown in Figure 1; only the essential differences from the design shown in Figure 1 are explained in detail.

[0124] Figure 3 shows an embodiment of an application system 1 according to the invention, wherein the cooling device 13 with a refrigerator 33 is formed on the storage cryostat 2. The refrigerator 33 is arranged in a helium circuit 34, which is operated by a pump 35. This pump pumps helium in the helium circuit 34 through the precoolers 36 to the refrigerator 33. There, the helium expands, thereby generating cold. The refrigerator 33 acts as a heat sink 38 and is arranged in a lower fifth of the helium tank 6, here below the convection damping system 9. The precoolers 36 are thermally coupled, in a manner not shown in detail, to cooling stages 37 of a cold head 14; the cold head 14 is arranged here in an upper region of the storage cryostat 2. The refrigerator 33 becomes cold enough to cool the liquid helium 7 in a lower part to a temperature of 3.39 K or less.

[0125] Figure 4 shows an embodiment of an application system 1 according to the invention, wherein the storage cryostat 2 is equipped with a heating system 39. The heating system 39 comprises a continuous heating element 40 through which electric current from a heating current source 41 can flow. The heating element 40 extends over a height interval IHZ with a vertical height HHZ, here approximately HHZ = 0.78 * HHB. The heating system 39 is activated when the gas pressure PVOR in the gas chamber 15 of the helium container 6 of the storage cryostat 2 is to be increased, in particular to drive the transfer of the liquid helium 7 into the application cryostat 3.

[0126] The continuous heating element 40 is made of a material that has its highest electrical resistance at 4.2 K. Below and above 4.2 K, the resistance is lower. The heat output in the heating element 40 is distributed according to the local resistance within the heating element. In the liquid helium 7, the temperature in the upper part OT is 4.2 K; accordingly, the heating power is highest there, and the liquid helium is vaporized there by the concentrated heating power. In the middle part MT and the lower part UT, the heating power is lower, corresponding to the lower resistance there due to the lower temperature. In the gas chamber 15, the gaseous helium 8 also has a (global) temperature of approximately 4.2 K.When heating power is dissipated in the heating element 40, it heats up quickly because the thermal coupling in the gas is not as good as in the liquid, and then the resistance in the heating element 40 in the area of ​​the gas space 15 decreases, and the gas space 15 is no longer heated as much.

[0127] Due to these relationships, the heating element is "self-regulating" and concentrates its heat input on the upper part OT of the liquid helium 7 at 4.2 K. The continuous heating element 40 can be understood as an uninterrupted sequence of heating elements, whose respective heating power is determined by the temperature dependence of the resistance of their material and also changes depending on the fill level of the liquid helium.

[0128] Figure 5 shows a schematic side view of an embodiment of a storage cryostat 2 according to the invention. In this storage cryostat 2, the convection inhibition system 9 is formed by a plurality of vertical divider structures 42. Here, the divider structures 42 are each designed as vertically oriented tubes 43. The divider structures 42, or the tubes 43, are open at the top and bottom, so that liquid helium 7 can flow in and out of the tubes according to the current fill level.

[0129] Fig. 6 shows a top view of the convection damping system 9 alone. A chamber 44 is formed inside each tube 43. The maximum inner diameter IDK of each chamber 44 and the maximum container diameter BDM of the helium container 6 are both IDK = 0.06 * BDM. Preferably, IDK < 0.1 * BDM, and preferably IDK < 0.05 * BDM. Typically, the storage cryostat 2 is operated such that the liquid level 10 of the liquid helium 7 is always lower than the upper ends of the divider structures 42.

[0130] The divider structures 42 allow closed convection currents of liquid helium to be confined to the area (and especially the horizontal diameter) of a chamber 44, thereby also severely restricting vertical convection. Upward and downward flowing sub-currents would have to form in close spatial proximity, leading to turbulence and a weakening of the closed-circuit current in the chamber 44.

[0131] Figure 7 shows a further embodiment of a storage cryostat 2 according to the invention, wherein the convection inhibition system 9 is formed by a packing of hollow bodies 45. The hollow bodies 45 are here designed as hollow spheres 46, see also the enlargement at the top left. The hollow bodies 45 are provided with a plurality of holes 47, typically at least four holes, preferably at least eight holes, wherein the holes 47 are evenly distributed on the outside of the hollow bodies 45.

[0132] The holes 47 allow the interior of the hollow bodies 45 to be filled with liquid helium 7, and the liquid helium 7 can also easily drain out of the hollow bodies 45 through the holes 47. At the same time, the hollow bodies 45 prevent the formation of circulating flows of liquid helium 7 due to convection.

[0133] The holes 47 have a maximum diameter DL, and the hollow bodies 45 have a maximum diameter DHK. In the illustrated configuration, DL = 0.15 * DHK. Generally, DL < 0.2 * DHK is preferred. The hollow bodies 45 are typically made of a plastic with low thermal conductivity, e.g., nylon. The hollow bodies 45 are an example of an open-pore filler material 60 for the convection inhibition system 9.

[0134] The storage cryostat 2 has a neck tube 61 through which the interior of the helium tank 6 is accessible. The inner diameter IDH of the neck tube 61 is large enough to allow the hollow bodies 45 to be inserted through the neck tube 61 into the helium container 6, where IDH > DHK.

[0135] Figure 8 shows another embodiment of a storage cryostat 2 for the invention, wherein the convection inhibition system 9 is formed by an accumulation 48 of a fibrous material 49 in the helium container 6. The fibrous material 49 is glass wool and is arranged directly in the helium container 6. The fibrous material 49 can be easily permeated (saturated) by liquid helium 7, and liquid helium 7 can easily escape from the fibrous material 49, in particular, flow out of it. At the same time, however, the fibrous material 49 disrupts the formation of convection currents in the liquid helium 7. The fibrous material 49 is another example of an open-pore filling material 60 for the convection inhibition system 9.

[0136] A sintered filter 50 is formed at the inlet opening 20 of the transfer line 4. This allows liquid helium 7 to pass through, but retains any fragments and any abrasion of the fiber material 49, so that fragments and abrasion cannot enter the transfer line 4 and the application cryostat, or only in small quantities.

[0137] Furthermore, this design incorporates a horizontal heat-conducting element 51. Here, this element is designed as a horizontally oriented copper grid. The heat-conducting element 51 is thermally coupled to the heat sink 16 of the cold head 14 and extends below the convection damping system 9, essentially covering the entire (horizontal) cross-section of the helium container 6. The heat-conducting element 51 enables a balanced temperature distribution in the liquid helium 7 in the horizontal plane. If desired, a multitude of heat-conducting elements can be arranged vertically distributed within the helium container 6, particularly in the area of ​​the height interval IKS of the convection damping system 9 (not shown in detail). Note that instead of filling with fiber material 49, the helium container 6 could also be filled with an open-pore foam (not shown in detail).

[0138] Figure 9 shows a further embodiment of a storage cryostat 2 for the invention, wherein the convection inhibition system 9 is formed by several accumulations 48 of a fibrous material 49 in the helium container 6. Each accumulation 48 is enclosed in a fabric sheath 52. The fabric sheath

[0139] 52 is permeable to liquid helium 7, but retains fragments and abrasion of the fiber material 49. The fabric casing 52 can be made of a nylon fabric in particular.

[0140] At room temperature, the filled fabric sheaths 52 can be easily compressed elastically and inserted into the helium container 6 through a neck tube (not shown in detail in Fig. 9, but see Fig. 7 for further information).

[0141] Figure 10 shows a further embodiment of an application system 1 according to the invention, wherein the storage cryostat 2 is equipped with a heating system 39. The heating system 39 comprises a plurality of discrete heating sections 53, which are arranged vertically distributed in the helium reservoir 6 of the storage cryostat 2. The heating sections 53 are distributed in a height interval IHZ with a height HHZ, where HHZ = 0.83 * HHB. At each heating section

[0142] 53 The heating output can be individually adjusted here by means of an electronic control unit 54.

[0143] Furthermore, a sensor device 55 is arranged in the helium container 6, with which the current fill level of liquid helium 7, i.e., the position of the liquid level 10 of the liquid helium 7, can be determined. The sensor device 55 is also called a fill level sensor.

[0144] The sensor device 55 can be configured, in particular, as a wire made of superconducting material through which a short current pulse flows for measurement. Over the length in which the wire is immersed in liquid helium 7, the wire remains superconducting (zero resistance). Over the length in which the wire is immersed in gaseous helium 8 in the gas chamber 15, the wire becomes normally conducting (resistance > 0). The resistance of the entire wire is then measured. From the resistance value of the entire wire, the length of the normally conducting portion of the wire can be determined, and thus the fill level of liquid helium 7 can be ascertained.

[0145] If the gas pressure PVOR in the storage cryostat n 2 in the gas chamber 15 is to be increased, the control device 54 concentrates the heating power on the heating section 53 that is currently located furthest above the liquid level 10, i.e., closest to the liquid level 10. This means that the heating power is essentially directed to the upper part OT of the liquid helium 7, which has a temperature of 4.2 K.

[0146] The cooling device 13, here designed as a cold head 14, is arranged in the design shown in a lower third of the helium container 6, slightly below the middle of the convection inhibition system 9.

[0147] Figures 11, 12, and 13 illustrate the transfer of liquid helium from the storage cryostat 2 to the application cryostat 3 in detail over time. The application system 1 of Figures 11 to 13 corresponds in its structure to the application system of Figure 1.

[0148] Fig. 11 shows the application system 1 at the beginning of the transfer of liquid helium 7.

[0149] At the start of the transfer, the liquid helium 23 in the application helium container 22 of the application cryostat 3 is almost exhausted; the fill level in the example shown is only about 5%. The liquid helium 23 in the application helium container 22 has a temperature of 4.2 K. Above the liquid helium 23 in the gas space 25 is gaseous helium 24 with a temperature of 4.2 K and a pressure pANw of about 1.03 bar. In contrast, a larger quantity of liquid helium 7 has been provided in the helium container 6 of the storage cryostat 2, here by conveying purified helium gas from an intermediate storage tank 27 through the feed line 28 into the storage cryostat 2 and liquefying it there with the cooling device 13. The fill level of the helium container 6 is about 70% here.

[0150] The cooling device 13 cooled the liquid helium 7 in a lower part UT to a temperature < 3.39 K. In an upper part OT, the temperature of the liquid helium 7 is 4.2 K. In a middle part MT, the temperature of the liquid helium 7 decreases from top to bottom from 4.2 K to 3.39 K.

[0151] The different parts UT, MT and OT of the liquid helium are marked with different hatching in Fig. 11 (and Fig. 12, 13).

[0152] The stratification of the liquid helium 7 in the storage cryostat 2 is stabilized by the convection damping system 9, which here consists of vertically stacked, perforated horizontal plates. The liquid level 10 is located slightly above the height interval IKS of the convection damping system 9. A lower edge 58 of the upper part OT lies at the upper end of the height interval IKS, and the lower edge 57 of the middle part MT lies in the upper half of the height interval IKS. In the gas space 15 above the liquid level 10, gaseous helium 8 is present in the helium container 6 at 4.2 K and a gas pressure PVOR of approximately 1.06 bar.

[0153] The slight overpressure of the helium gas in the storage cryostat 2 compared to the application cryostat 3 causes liquid helium 7 to be drawn from the lower part UT through the transfer line 4 into the application cryostat 3 during the transfer process. This causes the liquid level 56 of liquid helium 23 in the application helium container 22 to gradually rise, and the liquid level 10 in the helium container 6 of the storage cryostat 2 to gradually fall. Due to the subcooling of the transferred liquid helium 31, gaseous helium 24 condenses to liquid helium 23 simultaneously with the transfer in the application helium container 22, causing the liquid level 56 in the application helium container 22 to rise further. The subcooling and the resulting condensation are sufficient so that no helium gas 24 is forced out of the application cryostat 3 during the transfer (and would have to be e.g. vented).

[0154] Fig. 12 shows the state of the application system 1 after approximately half of the desired amount of liquid helium 7 has been transferred into the application cryostat 3.

[0155] This results in a liquid level of 10 of the liquid helium 7 in the helium container.

[0156] The liquid helium 7 in storage cryostat n 2 has sunk somewhat, into the area of ​​the height interval IKS of the convection inhibition system 9. The stratification of the liquid helium 7 in the helium tank 6 has been maintained thanks to the convection inhibition system 9. In particular, the upper part OT and the middle part MT have essentially retained their respective layer thicknesses (in the vertical direction). In contrast, the layer thickness of the lower part UT has decreased, since the transferred supercooled liquid helium 31 originates from this lower part UT, corresponding to the position of the inlet opening 20 of the transfer line 4 in the area of ​​the lower part UT, at the lower end of the height interval IKS of the convection inhibition system 9. The lower edge 57 of the middle part MT of the liquid helium

[0157] 7 now lies in a lower half of the height interval IKS of the convection inhibition system 9.

[0158] If the gas pressure PVOR in the storage cryostat 2 should drop too low during the transfer, some helium gas can be introduced from the gas pressure reservoir 5 into the gas chamber 15 via the helium gas line 29 to raise the gas pressure PVOR. Since the liquid helium 7 in the upper part OT is at 4.2 K, no significant condensation of helium gas 8 to liquid helium 7 occurs in the helium container 6, and the pressure build-up in the gas chamber 15 can proceed without problems. Finally, Fig. 13 shows the state of the application system 1 after the desired quantity of liquid helium 7 has been transferred into the application cryostat 3.

[0159] In the example shown, the application helium container 22 of the application cryostat 3 is now approximately 75% filled with liquid helium 23.

[0160] In contrast, the helium reservoir 6 of the storage cryostat 2 is now only approximately 30% filled with liquid helium 7. The layering of the liquid helium 7 in the helium reservoir 6, consisting of the upper part OT, the middle part MT, and the lower part, remains intact. However, the layer thickness of the lower part UT has decreased further, and the position of the lower edge 57 of the middle part MT has dropped further. The lower edge 57 of the middle part MT is now located at the lower end of the height interval IKS of the convection damping system 9.

[0161] The central part MT of the liquid helium 7 in the helium container 6 has always remained within the height interval IKS of the convection inhibition system 9 with its lower edge 57 during the transfer; in the example shown, even the central part MT as a whole has always remained within the height interval IKS of the convection inhibition system 9, which is preferred within the scope of the invention.

[0162] Figure 14 schematically shows an exemplary storage cryostat 2 for an application system according to the invention in a longitudinally sectional side view. A convection inhibition system 9 is arranged in the helium container 6 of the storage cryostat 2, similar to the one shown in Figure 5. The convection inhibition system 9 occupies a space BAU in the helium container 6, which is outlined here with dotted lines. The helium container 6 has an internal volume INV. In the illustrated design, BAU is approximately 0.60 * INV. According to the invention, BAU typically > 40% * INV.

[0163] Fig. 15 schematically shows a horizontal cross-section of another storage cryostat 2 for an application system according to the invention. A convection inhibition system 9, similar to that shown in Fig. 5, is arranged in the helium container 6 of the storage cryostat 2. The cross-section lies within the height interval of the convection inhibition system 9. The convection inhibition system 9 occupies a cross-sectional area BFL, which is shown here outlined with dots. The helium container 6 has an internal cross-sectional area QFL. In the illustrated design, BFL is approximately 0.80 * QFL. According to the invention, BFL typically > 60% * QFL, at least locally within the height interval of the convection inhibition system 9, and preferably throughout the entire height interval of the convection inhibition system. ist

[0164] 1 Application system

[0165] 2 Storage Cryostat

[0166] 3 Application cryostat

[0167] 4 Transfer line

[0168] 5 gas pressure storage tanks

[0169] 6 helium containers (of the storage cryostat)

[0170] 7 liquid helium (in the storage cryostat)

[0171] 8 Helium gas (in the storage cryostat)

[0172] 9 Convection inhibition system

[0173] 10 Liquid level (of liquid helium in the storage cryostat)

[0174] 11 Storage vacuum tank

[0175] 12 Radiation shield (of the storage cryostat)

[0176] 13 Cooling device

[0177] 14 Cooling head

[0178] 15a First heat sink (for radiation shield)

[0179] 15b Second heat sink (for helium tank)

[0180] 16 Locking structure

[0181] 16a Interruption

[0182] 17 Blocking structure

[0183] 17a Interruption

[0184] 18 Plate 18a Bore

[0185] 19 plates

[0186] 19a Borehole

[0187] 20 Inlet opening

[0188] 21 Outlet opening

[0189] 22 Application Helium Containers

[0190] 23 liquid helium (in the application cryostat)

[0191] 24 gaseous helium (in the application cryostat)

[0192] 25 Gas space (in the application cryostat)

[0193] 26 Application vacuum tank

[0194] 27 intermediate storage

[0195] 28 Feed line

[0196] 29 Helium gas pipeline

[0197] 31 transferred liquid helium

[0198] 32 Heating device (in the application cryostat)

[0199] 33 Refrigerator

[0200] 34 Helium cycle

[0201] 35 pump

[0202] 36 pre-coolers

[0203] 37 cooling levels

[0204] 38 Heat sink (refrigerator)

[0205] 39 Heating system

[0206] 40 continuous heating element

[0207] 41 heating power source

[0208] 42-part structure

[0209] 43 pipe

[0210] 44th Chamber

[0211] 45 hollow bodies

[0212] 46 Hollow sphere

[0213] 47 holes

[0214] 48 collection

[0215] 49 Fiber material

[0216] 50 Sintered filters 51 Thermal conducting element

[0217] 52 Fabric cover

[0218] 53 Heating section

[0219] 54 Control unit

[0220] 55 Sensor device / level sensor

[0221] 56 Liquid level (of liquid helium in the application cryostat)

[0222] 57 Lower edge of the middle part

[0223] 58 Lower edge of the upper part

[0224] 59a Pressure sensor (in the storage cryostat)

[0225] 59b Pressure sensor (in the application cryostat)

[0226] 60 open-pore filler material

[0227] 61 Neck tube

[0228] CONSTRUCTION Installation space of the convection inhibition system

[0229] BDM maximum diameter of the helium container

[0230] BFL construction area of ​​the convection inhibition system in the horizontal cross-section

[0231] DHK maximum diameter of the hollow body

[0232] DL maximum diameter of the hole

[0233] HHB vertical height of the helium tank

[0234] HHZ vertical height of the height interval of the heating sections

[0235] HKS vertical height of the height interval of the convection inhibition system

[0236] IDH inner diameter of the neck tube

[0237] IDK maximum inner diameter of the chamber

[0238] IHZ height interval of the heating sections

[0239] IKS altitude interval of the convection inhibition system

[0240] INV Internal volume of the helium container

[0241] MT middle section

[0242] OT upper part

[0243] QFL inner horizontal cross-sectional area of ​​the helium container

[0244] UT lower part

Claims

Patent claims 1. Storage cryostat (2) for liquid helium (7), suitable for transferring liquid helium (7) from the storage cryostat (2) to an application cryostat (3), wherein the storage cryostat (2) comprises - a vacuum-insulated helium container (6) for liquid helium (7), wherein the helium container (6) has a vertical height HHB that can be filled with liquid helium (7), - a transfer line (4) for liquid helium (7), with an inlet opening (20) that opens into a lower region of the helium container (6), in particular into a lower fifth of the helium container (6), and - a convection inhibition system (9) which is arranged in the helium container (6) and hinders vertical convection of liquid helium (7) in the helium container (6), characterized in that the convection inhibition system (9) is formed in the helium container (6) in a height interval (IKS) with a vertical height HKS, with HKS > 0.50*HHB, and that the convection inhibition system (9) hinders the vertical convection of liquid helium (7) in the helium container (6) over the area of ​​the height interval (IKS) of the convection inhibition system (9).

2. Storage cryostat (2) according to claim 1, characterized in that HKS>0.75*HHB, preferably where HKS>0.90*HHB.

3. Storage cryostat (2) according to claim 1 or 2, characterized in that the storage cryostat (2) further comprises a cooling device (13).

4. Storage cryostat (2) according to claim 3, characterized in that a heat sink (15b; 38) of the cooling device (13) is arranged in a lower region of the helium container (6), in particular in a lower fifth of the helium container (6).

5. Storage cryostat (2) according to one of the preceding claims, characterized in that the convection inhibition system (9) is arranged in a fixed position in the storage cryostat (2).

6. Storage cryostat (2) according to one of the preceding claims, characterized in that the convection inhibition system (9) has a plurality of vertically arranged, horizontally or approximately horizontally extending barrier structures (16, 17), wherein the barrier structures (16, 17) are liquid-tight except for some interruptions (16a, 17a), and that in projection onto a horizontal plane each barrier structure (16, 17) occupies an area FHS and the associated interruptions of this barrier structure (16, 17) together occupy an area FUN, with FHS>10*FUN, preferably FHS>50*FUN.

7. Storage cryostat (2) according to claim 6, characterized in that the barrier structures (16, 17) are designed as planar plates (18, 19), and the interruptions (16a, 17a) are formed as bores (18a, 19a) in the plates (18, 19) are trained.

8. Storage cryostat (2) according to claim 6 or 7, characterized in that the interruptions (16a, 17a) of vertically adjacent blocking structures (16, 17) are arranged offset from each other in at least one horizontal direction.

9. Storage cryostat (2) according to one of the preceding claims, characterized in that the convection inhibition system (9) has a plurality of vertically or approximately vertically oriented divider structures (42) by which a plurality of top and bottom open, but horizontally liquid-tight chambers (44) are formed in the helium container (6), and that for a respective maximum inner diameter IDK of the chambers (44) and a maximum container diameter BDM of the helium container (6), each measured in the horizontal plane, the following applies: BDM>10*IDK, preferably BDM>20*IDK.

10. Storage cryostat (2) according to claim 9, characterized in that the divider structures (42) are formed by vertically or approximately vertically oriented tubes (43), in particular wherein the tubes (43) are bundled.

11. Storage cryostat (2) according to one of the preceding claims, characterized in that the convection inhibition system (9) comprises a packing of hollow bodies (45), in particular hollow spheres (46), wherein the walls of the hollow bodies (45) each have a plurality of holes (47).

12. Storage cryostat (2) according to one of the preceding claims, characterized in that the convection inhibition system (9) comprises at least one accumulation (48) of open-pore filling material (60).

13. Storage cryostat (2) according to claim 12, characterized in that the filling material (60) comprises a fiber material (49), in particular wherein the fiber material (49) is glass wool.

14. Storage cryostat (2) according to claim 12 or 13, characterized in that the filling material (60) comprises an open-pore foam, in particular wherein the open-pore foam is made of a plastic material.

15. Storage cryostat (2) according to claim 12, 13 or 14, characterized in that a filter, in particular a sintered filter (50), is arranged at the inlet opening (20) of the transfer line (4), wherein the filter is permeable to liquid helium (7) but retains fragments and / or abrasion of the filling material (60).

16. Storage cryostat (2) according to one of claims 12 to 15, characterized in that a respective accumulation (48) of filling material (60) is arranged in a fabric shell (52), wherein the fabric shell (52) is permeable to liquid helium (7) but retains fragments and / or abrasion of the filling material (60).

17. Storage cryostat (2) according to one of the preceding claims, characterized in that the storage cryostat (2) has a neck tube (61) through which the interior of the helium container (6) is accessible, and that the convection inhibition system (9) is designed such that it is introduced into the helium container (6) through the neck tube (61). can be, in particular wherein the convection inhibition system (9) comprises a plurality of unconnected individual elements, each of which is small enough to be passed through the neck tube (61) and / or the convection inhibition system (9) is wholly or partially flexible at room temperature.

18. Storage cryostat (2) according to one of the preceding claims, characterized in that for a space BAU occupied by the convection inhibition system (9) in the helium container (6) and a maximum volume MW of liquid helium displaced by the convection inhibition system (9) in the helium container (6) the following applies: BAU>5*MVV, preferably BAU>20*MVV.

19. Storage cryostat (2) according to one of the preceding claims, characterized in that the convection inhibition system (9) is made at least partially, preferably completely, of a material or materials with a specific thermal conductivity X measured at 4.2 K, with X < 0.1 W / (cm*K), preferably X < 0.01 W / (cm*K), in particular wherein the convection inhibition system (9) is made at least partially of plastic, preferably nylon.

20. Storage cryostat (2) according to one of the preceding claims, characterized in that the convection inhibition system (9) is constructed such that, on average, for a horizontal thermal conductivity HWL of the convection inhibition system (9) and a vertical thermal conductivity VWL of the convection inhibition system (9), VWL < 0.33 * HWL, preferably VWL<0.2*HWL.

21. Storage cryostat (2) according to one of the preceding claims, characterized in that one or more horizontal heat conducting elements (51) are present in the area of ​​the height interval (ICS) of the convection inhibition system (9) and / or below the convection inhibition system (9), which are horizontally or substantially horizontally oriented, in particular wherein one or more of the horizontal heat conducting elements (51) are connected to a heat sink (15b; 38) of a cooling device (13).

22. Storage cryostat (2) according to one of the preceding claims, characterized in that a heating system (39) is arranged in the helium container (6), that the heating system (39) comprises a plurality of heating sections (53) which are arranged in the helium container (6) distributed over a height interval (IHZ) of the heating sections (53) in a vertical direction, wherein the height interval (IHZ) of the heating sections (53) has a vertical height HHZ, wherein HHZ>0.5*HHB, preferably HHZ>0.75*HHB, particularly preferably HHZ>0.9*HHB, and that the heating system (39) is configured to change a distribution of a relative heating power on the heating sections (53) along the vertical direction.

23. Storage cryostat (2) according to claim 22, characterized in that the heating system (39) is configured to change the distribution of the relative heating power depending on a fill level of liquid helium (7) in the helium container (6).

24. Storage cryostat (2) according to one of claims 22 or 23, characterized in that the heating powers at the heating sections (53) are temperature-dependent and are maximum at 4.2 K.

25. Storage cryostat (2) according to one of claims 22 to 24, characterized in that the heating system (39) comprises a control device (54) with which the distribution of the relative heating power to the heating sections (53) can be variably controlled, in particular wherein the heating power of a respective heating section (53) can be individually adjusted with the control device (54).

26. Storage cryostat (2) according to claim 25, characterized in that the storage cryostat (2) has a sensor device (55) for determining a current fill level of liquid helium (7) in the helium container (6), and that the control device (54) is configured to distribute the relative heating power in such a way that the heating power is concentrated on the heating section (53) or heating sections (53) that are currently below a liquid level (10) of liquid helium (7) in the helium container (6) and are closest to the liquid level (10).

27. Storage cryostat (2) according to one of the preceding claims, wherein the helium container (6) is at least partially filled with liquid helium (7), wherein at least a lower part (UT) of the liquid helium (7) is present as supercooled liquid helium, in particular with a temperature <3.39K.

28. Application system (1), comprising - a storage cryostat (2) according to any of the preceding claims, and - an application cryostat (3), wherein the application cryostat (3) comprises a vacuum-insulated application helium container (22), and wherein an outlet opening (21) of the transfer line (4) opens into the application helium container (22).

29. Application system (1) according to claim 28, characterized in that a heating device (32) is provided with which helium in the transfer line (4) and / or in the application helium container (22) can be heated.

30. Application system according to claim 28 or 29, characterized in that a pressurized gas storage tank (5) for gaseous helium is provided, and that a helium gas line (29) connects the pressurized gas storage tank (5) to the helium container (6) of the storage cryostat n (2).

31. Method for transferring liquid helium (7) from a storage cryostat (2) to an application cryostat (3), in particular wherein the storage cryostat (2) and the application cryostat (3) are configured in an application system (1) according to any one of claims 28 to 30, wherein the storage cryostat (2) comprises - a vacuum-insulated helium container (6) for liquid helium (7), wherein the helium container (6) has a vertical height HHB that can be filled with liquid helium (7), and - a transfer line (4) for liquid helium (7), with an inlet opening (20) that opens into a lower region of the helium container (6), in particular into a lower fifth of the helium container (6), wherein the application cryostat (3) comprises a vacuum-insulated application helium container (22), and wherein an outlet opening (21) of the transfer line (4) opens into the application helium container (22), with the following steps: Step a) in the helium container (6) of the storage cryostat n (2) liquid helium (7) is provided, wherein at least a lower part (UT) of the liquid helium (7) in the helium container (6) is present as supercooled liquid helium and has a temperature <3.39 K everywhere in the lower part (UT), Step b) supercooled liquid helium from the lower part (UT) is transferred through the transfer line (4) into the application cryostat (3), the supercooling of the transferred liquid helium (31) alone being sufficient to liquefy a gas volume (GV) of gaseous helium (24) in the application helium container (22), which corresponds to a liquid volume (FVtrans) that the supercooled liquid helium (31) fills after transfer into the application helium container (22) and heating to the saturation temperature at the desired final pressure in the application helium container (22), plus a liquid volume (FVkond) that is obtained from the gas volume of gaseous helium (24) after its liquefaction.

32. Method according to claim 31, characterized in that at least during step b) an upper part (OT) of the liquid helium (7) in the helium container (6) of the storage cryostat (2) has a temperature > 4.2 K, and helium gas (8) with a temperature > 4.2 K is present in a gas space (15) of the helium container (6) of the storage cryostat (2) above a liquid level (10) of the liquid helium (7), and a gas pressure PVOR of the helium gas (8) is set to transfer the supercooled liquid helium (7) in the gas space (15) of the helium container (6) of the storage cryostat (2) which is sufficient to convey the liquid helium (7) of the lower part (UT) through the transfer line (4) into the application helium container (22).

33. Method according to claim 32, characterized in that the storage cryostat (2) comprises a convection inhibition system (9) which is arranged in the helium container (6) and inhibits vertical convection of liquid helium in the helium container (6), wherein the convection inhibition system (9) is formed in the helium container (6) in a height interval (IKS) with a vertical height HKS, with HKS > 0.50*HHB, and the convection inhibition system (9) inhibits the vertical convection of liquid helium (7) in the helium container (6) over the area of ​​the height interval (IKS) of the convection inhibition system (9), such that between the upper part (OT) and the lower part (UT) of the liquid helium (7) in the helium container (6) of the storage cryostat (2) there is a middle part (MT) of the liquid helium (7) in which a temperature of the liquid helium (7) is present. a vertical temperature gradient from a first temperature >4.2K to a second temperature < 3.39K,and that during the transfer of supercooled liquid helium in step b), the liquid level (10) of the liquid helium (7) in the helium container (6) gradually decreases, and the middle part (MT) of the liquid helium (7) always remains above and / or within the area of ​​the height interval (IKS) of the convection inhibition system (9).

34. Method according to claim 33, characterized in that, for the purpose of adjusting the gas pressure PVOR, helium gas from a pressurised gas storage (5) is admitted at least occasionally into the helium container (6) of the storage cryostat (2).

35. Method according to one of claims 33 or 34, characterized in that, for the purpose of adjusting the gas pressure PVOR, the helium in the helium container (6) of the storage cryostat (2) is heated at least occasionally by a heating system (39), and that a heating power of the heating system (39) is introduced exclusively or at least predominantly directly into the upper part (OT) of the liquid helium (7), which has a temperature T>4.2K, and / or the gas space (15) of the helium container (6), preferably wherein a heating power of the heating system (39) is introduced exclusively or at least predominantly directly into the upper part (OT) of the liquid helium (7), which has a temperature T>4.2K.

36. Method according to claim 35, characterized in that the heating system (39) comprises a plurality of heating sections (53) arranged in the helium container (6) distributed vertically over a height interval (IHZ) of the heating sections (53), wherein the height interval (IHZ) of the heating sections (53) has a vertical height HHZ, wherein HHZ>0.5*HHB, preferably HHZ>0.75*HHB, particularly preferably HHZ>0.9*HHB, and that a distribution of a relative heating power on the heating sections (53) along the vertical direction is changed during step b), in particular wherein the change of the distribution of the heating power is made as a function of repeated level measurements of liquid helium (7) in the helium container (6) of the storage cryostat (2).

Images