APPARATUS AND METHOD FOR TRANSFERRING LIQUID Helium INTO AN APPLICATION CRYOSTAT

Abstract

The invention relates to an apparatus and a method for transferring liquid helium into an application cryostat, the apparatus comprising: a reservoir; a transfer line comprising a first transfer line end and a second transfer line end in the storage, the second transfer line end for insertion into an application cryostat; means for generating a pressure difference between the storage and the application cryostat; the condensation heat exchanger is used for condensing helium into liquid helium; the low-temperature cooler is used for cooling the condensation heat exchanger; and a control device having a measurement input for the pressure sensor and a control output for the device, the control device being programmed to control the device, such that the volume of liquid helium transferred through the transfer line per unit time is substantially equal to a change in volume of helium condensed into liquid helium from helium per unit time at the condensation heat exchanger. By means of the device, the loss of helium during the transfer of liquid helium is minimized in a simple manner.

Description

Technical Field

[0001] The present invention relates to a device for transferring liquid helium into an application cryostat, the device comprising:

[0002] - a storage for liquid helium;

[0003] - a transfer line for liquid helium for transferring liquid helium from the storage into the application cryostat, the transfer line comprising a first transfer line end and a second transfer line end, the first transfer line end being arranged in the storage and the second transfer line end being adapted to be inserted into the application cryostat; and

[0004] - a device for generating a pressure difference between the storage and the application cryostat. Background Art

[0005] Such a device is known from chapter 12 of the "User Manual for NMR Magnet System UltraShield Magnet (English version)", edition 006 (October 12, 2004) of the company publication of Bruker BioSpin AG, Fällanden, Switzerland.

[0006] Superconducting magnets, such as those used for NMR spectroscopy (NMR = nuclear magnetic resonance) or magnetic resonance imaging (also known as MRI (MRI = magnetic resonance imaging)), need to be cooled to ensure the superconducting state of the magnet. In many cases, the superconducting magnet is arranged in an application cryostat in which liquid helium is stored, typically at a temperature of about 4.2 K, which corresponds to the boiling point of liquid helium at atmospheric pressure. Cooling with liquid helium is also known from other application areas.

[0007] Since the application cryostat cannot effect perfect thermal insulation, or heat is introduced into the application cryostat through the corresponding application, the liquid helium vaporizes during operation. If the liquid level of the liquid helium in the application cryostat drops too much for continued operation, the application cryostat is refilled with liquid helium.

[0008] It should be noted here that helium is a scarce resource. Helium is a by-product of natural gas extraction. The available supply of helium on the world market is decreasing and the price of helium is rising, see "Helium Supply Tightens Again" by D. Kramer, Physics Today, American Physical Society, April 4, 2022, https: / / doi.org / 10.1063 / PT.6.2.20220404a.

[0009] Therefore, efforts are made to minimize the consumption of helium used for the operation of the cryostat. Many consumers invest in equipment for helium recovery, which can capture and reliquefy the vaporized helium.

[0010] As described in the company publication "User Manual for NMR Magnet System UltraShield Magnet (English Version)" mentioned above, a large amount of helium loss occurs during the common process of refilling liquid helium from the storage (storage Dewar) into the application cryostat. This common process can be outlined as follows:

[0011] Step a): Bring the storage ("transport reservoir") near the application cryostat, near the NMR magnet in the company publication, up to a distance of several meters.

[0012] Step b): Insert the hot transfer line into the transport reservoir so that its (first) end is below the liquid level of the contained liquid helium.

[0013] Step c): Vaporize the helium in the transport reservoir by the heat input through the hot transfer line. Thus, the pressure in the transport reservoir rises, and the liquid helium is pressed into the transfer line, which is thereby cooled. The helium escaping from the end of the transfer line during the cooling process is usually not captured but lost to the atmosphere. For a typical transfer line several meters long, several liters of liquid helium are required for cooling.

[0014] Step d): Once the helium escaping from the (second) end of the line away from the transport reservoir is sufficiently cold (i.e., the transfer line is sufficiently cooled), the transfer line is connected to the application cryostat (e.g., NMR magnet), i.e., the second end is inserted into the application cryostat.

[0015] Step e): After the transfer line is connected to the application cryostat, the liquid helium flows from the transport reservoir into the application cryostat. The mass flow is driven by the pressure difference existing between the transport reservoir and the application cryostat. As mentioned above, due to the insertion of the transfer line, an overpressure is established in the transport reservoir. However, the pressure build-up in the transport reservoir usually occurring through heat input during the insertion of the transfer line is not sufficient to transfer the desired amount of liquid helium. Therefore, helium gas is charged into the transport reservoir from a pressure cylinder through a pressure regulator, so that the pressure in the transport reservoir is constantly maintained high. Usually, the overpressure regulated in the transport reservoir is about 50 - 100 mbar. During the transfer of liquid helium, the gaseous helium corresponding to the volume of the incoming liquid helium is pressed out of the application cryostat at the output end.

[0016] For illustration: When starting to transfer liquid helium into an application cryostat, the application cryostat or its helium storage tank is usually not empty but still contains a small amount of liquid helium and, in addition, is filled with gaseous helium at a temperature of 4.2 K and a pressure of approximately 1 bar. As the helium storage tank is slowly filled with liquid helium during the transfer, the cold gaseous helium present in the helium storage tank before the transfer starts is gradually pressed out of the helium storage tank and escapes through the outlet of the application cryostat.

[0017] Gaseous helium has a density of 16.5 g / l at 4.2 K and atmospheric pressure. Liquid helium at 4.2 K and atmospheric pressure has a density of 125 g / l. If, for example, 100 liters of liquid helium (i.e., 12.5 kg of helium) are transferred, then 100 liters of gaseous helium (i.e., 1.65 kg) are thus pressed out of the application cryostat. This corresponds to 13.2 liters of liquid helium or 13.2% of the transfer amount.

[0018] In most cases, these amounts of helium simply escape through the outlet of the application cryostat into the atmosphere, which is not sustainable and also makes the operation of the application cryostat expensive.

[0019] Alternatively, for example, a balloon storage can be installed, which is dimensioned large enough to capture the helium ("transfer losses") occurring during helium transfer at the outlet and supply it to a high-pressure storage or a liquefier. In the pipeline system leading to the balloon and in the balloon itself, the gaseous helium is heated to room temperature, which results in a significant increase in the gas volume. 100 liters of gaseous helium at atmospheric pressure and 4.2 K correspond to approximately 10,000 liters (i.e., 10 m 3 ) at atmospheric pressure and room temperature.

[0020] When usually transferring helium to an NMR magnet - depending on the magnet type - between 100 and 400 liters of liquid helium are transferred. A typical transfer usually lasts about one hour. During this time, 10 to 40 cubic meters of gaseous helium at room temperature are thus produced, which must be stored in the balloon or processed by a recovery system (e.g., compressed in a pressure storage). This corresponds to 13 liters / hour to 50 liters / hour of liquid helium (or approximately between 1.6 and 6.6 kg of helium per hour). Correspondingly, large balloons or powerful recovery systems are very space-consuming and also very expensive.

[0021] It is proposed in the later published German published text DE102022209941A1 that during the transfer of liquid helium from a storage container to an application cryostat, the gaseous helium pressed out at the application cryostat is led through a return pipeline to the storage container.

[0022] It should also be noted that a cryocooler can be used to actively cool an application cryostat during continuous operation (such as a superconducting magnet for NMR applications). For example, see US2002 / 0002830A1. In this case, there is no need to refill liquid helium, and the problem of helium loss during refilling is eliminated.

[0023] However, active cooling has various disadvantages compared to passive operation using a liquid helium bath. In particular, vibrations caused by the cryocooler are introduced into the application cryostat, the energy consumption is high (about 8 kW during continuous operation), the maintenance cost is relatively high, and the downtime during maintenance activities is relatively long. In the case of a superconducting magnet with active cooling without cryogenics (i.e., a superconducting magnet without a liquid helium buffer volume), the time from a possible current failure until the superconductivity in the superconducting magnet collapses ("quenching time") is also very short.

[0024] US8671698 describes a helium re-liquefier with a pulse tube cooler that is separate from the application cryostat.

[0025] A modifiable re-liquefier for helium is known from US2007 / 0107445A1. The installation of such a device is quite complex. Additionally, vibrations are also introduced into the application cryostat here, and high energy and maintenance costs are generated.

[0026] US8375742B2 describes a helium re-liquefier equipped with its own isolation sheath. Helium vaporized from the application cryostat is liquefied by the re-liquefier and returned through a transfer tube also surrounded by the isolation sheath. In a variant, an interface for an external gas source is additionally provided.

[0027] US2009 / 0301129A1 describes a helium re-liquefier for retrofitting a magnetic resonance system, through which vaporized nitrogen and vaporized helium should be re-liquefied.

[0028] A condensation heat exchanger is known from EP0245057B1 and EP0396624B1, which is connected to a cold head through a cooling circuit and inserted into a cryostat with liquid helium.

[0029] DE102021205423A1 additionally describes a device in which helium is purified and liquefied using a single cold head.

[0030] DE4039365A1 describes an NMR magnet with a cryostat, in which supercooled liquid helium is arranged in a first lower cavity, liquid helium at 4.2 K under atmospheric pressure is arranged in a second upper cavity, and a thermally insulating but pressure-permeable barrier is arranged between the two cavities.

[0031] For example, the thermophysical properties of different fluid systems for helium can be queried on the website https: / / webbook.nist.gov / chemistry / fluid / . This website is operated by the National Institute of Standards and Technology (NIST) of the United States Department of Commerce.

[0032] DE102020204186A1 discloses a mobile liquefaction device for liquefying helium. The liquefaction device includes a liquefaction unit for liquefying helium, an intermediate memory for the liquefied helium, a purification unit for helium, and an additional collection unit for gaseous helium. The additional collection unit for gaseous helium includes a container with a flexible wall. Using the liquefaction unit and the purification unit, the helium that is stored at the location of the application cryostat and vaporizes during operation can be purified and liquefied and collected in the intermediate memory. When filling the application cryostat with liquid helium from the intermediate memory, the vaporized helium gas can be captured using the additional collection unit.

[0033] DE69926087T2 describes a device for re - condensing liquid helium, wherein the liquid helium is stored in a container. The gaseous helium vaporized in the container is guided through a pipeline to a cooling device arranged outside the container and liquefied there. The liquefied helium is guided back into the container through another pipeline. Summary of the Invention

[0034] The object of the present invention is to minimize helium losses in a simple manner when transferring liquid helium from a storage memory to an application cryostat.

[0035] According to the present invention, this object is solved by a device of the type described at the beginning, characterized in that

[0036] the device further comprises:

[0037] - a condensation heat exchanger for condensing helium gas into liquid helium, which is adapted to be inserted into an application cryostat;

[0038] - a cryogenic cooler for cooling the condensation heat exchanger, and

[0039] - a control device having at least one measurement input for a pressure sensor for measuring the air pressure (gas pressure) in the application cryostat and a control output for a device for generating a pressure difference, wherein the control device is programmed to control the device for generating a pressure difference such that the volume of liquid helium transferred per unit time through the transfer pipeline is approximately equal to the volume change of helium condensed from helium gas into liquid helium at the condensation heat exchanger per unit time.

[0040] It is possible to achieve with the device according to the invention that during the transfer of liquid helium from a storage reservoir into an application cryostat having a condensation heat exchanger, which is inserted into the application cryostat, the liquefaction of gaseous helium to liquid helium is carried out in situ in the application cryostat. On the one hand, the cooling power of the condensation heat exchanger (or cryocooler) and on the other hand the transfer rate of the liquid helium into the application cryostat can be coordinated with each other such that the volume change (volume reduction) of the helium condensed per unit time in the application cryostat at least substantially (and preferably exactly) corresponds to the volume of the liquid helium transferred from the storage reservoir through the transfer line by means of the device for generating a pressure difference into the application cryostat ("equilibrium state"). By adjusting and maintaining the equilibrium state caused by the control device during the transfer of the liquid helium, it is achieved that during the transfer of the liquid helium, the gaseous helium is not (or only very little) pressed out of the application cryostat by the inflowing liquid helium. Correspondingly, the necessity of capturing and processing the pressed-out gaseous helium for recovery is dispensed with. In particular, large balloons for capturing the pressed-out gaseous helium are no longer required for the transfer of liquid helium.

[0041] By means of the pressure difference adjusted by the device for generating a pressure difference between the storage reservoir and the application cryostat (wherein a higher pressure is provided in the storage reservoir than in the application cryostat, mostly having a pressure difference of 50 - 100 mbar), the liquid helium is pressed into the application cryostat through the transfer line. The device for generating (or adjusting) the pressure difference is connected to the control output of the control device and is controlled by the control device. By increasing the pressure difference, the transfer rate of the liquid helium can be increased, and by reducing the pressure difference, the transfer rate of the liquid helium can be reduced. It is noted that such a pressure difference does not need to be known within the scope of the present invention. Nevertheless, it is preferably provided that the control device additionally also monitors the pressure in the storage reservoir by means of a further pressure sensor.

[0042] The (at least approximate) maintenance of the equilibrium state is preferably ensured by keeping the pressure (helium pressure) in the application cryostat at least substantially constant or at least within a predetermined pressure range. The control device typically correspondingly uses the pressure in the application cryostat as an input variable (control variable) or at least as one of the input variables for controlling the device for generating a pressure difference.

[0043] Devices for generating a pressure difference are generally configured to change the pressure (gas pressure) in a storage reservoir, for example by changing the current of an electric heater in the storage reservoir or by changing the position of a regulating valve (inlet valve) in the helium gas line from a helium gas reservoir (in particular a helium pressure gas reservoir) to the storage reservoir. The cooling power at the condensation heat exchanger or the cooling power of the cryocooler of the condensation heat exchanger is generally kept constant. However, it is also possible to alternatively or additionally change the pressure in the application cryostat by means of the device for generating a pressure difference, for example by changing the current of an electric heater in the application cryostat or by changing the cooling power at the condensation heat exchanger.

[0044] A cryocooler generally includes a cold head and a compressor. The cryocooler can in particular include a Gifford-McMahon cryocooler or a pulse tube cryocooler. The cold head is thermally coupled to the condensate (heat) exchanger to cool the condensate (heat) exchanger, preferably by means of a cooling circuit. The cryocooler provides the cooling power required for the condensation of gaseous helium in the application cryostat.

[0045] If, for example, 100 liters of liquid helium are to be refilled into the application cryostat within the scope of the present invention, 100 liters of gaseous helium (gaseous helium at a temperature of 4.2 K) must be liquefied correspondingly in the application cryostat during the transfer of the liquid helium in order to prevent helium gas from flowing out of the application cryostat. The density of gaseous helium at 4.2 K and 1 bar is 16.5 g / l; correspondingly, approximately 1.65 kg of helium must be liquefied. Helium has a latent heat of 20.6 kJ / kg, and correspondingly approximately 34 kJ of energy must be absorbed from the cryocooler at a temperature of 4.2 K during the transfer of the liquid helium. If, for this purpose, a commercially available cryocooler with a cooling power of 2 watts is used, these energies can be absorbed in approximately 4.7 hours. The liquid helium transfer rate to be used within the scope of the present invention is then approximately 21.3 l / h. In practice, the power to be absorbed is slightly higher than the 34 kJ mentioned, because, for example, additional heat input into the system occurs via the helium transfer line and the inserted condensation heat exchanger (for example arranged on a cooling rod). The transfer time is correspondingly slightly extended or the transfer rate is reduced.

[0046] The time required for transferring liquid helium within the scope of the present invention, as can be seen from the above examples, depends in particular on the amount of liquid helium to be refilled, the cooling power of the cryocooler, and the additional heat input caused by incomplete insulation. The transfer of liquid helium can be planned according to the expected transfer time, especially as an "overnight" automated transfer even when the application cryostat is not being utilized for an application (such as NMR measurements). The typical transfer time within the scope of the present invention is from 1 h to 16 h, and preferably from 2 h to 12 h. It is noted that when supercooled liquid helium is transferred from the storage reservoir to the application cryostat, the transfer time can be reduced hereby (see also further below).

[0047] The storage reservoir is typically configured to be transportable ("transport reservoir"), preferably equipped with rollers so that it can be moved back and forth between different laboratories and can thus be used particularly easily for refilling multiple application cryostats. Preferably, the storage reservoir and the cryocooler are combined into an integrated transportable structural assembly (e.g., arranged on a common platform with rollers), especially when the storage reservoir also serves as a helium liquefier.

[0048] Typically, for the volume dV(LHe trans ) / dt of liquid helium transferred per unit time through the transfer line during the transfer of liquid helium and the volume change dV(He cond ) / dt of helium condensed from helium gas into liquid helium per unit time at the condensation heat exchanger, the following applies:

[0049] |dV(He cond ) / dt| ≥ 0.75 * |dV(LHe trans ) / dt|,

[0050] Preferably, |dV(He cond ) / dt| ≥ 0.9 * |dV(LHe trans ) / dt|.

[0051] In addition, the following generally also applies:

[0052] |dV(He cond ) / dt| ≤ 1.25 * |dV(LHe trans ) / dt|,

[0053] Preferably, |dV(He cond ) / dt| ≤ 1.1 * |dV(LHe trans ) / dt|.

[0054] Preferred embodiments of the device according to the invention

[0055] In a preferred embodiment of the device according to the invention, the control device is programmed to keep the pressure in the application cryostat approximately constant during the transfer of liquid helium into the application cryostat. It can thereby be achieved in a particularly simple manner that the transfer process is kept in equilibrium, i.e. it is carried out such that the volume of liquid helium transferred through the transfer line per unit time is approximately equal to the volume change of helium condensed from helium gas into liquid helium at the condensation heat exchanger per unit time. The pressure usually measured in the application cryostat is adjusted by the control device to a predetermined, fixed target value. It is noted that the target value should be (e.g. by 5 to 50 mbar) above the ambient atmospheric pressure in order to avoid air being drawn into the application cryostat. Alternatively, it may also be possible, for example, to adjust the measured pressure to a target value that is tracked during the transfer and that has a fixed distance, for example, from the ambient atmospheric pressure.

[0056] Furthermore, a preferred embodiment is one in which the application cryostat is sealed to prevent the outflow of gaseous helium without damaging any possible safety devices. This simplifies the construction of the entire system during the transfer of liquid helium and no expensive helium is lost during the transfer process.

[0057] In an advantageous embodiment, it is provided that the control device has a pressure sensor for measuring the ambient atmospheric pressure and that the control device is programmed to keep the pressure in the application cryostat at all times above the ambient atmospheric pressure, in particular by correspondingly controlling the device for generating the pressure difference. Thereby, air is prevented from being drawn into the application cryostat; the ingress of air causes the air components (e.g. moisture) in the application cryostat to freeze and thus causes a blockage of the gas flow. Preferably, the pressure can also be controlled directly in the application cryostat, for example by means of an electric heater installed at the condensation heat exchanger or elsewhere in the application cryostat. It is thus possible to avoid, in the event of a fault, an unreliable drop in the pressure in the application cryostat (e.g. when the transfer line freezes and becomes completely blocked).

[0058] In a preferred embodiment, the device for generating a pressure difference includes a regulating valve in the helium gas pipeline, wherein the helium gas pipeline includes a first helium gas pipeline end connected to the storage and a second helium gas pipeline end connected to the helium gas storage, in particular a helium pressure gas storage. By using the regulating valve leading to the helium gas storage, the pressure in the transport reservoir can be changed simply and quickly. The regulating valve can be automatically controlled and adjusted by a control device, for example, using an electric motor. It is noted that the helium flowing from the helium gas storage into the transport reservoir should be pre-purified so that impurities (such as water vapor or nitrogen) cannot reach the transport reservoir and the application cryostat and freeze there. Preferably, the transport reservoir is configured such that the gaseous helium entering from the helium gas storage can be liquefied in the transport reservoir, preferably by using the cold head of a cryocooler, which is also used to cool the condensation heat exchanger. Preferably, a common cryocooler is used to operate the cold trap for purifying helium gas and to liquefy the helium gas in the transport reservoir; for this purpose, in particular, a device as described in DE102021205423A1 can be used.

[0059] In an advantageous embodiment, the device for generating a pressure difference includes an electric heater in the storage. By heating with the electric heater in the storage (or in its helium container), the liquid helium stored in the storage vaporizes, which increases the pressure in the storage, thereby driving the transfer of the liquid helium. Such a process is particularly simple.

[0060] A particularly preferred embodiment is one in which the device further includes:

[0061] - A closed cooling circuit for the coolant, the cooling circuit including a forward pipeline from the cold head of the cryocooler to the condensation heat exchanger and a return pipeline from the condensation heat exchanger to the cold head of the cryocooler, wherein the cryocooler is configured to directly or indirectly cool the coolant using the cold head.

[0062] In particular, the cold head of the cryocooler is arranged separately from the application cryostat. By establishing a cooling circuit, the actual refrigeration location (at the cold head) can be spatially separated from the helium condensation location (at the condensation heat exchanger) in a simple manner; the condensation heat exchanger can be established especially at the end of a rigid cooling rod, and the cooling rod can be introduced into the application cryostat in a simple manner. The cold head does not need to be pushed into the application cryostat, which can save a great deal of space in the application cryostat and is also impossible in many cases because the opening in the application cryostat is preferably configured with a very small cross-section (significantly smaller than a commercially available cold head). Usually, the cold head is also arranged separately from the application cryostat, which simplifies the construction of the entire system. Additionally, the vibration input into the application cryostat can be minimized. A part of the forward line and the return line can be integrated into the cooling rod, and if necessary, a part of the transfer line can also be integrated. It is noted that the cooling circuit mostly also includes a compressor forward line from a separate compressor to the cold head and a compressor return line from the cold head to the compressor.

[0063] In a preferred expansion of this embodiment, the forward line, the return line, and the transfer line extend as a line bundle from the storage in a common isolation vacuum section. Such a configuration enables the isolation of the forward line, the return line, and the transfer line in a simple manner. The line bundle can be manipulated particularly simply. In particular, the second transfer line end (outflow end) of the transfer line and the condensation heat exchanger (the end of the forward line / start of the return line) can be inserted into the application cryostat particularly simply together. Mostly, the line bundle is arranged in a rigid tube ("cooling rod") in the rear region, i.e., near the second transfer line end of the transfer line and the condensation heat exchanger, which further simplifies the manipulation.

[0064] Furthermore, a sub-variant of this expansion is preferred, in which the forward line and the transfer line are thermally coupled to each other in the common isolation vacuum section, especially through a plurality of coupling bridges. Thereby, it is possible to pre-cool the transfer line using the cooling circuit or the coolant in the forward line before starting the transfer of liquid helium, so that when the helium transfer line is flowed through at the start of the liquid helium transfer, the helium transfer line is already cold. Thereby, no liquid helium is consumed (i.e., vaporized) for cooling the transfer line.

[0065] Furthermore, a preferred embodiment is provided, wherein the device further includes a helium memory, which is connected to the storage memory via a helium pipeline. In particular, the helium memory is a helium pressure gas memory. Thereby, it is possible to introduce helium into the storage memory, in particular to increase the pressure in the storage memory (so the helium memory is mostly a helium pressure gas memory) and / or to liquefy the gaseous helium introduced into the storage memory (for this purpose, usually the cold head of a cryocooler extends into the storage memory or its storage cryostat, see also below).

[0066] A particularly preferred embodiment is provided, wherein the cold head of the cryocooler and the helium container of the storage memory are arranged in a common storage cryostat, and the cold head of the cryocooler is configured to liquefy helium gas into liquid helium in the storage memory. If helium can be liquefied in the storage memory, there is no need to transport the liquid helium over a long distance (e.g., using a truck) to the location of the application cryostat, which is technically costly. Thus, the operation of the application cryostat can be significantly cheaper. Instead, it is possible to more easily transport the gaseous helium to be transported to the application cryostat (e.g., in a pressure gas cylinder), and / or the helium vaporized during the normal operation of the application cryostat (usually after intermediate storage) can be liquefied in the application cryostat, which is particularly sustainable.

[0067] In addition, an extension of this embodiment is advantageous, wherein the helium container and the cold head are configured to provide a volume of supercooled liquid helium in the helium container. The temperature of the supercooled helium is lower than the boiling point at the pressure present in the helium container. Mostly, the pressure in the helium container is approximately (but slightly higher than) 1 bar, corresponding to a boiling point of 4.2K. The supercooled liquid helium thus has a temperature lower than 4.2K. Preferably, the supercooled liquid helium in the helium container has a temperature of 4.0K or lower, particularly preferably 3.8K or lower. However, providing supercooled liquid helium is more energy-consuming than providing liquid helium at the boiling point (4.2K), and the energy consumption increases strongly as the temperature of the supercooled liquid helium decreases. Therefore, the supercooled liquid helium in the helium container preferably also has a temperature of 3.7K or higher. When the supercooled liquid helium is transported to the application cryostat, additional cooling power for condensing gaseous helium into liquid helium is provided in the application cryostat, corresponding to the temperature difference to the boiling point and the specific heat capacity of the liquid helium. Thereby, the transfer of the liquid helium can be carried out faster than using liquid helium at the boiling point with the given cooling power of the cryocooler.

[0068] A sub-variant of this expansion solution is particularly preferred, in which a thermal insulation barrier is arranged in the helium container. By means of the thermal insulation barrier, the supercooled helium volume is separated from the liquid saturated helium volume above the thermal insulation barrier below the thermal insulation barrier. With such a configuration, supercooled liquid helium can be provided particularly effectively and also relatively simply. The thermal insulation barrier that can be used within the scope of the present invention is described, for example, in DE4039365A1. The thermal insulation barrier is thermally insulating, but pressure-permeable. The cooling head of the cryocooler can be arranged in a separate vacuum chamber here, and the vacuum chamber extends through the thermal insulation barrier, so that the coldest stage of the cold head can provide cooling power below the thermal insulation barrier.

[0069] In a further sub-variant, it is provided that the forward line of the cooling circuit for the coolant of the cryocooler extends through the region of the liquid supercooled helium volume. Thus, a large "cold energy" storage with a temperature below 4.2 K is provided for the cooling of the condensation heat exchanger. The heat transfer at the condensation heat exchanger can be designed particularly effectively by the lower operating temperature.

[0070] In a further sub-variant, the end of the first transfer line leads into the region of the liquid supercooled helium volume in the storage, in particular near the bottom of the helium container. Correspondingly, supercooled liquid helium can be simply input into the application cryostat through the transfer line.

[0071] Furthermore, an embodiment is advantageous, in which the transfer line has a purge valve in the region near the end of the first transfer line. Before starting the transfer of liquid helium, the air present in the transfer line can be purged through the purge valve. For this purpose, some gaseous helium from the application cryostat - which is at a low overpressure relative to the ambient atmosphere - is guided through the transfer line and through the purge valve. Thereby, the introduction of air into the application cryostat can be minimized. In the simplest case, the purge valve leads to the ambient atmosphere, or alternatively to a helium recovery system (the helium recovery system is equipped with a purification function for separating air components).

[0072] Application system according to the invention

[0073] An application system also falls within the scope of the present invention, which application system includes the device described above according to the present invention and an application cryostat,

[0074] wherein the transfer line and the condensation heat exchanger are inserted into the application cryostat,

[0075] In particular, it is inserted into a common inlet pipe of an application cryostat. In the application system according to the present invention, liquid helium can be transferred from the storage to the application cryostat in a simple manner, and helium loss can be minimized. If the condensation heat exchanger (usually arranged at the cooling rod) and the transfer pipeline for liquid helium use the same inlet pipe (especially the suspension pipe of the NMR magnet), a sufficiently large outflow cross-section for the quenching situation (sudden loss of superconductivity of the NMR magnet) can be provided in a simple manner, that is, at the second inlet pipe (especially the suspension pipe) that is not blocked. In addition, the thermal coupling between the transfer pipeline and the forward pipeline of the coolant of the condensation heat exchanger can be more easily achieved.

[0076] A particularly preferred embodiment of the application system according to the present invention is provided, wherein the application cryostat includes a superconducting magnetic coil and an NMR sample head extends into the magnetic hole of the magnetic coil. The application cryostat can then be used for NMR measurements, and the cost for NMR measurement samples can be reduced based on the relatively low operating costs within the scope of the present invention. Usually, the NMR sample head extends into the room temperature hole of the application cryostat, and the room temperature hole is coaxial with the magnetic hole.

[0077] Method for transferring liquid helium according to the present invention

[0078] The method for transferring liquid helium into an application cryostat also falls within the scope of the present invention.

[0079] The method especially uses the above-described device according to the present invention or the above-described application system according to the present invention.

[0080] Wherein, the transfer pipeline for liquid helium is connected to the storage containing liquid helium at the first transfer pipeline end, and is inserted into the application cryostat at the second transfer pipeline end.

[0081] Wherein, liquid helium is transferred from the storage to the application cryostat through the transfer pipeline.

[0082] Wherein, the flow rate of liquid helium through the transfer pipeline is adjusted by a device for changing the pressure difference between the storage and the application cryostat.

[0083] It is characterized in that

[0084] The condensation heat exchanger cooled by a cryogenic cooler is inserted into the application cryostat, and gaseous helium is liquefied into liquid helium in the application cryostat.

[0085] And the control device measures the pressure in the application cryostat and thus controls the device for changing the pressure difference such that the volume of liquid helium transferred per unit time through the transfer line is approximately equal to the volume change of helium condensing from helium gas to liquid helium at the condensation heat exchanger per unit time. This is achieved within the scope of the method according to the invention such that when refilling liquid helium from the storage, no or only little helium gas is pressed out of the application cryostat by the incoming liquid helium. This is achieved in that the helium gas present in the application cryostat during the filling of liquid helium is liquefied using the condensation heat exchanger, so that the associated volume / volume change approximately corresponds ("equilibrium state"). Correspondingly, no or only little helium gas is lost during the transfer of liquid helium. A possible helium recovery system for storing and re-liquefying the pressed-out helium gas is not necessary or can be designed relatively small and low-cost.

[0086] A variant of the method according to the invention is particularly preferred, in which the control device keeps the pressure in the application cryostat approximately constant during the transfer of liquid helium into the application cryostat. By this process, it can be achieved in a simple manner that the volume of liquid helium transferred per unit time through the transfer line is approximately equal to the volume change of helium condensing from helium gas to liquid helium at the condensation heat exchanger per unit time ("equilibrium state").

[0087] In a preferred variant, no gaseous helium flows out of the application cryostat during the transfer of liquid helium. Thereby, helium losses can be completely eliminated during the transfer of liquid helium without the need for a helium recovery system.

[0088] A variant is also advantageous, which provides that the control device measures the atmospheric pressure of the surroundings and the control device keeps the pressure in the application cryostat at all times higher than the atmospheric pressure of the surroundings, in particular by correspondingly controlling the device for generating the pressure difference. Thereby, air is prevented from being sucked into the application cryostat from the surroundings. If the pressure in the application cryostat faces an overly strong drop, usually the transfer of liquid helium into the application cryostat is increased (by increasing the pressure in the storage); in an emergency (e.g., when the transfer line is blocked), the electric heater in the application cryostat (if present) can be switched on and / or turned up.

[0089] In a preferred variant, it is provided that the control device controls the regulating valve in the helium gas line as the device for changing the pressure difference, the helium gas line leading from a helium gas storage, in particular a helium pressure gas storage, to the storage. Thereby, the pressure in the storage can be directly and rapidly increased to start or increase the transfer of liquid helium.

[0090] A variant is also advantageous, in which the control device actuates an electric heater in the storage reservoir as a device for changing the pressure difference. The electric heater can be installed simply and cost-effectively. By means of the heater, the helium in the storage reservoir can be vaporized, which increases the gas pressure in the storage reservoir. A helium pressure gas reservoir is not required (although a helium pressure gas reservoir can also be provided).

[0091] Also preferred is a variant, in which the coolant in a closed cooling circuit is guided from the cold head of the cryocooler to the condensation heat exchanger via the forward line and back to the cooling head of the cryocooler via the return line, where the cold head of the cryocooler directly or indirectly cools the coolant, in particular where the cold head is arranged separately from the application cryostat. By means of the cooling circuit, the cold head can be spatially separated from the condensation heat exchanger, which saves structural space in the application cryostat (especially in the area of the feed line). In addition, the cold head can be easily used for other purposes, especially for liquefying the helium in the storage reservoir.

[0092] Particularly preferred is a variant, in which the transfer line between the storage reservoir and the application cryostat is thermally coupled to the forward line. Thereby, the transfer line for the liquid helium can be cooled by means of the cooling circuit.

[0093] A further development of this variant provides that, before the transfer of liquid helium is started via the transfer line, the transfer line is first pre-cooled by means of the coolant in the forward line. Then, when the liquid helium is first guided through the transfer line for the purpose of transfer, the transfer line is already cold and little or no liquid helium vaporizes on the path to the application cryostat. Thereby, liquid helium can be saved.

[0094] Also preferred is a variant, which provides that

[0095] the cold head of the cryocooler and the helium container of the storage reservoir are arranged in a common storage cryostat

[0096] and, before the transfer of liquid helium is started, gaseous helium is supplied from a helium gas reservoir, in particular a helium pressure gas reservoir, to the storage reservoir and the gaseous helium is condensed to liquid helium in the storage reservoir by means of the cold head. In this variant, the liquid helium can be produced on-site in the storage reservoir and the more costly and difficult transport of liquid helium to the application location can be avoided. If necessary, helium can be processed in a virtually closed circuit at the application location, which is sustainable and cost-effective.

[0097] A particularly preferred variant provides that a liquid supercooled helium volume is provided in the helium container of the storage reservoir, and the liquid helium transferred through the transfer line is withdrawn from the liquid supercooled helium volume. The supercooled helium volume provides additional cooling power in the application cryostat, and the additional cooling power supports the liquefaction of helium gas in the application cryostat, and the transfer of the liquid helium can be carried out particularly quickly.

[0098] A further development of the above-mentioned variant is also advantageous, which provides that the condensation heat exchanger is cooled by a coolant circulating in a closed cooling circuit.

[0099] And the coolant in the forward line is guided through the region of the liquid supercooled helium volume. Thus, a storage reservoir of particularly large cold energy at a temperature <4.2 K can be used for liquefaction in the application cryostat. The condensation heat exchanger is efficient and powerful.

[0100] A variant is also advantageous, in which, before starting the transfer of the liquid helium, the transfer line is first purged with gaseous helium from the application cryostat via a purge valve, which is arranged in the transfer line near the first transfer line end. Thereby, the input of impurities (air components) into the application cryostat is minimized. The branch line leading to the purge valve is usually located in the region of the storage reservoir. Usually, more than 3 / 4 of the length of the transfer line can be purged through the purge valve.

[0101] A variant is also preferred, in which the application cryostat is alternately used for applications during normal operation and filled with liquid helium during refilling operation.

[0102] Wherein, during normal operation, the condensation heat exchanger and the second transfer line end are not inserted into the application cryostat, and during refilling operation, the condensation heat exchanger and the second transfer line end are inserted into the application cryostat. The condensation heat exchanger and the transfer line are only inserted when they are needed. Thus, the heat input into the application cryostat during normal operation can be minimized.

[0103] In addition, a further development of the above-mentioned variant is preferred, which provides that a superconducting magnetic coil is arranged in the application cryostat, and during normal operation, NMR measurements on a sample are carried out using an NMR sample head as an application, and the sample is arranged in the magnetic hole of the superconducting magnetic coil. Within the scope of the present invention, sustainable and cost-effective NMR measurements on the sample are possible.

[0104] Additional advantages of the present invention result from the description and the drawings. Also, according to the present invention, the features mentioned above and further described can be used individually by themselves or in any combination in multiples. The embodiments shown and described should not be understood as exhaustive, but rather have exemplary features for the description of the present invention. Description of the Drawings

[0105] The embodiments of the present invention will be described in more detail below with reference to the drawings. The drawings are as follows:

[0106] Figure 1 A schematic view showing a first embodiment of an application system according to the present invention, the application system including a device for transferring liquid helium according to the present invention and an application cryostat, wherein the cryocooler has a separate cryocooler - cryostat;

[0107] Figure 2 A bundle of pipes showing the transfer pipe, the forward pipe, and the return pipe for the present invention;

[0108] Figure 3 A schematic view showing a second embodiment of an application system according to the present invention, the application system including a device for transferring liquid helium according to the present invention and an application cryostat, wherein the cold head of the cryocooler and the helium container of the storage are arranged in a common storage cryostat;

[0109] Figure 4 A structural form showing the storage of a device for transferring liquid helium according to the present invention, the storage having a heat insulation barrier in the helium container of the storage. Detailed Description of the Embodiments

[0110] Figure 1 A first embodiment of an application system 100 according to the present invention during the transfer of liquid helium is schematically shown, including a device 101 for transferring liquid helium and an application cryostat 102.

[0111] The device 101 includes a storage 1 having a helium container 2, and the helium container is thermally decoupled from the surrounding environment 4 through an isolation vacuum section 3. Here, in the surrounding environment 4, there is a room temperature (20 °C) and an atmospheric pressure p of 1.00 bar atm . One or more radiation shielding sections or multi - layer super - isolation sections (not shown in more detail) can be provided in the isolation vacuum section 3.

[0112] Liquid helium 5 is stored in the lower region of the helium container 2, and gaseous helium 6 is located above the liquid helium 5 in the upper region. In the shown embodiment, the liquid helium 5 and the gaseous helium 6 have a temperature of approximately 4.2 K in the storage 1, and here there is a pressure p of approximately 1.08 bar in the storage 1vorrat In the illustrated embodiment, an electric heater 7 is additionally arranged in the storage container 1, and the electric heater can be controlled by an electronic control device 8.

[0113] A transfer line 9 for liquid helium extends into the storage container 1. A first end 9a of the transfer line opens into the liquid helium 5 near the bottom of the helium container 2. The transfer line 9 is provided with a vacuum isolation section 23. The storage container 1 is configured to be transportable, and rollers 37 ("transport reservoir") are configured here.

[0114] A second end 9b of the transfer line 9 is inserted into the application cryostat 102 through an inlet tube 15a and opens into the helium storage tank 10 of the application cryostat 102. The helium storage tank 10 is thermally isolated from the surrounding environment 4 by an isolation vacuum section 13. One or more radiation shielding sections (not shown in more detail) may be provided in the isolation vacuum section 13.

[0115] Liquid helium 11 is present in the lower region of the helium storage tank 10 of the application cryostat 102, and gaseous helium 12 is present in the upper region. In the illustrated embodiment, the liquid helium 11 and the gaseous helium 12 each have a temperature of approximately 4.2 K in the helium storage tank 10, and a pressure p of approximately 1.03 bar exists in the helium storage tank. anwend .

[0116] For each pressure (for transferring liquid helium through the transfer line 9), generally p atm < p anwend < p vorrat .

[0117] Because the pressure p existing in the storage container 1 vorrat is slightly greater than the pressure p existing in the application cryostat 102 anwend , the liquid helium 5 is pressed from the storage container 1 into the application cryostat 102 through the transfer line 9, see the liquid helium 14 flowing out at the second end 9b of the transfer line. Thus, the liquid helium is transferred from the storage container 1 to the application cryostat 102 by the pressure difference between the storage container 1 and the application cryostat 102.

[0118] Through the inlet tube 15a, here not only the transfer line 9 but also the cooling rod 16 extends into the application cryostat 102; the inlet tube 15a is therefore also referred to as the common inlet tube 15a. A condensation heat exchanger 17 is configured at the lower end of the cooling rod 16. The gaseous helium 12 in the helium storage tank 10 is continuously liquefied during the transfer of liquid helium by means of the condensation heat exchanger 17.

[0119] The condensation heat exchanger 17 is cooled by a coolant that circulates in a cooling circuit 19. The cooling circuit 19 extends from a cold head heat exchanger 25a at the cold head 25 to the condensation heat exchanger 17 via a forward line 20 and extends back from the condensation heat exchanger 17 to the cold head heat exchanger 25a at the cold head 25 via a return line 21. The end regions of the forward line 20 and the return line 21 near the condensation heat exchanger 17 extend in the cooling rod 16. The forward line 20 and the return line 21 are surrounded by a vacuum isolation section 22. The coolant circuit 19 is driven here by a compressor 28, wherein a compressor forward line 26 leads from the compressor to the cold head heat exchanger 25a or the forward line 20, and a compressor return line 27 leads from the return line 21 or from the cold head heat exchanger 25a to the compressor 28. The coolant in the cooling circuit 19 can be in particular helium. The cold head 25 and the compressor 28 form a cryocooler 29 of the device 101.

[0120] The compressor 28 operates the cold head 25 here, wherein separate cold head lines 35, 36 are provided between the compressor 28 and the cold head 25 and additionally are responsible for the circulation of the coolant in the cooling circuit 19 of the condensation heat exchanger 17. This is particularly cost-effective. Here, the cooling circuit 19 can be separately activated and deactivated by a cooling circuit valve 19a, which is arranged here in the compressor forward line 26.

[0121] The cold head 25 and the cold head heat exchanger 25a are arranged here in a cryocooler-cryostat 30, which is separate from the application cryostat 102 and the storage 1. The cryocooler 29 can in particular be configured as a Gifford-McMahon cooler or a pulse tube cooler. The cooling of the cooling rod 16 or the condensation heat exchanger 17 is provided by a refrigerator outside the cryocooler 29 or the application cryostat 102.

[0122] The control device 8 monitors the pressure p in the application cryostat 102 using a pressure sensor 18 anwend , and the pressure sensor is arranged here on the second access tube 15b of the application cryostat 102. Additionally, the second access tube 15b is free and can in particular be well used as an emergency outlet for helium (for example in the case of a quench). The pressure sensor 18 is connected to the control device 8 at the measurement input 18a. Additionally, in the illustrated embodiment, the control device 8 monitors the pressure p in the surroundings 4 using a pressure sensor 8a integrated into the control device 8 atm .

[0123] In the embodiment shown, the control device 8 controls the heating power of the electric heater 7 in the storage tank 1 when transferring the liquid helium. The pressure in the storage tank 1 can be changed by the heating power of the heater 7, and thus also the pressure difference between the storage tank 1 and the application cryostat 102. The heater 7 here therefore constitutes a means 31 for generating a pressure difference between the storage tank 1 and the application cryostat 102. The heater 7 is connected to a control output 31a of the control device 8.

[0124] The heating power is regulated and monitored by the control device 8 in such a way that, when the cryostat 102 is used, the pressure p there is anwend Adjust to the predefined setpoint value p anwend soll . The predetermined rated value p anwend soll Here it is 1.03 bar and is selected such that it slightly (here by 0.03 bar) exceeds the pressure p of the surroundings 4 atm In the simplest case, the predetermined nominal value p anwend soll If the weather and thus the air pressure in the surroundings 4 or the pressure p monitored by the sensor 8a is constant over the entire duration of the transfer of liquid helium. atm If the change during the transfer is to be significant, the predetermined setpoint value p can also be changed if necessary. anwend soll , so that the pressure p in the cryostat 102 is applied anwend The pressure of the surrounding environment p atm The desired distances (minimum distances and / or maximum distances) are maintained, in particular to avoid the inhalation of ambient air into the application cryostat 102 and / or to prevent overpressure safety devices (overpressure valves, bursting disks, not shown in greater detail) on the application cryostat 102 from being triggered.

[0125] If during the period when liquid helium is input into the application cryostat 102 through the transfer line 9, the pressure p anwend Basically keep in p anwend soll , then the volume of liquid helium input per unit time dV(LHe trans ) / dt is substantially related to the volume change dV(He) of helium condensed in the condensing heat exchanger 17 per unit time. cond ) / dt corresponds (“equilibrium state”). In this case, during the period when liquid helium is input into the application cryostat 102 , no gaseous helium escapes from the application cryostat 102 .

[0126] If the pressure p anwend Drop below p anwend soll, the control device 8 increases the heating power at the heater 7, such that the additional helium vaporizes in the storage reservoir 1, and the pressure p in the storage reservoir vorrat rises, the flow rate of the liquid helium through the transfer line 9 increases, and the gas pressure in the cryostat 102 rises. If the pressure p anwend rises above p anwend soll , the control device 8 reduces the heating power at the heater 7 or completely shuts off the heater 7, so that less helium in the storage reservoir 1 vaporizes or does not vaporize at all, and the pressure in the storage reservoir 1 decreases (which is also the result of subsequently outputting the liquid helium 5), the flow rate of the liquid helium through the transfer line 9 decreases, and the gas pressure in the cryostat 102 decreases.

[0127] In the illustrated embodiment, the cooling power of the cryocooler 29 remains constant during the transfer of the liquid helium.

[0128] In the illustrated embodiment, a superconducting magnetic coil 32 (also simply referred to as a magnet) is arranged in the cryostat 102. In normal operation, the NMR sample head 33 extends into the room temperature bore (not shown in more detail) of the cryostat 102, so that the sample 34 can undergo NMR measurement in the magnetic bore of the magnet 32 in the magnetic field of the magnet. It is noted that in normal operation, the transfer line 9 and the cooling rod 16 are pulled out of the feed tube 15a, and the transfer line 9 and the cooling rod 16 are only inserted into the feed tube 15a during the refill operation (the feed tube is shown in Figure 1 ).

[0129] In the cryostat 102 and in the storage reservoir 1, a liquid level sensor may additionally be provided, and the liquid level sensor is read by the control device 8 (not shown in more detail).

[0130] Figure 2 The rear section of the illustrated line bundle 40, which can be used in the device for transferring liquid helium according to the invention within the scope of the invention (for this also see Figure 3 ).

[0131] The forward line 20 and the return line 21 of the cooling circuit for the condensation heat exchanger 17 and the transfer line 9 for the liquid helium 14 extend in the line bundle 40, and the liquid helium flows out at the second transfer line end 9b into the cryostat. The line bundle 40 forms a common isolation vacuum section 41 for the lines 9, 20, 21. A plurality of coupling bridges 42 made of a well - thermally - conductive material, for example, made of high - purity copper, are provided between the transfer line 9 and the forward line 20, and a thermal coupling is established between the forward line 20 and the transfer line 9 through the coupling bridges. Thus, it is especially possible to pre - cool the transfer line 9 using the forward line 20 before starting the transfer of the liquid helium.

[0132] The vertically extending portion of the line bundle 40 forms here the refrigeration bar 16 that can be easily operated. It is noted that the line bundle on the other side (except for the refrigeration bar) of the cooling bar is preferably configured to be flexible. The line bundle can have a so-called super insulation section. Additionally, a distance maintaining member with low heat conduction capacity is provided to keep each line spaced apart from the external isolation sheath.

[0133] Figure 3 A second embodiment of the application system 100 according to the present invention is schematically shown, and this application system includes a device 101 for transferring liquid helium and an application cryostat 102. The application system 100 largely corresponds to Figure 1 the application system, so only the main differences will be described hereinafter. For simplicity, the compressor and the part of the line guiding the coolant are not shown in more detail in Figure 3 the figure.

[0134] In Figure 3 the embodiment, a common storage cryostat 50 is established, and not only the cold head 25 but also the helium container 2 are arranged in the storage cryostat. The cold head 25 is arranged here in the receiving area 51, and the receiving area is open towards the helium container 2, so that gaseous helium 6 is distributed in the upper part of the helium container 2 and in the receiving area 51. The storage cryostat 50 has here a radiation shield 58, and the radiation shield is thermally coupled to the hotter cooling stage of the cold head 25 (the coupling is not shown in more detail).

[0135] The helium gas line 54 leads from the helium gas storage 52 configured as a helium pressure gas storage 53 to the storage 1. The first helium gas line end 54a extends into the upper part of the helium container 2, and the second helium gas line end 54b is connected to the helium pressure gas storage 53. The helium pressure gas storage 53 can be configured to be transportable, for example, constructed with rollers (not shown in detail).

[0136] The helium gas line 54 has a regulating valve 55 near its second helium gas line end 54b, and the regulating valve can be automatically controlled by the control device 8, and here it is automatically controlled by an electric motor (not shown in detail).

[0137] The helium gas line 54 passes through the receiving area 51 beside the cold head 25 and is thermally coupled to the two cold stages 25 of the cold head by means of a helium supply heat exchanger 56. The helium gas 6a flowing into the storage 1 through the helium gas line 54 (or the helium gas 6 already existing in the storage 1) can be liquefied by the cold head 25.

[0138] It is noted that the helium gas 6a should be purified before liquefaction, for example, by means of a cold trap (not shown in more detail); here, for example, the device described in DE102021205423A1 can be used.

[0139] In the illustrated embodiment, a pressure sensor 57 is additionally provided, and the pressure p in the storage 1 vorrat is measured by the pressure sensor and monitored by the control device 8; the control device 8 ensures that p vorrat is always kept higher than p atm (see also below), thereby preventing ambient air from being sucked into the storage 1. Additionally, the control device 8 also monitors the pressure p in the application cryostat 102 using the pressure sensor 18 anwend . Furthermore, the control device 8 can control the heater 7 in the storage 1

[0140] The control device 8 can use the heater 7 (see above) or the regulating valve 55 here respectively as the device 31 for generating a pressure difference between the storage 1 and the application cryostat 102. By increasing the opening cross-section of the regulating valve 55, additional helium (helium gas and / or liquefied helium) can be introduced into the storage 1, which increases the pressure p in the storage 1 vorrat . By reducing the opening cross-section of the regulating valve 55 or closing the regulating valve 55, the pressure p in the storage 1 can be reduced (when subsequently outputting liquid helium to the application cryostat through the transfer line 9) vorrat .

[0141] The forward line 20, the return line 21, and the transfer line 9 extend here as a line bundle 40 between the storage 1 and the application cryostat 102 in a common vacuum isolation section 41 (see Figure 2 ). Additionally, the transfer line 9 has a branch 60 leading to the purge valve 59 near its first transfer line end 9a, where the branch 60 is located within the common storage cryostat here. Through the purge valve 59, the transfer line 9 can be purged with helium 12 (the helium originating from the application cryostat 102) between the second transfer line end 9b and the branch 60, which is carried out through the transfer line 9 before starting the transfer of liquid helium; it is noted that for this purpose p anwend >p atm . To completely eliminate helium loss, the output end of the purge valve 59 can be connected to a helium recovery system; the air purged into the helium recovery system can be separated in the cold trap connected upstream when the helium from the recovery system is re-liquefied (the helium recovery system and the cold trap are not shown in more detail).

[0142] Method flow according to the present invention

[0143] Hereinafter, the process when re-filling liquid helium from the storage 1 into the application cryostat 102 will be exemplarily described within the scope of the method according to the present invention. The exemplary process can especially be on the application system 100 as in Figure 3occur as shown. Steps 2 to 6 can be assigned to the transfer operation, and step 7 is assigned to the normal operation of the application cryostat 102. Step 1 can occur in parallel with the normal operation or as part of the transfer operation.

[0144] Step 1) Helium is introduced from the helium pressure gas reservoir 53 via the helium pipeline 54 into the reservoir 1, where the helium is liquefied by the cold head 25. The liquid helium 5 is collected in the helium container 2.

[0145] Step 2) Once the liquefaction is complete (e.g., because the helium container 2 is full or the helium pressure gas reservoir 53 is empty), the transfer of the liquid helium 5 can be prepared. For this purpose, the user first inserts the cooling rod 16 together with the transfer pipeline 9 and the condensation heat exchanger 17 into the application cryostat 102 into the access pipe 15a.

[0146] Step 3) The purge valve 59 is opened, and the helium gas from the application cryostat 102 presses the air out of the transfer pipeline 9 through the purge valve 59. If the existing air escapes, the purge valve 59 is closed.

[0147] Step 4) Then the coolant cooling circuit valve ( Figure 1 reference numeral 19a in Figure 1 is opened, whereby a part of the air flow provided by the compressor (

[0148] reference numeral 28 in

[0149] branches off, and the coolant circulation in or through the condensation heat exchanger 17 in the cooling circuit 19 is activated. Since the forward pipeline 20 is thermally connected to the transfer pipeline 9, the transfer pipeline 9 is cooled here.

[0150] Step 4) Once the condensation heat exchanger 17 and the transfer pipeline 9 are cold, the transfer of the liquid helium ("helium transfer") begins. This can occur either automatically when the pressure in the helium storage tank 10 of the application cryostat 102 drops due to the start of condensation, or when the pressure in the reservoir 1 is actively increased, for example, by using the heater 7 or by introducing helium gas 6a from the helium pressure gas reservoir 53.

[0151] Step 7) Now it is possible to continue with the measurements only a few hours after the start of the helium transfer, using the application cryostat 102 and, in particular, using the NMR magnet (reference numeral 32 in Figure 1 ) contained in the application cryostat 102. Compared to a conventional helium transfer, in which gaseous helium is discharged through one of the feed tubes 15a, 15b, the application cryostat 102 stabilizes significantly faster within the scope of the present invention because no large amounts of cold gas escape through the feed tubes (suspension tubes) 15a, 15b (large amounts of cold gas usually cause strong cooling of the feed tubes during a conventional helium transfer and magnetic field instability during the return to thermal equilibrium).

[0152] Figure 4 shows an alternative structural form of the storage reservoir 1 for the present invention, which can be used, for example, in Figure 3 an embodiment of the application system of Figure 3 . Only the main differences from the

[0153] structural form are explained. Figure 4 In the structural form shown in

[0154] , a heat insulation barrier 70 is arranged in the helium container 2 of the storage reservoir 1. The heat insulation barrier 70 is pressure-permeable (i.e., can be penetrated by liquid helium), but is heat-insulating. The heat insulation barrier 70 can be constructed, in particular, as described in DE4039365A1. vorrat below.

[0155] The transfer line (line tube) 9 extends deeply into the region of the supercooled liquid helium 74 until it is not far from the bottom of the helium container 2. In the section of the region of the saturated helium volume 75 through which the transfer line 9 passes, the transfer line 9 is thermally insulated from the saturated helium volume 75 (not shown in more detail). Thus, within the scope of the helium transfer, the supercooled liquid helium 74 is fed into the application cryostat through the transfer line 9.

[0156] By means of supercooled liquid helium 74 fed into the application cryostat, thermal energy can be extracted from the application cryostat when the supercooled liquid helium is reheated to 4.2 K again. Then a small cooling power must be applied to the condensation heat exchanger in order to condense the gaseous helium at the condensation heat exchanger. If, for example, 100 l of liquid helium (12.5 kg) with a temperature of 3.7 K are transferred, then approximately 26.3 kJ of additional cold energy are available for use, and this additional cold energy can be used for the approximately 34 kJ required for the condensation heat (see above). However, the lower the temperature of the supercooled liquid helium 74, the more energy-consuming it is to provide the supercooled liquid helium 74.

[0157] The forward line 20 of the cooling circuit for the condensation heat exchanger extends through the region of the supercooled liquid helium 74 in the application cryostat. Thus, the thermal energy of the condensation heat exchanger can be removed particularly effectively by the coolant.

[0158] It is noted that supercooled helium for use in the present invention can also be produced, for example, by reducing the pressure of helium in a throttle (not shown in more detail).

[0159] In summary, the present invention relates to a device (101) for transferring liquid helium (14) in an application cryostat (102), the device comprising:

[0160] - a storage (1),

[0161] - a transfer line (9) which includes a first transfer line end (9a) in the storage (1) and a second transfer line end (9b) for insertion into the application cryostat (102),

[0162] - means (31) for generating a pressure difference between the storage (1) and the application cryostat (102),

[0163] characterized in that

[0164] - a condensation heat exchanger (17) for condensing helium gas (12) into liquid helium (11), the condensation heat exchanger for insertion into the application cryostat (102);

[0165] - a cryocooler (29) for cooling the condensation heat exchanger (17), and

[0166] - A control device (8), having a measurement input (18a) for a pressure sensor (18) for measuring the air pressure in an application cryostat (102) and a control output (31a) for a device (31) for generating a pressure difference, wherein the control device (8) is programmed to control the device (31) for generating a pressure difference such that the volume of liquid helium (14) transferred per unit time through the transfer line (9) is approximately equal to the volume change of helium condensed from helium gas (12) to liquid helium (11) at the condensation heat exchanger (17). With this device, the helium loss during the transfer of liquid helium is minimized in a simple manner.

[0167] List of reference numerals

[0168] 1 Storage

[0169] 2 Helium container

[0170] 3 Isolation vacuum section (on the storage)

[0171] 4 Surroundings / Ambient atmosphere

[0172] 5 Liquid helium (in the storage)

[0173] 6 Gaseous helium (in the storage)

[0174] 6a Gaseous helium (coming out of the storage)

[0175] 7 Electric heater (in the storage)

[0176] 8 Electronic control device

[0177] 8a Pressure sensor for the ambient atmosphere

[0178] 9 Transfer line for liquid helium

[0179] 9a First transfer line end (inserted into the storage)

[0180] 9b Second transfer line end (inserted into the application cryostat)

[0181] 10 Helium storage tank

[0182] 11 Liquid helium (in the application cryostat)

[0183] 12 Gaseous helium (in the application cryostat)

[0184] 13 Isolation vacuum section (on the application cryostat)

[0185] 14 (Outflowing / Transferred) liquid helium

[0186] 15a First / common inlet pipe

[0187] 15b Second inlet pipe

[0188] 16 Cooling rod

[0189] 17 Condensation heat exchanger

[0190] 18 Pressure sensor for applying a cryostat

[0191] 18a Measurement input (for pressure sensor 18)

[0192] 19 Cooling circuit

[0193] 19a Cooling circuit valve

[0194] 20 Forward line for coolant

[0195] 21 Return line for coolant

[0196] 22 Vacuum isolation section (of forward and return lines)

[0197] 23 Vacuum isolation section (of transfer line)

[0198] 25 Cold head

[0199] 25a Cold head heat exchanger (for cooling circuit)

[0200] 26 Compressor forward line

[0201] 27 Compressor return line

[0202] 28 Compressor

[0203] 29 Cryocooler

[0204] 30 Cryocooler - cryostat

[0205] 31 Device for generating a pressure difference

[0206] 31a Control output (for device 31)

[0207] 32 Superconducting magnetic coil / magnet

[0208] 33 NMR sample head

[0209] 34 Measurement sample

[0210] 35, 36 Cold head lines

[0211] 37 Roller

[0212] 40 Line bundle

[0213] 41 Common isolation vacuum section

[0214] 42 Coupling bridge

[0215] 50 Common storage cryostat

[0216] 51 Receiving area

[0217] 52 Helium storage

[0218] 53 Helium pressure gas storage

[0219] 54 Helium pipeline

[0220] 54a First end of the helium pipeline

[0221] 54b Second end of the helium pipeline

[0222] 55 Control valve

[0223] 56 Helium supply heat exchanger

[0224] 57 Pressure sensor for the storage

[0225] 58 Radiation shielding section

[0226] 59 Purge valve

[0227] 60 Branch for the purge valve

[0228] 70 Thermal insulation shielding section

[0229] 71 Vacuum vessel

[0230] 73 Lowest / coldest cooling stage

[0231] 74 Subcooled liquid helium / helium volume

[0232] 75 Saturated liquid helium / helium volume

[0233] 100 Application system

[0234] 101 Equipment for transferring liquid helium

[0235] 102 Application cryostat

Claims

1. A device (101) for transferring liquid helium (14) into an application cryostat (102), the device comprising: - a storage tank (1) for liquid helium (5); a transfer line (9) for liquid helium (14) for transferring liquid helium (5) from a storage reservoir (1) to an application cryostat (102), the transfer line comprising a first transfer line end (9a) and a second transfer line end (9b), the first transfer line end being arranged in the storage reservoir (1) and the second transfer line end being intended to be inserted into the application cryostat (102); - means (31) for generating a pressure difference between the storage reservoir (1) and the application cryostat (102); It is characterized in that The device (101) further comprises: a condensing heat exchanger (17) for condensing helium gas (12) into liquid helium (11), the condensing heat exchanger being intended to be inserted into an application cryostat (102); - a cryocooler (29) for cooling the condensing heat exchanger (17), and - a control device (8) having at least one measuring input (18a) for a pressure sensor (18) for measuring the gas pressure in the application cryostat (102) and a control output (31a) for a means (31) for generating a pressure difference, the control device (8) being programmed to control the means (31) for generating a pressure difference in such a way that the volume of liquid helium (14) transferred via the transfer line (9) per unit time is approximately equal to the change in volume of helium condensed from helium gas (12) to liquid helium (11) at the condensing heat exchanger (17) per unit time.

2. The device (101) according to claim 1, characterized in that The control device (8) is programmed to adjust the pressure (p) in the application cryostat (102) during the transfer of the liquid helium (14) into the application cryostat (102). anwend ) remains roughly constant.

3. The device (101) according to any one of the preceding claims, characterized in that The control device (8) has a sensor for measuring the atmospheric pressure (P atm ), and the control device (8) is programmed to - in particular by correspondingly actuating the means (31) for generating a pressure difference - apply a pressure (p anwend ) at all times maintains a higher atmospheric pressure than the surrounding environment (P atm ).

4. The device (101) according to any one of the preceding claims, characterized in that The device (31) for generating a pressure difference comprises a regulating valve (55) in a helium pipeline (54), wherein the helium pipeline (54) comprises a first helium pipeline end (54a) and a second helium pipeline end (54b), wherein the first helium pipeline end is connected to a storage tank (1), and the second helium pipeline end is used to be connected to a helium storage tank (52), in particular a helium pressure gas storage tank (53).

5. The device (101) according to any one of the preceding claims, characterized in that The means (31) for generating a pressure difference comprises an electric heater (7) in the storage reservoir (1).

6. The device (101) according to any one of the preceding claims, characterized in that The device (101) also includes a closed cooling circuit (19) for the coolant, which includes a forward pipeline (20) from the cold head (25) of the low-temperature cooler (29) to the condensing heat exchanger (17) and a return pipeline (21) from the condensing heat exchanger (17) to the cold head (25) of the low-temperature cooler (29), wherein the low-temperature cooler (29) is designed to directly or indirectly cool the coolant using the cold head (25), and in particular, wherein the cold head (25) of the low-temperature cooler (29) is arranged separately from the application low-temperature thermostat (102).

7. The device (101) according to claim 6, characterized in that Starting from a storage tank (1), a forward line (20), a return line (21) and a transfer line (9) extend as a line bundle (40) in a common insulating vacuum section (41), in particular, the forward line (20) and the transfer line (9) are thermally coupled to each other in a common insulating vacuum section (41), preferably thermally coupled to each other via a plurality of coupling bridges (42).

8. The device (101) according to any one of the preceding claims, characterized in that The device (101) further comprises a helium gas storage (52), which is connected to the storage tank (1) via a helium gas pipeline (54), and in particular, the helium gas storage (52) is a helium pressure gas storage (53).

9. The device (101) according to one of the preceding claims, characterized in that The cold head (25) of the cryocooler (29) and the helium container (2) of the storage tank (1) are arranged in a common storage cryostat (50), wherein the cold head (25) of the cryocooler (29) is designed to liquefy helium gas (6, 6a) into liquid helium (5) in the storage tank (1).

10. The device (101) according to claim 9, characterized in that The helium container (2) and the cold head (25) are designed to provide a liquid, supercooled helium volume (74) in the helium container (2).

11. The device (101) according to claim 10, characterized in that A thermal insulation barrier (70) is arranged in the helium container (2), by which a subcooled helium volume (74) below the thermal insulation barrier (70) is separated from a liquid, saturated helium volume (75) above the thermal insulation barrier (70).

12. An application system (100), comprising a device (101) according to any one of the preceding claims and an application cryostat (102), wherein: The transfer line (9) and the condensation heat exchanger (17) are inserted into the application cryostat (102), in particular into a common inlet pipe (15a) of the application cryostat (102), and the application cryostat (102) includes a superconducting magnetic coil (32) and the NMR sample head (33) extends into the magnetic hole of the magnetic coil (32).

13. A method for transferring liquid helium (14) into an application cryostat (102), in particular when using an apparatus (101) or an application system (100) according to any of the preceding claims, wherein: A transfer line (9) for liquid helium (14) is connected to a storage tank (1) containing liquid helium (5) via a first transfer line end (9a) and is inserted into an application cryostat (102) via a second transfer line end (9b), wherein the liquid helium (14) is transferred from the storage tank (1) to the application cryostat (102) via the transfer line (9), wherein the flow rate of the liquid helium (14) through the transfer line (9) is regulated by means of a device (31) for varying the pressure difference between the storage tank (1) and the application cryostat (102), It is characterized in that A condensing heat exchanger (17) cooled by a cryocooler (29) is inserted into an application cryostat (102), and gaseous helium (12) is liquefied into liquid helium (11) in the application cryostat (102), and a control device (8) measures the pressure (p anwend ) and controlling the device (31) for changing the pressure difference so that the volume of liquid helium (14) transferred through the transfer line (9) per unit time is approximately equal to the change in volume of helium condensed from helium gas (12) to liquid helium (11) at the condensing heat exchanger (17) per unit time.

14. The method according to claim 13, characterized in that During the transfer of the liquid helium (14) into the application cryostat (102), the control device (8) adjusts the pressure (p anwend ) remains roughly constant.

15. The method according to claim 13 or 14, characterized in that During the transfer of the liquid helium (14), no outflow of gaseous helium (12) from the application cryostat (102) occurs.

16. The method according to any one of claims 13 to 15, characterized in that The control device (8) measures the atmospheric pressure (p atm ), and the control device (8) - in particular by correspondingly controlling the device (31) for generating a pressure difference - applies the pressure (p anwend ) at all times maintains a higher atmospheric pressure than the surrounding environment (p atm ).

17. The method according to any one of claims 13 to 16, characterized in that The control device (8) controls a regulating valve (55) in a helium pipeline (54) as a device (31) for changing the pressure difference, wherein the helium pipeline leads from a helium storage tank (52), in particular a helium pressure gas storage tank (53), to the storage tank (1), and / or the control device (8) controls an electric heater (7) in the storage tank (1) as a device (31) for changing the pressure difference.

18. The method according to any one of claims 13 to 17, characterized in that In a closed cooling circuit (19), a coolant is conducted from a cold head (25) of a cryocooler (29) to a condensing heat exchanger (17) via a forward line (20) and is conducted back to the cold head (25) of the cryocooler (29) via a return line (21), wherein the cold head (25) of the cryocooler (29) directly or indirectly cools the coolant, in particular wherein the cold head (25) is arranged separately from an application cryostat (102).

19. The method according to claim 18, characterized in that The transfer line (9) between the storage tank (1) and the application cryostat (102) is thermally coupled to the forward line (20), and before the liquid helium (14) starts to be transferred through the transfer line (9), the transfer line (9) is first pre-cooled using the coolant in the forward line (20).

20. The method according to any one of claims 13 to 19, characterized in that The cold head (25) of the cryocooler (29) and the helium container (2) of the storage tank (1) are arranged in a common storage cryostat (50), and before the transfer of liquid helium (14) begins, gaseous helium (6a) is supplied to the storage tank (1) from a helium gas storage tank (52), in particular a helium pressure gas storage tank (53), and the gaseous helium (6, 6a) is condensed into liquid helium (5) in the storage tank (1) by means of the cold head (25).

21. The method according to any one of claims 13 to 20, characterized in that A liquid subcooled helium volume (74) is provided in a helium container (2) of a storage tank (1), and liquid helium (14) transferred via a transfer line (9) is removed from the liquid subcooled helium volume (74).

22. The method according to any one of claims 13 to 21, characterized in that An application cryostat (102) is alternately used for an application in normal operation and filled with liquid helium (14) in refilling operation, wherein during normal operation, a condensing heat exchanger (17) and a second transfer line end (9b) are not inserted into the application cryostat (102), while during refilling operation, the condensing heat exchanger (17) and the second transfer line end (9b) are inserted into the application cryostat (102), a superconducting magnetic coil (32) is arranged in the application cryostat (102), and during normal operation, an NMR measurement is performed as an application on a sample (34) arranged in a magnetic bore of the superconducting magnetic coil (32) using an NMR sample head (33).

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