Apparatus and method for transferring liquid helium to an application cryostat

Abstract

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

Description

TECHNICAL FIELD

[0001] The invention relates to an apparatus for transferring liquid helium into an application cryostat, the apparatus comprising

[0002] - a storage reservoir for liquid helium;

[0003] - a transfer line for liquid helium for transferring liquid helium from the storage reservoir into the application cryostat, the transfer line comprising a first transfer line end arranged in the storage reservoir and a second transfer line end for insertion into the application cryostat; and

[0004] - means for generating a pressure difference between the storage reservoir and the application cryostat. BACKGROUND

[0005] Such an apparatus is known from chapter 12 of the company publication "User Manual for NMR Magnet Systems UltraShield Magnets (English version) 006th edition, October 12, 2004" of Bruker BioSpin GmbH, Flawil, Switzerland.

[0006] Superconducting magnets, for example for NMR spectroscopy (NMR = nuclear magnetic resonance) or magnetic resonance imaging (also referred to as MRI (MRI = magnetic resonance imaging)), require cooling 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, usually at a temperature of approximately 4.2 K, which corresponds to the boiling point of liquid helium at atmospheric pressure. Cooling with liquid helium is also known from other fields of application.

[0007] Because the application cryostat cannot be perfectly thermally isolated, or heat is introduced into the application cryostat by the respective application, liquid helium evaporates during operation. If the level of liquid helium in the application cryostat falls too much for continued operation, the application cryostat is refilled with liquid helium.

[0008] It is pointed out here that helium is a scarce resource. Helium is a by-product of natural gas extraction. The supply of helium on the world market is becoming increasingly scarce, and the price of helium is rising, see "Helium supply tight again" by D. Kramer, April 4, 2022, Physics Today, https: / / doi.org / 10.1063 / PT.6.2.20220404a.

[0009] Therefore, efforts are being made to minimize helium consumption for the operation of cryogenic systems. Many consumers are investing in helium recovery equipment, which captures and reliquefies vaporized helium.

[0010] As described in the aforementioned company publication, "UltraShield Magnet (English Version) User Manual for NMR Magnet Systems," significant helium loss occurs during the common process of refilling liquid helium from a storage container (storage Dewar) into a cryostat. This common process can be summarized as follows:

[0011] Step a) Bring the storage device (“transport storage”) to the vicinity of the cryostat, or, in the company’s publication, to the vicinity of the NMR magnet, up to a distance of several meters.

[0012] Step b) Insert the heat transfer line into the transport reservoir such that its (first) end is below the liquid helium contained therein.

[0013] Step c) The helium in the transport reservoir is vaporized by the heat input through the heat transfer line. This increases the pressure in the transport reservoir, and the liquid helium is forced into the transfer line, which is then cooled. Helium escaping from the end of the transfer line during cooling is typically not captured but lost into 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 pipeline away from the transport reservoir is sufficiently cooled (i.e., the transfer pipeline is sufficiently cooled), the transfer pipeline is connected to the application cryostat (e.g., an 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, liquid helium flows from the transport reservoir to the application cryostat. The mass flow is driven by the pressure differential between the transport reservoir and the application cryostat. As mentioned above, an overpressure is established in the transport reservoir due to the insertion of the transfer line. However, the pressure buildup in the transport reservoir due to heat input at the time of transfer line insertion is typically insufficient to transfer the desired amount of liquid helium. Therefore, helium is introduced from the pressurized gas cylinder into the transport reservoir via a pressure regulator, thereby maintaining a constant high pressure in the transport reservoir. Typically, the overpressure regulated in the transport reservoir is approximately 50-100 mbar. During the transfer of liquid helium, the volume of gaseous helium corresponding to the incoming liquid helium is expelled from the application cryostat at the output.

[0016] For illustration: At the beginning of the transfer of liquid helium to the application cryostat, the application cryostat or its helium reservoir 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 reservoir is slowly filled with liquid helium during the transfer, the cold gaseous helium located in the helium reservoir before the transfer is gradually pressed out of the helium reservoir and escapes through the output of the application cryostat.

[0017] Gaseous helium has a density of 16.5 g / l at 4.2 K and atmospheric pressure. Liquid helium has a density of 125 g / l at 4.2 K and atmospheric pressure. If, for example, 100 liters of liquid helium are transferred (i.e. 12.5 kg of helium), 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 transferred amount.

[0018] In most cases, these amounts of helium simply escape into the atmosphere through the output of the application cryostat, 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 that occurs at the output during the helium transfer (“transfer loss”) and to supply it to a high-pressure storage or liquefier. In the pipe system to the balloon and the balloon itself, the gaseous helium is heated to room temperature, which leads to a considerable increase in gas volume. 100 liters of gaseous helium at atmospheric pressure and 4.2 K correspond to approximately 10,000 liters at atmospheric pressure and room temperature (i.e. 10 m 3 ).

[0020] In the usual transfer of helium to an NMR magnet - depending on the magnet type - between 100 and 400 liters of liquid helium are transferred. A usual transfer usually lasts about an hour. In this time, therefore, 10 to 40 cubic meters of gaseous helium at room temperature are produced, which must be stored in a balloon or processed by a recovery system (e.g. compressed in a pressure storage), corresponding 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 publication DE 102022209941 Al that the gaseous helium pressed out at the application cryostat during the transfer of liquid helium from the storage container to the application cryostat is passed through a return line to the storage container.

[0022] It is additionally noted that it is also possible to use a cryocooler for actively cooling an application cryostat (e.g. comprising a superconducting magnet for NMR applications) in continuous operation, see e.g. US 2002 / 0002830 Al. In this case, no refill of liquid helium is required and the problem of helium loss upon refilling is eliminated.

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

[0024] US 8 671 698 describes a helium reliquefier with a pulse tube cooler, which is separate from the application cryostat.

[0025] From US 2007 / 0107445 Al a retrofittable reliquefier for helium is known. The installation of this device is rather complex. In addition, here too vibrations are introduced into the application cryostat and high energy and maintenance costs are incurred.

[0026] US 8 375 742 B2 describes a helium reliquefier, which is equipped with its own insulation jacket. Helium vaporized from the application cryostat is liquefied by the reliquefier and led back through a transfer tube, which is also surrounded by an insulation jacket. In a variant, an interface for an external gas source is additionally provided.

[0027] US 2009 / 0301129 Al describes a helium reliquefier for retrofitting a magnetic resonance system, through which vaporized nitrogen and vaporized helium should be reliquefied.

[0028] From EP 0 245 057 B1 and EP 0 396 624 B1 a condensation heat exchanger is known, which is connected with a cold head by means of a cooling circuit and is inserted into a cryostat with liquid helium.

[0029] DE 10 2021 205 423 Al additionally describes a device in which helium is purified and liquefied with one single cold head.

[0030] DE 40 39 365 Al describes an NMR magnet with a cryostat, in which supercooled liquid helium is arranged in a first lower chamber, liquid helium at 4.2 K at atmospheric pressure is arranged in a second upper chamber, and a thermally insulating but pressure-permeable barrier is arranged between the two chambers.

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

[0032] A portable liquefaction device for liquefying helium is known from DE102020204186A1. This liquefaction device includes a liquefaction unit for liquefying helium, an intermediate storage unit for liquefied helium, a purification unit for helium, and an additional collection unit for gaseous helium, the additional collection unit comprising a container with flexible walls. Using the liquefaction unit and the purification unit, helium vaporized during operation and stored at the location of the applied cryostat can be purified and liquefied, and collected in the intermediate storage unit. When filling the applied cryostat with liquid helium from the intermediate storage unit, the additional collection unit can capture the vaporized helium.

[0033] DE69926087T2 describes an apparatus for recondensing liquid helium, wherein liquid helium is stored in a container. Gaseous helium, vaporized in the container, is guided through a pipe to a cooling device located outside the container and liquefied there. The liquefied helium is then guided back into the container through another pipe. Summary of the Invention

[0034] The objective of this invention is to minimize helium loss in a simple manner when transferring liquid helium from a storage device to an applied cryostat.

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

[0036] The device also includes:

[0037] - A condensing heat exchanger for condensing helium gas into liquid helium, the condensing heat exchanger being inserted into an application cryostat;

[0038] - Low-temperature coolers for cooling condensing heat exchangers, and

[0039] - A control device having at least one measurement input for a pressure sensor used to measure the gas pressure (gas pressure) in an applied cryogenic thermostat and a control output for a device used to generate a pressure difference, wherein the control device is programmed to control the device used to generate a 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 condensed into liquid helium at the condensing heat exchanger per unit time.

[0040] With the device according to the application it is possible to achieve, during the transfer of liquid helium from the storage reservoir into the application cryostat with the condensation heat exchanger inserted into the application cryostat, in which the liquefaction of the gaseous helium on site to liquid helium is carried out, that the cooling power of the condensation heat exchanger (or rather the cryocooler) on the one hand and the transfer rate of the liquid helium into the application cryostat on the other hand can be coordinated with each other in such a way that the volume change (volume reduction) of the helium condensed in the application cryostat per unit of time at least substantially (and preferably exactly) corresponds to the volume of the liquid helium transferred from the storage reservoir into the application cryostat by means of the means for generating a pressure difference through the transfer line ("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 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 recycling is dispensed with. In particular, a large balloon for capturing the pressed-out gaseous helium is no longer required for the transfer of the liquid helium.

[0041] The liquid helium is pressed into the application cryostat through the transfer line by means of the pressure difference between the storage reservoir and the application cryostat, which is adjusted with the means for generating a pressure difference, wherein a higher pressure prevails in the storage reservoir than in the application cryostat, mostly with a pressure difference of 50-100 mbar. The means for generating (or adjusting) the pressure difference are connected to the control output of the control device and are 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 in the scope of the present application. Nevertheless, it is preferred to provide that the control device additionally also monitors the pressure in the storage reservoir with a further pressure sensor.

[0042] The (at least approximate) maintenance of the equilibrium state is preferably ensured in that the pressure (helium gas pressure) in the application cryostat is kept at least approximately constant, or at least in a predetermined pressure interval. The control device correspondingly uses the pressure in the application cryostat as an input variable (control variable) or at least as one of the input variables for operating the means for generating a pressure difference.

[0043] The means for generating a pressure difference is usually configured to change the pressure (gas pressure) in the storage reservoir, for example by changing the current of an electrical heater in the storage reservoir or by changing the position of a regulating valve (inlet valve) in the helium gas line from the helium storage 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 usually kept constant. It is also possible, however, for the pressure in the applied cryostat to be changed alternatively or additionally by the means for generating a pressure difference, for example by changing the current of an electrical heater in the applied cryostat or by changing the cooling power at the condensation heat exchanger.

[0044] The cryocooler generally comprises a cold head and a compressor. The cryocooler can in particular comprise a Gifford-McMahon cooler or a pulse tube cooler. The cold head is thermally coupled to the condensate (heat) exchanger in order 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 applied cryostat.

[0045] If, for example, 100 litres of liquid helium are to be refilled into the applied cryostat in the context of the application, 100 litres of gaseous helium (gaseous helium at a temperature of 4.2 K) must be liquefied in the applied cryostat during the transfer of the liquid helium in order to avoid helium gas flowing out of the applied cryostat. The density of gaseous helium at 4.2 K and 1 bar is 16.5 g / l; approximately 1.65 kg of helium must be liquefied accordingly. Helium has a latent heat of 20.6 kJ / kg, and 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 accordingly. If a commercially available cryocooler having a cooling power of 2 watts is used for this purpose, for example, these energies can be absorbed in approximately 4.7 hours. The transfer rate of the liquid helium to be used in the context of the application is then approximately 21.3 l / h. The power to be absorbed in practice is also slightly higher than the 34 kJ, since additional heat inputs into the system occur, for example, through the helium transfer line and the inserted condensation heat exchanger (for example arranged on a cooling rod). The transfer time is accordingly slightly extended or the transfer rate is reduced as a result.

[0046] The time required for the transfer of liquid helium in the context of the present application, as can be seen from the above examples, depends, inter alia, on the amount of liquid helium to be refilled, the cooling power of the cryocooler and the additional heat input caused by the incomplete insulation. The transfer of liquid helium can be planned in accordance with the intended transfer time, in particular also as an "overnight" automated transfer when no application using the application cryostat is present (for example NMR measurements). Typical transfer times in the context of the present application are 1 h to 16 h and preferably 2 h to 12 h. It is noted that the transfer time can be reduced here when supercooled liquid helium is transferred from the storage reservoir into the application cryostat (see also further below).

[0047] The storage reservoir is generally configured to be transportable ("transportable reservoir"), preferably configured with rollers, so that it can be moved back and forth between different laboratories and can thus be used in particular easily for refilling a plurality of application cryostats. The storage reservoir is preferably combined with the cryocooler into an integrated transportable structural assembly (for example arranged on a common platform with rollers), in particular when the storage reservoir also serves as a helium liquefier.

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

[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, it is generally also applicable that:

[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 present application

[0055] In a preferred embodiment of the apparatus according to the application, the control device is programmed for keeping the pressure prevailing in the application cryostat substantially constant during the transfer of liquid helium into the application cryostat. Thereby it is achieved in a particularly simple manner that the transfer process is kept in equilibrium, i.e. is carried out such that the volume of liquid helium transferred through the transfer line per unit of time is substantially equal to the volume change of helium condensed from helium gas into liquid helium at the condensation heat exchanger per unit of time. The pressure prevailing 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 higher (e.g. by 5 to 50 mbar) than the atmospheric pressure of the surrounding environment in order to avoid air suction into the application cryostat. Alternatively it is also possible, for example, to adjust the measured pressure to a target value which is tracked during the transfer, which has a fixed distance, for example, from the atmospheric pressure of the surrounding environment.

[0056] Furthermore, an embodiment is preferred in which the application cryostat is sealed against outflow of gaseous helium without damaging 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 atmospheric pressure of the surrounding environment and that the control device is programmed for keeping the pressure in the application cryostat at any time above the atmospheric pressure of the surrounding environment, in particular by correspondingly operating the means for generating a pressure difference. Thereby it is avoided that air is sucked into the application cryostat; the suction of air leads to freezing of the air constituents (e.g. moisture) in the application cryostat and thus to a blockage of the gas flow. It is also possible to control the pressure directly in the application cryostat, for example by means of an electric heater installed in the application cryostat at the condensation heat exchanger or elsewhere. Thus it is possible to avoid in a fault situation that the pressure in the application cryostat drops untrustworthy low (e.g. when the transfer line is frozen and completely blocked).

[0058] In a preferred embodiment, the means for generating a pressure difference comprises a regulating valve in the helium line, wherein the helium line comprises a first helium line end connected to the storage reservoir and a second helium line end connected to a helium reservoir, in particular a helium pressure gas reservoir. With the regulating valve to the helium reservoir the pressure in the transport reservoir can be changed simply and quickly. The regulating valve can be automatically operated and regulated by a control device, for example with an electric motor. It is noted that the helium flowing from the helium reservoir into the transport reservoir should be pre-purified so that impurities, for example water vapor or nitrogen, cannot reach the transport reservoir and the cryostat and freeze there. The transport reservoir is preferably so set up that the gaseous helium entering from the helium reservoir can be liquefied in the transport reservoir, preferably with the cold head of a cryocooler, which is also used to cool the condensation heat exchanger. A common cryocooler is preferably used to operate the cold trap for purifying the helium and to liquefy the helium in the transport reservoir; for this, an apparatus as described in DE 102021205423 A1 can be used, in particular.

[0059] In an advantageous embodiment, the means for generating a pressure difference comprises an electric heater in the storage reservoir. By heating with the electric heater in the storage reservoir (or in its helium container), the liquid helium stored in the storage reservoir is vaporized, which increases the pressure in the storage reservoir, whereby the transfer of liquid helium can be driven. Such a process is particularly simple.

[0060] Particularly preferred is an embodiment in which the apparatus furthermore comprises:

[0061] a closed cooling circuit of the coolant, which cooling circuit comprises a forward line from the cold head of the cryocooler to the condensation heat exchanger and a return line from the condensation heat exchanger to the cold head of the cryocooler, wherein the cryocooler is set up to cool the coolant directly or indirectly with the cold head,

[0062] In particular, the cold head of the cryocooler is arranged separately from the application cryostat. By setting up the cooling circuit, the actual location of the refrigeration (at the cold head) can be spatially separated from the location of the helium condensation (at the condensation heat exchanger) in a simple manner; the condensation heat exchanger can be set up in particular at the end of a rigid cooling rod, which 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 not possible in many cases, since the opening in the application cryostat is preferably configured with a very small cross section (significantly smaller than a commercial, general-purpose cold head). The cold head is also arranged separately from the application cryostat as a rule, which simplifies the construction of the entire system. In addition, the input of vibrations into the application cryostat can be minimized. A portion of the forward line and the return line can be integrated in the cooling rod, and if necessary also a portion of the transfer line. It is noted that the cooling circuit also comprises a compressor forward line from the separate compressor to the cold head and a compressor return line from the cold head to the compressor as a rule.

[0063] In a preferred extension of this embodiment, the forward line, the return line and the transfer line extend as a line bundle from the storage reservoir in a common evacuated vacuum portion. Such a construction enables the evacuation of the forward line, the return line and the transfer line in a simple manner. The line bundle can be handled particularly simply, in particular the second transfer line end (outflow end) of the transfer line and the condensation heat exchanger (end of the forward line / beginning of the return line) can be inserted particularly simply together into the application cryostat. As a rule, the line bundle is arranged in a rigid tube (cooling rod) in the rear region, i.e. in the vicinity of the second transfer line end of the transfer line and the condensation heat exchanger, which further simplifies handling.

[0064] In addition, a sub-variant of this extension is preferred, in which the forward line and the transfer line are thermally coupled to one another in the common evacuated vacuum portion, in particular by means of a plurality of coupling bridges. It is thereby possible to pre-cool the transfer line with the cooling circuit or with the coolant in the forward line before the transfer of liquid helium is started, so that the helium transfer line is already cold when it is flowed through when the transfer of liquid helium is started. Liquid helium for cooling the transfer line is thereby not consumed, i.e. vaporized.

[0065] Furthermore, an embodiment is preferred, wherein the device furthermore comprises a helium reservoir, which is connected to the storage reservoir by means of a helium line, in particular wherein the helium reservoir is a helium pressure gas reservoir. Thereby it is possible to introduce helium into the storage reservoir, in particular to increase the pressure in the storage reservoir (whereupon the helium reservoir is mostly a helium pressure gas reservoir) and / or to liquefy gaseous helium introduced in the storage reservoir (for this purpose the cold head of the cryocooler mostly reaches into the storage reservoir or into a storage cryostat thereof, see also below).

[0066] Particularly preferred is an embodiment, wherein the cold head of the cryocooler and the helium container of the storage reservoir are arranged in a common storage cryostat, wherein the cold head of the cryocooler is designed for liquefying helium gas to liquid helium in the storage reservoir. If helium can be liquefied in the storage reservoir, it is not necessary to bring liquid helium over long distances (for example by means of a lorry) to the location of the application cryostat, which is technically costly, so that the operation of the application cryostat can be significantly cheaper. Instead, it is easier to transport gaseous helium to be transported to the application cryostat (for example in a pressure gas bottle) and / or helium vaporized in the normal operation of the application cryostat (usually after intermediate storage) is 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 designed for providing a volume of supercooled liquid helium in the helium container. The supercooled helium has a temperature below the boiling point at the prevailing pressure in the helium container. Mostly, the pressure in the helium container is approximately (but slightly above) 1 bar, which corresponds to a boiling point of 4.2 K. The supercooled liquid helium then has a temperature of less than 4.2 K. The supercooled liquid helium in the helium container preferably has a temperature of 4.0 K or less, particularly preferably 3.8 K or less. However, it is more energy-consuming to provide supercooled liquid helium than to provide liquid helium at the boiling point (4.2 K), wherein the energy consumption rises strongly as the temperature of the supercooled liquid helium falls. Therefore, the supercooled liquid helium in the helium container preferably also has a temperature of 3.7 K or more. When the supercooled liquid helium is delivered to the application cryostat, additional cooling power is provided in the application cryostat for condensing gaseous helium to liquid helium, corresponding to the temperature difference to the boiling point and the specific heat capacity of the liquid helium. Thereby the transfer of liquid helium can take place more quickly with the given cooling power of the cryocooler than with liquid helium at the boiling point.

[0068] A particularly preferred sub-variant of this expansion provides that a thermally insulating barrier is arranged in the helium container, with which the supercooled helium volume is separated below the thermally insulating barrier from the liquid, saturated helium volume above the thermally insulating barrier. With such a configuration it is possible to provide supercooled liquid helium particularly effectively and also relatively simply. Thermally insulating barriers which can be used in the context of the application are described, for example, in DE 40 39 365 A1. The thermally insulating barrier is thermally isolated, but pressure-tight. The cold head of the cryocooler can here be arranged in a separate vacuum chamber which projects through the thermally insulating barrier, so that the coldest stage of the cold head can provide cooling power below the thermally insulating 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. A large "cold energy" reservoir at a temperature of less than 4.2 K is thus 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 first transfer line end opens into the region of the liquid, supercooled helium volume in the storage reservoir, in particular in the vicinity of the bottom of the helium container. Supercooled liquid helium can be fed into the application cryostat in a simple manner by means of the transfer line accordingly.

[0071] Further, an embodiment is advantageous in which the transfer line has a purge valve in the region of the first transfer line end. Air present in the transfer line can be purged out before the transfer of liquid helium is started by means of 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. Air introduction into the application cryostat can thus be minimised. The purge valve opens in the simplest case into the ambient atmosphere, or alternatively into a helium recovery system which is equipped with a purification function for separating the air components.

[0072] Application system according to the application

[0073] An application system also falls within the scope of the application which comprises the above-described apparatus according to the application and an application cryostat,

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

[0075] In particular into a common feedthrough of an application cryostat. In the application system according to the application, liquid helium can be transferred from the storage reservoir to the application cryostat in a simple manner, wherein the helium loss can be minimized. If the condensation heat exchanger (usually arranged at the cooling rod) and the transfer line for the liquid helium use the same feedthrough (in particular the suspension tube of the NMR magnet), a sufficiently large outflow cross section for quench situations (sudden loss of superconductivity of the NMR magnet) can be provided in a simple manner, i.e. at the second feedthrough (in particular the suspension tube) which is not blocked. In addition, a thermal coupling of the transfer line to the forward line of the coolant of the condensation heat exchanger can be realized more easily.

[0076] Particularly preferably, an embodiment of the application system according to the application, wherein the application cryostat contains superconducting magnetic coils and the NMR sample head extends into a magnetic bore of the magnetic coils. The application cryostat can then be used for NMR measurements, and the costs for NMR measurement samples can be reduced based on the comparatively low operating costs in the scope of the application. Usually the NMR sample head extends into a room temperature bore of the application cryostat, which is coaxial to the magnetic bore.

[0077] Method for transferring liquid helium according to the application

[0078] A method for transferring liquid helium into an application cryostat likewise falls within the scope of the application,

[0079] In particular using the above-described apparatus according to the application or the above-described application system according to the application,

[0080] wherein the transfer line for the liquid helium is connected with a first transfer line end to a storage reservoir containing liquid helium and with a second transfer line end into the application cryostat,

[0081] wherein liquid helium is transferred from the storage reservoir to the application cryostat by means of the transfer line,

[0082] wherein the flow of liquid helium through the transfer line is regulated by means for changing the pressure difference between the storage reservoir and the application cryostat,

[0083] characterized in that

[0084] a condensation heat exchanger cooled with a cryocooler is inserted into the application cryostat and gaseous helium is liquefied to liquid helium in the application cryostat,

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

[0086] Particularly preferred is a variant of the method according to the application 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 procedure it can be achieved in a simple manner that the volume of liquid helium transferred through the transfer line per unit of time is approximately equal to the change in the volume of helium condensed from the helium gas into liquid helium at the condensation heat exchanger per unit of 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 when transferring liquid helium without the need for a helium recovery system.

[0088] A variant is also advantageous which provides that the control device measures the ambient atmospheric pressure and the control device keeps the pressure in the application cryostat at any time above the ambient atmospheric pressure, in particular by correspondingly operating the means for generating the pressure difference. Thereby air suction into the application cryostat from the ambient is prevented. If the pressure in the application cryostat is faced with too strong a drop, the transfer of liquid helium into the application cryostat is generally increased (in that the pressure in the storage reservoir is increased); in an emergency (for example when the transfer line is blocked) an electric heater in the application cryostat (if present) can be switched on and / or increased.

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

[0090] A variant is also advantageous, wherein the control device actuates an electric heater in the storage reservoir as a means for changing the pressure difference. The electric heater can be installed simply and cost advantageously. 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 (but can likewise be provided).

[0091] A variant is also preferred, wherein the coolant in the closed cooling circuit is guided from the cold head of the cryocooler to the condensation heat exchanger by means of a forward line and is guided back to the cold head of the cryocooler by means of a return line, wherein the cold head of the cryocooler cools the coolant directly or indirectly, in particular wherein the cold head is arranged separately from the application cryostat. With the cooling circuit, the cold head can be spatially separated from the condensation heat exchanger, which saves construction space at the application cryostat (in particular in the region of the inlet tube). In addition, the cold head can easily be used for other purposes, in particular for liquefying helium in the storage reservoir.

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

[0093] A further development of this variant provides that the transfer line is first pre-cooled with the coolant in the forward line before the transfer of liquid helium is started by means of the transfer line. The transfer line is then already cold when liquid helium is first guided through the transfer line in order to carry out the transfer, and no or only little liquid helium vaporizes on the way to the application cryostat. Thereby liquid helium can be saved.

[0094] A variant is also preferred, 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 gaseous helium is supplied to the storage reservoir from a helium gas reservoir, in particular a helium pressure gas reservoir, before the transfer of liquid helium is started, and the gaseous helium is condensed into liquid helium in the storage reservoir with the cold head. In this variant, liquid helium can be produced on site in the storage reservoir, and the relatively costly and difficult transport of liquid helium to the application site can be avoided. If necessary, the helium can be processed at the application site in an actually closed circuit, which is sustainable and cost-advantageous.

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

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

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

[0100] A variant is also advantageous in which the transfer line is first purged with gaseous helium from the cryostat of application via a purge valve which is arranged in the transfer line near the first transfer line end before the transfer of liquid helium is started. Thereby the input of impurities (air components) into the cryostat of application is minimised. The branch 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 by means of the purge valve.

[0101] Also preferred is a variant in which the cryostat of application is alternately used for application in normal operation and filled with liquid helium in a refilling operation,

[0102] wherein the condensation heat exchanger and the second transfer line end are not inserted into the cryostat of application during normal operation and the condensation heat exchanger and the second transfer line end are inserted into the cryostat of application during the refilling operation. The condensation heat exchanger and the transfer line are only inserted when they are needed. Thereby the thermal input into the cryostat of application in normal operation can be minimised.

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

[0104] Further advantages of the present application result from the description and the drawings. Also, the features mentioned above and described further below can be used on their own, but also in combination with each other, in accordance with the application. The embodiments shown and described are not to be understood as exhaustive, but rather have exemplary features for the description of the application. BRIEF DESCRIPTION OF DRAWINGS

[0105] Embodiments of the application are explained in more detail below with reference to the drawings. The drawings are as follows:

[0106] Figure 1 a schematic view of a first embodiment of an application system according to the application, comprising a device for transferring liquid helium according to the application and an application cryostat, wherein the cold head of the cryocooler and the helium container of the storage reservoir are arranged in one common storage cryostat;

[0107] Figure 2 a tube bundle for the transfer line, the forward line and the return line of the application;

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

[0109] Figure 4 a construction form of a storage reservoir for a device for transferring liquid helium according to the application, the storage reservoir having a thermal barrier in the helium container of the storage reservoir. DETAILED DESCRIPTION

[0110] Figure 1 a schematic view of a first embodiment of an application system 100 according to the application during the transfer of liquid helium, comprising a device 101 for transferring liquid helium and an application cryostat 102.

[0111] The device 101 comprises a storage reservoir 1 having a helium container 2, which is thermally decoupled from the surroundings 4 by an isolating vacuum 3. Here, there is room temperature (20°C) and an atmospheric pressure p of 1.00 bar in the surroundings 4. atm One or more radiation shields or a multilayer superinsulation (not shown in more detail) can be provided in the isolating vacuum 3.

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

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

[0114] A second transfer line end 9b of the transfer line 9 is inserted into the application cryostat 102 through a penetration tube 15a and opens into the helium reservoir 10 of the application cryostat 102. The helium reservoir 10 is thermally isolated from the surroundings 4 by an isolation vacuum 13. One or more radiation shields (not shown in more detail) can be provided in the isolation vacuum 13.

[0115] In the helium reservoir 10 of the application cryostat 102, there is liquid helium 11 in a lower region and gaseous helium 12 in an upper region. In the embodiment shown, the liquid helium 11 and the gaseous helium 12 each have a temperature of approximately 4.2 K in the helium reservoir 10, and there is a pressure p anwend .

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

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

[0118] Through the penetration tube 15a, not only the transfer line 9, but also the cooling rod 16 extends into the application cryostat 102; the penetration tube 15a is therefore also referred to as a common penetration tube 15a. On the lower end of the cooling rod 16, a condensation heat exchanger 17 is configured. Using the condensation heat exchanger 17, the gaseous helium 12 in the helium reservoir 10 is continuously liquefied during the transfer of liquid helium.

[0119] The condenser heat exchanger 17 is cooled with a coolant which circulates in a cooling circuit 19. The cooling circuit 19 extends from the cold head heat exchanger 25a at the cold head 25 with a forward line 20 to the condenser heat exchanger 17 and with a return line 21 from the condenser heat exchanger 17 back to the cold head heat exchanger 25a at the cold head 25. The end regions of the forward line 20 and the return line 21 in the vicinity of the condenser heat exchanger 17 extend in the cooling bar 16. The forward line 20 and the return line 21 are surrounded by a vacuum insulation 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 to 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 helium, in particular. The cold head 25 and the compressor 28 form a cryocooler 29 of the apparatus 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, in addition, are responsible for the coolant circulation in the cooling circuit 19 of the condenser heat exchanger 17. This is particularly cost-advantageous. Here, the cooling circuit 19 can be activated and deactivated separately by means of 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 be configured as a Gifford-McMahon cooler or a pulse tube cooler, in particular. The cooling of the cooling bar 16 or the condenser heat exchanger 17 is provided with a refrigerator which is separate from the cryocooler 29 or the application cryostat 102.

[0122] The control device 8 monitors the pressure p in the application cryostat 102 with a pressure sensor 18 anwend which is arranged here on the second inlet tube 15b of the application cryostat 102. In addition, the second inlet tube 15b is free and can be used as an emergency outlet for helium gas, in particular, for example in the event of a quench fall. The pressure sensor 18 is connected to the control device 8 at a measurement input 18a. In addition, in the embodiment shown, the control device 8 monitors the pressure p atm in the surroundings 4 with a pressure sensor 8a which is integrated into the control device 8.

[0123] In the embodiment shown, the control device 8 controls the heating power of the electrical heater 7 in the storage reservoir 1 when transfer of liquid helium is being carried out. By means of the heating power on the heater 7, the pressure in the storage reservoir 1 can be changed and, as a result, also the pressure difference between the storage reservoir 1 and the application cryostat 102. The heater 7 thus constitutes a means 31 for generating a pressure difference between the storage reservoir 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 tracked by the control device 8 in such a way that in the application cryostat 102, the pressure p anwend is regulated to a predetermined nominal value p anwend soll . The predetermined nominal value p anwend soll is here 1.03 bar and is chosen in such a way that it slightly (here by 0.03 bar) exceeds the pressure p atm of the surroundings 4. In the simplest case, the predetermined nominal value p anwend soll is constant during the entire duration of the transfer of liquid helium. If the weather and thus the air pressure in the surroundings 4 or the pressure p atm monitored with the sensor 8a changes strongly during the transfer, the predetermined nominal value p anwend soll can also be changed if necessary in order to keep the pressure p anwend in the application cryostat 102 at a desired distance (minimum distance and / or maximum distance) from the pressure p atm of the surroundings, in particular in order to avoid the intake of ambient air into the application cryostat 102 and / or to prevent triggering of an overpressure safety device (overpressure valve, burst disc, not shown in more detail) on the application cryostat 102.

[0125] If the pressure p anwend remains substantially at p anwend soll during the input of liquid helium into the application cryostat 102 via the transfer line 9, the volume dV(LHe trans ) / dt of liquid helium input per unit of time substantially corresponds to the change in volume dV(He cond ) / dt of helium condensed per unit of time at the condensation heat exchanger 17 ("equilibrium state"). In this case, no gaseous helium escapes from the application cryostat 102 during the input of liquid helium into the application cryostat 102.

[0126] If the pressure p anwend drops below p anwend sollthen the control device 8 increases the heating power at the heater 7, so that additional helium is vaporized in the storage reservoir 1, the pressure p vorrat increases, the flow of liquid helium through the transfer line 9 increases, and the gas pressure in the cryostat 102 increases. If the pressure p anwend increases beyond p anwend soll then the control device 8 reduces the heating power at the heater 7 or switches off the heater 7 completely, so that less or no helium is vaporized in the storage reservoir 1, the pressure p

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

[0128] In the shown embodiment, a superconducting magnetic coil 32 (also referred to as magnet) is arranged in the cryostat 102. In normal operation, an NMR sample head 33 projects into a room temperature bore (not shown in more detail) of the cryostat 102, so that a sample 34 can be subjected to an NMR measurement in a magnetic bore of the magnet 32 in a 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 access tube 15a, and that the transfer line 9 and the cooling rod 16 are inserted into the access tube 15a only in a refilling operation (the access tube is shown in Figure 1 ).

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

[0130] Figure 2 A rear section of a tube bundle 40 is shown, which can be used in the context of the present application on an apparatus for transferring liquid helium according to the present application (see also Figure 3 ).

[0131] The forward tube 20 and the return tube 21 of the cooling circuit for the condenser heat exchanger 17 and the transfer line 9 for the liquid helium 14, which flows out of the second transfer line end 9b into the cryostat, extend in the tube bundle 40. The tube bundle 40 constitutes a common evacuated insulation 41 for the tubes 9, 20, 21. Between the transfer line 9 and the forward tube 20, a plurality of coupling bridges 42 made of a well thermally conductive material, for example high-purity copper, are provided, by means of which a thermal coupling between the forward tube 20 and the transfer line 9 is established. It is thereby possible, among other things, to pre-cool the transfer line 9 with the forward tube 20 before the transfer of liquid helium is started.

[0132] The vertically extending part of the tube bundle 40 here constitutes a readily operable cooling rod 16. It is noted that the tube bundle on the other side of the cooling rod (apart from the cooling rod) is preferably constructed to be flexible. The tube bundle can have so-called super insulation. In addition, distance holders with low thermal conduction capacity are provided in order to keep the individual tubes spaced apart from the outer insulation jacket.

[0133] Figure 3 A second embodiment of an application system 100 according to the application is schematically shown, which comprises a device 101 for transferring liquid helium and an application cryostat 102. The application system 100 largely corresponds to the application system of Figure 1 , so that in the following only the main differences are set out. For the sake of simplicity, the compressor and the tube for partially guiding the coolant are not shown in more detail in Figure 3 .

[0134] In the embodiment of Figure 3 , a common storage cryostat 50 is set up, in which not only the cold head 25 but also the helium container 2 is arranged. The cold head 25 is here arranged in a receiving region 51, which 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 region 51. The storage cryostat 50 here has a radiation shield 58, which is thermally coupled on a warmer cooling stage of the cold head 25 (coupling not shown in more detail).

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

[0136] The helium tube 54 has a regulating valve 55 in the vicinity of the second helium tube end 54b, which can be automatically operated with the control device 8, here with an electric motor (not shown in detail).

[0137] The helium tube 54 leads past the cold head 25 through the receiving region 51 and is thermally coupled to the two cooling stages 25 of the cold head by means of a helium supply heat exchanger 56. The helium 6a that flows into the storage reservoir 1 via the helium tube 54 (or the helium 6 already present in the storage reservoir 1) can be liquefied with the cold head 25.

[0138] It is noted that the helium 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 DE 102021205423 A1 can be used.

[0139] In the shown embodiment, additionally a pressure sensor (pressure sensor) 57 is provided, which measures the pressure (pressure) p in the storage reservoir 1 vorrat is measured with the pressure sensor and monitored by the control device 8; the control device 8 ensures that p vorrat is always maintained above p atm (see also below), whereby an ambient air suction into the storage reservoir 1 is prevented. Additionally, the control device 8 also monitors the pressure p anwend in the application cryostat 102 with the pressure sensor 18. Furthermore, the control device 8 can actuate the heater 7 in the storage reservoir 1.

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

[0141] The feed line 20, the return line 21 and the transfer line 9 here extend between the storage reservoir 1 and the application cryostat 102 as a line bundle 40 in a common vacuum insulation 41 (see Figure 2 ). Additionally, the transfer line 9 has a branch 60 to the purge valve 59 in the vicinity of the first transfer line end 9a, wherein the branch 60 here is located within the common storage cryostat. The transfer line 9 between the second transfer line end 9b and the branch 60 can be purged with helium 12 (which originates from the application cryostat 102) via the purge valve 59, which is performed before the transfer of liquid helium via the transfer line 9 is started; it is noted that for this p anwend >p atm . In order to completely eliminate helium losses, the output of the purge valve 59 can be connected to a helium recovery system; the air purged into the helium recovery system can be separated off in a cold trap connected upstream when helium from the recovery system is re-liquefied (helium recovery system and cold trap not shown in more detail).

[0142] Method flow according to the application

[0143] In the following, a flow will be described exemplarily in the scope of the method according to the application when liquid helium is refilled from the storage reservoir 1 into the application cryostat 102. The exemplary flow can be performed in particular on the application system 100 as in Figure 3It occurs as shown in the diagram. Steps 2 through 6 can be configured for transfer operation, and step 7 is configured for normal operation of the cryostat 102. Step 1 can occur in parallel with normal operation or as part of transfer operation.

[0144] Step 1) Helium gas is introduced from the helium pressure gas storage device 53 into the storage device 1 via the helium pipeline 54, wherein the helium gas is liquefied by the cold head 25. Liquid helium 5 is collected in the helium container 2.

[0145] Step 2) Once liquefaction is complete (e.g., because helium container 2 is full or helium pressure gas storage 53 is empty), the transfer of liquid helium 5 can be prepared. For this purpose, the user first introduces the cooling rod 16 along with the transfer line 9 and the condenser heat exchanger 17 into the inlet pipe 15a through the cryostat 102.

[0146] Step 3) Open purge valve 59, and helium from the applied cryostat 102 forces air through purge valve 59 out of transfer line 9. If any air is present and escapes, purge valve 59 closes.

[0147] Step 4) Then open the cooling circuit valve for the coolant. Figure 1 (see attached figure 19a), thereby caused by the compressor ( Figure 1 A portion of the airflow provided by reference numeral 28 in the attached diagram branches off and is activated in the cooling circuit 19, or rather, through the condenser heat exchanger 17. The forward line 20 is thermally connected to the transfer line 9, which is cooled in this transfer line 9.

[0148] Step 4) Once the condenser heat exchanger 17 and transfer line 9 are cold, the transfer of liquid helium (“helium transfer”) begins. This can occur either spontaneously when the pressure in the helium storage tank 10, to which the cryostat 102 is applied, decreases due to the initial condensation, or when the pressure in the storage tank 1 is actively increased, for example, by using the heater 7 or by using helium gas 6a introduced from the helium pressure gas storage tank 53.

[0149] Step 5) The helium transfer is now controlled by the control device 8 such that the transfer rate of liquid helium through the transfer line 9 corresponds to the rate at which gaseous helium 12 condenses in the cryostat 102, so that no helium 12 escapes from the cryostat 102 during the helium transfer. Accordingly, the helium transfer according to the invention can be carried out so that the helium transfer can be performed without damage without the need for a storage balloon.

[0150] Step 6) Once the helium transfer is complete (e.g., because the cryostat 102 is completely filled with liquid helium 11 or the liquid helium 5 in the storage tank 1 is depleted), the user removes the cooling rod 16, along with the transfer line 9 and the condenser heat exchanger 17, from the cryostat 102.

[0151] Step 7) The measurement can now be continued only a few hours after the helium transfer has started using the cryostat 102 and especially using the NMR magnet (designated by reference numeral 32 in Figure 1 the drawing) contained in the cryostat 102. In contrast to the conventional helium transfer, in which gaseous helium escapes through one of the feedthrough tubes 15a, 15b, the cryostat 102 stabilizes significantly faster in the context of the present application, since no large amounts of cold gas escape through the feedthrough tubes (suspension tubes) 15a, 15b (large amounts of cold gas typically cause a strong cooling of the feedthrough tubes during conventional helium transfers and a destabilization of the magnetic field during the return to thermal equilibrium).

[0152] Figure 4 An alternative structural form for the storage reservoir 1 according to the application is shown, which can be used, for example, in the context of the embodiment of the application system of Figure 3 . Only the main differences from the structural form of Figure 3 are explained.

[0153] In the structural form shown in Figure 4 , a thermally insulating barrier 70 is arranged in the helium container 2 of the storage reservoir 1. The thermally insulating barrier 70 is pressure- permeable (i.e. can be flowed through by liquid helium), but is thermally insulating. The thermally insulating barrier 70 can be configured, in particular, as described in DE 40 39 365 A1.

[0154] The cold head 25 is arranged in a closed vacuum vessel 71, wherein the vacuum vessel 71 reaches beyond the thermally insulating barrier 70 (below). The lowest (coldest) cooling stage 73 of the cold head 25 can thereby cool liquid helium 74 below the thermally insulating barrier 70. This liquid helium 74 below the thermally insulating barrier 70 is supercooled and has a temperature of approximately 3.7 K here. The supercooled liquid helium 74 is also referred to as supercooled liquid helium volume 74 in its entirety. Above the thermally insulating barrier 70, saturated liquid helium 75 having a temperature of approximately 4.2 K is located; the saturated liquid helium 75 is also referred to as saturated liquid helium volume 75 in its entirety. Above the saturated liquid helium, gaseous helium 6 likewise has a temperature of approximately 4.2 K and is at a pressure p vorrat of approximately 1.08 bar.

[0155] The transfer line (line tube) 9 extends deeply into the region of the supercooled liquid helium 74 up to just before 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 is guided, the transfer line 9 is thermally insulated from the saturated helium volume 75 (not shown in more detail). Thus, in the context of the helium transfer, the supercooled liquid helium 74 is fed through the transfer line 9 into the cryostat.

[0156] By inputting the supercooled liquid helium 74 into the application cryostat, heat energy can be extracted from the application cryostat when the supercooled liquid helium is warmed up again to 4.2 K. Then a small cooling power has to be applied on the condensation heat exchanger in order to condense the gaseous helium at the condensation heat exchanger. If for example 100 1 of liquid helium with a temperature of 3.7 K (12.5 kg) are transferred, approximately 26.3 kJ of additional cold energy are available, which 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 is consumed to provide the supercooled liquid helium 74.

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

[0158] It is noted that the supercooled helium for the application can also be produced, for example, by means of a pressure reduction of the helium to low pressure in a throttle

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

[0160] - a storage reservoir (1),

[0161] - a transfer line (9) comprising a first transfer line end (9a) in the storage reservoir (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 reservoir (1) and the application cryostat (102),

[0163] characterized in that

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

[0165] - a cryogenic cooler (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 gas pressure in the cryostat (102) and a control output (31a) for the means (31) for generating a pressure difference, wherein the control device (8) is programmed to control the means (31) for generating a pressure difference such that the volume of liquid helium (14) transferred per unit of time through the transfer line (9) is approximately equal to the change in volume of helium condensed from helium gas (12) to liquid helium (11) at the condensation heat exchanger (17) per unit of time. With the device, the helium loss when transferring liquid helium is minimized in a simple manner.

[0167] LIST OF REFERENCE NUMERALS

[0168] 1 storage reservoir

[0169] 2 helium container

[0170] 3 insulation vacuum (on the storage reservoir)

[0171] 4 ambient atmosphere

[0172] 5 liquid helium (in the storage reservoir)

[0173] 6 gaseous helium (in the storage reservoir)

[0174] 6a gaseous helium (out of the storage reservoir)

[0175] 7 electric heater (in the storage reservoir)

[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 reservoir)

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

[0181] 10 helium reservoir

[0182] 11 liquid helium (in the cryostat)

[0183] 12 gaseous helium (in the cryostat)

[0184] 13 insulation vacuum (on the cryostat)

[0185] 14 liquid helium (outflowed / transferred)

[0186] 15a first / common access tube

[0187] 15b second access tube

[0188] 16 cooling rod

[0189] 17 condenser heat exchanger

[0190] 18 pressure sensor for use with cryostat

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

[0192] 19 cooling loop

[0193] 19a cooling loop valve

[0194] 20 forward line for coolant

[0195] 21 return line for coolant

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

[0197] 23 vacuum isolation (of transfer line)

[0198] 25 cold head

[0199] 25a cold head heat exchanger (for cooling loop)

[0200] 26 compressor forward line

[0201] 27 compressor return line

[0202] 28 compressor

[0203] 29 cryocooler

[0204] 30 cryocooler-cryostat

[0205] 31 means for generating pressure differential

[0206] 31a control output (for means 31)

[0207] 32 superconducting magnetic coil / magnet

[0208] 33 NMR sample head

[0209] 34 measurement sample

[0210] 35, 36 cold head line

[0211] 37 roller

[0212] 40 line bundle

[0213] 41 common isolated vacuum section

[0214] 42 coupling bridge

[0215] 50 common storage cryostat

[0216] 51 receiving area

[0217] 52 helium reservoir

[0218] 53 helium pressure gas reservoir

[0219] 54 helium line

[0220] 54a first helium line end

[0221] 54b second helium line end

[0222] 55 regulating valve

[0223] 56 helium supply heat exchanger

[0224] 57 pressure sensor for storage reservoir

[0225] 58 radiation shield

[0226] 59 purge valve

[0227] 60 bypass for purge valve

[0228] 70 thermal shield

[0229] 71 vacuum vessel

[0230] 73 lowest / coolest cooling stage

[0231] 74 supercooled liquid helium / helium volume

[0232] 75 saturated liquid helium / helium volume

[0233] 100 application system

[0234] 101 device for transferring liquid helium

[0235] 102 application cryostat

Claims

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

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

3. The device (101 ) according to claim 1 or 2, characterized in that The application cryostat (102) is sealed against the outflow of gaseous helium without damaging safety devices.

4. The device (101) according to claim 1 or 2, characterized in that The control device (8) has a pressure sensor (8a) for measuring the ambient atmospheric pressure P atm and is programmed to apply a pressure p anwend in the cryostat (102) which is at all times higher than the ambient atmospheric pressure P atm .

5. The device (101) according to claim 1 or 2, characterized in that The means (31) for generating a pressure difference comprise a regulating valve (55) in a helium gas line (54), wherein the helium gas line (54) comprises a first helium gas line end (54a) connected to the storage reservoir (1) and a second helium gas line end (54b) for connection to a helium gas reservoir (52).

6. The device (101) according to claim 1 or 2, characterized in that The means (31) for generating a pressure difference comprise an electric heater (7) in the storage reservoir (1).

7. The device (101) according to claim 1 or 2, characterized in that The apparatus (101) further comprises a closed cooling circuit (19) of a coolant, the closed cooling circuit comprising a forward line (20) from a cold head (25) of the cryocooler (29) to the condensation heat exchanger (17) and a return line (21) from the condensation heat exchanger (17) to the cold head (25) of the cryocooler (29), wherein the cryocooler (29) is designed for cooling the coolant directly or indirectly with the cold head (25).

8. The device (101) according to claim 7, characterized by The forward line (20), the return line (21) and the transfer line (9) extend as a line bundle (40) in a common evacuated vacuum section (41) from the storage reservoir (1).

9. The device (101) according to claim 8, characterized in that The forward line (20) and the transfer line (9) are thermally coupled to each other in the common evacuated vacuum section (41).

10. The device (101) according to claim 1 or 2, characterized in that, The device (101) further comprises a helium reservoir (52) which is connected to the storage reservoir (1) by means of a helium line (54).

11. The device (101) according to claim 1 or 2, characterized in that The cold head (25) of the cryocooler (29) and the helium vessel (2) of the storage reservoir (1) are arranged in a common storage cryostat (50), wherein the cold head (25) of the cryocooler (29) is designed for liquefying helium (6, 6a) in the storage reservoir (1) to liquid helium.

12. The device (101) according to claim 11, characterized by The helium vessel (2) and the cold head (25) are designed for providing a volume of supercooled helium (74) in the helium vessel (2) in liquid state.

13. The device (101 ) according to claim 12, characterized by A thermally insulating barrier (70) is arranged in the helium vessel (2), by which the volume of supercooled helium (74) below the thermally insulating barrier (70) is separated from a volume of liquid saturated helium (75) above the thermally insulating barrier (70).

14. The device (101) according to claim 12, characterized by A front line (20) of a cooling circuit (19) for a coolant of the cryocooler (29) extends through the region of the volume of supercooled helium (74) in liquid state.

15. The device (101) according to claim 12, characterized by The first transfer line end (9a) opens into the region of the volume of supercooled helium (74) in liquid state in the storage reservoir (1).

16. The device (101) according to claim 1 or 2, characterized by The transfer line (9) has a purge valve (59) in the region near the first transfer line end (9a).

17. An application system (100) comprising a device (101) according to any one of the preceding claims 1 to 16 and an application cryostat (102), wherein, The transfer line (9) and the condensation heat exchanger (17) are inserted into an application cryostat (102).

18. The application system (100) according to claim 17, characterized in that The application cryostat (102) comprises a superconducting magnet coil (32) and an NMR sample head (33) extends into a magnetic bore of the magnet coil (32).

19. A method for transferring liquid helium (14) into an application cryostat (102), wherein, The transfer line (9) for liquid helium (14) is connected to the storage reservoir (1) containing liquid helium by means of the first transfer line end (9a) and is inserted into the application cryostat (102) by means of the second transfer line end (9b), wherein liquid helium (14) is transferred from the storage reservoir (1) to the application cryostat (102) by means of the transfer line (9), wherein the flow of liquid helium (14) through the transfer line (9) is regulated by means of a device (31) for changing the pressure difference between the storage reservoir (1) and the application cryostat (102), characterized in that The condensation heat exchanger (17) cooled with the cryocooler (29) is inserted into the application cryostat (102) and in the application cryostat (102) gaseous helium is liquefied to liquid helium (11) and the control device (8) measures the pressure p in the application cryostat (102) anwend and the means (31) for changing the pressure difference are actuated so that the volume of liquid helium (14) transferred per unit of time through the transfer line (9) is approximately equal to the variation in volume of helium condensed per unit of time at the condensation heat exchanger (17) from the helium gas (12) to liquid helium (11).

20. The method of claim 19, wherein, During the transfer of the liquid helium (14) into the application cryostat (102), the control device (8) keeps the pressure p anwend approximately constant in the application cryostat (102).

21. The method of claim 19 or 20, wherein, During the transfer of liquid helium (14), no gaseous helium flows out of the application cryostat (102).

22. The method of claim 19 or 20, wherein, The control device (8) measures the atmospheric pressure p of the surrounding environment atm and the control device (8) will apply a pressure p in the cryostat (102) anwend which is at all times higher than the atmospheric pressure p of the surrounding environment atm .

23. The method of claim 19 or 20, wherein, The control device (8) actuates a regulating valve (55) in a helium line (54) leading from a helium reservoir (52) to the storage reservoir (1) as the device (31) for changing the pressure difference.

24. The method of claim 19 or 20, wherein, The control device (8) actuates an electric heater (7) in the storage reservoir (1) as the device (31) for changing the pressure difference.

25. The method of claim 19 or 20, wherein, In the closed cooling circuit (19), the coolant is guided from the cold head (25) of the cryocooler (29) to the condensation heat exchanger (17) by means of the front line (20) and is guided back to the cold head (25) of the cryocooler (29) by means of the return line (21), wherein the cold head (25) of the cryocooler (29) directly or indirectly cools the coolant.

26. The method of claim 25, wherein, The transfer line (9) between the storage reservoir (1) and the application cryostat (102) is thermally coupled to the front line (20).

27. The method of claim 26, wherein, Before the liquid helium (14) starts to be transferred through the transfer line (9), the transfer line (9) is first pre-cooled with coolant from the preceding line (20).

28. The method of claim 19 or 20, wherein, The cold head (25) of the cryocooler (29) and the helium container (2) of the storage reservoir (1) are arranged in a common storage cryostat (50), and before the liquid helium (14) starts to be transferred, gaseous helium (6a) is supplied from a helium storage reservoir (52) to the storage reservoir (1) and condensed into liquid helium (6, 6a) in the storage reservoir (1) with the cold head (25).

29. The method of claim 19 or 20, wherein, A volume of liquid supercooled helium (74) is provided in the helium container (2) of the storage reservoir (1), and the liquid helium (14) transferred through the transfer line (9) is taken from the volume of liquid supercooled helium (74).

30. The method of claim 29, wherein, The condensation heat exchanger (17) is cooled with coolant circulating in a closed cooling circuit (19), and the coolant in the preceding line (20) is guided through a region of the volume of liquid supercooled helium (74).

31. The method of claim 19 or 20, wherein, Before the liquid helium (14) starts to be transferred, the transfer line (9) is first purged with gaseous helium from the application cryostat (102) via a purge valve (59) arranged in the transfer line (9) near the first transfer line end (9a).

32. The method of claim 19 or 20, wherein, The application cryostat (102) is alternately used for application in normal operation and filled with liquid helium (14) in a refill operation, wherein during normal operation the condensation heat exchanger (17) and the second transfer line end (9b) are not inserted into the application cryostat (102), and during the refill operation the condensation heat exchanger (17) and the second transfer line end (9b) are inserted into the application cryostat (102).

33. The method of claim 32, wherein, A superconducting magnetic coil (32) is arranged in the application cryostat (102), and during normal operation NMR measurements are carried out on a sample (34) arranged in a magnetic bore of the superconducting magnetic coil (32) as application with an NMR sample head (33). A superconducting magnetic coil (32) is arranged in the application cryostat (102), and during normal operation NMR measurements are carried out on a sample (34) arranged in a magnetic bore of the superconducting magnetic coil (32) as application with an NMR sample head (33).

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