Device and method for transferring liquid helium to practical cryostat

Abstract

To provide a device for transferring liquid helium into a practical cryostat.SOLUTION: A device 101 for transferring liquid helium 14 into a practical cryostat 102 comprises: a storage dewar 1; a transfer line 9 including a first transfer line end 9a located in the storage dewar and a second transfer line end 9b for insertion into the practical cryostat; a device 31 for generating a pressure difference between the storage dewar and the practical cryostat; a condensation heat exchanger 17; a cryocooler; a pressure sensor 18 for measuring a gas pressure in the practical cryostat; and a control device 8 configured to make a volume of the liquid helium 14 become substantially equal to a volume change per unit time of the helium being condensed from helium gas 12 into liquid helium 11 in the condensation heat exchanger.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an apparatus for transferring liquid helium into a practical cryostat.

Background Art

[0002] An apparatus for transferring liquid helium into a practical cryostat includes the following. - A storage dewar for liquid helium, - A transfer line for liquid helium for transferring liquid helium from the storage dewar into the practical cryostat, comprising a first transfer line end disposed within the storage dewar and a second transfer line end for insertion into the practical cryostat, and - An apparatus for generating a pressure difference between the storage dewar and the practical cryostat. This type of apparatus is well-known from the company publication "NMR Magnet System UltraShield Magnets (English Version) User Manual", Edition 006, Chapter 12 (December 10, 2004) from Bruker BioSpin AG, Fällanden, Switzerland.

[0003] For example, superconducting magnets for nuclear magnetic resonance imaging (also known as NMR spectroscopy (NMR = nuclear magnetic resonance) or MRI) require cooling to maintain the superconducting state of the magnet. In many cases, the superconducting magnet is disposed within a practical cryostat, and the practical cryostat typically stores liquid helium 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 well-known in other practical fields.

[0004] A practical cryostat cannot provide complete insulation, and heat is transferred to the practical cryostat by the associated application, so liquid helium evaporates during operation. If the level of liquid helium in the practical cryostat drops too low to continue operation, the liquid helium is replenished in the practical cryostat.

[0005] Here, it should be noted that helium is a scarce resource. Helium is a by-product of natural gas production. The availability of helium in the world market is increasingly limited, and the price of helium is rising. See "Helium is again short in supply" by D. Kramer, Physics Today, April 4, 2022, American Institute of Physics, https: / / doi.org / 10.1063 / PT.6.2.20220404a.

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

[0007] As described in the above company publication "NMR Magnet System UltraShield Magnets (English Version) User Manual", significant losses of helium occur during the normal procedure of replenishing liquid helium from the storage dewar to the practical cryostat. This normal procedure can be summarized as follows.

[0008] Step a): Move the storage dewar ("transport dewar") close to the practical cryostat in the NMR magnet of the above company publication to a distance of several meters.

[0009] Step b): Insert a warm transfer line into the transport dewar, thereby positioning the (first) end of the line below the liquid surface of the contained liquid helium.

[0010] Step c) Due to the heat input from the warm transfer line, the helium in the transport dewar evaporates. As a result, the pressure in the transport dewar increases, and the liquid helium is pushed into the transfer line, and as a result, the transfer line is cooled. The helium pushed out from the end of the transfer line during the cooling process is usually not collected and is lost to the atmosphere. For a typical transfer line with a length of several meters, several liters of liquid helium are required for cooling.

[0011] Step d) When the helium pushed out from the (second) end of the line facing away from the transport dewar becomes cold enough (i.e., when the transfer line is sufficiently cooled), the transfer line is connected to a practical cryostat (e.g., an NMR magnet), i.e., the second end is inserted into the practical cryostat.

[0012] Step e) After the transfer line is connected to the practical cryostat, the liquid helium flows from the transport dewar to the practical cryostat. The mass flow rate is driven by the pressure difference existing between the transport dewar and the practical cryostat. In the transport dewar, an overpressure is generated by inserting the transfer line as described above. Usually, the pressure increase in the transport dewar caused by the heat input when the transfer line is inserted is not sufficient to transfer the desired amount of liquid helium. Therefore, helium gas is introduced into the transport dewar from a compressed gas cylinder through a pressure regulator, and thereby the pressure in the transport dewar is always kept high. Typically, the overpressure generated in the transport dewar is about 50 - 100 mbar. During the transfer of liquid helium, the gaseous helium is pushed out from the outlet of the practical cryostat at a rate corresponding to the volume of the inflowing liquid helium.

[0013] To be clear, when starting the transfer of liquid helium to a practical cryostat, the practical cryostat or rather its helium tank is typically not empty, but rather still contains a small amount of liquid helium, or else is filled with gaseous helium at a temperature of 4.2 K and a pressure of about 1 bar. As the helium tank is slowly filled with liquid helium during the transfer, the cold gaseous helium that was located inside the helium tank before the start of the transfer is continuously pushed out of the helium tank and pushed out through the outlet of the practical cryostat.

[0014] Gaseous helium at 4.2 K and atmospheric pressure has a density of 16.5 g / l. Liquid helium at 4.2 K and atmospheric pressure has a density of 125 g / l. For example, when 100 liters of liquid helium, i.e., 12.5 kg of helium, is transferred, 100 liters of gaseous helium, i.e., 1.65 kg, is pushed out of the practical cryostat as described above. This corresponds to 13.2 liters of liquid helium, i.e., 13.2% of the transfer volume.

[0015] In most cases, this amount of helium is simply pushed out into the atmosphere through the outlet of the practical cryostat, which is not sustainable and also increases the cost of operating the practical cryostat.

[0016] Alternatively, it is possible to install, for example, a gas balloon reservoir. The gas balloon reservoir is sized to be large enough to collect at the outlet the helium ("transfer losses") that accumulates during the helium transfer and supply it to a high-pressure reservoir or a liquefier. In the line equipment connected to the gas balloon and the gas balloon itself, the gaseous helium warms up to room temperature, resulting in a significant increase in the volume of the gas. 100 liters of gaseous helium at atmospheric pressure and 4.2 K corresponds to about 10,000 liters (i.e., 10 m 3 ) at atmospheric pressure and room temperature.

[0017] During the typical transfer of helium to an NMR magnet, depending on the type of magnet, 100 to 400 liters of liquid helium are transferred. A typical transfer takes about one hour. During this period, 10 to 40 cubic meters of gaseous helium accumulates at room temperature and an amount corresponding to 13 l / h to 50 l / h of liquid helium (or about 1.6 to 6.6 kg of helium / hour) must be stored in a gas balloon or processed (e.g., compressed in a pressure reservoir) by a recovery system. Therefore, a large gas balloon or a powerful recovery system will occupy a lot of space and will also be very expensive.

[0018] Subsequently, German Patent Application Publication No. 102022209941 proposes supplying the gaseous helium pushed out from a practical cryostat to a storage dewar through a return line while transferring liquid helium from the storage dewar to the practical dewar.

[0019] It should also be noted that it is possible to actively cool a practical cryostat (e.g., including a superconducting magnet for NMR practical use) during continuous operation of a cryocooler. See, for example, U.S. Patent Application Publication No. 2002 / 0002830. In this case, there is no need to replenish liquid helium, and the problem of helium loss during liquid helium replenishment is eliminated.

[0020] However, active cooling has several disadvantages compared to passive operation using a liquid helium bath. In particular, there is vibration introduced to the practical cryostat by the cryocooler, high energy consumption (about 8 kW in continuous operation), relatively high maintenance costs, and a relatively long downtime during maintenance work. When actively cooling a superconducting magnet without using a refrigerant (i.e., when the superconducting magnet does not have a buffer volume for liquid helium), the time from a possible power outage to the destruction of superconductivity of the superconducting magnet (the "time to quench") becomes very short.

[0021] U.S. Patent No. 8,671,698 describes that a helium re-liquefaction device includes a pulse tube refrigerator separate from a practical cryostat.

[0022] A retrofit re-liquefaction device for helium is well-known from U.S. Patent Application Publication No. 2007 / 0107445. Installing such a device is very cumbersome. In addition, in this case, it may also cause vibrations in the practical cryostat, resulting in high energy and maintenance costs.

[0023] U.S. Patent No. 8,375,742 discloses a helium re-liquefaction device having its own insulation jacket. Helium evaporating from the practical cryostat is liquefied by the re-liquefaction device and returned through a transfer pipe also covered by the insulation jacket. In one variant, a connection to an external gas source is also provided.

[0024] U.S. Patent Application Publication No. 2009 / 0301129 describes a helium re-liquefaction device for retrofitting to a magnetic resonance system, whereby the evaporating nitrogen and the evaporating helium are re-liquefied.

[0025] European Patent No. 0245057 and European Patent No. 0396624 disclose a condensation heat exchanger which is connected to a cold head via a cooling circuit and inserted into a cryostat having liquid helium.

[0026] German Patent Application Publication No. 102021205423 also describes a device for purifying and liquefying helium using a single cold head.

[0027] German Patent Application Publication No. 4039365 describes an NMR magnet having a cryostat in which supercooled liquid helium is arranged in a first lower chamber, liquid helium at atmospheric pressure and 4.2 K is arranged in an upper second chamber, and a heat-insulating but pressure-permeable barrier is arranged between the chambers.

[0028] The thermophysical properties of various fluid systems, for example, the thermophysical properties of helium, can be investigated 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.

[0029] A mobile liquefaction plant for liquefying helium is well-known from German Patent Application Publication No. 102020204186. The plant comprises a liquefaction device for liquefying helium, an intermediate storage device for liquefied helium, a purification device for helium, and an additional collection device for gaseous helium with a container having a flexible wall. By means of the liquefaction device and the purification device, the helium gas stored at the location of the practical cryostat during operation and evaporated can be purified, liquefied, and further collected in the intermediate storage device. When filling the practical cryostat with the liquid helium from the intermediate storage device, the evaporated helium gas can be collected by the additional collection device.

[0030] German European Patent Translation No. 69926087 describes, as a device for recondensing liquid helium, storing liquid helium in a container. The gaseous helium evaporated in the container is led through a line to a cooling device arranged outside the container, where it is liquefied. The liquefied helium is returned to the container through another line.

Prior Art Documents

Patent Documents

[0031]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

[0032] [Non-Patent Document 1] Bruker Biospin AG, "NMR Magnet System UltraShield Magnets (English Version) User Manual", 006 Edition, Chapter 12 (December 10, 2004) [Non-Patent Document 2] D. Kramer, "Helium is again short in supply", Physics Today, April 4, 2022, American Institute of Physics [Summary of the Invention] [Problems to be Solved by the Invention]

[0033] An object of the present invention is to minimize helium loss during the transfer of liquid helium from a storage dewar to a practical cryostat in a simple manner.

Means for Solving the Problem

[0034] The object of the present invention is achieved by a device of the type described at the beginning, which is characterized by further comprising the following. - A condensation heat exchanger inserted into a practical cryostat for condensing helium gas into liquid helium, - A cryocooler for cooling the condensation heat exchanger, and - A control device having at least one measurement input part for a pressure sensor for measuring the gas pressure in the practical cryostat and a control output part for a device for generating a pressure difference, the control device being programmed to control the device to generate a pressure difference such that the volume of liquid helium transferred through the transfer line per unit time is approximately equal to the volume change of helium condensing from helium gas to liquid helium per unit time in the condensation heat exchanger.

[0035] The device according to the invention enables on-site liquefaction of gaseous helium to liquid helium in a practical cryostat using a condensation heat exchanger inserted into the practical cryostat while transferring liquid helium from a storage dewar into the practical cryostat. The cooling capacity of one condensation heat exchanger (or rather a cryocooler) and the transfer rate of liquid helium to the other practical cryostat are adjusted so that the volume change (volume reduction) of helium condensed per unit time in the practical cryostat is at least substantially (preferably exactly) in agreement with (is in an "equilibrium state") the volume of liquid helium transferred from the storage dewar through the transfer line to the practical cryostat by a device for generating a pressure difference. By setting and further maintaining the equilibrium state during the transfer of liquid helium performed by the control device, it is ensured that the gaseous helium is not (or is only very slightly) pushed out of the practical cryostat by the liquid helium flowing in during the transfer of liquid helium. Thus, there is no need to collect and process the pushed-out gaseous helium for recovery. In particular, a large gas balloon for collecting the pushed-out gaseous helium is no longer required for the transfer of liquid helium.

[0036] Liquid helium is pushed into the practical cryostat through a transfer line by a pressure difference (usually a pressure difference of 50 to 100 mbar, with a higher pressure being applied in the storage dewar than in the practical cryostat) between a storage dewar provided with a device for generating a pressure difference and the practical cryostat. The device for generating (or setting) 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 liquid helium can be increased, and by decreasing the pressure difference, the transfer rate of liquid helium can be decreased. It should be noted that within the scope of the present invention, there is no need to know such a pressure difference. Nevertheless, it is also preferable that an additional pressure sensor is provided in the control device to monitor the pressure in the storage dewar.

[0037] The maintenance of the balance (at least approximately) is preferably ensured by maintaining the pressure (helium gas pressure) in the practical cryostat at least approximately constant or within at least a predetermined pressure interval. Thus, the control device typically uses the pressure in the practical cryostat as an input variable (controlled variable) for operating a device for generating a pressure difference, or as at least one input variable.

[0038] The device for generating a pressure difference is typically designed to change the pressure (gas pressure) in the storage dewar. For example, change the current of the electric heater in the storage dewar. Or change the valve position of the control valve (inlet valve) in the helium gas line from the helium gas reservoir (especially a compressed helium gas reservoir) to the storage dewar. The cooling capacity of the condensation heat exchanger, or rather the cooling capacity of its cryocooler, typically remains constant. However, alternatively or additionally, it is also possible to change the pressure in the practical cryostat. For example, use a device for generating a pressure difference to change the current of the electric heater in the practical cryostat. Or change the cooling capacity of the condensation heat exchanger.

[0039] The cryocooler generally comprises a cold head and a compressor. The cryocooler may particularly comprise a Gifford-McMahon cooler or a pulse tube refrigerator. The cold head is thermally coupled to the condensation heat exchanger and preferably cools the condensation heat exchanger through a cooling circuit as well. The cryocooler provides the cooling capacity required for the condensation of gaseous helium in the practical cryostat.

[0040] For example, when 100 liters of liquid helium are replenished into a practical cryostat within the scope of the present invention, the corresponding 100 liters of gaseous helium (at a temperature of 4.2 K) must be liquefied within the practical cryostat. This prevents helium gas from being pushed out of the practical cryostat during the transfer of liquid helium. The density of gaseous helium at 4.2 K and 1 bar is 16.5 g / l. Therefore, approximately 1.65 kg of helium must be liquefied. Helium has a latent heat of 20.6 kJ / kg. Therefore, during the transfer of liquid helium, approximately 34 kJ of energy must be absorbed by the cryocooler at a temperature of 4.2 K. Thus, for example, when using a commercially available cryocooler with a cooling capacity of 2 watts, this energy can be absorbed in approximately 4.7 hours. Therefore, the transfer rate of liquid helium used within the scope of the present invention is about 21.3 l / h or less. In practice, the energy to be absorbed is slightly higher than the aforementioned 34 kJ. This is because additional heat is transferred to the system, for example, through the helium transfer line and the inserted condensation heat exchanger (e.g., arranged on the cooling rod). This will accordingly extend the transfer time or rather slightly reduce the transfer rate.

[0041] As can be seen from the above example, the time required for the transfer of liquid helium within the scope of the present invention depends particularly on the amount of liquid helium to be replenished, the cooling capacity of the cryocooler, and the additional heat input from imperfect insulation. Depending on the expected transfer time, the transfer of liquid helium can be planned. In particular, when no practical use (e.g., NMR measurement) using a practical cryostat is performed in any form, it can also be planned as an "overnight" automatic transfer. Typical transfer times within the scope of the present invention are from 1 hour to 16 hours, preferably from 2 hours to 12 hours. It should be noted that the transfer time can be shortened when supercooled liquid helium is transferred from the storage dewar to the practical cryostat (see also below).

[0042] Storage dewars are typically designed to be transportable (a "transport dewar"), preferably using rollers. Thereby, the storage dewar can be moved back and forth between different laboratories and, moreover, can be used particularly easily to replenish multiple cryostats. Especially when the storage dewar is also used as a helium liquefier, the storage dewar preferably forms a transportable structure in combination with a cryocooler and integrated (e.g., arranged on a common platform with rollers).

[0043] (While transferring liquid helium through the transfer line) Let the volume of liquid helium transferred per unit time through the transfer line be dV (LHe trans ) / dt, and let the volume change of helium condensing from helium gas to liquid helium per unit time in the condensation heat exchanger be dV (He cond ). Typically, the following applies. |dV(He cond ) / dt| ≧ 0.75 * |dV(LHe trans ) / dt|, Preferably |dV(He cond ) / dt| ≧ 0.9 * |dV(LHe trans ) / dt|. In addition, the following also typically applies. |dV(He cond ) / dt| ≦ 1.25 * |dV(LHe trans ) / dt|, Preferably |dV(He cond ) / dt| ≦ 1.1 * |dV(LHe trans ) / dt|.

[0044] (The apparatus of a preferred embodiment of the present invention) In the apparatus according to a preferred embodiment of the present invention, the control device is programmed to keep the pressure in the utility cryostat substantially constant while transferring liquid helium to the utility cryostat. This makes it particularly easy to keep the transfer process in balance. That is, it becomes particularly easy for the volume of liquid helium transferred through the transfer line per unit time to proceed so as to be approximately equal to the volume change of helium condensed from helium gas to liquid helium per unit time in the condensation heat exchanger. Typically, the measured pressure in the utility cryostat is adjusted by the control device to a predetermined fixed target value. It should be noted that the target value should be higher than the ambient atmospheric pressure (for example, by 5 to 50 mbar) to avoid air being sucked into the utility cryostat. Alternatively, for example, it is also possible to adjust the measured pressure to be a target value that is adjusted again while the transfer is being carried out so as to have a constant difference with respect to the ambient atmospheric pressure. Furthermore, an embodiment in which the utility cryostat is sealed against the outflow of gaseous helium without damaging the safety device is preferred. This simplifies the overall configuration of the system during the transfer of liquid helium and prevents expensive helium from being lost during the transfer process.

[0045] In an advantageous embodiment, it is presented that the control device has a pressure sensor for measuring the ambient atmospheric pressure, and the control device is programmed to keep the pressure in the utility cryostat always higher than the ambient atmospheric pressure, particularly by appropriately operating a device for generating a pressure difference. This prevents air from being sucked into the utility cryostat. If air is sucked in, air components (for example, moisture) may freeze inside the utility cryostat and block the gas flow. Preferably, the pressure can also be directly controlled inside the utility cryostat by, for example, an electric heater attached to the condensation heat exchanger or attached to other locations inside the utility cryostat. This can prevent the pressure inside the utility cryostat from dropping to an unacceptable low level (for example, to a level where the transfer line freezes and is completely blocked) in case of a failure.

[0046] In a preferred embodiment, the device for generating a pressure difference includes a control valve in a helium gas line, the helium gas line having a first helium gas line end connected to a transport dewar and a second helium gas line end for connection to a helium gas reservoir, in particular a compressed helium gas reservoir. By means of the control valve for the helium gas reservoir, the pressure in the transport dewar can be changed quickly and easily. The control valve can be automatically operated and adjusted by a control device, for example using an electric motor. It should be noted that the helium introduced from the helium gas reservoir into the transport dewar should be pre-purified so that impurities (such as water vapor or nitrogen) do not enter the transport dewar and the utility cryostat and freeze there. Preferably, the transport dewar is designed such that the gaseous helium introduced from the helium gas reservoir can be liquefied therein. Preferably, it is designed such that it can be liquefied therein by the cold head of a cryocooler which is also used to cool the condensation heat exchanger. Preferably, a common cryocooler is used in the transport dewar to operate a cooling trap to purify the helium gas and to liquefy the helium gas. For this purpose, a device as described in particular in German Patent Application Publication No. 102021205423 can be used.

[0047] In an advantageous embodiment, the device for generating a pressure difference comprises an electric heater in a storage dewar. By heating the interior of the storage dewar (or rather the helium container therein) with the electric heater, the liquid helium stored in the storage dewar can evaporate, increasing the pressure in the storage dewar and propelling the transfer of the liquid helium. This method is particularly simple.

[0048] In a particularly preferred embodiment, the device further comprises the following. - A closed cooling circuit for a refrigerant, comprising a supply line from the cold head of a cryocooler to a condensation heat exchanger and a return line from the condensation heat exchanger to the cold head of the cryocooler. The cryocooler is designed to cool the refrigerant directly or indirectly by means of the cold head. In particular, the cold head of the cryocooler is arranged separately from the practical cryostat. By providing the cooling circuit, the position where a low temperature is actually generated (at the cold head) can be easily spatially separated from the position of helium condensation (at the condensation heat exchanger). In particular, the condensation heat exchanger can be attached to the end of a rigid cooling rod that can be easily inserted into the practical cryostat. The cold head does not need to be inserted into the practical cryostat, thereby saving a lot of space in the practical cryostat. In many cases, the opening of the practical cryostat is preferably designed with a very small cross-section (significantly smaller than a commercially available cold head), so that insertion is impossible in any case. Typically, the cold head is also arranged separately from the practical cryostat, which simplifies the design of the entire system. In addition, the transmission of vibrations to the practical cryostat can be minimized. Part of the supply line and the return line, and optionally also part of the transfer line, may be integrated with the cooling rod. It should be noted that the cooling circuit also usually comprises a compressor supply line from a separate compressor to the cold head and a compressor return line from the cold head to the compressor.

[0049] In a preferred development of this embodiment, the supply line, the return line, and the transfer line extend from the storage dewar as a line bundle within a common vacuum insulation. This design enables easy insulation of the supply line, the return line, and the transfer line. The line bundle is particularly easy to handle. In particular, the second transfer line end (outlet end) of the transfer line and the condensation heat exchanger (end of the supply line / start of the return line) can be inserted particularly easily together into the practical cryostat. Usually, the line bundle is arranged within a rigid pipe ("cooling rod") in the rear region, i.e., near the second transfer line end of the transfer line and the condensation heat exchanger. This makes handling even easier.

[0050] A secondary variant of this development is also preferred, in which the supply line and the transfer line are thermally coupled to each other within a common vacuum insulation, in particular using a plurality of coupling bridges. This enables the transfer line to be pre-cooled by a cooling circuit or rather by the refrigerant in the supply line before the start of liquid helium transfer. As a result, when transfer is started and liquid helium flows, the helium transfer line is already at a low temperature. This means that no liquid helium is consumed (i.e., evaporated) to cool the transfer line.

[0051] Furthermore, in a preferred embodiment, the device further comprises a helium gas reservoir connected to the storage dewar via a helium gas line. In particular, the helium gas reservoir is a compressed helium gas reservoir. This enables helium gas to be introduced into the storage dewar, in particular to increase the pressure in the storage dewar (the helium reservoir is usually a compressed helium gas reservoir at this time), and / or to liquefy the gaseous helium introduced into the storage dewar (the cold head of the cryocooler typically protrudes into the storage dewar or rather its storage cryostat. See also below).

[0052] An embodiment in which the cold head of the cryocooler and the helium container of the storage dewar are arranged in a common storage cryostat is particularly preferred. The cold head of the cryocooler is designed to liquefy helium gas into liquid helium within the storage dewar. If helium can be liquefied within the storage dewar, there is no need to transport the liquid helium over long distances (e.g., by truck) to the location of the practical cryostat. This transportation is technically complex. Therefore, the cost of operating the practical cryostat can be significantly reduced. Instead, gaseous helium, which is easier to transport, can be transported to the practical cryostat (e.g., within a compressed gas cylinder). And / or the helium that evaporates during the normal operation of the practical cryostat is liquefied within the practical cryostat (typically after intermediate storage). This is particularly sustainable.

[0053] In a further advantageous development of this embodiment, the helium container and the cold head are also designed to supply a volume of supercooled liquid helium within the helium container. The supercooled helium has a temperature below its boiling point at the actual pressure within the helium container. Typically, the pressure within the helium container is about 1 bar (but slightly above), and the corresponding boiling point is 4.2 K. The temperature of the supercooled liquid helium is then below 4.2 K. Preferably, the temperature of the supercooled liquid helium within the helium container is 4.0 K or less, particularly preferably 3.8 K or less. However, the supply of supercooled liquid helium is more energy - demanding than the supply of liquid helium at its boiling point (4.2 K). As the temperature of the supercooled liquid helium decreases, the energy demand increases rapidly. Therefore, it is also preferred that the supercooled liquid helium within the helium container also has a temperature of 3.7 K or more. When the supercooled liquid helium is supplied to the practical cryostat, additional cooling capacity becomes available for condensing gaseous helium into liquid helium within the practical cryostat. The additional cooling capacity depends on the temperature difference with respect to the boiling point of the liquid helium and its specific heat capacity. This enables a faster transfer of liquid helium compared to using liquid helium at its boiling point under the cooling capacity provided by the cryocooler.

[0054] In a secondary deformation mode of this development form, it is particularly preferred that a thermal barrier be arranged within the helium container. Thereby, the volume of supercooled helium below the thermal barrier is separated from the volume of liquid saturated helium above the thermal barrier. In this configuration, the supply of supercooled liquid helium can be carried out particularly efficiently and relatively easily. The thermal barrier that can be used in the context of the present invention is described, for example, in German Patent Application Publication No. 4039365. The thermal barrier is thermally insulating but pressure permeable. The cooling head of the cryocooler can be arranged in a separated vacuum chamber, protruding through the thermal barrier such that the coldest stage of the cold head can apply a cooling power below the thermal barrier.

[0055] In a further secondary deformation mode, it is provided that the supply line of the refrigerant of the cooling circuit of the cryocooler extends through the region of the volume of liquid supercooled helium. This means that a large reservoir of "cooling energy" at a temperature below 4.2 K is available for cooling the condensation heat exchanger. Due to the low operating temperature, heat transfer in the condensation heat exchanger can be carried out particularly efficiently.

[0056] In a further secondary deformation mode, the end of the first transfer line opens into the storage dewar in the region of the volume of liquid supercooled helium, particularly near the bottom of the helium container. Thereby, the supercooled liquid helium can be easily transported into the practical cryostat through the transfer line.

[0057] In another embodiment, it is advantageous for the transfer line to have a purge valve in the region near the end of the first transfer line. The air present in the transfer line can be blown out through the purge valve before the start of liquid helium transfer. For this purpose, some gaseous helium passes through the purge valve through the transfer line from the cryostat, which is under a slight overpressure compared to the ambient atmosphere. Thereby, the entry of air into the cryostat can be minimized. The purge valve leads to the ambient atmosphere in the simplest case, or alternatively to a helium recovery system (equipped with a purification function for separating air components).

[0058] (Practical system according to the present invention) A practical system comprising an apparatus according to the present invention and a cryostat as described above is also within the scope of the present invention, The transfer line and the condensation heat exchanger are inserted into the cryostat, In particular, it is inserted into the common access pipe of the cryostat. In the practical system according to the present invention, liquid helium can be transferred from the storage dewar to the cryostat in a simple manner while minimizing helium loss. When the condensation heat exchanger (typically arranged on a cooling rod) and the transfer line for liquid helium use a common access pipe (in particular, the suspension pipe of the NMR magnet), in the event of a quench (sudden loss of superconductivity of the NMR magnet), a sufficiently large outflow cross-section can be easily provided immediately in the second non-blocked access pipe (in particular, the suspension pipe). Furthermore, the thermal coupling between the transfer line and the supply line for the refrigerant of the condensation heat exchanger can be facilitated.

[0059] In one embodiment of the practical system according to the present invention, it is particularly preferable that the practical cryostat includes a superconducting magnet coil and the NMR probe head protrudes into the magnet bore of the magnet coil. Thereby, the practical cryostat can be used for NMR measurement, and since it has a relatively low operating cost within the scope of the present invention, the cost of NMR measurement of the sample can be reduced. Typically, the NMR probe head protrudes into the room-temperature bore of the practical cryostat that is coaxial with the magnet bore.

[0060] (Method according to the present invention for transferring liquid helium) A method for transferring liquid helium into a practical cryostat is also within the scope of the present invention, In particular, using the device according to the present invention or the practical system according to the present invention described above, The transfer line for liquid helium is connected to a storage dewar that stores liquid helium at the first transfer line end and is inserted into the practical cryostat at the second transfer line end, Liquid helium is transferred from the storage dewar through the transfer line to the practical cryostat, The flow of liquid helium through the transfer line is adjusted by a device for changing the pressure difference between the storage dewar and the practical cryostat. Further, The condensation heat exchanger cooled by the cryocooler is inserted into the practical cryostat to liquefy gaseous helium into liquid helium within the practical cryostat, The control device measures the pressure within the practical cryostat and operates the device for changing the pressure difference, whereby 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 to liquid helium per unit time in the condensation heat exchanger. It is characterized by this. Within the scope of the method according to the present invention, when replenishing liquid helium from the storage dewar, it is realized that almost no or only a small amount of helium gas is pushed out from the practical cryostat by the inflowing liquid helium. This is achieved by the fact that when filling the practical cryostat with liquid helium, the related volume / volume changes almost coincide with each other, and the helium gas present in the practical cryostat is liquefied by using a condensation heat exchanger ( "equilibrium state"). Therefore, the helium gas is hardly or not lost at all while transporting the liquid helium. A helium recovery system for storing and reliquefying the pushed-out helium gas is not necessary, or can be designed to be relatively small so as to obtain cost-effectiveness.

[0061] A variant of the method according to the present invention is particularly preferably that the control device keeps the pressure in the practical cryostat almost constant while transporting the liquid helium to the practical cryostat. By this method, it becomes easy for the volume of liquid helium transported through the transfer line per unit time to be almost equal to the volume change of helium condensed from helium gas to liquid helium per unit time in the condensation heat exchanger ( "equilibrium state").

[0062] In a preferred variant, there is no outflow of gaseous helium from the practical cryostat while transporting the liquid helium. This makes it possible to completely eliminate the helium loss during liquid helium transfer without the need for a helium recovery system.

[0063] It is also advantageous to have a variant in which the control device measures the ambient atmospheric pressure and keeps the pressure inside the practical cryostat always higher than the ambient atmospheric pressure, and in particular operates appropriately the device for generating a pressure difference. This prevents air from the surrounding environment from being sucked into the practical cryostat. When there is a risk that the pressure inside the practical cryostat may become quite low, the transfer of liquid helium into the practical cryostat usually increases (by increasing the pressure in the storage dewar). If necessary (for example, when the transfer line is blocked), the electric heater inside the practical cryostat is switched on and / or strengthened if available.

[0064] In a preferred variant, it is proposed that the control device operates the control valve in the helium gas line as the device for changing the pressure difference. The helium gas line leads from a helium gas reservoir, in particular a compressed helium gas reservoir, to the storage dewar. Thereby, the pressure in the storage dewar increases directly and rapidly, starting or increasing the transfer of liquid helium.

[0065] It is also advantageous to have a variant in which the control device operates the electric heater in the storage dewar as the device for changing the pressure difference. The electric heater is easy to install and inexpensive. The heater can evaporate the helium in the storage dewar, which increases the gas pressure in the storage dewar. The compressed helium gas reservoir is not necessary (however, it may still be provided).

[0066] Also, a variant is preferred in which the refrigerant is guided through a supply line from the cold head of the cryocooler to the condensation heat exchanger and a return line to the cooling head of the cryocooler within a closed cooling circuit, and the cold head of the cryocooler directly or indirectly cools the refrigerant, especially when the cold head is arranged separately from the practical cryostat. Using the cooling circuit, the cold head can be spatially separated from the condensation heat exchanger. Thereby, the installation space within the practical cryostat (especially in the area of the access pipe) is saved. Furthermore, the cold head can be easily used for other purposes. In particular, it can be used to liquefy helium in the storage dewar.

[0067] A variant is particularly preferred in which the transfer line between the storage dewar and the practical cryostat is thermally coupled to the supply line. Thereby, the transfer line for liquid helium can be cooled by the cooling circuit.

[0068] A further development of this variant presents that before the start of the transfer of liquid helium through the transfer line, the transfer line is first precooled by the refrigerant in the supply line. When the liquid helium first passes through the transfer line for transfer, the transfer line is already at a low temperature, and the liquid helium does not evaporate or only evaporates slightly on the path to the practical cryostat. Thereby, liquid helium can be saved.

[0069] The following variants are also preferred. The cold head of the cryocooler and the helium container of the storage dewar are arranged within a common storage cryostat. Before the start of the transfer of liquid helium, gaseous helium from the helium gas reservoir, especially from the compressed helium gas reservoir, is supplied to the storage dewar, and the gaseous helium is condensed into liquid helium in the storage dewar by the cold head. In this variant, liquid helium can be generated in situ within the storage dewar. Transportation of liquid helium to complex and difficult locations of use can be avoided. If necessary, helium can be processed in a substantially closed circuit at the location of use. This is sustainable and cost-effective.

[0070] A variant is particularly preferred which presents that the volume of supercooled liquid helium is provided to the helium container of the storage dewar and the liquid helium transferred through the transfer line is withdrawn from the volume of supercooled liquid helium. The volume of supercooled helium provides additional cooling power within the practical cryostat. This assists in the liquefaction of the helium gas within the practical cryostat. The transfer of liquid helium can be carried out particularly rapidly.

[0071] A further development of the aforementioned variant advantageously presents that the condensation heat exchanger is cooled by a refrigerant circulating within a closed cooling circuit, and the refrigerant is led to a supply line passing through the region of the volume of supercooled liquid helium. Thereby, a particularly large reservoir of cooling energy at a temperature below 4.2 K becomes available for use in liquefaction in the practical cryostat. The condensation heat exchanger becomes very efficient and powerful.

[0072] Before starting the transfer of liquid helium, a variant is also advantageous in which the transfer line is first purged of gaseous helium from the practical cryostat by a purge valve arranged near the first transfer line end within the transfer line. Thereby, the entry of contaminants (air components) into the practical cryostat is minimized. The branch to the purge valve is typically arranged in the region of the storage dewar. Typically, more than 3 / 4 of the length of the transfer line can be purged by the purge valve.

[0073] It is also preferable to have a modified form in which the practical cryostat is used alternately with normal operation for practical use and liquid helium is filled by a replenishment operation. During normal operation, the condensation heat exchanger and the end of the second transfer line are not inserted into the practical cryostat. During the replenishment operation, the condensation heat exchanger and the end of the second transfer line are inserted into the practical cryostat. The condensation heat exchanger and the transfer line are inserted only when necessary. Therefore, the heat input to the practical cryostat during normal operation can be minimized.

[0074] It is also preferable to have a further developed form of the above-described modified form, in which a superconducting magnet coil is arranged in the practical cryostat, and during normal operation as a practical use using an NMR probe head, the NMR probe head is arranged in the magnet bore of the superconducting magnet coil, and NMR measurement on a sample is performed. NMR measurement of a sample that is sustainable and cost-effective is possible within the scope of the present invention.

[0075] Further advantages of the present invention can be found in the specification and the drawings. Similarly, the above-described features and the features detailed below can be used individually or collectively in any combination according to the present invention. The illustrated and described embodiments should not be understood as an exhaustive list, but rather have an exemplary nature for the description of the present invention.

Brief Description of the Drawings

[0076]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0077] FIG. 1 schematically shows a practical system 100 according to a first embodiment of the present invention, which includes an apparatus 101 for transferring liquid helium and a practical cryostat 102 during the transfer of liquid helium.

[0078] The apparatus 101 includes a storage dewar 1 having a helium container 2, and the helium container 2 is thermally separated from the surrounding environment 4 by a vacuum insulation material 3. Here, the surrounding environment 4 is at room temperature (20°C) and an atmospheric pressure p of 1.00 bar atm and is. One or more radiation shields or multilayer superinsulators may be provided in the vacuum insulation material 3 (not shown in detail).

[0079] In the helium container 2, liquid helium 5 is stored in the lower region, and gaseous helium 6 exists in the upper region above the liquid helium 5. In the illustrated embodiment, the liquid helium 5 and the gaseous helium 6 in the storage dewar 1 have a temperature of about 4.2 K. The pressure p in the storage dewar 1 in this case vorrat is about 1.08 bar. In the illustrated embodiment, an electric heater 7 is also arranged in the storage dewar 1. The electric heater 7 can be controlled by an electronic control device 8.

[0080] The transfer line 9 for liquid helium protrudes into the storage dewar 1. The first transfer line end 9a opens into the liquid helium 5 near the bottom of the helium container 2. The transfer line 9 is provided with a vacuum heat insulator 23. The storage dewar 1 is designed to be transportable (a "transport dewar") by means of rollers 37 in this case.

[0081] The second transfer line end 9b of the transfer line 9 is inserted into the utility cryostat 102 through the access pipe 15a and opens into the helium tank 10 of the utility cryostat 102. The helium tank 10 is thermally insulated from the ambient environment 4 by a vacuum heat insulator 13. One or more radiation shields may be provided in the vacuum heat insulator 13 (not shown in detail).

[0082] In the helium tank 10 of the utility cryostat 102, liquid helium 11 is located in the lower region and gaseous helium 12 is located in the upper region. In the illustrated embodiment, the liquid helium 11 and the gaseous helium 12 in the helium tank 10 have a temperature of about 4.2 K in any state, and the pressure p anwend in the helium tank is about 1.03 bar.

[0083] (For transferring liquid helium through the transfer line 9), the pressure is generally p atm <p anwend <p vorrat is.

[0084] The pressure p in the storage dewar 1 vorrat is slightly higher than the pressure p anwend in the utility cryostat 102, so the liquid helium 5 is pushed out from the storage dewar 1 into the utility cryostat 102 through the transfer line 9. See the liquid helium 14 flowing out at the second transfer line end 9b. Propelled by the pressure difference between the storage dewar 1 and the utility cryostat 102, the liquid helium is consequently transferred from the storage dewar 1 to the utility cryostat 102.

[0085] Not only the transfer line 9 but also the cooling rod 16 extends into the practical cryostat 102 through the access pipe 15a. Therefore, the access pipe 15a is also called the common access pipe 15a. The condensation heat exchanger 17 is provided at the lower end of the cooling rod 16. The condensation heat exchanger 17 continuously liquefies the gaseous helium 12 in the helium tank 10 while transferring the liquid helium.

[0086] The condensation heat exchanger 17 is cooled by a refrigerant circulating in the cooling circuit 19. The cooling circuit 19 extends by a supply line 20 from the cold head heat exchanger 25a of the cold head 25 to the condensation heat exchanger 17 and a return line 21 returning from the condensation heat exchanger 17 to the cold head heat exchanger 25a of the cold head 25. The end regions of the supply line 20 and the return line 21 close to the condensation heat exchanger 17 extend in the cooling rod 16. The supply line 20 and the return line 21 are covered by the vacuum heat insulation material 22. In the refrigerant circuit 19 driven by the compressor 28, the supply line 26 of the compressor extends from the compressor to the cold head heat exchanger 25a or the supply line 20, and the return line 27 of the compressor extends from the return line 21 or the cold head heat exchanger 25a to the compressor 28. The refrigerant in the cooling circuit 19 may be particularly helium. The cold head 25 and the compressor 28 constitute the cryocooler 29 of the device 101.

[0087] In this case, the compressor 28 operates the cold head 25 and is divided into separate cold head lines 35, 36 provided between the compressor 28 and the cold head 25 to ensure the circulation of the refrigerant in the cooling circuit 19 for the condensation heat exchanger 17. This is particularly cost-effective. The cooling circuit 19 is divided into operation and stop by a cooling circuit valve 19a provided in the supply line 26 of the compressor in this case.

[0088] In this case, the cold head 25 and the cold head heat exchanger 25a are arranged within the cryostat 30 of the cryocooler. The cryostat 30 of the cryocooler is separate from the utility cryostat 102 and the storage dewar 1. The cryocooler 29 may be configured in particular as a Gifford-McMahon refrigerator or a pulse tube refrigerator. The cooling of the cooling rod 16 or the condensation heat exchanger 17 is effected by the cryocooler 29 or a refrigerator external to the utility cryostat 102.

[0089] In this case, the control device 8 uses a pressure sensor 18 provided in the second access pipe 15b of the utility cryostat 102 to monitor the pressure p within the utility cryostat 102. anwend Furthermore, the second access pipe 15b is open and can effectively serve as an emergency exit for helium gas (for example, in the case of a quench). The pressure sensor 18 is connected to the measurement input section 18a of the control device 8. Furthermore, in the illustrated embodiment, the control device 8 uses a pressure sensor 8a incorporated in the control device 8 to monitor the pressure p of the ambient environment 4. atm

[0090] In the illustrated embodiment, the control device 8 controls the heating capacity of the electric heater 7 in the storage dewar 1 when the transfer of liquid helium is being carried out. The pressure in the storage dewar 1 and hence also the pressure difference between the storage dewar 1 and the utility cryostat 102 can be changed by the heating capacity of the heater 7. Thus, the heater 7 constitutes a device 31 for generating a pressure difference between the storage dewar 1 and the utility cryostat 102. The heater 7 is connected to the control output section 31a of the control device 8.

[0091] The heating capacity is adjusted and readjusted by the control device 8 such that the pressure p within the utility cryostat 102 is regulated to a specified target value p. anwend anwend soll The specified target value p is regulated by the control device 8. The specified target value p anwend soll is 1.03 bar in this case, and the pressure p of the ambient environment 4atm In the simplest case, the specified target value p anwend soll is constant for the entire duration of the liquid helium transfer. atm If changes significantly during the transfer, the specified target value p anwend soll may be changed as needed. The pressure p anwend and the pressure of the surrounding environment p atm , in particular to avoid drawing ambient air into the operational cryostat 102 and / or to prevent activation of overpressure safety devices (such as pressure relief valves, rupture disks, etc., not shown in detail) in the operational cryostat 102.

[0092] During the introduction of liquid helium through transfer line 9 into the practical cryostat 102, pressure p anwend is effectively p anwend soll This keeps the volume of liquid helium introduced per unit time dV (LHe trans ) / dt is the change in volume of helium condensed per unit time in the condensing heat exchanger 17, dV(He cond ) / dt ("equilibrium condition"), in which no gaseous helium escapes from the operational cryostat 102 while liquid helium is being introduced into the operational cryostat 102.

[0093] Pressure p anwend ga p anwend soll If the pressure in the storage dewar 1 drops below this value, the controller 8 increases the heating power of the heater 7. This causes more helium to evaporate in the storage dewar 1, increasing the pressure p vorrat increases, the flow of liquid helium through the transfer line 9 increases, and the gas pressure in the working cryostat 102 increases.anwend is p anwend soll When it rises so as to exceed p, the control device 8 reduces the heating capacity of the heater 7 or completely switches it off. As a result, in the storage dewar 1, the amount of helium that evaporates decreases or stops evaporating completely, the pressure in the storage dewar 1 decreases (and also decreases as a result of the subsequent discharge of the liquid helium 5), the flow of liquid helium through the transfer line 9 decreases, and the gas pressure in the practical cryostat 102 decreases.

[0094] In the illustrated embodiment, the cooling capacity of the cryocooler 29 is kept constant during the transfer of liquid helium.

[0095] In the illustrated embodiment, the superconducting magnet coil 32 (also abbreviated as the magnet) is disposed within the practical cryostat 102. In normal operation, the NMR probe head 33 protrudes into the room-temperature bore (not shown in detail) of the practical cryostat 102. Thereby, the measurement sample 34 can be subjected to NMR measurement in the magnetic field within the magnet bore of the magnet 32. During normal operation, the transfer line 9 and the cooling rod 16 are drawn out from the access pipe 15a. Only during the replenishment operation are the transfer line 9 and the cooling rod 16 inserted into the access pipe 15a (the latter is shown in FIG. 1).

[0096] Filling height sensors can also be provided within the practical cryostat 102 and within the storage dewar 1, and these sensors are read by the control device 8 (not shown in more detail).

[0097] FIG. 2 shows the rear part of the line bundle 40 that can be used within the scope of the present invention on the apparatus for transferring liquid helium according to the present invention (see also FIG. 3).

[0098] The supply 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 flowing out into the practical cryostat at the second transfer line end 9b, extend within the line bundle 40. The line bundle 40 forms a common vacuum insulation 41 for the lines 9, 20, 21. A plurality of coupling bridges 42 made of a material having good thermal conductivity, for example, a plurality of coupling bridges 42 made of high-purity copper, are arranged between the transfer line 9 and the supply line 20. A thermal coupling is established between the supply line 20 and the transfer line 9 by the coupling bridge. Thereby, it becomes possible to pre-cool the transfer line 9 by the supply line 20, particularly before the start of the transfer of liquid helium.

[0099] In this case, the vertically extending portion of the line bundle 40 forms a cooling rod 16 that is easy to handle. Note that the line bundle outside the range of the cooling rod is preferably designed to be flexible. The line bundle may have so-called super-insulation properties. Also, spacers with low thermal conductivity are provided so that the lines are separated from the outer heat-insulating coating.

[0100] FIG. 3 schematically shows a practical system 100 according to a second embodiment of the present invention, which includes an apparatus 101 for transferring liquid helium and a practical cryostat 102. Since most of the practical system 100 coincides with the practical system of FIG. 1, only the important differences will be described below. For the sake of brevity, a part of the compressor and the lines carrying the refrigerant are not shown in detail in FIG. 3.

[0101] In the embodiment of FIG. 3, a shared storage cryostat 50 is installed. Both the cold head 25 and the helium container 2 are arranged in the shared storage cryostat 50. The cold head 25 is arranged in an acceptance region 51 that opens toward the helium container 2. Thereby, the gaseous helium 6 is distributed between the upper part of the helium container 2 and the inside of the acceptance region 51. The storage cryostat 50 in this case has a radiation shield 58 that is thermally coupled to the warmer cooling stage of the cold head 25 (the coupling part is not shown in detail).

[0102] The helium gas line 54 from the helium gas reservoir 52 leads into the storage dewar 1. The helium gas line 54 is designed as a compressed helium gas reservoir 53. The first helium gas line end 54a projects above the helium container 2. The second helium gas line end 54b is connected to the compressed helium gas reservoir 53. The compressed helium gas reservoir 53 can be designed to be transportable, for example, by rollers (not shown in detail).

[0103] Near the second helium gas line end 54b, the helium gas line 54 has a control valve 55 (not shown in detail). The control valve 55 is automatically actuated by the control device 8. In this case, the control valve 55 is actuated by an electric motor.

[0104] The helium gas line 54 passes through the cold head 25 through the receiving region 51 and is thermally coupled to the two cold stages of the cold head 25 by the helium supply heat exchanger 56. The helium gas 6a flowing into the storage dewar 1 through the helium gas line 54 can be liquefied by the cold head 25 (or the helium gas 6 already present in the storage dewar 1 can be liquefied).

[0105] It should be noted that the helium gas 6a should be purified before liquefaction, for example, by a cold trap (not shown in detail). For example, the device described in German Patent Application Publication No. 102021205423 can be used in such cases.

[0106] In the illustrated embodiment, a pressure sensor 57 is also provided. Thereby, the pressure p vorrat in the storage dewar 1 is measured and monitored by the control device 8. The control device 8 ensures that p vorrat is always p atmEnsure that it is above (see also below). This prevents ambient air from being sucked into the storage dewar 1. In addition, the control device 8 also monitors the pressure p anwend in the utility cryostat 102 by means of the pressure sensor 18. The control device 8 can also activate the heater 7 in the storage dewar 1.

[0107] The control device 8 can use the heater 7 (see above) or, similarly, the control valve 55 as a device 31 for generating a pressure difference between the storage dewar 1 and the utility cryostat 102 in either case. By increasing the opening cross-sectional area of the control valve 55, additional helium (helium gas and / or liquid helium) can be introduced into the storage dewar 1. Thereby, the pressure p vorrat in the storage dewar 1 increases. By decreasing the opening cross-sectional area of the control valve 55 or closing the control valve 55, (subsequently discharging the liquid helium in the utility cryostat through the transfer line 9), the pressure p vorrat in the storage dewar 1 can decrease.

[0108] In this case, the supply line 20, the return line 21, and the transfer line 9 extend between the storage dewar 1 and the utility cryostat 102 as a line bundle 40 within a common vacuum insulation 41 (see Fig. 2). In addition, the transfer line 9 has a branch 60 to the purge valve 59 near its first transfer line end 9a. The branch 60 is located in the common storage cryostat 50 in this case. The purge valve 59 can be used to purge the helium gas 12 in the transfer line 9 between the second transfer line end 9b and the branch 60, (the helium gas 12 sourced from the utility cryostat 102). This is done before the start of the transfer of liquid helium through the transfer line 9. For this purpose, p anwend > p atmIt should be noted that in order to completely eliminate the loss of helium, the outlet of the purge valve 59 may be connected to a helium recovery system. The air purged into the helium recovery system can be separated by an upstream cold trap during the reliquefaction of helium from the recovery system (the helium recovery system and the cold trap are not shown in detail).

[0109] (Procedure according to the present invention) Hereinafter, an example of a procedure for replenishing liquid helium from the storage dewar 1 to the practical cryostat 102 within the scope of the method according to the present invention will be described. The exemplary procedure can be performed in a practical system 100 as particularly shown in FIG. 3. Transfer operations may be assigned to steps 2 to 6, and normal operation of the practical cryostat 102 may be assigned to step 7. Step 1 can be executed in parallel with the normal operation or as part of the transfer operation.

[0110] Step 1) Helium gas is supplied from the compressed helium gas reservoir 53 through the helium line 54 to the storage dewar 1, and the helium gas is liquefied by the cold head 25. Liquid helium 5 accumulates in the helium container 2.

[0111] Step 2) As soon as the liquefaction is completed (for example, because the helium container 2 is full or the compressed helium gas reservoir 53 is empty), it is possible to prepare for the transfer of liquid helium 5. To do this, the user first inserts a cooling rod 16 having a transfer line 9 and a condensation heat exchanger 17 into the access pipe 15a of the practical cryostat 102.

[0112] Step 3) The purge valve 59 is opened. Helium gas from the practical cryostat 102 pushes air out of the transfer line 9 through the purge valve 59. When the existing air has escaped, the purge valve 59 is closed.

[0113] Step 4) Next, the valve of the cooling circuit (reference numeral 19a in FIG. 1) is opened for the refrigerant. Thereby, a part of the gas flow supplied by the compressor (reference numeral 28 in FIG. 1) is diverted. The circulation of the refrigerant in the cooling circuit 19, or rather the circulation of the refrigerant through the condensation heat exchanger 17, is activated. Since the supply line 20 is thermally coupled to the transfer line 9, the transfer line 9 is cooled in this process.

[0114] Step 4) Once the condensation heat exchanger 17 and the transfer line 9 are cooled, the transfer of liquid helium ("helium transfer") is started. This can be automatically performed either because the pressure in the helium tank 10 of the practical cryostat 102 decreases due to the start of condensation, or because the pressure in the storage dewar 1 is actively increased, for example, by the heater 7 or by the helium gas 6a supplied from the compressed helium gas reservoir 53.

[0115] Step 5) Next, the helium transfer is controlled by the control device 8 such that the transfer rate of the liquid helium through the transfer line 9 corresponds to the rate at which the gaseous helium 12 condenses within the practical cryostat 102. Thereby, the helium gas 12 is not pushed out from the practical cryostat 102 during the helium transfer. Therefore, the helium transfer according to the present invention can be carried out without the need for a storage balloon for performing lossless helium transfer.

[0116] Step 6) Once the helium transfer is completed (for example, when the practical cryostat 102 is completely filled with liquid helium 11 or the liquid helium 5 in the storage dewar 1 is exhausted), the user removes the cooling rod 16 having the transfer line 9 and the condensation heat exchanger 17 from the practical cryostat 102.

[0117] Step 7) Next, using the practical cryostat 102, particularly the NMR magnet (reference numeral 32 in FIG. 1) included in the practical cryostat 102, NMR measurements can be performed. The NMR measurements can be carried out continuously, starting just a few hours after the start of helium transfer. Compared with the conventional helium transfer accompanied by leakage of gaseous helium through one of the access pipes 15a, 15b, the stabilization of the practical cryostat 102 within the scope of the present invention occurs significantly faster. This is because a large amount of cryogenic gas does not leak through the access pipes (suspension pipes) 15a, 15b, (in the latter case, the access pipes can usually be significantly cooled during conventional helium transfer. The magnetic field during the period of returning to thermal equilibrium is unstable).

[0118] FIG. 4 shows an alternative design of the storage dewar 1 of the present invention. This alternative design can be used, for example, in the embodiment of the practical system of FIG. 3. Only the main differences from the design of FIG. 3 will be described.

[0119] In the design shown in FIG. 4, a thermal barrier 70 is arranged inside the helium container 2 of the storage dewar 1. The thermal barrier 70 has pressure permeability (i.e., liquid helium can flow through it) but has heat insulation properties. The thermal barrier 70 can be designed as described, in particular, in German Patent Application Publication No. 4039365.

[0120] The cold head 25 is disposed within a closed vacuum vessel 71. The vacuum vessel 71 extends beyond (downward) the thermal barrier 70. Thus, the lowest (coldest) cooling stage 73 of the cold head 25 can cool the liquid helium 74 below the thermal barrier 70. The liquid helium 74 below the thermal barrier 70 is supercooled and has a temperature of about 3.7 K. The entire supercooled liquid helium 74 is also referred to as the volume 74 of supercooled liquid helium. Above the thermal barrier 70 is saturated liquid helium 75, which has a temperature of about 4.2 K. The entire saturated liquid helium 75 is also referred to as the volume 75 of saturated liquid helium. The gaseous helium 6 above them also has a temperature of about 4.2 K and a pressure p vorrat is.

[0121] The transfer line (pipe) 9 extends deep into the region of the supercooled liquid helium 74, up to just before the bottom of the helium vessel 2. The portion of the transfer line 9 passing through the region of the volume 75 of saturated helium is such that the transfer line 9 is thermally insulated from the volume 75 of saturated helium (not shown in detail). Thus, during helium transfer, the supercooled liquid helium 74 is carried through the transfer line 9 into the utility cryostat.

[0122] The supercooled liquid helium 74 carried into the utility cryostat can extract thermal energy from the utility cryostat when the supercooled liquid helium is reheated to 4.2 K again. Therefore, the condensation heat exchanger should be given less cooling capacity to condense gaseous helium within the condensation heat exchanger. For example, when 100 l of liquid helium (12.5 kg) having a temperature of 3.7 K is transferred, about 26.3 kJ of additional cooling energy is available for about 34 kJ required for the condensation heat (see above). However, the lower the temperature of the supercooled liquid helium 74, the more energy-intensive the supply of the supercooled liquid helium 74 becomes.

[0123] The supply line 20 of the cooling circuit for the condensation heat exchanger within the practical cryostat extends through the region of supercooled liquid helium 74. Therefore, the refrigerant can be used particularly efficiently for carrying thermal energy away from the condensation heat exchanger.

[0124] It should be noted that the supercooled helium of the present invention can also be obtained, for example, by expanding helium at low pressure within a throttle (not shown in detail).

[0125] In summary, the present invention relates to an apparatus (101) for transferring liquid helium (14) to a practical cryostat (102), - a storage dewar (1), - a transfer line (9) having a first transfer line end (9a) within the storage dewar (1) and a second transfer line end (9b) for insertion into the practical cryostat (102), - an apparatus (31) for generating a pressure difference between the storage dewar (1) and the practical cryostat (102), - a condensation heat exchanger (17) for condensing helium gas (12) into liquid helium (11) suitable for insertion into the practical cryostat (102), - a cryocooler (29) for cooling the condensation heat exchanger (17), and - a control device (8) having a measurement input part (18a) for a pressure sensor (18) for measuring the gas pressure within the practical cryostat (102) and a control output part (31a) for the apparatus (31) for generating a pressure difference, the control device (8) being programmed to control the apparatus (31) for generating a pressure difference such that the volume of liquid helium (14) transferred through the transfer line (9) per unit time is approximately equal to the volume change of helium condensed per unit time from helium gas (12) to liquid helium (11) in the condensation heat exchanger (17). characterized by. This apparatus facilitates minimizing helium loss during the transfer of liquid helium.

Description of the reference numerals

[0126] 1 Storage Dewar 2 Helium Container 3 Vacuum Insulation Material (of Storage Dewar) 4 Surrounding Environment / Ambient Atmosphere 5 Liquid Helium (inside Storage Dewar) 6 Gaseous Helium (inside Storage Dewar) 6a Gaseous Helium (from Helium Gas Reservoir) 7 Electric Heater (inside Storage Dewar) 8 Electronic Control Device 8a Pressure Sensor for Ambient Atmosphere 9 Transfer Line for Liquid Helium 9a First Transfer Line End (inserted into Storage Dewar) 9b Second Transfer Line End (inserted into Practical Cryostat) 10 Helium Tank 11 Liquid Helium (inside Practical Cryostat) 12 Gaseous Helium (inside Practical Cryostat) 13 Vacuum Insulation Material (of Practical Cryostat) 14 Liquid Helium (flowed out / transferred) 15a First / Common Access Pipe 15b Second Access Pipe 16 Cooling Rod 17 Condensation Heat Exchanger 18 Pressure Sensor for Practical Cryostat 18a Measurement Input Part (for Pressure Sensor 18) 19 Cooling Circuit 19a Cooling Circuit Valve 20 Refrigerant Supply Line 21 Refrigerant Return Line 22 Vacuum Insulation Material (of Supply Line and Return Line) 23 Vacuum Insulation Material (of Transfer Line) 25 Cold Head 25a Heat Exchanger (for Cooling Circuit of Cold Head) 26 Compressor Supply Line 27 Compressor Return Line 28 Compressor 29 Cryocooler 30 Cryostat of the cryocooler 31 Device for generating a pressure difference 31a Control output section (for device 31) 32 Superconducting magnet coil / magnet 33 NMR probe head 34 Measurement sample 35, 36 Cold head line 37 Roller 40 Line bundle 41 Common vacuum insulation material 42 Coupling bridge 50 Common storage cryostat 51 Receiving area 52 Helium gas reservoir 53 Compressed helium gas reservoir 54 Helium gas line 54a First helium gas line end 54b Second helium gas line end 55 Control valve 56 Helium supply heat exchanger 57 Pressure sensor of the storage dewar 58 Radiation shield 59 Purge valve 60 Branch section for the purge valve 70 Thermal barrier 71 Vacuum vessel 73 Lowest / coldest cooling stage 74 Subcooled liquid helium / helium volume 75 Saturated liquid helium / helium volume 100 Practical system 101 Device for transferring liquid helium 102 Practical cryostat

Claims

1. An apparatus (101) for transferring liquid helium (14) into a practical cryostat (102), comprising: a storage dewar (1) for liquid helium (5), a transfer line (9) for liquid helium (14) with a first transfer line end (9a) arranged in the storage dewar (1) and a second transfer line end (9b) for insertion into the working cryostat (102) for transferring liquid helium (5) from the storage dewar (1) into the working cryostat (102); - a device (31) for creating a pressure difference between said storage dewar (1) and said working cryostat (102), The device (101) further comprises: - a condensing heat exchanger (17) suitable for insertion into said practical cryostat (102) for condensing helium gas (12) into liquid helium (11); - a cryocooler (29) for cooling said condenser 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 said practical cryostat (102) and a control output (31a) for said device (31) for generating a pressure difference, said control device (8) being programmed to control said device (31) for generating a pressure difference such that the volume of liquid helium (14) transferred through said transfer line (9) per unit time is approximately equal to the volume change of said helium condensing per unit time from helium gas (12) to liquid helium (11) in said condensation heat exchanger (17); The apparatus (101),

2. The control device (8) controls the pressure (p) in the operational cryostat (102) during the transfer of liquid helium (14) into the operational cryostat (102). ａｎｗｅｎｄ ) is programmed to keep it nearly constant.

2. The device (101) according to claim 1, characterized in that

3. The control device (8) controls the ambient atmospheric pressure (p ａｔｍ ) a pressure sensor (8a) for measuring The control device (8) controls the pressure (p) in the working cryostat (102) by appropriately operating, in particular, the device (31) for generating a pressure difference. ａｎｗｅｎｄ ) to the ambient atmospheric pressure (p ａｔｍ ) will be programmed to always remain higher than An apparatus (101) according to any one of claims 1 to 2, characterized in that

4. The device (31) for creating a pressure difference comprises a control valve (55) in a helium gas line (54); the helium gas line (54) comprises a first helium gas line end (54a) connected to the storage dewar (1) and a second helium gas line end (54b) for connection to a helium gas reservoir (52), in particular a compressed helium gas reservoir (53); An apparatus (101) according to any one of claims 1 to 3, characterized in that

5. said device (31) for generating a pressure difference comprises an electric heater (7) in said storage dewar (1); An apparatus (101) according to any one of claims 1 to 4, characterized in that

6. The device (101) comprises: - a closed cooling circuit (19) for a refrigerant comprising a supply line (20) from the cold head (25) of the cryocooler (29) to the condensing heat exchanger (17) and a return line (21) from the condensing heat exchanger (17) to the cold head (25) of the cryocooler (29), The cryocooler (29) comprises: designed to cool the refrigerant directly or indirectly through the cold head (25); In particular, the cold head (25) of the cryocooler (29) is arranged separately from the operational cryostat (102).

6. An apparatus (101) according to any one of claims 1 to 5, characterized in that

7. the supply line (20), the return line (21) and the transfer line (9) extend from the storage dewar (1) as a line bundle (40) within a common vacuum insulation (41); In particular, the supply line (20) and the transfer line (9) are thermally coupled to each other within the common vacuum insulation (41), preferably by means of a plurality of coupling bridges (42).

7. The device (101) according to claim 6, characterized in that

8. The apparatus (101) further comprises a helium gas reservoir (52) connected to the storage dewar (1) through a helium gas line (54); In particular, the helium gas reservoir (52) is a compressed helium gas reservoir (53). An apparatus (101) according to any one of claims 1 to 7, characterized in that

9. the coldhead (25) of the cryocooler (29) and the helium vessel (2) of the storage dewar (1) are disposed within a common storage cryostat (50); the cold head (25) of the cryocooler (29) is designed to liquefy helium gas (6, 6a) into liquid helium (5) in the storage dewar (1); An apparatus (101) according to any one of the preceding claims, characterized in that

10. the helium vessel (2) and the cold head (25) are designed to provide a (74) volume of liquid subcooled helium into the helium vessel (2); 10. Apparatus (101) according to claim 9, characterized in that

11. a thermal barrier (70) disposed within said helium vessel (2); a thermal barrier separates the volume (74) of subcooled helium below the thermal barrier (70) from a volume (75) of liquid saturated helium above the thermal barrier (70); 11. Apparatus (101) according to claim 10, characterized in that

12. A practical system (100) comprising an apparatus (101) according to any one of claims 1 to 11 and a practical cryostat (102), said transfer line (9) and said condensing heat exchanger (17) are inserted in said utility cryostat (102), in particular in a common access pipe (15a) of said utility cryostat (102); The practical cryostat (102) includes a superconducting magnet coil (32) and an NMR probe head (33) that projects into a magnet bore of the magnet coil (32). A practical system (100).

13. A method for transferring liquid helium (14) into a practical cryostat (102), comprising the steps of: In particular, the device (101) or practical system (100) according to any one of claims 1 to 12 is used, a transfer line (9) for liquid helium (14) connected at a first transfer line end (9a) to a storage dewar containing liquid helium (5) and inserted at a second transfer line end (9b) into said working cryostat (102); Liquid helium (14) is transferred from the storage dewar (1) through the transfer line (9) to the working cryostat (102); the flow of liquid helium (14) through the transfer line (9) being regulated by a device (31) for varying the pressure difference between the storage dewar (1) and the working cryostat (102); A condensing heat exchanger (17) cooled by a cryocooler (29) is inserted into the practical cryostat (102) for liquefying gaseous helium (12) into liquid helium (11) within the practical cryostat (102); The control device (8) controls the pressure (p ａｎｗｅｎｄ ) and operating the device (31) to change 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 volume change of the helium condensed from helium gas (12) to liquid helium (11) per unit time in the condensing heat exchanger (17). A method comprising:

14. The control device (8) controls the pressure (p) in the operational cryostat (102) during the transfer of liquid helium (14) into the operational cryostat (102). ａｎｗｅｎｄ ) is kept almost constant, 14. The method according to claim 13.

15. During the transfer of liquid helium (14), no outflow of gaseous helium (12) occurs from the utility cryostat (102).

15. The method according to claim 13 or 14, characterized in that

16. The control device (8) controls the ambient atmospheric pressure (p ａｔｍ ) is measured, The control device (8) is adapted to operate, in particular, the device (31) for generating a pressure difference to control the pressure (p ａｎｗｅｎｄ ) to the ambient atmospheric pressure (p ａｔｍ ) always higher than 16. The method according to any one of claims 13 to 15, characterized in that

17. said control device (8), as said device (31) for varying a pressure difference, actuates a control valve (55) in a helium gas line (54) leading from a helium gas reservoir (52), in particular a compressed helium gas reservoir (53), to said storage dewar (1); and / or The control device (8) operates an electric heater (7) in the storage dewar (1) as the device (31) for varying the pressure difference.

17. The method according to any one of claims 13 to 16, characterized in that

18. The refrigerant in the closed cooling circuit (19) through a supply line (20) from the cold head (25) of the cryocooler (29) to the condensing heat exchanger (17); and through a return line (21) to the cooling head (25) of the cryocooler (29); the cold head (25) of the cryocooler (29) directly or indirectly cools the refrigerant; In particular, the cold head (25) is arranged separately from the operational cryostat (102).

18. The method according to any one of claims 13 to 17, characterized in that

19. the transfer line (9) between the storage dewar (1) and the working cryostat (102) is thermally coupled to the supply line (20); the transfer line (9) is first pre-cooled by the refrigerant in the supply line (20) before the start of the transfer of liquid helium (14) through the transfer line (9); 20. The method according to claim 18.

20. the coldhead (25) of the cryocooler (29) and the helium vessel (2) of the storage dewar (1) are disposed within a common storage cryostat (50); gaseous helium (6a) from a helium gas reservoir (52), in particular a compressed helium gas reservoir (53), is supplied to the storage dewar (1) before the start of the transfer of liquid helium (14), and the gaseous helium (6, 6a) is condensed into liquid helium (5) in the storage dewar (1) by the cold head (25); 20. The method according to any one of claims 13 to 19, characterized in that

21. a volume (74) of liquid subcooled helium is provided into a helium vessel (2) of said storage dewar (1); the liquid helium (14) transferred through the transfer line (9) is drawn from a volume (74) of liquid subcooled helium; 21. The method according to any one of claims 13 to 20, characterized in that

22. The operational cryostat (102) is rotated for normal operation for practical use and is filled with liquid helium (14) by a refill operation; During normal operation, the condensing heat exchanger (17) and the second transfer line end (9b) are not inserted into the utility cryostat (102); During a refill operation, the condensing heat exchanger (17) and the second transfer line end (9b) are inserted into the utility cryostat (102); During normal operation for practical use with the NMR probehead (33), a superconducting magnet coil (32) is placed in the practical cryostat (102) and NMR measurements are performed on a sample (34) placed in a magnet bore of the superconducting magnet coil (32).

22. The method according to any one of claims 13 to 21, characterized in that

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