DEVICE AND METHOD FOR TRANSFERRING LIQUID HELIUM INTO AN APPLICATION CRYOSTAT

Abstract

A device for transferring liquid helium into an application cryostat comprises a storage dewar, a transfer line with a first transfer line end in the storage dewar and a second transfer line end for insertion into the application cryostat. An apparatus is provided for generating a pressure difference between the storage dewar and the application cryostat. A condensation heat exchanger, cooled by a cryocooler, condenses helium gas to liquid helium for insertion into the application cryostat. A control apparatus, using a measure of gas pressure in the application cryostat provides a control output to the apparatus for generating a pressure difference such that a volume of liquid helium transferred through the transfer line per unit of time is approximately equal to the change in volume of the helium which condenses from helium gas to liquid helium per unit of time at the condensation heat exchanger.

Claims

1. A device for transferring liquid helium into an application cryostat, comprising: a storage dewar for liquid helium, a transfer line for liquid helium for transferring liquid helium from the storage dewar into the application cryostat, comprising a first transfer line end arranged in the storage dewar and a second transfer line end for insertion into the application cryostat, an apparatus for generating a pressure difference between the storage dewar and the application cryostat, a condensation heat exchanger for condensing helium gas to liquid helium, for insertion into the application cryostat, a cryocooler for cooling the condensation heat exchanger, and a control apparatus having at least one measuring input from a cryostat pressure sensor for measuring a gas pressure in the application cryostat and a control output to the apparatus for generating a pressure difference, the control apparatus being programmed to control the apparatus for generating a pressure difference such that a volume of liquid helium transferred through the transfer line per unit of time is approximately equal to a change in volume of the helium which condenses from helium gas to liquid helium per unit of time at the condensation heat exchanger.

2. The device according to claim 1, wherein the control apparatus is programmed to keep the pressure (p.sub.anwend) in the application cryostat approximately constant during the transfer of liquid helium into the application cryostat.

3. The device according to claim 1, wherein the control apparatus has an ambient pressure sensor for measuring the ambient atmospheric pressure (p.sub.atm), and is programmed to keep the pressure (p.sub.anwend) in the application cryostat above an ambient atmospheric pressure (p.sub.atm) at all times.

4. The device according to claim 1, wherein the apparatus for generating a pressure difference comprises a control valve in a helium gas line, with the helium gas line comprising a first helium gas line end connected to the storage dewar, and a second helium gas line end for connection to a helium gas reservoir.

5. The device according to claim 1, wherein the apparatus for generating a pressure difference comprises an electric heater in the storage dewar.

6. The device according to claim 1, wherein the device further comprises a closed cooling circuit for a coolant, comprising a feed line from a 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, the cryocooler being designed to cool the coolant directly or indirectly by means of the cold head.

7. The device according to claim 6, wherein the feed line, the return line, and the transfer line extend from the storage dewar as a line bundle in a common insulation vacuum.

8. The device according to claim 1, wherein the device further comprises a helium gas reservoir which is connected to the storage dewar via a helium gas line.

9. The device according to claim 1, wherein a cold head of the cryocooler and a helium vessel of the storage dewar are arranged in a common storage cryostat, the cold head of the cryocooler being designed to liquefy helium gas into liquid helium in the storage dewar.

10. The device according to claim 9, wherein the helium vessel and the cold head are designed to provide a liquid supercooled helium volume in the helium vessel.

11. The device according to claim 10, wherein a thermal barrier is arranged in the helium vessel, by means of which thermal barrier the supercooled helium volume below the thermal barrier is separated from a liquid saturated helium volume above the thermal barrier.

12. An application system comprising a device according to claim 1 and an application cryostat, wherein the transfer line and the condensation heat exchanger are inserted into the application cryostat, and wherein the application cryostat contains a superconducting magnet coil, and an NMR probe head projects into a magnet bore of the magnet coil.

13. A method for transferring liquid helium into an application cryostat using a device according to claim 1, wherein a transfer line for liquid helium is connected by a first transfer line end to a storage dewar containing liquid helium, and is inserted into the application cryostat by a second transfer line end, wherein liquid helium is transferred from the storage dewar via the transfer line into the application cryostat, wherein a flow of liquid helium through the transfer line is adjusted by means of an apparatus for changing a pressure difference between the storage dewar and the application cryostat, wherein a condensation heat exchanger, which is cooled by means of a cryocooler, is inserted into the application cryostat and liquefies gaseous helium to liquid helium in the application cryostat, and wherein a control apparatus measures a pressure (p.sub.anwend) in the application cryostat and actuates the apparatus for changing a pressure difference such that a volume of liquid helium transferred through the transfer line per unit of time is approximately equal to the change in volume of the helium which condenses from helium gas to liquid helium per unit of time at the condensation heat exchanger.

14. The method according to claim 13, wherein the control apparatus keeps the pressure (p.sub.anwend) in the application cryostat approximately constant during the transfer of liquid helium into the application cryostat.

15. The method according to claim 13, wherein no outflow of gaseous helium from the application cryostat occurs during the transfer of liquid helium.

16. The method according to claim 13, wherein the control apparatus measures an ambient atmospheric pressure (p.sub.atm) and the control apparatus keeps the pressure (p.sub.anwend) in the application cryostat above the ambient atmospheric pressure (p.sub.atm) at all times.

17. The method according to claim 13, wherein the control apparatus, as the apparatus for changing a pressure difference, actuates a control valve in a helium gas line which leads from a helium gas reservoir to the storage dewar, and/or actuates an electric heater in the storage dewar.

18. The method according to claim 13, wherein a coolant is guided in a closed cooling circuit through a feed line from a cold head of the cryocooler to the condensation heat exchanger and through a return line back to the cooling head of the cryocooler, the cold head of the cryocooler cooling the coolant directly or indirectly.

19. The method according to claim 18, wherein the transfer line between the storage dewar and the application cryostat is thermally coupled to the feed line, and before the start of a transfer of liquid helium through the transfer line, the transfer line is first pre-cooled by means of the coolant in the feed line.

20. The method according to claim 13, wherein a cold head of the cryocooler and a helium vessel of the storage dewar are arranged in a common storage cryostat, and before the start of the transfer of liquid helium, gaseous helium from a helium gas reservoir is fed to the storage dewar and gaseous helium is condensed into liquid helium in the storage dewar by means of the cold head.

21. The method according to claim 13, wherein a liquid supercooled helium volume is provided in a helium vessel of the storage dewar, and the liquid helium transferred through the transfer line is drawn from the liquid supercooled helium volume.

22. The method according to claim 13, wherein the application cryostat is alternately used in normal operation for an application and is filled with liquid helium in a refill operation, wherein the condensation heat exchanger and the second transfer line end are not inserted into the application cryostat during normal operation, and are inserted into the application cryostat during a refill operation, and wherein a superconducting magnet coil is arranged in the application cryostat, and during normal operation as an application with an NMR probe head, NMR measurements are carried out on samples which are arranged in a magnet bore of the superconducting magnet coil.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0081] FIG. 1 shows a schematic view of a first embodiment of an application system according to the invention, comprising a device according to the invention for transferring liquid helium and also an application cryostat, a cryocooler having a separate cryocooler cryostat.

[0082] FIG. 2 shows a line bundle consisting of a transfer line, feed line, and return line for the invention.

[0083] FIG. 3 shows a schematic view of a second embodiment of an application system according to the invention, comprising a device according to the invention for transferring liquid helium as well as an application cryostat, a cold head of the cryocooler and a helium vessel of the storage dewar being arranged in a common storage cryostat.

[0084] FIG. 4 shows a design for the storage dewar for a device according to the invention for transferring liquid helium, having a thermal barrier in the helium vessel of the storage dewar.

DETAILED DESCRIPTION

[0085] FIG. 1 schematically shows a first embodiment of an application system 100 according to the invention, comprising a device 101 for transferring liquid helium and an application cryostat 102, during a transfer of liquid helium.

[0086] The device 101 comprises a storage dewar 1 having a helium vessel 2 which is thermally decoupled from the environment 4 by means of an insulation vacuum 3. Here, room temperature (20 C.) and an atmospheric pressure p.sub.atm of 1.00 bar prevail in the environment 4. One or more radiation shields or multi-layer superinsulation can be provided in the insulation vacuum 3 (not shown in detail).

[0087] In the helium vessel 2, liquid helium 5 is stored in a lower region, and gaseous helium 6 is above the liquid helium 5 in an upper region. In the shown embodiment, the liquid helium 5 and the gaseous helium 6 in the storage dewar 1 have a temperature of approximately 4.2 K, and in this case, a pressure p.sub.vorrat of approx. 1.08 bar prevails in the storage dewar 1. In the shown embodiment, an electric heater 7 is also arranged in the storage dewar 1, which can be controlled by means of an electronic control apparatus 8.

[0088] A transfer line 9 for liquid helium projects into the storage dewar 1. A first transfer line end 9a opens into the liquid helium 5 near the base of the helium vessel 2. The transfer line 9 is provided with vacuum insulation 23. The storage dewar 1 is designed to be transportable, in this case by means of rollers 37 (transportation dewar).

[0089] A second transfer line end 9b of the transfer line 9 is inserted into the application cryostat 102 through an access pipe 15a and opens into a helium tank 10 of the application cryostat 102. The helium tank 10 is thermally insulated from the environment 4 by an insulation vacuum 13. One or more radiation shields can be provided in the insulation vacuum 13 (not shown in detail).

[0090] In the helium tank 10 of the application cryostat 102, liquid helium 11 is located in a lower region, and gaseous helium 12 is located in an upper region. In the shown embodiment, the liquid helium 11 and the gaseous helium 12 in the helium tank 10 in each case have a temperature of approximately 4.2 K, and a pressure p.sub.anwend of approx. 1.03 bar prevails in the helium tank.

[0091] The pressures (for the transfer of liquid helium through the transfer line 9) are generally p.sub.atm<p.sub.anwend<p.sub.vorrat.

[0092] Since the pressure p.sub.vorrat prevailing in the storage dewar 1 is somewhat higher than the pressure p.sub.anwend prevailing in the application cryostat 102, liquid helium 5 is pushed out of the storage dewar 1 through the transfer line 9 and into the application cryostat 102; cf. the liquid helium 14 flowing out at the second transfer line end 9b. Driven by a pressure difference between the storage dewar 1 and the application cryostat 102, liquid helium is therefore transferred from the storage dewar 1 into the application cryostat 102.

[0093] Not only the transfer line 9, but also a cooling rod 16 extend through the access pipe 15a into the application cryostat 102; the access pipe 15a is therefore also referred to as the common access pipe 15a. A condensation heat exchanger 17 is formed at a lower end of the cooling rod 16. The condensation heat exchanger 17 continuously liquefies gaseous helium 12 in the helium tank 10 during the transfer of liquid helium.

[0094] The condensation heat exchanger 17 is cooled by means of a coolant which circulates in a cooling circuit 19. The cooling circuit 19 extends with a feed line 20 from a cold head heat exchanger 25a on a cold head 25 to the condensation heat exchanger 17, and with a return line 21 from the condensation heat exchanger 17 back to the cold head heat exchanger 25a on the cold head 25. End regions of the feed line 20 and return line 21 close to the condensation heat exchanger 17 extend in the cooling rod 16. The feed line 20 and the return line 21 are surrounded by vacuum insulation 22. The coolant circuit 19 is driven by a compressor 28, a compressor feed line 26 extending from the compressor to the cold head heat exchanger 25a or to the feed line 20, and a compressor return line 27 extending 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, in particular, be helium. The cold head 25 and the compressor 28 form the cryocooler 29 of the device 101.

[0095] The compressor 28 in this case operates the cold head 25, separate cold head lines 35, 36 being installed between the compressor 28 and the cold head 25, and also ensures the coolant circulation in the cooling circuit 19 of the condensation heat exchanger 17. This is particularly cost-effective. The cooling circuit 19 can be activated and deactivated separately by means of the cooling circuit valve 19a, in this case arranged in the compressor feed line 26.

[0096] In this case, the cold head 25 and the cold head heat exchanger 25a are arranged in a cryocooler cryostat 30 which is separate from the application cryostat 102 and from the storage dewar 1. The cryocooler 29 can, in particular, be constructed as a Gifford-McMahon refrigerator or pulse tube refrigerator. The cooling of the cooling rod 16 or the condensation heat exchanger 17 is installed with a cryocooler 29 or a refrigeration machine outside the application cryostat 102.

[0097] The control apparatus 8 monitors the pressure p.sub.anwend in the application cryostat 102 using a pressure sensor 18, which is in this case arranged on a second access pipe 15b of the application cryostat 102. Furthermore, the second access pipe 15b is free and can in particular serve effectively as an emergency outlet for helium gas (e.g., in case of quenching). The pressure sensor 18 is connected to the control apparatus 8 at a measuring input 18a. Furthermore, in the shown embodiment, the control apparatus 8 monitors the pressure p.sub.atm in the environment 4 using a pressure sensor 8a integrated in the control apparatus 8.

[0098] In the shown embodiment, the control apparatus 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 thus also the pressure difference between the storage dewar 1 and the application cryostat 102 can be changed via the heating capacity of the heater 7. The heater 7 thus constitutes an apparatus 31 for generating a pressure difference between the storage dewar 1 and the application cryostat 102. The heater 7 is connected to a control output 31a of the control apparatus 8.

[0099] The heating capacity is adjusted and readjusted by the control apparatus 8 such that the pressure p.sub.anwend in the application cryostat 102 is regulated to a specified target value p.sub.anwend.sup.soll. The specified target value p.sub.anwend.sup.soll is 1.03 bar in this case and is chosen such that it is slightly above (in this case by 0.03 bar) the pressure p.sub.atm in the environment 4. In the simplest case, the specified target value p.sub.anwend.sup.soll is constant throughout the entire duration of the liquid helium transfer. Should the weather, and thus the air pressure in the environment 4 or the pressure p.sub.atm monitored by means of the sensor 8a change significantly during the transfer, the specified target value p.sub.anwend.sup.soll can also be changed if required in order for a desired difference (minimum difference and/or maximum difference) to remain between the pressure p.sub.anwend in the application cryostat 102 and the pressure p.sub.atm in the environment, in particular in order to avoid sucking ambient air into the application cryostat 102 and/or to prevent the triggering of overpressure safety devices (pressure relief valves, rupture disks, not shown in detail) in the application cryostat 102.

[0100] If, during the introduction of liquid helium into the application cryostat 102 through the transfer line 9, the pressure p.sub.anwend remains substantially at p.sub.anwend.sup.soll, then the volume of liquid helium introduced per unit of time dV(LHe trans)/dt substantially corresponds to the change in volume of the helium dV(He.sub.cond)/dt which condenses per unit of time in the condensation heat exchanger 17 (state of equilibrium). In this case, no gaseous helium escapes from the application cryostat 102 during the introduction of the liquid helium into the application cryostat 102.

[0101] If the pressure p.sub.anwend falls below p.sub.anwend.sup.soll, the control apparatus 8 increases the heating capacity of the heater 7 such that additional helium is evaporated in the storage dewar 1, the pressure p.sub.vorrat in the storage dewar increases, the flow of liquid helium through the transfer line 9 is increased, and the gas pressure in the application cryostat 102 increases. If the pressure p.sub.anwend rises above p.sub.anwend.sup.soll, the control apparatus 8 reduces the heating capacity of the heater 7 or switches it off completely, such that less or no helium is evaporated in the storage dewar 1, the pressure in the storage dewar 1 drops (also as a result of the subsequent discharge of liquid helium 5), the flow of liquid helium through the transfer line 9 is reduced, and the gas pressure in the application cryostat 102 drops.

[0102] In the shown embodiment, the cooling capacity of the cryocooler 29 is kept constant during the transfer of liquid helium.

[0103] In the shown embodiment, a superconducting magnet coil 32 (also referred to as magnet for short) is arranged in the application cryostat 102. In normal operation, an NMR probe head 33 projects into a room temperature bore (not shown in detail) of the application cryostat 102, such that a measurement sample 34 can be subjected to an NMR measurement in the magnetic field of the magnet 32 in the magnet bore thereof. It should be noted that, in normal operation, the transfer line 9 and the cooling rod 16 are pulled out of the access pipe 15a, and only in refill operation are the transfer line 9 and the cooling rod 16 inserted into the access pipe 15a (the latter being shown in FIG. 1).

[0104] Fill level sensors can also be provided in the application cryostat 102 and in the storage dewar 1, which sensors are read by the control apparatus 8 (not shown in more detail).

[0105] FIG. 2 illustrates a rear portion of a line bundle 40 which can be used within the scope of the invention on a device according to the invention for the transfer of liquid helium (see also FIG. 3).

[0106] The feed line 20 and the return line 21 of the cooling circuit for the condensation heat exchanger 17 as well as the transfer line 9 for the liquid helium 14, which flows out into the application cryostat at the second transfer line end 9b, extend in the line bundle 40. The line bundle 40 forms a common insulation vacuum 41 for the lines 9, 20, 21. A plurality of coupling bridges 42 consisting of material having good thermal conductivity, for example high-purity copper, are installed between the transfer line 9 and the feed line 20, by means of which coupling bridges a thermal coupling is established between the feed line 20 and the transfer line 9. This makes it possible, in particular, to pre-cool the transfer line 9 by means of the feed line 20 before the start of the transfer of liquid helium.

[0107] In this case, the vertically extending part of the line bundle 40 forms an easy-to-handle cooling rod 16. It should be noted that the line bundle beyond the cooling rod is preferably designed to be flexible. The line bundle can have so-called superinsulation. In addition, spacers having low thermal conductivity are provided to keep the lines at a distance from the outer insulation sheath.

[0108] FIG. 3 schematically shows a second embodiment of an application system 100 according to the invention, comprising a device 101 for transferring liquid helium and an application cryostat 102. The application system 100 largely corresponds to the application system of FIG. 1, and therefore only the essential differences are explained below. For the sake of simplicity, the compressor and parts of the lines carrying the coolant are not shown in detail in FIG. 3.

[0109] In the embodiment of FIG. 3, a common storage cryostat 50 is installed, in which both the cold head 25 and the helium vessel 2 are arranged. The cold head 25 is arranged in a receiving region 51, which is open towards the helium vessel 2, such that the gaseous helium 6 is distributed in the upper part of the helium vessel 2 and in the receiving region 51. The storage cryostat 50 in this case has a radiation shield 58 which is thermally coupled to a warmer cooling stage of the cold head 25 (coupling not shown in detail).

[0110] A helium gas line 54 leads from a helium gas reservoir 52, which is designed as a compressed helium gas reservoir 53, into the storage dewar 1. A first helium gas line end 54a projects into the upper part of the helium vessel 2, and a 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 means of rollers (not shown in detail).

[0111] Near the second helium gas line end 54b, the helium gas line 54 has a control valve 55 which can be automatically actuated by the control apparatus 8, in this case by means of an electric motor (not shown in detail).

[0112] The helium gas line 54 leads through the receiving region 51 past the cold head 25 and is thermally coupled to the two cold stages of the cold head 25 by means of a helium supply heat exchanger 56. Helium gas 6a flowing into the storage dewar 1 through the helium gas line 54 (or helium gas 6 already present in the storage dewar 1) can be liquefied by means of the cold head 25.

[0113] It should be noted that the helium gas 6a should be purified before liquefaction, for example by means of a cold trap (not shown in detail); for example, the device described in DE 10 2021 205 423 A1 can be used in this case.

[0114] In the shown embodiment, a pressure sensor 57 is also provided, by means of which a pressure p.sub.vorrat in the storage dewar 1 is measured and monitored by the control apparatus 8; the control apparatus 8 ensures that p.sub.vorrat is above p.sub.atm at all times (see also below), which prevents ambient air from being sucked into the storage dewar 1. In addition, the control apparatus 8 also monitors the pressure p.sub.anwend in the application cryostat 102 by means of the pressure sensor 18. Furthermore, the control apparatus 8 can actuate the heater 7 in the storage dewar 1.

[0115] The control apparatus 8 can use the heater 7 (see above) or also the control valve 55 in each case as the apparatus 31 for generating a pressure difference between the storage dewar 1 and the application cryostat 102. By increasing the opening cross-section of the control valve 55, additional helium (helium gas and/or liquefied helium) can be introduced into the storage dewar 1, which increases the pressure p.sub.vorrat in the storage dewar 1. By reducing the opening cross-section of the control valve 55 or closing the control valve 55 (with subsequent discharge of liquid helium through the transfer line 9 into the application cryostat), the pressure p.sub.vorrat in the storage dewar 1 can be lowered.

[0116] The feed line 20, the return line 21, and the transfer line 9 extend in this case between the storage dewar 1 and the application cryostat 102 as a line bundle 40 in a common vacuum insulation 41 (cf. FIG. 2). In addition, the transfer line 9 has a branch 60 to a purge valve 59 near its first transfer line end 9a, the branch 60 being located in this case within the common storage cryostat 50. The purge valve 59 can be used to purge the transfer line 9 between the second transfer line end 9b and the branch 60 with helium gas 12 (which originates from the application cryostat 102), which takes place before the start of the transfer of liquid helium through the transfer line 9; it should be noted that p.sub.anwend>p.sub.atm for this purpose. In order to completely eliminate helium losses, the outlet of the purge valve 59 can be connected to a helium recovery system; the air that is purged into the helium recovery system can be separated in an upstream cold trap during the reliquefaction of the helium from the recovery system (helium recovery system and cold trap not shown in detail).

Procedure According to the Invention

[0117] In the following, the procedure of refilling liquid helium from the storage dewar 1 into the application cryostat 102 within the scope of a method according to the invention will be explained by way of example. The exemplary procedure can take place, in particular, in an application system 100 as shown in FIG. 3. Steps 2 to 6 can be assigned to transfer operation, and step 7 to normal operation of the application cryostat 102. Step 1 can take place in parallel with normal operation or as part of transfer operation.

[0118] Step 1) Helium gas is fed from the compressed helium gas reservoir 53 via the helium line 54 to the storage dewar 1, said helium gas being liquefied by the cold head 25. Liquid helium 5 collects in the helium vessel 2.

[0119] Step 2) As soon as the liquefaction is completed (e.g., because the helium vessel 2 is full or the compressed helium gas reservoir 53 is empty), it is possible to prepare for the transfer of the liquid helium 5. To do this, the user first inserts the cooling rod 16 with the transfer line 9 and the condensation heat exchanger 17 into the application cryostat 102 into the access pipe 15a.

[0120] Step 3) The purge valve 59 is opened, and helium gas from the application cryostat 102 pushes air through the purge valve 59 out of the transfer line 9. When the air present has escaped, the purge valve 59 is closed.

[0121] Step 4) Then, the cooling circuit valve (ref. sign 19a in FIG. 1) is opened for the coolant, whereby some of the gas stream supplied by the compressor (ref. sign 28 in FIG. 1) is diverted, and the circulation of the coolant in the cooling circuit 19 or rather through the condensation heat exchanger 17 is activated. Since the feed line 20 is thermally connected to the transfer line 9, the transfer line 9 cools down in the process.

[0122] Once the condensation heat exchanger 17 and the transfer line 9 are cold, the transfer of liquid helium (helium transfer) is started. This can either happen automatically when the pressure in the helium tank 10 of the application cryostat 102 drops due to the onset of condensation, or the pressure in the storage dewar 1 is actively increased, e.g., by means of the heater 7 or by means of supplied helium gas 6a from the compressed helium gas reservoir 53.

[0123] Step 5) The helium transfer is then controlled by the control apparatus 8 such that the transfer rate of the liquid helium through the transfer line 9 corresponds to the rate at which gaseous helium 12 condenses in the application cryostat 102, such that no helium gas 12 escapes from the application cryostat 102 during the helium transfer. Accordingly, the helium transfer can be carried out according to the invention such that no storage balloon is required for carrying out the helium transfer without losses.

[0124] Step 6) Once the helium transfer is completed (e.g., because the application 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 with the transfer line 9 and the condensation heat exchanger 17 from the application cryostat 102.

[0125] Step 7) Then, using the application cryostat 102, and in particular the NMR magnet (ref. sign 32 in FIG. 1) contained in the application cryostat 102, NMR measurements can be continued only a few hours after the start of the helium transfer. Compared to a conventional helium transfer with escape of gaseous helium through one of the access pipes 15a, 15b, the stabilization of the application cryostat 102 within the scope of the invention takes place significantly faster, since no large quantities of cold gas have escaped through the access pipes (suspension pipes) 15a, 15b (the latter usually leads to a significant cooling of the access pipes during a conventional helium transfer, and during the return to thermal equilibrium, the magnetic field is unstable).

[0126] FIG. 4 shows an alternative design of the storage dewar 1 for the invention, which can be used, for example, in the embodiment of the application system of FIG. 3. Only the main differences with respect to the design of FIG. 3 will be explained.

[0127] In the design shown in FIG. 4, a thermal barrier 70 is arranged in the helium vessel 2 of the storage dewar 1. The thermal barrier 70 is pressure-permeable (i.e., liquid helium can flow through), but thermally insulating. The thermal barrier 70 can be designed, in particular, as described in DE 40 39 365 A1.

[0128] The cold head 25 is arranged in a closed vacuum vessel 71, the vacuum vessel 71 extending beyond (below) the thermal barrier 70. The lowest (coldest) cooling stage 73 of the cold head 25 can thus cool the liquid helium 74 below the thermal barrier 70. Said liquid helium 74 below the thermal barrier 70 is supercooled and has a temperature of about 3.7 K. The supercooled liquid helium 74 is also referred to as a whole as a supercooled liquid helium volume 74. There is saturated liquid helium 75 above the thermal barrier 70 that is at a temperature of approximately 4.2 K; the saturated liquid helium 75 is also referred to as a whole as the saturated liquid helium volume 75. The gaseous helium 6 thereabove also has a temperature of about 4.2 K and is at the pressure p.sub.vorrat of approx. 1.08 bar.

[0129] The transfer line (pipe) 9 extends deep into the region of the supercooled liquid helium 74 until just before the base of the helium vessel 2. In the portion in which the transfer line 9 leads through the region of the saturated helium volume 75, the transfer line 9 is thermally insulated from the saturated helium volume 75 (not shown in detail). Accordingly, during the helium transfer, supercooled liquid helium 74 is conveyed through the transfer line 9 into the application cryostat.

[0130] The supercooled liquid helium 74 that is conveyed into the application cryostat can extract heat energy from the application cryostat when the supercooled liquid helium warms up again to 4.2 K. Less cooling capacity must then be applied to the condensation heat exchanger in order to condense gaseous helium in the condensation heat exchanger. For example, if 100 l of liquid helium (12.5 kg) with a temperature of 3.7 K are transferred, approximately 26.3 kJ of additional cooling 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-intensive the provision of supercooled liquid helium 74 becomes.

[0131] The feed line 20 of the cooling circuit for the condensation heat exchanger in the application cryostat extends through the region of the supercooled liquid helium 74. Accordingly, the coolant can be used to transport heat energy from the condensation heat exchanger in a particularly efficient manner.

[0132] It should be noted that supercooled helium for the invention can also result, for example, by expanding helium in a throttle at a low pressure (not shown in detail).

[0133] In summary, the invention relates to a device (101) for transferring liquid helium (14) into an application cryostat (102), comprising [0134] a storage dewar (1), [0135] a transfer line (9) comprising a first transfer line end (9a) in the storage dewar (1) and a second transfer line end (9b) for insertion into an application cryostat (102), [0136] an apparatus (31) for generating a pressure difference between the storage dewar (1) and the application cryostat (102), characterized by [0137] a condensation heat exchanger (17) for condensing helium gas (12) to liquid helium (11), for insertion into the application cryostat (102), [0138] a cryocooler (29) for cooling the condensation heat exchanger (17), and [0139] a control apparatus (8), having a measuring input (18a) for a pressure sensor (18) for measuring the gas pressure in the application cryostat (102) and a control output (31a) for the apparatus (31) for generating a pressure difference, the control apparatus (8) being programmed to control the apparatus (31) for generating a pressure difference such that a volume of liquid helium (14) transferred through the transfer line (9) per unit of time is approximately equal to the change in volume of the helium which condenses from helium gas (12) to liquid helium (11) per unit of time at the condensation heat exchanger (17). The device makes it easy to minimize helium losses during the transfer of liquid helium.

LIST OF REFERENCE SIGNS

[0140] 1 Storage dewar [0141] 2 Helium vessel [0142] 3 Insulation vacuum (at the storage dewar) [0143] 4 Environment/surrounding atmosphere [0144] 5 Liquid helium (in the storage dewar) [0145] 6 Gaseous helium (in the storage dewar) [0146] 6a Gaseous helium (from the helium gas reservoir) [0147] 7 Electric heater (in the storage dewar) [0148] 8 Electronic control apparatus [0149] 8a Pressure sensor for the surrounding atmosphere [0150] 9 Transfer line for liquid helium [0151] 9a First transfer line end (inserted into the storage dewar) [0152] 9b Second transfer line end (inserted into the application cryostat) [0153] 10 Helium tank [0154] 11 Liquid helium (in the application cryostat) [0155] 12 Gaseous helium (in the application cryostat) [0156] 13 Insulation vacuum (at the application cryostat) [0157] 14 (Outflowing/transferred) liquid helium [0158] 15a First/common access pipe [0159] 15b Second access pipe [0160] 16 Cooling rod [0161] 17 Condensation heat exchanger [0162] 18 Pressure sensor for application cryostat [0163] 18a Measuring input (for pressure sensor 18) [0164] 19 Cooling circuit [0165] 19a Cooling circuit valve [0166] 20 Feed line for coolant [0167] 21 Return line for coolant [0168] 22 Vacuum insulation (feed line and return line) [0169] 23 Vacuum insulation (transfer line) [0170] 25 Cold head [0171] 25a Cold head heat exchanger (for cooling circuit) [0172] 26 Compressor feed line [0173] 27 Compressor return line [0174] 28 Compressor [0175] 29 Cryocooler [0176] 30 Cryocooler cryostat [0177] 31 Apparatus for generating a pressure difference [0178] 31a Control output (for apparatus 31) [0179] 32 Superconducting magnet coil/magnet [0180] 33 NMR probe head [0181] 34 Measurement sample [0182] 35, 36 Cold head lines [0183] 37 Rollers [0184] 40 Line bundle [0185] 41 Common insulation vacuum [0186] 42 Coupling bridges [0187] 50 Common storage cryostat [0188] 51 Receiving region [0189] 52 Helium gas reservoir [0190] 53 Compressed helium gas reservoir [0191] 54 Helium gas line [0192] 54a First helium gas line end [0193] 54b Second helium gas line end [0194] 55 Control valve [0195] 56 Helium supply heat exchanger [0196] 57 Pressure sensor for storage dewar [0197] 58 Radiation shield [0198] 59 Purge valve [0199] 60 Branch for purge valve [0200] 70 Thermal barrier [0201] 71 Vacuum vessel [0202] 73 Lowest/coldest cooling stage [0203] 74 Supercooled liquid helium/helium volume [0204] 75 Saturated liquid helium/helium volume [0205] 100 Application system [0206] 101 Device for transferring liquid helium [0207] 102 Application cryostat