DE102010028750B4 - Low-loss cryostat arrangement - Google Patents

Abstract

A cryostat arrangement (10) with at least one cryostat (11) which has at least one first chamber (1) with supercooled helium at a temperature of less than 4 K and at least one further chamber (2) with liquid helium at a temperature of contains about 4.2 K, a Joule-Thomson valve (3) being arranged in the first chamber, the first being separated from the further chamber by a heat-insulating barrier (4), with helium from the first or further chamber expands via the Joule-Thomson valve into a pump-out line (13) which is in thermal contact with the helium of the first chamber and subcooled it, and wherein the pump-out line is in direct or indirect thermal contact with the further chamber in its further course and is then connected to the input of a pump (14), is characterized in that the output of the pump and / or an output for evaporating helium via at least one of the cryostats a refrigerant line (15) is fluidically connected to the further chamber, and that the refrigerant line has a branching device (16) which guides a partial flow of the helium in the refrigerant line back into the further chamber. This reduces the helium consumption and thus also the operating costs, with the pressure in the first chamber remaining constant.

Description

The invention relates to a cryostat arrangement having at least one cryostat which has at least one first chamber filled with supercooled liquid helium at a temperature of less than 4 K, and at least one further chamber located above the first chamber, which i. W. At atmospheric pressure contained liquid helium having a temperature of about 4.2 K, wherein the pressure level in the first chamber is equalized to the pressure level in the other chamber, wherein in the first chamber, a Joule-Thomson valve is arranged, wherein the first from the further chamber is separated by a heat-insulating barrier, wherein helium from the first or the other chamber via the Joule-Thomson valve expands into a Abpumpleitung which is in thermal contact with the helium of the first chamber and this undercooled, and wherein the Abpumpleitung in its further course is directly or indirectly in thermal contact with the other chamber and is then connected to the input of a pump.

Such a cryostat arrangement is known from, for example DE 40 39 365 C2 ,

A similar Kryostatenanordnung with the features mentioned is also in the DE 10 2004 012 416 A1 or in the US 2006/0064989 A1 described.

In contrast, the DE 10 2004 060 832 B3 a cryostat assembly in which a Joule-Thomson valve located in the first chamber does not expand helium into a pumping line, but directly into the first chamber, such as in the first chamber 4 can be seen. In order for the Joule-Thomson valve to function properly, there is a considerable negative pressure in the first chamber opposite the further chamber arranged above it.

Magnetic systems for nuclear magnetic resonance apparatus are subject to the highest demands with regard to the achievable magnetic field strengths and their homogeneity.

At a resonance frequency of 600 MHz, a field strength of 14.1 T must be achieved. These high magnetic field intensities can technically best be achieved by superconducting magnet coils having a superconducting short-circuit switch.

The superconducting magnetic coils require energy only during the charging phase and can generate a high magnetic field for a long time in short-circuit operation after removal of the power supply line without further energy input. The cooldowns to reach half the original field strength are in the order of 5000 years for modern superconducting magnets. This means that virtually no change in the magnetic field strength occurs in short-circuit operation over the order of hours and days.

A high temporal stability is required especially for long-term measurements, especially in so-called 2D and 3D measurements. This can only be realized in superconducting short-circuit operation. In general, the magnetic coils are charged once and then produce a homogenous magnetic field for years with the supply lines disconnected. In routine operation typical helium service lives of the magnet system are several months, if it is a "low-loss" cryostat.

In order to obtain higher homogeneous magnetic fields and more stable superconductivity, a publication by Williams et al. in "Rev. Sci. Instrum. "52 (5), May 1981, American Institute of Physics, 649-656, proposed operating the superconducting magnet coil at a lower operating temperature than the normal temperature of liquid helium (T = 4.2K). This lower temperature is usually generated by pumping off the liquid helium.

In the cited document, a cryostat is proposed, which has two nested, concentric helium tanks. The outer tank contains liquid helium at T = 4.2 K under normal pressure (1 bar).

From this outer tank, a liquid helium filling line leads to the inner tank so that the liquid helium can be overfilled from the outer to the inner tank. In the inner tank, in which the superconducting coil is located, the helium is pumped off to a pressure of 40 mbar and cooled down to a temperature of 2.3 K.

A major disadvantage of this arrangement is that the supercooled helium in the inner tank is under negative pressure and therefore the electrical leads, in particular for the charging of the superconducting magnet coil must be passed through the cold vacuum system. In particular, sealing problems, but also insulation problems due to the heat input into the cold vacuum reservoir via the feed lines introduced from an environment with room temperature and atmospheric pressure, inevitably lead to greatly reduced helium service lives.

Another disadvantage is that no measures are provided which require the high, for the operation of these apparatuses Helium consumption could be reduced, so that on the one hand enormous operating costs incurred, on the other hand only relatively short service life between the intervals for refilling liquid helium can be achieved if the known equipment does not have to be permanently filled with fresh helium anyway in operation.

DE 40 39 365 C2 proposes a system in which two temperature ranges are provided in a first and a further chamber, wherein in the first chamber liquid helium, which flows from the other chamber at atmospheric pressure and a temperature of T = 4.2 K, by pumping over a throttle is cooled in a nonequilibrium state.

However, the pressure level in the first chamber is equalized to the pressure level in the other chamber. Since in the first chamber with the supercooled liquid helium prevails substantially atmospheric pressure, the problem of a vacuum feedthrough for the electrical leads to the superconducting solenoid does not occur.

Due to the vertical arrangement of the first chamber under the other chamber, the gravitation counteracts a backflow of denser and therefore heavier undercooled helium from the lower cold reservoir into the upper warmer reservoir. In this way, defined flow conditions are ensured and there is no undesirable mixing of cold with warm helium in the upper reservoir instead.

A heat-insulating barrier not only prevents convection between the two chambers, but also largely heat transfer from one chamber to the other via heat conduction.

The barrier consists of two separated by a vacuum plates made of a poor thermal conductivity material such. As stainless steel or plastic. The vacuum insulation prevents heat exchange between the upper and lower reservoirs.

In order to avoid unwanted cooling of the helium in the other chamber, an electric heating element is usually arranged in addition to the heat insulation in the other chamber.

The vacuum is part of the unitary vacuum part of the cryostat, so the barrier does not have to be evacuated separately. In contrast to continuous tank systems, the measures bring about a drastic reduction of the heat entering from outside and are the prerequisite for a cryostat with low operating losses ("low loss").

The electrical leads to the magnet system as well as the supply lines for liquid helium are carried out in the pipe which is in each case guided through the tower or towers. Through this hollow tube construction creates a dual cryostat, both at 4.2 K under atmospheric pressure and in the vacuum operation in the range of z. B. 1.8 K to 2.3 K can be used.

In both modes of operation of the cryostat has low-loss properties, since regardless of the respective proportion of the pumped or evaporating helium stream, the total, in both gas streams together existing enthalpy is largely released to the shield system of the cryostat.

Since the cryostat contains two chambers of helium at two different temperature levels, there are two exhaust streams at different pressure levels. An exhaust gas flow is formed by the helium evaporating from the further chamber at atmospheric pressure, the second exhaust gas flow is formed by the helium pumped off via the refrigerator at a pressure of about 40 mbar.

Depending on the operating state of the cryostat, the two exhaust gas streams are different in strength, wherein the exhaust gas flow from the other chamber may possibly come to a complete standstill. For a low-loss cryostat, it is essential that the enthalpy contained in the exhaust gas is utilized as completely as possible. For this purpose, it is necessary to distribute the two exhaust gas streams, regardless of their strength, evenly on the various towers and the associated shields.

Object of the invention

In contrast, the object of the present invention is to further reduce helium consumption and thus also the operating costs, wherein the pressure in the first chamber should remain as constant as possible.

Solution of the task:

The object of the invention is achieved with the features of patent claim 1.

Advantageous embodiments thereof are specified in the further claims.

Brief description of the invention

This object is achieved in that the output of the pump and / or an outlet for evaporating helium of or at least one of the cryostat via a refrigerant line is fluidly connected to the other chamber, and that the refrigerant line has a branch device, which returns a partial flow of the helium located in the refrigerant line in the further chamber.

Instead of releasing the entire pumped helium into the atmosphere as before, some of the helium is conducted into the first chamber in the cryostat arrangement according to the invention. The helium is thereby reliquefied into the refrigerant line, which is becoming increasingly colder within the cryostat. The heat energy of helium is supplied to the other chamber, whereby a heating element is unnecessary.

The helium for the re-liquefaction can come from the same cryostat, in which the partial flow is to be returned. This would be the case with only one existing cryostat. In an arrangement of a plurality of cryostat but it is also conceivable that the evaporated or pumped helium of one or more other cryostat is introduced into one of the cryostats for re-liquefaction.

Preferred embodiments of the invention

A particularly preferred embodiment is characterized in that a pressure regulating device is provided which keeps the pressure in the other chamber constant. This could be achieved by an active or passive regulated valve on the coolant line. Constant pressure is essential for a uniform temperature distribution and is especially important for highly sensitive NMR measurements.

In a further embodiment, a heating device is provided in the further chamber. Although the necessary heat supply in the other chamber can be done solely by the helium supplied to the cryostat, embodiments are conceivable in which the pressure is controlled by the evaporation rate of the helium from the other chamber.

It is advantageous if, in the abovementioned embodiments, the pressure regulating device adjusts the pressure in the further chamber to an adjustable desired pressure which is greater than or equal to the ambient pressure of the cryostat arrangement.

Alternatively, the pressure regulating device adjusts the pressure in the further chamber to a predetermined overpressure above the atmospheric pressure.

In a further embodiment, the coolant line has at least one pressure relief valve and / or at least one rupture disk. In the case of an unexpected sharp rise in pressure, this ensures a controlled reduction in pressure.

Also advantageous is an embodiment, which is characterized in that the coolant line contains a buffer tank for providing an additional volume for the flowing helium. In this way, a reserve volume is available when more helium must be supplied to the cryostat. In addition, the buffer volume represents another measure for keeping the pressure constant.

Particularly preferred is an embodiment in which the coolant line has at least one filter device for the separation of impurities in helium. Impurities entering the first chamber can be a significant heat input. In addition, solids or frozen substances can settle and constrict lines and valves or even clogged. Therefore, the helium used must be highly pure.

It is preferable if the partial flow led back into the further chamber comprises between 20% and 80%, preferably between 25% and 60%, of the total flow of helium conveyed via the pump.

In another conceivable embodiment, helium is introduced from at least one further, spatially separated cryostat into the coolant line. This embodiment is particularly advantageous when a plurality of cryostats are set up in a plant, such as a research facility. Then, for example, the evaporating helium can be passed from one cryostat into another cryostat and cooled in the manner described.

A preferred embodiment is characterized in that a superconducting magnet coil is arranged in the first chamber.

A development of this embodiment provides that the cryostat arrangement is part of an NMR, MRI or FTMS apparatus.

In a further development of the embodiment, the apparatus comprises a high-resolution high-field NMR spectrometer with a proton resonance frequency ≥ 800 MHz.

The first chamber and the further chamber can be arranged both above and next to each other.

Further advantages of the invention will become apparent from the description and the drawings. Likewise, the features mentioned above and those listed further can be used individually or in any combination. The embodiments shown and described are not to be understood as exhaustive enumeration, but rather have exemplary character for the description of the invention.

Detailed description of the invention and drawing

The invention is illustrated in the drawing and will be explained in more detail with reference to embodiments. Show it:

1 Embodiment of a cryostat arrangement according to the invention with a cryostat with supercooled helium;

2 Embodiment of a cryostat assembly according to the invention with a cryostat with subcooled helium and another helium cryostat, which are interconnected via a coolant line;

three Embodiment of a cryostat arrangement according to the invention with a cryostat with subcooled helium and another helium cryostat, which are connected to each other via a coolant line, which leads to a liquefaction;

4 Embodiment of a cryostat arrangement according to the invention with a plurality of cryostat with subcooled helium and a plurality of other cryostats with helium, which are interconnected via a coolant line;

5 Embodiment of a cryostat arrangement according to the invention with two cryostat with subcooled helium, which have a common pumping line, and another cryostat with helium, wherein a cryostat with subcooled helium and the cryostat with helium are connected to each other via a coolant line.

1 shows an embodiment of a cryostat arrangement according to the invention 10 with a cryostat 11 with supercooled helium. The cryostat 11 consists of a first chamber 1 with supercooled helium (temperature <4 K) and another chamber 2 with liquid helium (temperature approx. 4,2 K), which by a heat-insulating barrier 4 are separated from each other. In the first chamber 1 is a Joule-Thomson valve three arranged by the helium from the other chamber 2 in the pumping line 13 can expand while keeping the first chamber 1 supercooled. The helium gets out of the pumping line 13 through a pump 14 pumped off and a refrigerant line 15 fed. This comprises in the illustrated embodiment, a buffer tank 18 In order to provide the helium with an additional volume, which can serve as a pressure and / or reflux reserve. A pressure relief valve 6 with rupture disk 7 prevents excessive pressure in the refrigerant line 15 if the pressure control device 17 the branch device 16 fails or due to other circumstances can not keep the pressure constant. To impurities through the pump 14 to eliminate is in the refrigerant line 15 also a filter 5 arranged.

In 2 is another embodiment of a cryostat arrangement according to the invention 20 shown. Here, the helium of another cryostat steams 22 , which works with liquid helium (4.2 K) in a designed as a manifold refrigerant line 25 from, on the also a buffer tank 28 and a branch device 26 with pressure regulator 27 are connected. That from the further cryostat 22 evaporated helium can now partially the first cryostat 21 be supplied with supercooled helium, wherein the supercooling as in 1 represented by the expansion of helium in the Joule-Thomson valve three he follows. Also at the in 2 illustrated embodiment, the in the pumping line 23 expanded helium through a pump 24 Pumped out, but not the refrigerant line 25 supplied but released to the atmosphere. The helium consumption of the entire cryostat assembly 20 As a result, it drops from about 230 ml / h without recycling helium to about 170 ml / h.

three shows a further embodiment of a cryostat arrangement according to the invention 30 , Here, the helium of another cryostat steams 32 , which works with liquid helium (4.2 K) in a designed as a manifold refrigerant line 35 from that to an external condenser 39 leads (not explicitly shown). At the refrigerant line 35 are also a buffer tank 38 and a branch device 36 with pressure regulator 37 are connected: That from the further cryostat 32 evaporated helium can now partially the first cryostat 31 be supplied with supercooled helium. The first cryostat 31 supplied partial flow must now no longer from condenser 39 be liquefied, whereby this is relieved or can therefore be designed for a lower capacity. Also in this embodiment, the in the pumping line 33 expanded helium through a pump 34 pumped off and released to the atmosphere.

In 4 is now an embodiment of a cryostat arrangement according to the invention 40 shown in which several more cryostats 42 on a refrigerant line designed as a manifold 45 are connected. A branch device 46 with pressure regulator 47 regulates the pressure in the refrigerant line 45 and releases excess helium to the atmosphere. Part of the through the cryostat 42 evaporated helium is now the first cryostat 41 supplied and liquefied in this. Again, this is in the pumping line 43 expanded helium of the first cryostat 41 via a pump 44 delivered to the atmosphere. The total consumption of such an arrangement would thus fall from about 460 ml / h without recycling to a minimum of about 340 ml / h.

5 Finally, an embodiment of a cryostat arrangement according to the invention 50 in which another cryostat 52 via a refrigerant line 55 with a first cryostat 51 connected is. A branch device 56 with pressure regulator 57 regulates the amount of the first cryostat 51 supplied helium. The first cryostat 51 shares the pumping line 53 with another cryostat 51 ' who also works with subcooled helium. A pump 54 pumps the helium of the two cryostat 51 . 51 ' from the pumping line 53 to the atmosphere.

LIST OF REFERENCE NUMBERS

1

First Chamber (2 K He)

2

Further chamber (4.2 K he)

3

Joule-Thomson valve

4

Heat insulating barrier

5

filter

6

Pressure relief valve

7

rupture disc

10

cryostat

11

Cryostat (2K helium)

13

evacuation line

14

pump

15

Refrigerant line

16

branching device

17

Pressure control device

18

buffer tank

20

cryostat

21

First cryostat (2 K helium)

22

Another cryostat

23

evacuation line

24

pump

25

Refrigerant line

26

branching device

27

Pressure control device

28

buffer tank

30

cryostat

31

Cryostat (2K helium)

32

Cryostat (4.2 K helium)

33

evacuation line

34

pump

35

Refrigerant line

36

branching device

37

Pressure control device

38

buffer tank

39

condenser

40

cryostat

41

First cryostat (2 K helium)

42

Another cryostat

43

evacuation line

44

pump

45

Refrigerant line

46

branching device

47

Pressure control device

50

cryostat

51

First cryostat (2 K helium)

51 '

Another cryostat (2 k helium)

52

Another cryostat

53

evacuation line

54

pump

55

Refrigerant line

56

branching device

57

Pressure control device

Claims (13)

Cryostat arrangement ( 10 ; 20 ; 30 ; 40 ; 50 ), with at least one cryostat ( 11 ; 21 . 22 ; 31 . 32 ; 41 . 42 ; 51 . 51 ' . 52 ), which has at least one first chamber ( 1 ) filled with supercooled liquid helium at a temperature of less than 4 K and at least one above the first chamber ( 1 ), further chamber ( 2 ) containing atmospheric-pressure liquid helium at a temperature of 4.2 K, the pressure level in the first chamber being equalized to the pressure level in the further chamber, wherein in the first chamber ( 1 ) a Joule-Thomson valve ( three ), the first ( 1 ) from the other chamber ( 2 ) is separated by a heat-insulating barrier, with helium from the first ( 1 ) or the other chamber ( 2 ) via the Joule-Thomson valve ( three ) in a pumping line ( 13 ; 23 ; 33 ; 43 ; 53 ) expanded with the helium of the first chamber ( 1 ) is in thermal contact and this is undercooled, and wherein the pumping line ( 13 ; 23 ; 33 ; 43 ; 53 ) in its further course directly or indirectly in thermal contact with the further chamber ( 2 ) and then to the input of a pump ( 14 ; 24 ; 34 ; 44 ; 54 ), characterized in that the output of the pump ( 14 ; 24 ; 34 ; 44 ; 54 ) and / or an outlet for evaporating helium of the or at least one of the cryostats ( 11 ; 21 . 22 ; 32 ; 42 ; 52 ) via a refrigerant line ( 15 ; 25 ; 35 ; 45 ; 55 ) fluidically with the further chamber ( 2 ) and that the refrigerant line ( 15 ; 25 ; 35 ; 45 ; 55 ) a branching device ( 16 ; 26 ; 36 ; 46 ; 56 ) having a partial flow of the in the refrigerant line ( 15 ; 25 ; 35 ; 45 ; 55 ) helium in the further chamber ( 2 ). Cryostat arrangement according to claim 1, characterized in that a pressure regulating device ( 17 ; 27 ; 37 ; 47 ; 57 ) is provided, the pressure in the other chamber ( 2 ) constant. Cryostat arrangement according to claim 2, characterized in that in the further chamber ( 2 ) is provided a heater. Cryostat arrangement according to claim 2 or 3, characterized in that the pressure regulating device ( 17 ; 27 ; 37 ; 47 ; 57 ) the pressure in the further chamber ( 2 ) to an adjustable setpoint pressure that is greater than or equal to the ambient pressure of the cryostat arrangement ( 10 ; 20 ; 30 ; 40 ; 50 ). Cryostat arrangement according to claim 2 or 3, characterized in that the pressure regulating device ( 17 ; 27 ; 37 ; 47 ; 57 ) the pressure in the further chamber ( 2 ) to a predetermined pressure above the atmospheric pressure. Cryostat arrangement according to one of the preceding claims, characterized in that the refrigerant line ( 15 ; 25 ; 35 ; 45 ; 55 ) at least one pressure relief valve ( 6 ) and / or at least one rupture disc ( 7 ) having. Cryostat arrangement according to one of the preceding claims, characterized in that the refrigerant line ( 15 ; 25 ; 35 ; 45 ; 55 ) a buffer container ( 18 ; 28 ; 38 ) to provide an additional volume for the helium contained in the refrigerant line. Cryostat arrangement according to one of the preceding claims, characterized in that the refrigerant line ( 15 ; 25 ; 35 ; 45 ; 55 ) at least one filter device ( 5 ) for the separation of impurities in the flowing helium. Cryostat arrangement according to one of the preceding claims, characterized in that the in the further chamber ( 2 ) diverted partial flow between 20% and 80%, preferably between 25% and 60% of the pump ( 14 ; 24 ; 34 ; 44 ; 54 ) comprises total helium flow delivered. Cryostat arrangement according to one of the preceding claims, characterized in that helium from at least one further, spatially separated cryostat ( 22 ; 32 ; 42 ; 52 ) in the coolant line ( 15 ; 25 ; 35 ; 45 ; 55 ) is initiated. Cryostat arrangement according to one of the preceding claims, characterized in that in the first chamber ( 1 ) A superconducting magnetic coil is arranged. Cryostat arrangement according to claim 11, characterized in that the cryostat arrangement ( 10 ; 20 ; 30 ; 40 ; 50 ) Is part of an NMR, MRI or FTMS apparatus. Cryostat arrangement according to claim 12, characterized in that the apparatus comprises a high-resolution high-field NMR spectrometer with a proton resonance frequency ≥ 800 MHz.

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