CRYOSTAT ARRANGEMENT COMPRISING A NECK TUBE HAVING A SUPPORTING STRUCTURE AND AN OUTER TUBE SURROUNDING THE SUPPORTING STRUCTURE TO REDUCE THE CRYOGEN CONSUMPTION

Abstract

A cryostat arrangement (1) with a vacuum tank (2) and a cryogenic tank (3) are provided. The vacuum tank has at least one neck tube, (4) leading to the cryogenic tank, with a supporting structure (4a) and an outer tube (4b) surrounding the supporting structure. The neck tube provides a connection from the cryogenic tank to a region outside the vacuum tank to allow cryogenic fluid to flow from the cryogenic tank into a region outside the vacuum tank or vice versa. The neck tube mechanically suspends the cryogenic tank inside the vacuum tank, and parts of the neck tube form a diffusion barrier between the interior of the cryogenic tank and the interior of the vacuum tank. The neck tube can connect to other components of the cryostat arrangement in a fluid-tight manner. Heat input from the neck tubes into the cryogenic tank can be considerably reduced thereby.

Claims

1. A cryostat arrangement, comprising a vacuum tank and a cryogenic tank, which is arranged inside the vacuum tank, wherein the vacuum tank comprises at least one neck tube having a supporting structure surrounded by an outer tube, the neck tube leading to the cryogenic tank, wherein the neck tube connects an internal volume of the cryogenic tank to a region outside the vacuum tank so that cryogenic fluid can flow out of the cryogenic tank into a region outside the vacuum tank or from the region outside the vacuum tank into the cryogenic tank, wherein parts of the neck tube used to mechanically suspend the cryogenic tank inside the vacuum tank and parts of the neck tube used to construct a diffusion barrier between an interior of the cryogenic tank and an interior of the vacuum tank are arranged to be spatially separated from one another and are produced from materials which are optimized independently of one another, such that the supporting structure supports a weight of the cryogenic tank, and the outer tube is produced from a material through which the cryogenic fluid cannot diffuse, or through which essentially no cryogenic fluid can diffuse, and wherein the outer tube is configured to connect to other components of the cryostat arrangement in a fluid-tight manner.

2. The cryostat arrangement according to claim 1, wherein the supporting structure is in a form of an inner tube, and wherein the inner tube connects the internal volume of the cryogenic tank to a region outside the vacuum tank so that the cryogenic fluid from the cryogenic tank can flow into a region outside the vacuum tank or from outside the vacuum tank to flow into a region inside the cryogenic tank.

3. The cryostat arrangement according to claim 2, wherein the outer tube is in direct contact with the inner tube.

4. The cryostat arrangement according to claim 2, wherein the outer tube is at a distance from the inner tube, and a gap remains open between the inner tube and the outer tube.

5. The cryostat arrangement according to claim 4, wherein the outer tube and the inner tube are interconnected by a plurality of axially arranged, radially extending thermal bridges.

6. The cryostat arrangement according to claim 1, wherein the supporting structure is produced from plastics material that is fiber reinforced.

7. The cryostat arrangement according to claim 1, wherein the supporting structure made of plastics material comprises a metal extension at each of its two ends.

8. The cryostat arrangement according to claim 7, wherein the metal extensions each have a length of between 20 mm and 100 mm and a cross-sectional area of stress of between 50 mm.sup.2 and 500 mm.sup.2.

9. The cryostat arrangement according to claim 1, wherein the outer tube is produced from metal.

10. The cryostat arrangement according to claim 1, wherein inside an inner tube of the neck tube and/or between the supporting structure and the outer tube, baffles are installed, which absorb thermal radiation and prevent convection.

11. The cryostat arrangement according to claim 11, wherein the baffles are foldable.

12. The cryostat arrangement according to claim 2, wherein an upper end of the inner tube is closed in a fluid-tight manner in normal operation by a pressure relief valve or a rupture disk, allowing the cryogenic fluid flowing away in normal operation to flow through a gap between the inner tube and the outer tube.

13. The cryostat arrangement according to claim 1, wherein the cryostat contains a Joule-Thomson (JT) cooler, in which the cryogenic fluid is depressurized using a pump located outside the vacuum tank, and the gap between the supporting structure and the outer tube is part of a connecting line between the JT cooler and the pump.

14. The cryostat arrangement according to claim 4, wherein the gap between the inner tube and the outer tube comprises a flow restrictor at an end of the neck tube which is near the cryogenic tank.

15. The cryostat arrangement according to claim 1, wherein the outer tube comprises at least one bellows portion so that the outer tube does not absorb any axial forces.

16. The cryostat arrangement according to claim 1, wherein the neck tube is produced from a material for which: is a maximum permissible mechanical stress, and >100 MPa; is an integral of the thermal conductivity over the temperature range T between 300 K and 4 K, and <300 W/m; and wherein a ratio /> (MPa.Math.m)/W.

17. The cryostat arrangement according to claim 1, wherein an integral leakage rate out of the cryogenic tank into the vacuum tank is less than 10.sup.6 mbar.Math.l/s.

18. The cryostat arrangement according to claim 2, wherein the outer tube is in thermal contact with the inner tube.

19. The cryostat arrangement according to claim 6, wherein the fiber-reinforced plastics material is G10.

20. The cryostat arrangement according to claim 7, wherein the metal extension is made of stainless steel.

21. The cryostat arrangement according to claim 8, wherein the outer tube is made of stainless steel.

Description

DESCRIPTION OF THE DRAWINGS

[0038] Aspects of the invention are shown in the drawings and described with reference to exemplary embodiments. In the drawings:

[0039] FIG. 1 is a schematic vertical sectional view of a first embodiment of the cryostat arrangement according to an aspect of the invention.

[0040] FIG. 2 is a schematic vertical sectional view of a second embodiment of the cryostat arrangement comprising baffles in the neck tube according to an aspect of the invention.

[0041] FIG. 3 is a schematic vertical sectional view of a third embodiment of the cryostat arrangement comprising a JT cooler and a thermal barrier in the cryogenic tank according to an aspect of the invention.

[0042] FIG. 4 is a schematic vertical sectional view of a fourth embodiment of the cryostat arrangement comprising a bellows portion in the neck tube according to an aspect of the invention.

[0043] FIG. 5A is a graph of the thermal conductivity integral of stainless steel versus temperature.

[0044] FIG. 5B is a graph of the thermal conductivity integral of G10 versus temperature.

DETAILED DESCRIPTION

[0045] FIGS. 1 to 4 of the drawings each show, in a schematic view, embodiments of the cryostat arrangement according to an aspect of the invention for storing a cryogen fluid, in particular, for cooling a superconducting magnet arrangement.

[0046] A cryostat arrangement 1 according to an aspect of the invention comprises a vacuum tank 2 and a cryogenic tank 3, which is arranged inside the vacuum tank 2, the vacuum tank 2 comprising at least one neck tube 4 having a supporting structure 4a and an outer tube 4b surrounding the supporting structure 4a, the neck tube 4 leading to the cryogenic tank 3 and, wherein the neck tube 4 produces a spatial connection of an internal volume of the cryogenic tank 3 to a region outside the vacuum tank 2 so that cryogenic fluid can flow out of the cryogenic tank 3 into a region outside the vacuum tank 2 or vice versa (from a region outside the vacuum tank 2 into the cryogenic tank 3).

[0047] The cryostat arrangement 1 according to an aspect of the invention is characterized, in that, firstly the parts of the neck tube 4 used to mechanically suspend the cryogenic tank 3 within the vacuum tank 2, and secondly the parts of the neck tube 4 used to construct a diffusion barrier between the interior of the cryogenic tank 3 and the interior of the vacuum tank 2 are arranged so as to be spatially separated from one another and are produced from materials which are optimized differently in each case, in that the supporting structure 4a supports the weight of the cryogenic tank 3 and is produced from a material in the case of which, for the ratio / of a maximum permissible mechanical stress , where >100 MPa, to , where is the integral of the thermal conductivity over the temperature range T between 300 K and 4 K, where <300 W/m, the following applies: /> (MPa.Math.m)/W, and in that the outer tube 4b is produced from a material through which cryogenic fluid cannot diffuse, or through which only an unmeasurable amount of cryogenic fluid can diffuse in operation, and in which the neck tube can be connected to other components of the cryostat arrangement 1 in a fluid-tight manner so that the resulting integral leakage rate out of the cryogenic tank 3 into the vacuum tank 2 is less than 10.sup.6 mbar.Math.l/s.

[0048] In the embodiments of the invention shown in FIGS. 1 to 4 of the drawings, the supporting structure 4a is in the form of an inner tube, and wherein the inner tube produces a spatial connection of the internal volume of the cryogenic tank 3 to a region outside the vacuum tank 2 so that cryogenic fluid can flow out of the cryogenic tank 3 into a region outside the vacuum tank 2 or vice versa. In this case, the outer tube 4b can be in direct, preferably thermally well-conducting, contact with the inner tubebut this is not shown in the drawings. Alternatively, as shown in FIG. 1-4, the outer tube 4b can be at a distance from the inner tube, and a gap 4c can remain open between the inner tube and the outer tube 4b. In this case, the outer tube 4b and the inner tube are preferably interconnected by a plurality of axially arranged, radially extending thermal bridges.

[0049] As can be seen in FIGS. 1, 2 and 4, flow off cryogen may pass through the annular gap 4c between the inner tube 4a and the outer tube 4b in order to optimally use the enthalpy of the cold gas for absorbing the heat which flows from the outer tank (e.g., vacuum tank 2) along the neck tube 4 into the cryogenic tank 3.

[0050] The outer tube 4b produces a fluid-tight connection to the insulation vacuum. The wall thickness is designed in such a way that the maximum differential pressure between the annular gap 4c and the insulation vacuum can be absorbed, and no significant diffusion of the cryogen into the insulation vacuum takes place. The material is selected in such a way that a fluid-tight connection to other parts of the cryostat (e.g., the cover plate of the cryogenic tank 3) can be produced reliably and cheaply. The outer tube 4b can be produced e.g., from stainless steel which has excellent welding properties. The wall thickness of said tube can be selected so as to be very thin, since the tube does not have to accommodate the entire weight of the cryogenic tank 3 (and the components located in it).

[0051] The inner tube 4a supports the weight of the cryogenic tank 3. However, it does not have to be hermetically sealed, as a result of which a material can be selected which is primarily characterized by the high ratio of mechanical strength and thermal conductivity. In this case, for example, fiber-reinforced plastics materials are considered. Thus, for example, the supporting structure 4a can be produced in particular from GRP, more preferably from the fiber-reinforced composite G10.

[0052] The GRP tube is connected to a stainless-steel sleeve at its two ends. Connection options between GRP and a stainless-steel sleeve are known to a person skilled in the art. The stainless-steel sleeve must have a certain minimum length (typically 50 mm).

[0053] The drawings in FIGS. 5A and 5B show the thermal conductivity integrals for stainless steel (FIG. 5A) and for the fiber-reinforced composite G10 (FIG. 5B). As can be seen, the thermal conductivity integral of stainless steel is approximately 30 times greater than that of G10. However, stainless steel is also much stronger than G10, as a result of which the ratio of strength to thermal conductivity must be used as a key indicator. The 0.2% yield strength of stainless steel, which would be used for the design, is typically 360 MPa (for 1.4301); the tensile strength of G10 is approximately 270 Mpa.

[0054] Even under the conservative assumption that, in the case of G10, a safety factor of 3 is applied with respect to the tensile strength and that stainless steel can be loaded up to the yield strength, the thermal conduction of a stainless steel tube [(270/3 Mpa)/(1 W/cm)]/[(360 Mpa)/(30 W/cm)]=7.5 times as great as a GRP tube having the same load capacity.

[0055] Preferably, the supporting structure 4a made of plastics material will support a metal extension 5a, 5a, preferably made of stainless steel, at each of its two ends. The metal extensions 5a, 5a each have a length of between 20 mm and 100 mm, preferably approximately 50 mm, and a cross-sectional area of stress of between 50 mm.sup.2 and 500 mm.sup.2.

[0056] As shown in FIG. 1, in embodiments of the invention, the upper end of the inner tube 4a can be closed in a fluid-tight manner in normal operation, in particular by a pressure relief valve or a rupture disk 9 so that cryogenic fluid flowing away in normal operation has to flow through the gap 4c between the inner tube 4a and the outer tube 4b. The gap 4c between the inner tube 4a and the outer tube 4b comprises a flow restrictor 7 at the end of the neck tube 4 which is closer to the cryogenic tank 3.

[0057] FIG. 2 shows an embodiment of the invention which is an alternative thereto, in which, inside the neck tube 4, in particular inside the inner tube 4a and/or between the supporting structure 4a and the outer tube 4b, so-called baffles 6 are installed, which absorb thermal radiation and prevent convection. The baffles 6 are preferably foldable so that, in the case of a rapid flow-off of the cryogen (e.g., in the case of a quench), the baffles release the cross section of the inner tube 4a and, in this way, restrict the pressure increase in the cryogenic tank 3.

[0058] In other embodiments of the invention, the annular gap 4c can also be used as a pump line for supercooled systems. If the inlet of the pump line is protected by a restrictor, the quench pressure does not have to be taken into consideration when dimensioning the outer tube 4b. Absolute fluid-tightness between the pump line (annular gap 4c) and the cryogenic tank 3 (or the volume in the inner tube 4a) is not necessary. A low leakage flow is acceptable if it is minor by comparison with the flow which is pumped out by the refrigerator.

[0059] FIG. 3 shows an embodiment designed in this manner in which the cryostat contains a JT cooler, in which cryogenic fluid is depressurized using a pump located outside the vacuum tank 2 (not shown in the drawings), wherein the gap 4c between the supporting structure 4a and the outer tube 4b is part of the connecting line between the JT cooler and the pump. FIG. 3 shows a cryogenic tank which is divided into two regions using a thermal barrier 20. The thermal barrier 20 is thermally insulating but allows pressure equalization between the two regions (e.g., a flexible membrane made of thermally insulating material). Above the thermal barrier, cryogen is, for example, at atmospheric pressure in the saturation state. Below the barrier, the cryogen is in the supercooled state (e.g., atmospheric pressure, but a temperature which is below the equilibrium temperature). Therefore, heat must be conducted away from the JT cooler. Such an arrangement is ideally suited to the operation of superconducting magnet coils at temperatures below 4.2 K.

[0060] In order to avoid mechanical redundancy of the system, a bellows portion 8 can be provided in the outer tube 4b. The outer tube 4b thus cannot absorb any axial forces and therefore also cannot be unduly strained by axial forces. An embodiment of the invention which is configured in this way is shown in FIG. 4.

[0061] Also conceivable are embodiments of the invention in which, by omitting the exhaust-gas cooling in the annular gap 4c or the availability as a pump line, a variant without an annular gap is implemented, or in which the supporting structureunlike as shown in the drawingsis not in the form of a tube, but rather of an individual rod or a plurality of rods.

[0062] The features of all the above-described embodiments of the invention canlargelyalso be combined with one another.