Cryostat assembly with superconducting magnet coil system with thermal anchoring of the mounting structure

Abstract

A cryostat assembly with an outer container for a storage tank with a first cryogenic fluid and a coil tank for a superconducting magnet coil system. The magnet coil system is cooled by a second cryogenic fluid colder than the first cryogenic fluid, the coil tank being mechanically connected to the outer container and/or to radiation shields surrounding the coil tank via a mounting structure. Liquid helium at an operating temperature of approximately 4.2 K is the first cryogenic, fluid and helium at an operating temperature of <3.5 K is the second cryogenic fluid in the coil tank. The mounting structure has mounting elements with thermally conductive contact points thermally coupled to heat sinks having a temperature at or below that of the storage tank, via thermal conductor elements. This ensures long times to quench if malfunctions occur.

Claims

1. Cryostat assembly comprising: an outer container in which a storage tank with a first cryogenic fluid and a coil tank with a superconducting magnet coil system to be cooled are arranged, wherein the magnet coil system is cooled at least in an operating state by a second cryogenic fluid whose temperature is below that of the first cryogenic fluid, and a mounting structure mechanically connecting the coil tank to the outer container and/or to at least one radiation shield surrounding the coil tank at least during a transport state of the assembly, wherein the first cryogenic fluid is liquid helium at an operating temperature of approximately 4.2 K in the storage tank and the second cryogenic fluid is helium at an operating temperature of <3.5 K in the coil tank, and wherein the mounting structure comprises a plurality of mounting elements each of which has at least one thermally conductive contact point which is thermally coupled, through at least one thermal conductor element, to at least one heat sink, whose temperature is lower than or equal to that of the storage tank.

2. Cryostat assembly according to claim 1, wherein the second cryogenic fluid is subcooled helium, wherein the pressure of the subcooled helium is above a saturation vapor pressure corresponding to the temperature of the second cryogenic fluid.

3. Cryostat assembly according to claim 1, wherein the mounting elements are made of a material for which, for a ratio σ/θ of maximum permissible mechanical stress σ, with σ>100 MPa, to an integral θ of a thermal conductivity λ over a temperature range AT between 300 K and 4 K, with θ<300 W/m, the following applies: σ/θ>1/3 (MPa.Math.m)/W.

4. Cryostat assembly according to claim 1, wherein the mounting elements are made of plastics material.

5. Cryostat assembly according to claim 4, wherein the mounting elements are made of fiber-reinforced plastics material.

6. Cryostat assembly according to claim 1, wherein the mounting elements are designed as strut elements, and wherein the thermally conductive contact points are glued onto or into the strut elements or are co-wound in a wound structure of the strut elements.

7. Cryostat assembly according to claim 1, wherein the mounting elements are each shaped as a loop, each of the loops having at least one thermally conductive contact point.

8. Cryostat assembly according to claim 1, wherein the mounting elements each have, on an end thereof nearer the coil tank, a thermally conductive contact point which is in mechanical surface contact with the coil tank via a thermally insulating plate on a side thereof facing away from the mounting element.

9. Cryostat assembly according to claim 1, wherein the thermal conductor element is constructed from a strand or a rod and is made of a material with high thermal conductivity lambda at low temperatures.

10. Cryostat assembly according to claim 9, wherein the high thermal conductivity at low temperatures is lambda >250 W/(m*K) at a temperature of 4 K, and wherein the material is high-purity copper or high-purity aluminum.

11. Cryostat assembly according to claim 1, wherein the thermal conductor element comprises a heat pipe or is constructed from a heat pipe.

12. Cryostat assembly according to claim 1, wherein the thermal conductor element comprises a radiation shield or is constructed from a radiation shield.

13. Cryostat assembly according to claim 12, wherein the radiation shield comprises or is constructed from a 4.2 K radiation shield.

14. Cryostat assembly according to claim 1, wherein the at least one heat sink comprises or consists essentially of the storage tank.

15. Cryostat assembly according to claim 14, wherein the thermal conductor element comprises tube loops with which the contact points and the storage tank are thermally coupled, and wherein the tube loops branch away from the storage tank below a liquid surface of the first cryogenic fluid, lead to the contact points, and then return to a location on the storage tank which is above the liquid surface.

16. Cryostat assembly according to claim 1, further comprising: an active cooler comprising subcooling pumps, configured to operate with an uninterruptible power supply in the event of a power failure, wherein the at least one heat sink comprises an exhaust gas of the active cooler, and wherein the active cooler further comprises an exhaust gas line moved past the at least one contact point serially or in parallel with thermal contact.

17. Cryostat assembly according to claim 16, wherein the active cooler comprises a Joule Thomson refrigerator.

18. Cryostat assembly according to claim 16, wherein the thermal contact between the storage tank and the exhaust gas line is configured as a movable contact which is connected to an interior of the exhaust gas line and with which contact is alternatingly made or broken.

19. Cryostat assembly according to claim 18, wherein the thermal contact comprises a mechanically preloaded bellows element which is connected to the interior of the exhaust gas line such that thermal contact is made only above an exhaust gas line pressure of 100 mbar.

20. Cryostat assembly according to claim 1, further comprising a room temperature bore with a horizontal axis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is illustrated in the drawings and will be explained in more detail with reference to embodiments. In the drawings:

(2) FIG. 1 is a schematic vertical sectional view of an embodiment of the cryostat assembly according to the invention;

(3) FIG. 2 is a vertical sectional view of a cryostat assembly according to the prior art;

(4) FIG. 3 is a schematic detailed view of an embodiment of the cryostat assembly according to the invention with a mounting element in which the thermally conductive contact points are integrated;

(5) FIG. 4 is a detailed view of an embodiment with a mounting element which is provided, at its coil-tank-side end, with a contact point, and is in mechanical surface contact with the coil tank via a thermally insulating plate;

(6) FIG. 5 is a detailed view of an embodiment in which the thermal conductor element comprises tube loops;

(7) FIG. 6 is a detailed view of an embodiment in which the thermal conductor element comprises the exhaust gas line of an active cooler;

(8) FIG. 7 is a detailed view of an embodiment in which the exhaust gas line of an active cooler crosses the thermal conductor element; and

(9) FIG. 8 shows an embodiment in which a mechanically preloaded bellows element is arranged in the region where the exhaust gas line and thermal conductor element cross, over which bellows element thermal contact can be made or broken.

DETAILED DESCRIPTION

(10) FIGS. 1 and 3 to 8 of the drawings are each schematic views showing different details of preferred embodiments of the cryostat assembly according to the invention for cooling a superconducting magnet assembly, while FIG. 2 illustrates a generic cryostat assembly according to the closest prior art.

(11) A cryostat assembly 1 of this kind has an outer container 2 in which a storage tank 3 with a first cryogenic fluid and a coil tank 4 with a superconducting magnet coil system 5 to be cooled are arranged. The magnet coil system 5 is cooled, at least in an operating state, by a second cryogenic fluid whose temperature is lower than that of the first cryogenic fluid. The coil tank 4 is mechanically connected to the outer container 2 and/or to one or more radiation shields 6 surrounding the coil tank 4 with a mounting structure at least during a transport state.

(12) The present invention broadens this per se known assembly by the following elements associated with the invention. The cryostat assembly 1 according to the invention is distinguished from the apparatuses of the prior art in that the mounting structure has a plurality of mounting elements 7; 7′ which each have at least one thermally conductive contact point 7a; 7a′ which are thermally coupled respectively to at least one heat sink, whose temperature is lower than or equal to that of the storage tank 3, via at least one thermal conductor element 8; 8′.

(13) In embodiments of the invention, at least one heat sink to which the thermal conductor elements 8; 8′ are coupled may comprise the storage tank 3, in particular consist of the storage tank 3 itself.

(14) Subcooled helium is usually used as the second cryogenic fluid, the pressure of the subcooled helium being above that of the saturation vapor pressure corresponding to the temperature of the second cryogenic fluid.

(15) The outer container 2 is normally designed as a vacuum container and the mounting elements 7; 7′ attached to the coil tank 4 are mechanically mounted on the inside of a typically provided radiation shield 6, as can be clearly seen in FIG. 1.

(16) FIG. 3 illustrates the embodiment of FIG. 1 in the region of the coil tank 4 in greater detail. Each mounting element then comprises at least one thermally conductive contact point 7a which is thermally coupled to a heat sink with a temperature that is lower than or equal to that of the storage tank 3 via a thermal conductor element 8.

(17) The mounting elements 7; 7′ can also be designed as strut elements. The thermally conductive contact points 7a; 7a′ can then be glued onto or into the strut elements or can be co-wound in a wound structure of the strut elements.

(18) The mechanical suspensions are usually made of GFRP. Structures (specifically the contact points) are glued/co-wound directly into the GFRP struts at a suitable point, and thermal contacting takes place via these structures. For the structures, a material with high thermal conductivity at low temperatures is preferred, for example high-purity copper or high-purity aluminum.

(19) Details of another embodiment are shown in FIG. 4. Here, the mounting elements 7′ have, on their end nearer the coil tank 4, a thermally conductive contact point 7a′ which is in mechanical surface contact with the coil tank 4 via a thermally insulating plate 9, which acts as a distance piece, on the side facing away from the mounting element 7′.

(20) The thermal conductor elements 8; 8′ can be constructed from a strand or a rod, at least from a material with high thermal conductivity lambda at low temperatures. In other embodiments (not expressly shown in the drawings), the thermal conductor elements 8; 8′ may also comprise a heat pipe or be constructed from a heat pipe. The thermal conductor elements 8; 8′ may also comprise a radiation shield, in particular a 4.2 K radiation shield, or be constructed from such, which is also not expressly shown in the drawings.

(21) FIG. 5 shows an embodiment in which the thermal conductor element 8′ comprises tube loops over which the contact points 7a and the storage tank 3, acting as the heat sink, are thermally coupled. The tube loops branch away from the storage tank 3 below a liquid surface of the first cryogenic fluid, lead to the contact points 7a, and then are returned to a location on the storage tank 3 which is above the liquid surface.

(22) FIG. 6 shows an embodiment comprising an active cooler, in particular a Joule Thomson refrigerator JT. Subcooling pumps (not expressly shown in the drawings) are provided, which can continue to be operated using an uninterruptible power supply in the event of a power failure. In this embodiment, at least one heat sink comprises the exhaust gas of the active cooler, an exhaust gas line 8a of the active cooler being moved past the contact points 7a; 7a′ serially or in parallel with thermal contact.

(23) Thus, the unused cooling capacity between the temperature ranges of 2 K and 4.2 K of the LHe heat flow of 0.4 mW/(ml/h) is available to intercept the heat flowing through the supports in the coil tank 3. In an ideal case, this corresponds to almost half the cooling capacity of the refrigerator and can thus relieve it considerably, especially in an emergency. Even in normal operation, this assembly allows a significant reduction in heat flow. As a result, the exhaust gas from the JT cooler, as indicated in FIG. 6, can also be used to intercept the heat load in the neck tubes.

(24) Another, optionally also supplementary, variant of the invention is shown in FIG. 7 in which, an active cooler is used, preferably again a Joule Thomson refrigerator JT. The exhaust gas line 8a of this cooler is “crossed” by the thermal conductor element 8 on its way to the heat sink.

(25) In the event of a failure of the subcooling pumps, the exhaust gas line 8a runs full with LHe, the phase boundary (liquid-gaseous) then being set somewhere between the outlet from the coil tank 4 arranged below and the thermal coupling to the storage tank 3 arranged above. By suitable selection of the thermal positioning (for example by different conductivity of the thermally conductive contact points 7a on the one hand and the crossing region or the coupling region to the heat sink on the other hand), the system can be concerted between higher consumption reduction in continuous operation and loss reduction in the case of pump failure. In extreme cases, the thermal conductivity of the coupling region to the heat sink will be much greater than the conductivity of the thermal conductor element 8. In that case, the assembly is in an embodiment without heat flow coupling.

(26) An advantageous development of this embodiment is shown in FIG. 8: in this embodiment, the thermal contact between the storage tank 3 and the exhaust gas line 8a is designed to be movable. For this purpose, a preloaded (for example by a spring) bellows element 10 mechanically connected to the interior of the exhaust gas line 8a is provided, with which element thermal contact can be made or broken. The bellows element 10 should generally be designed such that thermal contact is made only above an exhaust gas line pressure of 100 mbar (i.e. if and only if the pumps are no longer running).

(27) The same principle is also feasable for vertical cryostats in which the mechanical suspensions engage directly on the coil tank, for example in order to make cold transportability possible.

(28) The features of all the above-described embodiments of the invention may also be combined with one another at least in most cases.

LIST OF REFERENCES

(29) Documents taken into consideration for the assessment of patentability

(30) [1] EP 1 742 234 B1, US 2010/0236260 A1

(31) [2] U.S. Pat. No. 5,220,800

(32) [3] U.S. Pat. No. 5,586,437

(33) [4] U.S. Pat. No. 6,011,454

LIST OF REFERENCE SIGNS

(34) 1 Cryostat assembly 2 Outer container 3 Storage tank 4 Coil tank 5 Superconducting magnet coil system 6 Radiation shield(s) 7; 7′ Mounting elements 7a; 7a′ Thermally conductive contact points 8; 8′ Thermal conductor element(s) 8a Exhaust gas line of the active cooler 9 Thermally insulating plate 10 Bellows element JT Joule Thomson refrigerator