Cryostat assembly having a resilient, heat-conducting connection element

Abstract

A cryostat assembly comprises an outer container that houses a coil tank with a superconducting magnet coil system and a first cryogenic fluid, and a storage tank with a second cryogenic fluid. The coil tank is secured to the outer container by a first suspension element and the storage tank is secured to the outer container by a second suspension element. The storage tank is thermally connected to a cover element having a mechanical and thermally-conductive connection to a tube element and to the first suspension element. The cover element connects to the storage tank via a resilient, heat-conducting connection that is in thermal contact with the cover element and the storage tank. This allows thermal coupling between the storage tank and cover element, and independent relative movements between the storage tank and cover element, while suppressing relative movements between the tube element and the superconducting magnet coil system.

Claims

1. A cryostat assembly comprising: an outer container; a coil tank located in the outer container and being secured thereto by a first suspension element, the coil tank containing a superconducting magnet coil system to be cooled and a first cryogenic fluid; a storage tank located in the outer container and being secured thereto by a second suspension element, the storage tank containing a second cryogenic fluid having a temperature higher than that of the first cryogenic fluid during operation of the magnet coil system; a tube element located within the outer container that surrounds a room temperature bore; and a cover element that is substantially fixed to the tube element and to the first suspension element by substantially thermally conductive connections such that relative movements between the tube element and the coil tank are prevented, and that is connected to the storage tank via a connection element that is substantially thermally conductive and that provides a substantially mechanically decoupled connection that enables relative movement between the cover element and the storage tank.

2. A cryostat assembly according to claim 1, wherein the connection element comprises a corrugated bellows, strands, or fabric made of thermally conductive material with a thermal conductivity of >100 W/mK.

3. A cryostat assembly according to claim 1, wherein the connection element transmits a force of ≤100 N/mm to the cover element when the storage tank is displaced.

4. A cryostat assembly according to claim 1, further comprising a flange element that provides a thermal and mechanical connection between the cover element and the tube element, said flange element consisting of a material that contracts more than a material of the tube element when the cryostat assembly is cooled.

5. A cryostat assembly according to claim 4, wherein the tube element is made of copper and the flange element is made of aluminum.

6. A cryostat assembly according to claim 4, wherein the flange element is screwed to the cover element and soldered or welded to the tube element.

7. A cryostat assembly according to claim 1, wherein the storage tank is thermally connected to the tube element via the cover element and via a base element located to an opposite side of the superconducting magnet coil system from the cover element.

8. A cryostat assembly according to claim 7, wherein the connection element is a first connection element, and wherein the base element is connected to the storage tank via a second connection element that is substantially thermally conductive and that provides a substantially mechanically decoupled connection that enables relative movement between the base element and the storage tank.

9. A cryostat assembly according to claim 7, wherein the base element is mechanically flexible and has slots extending radially with respect to the room temperature bore.

10. A cryostat assembly according to claim 1, further comprising a shim system for homogenizing the magnetic field generated by the magnet coil system.

11. A cryostat assembly according to claim 10, wherein the shim elements are radially attached to the tube element.

12. A cryostat assembly according to claim 10 wherein the shim system comprises shim elements of a magnetic material.

13. A cryostat assembly according to claim 10 wherein the shim system comprises electrical shim elements.

14. A cryostat assembly according to claim 13, wherein the electrical shim elements are made of copper.

15. A cryostat assembly according to claim 1, further comprising at least one radiation shield located between the storage tank and the coil tank which, during operation of the superconducting magnet coil system, has a temperature between that of the first cryogenic fluid and that of the second cryogenic fluid.

16. A cryostat assembly according to claim 1, wherein at least one cryocooler is present in the cryostat assembly for reducing consumption of the first and/or the second cryogenic fluid.

17. A cryostat assembly according to claim 1, wherein the cryostat assembly is part of an NMR apparatus for spectroscopy or imaging.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is illustrated in the drawings and is 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 the slotted base element from the side and from below;

(5) FIG. 4 is a schematic detailed view of the tube element with electrical shim elements applied thereon;

(6) FIG. 5 is a schematic vertical sectional view of an embodiment of the cryostat assembly according to the invention having a cryocooler; and

(7) FIG. 6 is an isometric view of the storage tank, which is connected to the cover element via resilient, heat-conducting connection elements.

DETAILED DESCRIPTION

(8) FIGS. 1 and 3-6 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 shows a generic cryostat assembly according to the closest prior art.

(9) A cryostat assembly 1 of this kind comprises an outer container 2 in which a coil tank 3, having a superconducting magnet coil system 4 to be cooled and a first cryogenic fluid 5, is arranged. The superconducting magnet coil system 4 is also cooled, at least in an operating state, by a second cryogenic fluid 7 located in a storage tank 6, the temperature of which fluid is above that of the first cryogenic fluid 5. The coil tank 3 is mechanically rigidly secured to the outer container 2 by means of at least one first suspension element 8 and the storage tank 6 is mechanically rigidly secured to the outer container 2 by means of at least one second suspension element 9. In addition, the storage tank 6 is thermally connected to a cover element 10 which is, via at least one coupling element 11, thermally conductively and mechanically rigidly connected to the first suspension element 8 and thermally conductively and mechanically rigidly connected to a tube element 13.

(10) Liquid helium, which has a lower operating temperature than the second cryogenic fluid—usually liquid nitrogen—is generally used as the first cryogenic fluid. The outer container 2 will normally be designed as a vacuum container.

(11) In order to generate high magnetic fields or to reduce the volume of superconducting magnet coil systems, it is often advantageous to subcool the liquid helium, since this increases the critical current density of the superconductor. The subcooling takes place either by generating a vacuum in the coil tank or by using a subcooling unit as described in DE 40 39 365 A1, for example. In particular, it may be the case that a further storage tank having, for example, liquid helium at normal pressure is provided. The present invention is also advantageous for such cryostat assemblies.

(12) The present invention broadens this per se known assembly by the following essential elements of the invention: The cryostat assembly 1 according to the invention is distinguished from the devices from the prior art in that the cover element 10 is mechanically connected to the storage tank 6 via a resilient, heat-conducting connection element 12, the connection element 12 being in thermal contact with both the cover element 10 and the storage tank 6.

(13) In embodiments of the invention—as can be clearly seen in FIG. 1—a flange element 14 can be present, which is used for both the thermal and the rigid mechanical connection of the cover element 10 to the tube element 13. The flange element 14 may be made of a material which contracts more than the material of the tube element 13 when the cryostat assembly 1 is cooled from room temperature to an operating temperature. For example, the tube element 13 can be made of copper and the flange element 14 can be made of aluminum. The flange element 14 can also be both screwed to the cover element 10 and soldered or welded to the tube element 13.

(14) As also shown in FIG. 1, the storage tank 6 can be thermally connected to the tube element 13 via both the cover element 10 and a base element 15. This base element 15 can in turn be mechanically connected to the storage tank 6 via a further resilient, heat-conductive connection element 12′, preferably with a spring constant of 100 N/mm.

(15) The base element 15 will preferably be mechanically flexible. In further developments, this can be achieved in that it has radially extending slots 15′ with respect to a room temperature bore 16 of the cryostat assembly 1. This is shown schematically in FIG. 3.

(16) Details of another embodiment are shown in FIG. 4. Here, a shim system for homogenizing the magnetic field generated by the superconducting magnet coil system 4 is present, said shim system comprising shim elements 17 made of magnetic material and/or electrical shim elements 17. The shim elements 17 can be attached to the tube element 13 radially on the inside or the outside. In the case of electrical shim elements 17, these will be made of copper and will be applied, for example in the form of loop-shaped electrical coils, to the outer circumference of the tube element 13.

(17) FIG. 5 also shows an embodiment in which at least one radiation shield 18 is provided between the storage tank 6 and the coil tank 3, said radiation shield, in an operating state of the superconducting magnet coil system 4, having a temperature between that of the first cryogenic fluid and that of the second cryogenic fluid.

(18) Additionally, this drawing also shows an active cooler in the form of a cryocooler 19 for reducing the consumption of the first cryogenic fluid and/or the second cryogenic fluid in the cryostat assembly 1. In the case of NMR magnets, a low-vibration pulse tube cooler can be used, for example.

(19) Finally, FIG. 6 is an isometric view of the storage tank 6, which is connected to the cover element 10 via resilient, heat-conducting connection elements 12. These connection elements are shown here as corrugated bellows. In another embodiment, strands, preferably made of copper, are used.

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