GB2545178A

GB2545178A - Cryostats for superconducting magnets

Info

Publication number: GB2545178A
Application number: GB1521520.5A
Authority: GB
Inventors: Simpkins Michael
Original assignee: Siemens Healthcare Ltd
Current assignee: Siemens Healthcare Ltd
Priority date: 2015-12-07
Filing date: 2015-12-07
Publication date: 2017-06-14
Also published as: GB201521520D0

Abstract

A cylindrical superconducting magnet structure 10 has a cryogen vessel 20, comprising a cylindrical bore tube 22, cylindrical outer shell 24, and end pieces 26, forming a hollow cylindrical chamber. Axially aligned superconducting coils 14 and a coil support arrangement 16 are housed within the vessel 20. A tensile strut 30 mechanically joins two locations on the inner surface of the cryogen tank 20, reducing its tendency for buckling or deformation at high pressures. The strut 30 may be joined between the end pieces 26, or between the cylindrical bore tube 22 and outer shell 24, extending between two coils 14 through an aperture of the coil support arrangement 16. The strut 30 may be in two parts, attached to the coil support arrangement 16. Metallic bars or rings may be welded to the outer or inner surface of the cryogen vessel 20 where the tensile member 30 is joined.

Description

CRYOSTATS FOR SUPERCONDUCTING MAGNETS

The present invention relates to cryostats for superconducting magnets. In particular, it relates to a cylindrical superconducting magnet structure comprising a magnet assembly, itself comprising a plurality of axially-aligned coils of superconducting wire and a coil support arrangement, housed within a cryogen vessel which comprises a cylindrical bore tube, a cylindrical outer shell and end pieces joining the cylindrical bore tube to the outer shell to form a hollow cylindrical vessel.

Cryogen vessels for cooling superconducting magnets are partially filled with a liquid cryogen. The cryogen is held at its boiling point. A superconducting magnet structure within the cryogen vessel is kept cool by boiling of the liquid cryogen, while the boiled-off cryogen is recondensed to liquid by a cryogenic recondensing refrigerator. In normal operating conditions, this process stabilises, and the superconducting magnet structure is held at a stable temperature and the cryogen gas pressure within the cryogen vessel reaches a stable value. Typical of current superconducting magnet arrangements, the cryogen is helium and the cryogen gas pressure is approximately atmospheric pressure. The cryogen vessel is typically suspended within a vacuum vessel for thermal insulation. There is, therefore, typically a pressure differential of about atmospheric pressure across the wall of the cryogen vessel.

The present invention provides structures of cryogen vessels which are capable of withstanding increased pressure with regard to their wall thickness. Alternatively, the invention enables the cryogen vessel to be made with thinner walls for a given pressure capability, reducing weight and material cost of the cryogen vessel. A conventional approach to the problem of providing cryogen vessels capable of withstanding higher cryogen pressures is to make the cryogen vessel of thicker or stronger material. This will significantly increase the weight and cost of the cryogen vessel. Additional thickness of the cryogen vessel may mean that the diameter of the coils of superconducting wire needs to increase, leading to an increase in wire consumption and an increase in the cost and weight of the coils of superconducting wire.

The present invention aims to provide a cryogen vessel which is capable of withstanding increased pressure but which does not require a change of material or an increase in vessel wall thickness; or one which has reduced wall thickness for a same pressure capability.

Accordingly, the present invention provides cylindrical superconducting magnet structures as defined in the appended claims .

The above, and further, objects, characteristics and advantages of the present invention will become more apparent from the following description of certain embodiments thereof, taken in conjunction with the appended drawings, wherein:

Fig. 1 shows an axial part-cross-section of a first embodiment of the present invention;

Fig. 2 shows an axial part-cross-section of a second embodiment of the present invention; and

Fig. 3 shows an axial part-cross-section of a third embodiment of the present invention.

In Fig. 1, a cylindrical superconducting magnet structure 10 is shown. The structure is essentially symmetrical about axis A-A. The structure comprises a magnet assembly 12, which itself comprises a plurality of axially-aligned coils of superconducting wire 14 and a coil support arrangement 16, housed within a cryogen vessel 20. The cryogen vessel 20 comprises a cylindrical bore tube 22, a cylindrical outer shell 24 and end pieces 26 joining the cylindrical bore tube 22 to the cylindrical outer shell 24 to form a hollow cylindrical cryogen vessel 20.

According to a feature of the present invention, a tensile member 30 is provided within the cryogen vessel, mechanically joining two locations 32 on an inner surface 34 of the cryogen vessel 20.

In the illustrated embodiment, a plurality of tensile members 30 are provided, and in each case one of the locations 32 is on the cylindrical bore tube 22 and the other of the locations 32 is on the cylindrical outer shell 24.

Preferably, and as illustrated, a strengthening piece 36 is provided, mechanically joined to the cryogen vessel at one or both of the locations 32 on the inner surface of the cryogen vessel, and the tensile member is joined to the strengthening piece(s) where provided.

Alternatively, the strengthening piece may be provided, mechanically joined to an outer surface of the cryogen vessel at a location corresponding to one of the locations 32 on the inner surface of the cryogen vessel.

The strengthening piece(s) may be metallic bars or rings, for example, welded to the material of the cryogen vessel.

As illustrated, the tensile member 30 may extend between two of the axially-aligned coils 14 of superconducting wire. Apertures may be provided in the magnet assembly 12 to allow the tensile members 30 to traverse the cryogen vessel between two of the axially-aligned coils 14 of superconducting wire. For example, the tensile member 30 may extend through an associated hole 38 in the coil support arrangement 16.

As shown in Fig. 2, the tensile member 30 may be in two parts, each attached to the coil support arrangement 16. One tensile member part 30' may join a location on the cylindrical bore tube 22 to the coil support arrangement 16, while another tensile member part 30' may join a location on the coil support arrangement 16 to a location on the cylindrical outer shell 24. Strengthening pieces 40 may be provided, either on respective surfaces of the coil support arrangement 16, or extending through the coil support arrangement to bear tension in the respective tensile member parts 30' . Other arrangements may be provided in which tensile members extend from one part to another within the cryogen vessel. The tensile members 30 may be structural, and may be used to position and retain the magnet assembly 12 in place within the cryogen vessel 20.

While Figs. 1 and 2 show the cryogen vessel 20 as relatively close-fitting to an inner magnet assembly 12, the invention may be applied to cryogen vessels which include inner magnet assemblies and larger-diameter shield coils. The tensile members 30 will need to be longer, as the difference in diameter between the bore tube 22 and the cylindrical outer shell 24 will be greater.

The embodiments of Figs. 1 and 2 reduce the tendency for buckling or deformation of the bore tube 22 and the cylindrical outer shell 24. The tensile members 30 retain these cylindrical structures against one another, preventing an increase in radial distance between bore tube 22 and the cylindrical outer shell 24. A higher pressure P may be tolerated within the cryogen vessel without risk of buckling of the cryogen vessel than would be possible in the absence of the tensile members 30. This allows a thinner material to be used for the bore tube 22 and the cylindrical outer shell 24 than would be possible in the absence of the tensile members 30.

Fig. 3 shows another embodiment of the present invention. In this embodiment, tensile member 30 is provided within the cryogen vessel, mechanically joining two locations 32 on respective end pieces of the cryogen vessel. As with the above-described embodiments, the tensile member 30 may extend directly between the two locations, or the tensile member 30 may be in two parts 30' , each attached to the coil support arrangement 16. The tensile member may serve to retain the magnet structure in place within the cryogen vessel.

One tensile member may join a location on one end piece 26 to the coil support arrangement 16, while another tensile member 30 may join a location on the coil support arrangement 16 to a location on the other end piece 26. Strengthening pieces 40 may be provided, either on respective surfaces of the coil support arrangement 16, or extending through the coil support arrangement to bear tension in the respective tensile member parts 30' . Other arrangements may be provided in which tensile members extend from one part to another within the cryogen vessel.

The embodiment of Fig. 3 prevents expansion or deformation of the end pieces 26. The tensile members 30 retain the end pieces 26 against one another, preventing an increase in axial distance between the end pieces 26. A higher pressure P may be tolerated within the cryogen vessel without risk of buckling or deformation of the cryogen vessel than would be possible in the absence of the tensile members 30. This allows a thinner material to be used for the end pieces 2 6 than would be possible in the absence of the tensile members 30.

The present invention accordingly provides arrangements in which a higher pressure may be tolerated by a cryogen vessel without increasing the thickness of the walls of the cryogen vessel.

Claims

CLAIMS :

1. A cylindrical superconducting magnet structure (10) comprising a magnet assembly (12), itself comprising a plurality of axially-aligned coils (14) of superconducting wire and a coil support arrangement (16), housed within a cryogen vessel (12) which comprises a cylindrical bore tube (22), a cylindrical outer shell (24) and end pieces (26) joining the cylindrical bore tube to the outer shell to form a hollow cylindrical vessel, characterised in that a tensile member (30) is provided within the cryogen vessel, mechanically joining two locations (32) on an inner surface of the cryogen vessel.

2. A cylindrical superconducting magnet structure according to claim 1 wherein a strengthening piece (36) is provided, mechanically joined to the cryogen vessel at one or both of the locations (32) on the inner surface of the cryogen vessel.

3. A cylindrical superconducting magnet structure according to claim 1 wherein a strengthening piece is provided, mechanically joined to an outer surface of the cryogen vessel at a location corresponding to one of the locations on the inner surface of the cryogen vessel.

4. A cylindrical superconducting magnet structure according to any preceding claim wherein one of the locations is on the cylindrical bore tube and the other of the locations is on the cylindrical outer shell.

5. A cylindrical superconducting magnet structure according to claim 4 wherein the tensile member extends between two of the axially-aligned coils of superconducting wire.

6. A cylindrical superconducting magnet structure according to claim 5, wherein the tensile member extends through an associated aperture (38) in the coil support arrangement.

7. A cylindrical superconducting magnet structure according to claim 5, wherein the tensile member is in two parts, each attached to the coil support arrangement.

8. A cylindrical superconducting magnet structure according to any of claims 1-3 wherein the locations are on respective end pieces of the cryogen vessel.

9. A cylindrical superconducting magnet structure according to claim 8, wherein the tensile member is in two parts, each attached to the coil support arrangement.

10. A cylindrical superconducting magnet structure substantially as described and/or as illustrated in Figs. 1-3 of the accompanying drawing.