Magnet assembly with cryostat and magnet coil system, with cold reservoirs on the current leads

Patent metadata

Field	Value
Publication number	US-10839998-B2
Application number	US-201816155262-A
Country	US
Kind code	B2
Filing date	Oct 9, 2018
Priority date	Oct 9, 2017
Publication date	Nov 17, 2020
Grant date	Nov 17, 2020

Abstract

A magnet assembly ( 1 ) with a cryostat ( 2 ) has a superconducting magnet coil system ( 3 ), an active cooling device ( 4 ) for the coil system, and current leads ( 5 a, 5 b ) for charging the coil system. The current leads have at least one normal-conducting region ( 15 a, 15 b ), wherein multiple cold reservoirs ( 20 ) are thermally coupled to the current leads along the normal-conducting region thereof, in order to absorb heat the normal-conducting region during charging of the magnet coil system. The current leads have a variable cross-sectional area B in the normal-conducting region along the extension direction thereof, wherein at least over a predominant fraction of their overall length in the normal-conducting region, the cross-sectional area B decreases from a cold end ( 18 a, 18 b ) toward a warm end ( 19 a, 19 b ). This provides a magnet assembly requiring reduced cooling power during charging, with less heat introduced into the magnet coil system in normal operation.

First claim

The invention claimed is:

1. A magnet assembly comprising:
a cryostat with a superconducting magnet coil system,
an active cooling device for the magnet coil system, and
current leads configured to charge the magnet coil system in the cryostat, wherein:
the current leads comprise at least one normal-conducting region,
multiple cold reservoirs are thermally coupled to the current leads along the normal-conducting region of the current leads, in order to absorb the heat arising in the normal-conducting region during the charging of the magnet coil system,
the current leads have a variable cross-sectional area B in the normal-conducting region along an extension direction of the current leads, and
at least over a predominant fraction of an overall length of the current leads in the normal-conducting region, the cross-sectional area B decreases from a cold end toward a warm end in the normal-conducting region.

2. The magnet assembly as claimed in claim 1 , wherein the current leads in the normal-conducting region each have N successive subsections, with N≥2, and wherein the subsections each have a constant cross-sectional area Bi within a subsection, and the cross-sectional areas Bi decrease from the cold end toward the warm end.

3. The magnet assembly as claimed in claim 2 , wherein different ones of the subsections are thermally coupled to different cold reservoirs.

4. The magnet assembly as claimed in claim 2 , wherein pairs of the subsections comprise respective transitions and each transition of two subsections is thermally coupled to at least one respective cold reservoir.

5. The magnet assembly as claimed in claim 4 , wherein the at least one cold reservoir is also thermally coupled onto the cold end of the current lead in the normal-conducting region.

6. The magnet assembly as claimed in claim 2 , wherein 3≤N≤7.

7. The magnet assembly as claimed in claim 1 , wherein K stages of the thermal coupling are configured along each of the current leads in the normal-conducting region, and wherein at least one cold reservoir is thermally coupled to the current leads at each stage, with K≥2.

8. The magnet assembly as claimed in claim 7 , wherein a heavy mass Mi of cold-storing material in the at least one cold reservoir of a respective stage of the thermal coupling decreases over the stages from the cold end toward the warm end.

9. The magnet assembly as claimed in claim 7 , wherein 3≤K≤7.

10. The magnet assembly as claimed in claim 1 , wherein the cryostat is configured as a cryogen-free cryostat.

11. The magnet assembly as claimed in claim 1 , wherein at least some of the cold reservoirs are formed as gas-tight containers, and wherein a part of the volumes of the gas-tight containers are filled with an evaporable substance.

12. The magnet assembly as claimed in claim 11 , wherein the current leads extend at least partially inside the containers in the normal-conducting region.

13. The magnet assembly as claimed in claim 8 , wherein at least some of the containers are thermally coupled, respectively, with a lower end via a heat conduction element to a heat sink of the active cooling device, and the boiling point of the substance contained in the containers is greater than the temperature of the heat sink.

14. The magnet assembly as claimed in claim 1 , wherein at least some of the cold reservoirs are formed as metallic bodies.

15. The magnet assembly as claimed in claim 14 , wherein a plurality of the cold reservoirs formed as metallic bodies are arranged spaced apart from one another in a vacuum region of the cryostat.

16. The magnet assembly as claimed in claim 1 , further comprising an active auxiliary cooling device, which is thermally coupled to respective sections of the current leads in the normal-conducting region.

17. The magnet assembly as claimed in claim 16 , wherein the auxiliary cooling device is furthermore thermally coupled to a radiation shield of the cryostat and/or to a vacuum container of the cryostat and/or to a temperature control device for a sample under study.

18. The magnet assembly as claimed in claim 16 , wherein a lowest working temperature AT hilf of the auxiliary cooling device is higher than a lowest working temperature AT mss of the active cooling device for the magnet coil system.

19. The magnet assembly as claimed in claim 1 , wherein the cross-sectional area B changes from the cold end toward the warm end by at least a factor of 3.

20. A method for operating a magnet assembly as claimed in claim 1 , comprising:
charging the magnet coil system via the current leads,
selecting a charging current, and
configuring the variable cross-sectional area B and/or the cold reservoirs such that: (i) for a thermal load WL load , which acts maximally on a coldest stage of the current leads in the normal-conducting region during the charging, and (ii) for a thermal load WL es on the coldest stage in an equilibrium state with charged magnet coil system, the following applies:
WL load ≤5* WL es .

21. The magnet assembly as claimed in claim 20 , wherein WL load ≤2*WL es .

22. The magnet assembly as claimed in claim 1 , wherein the current leads further comprise a high-temperature superconductor (HTS) region.

Assignees

• Bruker Biospin Ag
• Bruker Switzerland Ag

Inventors

• Wikus Patrick
• Hinderer Joerg
• Strobel Marco

Classifications

• H01F6/065 Primary

  Feed-through bushings, terminals and joints (leading of conductors or axles through casings of transformers H01F27/04) · CPC title

• H01F6/04

  Cooling · CPC title

• H01F6/06 Primary

  Coils, e.g. winding, insulating, terminating or casing arrangements therefor · CPC title