Magnet arrangement comprising an actively shielded superconducting magnet coil system and an additional current path for stray field suppression in case of a quench

• US 6,563,316 B2
• Filed: 11/08/2001
• Issued: 05/13/2003
• Est. Priority Date: 12/05/2000
• Status: Active Grant

• Current Assignee: Bruker Switzerland AG (Bruker Corporation)
• Original Assignee: Bruker Biospin AG (Bruker Corporation)
• Inventors: Schauwecker, Robert, Bovier, Pierre-Alain, Amann, Andreas
• Primary Examiner(s): Lefkowitz, Edward
• Assistant Examiner(s): Shrivastav, Brij B.
• Application Number:
  US09/986,249
• Publication Number:
  US 20020101239A1
• Time in Patent Office: 551 Days
• Field of Search: 324/318, 324/322, 324/309, 324/307, 335/301, 335/316, 307/91
• US Class Current: 324/318
• CPC Class Codes: G01R 33/3815 with superconducting coils, e.g. power supply therefor
• CPC Class Codes: G01R 33/421 of main or gradient magnetic field
• CPC Class Codes: H02H 7/001 for superconducting apparatus, e.g. coils, lines, machines
• CPC Class Codes: Y02E 40/60 Superconducting electric elements or equipment; Power systems integrating superconducting elements or equipment

Abstract

A magnet arrangement comprising an actively shielded superconducting magnet coil system (M) and a plurality of protective elements (R1, . . . , Rl) for protection in case of a quench, wherein the superconducting magnet coil system (M) comprises a radially inner partial coil system (C1) and a radially outer partial coil system (C2) which are electrically connected in series and arranged coaxially with respect to one another and which each produce a magnetic field of opposite direction, wherein the superconducting current path of the magnet coil system (M) is subdivided into several sections (A1, . . . , An) each of which is electrically connected in parallel with at least one of the protective elements (R1, . . . , Rl), and wherein at least one of these sections (A1, . . . , An) comprises windings of the radially inner partial coil system (C1) and also windings of the radially outer partial coil system (C2), is characterized in that at least one additional closed current path (C3) is provided which has a non-vanishing areal winding number and which has a non-zero inductive coupling L_Ai⇄C3 with at least one section Ai. This permits—in particular through selection of the dimensions of the additional current path (C3)—suppression of an excess stray field of the magnet arrangement in the case of a quench of the magnet coil system (M).

Claims

1. A magnet configuration having an actively shielded superconducting magnet coil system for generating a magnetic field in a direction of a z axis in a working volume disposed on the z axis about z=0, the configuration comprising:

a radially inner partial coil system;

a radially outer partial coil system, said radially inner and outer coil systems being electrically connected in series and arranged coaxially with respect to each other, each of said inner and outer coil systems generating a magnetic field of opposite direction along the z axis in the working volume;

a plurality of protective elements for protecting the superconducting magnet coil system in case of a superconductivity breakdown or quench, wherein the magnet coil system defines a superconducting current path which is divided into sections (A1, . . . , An) each of which is electrically connected in parallel to at least one of said protective elements, with at least one of said sections having windings of said radially inner and said radially outer partial coil systems; and

at least one additional closed current path (C3) said additional path having a non-vanishing areal winding number and a non-zero inductive coupling L<sub>Ai⇄

C3</sub> to at least one of said sections Ai.

2. The configuration of claim 1, wherein a coupling coefficient $K_i=\frac{L_{\mathrm{Ai}\leftrightarrow }}{}$

C3LAi

LC3

is larger than 0.01, wherein L_Ai characterizes a self-inductance of said section Ai and L_C3 characterizes a self-inductance of said additional current path.

3. The magnet configuration of claim 1, wherein said radially inner partial coil system and said radially outer partial coil system have dipole moments approximately equal in value and opposite in sign.

4. The magnet configuration of claim 1, further comprising means for high-resolution magnetic resonance spectroscopy.

5. The magnet configuration of claim 1, wherein said additional current path comprises a coil system which is not electrically connected to the magnet coil system and which is arranged coaxially thereto.

6. The magnet configuration of claim 1, wherein said additional current path is defined by a part of the magnet coil system, bridged with an additional switch.

7. The magnet configuration of claim 1, wherein said additional current path has a small ohmic resistance R3.

8. The magnet configuration of claim 7, wherein L_C3/R3≧

1s with L_C3 being a self-inductance of said additional current path.

9. The magnet configuration of claim 1, wherein said additional current path is superconducting.

10. The magnet configuration of claim 1, wherein said additional current path comprises a device for limiting a current induced therein.

11. The magnet configuration of claim 1, wherein said additional current path further comprises means for drift compensation of the magnetic field of the magnet configuration in the working volume.

12. The magnet configuration of claim 1, wherein said additional current path further comprises means for shimming the magnet configuration.

13. The magnet configuration of claim 1, wherein said additional current path further comprises means for compensating external magnetic field fluctuations in the magnet configuration.

14. The magnet configuration of claim 1, wherein said additional current path is inductively decoupled from the magnet coil system.

15. The magnet configuration of claim 1, wherein at least one said inductively coupled section Ai having an inductive coupling to said additional current path which is substantially different from zero, also has a magnetic dipole moment substantially different from zero, wherein a current which is induced in said additional current path in case of a quench of said inductively coupled section, produces a magnetic dipole moment which corresponds substantially to that of said inductively coupled section before the quench.

16. The magnet configuration of claim 1, wherein said additional current path is superconducting and is thermally decoupled from at least one of said sections.

17. The magnet configuration of claim 16, wherein in case of a quench in said thermally decoupled section, an amount of heat transferred to said additional current path is not more than 50% of an amount of heat which is required for triggering a quench in said additional current path.

18. The magnet configuration of claim 1, wherein said additional current path is superconducting and thermally coupled with at least one of said sections.

19. The magnet configuration of claim 18, wherein heat transferred to said additional current path during a quench in said thermally coupled section corresponds to at least twice an amount of heat required for triggering a quench in said additional current path.

20. The magnet configuration of claim 1, wherein a substantial portion of at least one of said sections comprises only windings of said radially inner partial coil system or windings of said radially outer partial coil system.

21. The magnet configuration of claim 20, wherein said substantial portion is equal to said section.

22. The magnet configuration of claim 1, further comprising a passive magnetic material shielding.

23. The magnet configuration of claim 22, wherein said passive shielding is an integral component of a cryostat in which the magnet coil system is located.

24. The magnet configuration of claim 22, wherein said passive shielding is not completely magnetically saturated during operation.

25. The magnet configuration of claim 22, wherein said passive shielding comprises at least one of ferromagnetic material and soft iron.

26. The magnet configuration of claim 22, wherein said passive shielding is disposed radially beyond a radially outermost winding of the magnet coil system.