USE OF SUPERCONDUCTOR WIRE FOR ELECTRICALLY CONNECTING ADJACENT FIELD COILS IN A MAGNETIC RESONANCE IMAGING CRYOSTAT

Abstract

The invention relates to an electrically conducting wire, the wire (4) being formed as a flexible helix with constant or changing slope, with constant or changing diameter and with straight or curved extension, wherein the wire comprises a superconductor. In this way, a wire is provided that comprises a superconductor and that allows small bending radii, especially lower than 15 cm.

Claims

1. Use of an electrically conducting wire being formed as a flexible helix with constant or changing slope, with constant or changing diameter and with straight or curved extension, wherein the wire comprises a superconductor or an electrically conducting wire assembly with two electrically conducting wires, wherein the two electrically conducting wires are formed as a double helix with alternating winding directions. for electrically connecting the windings of adjacent field coils, each comprising superconductive windings of a magnet in a magnetic resonance imaging cryostat.

2. The use according to claim 1, wherein the electrically conducting wire or the electrically conducting wire assembly is guided via a bending that is equal or greater than 90 and/or that comprises a bending radius of 15 cm or less.

3. An assembly for a magnetic resonance imaging apparatus, the assembly comprising. a cryostat, a magnet with multiple field coils with superconductive windings arranged within the cryostat and an electrically conducting wire being formed as a flexible helix with constant or changing slope, with constant or changing diameter and with straight or curved extension, wherein the wire comprises a superconductor, or an electrically conducting wire assembly wherein the two electrically conducting wires are formed as a double helix with alternating winding directions, wherein the electrically conducting wire or the electrically conducting wire assembly is electrically connected to windings of adjacent field coils of the magnet.

4. The assembly for a magnetic resonance imaging apparatus according to claim 3, wherein the wire comprises MgB.sub.2 as a superconductor.

5. The assembly for a magnetic resonance imaging apparatus according to claim 3, wherein the diameter of the helix is between 1.5 cm and 8 cm, preferably between 3.5 cm and 6.5 cm.

6. The assembly for a magnetic resonance imaging apparatus according to claim 3, wherein the diameter of the wire is between 0.4 and 1.6 mm.

7. The assembly for a magnetic resonance imaging apparatus according to claim 3, wherein the wire has a length such that the number of windings is between 6 and 12.

8. The assembly for a magnetic resonance imaging apparatus according to claim 3, wherein the helix is a helix with changing directions wherein winding direction of the helix changes after each full turn.

9. The assembly for a magnetic resonance imaging apparatus according to claim 8, wherein the wire is bent back by 180 towards its previous course after a full turn.

10. The assembly for a magnetic resonance imaging apparatus according to claim 3, wherein the diameter of the wire is between is between 0.4 and 1.6 mm.

11. The assembly for a magnetic resonance imaging apparatus according to claim 3, wherein the wire has a length such that the number of windings is between 8 and 10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. Such an embodiment does not necessarily represent the full scope of the invention, however, and reference is made therefore to the claims and herein for interpreting the scope of the invention.

[0030] In the drawings:

[0031] FIG. 1 schematically depicts a cryostat with two electrically conducting wires according to a preferred embodiment of the invention which are each formed as a flexible helix,

[0032] FIG. 2 schematically depicts an electrically conducting wire assembly with two electrically conducting wires according to a preferred embodiment of the invention, wherein the two electrically conducting wires are formed as a double helix with alternating winding directions.

[0033] FIG. 3 schematically depicts an electrically conducting wire according to a preferred embodiment of the invention, wherein the winding direction of the helix changes after each 360 winding,

[0034] FIG. 4 depicts the method steps of a manufacturing method for an electrically conducting wire according to a first preferred embodiment of the invention and

[0035] FIG. 5 depicts the method steps of a manufacturing method for an electrically conducting wire according to a second preferred embodiment of the invention;

[0036] FIG. 6 shows a diagrammatic representation of a magnet (2) with multiple field coils with superconductive windings in which the helix-shaped electrical wire of the invention is incorporated.

DETAILED DESCRIPTION OF EMBODIMENTS

[0037] FIG. 1 schematically depicts a MRI cryostat 1 with two electrically conducting wires 4 according to a preferred embodiment of the invention. The electrically conducting wires 4 are both formed as a flexible helix. Here, the term flexible helix does not only relate to such conventional helix shapes which are defined as a curve that winds around the mantle of a cylinder which defines a diameter and with a constant slope. Rather, here also such geometries are understood to be a flexible helix which show a changing slope and/or a changing diameter along their respective extension. Further, the extension of the helix does not have to be straight as is the axis of a cylinder. Rather, the invention also allows for a curved extension of the helix which does not follow a straight line.

[0038] As depicted in FIG. 1, the electrically conducting wires 4 are routed in the MRI cryostat 1 from two electric terminals 3 to a super conducting magnet 4. Though this routing of the electrically conducting wires 4 means bending the wires 4, there is only a small risk of breakage since the electrically conducting wires 4 are shaped as a flexible helix. Therefore, this preferred embodiment of the invention takes advantage from the fact that bending a helix instead of a straight wire puts less stress on the individual wire turns and therefore allows smaller bend radii than allowable for a straight wire. This means that the electrically conducting wires 4 may even be formed from a brittle material.

[0039] According to the preferred embodiment of the invention described here, the electrically conducting wires 4 both comprise MgB.sub.2 as a superconductor. As mentioned above, MgB.sub.2 becomes superconducting below 39 K which has the advantage that cooling capacity is much higher at 39 K than at 9.7 K which is required for cooling NbTi. In this way, the drawback of conventional MgB.sub.2 wires, i.e., that they are brittle and may, therefore, easily crack, is overcome due the shape of a flexible helix.

[0040] Here, the electrically conducting wire has a diameter of the helix which is 5 cm and the electrically conducting wire 4 has a diameter which is 1 mm. Further, as can be understood from FIG. 1, the number of windings of each electrically conducting wire 4 is six.

[0041] Further, FIG. 2 schematically depicts an assembly with two electrically conducting wires 4 according to another preferred embodiment of the invention. Here, the two electrically conducting wires 4 are formed as a double helix wire assembly 5 with alternating winding directions. Since the currents in such alternating windings may compensate each other such a design is advantageous for field sensitive applications.

[0042] FIG. 3 schematically depicts an electrically conducting wire 4 according to another preferred embodiment of the invention which is also advantageous for field sensitive applications. Here, a helix 6 is provided wherein the winding direction of the helix 6 changes after each 360 winding.

[0043] The method steps of a manufacturing method according to a first preferred embodiment of the invention is depicted in FIG. 4. This manufacturing method comprises the following method steps: [0044] S1) arranging material comprising i) pre-reacted MgB.sub.2 powder or ii) Mg powder and B powder in the form of a helix with constant or changing slope, with constant or changing diameter and with straight or curved extension, and [0045] S2) heat treating the arranged material.
This means that this preferred embodiment of the invention allows for two alternatives, i.e., using pre-reacted MgB.sub.2 powder or Mg powder and B powder. In both cases these materials are arranged in the form of a helix with constant or changing slope, with constant or changing diameter and with straight or curved extension. However, the heat treatment in step S2 is different for both cases. In case i), the heat treating is performed at a temperature of 965 C. for 4 min. In contrast to that, in case ii) the heat treating is performed at a temperature of 650 C. for 40 min.

[0046] FIG. 5 depicts the method steps of a manufacturing method according to a second preferred embodiment of the invention. This method comprises the following method steps: [0047] a) arranging a pure Mg rod at the center of a Ta or Nb tube, [0048] b) filling the area between the area between the Mg rod and the Ta or Nb tube with B and C, [0049] c) repeating steps a) and b) for additional Mg rods and Ta or Nb tubes, [0050] d) bundling the filled rods, [0051] e) inserting the bundled and filled rods into a CuNi tube, [0052] f) cold deforming the filled CuNi tube in the form of a helix with constant or changing slope, with constant or changing diameter and with straight or curved extension, and [0053] g) heat treating the arranged material.

[0054] Here, C is provided as a carbon layer on the surface of the B particles or as C.sub.4H.sub.12 powders. Further, the heat treatment is performed at 640 C. In this way, Mg diffuses into the B particles and reacts to form MgB.sub.2 layers of 10 to 30 m thickness along the inner wall of the Ta tube.

[0055] FIG. 6 shows a diagrammatic representation of a magnet (2) with multiple field coils with superconductive windings in which the helix-shaped electrical wire of the invention is incorporated. The magnet 2 includes several field coils 61, each of them containing windings of superconducting material, e.g., including MgB2 in a matrix of normal resistive metal. Electrical feeding connections 62-1, 62-2 is provided for connecting to a power supply outside of the magnet, and even outside the cryostat 1. A helix-shaped electrical wire 63 is provided between one of the feeding connections 62-2 and an outer field coil 61. Also, helix-shaped interconnects 64 are provided between adjacent field coil 61 to facilitate wire routing of mechanically brittle electrical connections between the field coils 61.

[0056] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope. Further, for the sake of clearness, not all elements in the drawings may have been supplied with reference signs.

REFERENCE SYMBOL LIST

[0057] MRI cryostat 1 [0058] magnet 2 [0059] electrical terminals 3 [0060] superconducting wire 4 [0061] double helix wire assembly 5 [0062] helix with changing winding directions 6