Directly coolable multifilament conductor

Abstract

A directly coolable multifilament conductor or a magnetic coil, having at least two electric conductors and at least one cooling tube disposed between the conductors adapted to carry a fluid coolant, wherein the cooling tube is a metal conductor having a lower conductivity than the conductors surrounding the tube.

Claims

1. A directly coolable multifilament conductor for a magnetic gradient coil of a magnetic resonance apparatus, comprising at least two electric conductors and at least one cooling tube disposed between the conductors and configured to carry a fluid coolant to provide cooling and to carry a current to minimized eddy currents, wherein the cooling tube is a metal conductor having a lower electrical conductivity than the conductors surrounding the tube, the cooling tube has a rectangular or a circular cross section, and the at least two electric conductors have a rectangular cross section.

2. The conductor according to claim 1, wherein the cooling tube comprises stainless steel, and the at least two conductors comprise copper or aluminum.

3. The conductor according to claim 1, wherein the cooling tube has a wall thickness of 0.5-1.5 mm.

4. The conductor according to claim 1, wherein the rectangular cooling tube has a width between 3 mm and 7 mm and a height between 3 mm and 7 mm.

5. The conductor according to claim 1, wherein the rectangular at least two electric conductors have a width between 1 mm and 5 mm and a height between 3 mm and 7 mm.

6. The conductor according to claim 1, wherein the at least two electric conductors are twisted around the cooling tube.

7. The conductor according to claim 1, wherein the at least two electric conductors comprise an isolating surface coating.

8. The conductor according to claim 7, wherein the isolating surface coating is a varnish or a polymer coating.

9. The conductor according to claim 1, wherein the at least two electric conductors and the cooling tube are embedded in a flexible casting or a flexible coating that allows the at least two electric conductors to be bent.

10. A directly cooled magnetic gradient coil comprising at least one directly coolable multifilament conductor according to claim 1 forming a coil winding.

11. The directly cooled magnetic gradient coil according to claim 10, wherein the directly cooled magnetic gradient coil is a directly cooled magnetic gradient coil for a magnetic resonance apparatus.

12. A magnetic resonance apparatus, comprising at least one directly cooled magnetic gradient coil according to claim 10.

13. The conductor according to claim 1, wherein the circular cooling tube has a diameter between 3 mm and 7 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages of the invention are explained below in combination with various embodiments shown in the figures. The figures show:

(2) FIG. 1: A principle sketch of an inventive magnetic resonance apparatus comprising an inventive gradient coil,

(3) and

(4) FIGS. 2-10: Various principle sketches of different conductor means comprising a metal tube adapted to carry a liquid cooling means and several conductors having a higher conductivity than the metal tube, which conductors are arranged around the tube.

DETAILED DESCRIPTION

(5) FIG. 1 shows a principle sketch of an inventive magnetic resonance apparatus comprising a housing 2 with a central bore 3 into which an object, for example a patient, to be imaged is arranged.

(6) In the housing 2 among others a gradient coil 4 is arranged comprising several magnetic coils 5, which are usually embedded in a hardened grouting material, usually a polymer. Each coil is made of an inventive conductor means 6 being wound into a respective geometry needed for creating the respective magnetic field. The setup and the properties of such a gradient coil 4 are known.

(7) FIG. 2 shows a first embodiment of an inventive conductor means 6. The conductor means is a directly coolable multifilament conductor means. It comprises a cooling tube 7 arranged in the center of the conductor means 6. The cooling tube 7 is adapted to carry a fluid cooling means through a central channel 10 which is issued to cool the conductor means 6 which gets heated under operations due to the current being carried by the conductor means 6 and due to eddy currents. The tube 7 is made of metal, preferably steel, especially stainless steel. It has a rectangular cross section, with the wall thickness being between 0.5-1 mm. The width of the tube 7, seen in the horizontal direction, is clearly smaller than its height. The width may for example be between 2-4 mm, while the height is between 6-10 mm.

(8) At the two opposing long sides of the tube 7 several conductors 8 also having a rectangular shape are arranged in a stacked manner. Each stack comprises for example four conductors 8. The conductors having a higher electrical conductivity than the metal tube are made of copper or aluminium. In case they are made of copper they preferably comprise an isolating surface coating 9, preferably a varnish or a polymer coating. In case they are made of aluminium such a coating is optional due to the passivation layer usually present on an aluminium surface.

(9) The rectangular conductors, which may also have a square cross section, for example have a width between 2-4 mm and a height between 2-4 mm, while also these geometry parameters are only exemplary.

(10) The conductors 8 are stacked above and adjacent to each other, but are not fixed to each other. They are also not fixed to the tube 7. This allows a certain movement of the respective components relative to each other, so that the conductor means 6 can be bent and wound into a coil form.

(11) The heat produced in operation of the conductor means respectively the coil is transported to the metal tube 7 having a low thermal resistance, so that the heat can be transferred to the cooling means flowing through the hollow tube 7. This allows for a very effective cooling of the cooling means 6. Aside that the metal tube 7 also acts as a filament carrying the operational current. As it has a lower conductivity compared to the electric conductivity of the copper or aluminium conductors it is possible, especially when the wall thickness of the tube 7 is small, that the tube 7 has an efficiently large hollow cross section, so that the necessary flow rate of cooling fluid through the tube 7 can be realized.

(12) FIG. 3 shows another embodiment of an inventive conductor means 6, with the same reference numbers being used for the same components. Also, this conductor means comprises a hollow rectangular tube 7 being made of a metal having a lower electrical conductivity than the conductors 8 being arranged around all four sides of the rectangular tube 7. The conductors 8 are made of copper or aluminium with an optional isolating surface coating 9, for example a varnish or a polymer coating.

(13) FIG. 4 shows an embodiment of an inventive conductor means 6 which is comparable to the embodiment of FIG. 3. Different to FIG. 3 the hollow tube 7 of FIG. 4 has a circular or oval cross section. The conductors 8 are arranged around the tube 7, comparable to the embodiment of FIG. 3.

(14) FIG. 5 shows an embodiment of a cooling means 6 with a rectangular metal tube 7 and several conductors 8 also having a rectangular shape with a width and height comparable to the dimensions of the tube 7. In this embodiment at each long side of the tube 7 three conductors 8 are arranged, each comprising an optional isolating surface coating 9. Also, this embodiment allows a very good heat transfer to the cooling means flowing through the metal tube 7, which itself acts as a filament conductor.

(15) FIG. 6 shows an embodiment comparable to FIG. 5. It comprises a hollow tube 7 made of metal having a lower conductivity than the metal conductors 8. The tube 7 and the conductors 8 are arranged in a horizontal direction, with three conductors 8 being stacked above each other and arranged at each side of the tube 7. Also here the geometry of each conductor 7 is comparable to the tube geometry.

(16) FIG. 7 shows a conductor means 6, with a hollow tube 7 with a vertical orientation and with respective conductors 8 having a horizontal orientation, which are arranged at both long sides of the tube 7. In this embodiment at each side five conductors 8 are arranged. The conductor 8 in the middle of each conductor stack is thicker than the other conductors being arranged below and above the center conductor. By changing the cross section the electrical properties, especially the effective conductor cross section, may be varied and adjusted.

(17) FIG. 8 shows an embodiment of a conductor means 6 with a circular tube 7 being arranged in the center of the circular arrangement. Through its central channel 10 the liquid cooling means flows for transporting the heat away from the conductor means 6. The circular tube has an outer diameter between 2-10 mm, especially between 3-7 mm and is made of a metal having a lower electrical conductivity compared to the electrical conductivity of the conductors 8 arranged around the circular tube 7. The conductors 8 also have a circular cross section with a diameter also chosen between 2-10 mm, especially between 3-7 mm, but with a preferably smaller diameter compared to the diameter of the tube 7. The conductors 8 may also comprise an isolating surface layer 9, especially when they are made of copper. The conductors 8 may be twisted around the central tube 7.

(18) FIG. 9 shows an embodiment of a conductor means 6 which also comprises a hollow circular tube 7 around which the circular conductors 8 are arranged. In this embodiment the whole setup is casted into a flexible casting 11 made of a polymer or plastic material, which preferably also has elastic properties. The casting 11 fixes the conductors 8 relative to the tube 7, with the conductors still being in a thermal connection to the tube 7. Due to its flexibility and elasticity it is possible to bend the conductor means 6, while the flexibility and elasticity allow for stretching and compressing at the respective bends and also allows for a certain movement of the conductors 8 in the bending region.

(19) The conductors 8 may have an isolating surface coating 9, but this coating especially in this case is optional.

(20) Finally, FIG. 10 shows a conductor means 6 comprising a circular hollow tube 7 and circular conductors 8 being arranged around the tube 7. Again, the conductors are made of a metal having a higher electrical conductivity than the metal tube 7. The conductors 8 may have an optional isolating surface layer 9.

(21) In this embodiment a flexible or elastic coating 12 is arranged around the conductors 8 encasing the whole conductor means.

(22) Although the casting 11 or the coating 12 are shown only at the embodiments of FIGS. 9 and 10 with the circular tube 7 and the circular conductors 8, it is to be noted that also the other embodiments shown in FIGS. 2 to 7 may certainly be embedded in a casting 11 or in a coating 12 if need be.

(23) Although the present invention has been described in detail with reference to the preferred embodiment, the present invention is not limited by the disclosed examples from which the skilled person is able to derive other variations without departing from the scope of the invention.