GB2174248A - Superconducting coil for magnetohydrodynamic device - Google Patents

Abstract

In a superconducting coil 10 wound round a core 11, of e.g. iron, the arms 10a, 10b of the coil are spaced substantially equi-distant from adjacent parts of a yoke 12 and the core 11 so that the magnetic forces exerted on the coil arms are substantially zero and the mechanical support needed by the coil is minimised. The coil may be wound in a rectangular shape and used in a magnetohydrodynamic device with ducts 14, 15. <IMAGE>

Description

SPECIFICATION Improvements in magnetohydrodynamic devices This invention relates to high power magnets particularly for use in an application such as magnetohydrodynamic generation. Such magnets require a high intensity magnetic field of high homogeneity in an area of substantially rectangular cross-section.

The use of superconducting magnets gives the opportunity of producing the required field with a vey compact design of magnet.

According to the invention, there is provided a superconducting magnet comprising a superconducting coil having 'go' and 'return' arms, a core of magnetic material disposed between said 'go' and 'return' arms and a yoke of magnetic material surrounding said core and conductors and spaced from said core to define a pair of air spaces of substantially rectangular cross-section, wherein the 'go' and 'return' arms are spaced substantially equidistant from the adjacent surfaces of said core and yoke whereby to minimise the magnetic forces on said arms.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which, Figure 1 is a diagrammatic perspective view of a superconducting magnet constructed in accordance with the invention, Figure 2 is a cross-section through the magnet of Figure 1, and, Figure 3 is a flux path diagram of the magnet.

Referring first to Figure 1, the magnet comprises a superconducting coil 10 operating at cryogenic temperature, wound in an approximately rectangular shape around a soft iron core 11 which is at ambient temperature.

The magnetic circuit is completed by a soft iron yoke 12, which is also at ambient temperature, and core 11 is positioned within yoke 12 so as to define two air gaps 14, 15, each of substantially rectangular cross-section.

These gaps provide the working region of magnetic field and may thus be used to contain two identical MHD ducts.

Referring now to Figure 2, the coil 10 is enclosed in a cryostat comprising a helium vessel 16, radiation shield 1 7 and vacuum tank 18. The cryostat is rectangular in shape so that it entirely surrounds the coil 10 around its length.

Vessel 16 contains liquid helium so that the coil 10 can operate as a superconductor at 4.2 degrees Kelvin. The radiation shield 17 is made of high reflectivity material and vacuum tank 18 is the outer container of the cryostat and maintains the vessels within it under vacuum.

Referring more particularly again to Figure 1, the coil 10 has a 'go' arm 10a and a 'return' arm lOb. There are also two end connecting arms, one of which is shown at 21.

The positioning of 'go' and 'return' arms 10a, 10b, between the adjacent surfaces of core 11 and yoke 12, is selected so that there are substantially no magnetic forces on the arms tending to attract the arms towards either core 11 or yoke 12. When a current carrying conductor, like arm 10a or arm 10b, is positioned in air adjacent a ferro-magnetic member, forces are generated which attract the conductor towards the ferro-magnetic member.

In the present design each arm 10a, 10b, is positioned between two such members, namely core 11 and yoke 12, and as each arm is substantially equi-distant from the two attracting surfaces, the forces on the arm effectively cancel each other.

Each arm 10a, 10b is positioned to allow for the slight magnetic difference between the adjacent surface of yoke 12 and that of core 11 caused by the effect of air gaps 14, 15.

Because of the small sideways forces on arms 10a, 10b the supports for these arms can be relatively insubstantial. This minimises the need for structural support between the low temperature coil and the ambient temperature iron. The small amount of structural support needed minimises the heat leakage paths from the low temperature coil to the ambient temperature iron, thereby leading to improved cryogenic performance.

Members 21, 22, 23 and 24 support core 11 within the central aperture of yoke 12. In addition to supporting core 11 within yoke 12, members 21 to 24 define the side boundaries of gaps 14 and 15.

Figure 3 is a flux diagram of the magnet from which it will be seen that the magnetic field in gap 14 is substantially homogeneous and is of high intensity.

1. A superconducting coil having 'go' and 'return' arms, a core of magnetic material disposed between said 'go' and 'return' arms and a yoke of magnetic material completely surrounding said core and conductors, characterised in that said core (11) is spaced from said yoke (12) to define a pair of air spaces (14, 15) of substantially rectangular cross-section, and said 'go' and 'return' arms (10a, 10b) are spaced substantially equidistant from the adjacent surfaces of both said core (11) and said yoke (12) whereby to minimise the magnetic forces on said arms.

2. A superconducting coil as claimed in claim 1, characterised in that both said core (11) and said yoke (12) are at ambient temperature.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (2)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in magnetohydrodynamic devices This invention relates to high power magnets particularly for use in an application such as magnetohydrodynamic generation. Such magnets require a high intensity magnetic field of high homogeneity in an area of substantially rectangular cross-section. The use of superconducting magnets gives the opportunity of producing the required field with a vey compact design of magnet. According to the invention, there is provided a superconducting magnet comprising a superconducting coil having 'go' and 'return' arms, a core of magnetic material disposed between said 'go' and 'return' arms and a yoke of magnetic material surrounding said core and conductors and spaced from said core to define a pair of air spaces of substantially rectangular cross-section, wherein the 'go' and 'return' arms are spaced substantially equidistant from the adjacent surfaces of said core and yoke whereby to minimise the magnetic forces on said arms. An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which, Figure 1 is a diagrammatic perspective view of a superconducting magnet constructed in accordance with the invention, Figure 2 is a cross-section through the magnet of Figure 1, and, Figure 3 is a flux path diagram of the magnet. Referring first to Figure 1, the magnet comprises a superconducting coil 10 operating at cryogenic temperature, wound in an approximately rectangular shape around a soft iron core 11 which is at ambient temperature. The magnetic circuit is completed by a soft iron yoke 12, which is also at ambient temperature, and core 11 is positioned within yoke 12 so as to define two air gaps 14, 15, each of substantially rectangular cross-section. These gaps provide the working region of magnetic field and may thus be used to contain two identical MHD ducts. Referring now to Figure 2, the coil 10 is enclosed in a cryostat comprising a helium vessel 16, radiation shield 1 7 and vacuum tank 18. The cryostat is rectangular in shape so that it entirely surrounds the coil 10 around its length. Vessel 16 contains liquid helium so that the coil 10 can operate as a superconductor at 4.2 degrees Kelvin. The radiation shield 17 is made of high reflectivity material and vacuum tank 18 is the outer container of the cryostat and maintains the vessels within it under vacuum. Referring more particularly again to Figure 1, the coil 10 has a 'go' arm 10a and a 'return' arm lOb. There are also two end connecting arms, one of which is shown at 21. The positioning of 'go' and 'return' arms 10a, 10b, between the adjacent surfaces of core 11 and yoke 12, is selected so that there are substantially no magnetic forces on the arms tending to attract the arms towards either core 11 or yoke 12. When a current carrying conductor, like arm 10a or arm 10b, is positioned in air adjacent a ferro-magnetic member, forces are generated which attract the conductor towards the ferro-magnetic member. In the present design each arm 10a, 10b, is positioned between two such members, namely core 11 and yoke 12, and as each arm is substantially equi-distant from the two attracting surfaces, the forces on the arm effectively cancel each other. Each arm 10a, 10b is positioned to allow for the slight magnetic difference between the adjacent surface of yoke 12 and that of core 11 caused by the effect of air gaps 14, 15. Because of the small sideways forces on arms 10a, 10b the supports for these arms can be relatively insubstantial. This minimises the need for structural support between the low temperature coil and the ambient temperature iron. The small amount of structural support needed minimises the heat leakage paths from the low temperature coil to the ambient temperature iron, thereby leading to improved cryogenic performance. Members 21, 22, 23 and 24 support core 11 within the central aperture of yoke 12. In addition to supporting core 11 within yoke 12, members 21 to 24 define the side boundaries of gaps 14 and 15. Figure 3 is a flux diagram of the magnet from which it will be seen that the magnetic field in gap 14 is substantially homogeneous and is of high intensity. CLAIMS

1. A superconducting coil having 'go' and 'return' arms, a core of magnetic material disposed between said 'go' and 'return' arms and a yoke of magnetic material completely surrounding said core and conductors, characterised in that said core (11) is spaced from said yoke (12) to define a pair of air spaces (14, 15) of substantially rectangular cross-section, and said 'go' and 'return' arms (10a, 10b) are spaced substantially equidistant from the adjacent surfaces of both said core (11) and said yoke (12) whereby to minimise the magnetic forces on said arms.

2. A superconducting coil as claimed in claim 1, characterised in that both said core (11) and said yoke (12) are at ambient temperature.