Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Magnet structure or material
Patent
1986-11-14
1988-04-05
Harris, George
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Magnet structure or material
336232, 324320, H01F 720
Patent
active
047361760
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention, due to the collaboration of the National Intense Fields Dept. of the CNRS (Director M. Aubert) relates to a solenoidal magnet formed of a stack of annular disks, better known under the name of Bitter magnet; the invention relates more particularly to this type of magnet with a view to obtaining a magnetic field having the required homogeneity in a given volume in the region of the center of the magnet, one of the priviliged applications of the invention being image formation by nuclear magnetic resonance (NMR).
It is known that NMR image forming installations, among other things, require a large sized magnet capable of generating a uniform magnetic field in a given region of space. Typically, it is necessary to generate a field of 0.15 to 0.5 teslas with a homogeneity of 1 to 10 parts per million (ppm) in a sphere having a diameter a diameter of 40 cm at least.
2. Description of the Prior Art
Bitter coils are well known for the production of intense magnetic fields. In theory, the structure proposed by Bitter is a coil formed of annular metal disks (generally made from copper or aluminium), split so as to form as many turns and connected together so as to define a substantially helical winding with flat turns. The stack of disks is held in position by a plurality of tie rods. This structure is advantageous for it allows efficient cooling of the magnet, by forming holes in the disks (and in the insulators separating these disks), these holes being disposed in the same configuration from one disk to another so as to form an assembly of channels parallel to the axis of the coil, in which a cooling fluid flows, for example deioinized water, kerosene or oil.
In accordance to what is described in another patent application of the applicant, it is possible to calculate a magnet delivering a magnetic field of required homogeneity in a certain volume in the vicinity of its center of symmetry and formed of a certain number of Bitter coils joined side by side along a common longitudinal axis, these coils being constructed from disks all having the same inner and outer diameter, but of different thicknesses from one coil to another. The invention relates principally to a structure for connecting such coils, providing a perfectly rectilinear stack of said coils while distrubuting little the magnetic fields such as calculated from a theorectical model neglecting the technological constraints for connecting the coils and keeping the continuity of the cooling fluid channels.
SUMMARY OF THE INVENTION
In this spirit, the invention relates then essentially to a solenoidal magnet comprising Bitter type annular disks, of the same inner and outer diameters and including several coils of such disks joined side by side along a common longitudinal axis, wherein, with the disks of any two adjacent coils being of different thicknesses, two adjacent coils are connected together by means of a flat annular transition disk, forming a turn of the same inner and outer diameter as said disks and said transition disk has at least one thickness variation, depending on the difference of thickness of the disks of said adjacent coils.
The Bitter disks are conventionally stacked with interpositioning of insulators and all have the same configuration of holes for defining a cluster of channels parallel to the longitudinal axis of the magnet, in which the cooling fluid is caused to flow. Of course, said transition disks have the same configuration of holes for ensuring continuity of the cooling circuit inside all the series coils. In one possible embodiment, the transition disk may have a set-back on each of its faces, the height of this set-back corresponding to the helical pitch of the coil connected to this face. In another possibility, the transition disk may have a thickness of the same order of size as that of the disks of the adjacent coils and more particularly itself form one or more turns of regularily varying thickness, the thicknesses of the two ends of this or of
REFERENCES:
WO83/02522, PCT, Composite Coils for Toroidal Field Coils and Method of Using Same, R. Pericins et al.
Harris George
Thomson-CGR
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