Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Magnet structure or material
Patent
1987-01-06
1988-05-10
Harris, George
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Magnet structure or material
335300, 439883, H01F 500
Patent
active
047438797
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention, due to the collaboration of the Service National des Champs Intenses of the CNRS (Director M. AUBERT) generally relates to a solenoidal magnet with high magnetic field homogeneity, formed of several coils spaced apart from each other; it relates more particularly to a connection structure between the coils avoiding the creation of parasite field components.
It is known that NMR (nuclear magnetic resonance) image forming installations 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 magnetic field of 0.15 to 0.5 teslas with a homogeneity of 1 to 10 parts per million (ppm) in a sphere with a diameter of 40 cm at least.
2. Description of the Prior Art
It is known to form such a magnet from an assembly of coils spaced apart from each other by chosen distances along a common axis. In another patent application, the applicant describes a method for calculating the characteristics of such a magnet formed of coils all having the same inner and outer diameter and formed more particularly of Bitter type coils. In calculating such a magnet, it is assumed that no current flowing in the spaces between the coils is likely to create a magnetic field. Now, the coils are connected together in series and connecting conductors necessarily pass through these spaces. The invention relates more specifically to a connection structure between coils, adapted so as to avoid the formation of parasite field components between said coils.
SUMMARY OF THE INVENTION
With this in mind, the invention relates to a solenoidal magnet with high magnetic field homogeneity having several coils of the same inner and outer diameter spaced along a common longitudinal axis, wherein said coils are connected together in series by first conductors disposed parallel to said axis and extending respectively through said spaces between said coils, second conductors are disposed longitudinally in the vicinity of said first conductors and these second conductors are connected to third conductors formed and/or disposed over the length of each coil so as to distribute a current flow substantially uniformly over a cylindrical surface coaxial to said axis, said second and third conductors being interconnected and connected together in series with said coils so as to ensure the current return towards an axial end of said magnet.
The coils forming the above described magnet are preferably Bitter coils. Bitter coils are well known for the production of intense magnetic fields. The structure proposed by Bitter is a coil formed of annular metal disks (generally made from copper or aluminum), 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 together 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 materialize an assembly of channels parallel to the axis of the coil, in which flows a cooling fluid, for example deionized water, kerosene or oil.
The invention applies preferably to a magnet constructed from such Bitter coils to the extent that, more particularly, at least some of said tie rods may be used for forming said third conductors, distributing the return current over a substantially cylindrical surface coaxial with the coils, in the sections of the magnet occupied by these latter. In this embodiment, the ends of the tie rods may be connected electrically together by placing at each axial end of each coil an open ring, that is to say having a radial slit through which is established the connection point between said first corresponding conductor and said coil. The ring is of course isolated from the coil and a pair of said second conductors is disposed on each side of said first con
REFERENCES:
patent: 3281737 (1966-10-01), Swartz
Journal of Physics E, Scientific Instr., vol. 6, No. 4, Apr., 1973, C. B. Wheeler et al., Multiply Crowbarred Solenoids for Plasma Research, pp. 332-338.
Harris George
Thomson-CGR
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