Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Magnet structure or material
Patent
1986-10-16
1989-04-18
Harris, George
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Magnet structure or material
79DIG22, 403272, H01F 500
Patent
active
048231010
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of manufacturing a Bitter type coil, entering more particularly into the construction of a large sized magnet able to be used in a nuclear magnetic resonance (NMR) image forming installation. The invention also relates to a solenoid magnet having at least one Bitter type coil constructed by using this method.
2. Description of the Prior Art
It is known that NMR 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 having a diameter of 40 cm at least.
Furthermore, Bitter coils are well known for producing intense magnetic fields. The structure proposed by Bitter is a winding formed of metal annular disks (generally made from copper or aluminium) split so as to form as many turns and connected 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 are disposed in the same configuration from one disk to another so as to form a set of channels parallel to the axis of the coil. A cooling fluid, for example deionized water, kerosene or oil, flows in the channels.
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 number of such Bitter coils arranged along a common longitudinal axis. Methods of calculating such magnets are for example explained in other patent applications of the applicant.
SUMMARY OF THE INVENTION
The invention relates mainly to a method of constructing such a Bitter type coil, consisting in forming a winding of turns in the form of flat annular metal disks and jointingly stacking such disks, wherein such disks or parts of such disks are connected end to end by welding with indium as filler.
Indium welding may be carried out at a relatively low temperature (of the order of 200.degree. C.) so as to avoid deformation of the disks or disk portions, which allows a particularly regular winding to be obtained with jointing turns. In addition, indium has the additional advantage of an excellent electric conductivity.
Furthermore, the indium is preferably deposited before welding by electrolytic deposition on portions to be assembled together. Welding is then carried out by heating the portions in the assembled position, for example by means of a "HF turn". In one possible embodiment, the portions to be assembled together are provided with tongues and grooves of complementary shapes and dimensions, and the indium is deposited on these tongues and grooves.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and other advantages thereof will better appear from the following description, given solely by way of example with reference to the accompanying drawings in which:
FIG. 1 shows a disk part used for forming a Bitter type coil;
FIG. 2 is a detailed view illustrating the assembly of two similar disk parts, after the indium has been deposited and before welding the parts; and
FIG. 3 shows the winding of turns in the form of flat metal annular disks by jointingly stacking such disks.
DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
Referring to the drawings, the basic structure used in the invention has been shown for forming a large size Bitter coil usable more particularly in an NMR image forming installation for generating a uniform magnetic field of high homogeneity. Each coil is formed of the end to end assembly of flat annular disk parts 12. Each disk part 12 comprises, in the example shown, opposite tongues and grooves 14, 15, of complementary shapes and dimensions, at each of its ends respectively. T
REFERENCES:
patent: 2438967 (1948-04-01), Ellsworth
patent: 3497951 (1970-03-01), Reighter
patent: 3864507 (1975-02-01), Fox et al.
patent: 4165148 (1979-08-01), Campbell et al.
Centre National de la Recherche Scientifique
Harris George
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