Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F7/00—Magnets
  • H01F7/06—Electromagnets; Actuators including electromagnets
  • H01F7/20—Electromagnets; Actuators including electromagnets without armatures
  • H01F7/202—Electromagnets for high magnetic field strength

Definitions

• the invention due to the collaboration of the National Service of the Intensive Fields of the CNRS (Director M. AUBERT) generally relates to a solenoid magnet with high homogeneity of magnetic field, made up of several coils spaced from each other; more particularly, it relates to a connection structure between the coils, making it possible to avoid the creation of components of stray fields.
• NMR imaging installations require a large magnet capable of generating a uniform magnetic field in a determined 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 of at least 40 cm in diameter.
• the invention relates to a solenoid magnet with high homogeneity of magnetic field, consisting of a set of coils of the same internal and external diameter, spaced from each other by chosen distances along a common axis, said coils being connected in series, characterized in that two neighboring coils are connected by two groups of conductors symmetrical with respect to a plane passing through said axis and the ends of said neighboring coils, so that the current components perpendicular to said axis in said groups of conductors, create ampere-turns in opposition, at any point in the space between said coils.
• the two groups of aforementioned conductors are embodied by one or more circular conductive rings, each group thus comprising the parts of rings situated on either side of the aforementioned plane.
• This or (preferably) these rings are arranged substantially transversely to the axis while being slightly deformed to define, each, two substantially helical and opposite half-turns.
• this or these rings are connected to the ends of said coils on the one hand and / or between them on the other hand, by successively diametrically opposite junctions. In other words, if only one ring is used (case of a relatively small spacing between two adjacent coils), this is connected to the two ends of the two adjacent coils at diametrically opposite points.
• first ring is connected to a coil end at a first point and to an adjacent ring at a diametrically opposite second point and so continued until the last ring is connected with the end of the other coil.
• Bitter coils are well known for production. strong magnetic fields.
• the structure proposed by Bitter 0 is a winding made up of annular metal discs (generally made of copper or aluminum), split to form as many turns and connected to define a substantially helical winding with flat turns.
• the stack of discs is maintained by a plurality of tie rods.
• This structure is advantageous because it allows efficient cooling of the magnet, by making holes in the discs (and in the insulators separating these discs), these holes being arranged in the same configuration from a disc to the other to materialize a set of channels parallel to the axis of the coil, in which a 2 Q cooling fluid circulates, for example deionized water, etherene or
• the invention preferably applies to a magnet constructed from such Bitter coils insofar as, in particular, at least some of the above-mentioned tie rods can be used to make the current return conductors, distributing this current over a substantially cylindrical surface and coaxial with the coils, as indicated above.
• FIG. 1 is a general sectional view schematically showing a magnet made up of several Bitter type coils, separated from each other by distances chosen and connected by systems of conductors according to the invention;
• FIG. 2 is a partial perspective view of such a conductor system
• FIG. 3 is a detailed view of a junction point of the conductor system of FIG. 2.
• a solenoid magnet bia annular discs of Bitter consisting of seven coils 13a, l * a, 15a, 16, 13b, 14b, 15b aligned along the same main axis of symmetry z'z.
• NMR nuclear magnetic resonance
• the magnet is symmetrical with respect to a transverse plane passing through O.
• a possible method of calculating the characteristics of the coils of the magnet and the spacings between these coils is indicated in another French patent application N 9 84 19191 , filed by the Applicant, and is not part of the invention presently described.
• the term “Bitter coil” is understood to mean any coil corresponding to the definition mentioned above.
• the radially split discs constituting the turns are connected, for example welded, end to end and held in a tight stack by means of a plurality of tie rods 18a or 18b regularly distributed over a cylindrical surface with an axis z'z. All the coils are connected in series.
• the current source not shown, is for example connected to the outer end of the coil 13a.
• the tie rods 18a are in several sections specific to each coil; they do not extend into the spaces defined between them.
• the tie rods 18b extend over the entire length of the magnet and are therefore common to all the coils.
• This plate is also in electrical contact with the tie rods 18b so that this arrangement defines a sort of squirrel cage connected in series as a whole with the coils of the magnet, the tie rods 18b being traversed by substantially equal fractions of the neck. ⁇ total rant which crosses the coils.
• the tie rods of the Bitter coils it is not essential to use the tie rods of the Bitter coils to compensate for the axial component of the current. If this compensation is sought, a simple cylindrical tubular casing external to the coils and coaxial can be used to ensure the current return. It is also possible to use a "squirrel cage" defined from other conductive rods than the tie rods.
• each group of conductors mentioned above consists of the halves of two circular conductive rings 0, 28, 29 located respectively of a same side of plane P.
• each ring 28 or 29 consists of several (for example two) concentric circular conductors 30 and 31 fixed by any suitable means to connecting pieces 35, 36, 37.
• the ring 28 is fixed at the end 25 of coil 15b by a metallic connecting piece 35.
• the ring 29 is fixed to the end 26 of the coil 14b by a similar metallic connecting piece 36.
• the rings 28 and 29 are connected to each other by a metallic connecting piece 37 diametrically opposite to the pieces 35 and 36.
• Two tie rods 18a located in the plane P and belonging respectively to the two coils to be connected are used to fix the pieces connection 35 and 36 at the ends of these coils (mounting holes 40).
• one of the tie rods 18b provided with its spacer crosses the connecting piece 37 (hole 41).
• the other tie rods 18b pass between the two concentric conductors 30 and 31 of each ring. These are of rectangular section and are fixed by screws and / or welded to the various connection pieces (see Figures 2 and 3).
• the conductive rings 28 and 29 are arranged substantially transverse to the axis while being slightly deformed longitudinally to each define two approximately helical half-turns and opposite, symmetrical with respect to the plane P. Consequently, at the output of the coil 15b considered, the current is also shared in the two half-turns and the current components flowing in the two half-turns of a same ring create ampere-turns in opposition, this in any point of the space between the coils. Substantially no axial magnetic field is therefore generated by the connection system between the coils. Furthermore, as mentioned previously, the axial component of current, however weak it may be, can be fairly precisely compensated by the current return tie rods.
• connection structure in the case where the coils of the magnet are effectively Bitter coils, it may be advantageous to produce the conducting rings 28, 29 from the same annular Bitter discs used for the manufacture of the coils, not split and connected end to end at diametrically opposite points. Furthermore, the number of rings used in a given space between two coils will depend on the length of this space.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Magnetic Resonance Imaging Apparatus (AREA)

Applications Claiming Priority (2)

Publications (2)

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• 1985
  • 1985-03-19 FR FR8504050A patent/FR2579362B1/fr not_active Expired
• 1986
  • 1986-02-21 US US06/939,124 patent/US4774487A/en not_active Expired - Fee Related
  • 1986-02-21 WO PCT/FR1986/000057 patent/WO1986005624A1/fr active IP Right Grant
  • 1986-02-21 DE DE8686901415T patent/DE3674973D1/de not_active Expired - Fee Related
  • 1986-02-21 EP EP86901415A patent/EP0215832B1/de not_active Expired - Lifetime

Non-Patent Citations (1)

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