Patent Application
20080224807
This application claims Paris Convention priority of DE 10 2007 013 349.0 filed Mar. 16, 2007 the complete disclosure of which is hereby incorporated by reference.
The invention concerns a magnet arrangement comprising a superconducting magnet coil system for generating a magnetic field in the direction of a horizontal z-axis in a working volume disposed along the z-axis about z=0, with at least one radial access to the working volume perpendicular to the z-axis, wherein the magnet coil system comprises at least one partial coil winding disposed coaxially about the z-axis at z>0, and at least one partial winding disposed coaxially about the z-axis at z<0.
A magnet arrangement of this type for NMR experiments is disclosed e.g. in [6].
Horizontal magnet arrangements are used, in particular, for MRI and also for EPR experiments. The magnetic field is thereby generally generated using solenoid coils with horizontal axis (z-axis).
The documents [1]-[6] disclose so-called “split coil” magnet arrangements. They consist of two separate coils or coil systems which are disposed mirror-symmetrically with respect to a plane that is perpendicular to the z-axis. This permits radial access (perpendicular to the z-axis) to the working volume in order to transfer e.g. samples or measuring means into or out of the working volume. The coil systems are separately wound on two or more coil bodies which are held together by a mechanical structure (or a support body) [3, 4]. The documents [4, 5, 6] moreover disclose magnet arrangements whose mechanical structure or support bodies support the axial forces between the two coil systems.
One problem with conventional magnet arrangements consists in that the coil bodies, the flanges and the mechanical structure which hold the coil bodies together must be fixed together in the gap. This reduces the small space available in the gap.
The assembly of the various coil bodies also causes production inaccuracies which, in turn, affect the homogeneity of the magnetic field of the magnet arrangement. One further problem with respect to field homogeneity arises when the actually effective magnetic forces differ from the theoretically calculated values of the design, and the coil systems are displaced with respect to each other.
Moreover, the production becomes complex due to the development of the individual coil systems, the assembly and connection of these coil systems.
It is therefore the purpose of the present invention to propose a magnet arrangement of the above-mentioned type which eliminates these problems.
This object is achieved in accordance with the invention in that at least one of the partial coil windings at z>0 as well as at least one of the partial coil windings at z<0 are supported by a common coil body, wherein the coil body has at least one opening at z=0 which permits radial access to the working volume, wherein the coil body supports the axial magnetic forces between the partial coil windings and wherein the coil body is force-fit mechanically connected at a front side to a first side plate.
The partial coil windings of the inventive magnet arrangement are disposed, in particular wound, onto a common coil body. A mechanical structure or a support body for fixing the coil body is not required due to the use of a common coil body. In consequence thereof, no space is required for fixing means. The partial coil windings may therefore be wound directly up to the opening of the coil body, thereby rendering the magnet arrangement particularly compact. In contrast to prior art, the individual parts of the coil body need not be joined, such that these production steps can be omitted. The common coil body moreover provides good heat transfer between the individual partial coil windings. The forces acting on the partial coil windings are advantageously transferred to one single coil body, thereby preventing an undesired movement of different coil body parts relative to each other. The correspondence between the calculated fields and those actually generated is also improved due to the increased mechanical precision.
In a preferred embodiment of the inventive magnet arrangement, the area of the material cross-section of the coil body is at least 5% of a ring area with a surface area (ra2−ri2)π in the sectional area perpendicular to the z-axis at z=0, wherein ra: largest separation between the outer contour of the material cross-section and the z-axis at z=0, with ra>0 and ri: smallest separation between the inner contour of the material cross-section and the z-axis at z=0 with ri>=0. This ensures the required stability of the coil body, at the same time realizing a large opening for radial access.
The coil body is preferably form-fit mechanically connected to a second side plate. The side plates are used to fix the coil body and the partial coil windings disposed thereon to the housing of the magnet arrangement. In contrast to a form-fit mechanical connection of the second side plate, a force-fit connection of the first and also of the second side plate would have static redundancy.
In one particularly preferred embodiment of the inventive magnet arrangement, at least one channel is provided in at least one of the coil bodies for passage of a wire, which connects a first chamber of the coil body containing a partial coil winding at z>0, to a second chamber of the coil body containing a partial coil winding at z<0. In this fashion, the partial coil windings can be wound in one single process. This reduces the number of joints and thus the manufacturing and assembly expenses.
In one particularly preferred embodiment, the magnet coil system comprises at least one additional coil body with at least one radial opening at z=0, wherein the radial openings of the coil bodies are disposed collinearly with respect to each other and permit radial access to the working volume perpendicular to the z-axis. Compensation coils may e.g. be disposed on the second coil body for reducing the stray field of the magnet arrangement, or shim coils may be provided for improving the homogeneity of the overall magnetic field.
In one particular embodiment of this inventive magnet arrangement, two partial coil windings are disposed mirror-symmetrically on each side of the center plane of the coil bodies, wherein the center plane extends through z=0 and is perpendicular to the z-axis. Symmetrically arranged partial coil winding pairs on different coil bodies do not generate any resulting magnetic forces between the coil bodies.
In a particularly advantageous embodiment of this type, at least one of the partial coil windings at z>0 is connected in series with at least one of the partial coil windings at z<0 as a protection section, wherein the protection section is connected in parallel with a common protection element. The protection elements protect the superconducting partial coil coil systems in the respective protection section in case of a quench to prevent an excessive increase of the magnetic forces acting on the superconducting coils. The series connection of the partial coil windings at z>0 with the partial coil windings at z<0 causes maintenance of the symmetric force-free field distribution, even during a quench.
It is also advantageous to provide axial access to the working volume along the z-axis. An axial access may be used e.g. for sample transfer.
The magnet arrangement is advantageously part of an apparatus for electron paramagnetic resonance (EPR) or nuclear magnetic resonance (NMR).
One obtains an overall compact magnet arrangement which can be produced with simplified production methods, and has improved stability and homogeneity properties.
Further advantages of the invention can be extracted from the description and the drawing. The features mentioned above and below may be used individually or collectively in arbitrary combination. The embodiments shown and described are not to be understood as exhaustive enumeration but have exemplary character for describing the invention.
a shows a sectional view of an inventive magnet arrangement along the z-axis;
b shows a three-dimensional broken-out section of an inventive coil body;
c shows a sectional view of the coil body of
a shows a sectional view of the inventive magnet arrangement M for generating a magnetic field in the direction of a horizontal z-axis. The partial coil windings A1a, A1b, B1c, B1b, B1c are wound onto a rotationally symmetric coil body K1 disposed about the z-axis. The coil body K1 has an opening O1 at z=0 perpendicular to the z-axis. Samples can be transferred through this opening O1 into a working volume V disposed at z=0. The opening O1 may also be used as a passage for measuring means or for irradiating a sample disposed in the working volume V.
The partial coil windings A1a, A1b, B1a, B1b, B1c are distributed along the z-axis, such that part of the partial coil windings A1a, A1b are located in an axial area at z>0, and the other partial coil windings B1a, B1b, B1c in an axial area at z<0. The coil body K1 is used as a support body for the partial coil windings A1a, A1b, B1a, B1b, B1c and the coil body K1 also supports the axial magnetic forces that prevail between the partial coil windings A1a, A1b, B1a, B1b, B1c.
The coil body K1 is force-fit connected to a first side plate F1 at an axial end (front side) of the coil body K1. A second side plate F2 disposed opposite to the first side plate F1 is moreover connected to the coil body K1 through form-fit connection. Towards this end, recesses, in particular millings, are provided on the side of the second side plate F2 facing the first side plate F1, into which the projections Vo1, Vo2 of the coil body K1 engage. The side plates F1, F2 provide a connection to a housing or are themselves part of the housing, as in the present case.
b is a 3-dimensional illustration of the coil body K1 of
c shows a sectional view of the coil body K1 of
In order to guarantee the stability required for supporting the magnetic forces that act on the coil body K1, the area of the cross-section of the walls W1, W2, shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 013 349.0 | Mar 2007 | DE | national |
