Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Magnet structure or material
Reexamination Certificate
2001-09-17
2003-12-30
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Magnet structure or material
C335S216000, C600S410000, C324S318000
Reexamination Certificate
active
06670878
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a magnet arrangement comprising a superconducting magnet coil system for generating a magnetic field in the direction of a z axis in a working volume disposed on the z axis about z=0, wherein the superconducting magnet coil system comprises a radially inner partial coil system and a radially outer partial coil system which is coaxial thereto, and a field forming device of magnetic material which is disposed about the z axis and preferably cylindrically symmetrical thereto, and is located radially between the radially inner and the radially outer partial coil system and is coaxial with the two partial coil systems, wherein the radially inner partial coil system produces a homogeneous field in the working volume while the radially outer partial coil system per se produces an inhomogeneous field in the working volume. The invention also concerns various methods for dimensioning the magnetic field forming device.
U.S. Pat. No. 4,587,504 (Re. 36,782) discloses a superconducting magnet arrangement with a radially inner and a radially outer partial coil system and a magnetic shielding, wherein the magnetic field of the radially inner partial coil system is homogeneous.
U.S. Pat. No. 5,012,217 discloses a superconducting magnet arrangement comprising a radially inner and a radially outer partial coil system with a cylindrically symmetrical shielding disposed radially between the two partial coil systems, wherein the magnetic field of the radially outer partial coil system is inhomogeneous.
Superconducting magnet coil systems are used for different applications, in particular for magnetic resonance methods, wherein the local homogeneity of the magnetic field in the working volume of the magnet arrangement is usually important. The most demanding applications involve high-resolution nuclear magnetic resonance spectroscopy (NMR spectroscopy). One typically tries to obtain a magnetic field strength which varies by less than 10 ppm of the field strength in the working volume through a length of between 50 to 60 mm along the axis of the magnet coil system. Means for homogenizing the field of the magnet coil system increase the coil volume. In consequence thereof and due to the typically very large field strengths, coil systems for magnetic resonance applications have a large magnetic dipole moment and therefore produce a large stray field. To counteract this stray field, superconducting partial coil systems can be mounted which compensate for the dipole moment of the main coil system (actively shielded magnet coil system). Additional stray field reduction can be achieved with magnetic shielding. These measures for reducing stray fields must not impair the field homogeneity in the working volume of the magnet arrangement.
U.S. Pat. No. 4,587,504 (Re. 36,782) describes an actively shielded magnet coil system for nuclear magnetic resonance applications wherein the field homogeneity in the working volume is obtained either by individually homogenizing both the main coil system and the shielding coil system or in that both partial coil systems mutually compensate each others inhomogeneous field contributions. The first embodiment is directed towards improving control of the resulting field homogeneity in the working volume while the second embodiment permits construction of a more compact magnet coil system. Additional magnetic shielding optimizes stray field suppression without influencing the field homogeneity in the working volume.
U.S. Pat. No. 5,012,217 describes an actively shielded superconducting magnet arrangement with additional magnetic shielding, wherein the magnetic field in the working volume generated by the magnet coil system itself is inhomogeneous and is rendered homogeneous through the field contribution of the magnetic shielding. More compact magnet systems can be constructed through utilization of the magnetic shielding for field homogenization. The field inhomogeneity of the magnet coil system is typically produced by the main coil system and also by the shielding coil system. The magnetic shielding is partially located radially between the two partial coil systems to permit reduction in the ampere winding number of the shielding coil system with respect to other conventional magnetic shielding arrangements.
Magnetic shielding in actively shielded magnet arrangements according to prior art is used to improve the stray field suppression of the actively shielded magnet arrangement thereby facilitating the field homogenization in the working volume.
In contrast thereto, it is the object of the present invention to supplement a homogeneous but not actively shielded magnet coil system (referred to as the radially inner partial coil system below) with an inhomogeneous radially outer partial coil system such that the overall resulting magnet arrangement produces, together with a magnetic field forming device, a homogeneous magnetic field in the working volume of the magnet arrangement. The radially outer partial coil system provides e.g. active stray field compensation.
SUMMARY OF THE INVENTION
In accordance with the invention, this object is achieved in that the radially outer partial coil system produces, together with the magnetic field forming device, a homogeneous field in the working volume. To utilize the magnetic field forming device for homogenizing the radially outer partial coil system, its exact field profile in the working volume must be calculated. Towards this end, it is particularly important that no magnetic hysteresis or remanence effects occur and that simple and exact calculation algorithms can be applied for the shape of the field of the magnetic field forming device in the working volume.
The invention solves this partial problem in that the radially inner and outer partial coil systems are designed such that there is a region in the radial space between the two partial coil systems where the magnetic field largely extends in a direction along the axis of the magnet arrangement and its strength is sufficient to magnetically saturate the magnetic material used, wherein the magnetic field forming device is disposed in this region.
Since the magnetic field forming device with the radially outer partial coil system of an inventive arrangement produce a homogeneous magnetic field in the working volume, existing radially inner partial coil systems can be advantageously retrofitted with a radially outer partial coil system and magnetic field forming device. Additionally, a magnet system can be produced in two variants: one with and one without radially outer partial coil system and magnetic field forming device. Magnet arrangements can be manufactured e.g. with or without stray field compensation using the same radially inner partial coil system. Homogenization of the radially outer partial coil system with the magnetic field forming device has the advantage that the radially outer partial coil system can have a simple structure; typically one single solenoid coil. The magnetic saturation of the magnetic field forming device and orientation of its magnetization along the axis of the magnet arrangement as well as the cylindrical symmetry of the magnetic field forming device permit simulation of its magnetic field as fields from cylinder surface currents, thereby permitting simple and precise calculation of the field.
In one particularly preferred embodiment of the inventive magnet arrangement, the radially inner and outer partial coil systems are electrically connected in series and form one single current path which is bridged via a switch. Such a magnet arrangement guarantees, without any further measures, that currents of identical magnitude flow in both partial coil systems.
In another advantageous embodiment of the inventive magnet arrangement, the radially inner and outer partial coil systems are electrically separated to constitute two separate current paths, each of which is bridged with a superconducting switch. The current in the individual partial coil systems of such a magnet arrangement can be ch
Bovier Pierre-Alain
Eckert Daniel
Laukien Frank
Schauwecker Robert
Bruker Biospin AG
Donovan Lincoln
Rojas Bernard
Vincent Paul
LandOfFree
Magnet arrangement comprising a superconducting magnet coil... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnet arrangement comprising a superconducting magnet coil..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnet arrangement comprising a superconducting magnet coil... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3143031