Bruker Biospin Ag

Bruker Ag

Bruker Biospin Gmbh

Andreas Amann

Robert Schauwecker

Pierre-Alain Bovier

Werner H Tschopp

Klaus Schlenga

Gerhard Roth

Wolfgang Frantz

Daniel M Eckert

A magnet assembly for generating a magnetic field (H) in the direction of a z axis in a working volume (AV) comprises an actively shielded superconducting magnet coil system (M) and at least one current path (P , . . . , Pn) which is superconductingly closed in the operating state. The actively shielded superconducting magnet coil system (M) has a radially inner partial coil system (C ) and a radially outer partial coil system (C ) disposed coaxially with respect to each other. An external device supplies current to the current paths (P , . . . , Pn) to charge each path to a respective current (IP , . . . , IPn) in the operating state. When optimizing the fringe field behavior outside of the magnet system, the overall magnitude of magnetic dipole moments of the current paths (P , . . . , Pn), charged to their respective operating currents (IP , . . . , IPn), is at least 0.1% of the magnitude of the magnetic dipole moment of the charged partial coil system (C ). When charging the current paths (P , . . . ,Pn) to their respective operating current (IP , . . . , IPn), the resulting change &Dgr; of the coefficient of second order (H ) of the polynomial expansion of the magnetic field (H) of the magnet assembly is given by: &verbar;&Dgr; &verbar;<max (0.25T/m , 0.9&middot;&verbar;H (M)&verbar;), wherein H (M) designates the coefficient of second order of the polynomial expansion of the magnetic field of the actively shielded superconducting magnet coil system (M) in the operating state. This permits compensation for deviations of the fringe field of the magnet assembly from its design values due to deviations of coil parameters from their design values, through an appropriate design of the additional current paths (P , . . . , Pn) and setting their currents to a suitable value.

Actively shielded superconducting magnet assembly with a device for additional fringe field optimization

NMR magnet coil system with separate superconducting short-circuited regions for drift compensation as well as method for operation thereof

A magnet assembly for generating a magnetic field (H) in the direction of a z axis in a working volume (AV) disposed on the z axis about z&equals;0 with an actively shielded superconducting magnet coil system (M) and at least one current path (P , . . . , Pn) which is superconductingly closed in the operating state, wherein the actively shielded superconducting magnet coil system (M) comprises a radially inner partial coil system (C ) and a radially outer partial coil system (C ) disposed coaxially with respect to each other and whose magnetic dipole moments have opposite signs in the operating state and differ by an amount &Dgr; , with &verbar;&Dgr; &verbar;<2.5% of the magnitude of the magnetic dipole moment of the radially inner partial coil system (C ), is characterized in that the current paths (P , . . . ,Pn) are at least temporally superconductingly short-circuited during charging of the actively shielded superconducting magnet coil system (M) and that the current paths (P , . . . , Pn) are designed such that the currents induced therein due to the charging process of the magnet coil system (M) generate an overall magnetic dipole moment of a magnitude of at least 0.1% of the magnitude of the magnetic dipole moment of the charged radially outer partial coil system (C ). Suitable design of the additional current paths compensates for deviations of the fringe field from its design specification, due to deviations of coil parameters from their design values.

Actively shielded superconducting magnet assembly with improved fringe field compensation

In a magnet arrangement (M, D, P , . . . , Pn) having a magnet coil system (M) with at least one current-carrying superconducting magnet coil, with an additional current-carrying coil system (D) which can be fed by an external current source to produce a magnetic field in the working volume which differs substantially from zero, and optionally with additional superconductingly closed current paths (P , . . . , Pn), wherein the magnetic fields in the z direction, generated by the additional current paths (P , . . . , Pn) due to currents induced during operation and the field of the additional current-carrying coil system (D) do not exceed 0.1 Tesla in the working volume, the additional coil system (D) is designed such that its field contribution to the working volume is determined taking into account the diamagnetism of the superconductor in the main coil system. This permits as large as possible an effective field efficiency of the additional coil system (D).

Dimensioning of magnet arrangement comprising an additional current carrying coil system

A magnet arrangement comprising a superconducting magnet coil system (C) for generating a magnetic field in the direction of a z axis in a working volume (AV) disposed on the z axis about z&equals;0, wherein the field of the magnet coil system (C) in the working volume (AV) comprises at least one inhomogeneous contribution H &middot;z with n&gE;2 whose contribution to the total field strength on the z axis about z&equals;0 varies with the nth power of z, and wherein a field shaping device (P) of magnetic material is provided, which is substantially cylindrically symmetrical with respect to the z axis, is characterized in that the magnet coil system (C) is provided for use in an apparatus for high-resolution magnetic resonance spectroscopy and the field shaping device (P) has, at least partially, a radial separation from the z axis of less than 80 mm and compensates for at least one of the inhomogeneous field contributions H &middot;z of the magnet coil system (C) by at least 50%, wherein at least one additional coil system (S) is provided which acts as a shim device in the magnet arrangement. This permits realization of a field shaping device from magnetic material of a suitable geometry such that at least part of the notch structures for field homogenization can be omitted in the magnet coil system.

Magnet arrangement comprising a superconducting magnet coil system and a magnetic field shaping device for high-resolution magnetic resonance spectroscopy

A magnet arrangement comprising an actively shielded superconducting magnet coil system (M) and a plurality of protective elements (R , . . . , Rl) for protection in case of a quench, wherein the superconducting magnet coil system (M) comprises a radially inner partial coil system (C ) and a radially outer partial coil system (C ) which are electrically connected in series and arranged coaxially with respect to one another and which each produce a magnetic field of opposite direction, wherein the superconducting current path of the magnet coil system (M) is subdivided into several sections (A , . . . , An) each of which is electrically connected in parallel with at least one of the protective elements (R , . . . , Rl), and wherein at least one of these sections (A , . . . , An) comprises windings of the radially inner partial coil system (C ) and also windings of the radially outer partial coil system (C ), is characterized in that at least one additional closed current path (C ) is provided which has a non-vanishing areal winding number and which has a non-zero inductive coupling L with at least one section Ai. This permits&mdash;in particular through selection of the dimensions of the additional current path (C )&mdash;suppression of an excess stray field of the magnet arrangement in the case of a quench of the magnet coil system (M).

Magnet arrangement comprising an actively shielded superconducting magnet coil system and an additional current path for stray field suppression in case of a quench

A superconducting magnet arrangement (M, S, P1, . . . , Pn) for generating a magnetic field in the direction of a z axis in a working volume, disposed about z&equals;0, comprising a magnet coil system (M) with at least one current-carrying superconducting magnet coil, a shim device (S) with at least one superconducting shim coil and additional superconductingly closed current paths (P1, . . . , Pn), wherein the magnetic fields generated in the z direction and in the working volume by the additional current paths due to induced currents during operation, do not exceed a magnitude of 0.1 Tesla, and wherein the shim device generates a field which varies along the z axis with a k power of z for an even power of k>0, is characterized in that the shim device is designed such that the effective field efficiency g of the shim device is substantially zero taking into consideration the diamagnetism of the superconductor in the magnet coil system.

Dimensioning of a superconducting shim device in a superconducting magnet arrangement

A superconducting magnet system for generating a magnetic field in the direction of a z axis in a working volume disposed about z&equals;0 with at least one current-carrying magnet coil (M) and with at least one additional, superconductingly closed current path (P , . . . , Pn), which can react inductively to the changes of the magnetic flux through the area enclosed by it, wherein the magnetic fields in the z direction in the working volume which are produced by these additional current paths during operation and due to induced currents, do not exceed a magnitude of 0.1 Tesla, is characterized in that, when an additional disturbance coil (D) produces a substantially homogeneous disturbance field in the magnet volume, the diamagnetic expulsion of the disturbance field from the main magnet coil is taken into consideration when designing the magnet coil(s) and the current paths. This permits straightforward modification of a conventionally calculated magnet arrangement to optimize the actual disturbance behavior of the system.

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Zurich, Switzerland

Andreas Amann