Abstract: A subject receiving bore (12) of a magnetic resonance apparatus has an axial length to diameter ratio of less than 1.75:1 and preferably about 1:1. The temporally constant magnetic field generated by superconducting magnets (10) surrounding the bore has various magnetic field harmonic distortions including a Z12 harmonic distortion which is described generally by the equation Z.sup.12. In long bore magnets with a length to diameter ratio of 2:1 or more, harmonic distortions above Z6 are not present, or if present, not measured. A magnetic field probe (80 ) measures the magnetic field in the bore at a sufficient number of axial locations to measure at least the Z12 harmonic, e.g., 24 axially displaced locations. The probes are sampled at a sufficient number of angular increments, e.g., 32-36, that any present transverse spherical harmonics are sampled. Ferrous shims (62) are mounted in the bore in the pockets (58) of shim trays (44) to compensate for the Z12 and other sampled harmonics above Z6.

Abstract: A subject receiving bore (12) of a magnetic resonance apparatus has an axial length to diameter ratio of less than 1.75:1 and preferably about 2:1. The temporally constant magnetic field generated by superconducting magnets (10) surrounding the bore have various magnetic field harmonic distortions generally in the Z1-Z18 range. Shim trays (80) are disposed longitudinally around the bore (12). Each shim tray contains a number of shim pockets (84) which receive ferrous shims for shimming the magnetic field in the bore (12). An initialization system (60) calibrates the initial magnetic field within the bore (12). An initial shim distribution is determined which shims the inhomogeneous magnetic field toward a target more homogeneous magnetic field. An optimization system (66) determines a residual magnetic field from a difference between the present inhomogeneous magnetic field of the bore and the target magnetic field.

Abstract: A shield is provided for a magnet of the type used in magnetic resonance imaging or spectroscopy to limit the fringe field of a superconducting magnet to specified boundaries when the magnet is generating a magnetic field having a strength required for normal magnet operation. The shield includes a number of steel rectangular plates position around the magnet to form respective sides of a shield, the shield having a cross section in the form of a polygon such as a octrahedron. End caps having the shape of such polygon are joined to the ends of the plates. Structure is provided for supporting the magnet for movement as an integral unit relative to the shield. The supporting structure includes a first set of adjusting mechanisms for moving the magnet vertically and a second set of adjusting mechanisms for moving the magnet laterally, relative to the shield, to move the axis of the magnet into alignment with the shield axis, to avoid magnet quenching and inhomogeneities in the field generated by the magnet.

Abstract: A superconducting switch pack has six switch elements arranged with three in each of two planes. Each switch element is made of a length of cupro-nickel matrix multi-filamentary superconducting wire which is formed into a serpentine shape so as to be bifilar. Primary and back-up heater elements are positioned between the planes of switch elements, and all of the switch elements and heater elements are encapsulated in a solid resin body, with their leads extending outside of the body for connection to electrical circuits. This construction results in a stable superconducting switch pack which is non-inductive, has a high current carrying capability and off resistance. This reduces cryogen boil off of the superconductive circuits connected to the switch pack and makes the switch pack particularly suited for the shim coils of an MR magnet. Each section of the switch pack can also keep magnetic field drifts of the individual superconductive coils to less than 0.

Abstract: A superconducting switch is bifilarly wound with two cupro-nickel matrix superconductors. Three layers of the wire is wound, with each layer of windings wrapped with four wires in hand and input and output portions of the wires adjacent to one another. This configuration and relationship between adjacent wires is maintained throughout all the layers of the entire winding. The windings are started 180.degree. apart and input and output leads are extracted 180.degree. degrees apart. The switch also includes a core around which the wires and a heater are wound, a casing to enclose the core, heater and wire windings, and a solid epoxy body which fills substantially all of the voids in the switch. Switch leads are stabilized using a copper channel in which they are soldered to avoid quenching when they are subjected to a high current in a magnetic field, and the copper channel is surrounded and soldered to a copper braid.

Abstract: A method of forming a superconductive joint between superconductors made of filaments of superconducting material embedded in a matrix material utilizes two baths of molten metals. One of the baths of molten metal is used for etching the matrix material away from the superconducting filaments and is vibrated at an ultrasonic frequency. The other bath is also vibrated at an ultrasonic frequency and is used to mold the etched superconductors into a superconducting joint. Superconducting joints may thereby be made under ordinary atmospheric conditions between superconducting wires having similar and/or different matrix materials.