Abstract: A method is provided of designing a magnetic resonance imaging magnet. At least one correction coil is positioned about the axial bore of the magnet which receives patients. The correction coil is used in the design process to reduce lower order harmonics generated by the magnet. Homogeneity of the magnetic field is thereby improved at selected volumes around the magnet.

Abstract: A multi purpose interconnect assembly between upper and lower helium vessels in a recondensing superconducting magnet to provide isothermal connections to extend the ride-through period, and to provide for helium liquid and gas passage, electrical interconnections, and to accommodate differential thermal contraction and expansion.

Abstract: A method for shimming a magnetic resonance imaging magnet requiring higher magnetic field homogneity on a small imaging volume and by magnetic field measurements on a larger volume providing small measurement error and practical field strength measurements and utilizing the spherical harmonic coefficients of the measurements.

Abstract: An open magnet useful in magnetic resonance imaging (MRI) applications. The magnet has two spaced-apart assemblies. Each assembly has a shielding coil located longitudinally outward from a main coil, a magnetizable member not carrying an electric current and spaced apart from and proximate the main and shielding coils, and a magnetizable pole piece spaced apart from the magnetizable member: The method of the invention generates a magnetic field in a first area between the two assemblies while shielding a second area not between the two assemblies from a stray magnetic field by creating the previously-described open magnet.

Abstract: A magnet cartridge for an open architecture superconducting magnet including an iron ring sandwiched between two coil forms, and including radial and axial positioning and securing apparatus to position, secure and maintain the relative positions of the coils on the coil forms and the iron ring in the presence of the strong superconducting magnet field generated by superconducting operation of said magnet.

Abstract: An open magnet useful in magnetic resonance imaging (MRI) applications. The magnet has two spaced-apart assemblies. Each assembly has a shielding coil located longitudinally outward from a main coil, a magnetizable member not carrying an electric current and spaced apart from and proximate the main and shielding coils, and a magnetizable pole piece spaced apart from the magnetizable member: The method of the invention generates a magnetic field in a first area between the two assemblies while shielding a second area not between the two assemblies from a stray magnetic field by creating the previously-described open magnet.

Abstract: In the installation of a superconducting magnet for magnetic resonance imaging at a preselected position in a mobile van, preselected curvilinear magnetic segments are applied to preselected locations on the exterior of the magnet to counteract magnet inhomogeneities in the imaging bore which would otherwise occur because of magnetic material in the van structure.

Abstract: An open superconductive magnet useful in magnetic resonance imaging (MRI) applications. The magnet has two spaced-apart assemblies and preferably has a "C" shape. Each assembly has: a vacuum enclosure having a longitudinal axis and surrounding a bore; a magnetizable pole piece located within the bore and outside the vacuum enclosure; and a superconductive main coil, a superconductive shielding coil, and a magnetizable ring positioned within the vacuum enclosure. There is no magnetizable solid path between the two pole pieces. Preferably, the ring is positioned longitudinally between the main and shielding coils.

Abstract: A quench-protecting superconductive-magnet electrical circuit. An impregnated superconductive-switch wire is coupled to the leads of a cryostable superconductive-coil assemblage having series-coupled coil portions. Series-coupled fan-in resistive heaters are also coupled in parallel with corresponding coil portions and are positioned thermally proximate the superconductive-switch wire. Fan-out resistive heaters are coupled in parallel with corresponding coil portions and are positioned thermally proximate corresponding coil portions. A local quench in one coil portion activates its corresponding fan-in resistive heater which quenches the superconductive-switch wire which activates all of the fan-out resistive heaters which globally quenches all of the coil portions thereby preventing local quench damage.

Abstract: A magnetic resonance imaging superconducting magnet including a cryostat, a gradient coil and superconducting gradient shield positioned around the gradient coil with an active resistive shimming member contiguous to the cryostat vessel; and the gradient shield being selectively cooled to superconducting operation after the magnetic shimming fields generated by the shimming member for field homogeneity within the bore of the magnetic resonance imaging magnet are induced onto, and maintained by, the superconducting gradient shield and operation of the resistive shimming member discontinued.

Abstract: A method of forming a superconducting joint between the Nb.sub.3 Sn layer of a superconducting tape and a superconducting NbTi wire through use of a Pb-Bi bath, joint securing arrangement and mold around the joint.

Abstract: An improved actively shielded superconducting magnet in which the main and bucking coils are directly wound onto respective coil support structures made of glass fiber-reinforced epoxy. The main and bucking coil cartridges are held in a fixed concentric relationship via a pair of flanges located at opposite ends of a helium vessel. During manufacture of the main and bucking coil cartridges, the outer diameters of the respective coil support structures are machined with high precision. Also, the diameters of two concentric grooves are precisely machined on the inner surface of each helium vessel end flange to match the outer diameters of the main and bucking coil support structures, so that at room temperature the main and bucking coil cartridges can slide smoothly into these grooves. The helium vessel is made of aluminum alloy and has a coefficient of thermal expansion which is greater than that of the fiber-reinforced epoxy coil support structures.

Abstract: A magnet including spaced-apart first and second pole pieces with generally opposing first and second pole faces. The first pole face has an axis extending generally towards the second pole face and has a surface region which includes at least two frustoconical surfaces. The frustoconical surfaces are generally coaxially aligned about the axis, and radially-adjacent frustoconical surfaces abut each other. In a second embodiment, points on the surface region located an identical radial distance from the axis are also located a common axial distance along the axis, and a graph of axial distance along the axis versus radial distance from the axis for such points is a curve having a continuous slope with at least two sign reversals. Such contoured pole faces allow for a smoother magnetic field to better reduce axisymmetric magnetic field inhomogeneity.

Abstract: A magnetic resonance imaging magnet including a superconducting gradient shield positioned around the gradient coil and contiguous to the cryogen vessel, with the gradient shield being selectively placed in superconducting operation to shield the magnet coils and structures from the magnetic fields generated by firing the imaging gradient coil positioned within the bore of the magnetic resonance imaging magnet. A plurality of thermally conductive members are compressed between the cryogen vessel and the gradient shield.

Abstract: A stable superconducting switch suitable for use in a conduction-cooled superconducting magnet includes a tape wound in a coil with the tape including an Nb.sub.3 Sn conductor sandwiched between stabilizing layers of copper, bronze or brass and wound in layers, with groups of layers separated by a partial layer of electrically conductive material.

Abstract: This invention relates to a pole face design for superconducting magnets of the type that are C-shaped. Such structures of this type, generally, employ pole faces which homogenize the magnet field within the imaging volume.

Abstract: An open architecture Magnetic Resonance Imaging Magnet with a pair of spaced annular superconducting magnet assemblies utilizing a cantilevered main magnet coil and correction magnet coil within each assembly.

Abstract: An apparatus and method is disclosed for evaluating the superconducting quality of superconducting materials. The materials are wound on a bifilar spool and tested in a cryogenic atmosphere to determine when the material quenches. During the testing procedure, the electro-magnetic field, current and temperature imposed on the material are varied and the test results are compared with known results to determine if the material is superconductive. In this way, large samples can be tested in a non-destructive manner.