Shield for a magnet

A shield is provided for a magnet of the type used in magnetic resonance imaging or spectrsocopy 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.