Superconducting magnet with arrangements to reduce stray magnetic fields

A superconductive magnet comprises a magnet assembly about an axis 10 where, in use, radially inner components have a lower circumferential electrical conductance than radially outer components. The components may be tubular thermal shields 2, 3 and/or coil formers 1, 4. A thermal shield bore tube 2 located radially inward of a superconducting coil 7 may incorporate axial slits or slots. Alternatively, an inner tubular thermal shield 2 may be made from a material with a lower conductivity to that of an outer tubular thermal shield 3. Various grades of aluminium alloys such as Al 1200, Al 6082, Al 6982, Al 5083, LM25 and LM27 may be used to provide components with different electrical conductance values. The magnet may include a stainless steel helium enclosure 8, a vacuum vessel 6 and shield coils 5. The superconductive magnet may provide integrated field burst protection for the stray magnetic fields associated with the quenching of a superconducting magnet.