Abstract: A magnet system to generate a static, uniform magnetic field in the examination chamber of a nuclear spin tomograph has a pair of outer field coils (1a, 1b) arranged on a common axis (a) at a mutual axial distance (g.sub.1) and a pair of inner field coils (2a, 2b) coaxial with the outer ones which are also equal to each other, in which both pairs of coils are arranged symmetrically to a central plane (E) perpendicular to the common axis (a). The axial distance (g.sub.1) between the outer field coils (1a and 1b) is 40 to 60% of their inside diameter (da.sub.2). The axial distance (g.sub.2) between the inner field coils (2a and 2b) is, with a maximum deviation of 15%, equal to that (g.sub.1) between the outer coils (1a and 1b). The magnet system forms an almost eight-order coil system and there is at least one transverse access aperture running across the direction of the uniform magnetic field and between the inner field coils (2a, 2b).

Abstract: A magnet coil (30) comprises at least one first winding made of wire (34) which is superconductive at operating temperature and at least one second winding made of normally conductive wire (36). In addition, means are provided for supplying a current into the second winding, which is completely dead during superconductive operation of the magnet coil (30), when at least certain sections of the superconductive wire (34) assume the normally conductive state.In order to accelerate the spatial propagation of this transition in the magnet coil (30) and at the same time to provide the possibility to use low-cost wires having a relatively small proportion, related to the cross-sectional area, of normally conductive material, the first and the second winding are connected in parallel electrically.