Abstract: A magnetic field generating assembly comprising a set (A1-A3;B1-B3;C1-C3) of, typically substantially coaxial, coils substantially symmetrically arranged about a plane orthogonal to the axis. At least some of the coils carry working currents in the opposite sense to the other coils The arrangement of turns and working currents carried by the coils is such that a first working volume (10) with a substantially homogeneous magnetic field is generated within the envelope defined by the assembly, and two second working volumes (11) each with a substantially homogeneous magnetic field are generated outside the envelope, the homogeneity of each of the first and second working volumes being sufficient to perform a NMR experiment on a sample in the working volume.

Abstract: A magnetic field generating assembly comprises a magnetic field generation system (7, 8) for generating, in a first mode, a first, relatively strong static magnetic field in a working volume (71) located outside the assembly, and for generating, in a second mode, a second, static magnetic field in the working volume in a second mode. In the second mode the magnetic field in the working volume (71) is weaker but more uniform than the first relatively strong magnetic field.