Apparatus and process for generating a homogeneous magnetic field

A process for correcting a crude magnetic field of a main field generator having n correcting magnetic field generators associated therewith to produce a substantially homogeneous corrected field, said process comprising the steps of:

• measuring the intensity and direction of the crude magnetic field B of the main field generator at a plurality of different points within the field to obtain the distribution of the crude magnetic field;
• expressing the crude magnetic field B at each of the plurality of different measured points by the following equation, which contains a main homogeneous magnetic field component, successively higher order inhomogeneous magnetic field components, and a residual:
• Bz(x,y,z)=Bo+a.sub.1 f.sub.1 +a.sub.2 f.sub.2 + . . . +a.sub.n f.sub.n +Rn(x,y,z) . . . ;
• determining the magnetic field output for a first one of the correcting generators such that a first one of the successively higher order inhomogeneous magnetic field components a.sub.1 f.sub.1 of the crude magnetic field B is completely cancelled by the magnetic field output b.sub.1 f.sub.1 of the first one of the correcting generators;
• determining the magnetic field output for each of the remaining ones of the n correcting generators such that the successively higher order inhomogeneous magnetic field components a.sub.2 f.sub.2 . . . a.sub.n f.sub.n of the crude magnetic field B are completely cancelled by the magnetic field outputs b.sub.2 f.sub.2 . . . b.sub.n f.sub.n, respectively, of the remaining ones of the n correcting generators;
• producing the determined magnetic field outputs from the n correcting generators;
• and
• superpositioning on the crude magnetic field B of the main field generator the magnetic field outputs from the n correcting generators to provide a substantially homogeneous corrected field.