Patent Document ID: 4523166
Application ID: 06662744
Patent Flag: 1

Claim One:
1. A method for operating correction coils to achieve a uniform magnetic field comprising the following steps: (a) measuring the magnetic field, with no current in the correction coils, at a plurality N of points within the volume for which uniformity is desired, the value of the field at the i.sup.th measurement point p.sub.i being denoted by F(p.sub.i); (b) determining a preliminary estimate for correction coil current I.sub.1, I.sub.2,. .. , I.sub.S for S correction coils by a least squares minimization of ##EQU4## and where P.sub.n (p.sub.i) is a polynomial function expressing the field contribution of correction coil n at point p.sub.i with one unit of current in correction coil n, and where .delta..sub.i is a non-zero weight assigned to each point p.sub.i ; (c) determining a new set of weights .delta..sub.i.sup.(new) for each measurement point according to: EQU .delta..sub.i.sup.(new) =.delta..sub.i.sup.(old) [1+a.vertline.X.sub.i .vertline./R].sup.-1, where R=max(X.sub.1, X.sub.2,. .. , X.sub.N)-min(X.sub.1, X.sub.2,. .. , X.sub.N) and where a is a positive convergence constant less than 1; (d) repeating steps (b) and (c) at least once with .delta..sub.i in step (b) replaced by .delta..sub.i.sup.(new) from step (a), so as to determine new values for correction current I.sub.1, I.sub.2,. .. , I.sub.S ; and (e) applying said new values of currents I.sub.1, I.sub.2,. .. , I.sub.S to correction coils 1 through S, respectively.