Optimization of the magnetic field homogeneity of circular and conical coil pairs

The magnetic field generated by a pair of coaxial circular loops is analyzed in order to find the optimum separation between the loops for each value of a prescribed homogeneity. For the maximum heterogeneities considered here, 0.1%, 1%, and 10%, the optimum loop spacing is obtained following a graphical procedure so that the length of the homogeneous field region along the axis is the longest possible. This study is extended to regions near the axis and to the entire region surrounding the center, calculating the loop separation that produces the largest homogeneous volume. The field homogeneity of a pair of "Helmholtz" coaxial conical coils is also investigated to obtain the optimum spacing between the conical coils; the volumes calculated with the desired homogeneity are compared with those obtained with a single pair of optimum coaxial loops. A new arrangement is hereby proposed based on double conical coils with optimum separation between the coils and optimum aperture of the cones. Some of the proposed arrangements are carried out in the laboratory where the experimental results are in good agreement with the theoretical predictions.