Field quality of the end sections of SSC dipoles

The central or two-dimensional field of a dipole magnet can be calculated with some precision. The fields at the end of the magnet, which are three-dimensional in nature, provide a more complicated problem. Starting with an end design that produced a relatively good end in terms of multipole components, a method of extending parts of the straight section was used to reduce the most important harmonics, the sextupole and decapole, to a negligible level. In addition, the effect of extending an iron yoke over the ends of a magnet was investigated and it was found to have little effect on the harmonics, though it will raise the dipole field. These results are encouraging as they imply that good ends can be developed with relative ease should the two dimensional cross-section of a dipole magnet such as the SSC have to be changed.