Elliptically polarizing undulator end designs

The magnetic end design of pure-permanent magnet Apple-II elliptically polarizing undulators (EPU) is discussed. Constraints on end block dimensions and positions are presented that guarantee steering and displacement free systems in both transverse directions and at all gaps for mu = I material. For block material with mu > 1 some beam steering (i.e. integrated dipole) may occur due to the ends; in particular, the integrated dipole strength varies with EPU phase. An optimization process is presented that assumes small perturbations about the mu = 1 solution and minimizes the variation in steering with EPU phase. We present numerical and experimental results that quantify the reduction in integrated dipole variation with phase.