MAGNETIC DESIGN OF AN APPLE III UNDULATOR FOR SWISSFEL

For the SwissFEL at PSI beside the hard x-ray beamline to start with a soft x-ray line is planned to cover the wavelength between 0.7 and 7.0nm. For full control of the polarization of the FEL light, APPLE undulators are forseen. In this paper the design of these devices is introduced and the preliminary magnetic configuration together with the optimization strategy is presented in details.