A Fixed Gap APPLE II Undulator for SLS

To vary the polarization vector of an APPLE II undulator continuously from 0 – 180°, all four magnet arrays need to be movable. Following the adjustable‐phase undulator approach by R. Carr, a 3.4 m long fixed gap undulator for SLS with a gap of 11.6 mm has been constructed. It will be installed in fall 2006. The gap drive is replaced by a pair‐wise shift of the magnet arrays to change the energy, while the polarization is changed by shifts of diagonal arrays. The high injection efficiency and standard operation top‐up mode at the SLS allows this simplified undulator design. The design as well as the operational aspects will be discussed.