In order to assure constructive interference between the consecutive insertion devices in a segmented undulator system there are electromagnetic chicanes, called “phase shifters” installed in the intersections. Besides theses phase shifters the intersections comprise a set of small steerer coils, a quadrupole magnet mounted on a mover platform, beam loss monitors (BLMs), a beam position monitors (BPMs) and an ion getter pump. Along the vacuum chamber for each undulator there is an additional ambient field corrector coil.
The small steerer coils are integrated into the individual undulator control systems and compensate for residual field integral changes during gap movements based on the magnetic measurement data from the undulator lab. The magnetic performance of the phase shifters, as well as any field errors or hysteresis, has also been characterized in detail in the magnetic measurement laboratory.
In case of the FLASH 2 undulator system, a central undulator control server calculates all required gap and taper settings as well as the corresponding current settings for the phase shifters, based on the magnetic field data for each component, the current accelerator energy, and the desired photon wavelength. This undulator controls server also supports several different optics and taper schemes.
