Insertion Devices - NISUS

NISUS is a Rare Earth Permanent Magnet Hybrid Undulator using SmCo₅ magnet material and Vanadium Permadur Poles. The structure uses wedged poles to increase available peak field. Each group of 16 periods (32 poles) has 6 alternately canted pole tips (10.8 mrad) to provide a transverse field gradient located at the center of each subset of poles. The full length of the device is comprised of 16 of these smaller units joined by tuning fork flexures to allow tapered gap from one section to the next.

STI Optronics has recently remapped the magnetic field of the NISUS undulator at a working gap of 20.6 mm and a peak field of 0.31T, followed by reshimming to reduce trajectory and phase errors. By powering the built-in bias coils and making fine, local gap adjustments, the initially large trajectory wander has been reduced to less than one wiggle amplitude, and the phase error has been reduced to only 4° rms. Transverse (skew) fields have also been measured and an initial set of vertical steering corrections with the four-wire system has been determined. The magnetic field quality is now such that we can expect near-ideal performance from the undulator.