A versatile electromagnetic planar/helical crossed undulator optimized for the SU5 low energy/high resolution beamline at Super-ACO

We present here a planar/helical crossed overlapped undulator, composed of two identical 10 (25-cm long) periods crossed undulators whose magnetic fields are produced by electromagnets. Therefore the gaps are fixed, the tuning range being set by varying the field excitation current. Such a design is quite simple, with only one mechanical translational motion, and versatile in terms of polarization settings and switching. After the optimization of the period length for minimizing the thermal load on the optics, the general concept of the crossed undulator is introduced, followed by a description of its actual magnetic design imposed by tolerances on the stored positron beam. Finally, the expected performances in terms of flux and polarization capabilities are presented. It appears that any state of polarization can be produced, at least on the first harmonic, with a large total polarization rate and a potentially high polarization switching frequency.