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, compose d of two identical 10 (25-cm long) periods crossed undulators whose ma gnetic fields are produced by electromagnets. Therefore the gaps are f ixed, the tuning range being set by varying the field excitation curre nt. Such a design is quite simple, with only one mechanical translatio nal motion, and versatile in terms of polarization settings and switch ing. After the optimization of the period length for minimizing the th ermal load on the optics, the general concept of the crossed undulator is introduced, followed by a description of its actual magnetic desig n imposed by tolerances on the stored positron beam. Finally, the expe cted performances in terms of flux and polarization capabilities are p resented. It appears that any state of polarization can be produced, a t least on the first harmonic, with a large total polarization rate an d a potentially high polarization switching frequency.