COMMISSIONING OF ELLIPTICAL UNDULATORS IN ELETTRA

Six 2 m long elliptical undulators have been constructed for the generation of linearly and circularly polarized light. Of these, five have been installed in the ELETTRA storage ring. In this paper, the first results of the commissioning are presented. There has been an increasing interest on behalf of the users for the utilization of circularly polarized light for experiments, like circular dichroism or magnetic scattering. For this purpose, during the past year five elliptical insertion devices have been introduced in the ELETTRA lattice and a sixth one will be located in the ring by early autumn. The insertion devices are of the APPLE-2 type, made of two double arrays of permanent magnet blocks which are schematically shown in figure 1. By shifting longitudinally one of the upper arrays with respect to the lower one diagonally opposite to it, the phase of the magnetic fields changes, hence generating light which goes from linearly polarized horizontally to vertically polarized, passing through circular polarization. This renders the insertion device extremely flexible, permitting various types of experiments to be carried out, according to the polarization of the light. While the main parameters of the insertion devices introduced in the lattice are listed in Table 1, technical details on their construction may be found in the references (1, 2). The insertion devices are 2 m long and situated in couples, in the order in which they appear in the table, symmetrically around the center of three straights. EU12.5 and EU6.0 are rotated by 1.0 and -1.0 mrad with respect to the machine axis and a central chicane bump is set to place the beam on their axis. This will allow the radiation to be supplied