Magnetic Characterization of an APPLE-II Undulator Prototype for FERMI@Elettra

The FERMI@Elettra free-electron laserwill use APPLE-II undulators in the radiating sections to produce variably polarized coherent photon beams. In preparation of the manufacturing of the final devices, a prototype has been developed in order to test different field optimization methods. For this purpose, an existing variable-gap support structure was retrofitted with a new mechanical interface (see figure 1) providing the required capability to longitudinally shift two of the four magnetic arrays.