Model studies on the ELFA wiggler

A wiggler for the ELFA high-gain single-pass Compton FEL (free-electron laser) is under study. The preliminary design of the wiggler (λ_w=12 cm, B_w=3.6 kG, total length L=6-7 m) has shown the need for model studies in order to optimize the pole and the coil geometry. The main characteristics of an electromagnet model and the high-precision apparatus for magnetic measurements are described. The results of the model field measurement are presented and discussed. The data are also compared with theoretical predictions, based on 2-D codes and simple analytical models. The first set of measurements made on the model has shown good agreement with the main design goals. Peak field level, field waveform in the midplane, and transverse field pattern seem to be satisfactory