RESONATOR DESIGN AND CHARACTERIZATION FOR THE ISRAELI TANDEM ELECTROSTATIC FEL PROJECT

The design and measurements of a resonator operating near 100 GHz and intended for use in a tandem FEL are presented. The designed resonator employs two parallel curved plates as a waveguide. In FEL operation t he TE(01) mode is excited. The resonator employs two wave splitters as reflectors. The wave splitters are segments of an overmoded rectangul ar waveguide which is connected at one end to the waveguide as describ ed above, and is shorted at the other end by a metal plate with an ape rture in the center for e-beam passage. Gain calculations were made in the low gain regime. At the operating frequency the curvature of the plates and the gap size were chosen so as to maximize the gain. A mult imode analysis of the wave splitter was made. Calculations show, that the optimal splitter width and length allow achievement of very low di ffraction losses at the aperture (similar to 2%). This means that the aperture can be made sufficiently large to allow efficient beam entran ce into the resonator without degrading its Q-factor. A resonator prot otype was constructed and its performance was evaluated experimentally .