A double-layered, planar dielectric loaded accelerating structure

Recently, a method to tune dielectric-loaded accelerating (DLA) structures has been proposed [these proceedings]. In these structures, a ferroelectric layer backs a conventional ceramic layer, thus allowing the effective dielectric constant of the waveguide to be varied by applying a DC electric field to the ferroelectric layer. In this paper, we present a design for a planar version of this double-layered, tuneable DLA structure. The advantage of the planar waveguide is its spectral uniformity, ease of frequency tuning, and its simplicity of fabrication. The dispersion equation for the structure and the accelerating wakefield exited by a planar electron bunch has been calculated. Based on this work, we present simulation results for 13, 20 and 35 GHz structure parameters including tunability factor. The transverse deflecting wakefields caused by the beam offset have been studied as well. In addition, we present the results of cold test measurements for an 11.4 GHz, double-layered, ceramic- ferroelectric test device, including tuning range and Q measurements.