Design of a high power S-Band backward-wave oscillator with a metamaterial interaction circuit

Summary form only given. We present designs for a high power backward-wave oscillator (BWO) which use a metamaterial loaded waveguide as the interaction circuit. Metamaterials have unique electromagnetic properties not normally found in nature, and have been shown to support negative index modes (permittivity and permeability simultaneously less than zero) that could be used to interact with an electron beam. The design incorporates planar, all-metallic metamaterial elements that are compatible with both a vacuum and a high power microwave environment. A 500 kV 80 A gun will be used to test the device which has been designed to operate in the S-Band near 2.856 GHz. Electromagnetic simulations of the metamaterial loaded waveguide have been performed to investigate the negative dispersion of the guide and estimate the beam-wave coupling. In addition, PIC simulations are presented to evaluate device performance and output power. The PIC simulations predict a power output of 5 MW using the 500 kV electron gun operating in one microsecond pulses. Experimental measurements of low-power microwave transmission through two test metamaterial waveguide structures are presented that show very good agreement with simulation and verify the excitation of the negative index mode.