Metamaterial based negative refractive index traveling wave tube

Summary form only given. We will present theoretical and experimental results of our research on a Traveling Wave Tube (TWT) amplifier using a metamaterial (MTM) structure. MTM structures have unique properties such as high effective permittivity and permeability which can be harnessed in a slow wave structure (SWS) for enabling strong interaction with an electron beam to produce signal gain. The frequency selective properties of the MTM structure make it interesting to suppress parasitic oscillations usually encountered in a high gain amplifier. We will present the compact design of 6 GHz TWT amplifier. A rectangular waveguide is employed in transverse magnetic mode resulting in a strong axial electric field. The hollow waveguide in TM mode operation is treated as magnetic plasma in this work. The enclosed metal walls create effective negative permeability. As the frequency is reduced below the waveguide cut-off, the effective permeability exhibits very large absolute value. This property helps reduce the phase velocity at lower frequencies. A uniaxial electric metamaterial is designed with effective negative permittivity. The structure exhibits double negative permittivity and permeability while inserting the uniaxial electric metamaterial to the magnetic plasma waveguide. The structure therefore has negative refractive index with large absolute value. The phase velocity is reduced to ~0.15c. The calculated values of the on-axis Pierce impedance indicate a strong interaction beam-wave interaction. Cold and hot simulations were both implemented in Particle in Cell (PIC) code namely, CST Particle Studio. These simulations verified the properties of this MTM based TWT amplifier and show > 20 dB signal gain. A cold test structure is currently under fabrication and experimental cold test results will be presented.