Optimization studies on CSRR loaded waveguide for particle accelerator applications

Summary form only given. One of the most promising directions for metamaterials (MTMs) in particle accelerators is investigating the property of backward propagating Cherenkov radiation to develop novel coherent radiation sources and Cherenkov wakefield detectors. In this work, optimization studies are carried out on the design of a MTM loaded waveguide for a Cherenkov wakefield detector recently proposed. A WR-284 metallic waveguide is loaded with four sheets of metasurface comprising of complementary split ring resonators (CSRRs) designed for operation around 6 GHz. The CSRRs give rise to a negative permittivity below the plasma frequency and the metasurface layers form a narrow patterned waveguide that confines TM modes and gives rise to negative permeability. The resulting left handed behavior allows for backward propagation of Cherenkov radiation. The optimization is performed to reduce the surface current and increase the fabrication suitability of the MTM. This CSRR loaded waveguide has been optimized through the use of thicker metasurface sheets (1 mm) and an increased ring gap. In comparison to the set up initially presented, the increase in sheet thickness creates a significant reduction in hybrid modes through the damping of weaker modes, while increasing fabrication suitability and reducing the effect of resistive heating as a result of surface current build up. The loaded waveguide structure still exhibits a TM-like mode suitable for left handed behavior at 5.86 GHz, characterized by strong beam coupling parameters with an R/Q of 36 Ω and a shunt impedance of 177 kΩ. Wakefield simulations confirm strong coupling of this mode to the beam, with longitudinal wake impedance excitations at 6.49 GHz of 10 kΩ and negligible transverse excitations.