Complementary split-ring resonator-coupled traveling wave accelerating structure

Abstract

In this paper, we present theoretical and simulation-based analyses of a novel, normal-conducting, multiple-cell, traveling wave accelerating structure. Instead of the conventional circular apertures, we utilize asymmetric complementary split-ring resonators to couple pillbox cavities and bring the phase velocity below that of the speed of light in vacuo. We show that this architecture exhibits a low, negative, group velocity and that the 0 through π modes decrease in order of frequency—in contrast to conventional electrically coupled structures in which the 0 mode has the lowest frequency and the π mode the highest. We illustrate the efficacy of the proposed design via electromagnetic and particle simulation results for a four-cell structure operating around 1.9 GHz. Results are given for operation in the π, 2π/3, and π/3 modes. Our design achieves accelerating gradients of around 3.3 MV/m and a cavity voltage of 0.594 MV for an applied rf power of 82 kW (π mode). The accelerating gradients achieved are up to 3.3 times that of a conventional circular aperture-coupled design with the same phase velocity, rf excitation power, operating frequency, mode type, and number of cells.