Applications of Twisted Hollow Waveguides as Accelerating Structures

A new class of accelerating structures employing a uniformly twisted waveguide is considered. Such a twisted helical structure can be designed to have a specified longitudinal cross section. The design of twisted accelerating structures is discussed with regard to particle velocity and strength of the accelerating field. It is shown how to choose a cross section and twist rate in order to produce a slow wave with a given velocity. With two representative structures, obtained wave velocities range from the speed of light, $c$, down to 61% the speed of light, while ${{ R}/ { Q}}$ values of over 1,000 $\Omega/{\rm m}$ have been achieved. A novel two dimensional finite difference based solver is employed to analyze the twisted structures considered. Two twisted cavity prototypes are fabricated and measured, and good agreement is obtained between measured and predicted dispersion curves.