A tunable dielectric loaded structure with built in transverse mode suppression

Recently, a method for tuning dielectric-loaded accelerating (DLA) structures has been proposed [A. Kanareykin, I. Sheinman, A.Al´tmark. Technical Physics Letters, Vol. 28, N 11, pp. 916-918, 2002., A. Kanareykin, W. Gai, J. Power, A. Altmark and I. Sheinman. AIP Conference Proceedings No 647, AAC 2002, pp. 565-575, 2002.]. In these structures, a ferroelectric layer backs a conventional ceramic layer, thus allowing the effective dielectric constant of the waveguide to be varied by applying a DC electric field to the ferroelectric layer. In this paper, we present a design for a cylindrical version of this multilayered, tunable DLA structure that has the additional benefit of suppression of transverse deflecting modes [E. Chojnacki et al., Jorn. Appl. Phys., 69, 6257, 1991.,W. Gai, Ching-Hung Ho., Jorn. Appl. Phys., Vol. 70. N 7, pp. 3955-3957, 1991.] due to the axially segmented conducting wall. This structure consist of a layer of conventional ceramic, surrounded by a thin layer of a ferroelectric, that is in turn surrounded by axially-oriented, insulated microstrip electrodes and a layer of absorbing material (ferrite). The axial orientation of the microstrips means that transverse deflection modes are suppressed, since they require an azimuthal current, while longitudinal accelerating modes are allowed, since they only require axial currents. We will present calculations of the relevant accelerator parameters for a cylindrical DLA structure.