Transverse Dynamics of the Azimuthally Inhomogeneous Electron Bunch in a Multilayer Dielectric Cylindrical Waveguide

Abstract

In reference [1], a complete analytical solution for Cherenkov wakefields generated by an azimuthally asymmetric annular beam propagating in a coaxial two-channel dielectric structure was presented. A drive bunch generates Cherenkov radiation (wakefield) inside the dielectric loaded waveguide and a second (witness) bunch passing through the structure at an appropriate delay with respect to the drive bunch is accelerated by the wakefield. Use of a ring beam in a multi-layer waveguide can significantly increase the transformer ratio by providing different paths for the ring driver and the accelerated bunch to pass through the structure. The main challenge of this scheme originates in the transverse dynamics of the drive bunch because of its high charge and relatively low energy. To hold the inner dielectric tube inside the waveguide metal (titanium) threads are used. The threads are located inside the drive beam section of the waveguide that leads to the segmentation of the drive beam. In this paper, we study the transverse dynamics of the annular beam with various types of azimuthally asymmetries that depend on the specifics of the beam generation and multilayer waveguide parameters. The different types of beam asymmetry and hybrid mode dependencies are presented using the original BBU-3000 [7] beam dynamics code.