Paper  Title  Page 

WEPPR062  The Mode Matching Method Applied to Beam Coupling Impedance Calculations of Finite Length Devices  3069 


The infinite length approximation is often used to simplify the calculation of the beam coupling impedance of accelerator elements. This is expected to be a reasonable assumption for devices whose length is greater than the transverse dimension but may be less accurate approximation for segmented devices. This contribution presents the study of the beam coupling impedance in the case of a finite length device: a cylindrical cavity loaded with a toroidal slab of material. In order to take into account the finite length we will decompose the field in the cavity and in the beam pipe into a set of orthonormal modes and apply the mode matching method to obtain the impedance. To validate our method, we will present comparisons between analytical formulas and 3D electromagnetic CST simulations as well as applications to the impedance of short beam pipe inserts, where the longitudinal and transverse dimensions are difficult to model in numerical simulations.  