Beam impedance calculation and analysis of higher order modes (HOMs) damped RF cavities using MAFIA in time domain

A time domain method using MAFIA code has been developed to calculate narrow band beam impedance in RF cavities over a wide range of frequency spectrum. The impedance is obtained through Fast Fourier Transformation (FFT) of computed wakefields by the MAFIA. Analysis of the calculated impedance spectrum will be presented. Application of the method to a known RF cavity design (PEP-II cavity) has shown good agreements with bench and beam measurements. The method has been applied to the RF cavity design of of Damping Rings for Next Linear Collider (NLC).