Paper 
Title 
Page 
WEPPR074 
Effect of the TEM Mode on the Kicker Impedance 
3102 

 C. Zannini, G. Rumolo, V.G. Vaccaro
CERN, Geneva, Switzerland
 C. Zannini
EPFL, Lausanne, Switzerland



The kickers are major contributors to the CERN SPS beam coupling impedance. As such, they may represent a limitation to increasing the SPS bunch current in the frame of a luminosity upgrade of the LHC. The CMagnet supports a transverse electromagnetic (TEM) mode due to the presence of two conductors. Due to the finite length of the structure this TEM mode affects the impedance below a certain frequency (when the penetration depth in the ferrite becomes comparable to the magnetic circuit length). A theoretical model was developed to take into account also the impedance contribution due to the TEM mode. The model is found to be in good agreement with CST 3D electromagnetic (EM) simulations. It allows for generic terminations in the longitudinal direction. An example of kicker is analyzed taking into account also the external cables.



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

 N. Biancacci, E. Métral, B. Salvant
CERN, Geneva, Switzerland
 M. Migliorati, L. Palumbo
URLS, Rome, Italy
 V.G. Vaccaro
Naples University Federico II and INFN, Napoli, Italy



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.


