HOM damped 500 MHz cavity design for 3rd generation SR sources

Higher order mode (HOM) damped cavities are one option to avoid multibunch instabilities in modem synchrotron radiation (SR) sources, which can reduce their performance potential. Two different cavity shapes (spherical and cylindrical) both using ridged circular waveguides for HOM damping have been optimised to find a good compromise with respect to maximum fundamental mode shunt impedance and minimum HOM impedances. The properties of the two cavity designs are discussed and impedance thresholds for the excitation of multibunch instabilities are presented for several 3rd generation SR sources, which utilise 500 MHz RF-systems. As a result of this numerical study the transverse and longitudinal HOM impedance can be reduced below threshold for most of these sources.