Impedance measurements of a HOM-damped low power model cavity

In the frame of a European Community funded project a higher order mode (HOM) damped normal conducting 500 MHz cavity is under development optimized for the use in 3rd generation storage ring light sources. The relevant HOM-impedances have been measured with a fully scaled low power model made from aluminium. By using a cutoff frequency of 615 MHz for the damping waveguides we have found a good compromise between the preservation of the accelerating mode impedance and the efficient broadband damping of HOM's. Detailed experimental results are presented and compared with numerical simulations.