Measurements of higher-order mode damping in the PEP-II low-power test cavity

The paper describes the results of measurements of the higher-order mode (HOM) spectrum of the low-power test model of the PEP-II RF cavity and the reduction in the Q´s of the modes achieved by the addition of dedicated damping waveguides. All the longitudinal (monopole) and deflecting (dipole) modes below the beam pipe cut-off are identified by comparing their measured frequencies and field distributions with calculations using the URMEL code. Field configurations were determined using a perturbation method with an automated bead positioning system. The loaded Q´s agree well with the calculated values reported previously, and the strongest HOMs are damped by more than three orders of magnitude. This is sufficient to reduce the coupled-bunch growth rates to within the capability of a reasonable feedback system. A high-power test cavity will now be built to validate the thermal design at the 150 kW nominal operating level, as described elsewhere at this conference