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.<
>