Mode Damping in NAL Main Ring Accelerating Cavities

The application of a ferrite with strong dispersion of magnetic loss tangent to control the impedance of undesired modes in the main ring cavities of the National Accelerator Laboratory synchrotron is described. The impedances of 17 of 21 modes in the frequency range of interest have been damped to less than 0.5 percent of the main mode impedance. On the basis of low level measurements, the dissipation added due to mode damping is 2 kW for operation at a 200 kV gap voltage.