Fermilab 500-GeV Main Accelerator RF Cavity 128-MHZ Mode Damper

The Fermilab 500-GeV main accelerating system has been operating for a year now with the aid of 128-MHz mode dampers. Such dampers proved to be necessary to achieve stable operation and a reasonably smooth slow spill at intensities of ~2 ?? 1013 protons per pulse, and furthermore are low-cost and reliable. This paper describes the approach used to identify troublesome modes, mentions something about the observed beam blow-up without dampers, and outlines the steps taken to design and install suitable dampers on eighteen main ring cavities. Spectrum analyzer pictures help illustrate the performance.