Higher order mode dampers for the KAON booster cavity

A prototype higher order mode (HOM) damper cavity has been designed and tested on a ferrite tuned booster cavity proposed for the KAON factory at TRIUMF. The damper cavity has been designed to keep the overall length to a minimum and has been optimized by using the SUPERFISH code. Low level signal measurements of unloaded and loaded Q of the booster cavity without and with the damper cavity respectively have been reported and it has been demonstrated that nearly all modes up to 1 GHz which couple to the accelerating gap are damped by the mode damper. In order to reduce the coupling at the booster fundamental frequencies by this type of damper, a new concept of damping higher order modes in the KAON booster cavity by employing a high-pass filter is presented. Conceptual design, prototype realization of such a filter in coaxial form and measurements of damping are outlined. Preliminary measurements show that the higher order modes up to 900 MHz are damped significantly with very little power absorption at the fundamental frequencies