Coaxial coupling scheme for fundamental and higher order modes in superconducting cavities

Higher Order Modes generated by a particle beam passing through a superconducting accelerating cavity have to be damped to avoid beam instabilities. A coaxial coupler located in the beam pipes of the cavities provides for better propagation of HOMs and strong damping in appropriate HOM dampers. The whole damping device can be designed as a detachable system. If appropriately dimensioned, the RF currents can be minimized at the flange position. Additionally, the coaxial system also provides efficient coupling of fundamental mode RF power into the superconducting cavity. Compared to presently available solutions for HOM damping, this scheme provides for several advantages: stronger HOM damping, attachable solution, and exchangeability of the HOM damping device on a cavity, less complexity of the superconducting cavity, possible cost advantages. This contribution discusses modeling, which lead to an optimized layout of a cavity-coupler system and describes results from the room temperature and first cryogenic temperature measurements .