Balloon Cavity with Increased Q Factor

Superconducting spoke cavities are prone to multipactor – resonant raise of number of electrons due to secondary emission. Recently proposed and tested balloon type spoke cavity showed an outstanding multipactor suppression properties but unfortunately serious Q degradation at high fields. With this proposal, Euclid Beamlabs will develop a new spoke cavity with increased Q factor and efficient multipactor suppression. A complex of steps will be implemented: (1) a balloon cavity geometry will be used for extremely efficient multipactor suppression, (2) spoke connections to the outer shell will be modified for better cleaning results and to increase the Q factor, and (3) additional ports will be added to provide access for electro- polishing (EP). EP was previously successfully implemented for half-wave resonators for the PIP-II project, which resulted in extremely low residual resistance. The ability to perform EP will open up the possibility for other state-of-the-art surface treatment techniques, such as Nitrogen doping and infusion. The aforementioned steps will result in a SRF cavity with increased Q factor and reduced multipactor as a candidate for PIP-II (SSR2). Since a considerable part of the PIP-II linac consists of SSR2 cavities, the use of the higher Q factor cavities developed in this project will significantly reduce the cryogenic load of the linac. Phase I of the project will be fully devoted to cavity electromagnetic design optimization with ports for surface processing, multipactor simulations, and development of a helium vessel design concept. Mechanical design will be developed with ports for electro-polishing and “tuning during manufacturing” friendly design. The potential market for high Q spoke resonators is significant, with anticipated future uses in large SRF-based accelerators for fundamental and applied research, and for industry.