Electro Polishing of Niobium Cavities at DESY

At DESY a facility for electro polishing (EP) of the super conducting (s.c.) TESLA/TTF cavities has been built and is operational since summer 2003. The EP infrastructure is capable to handle single - cell structures and the standard TESLA/ TTF nine - cell cavities. Several electro polishing processes have been made since and acceleration voltage up to 40 MV/m have been reached in nine cell structures. We report on measurements and experiences gained since 2003 as well as on handling procedures developed for the preparation of electro polished resonators. Specific data like heat production, variation of current density and bath aging will be presented. Another important point for reproducible results is the quality control of the electro polishing process.