Electro-Polishing Surface Preparation for High Gradient Cavities at DESY

Improvement of acceleration gradients in super conducting accelerator structures was reached by applying electro polishing to the niobium surfaces. This technology is actually foreseen to serve as major surface preparation step for projects like the XFEL at DESY and the proposed ILC linear accelerator. At DESY an electro polishing apparatus was build up in 2003. After commissioning the apparatus operates regular for cavity surface treatment. We report on experiences with the electro-polishing set up, polishing parameters and results on the preparation of S. C. resonators for a high gradient module to be tested in the TTF2 accelerator at DESY.