First multicell coating with planar arc cathode

Superconducting cavities can be produced from Niobium sheet material. An alternative fabrication method is to coat copper cavities with a thin Niobium film. At low frequencies cavities are large so that considerable cost can be saved with the reduced amount of expensive Niobium. The sputter coating technology has been developed by CERN. At moderate gradient Niobium coated copper cavities showed low loss, i.e. high quality factor. But with increasing gradient the quality factor drops down. Vacuum arc coating is a well known alternative coating method but was never tried out with RF cavities. There is a hope that the high impact energy of arc produced ions might create a “better” Niobium film without reduced Q-drop. In this R&D activity cavities have been coated by vacuum arc technology. The Niobium films show reasonable superconducting properties. But sever adhesion problems of the coating could not be solved within the time frame of the project.