20 Years of experience with the Nb/Cu technology for superconducting cavities and perspectives for future developments

The first niobium-coated copper cavities were produced at CERN in the early 1980s. The sputter coating technology was chosen as a basis for development, first in the pure diode configuration and subsequently in the magnetron configuration, which was then adopted for the successful series production of the LEP and LHC cavities. In parallel, an intensive R and D effort was undertaken at CERN and other Laboratories in order to understand the advantages and limitations of this technique. Some highlights of the present understanding will be given. Several new developments in the coating technique are being pursued around the world, which will be discussed together with their motivations