Superconducting RF cavities: past, present and future

In the last two decades many laboratories around the world, notably Argonne (ANL), TJNAF (formerly CEBAF), CERN, DESY and KEK, undertook the development of the technology of superconducting (SC) accelerating cavities. The aim was either to increase the accelerator energy or to save electrical consumption or both. This technology has been used extensively in the operating machines showing good performances and strong reliability. At present, the technology using bulk niobium (Nb) or Nb coated on copper (Cu) is mature enough to be applied for many different applications, such as synchrotron light sources and spallation neutron drivers. Results, R&D work and future projects will be presented with emphasis on application to linear accelerators.