High gradient superconducting cavities for storage rings

Superconducting (SC) cavities for use in electron storage rings have advanced to the point where several laboratories are making definitive plans to use them on a large scale. Laboratory tests of multi-cell SC cavities, including input and higher-order-mode (HOM) couplers, have yielded accelerating fields up to 15.3 MeV/m (CW). Reasons for the improved performance are discussed. Since the 1983 International Accelerator Conference in August, 1983, four SC cavities have been tested in storage rings. The cavities have yielded accelerating gradients up to 6.5 MeV/m, in excess of the frequently-quoted objective of 5 MeV/m, in addition, the average gradient obtained in these four tests was 4 MeV/m, almost twice the average obtained in the four cavities tested in storage rings during 1982-1983