Superconducting RF cavity for KEKB application to high-intensity accelerators

KEKB is one of the most challenging accelerators in the world, aiming to achieve a peak luminosity of 1x1034 cm-2s-1 for the study of B-meson physics. To achieve such a high luminosity, ampere-class beams of electrons and positrons have to be accumulated in the 8 GeV-ring (HER) and the 3.5 GeV-ring (LER) separately, and must be controlled precisely to collide with each other in the BELLE detector located at the collision point. These intense beams need accelerating RF cavities that have sufficiently damped higher modes (HOM) so as not to excite uncontrollable beam instabilities caused by the field induced by the beam. Therefore, new accelerating cavities have been developed in KEKB for both superconducting (SC) and normal conducting (NC) cavities. Since the beginning of machine commissioning in 1998, the peak luminosity has been improved gradually by increasing the beam intensity of both rings, and a peak luminosity of 1.4x1034 cm-2s-1 with the beams of 1.2 A in HER and 1.6 A in LER have been achieved so far. In HER, eight SC-damped cavities have been installed together with 12 NC cavities, and share the RF voltage of 11 MV and the beam power of 2.4 MW. This superior accelerating performance has led to new application of high-intensity acceleration for the SC cavity. (author)