CRYOGENIC SYSTEM FOR THE KEKB CRAB CAVITIES

The superconducting crab cavities, which change the direction of beam bunches to increase the luminosity of the KEKB accelerator, are successfully installed in the KEKB and operated with the stable operation of the large helium refrigerator for the KEKB. Since the crab cavities requires unique devices, such as long coaxial couplers, the cryostats for the crab cavities have various special features in their design and also in their cooling schemes. This paper describes such features and cooling schemes of the cryogenic system for the KEKB superconducting crab cavities. Calorimetric measurements on Q-factors of the crab cavities and static heat load (static loss) measurements of the crab cavity cryostats are carried out after the cryostat assembly. The results of these measurements are acceptable, and from these results, it is found that the crab cavity performance does not degrade so much during the cryostat assembly.