KEK, Ibaraki
Hitachi Technologies and Services Co., Ltd., Kandatsu, Tsuchiura
Two superconducting crab cavities have been operated stably without any significant trouble for three years in KEKB since Feb/2007. At present (Dec/2009), maximum beam current with 'Crab ON' achieves 1200mA for HER (High Energy Ring, electron) and 1640mA for LER (Low Energy Ring, positron), respectively. RF trip rate per day due to crab cavity during 'physics run' was 2.8/day for HER and 0.4/day for LER at the beginning, and is 0.8/day for HER and 0.1/day for LER at present, respectively. Although Piezo actuator was frequently broken down at the beam abort with RF trip of the crab cavity, it was controlled stably by only LLRF (Low Level RF) feed-back system without Piezo actuator. Maximum HOM (Higher Order Mode) power, which is measured at HOM dampers made from ferrite, is 9.1kW for HER and 14.6kW for LER at the maximum beam current, respectively. LER crab voltage, which had suddenly dropped from 1.50MV to 1.10MV on March/2007, was gradually recovered from 1.14MV to 1.33MV in 2008.
KEK, Ibaraki
Hitachi Technologies and Services Co., Ltd., Kandatsu, Tsuchiura
Two superconducting crab cavities were successfully installed into the KEKB accelerator in January 2007. Since then the crab cavities have been in stable operation for 3 years up to now, thanks to reliable operation of the cryogenic system of the KEKB including a large-scale helium refrigerator. This means that the cryostat for the crab cavities was well designed and constructed properly, although there are some technical complexities in the cryostat, such as two helium vessels in a cryostat, a movable coaxial coupler which is cooled with liquid helium and so on. The KEKB cryogenic system was also appropriately modified to operate the two crab cavity cryostats stably. This cryogenic system is described in this presentation. A calorimetric method to measure the Q-factors of the crab cavities is suggested, which employs an electric compensation heater in the cryostat, instead of the conventional method, which measures the descending rate of liquid helium level. Measurement results of the Q-factors of crab cavities after being assembled in the cryostat and after being installed into the KEKB accelerator are compared with the vertical test results.