AVS 49th International Symposium
    Vacuum Technology Tuesday Sessions
       Session VT-TuA

Paper VT-TuA1
Present Status of the KEKB Vacuum System

Tuesday, November 5, 2002, 2:00 pm, Room C-104

Session: Vacuum System Architecture and Specialized Analytical Techniques
Presenter: Y. Suetsugu, High Energy Accelerator Research Organization (KEK), Japan
Authors: K. Kanazawa, High Energy Accelerator Research Organization (KEK), Japan
S. Kato, High Energy Accelerator Research Organization (KEK), Japan
Y. Suetsugu, High Energy Accelerator Research Organization (KEK), Japan
H. Hisamatsu, High Energy Accelerator Research Organization (KEK), Japan
M. Shimamoto, High Energy Accelerator Research Organization (KEK), Japan
M. Shirai, High Energy Accelerator Research Organization (KEK), Japan
Correspondent: Click to Email
The KEK B-Factory (KEKB) is an electron-positron collider with an asymmetric energies consisting of two rings, that is, the High Energy Ring (HER) for 8.0 GeV electrons and the Low Energy Ring (LER) for 3.5 GeV positrons. The design beam currents are 1.1 A and 2.6 A with 5120 bunches for HER and LER, respectively. Each ring has a circumference of 3016 m and most of beam chambers are made of oxygen free copper for its ability to withstand the intense heat load and to shield effectively the radiation from high beam currents. The pumping scheme is a combination of Non-Evaporable Getter (NEG) pumps and sputter ion pumps. The commissioning of KEKB started in December 1998. At the end of March 2002, the achieved stored currents were about 0. 93 A and 1.44 A for HER and LER, respectively, with 1200 bunches. The KEKB is now able to serve the world-record luminosity of 7.2 nb@super -1@ s@super -1@ for the BELLE detector. The vacuum system has been operating satisfactorily. The average pressure of about 1x10@super -7@ Pa is achieved now for both rings during the operation. The coefficient of the photon stimulated gas desorption (PSD) decreased steadily to almost 1x10@super -6@ molecules photon@super -1@ at the integrated linear photon flux of about 3x10@super 25@ photons m@super -1@. Most of vacuum components, such as Helicoflex sealing (Le Carbone Co. Ltd.) and the vacuum bellows with RF-shield structure, have been working well. The severest trouble had been the beam-induced troubles of the movable masks, but the newly developed masks were installed and are now in use without serious problem. One of the latest issues is the excess heating of bellows, chambers or pumps coming from the electromagnetic filed excited by the intense bunched beam. A non-linear dependence of pressure on beam current has been observed in LER. That seems to deeply relate to the electron multipactoring, which causes the electron cloud instability. Here we will summarize the experiences and the present status of KEKB vacuum system, and touch briefly the future plan.