The present condition of KEKB vacuum system

In the KEK B-factory (KEKB), a high luminosity double ring electron-positron collider has been in operation since December 1998. On 9 May 2003, KEKB achieved the design luminosity of 1031 cm-2s-1 and now aims at a higher luminosity. Vacuum components suffer damages caused by high stored current itself and by induced HOM. Direct damage by beam is seen at the surface of the movable mask. The penetration of the strongly induced TE mode through gaps of rf fingers causes heat up of bellows and gate valves. This sometimes results in a serious damage of the fingers. The grid structure of the cover of a pump port cannot damp the TE mode sufficiently. Therefore, a certain number of pump units shows high temperature. In the positron ring, solenoid field is applied along vacuum chambers to reduce the effect of electron cloud that causes serious growth of the beam size. However, the reduction is not sufficient to achieve a higher luminosity. (author)