VACUUM DESIGN FOR KEKB

摘要

In designing a vacuum system of a new asymmetrical collider for KEKB, the vacuum ducts deal with intense heat from synchrotron radiation because of high stored current. Due to the short bunch length, the requirement for the smoothness of the inner surface is tight. OFC is adopted for vacuum chambers. Acid etch or chemical polishing is applied to clean extruded surface. Using NEG strips as the main pump, pumping speed is designed as 100 1 s~(-1) m~(-1). When the photo-desorption coefficient is 10~(-6) a pressure of 10~(-9) Torr will be realized. All chambers are baked before installation. By adopting "dry-hood" technique, in situ bake out will be omitted. Pumping slots are backed up by grid to prevent the penetration of beam induced field which causes heat up of pumprnelements. A gap between flanges are filled using Helicoflex as a vacuum seal. Contact force of an RF finger in a bellows is assured by a spring finger.