KEKB vacuum system

For KEK B-factory (KEKB), two rings with a circumference of 3016 m, mainly made of copper have been constructed. One ring stores a maximum of 2.6 A positron beam with the energy at 3.5 GeV, the other stores 1.1 A, 8 GeVelectron beam. These stored currents far exceed those of existing electron storage rings. The inside of a beam duct is designed to minimize an effect of beam induced ®elds. A gap between ¯anges is ®lled using Helico¯ex as a vacuum seal. Contact force of a RF ®nger in a bellows is assured by the use of a spring ®nger. Pumping slots are backed by crossing bars to prevent the penetration of beam induced ®elds. To obtain a pressure of 10ÿ7 Pa with beam, a pumping speed is designed to realize 0.1 m3 sÿ1 mÿ1 assuming that the photodesorption coef®cient reaches 10ÿ6 molecules/photon. The NEG strip is used as a main pump element. Chemical polishing is applied to clean the extruded surface of copper chambers. Almost all chambers are baked before installation. Only ion pumps are baked in situ. From beginning to end, a completely oil free pumping system is used. The photodesorption coef®cient at the start of the commissioning was slightly higher than expected, but the decrease of the coef®cient is as expected on the whole. There is no trouble on the RF contact for bellows. # 2001 Elsevier Science B.V. All rights reserved.