Construction status of the SuperKEKB vacuum system

The SuperKEKB, the upgrade of the KEKB, is an electron-positron collider with asymmetric energies, that is, 4.0 GeV positrons and 7.0 GeV electrons, aiming an unprecedentedly high luminosity of 8 × 1035 cm−2s−1. The construction of the new vacuum system for SuperKEKB has been in progress since 2010, as a key item of the upgrade project. The major challenges in the vacuum system are the reduction of beam impedances of various components and the suppression of the electron cloud effects (ECE) in the positron ring, as well as the realization of ultra-high vacuum, under the high beam current. New beam pipes and bellows chambers basically have an antechamber structure. The main pump is a strip-type NEG installed in an antechamber of beam pipes. Various countermeasures against the electron cloud effect, such as coating of TiN film, grooved surfaces and so on, are prepared for the positron ring. Most of new components have been already ordered and delivered. All the new beam pipes are baked at 150 °C for one day before the installation into the tunnel. Approximately 73% of the beam pipes have been installed. The evacuation of beam pipes in the tunnel has also begun. The vacuum system will be almost completed by the end of this March.