SuperKEKB vacuum system in the final stage of the construction

The SuperKEKB, the upgrade of the KEKB, is an electron-positron collider with asymmetric energies, that is, 7.0 GeV electrons and 4.0 GeV positrons, aiming at a luminosity of 8 x 10³⁵ cm^-2 s^-1. The construction of the new vacuum system for the SuperKEKB has been ongoing since 2010, as a key item of the upgrade project. The fabrication of more than 1000 beam pipes, vacuum pumps and bellows chambers in each, and other various vacuum components had almost completed in 2014. Before the installation into the KEKB tunnel, all of the new beam pipes were basically baked. A thin TiN film was coated on the inner surface of the beam pipes for the positron ring as a countermeasure against the electron cloud effect (ECE). Although several problems, such as cracking of the welding lines of the aluminum beam pipes, the relatively high air-leak rate at the connection flanges, occurred during the construction work, approximately 99% of the beam pipes were successfully installed by the end of November 2015. The activation of the NEG pumps in the tunnel fully started at the beginning of 2015, and has also been completed in approximately 97% of the ring. The vacuum system will be ready in this year with the aim of starting the first commissioning in the beginning of 2016. (author)