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The ˆrst (Phase-1) commissioning of SuperKEKB, an asymmetric-energy electron-positron collider at KEK, began in February 2016, after more than 5 years of upgrade work on KEKB and successfully ended in June 2016. A major task of the Phase-1 commissioning was the vacuum scrubbing of new beam pipes in anticipation of a su‹ciently long beam lifetime in the next commissioning. The pressure rise per unit beam current decreased steadily with increasing beam dose, as expected. Another important task was to check the stabilities of various new vacuum components at high beam currents of approximately 1 A. The temperature increases of the bellows chambers, gate valves, connection ‰anges, and so on were less than several degrees at 1 A, and no serious problems were found. The eŠectiveness of the antechambers and TiN coating in suppressing the electron-cloud eŠect (ECE) in the positron ring was also conˆrmed. However, the ECE in the Al-alloy bellows chambers was observed where TiN had not been coated. The use of permanent magnets with an axial magnetic ˆeld of approximately 100 G successfully suppressed this eŠect. Pressure bursts accompanying beam losses were also frequently observed in the positron ring. The preparation for the next Phase-2 commissioning, such as the installations of new beam pipes at the collision point and of six more beam collimators, are now in progress.

Vacuum System in the First Operation of SuperKEKB