Achievements and problems in the first commissioning of superKEKB vacuum system

The first (phase-1) commissioning of SuperKEKB, an asymmetric-energy electron–positron collider at High Energy Accelerator Research Organization, known as KEK, Japan, began in February 2016 and successfully ended in June 2016. Three major tasks of the phase-1 commissioning were as follows: (1) vacuum scrubbing of the new beam pipes in anticipation of a sufficiently long beam lifetime in the next commissioning, (2) checking the stabilities of various new vacuum components at high beam currents of approximately 1 A, and (3) beam tuning to study stability and achieve low emittance. The coefficient of photon stimulated desorption rate, η (molecules photon−1), decreased steadily with increasing photon dose, as expected. The temperature increases of the bellows chambers, connection flanges, etc., were less than 5 °C at 1 A. The effectiveness of an antechamber, a TiN coating, and a clearing electrode to suppress the electron cloud effect (ECE) was confirmed. However, the ECE in the Al-alloy bellows chambers with...