SuperKEKB is an asymmetric-energy electron-positron double-ring collider constructed by upgrading the KEKB B-factory. A large-scale upgrade construction has been completed and beam commissioning for beam collision with physics data taking has been started. In this report, an overview of the design, construction and beam commissioning of SuperKEKB is described.

The high luminosity e⁺e⁻collisions at the SuperKEKB accelerator produce heavy flavor particles, the B and D mesons as well as the τ lepton, at the rate of about 10¹⁰ particles/year with the designed luminosity of 8×10³⁵ cm⁻² s⁻¹. These high statistics data provide rich physics programs at the Belle II experiment, to search for new phenomena beyond the Standard Model of particle physics. I present the physics program, recent status and prospect of the Belle II experiment.

The KEK injector linac has delivered electrons and positrons for particle physics and photon science experiments for more than 30 years. It was upgraded towards the SuperKEKB collider with its extremely high luminosity that demands improved injection beams with four-times higher current, hundred-times lower emittance. Many injector components have been newly developed to achieve the required beams, and the upgraded injector is being commissioned.

A positron damping ring (DR) is newly constructed in KEK Tsukuba campus to produce low emittance beam for the SuperKEKB main ring. The machine commissioning is started January 23rd 2018. Although unexpected results were obtained in beam optics measurement, the DR has been started up without any fundamental difficulty. It is qualitatively confirmed from a beam profile monitor that the beam size is decreased after the injection. After about 1 month of the machine commissioning period, DR started steady operation for the first beam collision tuning in SuperKEKB.

SuperKEKB is an electron-positron double-ring asymmetric-energy collider to study new physics phenomena appeared in B-meson decays. In order to accomplish this purpose, extremely high luminosity is necessary which can be realized by a novel “nano-beam” collision scheme. First of all, the commissioning in Phase 2 was focused on the verification of nano-beam scheme. Secondary, the beam related background for the Belle II detector was also studied for the preparation of the pixel vertex detector which will be installed before the Phase 3 operation. The outlook and accomplishments of the commissioning will be reported in this article.

The target luminosity of SuperKEKB, L=8×10³⁵ cm⁻² s⁻¹, is the 40 times higher than that of KEKB. In order to attain the extremely high luminosity, the new beam final focus system with the superconducting magnets was constructed based on the accelerator design of “Nano-beam scheme.” The beam focus process was performed by the quadrupole doublets with 8 superconducting quadrupole magnets in the interaction region. The final focus system was composed of 55 superconducting magnets in total. In this report, the configuration of this superconducting magnet system, the magnet functions and their performances are described.