The BEPCII: Status and early commissioning

BEPCII is the upgrade project of Beijing Electron Positron Collider (BEPC). The installation of its storage ring components except the superconducting (SC) insertion magnets was completed in early November, 2006. While the improvement of the cryogenic system for SC magnets is in progress, the commissioning of the synchrotron radiation (SR) mode for the so called back-up scheme with conventional magnets adopted in the interaction region (IR), started on Nov. 13, 2006. The first electron beam was stored on Nov. 18 and later beam was provided to SR users for about 1 month starting from Dec. 25, 2006. The commissioning of the collision mode including the electron and position rings started in Feb. 2007. The first beam collision was realized on Mar. 25. Then optimization of the beam parameters was done. On May 14, a 100 mA to 100 mA beam collision was achieved with 20 bunches for each beam. The luminosity estimated from the measured beam-beam parameters has reached that of BEPC. From May 25 the machine turns to the second run of the SR mode. This paper provides an overview of the construction and introduce the commissioning results of the backup scheme of BEPCII.