The BEPCII project, a major upgrade and natural extension of the Beijing Electron–Positron Collider (BEPC), has passed an important milestone with beam now circulating in the outer ring and the synchrotron radiation (SR) beam lines open to users. Obtaining colliding beams will be the next step.
BEPCII consists of two storage rings, with a new ring built inside the original BEPC ring. The two rings will cross at two points to form a collider, with one ring for electrons and one for positrons. BEPCII will operate with beam energy in the range 1.0–2.1 GeV, appropriate for charm production, and with a design luminosity of 1 × 1033 cm-2s-1 at 1.89 GeV. The upgraded collider will also provide improved SR performance with higher beam energy and photon intensity than at BEPC.
Construction work on BEPCII started at the beginning of 2004. Summer that year saw the installation of new hardware subsystems for the linac injector after the old devices had been removed and commissioning of the upgraded injector linac followed, demonstrating its design performance. Then, after 16 months’ hard work, most of the components for the new inner storage ring had been manufactured and tested.
Installation was completed in early November 2006 with conventional magnets installed in the interaction region to enable commissioning of the outer ring with electrons for SR operation. In the meantime, improvement of the cryogenic system and field mapping of the superconducting magnets will proceed at a position out of the beam line.
Commissioning of the outer ring started on 13 November and a beam position monitor revealed the signal for the first turn of beam on the same day. Then, in the early morning of 18 November, the operators obtained circulating beam without RF and stored beam with RF. At the same time, the hardware systems were tested and debugged. Vacuum conditioning with beam followed, and with improving vacuum, orbit correction and other measures, the beam current in the storage ring and the beam lifetime were increased step by step. At the time this issue went to press, the beam current had reached 200 mA with a lifetime of 4 h at 1.89 GeV.
For SR operation, the beam energy was ramped to the required 2.5 GeV and commissioning with the SR beam lines began. The SR beams were then opened to users from 25 December. “This is a milestone of the BEPCII construction towards its final goal,” stressed Nobel laureate Tsung-Dao Lee during his recent visit to Beijing.
Commissioning with electron and positron beams in preparation for the first collisions will be carried out after one month of operation for SR users. The plan is then to install the superconducting insertion quadrupoles into the interaction region in the summer and to move the new detector BESIII into place in autumn. The first physics run of BEPCII/BESIII is scheduled to start by the end of 2007.
