Progress of the BEPCII Linac Upgrade

BEPCII is the second phase construction of the Beijing Electron Positron Collider (BEPC). It requires its injector linac to have higher beam energy (1.89GeV) for on-energy injection and a higher beam current (40mA e+ beam) for a higher injection rate (≥ 50mA/min.). The low beam emittance (1.6πmm-mrad for e+ beam, and 0.2πmm-mrad for 300mA e-beam) and low beam energy spread (± 0.5%) are also required to meet the storage ring acceptance. Hence we need a new electron gun system, a new positron source, a much higher power and more stable RF system with its phasing loops, and a new beam tuning system with orbit correction. Up to date, all system design and fabrication work have been completed. And in five months from May 1^stof 2004, the positron production system— from the electron gun to the positron source, has been installed into the tunnel. In this paper, we will introduce major upgrades of each system, and present the recent beam commissioning.