Photoinjector as pre-injector for BEPCII

In order to use the two-bunch acceleration technology to further double the positron injection rate from BEPCII (Beijing Electron Positron Collider Upgrade Project) linac to the storage ring, a pre-injector with two SHBs (Sub-harmonic Buncher) is being constructed to replace the old BEPCII bunching system. In this paper, we propose a new scheme to use a photoinjector as the pre-injector, the performance of which is comparable with or better than the sub-harmonic bunching system, at most 25% emittance and energy spread, 100% transport efficiency, absence of satellite bunch, etc. Beam dynamics of the photoinjector based pre-injector in both low charge and high charge cases are studied and compared with both the pre-injector with SHBs and the old BEPCII pre-injector. The high charge beam produced by the new photoinjector can be used as drive beam for laser-plasma and for laser-dielectric wakefield acceleration studies in the future. (authors)