Study of DESY II as an injector option for PETRA IV storage ring

PETRA IV is the storage ring light source currently under design at DESY in Germany. The baseline injector is a 6-GeV synchrotron DESY IV, an upgrade to the existing injector DESY II. Even if the project progresses in developing the DESY IV, we studied the intensity limit of DESY II to investigate the feasibility of reusing the existing injector chain, in view of a possible upgrade to a laser plasma injector in the coming years. We identified the microwave instability-induced energy spread and the transient beam loading as a limiting mechanism of single-bunch intensity in a 12.5 Hz cycle synchrotron. This paper reports the numerical simulation, its analysis, and its follow-up experiments of high charge acceleration at DESY II and its subsequent injection into PETRA III. The injection efficiency of DESY II's beam into future PETRA IV is also computed assuming imperfect lattices with 5% beta-beating. To overcome the intensity limit set by the pre-accelerator PIA, we investigated the possibility of multi-cycle accumulation at low energy. In this regard, we measured the lifetime and emittance over cycles and the chromaticities of the lattice. These are also reported in the paper.