Comparison of different longitudinal injection scenarios for achieving optimal performance in SAPS

Abstract The Southern Advanced Photon Source (SAPS) is a proposed fourth-generation diffraction-limited storage ring (DLSR) designed with a modified hybrid multibend achromat lattice, achieving a natural emittance as low as 33 pm. Given its limited dynamic aperture, the SAPS is not well suited to off-axis injection, with on-axis injection schemes proving a more favourable option. This paper highlights the advantages of longitudinal injection for SAPS, which employs a fast pulse kicker and multi-frequency RF systems. A systematic comparison is presented of the longitudinal injection schemes for double-frequency and triple-frequency RF systems. The effects of these schemes on circulating beam stretching, the time structure of the fast pulse kicker, RF parameter stability requirements, storage ring acceptance, and injection efficiency are considered. Based on these results, reasonable hardware specifications for the fast stripline kicker and RF system, as well as injector parameter requirements, are provided. These findings are crucial for SAPS to achieve longitudinal injection and can also serve as a reference for similar light sources.