Modelling of the short bunch optics for bERLinPro

The Energy Recovery Linac principle allows compressing electron bunches to the length at least two orders of magnitude shorter compared to storage rings. At bERLinPro bunch compression and decompression can be done in two stages in the injector and main arcs. The distribution of compression between these two stages is subject to optimization. Simulations show that the length and shape of the bunch in the injector and before the linac are the limiting factors for minimal bunch length. Injector simulations have to consider space charge effects, whereas CSR effects are limiting compression in the arcs. Current status of injector optimization and effect on the compressed bunch are presented.