Dentical decelerating wakefields for driver-bunches and identical accelerating wakefields for witness-bunches for their periodic sequence

Acceleration by the wakefield in the plasma can provide compact sources of relativistic electron beams of high brightness. Free electron lasers and particle colliders, using plasma wakefield accelerators, require high efficiency and beams with low energy spread. Achieving both conditions can be ensured by the formation of identical fields for all accelerating bunches and identical fields for all decelerating bunches by controlled selection of bunch currents and their spatial distribution for a given plasma wave. We demonstrate such optimal bunch currents and their spatial distribution in the linear regime in a plasma accelerator with wakefield excited by electron bunches injected from the RF accelerator with high quality. (author)