Staging acceleration of plasma accelerators is a critical requirement for compact colliders. The achivements have been made based on two different staging accelerartion schemes (from a LWFA to another LWFA  or from a Linac to a PWFA ) in recent years, however, the capure efficiency is very low (few percent or even lower). Here we present the first successful demonstration of external injection from a linear accelerator into a laser wakefield accelerator and the subsequent acceleration with ~100% capture efficiency. Stable 31-MeV, 20-fC electron beams from a conventional radio-frequency accelerator were velocity bunched to the duration of ~15fs (r.m.s.) and then external injected into the linear wakefield excited by a 10TW, 42 fs laser. Nearly all the electrons are mono-energetically accelerated and the maximum energy gain reaches 1.8 MeV in a 6-mm long plasma. High capture efficiency of external injection acceleration has also been systematically validated by 3D PIC simulations. This result paves the way toward the development of a high efficiency high energy particle accelerator.
 S. Steinke, et al.,“ Multistage coupling of independent laser-plasma accelerators”, Nature, 530, 19 (2016)
 E. Adli, et al.,“ Acceleration of electrons in the plasma wakefield of a proton bunch”, Nature, 561, 363 (2018)
|Working group||Laser-driven electron acceleration|