Cascaded high-gradient terahertz-driven acceleration of relativistic electron beams

Terahertz (THz)-driven acceleration has recently emerged as a new route for delivering ultrashort bright electron beams efficiently, reliably, and in compact setup. Many THz-driven related working schemes key technologies have been successfully demonstrated are continuously being improved to limits. However, the achieved gradient energy gain remain low, potential physics technical challenges high field regime still under-explored. Here we report record of 170 keV single-stage configuration, demonstrate first cascaded relativistic beam with 204 two-stages Whole-bunch is accomplished an average accelerating 85 MV/m peak THz electric 1.1 GV/m. This proof-of-principle result crucial advance major impact on future sources scientific discoveries.