Ultrarelativistic electron beams accelerated by terawatt scalable kHz laser

We show the laser-driven acceleration of unprecedented, collimated (2 mrad divergence), and quasi-monoenergetic (25 % energy spread) electron beams with energy up to 50 MeV at 1 kHz repetition rate. The laser driver is a multi-cycle (15 fs) 1 kHz optical parametric chirped pulse amplification (OPCPA) system, operating at 26 mJ (1.7 TW). The scalability of the driver laser technology and the electron beams reported in this work pave the way towards developing high-brilliance x-ray sources for medical imaging, innovative devices for brain cancer treatment, and represent a step towards the realization of a kHz GeV electron beamline.