High Repetition-Rate Wakefield Electron Source Generated by Few-millijoule, 30 Femtosecond Laser Pulses on a Density Downramp

Abstract : We report on an experimental demonstration of laser wakefield electron acceleration using a sub-TW power laser by tightly focusing 30-fs laser pulses with 8 mJ pulse energy on a 100 µm scale gas target. The experiments are carried out at an unprecedented 0.5 kHz repetition rate, allowing " real time " optimization of accelerator parameters. Well-collimated and stable electron beams with quasi-monoenergetic peaks around 100 keV are measured. Particle-in-cell simulations show excellent agreement with the experimental results and suggest an acceleration mechanism based on electron trapping on the density downramp, due to the time varying phase velocity of the plasma waves.