Generation of short THz bunch trains in a RF photoinjector

A radiofrequency electron gun joined to a compressor can generate trains of THz sub-picosecond electron pulses by illuminating the photocathode with trains of laser pulses. Assuming a prompt electron emission, each laser pulse generates an electron disk at the cathode. The disk train evolves toward a slightly modulated slug having a peculiar sawtooth energy modulation. This kind of energy modulation is transformed into a density modulation within a velocity-bunching compressor recovering at a good extent the initial multi-disk profile. The electron beam evolution is analyzed through simulations looking at its features as function of pulse and frequency characteristics of the laser and of the accelerator parameters.