Ultra-High-Brightness and tuneable attosecond-long electron beams with the Laser Wake Field Acceleration

Ultra-low emittance and tuneable in length electron beams can be obtained with the Laser Wake Field Acceleration (LWFA) by employing advanced ionization injection techniques, such as the Two-Color and the Resonant Multi-Pulse Ionization injection (ReMPI) schemes. There, a tightly focused, short wavelength (ionization) pulse extracts electrons from a selected inner shells of a dopant, allowing them to be longitudinally compressed and trapped in the wakefield excited by a different (driver) pulse. In this work we demonstrate, by means of analytical results and Particle In Cell simulations, that 340~as long electron beams with 2.3~GeV energy, 6.1~pC charge, 0.15~$\%$ projected energy spread, 60~nm normalised emittance, and projected 6D-Brightness in excess of $3\times 10^{18}A/m^2/0.1\%bw$ can be generated with a ~200TW~Ti:Sa laser system. The beam slice analysis reveals its potentialities for driving a few-spikes attosecond X-ray Free Electron Laser. Furthermore, the ultra-high projected quality, and the extreme shortness of the beams makes them ideal candidates for the generation of attosecond and quasi-monochromatic $\gamma$ photons beams through Thomson/Compton backscattering, or for the injection in subsequent plasma wakefield structures so as to reach TeV energies from staged LWFA.