Experimental Observation of Direct Laser Acceleration in a Low Density Self-Modulated Laser Wakefield Acceleration Regime*

Direct Laser Acceleration (DLA) is observed in an experiment on the Titan laser system at the Jupiter Laser Facility in a low density (3x10$^{\mathrm{17}}$ cm$^{\mathrm{-3}})$ regime of a self-modulated laser wakefield accelerator. A forking structure is show in the highest energies (\textgreater 50 MeV) of an accelerated electron beam (\textless 50 mrad) previously shown to indicate the effects of DLA during the acceleration process. The experimental results are confirmed in a quasi-3D simulation using OSIRIS under similar conditions to the experiment, i.e. 1 ps laser pulse, and moderate a$_{\mathrm{0}} \quad =$ 2.7. The simulation results show a stable SM-LWFA for the length of a 10 mm accelerator and confirm DLA being the dominant acceleration mechanism for the highest energy electrons.