The Effect of Plasma Density Gradient on the Direct Laser Acceleration of Electrons*

Direct laser acceleration (DLA) is capable of generating superponderomotive energy electrons to hundreds of MeV, as well as secondary particles and radiation from high-intensity picosecond laser pulses interacting with underdense plasma. Experiments performed on the OMEGA EP facility using apodized beams and supersonic gas nozzle targets demonstrate the sensitivity of the complex process of DLA to the gradient of the plasma density ramps. 2D particle-in-cell OSIRIS simulations mimic the interaction using different plasma density profiles and provide insight into the laser channel creation, laser fields evolution, as well as the significant effect of the sheath fields on the corresponding electron dynamics. Our results show an optimal plasma density gradient and a path towards optimizing DLA conditions.