Optimum Condition of Sharp-Density-Transition Scheme for the Generation of a High-Quality Electron Bunch in the Laser Wakefield Acceleration

In this paper, the effects of scale length and density transition ratio on the generation of a high-quality electron bunch with a sharp density transition in the laser wakefield accelerator were analyzed using 2-D particle-in-cell simulations. The simulation results show the effect of the density transition on the quality of the beam, i.e., the total charge of the electron bunch depends on the scale length and the density transition ratio and the size of the electron bunch only depends on the density transition ratio. The simulations also show that the energy spread of the bunch in the first period can be reduced with a sharp scale length. For this paper, the optimum condition for the generation of a high-quality electron bunch was found in the parameter space of both the scale length and the density transition ratio.