Energy enhancement of the self-modulated laser wakefield acceleration by using the plasma density gradient

Abstract

If GeV electron energies are to be achieved in the laser wakefield accelerator (LWFA), it is necessary to propagate an intense laser pulse over a long distance in a plasma without disruption. Many LWFA experiments have been done in the high-power, long-pulse, self-modulated regions, where self-guiding due to relativistic focusing appears to play a role in extending the acceleration length. However, there are strong instabilities and an electron dephasing problem due to the velocity difference between the electron beam and the wake wave. Our study shows that the upward density gradient scheme can be used to avoid the dephasing problem. In the study, particle-in-cell simulations were performed to search for the optimal conditions of the density gradient for the ongoing experiment. The simulation results show that the maximum energy of the accelerated electrons can be increased by about 50 % in the upward density gradient case. Moreover, we present a brief plan of ongoing experimental research using the laser system at the Korea Electrotechnology Research Institute (KERI).