Jong Uk Kim

The Effect of Density Gradient on the Self-modulated Laser Wakefield Acceleration with Relativistic and Kinetic Effects

The propagation of an intense laser pulse through an upward density-gradient plasma in a self-modulated laser wakefield acceleration (SM-LWFA) is investigated by using particle-in-cell (PIC) simulations. In the fully relativistic and kinetic PIC simulations, the relativistic and kinetic effects including Landau damping enhance the electron dephasing. This electron dephasing is the most important factor for limiting the energy of accelerated electrons. However, the electron dephasing, which is enhanced by relativistic and kinetic effects in the homogeneous plasma, can be forestalled through the detuning process arising from the longitudinal density gradient. Simulation results show that the detuning process can effectively maintain the coherence of the laser wake wave in the spatiotemporal wakefield pattern, hence considerable energy enhancement is achievable. The spatiotemporal profiles are analyzed for the detailed study on the relativistic and kinetic effects. In this paper, the optimum slope of the density gradient for increasing electron energy is presented for various laser intensities.

Effects of Scale Length and Transition Density Ratio on the Electron Trapping and Acceleration with a Sharp Density Transition in Laser Wakefield Accelerator

In this paper, the effects of scale length and transition density ratio on the electron trapping and acceleration with a sharp density transition in laser wakefield accelerator (LWFA) have been studied using one-dimensional particle-in-cell (PIC) simulations. Simulation results show that the number of accelerated electrons depends on the plasma density in the high density region and the scale length of the density transition region. For the detailed investigation of the dynamical features of the electron trapping and acceleration, spatiotemporal patterns of the laser wake wave are also used. Throughout this work, the optimum condition for the electron acceleration could be found in the relevant parameter space of the scale length and the transition density ratio.

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.

Generation of maximum photon flux at the optimum plasma density in the laser-driven betatron oscillation

The plasma density effect on x-ray characteristics from betatron oscillation in a laser wakefield accelerator was studied via two-dimensional particle-in-cell simulations. Inside an ion cavity, accelerated electrons with betatron oscillatory motion produce synchrotron radiation. As the plasma density increases, both bunch charge and betatron oscillation amplitude increase in the laser unmodulated regime and decrease again in the laser modulated regime. The multicavitation and weaker field from the laser modulation result in a smaller bunch charge and a decrease in oscillation amplitude in the modulated regime. The photon flux and critical energy in the wiggler regime, where the ion cavity acts as a wiggler, can be optimized and controlled through plasma density. In this work, the mechanism of the optimum ratio of laser pulse duration to plasma wavelength for maximum photon flux was investigated.